EP1792010B1 - Method for the production of paper, paperboard and cardboard - Google Patents

Description

The invention relates to a process for the production of paper, paperboard and cardboard by dewatering a paper stock on a wire in the presence of at least one polymer as a retention agent with sheet formation and drying of the sheets.

From the US-A 4,421,602 is the use of partially hydrolyzed homopolymers of N-vinylformamide as retention, drainage and flocculant in the production of paper known.

It is also known to use in the production of paper from contaminants containing pulps fixer, cf. Tappi Journal, August 1988, pages 131-134 , Known fixing agents are, for example, condensates of dicyandiamide and formaldehyde or condensates of dimethylamine and epichlorohydrin. From the EP-A 438 707 It is also known to use hydrolyzed homopolymers and / or copolymers of N-vinylformamide having a degree of hydrolysis of at least 60% as a fixing agent in the production of paper. They can also be used in combination with a cationic retention agent. The K value of the hydrolyzed polymers of N-vinylformamide is at most 150 (measured in 5% aqueous sodium chloride solution at a polymer concentration of 0.5 wt .-% and a temperature of 25 ° C) corresponding to a molecular weight M _w of about 900 000th

Further known retention aids are, for example, polyamidoamines which are obtainable by condensation of adipic acid and diethylenetriamine, grafting of the condensation products with ethyleneimine and crosslinking of the reaction products thus obtainable with bischlorohydrin ethers of polyethylene glycols, high molecular weight polyethyleneimines, high molecular weight polyacrylamides and copolymers of acrylamide and dimethylaminoethyl acrylate methochloride having a molecular weight M. _w of at least 3 million, cf. Examples of EP-A 438 707 ,

According to the teaching of EP-A 649 941 the deposition of impurities in the paper machine, for example, on metallic surfaces, screening and felts is reduced by adding to the pulp, a water-soluble copolymer containing at least 5 mol% of an N-vinylcarboxamide or a hydrolyzate thereof. The degree of hydrolysis of the N-vinylcarboxamides is 5 to 20 mol% as reported in the examples.

In addition, various combinations of polymers and a finely divided, inorganic solid, such as bentonite, which acts as a flocculant, are used as retention aids. colloidal silica or silica. For example, in Wochenblatt für Papierfabrikation, Volume 13, 493-592 (1979 ) describes the use of cationic polyelectrolytes in combination with bentonite. In this process, first of all bentonite is metered into the paper stock and then the cationic polyelectrolyte, wherein the paper stock may optionally be subjected to a shear rate.

From the EP-B 235 893 It is known to first add to a stock a synthetic cationic polymer having a molecular weight of more than 500,000 in an amount of more than 0.03 wt .-%, based on dry pulp, to form flakes, which then in a subsequent shearing step Microflakes are parted. Bentonite is then added and the resulting paper stock is dewatered with foliar formation.

After the out of the EP-A 335 575 In known processes for the production of paper, the pulp is successively mixed with two different water-soluble, cationic polymers, namely a fixing agent and a retention agent, then subjected to at least one shear stage and then treated with bentonite. Only then is the drainage of the pulp under sheet formation.

From the EP-A 711 371 Another method for producing paper is known. In this process, a synthetic, cationic, high molecular weight polymer is added to a thick stock cellulose suspension. After dilution of the flocculated thick stock, a coagulant consisting of an inorganic coagulant and / or a second, low molecular weight and highly cationic water soluble polymer is added prior to dewatering.

In the EP-A 910 701 describes a process for the production of paper and board, wherein the paper pulp successively added a low molecular weight or medium molecular weight cationic polymer based on polyethyleneimine or polyvinylamine and then with a high molecular weight cationic polymer such as polyacrylamide, polyvinylamine or cationic starch. After this pulp has been subjected to at least one shear stage, it is flocculated by addition of bentonite and the pulp is dewatered.

From the EP-A 608 986 It is known that one doses a cationic retention agent to the thick stock in papermaking. Another method for the production of paper and cardboard is from the US-A 5,393,381 , of the WO 99/66130 and the WO 99/63159 known, which is also a microparticle system of a cationic polymer and bentonite used. The cationic polymer used is a water-soluble, branched polyacrylamide.

In the WO 01/34910 there is described a process for producing paper in which a polysaccharide or a synthetic, high molecular weight polymer is metered into the pulp suspension. Subsequently, a mechanical shear of the pulp must take place. The reflocculation is carried out by dosing an inorganic component such as silica, bentonite or clay and a water-soluble polymer.

From the US 6,103,065 discloses a method of improving the retention and dewatering of paper stocks by adding a cationic polymer having a molecular weight of 100,000 to 2 million and a charge density of more than 4.0 meq./g to a pulp after the last shearing, simultaneously or thereafter, adding a polymer having a molecular weight of at least 2 million and a charge density of less than 4.0 meq./g and thereafter metering in bentonite: it is not necessary in this process to shear the stock following addition of the polymers , After addition of the polymers and the bentonite, the pulp can be dewatered without further action of shearing forces.

From the WO 04/15200 Also, a microparticle system of a cationic polymer and a finely divided inorganic component is known as a retention aid in the production of paper. Suitable cationic polymers are, for example, cationic polyacrylamides, polymers containing vinylamine units and / or polydiallyldimethylammonium chloride having an average molecular weight M _w of at least 500 000 and a charge density of at most 4.0 meq / g.

WO 98/01623 describes a process for the production of paper and board by dewatering pulps, sheet formation and drying of the leaves, the pulps first with (a) polyethyleneimines molecular weight M _w of more than 500,000 or vinylamine units containing polymers of molecular weight from 5000 to 3 million and then with (b) cationic polyacrylamides or vinylamine units containing polymers are added, wherein the molecular weights M _{w of} the polymers each amount to at least 4 million, and then the pulp at least one shearing stage undulked and flocculated by the addition of bentonite, colloidal silica or clay.

US 6576086 describes a process for the production of paper, paperboard and cardboard by dewatering a paper pulp containing impurities in the presence of fixing agents, wherein as fixing agent reaction products are used by Reaction of polymers containing amino and / or ammonium groups selected from the group comprising the polymers containing vinylamine units, polyalkylenepolyamines, polyamidoamines, polyamidoamines grafted with ethyleneimine which are optionally crosslinked, polydiallyldimethylammonium chlorides, dialkylaminoalkylacrylamide units or polymers containing dialkylaminoalkylmethacrylamide units; Polyallylamines and dicyandiamide and formaldehyde condensates with reactive sizing agents for paper in the ratio of polymer to reactive size of 15000: 1 to 1: 1 are available and use of the resulting reaction products as a fixer for water-soluble and water-insoluble impurities in the manufacture of paper, cardboard and cardboard from contaminants containing paper materials.

The microparticle systems described above are technically complicated because special devices are required for the metering of the finely divided inorganic flocculants.

It is an object of the present invention to provide another method of making paper, which provides a shorter drainage time, an improved filler retention, and papers having an improved formation over the prior art.

1. (a) durch Hydrolyse von Poly-N-vinylformamiden erhältliche kationische Vinylamineinheiten enthaltende Polymere mit einer Molmasse M_w von mindestens 1.2 Millionen, die durch Homopolymerisation von N-Vinylformamid zu Poly-N-vinylformamid und anschliessende Hydrolyse der einpolymerisierten Vinylformamideinheiten zu Vinylamineinheiten hergestellt werden, wobei der Hydrolysegrad dieser Polymeren 1 bis 50 % beträgt, und wobei die Polymeren eine Ladungsdichte (bestimmt bei pH 7) von 0,2 bis 4 meq/g haben,
   und
2. (b) mindestens ein kationisches Polyacrylamid und/oder ein kationisches Polymethacrylamid mit einer Molmasse M_w von jeweils mindestens 3 Millionen, wobei die kationischen Polyacrylamide bzw. die kationischen Polymethacrylamide 7 bis 30 Mol-% mindestens eines kationischen Monomeren einpolymerisiert enthalten, und wobei die kationischen Poly(meth)acrylamide mindestens ein kationisches Monomer aus der Gruppe Dimethylaminoethylacrylat und Dimethylaminoethylmethacrylat, in Form der freien Basen, Salze und/oder in quaternierter Form einpolymerisiert enthalten,

einsetzt,
wobei man pro Gewichtsteil der Komponente (a) 0,25 bis 0,4 Gewichtsteile der Komponente (b) verwendet.The object is achieved by a method for producing paper, cardboard and cardboard by dewatering a paper stock on a screen in the presence of at least one polymer as a retention agent with sheet formation and drying of the leaves, if one makes the sheet formation in the absence of finely divided inorganic flocculants and as retention agents

1. (a) polymers having a molecular weight M _w of at least 1.2 million and obtainable by hydrolysis of poly-N-vinylformamides, obtained by homopolymerization of N-vinylformamide to poly-N-vinylformamide and subsequent hydrolysis of the copolymerized vinylformamide units to vinylamine units, the degree of hydrolysis of these polymers being from 1 to 50% and the polymers having a charge density (determined at pH 7) of from 0.2 to 4 meq / g,
   and
2. (b) at least one cationic polyacrylamide and / or one cationic polymethacrylamide having a molecular weight M _w of at least 3 million, the cationic polyacrylamides or the cationic polymethacrylamides containing from 7 to 30 mol% of at least one cationic monomer in copolymerized form, and the cationic polymethacrylamide Poly (meth) acrylamides at least one cationic monomer from the group dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate, in the form of the free bases, salts and / or in copolymerized form in quaternized form,

uses,
wherein 0.25 to 0.4 parts by weight of component (b) is used per part by weight of component (a).

Polymers of cationic vinylamine units containing poly-N-vinylformamides and having a molecular weight M _w of at least 1.2 million each are known. They are prepared by homopolymerization of N-vinylformamide to poly-N-vinylformamide and subsequent hydrolysis of the copolymerized vinylformamide units to vinylamine units. Vinylamine-containing polymers are the cationic polymers obtainable by hydrolysis of poly-N-vinylformamides. The degree of hydrolysis of these polymers is 1 to 50% and is usually in the range of 2 to 40, especially 2 to 30%. The polymers of component (a) have a charge density (determined at pH 7) from 0.2 to 4 meq / g. The polymers containing vinylamine units and poly-N-vinylformamides of component (a) of the retention agent have a molecular weight M _w of at least 1.2 million. The preparation of homopolymers of N-vinylformamide having the abovementioned specifications is described, for example, in US Pat US 6,132,558 , Column 2, line 36 to column 5, line 25 described in detail. The statements made there are hereby incorporated by reference into the disclosure of the present invention.

As component (b) of the retention agent system, cationic polyacrylamides, cationic polymethacrylamides and mixtures of the compounds mentioned come into consideration, if they each have a molecular weight M _w of at least 3 million. Polymers of this type are mentioned in the prior art EP-A 335 575 described. In addition, such polymers are commercial products. They are known to be prepared by polymerizing acrylamide or methacrylamide in the presence of cationic monomers.

Suitable cationic monomers are, for example, the esters and amides of ethylenically unsaturated C ₃ - to C ₆ -carboxylic acids with aminoalcohols. Examples of cationic monomers are dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminopropyl methacrylate, diethylaminopropyl methacrylate, dimethylaminoethylacrylamide, diethylaminoethylacrylamide, dimethylaminoethylmethacrylamide, diethylaminoethylmethacrylamide, dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide and diethylaminopropylmethacrylamide.

The cationic monomers can be used in the copolymerization in the form of the free bases, the salts with mineral acids such as sulfuric acid, hydrochloric acid or phosphoric acid, the salts with organic acids such as formic acid, acetic acid, propionic acid, benzenesulfonic acid or p-toluenesulfonic acid and / or in quaternized form. Suitable quaternizing agents are, for example, C ₁ - to C ₁₈ -alkyl halides, such as methyl chloride, ethyl chloride, n-propyl chloride, isopropyl chloride and / or stearyl chloride and benzyl chloride,

The cationic polyacrylamides or the cationic polymethacrylamides contain from 7 to 30 mol% of at least one cationic monomer in copolymerized form. The molecular weights of the cationic polymers and nonionic polymers are at least 3 million and are mostly in the range of 5 million to 15 million.

1. (a) ein hydrolysiertes Polyvinylformamid mit einem Hydrolysegrad von 1 bis 50 % und einer Molmasse M_w von mindestens 1,2 Millionen
   und als Komponente
2. (b) ein Copolymerisat aus 93 bis 70 Mol-% Acrylamid und 7 bis 30 Mol-% mindestens eines kationischen Monomeren mit einer Molmasse M_w von mindestens 3 Millionen.

The retention agent contains in particular as a component

1. (a) a hydrolyzed polyvinylformamide having a degree of hydrolysis of from 1 to 50% and a molecular weight M _w of at least 1.2 million
   and as a component
2. (B) a copolymer of 93 to 70 mol% acrylamide and 7 to 30 mol% of at least one cationic monomer having a molecular weight M _w of at least 3 million.

The cationic polyacrylamides and the cationic polymethacrylamides preferably contain copolymerized as cationic monomer dimethylaminoethyl acrylate methochloride or dimethylaminoethylacrylamide methochloride. These methochlorides are easily accessible by alkylation of dimethylaminoethyl acrylate or of dimethylaminoethylacrylamide with methyl chloride.

1. (a) 0,001 bis 0,8 Gew.-%, vorzugsweise 0,01 bis 0,5 Gew.-%
   und
2. (b) 0,001 bis 0,8 Gew.-%, vorzugsweise 0,01 bis 0,2 Gew.-%

zugesetzt. Das Verhältnis der Komponenten (a) und (b) beträgt pro Gewichtsteil der Komponente (a) 0,25 bis 0,4 Gewichtsteile der Komponente (b). Das Retentionsmittel kann dem Papierstoff - in aller Regel erfolgt die Dosierung des Retentionsmittels erfindungsgemäß in den Dünnstoff - beispielsweise in Form einer Mischung aus den Komponenten (a) und (b) zugeführt werden. Man kann jedoch auch so vorgehen, dass man zunächst beispielsweise nach der letzten Scherstufe vor dem Stoffauflauf die Komponente (a) und anschließend die Komponente (b) dosiert. Beide Komponenten können jedoch auch getrennt voneinander aber gleichzeitig vor oder nach einer Scherstufe in den Dünnstoff eingebracht werden. Am vorteilhaftesten dosiert man zunächst mindestens eine Verbindung der Komponente (a) und anschließend mindestens eine Verbin dung der Komponente (b). Die Verbindung der Komponente (a) kann dabei beispielsweise vor einer Scherstufe und die Verbindung der Komponente (b) nach der letzten Scherstufe vor dem Stoffauflauf dem Papierstoff zugeführt werden. Beide Verbindungen können jedoch auch vor der letzten Scherstufe vor dem Stoffauflauf oder nach der letzten Stufe vor dem Stoffauflauf zum Papierstoff dosiert werden, Man kann jedoch auch die Komponente (a) an verschiedenen Stellen in den Dünnstoff dosieren und Scherkräfte auf das System einwirken lassen und die Komponente vor der letzten Scherstufe vor dem Stoffauflauf oder danach zufügen. Ebenso ist es möglich, zunächst die Komponente (b) dem Papierstoff zuzugeben und danach die Komponente (a) des Retentionsmittels zu dosieren.The components (a) and (b) of the retention agent are added to the paper stock, based on dry paper stock, in an amount of

1. (a) 0.001 to 0.8% by weight, preferably 0.01 to 0.5% by weight
   and
2. (b) 0.001 to 0.8% by weight, preferably 0.01 to 0.2% by weight

added. The ratio of components (a) and (b) per part by weight of component (a) is 0.25 to 0.4 part by weight of component (b). The retention agent can be fed to the paper stock-as a rule the metering of the retention agent takes place in the thin material-for example in the form of a mixture of components (a) and (b). But you can also do that in the first place For example, after the last shear stage before the headbox, the component (a) and then the component (b) dosed. However, both components can also be introduced into the thin material separately from one another before or after a shear stage. Most advantageously, at least one compound of component (a) is added first, followed by at least one verbin Component (b). The compound of component (a) can be supplied to the stock, for example, before a shear stage and the compound of component (b) after the last shear stage before the headbox. However, both compounds can be dosed before the last shear stage before the headbox or after the last stage before the headbox for pulp, but you can also dose the component (a) at different locations in the thin and shear forces act on the system and the Add the component prior to the last shear stage before the headbox or afterwards. It is likewise possible first to add component (b) to the paper stock and then to meter component (a) of the retention agent.

1. (a) durch Hydrolyse von Poly-N-vinylformamiden erhältliche kationische Vinylamineinheiten enthaltende Polymere mit einer Molmasse M_w von mindestens 1,2 Millionen, die durch Homopolymerisation von N-Vinylformamid zu Poly-N-vinylformamid und anschliessende Hydrolyse der einpolymerisierten Vinylformamideinheiten zu Vinylamineinheiten hergestellt werden, wobei der Hydrolysegrad dieser Polymeren 1 bis 50 % beträgt, und wobei die Polymeren eine Ladungsdichte (bestimmt bei pH 7) von 0,2 bis 4 meq/g haben,
   und
2. (b) mindestens ein kationisches Polyacrylamid und/oder ein kationisches Polymethacrylamid mit einer Molmasse M_w von jeweils mindestens 3 Millionen, wobei die kationischen Polyacrylamide bzw. die kationischen Polymethacrylamide 7 bis 30 Mol-% mindestens eines kationischen Monomeren einpolymerisiert enthalten, und wobei die kationischen Poly(meth)acrylamide mindestens ein kationisches Monomer aus der Gruppe Dimethylaminoethylacrylat und Dimethylaminoethylmethacrylat, in Form der freien Basen, Salze und/oder in quaternierter Form einpolymerisiert enthalten,

einsetzt,
wobei man pro Gewichtsteil der Komponente (a) 0,25 bis 0,4 Gewichtsteile der Komponente (b) verwendet
als alleiniges Retentionsmittel bei der Herstellung von Papier, Pappe und Karton.The invention is also the use of combinations of

1. (a) polymers containing cationic vinylamine units obtainable by hydrolysis of poly-N-vinylformamides and having a molecular weight M _w of at least 1.2 million, prepared by homopolymerization of N-vinylformamide to poly-N-vinylformamide and subsequent hydrolysis of the copolymerized vinylformamide units to vinylamine units wherein the degree of hydrolysis of these polymers is 1 to 50%, and wherein the polymers have a charge density (determined at pH 7) of 0.2 to 4 meq / g,
   and
2. (b) at least one cationic polyacrylamide and / or one cationic polymethacrylamide having a molecular weight M _w of at least 3 million, the cationic polyacrylamides or the cationic polymethacrylamides containing from 7 to 30 mol% of at least one cationic monomer in copolymerized form, and the cationic polymethacrylamide Poly (meth) acrylamides at least one cationic monomer from the group consisting of dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate, in the form of the free bases, salts and / or in copolymerized form in quaternized form,

uses,
wherein 0.25 to 0.4 parts by weight of component (b) is used per part by weight of component (a)
as sole retention agent in the production of paper, cardboard and cardboard.

According to the invention, all paper grades, paperboard and paperboard can be produced, for example papers for newspaper printing, so-called medium-fine writing and printing papers, natural gravure printing papers and also lightweight coating base papers. For example, wood pulp, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressure pulp (PGW) and sulfite and sulfate pulp can be used. As raw materials for the production of pulp and pulp and mechanical pulp as well as waste paper and coated broke into consideration. Pulp and pulp are being used in more or less in the so-called integrated paper mills less moist form directly without prior thickening or drying further processed into paper. Due to the impurities not completely removed therefrom, these fiber materials still contain substances that greatly disrupt the usual papermaking process. If such pulps are used, it is advisable to work in the presence of a fixative.

Both unfilled and filler-containing papers can be produced by the process according to the invention. The filler content in the paper may be up to a maximum of 40% by weight and is preferably in the range of 5 to 30% by weight. Examples of suitable fillers are clay, kaolin, native and precipitated chalk, titanium dioxide, talc, calcium sulfate, barium sulfate, aluminum oxide, satin white or mixtures of the stated fillers.

The papermaking can be carried out in the presence of the usual process chemicals in the usual amounts, e.g. bulk sizing agents, such as in particular alkyldiketene dispersions, rosin size, alkenylsuccinimide dispersions or sizing polymer dispersions, solidifying agents such as epichlorohydrin-crosslinked polyamidoamines, polyvinylamines of average molecular weight or strength, fixatives, biocides, dyes and fillers. The dosage of the usual process auxiliaries is preferably carried out in the thin material.

The process according to the invention gives papers with improved formation, improved filler distribution, better opacity and improved printability as compared to the products prepared by known processes. The process according to the invention is simpler to carry out than the microparticle processes and results in improved filler retention and formation compared with the prior art.

In the examples, the percentages for the starting materials always mean percent by weight. The molar masses M _{w of} the polymers were determined by means of static light scattering.

The drainage time was determined by dewatering a sample of the stock in a Schopper-Riegler tester and determining the time in seconds within the 300 ml of filtrate.

Ash retention (First Pass Ash Retention) was determined by calculating the difference between the ash concentration of the stock in the headbox and the ash concentration in the white water divided by the ash concentration of the stock in the headbox and multiplying by 100. It is expressed as a percentage. Formation (On-line Formation Index) was determined by measuring the sheets to be tested using Measure IT Optical Properties Measurement OP 4255 (Formation Sensor from ABB). The lower the measured value, the better the formation.

The following polymers were used in the examples: PVAm 1: Polyvinylamine with a molecular weight M _w of 1.2 million and a charge density of 3.0 meq / g PAM 1: Copolymer of 70% by weight of acrylamide and 30% by weight of dimethylaminoethyl acrylate methochloride having a molecular weight M _w of 8 million and a charge density of 1.7 meq / g

The bentonite used had been activated with aqueous sodium carbonate solution.

Examples

On a twin-wire paper machine which produced wood-containing printing paper at a speed of 1500 m / min., A pulp of 50% TMP, 30% deinked waste paper, 20% bleached kraft pulp and calcium carbonate filler and those in Example 1 and Comparative Examples 1 to 3, respectively dehydrated specified additives. The solids content of the white water was always 0.55%. The filler content of the paper was 30%. The paper had a basis weight of 52-56 g / m ² .

example 1

0.03% PVAm 1 and 0.01% PAM 1 were added to the stock indicated above after the last shear stage and before the headbox. The drainage time was 31 seconds, the ash retention 42% and the formation index 5.9.

Comparative Example 1

According to the teaching of EP-A 235 893 0.04% PVAm 1 and 0.015% PAM 1 were metered into the above-described paper stock before the last shear stage and then 0.3% bentonite before the headbox. The dewatering time of a sample containing the bentonite was 38 seconds, the ash retention 37%, and the formation index 6.9.

Comparative Example 2

To the paper stock described above 0.025% PAM 1 was metered after the last shear stage and before the headbox. The drainage time of this stock was 41 seconds, the ash retention 36% and the index for the formation 7.4.

Comparative Example 3

0.05% PVAm 1 was metered to the stock described above after the last shear stage in front of the headbox. The drainage time of this stock was 38 seconds, the ash retention 39% and the index for the formation 6.4.

Claims (2)

1. A process for the production of paper, board and cardboard by draining a paper stock on a wire in the presence of at least one polymer as a retention aid with sheet formation and drying of the sheets, wherein the sheet formation is carried out in the absence of finely divided inorganic flocculants and

   (a) cationic polymers comprising vinylamine units, obtainable by hydrolysis of poly-N-vinylformamides, and having a molar mass M_w of at least 1.2 million, which are prepared by homopolymerization of N-vinylformamide to give poly-N-vinylformamide and subsequent hydrolysis of the polymerized vinylformamide units to vinylamine units, where the degree of hydrolysis of these polymers is from 1 to 50%, and where the polymers have a charge density (determined at pH 7) of from 0.2 to 4 meq/g,
   and

   (b) at least one cationic polyacrylamide and/or one cationic polymethacrylamide having a molar mass M_w of, in each case, at least 3 million, where the cationic polyacrylamides or the cationic polymethacrylamides comprise from 7 to 30 mol% of at least one cationic monomer incorporated in the form of polymerized units, and where the cationic poly(meth)acrylamides comprise at least one cationic monomer in the form of the free bases, salts and/or in quaternized form from the group dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate incorporated in the form of polymerized units are used as retention aids, where from 0.25 to 0.4 part by weight of component (b) is used per part by weight of component (a).
2. The use of combinations of

   (a) cationic polymers comprising vinylamine units, obtainable by hydrolysis of poly-N-vinylformamides, and having a molar mass M_w of at least 1.2 million, which are prepared by homopolymerization of N-vinylformamide to give poly-N-vinylformamide and subsequent hydrolysis of the polymerized vinylformamide units to vinylamine units, where the degree of hydrolysis of these polymers is from 1 to 50%, and where the polymers have a charge density (determined at pH 7) of from 0.2 to 4 meq/g,
   and

   (b) at least one cationic polyacrylamide and/or one cationic polymethacrylamide having a molar mass M_w of, in each case, at least 3 million where the cationic polyacrylamides or the cationic polymethacrylamides comprise from 7 to 30 mol% of at least one cationic monomer incorporated in the form of polymerized units, and where the cationic poly(meth)acrylamides comprise at least one cationic monomer in the form of the free bases, salts and/or in quaternized form from the group dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate incorporated in the form of polymerized units
   where from 0.25 to 0.4 part by weight of component (b) is used per part by weight of component (a),
   as a sole retention aid in the production of paper, board and cardboard.