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FLEXO Magazine : May 2012
choices of materials used in any ink or coating formulation will determine that formulation’s fitness use for any particular application. PERFECT COVER-UP The first consideration for determin- ing ink’s fitness for use would be to ask: “Does the ink make the product look good?” “Does the ink cover the substrate well?” These may be over- simplistic questions, but if the ink does not cover the substrate well, more work is necessary. The nature of the substrate plays a vital role in determining any ink formula’s fitness for an application. Substrate composition, roughness, surface tension, and strength, all have an impact on the decisions made by an ink formulator. When an ink supplier asks for a sample of the substrate, there are valid reasons. Even substrates of the same composition can have an impact on an ink. Paper substrates, both coated and uncoated, can vary greatly when it comes to porosity, roughness, surface tension, holdout, and so forth. Some variation of these attributes can even occur among different lots from the same paper mill. Film substrates can vary as well. Plasticizer content, surface treatment and dimensional stability will affect the ink films in ways that the inkmaker must understand. So, how does one even begin to account for all these attributes? The easiest way to determine the important characteristics is to run a press trial with the ink and substrate combination. This is not always possible because of limitations in time and mate- rials. Testing a proof prepared off-line is often considered to be a quicker option. As part of the press correlation process, the ink supplier should be able to deter- mine a proper method for creating a lab proof that will mimic closely how the ink will print on press. Testing such proofs may be thought of as the next best thing after a full press trial. However, ink transfer and drying mechanics can often affect the performance of proofs printed off-line, especially if created by hand-proofing techniques. In order to minimize variation, due to operator error, it is highly recommended that some type of automated proofing device be used to create proofs for fitness of use testing. Several options are available, from units that mimic mini-presses in size and cost, to simpler units designed to regulate speeds and application pres- sures to consistent and reproducible levels. That being said, what tests can be done with the proof to determine how the ink interacts with the substrate? Many organizations have specific tests outlined for coverage evaluation. Most relate to density or color measure- ments of the ink on the substrate, or analysis of how much of the substrate shows through. Suppliers will often establish internal standards for both ink and substrates to judge alternatives against using the same methodology. Substrates are often easier to judge in this manner. Ink coverage can vary www.flexography.org may 2012 FLEXO 45 The world’s finest selection of flexo materials. A&V offers the world’s finest selection of flexo materials. Like nyloflex® NExT high-output UV technology and thin plate technology from Flint Group; new flat dot tech- nology from Toyobo; plus in-the-round technology and direct laser engraving. A&V supports these materials with 50 years of flexo experience and the finest technical support. Great materials and great service... that’s a hard combination to beat. get social theDiff erence! Experienc e 866.282.7697 fx: 800.223.6869 www.AndVre.com info@AndVre.com AV 9637.5 Materials ad.indd 1 3/25/12 2:03:08 PM