Advantages of using powder coating level agents

2021-09-15   Pageview:256

Due to the different polymerization monomers and different polymerization methods, there is a possibility of incompatibility between different leveling agents. In order to ensure good wetting performance, leveling agent should be uniformly dispersed in the powder system, good dispersion is necessary in the production process. Contaminants with low surface tension can seriously affect the surface properties of the coating. Therefore, during the production or processing process, try to avoid the introduction of low surface tension substances into the coating, such as oil, water vapor, silicone oil, etc.

 

 

 

 

 

 

 

 

 

 

Without leveling agent, the powder coating not only has poor fluidity and orange peel, but also tends to produce pinholes on the surface of the coating film. This is due to the difference in the surface tension of the powder coating melt, which tends to flow in the direction of higher surface tension, resulting in a very rough surface. The film formation of powder coatings can be divided into a melt phase and a flow phase immediately afterwards. Poor flowability mainly originates in the second phase. These problems usually arise in the first phase of film formation (melt phase) and are enhanced in the flow phase. Surface defects are substrate-independent and therefore cannot be considered as a result of poor wetting of the substrate, but rather as a result of very poor flow. High surface tension promotes leveling. A low surface tension also increases wettability and reduces defect generation, while a low melt viscosity also promotes better leveling. Therefore, a combination of these factors should be considered in practice to balance the final performance. The best way to solve the problem is to add the right amount of leveling agent.

Different powder systems have different surface tensions and may interfere with each other. In the actual production arrangement, the application of high surface tension varieties to low surface tension varieties in order to reduce the occurrence of cross-contamination phenomenon. The current leveling agents are mostly homopolymers or copolymers of acrylates, while some acrylic-silicone resins and pure silicone resins are considered/hazardous.0 In early tests, highly reactive or incompatible silicone resins (e.g., polysilanes) have led to plant-wide contamination, so there has been a resistance to the use of silicone resins.

However, there are modified polysiloxanes (e.g., polyethers and polyester-modified polysiloxanes, ptfe modified wax) that can improve the leveling properties of powder coatings without contamination. Generally, leveling agents are viscous liquids, so they are usually added to the resin in a single batch at a concentration of 5% to 15% or precipitated onto fumed silica at a concentration of 60% to 70% as a master batch. This makes it easier to meter and to disperse uniformly during the pre-mixing phase of the powder coating. Because silica tends to create a haze on transparent powders, resin is preferred as a carrier when high transparency is required.

Some high molecular weight thermoplastic polymers are also very effective in preventing shrinkage of powder coatings. For example, polyvinyl butyral used as leveling agent, because of their high melting point, it is difficult to disperse into the resin melt during extrusion, so it is soon replaced by liquid polyacrylic acid.

 

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