The market for ultraviolet (UV) and electron beam (EB) technology has been growing at double-digit rates the last 10 years. A significant reason for the technology's growth is its unique process characteristics, which allow UV coatings to be applied on virtually any substrates. Plastic, metal, composite, wood, paper, leather, vinyl, glass, magnetic recording tape and even human teeth are substrates finished with this technology. Application methods run the gamut from the more primitive "dip and wipe" approach to curtain coating, roller coating, silkscreening, printing and spraying.
The original driving forces behind the commercialization of UV/EB technology were energy savings and freedom from solvents. These benefits are complemented by high productivity and subsequently higher profits that can be obtained with the processes ever-increasing line speeds, just-in-time benefits and immediate "pack-and ship" capabilities.
In contrast to convection ovens, which are used to drive off solvents or water and to apply heat to cure coatings, UV and EB energy interacts directly with specially formulated materials that are often applied as near 100% solid systems containing low levels of volatile compounds. This direct action initiates a chemical reaction in fractions of a second. The space required for either a UV or EB curing unit is considerably smaller than that required for convection ovens. With UV/EB curing, electrical energy is efficiently used and no costly solvent recovery or emission control systems are needed.
One significant and rapidly growing application area involves the use of UV coatings with exterior weatherability for galvanized steel pipe for fence posts, highway guardrails, road signs and parking meters. These coatings see severe service requirements for resistance to salt corrosion, sunlight and moisture.
While well established in many industries, some individuals are still unfamiliar with UV and EB processing. Because this technology represents a different way of thinking about curing inks, coatings and adhesives, many myths and misconceptions about the technology have been spread.
UV/EB Materials are Dangerous
Overall, UV/EB materials are much less toxic than solvent-borne and some waterborne coatings. UV/EB coatings exhibit the following properties:
- have a very high or no flash point;
- emit little to no VOCs;
- have very low systemic toxicity;
- are mostly not mutagens;
- are not, as a class, carcinogens(recent long-term skin painting tests showed no carcinogenic effect);
- are not fetal or reproductive toxins;
- are not regulated as hazardous waste; and
- don't appear on any Community Right to Know list.
UV/EB curing materials are not absorbed through the skin as solvents are. Plus, they have very low vapor pressures, making inhalation less likely. Good industrial hygiene practices, knowledge of safe handling procedures and worker training are essential for safe handling of any chemical. When these principles are followed, experience has shown that UV/EB curing materials are safe.
UV Light Used in UV Curing is a Significant Hazard
The biological effects of exposure to UV light resemble the typical symptoms of sunburn. We are all familiar with sunburn, so anyone who might be inadvertently exposed to excessive UV light would be quickly aware of it. The American Council of Government and Industrial Hygienists (ACGIH) and National Institute for Occupational Safety and Health (NIOSH) have established exposure limits for UV light that are easily met with shielding to minimize escape of UV light into the workplace.
UV/EB Preparations are More Expensive than Conventional Coatings
A quick comparison of the cost per gallon is usually the reason that energy-cured 100% solids materials are considered higher cost. However, a more realistic approach is to look at actual applied cost per dry mil (or per item coated).
For example, let's assume that we are using a roll coating application, the transfer efficiency is the same and 1,604 ft2/gal per mil will be applied for both a UV and thermoplastic coating. For the thermoplastic coating the total solids by volume is 32.62% and the cost per gallon is $13.67. For the UV coating the total solids by volume is 99.69% and the cost per gallon is $35. Therefore the applied cost of the thermoplastic coating is $0.0262/ft2 per dry mil compared to $0.0218/ft2 per dry mil for the UV coating. This adds up to an approximate savings of 17% by using the UV coating.
UV Finishes are Prone to Cracking and Yellowing
While this may have been true several years ago, the rapid growth and advancement of the industry (with many chemical companies offering new raw material products) and resulting advances in UV/EB chemistry have given the formulator a number of chemical classes from which to choose. With this flexibility, the industry is now able to easily meet customer requirements and develop products that best fit customer applications, including requirements for non-yellowing and resistance to cracking. In fact, on certain poor weathering substrates like extruded vinyl, UV clearcoats are used to prevent premature yellowing as well as improve stain and abrasion resistance. In another example, the headlights on your car have a UV coating to prevent scratches, cracks and yellowing.
UV/EB Equipment is too Expensive
During the last few years, the prices of capital equipment have come down considerably. In addition, when considering capital equipment costs, one must also look at the space required and the energy consumed by the equipment.
Space. A drying oven for a conventional thermal cure system may extend for 50-100 ft, resulting in a footprint of 500-1,000 ft2. At a floor space cost of only $0.50/ft2 per month, that costs $3,000-6,000 per year. The equivalent UV "oven" would require significantly less space (50-100 ft2) at dramatically reduced costs.
Energy Consumption. One of the most significant cost factors when comparing thermal curing to UV curing is the energy cost. A large gas curing oven consumes 1.10 MBtu/hr (and requires large blowers), while the same production capacity can be achieved with a UV dryer requiring only 82 kW total.
There are other considerations regarding UV/EB technology as well. UV/EB users enjoy an increase in uptime and productivity due to the nature of the chemistry (doesn't skin over in applicator, no need to clean up between shifts/weekends and faster startups). Increased productivity means more profits, which quickly pay for any initial capital equipment costs.
Other areas of cost savings come from a reduced number of parts in the process and a shorter processing time, which directly relates to lower inventories. Quicker cure allows for fewer particles to contaminate the surface finish, which directly relates to reduced rework and scrap costs.
In summary, there are both tangible and intangible benefits to deciding to go to UV/EB curing. When factoring these benefits into the selection criteria, UV/EB typically becomes the most economical andenvironmentally safe solution!
To learn more about UV and EB curing please visit our web site, www.radtech.org, and join us at the world's largest event devoted to this fast growing technology-RadTech 2002 Conference and Exhibition scheduled for April 28-May 1, 2002 at the Indiana Convention Center in Indianapolis, IN.