Mechanical and Optical Properties of UV-Curable Modified Acrylic Adhesives

Abstract

Ultraviolet (UV) curable modified acrylics constitute a unique class of polymers for optical bonding applications due to their transparency. To elucidate their adhesion characteristics two UV-curable modified acrylics, including rigid and flexible formulations, were evaluated. Two main aspects were investigated. First, durability in hot-humid environment, in combination with epoxy, amine and methacryl terminated silanes, was assessed. Secondly, the optical transparency of the modified acrylic adhesives in the visible and infra-red regions of the spectra was measured. Transmittance was evaluated for the neat adhesives and for the cases where silanes were used both as surface primers as well as additives incorporated into the adhesives.

Experimental results show conclusively that enhanced mechanical properties are obtained when silanes are utilized as primers, especially for strength endurance in humid environments. Best performance for the rigid and flexible UV-curable adhesives was obtained when the methacrylic-terminated silane was used. Furthermore, when silanes were used as primers or directly incorporated into the adhesives, some improvement in transmittance was observed in all regions of the spectra. Generally, the UV-curable adhesives studied exhibited more than 90% transparency in the visible and near infra-red regions. Due to inherent absorbing bands, close to 3.5 and 5.5 μm and in the whole range of 8 to 12 μm, transmittance levels are low in these regions. These results indicate that acrylic adhesives in particular and polymer adhesives generally are inadequate optical adhesives in the latter region.

Key Words:

• UV-curing
• acrylic adhesives
• silanes
• optical properties
• mechanical properties
• durability