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Introduction To Ink
Introduction To Ink; Water Based & Plastisol Screen Printing Inks
For screen printing shirts at home, we can say there are two common types of inks used. There are air dry textile inks and plastisol textile inks. For printing posters and paper type flat work, you would use poster ink which is also an air dry ink. Either of the two textile inks may be used for screen printing shirts but the poster ink is used only for flat work and graphics printed on porous or glossy paper materials. The screen printing process for printing shirts and flat work will be very similar. It is the same process in general but there will be differences in materials used, beginning with the ink.
The air dry inks are made for many different applications and in general will be the most popular for hobby and home applications. These include inks like Speedball, Jantexinks and Permaset. These are manufacturers of poster and textile inks often referred to as water based inks. Some of these may be 100% water based. However, many inks considered to be water based are often a combination of solvents including but not limited to water. Many air dry inks may actually need to be heat set or don't really air dry per say, but cure in a way. To make things easier, from here on we will refer to the aforementioned air dry inks as water based.
As stated earlier, certain water based inks may also contain other solvents and/or do not "dry" by evaporation alone. Ultimately all air dry inks, even solvent based inks, fall into two categories; non oxidizers and oxidizers. Non oxidizers dry only by the evaporation of the solvents. There isn't any chemical process involved. The solvents act as a carrier only. Oxidizing ink, often found in industrial printing, may contain common solvents that evaporate but they also contain chemicals which dry by the process of oxidation much like rusting. Now they don't really rust but they dry by reacting with oxygen to harden the ink. Non oxidizing inks are most popular today as they are easier to work with. Textile and poster inks will be non oxidizing but textile inks may require heat setting for permanency. This can be done with an iron or a heat press.
Plastisol inks are limited to textiles. Manufactures of these inks include Wilflex, Union, and QVC. Most plastisol inks may be used at home when screen printing tee shirts. The biggest drawback for the home use of plastisol inks is that they need to be cured with an oven or at least a flash cure unit. Plastisol inks will never dry even when exposed to air until they are cured with heat. Plastisol ink has to reach a temperature of 320 to 330 degrees Fahrenheit so that it will cure and be dry to the touch. However, this ink is often considered to be easier to work with just because it won't dry in the screen during printing. Plastisol ink is also known to have excellent color, coverage, and durability.
There are different ways of curing plastisol inks. This is traditionally the problem for most home based screen printers. The machine of choice to have is a belt dryer. The shirt is simply pulled off the pallet and placed on a moving belt which carries it into the oven chamber where the ink reaches proper curing temperature. This is the easiest, most consistent method to cure large quantities of screen printed shirts. But it costs money and it requires space. Many home printers choose to use a flash cure unit to cure their plastisol printed shirts. This can be done on press or after the shirt has been pulled off of the pallet. Yet other residential printers use space heaters, heat guns, blow dryers and more to cure plastisol inks. Many of these "garage boy" techniques may work at home but they are not well suited for high volume commercial work.
Most water based inks will be thinner in comparison to plastisol inks and may require the use of a different mesh count for optimum results depending on your application. Many people recommend using an open mesh for water based inks to prevent drying in the screen but others prefer to use high mesh counts due to the ease of which you can print water based inks with them. Using an open mesh with a thinner ink will make flooding of the design a problem. Ink drying in the screen can often be solved by using a retarder or by back flooding the screen with ink in between prints.
Choosing which ink to use at home will ultimately depend on your application, economic limitations, space restrictions and/or your end goals. Many people choose to use water based ink for printing shirts because they have an eco friendly reputation. But there are plastisol inks that are manufactured today which are much more environmentally safe than you would think and comply with many government regulations regarding children.