Adhesion of UV-Cured Ink to UV-Cured Coating

Question:

I am a printing shop supervisor searching for a UV-cured ink, which can be printed onto a metal substrate that has been powder coated with a polyester paint. Is there such an animal? Would a UV-cured ink stick to a UV-cured powder coating? C. N.

Answer:

To answer your question in one word, Yes. Since this is a frequently asked question, I will also answer your question in more than one word. Inks and paints use the same raw materials but their end use is different. Paints are protective and decorative, while inks are informative and decorative. In that sense, inks can be treated like coatings.

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The rule is: “Any coating will ‘stick’ (spelled adhere) to any other coating if they are compatible.” That means, if the second coating adheres to and does not dissolve, lift, blister or otherwise destroy the original coating, they are compatible. Furthermore, it doesn’t matter whether either coating film is air dried, baked or UV cured.

As with any rule, there are exceptions. If the original coating has been modified to increase its mar-resistance, by having a wax or polyolefin on its surface, it will act as an interference coating. This will diminish any chance of adhesion of the second coating to the original. In this case, you would also say they are incompatible. Hopefully, this will not only answer your question, but also tell you why it happens and what to look for when checking compatibility of coatings.