EP2393982B1 - Method for producing paper, card and board with high dry strength - Google Patents

Description

The invention relates to a process for the production of paper, cardboard and cardboard with high dry strength by adding water-soluble cationic polymers and anionic polymers to a pulp, draining the pulp and drying the paper products.

To increase the dry strength of paper, a dry strength agent may either be applied to the surface of already dried paper or added to a stock prior to sheet formation. The dry strength agents are usually used in the form of a 1 to 10% aqueous solution. If such a solution of a dry strength agent is applied to the surface of a paper, considerable amounts of water must be evaporated during the subsequent drying process. Since the drying step is very energy consuming and since the capacity of the usual drying equipment on paper machines is usually not so large that you can drive at the maximum possible production speed of the paper machine, the production speed of the paper machine must be lowered so that dried dry-treated paper dried sufficiently becomes.

On the other hand, if the dry strength agent is added to a paper stock prior to sheet formation, the finished paper only has to be dried once. From the DE 35 06 832 A1 discloses a process for the production of paper with high dry strength, in which one adds to the stock first a water-soluble cationic polymer and then a water-soluble anionic polymer. Polyethyleneimine, polyvinylamine, polydiallyldimethylammonium chloride and epichlorohydrin-crosslinked condensation products of adipic acid and diethylenetriamine are described in the examples as water-soluble cationic polymers. Suitable water-soluble anionic polymers are, for example, homopolymers or copolymers of ethylenically unsaturated C ₃ - to C ₅ -carboxylic acids. The copolymers contain, for example, from 35 to 99% by weight of an ethylenically unsaturated C ₃ - to C ₅ -carboxylic acid, for example acrylic acid.

Out WO 04/061235 A1 discloses a process for the production of paper, in particular tissue, with particularly high wet and / or dry strengths, in which the first admixture of a water-soluble cationic polymer which contains at least 1.5 meq / g of polymer to primary amino functionalities and a molecular weight of at least 10,000 daltons. Particularly emphasized here are partially and fully hydrolyzed homopolymers of N-vinylformamide. Subsequently, a water-soluble anionic polymer is added, which contains anionic and / or aldehydic groups. The advantage of this method is mainly the variability of the two-component systems described in terms of various paper properties, including wet and dry strength, exposed.

in der R¹, R² = H oder C₁- bis C₆-Alkyl bedeuten,
mindestens einem Säuregruppen enthaltenden monoethylenisch ungesättigten Monomeren und/oder dessen Alkalimetall-, Erdalkalimetall- oder Ammoniumsalzen, und gegebenenfalls
anderen monoethylenisch ungesättigten Monomeren, und gegebenenfalls Verbindungen, die mindestens zwei ethylenisch ungesättigte Doppelbindungen im Molekül aufweisen.From the WO 06/056381 A1 discloses a process for making paper, paperboard and paperboard having high dry strength by separately adding a water-soluble vinylamine units-containing polymer and a water-soluble polymeric anionic compound to a pulp, dewatering the pulp and drying the paper products, using at least one water-soluble polymer anionic compound Copolymer obtainable by copolymerizing
at least one N-vinylcarboxamide of the formula

in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,
at least one acid group-containing monoethylenically unsaturated monomer and / or its alkali metal, alkaline earth metal or ammonium salts, and optionally
other monoethylenically unsaturated monomers, and optionally compounds which have at least two ethylenically unsaturated double bonds in the molecule.

From the older European application with the file number EP 09 150 237.7 discloses a process for producing high dry strength paper by separately adding a water-soluble cationic polymer and an anionic polymer to a stock, said anionic polymer being an aqueous dispersion of a water-insoluble polymer having an acid group content of at most 10 mol% or one anionic adjusted aqueous dispersion of a nonionic polymer is. Subsequently, the dehydration of the pulp and the drying of the paper products.

The invention has for its object to provide a further process for the production of paper with high dry strength and lowest possible wet strength available, the dry strength of the paper products over the prior art is further improved as possible.

The object is achieved by a method according to claim 1 for the production of paper, paperboard and cardboard with high dry strength by adding a water-soluble cationic polymer and an anionic polymer to a paper stock, draining the stock and drying the paper products, being an anionic polymer aqueous dispersion of at least one anionic latex and at least one degraded starch.

While the cationic polymer is added to the stock in the form of dilute aqueous solutions having a polymer content of e.g. 0.1 to 10 wt .-% is added, the addition of the anionic polymer is always carried out as an aqueous dispersion. The polymer concentration of the aqueous dispersion can be varied within a wide range. The aqueous dispersions of the anionic polymer are preferably metered in diluted form; for example, the polymer concentration of the anionic dispersions is 0.5 to 10% by weight.

Suitable cationic polymers are all water-soluble cationic polymers mentioned in the cited prior art. It is z. B. to amino or ammonium compounds carrying compounds. The amino groups may be primary, secondary, tertiary or quaternary groups. For the polymers are essentially polymers, polyaddition compounds or polycondensates into consideration, wherein the polymers may have a linear or branched structure up to hyperbranched or dendritic structures. Furthermore, graft polymers are also applicable. The cationic polymers are referred to in the present context as water-soluble, if their solubility in water under normal conditions (20 ° C, 1013 mbar) and pH 7.0, for example, at least 10% by weight.

The molecular weights M _{w of} the cationic polymers are, for example, at least 1000 g / mol. For example, they are mostly in the range of 5,000 to 5 million g / mol. The charge densities of the cationic polymers are, for example, 0.5 to 23 meq / g of polymer, preferably 3 to 22 meq / g of polymer and most often 6 to 20 meq / g of polymer.

• Ester von α,β-ethylenisch ungesättigten Mono- und Dicarbonsäuren mit Aminoalkoholen, vorzugsweise C₂-C₁₂-Aminoalkoholen. Diese können am Aminstickstoff C₁-C₈-monoalkyliert oder dialkyliert sein. Als Säurekomponente dieser Ester eignen sich z. B. Acrylsäure, Methacrylsäure, Fumarsäure, Maleinsäure, Itaconsäure, Crotonsäure, Maleinsäureanhydrid, Monobutylmaleat und Gemische davon. Bevorzugt werden Acrylsäure, Methacrylsäure und deren Gemische eingesetzt. Dazu zählen beispielsweise N-Methylaminomethyl(meth)acrylat, N-Methylaminoethyl(meth)acrylat, N,N-Dimethylaminomethyl(meth)acrylat, N,N-Dimethylaminoethyl(meth)acrylat, N,N-Diethylaminoethyl(meth)acrylat, N,N-Dimethylaminopropyl(meth)acrylat, N,N-Diethylaminopropyl(meth)acrylat und N,N-Dimethylaminocyclohexyl(meth)acrylat.

Suitable monomers for the preparation of cationic polymers are, for example:

• Esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with aminoalcohols, preferably C ₂ -C ₁₂ -aminoalcohols. These may be C ₁ -C ₈ monoalkylated or dialkylated on the amine nitrogen. As the acid component of these esters are z. For example, acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, maleic anhydride, monobutyl maleate and mixtures thereof. Preference is given to using acrylic acid, methacrylic acid and mixtures thereof. These include, for example, N-methylaminomethyl (meth) acrylate, N-methylaminoethyl (meth) acrylate, N, N-dimethylaminomethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate and N, N-dimethylaminocyclohexyl (meth) acrylate.

Also suitable are the quaternization products of the above compounds with C ₁ -C ₈ alkyl chlorides, C ₁ -C ₈ dialkyl sulfates, C ₁ -C ₁₆ epoxides or benzyl chloride.

In addition, as further monomers 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.

Also suitable are the quaternization products of the above compounds with C ₁ -C ₈ alkyl chloride, C ₁ -C ₈ dialkyl sulfate, C ₁ -C ₁₆ epoxides or benzyl chloride.

Suitable monomers are furthermore N-vinylimidazoles, alkylvinylimidazoles, in particular methylvinylimidazoles such as 1-vinyl-2-methylimidazole, 3-vinylimidazole N-oxide, 2- and 4-vinylpyridines, 2- and 4-vinylpyridine N-oxides and betainic derivatives and Quaternization products of these monomers.

worin

R

für Wasserstoff oder C₁- bis C₄-Alkyl steht,

-[Al-]_m

eine lineare oder verzweigte Oligoalkyleniminkette mit m Alkylenimineinheiten bedeutet,

m

für eine ganze Zahl im Bereich von 1 bis 20 steht, und das Zahlenmittel m in den Oligoalkyleniminketten wenigstens 1,5 beträgt,

Y

das Anionäquivalent einer Mineralsäure bedeutet und

n

für eine Zahl von 1 ≤ n ≤ m steht.

Other suitable monomers are allylamine, dialkyldiallylammonium chlorides, in particular dimethyldiallylammonium chloride and diethyldiallylammonium chloride and those from the WO 01/36500 A1 known monomers containing alkyleneimine units of the formula (II)

wherein

R

is hydrogen or C ₁ - to C ₄ -alkyl,

- [Al-] _m

a linear or branched oligoalkylenimine chain with m alkyleneimine units,

m

is an integer in the range of 1 to 20, and the number average m in the oligoalkyleneimine chains is at least 1.5,

Y

the anion equivalent of a mineral acid means and

n

is a number of 1 ≤ n ≤ m.

Monomers or monomer mixtures in which in the above formula (II) the number average of m is at least 2.1, usually 2.1 to 8, are preferred. she are obtainable by reacting an ethylenically unsaturated carboxylic acid with an oligoalkyleneimine, preferably in the form of an oligomer mixture. The resulting product may optionally be converted with a mineral acid HY in the acid addition salt. Such monomers can be polymerized in an aqueous medium in the presence of an initiator which initiates a free radical polymerization to cationic homo- and copolymers.

[Al-]_n

für eine lineare oder verzweigte Oligoalkyleniminkette mit n Alkylenimineinheiten steht,

n

eine Zahl von mindestens 1 bedeutet und

X

für eine geradkettige oder verzweigte C₂- bis C₆-Alkylengruppe steht sowie

Other suitable cationic monomers are from the older EP application 07 117 909.7 known. These are alkyleneimine units containing aminoalkyl vinyl ethers of the formula (III)

H ₂ C = CH-OX-NH- [Al-] _n -H (III),

wherein

[Al-] _n

represents a linear or branched oligoalkyleneimine chain having n alkyleneimine units,

n

a number of at least 1 means and

X

represents a straight-chain or branched C ₂ - to C ₆ -alkylene group and

Salts of the monomers (III) with mineral acids or organic acids and quaternization products of the monomers (III) with alkyl halides or dialkyl sulfates. These compounds are accessible by addition of alkyleneimines to amino C ₂ to C ₆ alkyl vinyl ethers.

The abovementioned monomers can be polymerized to water-soluble cationic homopolymers alone or together with at least one other neutral monomer to form water-soluble cationic copolymers or with at least one acid group-containing monomers to form amphoteric copolymers which carry a total cationic charge in a molar excess of copolymerized cationic monomers.

Suitable neutral monomers which are copolymerized with the abovementioned cationic monomers for the preparation of cationic polymers are, for example, esters of α, β-ethylenically unsaturated mono- and dicarboxylic acids with C ₁ -C ₃₀ -alkanols, C ₂ -C ₃₀ -alkanediols, 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 saturated C ₁ -C ₃₀ monocarboxylic acids, vinyl aromatics, vinyl halides, vinylidene halides, C ₂ -C ₈ monoolefins and Mixtures thereof.

Further suitable comonomers are, for example, methyl (meth) acrylate, methyl methacrylate, ethyl (meth) acrylate, ethyl methacrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, tert-butyl ethacrylate, n-octyl (meth) acrylate, 1,1,3,3-tetramethylbutyl (meth) acrylate, ethylhexyl (meth) acrylate, and mixtures thereof.

Also suitable are acrylamide, substituted acrylamides, methacrylamide, substituted methacrylamides such as, for example, acrylamide, methacrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, N- (n-butyl) ( meth) acrylamide, tert-butyl (meth) acrylamide, n-octyl (meth) acrylamide, 1,1,3,3-tetramethylbutyl (meth) acrylamide and ethylhexyl (meth) acrylamide and also acrylonitrile and methacrylonitrile and mixtures of the stated monomers.

Further monomers for modifying the cationic polymers are 2-hydroxyethyl (meth) acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, etc., and mixtures thereof.

Further suitable monomers for the copolymerization with the abovementioned cationic monomers are N-vinyllactams and derivatives thereof which contain, for example, one or more C ₁ -C ₆ -alkyl substituents, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec. Butyl, tert-butyl, etc. may have. These include, for example, 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, etc.

Suitable comonomers for the copolymerization with the abovementioned cationic monomers are furthermore ethylene, propylene, isobutylene, butadiene, styrene, α-methylstyrene, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and mixtures thereof.

Another group of comonomers are ethylenically unsaturated compounds bearing a moiety from which an amino group can be formed in a polymer-analogous reaction. These include, for example, N-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide, N-vinylpropionamide, N-vinyl-N-methylpropionamide and N-vinylbutyramide and mixtures thereof. The polymers formed therefrom can, as in EP 0 438 744 A1 described, by acidic or basic hydrolysis in vinylamine and amidine units (formulas IV - VII) containing polymers are transferred.

In the formulas IV-VII, the substituents R ¹ , R ^{2 are} H, C ₁ - to C ₆ -alkyl and X ^{- is} an anion equivalent of an acid, preferably a mineral acid.

For example, polyvinylamines, polyvinylmethylamines or polyvinylethylamines are formed during the hydrolysis. The monomers of this group may be polymerized in any manner with the cationic monomers and / or the above-mentioned comonomers.

Cationic polymers in the context of the present invention are also to be understood as meaning amphoteric polymers which carry a total cationic charge. In the case of the amphoteric polymers, the content of cationic groups is, for example, at least 5 mol% higher than the content of anionic groups in the polymer. Such polymers are z. B. accessible by copolymerizing a cationic monomer such as N, N-dimethyl-aminoethylacrylamide in the form of the free base, partially neutralized with an acid or in quaternized form with at least one acid group-containing monomer, wherein the cationic monomer in a molar excess is used so that the resulting polymers carry a total cationic charge.

• (a) mindestens einem N-Vinylcarbonsäureamid der Formel (I)
  
  in der R¹, R² = H oder C₁- bis C₆-Alkyl bedeuten,
• (b) mindestens einer monoethylenisch ungesättigten Carbonsäure mit 3 bis 8 C-Atomen im Molekül und/oder deren Alkalimetall-, Erdalkalimetall- oder Ammoniumsalzen und gegebenenfalls
• (c) anderen monoethylenisch ungesättigten Monomeren, und gegebenenfalls
• (d) Verbindungen, die mindestens zwei ethylenisch ungesättigte Doppelbindungen im Molekül aufweisen,

und anschließend teilweise oder vollständige Abspaltung von Gruppen -CO-R¹ aus den in das Copolymerisat einpolymerisierten Monomeren der Formel (I) unter Bildung von Aminogruppen, wobei der Gehalt an kationischen Gruppen wie Aminogruppen im Copolymerisat mindestens 5 Mol-% über dem Gehalt an einpolymerisierten Säuregruppen der Monomere (b) beträgt. Bei der Hydrolyse von N-Vinylcarbonsäureamidpolymeren entstehen in einer sekundären Reaktion Amidineinheiten, indem Vinylamineinheiten mit einer benachbarten Vinylformamideinheit reagieren. Im Folgenden bedeutet die Angabe von Vinylamineinheiten in den amphoteren Copolymerisaten immer die Summe aus Vinylamin- und Amidineinheiten.Amphoteric polymers are also obtainable by copolymerizing

• (a) at least one N-vinylcarboxamide of the formula (I)
  
  in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,
• (B) at least one monoethylenically unsaturated carboxylic acid having 3 to 8 carbon atoms in the molecule and / or their alkali metal, alkaline earth metal or ammonium salts and optionally
• (c) other monoethylenically unsaturated monomers, and optionally
• (d) compounds which have at least two ethylenically unsaturated double bonds in the molecule,

and then partial or complete cleavage of groups -CO-R ¹ from the copolymerized in the copolymer monomers of formula (I) to form amino groups, wherein the content of cationic groups such as amino groups copolymerized in the copolymer at least 5 mol% above the content of polymerized Acid groups of the monomers (b) is. In the hydrolysis of N-vinylcarboxamide polymers, amidine units are formed in a secondary reaction by reacting vinylamine units with an adjacent vinylformamide unit. In the following, the indication of vinylamine units in the amphoteric copolymers always means the sum of vinylamine and amidine units.

• (a₁) gegebenenfalls nicht hydrolysierte Einheiten der Formel (I)
• (a₂) Vinylamin- und Amidineinheiten, wobei der Gehalt an Amino- plus Amidingruppen im Copolymerisat mindestens 5 Mol-% über dem Gehalt an einpolymerisierten Säuregruppen enthaltenden Monomeren liegt,
• (b) Einheiten eines Säuregruppen enthaltenden monoethylenisch ungesättigten Monomeren und/oder deren Alkalimetall-, Erdalkalimetall- oder Ammoniumsalzen,
• (c) 0 bis 30 Mol-% Einheiten mindestens eines anderen monoethylenisch ungesättigten Monomeren und
• (d) 0 bis 2 Mol-% mindestens einer Verbindung, die mindestens zwei ethylenisch ungesättigte Doppelbindungen in Molekül aufweist.

The amphoteric compounds thus obtained contain, for example

• (a ₁ ) optionally unhydrolyzed units of the formula (I)
• (a ₂ ) vinylamine and amidine units, wherein the content of amino plus amidine groups in the copolymer is at least 5 mol% above the content of polymerized monomers containing copolymerized groups,
• (b) units of an acid group-containing monoethylenically unsaturated monomer and / or their alkali metal, alkaline earth metal or ammonium salts,
• (c) 0 to 30 mol% of units of at least one other monoethylenically unsaturated monomer and
• (d) 0 to 2 mol% of at least one compound having at least two ethylenically unsaturated double bonds in molecule.

The hydrolysis of the copolymers can be carried out in the presence of acids or bases or else enzymatically. In the case of hydrolysis with acids, the vinylamine groups formed from the vinylcarboxamide units are present in salt form. The hydrolysis of vinylcarboxylic acid amide copolymers is described in U.S. Pat EP 0 438 744 A1 , Page 8, line 20 to page 10, line 3, described in detail. The statements made there apply correspondingly to the preparation of the amphoteric polymers to be used according to the invention having a total cationic charge.

These polymers have, for example, K values (determined according to H. Fikentscher in 5% aqueous saline solution at pH 7, a polymer concentration of 0.5% by weight and a temperature of 25 ° C.) in the range from 20 to 250, preferably 50 to 150.

The cationic homopolymers and copolymers can be prepared by solution, precipitation, suspension or emulsion polymerization. Preference is given to solution polymerization in aqueous media. Suitable aqueous media are water and mixtures of water and at least one water-miscible solvent, e.g. As an alcohol such as methanol, ethanol, n-propanol, etc.

The polymerization temperatures are preferably in a range of about 30 to 200 ° C, more preferably 40 to 110 ° C. The polymerization is usually carried out under atmospheric pressure, but it can also proceed under reduced or elevated pressure. A suitable pressure range is between 0.1 and 5 bar.

To prepare the cationic polymers, the monomers can be polymerized by means of free-radical initiators.

As initiators for the radical polymerization, the peroxo and / or azo compounds customary for this purpose can be used, for example alkali 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 permalate, 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-amidinopropane) dihydrochloride or 2-2'-azobis (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 / Cu-I or iron II -Links.

To adjust the molecular weight, the polymerization can be carried out in the presence of at least one regulator. As a regulator, the usual compounds known in the art, such. B. sulfur compounds, for. As mercaptoethanol, 2-ethylhexyl thioglycolate, thioglycolic acid, sodium hypophosphite, formic acid or dodecyl mercaptan and Tribromchlormethan or other compounds which act regulating the molecular weight of the polymers obtained, are used.

Cationic polymers such as polyvinylamines and their copolymers can also be prepared by Hofmann degradation of polyacrylamide or polymethacrylamide and their copolymers, cf. H. Tanaka, Journal of Polymer Science: Polymer Chemistry Edition 17,1239-1245 (1979 ) and EI Achari, X. Coqueret, A. Lablache-Combier, C. Loucheux, Makromol. Chem., Vol. 194, 1879-1891 (1993 ).

All of the abovementioned cationic polymers can be modified by carrying out the polymerization of the cationic monomers and, if appropriate, of the mixtures of cationic monomers and the comonomers in the presence of at least one crosslinker. A crosslinker is understood as meaning those monomers which contain at least two double bonds in the molecule, e.g. Methylenbisacrylamid, glycol diacrylate, glycol dimethacrylate, glycerol triacrylate, pentaerythritol triallyl ether, at least two times with acrylic acid and / or methacrylic acid esterified polyalkylene glycols or polyols such as pentaerythritol, sobait or glucose. If at least one crosslinker is used in the copolymerization, the amounts used, for example, up to 2 mol%, z. B. 0.001 to 1 mol%.

• Di- und Polyglycidylverbindungen,
• Di- und Polyhalogenverbindungen,
• Verbindungen mit zwei oder mehr Isocyanatgruppen, eventuell blockierte Kohlensäurederivate,
• Verbindungen, die zwei oder mehrer Doppelbindungen aufweisen, die für eine Michael-Addition geeignet sind,
• Di-und Polyaldehyde,
• monoethylenisch ungesättigte Carbonsäuren, deren Ester und Anhydride.

Furthermore, the cationic polymers can be modified by the subsequent addition of crosslinkers, ie by the addition of compounds which have at least two amino groups reactive groups, such as

• Di- and polyglycidyl compounds,
• Di- and polyhalogen compounds,
• Compounds with two or more isocyanate groups, possibly blocked carbonic acid derivatives,
• Compounds having two or more double bonds suitable for Michael addition,
• Di- and polyaldehydes,
• monoethylenically unsaturated carboxylic acids, their esters and anhydrides.

Also suitable as cationic compounds are polymers which can be produced by polyaddition reactions, in particular polymers based on aziridines. Both homopolymers can be formed but also graft polymers which are produced by grafting aziridines to other polymers. Again, it may be advantageous to add crosslinkers during or after the polyaddition which have at least two groups capable of reacting with the aziridines or the amino groups formed, e.g. Epichlorohydrin or dihaloalkanes (see Ullmann's Encyclopedia of Industrial Chemistry, VCH, Weinheim, 1992, chapter on aziridines).

Preferred polymers of this type are based on ethyleneimine, e.g. homopolymers of ethyleneimine prepared by polymerization of ethyleneimine or polymers grafted with ethyleneimine such as polyamidoamines.

Further suitable cationic polymers are reaction products of dialkylamines with epichlorohydrin or with difunctional or polyfunctional epoxides, such as, for example, reaction products of dimethylamine with epichlorohydrin.

Also suitable as cationic polymers are polycondensates, e.g. Homopolymers or copolymers of lysine, arginine and histidine. They can be used as homopolymers or as copolymers with other natural or synthetic amino acids or lactams. For example, glycine, alanine, valine, leucine, phenylalanine, tryptophan, proline, asparagine, glutamine, serine, threonine or else caprolactam are suitable for the copolymerization.

As cationic polymers it is also possible to use condensates of difunctional carboxylic acids with polyfunctional amines, the polyfunctional amines having at least two primary amino groups and at least one further less reactive, ie. secondary, tertiary or quaternary amino group wear. Examples are the polycondensation products of diethylenetriamine or triethylenetetramine with adipic, malonic, glutaric, oxalic or succinic acid.

Also amino-carrying polysaccharides such. Chitosan are suitable as cationic polymers.

Furthermore, all the polymers described above, which carry primary or secondary amino groups, can be modified by means of reactive oligoethyleneimines as in the older one EP application 07 150 232.2 described. In this application, graft polymers are described whose graft base is selected from the group of polymers comprising vinylamine units, polyamines, polyamidoamines and polymers of ethylenically unsaturated acids, and which contain exclusively oligoalkyleneimine side chains as side chains. The preparation of graft polymers with Oligoalkyleniminseitenketten done by grafting on one of said grafting at least one Oligoalkylenimin containing a terminal Aziridinruppe.

In a preferred embodiment of the process according to the invention, the water-soluble cationic polymer used is a polymer containing vinylamine units.

In addition to the water-soluble cationic polymers described above, anionic polymers are also added to a paper stock in the process according to the invention.

The anionic polymer according to the invention contains at least one anionic latex and at least one degraded starch.

The term latex in the context of the present invention is understood to mean water-insoluble homopolymers and copolymers which are preferably used in the form of dispersions or emulsions.

For the purposes of the present invention, the term degraded starch is understood to mean starches which have an average molecular weight Mw of from 1,000 to 65,000.

The latex is preferably at least 40 wt .-%, preferably at least 60 wt .-%, more preferably at least 80 wt .-% of so-called main monomers (a).

The main monomers (a) are selected from C ₁ -C ₂₀ -alkyl (meth) acrylates, vinyl esters of carboxylic acids containing up to 20 C atoms, vinylaromatics having up to 20 C atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of 1 to 10 C-containing alcohols, aliphatic hydrocarbons having 2 to 8 carbon atoms and one or two double bonds or mixtures of these monomers.

To name a few are z. B. (meth) acrylic acid alkyl ester having a C ₁ -C ₁₀ alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, isobutyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.

In particular, mixtures of (meth) acrylic acid alkyl esters are also suitable.

Vinyl esters of carboxylic acids having 1 to 20 carbon atoms are, for. As vinyl laurate, stearate, vinyl propionate, vinyl versatate and vinyl acetate.

Suitable vinylaromatic compounds having up to 20 carbon atoms are vinyltoluene, α- and p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and preferably styrene. Examples of ethylenically unsaturated nitriles are acrylonitrile and methacrylonitrile.

The vinyl halides are chloro, fluoro or bromo substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride.

To name as vinyl ethers of alcohols containing 1 to 10 carbon atoms are, for. As vinyl methyl ether or vinyl isobutyl ether. Preferred are vinyl ethers of alcohols containing 1 to 4 carbon atoms.

As aliphatic hydrocarbons having 2 to 8 carbon atoms and one or two olefinic double bonds may be mentioned ethylene, propylene, butadiene, isoprene and chloroprene.

Preferred main monomers (a) are C ₁ -C ₂₀ -alkyl (meth) acrylates and mixtures of the alkyl (meth) acrylates with vinylaromatics, especially styrene (collectively also referred to as polyacrylate latex) or hydrocarbons having 2 double bonds, especially butadiene, or mixtures of such hydrocarbons with vinyl aromatics, especially styrene (collectively referred to as polybutadiene latex).

In addition to the main monomers (a), the latex may contain other monomers (b), e.g. Example, hydroxyl-containing monomers, in particular C ₁ -C ₁₀ hydroxyalkyl (meth) acrylates, and monomers having alkoxy groups, as they are obtainable by alkoxylation of hydroxyl-containing monomers with alkoxides, in particular ethylene oxide or propylene oxide.

Further monomers (b) are compounds which have at least two free-radically polymerizable double bonds, preferably 2 to 6, particularly preferably 2 to 4, very particularly preferably 2 to 3 and in particular 2. Such compounds are also referred to as crosslinkers.

The at least two free-radically polymerizable double bonds of the crosslinkers (b) can be selected from the group consisting of (meth) acrylic, vinyl ether, vinyl ester, allyl ether and allyl ester groups. Examples of crosslinkers (b) are 1,2-ethanediol di (meth) acrylate, 1,3-propanediol di (meth) acrylate, 1,2-propanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1.6 Hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane trioldi (meth) acrylate, pentaerythritol tetra (meth) acrylate, 1,4-butanediol divinyl ether, 1,6-hexanediol divinyl ether, 1,4-cyclohexanediol divinyl ether, divinylbenzene, allyl acrylate, allyl methacrylate , Methallyl acrylate, methallyl methacrylate, (meth) acrylic acid but-3-en-2-yl ester, (meth) acrylic acid but-2-en-1-yl ester, (meth) acrylic acid 3-methyl-but-2-en-1-yl ester Esters of (meth) acrylic acid with geraniol, citronellol, cinnamyl alcohol, glycerol mono- or diallyl ether, trimethylolpropane mono- or diallyl ether, ethylene glycol monoallyl ether, diethylene glycol monoallyl ether, propylene glycol monoallyl ether, dipropylene glycol monoallyl ether, 1,3-propanediol monoallyl ether, 1,4-butanediol monoallyl ether and furthermore itaconic acid diallyl ester. Allyl acrylate, divinylbenzene, 1,4-butanediol diacrylate and 1,6-hexanediol diacrylate are preferred.

In addition, the anionic latex may contain other monomers (c), e.g. As monomers with carboxylic acid groups, their salts or anhydrides. Called z. For example, acrylic acid, methacrylic acid, itaconic acid, maleic acid or fumaric acid and aconitic acid. The content of ethylenically unsaturated acids in the latex is generally less than 10% by weight. The proportion of these monomers (c) is for example at least 1 wt .-%, preferably at least 2 wt .-% and particularly preferably at least 3 wt .-%. The acid groups of the latex may optionally be at least partially neutralized prior to later use. Preferably, at least 30 mol%, particularly preferably 50-100 mol% of the acid groups are neutralized. Suitable bases are volatile bases such as ammonia or non-volatile bases such as alkali metal hydroxides, in particular sodium hydroxide solution.

In a first embodiment of the present invention, the anionic latex consisting of the above-mentioned monomers has a glass transition temperature (measured by DSC) of -50 to +50 ° C, preferably -50 to +10 ° C, more preferably -40 to + 5 ° C and most preferably from -30 to 0 ° C on.

The glass transition temperature T _g is generally known to the person skilled in the art. This means the limit value of the glass transition temperature, according to which these G. Kanig (Colloid Journal & Zeitschrift fur Polymere, vol. 190, page 1, equation 1 ) tends with increasing molecular weight. The glass transition temperature is determined by the DSC method (differential scanning calorimetry, 20 K / min, midpoint measurement, DIN 53765).

wobei x¹, x², .... xⁿ die Massenbrüche der Monomeren 1, 2, .... n und T_g ¹, T_g ², .... Tgⁿ die Glasübergangstemperaturen der jeweils nur aus einem der Monomeren 1, 2, .... n aufgebauten Polymerisaten in Grad Kelvin bedeuten. Die T_g-Werte für die Homopolymerisate der meisten Monomeren sind bekannt und z. B. in Ullmann's Encyclopedia of Industrial Chemistry, Bd. 5, Vol. A21, Seite 169, VCH Weinheim, 1992 , aufgeführt. Weitere Quellen für Glasübergangstemperaturen von Homopolymerisaten bilden z. B. J. Brandrup, E. H. Immergut, Polymer Handbook, 1st Ed., J. Wiley, New York, 1966 , 2nd Ed., J. Wiley, New York, 1975 , und 3rd Ed., J. Wiley, New York, 1989 .After Fox ( TG Fox, Bull. Phys. Soc. 1956 [Ser. II] 1, page 123 and according to Ullmann's Encyclopedia of Industrial Chemistry, Vol. 19, page 18, 4th edition, Verlag Chemie, Weinheim, 1980 ) applies to the glass transition temperature of at most weakly crosslinked copolymers in a good approximation: $$\mathrm{1}\mathrm{/}{\mathrm{T}}_{\mathrm{G}}\mathrm{=}{\mathrm{x}}^{\mathrm{1}}\mathrm{/}{{\mathrm{T}}_{\mathrm{G}}}^{\mathrm{1}}\mathrm{+}{\mathrm{x}}^{\mathrm{2}}\mathrm{/}{{\mathrm{T}}_{\mathrm{G}}}^{\mathrm{2}}\mathrm{+}\mathrm{...}\mathrm{,}\mathrm{+}{\mathrm{x}}^{\mathrm{n}}\mathrm{/}{{\mathrm{T}}_{\mathrm{G}}}^{\mathrm{n}}\mathrm{.}$$

where x ¹ , x ² , .... x ^{n are} the mass fractions of the monomers 1, 2, .... n and T _g ¹ , T _g ² , .... Tg ⁿ the glass transition temperatures of each of only one of the monomers 1, 2, .... n constructed polymers in degrees Kelvin. The T _g values for the homopolymers of most monomers are known and z. In Ullmann's Encyclopedia of Industrial Chemistry, Vol. 5, Vol. A21, page 169, VCH Weinheim, 1992 listed. Other sources of glass transition temperatures of homopolymers form z. B. J. Brandrup, EH Immergut, Polymer Handbook, 1st Ed., J. Wiley, New York, 1966 . 2nd Ed., J. Wiley, New York, 1975 , and 3rd Ed., J. Wiley, New York, 1989 ,

A person skilled in the art is familiar with the aid of the abovementioned literature on how anionic latices having the corresponding glass transition temperature are obtained by the choice of monomers.

1. (1) Styrol und/oder Acrylnitril oder Methacrylnitril,
2. (2) Acrylsäureestern und/oder Methacrylsäureestern von C₁- bis C₁₀-Alkoholen, und gegebenenfalls
3. (3) Acrylsäure, Methacrylsäure, Maleinsäure und/oder Itaconsäure.

Preferred anionic latexes of this first embodiment are, for example, aqueous dispersions

1. (1) styrene and / or acrylonitrile or methacrylonitrile,
2. (2) acrylic acid esters and / or methacrylic acid esters of C ₁ to C ₁₀ alcohols, and optionally
3. (3) acrylic acid, methacrylic acid, maleic acid and / or itaconic acid.

• (1) Styrol und/oder Acrylnitril,
• (2) Acrylsäureestern von C₁- bis C₄-Alkoholen, und gegebenenfalls
• (3) Acrylsäure.

Particularly preferred are aqueous dispersions of anionic latices

• (1) styrene and / or acrylonitrile,
• (2) acrylic acid esters of C ₁ to C ₄ alcohols, and optionally
• (3) acrylic acid.

For example, such particularly preferred polyacrylate latices contain 2-20% by weight of styrene, 2-20% by weight of acrylonitrile, 60-95% by weight of C ₁ -C ₄ -alkyl acrylates, preferably C ₄ -acrylates such as n-butyl acrylate , Isobutyl acrylate and / or tert. Butyl acrylate and 0-5 wt .-% acrylic acid.

In a second embodiment of the present invention, in addition to the abovementioned monomers, the anionic latex comprises, in copolymerized form, at least one monomer comprising phosphono and / or phosphoric acid groups, both monomers having a free acid group and salts, esters and / or anhydrides thereof can.

X

eine geradkettige oder verzweigte C₂-C₆-Alkylenoxideinheit und

n

eine ganze Zahl von 0 bis 20

bedeuten.Preference is given to using phosphon- and / or phosphoric acid-group-containing monomers which are obtainable by esterification of monoethylenically unsaturated C ₃ -C ₈ -carboxylic acids with optionally monoalkoxylated phosphonic and / or phosphoric acids. Particular preference is given to monoalkoxylated phosphoric acid group-containing monomers which are obtained by esterification of monoethylenically unsaturated C ₃ -C ₈ -carboxylic acids with optionally monoalkoxylated phosphoric acids of the general formula (VIII)

H- [X] _n -P (O) (OH) ₂ (VIII)

are available in which

X

a straight-chain or branched C ₂ -C ₆ -alkylene oxide unit and

n

an integer from 0 to 20

mean.

Preference is given to using monoalkoxylated phosphoric acids of the formula (VIII) in which X is a straight-chain or branched C ₂ -C ₃ -alkylene oxide unit, and n is an integer between 5 and 15. Particularly preferably, X is an ethylene or propylene oxide unit, more preferably a propylene oxide unit.

Of course, any mixtures of different optionally monoalkoxylated phosphonic acids and optionally monoalkoxylated phosphoric acids of the formula (VIII) for esterification with a monoethylenically unsaturated C ₃ -C ₈ carboxylic acid can be used. Preference is given to mixtures of monoalkoxylated Phosphoric acids of the formula (VIII) are used which contain the same alkylene oxide unit, preferably propylene oxide, but have a different degree of alkoxylation, preferably degree of propoxylation. Particularly preferred mixtures of monoalkoxylated phosphoric acids contain 5-15 units of propylene oxide, ie n is an integer between 5 and 15.

For the preparation of the monomers containing phosphonic and / or phosphoric acid groups, monoethylenically unsaturated carboxylic acids having 3 to 8 carbon atoms are esterified with the abovementioned optionally monoalkoxylated phosphonic and / or phosphoric acids, preferably with the optionally monoalkoxylated phosphoric acids of the general formula (VIII). Such monoethylenically unsaturated C ₃ -C ₈ -carboxylic acids are, for example, acrylic acid, methacrylic acid, dimethylacrylic acid, ethacrylic acid, maleic acid, citraconic acid, methylenemalonic acid, crotonic acid, fumaric acid, mesaconic acid and itaconic acid. Preference is given to using acrylic acid and methacrylic acid.

Of course, mixtures of monoethylenically unsaturated C ₃ -C ₈ carboxylic acids for esterification with optionally monoalkoxylated phosphonic and / or phosphoric acids, preferably with optionally monoalkoxylated phosphoric acids of the formula (VIII) can be used. However, preference is given to using only one monoethylenically unsaturated carboxylic acid, for example acrylic acid or methacrylic acid.

• (1) Styrol und/oder Acrylnitril oder Methacrylnitril,
• (2) Acrylsäureestern und/oder Methacrylsäureestern von C₁- bis C₁₀-Alkoholen, und gegebenenfalls
• (3) Acrylsäure, Methacrylsäure, Maleinsäure und/oder Itaconsäure, und
• (4) (Meth)acrylsäureestern von gegebenenfalls monoalkyoxylierten Phosphorsäuren der Formel (VIII), worin X und n die zuvor genannte Bedeutung haben.

Preferred anionic latexes of this second embodiment are, for example, aqueous dispersions

• (1) styrene and / or acrylonitrile or methacrylonitrile,
• (2) acrylic acid esters and / or methacrylic acid esters of C ₁ to C ₁₀ alcohols, and optionally
• (3) acrylic acid, methacrylic acid, maleic acid and / or itaconic acid, and
• (4) (meth) acrylic esters of optionally monoalkyoxylated phosphoric acids of the formula (VIII) in which X and n have the abovementioned meaning.

• (1) Styrol und/oder Acrylnitril,
• (2) Acrylsäureestern von C₁- bis C₄-Alkoholen, und gegebenenfalls
• (3) Acrylsäure, und
• (4) (Meth)acrylsäureestern von monoalkoxylierten Phosphorsäuren der Formel (VIII), worin X eine Propylenoxideinheit ist, und n eine ganze Zahl zwischen 5 und 15 ist.

Particularly preferred are aqueous dispersions of anionic latices

• (1) styrene and / or acrylonitrile,
• (2) acrylic acid esters of C ₁ to C ₄ alcohols, and optionally
• (3) acrylic acid, and
• (4) (meth) acrylic acid esters of monoalkoxylated phosphoric acids of the formula (VIII), wherein X is a propylene oxide unit, and n is an integer between 5 and 15.

For example, such particularly preferred polyacrylate latexes contain 2-25% by weight of styrene, 2-25% by weight of acrylonitrile, 50-95% by weight of C ₁ -C ₄ -alkyl acrylates, preferably C ₄ -acrylates such as n-butyl acrylate , Isobutyl acrylate and / or tert. Butyl acrylate, 0-5% by weight of acrylic acid and 0.1-5% by weight of (meth) acrylic acid esters of monoalkoxylated phosphoric acids of the formula (VIII) wherein X is a propylene oxide unit, and n is an integer between 5 and 15.

Usually, the glass transition temperature (measured by DSC) of the anionic latices of the second embodiment is in the range of -40 to + 50 ° C. Anionic latices having a glass transition temperature of from -20 to +20 ° C. and particularly preferably from -10 to +10 ° C. are preferably used in the aqueous slurries of finely divided fillers according to the invention.

Independently of the abovementioned two embodiments, the anionic latices are generally prepared by emulsion polymerization, and are therefore an emulsion polymer. The preparation of aqueous polymer dispersions by the process of free-radical emulsion polymerization is known per se (cf. Houben-Weyl, Methods of Organic Chemistry, Volume XIV, Macromolecular Substances, loc. cit., pages 133ff ).

In the emulsion polymerization for the preparation of latices, ionic and / or nonionic emulsifiers and / or protective colloids or stabilizers are used as surface-active compounds. The surface-active substance is usually used in amounts of from 0.1 to 10% by weight, in particular from 0.2 to 3% by weight, based on the monomers to be polymerized.

Common emulsifiers are z. B. ammonium or alkali metal salts of higher fatty alcohol sulfates, such as Na-n-lauryl sulfate, fatty alcohol phosphates, ethoxylated C ₈ - to C ₁₀ alkylphenols having a degree of ethoxylation of 3 to 30 and ethoxylated C ₈ - to C ₂₅ -fatty alcohols having a degree of ethoxylation of 5 to 50. Also conceivable are mixtures of nonionic and ionic emulsifiers. Also suitable are phosphate- or sulfate-containing, ethoxylated and / or propoxylated alkylphenols and / or fatty alcohols. Other suitable emulsifiers are in Houben-Weyl, Methods of Organic Chemistry, Volume XIV, Macromolecular Materials, Georg Thieme Verlag, Stuttgart, 1961, pages 192 to 209 listed.

Water-soluble initiators for the emulsion polymerization for the preparation of latices are, for. For example, ammonium and alkali metal salts of peroxodisulfuric, z. For example, sodium peroxodisulfate, hydrogen peroxide or organic peroxides, z. B. tert-butyl hydroperoxide. Also suitable are so-called reduction-oxidation (red-ox) initiator systems.

The amount of initiators is generally 0.1 to 10 wt .-%, preferably 0.5 to 5 wt .-%, based on the monomers to be polymerized. It is also possible to use a plurality of different initiators in the emulsion polymerization.

In the emulsion polymerization regulators can be used, for. B. in amounts of 0 to 3 parts by weight, based on 100 parts by weight of the monomers to be polymerized, by which the molecular weight is reduced. Suitable z. B. Compounds with a thiol group such as tert-butylmercaptan, thioglycolic acid ethylacrylic ester, mercaptoethynol, mercaptopropyltrimethoxysilane or tert-dodecylmercaptan or regulator without thiol group, in particular z. B. terpinolene.

The emulsion polymerization for preparing the latexes is generally carried out at 30 to 130 ° C, preferably at 50 to 100 ° C. The polymerization medium may consist of water only, as well as of mixtures of water and thus miscible liquids such as methanol. Preferably, only water is used. The emulsion polymerization can be carried out both as a batch process and in the form of a feed process, including a stepwise or gradient procedure. Preferably, the feed process in which one submits a portion of the polymerization, heated to the polymerization, polymerized and then the rest of the polymerization, usually over several spatially separate feeds, one or more of which monomers in pure or in emulsified form, continuously , gradually or with the addition of a concentration gradient while maintaining the polymerization of the polymerization zone supplies. In the polymerization can also z. B. be presented for better adjustment of the particle size of a polymer seed.

The manner in which the initiator is added to the polymerization vessel in the course of the free radical aqueous emulsion polymerization is known to one of ordinary skill in the art. It can be introduced both completely into the polymerization vessel, or used continuously or in stages according to its consumption in the course of the free radical aqueous emulsion polymerization. In detail, this depends on the chemical nature of the initiator system as well as on the polymerization temperature. Preferably, a part is initially charged and the remainder supplied according to the consumption of the polymerization.

To remove the residual monomers is usually after the end of the actual emulsion polymerization, d. H. after a conversion of the monomers of at least 95%, initiator added.

The individual components can be added to the reactor in the feed process from above, in the side or from below through the reactor bottom.

Following the copolymerization, the acid groups contained in the latex can still be at least partially neutralized. This can be done, for example, with oxides, hydroxides, carbonates or bicarbonates of alkali metals or alkaline earth metals, preferably with hydroxides to which any one or more counterions may be associated, eg Li ⁺ , Na ⁺ , K ⁺ , Cs ⁺ , Mg ²⁺ , Ca ^{2 +} or Ba ²⁺ . Also suitable for neutralization are ammonia or amines. Preference is given to aqueous ammonium hydroxide, sodium hydroxide or potassium hydroxide solutions.

In the emulsion polymerization, aqueous dispersions of the latex are generally obtained with solids contents of from 15 to 75% by weight, preferably from 40 to 75% by weight.

The particle size of the latices is preferably in the range of 10 to 1000 nm, more preferably in the range of 50 to 300 nm (measured using a Malvern ^® Autosizer 2 C).

The anionic polymers which can be used according to the invention comprise at least one anionic latex and at least one degraded starch. As described above, the degraded starches have an average molecular weight M _{w of} from 1,000 to 65,000 g / mol. The average molecular weights _{M.sub.w of} the degraded starches can easily be determined by methods known to the person skilled in the art, eg. By gel permeation chromatography using a multi-angle light scattering detector.

To obtain such a starch, one can start with all types of starch, e.g. of native, anionic, cationic or amphoteric starch. The starch can e.g. derived from potatoes, maize, wheat, rice, tapioca, sorghum, or may be waxy starches having an amylopectin content of> 80, preferably> 95% by weight, such as waxy maize starch or waxy potato starch. The starches may be anionically and / or cationically modified, esterified, etherified and / or crosslinked. Preference is given to cationized starches.

If the molecular weight M _{w of} the starches is not already in the range of 1,000 to 65,000 g / mol, they are subjected to molecular weight degradation. This molecular weight reduction can be carried out oxidatively, thermally, acidolytically or enzymatically. Preference is given to a procedure in which a starch is degraded enzymatically and / or oxidatively. The molecular weight Mw of the degraded starch is preferably in the range of 2,500 to 35,000 g / mol.

Particularly preferred is the use of anionic or cationic starches. Such strengths are known. Anionic starches are accessible, for example, by oxidation of native starches. Cationic starches are obtained, for example, by reacting native starch with at least one quaternizing agent, such as 2,3-Epoxipropyltrimethylammoniumchlorid prepared. The cationized starches contain quaternary ammonium groups.

The proportion of cationic or anionic groups in substituted starch is indicated by means of the degree of substitution (DS). It is, for example, 0.005 to 1.0, preferably 0.01 to 0.4.

You can use a single degraded starch or mixtures of two or more degraded starches.

In a particularly preferred form, maltodextrins are used as degraded starch. For the purposes of the present invention, maltodextrins are water-soluble carbohydrates obtained by enzymatic degradation of starch, which consist of glucose units and have a dextrose equivalent.

The anionic polymers may be prepared in various ways from the at least one anionic latex and the at least one degraded starch. For example, the anionic latex is first prepared by emulsion polymerization from the aforementioned monomers. Subsequently, the degraded starch is added and the components are mixed together. The addition of the degraded starch is usually carried out at room temperature. It is also possible that the degraded starch is added to the aforementioned monomers and the emulsion polymerization thereby takes place in the presence of the degraded starch.

As pulps for the production of the pulps, all qualities which are customary for this purpose can be considered, e.g. Pulp, bleached and unbleached pulp and pulps from all annual plants. Wood pulp includes, for example, groundwood, thermomechanical pulp (TMP), chemo-thermo-mechanical pulp (CTMP), pressure groundwood, semi-pulp, high yield pulp, and refiner mechanical pulp (RMP). As pulp, for example, sulphate, sulphite and soda pulps come into consideration. Preferably, unbleached pulp, also referred to as unbleached kraft pulp, is used. Suitable annual plants for the production of pulps are, for example, rice, wheat, sugar cane and kenaf. Waste pulp is most often used to make the pulps, either alone or in admixture with other pulps, or by starting from fiber blends of primary and recycled coated broke, e.g. bleached pine sulfate in admixture with reclaimed coated broke.

The process according to the invention is of technical interest for the production of paper and board from recycled paper, because it significantly increases the strength properties of the recycled fibers and has special significance for the improvement Strength properties of graphic papers and packaging papers. The papers obtainable by the process according to the invention surprisingly have a higher dry strength than those according to the process of the earlier European application with the file reference 09 150 237.7 manufacturable papers. At the same time, the retention of the fillers and fillers from the material used for the production is significantly increased by the inventive method, without the strength properties of the paper are adversely affected.

The pH of the stock suspension is, for example, in the range of 4.5 to 8, usually 6 to 7.5. To adjust the pH, it is possible to use, for example, an acid, such as sulfuric acid or aluminum sulphate.

In the method according to the invention, the cationic polymer is preferably first metered to the paper stock. The cationic polymer can be added to the thick material (fiber concentration> 15 g / l, for example in the range from 25 to 40 g / l up to 60 g / l) or preferably to a thin material (fiber concentration <15 g / l, eg in in the range of 5 to 12 g / l). The point of addition is preferably in front of the screens, but may also be between a shearing stage and a screen or afterwards. The anionic polymer is preferably added to the paper stock only after the cationic polymer has been added, but it may also be metered into the stock at the same time but separately from the cationic polymer. Furthermore, it is also possible first to add the anionic and subsequently the cationic polymer.

The cationic polymer is used, for example, in an amount of 0.03 to 2.0 wt .-%, preferably 0.1 to 0.5 wt .-%, based on dry pulp. The water-insoluble anionic polymer is e.g. in an amount of 0.5 to 10 wt .-%, preferably 1 to 6 wt .-%, in particular from 2.5 to 5.5 wt .-%, based on dry pulp, used.

The weight ratio of water-soluble cationic polymer to water-insoluble anionic polymer is, for example, 1: 5 to 1:20, based on the solids content, and is preferably in the range of 1:10 to 1:15, and more preferably in the range of 1:10 to 1:12.

In the method according to the invention, the process chemicals commonly used in papermaking can be used in the usual amounts, for example retention agents, dehydrating agents, other dry strength agents such as starch, pigments, fillers, optical brighteners, defoamers, biocides and paper dyes.

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

Examples

The percentages in the examples are by weight unless otherwise indicated in the context.

The K value of the polymers was after Fikentscher, Cellulose-Chemie, Vol. 13, 58-64 and 71-74 (1932 ) at a temperature of 20 ° C in 5 wt .-% saline solutions at a pH of 7 and a polymer concentration of 0.5%. Where K = k × 1000.

Cationic polymer A

This polymer was prepared by hydrolysis of a poly-N-vinylformamide with hydrochloric acid. The degree of hydrolysis of the polymer was 50 mole%, i. the polymer contained 50 mole% of N-vinylformamide units and 50 mole% of vinylamine units in salt form. The K value of the water-soluble cationic polymer was 90.

Cationic polymer B

Preparation as described under cationic polymer A, except that the degree of hydrolysis of the polymer was 30 mol%. The water-soluble cationic polymer B contained 70 mol% of N-vinylformamide units and 30 mol% of vinylamine units in salt form. The K value of the water-soluble cationic polymer was 90.

Anionic polymer 1

411.6 g of demineralized water, 14.6 g of a polystyrene seed (solids content 33%, mean particle size 29 nm) and 1.4 g of a 45% strength by weight solution of dodecylphenoxybenzenedisulfonic acid sodium salt (in an anchor plate stirrer equipped with anchor stirrer ( Dowfax® 2A1, Dow Chemicals) and 15.4 g of a 7 wt .-% solution of sodium peroxydisulfate submitted. Via a controlled, external oil bath, the reaction vessel was heated to 93 ° C. with stirring. After reaching the temperature, a previously prepared monomer emulsion consisting of 534.4 g of deionized water, 22.4 g of a 15 wt .-% solution of sodium lauryl sulfate (Disponil ^® SDS 15, Cognis), 8 g of a 45 wt .-% Solution of Dodecylphenoxybenzoldisulfonsäure sodium salt (Dowfax ^® 2A1, Dow Chemicals), 12 g of a 10 wt .-% solution of sodium hydroxide, 35 g of acrylic acid, 168 g of styrene, 829 g of n-butyl acrylate and 168 g of acrylonitrile uniformly within 2 hours and 45 Minutes added. In parallel, 49.7 g of a 7 wt .-% solution of sodium peroxydisulfate were added. The batch was stirred while maintaining the temperature for a further 45 minutes. Subsequently, 93.6 g of a 10% by weight solution of sodium hydroxide were added and the reaction contents were cooled to 60 ° C. Subsequently, two feeds were in parallel consisting of a) 24 g of a 10 wt .-% solution of tert-butyl hydroperoxide and b) 33 g of a 13 wt .-% solution containing the addition product of 2.67 g of sodium and 1.62 g Acetone added within 30 minutes. The reactor contents were cooled to room temperature.

A practically coagulate-free polymer dispersion having a solids content of 51% by weight was obtained. The polymer had a TLC measured glass transition temperature of + 5 ° C.

By adding 810 g of deionized water, the solids content was lowered to 30% by weight. Subsequently, 404 g of a 30 wt .-% solution of a maltodextrin (Fa. Cargill MD 09015 ^®) were added.

The resulting blend had a solids content of 30% by weight and a pH of 6.5.

Anionic polymer 2

Polymer 2 was prepared analogously to polymer 1, but a mixture of maltodextrin diluted to 30% by weight (from Cerestar, strength 019 S1) was used in the blending.

Anionic polymer 3

411.6 g of demineralized water, 14.6 g of a polystyrene seed (solids content 33%, mean particle size 29 nm) and 1.4 g of a 45% strength by weight solution of sodium dodecylphenoxybenzenedisulfonate (in FIG. Dowfax ^® 2A1, Dow Chemicals) and 15.4 g of a 7 wt .-% solution of sodium peroxydisulfate presented. Via a controlled, external oil bath, the reaction vessel was heated to 93 ° C. with stirring. After reaching the temperature, a previously prepared monomer emulsion consisting of 534.4 g of deionized water, 22.4 g of a 15 wt .-% solution of sodium lauryl sulfate (Disponil ^® SDS 15, Cognis), 8 g of a 45 wt .-% Solution of Dodecylphenoxybenzoldisulfonsäure sodium salt (Dowfax ^® 2A1, Dow Chemicals), 12 g of a 10 wt .-% solution of sodium hydroxide, 36 g of acrylic acid, 60 g of styrene, 1044 g of n-butyl acrylate and 60 g of acrylonitrile dosed evenly over 2 hours , In parallel, 49.8 g of a 7 wt .-% solution of sodium peroxydisulfate were added in 2.5 hours. The approach was keeping the temperature constant stirred for another 45 minutes. Subsequently, 93.6 g of a 10% by weight solution of sodium hydroxide were added and the reaction contents were cooled to 60 ° C. Subsequently, two feeds were in parallel consisting of a) 24 g of a 10 wt .-% solution of tert-butyl hydroperoxide and b) 33 g of a 13 wt .-% solution containing the addition product of 2.67 g of sodium and 1.62 g Acetone added within 30 minutes. The reactor contents were cooled to room temperature.

A practically coagulate-free polymer dispersion having a solids content of 50% by weight was obtained. The polymer had a glass transition temperature of -25 ° C as measured by DSC.

By adding 810 g of deionized water, the solids content was lowered to 30% by weight. Subsequently, 404 g of a 30 wt .-% solution of a maltodextrin (Fa. Cargill MD 09015 ^®) were added.

The resulting blend had a solids content of 30% by weight and a pH of 6.4.

Anionic polymer 4

In a 41 flattened vessel equipped with anchor stirrer, 340.8 g of demineralized water, 14.6 g of a polystyrene seed (solids content 33%, mean particle size 29 nm) and 1.4 g of a 45% strength by weight solution of sodium dodecylphenoxybenzenedisulfonate ( Dowfax ^® 2A1, Dow Chemicals) and 15.4 g of a 7 wt .-% solution of sodium peroxydisulfate presented. Via a controlled, external oil bath, the reaction vessel was heated to 93 ° C. with stirring. After reaching the temperature, a previously prepared monomer emulsion consisting of 483.6 g of deionized water, 22.4 g of a 15 wt .-% solution of sodium lauryl sulfate (Disponil ^® SDS 15, Cognis), 8 g of a 45 wt .-% solution of Dodecylphenoxybenzoldisulfonsäure sodium salt (Dowfax ^® 2A1, Dow Chemicals), 12 g of a 10 wt .-% solution of sodium hydroxide, 12 g of a methacrylic acid ester having a terminally esterified with phosphoric acid Oligopropylenoxid (Sipomer ^® PAM 200: CH ₂ = C (CH ₃ ) -COO- (CH ₂ CH (CH ₃ ) O) _8-10 -P (O) (OH) ₂ , Rhodia), 24 g of acrylic acid, 168 g of styrene, 828 g of n-butyl acrylate and 168 g of acrylonitrile uniformly within metered in from 2 hours and 45 minutes. In parallel, 87 g of a 4 wt .-% solution of sodium peroxydisulfate were added. The batch was stirred while maintaining the temperature for a further 45 minutes. Subsequently, 62.4 g of a 10 wt .-% solution of sodium hydroxide was added, and the reaction contents cooled to 60 ° C. Subsequently, two feeds consisting of a) 80 g of a 3 wt .-% solution of tert-butyl hydroperoxide and b) 53.4 g of deionized water with 33 g of a 13 wt .-% solution containing the addition product of parallel 2.67 g of sodium disulfite and 1.62 g of acetone added within 30 minutes. The reactor contents were cooled to room temperature.

A practically coagulate-free polymer dispersion having a solids content of 50% by weight was obtained. The polymer had a TLC measured glass transition temperature of + 4 ° C.

By adding 810 g of deionized water, the solids content was lowered to 30% by weight. Subsequently, 404 g of a 30 wt .-% solution of a maltodextrin (Fa. Cargill MD 09015 ^®) were added.

The resulting blend had a solids content of 30% by weight, a pH of 6.5 and a particle size of 137 nm measured by dynamic light scattering (Malvern HPPS).

Anionic polymer 5

In a 41 flattened vessel equipped with anchor stirrer, 1064.6 g of demineralized water, 7.2 g of a polystyrene seed (solids content 33%, mean particle size 29 nm), 0.6 g of a 45% strength by weight solution of sodium dodecylphenoxybenzenedisulfonate ( submitted Dowfax ^® 2A1, Dow Chemicals) and 240.0 g maltodextrin (Fa. Cargill MD 09015 ^®) and 7.8 g of a 7 wt .-% solution of sodium peroxodisulfate. Via a controlled, external oil bath, the reaction vessel was heated to 93 ° C. with stirring. After reaching the temperature, a previously prepared monomer emulsion consisting of 267.2 g of deionized water, 11.2 g of a 15 wt .-% solution of sodium lauryl sulfate (Disponil ^® SDS 15, Cognis), 4 g of a 45 wt .-% Solution of Dodecylphenoxybenzoldisulfonsäure sodium salt (Dowfax ^® 2A1, Dow Chemicals), 6 g of a 10 wt .-% solution of sodium hydroxide, 18 g of acrylic acid, 84 g of styrene, 414 g of n-butyl acrylate and 84 g of acrylonitrile dosed evenly over 2 hours , In parallel, 34.8 g of a 2.5 wt .-% solution of sodium peroxydisulfate were added within 2.5 hours. The batch was stirred while maintaining the temperature for a further 45 minutes. Subsequently, 46.8 g of a 10% by weight solution of sodium hydroxide were added and the reaction contents were cooled to 60 ° C. Subsequently, two feeds were in parallel consisting of a) 30 g of a 2 wt .-% solution of tert-butyl hydroperoxide and b) 55.6 g of deionized water with 16.4 g of a 13 wt .-% solution containing the addition product of 2, 67 g of sodium disulfite and 1.62 g of acetone added within 30 minutes. The reactor contents were cooled to room temperature.

A practically coagulate-free polymer dispersion having a solids content of 29.3% by weight, a pH of 6.1, was obtained. The polymer had a DSC measured Glass transition temperature of + 5 ° C. The particle size measured by dynamic light scattering (Malvern HPPS) was 149 nm.

Preparation of a pulp suspension

From 100% mixed waste paper, a 0.5% aqueous pulp suspension was prepared. The pH of the suspension was 7.1, the freeness of the substance 50 ° Schopper-Riegler (° SR). The stock suspension was then divided into eight equal parts and in Examples 1 to 6 and in Comparative Examples 1 and 2 under the conditions specified in the Examples and Comparative Examples on a Rapid Köthen sheet former according to ISO 5269/2 to sheets of a basis weight of 120 gsm processed.

example 1

The temperature of the paper stock suspension was about 20 ° C. To the stock suspension was added 0.25% of polymer A (polymer, based on dry pulp). After a reaction time of 5 minutes, the dispersion of the anionic polymer 1 was diluted by a factor of 10. The diluted dispersion was then metered into the pulp suspension with gentle stirring. The amount of anionic polymer 1 used was 5% (polymer solid, based on dry pulp). After an exposure time of 1 minute leaves were formed, which were then dried at 90 ° C for 7 minutes.

Example 2

The temperature of the paper stock suspension was about 20 ° C. 0.25% of polymer B (polymer, based on dry pulp) was added to the stock suspension. After a reaction time of 5 minutes, the dispersion of the anionic polymer 1 was diluted by a factor of 10. The diluted dispersion was then metered into the pulp suspension with gentle stirring. The amount of anionic polymer 1 used was 5% (polymer solid, based on dry pulp). After an exposure time of 1 minute leaves were formed, which were then dried at 90 ° C for 7 minutes.

Example 3

Example 3 was carried out analogously to Example 2, but the anionic polymer 2 was used.

Example 4

Example 4 was carried out analogously to Example 2, but the anionic polymer 3 was used.

Example 5

Example 5 was carried out analogously to Example 2, but the anionic polymer 4 was used.

Example 6

Example 6 was carried out analogously to Example 2, but the anionic polymer 5 was used.

Comparative Example 1 (Comparison with the earlier European application with the file reference 09 150 237.7)

The stock was heated to a temperature of 50 ° C. To the thus heated stock suspension was added 0.25% of polymer B (polymer, based on dry pulp). After a reaction time of 5 minutes, the dispersion of an anionic acrylate resin (solid content 50%) obtainable by the suspension polymerization of 68 mol% of n-butyl acrylate, 14 mol% of styrene, 14 mol% of acrylonitrile and 4 mol% of acrylic acid was increased by a factor 10 diluted. The mean particle size of the dispersed polymer particles was 192 nm. Subsequently, the dilute dispersion was metered into the pulp suspension heated to 50 ° C. with gentle stirring. The amount of acrylate used was 5% (polymer solid, based on dry pulp). After an exposure time of 1 minute leaves were formed, which were then dried at 90 ° C for 7 minutes.

Comparative Example 2

From the stock suspension described above, which had a temperature of 20 ° C, a sheet was formed without further additions.

Examination of the paper sheets

After a storage time of the sheets produced according to Examples 1 to 6 and Comparative Examples 1 and 2 in a climate chamber at a constant 23 ° C and 50% humidity for 12 hours, the dry breaking length of the sheets was determined according to DIN 54540. The determination of the CMT value of the air-conditioned sheets was carried out according to DIN 53143, the dry burst pressure of the leaves was determined according to DIN 53141. The results are shown in Table 1. Table 1 example Dry breaking length [m] Burst pressure [kPa] CMT30 [N] Filler content [%] 1 5632 586 291 11.7 2 5455 558 276 11.3 3 5491 545 269 10.7 4 5521 534 265 10.1 5 5412 565 271 11.1 6 5491 542 266 10.4 Comparative Example 1 4987 506 244 7.8 Comparative Example 2 3376 288 146 6.1

The examples and comparative examples show that the sheets according to the comparative examples have inferior strength properties despite lower filler content.

Claims (13)

1. A process for the production of paper, board and cardboard having high dry strength by addition of a water-soluble cationic polymer and of an anionic polymer to a paper stock, draining of the paper stock and drying of the paper products, wherein an aqueous dispersion of at least one anionic latex and at least one degraded starch which has an average molecular weight M_w of from 1000 to 65 000 g/mol is used as the anionic polymer.
2. The process according to claim 1, wherein the molar mass M_w of the cationic polymers is in the range from 5000 to 5 million g/mol.
3. The process according to claim 1 or 2, wherein the charge densities of the cationic polymers are in the range from 0.5 to 23 meq/g of polymer.
4. The process according to any of the preceding claims, wherein the water-soluble cationic polymer used is a polymer having vinylamine units.
5. The process according to any of claims 1 to 4, wherein the anionic latices consist of

   a) styrene and/or acrylonitrile or methacrylonitrile,

   b) acrylates and/or methacrylates of C1- to C10-alcohols and optionally

   c) acrylic acids, methacrylic acid, maleic acid and/or itaconic acid.
6. The process according to claim 5, wherein the anionic latices consist of 2 - 20% by weight of styrene, 2 - 20% by weight of acrylonitrile, 60 - 95% by weight of C₁-C₄-alkyl acrylates and 0 - 5% by weight of acrylic acid.
7. The process according to any of claims 1 to 4, wherein the anionic latex comprises at least one monomer comprising phosphonic and/or phosphoric acid groups, incorporated in the form of polymerized units.
8. The process according to claim 7, wherein monomers which comprise phosphoric acid groups and are obtainable by esterification of monoethylenically unsaturated C₃-C₈-carboxylic acids with optionally monoalkoxylated phosphoric acids of the general formula (VIII)
   
           H-[X]_n-P(O) (OH)₂     (VIII)
   
   where
   X is a straight-chain or branched C₂-C₆-alkylene oxide unit and
   n is an integer from 0 to 20,
   are used.
9. The process according to claim 8, wherein monoalkoxylated phosphoric acids of the formula (VIII), where X is a straight-chain or branched C₂-C₃-alkylene oxide unit and n is an integer from 5 to 15 are used.
10. The process according to claim 8, wherein the monoethylenically unsaturated C₃-C₈-carboxylic acid is acrylic acid, methacrylic acid, dimethylacrylic acid, methacrylic acid, maleic acid, citraconic acid, methylenemalonic acid, crotonic acid, fumaric acid, mesaconic acid and/or itaconic acid.
11. The process according to any of claims 7 to 10, wherein the anionic latices consist of

    (1) styrene and/or acrylonitrile or methacrylonitrile,

    (2) acrylates and/or methacrylates of C₁- to C₁₀-alcohols and optionally

    (3) acrylic acid, methacrylic acid, maleic acid and/or itaconic acid and

    (4) (meth)acrylates of optionally monoalkoxylated phosphoric acids of the formula (VIII), where X and n have the abovementioned meaning.
12. The process according to claim 11, wherein the anionic latices consist of 2 - 25% by weight of styrene, 2 - 25% by weight of acrylonitrile, 50 - 95% by weight of C₁-C₄-alkyl acrylates, 0 - 5% by weight of acrylic acid and 0.1 - 5% by weight of (meth)acrylates of monoalkoxylated phosphoric acids of the formula (VIII), where X is a propylene oxide unit and n is an integer from 5 to 15.
13. The process according to claim 12, wherein the degraded starch is a maltodextrin.