In the formulation design of powder coatings, it is better to increase the hardness of the coating based on adhesion, flexibility and impact strength. Therefore, the following issues are mainly considered:
1. The selection and proportion of resin and curing agent, and the film forming system with high functionality shall be selected. The proper crosslinking degree is the best. If the crosslinking degree is too high, the coating will be brittle and the flexibility will be poor. The hardness of hydroxyl containing polyester resin and high content of NCO curing agent is good, and the glass transition temperature of other resins should also be considered. B1530 can react with a small amount of hydroxyl group in polyester by adding 1% to the carboxylic pure polyester (TGIC/HAA) system to increase crosslinking and hardness.
2. Add pigment filler with high hardness, and the proportion is slightly larger than usual. After considering the normal color and luster, wollastonite, kaolin, talcum powder, mica powder and the like are added to the filler, but the glossiness and flatness of some of these varieties are inferior to that of precipitated barium sulfate. While slightly increasing the proportion of pigments and fillers, it is necessary to take into account the standard of physical properties.
3. As for the addition of additives, the conventional additives in this kind of powder can be reduced. For example, leveling agent and wetting agent can only increase the lower limit. Other fine powder PTFE/PE that can increase smoothness and fill the gap can be extruded internally or added externally. Representative brands include Clariant 3920F, Lubrizol 1778F, Hubei Laisi 1440, etc. Domestic products have similar effects, but the price is nearly half cheaper.
4. The standardized operation of spraying construction is also very important, and the phosphating treatment, spraying thickness and curing conditions are met. The coated workpieces are sandblasted and then phosphatized, which will improve the adhesion after powder spraying; The coating thickness shall be controlled within 60~80 when meeting the coating coverage and the uniformity of powder on corners μ M is more appropriate; The conventional curing condition of powder coating is 180-200 ℃. The low temperature formula design requires lower curing temperature. The crosslinking density of coating curing can be improved by adding catalyst. The lystium phosphonium salt catalyst 305 is well dispersed in sheet form, with universal effect and high cost performance.
The hardness of the coating is mainly related to the type and curing degree of the powder coating. The hardness of the coating is usually about 1H-3H, and some coatings with special requirements can be above 3H. The hardness of common indoor powder is lower than that of outdoor powder, which is usually tested with a hardness tester.
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