Page 460 - Handbook of Adhesives and Sealants

Adhesives Families 397

an additive for tack. Butyl rubber is generally used in solvent solution.
It is often formulated as a pressure sensitive adhesive. Butyl adhe-
sives are normally low strength and tend to creep under load. They
are useful in packaging applications because of their low permeability
to gases, vapors, and moisture.
Butyl rubbers contain a small amount of unsaturation (double bonds
in the molecular chain). Polyisobutylene is a completely saturated
form of butyl rubber. (See polyisobutylene adhesives below.) Butyl
rubber is often formulated with polyisobutylene to provide the re-
quired adjustments relative to the degree of cohesive strength and
creep resistance (favorable to butyl rubber) vs. the degree of flexibility,
tack, and peel strength (favorable to polyisobutylene).

10.4.1.5 Styrene butadiene rubber (SBR). Styrene butadiene rubber is
often used as the primary component in elastomeric adhesives, and it
is also used as a major additive to adjust properties of other elasto-
meric resin based adhesives. SBR does not have the good adhesive
properties of natural, nitrile, or neoprene rubber. However, it is lower
in cost than these resins. Compared to natural rubber, SBR adhesives
have better heat aging properties and lower moisture absorption. They
have a useful temperature range of 40F to 160 F. However, they do
not have the oil, solvent, or oxidation resistance of neoprene or nitrile
based products. SBR resins do not naturally have a high degree of
tack. Often tackifiers and plasticizers are added to SBR adhesive for-
mulation when a high degree of tack is needed in the application.
SBR adhesives are available in a variety of formulations. Water dis-
persions are very common as are solvent solutions and hot melt for-
mulations. SBR adhesives are used as pressure sensitive adhesives
and laminating adhesives for paper, textile, leather, plastic films, and
metal foils.

10.4.1.6 Polychloroprene (neoprene). Neoprene has become the popu-
lar term for polychloroprene elastomer. Neoprene may be designed for
curing or noncuring properties. Curing cements are formulated with
crosslinking agents. Metal oxides and antioxidants are commonly
found in neoprene adhesive formulations. They are responsible for the
excellent resistance of neoprene films to ozone and oxidation.
Neoprene is generally used in organic solvents either as a contact
adhesive (sprayed or brushed) or as an extrudable mastic. The rate of
strength development is rapid for neoprene adhesives, and they can
sustain low loads at high temperatures soon after bonding. However,
tack retention and solvent or heat reactivating is generally inferior to
other rubber adhesives. As a contact adhesive, neoprene cements are
applied to both substrates, the solvent is allowed to evaporate, and
the bonding surfaces are carefully assembled and forced together un-