Heat activateable adhesive

Heat-activatable pressure-sensitive adhesives consisting of crosslinked Ci-Cis polymethacrylates were prepared by Husemann et al. (1) and used on polyester substrates. 

Additional block terpolymers containing propyl acrylate and star block terpo-lymers containing styrene were previously prepared by the author [2] and used in hot-melt pressure-sensitive and heat-activatable adhesives. 

Random terpolymers consisting of ethyl, butyl, and behenyl acrylate were prepared by the author [3] and used as heat-activatable adhesives. Randon terpolymers consisting of iso-octyl/acrylic acid/styrene macromonomer, 92/4/ 4 mol%, respectively, were prepared by Joseph [4] and used as a reinforced pressure sensitive adhesive. 

There are three main polymers presently used for structural adhesive bonding and they are phenolics, epoxies and urethanes. We can also include in our classification, the initial physical state of the uncured adhesive since it governs the type of application and curing conditions. Structural adhesives are manufactured in the form of films or pastes. The films are one-part adhesives, i.e., they contain a latent catalyst which requires heat for activation. Structural adhesive films are made in a number of different thicknesses and can either be supported (containing a scrim) or unsupported. In general, film adhesives require the application of pressure during cure in order to obtain ultimate properties. Paste adhesives are either one- or two-part materials. That is, pastes can either contain a latent heat activatable catalyst, or they can be a system which is separated into two parts, one of which contains the cur a t i ve/ca talys t. Two-part pastes cure at room temperature. In this section the chemistry of one-... 

Cationic iodonium and sulfonium salts of strong acids are well known as UV-activatable strong acid sources, but they have also found use as heat-activatable acid sources in epoxy resins. Diaryliodonium salts, such as diphenyliodonium tetrafluoroborate (67), have found use with activators, e.g., benzopinacol, in epoxy adhesive and coating formulations. Cure times of several minutes at 160 C were claimed, with good room temperature latency. In a series of patents issued to Asahi Denka Kogyo K.K., several strong acid salts of aliphatic sulfonium compounds have been described as catalysts in heat curing epoxy compositions (68). " The counteranions... 

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