Production of paper, card and board
View Patent ↗The present invention relates to a process for producing paper, card and board. The present invention is based on the discovery that controlling solids content during the process in a specified manner provide enhanced initial web strength of the paper prior to drying and allows for higher machine speeds in the paper production process as compared to known processes.
1. A process for producing paper, card and board having an enhanced initial wet web strength, comprising:
draining a paper stock comprising filler and at least one water-soluble polymer and having a fibrous concentration of 3.5 to 15 g/l on a wire section to form a sheet, and
pressing the sheet on a press section to a solids content of G(x) wt % or greater, wherein
G(x) is computed by the following equation:
G ( x )=48+( x− 15)·0.4,
x is the numerical value of the filler content of the dry paper, card or board,
the water-soluble polymer is obtainable by Hofmann degradation of an acrylamide- and/or methacrylamide-containing polymer with or without subsequent postcrosslinking, and
the acrylamide- and/or methacrylamide-containing polymer is obtainable by free-radically polymerizing a monomer mixture comprising:
(a) 50 to 90 mol % of acrylamide and/or methacrylamide,
(b) 10 to 50 mol % of one or more monoethylenically unsaturated monomers whose corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation, and/or diallyldimethylammonium chloride, and
(c) optionally up to 1.0 wt %, based on the total weight of monomers (a) and (b), of one or more compounds having two or more ethylenically unsaturated moieties whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation, and
the sheet has an INF index of 3.2 to 3.9 Nm/g.
2. The process of claim 1 , wherein (b) is diallyldimethylammonium chloride.
3. The process of claim 1 , wherein said monoethylenically unsaturated monomers whose corresponding structural unit in the polymer is stable under the reaction conditions of Hofmann degradation are selected from the group consisting of nitriles of α,β-ethylenically unsaturated mono- and dicarboxylic acids, amides of α,β-ethylenically unsaturated monocarboxylic acids and their N-alkyl and N,N-dialkyl derivatives, N-vinyllactams, nitrogenous heterocycles, vinylaromatics, C 2 -C 8 monoolefins, α,β-ethylenically unsaturated mono- and dicarboxylic acids and salts thereof, anhydrides of α,β-ethylenically unsaturated mono- and dicarboxylic acids, ethylenically unsaturated sulfonic acids and salts thereof, and ethylenically unsaturated phosphonic acids and salts thereof.
4. The process of claim 1 , wherein the acrylamide- and/or methacrylamide-containing polymer contains monomer (c).
5. The process of claim 4 , wherein said compounds having two or more ethylenically unsaturated moieties whose corresponding structural units in the polymer are stable under the reaction conditions of Hofmann degradation are selected from the group consisting of methylenebisacrylamides, triallylamine, tetraallylammonium chloride, and N,N′-divinylpropyleneurea.
6. The process of claim 1 , wherein the acrylamide- and/or methacrylamide-containing polymer does not contain monomer (c).
7. The process of claim 1 , further comprising preparing the paper stock comprising filler and at least one water-soluble polymer at a fibrous concentration of 20 to 40 g/l, and diluting the prepared stock comprising filler and at least one water-soluble polymer to a fibrous concentration of 3.5 to 15 g/l.
8. The process of claim 7 , wherein the water-soluble polymer is added to a paper stock comprising filler and having a fibrous concentration of 20 to 40 g/l.
9. The process of claim 7 , wherein the water-soluble polymer is added to a paper stock having a fibrous concentration of 20 to 40 g/l followed by adding the filler.
10. The process of claim 7 , wherein the paper stock comprises a fibrous material having a freeness of ≦30° SR.
11. The process of claim 7 , wherein the water-soluble polymer is added in an amount of 0.05 to 5.00 wt %, based on fibrous material.
12. The process of claim 7 , wherein the water-soluble polymer is obtainable by subsequent postcrosslinking with a crosslinker selected from multifunctional epoxides, multifunctional carboxylic esters, multifunctional isocyanates, multifunctional acrylic or methacrylic esters, multifunctional acrylic or methacrylic amides, epichlorohydrin, multifunctional acyl halides, multifunctional nitriles, α,ω-chlorohydrin ethers of oligo- or polyethylene oxides or of other multifunctional alcohols, divinyl sulfone, maleic anhydride or w-halocarbonyl chlorides, multifunctional haloalkanes and carbonates.
13. The process of claim 1 , wherein the draining of the paper stock on a wire section and the of the sheet on a press section are conducted in a papermaking machine.
14. The process of claim 1 , wherein x ranges from 20 to 40 wt %.
15. The process of claim 1 , wherein x ranges from 20 to 30 wt %.
16. The process of claim 1 , wherein x ranges from 15 to 20 wt %.
17. The process of claim 1 , wherein x ranges from 25 to 40 wt %.
18. The process of claim 1 , wherein the fibrous material has a freeness of 20 to 30° SR.
19. The process of claim 1 , wherein the paper stock contains 0.5 to 50 kg of the at least one water-soluble polymer per metric ton of dry fibrous material.
20. The process of claim 1 , wherein the filler comprises at least one metal oxide, silicate and/or carbonate.