Sign & Digital Graphics

June '17

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60 • June 2017 • S I G N & D I G I T A L G R A P H I C S DIGITAL PRINTING AND FINISHING DIGITAL GRAPHICS Ink Chemistry Strategies Selecting the right ink chemistry/chemistries to fit your needs Ray Work, Ph.D., heads Work Associates, a consultant firm specializing in inkjet printing technologies, applications and markets. He worked for more than 28 years in research, research management, busi- ness development and business manage- ment with DuPont. Dr. Work holds a Ph.D. in physical inorganic chemistry from the University of New Orleans. He can be reached via email at workassociates@, or visit his website B Y R A Y W O R K , P H . D . Think Ink Of course they are coupled to the inkjet printer system and cannot be chosen independently. You should know up front that no single ink technology can be used successfully for all printing applications. There is no magic bullet. Initially, there was only aqueous (water-based) inks and sol- vent-based inks: aqueous for indoor prints, hot solvent inks for vinyl outdoor applications. Hot solvents, though very effective, posed serious health con- cerns; however, as the technology matured, mild- or eco-solvent inks came to replace the harsher true solvents. Later, inks further evolved to include UV-curable and "Latex" ink systems. Here we will discuss the pros and cons of each of these technologies and look at the new option of UV LED ink technology. Aqueous or Solvent? Hewlett Packard, Epson and Canon are the dominant sup- pliers of aqueous inkjet printers today. Aqueous printers provide exceptional image quality, a wide color gamut and good image permanence for indoor applications and for some outdoor appli- cations when either a protective coating or laminate are used. Aqueous inks, however, require that substrates have an ink- jet coating to absorb the ink, control drop spread and hold the pigment on the surface so that good color density can be obtained. As with all inkjet technologies the best results are always achieved when the printer, software, ink and media are optimized. Commonly used substrates for wide-format inkjet are adhesive-backed vinyl and fabric-reinforced or "scrim" vinyl. With aqueous inkjet inks a coating is required for these mate- rials, however for mild- and eco-solvent ink sets no coating is required. This is an advantage for eco-solvent inkjet. Roland, Epson, Mimaki, OKI Data and Mutoh are major sup- pliers of mild solvent inkjet printers. Although mild solvent ink, once printed and dried, is not water sensitive, the very thin ink layer is still somewhat susceptible to physical damage and weath- ering so it is prudent to coat the printed vinyl to protect it. For canvas, paper and other films, a coating may still be required to ensure good performance. Mild solvent inks do contain volatile organic compounds ( VOCs), though not in the high con- centrations found in hot solvent inks, and although most have little or no smell they are still solvents, and they should be handled carefully, ventilated or sequestered, and waste ink needs to be disposed of properly. A re you confused by the choices you have in selecting the right printer technology to meet your needs? Fortunately, when it comes to ink sets you have choices and are not forced to "make do" with a system that may not fully meet your needs. For wide-format printing, there are now several ink chemistry choices.

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