Application of additives in water-based coatings (2)

1.4 desiccants
water-based coatings are more prone to bubbles than solvent-based coatings. The causes of water-based paint foam: the base material itself is easy to foam, the compatible and interaction of various additives have a great impact on the production and stability of foam, production and construction into the bubble, thickener use and so on.
the function of anti-foaming agent: penetrate into the thin layer formed by the surfactant substance, by reducing the surface pressure, destroy the stability of the thin layer, so as to achieve the goal of de-foaming.
used in water-based paint are: (1) metal soap, mineral oil wax: mainly used in high PVC system industrial primers. In coatings with high gloss requirements, transparency is affected; (2) composite defoulants: mineral oil/hydrophobic particles/silicones, with the advantage of good compatibleity and few paint film defects, and (3) silicone-type defogulants: polysilane and polyether modified silicones. Characterized by strong foam suppression capacity and good thermal stability, good compatible with the system, less paint film defects, does not affect re-painting; It is characterized by good compatible, less paint film defects, does not affect gloss, but the foam suppression performance is weak, mainly used in varnish and highlight system.
method of evaluating deboulants: drumming method, specific gravity method, roller coating method and shaking method, in color paint mainly use deverage method to determine de-foaming ability. Detection method of deblistering ability: high-speed stirring method. Fixed speed, stirring time, dosing, viscosity, and other parameters, and then compare the height of the foam and the time of elimination. The defoiling agent should be screened by experiment according to the resin type, other additives and formulation system, combined with the production process and construction method. The general principle is (1) strong de-foaming ability, (2) good stability, (3) does not affect gloss, (4) no heavy painting obstacles.
dosage and addition method of anti-foaming agent: water-soluble coating and low viscosity latex paint dosage of 0.01% to 0.2%, high viscosity latex paint dosage of 0.3% to 1.0%, other water-based paint dosage of about 0.1%. Deblistering agents generally can not be directly added to diluted water-based coatings, need to be added at a high viscosity, and have a good dispersion. In the water-based system, the de-foaming agent containing machine-silicon components has obvious anti-foaming effect, which can be de-bubbled in the production stage, the de-foaming agent with good water dispersion or hydrophobic particles has a significant de-foaming effect, the de-foaming effect is significant in the construction phase, usually the dispersion phase plus 1/3 to 1/2, the coating deployment phase plus 2/3 to 1/2.
the key to choosing a deboulant: the desiccant has a suitable compatible balance with the system. If the deboulator is fully compatible with the system, then it can not penetrate well into the thin layer, the deboping effect is not ideal, if the compatible between the two is too poor, although it can achieve the purpose of deblistering, but may cause surface defects.
1.5 thickener
thickener effect: make the coating have the appropriate viscosity to improve its construction performance, leveling performance and storage stability;
commonly used thickeners can be divided into: (1) cellulose ethers: the advantages are high thickening efficiency, good storage stability, good compatible, anti-flow hanging and so on. The disadvantage is easy to corrupt long mold, poor leveling, (2) polyurethane thickener: the advantage is relatively low molecular mass, roller coating is not easy to produce splashes, can contract with latex particles, will not produce flocculation, smoothness, high gloss, Hydrophobic, wash-resistant, scratch-resistant and bio-stable, (3) polyacrylates (e.g. ASE 1135), good anti-mold invasive, but sensitive to pH, at pH of 8 to 10, Thickening works well, but when the pH is greater than 10, Dissolved in water, loses thickening. When using such thickeners, the effect of pH can be reduced with organic amines, and (4) inorganic thickeners (e.g. sodium-based bentonized soil, bumpy rod soil, silica dioxide, soil, etc.) can form a denatured gel body in the water system, limiting the flow of water, resulting in a thickening effect. Its thickening effect is better than the same amount of polyurethane thickeners and alkali-soluble acrylics. Can also be anti-floating hair flower, anti-sink, anti-flow hanging, but also has a wide range of pH adaptability, good freezing and thawing stability and biological stability, mainly used in water-based building coatings. Cellulose and alkali-soluble thickeners focus on water thickening, while polyurethanes focus on emulsion thickening.
1.6 anti-lighting agent
water-based coatings to ultra-fine silicon dioxide (also known as silicon micro-powder) as the main, non-stereotyped silicon dioxide is the first choice of high-grade coating anti-lighting agent, refractive index of 1.46. The porosity and granularity of the light-eliminating powder have a great influence on the light-eliminating effect, and the commonly used light-eliminating powder porosity is between 1.2 and 2.0 mL/g, with a particle size range of 3 to 7 m, with the best light-de-lighting effect around 5 m.
selection criteria for anti-lighting agents in water-based coatings: (1) the refractive index of the anti-light dissipant should be as close as possible to the refractive index of the film resin (1.4 to 1.6) ;(2) with wear resistance, scratch resistance;
of the anti-light effect: (1) The larger the particle size of the anti-light powder, the better the anti-light effect. However, the particle size should be adapted to the thickness of the coating film, the particle size is much larger than the film thickness of the anti-light effect is not good, and will worsen the appearance and feel of the paint film;
the amount of anti-light powder, the worse the transparency of the paint film, and the greater the effect of large particle size on the transparency. Fine-grained anti-light powder is good for anti-sinking.2 Additive selection techniques
give full play to the application characteristics of additives, the use of additives selectivity, sensitivity, synergy effects, highlighting effects and characteristic overlay effects and other application characteristics, the selection of suitable matching additive system, is the key technology for the selection of additives. In the application process of additives, we should actively explore the use of new additives, environmentally friendly additives and matching additives to overcome the dependence on existing additives. When applying matching aids, we should give full play to the positive effect of matching additive system, and also ensure the stability of matching additive system. The application of additives should pay special attention to the interaction between additives, the interaction and restriction between the various components of additives and coatings. Additive selection is premised on maintaining the essential properties of participating matching additives and the stability of the coating system.
the characteristics of pigments, the properties of dispersed media, the interaction between components, and the influence of external conditions should be taken into account in the selection of additives to minimize the negative effects of additives. According to different paint varieties, paint production, storage and transportation and construction requirements, through test comparison, to determine the variety of additives, addition and addition methods. Reasonably determine the relationship between coating and coating properties and additive varieties and dosages, and find the best balance between performance and dosage.3 Conclusion
the research direction of water-based coating additives in the future is efficient, safe, environmentally friendly and easy to construct. Performance is also moving towards compounding, protecting one performance while improving others. Strengthening the development and application of silicon-modified and fluorine-modified series of additives will be the development direction of the additive industry in the future. The development of water-based coating additive industry has a great effect on the development of water-based coating industry, the rational selection, accurate and appropriate use of additives is particularly important..