EP2443284B1 - 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 consisting of (i) vinylamine units polymers and (ii) Ethylenimineinheiten and (c) at least one water-soluble amphoteric polymer to a pulp, dewatering the stock to form sheets, and drying the resulting paper product.

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

Out JP 54-030913 a method for the production of paper with high dry strength is known in which the paper stock is first added an aluminum sulfate solution. Thereafter, a water-soluble amphoteric polymer is added. Subsequently, the paper stock is dewatered on the paper machine to form sheets, and the paper products are dried. Suitable amphoteric polymers are, for example, copolymers of acrylamide, acrylic acid and dimethylaminoethyl (meth) acrylate.

From the DE 35 06 832 A1 discloses a process for the production of paper with high dry strength, in which one adds to the stock first a water-soluble cationic polymer and then a water-soluble anionic polymer. Suitable anionic polymers are, for example, homopolymers or copolymers of ethylenically unsaturated C ₃ -C ₅ -carboxylic acids. The copolymers contain at least 35 wt .-% of an ethylenically unsaturated C ₃ - C ₅ carboxylic acid (eg acrylic acid) in copolymerized form. The cationic polymers described in the examples are polyethyleneimine, polyvinylamine, polydiallyldimethylammonium chloride and epichlorohydrin-reacted condensation products of adipic acid and diethylenetriamine. 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 board, wherein dosing alum, a polyallylamine and an anionic or amphoteric polymer to a fiber suspension. The combination produces papers with a high strength.

In JP 05-272092 discloses a process for producing high dry strength paper by first adding an aluminum sulphate solution to the stock followed by a high molecular weight, water soluble, amphoteric polymer dosed, then drained the paper stock on the paper machine with sheet formation and the paper products dried. Examples of amphoteric polymers include copolymers of acrylamide, acrylic acid, dimethylaminoethyl (meth) acrylate, (meth) acrylamide and sodium (meth) allylsulfonate. These amphoteric polymers are characterized by very high molecular weights and low solution viscosities.

A variant of in JP 05-272092 described method is in JP 08-269891 disclosed. In this method of producing paper having a high dry strength, an aluminum sulfate solution is also added to the paper stock first, followed by metering in a high molecular weight water-soluble amphoteric polymer, followed by dewatering of the paper stock on the paper machine and drying of the paper products. Copolymers of acrylamide, acrylic acid, dimethylaminoethyl methacrylates, (meth) acrylamide, sodium (meth) allylsulfonate and a crosslinker such as methylenebisacrylamide or triallylamine are used as amphoteric polymers, for example. 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 preparing polymers having 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), wherein the ratio (b) / (a) ≤ 0 , 00004, and their use as solidifying agents.

WO 98/06898 A1 describes a process for papermaking in which a cationic starch or a cationic wet strength agent and a water-soluble amphoteric polymer is added to the stock. This amphoteric polymer is composed of the nonionic monomers acrylamide and methacrylamide, an anionic monomer, a cationic monomer and a crosslinker, the amount of anionic and cationic monomer not exceeding 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 board, wherein to improve the strength properties of a paper product to the pulp 0.05 to 0.5 wt .-%, based on dry pulp, of a polyvinylamine obtained by hydrolysis of polyvinylformamide having a degree of hydrolysis of 25 to 100 %, is added in combination with an anionic polyacrylamide, the stock is then dewatered to form sheets and the paper is dried.

The EP 0 919 578 A1 relates to amphoteric polymers (type B) prepared by a two-stage polymerization. First, in a first stage, a polymer (type A) is prepared by the copolymerization of methallylsulfonic acid with others Vinyl monomers, then in the presence of the type A polyamor there is a further polymerization of vinyl monomers to the B-type polymer wherein the type A polymers have a molecular weight of from 1,000 to 5,000,000 and the type B polymers have a molecular weight of from 100,000 to 10,000,000 exhibit. Furthermore, this document comprises the use of the polymers of type B as solidifying agents for papermaking and the papers produced therewith, whereby the possibility of a combination with alum and anionic polyacrylamides is also described. Finally, the possibility of modifying the type B polymers by Hofmann degradation is also mentioned.

From the JP 2001-279595 For example, a paper product having improved strength properties is known which is obtained by dosing 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 producing high-strength paper wherein a mixture of a cationic, anionic or amphoteric polyacrylamide with a water-soluble aluminum compound is added to the fibers. This is followed by a metered addition of another polyacrylamide. This not only increases the strength, but also improves drainage at the same time.

From the WO 03/052206 A1 discloses a paper product having improved strength properties obtainable by applying to the surface of a paper product a polyvinylamine and a polymeric anionic compound which can form a polyelectrolyte complex with polyvinylamine, or a polymeric compound having aldehyde functions such as aldehyde group-containing polysaccharides. Not only does the paper improve its dry and wet strength, it also observes a sizing effect of the treating agents.

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

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 Another method for improving the dry strength of paper is disclosed. In this process, a separate addition of a Vinylamineinheiten polymers and a polymeric anionic compound to a pulp, dewatering of the pulp and drying of the paper products, wherein the polymeric anionic compound is at least one copolymer obtained 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 acid group-containing monoethylenically unsaturated monomer and / or their alkali metal, alkaline earth metal or ammonium salts and optionally
3. (c) other monoethylenically unsaturated monomers, and optionally
4. (d) compounds having at least two ethylenically unsaturated double bonds in the molecule.

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

In WO 2006/120235 A1 discloses a process for producing papers having a filler content of at least 15% by weight, in which filler and fibers are treated together with cationic and anionic polymers. The treatment is carried out 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 producing paper and paperboard having high dry strength, wherein three components are added to the stock:

1. (a) a polymer having primary amino groups and a charge density of> 1.0 meq / g,
2. (b) a second, different cationic polymer having 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 Also, there is known a paper additive for strengthening which 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.

Although many methods are known in the literature for producing high dry strength papers, there is a continuing need in the paper industry for new, alternative methods to those already known.

It is an object of the present invention to provide another process for the production of high dry strength paper, paperboard and paperboard which further improves the dry strength properties of the paper products over those of known products and at the same time provides faster dewatering of the paper Papierstoffs is 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.The objects are achieved by a method for producing paper, cardboard 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

to the pulp, dewatering of the pulp with sheet formation and subsequent drying of the paper products, wherein the water-soluble cationic polymer (b) is selected from the group of (i) vinylamine units containing polymers and (ii) polymers containing ethyleneimine units.

The said components of the solidification system may be added to the stock in any order or else as a mixture of two or more components.

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

The metal and semimetal 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, polyaluminum chloride or aluminum lactate.

Of course, any mixtures of said trivalent metal cations can be used, but preferably only a trivalent metal cation is 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 in one of the described salt forms is used.

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

The water-soluble cationic polymer (b) is selected from the group of polymers containing (i) 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 of 4 to 10 meq / g.

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

• durch Polymerisieren mindestens eines Monomeren der Formel
  
  in der R¹, R² = H oder C₁- bis C₆-Alkyl bedeuten,
  und anschließende teilweise oder vollständige Abspaltung der Gruppen -CO-R¹ aus den in das Polymerisat einpolymerisierten Einheiten der Monomeren (I) unter Bildung von Aminogruppen
  und/oder
• durch Hofmann-Abbau von Polymeren, die Acrylamid- und/oder Methacrylamideinheiten aufweisen.

Vinylamine-containing polymers (i) are known, cf. the state of the art DE 35 06 832 A1 and DE 10 2004 056 551 A1 , In the process according to the invention, polymers which contain (i) vinylamine units are reaction products which are obtainable

• by polymerizing at least one monomer of the formula
  
  in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,
  and subsequent partial or complete cleavage of the groups -CO-R ¹ from the polymerized in the polymer units of the monomers (I) to form amino groups
  and or
• by Hofmann degradation of polymers having acrylamide and / or methacrylamide units.

1. (1.) mindestens eines Monomeren der Formel
   
   in der R¹, R² = H oder C₁- bis C₆-Alkyl bedeuten,
2. (2.) gegebenenfalls mindestens eines anderen monoethylenisch ungesättigten Monomeren und
3. (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.In one embodiment of the invention, polymers containing (i) vinylamine units are, for example, the reaction products obtainable by polymerizing

1. (1.) at least one monomer of the formula
   
   in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,
2. (2.) optionally at least one other monoethylenically unsaturated monomer and
3. (3.) optionally at least one crosslinking monomer having at least two double bonds in the molecule

and subsequent partial or complete cleavage of the groups -CO-R ¹ from the polymerized in the polymer units of the monomers (I) to form amino groups.

1. (1.) N-Vinylformamid und
2. (2.) Acrylnitril

und anschließende Abspaltung von Formylgruppen aus den in das Copolymerisat einpolymerisierten Vinylformamideinheiten unter Bildung von Aminogruppen erhältlich sind.Preferably, as polymers containing (i) vinylamine units, the reaction products obtainable by polymerizing N-vinylformamide and subsequent cleavage of formyl groups from the vinylformamide units polymerized into the polymer to form amino groups are used, or the reaction products obtained by copolymerizing

1. (1.) N-vinylformamide and
2. (2.) Acrylonitrile

and subsequent cleavage of formyl groups from the copolymerized in the copolymer vinylformamide units to form amino groups are available.

• (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 may also be amphoteric if they have a total 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, for example, 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 acid-functional monomer 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 alkali metal, alkaline earth metal or ammonium salts,
• (2.2) optionally at least one other neutral and / or cationic monomer and
• (3.) optionally at least one crosslinking monomer having at least two double bonds in the molecule

and subsequent partial or complete cleavage of the groups -CO-R ¹ from the polymerized in the polymer units of the monomers (I) to form amino groups, wherein the content of amino groups in the copolymer at least 5 mol% above the content of copolymerized 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 a total 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 cleavage of formyl groups from the copolymerized in the polymer N-vinylformamide to form amino groups are obtainable, wherein the content of amino groups in the copolymer is at least 5 mol% above the content of copolymerized acid groups of the monomers (2.1).

Examples of monomers of the formula (I) are N-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinylpropionamide and N-vinyl-N methylpropionamide and N-vinylbutyramide. The monomers of group (a) may be used alone or in admixture in the copolymerization with the monomers of the other groups. Preferably used monomer of this group is N-vinylformamide.

These polymers may 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 copolymerized vinylcarboxamide units is carried out so far that the molar excess of amine units compared to 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 -aminoalcohols, 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-vinyllactams, nitrogen-containing heterocycles having α, β-ethylenically unsaturated double bonds, vinylaromatics, 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 methacrylate, 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 the group (2) are furthermore the esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with aminoalcohols, preferably C ₂ -C ₁₂ -aminoalcohols. These may be C ₁ -C ₈ monoalkylated or dialkylated on the amine nitrogen. Suitable acid components of these esters are, for example, 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.

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

Further suitable monomers of group (2) are acrylamide, 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 and mixtures thereof.

In addition, as further monomers of the 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.

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 during or after the hydrolysis to products which have amidine units, cf. eg EP 0 528 409 A1 or DE 43 28 975 A1 , Namely, in the hydrolysis of N-vinylcarboxylic acid amide polymers, amidine units are formed in a secondary reaction by reacting vinylamine units with an adjacent vinylformamide unit or, if a nitrile group is present as an adjacent group in the polymer. In the following, the indication of vinylamine units in the amphoteric copolymers or in unmodified homo- or copolymers always means the sum of vinylamine and amidine units.

Suitable monomers of group (2) are furthermore N-vinyllactams and derivatives thereof which may 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.

Further suitable monomers of group (2) 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 also 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. Typically, they are used in amounts of 1 to 90 mol%, preferably 10 to 80 mol% and particularly preferably 10 to 60 mol%.

For the preparation of amphoteric Copoylmerisaten come as other monoethylenically unsaturated monomers of group (2.) and anionic monomers into consideration, which are referred to above as monomers (2.1). They may optionally 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 resulting amphoteric copolymer has a total cationic charge.

Examples of anionic monomers of group (2.1) are ethylenically unsaturated C ₃ -C ₈ -carboxylic acids such as, for example, 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. Also suitable as monomers of this group are monomers containing sulfonic groups, such as vinylsulfonic acid, acrylamido-2-methylpropanesulfonic acid and styrenesulfonic acid, and monomers containing phosphonic groups, such as vinylphosphonic acid. The monomers of this group can be used alone or in admixture with each other, in partially or completely neutralized form in the copolymerization. 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.

A further modification of the copolymers is possible by using in the copolymerization 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, sobait or glucose. These are so-called crosslinkers. If at least one monomer of the above group is used in the polymerization, the amounts used are up to 2 mol%, e.g. 0.001 to 1 mole%.

Furthermore, to modify the polymers, it may be useful to combine the use of the above crosslinked with the addition of regulators. Typically, from 0.001 to 5 mole percent is used. All regulators known from the literature can be used, for example sulfur compounds such as mercaptoethanol, 2-ethylhexyl thioglycolate, thioglycolic acid and dodecylmercaptan 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 are obtainable by free-radically polymerizing, for example, N-vinylformamide in aqueous medium in the presence of at least one of the stated grafting bases together with copolymerizable other 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 vinylcarboxylic acid amide copolymers is described in U.S. Pat EP 0 438 744 A1 , Page 8, line 20 to page 10, line 3, described in detail. The explanations made there apply correspondingly to the preparation of the cationic and / or amphoteric polymers containing vinylamine units to be used according to the invention and having a total cationic charge.

The homo- and copolymers (i) containing the vinylamine units described above can be prepared 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 or isopropanol.

As described above, (i) vinylamine units also include the reaction products obtained by Hofmann degradation of homo- or copolymers of acrylamide or methacrylamide in an aqueous medium in the presence of sodium hydroxide and sodium hypochlorite and subsequent decarboxylation of the carbamate groups of the reaction products in the presence of a Acid are available. Such polymers are for example made EP 0 377 313 and WO 2006/075115 A1 known. The preparation of polymers containing vinylamine groups is described, for example, in WO 2006/075115 A1 , Page 4, line 25 to page 10, line 22 and in the examples on pages 13 and 14 are treated in detail. The information given there applies to the characterization of the polymers containing vinylamine units prepared by Hofmann degradation.

It is based on polymers containing acrylamide and / or methacrylamide units. These are homopolymers or copolymers of acrylamide and methacrylamide. Suitable comonomers are, for example, dialkylaminoalkyl (meth) acrylamides, diallylamine, methyldiallylamine and also the salts of the amines and the quaternized amines. Also suitable as comonomers Dimethyldiallylammonium salts, acrylamidopropyltrimethylammonium chloride and / or Methacrylamidopropyltrimethylammoniumchlorid, N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, vinyl acetate and acrylic and methacrylic acid esters. Also suitable as comonomers are anionic monomers such as acrylic acid, methacrylic acid, maleic anhydride, maleic acid, itaconic acid, acrylamidomethylpropanesulfonic acid, methallylsulfonic acid and vinylsulfonic acid and also the alkali metal, alkaline earth metal and ammonium salts of said acidic monomers, not more than 5 mol% of these monomers being included the polymerization can be used. The amount of water-insoluble monomers is chosen in the polymerization so that the resulting polymers are soluble in water.

If appropriate, comonomers may also be used crosslinkers, e.g. ethylenically unsaturated monomers containing at least two double bonds in the molecule, such as triallylamine, methylenebisacrylamide, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate and trimethylol trimethacrylate. If a crosslinker is used, the amounts used are, for example, 5 to 5000 ppm. The polymerization of the monomers can be carried out by any known method, e.g. by free-radical initiated solution, precipitation or suspension polymerization. If appropriate, it is possible to work in the presence of customary polymerization regulators.

When Hofmann degradation is for example from 20 to 40 wt .-% aqueous solutions of at least one acrylamide and / or methacrylamide units containing polymers. The ratio of alkali metal hypochlorite to (meth) acrylamide units in the polymer is decisive for the resulting content of amine groups in the polymer. The molar ratio of alkali metal hydroxide to alkali metal hypochlorite is for example 2 to 6, preferably 2 to 5. For a certain amine group content in the degraded polymer is calculated for the degradation of the polymer required amount of alkali metal hydroxide.

The Hofmann degradation of the polymer is carried out, for example, in the temperature range from 0 to 45 ° C, preferably 10 to 20 ° C in the presence of quaternary ammonium salts as a stabilizer to prevent a side reaction of the resulting amino groups with the amide groups of the starting polymer. After completion of the reaction with alkali metal hydroxide / alkali metal hypochlorite, the aqueous reaction solution is passed into a reactor in which an acid is introduced for the decarboxylation of the reaction product. The pH of the reaction product containing vinylamine units is set to a value of 2 to 7. The concentration of the decomposition products containing vinylamine units is, for example, more than 3.5% by weight, in most cases above 4.5% by weight. The aqueous polymer solutions can be concentrated for example by means of ultrafiltration.

The polymers (ii) containing ethyleneimine units include all polymers obtainable by polymerization of ethyleneimine in the presence of acids, Lewis acids or haloalkanes, such as homopolymers of ethyleneimine or graft polymers of ethyleneimine, cf. US 2,182,306 or US 3,203,910 , If desired, these polymers can subsequently be subjected to crosslinking. Suitable crosslinkers are, for example, all multifunctional compounds which contain reactive groups relative to primary amino groups, for example multifunctional epoxides such as bisglycidyl ethers of oligo- or polyethyleneoxides or other multifunctional alcohols such as glycerol or sugars, multifunctional carboxylic esters, mulifunctional isocyanates, polyfunctional acrylic or methacrylic acid esters, multifunctional acrylic acid - or methacrylic acid amides, epichlorohydrin, multifunctional acid halides, multifunctional nitriles, α, ω-chlorohydrin ethers of oligo- or polyethylene oxides or other multifunctional alcohols such as glycerol or sugars, divinylsulfone, maleic anhydride or ω-Halogencarbonsäurechloride, multifunctional haloalkanes in particular α, ω-dichloroalkanes. Other crosslinkers are in WO 97/25367 A1 , Pages 8 to 16 described.

For example, polymers containing ethyleneimine units are made EP 0 411 400 A1 . DE 24 34 816 A1 and US 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.

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

• Homopolymers of ethyleneimine,
• polyethyleneimines reacted with at least bifunctional crosslinkers,
• ethyleneimine grafted polyamidoamines reacted with at least bifunctional crosslinkers,
• Reaction products of polyethylenimines with monobasic carboxylic acids to amidated polyethylenimines,
• 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.

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

Particularly preferred are products of the two above types which have been subjected to ultrafiltration and thus optimized in their molecular weight distribution. Such ultrafiltered products are detailed in WO 00/67884 A1 and WO 97/25367 A1 described. These publications and the disclosure contained therein are expressly incorporated herein by reference.

Reaction products of polyethylenimines with monobasic carboxylic acids to amidated polyethylenimines are known from the WO 94/12560 A1 known. Michael addition products of polyethyleneimines to ethylenically unsaturated acids, salts, esters, amides or nitriles of monoethylenically unsaturated carboxylic acids are the subject of WO 94/14873 A1 , Phosphonomethylated polyethylenimines are described in detail in U.S. Pat WO 97/25367 A1 described. Carboxylated polyethyleneimines are obtainable, for example, by means of a stretching synthesis by reacting polyethyleneimines with formaldehyde and ammonia / hydrogen cyanide and hydrolysing the reaction products. Alkoxylated polyethyleneimines can be prepared by reacting Polyethyleiminen 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 may be, in each case, the polymers containing (i) vinylamine units or polymers containing (ii) ethyleneimine units. Of course, it is also possible to use any desired mixture of (i) vinylamine units-containing polymer 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 of 5: 1 to 1: 5, and more preferably in the range of 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 wt .-%, each based on dry pulp, 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.

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

1. (A) structural units which carry a permanently cationic or a protonatable group in aqueous medium,
2. (B) structural units bearing a group deprotonatable in an aqueous medium, and
3. (C) nonionic structural units.

In addition, the water-soluble amphoteric polymers (c) may also contain crosslinkers and / or regulators. Such crosslinkers and regulators are also those 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 -aminoalcohols, amides of α, β-ethylenically unsaturated monocarboxylic acids and their N-alkyl and N, N-dialkyl derivatives, nitrogen-containing heterocycles having 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 aminoalcohols, preferably C ₂ -C ₁₂ -aminoalcohols. These may be C ₁ -C ₈ monoalkylated or dialkylated on the amine nitrogen. Suitable acid components of these esters are, for example, 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 of this group 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.

Further suitable monomers 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 also betaine derivatives and quaternization products of these monomers and mixtures from that.

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, e.g. with methyl chloride, benzyl chloride, ethyl chloride, butyl bromide, dimethyl sulfate and diethyl sulfate or Alkylepoxiden.

Examples of monomers whose polymers contain structural units (B) are those which carry an acid function. These are 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 alkali metal, alkaline earth metal or ammonium salts.

Examples of such monomers of this group 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. Also suitable as monomers of this group are monomers containing sulfonic groups, such as vinylsulfonic acid, acrylamido-2-methylpropanesulfonic acid and styrenesulfonic acid, and monomers containing phosphonic groups, such as vinylphosphonic acid.

worin

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

Sulfonic group-containing monomers are, in particular, those of the formula (II) and salts thereof

wherein

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

The monomers of this group can be used alone or in admixture with each other, in partially or completely neutralized form in the copolymerization. For neutralization, for example, alkali metal or alkaline earth metal bases, ammonia, amines and / or alkanolamines are used. Examples of this are caustic soda, Potassium hydroxide, soda, potash, sodium bicarbonate, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine, morpholine, diethylenetriamine or tetraethylenepentamine.

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-vinyllactams and mixtures thereof.

Monomers of the formula (I) are, for example, N-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinylpropionamide and N-vinyl-N- methylpropionamide and N-vinylbutyramide. These monomers may be used alone or in admixture in the copolymerization with the monomers of the other groups. Preferably used monomer of this group is N-vinylformamide.

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

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

Further suitable monomers are acrylamide, 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, 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 furthermore N-vinyllactams and derivatives thereof which may 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.

Usually, the proportion of monomers whose polymers contain the structural units (C) in the water-soluble amphoteric polymer is at least 50% by weight, 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 especially 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 for the preparation of the water-soluble Polymweren (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 of 5: 1 to 1: 5, preferably 2: 1 to 1: 2 and more preferably 1: 1.

Such water-soluble amphoteric polymers (c) are known in the literature, as well as 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 manufacture is among others in JP 54-030913 whose disclosure is expressly incorporated herein by reference.

In the method according to the invention are preferably used as water-soluble amphoteric polymers (c) such 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 from 0.01 to 2.0% by weight, preferably from 0.03 to 1.0% by weight 0.1 to 0.5 wt .-%, each based on dry pulp, used.

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

For papermaking, suitable fibrous materials for the production of the pulps are all qualities customary for this purpose, eg wood pulp, bleached and unbleached pulp and pulps from all annual plants. Wood pulp includes, for example, groundwood, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressure groundwood, semi-pulp, high yield pulp, and refiner mechanical pulp (RMP). As pulp, for example, sulphate, sulphite and soda pulps. For example, unbleached pulp, also referred to as unbleached kraft pulp, is used. Suitable annual plants for the production of pulps are, for example, rice, wheat, sugar cane and kenaf.

The inventive method is particularly suitable for the production of dry-proof papers from waste paper (including deinked waste paper), which is used either alone or in admixture with other fibers. It is also possible to start with fiber blends of primary and recycled coated broke, e.g. bleached pine sulfate in admixture with reclaimed coated broke. The inventive method is for the production of paper, cardboard and cardboard from waste paper and in special cases from deinked waste paper of technical interest, 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 stock suspension is, for example, in the range of 4.5 to 8, usually 6 to 7.5. To adjust the pH, it is possible to use, for example, an acid, such as sulfuric acid or aluminum sulphate.

In the method according to the invention, the order of addition of the components (a), (b) and (c) is arbitrary, wherein the components can be added to the fiber suspension individually or in each mixture. For example, in the process according to the invention, first the cationic components, namely the (a) trivalent cations in the form of a salt and (b) water-soluble cationic polymers, are metered into the pulp. The addition of the cationic components (a) and (b) may be carried out separately or in admixture with the thick material (fiber concentration> 15 g / l, for example in the range of 25 to 40 g / l up to 60 g / l) or preferably in the Thin material (fiber concentration <15 g / l, for example in the range of 5 to 12 g / l) take place. The point of addition is preferably in front of the screens, but it can also be between a shearing stage and a screen or afterwards. The metering of the cationic components (a) and (b) to the paper stock can be carried out successively, simultaneously or as a mixture of (a) and (b) as described above. If, in the case of the water-soluble component (b), a mixture of (i) polymers containing vinylamine units and (ii) polymers containing ethyleneimine units is used, it is likewise possible to meter these in succession, simultaneously or as a mixture of (i) and (ii).

The water-soluble amphoteric polymer (c) is usually added only after the addition of the cationic components (a) and (b) to the pulp, but can also be added to the pulp simultaneously and also in admixture with (a) and (b).

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

In a preferred embodiment of the process according to the invention, it is preferable first to add the (a) trivalent cation 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 addition of the (a) trivalent cation in the form of a salt, followed by the (c) water-soluble amphoteric polymer and finally the (b) water-soluble cationic polymer.

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

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

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

The invention will be further illustrated by the following non-limiting examples.

The percentages in the examples are by weight unless otherwise specified. Of the K value of the polymers was determined according to Fikentscher, Cellulose Chemie, 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%. Where 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 laboratory tests in a Rapid-Köthen laboratory sheet former. The leaves were stored for 24 hours at 23 ° C and a humidity of 50%. Thereafter, the following strength tests were carried out:

• Bursting 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
• Dewatering time according to ISO standard 5267 (determined with a Schopper-Riegler test apparatus, in which in each case 1 l of the fiber slurry to be tested with a consistency of 10 g / l dewatered in it determined the time in seconds necessary for the passage of 600 ml of filtrate was)

Examples

In the examples, the following components or polymers were used:

Cation 1

Alum (aluminum sulfate technical 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, partially hydrolyzed to 30 mol%, molecular weight about 350,000 daltons, solids content 16.4 wt.% (Luredur® PR 8095 from BASF SE)

Polymer K2

Cationic polyethyleneimine, molecular weight about 1,000,000 daltons (Polymin® SK from BASF SE)

Polymer K3

Cationic polyvinylamine, Hofmann degradation product, molecular weight about 25,000 daltons, 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)

If appropriate, the following comparative polymers were additionally used in the comparative examples:

Polymer V1

Cationic polyacrylamide, molecular weight about 1 000 000 daltons, (Polymin® KE 440 from BASF SE)

Polymer V2

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

Polymer V3

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

Preparation of the paper stock for the examples and comparative examples

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

drainage test

In the examples and comparative examples, in each case 1 liter of the paper stock described above was used and in each case successively added with the trivalent cations and water-soluble polymers indicated in the table with stirring and then dewatered using a Schopper-Riegler dewatering tester, wherein the time in seconds for a flow rate (filtrate) of 600 ml. The concentration of the water-soluble cationic and amphoteric polymers each tested as a dry strength agent 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, where the data for the bursting pressure, SCT and CMT respectively as an increase in% relative to the zero value determination (Comparison 0) are shown. The values for the wet rice length are given in m, namely as difference measurement for zero value determination (comparison 0).

sheet formation

In the Examples and Comparative Examples, the trivalent cations and polymers shown in the Tables were added successively to the 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 examples and comparative examples. In the table, the amounts of the trivalent cations and polymers used in each case are given in percent by weight, based on the solids content of the paper stock. After the last addition of a water-soluble polymer to the stock, as much stock was removed (approximately 500 mL) to produce a sheet having a basis weight of 120 g / m ² on a Rapid-Kothen sheet former. The leaves were, as usual in Rapid-Köthen method, abgegautscht and dried for 8 minutes at 110 ° C in a drying cylinder. The results are given in Tables 1, 2a and 2b, where the data for the bursting pressure, SCT and CMT are each shown as an increase in% relative to the zero value determination (comparison 0). The values for the wet rice length are given in m, and also as an increase to the zero value determination (comparison 0).

Examples 1 to 10 according to the invention show in particular the surprisingly good effect of the system consisting of three components on the dry strength and at the same time on the dewatering. 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 18 16 18 145 Comparison 2 Cation 1 0.7 Polymer K1 0.15 - Polymer V2 0.15 15 13 16 155 Comparison 3 Cation 1 0.7 - Polymer A1 0.3 - 24 22 13 34 example 1 Cation 1 0.7 Polymer K1 0.15 Polymer A1 0.15 - 24 26 23 92 Example 2 Cation 2 0.14 Polymer K1 0.15 Polymer A1 0.15 - 23 21 23 98 Example 3 Cation 1 0.7 Polymer K1 0.15 Polymer A1 0.15 - 19 18 22 116 Example 4 Cation 1 0.7 Polymer K1 0.15 Polymer A1 0.15 - 22 24 20 131 Example 5 Cation 1 0.7 Polymer K1 0.15 Polymer A1 0.15 - 20 23 21 125 Comparison 0: zero value determination
Comparison 1: Comparison after DE 10 2004 056 551 A1
Comparison 2: Comparison analog DE 10 2004 056 551 A1 and additionally predosing a trivalent cation
Comparison 3: Comparison after EP 1849 803 A1
Example 1: Dosing order: cation 1, polymer K1, polymer A1
Example 2: Dosing order: cation 2, polymer K1, polymer A1
Example 3: Dosing order: polymer K1, cation 1, polymer A1
Example 4: Dosing order: Mixture of cation 1 and polymer K1, polymer A1
Example 5: Dosing order: 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: Comparison analog DE 10 2004 056 551 A1 and additionally predosing 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: Comparison analog JP 02-112498 A1
Examples 6 to 10: Dosing order in each case: trivalent cation, cationic polymer, amphoteric polymer 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 19 17 10 136 7.8 51 Comparison 5 15 8th 9 123 8.0 50 Comparison 6 24 22 13 34 6.8 78 Comparison 7 13 18 14 60 7.1 60 Comparison 8 17 25 17 75 7.5 82 Comparison 9 7 9 16 98 7.9 50 Comparison 10 8th 7 9 126 8.2 38 Example 6 24 26 23 110 8.0 30 Example 7 22 23 21 140 7.8 33 Example 8 23 24 23 135 7.9 40 Example 9 19 20 19 83 8.2 41 Example 10 21 19 20 91 7.9 47

Claims (22)

1. A process for the production of paper, board and cardboard having high dry strength by addition of

   (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, draining of 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 consisting of the (i) polymers comprising vinylamine units and (ii) polymers comprising ethylenimine units.
2. The process according to claim 1, wherein the (a) at least one trivalent cation is selected from Al³⁺, Zr³⁺ and Fe³⁺.
3. The process according to claim 2, wherein the (a) at least one trivalent cation is in the form of an aluminum sulfate, polyaluminum chloride or aluminum lactate salt.
4. The process according to any of the preceding claims, wherein the (a) at least one trivalent cation in the form of a salt is added to the paper stock in amounts of from 3 to 100 mol per t of dry paper.
5. The process according to any of the preceding claims, wherein reaction products which are obtainable

   - by polymerization of at least one monomer of the formula

   

   in which R¹, R² are H or C₁- to C₆-alkyl,
   and subsequent partial or complete elimination of the groups -CO-R¹ from the units of the monomers (I) incorporated in the form of polymerized units into the polymer with formation of amino groups
   and/or

   - by Hofmann degradation of polymers which have acrylamide and/or methacrylamide units are used as (i) polymers comprising vinylamine units.
6. The process according to claim 5, wherein reaction products which are obtainable by polymerization of

   (1.) at least one monomer of the formula

   

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

   (2.) optionally at least one other monoethylenically unsaturated monomer and

   (3.) optionally at least one crosslinking monomer having at least two double bonds in a molecule

   and subsequent partial or complete elimination of the groups -CO-R¹ from the units of the monomers (I) incorporated in the form of polymerized units into the polymer with formation of amino groups are used as (i) polymers comprising vinylamine units.
7. The process according to claim 6, wherein the reaction products which are obtainable by polymerization of N-vinylformamide and subsequent elimination of formyl groups from the vinylformamide units incorporated in the form of polymerized units into the polymer with formation of amino groups are used as (i) polymers comprising vinylamine units.
8. The process according to claim 6, wherein the reaction products which are obtainable by copolymerization of

   (1.) N-vinylformamide and

   (2.) acrylonitrile

   and subsequent elimination of formyl groups from the vinylformamide units incorporated in the form of polymerized units into the copolymer with the formation of amino groups are used as (i) polymers comprising vinylamine units.
9. The process according to claim 5, wherein reaction products which are obtainable by polymerization of

   (1.) at least one monomer of the formula

   

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

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

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

   (3.) optionally at least one crosslinking monomer having at least two double bonds in a molecule

   and subsequent partial or complete elimination of the groups -CO-R¹ from the units of the monomers (I) incorporated in the form of polymerized units into the polymer with the formation of amino groups, the content of amino groups in the copolymer being at least 5 mol% above the content of acid groups of the monomers (2.1) incorporated in the form of polymerized units, are used as (i) polymers comprising vinylamine units.
10. The process according to claim 9, wherein reaction products which are obtainable by polymerization of

    (1.) N-vinylformamide,

    (2.1) acrylic acid, methacrylic acid and/or the alkali metal, alkaline earth metal or ammonium salts thereof and

    (2.2) optionally acrylonitrile and/or methacrylonitrile

    and subsequent partial or complete elimination of formyl groups from the N-vinylformamide incorporated in the form of polymerized units into the polymer with the formation of amino groups, the content of amino groups in the copolymer being at least 5 mol% above the content of acid groups of the monomers (2.1) incorporated in the form of polymerized units, are used as (i) polymers comprising vinylamine units.
11. The process according to claim 5, wherein the reaction products which are obtainable by Hofmann degradation of homo- or copolymers of acrylamide or of methacrylamide in an aqueous medium in the presence of sodium hydroxide solution and sodium hypochlorite and subsequent decarboxylation of the carbamate groups of the reaction products in the presence of an acid are used as (i) polymers comprising vinylamine units.
12. The process according to any of the preceding claims, wherein at least one water-soluble cationic polymer from the group consisting of the

    - homopolymers of ethylenimine,

    - polyethylenimines reacted with at least bifunctional crosslinking agents,

    - polyamidoamines which have been grafted with ethylenimine and reacted with at least bifunctional crosslinking agents,

    - reaction products of polyethylenimines with monobasic carboxylic acids to give amidated polyethylenimines,

    - Michael adducts of polyethylenimines with ethylenically unsaturated acids, salts, esters, amides or nitriles of monoethylenically unsaturated carboxylic acids,

    - phosphonomethylated polyethylenimines,

    - carboxylated polyethylenimines and

    - alkoxylated polyethylenimines

    is used as (ii) polymers comprising ethylenimine units.
13. The process according to claim 12, wherein homopolymers of ethylenimine and/or polyamidoamines grafted with ethylenimine and subsequently reacted with at least bifunctional crosslinking agents are used as (ii) polymers comprising ethylenimine units.
14. The process according to any of claims 5 to 13, wherein the (b) at least one water-soluble cationic polymer is used in an amount of from 0.01 to 2.0% by weight, based on the dry paper stock.
15. The process according to any of the preceding claims, wherein water-soluble amphoteric polymers which are composed of at least three structural units:

    (A) structural units which carry a permanently cationic group or group protonatable in an aqueous medium,

    (B) structural units which carry a group deprotonatable in an aqueous medium, and

    (C) nonionic structural units.

    are used as (c).
16. The process according to claim 15, wherein the proportion of monomers whose polymers comprise the structural units (C), in the water-soluble amphoteric polymer, is at least 50% by weight, based on the total weight of the monomers which are used for the preparation of the water-soluble amphoteric polymer (c).
17. The process according to claim 15, wherein monomers of the formula (II) and salts thereof

    

    in which

    R¹ is H or a C₁-C₄-alkyl group and

    n is an integer in the range from 1 to 8,

    are used as monomers whose polymers comprise structural units (B).
18. The process according to claim 15 or 16, wherein the (c) at least one water-soluble amphoteric polymer is used in an amount of from 0.01 to 2.0% by weight, based on the dry paper stock.
19. The process according to any of the preceding claims, wherein first the (a) trivalent cation in the form of a salt is added to the paper stock, thereafter the (b) water-soluble cationic polymer and then the (c) water-soluble amphoteric polymer.
20. The process according to any of claims 1 to 18, wherein first the (a) trivalent cation in the form of a salt is added to the paper stock, thereafter the (c) water-soluble amphoteric polymer and then the (b) water-soluble cationic polymer.
21. The process according to any of claims 1 to 18, wherein first the mixture of the (a) trivalent cation in the form of a salt and of the (c) water-soluble amphoteric polymer is added to the paper stock and then the (b) water-soluble cationic polymer.
22. A paper which is obtainable by a process according to any of claims 1 to 21.