Title of Invention	A MOLD DEVICE, A DISK SUBSTATE, A METHOD OF MAKING A DISK SUBSTRATE BY USING A MOLD DEVICE
Abstract	A mold device (3) for forming a disk substrate (4) from a synthesized resin, comprising: a fixed mold (1); and a movable mold (2), said movable mold and the fixed mold forming a cavity (5) in which the disk substrate (4) is molded, wherein a separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold (1) and the movable mold (2) corresponding to an outer circumferential surface of the disk substrate (4) held on one of the fixed mold (1) and the movable mold (2).

Title of Invention

A MOLD DEVICE, A DISK SUBSTATE, A METHOD OF MAKING A DISK SUBSTRATE BY USING A MOLD DEVICE

Abstract

A mold device (3) for forming a disk substrate (4) from a synthesized resin, comprising: a fixed mold (1); and a movable mold (2), said movable mold and the fixed mold forming a cavity (5) in which the disk substrate (4) is molded, wherein a separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold (1) and the movable mold (2) corresponding to an outer circumferential surface of the disk substrate (4) held on one of the fixed mold (1) and the movable mold (2).

Full Text	-2- BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a mold device, a disk substrate, a method of making a disk substrate by using a mold device, and specifically, to a disk substrate used for fabricating an optical disk, being molded from a synthesized resin, a mold device for forming the disk substrate, and a method of molding the substrate. Description of the Related Art Generally, a disk substrate used for fabricating an optical disk is formed from a synthesized resin such as a polycarbonate resin, by using an injection molding device. The injection molding device includes a fixed mold and a movable mold, which form a cavity corresponding to the disk substrate to be molded. For example, on a surface of the fixed mold that defines the cavity, a projecting and depressed pattern corresponding to musical signals or other information signals is formed, and this is the so-called stamper, which is used for forming pits or pre-grooves constituting tracks representing desired information signals. On the side of the movable mold, a punch is provided to open a hole for locking a centering member at a projecting center portion. When molding the disk substrate using such a -3- mold device, a molten synthesized resin is injected to fill the cavity via a sprue bushing injection port arranged on the fixed mold. Then, after molding the disk substrate in the cavity, the punch is moved to punch the hole for locking the centering member at the center portion, and then pits or pre-grooves are formed on the primary surface of the disk substrate. Concerning this kind of disk substrate mold device, for example, Japanese Patent Gazette No. 03301103 discloses an invention in which on the side of the movable mold, a separation resistance caused by point-like projections and holes, or ring-shaped projections and grooves formed along the circumferential direction of the movable mold is provided on the outer surface of the disk substrate or on the inner surface of a projection at the center. In the invention disclosed in the aforesaid Japanese Patent Gazette No. 03301103, the molded disk substrate is separated easily and reliably from the stamper (this is the so-called "first separation"). Here, the disk substrate is molded by a stamper, which has a projecting and depressed pattern for forming pits or pre-grooves as the recording tracks. However, if it is desired to reduce the time length of the molding cycle, after the step of -4- separation of the disk substrate from the stamper, and when separating the disk substrate from the movable mold (this is the so-called "second separation"), the separation resistance, which is caused by point-like projections and holes, or ring-shaped projections and grooves formed along the circumferential direction of the movable mold, increases, and the disk substrate cannot be separated from the movable mold easily. Due to this, as is known, planarity of the disk substrate declines; moreover, the mechanical characteristics vertical vibration, circumferential tilt, and radial tilt decline, and the resulting disk substrate cannot be used to fabricate an optical disk. Especially, recently and continuing, DVD disks such as DVD+R/RW are widely used, and the DVD disks require high speed recording. In order to achieve the high speed recording, the planarity of the disk substrate is important, and disk substrates with the above problems are not suitable. That is, in the invention disclosed in the aforesaid Japanese Patent Gazette No. 03301103, there exists a resistance against separation of the disk substrate from the stamper due to the separation resisting portion, and the invention is not able to reduce the time length of the molding cycle, but merely -5- focuses on performance of separating the disk substrate from the stamper (the first separation). SUMMARY OF THE INVENTION It is a general object of the present invention to solve one or more problems of the related art. A specific object of the present invention is to provide a method capable of reducing a time length of a molding cycle while maintaining planarity of a disk substrate molded via a separation process. According to a first aspect of the present invention, there is provided a mold device for forming a disk substrate from a synthesized resin that includes a fixed mold and a movable mold, and the movable mold and the fixed mold form a cavity in which the disk substrate is molded. A separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate held on the one of the fixed mold and the movable mold. In the present invention, the separation resisting part having a roughened surface is provided on an inner surface of the fixed mold or the movable -6- mold corresponding to an outer circumferential surface of the disk substrate. The separation resisting part generates a resistance on the outer circumference of the disk substrate when separating the disk substrate, which is formed from a synthesized resin filling the cavity, from a stamper, which acts as a side surface of the cavity, thereby maintaining the planarity of the disk substrate when separating the disk substrate from the stamper. The separation resisting part improves separation ability of the outer circumferential surface of the disk substrate when separating the disk substrate from the mold device. As a result, even when the time length of the molding cycle is reduced for rapid molding, the disk substrate can be separated from the mold device while the planarity of the disk substrate is maintained. In contrast, the separation resisting portion in the aforesaid Japanese Patent Gazette No. 03301103 merely generates a resistance on the outer circumference of the disk substrate when separating the disk substrate from the stamper. As an embodiment, the roughened surface of the separation resisting part has a plurality of dotlike projections or dot-like depressions, or a plurality of line-shaped projections or line-shaped -7- depressions, or a combination of the dot-like and line-shaped projections or depressions distributed on a surface of the separation resisting part. As an embodiment, the roughened surface of the separation resisting part has a resistance generation area not less than 18 mm2, the roughened surface of the separation resisting part includes at least two rows of projections or depressions in the direction of pulling out the molded disk substrate, and the depth of each of the projections or depressions is in a range from 3 µm to 90 µm. More preferably, the depth of each of the projections or depressions on the roughened surface of the separation resisting part is in a range from 3 µm to 20 µm. As an embodiment, the roughened surface of the separation resisting part is formed by a roughening treatment on the inner surface of at least one of the fixed mold and the movable mold. Preferably, the roughening treatment may include WPC (Wide Peening and Cleaning) processing, bead blast processing, shot peening processing, micro dimple processing, cutting or polishing by using a cutter having a fine rough surface, and processing by using chemical elements or solutions capable of roughening a metal surface. According to a second aspect of the present -8- invention, there is provided a disk substrate formed from synthesized resin by using a mold device, including an outer circumferential surface roughened by a separation resisting part of the mold device, the separation resisting part having a roughened surface. According to a third aspect of the present invention, there is provided a method of molding a disk substrate by using a mold device including a fixed mold and a movable mold. The method includes the steps of filling a molding cavity, formed by the fixed mold and the movable mold and having a stamper for use of transfer as a side surface, with a synthesized resin; separating the disk substrate formed from the synthesized resin in the cavity from the stamper; and separating the disk substrate from the mold device. In the step of filling the cavity, the mold device includes a separation resisting part arranged on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate, and the separation resisting part has a roughened surface. As an embodiment, the roughened surface of the separation resisting part includes a plurality of dot-like projections or dot-like depressions, or a plurality of line-shaped projections or line-shaped -9- depressions, or a combination of the dot-like and line-shaped projections or depressions distributed on a surface of the separation resisting part. As an embodiment, the roughened surface of the separation resisting part includes a resistance generation area not less than 18 mm2; the roughened surface of the separation resisting part includes at least two rows of projections or depressions in the direction of pulling out the molded disk substrate; and a depth of each of the projections or depressions is in a range from 3 µm to 90 µm. More preferably, the depth of each of the projections or depressions on the roughened surface of the separation resisting part is in a range from 3 µm to 20 µm. Accordingly, the present invention provides a mold for forming a disk substrate from a synthesized resin, comprising: a fixed mold; and a movable mold, said movable mold and the fixed mold forming a cavity in which the disk substrate is molded, wherein a separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate held on one of the fixed mold and the movable mold. -9A- The present invention also provides a disk substrate formed by using a mold device from a synthesized resin, comprising: an outer circumferential surface roughened by a separation resisting part having a roughened surface of the mold device. The present invention further provides a method of molding a disk substrate by using a mold device including a fixed mold and a movable mold, said method comprising the steps of: filling a molding cavity with a synthesized resin, said molding cavity being formed by the fixed mold and the movable mold and having a stamper for use of transfer as a side surface thereof, said mold device including a separation resisting part arranged on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate, said separation resisting part having a roughened surface; separating the disk substrate formed from the synthesized resin in the cavity from the stamper; and separating the disk substrate from the mold device. These and other objects, features, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments given with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS FIGs. 1A and 1B are side cross-sectional views of an exemplary structure of a mold device for forming a disk substrate according to an embodiment of the present invention, where FIG. 1A shows an open -10- state of the mold device, and FIG. 1B shows a closed state of the mold device; FIG. 2 is a table showing characteristics of samples for explaining the separation resisting part 15, of the present embodiment in comparison with the related art; FIG. 3 is a table showing shapes and characteristic values of the separation resisting part 15 of the present embodiment in comparison with the related art. FIGs. 4A and 4B show examples of measured surface roughness; FIG. 5 shows a relation between shapes of the roughened surface and the time length of the molding cycle; FIG. 6 shows a relation between the depth of the unevenness on the roughened surface and the time length of the molding cycle, illustrating effects of the second separation; FIG. 7 is a perspective view of the cavity-ring 12; FIG. 8 is a cross-sectional view of the roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 processed by WPC with a square material being used; -11- FIG. 9 is a cross-sectional view of the roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 processed by WPC with a spherical material being used; and FIGs. 10A through 10D are cross-sectional views of the roughened surface of the separation resisting part 15 along the arrow B in FIG. 7, illustrating examples of shapes of the roughened surface of the separation resisting part 15 processed by cutting or polishing. DESCRIPTION OF THE PREFERRED EMBODIMENTS Below, preferred embodiments of the present invention are explained with reference to the accompanying drawings. In the following, as an example, descriptions are made of a mold device for forming a disk substrate used in fabrication of an optical disk such as a DVD-related disk (DVD+R or others), and a method of molding the disk substrate by using the mold device. FIGs. 1A and 1B are side cross-sectional views of an exemplary structure of a mold device 3 for forming a disk substrate according to an embodiment of the present invention, where FIG. 1A shows an open -12- state of the mold device, and FIG. 1B shows a closed state of the mold device. As illustrated in FIG. 1A, the mold device includes a fixed mold 1 and a movable mold 2 that is movably supported by a hydraulic mechanism (not shown) and is able to move in directions approaching toward and moving away from the fixed mold 1. Between the fixed mold 1 and the movable mold 2, there is formed a cavity 5 where a disk substrate 4 is to be molded. On the side of the fixed mold 1, a sprue bushing 6 is provided at the center of the cavity 5 through which flows synthesized resin, such as molten polycarbonate resin, supplied from a not-illustrated injection molding apparatus. At the center of the sprue bushing 6, there is a nozzle 6a for injecting resin, and the synthesized resin supplied from the not-illustrated injection molding apparatus is injected into the cavity 5 through the nozzle 6a. Around the outer circumference of the sprue bushing 6, a not-illustrated holder is provided, into which a not-illustrated inner side stamper support is fit to support the inner side of a stamper 7 (described below). On a surface of the fixed mold 1 that defines the cavity 5, the stamper 7 is mounted, which -13- is for molding a projecting and depressed pattern corresponding to information signals recorded on an optical disk, the projecting and depressed pattern including pits or pre-grooves constituting recording tracks on the signal recording area of the optical disk. The inner circumference of the center hole of the stamper 7 is supported by the not-illustrated inner side stamper support that is fit into the not-illustrated holder, and the outer circumference of the center hole of the stamper 7 is fixed by suction of air coming from a suction port (not illustrated). At the center of a surface of the movable mold 2 that defines the cavity 5, a recess 9 is provided to form, together with the fixed mold 1, a projecting portion on the other primary surface of the disk substrate 4. At the center of the recess 9, a punch mechanism 10 is provided to punch a hole for locking a centering member at the center of the projecting portion. The punch mechanism 10 is arranged in the movable mold 2 and is movable in a sleeve 11. An ejector 14 is supported by the sleeve 11 to be able to move relative to the movable mold 2 so as to stick out and separate the disk substrate 4 after being molded. On the outer surface of the movable mold 2, a cavity-ring 12 is provided that defines the cavity 5 -14- and molds the outer circumference of the disk substrate 4 to be molded. The front end surface of the cavity-ring 12 functions as a flat impacting surface, and is arranged so as to be able to contact the periphery of the stamper 7 attached to the fixed mold 1. When the movable mold 2 is moved to make contact with the fixed mold 1 so that of the mold device 3 is in a closed state, as illustrated in FIG. 1B, the flat impacting surface is brought into contact with the stamper 7 to form a closed cavity 5. The molding surface of the movable mold 2 is for forming the other primary surface of the disk substrate 4, which is a precise flat surface acting as a laser beam incident surface of the disk substrate 4. Therefore, the molding surface of the movable mold 2 is also a precise flat surface, for example, a mirror surface 13. After the disk substrate 4 is molded, and when the movable mold 2 is moved away from the fixed mold 1 (the first separation), the disk substrate 4 is held on the side of the movable mold 2, and then the ejector 14 in the movable mold 2 is stuck out to separate the disk substrate 4 from the movable mold 2 (the second separation). With the above basic structure of the mold -15- device 3, when molding the disk substrate 4, the movable mold 2 is moved and brought into contact with the fixed mold 1, and the mold device 3 is in the closed state, as illustrated in FIG. 1B. In this state, synthesized resin, such as molten polycarbonate resin, supplied from a not-illustrated injection molding apparatus is injected into the cavity 5 through the nozzle 6a. Then, the punch mechanism 10 is moved to punch the hole for locking the centering member at the center of the projecting portion of the disk substrate. After that, the movable mold 2 is further moved toward the fixed mold 1 to compress the synthesized resin filling the cavity 5 for clamping. Therefore, the disk substrate 4 corresponding to the cavity 5 is molded. After the disk substrate 4 is molded, the movable mold 2 is moved away from the fixed mold 1 (the first separation), and thereby, the disk substrate 4 is separated from the stamper 7. At this moment, the disk substrate 4 is held on the side of the movable mold 2. Subsequently, the ejector 14 in the movable mold 2 is stuck out to separate the disk substrate 4 from the movable mold 2 (the second separation). In the present embodiment, a separation resisting part 15 having a roughened surface is formed on the inner surface of the cavity-ring 12 -16- corresponding to the outer circumference of the disk substrate 4. The inner surface of the separation resisting part 15 is roughened by distributing dots, or lines, or their combinations on the inner surface of the cavity-ring 12, specifically, by small point-like projections and depressions scattering on the inner surface of the cavity-ring 12, or projecting and depressed lines scattering or crossing with each other on the inner surface of the cavity-ring 12, or their combinations. For example, the separation resisting part 15 has a roughened surface of an area of 18 mm2 or more to generate a resistance in the direction of pulling out the disk substrate 4, and the size of the roughness is 3 µm to 90 µm. The separation resisting part 15 generates a resistance on the outer circumference of the disk substrate 4 when separating the disk substrate 4 formed from the synthesized resin filling the cavity 5 from the stamper 7, and indicates separation ability of the outer circumference of the disk substrate 4 when separating the disk substrate 4 from the movable mold 2. By providing the separation resisting part 15 on the inner surface of the cavity-ring 12, when -17- molding the disk substrate 4, the outer circumference of the disk substrate 4 is roughened, generating a roughened portion 4a, corresponding to the roughness of the separation resisting part 15. Then, when separating the molded disk substrate 4 from the stamper 7, the separation resisting part 15 generates a resistance on the roughened portion 4a of the outer circumference of the disk substrate 4 to maintain the state of the disk substrate 4 being held to the movable mold 2. Thereby, the disk substrate 4 can be separated from the stamper 7 reliably without declination of the vertical vibration, peripheral tilt, and radial tilt characteristics, accordingly maintaining sufficiently high planarity, and therefore, the resulting disk substrate can be transferred to the movable mold 2 reliably (first separation). Furthermore, when separating the disk substrate 4 from the movable mold 2 (second separation), because the roughness of the separation resisting part 15 shows the ability to separate from the roughened portion 4a of the outer circumference of the disk substrate 4, even if the time for the disk substrate 4 to contract is not so long, in other words, even if the time length of the molding cycle is reduced for rapid molding, the disk substrate 4 can be -18- separated easily with the outer end surfaces of the disk substrate 4 not being impeded by the cavity-ring 12, and maintaining sufficiently high planarity. It should be noted that although the roughened portion 4a is formed on the outer end surfaces of the disk substrate 4 corresponding to the separation resisting part 15, because information signals are not recorded on the outer end surfaces of the disk substrate 4, the roughened portion 4a does not influence the signal recording area on the disk substrate. In the above, although it is described that the stamper 7 is mounted on the fixed mold 1, and the punch mechanism 10 is arranged on the movable mold 2, an arrangement in the opposite way can also be adopted. Below, methods of fabricating the separation resisting part 15 and quantitative characteristics of the roughness of the separation resisting part 15 are described in comparison with the related art. For the purpose of comparison, mold samples No. 1, No. 2, and No. 3 were made in accordance with the aforesaid Japanese Patent Gazette No. 03301103, and mold samples No. 4 and No. 5 were made in accordance with the present embodiment. Characteristics of these mold samples are summarized in a table in FIG. 2. -19- FIG. 2 is a table showing characteristics of samples for explaining the separation resisting part 15 of the present embodiment in comparison with the related art. FIG. 3 is a table showing shapes and characteristic values of the separation resisting part 15 of the present embodiment in comparison with the related art. As shown in the table in FIG. 2, in the first sample, 24 square recesses each having an area of 0.2 x 0.2 mm2 are uniformly arranged on the inner surface of the cavity-ring in one row along a circumference of the cavity-ring. The total length a of the recesses along a circumference of the cavity-ring amounts to 4.8 mm, and the depth b of the recesses is 0.2 mm, hence the total area of the recesses, which contributes to generation of a resistance (below, referred to as "resistance area"), amounts to 0.96 mm2. In the second sample, a ring-shaped recess having a 0.1mm x 0.1 mm square cross section (referring to FIG. 3) is formed on the inner surface of the cavity-ring along a circumference of the cavity-ring, the length a of the ring-shaped recess along the circumference of the cavity-ring is 376.99 mm, and the depth b of the recess is 0.1 mm; hence the total area -20- of the ring-shaped recess contributing to generation of a resistance (that is, the resistance area) amounts to 37.70 mm2. In the third sample, a ring-shaped recess having a 0.05 mm x 0.05 mm square cross section (referring to FIG. 3) is formed on the inner surface of the cavity-ring along a circumference of the cavity-ring, the length a of the ring-shaped recess along the circumference of the cavity-ring is 376.99 mm, and the depth b of the recess is 0.05 mm; hence, the total area of the ring-shaped recess contributing to generation of a resistance (that is, the resistance area) is 18.85 mm2. In the fourth sample, as the separation resisting part 15, the entire inner surface of the cavity-ring 12 is roughened along the circumference of the cavity-ring 12, and the roughness (an averaged depth of the projecting or depressed portions) of the roughened surface is 0.020 mm. The length a of the separation resisting part 15 along the circumference of the cavity-ring 12 is 376.99 mm, the average depth b of the projecting or depressed portions is 0.02 mm, and there are twelve rows of the projecting or depressed portions along the direction of pulling out the disk substrate 4; therefore, the total area of the roughened -21- surface of the separation resisting part 15 (that is, the resistance area) amounts to 45.24 mm2. In the fifth sample, as the separation resisting part 15, the entire inner surface of the cavity-ring 12 is roughened along the circumference of the cavity-ring 12 (referring to FIG. 3), and the roughness (an averaged depth of the projecting or depressed portions) of the roughened surface is 0.012 mm. The length a of the separation resisting part 15 along the circumference of the cavity-ring 12 is 376.99 mm, the average depth b of the projecting or depressed portions is 0.012 mm, and there are about thirteen rows of the projecting or depressed portions along the direction of pulling out the disk substrate 4; therefore, the total area of the roughened surface of the separation resisting part 15 (that is, the resistance area) amounts to 29.41 mm2. When estimating the resistance areas of the fourth sample and the fifth sample, because a cross section of each depressed portion on the inner surface of the cavity-ring 12 can be approximated to be a triangle, the resistance area d of each depressed portion was calculated by using the formula d=(ab)/2c. The surface roughness mentioned above was -22- measured by using a Form Taly-Surf S6 (produced by Taylor Hobson) surface roughness measurement instrument. FIGs. 4A and 4B show examples of measured surface roughness. FIG. 4A and FIG. 4B show the surface roughness of the same location of the separation resisting part 15, but data shown in FIG. 4A were obtained by making a measurement every 3 mm, whereas data shown in FIG. 4B were obtained by making a measurement every 1 mm in order to more clearly display the surface roughness by a graph. The numbers of rows in the fourth sample and the fifth sample, which are displayed in the table in FIG. 2, were obtained by counting on the actually measured graph assuming the thickness of the disk substrate to be 0.6 mm. Below, based on the above results of the five samples, evaluation was made on the relation between the samples and the time for a molding cycle, and on mechanical characteristics of the samples. For evaluation of the mechanical characteristics, as illustrated in FIG. 3, the time length of molding cycle, peripheral axial acceleration, peripheral radial tilt and the peripheral circumferential tilt were measured, and the mechanical characteristics were -23- evaluated based on these measured quantities. Here, the "peripheral radial tilt" indicates bending of the disk substrate in the radial direction in terms of angle. A small value of the peripheral radial tilt is desirable, because if the peripheral radial tilt becomes too large, it influences the offset and amplitudes of a push-pull signal obtained from an optical disk fabricated with the subject substrate. The "peripheral circumferential tilt" indicates bending of the disk substrate in the circumferential direction in terms of angle. Similarly, a small value of the peripheral circumferential tilt is desirable. The "peripheral axial acceleration" indicates the acceleration of a recording layer in a direction perpendicular to a reference plane when the rotational speed is 16 Hz (960 rpm, CAV control). If the peripheral axial acceleration becomes too large due to unevenness of the disk surface, response performance, tracking performance, and stability of focus servo or tracking servo may be influenced for an optical disk fabricated with the subject substrate. Recently and continuing, in DVD disks, which require high speed recording, quality related to the peripheral axial acceleration is attracting more and -24- more attention. For example, according to the Orange Book, in DVD+R/RW, a residual focus/tracking error is defined; converting this quantity into the peripheral axial acceleration, it turns out that a peripheral axial acceleration less than 2.1 m/s2 is required. In the present embodiment, when the peripheral axial acceleration is less than 2.1 m/s2, the mechanical characteristic is evaluated to be good. As for "time length of molding cycle", an object value is set to be 5.5 seconds. The above mechanical characteristics are measured by using an instrument called "Brief-126P" fabricated by Dr. Schenk. First, it is found that when the speed of opening the mold is constant, a reference of determining whether a resistance arises when separating the disk substrate from the stamper (the first separation) is that the resistance area in the direction of pulling out the disk substrate is greater than 18 mm2. In the first separation, if the resistance area is less than 18 mm2 in the direction of pulling out the disk substrate, it is found that the disk substrate cannot be separated from the stamper properly. Therefore, because the resistance area of -25- the first sample is less than 18 mm2 in the direction of pulling out the disk substrate, no matter how much is the time length of the molding cycle when using this mold sample, it is sure that the first mold sample cannot form disk substrates meeting predetermined requirements. Concerning the second sample, as illustrated in FIG. 3, if the time length of molding cycle is 9.6 seconds, the peripheral axial acceleration is 1.4 m/s2. As for the third sample, as illustrated in FIG. 3, if the time length of molding cycle is 8.4 seconds, the peripheral axial acceleration becomes 1.6 m/s2. For comparison, if the time length of molding cycle is reduced to be 6.7 seconds, the peripheral axial acceleration becomes 4.7 m/s2; furthermore, bending (tilt) occurs on the surface of the disk substrate in a region with the disk radius R ranging from 50 mm to 57 mm, and hence the mechanical characteristics of the third sample were evaluated to be bad. On the other hand, in the case of the fifth sample, as illustrated in FIG. 3, even when the time length of molding cycle is reduced to be 5.5 seconds, which is the object value, the peripheral axial acceleration becomes 1.7 m/s2, and the peripheral -26- radial tilt and the peripheral circumferential tilt are also sufficiently small; thus, the mechanical characteristics of the fifth sample are evaluated to be good. FIG. 5 shows a relation between shapes of the roughened surface and the time length of the molding cycle. According to the above description and as illustrated in FIG. 5, it is necessary to provide a plurality of rows of projections or depressions (unevenness) along the direction of pulling out the disk substrate; furthermore, when the depth of the unevenness is 0.09 mm or so, the time length of the molding cycle can be reduced to 9 seconds, when the depth of the unevenness is 0.05 mm or so, the time length of the molding cycle can be reduced to 7 seconds, and when the depth of the unevenness is 0.02 mm or so, the time length of the molding cycle can be reduced to 5.5 seconds, which is the object value. In other words, with a fine roughened surface, as those of the fourth sample and the fifth sample, the resistance area increases, and accordingly, the resistance increases. On the other hand, shallow unevenness results in good mechanical characteristics. When separating the disk substrate from the stamper -27- (the first separation), a large resistance area in the direction of pulling out the disk substrate is desirable. When taking the disk substrate out from the mold device 3 (the second separation), shallow unevenness is desirable especially when the time length of the molding cycle is reduced in order to achieve rapid molding, and there is not a sufficiently long time for the disk substrate to cool and contract. Because the shallow unevenness results in a small resistance, it is easy to pull the disk substrate out. In comparison, with a mold according to the above-mentioned Japanese Patent Gazette No. 03301103, which includes a separation resisting part having only one row of ring-shaped unevenness in the direction of pulling out the disk substrate being desirable, as in the second and third samples illustrated in the table in FIG. 2, even when the time length of the molding cycle is still as long as 6.7 seconds as in the case of the third sample, declination of quality of mechanical characteristics in the peripheral radial direction occurs due to the resistance in the second separation. Because the disk substrate is pulled out with the end surface of the disk substrate being jammed, bending (tilt) occurs on the surface of the disk substrate in a -28- region with the disk radius R from 50 mm to 57 mm. To the contrary, with a fine roughened surface, as that of the fifth sample, the resistance area increases in the direction of pulling out the disk substrate. In addition, with shallow unevenness, good mechanical characteristics are obtainable even when the time length of the molding cycle is reduced to 5.5 seconds. The quantity of depth of unevenness is further examined below. When the depth of the unevenness is in a range from 3 µm to 90 µm, preferably, from 3 µm to 20 µm, the separation resisting part 15 shows sufficiently good performance. For example, the depth of the unevenness is 12 µm in the fifth sample 5. If the depth of unevenness is less than 3 µm, the projections of the roughened surface are so fine that they do not have sufficient strength and can be crushed easily. For this reason, a sufficiently large resistance cannot be obtained when separating the disk substrate from the stamper. To the contrary, if the depth of unevenness is not less than 3 µm, a sufficiently large resistance can be generated when separating the disk substrate from the stamper. If the depth of unevenness is greater than -29- 90 µm, with a short molding cycle, the resistance is too large, that is, the ability of separation is too low, when separating the disk substrate from the movable mold. While, if the depth of unevenness is not greater than 90 µm, even if the molding cycle is shortened, a sufficiently large ability of separation can be obtained. FIG. 6 shows a relation between the depth of the unevenness on the roughened surface and the time length of the molding cycle, illustrating effects of the second separation, where the abscissa indicates the time length of the molding cycle and the ordinate indicates the depth of the unevenness. In the example shown in FIG. 6, it is assumed that the disk substrate shrinks by 90 µm when the time length of the molding cycle is 9 seconds, by 50 µm when the time length of the molding cycle is 7 seconds, and by 20 µm when the time length of the molding cycle is 9 seconds. As illustrated in FIG. 6, under the conditions that the resistance area is not less than 18 mm2, and there are more than two rows of projections or depressions (unevenness) in the direction of pulling out the disk substrate, when the depth of the unevenness decreases, even when the time length of -30- molding cycle is shortened and there is not a sufficiently long time for the disk substrate to cool and shrink, because of a small resistance due to the shallow unevenness, it is easy to pull the disk substrate out in the second separation. In FIG. 6, regions X, Y and Z are preferable for molding. Nevertheless, the regions X and Y are preferable for a reduced molding cycle, because in the regions X and Y, the depth of the unevenness is in a range from 3 µm to 20 µm, being suitable for a shortened molding cycle, particularly, a molding cycle less than the object value of 5.5 seconds. Furthermore, the region X is a preferable region, because in the region X, the resistance area, which is important to the first separation, is not less than 18 mm2, and the depth of the unevenness is in a range from 12 µm to 20 µm. The separation resisting part 15 of the fourth sample and the fifth sample, which include roughened surfaces, can be formed by various roughening treatments. In the present embodiment, a WPC (Wide Peening and Cleaning) process is used to form the separation resisting part 15. In the present embodiment, in order to obtain ideal surface roughness, the roughening process -31- is performed through two steps with materials having different roughness and shapes. For example, in the first step, use is made of a square aluminum oxide having an average granular size of 300 µm, while in the second step, use is made of spherical ceramic beads having an average granular size of 45 Mm. The shot pressure is 4.0 gf/cm2 in both the first step and the second step. The spray distance of the nozzle (that is, the distance to the object to be processed) is 7 cm. As for the processing time, the object is rotated twice so that each part thereof is processed for 30 seconds. Although sufficient roughness can be obtained in the first rotation, the roughness is made stable in the second rotation. By such a WPC processing, uniform surface roughness can be obtained easily. FIG. 7 is a perspective view of the cavity-ring 12. FIG. 8 is a cross-sectional view of the roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 processed by WPC. In FIG. 8, a roughened surface of point-like projections and depressions is formed by the WPC, and a square material is used in the WPC. The roughened surface of the separation -32- resisting part 15 along the arrow B in FIG. 7 processed by WPC has the same cross-section as that in FIG. 8. The method of forming the separation resisting part 15 is not limited to the WPC. For example, use can be made of any of bead blast, shot peening, micro-dimple processing, cutting or polishing with a cutter having a fine rough surface, or processing by using chemical elements or solutions capable of roughening a metal surface. The bead blast, in which air is blasted on the mold, shot peening, and micro-dimple processing, are substantially the same as the aforesaid WPC, and the injection pressure, materials, and processing procedures are also the same as those of WPC. In WPC, shot peening, micro-dimple processing, and bead blast, if square materials are used to impinge a metal surface at high speed to form a roughened surface having point-like projections and depressions, the obtained roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 has the same cross-section as that in FIG. 8, that is, the same as that produced by WPC. FIG. 9 is a cross-sectional view of the roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 when using spherical -33- material. That is, in WPC, shot peening, micro-dimple processing, and bead blast, if spherical materials are used to impinge a metal surface at high speed to form a roughened surface having point-like projections and depressions, the obtained roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 has the cross-section as shown in FIG. 9. As long as the resistance area is not less than 18 mm2, either of the separation resisting parts 15 in FIG. 8 or FIG. 9 is adoptable. In FIG. 8, because the cross section of each depression can be approximated to be a simple triangle, the resistance area d of each of the depressions can be simply calculated by using the formula d=(ab)/2c, where, a is the average depth of the unevenness, b is the circumference of the roughened surface, and c is the number of rows of the unevenness in the direction of pulling out the disk substrate 4. FIGs. 10A through 10D are cross-sectional views of the roughened surface of the separation resisting part 15 along the arrow B in FIG. 7, illustrating examples of shapes of the roughened surface of the separation resisting part 15 processed by cutting or polishing. -34- During the cutting or polishing process, the inner surface of the cavity-ring 12 is cut while the cavity-ring 12 is being rotated, thus forming roughened surfaces having the same shapes as those of the cutter. In FIG. 10A and FIG. 10B, the cutter has a fine rough surface. As long as the resistance area is not less than 18 mm2, any of the roughened surfaces in FIGs. 10A through 10C is adoptable. The roughened surface in FIG. 10D, however, is not usable because the disk substrate cannot be separated even after the disk substrate cools and contracts. Similarly, in the process using chemical elements or solutions capable of roughening a metal surface, the resistance area can be obtained in the following way. First, the resistance area generated per unit of the chemical element or solution is determined, and this quantity is multiplied by the circumference b of the roughened surface and by the number (c) of rows of the unevenness in the direction of pulling out the disk substrate 4. With the obtained resistance area, it can be determined whether the obtained roughed surface is usable or not. While the present invention is described with reference to specific embodiments chosen for -35- purpose of illustration, it should be apparent that the invention is not limited to these embodiments, but numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention. According to the present invention, the separation resisting part having a roughened surface is provided on an inner surface of the fixed mold or the movable mold corresponding to an outer circumferential surface of the disk substrate. When separating the disk substrate formed from synthesized resin filling the cavity from a stamper, which acts as a side surface of the cavity, the separation resisting part generates a resistance on the outer circumference of the disk substrate, thereby maintaining the planarity of the disk substrate when separating the disk substrate from the stamper. The separation resisting part improves separation ability of the outer circumferential surface of the disk substrate when separating the disk substrate from the mold device. As a result, even when the time length of the molding cycle is reduced for rapid molding, the disk substrate can be separated from the mold device while the planarity of the disk substrate is maintained. Therefore, even when the time length of molding cycle is reduced in order for rapid -36- molding to occur, it is possible to fabricate disks with high planarity of the disk substrate for use as high speed DVD disks. In addition, the roughened surface of the separation resisting part has a plurality of dot-like projections or dot-like depressions, or a plurality of line-shaped projections or line-shaped depressions, or a combination of the dot-like and line-shaped projections or depressions distributed on a surface of the separation resisting part, and the roughened surface of the separation resisting part has a resistance generation area not less than 18 mm2. The roughened surface of the separation resisting part includes at least two rows of projections or depressions in the direction of pulling out the molded disk substrate, and the depth of each of the projections or depressions is in a range from 3 µm to 90 µm, more preferably, from 3 µm to 20 µm. Therefore, the separation resisting part is able to reliably generate the resistance in the first separation and improve separation ability of the disk substrate in the second separation. Specifically, if the depth of unevenness is less than 3 µm, the projections of the roughened surface are so fine that they do not have sufficient -37- strength and can be crushed easily, and a sufficiently large resistance cannot be obtained when separating the disk substrate from the stamper. To the contrary, if the depth of unevenness is not less than 3 µm, a sufficiently large resistance can be generated when separating the disk substrate from the stamper. If the depth of unevenness is greater than 90 µm, in a short molding cycle, the resistance is too large, that is, the ability of separation is too low, when separating the disk substrate from the movable mold. In contrast, if the depth of unevenness is not greater than 90 µm, even when the molding cycle is shortened, a sufficiently large ability of separation can be obtained. The roughened surface of the separation resisting part can be formed by a roughening treatment, for example, by WPC (Wide Peening and Cleaning) processing, bead blast processing, shot peening processing, micro dimple processing, cutting or polishing by using a cutter having a fine rough surface, and processing by using chemical elements or solutions capable of roughening a metal surface. By these processing methods, uniform surface roughness capable of generating the resistance in the first separation and improving separation ability of the disk -38- substrate in the second separation can be obtained easily. -39- WE CLAIM: 1. A mold device for forming a disk substrate from a synthesized resin, comprising: a fixed mold; and a movable mold, said movable mold and the fixed mold forming a cavity in which the disk substrate is molded, wherein a separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate held on one of the fixed mold and the movable mold. 2. The mold device as claimed in claim 1, wherein the roughened surface of the separation resisting part has a plurality of dot-like projections or dot-like depressions, or a plurality of line-shaped -40- projections or line-shaped depressions, or a combination of the dot-like and line-shaped projections or depressions distributed thereon. 3. The mold device as claimed in claim 1 or claim 2, wherein the roughened surface of the separation resisting part has a resistance generation area not less than 18 mm2; and the roughened surface of the separation resisting part includes at least two rows of the projections or depressions in the direction of pulling out the molded disk substrate, and a depth of each of the projections or depressions is in a range from 3 µm to 90 µm. 4. The mold device as claimed in claim 1 or claim 3, wherein the depth of each of the projections or depressions on the roughened surface of the -41- separation resisting part is in a range from 3 µm to 20 µm. 5. The mold device as claimed in any of claims 1 through 4, wherein the roughened surface of the separation resisting part is formed by roughening treatment on the inner surface of at least one of the fixed mold and the movable mold. 6. The mold device as claimed in claim 5, wherein the roughening treatment includes WPC (Wide Peening and Cleaning) processing. 7. The mold device as claimed in claim 5, wherein the roughening treatment includes bead blast processing. -42- 8. The mold device as claimed in claim 5, wherein the roughening treatment includes shot peening processing. 9. The mold device as claimed in claim 5, wherein the roughening treatment includes micro dimple processing. 10. The mold device as claimed in claim 5, wherein the roughening treatment includes cutting or polishing by using a cutter having a fine rough surface. -43- 11. The mold device as claimed in claim 5, wherein the roughening treatment includes processing by using chemical elements or solutions capable of roughening a metal surface. 12. A disk substrate formed by using a mold device from a synthesized resin, comprising: an outer circumferential surface roughened by a separation resisting part having a roughened surface of the mold device. 13. A method of molding a disk substrate by using a mold device including a fixed mold and a movable mold, said method comprising the steps of: filling a molding cavity with a synthesized resin, said molding cavity being formed by the fixed mold and the movable mold and having a stamper for use of transfer as a side surface thereof, said mold device -44- including a separation resisting part arranged on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate, said separation resisting part having a roughened surface; separating the disk substrate formed from the synthesized resin in the cavity from the stamper; and separating the disk substrate from the mold device. 14. The method as claimed in claim 13, wherein the roughened surface of the separation resisting part includes a plurality of dot-like projections or dot-like depressions, or a plurality of line-shaped projections or line-shaped depressions, or a combination of the dot-like and line-shaped projections or depressions distributed on a surface of the separation resisting part. -45- 15. The method as claimed in claim 13 or claim 14, wherein the roughened surface of the separation resisting part includes a resistance generation area not less than 18 mm2; and the roughened surface of the separation resisting part includes at least two rows of projections or depressions in the direction of pulling out the molded disk substrate, and a depth of each of the projections or depressions is in a range from 3 µm to 90 µm. 16. The method as claimed in claim 15, wherein the depth of each of the projections or depressions on the roughened surface of the separation resisting part is in a range from 3 µm to 20 µm. 17. A mold device, substantially as herein described, particularly with reference to the accompanying drawings. 18. A disk substrate, substantially as herein described, particularly with reference to the accompanying drawings. 19. A method of molding a disk, substantially as herein described, particularly with reference to the accompanying drawings. 46 A mold device (3) for forming a disk substrate (4) from a synthesized resin, comprising: a fixed mold (1); and a movable mold (2), said movable mold and the fixed mold forming a cavity (5) in which the disk substrate (4) is molded, wherein a separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold (1) and the movable mold (2) corresponding to an outer circumferential surface of the disk substrate (4) held on one of the fixed mold (1) and the movable mold (2).

Full Text

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BACKGROUND OF THE INVENTION FIELD OF THE INVENTION
The present invention relates to a mold device, a disk substrate, a method of making a disk substrate by using a mold device, and specifically, to a disk substrate used for fabricating an optical disk, being molded from a synthesized resin, a mold device for forming the disk substrate, and a method of molding the substrate.
Description of the Related Art Generally, a disk substrate used for fabricating an optical disk is formed from a synthesized resin such as a polycarbonate resin, by using an injection molding device. The injection molding device includes a fixed mold and a movable mold, which form a cavity corresponding to the disk substrate to be molded. For example, on a surface of the fixed mold that defines the cavity, a projecting and depressed pattern corresponding to musical signals or other information signals is formed, and this is the so-called stamper, which is used for forming pits or pre-grooves constituting tracks representing desired information signals. On the side of the movable mold, a punch is provided to open a hole for locking a centering member at a projecting center portion.
When molding the disk substrate using such a

-3-
mold device, a molten synthesized resin is injected to fill the cavity via a sprue bushing injection port arranged on the fixed mold. Then, after molding the disk substrate in the cavity, the punch is moved to punch the hole for locking the centering member at the center portion, and then pits or pre-grooves are formed on the primary surface of the disk substrate.
Concerning this kind of disk substrate mold device, for example, Japanese Patent Gazette No. 03301103 discloses an invention in which on the side of the movable mold, a separation resistance caused by point-like projections and holes, or ring-shaped projections and grooves formed along the circumferential direction of the movable mold is provided on the outer surface of the disk substrate or on the inner surface of a projection at the center.
In the invention disclosed in the aforesaid Japanese Patent Gazette No. 03301103, the molded disk substrate is separated easily and reliably from the stamper (this is the so-called "first separation"). Here, the disk substrate is molded by a stamper, which has a projecting and depressed pattern for forming pits or pre-grooves as the recording tracks.
However, if it is desired to reduce the time length of the molding cycle, after the step of

-4-
separation of the disk substrate from the stamper, and when separating the disk substrate from the movable mold (this is the so-called "second separation"), the separation resistance, which is caused by point-like projections and holes, or ring-shaped projections and grooves formed along the circumferential direction of the movable mold, increases, and the disk substrate cannot be separated from the movable mold easily. Due to this, as is known, planarity of the disk substrate declines; moreover, the mechanical characteristics vertical vibration, circumferential tilt, and radial tilt decline, and the resulting disk substrate cannot be used to fabricate an optical disk. Especially, recently and continuing, DVD disks such as DVD+R/RW are widely used, and the DVD disks require high speed recording. In order to achieve the high speed recording, the planarity of the disk substrate is important, and disk substrates with the above problems are not suitable.
That is, in the invention disclosed in the aforesaid Japanese Patent Gazette No. 03301103, there exists a resistance against separation of the disk substrate from the stamper due to the separation resisting portion, and the invention is not able to reduce the time length of the molding cycle, but merely

-5-
focuses on performance of separating the disk substrate from the stamper (the first separation).
SUMMARY OF THE INVENTION
It is a general object of the present invention to solve one or more problems of the related art.
A specific object of the present invention is to provide a method capable of reducing a time length of a molding cycle while maintaining planarity of a disk substrate molded via a separation process.
According to a first aspect of the present invention, there is provided a mold device for forming a disk substrate from a synthesized resin that includes a fixed mold and a movable mold, and the movable mold and the fixed mold form a cavity in which the disk substrate is molded. A separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate held on the one of the fixed mold and the movable mold.
In the present invention, the separation resisting part having a roughened surface is provided on an inner surface of the fixed mold or the movable

-6-
mold corresponding to an outer circumferential surface of the disk substrate. The separation resisting part generates a resistance on the outer circumference of the disk substrate when separating the disk substrate, which is formed from a synthesized resin filling the cavity, from a stamper, which acts as a side surface of the cavity, thereby maintaining the planarity of the disk substrate when separating the disk substrate from the stamper. The separation resisting part improves separation ability of the outer circumferential surface of the disk substrate when separating the disk substrate from the mold device. As a result, even when the time length of the molding cycle is reduced for rapid molding, the disk substrate can be separated from the mold device while the planarity of the disk substrate is maintained.
In contrast, the separation resisting portion in the aforesaid Japanese Patent Gazette No. 03301103 merely generates a resistance on the outer circumference of the disk substrate when separating the disk substrate from the stamper.
As an embodiment, the roughened surface of the separation resisting part has a plurality of dotlike projections or dot-like depressions, or a plurality of line-shaped projections or line-shaped

-7-
depressions, or a combination of the dot-like and line-shaped projections or depressions distributed on a surface of the separation resisting part.
As an embodiment, the roughened surface of the separation resisting part has a resistance generation area not less than 18 mm2, the roughened surface of the separation resisting part includes at least two rows of projections or depressions in the direction of pulling out the molded disk substrate, and the depth of each of the projections or depressions is
in a range from 3 µm to 90 µm. More preferably, the depth of each of the projections or depressions on the roughened surface of the separation resisting part is
in a range from 3 µm to 20 µm.
As an embodiment, the roughened surface of the separation resisting part is formed by a roughening treatment on the inner surface of at least one of the fixed mold and the movable mold. Preferably, the roughening treatment may include WPC (Wide Peening and Cleaning) processing, bead blast processing, shot peening processing, micro dimple processing, cutting or polishing by using a cutter having a fine rough surface, and processing by using chemical elements or solutions capable of roughening a metal surface.
According to a second aspect of the present

-8-
invention, there is provided a disk substrate formed from synthesized resin by using a mold device, including an outer circumferential surface roughened by a separation resisting part of the mold device, the separation resisting part having a roughened surface.
According to a third aspect of the present invention, there is provided a method of molding a disk substrate by using a mold device including a fixed mold and a movable mold. The method includes the steps of filling a molding cavity, formed by the fixed mold and the movable mold and having a stamper for use of transfer as a side surface, with a synthesized resin; separating the disk substrate formed from the synthesized resin in the cavity from the stamper; and separating the disk substrate from the mold device.
In the step of filling the cavity, the mold device includes a separation resisting part arranged on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate, and the separation resisting part has a roughened surface.
As an embodiment, the roughened surface of the separation resisting part includes a plurality of dot-like projections or dot-like depressions, or a plurality of line-shaped projections or line-shaped

-9-
depressions, or a combination of the dot-like and line-shaped projections or depressions distributed on a surface of the separation resisting part.
As an embodiment, the roughened surface of the separation resisting part includes a resistance generation area not less than 18 mm2; the roughened surface of the separation resisting part includes at least two rows of projections or depressions in the direction of pulling out the molded disk substrate; and a depth of each of the projections or depressions is in
a range from 3 µm to 90 µm. More preferably, the depth of each of the projections or depressions on the roughened surface of the separation resisting part is in a range from 3 µm to 20 µm.
Accordingly, the present invention provides a mold for forming a disk substrate
from a synthesized resin, comprising: a fixed mold; and a movable mold, said movable mold and the fixed mold forming a cavity in which the disk substrate is molded, wherein a separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate held on one of the fixed mold and the movable mold.

-9A-
The present invention also provides a disk substrate formed by using a mold device from a synthesized resin, comprising: an outer circumferential surface roughened by a separation resisting part having a roughened surface of the mold device.
The present invention further provides a method of molding a disk substrate by using a mold device including a fixed mold and a movable mold, said method comprising the steps of: filling a molding cavity with a synthesized resin, said molding cavity being formed by the fixed mold and the movable mold and having a stamper for use of transfer as a side surface thereof, said mold device including a separation resisting part arranged on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate, said separation resisting part having a roughened surface; separating the disk substrate formed from the synthesized resin in the cavity from the stamper; and separating the disk substrate from the mold device.
These and other objects, features, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments given with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIGs. 1A and 1B are side cross-sectional views of an exemplary structure of a mold device for forming a disk substrate according to an embodiment of the present invention, where FIG. 1A shows an open

-10-
state of the mold device, and FIG. 1B shows a closed state of the mold device;
FIG. 2 is a table showing characteristics of samples for explaining the separation resisting part 15, of the present embodiment in comparison with the related art;
FIG. 3 is a table showing shapes and characteristic values of the separation resisting part 15 of the present embodiment in comparison with the related art.
FIGs. 4A and 4B show examples of measured surface roughness;
FIG. 5 shows a relation between shapes of the roughened surface and the time length of the molding cycle;
FIG. 6 shows a relation between the depth of the unevenness on the roughened surface and the time length of the molding cycle, illustrating effects of the second separation;
FIG. 7 is a perspective view of the cavity-ring 12;
FIG. 8 is a cross-sectional view of the roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 processed by WPC with a square material being used;

-11-
FIG. 9 is a cross-sectional view of the roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 processed by WPC with a spherical material being used; and
FIGs. 10A through 10D are cross-sectional views of the roughened surface of the separation resisting part 15 along the arrow B in FIG. 7, illustrating examples of shapes of the roughened surface of the separation resisting part 15 processed by cutting or polishing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Below, preferred embodiments of the present invention are explained with reference to the accompanying drawings.
In the following, as an example, descriptions are made of a mold device for forming a disk substrate used in fabrication of an optical disk such as a DVD-related disk (DVD+R or others), and a method of molding the disk substrate by using the mold device.
FIGs. 1A and 1B are side cross-sectional views of an exemplary structure of a mold device 3 for forming a disk substrate according to an embodiment of the present invention, where FIG. 1A shows an open

-12-
state of the mold device, and FIG. 1B shows a closed state of the mold device.
As illustrated in FIG. 1A, the mold device includes a fixed mold 1 and a movable mold 2 that is movably supported by a hydraulic mechanism (not shown) and is able to move in directions approaching toward and moving away from the fixed mold 1. Between the fixed mold 1 and the movable mold 2, there is formed a cavity 5 where a disk substrate 4 is to be molded.
On the side of the fixed mold 1, a sprue bushing 6 is provided at the center of the cavity 5 through which flows synthesized resin, such as molten polycarbonate resin, supplied from a not-illustrated injection molding apparatus. At the center of the sprue bushing 6, there is a nozzle 6a for injecting resin, and the synthesized resin supplied from the not-illustrated injection molding apparatus is injected into the cavity 5 through the nozzle 6a.
Around the outer circumference of the sprue bushing 6, a not-illustrated holder is provided, into which a not-illustrated inner side stamper support is fit to support the inner side of a stamper 7 (described below).
On a surface of the fixed mold 1 that defines the cavity 5, the stamper 7 is mounted, which

-13-
is for molding a projecting and depressed pattern corresponding to information signals recorded on an optical disk, the projecting and depressed pattern including pits or pre-grooves constituting recording tracks on the signal recording area of the optical disk. The inner circumference of the center hole of the stamper 7 is supported by the not-illustrated inner side stamper support that is fit into the not-illustrated holder, and the outer circumference of the center hole of the stamper 7 is fixed by suction of air coming from a suction port (not illustrated).
At the center of a surface of the movable mold 2 that defines the cavity 5, a recess 9 is provided to form, together with the fixed mold 1, a projecting portion on the other primary surface of the disk substrate 4. At the center of the recess 9, a punch mechanism 10 is provided to punch a hole for locking a centering member at the center of the projecting portion. The punch mechanism 10 is arranged in the movable mold 2 and is movable in a sleeve 11. An ejector 14 is supported by the sleeve 11 to be able to move relative to the movable mold 2 so as to stick out and separate the disk substrate 4 after being molded.
On the outer surface of the movable mold 2, a cavity-ring 12 is provided that defines the cavity 5

-14-
and molds the outer circumference of the disk substrate 4 to be molded. The front end surface of the cavity-ring 12 functions as a flat impacting surface, and is arranged so as to be able to contact the periphery of the stamper 7 attached to the fixed mold 1. When the movable mold 2 is moved to make contact with the fixed mold 1 so that of the mold device 3 is in a closed state, as illustrated in FIG. 1B, the flat impacting surface is brought into contact with the stamper 7 to form a closed cavity 5.
The molding surface of the movable mold 2 is for forming the other primary surface of the disk substrate 4, which is a precise flat surface acting as a laser beam incident surface of the disk substrate 4. Therefore, the molding surface of the movable mold 2 is also a precise flat surface, for example, a mirror surface 13.
After the disk substrate 4 is molded, and when the movable mold 2 is moved away from the fixed mold 1 (the first separation), the disk substrate 4 is held on the side of the movable mold 2, and then the ejector 14 in the movable mold 2 is stuck out to separate the disk substrate 4 from the movable mold 2 (the second separation).
With the above basic structure of the mold

-15-
device 3, when molding the disk substrate 4, the movable mold 2 is moved and brought into contact with the fixed mold 1, and the mold device 3 is in the closed state, as illustrated in FIG. 1B. In this state, synthesized resin, such as molten polycarbonate resin, supplied from a not-illustrated injection molding apparatus is injected into the cavity 5 through the nozzle 6a. Then, the punch mechanism 10 is moved to punch the hole for locking the centering member at the center of the projecting portion of the disk substrate. After that, the movable mold 2 is further moved toward the fixed mold 1 to compress the synthesized resin filling the cavity 5 for clamping. Therefore, the disk substrate 4 corresponding to the cavity 5 is molded.
After the disk substrate 4 is molded, the movable mold 2 is moved away from the fixed mold 1 (the first separation), and thereby, the disk substrate 4 is separated from the stamper 7. At this moment, the disk substrate 4 is held on the side of the movable mold 2. Subsequently, the ejector 14 in the movable mold 2 is stuck out to separate the disk substrate 4 from the movable mold 2 (the second separation).
In the present embodiment, a separation resisting part 15 having a roughened surface is formed on the inner surface of the cavity-ring 12

-16-
corresponding to the outer circumference of the disk substrate 4. The inner surface of the separation resisting part 15 is roughened by distributing dots, or lines, or their combinations on the inner surface of the cavity-ring 12, specifically, by small point-like projections and depressions scattering on the inner surface of the cavity-ring 12, or projecting and depressed lines scattering or crossing with each other on the inner surface of the cavity-ring 12, or their combinations.
For example, the separation resisting part 15 has a roughened surface of an area of 18 mm2 or more to generate a resistance in the direction of pulling out the disk substrate 4, and the size of the
roughness is 3 µm to 90 µm.
The separation resisting part 15 generates a resistance on the outer circumference of the disk substrate 4 when separating the disk substrate 4 formed from the synthesized resin filling the cavity 5 from the stamper 7, and indicates separation ability of the outer circumference of the disk substrate 4 when separating the disk substrate 4 from the movable mold 2.
By providing the separation resisting part 15 on the inner surface of the cavity-ring 12, when

-17-
molding the disk substrate 4, the outer circumference of the disk substrate 4 is roughened, generating a roughened portion 4a, corresponding to the roughness of the separation resisting part 15. Then, when separating the molded disk substrate 4 from the stamper 7, the separation resisting part 15 generates a resistance on the roughened portion 4a of the outer circumference of the disk substrate 4 to maintain the state of the disk substrate 4 being held to the movable mold 2. Thereby, the disk substrate 4 can be separated from the stamper 7 reliably without declination of the vertical vibration, peripheral tilt, and radial tilt characteristics, accordingly maintaining sufficiently high planarity, and therefore, the resulting disk substrate can be transferred to the movable mold 2 reliably (first separation).
Furthermore, when separating the disk substrate 4 from the movable mold 2 (second separation), because the roughness of the separation resisting part 15 shows the ability to separate from the roughened portion 4a of the outer circumference of the disk substrate 4, even if the time for the disk substrate 4 to contract is not so long, in other words, even if the time length of the molding cycle is reduced for rapid molding, the disk substrate 4 can be

-18-
separated easily with the outer end surfaces of the disk substrate 4 not being impeded by the cavity-ring 12, and maintaining sufficiently high planarity.
It should be noted that although the roughened portion 4a is formed on the outer end surfaces of the disk substrate 4 corresponding to the separation resisting part 15, because information signals are not recorded on the outer end surfaces of the disk substrate 4, the roughened portion 4a does not influence the signal recording area on the disk substrate.
In the above, although it is described that the stamper 7 is mounted on the fixed mold 1, and the punch mechanism 10 is arranged on the movable mold 2, an arrangement in the opposite way can also be adopted.
Below, methods of fabricating the separation resisting part 15 and quantitative characteristics of the roughness of the separation resisting part 15 are described in comparison with the related art.
For the purpose of comparison, mold samples No. 1, No. 2, and No. 3 were made in accordance with the aforesaid Japanese Patent Gazette No. 03301103, and mold samples No. 4 and No. 5 were made in accordance with the present embodiment. Characteristics of these mold samples are summarized in a table in FIG. 2.

-19-
FIG. 2 is a table showing characteristics of samples for explaining the separation resisting part 15 of the present embodiment in comparison with the related art.
FIG. 3 is a table showing shapes and characteristic values of the separation resisting part 15 of the present embodiment in comparison with the related art.
As shown in the table in FIG. 2, in the first sample, 24 square recesses each having an area of 0.2 x 0.2 mm2 are uniformly arranged on the inner surface of the cavity-ring in one row along a circumference of the cavity-ring. The total length a of the recesses along a circumference of the cavity-ring amounts to 4.8 mm, and the depth b of the recesses is 0.2 mm, hence the total area of the recesses, which contributes to generation of a resistance (below, referred to as "resistance area"), amounts to 0.96 mm2.
In the second sample, a ring-shaped recess having a 0.1mm x 0.1 mm square cross section (referring to FIG. 3) is formed on the inner surface of the cavity-ring along a circumference of the cavity-ring, the length a of the ring-shaped recess along the circumference of the cavity-ring is 376.99 mm, and the depth b of the recess is 0.1 mm; hence the total area

-20-
of the ring-shaped recess contributing to generation of a resistance (that is, the resistance area) amounts to 37.70 mm2.
In the third sample, a ring-shaped recess having a 0.05 mm x 0.05 mm square cross section (referring to FIG. 3) is formed on the inner surface of the cavity-ring along a circumference of the cavity-ring, the length a of the ring-shaped recess along the circumference of the cavity-ring is 376.99 mm, and the depth b of the recess is 0.05 mm; hence, the total area of the ring-shaped recess contributing to generation of a resistance (that is, the resistance area) is 18.85 mm2.
In the fourth sample, as the separation resisting part 15, the entire inner surface of the cavity-ring 12 is roughened along the circumference of the cavity-ring 12, and the roughness (an averaged depth of the projecting or depressed portions) of the roughened surface is 0.020 mm. The length a of the separation resisting part 15 along the circumference of the cavity-ring 12 is 376.99 mm, the average depth b of the projecting or depressed portions is 0.02 mm, and there are twelve rows of the projecting or depressed portions along the direction of pulling out the disk substrate 4; therefore, the total area of the roughened

-21-
surface of the separation resisting part 15 (that is, the resistance area) amounts to 45.24 mm2.
In the fifth sample, as the separation resisting part 15, the entire inner surface of the cavity-ring 12 is roughened along the circumference of the cavity-ring 12 (referring to FIG. 3), and the roughness (an averaged depth of the projecting or depressed portions) of the roughened surface is 0.012 mm. The length a of the separation resisting part 15 along the circumference of the cavity-ring 12 is 376.99 mm, the average depth b of the projecting or depressed portions is 0.012 mm, and there are about thirteen rows of the projecting or depressed portions along the direction of pulling out the disk substrate 4; therefore, the total area of the roughened surface of the separation resisting part 15 (that is, the resistance area) amounts to 29.41 mm2.
When estimating the resistance areas of the fourth sample and the fifth sample, because a cross section of each depressed portion on the inner surface of the cavity-ring 12 can be approximated to be a triangle, the resistance area d of each depressed portion was calculated by using the formula d=(a*b)/2*c.
The surface roughness mentioned above was

-22-
measured by using a Form Taly-Surf S6 (produced by Taylor Hobson) surface roughness measurement instrument.
FIGs. 4A and 4B show examples of measured surface roughness.
FIG. 4A and FIG. 4B show the surface roughness of the same location of the separation resisting part 15, but data shown in FIG. 4A were obtained by making a measurement every 3 mm, whereas data shown in FIG. 4B were obtained by making a measurement every 1 mm in order to more clearly display the surface roughness by a graph. The numbers of rows in the fourth sample and the fifth sample, which are displayed in the table in FIG. 2, were obtained by counting on the actually measured graph assuming the thickness of the disk substrate to be 0.6 mm.
Below, based on the above results of the five samples, evaluation was made on the relation between the samples and the time for a molding cycle, and on mechanical characteristics of the samples. For evaluation of the mechanical characteristics, as illustrated in FIG. 3, the time length of molding cycle, peripheral axial acceleration, peripheral radial tilt and the peripheral circumferential tilt were measured, and the mechanical characteristics were

-23-
evaluated based on these measured quantities.
Here, the "peripheral radial tilt" indicates bending of the disk substrate in the radial direction in terms of angle. A small value of the peripheral radial tilt is desirable, because if the peripheral radial tilt becomes too large, it influences the offset and amplitudes of a push-pull signal obtained from an optical disk fabricated with the subject substrate.
The "peripheral circumferential tilt" indicates bending of the disk substrate in the circumferential direction in terms of angle. Similarly, a small value of the peripheral circumferential tilt is desirable.
The "peripheral axial acceleration" indicates the acceleration of a recording layer in a direction perpendicular to a reference plane when the rotational speed is 16 Hz (960 rpm, CAV control). If the peripheral axial acceleration becomes too large due to unevenness of the disk surface, response performance, tracking performance, and stability of focus servo or tracking servo may be influenced for an optical disk fabricated with the subject substrate.
Recently and continuing, in DVD disks, which require high speed recording, quality related to the peripheral axial acceleration is attracting more and

-24-
more attention. For example, according to the Orange Book, in DVD+R/RW, a residual focus/tracking error is defined; converting this quantity into the peripheral axial acceleration, it turns out that a peripheral axial acceleration less than 2.1 m/s2 is required. In the present embodiment, when the peripheral axial acceleration is less than 2.1 m/s2, the mechanical characteristic is evaluated to be good.
As for "time length of molding cycle", an object value is set to be 5.5 seconds.
The above mechanical characteristics are measured by using an instrument called "Brief-126P" fabricated by Dr. Schenk.
First, it is found that when the speed of opening the mold is constant, a reference of determining whether a resistance arises when separating the disk substrate from the stamper (the first separation) is that the resistance area in the direction of pulling out the disk substrate is greater than 18 mm2. In the first separation, if the resistance area is less than 18 mm2 in the direction of pulling out the disk substrate, it is found that the disk substrate cannot be separated from the stamper properly.
Therefore, because the resistance area of

-25-
the first sample is less than 18 mm2 in the direction of pulling out the disk substrate, no matter how much is the time length of the molding cycle when using this mold sample, it is sure that the first mold sample cannot form disk substrates meeting predetermined requirements.
Concerning the second sample, as illustrated in FIG. 3, if the time length of molding cycle is 9.6 seconds, the peripheral axial acceleration is 1.4 m/s2.
As for the third sample, as illustrated in FIG. 3, if the time length of molding cycle is 8.4 seconds, the peripheral axial acceleration becomes 1.6 m/s2. For comparison, if the time length of molding cycle is reduced to be 6.7 seconds, the peripheral axial acceleration becomes 4.7 m/s2; furthermore, bending (tilt) occurs on the surface of the disk substrate in a region with the disk radius R ranging from 50 mm to 57 mm, and hence the mechanical characteristics of the third sample were evaluated to be bad.
On the other hand, in the case of the fifth sample, as illustrated in FIG. 3, even when the time length of molding cycle is reduced to be 5.5 seconds, which is the object value, the peripheral axial acceleration becomes 1.7 m/s2, and the peripheral

-26-
radial tilt and the peripheral circumferential tilt are also sufficiently small; thus, the mechanical characteristics of the fifth sample are evaluated to be good.
FIG. 5 shows a relation between shapes of the roughened surface and the time length of the molding cycle.
According to the above description and as illustrated in FIG. 5, it is necessary to provide a plurality of rows of projections or depressions (unevenness) along the direction of pulling out the disk substrate; furthermore, when the depth of the unevenness is 0.09 mm or so, the time length of the molding cycle can be reduced to 9 seconds, when the depth of the unevenness is 0.05 mm or so, the time length of the molding cycle can be reduced to 7 seconds, and when the depth of the unevenness is 0.02 mm or so, the time length of the molding cycle can be reduced to 5.5 seconds, which is the object value.
In other words, with a fine roughened surface, as those of the fourth sample and the fifth sample, the resistance area increases, and accordingly, the resistance increases. On the other hand, shallow unevenness results in good mechanical characteristics. When separating the disk substrate from the stamper

-27-
(the first separation), a large resistance area in the direction of pulling out the disk substrate is desirable.
When taking the disk substrate out from the mold device 3 (the second separation), shallow unevenness is desirable especially when the time length of the molding cycle is reduced in order to achieve rapid molding, and there is not a sufficiently long time for the disk substrate to cool and contract. Because the shallow unevenness results in a small resistance, it is easy to pull the disk substrate out.
In comparison, with a mold according to the above-mentioned Japanese Patent Gazette No. 03301103, which includes a separation resisting part having only one row of ring-shaped unevenness in the direction of pulling out the disk substrate being desirable, as in the second and third samples illustrated in the table in FIG. 2, even when the time length of the molding cycle is still as long as 6.7 seconds as in the case of the third sample, declination of quality of mechanical characteristics in the peripheral radial direction occurs due to the resistance in the second separation. Because the disk substrate is pulled out with the end surface of the disk substrate being jammed, bending (tilt) occurs on the surface of the disk substrate in a

-28-
region with the disk radius R from 50 mm to 57 mm.
To the contrary, with a fine roughened surface, as that of the fifth sample, the resistance area increases in the direction of pulling out the disk substrate. In addition, with shallow unevenness, good mechanical characteristics are obtainable even when the time length of the molding cycle is reduced to 5.5 seconds.
The quantity of depth of unevenness is further examined below.
When the depth of the unevenness is in a range from 3 µm to 90 µm, preferably, from 3 µm to 20 µm, the separation resisting part 15 shows sufficiently good performance. For example, the depth
of the unevenness is 12 µm in the fifth sample 5.
If the depth of unevenness is less than 3
µm, the projections of the roughened surface are so fine that they do not have sufficient strength and can be crushed easily. For this reason, a sufficiently large resistance cannot be obtained when separating the disk substrate from the stamper. To the contrary, if the depth of unevenness is not less than 3 µm, a sufficiently large resistance can be generated when separating the disk substrate from the stamper.
If the depth of unevenness is greater than

-29-
90 µm, with a short molding cycle, the resistance is too large, that is, the ability of separation is too low, when separating the disk substrate from the movable mold. While, if the depth of unevenness is not greater than 90 µm, even if the molding cycle is shortened, a sufficiently large ability of separation can be obtained.
FIG. 6 shows a relation between the depth of the unevenness on the roughened surface and the time length of the molding cycle, illustrating effects of the second separation, where the abscissa indicates the time length of the molding cycle and the ordinate indicates the depth of the unevenness.
In the example shown in FIG. 6, it is
assumed that the disk substrate shrinks by 90 µm when the time length of the molding cycle is 9 seconds, by 50 µm when the time length of the molding cycle is 7 seconds, and by 20 µm when the time length of the molding cycle is 9 seconds.
As illustrated in FIG. 6, under the conditions that the resistance area is not less than 18 mm2, and there are more than two rows of projections or depressions (unevenness) in the direction of pulling out the disk substrate, when the depth of the unevenness decreases, even when the time length of

-30-
molding cycle is shortened and there is not a sufficiently long time for the disk substrate to cool and shrink, because of a small resistance due to the shallow unevenness, it is easy to pull the disk substrate out in the second separation.
In FIG. 6, regions X, Y and Z are preferable for molding. Nevertheless, the regions X and Y are preferable for a reduced molding cycle, because in the regions X and Y, the depth of the unevenness is in a range from 3 µm to 20 µm, being suitable for a shortened molding cycle, particularly, a molding cycle less than the object value of 5.5 seconds.
Furthermore, the region X is a preferable region, because in the region X, the resistance area, which is important to the first separation, is not less than 18 mm2, and the depth of the unevenness is in a
range from 12 µm to 20 µm.
The separation resisting part 15 of the fourth sample and the fifth sample, which include roughened surfaces, can be formed by various roughening treatments. In the present embodiment, a WPC (Wide Peening and Cleaning) process is used to form the separation resisting part 15.
In the present embodiment, in order to obtain ideal surface roughness, the roughening process

-31-
is performed through two steps with materials having different roughness and shapes. For example, in the first step, use is made of a square aluminum oxide
having an average granular size of 300 µm, while in the second step, use is made of spherical ceramic beads
having an average granular size of 45 Mm.
The shot pressure is 4.0 gf/cm2 in both the first step and the second step. The spray distance of the nozzle (that is, the distance to the object to be processed) is 7 cm. As for the processing time, the object is rotated twice so that each part thereof is processed for 30 seconds. Although sufficient roughness can be obtained in the first rotation, the roughness is made stable in the second rotation. By such a WPC processing, uniform surface roughness can be obtained easily.
FIG. 7 is a perspective view of the cavity-ring 12.
FIG. 8 is a cross-sectional view of the roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 processed by WPC.
In FIG. 8, a roughened surface of point-like projections and depressions is formed by the WPC, and a square material is used in the WPC.
The roughened surface of the separation

-32-
resisting part 15 along the arrow B in FIG. 7 processed by WPC has the same cross-section as that in FIG. 8.
The method of forming the separation resisting part 15 is not limited to the WPC. For example, use can be made of any of bead blast, shot peening, micro-dimple processing, cutting or polishing with a cutter having a fine rough surface, or processing by using chemical elements or solutions capable of roughening a metal surface.
The bead blast, in which air is blasted on the mold, shot peening, and micro-dimple processing, are substantially the same as the aforesaid WPC, and the injection pressure, materials, and processing procedures are also the same as those of WPC.
In WPC, shot peening, micro-dimple processing, and bead blast, if square materials are used to impinge a metal surface at high speed to form a roughened surface having point-like projections and depressions, the obtained roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 has the same cross-section as that in FIG. 8, that is, the same as that produced by WPC.
FIG. 9 is a cross-sectional view of the roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 when using spherical

-33-
material.
That is, in WPC, shot peening, micro-dimple processing, and bead blast, if spherical materials are used to impinge a metal surface at high speed to form a roughened surface having point-like projections and depressions, the obtained roughened surface of the separation resisting part 15 along the arrow A in FIG. 7 has the cross-section as shown in FIG. 9.
As long as the resistance area is not less than 18 mm2, either of the separation resisting parts 15 in FIG. 8 or FIG. 9 is adoptable.
In FIG. 8, because the cross section of each depression can be approximated to be a simple triangle, the resistance area d of each of the depressions can be simply calculated by using the formula d=(a*b)/2*c, where, a is the average depth of the unevenness, b is the circumference of the roughened surface, and c is the number of rows of the unevenness in the direction of pulling out the disk substrate 4.
FIGs. 10A through 10D are cross-sectional views of the roughened surface of the separation resisting part 15 along the arrow B in FIG. 7, illustrating examples of shapes of the roughened surface of the separation resisting part 15 processed by cutting or polishing.

-34-
During the cutting or polishing process, the inner surface of the cavity-ring 12 is cut while the cavity-ring 12 is being rotated, thus forming roughened surfaces having the same shapes as those of the cutter. In FIG. 10A and FIG. 10B, the cutter has a fine rough surface.
As long as the resistance area is not less than 18 mm2, any of the roughened surfaces in FIGs. 10A through 10C is adoptable. The roughened surface in FIG. 10D, however, is not usable because the disk substrate cannot be separated even after the disk substrate cools and contracts.
Similarly, in the process using chemical elements or solutions capable of roughening a metal surface, the resistance area can be obtained in the following way. First, the resistance area generated per unit of the chemical element or solution is determined, and this quantity is multiplied by the circumference b of the roughened surface and by the number (c) of rows of the unevenness in the direction of pulling out the disk substrate 4. With the obtained resistance area, it can be determined whether the obtained roughed surface is usable or not.
While the present invention is described with reference to specific embodiments chosen for

-35-
purpose of illustration, it should be apparent that the invention is not limited to these embodiments, but numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.
According to the present invention, the separation resisting part having a roughened surface is provided on an inner surface of the fixed mold or the movable mold corresponding to an outer circumferential surface of the disk substrate. When separating the disk substrate formed from synthesized resin filling the cavity from a stamper, which acts as a side surface of the cavity, the separation resisting part generates a resistance on the outer circumference of the disk substrate, thereby maintaining the planarity of the disk substrate when separating the disk substrate from the stamper. The separation resisting part improves separation ability of the outer circumferential surface of the disk substrate when separating the disk substrate from the mold device. As a result, even when the time length of the molding cycle is reduced for rapid molding, the disk substrate can be separated from the mold device while the planarity of the disk substrate is maintained. Therefore, even when the time length of molding cycle is reduced in order for rapid

-36-
molding to occur, it is possible to fabricate disks with high planarity of the disk substrate for use as high speed DVD disks.
In addition, the roughened surface of the separation resisting part has a plurality of dot-like projections or dot-like depressions, or a plurality of line-shaped projections or line-shaped depressions, or a combination of the dot-like and line-shaped projections or depressions distributed on a surface of the separation resisting part, and the roughened surface of the separation resisting part has a resistance generation area not less than 18 mm2. The roughened surface of the separation resisting part includes at least two rows of projections or depressions in the direction of pulling out the molded disk substrate, and the depth of each of the projections or depressions is in a range from 3 µm to 90 µm, more preferably, from 3 µm to 20 µm. Therefore, the separation resisting part is able to reliably generate the resistance in the first separation and improve separation ability of the disk substrate in the second separation.
Specifically, if the depth of unevenness is less than 3 µm, the projections of the roughened surface are so fine that they do not have sufficient

-37-
strength and can be crushed easily, and a sufficiently large resistance cannot be obtained when separating the disk substrate from the stamper. To the contrary, if
the depth of unevenness is not less than 3 µm, a sufficiently large resistance can be generated when separating the disk substrate from the stamper.
If the depth of unevenness is greater than 90 µm, in a short molding cycle, the resistance is too large, that is, the ability of separation is too low, when separating the disk substrate from the movable mold. In contrast, if the depth of unevenness is not greater than 90 µm, even when the molding cycle is shortened, a sufficiently large ability of separation can be obtained.
The roughened surface of the separation resisting part can be formed by a roughening treatment, for example, by WPC (Wide Peening and Cleaning) processing, bead blast processing, shot peening processing, micro dimple processing, cutting or polishing by using a cutter having a fine rough surface, and processing by using chemical elements or solutions capable of roughening a metal surface. By these processing methods, uniform surface roughness capable of generating the resistance in the first separation and improving separation ability of the disk

-38-
substrate in the second separation can be obtained
easily.

-39-
WE CLAIM:
1. A mold device for forming a disk
substrate from a synthesized resin, comprising:
a fixed mold; and
a movable mold, said movable mold and the fixed mold forming a cavity in which the disk substrate is molded,
wherein a separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate held on one of the fixed mold and the movable mold.
2. The mold device as claimed in claim 1,
wherein the roughened surface of the separation
resisting part has a plurality of dot-like projections
or dot-like depressions, or a plurality of line-shaped

-40-
projections or line-shaped depressions, or a combination of the dot-like and line-shaped projections or depressions distributed thereon.
3. The mold device as claimed in claim 1 or
claim 2, wherein
the roughened surface of the separation resisting part has a resistance generation area not less than 18 mm2; and
the roughened surface of the separation resisting part includes at least two rows of the projections or depressions in the direction of pulling out the molded disk substrate, and a depth of each of the projections or depressions is in a range from 3 µm to 90 µm.
4. The mold device as claimed in claim 1 or
claim 3, wherein the depth of each of the projections
or depressions on the roughened surface of the

-41-
separation resisting part is in a range from 3 µm to 20 µm.
5. The mold device as claimed in any of claims 1 through 4, wherein the roughened surface of the separation resisting part is formed by roughening treatment on the inner surface of at least one of the fixed mold and the movable mold.
6. The mold device as claimed in claim 5, wherein the roughening treatment includes WPC (Wide Peening and Cleaning) processing.
7. The mold device as claimed in claim 5, wherein the roughening treatment includes bead blast processing.

-42-
8. The mold device as claimed in claim 5, wherein the roughening treatment includes shot peening processing.
9. The mold device as claimed in claim 5, wherein the roughening treatment includes micro dimple processing.
10. The mold device as claimed in claim 5,
wherein the roughening treatment includes cutting or
polishing by using a cutter having a fine rough
surface.

-43-
11. The mold device as claimed in claim 5, wherein the roughening treatment includes processing by using chemical elements or solutions capable of roughening a metal surface.
12. A disk substrate formed by using a mold
device from a synthesized resin, comprising:
an outer circumferential surface roughened by a separation resisting part having a roughened
surface of the mold device.
13. A method of molding a disk substrate by using a mold device including a fixed mold and a movable mold, said method comprising the steps of:
filling a molding cavity with a synthesized resin, said molding cavity being formed by the fixed mold and the movable mold and having a stamper for use of transfer as a side surface thereof, said mold device

-44-
including a separation resisting part arranged on an inner surface of at least one of the fixed mold and the movable mold corresponding to an outer circumferential surface of the disk substrate, said separation resisting part having a roughened surface;
separating the disk substrate formed from the synthesized resin in the cavity from the stamper; and
separating the disk substrate from the mold device.
14. The method as claimed in claim 13, wherein the roughened surface of the separation resisting part includes a plurality of dot-like projections or dot-like depressions, or a plurality of line-shaped projections or line-shaped depressions, or a combination of the dot-like and line-shaped projections or depressions distributed on a surface of the separation resisting part.

-45-
15. The method as claimed in claim 13 or
claim 14, wherein
the roughened surface of the separation resisting part includes a resistance generation area not less than 18 mm2; and
the roughened surface of the separation resisting part includes at least two rows of projections or depressions in the direction of pulling out the molded disk substrate, and a depth of each of the projections or depressions is in a range from 3 µm to 90 µm.
16. The method as claimed in claim 15,
wherein the depth of each of the projections or
depressions on the roughened surface of the separation
resisting part is in a range from 3 µm to 20 µm.

17. A mold device, substantially as herein described, particularly with reference to the accompanying drawings.
18. A disk substrate, substantially as herein described, particularly with reference to the accompanying drawings.
19. A method of molding a disk, substantially as herein described, particularly with reference to the accompanying drawings.
46
A mold device (3) for forming a disk substrate (4) from a synthesized resin, comprising: a fixed mold (1); and a movable mold (2), said movable mold and the fixed mold forming a cavity (5) in which the disk substrate (4) is molded, wherein a separation resisting part having a roughened surface is provided on an inner surface of at least one of the fixed mold (1) and the movable mold (2) corresponding to an outer circumferential surface of the disk substrate (4) held on one of the fixed mold (1) and the movable mold (2).

Documents:

00595-kol-2004 abstract.pdf

00595-kol-2004 assignment.pdf

00595-kol-2004 claims.pdf

00595-kol-2004 correspondence.pdf

00595-kol-2004 description(complete).pdf

00595-kol-2004 drawings.pdf

00595-kol-2004 form-1.pdf

00595-kol-2004 form-18.pdf

00595-kol-2004 form-2.pdf

00595-kol-2004 form-3.pdf

00595-kol-2004 form-5.pdf

00595-kol-2004 letters patent.pdf

00595-kol-2004 p.a.pdf

00595-kol-2004 priority document others.pdf

00595-kol-2004 priority document.pdf

00595-kol-2004 riply f.e.r.pdf

595-KOL-2004-CORRESPONDENCE.pdf

595-KOL-2004-FORM 27.pdf

595-KOL-2004-FORM-27.pdf

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Patent Number

207102

Indian Patent Application Number

595/KOL/2004

PG Journal Number

21/2007

Publication Date

25-May-2007

Grant Date

23-May-2007

Date of Filing

27-Sep-2004

Name of Patentee

RICOH COMPANY LTD.

Applicant Address

3-6, NAKAMAGOME 1-CHOME,OHTA-KU,TOKYO 143-8555

Inventors:

#	Inventor's Name	Inventor's Address
1	KOGA NOBORU	2-1-13,MIWAMIDORIYAMA,MACHIDA-SHI,TOKYO,

PCT International Classification Number

B29C 45/24

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2003-339565	2003-09-30	Japan
2	2004-251861	2004-08-31	Japan