Patent ID: 8753479
Filing Date: 2014-06-17
Classification: D21H

Abstract:
1. A process for producing paper, card and board, the process comprising draining a filler-containing paper stock comprising at least one water-soluble amphoteric copolymer with sheet formation in the wire section and then pressing the paper in the press section to form a product, wherein: a paper stock having a fibrous concentration in the range from 20 to 40 g/l has the at least one water-soluble amphoteric copolymer added to it, then the paper stock is diluted to a fibrous concentration in the range from 5 to 15 g/l, the diluted paper stock is drained to form a sheet, and the sheet is pressed in the press section to a solids content G(x) wt % or greater and G(x) computes according to: where x is a filler content of the product (in wt %) and G(x) is a minimal solids content (in wt %) to which the sheet is pressed; the water-soluble amphoteric copolymer is obtained by polymerizing a mixture of a) 20 to 60 mol % of acrylamide, based on a total number of moles of monomers in the polymerizing, b) 20 to 60 mol %, based on the total number of moles of monomers in the polymerizing, of at least one cationic monomer, c) 20 to 60 mol %, based on the total number of moles of monomers in the polymerizing, of at least one anionic monomer selected from the group consisting of a monoethylenically unsaturated C d) 0 to 30 mol %, based on the total number of moles of monomers in the polymerizing, of one or more monoethylenically unsaturated monomers other than said monomers (a), (b) and (c), and e) 0 to 5 mol %, based on the total number of moles of monomers in the polymerizing, of one or more compounds comprising two or more ethylenically unsaturated double bonds; a difference between the fractions of the cationic monomer and the anionic monomer in mol %, based on the total number of moles of monomers in the polymerizing, is not more than 10 mol %; the at least one cationic monomer b) is selected from the group consisting of an ester of an α,β-ethylenically unsaturated monocarboxylic acid with an amino alcohol, an ester of an α,β-ethylenically unsaturated dicarboxylic acid with an amino alcohol, an amide of an α,β-ethylenically unsaturated monocarboxylic acid with a diamine, an amide of an α,β-ethylenically dicarboxylic acid with a diamine, an N—C the product has an initial wet web strength index of ≧2.9 Nm/g.