Process for making hard, abrasionresistant paperboard

Claim 1

THE PROCESS FOR FABRICATING A HARD, STRONG, ABRASIONRESISTANT SHEET MATERIAL WHICH COMPRISES THE STEPS OF SATURATING A PLURALITY OF CARDBOARD SHEETS SUBSTANTIALLY FREE FROM NATURAL ACIDS WITH AN AQUEOUS SOLUTION CONSISTING PRINCIPALLY OF ONE PART OF ACETIC ACID DISPERSED IN THREE PARTS OF WATER TO ATTAIN A UNIFORM ACID DISTRIBUTION THROUGHOUT THE SHEET, DRYING THE SHEETS FOR ABOUT TWENTYFOUR HOURS, SATURATING THE DRIED SHEETS WITH A UREA RESIN SOLUTION CONTAINING APPROXIMATELY FOUR PARTS OF DIMETHYLOL UREA, ABOUT ONE PART OF UREA, AND ABOUT TEN PARTS WATER BY WEIGHT SO AS TO REACT WITH THE ACID IN THE SHEET, DRYING THE SHEETS FOR ABOUT TWELVE HOURS, SUPERPOSING THE SHEETS AND THEN SUBJECTING THE SUPERPOSED ASSEMBLY OF SHEETS TO NOT LESS THAN TWENTY-FIVE POUNDS PER SQUARE INCH PRESSURE AT A TEMPERATURE OF APPROXIMATELY 300*F.