Grey blocker slows the passage of dyes along the polyester fibres but can also alter the colour of inks printed on top It’s like a teenager without wi-fi: it looks okay right now, but it could blow at any moment TIPS & TECHNIQUES JULY 2019 images 47 stops halfway up, the divine white you took hours to place perfectly on the ‘Codfather Fish & Chip Shop’ sponsored navy running vests won’t turn a delightful shade of ice blue right before your eyes. There are many products on the market that claim to be suitable for screen printing on 100% polyester and I am sure they are. They have probably been tested in the best labs in the world by all the people that did so much better than me at school and became scientists rather than practising the dark art of squeegee pulling (don’t be a pusher, it’s just wrong), but my best advice would be: find the one that works for you. Grey blocker base is fantastic for slowing down the rampant march of the eager-to-be-seen dyes as it contains chemicals that basically stick a foot out near the door and trip up the running catcher before he can clock out. It can, however, change the colour of inks printed on top, which means using an extra screen for white base, which also means extra heat to gel it... The endless cycle continues. A better option is to lower the required temperature needed to get the ink to stick to the substrate (the scientists’ word for vest). This can be done with either a ready-to-use ink that cures at or around the 140°C mark (there are Tony Palmer has been in the garment decoration industry for over 30 years and is now an independent print consultant working closely with print shops to get the most from existing processes and techniques. Tony is passionate about keeping and enhancing production skill levels within the industry. He is the owner and consultant at Palmprint Consultants, offering practical help and assistance to garment decorators all over the globe. plenty on the market now) or by adding a catalyst to the ink: this will allow it to cure at really low temperatures, but it will also shorten the shelf life of the ink to hours instead of years. Heat management It’s imperative that your dryer is reliable. If it says 140°C on the display, it’s important that it doesn’t really reach 160°C inside the oven. Use a donut-type thermoprobe as this will accurately tell you what the ink film temperature is rather than the ambient temperature in the oven. The heat management doesn’t stop there: flash times need to be low to avoid shrinking and at the end of the dryer the ‘Codfather’ vests need to be stacked in very small piles. If you have the room for a table, make ten stacks and place a vest on each pile in succession – this allows the heat to dissipate quickly. We have all come into the print shop on a cold morning and felt the heat still locked into that huge stack of shirts that were printed the previous day. The heat locked into the shirts is basically the fuel for the dye to keep running up the straws. Kill the heat as quickly as possible: use a fan, hook up an airline, put the table on wheels and run it round the car park... Whatever it takes. Just get the vests up to temperature to cure the ink, and then cool them down as quickly as possible. In one shop, I even saw a chest freezer used to cool down wayward prints. In summary: control the heat and you control the bleedin’ polyester – there are tools out there to help you, so use them. Keep the temperature under control and you will be happier than the teenager when the wi-fi returns to full strength. A mixture of dye blockers, low-cure additives and finely tuned drying equipment will ensure you don’t walk into your shop the following day after a successful print run, open the box and utter those immortal words: “Are these Codfather vests supposed to be light blue?” Use a thermoprobe to measure ink film temperature rather than ambient temperature in the oven Create multiple stacks of T-shirts to allow the heat to dissipate as quickly as possible