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
  • D21H23/08—Controlling the addition by measuring pulp properties, e.g. zeta potential, pH
• • 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
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/14—Secondary fibres
• • 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
  • D21H17/01—Waste products, e.g. sludge
• • 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
  • D21H17/21—Macromolecular organic compounds of natural origin; Derivatives thereof
  • D21H17/24—Polysaccharides
• • 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
  • D21H17/21—Macromolecular organic compounds of natural origin; Derivatives thereof
  • D21H17/24—Polysaccharides
  • D21H17/28—Starch
• • 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
  • D21H17/21—Macromolecular organic compounds of natural origin; Derivatives thereof
  • D21H17/24—Polysaccharides
  • D21H17/31—Gums
  • D21H17/32—Guar or other polygalactomannan gum
• • 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
  • D21H17/44—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups cationic
  • D21H17/45—Nitrogen-containing groups
  • D21H17/455—Nitrogen-containing groups comprising tertiary amine or being at least partially quaternised
• • 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
  • 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
  • D21H23/08—Controlling the addition by measuring pulp properties, e.g. zeta potential, pH
  • D21H23/10—Controlling the addition by measuring pulp properties, e.g. zeta potential, pH at least two kinds of compounds being added

Definitions

• an aqueous suspension containing cellulosic fibres, and optional fillers and additives referred to as stock
• 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
• white water which usually contains fine particles, e g fine fibres, fillers and additives, is normally recirculated in the papermaking process
• Drainage and retention aids are conventionally introduced into the stock in order to facilitate drainage and increase adsorption of fine particles onto the cellulosic fibres so that they are retained with the fibres on the wire
• Cationic organic polymers like cationic starch and cationic acrylamide-based polymers are widely used as drainage and retention aids
• the present invention relates to a process for the production of paper from a suspension containing cellulosic fibres, and optional fillers, which comprises adding to the suspension a drainage and retention aid comprising a cationic organic polymer, forming and dewatering the suspension on a wire, the process being characterised in that the cationic organic polymer has an aromatic group and the suspension being dewatered on the wire has a conductivity of at least 2 0 mS/cm
• the present invention also relates to a process as described in the pre- characte ⁇ sing clause above, the process being further characterised in that it comprises forming and dewatering the suspension on a wire to obtain a wet web containing cellulos
• the present invention results in improved drainage and/or retention when using stocks having high contents of salt, and thus having high conductivity levels, and colloidal materials
• the present invention also results in improved drainage and/or retention when applied to papermaking processes with extensive white water recirculation and limited fresh water supply and/or processes using fresh water having high salt contents, in particular salts of di- and multivalent cations like calcium
• the present invention makes it possible to increase the speed of the paper machine and to use lower dosages of additives to give a corresponding drainage and/or retention effect, thereby leading to an improved papermaking process and economic benefits
• the cationic organic polymer having an aromatic group according to this invention herein herein also referred to as "main polymer”
• drainage and retention aid refers to one or more components (aids, agents, or additives) which, when being added to a stock, give better drainage and/or retention than is obtained when not adding the said one or more components Accordingly, the main polymer provides improved drainage and/
• the main polymer can be selected from homopolymers and copolymers prepared from one or more monomers comprising at least one monomer having an aromatic group suitably an ethylenically unsaturated monomer, and the main polymer is suitably a vinyl addition polymer
• R 3 wherein R, is H or CH 3 , R 2 and R 3 are each or, preferably, an alkyl group having from 1 to 3 carbon atoms, usually 1 to 2 carbon atoms, A., is O or NH, B-, is an alkylene group having from 2 to 8 carbon atoms, suitably from 2 to 4 carbon atoms, or a hydroxy propylene group,
• Q is a substituent containing an aromatic group, suitably a phenyl or substituted phenyl group, which can be attached to the nitrogen by means of an alkylene group usually having from 1 to 3 carbon atoms, suitably 1 to 2 carbon atoms, and preferably Q is a benzyl group
• Suitable monomers represented by the general formula (I) include quaternary monomers obtained by treating dialkylaminoalkyl (meth)acrylates, e g dimethylaminoethyl (meth)- acrylate diethylaminoethyl (meth)acrylate and dimethylaminohydroxypropyl (meth)acrylate and dialkylaminoalkyl (meth)acrylam ⁇ des, e g dimethylaminoethyl (meth)acrylam ⁇ de diethylaminoethyl (meth)acrylam ⁇ de, dimethylaminopropyl (meth)acrylam ⁇ de, and diethyl- aminopropyl (meth)acrylam ⁇ de, with benzyl chloride
• Preferred cationic monomers of the 4 general formula (I) include dimethylaminoethylacrylate benzyl chloride
• Preferred cationic monomers of the 4 general formula (I) include dimethylaminoethylacryl
• the main polymer can be a homopolymer prepared from a cationic monomer having an aromatic group or a copolymer prepared from a monomer mixture comprising a cationic monomer having an aromatic group and one or more copolyme ⁇ zable monomers
• Suitable copolyme ⁇ zable non-ionic monomers include monomers represented by the general formula (II)
• I I 0 C— A 2 - - B 2 — N
• suitable copolyme ⁇ zable monomers of this type include (meth)acrylam ⁇ de, acrylamide-based monomers like N-alkyl (meth)acrylam ⁇ des and N,N-d ⁇ alkyl (meth)acrylam ⁇ des, e g N-n-propylacrylamide, N- isopropyl (meth)acrylam ⁇ de, N-n-butyl (meth)acrylam ⁇ de, N-isobutyl (
• Suitable copolyme ⁇ zable cationic monomers include the monomers represented by the general formula (III)
• R 7 is H or CH 3
• R 8 , R 9 and R 10 are each H or, preferably, a hydrocarbon group, suitably alkyl, having from 1 to 3 carbon atoms, usually 1 to 2 carbon atoms
• a 3 is O or NH 5
• B 3 is an alkylene group of from 2 to 4 carbon atoms, suitably from 2 to 4 carbon atoms, or a hydroxy propylene group
• X " is an anionic countenon, usually methylsulphate or a halide like chloride
• suitable cationic copolymenzable monomers include acid addition salts and quaternary ammonium salts of the dialkylaminoalkyl (meth)acrylates and dialkylaminoalkyl (meth)acrylam ⁇ des mentioned above, usually prepared using acids like HCI, H 2 S0 4 , etc , or quaternizing agents like methyl chloride, dimethyl sulphate, etc , and diallyldimethylammonium chloride Preferred
• the main polymer according to this invention can be prepared from a monomer mixture generally comprising from 1 to 99 mole%, suitably from 2 to 50 mole% and preferably from 5 to 20 mole% of cationic monomer having an aromatic group, preferably represented by the general formula (I), and from 99 to 1 mole%, suitably from 98 to 50 mole%, and preferably from 95 to 80 mole% of other copolymenzable monomers which preferably comprises acrylamide or methacrylamide ((meth)acrylam ⁇ de), the monomer mixture suitably comprising from 98 to 50 mole% and preferably from 95 to 80 mole% of (meth)acrylam ⁇ de, the sum of percentages being 100
• the main polymer can also be selected from polymers prepared by condensation reaction of one or more monomers containing an aromatic group Examples of such monomers include toluene dnsocyanates, bisphenol A, phtha c acid, phthalic anhydride etc , which can be used in the preparation of cationic poly
• the charge density of the main polymer is within the range of from 0 1 to 6 0 meqv/g of dry polymer, suitably from 0 2 to 4 0 and preferably from 0 5 to 3 0 6
• the weight average molecular weight of synthetic main polymers is usually at least about
• the main polymer of this invention may be in any state of aggregation such as, for example, in solid form, e g powders, in liquid form, e g solutions, emulsions, dispersions, including salt dispersions, etc
• suitable main polymers for use in this invention include those described in U S Patent Nos 5,169,540, 5,708,071 , and European Patent Applications 183,466, 525,751 and 805,234, the disclosures of which are hereby incorporated herein by reference
• the main polymer is suitably in liquid form, e g in the form of an aqueous solution or dispersion
• the main polymer can be added into the stock to be dewatered in amounts which can vary within wide limits depending on, inter alia, type of stock, salt content, type of salts, filler content, type of filler, point of addition, etc Generally the main polymer is added in an amount that give better retention than is obtained when not adding it
• the main polymer is usually added in an amount of at least 0 001 %, often at least 0 005% by weight, based on dry stock substance, whereas the upper limit is usually 3% and suitably 1 5% by weight
• the main polymer is used in conjunction with an additional stock additive, thereby forming a drainage and retention aid comprising two or more components, usually referred to as drainage and retention aids
• drainage and retention aids refers to two or more components (aids, agents or additives) which, when being added to a stock, give better drainage and/or retention than is obtained when not adding the components
• suitable stock additives of this type include anionic microparticulate materials, e g anionic organic particles and anionic inorganic particles, water-soluble anionic vinyl addition polymers, low molecular weight cationic organic polymers, aluminium compounds, and combinations thereof
• the main polymer is used in conjunction with an anionic microparticulate material, notably with anionic inorganic particles
• the mam polymer is used in conjunction with anionic inorganic particles and a low molecular weight cationic organic polymer
• the mam polymer is used in conjunction with anionic inorganic particles and a low molecular weight cationic organic polymer
• the mam polymer is used
• Anionic inorganic particles that can be used according to the invention include anionic silica-based particles and clays of the smectite type It is preferred that the anionic inorganic particles are in the colloidal range of particle size
• Anionic silica-based particles, i e particles based on S ⁇ 0 2 or silicic acid, are preferably used and such particles are usually 7 supplied in the form of aqueous colloidal dispersions, so-called sols
• suitable silica-based particles include colloidal silica and different types of polysilicic acid
• the silica- based sols can also be modified and contain other elements, e g aluminium and/or boron, which can be present in the aqueous phase and/or in the silica-based particles
• Suitable silica-based particles of this type include colloidal aluminium-modified silica and aluminium silicates Mixtures of such suitable silica-based particles can also be used Drainage and retention aids comprising suitable anionic silica
• Anionic silica-based particles suitably have an average particle size below about 50 nm, preferably below about 20 nm and more preferably in 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 specific surface area of the silica-based particles is suitably above 50 m 2 /g and preferably above 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 can be measured by means of titration with NaOH in known manner, e g as described by Sears in Analytical Chemistry 28(1956) 12, 1981-1983 and in U S Patent No 5,176,891 The given area thus represents the average specific surface area of the particles
• the anionic inorganic particles are silica-based particles having a specific surface area within the range of from 50 to 1000 m 2 /g, preferably from 100 to 950 m 2 /g Sols of silica-based particles these types also encompass modified sols like aluminium-containing silica-based sols and boron-containing silica-based sols
• the silica-based particles are present in a sol having an S- value in the range of from 8 to 45%, preferably from 10 to 30%, 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 2 /g, and preferably from 750 to 950 m 2 /g, which sols can be modified with aluminium and/or boron as mentioned above
• the particles can be surface- modified with aluminium to a degree of from 2 to 25% substitution of silicon atoms
• the S- value can be measured and calculated as described by Her
• the silica-based particles are selected from polysilicic acid and modified polysilicic acid having a high specific surface area, suitably above about 1000 m 2 /g
• the specific surface area can be within the range of 8 from 1000 to 1700 m 2 /g and preferably from 1050 to 1600 m 2 /g.
• the sols of modified polysilicic acid can contain other elements, e.g. aluminium and/or boron, which can be present in the aqueous phase and/or in the silica-based particles.
• polysilicic acid is also referred to as polymeric silicic acid, polysilicic acid microgel, polysilicate and polysilicate microgel, which are all encompassed by the term polysilicic acid used herein.
• Aluminium-containing compounds of this type are commonly also referred to as poly- aluminosilicate and polyaluminosilicate microgel, which are both encompassed by the terms colloidal aluminium-modified silica and aluminium silicate used herein.
• Clays of the smectite type that can be used in the process of the invention are known in the art and include naturally occurring, synthetic and chemically treated materials.
• suitable smectite clays include montmorillonite/bentonite, hectorite, beidelite, nontronite and saponite, preferably bentonite and especially such bentonite which after swelling preferably has a surface area of from 400 to 800 m 2 /g.
• Suitable clays are disclosed in U.S. Patent Nos. 4,753,710; 5,071 ,512; and 5,607,552, which are hereby incorporated herein by reference.
• Anionic organic particles that can be used according to the invention include highly cross-linked anionic vinyl addition polymers, suitably copolymers comprising an anionic monomer like acrylic acid, methacrylic acid and sulfonated or phosphonated vinyl addition monomers, usually copolymerized with nonionic monomers like (meth)acrylamide, alkyl (meth)acrylates, etc.
• Useful anionic organic particles also include anionic condensation polymers, e.g. melamine-sulfonic acid sols.
• Water-soluble anionic vinyl addition polymers that can be used according to the invention include copolymers comprising an anionic monomer like acrylic acid, methacrylic acid and sulfonated vinyl addition monomers, usually copolymerized with nonionic monomers like acrylamide, alkyl acrylates, etc., for example those disclosed in U.S. Patent Nos. 5,098,520 and 5,185,062, the teachings of which are incorporated herein by reference.
• LMW cationic organic polymers that can be used according to the invention include those commonly referred to and used as anionic trash catchers (ATC).
• ATC's are known in the art as neutralizing and/or fixing agents for detrimental anionic substances present in the stock and the use thereof in combination with drainage and/or retention aids often provide further improved drainage and/or retention.
• the LMW cationic organic polymer can be derived from natural or synthetic sources, and preferably it is an LMW synthetic polymer.
• Suitable organic polymers of this type include LMW highly charged cationic organic polymers such as polyamines, polyamidoamines, polyethyleneimines, homo- and copolymers based on diallyldimethyl ammonium chloride, (meth)acrylamides and (meth)acrylates.
• LMW highly charged cationic organic polymers such as polyamines, polyamidoamines, polyethyleneimines, homo- and copolymers based on diallyldimethyl ammonium chloride, (meth)acrylamides and (meth)acrylates.
• the molecular weight of the LMW cationic organic polymer is preferably lower, it is suitably at least 2,000 and preferably at least 10,000
• the upper limit of the molecular weight is usually about 700,000, suitably about 500,000 and usually about 200,000
• Aluminium compounds that can be used according to the invention include alum, aluminates, aluminium chloride, aluminium nitrate and polyaluminium compounds, such as polyaluminium chlorides, polyaluminium sulphates, polyaluminium compounds containing both chloride and sulphate ions, polyaluminium silicate-sulphates, and mixtures thereof
• the polyaluminium compounds may also contain other anions than chloride ions, for example anions from sulfu ⁇ c acid, phosphoric acid, organic acids such as citric acid and oxalic acid
• Components of drainage and retention aids according to the invention can be added to the stock in conventional manner and in any order
• drainage and retention aids comprising a main polymer and an anionic microparticulate material, notably anionic inorganic particles
• the main polymer before a shear stage which can be selected from pumping, mixing, cleaning, etc , and to add the anionic particles after that shear stage
• such components are preferably introduced into the stock prior to introducing the mam polymer, optionally used in conjunction with an anionic microparticulate material
• the LMW cationic organic polymer and the main polymer can be introduced into stock essentially simultaneously, either separately or in admixture, for example as disclosed in U S Patent No 5,858,174, which is hereby incorporated herein by reference
• the LMW cationic organic polymer and the main polymer can be introduced into stock essentially simultaneously, either separately or in admi
• the drainage and retention a ⁇ d(s) according to the invention can be added to the stock to be dewatered in amounts which can vary within wide limits depending on, inter alia, type and number of components, type of stock, salt content, type of salts, filler content, type of filler, point of addition, degree of white water closure, etc Generally the a ⁇ d(s) are added in amounts that give better drainage and/or retention than is obtained when not adding the components
• the main polymer is usually added in an amount of at least 0 001% often at least 0 005% by weight, based on dry stock substance, and the upper limit is usually 3% and suitably 1 5% by weight Similar amounts are suitable for water-soluble anionic vinyl addition polymers, if used When using an anionic microparticulate material in the process, the total amount added is usually at least 0 001% by weight, often at least 0 005% by weight, based on dry substance of the stock, and the upper limit is usually 1 0% 10 and suitably 0 6% by weight When using ani
• an LMW cationic organic polymer When using an LMW cationic organic polymer in the process, it can be added in an amount of at least 0 05%, based on dry substance of the stock to be dewatered Suitably, the amount is in the range of from 0 07 to 0 5%, preferably in the range from 0 1 to 0 35%
• the total amount introduced into the stock to be dewatered depends on the type of aluminium compound used and on other effects desired from it It is for instance well known in the art to utilize aluminium compounds as precipitants for rosin-based sizing agents
• the total amount added is usually at least 0 05%, calculated as AI 2 O 3 and based on dry stock substance
• the amount is in the range of from 0 5 to 3 0%, preferably in the range from 0 1 to 2 0%
• the process of this invention is preferably used in the manufacture of paper from a suspension containing cellulosic fibers, and optional fillers, i e a stock, which has a high conductivity
• the conductivity of the stock that is dewatered on the wire is at least 2 0 mS/cm, suitably at least 3 5 mS/cm, preferably at least 5 0 mS/cm and most preferably at least 7 5 mS/cm
• Conductivity can be measured by standard equipment such as, for example, a WTW LF 539 instrument supplied by Christian Berner
• the values referred to above are suitably determined by measuring the conductivity of the cellulosic suspension that is fed into or present in the headbox of the paper machine or, alternatively, by measuring the conductivity of white water obtained by dewatering the suspension
• High conductivity levels mean high contents of salts (electrolytes), where the various salts can be based on mono-, di- and multivending cations like alkali metal
• the present invention further encompasses papermaking processes where white water is extensively recirculated (recycled), 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, suitably less than 15, preferably less than 10 and notably less than 5 tons of fresh water per ton of paper
• Recirculation of white water obtained in the process suitably comprises mixing the white water with cellulosic fibres and/or optional fillers to form a suspension to be dewatered, preferably it comprises mixing the white water with a suspension containing cellulosic fibres, and optional fillers, before the suspension enters the forming wire for dewatering
• the white water can be mixed with the suspension before, between, simultaneous with or after introducing the components of drainage and retention aids, if used, and before, simultaneous with or after introducing the main polymer
• Fresh water can be introduced in the process at any stage, for example, it can be mixed with cellulosic fibres in order to
• the process of this invention is used for the production of paper
• the process can be used in the production of paper from different types of suspensions of cellulose-containing fibres and the suspensions should suitably contain at least 25% by weight and preferably at least 50% by weight of such fibres, based on dry substance
• the suspension can be based on fibres from chemical pulp such as sulphate, sulphite and organosolv pulps, mechanical pulp such as thermomechanical pulp, chemo-thermomechanical pulp, refiner pulp and groundwood 12 pulp, from both hardwood and softwood, and can also be based on recycled fibres, optionally from de-inked pulps, and mixtures thereof
• DDA Dynamic Drainage Analyser
• the furnish used was based on 70% by weight of pulp of bleached birch/pine sulphate (60/40) refined to 200°CSF and 30% by weight of ground marble Stock volume was 800 mi, consistency 0 3% and pH about 8 Conductivity of the stock was adjusted to 0 47 mS/cm by addition of sodium sulphate The stock was stirred in a baffled jar at a speed of 1500 rpm throughout the test and chemicals additions were conducted as follows i) adding cationic polymer to the stock following by stirring for 30 seconds, n) adding anionic inorganic particles to the stock followed by stirring for 15 seconds, in) draining the stock while automatically recording the drainage time
• the polymers used for in the test series were P1) a cationic copolymer prepared by polymerisation of acrylamide (90 mole%) and acryloxyethyldimethylbenzylammonium chloride (10 mole%) and having an average molecular weight of about 6,000,000, and P2) a cationic copolymer prepared by polymerisation of acrylamide (90 mole%) and acryloxyethyltnmethylammonium chloride (10 mole%) and having an average molecular weight of about 6,000,000
• the polymers P1 and P2 were dissolved in water and used as 0 1 % aqueous solutions
• the anionic inorganic particles used were silica-based particles of the type disclosed in U S Patent No 5,368,833
• the sol had an S-value of about 25% and contained silica particles with a specific surface area of about 900 m 2 /g which were surface-modified with aluminium to a degree of 5%
• the silica-based particles were added in an amount of 1 0 kg/ton, calculated as S ⁇ 0 2 and based on dry stock system
• Table 1 shows the drainage time at various dosages of P1 and P2, calculated as dry polymer on dry stock system 13 Table 1
• Dewatering and retention effect was evaluated by means of the DDA used in Example 1 in combination with a nephelometer.
• First pass retention was evaluated by measuring the turbidity of the filtrate, the white water, obtained by draining the stock.
• the furnish used was based on 56% by weight of peroxide bleached TMP/SGW pulp (80/20), 14% by weight of bleached birch/pine sulphate pulp (60/40) refined to 200° CSF and 30% by weight of china clay.
• To the stock was added 40 g/l of a colloidal fraction, bleach water from an SC mill, filtrated through a 5 ⁇ m screen and concentrated with an UF filter, cut off 200,000.
• Stock volume was 800 ml, consistency 0.14% and pH was adjusted to 4.0 using dilute sulphuric acid.
• the conductivity was adjusted by addition of calcium chloride (60 ppm Ca 2+ ), magnesium sulphate (18 ppm Mg + ) and sodium bicarbonate (134 ppm HCO 3 " ).
• the polymers and anionic inorganic particles according to Example 1 were similarly used in this test series. Two dosages of polymers were used, 1 kg/t and 2 kg/t, respectively, calculated as dry polymer on dry stock system.
• Table 2 shows the dewatering and retention effect at various dosages of silica-based particles, calculated as SiO 2 and based on dry stock system. Table 2
• the furnish used was the same as used in Example 2.
• Stock volume was 800 ml and pH about 7.
• the conductivity was adjusted by addition of calcium chloride, thus simulating a very high electrolyte content and a high degree of white water closure.
• Table 3 shows the dewatering and retention effect at various dosages of silica- based particles, calculated as SiO 2 and based on dry stock system.
• Example 3 the dewatering effect was evaluated as in Example 3, except that both sodium acetate (550 ppm Na + ) and calcium chloride (1300 ppm Ca 2+ ) was used to adjust the conductivity.
• Table 5 shows the dewatering effect at various dosages of silica-based particles, calculated as Si0 2 and based on dry stock system.
• Example 3 the dewatering and retention effect was evaluated as in Example 3, using a combination of sodium acetate (550 ppm Na + ) and calcium chloride (1300 ppm Ca + ) to adjust the conductivity.
• the polymers according to Example 1 were similarly used in this test series.
• the anionic microparticulate material used was hydrated suspension of powdered Na- bentonite in water.
• the bentonite had a surface charge of about 0.33 meq/g and a 16 swelling ability of 41 ml (2 g)
• the bentonite particles were added in an amount of 8 0 kg/ton, calculated as dry bentonite on dry stock system
• Table 6 shows the dewatering and retention effect at various dosages of P1 and P2, calculated as dry polymer on dry stock system
• Example 3 the dewatering effect was ealuated as in Example 3, except that zink chloride was used to adjust the conductivity
• the polymers and anionic inorganic particles according to Example 1 were similarly used in these tests 17
• Table 8 shows the results of the dewatering tests at various dosages of silica- based particles, calculated as as Si0 2 and based on dry stock system.

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