Paper has voids, and the voids penetrating the paper in its thickness direction, in particular, influence barrier properties against oxygen and steam, or permeability to a coating material. Patent Literature 1 discloses use of a carboxymethylcellulose sodium salt having a degree of carboxymethyl substitution of 0.25 to 0.5 and a viscosity of 5 to 300 mPa·s as an aqueous solution at a concentration of 1%, as a permeation suppressant suppressing permeation of a paint through base paper. As a method for improving the air resistance which is an indicator of voids in paper, Patent Literature 2 discloses base paper for release paper incorporating ungelatinized granular starch. Patent Literature 3 discloses an improver for paper surface quality comprising an anionic polyacrylamide resin.    Patent Document 1: JP 2004-300624 A    Patent Document 2: JP 1992-57798 B    Patent Document 3: JP 2003-49390 A
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