How is a Tagless Pad Printing Plate Chemically Etched?
Chemically etching a plate requires the use of a photopolymer plate material. Photopolymer is more of a hands-on method of etching a plate. The process requires the artwork to be printed onto a film positive. A film positive is a transparent sheet with the artwork printed on it in complete black. The film positive is placed over the plate and cured under UV light for 5-10 minutes. The exposed plate (not covered by the print on the film positive) will harden.
After the first round of exposure, the film positive is swapped out for screen film. Screen film is a transparent sheet with thousands of tiny dots, available in either 200 lines per inch or 300 lines per inch depending upon how bold or fine the image is. The general purpose of line screen is to add a dot pattern to the inside of the artwork. The dot pattern will improve plate doctoring and image quality as well as reduce the chance of common printing problems such as scooping. The line screen is placed over the plate and is again exposed under UV light for 5-10 minutes.
Once the tagless printing plate has been exposed, the etch must be washed. The wash can either be an alcohol-based washing solution (developer) or a water-wash solution. The wash is determined by the plate material. The plate is then carefully cleaned and the uncured plate material is washed-out leaving a final etched plate. The plate must be dried and free of any moisture before use. Often a plate is placed in a drying oven for 10 – 15 minutes.
Polymer plate-making is a time-consuming process that requires the use of many consumables. It is, however, a much lower start-up cost than laser plate-making. Polymer plate-making has a lot of room for error, therefore it is important to keep exposure times as accurate as possible.