AS YOU PROBABLY KNOW, the garment decoration industry is moving away from PVC-based inks. Fashion and sports brands such as Nike and Adidas led the charge some years ago, mandating their suppliers move completely away from plastisol and PVC. The trend is intensifying and moving into the mainstream, leaving printers with some choices to make.
PVC plastisols became popular because they are so simple to print and cure. Frankly, they are way too easy to use. They have a wide curing window, don’t dry on press, are available ready for use (RFU), have extended screen life, print wet on wet, and work on almost any fabric or color. No wonder they dominated the market for decades – they were almost God’s gift to screen printers.
Although plastisols are still commonly used, the reality is they are no longer aligned with market expectations and regulatory trends, and haven’t been for some time. About a decade ago, the Consumer Product Safety Improvement Act led to the removal of phthalates from plastisols, altering the formulation, price point, and printability of the inks. Now, brands are demanding the removal of PVC – the very resin that makes up plastisol – altogether.
The Search for a Substitute
The biggest challenge for ink manufacturers has been the race to provide a non-PVC solution that acts like plastisol in production. A number of alternatives are available today.
One option is non-PVC plastisols, also known as acrysols. Basically, these inks replace the vinyl resin with acrylic polymers. They have a number of advantages beyond removing the PVC, including the feel on press and especially the ability to stay wet in the screen like a plastisol. But they are expensive and, for the most part, must be flashed after every color, which requires substantially more energy and larger equipment. There aren’t a lot of low-cure optionsand the ink film tends to be weaker than other ink systems, raising durability concerns. I see them as more of an evolution of plastisol technology than an innovation.
Silicone inks are another appropriate non-PVC option and they’re aligned with the ecological demands of the market, though they are typically used on a narrow range of fabrics. Compression fabrics prone to dye sublimation fit very well with the technology since silicone inks can cure as low as 250 degrees. Cotton and brushed fabrics are more difficult to print because the ink coats the fibers. Silicone inks require a fixative or catalyst in order to cure, which gives them a shelf life and creates some waste. Silicones should be used when a specific application requires them. Stretch fabrics such as yoga pants come to mind, and they’re also suitable on performance wear made from technical synthetic fabrics. The elasticity, washability, and resistance to bleeding and cracking of silicone inks are superb, though they come with a hefty price tag.
Let’s Talk About Water
Many years ago, I was having a discussion with my friend Mark Gervais, director of screen print for Ningbo Shenzhou Knitting, about alternatives to PVC plastisol and he said something that I repeat often: “It’s H2O, stupid!” He may have added some expletives at the time, but yes – it’s all about water. It’s eco-friendly, has been around for a long time, and is definitely PVC free. Kind of a no-brainer, in hindsight.
Technological advancements have made water-based ink increasingly more attractive. A decade ago, we wouldn’t have expected water-based inks to perform as well as, or sometimes even better than, plastisol, but they’ve come a long way. Along with their perceived environmental benefits, the performance of water-based inks has improved tenfold.
When garment printing was in its infancy, the only available inks were water based. They were economical but they dried very quickly in the screen, had weak washfastness, and were prone to fading. They were also very transparent and suitable for printing only light-colored, 100-percent-cotton materials. These traditional, pigmented water-based inks are still used on all-over prints and deliver a soft hand on lights and whites.
Printers who were raised on plastisols have always found water-based inks challenging to work with. Ray Smith, senior business development manager, specialty inks and polymer systems for PolyOne Corporation, says, “The reason printers seem to fail or succeed with different ink types is because when they learn how to print, the ink they were trained on is the type they most embrace. They learn the traits and behavior of that ink.”
Now that water-based printing is finally growing quickly in the US, many shops are adjusting to the learning curve. One of the biggest challenges for a printer is controlling heat and evaporation. The goal is to cure the ink and evaporate the water in the dryer, not on press. Though water-based products have improved vastly, one reason plastisol printers avoid them is because of the care they require to prevent the ink from drying in the screen. However, the techniques for controlling this potential problem are easy to learn. Controlling the platen heat and using the correct dryer temperature, belt speed, and chamber time are very important.
The final aesthetics of a water-based print – the hand, surface, and drape – are very pleasing after cure. Apparel brands are beginning to realize the inks aren’t just more ecologically friendly; they also produce prints with a superior feel and breathability. Further, water-based technology can be used on nearly any fabric if the correct ink and techniques are employed.
Water-based ink typically uses dyes or pigments in a suspension with water as the solvent. The solvent is designed to evaporate, leaving just the pigment or dye behind. Newer inks have a look and feel comparable to plastisol on press, with improved open screen time, but the print processes are very different. The details reflect how ink formulation, prepress processes, and print parameters all play into successfully working with these inks. I am always preaching process! Selecting the right tool for the right function is critical.
A Wide Range of Options
One commonly used water-based ink system is known as discharge. These inks chemically remove the color from the garment, replacing the dye being withdrawn with the colorant in the ink while retaining a soft feel. Discharge inks have been traditionally used in conjunction with plastisol and reduce the need for an underbase when printing on dark, natural-fiber garments. Most common formulations require the addition of zinc formaldehyde sulfoxylate as an activator, though formaldehyde-free formulas are available. These inks are reasonably easy to handle, assuming you have a water-resistant stencil that has been fully cross-linked and dried. According to Jesse Martinez, sales manager for Matsui International, the color values of discharge tend to give a somewhat unstable, vintage look, noting that they also have weak washfastness.
Newer, more sophisticated water-based ink systems are now available from various manufacturers on a large scale. For years, these were referred to as rubber inks in Asia, though the correct name is HSA (high solids acrylic). HSA inks are known for having similar performance characteristics as plastisol. Though they are water-based, they are opaque and vibrant. They can be used on both dark and light fabrics. They provide a soft feel and desirable drape. They are also suitable for use on polyester and poly/cotton blends, in addition to 100-percent cotton. HSA inks are flexible enough to be used on stretch materials containing blends of Lycra or spandex that are increasingly popular in performance apparel. They also have excellent fiber-matting properties and washfastness. Based on these characteristics, HSA inks are now often specified for use by marketers, contract printers of licensed goods, and many brands themselves.
Still, HSA technology isn’t the same as plastisol. For years, we have come up with creative ways to massage the separations and screens in order to do some wet-on-wet printing using HSA inks, with limited success. Recent innovations have led to the development of hybrid HSA/polyurethane blends, beginning with Virus and its WOW product line and now emulated by other companies taking a similar approach. We’ve been able to get up to eight colors to print wet on wet with these inks. According to Beppe Quaglia of Virus, the WOW project is much broader than simply enabling wet-on-wet printing, encompassing other considerations such as sustainability, ecology, costs, and reduction of consumables.
With regard to specialty inks, the variety and selection out there is incredible. Some water-based special-effect inks, including metallic, color-shifting shimmers, sparkles, and glitters, are impressive because the water, binders, and resins flash off or melt down and really allow the “particles” to shine. Also available are water-based high-density inks, clears, puff, foil and flock adhesives, and resists. The options are limitless.
Mastering Water-Based Inks on Press
As far as water-based technology has come, printers can’t just put the inks in their screens and expect them to behave like plastisol. Gervais comments, “With water-based inks, sometimes you need to do different things and sometimes you need to do things differently. That’s not a play on words – it’s just how it is.” Understanding the difference as well as the specific requirements at each step will give you the experience to succeed with water-based systems.
Danny Gruninger from Denver Print House made a commitment last year to become a 100-percent PVC-free, water-based shop. The company currently runs four automatics. Due to Denver’s dry climate and high elevation, several items needed to be addressed prior to making the transition. Controlling shop conditions is a high priority with water-based inks. Airflow, heat, and humidity play a significant role in their performance and printability.
As most water-based printers know, once you start a job, it’s problematic to stop and then start again. When team members need to take breaks from a press, it must be orchestrated so the job can continue to run. Gruninger found it necessary to do as much R&D as possible; his team is currently working with several ink manufacturers trying to determine what works best in their environment. Each ink has its own printing characteristics, he explains: “It takes a very disciplined crew and the determination to always be better.”
The basic art creation and separation process is similar to that of conventional plastisol printing. However, the final color sequence and additional flashes impact the decision-making process. The separator must work closely with production to determine how many heads will be needed on press. The pigment loads are lower than those of plastisol, which can affect strategies for separations, print orders, and of course, flashing.
The lack of opacity may require multiple underbase techniques. It’s common to print a first-down clear or a low-opacity white base overprinted with a high-opacity white to create a smooth, white underbase with transitions. The less opaque white would be printed through a higher mesh, then flashed, with the more opaque white printed through a lower mesh count. Highlight whites are sometimes employed as well. The secondary underbase should include the brightest and whitest areas of the image. Many dark colors will overprint only on the first white. Additional screens may be required as dye blockers for polyester and blended fabrics. Transparent and fluorescent colors may require additional screens as well.
Jamie McCrae from Latitudes says, “Opacity is the big one for HSA. Choose wisely. Most plastisol printers are used to printing one to two screens of white and one screen per color. With HSA, it’s more like two to three screens of white and one to three screens of color – fluorescent colors being the worst.” We’ve seen that dynamic at Graphic Elephants. In order to get a fluorescent yellow on a black or red polyester shirt, the print sequence might be as complicated as this: Clear (to mat down fibers), flash, blocker (to control bleed), flash, blocker, flash, white, flash, white, flash, fluorescent color with white mixed in, flash, fluorescent yellow, flash, yellow.
The color mixing process for HSA and polyurethane hybrids will be familiar. Pigment percentage guidelines and a formula guide help in creating color matches. Most manufacturers provide RFU colors, though rarely is an ink ready to go straight from the bucket. Typically, inks require additives to combat in-screen dry time, washfastness, anticrocking, and/or lower curing temperatures for difficult fabrics. These and other additives are resourceful tools. HSA water-based inks and hybrids are easy to mix and store for future use.
Water-based inks can contain any number of additives and components including solvents to inhibit premature drying in the screen, assist in curing, and improve durability, among other things. These chemicals, combined with the water in the ink, can be extremely aggressive toward the stencil. Selecting the right stencil system is critical to producing durable, reclaimable screens for use with water-based inks.
Diazo-sensitized stencils hold up to the water, but they have minimal solvent resistance. The use of an emulsion hardener as a post treatment isn’t necessarily effective, as it only further improves the stencil’s water resistance, not solvent resistance.
Dual-cure emulsions are supposed to be solvent and water resistant, but in my experience, they don’t have the level of water resistance needed. The use of a hardener can increase its water resistance, but such a screen may not be reclaimable (though reclaimable hardeners are available).
It seems to me that hybrid photopolymer emulsions are the direction to go with these inks. Hybrid means they have been engineered to be solvent and water resistant. Photopolymer emulsions have a high solids content and are easy to coat. Their fast exposure enables the use of computer-to-screen technology and LED exposure.
Producing a durable screen for water-based inks also requires proper mesh preparation. Using a mesh prep and degreaser not only cleans the mesh, but also primes it to accept the coating for good adhesion. After coating, the stencil must be completely dried before exposure. Fully exposing the stencil is also very important with water-based inks. Underexposure will not work with these products; do exposure tests to be sure the emulsion is completely cured. After developing and fully drying the stencil, block out unwanted open areas with the same emulsion. I like to do a post exposure to help harden and fully crosslink the stencil. Taping the inside of the screen where the squeegee and flood bar travel, as well as where they “chop,” helps alleviate premature breakdown during the run.
Water-based ink is less opaque and will require some additional flashing. When you’re working out the color sequence, it’s important to put colors that are less opaque, have the biggest coverage, or are most important at the end or before a flash station. Water-based setups can be difficult and frustrating at times, especially when the humidity level in the shop is low. When HSA inks are exposed to the environment, the water in the ink begins to evaporate. This can be a problem if the registration process takes some time. New developments have improved the ink’s open screen time and re-wetting abilities.
Once the job is running, these inks will keep the image open unless it stops flooding, so be sure to keep the screens wet with ink. HSA inks have a tendency to move to the sides of the squeegee, so it’s important to have a person tend the screens and use winged flood bars to keep ink in the center of the screen. Refresh ink in the screen by moving it into the print area and adding new ink. One common problem is overloading the screen with ink, as it can dry out. Misting the ink with water can help, but a more effective method is using a fogging type of system that utilizes vapor rather than airborne water.
Squeegee pressure is another variable to consider. The first screen seals the garment so the pressure on that screen should be the highest. The subsequent screens need to build opacity, so use as little pressure as possible on them. Typically, double-stroke printing is necessary to clear the ink completely from the mesh openings.
We want the flood bar to hover above the screen mesh and not force it into the stencil. As the ink runs, it will be going through an evaporation process. Depending on the humidity level, this process may be fast or slow.
The combination of heat and airflow promotes water evaporation, which is the key to flashing these inks. Controlling the ink film and platen temperature is critical, however. The heat you need to properly set the ink at the flash station is totally unwanted at the press, where it can cause print performance problems including accelerated drying in the screen. Using flash time, temperature control, distance, upper limits, and all the other tools on the flash, we can achieve that delicate balance of controlling the heat and ink film temperature.
Curing and Drying
If your inks are wet and printing correctly, the next issue is curing. It’s not a requirement, but having a forced-air gas dryer with enough belt to accommodate a chamber time of two to three minutes is best. Without that time in the dryer, you run the risk of undercuring and adhesion issues, as well as washfastness problems. Water-based inks don’t cure until all of the water has evaporated, leaving the binder and pigment on the shirt. The right temperature setting and belt speed will depend on the length of your drying tunnel, so use a digital thermometer to establish the temperature and chamber time you need.
When a job on press is completed, process the screens immediately. You will likely cause stains on the screen mesh if ink is left in the print area. Wiping the print areas with a wet rag helps minimize this, so keep buckets around the press with water and rags for cleanup. And don’t assume water-based ink alleviates any disposal concerns. It contains dyes/pigments, binders, resins, and the like. Just because it has water in the name doesn’t mean it’s drain safe.
My best advice for those unfamiliar with these inks is to walk before you run and crawl before you walk. Start by printing single or multicolor designs on light garments using only dark water-based inks. Next, get a bright white print on dark fabric. Try printing vector art with bold block colors, a more complex use of water-based inks. Then take another big step and experiment with water-based simulated process color on dark garments.
Most importantly, don’t wait. Water-based printing opens up new opportunities that help to differentiate your product in the market. They deliver an arguably better finish and offer more variety in special effects. There is little that cannot be achieved using water-based inks. Regardless of regulations, performance and responsibility can go hand in hand. Water-based inks today have advanced properties that enable them to be used for just about any application.
“The world changes, with or without our blessing,” Quaglia observes. “It is a fact and is vital to thinking about how we can adjust our approach. The increasing chemical substance limitations, the growing concepts of sustainability, personal awareness about ecology, and generation renewal could be properly sustained just by lifting the bar of our skills and knowledge through a different mental approach. The past is a wonderful place where we built ourselves, our profession, our dreams, and we never have to forget about that, but now our vision must be projected to the future, because it is exactly where we are going to spend the rest of our lives.”
Adds Michelle Moxley, M&R’s innovation director, “Always be willing to try anything new, and always be willing to stop trying and move on. As they say, timing is everything, and if struggles outweigh gains, plan to revisit tests in the future. Use a structured plan to integrate anything new into your shop; a step-by-step approach is key. Even if your most trusted partner tells you what the correct step is, still prove it and do it yourself. This is where true knowledge and innovation live. If failure presents itself, be open to the possibility that more change is needed, either with mindset, gaining knowledge, or the technology you’ve tested. Also keep in mind, failure can ultimately be success; it’s all about perspective.”
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