The purpose of pre-treatment for coating is to improve the adhesion between the coating and the plastic surface and to form a conductive metal substrate on the plastic surface.
Author: Marisa
The purpose of pre-treatment for coating is to improve the adhesion between the coating and the plastic surface and to form a conductive metal substrate on the plastic surface. The pre-treatment processes mainly include mechanical roughening, chemical degreasing, chemical roughening, sensitization treatment, activation treatment, reduction treatment, and chemical plating. The first three items are to improve the adhesion of the coating, while the last four items are to form a conductive metal substrate.
(1) Mechanical roughening and chemical roughening. Mechanical roughening and chemical roughening treatment are the use of mechanical and chemical methods to roughen the surface of plastics, respectively, in order to increase the contact area between the coating and the substrate. It is generally believed that the binding force achieved by mechanical roughening is only about 10% of that achieved by chemical roughening.
(2) Chemical degreasing. The method of removing oil before coating on plastic surface is the same as that of removing oil before coating.
(3) Sensitization. Sensitization is the process of adsorbing easily oxidizable substances, such as tin dichloride and titanium trichloride, onto the surface of plastics with a certain adsorption capacity. These easily oxidizable substances that are adsorbed are oxidized during activation treatment, while the activator is reduced to catalytic crystal nuclei and left on the surface of the product. The function of sensitization is to lay the foundation for subsequent chemical plating of metal layers.
(4) Activation. Activation is achieved by treating sensitized surfaces with a solution of catalytically active metal compounds. The essence is to immerse the product adsorbed with a reducing agent into an aqueous solution containing an oxidizing agent containing a precious metal salt. As a result, the precious metal ions are reduced by S2+n as the oxidizing agent, and the reduced precious metal is deposited as colloidal particles on the surface of the product, which has strong catalytic activity. When this surface is immersed in a chemical plating solution, these particles become catalytic centers, accelerating the reaction rate of chemical plating.
(5) Restoration processing. After activation treatment and washing with clean water, the product is immersed in a certain concentration of reducing agent solution used during chemical plating before chemical plating, in order to reduce and remove the uncleaned activating agent. This is called reduction treatment. During chemical copper plating, formaldehyde solution is used for reduction treatment, while during chemical nickel plating, sodium hypophosphite solution is used for reduction treatment.
(6) Chemical plating. The purpose of chemical plating is to generate a conductive metal film on the surface of plastic products, creating conditions for electroplating metal layers on plastic products. Therefore, chemical plating is a key step in plastic electroplating.