Find out how using an industrial-grade pressure washer to develop stencils and reclaim mesh will improve the quality of your prints and prolong the life of your high-tension screens.
Moiré reduction is one of the most significant improvements. Using a powerful wash allows us to develop a more fully formed halftone dot by clearing all available stencil transfer openings and fully developing the gasket-cavity profile by removing all unexposed emulsion resin.
A high-pressure wash plays a huge role in reclaiming and ghost removal. Some printers think 3000 psi is overkill during the reclaiming process. They point out that ink degradents and stencil removers soften or dissolve the emulsion. They're right, but these products should be the foundation of the process, not the only part of the workflow.
Working with very high pressure at the reclaiming stage forces mesh knuckles apart and strips out any trapped emulsion or ink. The result is a much cleaner mesh with little, if any, ghosting. The higher the initial printing tension, the better the results will be.
Another objection I frequently hear is that high pressure rips the mesh. Screens can tear during reclaiming, but high-pressure washout isn't necessarily to blame. Screens rip during reclaiming as mesh tension drops. The lower the mesh tension, the greater the probability of a tear. Low-tension screens are more elastic, sort of like a trampoline. When you hit a low-tension screen with a high-pressure wash, the mesh will snap back as it absorbs the force of the water. This rapid snapping shocks the mesh and initiates the tear. On the other hand, high-tension screens (25 N/cm and more) exhibit very little elasticity. A high-pressure wash essentially applies a cutting or shearing action to high-tension mesh, which is why ghost images are so effectively stripped away.
To minimize the chance of ripping a screen during reclaiming, start at the bottom of the screen with the washer's wand at least 12 in. away from the mesh. With water pressure on, bring the wand toward the mesh until the washer's tip is 1-2 in. from the screen's surface. Finally, begin a deliberate, side-to-side sweep up the screen until the image is completely removed.
The combination of high mesh tension and high water pressure in the screenroom can result in longer screen life, better image quality, and less moiré. You will also benefit from more consistent printing tension and less ghosting on future runs.
© 2005 Mark Coudray. Republication of this material in whole or in part, electronically or in print, without the permission of the author is forbidden.
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