JPS643022B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method of manufacturing a shadow mask for a color picture tube. Technical Background and Problems of the Invention As shown in FIG. 1, a general color picture tube has three electron beams 1, 2 corresponding to red, green, and blue emitted from an electron gun (not shown). 3 is a regularly arranged fine aperture 5 of a shadow mask 4
The structure is such that a color image is projected by causing the phosphors 7, 8, and 9 that emit red, green, and blue light, which are attached to the inner surface of the panel 6, to emit light in a corresponding manner. . This type of color picture tube shadow mask is
It is necessary to accurately drill regularly arranged fine holes, to form a curved surface similar to the inner surface of the panel without any shape distortion, and to maintain the distance from the inner surface of the panel (hereinafter referred to as the q value) to a predetermined value. It is required to hold it correctly. As a material for such a shadow mask, generally used is aluminized decarburized steel having a thickness of about 0.10 mm to 0.3 mm, which mainly contains high-purity iron. These are comprehensively determined based on material supply capacity, cost, workability, strength, etc. However, the shadow mask for a color picture tube still has several problems even if all of the above conditions are controlled within the permissible range in each step up to the installation into the tube. One of these problems is the problem of thermal expansion caused by the rise in temperature of the shadow mask. In other words, when a color picture tube is operated, less than 1/3 of the electron beams pass through the apertures in the shadow mask, and the remaining electron beams impinge on the shadow mask, which can sometimes reach temperatures as high as 80 degrees Celsius. heated. As a result, the shadow mask undergoes thermal expansion and deviates from the correct q value. This causes a so-called doming phenomenon and deteriorates color purity. The expansion coefficient of conventionally commonly used materials whose main component is iron is 0~
Since it is quite large at about 12×10 ^-6 /deg at 100°C, this doming phenomenon is likely to occur and has become an important problem. Therefore, various proposals have been made in the past to reduce the purity drift, that is, the deterioration of color purity caused by this doming phenomenon, but no effective measures have been found, especially for the initial stage of tube operation and localized doming. Not served. Therefore, an example of using a material with a small coefficient of thermal expansion, such as an iron-nickel alloy, for the material itself of the shadow mask was published in 1973.
25446, JP-A-50-58977, and JP-A-Sho.
Although it has been proposed in Publication No. 50-68650, it has not yet reached the point where it satisfies practical conditions. One of the reasons for this is the difficulty in processing metal plates made of iron-nickel alloy. That is, in order to keep the q value within the allowable range, the curved surface of the shadow mask is required to have high precision, and the allowable tolerance is extremely strict, ±5 mm for a radius of curvature (R) of 1000 mm. However, iron-nickel alloys have the disadvantage of being inferior in formability into a spherical shape by pressing or the like because they retain considerable elasticity after annealing compared to conventional alloys whose main component is iron. For example, as shown in Figure 2, when a 0.2 mm thick iron-nickel plate is formed into a spherical surface, a local dent is created with respect to the standard radius.If the amount of dent (d) is 20 μm or less, it is essentially It has been determined that the degradation of color purity is acceptable. Regarding the amount of depression (d) and the yield point strength of the shadow mask material, for example, a 14-inch shadow mask exhibits the characteristics as shown in FIG. That is, in order to make the amount of depression 20 μm or less, the yield point strength needs to be suppressed to 20 Kg/mm ² or less. However, when a shadow mask made of an iron-nickel alloy is annealed in a mask annealing furnace in hydrogen in the same way as a conventional shadow mask made of aluminium-killed decarburized steel, the yield point strength is as shown in Figure 4. Compared to the characteristics (a) of aluminum killed decarburized steel, iron. Properties (b) of nickel-based alloys are very high. That is,
Even after annealing at a high temperature of 900℃, the yield point strength is still 29 ~
It only decreases to 30Kg/ ^mm2 . In FIG. 3, since a clear boundary cannot be obtained for the yield point strength of the iron-nickel alloy, the tensile strength at 0.2% elongation is used instead. In this way, shadow masks made of iron-nickel alloys have large deformations and dents, especially around the effective part, so
Deterioration of color purity caused by thermal expansion of the mask due to a small expansion prime number is almost no problem, but deterioration of color purity due to deformation is considered to be a major problem. OBJECTS OF THE INVENTION An object of the present invention is to improve the curved surface formability of a shadow mask whose main component is an iron-nickel alloy, and to provide a method for manufacturing a shadow mask with high precision in which deformation is prevented. Summary of the invention The present invention reduces the yield point strength by forming a large number of holes in a metal plate mainly composed of an iron-nickel alloy, annealing it in a vacuum (including reduced pressure), and then forming it. This is a highly accurate shadow mask that does not cause deformation and prevents deterioration of color purity. Embodiments of the Invention An embodiment in which an amber alloy is used as a material for a shadow mask whose main component is an iron-nickel alloy will be described below. Table 1 shows the weight composition ratio of the amber alloy used as an example and the conventional aluminum killed decarburized steel.

[Table] Figure 5 shows the yield point strength of a shadow mask made of 36Ni amber alloy with the above composition when the temperature of the annealing process in a conventional mask annealing furnace in a hydrogen atmosphere is raised. As is clear from the figure, even when annealed at temperatures as high as 1200°C, the yield point strength decreases only to 24 kg/mm ² . Therefore, in order to set the yield point strength to 20Kg/mm2 ^or less without any problems with formability, extrapolate from Figure 5 and set the annealing temperature to 1500℃ to 1700℃.
It is necessary to do so. However, since the melting point of this amber alloy is 1440°C to 1455°C, it is not possible to simply increase the temperature. In Figures 6 to 8, the annealing temperature is 1000, respectively.
3 is a micrograph showing the crystal structure of a sample at temperatures of 1100°C, 1100°C, and 1200°C. In FIGS. 6 to 8, a indicates a cross section, and b indicates a surface crystal structure, respectively. As is clear from FIGS. 6 to 8, it can be seen that the growth of crystal grains progresses as the annealing temperature increases. However, while the crystal grains in the cross section have grown significantly, the crystal grains on the surface have hardly grown. That is, this insufficient growth of surface crystal grains is related to the yield point strength, and this deviation in crystal growth is thought to be due to subtle segregation of impurities in the thickness direction of the alloy plate, particularly between the vicinity of the temperature and the inside thereof. Therefore, in this example, annealing was performed in a vacuum by exhausting the annealing atmosphere to the atmosphere. Degree of vacuum
10 at 1000℃, 1100℃ and 1200℃ respectively at 10 ^-3 Torr
Microscopic photographs showing the crystal structure when annealed for 1 minute are shown in FIGS. 9 to 11, respectively. The thin plate thickness is
It is 0.2mm. In addition, in FIGS. 9 to 11,
A shows a cross section, and b shows a surface crystal structure. As is clear from FIGS. 9 to 11, the annealing resulted in good growth of crystal grains not only in the cross section but also on the surface. FIG. 12 shows the yield point strength of the shadow mask annealed in vacuum as described above. A yield point strength of 20 Kg/mm ² without any problem in formability can be obtained by annealing at 1000° C. or higher. Table 2 shows the results of an analysis of impurities on the surface (layer less than 1/20th of the thickness) that are thought to inhibit the growth of crystal grains on the surface.

[Table] As is clear from Table 2, iron after annealing in vacuum -
Impurities other than nickel have generally decreased, and in particular, manganese (Mn) has decreased to about 1/10, and phosphorus (P) and sulfur (S) have decreased to undetectable levels. This is because by annealing in vacuum, Mn, P, S, etc. with high vapor pressure evaporate from the grain boundaries and facilitate the growth of crystal grains. This is thought to be because impurity oxides and the like are difficult to form in the surface layer. When a shadow mask with a yield point strength of 20 Kg/mm ² or less was formed into a predetermined curved shape using the amber alloy obtained by annealing in a vacuum as described above, a mask with no problem in the quality of the curved surface was obtained. The color picture tube incorporating the shadow mask obtained in this way has a very low thermal expansion coefficient of 1 to 2 × 10 ^-6 /deg at 0 to 100°C, so the color purity is affected by the thermal expansion of the shadow mask. There is no problem with deterioration.
Furthermore, a product was obtained in which there was no problem of deterioration of color purity due to mechanical deformation of the shadow mask. In the above examples, an example was described in which annealing was performed in a vacuum of 10 ^-3 Torr, but it was confirmed that similar effects can be achieved if the degree of vacuum is 10 ^-1 Torr or less. At this degree of vacuum, the residual gas may be oxidizing, reducing, or inert gas. If the pressure is increased more than this, impurities will not be evaporated sufficiently and the effect will be weakened. This annealing step may also be performed before drilling the multiple holes in the shadow mask. Furthermore, the shadow mask material applied to the present invention is not limited to 36Ni amber alloy,
Needless to say, any material whose main component is an iron-nickel alloy other than the 41Ni alloy can be similarly applied. Effects of the Invention As described above, according to the present invention, it is possible to improve the curved surface formability of a shadow mask mainly composed of an iron-nickel alloy, prevent deformation, and provide a highly accurate curved surface quality. It is possible to obtain a color picture tube without.

[Brief explanation of drawings]

Figure 1 is a schematic diagram to explain the operation of a color picture tube, Figure 2 is a schematic diagram of the main parts to explain the deformation of a shadow mask, and Figure 3 is a diagram showing the relationship between the amount of deformation of the shadow mask material and the yield point strength. FIGS. 4 and 5 are characteristic diagrams showing the relationship between the annealing temperature and yield point strength of the shadow mask. FIGS. 6 to 8 and 9 to 11 are characteristic diagrams for the conventional and present invention. FIGS. 6 to 11 are diagrams showing the metal crystal structure of the shadow mask material according to the annealing temperature according to the respective examples. In FIGS. 6 to 11, a shows the cross section and b shows the surface, respectively. FIG. FIG. 3 is a characteristic diagram showing the relationship between annealing temperature and yield point strength in Examples. 4...Shadow mask, 5...Open hole.

Claims (1)

[Claims] 1. A step of providing a large number of holes in a thin metal plate mainly composed of iron and nickel, annealing the metal plate having the large number of holes, and the annealed metal plate. 1. A method for manufacturing a shadow mask comprising at least a step of molding a shadow mask, wherein the annealing is performed in a vacuum. 2. Claim 1, wherein the annealing is performed in a vacuum at a pressure of 10 ^-1 Torr or less
2. Method for manufacturing a shadow mask as described in Section 1. 3. The method of manufacturing a shadow mask according to claim 2, wherein the annealing is performed at a temperature of 1000° C. or higher.