Process chemical for use in the production of paper or board

Abstract

The invention relates to a process for producing paper or board from an aqueous fibre suspension, which process includes the step of adding a process chemical to the aqueous fibre suspension, said process chemical being a polymer obtained by controlled radical polymerization technique from an ethylenically unsaturated monomer, a chain transfer agent, and an initiator in a liquid medium or by controlled photopolymerization technique from an ethylenically unsaturated monomer and a photoiniferter in a liquid medium. The process chemical improves the runnability and productivity of the paper or board machine.

1 . A process for producing paper or board from an aqueous fibre suspension, which process comprises adding a process chemical to the aqueous fibre suspension, feeding the obtained aqueous fibre suspension to the headbox of a paper or board machine, feeding the aqueous fibre suspension from the headbox to a wire, dewatering the aqueous fibre suspension on the wire to form a paper or board web, and drying the paper or board web, said process chemical being a polymer obtained by controlled radical polymerization technique, which is Reversible Addition-Fragmentation Chain Transfer (RAFT), Macromolecular Design via Interchange of Xanthates (MADIX), Atom Transfer Radical Polymerization (ATRP) or nitroxide-mediated radical polymerization (NMRP), from an ethylenically unsaturated monomer, a chain transfer agent, and an initiator in a liquid medium or by controlled photopolymerization technique from an ethylenically unsaturated monomer and a photoiniferter in a liquid medium. 
     
     
         2 . The process according to  claim 1  wherein the liquid medium comprises an aqueous solution. 
     
     
         3 . The process according to  claim 1  wherein the radicals in the radical polymerization are generated by thermal means. 
     
     
         4 . The process according to  claim 1  wherein the chain transfer agent comprises a compound having a segment having the formula
   —X—C(═S)—S—  I
 
 wherein X is C, O, N or S. 
 
     
     
         5 . The process according to  claim 4  wherein the chain transfer agent comprises S,S′-bis(α,α′-dimethyl-α″-acetic acid) trithiocarbonate, 4-cyanopentanoic acid dithio-benzoate (CPA) or a salt thereof or 2-(2-methyl-2-thiobenzoylsulfanylpropionylimino)-ethanesulfonate. 
     
     
         6 . The process according to  claim 1  wherein the photoiniferter comprises a compound having a segment having the formula
   —N—C(═S)—S—  II
 
 
     
     
         7 . The process according to  claim 6  wherein the photoiniferter comprises 2-(N,N-diethyldithiocarbamyl)isobutyric acid or 2-(N,N-dimethyldithiocarbamyl)-isobutyric acid or a salt thereof. 
     
     
         8 . The process according to  claim 1  wherein the ethylenically unsaturated monomer comprises acrylamide, acrylic acid, dimethyl acrylamide, 2-(dimethylamino)ethyl methacrylate, [2-(acryloyloxy)ethyl]trimethylammonium chloride, 2-(methacryloyloxy)ethyl]trimethylammonium chloride or diallyldimethylammonium chloride. 
     
     
         9 . The process according to  claim 1  wherein the polymer comprises a homopolymer or copolymer. 
     
     
         10 . The process according to  claim 9  wherein the copolymer comprises a block copolymer or a multiblock copolymer. 
     
     
         11 . The process according to  claim 1  wherein the polymer has a molecular weight in the range of about 1000 to about 1 000 000. 
     
     
         12 . The process according to  claim 1  wherein the polymer is added to the aqueous fibre suspension in an amount of about 25 to 10 000 g/ton of dry matter of the aqueous fibre suspension. 
     
     
         13 . The process according to  claim 1  wherein the process chemical functions as a coagulant or fixative for the binding of disturbing substances to the fibres. 
     
     
         14 . The process according to  claim 1  wherein the aqueous fibre suspension comprises chemical pulp, mechanical pulp, chemo-mechanical pulp, recycled fibres or a mixture thereof. 
     
     
         15 - 16 . (canceled)