To obtain valuable plastic electroplating coatings, coarsening is crucial in plastic electroplating. For ABS plastics, chemical roughening method is often used, which is to use a mixture of chromic acid and sulfuric acid as the roughening solution. This roughening solution dissolves the spherical particles of butadiene in ABS, forming a concave shaped micro rough surface, greatly increasing the surface area and enhancing the adhesion between the substrate and the coating.
Due to the various grades of ABS plastic, the butadiene content varies among different grades. Therefore, different concentrations and ratios of roughening solutions should be selected during roughening. There are generally two types of roughening fluids, namely high chromic acid type and high sulfuric acid type. The former has a chromic acid content of 400-6009/L and sulfuric acid of 200-3009/L, while the latter has a sulfuric acid content of 10009/L and chromic acid only contains 50-2009/L. The coarsening temperature of both is between 60-70 ℃ and the time is 10-30 minutes.
For ABS that is difficult to roughen, a high chromic acid type can be used, while for ABS that is easy to roughen, a high sulfuric acid type roughing solution can be used.
In addition, the coarsening temperature and time are also important conditions, and the temperature should not exceed 70 ℃. Otherwise, not only will excessive coarsening occur, but also plastic deformation will occur. Generally, when the temperature is high, the roughening time should be shortened, while when the temperature is low, the roughening time should be extended. The old roughening solution should also extend the roughening time.
Before roughening, it is best to perform oil removal or pre roughening treatment to enhance the roughening effect and shorten the roughening time. The general pre-treatment process includes 509 potassium dichromate, 1L sulfuric acid, 70mL water, room temperature, and time of 0.1 to 1min. After this process, the plastic surface can be hydrophilic, but the plating piece after alkaline degreasing must be cleaned before adding the roughening solution, otherwise it may cause premature failure of the roughening solution.