Date: 2020-10-29
Low temperature curing and ultra-low temperature curing of powder coatings are currently the main directions and goals of research and development for various raw material and powder manufacturers. Their advantages not only meet the on-site application needs of customers, but also respond to national energy conservation and emission reduction policies. Moreover, their application fields are relatively wide, such as the construction machinery (ACE) industry, medium density fiberboard (MDF), and 5G special heat dissipation materials.
At present, there are few reports on the research of outdoor low-temperature curing extinction powder coatings at home and abroad, and domestic suppliers of outdoor low-temperature curing extinction agents are also in the preliminary research and development stage. However, the effect of outdoor room temperature curing extinction agents under low-temperature curing conditions is minimal.
At present, the common production process for outdoor low-temperature curing extinction powder coatings is a two-component dry blend extinction of hydroxyalkylamide (HAA) or tri glycidyl isocyanurate (TGIC), which cannot achieve a dull luster; Another process is one-step high and low acid value low-temperature curing extinction, and there are very few raw material manufacturers who can achieve this technology; However, pure low-temperature curing extinction agent products are still in the research and development stage, and there are still many challenges that need to be tackled.
The author of this article has developed an outdoor ultra-low temperature curing (140 ℃ x15 minutes) extinction powder coating with the joint support of raw material manufacturers and peer elites. It has been applied in the fields of lighting and outdoor furniture and has gained widespread recognition from end users.
Research progress on outdoor low-temperature extinction powder coatings
1.1 HAA&TGIC two-component dry mixed low-temperature extinction
The HAA two-component dry mixing low-temperature extinction technology is relatively mature. Manufacturers such as Allnex, DSM, Synthomer, etc. all have such products. Among them, Xintema dry mixed low-temperature extinction technology can achieve a gloss of 15% and a smooth and delicate surface; The TGIC two-component dry mixing low-temperature extinction technology is difficult to control due to its poor reaction rate. Only manufacturers such as Allnex and DSM have such products.
1.2 One step method for low temperature extinction of high and low acid values
At present, there are mature products for one-step high and low acid value room temperature extinction, but there are still few reports on one-step low-temperature extinction. Allnex and DSM have only recently acquired this technology, which can achieve a white glossiness of 20% (60°).
1.3 Low temperature curing matting agent
At present, domestic manufacturers of outdoor low-temperature curing matting agents are still in the research and development stage. Although the gloss can achieve matte under low-temperature conditions, its mechanical properties are very poor and cannot meet customer needs at all; However, only one or two foreign companies have just released new outdoor low-temperature curing (160 ℃ x15min) extinction products.
2 Experimental section
2.1 Formula raw materials
This article uses imported low-temperature polyester resin and special additives combined with imported low-temperature matting agents to prepare outdoor ultra-low temperature curing matting powder coatings, and compares the physical and chemical performance differences between different types of curing agents and room temperature polyester resins. The raw materials and basic ratios used are shown in Table 1.
2.2 Experimental Equipment
Experimental equipment: electronic balance, mixer, extruder, powder mill, electrostatic spray gun, oven, film thickness gauge, gloss gauge, impact gauge, bending gauge, cupping gauge, UVB aging chamber, PCI standard board.
2.3 Experimental Methods
According to the design formulas A, B, and C, resin, curing agent, matting agent, various additives, and pigments are pre mixed, melted and extruded, cooled and crushed, ground into powder, and then sprayed with an electrostatic spray gun for solidification to obtain an outdoor ultra-low temperature curing matting powder coating sample. The curing conditions are 140 ℃ x 15min. Cool the prepared sample to room temperature and conduct various performance tests. The main performance is listed in Table 2, and the mechanical performance test sample image is shown in Figure 1.
Figure 1 shows a sample image of the mechanical performance test of formula A. After a large number of tests comparing different raw materials and dosage ratios, it can be concluded that the type and dosage ratio of raw materials used in formula A are the optimal formula, with the best extinction performance, mechanical performance, weather resistance, and surface smoothness. This article continuously optimizes the formula to ultimately produce an outdoor ultra-low temperature curing extinction powder coating with excellent leveling, mechanical properties, extinction, and weather resistance.
By comparing different types of curing agents 1 and 2, it can be seen that the ultra-low temperature extinction powder produced by both agents has excellent flatness and fineness in appearance. The ultra-low temperature extinction powder produced by curing agent 1 has better mechanical properties, while the ultra-low temperature powder produced by curing agent 2 has better extinction properties.
By comparing the low-temperature curing and room temperature curing polyester resins, it can be seen that there is no significant difference in the mechanical and weather resistance properties of the ultra-low temperature extinction powder produced by the two. However, the ultra-low temperature extinction powder produced by low-temperature curing polyester has better leveling performance and a smoother and more delicate surface.
At the same time, several outdoor low-temperature extinction agents provided by domestic suppliers were also tested. Although their extinction performance and leveling performance can meet the research requirements, their mechanical properties are very unsatisfactory, which will not be elaborated here.
This article provides a detailed introduction to the research progress and extinction methods of outdoor low-temperature curing (160 ℃ x15 min) extinction powder coatings at home and abroad. It further introduces the development process and physicochemical properties of outdoor ultra-low temperature curing (140 ℃ x15 min) extinction powder coatings. Through testing, the outdoor weather resistance of this product has reached the Qualicoat class 1 performance index requirements and can be widely used in industries such as building materials, outdoor furniture, display cabinets, lighting, etc.
Due to the recent introduction of imported low-temperature polyester resin and low-temperature matting agent, their raw material prices are relatively expensive and difficult for end customers to accept. Therefore, it is difficult for powder manufacturers to promote them, and currently only used for some high-end customers and markets. At the same time, we hope that domestic polyester manufacturers and matting agent manufacturers can increase their research and development efforts for such products, localize them as soon as possible, and contribute to the domestic market.
Due to the significant energy-saving and environmental advantages of low-temperature and ultra-low temperature curing, which can greatly reduce coating costs, outdoor low-temperature and ultra-low temperature curing extinction powder coatings have always been a key research topic for raw material manufacturers and powder peers. This article aims to provide some reference opinions for peer researchers through test data, and then select suitable resins and low-temperature extinction agents in subsequent low-temperature extinction research and development projects.