WO2012175392A1

WO2012175392A1 - Method for producing paper, paperboard, and cardboard

Info

Publication number: WO2012175392A1
Application number: PCT/EP2012/061248
Authority: WO
Inventors: Anton Esser; Hans-Joachim HÄHNLE
Original assignee: Basf Se
Priority date: 2011-06-21
Filing date: 2012-06-14
Publication date: 2012-12-27
Also published as: BR112013032550A2; CN103620115A; BR112013032550A8; EP2723943B1; PT2723943T; ES2692543T3; CN103620115B; BR112013032550B1; PL2723943T3; EP2723943A1

Abstract

The invention relates to a method for producing paper, paperboard, and cardboard, comprising dewatering a paper material having filler material and having at least one water-soluble amphoteric copolymer, forming sheets in the wire section, and then pressing the paper in the press section, wherein the at least one water-soluble amphoteric copolymer is metered and added to a paper material having a fiber concentration in the range from 20 to 40 g/L, then the paper material is diluted to a fiber concentration in the range from 5 to 15 g/L, the diluted paper material is dewatered to form a sheet and the sheet is pressed in the press section to a solids content of G(x) wt % or greater, and G(x) is calculated as G(x) = 48 + (x - 15) · 0.4, where x stands for the numerical value of the minimum solids content (in wt%) to which the sheet is pressed, wherein the water-soluble amphoteric copolymer can be obtained by polymerizing a mixture of a) 20 to 60 mol% of acrylamide relative to the total moles of the monomers used for polymerization, b) 20 to 60 mol%, relative to the total moles of the monomers used for polymerization, of at least one cationic monomer, c) 20 to 60 mol%, relative to the total moles of the monomers used for polymerization, of at least one anionic monomer selected from monoethylene unsaturated C₃- to C₅-carbolic acids, monoethylene unsaturated C₃- to C₅-dicarbolic acids, sulfonic acids, phosphonic acids, and/or the salts of said acids, d) 0 to 30 mol%, relative to the total moles of the monomers used for polymerization, of one or more monoethylene unsaturated monomers different from the monomers (a), (b), and (c), and e) 0 to 5 mol%, relative to the total moles of the monomers used for polymerization, of one or more compounds comprising at least two ethylene unsaturated double bonds in the molecule, wherein the amount of the difference between the proportions of the cationic and the anionic monomers in mol%, each relative to the total moles of the monomers used for polymerization, is a maximum of 10 mol%.

Description

The invention relates to a process for the production of paper, paperboard and paperboard comprising dewatering a filler-containing paper stock comprising at least one water-soluble amphoteric copolymer with formation of sheets in the wire section and subsequent pressing of the paper in the paper press section. The development of new processes for the production of paper takes place at various points in the process. Improved papers are achieved by new ingredients or modified dosing. But even faster and faster paper machines make new demands on the manufacturing process. A limiting factor on the way to further increasing the speed of paper machines is the initial wet texture strength. It limits the maximum applicable force that can be exerted on a sheet just formed in the paper machine that has passed through the wire and press sections of the machine and is being transferred to the dryer section. In this case, the sheet must be pulled off the press rollers. In order to be able to reliably ensure tear-free operation of a paper machine, the applied peel force at this point must be significantly smaller than the initial wet texture strength of the wet paper. An increase in the initial wet structure strength allows the use of higher take-off forces and thus a faster operation of the paper machine, cf. EP-B-0 780 513.

Initial wet web strength refers to the strength of a wet paper that has never been dried. This is the strength of a wet paper, as is the case in papermaking after passing through the wire and press section of the paper machine.

In the press section, the wet nonwoven fabric is doffed onto the press felt by a suction cup (suction roll or static vacuum element). The task of the press felt is the transport of the fibrous web by press nips of various modifications. Depending on the design of the press section and the composition of the paper stock, the dry content of the web is up to a maximum of 55%. The dry content increases with the pressure exerted on the continuous paper web in the press. Printing and thus the dry content of the paper web can be varied over a relatively large range in many paper machines. It is known that the initial wet structural strength can be increased by increasing the solids content of the paper at the point between the press and dryer sections in the manufacturing process. There is also the possibility of the solids content improve this point of the process through additives to increase drainage. But there are limits to this possibility.

WO 2009/156274 teaches the use of amphoteric copolymers obtainable by copolymerization of N-vinylcarboxamide with anionic comonomers and subsequent hydrolysis of the vinylcarboxamide as a stock additive to increase the initial wet strength of paper. The treatment is e.g. in thick stock or thin paper in the papermaking process. Amphoteric copolymers based on acrylamide are widely known as retention agents. DE 1948994 describes amphoteric copolymers based on acrylamide with a K value according to Fikentscher of 200 to 250 as dehydrating agent. They thus have a molecular weight for retention agents usual in the range of 500 000 to 10 000 000 daltons and are usually added to the thin material.

Furthermore, for example, the use of amphoteric copolymers based on acrylamide for solidification is known. Their molecular weight is typically in the range of 50,000 to 500,000 daltons. The invention has for its object to increase in the production of paper, the initial wet structural strength of the still wet paper web before the transition to the dryer section, in order to achieve higher machine speeds compared to known methods in the papermaking process. Accordingly, there has been found a process for producing paper, paperboard and paperboard comprising dewatering a filler-containing stock containing at least one water-soluble amphoteric copolymer, sheet forming in the wire section and then pressing the paper in the press section to produce a stock having a pulp concentration in the range of 20 to 40 g / l, the at least one water-soluble, amphoteric copolymer is metered, then the paper stock is diluted to a pulp concentration in the range of 5 to 15 g / l, the diluted paper stock is dewatered to form a sheet and the sheet in the Press section to a solids content G (x) wt .-% or greater presses and G (x) calculates after

G (x) = 48 + (x - 15) x 0.4 where x is the numerical value of the filler content of the dry paper, paperboard or paperboard (in% by weight) and

and G (x) is the number of minimum solids (in% by weight) on which the sheet is pressed, wherein the water-soluble, amphoteric copolymer is obtainable by polymerizing a mixture of

From 20 to 60 mol% of acrylamide, based on the total number of moles of monomers used for the polymerization,

From 20 to 60 mol%, based on the total number of moles of monomers used for the polymerization, of at least one cationic monomer,

20 to 60 mol%, based on the total number of moles of the monomers used for the polymerization, of at least one anionic monomer which is selected from monoethylenically unsaturated C3 to C5 carboxylic acids, monoethylenically unsaturated C3 to Cs dicarboxylic acids, sulfonic acids, phosphonic acids and / or the salts of these acids,

0 to 30 mol%, based on the total number of moles of the monomers used for the polymerization, of one or more monoethylenically unsaturated monomers which are different from the monomers (a), (b) and (c), and

0 to 5 mol% based on the total number of moles of the monomers used for the polymerization, one or more compounds having at least two ethylenically unsaturated double bonds in the molecule, wherein the amount of the difference of the proportions of the cationic and the anionic monomer in mol%, respectively to the total moles of monomers used for the polymerization, a maximum of 10 mol%.

The present invention further relates to a process for the production of paper, paperboard and paperboard comprising dewatering a full-bodied pulp containing at least one water-soluble amphoteric copolymer, sheet forming in the wire section and then pressing the paper in the press section to form a pulp a pulp concentration in the range of 20 to 40 g / l which doses at least one water-soluble, amphoteric copolymer, then the pulp diluted to a pulp concentration in the range of 5 to 15 g / l, dewatered the diluted pulp to form a sheet and the sheet in the Press section to a solids content of> 48 wt .-%, preferably from 49 to 53 wt% pressed, wherein the water-soluble, amphoteric copolymer is obtainable by polymerizing a mixture of a) 20 to 60 mol% of acrylamide, based on the total number of moles the monomers used for the polymerization, b) from 20 to 60 mol%, based on the total number of moles of monomers used for the polymerization, of at least one cationic monomer, c) from 20 to 60 mol%, based on the total moles of monomers used for the polymerization, of at least one anionic monomer selected is from monoethylenically unsaturated C 3 - to C 5 -carboxylic acids, monoethylenically unsaturated C 3 - to C 8 -dicarboxylic acids, sulfonic acids, phosphonic acids and / or the salts of these acids, d) 0 to 30 mol%, based on the total number of moles of the monomers used for the polymerization, one or more monoethylenically unsaturated monomers other than the monomers (a), (b) and (c); and e) 0 to 5 mol%, based on the total moles of monomers used for the polymerization, of one or more compounds have at least two ethylenically unsaturated double bonds in the molecule, wherein the amount of the difference in the proportions of the cationic and the anionic monomers Rs in mol%, in each case based on the total number of moles of the monomers used for the polymerization, a maximum of 10 mol%.

The term paper stock is understood below as meaning a mixture of water and fibrous material which, depending on the stage in the production process of the paper, paperboard or paperboard, still contains the water-soluble amphoteric copolymer, filler and optionally paper auxiliaries.

The dry content of the paper is understood as meaning the solids content of paper, board and pulp with the heat-barrier method as determined in accordance with DIN EN ISO 638 DE.

In the context of this application, the term pigment is used synonymously with the term filler, since in the production of paper the pigments are used as fillers. As used in papermaking, the term "filler" is understood to mean inorganic pigment.

The inventive method is used to produce paper, cardboard and cardboard comprising dewatering a filler-containing paper stock. The filler content (x) of the paper, cardboard and paperboard can amount to 5 to 40% by weight, based on the paper, the cardboard or the cardboard. According to a preferred embodiment, a process for the production of paper is preferred whose filler content is 20 to 30 wt .-%. Such papers are, for example, wood-free papers. According to a further preferred embodiment, a process for the production of paper is preferred whose filler content is 10 to 20 wt .-%. Such papers are used primarily as packaging papers.

According to a further preferred embodiment, preference is given to a process for the production of paper whose filler content is 5 to 15% by weight. Such papers are used primarily for newspaper printing.

According to a further preferred embodiment, preference is given to a process for producing paper whose filler content is from 25 to 40% by weight, for example SC papers.

The aqueous paper pulp containing at least one water-soluble amphoteric polymer, pulp and filler is dehydrated in the wire section to form a sheet and the sheet is pressed in the press section, that is, it is further dewatered. The dewatering in the press section takes place up to a minimum solids content, but can also go beyond that. This lower limit of the solids content up to which the product must be pressed is also referred to hereinafter as the limit dry content or else as the minimum solids content G (x) and is based on the compressed sheet which is a mixture of paper stock and water. This Grenztrockengehalt to which at least dehydrated, it depends on the amount of filler. Thus, the limit dry content G (x) for a paper with a filler content of 30 or 15 wt .-% calculated according to the formula

G (x) = 48 + (x - 15) x 0.4

to G (30) = 48 + (30-15) * 0.4 = 54

or to G (15) = 48 + ( ^15-15 ) ^■ 0.4 = 48.

In other words, in the production of paper having a filler content of 30% by weight, according to the invention, a solids content of at least 54% by weight is pressed in the press section in order to obtain paper with good initial wet structural strength.

In contrast, according to the invention, in the production of paper having a filler content of 15 or smaller in the press section, a solids content of at least 48% by weight is pressed in order to obtain paper with good initial wet structural strength. According to one embodiment of the invention, for the production of paper, paperboard and cardboard having a filler content of 17 to 32 in the press section to a minimum solids content in the range of 49 to 55 pressed. According to another embodiment of the invention, for the production of paper, paperboard and cardboard having a filler content of 15 or smaller in the press section, at least a solids content of 48% by weight is pressed.

The treatment of the fibers according to the invention is carried out by metering the amphoteric copolymer to the pulp at a pulp concentration in the range of 20 to 40 g / l. In a pulp concentration of 20 to 40 g / l (corresponds to a pulp concentration of 2 to 4 wt .-% based on the aqueous pulp) is usually understood in the papermaking the thick material. This is distinguished from the thin material, which is to be understood below as a fiber concentration in the range of 5 to 15 g / l. Following treatment with amphoteric copolymer, the stock is diluted with water to a pulp concentration in the range of 5 to 15 g / L.

According to the invention, native and / or recovered fibers can be used as the fibrous material. All fibers of coniferous and hardwoods commonly used in the paper industry can be used, for example. Pulp, bleached and unbleached pulp and pulp from all annual plants. Wood pulp includes, for example, groundwood, thermomechanical pulp (TMP), chemo-thermo-mechanical pulp (CTMP), pressure groundwood, semi-pulp, high yield pulp and refiner mechanical pulp (RMP). As pulp, for example, sulphate, sulphite and soda pulps come into consideration. Preferably, unbleached pulp, also referred to as unbleached kraft pulp, is used. Suitable annual plants for the production of fibrous materials are for example rice, wheat, sugarcane and kenaf. Waste paper may also be used to make the pulps, either alone or blended with other pulps. For example, the waste paper can come from a deinking process. But it is not necessary that the waste paper to be used is subjected to such a process. Furthermore, it is also possible to start from fiber blends of a primary material and recycled coated broke.

In the case of bleached or unbleached pulp, a pulp having a freeness of 20 to 30 SR can be used. In general, a pulp with a freeness of about 30 SR is used, which is ground during the production of the pulp. Preferably, pulp is used which has a freeness of <30 SR.

The treatment of the pulp with the water-soluble amphoteric polymer is carried out in aqueous suspension, preferably in the absence of other process Chemicals commonly used in papermaking. It takes place in the papermaking process by adding at least one water-soluble amphoteric copolymer to an aqueous paper stock having a pulp concentration of 20 to 40 g / l. Particularly preferred is a process variant in which an amphoteric copolymer is added to the aqueous paper stock at a time prior to the addition of the filler. Very particularly preferably, the addition takes place after the addition of the dry strength agent, for example the starch.

The water-soluble, amphoteric copolymers are preferably added in an amount of 0.05 to 5.00 wt .-%, based on pulp (solid).

Typical application rates are, for example, from 0.5 to 50 kg, preferably from 0.6 to 10 kg, of at least one water-soluble, amphoteric copolymer, per ton of dry pulp. The amounts of amphoteric copolymer used are particularly preferably 0.6 to 3 kg of polymer (solid), based on one ton of dry pulp.

The exposure time of the amphoteric copolymer to a pure pulp or pulp after metering to sheet formation is, for example, 0.5 seconds to 2 hours, preferably 1.0 seconds to 15 minutes, more preferably 2 to 20 seconds.

In addition to the amphoteric polymer, inorganic pigment is added as filler to the pulp. Inorganic pigments are all pigments customarily used in the paper industry on the basis of metal oxides, silicates and / or carbonates, in particular of pigments from the group consisting of calcium carbonate, in the form of ground (GCC) lime, chalk, marble or precipitated calcium carbonate (PCC). talc, kaolin, bentonite, satin white, calcium sulfate, barium sulfate and titanium dioxide. It is also possible to use mixtures of two or more pigments.

According to the invention, inorganic pigments having an average particle size (Z average) <10 μm, preferably from 0.3 to 5 μm, in particular from 0.5 to 2 μm, are used. The determination of the average particle size (Z-average) of the inorganic pigments and of the particles of the powder composition is carried out in the context of this document generally by the method of quasi-elastic light scattering (DIN-ISO 13320-1), for example with a Mastersizer 2000 from. Malvern Instruments Ltd. ,

The inorganic pigment is preferably metered after the addition of the water-soluble amphoteric copolymer. In this case, according to a preferred embodiment, the addition takes place in the stage in which the pulp is already present as a thin material, ie at a pulp concentration of 5 to 15 g / l. According to a further preferred embodiment, the inorganic pigment is metered both in the thin and in the thick matter, wherein the ratio of the two addition amounts (adding thick matter / adding thin material) is preferably 5/1 to 1/5. In addition to the amphoteric copolymers, conventional paper auxiliaries can optionally be mixed with the paper stock, generally at a pulp concentration of 5 to 15 g / l. Conventional paper auxiliaries are, for example, sizing agents, wet strength agents, cationic or anionic retention aids based on synthetic polymers, and dual systems, dehydrating agents, other dry strength agents, optical brighteners, defoamers, biocides and paper dyes. These conventional paper additives can be used in the usual amounts.

The sizing agents are alkylketene dimers (AKD), alkenylsuccinic anhydrides (A-SA) and rosin size.

Suitable retention agents are, for example, anionic microparticles (colloidal silicic acid, bentonite), anionic polyacrylamides, cationic polyacrylamides, cationic starch, cationic polyethyleneimine or cationic polyvinylamine. In addition, any combination thereof is conceivable, for example, dual systems consisting of a cationic polymer with an anionic microparticle or an anionic polymer with a cationic microparticle. In order to achieve a high filler retention, it is recommended to add retention aids of this kind, which can be added to the thick material, for example, but also to the thin material.

Dry strength agents are to be understood as meaning synthetic dry strength agents such as polyvinylamine, polyethyleneimine, glyoxylated polyacrylamide (PAM) or natural dry strength agents such as starch. In the paper machine, these dry contents are set when passing through the press section. In the press section, the wet nonwoven fabric is abraded onto the press felt by a suction cup (suction roll or static vacuum element). The task of the press felt is the transport of the fibrous web through press nips of various modifications. Depending on the design of the press section and the composition of the paper stock, the dry content of the web is up to a maximum of 55%. The dry content increases with the pressure exerted on the continuous paper web in the press. Printing and thus the dry content of the paper web can be varied over a relatively large range in many paper machines.

The water-soluble amphoteric copolymers used in the process according to the invention generally contain at least 20 mol%, preferably at least 25 mol% and in a particularly preferred form at least 30 mol% and in Generally at most 60 mol%, preferably at most 55 mol% and in a particularly preferred form at most 50 mol% of copolymerized acrylamide (monomers a), based on the total moles of monomers. The water-soluble amphoteric copolymers used in the process according to the invention furthermore generally contain at least 20 mol%, preferably at least 25 mol% and generally at most 60 mol%, preferably at most 55 mol% and in a particularly preferred form at most 50 mol% % of a cationic monomer (monomers b) copolymerized, based on the total number of moles of monomers.

In addition, the water-soluble amphoteric copolymers generally contain at least 20 mol%, preferably at least 25 mol%, and generally at most 60 mol%, preferably at most 55 mol% and more preferably at most 50 mol% of an anionic monomer ( Monomer c), which is selected from the group consisting of monoethylenically unsaturated C3 to C5 monocarboxylic acids, monoethylenically unsaturated C3 to Cs dicarboxylic acids, sulfonic acids, phosphonic acids and / or the salts of these acids copolymerized, based on the total moles of monomers ,

In addition, the water-soluble amphoteric copolymers can be up to 30 mol%, preferably up to 20 mol%, in particular up to 15 mol%, particularly preferably 0 to 10 mol% of one or more monoethylenically unsaturated monomers (monomer d), the of the monomers a), b) and c) are different, in copolymerized form, based on the total moles of monomers.

In addition, the water-soluble amphoteric copolymers can be up to 5 mol%, preferably up to 3 mol%, in particular up to 1 mol%, particularly preferably 0.5 mol% of one or more ethylenically unsaturated monomers (monomer e), the min - contain at least two ethylenically unsaturated double bonds in the molecule, in copolymerized form, based on the total number of moles of the monomers used for the polymerization.

According to the invention, the amount of cationic and anionic monomer is chosen so that the amount of the difference in the proportions of the cationic and anionic monomers in mol%, in each case based on the total moles of monomers used for the polymerization, is at most 10 mol%.

The resulting amphoteric polymers are predominantly neutrally charged at pH 7 and 20 ° C.

In the context of the present invention, the term alkyl includes straight-chain and branched alkyl groups. Suitable alkyl groups are, for. As Ci-C6-alkyl and special it preferably Ci-C4-alkyl groups. These include in particular methyl, ethyl, propyl, isopropyl, n-butyl, 2-butyl, sec-butyl, tert-butyl, n-pentyl, 2-pentyl, 2-methylbutyl, 3-methylbutyl, 1, 2-dimethylpropyl , 1, 1-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 2-hexyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1, 2-dimethylbutyl, 1, 3-dimethylbutyl, 2 , 3-dimethylbutyl, 1, 1-dimethylbutyl, 2,2-dimethylbutyl, 3,3-

Dimethylbutyl, 1, 1, 2-trimethylpropyl, 1, 2,2-trimethylpropyl, 1-ethylbutyl, 2-ethylbutyl, 1-ethyl-2-methylpropyl, etc.

In the following, compounds which can be derived from acrylic acid and methacrylic acid are sometimes abbreviated by inserting the syllable "(meth)" into the compound derived from the acrylic acid.

Depending on the type of dissociable groups, a distinction is made between cationic and anionic monomers. Considered is the charge of the unsaturated monomer.

Under cationic monomers below basic group-containing monomers which are quaternized or protonated or protonatable to understand.

In the following, anionic monomers are to be understood as meaning monomers with acid groups, ie, radicals with a cleavable or split off proton.

Preferred cationic monomers are selected from esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with aminoalcohols, preferably C 2 -C 12 -aminoalcohols, amides of α, β-ethylenically unsaturated mono- and dicarboxylic acids with diamines, and the N-d -Cs-monoalkylated or Nd-Cs-dialkylated derivatives of the esters or amides.

As the acid component of these esters, e.g. Acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, maleic anhydride, monobutyl maleate and mixtures thereof. Preference is given to using acrylic acid, methacrylic acid and mixtures thereof. These include, for example, N-methylaminomethyl (meth) acrylate, N-methylaminoethyl (meth) acrylate, N, N-dimethylaminomethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N , N-dimethylaminopropyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate and N, N-dimethylaminocyclohexyl (meth) acrylate.

In addition, as further monomers (b) are N- [2- (dimethylamino) ethyl] acrylamide, N- [2- (dimethylamino) ethyl] methacrylamide, N- [3- (dimethylamino) propyl] acrylamide, N- [3- (Dimethylamino) propyl] methacrylamide, N- [4- (dimethylamino) butyl] acrylamide, N- [4- (dimethylamino) butyl] methacrylamide, N- [2- (diethylamino) ethyl] acrylamide, N- [2- (diethylamino ) ethyl] methacrylamide and mixtures thereof. Of the aforementioned monomers, the respective quaternary compounds are also suitable. The quaternary compounds of the monomers are obtained by reacting the monomers with known quaternizing agents, for example with methyl chloride, benzyl chloride, ethyl chloride, butyl bromide, dimethyl sulfate and diethyl sulfate or Alkylepoxiden.

Also suitable as monomers (b) are N-vinylimidazoles and alkylvinylimidazoles, in particular methylvinylimidazoles such as, for example, 1-vinyl-2-methylimidazole, 3-vinylimidazole N-oxide, 2- and 4-vinylpyridine N-oxides and betaine derivatives and quaternization products of these monomers ,

Examples of ethylenically unsaturated anionic monomers (c) which are used are monoethylenically unsaturated C 3 - to C 8 -carboxylic acids, such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, allylacetic acid and vinylacetic acid, monoethylenically unsaturated C 3 - to C 8 -dicarboxylic acids, such as maleic acid, itaconic acid, fumaric acid, mesaconic acid, Citraconic acid and methylenemalonic acid, sulfonic acids such as vinylsulfonic acid, styrenesulfonic acid, acrylamidomethylpropanesulfonic acid, allylsulfonic acid and methallylsulfonic acid, phosphonic acids such as vinylphosphonic acid and / or the salts of these acids, in particular the alkali metal, alkaline earth metal and / or ammonium salts of these acids. For neutralization, for example, alkali metal or alkaline earth metal bases, ammonia, amines and / or alkanolamines are used. Examples of these are sodium hydroxide solution, potassium hydroxide solution, soda, potash, sodium bicarbonate, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine, morpholine, diethylenetriamine or tetraethylenepentamine.

Preferred anionic monomers include acrylic acid, methacrylic acid, maleic acid, itaconic acid and acrylamido-2-methylpropanesulfonic acid. Particular preference is given to polymers based on acrylic acid. The copolymers may optionally contain at least one further monomer of group (d) in copolymerized form which does not fall under any of monomers (a), (b) and (c) but is a monoethylenically unsaturated monomer other than these. Examples of monomers (d) are nitriles of α, β-ethylenically unsaturated mono- and dicarboxylic acids, for example acrylonitrile and methacrylonitrile.

Further suitable monomers of group (d) are:

Esters α, β-ethylenically unsaturated mono- and dicarboxylic acids with monohydric C1-C30 alkanols, C2-C3o-alkanediols and esters of vinyl alcohol and allyl alcohol with C1-C30 monocarboxylic acids, N-vinyl amides, methacrylamide and N-mono- and disubstituted acrylamides and methacrylamides, N-vinyl lactams, lactones having α, β-ethylenically unsaturated double bonds, vinyl aromatics, vinyl halides, vinylidene halides, C 2 -C 8 monoolefins and mixtures thereof. Examples of representatives of this group (d) are, for example, methyl (meth) acrylate, methyl acrylate, ethyl (meth) acrylate, ethyl methacrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, tert-butyl methacrylate, n-ocytl (meth) acrylate, 1,1,3,3-tetramethylbutyl (meth) acrylate, ethylhexyl (meth) acrylate, methacrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, n-Propyl (meth) acrylamide, N- (n-butyl) (meth) acrylamide, tert-butyl (meth) acrylamide, n-octyl (meth) acrylamide, 1,1,3,3-tetramethylbutyl (meth) acrylamide , Ethylhexyl (meth) acrylamide, vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinylpropionamide and N-vinyl-N-methylpropionamide and N Vinyl butyramide, 2-hydroxyethyl (meth) acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate,

Hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate and mixtures thereof.

Suitable monomers (d) are also N-vinyl lactams and their derivatives, e.g. may have one or more C 1 -C 6 -alkyl substituents (as defined above). These include N-vinylpyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, N-vinyl-5-methyl-2-pyrrolidone, N-vinyl-5-ethyl-2-pyrrolidone, N-vinyl-6-methyl-2-piperidone, N-vinyl-6-ethyl-2-piperidone, N-vinyl-7-methyl-2-caprolactam, N-vinyl-7-ethyl-2-caprolactam and mixtures thereof.

Suitable additional monomers (d) are also ethylene, propylene, isobutylene, butadiene, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and mixtures thereof.

The aforementioned monomers (d) can be used individually or in the form of any mixtures. A further modification of the copolymers is possible by using in the copolymerization monomers (e) which contain at least two double bonds in the molecule, for example triallylamine, tetraallylammonium chloride, methylenebisacrylamide, glycol diacrylate, glycol dimethacrylate, glycerol triacrylate, pentaerythritol triallyl ether, at least twice with acrylic acid and / or Methacrylic acid esterified polyalkylene glycols or polyols such as pentaerythritol, Sobit or glucose. Also suitable are allyl and vinyl ethers of polyalkylene glycols or polyols such as pentaerythritol, soudite or glucose. If at least one monomer of group (d) is used in the copolymerization, the amounts used are up to 2 mol%, for example 0.001 to 1 mol%. In a preferred embodiment, copolymers obtainable by polymerization of From 20 to 50 mol% of acrylamide, based on the total number of moles of monomers used for the polymerization,

From 25 to 40 mol%, based on the total number of moles of monomers used for the polymerization, of at least one cationic monomer,

25 to 40 mol%, based on the total moles of monomers used for the polymerization, of at least one anionic monomer which is selected from monoethylenically unsaturated C3 to C5 carboxylic acids, monoethylenically unsaturated C3 to Cs dicarboxylic acids, sulfonic acids, phosphonic acids and / or the salts of these acids,

The preparation of the water-soluble amphoteric copolymers is carried out by customary methods known to the person skilled in the art. The preparation of the water-soluble amphoteric copolymers can be carried out by solution, precipitation, suspension or emulsion polymerization. Preference is given to solution polymerization in aqueous media. Suitable aqueous media are water and mixtures of water and at least one water-miscible solvent, e.g. an alcohol such as methanol, ethanol, n-propanol, isopropanol, etc.

The polymerization temperatures are preferably in a range of about 30 to 200 ° C, more preferably 40 to 1 10 ° C. The polymerization can take place under atmospheric pressure but also under reduced or elevated pressure. A suitable pressure range is between 0.1 and 5 bar.

The anionic monomers (c) are preferably used in the salt form. The pH is preferably adjusted to a value in the range of 3 to 8 for copolymerization. By using a standard buffer or by measuring the pH and corresponding addition of acid or base, the pH can be kept constant during the polymerization. To prepare the copolymers, the monomers can be polymerized by means of free-radical initiators. As initiators for the radical polymerization, the peroxo and / or azo compounds customary for this purpose can be used, for example alkali metal or ammonium peroxidisulfates, diacetyl peroxide, dibenzoyl peroxide, succinyl peroxide,

Di-tert-butyl peroxide, tert-butyl perbenzoate, tert-butyl perpivalate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl permalate, cumene hydroperoxide, diisopropyl peroxidicarbamate, bis (o-toluoyl) peroxide, didecanoyl peroxide, dioctanoyl peroxide , Dilauroyl peroxide, tert-butyl perisobutyrate, tert-butyl peracetate, di-tert-amyl peroxide,

tert-butyl hydroperoxide, azo-bis-isobutyronitrile, azo-bis (2-amidonopropane) dihydrochloride or 2-2'-azobis (2-methyl-butyronitrile). Also suitable are initiator mixtures or redox initiator systems, e.g. Ascorbic acid / iron (II) sulfate / sodium peroxodisulfate, tert-butyl hydroperoxide / sodium disulfite, tert-butyl hydroperoxide / sodium hydroxymethanesulfinate, H2O2 / CUI and sodium or ammonium peroxodisulfate / sodium disulfite.

To adjust the molecular weight, the polymerization can be carried out in the presence of at least one regulator. As a regulator, the usual compounds known in the art, such. B. sulfur compounds, for. Mercaptoethanol,

2-Ethylhexylthioglycolat, thioglycolic acid, sodium hypophosphite, formic acid or Dodecylmercaptan and Tribromchlormethan or other compounds which act regulating the molecular weight of the polymers obtained, are used.

The molecular weight of the water-soluble amphoteric copolymers is, for example, at least 10,000, preferably at least 100,000 daltons and in particular at least 250,000 daltons. The molecular weights of the copolymers are then e.g.

10,000 to 10 million, preferably 100,000 to 5 million (as determined by light scattering). This molar mass range corresponds, for example, to K values of 5 to 300, preferably 10 to 200 (determined according to H. Fikentscher in 5% strength aqueous sodium chloride solution at 25 ° C. and a polymer concentration of 0.1% by weight).

The water-soluble, amphoteric copolymers can carry an anionic or a cationic excess charge or else be electrically neutral if the same number of anionic and cationic groups are present in the copolymer.

The method according to the invention enables a tear-free operation of the paper machine. The paper web or paper sheet produced in the process shows a significantly increased wet texture strength. The following examples are intended to explain the present invention in more detail. The percentages in the examples are by weight unless otherwise specified. Examples

Preparation of the copolymers

Example P1: Preparation of Polymer I

In a 2 l 5-neck flask equipped with an anchor stirrer, a thermometer, a descending condenser and a nitrogen inlet 400 g of deionized water were submitted. Furthermore, the following feeds were provided:

Feed 1: The following components were mixed in a beaker:

250 g of deionized water

95.6 g 50% strength by weight aqueous acrylamide solution

121, 9 g 80 wt .-%, aqueous solution of acryloyloxyethyltrimethylammonium chloride

148.1 g 32 wt .-%, aqueous sodium acrylate solution

0.2 g of 1% strength by weight aqueous solution of diethylenetriaminepentaacetic acid

By adding about 32 g of 37% hydrochloric acid, the pH was adjusted to 4.1

Feed 2: 60.0 g of a 1 wt .-% aqueous solution of ^2,2'-azobis (2-amidinopropane) dihydrochloride

Feed 3: 16.5 g of a 1 wt .-% aqueous solution of ^2,2'-azobis (2-amidinopropane) dihydrochloride

The original was heated to 63 ° C and the pressure was lowered by means of a water jet pump so far that the water just started to boil. The feeds 1 and 2 were started simultaneously, the feed 1 in 2 hours and the feed 2 in 3 hours at a constant internal temperature to the template. After the end of feed 2, the reaction was held at 63 ° C. for a further hour, then the mixture was heated to 72 ° C. and the vacuum was reduced correspondingly. The reaction mixture was kept at 72 ° C for a further 2 hours, then feed 3 was added all at once and postpolymerized at 72 ° C for a further 2 hours. Then the vacuum was released, the batch was diluted with 500 g of deionized water and cooled to room temperature. During the entire polymerization, 208 g of water were distilled off. A clear, colorless, viscous solution of a polymer having the composition of 40 mol% of acrylamide, 30 mol% of acryloyloxyethyltrimethylammonium chloride and 30 mol% of sodium acrylate was obtained. Solids content: 14.5% by weight

Viscosity: 10,600 mPas (Brookfield, spindle 7, 50 rpm, room temperature)

K value 120 (0.1% solution of the polymer in a 5 wt .-% aqueous

Saline)

Example P2: Preparation of Polymer II

Feed 1: The following components were mixed in a beaker:

250 g of deionized water

1 19.5 g 50% strength by weight aqueous acrylamide solution

1 13.8 g 80 wt .-%, aqueous solution of acryloyloxyethyltrimethylammonium chloride

108.6 g 32% strength by weight aqueous sodium acrylate solution

0.2 g of 1% strength by weight aqueous solution of diethylenetriaminepentaacetic acid. The addition of about 38 g of 37% strength hydrochloric acid adjusted the pH to 4.1

Feed 2: 63.5 g of a 1% aqueous solution of ^2,2'-azobis (2-amidinopropane) - dihydrochloride

Feed 3: 17.0 g of a 1% aqueous solution of ^2,2'-azobis (2-amidinopropane) - dihydrochloride

The original was heated to 66 ° C and the pressure was lowered by means of a water jet pump so far that the water just started to boil. The feeds 1 and 2 were started simultaneously, the feed 1 in 2 hours and the feed 2 in 3 hours at a constant internal temperature to the template. After the end of feed 2, the reaction was held for a further hour at 66 ° C, then was heated to 78 ° C and correspondingly reduced the vacuum. The reaction mixture was kept for a further 2 hours at 78 ° C, then feed 3 was added all at once and postpolymerized at 78 ° C for a further 2 hours. The vacuum was then released, the batch was diluted with 500 g of deionized water and cooled to room temperature. During the entire polymerization, 200 g of water were distilled off.

A clear, colorless, viscous solution of a polymer having the composition of 50 mol% of acrylamide, 28 mol% of acryloyloxyethyltrimethylammonium chloride and 22 mol% of sodium acrylate was obtained.

Solids content: 14.1% by weight

Viscosity: 42,000 mPas (Brookfield, spindle 7, 50 rpm, room temperature) 125 (0.1% solution of the polymer in a 5% aqueous saline solution)

Example P3: Preparation of Polymer III

Feed 1: The following components were mixed in a beaker:

250 g of deionized water

71.7 g 50% strength by weight aqueous acrylamide solution

130.1 g 80% strength by weight aqueous solution of acryloyloxyethyltrimethylammonium chloride

187.8 g 32 wt .-%, aqueous sodium acrylate solution

By adding about 34 g of 37% hydrochloric acid, the pH was adjusted to 4.1

Feed 2: 60.3 g of a 1 wt .-% aqueous solution of ^2,2'-azobis (2-amidinopropane) dihydrochloride

Feed 3: 16.0 g of a 1 wt .-% aqueous solution of ^2,2'-azobis (2-amidinopropane) dihydrochloride

The original was heated to 63 ° C and the pressure was lowered by means of a water jet pump so far that the water just started to boil. The feeds 1 and 2 were started simultaneously, the feed 1 in 2 hours and the feed 2 in 3 hours at a constant internal temperature to the template. After the end of feed 2, the reaction was held at 63 ° C. for a further hour, then the mixture was heated to 72 ° C. and the vacuum was reduced correspondingly. The reaction mixture was kept at 72 ° C for a further 2 hours, then feed 3 was added all at once and postpolymerized at 72 ° C for a further 2 hours. Then the vacuum was released, the batch was diluted with 500 g of deionized water and cooled to room temperature. During the entire polymerization, 200 g of water were distilled off. A clear, fabeless, viscous solution of a polymer having the composition of 30 mol% of acrylamide, 32 mol% of acryloyloxyethyltrimethylammonium chloride and 38 mol% of sodium acrylate was obtained.

Solids content: 14.8% by weight

Viscosity: 12,000 mPas (Brookfield, spindle 7, 50 rpm, room temperature)

K value 1 17 (0.1% solution of the polymer in a 5% strength by weight aqueous

Saline) Example P4: Preparation of Polymer IV (Not According to the Invention)

Feed 1: The following components were mixed in a beaker:

287.7 g of deionized water

214.3 g 50% strength by weight aqueous acrylamide solution

78.1 g 80% strength by weight aqueous solution of acryloyloxyethyltrimethylammonium chloride

94.9 g of 32% strength by weight aqueous sodium acrylate solution

0.3 g of 1% strength aqueous solution of diethylenetriaminepentaacetic acid The pH was adjusted to 4.1 by the addition of about 20 g of a 37% strength hydrochloric acid.

Feed 2 67.1 g of a 1 wt .-% aqueous solution of ^2,2'-azobis (2-amidinopropane) dihydrochloride

Feed 3: 17.7 g of a 1 wt .-% aqueous solution of ^2,2'-azobis (2-amidinopropane) dihydrochloride The initial charge was heated to 64 ° C and the pressure by means of a water jet pump lowered so far, the Water just started to boil. The feeds 1 and 2 were started simultaneously and he feed 1 in 2 hours and the feed 2 in 3 hours at a constant internal temperature to the template. After the end of feed 1, the feed vessel was rinsed with 50 ml of deionized water. After the end of feed 2, the reaction was maintained at 64 ° C. for a further 30 minutes, then 100 ml of deionized water were added and the mixture was heated to 72 ° C. and the vacuum was reduced correspondingly. The reaction mixture was held at 72 ° C for an additional 1.5 hours. Then feed 3 was added all at once and postpolymerized at 72 ° C. for a further 2 hours. The vacuum was then released, the batch was diluted with 500 g of deionized water and cooled to room temperature. During the entire polymerization, 220 g of water were distilled off.

A clear, colorless, viscous solution of a polymer having the composition of 70 mol% of acrylamide, 15 mol% of acryloyloxyethyltrimethylammonium chloride and 15 mol% of sodium acrylate was obtained.

Solids content: 13.6% by weight

Viscosity: 21,600 mPas (Brookfield, spindle 7, 50 rpm, room temperature)

K value 129 (0.1% solution of the polymer in a 5 wt .-% aqueous

Saline)

Example P5: Preparation of Polymer V (Not According to the Invention) In a 2 l 5-neck flask equipped with an anchor stirrer, a thermometer, a descending condenser and a nitrogen inlet 400 g of deionized water were submitted. Furthermore, the following feeds were provided:

Feed 1: The following components were mixed in a beaker:

290.2 g deionized water

183.7 g 50% strength by weight aqueous acrylamide solution

158.1 g of 32% strength by weight aqueous sodium acrylate solution

0.2 g of 1% strength aqueous solution of diethylenetriaminepentaacetic acid The pH was adjusted to 4.1 by the addition of about 20 g of 37% strength hydrochloric acid.

Feed 2: 75.1 g of a 1 wt .-% aqueous solution of ^2,2'-azobis (2-amidinopropane) dihydrochloride

Feed 3: 18.0 g of a 1 wt .-% aqueous solution of ^2,2'-azobis (2-amidinopropane) dihydrochloride

The original was heated to 66 ° C and the pressure was lowered by means of a water jet pump so far, so the water just began to boil. The feeds 1 and 2 were started simultaneously and he feed 1 in 2 hours and the feed 2 in 3 hours at a constant internal temperature to the template. After the end of feed 1, the feed vessel was rinsed with 50 ml of deionized water. After the end of feed 2, the reaction was held at 66 ° C. for a further 30 minutes, then 100 ml of deionized water were added and the mixture was heated to 75 ° C. and the vacuum was reduced correspondingly. The reaction mixture was held at 75 ° C for an additional 1.5 hours. Then feed 3 was added all at once and postpolymerized at 75 ° C. for a further 2 hours. The vacuum was then released, the batch was diluted with 500 g of deionized water and cooled to room temperature. During the entire polymerization, 220 g of water were distilled off.

A clear, colorless, viscous solution of a polymer having the composition of 60 mol% of acrylamide, 15 mol% of acryloyloxyethyltrimethylammonium chloride and 25 mol% of sodium acrylate was obtained. Solids content: 12.1% by weight

Viscosity: 33,500 mPas (Brookfield, spindle 7, 50 rpm, room temperature) K value 125 (0.1% solution of the polymer in a 5% strength by weight aqueous solution)

Saline)

Testing of the polymers I to V described above to increase the initial wet strength of paper To simulate the sheet formation process on a laboratory scale, the pulp concentration of the thin material in the examples must be set at 3.5 g / l.

Pretreatment of the pulp suspension

Bleached birch sulphate was beaten nip-free at a pulp concentration of 4% in the laboratory pulp until a freeness of 30 ° SR was reached. The opened substance is an optical brightener (Blankophor ^® PSG) and a fully digested cationic starch (HICAT ^® 5163 A) were then added and allowed to act for 5 minutes. The digestion of the cationic starch was previously carried out as a 10% starch slurry in a jet cooker at 130 ° C and 1 minute residence time. The metered amount of the optical brightener was 0.5 wt .-% commercial goods, based on the solids content of the pulp suspension. The dosage of the cationic starch was 0.8% starch (solid), based on the solids content of the pulp suspension. The pulp content of the pulp suspension after addition of starch and optical brightener was 3.5% (35 g / l).

Examples 1 to 3

Three beakers were each filled with 50 g of the pretreated pulp suspension described above. 2 g of a 1% strength by weight aqueous solution of one of the polymers I-III described above were metered into each of the beakers with slight stirring of the pulp suspension (corresponds to 1% polymer (solid) on pulp (solid)). Subsequently, the pulp suspensions were diluted by addition of water to a pulp concentration of 0.35% each. Thereafter, a 20% strength by weight carbonate pigment slurry (PCC, Syncarb F474 from Omya) was added. The added amount of the pigment suspension (equivalent to filler suspension) was adjusted in several preliminary experiments so that the pigment content in the laboratory sheets subsequently formed was about 20%. The pulp suspensions were processed two minutes after the pigment addition to a Rapid-Köthen sheet former according to ISO 5269/2 to sheets of a basis weight of 100 g / qm. The wet leaves were then removed from the screen frame and placed between two absorbent felts. The package consisting of absorbent felts and the wet paper was then pressed in a static press at a press pressure of 6 bar. It was pressed in each case up to a solids content of 50 wt .-% of the wet leaves.

Examples 4, 5 and 7 (not according to the invention)

Three beakers were each filled with 50 g of the pretreated pulp suspension described above. In each case 2 g of a 1% strength by weight aqueous solution of one of the above-described polymers IV and V were metered into two of the beakers with slight stirring of the pulp suspension. The pulp in the third beaker served as a reference and remained untreated (Example 7). Subsequently, the pulp suspensions in all 3 beakers were diluted by addition of water to a pulp concentration of 0.35% each. Thereafter, in each case a 20% strength by weight carbonate pigment slurry (PCC, Syncarb F474 from Omya) was added to the mixture. The added amount of pigment suspension was adjusted in several preliminary experiments so that the pigment content in the laboratory sheets subsequently formed was about 20%. The pulp suspensions were processed two minutes after the pigment addition to a Rapid-Köthen sheet former according to ISO 5269/2 to sheets of a basis weight of 100 g / qm.

The wet leaves were then removed from the screen frame and placed between two Saugfilze. The package consisting of absorbent felts and the wet paper was then pressed in a static press at a press pressure of 6 bar. By adjusting the residence time of the papers within the press arrangement, in each case up to a solids content of 50% by weight of the wet leaves was pressed.

Example 6 (not according to the invention - dosage in the thin material)

50 g of the pretreated pulp suspension (thick stock) was diluted by the addition of 450 g of water to a pulp concentration of 0.35% (corresponding to 3.5 g / l). 2 g of a 1% strength by weight aqueous solution of polymer I were added to 500 g of the diluted pulp suspension (thin material) (corresponds to 1% by weight of polymer (solid) based on pulp (solid).

Thereafter, in each case a 20% strength by weight carbonate pigment slurry (PCC, Syncarb F474 from Omya) was added to the mixture. The added amount of pigment suspension was adjusted in several preliminary experiments so that the pigment content in the laboratory sheets subsequently formed was about 20%.

The pulp suspension was processed two minutes after the pigment addition on a Rapid-Kothen-Blattbildner according to ISO 5269/2 to sheets of a basis weight of 100 g / qm. The wet leaves were then removed from the screen frame and placed between two Saugfilze. The package consisting of absorbent felts and the wet paper was then pressed in a static press at a press pressure of 6 bar. By adjusting the residence time of the papers within the press arrangement in each case up to a solids content of 50 wt .-% of the wet leaves was pressed.

Examples 8, 9 and 10 (not according to the invention)

Three beakers were each filled with 50 g of the pretreated pulp suspension described above. 2 g of a 1% strength by weight aqueous solution of one of the polymers I-III described above were metered into each of the beakers, with slight stirring of the pulp suspension (corresponds to 1% polymer (solid) on pulp (solid)). Subsequently, the pulp suspensions by addition of water was a pulp concentration of 0.35% each diluted. Thereafter, a 20% strength by weight carbonate pigment slurry (PCC, Syncarb F474 from Omya) was added. The added amount of the pigment suspension was adjusted in several preliminary experiments so that the pigment content in the laboratory sheets subsequently formed was about 20%. The pulp suspensions were processed two minutes after the pigment addition to a Rapid-Köthen sheet former according to ISO 5269/2 to sheets of a basis weight of 100 g / qm. The wet leaves were then removed from the screen frame and placed between two Saugfilze. The package consisting of absorbent felts and the wet paper was then pressed in a static press at a press pressure of 6 bar. By adjusting the residence time within the press arrangement, in each case up to a solids content of the wet leaves was pressed, which is shown in Table 1.

Example 1 1

The procedure was as in Example 7 and untreated pigment (PCC, Syncarb F474 from Omya) used. The press duration in the static press was adjusted so that the solids content of the wet leaves was below the limit dry content, taking into account the pigment content. In this case, below 50%, at 48.7%.

Application testing: Determination of initial wet texture strength

The wet strength and the initial wet strength of paper are to be distinguished from the initial wet texture strength because both properties are measured on papers which are moistened again after drying to a defined water content. The initial wet strength is an important parameter in the assessment of non-permanent wet-strength papers. A dried and then re-wetted paper has a very different wet strength than a wet paper that is present just after passing through the wire and press section of a paper machine.

The determination of the initial wet texture strength on the wet paper takes place in each case according to the Voith process (see M.Schwarz and K. Bechtel "Initial structural strength in sheet formation", in Wochenblatt fur Papierfabrikation 131, pages 950-957 (2003) no 16. The wet leaves were then chipped onto a plastic backing after pressing in the static press and transferred to a cutting pad, and then the test strips were cut out of the sheet at a defined length and width, and pressed under constant pressure. For the examination of the paper sheets obtained according to the examples given above, in each case four dry contents were set in the range of between 42% and 58% From these values, the adaptation method described in the above reference was used Initial wet texture strength determined at 50% dry content. The actual measurement of the initial wet structural strength was made on a vertical tensile testing machine with a special clamping device. The force determined in the tractor was converted into the area-mass-independent so-called INF index. For a detailed description of the clamping device, the measuring procedure, the determination of the dry content in the paper and the data processing, the reference cited above can be used.

The results of the tests are shown in Table 1

Table 1: Results of the performance test for the production of paper with a filler content of 20 wt .-%. According to the calculation of the limit dry content G (x) = G (20), according to the invention, a solids content of at least 50% by weight is to be pressed:

G (20) = 48 + (20-15) 0.4 = 50

Example Polymer INF Index Solids content

[Nm / g] to which was pressed [%]

1 I 3,3 50,3

2 II 3.1 50.5

3 III 2.9 50.2

4

IV 2.1 50.9 not according to the invention

5

V 2.0 51, 2 not according to the invention

6

not according to the invention I 2,2 50,6 (polymer I in the thin material)

7

- 1, 7 51, 3 not according to the invention

8th

I 1, 5 48.6 not according to the invention

9

II 1, 4 48.8 not according to the invention

10

III 1, 3 48.3 not according to the invention

1 1

- 1, 4 48.7 not according to the invention

Claims

Claims 1. A process for producing paper, paperboard and cardboard comprising dewatering a filler-containing paper stock comprising at least one water-soluble amphoteric copolymer, forming a sheet in the wire section and then pressing the paper in the press section, resulting in a stock having a pulp concentration in the range from 20 to 40 g / l the at least one water soluble, amphoteric copolymer is metered, then the stock is diluted to a pulp concentration in the range of 5 to 15 g / l, the diluted stock is dewatered to form a sheet and the sheet in the press section to a solids content G (x) wt% or greater presses and G (x) calculates after

G (x) = 48 + (x - 15) x 0.4 where x is the number value of the filler content of the dry paper, paperboard or paperboard (in% by weight) and

and G (x) is the minimum solids (in% by weight) number count on which the sheet is pressed, the water-soluble, amphoteric copolymer being obtainable by polymerizing a mixture of a) from 20 to 60 molar % Acrylamide, based on the total number of moles of the monomers used for the polymerization, b) 20 to 60 mol%, based on the total number of moles of the monomers used for the polymerization, of at least one cationic monomer, c) 20 to 60 mol%, based on the total number of moles the monomers used for the polymerization, of at least one anionic monomer selected from monoethylenically unsaturated C 3 - to C 5 -carboxylic acids, monoethylenically unsaturated C 3 - to C 8 -dicarboxylic acids,

Sulfonic acids, phosphonic acids and / or the salts of these acids d) 0 to 30 mol%, based on the total number of moles of the monomers used for the polymerization, of one or more monoethylenically unsaturated monomers of the monomers (a), (b) and (c ) are different, and e) 0 to 5 mol%, based on the total number of moles of the monomers used for the polymerization, of one or more compounds which have at least two ethylenically unsaturated double bonds in the molecule, the amount of the difference in the proportions of the cationic and anionic monomers in mol%, in each case based on the total number of moles of the monomers used for the polymerization, a maximum of 10 mol%.

A process for producing paper, paperboard and cardboard comprising dewatering a filler-containing paper stock comprising at least one water-soluble amphoteric copolymer, forming a sheet in the wire section and then pressing the paper in the press section, resulting in a stock having a pulp concentration in the range from 20 to 40 g / l the at least one water soluble, amphoteric copolymer is metered, then the stock is diluted to a pulp concentration in the range of 5 to 15 g / l, the diluted stock is dewatered to form a sheet and the sheet in the press section to a solids content of> 48% by weight, the water-soluble, amphoteric copolymer being obtainable by polymerizing a mixture of a) from 20 to 60 mol% of acrylamide, based on the total number of moles of monomers used for the polymerization, b) from 20 to 60 mol% , based on the total number of moles of Mo used for the polymerization c) 20 to 60 mol%, based on the total number of moles of the monomers used for the polymerization, of at least one anionic monomer selected from monoethylenically unsaturated C3 to C5 monocarboxylic acids, monoethylenically unsaturated C3 to C5 Dicarboxylic acids, sulfonic acids, phosphonic acids and / or the salts of these acids d) 0 to 30 mol%, based on the total number of moles of the monomers used for the polymerization, of one or more monoethylenically unsaturated monomers selected from the monomers (a), (b) and (c) are different, and e) 0 to 5 mol%, based on the total number of moles of monomers used for the polymerization, of one or more compounds which have at least two ethylenically unsaturated double bonds in the molecule, wherein the amount of the difference in the proportions of the cationic and the anionic monomer in mol%, in each case based on the total moles of the monomers used for the polymerization, a maximum of 10 mol%.

A method according to claim 1 or 2, characterized in that the pulp contains as pulp exclusively a pulp having a freeness of <30 ° SR.

Method according to one of claims 1 to 3, characterized in that the water-soluble, amphoteric copolymer are added to the paper stock with a pulp concentration in the range of 20 to 40 g / l and before the addition of a filler.

Method according to one of claims 1 to 4, characterized in that the water-soluble, amphoteric copolymer in an amount of 0.05 to 5.00 wt .-%, based on pulp, is added.

Process according to any one of Claims 1 to 5, characterized in that the water-soluble, amphoteric copolymer is obtainable by polymerizing a mixture with at least one cationic monomer selected from the esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with amino alcohols, Amides of α, β-ethylenically unsaturated mono- and dicarboxylic acids with diamines, and the N-d-Cs-monoalkylated or Nd-Cs-dialkylated derivatives of these esters or these amides.

Method according to one of claims 1 to 6, characterized in that the water-soluble, amphoteric copolymer is obtainable by polymerizing a mixture with at least one anionic monomer selected from acrylic acid, methacrylic acid, maleic acid, itaconic acid and acrylamido-2-methylpropanesulfonic acid and the salts thereof acids.

Method according to one of claims 1 to 7, characterized in that the water-soluble, amphoteric copolymer is obtainable by polymerizing a mixture of a) from 20 to 50 mol% of acrylamide, based on the total number of moles of the monomers used for the polymerization,

From 25 to 40 mol%, based on the total number of moles of monomers used for the polymerization, of at least one cationic monomer, c) 25 to 40 mol%, based on the total moles of monomers used for the polymerization, of at least one anionic monomer which is selected from monoethylenically unsaturated C3 to C5 monocarboxylic acids, monoethylenically unsaturated C3 to C5 dicarboxylic acids, sulfonic acids, phosphonic acids and or the salts of these acids, d) 0 to 30 mol%, based on the total moles of the monomers used for the polymerization, of one or more monoethylenically unsaturated monomers which are different from the monomers (a), (b) and (c) , and e) 0 to 5 mol%, based on the total number of moles of the monomers used for the polymerization, one or more compounds having at least two ethylenically unsaturated double bonds in the molecule, wherein the amount of the difference in the proportions of the cationic and the anionic monomer in mol %, in each case based on the total number of moles of the monomers used for the polymerization, a maximum of 10 mol%.

9. The method according to any one of claims 2 to 8 for the production of paper, paperboard and cardboard having a filler content of 17 to 32, characterized in that one presses in the press section to at least a solids content in the range of 49 to 55.

10. The method according to any one of claims 2 to 8 for the production of paper, board and cardboard having a filler content of 15 or smaller, characterized in that one presses in the press section to at least a solids content of 48 wt .-%.