Company: Liaoyang Xinyu Chemical Co., Ltd.
Address: No. 29 Vanward two road, Hongwei District, Liaoyang, Liaoning, China.
Abstract: A new ultra-low temperature curing agent for powder coatings and the properties of powder coatings made of crystalline epoxy resin were introduced. Its successful development has greatly expanded the application range of powder coatings, and has obvious economic and social benefits.
Powder coatings have become the second largest producer in the world after the United States after decades of development in China. Their applications have gradually developed rapidly from the initial field of household electrical appliances to various industries, extending to petrochemical, mechanical and electrical instruments, ships, electronic devices, construction, transportation, machinery, automobiles, and assembly. Boxes, packaging, aerospace, water conservancy, computers, railways, weapons and dozens of other industries.
Although powder coatings have four "E" (economic, environmental protection, high efficiency, excellent performance) advantages, but some of its weaknesses are obvious. If the curing conditions are relatively harsh, the curing temperature is generally between 180 ~200 C. High curing temperature not only leads to high energy consumption, but also restricts the application of powder coatings in some occasions which can not be cured at high temperature, such as plastics and wood coating. Therefore, the low temperature curing of powder coatings has become the long-term goal of the powder coatings industry.
Powder coatings can't be cured at low temperature like liquid coatings because of its own process characteristics. Generally speaking, we define the powder coatings cured at 180 ~200 ~C as standard curing powder coatings, 130 ~160 ~C as low temperature curing powder coatings, and 110 ~130 ~C as ultra-low temperature curing powder coatings. Curing type.
It is technically difficult to achieve ultra-low temperature curing of powder coatings. The curing system of powder coatings is a kind of latent curing system at low temperature. If the reactivity of this system is high at low temperature, it will affect the stability of powder extrusion and storage. On the other hand, the epoxy resin and curing agent used in powder coatings are solids with higher softening point, which have higher melting viscosity at low temperature and lower melting viscosity. When the temperature is cured, the coating is hard to flatten and affect the surface effect. If the resin and curing agent with lower softening point are used, the melting viscosity can be reduced, but the storage stability of the powder becomes worse, so it needs to be kept in cold storage at low temperature, which brings a lot of inconvenience to use. Therefore, the key to prepare low-temperature curing powder coatings is to find an epoxy resin and curing agent suitable for powder storage with both high softening point and suitable reactive activity. With the help of modern analytical methods, the chemical properties and thermal properties of materials are analyzed. After a year of repeated formula selection, an ideal formulation system of low temperature curable powder coatings is found. The powder coatings can be cured at 110 C, but the curing time is slightly longer. At 120 C, they can be compared with standard powder coatings. The curing time is equal.
2. experimental conditions and methods
3.1 preparation of powder coatings
After accurately weighing the raw materials such as resin, curing agent, additives, pigments and fillers, mixing them in a high-speed mixer for 5-8 minutes, mixing and extruding the finished powder coating on the extruder (the temperature in zone I is set at 100 6550
3.2 template preparation
Phosphating and drying are required before spraying. The prepared powder was sprayed to the specified thickness by electrostatic spraying. The film thickness was controlled between 60 and 90 microns. The baking conditions were set at 110 C for 30 minutes, 120 C for 20 minutes and 130 C for 10 minutes, respectively.
4. test results and discussion
4.1 determination of the basic formulation of powder coatings
Considering the production cost and usage habit, bisphenol A epoxy resin E-12 was selected as the main epoxy resin, and a macromolecule compound with hydroxyl and amine-terminated group was used as the curing agent to adjust the reaction rate according to different curing conditions. Because of the softening point between epoxy resin and curing agent, the prepared powders have better storage stability. A certain number of amines in the molecular structure of curing agent have higher reactivity and better catalytic activity. In addition, because of its large molecular structure, the film formed will not be solidified like imidazole curing agent. The coating is crisp and has better mechanical properties. Typical recipes are shown in Table 1.