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The Benefits of High-Pressure Washes and High-Tension Screens

(July 2006) posted on Tue Aug 08, 2006

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.

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By Mark A. Coudray

Your screens can experience a 10- to 15-N/cm drop in tension the first time you clean them with a high-pressure washer. Water pressure greater than 2400 psi forces the knuckles open and lubricates the mesh thread, causing the thread to slip and the tension to drop. You can observe the same phenomenon during the first 150 prints on brand new mesh. The continual off-contact fatigue cycle causes the same knuckle release to occur, resulting in a large tension drop.

You should adjust the screen to its final tension after abrading and a high-pressure wash. My shop has experienced a marked improvement in virgin mesh's performance by following this practice. You can reduce the initial tension drop on press by up to 80% by using a high-pressure rinse, retensioning the mesh to its target level, and then degreasing. If you use static frames, you won't be able to make corrections. You'll simply have to live with the drop in tension.

Stencil developing

My shop recently changed screen-washout practices with noticeable improvement to image quality and moiré reduction on high-density stencils and halftone images. Like many screenmakers, we were under the impression that extreme care was necessary when washing out exposed images—and I have always been very strict about how we prepare our screens, the environmental condition of the screenroom, and the quality of the exposure systems we use.

We now soak our exposed screens in a water tank for two minutes or longer after exposure in an effort to more thoroughly rehydrate the unexposed areas. We also use a power-assisted spray to wash out the screens and further improve the irrigation and removal of any unexposed resin. We use 500 psi at about 9-12 in. when washing from the print side.

The changes my shop made to the stencil-developing routine resulted in noticeable improvements to edge definition, stencil bridging, and halftone sharpness. Line water pressure simply doesn't have enough energy to dig down into the very fine capillary crevices of the mesh's knuckle intersections or into the areas where the round stencil dot edge intersects with the mesh. We're now fully exploiting these areas and greatly enhancing print quality.


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