Page 472 - Handbook of Adhesives and Sealants

408 Chapter Ten

Polyester hot-melt adhesives are based on terephthalic acid, but
other diacids are also used. Polyester hot-melt resins have a relatively
high melting point of approximately 500 F. Thus, they are generally
used as a heat activated film. They can be formulated to have high
tensile strength and are often employed where high strength and high
temperature resistance are required.

10.4.2.9 Polyolefins. Polyolefins are generally not thought of as ad-
hesives because they are so hard to bond as a substrate. However,
polyolefin resins make excellent hot melt adhesives because they do
have a low surface energy and wet most polymeric and metallic sub-
strates. However, commercial grade standard polyolefin resins cannot
be used in these applications. Standard polyolefin products (film for
example) have low molecular weight constituents that will contribute
to a weak boundary layer. Polyolefins that are used for adhesives are
relatively pure compounds with high molecular weight.
Adhesives that are based on polyolefin resins are used mainly as
hot melt adhesives in either block or film form. In film form, they
provide excellent peel strength as a hot laminating adhesive for plastic
films and metallic foils. Polyethylene adhesive films are also used in
extrusion coating. In this application, a ply of polyethylene is extruded
onto a structure to provide a heat sealing medium for later bonding.

10.4.2.10 Polysulfone. Polysulfone resins, like polyesters, are temper-
ature resistant thermoplastic adhesives that require fairly high tem-
perature for heat activation after all solvents have been removed.
These very tough, high strength resins have excellent resistance to
creep. They maintain their structural strength (more than 60% of
their room temperature strength) up to 375 F. They also have creep
resistance at 300 F. Tensile shear strengths of over 4,000 psi have
been obtained with stainless steel after pressing at 700 F. Polysulfone
adhesives are resistant to strong acids and alkalis. They are attacked
by polar organic solvents and aromatic hydrocarbons.
Polysulfone adhesives have good gap filling properties. They are of-
ten chosen for applications where the high temperature structural
properties of thermosetting adhesives are required, but where the
processing speed and toughness of a thermoplastic are also necessary.

10.4.2.11 Phenoxy. Phenoxy adhesives are thermoplastics similar to
the epoxy family. They are a one component material supplied in pow-
der, pellet, or film form. They can be used as a hot melt or applied as
a solvent solution.
Phenoxy adhesives withstand weathering well and have excellent
resistance to water, alcohols, and aliphatic hydrocarbons. Service tem-