JPH0543647B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a novel conductive material. Transparent conductive films made of conductive materials that have both electrical conductivity and optical transparency are industrial materials whose demand has been rapidly increasing in recent years, along with the remarkable development of electro-optical devices. Among these, transparent conductive films made of tin oxide-based conductive materials are widely used because they have better physical and chemical durability than indium oxide-based materials and are inexpensive. (Prior art) A transparent conductive film made of such a conductive material is usually formed on a substrate by a film forming method such as a vapor phase method, such as a CVD method, a vacuum evaporation method, a reactive ion plating method, or a sputtering method. It is coated with a film and put into practical use. However, all of these methods not only have the drawbacks of complicated equipment and slow film formation speed, but also have the problem of forming a film on a small area and not being able to obtain a film with a large area. . On the other hand, the so-called coating method, in which a film is formed by coating a substrate with a liquid raw material, has the advantage that a large-area thin film can be obtained through a relatively simple process, and is an industrially promising method. This coating method has been widely studied for tin oxide based materials as well, and the thermal decomposition behavior of liquid tin based compounds for a wide variety of uses has been studied. The main ones include aqueous solutions of tin salts of inorganic or organic acids, organic tin compounds that are liquid at room temperature, tin alkoxides, and their hydrolysates, but all of them have drawbacks as conductive materials for use in coatings. However, it has not yet been put into practical use. With such materials, the salt crystals tend to crystallize on the substrate in the drying process after coating the substrate, making it difficult to obtain a uniform film. With other materials, it is difficult to control the film thickness because a dry thin film cannot be obtained, and there are also problems in how to hold the substrate during firing. Although these materials have recently been developed, they have many industrial problems, such as the coating liquid being very unstable and the need for strict moisture control in order to form a uniform and transparent film. (Problems to be Solved by the Invention) In view of these circumstances, the present inventors have conducted extensive research to obtain a conductive material from which an excellent transparent conductive film can be easily obtained, and as a result, the present invention has been developed. This is what I have come to complete. (Means for Solving the Problems) That is, the present invention relates to a conductive material made of an ammonium stannate solution. (Function) The present invention will be explained in more detail below. Characteristics of materials desired not only for use in transparent conductive films but also as coating agents in general are that they have excellent film formability during coating, that a uniform film can be obtained, and that the film thickness can be easily controlled. The present inventors investigated various tin compound aqueous solutions as transparent conductive coating agents, and as a result, they obtained ammonium stannate, which is a novel compound not previously known, and found that it satisfies the above two characteristics. As mentioned above, even if a conventionally known aqueous solution of a tin salt of an inorganic or organic acid is coated on a substrate, crystals of the salt precipitate on the substrate, and a uniform transparent dry film cannot be obtained. Furthermore, even if the drying conditions are specially devised to prevent crystallization from a macroscopic perspective, it is essentially unavoidable that the crystals will precipitate as microcrystals. In this case, the crystals become bulky and a microscopically uniform film cannot be obtained. It is clear that these non-uniformities have a negative impact on both electrical conductivity and optical transparency. On the other hand, sodium stannate (Na ₂ SnO ₃ ) and potassium stannate (K ₂ SnO ₃ ) are water-soluble stannate salts.
Alkali metal salts such as the following are conventionally known. However, as a matter of course, even if these are dried and fired, only a composite oxide of alkali metal and tin can be obtained, but not tin oxide having electrical conductivity. In contrast, according to the coating using ammonium stannate solution newly discovered by the present inventors,
The dried film is uniform both macroscopically and microscopically, and the fired product is obtained as a film with a uniform tin oxide composition. The composition of the ammonium stannate of the present invention is the molar ratio of ammonia to tin (NH ₃ /SnO ₂ molar ratio)
is 0.2 or more. In this case, if this molar ratio is less than 0.2, the solubility in water will be low, making it unsuitable as a coating liquid. Further, although there is no particular upper limit, even if a material containing too much ammonia is used, there will be no change in the properties as a conductive material, and it is not economically preferable. The minimum compositional limitations that the ammonium stannate of the present invention should have are only those mentioned above, but the present invention is not limited to only tin-based compounds. That is, generally, antimony or the like is often added for the purpose of improving the electrical conductivity of tin oxide, but in the case of the present invention, ammonium stannate containing antimony, which exhibits better electrical conductivity, is added by the method described below. can be manufactured. Further, the conductive material of the present invention can also be used in combination with additives for improving the physical properties of the transparent conductive film, particularly its strength. Examples include silicate-based materials, silica sol, low-melting glass compositions, and organic silicates that develop bonding strength upon firing. Furthermore, in order to improve the wettability with the substrate during coating, a suitable organic solvent such as alcohol, cellosolve, or a compatible surfactant may be added to the conductive material of the present invention to improve workability. It is also possible to make it easier. Furthermore, in order to improve the adhesion with organic films, plastics, and fibers, a resin with the same composition as the object to be coated, a resin with reactivity, a plastic additive, etc. is added, and the coating is applied as an antistatic paint to the object to be coated. Then, a product with excellent adhesion can be obtained. Furthermore, the conductive material of the present invention may be added to raw materials for films, plastics, fibers, and processed and molded to produce films, plastics, fibers, and the like. The components of these organic films, plastics, and fibers include polyethylene, polyester,
Polystyrene, polypropylene, vinylidene chloride, vinyl acetate, polyamide, polyacrylate, polycarbonate, butadiene resin, polyacetal resin, methacrylic resin, furan resin, phenolic resin, melamine resin, urea resin, polyurethane resin, ketone resin, epoxy resin, xylene resin, Examples include polyvinyl alcohol, cellophane, cellulose acetate, and various monomers used in the production of these polymers, but the components are not limited to these. The conductive material of the present invention is completely unknown in the past, and creates new uses in the field of application of transparent conductive materials. The characteristics of the conductive material of the present invention are listed below. First, as mentioned above, a uniform coating film can be obtained by the coating method. Furthermore, the film thickness can be freely controlled by changing the concentration of the coating liquid. Second, it does not generate corrosive gas during drying or firing. The conductive material of the present invention consists essentially of tin, ammonia, and water as a solvent. Therefore, the gases generated in the process of drying and calcining this to form tin oxide are only ammonia and water, and no countermeasures are required. In contrast, when stannic chloride, for example, is used as the inorganic tin salt aqueous solution, a large amount of harmful and corrosive hydrogen chloride gas is generated during firing, which is unfavorable in terms of furnace selection and working environment. For these reasons, the conductive material of the present invention is industrially useful. Thirdly, it has excellent stability. Tin alkoxide is extremely unstable and has a fatal defect of poor stability over time. The conductive material of the present invention has not only high purity but also good stability, and can be said to be of higher quality. The conductive material of the present invention having the above-mentioned excellent characteristics is not only very useful as a transparent conductive film material, but also can be used as a conductivity imparting agent by coating various fillers, and can also be used as an electroconductor for gas sensor materials, etc. It is also useful for application in the ceramics field, and is a novel substance that can be applied to many other uses. The ammonium stannate solution of the present invention can be produced by the following method. First of all, a gel is produced by reacting a tin compound with an alkali metal bicarbonate or an ammonium bicarbonate salt. Examples of the tin compound include stannic chloride and stannic sulfate, and examples of the alkali metal bicarbonate include sodium bicarbonate and potassium bicarbonate. The proportion used is preferably such that the pH of the reaction solution at the end of the gel formation reaction is 6. If the amount of the alkali metal bicarbonate or ammonium bicarbonate used is smaller than this, the tin will not be completely gelled and the yield will be poor, which is also undesirable for economic reasons. The gel thus produced is then washed to remove impurities. Regarding the amount of residual impurities, it is preferable to have a small amount from the viewpoint of production and usage of the ammonium stannate solution. The cleaning means is not particularly limited, and any commonly used methods such as water filtration and repulp centrifugation can be used. Alternatively, a method of removing impurities by contacting with a suitable ion exchange resin or the like may also be adopted. The ammonium stannate solution of the present invention can be obtained by adding and dissolving ammonia water and, if necessary, water to the washed gel. Here, the amount of ammonia used is such that the composition of the product is a molar ratio of ammonia to tin of 0.2 or more. Further, the concentration and amount of ammonia water may be appropriately used to obtain a desired concentration. Furthermore, in order to improve the solubility of the gel, heating may be performed as necessary. As mentioned above, when the conductivity is improved by incorporating antimony into the material of the present invention, the following method may be used for manufacturing. First, in the step of gelling a tin compound, antimony is simultaneously gelled to produce a gel containing tin and antimony. Next, this is dissolved in aqueous ammonia. In this case, a soluble antimony compound, such as antimony trichloride, is added to an aqueous solution of a tin compound,
A mixed solution of tin and antimony is prepared and used as a starting material. The steps after gelation may be the same as for ammonium stannate solution. Alternatively, antimony trioxide may be added to the washed gel and then dissolved in aqueous ammonia. In this case, it is desirable that the antimony trioxide used be active and highly reactive. Also, its hydrate called antimonic acid can be used. Although some undissolved substances may remain after the dissolution step, they can be easily removed by means such as filtration. (Example) The present invention will be further explained below with reference to Examples, but the present invention is not limited thereto. Moreover, all percentages indicate weight % unless otherwise specified. Example 1 Ammonium bicarbonate aqueous solution (NH ₃ 2.9%) 1000
300 parts of an aqueous solution of stannic chloride (SnO ₂ 16.5%) was gradually added to the mixture while stirring. After filtering the generated gel, water injection filtration and cleaning were performed until no chlorine was found in the gel. As a result, a gel containing 36.5% SnO ₂ and 0.53% NH ₃ was obtained. Next, ammonium stannate aqueous solutions of various compositions were prepared using this gel, and their performance as conductive materials was investigated. The method was to add and mix aqueous ammonia (NH ₃ 2.0%) and water in the amounts shown in Table 1 to 100 parts of gel, and stir to dissolve the gel. As a result, an ammonium stannate aqueous solution having a SnO ₂ concentration of 8% and a molar ratio of ammonia and tin of 1.50, 0.50, and 0.20, respectively, was obtained. Further, as a comparative example, a composition having the same molar ratio of 0.15 was obtained by the same operation as described above, except that the amounts of ammonia water and water added were changed to the amounts shown in Table 1. The properties of these products are shown in Table 1. The following tests were conducted using these compositions and a sodium stannate aqueous solution containing 8% SnO ₂ for comparison. These aqueous solutions were spin-coated onto a 76×26 mm slide glass at a rotation speed of 1000 rpm, dried at 100° C., and the surface condition was observed. Furthermore, these were heat-treated at 600° C. for 30 minutes, and the surface resistance and light transmittance of the obtained transparent conductive coated glass were measured. The results are shown in Table 2.

【table】

[Table] Results As is clear from Tables 1 and 2, the ammonium stannate of the present invention in which the molar ratio of ammonia to tin was 0.2 or more was a uniform, transparent solution. Moreover, although the coating treatment of the present invention yields a good transparent conductive glass, the molar ratio is
When it was 0.15, the liquid was non-uniform and therefore both surface resistance and light transmittance were poor. Furthermore, when sodium tin oxide was used in place of the product of the present invention, the coating film did not exhibit electrical conductivity. Example 2 In order to improve conductivity, antimony was added to the conductive material of the present invention, and a test was conducted in the same manner as in Example 1. To 1000 parts of stannic chloride aqueous solution (SnO ₂ 17.6%),
5.4 parts of antimony trichloride was added and dissolved by heating to 80°C. After cooling, this was gradually added to 3494 parts of an aqueous ammonium bicarbonate solution (NH ₃ 3.0%) while stirring to form a gel. The generated gel was filtered, about 1000 parts of water was added thereto, the pulp was mixed, and solid-liquid separation was performed using a centrifuge. This operation was repeated until no chlorine was observed in the gel, and as a result, SnO ₂ 32.1%, Sb 0.52
%, a gel containing 0.38% _NH3 was obtained. Next, 25 parts of ammonia water (NH ₃ 10.0%) and 196 parts of water were added and mixed to 100 parts of the gel, and the mixture was heated at 50° C. with stirring to dissolve the gel. As a result, an aqueous ammonium stannate solution containing antimony with 10% SnO ₂ , 0.90% NH ₃ , a molar ratio of ammonia to tin of 0.8, and 0.16% Sb was obtained. This was coated on glass in the same manner as in Example 1 to obtain transparent conductive coated glass. As a result of measuring the surface resistance and light transmittance of this glass, the surface resistance was 4.8kΩ/□, and the light transmittance was
It was 92%. Example 3 To 100 parts of the antimony-containing ammonium stannate aqueous solution obtained in Example 2, 20 parts of a 10% acrylic resin emulsion was added to prepare an antistatic paint. This paint was roll coated onto an acrylic plate and dried to obtain an acrylic plate with a coating thickness of 0.4 μm and subjected to antistatic treatment. As a result of measuring the surface resistance of this coating surface, the resistance value was 5.2×10 ⁹ Ω/□.

Claims (1)

[Claims] 1 A conductive material made of ammonium stannate solution.