JPH09263753A - Method for surface-coating phosphor particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain phosphor particles excellent in moistureproofness, etc., by fludizing phosphor particles and spraying a metal alkoxide oligomer on the surfaces of the particles to form metal oxide films thereon. SOLUTION: Phosphor particles (e.g. copper-activated zinc sulfide phosphor particles) are fed into a cylindrical fluidized bed apparatus having a filter mesh on its bottom, and heated nitrogen or the like is passed through the filter mesh and blown into the particles to form a fluidized bed. A solution of an oligomer of a metal alkoxide (e.g. an oligomer of aluminum isopropoxide) is sprayed on the fluidized bed, and the particles are dried, whereby the oligomer undergoes a hydrolysis reaction and a condensation reaction on the surfaces of the particles to form films of a metal oxide on their surfaces. A phosphor produced by using the obtained phosphor particles surface-coated with a metal oxide is not deteriorated by moisture.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for coating the surface of phosphor particles with an inorganic oxide, and more specifically,
The present invention relates to a method for making the surface of phosphor particles moisture-proof by forming a continuous film of such an oxide.

[0002]

2. Description of the Related Art A phosphor emits fluorescence when excited by an electron beam, an ultraviolet ray or an electric field, and is therefore used in various applications as a cathode ray tube, a fluorescent lamp and a thin flat light source.

For example, when the electroluminescent phosphor (hereinafter referred to as EL phosphor) is used in an electroluminescent lamp (hereinafter referred to as EL lamp) such as an electroluminescent panel (hereinafter referred to as EL panel), it is typical. The structure is such that an EL phosphor layer is interposed between the front transparent electrode and the back electrode, and a dielectric layer such as barium titanate is interposed between the phosphor layer and the back electrode. The luminous efficiency of this EL lamp is
When it emits light in a high humidity state, it deteriorates more rapidly than when used in a dry state. Therefore, the EL lamp
Generally, it is used after being packaged with a moisture-proof and water-resistant material having a thickness of 100 to 200 μm, for example, polytrifluorochloroethylene. However, such packaging materials are expensive,
Moreover, since CFCs, which are pollution control substances, are used as raw materials, an alternative method is required. For this reason, it has been attempted to form a moisture-proof coating on the phosphor particles used instead of covering the EL lamp with a moisture-proof material.

For example, in US Pat. No. 4,585,673, aluminum or aluminum entrained in the carrier gas as a precursor of a metal oxide is formed on the surface of phosphor particles fluidized with the carrier gas. The phosphor particles by depositing a volatile organometallic compound or metal alkoxide of yttrium, such as trimethylaluminum, at a temperature below its decomposition temperature and then heating to or above its decomposition temperature, such as 400 ° C. It is disclosed that a metal oxide film is formed on the surface of.

Further, Japanese Patent Application Laid-Open No. 6-25857 discloses that
Similarly, on a surface of phosphor particles fluidized with a carrier gas, titanium tetraisopropoxide entrained in the carrier gas is used as a precursor at a temperature of 300 ° C. or lower to form a titanium oxide film. are doing.

Further, in Japanese Patent Application Laid-Open No. 4-230996, a chloride and / or an alkoxide of silicon, titanium or zirconium is used as a precursor of an oxide,
At the surface of the fluidized phosphor particles, the precursor is heated to a temperature of 1
It is disclosed to react with water vapor at 20 to 140 ° C. to form an oxide film.

[0007]

In such a method,
Since a compound such as a metal chloride, a metal alkoxide, or a trialkylaluminum having a relatively small molecular weight, a high hydrolysis rate, and a large relative ratio of a portion released by hydrolysis is used as a precursor, The precursor attached to the surface undergoes a remarkable volume reduction during the formation of an oxide film due to hydrolysis and condensation reactions, and when an attempt is made to form a film with a thickness necessary for moisture prevention, cracks occur and a completely continuous film is formed. Therefore, the phosphor particles cannot be wrapped. Therefore, the moisture-proof effect due to the formation of such a film is insufficient.

Trialkylaluminum such as trimethylaluminum is inconvenient to handle because it ignites in air and has a high hydrolysis rate. The method using chloride requires hydrogen chloride as a by-product during hydrolysis, and thus requires a treatment device of a special material. Further, when exposed to a high temperature for forming a film, there is a problem that various characteristics of the phosphor are adversely affected by heat.

The present invention has been made to solve the above problems, and has practically sufficient moisture resistance and phosphor characteristics without adversely affecting the various characteristics of the phosphor and the optical properties of the particles. An object of the present invention is to provide a method for producing phosphor particles having

[0010]

Means for Solving the Problems As a result of repeated studies to achieve this object, the present inventors have found that the object can be achieved by using a metal alkoxide oligomer as a precursor of a metal oxide. The present invention has been completed and the present invention has been completed.

That is, the surface coating method of the phosphor particles of the present invention is a method of coating the surface of the phosphor particles with a metal oxide, wherein the surface of the fluidized phosphor particles is
It is characterized in that a metal oxide film is formed from a metal alkoxide oligomer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The phosphor particles used in the present invention may be of any type, but the surface coating method of the present invention is particularly susceptible to deterioration due to the influence of humidity. Is effective for. Examples of such EL phosphor particles include zinc sulfide, zinc selenide, and the like as base materials, copper, silver, manganese, and the like as activators, and chlorine, bromine, iodine, and co-activators as necessary. Examples of the phosphor particles include aluminum.

In the present invention, the metal oxide film formed on the surface of the phosphor is an oxide containing one or more metal atoms selected from aluminum, silicon, titanium and magnesium, such as aluminum oxide. Included are coatings of silicon dioxide, titanium dioxide and magnesium oxide, as well as hybrid coatings of their oxides.

As a precursor of such a metal oxide, an oligomer of a metal alkoxide having a metal atom of the oxide is used. Examples of the metal atom include aluminum, silicon, titanium and magnesium, and 1
One kind or two or more kinds may be used. The alkyl group may be linear or branched and is exemplified by methyl, ethyl, propyl, butyl, hexyl, heptyl and octyl.
One kind or two or more kinds may be used. Such precursors include aluminum triethoxide, aluminum tri-n-propoxide, aluminum triisopropoxide, aluminum tri-n-butoxide, aluminum triisobutoxide, sec-butoxyaluminium diisopropoxide, aluminum triisobutoxide. -Sec-Butoxide, aluminum trialkoxides such as aluminum-tert-tributoxide; silicon tetraalkoxides such as methyl silicate, ethyl silicate, -n-propyl silicate, isopropyl silicate, -n-butyl silicate;
Titanium tetraethoxide, titanium tetra-n-propoxide, titanium tetraisopropoxide, titanium tetra-
titanium tetraalkoxides such as n-butoxide and titanium tetra-tert-butoxide; and respective oligomers of magnesium dialkoxide such as magnesium diethoxide and magnesium isopropoxide,
Alternatively, it is a hybrid oligomer composed of two or more metal alkoxides. The metal alkoxide oligomer has a molecular structure composed of a chain, branched or cyclic molecular skeleton in which metal atoms and oxygen atoms are alternately bonded and an alkoxy group bonded to the metal atom, and the degree of condensation is usually 2 to 10, It is preferably an oligomer of 3 to 8, and may be a pure product such as a dimer, trimer or tetramer, or a mixture of oligomers having different degrees of condensation, and a metal alkoxide monomer may be partially present.

Such a metal alkoxide oligomer can be obtained by partially hydrolyzing one or more metal alkoxides with a required amount of water in the presence of a catalyst, if necessary, and then condensing the same. Also,
For example, it can also be obtained by reacting the corresponding metal chloride with the corresponding alcohol under conditions such that condensation occurs.

Aluminum isopropoxide, which has moderate reactivity and can easily form a metal oxide,
Oligomers of metal alkoxides such as ethyl silicate, titanium tetraethoxide, titatetraisopropoxide are preferred. In the case of an ethyl silicate oligomer, those having an average molecular weight of 700 to 1,000 are particularly preferable.

In the present invention, the phosphor particles are fluidized and processed. For example, phosphor particles are charged into a cylindrical fluidized bed processing apparatus having a dispersion means such as a filter mesh at the bottom, and an inert gas such as nitrogen or argon is fed as a flowing gas through the filter mesh. Allow to form a fluidized bed of phosphor particles. The temperature is not particularly limited, but a range of 100 to 200 ° C is preferable.

Then, a metal alkoxide oligomer is introduced as a precursor of the metal oxide. The introduction of the precursor is preferably sprayed directly onto the fluidized bed, and in order to perform uniform treatment on the surface of the phosphor particles, it is more preferable to dissolve the precursor in an organic solvent and spray it. . The solvent is not particularly limited as long as it dissolves the precursor to be used and can be easily volatilized at the processing temperature. Hydrocarbon-based solvents such as toluene, xylene, gasoline and naphtha; ketones such as acetone and methyl ethyl ketone. Examples include system solvents; and alcohol solvents such as methanol, ethanol and isopropanol.

The precursor sprayed on the phosphor particles in the fluidized bed adheres to the surface of the particles and forms a metal oxide film on the surface of the particles by hydrolysis and condensation of the alkoxy groups. The thickness of the coating is the thickness required to obtain the necessary moisture resistance depending on the type of phosphor particles and the use conditions. The amount of precursor introduced is calculated from the amount that gives the required coating thickness.

The method of the present invention does not require a firing step in particular for forming the metal oxide film, but firing may be carried out, if necessary, within a range not impairing the characteristics of the phosphor.

[0021]

The metal alkoxide oligomer sprayed on the surface of the fluidized phosphor particles is
It is possible to form a metal oxide film by a hydrolysis reaction and a condensation reaction, impart moisture resistance to the phosphor particles, and prevent deterioration of the phosphor due to moisture.

[0022]

The present invention will be described in more detail with reference to the following examples. The present invention is not limited by these examples.

Example 1 A ZnS powder was used as a base material, and CuSO was used as an activator.
₄ , NaBr and KBr as a co-activator are wet-mixed, and the obtained slurry is dried, and then, in an H ₂ S atmosphere,
It was baked at 900 ° C. for 80 minutes to obtain ZnS: Cu, Br type EL phosphor particles.

5,000 g of the above ZnS: Cu, Br type EL phosphor particles was charged into a cylindrical fluidized bed processing apparatus equipped with a filter mesh at the bottom. Nitrogen at a temperature of 170 ° C. and a blowing rate of 0.7 m / s was blown through the filter mesh to form a fluidized bed of phosphor particles. Then, a solution prepared by dissolving 1,200 g of an ethyl silicate oligomer mixture having an average molecular weight of 745 in 5,000 ml of ethanol was sprayed on the fluidized bed at a spraying rate of 50 g / min. After the spraying was completed, the film-forming reaction was completed by further drying for 30 minutes while maintaining the fluid state. Then, the treated particles were taken out and sieved to obtain treated phosphor particles. The phosphor particles thus treated had a completely continuous silicon dioxide film formed on the surface without cracks or defects.

The thus obtained EL phosphor particles having a silicon dioxide coating and untreated EL for comparison
EL using phosphor particles and cyanoethyl cellulose as binder without using a moisture-proof film
A panel was prepared. To these EL panels, 100V,
The initial emission brightness and the brightness half-life were measured by applying an AC voltage of 400 Hz.

As a result, E which forms a silicon dioxide film
The EL panel using the L phosphor had almost the same initial emission luminance and the luminance half-life improved to 5.2 times as compared with the one using the untreated EL phosphor particles.

Example 2 ZnS: Cu, Br type EL similar to that used in Example 1
The phosphor particles of 5,000 g were treated with the same fluidized bed treatment apparatus as in Example 1, except that the temperature was 150 ° C., the precursor was titanium tetraethoxide tetramer, and the spray rate of the ethanol solution was 100 g / min. Similar to 1,
EL phosphor particles having a titanium dioxide coating were obtained.

The surface-coated EL phosphor particles thus obtained were evaluated in the same manner as in Example 1. As a result, the EL phosphor having the titanium dioxide coating was used.
The panel has almost the same initial emission luminance and a luminance half-life of 7. compared to those using the untreated EL phosphor particles.
It was 5 times better.

Example 3 ZnS powder was used as a base material and CuSO was used as an activator.
₄ , NaCl and KCl are mixed as a co-activator by a wet method, and the obtained slurry is dried, and then, in an H ₂ S atmosphere,
It was baked at 900 ° C. for 80 minutes to obtain ZnS: Cu, Cl type EL phosphor particles.

5,000 g of the above ZnS: Cu, Cl type EL phosphor particles were heated to 150 ° C. in the same fluidized bed treatment apparatus as in Example 1, and the trimer and tetramer of aluminum triisopropoxide were used as the precursor solution. 1,000 g of a 60:40 weight ratio mixture of xylene 5,0
Using the one dissolved in 00 ml, the spraying speed is 100
EL phosphor particles having an aluminum oxide film were obtained in the same manner as in Example 1 except that g / min was set.

The surface-coated EL phosphor particles thus obtained were evaluated in the same manner as in Example 1. As a result, an EL panel using the EL phosphor having an aluminum oxide film was untreated EL. The initial emission luminance was almost the same as that using the phosphor particles, and the luminance half-life was improved by 6.8 times.

Example 4 ZnS: Cu, Cl type EL similar to that used in Example 3
An average molecular weight of 5,000 g of phosphor particles was set to 900 as a precursor solution by the same fluidized bed processing apparatus as in Example 1.
600 g of the ethyl silicate oligomer mixture of Example 3
A mixture of silicon dioxide and aluminum oxide was used in the same manner as in Example 1 except that 500 g of the aluminum triisobutoxide oligomer mixture used in Example 1 was dissolved in 5,000 ml of xylene and the spraying rate was 100 g / min. EL phosphor particles having a coating film were obtained.

The surface-coated EL phosphor particles thus obtained were evaluated in the same manner as in Example 1. As a result, the EL panel using the EL phosphor having the metal oxide film was not treated. Compared to the one using EL phosphor particles,
The initial emission luminance was almost the same, and the luminance half-life was improved by 6.9 times.

Table 1 shows the relative values of the initial emission brightness and the brightness half-life of the surface-coated EL phosphor particles obtained in Examples 1 to 4 with respect to the corresponding untreated EL phosphor particles.

[0035]

[Table 1]

[0036]

According to the present invention, the moisture-proof property of the metal oxide, which does not have defects such as cracks, on the entire surface of the phosphor particles without adversely affecting various properties of the phosphor and the optical properties of the particles. It is possible to form a continuous coating of. The phosphor manufactured by using the phosphor particles whose surface is coated according to the present invention, particularly the EL phosphor, has sufficient moisture resistance in practical use.

Therefore, the phosphor using the phosphor particles surface-coated according to the present invention is not affected by humidity and has a long life without using a packaging material such as polytrifluorochloroethylene. Applied products such as EL
It can be used for panels.

Claims (6)

[Claims] 1. A method for coating the surface of a phosphor particle with a metal oxide, which comprises forming a metal oxide film from a metal alkoxide oligomer on the surface of the fluidized phosphor particle. Surface coating method for phosphor particles. 2. The surface coating method according to claim 1, wherein the metal oxide is aluminum oxide, silicon dioxide, titanium dioxide or magnesium oxide. 3. The surface coating method according to claim 1, wherein the metal alkoxide oligomer is a metal alkoxide oligomer of aluminum, silicon, titanium or magnesium. 4. The surface coating method according to claim 1, wherein the phosphor particles are electroluminescent phosphor particles. 5. The surface coating method according to claim 1, wherein the phosphor particles are copper-activated zinc sulfide phosphor particles. 6. The surface coating method according to claim 1, wherein the metal alkoxide oligomer is sprayed on the fluidized phosphor particles.