JPH0143978B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phosphor screen for a display cathode ray tube in which the light emitting elements are formed from a mixture of two or more different phosphors.

In recent years, with the expansion of cathode ray tubes for use in computer terminal devices and other uses, cathode ray tubes for displays have come to be used with phosphor screen characteristics different from those of ordinary commercial televisions. That is, instead of the usual three primary colors of green, red, and blue, three-color phosphor screens are made with light gray or white instead of blue. In this case, two or more types of phosphors must be mixed in order to obtain a predetermined luminescent color.

In addition, when using a vertical scanning frequency lower than the normal 60Hz, phosphors with a long afterglow time are used to prevent flicker, but generally, phosphors with a long afterglow time have low brightness, so they are not suitable for commercial television. P22 phosphor used in cathode ray tubes may be used in combination.

In this way, when manufacturing a phosphor screen by mixing two or more types of phosphors to form one light emitting element, the slurry method that is currently commonly used for manufacturing color cathode ray tube phosphors produces an excessive amount of material on the inner surface of the panel. Because the coated slurry is collected and reused, the mixing ratio of two or more different types of phosphors contained in the collected slurry is different from the phosphor mix ratio of the slurry used for coating, so the characteristics always remain constant. It was difficult to manufacture phosphor screens. In other words, if the mixing ratio of phosphors changes, the emitted light color will change, and if a phosphor with a long afterglow time and a phosphor with a short afterglow time are mixed, the afterglow time and brightness will change. There were flaws.

In the slurry method, a phosphor screen is manufactured through the steps shown in FIG. That is, with the inner surface of the panel facing upward, a slurry of a phosphor suspended in a mixed solution of polyvinyl alcohol (PVA) and ammonium dichromate (ADC) is applied to the inner surface of the panel. The slurry is applied to the entire inner surface of the panel while rotating slowly, and then the panel is rotated at high speed to shake off excess slurry using centrifugal force. The film is then dried using a heater, a shadow mask is attached to the panel, exposed to light, and developed using hot water. This process is repeated three times to form a three-color phosphor screen.

The slurry shaken off by rotating the panel at high speed is recovered and reused, but the phosphor content of this slurry is lower than the phosphor content of the slurry at the time of coating. Therefore, it is mixed with a slurry having a high phosphor content and used for recoating with a predetermined phosphor content. If the slurry contains only one type of phosphor, no particular problem will occur with the conventional method, but if two or more types of phosphors are mixed, the ratio of phosphors contained in the slurry to be recovered may differ from the original one. It becomes different. After examining the cause of this, we found that it was due to differences in the specific gravity and particle size of the phosphors used. That is, when a slurry is coated with one type of phosphor, the proportion of the phosphor contained in the recovered phosphor slurry decreases, and the average particle size becomes smaller. (Figure 2) In these cases, the phosphor settles between the time the slurry is applied to the inner surface of the panel and the time it is shaken off. Many bodies are recovered. When using a slurry containing two types of phosphors, different phosphors generally have different specific gravity, so the phosphor with higher specific gravity settles first and adheres more to the panel. The recovered phosphor slurry contains many phosphors with low specific gravity.
Therefore, the ratios of the two types of phosphors contained in the recovered phosphor will differ.

Based on the above study results, the present invention has been developed by making the average particle size of the phosphor with a large specific gravity smaller than that of the phosphor with a small specific gravity, and the phosphor mixing ratio of the recovered phosphor is adjusted to the phosphor mixing ratio of the slurry when applied. This is done so that it does not change. By reducing the average particle size of a phosphor with a large specific gravity, the sedimentation rate can be made the same as that of a phosphor with a small specific gravity and a large average particle size. Therefore, if the sedimentation speed is made the same, it is possible to recover a slurry having the same mixing ratio of phosphors as that of the coating slurry, making it easy to reuse it.

According to the present invention, when two or more types of phosphors are mixed to form one light emitting element, the mixing ratio of the phosphors can be kept constant even in the recovered phosphors, which is very beneficial. In particular, since rare earth phosphors generally have a high specific gravity, it is particularly effective when rare earth phosphors are mixed with other phosphors.

The present invention will be explained below with reference to Examples.

Example 1 Average particle size of 8-2μ in blue light-emitting element of three-color phosphor screen
silver-activated zinc sulfide phosphor (specific gravity 4.1, CIE chromaticity x=
0.148, y=0.062) 66% by weight, copper aluminum activated zinc sulfide phosphor with average particle size 8.2μ (specific gravity 4.1, CIE chromaticity x
=0.280, y=0.600) 19% by weight, average particle size 6-0μ
europium-activated yttrium oxysulfide phosphor (specific gravity 4-95, CIE chromaticity x=0.620, y=0.350)15
A fluorescent film was formed by mixing % by weight and using a slurry method.
The emission color at this time is CIE chromaticity: x=0.180, y=
It was 0.140. This phosphor slurry was recovered and used for production, but the CIE chromaticity was x=0.180±
0.005, y=0.140±0.005. This range is a range in which almost no change in chromaticity is observed during use.

Example 2 80% by weight of manganese-activated zinc phosphate phosphor (specific gravity 3.9, CIE chromaticity x=0.645, y=0.350) with an average particle size of 7.0μ and an average particle size of 5.2μ in a red light-emitting element of a three-color phosphor screen.
europium-activated zinc oxysulfide phosphor (specific gravity
4.95, CIE chromaticity x=0.620, y=0.350) 20% by weight
A fluorescent film was formed using a slurry method. The luminescent color at this time is CIE chromaticity x = 0.637, y = 0.350, and the brightness is higher than when using manganese activated zinc phosphate phosphor alone.
It became 30% brighter. Although production was carried out using this phosphor slurry, no change was observed in the brightness or the frame frequency at which flicker occurs.

As described above, according to the present invention, when one light emitting element is formed using a slurry method using mixed phosphors, it is very useful when mass producing phosphor screens with the same characteristics.

[Brief explanation of drawings]

Figure 1 is a flow sheet of the fluorescent film manufacturing process, Figure 2
The figure shows the particle size distribution of the coated phosphor and the recovered phosphor. 1... Particle size distribution of coated phosphor, 2... Particle size distribution of recovered phosphor.

Claims (1)

[Claims] 1. When a light emitting element is formed from a mixture of two or more different types of phosphors, the device is characterized by having a phosphor screen in which the average particle size of the phosphor with higher specific gravity is smaller than the average particle size of the phosphor with lower specific gravity. Cathode ray tube for display.