by Scott Sabreen, the Sabreen Group
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Question: What is the difference between Continuous Inkjet and Drop-on-Demand Inkjet?
One of the earliest inkjet technologies, dating back to the mid-1980s, is termed Continuous Inkjet (CIJ) printing. At that time non-contact CIJ was used for general purpose printing of variable information on flat packaging and direct mailing (paper stock, cardboard, and related porous substrates). A few, but limited, plastics applications used CIJ but in general, there was poor ink adhesion. With CIJ, printheads incorporate a single jet and can run at very fast speeds using air- drying solvent-based inks, although alternative heat-cure inks also are used. As the terminology implies, CIJ operates in a continuous stream mode. CIJ is a very fast inkjet method but lacks high quality printing.
The newest generation of inkjet technology is termed Drop-on-Demand (DOD), or piezoelectric DOD inkjet. It is DOD inkjet printing which provides newfound excitement for high resolution, variable information, decorating on two-dimensional and three-dimensional plastics applications. At present its primary usage remains in printing flat products such as billboards and signage.
DOD inkjet also is a non-contact printing technology, but in contrast to CIJ, dots of ink are precisely controlled which yields very high resolution, 600 to 1400dpi and higher. Individual droplets of ink are jetted from small diameter vessels directly to a specified position on the substrate to create the image or alphanumeric text (and machine vision codes). The vessels can range in quantity from 128 to 768 and greater depending upon the print area and speed requirements. Thus, the main difference between CIJ and DOD is the multi-nozzle drop-on-demand printhead nozzles that are in intermittent use.
Question: What is the difference between Binary and Grayscale Inkjet Printing?
In Binary inkjet, every pixel on the substrate to be marked is either covered with an ink drop or its not, thus an either/or binary choice. In contrast to Binary, Grayscale inkjet has the capability to fire a range of individual drop sizes. Some printhead manufacturers have the capability to fire up to 16 levels of grayscale. Grayscale inkjet can be preferred versus Binary for exceptionally high resolution as measure in dots-per-inch (dpi).
Question: What types of inks can be used for Inkjet Printing?
Depending upon the specific type of inkjet printhead, UV (ultra-violet) inks, solvent-base inks, water-base inks, and hybrid inks can be used. Ink chemistry is a critical factor when determining which type of printhead to procure for each application. Inks are normally formulated to be used in specific printheads. This is due, in part, because printheads will function best when the optimal visco-elastic properties are achieved including temperature, viscosity, drop size, and shear forces just to mention a few of the important variables. Many printheads can utilize either UV, solvent-, or water-base inks.
Scott R. Sabreen is founder and president of The Sabreen Group, Inc., which is an engineering company specializing in secondary plastics manufacturing processes surface pretreatments, bonding decorating and finishing, laser marking, and product security. He has been developing new technologies and solving manufacturing problems for over 25 years. He can be contacted at (888) SABREEN or by visiting www.sabreen.com or www.plasticslasermarking.com.