JPH0710956B2 - Inorganic film forming composition - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an alkali silicate-based composition for forming an inorganic film, and more particularly to a composition of several μm to 100 μm without foaming or pinholes during heat curing. The present invention relates to a film-forming composition for forming an inorganic film having a moderate film thickness.

The composition according to the present invention can be used for the purpose of forming a colored film by adding a colorant to the composition, and can also be used as a heat-resistant paint or a cosmetic paint for glass, ceramics, metals and the like.

(Prior Art) A wide variety of inorganic coating materials have been proposed as an inorganic coating material using alkali silicate as a film-forming binder, depending on the combination of the alkali silicate and a filler or curing agent.

In this type of inorganic coating, the aqueous alkali silicate solution as a binder for film formation forms a strong skin on the film surface before drying inside the film during heat curing, so if the drying speed is fast, the water content inside will cause the above skin to form. When exiting, there is a drawback that foaming and pinholes tend to occur. Therefore, these alkali silicate-based paints have taken the following measures in order to obtain a film free from bubbles and pinholes.

1) A method in which a large amount of various minerals and the like that are insoluble at room temperature in an aqueous alkali silicate solution are used as fillers and are mixed in a large amount into a coating composition. As the filler, those having an average particle size of about several μm to several tens of μm are generally used, and the lower limit of the particle size of even fine particles such as TiO ₂ is about 0.1 to 0.5 μm. There is no known filler containing colloidal ultrafine particles having a particle size of about 0.02 μm.

2) A method of making the film thickness extremely thin, for example, several μm or less.

3) A method in which heating and heating are performed extremely slowly during curing.

(Problems to be Solved by the Invention) However, the above three methods have the following problems.

First, according to the method 1), that is, a method using a large amount of filler, a film having a strong hiding power, that is, a high reflectance, and a transparent feeling cannot be obtained.

Further, in the above method 2), that is, the method of making the film thickness extremely thin, the allowable range of the coating film thickness at the time of coating is very narrow, and severe working conditions are required.

Further, the above method 3), that is, the method of slowly increasing the temperature during heating is not practical because the drying and curing takes too much time.

(Means for Solving the Problem) The present invention uses an aqueous solution containing an alkali silicate as a main component as a film-forming binder, and mixes an appropriate amount of colloidal particles insoluble at room temperature with the alkaline silicate solution to increase the amount of the filler. We have obtained the knowledge that the same effect as that of the mixture can be obtained, and that a very smooth film with a film thickness of several μm to 100 μm can be formed without foaming and pinholes during the heating effect. It was done.

That is, the present invention relates to 100 parts of alkali silicate represented by the general formula R ₂ O · nSiO ₂ (R is an alkali metal, n is a number of 0.5 or more), colloid particles 5 insoluble in an alkali silicate aqueous solution at room temperature.
An inorganic film-forming composition comprising 50 parts and a curing agent.

In the present specification, all parts expressing ratios are on a weight basis.

Examples of the alkali silicate include commercially available liquid products such as water glass Nos. 1, 2, and 3, a calcium silicate solution, and a lithium silicate solution. These alkali silicates may be used alone or in combination of two or more.

As colloidal particles insoluble in an aqueous solution of alkali silicate at room temperature, colloidal alumina (Aluminum Oxide C manufactured by Degussa) prepared by thermally decomposing a compound such as aluminum chloride in a gas phase, or dried alumina sol. Things can be used. However, colloidal silica (aerosil or the like), which is a typical colloidal particle, is gradually dissolved when mixed with an aqueous alkali silicate solution, and therefore foaming and pinhole formation during heat curing cannot be suppressed.
The preferred average particle size of the colloidal particles is 0.001 to 0.06 μm.

Also, while the refractive index of alkali silicate is 1.49 to 1.54, the refractive index of colloidal alumina is 1.67, and although the difference in refractive index between the two is very large, the average particle diameter of colloid particles is 0.02 μm. And the wavelength of visible light (0.4 to 0.7 μm)
Since it is sufficiently smaller than that of, the light penetrates the particles due to the phenomenon of light diffraction, and a transparent film is formed.

Regarding the composition ratio of the components of the composition, alkali silicate 100
If the amount of colloidal particles is less than 5 parts per part, foaming or pinholes tend to occur during drying and curing.
If it is more than the amount, the film forming ability of the composition will be weakened and the strength and durability of the cured film will be reduced. Therefore, colloidal particles are limited to the range of 5 to 50 parts with respect to 100 parts of alkali silicate. A particularly preferable mixing ratio is in the range of 10 to 40 parts of colloidal particles to 100 parts of alkali silicate.

As the curing agent, one or a combination of two or more known curing agents such as various phosphates, colloidal silica, silicofluoride, and multi-metal oxides can be used. By properly selecting the type and amount of curing agent, water resistance,
The durability such as acid resistance and alkali resistance can be remarkably improved. The mixing ratio of the curing agent is appropriately selected within the range of 8 to 50 parts with respect to 100 parts of alkali silicate.

The film-forming composition according to the present invention is applied as a paint in the form of an aqueous solution or an aqueous dispersion on the surface of an article to be coated such as a metal product by a method such as spraying or dipping.
The ratio of water to the solid content of 100 parts by weight of this composition is 30 to 3
It is 50 parts, and the film thickness can be adjusted by increasing or decreasing the proportion of water. The applied water-based composition is usually cured by heating it at a temperature of 200 to 300 ° C. for 10 to 30 minutes to form a film having desired properties.

The composition of the present invention can be applied not only to metal products but also to coated products such as ceramic products and glass products.

(Effects of the Invention) The composition for forming a film according to the present invention is applied to the surface of a product such as glass, ceramics or metal by a spray method or a dipping method, and dried (baked), so that the composition can be very easily heated and cured. It is possible to form an inorganic film having a film thickness of about several μm to 100 μm without foaming or pinholes.

(Examples) Next, some examples of the present invention and comparative examples for showing a comparison with the examples will be given in order to demonstrate the above effects.

Example 1 No. 3 sodium silicate 40% aqueous solution 100 parts Colloidal alumina (Aluminum Oxide C manufactured by Dexa) 15
Parts Aluminum phosphate (average particle size 2 μm) 15 parts Water 110 parts The above composition was pulverized and mixed for 30 minutes by a ball mill to prepare a coating material comprising the film forming composition of the present invention. This paint is spray-coated on a glass plate and a degreased steel plate (application amount: 200 g /
m ² ), and baked and cured at 250 ° C. for 10 minutes to prepare a test piece 1.

Example 2 100 parts of No. 3 sodium silicate 20% aqueous solution was mixed with 10 parts of powdered colloidal silica, and the resulting mixture was placed in a flask equipped with a reflux device and heat-treated at 100 ° C. for 1 hour to obtain a colorless transparent modified silicic acid. An aqueous sodium solution was prepared.

The above modified sodium silicate aqueous solution 110 parts Colloidal alumina 4 parts Water 100 parts The above composition was pulverized and mixed for 30 minutes by a ball mill to prepare a coating composition comprising the composition of the present invention. This paint is spray applied to a transparent glass plate and degreased steel plate (application amount: 100 g /
m ² ), and baked and cured at 250 ° C. for 10 minutes to prepare a test piece 2.

Example 3 No. 3 40% aqueous solution of potassium silicate 100 parts Colloidal alumina 10 parts Activated zinc white 10 parts Water 70 parts The above composition was ground and mixed for 30 minutes by a ball mill to prepare a coating composition comprising the composition of the present invention. This paint is spray applied to a transparent glass plate and degreased steel plate (application amount: 80 g /
m ² ), and baked and cured at 300 ° C. for 5 minutes to prepare a test piece 3.

Comparative Example 1 No. 3 sodium silicate 40% aqueous solution 100 parts Aluminum phosphate (average particle size 2 μm) 10 parts Water 30 parts The above composition was ground and mixed in a ball mill for 30 minutes to prepare a paint. This paint was spray-coated on a glass plate and a degreased steel plate (coating amount: 100 g / m ² ), and baked and cured at 250 ° C. for 10 minutes to prepare a test piece 4.

Comparative Example 2 No. 3 40% sodium silicate aqueous solution 100 parts Colloidal silica (Aerosil) 15 parts (manufactured by Nippon Aerosil Co., Ltd.) Aluminum phosphate 20 parts Water 110 parts The above composition is ground and mixed for 30 minutes by a ball mill to prepare a coating material. did. This coating material was spray-coated on a transparent glass plate and a degreased steel plate (coating amount: 100 g / m ² ), and baked and cured at 250 ° C. for 10 minutes to prepare a test piece 5.

Comparative Example 3 No. 3 sodium silicate 40% aqueous solution 100 parts Colloidal alumina 25 parts Aluminum phosphate (average particle size 2 μm) 15 parts Water 300 parts The above composition was ground and mixed in a ball mill for 30 minutes to prepare a coating material. This coating material was spray-coated on a transparent glass plate and a degreased steel plate (coating amount: 70 g / m ² ) and baked and cured at 250 ° C. for 10 minutes to prepare a test piece 6.

Performance Test Each test piece obtained in Examples and Comparative Examples was evaluated by the following tests. However, in the film thickness measurement of 2) below, a test piece with a steel plate as a coating object was used, and in other tests, a test piece with a glass plate as a coating object was used.

1) The presence or absence of bubbles and cracks in the film appearance was evaluated by visual observation and optical microscope observation.

2) The film thickness was measured with an electromagnetic film thickness meter.

3) Adhesion was measured according to the basic test of JIS K-5400 (General paint test method). That is, 100 pieces of 1 mm square base mesh are made on the coating film of the test piece, cellophane tape is stuck on this base mesh, the tape is peeled off, the number of base meshes remaining on the test piece side is counted, and the original base mesh The adhesiveness was evaluated by the residual rate of the coating film with respect to the number.

4) The boiling water resistance was measured by immersing the test piece in boiling water for 5 hours,
After drying, changes in the film appearance were visually observed and evaluated.

5) For acid resistance, the test piece was immersed in a 10% aqueous solution of sulfuric acid at 25 ° C. for 24 hours, washed with water and dried to visually evaluate the change in the film appearance.

6) The alkali resistance was evaluated by immersing the test piece in a 10% sodium hydroxide aqueous solution at 25 ° C. for 24 hours, washing it with water and drying it, and visually observing the change in the film appearance.

The test results are summarized in the table below.

As is clear from this table, according to the film-forming composition of the present invention, it is possible to form an inorganic film having a required film thickness without bubbles, pinholes, and cracks and having excellent adhesion and durability. It is recognized that

Claims (2)

[Claims] 1. The general formula R ₂ O.nSiO ₂ (R is an alkali metal, n
Is a number of 0.5 or more) 100 parts of alkali silicate, colloidal particles 5 which are insoluble in the alkali silicate aqueous solution at room temperature
An inorganic film-forming composition comprising 50 parts and a curing agent. 2. A composition according to claim 1, wherein the colloidal particles are dry process colloidal alumina prepared by thermal decomposition of an aluminum compound.