EP2087169A1

EP2087169A1 - Method for producing a multi layer fiber web from cellulose fibers

Info

Publication number: EP2087169A1
Application number: EP07847084A
Authority: EP
Inventors: Simon Champ; Wolfgang Gaschler; Marc Leduc; Ellen KRÜGER; Christoph Hamers; Hans-Peter Hentze
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2006-10-31
Filing date: 2007-10-29
Publication date: 2009-08-12
Also published as: WO2008052970A1; CA2665712A1; US20100000693A1; CN101529020A

Abstract

The invention relates to the production of a multi layer fiber web from cellulose fibers by separately feeding of at least two different fiber suspensions and water into a multi layer head box, wherein separating elements separate them from each other and from the water. After leaving the nozzle mouth of the head box, they are transported to a device on which a web is formed. The water is guided in a way, such that it ends up in form of a layer between two layers of fiber suspensions on the web forming device after exiting the nozzle mouth and thus prevents mixing of the different fiber suspensions. At least one retention agent and/or at least one dehydrating agent is dosed to the fiber suspension and/or to the added water to increase the retention, dehydration and formation.

Description

Process for producing a multilayer fibrous web of cellulosic fibers

description

The invention relates to a method for producing a multi-layer fibrous web of cellulose fibers by separately feeding at least two different fiber suspensions and water into a multi-layer headbox, wherein they are separated from each other and from the water by separating elements and reach a device after leaving the headbox nozzle orifice a web is formed, wherein the water is guided so that it comes after exiting the nozzle orifice in the form of a layer between two layers of fiber suspensions on the web forming device and thus counteracts a mixing of the different fiber suspensions.

In order to produce multilayer papers in a paper machine, they must be equipped with a multi-layer discharge box, the discharge nozzle chambers of which are subdivided into separate flow channels and which extend over the entire width of the machine. So you can, for example make a paper consisting of three layers, by passing three differently composed pulps separately through a three, separate flow channels having Auslaufdüsenkammer and then drained on a wire of a paper machine, see. EP-A-0 939 842 and DE-A-10 2004 051 255.

From DE-A-101 26 346 a method and a Stoffzuführsystem for feeding a Mehrschichtstoffauflaufs a paper machine is known, being introduced by means of a single pump white water and the Siebwasserstrom is divided into several Siebwasserteilströme, then metered in thick matter and the thus obtained Partial streams via distributor the multilayer headbox feeds.

From WO-A-03/048452 a method for producing a multilayer fibrous web from at least two different fiber suspensions is known. The fiber suspensions and water are each fed separately to a multi-layer headbox, wherein they are separated by separating elements and after leaving the nozzle mouth of the headbox on a device on which a web is formed, wherein the water is guided so that it after the Exits the nozzle orifice in the form of a layer between two layers of fiber suspensions on the web forming device and prevents mixing of the various fiber suspensions. The separating elements in the multi-layer headbox are designed so that they are movable in the vertical direction and thus allow in the headbox a change in pressure between the pulp suspensions. However, in the references cited above, nothing more is disclosed about the fiber suspensions. When using a multilayer headbox for producing multilayer papers, there is always the danger that the individual fiber streams will be mixed between the end of the fabric outlet nozzle and the drainage part of the paper machine.

In the production of paper, which consists of only a single layer, various process chemicals such as sizing agents, dehydrating agents, flocculants, retention aids and dry and wet strength or mixtures of said process chemicals and biocides and / or dyes and color pigments are known to be used depending on the paper , see. Ullmann ^'s Encyclopedia of Industrial Chemistry, Sixth, Completely Revised Edition, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2003, Volume 25, pages 1 to 157, and optical brighteners, means for increasing the volume of the paper (so-called Bulk Promoters, see US-B-6,273,995) and modified fibers as described, for example, in WO-A-2006/048280.

Not only the composition of the process chemicals, but also the timing of metering such products into a pulp is an important feature in papermaking. The type and timing of dosing of retention and dewatering agents into a stock has e.g. an influence on the retention, the drainage rate and the formation. Thus, for example, EP-AO 235 893, EP-AO 335 575, EP-AO 310 959, US Pat. No. 4,388,150 and WO-A-94/05595 disclose a process for the production of paper using a microparticle system, in which case dosed a cationic polymer to the paper stock, then subjecting the mixture to the action of a shear field, then adding bentonite or silica and dewatering the pulp so obtainable without further action of shearing forces.

According to the process known from DE-A-102 36 252 for the production of paper, a microparticle system comprising a cationic polymer and a finely divided inorganic component is metered to the pulp after the last shear stage in front of the headbox and then the pulp is dewatered.

From EP-A-0462 365 organic microparticles are known, which may be uncrosslinked or crosslinked and each containing at least 1 wt .-%, but usually at least 5 wt .-% of an ionic comonomer in copolymerized form. The particle size of the uncrosslinked, water-insoluble microparticles is below 60 nm, while it is less than 750 nm for the crosslinked microparticles. The organic microparticles are used in papermaking together with a high molecular weight ionic polymer as a retention aid system, which may optionally additionally contain inorganic microparticles such as bentonite or silica. Furthermore, DE-A-10 2004 063 005 discloses a process for the production of paper, paperboard and paperboard using a microparticle system composed of a cationic polymeric retention agent having a molecular weight of at least 2 million and a finely divided inorganic component. The polymeric retention aid is metered into the stock and the finely divided inorganic component at least two times before or after the addition of the polymeric retention aid, subjecting the stock to at least one shear stage either before or after the addition of the retention agent. Further microparticle systems which are used as retention aids in papermaking are known, for example, from US Pat. No. 6,103,065 and WO-A-2004/015200.

From DE-A-10 2004 063 000 a process for engine sizing of paper, board and paperboard is known, wherein successively continuous addition of 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 substance concentration of at most 2 wt .-%, based on dry fibers, and dewatering of the paper stock under sheet formation in such a way that one doses the reactive sizing agent and the retention agent under turbulent flow at a point in the stock flow, after the last shear stage and before Beginning of the dewatering process is.

The invention has for its object to provide a method for producing multilayer papers with an improved formation available, wherein the mixing of the individual fiber streams during the web forming process does not take place as much as in known methods.

The object is achieved with a method for producing a multilayer fibrous web of cellulose fibers by separately feeding at least two different fiber suspensions and water in a Mehrla- genstoffauflaufkasten, wherein they are separated by separating elements from each other and supplied water and after leaving the nozzle orifice of Headbox on a dewatering device on which a multi-layer fibrous web is formed, wherein the water is guided so that it passes after exiting the nozzle orifice in the form of a layer between two layers of fiber suspensions on the web forming device and thus counteracts a mixing of the different fiber suspensions if, in order to improve the retention, drainage and formation, at least one retention agent and / or at least one dehydrating agent in the fiber suspensions and / or in the water supplied d osiert. According to the invention, a retention agent or a dehydrating agent or both products are metered into fiber suspensions. The addition of these agents may occur in the papermaking process prior to shear of the stock, between two shear stages, or after the last shear of the stock. Preferably, an aqueous solution of at least one retention agent and / or at least one dewatering agent is metered into the stock stream at a location downstream of the last shear stage of the stock and upstream of the headbox mouth. The addition of retention agent and / or dehydrating agent to the paper material is particularly advantageous under turbulent flow of the aqueous formulations of process chemicals. This achieves the most uniform possible distribution of these products in the pulp. For example, to create a turbulent flow one may use the device described in US-B-6,659,636. It consists, for example, of a two-component or multi-fluid nozzle through which water recycled from the paper machine and retention agent and / or dehydrating agent are passed into a laminar flowing paper stream. 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.

A method for producing a multilayer fibrous web of cellulosic fibers by separately feeding at least two different fiber suspensions and water into a multi-layer headbox wherein they are separated from each other and from supplied water by separating elements and reach a dewatering device after leaving the headbox nozzle mouth, on which a multilayer fibrous web is formed, wherein the water is guided so that it after leaving the nozzle orifice in the form of a

Layer passes between two layers of fiber suspensions on the web forming device and thus counteracts a mixing of the various fiber suspensions, is known from the prior art WO-A-03/048452 known. For details, reference is made to this publication, in particular page 2, line 2 to page 5, line 32 and the claims. As described therein, the flow of the supplied water is guided within the headbox by so-called "blade means" and passes between two streams of pulp suspensions into the dewatering section of the paper machine. The speed of the water flow is adapted to the speed of the fiber streams and is, for example, in the range of 2 to 10 m / sec, preferably 3 to 8 m / sec. The velocity of the water stream separating the fiber streams is preferably from 1 to 25%, most often from 5 to 10%, higher than the velocity of the individual fiber streams.

At least two fiber suspensions which are processed into a multilayer fibrous web have a different composition. Thus, for example, the middle layer of a three-layer fibrous web may consist of a cheap fibrous material such as waste paper, and the upper and lower side of the fibrous web may consist of a high-quality fibrous web. gene pulp, such as bleached pine sulfate are formed. Through the selection of fibers and the additional use of other process chemicals such as engine sizing agents and / or solidifiers, it is possible to produce various types of multi-layer fibrous webs.

When using different fiber suspensions, which differ for example only by the nature of the suspended fibers or their concentration, it is possible according to the invention to add the same retention agent to all streams of fiber suspensions and meter it in such a way that at least two streams of fiber suspensions contain a different concentration of this retention agent. A further variant of the method according to the invention consists in metering at least two mutually different retention agents into at least two streams of fiber suspensions. These fiber suspensions may be composed of the same or different fibers. In addition, it is possible for at least two streams of fiber suspensions to contain a different concentration of retention aid.

In another embodiment of the process according to the invention, an aqueous solution of a retention agent and an aqueous dispersion of at least one filler are metered apart from one another or as a mixture into the paper stock.

However, retention aids and dehydrating agents can also be metered into at least one stream of the water supplied. Thus, it is possible, for example, to separate an aqueous solution of a retention agent and an aqueous dispersion of at least one filler from one another or to meter it as a mixture into at least one stream of the water supplied. However, one can also proceed by metering an aqueous dispersion of a filler into at least one stream of the fiber suspension and that the water supplied contains at least one retention agent. The retention aid supplied with the water can also be withdrawn as an aqueous solution from a storage vessel or metered separately into the water supplied.

Further process variants consist of using at least one retention agent in combination with at least one dehydrating agent or by using at least one retention agent in combination with a fixing agent. Fibers are used in particular when the pulp has a high cationic demand, for example having a COD of from 300 to 30,000, usually from 1000 to 20,000 mg of oxygen / kg of the aqueous phase of the pulp.

Examples of fixing agents are condensates of dicyandiamide and formaldehyde, condensates of dimethylamine and epichlorohydrin, cationic polyacrylamides having molecular weights Mw 1 000 to 20 000, or hydrolyzed homopolymers and copolymers of N-vinylformamide having a K value of 30 to 150, preferably 60 to 90 (determined according to H. Fikentscher, Cellulosic Chemistry, Vol. 13, 48-64 and 71-74 (1932) in 5% strength by weight aqueous common salt solution at a temperature of 25 ° C. and a polymer concentration of 0.5% by weight) , Fixing agents are used, for example, in an amount of 0.02 to 2 wt .-%, preferably 0.05 to 0.5 wt .-%, based on dry pulp.

For the method according to the invention, it is possible to use all retention aids which are known from the practice of papermaking or from the literature for this purpose. They are used for example in an amount of 0.01 to 0.3, preferably 0.01 to 0.05 wt .-%, based on dry pulp. The retention agent may, for example, be selected from the group of cationic, anionic, nonionic and amphoteric polymeric organic compounds or a microparticle system. The most common retention aids belong, for example, to the group of the polyacrylamides, the polymethacrylamides, the polymers containing vinylamine units and / or the microparticle systems.

Polyacrylamides and polymethyacrylamides can be nonionic, cationic, anionic or amphoteric. Polymers suitable as retention aids have an average molecular weight M _w of at least 1 million, preferably at least 2 million and in particular at least 5 million. Nonionic polyacrylamides or polymethacrylamides are prepared, for example, by polymerizing N-vinylformamide, acrylamide and / or methacrylamide.

Cationic polyacrylamides are, for example, copolymers prepared by copolymerizing acrylamide and at least one di-C 1 -C 2 -alkylamino-C 2 -C 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 which are quaternized with alkyl halides or with dimethyl sulfate. 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, 5 to 40 mol% of at least one cationic monomer, such as dimethylaminoethyl acrylate or diallyldimethylammonium chloride, in copolymerized form. Cationic polymethacrylamides can be prepared by copolymerizing methacrylamide with at least one of the cationic monomers described above. Other cationic polymers used as retention aids are copolymers of N-vinylformamide and at least one of the abovementioned cationic monomers. Anionic polyacrylamides are obtainable, for example, by copolymerizing acrylamide with at least one ethylenically unsaturated C3- to C5-carboxylic acid, in particular acrylic or methacrylic acid and / or monomers containing sulfonic acid groups, such as vinylsulfonic acid or styrenesulfonic acid and / or a salt of said monomers , Suitable salts are preferably the alkali metal salts, in particular the sodium salts and ammonium salts, into consideration. Anionic polymethacrylamides are prepared in analogy by polymerizing methacrylamide with the monomers having the above acid groups. The anionic polymers contain, for example, copolymerized 1 to 50, preferably 5 to 40 mol% of at least one anionic monomer.

The anionic polymeric retention aids also include copolymers which are obtainable by copolymerizing

at least one N-vinylcarboxamide of the formula

in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,

at least one acid group-containing monoethylenically unsaturated monomer and / or their alkali metal, alkaline earth metal or ammonium salts and optionally other monoethylenically unsaturated monomers, and optionally compounds which have at least two ethylenically unsaturated double bonds in the molecule.

The copolymeric anionic compound of this group used is preferably a copolymer which is obtainable by copolymerizing N-vinylformamide, acrylic acid, methacrylic acid and / or their alkali metal or ammonium salts and optionally other monoethylenically unsaturated monomers,

for example, the polymeric anionic compound

(a) 10 to 95 mol% of the units of the formula I.

(B) 5 to 90 mol% of units of a monoethylenically unsaturated carboxylic acid having 3 to 8 carbon atoms in the molecule and / or their alkali metal, alkaline earth metal or ammonium salts and

(c) contains from 0 to 30 mol% of units of at least one other monoethylenically unsaturated monomer in copolymerized form. The compounds of this group may be modified such that they additionally contain at least one compound (d) in copolymerized form with at least two ethylenically unsaturated double bonds in the molecule. When the monomers (a) and (b) or (a), (b) and (c) are copolymerized in the presence of such a compound (d), branched copolymers are obtained. The proportions and reaction conditions are to be chosen so that water-soluble polymers are still obtained. Under certain circumstances it may be necessary to use polymerization regulators. All known regulators can be used, such as, for example, thiols, sec. Alcohols, sulfites, phosphites, hypophosphites, thioacids, aldehydes, etc. (further details can be found, for example, in EP-A-0 438 744, page 5, lines 7-12). The branched copolymers contain, for example

(a) 10 to 95 mol% of units of the formula I,

(b) 5 to 90 mol% of units of an acid group-containing monoethylenically unsaturated monomer and / or their alkali metal, alkaline earth metal or ammonium salts,

(c) 0 to 30 mol% of units of at least one other monoethylenically unsaturated monomer and

(D) 0 to 2 mol%, preferably 0.001 to 1 mol% of at least one compound having at least two ethylenically unsaturated double bonds

in copolymerized form.

Amphoteric polyacrylamides and amphoteric polymethacrylamides each contain units of cationic and of anionic monomers in copolymerized form. An example of this is a copolymer of acrylamide, dimethylaminoethyl acrylate hydrochloride and acrylic acid.

Vinylamine-containing polymers are obtainable by hydrolysis of vinylformamide units containing polymers. Polyvinylamines are prepared for example by hydrolysis of homopolymers of N-vinylformamide, 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, Methacrylsäuremethy- ester, acrylamide, acrylonitrile and / or methacrylonitrile, can be hydrolyzed to Vinylamineinheiten containing polymers and used according to the invention as a retention agent. The polymers containing vinylamine units are cationic. In the hydrolysis of polymers of N-vinylformamide with acids, the salts of the polymers (ammonium salts), while resulting in the hydrolysis with bases such as sodium hydroxide or potassium hydroxide amino-bearing polymers. The preparation of homo- and copolymers of N-vinylformamide and the preparation of the polymers obtainable therefrom by hydrolysis of amino or ammonium groups 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. Polymers containing vinylamine units are preferably used as retention aids in the process according to the invention.

Further cationic polymeric retention aids are polydiallyldimethylammonium chlorides (polyDADMAC) and branched polyacrylamides, which are e.g. can be prepared by copolymerization of acrylamide or methacrylamide with at least one cationic monomer in the presence of small amounts of crosslinkers. Such polymers are described, for example, in US-A-5,393,381, WO-A-99/66130 and WO-A-99/63159.

Also suitable as cationic retention aids are polyamines having a molecular weight of more than 50,000, modified polyamines grafted with ethyleneimine and optionally crosslinked, polyetheramides, polyvinylimidazoles, polyvinylpyrrolidines, polyvinylimidazolines, polyvinyltetrahydropyrines, poly (dialkylaminoalkylvinylether), poly (dialkylaminoalkyl (meth) acrylates) in protonated or in quaternized form and polyamidoamines from a dicarboxylic acid such as adipic acid and polyalkylenepolyamines such as diethylenetriamine, which are grafted with ethyleneimine and crosslinked with Polyethylenglykoldich- lorhydrinethern according to the teaching of DE-B-24 34 816 or polyamidoamines, with Epichlorohydrin are converted to water-soluble condensation products. Further retention aids are cationic starches, alum and polyaluminum chloride.

Further suitable retention aids are so-called microparticle systems made of a polymeric retention agent having 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-0 335 575, EP-A-711,371, WO-A-01/34910, US-A-6,103,065 and DE-A-102 36,252. Both components are typically added separately to the stock during the papermaking process. Suitable organic components of the microparticle system are the above-described polymers, for example retention aids from the group of polymers containing vinylamine units, polymers containing vinylguanidine units, nonionic, cationic and anionic polyacrylamides, polyethyleneimines, ethyleneimine-grafted, crosslinked polyamidoamines, cationic starches and poly-diallyldimethylammonium chlorides ,

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 montmorrillonite as well as similar clay minerals like

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 sodium hydroxide treated form, for example 1 to 2 microns, the thickness of the platelets is about 1 nm. Depending on the type and activation of the bentonite has a specific O- berfläche of 60 to 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 to 250 nm, normally in the range 40 to 100 nm. The production 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 ratio) of up to 30: 1. The particle size is e.g. at least 50% smaller than 2 μm.

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. PCC becomes for example by introducing 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 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 the two components are metered independently of one another either simultaneously or in succession. A suitable finely divided organic component with 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.

Instead of a retention agent or in combination with a retention agent, flocculants may also be metered into at least one stream of a fiber suspension and / or into at least one stream of the water supplied. Of particular interest here may be such flocculants, which are effective only at a higher temperature. An example is methyl cellulose as a flocculant is ineffective at about 20 ⁰ C and acts at 75 ° C as a flocculant, see. GV Franks, Journal of Colloid and Interface Science 292, 598-603 (2005). Another example of a thermosensitive flocculant is poly (N-isopropylacrylamide). In the method according to the invention, the thermosensitive flocculants can be metered, for example, into at least one stream of the water fed in, which has a temperature in the region in which the flocculant is effective. For example, the stream of pulps may have a temperature in the range of 20 to 45 ° C, while the flow of the feed water may have a temperature in the range of 60 to 75 ° C.

PH-sensitive flocculants can also be used in the process according to the invention. An example of such a flocculant is the polysaccharide chitosan. For example, it is ineffective as a flocculant at pH 4.5, but flocculates as soon as the pH is increased to, for example, 8. Suitable dehydrating agents are preferably polymers containing ethyleneimine units. Such polymers are already listed above with the cationic retention agents. They act both as retention aids and as draining agents. Since the dehydrating effect of this class of compounds is more pronounced than the retenierenden effect, they are referred to in the present context as a dehydrating agent. Polyethyleneimines which are obtainable by polymerizing ethyleneimine in aqueous solution in the presence of acidic catalysts such as mineral acids or halogen compounds such as methylene chloride, carbon tetrachloride, ethylene chloride or tetrachloroethane, as well as crosslinked condensation products of a polyamidoamine and one grafted with ethyleneimine, belong in particular to this class of compounds dicarboxylic acid. Such products are sold under the trademark Polymin® by BASF, Ludwigshafen. They are used in papermaking, for example, in an amount of at least 0.01% by weight, usually in the range from 0.1 to 0.3% by weight.

Depending on the respective fibrous materials used to produce multilayer papers, at least one stream of a fiber suspension is metered with a polyacrylamide and / or a polymer comprising vinylamine units and a polymer containing ethyleneimine units in a stream of another fiber suspension.

For example, to produce a three-layer fibrous web, one doses

(A) in the stream of fiber suspension, which forms the top of the fibrous web, a retention aid from the group polyacrylamides, polymethacrylamides, the

Vinylamine-containing polymers, microparticle systems and mixtures thereof,

(b) in the stream of the fiber suspension, which forms the middle layer of the fibrous web, a dehydrating agent from the group consisting of Ethylenimineinheiten containing polymers and / or a retention agent from the group of vinylamine units containing polymers, cationic, anionic, nonionic and amphoteric polyacrylamides, Polymethacrylamides and their mixtures, and

(C) in the stream of fiber suspension which forms the underside of the fibrous web, a retention agent from the group of polyacrylamides, polymethacrylamides, polymers containing vinylamine units, the microparticle systems and mixtures thereof.

Preferably, one doses in the production of a three-layer fibrous web

(a) in the stream of the fiber suspension, which forms the upper side of the fibrous web, as a retention agent, a polymer containing vinylamine units, (B) in the stream of the fiber suspension, which forms the middle layer of the fibrous web, as dehydrating a Ethylenimineinheiten-containing polymer, and

(C) in the stream of the fiber suspension which forms the underside of the fibrous web, as a retention agent, a polymer containing vinylamine units.

Paper webs having an improved formation are obtained, for example, by using a higher concentration of retention agent in the stream forming the middle fibrous web when producing a three-layer fibrous web than in the streams forming the top and bottom of the fibrous web , The amount of retention agent used for the middle layer of a three-layer fibrous web is, for example,> 0.01% by weight, usually 0.015 to 0.3% by weight, based on dry paper stock. For the production of the top and the bottom of a three-layer fibrous web, the amounts of retention agent are usually <0.01 wt .-%, for example in the range of 0.001 to 0.009 wt .-%, based on dry fiber.

According to another variant of the method, the addition of a retention agent or a filler takes place with the aid of the supplied water. Thus, at least one retention agent and at least one thickener are metered into the stream of the water supplied. However, one can mix these additives in the desired ratio in a reservoir and convey it into the nozzle chamber of the headbox. Suitable thickeners are, for example, high molecular weight polyacrylamides or high molecular weight polycarboxylic acids having molecular weights M _w of at least 1 million, preferably at least three million. The thickeners are preferably crosslinked polyacrylamides or crosslinked polycarboxylic acids which swell very strongly in an aqueous medium. An example of a known thickener is a crosslinked polyacrylic acid. Suitable crosslinkers are, for example, methylenebisacrylamide, glycol diacrylate, butanediol diacrylate, butanediol dimethacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, pentaerythritol triallyl ether or triallylamine. The amounts of thickening agent added to the water are, for example, from 0.001 to 10% by weight, preferably from 0.01 to 1% by weight. This achieves an increase in the viscosity of the water, which reduces the risk of mixing different fiber streams during the dewatering process.

In a further process variant, the paper stock, preferably the thin stock, and / or the stream of the supplied water contains at least one suspended filler. Suitable fillers are the finely divided inorganic substances customarily used in papermaking, for example titanium dioxide, ground calcium carbonate (marble), precipitated calcium carbonate, chalk, talc, montmorillonite, dolomite or clay. Filler may, for example, in an amount up to 40 wt .-%, usually in the range of 5 to 30 wt .-%, each on dry pulp, are used. The fillers are used, for example, in the form of an aqueous, pumpable slurry containing a dispersant such as polyacrylic acid having a molecular weight M _w of 5,000 to 12,000. The fillers may also be added by adding to the pulp in the preparation of the pulp. The finely divided inorganic fillers generally lead to an increase in the basis weight of the filler-containing paper compared to a filler-free paper.

However, it is also possible to increase the volume of the paper by, for example, adding thermally expandable microparticles directly to the paper stock or by metering according to the invention as an aqueous suspension together with a retention agent and / or a dehydrating agent at a point in the paper stock stream Last shear stage of the pulp and before the nozzle mouth of the headbox is. In a further variant of the method according to the invention, it is also possible to meter an aqueous suspension of thermally expandable microparticles into the stream of the water fed in, which counteracts a mixing of the fiber streams. The microparticles are used, for example, in an amount of from 2 to 50% by weight, preferably from 5 to 45% by weight, based on dry paper stock.

Thermally expandable microparticles are known. They have, for example, a mean particle diameter of 17 to 35 microns. They are prepared by polymerizing ethylenically unsaturated monomers in the presence of a blowing agent and optionally further substances such as silica, bentonite, clay, organic suspending agents such as methyl cellulose, carboxymethyl cellulose or polyvinyl alcohol, starch or oxides and hydroxides of aluminum, calcium, magnesium or barium. The blowing agent content of the microparticles is 17 to 40 wt .-%, see. US-A-2006/0102307. The microparticles described therein have a shell of a polymer of vinylidene chloride, acrylonitrile and methyl methacrylate. Further disclosures on expandable microparticles can be found in publications US-A-3,615,972, US-A-3,945,956, US-A-5,536,756, US 6,235,800, US 6,235,394, US 6,509,384 and EP-A-0 486,080. When drying papers containing expandable microparticles, an increase in volume of the paper occurs.

The effect of the dehydrating agents can be enhanced by using them together with at least one surfactant. Alkoxylation products of alcohols or amines are preferably suitable as surface-active agents. An example of this is Sursol® VL (BASF Aktiengesellschaft, Ludwigshafen). The amounts of surfactants are for example 0.01 to 10 wt .-%, based on dry pulp. Further agents of this category are quaternized alkanolamine fatty acid esters which are described, for example, in US Pat. No. 2006/0196624. or polyamine amides as described, for example, in Nordic Pulp and Paper Research Journal 2003, 18, 188-193.

In a further embodiment of the process according to the invention, at least one retention agent is used in combination with a sizing agent. Suitable engine sizes are preferably reactive sizes, in particular C 12 -C 22 alkyl ketene dimers, C 5 -C 22 -alkyl and / or C 5 -C 22 -alkenyl succinic anhydrides, C 12 -C 36 -alkyl isocyanates or mixtures of the abovementioned compounds. In addition, resin glue can be used as a mass sizing agent. The aqueous reactive size dispersions are stabilized, for example, with the aid of cationic starch, cf. EP-B-0 353 212, EP-B-0 369 328 and EP-B-0 437 764. The sizing agents employed are both cationic and in particular anionic aqueous dispersions of at least one C 12 -C 22 -alkyldiketene. Such dispersions are known, for example, from WO-A-00/23551, 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, use is made e.g. the usual homogenizers. 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 the condensation products

(a) naphthalenesulfonic acid and formaldehyde,

(b) phenol, phenolsulfonic acid and formaldehyde,

(c) naphthalenesulfonic acid, formaldehyde and urea; and (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, it being possible to use the corresponding alkali metal, alkaline earth metal or ammonium salts instead of the free acids. 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 with Formaldehyde preferably in a molar ratio of 1: 0.1 to 1: 2 and usually in a molar ratio of 1: 0.5 to 1: 1 condensed. 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, 0.1 to 5 moles 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 (i) 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 Cr to C24-alkylamines, vinyl esters of saturated monocarboxylic acids having 2 to 24 carbon atoms, diesters of maleic acid or fumaric acid with monohydric C to C24 alcohols, vinyl ethers of alcohols having 3 to 24 C atoms or mixtures of the named compounds.

The amphiphilic copolymers contain, as hydrophilic monomers (ii), 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 with an anionic one Group polymerized. Particularly preferred are aqueous sizing agent dispersions containing anionic dispersant amphiphilic copolymers

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

(Ii) 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 having an anionic group

contained in copolymerized form and have a molecular weight M _w of 1 500 to 100 000.

The anionic dispersants used are preferably copolymers of maleic anhydride with C ₄ - to C 12 -olefins, particularly preferably C ₂ -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 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 are not sufficiently soluble in water in the form of the free acid, 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, 50 to 500, preferably 150 to 300 mg KOH / g polymer.

The amphiphilic copolymers are used, for example, in amounts of 0.05 to 20, preferably 0.5 to 10 wt .-%, based on the reactive sizing agent, as an anionic dispersant for the preparation of sizing dispersions. 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. When amphiphilic copolymers alone are used as dispersants, aqueous sizing agent dispersions are obtained which are free from formaldehyde and stable in storage. In order to prepare aqueous anionic sizing dispersions can be present, for example, an aqueous solution of at least one condensation product or at least one amphiphilic copolymer and disperse therein the sizing agent at temperatures of for example 20 to 100, preferably 40 to 90 ⁰ C. 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, from 2 to 8, and is preferably in the range of from 3 to 4. This gives aqueous, anionically adjusted sizing agent dispersions having an average size of sizing agents in the range of 0.1 to 3, 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 selected such that the dispersion as a whole carries an anionic charge. Preferred cationic dispersant is cationic starch.

According to another variant of the method, the addition of a retention agent and / or a filler takes place in combination with a sizing agent and / or a solidifying agent with the aid of the supplied water. Thus, for example, at least one retention agent, a fixing agent and a sizing agent and / or a solidifying agent and optionally at least one thickener are metered into the stream of the water supplied. However, one can mix these additives in the desired ratio in a reservoir and convey it into the nozzle chamber of the headbox.

According to another variant of the method, the addition of a binder alone or in combination with a filler, a retention agent, a fixing agent, a sizing agent and / or a solidifying agent is preferably carried out with the aid of the supplied water or it is metered into the pulp. Thus, at least one binder and optionally a filler, a retention agent, a fixing agent, a sizing agent, a solidifying agent and optionally at least one thickener are preferably metered into the stream of the water supplied. However, these additives can be mixed in the desired ratio in a storage container and conveyed therefrom into the nozzle chamber of the headbox. Binders, for example, cause better binding of fillers to the paper fibers and, when metered into the fiber streams forming the outer layers of the paper, improve the printability of the paper. With the aid of the binders it is also possible to improve the barrier properties of paper, e.g. against the penetration of fats, oils and water and against the passage of gases, in particular oxygen or air.

Examples of suitable synthetic binders are polymers which contain at least 40% by weight of so-called main monomers selected from C 1 -C 20 -alkyl (meth) acrylates, vinyl esters of saturated carboxylic acids containing up to 20 C atoms, vinylaromatics up to 20 C atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols containing 1 to 10 C atoms, aliphatic hydrocarbons having 2 to 8 C atoms and one or two double bonds or mixtures of these monomers.

Suitable synthetic polymers are, in particular, polymers obtainable by free-radical polymerization of ethylenically unsaturated compounds (monomers).

The binder is preferably a polymer which consists of at least 40% by weight, preferably at least 60% by weight, particularly preferably at least 80% by weight, of so-called main monomers.

The main monomers are selected from C 1 -C 20 -alkyl (meth) acrylates, vinyl esters of saturated carboxylic acids containing up to 20 C atoms, vinylaromatics having up to 20 C atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of 1 to 10 C-containing alcohols, aliphatic hydrocarbons having 2 to 8 carbon atoms and one or two double bonds or mixtures of these monomers.

To name a few are z. B. (meth) acrylic acid alkyl ester having a Ci-Cio-alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate. In particular, mixtures of (meth) acrylic acid alkyl esters are also suitable.

Vinyl esters of carboxylic acids having 1 to 20 carbon atoms are, for. As vinyl laurate, vinyl stearate, vinyl propionate, vinyl versatate and vinyl acetate.

Suitable vinylaromatic compounds are vinyltoluene, α- and p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and preferably styrene. Examples of nitriles are acrylonitrile and methacrylonitrile.

The vinyl halides are chloro, fluoro or bromo substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride.

To name as vinyl ethers are, for. As vinyl methyl ether or vinyl isobutyl ether. Vinyl ether is preferably from 1 to 4 C-containing alcohols.

As hydrocarbons having 2 to 8 carbon atoms and one or two olefinic double bonds may be mentioned ethylene, propylene, butadiene, isoprene and chloroprene.

Preferred main monomers are C 1 -C 10 -alkyl (meth) acrylates and mixtures of the alkyl (meth) acrylates with vinylaromatics, especially styrene (polymers with these main monomers are collectively called polyacrylates for short) or, alternatively, hydrocarbons having 2 double bonds, in particular butadiene, or Mixtures of such hydrocarbons with vinyl aromatics, in particular styrene (polymers with these main monomers are collectively called polybutadienes for short).

For mixtures of aliphatic hydrocarbons (especially butadiene) with vinyl aromatics (especially styrene), the ratio z. B. between 10:90 to 90:10, in particular 20:80 to 80:20.

In addition to the main monomers, the polymer may contain monomers having at least one acid group (short acid monomer), z. As monomers with carboxylic acid, sulfonic acid or phosphonic acid groups. Preferred are carboxylic acid groups. Called z. For example, acrylic acid, methacrylic acid, itaconic acid, maleic acid or fumaric acid.

Other monomers are also z. As well as hydroxyl-containing monomers, in particular Ci-Cio-hydroxyalkyl (meth) acrylates, (meth) acrylamide. Accordingly, particularly preferred polymers are synthesized in the case of polybutadienes

From 10 to 90% by weight, preferably from 20 to 70% by weight, of aliphatic hydrocarbons having two double bonds, in particular butadiene,

From 10 to 90% by weight, preferably from 30 to 80% by weight, of vinylaromatic compounds, in particular styrene,

0 to 20 wt .-%, preferably 0 to 10 wt .-% acid monomer, and 0 to 20 wt .-%, preferably 0 to 10 wt .-% further monomers

or alternatively in the case of the polyacrylates

10 to 95% by weight, preferably 30 to 95% by weight, of C 1 -C 10 -alkyl (meth) acrylates, 0 to 60% by weight, preferably 0 to 50% by weight, of vinylaromatic compounds, in particular special styrene and

0 to 20 wt .-%, preferably 0 to 10 wt .-% acid monomer and 0 to 20 wt .-%, preferably 0 to 10 wt .-% further monomers.

Both the polybutadienes and the polyacrylates preferably contain acid monomers as comonomers, preferably in an amount of 1 to 5 wt .-%. The maximum amount of the above aliphatic hydrocarbons in the polybuadienes and the alkyl (meth) acrylates in the polyacrylates is reduced accordingly by the minimum amount of the acid monomers.

The polymers are prepared in a preferred embodiment by emulsion polymerization, it is therefore an emulsion polymer. However, the polymers can z. B. also be prepared by solution polymerization and subsequent dispersion of the polymer solution in water.

In the emulsion polymerization usually ionic and / or nonionic emulsifiers and / or protective colloids or stabilizers are used as surface-active compounds.

The surface-active substance is used, for example, in amounts of from 0.1 to 10% by weight, based on the monomers to be polymerized.

Water-soluble initiators for the emulsion polymerization are z. For example, ammonium and alkali metal salts of peroxodisulfuric, z. For example, sodium peroxodisulfate, hydrogen peroxide or organic peroxides, z. B. tert-butyl hydroperoxide.

Also suitable are so-called reduction-oxidation (red-ox) -initiator systems. The amount of initiators is generally 0.1 to 10 wt .-%, preferably 0.5 to 5 wt .-%, based on the monomers to be polymerized. It is also possible to use a plurality of different initiators in the emulsion polymerization.

In the polymerization regulators can be used, for. B. in amounts of 0 to 0.8 parts by weight, based on 100 parts by weight of the monomers to be polymerized, by which the molecular weight is reduced. Suitable z. B. Compounds with a thiol group such as tert-butylmercaptan, Thioglykolsäureethylacrylester, mercaptoethanol, mercaptopropyltrimethoxysilane or tert-dodecylmercaptan.

The emulsion is usually carried out at 30 to 130 ⁰ C, preferably 50 to 9O ⁰ C. The polymerization medium may consist of water only, as well as mixtures of water and thus miscible liquids such as methanol. Preferably, only water is used. The emulsion polymerization can be carried out both as a batch process and in the form of a feed process, including a stepwise or gradient procedure. Preferably, the feed process in which one submits a portion of the polymerization, heated to the polymerization, polymerized and then the rest of the polymerization, usually over several spatially separate feeds, one or more of which monomers in pure or in emulsified form, continuously , gradually or with the addition of a concentration gradient while maintaining the polymerization of the polymerization zone supplies. In the polymerization, it is also possible, for example for the purpose of better adjustment of the particle size, to introduce a polymer seed.

The manner in which the initiator is added to the polymerization vessel in the course of the free radical aqueous emulsion polymerization is known to one of ordinary skill in the art. It can be introduced both completely into the polymerization vessel, or used continuously or in stages according to its consumption in the course of the free radical aqueous emulsion polymerization. In particular, this depends on the chemical nature of the initiator system as well as on the polymerisation temperature. Preferably, a part is initially charged and the remainder supplied according to the consumption of the polymerization.

To remove the residual monomers is usually also after the end of the actual emulsion polymerization, d. H. after a conversion of the monomers of at least 95%, initiator added.

The individual components can be added to the reactor in the feed process from above, in the side or from below through the reactor bottom. In the emulsion polymerization, aqueous dispersions of the polymer are generally obtained with solids contents of 15 to 75 wt .-%, preferably from 40 to 75 wt .-%.

Suitable binders are in particular mixtures of various binders, eg. As well as mixtures of synthetic and natural polymers. Aqueous polymer dispersions are preferably used as binders, which are composed of at least 60 wt .-% of butadiene or mixtures of butadiene and styrene or aqueous dispersions of polymers containing at least 60 wt .-% d- to C20-alkyl (meth) acrylates or Mixtures of d- to C2o-alkyl (meth) acrylates in copolymerized form with styrene.

Other suitable binders are polymers containing N-vinylformamide and / or vinylamine units, which have an average molecular weight M _w of at least 10,000. These polymers can be in the form of an aqueous dispersion or as a solution in water. They are prepared, for example, by polymerizing N-vinylformamide alone or in the presence of at least one other nonionic, cationic and / or anionic monomer. The homopolymers and copolymers of N-vinylformamide which can be prepared in this way can be hydrolyzed in a polymer-analogous reaction with elimination of formyl groups from the copolymerized vinylformamide units to form amino groups. The hydrolysis is preferably carried out in an aqueous medium in the presence of at least one acid such as hydrochloric acid or sulfuric acid, enzymatically or in the presence of bases such as sodium hydroxide or potassium hydroxide. The vinylformamide units may be wholly or even partially hydrolyzed. For example, in a complete hydrolysis of homopolymers of N-vinylformamide, polyvinylamines are obtained.

Suitable anionic monomers are, for example, monomers containing acid groups. Examples thereof are acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, vinylphosphonic acid, acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, allylacetic acid, crotonic acid and ethacrylic acid. The anionic monomers can be used in the polymerization in the form of the free acids or in partially or completely neutralized with alkali metal, alkaline earth metal and / or ammonium bases form. The sodium salts or potassium salts of the acids are preferably suitable. Both the non-hydrolyzed copolymers of N-vinylformamide with anionic monomers and the partially or completely hydrolyzed copolymers of N-vinylformamide and anionic monomers, which are described, for example, in DE-A-103 15 363, cf. in particular page 5, line 39 to page 12, line 39, can be used as binders for the modification of inorganic see pigments. N-vinylformamide can also be copolymerized with cationic monomers such as dialkylaminoalkyl (meth) acrylates and / or diallyldimethylammonium chloride. The basic monomers are preferably used in the form of the salts with mineral acids or in form partially or fully quaternized with alkyl halides or with dimethyl sulfate. In the copolymerization of N-vinylformamide with anionic and / or cationic monomers may optionally be additionally used nonionic monomers such as methyl acrylate, ethyl acrylate, methyl methacrylate, vinyl acetate, acrylamide and / or methacrylamide. Both the hydrolyzed cationic and the nonhydrolyzed cationic copolymers can be used as binders for the modification of inorganic pigments. It is likewise possible to use amphoteric polymers which are obtainable, for example, by copolymerization of N-vinylformamide, dimethylaminoethyl acrylate methochloride and acrylic acid, or which are formed by complete or partial hydrolysis of the vinylformamide units of these copolymers. The polymers containing vinylformamide and / or vinylamine units which are used to modify pigments preferably have an average molecular weight M _w of at least 20,000. Mostly, the average molar masses of the copolymers are in the range from 30,000 to 5 million, in particular from 50 000 to 2 million. The molecular weights are determined, for example, with the aid of static light scattering at pH 7.6 in a 10 mmolar aqueous saline solution.

In addition, are suitable as binders ethylene copolymer waxes, the

(A ^' ) from 20.5 to 38.9% by weight, preferably from 21 to 28% by weight, of at least one ethylenically unsaturated carboxylic acid,

(B ') 60 to 79.4 wt .-%, preferably 70 to 78.5 wt .-% of ethylene and

(C) 0.1 to 15 wt .-%, preferably 0.5 to 10 wt .-% of at least one ethylenic

Contain unsaturated carboxylic acid ester in copolymerized form.

The ethylene copolymer waxes described above have, for example, a melt flow rate (MFR) in the range of 1 to 50 g / 10 min, preferably 5 to 20 g / 10 min, more preferably 7 to 15 g / 10 min, measured at 160 ^° C. and a load of 325 g according to EN ISO 1 133. Its acid value is usually 100 to 300 mg KOH / g wax, preferably 1 15 to 230 mg KOH / g wax, determined to DIN 53402.

They have a kinematic melt viscosity n of at least 45,000 mm ² / s, preferably of at least 50,000 mm ² / s. The melting ranges of the ethylene copolymer are, for example, in the range of 60 to 110 ⁰ C, preferably in the range of 65 to 90 ° C, determined by DSC in accordance with DIN 51,007th The melting ranges of the ethylene copolymer may be wide and, a temperature raturintervall of at least 7 to a maximum of 20 ⁰ C is preferred to have at least 10 ⁰ C and at most 15 ° C.

However, the melting points of the ethylene copolymer waxes may also have a small fluctuation range and be in a temperature range of less than 2 ° C, preferably less than 1 ° C, determined according to DIN 51007.

The density of the waxes is usually 0.89 to 1, 10 g / cm ³ , preferably 0.92 to 0.99 g / cm ³ , determined according to DIN 53479.

The ethylene copolymer waxes are e.g. alternating copolymers or block copolymers or, preferably, random copolymers.

Ethylene copolymer waxes of ethylene and ethylenically unsaturated carboxylic acids and optionally ethylenically unsaturated carboxylic acid esters can advantageously be prepared by free-radically initiated copolymerization under high-pressure conditions, for example in high-pressure autoclaves equipped with an agitator or in high-pressure tubular reactors. Production in high-pressure autoclaves equipped with a stirrer is preferred. Such high-pressure autoclaves are known per se, a description can be found in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, keywords: Waxes, Vol. A 28, p. 146 et seq., Verlag Chemie, Weinheim, Basel, Cambridge, New York, Tokyo , 1996. In them predominantly the ratio length / diameter at intervals of 5: 1 to 30: 1, preferably 10: 1 to 20: 1 behaves. The likewise applicable high-pressure tube reactors can likewise be found in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, keywords: Waxes, Vol. A 28, p. 146 ff., Verlag Chemie, Weinheim, Basel, Cambridge, New York, Tokyo, 1996.

Suitable pressure conditions for the polymerization are 500 to 4000 bar, preferably 1500 to 2500 bar. Conditions of this type are also referred to below as high pressure. The reaction temperatures are in the range from 170 to 300 ^° C., preferably in the range from 195 to 280 ^° C. The polymerization can also be carried out in the presence of a regulator. The above-mentioned waxes are described in detail, for example, in WO-A-04/108601, page 2, line 38 to page 12, line 10.

According to another variant of the method according to the invention, the addition of an unstabilized engine sizing agent takes place alone or in combination with a filler, a retention agent, a fixing agent and / or a solidifying agent with the aid of the water supplied. Thus, at least one unstabilized engine sizing agent is metered into the stream of water fed in, and optionally a filler, a retention agent, a fixing agent, a solidifying agent and at least one thickener. However, you can these additives in the desired ratio Mix in a reservoir and convey it into the nozzle chamber of the headbox.

Unstabilized engine sizing agents are to be understood as meaning the massing agents described above which contain no or very small amounts of stabilizers. If the metered-in emulsifier dispersion is metered into the stream of the water fed in directly after emulsification according to the above-described variant of the process according to the invention, the bulk emulsifying agent can be emulsified on site.

The aqueous dispersions of a size sizing agent may optionally be used together with a cationic synthetic polymer acting as fixer and promoter, wherein fixer and promoter are metered into the stock in admixture with at least one size sizing agent or separately therefrom. The dosage is usually in the thin material. For optimum metering, engine sizing agents and optionally promoters in combination with a retention agent are metered into the stock stream at a point downstream of the last shear stage of the stock and in front of the nozzle head of the headbox. The cationic polymers used as fixing agents and promoters for engine lubricants can be metered into the stock before or after the last shear stage, for example. Examples of cationic polymers of this type are polymers containing vinylamine units, polymers containing vinylguanidine units, polyethyleneimines, polyamidoamines grafted with ethyleneimine and / or polydiallyldimethylammonium chlorides. The amount of fixing agent is for example 0.02 to 2.0, preferably 0.05 to 0.5 wt .-%, based on dry pulp.

In another embodiment of the invention, at least one retention agent is used in combination with a solidifying agent for paper. Known solidifying agents for paper are, for example, urea-formaldehyde resins which, in addition to the wet strength, also increase the dry strength of the paper (cf EP-AO 123 196 and US-A-3,275,605), melamine-formaldehyde resins (cf. B-10 90 078) or other commercial products eg polyamidoamines crosslinked with epichlorohydrin (see the trademarks Luresin®, BASF Aktiengesellschaft, Ludwigshafen).

In order to produce multilayer webs of cellulose fibers one can assume all of the fibers commonly used in papermaking. The cellulose fibers are first suspended in water to produce a paper stock. Suitable cellulose fibers are, for example, wood pulp and all annual plants. Wood pulp includes, for example, groundwood, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressure groundwood, semi-pulp, high yield pulp, and refiner mechanical pulp (RMP), as well as recovered paper. In addition, pulps used in bleached or unbleached forms are suitable. such as sulphate, sulphite and soda pulps as well as recovered paper fibers. Preferably, unbleached pulps, also referred to as unbleached kraft pulp, are used. 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 pulp concentration, which is dewatered in the paper machine, is at most 2% by weight and is usually in the range of 0.5 to 1 , 0 wt .-%, based on dry pulp.

It is also possible to add to the pulp the process chemicals usually used in papermaking in the usual amounts, e.g. the previously mentioned fixing agents, sizing agents, dry and wet strength agents, biocides and / or dyes. The paper stock is in each case processed according to the invention into a multilayer fibrous web by dewatering it on a wire with formation of a web. The webs thus produced are dried. Dewatering of the stock and drying of the webs are part of the papermaking process, which is performed continuously.

By the process according to the invention, it is possible, for example, to produce papers which are composed of 2, 3, 4, 5 or more layers. Preference is given to three-layered papers. In this case, it is possible to inexpensively produce good quality papers by using cheap fibers for the middle layer and qualitatively better fibers for the top and bottom of the three-layered paper. Thus, for example, bleached fibers such as birch sulphate and / or pine sulphate bleached fibers may be used to form the top and bottom of a three-ply paper, while recycled paper, TMP and / or wood pulp fibers may be considered for the middle layer of the three-ply paper ,

The multilayer papers produced according to the invention are suitable, for example, as printing and writing papers, copying papers, inkjet papers, cardboard and paperboard, as well as for packaging on liquids and the production of folding boxes and corrugated cardboard as well as cardboard.

Claims

claims

1. A process for producing a multi-layer fibrous web of cellulose fibers by separately feeding at least two different Fersersuspensionen and water in a multi-layer headbox, wherein they are separated by separating elements from each other and supplied water and after leaving the nozzle mouth of the headbox on a dewatering device , on which a multilayer fibrous web is formed, wherein the water is guided so that it comes after emerging from the nozzle orifice in the form of a layer between two layers of fiber suspensions on the web forming device and thus counteracts a mixing of the different fiber suspensions, characterized in that at least one retention aid and / or at least one dewatering agent is metered into the fiber suspensions and / or into the water fed in order to improve the retention, dehydration and formation.

2. The method according to claim 1, characterized in that one doses an aqueous solution of at least one retention agent and / or at least one dehydrating agent at a point in the stock flow, which is after the last shear stage of the pulp and before the nozzle mouth of the headbox.

3. The method according to claim 1 or 2, characterized in that one adds the same retention agent to all streams of fiber suspensions and dosed in such a way that at least two streams of fiber suspensions contain a different concentration of this retention agent.

4. The method according to claim 1 or 2, characterized in that at least two different retention agents are metered into at least two streams of fiber suspensions.

5. The method according to claim 4, characterized in that at least two streams of fiber suspensions contain a different concentration of retention aid.

6. The method according to any one of claims 1 to 5, characterized in that one separates an aqueous solution of a retention agent and an aqueous dispersion of at least one filler from each other or metered as a mixture in the pulp.

7. The method according to any one of claims 1 to 5, characterized in that one comprises an aqueous solution of a retention agent and an aqueous dispersion at least one filler separated or dosed as a mixture in at least one stream of water supplied.

8. The method according to any one of claims 1 to 5, characterized in that one comprises an aqueous dispersion of a filler in at least one stream of

Dosed fiber suspension and that the supplied water contains at least one retention agent.

9. The method according to any one of claims 1 to 8, characterized in that one uses at least one retention agent in combination with at least one dehydrating agent.

10. The method according to any one of claims 1 to 9, characterized in that one uses at least one retention agent in combination with a fixing agent.

1 1. A method according to any one of claims 1 to 10, characterized in that one uses at least one retention agent in combination with a Masselei- mungsmittel.

12. The method according to any one of claims 1 to 1 1, characterized in that one uses at least one retention agent in combination with a solidifying agent for paper.

13. The method according to any one of claims 1 to 12, characterized in that the retention agent is selected from the group of cationic, anionic, nonionic and amphoteric polymeric organic compounds or a microparticle system.

14. The method according to any one of claims 1 to 12, characterized in that the retention agent is selected from the group of polyacrylamides, the polymethacrylamides, the vinylamine units containing polymers and / or a microparticle system.

15. The method according to any one of claims 1 to 12, characterized in that at least one retention agent is a polymer containing vinylamine units.

16. The method according to any one of claims 1 to 12, characterized in that the dehydrating agent is a Ethylenimineinheiten-containing polymer.

17. The method according to any one of claims 1 to 12, characterized in that in at least one stream of a fiber suspension, a polyacrylamide and / or vinylamine units containing polymer and in a stream of another fiber suspension an ethyleneimine units containing polymer is metered.

18. The method according to any one of claims 1 to 12, characterized in that one produces a three-layer fibrous web, wherein

(a) in the stream of the fiber suspension, which forms the upper side of the fibrous web, a retention agent from the group of polyacrylamides, polymethacrylamides, polymers containing vinylamine units, microparticle systems and mixtures thereof,

(b) in the stream of the fiber suspension, which forms the middle layer of the fibrous web, a dehydrating agent from the group of polymers containing ethyleneimine units and / or a retention agent from the

Group of polymers containing vinylamine units, cationic, anionic, nonionic and amphoteric polyarylamides, polymethacrylamides and mixtures thereof, and

(C) in the stream of the fiber suspension, which forms the underside of the fibrous web, a retention agent from the group of polyacrylamides, Polmethac- rylamide, vinylamine units containing the polymers, the Mikroparti- kelsysteme and their mixtures is metered.

19. The method according to any one of claims 1 to 12, characterized in that one produces a three-layer fibrous web, wherein

(a) in the stream of the fiber suspension, which forms the upper side of the fibrous web, as a retention agent, a polymer containing vinylamine units,

(B) in the stream of the fiber suspension, which forms the middle layer of the fibrous web, as a dehydrating agent containing a Ethylenimineinheiten

Polymer, and

(C) in the stream of the fiber suspension, which forms the underside of the fibrous web, as a retention agent, a polymer containing vinylamine units is metered.

20. The method according to any one of claims 1 to 12, characterized in that the stream of water supplied contains at least one retention agent and at least one thickener.

21. The method according to any one of claims 1 to 12, characterized in that the stream of water supplied contains at least one retention agent and at least one binder.

22. The method according to any one of claims 1 to 12, characterized in that the stream of water supplied contains at least one suspended filler.

23. The method according to any one of claims 1 to 12, characterized in that the stream of water supplied contains at least one retention agent, a fixing agent, a sizing agent, a solidifier and / or a thickener.

24. The method according to any one of claims 1 to 12, characterized in that one doses an unstabilized engine sizing agent in the flow of water supplied.

25. The method according to any one of claims 1 to 24, characterized in that a surface-active agent is used to improve the drainage.