No other process produces such soft, breathable, absorbent, bright prints on dark colored garments. Also, no other process has been as misunderstood and maligned as discharge printing. This paper honestly addresses the health and safety non issues of Zinc Formaldehyde Sulfoxylate (ZFS) based discharge inks and points out the overwhelming advantages of the process. This paper will also instruct you on how to print bright, opaque colors using the DSPCH-1000 as your underbase white for overprinting plastisol inks on dark garments.
What is Discharging?
Discharging is a chemical reaction that destroys the ability of selected dyes to reflect color. This reaction takes place at temperatures above 180 degrees Fahrenheit while water is present.
What Shirts Are Dischargeable?
Only selected dyes used on natural fibers are dischargeable. Fruit of the Loom and Lee are the only major garment manufacturers stating some colors of their 100% cotton T shirts will discharge well. Fruit of the Loom rates their black, navy, denim, burgundy and brick as being the most dischargeable and their wedgewood, cadet blue, royal, purple and yellowjacket as the poorest. Other colors fall somewhere between.
Lee rates their shirts on a 1-10 scale with ten being the most dischargeable. Lee colors rated as tens are: black, gold, navy, purple, english rose, primrose and powder blue. Colors rated at 7 and discharging ok are peacock, kelly, wine and true red. Colors rated as poorest dischargeable colors are royal, hunter and ash.
Printers are advised to test the dye lot of each new case of shirts by checking the dischargeability of the top and bottom garment in the area to be printed or on an inner seam and put aside undischargeable garments to other uses.
What Are The Advantages Of Using A Discharge Underbase Over a Normal Plastisol Underbase?
The discharge underbase will produce a softer feeling print which will not have the rubbery, bullet proof feel associated with a dark garment printed with a regular white plastisol underbase. The printer will also increase his production output because the absorbency of the discharge underbase into the shirt allows the printer to print each subsequent color on top of the discharge underbase wet on wet. To eliminate pick-up on screens overprinted onto the discharge underbase printers may elect to flash cure the underbase print for about 1 second. However, if printers decide to flash cure it negates part of the increased production advantages of this process.
Why Use A Plastisol Discharge Mixture Over A Waterbase Discharge?
Most textile printers are comfortable with plastisols and are familiar with the techniques of how to use them. Although a 100% waterbase discharge print yields the ultimate in softness, breathability and absorbency, prints produced by overprinting Union plastisols wet on wet through fine meshes over a plastisol discharge underbase come very close without the problems of drying in the screen and the pot life associated with straight waterbase discharge inks.
Mixing of DSPCH-1000 and ZFS Powder
DSPCH-1000 is a two part system and will not work without the addition of the ZFS powder. It is recommended printers add 6% by weight of the powder to the DSPCH-1000 and mix until completely dispersed. Even though the DSPCH-1000 has a shelf life of 6 months, it is advised printers only mix the amount of final product which can be used in a 24 hour period.
Water resistant stencils are required for both the underbase screen and each subsequent screen.
Recommended mesh size for the underbase screen is a 156T monofilament polyester. Overprint colors such as the Union Ink PLUS Series, AUTO Series or MIXO Series may be printed through mesh sizes ranging from 156T-350T monofilament polyester.
Printing the discharge underbase is directly opposite that of printing a regular plastisol underbase. Adjust your technique so the ink is driven into the fabric deep enough to destroy the garment color beyond visible depth and to avoid having undischarged sides of individual threads showing when the fabric is stretched. This is usually achieved with extra heavy squeegee pressure and a fast squeegee stroke. Plastisols may then be printed wet on wet on top of the discharge underbase. Printers have successfully flash cured the DSPCH-1000 for 1 second in order to eliminate picking up of the underbase on the subsequent screens.
Curing of Print
A minimum of 90 seconds in a well ventilated oven where the entire ink film temperature reaches 320 degrees Fahrenheit is required to perform the discharge process and at the same time cure the overprint plastisols. Caution: This is a critical phase of the discharge process. If your oven does not allow the garment to remain in the heat chamber for at least 90 seconds it could effect the results of the finished print.
Environmental Concerns Regarding ZFS
The following excerpt is directly from a federal EPA letter concerning zinc formaldehyde sulfoxylate which is the discharge agent used in DSPCH-1000.
"A review of the current office of water activities reveals that there are no current regulations specifically controlling zink formaldehyde sulfoxylate (ZFS). Also according to the Office of Pesticides and Toxic Substances Hot Line, which has a computer based Federal Register (FR) data base, there have not been any FR notices/publications over the past ten years discussing, proposing, or promulgating rules for ZFS. Further, we are not aware of any situation where state or local officials have established controls for ZFS or banned the release of ZFS into water.."
As the above excerpt from the letter is dated June 11, 1991, the Toxic Substance Hot Line and Federal EPA have been asked to keep us advised of any changes in the status of ZFS and we will call them to check every few months. If anyone wants to check the accuracy of the above statement and to make sure there has been no change for themselves, the telephone numbers are:
Federal EPA- 1-202-260-7120 Toxic Substance Hot Line- 1-202-554-1404
Giving the CASE# for ZFS (24887-06-7) along with the name (ZFS) will expedite matters. Even though there are no specific laws against putting ZFS into water it should not be taken as an invitation to dump it down a drain. All chemicals should be disposed of as specified by local laws and your MSDS.
Health and Safety Concerns Regarding ZFS
According to the Material Safety Data Sheets for ZFS, qualified experts and results of actual monitoring; formaldehyde in ZFS is not set free prior to, during or after the discharge reaction. Even if it is was set free it should combine with a scavenger built into all UNION discharge bases.
Possible products of decomposition include carbon monoxide, carbon dioxide, sulfur dioxide and zinc oxides. PEL and TLF for sulfur dioxide is 2ppm in any eight period (5ppm STEL). Sulfur dioxide can cause irritation of the respiratory tract. PEL and TVL for zinc oxide is 5 Mg/m to the third power in any eight hour period. Zinc oxides could theoretically cause metal fume fever. PEL is the abbreviation for Permissible Exposure Limit. TVL is the abbreviation for Threshhold Limit Value which is the maximum level recommended for a lifetime of exposure for 8 hours per day. STEL is the abbreviation for Short Term Limit Exposure which means maximum level recommended even for brief exposure.
Any fumes generated in a well ventilated oven should pose no problems. Adequate ventilation recommended for any shop area should be sufficient enough for a good air exchange rate. Air blowing directly on the screens should be avoided as this will cause the inks to dry in the screen.
Union DSPCH-1000 Discharge Underbase White is solvent free and made with the safest possible ingredients. However, prolonged contact could cause skin irritation in sensitive individuals especially after the ZFS is added. Additionally, dried prints contain chemicals that could irritate the skin of sensitive individuals if the garment is worn prior to washing. Prolonged contact with the ink or unwashed prints should be avoided.
Clean-up Of The Discharge Underbase Screen
Even though the DSPCH-1000 is a plastiol mixture the discharge underbase screen must be cleaned up using the same techniques as any waterbased ink. Simply use a sponge or rag saturated with clean water and wipe out the screen and image area until completely clean. Follow the same procedure for any other screen in the design Which may have picked up any of the underbase print on the print side of the screen.
Customer testing is required and should be mandatory with this product or any new product or process before running production. Our technical advice and recommendations given verbally, in writing, or by trials are believed to be correct. They are not binding also with regard to the possible rights of third parties and do not exempt you from your task of examining the suitability of our products for the intended use. We cannot accept any responsibility for application and processing methods which are beyond our control, nor can we accept responsibility for misuse by you of the products or use by you of the products outside the specified written instructions given with the products. User must protect sensitive skin, exposed wounds and eyes from contact with products.