Process for manufacturing paper or cardboard

A process for manufacturing a sheet of paper or cardboard, said process comprising, before said sheet is formed, adding at least one N-vinylformamide polymer, partially hydrolyzed in the form of an inverse emulsion in the presence of an anti-gelling agent, and having a cationic regain of between 30 and 150%, to a fibrous suspension at one or more injection points, the inverse emulsion having a partially hydrolyzed N-vinylformamide polymer/anti-gelling agent weight ratio of between 1,000,000/5,000 and 1,000,000/50,000,

• wherein the anti-gelling agent is sodium bisulfite, and
• wherein the cationic regain is the gain in cationicity between the theoretical and measured cationicity,
• the theoretical cationicity, in meq·g−1, being determined by colorimetric titration of a 5 g·L−1 solution of polymer in water after a high shear rate of 8,000 rpm for 10 minutes,
• the measured cationicity, in meq·g−1, being determined by colorimetric titration of a 5 g·L−1 solution of polymer in water.