David considers the recent history of water-based inks and dispels some of the myths about working with these formulations.
By Rick Davis
Last month, I discussed a specialty application that involves water-based inks. In hindsight, I feel that I may have jumped the gun because most textile screen printers either shelved water-based inks years ago or have yet to try them on garments. So for this edition, I'll take a few steps back to review the history of water-based screen inks, the benefits and disadvantages of working with these formulations, and what you need to know to print them successfully. Flowing in and out of favor Almost all textile printers used water-based inks before the introduction of plastisols in 1961. At that time, the screen printers who used water-based inks were masters of their medium. But plastisols changed the ink market, and their user-friendly nature is the reason why so few garment printers use water-based chemistries today. Water-based inks produce prints with a very soft hand and bright, vibrant colors on most light-color fabrics, but their transparent nature makes them unsuitable for dark fabrics. The initial appeal of plastisols came from the fact that they could be printed on both light and dark garments. Printers who used these new inks were so pleased with the bright images that plastisols produced on darks, few paid attention to the harsher hand that the inks created. In truth, the heavy prints of the day were as much the result of poor printing tools and procedures (e.g., use of unstable wood frames, low screen tensions, and excessive squeegee pressure) as of early plastisol chemistries. Nevertheless, once garment printers noticed the heavy hand of plastisol prints and began complaining about them to the ink manufacturers, the manufacturers quickly responded by adjusting components of their plastisols to meet the market demand for softer prints. Since then, providing a softer hand has been a continuing focus of plastisol ink development. Luckily, printing technology progressed along with the inks. The introduction of retensionable frames and improved press controls allowed screen shops to better manage ink deposits and produce softer prints. Garment-printing technology advanced to the point were printers could use meshes with thread counts as high as 300-400 threads/in. to produce supple, high-detail plastisol prints. As screen printers were conquering the challenges of printing soft-handed images with plastisols, consumers decided to complicate matters by requiring special-effect inks, including puffs, high-density inks, gel formulations, and other types that are characterized by a heavy hand. Today's garment printers have conquered these challenging formulations as well, only to find the tables turning once again as customer preferences return to soft prints. This latest trend is driven by European and Asian markets, where fashion preferences are for vibrant graphics with a non-existent hand. So now printers are faced with either striving for the softest hand achievable with plastisols or diving back into the inherent softness of water-based technologies. While water-based inks still bring some inherent disadvantages to production, these formulations have undergone some significant advancements that make them worthy of consideration for a variety of garment applications. Water-based inks are completely different animals than plastisols. Many printers who use plastisols avoid them, saying, "The ink will dry in my screen!" While water-based formulations can dry on press, such statements are usually made by printers who have limited or no experience working with these inks. Are water-based inks more work intensive than plastisols? Yes. Are they handled and applied differently? Yes. The real keys to working with water-based inks is understanding their nature and applying the appropriate procedures to integrate them into the production workflow. The advantages of water-based textile inks start with the cost, which is a fraction of that associated with plastisols. Still, many of the printers with whom I've spoken say they don't pass these savings on to customers because of the additional care and attention required during the printing process. Water-based inks have a much lower viscosity than plastisols and exhibit no sheering characteristics, which facilitates easy printing. Water-based inks are best applied to 100%-cotton fabrics, where they dye the cotton fibers during the printing process, giving the prints excellent washability. The greatest advantage for the consumer--and the reason for the current interest in water-based inks--is the virtually non-existent hand they produce. What little hand these inks exhibit is attributed to the color of the ink and the size of the pigment particles it employs in any given color. White inks, for instance, will carry a more noticeable feel than other colors because the white pigments tend to be among the largest used in water-based inks. But once the printed garment has been properly cured and washed, even this slight hand disappears, and the decoration will feel as soft as the rest of the garment. The greatest obstacle in working with water-based ink is the potential for these formulations to dry in the screen. But after a little experience with these inks, printers discover that the learning curve for avoiding this problem is quite small. The key is to keep the ink moving and prevent it from standing exposure to open air for extended periods. If the press must be stopped for more than a few minutes, the image area of each screen needs to be wiped out and dried. If the ink dries within the image area, it will be tough to remove from stencil openings. In the worst case scenario, the screen will be completely ruined. Using screens with lower mesh counts--in the 125-160 thread/in. range-- also reduces the change that water-based inks will dry in screens and supports good detail reproduction. Although these mesh counts don't support the same degree of detail as printing plastisols through 230-305 thread/in. meshes, the level of detail possible at the lower counts is more than adequate for the majority of applications a printer will face. It's also important to know that the variety of special-effect options available in water-based formulations is much more limited than with plastisols--the choices only include metallics, fluorescents, puffs, and reflectives. Drying techniques are the last major consideration in working with water-based inks. High-velocity, forced-air dryers are the best solution for drying water-based prints because they rapidly force water out of the ink and garment to ensure a proper cure. Radiant infrared dryers can also work, but the time required to get a complete cure with these systems is substantially greater. Conclusion As the needs of the consumer change and diversify, it is up to you to stay on top of all the solutions available to meet their needs. Water-based inks are one such solution that are ideal in satisfying today's fashion trends. As with any technology, you can only benefit from water-based inks if you have procedures in place to implement them properly. Once you do, you'll be able to leave the competition all wet.
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