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Tips for Direct Projection

(August 2003) posted on Fri Aug 08, 2003

Learn about the intricacies of direct-projection exposure systems, how to keep your mesh from deteriorating, and the secrets of pad printing on inflatable objects.

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By Carol Swift, Peter Kiddell

Using a direct-projection exposure system can be a real benefit to large-format screen printers. Direct-projection systems eliminate the need for costly full-size film by using smaller positives that are projected onto emulsion-coated screens, enlarging the image to actual size and exposing the screen at the same time. By eliminating exposure as a separate step in the procedure and relying on smaller film positives, direct projection has great potential to reduce screenmaking time and material costs.


Those who print wide-format graphics can realize even greater productivity from direct-exposure by automating other aspects of screenmaking. For example, the projection system can be one stop on a complete screen processing line that features automatic emulsion coating, drying, projection exposure, developing, and delivery of screens to the production floor in the correct print order. In such environments, special conveyor systems are generally used to move screens through each stage of the process.


To realize the full benefits of projection exposure, equipment care and maintenance is crucial. One area of concern is the condition of the exposure lamp in the system. Replacement lamps for projection-exposure equipment are considerably more expensive than for conventional exposure units, tempting users to go past the recommended operating lives of the bulbs (typically rated at about 1000 hr) and rely on their system's light integrator to compensate for any falloff in output.


Sorry, but it doesn't work that way. Not only does lamp power diminish over time, but the spectral output changes as well, to the point where it no longer matches the requirements of the photoinitiators in the emulsion. This can spell disaster in the form of weak stencils and pinholing, eventually leading to lost production time that will be far more costly than replacing the lamp in the first place. So pay attention to lamp operation time and replace the bulb on schedule.



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