Aqueous copolyester dispersions suited for the subbing of polyester film, subbed polyester film and photographic materials containing a subbed polyester base

摘要

An aqueous copolyester dispersion suitable for the subbing of polyesterfilm without the use of solvents, is characterized in that the copolyester essentially consists of recurring ester groups derived from ethylene glycol and a mixture of terephthalic acid, isophthalic acid and sulphoisophthalic acid whose sulpho group is in salt form, the said acid mixture containing from 20 to 60 mole %of isophthalic acid and from 6 to 10 mole % of said sulphoisophthalic acid, the remainder being terephthalic acid, the copolyester having a glass transition temperature above 45°C and an intrinsic viscosity of from 0.15 to 0.45 dl/g when measured at 25°C in a mixture of phenol/o-dichlorobenzene (60/40 by volume). The sulpho- salt group of the sulphoisophthalic acid may be an alkali metal or onium salt. The aqueous dispersion may be coated onto the polyester film before longitudinal stretching thereof.