Waterborne alicyclic epoxy resin coating spraying precautions
Water-based, that is, caprolactone polyols containing no VOC and HAPS resins and a narrow degree of polymerization distribution, such coatings can be applied by conventional equipment and may replace powder coatings. What are the points of attention in the preparation of water-based alicyclic epoxy liquid coatings? Experts from China Epoxy Resin Industry Association have made a special introduction.
The use of traditional liquid coating equipment can avoid the basic equipment investment necessary for a new powder coating line. These coatings can be diluted with water or thickened with aqueous thickeners. Compared with the traditional bisphenol A diglycidyl ether resin, the alicyclic epoxy has the following differences: it is an aliphatic backbone, which reacts rapidly with an acid, but is basically a curing agent with an amine/amide epoxy. No reaction, no chlorine, viscosity of 350 cps and bisphenol A diglycidyl ether resin of 11,000 cps, and it also has excellent weatherability. The use of low-viscosity alicyclic epoxys in cationic UV coatings has grown significantly, and there have been many reports on the formulation and performance of such 100% solids coatings without "va", which are among the heat-curing coatings. The application has few detailed literature. In principle, the formulation technology of cationic UV coatings can also be used in thermal curing systems, but the two are also different. For example, UV coatings are generally not sprayed, so the application viscosity can be higher than that of spray-coated thermal curing coatings. In baking cationic coatings, water can be used. As a diluent for VOC.
Caprolactone polyols are effective reactive diluents for solvent-based coatings and accelerate the curing of cationic UV coatings. In cationic UV coatings, the hydroxyl groups of such polyols accelerate the curing and result in a certain degree of humidity. Curing sensitivity. In the heat-cured coating, since the humidity in the oven is low, moisture does not inhibit solidification. The presence of polyols increases the tolerance to water, so water can be used as a VOC-free diluent in coating formulations consisting of cycloaliphatic epoxys and polyols. These coatings are actually high solids organic coatings diluted with water. . Dilution with water has two advantages: low viscosity without VOC, and common, well-known water-based paint measures can be used to achieve anti-sagging and rheology control. Since the components in the formulation are only partially miscible with water and thus the amount of water that can be absorbed is limited, care should be taken to avoid excessive phase water and phase separation.
Cellulosic thickeners are effective in controlling sagging in aqueous coatings, but it is unclear whether it is effective in 100% solids, water-diluted alicyclic epoxy coatings. Early work showed that the water-diluted 100% solid epoxy was thixotropic when measured with a Brookfield viscometer. Examination of various thickeners has shown that cellulosic thickeners give the best overall performance. When heated to 40 ~ 60 ° C, the best paint film appearance can be obtained by spray gun construction, and the low construction temperature makes the cured paint film produce more orange peel. Experts from China Epoxy Resin Industry Association said that the main advantage of powder coatings is that the coating efficiency is high. The high coating efficiency is mainly achieved by the recovery of powder. If it is equivalent to powder coating, such liquid coating needs some kind of Ways to recycle fly lacquer. Since the coating formulation mentioned here does not contain organic solvent recovery much easier, it is easy to adjust the water lost during the recovery process by measuring the conductivity, if necessary, compared to the powder coating. Higher baking temperatures required for such coatings can save energy compared to high baking temperatures. Another method that is being evaluated is to spray the anhydrous epoxy, polyol and pigment formulation products using the “Unicarb†method. The “Unicarb†method is more efficient to use than powder coatings. It is necessary to simply add a solvent to the above formulation without requiring a VOC-free coating.
Regarding the formulation note, experts from the China Epoxy Resin Industry Association said that for cationic curing, the alkali will terminate curing, so all additives and rheology control agents must be free of basic substances, alkaline pigments and amine-treated pigments. Inhibit curing. Alkaline rhodamine pigments also inhibit cationic curing. Basic pigments and auxiliaries cannot be used in cationically cured coatings. Curing depends on the volatilization of the catalyst FC. If the film is too thick or the oven is not ventilated, the amine cannot be completely removed from the lacquer. The film is released to inhibit curing. The viscosity increases with the increase of the degree of branching of the polyol: the viscosity of the diol is lower than that of the ternary or tetrahydric alcohol, and the amount of the epoxy resin is increased when the diol is used together, and the amount of the catalyst is increased. Will accelerate the curing speed but also reduce the corrosion resistance, the molar ratio of epoxy to hydroxyl R has a significant effect on the curing speed.
In summary, cycloaliphatic epoxy and caprolactone polyols can be formulated into low viscosity or even VOC free coatings that can be diluted with water to spray viscosity. Cellulose thickeners can be diluted with water by 100% solids epoxy and polystyrene. The alcohol coating has effective sag resistance. The curing speed of the system is determined by the following variables: the molar ratio of epoxy to hydroxyl, the functionality of the polyol and epoxy, the amount of catalyst and the curing temperature. The formulation can be easily used. The color paint is prepared, and since such paint is cationically cured, the alkaline pigment and the substrate inhibit the curing.
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