EP3332063B1 - Method for producing paper - Google Patents

Description

The invention relates to a process for the production of paper and board, comprising adding this aqueous suspension to a paper stock, dewatering the paper stock obtained and then pressing the paper sheet and drying it.

Paper production is a process in which a solid phase consisting of cellulose or wood fibers and various inorganic additives is separated from an aqueous phase. The initial concentration of the solid phase in the paper stock suspension (thin stock) is typically in a range between 15 g/l and 1.5 g/l. The separation of the solid phase and the aqueous phase takes place in several stages and can be modulated within these stages through the choice of mechanical parameters or the targeted addition of chemical additives. In the first stage, the paper stock is dewatered by spraying it onto a screen or by injecting it between two screens, which are referred to as the bottom screen or top screen, depending on their position relative to the injected paper stock. Depending on the design of the so-called wire section, the water is separated from the paper stock solely by gravity or by a combination of gravity and centrifugal forces and runs off through the openings of the wires.

The use of chemical additives, the so-called retention and drainage aids, also plays an important role in wire drainage. These include, in particular, high-molecular, slightly cationic polyacrylamides, cationic starch, but also polymers based on vinylformamide and ethyleneimine. That's how she describes it US6273998 the use of vinylamine copolymers in combination with microparticles such as bentonite as a retention aid that is added to the paper stock in the wet-end process.

Furthermore, she teaches EP-A-950138 the two-stage treatment of paper stock with a cationic polymer and microparticles and after shearing in the second stage with a cross-linked anionic polymer.

WO-A-04/087818 , WO-A-05/012637 and WO-A-2006/066769 describe aqueous slurries of finely divided fillers which have been treated with water-soluble amphoteric copolymers based on polyvinylamine. These slurries make it possible to increase the filler content in paper while retaining the paper properties, in particular dry strength.

The dryness achieved in the wire section depends not only on the mechanical requirements of the wire section and the choice of chemical additives, but also very much on the paper stock system and the basis weight of the paper web. Even if the primary goal is efficient dewatering of the paper stock, good end properties of the paper should continue to be achieved will. Dewatering too quickly can lead to premature immobilization of the paper fibers and thus lead to poor strength properties or poor optical properties.

An important property, which also depends on the dry content of the paper web, is the so-called initial wet structural strength INF. The wet strength and the initial wet strength of paper are to be distinguished from the initial wet structural strength, because both properties are measured on papers which, after drying, are moistened again to a defined water content. Initial wet web strength is the strength of a wet paper that has never been dried. This is the strength of a wet paper as it is in papermaking after it has passed through the wire and press sections of the paper machine. It typically contains about 50% water. An increase in the initial wet structure strength allows the application of higher pull-off forces and thus faster operation of the paper machine (cf. EP-A-0 780 513 ) or the use of larger amounts of filler.

the WO 2009/156274 teaches the use of amphoteric copolymers, which can be obtained by copolymerization of N-vinylcarboxamide with anionic comonomers and subsequent hydrolysis of the vinylcarboxamide, as a paper stock additive to increase the initial wet structural strength of paper. The treatment takes place, for example, in the thick stock or in the thin stock in the paper manufacturing process.

Furthermore, she teaches WO 2014/029593 a process for the production of paper with a high initial wet structural strength with the addition of a water-soluble amphoteric copolymer, which was obtained by Hofmann degradation of a polymer containing acrylamide and/or methacrylamide, and pressing the paper sheet formed in the press section to a defined solids content of ≥48 wt. -%.

the DE 60115692 T2 describes a process for making paper from paperboard, comprising forming a cellulosic suspension, flocculating the suspension, draining the suspension on a screen to form a sheet and then drying the sheet, characterized in that the suspension is flocculated using a flocculation system comprising a siliceous material and organic microparticles having an unswollen particle diameter of less than 750 nanometers.

The invention was based on the object of increasing the initial wet structure strength of the still moist paper web before the transition to the drying section during the production of paper, in order to achieve higher machine speeds in the paper production process compared to known methods.

• das Bereitstellen einer wässrigen Anschlämmung enthaltend Füllstoff, wenigstens ein wasserlösliches, amphoteres Polymer und Mikropartikel,
  • Zugabe dieser wässrigen Anschlämmung zu einem Papierstoff
• Entwässern des erhaltenen Papierstoffes, unter Blattbildung in der Siebpartie, bis zu einem Trockengehalt des Papierblattes auf mindestens 18 Gew.-%
  • und anschließendem Pressen des Papierblattes und Trocknen, wobei das wasserlösliche, amphotere Polymere erhältlich ist durch Copolymerisieren eines nomerengemisches umfassend
    1. a) wenigstens einem N-Vinylcarbonsäureamid der allgemeinen Formel
       
       worin R¹ und R² unabhängig voneinander für H oder C₁- bis C₆-Alkyl stehen,
    2. b) wenigstens einem monoethylenisch ungesättigten Monomer mit mindestens einer freien Säuregruppe oder mindestens einer Säuregruppe in Salzform
    3. c) gegebenenfalls wenigstens einem von den Komponenten (a) und (b) verschiedenen monoethylenisch ungesättigten Monomer, und
    4. d) gegebenenfalls wenigstens einer Verbindung, die mindestens zwei ethylenisch ungesättigte Doppelbindungen im Molekül aufweist,
  und anschließende teilweise oder vollständige Hydrolyse der Gruppen -CO-R¹ des Polymerisats, wobei die Differenz der Anteile der kationischen und der anionischen Monomereinheiten in Mol, jeweils bezogen auf die Gesamtmolzahl aller Monomereinheiten, absolut maximal 10 Mol% beträgt, wobei der Füllstoff Calciumcarbonat ist,
  wobei die Mikropartikel ein Copolymer aus Acrylamid und einem oder mehreren anionischen Monomeren sind, oder die Mikropartikel anorganische Mikropartikel sind, ausgewählt aus Bentonit, kolloidale Kieselsäure und Silikate.

Accordingly, a process for the manufacture of paper and board has been found comprising

• the provision of an aqueous suspension containing filler, at least one water-soluble, amphoteric polymer and microparticles,
  • Addition of this aqueous slurry to a paper stock
• Dewatering of the resulting paper stock, with sheet formation in the wire section, until the paper sheet has a dry content of at least 18% by weight
  • and then pressing the paper sheet and drying, wherein the water-soluble, amphoteric polymer is obtainable by copolymerizing a monomeric mixture comprising
    1. a) at least one N-vinylcarboxamide of the general formula
       
       wherein R ¹ and R ² independently represent H or C ₁ - to C ₆ -alkyl,
    2. b) at least one monoethylenically unsaturated monomer having at least one free acid group or at least one acid group in salt form
    3. c) optionally at least one monoethylenically unsaturated monomer different from components (a) and (b), and
    4. d) optionally at least one compound which has at least two ethylenically unsaturated double bonds in the molecule,
  and subsequent partial or complete hydrolysis of the -CO-R ¹ groups of the polymer, the difference in the proportions of the cationic and anionic monomer units in moles, based in each case on the total number of moles of all monomer units, being a maximum of 10 mol% in absolute terms, the filler being calcium carbonate ,
  wherein the microparticles are a copolymer of acrylamide and one or more anionic monomers, or the microparticles are inorganic microparticles selected from bentonite, colloidal silica and silicates.

It was found that the dry content of the paper web at the end of the wire section and before the mechanical pressing process has a major impact on the effect of filler treatment with a multi-component system.

Depending on the area-related mass, colloquially also referred to as basis weight, the designation for the molded body made of fibrous material changes. In the following, paper should be understood to mean a mass per unit area of 7 g/m ² to 225 g/m ² and cardboard should be understood to mean a mass per unit area of from 225 g/m ² .

Paper stock (also referred to as pulp) is understood below to mean a mixture of substances consisting of one or more types of fibrous substances, fillers and various auxiliary substances suspended in water before sheet formation.

Total paper stock is the paper stock after the addition of all filler slurries and auxiliaries. If it is a reference to the total dry paper stock, also referred to as total paper stock (solid), this is to be understood as the mass that results from the dryness determination according to DIN EN ISO 638 DE.

Fillers are provided as so-called aqueous slurry and mixed with the rest of the paper stock. In the context of this application, the term filler includes calcium carbonate, which can be used in the form of ground (GCC) lime, chalk, marble or precipitated calcium carbonate (PCC).

In the context of this invention, filler is to be understood as meaning particles with an average particle size (volume average) of ≧10 μm, preferably from 0.3 to 5 μm, in particular from up to 0.5 to 2 μm. The mean particle size (volume mean) of the fillers is generally determined in the context of this document using the method of quasi-elastic light scattering (DIN-ISO 13320-1), for example using a Mastersizer 2000 from Malvern Instruments Ltd. Fillers usually have a BET specific surface area of ≤20 m ² /g.

Aqueous slurry is understood to mean a composition containing filler, which generally has a filler content of ≧5% by weight, based on the aqueous slurry. The suspension preferably contains 10 to 70% by weight, in particular 20 to 60% by weight, of filler. The aqueous suspension of the filler can also contain additional organic or inorganic auxiliaries.

According to the invention, an aqueous slurry is provided which comprises at least one inorganic filler, a water-soluble amphoteric polymer and microparticles. The water-soluble amphoteric polymer can be obtained by copolymerizing the monomer mixture comprising the monomers a) and b) and subsequent complete or partial hydrolysis of the —CO—R ¹ groups of the polymer. The choice of the monomer composition and the degree of hydrolysis ensures that the difference in the proportions of the cationic and the anionic monomer units in moles, based in each case on the total number of moles of all monomer units, is an absolute maximum of 10 mol%.

• Amidineinheiten
  
• Amineinheiten
  
  wobei die Substituenten R¹ und R² in den Formeln II, II undVI die in Formel I angegebene Bedeutung haben und X^- in den Formeln II und III ein Anion bedeutet,

und Einheiten von ethylenisch ungesättigten Säuren der Gruppe (b) in Form der freien Säuren und/oder in Salzform.The water-soluble amphoteric polymers contain the following structural units:

• amidine units
  
• amine units
  
  where the substituents R ¹ and R ² in the formulas II, II and VI have the meaning given in formula I and X ^- in the formulas II and III is an anion,

and moieties of ethylenically unsaturated acids of group (b) in free acid form and/or in salt form.

In the case of the hydrolyzed copolymers, the ratio of amidine units to amine units is, for example, 100:1 to 1:30, preferably 40:1 to 1:15, particularly preferably 8:1 to 1:8.

In this context, cationic units are the sum of amine and amidine units, while anionic units include the acid units which are formed during the copolymerization from the monomers of group (b) and which are present in the form of the free acid groups and/or in present in salt form.

Examples of group (a) monomers are open-chain N-vinylamide compounds of the formula (I), such as 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) can be used alone or as a mixture in the copolymerization with the monomers of the other groups. From this group, preference is given to using N-vinylformamide in the copolymerization.

The copolymers to be used according to the invention contain at least one monomer from group (b) that is a monoethylenically unsaturated monomer having at least one free acid group or at least one acid group in salt form.

The acid group can be present as a free acid group or in a salt form. Preferred salts are the water-soluble salts such as alkali metal, alkaline earth metal or ammonium salts.

Suitable bases for the partial or complete neutralization of the acid groups of the monomers (b) are, for example, alkali metal or alkaline earth metal bases, ammonia, amines and/or alkanolamines. Examples of these are sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, magnesium hydroxide, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine, morpholine, diethylenetriamine or tetraethylenepentamine.

Suitable monomers of this group (b) are, for example, monoethylenically unsaturated sulfonic acids, phosphonic acids, monocarboxylic acids and dicarboxylic acids and their salts. Also suitable are monoethylenically unsaturated monoesters of phosphonic acids, monoamides of phosphonic acids, and dicarboxylic acid anhydrides. Suitable monomers (b) are also esters of phosphoric acid with alcohols having a polymerizable, α,β-ethylenically unsaturated double bond. One or the two remaining protons of the phosphoric acid group can be neutralized by suitable bases. In addition, another acid function can be esterified with alcohols that do not have any polymerizable double bonds.

Examples of suitable saturated alcohols for esterifying phosphoric acid are C ₁ -C ₆ -alkanols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, n-hexanol and their isomers.

Possible group (b) monomers are, for example, monoethylenically unsaturated carboxylic acids having 3 to 8 carbon atoms and the water-soluble salts such as alkali metal, alkaline earth metal or ammonium salts of these carboxylic acids. This group of monomers includes, for example, acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, α-chloroacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, mesaconic acid, citraconic acid, glutaconic acid, aconitic acid, methylenemalonic acid, allylacetic acid, vinylacetic acid and crotonic acid. The dicarboxylic acid anhydrides of the abovementioned acids are also suitable.

The monomers (b) also include, for example, vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-acryloxypropylsulfonic acid, 2-hydroxy-3-methacryloxypropylsulfonic acid, styrenesulfonic acid, acrylamidomethylenephosphonic acid, 2-acrylamido-2-methylpropanesulfone acid, vinylphosphonic acid, N-vinylaminomethylenephosphonic acid (CH ₂ =CH-NH-CH ₂ -PO ₃ H), vinylphosphonic acid monomethyl ester, allylphosphonic acid, allylphosphonic acid monomethyl ester, acrylamidomethylpropylphosphonic acid, (meth)acrylic ethylene glycol phosphate and phosphoric acid monoallyl ester.

The aforementioned monomers (b) can be used individually or in the form of any desired mixtures.

For modification, the copolymers can optionally contain at least one further monomer of group (c) in copolymerized form. Preferably, these monomers are nitriles of α,β-ethylenically unsaturated mono- and dicarboxylic acids such as acrylonitrile and methacrylonitrile. When such copolymers are hydrolyzed, 5 ring amidines are then obtained.

Further suitable monomers of group (c) are:
Esters of α,β-ethylenically unsaturated mono- and dicarboxylic acids with monobasic C ₁ -C ₃₀ alkanols, C ₂ -C ₃₀ alkanediols and C ₂ -C ₃₀ amino alcohols, amides of α,β-ethylenically unsaturated monocarboxylic acids and their N-alkyl and N,N-dialkyl derivatives, esters of vinyl alcohol and allyl alcohol with C ₁ -C ₃₀ monocarboxylic acids, N-vinyl lactams, nitrogen-containing heterocycles and lactones with α,β-ethylenically unsaturated double bonds, vinyl aromatic compounds, vinyl halides, vinylidene halides, C C ₂ -C ₈ mono-olefins and mixtures thereof.

Examples of representatives of this group (c) are, for example, methyl (meth)acrylate (the wording "...(meth)acrylate" means both "...methacrylate" and "...acrylate"), methyl ethacrylate, ethyl(meth )acrylate, ethyl ethacrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, tert-butyl ethacrylate, n-octyl (meth)acrylate, 1,1,3,3- tetramethylbutyl (meth)acrylate, ethylhexyl (meth)acrylate, and mixtures thereof.

Suitable additional monomers (c) are also the esters of α,β-ethylenically unsaturated mono- and dicarboxylic acids with amino alcohols, preferably C ₂ -C ₁₂ -amino alcohols. These can be C ₁ -C ₈ monoalkylated or dialkylated on the amine nitrogen. Examples of suitable acid components of these esters are acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, maleic anhydride, monobutyl maleate and mixtures thereof. Acrylic acid, methacrylic acid and mixtures thereof are preferably used. These include, for example, N-methylaminomethyl (meth)acrylate, N-methylaminoethyl (meth)acrylate, N,N-dimethylaminomethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)- acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate and N,N-dimethylaminocyclohexyl (meth)acrylate.

Suitable additional monomers (c) are also acrylamide, methacrylamide, N-methyl(meth)acrylamide (the wording "...(meth)acrylamide" stands for "...acrylamide" and for "...methacrylamide"), 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.

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

In addition, as further monomers (c) 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.

Suitable monomers (c) are also N-vinyllactams and their derivatives, which can have, for example, one or more C ₁ -C ₆ -alkyl substituents (as defined above). These include N-vinylpyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, N-vinyl-5-methyl-2-pyrrolidone, N-vinyl-5-ethyl-2-pyrrolidone, N-vinyl-6-methyl-2-piperidone, N-vinyl-6-ethyl-2-piperidone, N-vinyl-7-methyl-2-caprolactam, N-vinyl-7-ethyl-2-caprolactam and mixtures thereof.

Also suitable are esters of vinyl alcohol and allyl alcohol with C ₁ -C ₃₀ monocarboxylic acids.

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

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

The aforementioned monomers (c) can be used individually or in the form of any desired mixtures.

A further modification of the copolymers is possible by using, in the copolymerization, monomers (d) which contain at least two double bonds in the molecule, e.g Polyalkylene glycols or polyols such as pentaerythritol, sobit or glucose. Also suitable are allyl and vinyl ethers of polyalkylene glycols or polyols such as pentaerythritol, sobit or glucose. If at least one monomer of group (d) is used in the copolymerization, the amounts used are up to 2 mol%, for example 0.001 to 1 mol%.

In a preferred embodiment, a monomer mixture is used for the polymerization, with at least one monoethylenically unsaturated monomer selected as component (b). from the group consisting of monocarboxylic acids, dicarboxylic acids and dicarboxylic acid anhydrides, said monomer having at least one free acid group or at least one acid group in salt form.

In a further preferred embodiment, a monomer mixture is used for the polymerization whose monoethylenically unsaturated monomer with at least one free acid group or at least one acid group in salt form (component (b) is selected from the group consisting of sulfonic acids, phosphonic acids, monoesters of phosphonic acids, monoamides of phosphonic acids and esters of phosphoric acid with alcohols having a polymerizable α,β-ethylenically unsaturated double bond.

1. a) 1 bis 99 Gew.-%, bevorzugt 5 bis 95 Gew.-%, insbesondere 20 bis 90 Gew.-%, bezogen auf das Gesamtgewicht der zur Polymerisation eingesetzten Monomere, wenigstens eines N-Vinylcarbonsäureamids der allgemeinen Formel
   
   worin R¹ und R² unabhängig voneinander für H oder C₁- bis C₆-Alkyl stehen,
2. b) 1 bis 99 Gew.-%, bevorzugt 5 bis 95 Gew.-%, insbesondere 10 bis 80 Gew.-%, bezogen auf das Gesamtgewicht der zur Polymerisation eingesetzten Monomere, wenigstens eines monoethylenisch ungesättigten Monomers mit mindestens einer freien Säuregruppe oder mindestens einer Säuregruppe in Salzform, bevorzugt wenigstens eines Monomers, das ausgewählt ist aus der Gruppe bestehend aus Monocarbonsäuren, Dicarbonsäuren und Dicarbonsäureanhydriden,
3. c) 0 bis 90 Gew.-%, bevorzugt 0,1 bis 85 Gew.-%, insbesondere 1 bis 80 Gew.-%, bezogen auf das Gesamtgewicht der zur Polymerisation eingesetzten Monomere, wenigstens einem von den Komponenten (a) und (b) verschiedenen monoethylenisch ungesättigten Monomer, und
4. d) 0 bis 5 Gew.-%, bevorzugt 0,0001 bis 3 Gew.-%, bezogen auf das Gesamtgewicht der zur Polymerisation eingesetzten Monomere, wenigstens einer Verbindung, die mindestens zwei ethylenisch ungesättigte Doppelbindungen im Molekül aufweist,

besteht.Typical water-soluble amphoteric polymers are obtainable by copolymerizing a monomer composition and subsequent partial or complete hydrolysis of the -CO-R ¹ groups of the polymer, the monomer composition consisting of

1. a) 1 to 99% by weight, preferably 5 to 95% by weight, in particular 20 to 90% by weight, based on the total weight of the monomers used for the polymerization, of at least one N-vinylcarboxamide of the general formula
   
   wherein R ¹ and R ² independently represent H or C ₁ - to C ₆ -alkyl,
2. b) 1 to 99% by weight, preferably 5 to 95% by weight, in particular 10 to 80% by weight, based on the total weight of the monomers used for the polymerization, of at least one monoethylenically unsaturated monomer having at least one free acid group or at least an acid group in salt form, preferably at least one monomer selected from the group consisting of monocarboxylic acids, dicarboxylic acids and dicarboxylic acid anhydrides,
3. c) 0 to 90% by weight, preferably 0.1 to 85% by weight, in particular 1 to 80% by weight, based on the total weight of the monomers used for the polymerization, of at least one of components (a) and ( b) different monoethylenically unsaturated monomer, and
4. d) 0 to 5% by weight, preferably 0.0001 to 3% by weight, based on the total weight of the monomers used for the polymerization, of at least one compound which has at least two ethylenically unsaturated double bonds in the molecule,

consists.

1. a) wenigstens einem N-Vinylcarbonsäureamid der allgemeinen Formel
   
   worin R¹ und R² unabhängig voneinander für H oder C₁- bis C₆-Alkyl stehen,
2. b) wenigstens einem Monomer, das ausgewählt ist unter monoethylenisch ungesättigten Carbonsäuren mit 3 bis 8 C-Atomen und deren wasserlöslichen Salzen wie Alkalimetall-, Erdalkalimetall- und Ammoniumsalzen dieser Carbonsäuren,
3. c) gegebenenfalls wenigstens einem von den Komponenten (a) und (b) verschiedenen monoethylenisch ungesättigten Monomer, und
4. d) gegebenenfalls wenigstens eine Verbindung, die mindestens zwei ethylenisch ungesättigte Doppelbindungen im Molekül aufweist,

und anschließende teilweise oder vollständige Hydrolyse der Gruppen -CO-R¹ aus den in das Copolymerisat einpolymerisierten Monomeren (a) erhältlich sind.For example, preferred are those water-soluble amphoteric polymers obtained by copolymerizing

1. a) at least one N-vinylcarboxamide of the general formula
   
   wherein R ¹ and R ² independently represent H or C ₁ - to C ₆ -alkyl,
2. b) at least one monomer selected from monoethylenically unsaturated carboxylic acids having 3 to 8 carbon atoms and their water-soluble salts such as alkali metal, alkaline earth metal and ammonium salts of these carboxylic acids,
3. c) optionally at least one monoethylenically unsaturated monomer different from components (a) and (b), and
4. d) optionally at least one compound which has at least two ethylenically unsaturated double bonds in the molecule,

and subsequent partial or complete hydrolysis of the -CO-R ¹ groups from the monomers (a) polymerized into the copolymer.

1. a) N-Vinylformamid,
2. b) Acrylsäure, Methacrylsäure und/oder deren Allkalimetall- oder Ammoniumsalzen, und
3. c) gegebenenfalls anderen monoethylenisch ungesättigten Monomeren

und anschließende Abspaltung der -CO-R¹-Gruppe aus den Copolymerisaten.Particularly preferred are those water-soluble, amphoteric polymers that are obtainable by copolymerizing

1. a) N-vinylformamide,
2. b) acrylic acid, methacrylic acid and/or their alkali metal or ammonium salts, and
3. c) optionally other monoethylenically unsaturated monomers

and subsequent elimination of the -CO-R ¹ group from the copolymers.

wobei in den Amidineinheiten (II) bis (V) X^- jeweils ein Anion bedeutet und die Substituenten R¹ und R² in den Formeln II - VI jeweils die in Formel I angegebene Bedeutung haben.The hydrolysis of the polymers obtained by the process described above is carried out by known processes by the action of acids, bases or enzymes, for example hydrochloric acid, sodium hydroxide or potassium hydroxide. This results from the copolymerized monomers (a) of the above formula (I) by splitting off the -CO-R ¹ group, to give copolymers which contain vinylamine units (VI) and/or amidine units (II - V)

where in the amidine units (II) to (V) X ^- is in each case an anion and the substituents R ¹ and R ² in the formulas II - VI each have the meaning given in formula I.

The originally anionic copolymer receives cationic groups as a result of the hydrolysis and thus becomes amphoteric.

The amidine units (II) and (III) are formed by reacting adjacent vinylamine units of the formula (VI) with vinylformamide units or those of the formula IV and V by reacting adjacent vinylamine units of the formula (VI) with acrylonitrile or methacrylonitrile groups (if present in the polymer).

The hydrolysis of the copolymers is, for example, in EP-B-0 672 212 on page 4, lines 38 - 58 and on page 5, lines 1 - 25 and in the examples of EP 528 409 revealed in detail.

An amphoteric polymer is preferably used in which the hydrolysis was carried out in the presence of bases, preferably in the presence of sodium hydroxide solution.

Preference is given to partially and fully hydrolyzed polymers with a degree of hydrolysis of ≧10 mol %, preferably ≧20 mol %, in particular ≧30 mol %. Their degree of hydrolysis is equivalent to the molar percentage total content of the primary amino groups and amidine groups of the polymers, based on the N-vinylcarboxamide units originally present.

1. (i) 1 bis 98 Mol-%, vorzugsweise 1 bis 75 Mol-% Vinylcarbonsäureamideinheiten,
2. (ii) 1 bis 98 Mol-%, vorzugsweise 1 bis 55 Mol-% Einheiten von monoethylenisch ungesättigten Sulfonsäuren, Phosphonsäuren, Phosphorsäureestern, Derivaten davon, oder Einheiten von monoethylenisch ungesättigten Mono- und Dicarbonsäuren, deren Salzen und Dicarbonsäureanhydriden,
   bevorzugt 1 bis 98 Mol-%, vorzugsweise 1 bis 55 Mol-% Einheiten mindestens einer monoethylenisch ungesättigten Carbonsäure mit 3 bis 8 C-Atomen,
3. (iii) 1 bis 98 Mol-%, vorzugsweise 1 bis 55 Mol-% Vinylamineinheiten der Formel (VI) und/oder Amidineinheiten der Formel (II), (III), (IV) und/oder (V), und
4. (iv) bis zu 50 Mol-% Einheiten von anderen monoethylenisch ungesättigten Verbindungen.

The amphoteric polymer contains, for example

1. (i) 1 to 98 mol%, preferably 1 to 75 mol% of vinylcarboxamide units,
2. (ii) 1 to 98 mol%, preferably 1 to 55 mol% of units of monoethylenically unsaturated sulfonic acids, phosphonic acids, phosphoric acid esters, derivatives thereof, or units of monoethylenically unsaturated mono- and dicarboxylic acids, their salts and dicarboxylic acid anhydrides,
   preferably 1 to 98 mol%, preferably 1 to 55 mol% of units of at least one monoethylenically unsaturated carboxylic acid having 3 to 8 carbon atoms,
3. (iii) 1 to 98 mol%, preferably 1 to 55 mol% of vinylamine units of formula (VI) and/or amidine units of formula (II), (III), (IV) and/or (V), and
4. (iv) up to 50 mole % of units from other monoethylenically unsaturated compounds.

1. (i) 5 bis 70 Mol-% Vinylcarbonsäureamideinheiten,
2. (ii) 3 bis 30 Mol-% Einheiten von monoethylenisch ungesättigten Sulfonsäuren, Phosphonsäuren und Salzen davon, und
3. (iii) 10 bis 60 Mol-% Vinylamineinheiten der Formel VI in Salzform und gegebenenfalls Amidineinheiten der Formel (II) und/oder (III).

Particular preference is given to containing amphoteric polymers, in particular consisting of

1. (i) 5 to 70 mol% vinylcarboxamide units,
2. (ii) 3 to 30 mol% of units of monoethylenically unsaturated sulfonic acids, phosphonic acids and salts thereof, and
3. (iii) 10 to 60 mol% of vinylamine units of formula VI in salt form and optionally amidine units of formula (II) and/or (III).

1. (i) 5 bis 70 Mol-% Vinylcarbonsäureamideinheiten,
2. (ii) 5 bis 45 Mol-% Einheiten von Acrylsäure, Methacrylsäure, Salzen und Gemischen davon,
   und
3. (iii) 10 bis 60 Mol-% Vinylamineinheiten der Formel VI in Salzform und/oder Amidineinheiten der Formel (II) und/oder (III).

According to a further embodiment, amphoteric polymers are particularly preferred, containing, in particular consisting of

1. (i) 5 to 70 mol% vinylcarboxamide units,
2. (ii) 5 to 45 mol% units of acrylic acid, methacrylic acid, salts and mixtures thereof,
   and
3. (iii) 10 to 60 mol% of vinylamine units of formula VI in salt form and/or amidine units of formula (II) and/or (III).

According to all of the aforementioned embodiments, those amphoteric copolymers which contain N-vinylformamide in copolymerized form as component (a) are of particular industrial importance.

The water-soluble amphoteric polymers are prepared by customary methods known to those skilled in the art. Suitable methods are for example in EP-A-0 251 182 , WO-A-94/13882 and EP-B-0 672 212 described, to which reference is made here. Furthermore, the production of the in WO-A-04/087818 and WO-A-05/012637 described water-soluble amphoteric polymers.

The water-soluble amphoteric polymers can be prepared by solution, precipitation, suspension or emulsion polymerization. Solution polymerization in aqueous media is preferred. Suitable aqueous media are water and mixtures of water and at least one water-miscible solvent, e.g. an alcohol such as methanol, ethanol, n-propanol, isopropanol, etc.

The polymerization temperatures are preferably in a range from about 30 to 200.degree. C., particularly preferably 40 to 110.degree. The polymerization usually takes place under atmospheric pressure, but it can also take place under reduced or superatmospheric pressure. A suitable pressure range is between 0.1 and 5 bar.

The monomers (b) containing acid groups are preferably used in the salt form. The pH is preferably adjusted to a value in the range from 6 to 9 for the copolymerization. The pH can be kept constant during the polymerization by using a conventional buffer or by measuring the pH and adding acid or base accordingly.

To prepare the polymers, the monomers can be polymerized with the aid of free-radical initiators.

The peroxo and/or azo compounds customary for this purpose can be used as initiators for the radical polymerization, for example alkali metal or ammonium peroxydisulfates, diacetyl peroxide, dibenzoyl peroxide, succinyl peroxide, di-tert-butyl peroxide, tert-butyl perbenzoate, tert-butyl perpivalate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl permaleate, cumene hydroperoxide, diisopropyl peroxydicarbamate, bis-(o-toluoyl)-peroxide, didecanoyl peroxide, dioctanoyl peroxide, dilauroyl peroxide, tert-butyl perisobutyrate, tert-butyl peracetate, di-tert. -amyl peroxide, tert-butyl hydroperoxide, azo-bis-isobutyronitrile, azo-bis-(2-amidonopropane) dihydrochloride or 2-2'-azo-bis-(2-methyl-butyronitrile). Also suitable are initiator mixtures or redox initiator systems, such as, for example, ascorbic acid/iron(II) sulfate/sodium peroxodisulfate, tert-butyl hydroperoxide/sodium disulfite, tert-butyl hydroperoxide/sodium hydroxymethanesulfinate, H ₂ O ₂ /Cul.

To adjust the molecular weight, the polymerization can be carried out in the presence of at least one regulator. As regulators, the usual compounds known to those skilled in the art, such as sulfur compounds, e.g. B. mercaptoethanol, 2-ethylhexyl thioglycolate, thioglycolic acid, sodium hypophosphite, formic acid or dodecyl mercaptan and tribromochloromethane or other compounds which regulate the molecular weight of the polymers obtained can be used.

The average molar mass M _w of the water-soluble amphoteric polymer is, for example, at least 10,000, preferably at least 100,000 daltons and in particular at least 500,000 daltons. The molar masses of the polymers are then, for example, from 10,000 to 10 million, preferably from 100,000 to 5 million (determined, for example, by light scattering on their non-hydrolyzed precursor). This molar mass range corresponds, for example, to K values of 5 to 300, preferably 10 to 250 (determined according to H. Fikentscher in 5% strength aqueous common salt solution at 25° C. and a polymer concentration of 0.1% by weight).

Other components of the aqueous slurry are microparticles.

The microparticle can have either an organic or an inorganic character.

Suitable polymeric microparticles include anionic microparticles. These organic polymers have limited solubility in water and may be crosslinked. Unswollen organic microparticles have a particle size of less than 750 nm.

Anionic organic microparticles, such as those in U.S. 6,524,439 are obtainable by hydrolysis of an acrylamide polymer microparticle or by polymerization of anionic monomers such as (meth)acrylic acid and its salts, 2-acrylamido-2-methylpropanesulfonates, sulfoethyl (meth)acrylates, vinylsulfonic acid, styrenesulfonic acid, maleic acid or other dibasic acids or their salts and mixtures thereof.

These anionic monomers can also be copolymerized with nonionic monomers such as (meth)acrylamide, N-alkylacrylamides, N,N-dialkylacrylamides, methyl (meth)acrylate, acrylonitrile, N-vinylmethylacetamide, N-vinylmethylformamide, vinyl acetate, N- vinylpyrrolidone and mixtures thereof.

The polymerization of the monomers into microparticles is typically carried out in the presence of a multifunctional crosslinking agent. Such crosslinkers are for example in U.S. 6,524,439 described, and have at least two double bonds or one double bond and one reactive group or two reactive groups. For example, its N,N-methylene-bis-(meth)acrylamide, Polyethyleneglycoldi(meth)acrylate, N-vinylacrylamide, divinylbenzene, triallylammonium salts, N-methylallylacrylamideglycidyl(meth)acrylate, acrolein, methylolacrylamide, dialdehydes such as glyoxal, diepoxy compounds and epichlorohydrin.

The multifunctional crosslinking agent is used in an amount that gives a sufficiently crosslinked polymer. For example, at least 4 ppm of multifunctional crosslinking agent can be used per mole of monomer. A quantity of from 4 to 6000 ppm, particularly preferably from 20 to 4000 ppm, and in particular from 40 to 2000 ppm, of multifunctional crosslinking agent is preferably used per mole of monomers.

To adjust the molecular weight, the polymerization can be carried out in the presence of at least one regulator. Such polymerizations for the production of polymer particles are, for example, in U.S. 5,961,840 , U.S. 5,919,882 , 5,171,808 and U.S. 5,167,766 described.

As regulators, the usual compounds known to those skilled in the art, such as sulfur compounds, e.g. B. mercaptoethanol, 2-ethylhexyl thioglycolate, thioglycolic acid, sodium hypophosphite, formic acid or dodecyl mercaptan and tribromochloromethane or other compounds which regulate the molecular weight of the polymers obtained can be used.

The polymerisation to form a microparticle usually takes place by means of inverse emulsion polymerisation or inverse microemulsion polymerisation and is generally known to the person skilled in the art. Such polymerizations are for example in the US2003/0192664 (Page 6) whose teaching is expressly referred to.

1. a) Zubereiten einer W/O Emulsion mit einer Ölphase als kontinuierlicher Phase und einer wässrigen diskontinuierlichen Phase, indem eine wässrige Lösung der Monomere in einem Kohlenwasserstoff in Gegenwart eines Tensids emulgiert wird und
2. b) Durchführen einer freien radikalischen Polymerisation.

The microparticles are usually produced by means of

1. a) preparing a W/O emulsion having an oil phase as a continuous phase and an aqueous discontinuous phase, by emulsifying an aqueous solution of the monomers in a hydrocarbon in the presence of a surfactant and
2. b) performing a free radical polymerization.

Anionic organic microparticles are preferred, in particular copolymers of acrylamide and one or more anionic monomers.

Preferred anionic organic microparticles, when unswollen, have an average particle diameter of ≦750 nm, preferably ≦500 nm, particularly in the range from 25 to 300 nm.

The anionic organic microparticles preferably contain 0 - 99 parts by weight a nonionic monomer 1 - 100 parts by weight an anionic monomer each based on the total weight of all monomers.

The anionic organic microparticles particularly preferably contain 10 - 90 parts by weight a nonionic monomer 10 - 90 parts by weight an anionic monomer each based on the total weight of all monomers.

The anionic organic microparticles particularly preferably contain 20 - 80 parts by weight a nonionic monomer 20 - 80 parts by weight an anionic monomer each based on the total weight of all monomers.

The anionic organic microparticles have a charge density of at least 2 meq/g. A charge density in the range from 2 to 18 meq/g, preferably from 3 to 15 meq/g, in particular from 5 to 12 meq/g, is suitable.

In contrast to inorganic fillers, which have a BET specific surface area of ≤20 m ² /g, inorganic microparticles have a BET specific surface area of ≥100 m ² /g (BET measurement (DIN ISO 9277:2003-05) .

The inorganic microparticles are selected from bentonite, colloidal silica and silicates. Bentonite is generally understood to mean phyllosilicates which are swellable in water. These are primarily the clay mineral montmorillonite and similar clay minerals such as nontronite, hectorite, saponite, sauconite, beidellite, allevardite, illite, halloysite, attapulgite and sepiolite. These layered silicates are preferably activated prior to their use, i.e. converted into a water-swellable form, by treating the layered silicates with an aqueous base such as aqueous solutions of sodium hydroxide, potassium hydroxide, soda or potash.

The inorganic microparticles used are preferably bentonite in the form treated with sodium hydroxide solution. The flake diameter of the bentonite dispersed in water in the form treated with caustic soda is 1 to 2 μm, for example, and the flake thickness is about 1 nm. Depending on the type and activation, the bentonite has a specific surface area of 150 to 800 m ² /g. Typical bentonites are, for example, in the EP-B-0235893 described. In the papermaking process, bentonite is typically added to the cellulose suspension in the form of an aqueous bentonite slurry. This bentonite slurry can contain up to 10% by weight of bentonite. Normally, the slurries contain approx. 3 - 5% by weight of bentonite.

Products from the group consisting of silicon-based particles, silica microgels, silica sols, aluminum silicates, borosilicates, polyborosilicates or zeolites can be used as colloidal silicic acid. These have a specific surface area of 200-1000 m ² /g and an average particle size distribution of 1-250 nm, normally in the range 40-100 nm EP-A-0041056 , EP-A-0185068 and US-A-5176891 described.

Clay or kaolin is a hydrous aluminum silicate with a plate-like structure. The crystals have a layered structure and an aspect ratio (ratio of diameter to thickness) of up to 30:1. The particle size is at least 50% smaller than 2 μm.

In the case of inorganic microparticles, a weight ratio of fillers to inorganic microparticles of at least 30:1 is preferably selected.

The aqueous slurry generally has a solids content of ≧3% by weight, preferably ≧8% by weight, in particular ≧12% by weight, based on the aqueous slurry.

• 0,01 - 1 Gew.-% bezogen auf Füllstoff (fest). Bevorzugt wird ein Mikropartikelanteil von
• 0,05 - 0,6 Gew.-% bezogen auf den Füllstoff (fest).

The proportion of microparticles in the aqueous slurry is, for example

• 0.01 - 1% by weight based on filler (solid). A microparticle content of is preferred
• 0.05 - 0.6% by weight based on the filler (solid).

The proportion of the water-soluble, amphoteric polymer is generally 0.01-1% by weight, preferably 0.05-0.6% by weight, based on the filler (solid).

Preference is given to aqueous suspensions containing, preferably consisting of water, 5-70% by weight of filler, based on the aqueous suspension, and 0.001-1% by weight of water-soluble amphoteric polymer and 0.01-1% by weight of microparticles, each based on Filler (solid).

Preference is given to slurries in which the water-soluble amphoteric polymer/microparticle ratio is 5:1 to 1:5, preferably 3:1 to 1:3.

According to the invention, the aqueous slurry is metered into a paper stock.

All fibers from softwood and deciduous wood commonly used in the paper industry, for example mechanical pulp, bleached and unbleached cellulose and paper pulp from all annual plants, can be used as paper stock. Mechanical pulp includes, for example, groundwood, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressure groundwood, semi-chemical pulp, high-yield pulp, and refiner mechanical pulp (RMP). Sulphate, sulfite and soda pulp, for example, can be used as pulp. Preference is given to using unbleached pulp, which is also referred to as unbleached kraft pulp. Suitable annual plants for the production of paper pulp are, for example, rice, wheat, sugar cane and kenaf. Waste paper can also be used to produce the pulps, either on its own or in a mixture with other fibrous materials. The waste paper can come from a deinking process, for example. However, it is not necessary for the waste paper to be used to be subjected to such a process. Furthermore, fiber mixtures made from a primary material and recycled coated broke can also be used.

According to the invention, the aqueous slurry is added to an aqueous suspension of fibers. Preferably, this is done in the absence of other process chemicals commonly used in papermaking. The water-soluble, amphoteric polymers can be added in the papermaking process, for example, in an amount of 0.01 to 1.00% by weight, based on dry fiber.

Typical application rates are, for example, 0.1 to 10 kg, preferably 0.3 to 4 kg, of the water-soluble, amphoteric polymer per tonne of dry fibrous material. In most cases, the amounts of amphoteric polymer used are 0.5 to 2.5 kg of polymer (solid), based on ton of dry fiber.

The process chemicals customarily used in papermaking can be used in the usual amounts in the process according to the invention, e.g. These substances are preferably added to the paper stock only after the fibrous stock has been treated according to the invention.

Schematically, a paper machine consists of the following units: headbox, wire section, press section and dryer section. The dewatering effect within the wire section is achieved by mechanical forces (gravity, centrifugal force). In addition, hydrodynamic measures are also used. These usually lead to a negative pressure being created on the screens. These measures are particularly useful when dewatering has reached a level where the first capillary effects in the wet paper structure play a role.

According to the invention, sheet formation takes place in the wire section up to a dry content of the paper sheet of at least 18% by weight, preferably 19% by weight, in particular 20% by weight. Sheet formation in the wire section preferably takes place up to a dry content of the paper sheet of at most 25% by weight. According to a preferred variant, sheet formation takes place in the wire section up to a dry content of the paper sheet in the range from 19 to 22% by weight.

In the press section, the moist nonwoven is couched onto the press felt by a take-off suction device (suction roll or static vacuum element). The task of the press felt is to transport the fibrous web through press nips of various modifications. Depending on the design of the press section and the composition of the paper stock, the dry content of the web is up to a maximum of 55% by weight. The dry content increases with the pressure exerted on the paper web running through the press. The pressure and thus the dry content of the paper web can be varied over a relatively wide range in many paper machines.

The method according to the invention enables tear-free operation of the paper machine. The paper web or paper sheet produced in the process shows a significantly increased initial wet structural strength.

Percentages in the examples are by weight unless otherwise noted.

examples

The degree of hydrolysis of the water-soluble amphoteric polymers was determined by enzymatic analysis of the formic acid/formates released during the hydrolysis (test set from Boehringer Mannheim).

The structural composition of the polymers was calculated from the monomer mixture used, the degree of hydrolysis and the vinylamine/amidine ratio determined by means of ¹³ C-NMR spectroscopy. The composition ratio is in mol% unless otherwise specified.

The dry content is determined in accordance with DIN EN ISO 638 DE using the heating cabinet method. The dry content of the sheet of paper is the ratio of the mass of a sample that has been dried to a constant mass at a temperature of (105 ± 2) °C under defined conditions to the mass of the sample before drying. The dry content is given as a percentage by mass.

In analogy to the determination of the dry content of the paper sheet, the determination of the dry content of the total paper stock and the fibrous stock takes place. This results in the indication of total paper stock (solid) or fibrous stock (solid).

The K values were H. Fikentscher, Cellulose Chemistry, Volume 13, 48-64 and 71-74 measured under the specified conditions. The information in brackets indicates the concentration of the polymer solution and the solvent.

The solids content of the polymers was determined by distributing 0.5 to 1.5 g of the polymer solution in a metal lid with a diameter of 4 cm and then drying it in a circulating air drying cabinet at 140° C. for two hours. The ratio of the mass of the sample after drying under the above conditions to the mass when the sample was taken gives the solids content of the polymer.

Ash content: ISO 2144

The average molecular weight M _w is understood here, above and below, as the mass-average molecular weight M _w , as can be determined by light scattering. The molecular weight was determined on the unhydrolyzed precursor.

• Bentonit (Hydrocol^® der Fa. BASF)
• Colloidales Silica (EKA NP der Fa. Akzo Nobel)
• Acrylamid-haltiges strukturiertes anionisches Mikropartikel (Telioform^® M300 der Fa. BASF) Retentionsmittel: Percol^® 540. der Firma BASF SE) kationisches Polyacrylamid in Form einer 1 gew.-%igen Lösung

Materials used:

• Bentonite (Hydrocol ^® from BASF)
• Colloidal silica (EKA NP from Akzo Nobel)
• Acrylamide-containing structured anionic microparticle (Telioform® ^M300 from BASF) retention aid: ^Percol® 540 from BASF SE) cationic polyacrylamide in the form of a 1% strength by weight solution

Production of slurries A1 - A16

The following amphoteric polymers were used to produce slurries. Table 1: Water-soluble amphoteric polymers used polymer Composition vinyl formamide units/acrylic acid units/vinylamine + amidine units Mean Molecular Weight [daltons] P1 40/30/30 500000 p2 5/45/50 400000 P3 65/20/15 650000 P4 30/40/30 400000 P5 30/30/40 400000 P6 40/30/30 500000

Slurry A1

0.7 g of a 12% strength by weight aqueous solution of the polymer P1 were placed in a beaker and then diluted with 30 g of water. 150 g of a 20% strength by weight slurry of precipitated calcium carbonate (PCC) in water were then added. During and after the addition of the PCC slurry, the mixture was stirred at 1000 revolutions per minute (rpm) with the aid of a Heiltof stirrer. About 30 seconds after the addition of the PCC suspension, a 1% strength by weight suspension of bentonite (Hydrocoll from BASF) was added with the stirring unit running. The amount of berntonite suspension added was calculated in such a way that the proportion of bentonite (solid) corresponds to 0.3% by weight, based on PCC (solid). After a further 30 seconds, the number of revolutions of the Heiltof stirrer was reduced to 200 rpm. The bentonite suspension was prepared according to the recommendations in the technical data sheet (Hydrocoll) for use as microparticles to support flocculation processes. This applies in particular to the sufficient swelling of the bentonite before use. The pH of the mixture is then adjusted to 8.5.

Slurry A2 - A8

The procedure for preparing suspension A1 was followed, using the polymers P2 to P6 and microparticles listed in Table 1, the amounts or However, concentrations were maintained. Slurry 6 was made with ground calcium carbonate instead of precipitated calcium carbonate. Table 2 shows the compositions of the slurries produced. Table 2: Preparation of the slurries siltation polymer filler microparticles A1 P1 PCC bentonite A2 p2 PCC bentonite A3 P3 PCC bentonite A4 P4 PCC bentonite A5 P5 PCC bentonite A6 P6 GCC bentonite A7 P6 PCC silica sol A8 p2 PCC silica sol PCC: precipitated calcium carbonate
GCC: ground calcium carbonate

Slurry A9

0.7 g of a 12% strength by weight aqueous solution of the polymer P6 were placed in a beaker and then diluted with 30 g of water. 150 g of a 20% strength by weight slurry of precipitated calcium carbonate (PCC) in water were then added. During and after the addition of the PCC slurry, the mixture was stirred at 1000 revolutions per minute (rpm) using a Heiltof stirrer. About 30 seconds after the addition of the PCC slurry, a 1% by weight solution of an acrylamide-containing structured anionic micropolymer (Telioform M300 from BASF) was added with the stirring unit running. The amount of micropolymer solution added was calculated such that the solid fraction of micropolymer in the PCC slurry corresponds to 0.07% by weight of the solid PCC fraction. After a further 30 seconds, the number of revolutions of the Heiltof stirrer was reduced to 200 rpm and left at this until the slurry was used further. The pH of the mixture was then adjusted to 8.5.

Slurry A10

The procedure for preparing slurry A9 was repeated, with the difference that polymer P2 was now used instead of polymer P6.

Slurry A11

9 g of a 1% strength by weight slurry of bentonite (Hydrocoll from BASF) were placed in a beaker. The bentonite slurry was used as microparticles to support flocculation processes in accordance with the recommendations in the Technical Data Sheet (Hydrocoll). prepared. 150 g of a 20% strength by weight suspension of precipitated calcium carbonate (PCC) in water were then added. The ratio of the solids content of bentonite to PCC in the resulting slurry was 3 to 1000. During the addition of the PCC slurry and thereafter, the mixture was stirred at 1000 revolutions per minute (rpm) using a Heiltof stirrer. About 30 seconds after the addition of the PCC suspension, 21 g of a 0.4% strength by weight aqueous solution of the polymer P6 were added with the stirring unit running. After a further 30 seconds, the number of revolutions of the Heiltof stirrer was reduced to 200 rpm and left at this until the slurry was used further. The pH of the mixture was then adjusted to 8.5.

Slurry A12 - A14

The procedure for preparing slurry A11 was repeated, using the polymers P and microparticles listed in Table 1, but the amounts and concentrations were retained. Slurry A16 was made with ground calcium carbonate instead of precipitated calcium carbonate. Table 3 shows the compositions of the slurries produced. Table 3: Preparation of the slurries siltation polymer filler microparticles microparticles [g] A11 P6 PCC bentonite 0.09 A12 p2 PCC bentonite 0.09 A13 P6 PCC silica sol 0.09 A14 p2 PCC silica sol 0.09 PCC: precipitated calcium carbonate

Slurry A15

21 g of a 0.1% strength by weight solution of an acrylamide-containing structured anionic micropolymer (M300 from BASF) were placed in a beaker. 150 g of a 20% strength by weight suspension of precipitated calcium carbonate (PCC) in water were then added. The ratio of the solids content of micropolymer to PCC in the resulting slurry was 0.7 to 1000. During the addition of the PCC slurry and thereafter, the mixture was stirred at 1000 revolutions per minute (rpm) using a Heiltof stirrer. About 30 seconds after the addition of the PCC suspension, 21 g of a 0.4% strength by weight aqueous solution of the polymer P6 were added with the stirring unit running. After a further 30 seconds, the number of revolutions of the Heiltof stirrer was reduced to 200 rpm and left at this until the slurry was used further. The pH of the mixture was then adjusted to 8.5.

Slurry A16

The procedure for preparing suspension A15 was repeated, with the difference that polymer P2 was now used instead of polymer P6.

Slurry A17 (not according to the invention)

The procedure for preparing slurry A1 was followed, with the difference that no microparticles were added.

Slurry A18 (not according to the invention)

The procedure for preparing slurry A2 was followed, with the difference that no microparticles were added.

Slurry A19 (not according to the invention)

The procedure for preparing slurry A11 was followed, with the difference that no water-soluble, amphoteric polymer was added.

Pretreatment of the pulp suspension

A mixture of bleached birch sulphate and bleached pine sulphate in a ratio of 70/30 at a solids concentration of 4 wt. The pH of the fibrous material was in the range between 7 and 8. The ground material was then diluted to a solids concentration of 0.8% by weight by adding water. An optical brightener (Blankophor PSG) and a cationic starch (HiCat 5163 A) were then added to the diluted pulp.

The cationic starch was digested beforehand as a 10% strength by weight starch slurry in a jet cooker at 130° C. and a residence time of 1 minute. The dosage of the optical brightener was 0.3% by weight of commercial product, based on the total paper stock (solid). The dosage of the cationic starch was 0.8% by weight of starch (solids), based on the total paper stock (solids).

Production of paper sheets according to the method according to the invention:

In order to determine the behavior of the aqueous slurries described above in the production of paper containing filler, 500 ml of the diluted paper stock suspension were introduced and metered into this in each case one of the filler slurries described in the examples and comparative examples and a cationic polyacrylamide (Percol) as a retention aid. The dosage of the retention aid was 0.01% by weight of Percol, based on the total paper stock (solid). The amount of filler slurry metered into the paper stock suspension was adjusted with the aid of several preliminary tests so that the ash content of the paper sheets made from paper stock and slurry was 25% by weight.

For comparison, sheets were produced which each contained about 25% by weight of an untreated PCC and 25% by weight of an untreated GCC.

The sheets of paper with a basis weight of 100g/sqm were produced on a dynamic sheet former from TechPap France. The paper stock suspension was sprayed onto a screen that was clamped into a vertical, rapidly rotating drum is. The dewatering and sheet formation in this system is determined not only by the sheet structure but above all by the centrifugal forces within the rotating drum. By varying the speed of rotation of the drum, the centrifugal force acting on the resulting sheet structure can also be varied. The result is a variation in sheet drainage that leads to a variation in dryness in the wet paper structure. What is meant here is the dry content of the wet paper structure immediately after removal from a water-permeable base (wire) that is clamped in the drum of the dynamic sheet former.

The number of revolutions of the drum was varied in 5 steps between 600 and 1100 revolutions per minute, as a result of which dry contents in the range between 14% by weight and 21% by weight can be set. The amount of filler added for sheet formation must be slightly adjusted upwards as the number of revolutions of the drum increases, since filler retention decreases with increasing dewatering. A small portion of the sheet structure, while still wet, is used to determine the dryness immediately after the wet paper sheet is removed from the wire of the dynamic sheet former.

Application test: Determination of the initial wet structure strength

The wet strength and the initial wet strength of paper are to be distinguished from the initial wet structural strength, because both properties are measured on papers which, after drying, are moistened again to a defined water content. The initial wet strength is an important parameter when evaluating non-permanently wet-strength papers. A paper that has been dried and then moistened again has a completely different wet strength than a moist paper that is present immediately after it has passed through the wire and press sections of a paper machine.

The determination of the initial wet structure strength on the wet paper is carried out using the Voith method (cf. M. Schwarz and K. Bechtel "Initial structural strength during sheet formation", in Wochenblatt für Papierfabrikation 131, pages 950 - 957 (2003) No. 16 . to do this, the wet sheets, after pressing in the static press, were knocked off onto a plastic base and transferred to a cutting base. The sample strips were then cut from the sheet with a defined length and width. These were pressed under constant pressure until the desired dry content was reached. Four solids contents in the range between 42% and 58% were set in each case for examining the paper sheets obtained according to the examples given above. From these values, the initial wet structural strength at 50% dry content was determined using a fitting method described in the reference above. The actual measurement of the initial wet structure strength was carried out on a vertical tensile testing machine with a special clamping device. The force determined in the tractor was converted into the so-called INF index, which is independent of the area mass. For a precise description of the clamping device, the measuring procedure, the determination of the dry content in the paper and the data processing, the reference given above can be consulted.

The results of the tests are given in Table 4 Table 4 example siltation Dry content before press [% by weight] INF(50%) index [Nm/g] Reference PCC 1 PCC untreated 14.6 1.8 Reference PCC 2 PCC untreated 15.3 1.7 Reference PCC 3 PCC untreated 17.1 2.1 Reference PCC 4 PCC untreated 18.6 1.9 Reference PCC 5 PCC untreated 19.5 1.7 Reference GCC 6 GCC untreated 14.9 2.1 Reference GCC 7 GCC untreated 16.1 2.0 Reference GCC 8 GCC untreated 17.8 1.8 Reference GCC 9 GCC untreated 18.6 1.7 Reference GCC 10 GCC untreated 19.4 1.9 1 1 14.8 2.4 2 1 15.7 2.2 3 1 17.2 2.4 4E 1 18.3 3.9 5E 1 19.5 4.2 6 2 15.3 2.2 7 2 16.8 2.4 8th 2 17.5 2.5 9E 2 18.2 3.6 10E 2 19.4 3.9 11 3 15.5 1.9 12 3 16.2 2.3 13 3 17.6 2.6 14E 3 18.4 3.4 15E 3 20.1 3.8 16 4 15.3 2.1 17 4 15.9 2.1 18 4 17.4 2.4 19E 4 18.5 3.6 20E 4 19.7 3.8 21 5 14.9 2.1 22 5 16.3 2.4 23 5 17.2 2.3 24E 5 18.9 3.6 25E 5 19.8 3.7 26 6 15.8 2.2 27 6 16.5 2.3 28 6 17.3 2.7 29E 6 18.7 4.1 30E 6 19.5 4.5 31 7 15.2 2.3 32 7 16.6 2.3 33 7 17.4 2.6 34E 7 18.6 3.5 35E 7 19.4 3.8 36 8th 14.5 1.9 37 8th 15.3 2.4 38 8th 16.8 2.4 39E 8th 18.3 3.6 40E 8th 19.5 3.7 41 9 15.6 2.1 42 9 16.4 2.1 43 9 17.3 2.2 44E 9 18.3 3.6 45E 9 19.6 3.5 46 10 15.6 1.8 47 10 16.4 2.1 48 10 17.3 2.3 49E 10 18.7 3.4 50E 10 19.6 3.7 51 11 15.7 2.2 52 11 16.4 2.2 53 11 17.7 2.4 54E 11 18.6 3.6 55E 11 19.9 3.7 56 12 14.8 2.2 57 12 16.1 2.3 58 12 17.1 2.6 59E 12 18.2 3.5 60E 12 18.9 3.8 61 13 15.2 2.3 62 13 16.7 2.4 63 13 17.6 2.7 64E 13 18.6 3.8 65E 13 19.4 4.0 66 14 15.3 2.1 67 14 16.4 2.3 68 14 17.3 2.3 69E 14 18.4 3.5 70E 14 19.3 3.9 71 15 14.8 2.0 72 15 15.6 2.1 73 15 16.9 2.4 74E 15 18.4 3.5 75E 15 19.1 3.5 76 16 15.4 1.8 77 16 16.6 2.1 78 16 17.6 2.4 79E 16 18.4 3.3 80E 16 19.6 3.6 81 17 16.1 2.2 82 17 16.9 2.2 83 17 17.3 2.3 84 17 18.7 2.3 85 17 19.8 2.4 86 18 15.7 2.1 87 18 16.4 2.4 88 18 17.2 2.3 89 18 18.4 2.5 90 18 19.3 2.4 91 19 15.6 2.2 92 19 16.7 2.1 93 19 17.8 2.4 94 19 18.6 2.2 95 19 19.7 2.3

All examples according to the invention are marked with an "E" in the table.

The following conclusions can be drawn from the data presented in Table 4:
The examples carried out according to the invention show a significantly increased wet structural strength index INF(50%) of the sheets. If the dry content is significantly lower, the INF(50%) index is only slightly above that of an untreated filler slurry.

Reference examples PCC 4 and PCC5 and reference example GCC9 and GCC10 show that setting the dry content above 18% by weight alone (in this case by setting the rotational speed of the dynamic sheet former), without additional treatment of the filler slurry with a 2-component system, leads to none significant increase in the INF(50%) index.

Examples 84, 85, 89, 90, 94 and 95 show that treatment of the filler with only the water-soluble amphoteric polymer or only the microparticles also has no effect when the dry content exceeds 18%.

Claims (9)

1. Method for the production of paper and board comprising

   - providing an aqueous slurry comprising filler, at least one water-soluble amphoteric polymer and microparticles,

   - adding said aqueous slurry to a paper stock

   - dewatering the resulting paper stock, with sheet formation in the wire section, up to a dry content of the paper sheet of at least 18 % by weight

   - and subsequent pressing of the paper sheet and drying,

   wherein the water-soluble, amphoteric polymer is obtainable by copolymerizing a monomer mixture comprising

   a) at least one N-vinylcarboxamide of the general formula

   

   in which R¹ and R² independently of one another represent H or C₁ to C₆ alkyl,

   b) at least one monoethylenically unsaturated monomer having at least one free acid group or at least one acid group in salt form

   c) optionally at least one monoethylenically unsaturated monomer which is different from components (a) and (b), and

   d) optionally at least one compound having at least two ethylenically unsaturated double bonds in the molecule,

   followed by partial or complete hydrolysis of the -CO-R¹ groups of the polymerizate,

   wherein the difference between the proportions of cationic and anionic monomer units in moles, based in each case on the total number of moles of all monomer units, is not more than 10 mol% in absolute terms,

   wherein the filler is calcium carbonate,

   wherein the microparticles are a copolymer of acrylamide and one or more anionic monomers, or the microparticles are inorganic microparticles selected from bentonite, colloidal silica and silicates.
2. Method according to Claim 1, wherein the monomer mixture comprises

   a) 5 to 95% by weight, based on the total weight of the monomers used for the polymerization, of at least one N-vinylcarboxamide of the general formula

   

   in which R¹ and R² independently of one another are H or C₁ to C₆ alkyl,

   b) 5 to 95% by weight, based on the total weight of the monomers used for the polymerization, of at least one monoethylenically unsaturated monomer having at least one free acid group or at least one acid group in salt form,

   c) 0 to 90% by weight, based on the total weight of the monomers used for the polymerization, of at least one monoethylenically unsaturated monomer other than components (a) and (b), and

   d) 0 to 5% by weight, based on the total weight of the monomers used for the polymerization, of at least one compound having at least two ethylenically unsaturated double bonds in the molecule.
3. Method according to any one of Claims 1 to 2, wherein the water-soluble amphoteric polymer is obtainable by copolymerizing

   a) N-vinylformamide,

   b) at least one monoethylenically unsaturated monomer selected from acrylic acid, methacrylic acid, alkali metal salts of acrylic acid and/or methacrylic acid and ammonium salts of acrylic acid and/or methacrylic acid, and

   c) optionally other monoethylenically unsaturated monomers

   and subsequent partial or complete hydrolysis of the -CO-R¹ groups of the polymerizate,
   wherein the difference between the proportions of cationic and anionic monomer units in moles, in each case based on the total number of moles of all monomer units, in absolute terms is not more than 10 mol%.
4. Method according to Claim 1, wherein the water-soluble amphoteric polymer comprises

   (i) 1 to 98 mol% vinyl carboxamide units,

   (ii) 1 to 98 mol% of units of monoethylenically unsaturated sulfonic acids, phosphonic acids, phosphoric acid esters, derivatives thereof, or units of monoethylenically unsaturated mono- and dicarboxylic acids, salts thereof and dicarboxylic acid anhydrides,

   (iii) 1 to 98 mol% of vinylamine units and/or amidine units, and

   (iv) up to 50 mol% of units of other monoethylenically unsaturated compounds.
5. Method according to any one of Claims 1 or 4, wherein the water-soluble amphoteric polymer comprises

   (i) 5 to 70 mol% vinyl carboxamide units,

   (ii) 5 to 45 mol% of units selected from acrylic acid, methacrylic acid, salts of acrylic acid and salts of methacrylic acid, and

   (iii) 10 to 60 mol% of units of vinylamine units and optionally amidine units.
6. Method according to any one of Claims 1 to 5, wherein the proportion of microparticles in the aqueous slurry is 0.01 - 1% by weight based on the filler.
7. Method according to any one of Claims 1 to 6, wherein the proportion of the water-soluble, amphoteric polymer is 0.01 - 1% by weight based on the filler.
8. Method according to any one of Claims 1 to 7, wherein the aqueous slurry comprises water, 5 - 70% by weight filler based on the aqueous slurry, and 0.001 - 1% by weight water-soluble amphoteric polymer based on the filler and 0.01 - 1% by weight microparticles based on filler.
9. Method according to any one of Claims 1 to 8, wherein sheet formation in the wire section is carried out up to a dry content of the paper sheet of at least 19% by weight.