Лако-красочные материалы — производство

Additives are typically products added at levels of 0.1 to 0.5% to modify specific proper­ties. Most commonly used additives are defoamers, antisettling or wetting agents, thixo- tropes, and adhesion promoters. Use of antioxidants or preservatives is rare. Because of their minimal shrinkage, compressive strength of cured epoxies is very high. Since aeration will reduce this substantially, use of defoamers, especially in heavily filled systems, is quite common. Many defoamers are suitable, but silicone-based defoamers should be avoided on surfaces where adhesion in critical. Addition levels of 0.05 to 0.2% usually suffice.

Antisettling agents, pigment dispersers, or wetting agents may be included in filled formulations. Depending on the formula, particularly the selection of fillers, such products may reduce or eliminate settlement. Usuage will generally be at a level of 0.1 to 0.3% of formulation. These agents are best added prior to incorporation of the fillers. Various thixotropes are used in epoxy formulations to reduce or eliminate flow in products designed for use on vertical surfaces, to improve gap-filling properties, or to reduce set­tlement of fillers. Fumed silica is widely used at levels of 0.1 to 3%. At low levels, the effect on viscosity is small except in high-viscosity systems, but settlement will be reduced. At higher addition levels, even low-viscosity products can be converted to firm pastes. To improve the efficiency of fumed silica, especially in the resin component, small quantities of polar liquids may be added.

Other thixotroping agents include Bentones and Tixogels, of which a number of grades are available, and China clay or kaolin, usually added as a filler, but which imparts thixotropy to the formulated product. Organofunctional silanes are extremely effective

adhesion promoters. Added at levels of 0.05 to 0.2%, they can improve adhesion to certain nonporous substrates, such as glass, metals, and certain plastics. Formulators can select from a number of different functional groups, but generally epoxy functional types will be used in the resin component and amine functional grades in the hardener.