Page 461 - Handbook of Adhesives and Sealants

398 Chapter Ten

der pressure. Because of the exceptionally high early strength of the
neoprenes, it is difficult to correct a misalignment once the prepared
surfaces are in contact.
Neoprene is similar in physical properties to natural rubber, but it
is stronger and has better aging and high temperature properties. Ne-
oprene bonds are useful over a temperature range of 70 to 180 F.
Mechanically, neoprene bonds absorb vibration and display good shear
and peel strengths. Shear strengths on metal substrates can be as
high as 3,000 to 5,000 psi. Cured neoprene films are more rigid than
thermoplastic adhesives, but not as rigid as epoxy or phenolic adhe-
sives. Neoprenes deform slightly under stress and, therefore, exhibit
excellent fatigue and impact properties.
Neoprenes have good resistance to water, salt spray, commonly en-
countered chemicals, and biodeterioration. They are, therefore, often
used in building construction for decorative plastic laminates, wood
working, plywood and hardboard paneling to walls, etc. However, ne-
oprenes should be used in applications where the constant shear stress
is limited to 300 psi, because they are liable to cold flow. For structural
applications, neoprene elastomers are blended with synthetic resin to
promote mechanical strength and heat stability. Like nitrile elasto-
mers, neoprene is often blended with phenolic resins.
Certain neoprene adhesives have been designed specifically for
bonding metal to metal for structural purposes. Good bonds are
formed with a variety of metals such as aluminum, magnesium, steel,
and stainless steel. Some compounds are relatively poor on copper,
zinc, and chromium. Neoprene is the basic adhesive used in installing
laminated plastic counter tops in kitchens. The shoe industry is also
a large outlet for the neoprene cements.

10.4.1.7 Acrylonitrile butadiene (nitrile). Acrylonitrile butadiene or ni-
trile adhesives are the most versatile of the general purpose rubber
types, but they are less popular than neoprene based adhesives. Ni-
trile rubber adhesives are a copolymer of butadiene and acrylonitrile.
The adhesive properties can be increased by increasing the nitrile con-
tent. Nitrile resins are very compatible with a wide variety of fillers
and modifiers, thus giving the formulator a wide variety of properties.
Nitrile adhesives are generally available in solvent solutions of
varying viscosity. Once dried on a substrate, the adhesive can be re-
activated with heat or solvent before joining. Although an adequate
cure can be obtained at 325 F in about 20 mins, better strengths at
elevated temperatures are obtained if the adhesive is cured at higher
temperature. Nitrile adhesives are also available in tape form which
can be activated under heat and pressure.
Nitrile adhesive bond strength and creep resistance vary consider-
ably with the compounding agents used. High bond strengths are ob-