Printing with discharge ink is a fantastic way to create a vibrant print that's unbelievably soft. Discharge printing isn't for everyone though. Let's discover what is discharge, how it works, what's needed for it, garment selection, and when and when not to use it.
WHAT IS DISCHARGE AND HOW DOES IT WORK
Discharge ink is a traditional, low solids, water-based ink (compared to a high solids water-based ink like Green Galaxy). Unlike traditional water-based ink, discharge has a few extra ingredients and a discharge activator (Zinc-Formaldehyde-Sulfoxylate is the active ingredient) that removes the dyes in the shirt, stripping it to its natural fiber. The natural fiber is a light, brown shade (it won’t be white).
How does discharge remove the dyes, you ask? When the printed shirt is going under a heat source and the ink reaches 230°, the chemical process of stripping the dyes begins. The formaldehyde breaks off from the activator and destroys dye molecules. Typically, this process is finished when the ink reaches 250-260°. At this stage, the formaldehyde in the activator has done as much as it can with the dyes in the fabric. (Friendly reminder — all water-based inks cure once the entire ink film reaches 300°-320°. What can make this confusing is that the discharge process happens at 260°, so the print will look good, but it’s not completely cured; it’ll wash out after one wash.)
Next, the sulfur that’s in the discharge agent binds with the formaldehyde to make an inert molecule. Not all formaldehyde and sulfur will bond together. Because of this fact, it is VERY IMPORTANT to have excellent ventilation in your working space and to vent the fumes from the conveyor dryer to the outside.
Please note that printers may also have a sulfa allergy. They will have a reaction to the sulfur in the discharge agent. This is commonly why people complain about itching when wearing a discharge garment that hasn’t been washed. Even our print expert Colin Huggins has a sulfa allergy. When he touches the raw powder, his fingers swell, so he knows he has to be careful.
WHAT IS NEEDED TO PRINT DISCHARGE
If you’re ready to print with discharge, you need to have two, very important things — ventilation and a conveyor dryer. You need these pieces in place because of the chemical reactions that happen during the curing process as we have already addressed.
Insider’s Tip: Do not use discharge on children’s clothing. Discharge is not CPSIA certified because it can exceed the limits of part per million on formaldehyde residue. Non-formaldehyde discharge exists, but it doesn't break down the fabric dye molecules as well as formaldehyde solutions. Just don’t use discharge for kid’s apparel.
You will also need a water-resistant and discharge-ready emulsion like Baselayr Complete. You will need to follow the proper steps of obtaining a durable stencil (check out the video below to learn more about exposing screens).
I cannot stress how important it is to have a proper heat source. Ideally, it would be a conveyor dryer that’s vented to the outside. If you don’t have a conveyor dryer that’s properly vented, you will have to decide if you’re comfortable with printing with discharge ink, knowing the chemicals you are dealing with.
Pro Tip: When applying tape to the screen, do not apply tape to the bottom of the emulsion. Emulsion breathes and it soaks up some liquids from both plastisol and water-based ink (low or high solids). In the case of discharge, it’ll pull the water. If you have tape on the bottom, the discharge will build a vapor barrier. Think of it like putting tape on window with condensation, the condensation build up under tape. With discharge, the moisture that builds up will have discharge in it. As you run a squeegee over it, it'll squeeze discharge out of the side over time. Always put tape on the top. Use water resistant block out or finger nail polish if you don’t have tape.
TYPE OF FABRIC MATTERS
Discharge mainly works on 100% natural fabric like cotton and hemp. You can discharge print on shirts that have natural fibers combined with synthetic fibers like 50/50 or triblends, but there is a caveat. The synthetic fibers usually found in 50/50, triblends, or other garments on the market, will not discharge. You may see some cool effects. Not all synthetic fibers are dark. Some are light, like heathered garments, which encompasses a white, synthetic fiber. That fiber will not have much of an impact on the color within the discharge.
In the end, it’ll come down to testing and what you or your customer wants.
Discharge print by Rogue Lab.
Not all garments are created equally! Sometimes, garments are over-dyed. A t-shirt manufacturer might make a batch that is slightly off-color or a line doesn’t sell well, so they will dye it again to attempt to resell the shirt. You can't always tell when you have an over-dyed garment. Sometimes you can tell by the tag (if it has a tint), but not always. The only way to find out if a shirt is over-dyed is to do a swab test inside the hem. If the original color is "undischargable," it’ll show a tint of that color. To try to avoid receiving over-dyed garments, call manufacturer to double check you receive shirts that aren’t over-dyed. Buyer beware, sometimes the mills don’t relay proper information to the manufacturers (sometimes they hide the fact that it happen). The supplier doesn’t have perfect control over manufacturing. Always test garments before going into productions.
Not everyone can get their hands on a ton of shirts. You could also ask for a fabric color card from the vendor. Once you have the card, either discharge print on a tiny section of it or swab it with the discharge clear base and cure it. Again, you’ll be able to compare and contrast the results. You will also have a handy card to remind you of the effects in the future.
Pro Tip: Most major shirt manufacturers have a grading on how well a shirt discharges. They’ll rate the shirts with either an A, B, or C. “A” means it’s a solid shirt, you won’t have any issues whatsoever. “B” means you should hardly ever have a problem. “C” indicates that there might be some color issues, so you need to test it. Never go below a C level.
WHEN TO PRINT DISCHARGE
You’ll want to use discharge ink for an even softer hand than you’re currently able to produce with straight plastisol or high solids water-based inks. Removing the dyes from the garment allows you to create a light shirt color that then takes the place of a white base. As a result, you can print inks directly on the fabric, which allows us to get away with a thinner print. We can also modify the inks to be softer while maintaining good opacity. Fashion or retail are typical areas that would like discharge prints.
In the end, a printer would avoid printing with discharge ink if he or she is printing on children's apparel or does not have the proper ventilation and conveyor dryer. Printing with discharge is a great, fun way to achieve incredibly soft prints for retail. We'll dive into the different ways to print discharge in the future, so stick around!