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FLEXO Magazine : June 2013
dried ink film, such as might occur on a plate or anilox roll. This is more often a matter of concern for water-based inks, since UV curable inks are designed to stay “soluble” until cured, and solvent inks tend to be okay, as long as the appro- priate solvent blend is maintained at press. Compatibility is often considered an assumed property, but some inks may require special extenders or special bases in order to fulfill the requirements. Often, highly resistant inks must be designed from the start to use special resins, even in the pigment grind, which would not be compatible with other inks. In addition, some inks may need to be catalyzed in order to fulfill the printed specifications, which will cause the ink to build in viscosity over a time. These situations must be commu- nicated between the ink supplier and the printers, especially if the printer has existing dispersions that it would like to use. Also, a particular substrate may be sensitive to certain chemicals, such as with some thermal or carbonless sub- strates, and this can definitely impact how an ink is formu- lated. So, it is always best to evaluate an ink or coating on the actual substrate that is going to be used. This is especially important in flexography, due to the vast amounts of sub- strates used in the industry, from films, to foils, let alone all the various grades of coated and uncoated papers. The dry rate of an ink becomes very important with all the various types of substrates and presses being utilized, that it is becoming ever more popular to set specifications on ink dry rates. This can be as simple as pulling a print by hand and measuring the time it takes for the ink to dry to the touch, or it could be as sophisticated as using an automated device tracking a fine needle across a print with timing and data collection done by a computer. ENVIRONMENTAL IMPACT Regulatory concerns definitely impact the make-up of inks, and there is continual demand to reduce the environ- mental impacts of the inks. This includes pressures to further reduce VOC levels, drives to eliminate potentially hazardous intermediates such as bisphenol A, heightened demands for increased usage of biorenewable resources, and so forth. As businesses in North America adjust to the changing global environment, aspects of the European Union’s Regis- tration, Evaluation, Authorization and restriction of Chemical substances (REACH) legislation and the Globally Harmonized System (GHS) of classification and labeling of chemicals may require adjustments and refinements in ink formulations. This push for increased environmental and personal safety concerns does not have to be exclusively governmental. Many consumer product companies have taken it upon themselves to control the environmental impact of the packages, and have established their own specifications, which in many cas- es are far more cautious than the perspective governmental agencies have undertaken. This is done as a way to protect the company ’s brand image, as well as its financial status. Extraction tests may be expensive, but they would be far less costly than a total product recall or defending against a law- suit, both of which occurred in the past few years when various photoinitators were found to migrate into foods. To overcome this potential, some consumer product companies have initiat- ed programs of their own which require extensive testing, and some organizations have pooled their resources to conduct industry-wide testing on specific resins and photoinitiators. Radtech, for one example, coordinated testing to get Food Contact Notification status for key UV curable materials under FCN 772. REQUIREMENTS Once a job is printed, be it a package, a label, or a display item; it must meet certain requirements relating to its use, either in the supply chain or in the end use. So, from a perfor- mance specification standpoint, a simple differentiation might be to classify performance specifications amongst visual, physical, and chemical categories. The first category, visual, is easy. A big part of this deals with the aspect of color. The color has to be correct. This topic is discussed quite often, but any ink supplier will tell you that in order to provide good color matches, they must have ac- cess to the appropriate information from the printer, such as anilox volume, substrate, press configuration, etc. It cannot be understated that communication is vital. Having proper specifications before an ink is matched will definitely help the ink supplier to deliver the appropriate ink. That being said, the customer must understand the specifications, as well. Merely stating the CIELab specifications or a color difference specification without reference to the instrumentation and methodology is a prescription for disaster. The color measurement industry is working hard to reduce differences in color measurement amongst various instru- ments with the establishment of ISO 13655-2009 spectral measurement conditions M1 and M2, as well as establishing profiling techniques across the web allowing instruments to 98 FLEXO June 2013 www.flexography.org Ink Specifications Usage Performance Bulk Regulatory Visual Physical Chemical Color, metamerism, opacity, gloss, lay, trap, fade, yellowing, hazing, burn-out Abrasion, rub, slide angle, COF, adhesion, heat resistance, curl, blocking, crinkle Viscosity, pH, solids, foam, resolubility, stability, dry rate, cure rate, surface tension OSHA, CONEG, FDA, odor, REACH, CONEG, CEPA, EPA, Prop 65, SARA, TSCA, ROHS, and more Water resistance, chemical resistance, bleed Price, mileage, transfer Economic