JPH08176508A - Composition for forming silica-based coating film, silica-based coating film produced by using the composition and production of the composition - Google Patents

Abstract

PURPOSE: To obtain the subject composition containing a partial hydrolyzate of a tetraalkoxysilane and a specific alkyltrialkoxysilane, having excellent hydrophilicity and storage stability and useful for the preparation of a transparent silica-based coating film having high surface hardness. CONSTITUTION: This coating composition contains (A) a partial hydrolyzate of (i) a tetraalkoxysilane (preferably tetramethoxysilane) and (ii) an alkyltrialkoxysilane having a >=2C (preferably 2-6C) alkyl group directly bonded to silicon atom as a main raw material and preferably further (B) a monohydric aliphatic alcohol, (C) water and (D) an organic carboxylic acid having pKa of >1.0 and <=5.0 as essential components. The composition preferably has a contact angle of <=30 deg. with water. A hydrophilic silica-based coating film is produced by applying the composition to a substrate and heat-treating at >=300 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrophilic silica-based coating film forming composition, a hydrophilic silica-based coating film using the same, and a method for producing the same, which has a hydrophilic contact angle with water of 30 °. The following silica-based coating is produced by a heat treatment using a specific partial hydrolyzate.

[0002]

2. Description of the Related Art Various fields have been used in various fields to form silica coatings on the surface of various substrates including resins, metals and ceramics by using the sol-gel method with various silicates as raw materials. The main purposes of these are to prevent the occurrence of scratches on the substrate, to insulate electricity, and to prevent corrosion by water and various chemicals. The coating / film formation of the solution containing the silane compound on the substrate is performed by an impregnation method, a dipping method, a spin coating method, a spray method or the like.

[0003]

However, in general, a film using only tetraalkoxysilane has a very hard surface but is not sufficiently hydrophilic, and a film using only alkyltrialkoxysilane has insufficient hardness. And gives a hydrophobic surface.

[0004]

Therefore, as a result of diligent studies on these conventional problems, the present inventors have found that tetraalkoxysilane and an alkyltri having an alkyl group having 2 or more carbon atoms directly bonded to a silicon atom. It was found that a silica-based coating film having a contact angle with water of 30 ° or less can be obtained by using a partial hydrolyzate with an alkoxysilane as a main raw material, and the present invention was reached.

The present invention will be described in detail below. Specific examples of the tetraalkoxysilane used in the present invention include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetraisobutoxysilane, tetrasecbutoxysilane, and tetratertbutoxysilane. Etc., and those having four or more alkoxy groups directly bonded to a silicon atom can be used regardless of the difference of the alkoxy groups, but usually from the viewpoint of easy availability, etc., one or two of the above It is selected from the above. Examples of the alkoxy group include methoxy, ethoxy, isopropoxy, propoxy, butoxy, isobutoxy, sec butoxy, tert butoxy and the like. Specific examples of the alkyltrialkoxysilane having an alkyl group having 2 or more carbon atoms directly bonded to a silicon atom include ethyltrimethoxysilane,
It refers to ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, etc., and the alkyl group directly bonded to the silicon atom may be an alkyl group having 2 or more carbon atoms. Specifically ethyl, propyl, butyl,
Examples thereof include isobutyl, pentyl, and hexyl, with an alkyl group having 2 to 6 carbon atoms being particularly preferable. If the carbon number is too large, the hydrophilicity becomes low. In the present invention, one or more of these can be used. Also,
Alkoxyl groups are methoxy, ethoxy, isopropoxy,
Propoxy, butoxy, isobutoxy, sec butoxy, tert butoxy and the like can be mentioned. In the present invention, these alkoxysilanes are used as a partial hydrolyzate. The partial hydrolysis reaction can be carried out by a known method. For example, a predetermined amount of water is added to a mixture of the above tetraalkoxysilane and alkyltrialkoxysilane in the presence of an acid catalyst to distill off methanol as a by-product, and ,
The reaction is performed at room temperature to about 100 ° C. By this reaction, methoxysilane is hydrolyzed to silanol, and the subsequent condensation reaction causes a liquid substance (average degree of polymerization of 2).
To 8). The degree of hydrolysis can be appropriately adjusted according to the amount of water used, but in the present invention, it is usually about 10 to 90%, more preferably 20 to 90%.
It is selected from about 80%. The partially hydrolyzed alkoxysilane thus obtained usually contains about 2 to 10% of a monomer. These are further boiled oligomer,
The content of the monomer can be reduced to 1% or less by vaporizing the monomer and removing the monomer together with the inert gas. The ratio of tetraalkoxysilane to alkyltrialkoxysilane is preferably 5 g or more and 95 g or less of alkyltrialkoxysilane with respect to 100 g of the total amount of tetraalkoxysilane and alkyltrialkoxysilane. If it is less than 5 g, the surface contact angle is high, and if it exceeds 95 g, the surface hardness when cured is lowered.

Basically, only the above-mentioned partial alkoxysilane hydrolyzate is required, but an aliphatic monohydric alcohol, water, and an organic carboxylic acid having a pKa of more than 1.0 and not more than 5.0 are added thereto. Then, the film characteristics are improved. The aliphatic monohydric alcohol is not particularly limited as long as it can uniformly dissolve the alkoxysilane partial hydrolyzate. Specifically, methanol, ethanol, isopropyl alcohol, butanol, or 2-methoxyethanol, 2-ethoxyethanol, 2- (2-
Ethoxyethoxy) ethanol, 2- (2-methoxyethoxy) ethanol, 2-butoxyethanol, 2-
(2-butoxyethoxy) ethanol and the like can be mentioned.
These alcohols are excellent in solubility of the above-mentioned alkoxysilane and its partial hydrolyzate. In addition to using one kind or a mixture of two or more kinds among the above-exemplified solvents, other general solvents may be mixed and used with these solvents. Specific examples of the other solvent include ethers such as ethyl ether and butyl ether, polyhydric alcohols such as ethylene glycol and propylene glycol, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and ethyl acetoacetate. The kind is mentioned. However, the amount of these solvents used with respect to the aliphatic monohydric alcohol is 50 with respect to 100 parts by weight of the aliphatic monohydric alcohol from the viewpoint of the uniformity of the obtained film.
It is preferable that the content be not more than part by weight. A suitable amount of the solvent for the partial hydrolysis product of alkoxysilane is 100 parts of A component.
The solvent is preferably 50 to 1000 parts by weight with respect to parts by weight. When the amount of the solvent is less than 50 parts by weight, the spreadability of the liquid on the substrate is poor,
It will be difficult to apply a uniform thickness. On the other hand, the solvent is 1
If it is more than 000 parts by weight, only a film having an extremely small thickness can be obtained, and it becomes necessary to recoat the film.

Water is added to accelerate the hydrolysis reaction of the alkoxy group remaining in the partial hydrolyzate. The required amount of water varies depending on the amount of the alkoxy groups remaining in the partial hydrolyzate, but is 0 relative to 100% equivalent of the hydrolysis rate theoretically required to hydrolyze all the alkoxy groups. It is preferably at least 5 times the amount. If the amount of water is small, not only the thickness of the film obtained by heating and curing after coating becomes extremely small, but also the flatness of the film surface is significantly impaired.

An organic carboxylic acid having a pKa of more than 1.0 and not more than 5.0 is a useful catalyst for the progress of the hydrolysis reaction of the alkoxy group remaining in the partial hydrolyzate and the subsequent condensation / curing reaction. . pka exceeds 1.0 and 5.
The organic carboxylic acid of 0 or less is not particularly limited as long as it is soluble in the alcohol or water described above, and specifically, maleic acid, oxalic acid, trichloroacetic acid, fumaric acid, formic acid, Examples thereof include acetic acid and pivalic acid. In general, as a catalyst for the hydrolysis and condensation reaction of the alkoxysilane oligomer, an acid or base catalyst other than an organic carboxylic acid can be used, but a pka of 1.0 is particularly preferable.
An organic carboxylic acid having a viscosity of more than 5.0 and less than 5.0 is superior to other catalysts in terms of storage stability of the coating solution. The preferable addition amount is 0.3 parts by weight or more based on 100 parts by weight of the alkoxysilane partial hydrolyzate. When a film is formed from a composition having an amount of the above carboxylic acid less than this, the thickness of the obtained film becomes extremely small.

As a method of blending these components, it is general to dissolve the partial hydrolyzate in a solvent at room temperature and then add water and an organic carboxylic acid. The composition thus obtained is formed into a film on a substrate such as glass, a silicon wafer, a ceramic, and a metal by various coating methods, and then cured by heating, so that the contact angle with water is 30 ° or less and the hardness is An excellent silica coating can be easily obtained. The heating temperature at this time is preferably 300 ° C. or higher. If the temperature is lower than 300 ° C, the curing time may be too long or the curing may not be substantially achieved depending on the type of tetraalkoxysilane, alkyltrialkoxysilane and the like.

[0010]

The present invention will be described in more detail with reference to the following examples. (Synthesis example 1) 90 g of tetramethoxysilane, 10 g of propyltrimethoxysilane, 31.5 of methanol
Gram, 8.7 g of water, 0.13 g of 1N hydrochloric acid are heated at a liquid temperature of 65 ° C. for 2 hours, and then 100 ° C. and 150 ° C.
It was heated and distilled. After that, the content was cooled to room temperature and stirred under reduced pressure for 30 minutes to remove the monomer to obtain a partial hydrolyzate A.

(Synthesis Example 2) As in Synthesis Example 1, 80 g of tetramethoxysilane and 2 of propyltrimethoxysilane were used.
A partial hydrolyzate B was obtained using 0 g, 31.1 g of methanol, 8.6 g of water, and 0.13 g of 1N hydrochloric acid.

(Synthesis Example 3) As in Synthesis Example 1, 10 g of tetramethoxysilane and 9 of propyltrimethoxysilane were used.
A partial hydrolyzate C was obtained using 0 g, methanol 29.5 g, water 8.2 g, and 1N hydrochloric acid 0.12 g.

(Synthesis Example 4) Tetramethoxysilane 100
Grams, 31.6 grams of methanol, 8.8 grams of water,
0.13 g of 1N hydrochloric acid was heated at a liquid temperature of 65 ° C. for 2 hours and then heated to 100 ° C. and 150 ° C. for distillation. Then, the content was cooled to room temperature and stirred under reduced pressure for 30 minutes to remove the monomer, and thus a partial hydrolyzate D was obtained.

(Synthesis Example 5) 100 g of propyltrimethoxysilane, 29.3 g of methanol, 8.1 g of water and 0.12 g of 1N hydrochloric acid were heated at a liquid temperature of 65 ° C. for 2 hours and then heated at 100 ° C. and 150 ° C. Distilled by heating at ℃. Then, the content was cooled to room temperature and stirred under reduced pressure for 30 minutes to remove the monomer, and thus a partial hydrolyzate E was obtained.

Synthesis Example 6 Tetramethoxysilane 10 g, methyltrimethoxysilane 90 g, methanol 29.0 g, water 8.0 g, 1N hydrochloric acid 0.1
2 grams are heated at a liquid temperature of 65 ° C. for 2 hours and then 100
Distilled by heating at ℃, 150 ℃. After that, the content was cooled to room temperature and stirred under reduced pressure for 30 minutes to remove the monomer to obtain a partial hydrolyzate F.

Example 1 61.5 g of ethanol was mixed with 31.5 g of the partial hydrolyzate A obtained in Synthesis Example 1 above, and the mixture was stirred at room temperature and uniformly dissolved. 6.9 g of water and 0.32 g of maleic acid (pKa = 1.92)
Was added in this order, and the mixture was further stirred until maleic acid was dissolved to obtain a composition of a silica-based coating film forming coating liquid. This solution did not gel even when left at 23 ° C. for 100 days. After soaking the glass in this composition, the glass is pulled up at 300 mm / min at 23 ° C. and 55% relative humidity.
After evaporating the solvent for 2 minutes in a hot air oven at 20 ° C,
Further, it was heated and cured at 450 ° C. for 30 minutes in a hot air oven. The film was transparent and no cracks were found. The characteristics of the obtained film are shown in Table 2.

(Example 2) A composition was obtained according to Table 2 in the same manner as in Example 1 except that the partial hydrolyzate B was used, and a film was formed and cured by heating. The film was transparent and no cracks were found. The characteristics of the obtained film are shown in Table 2.

(Example 3) A composition was obtained according to Table 2 in the same manner as in Example 1 except that the partial hydrolyzate C was used, and a film was formed and heat-cured. The film was transparent and no cracks were found. The characteristics of the obtained film are shown in Table 2.

(Example 4) A composition was prepared according to Table 2 in the same manner as in Example 1 except that acetic acid was used instead of malein, and a film was formed and heat-cured. The film was transparent and no cracks were found. The characteristics of the obtained film are shown in Table 2.

(Comparative Example 1) In Example 1, when the partial hydrolyzate D was used instead of the partial hydrolyzate A, it solidified 9 days after the preparation of the solution and a film could not be formed. (Comparative Example 2) In Example 1, a partial hydrolyzate E was used in place of the partial hydrolyzate A to prepare a composition. The film was transparent and no cracks were found. The characteristics of the obtained film are shown in Table 2.

Comparative Example 3 36.2 g of the partial hydrolyzate A was dissolved in 66.5 g of ethanol, and 0.3 g of maleic acid was added without adding water to obtain a composition. A film was formed in the same manner as in Example 1. The thickness of the film was low and uneven. The characteristics of the obtained film are shown in Table 2.

Comparative Example 4 A liquid was prepared under the same conditions as in Example 1 except that the same amount of hydrazine (pKa = 7.97) was used instead of maleic acid in Example 1, and after mixing four components, 1
Over time, the composition thickened and became cloudy. As a result, a transparent film having a uniform thickness could not be obtained. (Comparative Example 5) In Example 1, a solution was prepared by using the partial hydrolyzate F instead of the partial hydrolyzate A to prepare a composition. The film was transparent and no cracks were found. The characteristics of the obtained film are shown in Table 2.

[0023]

[Table 1]

[0024]

[Table 2]

(1) The pencil hardness was based on JIS K5651. (2) Regarding the contact angle with water, the contact angle of a water drop obtained by gently adhering a water ball having a diameter of 20 mm to a sample formed on glass was measured with a microscope. Repeated three times, the average value was used as a representative value. As is clear from the table, by using the composition of the present invention, by further using it, it is possible to obtain a silica coating which is transparent, has no cracks, has a high surface hardness, and has a water contact angle of 30 ° or less.

[0026]

According to the present invention, a silica coating which has good storage stability as a coating solution and is transparent, has no cracks, has a high surface hardness, and has a water contact angle of 30 ° or less can be obtained by using the same. can get.

Claims (6)

[Claims] 1. A hydrophilic silica-based coating film-forming composition containing a partial hydrolyzate of a tetraalkoxysilane and an alkyltrialkoxysilane having an alkyl group directly bonded to a silicon atom and having 2 or more carbon atoms. 2. The silica film-forming composition according to claim 1, wherein the tetraalkoxysilane is tetramethoxysilane. 3. The alkyltrialkoxysilane having an alkyl group has a carbon number of 2 or more 6 directly bonded to a silicon atom.
The silica-based film-forming composition according to claim 1 or 2, which is as follows. 4. A. Partial hydrolyzate of tetramethoxysilane and alkyltrimethoxysilane B. Aliphatic monohydric alcohol C.I. Water D. A hydrophilic silica-based film-forming composition having an organic carboxylic acid having a pKa of more than 1.0 and 5.0 or less as an essential component and having a contact angle with water of 30 ° or less. 5. A method for producing a hydrophilic silica-based coating, which comprises heat-treating the composition for forming a silica-based coating according to claim 1 at a temperature of 300 ° C. or higher after coating. 6. A hydrophilic silica-based coating having a contact angle with water of 30 ° or less, which is obtained by coating the composition for forming a silica-based coating according to any one of claims 1 to 4.