A rather surprising feature of one polyester formulated as a metal adhesive, is the high tensile shear strength claimed for it, of the order of 235 kg/cm3 on aluminum alloy, the pressence of ether linkages in the polyester resin is considered to be an important factor in securing this high bond strength.
Polyester base adhesive giving strong bonds on concrete, stone and steel has been described in which two component are mixed in equal ratios, with hardening taking place at 20oC in twenty minutes. In other instance styrene/polyester adhesive is stated to give the high shear strength of 1,880 psi. in bonding a polycarbonate, and a tensile strength of 1,137 psi. in bonding polymethyl styrene.
Isophtalic acid, in partial or total subtitution, has been compared with phthalic acid in unsaturated polyester, and gives among other polyester properties, a higher heat resistance and better adhesive to glass fibres. Futhermore, the adhesion of isophthalic polyester to metal is claimed to be exceptionally good.
If is interesting to note that an early article on dially phthalate polymers sugested their use in the bonding of sanwich constructions. The possibility of the nature of an adherend inhabiting the curing of an unsaturated polyester is a factor to be considered, such as the sulfur in vulcanized rubber and phenolic compound in certain timbers.
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