Other Properties of Polyester Resin

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 20^oC 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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Properties and Applications of Polyester Resins

One of the first adhesive uses of saturated thermosetting polyester resins was the bonding of mica with glyptals to form electrical insulating materials. Because of certain difficulties associated with the high curing temperature and the removal of water of condensation, they did not find wide acceptance. Interest in the saturated polyesters was, however, revived with the introduction of the polyisocyanate adhesive.

Thermoplastic copolyesters based on mixed saturated dibasic acids, such as sebacic, terephtalic, isophtalic and hexahydrophtalic acids, and glycols have recently been introduced in adhesive compositions. They have created an interest in the shoe industry and in splicing thermoplastic tapes, in particular polyethylene terephtalate photographic film, which cannot easily be joined by solvent action.

Unsaturated polyesters also have certain adhesive uses but they suffer from relatively high shrinkage (compared, for example, with epoxy resins), and severe shrinkage in a bonded object can be the cause of joint failure or result in distortion. A method of reducing shrinkage by the incorporation of a vinyl polymer such as polyestyrene or polyvinyl methyl ether is described. Sugested adhesive applications include the gluing of metals and optical components, and use as binders for abrasive particles. A particularly interesting example of the use of a polyester adhesive is the construction of a steel canal bridge in a chemical works at Marl in Germany.