Decorated plastics may soon get a performance boost. DuPont Performance Materials'† Functional Aesthetics group has developed technologies that allow higher-performing semi-crystalline engineering plastics to be painted or plated for automotive, appliance, and consumer-products applications.
Plastic decorating processes like these have been mainstream for years, but they traditionally worked best with amorphous thermoplastics like ABS. Semi-crystalline thermoplastics often offer better mechanical properties than their amorphous counterparts. But they have been more difficult to paint or plate because their chemical resistance gives the decoration little chance of adhering to the plastic substrate.
To enable painting and plating semi-crystalline plastics, DuPont has started by formulating new DS grades of its Delrin acetal resin. These plateable Delrin grades offer an improvement over ABS, particularly when it comes to maximum elongation. ABS starts with an elongation of around 25 percent, but after plating, that figure plummets to around two percent. Delrin DS900M, a low molecular weight acetal, has an elongation of around five percent, which is unaffected by plating. Acetal grades under development with higher molecular weight will have even better elongation, predicts Josef Ros, DuPont Europe's development manager for EP Functional Aesthetics.
Beyond the materials development, DuPont has also had to develop a patented part etching process to make decorated acetal a reality. Etching helps provide a foothold for the decoration, but the etching processes used for amorphous plastics are too aggressive for acetals and tend to interfere with its mechanical properties. So DuPont worked with Rohm & Haas to develop an acetal-friendly etching system called Delrin Etch. This new etching process works at around 25-30 C, whereas previous etching processes required temperatures anywhere from 50 to 80 C. It is also chrome-free. Air oven aging shows that adhesion of the metal to the substrate is maintained over time, as is the performance of the part,†Ros reports.†
Rohm & Haas has a license to produce and sell the Delrin etching chemicals to DuPont customers or to contract decorating companies working for DuPont customers. DuPont, meanwhile, has already chalked up several European licensees for its acetal decorating technology and plans to offer it in North America as well. The first commercial applications are now beginning to go into production. One example is a one-piece painted handle with an integral latch for a washing machine front door. Slovenian company Secaplast molds and decorates the part entirely in Delrin for a local appliance producer, Gorenje. The part replaces an acetal/ABS assembly.
While many of the first commercial decorating techniques focus on acetal, DuPont has other technologies in the works for other semi-crystalline materials too. To take one example, the company has come up with a new stretchable ink for sublimation printing on PBT.
For more information on plateable Delrin grades, click here.
A comparison of samples subjected to scratch tests show how
metal adheres much better to a new plateable grade of Delrin acetal (left) than to a standard grade (