WHAT IS PLASTISOL INK FOR SCREEN PRINTING?

A basic guide to understanding the 3 unique characteristics of Plastisol and how they affect performance.

Before we get started with what plastisol is. Let’s begin with a quick overview of what plastisol does. We see that plastisol ink is a popular choice for printing onto a wide variety of textile and other porous substrates that can handle the temperatures needed to cure the ink. Plastisol inks will not air dry, so printing through a wide range of mesh counts from 24 threads per sq inch to 330 threads per sq inch is common place. Most colors have good opacity, so printing onto a wide variety of color substrates has been simplified. Once the inks are fully cured the colors can be very bright and the prints are extremely durable. This combination of features makes plastisol a popular choice for many types of apparel decorating from Athletic & Sportwear printing to High end fashion prints combining high resolution images and specialty effects inks and just about everything in between.

But that still leave us asking, “What is Plastisol ink?” Let’s begin with the basics in layman terms. Plastisol ink is basically nothing more than a liquid vinyl, made up primarily of 3 main ingredients, First is Resin, in its raw material form, it looks sort of like a coarse ground flour, this is the binder or body of our ink. Next is Plasticizer, it looks like corn syrup and this is what gives our ink the liquid nature, lastly is Pigment, in its raw material form it looks like colored powder, this as you may have guessed give our ink its color.

These 3 ingredients comprise, the majority of what makes up plastisol ink, but they also have a varying combination of other ingredients in smaller quantities. Including Optical Brighteners, Rheology modifiers, De-tackifiers, anti-bleed agents, adhesion promoters, plus fillers and occasionally other varied ingredients, for increased elongation, lower fusion, etc based on type of plastisol, and the specialty applications it was designed for.

Plastisol ink fuses as the resin in the ink is heated, the resin acts like a sponge and absorbs the liquid Plasticizer. With continued increasing temperatures the resin continues to grow, encapsulating or trapping the color pigment inside. Eventually the resin has grown until the resins themselves bond together forming a flexible and durable ink film.

If our “entire” ink film does not reach full cure temperature, all of the plasticizer will NOT be absorbed, and the resin will not have been able to bond together fully. Instead the resin and pigment will be laying in a jello like film that feels dry to the touch but has no tensile strength and will have minimal adhesion and abrasion resistance, which will then fail wash test as the ink fades & cracks.

Over curing plastisol being a primary concern for print failure, is a misnomer that has popped up a few times, over the past 30 years. Your temperature range for plastisol inks is dictated by the type of fabric as the garment will scorch and burn long before the ink film will blister or distort to the point that it causes print defects or fails wash test.

What we generally see with Over curing is an increased likely hood of poly fabrics to bleed but it won’t affect the ink cure or the strength of the ink film to provide a durable, long lasting print life. Now some specialty inks like puff inks can deflate if over cured.

Now plastisol ink has 3 unusual physical prosperities, the first is, plastisol ink is thixotropic, which means as the ink is agitated, stirred or as it is being shuttled forward and back across the screen image by the squeegee, the ink viscosity lowers, making it creamier and easier to print. (Be wary though, if you use electric drill to stir the ink, that you don’t stir too long or too fast, as speed creates friction and friction creates heat. Which can cause your ink to thicken, especially in the bottom of your ink container.)

Thixotropic, also referred to as a false body is critical to us achieving crisp high resolution prints, as the ink is agitated by the squeegee the viscosity drops, allowing it to more easily pass through the mesh with minimal distortions and then once it is on the shirt to slowly regain its thicker viscosity to maintain the detail without puddling out, or soaking into the shirt, resulting in dot gain or general loss of detail.

Second unique characteristic is regarding how the ink cures from thermal energy / heat. Plastisol ink can transition from a liquid ink, then at 180-220F to GEL, which means it is semi cured and turns into a viscous semi solid Plastisol ink, that is dry to the touch. Then as our temperatures continue to rise, the ink in layman terms, “re-wets” and once the ink is heated to it’s required fuse temp. The ink will fuse and turn into a permanent durable ink film or layer of colored vinyl that has bonded with our substrate / shirt.

Why does plastisol have both a GEL & FUSE temperatures? This is a critical function for screen printing as it allows us to flash an under base, causing the ink to GEL and be dry to the touch and then we can stack colors on top of each other. Then when the ink is inside the dryer the ink films can melt together before curing into ONE durable layer ink.

If plastisol ink didn’t have this characteristic, we would have 2 or more multiple layers of ink with poor to no inter-coat adhesion (inter-coat adhesion is the mechanical adhesion of ink to a substrate or to another layer of ink or coating) and the ink layers would separate or peel off from each during washing.

We occasionally see this phenomenon, when the under base is over flashed and instead of a GEL, we accidentally reach our FUSE Temp and the ink is fully cured / fused. Then our top color ink, peels, fades, or washes off as both layers of ink were fully cured but sadly the under base was fully cured before the other layers were printed. Our under base was unable to melt together forming one solid layer of ink.

Last unique characteristic, plastisol inks are 100% solids ink, as the ink GEL’s & FUSE’s to a full cure, we lose none of the ink. If we print water based or solvent based as the ink film dries, they shrink, as water or solvents are dispersed into the air. With plastisol ink, if we print 5 grams of ink onto a garment, once the ink is fully cured, we still have 5 grams. This allows us to achieve higher opacity easier and more consistently. It also contributes to a safe work environment as nothing is being dispelled into the air of our shop. Plastisol inks are nonhazardous, nonflammable, VOC Free, and most plastisol’s today are Non-phthalate to meet various government regulations.

The Achilles heel of 100% solid ink with high opacity, is the inks tend to be heavier and require more finesse to achieve a smooth, texture free print. An easy work around is to print through lower mesh counts, as the ink will clear the mesh more easily, but this increases the odds of us having a heavy hand or texturing. We can also add 5% of curable reducer, but if we are not careful, this can lower our viscosity too much and the ink soaks into the shirt and we run the risk of losing opacity and detail.

Goods news with proper mesh selection and reasonable tension, we can control our ink deposit by controlling our print variables, Speed, Angle and Pressure, using a standard 70 durometer squeegee.

Stay tuned for future posts on how to control these variables in screen printing with plastisol to make achieving beautiful prints, not only easier but ultimately more profitable!

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