Use the following tips to control the variables most commonly encountered in garment screen printing.
Measuring flash temperature
Measuring ink temperature during flashing is best achieved using a non-contact infrared thermometer immediately after the print exits the flash unit. These hand-held devices measure the infrared radiation coming off an object. Aimed a few inches away, they report readings as surface temperature. Lasers are available to ensure the sensor is properly aimed at the desired object (Figure 5). Small, inexpensive models with lasers sell for less than $50 and are quite effective.
To get a good reading on the flashed ink, set the thermometer to max temperature mode, then simply aim the reading sensor on the ink immediately after you rotate the platen from under the flash unit. Units with lasers are particularly useful to confirm you hit the ink itself and not just the shirt. The display will show the highest temperature read on the ink. Because ink will cool very quickly after being removed from the flash unit, the reading can not reflect the true temperature the ink reached. However, if the reading remains at or below 275°F (135°C) the ink is usually not being over flashed.
Best practices are to first adjust the flash settings so gel just occurs on the ink, then use the non-contact thermometer to measure the ink temperature as it comes out of the flash. This becomes your baseline for that set of conditions. Many variables come into play, so this temperature will be a bit different for each circumstance. Finally, check ink temperature during the run and adjust the flash time so the ink does not drastically exceed the baseline temperature originally measured.
Press platens progressively heat up as a run continues when flash units are in use. Warm platens preheat the plastisol ink before it is flashed, reducing the needed dwell time. Until the platens warm up, a longer flash time will be required during starting up. The best option is to pre-heat platens under the flash with four revolutions. If this is not possible, the flash time should be checked and adjusted once the platens are warm.
The five issues we have discussed here are just some of the variables that influence the garment-printing process. Perform an audit of these areas in your operation. Don’t assume they are running effectively. Take action to implement solutions to any problems you find. I guarantee you will see improvements in your print quality, efficiency, and production flow.
Dawn Hohl-Nowlin is a technical trainer and consultant on screen printing. Her industry experience includes 18 years with SPTF/SGIA, overseeing screen- printing workshops, developing training resources, and conducting process-related research. She is a member of the Academy of Screen Printing Technology. She can be reached at firstname.lastname@example.org.
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