The most widely used processes in apparel screen printing is probably solvent-based plastisol. Plastisol printing inks are typically based on the PVC polymer. So just what is PVC? PVC is the acronym for polyvinyl chloride, a tough, durable, low cost plastic that is the second most popular plastic (by volume) next to polyethylene. PVC has tens of thousands of consumer and commercial uses. It is found in vinyl siding, water based emulsion paints, pipe, wire coatings, and floor tile. Plastisized (softened) versions are used for vinyl fabrics, medical products, plastic wrapping and flexible coatings. Packaging applications include meat wrap, "blister packs" and bottles for edible oils and some non-food products. And many plastisol printing inks.
Pure PVC, with no additives or contaminants, is non-toxic. But you rarely see pure PVC in consumer products. Most of the time, PVC plastic is mixed with various auxiliary chemicals and plasticizers and then the health and safety story is not so rosy.
Unlike most commodity plastics that have only carbon and hydrogen atoms as their main component elements, PVC differs by the addition of chlorine, which increases its compatibility with a wide range of materials and suitability for shaping by a variety of techniques. But the addition of the chlorine also leads to one of the major environmental problems associated with PVC – the formation during its manufacture and disposal of Dioxins. PVC manufacture, use and disposal have been identified as the single biggest source of dioxin in the environment. During the PVC environmental life cycle, dioxins are formed during the production of the raw material and if a vinyl product ends up in an incinerator. Dioxins refer collectively to a family of 210 different chemicals including dioxins and furans. As a class, dioxins are among the most toxic chemicals known. Many dioxins are carcinogens and highly potent hormone disrupters. They are harmful to animals and fish, do not easily break down in the environment and, therefore, tend to accumulate. Since they are fat soluble they also tend to bioaccumulation in the food chain. Except for a few laboratory applications, dioxins are never made on purpose, but formed as unwanted wastes and by-products of many reactions involving chlorine, carbon containing molecules and heat.
To make matters worse, one of the basic building blocks for PVC is phosgene gas. Which is notoriously known as a nerve gas used during World War I and was the chemical accidentally released in Bhopal, India in the early 1980’s which resulted in the death’s of nearly 3,000 people and 100.000 injured in the world's worst industrial disaster.
Phosgene is used to product the vinyl chloride monomer that is polymerized in polyvinylchloride. In essence, it is what makes up the ?links? in the ?chain? of PVC. Studies show that vinyl chloride can damage the liver, nerves, and immune system – and that has been found to be a human carcinogen.
Most plastisol inks are solvent based. This means that they use one or more of the following chemicals to keep the color part of the ink suspended during the printing operations:
Yes, this is a big list. And most of these solvents are considered hazardous air pollutants. Some can help the formation of smog. Most are either acutely or chronically toxic to humans. Several are known or suspected carcinogens, teratogens and mutanogens.
Many printing processes use heat to drive off these solvents. This processes dries or ?sets? the ink. This can lead to health and air quality problems if the solvent emitted are not properly taken care of or treated.
PVC is a hard, ridged material. Think of PVC sprinkler pipes. In many instances a chemical must be added to make the PVC soft and pliable. As mentioned previously, common chemicals used to soften PVC are phthalates, fatty acids, and alcohols. Of special concern are certain which are known hormone disrupters. These chemicals mimic or interfere with our own delicate hormone system. As a class, phthalates are one of the most prevalent of the hormone disrupting chemicals found in the environment. Hormone disrupting chemicals can lead to a variety of health problems including developmental problems, reproductive problems, increased susceptibility to a verity of cancers, as well as broad implications in lower sperm count in men and fertility difficulties in women.
Many pigments that are used as colorants in printing inks are based on the chemistry of heavy metals. Typical heavy metals include:
Like solvents, this is big list and each of these metals has environmental health and safety issues in their lifecycle. Many of these are actually or chronically toxic to humans, can be toxic to wildlife if released to the environment in wastewater and some known human carcinogens.
The good news is that many companies are facing the challenge of replacing PVC, solvents, phthalates and heavy metal containing pigments and inks in their products because of both possible legal restrictions as well as environmental considerations.
Some manufactures are lowering the total volume or solvents in their ink formulations to nearly zero. The good news is that the solvents, and their negative affects, are reduced or eliminated. One possible drawback is that it takes more water to clean processes equipment and screens than solvent based inks. And that the increased water use and the wastes are now going down the drain – to be either treated – or worse, released untreated into the environment.
Here again, companies have found replacements for dangerous phthalates by using other phthalates or entirely different, less toxic chemistries. These are preferred.
Some manufacturers are producing harmful heavy metal free – or reduced metal content inks. These too are preferred.
Attention and concern regarding PVC content has motivated some ink manufacturers to find a replacement for PVC for traditional ?plastisol? printing applications. These inks are being developed primarily around acrylic chemistry. In most cases, this is preferred to anything containing PVC polymers.