WO1992014881A1

WO1992014881A1 - Aqueous sludges of finely-ground fillers and their use for producing filler-containing paper

Info

Publication number: WO1992014881A1
Application number: PCT/EP1992/000328
Authority: WO
Inventors: Sigberg Pfohl; Werner Auhorn; Andreas Stange; Friedrich Linhart
Original assignee: Basf Aktiengesellschaft
Priority date: 1991-02-26
Filing date: 1992-02-17
Publication date: 1992-09-03
Also published as: DE4105919A1; DE59202742D1; EP0573458B1; ATE124484T1; EP0573458A1

Abstract

Aqueous sludges of finely-ground fillers that are at least partially coated with polymers are produced by successively adding to an aqueous filler sludge 0.1 to 5 wt % of a cationic paper consolidating agent, 0.1 to 5 wt % of a non-ionic and/or anionic paper consolidating and/or sizing agent, with respect to the weight of fillers. The cationic consolidating agent is used in such an amount, with respect to the anionic consolidating and/or sizing agents, that the finely-ground fillers have a cationic charge. Also disclosed is the use of the thus obtained aqueous sludges of finely-ground fillers for producing filler-containing paper, cardboard and/or paperboard by adding the aqueous sludges to a paper pulp and by draining the paper pulp.

Description

Aqueous slurries of finely divided fillers and their use in the manufacture of filler-containing paper

description

The invention relates to aqueous slurries of finely divided fillers which are at least partially coated with polymers, and to the use of the aqueous slurries for the production of filler-containing paper or cardboard and filler-containing cardboard.

GB-A-2 125 838 discloses the treatment of fillers which are used for the production of paper with cationic polyelectrolytes and aluminum salts and, if appropriate, aluminates. Suitable polyelectrolytes are, for example, cationic polyacrylamides, which are used in amounts of 0.1 to 6% by weight, based on the mixture. The individual components are mixed in a dry state. When the filler mixture is introduced into a paper stock, the surfaces of the filler particles show a positive charge. This

Filler mixtures result in papers with improved strength. However, the effects that can be achieved in this way are still unsatisfactory in practice. From EP-B-0 227 465 a process for the production of a filled paper is known, in which both the paper fibers and separately the fillers are each treated in an aqueous medium with synthetic polymers which carry a charge. Possible synthetic polymers are flocculants or retention agents which are usually used in paper manufacture. The amounts used are 0.2 to 1% by weight, based on the dry weight of the fillers. The effects of an improvement in the dry strength of the paper which can be achieved with this method are still in need of improvement.

EP-A-278 602 discloses a process for the production of aqueous suspensions of fillers containing finely divided calcium carbonate, in which slurries containing at least 60% by weight of fillers are added an anionic and cationic polyelectrolyte in such a ratio that the filler particles carry a cationic charge. Suitable cationic polyelectrolytes are, for example, polydiallyldimethylammonium chlorides with molecular weights of about 10,000 to 100,000. The anionic polyelectrolytes are used in quantities of 0.01 to 0.1% by weight, based on filler, while the cationic polyelectrolytes in quantities of 0.01 to about 1.5 wt .-%, based on filler can be used. These highly concentrated pigment slurries have a relatively low viscosity, however they cannot be used to produce papers with high dry strength.

DE-A-2 115 409 discloses the treatment of fillers which are used in the production of paper in aqueous slurry with water-soluble compounds which are deposited on the particulate fillers by adding aluminum sulfate, calcium chloride or borax. Suitable water-soluble polymers are, for example, polyacrylates, which can be converted into a clear solution or into a clear gel by adding sodium hydroxide or ammonia, and also polyvinyl alcohol, casein or alginates. The treated like this

In this way, pigments are coated with polymers. With the pigments treated in this way, papers with higher strength are obtained. The disadvantage here is the high amount of aluminum sulfate that is required for fixing the polymers to the pigment particles. The strength properties of the papers produced with these treated fillers still leave something to be desired.

From CA-A-1 110 019 a process for the production of paper with high dry strength is known, in which a water-soluble cationic polymer, e.g. Polyethyleneimine, and then a water-soluble anionic polymer, e.g. adds a hydrolyzed polyacrylamide and the paper stock on a paper machine

Leaf formation drained. The anionic polymers contain up to 30 mol% of polymerized acrylic acid.

EP-B-0 193 111 describes a process for producing paper with high dry strength and as low as possible

Wet strength is known, in which the paper stock is treated in succession with cationic polymers and then anionic polymers and dewatered to form sheets. As an anionic See polymers include, for example, homopolymers of ethylenically unsaturated C ₃ to C ₅ carboxylic acids or copolymers of these carboxylic acids with amides, nitriles and / or esters of ethylenically unsaturated C ₃ to C ₅ carboxylic acids

Consider, the copolymers containing 35 to 99 wt .-% of an ethylenically unsaturated C ₃ to C ₅ carboxylic acid. When using the latter two methods in practice, however, it has been found that the achievable effects with respect to dry consolidation are not satisfactory because of the very high shear forces in the high-speed paper machines and because of the high load of impurities in largely closed paper machine water circuits.

The present invention has for its object to provide improved aqueous slurries of finely divided fillers for the production of filler-containing papers compared to the prior art. The filler slurries should in particular be processable for the production of filled papers with high dry strength. Another object is to make the fillers less sensitive to pH changes in paper manufacture and, in particular, to reduce the solubility of calcium sulfate pigments in water. The object is achieved according to the invention with aqueous slurries of finely divided fillers, which are at least partially coated with polymers, for the production of filler-containing paper, which are obtainable by successive addition of

[a] 0.5 to 5% by weight of a cationic strengthener for paper and

(b) 0.5 to 5% by weight of a nonionic and / or anionic strengthening agent for paper, a nonionic and / or anionic sizing agent for paper or mixtures of the nonionic or anionic strengthening agents and

Sizing agents or by adding the hardener in reverse order to aqueous slurries of the fillers, the cationic hardener (a) compared to the compounds (b) in such a Amount used that the finely divided fillers carry a cationic charge. Such filler slurries are used for the production of filler-containing paper or cardboard or filler-containing cardboard by adding the aqueous slurry to a paper stock and dewatering the paper stock. This gives papers with high dry strength. The coating of the fillers with the polymer has the effect that the fillers are incorporated into the fiber structure of the paper significantly better than untreated fillers, so that with the aqueous pigment slurries according to the invention, compared to known pigment slurries, significantly higher paper strengths can be achieved with the same filler content in the paper. Suitable fillers are all those finely divided minerals that are usually used for the production of filler-containing paper. These are, for example, calcium carbonate, chalk, titanium dioxide, kaolin, china clay, satin white, calcium sulfate, barium carbonate and

Barium sulfate. The average particle size of the fillers is usually in the range from 0.1 to 5.0 μm. The finely divided fillers are suspended in water. For economic reasons, the filler concentration of the aqueous slurry should be at least 10% by weight. Filler concentrations of up to 70% by weight are possible, but it is advisable to use a dispersant for more highly concentrated pigment slurries in order to be able to produce aqueous pigment slurries with a relatively low viscosity. Suitable dispersants are, for example, polymers of acrylic acid with a K value of 8 to 40 or cationic dispersants such as low molecular weight polymers of diallyldimethylammonium chloride with average molecular weights of 1000 to 40,000. The dispersants are used in quantities of 0.01 to 0.3, preferably 0.02 up to 0.05% by weight, based on the fillers. However, they are only used if the viscosity of the aqueous slurries of the finely divided pigments becomes too high.

The aqueous pigment slurries described above are successively (a) with cationic strengthening agents and then (b) with nonionic or anionic strengthening agents, sizing agents or their mixtures or in reverse order, that is, first treated with the anionic component (b) and then with katicnic solidifiers (a). For this purpose, the respective compounds in question are added to the pigment slurries in the form of an aqueous solution or an aqueous dispersion and are distributed as evenly as possible therein. This can be done, for example, with the aid of shaving units, such as ultraturrax devices, or in practice in a deliteur. As soon as the compounds (a) or (b) added first for slurrying the fillers largely from the suspended ones

Fillers are added, first add the other component (a) or (b) required for the treatment of the fillers, so that at least partially coated suspended filler particles are present. For example, people treated in this way

Calcium carbonate fillers also in the acidic pH range, e.g. at pH 5 to 6, practically without damage to the fillers used in papermaking. Calcium sulfate fillers which have been provided with a coating in accordance with the invention therefore have a significantly reduced solubility in water in comparison with untreated calcium sulfate fillers. The calcium sulfate pigments treated according to the invention are therefore of particular interest for the production of filled papers and paper products, such as cardboard and cardboard. Calcium carbonate fillers and calcium sulfate fillers are preferably mixed with (a) cationic strengthening agents, e.g. Polyethyleneimine or water-soluble, crosslinked polyamidoamines followed by (b) alkydiketen emulsions, e.g. Stearyl diketene emulsions, or copolymers of acrylamide and acrylic acid (the copolymerized acrylic acid content is 5 to 20% by weight). The temperature of the aqueous suspensions of the fillers can be varied over a wide range of temperatures during the action of compounds (a) and (b), e.g. between 5 and 95 ° C. Usually the dry setting agents are brought together with the aqueous pigment slurries at temperatures in the range from 15 to 40 ° C.

Solidifiers (a) and (b) are all those polymers which reduce the dry strength of paper when added to the pulp in an amount of 0.5% by weight, based on dry fibers (for example bleached pine sulphate pulp as standard) increase at least 10%. In addition to increasing the dry strength, the wet strength of the paper can also be increased by the strengthening agents (a) or (b) which are considered according to the invention.

Suitable cationic hardeners (a) are, for example, polyethyleneimines which contain at least 5 ethyleneimine units. Both low molecular weight and very high molecular weight polyethyleneimines can be used. The polyethyleneimines can be mixed with organic acids such as formic acid, acetic acid or propionic acid or also with inorganic acids such as hydrochloric acid.

Sulfuric acid or phosphoric acid can be neutralized. Suitable polyethyleneimines in 10% by weight aqueous solution at 20 ° C have viscosities of 5 to 1500, preferably 25 to 700 mPas (Brookfield viscometer, 20 rpm).

Suitable cationic hardeners are also partially to completely hydrolyzed homopolymers and copolymers of N-vinylformamide. The degree of hydrolysis of the N-vinylformamide in these polymers is at least 2 mol% and is preferably in the range from 50 to 100 mol%. For example, if one starts from a homopolymer of N-vinylformamide and hydrolyzes it to 100%, a polyvinylamine is obtained. Copolymers of N-vinylformamide with other monomers, for example vinyl acetate, vinyl propionate, acrylonitrile, methacrylonitrile, acrylamide and methacrylamide can also be hydrolyzed by the action of acids or bases. The degree of hydrolysis, which was given above, always refers to the N-vinylformamide content of the copolymer in the copolymer. In the hydrolysis of copolymers of N-vinylformamide and vinyl acetate or vinyl propionate, polymers are obtained which, in addition to the units of the monomers on which these polymers are based, also have units of vinylamine and vinyl alcohol. Suitable homopolymers of N-vinylformamide and copolymers of N-vinylformamide with other ethylenically unsaturated monomers have a K value of 50 to 200, preferably 80 to 150. The K value of the hydrolyzed and the non-hydrolyzed N-vinylformamide polymers is correct within the error limits match. Such polymers are known, for example, from US Pat. No. 4,421,602 and US Pat. No. 4,444,667. Suitable hardeners (a) are also homopolymers and copolymers of N-vinylimidazole and N-vinylimidazole and their derivatives. The cooo lers contain at least 30% by weight of N-vinylimiαazole or N-vinylimidazoline or their derivatives in the form of the salts polymerized with inorganic or organic acids or in the form of quaternization products. Suitable comonomers for the preparation of the copolymers are, for example, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate and C ₁ -C ₄ -alkyl vinyl ether, for example vinyl methyl ether. Suitable derivatives of N-vinyl imidazole and N-vinylimidazoline are, for example, the compounds which are substituted in the 2-position C ₁ - to C ₃ -alkyl or phenyl-substituted compounds, for example 1-vinyl-2-methylimidazoline in the form of the salt with hydrochloric acid.

Other water-soluble cationic strengthening agents (a) which increase both the dry strength and the wet strength of paper are polyamidoamines which are crosslinked with epichlorohydrin. Suitable products of this type are known, for example, from US Pat. No. 2,926,116. They are made by combining a dicarboxylic acid such as adipic acid with a polyamine e.g.

Diethylenetriamine or tetraethylene pentamine, condensed and the resin obtained crosslinked with epichlorohydrin to the extent that water-soluble reaction products are still obtained. In 10% by weight aqueous solution at a temperature of 20 ° C., these polymers have a viscosity of 20 to 200 mPas (measured with a rotary viscometer at 20 rpm).

This group of cationic solidifiers also includes polyamidoamines grafted with ethyleneimine, which are crosslinked with epichlorohydrin or, according to DE-PS 24 34 816, with reaction products which, by reacting the terminal OH groups of

Polyalkylene oxides with 8 to 100 alkylene oxide units (preferably polyethylene oxides) with at least equivalent amounts of epichlorohydrin can be obtained. These are polyalkylene oxides end capped on both sides with epichlorohydrin. The viscosity of the water-soluble products grafted and crosslinked with ethyleneimine - measured with a rotary viscometer at 20 rpm and a concentration of polycondensate of 10% by weight and 20 ° C. - is 300 to 2500 mPas. In addition, homopolymers of diallyldi-C ₁ -C ₃ -alkylammonium compounds and diaikylmono-C ₁ -C ₃ -amines are suitable as cationic solidifiers (a). Either the free bases or the halides, in particular the chlorides or quaternized products can be used. Homopolymers of diallyldimethylammonium chloride and diallyidiethylammonium chloride are particularly suitable.

Copolymers of acrylamide which have up to 45, preferably 2 to

30% by weight of a basic di-C ₁ - to C ₃ -alkylamino-C ₂ - bis

C ₄ alkyl (meth) acrylate copolymerized. The basic acrylates are used in the form of the salts with inorganic or organic acids or in quaternized form. Of particular interest here are copolymers of acrylic amide and diethyl aminoethyl acrylate or diethylaminoethyl methacrylate in the form of the hydrochloride or in the form quaternized with methyl chloride, copolymers of acrylamide and diethylaminoethyl acrylate as sulfate, chloride and methosulfate, copolymers of acrylamide and dimethylaminopropyl sulfate as or methochloride, copolymers of acrylamide and aminoethyl acrylate hydrochloride, copolymers of acrylamide and diethylaminoethyl methacrylate sulfate and copolymers of acrylamide and diethylaminopropylacrylate hydrochloride.

Copolymers of acrylamide and dialkylaminoalkylacrylamides are also of interest as cationic hardeners (a), e.g. Copolymers of acrylamide which contain up to 30% by weight of polymerized dimethylaminoethyl acrylamide, dimethylaminoethyl methacrylamide, dimethylaminopropylacrylamide, dimethylaminobutylacrylamide or aminoethyl acrylamide. These hardeners are also used in salt form or in quaternized form.

The homopolymers and copolymers described above are known as strengthening agents for paper. They have K values of 50 to 200, preferably 80 to 150 (measured according to H. Fikentscher in a 1% strength aqueous solution of the polymer at 25 ° C. and pH 7).

Some of the polymers mentioned can also be used for other applications, for example polyamidoamines grafted with ethyleneimine which are crosslinked are used in practice predominantly as retention aids. In the higher according to the invention The quantities of polymers used are these compounds, strengthening agents which, for example, increase the dry and wet strength of the paper. Of the cationic solidifiers (a), preference is given to polyethyleneimine with at least 5 polymerized ethylene lenimine units, water-soluble polyamidoamines onto which ethyleneimine is optionally grafted and which are crosslinked with epichlorohydrin or with a polyalkylene oxide which is closed on both sides with epichlorohydrin end groups, or copolymers of acrylamide and dimethylaminoethylacrylacrylate quaternized form with K values from 50 to 200. In some cases, an increase in filler retention can be achieved if mixtures of strengthening agents are used, e.g. a mixture of polyethyleneimine that contains 500 ethyleneimine units and a copolymer of acrylamide and 20% by weight dimethylaminoethyl acrylate methochloride with a K value of 190.

The cationic solidifiers are added to the aqueous slurries of the finely divided fillers in amounts of 0.1 to 5, preferably 1 to 2,% by weight. It is essential that they are used in such an amount that the finely divided fillers treated with them still carry a cationic charge even after the addition of the dry strength agent (b). The charge of fillers which have been treated according to the invention can be determined, for example, by isolating the fillers from the aqueous slurry and determining the charge in the filtrate using electrolyte titration, cf. D. Hörn, Polyethylenimine / Physicochemical Properties and Application (IUPAC) Polymeric amines and Ammonium Salts, Pergamon Press, Oxford and New York, 1980, pages 335-355. In practice, this is done with the help of a Mütek PCD device, Mütek laser and (opto) electronic devices GmbH, D-8036 Herrsching (cf. the associated brochure from 1988).

Suitable anionic hardeners (b) are, for example, homopolymeric seeds of ethylenically unsaturated C ₃ to C ₅ carboxylic acids. These include, for example, homopolymers

Acrylic acid, methacrylic acid, maleic acid, hydrolyzed homopolymers of maleic anhydride and homopolymers of itaconic acid. The ethylenically unsaturated carboxylic acids mentioned can be copolymerized with other monomers. For example, anionic solidifying copolymers of 1 to 99% by weight of ethylenically unsaturated C ₃ to C ₅ carboxylic acids, 99 to 1% by weight of an amide, nitrile and / or an ester of an ethylenically unsaturated C ₃ -bis are suitable C ₅ carboxylic acid and 0 to

15 wt .-% styrene or a Cι ~ to C ₄ alkyl vinyl ether. The copolymers preferably contain 5 to 20% by weight of an ethylenically unsaturated C ₃ to C ₅ carboxylic acid, 95 to

80% by weight of an amide, nitrile and / or an ester of an ethylenically unsaturated carboxylic acid and 0 to 15% by weight of styrene or a C ₁ to C ₄ alkyl vinyl ether. The sum of the percentages by weight in the copolymer is 100 in each case. The esters of ethylenically unsaturated C ₃ to C ₅ carboxylic acids of the copolymers are preferably derived from monohydric alcohols having 1 to 4 carbon atoms. Particularly preferred as component (b) are terpolymers made from (1) 5 to 30% by weight of acrylic acid, (2) 90 to 65% by weight of acrylamide and (3) 5 to 30% by weight of acrylonitrile. The anionic water-soluble polymers (b) have a K value (according to H. Fikentscher) from 50 to 200 and preferably from 80 to 150. The K value for the copolymers is determined in 1% strength aqueous solution at 25 ° C. The pH when determining the K values is 7. The anionic ones

Dry strength agents (b) can be used in the form of the free acids or in partially or completely neutralized form with bases. It is only important here that the partially or completely neutralized polymers are soluble in water. Suitable bases are alkali and alkaline earths, ammonia and amines, e.g. Sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide, barium hydroxide, ammonia, trimethylamine,

Ethanolamine and morpholine.

Nonionic hardeners (b) are polyvinyl alcohols which can be obtained, for example, by polymerizing vinyl acetate and saponifying the polymers. Other suitable nonionic solidifiers are polyacrylamides, which are obtained by polymerizing

Acrylamide can be produced. Like the cationic hardeners, the nonionic hardeners have K values in the range from 50 to 200, preferably 80 to 150. The hardeners (b) can be used individually or in a mixture, for example a mixture of polyacrylamide and a copolymer can be used as the dry hardener made of acrylamide and 20 wt .-% acrylic acid or a Use a mixture of an acrylamide homopolymer and acrylic acid homopolymer. The dry strength agents (b) are added to the aqueous suspension of fillers in amounts of 0.1 to 5, preferably 1 to 3,% by weight. To treat the aqueous slurries of finely divided fillers, one can of course also proceed by adding the finely divided fillers to an aqueous solution of the solidifier (a) or (b) and mixing the filler suspension obtained. In the treatment of finely divided fillers in an aqueous medium with solidifiers according to (a) and (b), the finely divided fillers are at least partially coated on the surface with polymers. The opposite charge of the compounds of (a) and (b) causes polymers to deposit on the filler particles and adhere to them. In order to achieve a further increase in the binding of the polymers to the fillers, aluminum sulfate (alum) can optionally also be added in amounts of 0.1 to 3% by weight, based on the filler.

Non-ionic and / or anionic sizing agents for paper can also be used as component (b) in amounts of 0.1 to 5% by weight, based on the fillers. If the aqueous slurries of finely divided fillers obtainable in this way are used in the production of filler-containing papers, a markedly reduced water absorption is found compared to such filler-containing papers, which can be obtained using glue-free aqueous slurries of fillers, which are subsequently treated with a hardener (a) and ( b) have been treated. Suitable sizing agents are, for example, aqueous emulsions of alkyldiketenes, e.g. Stearyldiketene, copolymers of diisobutene and maleic anhydride, which are used in hydrolyzed form as alkali or ammonium salts in aqueous solution, copolymers of styrene, maleic anhydride and

Acrylic acid, in which the maleic anhydride is also hydrolyzed and at least partially neutralized with sodium hydroxide solution or ammonia, and copolymers of butyl acrylate and acrylonitrile, which are obtained by polymerizing the monomers in aqueous

Solutions of degraded starches are available. Such sizing agents are described, for example, in EP-B 0 257 412. Resin glues (rosin) and aqueous dispersions of alkenyl succinic anhydrides are also suitable as component (b). A further modification of the fillers is possible by additionally treating 0.001 to 0.02% by weight of an acrylamide polymer with a K value of at least after treating the aqueous slurries of the finely divided fillers with the dry strength agents (a) and (b) 220 added as a flocculant. With the help of this measure, an increase in the ash content in the paper can be achieved when the finely divided fillers treated in this way are used during paper production.

The aqueous slurries of the finely divided fillers, which have been treated in succession with components (a) and (b) or in reverse order and which carry a cationic charge, are used to produce filler-containing paper or cardboard and filler-containing cardboard. The aqueous slurries become a paper stock which, in addition to the

Slurrying the fibers in water may also contain other additives customary in paper production, for example retention aids, defoamers or dyes, and added and mixed. The paper stock mixed with the aqueous slurries of finely divided fillers is then dewatered in the customary manner on the paper machine. The aqueous slurries of the pigments are added to the paper stock in such an amount that papers with filler contents of 5 to 70, preferably 20 to 40,% by weight are obtained. The aqueous pigment slurries are also used for the production of filler-containing cardboard and of filler-containing cardboard. The pigment slurries according to the invention can be used for the production of all filler-containing papers and paper products, for example for the production of writing, printing and packaging papers. The papers can consist of a large number of different types of fiber materials, for example of sulfite or sulfate pulp in the bleached or unbleached state, wood pulp, thermomechanical material (TMP), chemo-thermomechanical material (CTMP) and waste paper. The papermaking takes place in the pH range from 4 to 9, preferably at pH values from 6 to 7. To adjust a pH value in the acidic range, sulfuric acid or aluminum sulfate can be added to the stock suspension. The percentages in the examples mean percent by weight. The dry tear length was determined according to DIN 53 112, sheet 1. The whiteness of the paper was determined at 457 μm with a conventional color measuring device.

The charge density was determined using an electrolyte titration with a Mütek PCD device, Mütek laser and optoelectronic devices GmbH, D-8036 Herrsching.

The K values of the polymers were determined according to H. Fikentscher,

Cellulose-Chemie, Volume 13, 58-64 and 71-74 (1932) in 1% aqueous solution at 25 ° C and pH 7 determined.

Example 1 a) Aqueous suspension of china clay

Water is placed in a mixing vessel and enough china clay with an average particle size of 1 to 3 μm is added with stirring, so that a 20% aqueous suspension of china clay is formed. 0.6%, based on china clay, of a polyethyleneimine, which is in

10% aqueous solution has a viscosity of 30 mPas. The slurry is then stirred for 5 minutes and mixed with 1.8%, based on china clay, of a copolymer of 80% acrylamide and 20% acrylic acid, which in the form of

Sodium salt has a K value of 120 (anionic dry strength agent). The solid particles contained in the slurry had a polymer coating and had a positive charge. b) Production of paper

A paper made from 85% bleached wood pulp and 15% bleached pine sulfate pulp with a basis weight of 80 g / m ^{2 was} produced on a test paper machine with a working width of 75 cm at a speed of 60 m / min. The pH of the stock suspension was 7.5, the freeness 60 ° Schopper-Riegler (° SR). The aqueous suspension of china clay according to a) was metered in continuously in an amount such that the mixture prepared from the mixture was added to the fibrous suspension described above Paper had an ash content of about 30%. Before the headbox, 0.04% of a commercially available retention agent (condensation product of adipic acid and diethylenetriamine, grafted with polyethyleneimine and crosslinked with a polyalkylene oxide end-capped with epichlorohydrin) and 0.02%, based on the dry content of the paper stock, were added to the paper stock Copolymers of acrylamide and acrylic acid with a K value of 250. The basis weight, the ash content, the dry tear length and the whiteness were determined from the paper formed in this way. The values are given in Table 1.

Comparative Example 1 Example 1b) was repeated with the exception that an untreated 20% aqueous suspension of china clay was used instead of the aqueous slurry a) treated with dry strength agents to produce paper. The properties of paper made therefrom are given in Table 1.

Comparative Example 2 (according to the teaching of CA-A-1 110 019)

So much of an aqueous suspension of china clay was added to the pulp slurry described in Example 1b) in order to produce sheets with a filler content (determined by the ash content of the paper) of approximately 30%. 0.2% of polyethyleneimine, which had a viscosity of 30 mPas in 10% strength aqueous solution, was then added to the paper stock containing fibers and fillers, based on the dry content of the total paper stock. After the stock density controller, 0.6% of a copolymer of 80% acrylamide and 20% acrylic acid, based on the dry total fabric, was metered in continuously. This copolymer was in the form of the sodium salt and had a K value of 120. The properties of the paper produced from it are given in Table 1.

Example 2 a) aqueous slurry of china clay

By introducing china clay into water, a 20% aqueous slurry is first prepared and with vigorous stirring with 1.2%, based on china clay, with a copolymer of 80% acrylamide and 20% dimethylaminoethyl acrylate methochloride with a K value of 130 (cationic dry strength agent) added. After stirring for 5 minutes, 0.6%, based on, is added to the filler slurry

China clay, a copolymer of 90% acrylamide and 10% acrylic acid in the form of the sodium salt with a K value of 120 and stir the slurry for another 10 minutes. After this treatment, the suspended solid particles were coated with a polymer and had a cationic charge. b) Production of paper

Paper was produced in accordance with the instructions given in Example 1b), with the only exception that the China Clay slurry used in Example 2a) was used instead of the treated China clay slurry used therein, The properties of the paper thus obtainable are given in Table 2.

Comparative Example 3 (according to the teaching of CA-A-1 110 019)

To the fiber and filler suspension described in Comparative Example 2, 0.4% of a copolymer of 80% acrylamide and 20% dimethylaminoethyl acrylate methochloride with a K value of 130 and based on the consistency of the total pulp was first added continuously to the mixing chest 0.2% of a copolymer of 90% acrylamide and 10% acrylic acid in the form of the sodium salt with a K value of 120. The properties of the paper so produced are given in Table 2.

Comparative Example 4

Comparative Example 1 was repeated to obtain paper having the properties shown in Table 2.

Example 3 a) Aqueous suspension of china clay Sufficient china clay with an average particle size of 1 to 3 μm is introduced into water with vigorous stirring that a 20% aqueous suspension of china clay is formed. Then, with vigorous stirring, 1.2%, based on china clay, of a copolymer of 80% acrylamide and 20% dimethylaminoethyl acrylate methochloride with a K value of 130 (cationic dry strength agent) is added, the suspension is stirred for 5 minutes and mixed then with 0.6%, based on china clay, of a copolymer of 90% acrylamide and 10% acrylic acid in the form of the sodium salt with a K value of 100 (anionic dry strength agent). The solid particles are then covered with a polymer film and carry a positive charge. Aluminum sulfate was then added to the slurry until the pH was 4.5. b) Production of paper

Example 1b was repeated with the only exception that the china clay slurry obtained according to example 3a) was now used instead of the aqueous slurry used there. The properties of the paper thus obtained are shown in Table 3. Comparative Example 5 Comparative Example 1 was repeated. The properties of the paper obtained are given in Table 3.

Comparative Example 6 (comparison according to DE-A-32 43 904) A 20% aqueous slurry of china clay was mixed with 1.8% of a copolymer of 80% acrylamide and 20% dimethylaminoethyl acrylate methochloride with a K value of 130 and then adjusted to pH 4.5 by adding aluminum sulfate. This filler suspension was then used instead of the suspension la) specified in Example 1b) for the production of paper. The properties of the paper thus obtainable are given in Table 3.

Claims

Aqueous slurries of finely divided fillers, which are at least partially coated with polymers, for the production of filler-containing paper, characterized in that they are obtainable by successive addition of

(a) 0.1 to 5% by weight of a cationic strengthener for paper and

(b) 0.1 to 5% by weight of a nonionic and / or

anionic strengthener for paper, a nonionic and / or anionic sizing agent for paper or mixtures of the nonionic or anionic strengthening agents and the sizing agents or by adding components (a) and (b) in reverse order to aqueous slurries of the fillers, the cationic strengthening agents ( a) compared to the compounds (b) are used in such an amount that the finely divided fillers carry a cationic charge.

2. Aqueous slurries of finely divided fillers according to claim 1, characterized in that they additionally contain 0.01 to 0.3% by weight, based on the fillers, of a dispersant.

3. Aqueous slurries of finely divided fillers according to claim 1 or 2, characterized in that they

additionally contain 0.001 to 0.02% by weight of an acrylamide polymer with a K value of at least 220 as a flocculant.

4. Aqueous slurries of finely divided fillers according to claim 1 or 2, characterized in that as

Dry strengthener

(a) Polyethylenimine with at least 5 copolymerized ethyleneimine units, water-soluble polyamidoamines onto which ethyleneimine is optionally grafted and which is coated with epichlorohydrin or with one on both sides Epichlorohydrin end-capped polyalkylene oxide or copolymers of acrylamide and dimethylaminoethyl acrylate with K values from 50 to 200 and

(b) Homopolymers of acrylamide or anionically modified copolymers of acrylamide with K values from 50 to 200 (each determined according to H. Fikentscher in 1% by weight aqueous solution at 25 ° C. and pH 7).

5. Use of the aqueous slurries of finely divided

Fillers according to one of claims 1 to 4 for the production of filler-containing paper or cardboard and filler-containing cardboard by adding the aqueous slurries to a paper stock and dewatering the paper stock.