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FLEXO Magazine : November 2009
www.flexography.org NOVEMBER 2009 FLEXO 35 High pigmented inks printed at varying volumes on uncoated. FIGURE 1A. High pig- mented ink printed us- ing 360lpi/4bcm anilox on semi-gloss. FIGURE 1B. High pig- mented ink printed us- ing 360lpi/4bcm anilox on uncoated. FIGURE 1C. High pig- mented ink printed us- ing 360lpi/4bcm anilox on high gloss. of the aniloxes were typically very low; 200 to 400 line-screen levels were the norm. Very little process printing was done and what was done was far from photographic quality. Inks were made from pigments that were built to be lightfast and very opaque. Leaded pigments, such as moly orange, chrome yellow and lemon yellow, were widely used in pack- aging. Dyes were used in the label and envelope processes. Reds made from heavy metal pigments, including barium, were used everywhere. But all of these inks, as the formula- tor pushed to increase strength, became "short"---a term described to me by an old formulator that meant that the ink would not flow. A short ink had the consistency of mayon- naise, and pressmen were really challenged to keep these inks moving in their pumps and pans. Solvent inks cured well. The product off the end of the press was able to be tested for quality. The resins used had a wide range of adhesion to various substrates. Inks were printed with volumes of 3 to 6bcm, which would cover most substrates, even problematic uncoated substrates. However, those pesky marketing managers wanted more. In addition, the EPA had an issue or two with leaded, dye-based, and bari- um pigments, not to mention their issues with the chlorinated rubber resins and the solvents used to control their viscosities. Water-based inks, in the beginning, were used for basic printing on corrugated. They were limited in the selection of pigments, which were the same ones used with solvent inks. They were also limited by slow-drying polymers and low-air- flow dryers on the press. However, pressmen and formulators (and their wives) liked going home with clean hands. And the EPA liked the lower VOC emissions. Fast forwarding a bit as anilox technology was improved higher-line aniloxes with lower volumes were utilized to improve print for use on higher-line plates with water-based process inks. This was a challenge to increase the amount of pigments in the process inks while keeping the viscosity stable. The printers jumped immediately to the next logical step, which was integrating process and line work plates into one. By doing this, they could maximize the stations on their presses. The pigment challenge was further exasper- ated by the need to incorporate slow solvents and amines to print the process colors, which tend to cause the pigment to swell. Other issues for the pigments were the use of doctor blades. Their use increased consistently significantly, but also increased the shear forces significantly. This made it para- mount that the resins used in the formulations bonded well. UV inks progressed in much of the same way as water did to solvent. Initially, the same pigments were tried and when that failed, other pigments were developed specifically for UV. Due to the curing process, a lot of the nonsense in drying was averted. However, achieving a better flow and a more fluid rheology is always a focus and factor in the selection and development of UV inks. DOLLARS AND SENSE The final factor in this puzzle is the price. Due to the need to provide pigments that can withstand the exposure to sunlight and oxidation for longer periods of time, more expensive pigments are required, and work continues on solutions to bring better fluidity to the printer with these products. It seems that non-fade resistant (NFR) inks, unable to withstand more FIGURE 2A. High pigmented ink printed using 600lpi/3.7bcm anilox on semi-gloss. FIGURE2B. High pigmented ink printed using 600lpi/3.7bcm anilox on uncoated. FIGURE 2C. High pigmented ink printed using 600lpi/3.7bcm anilox on high gloss. TECHNOLOGIES & TECHNIQUES
Sustainable Fall 2009