As demands for new and exciting applications grow, so too must the research and development into ink formulations that are up to the task. This article highlights what's going on in UV.
By Mike Plier
But the story was much different in the 1990s. Raw-materials manufacturers at the time, even the largest in the market, said they couldn’t supply certain components or that particular ideas, such as providing inks with enough elongation for the screen print vacuum-forming process, could never come to fruition. But we did it and today’s situation is much different. Let’s take a look at the building blocks of screen and digital inks and then examine the changes that have shaped the specialty formulations that were supposed to be impossible to create.
All screen inks begin with the same set of components: monomers, oligomers, resins, initiators, pigments, and additives. These also happen to be the same components needed for digital. So what’s different?
Monomers This component makes up the majority of the ink system and is the basic building block of UV ink. It is a small molecule that may become chemically bonded to other monomers to form a polymer. Monomers have different levels of functionality that allow them to perform in different ways. Functionality describes the component’s adhesion range. Monofunctional adheres like a joystick—one gripping point. It promotes elongation (Figure 1). Di-, tri-, and multifunctional monomers have multiple gripping points, much like a hook-and-loop fastener. They go on glass and metal—rigid materials. Monomers enhance cure speed, improve adhesion, and adjust viscosity.
Oligomers This is a molecule or chemical compound of a complicated structure consisting of several monomeric units in chemical union. It is the base resin used in UV-ink formulations. Oligomers are the backbone of the screen-ink system. Oligomer selection is based on required adhesion, the need for flexibility or a harder surface, or level of lightfastness. They include urethane, polyester, epoxy, and acrylic. Oligomers tend to be of high viscosity, and need to be refined and their proportions limited in inkjet inks.
Resins These are a category of thermoplastic or thermosetting polymers or co-polymers of acrylic acid, methacrylic acid, esters of these acids, or acrylonitrile used to produce paints, synthetic rubbers, and lightweight plastics. Resins are generally inert components that help with adhesion and surface characteristics. Typically, only small amounts of resins are used in digital inks because of their high molecular weight.
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