EP2288750B1 - Method for producing paper, paperboard and cardboard with a 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-A-35 06 832 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, in copolymerized form.

Out WO-A-2004/061235 is a process for the production of paper, especially tissue, with particularly high wet and / or dry strengths known, in which one first adds to the paper a water-soluble cationic polymer which contains at least 1.5meq / g polymer of 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. As an advantage of this The method is mainly the variability of the two-component systems described in terms of various paper properties, including wet and dry strength, exposed.

DE 10 2005 029 010 teaches a method of making paper by separately adding a vinylamine moiety-containing polymer and a water-soluble polymeric anionic compound to the stock. The anionic copolymer is composed of the monomers N-vinylcarboxamide and acrylic acid, wherein the acrylic acid content of the monomer composition is 30%. Such acrylic acid contents render the copolymer water-soluble.

From the CA 1 110 019 discloses a process for the production of paper with high dry strength, in which one adds to the paper stock first a water-soluble cationic polymer and then a water-soluble anionic polymer. The anionic polymers are acrylamide / acrylic acid copolymers having an acrylic acid content of 2-30 mol%.

The US 5,185,062 teaches a papermaking process in which a mineral slurry, first a mineral filler, then a high molecular weight cationic polymer and then a water soluble anionic polymer of average molecular weight, is added to a cellulose slurry. The anionic polymers are polymers based on acrylic acid or copolymers which contain at least 65 mol% of anionically ionizable radicals.

The US 2003/0188840 teaches the addition of a mixture of a water-soluble anionic resin and a water-soluble cationic or amphoteric starch in the papermaking process. As anionic polymers copolymers based on acrylamide / acrylic acid are used, which are water-soluble.

The US 5,338,406 teaches a process for producing high dry strength paper using a polyelectrolyte complex formed from a water-soluble cationic polymer and a water-soluble anionic polymer.

in der R¹, R² = H oder C₁- bis C₆-Alkyl bedeuten,
mindestens eines Säuregruppen enthaltenden monoethylenisch ungesättigten Monomeren und/oder deren 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-A-2006/056381 discloses a process for making high dry strength paper, board and paperboard by separately adding a water-soluble vinylamine units-containing polymer and a water-soluble polymeric anionic compound to a stock, dewatering the paper stock and drying the paper products to yield at least one water-soluble polymeric 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 their 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.

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 according to the invention by a process for the production of paper, paperboard and cardboard with high dry strength by separately adding a water-soluble cationic polymer and an anionic polymer to a paper stock, dewatering the paper stock and drying the paper products, if the anionic polymer is an aqueous dispersion a water-insoluble polymer having an acid group content of 0.1 to 10 mol% or an anionic aqueous dispersion of a nonionic polymer.

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

Anionic polymers

The water-dispersed anionic polymers 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 of polymer / liter of water, usually at most 0.5 g / l and preferably not more than 0.1 g, dissolve / l. The dispersions are anionic due to the content of acid groups in the polymer. The water-insoluble polymer has a content of acid groups 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, for example, selected from carboxyl, sulfonic acid and phosphonic acid groups. Particularly preferred are carboxyl groups.

1. (a) mindestens ein Monomer aus der Gruppe von C₁- bis C₂₀-Alkylacrylaten, C₁ - bis C₂₀-Alkylmethacrylaten, Vinylestem 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 und gegebenenfalls
3. (c) 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 gegebenenfalls
4. (d) mindestens eine Monomer mit mindestens zwei ethylenisch ungesättigten Doppelbindungen im Molekül
   einpolymerisiert.

The anionic polymers contain, for example

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, vinylaromatics having up to 20 C atoms, ethylenically unsaturated nitrites, vinyl ethers of saturated monohydric alcohols, vinyl halides and aliphatic hydrocarbons containing 2 to 8 carbon atoms containing 1 to 10 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 and optionally
3. (C) at least one monomer selected from the group consisting of C ₁ to C ₁₀ hydroxyalkyl acrylates, C ₁ to C ₁₀ hydroxyalkyl methacyrylates, acrylamide, methacrylamide, NC _{1 to} C ₂₀ alkylacrylamides and NC _{1 to} C ₂₀ alkyl methacrylamides and possibly
4. (D) at least one monomer having at least two ethylenically unsaturated double bonds in the molecule
   in copolymerized form.

The anionic polymers contain z. B. at least 40 mol%, preferably at least 60 mol% and in particular at least 80 mol% of at least one monomer of group (a) copolymerized. These monomers are practically water-insoluble or, when homopolymerized, result in water-insoluble polymers.

The anionic polymers preferably 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 copolymerized 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 -C ₂₀ -alcohols such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, n-butyl 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, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, n-decyl acrylate, n-decyl methacrylate, dodecyl acrylate, dodecyl methacrylate, lauryl acrylate, lauryl methacrylate, palmityl acrylate, palmityl methacrylate, stearyl acrylate and stearyl methacrylate. Of these monomers, the esters of acrylic acid and of methacrylic acid with saturated, monohydric C ₁ - to C ₁₀ -alcohols are preferably used. Mixtures of these monomers are also used in the preparation of the anionic polymers, for example mixtures of n-butyl acrylate and ethyl acrylate or mixtures of n-butyl acrylate and at least one propyl acrylate.

• Vinylester von gesättigten Carbonsäuren mit 1 bis 20 C-Atomen z. B. Vinyllaurat, Vinylstearat, Vinylpropionat, Versaticsäurevinylester und Vinylacetat,
• vinylaromatische Verbindungen wie Styrol, α-Methylstyrol, p-Methylstyrol, α-Butylstyrol, 4-n-Butylstyrol und 4-n-Decylstyrol,
• Nitrile wie Acrylnitril und Methacrylnitril, Vinylhalogenide wie mit Chlor, Fluor oder Brom substituierte ethylenisch ungesättigte Verbindungen, bevorzugt Vinylchlorid und Vinylidenchlorid,
• Vinylether, z. B. Vinylether von 1 bis 4 C-Atome enthaltenden gesättigten Alkoholen wie Vinylmethylether. Vinylethylether, Vinyl-n-propylether, Vinylisopropylether, Vinyl-n-butylether oder Vinylisobutylether sowie
• eine oder zwei olefinische Doppelbindungen aufweisende aliphatische Kohlenwasserstoffe mit 2 bis 8 C-Atomen wie Ethylen, Propylen, Butadien, Isopren und Chloropren.

Further monomers of group (a) of the anionic polymers are:

• Vinyl esters of saturated carboxylic acids having 1 to 20 carbon atoms z. Vinyl laurate, vinyl stearate, vinyl propionate, vinyl versatate and vinyl acetate,
• vinyl aromatic compounds such as styrene, α-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene and 4-n-decylstyrene,
• Nitriles such as acrylonitrile and methacrylonitrile, vinyl halides such as chlorine, fluorine or bromine substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride,
• Vinyl ethers, e.g. B. vinyl ethers containing from 1 to 4 carbon atoms saturated alcohols such as vinyl methyl ether. Vinylethyl ether, vinyl n-propyl ether, vinyl isopropyl ether, vinyl n-butyl ether or vinyl isobutyl ether and
• one or two olefinic double bonds aliphatic hydrocarbons having 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 alkyl (meth) acrylates with vinylaromatics, in particular styrene and / or double bonds containing hydrocarbons, in particular butadiene, or mixtures of such hydrocarbons with vinylaromatics , in particular 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 in a mixture. In the case of monomer mixtures, the weight ratio of alkyl acrylates or alkyl methacrylates to vinyl aromatics and / or to double-bond hydrocarbons such as butadiene may be, for example, 10:90 to 90:10, preferably 20:80 to 80:20.

Examples of 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, methylenemalonic acid, allylacetic acid, vinylacetic acid and crotonic acid , Also suitable as monomers of group (b) are monomers containing sulfo groups, such as vinylsulfonic acid, acrylamido-2-methylpropanesulfonic acid and styrenesulfonic acid and vinylphosphonic acid. The monomers of this group can be used alone or in admixture with each other, in partially or completely neutralized form in the copolymerization. For neutralization, for example, alkali metal or alkaline earth metal bases, ammonia, amines and / or alkanolamines are used. Examples of these are sodium hydroxide solution, potassium hydroxide solution, soda, potash, sodium bicarbonate, magnesium oxide, calcium hydroxide, calcium oxide, triethanolamine, ethanolamine, morpholine, diethylenetriamine or tetraethylenepentamine.

The water-insoluble anionic polymers may optionally contain as further monomers (c) at least one monomer from the group of C ₁ to C ₁₀ hydroxyalkyl acrylates, C ₁ to C ₁₀ hydroxyalkyl methacyrylates, acrylamide, methacrylamide, NC _{1 to} C ₂₀ alkylacrylamides and NC _{1 to} C ₂₀ alkyl methacrylamides included. If these monomers are used to modify the anionic polymers, it is preferable to use acrylamide or methacrylamide. The amounts of polymerized 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, in the range of 1 to 5 mol%. Suitable monomers of group (d) are compounds having at least two ethylenically unsaturated double bonds in the molecule. Such compounds 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 may 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" here and in the following text means both "... Acrylate" and " methacrylic acid or 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 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, ester 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 monoally lether, 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. If a crosslinker is used to modify the polymers, the amounts polymerized in are up to 2 mol%. They are, for example, in the range of 0.001 to 2, preferably 0.01 to 1 mol%.

The water-insoluble anionic polymers preferably comprise, as monomers (a), mixtures of 20-50 mol% of styrene and 30-80 mol% of at least one alkyl methacrylate and / or at least one alkyl acrylate in copolymerized form. If appropriate, they may additionally contain up to 30 mol% of methacrylonitrile or acrylonitrile in copolymerized form. If appropriate, such polymers may also be modified with the amounts of methacrylamide and / or acrylamide stated 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.Preferably included anionic polymers

1. (a) at least 60 mol% of at least one monomer selected 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

in copolymerized form.

Particular preference is given to anionic polymers which comprise at least 80 mol% of at least one monomer of group (a) in copolymerized form. They 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-Butylstyrol, 4-n-butylstyrene, butadiene and / or isoprene in a weight ratio of 10: 90 to 90: 10 copolymerized.

The preparation of the anionic polymers is usually carried out by emulsion polymerization. It is therefore in the anionic polymers are emulsion polymers. 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 Materials, Georg Thieme Verlag, Stuttgart 1961, pages 133ff ).

In the emulsion polymerization for the preparation of the anionic polymers, 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 alkylhenols 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 anionic polymers 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, for example combinations of peroxides, hydroperoxides or hydrogen peroxide with reducing agents such as ascorbic acid or sodium bisulfite. These initiator systems may additionally contain metal ions such as iron (II) ions.

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

In the emulsion polymerization, if desired, regulators may be used, e.g. in amounts of from 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 z. B. Compounds with a thiol group such as tert-butyl mercaptan, Thioglycolsäureethylacrylester, mercaptoethanol, mercaptopropyltrimethoxysilane or tert-dodecyl mercaptan or regulator without thiol, in particular z. B. terpinolene.

The emulsion polymerization for the preparation of the anionic polymers 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 also after the end of the actual emulsion polymerization, ie after a conversion of the monomers of at least 95%, added again at least one initiator and the reaction mixture heated for a certain time to the polymerization or an overlying temperature.

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 (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 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 anionic polymer are generally obtained with solids contents of 15 to 75 wt .-%, preferably from 40 to 75 wt .-%. The molecular weight M _{w of} the anionic polymers is, for example, in the range of 100,000 to 1 million daltons. If the polymers have a gel phase, a molecular weight determination is not readily possible. The molar masses are then above the above-mentioned range.

The glass transition temperature Tg of the anionic polymers is for example in the range of -30 to 100 ° C, preferably in the range of -5 to 70 ° C and particularly preferably in the range of 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 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 may optionally contain polymerized small amounts of cationic monomer units, so that there are amphoteric polymers, but the total charge of the polymers must be anionic. For example, the net anionic charge is less than -0.2 meq / g. It is usually in the range of -0.5 to -2.0 meq / g. In addition, polymer dispersions of nonionic monomers which are emulsified with the aid of anionic surfactants or emulsifiers (such compounds have been described above in the emulsion polymerization for the preparation of anionic polymers) are also suitable as anionic polymers are. The surfactants or emulsifiers are used for this application, for example, in amounts of 1 to 15 wt .-%, based on the total dispersion.

Cationic polymers

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 polymer are in the main 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. For example, they are mostly in the range of 5,000 to 5 million. 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.
• Ebenfalls geeignet sind die Quarternierungsprodukte der vorstehenden Verbindungen mit C₁-C₈ Alkylchloriden, C₁-C₈-Dialkylsulfaten, C₁-C₁₆-Epoxiden oder Benzylchlorid.

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-A-01/36500 known alkyleneimine units containing monomers of the formula

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 the number average of m in the above formula is at least 2.1, usually 2.1 to 8, are preferred. They 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

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 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 group-containing monomer 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.

Other suitable comonomers are e.g. Methyl (meth) acrylate, methylethacrylate, ethyl (meth) acrylate, ethylethacrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, tert-butylethacrylate, n-octyl (meth) acrylate, 1,1,3,3-tetramethylbutyl (meth) acrylate, ethylhexyl (meth) acrylate and mixtures thereof.

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-A-0438744 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, polyvinyl-methylamines 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 should also 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-Dimethylaminoethylacrylamid 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 is used in a molar excess so that the resulting polymers carry a cationic total charge.

• (a) mindestens einem N-Vinylcarbonsäureamid der Formel
  
  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
  
  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 the formula I to form amino groups, wherein the content of cationic groups such as amino groups in the copolymer at least 5 mol% above the content of copolymerized acid groups of 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. Hereinafter the indication of vinylamine units in the amphoteric copolymers always means the sum of vinylamine and amidine units.

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

The amphoteric compounds thus obtained contain, for example

1. (a) optionally unhydrolyzed units of the formula I.
2. (b) vinylamine units and amidine units, wherein the content of amino plus amidine groups in the copolymer is at least 5 mol% higher than the content of copolymerized acid group-containing monomers,
3. (c) units of an acid group-containing monoethylenically unsaturated monomer and / or their alkali metal, alkaline earth metal or ammonium salts,
4. (d) 0 to 30 mol% of units of at least one other monoethylenically unsaturated monomer and
5. (e) 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-A-0 438 744 , 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 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. As already described in the case of the anionic polymers, a crosslinker is understood as meaning those monomers which contain at least two double bonds in the molecule, eg. As methylenebisacrylamide, 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, soba 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 2 oder mehr Isocyantgruppen, eventuell blockierte Kohlensäurederivate,
• Verbindungen, die 2 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 2 amino groups reactive groups, such as. B.

• Di- and polyglycidyl compounds,
• Di- and polyhalogen compounds,
• Compounds with 2 or more isocyanate groups, possibly blocked carbonic acid derivatives,
• Compounds having 2 or more double bonds suitable for Michael addition,
• Di- and polyaldehydes,
• monoethylenically unsaturated carboxylic acids, their esters and anhydrides.

Other suitable 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 during or after the polyaddition add crosslinkers having at least 2 groups that can react with the aziridines or the amino groups formed, such as. For example, 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. produced by polymerization of ethyleneimine homopolymers of ethyleneimine or grafted with ethyleneimine polymers such as polyamidoamines.

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

As cationic polymers are also polycondensates, eg. 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 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 bearing at least 2 primary amino groups and at least one further less reactive, ie 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 groups carrying polysaccharides such. B. 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.

papermaking

As fibrous materials for the production of pulps all conventional qualities come into consideration, for. B. wood 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. For the production of pulps, waste paper is mostly used, which is used either alone or in admixture with other fibers or it is based on fiber blends of a primary material and recycled coated Committee, z. B. bleached pine sulfate in admixture with recycled coated broke. The process according to the invention is of technical interest for the production of paper and paperboard because it significantly increases the strength properties of the recycled 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 according to the process of WO 2006/056381 manufacturable papers.

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

In the method according to the invention, the 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 component is usually added to the paper stock only after the cationic component has been added, but it can also be metered into the paper stock at the same time, but separately from the cationic component. Furthermore, it is also possible first to add the anionic and subsequently the cationic component.

Particularly advantageous is a process variant in which the pulp is heated to a temperature of at least 40 ° C, e.g. 45 to 55 ° C, preferably heated to at least 50 ° C and then dosed first the water-soluble cationic polymer and then or simultaneously, but separately, the water-insoluble anionic polymer. However, it is also possible to meter the water-insoluble anionic polymer and then the water-soluble cationic polymer into the paper stock heated to at least 40 ° C. first. The water-soluble cationic polymer used is preferably a polymer containing vinylamine units.

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. As retention aids, dehydrating agents, other dry strength such as starch, pigments, fillers, optical brighteners, defoamers, biocides and paper dyes.

The percentages in the examples are by weight unless otherwise specified. The K value of the polymers was calculated according to Fikentscher, Cellulose Chemistry, 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%. Where K = k 1000.

For the individual tests, sheets were produced in laboratory tests in a Rapid-Köthen laboratory sheet former. The dry breaking length was determined according to DIN 53 112, sheet 1. The determination of the CMT value was carried out according to DIN 53 143, the dry burst pressure was determined according to DIN 53 141.

Examples

In the examples and comparative examples, the following polymers were tested:

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 Polymer A, except that the degree of hydrolysis of the polymer was 30 mol%. The water-soluble cationic polymer 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.

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 8 equal parts and in Examples 1 to 3 and in Comparative Examples 1 to 5 under the conditions specified in the Examples and Comparative Examples on a Rapid Köthen sheet former according to ISO 5269/2 sheets of a basis weight of 120 gsm processed.

example 1

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 used

Acrylate resin amount 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

Another sample of the stock suspension described above was treated at a fabric temperature of 22 ° C with 0.25% Polymer B (polymer solids, based on dry pulp). After a residence 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, the temperature of which was about 20 ° C., was metered into the pulp suspension, which had a temperature of 22 ° 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.

Example 3

The dispersion of an anionic acrylate resin (solids 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 diluted by a factor of 10. The diluted dispersion was then added to the pulp suspension with gentle stirring. The amount of acrylate used was 5% (polymer solid), based on dry pulp. The mean particle size of the dispersed particles was 192 nm. The pulp suspension pretreated with the dispersion was then heated to 50 ° C. To the heated stock suspension was metered 0.25% polymer B (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 1

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

Comparative Examples 2 to 4 were according to Example 1 of WO 2006/056381 carried out.

Comparative Example 2

A sample of the stock suspension described above was mixed at a fabric temperature of 22 ° C. with 0.25% of polymer A (polymer solid, based on dry pulp). After a residence time of 5 minutes, 0.25% of a water-soluble copolymer of 30% acrylic acid and 70% vinylformamide was added. The copolymer was in the form of a sodium salt and had a K value of 90. After an exposure time of 1 minute, leaves were formed, which were then dried at 90 ° C. for 7 minutes.

Comparative Example 3

Another sample of the stock suspension described above was added at a fabric temperature of 22 ° C with 0.25% polymer B (polymer solid, based on dry pulp). After a residence time of 5 minutes, 0.5% of a water-soluble copolymer of 30% acrylic acid and 70% vinylformamide was added. The copolymer was in the form of a sodium salt and had a K value of 90. After an exposure time of 1 minute, leaves were formed, which were then dried at 90 ° C. for 7 minutes.

Comparative Example 4

Another sample of the stock suspension described above was treated at a material temperature of 22 ° C. with 1% of polymer B (polymer solid, based on dry pulp). After a residence time of 5 minutes, 1% of a water-soluble copolymer of 30% acrylic acid and 70% vinylformamide was added. The copolymer was in the form of a sodium salt and had a K value of 90. After an exposure time of 1 minute, leaves were formed, which were then dried at 90 ° C. for 7 minutes.

Comparative Example 5

Another sample of the stock suspension described above was mixed at a material temperature of 50 ° C. with 0.25% of polymer B (polymer solid, based on dry pulp). After a residence time of 5 minutes, 0.5% of a water-soluble Copolymer of 30% acrylic acid and 70% vinylformamide added. The copolymer was in the form of a sodium salt and had a K value of 90. After an exposure time of 1 minute, leaves were formed, which were then dried at 90 ° C. for 7 minutes.

Examination of the paper sheets produced according to Examples 1 to 3 and Comparative Examples 1 to 5

After a storage time of the leaves produced in the air conditioning room according to the examples and comparative examples at a constant 23 ° C and 50% humidity for 12 hours each of 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 53 143, the dry burst pressure of the sheets 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 5213 532 251 2 4844 474 233 3 5134 511 235 Comparative Example 1 3598 307 141 Comparative Example 2 4011 361 176 Comparative Example 3 4678 401 217 Comparative Example 4 4768 443 231 Comparative Example 5 4489 383 211

Claims (14)

1. A process for the production of paper, board and cardboard having high dry strength by separate 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 a water-insoluble polymer having a content of acid groups of from 0.1 to 10 mol% or an aqueous dispersion of a nonionic polymer, which dispersion has been made anionic, is used as the anionic polymer.
2. The process according to claim 1, wherein the water-insoluble polymer has a content of acid groups of from 0.1 to 9 mol%.
3. The process according to claim 1 or 2, wherein the water-insoluble polymer has a content of acid groups of from 0.5 to 6 mol%.
4. The process according to any of claims 1 to 3, wherein the water-soluble polymer has a content of acid groups of from 2 to 6 mol%.
5. The process according to any of claims 1 to 4, wherein the acid groups are selected from carboxyl, sulfo and phosphonic acid groups.
6. The process according to any of claims 1 to 5, wherein the anionic polymers comprise

   (a) at least one monomer from the group consisting of C₁- to C₂₀-alkyl acrylates, C₁- to C₂₀-alkyl methacrylates, vinyl esters of saturated carboxylic acids comprising up to 20 carbon atoms, vinylaromatics having up to 20 carbon atoms, ethylenically unsaturated nitriles, vinyl ethers of saturated, monohydric alcohols comprising 1 to 10 carbon atoms, vinyl halides and aliphatic hydrocarbons having 2 to 8 carbon atoms and one or two double bonds,

   (b) at least one anionic monomer from the group consisting of the ethylenically unsaturated C₃- to C₈-carboxylic acids, vinylsulfonic acid, acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylphosphonic acid and the salts thereof and optionally

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

   (d) at least one monomer having at least two ethylenically unsaturated double bonds in the molecule
   incorporated in the form of polymerized units.
7. The process according to any of claims 1 to 6, wherein the anionic polymers comprise

   (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-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, acrylonitrile, methacrylonitrile, butadiene and isoprene,

   (b) from 0.5 to 9 mol% of at least one anionic monomers from the group consisting of the ethylenically unsaturated C₃- to C₅-carboxylic acids
   incorporated in the form of polymerized units.
8. The process according to any of claims 1 to 7, wherein the anionic polymers comprise at least 80 mol% of at least one monomer of group (a) incorporated in the form of polymerized units.
9. The process according to claim 8, wherein the anionic polymers comprise, as monomer of group (a), mixtures of (i) a C₁- to C₂₀-alkyl acrylate and/or a C₁- to C₂₀-alkyl methacrylate and (ii) styrene, α-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, butadiene and/or isoprene in the weight ratio of from 10 : 90 to 90 : 10 incorporated in the form of polymerized units.
10. The process according to any of claims 1 to 9, wherein the anionic polymers have a glass transition temperature Tg of from -30 to 100°C (measured according to DIN EN ISO 11357).
11. The process according to any of claims 1 to 10, wherein the anionic polymers have a glass transition temperature of from -5 to 70°C.
12. The process according to any of claims 1 to 11, wherein the temperature of the paper stock is at least 40°C.
13. The process according to any of claims 1 to 11, wherein the temperature of the paper stock is at least 50°C.
14. The process according to any of claims 1 to 13, wherein a polymer having vinylamine units is used as the water-soluble cationic polymer.