JPS59140378A - Manufacture of protective film - Google Patents

Abstract

PURPOSE:To provide water repellency to the surface of a film by adding alkali methyl siliconate to a soln. of alkali metallic silicate to adjust the pH of the soln. to a specified value, applying the soln. to a metallic plate, baking it, and treating the resulting film with acid. CONSTITUTION:Alkali siliconate is added to a soln. of alkali metallic silicate to adjust the pH of the soln. to >=10. The soln. is applied to a metallic plate and baked at a high temp. to form a film. By treating the film with acid, all of alkali metallic ions are extracted from the film to provide water repellency to the surface of the film. Potassium silicate, sodium silicate or a mixture thereof is used as said alkali metallic silicate, and sodium siliconate, potassium siliconate or a mixture thereof is used as said alkali siliconate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for manufacturing a protective film formed on a metal plate such as an aluminum reflective mirror using an alkali metal silicate solution, and particularly to prevent dirt and moisture from adhering to the surface of the protective film. The present invention relates to a method for producing a protective coating that can be made water repellent so that it is difficult to remove and can be easily wiped off even if it adheres.

A method of forming a protective film on a metal plate such as an aluminum reflective mirror using an alkali metal silicate solution is already known and is described in detail in, for example, Japanese Patent Publication No. 30521/1983. Protective coatings produced by such methods are generally hard, glassy, adherent, transparent coatings that are also very chemically stable and resistant to attack by chemicals and contaminants. It has the great advantage of having extremely high resistance.

However, even objects with protective coatings manufactured by the method described above may corrode after long-term use, especially when used in locations where water and dust are likely to collect. It was found that there was a significant shift in the direction around 1. The reason why such a phenomenon occurs is considered to be due to the following reasons. In other words, when viewed microscopically, the surface of the protective film has small holes called "pinholes" caused by unevenness on the substrate, and microscopic cracks called "cracks" caused by foreign matter adhering to the substrate surface. Defects such as cracks are partially present. On the other hand, the surface of conventional alkali metal silicate coatings is hydrophilic for the following reasons. That is,
The chemical formula for the terminal end of an alkali metal silicate molecule is:
(-3(, -OM+) (where M is an alkali metal such as potassium or sodium)
A siloxane bond represented by 1 [: -3i-OSi] is formed, resulting in a three-dimensional structure and a hard film. However, the end of the molecule is C3i-ON)
At this time, the alkali metal M in this reacts with carbon dioxide gas in the air, causing clouding. Therefore, when the film is treated with an acid such as nitric acid to extract the alkali metals in the film, the end of the molecule, that is, the surface layer, is C-8i-OH:l.
1, the hydrophilic group (-0T()) faces outward, and the film becomes hydrophilic as a whole. Therefore, when water adheres to the surface of the protective film, the entire film is covered with water. As a result, the aforementioned defective areas of the film are also subject to water infiltration, and the water is difficult to run off due to its hydrophilic nature.In such a state, if dust or scum adheres to the film along with the water, a chemical reaction may occur. This causes corrosion to occur from the defective parts of the film, developing into pitting corrosion. Hydroxides of aluminum, etc., generated from this pitting corrosion part (d) firmly adhere to the hydrophilic film and are easily wiped off. It cannot be removed and the surface appearance of the metal plate is significantly contaminated.

To solve this problem, either apply a water-repellent protective film to the surface of the film to prevent water from adhering to it, which can cause corrosion, or thicken the film in areas where pinholes or cracks occur. By doing so, it is possible to prevent contact between water and the substrate. A common method of the former is to apply a water-repellent resin, such as silicone oil or varnish, to the surface of the completed protective coating. However, according to this method, the adhesion of the water-repellent film is poor, the durability is low, and the light transmittance is also low, so there is a major drawback that the reflectance decreases when applied to a front surface, etc. A common method for the latter method is to coat the same type of protective film three to five times, but this method reduces the reflectance due to clouding of the film and cracks in the film due to thermal shock. The disadvantage is that it does not occur.

The present invention was made in view of the above points, and has greater water repellency than conventional alkali metal silicate coatings,
It is an object of the present invention to provide a method for producing a protective coating having excellent properties such that the degree of corrosion is extremely low and even if corrosion products adhere, they can be easily wiped off.

In order to achieve this objective, the inventors conducted various experiments and conducted a certain treatment using a mixture of water-soluble silicone, especially alkali methyl siliconate, in an alkali metal silicate solution. The alkali methyl siliconate mentioned above is sold under the trade name Dry Seal Ej by Toray Silicon Co., Ltd. It is used to prevent cracks caused by frost damage by coating on the surface of water, or to make sake bottles, insulation materials, etc. water repellent by adding it to starch, water glass, etc.Alkali metal silicate solutions are also a type of hydropower. However, in order to produce a protective coating such as the one of the present invention, it is necessary to
Not only is it necessary to appropriately select n, but also acid treatment as described below is required, and it is not enough to simply add alkali methyl siliconate. In addition, in the present invention, when alkali methyl siliconate is selected as an additive, it is 1) soluble in water, 2) has a high pH and is stable;
■ Stable even when added to alkali metal silicate solutions,
■This is because good transparency can be obtained when applied to metal plates, etc.

Hereinafter, the method for manufacturing a protective film according to the present invention will be explained according to the steps.

First, a stock solution of alkali metal silicate solution is prepared, and a predetermined amount of water and alkali methyl siliconate are added thereto. The alkali metal silicate solution used in the experiment was a potassium silicate solution, and the stock solution had the following composition in terms of weight percent.

Potassium oxide K2O8,3% Silica S is also 0□ 208% water
70.9% Also, sodium methyl siliconate was used as the alkali methyl siliconate. As mentioned above, this is generally commercially available under the trade name "Dry Seal E", and has the following general characteristics.

Appearance Pale yellow transparent Specific gravity (25℃) ■, 26-1.27 solid content (%
) 30 pJI 13 The mixing ratio of the stock solution of potassium silicate solution, water and sodium methyl siliconate in terms of volume is as follows.

Potassium silicate solution stock solution 26% water
73% Sodium methyl siliconate 1% In this case, the mixing ratio of sodium methyl siliconate can be appropriately selected within the range of 0.05 to 10% by weight. If this lower limit is too low, it will not be possible to obtain sufficient water repellency, and if it is higher than the upper limit, transparency will decrease.
This makes it unsuitable for forming protective coatings on reflective mirrors, etc.

Furthermore, in the present invention, care must be taken that the pi of the above-mentioned liquid mixture must be 10 or more. This is because when the pH is less than 10, especially 8 to 9 or less, the alkali metal silicate solution causes a polymerization or condensation reaction, and the resulting precipitation and gelation of free silicic acid make the solution opaque and form a coating. This is because it becomes impossible to configure.

After preparing the above-mentioned liquid mixture, next, dip a metal plate such as an aluminum reflector into the liquid mixture, and after coating the surface of the metal plate with enough solution, pull up the metal plate and place it in a drying room. Dry for 10 minutes at a temperature of approximately 32°C. This causes the water to dissipate and the alkali metal silicate to coagulate with the alkali methyl siliconate to begin to form a film. Next, the metal plate was placed in a heating furnace at 250-320°C.
The film is heated for 10 minutes at a temperature of 100 to completely remove water from the film and harden the film. This heating causes a condensation reaction in the aggregate of the alkali metal silicate and alkali methyl siliconate, resulting in a strong siloxane bond CS4.
O-Si] is generated to form a strong film that is difficult to dissolve in water.

Next, the heated metal plate is taken out and immersed in a 3% nitric acid solution at a temperature of about 70° C. for 3 minutes to perform acid treatment, and then washed with water.

By this acid treatment and washing with water, alkali metal ions present in the coating, ie, potassium ions and sodium ions in the examples, are extracted and removed. What is important in the present invention is not simply to add alkali methyl siliconate as in the conventional general usage method, but to utilize a process of extracting and removing alkali metal ions from the alkali metal silicate coating. , the alkaline content present in the alkali methyl siliconate is also extracted and removed at the same time. As mentioned above, when alkali metal ions are extracted and removed from a film formed using only an alkali metal silicate solution, the surface of the film becomes strongly hydrophilic. Even when alkali metal ions were extracted and removed from the coating formed using the mixed solution, not only was there no adverse effect, but the coating surface became highly water repellent, which was a better result than expected. As described above, the reason why the protective coating produced according to the present invention exhibits strong water repellency is due to the presence of methyl siliconate, which has a methyl group that provides water repellency, on the surface of the protective coating. In addition, the methyl group of methyl siliconate is inactive and non-adhesive to aluminum hydroxide, etc., which is a waste food product. Since the protective coating is resistant to corrosion, corrosion products will not adhere to the surface of the protective coating, and it can be easily wiped off with water etc. no matter how many times it is worn. Even if a protective film is formed using a mixed solution of When combined with water, it becomes a corrosive solution such as potassium hydroxide or sodium hydroxide, which also attacks the siloxane bonds in the film and the methyl groups that provide water repellency.

The method for manufacturing the protective coating according to the present invention is almost the same as the conventional protective coating using an alkali metal silicate solution in terms of the manufacturing process, and does not require any additional steps. Namely, ■ immersion of the metal plate in solution, ■ drying, ■ high temperature heating,
■A protective film is formed through a series of steps of acid treatment and water washing, and has the advantage that conventional manufacturing equipment can be used as is. Furthermore, as mentioned above, the protective coating produced according to the present invention has extremely superior properties compared to conventional protective coatings, and this can also be supported by the experimental results described below.

Note that the thickness of the protective film formed by performing the above series of steps only once is usually about 1 to 2 μm, which is not necessarily satisfactory in terms of mechanical strength. Therefore,
In order to increase the mechanical strength of the coating, colloidal silicone force may be further added to the mixed solution to improve the adhesion and strength of the coating, or the series of steps described above may be repeated two or more times to form a multilayer coating. That's a shame. However, in the latter case, if the first layer of protective film formed on the surface of the metal plate is water repellent, most of the alkali metal silicate solution that would otherwise be used to form the second layer of protective film is water repellent. The problem arises that it does not stick. In order to solve these problems, for example, the first protective coating should be made hydrophilic by using an alkali metal silicate solution without adding alkali methyl siliconate, and the second protective coating should be made hydrophilic. A water-repellent coating may be obtained by adding alkali methyl siliconate. In the present invention, it is also possible to use a sodium silicate solution or a mixture of this and a potassium silicate solution instead of the potassium silicate solution, and potassium methylsiliconate can be used instead of sodium methylsiliconate. It is also possible to use esters or mixtures thereof with sodium methyl siliconate.

Finally, the effects of the present invention will be explained based on experimental data.

The experiment involved applying an alkali metal silicate solution without adding alkali methyl siliconate to the surface of an aluminum reflector, drying it, baking it, and then performing an acid treatment and water washing process only once. The above steps were repeated using a protective film formed from K (sample 1), a protective film formed by repeating the above steps twice (sample 2), and an alkali metal silicate solution to which alkali methyl siliconate was added. The protective coating according to the present invention (Sample 3) was applied only once to each cast corrosion resistance test (JISH).
8681,) and was tested with Late Namper (R
,N,), the degree of pitting corrosion, the appearance after the test, the water wiping property of the corroded area, and the reflectance of the reflector.

The results are shown in Table 1.

Table 1 As is clear from Table 1, the reflector (Sample 3) with the protective coating manufactured according to the present invention has a protective coating manufactured using an alkali metal silicate solution without the addition of alkali methyl siliconate. (Sample 1) has significantly superior edibility, and also has a protective coating obtained by repeating the conventional process twice (Sample 2).
) is superior compared to In particular, the degree of pitting corrosion is smaller than that obtained by conventional methods, and the appearance after the test is also clean. Note that the reflectance of sample 3 is that of sample 1,
:27':,, As the table shows, there is almost no difference between 1 and 1. As described above, the method for manufacturing a protective film according to the present invention can produce a protective film with superior performance in just one manufacturing process, compared to the conventional method of repeating the same process twice, and can reduce production. There are also great benefits in terms of gender.

Claims (1)

[Claims] 1. Adding alkali methyl siliconate to an alkali metal silicate solution to maintain the pII of the entire solution at 10 or more, and applying the solution onto a metal plate and baking it at a high temperature to form a coating. 1. A method for producing a protective film, which comprises forming a protective film, and then treating the film with an acid to extract substantially all alkali metal ions from the film to make the surface of the film water repellent. 2. The alkali metal silicate solution is a potassium silicate solution, a sodium silicate solution, or a mixed solution thereof, and the alkali methyl siliconate is sodium methyl siliconate, potassium methyl siliconate, or a mixture thereof. A method for producing a protective coating according to claim 1, characterized in that: