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Screen Printing: Production
The Advantages of Apparel Decorators Utilizing Plastisol Textile Inks When Screen PrintingEase of use and wash-fastness are just two of the numerous reasons plastisol still remains a go-to ink system for apparel decorators when screen printing
Adjustable viscosity is an advantage of plastisol inks. Screen printers graduated from printing through multifilament mesh counts, such as 8xx, 10xx and 12xx, to 125-305 multifilament screen mesh counts.
During the past two decades, there has been a push from different organizations — including environmental agencies and large sporting goods companies — to have traditional plastisol inks either modified or replaced.
One primary concern was the banning of certain phthalates that have been deemed harmful. Our industry wasted no time in eliminating those components to meet those demands. Today, most ink manufacturers only offer phthalate-compliant products to meet with the Consumer Products Safety Improvement Act (CPSIA) requirements that were originally passed in 2008.
In pursuit of business with large sports companies, some screen printers have tried and, in some cases, completely converted to alternatives, such as high-solids, water-based, acrylic-based and discharge ink systems. Although these new alternatives have gained popularity during the past few years, plastisol still is the most popular and widely used ink system on the textile screen-printing market. Let’s look at the advantages plastisols have compared to alternative ink lines currently on the market.
Screen printers concern themselves with two primary aspects of printing performance: Inks that do not air dry (plastisols and acrylics) and those that do (water-based and discharge). When plastisols were initially introduced to the apparel decorating industry more than 40 years ago, the only composition for textiles were standard water-based dyes. Some decorators were printing athletic jerseys with acrylic paint, which initially looked impressive but lacked elasticity or durability.
The advent of plastisol inks offered advantages that had never been previously experienced. The primary advantage was that the ink did not dry in the screen, which was an aspect of water-based dyes that printers had grown accustomed to out of necessity. Plastisol inks eliminated that situation and made the printing process considerably easier. For the first time, printers could walk away from the press without going through the time-consuming procedure of wiping the water-based inks from the screens to ensure they would not dry out.
Plastisol ink also has screen-making advantages. Prior to plastisols, the only screen-printing photo emulsions needed were those that were water resistant. They worked well for their intent, but were not typically designed for long production runs. Thus, screen pinholes and breakdowns were common on larger jobs.
The early solution to this issue was to treat the screen with a diluted acid solution, which would make the screen stencil permanent. Although this would require restretching the screen mesh, it was deemed justified in order to print longer production runs with fewer backup sets of screens.
Today, there are countless photo emulsions available for any ink composition currently on the market, although those intended strictly for plastisols are the easiest with which to work. They also have fewer issues regarding longevity and stencil recycling.
Adjustable viscosity is a major advantage of plastisol ink. When veteran water-based printers opened their first plastisol ink can, their initial thought probably was, “How in the world will I ever get anything so thick through the screen?” The real eye-opening experience was that printers graduated from printing through multifilament mesh counts, such as 8xx, 10xx and 12xx, to 125-305 multifilament screen mesh counts. Although plastisols were more expensive than their water-based competitors, the increased mileage more than offset the cost difference.
From the standpoint of viscosity, plastisols typically will hold their original viscosity but can be adjusted by using different modifying agents. These currently are available to address any performance parameter that may be required. Water-based inks also have numerous modifying agents, but they still can increase in viscosity and decrease in performance as they are exposed to open air.
Although all ink systems available today (plastisol and water-based) have adjustable opacity levels, none possess that of plastisols. Water-based ink lines are offered in both standard and high-solids (opaque) content formats, but as separate ink lines. Plastisols also are offered as both all-purpose and high-opacity/low-bleed lines, but are far more versatile from the standpoint of modification. The bases used in plastisol mixing systems are formulated with different fillers and modifiers, which allow the manufacturer to pre-determine the base opacity in the initial formulation process. Thus, the printer has the choice of product to use to determine the performance and opacity level prior to mixing.
Although standard water-based and discharge products have their applications and individual advantages when it comes to performance, they lack the versatility that plastisol bases offer with regard to printing on difficult substrates like nylon and polyester. Plastisols also offer the versatility to inventory bases for different special effects and applications, and mix only what is needed for a particular production run. The advantage here is inventory and cost control, as well as the ability to mix as needed.
Flashing and Curling
With the introduction of plastisols came the need to print an underbase and flash it for overprinting with semi-opaque colors. Today’s plastisols will flash at lower temperatures and with minimal after-flash tack, allowing for high-speed production on automatic presses. Although there are flash units with forced hot air, it generally takes more time to drive the water content from a water-based ink film than with plastisol ink.
In addition, there’s an increased platen temperature on post-flash screens when using water-based ink. Although today’s water-based inks have anti-drying agents built into them, the residual heat will have a negative impact on their evaporation rate in the screens as opposed to plastisol. They typically are unaffected unless excessive flash temperatures are reached.
When it comes to curing, there are two basic types of dryers that commonly are used in textile screen printing: radiant heat (infrared) and hot forced air. Today, we also have combination dryers with hot forced air and radiant heat panels to “bump” the curing process. Of these options, the hot forced air or combination units have proven to be the most effective for plastisol and water-based applications.
Plastisol offers the versatility of curing with any of the previously mentioned units. This ink type requires sufficient heat to ensure the plasticizers within the ink film are completely and properly absorbed by the PVC resin. This will achieve the proper cure and durability.
Water-based ink, on the other hand, requires hot forced air to properly drive the moisture content out of the ink film and fabric to achieve a proper cure. It’s possible for water-based ink to be properly cured with radiant heat dryers, but the retention time is considerably greater.
The wash-fastness, or durability, of a print can be determined by the difference in the two respective inks’ compositions. Plastisol inks are, in essence, liquid plastic, which is intended to be deposited onto the surface of the fabric in the thinnest manner possible. Water-based inks are intended to penetrate the fabric and convert (dye) its color into the ink color.
When properly cured, plastisols create a permanent layer of plastic, which is resistant to wash and wear. Water-based inks are intended to be permanently set into the fabric, but can fade over time from fibrillation and degrading within the garment’s fibers. Although both ink systems are subject to this kind of deterioration, plastisol will retain a greater degree of color due to its composition.
Another major advantage of plastisol compared to water-based ink lies in its ease of removal in the case of small smears or pinholes. Plastisol ink is removed with a spot-cleaning gun and one of the many available spot-removal fluids on the market. Although there also are spot-cleaning compounds available for water-based printing, removal is much easier with plastisols.
This information is by no means intended to place water-based inks in a dim light, but, rather, to point out the positive aspects that plastisol ink offers in an age where many detractors try to divert printers to water-based or non-PVC printing configurations. Although some have converted partially or completely to non-conventional ink systems, plastisol remains the primary ink of choice among today’s textile screen printers.
Rick Davis is the southeastern regional sales manager for Triangle Ink Co. He is a 35-year veteran of the textile screen-printing and apparel manufacturing industries. His background includes plant design, management and troubleshooting, and he also is a member of the Academy of Screen Printing Technology. For more information or to comment on this article, email Rick at email@example.com.
Hear Rick speak on screen printing topics at the 2015 Imprinted Sportswear Shows(ISS). Individual seminars are just $25 if you pre-register at issshows.com. — J.B.
Article updated Oct. 30, 2023
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