Manufacture of wet strength paper

Claim 1

METHOD OF SIZING CELLULOSIC PAPER TO INCREASE IT WET-STRENGTH WHICH COMPRISES MIXING AN AQUEOUS SUSPENSION OF CELLULOSIC PAPER FIBERS HAVING A NEGATIVE ELECTRIC CHARGE WITH A DILUTE AQUEOUS ALKALINE SOLUTION OF A RESIN WHICH IS THE REACTION PRODUCT OF: (1) A WATER-SOLUBLE HEATCONVERTIBLE CONDENSATE OF ONE MOL UREA AND BETWEEN ONE AND FOUR MOLS FORMALDEHYDE AND, (2) A POLYHYDRIC PHENOL HAVING AT LEAST TWO HYDROXYL GROUPS IN A METAL POSITION TO EACH OTHER, EACH HYDROXYL GROUP HAVING AN INDIVIDUAL HYDROGEN ATOM ORTHO THERETO ON THE PHENOLIC RING IN AMOUNT BETWEEN 2 AND 20% BY WEIGHT OF SAID CONDENSATE AND SAID RESIN BEING ONLY PARTLY SOLUBLE IN WATER, BUT SOLUBLE IN AQUEOUS ALKALINE SOLUTIONS, ACIDIFYING THE AQUEOUS MIXTURE OF PAPER FIBERS AND SAID RESIN TO FORM A COLLOIDAL DISPERSION OF THE RESIN WHEREIN THE COLLOIDAL RESIN PARTICLES EXHIBIT A POSITIVE ELECTRIC CHARGE CAUSING RAPID PRECIPITATION OF THE RESIN PARTICLES ON TO THE NEGATIVELY CHARGED PAPER FIBERS, FORMING A SHEET FROM THE PAPER FIBERS AFTER THE RESIN PARTICLES HAVE PRECIPITATED THEREON AND THEN DRYING THE SHEET AT AN ELEVATED TEMPERATURE.