"A few years ago, I spent several days at a very large powder coating manufacturing facility. The plant was doing 'in-mold coating,' in which they took sheets of plastic, placed them in a mold, and closed the mold. I am curious to know if this process is being used elsewhere at this time."
I have a customer that wants me to powder coat a set of wheels for his truck. I have asked my suppliers if they could provide a chrome powder and was told they couldn’t. Is it possible to achieve a chrome finish with powder?
Sounds like a neat project. You can’t perfectly emulate a chrome finish with powder; however, you can approximate it with a cool metallic patina. Powder suppliers can formulate a product with a leafing aluminum pigment that provides a bright, continuous metallic sheen. You need to topcoat most of these with a durable clear to achieve resistance to the elements. The finish won’t have the reflectivity and hardness of a chrome finish, but it still looks pretty cool.
As the originator of the Powder Coating Forum forFinishing Todaywhen it was stillIndustrial Paint & Powdermagazine, I really enjoy your column. A few years ago, I spent several days at a very large powder coating manufacturing facility. The plant was doing “in-mold coating,” in which they took sheets of plastic, placed them in a mold, and closed the mold. After the part was formed, and while it was still hot, they opened the mold slightly and injected powder into the mold. They then closed the mold, and the powder coated the part and cured under the heat of the mold. When the mold was opened, they had a part that was the color that they wanted. They were making bath fixtures (sinks), but the process would work on just about any product. I am curious to know if this process is being used elsewhere at this time.
--Bob Collins, President, Metal Finishing Services, Inc., Gallatin, TN
I remember reading your columns over the years. I always enjoyed your helpful knowledge and wit. I am somewhat familiar with in-mold powder coating technology. Ferro also pursued this technology in the 80’s and 90’s. They had at least one commercial application - a fast-cure system that I believe was based on unsaturated polyester chemistry. The process was not quite quick enough for widespread commercialization. Perhaps it will someday be resurrected in another application.
I have developed crackle finishes with both solvent- and water-based liquid systems. Is it possible to develop a crackle finish with powder coatings?
I would recommend starting with an OH-polyester-TMMGU system and modifying it with various other resins to vary the degree of wrinkling that this system produces. TMMGU is tetra methoxy methyl glycoluril and is supplied by Cytec as Powderlink 1174. It requires an acidic catalyst that is usually buffered by a base. The main polyester suppliers (DSM, Cytec, Hexion and Sun Polymer) have recommendations for the most suitable OH-polyesters to use with TMMGU. You typically want a lower OH material (25 to 35 hydroxyl number) because TMMGU can seriously depress the Tg of your powder.
This system provides a fairly tight wrinkle. Dilution with other resins (acrylic, COOH-polyester, etc) opens up the wrinkle, producing more of a crackle finish.
Ask Joe Powder is a regular feature of Finishing Today magazine. Please send your questions to firstname.lastname@example.org.
FINISHING ANSWERS: Ask Joe Powder
December 1, 2007