The Screen Print Column
Curing screen printing inks for textiles
Managing director of Screen Print World, Dave Roper, takes a look at curing your prints and why this is crucial in ensuring they remain bright.
C
uring your prints after the printing process is complete is crucial in ensuring the inks you have printed are going to remain bright and not wash off the garment.
Textile inks, whether plastisol or water-based inks can crack, wash out and generally look terrible if they have not been fully cured which can result in costly losses to any business if they come back to you. You can ensure you get the best results from your inks following a few basic steps.
What is curing?
Firstly, lets discuss what curing is. Curing is the fusing of the ink to the garment, that results in its resistance to washing or abrasion, this is reached at the magic number of 160°C for a specified time – this will vary depending on whether you’re printing water-based inks or plastisols, and what you are curing with. Textile Inks can be cured using conveyor dryers, heat presses, heat guns or flash dryers, even a hot iron, but the key to success is reaching the right temps over the right time. Using heat presses will require a print to lightly dried and cured using moderate pressure for 20 to 30 seconds (water-based inks may require two passes). A sheet of transfer paper would need to be placed on top of the print, and the finish of a heat pressed plastisol print once heat pressed is quite smooth.
Curing is the fusing of the ink to the garment
Plastisol inks will cure once the entire ink film reaches the magic number, this will ensure the ink film fuses to the garment. Most plastisols will take on a slight shine when fully cured, and can generally be tested by stretching the garment a bit – cured plastisol will offer a slight stretch when cured, and if not fully cured will look dull and crack when stretched.
Water-based inks are a slightly different and will require stable heat at the required temperature over a specific time in order for the binders and cross-linkers to fuse. For this reason, water-based inks usually require longer chambered conveyor dryers, and slower curing speeds, than can traditionally be used for plastisol print shops. Using a shorter conveyor dryer for curing water-based inks will probably require multiple passes in order to achieve a final cure.
Although inks can theoretically be cured using a heat gun or flash dryer, it is always a bit ‘hit and miss’ as it’s difficult to replicate the numbers accurately time after time and this results in some areas of the garment current and other areas being at risk of washing out. This is why conveyors and heat presses are far superior for curing as they enable the printer to accurately dial in the numbers and time required to get the correct results every time. Once you have wash tested your print and have set the conveyer or heat press to get the results you need, you are assured that every garment that you are curing is reaching the same heat and time parameters needed and you will have the peace of mind that your customer is not going to be back with garments that are washing out.
Specialist inks and additives
Specialist inks and additives are also available to aid the curing process on garments that are heat sensitive or prone to dye migration. Low bleed inks will block out the migration of unstable dyes on garments which would migrate into the print once heated. Also available are low temperature inks which will cure at a lower temperature than traditional plastisols – these usually fully cure at around 130°C and are useful on heat sensitive fabrics.
Also available are catalysts for water-based inks which can be added to achieve a final cure by air drying or reduced heat. These products are very useful to smaller production facilities that do not want to spend additional cash on equipment and still have peace of mind that their prints are stable when they reach the customer.
When setting up curing any textile ink, it is always advisable to wash test often to ensure your print shop is sending out garments which are curing correctly.
| 66 | May 2023
www.printwearandpromotion.co.uk
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