Displace and replace

Dave Roper provides a primer on textile screen printing with discharge ink

Discharge ink produces soft hand prints and offers the ability to create both bold and vintage looks. However, it’s also acquired an undeserved reputation as a process that requires a higher level of skill compared with printing plastisol. This can lead some printers to question whether it’s really worth the hassle. But they’d be wrong about the need for special skills, and mastering printing with discharge ink is most definitely worth the effort, explains Dave Roper, managing director of Dave Roper Ltd.

A water-based product, discharge ink contains an active ingredient which, when put through the dryer, drives the dye out of the garment’s cotton fibres (ie. discharges the dye) returning them to their original ‘ecru’ (natural) colour. If a pigment has also been added to the ink – and it usually is – then the pigment will colour the fabric in the areas from which the dye has been discharged.

Discharge ink is usually only used on dark cotton garments: cotton, because discharge ink isn’t capable of bleaching out the colour in polyester, and darker fabrics because on lighter ones there’s no requirement to discharge the dyes and an equivalent soft hand feel could be achieved using slightly cheaper water-based ink. Discharge inks can also be used on polycottons or tri-blends where they will produce a vintage look, as only the colour in the cotton fibres will be discharged and replaced by the pigment in the ink; the polyester will remain unaffected.

While printing with discharge ink is straightforward once you know how, there are a few factors to consider. Once activated, the ink has to be used within six hours. So you need to measure out what you need carefully to avoid wastage, recommends Dave. The ratio used in this step-by-step – 5% pigment, 8% discharge activator and the rest discharge base – is a good guide. Dave used Amex inks for this example.

There is a small amount of formaldehyde used in discharge inks and so you must also ensure that the printing area is well ventilated. However, as Dave points out, “All print shops using any type of ink should be well ventilated anyway”.

A coarser mesh is recommended when printing discharge ink. In addition, the off -contact, (the distance between the shirt and the screen), needs to be reduced because discharge is a water-based ink and so needs to be pushed into the fabric. By contrast, plastisol ink sits on top of the fabric and therefore needs to be printed with higher off -contact. Multiple colours can be layered on top of each other to create different shades. Bear in mind, though, that the print that’s visible before curing will appear light and dull compared to the finished (cured) result. Dave strongly encourages printers to run one garment through the dryer before commencing a large run with discharge ink to check for mistakes: the lightness of the print makes it more difficult to spot errors prior to curing.

While a heat press or flash dryer can be used, Dave explains that a conveyor (tunnel) dryer is the best choice as it allows precise control over the temperature and speed. The temperature needs to reach 160ºC and remain there for at least 45 seconds. The cured T-shirt will have a soft hand that will only get softer as it’s washed, he adds.

One area where discharge ink works particularly well is to create a white base on a dark tee on which multiple colours can then be printed. While many printers lay down a white plastisol on a dark tee and then add coloured plastisol inks, using discharge ink first (and drying it so it’s activated and thus bleaches out the tee’s colour) before using the coloured plastisol inks gives a less layered feel and look.

STEP-BY-STEP: PRINTING WITH DISCHARGE INK