JPH0312474A - Bonding coloring agent particles to fludrescent material particles - Google Patents

Abstract

PURPOSE: To obtain a non-flocculent and freely flowable phosphor powder fitted with a coloring agent economically and easily by separating a solid from an aq. slurry consisting of phosphor particles, coloring agent particles and a binder to dry the same.

CONSTITUTION: Phosphor particles (A), coloring agent particles (B) and a binder (C) composed of a latex (co)polymer having glass transition temp. of about 20°C or higher are stirred and mixed to form an aq. slurry. A solid is separated from this slurry by decantation and dried at temp. equal to or higher than the min. film forming temp. (e.g. 130-150°C) of latex to obtain phosphor particles to which the coloring agent particles are bonded. As an example of a combination of the components A, B, a zinc sulfide phosphor and cobalt aluminate or a yttrium oxide sulfide and ferric oxide is designated.

COPYRIGHT: (C)1991,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for bonding colorant particles to phosphor particles using a polymer or copolymer coated as a latex, with the phosphor particles and colorant particles in an aqueous suspension. It is.

In particular, the binder is a latex polymer with a glass transition temperature above 20°C. These polymeric binders produce colored phosphor powders that are tacky, non-agglomerated, and free-flowing.

Section 1: Colorant or pigment particles on phosphor particles
Many methods of combining are described in the literature.

These materials are primarily used in cathode ray tubes, where the colorant or pigment acts as a filter to improve the color purity and contrast of the emitted light. Both organic and inorganic colorant binders are used in the art.

U.S. Patent No. 4.473. - No. 634 describes an inorganic binder system using water glass (potassium silicate) as the binder. Organic binder systems such as gelatin as described in U.S. Pat. No. 3,275,466 and various organic polymers coated as latexes as described in U.S. Pat. No. 4,049,845 are also used in the art. It has been found to be useful. However, U.S. Patent No. 4.049.84
The method taught in No. 5 uses latex polymers that exhibit glass transition temperatures well below room temperature. Therefore,
These polymers are rather soft and viscous, resulting only in colored phosphor powders that are not free-flowing and easily agglomerate.

As a result, these powders cannot be screened through dry sieving, which is the usual method used to ensure that colorant phosphor powders are deagglomerated in conventional methods. The separation step is usually the final step in product manufacturing.Also, these colored phosphor powders tend to reagglomerate after separation due to the stickiness of the polymer binder. No. 4,049,845 discusses this problem and discusses tack reduction methods including additional treatments such as by the application of inorganic and organic crosslinkers.

These steps add complexity to the process and are not always effective.

Phosphors prepared according to U.S. Pat. No. 4,049,845 undergo a high degree of reagglomeration and require extensive wet ball milling of these materials in the coating slurry prior to coating onto cathode ray tube faceplates. be.

If such a deagglomeration stage is not used, the phosphor coating becomes grainy and grainy and unacceptable. This method also required additional labor and effort since the phosphor slurry had to be sent to the mill for milling once and then pumped from the mill to a container where it was stored until the coating operation.

It is desirable to eliminate the wet ball milling step prior to phosphor coating to reduce unnecessary handling that can degrade the phosphor and also to reduce cost.

Therefore, it would be desirable to develop a method for coating phosphors with colorants that eliminates the problems associated with viscous polymeric binders, such as poor dry sieving properties and susceptibility to reagglomeration after sieving. , will make a major contribution to this field. Such an improved phosphor would eliminate the need to mill the phosphor slurry before use.

Such phosphors are known in the industry as ``no-milling''.
mil1) J or “non-cohesive (stir-in)”
It is known as J.

According to one aspect of the present invention, a method for bonding colorant particles to phosphor particles is provided. The method includes forming an aqueous slurry of phosphor particles, colorant particles, and a binder (e.g., a latex polymer or copolymer) having a glass transition temperature greater than 20°C, stirring the slurry,
It involves separating the solids from the product liquid and drying the solids at a temperature above the minimum film forming temperature of the latex to produce colored phosphor particles with bound colorant particles.

It has been found that organic polymer latexes of various compositions can be used to attach colorant particles to phosphor particles as long as they have glass transition temperatures above room temperature. Such latex polymers are easily and inexpensively coated, require no additional processing steps to reduce binder viscosity, and produce "no-milling" or "non-agglomerated" colored phosphors. It is appropriate for

Examples of some preferred phosphor and colorant combinations that are particularly suitable for the practice of the present invention include zinc sulfide phosphors such as silver-activated zinc sulfide phosphors and cobalt aluminate as a blue colorant and europium-activated acid. Includes yttrium oxysulfide phosphors such as yttrium (oxy)sulfide and ferric oxide as a red colorant.

Typically, the colorant is about 0.1-2.5% by weight of the phosphor.
and the binder comprises about 0.05-0.5% by weight of the phosphor.1 The average phosphor particle size is preferably about 4-15 μm in diameter, and the average particle size of the colorant particles is Approximately 0.1
Preferably, the diameter is ˜1.0 μm.

The binder is a latex polymer or copolymer.

"Latex" is defined herein as an aqueous colloidal suspension of an organic polymer or copolymer. For the reasons mentioned above, it is important that the binder has a glass transition temperature above about 20°C. "Glass transition temperature (Tg)
J means the temperature at which the amorphous polymeric material locally undergoes an abrupt change in properties associated with cessation of molecular motion. Below the glass transition temperature (Tg), polymeric materials behave as hard, brittle, and rigid solids. Above the glass transition temperature (Tg), amorphous polymeric materials behave as viscous, plastic solids. Examples of these types of binders are (1) 1(ycar 2600X
(2) Tylac 68-15, an acrylic polymer manufactured by Goodrich under the trade name B, F, 256 (which has a Tg of +45°C);
(3) Polystyrene latex manufactured by Relchhold under the trade name Synthemul (which has a Tg of +100°C) and (3) R under the trade name Synthemul.
Carboxylated acrylate acrylonitrile copolymer manufactured by Elchhold (which is +2
has a Tg of 0°C).

The aqueous slurry has phosphor particles to which a colorant is attached;
Formed from colorant particles and a binder.

This is preferably done by first forming an aqueous slurry of phosphor and colorant. The usual practice is to form a slurry of phosphor, deagglomerate the colorant to form another aqueous slurry of colorant, and mix these 2m slurries together. A binder, which is latex, is then added. Colloidal particles typically have a particle size of about 0.05-2.0 μm in diameter. The resulting phosphor-colorant-binder slurry is agitated so that the colloidal polymer or copolymer particles bind the colorant particles to the phosphor particles.

After typically (but not exclusively) about 172 hours of stirring,
The product solids, which are phosphor particles with colorant attached by a binder, are separated from the product liquid by standard techniques.

This is usually done by allowing the solids to settle out and then decanting the liquid.

It is preferred to wash the solids one or more times with deionized water to remove water-soluble impurities such as dispersants added by the manufacturer to stabilize the latex.

The solid is then heated to the minimum film forming temperature (MFT) of the latex.
) for about 8 hours. The minimum film forming temperature (MFT) is the lowest temperature at which the latex dries to form a continuous, non-porous film. Drying is usually done at a temperature of at least about 110°C. Most typically,
The drying temperature is approximately 130-150°C.

After the resulting dry phosphor is cooled, the resulting phosphor is sieved to remove oversized materials. The phosphor powder thus obtained is now ready for use.

Approximately 1 kg of ZnS:Ag phosphor was slurried in approximately 412 kg of deionized water per step. Approximately 1.5% by weight of the phosphor weight, or 15 g, of the blue colorant CoAlaOn was deagglomerated by dispersing it in approximately 250 mβ of deionized water using an ultrasound probe. A colorant slurry was added into the stirred phosphor dispersion. After R, 0.25% by weight or about 2.5 grams of a commercially available latex manufactured by B, F. Goodrich was added to the stirred phosphor and colorant slurry. This latex is 1ycar2600X25
6 acrylic cobolymer, with a T of +45°C, and approximately 42
It had an MFT of °C. The resulting phosphor-colorant-binder copolymer slurry was stirred for approximately 10 minutes and the solids allowed to settle.

Two cold deionized water washes (44 each) were performed by slurrying the phosphor for several minutes, allowing the solids to settle and decanting.

The solids were transferred to a tray and dried at about 130° C. for about 8 hours. After cooling, the phosphor was sieved. The produced phosphor can now be used at any time.

Approximately 1 kg of YmO*S:εU cathode ray tube phosphor (approximately 412 kg)
slurried in deionized water. Approximately 0.0 of the fluorescent weight.
15% by weight or 1.5 g of the red colorant Fears was dispersed into approximately 250 mI2 of deionized water using an ultrasonic probe. A colorant is then added to the phosphor slurry and about 0.10% by weight or about 1.0 g of Relnh
A commercially available latex manufactured by Old Company was added to the phosphor and colorant slurry. This latex has a product name of Tylac6.
g-157, polystyrene polymer, +100°C
It had a T of +40°C and an MFT of +40°C. Example 1: A phosphor with zero colorant, in which the resulting phosphor-colorant-binder polymer slurry was stirred for several minutes and the solids were allowed to settle.
and dried at about 130° C. for about 16 hours. After cooling, the phosphor was sieved to remove material outside the target dimensions. The produced phosphor is now ready for use.

``Medicine.''

Approximately 1 kg of ZnS: Ag cathode ray tube phosphor and approximately 1.5 g
and the blue colorant CoAl*O+ were slurried according to Example 1. At this point, 0.20% by weight or approximately 2.0 grams of commercial latex manufactured by Relnhold was added to the slurry. This latex is 5ynthe++
vl DL-0685, a carboxylated acrylate acrylonitrile copolymer. This polymer T
1 was +20°C and MFT was +40°C. The colored phosphor was washed, dried and sieved according to the procedure of Example 1. The produced phosphor was now ready for use.

1. We succeeded in eliminating the wet ball milling step prior to phosphor coating in order to reduce unnecessary handling that could degrade the phosphor and also to reduce costs. It has become possible to easily produce a phosphor that retains its dispersion ability.

Although specific examples of the invention have been described above, it should be noted that many changes may be made within the scope of the invention.

Claims (1)

Claims: 1) A method of bonding colorant particles to phosphor particles, comprising: (a) phosphor particles, colorant particles and latex polymers and copolymers having a glass transition temperature greater than about 20°C; forming an aqueous slurry of a binder selected from the group consisting of and agitating the slurry; (b) separating solids from the product liquid; and (c) exceeding the minimum film forming temperature of the latex. drying the solid at a temperature to produce phosphor particles having bound colorant particles; and a method of binding colorant particles to the phosphor particles comprising: