In the powder coating formula, resin and curing agent are the basic film-forming substances, and the matching between them is an important factor to determine the properties of powder coating and film. Generally speaking, the selection and matching of resin and curing agent can be considered according to the following contents.
1. From the point of view of the use of powder coatings, first of all, understand whether the coating products are used outdoors or indoors.
Outdoor products must choose weather-resistant resin and curing agent system, then polyester, polyurethane, (aliphatic polyurethane curing system) or acrylic powder coating should be selected. For indoor products, epoxy and epoxy-polyester powder coating systems can be considered. If used in decoration, epoxy-polyester powder coatings are selected; if used in anticorrosion, epoxy powder coatings are selected. For high requirements of indoor powder coatings (such as aluminum profile ceiling powder), if the price is reasonable, you can also choose polyester and other weather-resistant powder coatings.
2. In order to meet the requirements of users, it is necessary to understand the curing process conditions of coating products.
For example, baking temperature and time, it is impossible for the user to change the coating conditions with the design of the powder coating formula. From the point of view of labor efficiency, users want the baking time to be short, but the baking temperature can be increased to meet the requirements of complete curing of the film. When the baking temperature is increased, new requirements are put forward for the heat resistance of raw materials such as resins, curing agents, pigments and auxiliaries, which brings a lot of trouble to the formula design, and generally do not change the coating process conditions easily.
3. Considering the cost, the coating cost is an important factor to popularize and apply the product and to ensure the economic interests of both supply and demand.
The varieties of powder coatings with reasonable cost should be fully considered in the selection of resins and curing agents. In the selection of epoxy-polyester powder coatings, based on the price of polyester powder coatings and epoxy resin and the requirements for film properties, we can decide to choose polyester resin: epoxy resin = 50:50 (quality). At 60:40 or 70:30, the performance / price ratio of powder coatings is also an important factor to be considered. .
4. Considering the appearance of the coating film, when the requirement of convective leveling is high, the resin and curing agent system with low melting viscosity and low reaction activity should be selected in the selection of resin and when the glass transition temperature of resin meets the requirement. The film leveling property of general powder coating is good when the gelation time is long and the fluidity of melting level is large.
5. Considering the physical and mechanical properties and chemical resistance of the film, for the products with high performance requirements, the resin system with high epoxy value, hydroxyl value and acid value should be selected as far as possible, that is, after the coating is cured, A system with high cross-linking density of the film. For example, in epoxy-polyester powder coatings, the ratio of polyester resin with high acid value (polyester resin: epoxy resin = 50:50) is lower (polyester resin: epoxy resin = 70:30 polyester resin). The film crosslinking density is high and the corresponding performance is good.
6. From the safety and hygiene considerations in the use of powder coatings, try to select non-toxic or irritating curing agents, and after the preparation of powder coatings, the toxicity is less, and the film should be a non-toxic curing agent after curing.