Process for the production of articles covered with...

Details Process for the production of articles covered with... Process for the production of articles covered with...

1999-07-26

2002-10-15

Dawson, Robert (Department: 1712)

Stock material or miscellaneous articles

Composite

Of silicon containing

C428S446000, C428S447000, C428S428000, C428S429000, C427S387000, C427S164000, C427S165000, C106S287160

Reexamination Certificate

active

06465108

ABSTRACT:

TECHNICAL FIELD
The present invention related to a method for producing an article comprising a substrate such as ceramics, plastics, metals or the like supporting thereon a silica-based film coated article, a silica-based film-coated article, a liquid composition for silica-based film coating, a method for producing an article comprising the silica-based film supporting thereon a functional film coated, and a functional film-coated article.
BACKGROUND ART
There are known various technologies in which a silica primer film or other oxide primer films are provided between a substrate and a functional film in forming a functional film on the surface of the substrate such as glass or other material, for the purpose of improving bonding strength between the substrate and the functional film, and preventing diffusion of an alkali component and improving durability of the functional film when the substrate contains an alkali component.
As methods for providing this oxide primer film, there are known sol-gel methods (Japanese Patent Publication No. 20781 of 1992, Japanese Laid-Open Patent No.311332 of 1990), methods in which a solution prepared by dissolving chlorosilane in a non-aqueous solvent is applied (Japanese Laid-Open Patent No. 86353 of 1993, Japanese Patent No. 2525536 (Japanese Laid-Open Patent No.238781 of 1993)), CVD methods, vapor deposition methods and the like.
In these methods, the main point thereof is the increase in the number of hydroxyl groups on the surface of the primer film for improving bonding strength with the functional film. However, there have been problems in that the hydroxyl group on the surface of the primer film tends to adsorb water contained in air, if water is once adsorbed, it is difficult to remove it with any ease, so heating is necessary at about 100 to 200° C. in applying the functional film (the abovementioned Japanese Patent Publication No.20781 of 1992, Japanese Laid-Open Patent No. 311332 of 1990, Japanese Laid-Open Patent No. 238781 of 1993) or treatment for a long period of time is necessary even when heating is not necessary (the abovementioned Japanese Laid-Open Patent No. 86353 of 1993).
In the methods in which the oxide primer film is formed (the abovementioned Japanese Laid-Open Patent No. 311332 of 1990, Japanese Patent No. 2525536), strength of the primer film itself is low by only applications at normal temperatures, therefore, baking at a temperature of about 500 to 600° C. after the application is indispensable when increasing strength. Furthermore, when the substrate contains an alkali, it is necessary to form an oxide primer film having a thickness of 100 nm or more for preventing diffusion of the alkali during the baking. However, there have been problems in that when the thickness of the primer film increases, the film thickness tends to become uneven, appearance failures such as reflection unevenness and the like tend to occur, production cost increases, and the like.
Furthermore, in the method in which a solution prepared by dissolving tetrachlorosilane into a non-aqueous solvent such as perfluorocarbon, methylene chloride and hydrocarbon is applied (the abovementioned Japanese Patent No. 2525536), scratch resistance is low though a silica primer film is obtained at normal temperatures. A chlorosilyl group has extremely high reactivity, and in the case of a coating solution, it is necessary to conduct the coating under an environment containing no storage water, whereby the production cost is consequently undesirable.
An object of the present invention is to solve the abovementioned problems of the prior art and to provide a method for producing in a short period of time and with ease a silica-based film-coated article excellent as a primer film and a functional film-coated article excellent in durability without requiring treatment leading to an increase in production costs such as baking and the like.
DISCLOSURE OF INVENTION
In the present invention, a silica-based film which is durable and has an alkoxyl group on the surface is coated on the surface of a substrate by applying on the substrate an alcohol solution composed of a silicon alkoxide in low concentration and a volatile acid in high concentration and drying at a normal temperature, and a functional film is allowed to be bonded to the substrate securely by applying on this silica-based film an organosilane having a hydrolyzable group and a functional group having a specific function, for solving the abovementioned problems.
Namely, the present invention is a method for producing a silica-based film-coated article by applying on a substrate a coating liquid composed of an alcohol solution containing a silicon alkoxide and an acid, wherein said coating liquid comprises;
(A) silicon alkoxides having at least two alkoxide groups or hydrolyzates thereof (including a partial hydrolyzate), 0.010 to 3% by weight (in terms of silica)
(B) an acid 0.0010 to 1.0 normality, and
(C) water 0 to 10% by weight.
The phrase “in terms of silica,” as used herein, is understood to mean that the Si content is calculated as SiO
2
as if all the Si contained in silicon alkoxide were to be converted to SiO
2
.
The contents of the component (A) of 0.010 to 3% by weight (in terms of silica) is applicable when a silicon alkoxide and a hydrolyzate thereof are used alone, respectively, and also when they are mixed for use.
In the present invention, the silicon alkoxide used in the abovementioned coating liquid is not particularly restricted, and examples thereof include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like, and preferably, silicon alkoxides having relatively low molecular weight, for example, tetraalkoxysilanes having an alkoxyl group with 3 or less carbon atoms is used since they tend to form a compact film. Furthermore, polymers of these tetraalkoxisilanes having an average polymerization degree of 5 or less are preferably used.
As the acid catalyst used in the abovementioned coating liquid, volatile acids such as hydrochloric acid, hydrofluoric acid, nitric acid, acetic acid, formic acid, trifluoroacetic acid and the like are preferable since they vaporize and do not remain in the film by drying at normal temperatures, and among them, hydrochloric acid which has high volatility and of which handling is relatively easy is particularly preferable.
Furthermore, the alcohol solvent used in the abovementioned coating liquid is not particularly restricted, and examples thereof include methanol, ethanol, 1-propanol, 2-propanol, butyl alcohol, amyl alcohol and the like. Among them, linear saturated monohydric alcohol having 3 or less carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol and the like is preferably used since evaporation speed thereof at normal temperatures is high.
In the coating liquid composed of an alcohol solution containing a silicon alkoxide, an acid and water (including that used for dissolution of the acid, that is generated from impurities in the solvent and from the atmosphere, and the like), hydrolysis reaction represented by the following formula (1) between a silicon alkoxide and water is carried out, during preparation, during storage and after application of the liquid. In the formula, R represents an alkyl group.
(—Si—OR)+(H
2
O)→(—Si—OH)+(ROH)  (1)
The hydrolyzed silanol groups (—Si—OH) mutually cause dehydration condensation reaction as shown in the following formula (2) to form a siloxane bond (—Si—O—Si—).
(—Si—OH)+(—Si—OH)→(—Si—O—Si—)+(H
2
O)  (2)
Whether or not the coating liquid composed of an alcohol solution containing a silicon alkoxide, an acid and water, the alkoxy group in the silicon alkoxide causes hydrolysis reaction as shown in the abovementioned formula (1), or whether the hydrolyzed groups (—Si—OH) mutually cause dehydration condensation reaction as shown in the abovementioned formula (2) in the abovementioned coating liquid or more depends significantly on the acid concentration of the solution, the concentration of the silicon alkoxi

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