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FLEXO Magazine : June 2013
to meet. I would urge everyone to make sure to have a copy. Additionally, there are numerous reference texts that discuss such things as fluid dynamics of ink transfer, organic chem- istry of pigments and dyes, and optical properties of polymer films. This level of depth is of little value to the printer or print buyer trying to produce a printed product for sale within a short period of time. Outside of the ink producers’ world, what the customers want to know is if the ink will satisfy the needs of the applica- tion. In other words, one must think of where the label, pack- age, corrugated box, or design might live once it has been printed. Before the ink can be judged against the set expecta- tions, the printer must be able to print it. So, the first differen- tiation in ink specifications is between the usage properties (or core physical virgin ink properties) of the ink, versus the performance properties (or core printed ink properties) of the ink on the substrate. INK’S PROPERTIES Usage properties are those that are needed by the printer, in order to transfer the ink appropriately to the substrate. Such properties may be different for various presses, sub- strates, plates, anilox volumes, etc. Performance properties are those requirements needed for the dried or cured ink to meet the desired end-use application. Both usage properties and performance properties are important to keep in mind, because even if the dried ink can meet the end-use require- ments, if it cannot be printed, there is still a problem. Usage properties of the ink can include those discussed in the text of FIRST 4.0 , such as viscosity, pH, dry rate, and the cure rate for UV inks. Some others that are not specifically mentioned are resolubility, compatibility, pricing, as well as regulatory considerations. In fact, the regulatory environment can be a considerable factor in determining the suitability of ink for a particular printer. For instance, there are many locations that have strict limits on the amount of copper that can be present in a plant’s efflu- ent. So, these printers must either commit significant amounts of capital in abatement facilities, or must limit themselves to low copper inks. Since the most common, and often the most economical, blue colorant used in flexographic inks is copper phthalocyanine blue, this can significantly impact the ink for- mulation, properties, and cost. Other regulatory concerns can also affect which inks a particular printer could use. Thus, a logical differentiation in the usage property specifications might be between bulk property considerations, economic considerations, and regulatory considerations. Bulk properties would be those that the ink physically would need to have in order for the printer to be able to use it with its equipment and substrate. Regulatory properties would include those that the ink would need to fulfill in order for the printer to legally use it for the intended application. Economic considerations would obviously involve as- pects such as pricing, mileage, inventory, and transfer concerns. Since not all presses print alike, the bulk physical property considerations may be very specific. Presses with high air flow through the press, such as some vacuum trans- fer presses, may have more demands on the ink from a resolubility standpoint. There are several ways in which this can be tested. Several spot tests for resolubility have been proposed, along with Geiger press rewet methodologies. Basi- cally, one is looking for how long the ink will resolubilize a partially www.flexography.org June 2013 FLEXO 97 Dr. Franklin J. Maisel is shown in front of the replica Gutenberg’s printing press that he built and exhibited in the Vatican in 2012 alongside His eminence, Cardinal Raffaele Farina, librarian of the Vatican Library. Dr. Maisel serves as the associate curator of amncient manuscripts, writing, and early Bible collections at The Legacy Museum in Atlanta, GA.