Title of Invention

"A METHOD OF MANUFACTURING A MATERIAL FOR AN APERTURED GRILL IN A COLOR PICTURETUBE"

Abstract The object of the present invention is to provide a material for an aperture grille for use in a color picture tube, which has an excellent yield strength and high temperature creep strength and superior magnetic characteristics to currently used materials. The other objects are to provide a producing method of the above mentioned material for an aperture grille, and to provide an aperture grille made thereof and a color picture tube incorporating the aperture grille. The method comprises the steps of cold-rolling a low carbon steel sheet containing 0.05 to 2.5 wt% of Cu, or 0.5 to 2.5 wt% of Cu and 0.001 to 0.4 wt% of P, and subjecting same to ageing at a temperature of 300 to 700" C. Alternatively, the method comprises the steps of: cold-rolling the low carbon steel sheet same as mentioned above, and subjecting same to process-annealing at a temperature of 500 to 800" C, then another cold-rolling, and ageing thereafter.
Full Text [Detailed description of the Invention]
The present invention relates to a material for an aperture grille for use in a color picture tube, a producing method therefor, an aperture grille, and a color picture tube incorporating the aperture grille. More particularly, it relates to a material for an aperture grille for use in a color picture tube which has an exceDent tensile strength and high temperature creep strength and besides good magnetic characteristics, and relates to a producing method therefor, an aperture grille made thereof, and a color picture tube incorporating this aperture grille.
[Problem to be solved by the Invention]
IS
When an aperture grille is incorporated into a color picture tube, it
welded to a frame of the color picture tube while being applied with a great tention. Therefore, a material for aperture grille for color picture tube is essentially required to have a tensile strength of at least 60 kgf/mrri. Accordingly, the material currently used for the aperture grille of a color picture tube consists of a low carbon steel sheet which has been reinforced by strengthening-forming.
Further, after welded to the frame of the color picture tube, the aperture grille is subjected to a heat treatment for blackening. This heat treatment is carried out at 455 ° C which is below the recrystalization temperature of steel for only a short time of about 15 minutes so that after blackening the tapes constituting the aperture grille may not be loosened but can be maintained with its loaded tensile strength. However, under such heat treatment conditions for blackening, the tapes cannot be entirely free from a recovery phenomenon but involve elongation of it by the recovery, thereby suffering cuts and twists. For this reason, a material for an aperture grille for use in a color picture tube is required to have a tensile strength of not less than 60 kgf/m m2 and a creep strength capable to cause no elongation even when subjected to such a heat treatment for blackening as conducted at a temperature of 455 ° C for a time of 15 minutes, and to control its elongation of not more than 0.4% when the aperture grille is applied with a tensile strength of 30 kgf/m
m2
The color picture tube comprises an electron gun and a luminiscent screen which converts electron beam into picture images. The inside of the picture tube is covered with a magnetic shield member so as to prevent the electron beam from being biased by geomagnetism. The aperture grille is also required to serve as the magnetic shield member and, therefore, should be made of a material having a great magnetic flux density (Br) and a small coercive
force (Hc) which represent magnetic characteristics, in other words, a material having a great ratio of magnetic flux density to coercive force (Br/Hc). However, such a low carbon steel sheet as mentioned above, which has been subjected to strengthening-forming for obtaining a high tensile strength and also subjected to the heat treatment for blackening at a temperature below its recrystalization temperature, has a small magnetic flux density of up to 8 kG and a great coercive force of about 5 Oe, that is, the value of Br(kG)/Hc(Oe) is as small as about 1.6. These values indicate that such a low carbon steel sheet is inferior as a magnetic shield material.
So far, methods for improving a tensile yield strength of a low carbon steel sheet includes a solid solution strengthening method by means of carbon and nitrogen. The more the carbon or the nitrogen increases in the steel, the more increases carbide or nitride so that the movement of ferromagnetic domain walls will be prevented, inducing the impairment of the magnetic characteristics of the steel. Besides, methods for improving a creep strength of a low carbon steel sheet include that of precipitating carbide and others in the steel. These precipitates have mostly a large grain size in micron order, which prevent the movement of ferromagnetic domain walls, remarkably impairing the magnetic characteristics of the steel. Therefore, this method has not been applied as methods of producing a material for an aperture grille for use in a color picture
tube.
The present invention has an object to provide a material for an aperture grille for use in a color picture tube which has an excellent tensile strength and high temperature creep strength and superior magnetic characteristics to prior materials, and provide a producing method therefor, an aperture grille made thereof, and a color picture tube incorporating this aperture grille.
[Means for solving the problem]
An invention as claimed in claim 1 relates to a material for an aperture grille for use in a color picture tube made of a low carbon steel sheet containing 0.05 to 2.5 wt% of Cu.
An invention as claimed in claim 2 relates to a material for an aperture grille for use in a color picture tube made of a low carbon steel sheet containing 0.05 to 2.5 wt% of Cu and 0.001 to 0.4 wt% of P.
An invention as claimed in 3 relates to a method of producing a material for an aperture grille for use in a color picture tube comprising the steps of cold-rolling a hot-rolled low carbon steel strip containing 0.05 to 2.5 wt% of Cu, and then subjecting same to ageing at a temperature of 300 to 700 ° C.
An invention as claimed in 4 relates to a method of producing a material for an aperture grille for use in a color picture tube comprising the steps of: cold-rolling a hot-rolled low carbon steel strip containing 0.05 to 2.5 wt% of Cu and 0.001 to 0.4 wt % of P, and then subjecting same to ageing at a temperature of 300 to 700 ° C.
An invention as claimed in claim 5 relates to a method of producing a material for an aperture grille for use in a color picture tube comprising the steps of cold-rolling a hot-rolled low carbon steel strip containing 0.05 to 2.5 wt% of Cu, subsequently subjecting same to process-annealing at a temperature of 500 to 800 ° C and then another cold-rolling, and subjecting same to ageing at a temperature of 300 to 700 ° C.
An invention as claimed in claim 6 relates to a method of producing a material for an aperture grille for use in a color picture tube comprising the steps of cold-rolling a hot-rolled low carbon steel strip containing 0.05 to 2.5 wt% of Cu and 0.001 to 0.4 wt % of P, subsequently subjecting same to process-annealing at a temperature of 500 to 800° C and then another cold-rolling, and subjecting same to ageing at a temperature of 300 to 700 C.
An invention as claimed in claim 7 relates to an aperture grille for use in a color cathode ray tube made of a low carbon steel sheet containing 0.05 to 2.5 wt% of Cu , and another invention as claimed in claim 8 relates to an

perture grille for use m a color cathode ray tube made of a low carbon steel sheet containing 0.05 to 2.5 wt% of Cu and 0.001 to 0.4 wt% of P
An invention as claimed in claim 9 relates to a color picture tube incorporating an aperture grille for use in a color picture tube, which is made of a low carbon steel sheet containing 0.05 to 2.5 wt% of Cu , and another invention as claimed in claim 10 relates to a color picture tube incorporating an aperture grille for use in a color picture tube, which is made of a low carbon steel sheet containing 0.05 to 2.5 wt% of Cu and 0.001 to 0.4 wt% of P .
[Preferred embodiments of the Invention]
According to the present invention it proved that hyper low carbon Steel to which Cu is added is subjected to ageing to precipitate a micro Cu phase ( £ phase) in a nanometer (nm) order, or alternately the thus treated hyper low carbon steel to which further P is added is subjected to solid solution strengthening of phosphorus so that the steel could obtain a tensile strength of not less than 60 kgf/m ni and excellent magnetic characteristics as represented by a ratio of Br(kG)/Hc(Oe) of not less than 2.5 through the annealing by the ageing.
The present invention is now described in detail below.
In the present invention, a material for an aperture grille for use in a color picture tube consists preferably of hyper low carbon steel obtained by the step of subjecting the steel to a decarburization and denitrification treatment by use .of a vacuum degassing process to decrease the carbide and nitride in the steel and accelerate the growth of crystal grains during hot-rolling and continuous annealing. In addition, since the carbide and nitride finely dispersed in the steel prevent the movement of ferromagnetic domain walls to thereby impair the magnetic characteristics of the steel, it is necessary to limit the elements included in the steel beforehand and reduce them to the least. Now the explanation begins with sorts and amounts of the elements to be added to the steel which is to be used for the material for the aperture grille for use in

the color picture tube of the present invention.
As for C, the more the carbon exists in the steel sheet after cold-rolling, the more the carbide is produced to thereby prevent the movement of ferromagnetic domain walls and inhibit the growth of crystal grains, resulting in the impairment of the magnetic characteristics of the steel. For this reason, the upper limit of the addition amount of carbon is determined to be 0.01 wt%. The lower limit of the addition amount of carbon is desirably as little as it can be practically controlled through the vacuum degassing process.
As for Mn, manganese is essentially added to steel to react with sulfur in the steel so as to stabilize the sulfur as MnS, thus keeping the steel from the embrittlement during hot-rolling. However, it is desirable for improving the magnetic characteristics of the steel to lessen the amount of manganese. So the addition amount of the manganese is limited up to 0.5 wt%.
As for Si, silicon impairs the adhesion of a black oxide film, so the addition amount of the silicon is limited up to 0.3 wt%. As for S, sulfur is desirably less included in the steel in an aspect of the growth of crystal grains, so the addition amount of the sulfur is limited up to 0.05 wt%. Also, the addition amount of nitrogen is desirably up to 0.05 wt% in the same aspect.
As for Cu, the more the copper is added to the steel, the more amount of £ phase is precipitated during ageing so that the yield strength and creep strength of the steel remarkably increases. Since the £ phase is an extremely fine precipitate in a nanometer order, it scarcely prevents the movement of ferromagnetic domain walls, thus inducing extremely little impairment of the magnetic characteristics of the steel, in contrast to a precipitate in a micron order. Therefore, it is possible to improve the yield strength and creep strength without lowering the magnetic characteristics of the steel by adding an increased amount of copper. When the addition amount of copper is less than 0.05 wt%, it effects not enough improvement in the strength. On the other hand, when the addition amount of copper is rather large, the precipitate exceeds, thus inducing the impairment of the magnetic characteristics of the

steel. Therefore, the addition amount of copper is preferably limited up to 2.5
wt%.
As for P, phosphorus is effective in improving the strength of steel by means of solid solution strengthening. Since the addition of phosphorus to steel makes it possible to improve the tensile strength and creep strength of the steel, the solid solution strengthening by use of phosphorus can be applied together with the strengthening through the ageing precipitation by means of adding copper to steel, which is a desired object of the present invention. When the addition amount of phosphorus is not less than 0.001 wt%, the steel can obtain enough strength. When the addition amount of phosphorus exceeds 0.4 wt%, unevenly mixed grains will appear due to the segregation, so the addition amount of phosphorus is limited up to 0.4 wt%.
Next, a producing method of a thin steel sheet as a material for an aperture grille for use in a color picture tube of the present invention is explained.
The producing method comprises the steps of hot-rolling hyper low carbon steel containing the above mentioned chemical components which has been subjected to a vacuum melting process or vacuum degassing process to be melted, pickling same to remove an oxide film formed during the hot-rolling, subsequently cold-rolling same to form a thin steel sheet of 0.035 to 0.2mm thickness, and ageing same at a temperature of 300 to 700" C for a time of 10 minutes to 20 hours. In a case where a large amount of Cu, or Cu and P are added to the steel, the re crystallization temperature of the steel is elevated. Therefore, the ageing may be carried out even at the upper limit temperature of around 700' C, but preferably at a temperature of 450 to 550 ° C considering the amount of preciptated Cu and the grain size of the preciptated material. When the ageing temperature is lower than 300 ° C, the 8 phase cannot be precipitated enough so that a desired tensile strength cannot be attained. On the other hand, the ageing temperature is elevated above 700' C, over-ageing takes place to solve the £ phase again into the steel, thus decreasing the

ensile yield resisting strength of the steel. The ageing may be carried out using either box annealing furnace or continuous annealing furnace, depending on heating temperature and heating time.
There may be another embodiment of the producing method of the present invention, which comprises the steps of hot-rolling the above mentioned hyper low carbon steel, pickling same, cold-rolling same to form a steel sheet of 0.1 to 0.6mm thickness, subsequently subjecting same to process-annealing at a temperature of 500 to 800" C to control crystal grain sizes, subjecting same to another cold-rolling to form a thin steel sheet of 0.035 to 0.2mm thickness, and ageing same in the manner as mentioned above. When the process-annealing temperature is lower than 500 ° C, the steel sheet cannot be softened enough. If this steel sheet is subjected to the above mentioned ageing after the secondary cold-rolling, its tensile strength is exteremly raised. On the other hand, when the process-annealing temperature is higher than 800 ° C, the steel sheet cannot attain a desired yield strength even after it is subjected to the secondary cold-rolling and then the above mentioned ageing.
[Examples]
The present invention is described more in detail with regard to
examples below.
(Example)
Nine different kinds of steel (A ~ I) which respectively contain chemical compositions as shown in Table 1 were vacuum-degassed and melted into slabs, which were hot-rolled to form hot-rolled sheets each having a thickness of 2.5mm. These hot-rolled sheets were subjected to sulfuric acid pickling and then cold-rolling to form two kinds of cold-rolled sheets each having a thickness of 0.lmm or 0.3mm. Thereafter, the cold-rolled steel sheets of 0.lmm thick were directly subjected to ageing, while the cold-rolled steel sheets of 0.3mm thick were subjected to process-annealing, another cold-rolling to form

steel sheets each having a thickness of 0.lmm, and ageing. The thus obtained steel sheet samples were applied with 10 oersted of magnetic field using a compact type Epstein magnetism measuring apparatus to measure their magnetic flux densities and coercive forces and calculate values of Br(kG)/Hc(Oe). The samples were further measured to obtain their tensile strengths by use of TENSILON, and to obtain their creep strengths by use of Creep tester (made by TOKAI SEISAKUSHO) such that they were applied with a load of 30kgf/m m2 and maintained at 455 ° C in the atmosphere for 15 minutes to measure and evaluate their elongation (%). Conditions for the process-annealing and ageing, and characteristics of the steel sheets samples are shown in Table 2.
[Table 1] [Table 2]
[Effect of the Invention]
The material for an aperture grille as claimed in claim 1 consists of a low carbon steel sheet containing 0.05 to 2.5 wt% of Cu and the material for an aperture grille as claimed in claim 2 consists of a low carbon steel sheet containing 0.05 to 2.5 wt% of Cu and 0.001 to 0.4 wt% of P.
The method of producing as claimed in claim 3 comprises the steps of cold-rolling a hot-rolled low carbon steel strip containing 0.05 to 2.5 wt% of Cu, and then subjecting same to ageing at a temperature of 300 to 700 ° C.
The method of producing as claimed in claim 4 comprises the steps of cold-rolling a hot-rolled low carbon steel strip containing 0.05 to 2.5 wt% of Cu and 0.001 to 0.4 wt % of P, and then subjecting same to ageing at a temperature of 300 to 700 ' C.
The method of producing as claimed in claim 5 comprises the steps of cold-rolling a hot-rolled low carbon steel strip containing 0.05 to 2.5 wt% of Cu,

subsequently subjecting same to process-annealing at a temperature of 500 to 800 C and then another cold-rolling, and subjecting same to ageing at a temperature of 300 to 700 * C.
The method of producing as claimed in claim 6 comprises the steps of cold-rolling a hot-rolled low carbon steel strip containing 0.05 to 2.5 wt% of Cu and 0.001 to 0.4 wt % of P, subsequently subjecting same to process-annealing at a temperature of 500 to 800 * C and then another cold-rolling, and subjecting same to ageing at a temperature of 300 to 700' C. Consequently, these methods can produce a material for an aperture grille for use in a color picture tube having an excellent tensile strength and excellent high temperature creep strength, and good magnetic characteristics.
In the aperture grille and/or the color picture tube as claimed in claims 7 to 10, the tapes constituting the aperture grille are never loosened even after the aperture grille is welded to the frame of the color picture tube and subjected to the heat treatment for blackening.

(Table 1)
Chemical compositions of samples (steel sheet)
(Table Removed)
(Table2)
Conditions for ageing and process-annealing and Characteristic of samples
(Table Removed)






WE CLAIM:
1. A method of manufacturing a material for an aperture grill for
use in a color picture tube, comprising cold rolling a low carbon
steel comprising 0.05 to 2.5% by weight of Cu, 0.01% by weight
or less of C and other inevitable impurities, applying an
intermediate annealing at a temperature of 500 to 800°C, then
applying secondary cold rolling, and subsequently applying an
ageing treatment at a temperature of 300 to 700°C.
2. A method of manufacturing a material for an aperture grill for
use in a color picture tube, comprising cold rolling low carbon
steel comprising 0.05 to 2.5% by weight of Cu, 0.001 to 0.4% by
weight of P, 0.01% by weight or less of C, and other inevitable
impurities, then applying an intermediate annealing at a
temperature of 500 to 800°C, then applying secondary cold
rolling, and subsequently applying an ageing treatment at a
temperature of 300 to 700°C.
3. A method of manufacturing a material for an aperture grill in a
color picture tube substantially as herein described with
reference to the foregoing examples.







Documents:

252-del-1998-abstract.pdf

252-del-1998-claims.pdf

252-del-1998-correspondence-others.pdf

252-del-1998-correspondence-po.pdf

252-del-1998-description (complete).pdf

252-del-1998-form-1.pdf

252-del-1998-form-13.pdf

252-del-1998-form-19.pdf

252-del-1998-form-2.pdf

252-del-1998-form-3.pdf

252-del-1998-form-4.pdf

252-del-1998-form-6.pdf

252-del-1998-gpa.pdf

252-del-1998-petition-138.pdf


Patent Number 215323
Indian Patent Application Number 252/DEL/1998
PG Journal Number 11/2008
Publication Date 14-Mar-2008
Grant Date 25-Feb-2008
Date of Filing 29-Jan-1998
Name of Patentee TOYO KOHAN CO., LTD.,
Applicant Address 4-3 KASUMIGASEKI 1-CHOME, CHIYODA-KU, TOKYO 100, JAPAN.
Inventors:
# Inventor's Name Inventor's Address
1 HIRONAO OKAYAMA TOYO KOHAN CO. LTD. TECHNICAL RESEARCH LABORATORY, 1296-1 HIGHASHITOYOI, KUDAMATSU-SHI YAMAGUCHI-KEN, JAPAN.
2 TSUNEYUKI IDE TOYO KOHAN CO. LTD. TECHNICAL RESEARCH LABORATORY, 1296-1 HIGHASHITOYOI, KUDAMATSU-SHI YAMAGUCHI-KEN, JAPAN.
3 HIROSHI FUJISHIGE C/O TOYO KOHAN CO. LTD. OF KUDAMATSU PLANT, 1302, HIGASSHITOYOI, KUDAMATSU-SHI, YAMAGUUCHI-KEN, JAPAN.
4 SETSUO TAKAKI C/O KYUSHU UNIVERSITY FACULTY OF ENGINEERING, 10-1 HAKOZAKI 6-CHOME, HIGASHI-KU, FUKUOKA-KU, FUKUOKA-SHI, FUKUOKA-KEN, JAPAN.
5 YASUO TAHARA TOYO KOHAN CO. LTD. TECHNICAL RESEARCH LABORATORY, 1296-1 HIGHASHITOYOI, KUDAMATSU-SHI YAMAGUCHI-KEN, JAPAN.
6 AKIRA IKEDA C/O TOYO KOHAN CO. LTD., 4-3 KASUMIGASEKI 1-CHOME, CHIYODA-KU, TOKYO, JAPAN.
PCT International Classification Number H01J 29/07
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 TOKU-GAN-HEI 9-36929 1997-02-06 Japan