23.02.2015
Since 2006, there has been a incredible rush toward the use of UV-curable inks in most of the printing markets. Digital printing today is the de facto method for short-run, wide- and grand-format or variable-data print production. In the inkjet arena of narrow format, there is Screen (Dainippon), HP, Kodak Versamark and Agfa Dotrix. Wide- and grand-format printing applications have flourished because of the flexible nature of inkjet technology and adaptability of inkjet chemistries to various substrates. The capability to control this change only when the printer needs it to happen makes the ink appealing to anyone occupied in the use or formulation of inks.
Sales of UV inks have been given considerable momentum by new European Union legislation on the emissions of volatile organic compounds (VOC).
Second, UV-curable inks can be printed at higher speeds in both narrow- and wide-format sizes without the need for cumbersome drying systems.
Coupled with that flexibility is the wider range of rigid substrates that these inks have superior adhesion to. Let?s go over some of the verbiage associated with UV inks, and how the UV curable process works. In starting and completing the UV-curing process, photoinitiators are the prime components. The types of photoinitiators most commonly used in inkjet inks have been of the free-radical nature. A monomer (from Greek mono ?one? and meros ?part?) is a small, single molecule that may become chemically bonded to other monomers to form a polymer.
Depending on the UV ink formulation, other additives can also be included, such as flow and wetting aids, antioxidants and stabilizers. Stabilizers are used to help with the ink?s shelf-life and increase the tolerance to heat, which is important at higher jetting temperatures. Presently, the majority of flatbed inkjet systems use what are called free-radical UV inks, rather than cationic (containing positively charged electrons) UV inks. Free-radical UV inks use an acrylate or urethane resin, which polymerizes rapidly when exposed to UV radiation. Free-radical UV inks typically use a shuttered mercury-vapor lamp on either side of the print head to produce enough UV output to complete the curing process. A UV lamp?s peak intensity will have a drop off in performance that is related to the bulb type, usage and duty cycle of the printer. Even though the UV-curing process is fundamentally an immediate process ? inks are certainly ?dry to the touch? right after printing ? some post-curing does take place.
Cationic inks, which generally use epoxy resins instead of urethanes, also are virtually odor-free. The curing process is best described as the following: The protons, generated from the photoinitiator during UV exposure, continue to be active after exposure. These inks typically have better adhesion to the traditional ?difficult? substrates, like expanded plastics and glass. Cationic inks cure from UV lamps that are ?tuned? to the specific wavelength of UV radiation needed by the photoinitiator.
These two UV curing lamp systems do not generate the high temperatures associated with mercury-vapor lamps.
This article appeared in the SGIA Journal, 2nd Quarter 2008 Issue and is reprinted with permission. Short wave infrared heating elements, or infrared emitters comprise a linear coiled metal filament surrounded by a clear quartz envelope (tube). The power savings of a short wave heating system can be substantial compared to convection heating. The construction of a short wave infrared heating lamp means that large amounts of heat are delivered quickly, but also with extreme efficiency. One of the main advantages of short wave infrared heating is the small size of the installation.


This increase has been driven by new developments in ink technology and demand from printer manufacturers and end users. Technologies driving these applications include toner (electro-photography) and inkjet-based printing systems. Ink research and development for inkjet printing has never been greater, with a migration from the original water-based dye and pigment inks to the presently popular mid- and high-solvent and UV-curable inkjet ink types.
Within the last two years, there has been a incredible rush toward the use of UV-curable inks in most of the printing markets.
UV-curable inks, which were already being used extensively in the screen printing field, are replacing much of the solvent inkjet ink currently in use.
Lastly, the flexibility now being seen in the UV ink formulations allows roll-to-roll capability, opening up fleet graphics applications in the areas of wide- and grand-format printing. Compared to solvent inks, UV does not dry up in the inkjet head and exhibits a lower rate of nozzle failure caused by blockage.
A polymer can be any of numerous natural and synthetic compounds of high-molecular weight, consisting of up to millions of repeated linked units ? each a relatively light and simple molecule.
After absorbing UV energy from the light source located on the print head, the photoinitiators fragment into reactive materials that start the chemical reaction known as polymerization.
Ink formulators work with photoinitiator suppliers to develop inks that are compatible with the UV output of medium-pressure, mercury-vapor bulbs found in most curing systems for inkjet printing. Monomers provide many specific functions within an inkjet formulation, depending on their viscosity and chemistry. Oligomers determine the final properties of the cured ink film, including its elasticity, outdoor performance characteristics and chemical resistance. Usually, the colorant is pigment-based because of the greater light fastness and durability of pigments compared with dyes. Surfactants (surface active agents) are included to ensure the ink film spreads in a controlled fashion, and coats the media or substrate uniformly. Simplistically, stabilizers neutralize or absorb reactive molecules in the ink during storage and prevent polymerization.
Recent innovations of new performance-enhancing, cationic-ink chemistry have stimulated their development for inkjet-type applications. These bulbs are unbelievably hot, and that temperature gets transmitted to the substrate with each pass of the print head.
UV curing lamps age, and with subsequent changes in output, they may reach a point in which inadequate energy is emitted to fully cure the ink layer. Dust and ink residues on lamp windows and reflectors also can have an impact on the lamp unit?s output, requiring periodic maintenance to prevent any reduction in cure efficiency. UV-curable inks are essentially on top of the substrate (unlike solvents that etch into the substrate), and the interface between the ink and the substrate is not as strong as solvent inks. They start to polymerize when exposed to UV radiation in the nanometer range which stimulates the photo initiator chemistry. The excellent adhesion to difficult substrates is related to the ink?s reduction in shrinkage (due to heat), which is roughly one-third of that experienced by free-radical UV ink systems.
Manufacturers also are utilizing UV-light emitting diodes (LED) lamp blocks to supply the necessary UV energy. Cold curing mitigates the heat issue associated with free-radical UV cure inks while, at the same time, the cured ink is more robust at its cured endpoint. Infrared heat is actually light, whereby heat is the result of the product absorbing the infrared light. Major trans-promotional marketing players generally utilize toner-based systems and include such names as Xerox IGen3, Kodak Nexpress, HP and HP Indigo, Oce, Konica-Minolta, Ricoh, Kyocera and Xeikon.
Driving the shift to UV is its ability to almost immediately change the ink state from a liquid to an extremely resilient hard film. Solvent- and water-based inks dry by evaporation and upwards of 80 to 90 percent of those ingredients go into the atmosphere as vapors during the printing process. Ultraviolet light is electro-magnetic radiation, situated between 200 and 380 nm of the light spectrum.


But there are downsides, including UV-light exposure hazards and possible sensitization issues related to the handling of uncured UV ink.
Disadvantages from this type of light source include excessive substrate heating, high power consumption and the need for scheduled lamp replacement.
Most mono-functional monomers are used as ?solvents,? or flow modifiers, because of their ability to reduce viscosity and combine with other ink components.
Pigments used in outdoor advertising and display applications have similar requirements to those used in automotive paints.
Careful control of drop-spreading behavior contributes to the dot-gain control, which is vitally important for image quality. There are limitations to free-radical UV inks, which include oxygen inhibition, poor adhesion to difficult substrates and residual odor.
If the ink layer is not cured completely, the ink will not reach its intended hardness potential. Moreover, the effects of exposure time to UV radiation are cumulative: If an ink is over-cured, it can become fragile and flake off.
In the past, cationic inks have been available for UV-curable analog printing, but the polymerization process could take hours from initiation to completion. That means a coating does not need to be fully cured after it leaves the light source, just dry to the touch.
Cationic inks are sensitive chemistries, and can react with the bases and acids present in inkjet media, resulting in poor adhesion. This feature enables UV inkjet systems to be used on substrates that, until now, had been considered unsuitable, including vehicle graphics, uncoated glass materials and other slick or heat-sensitive substrates.
His extensive background in digital imaging, electronic pre-press for print, professional photography and computers, serves members by supplying individualized solutions to their daily business problems. A short wave infrared heating is one of themost efficient form of heating, delivering large amounts of energy instantly to where it matters most : onto the product, and no unnecessary heating of  the surrounding infrastructure.
When we designan infrared heatingsystem the properties of light must be considered: absorption, transmission and reflection. For example , consider a standard  powder coating application: a typical convection oven will be atleast 10-20 meters in length. The advantages of UV-curable inks overshadow any disadvantages, marking them as the dominant ink system for the future of industrial inkjet printing.
Burton received his Bachelor of Science in Photographic Science from the Rochester Institute of Technology. Because the system has a zero warm up time, it can be switched off during times when there is no product on the line, when there is a breakdown or even when operators go to lunch. Quartz is translucent to IR radiation, which means the quartz envelope of the infrared lamp does not absorb the infrared radiation. While a pigment is selected on the basis of the required application, size control and reduction along with dispersion technique are major components of ink formulation. Convection systems need hours to reach operating temperature and cannot be switchedoff without compromising production time.
Typical heating elements like stainless steel, silicide, ceramic tiles, 50% of the energy is wasted just heating up the element itself.
Infrared heating systems are small, compact and easily retrofitted into existing processes. These ?higher functions? of a monomer add improved film hardness and resistance properties, but may also increase the viscosity of the chemistry. Unlike gas convection systems, electric infrared heating requires no maintenance and ongoing compliance is not required. The lifetime of the quartz infraredtwin tube, when installed correctly will be in excess of 100000 hours.



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Comments Uv curing lamp temperature control

  1. Lelli
    Making small repairs to lines with cuts currency, or forgery of important documents.
  2. WiND
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