Friday, December 11, 2009

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.