In the processing of plastic extrusions, the purpose of coating pre-treatment is to improve the adhesion of the coating to the plastic surface and to form a conductive metal underlayer on the plastic surface. The pretreatment process mainly includes: mechanical roughening, chemical degreasing, chemical roughening, sensitization treatment, activation treatment, reduction treatment, and electroless plating. The following is a detailed description of the pre-coating process for the coating of plastic extrusions.
1. Mechanical roughening and chemical coarsening. Mechanical roughening and chemical roughening treatment are to mechanically and chemically thicken the surface of the plastic to increase the contact area between the coating and the substrate. It is generally believed that the bonding force that can be achieved by mechanical roughening is only about 10% of chemical coarsening.
2. Chemical degreasing. The method of pre-treatment degreasing of the plastic surface coating is the same as the pre-treatment degreasing method of the coating.
3. Sensitization. Sensitization is the adsorption of some easily oxidizable substances such as tin dichloride and titanium trichloride on the surface of plastics with certain adsorption capacity. These adsorbed oxidizable species are oxidized during the activation treatment, and the activator is reduced to a catalytic nucleus which remains on the surface of the article. The role of sensitization is to lay the foundation for subsequent electroless plating of metal layers.
4. Activation. Activation is by treating the sensitized surface with a solution of a catalytically active metal compound. The essence is that the product adsorbing the reducing agent is immersed in an aqueous solution of an oxidizing agent containing a noble metal salt, so that the noble metal ion is reduced as S2 n as an oxidizing agent, and the reduced noble metal is deposited on the surface of the product as colloidal particles, which has a strong Catalytic activity. When such a surface is immersed in an electroless plating solution, these particles become a catalytic center, and the reaction speed of the electroless plating is accelerated.
5. Restore treatment. The product after activation treatment and washing with water is immersed in a certain concentration of a reducing agent solution for electroless plating before electroless plating, so as to reduce and remove the unwashed activator, which is called reduction treatment. . When electroless copper plating, it is reduced by a formaldehyde solution, and when electroless nickel plating is treated with a sodium hypophosphite solution.
6, electroless plating. The purpose of electroless plating is to create a layer of conductive metal film on the surface of plastic products to create conditions for plating metal layers on plastic products. Therefore, electroless plating is a key step in plastic plating.