JPH0240696B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel coating solution for forming a silica film, a method for producing the same, and a method for forming a silica film on a substrate using the same. The method for forming a silica film on a substrate is as follows:
Vapor phase growth method and coating method are known. Since the vapor phase growth method requires special equipment, has limitations on the size of the substrate, and is difficult to mass-produce, the coating method has attracted attention in recent years. The silica film formed by the coating method is required to be uniform and free from pinholes and cracks. Furthermore, due to the increasing size of substrates and mass production due to recent coating methods, safety issues have arisen.
From a hygienic standpoint, there is a demand for coating liquids that have less solvent volatilization during work, are less flammable, and are less toxic. In order to meet the former requirement, various coating solutions for forming a silica film have been proposed. For example, a reaction product obtained by reacting an alkoxysilane, a lower carboxylic acid or an acid anhydride, and a lower alcohol in the presence of an organic acid reaction promoter has been proposed (JP-A-55-34258; -24831, 55-34276). However, these all contain large amounts of low-boiling esters, such as ethyl acetate, and lower alcohols, such as ethanol, and are far from meeting the latter requirement. An object of the present invention is to provide a hydroxysilane condensate solution that provides a uniform silica coating free of pinholes and cracks and has low volatility, and a method for producing the same. The first aspect of the present invention has the general formula R ¹ (OR ² ) _o OH
(Here, R ¹ is an alkyl group having 1 to 4 carbon atoms or an acyl group having 2 to 4 carbon atoms, R ² is an alkylene group having 2 to 4 carbon atoms, and when there are two or more in the same molecule (n≧2 ) They may be the same or different, and n is an integer from 1 to 4. A coating liquid for forming a silica film with a boiling point of 100~
The gist is that the temperature is 500℃. The hydroxysilane condensate is obtained by reacting a silane derivative described below such as an alkoxysilane in the presence of an alcohol and water or a lower carboxylic acid in an amount of about 2 times or more moles or more relative to the alkoxysilane, and an acid as a reaction accelerator. It is a condensation compound that can be obtained dissolved in a suitable organic solvent such as ethanol, and can form a silica coating by applying the solution to a surface of glass, metal, plastic, etc. and heating it. degree or molecular weight. Ethanol or methanol has been well known as the above-mentioned suitable organic solvent, but its types are limited, and ethyl acetate, ethyl ether, and hydrocarbons, which are often used as organic solvents, cannot be used alone. It's inappropriate. As mentioned above, ethanol and methanol have a low boiling point and are highly volatile, so they pose the above-mentioned problems. The present invention uses the main solvent in place of part or all of ethanol etc.,
This not only solves the problems of the prior art described above, but also provides the naturally required good stability of the hydroxysilane condensate in solution. In order to make the boiling point of the solution of the present invention higher than 100°C and to give it good stability, the quantitative ratio in which the main solvent should be present in the solvent in the solution depends on the objective. It generally depends on the boiling point or flash point of the solution of the present invention, the boiling point and molecular weight of the main solvent used, the boiling point and molecular weight of the coexisting low-boiling solvent, the affinity with the main solvent based on the molecular weight and its chemical structure, the amount of water used, etc. Although it is not possible to say, it is about 20% by weight or more, preferably about 30% by weight or more, and more preferably 50% by weight or more.
It is preferable that it is present in an amount of % by weight or more. Examples of the main solvent include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether,
Examples include propylene glycol monomethyl ether, propylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monoacetate, or a mixture of two or more thereof. All of these have boiling points higher than 100°C. The main solvent is the hydroxysilane condensate,
It has the property of uniformly dissolving the silane derivatives mentioned below, their partial condensates, and water, which are raw materials. On the other hand, there are solvents (hereinafter referred to as sub-solvents) which have relatively high boiling points, but lack the ability to dissolve them when used alone, and are therefore preferably used in combination with the main solvent. As the subsolvent, monohydric alcohols with 4 to 10 carbon atoms, polyhydric alcohols with 2 to 6 carbon atoms (including cases where an ether bond or -COO- bond exists in the carbon chain), general formula R ¹ O (R ² O) _o R ¹ (here
R ¹ , R ² and n have the same meaning as stated above,
Multiple R ^1s present in the same molecule may be different from each other. ), fatty acids having 4 to 10 carbon atoms, acetoacetic acid, alkyl (1 to 4 carbon atoms) esters of acetoacetic acid, acetylacetone, and the like can be used. The solvent component in the solution of the present invention may contain water or a low-boiling organic solvent in addition to the main solvent and subsolvent. These often come into the solution according to the invention during the production of the hydroxysilane condensate. In addition, some of the above-mentioned low-boiling point organic solvents, such as monohydric alcohols having 1 to 3 carbon atoms, may be used within a range where the boiling point of the solution can be maintained at 100°C or higher in order to stabilize the solution, which is the object of the present invention. , may be added to the desired solution. Among the low boiling point organic solvents, those having a relatively high boiling point can be present in a relatively large amount in the solution of the present invention compared to those having a low boiling point. Examples of the low-boiling organic solvent include ethanol, methanol, methyl acetate, ethyl acetate, ethyl ether, isopropyl alcohol, acetone, and the like. The amount of these substances present in the solvent in the solution of the present invention is desirably 40 mol% or less, preferably 30 mol% or less. The amount of water present in the solvent in the solution of the present invention is preferably 50% by weight or less, preferably 20% by weight or less. Too much water will make the solution unstable,
This is because gelation may occur during storage. The concentration of the hydroxysilane condensate in the solution of the present invention is preferably 1 to 20% by weight. 1% by weight
If it is smaller, when this solution is used as a coating liquid, the thickness of the silica film obtained by one application will be thin, and there is a possibility that repeated application may be necessary depending on the application. On the other hand, if it is more than 20% by weight, the solution becomes unstable and gelation tends to occur. A second aspect of the present invention is a method for producing the high boiling point solution according to the present invention, which has the general formula R ⁴ rSi
[(OR ² ) _o OR ¹ ] _s [OR ³ ] _u (here R ¹ is carbon number 1~
4 alkyl group or acyl group having 2 to 4 carbon atoms, R ² is an alkylene group having 2 to 4 carbon atoms, R ³ and
R ⁴ is an alkyl group having 1 to 8 carbon atoms, an alkenyl group,
Aryl group or alkyl group, R ¹ , R ²
and ^R3 , when there are two or more of each in the same molecule, they may be the same or different, n is an integer from 1 to 4, r is 0 or 1, s and u are An integer from 0 to 4, r+s+u=
It is 4. ) or a partial condensate thereof in an organic solvent containing or not containing a main solvent in an amount of 0.8 to 16 times the weight of the silane derivative or a partial condensate thereof, based on the silicon atom of the silane derivative or partial condensate thereof. 2-r/2-(m-1)/m to 90 times the mole of water (where r has the same meaning as above, m is 1 in the case of the silane derivative, and 1 in the case of the partial condensate) This indicates that it is an m-mer.)
and reacting in the presence of an acid as a reaction promoter,
If necessary, the main solvent is added during or after the reaction, or the low-boiling components are evaporated or added, and the main solvent is contained in the solvent component of the hydroxysilane condensate solution in an amount of 20% by weight or more. The main solvent is used so that the boiling point of the solvent component is 100 to 500°C. In the method, u of the silane derivative or its partial condensate is as small as possible (preferably less than 3, more preferably less than 2) from the viewpoint of increasing the boiling point of the hydroxysilane condensate solution as the reaction product liquid as much as possible. , more preferably 1
less than, most preferably zero. ), n should be as large as possible. On the other hand, from the viewpoint of increasing the reaction rate, the molecular weights of R ⁴ , [(OR ² ) _o OR ¹ ], and OR ³ should be as small as possible;
The number of carbon atoms in R ¹ to ^{R 4} is small, n is small, and when the molecular weight of R ³ is smaller than that of [(OR ² ) _o OR ¹ ], it is better for u to be larger. R ³ (when present) is an alcohol R ³ OH liberated by hydrolysis of the silane derivative or partial condensate thereof;
It is a good solvent for the silane derivative or its partial condensate, the reaction product hydroxysilane condensate, and water, and also for improving the stability of the coating solution for forming a silica film obtained by the method of the present invention. Those having 1 to 3 carbon atoms are preferred. The partial condensate can be obtained by reacting the silane derivative with a very small amount of water and an acid as a reaction accelerator. It is sold under the trademark ``Ethyl Silicate 40''. During and after the reaction, the organic solvent used in the method of the present invention is capable of removing the silane derivative, its partial condensate, the hydroxysilane condensate produced by these reactions, and the water present together with them during and after the reaction. Uniformly dissolves. Examples include the main solvent, a mixture of the main solvent and the subsolvent, a lower monohydric alcohol having 1 to 3 carbon atoms,
and mixtures thereof, but it is not excluded that these may be mixed with a small amount of other organic solvent as long as the above-mentioned properties are not lost. If a relatively large amount of a low boiling point organic solvent such as ethanol or methanol is used in the method of the present invention, the boiling point of the reaction product liquid may become lower than 100°C. Afterwards, it is necessary to raise the boiling point of the reaction product liquid to 100° C. or higher by volatilizing them or adding the main solvent or subsolvent. Since the operation of volatilization removal is troublesome, from the viewpoint of avoiding such an operation as much as possible, the organic solvent used is one whose main component is a main solvent or a mixture of a main solvent and a subsolvent. is preferred. The amount of the organic solvent used in the method of the present invention is 0.8 based on the silane derivative or partial condensate thereof.
~16 times by weight, preferably 0.95 to 12 times by weight.
If it is less than 0.8 times by weight, as the reaction progresses and the concentration of hydroxysilane or its condensate in the reaction mixture increases, the viscosity of the reaction mixture will gradually increase, and there is a risk that gelation will eventually occur. . On the other hand, if the amount is more than 16 times the weight, the concentration of the hydroxysilane condensate obtained by the reaction will be low, and if this is used as a coating solution, the thickness of the coating will be thin, and depending on the application, the desired coating may be difficult to obtain. This is not preferable since it may be necessary to repeat coating several times in order to obtain a sufficient thickness. When the amount of water used in the method of the present invention is less than [2-r/2-(m-1)/m] times the mole of silicon atoms of the silane derivative or partial condensate thereof, Since the degree of hydroxysilane condensation generated in the reaction is difficult to increase, when coated on basic surfaces, it takes a long time at high temperatures to form a film, the desired hardness of the silica film cannot be obtained, and the uniformity of the film surface cannot be obtained. This is not preferable because there are disadvantages such as the absence of For the same reason, the amount of water used is more preferably [3-r/2-(m-1)/m] times or more by mole. On the other hand, if it is larger than 90 times by mole, the above-mentioned organic solvent must also be present in a large amount, and the concentration of the hydroxysilane condensate obtained by the reaction becomes low, so it is used as a coating solution. In this case, the thickness of the coating becomes thin and, depending on the application, it may be necessary to apply the coating several times to obtain the desired thickness, which is not preferable. For the same reason, the amount of water used is more preferably 10 moles or less, still more preferably 6 moles or less, and most preferably 4 moles or less. Examples of the reaction accelerator used in the method of the present invention include inorganic acids, organic acids, acidic ion exchange resins, and solid acidic catalysts in which an inorganic acid is supported on a carrier. Examples of the inorganic acid include hydrochloric acid, phosphoric acid, phosphoric anhydride, and boric acid, and the amount thereof varies depending on the degree of dissociation of the inorganic acid, but is usually used for a mixture of a silane derivative, water, and an organic solvent. , 0.005~
It is preferable to use 1.0% by weight. Examples of the organic acids include acetic acid, propionic acid, benzenesulfonic acid, toluenesulfonic acid, and naphthalenesulfonic acid, and the amount used in this case is preferably in the range of 0.05 to 3% by weight based on the mixed liquid. The acidic ion exchange resins include sulfonic acid-based strong acid cation exchange resins and super strong acid cation exchange resins, such as the product name Diaion -SKIB-.
H, -SK-228-H, Amberlite-IR-
Examples include 120B, -118, -112, -122, -124, -200C, and naphion-H. Note that commercially available acidic ion exchange resins are substituted with H type, but not completely substituted. Therefore, if the substitution to the H type is incomplete, Na ions will be eluted into the reaction solution and mixed as impurities, which will limit its use in the field of electronic materials, where Na ions are a problem. Before use, it is desirable to increase the degree of substitution to H type. When using the acidic ion exchange resin in the present invention by dispersing it in the form of particles while stirring in the reaction mixture, the amount of the acidic ion exchange resin to be used is 5 to 25% by weight of the reaction mixture, which is packed into a column in the form of particles. Or, when the reaction mixture is made to flow between these layers in the form of a multi-layered thin film, it is preferable to use the reaction mixture in an amount of 5% by weight or more up to the upper limit that allows the above-mentioned flow. As the catalyst in which an inorganic acid is supported on the carrier,
Silica, alumina-silica, zirconia, and activated carbon supported with sulfuric acid or phosphoric acid can be used. The amount of the inorganic acid supported is usually preferably about 1 to 10% by weight, and the amount of the supported solid acid catalyst is 5 to 25% by weight based on the reaction mixture.
It is preferable to use it within a range of % by weight. To describe the operation for manufacturing the coating liquid of the present invention, when the reaction accelerator is an organic acid, an acidic ion exchange resin, or a solid acid catalyst, a predetermined amount of a silane derivative, a predetermined amount of an organic solvent, and a predetermined amount of a reaction promoter are used. It is best to mix the mixture with the accelerator and slowly drip water into the mixture while stirring. When the reaction promoter is an inorganic acid, it is preferable to mix and stir a predetermined amount of alkoxysilane and a predetermined amount of an organic solvent, and gradually drop the inorganic acid-containing aqueous solution into the mixture. By dropping water or an aqueous solution containing an inorganic acid, an exothermic reaction occurs, and the silane derivative reacts to produce alcohol and hydroxysilane. The alcohol produced at this time and the alcohol contained in the main solvent added at the beginning of the reaction are effective in making the hydroxysilane exist stably. By continuing the reaction further, condensation of hydroxysilane progresses and the amount of silane derivative decreases. By continuing the reaction until the content of the silane derivative in the reaction solution becomes 1% or less, a reaction product containing a hydroxysilane condensate as a main component can be obtained. In this case, the reaction temperature is suitably from room temperature to the boiling point of the reaction solution, more preferably from room temperature to 100°C or less. The obtained reaction solution can be used as a coating solution after being adjusted to a desired solvent composition and concentration by partially removing or adding an organic solvent as required, and filtered through a 0.2μ filter. At this time, as an example of the solvent added for concentration adjustment, the main solvent or subsolvent described above is preferable. Next, the present invention will be explained in more detail with reference to Examples. In addition, in the following examples, the solid content concentration of the hydroxysilane condensate solution is expressed as the weight percent of the solid content obtained when heated at a predetermined temperature for a predetermined time, based on the initial solution of solid content, and the temperature and heating time are, for example, (200 ℃; 3 hours). Example 1 HCl was added to a mixture of 1 mole of tetraethoxysilane and 470 g of ethyl cellosolve (2.26 times the weight of tetraethoxysilane) while stirring at room temperature.
A reaction accelerator prepared by dissolving 0.075 g in 4 moles of water is added dropwise. At this time, an exothermic reaction occurs and the reaction proceeds, raising the liquid temperature to 46°C. Once the heat generation subsides, heat the liquid to 65℃. As the reaction progresses, tetraethoxysilane disappears and ethanol is produced. When the reaction progress was analyzed by gas chromatography and high performance liquid chromatography, it was confirmed that tetraethoxysilane disappeared after 1 hour at 65°C, and the formation of a hydroxysilane condensate after 2 hours at 65°C. The reaction was further continued at 65°C for a total of 20 hours, and was then terminated. The solid content of the reaction solution at this time was 9.2
It was in weight%. Next, cellosolve acetate was added to the reaction solution obtained as described above, and the solid content concentration (200℃; 3 hours) was adjusted.
The content was adjusted to 8.0% by weight and filtered using a 0.2μ filter to obtain a coating solution for silica coating.
The solvent composition of the coating liquid thus obtained was analyzed by gas chromatography and found to be 24% by weight of ethanol, 76% by weight of ethyl cellosolve and cellosolve acetate.The boiling point of this coating liquid was 110°C, and the flash point was determined by the Tensky-Martens method. (closed) and the temperature was 26℃. Cl
Anion concentration is 60ppm/g, Na ion is <
It was 0.2 ppm/g. The coating solution obtained in this way was applied onto a glass plate using a spinner (rotation speed: 3000 rpm) at 200°C for 30 minutes, and then at 500°C for 30 minutes.
After baking for a minute, a silica film with a thickness of 1150 Å was obtained. When these films were observed using a scanning electron microscope, no cracks or pinholes were observed, and the film surface was smooth and uniform. The physical properties of this film were as follows, and were almost the same as those obtained when a conventionally known alcohol-based coating solution (using methanol or ethanol) was used. Etching rate 450 Å/min (1 mol% HF aqueous solution) Thermal expansion number 8×10 ^-7 /℃ Specific resistance 1×10 ¹⁴ Ω・cm Example 2 1 mol of monoethoxytri(2-ethoxyethoxy)silane and 476 g of butyl cellosolve (alkoxy 1.4 times the weight of silane) at 60°C.
While stirring, add 0.1 as HCl (reaction accelerator).
g dissolved in 4 mol of water is added dropwise. The reaction progresses rapidly, the alkoxysilane disappears,
Ethanol and ethyl cellosolve are produced.
When the reaction progress was analyzed by gas chromatography and high-speed liquid chromatography, the alkoxysilane disappeared after about 1 hour at 60℃, and about 2
After some time, the formation of a hydroxysilane condensate was confirmed. After further heating at 60°C for a total of 8 hours, heating was continued at 80°C for 10 hours to complete the reaction. The solid content concentration of the reaction solution at this time (200℃; 3 hours) is
It was 7.8% by weight. The reaction solution thus obtained was filtered through a 0.2μ filter to obtain a coating solution for silica coating. The solvent composition of this coating liquid was 5.5% by weight of ethanol and 94.5% by weight of butyl cellosolve and ethyl cellosolve, and the boiling point of this coating liquid was 140°C and the flash point was 49°C.
In addition, the Cl anion concentration is 50 ppm/g, and the Na ion concentration is <
It was 0.2 ppm/g. The coating liquid thus obtained was applied onto a glass plate using a spinner (3000 rpm) and baked at 200°C for 30 minutes and then at 500°C for 430 minutes to obtain a film of 1050 Å. When this film was observed using a scanning electron microscope, neither cracks nor pinholes were observed, and the film surface was smooth and uniform. The physical properties of this film were as follows. Etching rate 400 Å/min (1 mol% HF aqueous solution) Thermal expansion number 5×10 ^-7 /℃ Specific resistance 4×10 ¹⁴ Ω・cm Examples 3, 4 Solid content concentration obtained in Example 2 (250℃; 3 hours )
7.8% by weight of the coating solution was diluted with ethyl acetoacetate to a solid content concentration (250°C; 3 hours) of 6.0% by weight and 3.0% by weight.
The boiling points and flash points of each coating solution were measured and found to be as follows.

[Table] After coating these two types of coating liquids on a glass plate using a spinner (3000 rpm), they were heated at 200℃.
After baking at 500°C for 38 minutes and 30 minutes, films with thicknesses of 800 Å and 400 Å were obtained, respectively. When these films were observed with a scanning electron microscope, no cracks or pinholes were observed, and they were smooth and uniform. It was hot on the face. Example 5 1 mole of tetraethoxysilane and carbitol
Add 400ml of ion exchange resin Diaion PK-228LH to 670g (3.22 times the weight of Si (OEt) ₄ ),
Stir slowly. The contents are quickly heated, and when the temperature reaches 85°C, water is injected into the system at a rate of 20g/hr. As water is added, the reaction occurs slowly, reducing tetraethoxysilane and producing ethanol. After injecting 4 mol of water, it was confirmed by gas chromatography that tetraethoxysilane completely disappeared in about 2 hours. The reaction was further continued at 85°C for a total of 24 hours to complete the reaction. The solid content concentration of the reaction solution at this time (250℃; 3 hours) was 5.6% by weight.
It was hot. Filter this liquid with a 0.2μ filter,
It was used as a coating liquid for silica coating. The solvent composition of the coating liquid thus obtained was analyzed by gas chromatography and found to be 21.5% by weight of EtOH (ethanol) and 78.5% by weight of carbitol, and the boiling point of this coating liquid was 126°C and the flash point was 28°C. In addition, the impurity concentration is extremely low due to the use of ion exchange resin, with Cl ^- concentration <0.1ppm and Na ⁺
The concentration was <0.2 ppm. This coating solution was applied onto a glass plate in the same manner as in Example 1, and the resulting silica film was baked and was free of cracks and pinholes, and was a uniform film. Example 6 Ethylsilicate-40 (trademark for a solution of tetra- to pentamer partial condensate of tetraethoxysilane)
HCl 0.15g in 140g and Carbitol 489g
-Add as an ethanol solution and stir gently. 54 g of water is poured into this solution over 2 hours at room temperature. The liquid temperature rises to 40℃. When the heat generation subsides, heat the reaction solution to 60°C to carry out the reaction. The progress of the reaction is monitored by gas chromatography and is terminated after 24 hours. Thereafter, the by-produced EtOH was removed under reduced pressure. The solid content of the reaction solution after EtOH removal is
Butyl cellosolve was added to this at 8.9% by weight,
The solid content was adjusted to 8.0% by weight and filtered through a 0.2μ filter to obtain a coating liquid. The boiling point of the coating liquid thus obtained is 175℃, and the flash point is 82.
At °C, impurity concentration is Cl ^- 84ppm/g, Na ⁺ <0.2ppm
It was hot. This coating solution was applied onto a glass plate using a spinner (3000 rpm) in the same manner as in Example 1, and then baked.
A silica film with a thickness of 1150 Å was obtained. The silica film had a uniform surface with no cracks or pinholes. The physical properties of this film were as follows. Etching rate 400 Å/min (1 mol% HF aqueous solution) Thermal expansion number 5×10 ^-7 /℃ Specific resistance 7×10 ¹⁵ Ω・cm Example 7 A mixture of 2.5 moles of tetraethoxysilane, 600 g of acetic acid, and 925 g of cellosolve was added at room temperature. While stirring slowly, add 0.2 g of HCl as an HCl-EtOH solution. After the addition was completed, the reaction solution was heated to 60°C and the progress of the reaction was analyzed and followed by gas chromatography. Tetraethoxysilane and acetic acid decreased.
It is observed that ethyl acetate and cellosolve acetate are produced. The reaction was continued at 60°C for 28 hours, and the reaction was completed. Next, the system was reduced in pressure and the liquid temperature was reduced to 60°C.
Part of the by-produced ethanol and ethyl acetate was removed below, and diluted with cellosolve so that the solid content concentration was 8.1% by weight when heated at 150°C for 3 hours, and filtered using a 0.2μ filter. It was filtered to obtain a coating solution for silica coating. The solvent composition of the coating solution thus obtained was 8.1% by weight of ethanol in gas chromatography area ratio;
Ethyl acetate 10.4% by weight, acetic acid 3.8% by weight, cellosolve 58.4% by weight, cellosolve acetate 18.9% by weight,
This coating liquid had a boiling point of 115°C and a flash point of 26°C. In addition, the Cl ^- concentration of this coating solution was determined by potentiometric titration method.
It was 23 ppm/g. When the coating liquid thus obtained was applied onto a glass plate in the same manner as in Example 1 and baked, a smooth and uniform film free of cracks and pinholes was obtained. The thickness of this silica film was 950 Å, and the etching rate when using a 1 mol% HF aqueous solution was 400 Å/min. Example 8 1 mole of tetraethoxysilane is dissolved in 300 g of butyl cellosolve and 280 g of cellosolve acetate, and while stirring at room temperature, a reaction accelerator prepared by dissolving 0.086 g of HCl in 4 moles of water is added dropwise. At this time, the reaction proceeds with exothermic heat, and the liquid temperature rises to 42°C. Once the heat generation subsides, heat the liquid to 65°C and continue the reaction. The reaction was continued at 65°C for 10 hours, and then at 80°C for 5 hours, while monitoring the progress of the reaction based on the amount of ethanol produced. At this time, the solid content concentration of the reaction solution is
It was 8.0% by weight. The reaction solution thus obtained was filtered through a 0.2μ filter to obtain a coating solution for silica coating. The ethanol content in the coating solution thus obtained was 22% by weight.
The coating liquid had a boiling point of 120°C and a flash point of 28°C. Comparative Example 1 1 mol of tetraethoxysilane, 240 g of acetic acid, 360 g of ethanol, and 0.084 g of HCl are mixed into a reaction vessel, and while stirring, the mixture is quickly heated to bring the reaction solution to 60°C. As the reaction progresses,
The progress of the reaction, in which tetraethoxysilane disappeared and ethyl acetate was produced, was analyzed by gas chromatography, and the reaction was continued until the acetic acid content was 1% by weight or less. The solid content concentration of the reaction solution after 14 hours at 60°C (200°C; 3 hours) was 8.6% by weight. Next, this mixture was adjusted to a concentration of 6.1% by weight with a 6:4 mixed solvent of ethanol and ethyl acetate, and filtered using a 0.2μ filter to obtain a silica coating solution. The solvent composition ratio of this liquid was analyzed by gas chromatography, and the area ratio was 6 ethanol: 4 ethyl acetate, with a boiling point of 72°C and a flash point of about 2°C. Moreover, the ^impurity concentration was 73 ppm.

Claims (1)

[Claims] 1 General formula R ¹ (OR ² ) _o OH (where R ¹ has 1 to 1 carbon atoms)
4 alkyl group or acyl group having 2 to 4 carbon atoms,
^R2 is an alkylene group having 2 to 4 carbon atoms, and when there are two or more in the same molecule (n≧2), they may be the same or different, and n is an integer of 1 to 4. ) A solution consisting of a hydroxysilane condensate dissolved in a solvent containing 20% by weight or more of the compound (hereinafter referred to as the main solvent), which has a boiling point.
A coating liquid for forming a silica film at a temperature of 100 to 500℃. 2 In paragraph 1, the solvent serves as a subsolvent;
Monohydric alcohol with 5 to 10 carbon atoms, 2 to 10 carbon atoms
6 polyhydric alcohol (including cases where there is an ether bond in the carbon chain), general formula R ¹ O (R ² O) _o R ¹ (where R ¹ , R ² and n have the same meanings as above) , multiple R ^1s present in the same molecule may be different from each other), fatty acids having 4 to 10 carbon atoms, acetoacetic acid, alkyl (1 to 4 carbon atoms) esters of acetoacetic acid, and acetylacetone. 3 In item 1 or 2, the solvent is 50% by weight
The coating liquid characterized in that it contains the following water. 4. The coating liquid according to any one of Items 1 to 3, wherein the solvent contains methyl acetate, ethyl acetate, methanol, and ethanol in a total amount of 40 mol% or less. 5. The coating liquid according to any one of Items 1 to 4, wherein the solvent contains the main solvent in an amount of 30% by weight or more. 6. The coating liquid according to any one of Items 1 to 5, wherein the concentration of the hydroxysilane condensate is 1 to 20% by weight. 7 General formula R ⁴ rSi [(OR ² ) _o OR ¹ ] _s [OR ³ ] _u (here
R ¹ is an alkyl group having 1 to 4 carbon atoms or an acyl group having 2 to 4 carbon atoms, R ² is an alkylene group having 2 to 4 carbon atoms, R ³ and R ⁴ are alkyl groups having 1 to 8 carbon atoms,
It is an alkenyl group, an aryl group, or an alkyl group, and when two or more of R ¹ , R ² and R ³ exist in the same molecule, they may be the same or different, and n is an integer of 1 to 4, r is 0 or 1, s and u are integers of 0 to 4,
r+s+u=4. ) of the silane derivatives or partial condensates thereof in an organic solvent of 0.8 to 16 times their weight with or without the main solvent, hydrolysis of the silicon atoms of the silane derivatives or partial condensates thereof; As an agent for these, 2-r/2-(m-1)/m to 90 times the amount of water (however, r has the same meaning as above, m is 1 in the case of the above silane derivative, In the case of a partial condensate, it is an m-mer) and reacted in the presence of an acid as a reaction promoter, and if necessary, the main solvent is added during or after the reaction, or Evaporating or adding low boiling point components,
The main solvent is used so that the solvent component in the hydroxysilane condensate solution thus obtained contains 20% by weight or more of the main solvent and the boiling point of the solvent component is 100 to 500°C. A method for producing a coating liquid for forming a silica film. 8. The method according to item 7, wherein r in the general formula of the silane derivative is 0. 9 In item 8, in the general formula of the silane derivative, u is 3 or less, preferably 2 or less, more preferably 1
The method described above is characterized in that the following is more preferably 0. 10. The method according to item 9, wherein r in the general formula of the silane derivative is 1. 11 In item 10, u in the silane derivative
is 2 or less, preferably 1 or less, and more preferably 0. 12. The method according to any one of items 7 to 11, wherein when u in the general formula of the silane derivative is greater than 1, the number of carbon atoms in R ³ is 1 to 3. 13. The method according to any one of items 7 to 12, characterized in that the silane derivative is used as a raw material for the hydroxysilane condensate, which is the reaction product. 14. The method according to any one of items 7 to 12, characterized in that a partial condensate of the silane derivative is used as a raw material for the hydroxysilane condensate, which is the reaction product. 15. The method according to any one of items 7 to 14, characterized in that the organic solvent contains a main solvent as a main component. 16. The method according to any one of items 7 to 14, wherein the organic solvent is a mixture of a main solvent and an auxiliary solvent. 17. The method according to any one of items 7 to 16, characterized in that water itself is used as the hydrolyzing agent. 18. The method according to any one of items 7 to 16, wherein a lower carboxylic acid or an acid anhydride thereof is used as the hydrolyzing agent. 19. The method according to any one of items 7 to 16, characterized in that an acidic ion exchange resin is used as the reaction promoter. 20. The method according to any one of items 7 to 16, characterized in that a solid acidic catalyst in which an inorganic acid is supported on a carrier is used as the reaction promoter. 21. The method according to any one of items 7 to 16, characterized in that an inorganic acid is used as the reaction accelerator. 22. The method according to any one of items 7 to 16, characterized in that an organic acid is used as the reaction accelerator.