Frequently Asked Questions
Select a question below to find the answer
Q: Science behind UV Curing ?
A: Using light instead of heat, the UV curing process is based on a photochemical reaction. Liquid monomers and oligomers are mixed with a small percent of photoinitiators, and then exposed to UV energy. In a few seconds, the products - inks, coatings or adhesives instantly harden.
Q: Why use UV?
A: The UV process enables the press to deliver higher-quality work—better color density with very little dot gain (as low as 3%) at faster press speeds. Additionally, startup is faster and clean-up is less time-consuming, so labor is reduced. Finally, the cost of UV chemistry on a coverage basis is less expensive than with solvent- or water-based inks and coatings, and the UV curing process consumes less electrical energy than that of hot air of IR ovens to effect drying. UV emits little to no volatile organic compounds or Hazardous Air Pollutants, hence Environment friendly.
Q: What size UV lamp do I need?
A: We recommend a UV lamp at least two inches longer than your product or print size.
Q: What type of UV lamp do I need— Mercury, Gallium or Metal Halide (Iron)—and what wattages ?
A: We recommend that you ask your coating and Ink supplier if they can guide you in the right direction. If not, please call us and we will be happy to assist you.
Q: How much light per inch does a UV lamp give off?
A: There is a difference between operating power—expressed in watts per inch—and UV energy delivered to the substrate—integrated energy and peak irradiance. Although operating power (watts per inch) and UV energy delivered to the substrate are relational, all systems do not operate at equivalent efficiencies and do not provide equivalent UV energy to the substrate for equivalent input power. UV energy delivered to the substrate is a function of optics, lamp housing and bulb dimension. The UV Cure delivers superior UV energy to the web/substrate at any given input power level. The UV energy output is measured in milli-joules per centimeter squared (mJ/cm2) for the integrated energy (or dose) and watts per centimeter squared (W/cm2) for the peak irradiance (or focused power directly under the lamp). Each measure can be broken down into individual bandwidth (UV A, UV B, UV C, and UV V) which is used to confirm a proper bulb-to-chemistry match. Note: the integrated energy is a function of time (i.e. the longer the time exposure the more dose-energy imparted to the substrate) whiles the irradiance stays the same at all speeds, as it is not time dependant.
Q: Is the heat around the press excessive?
A: No, although all arc lamps that generate UV operate at high temperatures, proper system design includes lamp cooling, via air or water or both, to extract and exhaust the heat away from the press area. This keeps the outer lamp housing from becoming dangerously hot. Exhaust air is generally drawn out of the facility, thereby removing the heat. Similarly, the water-cooled design relies on chilled water flow through the lamp housing to remove heat, and the heated water is passed through a closed-loop chiller.
Q: What is the average bulb life?
A: Most lamps are warranted for 1,000 hours of use, but UV CURE users attain as much as 1200 hours of useful life. Actual life will depend on power levels used to cure (using only low and medium power levels will extend the life of a lamp); maintenance programs that include regular cleaning of the bulbs and reflectors (if allowed to remain dirty, the power level needed to cure must be increased, which will shorten lamp life); excessive heat in the lamp housing caused by improper airflow (i.e., the blower is not functioning, or the air hoses are damaged or blocked), which will shorten lamp life.
Q: Can I cure my water- or solvent-based ink with UV?
A: No, although there is a heat emitted from the UV system, it is not an effective way to thermally cure inks or coatings. A combination dryer with hot air or IR in addition to the UV lamps is the recommended solution for those applications that require frequent switching from one type of chemistry to another.
Q: How do the costs associated with UV curing compare to conventional inks?
A: Although UV inks are typically more expensive than solvent- or water-based inks, they provide more useable coverage, as they are 100% solids—that is, they require less ink to attain the same color density as a thermal-cured ink because a portion of the thermal-cured ink evaporates. Additionally, UV inks do not dry in the ink train and therefore do not require daily wash ups, and most printers are able to run at faster speeds using UV inks. The net result is that when the labor to perform wash-ups, startup time and production are factored in along with the ink usage, UV inks are actually less costly to a printing operation than solvent- or water-based inks.
Q: What maintenance items are typically associated with UV curing systems?
A: The bulb and reflector liners require regular maintenance to keep them clean, with the service interval depending on the process. Bulbs and reflector liners should be cleaned with alcohol and clean paper towels. Other maintenance items include mercury relays, pneumatic valves, and filters and limit switches on a very infrequent interval.
Q: Can UV be used with thin film substrates that are heat- sensitive?
A: Absolutely. There are a number of means to abate the heat emitted to the substrate from the UV lamp. With the combination of dichroic shutters and dichroic quartz filter allows use of filmic materials.
Q: How do you know if the cure is complete?
A: There are two common tests for completeness of cure or the polymerization process. They are a tape test to determine adhesion of the ink or coating to the substrate and a scratch test to determine that the cure is full depth. Additionally, many UV chemistries continue to cure after exposure to UV lamps—this is known as a post cure. Post cure takes place off-press and further enhances the physical properties of the ink or coating in terms of toughness and adhesion.
Q: How much power is needed to attain full cure?
A: That depends on the thickness or lay-down of the ink or coating, as well as the press speed. If thickness or press speed increases the UV power may also need to increase. This can only be determined on-press and should include sampling as per the tape and scratch tests for full cure described above.
Q: Does it cost more to operate a UV system than a conventional thermal oven for curing?
A: No, in fact, just the opposite. New UV systems have become even more energy-efficient and so have increased the savings of operating a UV system rather than a hot-air or IR dryer.