Page 459 - Handbook of Adhesives and Sealants

396 Chapter Ten

10.4.1.2 Asphalt. Asphalt adhesives are low cost thermoplastic for-
mulations that generally consist of asphaltic resin compounded with
thermoplastic rubber such as butyl or polyisobutylene. These adhe-
sives are inherently tacky. Adhesion is very good to a wide variety of
materials, such as concrete, glass, metal, and paper products.
Asphalt adhesives should be used only where there is little or no
stress. Bond strengths are low and fall rapidly as temperature is
raised. The high temperature properties of asphalt adhesives are de-
pendent on the particular asphalt used and on the compounding of the
adhesive. Asphalt adhesives become brittle at about 20–30 F. Water
and alkali resistance of asphalt adhesives are very good. Thick films
are impermeable to moisture vapor. Oils, greases, and common sol-
vents will soften asphalt products.
Water emulsion, solvent solutions, and hot melts are widely used
forms of asphalt adhesives. Such mixtures are useful as sealants, but
asphalt emulsions have also been used for laminating paper and other
packing materials where a water barrier is needed. They are used in
many applications where strength is secondary to resistance to water,
alkali, or acid. Hot melts have been used for bonding insulation and
for lamination of paper and foil. Emulsions have been used as binders
in roads, for installation of asphalt tile, and for bonding of waterproof
packages. Another important application is in low cost roofing and
flooring.

10.4.1.3 Reclaimed rubber. Adhesives based on reclaimed rubber are
manufactured primarily from devulcanized rubber. They are generally
made from scrap rubber products, such as automobile tires, and var-
ious additives to provide characteristics required for the application.
Often new elastomeric resins will be blended with the devulcanized
rubber to achieve better properties. The primary characteristic of re-
claimed rubber adhesives is their low cost.
Formulations mostly consist of solvent solutions or water disper-
sions. They have properties similar to natural rubber. However, their
elasticity is not as great as natural rubber. Reclaimed rubber adhe-
sives are generally not considered for structural applications because
of their relatively weak shear strength and poor resistance to sunlight
and to temperatures greater than 158 F. As a result, they find appli-
cations in low strength, cost sensitive applications. Reclaimed rubber
adhesives are used in the automobile industry for bonding carpets to
floors, body sealers and sound deadeners, and bonding flexible trim to
metal. They generally bond well to most metals, wood, paper, fabric,
leather, and natural rubber.

10.4.1.4 Butyl rubber. Butyl rubber is an elastomer used in adhesives
and sealants. It is a copolymer of a diene such as butadiene and an
olefin such as isobutylene. It is used both as a primary resin and as