Pressure-sensitive polyisobutylene, butyl rubber

Nitrile rubber is used preferably for contact adhesives with improved plasticizer resistance. Polyisobutylene is used in pressure-sensitive adhesives. Butyl rubber is sometimes added to pressure-sensitive and hot-melt adhesives, although it is mainly used in sealing compounds. Epoxy resins and reactive (meth)acrylate adhesives (reactive adhesives) are modified with polychloroprene, butyl, and nitrile rubber. Chlorinated rubber is added in small quantities to contact adhesives and also to rubber-to-metal bonding agents for improving the adhesion properties. 

Butyl Rubber. Butyl rubber is used in conjunction with other thermoplastic hydrocarbon rubbers (for example, polyisobutylene) to make pressure-sensitive hot-melt adhesives. Such formulations include also tackifying resins and oils. Adhesives of low viscosity are produced, and these may be applied by the hot-melt spray technique (see page 106). 

In the hot-melt type, two principal polymer types are used polyolefin and ethylene co-polymer based and polyester and polyamide type. In the solvent-based type, the most prominent are neoprene (polychloroprene)-based solvent and latex types, and polyvinyl acetate emulsions. For pressure-sensitive adhesives, the most favored are acrylic adhesives and butyl rubber/polyisobutylene types. 

Polyisobutylene and Butyl Rubber. Polyisobutylenes are polymers of low polarity and low Tg and are available in a wide range of molecular masses. For pressure-sensitive adhesives, polymers with a viscosity average molecular mass My of at least 10 are used in combination with low molecular mass types. 

Elastomeric adhesives are natural or synthetic polymers with superior toughness and elongation. Examples of elastomeric adhesives include natural rubber, reclaimed rubber, butyl rubber, polyisobutylene, nitrile rubber, styrene-butadiene-rubber, etc.l Elastomeric adhesives are supplied as solvent solutions, latex cements, pressure sensitive tapes, and single- or multi-component nonvolatile liquid or pastes.[ 1 However, they are usually supplied in liquid form. Most are solvent dispersions or water emulsions. The service temperature is up to 204°C (400°F). They never melt, have excellent flexibility, but low bond strength. The main application of elastomeric adhesives is on unstressed joints on lightweight materials (e.g., joints in flexure). Hence, they are not considered structural adhesives. 

Two important parameters in the formulation of pressure sensitive adhesives are tack and hold, which is the ability to resist creep under deadload. As noted, butyl and polyisobutylene are inherently tacky polymers. This tack can be enhanced with a wide variety of resins and other tackifiers. The hold or cohesive strength is low compared to some other pressure sensitive adhesive polymers, such as natural rubber, but can be increased if required by (1) incorporation of high molecular weight PIB or natural rubber, (2) the choice of the other ingredients, particularly resins and fillers, and (3) the partial or preferential curing techniques noted previously. The poly isobutylene polymers are primarily used in label pressure sensitive adhesives and in certain tapes where high cohesive strength is not necessary. 

Higgins, J. J., Jagisch, F. C., and Stucker, N. E., Butyl Rubber and Polyisobutylene, in Handbook of Pressure-Sensitive Adhesive Technology, Second Edition, D. Satas, ed., p. 374, New York, Van Nostrand Reinhold, 1989. 

---