Troubleshooting the pad-printing process requires the identification and control of associated variables. The tips presented here will help you avoid some of the persistent problems you encounter on press.
By Julian Joffe
When choosing the size of the pad, always choose one that is at least 20% to 25% larger than the image being printed. If a pad is too small, your image pick up will be too close to the edge of the pad where the silicone is not as firm and where it tends to stretch more. This can cause distortion such as the smiles or frowns of the image one often encounters (Figure 2). A pad that is too large can pick up excessive ink often left on the cliche around the inkcup travel. Therefore, it is important to make sure that the image you are printing is not so large that it comes too close to the edge of the ink cup outline.
A pad that is short requires more pressure to compress. If you are trying to pick up an image that covers a large area of the pad, and especially if the pad is fairly steep (pointed), pick one that is taller. In this case, your pad will not exert too much force onto the cliche etching. Ink tends to move in the direction of pad roll out.
Higher durometer (harder) pads tend to work better than softer ones because softer pads vibrate slightly as they move back and forth on the machine. This can cause an effect known as pinholing (Figure 3).
Harder pads tend to trap less air due the pressure they exert onto the etched surface of the cliche. They also allow the image to be transferred off the pad surface more readily, thus allowing for crisper images with sharper definition. A simple rule of thumb: As the pad gets softer, it should be pointier. When printing onto rougher surfaces, harder pads tend to drive the ink into the nooks and crannies more readily and thus prevent the image from looking pinholed. Always review the image on the pad before and after the print.
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