Aqueous cycloaliphatic epoxy resin coating spraying notes

Water-based coatings, which are free from VOC and HAPS (high-level pollution solvents), can be made from liquid cycloaliphatic epoxy resins and caprolactone polyols with a narrow degree of polymerization. Such coatings can be constructed using conventional equipment and may be substituted. Powder coating. What are the points of attention when making water-based epoxy epoxy liquid coatings?

The use of traditional liquid paint spraying equipment can avoid the investment in basic equipment necessary for a new powder coating line, which can be diluted with water after modification, or can be thickened with a cellulose thickener for aqueous coatings. Compared with the traditional bisphenol A diglycidyl ether resin, the cycloaliphatic epoxy has the following differences: it is an aliphatic main chain and reacts quickly with acid, but it is basically a curing agent with amine/amide epoxy. It does not react, contains no chlorine, has a viscosity of 350 centipoise, and bisphenol A diglycidyl ether resin has a viscosity of 11,000 centipoise. It also has excellent weather resistance. The use of low-viscosity cycloaliphatic epoxy in cationic UV coatings has grown significantly. There have been many reports on the formulation and properties of such non-vapor-containing 100% solid coatings, which are used in heat-cured coatings. There are few detailed documents for the application. In principle, the formulation technology of cationic UV coatings can also be used for thermal curing systems, but they are also different. For example, UV coatings are generally not applied by spraying. Therefore, the application viscosity can be higher than that of spray-cured coatings, and water can be used in baked cationic coatings. As a diluent for VOCs.

Caprolactone polyol is an effective reactive diluent that has been used in solvent-based coatings and can accelerate the curing of cationic UV coatings. The hydroxyl groups of such polyols in cationic UV coatings can both accelerate cure and at the same time result in a certain degree of humidity. Curing sensitivity. In the heat-curable coating, since the humidity in the oven is low, the moisture does not inhibit the curing. The presence of polyols increases the water tolerance so that water can be used as a VOC-free diluent in coating formulations consisting of cycloaliphatic epoxies and polyols. Such coatings are actually high-solid organic coatings diluted with water. . Dilution with water has two advantages: low viscosity without VOC, which can be achieved with common, well-known water-based paint measures to prevent sagging and rheological control. Since the ingredients in the formulation are only partially miscible with water and therefore the amount of water that can be absorbed is limited, care should be taken to avoid adding too much water to cause phase separation.

Cellulose thickeners can effectively control sagging in aqueous coatings, but it is unclear whether it is effective in 100% solids, water-diluted cycloaliphatic epoxy coatings. Early work showed that water-diluted 100% solids epoxy had thixotropic behavior when measured with a Brookfield viscometer. Examination of various thickeners showed that cellulosic thickeners gave the best overall performance. When heated to 40-60 °C with the spray gun construction can get the best film appearance, low construction temperature makes the cured paint film produce more orange peel.

The main advantage of powder coatings is their high coating efficiency. The high coating efficiency is mainly achieved through the recovery of powders. To be equivalent to powder coatings, such liquid coatings need some way to recover the flying paint. Since the coating formulation mentioned here does not contain much organic solvent, it is much easier to recover. By measuring the conductivity, if necessary, water can be used to make the water lost during the recovery easy to adjust. This is in contrast to powder coatings. The lower bake temperature required for such coatings compared to high baking temperatures saves energy. Another project under evaluation is to use the “Unicarb” method to spray-dry epoxy-, polyol-, and pigment-containing formulations. The “Uni carb” method is more efficient than powder coatings, such as Do not need VOC-free coatings simply add the solvent in the above formula.

With regard to the formulation note, experts from the China Epoxy Resin Industry Association stated that for the cationic cure, the base will stop curing, so all additives and rheology control agents must be free of alkaline substances. Basic and amine-treated pigments will Inhibit curing. Alkaline rhodamine pigments also inhibit cationic curing. Basic pigments and additives cannot be used in cationic curing coatings. Curing depends on the volatilization of a small amount of amine blocking agent in catalyst FC-520. If the film is too thick or the oven is not Ventilation allows the amine to not completely escape from the paint film and inhibit curing. The viscosity increases with the increase in the degree of polyol branching: diols have lower viscosities than ternary or tetrahydric lacquers, and need to increase the amount of epoxide (R value) when combined with diols. The film, high epoxy dosage can improve the corrosion resistance, the increase in the amount of catalyst will accelerate the curing rate but will also reduce the corrosion resistance, the molar ratio of epoxy to hydroxyl R has a significant effect on the curing speed.

In short, cycloaliphatic epoxy and caprolactone polyols can be formulated into low viscosity or even VOC-free coatings. The coating can be diluted with water to spray viscosity. Cellulose thickener can be diluted with water to give 100% solids of epoxy and multiples. The alcohol coating has an effective sag resistance. The curing rate of the system is determined by the following variables: the mole ratio of epoxy to hydroxyl, the functionality of polyol and epoxy, the amount of catalyst used, and the curing temperature. The formulation can be easily used Color paints are prepared. Since these coatings are cationically cured, basic pigments and substrates inhibit curing.

Source: Ink Information