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NEW DEVELOPMENTAL UV CURABLE PRESSURE SENSITIVE ADHESIVES [2006]

2006 Dahlquist Award Winner

Victor Lu, Jeffrey Wang, Brian Maxwell, Sarah Shinkwin, Jim Stockhausen

Commercial interest in UV-curable pressure sensitive adhesives (PSA) continues to grow in recent years due to the potential for this technology to deliver a better cure control, higher coating productivity, lower overall production cost, and lower VOC emissions. A number of UV-curable PSA systems have been developed to meet the needs for different PSA applications. Those systems include UV-curable styrenic block copolymers(1), cationic UV-curable epoxy-functional liquid rubbers(2), acrylic polymers with grafted photo-initiator(3), acrylic polymer/monomers syrups(4), and various acrylated oligomers(5). However, the UV PSA technology is still in its infancy stage and thus needs continuous improvement in several key areas including wider cure window, decreased sensitivity to air or moisture, more uniform cure for thick coating, and better adhesion/cohesion performance.

Conventional polyurethane has been widely used for many adhesive applications because of its good adhesion and high cohesion. Such a unique property is mainly a result of a two-phase microstructure of flexible polyurethane. Flexible polyurethane normally consists of both the hard segments (HS) and the soft segments (SS). The strong hydrogen bonding within the HS and the incompatibility between the SS and HS drive the formation of a two-phase structure where many nanosize hard phases are dispersed in a soft continuous domain(6). By carefully designing the compatibilities, it is possible to have the UV reactive components to stay selectively with the HS micro-phase and the tackifiers to be miscible only with the SS domain. This two-phase UV curable system is expected to offer several important advantages including better curability, less sensitivity to curing environment, and a higher adhesion performance.

This paper describes a new developmental UV-curable PSA based on an acrylic urethane polymer from Cytec. This new UV- curable PSA exhibits excellent UV curability, workable viscosity at warm-melt temperature (100^oC to 130^oC), and good adhesion to both high and low surface energy substrates. By modifying the formulation, a wide range of UV curable adhesives can be developed from this new technology to fit with different industrial applications.