Process for manufacturing paper and board having improved retention and drainage properties

A method for manufacturing at least one of a sheet of paper and a board, comprising, before the formation of the at least one of the sheet and the board, the step of adding at least two retention aids to a fibrous suspension, at one or more injection points, the at least two retention aids comprising:

• a main retention aid comprising a (co)polymer having a cationic charge density above 2 meq/g, obtained by the Hofmann degradation reaction, in aqueous solution, in the presence of at least one of an alkaline-earth and alkali hydroxide and of at least one of an alkaline-earth and alkali hypohalide, on a base (co)polymer comprising at least one nonionic monomer selected from the group consisting of acrylarnide, methacrylarnide, N,N dimethylacrylarnide and combinations thereof, and
• a secondary retention aid comprising a water-soluble or water-swellable polymer having an anionic charge density above 0.1 meq/g,
• wherein:
• the main retention aid has a molecular weight of less than 100,000 g/mol, and is introduced into the fibrous suspension in a proportion of 100 to 800 g/t of dry pulp,
• the secondary retention aid is introduced into the fibrous suspension in a proportion of 50 to 800 g/t of dry pulp and has an intrinsic viscosity IV above 3 dl/g,
• the main retention aid is introduced into a thin stock in a concentration not exceeding 2%;
• and
• the introduction of the main and secondary retention aids is separated by a shear step.