Producers and converters of goods are constantly looking for process improvements that allow them to increase productivity. Ultraviolet/electron beam (UV/EB) curing can increase the speed of production while decreasing the overall environmental impact. While UV/EB curing is well-known to producers and converters of essentially two-dimensional surfaces—such as flooring, optical media, and printed surfaces—the technology can enable process improvements in less obvious applications, like sealants and potting compounds. Industrial sealants and potting compounds, such as those used in equipment, automotive, and electric grid construction, have thus far been considered niche applications.
These applications have a different set of requirements than other UV/EB areas. In traditional UV/EB applications, the coating, adhesive, or ink is typically applied at a very thin coat weight and provides surface modification or protection. In the case of sealants, the applied chemistry is expected to bridge the gap between solid surfaces and possibly tie them together. The sealant should have a certain surface hardness that will allow compression during assembly, and it should be able to withstand mechanical stresses. Potting compounds fill in pre-determined areas to protect the contents or users of the goods.
Sealants and potting compounds are expected to perform in more adverse environments than standard UV-cured systems. These systems could be exposed to high temperature and high humidity for extended periods of time. There is also potential exposure from liquids, such as water, cooling fluids or lubricating oils. It is therefore necessary to understand the resistance of the UV-cured system to all of these potential exposures. As with any system, changes in mechanical or adhesion properties over the service life are undesirable. Understanding how certain monomers and oligomers can hold up under these adverse conditions becomes critical in assembling the best solution possible.
A study was undertaken to understand the key differences in monomer and oligomer backbone structure as heat aging is applied to the UV-cured sealant. The focus of the oligomer evaluations was on aliphatic urethane acrylates, as these backbones allow for differentiation of the molecular weight, backbone chemistry and functionality. By varying these oligomer design elements, applications chemists can achieve a wide range of tensile, viscoelastic, solvent resistance and liquid properties. A plethora of monomer structures could potentially be used in these applications. Table 1 shows a list of the prospective products.