Resin for wet strength paper and process for making it

Claim 1

THE PROCESS FOR THE PRODUCTION OF A STABLE AQUEOUS SOLUTION OF A UREA-FORMALDEHYDE CONDENSATE SELECTIVELY ADSORBABLE FROM ACIDIC AQUEOUS SOLUTIONS BY CELLULOSE FIBERS, WHICH COMPRISES (1) MAINTAINING FROM A PERIOD OF AT LEAST ONE HOUR AT TEMPERATURES IN THE RANGE 10* C. TO 35* C. AN AQUEOUS SOLUTION INITIALLY CONTAINING FORMALDEHYDE AND UREA IN THE MOL RATIO OF 1.65 TO 3 MOLS FORMALDEHYDE FOR EVERY 1 MOL UREA AND AN ACIDIC BUFFER SALT WHICH MAINTAINS THE HYDROGEN ION CONCENTRATION OF SAID SOLUTION WITHIN THE RANGE PH 4.5 TO 6.9, SAID SOLUTION HAVING BEEN PREPARED BY MIXING THE UREA WITH THE FORMALDEHYDE IN AN AQUEOUS SOLUTION HAVING A PH WITHIN THE AFORESAID RANGE AND BEING MAINTAINED AT THE AFORESAID TEMPERATURES AND HYDROGEN ION CONCCENTRATION FOR A PERIOD OF TIME THROUGHOUT WHICH THE REACTION PRODUCTS OF THE UREA AND FORMALDEHYDE REMAIN DISSOLVED IN THE AQUEOUS SOLUTION; (2) THEN HEATING THE LIQUID PRODUCT OF STEP 1 TO TEMPERATURES ABOVE 50* C. AND MAINTAINING IT AT THOSE TEMPERATURES AND AT ACIDITIES IN THE RANGE PH 4.5 TO 6.5 TO CAUSE FURTHER CONDENSATION OF THE UREA AND FORMALDEHYDE; AND (3) COOLING THE THUS HEATED LIQUID REACTION MIXTURE TO ATMOSPHERIC TEMPERATURES AND THUS ARRESTING THE CONDENSATION REACTIONS WHEN THE PRECIPITATION TIME OF THE HEREINDESCRIBED REACTION TIME TEST IS SUBSTANTIALLY AT ITS MINIMUM VALUE FOR SAID REACTION MIXTURE.