Hernon
Cyanoacrylate Adhesives
Instant Bonding Adhesives
Hernon offers a very complete selection of cyanoacrylate
adhesives. Two different categories are offered: Instantbond TM & Quantum (TM). The Instantbond
TM 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 (TM) 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
infleuence 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
adhesives.
Instantbond TM 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 TM cyanoacrylates
require sufficient atmospheric moisture to cure or catalyze the liquid adhesive.
The Instantbond TM 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
TM cyanoacrylate types. Hernon's Quantum (TM) 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" ox jelly-like consistency. Gels do
not 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 chemistxies, and the use of
Accelerators.
Less is better. Always use cyanoacrylates sparingly. One drop is sufficient for bonding
approximately one square inch of surface. |
