Most of us grab the sunscreen before heading out to the pool or working in the yard. We’ve all heard of it. UV radiation creates free radicals, which cause damage in living systems. If you are a living system, this is generally not regarded as a good thing. In the world of UV-curable coatings, however, the generation of free radicals and the subsequent breaking and remaking of bonds is not only desirable, but necessary. Historically that task has been accomplished by the use of synthetic materials, most of them originating from fossil fuels. The most commonly used materials are acrylates and methacrylates.
Some acrylates and methacrylates may be derived in some part from bio-based materials. Such materials derived from soy have been around for over 20 years. Ecology incorporates such materials wherever possible. These materials, however, have not been the major thrust of our bio-based research.
In the 1990s, a great deal of attention was paid to the possible irradiation of foodstuffs for safety. As a result, a flurry of papers was released describing the effects of radiation, mostly gamma, on various foodstuffs. We began to wonder if some foodstuffs, especially those showing polymerization with ionizing radiation or even thermal energy, might be coaxed to polymerize with the application of UV radiation as well. It is indeed the case that such polymerization takes place.
DiscoveryWe have identified mixtures of proteins, (which have been designated EQ-6000), available as foodstuffs, that may be incorporated into coatings in several ways. One use for EQ-6000 is as a self-photoinitiating film former. Natural proteins tend to be tightly curled. In order to make them more active groups available for crosslinking, it is necessary to relax or denature the protein structure. This can be done with the use of a mild acid. Such acids can also be derived from foodstuffs. The denatured EQ-6000 may be dispersed in a water carrier. A bio-derived emulsifier may be added as well. Such a coating has been demonstrated to cure at 400 feet per minute with 600-Watt UV lamps. The coating has shown barrier properties to air and solvents.
Other ApplicationsSimilar coatings may be further modified with other foodstuff-type materials to resist water or grease. These coatings are potentially edible. Flavorings have been added as well and cured into the resulting coating. These “GRAS” coatings may be and have been made of components considered as food rather than additives and thus have potential for food contact without the monitoring of extractables. This could be a great boon for label and package converters who don’t have the resources to determine extractables.
A second use for EQ-6000 is as a photoinitiator with conventional UV-curable materials. This is particularly notable for materials covered under FCN 772, which can be used for food contact under prescribed conditions. Two monomers covered under FCN 772 are TMPTA and TMPEOTA. Both of these monomers may be cured by using EQ-6000 as a photoinitiator or co-initiator. In this case, curing proceeds better without a denaturing agent. An amino acid found to be an active element in this mix may be used to boost curing as well.
A third use for EQ-6000 is the extension of coverage by conventional pigments. Pigmentation of UV-curable coatings presents difficulties. Some pigments absorb the very frequencies of light, which are needed to cure the coating. There are established ways of handling this problem. One is by the use of doped lamps, which deliver frequencies that are not absorbed by the pigments. Another is to use photoinitiators that absorb in different frequency ranges. These methods may also be combined. EQ-6000 adds another weapon to this arsenal. Suspended in powder form it can increase coverage. Since it also is self-curing and acts as a photoinitiator, rather than interfering with the curing process it actually promotes it.
The final use highlighted in this discussion is that of EQ-6000 as a matting agent. When used in powdered form, there are multiple advantages to be seen. The first is that, as in the use with pigments, it enhances rather than interferes with UV cure. Since it does actually cure into the finished film, it does not migrate. In many systems, it does not appear to substantially raise viscosity. It may also be combined with other bio-based additives to provide a rough surface that produces a release surface. This is unusual, as most release surfaces, such as silicones or fluorinated hydrocarbons, are smooth. By the manipulation of the additives the roughened surface may also resist water or grease.
ValueThe big question in the case of a new technology such as this always is: “What is the value proposition?” The material in EQ-6000 is available as a commodity in bulk quantities from both China and South America. Raw materials for analogs are available in bulk as commodities as well. Since none of these materials are petroleum based, the prices do not fluctuate with oil. In addition, since acrylates are not involved, the current supply problem and price squeeze for acrylic acid has no impact. As a film former, coatings are substantially less expensive than those from conventional UV-curable materials; EQ-6000 is less expensive than many pigments and some matting agents. The familiar cry of, “I’d love to go green but I just can’t afford it,” could not be justified for EQ-6000.
Ecology Coatings does not consider EQ-6000 the endpoint of our research in this area. Rather it is an encouraging start to a whole new family of safer and more sustainable products. We look forward to both the products and new applications in a greener world.
For more information, visit www.ecologycoatings.com.