By: Kevin Kauth
Humidity is a problem many screen printers battle; however, most do not fully understand how it affects their screens. Many want to blame the emulsion, but in most cases, it is their environment not the product causing their troubles.
Emulsion is hygroscopic, which means it absorbs moisture from the environment it is in. A screen could be completely dry in one area of your shop or in a drying cabinet and if it is taken to another area where humidity is higher it will take on that moisture and rewet. This also holds true if you have dry screens in an area, coat more fresh screens, and place them in the same area to dry. As the water evaporates out of the freshly coated screens it will raise the humidity and rewet the dry screens next to them.
PVA, the main component in all emulsions, is very good at absorbing water from its environment and holding it. The battle to ensure your screens are dry is constant. Even with a screen that is exposed and fully cross-linked the PVA still will absorb water, just at a slower rate and slightly less than a screen that is not exposed and cross-linked.
Screens exposed before fully drying may look good visually when looking at exposure times and resolution; however, may not have achieved a thorough cure. This can lead to the screen acting like it was underexposed and lead to early breakdown on press. Moisture in screens also affects exposure times. The water present in the emulsion interferes with proper cross-linking. If you are using a diazo or dual cure emulsion humidity will make your screens expose slower, requiring more time. The opposite is true if you are using a photopolymer emulsion. Photopolymers require less time and expose faster under humid conditions.
Your best chance at success in the screen room is understanding the battle with humidity and monitoring your environment. Use a hygrometer to monitor your relative humidity and temperature. Ideal screen room conditions are between 30%-40% RH and 60°F to 80°F. Also, in my opinion, every screen room should have a dehumidifier in it. By using a dehumidifier, it will keep your environment at a more consistent level. Finally, keep your “wet processes” (developing, reclaiming, etc.) separate from your “dry processes” (storing and exposing screens). By using separate areas, it will help contain moisture and humidity away from your screens and will minimize variables.
A great guy once said, “If you’re hot and sticky so are your screens!”
Nobody likes to be hot and sticky and neither do your screens!
Kevin Kauth is Chromaline’s Technical Sales Representative for the Midwest region. Kevin has a strong background in screen printing and graphic arts. Prior to Chromaline, Kevin was employed at SEFAR where he was an Applications Specialist in their Technical Service and Marketing Department. At SEFAR, he interfaced with clients doing technical training and process control and improvement. He also has a strong digital background and can assist with outputting high-quality artwork for photopositives and photonegatives.
Contact Chromaline Today
If you have any further questions about understanding humidity for screen printing, please contact us today.