JP3016939B2 - Low viscosity cyanoethyl pullulan and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing low-viscosity cyanoethyl pullulan, and more particularly to a method for producing low-polymerization cyanoethyl pullulan which is suitable as a binder used for producing an electroluminescence element.

[0002]

2. Description of the Related Art In recent years, a separation type electroluminescent element (hereinafter abbreviated as EL light emitting element) which is thin and easy to mount as a backlight for a liquid crystal display or the like has been attracting attention. As a binder used in the manufacture of EL light-emitting devices, it has a high dielectric constant, has excellent film forming properties, has appropriate viscoelastic properties, has excellent coating suitability, and has a suitable thermoplasticity. It is required to be excellent in thermocompression bonding property, and to have less ionic impurities and less dielectric loss. An EL light emitting device manufactured using a binder having a high dielectric constant has high brightness, but without appropriate viscoelastic properties and thermoplasticity, uneven coating at the time of coating, and thermocompression bonding between a light emitting layer and a surface electrode. There is a problem that the unevenness of light emission is increased due to a defect or the like, and the dielectric loss at the interface between the light emitting layer and the surface electrode is increased due to poor adhesion. It should be noted that ionic impurities contained in such a high dielectric constant binder cause an increase in dielectric loss, and have a significant effect on the luminous efficiency, lifetime, and the like of the obtained EL light emitting device.

Conventionally, as binders for EL light emitting devices, cyanoethyl cellulose, cyanoethyl starch,
Various cyanoethylated compounds such as cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl pullulan have been proposed. Among them, cyanoethyl pullulan is most excellent in dielectric properties, but has a very high degree of polymerization, has poor coating suitability and thermocompression bonding properties, and has various practical problems. In order to improve this point, various developments have been demanded for producing low-viscosity cyanoethyl pullulan. For example, the method described in JP-A-59-96104 has been generally adopted at present. Pullulan is a high molecular chain polymer in which a unit of maltotriose, which is a trimer of glucose, is linked repeatedly by α-1,6 bonds which are different from the trimer. It is accumulated as a viscous substance outside the cells by culturing the strain with aeration and agitation, and is obtained by separating and purifying the cells. In this case, the molecular weight of pullulan differs depending on various conditions during culturing, but usually has a very high degree of polymerization, and the high degree of polymerization (that is, high viscosity) cyanoethylated pullulan obtained by directly cyanoethylating contains practical problems. Is as described above. As a method for obtaining low polymerization degree (that is, low viscosity) cyanoethyl pullulan, a method of depolymerizing high polymerization degree cyanoethyl pullulan is not conceivable, but a low polymerization degree pullulan obtained by depolymerizing high polymerization degree pullulan is used as cyanoethyl pullulan. Is generally used.

It is expected that the properties of such low-viscosity cyanoethyl pullulan are firstly governed by the method of depolymerization of pullulan and the method of cyanoethylation of depolymerized pullulan. Conventionally known methods for depolymerizing pullulan are roughly classified as follows. First method: A method in which pullulan having a low degree of polymerization is obtained by bringing hydrogen halide gas into contact with powdery pullulan and hydrolyzing it. However, it is easily understood that this method is basically a depolymerization in an uneven system, and the uniformity of the depolymerization is inferior. Method 2: In the aqueous pullulan solution,
In this method, pullulan having a low degree of polymerization is obtained using an enzyme that decomposes pullulan, such as pullulanase, isoamylase, or glucoamylase. On the other hand, as the cyanoethylation reaction conditions, for example, as described in JP-A-59-96104, a depolymerized raw material pullulan is dissolved in an aqueous solution of caustic alkali such as sodium hydroxide, and a solvent compatible with acrylonitrile and water and acrylonitrile, for example, A method of adding acetone, dioxane, etc. and reacting at around room temperature, or dispersing the starting material pullulan in a solvent such as hexane, benzene, etc., adding acrylonitrile and an aqueous caustic solution to 40 to 60 ° C.
Are known. However, the low-viscosity cyanoethyl pullulan obtained by such a method has low viscosity and therefore has excellent properties not found in high-viscosity cyanoethyl pullulan, and is currently widely used as a binder for EL light emitting devices. Because of insufficient elasticity and thermoplastic properties, as described above, there was a problem that emission spots and dielectric loss were large.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to provide a binder for an EL light-emitting element which has a short lifespan and a high luminous efficiency with less uneven spots accompanying an increase in demand for the EL light-emitting element. The technical means of the present invention that meets this requirement is as follows. A The degree of substitution of cyanoethyl groups in anhydroglucose units is 2.0 to 3.0, and the viscosity of a 30% by weight N, N'-dimethylacetamide solution at 25 ° C is 1700.
± 500 centipoise and the viscosity of the solution is η
₆₀ / η ₆ ≦ 1 Low viscosity cyanoethyl pullulan, wherein η ₆₀ is 25 using a B-type viscometer (rotor No. 3).
° C, viscosity at 60 rpm, η ₆ is also 25
Indicates the viscosity at 6 ° C. and ° C. B. The process for producing low-viscosity cyanoethyl pullulan according to A, wherein the low-polymerized pullulan obtained by hydrolysis with sulfuric acid in an aqueous solution system is reacted with acrylonitrile in the presence of a caustic catalyst. In the method described in CB, when pullulan is reacted with acrylonitrile in the presence of a caustic alkali catalyst, the caustic alkali of the reaction system is 0.05 to 0.10 mol per hydroxyl group of pullulan and water is also 0.1 to 0.1 mol. 2
0 to 0.50 mol, acrylonitrile was also used at 5.0 to
The process for producing low-viscosity cyanoethyl pullulan according to A, wherein the amount is 10.0 mol and the reaction temperature is 40 to 60 ° C.

[0006] By the above-mentioned means, a low-viscosity cyanoethyl pullulan having excellent solution viscosity dependency on mechanical shear stress can be obtained. The reason is not clear, but is presumed as follows. 1) Uniform depolymerization of pullulan: The conventionally known method of hydrolyzing powdery pullulan with a hydrogen halide gas is basically a solid phase heterogeneous depolymerization, whereas in the present method, a homogeneous aqueous solution is used. By adopting the depolymerization method in the system,
A more uniform hydrolysis reaction is performed. 2) Cyanoethylation reaction: The difference from the conventionally known method is as follows.
The difference in the reaction solvent is first mentioned. Whereas conventionally known methods react simultaneously with acrylonitrile in the presence of any organic solvent, the method of the present invention uses a single solvent system of acrylonitrile alone. That is, in the polymer reaction such as the present reaction, it is expected that the conformation of the polymer chain accompanying the reaction greatly differs depending on the solvent type of the reaction system. Therefore, it is expected that the substituent distribution of the cyanoethyl group is different from that of cyanoethyl pullulan obtained by a conventionally known method. It can be easily understood that such a difference in substituent distribution has a great effect on solution viscosity and suitability for blending with a plasticizer. Also, the amount of water and the amount of caustic alkali in the reaction system can easily affect the conformation of the pullulan polymer chain in the reaction system and side reactions during the reaction (by-products of carboxyl groups due to hydrolysis of cyanoethyl groups). Presumed.
It is not preferable to use excess amounts of water and caustic in the reaction system more than necessary amounts from the viewpoint of uniformity of the reaction and suppression of side reactions. It is possible to obtain high-quality low-viscosity cyanoethyl pullulan that meets such a purpose. On the other hand, if the water content and the caustic alkali content are less than the required amounts, the reaction does not proceed smoothly, which is not preferable.

[0007]

The operation and effect of the present invention will be described in relation to the manufacture of the EL device.
It can be obtained by interposing at least one light emitting layer containing a phosphor such as Cl between electrodes that are transparent. in this case,
First, on one electrode, a luminescent layer sheet obtained by applying a paste obtained by dispersing a phosphor powder and a high dielectric constant binder in an organic solvent by an appropriate method such as a screen printing method or a bar coating method, and further, The electrode plate is manufactured by bonding the above-mentioned electrode plates by means such as heating and pressure bonding. The use of the low-viscosity cyanoethyl pullulan of the present invention as a high dielectric constant binder has the following effects. 1) The greatest characteristic of the low-viscosity cyanoethyl pullulan obtained in the present invention is that the solution viscosity depends on the mechanical shearing force, that is, the above-mentioned viscosity characteristic shows η ₆₀ / η ₆ ≦ 1. Conventionally known low-viscosity cyanoethyl pullulan has η ₆₀ / η
₆ > 1 clearly shows viscous properties different from the low viscosity cyanoethyl pullulan of the present invention. That is, at the time of coating, regardless of the method of the coating method, some mechanical shear stress is always applied to the coating paste, but the viscosity of the low-viscosity cyanoethyl pullulan of the present invention is η ₆₀ / η
₆ ≦ 1, and the viscosity is lower when a mechanical shear stress is applied. Therefore, when the low-viscosity cyanoethyl pullulan of the present invention is used for a phosphor paste or an insulating layer paste, a decrease in coating aptitude due to an increase in viscosity during coating such as a conventionally known binder is not observed, and stable. Coating can be performed, and luminescent spots based on coating spots are significantly improved. 2) Excellent blending properties with a plasticizer, and when the same plasticizer is used, the resulting coating film is more excellent in thermocompression bonding property than in the case of using a conventionally known low-viscosity cyanoethyl pullulan, and more uniform thermocompression bonding property is obtained. It is significantly improved. Therefore,
The unevenness of light emission and the dielectric loss of the EL light emitting element due to the poor pressure bonding are remarkably improved, and it becomes possible to obtain an EL light emitting element having high luminous efficiency, long life, and excellent uniform light emitting characteristics.

[0008]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but it is needless to point out that the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded. Example 1 800 g of water was charged into a glass reactor equipped with a stirrer, 100 g of pullulan powder having a viscosity of 110 centipoise of a 10% by weight aqueous solution at 25 ° C was added, and the mixture was heated to 60 ° C and uniformly dissolved. Subsequently, dilute sulfuric acid obtained by dissolving 2.55 g of 96% sulfuric acid in 100 g of water was added, and depolymerized until the viscosity at 25 ° C. became 25 centipoise. Next, sulfuric acid was neutralized with a sodium hydroxide aqueous solution, and then the depolymerization reaction liquid was poured into a large amount of acetone to precipitate low-viscosity pullulan. After solid-liquid separation, it was sufficiently washed with water to remove impurities such as neutralized salts, and then dried to obtain low-viscosity pullulan. In a reactor equipped with a stirrer, 81.6 g of the above low-viscosity pullulan and 3.892 g of caustic soda were added to 1 part of water.
An aqueous solution of caustic soda dissolved in 0.025 g was added, and the mixture was stirred at room temperature for 30 minutes. Then 720 g of acrylonitrile
The mixture was added and reacted at 55 ± 3 ° C. for 3 hours. Then, after cooling to room temperature, excess caustic soda was neutralized with acetic acid, and excess acrylonitrile was distilled and recovered while adding water as needed. After the yield of the recovery operation, impurities such as neutralized salts were washed and removed with a large amount of water, followed by solid-liquid separation. The obtained solid was dissolved in a large amount of acetone, and the undissolved material was separated by filtration and poured into a large amount of water with stirring to precipitate cyanoethyl pullulan. The washing and dehydration were repeated with pure water and dried under reduced pressure to obtain the desired low-viscosity cyanoethyl pullulan. The degree of substitution of the cyanoethyl group in the anhydrous glucose unit was 2.80, and the viscosity of the 30% by weight N, N′-dimethylacetamide solution at 25 ° C. was 2000 centipoise.

For reference, an EL light-emitting device was manufactured by using the low-viscosity cyanoethyl pullulan obtained in Example 1 by the following method. 20 parts by weight of BaTiO ₃ fine powder, 1.5 parts by weight of cyanoethyl polyvinyl alcohol (Cyanoresin CR-V manufactured by Shin-Etsu Chemical Co., Ltd.), 3.5 parts by weight of low-viscosity cyanoethyl pullulan obtained in Example 1, N, N′-dimethyl A paste consisting of 12 parts by weight of formamide was applied on an Al foil having a thickness of 0.1 mm by a screen printing method to form a reflective insulating layer having a thickness of 20 μm. Further, ZnS: Cu, C having an average particle diameter of 27.0 μm is formed on the reflective insulating layer.
20 parts by weight of phosphor, 1.5 parts by weight of cyanoethyl polyvinyl alcohol (Cyanoresin CR-V manufactured by Shin-Etsu Chemical Co., Ltd.), 3.5 parts by weight of low-viscosity cyanoethyl pullulan obtained in Example 1, N, N'-dimethylformamide A paste consisting of 12 parts by weight was applied by a screen printing method to form a light emitting layer having a thickness of 60 μm. ITO-coated transparent PET using a 75 μm thick transparent PET film
A silver paste is applied to the surface of the TO layer to form a current collecting zone having a thickness of 10 μm, and the current collecting zone is further formed of a phosphor bronze foil having a thickness of 10 μm.
A surface electrode was prepared by connecting a lead terminal of 0 μm. Next, after the light emitting layer and the surface electrode were heat-pressed with a hot roll laminator, lead terminals similar to those described above were connected to the Al foil to produce a dispersed EL light emitting device body. Next, a nylon 6-based transparent film (Daiamide ZS-185, manufactured by Daicel Chemical Co., Ltd.) was heat-pressed on both surfaces of the element body using a thermocompression laminator to laminate the element body and the water refill layer. Next, the upper laminate was wrapped with a moisture-proof film (Nitoflon 4820 manufactured by Nitto Denko Corporation) and subjected to heat compression to produce a dispersion-type EL light-emitting device. Tables 1 to 3 show the reaction conditions, cyanoethyl pullulan characteristics, and EL device characteristics of Example 1.

Examples 2-3 Using a low-viscosity pullulan obtained in exactly the same manner as in Example 1, a cyanoethylation reaction was carried out. All the cyanoethylation reaction conditions were the same as in Example 1 except for the portions described in Table 1, to obtain the desired low-viscosity cyanoethyl pullulan. The degree of substitution of the cyanoethyl group in the anhydrous glucose unit was 2.75 and 2.85.
0% by weight of N, N′-dimethylacetamide solution at 25 ° C.
Were 1800 and 1900 centipoise. In addition, an EL light emitting device was manufactured in the same manner as described above except that the cyanoethyl pullulan obtained in Examples 2 and 3 was used. Tables 1 to 3 show the reaction conditions, cyanoethyl pullulan characteristics and EL device characteristics of Examples 2 and 3.

Comparative Example 1 The same raw pullulan as used in Example 1 was obtained by
Depolymerization was carried out according to the method of Example 1 described in No. 9-96104. That is, 150 g of the raw material pullulan was charged into a glass reactor, 15 g of anhydrous methanol containing 13% by weight of hydrogen chloride was injected under stirring, and depolymerization was performed at 40 ° C. for 3 hours. Upon volatilization, a low-viscosity pullulan with a viscosity of 23 centipoise at 25 ° C. of a 10% by weight aqueous solution was obtained. Except that this low-viscosity pullulan was used, the same treatment as in Example 1 was carried out to obtain a target low-viscosity cyanoethylpullulan. The degree of substitution of the cyanoethyl group in the anhydrous glucose unit was 2.72, and the viscosity at 25 ° C. of a 30% by weight N, N′-dimethylacetamide solution was 2,200 centipoise. or,
Except for using the cyanoethyl pullulan obtained in Comparative Example 1, an EL device was manufactured in the same manner as described above. Tables 1 to 3 show the reaction conditions, the cyanoethyl pullulan characteristics, and the EL device characteristics of Comparative Example 1.

Comparative Example 2 Using the low viscosity pullulan obtained in Comparative Example 1,
The cyanoethylation reaction was carried out according to the method of Example 1 described in No. 6104. That is, 100 g of the low-viscosity pullulan and 30% of an 8% by weight aqueous sodium hydroxide solution were placed in a reactor equipped with a stirrer.
0 g, acrylonitrile 500 g, and acetone 200 g were charged and reacted at 20 ° C. for 24 hours. Then, the reaction solution was neutralized with glacial acetic acid, and then poured into a large amount of water with stirring to precipitate cyanoethyl pullulan. Thereafter, the same treatment as in Example 1 was performed to obtain a target low-viscosity cyanoethyl pullulan. The substitution degree of the cyanoethyl group in the anhydrous glucose unit was 2.80, and 30% by weight of N, N'-
The viscosity of the dimethylacetamide solution at 25 ° C. is 2400.
It was centipoise. In addition, an EL light emitting device was manufactured in the same manner as described above except that the cyanoethyl pullulan obtained in Comparative Example 2 was used. Tables 1 to 3 show reaction conditions, cyanoethyl pullulan characteristics, and EL device characteristics of Comparative Example 2.

Comparative Example 3 The same raw pullulan as used in Example 1 was obtained by
Depolymerization was carried out according to the method of Example 2 described in No. 9-96104, and further cyanoethylation was carried out according to the same method to obtain the desired low-viscosity cyanoethyl pullulan. That is, 100 g of the same raw material pullulan used in Example 1 was
g of water, and then 3 ml of a 1 wt% aqueous solution of isoamylase was added so that the isoamylase became 300 ppm with respect to pullulan. To depolymerize to 24 centipoise. Next, 100 g of a 25% by weight aqueous sodium hydroxide solution was added, and 600 g of acrylonitrile was further added.
400 g of acetone was added and reacted at 25 ° C. for 12 hours with stirring. Next, the reaction solution was neutralized with 20% by weight hydrochloric acid, and the reaction solution was poured into a large amount of water to precipitate cyanoethyl pullulan. Thereafter, the same treatment as in Example 1 was performed to obtain a target low-viscosity cyanoethyl pullulan. The degree of substitution of the cyanoethyl group in the anhydrous glucose unit was 2.73, and the viscosity at 25 ° C. of the 30% by weight N, N′-dimethylacetamide solution was 2,500 centipoise. In addition, except that the cyanoethyl pullulan obtained in Comparative Example 3 was used, EL was prepared according to the method described above.
A light-emitting element was manufactured. Tables 1 to 3 show the reaction conditions, the cyanoethyl pullulan characteristics, and the EL device characteristics of Comparative Example 3.

[0014]

[Table 1]

[0015]

[Table 2] * Cyanoethyl pullulan properties: solution viscosity is 30% by weight
The value obtained by measuring the N, N′-dimethylacetamide solution in an environment at 25 ° C.

[0016]

[Table 3] * EL element characteristics: A value measured under an environment of a temperature of 20 ° C. and a humidity of 65% RH when an AC electric field of 100 V and 400 Hz is applied. The service life is 1/1 of the initial brightness under continuous lighting under the same conditions.
2 shows the time required to reach the luminance.

As summarized in Tables 1 to 3, it is clear that the low-viscosity cyanoethyl pullulan of the present invention is extremely excellent as a binder for EL light-emitting elements, compared with the conventionally known low-viscosity cyanoethyl pullulan. The industrial significance of the invention is extremely large.

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein the degree of substitution of the cyanoethyl group in the anhydrous glucose unit is 2.0 to 3.0, and 30% by weight of N,
A low-viscosity cyanoethyl pullulan, wherein the viscosity of the N-dimethylacetamide solution at 25 ° C. is 1700 ± 500 centipoise and the viscosity property of the solution is η ₆₀ / η ₆ ≦ 1.0. However, η ₆₀ is 2 using a B-type viscometer.
The viscosity at 5 ° C. and 60 rpm, η ₆ is also ₆ r
Shows the viscosity in pm.