Coatings World - April 2012

A UV Curable Grease
Resistant Coating Comprised
of GRAS Components

by Sally W. Ramsey, Ecology Coatings. Inc.

There has been a continuing concern in the UV curable community to develop materials that might safely be used in contact with food. The Rad Tech Food Contact Alliance has addressed this problem through FCN 772. However, coatings, inks and adhesives so formulated are permitted a migration level for each monomer or photoinitiator of up to 1 ppm. The total level of nonvolatile extractables from a finished coating may not exceed 1ppm after correction for migration levels of whatever monomer or photoinitiator was included in the formulation. The specified UV and EB cured coatings and inks may be used in direct contact with food, subject to these requirements. FCN 772 does not apply to every user of these materials. Under FDA regulations, only members of the Alliance and their customers may claim clearance for materials and or formulations covered under FCN 772.1 Many businesses may find these requirements difficult to meet. Coatings created from foodstuff materials that are generally regarded as safe (GRAS) under 21 CFR 175 would create no such difficulties.

Origin of an Idea

Although first explored in the 1930s, in the 1950s food irradiation research was growing under the “Atoms for Peace” program. The first petition for treatment of foods by irradiation was submitted in the 1960s.2 A task group established in 1981 concluded that studies with irradiated foods do not show adverse toxicological effects. 3 Nonetheless, over the years there has been considerable concern over the effects of ionizing radiation on foodstuffs. A study in 2000 explored the structural changes, such as cross linking, induced in ovalbumin, ovomucoid, and ovo-transferrin by the effect of oxygen radicals generated by gamma radiation. 4 It occurred to this researcher that if such changes could be induced by the use of ionizing radiation, perhaps similar changes could be induced with ultra-violet (UV) radiation.

In addition to food contact concerns, a justification for the exploration of these materials is increasing public demand for more non-petroleum based products. Bio-based content is of increasing popularity.

Forming a Film

Some proteins contain the amino acid cysteine which has an S-H bond. Albumin is one such protein. While most familiarly found in animal products, albumin and other proteins may also be extracted from vegetable products such as oats. S-H bonds from cysteine (Figure 1), may be oxidized to form S-S bonds. Natural proteins are usually tightly curled. Such a structure may shield S-H bonds from reactions. A curled structure may be relaxed mechanically, thermally, or by treatment with a GRAS mild acid such as 2, 3 dihydroxysuccinic acid, ethanoic acid, 3-hy- droxypentanedioic acid, salts of these acids or mixtures thereof. Albumin, transferrin, ovomucin, lysozyme, or combinations of these proteins in powdered form may be mixed with a mild acid and dissolved in water.

Figure 1: Cysteine Cross Linking5

Grease Resistance

Special attention was paid to the development of grease resistance. At present, bags for greasy foods such as dry pet food, use barriers such as polyethylene to prevent the migration of grease to the outside of the bag. Using the protein mix as the basic film former, various additives were used to block such migration. Since the creasing of bags may crack a coating and allow grease to pass, all testing was done on creased paper. Some samples were creased prior to coating and some samples were creased after coating. A kraft paper, such as that used in pet food bags was used for test purposes.