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

Claim 1

A PROCESS FOR PRODUCING AN ESSENTIALLY COLORLESS TRANSLUCENT TO TRANSPARENT HYDROPHILIC SURFACE ON A HYDROPHOBIC FILM ESSENTIALLY COMPOSED OF A HIGHLY POLYMERIC POLYESTER OF (1) AT LEAST ONE DIHYDRIC ALCOHOL OF THE FORMULA HOCH2-WN-CH2OH WHERE W IS A DIVALENT HYDROCARBON RADICAL TAKEN FROM THE GROUP CONSISTING OF METHYLENE, POLYMETHYLENE AND ALKYL-SUBSTITUTED POLYMETHYLENE OF 1-8 CARBON ATOMS AND CYCLOALIPHATIC RADICALS OF 5-6 CARBON ATOMS AND N IS ONE OF THE CARDINAL NUMBERS 0 AND 1 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 (A) CONTACTING AT LEAST ONE SURFACE OF SAID FILM WITH A 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 SELECTED FROM THE GROUP CONSISTING OF CHROMIUM TRIOXIDE, CHROMIC ACID SALTS AND DICHROMIC ACID SALTS EQUIVALENT TO 0.1-4.0 PARTS BY WEIGHT CR2O3 UNTIL A HYDROPHILIC SURFACE IS FORMED ON THE FILM, (B) CONTACTING SAID TREATED SURFACE OF THE FILM WITH AN EXCESS OF WATER FOLLOWED BY (C) CONTACTING SAID RESULTING TREATED SURFACE OF THE FILM WITH A 0.5%-30% AQUEOUS ALKALI METAL HYDROXIDE SOLUTION TO REMOVE RESIDUAL COLOR.