Tack and Viscoelasticity of Block Copolymer Based Adhesives

Tackification of block copolymers of the linear ABA or radial (AB) x type, in which the center block (B) is in the rubbery state at use temperature, follows principles established for other rubbery polymers except for peculiarities of the systems introduced by the block polymer domain structure. Successful pressure-sensitive adhesives result wherever the tackifer is compatible with the rubbery phase, which forms the continuum. Connectivity of the hard phase generally leads to loss in compliance, making tack ultimately contact-limited; whereas tack is low, adhesion can be developed by control of dwell time, temperature and contact pressure. A previously explored criterion for contact limitation, defining a critical minimum 1-second creep compliance, appears to be valid for block polymer-based adhesives, as is the rule that an effective tackifier must raise Tg (in the present case of the rubbery continuum) while also acting as a plasticizer.