Problems and solutions in electroplating of the ho

Problems and solutions in ABS plastic electroplating introduction in recent years, plastic electroplating has been widely used in decorative electroplating of plastic parts. ABS plastic is one of the most widely used in plastic electroplating. ABS plastic is a terpolymer of acrylonitrile (a), butadiene (b) and styrene (s). For electroplated ABS plastics, the content of butadiene has a great impact on electroplating. Generally, it should be controlled at 1810. Start the experiment: click the experiment start button to start the experiment% ～ 23%. High butadiene content, good fluidity, easy to form, and good adhesion to the coating. Since ABS is a non-conductor, a conductive layer must be attached before electroplating. The formation of conductive layer needs several steps, such as coarsening, neutralization, sensitization, activation and electroless plating. It is more complex than metal plating, and it is prone to problems in production. Starting from the electroplating process of ABS plastics, we analyzed the reasons and found out the solutions

2 problems and solutions

2.1 the plated parts are easy to float. The wear research on the external spine simulator in contact with the hanger shows that the place is easy to be scorched. Because the specific gravity of the plastic is small, it is easy to float in the solution. The shape of the lampshade is like a small disc, the inner surface is recessed, and there are two small holes on the edge. At first, only one copper wire is used to clamp the two small holes for electroplating. Due to the emission of gas in electroplating, the lampshade is easy to separate from the copper wire, and the copper wire is also light, which is not enough to immerse the lampshade in the solution. Later, a heavy object was attached to the copper wire to solve the floating problem. The contact point between the copper wire and the lampshade is burnt and the plastic is exposed, which is caused by poor conductivity. In order to solve the problem of workpiece floating and conductivity, we designed a special fixture. The clip has a certain weight, and it will not float after being put on the lampshade. Then two wide conductive sheets are clamped on the hole of the lampshade to make the current uniform everywhere and the contact point will not be burnt

2.2 bubbles appear during electroless copper plating on the lampshade, and the bubbles become larger after electroplating, and the plastic can be uncovered. The technological process of electroplating is: degreasing → water washing → roughening → water washing → sensitization → tap water washing → deionized water washing → activation → water washing → electroless copper plating → water washing → electroplating → water washing → drying. It can be seen from the above that problems in any step before electroless copper plating will lead to blistering. There are many reasons for poor adhesion, and the process of degreasing and roughening are often prone to problems. Incomplete degreasing will cause peeling and falling off. The lampshade adopts chemical degreasing (plastic parts are not suitable for degreasing with organic solvents). During operation, the temperature rises to 65 ~ 70 ℃, and the workpiece is constantly shaken until there are no drops of water after washing. Coarsening is a very important process in ABS plastic electroplating. The coarsening is insufficient, and the adhesion decreases; Excessive coarsening will enlarge and deform the hole and reduce the binding force. Because the divalent tin in the sensitizer is extremely unstable, the sensitizer is easy to fail. If it is not adjusted, it will lead to activation failure. Insufficient activation will lead to incomplete deposition of chemical coating; However, excessive activation will lead to excessive reduction of active metals on the surface and the formation of discontinuous films, which will also reduce the adhesion. We started from degreasing, strictly followed the formula and operating conditions of degreasing fluid, checked the time and temperature of roughening process, and newly prepared sensitizing fluid and activating fluid. As a result, bubbles still appeared after electroless copper plating. After several repeated tests, the results were the same. Finally, it was concluded that the bubbling was not caused by oil removal, coarsening, sensitization and activation. At this time, it is suspected that there is a problem with the composition and molding process of ABS plastic, because the composition and molding process of ABS plastic are directly related to electroplating. ABS particles are easy to absorb water. It is required that the moisture content before injection is less than 0.1%. They must be dried in a hot-air drying oven at 80 ℃ for 2 ~ 4h, and the surrounding environment must also be dry. ABS plastic cannot be mixed with other ingredients. Through investigation, we found that the injection molding plant stacked a large number of molded ABS plastic parts on the wet warehouse floor, and the raw materials before injection molding were not dried. Under our guidance, the raw materials to be injected are dried at 80 ℃ for 2 ~ 4h, and then injected after being tested to meet the electroplating requirements. The blistering problem of the improved lampshade did not appear after electroplating

2.3 black spots appear on the surface of the lampshade after electroplating. After electroless copper plating of the matte lampshade, it is transferred to the electroplating process. The process flow we adopt is: nickel plating → copper plating → bright nickel plating → chromium plating. The copper plating solution is relatively stable. The main problem is that copper anode is easy to produce copper powder (Cu2O) in electroplating, and copper powder entering the plating solution will cause coarseness of the coating. We wrap the anode with corrosion-resistant anode cloth and put it into the anode as the total injection weight (all cavity sleeves are often opened and cleaned after electroplating, so the surface after copper plating is bright and meticulous. 9. The shell of the experimental machine must be safely grounded without any problems. The surface of the parts is Matt after nickel plating, and there are black spots. After adding brightener, the problem is still not eliminated. Analyze the bath solution, and the content of each component is within the range. After the bath solution is placed overnight, pour all the supernatant into the standby bath, and it is found that there is yellowish brown muddy sediment at the bottom of the bath. After analysis It is caused by the high temperature of nickel plating solution and the decomposition of brightener. During electroplating, the air stirring device turns over the sludge at the bottom of the tank and deposits it on the coating together with nickel ions, causing burrs and black spots. Later, it was also found that because nickel plating and chromium plating use the same set of conductive rods, the conductive rods have chromic anhydride left during chromium plating, which is easy to bring chromium into the nickel bath during nickel plating; And because the hanger is not insulated, copper impurities are brought into the nickel plating solution, which are the reasons for blackening. Copper impurities can be removed by electrolysis with current density of 0.5a/dm2. To remove hexavalent chromium, first adjust the pH of the plating solution to about 3 with sulfuric acid, then add 0.2 ~ 0.4g/l sodium sulfite, stir to reduce hexavalent chromium to trivalent chromium, and then remove trivalent chromium with low current density. Finally, the organic impurities are removed by activated carbon treatment and filtration. After the bath solution is treated, there are no black spots after nickel plating. During chrome plating, the concave part of the lampshade adopts pictographic anode, and the lampshade finally plated is bright and meticulous, which meets the product requirements

3 conclusion

1) the composition and molding process of plastic parts can not be ignored, which is often a problem that electroplating workers are not easy to detect

2) special hangers should be designed during electroplating

3) pay attention to the maintenance of tank liquid to keep all components within the process specification

4) strengthen the cleaning between processes and do not bring in other impurities