JPH075650B2 - Organic binder - Google Patents

Description

TECHNICAL FIELD The present invention relates to cyanoethylated polyvinyl alcohol having a low dielectric loss tangent.

[Prior art]

The electroluminescent light emitting device (hereinafter abbreviated as EL device) is a back electrode made of a thin metal plate or a metal foil, high dielectric constant powder such as titanium oxide or barium titanate, cyanoethylated polyvinyl alcohol, cyanoethylated cellulose, vinylidene fluoride. A reflective insulating layer in which a thin film is formed by dispersing it in a high dielectric constant organic binder such as a copolymer, a fluorescent layer in which a fluorescent substance powder is dispersed in a high dielectric constant organic organic binder to form a thin film, and Au. A film with low moisture permeability such as polychlorotrifluoroethylene for protecting the fluorescent body from external moisture in a laminate consisting of transparent electrodes formed by vapor-depositing Al, ITO, etc. on an insulating film such as polyester film. It has a structure in which it is sealed with a transparent moisture-proof film consisting of. By applying an AC voltage between both electrodes of such EL element, The fluorescent material emits light.

[Problems to be solved by the invention]

The properties required of the high dielectric constant organic binder used in the EL device having the above-described structure include a high dielectric constant, a low dielectric loss tangent (hereinafter abbreviated as tan δ), and a substrate (backside voltage, Adhesiveness with the transparent electrode) is good. When an organic binder having a small dielectric constant is used, it is necessary to apply a high voltage to the device. Also,
When an organic binder having a large tan δ is used, the current flowing through the phosphor layer becomes large, which shortens the life of the phosphor because it causes deterioration of the binder, and also increases the power consumption and decreases the luminous efficiency. It is known that the element has a bad influence on the heat generation of the element and the characteristics inherent to the EL element are impaired. When an organic binder having a poor adhesion to the base material is used, the workability in producing the element is poor and the base material and the phosphor layer are peeled off during lighting, resulting in uneven brightness on the light emitting surface.

Currently, as organic binders for EL, cyanoethylated cellulose, cyanoethylated pullulan, polyvinylidene fluoride, cyanoethylated polyvinyl alcohol, etc., which have a large dielectric constant, are used. Since cyanoethylated cellulose and cyanoethylated pullulan have very poor properties and improve adhesion,
As a method of adding an additive, a method of copolymerizing polyvinylidene fluoride has been proposed, but its effect is not sufficient. On the other hand, cyanoethylated polyvinyl alcohol has a high dielectric constant and good adhesion to a substrate, and is the most useful organic binder for EL currently used.

However, the element using cyanoethylated polyvinyl alcohol has a problem that the life is extremely short when it is lit in a high temperature environment as compared with when it is lit in a normal temperature environment.

[Means for solving problems]

As a result of intensive studies in view of the above problems, the present inventors have found that the life of an element using cyanoethylated polyvinyl alcohol as a binder is extremely long when it is lit under a high temperature environment as compared to when it is lit under a room temperature environment. The inventors of the present invention have found that the cause of the shortening is due to the large temperature dependence of tan δ of cyanoethylated polyvinyl alcohol.

That is, the present invention has a tan δ value of 0.1 or less at 20 ° C.,
0.4 or less at 50 ° C, 2 or less at 70 ° C, or 100 ° C
It relates to a cyanoethylated polyvinyl alcohol having 10 or less, and to a production method for obtaining the cyanoethylated polyvinyl.

Conventionally, cyanoethylated polyvinyl alcohol was obtained by a method of reacting polyvinyl alcohol and acrylonitrile under an alkaline catalyst after the reaction, neutralizing with an acid, and washing with water, but tan δ of the cyanoethylated polyvinyl alcohol thus obtained is It was as large as 0.2 at 20 ° C, and was as high as 2 at 50 ° C and 20 at 70 ° C at high temperatures. Generally, in order to remove residual alkalis, acids and salts, cyanoethylated polyvinyl alcohol is dissolved in a solvent to form a 2 to 5 weight percent solution, and this solution is added to a large amount of water to give cyanoethylated polyvinyl alcohol. The reprecipitation method of precipitation was used, but there was almost no effect on the reduction of tan δ.

That is, in the purification method of the present invention, cyanoethylated polyvinyl alcohol is dissolved in a solvent to prepare a 1 to 20 wt% solution, and 1 to 10 parts by weight, preferably 1 to 3 parts by weight per 1 part by weight of this solution. Of the precipitant of
This is a method of obtaining cyanoethylated polyvinyl alcohol having a small tan δ value and a small temperature dependence by precipitating cyanoethylated polyvinyl alcohol. The cyanoethylated polyvinyl alcohol obtained by this method has only the tan δ value improved without impairing the inherent properties of the cyanoethylated polyvinyl alcohol such as dielectric constant and adhesiveness. When 10 parts by weight or more of the precipitant was used per 1 part by weight of the cyanoethylated polyvinyl alcohol solution, the tan δ value was hardly improved. The solvent used in the present invention is one that dissolves cyanoethylated polyvinyl alcohol in an amount of at least 1% by weight and mixes well with the precipitating agent shown below, and examples thereof include acetone, methyl ethyl ketone, acetonitrile, dimethylformamide, and dimethylacetamide. . As the precipitating agent, a precipitant that does not dissolve the binder but dissolves only the impurities well and has a relatively low boiling point, such as water, methanol, or ethanol, is used. The tan δ value of the cyanoethylated polyvinyl alcohol obtained by the above method is 0.1 or less at 20 ° C., 0.4 or less at 50 ° C., 2 or less at 70 ° C., or 100.
By repeating the above method at 10 ° C. or less, a cyanoethylated polyvinyl alcohol having a smaller tan δ value and a smaller tan δ temperature rise dependency can be obtained.

A method for producing an element using the cyanoethylated polyvinyl alcohol obtained by the above method as a binder will be described.

FIG. 1 shows a sectional view of the EL device. 1 is a back electrode made of a thin metal plate or metal foil such as Al, Cu, Au, 2 is high dielectric constant powder such as titanium oxide or barium titanate, cyanoethylated polyvinyl alcohol, cyanoethylated cellulose, vinylidene fluoride copolymer, etc. A reflective insulating layer in which a thin film is formed by dispersing it in a high dielectric constant organic binder, and 3 is a phosphor in which Cu, Mn, Al, Cl, Br activators and activators are injected into zinc sulfide or zinc selenide. A phosphor layer formed by dispersing a powder in the high dielectric constant organic binder to form a thin film, 4 is a transparent electrode formed by vapor-depositing Au, Al, ITO or the like on an insulating film such as a polyester film, and 6 is a moisture film. It is a transparent moisture-proof film made of a film having low moisture permeability such as polychlorotrifluoroethylene for protecting sensitive fluorescent substances from external moisture.

In the EL device having the above-mentioned structure, by applying an alternating current between 1 and 4 to form a phosphor layer or a reflective insulating layer in which the phosphor emits light, the high dielectric constant organic binder is acetone, It is dissolved in a solvent such as dimethylformamide, and in the case of a phosphor layer, the phosphor powder is added, and in the case of a reflective insulating layer, the high dielectric constant powder is added and sufficiently stirred and mixed to form a space, which is screen-printed. Apply with a doctor blade, roll coater, etc. and dry.

There are various combinations in the order of forming the back electrode, the reflective insulating layer, the fluorescent material layer, and the transparent electrode, but as an example, the reflective insulating layer and the fluorescent material layer are formed in this order on the back electrode, and the transparent electrode is laminated. In this case, the transparent electrode provided on the insulating film such as polyester and the fluorescent layer are overlapped with each other so that they face each other, and they are heat-pressed, and then the electrode is attached and the whole is sealed with a moisture-proof film.

[Action and effect]

Although it is not clear why tanδ of the cyanoethylated polyvinyl alcohol obtained by the purification method of the present invention is small, the present inventors presume as follows.

That is, tan of cyanoethylated polyvinyl alcohol
As a cause of increasing the value of δ, the presence of metal salts and low molecular weight cyanoethylated polyvinyl alcohol derivatives that are by-produced in the cyanoethylation process is considered, and the metal salts are conventionally removed by reprecipitation using a large amount of water. However, the latter low molecular weight cyanoethylated polyvinyl alcohol derivative is rather difficult to dissolve by reprecipitation with a large amount of water or alcohol as in the conventional method, and a solvent and water, a precipitant such as alcohol as in the present invention. It is considered that the target high molecular weight cyanoethylated polyvinyl alcohol precipitates and the metal salt and the low molecular weight cyanoethylated polyvinyl alcohol derivative elute by limiting the mixing ratio of the above to a certain range.

It is considered that the EL light-emitting device using the cyanoethylated polyvinyl alcohol having a small tan δ thus obtained as a binder has a small current flowing through the light-emitting layer, little deterioration of the light-emitting layer, and a long life.

〔Example〕

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

Reference Example 1. (Production of cyanoethylated polyvinyl alcohol) Commercially available polyvinyl alcohol (polymerization degree 2000, saponification degree 9
8.5%) 1 part by weight and 1% 5% aqueous solution of sodium hydroxide
Part by weight, 10 parts by weight of acrylonitrile are mixed, and 50-60 ° C
The reaction was terminated by stirring within the range of 3 hours. After cooling the reaction solution to room temperature, 2 parts by weight of 5% acetic acid aqueous solution was added to neutralize the catalyst (sodium hydroxide), and then acrylonitrile was distilled off while adding 2 parts by weight of each water, washed with water and dried. Thus, cyanoethylated polyvinyl alcohol was obtained.

The N element component of this cyanoethylated polyvinyl alcohol was 14.2% as a result of analysis by the Kjeldahl method, and was 96.5% when converted to the degree of cyanoethylation.

Example 1 1 part by weight of the cyanoethylated polyvinyl alcohol obtained in the above Reference Example was dissolved in 9 parts by weight of acetone, and then 10 parts by weight of pure water was added little by little while stirring to precipitate cyanoethylated polyvinyl alcohol. Vacuum drying (60 ℃ 7T
orr, 24 hours) to obtain purified cyanoethylated polyvinyl alcohol.

The cyanoethylated polyvinyl alcohol obtained by the above method was dissolved in acetone to form a film by the casting method, and an Al foil was attached as an electrode, and tan δ was measured by an LCR meter to be 0.1 at 20 ° C, 0.4 at 50 ° C, 70
It was 1.8 at ℃ and 9.1 at 100 ℃.

Then, 10 parts by weight of the cyanoethylated polyvinyl alcohol obtained by the above method for preparing a device was dissolved in 20 parts by weight of dimethylformamide to prepare a binder solution, and 10 parts by weight of the binder solution was fluorinated mainly with ZnS. Body 1
A fluorescent paste was prepared by adding 0 parts by weight and sufficiently stirring and mixing, and an insulating paste was similarly prepared by similarly adding 10 parts by weight of barium titanate to 10 parts by weight of a binder solution and sufficiently stirring and mixing.

The above insulating paste is applied by screen printing on an Al foil with a thickness of 100 μ and dried to form a reflective insulating layer with a thickness of 20 μ, and the fluorescent paste is applied by screen printing on the insulating reflective layer in the same manner and dried by a thickness of 40 μ. A phosphor layer of. Next, a transparent conductive film made of indium oxide and tin oxide was attached to the surface of the polyester film by a vapor deposition method so that the conductive surface of the transparent conductive film faces the fluorescent material layer and is heated through a thermocompression roll. Crimping was performed.
Then, after attaching a lead wire for an electrode, the whole was covered with a laminated film of polyethylene film and polychlorotrifluoroethylene and sealed by heat sealing.

The device manufactured in this way is kept at 100 ° C in an environment of 20 ° C and 65% RH.
The brightness half-life when connected to a V × 400Hz power source and lit
The brightness half-life was 4200 hours, and the brightness half-life was 410 hours when the lamp was lit at 50 ° C and 90% RH.

Example 2 1 part by weight of crude cyanoethylated polyvinyl alcohol obtained in the same manner as in Example 1 was dissolved in 49 parts by weight of acetonitrile, and 150 parts by weight of methanol was added little by little to this with stirring to add cyanoethylated polyvinyl alcohol. After the alcohol was precipitated and separated, vacuum drying (60 ° C., 7 Torr, 24 hours) was performed to obtain a purified cyanoethylated polyvinyl alcohol. The result of measuring tan δ by the same method as in Example 1 was 20 ° C.
At 0.1 and 0.6 at 50 ° C. Further, the luminance half-life of the device manufactured by using the above-mentioned purified cyanoethylated polyvinyl alcohol in the same manner as in Example 1 under lighting at 20 ° C. and 65% RH environment is 4100 hours, and 50 ° C. and 90%. The brightness half-life was 350 hours when the light was turned on in the RH environment.

Example 3. Cyanoethylated polyvinyl alcohol obtained by repeating purification 10 times in the same manner as in Example 1.
As a result of measuring nδ, it was 0.05 at 20 ° C and 0.1 at 50 ° C.

The brightness half-life is 4700 hours when the device manufactured using this binder is lit under the environment of 20 ° C and 65% RH.
The brightness half-life was 650 hours when the lamp was turned on at 90 ℃ and 90% RH.

Comparative Example 1. 1 part by weight of the cyanoethylated polyvinyl alcohol obtained in Reference Example was synthesized in a similar manner, and after washing only with water, tan δ was measured for cyanoethylated polyvinyl alcohol not subjected to reprecipitation purification. It was 2 at 50 ° C and 20 at 70 ° C.

The luminance half-life is 2500 hours when the device manufactured using the above binder is lit under the environment of 20 ° C and 65% RH.
%, 90% RH, the brightness half-life was 150 hours.

As described above, the EL element using cyanoethylated polyvinyl alcohol having a small tan δ of the present invention as a binder has less heat generation due to a loss current and a longer half-life of luminance, and the effect of improving the half-life under high temperature conditions is particularly remarkable.

Claims (4)

[Claims] 1. The dielectric loss tangent value is 0.1 or less at 20 ° C. and 0.4 at 50 ° C.
A cyanoethylated polyvinyl alcohol that is: 2. The cyanoethylated polyvinyl alcohol according to claim 1, which has a dielectric loss tangent value of 2 or less at 70 ° C. 3. A solvent which can dissolve at least 1% by weight or more of cyanoethylated polyvinyl alcohol and is well mixed with a precipitating agent (consisting of one or more selected from the group consisting of water, methanol and ethanol). A method for purifying cyanoethylated polyvinyl alcohol, characterized in that 1 to 10 parts by weight of a 1 to 20% by weight solution of cyanoethylated polyvinyl alcohol dissolved therein is added to 1 to 10 parts by weight of the above-mentioned precipitating agent to carry out reprecipitation purification. 4. The method for purifying cyanoethylated polyvinyl alcohol according to claim 3, wherein the solvent is acetone, methyl ethyl ketone, acetonitrile, dimethylformamide, or dimethylacetamide.