Page 473 - Handbook of Adhesives and Sealants

Adhesives Families 409

perature ranges from 52 to 180 F. Resistance to creep is high, even
at 176 F. These adhesives provide rigid, tough glue lines with high
adhesive strength. In hot melt form, plasticizers are generally used to
reduce the melt temperature. Good adhesion has been obtained with
copper, brass, steel, aluminum, wood, and many other substrates.
Phenoxy resins are used as structural adhesives for rapid assembly
of metals and rigid materials, for continuous lamination of metal to
metal or wood, and for flexible substrates. Other applications are in
pipe forming, assembly of automotive components, and bonding of
polymeric materials.

10.4.2.12 Acrylic. Thermoplastic acrylics have excellent adhesive
qualities. Acrylic adhesives are available as solutions, as emulsions,
or as polymer-monomer mixtures, which may be cured by ultraviolet
light, heat, or chemical catalysts.
Pressure sensitive adhesives are based on solvent systems. Bonding
consists of drying to the point of tackiness and then joining the two
tacky surfaces. The acrylics have medium water resistance, good re-
sistance to oil and thermal shock, and poor resistance to organic sol-
vents. Temperature resistance varies with the nature of the base
resin. Acrylic adhesives have excellent outdoor weathering and aging
characteristics. One of their main applications is on automobile
‘‘bumper stickers’’ or for outdoor name tags, labels, signs, etc.
Polyacrylate elastomers are used to make high performance pres-
sure sensitive adhesives. These are used for holding a wide variety of
substrates including, automobile identification tags, mounting tape,
protective moldings, etc. These adhesives have excellent strength and
outdoor aging resistance.
Acrylic hot-melt pressure-sensitive adhesives are relatively new.
These adhesives can be applied as a hot melt, but once on the sub-
strate they act as a pressure-sensitive adhesive. In this method of
application, the use of solvent simply as a carrier to apply resin to the
substrate is eliminated. Acrylic hot-melt adhesives provide higher
thermal, oxidative, and UV stability than other hot-melt or pressure-
sensitive adhesives.

10.4.3 Naturally occurring resins
Naturally occurring adhesives are still used today in many applica-
tions. These are usually based on natural organic products or inor-
ganics. They are used primarily when a low cost adhesive is required.
However, some non-polymeric adhesives such as ceramic cements have
very specific properties (e.g., high temperature resistance) that find
use in niche applications.