Does screen printing crack?

Are those little cracks you sometimes see when screenprinting with water-based inks normal? Yes. But there is a way to stop it from happening.

We received this message from a customer: I screen print on cotton T-shirts using water-based inks. When the ink dries, the print tends to crack or split. What’s causing this? And how can I stop it from happening?

Furthermore, the customer continued, if I look at the T-shirt against the sun, I can see lots of tiny holes on the areas where I applied the ink. Is it possible to cover these, or is there just no way of getting rid of them?

First of all, about the “tiny holes”, this depends on the weight of the fabric, i.e. whether the fabric’s thread count is high or low. So, depending on the cotton you’re printing on, it is sometimes possible for these tiny holes to appear. Indeed, what the ink does is it dyes the fibres, so if the density of the fibres is relatively low, the weave will be fairly easy to distinguish.

As for the cracks, all water-based acrylic inks, if used with low thread count screens, tend to develop cracks after drying.
This means that the layer of ink, due to its thickness, doesn’t expand along with the fabric as it expands, and so it splits.

It splits, but it doesn’t come away: indeed, water-based inks are actually very resistant to washing, even more so when heated with an iron (or even better with a heat press).
Furthermore, don’t wash the garment within the first 72 hours, as this is the time needed for the ink to harden completely.

To resolve the problem of cracking, one solution is to use water-based inks that have more elasticity. Modatex inks, for example, are available in a number of elastic versions in a variety of colours: Transparent Base, Elastic White, Elastic Black, Colours for four-colour process printing.

If printing on light-coloured materials, we recommend mixing some transparent base with the normal colours to achieve the required elasticity.

If printing on dark materials, it’s a good idea to print a background using the elastic white and then print on this with the normal colours. It’s common for the elastic colours to be less opaque than the normal colours.

Alternatively, there’s also a professional water-based ink that you can use, Aquatech, it has a matt finish, is soft hand, smooth to the touch, and is partially elastic. 

I got a request last week to help someone figure out why their ink cracked. They thought it was the shirts. I have never seen a shirt that would cause the ink to crack all by itself. There is always an ink solution for cracking.

WHAT CAUSES INK TO CRACK?

Primarily the cause of the ink cracking is from the ink not curing. Ink that is not cured will crack when you pull at the shirt (after it has cooled down) or will crack when washed.

Reasons it might not be cured:

• Dryer temperature too low.
• Dryer belt speed too fast.
• Dryer chamber is too short.
• Dryer electric heating elements are too high off the belt (heat not really getting to the ink.)
• Dryer electric heating elements too low (might cause scorching if the shirt is too long under    the heat, and can also cause overcuring and more inconsistent curing when heating element kicks off and on.)
• Poor air flow in the Dryer.
• Moisture in the shirt: What happens is that the moisture in the shirt evaporates and in the process it will cool the shirt. This is one of the most common reasons that ink does not cure. It is a difficult thing to realize because you cannot see or feel the moisture in the garment, and no shop I have ever seen has instruments which can measure this. It is very common with shirts that come through rainy weather in trucks, sit in damp warehouses, or are garment dyed (which can leave moisture in the shirt.) Thicker shirts and particularly canvas is more likely to have absorbed moisture. Moisture problems are also made worse by dryers with poor air flow.
• Shirts that enter the dryer at a low temperature. You might have been printing shirts on Friday that are at a room temperature of 80 degrees in your shop at the end of the day and they might be curing well at with your dryer settings. Then,  after a damp cold weekend in Maine on Monday morning the shirts might have absorbed moisture and they might be 39 degrees. So then they are both having moisture and are entering the dryer at 40 degrees or lower of a temperature than the previous Friday. The ink then has to go from 40 degrees to 320 in the dryer instead of 100 to 320 in the dryer.
• Too much modification of the ink. Too much non-curable reducer, extra pigments, etc can change the cure temperature or even make the ink so it won’t ever cure all the way.
• Shirt color or type of fabric: not usually a problem, but shirts that reflect or absorb heat particularly in short electric dryers can affect the cure of the ink.
• Ink color: particularly metallics or reflective inks can also deflect heat and make curing take longer, again particularly with electric dryers.
• Ink film which is too thick. The ink has to cure all the way through, not just on the top. (and…By the way, three thin coats of ink generally can be made thinner in the end than one or two coats can be printed.)

Secondarily (and rarely) inks can crack if the shirts are too stretchy or have a low stitch density.

Some inks are more elastic than others and can deal with the stretch: try a diffent ink after consulting with your ink supplier. You can add things to increase stretch, for example Rutland makes “spandisol” which can be added to standard plastisol to make it stretch more.

Other solutions:

You can always use silicone inks which are extremely stretchy.

You can sometimes use certain water-based inks which will coat the shirt fibers rather than sit in a film on the surface of the shirt.

Ink Can Crack if Overcured

• Not nearly as common as undercuring, plastisol can be overheated and overcured. This will make the ink film brittle and it will crack when you pull on the shirt or when washed.