Screen Printing: Production

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November 12, 2012

Editor’s Note: The following article is not meant to discredit or discourage compliance with the federal Consumer Product Safety Improvement Act. Impressions encourages all apparel decorators to thoroughly research all ink systems and make the best choice for their shops.

Screen printers work with chemical systems daily. However, there’s been a big push to become more environmentally conscious, as well as reduce waste and the impact of the things we use.

In our industry, water-based inks have been touted as the sustainable option and, for some reasons, that makes sense; even the name sounds friendlier. However, water-based inks are compared many times to the plastisol ink that was prevalent decades ago, which no longer makes it a fair comparison. I wonder if we shouldn’t take a fresh look at plastisol to see if it actually could be considered a sustainable ink system.

Clearly, both ink systems include industrial chemicals. Both also must adhere to Consumer Product Safety Improvement Act (CPSIA) requirements, both ink systems are considered to be hazardous chemicals when in their uncured states and each must adhere to the laws governing such things when they are handled and disposed. Thanks to CPSIA, lead-free and phthalate-free plastisol is now the industry standard, and the use of PVC-free plastisol is quite common and still growing. Much of the bad rap associated with plastisol has to do with phthalates or PVC, factors that now are not largely relevant.

Comparing Composition and Screen Prep
Water-based ink uses water as its main solvent, but it also contains pigments, binders, thickeners and sometimes co-solvents, which can be petroleum-based. Some water-based inks contain volatile organic compounds (VOCs) that evaporate as the ink dries and can contaminate the air. Many water-based inks also contain additives that inhibit mold growth, since this ink system can experience the problem of mold growing on the surface or even in the product itself. If the latter problem occurs, it renders the ink unusable. Water-based inks also can have additional additives, which could help with curing or print performance. Just as you must consider which plastisol to use in order to cut down on chemicals, the same holds true for water-based ink.

There also is a difference in the screen preparation used with each ink system. Your average screen emulsion is formulated for use with plastisol and will degrade if you try to use it with water-based ink. Special screen emulsions are required for use with water-based inks, but they can degrade. Therefore, it’s common to add another chemical to the mix with water-based ink that hardens the emulsion. This will ensure your stencil does not break down in the middle of a production run, which may cost time and additional product. Sometimes though, the hardener will make screen reclamation impossible, forcing printers to cut out the mesh and make a new screen.

Lifespans and Cleanup
Water-based ink has a definite shelf life and the potential to evaporate out of the bucket or in a screen (thus, ruining the screen). It can be reused only if it has not been catalyzed. And even though water-based ink messes can be cleaned using water, it does not mean the solids in the ink residue can go down the drain. Plastisol will not dry in the bucket or the screen, will likely last until you can use it (although manufacturers recommend testing beyond a year of shelf life), can be reused, mixed to make a new color or, ultimately, you can cure it and recycle it. Plastisol cleanup generally requires mineral spirits, although there are plastisol products on the market that can be cleaned up with water.

The amount of waste obviously will be determined entirely by how you use either system, but when you take a wider view of the entire process, it seems the potential for waste is much larger with water-based ink than plastisol ink.

The Discharge Debate
There’s also the matter of opacity with each system. When printing light colors on dark-colored garments, plastisol simply requires a white underbase. Water-based ink, however, requires discharge to remove the dye of the garment. There has been a lot of debate regarding whether discharge is a safe product. Officially, it is considered safe — if handled correctly. However, most types of discharge contain formaldehyde as a part of the active ingredient, Zinc Formaldehyde Sulfoxylate (ZFS). This composition means that after use, some of the formaldehyde will be left in the garment. The amount is not considered enough to harm a person, but when the consumer washes the garment, traces of formaldehyde go into municipal waste water systems.

Discharge works because it reacts when heated and, while it has not been proven that it releases formaldehyde into the air, there is evidence that greenhouse gases like carbon dioxide and carbon monoxide are released, as well as sulfur dioxide, other sulfur oxides and zinc oxides, which can be harmful if inhaled.

Arguments can be made that proper ventilation and air filters around dryers and flash units (if used) will minimize these gases’ effects on workers, and that the amount released is not significant per shirt. However, is there an environmental impact involved with very large production runs of water-based printing that require a discharge base? It seems logical that the buildup of trace amounts of formaldehyde and vented gases could have an impact in the long run. There are discharge products that do not contain formaldehyde, but these versions don’t tend to perform as well.

Curing temperature between the two differs as well, but may not have much bearing on the topic of overall sustainability. Plastisol ink requires a higher curing temperature, while water-based ink requires more time to cure at a lower temperature. However, I have not seen any data comparing the energy usage difference to the difference in time and temperature.

If you look at the big picture, a case can be made for the sustainable use of plastisol ink. That’s not to say that the eco-friendly claims of water-based ink are false. However, so much has been made of water-based being the “green” ink system that I think there’s a false perception that you can grab any water-based ink and call your process sustainable. Sustainability doesn’t come easily in an industry such as ours, where industrial chemical systems are necessitated. CPSIA compliance may be a challenge for many, but the benefit is that it has changed the chemicals we use in our industry.

Sustainability isn’t just about the inks you use, but how you use your ink system. Do you want to use fewer chemicals and dislike the formaldehyde in discharge? Do you want the ability to reuse ink? If so, plastisol could be your sustainable option. However, if you want a biodegradable ink that cleans up with water, an eco-friendly water-based ink is certainly a valid option, particularly if you find a formaldehyde-free discharge that works well for you.

Perhaps it comes down to the sustainability of the process vs. the sustainability of the end product. Many things factor into sustainability, and I think it’s important to look at the entire process and carefully examine each step. You also must weigh the chemicals necessary in one system against the chemicals necessary in the other. However, it’s unfair to continue to associate plastisol with its past, particularly when we forget that water-based inks often contained carcinogens in their past formulations.

At the very least, if you use plastisol ink, I think it’s fair to say you still have the opportunity to be a sustainable printer — especially if you are transparent in your process and educate your customers.

Tessa Sainz has been a screen printing enthusiast since she was an undergraduate student at Notre Dame. She now works as an assistant manager for a Fortune 500 company in the apparel industry. She also started Krmbal, an eco-conscious indie graphic T-shirt brand. For more information or to comment on this article, email Tessa at tessasainz@gmail.com, or check out her blog at krmbal.com/blog.