Patent ID: 6375775
Filing Date: 2002-04-23
Classification: C08G,C08L,C09J,Y10T

Abstract:
A process for preparing corrugated paperboard comprising the steps of:a) applying to the tips of the corrugations of a fluted paper strip, a water-resistant, viscosity stable alkaline curing, starch-based corrugating adhesive composition comprising: i) from about 10 to 40% by weight, based on the total weight of the adhesive, of starch; ii) from about 0.3 to 5% by weight, based on the total weight of starch, of an alkali; iii) from about 0.3 to 12% by weight, dry basis, based on the weight of starch, of a crosslinking additive prepared by reacting a ketone and formaldehyde in a molar ratio of 1 mole of ketone to about 1.5 to 6 moles of formaldehyde under aqueous alkaline conditions at about 20 to 80Â° C. to obtain a water-soluble ketone-formaldehyde condensate containing about 1 to 4% by weight of unreacted formaldehyde and wherein from about 2 to 6.5 parts by weight of a water-soluble alkali metal or alkaline earth metal sulfite per part by weight of unreacted formaldehyde is added to the condensate to react with the unreacted formaldehyde present and allowing the reaction to proceed at about 20 to 45Â° C. at a pH of about 5 to 9 until the unreacted formaldehyde is reduced to less than about 0.6% by weight, based on the weight of condensate, and iv) from about 54 to 89% by weight of water, based on the total weight of the adhesive; wherein the viscosity of the adhesive composition does not increase more than 32% over 24 hours; andb) applying a facing to the adhesive coated tips of the fluted paper strip to form an adhesive bond.