What is Discharge Screen Printing?
Discharge inks work by removing the dyed areas of reactive dyed dark garments to create a different colour in its place. The pigments used in discharge inks are impervious to the discharge process so essentially, they replace the colour that was there previously on the garment. Some refer to it as a ‘bleaching’ process, however discharge inks don’t damage the cotton fibres. The end result is an extremely soft print that can have little to no handle on the garment, whilst offering extremely bright colours.
For this step-by-step guide, we used our latest discharge formulation MagnaPrint® Discharge LO. LO stands for low odour, as this ink system was developed not to have the unpleasant aroma when printing that discharge inks are often associated with. Instead Discharge LO offers a mildly sweet aroma that’s far more preferable for the shop floor!
Check out our video guide below!
Step 1: Artwork and Screen Selection
Discharge ink is extremely versatile when it comes to the type of artwork you can screen print, ranging from solid, vector style designs to photographic halftones and detailed designs. We chose a playful motif with plenty of colour to show off the bright effects you can achieve with discharge inks. We recommend using 43-62T (110-158) mesh screens for solid areas and 77 – 90T (196-230) mesh for halftones when printing with discharge inks. As this design was made up of completely solid print areas, we used 62T (158) screens for all colours.
Step 2: Mixing Inks
Once we selected the five different colour references for our design (plus Super White for the white areas), we were able to mix the colours using MagnaPrint Eco-Pigments and the Discharge LO ink system. We generated the recipes using the MagnaMix software and selected our required quantities, then used an automatic MagnaTint pigment dispenser to add the colours to our ink pots. The ink then needs to be thoroughly mixed. If you don’t have a dispenser, you can weigh out each pigment – MagnaMix provides accurate recipes for thousands of different colours.
Step 3: Choosing Your Garments
Not all fabrics are suitable for discharge printing. It’s always a good idea to test out the garments you are going to print beforehand. Remember, only cellulosic fibres like cotton can be printed with discharge inks, and they need to be dyed with reactive dyestuffs – but this doesn’t mean you can’t use blends (and this can create a nice vintage look where the polyester fibres don’t discharge). Another consideration is the colour of your fabrics, some may discharge better than others – another good reason to test prior to production. For this guide we used four different colour shirts, 100% cotton black, 100% cotton navy, 90% cotton/10% polyester heather blue, 50% cotton/50% polyester grey. This selection should provide a nice range of results and effects.
Step 4: Press Set Up
When setting up the screens on your press, make sure that there is around 3-5mm of off-contact distance between the mesh and the garment. We used a medium 60-90-60 shore rectangular squeegee and set the blade angle to 15° (10-15° is ideal). Screen order in the machine should go from smallest to largest print areas and white should always be placed as the last screen to pick-up.
Step 5: Activating Your Inks
Discharge LO (like other discharge inks) is ‘2-pack’ system and uses 6% activator (Activator AB) which is mixed with the base ink before printing. Following activation, the ink should be left for 10-30 minutes to dissolve and have an active life of up to 8 hours (depending on environmental conditions). To avoid wastage, only activate the amount of ink needed for your run (usually 1-2 kg per screen). Always keep activated ink next to the print station in a sealed container.
Step 6: Wet-On-Wet Discharge Screen Printing
A great advantage of discharge inks is that they can printed wet-on-wet and don’t require flash units in between stations or an underbase. We recommended printing with a single or double stroke – dependent on how absorbent the fabric is. We used a medium squeegee speed and medium to high pressure when printing. Unlike high solids inks, discharge inks should be driven into the fabric – if necessary, you can reduce squeegee speed and increase the pressure. We used an eight station M&R Sportsman EX press to print this design.
Step 7: Before Curing
When printing with discharge systems, inks initially printed onto the fabric will appear muted or dull until they have been cured. Curing discharge prints activates the ‘bleaching’ process.
Step 8: Time to Cure Your Prints
It’s now time to send the garments down your dryer. We used an M&R MiniSprint 2000 dryer at 170°C (340°F) for 2.5 minutes. Depending on the size of your dryer you may need to adjust your process, but we recommend aiming for the above 2.5 to 3 minutes at that temperature overall.
Step 9: The End Product
Once cured, the colours really start to sing and show how the heat has activated the discharge process and replace the colour in the shirt. The different shirts show some variables in the effects you can achieve. The black and navy 100% cotton shirts provided really bright and solid colours, whereas the lighter colours and polyester content in the other shirts created a more muted and vintage look discharge effect.
Check out the article featured in the April 2022 edition of Images Magazine!
