JPH02242880A - Production of fluorescent substance coated with silicon dioxide - Google Patents

Abstract

PURPOSE:To obtain a fluorescent substance for cathode ray tubes coated with a homogeneous and smooth thin film by keeping a dispersion prepared by dispersing a fluorescent substance in a liquid containing an alcohol under specific conditions, slowly dripping an organosilicon into the dispersion and forming a thin film of silicon dioxide. CONSTITUTION:The objective fluorescent substance is obtained by initially dispersing a fluorescent substance, such as zinc sulfide-based fluorescent substance, in ethyl alcohol (preferably a solution at >=0.7 volume ratio of ethyl alcohol/water), adding aqueous ammonia to the dispersion while stirring the dispersion, regulating the pH to >=8, further keeping the temperature at 40-70 deg.C and slowly dripping an organosilicon (e.g. methyl silicate) into the above- mentioned dispersion, requiring a time of >=10min.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for manufacturing a phosphor suitable for use in phosphor screens of color picture tubes and other cathode ray tubes.

[Conventional technology and its problems]

Phosphors used in color picture tubes are subjected to various surface treatments in order to improve coating properties and prevent discoloration during coating. As surface treatment substances, silicate compounds, aluminate compounds, phosphate compounds, metal oxides, etc. are used. In particular, silicate compounds are widely used because they are easy to process. Silicon dioxide, zinc silicate, aluminum silicate, and the like are known as silicate compounds. A technique for attaching silicon dioxide to the surface of a phosphor has been developed (Japanese Unexamined Patent Publication No. 115683/1983). This publication states that organic silicon is hydrolyzed to form silicon dioxide,
A technique for attaching this to the surface of a phosphor has been disclosed. Ethyl silicate and the like are used as organosilicon. In this method, organic silicon is hydrolyzed using ammonium carbonate or adsorbed water to form silicon dioxide, which is attached to the surface of the phosphor. However, with this method, a uniform thin film of silicon dioxide cannot be deposited on the surface of the phosphor, resulting in an uneven surface coating. The silicon dioxide coating the surface of the phosphor is preferably a thin film that uniformly covers the surface of the phosphor more completely. A phosphor coated with a non-uniform silicon dioxide film cannot cover the front side of the phosphor unless the silicon dioxide deposit is increased. If the amount of silicon dioxide attached is small,
There are many parts that are not covered. When the amount of the surface treatment substance attached increases, the characteristics of the fluorescent film deteriorate. In particular, the luminance of light emission decreases. This is because the surface coating material is attached as an auxiliary material to improve the characteristics of the phosphor, and does not emit light itself. When attaching silicon dioxide to the surface of a phosphor, it is important to completely cover the front surface of the phosphor with a small amount of surface treatment substance. If silicon dioxide coated on the surface of the phosphor can be formed into a thin film, the coating film can transmit the emitted light from the phosphor without absorbing it, thereby reducing the reduction in luminance. Moreover, silicon dioxide covering the entire surface of the phosphor protects the phosphor in an ideal state. When the entire surface of the phosphor is protected by a thin film, contamination of the phosphor during coating is prevented and discoloration is reduced. Another feature is that the coating prevents deterioration due to electron beam irradiation and reduces the decrease in brightness. Furthermore, it achieves a number of excellent effects, such as improved coating properties and higher brightness when used as a fluorescent film. It can be easily considered theoretically that a thin, uniform silicon dioxide film exhibits excellent properties, but all the methods developed so far have been based on observing the coated phosphor with an electron microscope. A smooth silicon dioxide film could not be formed on the surface.

[Purpose of the invention]

This invention was developed to satisfy this requirement, and an important objective of the invention is to provide a method for manufacturing a phosphor that can coat the surface of the phosphor with a uniform thin film of silicon dioxide. be.

[Means to solve conventional problems]

This invention utilizes organic silicon hydrolysis to attach silicon dioxide to the surface of a phosphor for a cathode ray tube. In order to coat the phosphor with a thin and uniform silicon dioxide film, the phosphor is dispersed in a liquid containing alcohol, the pH of this phosphor dispersion is adjusted to 8 or higher, and the heating temperature is set to 4.
The temperature is maintained at 0 to 70°C, and organosilicon is added. The pH of the phosphor dispersion can be adjusted by dropping aqueous ammonia. This invention does not mix organosilicon together with the phosphor dispersion liquid, but maintains the pH of the phosphor dispersion liquid at 8 or higher and the heating temperature at 40 to 70°C, and injects the organosilicon for a period of 10 minutes or more. It is added slowly and gradually dropwise. This is because if the dropping time of organosilicon is short, silicon dioxide will not form a film but will adhere to the surface of the phosphor in the form of particles. The pH of the phosphor dispersion is adjusted to 8 or higher, preferably 9 or higher. This is because when the pH is below 8, hydrolysis of organosilicon is difficult to proceed. The temperature of the phosphor dispersion liquid is preferably adjusted to a range of 40°C to 70°C. This is because when heated to 40° C. or higher, hydrolysis of organosilicon tends to proceed, and when heated above 70° C., aqueous ammonia evaporates and the pH decreases. In the above manufacturing method, the amount of the surface treatment substance deposited is preferably adjusted to a range of 0.01 to 5 parts by weight per 100 parts by weight of the phosphor. If the amount of silicon dioxide deposited is too small, the effect of surface treatment will be low, while if it is too large, the brightness will be reduced. The method of this invention allows silicon dioxide to be attached to the surface of a phosphor without the use of a binder. This is because silicon dioxide is formed in a film form and adhered to the surface of the phosphor. However, it goes without saying that it is also possible to attach silicon dioxide to the surface of the phosphor using a binder. The binder includes, for example, a zinc compound, an aluminum compound, an alkaline earth metal compound such as Mg, Ca, or Sr;
At least one of phosphate compounds and borate compounds can be used. As the zinc compound, water-soluble zinc salts such as zinc sulfate, zinc nitrate, and zinc acetate can be used. As the aluminum compound, water-soluble aluminum salts such as aluminum nitrate and aluminum sulfate can be used. Furthermore, water-soluble salts such as sodium pyrophosphate can be used as the phosphoric acid compound. As the boric acid compound, sodium borate or the like can be used. Since the phosphor used in the present invention exhibits excellent characteristics when used in color picture tubes, it goes without saying that it can be used not only in color picture tubes but also in monochrome picture tubes. Examples of phosphors include: ■ Oxide-based phosphors such as zinc sulfide phosphors, europium-activated yttrium oxide phosphors, manganese-activated zinc phosphate phosphors, and manganese-activated zinc silicate phosphors; ■ Europium-activated phosphors Sulfide-based phosphors such as active yttrium oxysulfide phosphors and terbium-activated yttrium oxysulfide phosphors can be used. As the organosilicon used in this invention, methyl silicate, ethyl silicate, or propyl silicate can be used. Particularly suitable is ethyl silicate. In this invention, the surface of the phosphor is treated in the following steps. ■ Disperse the phosphor in ethyl alcohol. This liquid preferably has an ethyl alcohol/water volume ratio of 0.7 or more. (2) While stirring the phosphor dispersion, add ammonia water to adjust the pH. ■ Slowly drop organosilicon and aqueous ammonia separately over time into the phosphor dispersion. In steps ① to ②, a thin film of silicon dioxide is formed on the surface of the phosphor. Electron micrographs of the phosphors whose surfaces were coated with a silicon dioxide film in this step are shown in Figures 1a and b. It is. As shown in FIGS. 1a and 1b, the phosphor produced by the method of the invention is coated with a thin film of silicon dioxide with an extremely smooth surface. For reference, the above-mentioned JP-A-60-115
FIG. 2 shows an electron micrograph of a phosphor coated with silicon dioxide using the conventional method disclosed in Japanese Patent No. 683. As shown in Fig. 2, conventional phosphors have granular irregularities of silicon dioxide on their surfaces, but the phosphors produced by the method of this invention have extremely smooth and smooth surfaces, as shown in Fig. 1. A thin film is formed.

[effect]

The phosphor produced by the method of this invention is coated with a smooth thin film of silicon dioxide, as shown in FIG. Phosphors coated with a thin film of silicon dioxide
Contamination of the phosphor during application is prevented and discoloration is reduced. Further, the coating film prevents deterioration due to electron beam irradiation, thereby reducing reduction in brightness. Furthermore, the coating properties can be improved, and the brightness when used as a fluorescent film can be increased. These properties change depending on the amount of silicon dioxide deposited on the surface. FIGS. 3 and 4 show the amount of Cr adsorbed by the phosphor and the degree of discoloration caused by Cu ions. FIG. 3 measures the amount of Cr adsorbed on the phosphor coated as a phosphor film. That is, after attaching the phosphor to the face plate using a mixed aqueous solution of dichromate and polyvinyl alcohol, the phosphor was peeled off from the face plate, and the amount of Cr adsorbed on the phosphor was measured. As shown in this figure, the phosphor produced by the method of the present invention can have only 1 part by weight or less of silicon dioxide attached to it, as shown by curve A, to drastically reduce the amount of Cr adsorbed. . If a large amount of Cr is adsorbed, the fluorescent film becomes slightly brownish (
Cr ion color). However, the phosphor produced by the method of the present invention can prevent interference with light emission due to the influence of Cr. Curve B shows the characteristics of a phosphor obtained by mixing ethyl silicate and ethyl alcohol together in a phosphor dispersion, and adding an ammonium carbonate solution dropwise thereto to adhere silicon dioxide to the surface. FIG. 4 measures the extent to which the color changes due to the influence of Cu ions. A ZnS:Ag blue-emitting phosphor is used for this measurement. Zinc sulfide phosphor emits blue light when activated with silver and green light when activated with copper, so ZnS:
The emission color of the Ag phosphor changes to green due to the influence of a very small amount of Cu ions. The measurements shown in Figure 4 were carried out during the process of coating the phosphor by precipitation using the potassium silicate and barium method.
12 ppm of copper ions (acid copper) are added to the cushion liquid and applied to the glass. The phosphor applied to the glass was dried and baked at 450° C. for 30 minutes, the color tone before and after baking was measured, and the change in y value Δy was measured. The larger Δy is, the greater the degree of discoloration. As shown in this figure, the phosphor produced by the method of this invention is only 1! Coating with a trace amount of silicon dioxide of 11 parts or less can effectively prevent discoloration of copper ions. Song & IB
shows the characteristics of a phosphor in which ethyl silicate and ethyl alcohol are mixed together in a phosphor dispersion liquid, and an ammonium carbonate solution is added dropwise to this to adhere silicon dioxide to the surface. Furthermore, FIG. 5 shows the change in brightness with respect to the amount of silicon dioxide deposited. A face plate was prototyped by applying a phosphor to the face plate in the same manner as the test shown in FIG. 3, and depositing aluminum on the surface of the phosphor. The back side of this face plate was heated at an accelerating voltage of 12 kV and a current density of 1.
．． The brightness of the face plate surface was measured by exciting with an electron beam to 0μ. Curve A shows the brightness characteristics of the phosphor produced by the method of this invention. In this way, although the phosphor produced by the method of the present invention has silicon dioxide attached thereto, which itself does not emit light, it is possible to improve the luminance by adjusting the amount of silicon dioxide attached to the phosphor to a specific amount. The reason why the brightness can be increased by attaching a silicon dioxide thin film is that the surface treatment improves the coating condition of the phosphor, the silicon dioxide thin film on the surface does not scatter the emitted light from the phosphor, and it also prevents impurities such as Cr from scattering. The reason is to suppress interference with light emission caused by Furthermore, FIG. 6 shows the deterioration characteristics of the phosphor to which silicon dioxide is attached. For the deterioration characteristics, the same face plate used for the measurement in FIG. 5 was used. However, in order to forcibly degrade the fluorescent film, the fluorescent film was stimulated for 30 minutes under conditions that were more severe than under normal usage conditions. Excite the fluorescent film
For the electron beam, the acceleration voltage is 15kV and the current density is 10μ.
A/cm2. The brightness after stimulation with an electron beam is displayed with the brightness before forced stimulation being 100. As is clear from this figure, the phosphor prototyped using the method of this invention is
Coating with less than 1 part by weight of silicon dioxide significantly improves the deterioration characteristics. Furthermore, the phosphor produced by the method of the present invention can be coated with silicon dioxide on the surface after the pigment is attached, thereby preventing the pigment from peeling off. FIG. 7 shows the measurement of the pigment peeling rate of the phosphor to which silicon dioxide is attached. This measurement uses a pigmented phosphor whose surface is coated with silicon dioxide. This measurement is
A slurry of dichromate and polyvinyl alcohol in which a pigmented phosphor was dispersed was forcibly dispersed using a disperser, and the peeling rate of the pigment was measured before and after the dispersion. As shown in this figure, the phosphor prototyped by the method of the present invention has 1 part by weight or less of silicon dioxide attached to it, thereby minimizing the peeling rate of the pigment.

[Preferred embodiment]

The present invention will be explained in detail below. (Example 1) A phosphor coated with a silicon dioxide thin film was manufactured using the following steps. , ■ Ethanol...e o o g. Ammonia water (18%) 30 g 1 green light-emitting phosphor (ZnS: Cu) 300 g or more were placed in a container and heated to 50° C. while stirring. ■ Mix ethyl panolicate and ethyl alcohol,
Prepare the stirred solution and 5% ammonia water. The amount of ethyl silicate mixed is 22.5g, the amount of ethyl alcohol mixed is 120g, and the amount of ammonia water is 1.5g.
Let it be 0 g. ■ Drop the mixture of ethyl silicate, ethyl alcohol, and ammonia water into the stirring phosphor mixture. The dropping time is 30 minutes. During the dropping, the temperature of the phosphor mixture is maintained at 50 to 55°C. Keep the pH between 9.2 and 9.4. (2) After being allowed to stand, the supernatant liquid was removed by decantation, dehydrated, dried at a temperature of 110°C to 120°C for 8 to 12 hours, and separated through a sieve. The thus obtained phosphor had a thin film of silicon dioxide attached to its surface. The phosphor obtained in this step is shown in FIG. 1a. The obtained phosphor has a weight ratio of 2.5 to 100 phosphor weight parts.
% by weight of silicon dioxide was deposited. Further, silicon dioxide having a thickness of 50 mμ was adhered to the surface of this phosphor. When measuring the amount of Cr adsorption, brightness, Δy due to Cu contamination, and brightness after forced deterioration test for this phosphor, the results were as follows: ■ Adsorption amount of 3pprn, ■ Brightness of 110%, ■ Discoloration Δy due to Cu contamination. was 0.002, and ■ the brightness after forced deterioration was 97.5%. By the way, the phosphor that does not have silicon dioxide attached is ■ C
The adsorption amount of r was 200 ppm, (1) the brightness was 100% (based on the brightness of this phosphor), (2) the Δy due to Cu contamination was 0.03, and (2) the brightness after the forced deterioration test was 92.0%. (Example 2) A phosphor coated with a silicon dioxide thin film was manufactured using the following steps. ■ Ethanol...4.8kg. Ammonia water (18%) 200 g. Blue-emitting phosphor (ZnS:Ag)-2kg,
was placed in a container and heated to 50°C while stirring;■
Prepare a mixed and stirred solution of ethyl silicate and ethyl alcohol, and 5% ammonia water. The amount of ethyl silicate mixed is 25g, and the amount of ethyl alcohol mixed is 2
00g, and ammonia water is 250g. (2) Separately drop a mixture of ethyl silicate and ethyl alcohol and ammonia water into the stirring phosphor mixture. The dropping time is 30 minutes. During the dropping, the temperature of the phosphor mixture is maintained at 50 to 53°C. pH is 9.
Keep it at 3. (2) After being allowed to stand, the supernatant liquid was removed by decantation, dehydrated, dried at a temperature of 110°C to 120°C for 8 to 12 hours, and separated through a sieve. The thus obtained phosphor had a thin film of silicon dioxide attached to its surface. The phosphor obtained in this step is shown in Figure 1. The obtained phosphor has a weight ratio of 0.4 to 100 parts by weight of the phosphor.
5% by weight of silicon dioxide was deposited. Further, the thickness of the silicon dioxide film attached to the surface of the phosphor was 10 mμ. Regarding this phosphor, we measured the adsorption amount, brightness, △y due to Cu contamination, and brightness after forced deterioration test, and found that: ■ Cr adsorption amount is 10 ppm, ■ Brightness is 105%, ■ Cu contamination The color change Δy was 09005°■ The brightness after forced deterioration was 95%. (Example 3) A phosphor coated with a thin film of silicon dioxide was manufactured using the following process. ■ Ethanol... 800g, ammonia water (
18%)...30g, blue-emitting phosphor (ZnS
: Ag)-300g, 10% cobalt aluminate dispersion...48mQ, 10% cobalt aluminate dispersion 4
For 8mα, cobalt aluminate and phosphor 100!1
1 for 1 part. Contains 6 parts by weight. These raw materials were placed in a container and heated to 50°C while stirring. ■ Mix ethyl silicate and ethyl alcohol,
Prepare a stirred solution and 5% aqueous ammonia. The amount of ethyl silicate mixed is 22.5g, the amount of ethyl alcohol mixed is 120g, and the amount of ammonia water is 150g.
shall be. This liquid is 3 parts by weight per 100 parts by weight of the phosphor.
Contains parts by weight of silicon dioxide. ■ Separately drop a mixture of ethyl silicate and ethyl alcohol and aqueous ammonia into the stirring phosphor mixture. The dropping time is 30 minutes, and the temperature of the phosphor mixture is maintained at 50 to 53° C. during the dropping. pH is 9.2
Keep at ~9.4. (2) After being allowed to stand, the supernatant liquid was removed by decantation, dehydrated, dried at a temperature of 110°C to 120°C for 8 to 12 hours, and separated through a sieve. The thus obtained phosphor had a Wi film of silicon dioxide attached to its surface. The obtained phosphor has a weight ratio of 2.8 to 100 phosphor weight parts.
% by weight of silicon dioxide was deposited. The silicon dioxide film thickness was approximately 60 mμ. For this phosphor, we measured the Cr adsorption amount, brightness, Δy due to Cu contamination, and brightness after forced deterioration test, and found that: ■ Adsorption amount is 5 ppm, ■ Brightness is 110%, ■ Discoloration Δy due to Cu contamination. ■ The brightness after forced deterioration was 97.4%.■ The peeling rate of the pigment was 3%.By the way, the peeling rate of the pigment of the pigmented phosphor without silicon dioxide was 80%. ,
The pigment peeling rate of phosphors with pigments attached using conventional methods is 3.
It was 0%.

[Brief explanation of drawings]

Figures 1a and b are electron micrographs of a phosphor produced by the method of the present invention, Figure 2 is an electron micrograph of a phosphor to which silicon dioxide has been attached by a conventional method, and Figures 3 to 6 are A graph showing the adsorption amount of Cr, discoloration Δy due to Cu contamination, brightness, and deterioration characteristics with respect to the amount of silicon dioxide adhesion. FIG. 7 is a graph showing the pigment peeling rate of the pigmented phosphor against the amount of silicon dioxide adhesion. Tate 2 < S! 0dlltl/ii light body ioo weightff1aiE diagram S iQ, weight WI/fluorescent fluorescent body 1 member05102 parts by weight/fluorescent body 100 parts by weightS io, weight parts/it light body ioo weight! Department! ．． Description of the case 2, Title of the invention 3, Person making the amendment 4, Substitute amendment (spontaneous) 1999 Patent Application No. 064417 Method for manufacturing phosphor coated with silicon dioxide 491 Kaminakamachioka, Anan City, Tokushima Prefecture Address 100 Nichia Kagaku Kogyo Co., Ltd. Representative Nobuo Ogawa Attachment 1, page 3, line 10 of the specification, "front" is corrected to "surface." 2. "Front" on page 3, line 19 of the specification is corrected to "surface." 3. Insert the following sentence between page 7, line 8 and line 9 of the specification. ``Magnesium nitrate, calcium nitrate, strontium nitrate, etc. can be used as alkaline earth metal compounds.'' 4. ``For boric acid compounds,
"Sodium borate" is corrected to "Boric acid compounds include boric acid and sodium borate." 5. From page 7, line 18 to page 8, line 2 of the specification, "■ Zinc sulfide-based phosphor, europium-activated yttrium oxide phosphor,......8 , Details of the correction The phosphor as shown in the attached sheet, ■Europium-activated yttrium oxysulfide fluorescence” will be corrected as follows. ■ Sulfide-based phosphors such as zinc sulfide-based phosphors and zinc cadmium sulfide phosphors; ■ Oxides such as europium-activated yttrium oxide phosphors, manganese-activated zinc phosphate phosphors, and manganese-activated zinc silicate phosphors. "Europium-activated oxidized yttrium fluorescence" 6. In the second line of page 11 of the specification, "together with alcohol" is corrected to "together with alcohol." 7. Correct "Curve A is" on page 12, line 13 of the specification to "Curve in FIG. 5." 8. On page 15, line 4 of the specification, “Ammonia water is 15
Set to 0g. " is corrected to "The amount of ammonia water is 150 g. This liquid contains 3 parts by weight of silicon dioxide per 100 parts by weight of the phosphor." 9. “Drop into the mixed liquid” on page 15, line 7 of the specification
is corrected to ``Drop them separately into the mixture.'' 10. On page 17, line 4 of the specification, “Nia water is 250
Let it be g. " is 250 g of near water. This liquid contains 0.5 parts of heavy electricity per 100 parts of phosphor by weight of silicon dioxide. Corrected to J. 1. Indication of the incident 2. Invention of the invention Name Address Procedures Correction Book Type) % Formula % Manufacturing method of phosphor coated with silicon dioxide , page 20, lines 11 to 13 of the specification
Figures a and b are electron micrographs of a phosphor produced by the method of the present invention, and Figure 2 is an electron micrograph of a phosphor to which silicon dioxide has been deposited by a conventional method.
) is an electron micrograph showing the particle structure of the phosphor produced by the method of the present invention, and FIG. 2 is an electron micrograph showing the particle structure of the phosphor to which silicon dioxide has been attached by the conventional method.'' 8. Details of the amendment as shown in the attached sheet.

Claims (1)

[Claims] A method for attaching silicon dioxide to the surface of a phosphor for a cathode ray tube by utilizing hydrolysis of organosilicon, comprising: (1) dispersing the phosphor in a liquid containing alcohol;
2) The pH of this phosphor dispersion is set to 8 or higher, (3)
Furthermore, the temperature of the dispersion liquid is maintained at 40 to 70°C, and (4) organosilicon is gradually dropped over a period of 10 minutes or more to form a thin film of silicon dioxide on the surface of the phosphor. A method for producing a phosphor coated with silicon dioxide.