With the advancement of science and technology, people have put forward higher benefits and requirements for the preparation and use of coatings. Various additives are used in the formulation of water-based coatings and solvent-based coatings, such as additives to improve pigment wetting and dispersing, additives to help the storage and stability of finished coatings, coatings defoamers to eliminate pores, and additives to adjust the appearance of paint films.
Because the coating requires various high-speed stirring mixers, such as three-roller, sand mill and ball mill, etc. In the process of air spraying, airless spraying, roller coating, flow coating and curtain coating, the free energy of the coating system will be increased to varying degrees to help generate foam, which is also the external factor of coating foaming. The foam problem of water-based latex paint is the most prominent, which is caused by its special formula and special production process.
(1) The latex paint uses water as the diluent, and a large amount of emulsifier is used in the emulsion polymerization, which greatly reduces the surface tension of the emulsion, resulting in the generation of foam;
(2) The wetting and dispersing agents used to disperse pigments in latex paints are also substances that reduce surface tension, which contributes to the generation and stabilization of foam in latex paints;
(3) If the viscosity of latex paint is too low in the use stage, it is inconvenient for construction, but after the thickener is used, the film wall of the foam will be thicker and more elastic, and the formed foam will not be easy to eliminate;
(4) Because the latex paint will be fully stirred and dispersed during the preparation, coupled with the spraying, brushing, rolling and other operations during the construction process, it is very easy to form foam.
The generation of latex paint foam not only has a great impact on our construction, but the air in the foam also hinders the dispersion of pigments and fillers, making the utilization rate of equipment insufficient and affecting the quality of latex paint; due to excessive foam during canning, Multiple canning is required; during the construction process, pinhole-like surface defects will be left on the surface of the paint film, which is not aesthetically pleasing, and also affects the weather resistance and corrosion resistance of the paint film. Therefore, most paint manufacturers will add paint defoamer when producing latex paint to eliminate and suppress foam. So what types of paint defoamer are there?
Coating defoamers are generally divided into water-based and solvent-based oil-based. for coating additives Currently, the following four types of defoamer are commonly used in the domestic market.
1. Lower alcohols and esters
Including isopropyl alcohol, butanol, tributyl phosphate, etc., but they have certain toxicity and VOC, and the defoaming performance is poor, and now they have gradually faded out of people’s sight and are no longer used.
2. Organic polar compounds
Refers to some surfactants with low HLB values, such as polyether surfactants, polyethylene glycol fatty acids, etc., which are rare in the market.
3. Mineral oils
Mineral oil defoamer is a frequent visitor in coatings. In addition to its good defoaming performance, it also contains some hydrophobic particles, which will not affect the use of coatings. It is relatively common and used in the market.
It mainly uses hydrophobic silicone and polyether modified silicon as active ingredients, and some other carrier surfactants are used together, which has good defoaming effect, excellent compatibility, low dosage, easy dispersion, and excellent breaking Foaming and anti-foaming ability. It will not produce coating (fish-eye) defects or affect film formation, no shrinkage crater, no oil slick, demulsification, etc. It has a special effect on the coating system and is one of the more commonly used coating defoamers.
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