| Title of Invention | "OPTICAL INFORMATION RECORDING MEDIA" |
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| Abstract | An optical information recording medium which comprises a substrate, an information layer carried on one side of the substrate, and a protective layer covering the outer surface of the information layer wherein the protective layer is constituted by a first protective layer covering the outer surface of the information layer, a second protection layer covering the outer surface of the first protective layer, and a third protective layer covering the outer surface of the second protective layer, and the hardness of the second protective layer is made lower than those of the first and the third protective layer, wherein composition of matter as a first protective layer includes at least a kind of resin among acryl ester, acrylic special acrilate, acrilate ester, monomer ester and alicyclic monomer, composition of matter as a second protective layer includes at least a kind of resin among polyurethane acrilate and esthers acrilate, composition of matter as a third protective layer includes at least a kind of resin among acryl ester, acrylic special acrilate, acrilate ester, monomer ester and alicyclic monomer. |
| Full Text | - 1 - The Present Application rates to "An Optical information Recording Medium". FIELD OF THE INVENTION This invention also relates to optical information recording media such as optical disk, magneto-optical disk, and magnetic disk, and particularly relates to bare-type optical information recording media to be mounted into a disk drive without being housed in a cartridge case. BACKGROUND OF THE INVENTION Conventionally, various bare-type optical information recording media to be mounted into a disk drive without being housed in a cartridge case are commercially made available, such as CD (Read only type compact disk), CD-R (Recordable type compact disk), and CD-RW (Rewritable compact disk). Such optical information recording media are susceptible to damage of disk and reduced medium life time, compared with optical information recording media held in a cartridge case and to be mounted into a disk drive as housed in the cartridge case such as MO (3.5 inch magneto-optical recording media). Therefore, reinforcement of protective layer covering the information layer is conventionally attempted. Reinforcing measures proposed before include (a) covering the information layer with a plurality of - 2 - hard protective layers, (b) covering the surface of the information layer with a soft first protective layer and covering the surface of the first protective layer with a hard second layer, and (c) covering the surface of the information layer with a hard first layer and covering the surface of the first protective layer with a soft second protective layer. Covering the information layer with a plurality of hard protective layers increase the rigidity of the protective layer so that the point pressure applied to the protective layer can be widely dispersed and the point pressure acting on the information layer can be released. Further, a hard protective layer is located on the surface so that the protective layer is insusceptible to scratches. This measure, however, can not absorb the point pressure applied to the surface of the protective layer. In addition, the thickness of the protective layer is limited by the standard, cost, characteristic etc., and the rigidity of the protective layer can not be unlimitedly increased, so it is difficult to release enough the point pressure acting on the information layer, so that the destruction of the information layer due to the point pressure can not be eliminated. On the other hand, covering the outer surface of the information layer with a first soft layer and covering the surface of the first protective layer with a second hard protective layer can absorb the point - 3 - pressure acting on the second protective layer by the first protective layer, so that the point pressure acting on the information layer can be released and the destruction of the information layer due to the" point pressure can be reduced. Further, a hard protective layer is located on the surface so that the protective layer is insusceptible to scratches. In this measure, however, a first soft protective layer is located on the surface of the information layer and the force in the facial direction caused by the deformation of the first protective layer acts directly on the information layer, so that the destruction of the information layer can not effectively prevented if the information layer is formed of a soft organic compound such as a dye. In addition, it is susceptible to a peeling of the first protective layer from the information layer. Further, covering the outer surface of the information layer with a first hard protective layer and covering the first protective layer with a second soft protective layer can absorb the point pressure acting on the second protective layer by the softly of the second protective layer, so that the point pressure acting on the information layer can be released and the destruction of the information layer due to the point pressure can be reduced. In this measure, however, a soft layer is located on the surface so that it is susceptible to scratches in the second protective layer when a hard material slip-contacts with it and is - 4 - susceptible to poor esthetic appearance of the optical information recording medium. In addition, this measure has a problem that once a scratch occurs, the point pressure acting on the information layer increases quickly because a hard material directly contacts with the first hard protective layer, so it is susceptible to the destruction of the information layer. SUMMARY OF THE INVENTION This invention is made in view of these inconveniences of the prior art, and it is an object of the present invention to provide an optical information recording medium that is insusceptible to destruction or peeling of the information layer, when a point pressure is applied to it, and also insusceptible to scratches on the surface of the protective layer when a hard material slip-contacts with it. To accomplish the object, this invention is configured that an optical information recording medium comprising a substrate, an information layer carried on one side of the substrate, and a protective layer covering the outer surface of the information layer wherein the protective layer is constituted by a first protective layer covering the surface of the information layer, a second protective layer covering the surface of the first protective layer, and a third protective layer covering the surface of the second - 5 - protective layer, and the hardness of the second protective layer is made lower than those of the first and the third protective layers. When the protective layer is constituted by a first hard protective layer, a second soft protective layer, and a third hard protective layer in this way, any point pressure acting on the outermost third protective layer is absorbed by the second soft protective layer disposed under the third protective layer and also dispersed by the first hard protective layer disposed under the second protective layer, so that the destruction of the information layer due to the action by the point pressure can be effectively prevented. Further, even if the second soft protective layer is deformed by the point pressure and a force in the facial direction arises, the first hard protective layer disposed under the second protective layer prevent the force in the facial direction from acting on the information layer and the peeling of the protective layers from the information layer, even when the information layer is formed of an organic material such as a dye. In addition, the third hard protective layer disposed on the surface makes the medium insusceptible to scratches on the protective layers when contacting with a hard material so that the good appearance of the optical information recording medium can be maintained for a long time. The second and the third protective layers - 6 - can be not only formed of a transparent colorless resin layer, but also formed with a printing layer for performing color printing or design printing on the optical information recording medium. Further, the information layer can be not only formed with a single recording layer made of a heat mode or photon mode recording material, but also formed of the recording layer and a reflective layer covering the surface of the recording layer, or of a combination of the recording layer and another layer, for example a reflective layer or a dielectric layer. According to an embodiment of this invention set forth in Claim 1, a protective layer is constituted by a first hard protective layer, a second soft protective layer, and a third hard protective layer, so that any point pressure acting on the outermost third protective layer is absorbed by the second soft protective layer disposed under the third protective layer and also dispersed by the first hard protective layer disposed under the second protective layer, so that the distraction of the information layer due to the action by the point pressure can be effectively prevented. Further, even if the second soft protective layer is deformed by the point pressure and a force in the facial direction arises, the first hard protective layer disposed under the second protective layer prevent the force in the facial direction from acting on the information layer and peeling of the protective - 7 - layers from the information layer, even when the information layer is formed of a organic material such as a dye. In addition, the third hard protective layer disposed on the surface makes the medium insusceptible to scratches on the protective layers when contacting with a hard material so that the good appearance of the optical information recording medium can be maintained for a long time. According to an embodiment of this invention set forth in Claim 2, besides having the same effect as mentioned above, the second and the third protective layers are replaced by printing layers so that the layer structure and the manufacturing process can be simplified and desired optical information recording medium can be manufactured inexpensively. According to an embodiment of this invention set forth in Claim 3, besides having the same effect as mentioned above, the information layer is formed of a combination of a recording layer made of a heat mode or photon mode recording material and a metallic reflective and/or dielectric layer so that the reproduced signal level of the optical information recording medium and the recording reproduction sensitivity can be improved. BRIEF DESCRIPTION OF THE Accompanying DRAWINGS Fig. 1 is a plan view of optical information recording medium according to an exemplary embodiment - 8 -of this invention; Fig. 2 is a cross sectional view of optical information recording medium according to an exemplary embodiment of this invention; Fig. 3 is an enlarged cross sectional view of the principal parts of optical information recording medium according to an exemplary embodiment of this invention; Fig. 4 is a schematic view illustrating an apparatus and method according to this invention; and Fig. 5 is a plot showing the test results. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, an embodiment of information recording medium according to this invention will be described with reference to Figs. 1 to 3. Fig. 1 is a plan view of information recording medium according to the exemplary embodiment. Fig. 2 is a cross sectional view of information recording medium according to the exemplary embodiment. Fig. 3 is an enlarged cross sectional view showing the details of the layer structure of information recording medium according to the exemplary embodiment. As will be apparent from Figs. 1 and 2, the optical information recording medium 1 of this embodiment is constructed with a substrate 2 having a Preformatted pattern on one side, an information layer 3 formed on the surface having a preformatted pattern - 9 - of the substrate 2, and a protective layer 4 covering the surface of the information layer 3. The substrate 2 is formed in a shape of a disk having a center hole 2a, and in a ring-shaped data recording area 5 of its one side except the innermost and outermost portions formed a preformatted pattern 6 comprising a set of fine pit patterns in a spiral or concentric shape centered at the center hole 2a. The substrate 2 is formed of a hard material such as glass and plastics. The information layer 3 is formed on the preformatted patterned surface of the substrate 2 over a slightly wider area than the data recording area 5. In the optical information recording medium 1 according to this embodiment, the information layer 3 is constituted by a recording layer 3a made of a desired heat mode or photon mode recording material and a reflective layer 3b covering the surface of the recording layer 3a as shown in Fig. 3. This configuration shows a layer structure of the information layer 3 particularly suited for CD-R or CD-RW, where a CD-R can be produced by using an organic dye material for the recording layer 3a, and a CD-RW can be produced by using a phase change type recording material for the recording layer 3a. The recording film layer 3a made of an organic dye material can be formed by spin coating, and the recording layer 3a made of a phase change type recording material can be formed - 10 - by sputtering or vacuum deposition. On the other hand, the reflective layer 3b is provided to improve the reproduction sensitivity by increasing the intensity of the reflected light incident to the photodetector disposed on the recording/reproducing apparatus, and made of aluminum, silver, gold or an alloy containing these metals for example. This reflective layer 3b can also be formed by sputtering or vacuum deposition. The protective layer 4 is provided to protect the information layer 3 from mechanical impact or chemical deterioration, and formed to cover the entire surface of the information layer 3 as shown in Fig. 2. In the optical information recording medium 1 according to this embodiment, the protective layer 4 has a three-layer structure constituted by a first protective layer 4a, a second protective layer 4b, and a third protective layer 4c as shown in Fig. 3. The first and the third protective layers 4a and 4c are formed of a resin material harder than that of the second protective layer 4b, and the second protective layer 4b is formed of a resin material more soft than those of the first and the third protective layers 4a and 4c. As a resin material to form the first and the third protective layers 4a and 4c can be used a composition containing at least one resin selected from the group consisting of acrylate ester, difunctional acrylic acrylate, ester acrylate, ester monomer, and alithatic cyclic monomer- And as a resin material to form the - 11 - second protective layer 4b can be used a composition containing at least one resin selected from the group consisting of urethan acrylate and ether acrylate. In addition, the second and the third protective layers 4b and 4c can be formed by printing with an ink obtained by adding a pigment to a desired resin material, thereby allowing color printing or design printing on the optical information recording medium 1. The thicknesses of respective sublayers constituting the protective layer 4 are preferably thick to improve the protective effect for the information layer 3, but if it is too thick, the substrate 2 is susceptible to deformation due to the stress arising when curing the protective layer 4, and if too thin, the protective effect required practically can not be attained. Therefore, the first, the second and the third protective layers 4a, 4b, and 4c are preferably about 2 to 15 microns thick depending on the physical properties of the material used. In the following, the effects of the optical information recording medium according to this invention will be demonstrated by way of test examples. (1) Specimen a. Sample obtained according to this invention: Disk material from which a disk-form optical information recording medium is made was obtained by forming a recording layer made of an organic dye by - 12 - spin coating on the surface having a preformatted pattern of an injected polycarbonate substrate and then forming a silver reflective layer by sputtering on the recording layer. On the disk material were sequentially formed a first protective layer having a thickness of 5 micron made of a composition containing an acrylate ester, a second protective layer having a thickness of 8 micron made of a composition containing a pigment, an urethan acrylate, an ether acrylate, a photo initiator, and an additive, and a third protective layer having a thickness of 8 micron made of a composition containing a pigment, a difunctional acrylic acrylate, an ester acrylate, an ester monomer, an aliphatic cyclic monomer, a photo initiator, and an additive in this order to obtain a desired CD-R. The first protective layer was formed by spin coating and the second and the third protective layers were formed by screen printing, b. Comparative Example 1: On the disk material were sequentially formed a first protective layer having a thickness of 5 micron made of a composition containing an acrylate ester, a second protective layer having a thickness of 8 micron made of a composition containing a pigment, a difunctional acrylic acrylate, an ester acrylate, an ester monomer, an aliphatic cyclic monomer, a photo initiator, and an additive, and a third protective layer having a thickness of 8 micron made of a - 13 - composition containing an acrylate ester in this order to obtain a desired CD-R. The first and the third protective layers were formed by spin coating and the second protective layer was formed by screen printing. c. Comparative Example 2: On the disk material were sequentially formed a first protective layer having a thickness of 5 micron made of a composition containing an acrylate ester, and a second protective layer having a thickness of 8 micron made of a composition containing a pigment, a difurctional acrylic acrylate, an ester acrylate, an ester monomer, an aliphatic cyclic monomer, a photo initiator, and an additive in this order to obtain a desired CD-R. The first protective layer was formed by spin coating and the second protective layer was formed by screen printing. d. Comparative Example 3: On the disk material were sequentially formed a first protective layer having a thickness of 8 micron made of a composition containing a pigment, an urethan acrylate, an ether acrylate, a photo initiator, and an additive, and a second protective layer having a thickness of 8 micron made of a composition containing a pigment, a difunctional acrylic acrylate, an ester acrylate, an ester monomer, an aliphatic cyclic monomer, a photo initiator, and an additive in this order to obtain a desired CD-R. The first and the second protective layers were formed by screen - 14 -printing. e. Comparative Example 4: On the disk material were sequentially formed a first protective layer having a thickness of 5 micron made of a composition containing an acrylate ester, and a second protective layer having a thickness of 8 micron made of a composition containing a pigment, an urethan acrylate, an ether acrylate, a photo initiator, and an additive in this order to obtain a desired CD-R. The first protective layer was formed by spin coating and the second protective layer was formed by screen printing. (2) Test Apparatus and Method Test was conducted by fixing a sample, that is a CD-R 1 having data recorded on it on a table 10 with nonwoven fabric 11 interposed inbetween, pushing sapphire glass 13 having a point angle of 60 degrees attached to an end of a loading device 12 against a protective layer of the CD-R 1, translating the table 10 to its facial direction while maintaining the condition to move the sapphire glass 13 relatively to the radial direction of the CD-R 1, and counting the error count of the CD-R 1 after loading, as shown in Fig. 4. CD-R 1 was loaded by putting a weight 14 having a weight of 10 to 50 gram on the axial center of the sapphire glass 13 over the areas having a radius of 26 to 29 mm, 31 to 34 mm, 36 to 39 mm, 41 to 44 mm, 46 - 15 -to 49 mm, and 51 to 54 mm about the center hole 2a. Information was recorded on the CD-R 1 with a CD writer "PLEXTER PX-R820" manufactured by SINANOKENSI Co. and error measurement was conducted with "CD-CATS" manufactured by AUDIO DEVELOPMENT Co. (3) Test Results Fig. 5 shows the test results. The lines in the graph showing the test result represent average values of test data obtained for each area concerned. As can be seen from this graph, while in the CD-Rs according to the Comparative Examples 1 to 4 errors were generated in reproduced signals by loading them with a load of about 0.25 to 0.30 N or more, in the Sample according to this invention no error was generated in reproduced signals even if it was loaded with a load of 0.5 N, showing a substantial improvement in the scratch resistance. It is considered that this is because the Sample according to this invention has a three-layer construction comprising a first hard protective layer, a second soft protective layer, and a third hard protective layer, and therefore any point pressure acting on the outermost third protective layer is absorbed by the second soft protective layer disposed under the third protective layer and also dispersed by the first hard protective layer disposed under the second protective layer, so that the distraction of the information layer due to the action by the point pressure can be effectively prevented. - 16 -The CD-R according to the Comparative Example 3 having a first soft protective layer and a second hard protective layer formed in this order on a silver reflective layer suffered partial peeling between the silver reflective layer and the first protective layer, while the Sample according to this invention suffered no peeling. It is considered that this is because even if the second soft protective layer is deformed by the point pressure and a force in the facial direction arises, the first hard protective layer having good adhesion to the second protective layer disposed under the second protective layer prevent the force in the facial direction from acting on the silver reflective layer. The CD-R according to the Comparative Example 4 having a first hard protective layer and a second soft protective layer formed in this order on a silver reflective layer suffered scratching on the second protective layer by the sapphire glass 13, while the Sample according to this invention having a third hard protective layer on the surface suffered no scratching by the sapphire glass 13, so that the good appearance of the CD-R was maintained well. For the Sample according to this invention, the same results as afore-mentioned were obtained even if the thickness of the first, the second, and the third protective layers respectively in a range of 2 to 15 microns. Further, the same results as afore- - 17 - mentioned were obtained even if the materials used to form the first, the second, and the third protective layers were changed within a scope described in the Detailed Description of the Invention. The exemplar embodiment has been described with reference to an optical information recording medium with a single-sheet configuration, but an optical information recording medium with a double-side recording configuration having two single-plate optical information recording media laminated concentrically can be also realized similarly. The exemplar embodiment has been described with reference to a recordable or rewritable optical information recording medium with a recording layer 3a, but this invention is not limited to them, and a read only optical information recording medium with a reflective layer 3b only (CD) can be also realized similarly. In addition, the exemplar embodiment has been described with reference to CD-R or CD-RW, an optical information recording medium comprising a magnetic layer as a recording layer 3a can be also realized similarly. In this case, the information layer 3 can be constituted by a combination of a magneto-optical recording layer, a dielectric layer, and a reflective layer. -18- WE CLAIM: 1. An optical information recording medium comprising a substrate, an information layer carried on one side of the substrate, and a protective layer covering the outer surface of the information layer wherein the protective layer is constituted by a first protective layer covering the outer surface of the information layer, a second protection layer covering the outer surface of the first protective layer, and a third protective layer covering the outer surface of the second protective layer, and the hardness of the second protective layer is made lower than those of the first and the third protective layer, wherein composition of matter as a first protective layer includes at least a kind of resin among acryl ester, acrylic special acrilate, acrilate ester, monomer ester and alicyclic monomer. Composition of matter as a second protective layer includes at least a kind of resin among polyurethane acrilate and esthers acrilate, Composition of matter as a third protective layer includes at least a kind of resin among acryl ester, acrylic special acrilate, acrilate ester, monomer ester and alicyclic monomer. 2. The optical information recording medium set forth in claim 2 wherein said second and third protective layers are printing layers. 3. The optical information recording medium set forth in claim 2 wherein said information layer is formed of a combination of a recording layer made of a heat mode or photon mode recording material and a reflection and/or dielectric layer. An optical information recording medium which comprises a substrate, an information layer carried on one side of the substrate, and a protective layer covering the outer surface of the information layer wherein the protective layer is constituted by a first protective layer covering the outer surface of the information layer, a second protection layer covering the outer surface of the first protective layer, and a third protective layer covering the outer surface of the second protective layer, and the hardness of the second protective layer is made lower than those of the first and the third protective layer, wherein composition of matter as a first protective layer includes at least a kind of resin among acryl ester, acrylic special acrilate, acrilate ester, monomer ester and alicyclic monomer, composition of matter as a second protective layer includes at least a kind of resin among polyurethane acrilate and esthers acrilate, composition of matter as a third protective layer includes at least a kind of resin among acryl ester, acrylic special acrilate, acrilate ester, monomer ester and alicyclic monomer. |
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| Patent Number | 202491 | ||||||||
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| Indian Patent Application Number | 213/CAL/2001 | ||||||||
| PG Journal Number | 08/2007 | ||||||||
| Publication Date | 23-Feb-2007 | ||||||||
| Grant Date | 23-Feb-2007 | ||||||||
| Date of Filing | 11-Apr-2001 | ||||||||
| Name of Patentee | HITACHI MAXELL ,LTD | ||||||||
| Applicant Address | A CORPORATION ORG.UNDER THE LAWS OF JAPAN 1-83,USHITORA -1-CHOME IBARAKI-SHI OSAKA | ||||||||
Inventors:
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| PCT International Classification Number | G 11 B 7/24 | ||||||||
| PCT International Application Number | N/A | ||||||||
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