WO2006069657A2

WO2006069657A2 - Paper mass-gluing method

Info

Publication number: WO2006069657A2
Application number: PCT/EP2005/013625
Authority: WO
Inventors: Simon Champ; Roland Ettl
Original assignee: Basf Aktiengesellschaft
Priority date: 2004-12-22
Filing date: 2005-12-17
Publication date: 2006-07-06
Also published as: DE102004063000A1; WO2006069657A3

Abstract

The invention relates to a method for mass-gluing paper, paperboard and cardboard by successively and continuously adding the aqueous dispersion of at least one type or reactive gluing agent and at least one type of retention agent into a laminar running pulp flow whose substance concentration is equal or less than 2 % by weight with respect to dry fibres, dewatering the paperboard and by forming sheets, wherein the inventive method consists in dosing the reactive gluing agent and the retention agent in the form of a turbulent flow into a pulp flow at a point located after a last shearing stage and prior to the beginning of a dewatering process.

Description

Method for sizing paper

description

The invention relates to a process for engine sizing of paper, cardboard and paperboard by successively adding an aqueous dispersion of at least one reactive sizing agent and at least one retention agent to a laminar flow of paper stock having a fabric concentration of at most 2% by weight, based on dry fibers, and Dewatering of the pulp under foliation.

Reactive sizing agents include, for example, alkyl ketene dimers (AKD) and alkyl and alkenyl succinic anhydrides (ASA). Both classes of substances are added in the form of aqueous dispersions to the paper stock prior to sheet formation. The AKD dispersions can be both cationically e.g. with the aid of cationic starch as well as anionic e.g. be stabilized by means of condensation products of naphthalenesulfonic acid and formaldehyde. In Nordic PuIp and Paper Research Journal no. 2/1986, pages 31-38, reported the mechanism of sizing with cationically-adjusted AKD dispersions. Among other things, the influence of retention aids, pH, electrolytes and type of AKD addition, such as contact time and shear intensity, on the AKD retention in the paper was investigated. In two examples, the contact times were 30 and 60 seconds, respectively. An exposure time of AKD to a stock of more than 5 minutes showed no increase in AKD retention, but led to a decrease in AKD retention, while the use of highly cationically charged polyelectrolytes together with AKD dispersions the retention of AKD in the Paper increased considerably.

Since AKD and ASA tend to hydrolyze in an aqueous medium and since a good retention of both sizing agents in the papermaking process is desired, the metering points on the paper machine for these sizing agents must be selected accordingly, cf. Lecture by George J. Batten, Jr., 1997 TAPPI Sizing Short Course. Thus, for the addition of AKD, a position between the chest and the pressure sorters and, for ASA, a location between pressure sorter and before the last shear stage (screen) is proposed.

From US-B-6,659,636 a method and an apparatus for a continuous addition of retention aids in a fiber suspension is known, which is pumped to the headbox. Before the retention agent comes into contact with the fiber suspension, it is brought together with water from the paper machine cycle in a mixing device. As a mixing device, for example, a multi-fluid nozzle is described by the recycled water from the paper machine cycle and an aqueous solution of a retention agent continuously into the fiber suspension be directed. This achieves a homogeneous distribution of the retention agent in the pulp.

From EP-A-1 422 337 a headbox for a paper or board machine is known, the headbox comprising at least one mixing chamber into which a liquid, e.g. a fiber suspension, flows in and in the over at least partially in different height (z) opening metering channels another fluid, e.g. An aqueous solution of a retention agent can be added to the fiber suspension.

From DE-A-102 25 702 a method and an apparatus for measuring the retention of at least one additive to a fiber suspension is known. In this method, an additive such as AKD or a retention agent is added continuously to a fiber suspension stream under the action of high shear forces. The mixture then flows through a tube in laminar flow and is then passed through a filter system, for example. The filter system has a flow chamber in which the mixture of fiber suspension and at least one additive flows along a sieve in the direction of the surface area of the sieve. The sample separated in the filter unit is then examined online to determine, for example, the retention.

The object of the invention is to provide an improved process for the production of paper products, wherein the efficiency of mass-producing agent and retention agent is coordinated with one another.

The object is achieved by a method for engine sizing of paper, board and cardboard by successively continuous addition of an aqueous dispersion of at least one reactive sizing agent and at least one retention agent to a laminar flowing stock flow with a concentration of at most 2 wt .-%, based on dry Fibers, and dewatering the stock under sheet formation, by metering the reactive sizing agent and the retention agent under turbulent flow at a location in the paper stock stream that is after the last shear stage and before the start of the dewatering process. The dewatering process of the pulp begins with the impact of the pulp on the wire. The contact time of reactive sizing agent and retention agent in the paper stock in the method according to the invention from the metering point to the beginning of the dewatering process is at most 30 seconds and preferably at most 10 seconds.

To prepare the pulp, for example, starting from cellulose fibers, which are suspended in water. Suitable cellulose fibers are, for example, wood pulp and all annual plants. Wood pulp includes, for example, groundwood, thermo-mechanical pulp (TMP), chemothermomechani- shear fabric (CTMP) ₁ pressure sanding, semi-pulp, high-yield pulp and refiner mechanical pulp (RMP) and waste paper. Also suitable are pulps that can be used in bleached or unbleached form as well as recovered paper fibers. Examples include sulphate, sulphite and soda pulps. Preference is given to using unbleached pulps, which are also referred to as unbleached kraft pulp. The fibers mentioned can be used alone or in a mixture. Particularly preferred is the use of kraft pulp as well as TMP and CTMP. The pH of the cellulose fiber slurry is, for example, 4 to 8, preferably 6 to 8. The substance concentration is at most 2% by weight and most often in the range of 0.5 to 1.0% by weight based on dry stock.

The stock may optionally contain fillers. Suitable fillers are all insoluble products which are commonly used in papermaking, e.g. Calcium carbonate, chalk, precipitated calcium carbonate, calcium sulfate, titanium dioxide, dolomite, clay and / or talc. The filler content may, for example, be from 0 to 35, preferably from 10 to 30,% by weight, based on dry paper stock. The fillers are usually dosed to the thick matter or at a point between the sieves and the headbox in the thin material.

According to the invention, at least one reactive sizing agent is initially metered into the paper stock and then at least one retention agent is added. The retention agent may be added to the stock at a single location, or preferably at two successive locations. In some cases it has proved to be advantageous if the retention agent is metered into the stock at three or four locations arranged one after the other. By having at least two retention agent dosing sites available, the reactive sizing agent dosing station and the first retention agent dosing station may be virtually equidistant from the headbox or drainage on the wire so that the sizing agent and the retention agent added first is practical have the same contact time in the pulp. Preferably, the contact time of sizing agent and retention agent in the pulp 0.1 to 30 seconds and is chosen so that the optimum effect of sizing agent and retention agent is achieved.

An important feature of the method according to the invention is the fact that sizing agent and retention agent are each metered in a turbulent flow to the pulp. A suitable device for this is known from the above-mentioned US-B-6, 659,636. Both sizing agent and retention agent are each metered into the laminar flow of paper stock in a mixing device in which a turbulent flow prevails. The flow rate of the paper stock flow is, for example, at least 2 m / sec in the case of conventional paper machines and is usually in the range of 3 to 7 m / sec. The mixing device stands, for example, from a two-component or multi-fluid nozzle, are passed through the recycled from the paper machine water and sizing agent or retention agent in turbulent flow in the laminar flowing stock flow.

For the dosage of reactive sizing agent and retention agent according to the invention, it is also possible to use the mixing chambers which are known from the EP-A-1 422 337 assigned to the prior art. Also in this embodiment of the invention, the addition of reactive sizing agent and retention aid to the stock takes place in a turbulent flow.

As reactive come particular C ₂ - to C ₂₂ -alkylketene, C ₅ - to C ₂₂ alkyl and / or C ₅ - to C ₂₂ -Alkenylbernsteinsäureanhydride, C ₂ - to C ₃₆ - alkyl isocyanates or mixtures of said compounds. Reactive sizing agents are described in greater detail in the references cited in the prior art, for example. The aqueous reactive size dispersions are stabilized, for example, with the aid of cationic starch, cf. EP-BO 353 212, EP-B-0369328 and EP-BO 437 764. As sizing agents are particular anionic adjusted aqueous dispersions of a C _2- C ₂₂ used at least until -Alkyldiketens. Such dispersions are known, for example, from WO-A-00/23651, pages 2 to 12. For the preparation of sizing dispersions, the reactive sizing agents are usually heated to a temperature above their melting point and then emulsified in water under the action of shear forces. Liquid alkenylsuccinic anhydrides can already be emulsified at room temperature. For emulsifying, for example, the conventional homogenizers are used. To stabilize the dispersed sizing agents in the aqueous phase, dispersants are used. Thus, for example, at least one anionic dispersant is used for the preparation of anionic sizing dispersions, for example a dispersant from the group of condensation products

(a) naphthalenesulfonic acid and formaldehyde,

(b) phenol, phenolsulfonic acid and formaldehyde,

(c) naphthalenesulfonic acid, formaldehyde and urea, as well

(d) phenol, phenolsulfonic acid, formaldehyde and urea.

The anionic dispersants may be in the form of the free acids, the alkali metal, alkaline earth metal and / or ammonium salts. The ammonium salts can be derived from both ammonia and from primary, secondary and tertiary amines, for example, the ammonium salts of dimethylamine, trimethylamine, hexylamine, cyclohexylamine, dicyclohexylamine, ethanolamine, diethanolamine and triethanolamine are. The condensation products described above are known and commercially available. They are prepared by condensing said components, wherein instead of the free acids and the corresponding alkali metal, Alkaline earth metal or ammonium salts can use. Suitable catalysts for the condensation are, for example, acids such as sulfuric acid, p-toluenesulfonic acid and phosphoric acid. Naphthalenesulfonic acid or its alkali metal salts are condensed with formaldehyde preferably in a molar ratio of 1: 0.1 to 1: 2 and usually in a MoI ratio of 1: 0.5 to 1: 1. The molar ratio for the production of condensates of phenol, phenolsulfonic acid and formaldehyde is also in the range given above, using any mixtures of phenol and phenolsulfonic acid instead of naphthalenesulfonic acid in the condensation with formaldehyde. Instead of phenolsulfonic acid, it is also possible to use the alkali metal and ammonium salts of phenolsulfonic acid. The condensation of the abovementioned starting materials may optionally be carried out additionally in the presence of urea. For example, based on naphthalenesulfonic acid or on the mixture of phenol and phenolsulfonic acid, from 0.1 to 5 mol of urea are used per mole of naphthalenesulfonic acid or per mole of the mixture of phenol and phenolsulfonic acid.

The condensation products have, for example, molar masses in the range from 800 to 100,000, preferably 1,000 to 30,000 and in particular from 4,000 to 25,000. Preferably used as anionic dispersants are salts which are obtained, for example, by neutralizing the condensation products with lithium hydroxide, Sodium hydroxide, potassium hydroxide or ammonia receives. The pH of the salts is, for example, in the range of 7 to 10.

Also suitable as anionic dispersants are amphiphilic copolymers

(i) hydrophobic monoethylenically unsaturated monomers and (ii) hydrophilic monomers having an anionic group such as monoethylenically unsaturated carboxylic acids, monoethylenically unsaturated sulfonic acids, monoethylenically unsaturated phosphonic acids or mixtures thereof.

Suitable hydrophobic monoethylenically unsaturated monomers

(a) are, for example, olefins having 2 to 150 carbon atoms, styrene, α-methylstyrene, ethylstyrene, 4-methylstyrene, acrylonitrile, methacrylonitrile, esters of monoethylenically unsaturated C ₃ - to C ₅ -carboxylic acids and monohydric alcohols, amides of

Acrylic acid or methacrylic acid with C ₁ - to C ₂₄ -alkylamines, vinyl esters of saturated monocarboxylic acids having 2 to 24 C atoms, diesters of maleic acid or fumaric acid with monohydric C ₁ - to C ₂₄ -alcohols, vinyl ethers of alcohols having 3 to 24 C- Atoms or mixtures of the compounds mentioned.

The amphiphilic copolymers contain as hydrophilic monomers (b), for example C ₃ - to C ₁₀ - monoethylenically unsaturated carboxylic acids or their anhydrides, 2-acrylamido 2-methylpropanesulfonic acid, vinylsulfonic acid, styrenesulfonic acid, vinylphosphonic acid, salts of said monomers or mixtures thereof as hydrophilic monomers copolymerized with an anionic group.

Particularly preferred are aqueous sizing agent dispersions containing anionic dispersant amphiphilic copolymers

(a) α-olefins having 4 to 12 C atoms, styrene or mixtures thereof as hydrophobic

Monomers and (b) maleic acid, acrylic acid, methacrylic acid, half esters of maleic acid and alcohols having 1 to 25 carbon atoms or alkoxylation of such alcohols, hemiamides of maleic acid, salts of said monomers or mixtures of these compounds as hydrophilic monomers copolymerized with an anionic group, and have a molecular weight M _w of 1 500 to 100 000.

As anionic dispersants are preferably copolymers of maleic anhydride with C ₄ - to C ₁₂ olefins, more preferably C ₈ olefins such as octene-1 and diisobutene. Most preferred is diisobutene. The molar ratio between maleic anhydride and olefin is for example in the range 0.9: 1 to 3: 1, preferably from 0.95: 1 to 1, 5: 1. These copolymers are preferably used in hydrolyzed form as aqueous solution or dispersions, wherein the anhydride group is present open and the carboxyl groups are preferably partially or completely neutralized. The following bases are used for neutralization: alkali metal bases, such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, alkaline earth salts, such as calcium hydroxide, calcium carbonate, magnesium hydroxide, ammonia, primary, secondary or tertiary amines, such as triethylamine, triethanolamine, diethanolamine, ethanolamine, morpholine etc.

If the amphiphilic copolymers in the form of the free acid are not sufficiently water-soluble, they are used in the form of water-soluble salts, for example using the corresponding alkali metal, alkaline earth metal and ammonium salts. The molecular weight M _{w of} the amphiphilic copolymers is, for example, 800 to 250,000, usually 1,000 to 100,000, and is preferably in the range from 3,000 to 20,000, in particular from 1,500 to 10,000. The acid numbers of the amphiphilic copolymers are, for example, from 50 to 500, preferably 150 to 300 mg KOH / g polymer.

The amphiphilic copolymers are used, for example, in amounts of from 0.05 to 20, preferably from 0.5 to 10,% by weight, based on the reactive sizing agent, of the anionic dispersant Production of sizing agent dispersions used. Preferably, the amphiphilic copolymers are used in amounts of 0.1 to 2, in particular 0.6 to 1 wt .-%, based on the sizing agent to be dispersed. The sole use of amphiphilic copolymers as dispersants gives aqueous solvent dispersions which are formaldehyde-free and storage-stable.

In order to prepare aqueous anionic sizing dispersions may be for example an aqueous solution of at least one condensation product or at least one amphiphilic copolymer present therein at temperatures of for example 20 to 100, preferably 40 to 90 ⁰ C disperse the sizing agents. The sizing agent is preferably added in the form of a melt and dispersed with vigorous stirring or shearing. The resulting dispersion is cooled in each case. In this way it is possible, for example, to prepare aqueous, anionically adjusted sizing dispersions which contain 6 to 65% by weight of an alkyldiketene or 0.1 to 65% by weight of an alkenylsuccinic anhydride dispersed as sizing agent. Preference is given to highly concentrated size dispersions containing, for example, from 25 to 60% by weight of an alkyldiketene sizing agent in the presence of from 0.1 to 5.0% by weight of a condensation product of naphthalenesulfonic acid and formaldehyde or at least one condensation product of (b) , (c) and / or (d) dispersed.

Further preferred sizing agent dispersions contain from 25 to 60% by weight of an alkyldiketene sizing agent and from 0.1 to 5.0% by weight of an amphiphilic copolymer

(I) 95 to 50 wt .-% of isobutene, diisobutene, styrene or mixtures thereof and (ii) 5 to 50 wt .-% acrylic acid, methacrylic acid, maleic acid, half esters of maleic acid or mixtures thereof or a water-soluble salt of such a copolymer.

Such highly concentrated size dispersions have a relatively low viscosity, for example in the range of 20 to 100 mPas (measured with a Brookfield viscometer and a temperature of 2O ⁰ C). In the preparation of the aqueous dispersions, the pH is, for example, 2 to 8, and is preferably in the range of 3 to 4. An aqueous anionic sizing agent dispersion having an average sizing size in the range of 0.1 to 3 is obtained , preferably 0.5 to 1, 5 microns.

If appropriate, the anionically dispersed reactive sizing agents may additionally contain at least one cationic dispersant, but the amount of cationic dispersant must be chosen such that the total dispersion carries an anionic charge. Preferred cationic dispersant is cationic starch.

If appropriate, the aqueous dispersions of a reactive sizing agent can be used together with a cationic, synthetic polymer which acts as a fixing agent and promoter, wherein fixing agent and promoter are metered in a mixture with at least one reactive sizing agent or separately therefrom. For optimum dosing, these additives are also mixed in a turbulent flow with the stock. For this purpose, the same devices can be used as for the addition of reactive sizes and retention agents. The cationic polymers used as fixing agents and promoters can be metered into the paper stock, for example, before or after the last shear stage. Examples of cationic polymers of this type are polymers containing vinylamine units, polymers containing vinyl guanidine units, polyethyleneimines, polyamidoamines grafted with ethyleneimine and / or polydiallyldimethylammonium chlorides. The amount of cationic polymers is for example 0.001 to 2.0, preferably 0.01 to 0.1 wt .-%, based on dry pulp.

The cationic polymers which are used as fixing agents and as promoters are known, cf. WO-A-2004/022848, page 6, line 39 to page 12, line 24. They preferably have K-values according to Fikentscher of 50 to 135 (determined in 5% aqueous saline solution at 25 ⁰ C, a pH of 7 and a polymer concentration of 0.5% by weight). Cationic polymers preferably used as fixing agents and promoters are hydrolyzed polyvinylformamides having a degree of hydrolysis of, for example, from 5 to 100% and polyethyleneimines.

The dewatering of the paper stock is carried out according to the invention, in the presence of at least one reactive sizing agent and at least one retention agent. In addition to anionic retention aids or nonionic retention aids such as polyacrylamides, cationic polymers are preferably used as retention aids and as dehydrating agents. This achieves a significant improvement in the runnability of the paper machine. In contrast to the fixatives, the retention agents have a higher molecular weight. For example, they have Fikentscher K values of at least 140, usually from 170 to 300 (determined in 5% strength aqueous sodium chloride solution at 25 ° C., a polymer concentration of 0.5% by weight and a pH of 7 ). They are preferably used in amounts of from 0.01 to 0.03% by weight, based on dry paper stock.

Suitable retention agents are all polymers which are commercially available for this purpose, in particular cationic polyacrylamides, polydiallyldimethylammonium chlorides, high molecular weight polyvinylamines, polyethyleneimines, polyamines having a molecular weight of more than 50,000, modified polyamines grafted with ethyleneimine and optionally crosslinked, polyetheramides, polyvinylimidazoles, polyvinylpyrrolidines, polyvinylimidazolines, polyvinyltetrahydropyrines, poly (dialkylaminoalkylvinyl ethers), poly (dialkylaminoalkyl (meth) acrylates) in protonated or in quaternized form and polyamidoamines of a dicarboxylic acid such as adipic acid and polyalkylenepolyamines such as diethylenetriamine grafted with ethyleneimine and cross-linked with polyethylene glycol dichlorohydrin ethers according to the teaching of DE-B-24 34 816 or polyamidoamines which have been reacted with epichlorohydrin to give water-soluble condensation products and also copolymers of acrylamide or methacrylamide and dialkylaminoethyl acrylates or methacrylates, for example copolymers of acrylamide and dimethylaminoethyl acrylate in the form of the salt with hydrochloric acid or in methylated quaternized form.

Further suitable retention aids are so-called microparticle systems consisting of a polymeric retention agent with a molecular weight M _w of at least 1 million, preferably at least 2 million, and a finely divided inorganic or organic component. Such systems are known, cf. US-A-3,052,595, EP-A-017353, EP-A-223,223, EP-A-335,575, EP-A-711,371, WO-A-01/34910, US-A-6, 103,065 and DE-A-102 Examples of suitable organic components of the microparticle system are retention aids selected from the group consisting of vinylamine units, polymers containing vinylguanidine units, nonionic, cationic and anionic polyacrylamides, polyethyleneimines, ethyleneimine-grafted, crosslinked polyamidoamines, cationic starches and polydiallyldimethylammonium chlorides ,

The retention aid of the microparticle system may be cationic, anionic, amphoteric or nonionic. At least one polymer from the group of nonionic polyacrylamides, the nonionic polymethacrylamides, the cationic polyacrylamides, the cationic polymethacrylamides, the anionic polyacrylamides, the anionic polymethacrylamide, the poly (N-vinylformamide), and the vinylamine units contains, for example, as the polymeric, synthetic retention aid Polymers and the Polydiallyldimethylammoniumchloride into consideration. The average molecular weight M _{w of} the polymeric retention aids is preferably at least 2 million daltons, in particular at least 3 million, and is usually in the range of, for example, 3.5 million to 15 million. The charge density of the polymers in question is, for example, at most 4.0 meq./g.

Particularly preferred are cationic polyacrylamides having an average molecular weight M _w of at least 5 million daltons and a charge density of 0.1 to 3.5 meq./g and polyvinylamines obtainable by hydrolysis of vinylformamide units containing polymers and having an average molecular weight of at least Have 2 million daltons. The polyvinylamines are preferably obtained by hydrolysis of homopolyamines. mers of N-vinylformamide produced, wherein the degree of hydrolysis, for example, up to 100%, usually 70 to 95%. High molecular weight copolymers of N-vinylformamide with other ethylenically unsaturated monomers such as vinyl acetate, vinyl propionate, methyl acrylate, methyl methacrylate, acrylamide, acrylonitrile and / or methacrylonitrile can also be hydrolyzed to give polymers containing vinylamine units and used according to the invention. For example, all polyvinylamines having a molecular weight M _w of at least 2 million can be used according to the invention, which are obtainable by hydrolysis of vinylformamide units-containing polymers, the degree of hydrolysis of the vinylformamide units being 0.5 to 100 mol%. The preparation of homopolymers and copolymers of N-vinylformamide is known. It is described in detail in, for example, US Pat. No. 6,132,558, column 2, line 36 to column 5, line 25. The statements made there are hereby incorporated by reference into the disclosure content of the present application.

Cationic polyacrylamides are, for example, copolymers prepared by copolymerizing acrylamide and at least one di-C ₁ -C ₂ -alkylamino-C ₂ -bisC ₄ -alkyl (meth) acrylate or a basic acrylamide in the form of the free bases, the salts with organic or inorganic acids or the compounds quaternized with alkyl halides. Examples of such compounds are dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylate, dimethylaminopropyl acrylate, diethylaminopropyl methacrylate, diethylaminopropyl acrylate and / or dimethylaminoethylacrylamide, dimethylaminoethylmethacrylamide, dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide and / or diallyldimethylammonium chloride. The comonomers mentioned can also be copolymerized with methacrylamide to form cationic polymethacrylamides containing, for example, from 5 to 40 mol% of at least one cationic monomer, such as dimethylaminoethyl acrylate or diallyldimethylammonium chloride, in copolymerized form. Cationic polymethacrylamide can also be used as a polymeric retention agent of the microparticle system.

Further examples of polymers containing cationic polyacrylamides and vinylamine units can be found, for example, in the references such as EP-A-0 910 701 and US Pat. No. 6,103,065. One can use both linear and branched polyacrylamides. Such polymers are commercial products. Branched polymers, e.g. can be prepared by copolymerization of acrylamide or methacrylamide with at least one cationic monomer in the presence of small amounts of crosslinking agents, for example, in the references cited in the prior art US Pat. No. 5,393,381, WO-A-99/66130 and WO-A-99 / 63159 described.

Further suitable cationic polymeric retention aids of the microparticle system are polydiallyldimethylammonium chlorides (polyDADMAC) with an average molecular weight. at least 2 million daltons. Polymers of this type are commercial products. Preferably used polymers of the microparticle system are cationic polyacrylamides, vinylamine units containing polymers and mixtures thereof, wherein the molecular weights M _{w of} the polymers amount to at least 2 million.

The polymeric retention aids of the microparticle system are added to the paper stock, for example, in an amount of 0.005 to 0.5% by weight, preferably in an amount of 0.01 to 0.25% by weight, based on dry paper stock.

Benetonit, colloidal silicic acid, silicates and / or calcium carbonate may be considered as an inorganic component of the microparticle system. Colloidal silicic acid is to be understood as meaning products based on silicates, for example silica microgel, silical sol, polysilicates, aluminum silicates, boron silicates, polyboron silicates, clay or zeolites. Calcium carbonate can be used, for example, in the form of chalk, ground calcium carbonate or precipitated calcium carbonate as the inorganic component of the microparticle system. Bentonite is generally understood to be phyllosilicates which are swellable in water. These are mainly the clay mineral montmorillonite and similar clay minerals such as nontronite, hectorite, saponite, sauconite, beidellite, allevardite, illite, halloysite, attapulgite and sepiolite. These phyllosilicates are preferably activated before use, ie converted into a water-swellable form in which the phyllosilicates are treated with an aqueous base such as aqueous solutions of caustic soda, potassium hydroxide, soda, potash, ammonia or amines. Bentonite in the form treated with sodium hydroxide solution is preferably used as the inorganic component of the microparticle system. The platelet diameter of the water-dispersed bentonite is in the group treated with Natromlauge form, for example 1 to 2 microns, the thickness of the flakes is nm at about first depending on the type and activation has the bentonite has a specific O- berfläche 60-800 m ² / G. Typical bentonites are described, for example, in EP-B-0235893. In the papermaking process, bentonite is added to the cellulosic suspension, typically in the form of an aqueous bentonite slurry. This bentonite slurry may contain up to 10% by weight of bentonite. Normally, the slurries contain about 3 to 5 wt .-% bentonite.

As colloidal silica, products from the group of silicon-based particles, silica microgels, silica sols, aluminum silicates, borosilicates, polyborosilicates or zeolites can be used. These have a specific surface area of 50 to 1000 m ² / g and an average particle size distribution of 1 - 250 nm, usually in the range 40 - 100 nm. The preparation of such components is described, for example, in EP-AO 041 056, EP-AO 185 068 and US-A-5,176,691.

Clay or kaolin is a hydrous aluminum silicate with a platelet-like structure. The crystals have a layer structure and an aspect ratio Diameter to thickness) of up to 30: 1. The particle size is for example at least 50% less than 2 microns.

Carbonates used are preferably natural calcium carbonate (ground calcium carbo- nate, GCC) or precipitated calcium carbonate (PCC). GCC is produced, for example, by grinding and visual processes using grinding aids. It has a particle size of 40 - 95% less than 2 microns, the specific surface area is in the range of 6 - 13 m ² / g. For example, PCC is made by passing carbon dioxide into an aqueous calcium hydroxide solution. The average particle size is in the range of 0.03-0.6 μm. The specific surface area can be greatly influenced by the choice of precipitation conditions. It is in the range of 6 to 13 m ² / g.

The inorganic component of the microparticle system is added to the paper stock in an amount of 0.01 to 2.0% by weight, preferably in an amount of 0.1 to 1.0% by weight, based on dry paper stock.

Also suitable as a microparticle system are also combinations of an organic polymer having a molecular weight M _w of at least 2 million and a mixture of a finely divided inorganic component and a finely divided organic component, wherein both components are metered independently of one another either simultaneously or in succession. A suitable finely divided organic component having an anionic charge is described, for example, in WO-A-98/29604. At least one finely divided crosslinked copolymer of acrylamide and at least one monoethylenically unsaturated anionic monomer is preferably used as finely divided, organic component of the microparticle system.

Examples of microparticle systems are combinations of cationic polymers such as cationic starch and finely divided silica or of cationic polymers such as cationic polyacrylamide and bentonite.

It is possible to add to the pulp the process chemicals usually used in papermaking in the usual amounts, e.g. the already mentioned fixatives, as well as dry and wet strength agents, biocides and / or dyes. Of the

Paper stock is dewatered on a sieve with formation of sheets. The leaves thus produced are dried. Dewatering the stock and drying the sheets are part of the papermaking process and are performed continuously in the art.

Compared with the prior art, the advantage of the process according to the invention is that reactive sizes, retention aids and optionally xiermittel and other process aids used in the optimum for the respective substances residence time in the pulp and thus the maximum possible with these substances effect such as sizing grade of the paper and retention of fillers can achieve.

Claims

claims

Anspruch [en] A method for sizing paper, board and board by successively adding an aqueous dispersion of at least one reactive sizing agent and at least one retention agent to a laminar flow of stock with a fabric concentration of at most 2% by weight of dry fibers and dewatering the paper Paper stock under sheet formation, characterized in that the Reaktivleimungsmittel and the retention agent metered under turbulent flow at a point in the paper pulp flow, which is after the last shear stage and before the start of the dewatering process.

2. The method according to claim 1, characterized in that the contact time of reactive sizing agent and retention agent in the paper stock from the metering point to the beginning of the dewatering process is at most 30 seconds.

3. The method according to claim 2, characterized in that the contact time of reactive sizing agent and retention agent in the pulp from the metering point to the beginning of the dewatering process is at most 10 seconds.

4. The method according to any one of claims 1 to 3, characterized in that the reactive sizing agent in the paper has a 0.5 to 20 seconds higher contact time than the retention agent.

5. The method according to any one of claims 1 to 4, characterized in that a contact time of sizing agent and retention agent in the paper stock in the range of 0.1 to 30 seconds is selected so that the optimum effect of sizing agent and retention agent is achieved.

6. The method according to any one of claims 1 to 5, characterized in that the sizing agent C ₁₂ - to C ₂₂ -Alkylketendimere, C ₅ - to C ₂₂ alkyl and / or C ₅ - to C ₂₂ -Alkenylbemsteinsäureanhydride, C ₁₂ - to C ₃₆ - alkyl isocyanates or mixtures of the compounds mentioned.

7. The method according to any one of claims 1 to 6, characterized in that one uses as sizing anionically adjusted aqueous dispersions of at least one C ₁₂ to C ₂₂ alkyldiketene.

8. The method according to any one of claims 1 to 7, characterized in that at least one retention agent from the group of vinylamine units containing polymers, vinylguanidine units containing polymers, nonionic, cationic and anionic polyacrylamides, polyethyleneimines, ethyleneimine-grafted, crosslinked polyamidoamines and polydiallyldimethylammonium chlorides.