Share the surface treatment technology before electroplating of plastic products
The surface treatment of plastic products processing mainly includes coating treatment and coating treatment.
Generally speaking, plastics have large crystallinity, small polarity or non-polarity, and low surface energy, which will affect the adhesion of the coating. Since plastic is a non-conductive insulator, it cannot be directly coated on the surface of the plastic according to the electroplating process regulations. Therefore, before the surface treatment, the necessary pretreatment should be carried out to improve the adhesion of the coating and provide a conductive bottom layer with good adhesion to the coating.
The pretreatment of the coating includes the degreasing of the plastic surface, that is, the cleaning of the surface with oil stains and mold release agents, and the activation of the plastic surface to improve the adhesion of the coating.
One. Degreasing of plastic products
Similar to the degreasing of metal products. The degreasing of plastic products can be cleaned with organic solvents or alkaline aqueous solutions containing surfactants. Organic solvent degreasing is suitable for cleaning organic dirt such as paraffin, beeswax, grease and other organic dirt on the plastic surface. The organic solvents used do not dissolve, expand or crack plastics, have low boiling point, volatility, non-toxicity and non-flammability.
Alkaline aqueous solutions are suitable for degreasing alkali-resistant plastics. The solution contains caustic soda, alkali salts and various surfactants. The most commonly used surfactant is the OP series, i.e. alkylphenol ethoxylate, which does not form foam or remain on the plastic surface.
2。 Surface activation of plastic products
This activation is to increase the surface energy of the plastic, that is, to form some polar groups on the surface of the plastic or make it thicker, so that the coating is easier to wet and adsorb on the surface of the part. There are various methods of surface activation, such as chemical oxidation, flame oxidation, solvent vapor etching and corona discharge oxidation. Among them, the most commonly used method is chemical crystal oxidation, which is usually used as a chromic acid treatment solution. Its typical formula is potassium dichromate 4.5%, water 8.0%, concentrated sulfuric acid (more than 96%) 87.5%.
Some plastic products, such as polystyrene and ABS plastics, can be coated directly without chemical oxidation.
In order to obtain a high-quality coating, it is also suitable for chemical oxidation treatment. For example, after degreasing ABS plastics, they can be etched with dilute chromic acid treatment solution. Typical treatment formulations are 420 g L of chromic acid and 200 ml L of sulfuric acid (specific gravity 1.83). Typical treatment processes are 65°C, 70°C5min, 10min, washing, drying.
The advantage of chromic acid treatment solution etching is that it can be treated uniformly, no matter how complex the shape of the plastic product. Its disadvantage is that there are hazards and pollution problems in operation.
The purpose of coating pretreatment is to improve the adhesion between the coating and the plastic surface and to form a conductive metal substrate on the plastic surface.
The pretreatment process mainly includes mechanical roughening, chemical degreasing and chemical roughening, sensitization treatment, activation treatment, reduction treatment and electroless plating. The last three are to improve the adhesion of the coating, and the last four are to form a conductive metal substrate.