Just like baking a cake, drying a screen requires that you follow a specific recipe.
By Mick Orr
Some screen printers ask if red safe lights are okay to use. Sure they are. But have you ever been in a darkroom with a red light on? It's almost impossible to see anything! These lights are designed for working with camera film, which is very sensitive to white light. For screenmaking, use yellow lights, which are easier on the eyes and allow you to see what you're doing. Just keep your screens away from them when you're drying emulsion.
Checking for hot spots
For those thinking about adding a factory-made screen-drying cabinet or making their own, heating is a consideration that deserves some attention. While most heated factory models have been tested to ensure that they will provide uniform temperatures throughout, homemade cabinets often incorporate a small space heater to facilitate the drying process. If the heater is poorly directed inside the cabinet, you will experience hot spots and wide temperature swings throughout the cabinet.
Screens directly in the path of a heater's output may get exposed to higher temperatures on one side than the other and end up with nonuniform drying across the coating. Also, if the circulation within the unit is poor, the screens on the lower levels are likely to be subjected to a lower temperature, while the screens placed higher up get damaged from excessive heat that rises to the top. Make sure that the cabinet you use has both adequate airflow and heat displacement to prevent these conditions.
To ensure your heated drying cabinet works properly, get a thermometer and measure just how hot the cabinet gets. Check for hot spots by taking multiple readings in several locations throughout the cabinet.
One more piece of equipment
In most screenmaking rooms, including those with automated drying cabinets, one important piece of equipment that will greatly improve the longevity of coated screens is usually missing. That piece of equipment is a second cabinet for holding the dry screens. This cabinet protects the screens from premature exposure and guards them from excessive heat while freeing the drying cabinet for processing additional screens.
Another function served by such a storage cabinet is that it allows screens to adjust to the shop's climate prior to exposure. Screen frames often expand and contract in response to temperature changes, and humidity can affect the stencil by causing it to swell. If screens aren't allowed to acclimate prior to exposure, distortion of the stencil image and registration problems become much more likely. Giving screens time to adjust in a protective cabinet is an easy way to avoid these problems.
In order to make a high-quality stencil, it is important to maintain proper drying conditions in your shop. Be sure to dry your coated screens in an environment that is dust-free, protect them from UV light, and dry at low temperatures to prevent premature crosslinking of the emulsion. Also make sure your drying area or cabinet has adequate airflow and that you control temperature and humidity throughout your operation. Finally, use dried screens as soon as possible or store them in a light-safe storage area or holding cabinet. By following these suggestions, you can eat your cake and dry a screen, too.
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