Discussion on low temperature curing powder coating

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Although powder coatings have the advantages of four "E" (Economical-Environmental-Environmental-Efficient-Efficient-Excellent Performance-Performance), some of its weaknesses are obvious. If the curing conditions are harsh, the curing temperature is generally between 180 and 200 °C. If the curing temperature can be lowered, the energy consumption can be reduced, which is the need for environmental protection, energy saving and emission reduction. The high curing temperature, in addition to high energy consumption, limits the coating of some substrates that cannot withstand high temperatures, such as plastics and wood, which greatly affects the expansion of powder coating applications. From the perspective of further improving the efficiency, the powder coating which can be cured at a low temperature can greatly shorten the curing time and improve the production efficiency while maintaining the temperature constant. Therefore, achieving low temperature curing of powder coatings has become one of the development directions of the powder coating industry.

For a long time, in the powder coatings and related supporting fields such as raw materials, equipment, the efforts of the colleagues, in the low-temperature curing of powder coatings has made great progress. Now pure epoxy system sand effect products can be cured at 130 ° C / 15 minutes. The flat high gloss epoxy system can be cured at 140 ° C / 15 minutes. However, epoxy has poor yellowing resistance and weather resistance and cannot be used outdoors. The polyester/epoxy hybrid system sand product which is better than the epoxy system can also be made at 135 ° C / 15 minutes, and the flat high gloss product can be cured at 150 ° C / 15 minutes (slightly flat). The pure polyester system sand product can be cured at 140 ° C / 15 minutes, and the flat high light can be cured at 160 ° C / 15 minutes. However, pure polyester system flat low-light products are still very difficult.

It is technically difficult to achieve ultra-low temperature curing of powder coatings. First of all, the curing system of powder coating is a low-temperature latent curing system. If the system has high low-temperature reaction activity, it will affect the powder baking extrusion and storage stability. On the other hand, the resin and curing used in powder coating. The agents are solids with higher softening point, and the melt viscosity is higher at low temperature. When curing at low temperature, the coating film is difficult to level and affect the surface effect. If a resin having a lower softening point and a curing agent are used, the melt viscosity can be lowered, but the storage stability of the powder is deteriorated, and it is required to be stored at a low temperature for refrigerating, which causes inconvenience to the use. Therefore, the search for a resin and a curing agent that are suitable for powder storage with both a high softening point and a suitable reactivity is the key to preparing a low temperature curing powder coating.

Low-temperature curing powder coating development direction

To reduce the curing temperature of the powder coating, the following discussion will be made from the main resin, curing agent, catalyst, infrared light curing, ultraviolet curing, spray drying method for powder coating production of powder coating and radical reaction curing.

Whether the powder coating is thermoplastic or thermosetting, the film forming temperature is about 180-200 ° C, and the curing time is long (10-20 min), which limits its use only to heat-resistant substrates such as metal, and time-consuming, relative energy consumption. Larger. For every 10°C reduction, the curing temperature is about 10% energy saving. In order to save energy and reduce costs, the coating range of powder coatings is expanded, and the solvent-based coating line is better aligned. Powder coatings must be developed in the direction of low-temperature curing. The low-temperature curing of the powder coating can be achieved by reducing the melting temperature, viscosity, softening point of the resin itself, increasing the functional group of the resin, increasing the degree of crosslinking, adding appropriate auxiliaries, and applying appropriate catalysts. Reducing the curing temperature of the powder coating not only accelerates the production speed of the automatic production line and improves the production efficiency, saves energy, but also greatly increases the application range of the powder coating.

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