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Pretreatment of automotive plastic parts before painting to strengthen coating adhesion method

Update:14-07-2022
Summary:In recent years, with the fiery heating up of the domestic automobile market, my...
In recent years, with the fiery heating up of the domestic automobile market, my country's automobile industry has developed rapidly, which also makes people put forward higher requirements for the appearance, safety, energy saving and environmental protection of automobiles. The use of lightweight plastic materials can not only reduce the quality of the car, save energy, and make the car safer and more comfortable, but also more resistant to atmospheric corrosion and gasoline than metals, and easy to process and shape to reduce production costs. The application is more and more extensive.
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 function and decorative effect, and prolong the life of plastic parts, the surface coating of plastic products must be carried out. Most plastics have the characteristics of small polarity, large crystallinity, low surface tension, poor wettability, and smooth surface, which lead to poor coating adhesion of plastic parts. Therefore, how to improve the adhesion of plastic parts coating is one of the key problems to be solved in plastic part coating.
In order to solve the problem of coating adhesion of automotive plastic parts, you must have some understanding of the process of coating automotive plastic parts. The process of automotive plastic parts can be roughly divided into the following parts:
Grinding of blanks, chemical treatment, dust removal, primer spraying, one-color paint (or metallic flash paint), varnishing, baking, handover inspection, storage of qualified products, repair or paint stripping of unqualified products. It is understood that among these many process links, the most important link to improve the adhesion of plastic parts coating is pre-painting. The purpose of pre-treatment of automotive plastic parts is to improve the adhesion of coatings to plastics through a series of physical and chemical methods, reduce various defects of coatings, and thus improve the quality of plastic coatings. The pretreatment of plastic parts paint 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. Plastics are poor conductors and are prone to static electricity. During storage and transportation, they absorb dust or debris from product trimming, 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 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, so that the surface is oxidized and introduced into hydrophilic functional groups, thereby improving the 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
Flame treatment is to spray flame on the plastic surface, so that the surface temperature reaches 1000-2800 ℃, but the treatment time is very short (in seconds) to avoid damage and melting of automobile plastic parts. This allows local oxidation of molecules on the surface of automotive plastic parts, thereby improving wetting and adhesion
4. Surfactant treatment method
The 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, wetting and adhesion to plastics.
5. Hot melt treatment
Thermal solvent treatment refers to the use of specific solvents for short-term treatment of plastics at high temperatures. During the treatment, the plastic surface undergoes violent expansion, or a rough surface containing corroded amorphous parts and less affected crystalline parts appears, thereby improving the adhesion of the paint.
6. Ultraviolet treatment
The 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 automobile plastic parts, increase the surface tension, reduce the contact angle of the coating, and improve the adhesion of the coating film.
7. Plasma treatment
Plasma equipment is mainly composed of plasma generator, gas delivery system and plasma shower head. The working principle of the method is as follows: high-voltage high-frequency energy is generated by a plasma generator, low-temperature plasma is generated by glow discharge, and the plasma is sprayed on the surface of the plastic part with the help of compressed air to eliminate the static electricity on the surface of the plastic part and remove the surface of the plastic part. of hydrocarbon pollutants (such as grease and auxiliary additives in plastic materials, etc.).
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