The surface treatment of plastic products mainly includes coating treatment and coating treatment。 Generally, the crystallinity of plastics is larger, the polarity is smaller or non-polar, and the surface energy is lower, which will affect the adhesion of coating。 Because plastic is a non-conductive insulator, it can not be directly coated on the plastic surface according to one-stream electroplating process specifications。 Therefore, before surface treatment, necessary pretreatment should be carried out to improve the bonding force of coating and provide a conductive undercoat with good bonding force for coating。 The first part talks about the pretreatment process of coating, this part talks about the pretreatment process of coating。
2. Pretreatment of coating
The purpose of coating pretreatment is to improve the adhesion between the coating and the plastic surface and to form a conductive metal bottom layer on the plastic surface. The pretreatment process mainly includes mechanical coarsening, chemical deoiling, chemical coarsening, sensitization, activation, reduction and electroless plating. The first three are to improve the adhesion of the coating, and the last four are to form a conductive metal bottom.
1. Mechanical and Chemical Coarsening
Mechanical coarsening and chemical coarsening are mechanical and chemical methods to coarsen the surface of plastics, respectively, in order to increase the contact area between coating and matrix。 It is generally believed that the binding force of mechanical coarsening is only about 10% of chemical coarsening。
2. Chemical degreasing
The degreasing method of coating pretreatment on plastic surface is the same as that of coating pretreatment.
Sensitization is the adsorption of oxidizable substances such as tin dichloride and titanium trichloride on the surface of plastics with certain adsorption capacity. These adsorbed readily oxidized substances are oxidized during activation treatment, while the activator is reduced to catalytic nuclei and left on the surface of the product. The role of sensitization is to lay the foundation for subsequent electroless metal plating.
Activation is the treatment of sensitized surfaces by catalyzing the solution of active metal compounds. Its essence is to immerse the products adsorbed with reductant into the aqueous solution containing oxidant containing noble metal salts. As an oxidant, noble metal ions are reduced by S2+n. The reduced noble metal is deposited on the surface of the products as colloidal particles, which has strong catalytic activity. When the surface is immersed in electroless plating solution, these particles become catalytic centers, which accelerates the reaction rate of electroless plating.