Material selection and Electroplating texture Analysis of Electroplated Plastics.
There are many kinds of plastics, but not all of them can be electroplated.
Some plastics have poor adhesion to the metal layer and have no practical value; some of the physical properties of some plastics and metal coatings, such as the coefficient of expansion, are too different, so it is difficult to guarantee their performance in a high-temperature difference environment.
ABS is the most commonly used in electroplating, followed by PP.
In addition, PSF, PC, PTFE and so on also have successful electroplating methods, but they are difficult.
Material analysis.
International plastic electroplating formed large-scale production in the 1950s, and China also began to produce plastic electroplating in the mid-1960s, which was mainly used for buttons, buckles and other small products at that time. The quality requirements are as good as metal.
With the development of the times and the continuous improvement of product quality, the requirements for coating quality should be improved accordingly.
Before the reform and opening up, the improvement of product quality was achieved in the form of targets issued by administrative orders, but the situation after the reform and opening up was different. The “superiors” were gone, and the indicators were gone. The requirements of customers have become the indicators of product quality, which you can or may not achieve, but it is related to the survival or elimination of manufacturers and their processes.
Therefore, all the proposed quality requirements are very substantive or really effective and are also economically feasible.
Nowadays, the driving force for the continuous improvement of the quality requirements of plastic plating lies in the development of foreign-funded enterprises in China, because the world, especially Japan and Taiwan Province, which are close to China, all hope to make use of the existing conditions in the mainland to process products and reach the required level of quality, which exposes the deficiency of our plastic plating quality and forces us to improve our quality.
The present situation of the quality of plastic electroplating: the quality level of plastic electroplating in advanced industrial countries is indeed very high, and the quality level of plating parts of some foreign-funded units in Guangdong is also good, and some units in Zhejiang are not poor.
Mainly manifested in the appearance can be comparable with foreign advanced products, and can meet the quality requirements of foreign-funded enterprises.
As for the internal quality, the quality is uneven due to the imperfection of testing methods and testing standards.
In recent years, plastic electroplating has been widely used in the decorative electroplating of plastic parts.
ABS plastic is the most widely used in plastic electroplating.
ABS plastic is a terpolymer of acrylonitrile (A), butadiene (B), and styrene (S).
For electroplating grade ABS plastics, the content of butadiene has a great influence on electroplating, which should be controlled at 18%-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 the conductive layer goes through several steps such as coarsening, neutralization, sensitization, activation, and electroless plating, which is more complex than metal plating and is prone to problems in production.
Starting from the process of plastic electroplating, we analyze the reasons and find out solutions.
- The plated parts are easy to float, and the place in contact with the hanger is easy to be charred because the proportion of plastic is small, so it is easy to float in the solution.
The lampshade is shaped like a small plate, the inner surface is concave, and there are two small holes on the edge. at first, only one copper wire is stuck with two small holes for electroplating.
Due to the release 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 make the lampshade immersed 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 is scorched and the plastic is exposed, which is caused by poor conductivity.
In order to solve the problem of the workpiece floating and conductive, we have designed a special fixture.
The fixture has a certain weight, it no longer floats after putting on the lampshade, and then two wide conductive plates are stuck on the hole of the lampshade, so that the current is uniform everywhere, and the contact point will not be charred. - The bubble appears during the electroless copper plating of the lampshade, and the bubble becomes larger after electroplating, and the technological process of plastic electroplating can be uncovered as follows: deoiling, water washing, coarsening, water washing, sensitizing, tap water washing, deionization 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 bubbling.
There are many reasons for poor adhesion, and the problems are often caused by the deoiling process and coarsening process.
If the oil is not removed thoroughly, it will cause peeling and falling off.
The lampshade uses chemical deoiling (plastic parts are not suitable to be deoiled with organic solvents). During operation, the temperature rises to 65 ℃ and 70 ℃, shaking the workpiece continuously until no water droplets are hung after washing.
Coarsening is a very important process in ABS plastic electroplating.
If the coarsening is insufficient, the binding force will decrease; if the coarsening is excessive, the hole will become larger and deformed, and the binding force will also be reduced.
Because the divalent tin in the sensitizing solution is extremely unstable, the sensitizing solution is easy to fail, if not adjusted, it will lead to activation failure.
Insufficient activation will lead to incomplete deposition of electroless coating, while excessive activation will lead to excessive reduction of active metals on the surface to form a discontinuous film, which will also reduce adhesion.
Starting from the deoiling, we strictly follow the deoiling formula and operating conditions, check the time and temperature of the coarsening process, and prepare a new sensitizing solution and activation solution. As a result, bubbles still appear after electroless copper plating.
After several repeated experiments, it was concluded that bubbling was not caused by deoiling, coarsening, sensitization, and activation.
At this time, it is suspected that there is a problem with the composition and molding process of the material because the composition and molding process of ABS plastic is directly related to electroplating.
ABS particles are easy to absorb water, and the moisture content is required to be less than 0.1% before injection. It must be dried in a hot air drying box at 80 ℃ for 2 to 4 hours, and the surrounding environment must also be dry.
ABS plastics cannot be mixed with other ingredients.
Through the investigation, we found that the injection molding factory piled 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 hours, and then injection molding is carried out after being tested to meet the electroplating requirements.
The bubbling problem did not appear after electroplating of the improved lampshade.