JP2880195B2 - 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 capable of 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

Conventionally, as a method for forming these silica-based coatings, a vapor-phase method such as a vapor deposition method, a CVD method, and a sputtering method, or a coating liquid for forming a silica-based coating is applied to a substrate, and heated and fired to form a silica-based coating. Forming coating methods are known. Among them, the coating method has advantages that the operation of forming a film is simpler than the vapor phase method, and there is no restriction on the size of the base material used.

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 partially adding an alkali or an acid to partially hydrolyze the alkoxysilane 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). It is characterized in that it is partially hydrolyzed in the presence, then the obtained partially hydrolyzed solution is brought into contact with an alkali, and the obtained coating solution is acidified by adding an acid.

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.

Specific examples of the acid include an inorganic acid such as hydrochloric acid, nitric acid, and sulfuric acid; an organic acid such as acetic acid and oxalic acid; and a compound which is acidic in an aqueous solution such as metallic soap.

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

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 to 1 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 acid is preferably used in such an amount that the pH of the reaction mixture is between 0 and 6, preferably between 2 and 4. The lower 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 is extremely fast at high temperature and low pH, but is usually performed within 5 hours, preferably within 3 hours.

When the alkoxysilane is partially hydrolyzed in the presence of an acid as described above, the alkoxysilane is partially hydrolyzed to produce a condensation polymerized product of the partially hydrolyzed alkoxysilane. The molecular weight (polystyrene-equivalent weight average molecular weight) of this polycondensate is 100 to 5,000, preferably 500 to 2,000.
It is preferably 00.

If the molecular weight of the polycondensate of the alkoxysilane partial hydrolyzate generated at this time is less than 100, organic residues (for example, 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 the alkoxysilane in the presence of an organic solvent, water and an acid as described above is then contacted with an alkali. At this time, water may be added to the reaction mixture as needed, or new alkoxysilane may be added.

When the reaction mixture obtained by partial hydrolysis as described above is brought into contact with an alkali, partial hydrolysis of the remaining alkoxysilane, partial hydrolysis of new alkoxysilane added as necessary, It is considered that the conversion of OH groups and OR groups remaining in the polycondensate obtained in the above into siloxane bonds, acceleration of the polycondensation reaction and the like proceed.

As the alkali, specifically, ammonia, amine,
A compound exhibiting alkalinity in an aqueous solution, such as an alkali metal hydroxide, a quaternary ammonium compound, or an amine-based coupling agent, is used in an amount such that the pH of the reaction mixture is 6 to 11, preferably 6 to 9. Can be

Contact with alkali, 10 ~ 100 ℃, preferably 20 ~ 60 ℃
It is desirable to carry out at a temperature of Although the contact time varies greatly depending on the contact temperature, it is usually 0.5 to 5 times.
The time is preferably about 1 to 3 hours.

When the alkoxysilane is partially hydrolyzed in the presence of an acid in this manner and then brought into contact with an alkali, a coating solution for forming a silica-based film containing a condensation polymer of the alkoxysilane partially hydrolyzed product is obtained. The liquid usually shows alkaline. Then, when the coating liquid is added again with acid to make the coating liquid acidic, preferably at pH 6 or lower, the pot life of the coating liquid is improved, and longer-term storage becomes possible.

The coating solution for forming a silica-based film obtained as described above is applied to a substrate, and then 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, a general method such as a spray method, a spin coating method, a dip coating method, a roll coating method, a screen printing method, and a transfer printing method 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 is obtained because the alkoxysilane is partially hydrolyzed in the presence of an acid and then contacted with an alkali to obtain a coating solution having a low content of organic residues. It is considered that when baking the coating film with this 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, a trialkoxysilane alone such as monomethyltrimethoxysilane, or a mixture of a tetraalkoxysilane and a trialkoxysilane such as monomethyltrimethoxysilane or a dialkoxysilane such as dimethyldimethoxysilane,
Alternatively, it is preferable to use a mixture of tetraalkoxysilane, trialkoxysilane, and dialkoxysilane. 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.

The tetraalkoxysilane and the trialkoxysilane or dialkoxysilane may be mixed and used from the beginning. For example, the partial hydrolysis step using an acid is performed using only the tetraalkoxysilane, and upon contact with an alkali, Alkoxysilane 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.

Reference Example 1 357 g of tetraethoxysilane (ethyl silicate-28, manufactured by Tama Chemical Industry, 28% by weight of tetraethoxysilane in terms of SiO ₂ ), 120 g of water, and 523 g of IPA were mixed and stirred, and then concentrated nitric acid was added. Adjusted to pH1. 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 in terms of polystyrene of 1500.

Then add 1% aqueous ammonia to the reaction mixture
After the pH was adjusted to 6, it was kept at 30 ° C. for 12 hours to prepare a coating solution for forming a silica-based film.

The molecular weight of the alkoxysilane partially hydrolyzed polycondensate in this coating solution was 4,200.

Example 1 250 g of tetraethoxysilane (ethyl silicate-40, manufactured by Tama Chemical Industries, tetraethoxysilane concentration in terms of SiO _{2 of} 40% by weight), 60 g of water and 690 g of ethyl cellosolve were mixed and stirred, and concentrated hydrochloric acid was added. Adjusted to pH2. The obtained mixture was kept at 50 ° C. for 2 hours to partially hydrolyze tetraethoxysilane. The condensation polymerization product of the alkoxysilane partial hydrolyzate obtained after the partial hydrolysis has a molecular weight of
1000.

Next, 1% monoethanolamine was added to the reaction mixture [I] to adjust the pH to 7, and the mixture was kept at 50 ° C. for 2 hours. Concentrated hydrochloric acid is added again to the liquid thus obtained,
The pH was adjusted to 4, and a coating solution for forming a silica-based film was prepared. The molecular weight of the alkoxysilane partially hydrolyzed polycondensate in this coating solution was 3,800.

Reference Example 2 98 g of tetraethoxysilane (methyl silicate-51, manufactured by Tama Chemical Industries, 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 tin octylate was mixed. (TN-12 manufactured by Sakai Chemical Industry Co., Ltd.) was added to adjust the pH to 3. The obtained mixture was kept at 50 ° C. for 30 minutes to partially hydrolyze tetramethoxysilane. The polycondensate of the partially hydrolyzed alkoxysilane obtained after the partial hydrolysis had a molecular weight of 800.

Next, 1% triethanolamine was added to the reaction mixture to adjust the pH to 7, and then kept at 30 ° C. for 1 hour to prepare a coating solution for forming a silica-based film. The molecular weight of the alkoxysilane partially hydrolyzed polycondensate in this coating solution was 2,600.

Reference Example 3 118 g of methyl silicate-51 used in Reference Example 2 and water 7
2 g and 556 g of ethyl cellosolve were mixed and stirred, and the pH was adjusted to 1 by adding concentrated nitric acid. Bring the resulting mixture to 50 ° C for 1
After a certain time, partial hydrolysis of tetramethoxysilane was performed. The polycondensation product of the partially hydrolyzed alkoxysilane obtained after the partial hydrolysis had a molecular weight of 1200.

Then add 1% aqueous ammonia to the reaction mixture
After adjusting the pH to 6, 30 g of dimethyldimethoxysilane, 170 g of methyltrimethoxysilane, and 54 g of water were added with stirring, and kept at 50 ° C. for 3 hours to prepare a coating solution for forming a silica-based film. The molecular weight of the alkoxysilane partially hydrolyzed polycondensate in this coating solution was 4,000.

Reference Example 4 Methyl silicate-51 used in Reference Example 2 118 g and water 72 g
And 491 g of propylene glycol monopropyl ether were mixed and stirred, and concentrated nitric acid was added to adjust to pH2. 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, 1% monoethanolamine was added to the reaction mixture to adjust the pH to 7, and then methyltrimethoxysilane 2 was added.
05 g and 54 g of water were added with stirring, and kept at 50 ° C. for 1 hour to prepare a coating solution for forming a silica-based film. The molecular weight of the alkoxysilane partially hydrolyzed polycondensate in this coating solution was 3,000.

Example 2 In Example 1, instead of adding 1% monoethanolamine to the reaction mixture [I], 10 g of an anion exchange resin (DIAION-SA10A manufactured by Mitsubishi Kasei) was added to the reaction mixture [I], and the mixture was adjusted to pH7. After adjusting and then removing the ion exchange resin
Example 1 was repeated except that the solution was kept at 0 ° C. for 2 hours, and concentrated hydrochloric acid was again added to the solution to prepare a coating solution for forming a silica-based film having a pH of 4.
Same as. The molecular weight of the alkoxysilane partially hydrolyzed polycondensate in this coating solution was 3,900.

Example 3, Reference Example 5 In order to compare the pot lives of the coating solutions obtained in Examples 1 and 2 and Reference Examples 1 to 4, the viscosities of each coating solution were measured immediately after preparation and after storage for one month.

The storage was placed in a thermostat at 25 ° C. Viscosity is 25
It is a value at ° C. Table 1 shows the results.

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 to adjust the pH to 1.
Was adjusted. The obtained mixture was kept at 50 ° C. for 1 hour to partially hydrolyze tetraethoxysilane 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
Was mixed and stirred, 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 film thickness of the obtained coating was 2,000 ° in Example (1), Reference Examples (1) and (2) and Comparative Example (1), and was 2,000 ° in Reference Example (3).
(4) and Comparative Example (2) and Comparative Example (2)
It was 0Å.

 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.

 Table 2 shows the results.

From Table 2, 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 by using a coating solution only with tetraalkoxysilane. As can be seen from the fact that the refractive index of the formed film (Example 1 and Reference Examples 1 and 2) is higher than the film of Comparative Example 1, there is almost no pinhole and a dense film is formed. I understand.

In addition, the dielectric constant is the same as that of the conventional coating liquid (comparative example).
It turns out that it is low compared with.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C09D 183/04 C09D 183/02

Claims (1)

(57) [Claims] 1. A compound of 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 acid, and the obtained partially hydrolyzed solution is contacted with an alkali to obtain A method for producing a coating liquid for forming a silica-based film, comprising a condensation polymerized product of an alkoxysilane partial hydrolyzate, wherein the coating liquid is acidified by adding an acid.