KR20060009008A - A process for the production of paper - Google Patents

Abstract

The invention relates to a process for the production of paper which comprises (i) providing a main aqueous flow containing cellulosic fibres; (i) introducing one or more retention components into the main aqueous flow to form a main aqueous flow containing one or more retention components; (iii) providing a diluting aqueous flow; (iv) introducing a low molecular weight cationic organic polymer into the diluting aqueous flow to form a diluting aqueous flow containing a low molecular weight cationic organic polymer, the low molecular weight cationic organic polymer having a weight average molecular weight up to 5,000,000; (v) introducing the diluting aqueous flow containing a low molecular weight cationic organic polymer into the main aqueous flow containing one or more retention components to form a resulting aqueous flow; and then (vi) ejecting the resulting aqueous flow onto a wire and dewatering the resulting aqueous flow to form a web of paper. The invention further relates to a process for the production of paper on a paper machine containing a dilution headbox which comprises (i) introducing one or more retention components into a main aqueous flow containing cellulosic fibres, and feeding the obtained main aqueous flow into the dilution headbox; (ii) introducing low molecular weight cationic organic polymer having a weight average molecular weight up to 5,000,000 into a diluting aqueous flow and feeding the obtained diluting aqueous flow into the dilution headbox; (iii) mixing the obtained main aqueous flow with the obtained diluting aqueous flow in the headbox to form a resulting aqueous flow; and (iv) ejecting the resulting aqueous flow onto a wire and dewatering the resulting aqueous flow to form a web of paper. The invention also relates to a process for the production of paper from an aqueous suspension containing cellulosic fibres, and optional filler, which comprises introducing one or more retention components into the suspension followed by introducing into the suspension a low molecular weight cationic organic polymer having a weight average molecular weight up to 5,000,000, and then forming and draining the suspension on a wire.

Description

Manufacturing method of paper {A PROCESS FOR THE PRODUCTION OF PAPER}

Field of invention

The present invention relates to a process for making paper, wherein a papermaking additive is introduced into a cellulosic stock before the cellulose stock is discharged onto the wire from the headbox and dehydrated to form paper paper.

Background of the Invention

In papermaking technology, an aqueous suspension called stock containing cellulose fiber and optional fillers and additives is fed to a headbox which discharges the stock on the forming wire. Water is dewatered from the stock to form a wet paper web on the wire, and the paper is further dewatered to dry in the drying zone of the paper machine.

Retention agents are generally introduced into the stock to increase the adsorption of fine particles such as fine fibers and filler particles, for example, to allow the cellulose fibers to be retained with the fibers on the wire. A wide variety of retention agents are known in the art, examples of which are anionic, non-ionic, amphoteric and cationic organic polymers of different molecular weight, inorganic materials, and combinations thereof. Water, called white water obtained by dewatering stock and wet paper, contains fine particles that are not retained on the wire due to incomplete retention, and the white water is typically recycled in different flow circuits.

In paper machines with a dilution headbox, white water is used to dilute the stock in the headbox. As a result, a high concentration of stock stream is diluted with a low concentration stream originating from white water. The headbox may have a series of mixing zones or dilution lines distributed over the width of the headbox. White water is injected into the mixing zone to control the stock dilution locally to form various concentration profiles exiting the slice openings of constant volume flow. The dilution headbox design provides better control of paper properties by controlling the amount of dilution, ie the ratio of high flow to low flow, at multiple points in the dilution headbox through the paper machine, and improves the basis weight of the paper. Can be controlled in a controlled manner, and can be made essentially uniform in the cross direction of the paper machine. However, when using high performance retention agents, it was found that the papermaking process and the properties of the paper produced were still not completely satisfactory and contributed to inadequate pitch precipitation control.

The problems caused by pitch accumulation on the paper machine and the formation of pitch globules in the final paper in all kinds of paper production are already recognized. Pitch generally refers to emulsified hydrophobic organic compounds. Pitch can be defined as a sticky resinous material released from wood during the pulp process. In addition, the pitch will contain a viscous material such as an adhesive coating resulting from the playing piece and the fibrous component, often referred to as sticky switch (stickies) and select kiss (tackies). In the papermaking process, the pitch is present as an unstable colloidal dispersion of hydrophobic particles. Thus, typical papermaking process conditions such as hydrodynamic and mechanical shear forces and temperature fluctuations, chemical environment and equilibrium can cause the colloidal pitch particles to aggregate in the cellulose suspension or to precipitate on the surface of a wire or other device. This can lead to material defects such as the formation of holes or spots in the final product and poor paper surface, and shortened equipment life, capacity problems, paper machine downtime and ultimately loss of benefits for paper machine. These problems are magnified in paper machines with high process water closures, such as large-scale white water recycling.

Summary of the Invention

The present invention generally relates to a process for making paper, comprising:

(i) providing a main aqueous flow containing cellulose fibers;

(Ii) introducing one or more retention components into the primary aqueous stream to form a primary aqueous stream containing one or more retention components;

(Iii) providing an aqueous stream for dilution;

(Iii) introducing a low molecular weight cationic organic polymer having an average molecular weight of up to 5,000,000 into the dilution aqueous stream to form an aqueous dilution stream containing a low molecular weight cationic organic polymer;

(Iii) introducing a dilute aqueous stream containing said low molecular weight cationic organic polymer into a primary aqueous stream containing said at least one retained component to form a resulting aqueous stream; And after

(Iii) draining the resulting aqueous stream on a wire and dewatering the resulting aqueous stream to form a paper paper.

The present invention also includes the following and is directly connected to the process of making paper in a paper machine containing a dilution headbox:

(i) introducing one or more retention components into the main aqueous stream containing cellulose fibers and feeding the obtained main aqueous stream to the dilution headbox;

(Ii) introducing a low molecular weight cationic organic polymer having an average molecular weight of up to 5,000,000 into an aqueous dilution stream and feeding the obtained aqueous dilution stream to a dilution headbox;

(Iii) mixing the obtained main aqueous stream in the headbox with the obtained aqueous stream for dilution to form the resulting aqueous stream; And

(Iii) draining the resulting aqueous stream on a wire and dewatering the resulting aqueous stream to form a paper paper.

The present invention also relates to a process for making paper from an aqueous suspension containing cellulose fibers and an optional filler, which process comprises introducing at least one retained component into the suspension, followed by an average molecular weight of up to 5,000,000 Introducing a low molecular weight cationic organic polymer having into the suspension, thereafter forming a suspension, and then draining the suspension onto a wire.

Detailed description of the invention

In accordance with the present invention, it has been found that the pitch problem can be reduced by introducing additives into the stock in a particular manner, prior to dewatering the stock from the wire to form paper paper. This finding is particularly applicable to papermaking processes for making paper in paper machines with dilution headboxes. It has also been found that pitch precipitation in papermaking systems can be better controlled according to the present invention. The process of the present invention also makes it possible to produce paper with improved properties.

The dilution headbox generally includes one or more inlets for the first partial volume flow, one or more inlets for the second partial volume flow, one or more zones for mixing the partial volume flows to form a mixture volume flow, and the mixture volume. One or more outlets for discharging the flow. Preferably the dilution box comprises a plurality of said inlets, mixing zones, and outlets across the working width of the dilution box. Examples of suitable dilution headboxes are described in US Pat. No. 4,909,904; 5,196,091; 5,316,383; 5,545,293; And 5,549,793.

As used herein, the term "main aqueous stream" refers to the main stream of stock entering a headbox containing cellulose fibers and optional filler and having a high concentration (hereinafter HC), ie a high solids HC stock, which is high concentration. The flow (hereinafter HC flow) is shown. The concentration of the HC flow can be from 0.1% to 3.5% by weight, suitably from 0.3% to 2.2% by weight, and preferably from 0.4% to 1.9% by weight. As used herein, the term "diluting aqueous flow" is used to dilute the HC flow and refers to an aqueous flow having a low concentration (LC), ie, a low solids content LC stock in relation to the HC flow. This represents a low concentration of flow (hereinafter referred to as LC flow). The concentration of the LC stream may be within the range of 0-1.5 wt%, suitably 0.002-0.9 wt%, and preferably 0.005-0.8 wt%, provided that the concentration of the LC stream is lower than the concentration of the HC flow. . Preferably, in the headbox, the HC flow is mixed and diluted with the LC flow, for example just before the turbulence generator, to produce the resulting flow that is discharged onto the wire for dehydration. The volume ratio of HC flow to LC flow may be in the range of 99: 1 to 50:50, suitably 97: 3 to 60:40, preferably 95: 5 to 75:25, typically about 85:15. Traditionally in dilution headbox designs, the volume ratio of HC flow to LC flow is preferably different at multiple points in the headbox across the width of the headbox to control the dilution amount, thereby crossing the basis weight of the paper paper formed. Allows better control of the profile. Preferably the partial volume flows, ie HC flow and LC flow, are mixed in the headbox to form the resulting HC / LC mixture volume flow, which exits the headbox and essentially cross-machine direction. Is constant.

The aqueous LC stream used for dilution can be selected from fresh water, white water and other types of aqueous streams regenerated in the process. The dilution LC stream may contain fibrous microparticles and fillers and may be treated by a purification step prior to feeding to the headbox. Examples of suitable steps that can be used for the purification or purification of this type of aqueous stream include filtration, floatation, precipitation, anaerobic and aerobic treatment. Preferably, the LC stream is white water containing, for example, cellulose microparticles, extracts and other additives that are released from wood during the pulp process, fillers and other additives that are introduced into the HC stream but are not retained on the wire. The white water used is preferably obtained by dehydrating stock and / or wet paper on the wire and can be purified as mentioned above before feeding to the dilution headbox. LC flows generally have a different composition than HC flows. When filler is used in the process, the filler content of the LC stream is generally different from the filler content of the HC stream; LC flows typically have a higher filler content than HC flows, where the filler content is expressed as a percentage of dry matter in the flow.

In addition to the HC flow and LC flow entering the headbox as described above, there may be one or more additional flows entering the headbox in accordance with the present invention. The addition stream is preferably a flow containing only water. The additional stream may also be a stream of stock or pulp of a different concentration and / or composition than the HC stream.

The retention component introduced into the HC stream in accordance with the present invention can be, for example, one retention agent or retention system defined later. One component may be any component that functions as a retention agent, and may preferably be, for example, a cationic polymer such as those defined herein. In this embodiment, the amount of component introduced into the main aqueous stream should be sufficient to provide a retention better than that obtained when no component is added.

In a preferred embodiment of the invention, a retention system is used. As used herein, the term "holding system" refers to two or more components or agents that, when added to a stock, provide better retention than those obtained when not added. The components of the retention system are preferably selected from two or more organic polymers and one or more organic polymers in combination with aluminum compounds and / or inorganic microparticles.

In a preferred embodiment of the invention, a microparticle retention system is used. As used herein, the term “microparticle retention system” refers to a retention system that includes microparticles or microparticulate materials such as, for example, anionic inorganic particles, cationic inorganic particles, and organic microparticles as defined herein. Microparticulate materials are used in combination with one or more additional components, typically one or more organic polymers, also referred to herein as main polymers, preferably cationic, amphoteric or anionic polymers. Anionic microparticles are preferably used in combination with one or more amphoteric and / or cationic polymers, and cationic microparticles are preferably used in combination with one or more amphoteric and / or anionic polymers. Preferably the microparticles are anionic inorganic particles. More preferably, the microparticles have a particle size in the colloidal range. Retention systems, eg, systems comprising microparticles, may comprise two or more components; For example, the retention system may be a three or four component retention system. Such suitable additional components include, for example, aluminum compounds and low molecular weight cationic organic polymers. Retention systems, including microparticle retention systems, typically provide better dehydration than those obtained when no such ingredients are added, which systems are commonly referred to as retention and dehydration systems.

In another preferred embodiment of the invention, a retention system comprising at least one cationic organic polymer and at least one anionic organic polymer is used. Suitably such retention systems include cationic organic polymers having one or more aromatic groups and / or anionic organic polymers having one or more aromatic groups, as defined herein.

Anionic inorganic particles that can be used according to the present invention include anionic silica-based particles and clays of the smectite type. Preferably, colloidal silica and anionic silica-based particles of different types comprising polysilicic acid and polysilicates, ie particles based on SiO ₂ or silicic acid, are used. Anionic silica-based particles are generally provided in the form of an aqueous colloidal dispersion, so-called sol. Also in accordance with the present invention suitable silica-based sols may contain other elements such as, for example, nitrogen, aluminum and boron. These elements may exist as a result of modifications with organic nitrogen-containing organic compounds, aluminum-containing compounds and boron-containing compounds, respectively. Such compounds may exist as aqueous sol and / or silica-based particles. Retention and dehydration systems comprising suitable anionic silica-based particles are described in US Pat. No. 4,388,150; 4,927,498; 4,954,220; 4,961,825; 4,980,025; 5,176,891; 5,368,833; 5,447,604; 5,470,435; 5,543,014; 5,571,494; 5,584,966; 5,603,805; And 6,379,500, all of which are incorporated herein by reference.

The anionic silica-based particles suitably have an average particle size in the range of about 50 nm or less, preferably about 20 nm or less, and more preferably in the range of about 1 to about 10 nm. Traditionally in silica chemistry, particle size refers to the average size of aggregated or non-aggregated primary particles. The specific surface area of the silica-based particles is suitably at least 50 m ² / g, preferably at least 100 m ² / g. Typically the specific surface area is at most about 1700 m ² / g, preferably at most 1000 m ² / g. The specific surface area may interfere with the titration, such as aluminum and boron species present in the sample, by known methods as described, for example, in Sears in Analytical Chemistry 28 (1956): 12, 1981-1983 and US Pat. No. 5,176,891. After appropriate removal or adjustment of the possible elements or compounds, the determination is made by titration with NaOH. Thus a given zone represents the average specific surface area of the particles.

In a preferred embodiment of the invention, the anionic inorganic particles are silica-based particles having a specific surface area in the range of 50 to 1000 m ² / g, preferably 100 to 950 m ² / g. Preferably, the anionic inorganic particles have an S-value in the range of 8 to 45%, preferably 10 to 35%, and a ratio in the range of 300 to 1000 m ² / g, suitably 500 to 950 m ² / g. It contains silica-based particles having a surface area, and the silica-based particles are present in silica-based sols which are not aluminum-modified or aluminum-modified, suitably surface-modified with aluminum. S-values are calculated from Iler & Dalton in J. Phys. Chem. It is measured and calculated as described in 60 (1956), 955-957. S-values indicate the degree of aggregation or microgel formation, and lower S-values indicate the higher degree of aggregation.

In still another embodiment of the present invention, the anionic inorganic particles are selected from polysilicic acids having a high specific surface area, suitably at least about 1000 m ² / g, which are selectively reacted with aluminum. The specific surface area may be in the range of 1000 to 1700 m ² / g, preferably 1050 to 1600 m ² / g. In the art, polysilicates may also be referred to as polymeric silicic acid, polysilicate microgels, polysilicates and polysilicate microgels, all of which are included in the polysilicate terminology used herein.

Smectite type clays that can be used in the process of the present invention are known in the art and include natural, synthetic and chemically treated materials. Examples of suitable smectite clays include montmorillonite / bentonite, hectorite, baydelite, nontronite and saponite, preferably benzonitite, particularly preferably 400 to 800 m ² / g after swelling Has a surface area of. Suitable clays are described in US Pat. No. 4,753,710, incorporated herein by reference; 5,071,512; And 5,607,552, the last patent discloses a mixture of anionic silica-based particles and smectite clay, preferably natural bentonite. Cationic inorganic particles that can be used include cationic silica-based particles, cationic alumina, and cationic zirconia.

Organic polymers suitable for use as part of a retention agent or retention system according to the present invention may be anionic, non-ionic, amphoteric or cationic in nature, which may be derived from natural or synthetic sources and may be linear, branched. Or cross-linking such as in the form of microparticles. Preferably the polymer is water soluble or water-dispersible.

Examples of suitable cationic polymers are, for example, starch, guar gum, cellulose, chitin, chitosan, glycan, galactan, glucan, xanthan gum, pectin, mannan, dextrin, preferably starch and guar gum, suitably potatoes, Cationic polysaccharides such as corn, wheat, tapioca, rice, waxy corn, barley, and the like; Cationic chain-grown polymers which are cationic vinyl addition polymers such as, for example, acrylate-, acrylamide-, vinylamine-, vinylamide- and allylamine-based polymers, and cationic polyamidoamines, polyethylene imines, Cationic synthetic organic polymers such as cationic step-growth polymers such as polyamines and polyurethanes. Cationic starch and cationic acrylamide-based polymers are particularly preferred cationic polymers as single retention components as well as retention systems with or without anionic inorganic particles. Examples of suitable cationic organic polymers having one or more aromatic groups include the polymers disclosed in WO 02/12626. In particular, the weight average molecular weight of the cationic organic polymer may vary within wide limits depending on the type of polymer used, which is typically at least 2,000,000, more often at least 3,000,000, suitably at least 5,000,000. The upper limit is not strict; About 600,000,000, typically 150,000,000, suitably 100,000,000.

Examples of more suitable cationic polymers that can be introduced into the HC stream in accordance with the present invention include cationic organic polymers having a low molecular weight. Such cationic organic polymers include polymers called anionic contaminant removers (hereinafter ATC). The weight average molecular weight of the ATC cationic organic polymer is usually at least 2,000, suitably at least 10,000, preferably at least 50,000, generally at most 2,000,000 and often at most 1,500,000. Suitable ATCs include linear, branched, and cross-linked polymers and are generally highly charged and can be derived from natural and synthetic sources. Examples of suitable ATCs are, for example, starch, guar gum, cellulose, chitin, chitosan, glycan, galactan, glucan, xanthan gum, pectin, mannan, dextrin, preferably starch and guar gum, suitably potatoes, corn, Low molecular weight degraded polysaccharides based on starch, including wheat, tapioca, rice, waxy corn, barley, and the like; Cationic chain-grown polymers such as, for example, diallyldimethyl ammonium chloride, such as acrylate-, acrylamide-, vinylamine-, vinylamide-, and allylamine-based polymer-like cationic vinyl addition polymers. Diallyldialkyl ammonium halides, homo- and copolymers based on (meth) acrylamide and (meth) acrylates); And cationic synthetic organic polymers such as, for example, cationic polyamidoamines, polyethylene imines, polyamines such as dimethylamine-epichloridrin copolymers, and cationic step-growth polymers such as polyurethanes.

Examples of suitable anionic organic polymers according to the present invention may be selected from step-growth polymers, chain-growth polymers, polysaccharides, natural aromatic polymers and variants thereof. Examples of suitable anionic step-growth polymers include anionic benzene-based condensation polymers and naphthalene-based condensation polymers, preferably naphthalene-sulphonic acid based condensation polymers and naphthalene-sulfonate based condensation polymers; And additive polymers such as anionic polyurethanes, ie polymers obtained by step-growth addition polymerization. Examples of suitable anionic chain-grown polymers are, for example, acrylate- and acrylamide-based polymers including anionic or potentially anionic monomers such as (meth) acrylic acid and paravinyl phenol (hydroxy styrene). Anionic vinyl addition polymers. Examples of suitable natural aromatic polymers according to the invention and their modifications, ie modified natural aromatic anionic polymers, are lignin-based polymers, preferably for example lignosulfonates, kraft lignin, sulfonated kraft lignin, And sulfonated lignin, such as tannin extract. Examples of other suitable anionic organic polymers having one or more aromatic groups include the polymers disclosed in WO 02/12626. In particular, the weight average molecular weight of the anionic polymer may vary within wide limits depending on the type of polymer used and is typically at least about 500, suitably at least about 2,000, preferably at least about 5,000. The upper limit is not strict; About 600,000,000, generally 150,000,000, suitably 100,000,000, preferably 10,000,000.

As used herein, the term "step-growth polymer (also called step-reaction polymer)" refers to a polymer obtained by step-growth polymerization (also called step-reaction polymerization). The term "chain-grown polymer (also called chain reaction polymer)" as used herein refers to a polymer obtained by chain-growth polymerization (also called chain reaction polymerization).

Aluminum compounds that can be used according to the invention include alum, aluminate, aluminum chloride, aluminum nitrate and polyaluminum chloride, polyaluminum sulfate, polyaluminum compounds containing both chlorine and sulfate ions, polyaluminum silicate- Polyaluminum compounds such as sulphates and mixtures thereof. The polyaluminum compound may also contain other anions such as anions of organic acids such as phosphoric acid, sulfuric acid, citric acid and oxalic acid.

Preferred retention systems according to the present invention include:

(i) anionic silica-based particles in combination with cationic starch, cationic guar gum or cationic acrylamide-based polymers, optionally in combination with anionic organic particles and / or ATC and / or aluminum compounds;

(Ii) anionic silica-based particles in combination with anionic chain-grown polymers, preferably cationic organic polymers and / or anionic acrylamide-based polymers in combination with ATC;

(Iii) bentonite in combination with cationic acrylamide-based polymers and optionally in combination with ATC and / or aluminum compounds;

(Iii) combined with an anionic step-growth polymer, preferably an anionic naphthalene-based condensation polymer; Cationic polysaccharides, preferably cationic starch, optionally mixed with ATC and / or aluminum compounds;

(Iii) cationic polysaccharides, preferably cationic starches, in combination with natural aromatic anionic polymers and variants thereof, preferably sulfonated lignin, and optionally in combination with ATC and / or aluminum compounds;

(Iii) cationic chain-growth polymers, preferably cationic acrylics, in combination with anionic step-growth polymers, preferably anionic naphthalene-based condensation polymers and optionally in combination with ATC and / or aluminum compounds Amide-based polymers; And

(Iii) cationic chain-grown polymers, preferably cationic acrylamides, in combination with natural aromatic anionic polymers and their modifications, preferably sulfonated lignin, and optionally in combination with ATC and / or aluminum compounds. Based polymers;

(Iii) a cationic chain-grown polymer in combination with ATC, preferably a cationic acrylamide-based polymer; And

(Iii) cationic chain-grown polymers, preferably cationic acrylamide-based polymers in combination with anionic organic particles.

In the process of the invention, the retained component is preferably introduced into the HC stream which is mixed with the LC stream in the headbox, thereby introducing the component into the resulting aqueous stream in the dilution process. When using a retention system comprising one or more components, the components can be added to the stock flow in a traditional manner, preferably at different points and in any order. When using retention systems comprising anionic inorganic particles and cationic polymers, it is desirable to add cationic polymers to the HC stock stream before adding microparticulate materials, although the reverse order of addition may be used. When using retention systems comprising cationic and anionic organic polymers, it is desirable to add cationic polymers to the HC stock stream before adding anionic polymers, although the reverse order of addition may be used. It is also preferred to add a first component, such as a cationic polymer, before the shearing step, which may be selected for pumping, mixing, purifying, etc., and adding a second component, such as anionic inorganic microparticles or organic polymer, after the shearing step. It is desirable to. When using a low molecular weight cationic organic polymer such as ATC, it is preferred that the organic polymer is introduced into the HC stock stream prior to or simultaneously with the other retained components. When using an aluminum compound, the aluminum compound is preferably introduced into the HC stock stream prior to or simultaneously with the other retained components.

The components of the retention system may vary within wide limits, particularly depending on the type and number of components, the type of stock, the type of filler, the filler content, the point of addition, and the like. In general, the components are added in an amount that provides a retention better than the retention obtained when the components are not added. When using anionic inorganic particles as the microparticulate material, the total amount added is generally at least 0.001% by weight, often at least 0.005% by weight, based on the dry material of the stock. The upper limit is generally 1.0% by weight, preferably 0.6% by weight. When using anionic silica-based particles, the total amount is suitably within the range of 0.005 to 0.5% by weight, preferably within the range of 0.01 to 0.2% by weight, calculated on the basis of SiO ₂ and dry stock material. Organic polymers, such as cationic and anionic polymers, are generally added in total amounts of at least 0.001% by weight, often at least 0.005% by weight, based on the dry stock material. The upper limit is generally 3% by weight, suitably 1.5% by weight. When using a low molecular weight cationic organic polymer as ATC, it can be introduced into the HC stock flow in an amount of at least 0.01%, suitably in the range of 0.05% to 0.5%, based on the dry stock material. When using aluminum compounds in the process, the total amount introduced into the stock for dehydration depends on the type of aluminum compound used and other effects desired from the aluminum compound. The use of aluminum compounds as precipitants for rosin-based sizing agents is known in the art. The total amount added is generally at least 0.05% calculated on the basis of Al ₂ O ₃ and dry stock material. Suitably the total amount is in the range of 0.08 to 2.8, preferably in the range of 0.1 to 2.0%.

According to the invention, the low molecular weight cationic organic polymer is preferably introduced into the LC stream for mixing with the HC stream in the dilution headbox. Suitable low molecular weight (LMW) cationic organic polymers include linear, branched and cross-linked polymers and generally include highly charged ones that can be derived from natural and synthetic sources. Examples of suitable LMW cationic organic polymers are, for example, starch, guar gum, cellulose, chitin, chitosan, glycan, galactan, glucan, xanthan gum, pectin, mannan, dextrin, preferably starch and guar gum, suitably LMW degraded polysaccharides based on starch, including potatoes, corn, wheat, tapioca, rice, waxy corn, barley, and the like; Cationic chain-grown polymers such as, for example, diallyldimethyl ammonium chloride, such as acrylate-, acrylamide-, vinylamine-, vinylamide-, and allylamine-based polymer-like cationic vinyl addition polymers. Diallyldialkyl ammonium halides, homo- and copolymers based on (meth) acrylamide and (meth) acrylates); And cationic synthetic organic polymers such as, for example, cationic polyamidoamines, polyethylene imines, polyamines such as dimethylamine-epichloridrin copolymers, and LMW cationic step-growth polymers such as polyurethanes. The weight average molecular weight of the LMW cationic organic polymer is generally at least 100,000, suitably at least 500,000, preferably at least 1,000,000, and generally at most 5,000,000, suitably at most 3,000,000 and preferably at most 2,000,000. In general, when a cationic organic polymer is added to the HC stream as part of a retention agent or retention system, the weight average molecular weight of the LMW cationic organic polymer added to the LC stream is the weight average of the cationic organic polymer added to the HC stream. Smaller than molecular weight

LMW cationic organic polymers are generally added to the LC stream in an amount of at least 0.01%, based on the dry matter of the stock to be dehydrated. Suitably the amount is in the range from 0.05 to 1.0%, preferably in the range from 0.1 to 0.5%.

In a preferred embodiment of the invention, following the step of introducing the LC stream containing the LMW cationic organic polymer into the HC stream containing one or more retention components to form the resulting aqueous stream, the retention component is no longer the resultant aqueous stream. It is not introduced. The formation of the resulting aqueous stream preferably takes place in the dilution headbox, but may also occur outside the headbox.

The process of the present invention is applicable to all papermaking processes and cellulose suspensions, and is particularly useful for making paper from stocks with high conductivity. In this case, the conductivity of the stock dehydrated on the wire is at least about 1.5 mS / cm, suitably at least 3.5 mS / cm, preferably at least 5.0 mS / cm. Conductivity can be measured, for example, by standard equipment such as the WTW LF 539 device supplied by Christian Berner. The above mentioned values are determined by measuring the conductivity of the resulting aqueous flow which is discharged on the wire to be dehydrated. High conductivity levels refer to a high content of salts (electrolytes) derived from the materials used to form the stock, the various additives introduced into the stock, the fresh water supplied to the process, and the like. In addition, the salt content is generally higher in processes where white water is recycled extensively, which can lead to significant salt accumulation in the water cycle of the process.

The present invention also provides that the white water is recycled or recycled extensively, ie having a high number of white water closures, for example 0 to 30 tonnes, generally less than 20 tonnes, preferably less than 15 tonnes per tonne of dry paper produced. And, preferably, less than 10 tonnes, notably less than 5 tonnes of fresh water is used. Fresh water can be introduced into the process at any stage; For example, fresh water may be mixed with cellulose fibers to form a suspension, and fresh water may be mixed with a turbid suspension containing cellulose fibers to dilute the suspension to form a pale suspension that is fed to the headbox as a high concentration stream. Can be mixed.

The process according to the invention is used for the manufacture of paper. The term "paper" as used herein, of course, includes paper and their manufacture, as well as other paper-like products such as, for example, boards and paperboard, and their manufacture. The process can be used for the production of paper from different types of cellulose suspension, which suspension should contain at least 25%, preferably at least 50%, by weight of each fiber based on the dry matter. The suspension may be chemical pulp, such as sulphate and sulphite pulp, thermodynamic pulp, chemical-thermomechanical pulp, organosolve pulp, refiner pulp or groundwood pulp from both hardwood and softwood, or elephant grass, bagasse, Flax may be based on fibers from fibers derived from annual plants such as straw and the like, and suspensions may also be used in suspensions based on recycled fibers. The present invention is preferably applicable to the process of making paper from wood-containing suspensions. Suspensions may also be used in traditional types of mineral fillers such as, for example, kaolin, clay, titanium dioxide, gypsum, talc, and natural and minerals such as, for example, chalk, ground marble, ground calcium carbonate, and precipitated calcium carbonate. It contains synthetic calcium carbonate. Of course, the stock may also contain stock size agents based on traditional types of papermaking additives such as wet-strength agents, rosin, ketene dimers, ketene multimers, alkenyl succinic anhydrides and the like.

Suitably, the present invention is directed to paper machine for making wood-based paper and paper based on recycled fibers such as SC, LWC and other types of book and newspaper paper, and paper machine for producing wood-free printing paper and writing paper. Applicable, the term 'wood-free' means less than about 15% of wood-containing fiber. The invention is also applicable to the manufacture of paper or boards in multilayer headboxes as well as to the manufacture of boards in machines with multiple headboxes, in which one or more layers are essentially recycled fibers. It is composed. In machines using multiple headboxes or multiple headboxes in which one or more layers are made of a dilution type headbox, the present invention can be applied to one or more such layers. Suitably the invention applies to paper machines operating at a speed of 300 to 2500 m / min, preferably 1000 to 2000 m / min.

The invention is further illustrated in the following examples, which, however, are not intended to limit the invention. Unless stated otherwise, parts and% relate to weight parts and weight percentages, respectively.

The process of the present invention was tested using different LMW cationic organic polymers as additives to LC stocks.

Paper was made from cellulose suspensions in paper machines using dilution headboxes to make SC grades. The following retention agents were added to the HC stock; First, a dimethylamine-epichloridrin copolymer having a weight average molecular weight of about 1 million was dried, and the cationic polyacrylamide having a weight average molecular weight of 4.6 million was dried based on the dry finish. 0.36 kg / ton based on feed stock. LC stock was obtained by draining the stock.

500 ml of LC stock was added to the Dynamic Drainage Jar and mixed at 1000 rpm for 15 seconds, then LMW cationic organic polymer was added to the stock and mixed for 30 seconds. In a blank test, LC stock was added to the dynamic drain jar and mixed for 45 seconds at 1000 rpm without addition of the LMW cationic organic polymer. The LC stock obtained was then drained and the filtrate collected and passed through a 1 micron filter. The Ocean Optics S2000 UV Spectrophotometer with fast scan rate was used to measure the UV absorption as showing the pitch content of the filtered aliquots.

Various LMW cationic organic polymers were tested at the same dry capacity (4 kg / ton based on LC stock dry material and about 2 kg / ton based on total dry material reel tonnage) and the results are summarized below.

LMW-1 was a dimethylamine-epichloridrin copolymer with a weight average molecular weight of about 120,000;

LMW-2 was a dimethylamine-epichloridrin copolymer with a weight average molecular weight of about 1,000,000;

LMW-3 was polydiallyldimethylammonium chloride with a weight average molecular weight of about 680,000;

LMW-4 was polydiallyldimethylammonium chloride with a weight average molecular weight of about 1,800,000.

Compared with the control test, all processes according to the present invention showed a decrease in UV absorption. The most effective process according to the invention was to use polydiallyldimethylammonium chloride with a weight average molecular weight of about 1,800,000.

The tests are summarized in Table 1, which shows UV absorption at different wavelengths for the process according to the invention, with the control corresponding to the prior art.

 Table 1. UV Absorption at Different Wavelengths

The present invention relates to a process for making paper, wherein a papermaking additive is introduced into a cellulosic stock before the cellulose stock is discharged onto the wire from the headbox and dehydrated to form paper paper.

Claims (13)

Process for making paper in paper machines containing a dilution headbox, comprising: (i) introducing one or more retention components into a main aqueous flow containing cellulose fibers and feeding the obtained main aqueous flow to the dilution headbox; (Ii) introducing a low molecular weight cationic organic polymer having a weight average molecular weight of up to 5,000,000 into a diluting aqueous flow and feeding the obtained dilution aqueous flow to a dilution headbox; (Iii) mixing the obtained main aqueous stream with the obtained dilution aqueous stream in a headbox to form the resulting aqueous aqueous flow; And (Iii) draining the resulting aqueous stream on a wire and dehydrating the resulting aqueous stream to form a web of paper. Paper manufacturing method comprising: (i) providing a primary aqueous stream containing cellulose fibers; (Ii) introducing one or more retention components into the primary aqueous stream to form a primary aqueous stream containing one or more retention components; (Iii) providing an aqueous stream for dilution; (Iii) introducing a low molecular weight cationic organic polymer having a weight average molecular weight of up to 5,000,000 into the dilution aqueous stream to form an aqueous dilution stream containing a low molecular weight cationic organic polymer; (v) introducing a dilution aqueous stream containing said low molecular weight cationic organic polymer into a primary aqueous stream containing said one or more retained components to form a resulting aqueous stream; And after that (Iii) discharging the resulting aqueous stream onto a wire and dehydrating the resulting aqueous stream to form a paper web From an aqueous suspension containing cellulose fiber and an optional filler, introducing one or more retention ingredients into the suspension, subsequently introducing a low molecular weight cationic organic polymer having a weight average molecular weight of up to 5,000,000 into the suspension. And then forming a suspension and draining the suspension on a wire. The method of claim 1, wherein the main aqueous stream has a higher concentration than the dilution aqueous stream. 5. The method of claim 1, wherein the aqueous stream for dilution is white water obtained by dehydrating the resulting aqueous stream. 6. The method of claim 1, wherein the retention component is selected from the group consisting of a microparticle retention system and a retention system comprising two or more organic polymers. The method of claim 1, wherein the retention component comprises one or more cationic organic polymers and anionic silica-based particles. The method of claim 1, wherein the retention component comprises a cationic organic polymer that is a cationic starch or a cationic acrylamide-based polymer. The method of claim 1, wherein the low molecular weight cationic organic polymer has a weight average molecular weight in the range of 500,000 to 3,000,000. The method of claim 1, wherein the low molecular weight cationic organic polymer is a homopolymer or copolymer based on diallyldimethylammonium chloride. The method of claim 1, wherein the retention component comprises one or more organic polymers containing one or more aromatic groups. The method of any one of the preceding claims, comprising producing paper at a machine speed of 300 to 2500 m / min. Method according to any of the preceding claims, comprising introducing 0 to 30 tonnes of fresh water per tonne of dry paper produced and recycling the white water.