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Cyanoacrylate information and tips on
dealing with a difficult - but important - material.
Cyanoacrylates are single component moisture
curing adhesives which cure rapidly to form tough, durable, high performance
bonds and Cyanoacrylates are chosen for versatility and
ability to bond a wide variety of substrates including; metals, woods,
ceramics, rubbers, plastics and textiles. The rapid bonding of parts ensures efficient production
levels and accurate control of costs. Cyanoacrylate
adhesives (CA), a member of the acrylic family, have been used for many
years. CA will cure rapidly when exposed to moisture and are especially good
with metals, ceramics and glass. CA will also bond human skin almost
immediately and are used in wound closure. Mixed CA resins feature better
molecular compatibility with plastic surfaces, but even with these
improvements, most CA bonding is done on metals and glasses.
CA gels quickly, depending on the surface, and is excellent for staking or
quick-fixturing of certain materials. Most CA is a one-part system, which
means less waste from mixing and problems with needing to use it
quickly (pot life) before it is unusable. Most CA functions well up to 180°
F and does not need a post-cure operation. Secondary oven cure is necessary
for adhesives featuring high temperature resistance—up to 350° F.
CA does not typically require mixing, refrigeration, or other special
handling pre-use, but should always be kept in a low-humidity environment.
Caution should be strictly observed in handling, especially bonding to skin,
and while the odor can be unpleasant, there are usually no fire hazards with
fumes. Good ventilation is necessary, however, for operator comfort.
Though the bond appears instant, the actual full cure takes place over a
period of hours and can sometimes be accelerated by heating. Fast-tack
fixturing is sometimes very important to processes because it allows
increased throughput in assembly, lowering the amount of time the bond is
vulnerable to movement during handling or other
process movement as the CA sets.
Most CA's have low viscosity (10 to 500 Centipoise) so they spread easily and
can even penetrate some joints by capillary action., which means that
dispensing by syringe or specially designed Teflon valves is commonplace.
Automated dispensing equipment is available at extremely modest costs and is
also good for patterned, automated dispensing on X-Y-Z and rotary tables.
CA may seem expensive, but they can repay the user in reduced labor cost,
capital investment and quality because of their ease of low cost dispensing,
speed and fast cure. Any product that requires rapid assembly might benefit
from using a CA adhesive in assembly.
Costs can be also be lowered with reproducible and precise
automated dispensing.
CA do not cure on acidic surfaces and as a result, some
substrates (such as pickled metals) require neutralizing treatments before
bonding. Plastics and rubber, too, have little adsorbed moisture, so primers
are necessary to provide surface reactivity. Caution must also be used to
avoid “crazing” or “clouding” on some plastics, due to solvents.
Curing on less compatible surfaces might require more
testing, through trial and consultation, but when the application calls for
the quick-cure, it can be rewarding in terms of overall process.
Acrylic chemistry is quite flexible and can be “tweaked” by formulators. New
chemistry and secondary heat curing have increased temperature limits of CA,
and there have been many advances in formulating materials for thicker bond
lines. While close-fitting joints and bond lines less than 0.01 inch are
still favored, there can be some cases when the formula can be modified to
perform in a thicker content.
Advances in CA formulas have made them easier to use and dispense and are
readily available, versatile and worth considering for assembly.
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