The surface of the treated plastic article is treated with two coating treatments and a coating coating. The plastic has a large degree of crystallinity, a small polarity or no polarity, and the surface energy of the plastic product is low, which affects the adhesion of the coating. Since plastic is a non-conductive insulator, it is not possible to directly coat the surface of a plastic product according to a plating process specification. Therefore, before the surface treatment of the plastic product, the necessary pre-treatment should be performed to improve the adhesion of the coating coating and A conductive underlayer that provides good adhesion to the coating process.
1. Pretreatment of coated coating of plastic products
The pretreatment includes degreasing treatment of the surface of the plastic product, that is, cleaning of the oil stain and release agent on the surface of the plastic product, and activation treatment of the surface of the plastic product for the purpose of improving the adhesion of the coating.
(1) Degreasing of plastic products. Similar to the degreasing of metal products, the degreased plastic products can be cleaned with an organic solvent or degreased with an alkaline aqueous solution containing a surfactant. Organic solvent degreasing is suitable for cleaning paraffin, beeswax, fat and other organic soils from the surface of plastic products. The organic solvent used should not dissolve, swell or crack the plastic products. It has low boiling point, is volatile, and is non-toxic. Not flammable.
The alkaline aqueous solution is suitable for degreasing of alkali-resistant plastic products. Because this solution contains caustic soda, basic salts and various surface active substances. The most commonly used surface active material is the OP series, an alkyl phenol ethoxylate, which does not form a foam and does not remain on the surface of the plastic article.
(2) Activation of the surface of plastic products. Activation is to improve the surface energy of plastic products. It is to create some polar groups on the surface of plastic products or to roughen them to make the coatings more wettable and adsorbed on the surface of the parts. There are many methods for surface activation of plastic products, such as chemical oxidation, flame oxidation, solvent vapor etching and corona discharge oxidation. The most widely used one is chemical crystal oxidation treatment. This method is commonly used as a chromic acid treatment liquid. Its typical formula is 4.5% potassium dichromate, 8.0% water, and 87.5% concentrated sulfuric acid (96% or more).
Some plastic products, such as polystyrene plastic products and aBS plastic products, can also directly coat the surface of plastic products without chemical oxidation treatment. In order to obtain high-quality coating coating, it can also be treated with chemical oxidation. For example, aBS plastic products can be etched with rare chromic acid treatment solution after degreasing. The typical treatment formula is chromic acid 420g/L, sulfuric acid. (specific gravity 1.83) 200ml / L. The typical treatment process is 65 ° C 70 ° C / 5 min 10 min, washed with water and dried.
The advantage of etching with chromic acid treatment solution is that no matter how complicated the shape of the plastic product is, it can be uniformly treated, but there is a certain danger in operation, and there is also a problem of pollution.
2. Pretreatment of plating coating
The purpose of the coating pre-treatment is to improve the adhesion of the coating to the surface of the plastic article and to form a conductive metal underlayer on the surface of the plastic article. The pretreatment processes mainly include: mechanical roughening, chemical degreasing, chemical roughening, sensitization treatment, activation treatment, reduction treatment, and electroless plating. The first three are to improve the adhesion of the coating, and the last four are to form a conductive metal underlayer.
(1) Mechanical roughening and chemical coarsening. The mechanical roughening and chemical roughening treatment are to coarsely thicken the surface of the plastic product by mechanical and chemical methods, respectively, to increase the contact area between the plating layer 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 surface coating of the plastic product is the same as the method of pre-treatment degreasing of the coating.
(3) Sensitization. Sensitization has a certain adsorption capacity, and some easily oxidized substances such as tin dichloride and titanium trichloride are adsorbed on the surface of plastic products. These adsorbed oxidizable substances are oxidized during the activation treatment, and the activator is reduced to the catalytic nucleus and remains on the surface of the plastic article.
(4) Activation. Activation is by treating the surface of the sensitized plastic article with a solution of the catalytically active metal compound. The essence is that the plastic product adsorbing the reducing agent is immersed in the aqueous solution of the oxidizing agent containing the precious metal salt, so that the noble metal ion is reduced by S2+n as the oxidizing agent, and the reduced precious metal is deposited on the surface of the product as colloidal particles, which is 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) Reduction treatment. The plastic product after activation treatment and washing with water is immersed in a certain concentration of a reducing agent solution for electroless plating before the electroless plating, so as to remove the unwashed activator, which is called Restore processing. When electroless copper plating is carried out, 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 the electroplating of plastic products.
N-Methylimidazolium Chloride,N-Methylimidazolium Chloride 99%,N-Methylimidazolium Chloride In Stock,Imidazole Ionic Liquids
Henan Tianfu Chemical Co.,Ltd , https://www.tianfuchem.com