Process for preparing corrugated paperboard

A process for preparing corrugated paperboard comprising the steps of:

• (1) applying to the tips of the corrugations of a fluted paper strip a water-resistant alkaline curing corrugating adhesive composition comprising:
• A. from about 10 to 40%, based on total weight of the adhesive, of starch, this including the ungelatinized as well as the gelatinized portions of the starch;
• B. from about 0.3 to 5%, based on total weight of the starch, of an alkali;
• C. from about 54 to 89%, based on total weight of the adhesive, of water;
• and
• D. from about 0.3 to 10%, based on total weight of the starch, dry basis, of a crosslinking additive prepared by reacting acetone and formaldehyde in a molar ratio of 1 mole of acetone to about 2 to 5.5 moles of formaldehyde under aqueous alkaline conditions at about 20.degree.-80.degree. C. to obtain a water-soluble acetone-formaldehyde condensate containing about 1-10% unreacted formaldehyde;
• adding to the condensate at least an effective amount of dihydroxyethylene urea to react with the unreacted formaldehyde present therein;
• and allowing the reaction to proceed at about 20.degree.-80.degree. C. until the unreacted formaldehyde remaining is reduced to about 0.1-2% by weight;
• and
• (2) applying a facing to the adhesive-coated tips of said fluted paper strip to form an adhesive bond.