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![]() Getting into Ink
Fortunately, there is a lot of information available. Every ink manufacturer provides some sort of brochure about their products, and discussions about ink turn up in almost every screenprinting trade journal and forum. Within this free library you'll find information that can not only help you improve your present screenprinting operation, but can provide you with ideas about additional screenprinting opportunities you might want to consider.
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You will, however, be encountering a few unfamiliar ink-related terms. Information sources are often aimed at experienced audiences so they sometimes overlook the need to supply basic definitions. That's what we're going to do here.
Adhesion and Cohesion: Factors that make ink work
I. WHAT INK IS MADE OF:
Vehicle The binder is a solid, or heavy liquid that provides body to the ink. Its most important job is getting the pigment to adhere to the substrate. Binders are film-forming resins like ethyl cellulose and nitro cellulose, which are used in most screenprinting inks. Some product literature will call them film-formers rather than binders. The vehicle undergoes changes as the ink dries. Solvents evaporate, leaving only resins and pigment on the surface of the substrate.
Rheology Viscosity is how a liquid flows. Liquids with low viscosity flow quite easily; liquids with high viscosity are thick and tend to stay put. Viscosity can change. Inks, for example, react to a number of factors from outside temperature to the force of the squeegee. Probably no other single characteristic influences how ink prints as much as its viscosity. If you work with different types of screenprinting inks, you will soon discover that the viscosities of screenprinting inks can vary widely.
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The long and short of it
Thixotropy
Shear
II. Additives But caution should be the rule when you begin to modify your ink. The additives that can be used with a particular type of ink and the proportions that can be safely added will be detailed in the product information supplied by the manufacturer. The proportions for additives are often given as a range rather than a single figure and usually in the form of a percentage of the total mix by weight. The purchase of an accurate electronic scale is very useful for obtaining consistent results in mixing in additives, and is essential when you get into mixing colors. Color formulas -- for matching Pantone colors, for example -- are given by weight. Once an ink has been modified, any leftovers must be carefully labeled with the additives used and the percentages. You now have separate versions of that ink and you don't want to mix them up. Mistakes are easy to make and unfortunately are common.
Thinners A thinner's job is simply to lower an ink's viscosity. But you have to be careful. By altering an ink's viscosity you can change almost everything about it: how it flows through the mesh, how it dries, and how well it adheres to the substrate. The addition of significant amounts of thinner can make an ink more transparent or make it dull. Add too much and the ink begins to break down. Thinners often include several different solvents, and manufacturers have developed specialized thinners to match every kind of ink they produce. When purchasing thinner, it is important to get the right one. To be on the safe side use only the specified thinner and never add more than the recommended proportions. Thinners from other manufacturers may not be compatible, and using inexpensive thinners from a paint store is definitely not a good idea.
Fast thinners and slow thinners One solution is to by mix up a thinned-down version of your ink before you start printing, and add that when you have to replenish your supply. The thinned ink will blend in with the ink already in your screen and the extra thinner will help replace the thinner it has lost to evaporation. When temperatures rise especially high, an even better solution is to replace your normal thinner with one specifically designed to evaporate more slowly. These are called slow thinners or retarders. Some printers automatically add retarders to their ink anytime they will be printing fine details or when they expect to be printing at a slower speed.
Transparent bases
Thickening agents Now that you're equipped with some of these basic definitions, you're ready to tackle some of those technical ink-related articles. Remember that there are many types of ink out there, but the ones you need to focus on are the lacquers, enamels, or epoxies. Those are the ones most often used in sign printing.
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