JPS6310090B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming a silicon oxide film on the surface of an inorganic substrate. Conventionally, methods for forming a silicon oxide film on the surface of an inorganic substrate have been based on sputtering or vapor phase growth. However, all of these devices require complicated devices, and it is difficult to form a uniform coating over a wide area. In recent years, in order to improve these drawbacks, a method has been proposed in which, for example, a reaction product of an alkoxysilane or a halogenated silane, a lower carboxylic acid, and an alcohol is applied to a substrate and then heat treated to form a silicon oxide film. (Unexamined Japanese Patent Publication 1973)
-103533 Publication, 1982-104521 Publication, 1982 Publication
Publication No.-34276, Publication No. 55-34258). but,
The silicon oxide coating formed using the coating liquid obtained by the above method does not have a complete coating without pinholes, cracks, etc., and is not necessarily completely satisfactory. The cause of this is not certain, but
This is thought to occur because alkoxy groups remain in hydroxysilanes produced from alkoxysilanes or halogenated silanes, and these alkoxy groups decompose and scatter during heat treatment. When producing a coating liquid by the above method, there is also the disadvantage that the reaction requires an extremely long time (about 24 hours or more) and the productivity is extremely low. A method has also been proposed in which a coating solution is prepared by hydrolyzing a product of 8 moles or less of water per mole of alkoxysilane. (Japanese Unexamined Patent Publication No. 51-93922) However, there is a drawback that the silicon oxide film formed using the coating liquid obtained by this method does not become a complete film. This means that the amount of water used for hydrolysis is water/alkoxysilane <8 (molar ratio)
It is thought that this is because hydrolysis does not proceed completely under these conditions, and as a result, alkoxy groups remain in the hydroxysilane produced, and these alkoxy groups are decomposed and scattered during heat treatment. Furthermore, since all of the above methods use a product that has not been sufficiently hydrolyzed as a coating solution, repellency and unevenness occur on the surface of the inorganic substrate, making it impossible to obtain a homogeneous film, and the coating solution is exposed to moisture during storage. It has the disadvantage that it decomposes. As a result of intensive research to overcome the above-mentioned drawbacks, the inventors of the present invention have developed an aqueous solution of silicic acid by acidifying a silicon compound as a raw material, and then removing and separating water from the aqueous solution. It was discovered that a polar organic solvent solution is suitable as a coating liquid, and the present invention was completed. That is, the present invention provides a method in which a coating solution containing a silicon compound is applied to the surface of an inorganic substrate, and then a silicon oxide film is formed by heat treatment, in which one or two selected from silicic acid and silicates are used as the coating solution. Use a coating solution in which the above silicon compound is acidified to form water-soluble silicic acid, and then the silicic acid aqueous solution is dehydrated to form a polar organic solvent solution with a water/silicon molar ratio of 5 or less. The present invention provides a method for forming a silicon oxide film on the surface of an inorganic substrate, which is characterized by high productivity, high stability, and can provide an excellent coating film. When forming a film using the coating solution of the present invention, since the raw material itself has no organic moieties, there are no problems caused by residual alkoxy groups that occur when alkoxysilane is used as a raw material. There is no need to consider this, and in addition, a uniform coating with high surface hardness without pinholes or cracks can be obtained.In addition, the time required to produce the coating solution is short, and the resulting coating solution is easy to use. has the advantage of being stable even when stored for long periods of time. The silicon compounds used in carrying out the method of the invention are silicic acid and/or silicates. Examples of these compounds include silicic acid, silica sol,
Lithium silicate, potassium silicate, sodium silicate, ammonium silicate, calcium silicate,
Magnesium silicate, JIS No. 1, No. 2, No. 3, No. 4 water glass, lithium water glass, potassium water glass, synthetic silicates such as zeolite X, zeolite Y, zeolite A, zeolite L, olivine, olivine Mention may be made of natural silicate minerals such as , mica, talc, wollastonite, albite, serpentine, and asbestos. These may be used alone or in combination of two or more. In carrying out the method of the present invention, the method of acidifying the silicon compound includes a method of treating the silicon compound with a monovalent or polyvalent acid that is soluble in water and capable of neutralizing the base of the silicate; A method such as treatment with a cation exchange resin can be adopted. Such acids include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, sulfonic acid, chlorosulfonic acid, bromic acid, acetic acid, chloroacetic acid, formic acid, oxalic acid, propionic acid, acrylic acid, methacrylic acid, acetoacetic acid, and citric acid. , gluconic acid, glycolic acid, caprylic acid, caproic acid and the like. The amount of acid can be appropriately selected depending on the type of raw material silicon compound, the strength of the acid used, the acid treatment conditions, etc., but in general, it is preferably in the range of 1 equivalent to 100 equivalents per 1 mole of silicon. used. When the raw material silicon compound is water-insoluble, it is preferable to use a relatively large amount of acid in order to increase the yield of the product. This acidification treatment is generally carried out at a temperature in the range of 0°C to 100°C, and although the required time varies depending on the type of raw material, it can usually be carried out in a range of 10 minutes to 5 hours. The acidification treatment is carried out in an acidic region with a pH of 4 or lower, because if the pH becomes 4 or higher during the treatment, a silicic acid gel will be generated, making it impossible to obtain the desired coating solution in the method of the present invention. In carrying out the method of the present invention, the acidified solution is then subjected to a dehydration treatment to form a coating solution having a water/silicon molar ratio of 5 or less, preferably 3 or less. If fine precipitates are present in the liquid during dehydration, it is preferable to separate them by filtration or the like in advance. As a dehydration treatment method, generally a method of adding an inorganic electrolyte and salting out is preferably adopted, but
Of course, other methods such as adding a dehydrating agent can also be used. In order to perform salting out, a polar organic solvent may be added to the acidified solution, an inorganic electrolyte may be added thereto, the mixture may be mixed, and then left to stand. The amount of polar solvent and the amount of inorganic electrolyte during salting out may be such that the silicic acid produced is sufficiently recovered and the water/silicon molar ratio in the coating solution after dehydration is 5 or less. However, in general, 5 parts by weight of polar organic solvent are used per 1 part by weight of silicon oxide.
~100 parts by weight and 1 to 20 parts by weight of inorganic electrolyte are used. If the water/silicon molar ratio in the coating solution is greater than 5, it is not preferable to form a film free of pinholes and cracks, and the film becomes uneven. Examples of the polar organic solvent include methanol, ethanol, propanol, butanol, tetrahydrofuran, dioxane, acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, methyl acetate, and ethyl acetate.
In particular, methanol and tetrahydrofuran are preferably used. The inorganic electrolyte may be one commonly used as a salting-out agent, such as sodium chloride, potassium chloride, ammonium chloride, calcium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, magnesium sulfate, and the like. The salting-out operation as a dehydration treatment usually only needs to be carried out once, but in order to increase the extraction rate of the silicic acid component, the extraction may be repeated several times. As a dehydrating agent,
Known solid dehydrating agents such as silica gel, activated alumina, molecular sieves, dehydrated sodium sulfate, and dehydrated copper sulfate can be used. The coating liquid thus obtained can be used as a coating liquid as it is, or after diluting with the above-mentioned organic solvent as desired and further adding suitable additives.
The concentration of silicic acid in the coating solution is expressed as silicon oxide.
Preferably, it is used in a range of 0.1 to 20 weight percent. The diluting solvent for the coating solution may be the same as the extraction solvent or may be different. The coating solution further contains polyhydric alcohols such as ethylene glycol, propylene glycol, triethylene glycol, and glycerin, as well as acetylacetone, ethyl acetoacetate,
chelating compounds such as diacetone alcohol and ethylene glycol monoethyl ether,
Add oxygen-containing high boiling point solvents such as diethylene glycol monoethyl ether and diethylene glycol diethyl ether, polymeric film forming agents such as polyvinyl butyral, polyvinyl pyrrolidone, and polyvinyl acetate, and other metal salts that are soluble in this coating solution. You can also do that. The concentration of these additive components varies depending on the usage conditions of the coating solution and the conditions of the silicon oxide film to be formed, but the oxygen-containing high-boiling solvent is in an amount of 30% by weight or less in the coating solution, and the polymeric film-forming agent is in an amount of 10% by weight or less.
It is preferable to use the amount within a weight percent range. Examples of inorganic substrates to which the coating solution according to the present invention can be applied include well-known inorganic solid surfaces such as glass, ceramics, minerals, and single crystals. In particular, it can be suitably used for glass surfaces. Before applying the coating solution of the present invention to the surface of these substrates, it is preferable to clean the substrate surface by washing or the like in advance in order to form a more complete coating. In order to apply the coating liquid to the surface of the substrate, known methods such as a spray method, a dip-and-lift method, a spin-on method, and a roll coater method can be used. At this time, it is also effective to take measures such as appropriately adjusting the moisture content of the coating atmosphere and the concentration of solvent vapor as necessary in order to obtain uniformity of the coating film. A silicon oxide film is formed by heat-treating the coated inorganic substrate at a temperature of 150°C or higher. With the coating solution according to the present invention, a transparent silicon oxide film having a thickness of 0.02 to 5 μm can be easily obtained as a homogeneous film without pinholes or cracks. The silicon oxide film produced by the method of the present invention chemically and mechanically protects the glass surface, prevents impurity diffusion from semiconductors and glass, controls electrical conductivity through electrical insulation or impurity doping, and forms a smooth surface without polishing. It can be effectively used when obtaining Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. Example 1 In a 500 ml flask with a stirrer, 0.64 mol/
Pour 200ml of sulfuric acid and add 100ml of 0.8mol/
No. 2 water glass was added dropwise over 10 minutes to obtain an aqueous silicic acid solution with a water/silicon molar ratio of 80. Next, 200 ml of tetrahydrofuran and a salting-out agent of the type and amount shown in Table 1 were added, stirred vigorously and left to stand, and then the tetrahydrofuran layer containing silicic acid was extracted and separated. The water/silicon molar ratios in this liquid were as shown in Table 1. Next, the silicic acid content in this liquid was diluted with tetrahydrofuran to a concentration of 3% by weight as silicon oxide. A glass plate was immersed in this liquid as a coating liquid, and after being pulled up at a constant speed, it was fired at 450°C for 30 minutes.
A silicon oxide film with a thickness of 1000 Å was formed. The resulting coating film was mixed with 15 g of 55% HF and 10 _g of 60% HNO.
The sample was treated with an etching solution containing 600 g of water and 600 g of water, and the etching rate was measured. Table 1 shows the results of observing the surface condition with the naked eye and with an optical microscope.

[Table] Example 2 Add 20 g of dry silica gel to 100 g of the coating solution obtained in Comparative Example 1, leave it for a day and night, filter it to obtain a coating solution, and apply the same method as in Example 1 (water/silicon molar ratio 3). A silicon oxide film was formed. The surface condition of this silicon oxide film was good, and the etching rate was 600 Å/min. Example 3 Amberlite IR-120B H-type cation exchange resin was packed in a column with a diameter of 25 mmφ and a length of 500 mm with a bottom cap, and 0.8 mol/No. 2 water glass was passed through the column for acidification treatment. 100 ml of this acidified solution (water/silicon molar ratio 24) was mixed with 200 ml of tetrahydrofuran. This solution was transferred to a separatory funnel, 80 g of sodium chloride was added thereto, and after vigorous shaking and standing, the tetrahydrofuran layer containing silicic acid was separated. The water/silicon molar ratio in this liquid is
It was less than 0.5. Next, the silicic acid content in this liquid was adjusted to 3% by weight as silicon oxide with tetrahydrofuran, and a coating liquid was prepared. The etching rate of a silicon oxide film formed using this coating solution in the same manner as in Example 1 was 450 Å/min, and the surface condition was good. For comparison, the ion exchange flowing liquid of this example was
The procedure was exactly as in this example except that 100 ml was introduced into 200 ml of tetrahydrofuran and no sodium chloride was added. The silicon oxide coating using this coating liquid causes cracks around the glass substrate.
The etching rate was 1100 Å/min. Example 4 500ml of concentrated hydrochloric acid in a 1000ml flask with a stirrer,
20g of powder under 200 mesh of A4 type synthetic zeolite
and stirred at room temperature for 2 hours. After adjusting the pH to 1 to 1.5 with aqueous ammonia, the reaction residue was over-separated, and 200 ml of tetrahydrofuran and 120 g of sodium chloride were added to the liquid (water/silicon molar ratio 125), stirred vigorously, and after standing still, the silicic acid The tetrahydrofuran layer containing was separated. The water/silicic acid molar ratio in this liquid was 2. After adjusting the silicic acid content in this solution to 3% by weight as silicon oxide, a silicon oxide film was formed in the same manner as in Example 1. The surface condition was good and the etching rate was 600%.
The temperature was Å/min. Furthermore, for comparison, a silicon oxide film formed in the same manner as in this example except that no salt was added during extraction had significant cracks in the periphery, and the etching rate was 1100 Å/min. It was hot.

Claims (1)

[Claims] 1. In a method of applying a coating solution containing a silicon compound to the surface of an inorganic substrate and then heat-treating it to form a silicon oxide film, a type selected from silicic acid and silicates is used as the coating solution. Alternatively, a coating solution is obtained by acidifying two or more silicon compounds to form water-soluble silicic acid, and then dehydrating the silicic acid aqueous solution to form a polar organic solvent solution with a water/silicon molar ratio of 5 or less. A method for forming a silicon oxide film on the surface of an inorganic substrate, the method comprising using: 2. The method for forming a silicon oxide film on the surface of an inorganic substrate according to claim 1, characterized in that water glass, sodium silicate, potassium silicate, or potassium water glass is used as the silicon compound. 3. The method for forming a silicon oxide film on the surface of an inorganic substrate according to claim 1, characterized in that hydrochloric acid, sulfuric acid, or nitric acid is used as the acid used in the acidification treatment. 4. Claim 1, characterized in that the dehydration treatment is performed such that the water/silicon molar ratio is 3 or less.
A method for forming a silicon oxide film on the surface of an inorganic substrate as described in 1. 5. The method of forming a silicon oxide film on the surface of an inorganic substrate according to claim 1, characterized in that the dehydration treatment method is a method of salting out using an inorganic electrolyte.