JPS639018B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composition necessary for forming a transparent conductive film by applying the composition to the surface of a glass or ceramic substrate and then baking the composition. Display elements such as liquid crystal display elements, plasma display elements, electroluminescence elements, photovoltaic cells,
2. Description of the Related Art Conductive films that are transparent to light are used in photosensitive elements such as image pickup tubes, resistive heating elements used in anti-fog window glasses for airplanes, automobiles, homes, etc., and the like. Materials used for this transparent conductive film include a system in which tin oxide is doped with antimony and a system in which indium oxide is doped with tin, but indium oxide, which has high electrical conductivity, is widely used. Conventionally, there are the following two composition liquids used to form a transparent conductive film by coating and baking. (1) Organic solutions of alkoxides or carboxylates of indium. (2) Thinner or alcohol solution containing tin octylate or tin caprylate added to indium naphthenate or diethylmonoethoxyindium. However, these have problems such as being easily repelled on glass substrates, making it difficult to obtain a uniform coating, and having high electrical resistance. An object of the present invention is to eliminate the drawbacks of the above-mentioned compositions and to provide a composition from which a uniform transparent conductive film with low electrical resistance can be obtained. To achieve this objective, the composition of the present invention comprises indium nitrate, dicarboxylic acid, and
At least one organic solvent among monohydric alcohols, esters, and ketone ethers with a boiling point of 130°~
At least one organic solvent selected from cellosolves, carbitols, and glycols at 250°C, and tin 2-ethylhexanoate, tin caproate, dimethyl diacetate, and dimethyltin octanate. and one type of tin compound. When a solution with such a composition is used, (1) indium nitrate reacts with dicarboxylic acid to form an indium complex in which nitrate ions are partially substituted with dicarboxylic acid, and (2) this complex , because it has the property of becoming glassy when the solvent is removed,
(3) It is completely oxidized and decomposed by heating without precipitating as crystals, so a uniform indium oxide film can be formed. Also, (4)
Contains an organic solvent with a boiling point of 100°C or less, so the solvent evaporates rapidly after application, increasing the viscosity of the coating, so it does not repel, and (5) has a boiling point of 130°C.
Since it also contains an organic solvent with a temperature of ℃ or higher, it is difficult to cause clouding of the coating film caused by premature drying, and therefore a homogeneous transparent conductive film without pinholes or clouding can be obtained. Next, materials used in the present invention will be explained. (1) Dicarboxylic acids; those with 3 to 10 carbon atoms are preferred; dicarboxylic acids with fewer carbon atoms have poor solubility in organic solvents of the reaction product of dicarboxylic acids with indium nitrate; , the resistance value of the resulting transparent conductive film increases. Further, a dicarboxylic acid having a double bond or a side chain may also be used. Specifically, malonic acid, succinic acid, methylmalonic acid, glutaric acid, methylsuccinic acid, adipic acid, pimelic acid, suberic acid,
Azelaic acid, sebacic acid, maleic acid, citraconic acid, itaconic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, and the like. Among these, methylsuccinic acid,
Citraconic acid is most preferred. In addition, anhydrides of these dicarboxylic acids are hydrolyzed by stirring with indium nitrate in an organic solvent and behave similarly to dicarboxylic acids, and their esters, especially monoesters, are hydrolyzed to form dicarboxylic acids. It is thought that dicarboxylic acids behave in the same way as acids, and dicarboxylic acids may also be esterified when alcohols are used as organic solvents. Such dicarboxylic acid is preferably added in a molar ratio of 0.3 to 2.0 with respect to indium nitrate.If it is less than this, the solubility of indium nitrate will be poor and the transparent conductive film will become cloudy, and if it is more than this, the transparent conductive film will become cloudy. Conductivity deteriorates. (2) Organic solvent: At least one of alcohols, ketones, esters, and ethers with a boiling point of 30° to 100°C, and cellosolves, carbitols, and glycols with a boiling point of 130° to 250°C. A mixed system with at least one selected from these is used. Since these organic solvents have polarity, they serve as good solvents for indium nitrate, dicarboxylic acids, or their reactants, and can dissolve them up to a fairly high concentration range. Specifically, organic solvents with a boiling point of 30° to 100°C include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone, ethyl formate, propyl formate, methyl acetate, ethyl acetate, diethyl ether, dipropyl ether, Examples include diisopropyl ether and tetrahydrofuran. Further, examples of organic solvents having a boiling point of 130° to 250°C include ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, and the like. In this way, by creating a mixed system of a low-boiling point solvent and a high-boiling point solvent, rapid solvent evaporation can be moderately suppressed, preventing clouding of the coating film, and moreover, when only a high-boiling point solvent is used, At the same time, it is possible to eliminate unevenness in the thickness of the coating film, which tends to occur. Furthermore, since the viscosity of the coating film increases with the evaporation of the low boiling point solvent, it is less likely to be repelled, but it is effective to add a surfactant to further improve the wettability to the substrate.
The surfactant is preferably a nonionic surfactant, and a fluorine-based surfactant is particularly effective since it can significantly lower the surface tension of the organic solvent by adding a small amount. The appropriate mixing ratio of the high boiling point solvent to these low boiling point solvents is 30wt% or less, especially 3 to 30% by weight.
Preferably it is in the range of 20wt%. If the amount is more than this, unevenness in film thickness tends to occur when coating. In addition, the amount of these solvents added is 100 parts by weight in total of low boiling point solvent and high boiling point solvent.
Indium nitrate is preferably added in an amount of 2 to 50 parts by weight. (3) Tin compound; added to improve the conductivity of the transparent conductive film. Examples of such tin compounds include tin halides, organic tin acids, and alkoxides. However, when tin halides such as stannic chloride are used, the tin chloride evaporates when formed into a transparent conductive film. Otherwise, chlorine may remain in the film, resulting in poor conductivity of the film, which is undesirable.
Furthermore, alkoxides have poor solubility and it is difficult to obtain a uniform composition. When organic acid tin is used, it does not evaporate and is oxidized and decomposed into tin oxide when heated to 350 to 400°C, making it possible to obtain a transparent conductive film with excellent light transmission and high conductivity. can. Among organic tin acids, those with a small number of carbon atoms, such as tin acetate, have poor solubility, and conversely, if the number of carbon atoms is too large, the conductivity of the transparent conductive film tends to deteriorate. Specifically, tin 2-ethylhexanoate and tin caproate are preferred. Furthermore, organic acid salts of organotin compounds having Sn--C bonds also exhibit the same tendency as organic tin acids. Examples of such tin compounds include dimethyltin diacetate and dimethyltin dioctanate. These tin compounds are preferably added in an Sn/(In+Sn) ratio of 5 to 20 wt%, and if the amount is greater or less than this, the conductivity of the transparent conductive film will deteriorate. To obtain a composition for forming a transparent conductive film using the above materials, indium nitrate, dicarboxylic acid, and an organic solvent are completely dissolved by mixing and stirring at room temperature or under heating, and a tin compound is added to this. Prepared by method. Next, when forming a transparent conductive film, in order to apply the composition of the present invention to a substrate, a dipping and pulling method,
Usual coating techniques such as spin coating, spraying, and brush coating can be applied. In addition, the coating film of the composition of the present invention is baked in an oxygen-containing atmosphere such as the atmosphere for a temperature of 200 to
It is preferable to carry out this by irradiating ultraviolet rays for 1 minute to 5 minutes while heated to 400°C, and then holding the temperature at 450 to 700°C for 5 minutes to 1 hour. Next, the present invention will be explained with reference to Examples. Example 1 Indium nitrate and the dicarboxylic acids shown in Table 1 (a) to (d) were combined in equimolar amounts and dissolved in a 9:1 mixture of ethyl alcohol and ethylene glycol, and (e) to (f) were added to the mixture. By adding the tin compounds shown in Table 1,
Compositions No. 1 to No. 7 were prepared. These compositions were applied to a thoroughly cleaned quartz glass substrate using a dipping and pulling method (pulling speed: 20
cm/min), then heated to approximately 350°C, exposed to ultraviolet light for 5 minutes, and further exposed to 500°C in air.
℃ for 1 hour to create a transparent conductive film. The resulting transparent conductive films all had a film thickness of 500 Å or less and a sheet resistance of 20 KΩ/2. In addition, translucency,
The film strength was also sufficiently satisfactory.

【table】

[Table] Note: ( ) indicates molar ratio Example 2 Using the component material No. 3 in Table 1, compositions were prepared with various blending ratios of each component, and the results were as shown in Example 1. A transparent conductive film was formed in the same manner. Table 2 Nos. 8 to 12 show cases where the blending ratio of citraconic acid to indium nitrate was changed. When citraconic acid is not added, indium nitrate cannot be completely dissolved, and indium nitrate 1
When about 0.5 mol of citraconic acid is added, the lowest sheet resistance value is obtained, and as the blending ratio of citraconic acid is further increased, the sheet resistance value becomes higher. Table 2 No. 13 to No. 17 are cases where the amount of tin 2-ethylhexanoate added was changed. Sn/(In＋
With Sn), the lowest sheet resistance value is obtained at 10 to 15 wt%, but a practical level sheet resistance value can be obtained even at 5 to 20 wt%. When the amount is more than or less than 5 to 20 wt%, the sheet resistance value increases. Table 2 No. 18 to No. 19 are cases where the amount of solvent was changed. The thickness of the transparent conductive film obtained changes depending on the amount of solvent, and the sheet resistance is 0.5KΩ/0 at a film thickness of 800Å.
It is possible to form the transparent conductive film (B) in one application.

【table】

[Table] Note) No. 8 is insoluble in indium nitrate. The values in parentheses in the table are molar ratio Example 3. In this example, compositions were prepared by changing the type of solvent in Example 2, and the compositions of Examples 1 and 2 were A transparent conductive film was formed in the same manner. The results are shown in Table 3. Solvents with a boiling point of 30-100℃, acetone, methyl acetate,
The mixed system of diethyl ether, ethyl alcohol and ethylene glycol is almost the same as the mixed system of ethyl alcohol and ethylene glycol. On the other hand, when ethyl cellosolve or ethyl carbitol is used instead of ethylene glycol as a solvent with a boiling point of 130° to 250°C, and a mixture of this and ethyl alcohol is used, the film becomes cloudy even at a film thickness of 500 Å. A transparent conductive film was obtained that was free of porosity, was uniform, and had a low sheet resistance value. Furthermore, when the amount of ethylene glycol was increased, unevenness in film thickness occurred. However, by decreasing the amount of ethylene glycol and increasing the ratio of indium nitrate to the solvent, it is possible to obtain a transparent conductive film that is uniform, fairly thick, and has no uneven thickness.

[Table] Comparative Examples As comparative examples, monocarboxylic acid was used instead of dicarboxylic acid, no additive was used, stannic chloride was used instead of organic acid tin, and ethyl alcohol alone was used as the solvent. Each composition was prepared for each case, and a transparent conductive film was formed.
The results are shown in Table 4. When no dicarboxylic acid was added and when a monocarboxylic acid was used, the film became cloudy. Furthermore, when stannic chloride is used, the sheet resistance value of the resulting transparent conductive film is high. Furthermore, in the case of using ethyl alcohol alone, the amount of ethyl alcohol relative to indium nitrate must be reduced in order to obtain a film thickness of approximately 500 Å under the same coating conditions. In this way, when the film thickness is reduced to approximately 500 Å, the film becomes cloudy.

[Table] By using the composition of the present invention, a transparent conductive film that has high conductivity after one application, has excellent light transmittance, and has a film strength comparable to that of a vapor-deposited film can be baked in air. You can get it at Furthermore, by applying the composition of the present invention to a dip-and-pull coating method, it is possible to apply it to large-area substrates, and it is inexpensive.
Transparent conductive films with excellent properties can be produced in large quantities, which is extremely advantageous industrially.

Claims (1)

[Claims] 1 97 to 80 wt% of at least one organic solvent among monohydric alcohols, esters, ketones, and ethers with a boiling point of 30°C to 100°C, and cellosolves, carbitols, and glycols with a boiling point of 130°C to 250°C At least one selected organic solvent 3~
100 parts by weight of a mixture of 20 wt%, 2 to 50 parts by weight of indium nitrate, dicarboxylic acid with a molar ratio of 0.3 to 2.0 moles to indium nitrate, tin 2-ethylhexanoate, tin cabroate, dimethyltin diacetate, at least one tin compound selected from dimethyltin dioctanate;
A composition for forming a transparent conductive film, characterized by having a Sn/(In+Sn) ratio of 5 to 20 wt%.