RESIN COMPOSITIONS OF OPTICALLY ISOTROPIC FILMS WITH HIGH SOLVENT RESISTIVITIES

Abstract

In order to prepare transparent and optically isotropic films with high heat and solvent resistivities and good mechanical properties, many kinds of polymer resins were studied. Phenoxy resins crosslinked with isocyanate curing agents were found to give films with desired properties. The following isocyanate curing agents were used: trimethylolpropane adducted with toluenediisocyanate (TDIT), xylene diisocyanate (XDIT), hexamethylene diisocyanate (HDIT). The effects of these curing agents on the properties of resulted films were appreciable, regardless of the degree of the reaction, suggesting the importance of the chemical structure of the curing agent. The films with the best qualities were obtained by TDIT curing. HDIT cured films had high tear strength but were inferior in the heat and solvent resistivities. The superior characteristics of film cured with TDIT may be mainly due to the rigidity of the aromatic rings of TDIT.
The following results were obtained for TDIT cured films: (1) The optimum mole ratio of TDIT to phenoxy resin was between 0.8 and 1.0. (2) In the case of mole ratio 1:1, the empirical relation, logt=5.127-0.026 T was found between curing temperature (T) and aging time required for high solvent resistivity (t). (3) The films cured at 150°C had higher heat resistivity and better mechanical properties than those cured at 90°C, suggesting that higher temperature curing is more effective.