EP2443284B2 - Method for increasing dry strength of paper, paperboard and cardboard - Google Patents

Description

The invention relates to a process for the production of paper, paperboard and cardboard with high dry strength by adding (a) at least one trivalent cation, (b) at least one water-soluble cationic polymer selected from the group of (i) polymers containing vinylamine units and (ii) ethyleneimine units containing polymers and (c) at least one water-soluble amphoteric polymer to form a paper stock, dewatering the paper stock with sheet formation and drying the paper product obtained, wherein the (i) vinylamine-containing polymer and (c) at least one water-soluble amphoteric polymer as in claims 1 and 2 are defined.

Numerous papers with high dry strength and the processes for their production are already known from the literature.

Out JP 54-030913 a process for producing paper with high dry strength is known in which an aluminum sulfate solution is first added to the paper stock. A water-soluble amphoteric polymer is then metered in. The paper stock is then dewatered on the paper machine to form sheets, and the paper products are dried. Examples of suitable amphoteric polymers are copolymers of acrylamide, acrylic acid and dimethylaminoethyl (meth) acrylate.

From the DE 35 06 832 A1 a process for producing paper with high dry strength is known, in which first a water-soluble cationic polymer is added to the paper stock and then a water-soluble anionic polymer is added. Suitable anionic polymers are, for example, homopolymers or copolymers of ethylenically unsaturated C ₃ -C ₅ carboxylic acids. The copolymers contain at least 35% by weight of an ethylenically unsaturated C ₃ -C ₅ carboxylic acid (for example acrylic acid) in copolymerized form. The cationic polymers described in the examples are polyethyleneimine, polyvinylamine, polydiallyldimethylammonium chloride and condensation products of adipic acid and diethylenetriamine reacted with epichlorohydrin. The use of partially hydrolyzed homo- and copolymers of N-vinylformamide has also been considered.

The JP 02-112498 relates to a process for the production of corrugated cardboard, in which alum, a polyallylamine and an anionic or amphoteric polymer are added to a fiber suspension. The combination results in papers with a high strength.

In JP 05-272092 describes a process for the production of paper with high dry strength, in which an aluminum sulfate solution is first added to the paper stock, and then a water-soluble amphoteric polymer with high molecular weight is metered in, then the paper stock is dewatered on the paper machine with sheet formation and the paper products are dried. Examples of amphoteric polymers which are mentioned are copolymers of acrylamide, acrylic acid, dimethylaminoethyl (meth) acrylate, (meth) acrylamide and sodium (meth) allyl sulfonate. These amphoteric polymers are characterized by very high molecular weights and low solution viscosities.

A variant of the in JP 05-272092 procedure is described in JP 08-269891 disclosed. In this process for producing paper with high dry strength, an aluminum sulfate solution is also first added to the paper stock, and then a water-soluble amphoteric polymer with a high molecular weight is added, then the paper stock is dewatered on the paper machine to form sheets and the paper products are dried. The amphoteric polymers used are, for example, copolymers of acrylamide, acrylic acid, dimethylaminoethyl methacrylate, (meth) acrylamide, sodium (meth) allyl sulfonate and a crosslinker such as methylenebisacrylamide or triallylamine. These amphoteric polymers have a very high molecular weight and one opposite JP 05-272092 further reduced solution viscosity.

The EP 0 659 780 A1 describes a process for the preparation of polymers with a weight average molecular weight of 1,500,000 to 10,000,000 (a) and a weight average root mean square radius of 30 to 150 nm (b), the ratio (b) / (a)) 0 , 00004, and their use as a solidifying agent.

WO 98/06898 A1 describes a process for paper manufacture in which a cationic starch or a cationic wet strength agent and a water-soluble amphoteric polymer are added to the paper stock. This amphoteric polymer is made up of the nonionic monomers acrylamide and methacrylamide, an anionic monomer, a cationic monomer and a crosslinker, the amount of anionic and cationic monomer not being more than 9% by weight of the total monomers used in the amphoteric polymer.

The JP-A-1999-140787 relates to a process for the production of corrugated cardboard, whereby to improve the strength properties of a paper product to the paper stock 0.05 to 0.5% by weight, based on dry paper stock, of a polyvinylamine obtained by hydrolysis of polyvinylformamide with a degree of hydrolysis of 25 to 100 % is accessible, is added in combination with an anionic polyacrylamide, the paper stock is then dewatered with sheet formation and the paper dries.

The EP 0 919 578 A1 relates to amphoteric polymers (type B), which are produced by means of a two-stage polymerization. First, in a first stage, a polymer (type A) is produced by the copolymerization of methallylsulfonic acid with other vinyl monomers, then, in the presence of the type A polymer, a further polymerization of vinyl monomers to form the type B polymer takes place, the type A polymers having a molecular weight of 1,000 to 5,000,000 and the type B polymers have a molecular weight of 100,000 to 10,000,000. This document also includes the use of type B polymers as strengthening agents for papermaking, as well as the papers produced therewith, the possibility of a combination with alum and anionic polyacrylamides also being described. Finally, the possibility of modifying type B polymers through Hofmann degradation is also mentioned.

From the JP 2001-279595 a paper product with improved strength properties is known, which is obtained by adding a mixture of an amphoteric, cationic or anionic polymer and a water-soluble aluminum solution to the pulp.

The JP 2001-279595 relates to a process for the production of paper with high strength, wherein a mixture of a cationic, anionic or amphoteric polyacrylamide with a water-soluble aluminum compound is added to the fibers. A further polyacrylamide is then metered in. This not only increases strength, but also improves drainage at the same time.

From the WO 03/052206 A1 a paper product with improved strength properties is known, which can be obtained by applying a polyvinylamine and a polymeric anionic compound which can form a polyelectrolyte complex with polyvinylamine, or a polymeric compound with aldehyde functions such as polysaccharides containing aldehyde groups, to the surface of a paper product. Not only is an improvement in the dry and wet strength of the paper obtained, but a sizing effect of the treatment agents is also observed.

In JP 2005-023434 describes a process for the production of paper with high strength, which is obtained by metering two polymers. The first polymer is a branched amphoteric polyacrylamide. As the second polymer, a copolymer of a cationic vinyl monomer can be considered as the main monomer.

1. (a) mindestens eines N-Vinylcarbonsäureamids der Formel
   
   in der R¹, R² = H oder C₁- bis C₆-Alkyl bedeuten,
2. (b) mindestens eines Säuregruppen enthaltenden monoethylenisch ungesättigten Monomeren und/oder deren Alkalimetall-, Erdalkalimetall- oder Ammoniumsalzen und gegebenenfalls
3. (c) anderen monoethylenisch ungesättigten Monomeren, und gegebenenfalls
4. (d) Verbindungen, die mindestens zwei ethylenisch ungesättigte Doppelbindungen im Molekül aufweisen.

In the DE 10 2004 056 551 A1 discloses another method of improving the dry strength of paper. In this process, a polymer containing vinylamine units and a polymeric anionic compound are added separately to a paper stock, the paper stock is dewatered and the paper products are dried, using at least one copolymer as the polymeric anionic compound which is obtainable by copolymerizing

1. (A) at least one N-vinylcarboxamide of the formula
   
   in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,
2. (b) at least one monoethylenically unsaturated monomer containing acid groups and / or their alkali metal, alkaline earth metal or ammonium salts and optionally
3. (c) other monoethylenically unsaturated monomers, and optionally
4. (d) Compounds which have at least two ethylenically unsaturated double bonds in the molecule.

From the WO 2006/075115 A1 the use of Hofmann degradation products of copolymers of acrylamide or methacrylamide in combination with anionic polymers with an anionic charge density of> 0.1 meq / g for the production of paper and cardboard with a high dry strength is known.

In WO 2006/120235 A1 describes a process for producing papers with a filler content of at least 15% by weight, in which the filler and fibers are treated together with cationic and anionic polymers. The treatment takes place alternately with cationic and anionic polymers and comprises at least three steps.

1. (a) ein Polymer mit primären Aminogruppen und einer Ladungsdichte von > 1,0 meq/g,
2. (b) ein zweites, anderes kationisches Polymer mit einer Ladungsdichte von > 0,1 meq/g, das durch radikalische Polymerisation von kationischen Monomeren erhältlich ist, und
3. (c) ein anionisches Polymer mit einer Ladungsdichte von > 0,1 meq/g.

The WO 2006/090076 A1 also relates to a process for the production of paper and cardboard with high dry strength, whereby three components are added to the paper stock:

1. (a) a polymer with primary amino groups and a charge density of> 1.0 meq / g,
2. (b) a second, different cationic polymer with a charge density of> 0.1 meq / g, which is obtainable by free radical polymerization of cationic monomers, and
3. (c) an anionic polymer with a charge density of> 0.1 meq / g.

Out EP 1 849 803 A1 is also known a paper additive for strengthening that is obtained as a water-soluble polymer by polymerizing (meth) acrylamide, an α, β-unsaturated mono- or dicarboxylic acid or salts thereof, a cationic monomer and a crosslinking monomer. In a second stage, the remaining residual monomer is polymerized with further persulfate catalyst.

Even if there are already numerous processes in the literature for the production of papers with high dry strength are known, there is a continuous need in the paper industry for new, alternative processes to those already known.

The present invention was therefore based on the object of providing a further process for the production of paper, paperboard and cardboard with high dry strength, in which the dry strength properties of the paper products are further improved compared to those of known products, and in which at the same time faster drainage of the Paper stock is made possible.

1. (a) mindestens eines trivalenten Kations in Form eines Salzes,
2. (b) mindestens eines wasserlöslichen kationischen Polymeren und (c) mindestens eines wasserlöslichen amphoteren Polymeren

zum Papierstoff, Entwässern des Papierstoffs unter Blattbildung und anschließende Trocknen der Papierprodukte, wobei das wasserlösliche kationische Polymere (b) ausgewählt ist aus der Gruppe der (i) Vinylamineinheiten enthaltende Polymere und (ii) Ethylenimineinheiten enthaltende Polymere, wobei das (i) Vinylamineinheiten enthaltende Polymer und das (c) mindestens eine wasserlösliche amphotere Polymer wie in den Ansprüchen 1 und 2 definiert sind.The objects are achieved according to the invention with a process for the production of paper, paperboard and cardboard with high dry strength, by adding

1. (a) at least one trivalent cation in the form of a salt,
2. (b) at least one water-soluble cationic polymer and (c) at least one water-soluble amphoteric polymer

for paper stock, dewatering of the paper stock with sheet formation and subsequent drying of the paper products, the water-soluble cationic polymer (b) being selected from the group of (i) polymers containing vinylamine units and (ii) polymers containing ethyleneimine units, the (i) polymer containing vinylamine units and (c) at least one water-soluble amphoteric polymer as defined in claims 1 and 2 are.

The stated components of the consolidation system can be added to the paper stock in any order or as a mixture of two or more components.

In principle, all trivalent metal or semimetal cations are suitable as trivalent cations in the process according to the invention. Preferred metal cations are Al ³⁺ , Zr ³⁺ and Fe ³⁺ . Al ³⁺ is very particularly preferred.

The metal and semi-metal cations are used in the form of their salts. In the case of Al ³⁺ , this can be used, for example, in the form of aluminum sulfate, polyaluminium chloride or aluminum lactate.

Of course, any mixtures of the trivalent metal cations mentioned can also be used, but only one trivalent metal cation is preferably used in the process according to the invention. In addition, different salts of this metal cation can be used in any mixtures. In a preferred embodiment of the method according to the invention, a trivalent metal cation is used in one of the salt forms described.

The trivalent cations are usually added to the paper stock in amounts between 3 and 100 mol per ton of dry paper, preferably in the range from 10 to 30 mol per ton of dry paper.

The water-soluble cationic polymer (b) is selected from the group of (i) polymers containing vinylamine units and (ii) polymers containing ethyleneimine units.

The cationic polymers (b) are water-soluble. The solubility in water under normal conditions (20 ° C., 1013 mbar) and pH 7.0 is, for example, at least 5% by weight, preferably at least 10% by weight.

The charge density of the cationic polymers (without counterion) is, for example, at least 1.0 meq / g and is preferably in the range from 4 to 10 meq / g.

The water-soluble cationic polymers (b) usually have average molecular weights in the range from 10,000 to 10,000,000 Daltons, preferably in the range from 20,000 to 5,000,000 Daltons, particularly preferably in the range from 40,000 to 3,000,000 Daltons.

Polymers (i) containing vinylamine units are known, cf. those mentioned in relation to the prior art DE 35 06 832 A1 and DE 10 2004 056 551 A1 .

As polymers containing (i) vinylamine units, preference is given to using the reaction products which are obtainable by polymerizing N-vinylformamide and subsequent cleavage of formyl groups from the vinylformamide units polymerized into the polymer with the formation of amino groups.

• (1.) mindestens eines Monomeren der Formel
  
  in der R¹, R² = H oder C₁- bis C₆-Alkyl bedeuten,
• (2.1) mindestens jeweils eines eine Säurefunktion tragenden Monomeren ausgewählt aus monoethylenisch ungesättigten Sulfonsäuren, monoethylenisch ungesättigten Phosphonsäuren und monoethylenisch ungesättigten Carbonsäuren mit 3 bis 8 C-Atomen im Molekül und/oder deren Alkalimetall-, Erdalkalimetall- oder Ammoniumsalzen,
• (2.2) gegebenenfalls mindestens eines anderen neutralen und/oder eines kationischen Monomeren und
• (3.) gegebenenfalls mindestens eines vernetzend wirkenden Monomeren mit mindestens zwei Doppelbindungen im Molekül

und anschließende teilweise oder vollständige Abspaltung der Gruppen -CO-R¹ aus den in das Polymerisat einpolymerisierten Einheiten der Monomeren (I) unter Bildung von Aminogruppen, wobei der Gehalt an Aminogruppen im Copolymerisat mindestens 5 Mol-% über dem Gehalt an einpolymerisierten Säuregruppen der Monomere (2.1) beträgt.In another embodiment of the invention, the polymers containing vinylamine units are amphoteric if they have an overall cationic charge. The content of cationic groups in the polymer should be at least 5 mol%, preferably at least 10 mol%, above the content of anionic groups. Such polymers are obtainable by polymerizing

• (1.) at least one monomer of the formula
  
  in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,
• (2.1) at least one monomer bearing an acid function selected from monoethylenically unsaturated sulfonic acids, monoethylenically unsaturated phosphonic acids and monoethylenically unsaturated carboxylic acids with 3 to 8 carbon atoms in the molecule and / or their alkali metal, alkaline earth metal or ammonium salts,
• (2.2) optionally at least one other neutral and / or one cationic monomer and
• (3.) optionally at least one crosslinking monomer with at least two double bonds in the molecule

and subsequent partial or complete cleavage of the -CO-R ^{1 groups} from the units of the monomers (I) polymerized into the polymer with the formation of amino groups, the content of amino groups in the copolymer at least 5 mol% above the content of polymerized acid groups of the monomers (2.1) is.

• (1.) N-Vinylformamid,
• (2.1) Acrylsäure, Methacrylsäure und/oder deren Alkalimetall-, Erdalkalimetall- oder Ammoniumsalzen und
• (2.2) gegebenenfalls Acrylnitril und/oder Methacrylnitril

und anschließende teilweise oder vollständige Abspaltung von Formylgruppen aus dem in das Polymerisat einpolymerisierten N-Vinylformamid unter Bildung von Aminogruppen erhältlich sind, wobei der Gehalt an Aminogruppen im Copolymerisat mindestens 5 Mol-% über dem Gehalt an einpolymerisierten Säuregruppen der Monomere (2.1) beträgt.Also of interest are polymers containing amphoteric vinylamine units, which carry an overall cationic charge and which, for example, by copolymerizing

• (1.) N-vinylformamide,
• (2.1) Acrylic acid, methacrylic acid and / or their alkali metal, alkaline earth metal or ammonium salts and
• (2.2) optionally acrylonitrile and / or methacrylonitrile

and subsequent partial or complete splitting off of formyl groups from the N-vinylformamide polymerized into the polymer with the formation of amino groups are obtainable, the content of amino groups in the copolymer being at least 5 mol% above the content of polymerized acid groups of the monomers (2.1).

Examples of monomers of the formula (I) are N-vinylformamide, N-vinyl-N-methylformamide, N-vinyl acetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinyl propionamide and N-vinyl-N -methylpropionamide and N-vinylbutyramide. The monomers of group (a) can be used alone or as a mixture in the copolymerization with the monomers of the other groups. Preferred monomer of this group is N-vinylformamide.

These polymers can optionally be modified by copolymerizing the N-vinylcarboxamides (1.) together with (2.) at least one other monoethylenically unsaturated monomer and then hydrolyzing the copolymers to form amino groups. If anionic monomers are used in the copolymerization, the hydrolysis of the polymerized vinylcarboxamide units is carried out to such an extent that the molar excess of amine units over the anionic units in the polymer is at least 5 mol%.

Examples of monomers of group (2) are esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with C ₁ -C ₃₀ alkanols, C ₂ -C ₃₀ alkanediols and C ₂ -C ₃₀ amino alcohols, amides of α , β-ethylenically unsaturated monocarboxylic acids and their N-alkyl and N, N-dialkyl derivatives, nitriles of α, β-ethylenically unsaturated mono- and dicarboxylic acids, esters of vinyl alcohol and allyl alcohol with C ₁ -C ₃₀ monocarboxylic acids, N-vinyl lactams, nitrogen-containing heterocycles with α, β-ethylenically unsaturated double bonds, vinyl aromatics, vinyl halides, vinylidene halides, C ₂ -C ₈ monoolefins and mixtures thereof.

Suitable representatives are e.g. Methyl (meth) acrylate (in which (meth) acrylate in the context of the present invention means both acrylate and methacrylate), methyl ethacrylate, ethyl (meth) acrylate, ethyl ethacrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert. -Butyl (meth) acrylate, tert-butyl ethacrylate, n-octyl (meth) acrylate, 1,1,3,3-tetramethylbutyl (meth) acrylate, ethylhexyl (meth) acrylate and mixtures thereof.

Suitable additional monomers of group (2.) are also the esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with amino alcohols, preferably C ₂ -C ₁₂ -amino alcohols. These can be C ₁ -C ₈ monoalkylated or dialkylated on the amine nitrogen. Acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, maleic anhydride, monobutyl maleate and mixtures thereof are suitable as acid components of these esters. Acrylic acid, methacrylic acid and mixtures thereof are preferably used. 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.

Also suitable as monomers of group (2.) are 2-hydroxyethyl (meth) acrylate, 2-hydroxyethyl ethacrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and mixtures thereof.

Suitable additional monomers of group (2.) are also acrylic acid amide, methacrylic acid amide, 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, and mixtures thereof.

In addition, as further monomers of group (2.) 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 are suitable.

Further examples of monomers of group (2) are nitriles of α, β-ethylenically unsaturated mono- and dicarboxylic acids, such as, for example, acrylonitrile and methacrylonitrile. The presence of units of these monomers in the copolymer leads to products which have amidine units during or after the hydrolysis, cf. e.g. EP 0 528 409 A1 or DE 43 28 975 A1 . In the hydrolysis of N-vinylcarboxamide polymers, amidine units are formed in a secondary reaction in that vinylamine units react with an adjacent vinylformamide unit or - if a nitrile group is present as an adjacent group in the polymer - with it. In the following, the specification of vinylamine units in the amphoteric copolymers or in unmodified homopolymers or copolymers always means the sum of vinylamine and amidine units.

Suitable monomers of group (2.) are also N-vinyl lactams and their derivatives, which can have, for example, 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.

Furthermore, N-vinylimidazoles and alkylvinylimidazoles are suitable as monomers of group (2.), 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 these monomers as well as 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 can be used individually or in the form of any mixtures. They are typically used in amounts of 1 to 90 mol%, preferably 10 to 80 mol% and particularly preferably 10 to 60 mol%.

For the production of amphoteric copolymers, other monoethylenically unsaturated monomers of group (2.) also include anionic monomers, which are referred to above as monomers (2.1). If appropriate, they can be copolymerized with the neutral and / or cationic monomers (2.2) described above. However, the amount of anionic monomers (2.1) is at most 45 mol%, so that the amphoteric copolymer formed has an overall cationic charge.

Examples of anionic monomers of group (2.1) are ethylenically unsaturated C _{3 to} C ₈ carboxylic acids such as acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, maleic acid, fumaric acid, itaconic acid, mesaconic acid, citraconic acid, methylenemalonic acid, allylacetic acid, vinylacetic acid and crotonic acid. Suitable monomers of this group are also monomers containing sulfonic groups, such as vinylsulfonic acid, acrylamido-2-methylpropanesulfonic acid and styrene sulfonic acid, and monomers containing phosphonic groups, such as vinylphosphonic acid. The monomers of this group can be used alone or in a mixture with one another, in partially or completely neutralized form, in the copolymerization. For example, alkali metal or alkaline earth metal bases, ammonia, amines and / or alkanolamines are used for neutralization. Examples are caustic soda, potassium hydroxide, soda, potash, sodium hydrogen carbonate, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine, morpholine, diethylenetriamine or tetraethylene pentamine.

A further modification of the copolymers is possible by using monomers of group (3.) which contain at least two double bonds in the molecule, e.g. Triallylamine, methylenebisacrylamide, glycol diacrylate, glycol dimethacrylate, glycerol triacrylate, pentaerythritol triallyl ether, polyalkylene glycols esterified at least twice with acrylic acid and / or methacrylic acid, or polyols such as pentaerythritol, sobitol or glucose. These are so-called crosslinkers. If at least one monomer from the above group is used in the polymerization, the amounts used are up to 2 mol%, e.g. 0.001 to 1 mole percent.

Furthermore, to modify the polymers, it can be useful to combine the use of the above crosslinkers with the addition of regulators. Typically 0.001 to 5 mol% are used. All controllers known from the literature can be used, e.g. Sulfur compounds such as mercaptoethanol, 2-ethylhexyl thioglycolate, thioglycolic acid and dodecyl mercaptan and sodium hypophosphite, formic acid or tribromochloromethane and terpinolene.

The polymers (i) containing vinylamine units also include hydrolyzed graft polymers of, for example, N-vinylformamide on polyalkylene glycols, polyvinyl acetate, polyvinyl alcohol, polyvinylformamides, polysaccharides such as starch, oligosaccharides or monosaccharides. The graft polymers can be obtained by free-radical polymerizing, for example, N-vinylformamide in an aqueous medium in the presence of at least one of the graft bases mentioned, optionally together with other copolymerizable monomers, and then hydrolyzing the grafted vinylformamide units in a known manner to give vinylamine units.

The hydrolysis of the copolymers described above can be carried out in the presence of acids or bases or else enzymatically. In the case of hydrolysis with acids, the vinylamine groups formed from the vinylcarboxamide units are present in salt form. The hydrolysis of vinylcarboxamide copolymers is in the EP 0 438 744 A1 , Page 8, line 20 to page 10, line 3, described in detail. The statements made there apply accordingly to the preparation of the purely cationic and / or amphoteric polymers containing vinylamine units to be used according to the invention and having an overall cationic charge.

The above-described homopolymers and copolymers (i) containing vinylamine units can be prepared by solution, precipitation, suspension or emulsion polymerization. Solution polymerization in aqueous media is preferred. Suitable aqueous media are water and mixtures of water and at least one water-miscible solvent, for example an alcohol such as methanol, ethanol, n-propanol or isopropanol.

The polymers (ii) containing ethyleneimine units include all polymers obtainable by polymerizing ethyleneimine in the presence of acids, Lewis acids or haloalkanes, such as homopolymers of ethyleneimine or graft polymers of ethyleneimine, cf. U.S. 2,182,306 or U.S. 3,203,910 . These polymers can optionally be subsequently subjected to crosslinking. Suitable crosslinkers are, for example, all multifunctional compounds which contain groups reactive toward primary amino groups, for example multifunctional epoxides such as bisglycidyl ethers of oligo- or polyethylene oxides or other multifunctional alcohols such as glycerol or sugars, multifunctional carboxylic esters, multifunctional isocyanates, multifunctional acrylic or methacrylic esters - or methacrylic acid amides, epichlorohydrin, multifunctional acid halides, multifunctional nitriles, α, ω-chlorohydrin ethers of oligo- or polyethylene oxides or of other multifunctional alcohols such as glycerol or sugars, divinyl sulfone, maleic anhydride or ω-halo-acid chlorides, ω-halogenoalkanes, in particular, multifunctional haloalkanes, α-dichlorocarboxylic acid chlorides, multifunctional haloalkanes. Further crosslinkers are in WO 97/25367 A1 , Pages 8 to 16.

Polymers containing ethyleneimine units are, for example, from EP 0 411 400 A1 , DE 24 34 816 A1 and U.S. 4,066,494 known.

• Homopolymerisate des Ethylenimins,
• mit mindestens bifunktionellen Vernetzern umgesetzten Polyethylenimine,
• mit Ethylenimin gepfropften Polyamidoamine, die mit mindestens bifunktionellen Vernetzern umgesetzt sind,
• Umsetzungsprodukte von Polyethyleniminen mit einbasischen Carbonsäuren zu amidierten Polyethyleniminen,
• Michaeladditionsprodukte von Polyethyleniminenen an ethylenisch ungesättigte Säuren, Salze, Ester, Amide oder Nitrile von monoethylenisch ungesätitgten Carbonsäuren,
• phosphonomethylierten Polyethylenimine,
• carboxylierten Polyethylenimine und
• alkoxylierten Polyethylenimine.

The polymers containing (ii) ethyleneimine units are used, for example, in the process according to the invention at least one water-soluble cationic polymer from the group of

• Homopolymers of ethyleneimine,
• Polyethyleneimines reacted with at least bifunctional crosslinkers,
• polyamidoamines grafted with ethyleneimine which are reacted with at least bifunctional crosslinkers,
• Reaction products of polyethyleneimines with monocarboxylic acids to form amidated polyethyleneimines,
• Michael addition products of polyethyleneimines with ethylenically unsaturated acids, salts, esters, amides or nitriles of monoethylenically unsaturated carboxylic acids,
• phosphonomethylated polyethyleneimines,
• carboxylated polyethyleneimines and
• alkoxylated polyethyleneimines.

Polymers that are obtained by first condensing at least one polycarboxylic acid with at least one polyamine to polyamidoamines, then grafting them with ethyleneimine and then crosslinking the reaction products with one of the above-mentioned compounds belong to the preferred compounds containing ethyleneimine units. A method for producing such compounds is for example in DE 24 34 816 A1 described, where α, ω-chlorohydrin ethers of oligo- or polyethylene oxides as crosslinkers application Find.

Products of the two above types which have been subjected to ultrafiltration and have thus been optimized in terms of their molecular weight distribution are particularly preferred. Such ultrafiltered products are discussed in detail in WO 00/67884 A1 and WO 97/25367 A1 described. Reference is expressly made at this point to these publications and the disclosure contained therein.

Reaction products of polyethyleneimines with monocarboxylic acids to form amidated polyethyleneimines are from the WO 94/12560 A1 known. Michael addition products of polyethyleneimines with ethylenically unsaturated acids, salts, esters, amides or nitriles of monoethylenically unsaturated carboxylic acids are the subject of the WO 94/14873 A1 . Phosphonomethylated polyethyleneimines are extensively described in WO 97/25367 A1 described. Carboxylated polyethyleneimines can be obtained, for example, with the aid of a stretchers synthesis by reacting polyethyleneimines with formaldehyde and ammonia / hydrogen cyanide and hydrolyzing the reaction products. Alkoxylated polyethyleneimines can be prepared by reacting polyethyleneimines with alkylene oxides such as ethylene oxide and / or propylene oxide.

In the process according to the invention, the water-soluble cationic polymer (b) used can be the (i) polymers containing vinylamine units or (ii) polymers containing ethyleneimine units in each case alone. It is of course also possible to use any mixture of (i) polymer containing vinylamine units and (ii) polymer containing ethyleneimine units. In such a mixture the weight ratio of (i) polymers containing vinylamine units to (ii) polymers containing ethyleneimine units is, for example, 10: 1 to 1:10, preferably in the range from 5: 1 to 1: 5, and particularly preferably in the range from 2: 1 to 1: 2.

The at least one water-soluble cationic polymer (b) is particularly preferred in the process according to the invention for producing paper, for example in an amount of 0.01 to 2.0% by weight, preferably 0.03 to 1.0% by weight 0.1 to 0.5% by weight, based in each case on dry paper stock, are used.

The amphoteric polymers (c) are water-soluble. The solubility in water under normal conditions (20 ° C., 1013 mbar) and pH 7.0 is, for example, at least 5% by weight, preferably at least 10% by weight.

1. (A) Struktureinheiten, die eine permanent kationische oder eine in wässrigen Medium protonierbare Gruppe tragen,
2. (B) Struktureinheiten, die eine in wässrigem Medium deprotonierbare Gruppe tragen, und
3. (C) nichtionische Struktureinheiten,

wobei man als Monomere, deren Polymere Struktureinheiten (B) enthalten, Monomere der Formel (II) sowie deren Salze.

• wobei R¹ = H oder eine C₁-C₄-Alkylgruppe und
• n eine ganze Zahl im Bereich von 1 bis 8ist,
• verwendet.

The water-soluble amphoteric polymers (c) which can be used in the process according to the invention are made up of at least three structural units:

1. (A) structural units which carry a permanently cationic group or a group which can be protonated in an aqueous medium,
2. (B) structural units which carry a group which can be deprotonated in an aqueous medium, and
3. (C) nonionic structural units,

where the monomers whose polymers contain structural units (B) are monomers of the formula (II) and their salts.

• where R ¹ = H or a C ₁ -C ₄ alkyl group and
• n is an integer in the range from 1 to 8,
• used.

In addition, the water-soluble amphoteric polymers (c) can also contain crosslinkers and / or regulators. Such crosslinkers and regulators are also those which are already used in the water-soluble cationic polymers (b).

Examples of monomers whose polymers contain structural units (A) are esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with C ₂ -C ₃₀ -amino alcohols, amides of α, β-ethylenically unsaturated monocarboxylic acids and their N-alkyl and N, N-dialkyl derivatives, nitrogen-containing heterocycles with α, β-ethylenically unsaturated double bonds and mixtures thereof.

Suitable monomers of this group are the esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with amino alcohols, preferably C ₂ -C ₁₂ -amino alcohols. These can be C ₁ -C ₈ monoalkylated or dialkylated on the amine nitrogen. Acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, maleic anhydride, monobutyl maleate and mixtures thereof are suitable as acid components of these esters. Acrylic acid, methacrylic acid and mixtures thereof are preferably used. 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 of this group 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 are suitable.

N-vinylimidazoles and alkylvinylimidazoles are also suitable as monomers, in particular methylvinylimidazoles such as 1-vinyl-2-methylimidazole, 3-vinylimidazole-N-oxide, 2- and 4-vinylpyridine-N-oxides and betaine derivatives and quaternization products of these monomers and mixtures from that.

The particular quaternary compounds of the aforementioned monomers 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 alkyl epoxides.

worin

• wobei R¹ = H oder eine C₁-C₄-Alkylgruppe und
• n eine ganze Zahl im Bereich von 1 bis 8 ist,
• bedeuten,
• bevorzugt.

Monomers whose polymers contain structural units (B) are those of the formula (II) and their salts

wherein

• where R ¹ = H or a C ₁ -C ₄ alkyl group and
• n is an integer ranging from 1 to 8,
• mean,
• prefers.

The monomers of this group can be used alone or in a mixture with one another, in partially or completely neutralized form, in the copolymerization. Alkali metal or alkaline earth metal bases, ammonia, amines and / or alkanolamines, for example, are used for neutralization. Examples are caustic soda, potassium hydroxide, soda, potash, sodium hydrogen carbonate, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine, morpholine, diethylenetriamine or tetraethylene pentamine.

Monomers whose polymers contain structural units (C) are monomers of the formula (I), esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with C ₁ -C ₃₀ alkanols and C ₂ -C ₃₀ alkanediols, (meth) acrylamides, nitriles of α, β-ethylenically unsaturated mono- and dicarboxylic acids, esters of vinyl alcohol and allyl alcohol with C ₁ -C ₃₀ monocarboxylic acids, N-vinyl lactams and mixtures thereof.

Monomers of the formula (I) are, for example, N-vinylformamide, N-vinyl-N-methylformamide, N-vinyl acetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinyl propionamide and N-vinyl-N- methylpropionamide and N-vinylbutyramide. These monomers can be used alone or in a mixture in the copolymerization with the monomers of the other groups. Preferred monomer of this group is N-vinylformamide.

Suitable representatives of this monomer group are e.g. Methyl (meth) acrylate, methyl ethacrylate, ethyl (meth) acrylate, ethyl ethacrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, tert-butyl ethacrylate, n-octyl (meth) acrylate, 1,1,3,3-tetramethylbutyl (meth) acrylate, ethylhexyl (meth) acrylate, and mixtures thereof.

Also suitable as monomers of this group are 2-hydroxyethyl (meth) acrylate, 2-hydroxyethyl ethacrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate , 6-hydroxyhexyl (meth) acrylate and mixtures thereof.

Suitable additional monomers are also acrylic acid amide, methacrylic acid amide, 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, and mixtures thereof.

In addition, nitriles of α, β-ethylenically unsaturated mono- and dicarboxylic acids such as acrylonitrile and methacrylonitrile are suitable.

Suitable monomers of this group are also N-vinyllactams and their derivatives, which can have, for example, 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.

The proportion of monomers whose polymers contain the structural units (C) is usually at least 50% by weight in the water-soluble amphoteric polymer, based on the total weight of the monomers used to prepare the water-soluble polymer (c). The proportion of monomers whose polymers contain the structural units (C) is preferably at least 60% by weight, particularly preferably at least 75% by weight and particularly preferably at least 85% by weight, but not more than 98% by weight , in each case based on the total weight of the monomers which are used to produce the water-soluble polymer (c).

The molar ratio of the monomers whose polymers contain the structural units (A) to those whose polymers contain the structural units (B) is usually in the range from 5: 1 to 1: 5, preferably 2: 1 to 1: 2 and is particularly preferably 1: 1.

Such water-soluble amphoteric polymers (c) are known in the literature, as is their preparation. For example, the amphoteric polymers can be prepared by radical polymerization of the aforementioned monomers in solution, as gel polymerization, precipitation polymerization, water-in-water polymerization, water-in-oil polymerization or by spray polymerization.

The production is carried out in JP 54-030913 , the disclosure of which is expressly referred to at this point.

In the process according to the invention, the water-soluble amphoteric polymers (c) used are preferably those as in EP 0 659 780 A1 , EP 0 919 578 A1 , EP 1 849 803 A1 , JP 08-269891 , JP 2005-023434 and JP 2001-1279595 disclosed.

The at least one water-soluble amphoteric polymer (c) is particularly preferred in the process according to the invention for producing paper, for example in an amount of 0.01 to 2.0% by weight, preferably 0.03 to 1.0% by weight 0.1 to 0.5% by weight, based in each case on dry paper stock, are used.

The present invention also relates to the papers produced by the process described above, as well as cardboard and cardboard.

For papermaking, all the usual qualities can be considered as fibrous materials for producing the pulps, e.g. Wood pulp, bleached and unbleached cellulose and paper pulp from all annual plants. Wood pulp includes, for example, ground wood, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressure pulp, semi-pulp, high-yield pulp, and refiner mechanical pulp (RMP). For example, sulfate, sulfite and soda cellulose can be used as the pulp. For example, unbleached pulp, also known as unbleached kraft pulp, is used. Suitable annual plants for the production of paper stocks are, for example, rice, wheat, sugar cane and kenaf.

The process according to the invention is particularly suitable for the production of dry-resistant papers from waste paper (including deinked waste paper) which is used either alone or in a mixture with other fibrous materials. One can also start from fiber blends of a primary material and recycled coated broke, e.g. bleached pine sulphate mixed with recycled coated broke. The process according to the invention is of technical interest for the production of paper, paperboard and cardboard from waste paper and in special cases also from deinked waste paper, because it significantly increases the strength properties of the recycled fibers. It is of particular importance for improving the strength properties of graphic papers and packaging papers.

The pH of the pulp suspension is, for example, in the range from 4.5 to 8, mostly from 6 to 7.5. For example, an acid such as sulfuric acid or aluminum sulfate can be used to adjust the pH.

In the process according to the invention, the order in which components (a), (b) and (c) are added is arbitrary, and the components can be added to the fiber suspension individually or in any mixture. For example, in the process according to the invention, the cationic components, namely the (a) trivalent cations in the form of a salt and (b) water-soluble cationic polymers, are first metered into the paper stock. The cationic components (a) and (b) can be added separately or as a mixture to the thick stock (fiber concentration> 15 g / l, for example in the range from 25 to 40 g / l to 60 g / l) or preferably in the Thin material (fiber concentration <15 g / l, e.g. in the range from 5 to 12 g / l). The addition point is preferably in front of the sieves, but it can also be between a shear stage and a screen or after it. The addition of the cationic components (a) and (b) to the paper stock can, as described above, take place one after the other, simultaneously or also as a mixture of (a) and (b). If, in the case of water-soluble component (b), a mixture of (i) polymers containing vinylamine units and (ii) polymers containing ethyleneimine units is used, it is also possible to meter them in succession, simultaneously or as a mixture of (i) and (ii).

The water-soluble amphoteric polymer (c) is usually only added to the paper stock after the addition of the cationic components (a) and (b), but can also be added to the paper stock at the same time and also in a mixture with (a) and (b).

Furthermore, it is also possible to add the water-soluble amphoteric polymer (c) first and then the cationic components (a) and (b) or first to add one of the cationic components (a) or (b) to the paper stock, then the water-soluble amphoteric polymer (c) and then add the other cationic component (a) or (b).

In a preferred embodiment of the process according to the invention, the (a) trivalent cation is preferably added first in the form of a salt, then the (b) water-soluble cationic polymer and then the (c) water-soluble amphoteric polymer.

In another, likewise preferred variant of the process according to the invention, the (a) trivalent cation is added first in the form of a salt, then the (c) water-soluble amphoteric polymer and finally the (b) water-soluble cationic polymer.

In a third, likewise preferred embodiment, a mixture of (a) is added first trivalent cation in the form of a salt and the (c) water-soluble amphoteric polymer to the paper stock. Then the (b) water-soluble cationic polymer is metered in.

In the process according to the invention, the process chemicals usually used in papermaking can be used in the usual amounts, e.g. Retention aids, drainage aids, other dry strength agents such as starch, pigments, fillers, optical brighteners, defoamers, biocides and paper dyes.

The process according to the invention gives papers with a dry-strength finish whose dry strength has an increased dry strength compared with papers produced by known processes. In addition, the drainage rate is improved in the method according to the invention compared to known methods.

The invention is illustrated in more detail by means of the following non-limiting examples.

Unless stated otherwise, the percentages in the examples are percentages by weight. The The K value of the polymers was determined according to Fikentscher, CelluloseChemie, Volume 13, 58-64 and 71-74 (1932 ) at a temperature of 25 ° C in 5 wt .-% aqueous saline solutions at a pH of 7 and a polymer concentration of 0.5%. Here, K = k * 1000.

• Berstdruck nach DIN ISO 2758 (bis 600 kPa), DIN ISO 2759 (ab 600 kPa)
• SCT nach DIN 54518 (Bestimmung des Streifenstauchwiderstandes)
• CMT nach DIN EN 23035 (Bestimmung des Flachstauchwiderstandes)
• Naßreislänge nach TAPPI T 456
• Aschegehalt nach TAPPI T 413
• Entwässerungszeit nach ISO Standard 5267 (bestimmt mit einem Schopper-Riegler-Testgerät, in dem man jeweils 1l der zu prüfenden Faseraufschlämmung mit einer Stoffdichte von 10 g/l darin entwässerte ind die Zeit in Sekunden bestimmte, die für den Durchlauf von 600 ml Filtrat notwendig war)

For the individual tests, sheets were produced in a Rapid-Koethen laboratory sheet former in laboratory experiments. The leaves were stored for 24 hours at 23 ° C. and a humidity of 50%. The following strength tests were then carried out:

• Burst pressure according to DIN ISO 2758 (up to 600 kPa), DIN ISO 2759 (from 600 kPa)
• SCT according to DIN 54518 (determination of the strip crush resistance)
• CMT according to DIN EN 23035 (determination of the flat crush resistance)
• Wet rice length according to TAPPI T 456
• Ash content according to TAPPI T 413
• Drainage time according to ISO Standard 5267 (determined with a Schopper-Riegler test device, in which 1 l of the fiber slurry to be tested with a consistency of 10 g / l was dehydrated and the time in seconds was determined which was necessary for 600 ml of filtrate to pass through was)

Examples

The following components and polymers were used in the examples:

Cation 1

Alum (technical aluminum sulfate powder [Al ₂ (SO ₄ ) ₃ · 14H ₂ O])

Cation 2

Polyaluminum chloride with 18% Al ₂ O ₃ (Sedipur® PAC 18 from BASF SE)

Polymer K1

Cationic polyvinylformamide, 30 mol% partially hydrolyzed, molecular weight approx. 350,000 Dalton, solids content 16.4% by weight (Luredur® PR 8095 from BASF SE)

Polymer K2

Cationic polyethyleneimine, molecular weight approx. 1,000,000 Dalton (Polymin® SK from BASF SE)

Polymer K3 (for reference example *)

• [Table 2a] Marking added as a reference example (see replacement page 15)
• [Table 2b] Marking added as a reference example (see replacement page 15)

Cationic polyvinylamine, Hofmann degradation product, molecular weight approx. 25,000 Dalton, solids content 8% by weight (RSL HF 70D from SNF SAS)

Polymer A1

Amphoteric polyacrylamide, solids content 19.2% by weight (Harmide® RB 217 from Harima)

Polymer A2

Amphoteric polyacrylamide, solids content 20% by weight (Polystron® PS-GE 200 R from Arakawa)

Polymer A3

Amphoteric polyacrylamide, solids content 20% by weight (Polystron® PS-GE 300 S from Arakawa)

In the comparative examples, the following comparative polymers were optionally used:

Polymer V1

Cationic polyacrylamide, molecular weight approx. 1,000,000 Dalton, (Polymin® KE 440 from BASF SE)

Polymer V2

Anionic polyacrylamide, molecular weight approx. 600,000 Dalton, solids content 16% by weight (Luredur® PR 8284 from BASF SE)

Polymer V3

Polyallylamine, molecular weight about 15,000 Dalton, solids content 93% by weight (PAA-HCI-3S from Nittobo)

Preparation of the paper stock for the examples and comparative examples

A paper made from 100% recovered paper (mixture of the types: 1.02, 1.04, 4.01) was whipped free of specks with drinking water at a consistency of 4% in a laboratory pulper and ground to a freeness of 40 ° SR in a laboratory refiner. This substance was then diluted with drinking water to a consistency of 0.7%.

Drainage test

In the examples and comparative examples, 1 liter of the paper stock described above was used in each case and the trivalent cations and water-soluble polymers indicated in the table were added one after the other with stirring and then dewatered using a Schopper-Riegler dewatering tester, the time being in seconds for a flow rate (filtrate) of 600 ml. The concentration of the water-soluble cationic and amphoteric polymers each tested as dry strength agents for paper was 1% each, and that of the trivalent cation in aqueous solution was 10% each. The measurement results are summarized in Tables 1, 2a and 2b, the data for the bursting pressure, SCT and CMT each being shown as an increase in% relative to the zero value determination (comparison 0). The values for the length of the wet rice are given in m, as a differential measurement for the determination of the zero value (comparison 0).

Foliage

In the examples and comparative examples, the trivalent cations and polymers indicated in the tables were added successively to the paper stock described above with stirring. The polymer concentration of the aqueous solutions of the cationic and anionic polymers was 1% each, and that of the trivalent cation in aqueous solution was 10% each. In addition, 0.27% of a commercially available defoamer (Afranil® SLO from BASF SE) was used in all of the examples and comparative examples. The table shows the amounts of the trivalent cations and polymers used in each case in percent by weight, based on the solids content of the paper stock. After the last addition of a water-soluble polymer to the paper stock, enough stock was removed (approx. 500 ml) to produce a sheet with a weight per unit area of 120 g / m ² on a Rapid-Koethen sheet former. As is customary in the Rapid-Koethen process, the leaves were drained and dried for 8 minutes at 110 ° C. in a drying cylinder. The results are given in Tables 1, 2a and 2b, the data for the bursting pressure, SCT and CMT each being shown as an increase in% relative to the determination of the zero value (comparison 0). The values for the wet rice length are given in m, also as an increase over the determination of the zero value (comparison 0).

The experiments according to the invention in Examples 1 to 10 show in particular the surprisingly good effect of the system consisting of three components on dry strength and, at the same time, on drainage. Table 1 example Trivalent cation Dosage [%] Cationic polymer Dosage [%] Amphoteric polymer Dosage [%] Comparative polymer Dosage [%] Burst pressure increase [%] SCT increase [%] CMT increase [%] Wet rice length increase Comparison 0 - - - Polymer V1 0.04 - - - - Comparison 1 - Polymer K1 0.15 - Polymer V2 0.15 18th 16 18th 145 Comparison 2 Cation 1 0.7 Polymer K1 0.15 - Polymer V2 0.15 15th 13 16 155 Comparison 3 Cation 1 0.7 - Polymer A1 0.3 - 24 22nd 13 34 example 1 Cation 1 0.7 Polymer K1 0.15 Polymer A1 0.15 - 24 26th 23 92 Example 2 Cation 2 0.14 Polymer K1 0.15 Polymer A1 0.15 - 23 21st 23 98 Example 3 Cation 1 0.7 Polymer K1 0.15 Polymer A1 0.15 - 19th 18th 22nd 116 Example 4 Cation 1 0.7 Polymer K1 0.15 Polymer A1 0.15 - 22nd 24 20th 131 Example 5 Cation 1 0.7 Polymer K1 0.15 Polymer A1 0.15 - 20th 23 21st 125 Comparison 0: zero value determination Comparison 1: Comparison after DE 10 2004 056 551 A1 Comparison 2: analogous comparison DE 10 2004 056 551 A1 and additional pre-metering of a trivalent cation Comparison 3: Comparison after EP 1849 803 A1 Example 1: Dosing sequence: cation 1, polymer K1, polymer A1 Example 2: Dosing sequence: cation 2, polymer K1, polymer A1 Example 3: Dosing sequence: polymer K1, cation 1, polymer A1 Example 4: Dosing sequence: mixture of cation 1 and polymer K1, polymer A1 Example 5: Dosing sequence: cation 1, polymer A1, polymer K1 example Trivalent cation Dosage [%] Cationic polymer Dosage [%] Amphoteric polymer Dosage [%] Comparative polymer Dosage [%] Comparison 0 - - - Polymer V1 0.04 Comparison 4 - Polymer K1 0.15 - Polymer V2 0.15 Comparison 5 Cation 1 0.5 Polymer K1 0.15 - Polymer V2 0.15 Comparison 6 Cation 1 0.5 - Polymer A1 0.3 - Comparison 7 Cation 1 0.5 - Polymer A2 0.3 - Comparison 8 Cation 1 0.5 - Polymer A3 0.3 Comparison 9 Cation 1 0.5 - - Polymer V3 0.15 Polymer V2 0.15 Comparison 10 Cation 1 0.5 - Polymer A1 0.15 Polymer V3 0.15 Example 6 Cation 1 0.5 Polymer K1 0.15 Polymer A1 0.15 - Example 7 Cation 1 0.5 Polymer K1 0.15 Polymer A2 0.15 - Example 8 Cation 1 0.5 Polymer K1 0.15 Polymer A3 0.15 - Example 9 Cation 1 0.5 Polymer K2 0.15 Polymer A1 0.15 - Example 10 * Cation 1 0.5 Polymer K3 0.15 Polymer A1 0.15 - Comparison 1: Zero value determination Comparison 4: Comparison after DE 10 2004 056 551 A1 Comparison 5: analogous comparison DE 10 2004 056 551 A1 and additional pre-metering of a trivalent cation Comparison 6: Comparison after EP 1 849 803 A1 Comparison 7: Comparison after JP 54-030913 A1 Comparison 8: Comparison after JP 54-030913 A1 Comparison 9: Comparison after JP 02-112498 A1 Comparison 10: analogous comparison JP 02-112498 A1 Examples 6 to 10: Dosing sequence in each case: trivalent cation, cationic polymer, amphoteric polymer * = Reference example example Burst pressure increase [%] SCT increase [%] CMT increase [%] Wet rice length increase [m] Ash content [%] Drainage time [s] Comparison 0 - - - - 7.6 58 Comparison 4 19th 17th 10 136 7.8 51 Comparison 5 15th 8th 9 123 8.0 50 Comparison 6 24 22nd 13 34 6.8 78 Comparison 7 13 18th 14th 60 7.1 60 Comparison 8 17th 25th 17th 75 7.5 82 Comparison 9 7th 9 16 98 7.9 50 Comparison 10 8th 7th 9 126 8.2 38 Example 6 24 26th 23 110 8.0 30th Example 7 22nd 23 21st 140 7.8 33 Example 8 23 24 23 135 7.9 40 Example 9 19th 20th 19th 83 8.2 41 Example 10 * 21st 19th 20th 91 7.9 47 * = Reference example

Claims (12)

1. Method for the production of paper, board and cardboard with high dry strength by adding

   (a) at least one trivalent cation in the form of a salt,

   (b) at least one water-soluble cationic polymer; and

   (c) at least one water-soluble amphoteric polymer
   to the paper stock, dewatering the paper stock with sheet formation and subsequent drying of the paper products, wherein the water-soluble cationic polymer (b) is selected from the group of (i) polymers containing vinylamine units and (ii) polymers containing ethyleneimine units,
   wherein the polymers used as (i) polymers containing vinylamine units are reaction products obtainable by polymerizing

   (1.) at least one monomer of the formula

   

   in which R¹, R² = H or C₁ ^- to C₆ ^- alkyl,

   (2.1) at least one monomer each carrying an acid function selected from monoethylenically unsaturated sulfonic acids, monoethylenically unsaturated phosphonic acids and monoethylenically unsaturated carboxylic acids having 3 to 8 C atoms in the molecule and/or their alkaline metal, alkaline earth metal or ammonium salts,

   (2.2) optionally at least one other neutral and/or cationic monomer, and

   (3.) if necessary at least one crosslinking monomer with at least two double bonds in the molecule and subsequent partial or complete separation of the groups -CO-R¹ from the units of the monomers (I) polymerized into the polymer with the formation of amino groups, the content of amino groups in the copolymer at least 5 mol% above the content of polymerized acid groups of the monomers (2.1), and is used as (c) water-soluble amphoteric polymers, which are composed of at least three structural units:

   (A) structural units which carry a permanently cationic group or a group that can be protonated in aqueous medium,

   (B) structural units carrying a group that is deprotonatable in aqueous medium, and

   (C) non-ionic structural units,

   wherein the monomers whose polymers contain structural units (B) are monomers of formula (II) and salts thereof

   

   wherein

   R¹ = H or a C₁ ^-C₄ ^- alkyl group and

   n is an integer ranging from 1 to 8.
2. Method for the production of paper, board and cardboard with high dry strength by adding

   (a) at least one trivalent cation in the form of a salt,

   (b) at least one water-soluble cationic polymer; and

   (c) at least one water-soluble amphoteric polymer
   for paper stock, draining the paper stock with sheet formation and subsequent drying of the paper products, wherein the water-soluble cationic polymer (b) is selected from the group of (i) polymers containing vinylamine units and (ii) polymers containing ethyleneimine units,
   wobei man als (i) Vinylamineinheiten enthaltende Polymere die Reaktionsprodukte einsetzt, die erhältlich sind durch Polymerisieren von N-Vinylformamid und anschließende Abspaltung von Formylgruppen aus den in das Polymerisat einpolymerisierten Vinylformamideinheiten unter Bildung von Aminogruppen, und man als (c) wasserlösliche amphotere Polymere einsetzt, die aus mindestens drei Struktureinheiten aufgebaut sind:

   wherein (i) the polymers containing vinylamine units are the reaction products obtainable by polymerizing N-vinylformamide and subsequently removing formyl groups from the vinylformamide units polymerized into the polymer to form amino groups, and (c) water-soluble amphoteric polymers are used consisting of at least three structural units:

   (A) structural units which carry a permanently cationic group or a group that can be protonated in aqueous medium,

   (B) structural units carrying a group that is deprotonatable in aqueous medium, and

   (C) non-ionic structural units, and

   wherein the monomers whose polymers contain structural units (B) are monomers of formula (II) and salts thereof

   

   wherein

   R¹ = H or a C₁ ^-C₄ ^- alkyl group and

   n is an integer ranging from 1 to 8.
3. Method according to claim 1 or 2, wherein the (a) at least one trivalent cation is selected from Al³⁺, Zr^3* and Fe³⁺.
4. Method according to claim 3, wherein the (a) is at least one trivalent cation in the form of a salt of aluminum sulphate, polyaluminum chloride or aluminum lactate.
5. Method according to any of the above claims, wherein the (a) at least one trivalent cation in the form of a salt is added to the pulp in amounts between 3 and 100 moles per ton of dry paper.
6. Method according to one of the preceding claims, wherein (ii) polymers containing ethyleneimine units, at least one water-soluble cationic polymer from the group

   - Homopolymers of ethyleneimine,

   - polyethyleneimines reacted with at least bifunctional crosslinkers,

   - polyamidoamines grafted with ethyleneimine, which are reacted with at least bifunctional crosslinkers,

   - Reaction products of polyethyleneimines with monobasic carboxylic acids to amidated polyethyleneimines,

   - Michael addition products of polyethyleneimines to ethylenically unsaturated acids, salts, esters, amides or nitriles of monoethylenically unsaturated carboxylic acids,

   - phosphonomethylated polyethyleneimines,

   - carboxylated polyethyleneimines and

   - alkoxylated polyethyleneimines
   is used.
7. Method according to claim 6, characterized in that homopolymers of ethyleneimine and/or polyamidoamines grafted with ethyleneimine and subsequently reacted with at least bifunctional crosslinkers are used as (ii) polymers containing ethyleneimine units.
8. Method according to any one of claims 1 to 7, wherein the (b) at least one water-soluble cationic polymer is used in an amount of 0.01 to 2.0% by weight, based on the dry paper stock.
9. Method according to any of the above claims, wherein first the (a) trivalent cation is added to the paper pulp in the form of a salt, then the (b) water-soluble cationic polymer and then the (c) water-soluble amphoteric polymer.
10. Method according to one of claims 1 to 8, wherein first the (a) trivalent cation is added to the paper pulp in the form of a salt, then the (c) water-soluble amphoteric polymer and finally the (b) water-soluble cationic polymer.
11. Method according to any one of claims 1 to 8, wherein first the mixture of the (a) trivalent cation in the form of a salt and the (c) water-soluble amphoteric polymer is added to the paper pulp and then the (b) water-soluble cationic polymer.
12. Papers obtainable by a method according to claims 1 to 11.