UV-curable Resins

Properties and Applications

A large number of UV-curable resins are commercially available including polyesters, epoxies, urethanes, silicones and polyethers. The majority of these resins are free-radical curing acrylic-functionalized oligomers which usually cure in a matter of seconds but only in the presence of radiation. Typically, only thin resin layers in the range of 5 - 10 mil can be cured because not enough photons penetrate beyond this depth to achieve full cure.¹ Another major drawback of free-radical curing systems is oxygen inhibition. Atmospheric and dissolved oxygen in the resin reacts with free radicals forming less reactive peroxy radicals. This not only reduces the rate of polymerization but also can result in incomplete cure which produces a tacky surface. Besides free-radical curing systems, cationic resin systems based on epoxy and/or vinyl ether compounds are employed. These resins can be cured with a much lower UV dose and are suitable for even thick bondlines (about 10 mil or more) and thick coatings due to UV initiated dark cure. Full strength, however, is only reached after several hours. Furthermore, only a limited number of monomers and oligomers are available for light induced cationic cure.

UV curing resins are used in a variety of applications in the coating, ink and adhesive industry. They have become very popular resin systems due to their high productivity, ease of application, and low(er) impact on the environment. They are often employed when fast drying and curing is needed and are extensively used in inks for UV flexo, screen, and lithographic printing, in over print varnishes as well as in products for potting and encapsulation of sensitive electronic elements. Other important applications include scratch resistant wood, concrete and plastic coatings and acrylic adhesives.

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