3M Adhesive and Tape Classifications
Classify by form
3M adhesives are available as liquids, pastes, tapes, films, and
shaped solids. Each has characteristics to be considered for
application effectiveness and efficiency.
Liquids and pastes readily fill voids to enhance mechanical
adhesion. Many liquids can be sprayed to cover large areas.
Films and pressure sensitive tapes offer advantages unique to their
form:
• Uniform thickness throughout the joint.
• Confinement of the adhesive to the immediate bonding area.
• Clean bonding without dripping or overflow.
• Minimum adhesive waste.
• Die-cut into unique shapes to facilitate bonding of complex
parts with narrow bonding surfaces.
Hot melts are supplied as solid sticks, cartridges, pellets, or similar
shapes. Handling and storage is easy and neat.
Classify by strength
Another classification for industrial applications is by relative
strength and solidification process. Generally, those adhesives that
bond through a chemical reaction are stronger than those that bond
through a physical change.
Structural adhesives bond by chemical reaction.
3M structural strength adhesives bond the load-bearing parts
of a product. As a rule of thumb, structural strength adhesives
reach a minimum of 1,000psi overlap shear strength. 3M
formulations include the following:
•
Epoxy adhesives
are available in one and two-part liquids and
pastes. Of all 3M adhesives, these provide the highest strength
and elevated temperature resistance.
•
Acrylic adhesives
are two-part liquids or pastes that bond the
widest variety of substrates including hard-to-bond plastics and
oily metals. The distinction is high strength bonding without
the surface preparation needed for epoxies and urethanes.
•
Cyanoacrylate adhesives
are high strength liquid formulations
known as instant adhesives. On rigid plastic, glass, metal,
rubber, and other low porosity substrates, they harden in
seconds through reaction with surface moisture.
Non-structural adhesives bond with a physical change.
Non-structural adhesives vary in strength from repositionable
to equal to or greater than the strength of the substrate being
bonded. These adhesives are typically less than 1,000psi and
bond materials in cushions, gaskets, insulation, veneers, and
general assembly. 3M formulations include the following:
•
Hot melt adhesives
melt and flow under heat to wet the
substrates and make bonds quickly upon cooling. Products
are available with a variety of characteristics such as short
set times, sprayable formulas, and permanent PSA properties.
Applications range from sealing to bonding automotive interior
trim.
•
Rubber adhesives
are solvent-based or water-based and solidify
through evaporation of the carrier. Products are designed
for: adhesion to various substrates; a variety of application
methods; and environmental resistance.
•
Contact bond adhesives
are usually rolled, brushed, or sprayed
on the two surfaces to be mated and permitted to become dry
to the touch with a variety of open times. When the surfaces
are pressed together, near ultimate bond strength is achieved.
Pressure sensitive adhesives
Pressure sensitive adhesives (PSAs) found in 3M tapes grip
immediately to mating services. With dwell time, the adhesive
conforms to surface irregularities.
3M hybrid classifications
•
Curing hot melts
(Polyurethane Reactive [PUR] adhesives) are
moisture-curing urethanes that apply like a hot melt adhesive
but cool to bond strength usually associated with two-part
structural adhesives.
•
Reclosable fasteners
combine adhesive and mechanical
fastening principles. Pressure sensitive adhesive permanently
bonds two reclosable mating strips to the substrates that need
to be opened and closed multiple times.
In most cases, adhesives require minimal training, and many
adhesives require little or no investment in major equipment.
Q
Do you want to bond and simultaneously seal between the
substrates?
With many adhesives and tapes, continuous contact between
mating surfaces effectively bonds and seals against dirt, dust,
water, and other environmental conditions. Adhesives and
tapes also provide a film barrier to reduce or prevent bimetallic
corrosion that often occurs in bonding two different types of metal.
Q
Does your part need to be disassembled for maintenance
or service?
When assembled with most adhesives or tapes, parts are generally
difficult or virtually impossible to disassemble without damaging
the part. As an exception, hot melt adhesives can be reheated and
reused, but in most instances reuse would be messy and
impractical. As already noted, repositionable adhesives are
available, but application is restricted to lighter duty attachment
or closure. Reclosable fasteners are a hybrid technology using
mechanical fastening and pressure sensitive adhesive. The adhesive
permanently bonds two reclosable mating strips to the substrates
that need to be opened and closed.
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