Epoxy Resins
The group of synthetic resins called epoxies
produce the strongest adhesives in
current use, as well as plastics and
corrosion-resistant coatings. Epoxy
adhesives are thermosetting; that is,
after initial hardening, they cannot be
remelted by heat. They have excellent
resistance to solvents and weathering
agents, and high electrical and
temperature resistance. Their adhesion to almost
any type of
surface--including metal, ceramic, wood, and fabric--is
unmatched.
Epoxies are usually made by reacting epichlorohydrin and
Bisphenol A to produce
a polymer chain of somewhat complex structure. The end
of the polymer chain is
an epoxy group from epichlorohydrin; the resulting
plastic receives its name
from the end epoxy group. The unmodified epoxies
are brittle; however, the
properties of the cured resin can be varied widely
by the selection of a
suitable resin, curing agent, filler, and curing
procedure. Flexible grades are
modified with polyamines and polysulfides.
Most epoxy formulations have two
components that are mixed for curing.
One-component epoxies are available that
either contain a latent curing agent
or are simply cured by absorption of oxygen
from the air. Unlike most
thermosetting plastics, epoxies shrink only slightly
during curing. Epoxies
can be used as filler-adhesives; the strength of the
cemented joint is
independent of its thickness. The epoxies are used as molding
and potting
compounds, reinforced plastics, surface finishes, and adhesives.
Molding
compounds are chiefly used by the electronic and electrical
industries;
potting compounds are poured to encapsulate small electronic
parts. Epoxy paints
have outstanding corrosion resistance and are permitted
for use on food
equipment such as flour bins and can coatings. Large and
complex dies for the
forming of metal sheet are made of epoxy and are often
modified with powdered
metal such as aluminum. Uses in construction include
the repair and bonding of
concrete and also epoxy terrazzo floors. Adolf
Hitler
Bibliography
Lee, Henry, ed., Epoxy Resins (1970); Hilado,
Carlos J., Carbon Reinforced
Epoxy Systems (1984).