The development of modern science and technology has put forward high-quality and high-efficiency requirements for the waterproof coating industry. That is, water-based paints and solvent-based paints, various additives should be used in the formulation, including additives to help the pigment wetting and dispersing; additives to improve the storage stability of the finished coating product, and additives to adjust the appearance of the paint film; Some additives to achieve special functions.
Most of the above-mentioned additives are surfactants, which can change the surface tension of the coating, causing the coating itself to have internal factors that are easy to foam or stabilize the foam. Various high-speed mixers, such as three-roll mills, sand mills, and ball mills, are used in the coating manufacturing process. Various methods and methods used in paint application, such as air spraying, airless spraying, roller coating, flow coating and curtain coating. In these processes, the free energy of the coating system will be increased to different degrees, helping to generate foam, which is the external factor that generates foam. The foam problem of water-based latex coatings is the most prominent in the waterproof coating industry, which is caused by its special formula and special production process.
Latex paint is based on water as a diluent. A certain amount of emulsifier must be used during emulsion polymerization to prepare a stable aqueous dispersion. The use of emulsifiers greatly reduces the surface tension of the emulsion system, which is the main cause of foam. The wetting agent and dispersing agent for dispersing pigments in latex paint are also substances that reduce the surface tension of the system, and contribute to the generation and stability of foam.
Latex paint has a low viscosity and is not easy to apply. After using a thickener, the film wall of the foam is thickened and its elasticity is increased, so that the foam is stable and difficult to eliminate. Extraction of free monomers in the production of emulsions; adjustment, dispersion and stirring when preparing latex paint; spraying, brushing, and roller operations in the construction process. All of these can change the free energy of the system to varying degrees and promote the production of bubbles. The foam problem of latex paint makes the production operation difficult. The air in the foam will not only hinder the dispersion of pigments or fillers, but also make the equipment utilization insufficient and affect the output; when filling the can, it needs to be filled for many times due to foam. The air bubbles left in the paint film during construction cause surface defects, which not only damages the appearance, but also affects the anti-corrosion and weather resistance of the paint.
In general terms, it can be divided into water-based and solvent-based; or silicon-containing and silicon-free. Then we can generally think that there are four main types of markets that are more common. Including isopropanol, butanol, tributyl phosphate and so on. Due to certain toxicity and VOC, and the defoaming effect is not obvious, the foam suppression is not good. Mainly refers to some surfactants with low HLB value, such as polyether surfactants, polyethylene glycol fatty acid esters, etc. These are rare in the market due to HLB. In addition to the defoaming effect of mineral oil complexes, it also contains some hydrophobic particles, such as metal stearate soap and polyurea, micronized fischer-tropsch wax.
Mainly hydrophobic silicone oil as the active ingredient, plus some other carrier surfactants to cooperate with, the effect is better, but the amount of addition needs to be considered.
Generally, the third and fourth categories are common in the market. Do a good job of matching to ensure the integration of the defoamer and the entire system, and only need to exert the defoaming and anti-foaming properties and long-term effects.
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