JPH08176541A - Fluorescent substance for cathode ray tube - Google Patents

Abstract

PURPOSE: To prepare a fluorescent substance for cathode ray tubes, obtained by adhereing at least pectin to the surfaces of a fluorescent particle, excellent in dispersibility and coating properties, particularly in coating of color cathode ray tubes. CONSTITUTION: This fluorescent substance is prepared by adhering (B) at least pectin, preferably pectin, silica and a divalent or trivalent metal hydroxide to the surface of (A) fluorescent particles. In order to adhere the component (B) to the component (A), for example, a solution of the component (B) dissoluting pectin is added to a slurry dispersing the component (A), further zinc ion is added to cause their gelling reaction to attain the adhesion. The addition amount of the pectin is preferably 0.01-0.5wt.%, optimally 0.03-0.08wt.% based on the fluorescent particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode fluorescent substance, and more particularly to a fluorescent substance excellent in coating properties on a color cathode ray tube.

[0002]

2. Description of the Related Art As is well known, a fluorescent surface of a color cathode ray tube is formed with green, blue, and red light emitting phosphors in a dot shape or a stripe shape. Generally, a slurry method is used to form the fluorescent screen. The slurry method is as follows. Mainly PVA (polyvinyl alcohol) and ADC (ammonium dichromate)
A phosphor is suspended in an aqueous solution containing and to prepare a coating slurry. The coating slurry is poured onto the inner surface of the face plate of the color cathode ray tube mounted on the spin coater and spread over the entire surface, and then the excess slurry is shaken off at a predetermined speed and dried to form a phosphor layer. Then, a predetermined pattern in the form of dots or stripes is exposed through an ultraviolet light source of a high-pressure mercury lamp through a shadow mask, and the unexposed excess phosphor layer is washed away by development to form a fluorescent film. This operation is green
This is sequentially performed for the blue and red light emitting phosphors.
The following characteristics are generally required for the phosphor screen formed by such a slurry method.

(1) A good summary. That is, fine dots or stripes should be formed with a uniform film thickness. The good brightness improves the brightness of the fluorescent screen of the cathode ray tube. (2) Good sharpness. That is, dots or stripes with a predetermined shape and width are formed at predetermined positions. (3) The adhesive force between the phosphor layer and the face plate is large. If the adhesive strength is small, dots or stripes are peeled off, and the yield of the phosphor screen forming process is reduced. (4) No color mixture. That is, phosphors forming dots or stripes of one light emitting component should not be mixed with phosphors of other light emitting components adjacent to each other. When this color mixture occurs, the color purity of the green, blue, and red light emitting components decreases, and as a result, the color reproduction range of the color cathode ray tube decreases. (5) There is no residue. That is, the phosphor layer should not remain on the face plate when the unexposed phosphor layer is washed away. This also leads to a reduction in the color reproduction range of the color cathode ray tube.

The above characteristics are affected by the surface condition of the phosphor. Therefore, various phosphors for cathode ray tubes have been developed in which various treatment substances are attached to the phosphor to improve the surface condition of the phosphor.

Currently, silicon dioxide (SiO ₂ ; hereinafter referred to as silica) is the most widely used surface treatment substance. Phosphors containing silica as a surface treatment substance are generally added to a phosphor suspension by adding an aqueous solution containing silicate ions or fine particle silica, and further adding an electrolyte solution containing Zn, Al ions and the like. It is obtained by aggregating a substance on the surface of a phosphor to generate a silicate compound.

For example, Japanese Examined Patent Publication No. 50-15747 discloses a method of coating a phosphor with zinc silicate by adding phosphorous water glass and zinc sulfate. Further, Japanese Patent Publication No. 61-46512 discloses a phosphor coated with silica and a zinc compound.

Further, in JP-A-5-179235, at least one water-soluble binder selected from the group consisting of gum arabic, gelatin, polymethacrylamide, and polyvinyl alcohol is provided on the particle surface of the phosphor. Disclosed is a phosphor coated with a metal alginate containing Zn, Zn, Al, and an alkali metal.

[0008]

The phosphor for a cathode ray tube whose particle surface is coated by the above-described method satisfies (1) the outline, (4) color mixture, and (5) residue characteristics to some extent, and therefore is still used. Although widely used, with the development of high-definition televisions, high-definition cathode ray tubes, and the like, there is a strong demand for the development of phosphors having even more excellent coating characteristics.

The present invention has been made in view of the above circumstances, and satisfies all the above characteristics, and particularly, (1) Summary,
(3) It is an object of the present invention to provide a phosphor for a cathode ray tube which is excellent in adhesive property.

[0010]

Means for Solving the Problems As a result of earnest studies on the modification of the particle surface of a cathode ray phosphor, the present inventor has found that the above-mentioned problems are caused by attaching pectin, which is one of many polysaccharides, to the surface of the phosphor. The present invention has been completed and the present invention has been completed.

That is, the phosphor for a cathode ray tube of the present invention is
At least pectin is attached to the surface of the phosphor particles.

[0012] Pectin is a colloidal polysaccharide widely distributed in plants such as inside the outer skin of citrus fruits.
It is the most main pectin and is composed of a linear polymer of D-galacturonic acid, and its carboxy group is partly a methyl ester. Pectin reacts with divalent metal ions such as calcium and zinc to form a strong gel, and the phosphor for a cathode ray tube of the present invention can be attached to the phosphor surface by utilizing such characteristics of pectin. For example, to a slurry in which the phosphor is suspended, a pectin solution is added, and further zinc ions are added,
Pectin can be attached to the phosphor by the gelation reaction described above.

Further, it is preferable that silica is attached to the coating characteristics of the cathode ray tube. For example, in order to attach silica to the phosphor, silica is added to the above reaction system in advance, sufficiently mixed with the phosphor, and the silica is attached to the phosphor surface by utilizing the gelation reaction. It is possible. However, it is necessary to control the amount of divalent ions such as zinc depending on the particle size and amount of silica.
P suitable for precipitating valent metals as hydroxide ions
It is necessary to control to H. For example, when zinc is used, the pH is 7.6 or more, when Mg is used, the pH is 10.5 or more, and when Ca is used, the pH is 10 or more.
It should be adjusted to a range of 11.

The addition amount of pectin used in the present invention is preferably in the range of 0.01 to 0.5% by weight based on the phosphor. If it is less than 0.01, the effect of the pectin coating is almost insignificant, and if it is more than 0.5% by weight, the tendency of aggregation appears, which is not good. Further, the range of 0.03 to 0.08% by weight is most preferable.

Further, by depositing a hydroxide of a trivalent metal ion typified by aluminum ions and rare earth ions on the surface, silica can be more firmly attached to the phosphor surface.

Further, a water-soluble binder such as gum arabic, gelatin, polymethacrylamide, polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose, polyethylene oxide, acrylic emulsion and the like is used together with pectin, whereby the face of the above-mentioned cathode ray phosphor is used. It is possible to control the balance of coating performance on the plate. actually,
Even though the method of forming the phosphor layer on the face plate of the color cathode ray tube is the same, a small amount of additive added to the phosphor suspension, the drying temperature of the coated surface, the exposure conditions, the development conditions, etc. individually affect these. This control may be necessary because the variables can not be ignored.

[0017]

In the present invention, by coating the surface of the phosphor for a cathode ray tube with pectin, the dispersibility is further improved as compared with the conventional product, and as a result, the adhesive force and the consistency of the coating characteristics are improved. Further, conventionally, when the dispersibility is strong, an inorganic surface treatment agent, for example, zinc silicate, zinc hydroxide, aluminum hydroxide, etc., tends to cause the above-mentioned color mixture, and the influence of the residue is large, but the present invention The above-mentioned pectin-attached phosphor does not have such a problem, and since the dispersion is good, the sharpness of dots and stripes is also improved.

As a typical method for evaluating the dispersibility of the phosphor, there is a method of measuring the sedimentation height (the height of the interface caused by the sedimentation of the phosphor). FIG. 1 compares the conventional cathode ray phosphor with the product of the present invention. The phosphor slurry is ordinary PV
A-ADC phosphor suspension, 30 cm in the sedimentation tube
This slurry is filled up to the height of, and the sedimentation height is measured over time and plotted. Than this,
The phosphor of the present invention is hard to settle and is well dispersed as compared with the conventional product. In particular, the amount of pectin attached to the fluorophore is 0.
The range of 03 to 0.08% by weight is preferable, and especially 0.0
5% by weight is most dispersed.

Another method for evaluating the dispersibility of the phosphor is the measurement of sedimentation volume, which is carried out by the following method.
First, 15 ml of the above-mentioned ordinary phosphor suspension was put in a test tube with a graduated volume, and the turning radius was 10 cm.
Spin for 15 minutes at 2000 rpm with a centrifuge and read the volume of the precipitate. The smaller the settling volume, the better the dispersion state of the powder such as the phosphor in the slurry, and the better the spread of the coated surface on the face plate of the cathode ray tube. The relationship between the amount of pectin attached to the phosphor of the present invention and the sedimentation volume is shown in the curve of FIG.
From this, when the amount of pectin attached is around 0.03 to 0.08% by weight, the sedimentation volume is small, which is favorable.

As another method for evaluating the dispersibility of the phosphor, the median particle diameter (Dm) of the phosphor in the above-mentioned phosphor suspension is used.
There is a way to measure. The median particle diameter is obtained by converting particles counted by the Coulter counter method from a number distribution to a volume distribution and obtaining a 50% value of an integrated distribution including secondary particles. The smaller the Dm of this phosphor suspension, the better the dispersed state. On the other hand, when Dm is large, it is considered that the phosphor particles were agglomerated because they aggregated. The relationship between Dm and the amount of pectin attached to the phosphor of the present invention is shown in the curve of FIG. From this, the adhesion amount of pectin is 0.03 ~
Around 0.08% by weight is preferable because Dm becomes small.

FIG. 4 shows the relationship between the amount of pectin attached to the phosphor of the present invention and the actual adhesive strength of the phosphor. Here, the adhesive force was measured by the following method. The ordinary phosphor suspension described above is poured onto the inner surface of the face plate of the color cathode ray tube installed in the spin coater, and after spreading the whole, the excess slurry is shaken off at a predetermined speed and dried to form the phosphor layer. Then, a predetermined dot-shaped pattern is exposed through a shadow mask by an ultraviolet light source of a high pressure mercury lamp. At the time of this exposure, a density filter NDF (neutral density filter) is attached between the shadow mask and the ultraviolet light source. By exposing in this state, the exposure amount of the phosphor coated surface on the face plate is adjusted depending on the location, and by subsequent development, one having a large dot diameter to one having a small dot diameter is formed. The smallest dot diameter of these is called the adhesive strength. As shown in the curve of FIG. 4, when the amount of pectin attached is in the range of 0.03 to 0.08% by weight, the minimum dot diameter becomes small, that is, the adhesive force becomes strong, which is preferable.

As a comparative example, the results of the tests already conducted on the phosphor to which the same amount of alginate as pectin was attached are shown by ● in FIGS. 2 to 4. Alginate is also a kind of many polysaccharides like pectin and shows the effect of dispersion,
Compared with the product of the present invention, the sedimentation volume and Dm are large, the dispersibility is small, and as a result, the minimum dot diameter is large and the adhesive strength is weak. That is, it can be understood that the effect of alginate on dispersibility does not reach that of pectin.

[0023]

【Example】

[Example 1] Z that has been dispersed and washed as a green light emitting phosphor
1 kg of nS: Cu, Al phosphor was suspended in 2.5 liters of deionized water, and colloidal silica was added to the phosphor.
Add 0.3%. Thereto, 0.1 g of pectin dissolved in warm water (0.01% by weight with respect to the phosphor) is added.
Further, an aqueous zinc sulfate solution is added to the phosphor while stirring at 0.05% by weight in terms of Zn, and then ammonia water is added dropwise to adjust the pH to 7.6. Then, the mixture was allowed to stand to sink the phosphor, the supernatant was removed, and the mixture was suction-separated with a Nutsche, dried at 110 ° C. for 15 hours, and passed through a 200-mesh sieve to obtain a phosphor.

[Examples 2 to 18], [Comparative Examples 1 to 4] Table 1 shows the amounts of pectin added, zinc added, calcium added, sodium alginate as an alginate, gelatin added, and silica added. A phosphor was obtained in the same manner as in Example 1 except that the phosphor was changed as shown in FIG. In addition, the sedimentation height, the slurry Dm, and the minimum dot diameter were measured by the method described above, and the results are summarized in Table 2.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

Since the present invention is configured as described above, it has the following effects.

The phosphor for a cathode ray tube of the present invention has a good dispersibility, and therefore, the coating surface on the face plate of the cathode ray tube is improved in the adhesion and the adhesive force of the phosphor to the face plate is increased. As a result, the brightness of the cathode ray tube can be improved and the yield in the coating process can be improved.

Further, conventionally, when the dispersibility is strong, an inorganic surface treatment agent such as zinc silicate, zinc hydroxide, aluminum hydroxide or the like is liable to cause the above-mentioned color mixture, and the influence of the residue is large. However, the pectin-attached phosphor of the present invention does not have such a problem, and since the dispersion is good, the sharpness of dots and stripes is also improved.

[0030]

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between sedimentation time and sedimentation height of suspensions using phosphors according to an example of the present invention and a comparative example.

FIG. 2 is a graph showing the relationship between the amount of pectin added and the sedimentation volume of the phosphor of the present invention.

FIG. 3 is a graph showing the relationship between the amount of pectin added to the phosphor of the present invention and Dm.

FIG. 4 is a graph showing the relationship between the amount of pectin added to the phosphor of the present invention and the minimum dot diameter.

Claims (3)

[Claims] 1. A phosphor for a cathode ray tube, characterized in that at least pectin is attached to the surface of phosphor particles. 2. The phosphor for a cathode ray tube according to claim 1, wherein the pectin is a salt with a divalent metal. 3. The phosphor for a cathode ray tube according to claim 1, wherein pectin, silica, and a hydroxide of a divalent or trivalent metal are attached to the surface of the phosphor particles.