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![]() We Put Ink on Paper
By Bob Flipse, Owner, Grafx Network
As a person whose life is governed by physics and chemistry (and I joke about this), I find the myriad concepts of inkjet printing fascinating, and I still get a kick out of watching a printer go back and forth with the image developing right before my eyes.
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In one form or another, this has been going on in a mechanized fashion since Johannes Gutenberg invented the printing press around 1440, but things have come a long way since then. Commercial drop-on-demand printing, as we know it, began in the 1980s. Both HP and Canon were developing thermal inkjet printheads, and the now-popular piezo printhead came along at roughly the same time. Even as advancements continue to be made to this day, each technology still requires different chemical and physical properties in the ink in order to fire properly. No doubt you have seen differences in print quality or color from one media to another or even from one roll to another. Variations in print quality can depend on the time of day, the length of print runs, changes in temperature or humidity, the age of the printer, different ink lot or third-party ink, and the list goes on. These make up the variety of physical and chemical factors, all of which can affect the final result, i.e. the quality of your finished print.
Printhead Technologies Enter piezo printheads. Again, simply put, the ink flows into a chamber and is fired out of the nozzle by a piezo membrane (derived from the Greek piezein, which means to squeeze or press), which, when excited or fired, mechanically forces the ink droplet through the nozzle. Compared to thermal printheads where the vaporization point of the ink is critical to the process, one can readily see that a mechanical means of firing the ink droplet could be far more friendly and adaptable to a variety of ink technologies, including solvent, UV-curable, dye-sublimation and aqueous.
Typical Printing Process Printing in single pass and putting down the full ink load to depict the image results in an overwhelming amount of ink that is incapable of drying quickly enough to depict a crisp image, not to mention having a softer featured edge that allows it to blend with the previous pass. I can't recall a single graphics printer I have worked with that even has a single-pass mode.
Temperature and Humidity Overview Keeping your print room at 85 degrees to optimize your drying will likely result in unhappy and sluggish employees and a loss in productivity. Frankly, we have seen printer performance deteriorate in warmer printing environments. One shop I visited in North Carolina with no air conditioning ran their jobs from midnight through 8:00 am. When it got over 85 degrees in his shop, the print quality became unusable. Extreme? Perhaps, but a good example nonetheless. Considering humidity, vapor-saturated air cannot readily absorb additional vapors (including solvents). Your prints won't dry as well on a damp day for obvious reasons. If you have a damp and cool day - imagine the results. Recommendation: For the best and most consistent printing results, keep your shop environment as consistent as possible. For most any print technology, the best numbers to aim for would be 72-75 degrees and 55-percent humidity, and invest in a hygrometer to measure your shop conditions. All this may mean air conditioning or dehumidifying as necessary, and humidifying in the winter when the humidity can get too low. Static is often a result of low humidity, usually with severe effects on print quality and even on the equipment itself.
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Your Printer in Winter Recommendation: Even if you have the need to keep your overall shop cooler, such as for a large bay or on weekends, invest in the necessary technology to maintain your print room at least at a temperature close to its usual operating range. Also, at a minimum, keep your commonly used materials and next upcoming rolls or sheets in the print room area so they can stabilize temperature and static prior to use. Not uncommonly, we go into print shops where the printer is near a door that opens frequently, causing large temperature and humidity fluctuations. Obviously it's pretty tough to maintain consistent quality under those conditions.
Environmental Effects on Color Several of the more popular RIP software companies are in Salt Lake City, which has an average elevation of 4,327 feet. Though right on the lake, it is generally a desert environment with an average low humidity of 22 percent on July afternoons. You can reasonably expect that the RIP software companies have air conditioning to cool down their facilities, but I do not recall that the ones I have visited have humidification equipment in their color labs where they generate their (which are actually your) color profiles. Read the fine print or expert articles on the subject. They often state that the "canned" profiles that you receive with the RIP are a good starting point or reference standard, but that you should recalibrate if you wish to have accurate color. Faster drying equals lower dot gain, so imagine that effect on print quality. Considering what you now know about the effect of temperature and humidity on dot gain, which both affect color rendering, do you think that a profile generated on July 15 in Salt Lake City would be color accurate in Baltimore on that same day? Fact and Hint: Many of the newer printers have built-in color measuring devices, also known as spectrophotometers. The better RIPs have built-in color engines, and some have a routine in the RIP where you can automatically use this device to recalibrate. Make friends with that device if you have one, and use it often! If you don't have one and your RIP readily supports it, buy one.
Print Passes
Printer Heaters This is a delicate balance, so consider the factors involved: the number of heaters on the printer and their surface area, the thickness of the media you are using, its backing material and overall ability to absorb the heat, the speed of transport of the media over the heaters (dwell time), not to mention the density of your prints in terms of overall ink load, etc. Remember also that overly high temperatures may cockle (warp) the material and cause head strikes or other anomalies. Considering all the factors involved in the printing and heating process, there are a few simple rules:
Walking the Walk A 25+ year industry veteran, Bob Flipse was an early innovator in wide format digital printing. Starting in aqueous, his knowledge now covers solvent, UV, and other ink technologies. Bob is a partner in Grafx Network, a nationwide service company for wide format printing equipment. Their services include maintenance, repair, training, color management, and moving and logistics. Much of their work is performed for dealers and manufacturers, some of outsource to them for overflow work while others use them as primary service providers. www.grafxnetwork.com This article appeared in the SGIA Journal, July / August 2015 Issue and is reprinted with permission. Copyright 2016 Specialty Graphic Imaging Association (www.sgia.org). All Rights Reserved.
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