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How to Dry a Screen

(May 2002) posted on Tue Apr 30, 2002

Just like baking a cake, drying a screen requires that you follow a specific recipe.

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By Mick Orr

Many types of drying cabinets can be used, from heated, thermostatically-controlled factory units to simple homemade ones. If you use such a device, just make sure that it provides good airflow, with an intake to draw in dry air and an exhaust for the wet air. When a drying cabinet is constructed correctly, it accelerates the drying process while saving space and preventing damage and contamination of coated screens.

Speaking of contamination, this is an especially important airflow issue for shops that dry screens in an open environment, such as companies that use large-format screens. As mentioned earlier, large-format printers frequently employ climate-controlled rooms in which they dry their large screens. They frequently accelerate the drying process by moving air around the room with one or more fans. The big problem with fans is that they not only push air around, but they push dirt, dust, and other debris along with it. A big wet screen is a giant target just waiting to be covered by this debris as it flies around the drying room. Therefore, if the drying room itself can't be made completely dust free, it's not a bad idea to at least put an air filter on the intake side of the fan(s). The filter will help capture these particles before they land on screens and become pinholes and other stencil defects during exposure or on press.

Lighting When drying a coated screen, the drying area or cabinet must be completely dark, because any light--specifically UV wavelengths--that strikes the coated screens can cause the emulsion to begin crosslinking and pre-expose the stencil. If this happens, you'll be left with an unusable screen. Even filtered fluorescent bulbs will lead to premature crosslinking if the coated screen is exposed to the light for too long. It usually takes hours before yellow lights create any serious pre-exposure. Still, it's not uncommon for coated screens to remain in drying areas with such lighting conditions for a day or more, which can lead to some significant problems.

Not only do yellow lights give off UV light, but over time, the yellow filtering material begins to fade. You'll notice the problem as a whitening of the bulb toward the ends, which is a sign that the bulbs should be changed. Testing devices are also available to check the light-quality of bulbs and determine whether they are emitting too much UV light.


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