JPS59536B2 - Improved silica sol paint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved silica gel coating using a stable silica sol as a binder.

The present inventors found that the silicate skeleton formed by 51-0 bonds has high thermal and chemical stability, and that inorganic heteronuclear polymers in particular have partial ionicity. Since the bond energy is higher by the amount of ion resonance than the single bond of the same nucleus, when bond energy is used to compare heat resistance, the bond energy of C-C covalent bond of organic polymer is 82.6Kc8
f,/mol, the Si-O bond energy of inorganic heteronuclear polymers is high at 106-/mol, which is stable against oxidation at high temperatures, but at low temperatures due to the presence of ionic impurities and water. We focused on the point where the bond breaks. Silica sol with a silicate skeleton is currently commercially available with an anhydrous silicic acid content of about 20 to 31%;
It freezes at temperatures below °C, and even after thawing, it does not return to a sol, making it unusable.The above-mentioned problem with its stability, particularly at low temperatures, limits its application, and a solution to this problem has been desired.

Various methods have been proposed for stabilizing silica sol, but methods using reagents such as organic amines,
Alternatively, it has been known to use a low molecular weight vaporizable nitrogen base such as quaternary ammonium hydroxide.

These reagents increase the pH of the silica sol due to their higher basicity, and due to their evaporative nature, the added evaporable nitrogen base is removed as the temperature rises during storage and water evaporates, while the silica sol The serious drawback is that the sol is concentrated, resulting in gelation of the sol and precipitation of silica crystals. Note that stabilization by adding a water-soluble organic liquid such as ethylene glycol is also known, but there are problems such as gelation depending on cooling conditions. Regarding the use of silica sol as a surface treatment agent, see Patent Application Publication No. 45-14897, ``Surface Treatment Method''.
has been proposed, but when coating the surface of an inorganic or organic substance with silica sol, methanol is added to the silica particles with a constant particle surface area in the silica sol and the dispersion liquid for the purpose of reinforcing and modifying the coated surface. One method is to limit the molar ratio of methanol and water to a certain range and apply silica sol to the treated surface to form and strengthen the film, and the other is to burn the methanol remaining on the treated surface immediately after application, thereby forming a film. This is a method that speeds up the process and improves the quality at the same time.

However, the strength of the coating produced by the former method is weak, and the latter method has problems in implementation in terms of work management. The present inventors have conducted various studies to improve the low-temperature or storage stability of silica sol, as well as to form a film with sufficient strength and adhesive strength when forming a film by adding a filler to silica sol. It was discovered that the low-temperature stability of silica sol was significantly improved when silica sol was added with a small amount of water-soluble melamine resin, and when this was used as a binder in a paint, the low-temperature stability and coating hardness were further improved. At the same time, they discovered that cracks were less likely to occur on the finished surface and completed the present invention. The present invention uses a stable silica sol obtained by adding one or more types of longer chain dihydric alcohols having 3 or more carbon atoms and a water-soluble melamine resin to silica sol as a binder, and aggregates, fillers, This paint is especially suitable for painting the interior and exterior walls of buildings, containing necessary materials such as water repellent, thickener, coloring pigment, and antifoaming agent.

The dihydric alcohol having 3 or more carbon atoms used in the present invention has a long carbon chain, such as propylene glycol, trimethylene glycol, triethylene glycol, etc. It is added in an amount of 5 parts by weight or more per 100 parts by weight (as a standard).

As water-soluble melamine resin, commercially available solid content is 50 weight?
The solid content is 1 to 100 parts by weight of silica sol.
2.5 parts by weight is added. Note that when the water-soluble melamine resin solid content was less than 1 part by weight, low-temperature stability was poor and gelation was observed. Moreover, if it exceeds 2.5 parts by weight, the strength of the coating will decrease.
A decrease in coating film drying speed, a decrease in water resistance, and a decrease in adhesion (interfacial strength) were observed. The silica sol used in the present invention does not use an organic amine or an evaporable nitrogen base for stabilization as in the past, so it does not affect the pH of the silica sol and does not cause performance deterioration due to evaporation of additives during storage. Not only does it not gel during storage, but it also does not gel when frozen.

Then, it increases the adhesive strength as a binder and produces an effect as a film-forming strengthening agent 3.

When producing a paint using stabilized silica sol as a binder, generally 10 to 30% by weight of this silica sol (based on 30% content as silicic anhydride) and 50 to 70% by weight of aggregate or filler. It can be produced by adding and adjusting water, thickeners, antifoaming agents, etc. according to various application methods such as spraying, roller coating, brush coating, etc. to a mixture of 4 and 4 appropriate amounts of pigments. .

Therefore, this paint does not require organic solvents, and the treatment process is only the coating process, without the need for a heating and drying process.
The constituent components are mainly inorganic and nonflammable, and have excellent properties as a paint for the interior and exterior walls of buildings, particularly slate, concrete, mortar, and the like. The present invention will be explained below with reference to Examples.

Example: Add 1009r silica sol (silicic acid anhydride content: 30% by weight, pH: 25°C: 8-10) into a polyvinyl beaker, add propylene glycol and water-soluble melamine resin as additives, and stir with a stick until uniform. A stabilized silica sol was obtained by stirring.

Next, samples according to the present invention and comparative samples were manufactured in the proportions shown in Table 1, and each sample was coated on a slate plate (50 mm x 150 mm) using a brush.
) to a thickness of 1 to 1.2 mm, humidity 80%, 20
A needleman test was performed on the film that had been cured for 7 days in a greenhouse at 70°C.

The measuring device shown in Fig. 1 was used for this needleman test, so I will explain it first. 1 is a diamond needle,
2 is a circular metal rod (length 25mm 1 diameter 4m7!L), 3
are circular metal rods (length 215 mm, diameter 10 mI!), which form a body. Reference numeral 4 denotes a pedestal for mounting a load weight, which is installed perpendicularly on the metal rod 3.

Using this equipment, the coating was coated with 1.0k9 and 2.2
．． A load of 0 kg was applied for 10 seconds, and the diameter of the stamp produced when a diamond needle penetrated the surface of the film was measured. The results were as shown in Table 1.

This measurement result shows that the hardness of the film is significantly improved by adding the water-soluble melamine resin.
Aggregate and other ingredients were added to the stabilized silica sol and stirred uniformly according to the formulations shown in Table 2 to produce paints A and B.

This paint was frozen at -20℃ for 24 hours and 60 hours in a constant temperature and humidity chamber, and after thawing, it was applied to a slate board with a brush.The resulting coatings were all in good condition, and the curing state was also good. It was hot.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an apparatus for measuring the hardness of a coating film. 1...Diamond needle, 2,3...
Circular metal rod, 4... Frame for mounting weights.

Claims (1)

[Claims] 1. An improvement characterized by comprising 100 parts by weight of silica gel, 5 parts by weight or more of one or more dihydric alcohols having 3 or more carbon atoms, and 1 to 2.5 parts by weight of a water-soluble melamine resin as a solid content. silica sol paint.