A new method based on application of cyclic strain to evaluate the durability of pressure sensitive adhesives

摘要

The development of PSAs suitable for specific applications requires an optimization of the two most essential properties: sufficient bond strength and clean resolvability. The latter is conveniently obtained by controlling the mode of debonding to an interfacial failure, yet the issue of bond strength is challenging since the optimum bond strength must be available in the same failure mode. More complication arises from the fact that the methods, such as peel and creep tests, used to evaluate the bond strength are often qualitative and he results obtained may not accurately reveal the effects of various PSA design parameters. In the presence study, a new method, named cyclic strain application (CSA) test, is devised to evaluate the durability of PSAs. A key feature of this test is that by applying a controlled cyclic strain on a PSA/substrate interface we can quantitatively monitor the temporal stress variation as well as the time for interfacial failure (t_f). As a result, the effects of various PSA design parameters, such as molar mass, blending with low molar mass fractions, adhesion promoters, and the level of crosslinking on PSA durability can be clearly seen. Other factors being equal, higher molar mass samples showed greater t_f, while, blending with low molar mass fractions let to a reduced t_f. The use of a strong adhesion promoter, as anticipated, increased t_f. However, it should be noted that excessive bond strength may lead to a cohesive failure, which is detrimental in the design of good PSAs. From a comparison of t_f with peel strength, it was clearly shown that t_f, the key parameter obtained from the CSA test, had a strong correlation with eel strength. In addition, some other information, such as the detailed influences of the level of crosslinking and molar mass on PSA durability was also obtained form the CSA test. Lastly, some important PSA design concepts and other examples utilizing the CSA test are presented.