Discharge Printing Demystified
What Shirts Are Dischargeable?
Discharge printing will only work properly on 100% cotton garments. Most screen printers are used to working with plastisols and are familiar with the techniques of how to use them properly. Even though a 100% water base discharge print will yield the best results in softness, breathability, and absorbency, prints produced by overprinting plastisols wet on wet through fine meshes over a plastisol discharge under base come very close, without the problems of drying in the screen and the pot life associated with straight water base discharge inks.
- discharge printing leaves a very soft hand; the material feels as though it has not been printed at all -
What Are The Advantages of Using a Discharge Under Base vs. a Plastisol Under Base?
The discharge process will produce a softer feeling print as well as very bright colors on darker garments. You can also increase your production output as the absorbency of a discharge under base into the shirt allows you to print each subsequent color on top of the discharge under base wet on wet. In order to eliminate pick-up on screens overprinted onto the discharge under base, you can flash cure the under base print. However, if you decide on this course of action it will negate part of the increased production advantage of this process. Re-died garments from shirt manufacturers will not discharge. Purple and royal garments will also not discharge as they are not reactive dyes.
Are There Special Screen Making Considerations?
Waterproof stencils are required for both the under base screen and each subsequent screen (must be waterproof, not simply water resistant). Our customer service representatives can help you choose an emulsion that can resist breaking down during production when performing this process.
How Do Discharge Inks Differ From Plastisol Inks?
Discharge inks are the exact opposite of plastisol inks. You have to adjust your technique so that the ink is driven into the fabric deep enough to destroy its color beyond visible depth and avoid having undischarged sides of individual threads showing when the fabric is stretched. This can easily be achieved with extra heavy squeegee pressure and a fast stroke. If you are using discharge ink as an under base, plastisols may be printed wet on wet on top of the discharge under base.
Curing
A minimum of 90 seconds in a well ventilated oven where the entire ink film temperature reaches 320 degrees is required to complete the discharge process. This is enough time to perform the discharge process and also cure plastisol as well (if applicable). This is a critical part of the discharge process. If your dryer does not allow the garment to remain in the heat chamber for at least 90 seconds if could affect your results negatively.
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Discharge Printing Steps
- Getting accurate weights is a critical step. Weigh your containers prior to adding chemicals, record these weights, and set scale to zero before adding chemicals.
- Add Discharge Base into container and record weight.
- Add your Activator to the base and make sure it fully disolves. Usually you will ad up to 8%, but you can start at lower percentages and test until it stops intensifying the color. Be sure to only produce what can be used in 24 hours as beyond that the mix will start to lose its vibrancy.
- Add a penetrant if desired. A penetrant helps the ink penetrate deeper in to the fabric for richer colors.
- Add a pigment if desired. Pigments can be added to make colored discharbge. Usually 12% is a good guideline but some manufacturers recommend up to 15% for whites.
- Print using a heavy stroke to make sure that the ink penetrates as deeply as possible into the garment, followed by a lighter stroke for a good surface deposit. You can flood the screen before moving on to the next color to prevent the ink from drying in the mesh. It is usually better to print darker colors early and work toward the lighter colors.
- Using a flash in not necessary between colors. However flashing after the last color may help keep your pigments on the surface and can result in a brighter print.
- Send to dryer for final cure.
Be sure to pay careful attention to your ink ratios. Some experimentation can yield dramatic results, but to maintain consistency you should always write down all ratios, weights, etc.
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