JPH07312287A - Surface treatment method for phosphor, and dispersion el element using this phosphor - Google Patents

Abstract

PURPOSE:To suppress the chemical change of a phosphor by moisture and a local peeling between a phosphor and an organic binder by temperature, and improve luminance deterioration. CONSTITUTION:When the surface of a phosphor 3 is covered with water glass, a mixed aqueous solution of water glass, aluminium sulfate, and sodium hydroxide is used to form a fine composite film with water glass containing Al. Thus, the shielding effect of moisture and the adhesion between the phosphor and the organic binder are improved, and the luminance deterioration under high humidity and high temperature environments can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for a phosphor and a long-life dispersion type EL device using the surface-treated phosphor.

[0002]

2. Description of the Related Art As a conventional technique, a method of coating a water glass film on a phosphor for a cathode ray tube is disclosed in JP-A-58-80375. This method relates to a method for coating a surface of an alkaline earth metal sulfide phosphor that is easily hydrolyzed or dissolved in water, such as CaS, and is composed of water glass.
By diluting with an alkaline aqueous solution of H9 to 14 and coating the surface of the phosphor with water glass using alkaline water glass with an optimized concentration of water glass, the water resistance is improved and luminance deterioration is suppressed, and stability is achieved. In addition, the coating property is improved.

[0003]

However, when the above-mentioned technique is applied to a phosphor for a dispersion type EL, the experimental results show that the denseness of the film is insufficient and the expected moisture resistance cannot be obtained. became. In addition to the chemical change on the surface of the phosphor due to water, a major cause of the deterioration in brightness in the dispersion type EL is a decrease in the adhesiveness between the phosphor and the organic binder due to temperature (local peeling), which is also sufficient. The effect was not obtained.

[0004]

DISCLOSURE OF THE INVENTION The present invention is intended to improve the moisture resistance of a dispersion type EL device and the adhesion between a phosphor and an organic binder, and when coating the surface of the phosphor with water glass, water glass and sulfuric acid are used. The present invention provides a method for surface treatment of a phosphor, which comprises coating with a mixed aqueous solution of aluminum and sodium hydroxide. The water glass film is a composite film containing Al. Further, the present invention is characterized in that it is a dispersion type EL device in which a phosphor coated with water glass composed of a composite film containing Al is used for a light emitting layer.

[0005]

By the above-mentioned method, a dense water glass composite film containing Al is formed on the surface of the phosphor, so that the composite film suppresses the chemical change of the phosphor due to infiltration moisture from the outside. Further, since the water glass film is strongly bonded to both the phosphor having fine pores and the organic binder, the occurrence of local peeling due to temperature is also suppressed. Therefore, the deterioration of the brightness of the dispersion type EL element can be suppressed, and the life can be greatly improved.

[0006]

EXAMPLE An example of the present invention will be described in detail below. First, 100 parts by weight of the phosphor ZnS: Cu, Cl was added to 500 parts by weight of pure water preheated to 50 ° C., and then 2.5 parts by weight of water glass (Water glass No. 2 manufactured by Kishida Chemical Co., Ltd.) was added. Stir for minutes. Then AL as a coagulant
9 parts by weight of 25% aqueous solution of 2 (SO4) 3 are added over 1 hour. Further, the inside is treated with an aqueous NaOH solution. At this time, unnecessary ions such as SO42- and SiO2 particles are removed. Finally, the phosphor coated with a water glass film containing an Al salt is obtained through the steps of washing with water, drying and sieving. Using the phosphor 3 obtained as described above, FIG.
A dispersion type EL device having the structure shown in is prepared. First, the insulating layer 2 containing a high dielectric material such as BaTiO3 is formed on the Al electrode 1. Next, the phosphor 3 is mixed and dispersed in a binder made of cyanoethyl cellulose and dimethylformamide, coated on the insulating layer 2 and dried for a certain period of time to form a light emitting layer 4.

The transparent electrode 6 provided with the electrode terminal 5 in advance is bonded thereto by thermocompression bonding. After that, both electrodes 1,
6 is sandwiched between water catching films 7 and 7, and the whole is sealed with moisture-proof outer covering films 8 and 8. This distributed EL
The frequency of the element is 800 in an environment of 70 ° C-90% relative humidity.
FIG. 2 shows the deterioration of luminance over time when the initial luminance was adjusted to 300 cd / m @ 2 and the lamp was turned on under Hz. The solid line is according to the invention and the dotted line is conventional (untreated). Since the moisture deterioration of the phosphor is suppressed, the luminance half-life time of the present invention is 30 hours to 100 hours of the present invention.
It has become time, and the life has been improved by about 3.3 times. Further, FIG. 3 shows the deterioration of luminance with time similarly examined under the environment of 50 ° C.-20% relative humidity. Since local peeling between the phosphor and the organic binder due to temperature is suppressed,
The luminance half-life has been reduced from 158 hours in the past to 244 hours in the present invention, and the life has been improved by about 1.5 times. When the water glass-coated phosphor in this example was analyzed by an EPMA apparatus (JED-2001 manufactured by JEOL Ltd.), Zn41.
4 mol%, S40.0 mol%, Si8.7 mol
%, Al 9.9 mol% were detected.

[0008]

Example 2 Water glass (Water glass No. 2 manufactured by Kishida Chemical Co., Ltd.)
Using 2.5 parts by weight and 12 parts by weight of an Al 2 (SO 2) 325% aqueous solution, the same treatment as in Example 1 was carried out, and EL
A device was produced and the life was evaluated. The results are shown in Figure 2.
As shown in FIG. The life was further improved as compared with the case of the first embodiment. EPMA analysis result is Zn 40.8 mol%, S
37.1 mol%, Si 9.7 mol%, Al12.4
It was mol%.

[0009]

Example 3 2.5 parts by weight of water glass and Al2 (SO4)
Using 15 parts by weight of a 25% aqueous solution, the same treatment as in Example 1 was carried out to fabricate an EL device, and its life was evaluated. The results are shown in FIGS. The life was further improved as compared with the cases of the first and second embodiments. The EPMA analysis results are Zn 34.8 mol%, S36.7 mol%, Si1
It was 1.1 mol% and Al17.4 mol%. As described above, Table 1 shows the results of comparing the brightness and efficiency of the EL devices produced in Examples 1 to 3 with those of the conventional (untreated) device. As described above, according to the first to third embodiments, the life is greatly improved as compared with the conventional example, but conversely, the luminance and efficiency are slightly lowered. It is presumed that as the water glass film becomes thicker, the capacitance component of the film itself decreases and the impedance component increases. In addition, each condition of the above-mentioned embodiment is not limited, for example, water glass concentration, Al
An effective water glass film can be formed even if the combination of 2 (SO4) 3 concentration, addition method, treatment temperature and time is changed. The desirable thickness of the water glass film in the present invention is 0.1 to 10 μm, particularly preferably 0.5 to 5 μm, and the contained Al has an Al / Si ratio of 0.5.
The range of ˜2 mol%, especially 1˜1.5 mol% is preferable. If it is too thin, a sufficient life improving effect cannot be obtained, and if it is too thick, there is a problem in that the luminance and efficiency decrease significantly.

Further, the binder component used in the EL device is other than cyanoethyl cellulose, such as styrene resin,
Silicone resin, epoxy resin, vinylidene fluoride resin, cyanoethyl saccharose, cyanoethyl pullulan,
Similar effects can be obtained with cyanoethyl polyvinyl alcohol or the like. Further, it is not necessary to use the water catching film 7 or the waterproof film 8, and the brightness half-life in this case is shorter than that in the above-mentioned embodiment, but the EL element is characterized by low cost and thinness.

[0011]

[Table 1]

[0012]

As described above, according to the present invention, it is possible to form a dense water glass film on the surface of the phosphor, and by using this phosphor in the light emitting layer of the dispersion type EL device, the brightness can be improved. The decrease is suppressed and the life is greatly improved. The reason is that the moisture blocking effect suppresses the moisture deterioration of the phosphor, and the adhesiveness between the phosphor and the organic binder is improved, so that the initial power reduction is suppressed.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a dispersion type EL device manufactured using a phosphor obtained according to the present invention.

FIG. 2 shows a dispersion-type EL device using the phosphors of Examples 1 to 3 and the conventional example, respectively, at 70 ° C.-90% relative humidity.
FIG. 9 is a diagram showing deterioration with time of the brightness when the initial brightness is adjusted to 300 cd / m 2 and the light is turned on in an environment of%.

FIG. 3 shows a dispersion type EL device using the phosphors of Examples 1 to 3 and a conventional example, respectively, at 50 ° C.-relative humidity 20.
FIG. 9 is a diagram showing deterioration with time of the brightness when the initial brightness is adjusted to 300 cd / m 2 and the light is turned on in an environment of%.

[Explanation of symbols]

 1 AL electrode 2 Insulating layer 3 Phosphor 4 Light emitting layer 5 Electrode terminal 6 Transparent electrode 7 Water catching film 8 Waterproof film

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Claims (3)

[Claims] 1. A method for treating a surface of a phosphor, which comprises coating the surface of the phosphor with water glass using a mixed aqueous solution of water glass, aluminum sulfate and sodium hydroxide. 2. A dispersion type EL element having a laminated body of a back electrode, an insulating layer, a light emitting layer and a transparent electrode, wherein a phosphor having a water glass film formed in the light emitting layer is used. EL device. 3. The dispersion type EL device according to claim 2, wherein the water glass film is a composite film containing Al.