Silk screen printing has been around for centuries. It dates back to Ancient China at the time of the Song Dynasty. The practice spread to Japan and neighbouring countries over the years, and by the 18th century, screen printing had gained public acceptance in Europe after silk mesh was brought in from the East.
Centuries later, silk screen printing continued to gain momentum and is now used in a variety of applications from car decals, balloons and even CDs. Perhaps the largest screen printing market is clothing, where silk screen is considered a primary method for producing unique designs for T-shirts, yardage, apparel, promotional merchandise and homewares.
Nowadays, there are two main chemistries of textile ink commonly used by professional printers, each with a set of advantages and disadvantages. How do you know which one is best for your needs? We’ll break down the pros and cons for you.
Plastisol inks are based on pigment with particles of PVC (plastic) dispersed in a plasticiser medium, and often contain no volatile components. All Plastisols are thermoplastic, which means that they must be heated to cure. Typically, curing a plastisol print occurs relatively quickly (20-60 seconds) at temperatures over 160 °C (320 °F), resulting in the formation of a continuous film that sits on the fabric. Plastisol inks remain a common choice for many professionals, as they allow for versatility in application and durability of finish.
The Pros of Plastisols
Plastisol inks can be applied equally to dark and light coloured fabrics with little to no effect on the colour of the print. This property means that Plastisols can be applied over other inks without bleeding or affecting opacity. However, the major benefit of Plastisols is that they do not dry out in the screen. This means they can be left out or on screens for long periods without clogging the mesh or affecting their ability to print. Other benefits of Plastisols include their durability and their forgivingness with most of the emulsions and/or adhesives used to fix screen stencils.
The Cons of Plastisols
Plastisol prints typically have a harder hand feel and zero breathability, both of which are considered undesirable. Also, because these prints leach plasticisers with every wash, older Plastisol prints are more likely to chip or crack. Further, printing over high nap fabrics or onto areas such as seams or creases on textiles can create problems because Plastisol films have a tendency to clump, crack, or rub. Due to their thermoplastic nature, Plastisols can also be affected by sources of high temperature such as irons and tumble dryers, which can cause films to become soft and smear. Plastisol prints can also stick together in the wash, even at relatively low water temperatures.
As well as a poor wearing experience, the biggest negative with Plastisols involves the chemicals used in the manufacture of Plastisols, during their curing process and with cleaning. Chemically, most Plastisols contain PVC resin and phthalate plasticisers, the latter having been widely recognised as harmful to health and to the environment. There is increasing pressure from governments and environmental agencies in many countries to restrict their usage.
During curing, Plastisols also give off Vinyl Chloride Monomer (VCM) fumes. These have also been widely recognised as having harmful health effects. In the short term, VCM is an irritant to mucous membranes (think eyes, nose, throat, lungs) and in the long term, widely reported as carcinogenic.
Solvents are typically used to clean up Plastisols and these too are considered hazardous. Both Plastisols and their cleaning solvents require specialised disposal, but many print shops do not observe proper practice, with ink wastes going into the trash and solvents being poured down the drain.
Once in the hands of the end user, with each wash, plasticiser is washed into the water waste stream where they have been implicated as endocrine disruptors causing environmental harm to the life cycles of fish, mammals and bird life. Plasticisers can also migrate from the garment to the skin of the user and in some cases, cause mild or severe skin irritation.
Water-based inks are dispersions of pigment or dye in a water-based medium with acrylic polymers as a typical resin. They generally cure first through the evaporation of water and/or other volatile components and then with heat to cross link. Water-based inks are recognised in textile printing for their soft hand leading to better wearing experience, environmental benefits and ease of clean up.
The Pros of Water-Based Inks
The superior penetration of water-based inks means that a print can be applied evenly over all areas on a variety of fabrics, including some notoriously difficult to print with Plastisols, such as towelling. This can also give water-based prints a more washed out look which is ideal for vintage or faded designs. After evaporation of the water, water-based ink films are thinner than plastisol ink films from the same screens, making them more flexible. Other properties, combined with their coverage and ease of use, also make water-based inks most desirable for roll-to-roll yardage printing.
Water-based inks have a softer hand and much better breathability, providing greater comfort in wearable textiles. Given a typically lower viscosity, water-based inks are easier to print with, particularly for manual printers, so less strain on wrists, shoulders and back. Even on autos, the lower pressure required means that all equipment (mesh, squeegee, clamps etc) last longer. Perhaps best of all, reduced pressure leads to less fabric bruising, to which plastisol prints are particularly prone.
In clean up, water-based inks are also more eco-friendly, being readily cleaned up with water. Some water-based inks, such as the PERMASET PERMATONE Ink range, have been granted formal Organic Approval, having successfully met the requirements of the Global Organic Textiles Standards (GOTS) for non-organic chemical inputs for use in organic textile processing.
The Cons of Water-based Inks
Water-based inks are viewed in plastisol circles as being harder to use. They are more likely to dry in the screen and typically take longer to cure than Plastisols. This extra curing requirement means more floor space for drying tunnels etc.
Whilst Plastisols are provided as a “one size fits all” product, water-based inks have evolved into two distinct branches; transparent and opaque (aka HSAs). For transparent inks, the colour of the fabric influences the colour of the print and on darker fabrics, prints with transparent inks will not appear as intended. However, this can be easily overcome by choosing an opaque/HSA water-based ink.
A misconception is that water-based colours do not appear as bold or vivid and do not have as high an opacity. With advances in technology, this is not the case. Transparent inks, properly printed, can be even more vibrant than comparable Plastisols.
For printing on dark garments, the PERMASET SUPERCOVER range is a ground breaking, high solids, high opacity water-based ink range that offers strong colour on dark backgrounds.
Another issue of water-based inks is that they require more care in screen prep. Water-based inks will dissolve most emulsions typically used for Plastisol screen stencils, as these are typically not water resistant. This is simply resolved by choosing a water resistant or dual cure emulsion, of which there are many. These include Fujifilm Dirasol® 916, KIWO POLYCOL® MULTI-TEX / VERSA-TEX™, ULANO® 925WR or Chromaline® CP-Tex. Ask your dealer for an appropriate product.
We believe that the positives of water-based inks far outweigh the negatives. In choosing water-based inks, you not only produce comfortable to wear and detailed prints, you avoid the harmful effects associated with Plastisol inks and help take steps to lighten the load on the planet.
Colormaker Industries offers a range of water-based textile printing inks in the PERMASET AQUA, PERMASET SUPERCOVER and PERMATONE.
Visit our PERMASET FAQs for answers, complete our contact form or email us at [email protected] if you have any technical questions.