Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2000-02-23
2001-10-23
Yee, Deborah (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S651000
Reexamination Certificate
active
06306229
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Technological Field
The present invention relates to an invar alloy steel sheet for a shadow mask for use in a color picture tube (hereinafter referred to as CRT), a method for producing same, a shadow mask made of the above mentioned invar alloy steel sheet, and a CRT incorporating the above mentioned shadow mask. More particularly, it relates to a steel sheet for a shadow mask made of an invar alloy having excellent etchability in forming dot holes (minute fine holes) of the shadow mask, method for producing the above mentioned invar alloy steel sheet, the above mentioned shadow mask, and a CRT incorporating the shadow mask.
2. Prior Art
As a material for a shadow mask for use in CRT, a thin sheet made of an invar alloy or aluminum killed steel is used. The sheet for a shadow mask made of invar alloy is produced by the steps of melting an invar alloy, casting the molten invar alloy, forging and hot rolling same, and then subjecting same to pickling and grinding for descaling, and thereafter cold rolling and annealing same. The thus obtained invar alloy thin sheet is perforated to form dot holes by the use of a photoetching method so that a flat mask can be produced. The flat mask is subjected to the steps of annealing, press-forming into a desired shape, and blackening, and then incorporated into a CRT.
A shadow mask serves as an anode for electron beams emitted from electron guns and as an iris diaphragm for allowing the electron beam that has passed through the dot holes to be projected onto dots of fluorescent coating spread over a front panel. Regarding the latter role, the dot holes directly affect sharpness, irregular color or irregular luminance of picture images displayed on the CRT, and therefore they require extremely high dimensional accuracy. A dot hole comprises a small hole diameter portion (hereinafter referred to as a small dot) provided on a surface of a thin plate-like mask sheet facing a cathodic side, i.e., opposed to the electron guns, a large hole diameter portion (hereinafter referred to as a large dot) provided on the other surface of the mask sheet facing the front panel, and a joint hole portion (Break Through Hole, hereinafter referred to as Br Th hole) at which the small dot and the large dot meet each other. The function of the iris diaphragm for the electron beam is substantially effected by this Br Th hole.
Generally, an invar allot steel sheet for shadow mask has a thickness of 100 to 250 &mgr;m and the pitch between both centers of the dot holes is approximately 250 &mgr;m in the case of a high definition shadow mask. The Br Th holes have each a diameter of about 120 &mgr;m and they should be round and have roundness uniform diameters. Further, the invar alloy steel sheet is strictly required to have an etched surface provided with a fine and uniform surface roughness in view of such a function if iris diaphragm. Accordingly, it is strongly required to improve characteristics for etching, i.e., etchability of such an invar alloy steel sheet for shadow mask.
As a method for improving etchability of an invar alloy sheet, some techniques for decreasing inevitable impurities in the invar alloy have been proposed in the disclosures such as Japanese Patent Publication No. Hei-2-51973 and Laid-open Japanese Patent No. Sho-61-190023, in which the amount of inevitable impurities such as C, O, and N is restricted. Truly, these proposed techniques are essential to a highly accurate etching technology for forming a shadow mask or the like, but even if the inevitable impurities are simply decreased, all the problem in etchability of the invar alloy cannot be solved. On the other hand, as a method for improving the metallurgical structure of an invar alloy, some techniques have been proposed in the disclosures such as Laid-open Japanese Patent No. Hei-61-39343, Japanese Patent Publication No. Hei-2-9655, and Laid-open Japanese Patent No. Hei-6-279946, in which grain size or crystal orientation is restricted. These techniques have been so far widely known and are also essential to the improvement in etchability of invar alloys. In a polycrystal material, the finer the crystal grain is, the rarer the chance for difference to occur among etching rates of grains with regard to crystal orientation, which enables the etching rates to be uniform. In addition, an invar alloy has a face-centered cubic lattice structure, which is the same kind of structure as that of austenitic stainless steel known as a stainless steel alloy in the steel material field. It is also well known that in a material having a face-centered cubic lattice structure, etching proceeds more uniformly in such high atomic density planes as {111} plane and {100} plane than other planes.
Thus, a simple combination of the above mentioned prior techniques cannot sufficiently provide an improvement in etchability of the invar alloy as a material for a high definition shadow mask. Besides, the industrial production of such invar alloys having minute and fine grain structures and crystal orientation structures requires complicated control systems throughout the processes of cold rolling, annealing, and so on, which constitutes a main factor of high cost. Today, there arises a stronger demand for a low cost shadow mask. A shadow mask and a shadow mask material of high grade and low cost are being sought after now.
Problem to Be Solved By the Invention
The present invention has an object to provide an industrially economical invar alloy steel sheet for a shadow mask material having more improved etchability, a method for producing the above mentioned invar alloy steel sheet, a shadow mask made of the invar alloy, and a color picture tube incorporating the above mentioned shadow mask.
Means for Solving the Problem
The invar alloy steel sheet for a shadow mask material according to claim
1
consists essentially of 33 to 40 wt % Ni and the balance being Fe, and the invar alloy steel sheet has a percentage of {100} texture of 60 to 80% in a rolled surface thereof.
The method for producing an invar alloy steel sheet material for a shadow mask as claimed in claim
2
comprises the steps of hot working an invar alloy slab consisting essentially of 33 to 40 wt % Ni and the balance being Fe, subjecting the hot worked invar alloy slab to a primary cold rolling at a rolling reduction ratio of not more than 80%, annealing same at a temperature of 550° C. or higher, and subjecting same to a secondary cold rolling at a rolling reduction ration of not more than 50%.
In the above mentioned method for producing an invar alloy steel sheet material for a shadow mask, the rolling reduction ratio in the primary cold rolling may preferably be 50 to 80% (as claimed in claim
3
), the temperature in the annealing may preferably be 650 to 950° C. (as claimed in claim
4
), and the rolling reduction ratio in the secondary cold rolling may preferably be 0.05 to 40% (as claimed in claim
5
).
The shadow mask for use in a color picture tube as claimed in claim
6
employs the above mentioned invar alloy steel sheet.
The color picture tube as claimed in claim
7
incorporates the above mentioned shadow mask.
Preferred Embodiment
First, Ni content in an invar alloy is limited to 33 to 40 wt %. When the Ni content in the invar alloy is within the above mentioned range, the invar alloy has a remarkably decreased coefficient of thermal expansion. As a consequence, when a shadow mask made of this invar alloy is incorporated in a CRT, it can be free from problems such as distortion or irregular color of picture images, even when the temperature changes. On the other hand, when the Ni content is less than 33 wt %, or the Ni content exceeds 40 wt %, the coefficient of thermal expansion of the invar alloy increases, resulting in the above mentioned problem such as the distortion of picture images. A technological problem in the production of the invar alloy steel sheet for shadow mask for use in CRT is how to improve the etchability of the invar alloy. However, when prio
Ide Tsuneyuki
Ikeda Akira
Ikenaga Hiroaki
Okayama Hironao
Sato Taizo
Browdy and Neimark
Toyo Kohan Co. Ltd.
Yee Deborah
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