JP2801660B2 - Method for producing coating liquid for forming silica-based coating - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a coating solution for forming a silica-based film, and more particularly, to a method having no defects such as pinholes and cracks, excellent mechanical strength and chemical resistance. The present invention relates to a method for producing a coating liquid for forming a silica-based film having excellent moisture resistance and insulation properties.

Technical background of the invention Silica-based coatings are formed on various substrates such as glass, plastic, ceramic or metal, and are used as a protective film for protecting the substrate from corrosion or an insulating film formed on a semiconductor substrate. Can be

Conventional methods for forming these silica-based coatings include a vapor-phase method such as a vapor deposition method, a CVD method, and a sputtering method, or a method for forming a silica-based coating by applying a coating liquid for forming a silica-based coating to a substrate and heating and baking the coating. There is a coating method to form. Among them, the coating method is easier to perform the film formation than the gas phase method,
There are advantages such as no restriction on the size of the substrate.

By the way, as a coating solution for forming a conventional silica-based film, an alkoxysilane solution such as tetraalkoxysilane or trialkoxysilane is dissolved in an organic solvent such as alcohol, ketone or ester to prepare an alkoxysilane solution. And an alkali catalyst or an acid catalyst are added, and the alkoxysilane is partially hydrolyzed in an organic solvent to produce a condensation polymerized product of the partially hydrolyzed alkoxysilane.

However, when the coating liquid for forming a silica-based coating obtained in this manner is applied to a substrate, dried and fired to form a coating, organic residues such as alkyl groups of alkoxysilane remaining in the coating immediately after application are obtained. The radicals decompose during firing, resulting in pinholes or voids in the coating [organic residues decomposing, imperfect Si-O-Si bonds, structural defects or pores]. However, there was a problem that a dense film could not be formed, and a silica-based film still not satisfactory in chemical resistance and the like could not be obtained. In addition, such voids easily adsorb moisture in the air, and thus, when used as, for example, an insulating film, there is a problem that the insulating property is reduced.

For this reason, it is possible to form a silica-based coating that is dense and has excellent mechanical strength, chemical resistance, moisture resistance, and insulating properties without generating pinholes or voids. The emergence of a coating solution for forming a system coating is desired.

Object of the Invention The present invention has been completed in view of the prior art as described above, does not generate pinholes or voids, is dense, mechanical strength, chemical resistance,
An object of the present invention is to provide a method for producing a coating liquid for forming a silica-based film, which is excellent in moisture resistance, insulation properties and the like and can form a silica-based film having a low relative dielectric constant.

SUMMARY OF THE INVENTION A method for producing a coating solution for forming a silica-based film containing a condensation polymerized product of an alkoxysilane partial hydrolyzate according to the present invention is represented by the general formula: R ¹ _n Si (OR ² ) _4-n (wherein R ¹ Is a hydrocarbon group, R ² is an alkyl group having 1 to 4 carbon atoms, and n is 0 to 3), in the presence of an organic solvent, water and an alkali catalyst. Then, the obtained partially hydrolyzed liquid is further partially hydrolyzed in the presence of water and an acid catalyst.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, a method for producing a coating solution for forming a silica-based film according to the present invention will be specifically described.

The alkoxysilane used in the present invention has a general formula R ¹ _n Si (OR ² ) _4-n (wherein R ¹ is a hydrocarbon group, R ² is an alkyl group having 1 to 4 carbon atoms, Is 0 to 3).

Specific examples of the hydrocarbon group for R ¹ include a methyl group, an ethyl group, and a vinyl group.

As such an alkoxysilane, specifically,
Tetramethoxysilane, tetraethoxysilane, monomethyltrimethoxysilane, monomethyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, monoethyltrimethoxysilane, monoethyltriethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, vinyltriethoxysilane Methoxysilane, vinyltriethoxysilane and the like are used.

These alkoxysilanes are used alone or in combination.

As the organic solvent for dissolving the alkoxysilane as described above, specifically, methanol, ethanol,
Alcohols such as propanol and butanol, ethylene glycol ethers such as methyl cellosolve and ethyl cellosolve, glycols such as ethylene glycol and propylene glycol, and esters such as methyl acetate, ethyl acetate and methyl lactate are used.

These organic solvents are used alone or as a mixture.

As the alkali catalyst, specifically, a compound exhibiting alkalinity in an aqueous solution such as ammonia, an amine, a metal hydroxide such as sodium hydroxide, potassium hydroxide or calcium hydroxide is used.

In the present invention, first, the above alkoxysilane is partially hydrolyzed in the presence of an organic solvent, water and an alkali catalyst.

Here alkoxysilane in the reaction mixture, as SiO ₂ 3 to 25 wt% preferably is preferably used in an amount of 5 to 20 wt%.

Water is added in an amount of 0.1 to 1 mol of Si-OR group of alkoxysilane.
It is used in an amount of 1-2 mol, preferably 0.5-1 mol. The amount of water is 0.1 mol per mol of Si-OR group of alkoxysilane.
When the amount is less than 2 moles, the hydrolysis of the alkoxysilane tends to be insufficient. On the other hand, when the amount exceeds 2 moles, the hydrolysis rate of the alkoxysilane becomes too fast, and it is difficult to control the degree of condensation polymerization of the alkoxysilane. Tend to occur.

The alkali catalyst is desirably used in such an amount that the pH of the reaction mixture is from 6 to 12, preferably from 7 to 10. The higher the pH of the reaction mixture, the faster the hydrolysis rate of the alkoxysilane, the smaller the amount of water added, and the lower the partial hydrolysis rate.

The partial hydrolysis reaction of alkoxysilane is performed at 10 to 100 ° C.
Preferably, the reaction is carried out at a temperature of 20 to 60 ° C. The above reaction time varies greatly depending on the reaction temperature, but is usually about 0.5 to 5 hours, preferably about 1 to 3 hours.

When a partial hydrolysis reaction of alkoxysilane is performed in the presence of an alkali catalyst as described above, the alkoxysilane is partially hydrolyzed to generate a condensation polymer of the partially hydrolyzed alkoxysilane. The molecular weight (weight average molecular weight in terms of polystyrene) of this polycondensate is preferably from 100 to 5,000, more preferably from 500 to 2,000.

If the molecular weight of the polycondensate of the alkoxysilane partial hydrolyzate generated at this time is less than 100, organic residues (eg, OR groups) remain in the silica-based coating finally obtained,
A dense coating tends not to be formed, while if it exceeds 5,000, the silica-based coating finally obtained tends to be porous.

In the present invention, the reaction mixture obtained by partially hydrolyzing alkoxysilane in the presence of an organic solvent, water and an alkali catalyst as described above is added with an acid catalyst, and the remaining alkoxysilane is partially removed. Perform hydrolysis.

Specific examples of the acid catalyst include inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid, and organic acids such as acetic acid and oxalic acid.

The acid catalyst is used when the pH of the reaction mixture is 0-6, preferably 1-5.
It is used in such an amount that

Since the partial hydrolysis reaction of the alkoxysilane becomes faster as the pH becomes lower, it is preferable to appropriately control the pH of the reaction system, the amount of water, and the partial hydrolysis temperature.

When the alkoxysilane is partially hydrolyzed in the presence of an acid catalyst as described above, water may be added to the reaction mixture as needed, or new alkoxysilane may be added.

The partial hydrolysis reaction of alkoxysilane with an acid catalyst is desirably performed at a temperature of 10 to 100 ° C, preferably 20 to 60 ° C. The above reaction time varies greatly depending on the reaction temperature, but is usually 0.5 to 5 hours, preferably 1 to 3 hours.
About an hour.

In this way, the alkoxysilane is partially hydrolyzed in the presence of an alkali catalyst, and then the alkoxysilane is partially hydrolyzed in the presence of an acid catalyst to form a silica-based coating containing a condensation polymer of the alkoxysilane partially hydrolyzed product. A coating solution is obtained. This coating solution is applied on a substrate, dried and fired to form a film on the substrate. The molecular weight of the condensation polymerization product of the alkoxysilane partial hydrolyzate is usually 100 to 10,000, preferably 500 to 5,000. In order to apply the coating liquid on the substrate,
Conventional methods such as spraying, spin coating, dip coating, roll coating, screen printing, and transfer printing can be employed.

The above firing temperature is usually 300 to 900 ° C., preferably 450 to 8
It is about 00 ° C.

The silica-based coating formed using the coating solution for forming a silica-based coating according to the present invention as described above is free from defects such as pinholes and cracks, is dense, has excellent mechanical strength, and has chemical resistance. Also excellent in moisture resistance and insulation. In the present invention, a dense silica-based coating as described above can be obtained by partially hydrolyzing alkoxysilane in the presence of an alkali catalyst and then an acid catalyst, thereby obtaining a coating liquid having a low content of organic residues, It is considered that, when the coating is baked with the coating solution, generation of voids caused by decomposition of these residues is suppressed.

The thickness of the silica-based coating formed in the present invention, various thickness of the coating is formed depending on the purpose, a relatively thick coating, for example, if a silica-based coating having a thickness of 5000 Å or more is required As the alkoxysilane, it is preferable to use a mixture of a tetraalkoxysilane and a trialkoxysilane such as monomethyltrimethoxysilane or a dialkoxysilane such as dimethyldimethoxysilane. In order to obtain a silica-based coating having a thickness of less than 5000 °, it is preferable to use a tetraalkoxysilane such as tetramethoxysilane or tetraethoxysilane as the alkoxysilane.

Tetraalkoxysilane and trialkoxysilane or dialkoxysilane may be mixed and used from the beginning, and for example, the partial hydrolysis step using an alkali catalyst is performed using only tetraalkoxysilane,
In the partial hydrolysis step using an acid catalyst, trialkoxysilane or dialkoxysilane may be added.

The mixing ratio of tetraalkoxysilane and trialkoxysilane or dialkoxysilane is 0.5 to 4.5: 5 to 9: 0 to 2 (weight ratio as SiO ₂ ) of tetraalkoxysilane: trialkoxysilane: dialkoxysilane. Desirably.

When the amount of tetraalkoxysilane is increased, the resulting silica-based coating is excellent in heat resistance and moisture resistance, but when a silica-based coating having a large film thickness is formed, cracks tend to occur easily. When the amount of silane or dialkoxysilane increases, the resulting silica-based coating tends to have poor heat resistance and moisture resistance.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Example 1 357 g of tetraethoxysilane (ethyl silicate-28, manufactured by Tama Chemical Industries, tetraethoxysilane concentration in terms of SiO _{2 of} 28% by weight), 120 g of water, and 523 g of IPA were mixed and stirred, and then 1% NH ₃ water was added. It was adjusted to pH 8 by addition. The obtained mixture was kept at 50 ° C. for 1 hour to partially hydrolyze tetraethoxysilane. The polycondensate of the partially hydrolyzed alkoxysilane obtained after the partial hydrolysis had a molecular weight of 800 in terms of polystyrene.

Next, concentrated nitric acid was added to the reaction mixture to adjust the pH to 2, and the mixture was maintained at 30 ° C. for 12 hours to further partially hydrolyze tetraethoxysilane to prepare a coating solution for forming a silica-based film. The molecular weight of the polycondensation product of the partially hydrolyzed tetraethoxysilane in this coating solution was 2,000.

Example 2 250 g of tetraethoxysilane (ethyl silicate-40, manufactured by Tama Chemical Industries, concentration of tetraethoxysilane in terms of SiO _{2 of} 40% by weight), 60 g of water and 690 g of ethyl cellosolve were mixed and stirred, and 1% monoethanolamine was added. To pH 9
Was adjusted. The obtained mixture was kept at 50 ° C. for 2 hours to partially hydrolyze tetraethoxysilane. The polycondensation product of the partially hydrolyzed alkoxysilane obtained after the partial hydrolysis had a molecular weight of 500.

Subsequently, concentrated hydrochloric acid was added to the reaction mixture to adjust the pH to 1, and the mixture was kept at 50 ° C. for 2 hours to further partially hydrolyze tetraethoxysilane to prepare a coating solution for forming a silica-based film. The molecular weight of the polycondensation product of the partially hydrolyzed tetraethoxysilane in this coating solution was 2,500.

Example 3 98 g of tetramethoxysilane (methyl silicate-51, manufactured by Tama Chemical Industry, tetramethoxysilane concentration in terms of SiO _{2 of} 51% by weight), 90 g of water and 812 g of propylene glycol monopropyl ether were mixed and stirred, and triethanolamine was added. Was added to adjust to pH7. Bring the resulting mixture to 50 ° C for 3
After holding for 0 minutes, partial hydrolysis of tetramethoxysilane was performed. The condensation-polymerized product of the partially hydrolyzed alkoxysilane obtained after the partial hydrolysis had a molecular weight of 2,000.

Next, phosphoric acid was added to the reaction mixture to adjust the pH to 2, and the mixture was maintained at 30 ° C. for 1 hour to further partially hydrolyze tetramethoxysilane to prepare a coating solution for forming a silica-based film. The molecular weight of the polycondensation product of the partially hydrolyzed tetramethoxysilane in this coating solution was 3,200.

Example 4 118 g of methyl silicate-51 used in Example 3 and water 7
2 g and 556 g of ethyl cellosolve are mixed and stirred, and 0.1% N
And adjusted to pH7 by the addition of H ₃ water. The obtained mixture is kept at 50 ° C
For 1 hour to partially hydrolyze tetramethoxysilane. The polycondensation product of the partially hydrolyzed alkoxysilane obtained after the partial hydrolysis had a molecular weight of 1200.

Next, acetic acid was added to the reaction mixture to adjust the pH to 4, and then 30 g of dimethyldimethoxysilane, 170 g of methyltrimethoxysilane, and 54 g of water were added with stirring, and then added.
The mixture was kept at 0 ° C. for 3 hours to further partially hydrolyze the alkoxysilane to prepare a coating solution for forming a silica-based film. The molecular weight of the polycondensate of the partially hydrolyzed alkoxysilane in this coating solution was 2,200.

Example 5 118 g of methyl silicate-51 used in Example 3 and water 7
2 g and propylene glycol monopropyl ether 491 g
Were mixed and stirred, and adjusted to pH 7 by adding 0.1% NH ₃ water. The obtained mixture was kept at 50 ° C. for 1 hour to partially hydrolyze tetramethoxysilane. The polycondensation product of the partially hydrolyzed alkoxysilane obtained after the partial hydrolysis had a molecular weight of 1,000.

Next, acetic acid was added to the reaction mixture to adjust the pH to 5, then 205 g of methyltrimethoxysilane and 54 g of water were added with stirring, and the mixture was kept at 50 ° C. for 1 hour to further partially hydrolyze the alkoxysilane. Then, a coating solution for forming a silica-based film was prepared. The molecular weight of the condensation polymerized product of the partially hydrolyzed alkoxysilane in this coating solution was 2,800.

Comparative Example 1 While mixing and stirring 357 g of ethyl silicate-28, 240 g of water, and 403 g of ethanol, concentrated nitric acid was added thereto to adjust the pH to 1.
Was adjusted. The obtained mixture was kept at 50 ° C. for 1 hour to partially hydrolyze tetriethoxysilane to prepare a coating solution for forming a silica-based film. The condensation polymerization product of the partially hydrolyzed alkoxysilane contained in this coating solution has a molecular weight of
1500.

Comparative Example 2 30 g of dimethyldimethoxysilane, 170 g of methyltrimethoxysilane, 118 g of methylsilicate-51 and 126 g of water
After stirring and mixing with g, acetic acid was added to adjust the pH to 4, and then the mixture was kept at 50 ° C. for 10 hours to partially hydrolyze the alkoxysilane to prepare a coating solution for forming a silica-based film. The polycondensation product of the alkoxysilane partial hydrolyzate contained in this coating solution had a molecular weight of 2,200.

The coating solutions obtained in the above Examples and Comparative Examples were applied to a glass substrate by a spin coating method, dried at 150 ° C. for 10 minutes, and baked in air at 350 ° C. for 30 minutes. The thicknesses of the obtained coatings were determined in Examples (1) to (3) and Comparative Example (1).
In Example (4), (5) and Comparative Example (2), it was 5,000.

 The obtained coating was evaluated for the following items.

(1) Crack: The film surface was visually observed.

(2) Boiling resistance: Observation of peeling of the film after immersion in boiling water for 1 hour.

(3) Alkali resistance: Observation of peeling of the film after immersion in a 5% NaOH aqueous solution at 50 ° C. for 10 minutes.

(4) Pencil hardness: according to JIS K-5400.

(5) Refractive index: by ellipsometer.

 The results are shown in Table 1.

From Table 1, the film formed using the coating solution of the present invention is excellent in moisture resistance by boiling resistance evaluation, chemical resistance by alkali resistance evaluation, and using a coating solution only with tetraalkoxysilane. (Example 1)
As can be seen from the fact that the refractive indexes of (3) to (3) are higher than that of the coating of Comparative Example 1, it is understood that there is almost no pinhole and a dense coating is formed.

In addition, the relative dielectric constant of the film using a conventional coating solution (comparative example)
It turns out that it is low compared with.

Claims (1)

(57) [Claims] A compound represented by the general formula: R ¹ _n Si (OR ² ) _{4 -n} (wherein R ¹ is a hydrocarbon group, R ² is an alkyl group having 1 to 4 carbon atoms, and n is 0 to 3) Is partially hydrolyzed in the presence of an organic solvent, water and an alkali catalyst, and then the obtained partially hydrolyzed solution is subjected to the hydrolysis in the presence of water and an acid catalyst. A method for producing a coating liquid for forming a silica-based film, comprising a condensation polymerized product of an alkoxysilane partially hydrolyzed product.