Process of preparing corrugated paper board with a particular polyvinyl alcohol modified starch-based corrugating adhesive

Claim 1

An improved continuous process of preparing corrugated board consisting of at least one liner and at least one fluted medium, which process includes the steps of (1) continuously applying to the tips of the corrugations of the fluted medium a composition comprising at least 15%, based upon the weight of the total solids on a dry basis, of a potentially adhesive ungelatinized starch and up to 85%, based upon the weight of the total solids on a dry basis, of a viscous gelatinized starch carrier therefor, (2) bringing a liner in contact with the adhesive coated tips of the corrugated medium; and (3) applying heat and pressure to bond said liner and fluted medium, the improvement consisting of employing in said composition from about 2 to about 20 percent, by weight of the total starch present, of polyvinyl alcohol having a degree of hydrolysis of from about 99 to about 100 percent, a 4 percent aqueous solution viscosity at 20° C. of from about 5 to about 60 centipoises, less than about 3 percent by weight cold water solubles at 30° C., at least about 80 percent by weight hot water solubles at 70° C., at least about 95 percent of said polyvinyl alcohol having a particle size less than about 45 microns and substantially all of said polyvinyl alcohol having a particle size less than about 75 microns.