In recent years, the plastic plating is widely used in decorative plating of plastic parts. ABS is the most widely used one. ABS is the terpolymer of acrylonitrile (A), butadiene (B), and styrene (S). For plastic ABS plating, the content of butadiene has great influence for plating and should generally be controlled at 18%to 23%. Butadiene has high content, good mobility, easy molding, and good coating adhesion. Since ABS is the non-conductor, the conductive layer should be made before plating. The conductive layer is made under the following procedure: roughening, neutralization, sensitization, activation, and chemical plating. It is more complex then metal plating and is easy to have problems. We analyze the reason and find the solutions from the point of ABS plating technique.

1. Problems and solutions

1.1 The plating piece is easy to float. The contact part is easy to be burned since the specific gravity of plastic is lighter; therefore, it is easy to float in liquid. The shape of the lamp cover is like a disk. The inner surface is concave and the sides have tow holes. One copper wire stops the two holes for plating. Because the gas is put out during the plating, the lamp cover separates with the copper wire. The copper wire is light and the lamp cover can not drop into the liquid. The float problem is solved by adding heavy matter on the copper wire. The contact point between copper wire and lamp cover is burned and the plastic is exposed. This is caused by bad conduction. To solve the floating and conduction problem, we design the special clamp. The clamp has certain weight and will not make it float; and two relative wide conductive plates are used on the holes on the lamp cover to make the current average. Therefore, the contact point can not be burned.

1.2 The bubble appears while lamp covering chemical copper plating. The bubble becomes large after plating. The lifting plastic plating technique flow is: oil removing→ water cleaning → roughening → water cleaning→ sensitization → water cleaning→ deionization cleaning→ activation→ water cleaning → chemical copper plating → water cleaning → plating → water cleaning →drying. From the above, we can know that if any procedure has problems, the bubble will appear. Many problems lead to bad adhesion force, especially the oil removing and roughening process. If the oil is not removed totally, it may cause falling and peeling off. The lamp cover uses chemical oil removing (the plastic piece can not be used with organic solution). During operation, the workers shake the piece till no bead is on the surface after washing under 65～70℃. The roughening is a very important processing for ABS plastic plating. If the roughening is not enough, the adhesion force reduces; if the roughening is over the standard, the hole will become large and be out of shape. Therefore, the adhesion force will reduce too. Since the stannous is not stable in sensitization solution, the sensitization solution is easy to cease to be effect. If it is not regulated, the activation will fail. If the activation is insufficient, the chemical plating sedimentation is not enough; if the activation is over, the active metal restores too much and forms un-successive film. Therefore, the adhesion force will reduce.

We begin with the oil-removing, and operate under oil removing preparation and operation condition. We check the roughening time, temperature and prepare the sensitization and activation solution. The bubble appears after chemical copper plating. The result is the same after many experiments. We make a conclusion that the bubble is not caused by oil-removing, roughening, sensitization and activation. Then, we doubt about the component and molding technique since the component and molding technique of ABS plastic is important to plating. The ABS kernel is easy to absorb the water. It is required that the water content is lower than 0.1% before pouring. It should be drying under 80℃ in hot wind drier for 2 to 4 hours with dry surrounding environment. The ABS plastic can not be mixed with other components. After investigation, we find that the injection factories put ABS in the humid store room and the material before injection is not dried. We suggest to drying the material under 80℃ for 2 to 4 hours. After the material passes the test, it can be injected. The bubble problem never happens after improvement.

1.3 The black spot appears after plating of the lamp cover. The unglazed lamp cover turns into plating procedure after chemical copper plating. Our technique flow is: nickel plating→ copper plating →light nickel plating →chrome plating. The copper plating solution is stable, but the copper anode produces copper powder (Cu2O) easily and the copper powder will cause rough plating layer after entering into the solution. We use corrosion resistant anode bag covers the anode, then we put it into anode suite. We clean it often after plating. Therefore, the surface of copper plating is light, fine without any problems. The surface after the light nickel plating has not luster but black spot. After adding the lighting agent, the problems can not be solved. We analyze the tank solution and all the component content are in the standard range. After keeping the tank solution for one night, we throw out the clear solution and find out that there is yellow muddy-like sediment at the bottom. From the analysis, we find out that this is caused by high temperature of nickel plating solution and decomposition of lighting agent. While plating, the air mixer turns the mud at the bottom and the mud deposit on the plating layer with nickel ion to form burr and black spot.

Later, we find out that the nickel and chrome plating use the same set of conductive bar. The conductive bar has left chromic anhydride and will bring chrome to nickel tank. The hanging tool is not insulated and it brings copper to the nickel plating solution. All theses contribute to black spot. The copper can be removed by using electrolysis of 0.5A/dm2 current density. If we want to remove hexavalent chromium, we must use sulphuric acid to make PH turn to 3; then we can add sodium sulfite 0.2～0.4g/L and mix to make the hexavalent chromium turn into trivalent chromium.Later, we use low current density to remove trivalent chromium. At last, we use active carbon to remove the organic impurities. The tank solution has no black spot after the treatment. During chrome sleeve processing, we use shape-imitation anodes. Therefore, the lamp cover is light, fine and up to the product standard.