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Etch-Depth Consistency on Pad-Printing Plates

(March 2002) posted on Sun Mar 31, 2002

Discover the negative effects of inconsistent etch-depth on plates and learn about considerations for sourcing, storing, and maintaining pad-printing pads.

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By Carol Swift, Peter Kiddell

Several factors influence the performance of the pad-printing process, including the condition of the ink, the condition of the pad (including shape and hardness), ambient conditions, machine cycling parameters, and the etch depth of the plates (cliches) that contain the printing image. Most of these elements are relatively easy to define and control. However, measuring the etch depth of the imaged plate is an important function that is overlooked by most users and by a great many plate providers as well.

One reason why few printers or suppliers verify that etch depths fall within acceptable tolerances is because the equipment required to measure etch depth accurately is fairly expensive, costing $7000-10,000. We are fortunate to have such equipment at our disposal, and the tests we have conducted with it on behalf of our clients has led to several interesting revelations.

For optimum printing results, the etch depth on an open-etch (line art) plate should be between 25-28 microns and on a screened (halftone) plate, 30-32 microns. On plates we've measured for clients, particularly screened plates, we've recorded readings from 16-30 microns on the same plate. The overall range on plates we've sampled runs from 13-35 microns for screened plates and 18-30 microns for open-etch types. Such variations can have disastrous effects on print quality since the amount of ink deposited during printing changes with the depth of etch.

Producing an etched steel plate is not a simple process. It requires careful control in all aspects of production. Key requirements include verifying the quality of the steel and the resist coating, assuring correct exposure time and development procedures, checking etchant condition, and making sure that the etching and rinsing processes are being completed correctly. Mistakes or oversights in any of these areas can affect the etch quality of the finished plate. Only rigorous final inspection by the supplier of the etched plate will ensure individual plate quality and consistency from plate to plate.


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