Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
  • D21H23/04—Addition to the pulp; After-treatment of added substances in the pulp
  • D21H23/06—Controlling the addition
  • D21H23/14—Controlling the addition by selecting point of addition or time of contact between components
  • D21H23/18—Addition at a location where shear forces are avoided before sheet-forming, e.g. after pulp beating or refining
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/37—Polymers of unsaturated acids or derivatives thereof, e.g. polyacrylates
  • D21H17/375—Poly(meth)acrylamide
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/41—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups
  • D21H17/42—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups anionic
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/41—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups
  • D21H17/44—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups cationic
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
  • D21H17/68—Water-insoluble compounds, e.g. fillers, pigments siliceous, e.g. clays
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/06—Paper forming aids
  • D21H21/10—Retention agents or drainage improvers
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/76—Processes or apparatus for adding material to the pulp or to the paper characterised by choice of auxiliary compounds which are added separately from at least one other compound, e.g. to improve the incorporation of the latter or to obtain an enhanced combined effect
  • D21H23/765—Addition of all compounds to the pulp

Definitions

• the present invention relates to a process for the production of paper. More specifically, the invention relates to a process for the production of paper which comprises adding first, second and third polymers to an aqueous cellulosic suspension after all points of high shear and dewatering the obtained suspension to form paper.
• an aqueous suspension containing cellulosic fibres, and optional fillers and additives referred to as stock
• stock is fed through pumps, screens and cleaners, which subject the stock to high shear forces, into a headbox which ejects the stock onto a forming wire.
• Water is drained from the stock through the forming wire so that a wet web of paper is formed on the wire, and the web is further dewatered and dried in the drying section of the paper machine.
• Drainage and retention aids are conventionally introduced at different points in the flow of stock in order to facilitate drainage and increase adsorption of fine particles such as fine fibres, fillers and additives onto the cellulose fibres so that they are retained with the fibres on the wire.
• Examples of conventionally used drainage and retention aids include organic polymers, inorganic materials, and combinations thereof.
• US 6,103,065 discloses a method for improving the retention and drainage of papermaking furnish comprising the steps of adding at least one cationic high charge density polymer of molecular weight 100,000 to 2,000,000 to said furnish after the last point of high shear; adding at least one polymer having a molecular weight greater than 2,000,000; and adding a swellable bentonite clay.
• EP 1 238 161 B1 discloses a process for making paper or paper board in which a cellulosic suspension is flocculated by addition to a thin stock stream of the cellulosic suspension of a substantially water-soluble cationic synthetic polymer of intrinsic viscosity of at least 4 dl/g, wherein the flocculated cellulosic suspension is subjected to mechanical shearing and then reflocculated by addition subsequent to the centri-screen of a reflocculating system comprising (i) a siliceous material and (ii) a substantially water soluble anionic polymer of intrinsic viscosity of at least 4 dl/g.
• the process is claimed to provide improvements in retention and drainage.
• WO 2004/015200 discloses a method for producing paper and board by shearing the paper material, adding a microparticle system made of cationic polymers and a fine- particle inorganic component to the paper material following the last shearing step before agglomerating the material, dewatering the paper material so as to form sheets, and drying said sheets.
• the method is claimed to provide improvements in retention and drainage.
• the present invention is directed to a process for producing paper which comprises: (i) providing an aqueous suspension comprising cellulosic fibres, (ii) adding to the suspension after all points of high shear: a first polymer being a cationic polymer having a charge density above 4.0 meq/g; a second polymer having a molecular weight above 500,000; and a third polymer being an anionic polymer; and (iii) dewatering the obtained suspension to form paper.
• the present invention is also directed to a process for producing paper which comprises: (i) providing an aqueous suspension comprising cellulosic fibres, (ii) adding to the suspension after all points of high shear: a first polymer being a cationic, acrylamide-based polymer having a charge density above 2.5 meq/g; a second polymer being an acrylamide-based polymer having a molecular weight above 500,000; and a third polymer being an anionic polymer; and (iii) dewatering the obtained suspension to form paper.
• the present invention is further directed to a process for producing paper which comprises: (i) providing an aqueous suspension comprising cellulosic fibres, (ii) adding to the suspension after all points of high shear: a first polymer being a cationic polymer having a charge density above 2.5 meq/g; a second polymer being a water-dispersible polymer; and a third polymer being an anionic polymer; and (iii) dewatering the obtained suspension to form paper.
• a process for producing paper which comprises: (i) providing an aqueous suspension comprising cellulosic fibres, (ii) adding to the suspension after all points of high shear: a first polymer being a cationic polymer having a charge density above 2.5 meq/g; a second polymer being a water-dispersible polymer; and a third polymer being an anionic polymer; and (iii) dewatering the obtained suspension to form paper.
• the present invention it has been found that drainage and retention can be improved without any significant impairment of formation, or even with improvements in paper formation, by a process which comprises adding drainage and retention aids comprising first, second and third polymers to a cellulosic suspension after all points of high shear and then dewatering the obtained suspension to form paper.
• the present invention provides improvements in drainage and retention in the production of paper from all types of stocks, in particular stocks containing mechanical or recycled pulp, and stocks having high contents of salts (high conductivity) and colloidal substances, and in papermaking processes with a high degree of white water closure, i.e. extensive white water recycling and limited fresh water supply.
• the present invention makes it possible to increase the speed of the paper machine and to use lower dosages of polymers to give corresponding drainage and/or retention effects, thereby leading to an improved papermaking process and economic benefits.
• drainage and retention aids refers to two or more components which, when added to an aqueous cellulosic suspension, give better drainage and retention than is obtained when not adding the said two or more components.
• the first polymer according to the present invention is a cationic polymer haying a charge density of at least 2.5 meq/g, suitably at least 3.0 meq/g, preferably at least 4.0 meq/g.
• the charge density is in the range of from 2.5 to 10.0, preferably from 3.0 to 8.5 meq/g.
• the first polymer can be selected from inorganic and organic cationic polymers.
• the first polymer is water-soluble.
• suitable first polymers include polyaluminium compounds, e.g. polyaluminium chlorides, polyaluminium sulphates, polyalu- minium compounds containing both chloride and sulphate ions, polyaluminium silicate- sulphates, and mixtures thereof.
• suitable first polymers include cationic organic polymers, e.g. cationic acrylamide-based polymers; poly(diallyldialkyl ammonium halides), e.g. poly(diallyldimethyl ammonium chloride); polyethylene imines; polyamidoamines; polyamines; and vinylamine- based polymers.
• suitable cationic organic polymers include polymers prepared by polymerization of a water-soluble ethylenically unsaturated cationic monomer or, preferably, a monomer mixture comprising one or more water-soluble ' ethylenically unsaturated cationic monomers and optionally one or more other water-soluble ethylenically unsaturated monomers.
• Suitable water-soluble ethylenically unsaturated cationic monomers include diallyldialkyl ammonium halides, e.g. diallyldimethyl ammonium chloride and cationic monomers represented by the general structural formula (I):
• R 4 wherein R-i is H or CH 3 ;
• R 2 and R 3 are each H or, preferably, a hydrocarbon group, suitably alky!, having from 1 to 3 carbon atoms, preferably 1 to 2 carbon atoms;
• A is O or NH;
• B is an alkyl or alkyiene group having from 2 to 8 carbon atoms, suitably from 2 to 4 carbon atoms, or a hydroxy propylene group;
• R 4 is H or, preferably, a hydrocarbon group, suitably alkyl, having from 1 to 4 carbon atoms, preferably 1 to 2 carbon atoms, or a substituent containing an aromatic group, suitably a phenyl or substituted phenyl group, which can be attached to the nitrogen by means of an alkyiene group usually having from 1 to 3 carbon atoms, suitably
• R 4 including a benzyl group (-CH 2 -C 6 H 5 ); and X " is an anionic counterion, usually a halide like chloride.
• Suitable monomers represented by the general structural formula (I) include quaternary monomers obtained by treating dialkylaminoalkyl (meth)acrylates, e.g. dimethyl- aminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate and dimethylaminohydroxypropyl (meth)acrylate, and dialkyiaminoalkyl (meth)acrylamides, e.g.
• Preferred cationic monomers of the general formula (I) include dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt and dimethylaminoethyl methacrylate benzyl chloride quaternary salt.
• the monomer mixture can contain one or more water-soluble ethylenically unsaturated non- ionic monomers.
• suitable copolymerizable non-ionic monomers include acrylamide and acrylamide-based monomers, e.g. methacrylamide, N-alkyl (meth)acrylamides, e.g.
• the monomer mixture can also contain one or more water-soluble ethylenically unsaturated anionic or potentially anionic monomers, preferably in minor amounts.
• the term "potentially anionic monomer”, as used herein, is meant to include a monomer bearing a potentially ionisable group which becomes anionic when included in a polymer on application to the cellulosic suspension.
• suitable copolymerizable anionic and potentially anionic monomers include ethylenically unsaturated carboxylic acids and salts thereof, e.g. (meth)acrylic acid and salts thereof, suitably sodium (meth)acrylate, ethylenically unsaturated sulphonic acids and salts thereof, e.g. 2-acrylamido ⁇ 2-methylpropanesulphonate ⁇ sulphoethyl-(meth)acrylate, vinylsulphonic acid and salts thereof, styrenesulphonate, and paravinyl phenol (hydroxy styrene) and salts thereof.
• preferred copolymerizable monomers include acrylamide and methacrylamide, i.e.
• (meth)acrylamide examples include cationic acrylamide-based polymer, i.e. a cationic polymer prepared- from a monomer mixture comprising one or more of acrylamide and acrylamide-based monomers
• the first polymer in the form of a cationic organic polymer can have a weight average molecular weight of at least 10,000, often at least 50,000. More often, it is at least 100,000 and usually at least about 500,000, suitably at least about 1 million and preferably above about 2 million. The upper limit is not critical; it can be about 30 million, usually 20 million.
• the second polymer according to the present invention is preferably an organic polymer which can be selected from non-ionic, cationic, anionic and amphoteric polymers.
• the second polymer can be water-soluble or water-dispersible.
• the second polymer is prepared by polymerization of one or more ethylenically unsaturated monomers, preferably one or more water-soluble ethylenically unsaturated monomers. Examples of preferred second polymers include acrylamide-based polymers.
• suitable second polymers include water-soluble and water-dispersible non-ionic organic polymers obtained by polymerizing one or more water-soluble ethylenically unsaturated non-ionic monomers.
• suitable non-ionic monomers include acrylamide and the above-mentioned non-ionic acrylamide-based and acrylate-based monomers and vinylamines.
• preferred non-ionic monomers include, acrylamide and methacrylamide, i.e., (meth)acrylamide, and examples of preferred second polymers include non-ionic acrylamide-based polymer.
• suitable second polymers include cationic organic polymers obtained by polymerizing a water-soluble ethylenically unsaturated cationic monomer or, preferably, a monomer mixture comprising one or more water-soluble ethylenically unsaturated cationic monomers and optionally one or more other water-soluble ethylenically unsaturated monomers.
• suitable cationic monomers include those represented by the above-mentioned general structural formula (I), wherein R 1 , R 2 , R 3 , R 4 , A, B and X " are as defined above, and diallyldialkyl ammonium halides, e.g. diallyldimethyl ammonium chloride.
• the monomer mixture can contain one or more water-soluble ethylenically unsaturated non- ionic monomers.
• suitable copolymerizable non-ionic monomers include acrylamide and the above-mentioned non-ionic acrylamide-based and acrylate-based monomers and vinylamines.
• the monomer mixture can also contain one or more water- soluble ethylenically unsaturated anionic or potentially anionic monomers, preferably in minor amounts.
• suitable copolymerizable anionic and potentially anionic monomers include ethylenically unsaturated carboxylic acids and salts thereof, and ethylenically unsaturated sulphonic acids and salts thereof, e.g. any one of those mentioned above.
• preferred copolymerizable monomers include acrylamide and methacrylamide,. i.e.' (meth)acrylamide, and examples of preferred second polymers include cationic acrylamide-based polymer.
• suitable second polymers include anionic organic polymers obtained by polymerizing a water-soluble ethylenically unsaturated anionic or potentially anionic monomer or, preferably, a monomer mixture comprising one or more water-soluble ethylenically unsaturated anionic or potentially anionic monomers and optionally one or more other water- soluble ethylenically unsaturated monomers.
• suitable anionic and potentially anionic monomers include ethylenically unsaturated carboxylic acids and salts thereof, and ethylenically unsaturated sulphonic acids and salts thereof, e.g. any one of those mentioned above.
• the monomer mixture can contain one or more water-soluble ethylenically unsaturated non-ionic monomers.
• suitable copolymerizable non-ionic monomers include acrylamide and the above-mentioned non-ionic acrylamide-based and acrylate-based monomers and vinylamines.
• the monomer mixture can also contain one or more water- soluble ethylenically unsaturated cationic and potentially cationic monomers, preferably in minor amounts.
• the term "potentially cationic monomer”, as used herein, is meant to include a monomer bearing a potentially ionisable group which becomes cationic when included in a polymer on application to the cellulosic suspension.
• suitable copolymerizable cationic and potentially cationic monomers include the monomers represented by the above general structural formula (I) and diallyldialkyl ammonium halides, e.g. diallyldimethyl ammonium chloride.
• suitable copolymerizable monomers include (meth)acrylamide, and examples of preferred second polymers include anionic acrylamide- based polymer.
• suitable second polymers include amphoteric organic polymers obtained by polymerizing a monomer mixture comprising one or more water-soluble ethylenically unsaturated anionic or potentially anionic monomers and one or more water-soluble ethylenically unsaturated cationic ' or potentially cationic monomers, and optionally one or more other water-soluble ethylenically unsaturated monomers.
• suitable anionic and potentially anionic monomers include ethylenically unsaturated carboxylic acids and salts thereof, and ethylenically unsaturated sulphonic acids and salts thereof, e.g. any one of those mentioned above.
• Suitable cationic and potentially cationic monomers include the monomers represented by the above general structural formula (I) and diallyldialkyl ammonium halides, e.g. diallyldimethyl ammonium chloride.
• the monomer mixture can contain one or more water-soluble ethylenically unsaturated non-ionic monomers.
• suitable copolymerizable non-ionic monomers include acrylamide and the above- mentioned non-ionic acrylamide-based and acrylate-based monomers and vinylamines.
• Examples of preferred copolymerizable monomers include (meth)acrylamide, and examples of preferred second polymers include amphoteric acrylamide-based polymer.
• the monomer mixture can also contain one or more polyfunctional crosslinking agents in addition to the above-mentioned ethylenically unsaturated monomers.
• the presence of a polyfunctional crosslinking agent in the monomer mixture renders possible preparation of second polymers that are water-dispersible.
• the polyfunctional crosslinking agents can be non-ionic, cationic, anionic or amphoteric.
• suitable polyfunctional crosslinking agents include compounds having at least two ethylenically unsaturated bonds, e.g.
• N,N-methylene-bis(meth)acrylamide polyethyleneglycol di(meth)acrylate, N-vinyl (meth)acrylamide, divinylbenzene, triallylammonium salts and N-methylaily!(rneth)acrylamide
• compounds having an ethylenically unsaturated bond and a reactive group e.g. glycidyl (meth)acrylate, acrolein and methylol(meth)acrylamide
• compounds having at least two reactive groups e.g. dialdehydes like glyoxal, diepoxy compounds and epichlorohydrin.
• Suitable water-dispersible second polymers can be prepared using at least 4 molar parts per million of polyfunctional crosslinking agent based on monomer present in the monomer mixture, or based on monomeric units present in the polymer, preferably from about 4 to about 6,000 molar parts per million, most preferably from 20 to 4,000.
• suitable water-dispersible organic polymers include those disclosed in U.S. Patent No. 5,167,766, which is hereby incorporated herein by reference.
• Further examples of suitable second polymers include water-dispersible anionic, cationic and amphoteric organic polymers, and preferred second polymers include water-dispersible anionic organic polymers, preferably water-dispersible anionic acrylamide- based polymers.
• the second polymers according to the invention can have a weight average molecular weight of at least about 500,000.
• the weight average molecular weight is at least about 1 million, suitably at least about 2 million and preferably at least about 5 million.
• the upper limit is not critical; it can be about 50 million, usually 30 million.
• the second polymer according to the invention can have a charge density less than about 10 meq/g, suitably less than about 6 meq/g, preferably less than about 4 meq/g, more preferably less than 2 meq/g.
• the charge density is in the range of from 0.5 to 10.0, preferably from 1.0 to 4.0 meq/g.
• Suitable second polymers include anionic organic polymers having a charge density less than 10.0 meq/g, suitably less than 6.0 meq/g, preferably less than 4.0 meq/g.
• Suitable second polymers further include cationic organic polymers having a charge density less than 6.0 meq/g, suitably less than 4.0 meq/g, preferably less than 2.0 meq/g.
• the third polymer according to the present invention is an anionic polymer which can be selected from inorganic and organic anionic polymers.
• suitable the third polymers include water-soluble and water-dispersible inorganic and organic anionic polymers.
• suitable third polymers include inorganic anionic polymers based on silicic acid and silicate, i.e., anionic silica-based polymers.
• Suitable anionic silica-based polymers can be prepared by condensation polymerisation of siliceous compounds, e.g. silicic acids and silicates, which can be homopolymerised or co-polymerised.
• the anionic silica- based polymers comprise anionic silica-based particles that are in the colloidal range of particle size.
• Anionic silica-based particles are usually supplied in the form of aqueous colloidal dispersions, so-called sols.
• the silica-based sols can be modified and contain other elements, e.g.
• silica-based particles aluminium, boron, nitrogen, zirconium, gallium and titanium, which can be present in the aqueous phase and/or in the silica-based particles.
• suitable anionic silica-based particles include polysilicic acids, polysilicic acid microgels, polysiiicates, polysilicate microgels, colloidal silica, colloidal aluminium-modified silica, polyaluminosilicates, polyaluminosiiicate microgels, polyborosilicates, etc.
• suitable anionic silica-based particles include those disclosed in U.S. Patent Nos.
• Suitable anionic silica-based particles include those having an average particle size below about 100 nm, preferably below about 20 nm and more preferablyin the range of from about 1 to about 10 nm.
• the particle size refers to the average size of the primary particles, which may be aggregated or non-aggregated.
• the anionic silica-based polymer comprises aggregated anionic silica-based particles.
• the specific surface area of the silica-based particles is suitably at least 50 m 2 /g and preferably at least 100 m 2 /g. Generally, the specific surface area can be up to about 1700 m 2 /g and preferably up to 1000 m 2 /g.
• the specific surface area is measured by means of titration with NaOH as described by G.W. Sears in Analytical Chemistry 28(1956): 12, 1981-1983 and in U.S. Patent No. 5,176,891 after appropriate removal of or adjustment for any compounds present in the sample that may disturb the titration like aluminium and boron species. The given area thus represents the average specific surface area of the particles.
• the anionic silica-based particles have a specific surface area within the range of from 50 to 1000 m 2 /g, more preferably from 100 to 950 m 2 /g.
• the silica-based particles are present in a sol having a S-value in the range of from 8 to 50 %, preferably from 10 to 40%, containing silica-based particles with a specific surface area in the range of from 300 to 1000 m 2 /g, suitably from 500 to 950 m z /g, and preferably from 750 to 950 m 2 /g, which sols can be modified as mentioned above.
• the S- value is measured and calculated as described by Her & Dalton in J. Phys. Chem. 60(1956),
• the S-value indicates the degree of aggregation or microgel formation and a lower
• S-value is indicative of a higher degree of aggregation.
• the silica-based particles have a high specific surface area, suitably above about 1000 m 2 /g.
• the specific surface area can be in the range of from 1000 to 1700 m 2 /g and preferably from 1050 to 1600 m 2 /g.
• suitable third polymers include water-soluble and water-dispersible organic anionic polymers obtained by polymerizing an ethylenically unsaturated anionic or potentially anionic monomer or, preferably, a monomer mixture comprising one or more ethylenically unsaturated anionic or potentially anionic monomers, and optionally one or more other ethylenically unsaturated monomers.
• the ethylenically unsaturated monomers are water-soluble.
• suitable anionic and potentially anionic monomers include ethylenically unsaturated carboxylic acids and salts thereof, ethylenically unsaturated sulphonic acids , and salts thereof, e.g. any one of those mentioned above.
• the monomer mixture can contain one or more water-soluble ethylenically unsaturated non-ionic monomers.
• suitable copolymerizable non-ionic monomers include acrylamide and the above-mentioned non-ionic acrylamide-based and acrylate-based monomers and vinylamines.
• the monomer mixture can also contain one or more water-soluble ethylenically unsaturated cationic and potentially cationic monomers, preferably in minor amounts.
• suitable copolymerizable ' cationic monomers include the monomers represented by the above general structural formula (I) and diallyldialkyl ammonium halides, e.g. diallyl- dimethyl ammonium chloride.
• the monomer mixture can ' also contain one or more polyfunctional crosslinking agents.
• a polyfunctional crosslinking agent in the monomer mixture renders possible preparation of third polymers that are water-dispersible.
• suitable polyfunctional crosslinking agents including the above-mentioned polyfunctional crosslinking agents. These agents can be used in the above-mentioned amounts.
• suitable water-dispersible organic anionic polymers include those disclosed in U.S. Patent No. 5,167,766, which is incorporated herein by reference.
• Examples of preferred copolymerizable monomers include (meth)acrylamide, and examples of preferred third polymers include water-soluble and water-dispersible anionic acrylamide- based polymers.
• the third polymer being an organic anionic polymer according to the invention preferably an organic anionic polymer that is water-soluble, has a weight average molecular weight of at least about 500,000.
• the weight average molecular weight is at least about 1 million, suitably at least about 2 million and preferably at least about 5 million.
• the upper limit is not critical; it can be about 50 million, usually 30 million.
• the third polymer being an organic anionic polymer can have a charge density less than about 14 meq/g, suitably less than about 10 meq/g, preferably less than about 4 meq/g.
• the charge density is in the range of from 1.0 to 14.0, preferably from 2.0 to 10.0 meq/g.
• Examples of preferred drainage and retention aids according to the invention include:
• first polymer being cationic acrylamide-based polymer
• second polymer being cationic acrylamide-based polymer
• third polymer being anionic silica-based particles
• first polymer being cationic polyaluminium compound, second polymer being cationic acrylamide-based polymer, and third polymer being anionic silica-based particles;
• first polymer being cationic acrylamide-based polymer, second polymer being water-soluble or water-dispersible anionic acrylamide-based polymer, and third polymer being anionic silica-based particles;
• first polymer being cationic polyaluminium compound, second polymer being water- soluble or water-dispersible anionic acrylamide-based polymer, and third polymer being anionic silica-based particles;
• first polymer being cationic acrylamide-based polymer
• second polymer being cationic acrylamide-based polymer
• third polymer being water-soluble or water- dispersible anionic acrylamide-based polymer
• first polymer being cationic polyaluminium compound
• second polymer being cationic acrylamide-based polymer
• third polymer being water-soluble or water- dispersible anionic acrylamide-based polymer
• the first, second and third polymers are added to the aqueous cellulosic suspension after it has passed through all stages of high mechanical shear and prior to drainage.
• high shear stages include pumping and cleaning stages.
• shearing stages are included when the cellulosic suspension is passed through fan pumps, pressure screens and centri-screens.
• the last point of high shear occurs at a centri-screen and, consequently, the first, second and third polymers are suitably added subsequent to the centri-screen.
• the cellulosic suspension is fed into the headbox which ejects the suspension onto the forming wire for drainage.
• additional materials in the process of the present invention.
• these materials are added to the cellulosic suspension before it is passed through the last point of high shear.
• additional materials include starches, e.g. cationic, anionic and amphoteric starch, preferably cationic starch; water- soluble organic polymeric coagulants, e.g. cationic polyamines, polyamideamines, polyethylene imines, dicyandiamide condensation polymers and low molecular weight highly cationic vinyl addition polymers; and inorganic coagulants, e.g. aluminium compounds, e.g. alum and polyaluminium compounds.
• starches e.g. cationic, anionic and amphoteric starch, preferably cationic starch
• water- soluble organic polymeric coagulants e.g. cationic polyamines, polyamideamines, polyethylene imines, dicyandiamide condensation polymers and low molecular weight highly cationic vinyl addition polymers
• the first, second and third polymers can be separately added to the cellulosic suspension.
• the first polymer is added to the cellulosic suspension prior to adding the second and third polymers.
• the second polymer can be added prior to, simultaneously with or after adding the third polymer.
• the first polymer is suitably added to the cellulosic suspension simultaneously with the second polymer and then the third polymer is added.
• the first, second and third polymers according to the invention can be added to the cellulosic suspension to be dewatered in amounts which can vary within wide limits. Generally, the first, second and third polymers are added in amounts that give better drainage and retention than is obtained when not adding the polymers.
• the first polymer is usually added in an amount of at least about 0.001 % by weight, often at least about 0.005 % by weight, calculated as dry polymer on dry cellulosic suspension, and the upper limit is usually about 2.0 and suitably about 1.5 % by weight.
• the second polymer is usually added in an amount of at least about 0.001 % by weight, often at least about 0.005 % by weight, calculated as dry polymer on dry cellulosic suspension, and the upper limit is usually about 2.0 and suitably about 1.5 % by weight.
• the third polymer is usually added in an amount of at least about 0.001 % by weight, often at least about 0.005 % by weight, calculated as dry polymer or dry SiO 2 on dry cellulosic suspension, and the upper limit is usually about 2.0 and suitably about 1.5 % by weight.
• such additives can be added in an amount of at least about 0.001% by weight, calculated as dry additive on dry cellulosic suspension.
• the amount is in the range of from about 0.05 up to about 3.0%, prefer- ably in the range from about 0.1 up to about 2.0%.
• the process of this invention is applicable to all papermaking processes and cellulosic suspensions, and it is particularly useful in the manufacture of paper from a stock that has a high conductivity.
• the conductivity of the stock that is dewatered on the wire is usually at least about 1.5 mS/cm, preferably at least 3.5 mS/cm, and more preferably at least 5.0 mS/cm.
• Conductivity can be measured by standard equipment such as, for example, a WTW LF 539 instrument supplied by Christian Berner.
• the present invention further encompasses papermaking processes where white water is extensively recycled, or recirculated, i.e. with a high degree of white water closure, for example where from 0 to 30 tons of fresh water are used per ton of dry paper produced, usually less than 20, preferably less than 15, more preferably less than 10 and notably less than 5 tons of fresh water per ton of paper.
• Fresh water can be introduced in the process at any stage; for example, fresh water can be mixed with cellulosic fibers in order to form a cellulosic suspension, and fresh water can be mixed with a thick cellulosic suspension to dilute it so as to form a thin cellulosic suspension to which the first, second and third polymers are added.
• the process according to the invention is used for the production of paper.
• paper as used herein, of course include not only paper and the production thereof, but also other web-like products, such as for example board and paperboard, and the production thereof.
• the process can be used in the production of paper from different types of suspensions of cellulosic fibers, and the suspensions should preferably contain at least 25% and more preferably at least 50% by weight of such fibers, based on dry substance.
• the suspensions can be based on fibers from chemical pulp, such as sulphate and sulphite pulp, thermo- mechanicai pulp, chemo-thermomechanical pulp, organosolv pulp, refiner pulp or groundwood pulp from both hardwood and softwood, or fibers derived from one year plants like elephant grass, bagasse, flax, straw, etc., and can also be used for suspensions based on recycled fibers.
• chemical pulp such as sulphate and sulphite pulp, thermo- mechanicai pulp, chemo-thermomechanical pulp, organosolv pulp, refiner pulp or groundwood pulp from both hardwood and softwood, or fibers derived from one year plants like elephant grass, bagasse, flax, straw, etc.
• the invention is preferably applied to processes for making paper from wood-containing suspensions.
• the suspension also contain mineral fillers of conventional types, such as, for example, kaolin, clay, titanium dioxide, gypsum, talc and both natural and synthetic calcium carbonates, such as, for example, chalk, ground marble, ground calcium carbonate, and precipitated calcium carbonate.
• the stock can of course also contain papermaking additives of conventional types, such as wet-strength agents, sizing agents, such as those based on rosin, ketene dimers, ketene multimers, alkenyl succinic anhydrides, etc.
• the invention is applied on paper machines producing wood-containing paper and paper based on recycled fibers, such as SC, LWC and different types of book and newsprint papers, and on machines producing wood-free printing and writing papers, the term wood-free meaning less than about 15% of wood-containing fibers.
• recycled fibers such as SC, LWC and different types of book and newsprint papers
• wood-free printing and writing papers the term wood-free meaning less than about 15% of wood-containing fibers.
• preferred applications of the invention include the production of paper and layer of multilayered paper from cellulosic suspensions containing at least 50 % by weight of mechanical and/or recycled fibres.
• the invention is applied on paper machines running at a speed of from 300 to 3000 m/min and more preferably from 500 to 2500 m/min.
• C-PAM 1 Cationic acrylamide-based polymer prepared by polymerisation of acrylamide (40 mole%) and acryloxyethyltrimethyl ammonium chloride (60 mole%), the polymer having a weight average molecular weight of about 3 million and cationic charge density of about 4.2 meq/g.
• C-PAM 2 Cationic acrylamide-based polymer prepared by polymerisation of acrylamide (60 mole%) and acryloxyethyltrimethyl ammonium chloride (40 mole%), the polymer having a weight average molecular weight of about 3 million and cationic charge of about 3.3 meq/g.
• C-PAM 3 Cationic acrylamide-based polymer prepared by polymerisation of acrylamide (88 mole%), acryloxyethyltrimethyl ammonium chloride (10 mole%) and dimethyl acrylamide (2 mole%), the polymer having a weight average molecular weight of about 6 million and cationic charge density of about 1.2 meq/g.
• C-PAM 4 Cationic acrylamide-based polymer prepared by polymerisation of acrylamide (90 mole%) and acryloxyethyltrimethyi ammonium chloride (10 mole%), the polymer having a wejght average molecular weight of about 6 million and cationic charge density of about 1.2 meq/g.
• PAC Cationic polyaluminium chloride with a cationic charge density of about 8.0 meq/g
• C-PAI 1 Cationic polyamine having a weight average molecular weight of about 200,000 and cationic charge density of about 7 meq/g.
• C-PAI 2 Cationic polyamine having a weight average molecular weight of about
• A-PAM Anionic acrylamide-based polymer prepared by polymerisation of acrylamide (80 mole%) and acrylic acid (20 mole%), the polymer having a weight average molecular weight of about 12 million and anionic charge density of about 2.6 meq/g.
• A-X-PAM Anionic crosslinked acrylamide-based polymer prepared by polymerisation of acrylamide (30 mole%) and acrylic acid (70 mole%), the polymer having a weight average molecular weight of about 100,000 and anionic charge density of about 8.0 meq/g.
• Silica Anionic inorganic condensation polymer of silicic acid in the form of colloidal aluminium-modified silica sol having an S value of about 21 and containing silica-based particles with a specific surface area of about 800 m 2 /g.
• Bentonite Bentonite
• DDA Dynamic Drainage Analyser
• the stock used in the tests was based on 75% TMP and 25% DIP fibre material and sedimented white water from a newsprint mill. Stock consistency was 0.78%. Conductivity of the stock was 1.5 mS/cm and pH was 6.8.
• Additions to the stock were made as follows: The first addition (addition level of 5kg/t) was made 15 seconds prior to dewatering, the second addition (addition level of 0.8 kg/t) was made 10 seconds prior to dewatering and the third addition (addition level of 0.5 kg/t) was made 5 seconds prior to dewatering.
• Table 1 shows the dewatering times at different modes of addition.
• the polymer and bentonite addition levels were calculated as dry product on dry stock system, and the sol of silica-based particles were calculated as SiO 2 and based on dry stock system.
• Test No. 1 shows the result without any additives.
• Test Nos. 2 to 4 illustrate processes used for comparison and Test Nos. 5 to 7 illustrate processes according to the invention.
• Table 1
• Table 1 shows that the process according to the present invention resulted in improved dewatering.
• the stock used in the test was based on 75% TMP and 25% DIP fibre material and bleach water from a paper mill. Stock consistency was 0.77%. Conductivity of the stock was 1.6 mS/cm and pH was 7.2.
• Additions to the stock were made as follows: The first addition, if any, was made 45 or 15 seconds prior to dewatering, the second addition, if any, was made 25 or 10 seconds prior to dewatering and the third addition, if any, was made 5 seconds prior to dewatering.
• Table 2 shows the dewatering times at different modes of addition. Addition times are given in seconds prior to dewatering and addition levels are given in kg/t for the first, second and third additions (1 st / 2 nd / 3 rd ), respectively.
• the polymer addition levels were calculated as dry product on dry stock system, and the silica-based particles were calculated as SiO 2 and based on dry stock system.
• Test No. 1 shows the result without any additives.
• Test Nos. 2 to 7 illustrate processes used for comparison and Test Nos. 8 to 10 illustrate processes according to the invention.
• Retention performance was evaluated by means of a nephelometer, available from Novasina, Switzerland, by measuring the turbidity of the filtrate, the white water, obtained by draining the stock.
• the turbidity was measured in NTU (Nephelometric Turbidity Units).
• Example 2 The stock and modes of stirring and addition used in Example 2 were similarly used in this example. Table 3 shows the dewatering effect at different modes of addition. Test No. 1 shows the result without any additives. Test Nos. 2 and 3 illustrate processes used for comparison and Test No. 4 illustrates the process according to the invention.
• Table 3 shows that process of the present invention resulted in improved drainage performance.
• Table 4 shows the dewatering effect at different modes of addition.
• Test No. 1 shows the result without any additives.
• Test Nos. 2 to 7 illustrate processes used for comparison and Test Nos. 8-9 illustrate processes according to the invention.
• Table 4 shows that the process according to the present invention resulted in improved drainage (dewatering) and retention performance.
• the stock used in this example was based on 75% TMP and 25% DIP fibre material and bleach water from a newsprint mill. Stock consistency was 0.82%. Conductivity of the stock was 1.7 mS/cm and pH was 7.2.
• Table 5 shows the dewatering effect at different modes of addition.
• Test Np. 1 shows the result without any additives.
• Test Nos. 2 to 8 illustrate processes used for comparison and Test No. 9 illustrates the process according to the invention.
• Table 5 shows that the process according to the present invention resulted in improved drainage (dewatering) and retention performance.
• Drainage performance was evaluated according to the procedure of Example 2.
• the stock and modes of stirring and addition used in Example 5 were similarly used in this example.
• Table 6 shows the dewatering effect at different modes of addition.
• Test No. 1 shows the result without any additives.
• Test Nos. 2 to 6 illustrate processes employing additives used for comparison (Ref.) and Test No. 7 illustrates the process according to the invention.
• Table 6 shows that the process according to the invention resulted in improved dewatering performance.
• Drainage performance was evaluated according to the procedure of Example 2.
• the stock and modes of stirring and addition used in Example 5 were similarly used in this example.
• Table 7 shows the dewatering effect at different modes of addition.
• Test No. 1 shows the result without any additives.
• Test Nos. 2 to 7 illustrate processes used for comparison and Test No. 8 illustrates the process according to the invention.
• Table 7 shows that the process according to the invention resulted in improved dewatering performance.

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