Ink Printing on Anodized Aluminum

Q. We anodize small sheets and then digitally print on them. We store the unsealed sheets for varying lengths of time, and the time between anodizing and printing can be weeks. After 2–3 weeks, the anodic layer does not seem to absorb the solvent dye as well as it does after 1 or 2 days. Could this be caused by insufficient rinsing? The rinsing is done manually with RO cold water at approximately 20°C. How can we prolong the time between anodizing and printing? P.B.

A. The unsealed anodic coating self-seals over time. This happens because the porous and very absorbent anodic coating essentially soaks up the humidity in the air. Sealing of the anodic coating is a hydration process. It is helped along by chemical and temperature means in the sealing bath, but simply leaving an unsealed anodic coating exposed to the air will also seal it to some degree, very slowly over time. This situation can be retarded somewhat if the sheets are stacked together after anodizing and drying. This limits the exposure to air. Make sure each sheet is absolutely dry, with no drops or puddles. If local temperature and humidity are high, perhaps the sheet can be stored in a controlled environment, such as an air conditioned room. You may want to establish a time limit between anodizing and printing. Establish a method to date the stacked sheet, and keep track of usage. You will probably be able to determine what the practical storage time limit is for your environment.