Plastisol inks have been a mainstay of the textile screen-printing industry for the past 40-plus years. Although new technologies are popular in some applications such as high-solids acrylic (HSA), silicones, discharge and new water-based inks, plastisols still are the go-to product for most of the imprinted sportswear market.
The plastisol screen-printing inks manufactured today come from a wide variety of performance factors. Each product line typically is designed to address a specific screen-printing application, including:
• Soft-hand applications
• Athletic-printing applications
• High-elongation fabrics
• Photographic reproduction
• Nylon and synthetic applications
• Special effect applications
Unlike the ink lines from the past, most all plastisols today are manufactured as ready-to-use products straight from the container. Although this is the case, a wide range of product modifiers still are available that enhance the ink’s performance based on the finished product’s desired effects.
Here, let’s look at the modifiers currently offered for plastisol screen printing, as well as their benefits, drawbacks and any caution that should be applied when using them.
One of the more popular additives on the market is soft-hand extenders. They originally were developed to minimize prints’ athletic feel. Prior to the onset of high-tension screen printing, many decorators used coarser mesh counts and excessive ink films, resulting in the introduction of soft-hand extenders to help minimize that effect.
These extenders particularly are helpful when printing on light-colored garments. As soft-hand extenders are lower in viscosity, they increase the ink film’s flow and penetration into the fabric. Keeping in mind that you want the ink film on the fabric’s surface and not excessively driven into the garment, higher-tension screens also contribute to this effect.
There is no actual limit to how much soft-hand extender can be added to an opaque plastisol as long as you know the ink’s overall opacity will decrease as the extender-to-ink ratio increases.
The most common modifier used by many plastisol screen printers is a viscosity reducer, which can be a great benefit when used properly. There are two basic kinds of viscosity reducers used in plastisol-printing applications: straight plasticizer reducers and curable reducers. The former can be beneficial when properly used and measured to the manufacturer’s recommendations.
The problem with straight plasticizer reducers was that many printers wouldn’t properly measure the required amount, which often resulted in an overly plasticized ink that wouldn’t properly cure and a finished print with poor washability characteristics.
This scenario led to the introduction of curable reducers in the 1980s. This kind of viscosity reducer is a liquid plasticizer with a balanced amount of resin that allows the reduced ink to properly cure. This removed the threat of a resulting print with poor washability, while also allowing screen printers to modify the ink to their liking.
Caution still must be taken, as adding an excessive amount of curable reducer can result in poor opacity if the ink’s viscosity is excessively thin. As with any plastisol modifier, you should strictly adhere to the manufacturer’s recommendations for proper mixing.
This type of plastisol additive is intended to decrease the flash time for standard plastisol inks. Flash additives are beneficial when printing on polyester or tri-blends, which are sensitive to heat and prone to scorching. When printing on tri-blends, minimizing the fabric’s heat exposure will help minimize the scorching risk.
Polyester fabrics, on the other hand, don’t tend to scorch as easily as tri-blends, but the risk of sublimating the polyester dyes — which only promotes the potential for dye sublimation or migration — must be considered. Therefore, any heat reduction that can be introduced to the process will benefit the finished product.
Flash additives can be added up to 10% by weight to a standard plastisol depending on the manufacturer. Again, it always is important to adhere to the manufacturer’s mixing recommendations.
Any plastisol textile screen printer who has ventured into the special-effects realm of foil applications has experienced working with foil-release additives. As foil had an inherent ability to stick to plastisol ink film’s surface, the ink must be modified to reject the foil’s bonding characteristics. Foil applications can be tricky due to several variables within the process, including:
• Plastisol brand
• Ink-film thickness on the fabric
• Foil brand
• Amount of foil-release additive in the ink
• Heat-transfer time, temperature and pressure
It’s not unusual to spend time upfront conducting research-and-development tests to find the optimal combination of
parameters to produce consistent results. The best starting point is with the manufacturer’s recommendations for both the amount of foil-release additive and the foil-transfer instructions. The aforementioned variables may need to be adjusted to achieve optimal, repeatable results.
Synthetic fabrics like nylon have an extremely smooth woven surface, as opposed to a T-shirt’s soft, knitted surface. This makes the process of properly fusing a plastisol ink to the fabric much more difficult. This fact is enhanced if the fabric has a waterproof treatment, such as Scotchgard, which makes the need for a nylon catalyst imperative. Nylon-catalyst additives not only will enhance a plastisol’s bonding capabilities to a nylon woven fabric’s surface, but also will lower the ink’s cure temperature. This is an advantage, as many synthetic fabrics like nylon can’t withstand the full curing temperatures of 320°F required for standard plastisols.
Specialty high-elongation inks and additives currently are offered across several different ink lines. The high-elongation clears and liquid additives are very effective when printing on fabrics such as spandex and Lycra.
When working with these components, it’s important to avoid dyed fabrics containing polyester, as high-elongation additives will promote dye migration. Although standard plastisol inks have a good degree of elongation, fabrics like spandex and Lycra require the ink to have an elongation factor up to 300% without cracking.
The percentage of additive or clear to be added to a standard ink will vary among manufacturers and — as with any additive — mixing instructions should be strictly followed to achieve the best results.
Although most plastisols are designed to be printed straight from the container, there always are situations where special modifications are needed to enhance the ink’s performance based on the application and substrate. When it comes to mixing in these additives, just remember to adhere to the manufacturer’s recommendations to achieve optimal results.
Rick Davis is an industry veteran with a background in plant and contractor management, quality control, process troubleshooting and consulting. He currently is the screen-print process manager at Scalable Press and is a member of the Academy of Screen and Digital Printing Technologies. For more information or to comment on this article, email Rick at rickd5050@yahoo.com.
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