In recent years, as the domestic automobile market heats up, China’s automobile industry has developed rapidly, which also makes people put forward higher requirements for the appearance, safety, energy conservation and environmental protection of automobiles. The use of lightweight plastic materials can not only reduce the quality of cars, save energy, and make cars safer and more comfortable. It is also more resistant to atmospheric corrosion and gasoline than metal, and is easy to process and shape and reduce production costs. Therefore, it has become more and more widely used. usage of.
Although the application of plastic parts has many advantages, the plastic parts themselves also face many problems, such as poor UV resistance and easy aging. Therefore, in order to improve the texture of plastic products, improve their protective functions and decorative effects, and extend the life of plastic parts, it is necessary to carry out surface coating on plastic products. Most plastics have the characteristics of low polarity, large crystallization, low surface tension, poor wettability, and smooth surface, which leads to poor adhesion of the plastic coatings. Therefore, how to improve the adhesion of plastic parts coating is one of the key problems that need to be solved in plastic parts coating.
In order to solve the problem of coating adhesion of automotive plastic parts, it is necessary to understand the process flow of automotive plastic parts coating. According to the author’s sorting and collection, the process flow of automotive plastic parts can be roughly divided into the following parts:
Blank polishing, chemical treatment, dust removal, primer, color paint (or metallic flash paint), finishing, baking, inspection, acceptance of qualified products, repairing or stripping of unqualified products.
It is understood that in these many process links, the most important link to improve the coating adhesion of plastic parts is pre-painting. The purpose of pre-treatment of automobile plastic parts is to improve the adhesion of the coating to the plastic through a series of physical and chemical methods, reduce various defects of the coating, and improve the quality of the plastic coating. The pretreatment of plastic parts before painting includes conventional treatment, acid treatment, flame treatment, surfactant treatment, hot solvent treatment, ultraviolet treatment and plasma treatment.
1, conventional treatment method
The so-called conventional treatment, that is, dust removal, static removal, and degreasing. Plastic is a poor conductor and is prone to static electricity. During storage and transportation, it absorbs dust or debris trimmed from the product, which will seriously affect the adhesion and hardness of the coating film. In order to clean the surface of the product, it can be washed with a chemical solution, and it can also remove dust and static electricity.
2, acid treatment
This method is to treat the surface of the plastic with an acidic substance to oxidize the surface to introduce hydrophilic functional groups, thereby improving surface wettability; at the same time, the surface is etched into a porous structure to improve the adhesion of the coating on the plastic.
3, flame treatment method
Flame treatment is to spray flame on the plastic surface to make the surface temperature reach 1000～2800℃, but the treatment time is very short (in seconds) to avoid plastic damage and melting. In this way, the molecules on the plastic surface layer can be locally oxidized, thereby improving the wettability and adhesion.
4. Surfactant treatment method
Surfactant treatment method is to add a surfactant to the plastic to form a monomolecular layer on the surface of the plastic to obtain a high-energy surface and improve the adhesion of the coating film. In addition, surfactants can simultaneously impart antistatic properties, wettability and adhesion to plastics.
5. Hot melt treatment method
Thermal solvent treatment method refers to the use of specific solvents for short-term treatment of plastics at high temperatures. During the treatment process, the plastic surface expands violently, or a rough surface with corroded non-crystalline part and less affected crystalline part appears, thereby improving the adhesion of the coating.
6. Ultraviolet treatment method
Ultraviolet treatment method is to irradiate the plastic with ultraviolet rays, and use the action of oxygen in the air to generate polar groups on the surface of the plastic, increase the surface tension, reduce the contact angle of the coating, and improve the adhesion of the coating.
7, plasma treatment method
Plasma equipment is mainly composed of plasma generator, gas delivery system and plasma nozzle. The working principle of this method is: high-voltage high-frequency energy is generated by the plasma generator, low-temperature plasma is generated by glow discharge, and the plasma is sprayed to the surface of the plastic part with the help of compressed air to eliminate static electricity on the surface of the plastic part and remove the surface of the plastic part Hydrocarbon contamination (such as grease and auxiliary additives in plastic materials, etc.).
In addition, in order to improve the adhesion of the coating, the surface treatment and construction environment of plastic parts before coating should be strictly controlled during the construction process to ensure the quality of coating. While using new plastic materials, attention should be paid to increasing its surface tension. And polarity, if necessary, change the pre-treatment process and primer varieties.
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Link to this article：How to solve the coating adhesion of automotive plastic parts
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