Screen Printing: Process + Techniques

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Not all inks are created equal. Lately, there’s been a lot of buzz regarding “eco-friendly” inks. Without going into too much detail on the make-up of these screen printing inks, I’d like to give a brief guideline of what to look for when switching to or using “eco-friendly” inks.

When considering purchasing an ink, it’s always a good idea to take a look at the product’s SDS (Safety Data Sheet). The SDS will give you a lot of information regarding the product’s ingredients and whether the chemicals are deemed toxic or not, or the level of toxicity. In addition, it will give first aid tips and how to safely use and dispose of the product. Just because an ink contains “water” for example, does not mean that there are no other chemicals in it. Unless a printer concocts their own ink and knows what goes into it, an ink will include binders, pigments, and fillers of some type.

I’ve seen many printers switch from a standard plastisol to an alternate ink without adjusting their print processes. This could spell out “disaster,” so let me list some of the items to look out for:

• Emulsion – can your new ink of choice be printed with your existing emulsion? If you are switching from a traditional plastisol ink to a “water-base” ink (including some of the high-solid water-base type inks), it will require a different type of emulsion – one that is more durable and can withstand contact with water.

With the extra durable emulsion, reclaiming the emulsion from the screens can be difficult or even impossible and the screen mesh would need to be torn out and re-stretched.

• Humidity – Water-base inks perform best when the humidity is higher than when it is lower. Some equipment manufacturers even offer humidifiers with their machines to help keep sensitive ink flowing. Take this into consideration when deciding on which ink system to purchase. (I would not recommend printing water-base inks in Arizona in August, for example.) The humidifiers can also corrode the machines over time.

• Flash – does the ink need to be flashed between each color? Many ink lines cannot be printed wet-on-wet due to the colors blending and becoming muddy. I’ve been to large print facilities where they include flash and cool-down stations after each color to get the desired print results. This type of set-up may not be possible or production-friendly at shops with smaller automatics or manual presses.

Let’s take printing a four-color print on a black shirt using the various types of inks as an example. When using standard plastisol inks, there are five ink stations and one flash. The same would be true if printing traditional water-base inks with a discharge underbase. For high-solids water-base inks and typical acrysol inks, the number of stations increases due to the need to flash after each color.

Some inks require that the pallets should be preheated to a certain temperature before printing can begin, thus requiring additional downtime before production can commence. The “eco-friendly” impact of the use of discharge or the additional energy output requirements for pre-heating pallets or the extra flash units needed should be considered in the analysis.

• Pantone Color Matching – does the ink system provide pantone color matches? If your shop offers to color match logos or artwork, the ability to mix PMS colors is essential to your business.

• Special Effects – does the ink line include specialty inks like high density, foil adhesive, gel gloss etc.? Many customers like adding texture and bling to even a small logo print and special effects make your shop stand out.

• Low-Cure – does the ink line accommodate cure at lower temperature? Not all shirts are 100% cotton, and many of today’s trendy eco-friendly or recycled material shirts are synthetic blends, requiring bleed blocking ink technology and/or low-cure capability.

• Halftone/Detail Printing – can the ink print through high mesh counts? This might be an important factor if your shop offers half-tone or photo-realistic or detailed prints.

• Test Certifications – Check whether the inks have passed any of the stringent tests which certify that the inks do not contain or contain only a certain amount of known hazardous or restricted substances.

• Complete System or Two-Part System – is the ink system a one-part complete system (ready-to-use) or does it require mixing in a catalyst such as some silicone ink systems require? Although certain inks may need to be mixed with a catalyst in order for them to adhere better to difficult substrates, or simply to cure, typically once the inks are mixed with a catalyst, they have a limited pot life. This means that after several hours or days, the ink becomes unusable and needs to be disposed of. If too much ink was mixed for the job at hand, it creates unnecessary waste. Plastisols and acrysols generally have much longer pot lives – months or even years – and are ready-to-use straight out of the bucket. The unused ink portion can also be returned to the bucket for reuse at a later time.

• Volatile organic compounds (VOCs) – How much VOCs does the ink system have? VOCs are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects.

VOCs are emitted by a wide array of products numbering in the thousands and are widely used as ingredients in common household products as well as cosmetics, paints and varnishes. The caution here is that concentrations of many VOCs are consistently higher in water-base ink products than standard ink products. As such, when the ink goes through the dryer to be cured, the VOCs can release a greater concentration of chemicals into the surrounding (indoor) space, which can affect the operators’ health over the long-term.

In summary, do the research before deciding on what type of ink is right for your shop. Consider what’s in the ink – not only after it is cured on the shirt, but before it is. Many are only interested in what is on the shirt after processing. However, they may not have the full understanding of what it took to process that imprint. In order to evaluate “eco-friendliness,” take into consideration all that it takes to get that embellishment completely processed.