Plastic electroplating has been widely used in decorative electroplating of plastic parts. ABS plastic is the most widely used type in plastic electroplating.
Author: Marisa
ABS plastic is a ternary copolymer of acrylonitrile (A), butadiene (B), and styrene (S). For electroplated ABS plastics, the content of butadiene has a significant impact on electroplating and should generally be controlled between 18% and 23%. High butadiene content, good fluidity, easy molding, and good adhesion to the coating. Due to ABS being non-conductive, a conductive layer must be attached before electroplating. The formation of a conductive layer requires several steps such as roughening, neutralization, sensitization, activation, and chemical plating, which are more complex than metal electroplating and prone to problems in production. We started from the process of ABS plastic electroplating, analyzed the reasons, and found a solution.
1--Plated parts are prone to floating, and the areas in contact with hangers are prone to burning due to the low specific gravity of plastic, making it easy to float in solution. The shape of the lampshade is like a small plate, with a concave inner surface and two small holes on the edges. Initially, only one copper wire was used to clamp the two small holes for electroplating. Due to the release of gases during electroplating, the lampshade is easily detached from the copper wire, and the copper wire is also light, which is not enough to immerse the lampshade in the solution. Later, heavy objects were attached to the copper wire to solve the floating problem. The contact point between the copper wire and the lampshade was burnt and the plastic was exposed, which was caused by poor conductivity. In order to solve the problems of workpiece floating and conductivity, we have designed specialized fixtures. The clamp has a certain weight and will no longer float when the lampshade is installed. Then, two wider conductive pieces are used to clamp the holes in the lampshade to ensure even current flow and prevent the contact points from burning.
2--Bubbles appear during the chemical copper plating of lampshades. After electroplating, the bubbles become larger and can be lifted up. The process flow of plastic electroplating is: degreasing → water washing → roughening → water washing → sensitization → tap water washing → deionized water washing → activation → water washing → chemical copper plating → water washing → electroplating → water washing → drying. From the above, it can be seen that any problems in the steps before chemical copper plating will lead to bubbling. There are many reasons that can cause poor adhesion, and the oil removal and roughening processes are often prone to problems. Incomplete oil removal can cause peeling and detachment. The lampshade adopts chemical degreasing (organic solvents are not suitable for degreasing plastic parts). During operation, the temperature is raised to 65-70 ℃, and the workpiece is continuously shaken until no water droplets hang after washing with water. Coarsening is an important process in ABS plastic electroplating. Insufficient coarsening and decreased adhesion; Excessive coarsening will cause the pores to enlarge and deform, and the bonding force will also decrease. Due to the instability of divalent tin in the sensitization solution, the sensitization solution is prone to failure. If not adjusted, it can lead to activation failure. Insufficient activation can result in incomplete deposition of chemical coatings; However, excessive activation can lead to excessive reduction of active metals on the surface, resulting in the formation of discontinuous film layers and a decrease in bonding strength.
We started with degreasing and strictly followed the degreasing liquid formula and operating conditions. We also checked the time and temperature of the roughening process and prepared a new sensitization solution and activation solution. However, bubbles still appeared after electroless copper plating. After several repeated experiments, the results were the same, and it was finally determined that the bubbling was not caused by oil removal, roughening, sensitization, or activation. At this point, it is suspected that there may be issues with the composition and molding process of the material, as the composition and molding process of ABS plastic are directly related to electroplating. ABS particles are prone to water absorption and require a moisture content of less than 0.1% before injection. They must be dried in an 80 ℃ hot air drying oven for 2-4 hours, and the surrounding environment must also be dry. No other components can be mixed into ABS plastic. We found through investigation that injection molding factories stack a large number of molded ABS plastic parts on damp warehouse floors, and the raw materials before injection molding are not dried. Under our guidance, the raw materials to be injected are dried at 80 ℃ for 2-4 hours, and after inspection, they meet the electroplating requirements before injection molding. The improved lampshade no longer experiences blistering after electroplating.