Page 431 - Handbook of Adhesives and Sealants

Adhesives Families 373

mulation. Temperature resistance increases with the epoxy content of
the system. Resistance to solvents, oil and grease, and exterior weath-
ering and aging are superior to that of most thermoplastic elastomers.
The epoxy-polysulfide adhesive is usually supplied as a two-part,
flowable paste that cures to a rubbery solid at room tempera-
ture. These systems can be heavily filled without adversely affecting
their properties. The polysulfide elastomer will cure epoxy resins by
itself, but the reaction is extremely slow. A tertiary amine is usually
used as a catalyst for room temperature curing. A sulfur odor is no-
ticeable during processing, making ventilation important.
Epoxy-polysulfides are often used in applications requiring a high
degree of elongation. They are generally used to bond concrete in
floors, roadways, and airport runways. Other principal uses include
sealing applications, bonding of glass, potting, and bonding of rubber
to metal.

10.3.2.5 Epoxy-vinyl. Epoxy resins may be blended with certain vinyl
polymers to improve the impact strength and peel strength of the ad-
hesives. Polyvinyl acetals, such as polyvinyl butyral and polyvinyl for-
mal, and polyvinyl esters are commonly used to modify DGEBA resins
at a 10–20% addition. Elevated temperature resistance is sacrificed
by the addition of the low Tg vinyl resins. These adhesives are gen-
erally available as films or solvent solutions. They are commonly used
as laminating adhesives for film or metallic foil.

10.3.3 Resorcinol formaldehyde and
phenol resorcinol formaldehyde
Resorcinol resins come from the phenolic resin family. They are more
expensive than their phenolic counterparts, but they are useful when
a room-temperature cure is necessary. They find application in bond-
ing wood, cellulose acetate, molded urea plastics, nylon, and various
plastic laminates to wood core. They also bond to porous materials
such as paper, textiles, leather, and fiberboard. They do not usually
bond to metal, although they will bond metal to wood if the metal is
first primed.
Resorcinol adhesives are primarily used for bonding wood struc-
tures. Adhesive bonds are usually as strong as the wood. Resorcinol
adhesives are suitable for exterior use, and they are resistant to boil-
ing water, oil, many solvents, and mold growth. Their service temper-
ature ranges from 300 to 350 F. Because of high cost, resorcinol
formaldehyde resins are often modified by the addition of phenolic
resins to form phenol resorcinol. Resorcinol formaldehyde resins are
also commonly used as a primer for bonding nylon with epoxy or pol-