WO2003074786A2

WO2003074786A2 - Aqueous slurries of fine-particulate fillers, method for production and use thereof for the production of papers comprising fillers

Info

Publication number: WO2003074786A2
Application number: PCT/EP2003/002043
Authority: WO
Inventors: Anton Esser; Rudolf Lorz; Rainer Blum; Chafiq Belouadi
Original assignee: Basf Aktiengesellschaft
Priority date: 2002-03-05
Filing date: 2003-02-28
Publication date: 2003-09-12
Also published as: AU2003215608A8; AU2003215608A1; WO2003074786A3; DE10209448A1

Abstract

The invention relates to aqueous slurries of fine-particulate fillers, at least partly coated with polymers and which may be obtained by treatment of aqueous slurries of fine-particulate fillers with at least one binder for paper coating inks, production of the aqueous slurries and use thereof for the production of paper comprising fillers, card comprising fillers and cardboards comprising fillers, by means of draining the pulp.

Description

Aqueous suspensions of finely divided fillers, processes for their manufacture and their use for the manufacture of filler-containing papers

description

The invention relates to aqueous slurries of finely divided fillers which are at least partially coated with polymers, processes for their preparation and their use as additives to the pulp in the manufacture of filler-containing paper, filler-containing cardboard and filler-containing cardboard.

From DE-B-25 16 097 it is known that aqueous suspensions of inorganic particles which have a positive zeta potential are mixed with an anionic latex of a resin, the balance of the negative and positive charges of the particles of the inorganic substance in the suspension and the resin in the latex during mixing is adjusted such that essentially all of the resin particles are bound to the surface of the particles of the inorganic substance and the coated particles thus obtained have a zeta potential of essentially zero. Treatment of the inorganic particles with a latex, however, presupposes that the inorganic particles are pretreated with a cationic agent, such as cationic starch, so that they have a positive zeta potential. The aqueous suspensions are added to the paper stock in the manufacture of filler-containing paper.

In order to produce highly concentrated aqueous pigment slurries such as calcium carbonate slurries with low viscosity, a dispersing agent, e.g. low molecular weight polyacrylic acids, cf. EP-A-0 002 771. The dispersed pigment particles have an anionic surface charge. The aqueous pigment slurries are used, for example, in the manufacture of paper. For this purpose, use is also made of aqueous dispersions of precipitated calcium carbonate, which is usually processed in the absence of dispersants.

EP-B-0 573 458 discloses a process for the preparation of aqueous slurries of finely divided fillers, which are at least partially coated with polymers, for the production of filler-containing papers. In this process, a cationic strengthener for paper is added to an aqueous slurry of fillers and then a nonionic and / or anionic strengthener for paper or a nonionic or anionic sizing agent for paper. However, the cationic feedstocks are always used in such an amount that the finely divided fillers carry a cationic charge.

DE-A-198 21 089 discloses another process for the preparation of aqueous slurries of finely divided fillers which are at least partially coated with polymers. In this process, an aqueous suspension of fillers is treated in the absence of cationic strengthers for paper with at least one polymeric agent in the form of an aqueous dispersion. However, such dispersions always contain polymeric emulsifiers, e.g. degraded starches or synthetic polymers.

The object of the invention is to provide further aqueous suspensions of finely divided fillers which, in papermaking, produce papers with improved tear length and printability compared to the known suspensions.

The object is achieved with aqueous

Slurries of finely divided fillers which are at least partially coated with polymers, the slurries being obtainable by treating aqueous slurries of finely divided fillers with at least one binder for paper coating slips.

The aqueous slurries contain, for example, 1 to 50% by weight, preferably 10 to 40% by weight, of at least one finely divided filler. The amount of binder is, for example, 0.1 to 5% by weight, preferably 0.5 to 3% by weight, based on fillers.

The invention also relates to a process for the preparation of the aqueous slurries, 0.1 to 5% by weight of at least one binder for paper coating slips, based on filler, being added to an aqueous slurry of at least one finely divided filler, or the aqueous slurry of at least one finely divided Filler in an aqueous dispersion of a binder for paper coating colors and mixes the components. The molar mass of the emulsifiers contained in the binders for paper coating colors is <2000.

Another object of the invention is the use of the aqueous slurries described above as an additive to the pulp in the production of filler-containing paper, filler-containing like cardboard or filler-containing cardboard by dewatering the paper stock.

All pigments commonly used in the paper industry are suitable as fillers, e.g. Calcium carbonate, which can be used in the form of lime, chalk, marble or precipitated calcium carbonate, talc, kaolin, bentonite, satin white, calcium sulfate, barium sulfate and titanium dioxide. The particle diameter of the finely divided fillers is, for example, between 10 40 and 90% less than 2 μm.

The fillers are processed, for example, by introducing them into water to form an aqueous slurry. Precipitated calcium carbonate is usually used in the absence of

15 slurried in water. To prepare aqueous slurries of the other fillers, an anionic dispersing agent, e.g. Polyacrylic acids with a molecular weight Mw of, for example, 1000 to 40,000. If an anionic dispersant is used,

20 to 0.01 to 0.5 wt .-%, preferably 0.2 to 0.3 wt .-% for the preparation of the aqueous filler slurries. The finely divided fillers dispersed in water in the presence of anionic dispersants are anionic. The aqueous slurries usually contain at least 15 to 25% by weight

25 of a filler.

In order to produce the aqueous slurries of finely divided fillers according to the invention, aqueous slurries of optionally anionically dispersed finely divided fillers are treated with at least one binder for paper coating slips.

For example, 0.1 to 5% by weight, based on fillers, of a binder for paper coating slips can be added to an aqueous slurry containing at least 1 to 50% by weight of a finely divided filler, or an aqueous slurry of a 5 finely divided filler in an aqueous dispersion Enter a binder for paper coating colors and mix the components. The treatment of the aqueous slurries of finely divided fillers with the binders for paper coating colors can be carried out continuously or batchwise. When bringing together aqueous suspensions of finely divided fillers and aqueous dispersions of binders for paper coating colors, the fillers are at least partially coated or impregnated with binders. The components are mixed, for example, in a shear field. In most cases it is sufficient to stir the components after they have been brought together or to treat them in a shear field of an Ultraturrax device. Bringing together and mixing the components of the aqueous slurries can take place, for example, in the temperature range from 0 ° C. to 95 ° C., preferably 10 to 70 ° C. The components are usually mixed at room temperature up to a temperature of 40 ° C. The pH of the aqueous slurries of fillers treated with coating color binders is, for example, 5 to 11, preferably 6 to 9, the pH of slurries containing calcium carbonate preferably being more than 6.5.

The binders preferably contain so-called main monomers copolymerized, selected from Ci to Cie alkyl (meth) acrylates, vinyl aromatics with up to 20 C atoms, vinyl esters of carboxylic acids with 1 to 20 C atoms, vinyl halides, ethylenically unsaturated nitriles, non-aromatic hydrocarbons with a or two conjugated double bonds or mixtures of these monomers. For example, (Meth) -acrylsäurealkylestern with a Cχ-Cιo-alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, isobutyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate. Mixtures of the (meth) acrylic acid alkyl esters are also particularly suitable.

The vinyl esters of carboxylic acids with 1 to 20 carbon atoms are, for example Vinyl laurate, vinyl stearate, vinyl propionate and vinyl acetate.

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

Vinyl halides are ethylenically unsaturated compounds substituted with chlorine, fluorine or bromine, preferably vinyl chloride and vinylidene chloride.

Butadiene, isoprene and chloroprene and ethylene may be mentioned as non-aromatic hydrocarbons with one or two conjugated olefinic double bonds.

In addition to the main monomers, the binders can optionally also contain other monomers in copolymerized form, for example monomers containing hydroxyl groups, such as hydroxyalkyl acrylates or monomers with alkoxy groups, as can be obtained by alkoxylating hydroxyl-containing monomers with alkoxides, in particular ethylene oxide or propylene oxide, monomers with acid or Anhydride groups or their salts, for example (meth) acrylic acid, maleic acid, vinyl sulfonic acid. The binders preferably consist of a polymer which contains at least 20% by weight of the main monomers, particularly preferably at least 35% by weight and very particularly preferably at least 50% by weight, of at least one main monomer.

The binder can also contain at least 1% by weight, particularly preferably at least 3% by weight, particularly preferably at least 15% by weight, of monomers copolymerized with at least one acid group (acid monomers for short). The acid groups of the polymer can, if appropriate, be at least partially neutralized before later use. Preferably at least 30 mol%, particularly preferably 50 to 100% of the acid groups are neutralized. Suitable bases are volatile bases such as ammonia or non-volatile bases such as alkali metal hydroxides, in particular sodium hydroxide solution.

Preferred binders are, for example, aqueous dispersions of copolymers

(a) styrene and / or acrylonitrile or methacrylonitrile,

(b) Acrylic acid esters and / or methacrylic acid esters of C ~ to Ciβ alcohols, and optionally

(c) acrylic acid, methacrylic acid, maleic acid and / or itaconic acid.

Further preferred binders are polymers of (a) styrene, (b) butadiene and (c) optionally acrylic acid or methacrylic acid. Copolymers based on (meth) acrylic esters or vinyl acetate and other monoethylenically unsaturated monomers are also of interest as binders for paper coating slips for the treatment of aqueous slurries of fillers. The glass transition temperature of the polymers is e.g. -40 to + 50 ° C and is preferably below 6 ° C.

The binders for paper coating slips are preferably prepared by free-radical polymerization of the above-mentioned monomers in an aqueous medium in the presence of protective colloids or emulsifiers. Suitable protective colloids are, for example, polyvinyl alcohols or partially hydrolyzed polyvinyl acetates. For the treatment of finely divided fillers according to the invention, preference is given to using binders which are stabilized with the aid of protective colloids or emulsifiers with a molecular weight Mw <2000. Aqueous dispersions of the binders which contain anionic emulsifiers such as sodium lauryl sulfate, disulfo-C 1 -alkyldiphenyl oxide or mixtures thereof as emulsifiers for the polymers are particularly preferred. However, it is also possible to use such aqueous dispersions of polymers as binders with the aid of nonionic, cationic or amphoteric Emulsifiers are stabilized. Common emulsifiers are, for example, ethoxylated fatty alcohols (degree of ethoxylation: 3 to 50, alkyl radical: Cβ- to C ₃₆ ) / ethoxylated mono-, di- and trialkylphenols (degree of ethoxylation: 3 to 50, alkyl radical: Cβ- to Cι ₂ ), alkali metal salts of Dialkyl esters of sulfosuccinic acid as well as alkali and ammonium salts of alkyl sulfates (alkyl radical: CQ to C ₂ ), of ethoxylated alkanols (degree of ethoxylation: 4 to 30, alkyl radical: C ₂ to Ci 6), of ethoxylated alkyl phenols (degree of ethoxylation: 3 to 50, alkyl radical : C to Cg), of alkylsulfonic acids (alkyl radical: Cι to Cia) and of alkylarylsulfonic acids (alkyl radical: C ₉ to Ciβ) • The particle size of the polymers contained in the aqueous dispersions is, for example, 50 to 300 nm, preferably 80 to 150nm. The binders contain, for example, 0.1 to 5, preferably 0.5 to 3% by weight of at least one emulsifier.

Aqueous slurries of precipitated calcium carbonate, which is free from dispersants, and of ground calcium carbonate, which can be obtained by grinding lumpy calcium carbonate or marble in the presence of anionic polymeric dispersants such as polyacrylic acids with molecular weights of 1000 to 15000, are particularly preferably prepared. Anionic aqueous dispersions of copolymers based on styrene and butadiene or styrene and acrylic esters which are stabilized with the aid of emulsifiers which have a molecular weight M w <2000 are preferably used as binders for this purpose.

The aqueous slurries of fillers produced in accordance with the invention are used as additives to the paper stock in the production of filler-containing paper, filler-containing cardboard or filler-containing cardboard by dewatering the paper stock. They can be stored for a longer period of time or can be prepared and processed directly in the paper mill immediately before paper production. They are added to the paper stock in such an amount that filler-containing papers are formed which contain, for example, 5 to 50% by weight, preferably 15 to 35% by weight, of filler. The aqueous slurries are particularly suitable for the production of papers with filler contents of 30 to 50% by weight. The aqueous slurries of fillers can be added to both the thick and the thin material in papermaking. They can be used in the presence of the additives commonly used in the paper industry, such as sizing agents, fixing agents, dewatering agents, strengthening agents or retention aids. The aqueous pigment slurries treated according to the invention with a binder for paper coating slips can be used for the production of all filler-containing paper grades, for example newspaper printing, SC paper (supercalendered paper), wood-free or wood-containing writing and printing papers. For the production of such papers, for example, the main raw material components are wood pulp, thermomechanical material (TMP), che thermomechanical material (CTMP), pressure grinding (PGW) and sulphite and sulphate pulp. In order to achieve high filler retention, the addition of retention aids to the paper stock is recommended. The retention aids can, for example, be added to the thick stock or also to the thin stock. The retention agent used is, for example, high molecular weight polyacrylamides (the molar masses of the polymers are above 2 million) or so-called microparticle systems are used, in which case a polymeric cationic retention agent is first added to the paper stock, the paper stock is then subjected to shear and then bentonite or finely divided silica is added Amounts up to 2% by weight, based on dry fiber, are added.

In the production of wood-free papers, optical brighteners can also be added to the paper stock. The amounts of optical brighteners are, for example, 0.3 to 3.0, preferably 0.6 to 1.5% by weight, based on dry paper stock.

Due to the treatment of the aqueous slurries of finely divided fillers with aqueous dispersions of binders for paper coating colors, aqueous filler slurries are obtained which can be processed into papers in which the dusting in the printing and copying process is reduced compared to filler-containing papers whose fillers have not been treated with a binder were.

The percentages in the examples mean percent by weight, unless the context indicates otherwise.

The aqueous slurries of fillers produced in Examples 1 to 5 and in Comparative Example 1 were then tested for their suitability for the production of filler-containing papers. The particle size of the dispersed fillers was <2 μm in the examples and in comparative example 1 for 90% of the particles. example 1

1.8 g of a 50% commercial aqueous dispersion of a copolymer of styrene and n-butyl acrylate stabilized with anionic emulsifiers and having a glass transition temperature of 5 ° C. (Acronal® S 504) were placed in a beaker and then with drinking water to a solids content of 10 % diluted. 150 g of a 20% slurry of precipitated calcium carbonate (PCC) in water were then added. During the addition of the slurry and thereafter the mixture was stirred with the aid of a medicinal stirrer at 1000 revolutions per minute (rpm). The pH of the mixture was then adjusted to 8.5.

Example 2

0.6 g of a 50% commercially available aqueous dispersion of a copolymer based on styrene and n-butyl acrylate stabilized with anionic emulsifiers and having a glass transition temperature of 5 ° C. (Acronal® S 504) were placed in a beaker and then poured into drinking water diluted a solids content of 10%. Then 150g of a 20% slurry of PCC in water was added to this solution. During the addition of the PCC slurry and thereafter, the mixture was stirred at 1000 rpm using a medicinal stirrer. The pH of the mixture was then adjusted to 8.5.

Example 3

1.8 g of a 50% commercial aqueous styrene-butadiene dispersion containing an anionic emulsifier

(Styronal® 8736) with a glass temperature of 5 ° C were placed in a beaker and then diluted with drinking water to a solids content of 10%. Then 150 g of a 20% aqueous PCC slurry were added to this solution. During and after the addition, the mixture was stirred using a medicinal stirrer at 1000 rpm. The pH of the mixture was then adjusted to 8.5.

Example 4

0.6 g of a 50% commercially available, aqueous styrene-butadiene dispersion (Styronal® 8736) containing an anionic emulsifier and having a glass transition temperature of 5 ° C. were placed in a beaker and then diluted with drinking water to a solids content of 10%. Then 150 g of a 20% aqueous PCC slurry were added to this solution. During the addition of the slurry and afterwards, the mixture was Stirrer stirred at 1000 rpm. The pH of the mixture was then adjusted to 8.5.

Example 5

1.8 g of a 50% commercially available aqueous styrene-acrylate dispersion (Acronal® S 504) with a glass transition temperature of 5 ° C. were placed in a beaker and then diluted with drinking water to a solids content of 10%. Then 150 g of a 20% aqueous suspension of finely divided calcium carbonate were added to this solution, which was prepared by grinding calcium carbonate in an aqueous medium in the presence of a low molecular weight polyacrylic acid as dispersant (anionically dispersed ground calcium carbonate - GCC -). During the addition of the GCC slurry and then the mixture was stirred at 1000 rpm using a Heiltof stirrer. The pH of the mixture was then adjusted to 8.5.

Comparative Example 1 according to the teaching of DE-A-198 21 089

3 g of a 33% commercially available, aqueous polymer sizing dispersion based on a graft polymer of acrylonitrile and n-butyl acrylate on degraded starch Basoplast® 250 D with a glass transition temperature of 45 ° C. were placed in a beaker and then with drinking water to a solids content diluted by 10%. Then 150 g of a 20% aqueous PCC slurry were added to this solution. During the addition of the slurry and thereafter, the mixture was stirred at 1000 rpm using a medicinal stirrer. The pH of the mixture was then adjusted to 8.5.

Manufacture of paper containing fillers

A mixture of TMP (thermo-mechanical pulp) and wood pulp was whipped in a ratio of 70/30 at a solids concentration of 4% in the laboratory pulper until a grind of 60-65 was reached. The pH of the substance was in the range between 7 and 8. The ground substance was then diluted with drinking water to a solids concentration of 0.35%.

In order to determine the behavior of the aqueous filler slurries described above in the production of filler-containing paper, 500 ml of the paper stock suspension were placed in each case and the slurries treated according to the examples and the comparative example and a cationic retention agent (Polymin KE 2020). The dosage amount of the retenti- Onsmittel was 0.01% polymer, based on the dry content of the pulp suspension. The amount of slurry was adjusted by means of several preliminary tests so that the ash content of the paper sheets made with the fabric was 32%.

Sheets were also made using the 20% aqueous slurries of precipitated calcium carbonate (PCC slurry) and ground calcium carbonate (GCC slurry) shown in Table 1.

The paper sheets were each produced on a Rapid-Köthen sheet former according to ISO 5269/2 with a sheet weight of 80g / m2 and then dried for 7 minutes at 90 ° C and then calendered with a line pressure of 200 N / cm.

Examination of the paper sheets

After a storage period in the climatic room at a constant 23 ° C and 50% humidity for 12 hours, the dry tear length of the leaves was tested according to DIN 54540 and the porosity of the leaves according to Bendtsen (ISO 5636-3). The dry pick resistance of the papers was determined with the IGT printability tester (ISO 3783).

The drop-away impact test, which is a measure of the water absorption behavior, was carried out on paper samples with a size of 50 x 50 mm. The samples were separated from each other and kept in the climatic room for at least 8 hours (normal climate for pretreatment and testing according to ISO 187). The sample to be tested is placed on the edge of a beaker. 5 μl of completely demineralized water is added dropwise to the paper surface with the aid of a syringe, and the drops should not fall onto the paper surface. At the same time, a stopwatch is started and the time is measured until the water level of the drop is no longer visible on the paper surface.

Table 1

As can be seen from Table 1, filler-containing papers can be significantly improved in their strength properties both with anionically dispersed GCC slurries and with PCC slurries, which have each been treated with a coating color binder, without the porosity and water absorption behavior of the papers being significantly influenced become.

Claims

claims

1. Aqueous slurries of finely divided fillers which are at least partially coated with polymers, characterized in that they are obtainable by treating aqueous slurries of finely divided fillers with at least one binder for paper coating colors.

2. Aqueous slurries according to claim 1, characterized in that they contain 1 to 50 wt .-% of at least one finely divided filler and that the amount of binder is 0.1 to 5 wt .-%, based on fillers.

3. Aqueous slurry according to claim 1 or 2, characterized in that they contain 10 to 40 wt .-% of at least one filler.

4. Aqueous slurries according to one of claims 1 to 3, characterized in that the binders for paper coating inks contain only emulsifiers with a molecular weight M _w <2000.

5. Aqueous slurry according to one of claims 1 to 4, characterized in that the binders for paper coating colors contain at least one anionic, cationic, nonionic and / or amphoteric emulsifier.

6. A process for the preparation of the aqueous slurries according to claims 1 to 5, characterized in that 0.1 to 5% by weight of at least one binder for paper coating slips, based on filler, is added to an aqueous slurry of at least one finely divided filler or the enters aqueous slurry of at least one finely divided filler into an aqueous dispersion of a binder for paper coating slips and mixes the constituents in each case.

7. The method according to claim 6, characterized in that the molar mass of the emulsifiers contained in the binders for paper coating colors is <2000.

8. Use of the aqueous slurry according to claims 1 to 5 as an additive to the paper stock in the production of filler-containing paper, filler-containing cardboard or filler-containing cardboard by dewatering the paper stock.