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Instant Adhesives
Bonding
Hernon offers a very complete selection of cyanoacrylate adhesives.
Two different categories are offered: Instantbond & Quantum.
The Instantbond grades offer "classic" performance,
while the Quantum grades deliver "special" or "advanced"
performance. The differences between the two categories are the
result of formulation, modification and molecular engineering.
Instantbond Cyanoacrylates
Classic cyanoacrylates are represented by the ethyl and methyl
chemistries. Generally, the methyls offer better bond strengths
on metals, the ethyls providing better strengths on everything
else. Substrate selection and bondline configuration directly
influence adhesive performance.
For example, two polished bare metal surfaces are
best bonded with a methyl grade. By comparison, better results
would be generated by an ethyl grade when bonding a single bare
metal surface, such as an emblem to an automobile fender. Why?
The automobile fender is painted, and while composed of metal,
the adhesive is in contact with the acrylic paint layer, a plastic
surface. To summarize; use methyls when bonding bare metal-to-metal,
ethyls for everything else. Surface chemistry plays an important
role in the cure of the classic cyanoacrylate adhesive.
Instantbond grades cure as the result of contact
with trace amounts of moisture. The reaction is called ionic
polymerization. Any surface capable of absorbing moisture is
a good surface for bonding.
The water molecule is V-shaped and orients itself
so that the two halves represent two OH- or "weak"
hydroxyl groups. Instantbond cyanoacrylates require sufficient
atmospheric moisture to cure or catalyze the liquid adhesive.
The Instant bond formulations cure best when  surface
pH is slightly alkaline or over 7.0. Poor bonding performance
results on acidic surfaces such as: plastics and rubber covered
by mold release agents, platings, wood and leather. These surface
conditions should be viewed as limitations for the Instantbond
Cyanoacrylate types. Hernon's Quantum cyanoacrylates, discussed
later, are formulated to overcome such limitations.
Adhesive viscosity plays a vital role in the fixture
time of cyanoacrylates. The lower the viscosity, the quicker
the adhesive will fixture. The higher the viscosity the slower
the bonding action. Water has a viscosity of 1 centipoise (cP),
and very thick maple syrup has a viscosity of approximately 2,500
cP. Fillers can be added to the adhesive to create a "gel"
or jelly-like consistency. Gels do no flow like liquids and can
be easily used on vertical or overhead surfaces without migration.
Gap fill ability is directly related to the viscosity
of the adhesive. Low viscosity adhesives have small gap filling
capabilities. High viscosity adhesives have greater gap filling
abilities. Gel grades have excellent gap filling properties.
Use of cyanoacrylate accelerators can enhance gap-filling abilities,
see page 70.
Cyanoacrylates are 100% adhesive and contain no
solvents. However, cyanoacrylate particles can become airborne
and can settle on surfaces during cure leaving a white residue.
This action is called "blooming". Blooming is minimized
by adequate ventilation at the bondline, selection of special
chemistries and the use of Accelerators.
Less is better. Always use cyanoacrylates sparingly.
One drop is sufficient for bonding approximately one square inch
of surface.
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