JP2006111851A - Solution for forming silica-based film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solution for forming silica-based film, capable of forming the silica-based film having hardness similar to that of molten glass by a sol-gel method. <P>SOLUTION: This solution for forming the silica-based film containing a silicon alkoxide, a strong acid, water and an alcohol is characterized in that the concentration of the silicon alkoxide is >3 and <9 mass% expressed by the SiO<SB>2</SB>concentration on converting the silicon atoms contained in the silicon alkoxide to those of the SiO<SB>2</SB>, the number of moles of the water is ≥4 and ≤10 folds of the total number of moles of the silicon atoms contained in the silicon alkoxide, and the concentration of the strong acid is 0.001-0.2 mol/kg range expressed by the mass molar concentration of proton on assuming that the proton completely dissociates from the strong acid. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solution for forming a silica-based film by a sol-gel method.

  General glass is produced by a melting method in which a raw material is melted at a high temperature exceeding 1500 ° C. and cooled. On the other hand, the sol-gel method is a relatively new method for producing glass and ceramics at a low temperature.

  In the sol-gel method, a solution of a metal organic or inorganic compound is used as a starting material, and the solution is made into a sol in which fine particles of metal oxide or hydroxide are dissolved by hydrolysis / polycondensation reaction of the compound in the solution. In this method, the reaction is allowed to progress to gelation and solidification, and the gel is heated to obtain an oxide solid.

  In the sol-gel method, it is possible to produce a thin film on various substrates in order to produce glass from a solution, and it is possible to produce glass at a lower temperature than the glass production temperature by the melting method. Has characteristics.

  Many methods for forming a silica-based coating film by this sol-gel method have been proposed. In the sol-gel method, the heat treatment is usually performed at a temperature of 500 ° C. or higher although it is at a lower temperature than the melting method (for example, JP-A-55-034258).

  Further, techniques for curing the silica-based coating film by heating at about 450 ° C. have been proposed (for example, Japanese Patent Application Laid-Open Nos. 63-241076 and 08-027422). In addition, techniques for curing the silica-based coating film in a low temperature range from room temperature to about 200 ° C. have been proposed (for example, JP-A-63-268772 and JP-A-2002-088304).

  Furthermore, in Japanese Patent Application Laid-Open Nos. 05-085714 and 06-052796, “a treatment liquid and a forming method of a silica coat film capable of forming a non-glare film that can be fired at a low temperature (room temperature to 100 ° C.)” are described. Proposed.

  Here, in Japanese Patent Laid-Open No. 05-085714, a value as a hydrolysis rate is defined, and by setting this to 300% to 1500%, a hard film having excellent adhesiveness can be obtained. . The hydrolysis rate defined here is a value indicating the addition ratio of water. When teramethoxysilane or water having a mole number twice that of tetraethoxysilane is added, 100 is added. It is a value converted as a percentage. A hydrolysis rate of 300% to 1500% indicates that water is added in an amount of 6 to 30 times the number of moles of teramethoxysilane or tetraethoxysilane.

  Japanese Patent Application Laid-Open No. 2002-088304 states that when a coating liquid having an average molecular weight of tetraalkoxysilane oligomer of 85000 to 500000 is used, a strong silica film without cracks can be obtained.

  Furthermore, Japanese Patent Application Laid-Open No. 63-168470 discloses a coating composition in which a film having a pencil hardness of 6H to 8H can be obtained by heating at 150 ° C. The composition includes colloidal silica.

  By the way, such a coating film by the sol-gel method is useful because it can impart a chemical protection function and optical characteristics to the target substrate surface. In addition, this coating film can be used as a base film for forming a functional film such as a water repellent film. Further, this coating film is used as a matrix, and functional fine particles are dispersed in the film. In addition, the coating film is also required to have mechanical durability.

Therefore, the present inventor has proposed a “method for producing a silica-based film-coated article” in Japanese Patent Application Laid-Open No. 11-269657. The content is intended to “manufacture excellent silica-based film-coated articles without the need for firing or pretreatment”, and includes “acid and silicon alkoxide dissolved in alcohol, At least one of the alkoxide and its hydrolyzate (including the partial hydrolyzate) contains 0.010 to 3% by weight in terms of silica, 0.0010 to 1.0N acid, and 0 to 10% by weight water. Is a method for producing an article coated with a silica-based film by applying a coating liquid to a substrate.
The silica-based film obtained by this method was able to withstand the dry cloth abrasion test.

JP 55-034258 (US Pat. No. 4,277,525) Japanese Patent Laid-Open No. 63-241076 (US Pat. No. 4,865,649) Japanese Patent Application Laid-Open No. 08-027422 Japanese Unexamined Patent Publication No. 63-268772 JP 2002-088304 A JP 05-085714 A Japanese Patent Application Laid-Open No. 06-052796 JP 63-168470 A JP-A-11-269657 (WO 99/28534, EP 0967297, US6465108)

  In order to obtain a dense silica-based film by the sol-gel method, heat treatment at 450 ° C. or higher is required. For this reason, the material of the base material used may be restricted. Furthermore, when functional fine particles are dispersed in a film even at a heat treatment at 450 ° C., the fine particles may be decomposed or the function thereof may be impaired depending on the type of functional fine particles. For example, it is the case of organic fine particles or ITO fine particles.

  In JP-A-63-241076, although heat treatment at 450 ° C. is performed in the examples, there is no description regarding film hardness. In JP-A-8-27422, heat treatment at 450 ° C. is performed in the examples, the film thickness is 300 nm, and the film hardness is 9H in pencil hardness.

  Furthermore, in Japanese Patent Application Laid-Open No. 63-268772, the film was cured at room temperature and the film thickness was unknown, but the film hardness was about 3H to 7H in pencil hardness. Japanese Patent Application Laid-Open No. 2002-88304 performs heat treatment at 80 ° C. in the examples. The evaluation of the film shows only the shrinkage rate and does not show the specific hardness. In addition, the film thickness in the Example was about 100 nm.

  In addition, according to Japanese Patent Laid-Open Nos. 05-085714 and 06-052796, “9H is obtained in pencil hardness in a film (thickness unknown) fired at a low temperature (room temperature to 100 ° C.). .

  Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 11-269657 by the present inventor, the obtained silica-based film can withstand the dry cloth abrasion test, but further improvement in film hardness has been required. In addition, the film thickness in an Example was 250 nm at maximum.

  Here, in the coating film by the sol-gel method, the film thickness obtained by one operation is generally about 100 to 200 nm.

  In a silica-based film by the sol-gel method, if it is desired to increase the film thickness, multiple coatings are necessary. Furthermore, since the crack is easily generated by increasing the film thickness, a countermeasure for the crack is also necessary. Therefore, for example, a production method for obtaining a silica-based film having a film thickness exceeding 250 nm by a single operation has also been demanded.

  Accordingly, the present invention has been made to solve the above-described problems, and a silica-based film forming solution capable of forming a silica-based film having hardness similar to that of molten glass by a sol-gel method is provided. provide.

  First, the sol-gel process will be described. As an example, formation of a silica-based film by a sol-gel method will be described.

  For example, in a sol-gel method using silicon alkoxide as a starting material, silicon alkoxide is converted into an oligomer via a siloxane bond in a solution by a hydrolysis reaction and dehydration condensation reaction with water and a catalyst to be in a sol state.

  When this solution is applied to the substrate, the water and the solvent are volatilized, whereby the oligomer is concentrated and the molecular weight is increased, and eventually the solution loses fluidity and becomes a semi-solid gel. Immediately after gelation, the gap between the siloxane polymer networks is filled with a solvent or water. When this gel dries and water and solvent volatilize, the siloxane polymer shrinks and solidifies.

  In the solidified gel, the gap filled with the solvent and water is not completely filled and remains as pores even when heat treatment up to about 400 ° C. is performed. For this reason, in the sol-gel method, a hard film cannot be obtained by heat treatment at about 400 ° C. In order to obtain a hard film, a heat treatment at a higher temperature, for example, 500 ° C. or more, was required.

The relationship between the reaction and temperature in the heat treatment of the silica-based film by the sol-gel method described above will be described in more detail.
First, in a temperature range of about 100 to 150 ° C., water, a solvent and the like contained in the solution are evaporated.
Subsequently, if the raw material contains an organic material in a temperature range of about 250 to 400 ° C., it decomposes and evaporates.
Further, when the temperature is about 500 ° C. or higher, the gel skeleton contracts and a dense film is formed.

  As described above, in a normal sol-gel reaction, a gap between the formed networks is filled with a solvent and water in a state after gelation. It is known that the size of the gap depends on the form of polymerization of silicon alkoxide in the solution.

Moreover, the form of polymerization varies greatly depending on the pH of the solution.
That is, in an acidic solution, the oligomer of silicon alkoxide is likely to grow in a straight chain. When such a solution is applied to a substrate, the linear oligomers are folded to form a network structure, and the resulting film becomes a dense film with relatively small gaps.
However, since the linear polymer is folded and solidified, the micro structure is not strong, and cracks are easily generated when the solvent or water volatilizes from the gap.

  On the other hand, spherical oligomers are likely to grow in an alkaline solution. When such a liquid is applied to the substrate, a structure in which spherical oligomers are connected to each other is formed, and a film having a relatively large gap is formed. Since this gap is formed by bonding and growing a spherical oligomer, when the solvent or water volatilizes from the gap, it is difficult for cracks to enter.

  The present inventors paid attention to the pH of the solution and examined the acid concentration and the amount of water in an acidic region where a relatively dense film can be formed. In a certain concentration region, even a thick film is dense and free of cracks. It has been found that a film can be formed, and further, when such a film is heat-treated at, for example, about 150 to 300 ° C., a film having a hardness comparable to that of molten glass can be obtained.

  Now, it is known that the isoelectric point of silanol is 2. This indicates that when the pH of the solution is 2, silanol can exist most stably in the solution. That is, even when a large amount of hydrolyzed silicon alkoxide is present in the solution, if the pH of the solution is about 2, the probability that an oligomer is formed by the dehydration condensation reaction is very low. As a result, the hydrolyzed silicon alkoxide can exist in the solution in a monomer or low polymerization state.

  For example, when a strong acid is added to the sol-gel solution and the proton of the strong acid is completely dissociated, the proton molar concentration (hereinafter simply referred to as proton concentration) is 0.001 to 0.1 mol / kg. Then, the pH of the solution is about 3 to 1. Therefore, an oligomer having a relatively low degree of polymerization can be stably present in this solution.

  For example, in Japanese Patent Application Laid-Open No. 2002-088304, it was recommended that the average molecular weight of the tetraalkoxysilane oligomer be 85,000 to 500,000, but in the present invention, it is much smaller, about 500 to 10,000. It is a molecular weight oligomer. The present inventors have found that it is important that a thick film without a strong crack is present in the solution as an oligomer having a relatively low polymerization degree.

  The acid used in the forming solution of the present invention must be a strong acid. Examples of the strong acid include the following. Examples include hydrochloric acid, nitric acid, trichloroacetic acid, trifluoroacetic acid, sulfuric acid, phosphoric acid, methanesulfonic acid, paratoluenesulfonic acid, and oxalic acid. Of the strong acids, volatile acids can be preferably used because they do not volatilize when heated and remain in the cured film. If an acid remains in the cured film, it may hinder the bonding of inorganic components and reduce the film hardness.

  The coating liquid of the present invention has a mixed solvent of water and alcohol, and other solvents can be added as necessary. In the case of such a mixed solvent, a strong acid is used and a strong acid is used. By setting the mass molar concentration of protons to be 0.001 to 0.2 mol / kg when it is assumed that protons are completely dissociated, the liquid can have a pH of around 2.

  In calculating the molar concentration of protons, it is not necessary to consider protons having an acid dissociation index of 4 or more in the acid used. For example, since the acid dissociation index of acetic acid, which is a weak acid, in water is 4.8, even when acetic acid is included in the forming solution, the proton of acetic acid is not included in the proton concentration. In the present specification, the strong acid specifically refers to an acid having a proton having an acid dissociation index of less than 4 in water.

  In the formation solution of the present invention, the reason why the proton concentration is defined as the concentration when the proton of the strong acid is completely dissociated as described above is that in the mixed solution of the organic solvent and water as in the present invention. This is because it is difficult to accurately determine the degree of acid dissociation.

  When the pH of the solution is 3 to 1, this is applied to the substrate surface and dried, the oligomer derived from silicon alkoxide having a low polymerization degree is densely filled, and a film without cracks is formed. As a result, the pores formed are small and a fairly dense film can be obtained.

  It is one of the important points of the present invention that such oligomers derived from silicon alkoxide having a low polymerization degree are closely packed. However, with this alone, a sufficiently high hardness film cannot be obtained even when heated at 200 to 300 ° C.

  As described above, the oligomer having a relatively low degree of polymerization is stably present by setting the pH of the solution to about 3 to 1. However, in such a pH range, even if water necessary for hydrolyzing all of the silicon alkoxide stoichiometrically is added, it is stabilized in a state where unreacted alkoxide remains. Even if heating is performed with insufficient hydrolysis, a siloxane bond cannot be sufficiently formed by the polymerization reaction, and a hard film cannot be obtained.

  Therefore, in the present invention, at least the stoichiometric amount of water necessary for hydrolysis is added in advance. That is, the number of moles required for hydrolysis, that is, four times or more of water is added to the number of moles of silicon atoms in the silicon alkoxide. In this way, the hydrolysis reaction is promoted, and as a result, the curing caused by the polymerization is sufficiently performed.

  Furthermore, in this invention, it is preferable to add water exceeding the 4 times mole number required for a hydrolysis. The reason for this is as follows. For example, in a low-viscosity solution, as long as there is a stoichiometrically sufficient amount of water, the hydrolysis reaction proceeds with sufficient diffusion. However, the fluidity of the liquid decreases during drying or heating, and the diffusion does not occur sufficiently, so that the hydrolysis reaction may not proceed sufficiently. As a result, there is a possibility that a film having high hardness cannot be obtained only by heat treatment at a temperature up to about 400 ° C.

  That is, at the time of drying, water evaporates in parallel with the volatilization of the solvent. Even if water is added to the solution in advance, if the amount is small, incompletely hydrolyzed silicon alkoxide is filled without being fully hydrolyzed at the stage where silicon alkoxide is concentrated. . Therefore, sufficient water is added to the solution in advance. Specifically, it is preferable to add 5 to 10 moles of water.

  For example, in the case of tetraalkoxysilane which is an example of silicon alkoxide, if 4 moles of water are present per mole of tetraalkoxysilane, all the alkoxyl groups are hydrolyzed stoichiometrically. Become. Therefore, in the present invention, the number of moles of water more than 4 times the number of moles of silicon atoms in the silicon alkoxide, preferably the number of moles of water exceeding 4 times is added. As a result, it is possible to obtain a film having a high hardness only by sufficiently proceeding with the hydrolysis reaction of silicon alkoxide and performing a heat treatment at a temperature up to about 400 ° C.

  Further, in the case of a tetraalkoxysilane polymer (for example, ethyl silicate 40 manufactured by Colcoat Co., Ltd.), assuming that the number of moles of Si in the polymer is n, the number of moles of water stoichiometrically required for hydrolysis. Is (2n + 2) moles. Therefore, as the alkoxysilane raw material having a higher degree of polymerization is used, the number of moles of water stoichiometrically required for hydrolysis is reduced with respect to 1 mole of Si.

  In the present invention, the reason for adding an excess amount of water of stoichiometrically more than the number of moles of water required for hydrolysis is to accelerate the hydrolysis reaction during drying or heating, and consequently to cure due to polymerization. There is enough to do. For example, in a low-viscosity solution, as long as there is a stoichiometrically sufficient amount of water, the hydrolysis reaction proceeds with sufficient diffusion. However, the fluidity of the liquid decreases during drying or heating, and the diffusion is not sufficiently performed, so that the hydrolysis reaction cannot proceed sufficiently. As a result, a film having high hardness cannot be obtained only by heat treatment at a temperature up to about 400 ° C.

  Therefore, even when using a silicon alkoxide raw material polymerized in advance, an excess amount of water, that is, a mole number exceeding 4 times, is added to 1 mol of Si. Preferably, 5 to 10 times the number of moles of water is added.

  Moreover, in the manufacturing method of the silica type film | membrane using the formation solution of this invention, it is good to perform the heat processing for hardening a film | membrane at the temperature of 400 degrees C or less. In this case, after the film is densified, the organic matter contained therein is burned and the portion becomes a void, so that the film hardness does not decrease. In other words, a dense and hard structure is maintained in a state containing organic matter.

  The heat treatment temperature may be appropriately selected according to the required film hardness. For example, a film hardness of about pencil hardness B can be obtained by drying at room temperature. Further, a film hardness of about H is obtained by heat treatment at 90 ° C. and a film hardness of 9H or more at 120 ° C. Furthermore, if a heat treatment at 150 ° C. or higher is performed, the film hardness exceeds the category of the pencil hardness test, so it is preferable to measure by a wear test in accordance with JIS R 3212. That is, it evaluates using a commercially available Taber abrasion tester. When heat treatment of about 150 ° C. or higher is performed, the haze ratio after performing a 1000-time wear test with a Taber abrasion tester with a load of 500 g becomes 4% or less, which is equivalent to the surface hardness of the molten glass plate. It is obtained.

  Further, this silica-based film forming solution may contain a small amount of phosphoric acid. This phosphorus acts as a curing catalyst particularly during curing. Phosphorus remains in the film without volatilization at a temperature of 400 ° C. or lower. Also, since there are many polymorphs of phosphorus, it is preferable because it does not increase the residual stress and does not lower the film hardness.

  The forming solution of the present invention may further contain at least one of functional fine particles, molecules or ions.

  The functional fine particles are preferably conductive oxide fine particles and / or organic fine particles. The functional molecule is preferably an organic dye.

From the above, the present invention can be grasped as follows.
That is, as an invention according to claim 1,
Including silicon alkoxide, strong acid, water and alcohol,
The concentration of the silicon alkoxide is a displayed by SiO ₂ concentration of less than 9% by weight greater than 3 mass% when converted to silicon atoms contained in the silicon alkoxide to SiO _2,
The number of moles of water is 4 to 10 times the total number of moles of silicon atoms contained in the silicon alkoxide,
Silica system characterized in that the concentration of the strong acid is in the range of 0.001 to 0.2 mol / kg, expressed by the molar concentration of protons on the assumption that protons are completely dissociated from the strong acid A film forming solution.

As invention of Claim 2,
The solution for forming a silica-based film according to claim 1, wherein the silicon alkoxide contains at least one of tetraalkoxysilane and a polymer thereof.

As invention of Claim 3,
3. The silica-based film forming solution according to claim 2, wherein the total amount of the tetraalkoxysilane and the polymer thereof is 3 to 30% by mass in terms of silica.

As invention of Claim 4,
The said formation solution is a formation solution of the silica type film according to any one of claims 1 to 3 which further contains phosphoric acid.

As invention of Claim 5,
5. The silica-based film forming solution according to claim 1, wherein the forming solution further includes at least one of functional fine particles, molecules, or ions.

As invention of Claim 6,
6. The silica-based film forming solution according to claim 5, wherein the functional fine particles are conductive oxide fine particles and / or organic fine particles.

As invention of Claim 7,
The solution for forming a silica-based film according to claim 5, wherein the functional molecule is an organic dye.

In this specification, the silica-based film refers to a film in which silica is a component having the highest content rate.
According to the present invention, it is possible to form a silica-based film excellent in mechanical strength despite being a thick film having a thickness exceeding 300 nm formed by a sol-gel method.

    The silica-based film by the forming solution of the present invention has a film hardness comparable to that of molten glass by heat treatment at a relatively low temperature. Even if this silica-based film is applied to window glass for automobiles or buildings, it is sufficiently practical.

  In the forming solution of the present invention, the hydrolysis and polymerization state of the silicon alkoxide in the solution is controlled by adding a strong acid and adjusting the pH. Further, during drying, a volatile strong acid is used so that the pH of the solution changes, and the water content is further adjusted. By doing so, a film having high hardness can be obtained by heat treatment at a relatively low temperature. Furthermore, it can be applied to the production of a silica-based film having a film thickness of more than 250 nm and several μm by one operation.

  Furthermore, a functional substance can be introduced into the resulting silica-based film as a matrix. At this time, a functional substance whose function is impaired after a heat treatment step of about 400 ° C. or higher can be introduced into the silica-based film without impairing the function.

  Furthermore, many organic substances that can be used as functional substances often start to decompose at a temperature of 200 to 300 ° C. Further, it is known that the heat shielding ability of the ITO fine particles is lowered by heating at, for example, 250 ° C. or more. In such a substance, it is possible according to the present invention to sufficiently cure the silica-based film even at a temperature lower than the temperature that impairs its characteristics such as the decomposition temperature, for example, 200 ° C. As a result, when the forming solution of the present invention is used, a thermally unstable functional substance can be introduced into a silica-based film having a hardness that can withstand a wide range of practical use without impairing its function.

Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
To 109.8 g of ethyl alcohol (manufactured by Katayama Chemical), 10.6 g of tetraethoxysilane (manufactured by Shin-Etsu Chemical), 7.0 g of pure water, and 0.05 g of concentrated hydrochloric acid (35% by mass, manufactured by Kanto Chemical) were added and stirred. A forming solution was obtained.

  The silicon alkoxide (tetraethoxysilane) content (silica conversion), proton concentration, and water content in this solution are as shown in Table 1. The water content is calculated by adding water (0.35% by mass) contained in ethyl alcohol. The proton concentration was calculated on the assumption that all protons contained in hydrochloric acid were dissociated. The calculation method of water content and proton concentration is the same in all of the following Examples and Comparative Examples.

(Table 1)
────────────────────────────────────────
Silicon proton water crack taber
Alkoxide concentration (vs. Si content; film thickness)
(Mass%) ^* (mol / kg) molar ratio) (nm) Film peeling ----------------------- ────────
Example 1 3.1 0.004 8 400 None None Comparative Example 1 5.0 0.0001 7 --------
Example 2 5.0 0.001 7 480 None None Example 3 5.0 0.01 7 510 None None Example 4 5.0 0.02 7 480 None None Example 5 5.0 0.03 7 450 None None Example 6 5.0 0.05 7 480 None None Example 7 5.0 0.1 7 460 Yes No Comparative Example 2 5.0 0.3 7 --- Yes Yes Comparative Example 3 5.00 .01 2 --- Yes Yes Example 8 5.0 0.01 4 430 No Yes Example 9 5.0 0.01 10 490 Yes No Comparative Example 4 5.0 0.01 15 460 Yes Yes Example 10 6.0 0.01 7 520 Yes No Example 11 7.0 0.01 7 630 Yes No Example 12 8.0 0.01 7 740 Yes No Comparative Example 5 9.0 0.01 7-Yes Yes Yes────────────── ──────────────────────────

  Subsequently, this forming solution was applied by a flow coating method on a cleaned soda-lime silicate glass substrate (100 × 100 mm) at a humidity of 30% and room temperature. As it was, after drying at room temperature for about 30 minutes, it was put into an oven preheated to 200 ° C., heated for 40 minutes, and then cooled. The obtained film was a film having a high transparency and no cracks having a thickness of 400 nm.

  The hardness of the film was evaluated by an abrasion test in accordance with JIS R 3212. That is, using a commercially available Taber abrasion tester (5150 ABRASER manufactured by TABER INDUSTRIES), abrasion was performed 1000 times with a load of 500 g, and the haze ratio before and after the abrasion test was measured. Table 1 shows the film thickness, the presence or absence of cracks, and the presence or absence of film peeling after the Taber test.

The haze ratio before the Taber abrasion test was 0.1%, and the haze ratio after the test was 3.3%.
In addition, when the haze rate before and behind the Taber test in a molten glass plate was measured as a blank, it was 0.0% before the test. It was 1.5% after the test. In addition, the haze rate was measured using HGM-2DP by Suga Test Instruments Co., Ltd.

  The glass plate with a silica film produced in Example 1 is sufficiently practical as a window glass for automobiles or buildings. In the window glass for automobiles, the haze ratio after the Taber test is required to be 4% or less.

(Examples 2-7) (Comparative Examples 1-2)
A film was formed in the same manner as in Example 1 except that the mixing ratio of the raw materials was changed. The blending ratio of the raw materials is shown in Table 1 together with the film thickness and the results of the Taber abrasion test.

  In Examples 2 to 7 and Comparative Examples 1 and 2, only the proton concentration was changed. In Comparative Example 1 in which the proton concentration was lowered, the forming solution was bounced off the glass plate and could not be applied. This is presumably because the hydrolysis of the silicon alkoxide was extremely insufficient. In Example 7 in which the proton concentration was increased, cracks occurred in a part of the film, but as a result of the Taber abrasion test performed on the area where no cracks occurred, the film did not peel off. In Comparative Example 2 in which the proton concentration was further increased, cracks were generated in the film in a wider region than in Example 7. As a result of the Taber abrasion test conducted on the region where no film thickness could be measured and cracks did not occur, Peeled off.

(Examples 8 to 9) (Comparative Examples 3 to 4)
A film was formed in the same manner as in Example 1 except that the mixing ratio of the raw materials was changed. The blending ratio of the raw materials is shown in Table 1 together with the film thickness and the results of the Taber abrasion test.

  In Examples 8 to 9 and Comparative Examples 3 to 4, only the amount of water added was changed. In Comparative Example 3, fine cracks accompanied with peeling occurred, and the film peeled by the Taber abrasion test. In Example 9 and Comparative Example 4, cracks occurred in a part of the film, but as a result of the Taber abrasion test performed on the area where no cracks occurred, the film was not peeled off in Example 9, and the film was not removed in Comparative Example 4. Peeled off.

(Examples 10 to 12) (Comparative Example 5)
A film was formed in the same manner as in Example 1 except that the mixing ratio of the raw materials was changed. The blending ratio of the raw materials is shown in Table 1 together with the film thickness and the results of the Taber abrasion test.

  In Examples 10 to 12 and Comparative Example 5, only the amount of silicon alkoxide added was changed. In all cases, cracks occurred in a part of the film, but as a result of the Taber abrasion test conducted on the area where no crack occurred, the film was not peeled off in Examples 10 to 12, and the film was peeled off in Comparative Example 5. . In Comparative Example 5, many cracks occurred to such an extent that the film thickness could not be measured.

  The examples and comparative examples described above are merely examples for explaining the present invention, and the present invention is not limited to these examples.

  For example, as the silicon alkoxide, tetramethoxysilane, methyl silicate, or the like may be used.

  Further, as the silicon alkoxide, an organically modified alkoxide may be used. However, in this case, it is preferable that the organically modified silicon alkoxide is in an amount of 10% or less of the number of moles of silicon atoms of the silicon alkoxide not organically modified.

As the acid, sulfuric acid, p-sulfonic acid, methanesulfonic acid and the like may be used.
As the alcohol, methyl alcohol, 1-propyl alcohol, isopropyl alcohol, t-butyl alcohol, or the like may be used.

Furthermore, a metal oxide other than silica may be added to the silica-based film according to the present invention.
For example, lithium, sodium, potassium, cesium, magnesium, calcium, cobalt, iron, nickel, copper, aluminum, gallium, indium, scandium, yttrium, lanthanum, cerium, zinc, and other metal chlorides, oxides, nitrates, etc. You may add to a coating liquid.

  With respect to boron, boric acid or boron alkoxide can be chelated with a β-diketone such as acetylacetone and added.

  Regarding titanium and zirconium, oxychloride, oxynitrate, or alkoxide can be chelated with β-diketone and added.

  As for aluminum, it is possible to add alkoxide by chelating with β-diketone.

  The article formed with the silica-based film according to the present invention is useful as a base film, a protective film, a low reflection film, an ultraviolet shielding film, an infrared shielding film, a colored film, and the like.

Claims (7)

Including silicon alkoxide, strong acid, water and alcohol,
The concentration of the silicon alkoxide is a displayed by SiO ₂ concentration of less than 9% by weight greater than 3 mass% when converted to silicon atoms contained in the silicon alkoxide to SiO _2,
The number of moles of water is 4 to 10 times the total number of moles of silicon atoms contained in the silicon alkoxide,
Silica system characterized in that the concentration of the strong acid is in the range of 0.001 to 0.2 mol / kg, expressed by the molar concentration of protons on the assumption that protons are completely dissociated from the strong acid Film forming solution.   The solution for forming a silica-based film according to claim 1, wherein the silicon alkoxide includes at least one of tetraalkoxysilane and a polymer thereof.   The solution for forming a silica-based film according to claim 2, wherein the total amount of the tetraalkoxysilane and the polymer thereof is 3 to 30% by mass in terms of silica.   The silica-based film forming solution according to claim 1, wherein the forming solution further contains phosphoric acid.   5. The silica-based film forming solution according to claim 1, wherein the forming solution further contains at least one of functional fine particles, molecules, or ions.   The silica-based film forming solution according to claim 5, wherein the functional fine particles are conductive oxide fine particles and / or organic fine particles.   The solution for forming a silica-based film according to claim 5, wherein the functional molecule is an organic dye.