Process for rendering polyester film receptive to photographic materials and resulting elements

Claim 1

A PROCESS FOR IMPARTING HYDROPHILIC PROPERTIES TO THE SURFACE OF A HYDROPHOBIC FILM ESSENTIALLY COMPOSED OF A HIGHLY POLYMERIC POLYESTER OF (1) AT LEAST ONE DIHYDRIC ALCOHOL OF THE FORMULA HOCH2-W-CH2OH WHEREIN W IS A DIVALENT HYDROCARBON RADICAL SELECTED FROM THE GROUP CONSISTING OF METHYLENE, POLYMETHYLENE AND ALKYL-SUBSTITUTED POLYMETHYLENE OF 0 TO 8 CARBONS AND CYCLOALKYLENE OF 5-6 CARBONS AND (2) AT LEAST ONE DICARBOXYLIC ACID, AT LEAST 15 MOLE PERCENT OF SAID ACID BEING TEREPHTHALIC ACID, UP TO 20 MOLE PERCENT BEING AN ALIPHATIC DICARBOXYLIC ACID AND THE REMAINING DICARBOXYLIC ACID BEING SELECTED FROM THE GROUP CONSISTING OF TEREPHTHALIC ACID AND ISOPHTHALIC ACID, WHICH COMPRISES CONTACTING AT LEAST ONE SURFACE OF SAID FILM FOR A PERIOD UP TO ABOUT 60 SECONDS WITH A TREATMENT SOLUTION COMPRISING 82-98.8 PARTS BY WEIGHT OF H2SO4, 1-14.5 PARTS BY WEIGHT OF WATER AND AN AMOUNT OF CHROMIC ACID YIELDING COMPOUND EQUIVALENT TO 0.1 TO 4.0 PARTS BY WEIGHT CR2O3 SELECTED FROM THE GROUP CONSISTING OF CHROMIUM TRIOXIDE, CHROMIC ACID SALTS AND DICHROMIC ACID SALTS, SAID COMPOUND YIELDING CHROMIC ACID IN WATER CONTAINING SULFURIC ACID, UNTIL A HYDROPHILIC SURFACE IS FORMED ON THE POLYESTER FILM AND CONTACTING THE TREATED SURFACE OF THE FILM WITH AN EXCESS OF WATER.