JPH0555566B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for manufacturing a shadow mask for a color picture tube, and particularly to an annealing method when the material is an iron-nickel alloy. [Technical background of the invention and its problems] High-purity, low-carbon steel plates such as rimmed steel or aluminum-killed steel are generally used as materials for shadow masks for color picture tubes, but this is limited by material supply capacity, cost, and processing. It is determined comprehensively based on characteristics, strength, etc. However, its biggest drawback is its large coefficient of thermal expansion (0 to 100℃, approximately 12×
10 ^-6 /℃). The electron beam passage rate of a typical shadow mask is 15 to 25%, and many electron beams collide with the shadow mask, raising the temperature of the shadow mask itself to 30 to 80 degrees Celsius. As a result, the shadow mask undergoes thermal deformation and the curvature of the curved surface facing the fluorescent surface collapses, causing a deterioration in color purity called purity drift (PD). A general color picture tube with a rough mask hole pitch has a large margin for deviations in the geometric positional relationship between the phosphor layer and the electron beam (hereinafter referred to as the guard band amount), and the shadow mask is subject to thermal deformation to a certain extent. However, deterioration of color purity is less likely to occur. However, in the case of high-definition color picture tubes used as display devices for characters and graphics, and color picture tubes for general consumer use that have improved screen flatness and have a finer pitch to accommodate teletext broadcasting, the above margin is required. Degree is not always sufficient.
In other words, in the case of high-definition color picture tubes, the hole size is small (for example, 140μ for 0.3mm pitch, 85μ for 0.2mm pitch) because the hole pitch is small (for example, 140μ for 0.3mm pitch, 85μ for 0.2mm pitch). When trying to obtain a mask with small hole dimensions, the mask plate thickness must be made thinner, resulting in a decrease in heat capacity, and the amount of thermal expansion under certain conditions is greater than in a thicker plate, resulting in a deterioration of color purity. There are some easy problems. On the other hand, in the case of a color picture tube with improved screen flatness, the radius of curvature of the mask is larger than that of a regular tube, so even if the same amount of mask undergoes the same amount of thermal expansion, the electron beam passing through the mask hole will The problem is that there is a large amount of deviation in the position of the target phosphor layer, and the amount of the guard band is also small due to the small pitch, so that color purity tends to deteriorate. Various methods are being considered to solve this problem, but the
Publication No. 25446, Japanese Patent Application Laid-Open No. 1983-58977, Japanese Patent Application Publication No. 1973
Iron-nickel alloy with a small coefficient of thermal expansion, such as 36% Ni-Fe amber alloy (0 to 100°C, approximately 0 to 2.0×10 ^-6 /°C) as shown in Publication No. 68650
Or 42% Ni-Fe alloy (0~100℃, approx. 5.0×
10 ^-6 /℃) has been proposed as a material, but it has not yet reached the point where it satisfies practical conditions. One of the reasons for this is the difficulty in processing masks made of iron-nickel alloy. The curved surface of the shadow mask requires high precision,
For a radius of curvature (R) of 1000mm, the allowable tolerance is ±5mm, which is extremely strict. However, iron-nickel alloys have the disadvantage that, compared to conventional alloys whose main component is iron, they have high mechanical strength and poor spherical formability by pressing etc. even when subjected to similar annealing. For example, the first
As shown in the figure, when an iron-nickel mask with a thickness of 0.2 mm is molded into a spherical surface and a local dent is created with respect to the standard radius, if the amount of dent (d) is less than 20 μm, it will substantially affect the color purity. Deterioration is acceptable. This amount of depression can be calculated as the yield point strength of the shadow mask material, for example.
A 14-inch shadow mask exhibits the characteristics shown in Figure 2. That is, in order to make the amount of depression 20 μm or less, it is necessary to suppress the yield point strength to 20 Kg/mm ² or less. However, when a shadow mask made of an iron-nickel alloy is annealed in an annealing furnace in the same hydrogen atmosphere as a conventional shadow mask made of aluminum-killed low carbon steel, the yield point strength obtained is as shown in Figure 3. Furthermore, property b of the iron-nickel alloy is much higher than property a of aluminum killed low carbon steel. That is, even when annealed at a high temperature of 900°C, the yield point strength decreases only to 29 to 30 kg/mm ² . In addition, in Figure 2, the yield point strength of the iron-nickel alloy is 0.2% because it does not exhibit the yield phenomenon peculiar to carbon steel.
The tensile strength when stretched is used as a substitute. As described above, a shadow mask made of an iron-nickel alloy has large deformations and dents, especially around the effective area, so deterioration of color purity due to deformation becomes a major problem.
On the other hand, in order to improve the corrosion resistance and heat radiation of the shadow mask incorporated into the tube, a black oxide film layer is formed on the mask surface after obtaining the desired curved surface by press molding. However, since iron-nickel alloy contains nickel, which has good corrosion resistance, it is less likely to form a black oxide film than aluminum killed low carbon steel. As a result, heat radiation from the mask deteriorates, and combined with the fact that the thermal conductivity is lower than that of aluminum killed low carbon steel, heat tends to accumulate. The temperature of the mask under the same imaging conditions tends to be higher than that of a mask made of low carbon steel, so the amount of thermal expansion will be higher than the desired value, and unless a black oxide film with good heat radiation is formed, it will be called low thermal expansion. The advantages of the material are not utilized, and color purity deterioration due to thermal deformation becomes a problem. [Object of the Invention] The present invention provides a method for manufacturing a shadow mask made of an iron-nickel alloy, which has good press formability, and facilitates the formation of a black oxide film with excellent corrosion resistance and thermal radiation resistance. The ultimate goal is to provide a color picture tube with good screen white uniformity (WU) quality and no PD problems. [Summary of the Invention] The present invention involves annealing a shadow mask made of an iron-nickel alloy in a vacuum before press forming.
By performing cooling after annealing in a furnace in a reducing atmosphere, the yield point strength of the shadow mask is lowered and the amount of deformation during press forming is suppressed, and at the same time, the formation of stainless steel on the surface of the shadow mask is suppressed and a good oxide film is created. growth. [Embodiments of the Invention] Examples 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 material compositions of the amber alloy and aluminum killed low carbon steel.

[Table] Figure 4 shows the yield point strength of a shadow mask made of 36Ni amber alloy with the above composition when the annealing temperature is increased using an annealing furnace in a hydrogen atmosphere (dew point 10°C). As is clear from Figure 4,
Even when annealed at a high temperature of 1200℃, the yield point strength is 24Kg/mm ²
It only decreases to. Therefore, in order to set the yield point strength to 20 Kg/mm ² or less without causing problems in formability, it is necessary to extrapolate from FIG. 4 and set the annealing temperature to 1500 to 1700°C. However, considering that the melting point of the amber alloy is 1440-1450°C, this is not practicable. The present inventors observed the crystal structure of a metal plate after annealing as shown in JP-A No. 59-27433, and found that in the case of hydrogen annealing, the crystal grains in the cross section change as the annealing temperature increases. Although it grows well,
It was found that the growth of crystal grains on the surface was negligible. This insufficient growth of surface crystal grains is related to the yield point strength, and we thought that if the same crystal growth as in the cross section could be achieved, the yield point strength would approach 20 Kg/mm ² . For this purpose, it is assumed that the growth of surface grains can be promoted by evaporating impurities that concentrate at the surface grain boundaries, such as Mn, P, and S, which have particularly high vapor pressure, from the grain boundaries. Annealing was performed. Annealing was performed at a vacuum degree of 10 ^-2 Torr and a temperature of 900 to 1200°C for 10 minutes each. As a result, as shown in FIG. 5, a yield point strength of 20 kg/mm ² or less was obtained at an annealing temperature of 1000° C. or higher. In addition, the growth of crystal grains on the surface is the same as that inside, and as can be seen from Table 2 showing the analysis results of impurities in the surface layer with a thickness of 1/20 or less, Mn,
Impurities such as P and S are significantly reduced. Although the degree of vacuum during the vacuum annealing was performed at 10 ^-2 Torr, the degree of vacuum during vacuum annealing can be lowered to 10 ^-1 Torr by increasing the annealing time. The growth of crystal grains changes depending on the contamination state of the grain boundaries.
Contamination inhibits its growth. By annealing this in a vacuum atmosphere, the concentrated impurities escape from the surface and are removed. This speed depends on the degree of vacuum as well as the ambient temperature, but it was found that the required degree of vacuum was 10 ^-1 Torr or less.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to easily form a black oxide film that has good press formability and excellent corrosion resistance and thermal radiation properties, has good white uniformity quality, and has no PD problem. A shadow mask made of nickel alloy can be obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the main parts to explain the deformation of the shadow mask, Figure 2 is a characteristic diagram showing the relationship between the amount of deformation of the shadow mask and the yield point strength, and Figures 3 and 4 are the annealing temperature of the shadow mask. FIG. 5 is a characteristic diagram showing the relationship between vacuum annealing temperature and yield point strength.

Claims (1)

[Scope of Claims] 1. A step of drilling a large number of holes in a thin metal plate mainly composed of iron and nickel, a step of annealing the metal plate in which the large number of holes have been drilled, and A method for manufacturing a shadow mask, comprising at least the steps of forming an annealed metal plate and forming a black oxide film on the formed metal plate,
A method for manufacturing a shadow mask, characterized in that the annealing is performed in a vacuum, and the cooling after the annealing is performed in a furnace in a reducing atmosphere. 2. The method of manufacturing a shadow mask according to claim 1, wherein the annealing is performed in a vacuum at a pressure of 10 ^-1 torr or less. 3. Production of a shadow mask according to claim 1, characterized in that hydrogen gas is continued to be introduced during furnace cooling after the annealing until the furnace temperature drops to 500°C, and a black oxide film is formed after the annealing process is completed. Method. 4. The method for manufacturing a shadow mask according to claim 2, wherein the annealing is performed at a temperature of 1000° C. or higher. 5. The method of manufacturing a shadow mask according to claim 3, wherein the shadow mask is stored in a deoxidizing atmosphere until the black oxide film is formed after the annealing.