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
Initiators Photoinitiators absorb UV energy from a light source, setting in motion a chemical reaction that quickly polymerizes and converts the liquid into a solid. Ultimately, initiators serve as spark plugs that cause crosslinking throughout the ink system. Ink manufacturers use a multitude of initiators, depending on the nanometer range at which they want the ink system to cure.
Additive package An additive is any chemical added to an ink to change the characteristics of the ink, such as cure speed, adhesion, or chemical or water resistance, to name a few. Screen inks contain additive packages that can include thickening powders, flattening powders, or flow controls that promote a smooth flow without surface imperfections. Additives also can provide specialty finishes in screen inks that are not yet available in inkjet inks. The flow-control and wetting agents used in digital inks tend to be in liquid form with a sub-micron particle size.
Pigments These are fine, solid particles used to give color, transparency, or opacity. They may be made of organic or inorganic materials, and they are grouped according to color using a color index and a grayscale rating of 1-8 (8 being the most lightfast or durable). They possess different properties of lightfastness, and they also can have similar properties to oligomers, including chemical resistance, heat and cold resistance, abrasion resistance, and more. Pigments tend to raise the viscosity of inkjet inks. For digital inks, manufacturers are now chemically treating pigments to help them break down before they go through the milling process. The pigment particulates are then milled down to a sub-micron size.
Turning peanut butter into a fine wine
Screen-printing ink can be compared to mayonnaise or even peanut butter in terms of thickness or viscosity. As a point of reference, screen-printing inks can range from 1,500- 19,000 centipoises. Digital inks, for the most part, are around 10-20 centipoises in viscosity. As a benchmark, water measures 0-2 centipoises—a huge difference in itself. Manufacturers have to reduce particle size to smaller than 1 μm to fire inks through inkjet printheads (Figure 2). This involves looking at raw materials that don’t have anything to do with the screen-printing industry but affect the physical characteristics of a fluid or ink system. The process also involves transferring the technology to digital—making a chocolate bar into chocolate milk.
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