EP2491177B1 - Process for fabricating paper, paperboard and cardboard with high wet strength - Google Patents

Description

The invention relates to a process for the production of paper, cardboard and cardboard with high dry strength by adding an aqueous composition of a nanocellulose and at least one polymer selected from the group of anionic polymers and water-soluble cationic polymers, dewatering the paper stock and drying the paper products.

In order to increase the dry strength of paper, a dry strength agent can either be applied to the surface of a paper that has already dried or added to a paper stock before the sheet is formed. The dry strength agents are usually applied in the form of a 1 to 10% strength aqueous solution. If such a solution of a dry strength agent is applied to the surface of a paper, then considerable amounts of water must be evaporated in the subsequent drying process. Since the drying step is very energy-intensive and since the capacity of the usual drying devices 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 reduced so that the dry-proofed paper dries to a sufficient extent becomes.

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

Out WO 04/061235 A1 A process for the production of paper, in particular tissue, with particularly high wet and / or dry strengths is known, in which a water-soluble cationic polymer is first added to the paper stock, which contains at least 1.5 meq / g polymer of primary amino functionalities and a molecular weight of at least 10,000 daltons. Partly and completely hydrolyzed homopolymers of N-vinylformamide are particularly emphasized. A water-soluble anionic polymer is then added, which contains anionic and / or aldehydic groups. The main advantage of this process is the variability of the two-component systems described with regard to various paper properties, including wet and dry strength.

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 gegebenenfallsVerbindungen, die mindestens zwei ethylenisch ungesättigte Doppelbindungen im Molekül aufweisen.From the WO 06/056381 A1 is a process for the production of paper, cardboard and cardboard with high dry strength by separately adding a water-soluble vinylamine unit-containing polymer and a water-soluble polymeric anionic compound to a paper stock, dewatering the paper stock and drying the paper products, wherein the polymeric anionic compound comprises at least one water-soluble Copolymer used, which is obtainable by copolymerizing
at least one N-vinylcarboxamide of the formula (I)

in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,
at least one monoethylenically unsaturated monomer containing acid groups and / or its alkali metal, alkaline earth metal or ammonium salts, and optionally
other monoethylenically unsaturated monomers, and optionally compounds that 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 A process for the production of paper with high dry strength by separately adding a water-soluble cationic polymer and an anionic polymer to a paper stock is known, the anionic polymer being an aqueous dispersion of a water-insoluble polymer with an acid group content of at most 10 mol% or an anionic adjusted aqueous dispersion of a nonionic polymer. The paper stock is then dewatered and the paper products dried.

In the older European application with the file number EP 09 152 163.3 discloses a process for producing paper, cardboard and cardboard with high dry strength, which is also characterized by adding a water-soluble cationic polymer and an anionic polymerate to a paper stock, dewatering the paper stock and drying the paper products. It is called anionic Polymer used an aqueous dispersion of at least one anionic latex and at least one degraded starch.

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

The object is achieved according to the invention with a method for producing paper, cardboard and cardboard with high dry strength according to claim 1.

In this document, nanocellulose is understood to mean cellulose forms which are converted by a process step from the state of the natural fiber with the usual dimensions (length approx. 2000 - 3000 μm, thickness approx. 60 μm) into a form in which the thickness dimension is particularly strong is reduced.

The production of nanocellulose is known in the literature. For example, in WO 2007/091942 A1 discloses a grinding process which can be carried out using enzymes. Processes are also known in which the cellulose is first dissolved in suitable solvents and then precipitated as nanocellulose in the aqueous medium (for example described in WO 2003/029329 A2 ).

In addition, nanocelluloses are commercially available, for example the products sold by J. Rettenmeier & Söhne GmbH & Co. KG under the trade name Arbocel®.

The nanocelluloses which are used in the process according to the invention can be dissolved and used in any suitable solvent, for example in water, organic solvents or in any mixtures thereof. Such solvents can also contain other constituents such as ionic liquids in any amount.

Nanocelluloses which contain ionic liquids are produced, for example, by micronizing celluloses present in ionic liquids in the form of the natural fibers in one of the processes described above. Celluloses in the form of natural fibers, which are present in ionic liquids, are among others US 6,824,599 B2 known. Reference is hereby expressly made to the content of this US patent.

In particular, in this document nanocellulose should be understood to mean those celluloses whose linear expansion is below 1000 μm, preferably below 500 μm, but above 100 nm. The linear expansion is accordingly preferably between 100 nm and 500 μm, particularly between 100 nm and 100 μm, particularly preferably between 100 nm and 50 μm and in particular between 100 nm and 10 μm. The thickness of the cellulose is, for example, in the range between 50 μm and 3 nm. The thickness is preferably between 1 μm and 5 nm. The values given here for thickness and linear expansion are of course average values, for example at least 50% of the cellulose fibers are in the ranges and preferably at least 80% of the cellulose fibers are in the ranges specified.

The nanocellulose of the process according to the invention is a nanocellulose whose fiber thickness of at least 80% of the cellulose fibers is between 50 μm and 3 nm, preferably between 1 μm and 5 nm, and between 5 ppm and 2% by weight, preferably between 10 ppm and Contains 1% by weight of ionic liquids.

The present invention therefore also relates to such a nanocellulose whose fiber thickness of at least 80% of the cellulose fibers is between 50 μm and 3 nm, preferably between 1 μm and 5 nm, and between 5 ppm and 2% by weight, preferably between 10 ppm and 1 wt .-% contains ionic liquids.

The length extension and the thickness of the cellulose fibers can be determined, for example, using Cryo-TEM images. As described above, a nanocellulose that can be used in the method according to the invention has fiber thicknesses of up to 5 nm and length extensions of up to 10 mm. These nanocellulose fibers can also be called fibrillia, the smallest superstructure in cellulose-based substances (5-30 nm wide depending on the plant variety; degrees of polymerization up to 10,000 anhydroglycose units). They typically have high moduli of elasticity of up to several hundred GPa, and the strength of such fibrils is in the GPa range. The high stiffness is a result of the crystal structure in which the long parallel polysaccharide chains are held together by hydrogen bonds. The cryo-TEM method is known to the person skilled in the art. In this context, cryo-TEM means that the aqueous dipsersions of cellulose are frozen and measured by means of an electron transmission. In the aqueous medium, the nanocellulose fibers are typically present in intertwined networks of several fibers. This leads to a gel at the macroscopic level. This gel can be measured rheologically, showing that the memory module is larger in magnitude than the loss module. This gel behavior is typically already present at concentrations of 0.1 mass percent nanocellulose in water.

In the process according to the invention, aqueous slurries of nanocelluloses are used which contain 0.1 to 25% by weight of nanocellulose, based on the total weight of the aqueous slurry. The aqueous slurries preferably contain 1 to 20% by weight, particularly preferably 1 to 10% by weight and in particular 1 to 5% by weight of the nanocellulose.

In addition to nanocellulose, the aqueous compositions which can be used in the process according to the invention comprise at least one polymer which is selected from the group of anionic and water-soluble cationic polymers.

In a preferred embodiment of the method according to the invention, the aqueous composition contains at least one anionic polymer in addition to the nanocellulose. It is also possible that the aqueous composition contains at least one water-soluble cationic polymer in addition to the nanocellulose and the anionic polymer.

In another embodiment of the method according to the invention, the aqueous composition contains a water-soluble cationic polymer in addition to the nanocellulose.

The anionic polymers for the purposes of this invention are practically insoluble in water. For example, at a pH of 7.0 under normal conditions (20 ° C, 1013 mbar) at most 2.5 g polymer / liter of water, mostly at most 0.5 g / l and preferably not more than 0.1 g / l. The dispersions are anionic due to the content of acid groups in the polymer. The water-insoluble polymer has, for example, an acid group content of 0.1 to 10 mol%, usually 0.5 to 9 mol% and preferably 0.5 to 6 mol%, in particular 2 to 6 mol%. The content of acid groups in the anionic polymer is usually 2 to 4 mol%.

The acid groups of the anionic polymer are selected, for example, from carboxyl, sulfonic acid and phosphonic acid groups. Carboxyl groups are particularly preferred.

1. (a) mindestens ein Monomer aus der Gruppe von C₁- bis C₂₀-Alkylacrylaten, C₁- bis C₂₀-Alkylmethacrylaten, Vinylestern von bis zu 20 C-Atome enthaltenden gesättigten Carbonsäuren, Vinylaromaten mit bis zu 20 C-Atomen, ethylenisch ungesättigten Nitrilen, Vinylethern von 1 bis 10 C-Atome enthaltenden gesättigten, einwertigen Alkoholen, Vinylhalogeniden und aliphatischen Kohlenwasserstoffen mit 2 bis 8 C-Atomen und ein oder zwei Doppelbindungen,
2. (b) mindestens ein anionisches Monomer aus der Gruppe der ethylenisch ungesättigten C₃- bis C₈-Carbonsäuren, Vinylsulfonsäure, Acrylamido-2-methylpropansulfonsäure, Styrolsulfonsäure, Vinylphosphonsäure sowie deren Salze,
3. (c) gegebenenfalls mindestens ein Monomer aus der Gruppe der C₁- bis C₁₀-Hydroxyalkylacyrylate, C₁- bis C₁₀-Hydroxyalkylmethacyrylate, Acrylamid, Methacrylamid, N-C₁-bis C₂₀-Alkylacrylamide und N-C₁-bis C₂₀-Alkylmethacrylamide, und
4. (d) gegebenenfalls mindestens eine Monomer mit mindestens zwei ethylenisch ungesättigten Doppelbindungen im Molekül einpolymerisiert.

The anionic polymers contain

1. (a) at least one monomer from the group of C ₁ - to C ₂₀ alkyl acrylates, C ₁ - to C ₂₀ alkyl methacrylates, vinyl esters of saturated carboxylic acids containing up to 20 C atoms, vinyl aromatics with up to 20 C atoms, ethylenic unsaturated nitriles, vinyl ethers of saturated to 1 to 10 carbon atoms, monohydric alcohols, vinyl halides and aliphatic hydrocarbons with 2 to 8 carbon atoms and one or two double bonds,
2. (b) at least one anionic monomer from the group of ethylenically unsaturated C ₃ to C ₈ carboxylic acids, vinylsulfonic acid, acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylphosphonic acid and salts thereof,
3. (c) optionally at least one monomer from the group of the C ₁ to C ₁₀ hydroxyalkylacyrylates, C ₁ to C ₁₀ hydroxyalkyl methacrylates, acrylamide, methacrylamide, NC _{1 to} C ₂₀ alkyl acrylamides and NC _{1 to} C ₂₀ alkyl methacrylamides , and
4. (d) optionally polymerized at least one monomer with at least two ethylenically unsaturated double bonds in the molecule.

The anionic polymers contain at least 60 mol% and in particular at least 80 mol% of at least one monomer from group (a) polymerized. These monomers are practically water-insoluble or, when homopolymerized with them, give water-insoluble polymers.

The anionic polymers contain, as monomer of group (a), mixtures of (i) a C ₁ to C ₂₀ alkyl acrylate and / or a C ₁ to C ₂₀ alkyl methacrylate and (ii) styrene, α-methylstyrene, p-methylstyrene , α-butylstyrene, 4-n-butylstyrene, butadiene and / or isoprene polymerized in a weight ratio of 10:90 to 90:10. Examples of individual monomers of group (a) of the anionic polymers are acrylic acid and methacrylic acid esters of saturated, monohydric C ₁ to C ₂₀ alcohols such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, n- Butyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-butyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, n-decyl acrylate, n-decyl methacrylate, 2-propylheptyl acrylate, 2-propylheptyl methacrylate, dodecyl acrylate, dodecyl methacrylate, lauryl acrylate, palmityl acrylate, palmityl acrylate, palmityl acrylate, palmityl acrylate, palmityl acrylate Of these monomers, the esters of acrylic acid and methacrylic acid with saturated monohydric C ₁ -C ₁₀ -alcohols are preferably used. Mixtures of these monomers are also used in the preparation of the anionic polymers, e.g. B. mixtures of n-butyl acrylate and ethyl acrylate or mixtures of n-butyl acrylate and at least one propyl acrylate.

Other monomers of group (a) of the anionic polymers are:
Vinyl esters of saturated carboxylic acids with 1 to 20 carbon atoms z. B. vinyl laurate, vinyl stearate, vinyl propionate, vinyl versatic acid and vinyl acetate,
vinyl aromatic compounds such as styrene, α-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene and 4-n-decylstyrene,
ethylenically unsaturated nitriles such as acrylonitrile and methacrylonitrile,
Saturated alcohols containing 1 to 10 carbon atoms, preferably 1 to 4 saturated alcohols containing vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl n-propyl ether, vinyl isopropyl ether, vinyl n-butyl ether or vinyl isobutyl ether,
Vinyl halides such as chlorine, fluorine or bromine substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride, and
one or two olefinic double bonds containing aliphatic hydrocarbons with 2 to 8 carbon atoms such as ethylene, propylene, butadiene, isoprene and chloroprene.

Preferred monomers of group (a) are C ₁ -C ₂₀ alkyl (meth) acrylates and mixtures of the alkyl (meth) acrylates with vinyl aromatics, in particular styrene and / or hydrocarbons having two double bonds, in particular butadiene, or mixtures of such hydrocarbons with vinyl aromatics , especially styrene. Particularly preferred monomers of group (a) of the anionic polymers are n-butyl acrylate, styrene and acrylonitrile, which can each be used alone or as a mixture. In the case of monomer mixtures, the weight ratio of alkyl acrylates or alkyl methacrylates to vinyl aromatics and / or to hydrocarbons having two double bonds, such as butadiene, can be, for example, 10:90 to 90:10, preferably 20:80 to 80:20.

Anionic monomers of group (b) of the anionic polymers are ethylenically unsaturated C ₃ - to C ₈ -carboxylic acids such as acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, maleic acid, fumaric acid, itaconic acid, mesaconic acid, citraconic acid, methylene malonic acid, allylacetic acid, vinyl acetic acid and crotonic acid. Suitable monomers of group (b) are also monomers containing sulfone groups, such as vinylsulfonic acid, acrylamido-2-methyl-propanesulfonic acid and styrene sulfonic acid and vinylphosphonic acid. The monomers of this group can be used alone or in a mixture with one another, in partially or in completely neutralized form in the copolymerization. For neutralization, for example, alkali metal or alkaline earth metal bases, ammonia, amines and / or are used Alkanolamines. Examples include sodium hydroxide solution, potassium hydroxide solution, soda, potash, sodium hydrogen carbonate, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine, morpholine, diethylene triamine or tetraethylene pentamine.

The water-insoluble anionic polymers can, if appropriate, as further monomers (c) at least one monomer from the group of the C ₁ -C ₁₀ -hydroxyalkylacyrylates, C ₁ -C ₁₀ -hydroxyalkyl methacrylates, acrylamide, methacrylamide, NC ₁ -C ₂₀ -alkyl acrylamides and Contain NC _{1 to} C ₂₀ alkyl methacrylamides. If these monomers are used to modify the anionic polymers, acrylamide or methacrylamide is preferably used. The amounts of copolymerized monomers (c) in the anionic polymer are up to, for example, 20 mol%, preferably up to 10 mol% and, if these monomers are used in the polymerization, are in the range from 1 to 5 mol%.

The anionic polymers can optionally also contain monomers of group (d). Suitable monomers of group (d) are compounds having at least two ethylenically unsaturated double bonds in the molecule. Such connections are also referred to as crosslinkers. They contain, for example, 2 to 6, preferably 2 to 4 and usually 2 or 3 free-radically polymerizable double bonds in the molecule. The double bonds can be, for example, the following groups: acrylic, methacrylic, vinyl ether, vinyl ester, allyl ether and allyl ester groups. Examples of crosslinkers are 1,2-ethanediol di (meth) acrylate (the notation "... (meth) acrylate" or "(meth) acrylic acid" means here both "... acrylate" and "in the text below." .. methacrylate "or acrylic acid as well as methacrylic acid), 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 triol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, 1,4-butanediol divinyl ether, 1,6-hexanediol divinyl ether, 1,4-cyclohexanediol divinyl ether, divinylbenzene, allyl acrylate, methallyl methacrylate, allyl 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, cinnamon alcohol, glycerol mono- or diallyl ether, trimethylolpropane mono- or diallyl ether, ethylene glycol monoallyl ether, diethylene glycol monoallyl ether, propylene glycol monoally lether, dipropylene glycol monoallyl ether, 1,3-propanediol monoallyl ether, 1,4-butanediol monoallyl ether and also diacetate of itaconate. Allyl acrylate, divinylbenzene, 1,4-butanediol diacrylate and 1,6-hexanediol diacrylate are preferred. If a crosslinker is used to modify the anionic polymers, the amounts polymerized in are up to 2 mol%. For example, they are in the range from 0.001 to 2, preferably 0.01 to 1, mol%.

The water-insoluble anionic polymers preferably contain, as monomers (a), mixtures of 20-50 mol% of styrene and 30-80 mol% of at least one alkyl methacrylate and / or polymerized at least one alkyl acrylate. If appropriate, they can also contain up to 30 mol% of copolymerized methacrylonitrile or acrylonitrile. Such polymers can optionally also be modified with the amounts of methacrylamide and / or acrylamide given above under monomers of group (c).

1. (a) mindestens 60 Mol-% mindestens eines Monomers aus der Gruppe bestehend aus einem C₁- bis C₂₀-Alkylacrylat, einem C₁- bis C₂₀-Alkylmethacrylat, Vinylacetat, Vinylpropionat, Styrol, α-Methylstyrol, p-Methylstyrol, α-Butylstyrol, 4-n-Butylstyrol, 4-n-Decylstyrol, Acrylnitril, Methacrylnitril, Butadien und Isopren und
2. (b) 0,5 bis 9 Mol-% mindestens eines anionischen Monomers aus der Gruppe der ethylenisch ungesättigten C₃- bis C₅-Carbonsäuren einpolymerisiert.

Contain the anionic polymers used in the process according to the invention

1. (a) at least 60 mol% of at least one monomer from the group consisting of a C ₁ to C ₂₀ alkyl acrylate, a C ₁ to C ₂₀ alkyl methacrylate, vinyl acetate, vinyl propionate, styrene, α-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, acrylonitrile, methacrylonitrile, butadiene and isoprene and
2. (b) 0.5 to 9 mol% of at least one anionic monomer from the group of ethylenically unsaturated C ₃ - to C ₅ -carboxylic acids are polymerized.

Anionic polymers which contain at least 80 mol% of at least one monomer from group (a) in copolymerized form are particularly preferred. They usually contain as a monomer of group (a) mixtures of (i) a C ₁ - to C ₂₀ -alkyl acrylate and / or a C ₁ - to C ₂₀ -alkyl methacrylate and (ii) styrene, α-methylstyrene, p-methylstyrene, Polymerized α-butylstyrene, 4-n-butylstyrene, butadiene and / or isoprene in a weight ratio of 10:90 to 90:10.

The anionic polymers are generally prepared by emulsion polymerization. The anionic polymers are therefore emulsion polymers. The preparation of aqueous polymer dispersions by the free-radical emulsion polymerization process is known per se (cf. Houben-Weyl, Methods of Organic Chemistry, Volume XIV, Macromolecular Substances, Georg Thieme Verlag, Stuttgart 1961, pages 133ff ).

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

Common emulsifiers are e.g. 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 with a degree of ethoxylation of 3 to 30 and ethoxylated C ₈ - to C ₂₅ -fatty alcohols with a degree of ethoxylation of 5 to 50. Mixtures are also conceivable from nonionic and ionic emulsifiers. Also suitable are phosphate or sulfate group-containing, ethoxylated and / or propoxylated alkylhenols and / or fatty alcohols. Other suitable emulsifiers are in Houben-Weyl, Methods of Organic Chemistry, Volume XIV, Macromolecular Substances, Georg Thieme Verlag, Stuttgart, 1961, pages 192 to 209 listed.

Water-soluble initiators for emulsion polymerization for the preparation of the anionic polymers are e.g. B. ammonium and alkali metal salts of peroxidic sulfuric acid, e.g. As sodium peroxodisulfate, hydrogen peroxide or organic peroxides, e.g. B. tert-butyl hydroperoxide.

So-called reduction-oxidation (red-ox) initiator systems are also suitable, for example combinations of peroxides, hydroperoxides or hydrogen peroxide with reducing agents such as ascorbic acid or sodium bisulfite. These initiator systems can additionally contain metal ions such as iron (II) ions.

The amount of initiators is generally 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the monomers to be polymerized. Several different initiators can also be used in emulsion polymerization.

In the emulsion polymerization, regulators can optionally be used, e.g. B. in amounts of 0 to 3 parts by weight, based on 100 parts by weight of the monomers to be polymerized. This reduces the molecular weight of the resulting polymers. Suitable regulators are e.g. B. Compounds with a thiol group such as tert-butyl mercaptan, ethyl thioglycolate, mercaptoethanol, mercaptopropyltrimethoxysilane or tert-dodecyl mercaptan or regulator without a thiol group, in particular, for. B. terpinolene.

The emulsion polymerization for the preparation of the anionic polymers generally takes place at 30 to 130 ° C., preferably at 50 to 100 ° C. The polymerization medium can consist only of water, as well as mixtures of water and thus miscible liquids such as methanol. Preferably only water is used. The emulsion polymerization can be carried out either as a batch process or in the form of a feed process, including a step or gradient procedure. Preference is given to the feed process, in which part of the polymerization batch is initially charged, heated to the polymerization temperature, polymerized and then the remainder of the polymerization batch, usually via a plurality of spatially separate feeds, one or more of which contain the monomers in pure or in emulsified form , gradually or with superposition of a concentration gradient while maintaining the polymerization of the polymerization zone. In the polymerization z. B. to better adjust the particle size, 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 the person skilled in the art. It can either be completely introduced into the polymerization vessel or, depending on its consumption, be used continuously or in stages in the course of the free-radical aqueous emulsion polymerization. Specifically, this depends on the chemical nature of the initiator system as well as on the polymerization temperature. A portion is preferably introduced and the remainder is fed to the polymerization zone in accordance with the consumption.

To remove the residual monomers, usually after the end of the actual emulsion polymerization, ie. H. after a conversion of the monomers of at least 95%, at least one initiator is again added and the reaction mixture is heated to the polymerization temperature or a temperature above it for a certain time.

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

Following the (co) polymerization, the acid groups contained in the anionic polymer can still be at least partially or completely 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 counterion or more can be associated, e.g. B. Li ⁺ , Na ⁺ , K ⁺ , Cs ⁺ , Mg ²⁺ , Ca ²⁺ or Ba ²⁺ . Ammonia or amines are also suitable for neutralization. Aqueous ammonium hydroxide, sodium hydroxide or potassium hydroxide solutions are preferred.

In emulsion polymerization, aqueous dispersions of the anionic polymer are generally obtained with solids contents of from 15 to 75% by weight, preferably from 40 to 75% by weight. The molecular weight M _{w of} the anionic polymers is, for example, in the range from 100,000 to 1 million daltons. If the polymers have a gel phase, it is not readily possible to determine the molar mass. The molecular weights are then above the range mentioned above.

The glass transition temperature Tg of the anionic polymers is, for example, in the range from -30 to 100 ° C, preferably in the range from -5 to 70 ° C and particularly preferably in the range from 0 to 40 ° C (measured by the DSC method according to DIN EN ISO 11357).

The particle size of the dispersed anionic polymers is preferably in the range from 10 to 1000 nm, particularly preferably in the range from 50 to 300 nm (measured with a Malvern® Autosizer 2 C).

The anionic polymers can optionally contain small amounts of cationic monomer units in copolymerized form, so that amphoteric polymers are present, but the total charge of the polymers must be anionic. Also suitable as anionic polymers are polymer dispersions of nonionic monomers which are emulsified with the aid of anionic surfactants or emulsifiers (such compounds were described above in the emulsion polymerization for the preparation of anionic polymers). For this application, the surfactants or emulsifiers are used, for example, in amounts of 1 to 15% by weight, based on the total dispersion.

As described above, in addition to or alternatively to the anionic polymer, the aqueous composition can also contain a water-soluble cationic polymer in addition to the nanocellulose.

All water-soluble cationic polymers mentioned in the prior art cited at the beginning are suitable as cationic polymers. It is e.g. B. to amino or ammonium-bearing compounds. The amino groups can be primary, secondary, tertiary or quaternary groups. Polymers, polyaddition compounds or polycondensates are essentially suitable for the polymers, it being possible for the polymers to have a linear or branched structure up to hyperbranched or dendritic structures. Graft polymers can also be used. 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 is, for example, at least 10% by weight.

The molecular weights M _{w of} the cationic polymers are, for. B. at least 1,000 g / mol. For example, they are usually in the range from 5,000 to 5 million g / mol. The charge densities of the cationic polymers are, for example, 0.5 to 23 meq / g polymer, preferably 3 to 22 meq / g polymer and mostly 6 to 20 meq / g polymer.

Suitable monomers for the preparation of cationic polymers are, for example:
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. As an acid component of these esters are, for. As 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 ,

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 are also suitable.

In addition, other monomers are N- [2- (dimethylamino) ethyl] acrylamide, N- [2- (dimethylamino) ethyl] methacrylamide, N- [3- (dimethylamino) propyl] acrylamide, N- [3- (dimethylamino) propyl] methacrylamide, N- [4- (dimethylamino) butyl] acrylamide, N- [4- (dimethylamino) butyl] methacrylamide, N- [2- (diethylamino) ethyl] acrylamide, N- [2- (diethylamino) ethyl] methacrylamide and mixtures thereof are suitable.

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 are also suitable.

Suitable monomers are also N-vinylimidazoles, alkylvinylimidazoles, especially methylvinylimidazoles such as 1-vinyl-2-methylimidazole, 3-vinylimidazole-N-oxide, 2- and 4-vinylpyridines, 2- and 4-vinylpyridine-N-oxides, and betaine 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 chloride, in particular dimethyldiallylammonium chloride and diethyldiallylammonium chloride, and those from WO 01/36500 A1 known monomers of formula (II) containing alkyleneimine units

wherein

R

represents hydrogen or C ₁ -C ₄ -alkyl,

- [Al-] _m

is a linear or branched oligoalkyleneimine chain with m alkyleneimine units,

m

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

Y

means the anion equivalent of a mineral acid and

n

stands for a number of 1 ≤ n ≤ m.

Monomers or monomer mixtures in which the number average of m in the above formula (II) 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 product obtained can optionally be converted into the acid addition salt using a mineral acid HY. Such monomers can be polymerized in an aqueous medium in the presence of an initiator which triggers a radical polymerization to give cationic homopolymers 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 WO 2009/043860 A1 known. These are aminoalkyl vinyl ethers of the formula (III) containing alkyleneimine units

H ₂ C = CH-OX-NH- [Al-] _n -H (III),

wherein

[Al-] _n

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

n

is a number of at least 1 and

X

represents a straight-chain or branched C ₂ -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 can be obtained by adding alkyleneimines to amino-C ₂ -C ₆ -alkyl vinyl ethers.

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

Suitable neutral monomers which are copolymerized with the above-mentioned 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 of these.

Other suitable comonomers are e.g. B. methyl (meth) acrylate, methylethacrylate, ethyl (meth) acrylate, ethylethacrylate, 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 acrylic acid amide, methacrylic acid amide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, N- (n-butyl) - (meth) acrylamide, tert-butyl (meth) acrylamide, n-octyl (meth) acrylamide, 1,1,3,3-tetramethylbutyl (meth) acrylamide and ethylhexyl (meth) acrylamide as well as acrylonitrile and methacrylonitrile and mixtures of the monomers mentioned ,

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

Other suitable monomers for copolymerization with the above-mentioned cationic monomers are N-vinyl lactams and their derivatives, which, for. B. can have one or more C ₁ -C ₆ alkyl substituents, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, etc. These include e.g. B. 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 above-mentioned cationic monomers are also ethylene, propylene, isobutylene, butadiene, styrene, α-methylstyrene, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and mixtures thereof.

In den Formeln IV - VII stehen die Substituenten R¹, R² für H, C₁- bis C₆-Alkyl und X für ein Anionäquivalent einer Säure, vorzugsweise einer Mineralsäure.Another group of comonomers are ethylenically unsaturated compounds which carry a group 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 from it can, as in EP 0 438 744 A1 described, by acid or basic hydrolysis in vinylamine and amidine units (formulas IV - VII) polymers are converted.

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.

The hydrolysis produces, for example, polyvinylamines, polyvinylmethylamines or polyvinylethylamines. The monomers of this group can be polymerized in any manner with the cationic monomers and / or the above-mentioned comonomers.

Cationic polymers for the purposes of the present invention are also to be understood as meaning amphoteric polymers which carry a total cationic charge. In the amphoteric polymers, the content of cationic groups is, for example, at least 5 mol% above the content of anionic groups in the polymer. Such polymers are e.g. B. accessible by copolymerizing a cationic monomer such as N, N-dimethylaminoethyl acrylamide in the form of the free base, in partially neutralized with an acid or in quaternized form with at least one monomer containing acid groups, the cationic monomer being used in a molar excess , so that the resulting polymers carry a total cationic charge.

1. (i) mindestens einem N-Vinylcarbonsäureamid der Formel (I)
   
   in der R¹, R² = H oder C₁- bis C₆-Alkyl bedeuten,
2. (ii) mindestens einer monoethylenisch ungesättigten Carbonsäure mit 3 bis 8 C-Atomen im Molekül und/oder deren Alkalimetall-, Erdalkalimetall- oder Ammoniumsalzen und gegebenenfalls
3. (iii) anderen monoethylenisch ungesättigten Monomeren, und gegebenenfalls
4. (iv) 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 (ii) 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

1. (i) at least one N-vinylcarboxamide of the formula (I)
   
   in which R ¹ , R ² = H or C ₁ - to C ₆ -alkyl,
2. (ii) at least one monoethylenically unsaturated carboxylic acid with 3 to 8 carbon atoms in the molecule and / or its alkali metal, alkaline earth metal or ammonium salts and optionally
3. (iii) other monoethylenically unsaturated monomers, and optionally
4. (iv) compounds which have at least two ethylenically unsaturated double bonds in the molecule,

and then partial or complete elimination of groups -CO-R ¹ from the monomers of formula (I) copolymerized into the copolymer to form amino groups, the content of cationic groups such as amino groups in the copolymer being at least 5 mol% above the content of copolymerized Acid groups of the monomers (ii). 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 specification of vinylamine units in the amphoteric copolymers always means the sum of vinylamine and amidine units.

• (i₁) gegebenenfalls nicht hydrolysierte Einheiten der Formel (I)
• (i₂) Vinylamin- und Amidineinheiten, wobei der Gehalt an Amino- plus Amidingruppen im Copolymerisat mindestens 5 Mol-% über dem Gehalt an einpolymerisierten Säuregruppen enthaltenden Monomeren liegt,
• (ii) Einheiten eines Säuregruppen enthaltenden monoethylenisch ungesättigten Monomeren und/oder deren Alkalimetall-, Erdalkalimetall- oder Ammoniumsalzen,
• (iii) 0 bis 30 Mol-% Einheiten mindestens eines anderen monoethylenisch ungesättigten Monomeren und
• (iv) 0 bis 2 Mol-% mindestens einer Verbindung, die mindestens zwei ethylenisch ungesättigte Doppelbindungen in Molekül aufweist.

The amphoteric compounds obtainable in this way contain, for example

• (i ₁ ) optionally non-hydrolyzed units of the formula (I)
• (i ₂ ) vinylamine and amidine units, the content of amino plus amidine groups in the copolymer being at least 5 mol% above the content of polymerized acid groups containing monomers,
• (ii) units of a monoethylenically unsaturated monomer containing acid groups and / or their alkali metal, alkaline earth metal or ammonium salts,
• (iii) 0 to 30 mol% of units of at least one other monoethylenically unsaturated monomer and
• (iv) 0 to 2 mol% of at least one compound which has at least two ethylenically unsaturated double bonds in the molecule.

The copolymers can be hydrolysed in the presence of acids or bases or also enzymatically. In the hydrolysis with acids, the vinylamine groups formed from the vinylcarboxamide units are in salt form. The hydrolysis of vinyl carboxamide copolymers is in the EP 0 438 744 A1 , Page 8, line 20 to page 10, line 3, described in detail. The statements made there apply accordingly to the production of the amphoteric polymers to be used according to the invention with 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. 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. B. an alcohol such as methanol, ethanol, n-propanol, etc.

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

To produce the cationic polymers, the monomers can be polymerized with the aid of initiators which form free radicals.

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 permaleinate, cumene hydroperoxide, diisopropyl peroxidicarbamate, bis- (o-toluoyl) peroxide, didecanoyl peroxide, dioctanoyl peroxide, dilauroyl peroxide, tert-butyl peris-butyl peroxide, tert-peryl butyl peroxide, tert. , tert-butyl hydroperoxide, azo-bisisobutyronitrile, azo-bis- (2-amidinopropane) dihydrochloride or 2-2'-azo-bis- (2-methylbutyronitrile). Initiator mixtures or redox initiator systems, such as, for. B. 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) compounds.

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 to those skilled in the art, such as, for. B. sulfur compounds, e.g. B. mercaptoethanol, 2-ethylhexylthioglycolate, thioglycolic acid, sodium hypophosphite, formic acid or dodecyl mercaptan and tribromochloromethane or other compounds which act regulatingly on the molecular weight of the polymers obtained.

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 aforementioned 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 crosslinking agent. A crosslinker is understood to mean those monomers which contain at least two double bonds in the molecule, e.g. B. methylene bisacrylamide, Glycol diacrylate, glycol dimethacrylate, glycerol triacrylate, pentaerythritol triallyl ether, at least twice polyalkylene glycols esterified with acrylic acid and / or methacrylic acid or polyols such as pentaerythritol, sobitol or glucose. If at least one crosslinker is used in the copolymerization, the amounts used are, for example, up to 2 mol%, for. B. 0.001 to 1 mole%.

• 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 crosslinking agents, ie by the addition of compounds which have at least two groups which are reactive toward amino groups, such as. B.

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

Polymers that can be produced by polyaddition reactions, such as, in particular, polymers based on aziridines, are also suitable as cationic compounds. Both homopolymers can be formed, but also graft polymers that are produced by grafting aziridines onto other polymers. Again, it may be advantageous to add during or after the polyaddition, which have at least two groups that can react with the aziridines or the amino groups formed, such as. B. epichlorohydrin or dihaloalkanes. Crosslinker (s. Ullmann's Encyclopedia of Industrial Chemistry, VCH, Weinheim, 1992 , Chapter on aziridines).

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

Other suitable cationic polymers are reaction products of dialkylamines with epichlorohydrin or with di- or multifunctional epoxides such as. B. reaction products of dimethylamine with epichlorohydrin.

Also suitable as cationic polymers are polycondensates, e.g. B. homo- 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 caprolactam.

Condensation of difunctional carboxylic acids with multifunctional amines can furthermore be used as cationic polymers, the multifunctional amines having at least two primary amino groups and at least one further less reactive, i.e. wear secondary, tertiary or quaternary amino group. Examples are the polycondensation products of diethylenetriamine or triethylenetetramine with adipic, malonic, glutaric, oxalic or succinic acid.

Also amino group-bearing polysaccharides such. B. Chitosan are suitable as cationic polymers.

Furthermore, all of the polymers described above which carry primary or secondary amino groups can be modified by means of reactive oligoethyleneimines, as in US Pat WO 2009/080613 A1 described. In this application graft polymers are described, the graft base of which is selected from the group of polymers containing vinylamine units, polyamines, polyamidoamines and polymers of ethylenically unsaturated acids and which contain only oligoalkyleneimine side chains as side chains. Graft polymers with oligoalkyleneimine side chains are prepared by grafting at least one oligoalkyleneimine which contains a terminal aziridine group onto one of the graft bases mentioned.

In the process according to the invention, a polymer having vinylamine units is used as the water-soluble cationic polymer.

The present invention also relates to an aqueous composition composed of a nanocellulose and at least one polymer, selected from the group of anionic polymers and water-soluble cationic polymer, as can be used in the process according to the invention described above.

All the usual qualities can be considered as pulps for the production of the pulps, for example wood pulp, bleached and unbleached cellulose and pulps from all annual plants. For example, pulp includes wood pulp, thermomechanical material (TMP), chemo-thermomechanical material (CTMP), pressure grinding, semi-pulp, high-yield pulp and refiner mechanical pulp (RMP). For example, sulfate, sulfite and soda pulps are suitable as pulp. Unbleached pulp, which is also referred to as unbleached kraft pulp, is preferably used. Suitable annual plants for the production of paper materials are, for example, rice, wheat, sugar cane and kenaf. Waste paper is mostly used to produce the pulps, either alone or as a mixture with others Fibrous materials are used or fiber mixtures of a primary material and recycled scrap are assumed, for example bleached pine sulfate in a mixture with recycled scrap.

The process according to the invention is of particular technical interest for the production of paper and cardboard from waste paper, because it significantly increases the strength properties of the returned fibers and is of particular importance for improving the 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 by the process of WO 2006/056381 A1 manufacturable papers.

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

In the method according to the invention, the aqueous composition is first prepared from a nanocellulose and at least one polymer. It is irrelevant whether the nanocellulose is initially introduced and the at least one polymer is added to the nanocellulose or vice versa. If both an anionic polymer and a water-soluble cationic polymer are added, the order is also irrelevant.

In a preferred embodiment of the method according to the invention, the aqueous suspension of the nanocellulose is first heated, for example up to 60 ° C., preferably up to 50 ° C. and particularly preferably in a range between 30 and 50 ° C. An aqueous dispersion of at least one anionic polymer is then metered in. It is also possible, if appropriate, to add at least one cationic polymer to this aqueous composition.

In another preferred embodiment of the process according to the invention, at least one cationic polymer is added to the aqueous composition, this at least one cationic polymer preferably being added to a heated aqueous slurry of nanocellulose as described above. The anionic polymer is then optionally added.

Irrespective of the above-mentioned embodiments, the addition of the aqueous composition in the process according to the invention to the thick matter (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, for example in the range of 5 to 12 g / l). The addition point is preferably in front of the sieves, but can also be between a shear step and a screen or after.

The water-insoluble anionic polymer is, for. B. in an amount of 0.1 to 10 wt .-%, preferably 0.3 to 6 wt .-%, in particular from 0.5 to 5.5 wt .-%, based on dry paper, used. The cationic polymer optionally used is used, for example, in an amount of 0.03 to 2.0% by weight, preferably 0.1 to 0.5% by weight, based on dry paper stock.

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

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

The invention is illustrated by the following, non-limiting examples.

Examples

Unless stated otherwise, the percentages in the examples mean percentages by weight.

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

The stated average particle sizes were determined according to ISO 13321 by quasi-elastic light scattering using a Malvern® Autosizer 2 C on 0.01% by weight samples.

The following polymers were tested in the examples and comparative examples:

Cationic polymer A

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

Anionic polymer B

The anionic polymer B was present as an anionic acrylate resin with a solids content of 50% and was obtained by the suspension polymerization of 68 mol% n-butyl acrylate, 14 mol% styrene, 14 mol% acrylonitrile and 4 mol% acrylic acid. The average particle size of the dispersed polymer particles was 192 nm.

Anionic polymer C

The anionic polymer C was present as an anionic acrylate resin with a solids content of 50% and was obtained by the suspension polymerization of 87 mol% of n-butyl acrylate, 5 mol% of styrene, 5 mol% of acrylonitrile and 3 mol% of acrylic acid. The average particle size of the dispersed polymer particles was 184 nm.

nanocellulose

For the production of the nanocellulose, a Spinnig disk reactor was used, which was equipped with an inlet for cellulose solution and four inlets for water. The feed for the cellulose solution was positioned centrally above the axis of the disc 1 mm from the disc surface. The water inlets were positioned at equal distances from each other, 5 cm from the axis and 1 mm from the disk surface. The disc surface and the jacket of the spinning disc reactor were heated to 95 ° C. The reactor was filled with nitrogen. At a disk rotation speed of 2500 revolutions per minute, warm solutions of cellulose in an ionic liquid (cellulose from Firmar Weyerhäuser, 1% by weight in 1-ethyl-3-methylimidazolium acetate, dosage 50 g / min at 2 bar nitrogen pressure) metered onto the disc. At the same time, water at a temperature of 80 ° C. was added via the four water inlets at a dosage of 1000 ml / min. After cooling, the product suspension obtained was filtered through a folded filter and washed in portions with a total of 1000 ml of water. The cellulose fibers were then washed with about 200 ml of isopropanol and filled with isopropanol. The nanocellulose still contained 0.4% by weight of 1-ethyl-3-methylimidizaolium acetate and about 95% of the cellulose fibers had a fiber thickness between 5 and 200 nm.

example 1

200 ml of a 10% nanocellulose suspension were heated to 50 ° C. 0.25% by weight of the cationic polymer A (polymer solid, based on dry nanocellulose) was added. In another container, the anionic polymer B was diluted by a factor of 10 with water. The dilute dispersion of anionic polymer B was then metered into the heated nanocellulose suspension with gentle stirring. The amount of acrylate resin used was 25% by weight (polymer solid, based on dry nanocellulose).

A 0.5% by weight aqueous stock suspension was produced from 100% mixed waste paper. The pH of the suspension was 7.1, the degree of grinding of the material was 50 ° Schopper-Riegler (° SR).

The treated nanocellulose suspension was added to the waste paper pulp with stirring. The metered amount of treated nanocellulose (solid) based on waste paper stock (solid) was 5%. Subsequently, sheets with a basis weight of 120 g / m ² were produced from the treated waste paper stock on a Rapid-Köthen sheet former according to ISO 5269/2. The sheets were dried over one-sided contact to a steam heated metal cylinder for 7 minutes at 90 ° C.

Example 2

200 ml of a 10% nanocellulose suspension were heated to 30 ° C. In another container, the anionic polymer C was diluted by a factor of 10 with water. The diluted dispersion was then metered into the heated nanocellulose suspension with gentle stirring. The amount of acrylate resin used was 25% by weight (polymer solid, based on dry nanocellulose).

A 0.5% by weight aqueous stock suspension was produced from 100% mixed waste paper. The pH of the suspension was 7.1, the degree of grinding of the material was 50 ° Schopper-Riegler (° SR).

The treated nanocellulose suspension is added to the waste paper pulp with stirring. The metered amount of treated nanocellulose (solid) based on waste paper stock (solid) was 5%. Subsequently, sheets with a basis weight of 120 g / m ² were produced from the treated waste paper stock on a Rapid-Köthen sheet former according to ISO 5269/2. The sheets were dried over one-sided contact to a steam heated metal cylinder for 7 minutes at 90 ° C.

Example 3

200 ml of a 10% nanocellulose suspension were placed at room temperature. 0.5% by weight of the cationic polymer A (polymer solid, based on dry nanocellulose) was added.

A 0.5% by weight aqueous stock suspension was produced from 100% mixed waste paper. The pH of the suspension was 7.1, the degree of grinding of the material was 50 ° Schopper-Riegler (° SR).

The treated nanocellulose suspension was added to the waste paper pulp with stirring. The metered amount of treated nanocellulose (solid) based on waste paper stock (solid) was 5%. Subsequently, sheets with a basis weight of 120 g / m ² were produced from the treated waste paper stock on a Rapid-Köthen sheet former according to ISO 5269/2. The sheets were dried over one-sided contact to a steam heated metal cylinder for 7 minutes at 90 ° C.

Comparative Example 1

A 0.5% by weight aqueous stock suspension was produced from 100% mixed waste paper. The pH of the suspension was 7.1, the degree of grinding of the material was 50 ° Schopper-Riegler (° SR). Sheets with a basis weight of 120 g / m ² were produced from the untreated waste paper stock on a Rapid Köthen sheet former according to ISO 5269/2. The sheets were dried over one-sided contact to a steam heated metal cylinder for 7 minutes at 90 ° C.

Comparative example 2, corresponding to the older European application with the file number EP 09 150 237.7

A 0.5% by weight aqueous stock suspension was produced from 100% mixed waste paper. The pH of the suspension was 7.1, the degree of grinding of the material was 50 ° Schopper-Riegler (° SR).

The cationic polymer A was added undiluted to this fiber suspension. The amount of polymer used, based on the fiber content, was 0.3% by weight (polymer, solid). The substance pretreated with the cationic polymer was stirred gently for about 30 seconds. In another container, the dispersion of anionic polymer B was diluted by a factor of 10 with water. The diluted dispersion was then added to the fiber suspension with gentle stirring. The amount of acrylate resin used was 5% by weight (polymer, solid, based on the fiber content).

Sheets with a basis weight of 80 g / m ² were produced from the pretreated fibrous material on a Rapid-Köthen sheet former according to ISO 5269/2. The sheets were dried over one-sided contact to a steam heated metal cylinder for 7 minutes at 90 ° C.

Examination of the paper sheets

After the leaves produced according to the examples and comparative examples had been stored in a climatic room at a constant 23 ° C. and 50% atmospheric humidity for 12 hours, the dry tear length of the leaves was determined in accordance with DIN 54 540. The determination The CMT value of the air-conditioned leaves was determined according to DIN 53 143, the dry burst pressure of the leaves was determined according to DIN 53 141. The results are shown in Table 1. Table 1 example Dry tear length [m] Burst pressure [kPa] CMT30 [N] 1 5341 468 241 2 5455 487 262 3 5245 449 235 Comparative Example 1 3412 289 162 Comparative Example 2 4611 403 211

Claims (9)

1. A process for the production of paper, board, and cardboard having high dry strength, characterized in that firstly, an aqueous composition formed from a nanocellulose which is used as an aqueous slurry containing 0.1 % to 25 % by weight of nanocellulose with respect to the total weight of the aqueous slurry and at least one polymer selected from the group formed by anionic polymers and water-soluble cationic polymers is produced, the aqueous composition is metered into the paper pulp, the paper pulp is dewatered and the paper product is dried, wherein the nanocellulose has a linear extent of less than 1000 µm and at least 80 % of the cellulose fibres of the nanocellulose have a fibre thickness in the range from 50 µm to 3 nm,
   wherein the anionic polymer contains, in the copolymerized form:

   (a) at least 60 mol % of at least one monomer from the group consisting of a C₁ to C₂₀ alkyl acrylate, a C₁ to C₂₀ alkyl methacrylate, vinyl acetate, vinyl propionate, styrene, α-methyl styrene, p-methyl styrene, α-butyl styrene, 4-n-butyl styrene, 4-n-decyl styrene, acrylonitrile, methacrylonitrile, butadiene and isoprene,

   (b) 0.5 to 9 mol % of at least one anionic monomer from the group formed by ethylenically unsaturated C₃ to C₅ carboxylic acids as well as the salts thereof,

   (c) optionally, at least one monomer from the group formed by C₁ to C₁₀ hydroxyalkyl acrylates, C₁ to C₁₀ hydroxyalkyl methacrylates, acrylamide, methacrylamide, N-C₁ to C₂₀ alkylacrylamides, and N-C₁ to C₂₀ alkylmethacrylamides, and

   (d) optionally, at least one monomer containing at least two ethylenically unsaturated double bonds in the molecule,

   wherein a polymer containing a vinylamine unit is used as the water-soluble cationic polymer.
2. The process as claimed in claim 1, characterized in that at least 80 % of the cellulose fibres of the nanocellulose have a fibre thickness in the range from 1 µm to 5 nm.
3. The process as claimed in claim 1, characterized in that the nanocellulose has a linear extent of less than 1000 µm, the fibre thickness is in the range from 50 µm to 3 nm, and the nanocellulose contains between 5 ppm and 2 % by weight of ionic liquids.
4. The process as claimed in claim 3, characterized in that at least 80 % of the cellulose fibres of the nanocellulose have a fibre thickness between 50 µm and 3 nm and contain between 5 ppm and 2 % by weight of ionic liquids.
5. The process as claimed in claim 1, characterized in that the anionic polymer comprises, in the copolymerized form, at least 80 mol % of a monomer from group (a) .
6. The process as claimed in claim 1 or claim 5, characterized in that the anionic polymer contains, as the monomer from group (a), mixtures formed by (i) a C₁ to C₂₀ alkyl acrylate and/or a C₁ to C₂₀ alkyl methacrylate, and (ii) styrene, α-methyl styrene, p-methyl styrene, α-butyl styrene, 4-n-butyl styrene, butadiene and/or isoprene, copolymerized in a weight ratio of 10:90 to 90:10.
7. The process as claimed in one of the preceding claims, characterized in that the molar mass M_w of the cationic polymer is in the range from 5000 to 5 million g/mol.
8. The process as claimed in one of the preceding claims, characterized in that the charge density of the cationic polymer is in the range from 0.5 to 23 meq/g.
9. An aqueous composition formed from a nanocellulose, wherein the nanocellulose, which is used as an aqueous slurry containing 0.1 % to 25 % by weight of nanocellulose with respect to the total weight of the aqueous slurry, has a linear extent of less than 1000 µm and at least 80 % of the cellulose fibres of the nanocellulose have a fibre thickness in the range from 50 µm to 3 nm, and at least one polymer selected from the group formed by anionic polymers and water-soluble cationic polymers,
   wherein the anionic polymer contains, in the copolymerized form:

   (a) at least 60 mol % of at least one monomer from the group consisting of a C₁ to C₂₀ alkyl acrylate, a C₁ to C₂₀ alkyl methacrylate, vinyl acetate, vinyl propionate, styrene, α-methyl styrene, p-methyl styrene, α-butyl styrene, 4-n-butyl styrene, 4-n-decyl styrene, acrylonitrile, methacrylonitrile, butadiene and isoprene,

   (b) 0.5 to 9 mol % of at least one anionic monomer from the group formed by ethylenically unsaturated C₃ to C₅ carboxylic acids as well as the salts thereof,

   (c) optionally, at least one monomer from the group formed by C₁ to C₁₀ hydroxyalkyl acrylates, C₁ to C₁₀ hydroxyalkyl methacrylates, acrylamide, methacrylamide, N-C₁ to C₂₀ alkylacrylamide, and N-C₁ to C₂₀ alkylmethacrylamides, and

   (d) optionally, at least one monomer containing at least two ethylenically unsaturated double bonds in the molecule,

   wherein a polymer containing a vinylamine unit is used as the water-soluble cationic polymer,
   for use in a process as claimed in claims 1 to 8.