EP1831459B1 - Method for the production of paper, cardboard and card - Google Patents

Description

The invention relates to a process for the production of paper, paperboard and cardboard by adding a microparticle system of a polymeric retention agent having a molecular weight M _w of at least 2 million and a finely divided inorganic component to a pulp having a maximum density of 20 g / l and dewatering the Papierstoffs, wherein the pulp before or after the addition of the cationic retention agent is subjected to at least one shear stage.

The use of combinations of nonionic or anionic polymers and bentonite as retention aids in the production of paper is known, for example, from US Pat US-A-3,052,595 and the EP-A-0 017 353 known.

From the EP-A-0 223 223 is a method for the production of paper and cardboard by dehydration of a paper material known, wherein first added to a paper stock with a concentration of 2.5 to 5 wt .-% bentonite, then diluted the paper stock, a highly cationic polymer with a charge density of min 4 meq / g is added and finally a high molecular weight polymer based on acrylamide is added and the resulting pulp is dewatered after thorough mixing.

After the out of the EP-A-0 235 893 In known processes for the production of paper, an essentially linear synthetic cationic polymer having a molecular weight of more than 500,000 in an amount of more than 0.03% by weight, based on dry paper stock, of an aqueous pulp suspension is first metered into the mixture then the action of a shear field, wherein the first formed flakes are cut into microflakes carrying a cationic charge, then dosed bentonite and dewatered the pulp thus obtained without further action of shear forces.

EP-A-0 335 575 describes a papermaking process in which a polymeric cationic fixing agent and then a water-soluble cationic polymer are metered into a pulp, the pulp thus obtained is then subjected to at least one shear stage and then flocculated by the addition of bentonite.

In the EP-A-0 885 328 describes a process for the production of paper, wherein initially dosed to an aqueous pulp suspension, a cationic polymer, then subjecting the mixture to the action of a shear field, then adding an activated bentonite and dewatering the pulp thus obtained.

From the EP-A 0 711 371 Another method for producing paper is known. In this process, a synthetic, cationic, high molecular weight polymer added to a thick-matter cellulose suspension. After dilution of the flocculated thick stock, a coagulant consisting of an inorganic coagulant and / or a second, low molecular weight and highly cationic water soluble polymer is added prior to dewatering.

In the EP-A-0 910 701 describes a process for the production of paper and board, wherein the paper pulp successively added a low molecular weight or medium molecular weight cationic polymer based on polyethyleneimine or polyvinylamine and then with a high molecular weight cationic polymer such as polyacrylamide, polyvinylamine or cationic starch. After this pulp has been subjected to at least one shear stage, it is flocculated by addition of bentonite and the pulp is dewatered.

From the EP-A-0 608 986 It is known that in the papermaking process, a cationic retention agent is added to the thick matter. Another method for the production of paper and cardboard is from the US Patent No. 5,393,381 , of the WO-A-99/66130 and the WO-A-99/63159 in which a microparticle system composed of a cationic polymer and bentonite is also used. The cationic polymer used is a water-soluble, branched polyacrylamide.

In the WO-A-01/34910 there is described a process for producing paper in which a polysaccharide or a synthetic, high molecular weight polymer is metered into the pulp suspension. Subsequently, a mechanical shear of the pulp must take place. The reflocculation is carried out by adding an inorganic component such as silica, bentonite or clay and a water-soluble polymer.

From the US-A-6,103,065 discloses a method of improving the retention and dewatering of paper stocks by adding a cationic polymer having a molecular weight of 100,000 to 2 million and a charge density of more than 4.0 meq./g to a pulp after the last shearing, simultaneously or thereafter adding a polymer having a molecular weight of at least 2 million and a charge density of less than 4.0 meq./g and then metering in bentonite. It is not necessary in this method to shear the stock after the addition of the polymers. After addition of the polymers and the bentonite, the pulp can be dewatered without further action of shearing forces.

From the DE-A-102 36 252 is a method for producing paper, paperboard and cardboard by shearing a stock, adding a microparticle system of a cationic polymer and a finely divided inorganic component to the pulp after the last shear stage before the headbox, dewatering the stock to form sheets and drying the sheets one as cationic Polymers of the microparticle system cationic polyacrylamides, vinylamine units containing polymers and / or polydiallyldimethylammonium chloride having an average molecular weight M _w of at least 500 000 daltons and a charge density of at most 4.0 meq./g used.

US 6719881 describes a microparticle system for use as a retention and drainage aid in the manufacture of alkaline and acid paper products containing a high molecular weight flocculant polymer, an acid colloid and a coagulant or flocculant having an average molecular weight. The acid colloid comprises an aqueous solution of the water-soluble polymer or copolymer of melamine-aldehyde, preferably melamine-formaldehyde, and is present in an amount ranging from 0.0005% by weight to 0.5% by weight, based on the dry weight of Solids in the substance entry, available.

EP 1039026 discloses the production of paper by the formation of a thick stock cellulose suspension, flocculation of the thick stock by adding a polymer having a relatively high molecular weight and a relatively low cationic charge density, diluting the flocculated thick stock to form a thin stock, and then dewatering the thin stock; to form a paper sheet. Usually, the coagulant is added to the slurry prior to dewatering and the best results are achieved by adding the coagulant followed by anionic colloidal material, such as bentonite.

In the known papermaking processes in which a microparticle system is used as a retention agent, larger amounts of polymer and bentonite are required. Those processes which necessarily require the co-use of cationic polymers with a charge density of more than 4.0 give papers which tend to yellow. The previously known microparticle processes for papermaking also have the disadvantage that they do not meet today's demands on formation and Füllstoff- or fines retention.

The present invention has for its object to provide a further method for the production of paper, cardboard and paperboard using a microparticle system, which gives better retention and papers having an improved formation compared to the known methods.

The object is achieved with a method for producing paper, cardboard and cardboard by adding a microparticle system consisting of at least one cationic polymeric retention agent having a molecular weight M _w of at least 2 million and a finely divided inorganic component to a pulp having a consistency of at most 20 g / l and dewatering the Papierstoffs, wherein the pulp before or after the addition of the retention agent is subjected to at least one shear stage, when dosed the retention agent at least two locations in the pulp and the finely divided inorganic component before or after the addition of the retention agent or between two dosing agents for retention aids, wherein one uses as finely divided inorganic component of the microparticle system at least one bentonite, colloidal silica, silicates, calcium carbonate or mixtures thereof.

By the method according to the invention, all paper qualities can be produced, for example cardboard, single or multilayer carton, single or multi-layer liners, corrugating medium, papers for newspaper printing, so-called medium-fine writing and printing papers, natural gravure papers and lightweight base papers. To produce such papers, you can, for example, from wood pulp, thermo-mechanical pulp (TMP), chemo-thermo-mechanical fabric (CTMP), pressure ground (PGW), wood pulp and sulfite and sulfate pulp emanate. The pulps can be short fiber as well as long fiber. However, it is also possible to use fibers recovered from recovered paper alone or in admixture with other fibers for the manufacture of paper, board and cardboard. Preferably, wood-free grades are produced by the process according to the invention, which yield highly white paper products.

The papers may optionally contain up to 40 wt .-%, usually 5 to 35 wt .-% fillers. Suitable fillers are e.g. Titanium dioxide, natural and pre-painted chalk, talc, kaolin, satin white, calcium sulfate, barium sulfate, clay or alumina.

The production of the paper products takes place continuously. Usually, one starts from a thick material having, for example, a consistency in the range of 3 to 6 wt .-%. The thick material is diluted to a substance density of at most 20 g / l and processed according to the invention to the respective desired paper product. The consistency is for example 3 to 15 g / l, preferably 5 to 12 g / l and is usually in the range of 6 to 10 g / l.

The microparticle system according to the invention consists of at least one polymeric retention agent having a molecular weight M _w of at least 2 million and a finely divided anionic component. The retention aid may be cationic, anionic, amphoteric or nonionic. At least one polymer from the group of nonionic polyacrylamides, the nonionic polymethacrylamides, the cationic polyacrylamides, the cationic polymethacrylamides, the anionic polyacrylamides, the anionic polymethacrylamides, the poly (N-vinylformamides), the polymers containing vinylamine units and, for example, at least one polymer, synthetic retention agent the Polydiallyldimethylammoniumchloride into consideration. The average molecular weight M _{w of} the polymeric retention aids is at least 2 million daltons, preferably at least 3 million, and is usually in the range of, for example, 3.5 million to 15 million. The charge density of the polymers in question is for example at most 4.0 meq./g.

Particularly preferred are cationic polyacrylamides having an average molecular weight M _w of at least 5 million daltons and a charge density of 0.1 to 3.5 meq./g and polyvinylamines obtainable by hydrolysis of vinylformamide units containing polymers and having an average molecular weight of at least Have 2 million daltons. The polyvinylamines are preferably prepared by hydrolysis of homopolymers of N-vinylformamide, wherein the degree of hydrolysis, for example, up to 100%, usually 70 to 95%. Also high molecular weight copolymers of N-vinylformamide with other ethylenically unsaturated monomers such as vinyl acetate, vinyl propionate, methyl acrylate, methyl methacrylate, acrylamide, acrylonitrile and / or methacrylonitrile, can be hydrolyzed to vinylamine units containing polymers and used according to the invention. For example, all polyvinylamines having a molecular weight M _w of at least 2 million can be used according to the invention, which are obtainable by hydrolysis of vinylformamide units-containing polymers, the degree of hydrolysis of the vinylformamide units being 0.5 to 100 mol%. The preparation of homopolymers and copolymers of N-vinylformamide is known. For example, in the US 6,132,558 , Column 2, line 36 to column 5, line 25 described in detail. The statements made there are hereby incorporated by reference into the disclosure content of the present application.

Cationic polyacrylamides are, for example, copolymers prepared by copolymerizing acrylamide and at least one di-C ₁ -bisC ₂ -alkylamino-C ₂ -bisC ₄ -alkyl (meth) acrylate or a basic acrylamide in the form of the free bases, the salts with organic or inorganic acids or the alkyl halides quaternized compounds are available. Examples of such compounds are dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylate, dimethylaminopropyl acrylate, diethylaminopropyl methacrylate, diethylaminopropyl acrylate and / or dimethylaminoethylacrylamide, dimethylaminoethylmethacrylamide, dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide and / or diallyldimethylammonium chloride. The comonomers mentioned can also be copolymerized with methacrylamide to form cationic polymethacrylamides containing, for example, 5 to 40 mol% of at least one cationic monomer, such as dimethylaminoethyl acrylate or diallyldimethylammonium chloride, in copolymerized form. Cationic polymethacrylamides can also be used as the polymeric retention aid of the microparticle system.

Further examples of polymers containing cationic polyacrylamides and vinylamine units may be the references cited in the prior art, such as EP-A-0 910 701 and US-A-6,103,065 be removed. One can use both linear and branched polyacrylamides. Such polymers are commercial products. Branched polymers which can be prepared, for example, by copolymerization of acrylamide or methacrylamide with at least one cationic monomer in the presence of small amounts of crosslinking agents are described, for example, in the references cited in the prior art US Patent No. 5,393,381 . WO-A-99/66130 and WO-A-99/63159 described.

Other suitable polymeric retention aids of the microparticle system are poly (N-vinylformamides). For example, they are prepared by polymerizing N-vinylformamide into homopolymers or by copolymerizing N-vinylformamide together with at least one other ethylenically unsaturated monomer. The vinylformamide units of these polymers are not hydrolysed, in contrast to the preparation of polymers containing vinylamine units. The copolymers can be cationic, anionic or amphoteric. Cationic polymers are obtained, for example, by copolymerizing N-vinylformamide with at least one of the basic monomers mentioned in the copolymerization of acrylamide. Anionic polymers of N-vinylformamide are obtainable by copolymerizing N-vinylformamide in the presence of at least one acid monoethylenically unsaturated monomer. Such comonomers are, for example, monoethylenically unsaturated C ₃ -bis C ₅ carboxylic acids, acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid or sulfopropyl acrylate. The acidic monomers can also be used in completely neutralized with alkali metal, alkaline earth metal and / or ammonium bases in the copolymerization with N-vinylformamide. The copolymers mentioned contain units of anionic or cationic monomers, for example, in amounts of 0.5 to 50, preferably 5 to 40 mol% copolymerized. Copolymers of N-vinylformamide can also be amphoteric if they contain units of anionic and cationic monoethylenically unsaturated monomers in copolymerized form.

Other suitable retention aids are nonionic polyacrylamides and nonionic polymethacrylamides obtainable by polymerizing acrylamide and / or methacrylamide, as well as anionic polyacrylamides and anionic polymethacrylamides. The anionic poly (meth) acrylamides are obtainable, for example, by polymerizing acrylamide or methacrylamide with at least one anionic monomer. Suitable anionic monomers are, for example, monoethylenically unsaturated C ₃ -C ₅ -carboxylic acids, such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, vinylacetic acid or ethacrylic acid, and vinylphosphonic acid, styrenesulfonic acid, acrylamido-2-methylpropanesulfonic acid, sulfopropyl acrylate or sulfopropyl methacrylate and the alkali metal, alkaline earth metal and ammonium salts of the acid group-containing monomers into consideration. The anionic copolymers contain, for example, 1 to 50 mol%, preferably 5 to 40 mol% of at least one anionic monomer in copolymerized form. In addition, amphoteric copolymers of acrylamide and methacrylamide can be used as the polymeric retention aid of the microparticle system. Such copolymers are obtainable by copolymerizing acrylamide or methacrylamide in the presence of at least one anionic and at least one cationic ethylenically unsaturated monomer.

Other suitable cationic polymeric retention aids of the microparticle system are polydiallyldimethylammonium chlorides (PolyDADMAC) with an average molecular weight of at least 2 million daltons. Polymers of this type are commercial products.

The polymeric retention aids of the microparticle system are added to the paper stock in an amount of 0.005 to 0.5% by weight, preferably in an amount of 0.01 to 0.25% by weight, based on dry paper stock.

Suitable inorganic components of the microparticle system are, for example, bentonite, colloidal silicic acid, silicates and / or calcium carbonate. Colloidal silicic acid is to be understood as meaning products based on silicates, for example silica microgel, silical sol, polysilicates, aluminum silicates, boron silicates, polyborosilicates, clay or zeolites. Calcium carbonate can be used, for example, in the form of chalk, ground calcium carbonate or precipitated calcium carbonate can be used as the inorganic component of the microparticle system. Bentonite is generally understood to be phyllosilicates which are swellable in water. These are mainly the clay mineral montmorillonite and similar clay minerals such as nontronite, hectorite, saponite, sauconite, beidellite, allevardite, illite, halloysite, attapulgite and sepiolite. These phyllosilicates are preferably activated before use, ie converted into a water-swellable form in which the phyllosilicates are treated with an aqueous base such as aqueous solutions of caustic soda, potassium hydroxide, soda, potash, ammonia or amines. Bentonite in the form treated with sodium hydroxide or those bentonites which are already obtained in the sodium form, so-called Wyoming bentonites, are preferably used as the inorganic component of the microparticle system. The platelet diameter of the water-dispersed bentonite in the sodium hydroxide-treated form is, for example, at most 1 to 2 μm, the thickness of the platelets is approximately 1 nm. Depending on the type and activation, the bentonite has a specific surface area of 60 to 800 m ² / g , Typical bentonites are used in the EP-B-0235893 described. In the papermaking process, bentonite is added to the cellulosic suspension, typically in the form of an aqueous bentonite slurry. This bentonite slurry may contain up to 10% by weight of bentonite. Normally, the slurries contain about 3 to 5 wt .-% bentonite.

As colloidal silica, products from the group of silicon-based particles, silica microgels, silica sols, aluminum silicates, borosilicates, polyborosilicates or zeolites can be used. These have a specific surface area of 50 to 1500 m ² / g and an average particle size distribution of 1-250 nm, normally in the range 5-100 nm. The preparation of such components is described, for example, in US Pat EP-A-0 041 056 . EP-A-0 185 068 and US-A-5,176,891 described.

Clay or kaolin is a hydrous aluminum silicate with a platelet-like structure. The crystals have a layer structure and an aspect ratio (diameter to thickness ratio) of up to 30: 1. The particle size is e.g. at least 50% smaller than 2 μm.

The carbonates used are preferably natural calcium carbonate (ground calcium carbonate, GCC) or precipitated calcium carbonate (PCC). GCC is produced, for example, by grinding and visual processes using grinding aids. It has a particle size of 40 - 95% less than 2 microns, the specific surface area is in the range of 6-13 m ² / g. For example, PCC is made by passing carbon dioxide into an aqueous calcium hydroxide solution. The average particle size is in the range of 0.03-0.6 μm. The specific surface area can be greatly influenced by the choice of precipitation conditions. It is in the range of 6 to 13 m ² / g.

The inorganic component of the microparticle system is added to the stock in an amount of 0.01 to 2.0% by weight, preferably in an amount of 0.1 to 1.0% by weight, based on dry stock.

In the process of the invention, the aqueous fiber slurry, optionally containing a filler, is subjected to at least one shear stage. It goes through at least one cleaning, mixing and / or pumping stage. The shearing of the pulp (thin material) can be done for example in a pulper, classifier or in a refiner. The retention agent is metered according to the invention in at least two places in the thin and the finely divided inorganic component before or after the addition of the retention agent or between two dosing sites for retention aid. The process can be carried out, for example, by adding the retention agent after the last shear stage to at least two successive points and then metering the finely divided inorganic component. In another embodiment of the method according to the invention, the retention agent after the last shear stage is added to at least two points which have the same distance from the shear stage, and then dosed the finely divided inorganic component. However, the process can also be carried out by adding the retention agent before the last shear stage at at least two points, which are arranged in a plane perpendicular to the stock flow or behind one another, and by metering the finely divided inorganic component after the last shear stage. In addition, before the last shear stage, it is possible first to meter the finely divided inorganic component and then at least one retention agent or a subset of the retention agent to be used in total, and to add the same or another retention agent or the remaining retention agent after the last shear stage. However, it is also possible first to dose at least one retention agent to the thin material, to subject the system to shear, then to add at least one retention agent (identical or preferably different to the first-dosed retention agent) and then to add at least one finely divided inorganic component.

For example, in the process according to the invention, it is possible first to meter 25 to 75% by weight of the total retention agent before the last shear stage and the remaining portion of the retention agent and then to add the finely divided inorganic component or to meter it first before the last Scherstufe the finely divided inorganic component and 25 to 75 wt .-% of the retention agent and after the last shear stage the remaining portion of the retention agent.

In another embodiment of the method according to the invention, the finely divided inorganic component is metered in each case before the last shearing stage, followed by the retention agent at least two in a plane perpendicular to the first Papierstoffstrom or at successively arranged locations. The flow rate of the paper pulp stream is, for example, at least 2 m / sec in most paper machines and is usually in the range of 3 to 7 m / sec. The dosage of the retention agent can be made for example by means of single or multi-fluid nozzles in the paper stream. This achieves a rapid distribution of the retention agent in the pulp.

The distance between the center of the metering points of the retention agent is, for example, at least 20 cm in successive addition of retention agent. The distance between the center of a metering point for retention agent and the center of a metering point for the finely divided inorganic component, for example, also at least 20 cm. However, the retention sites for retention aids can also be arranged in a plane perpendicular to the stock flow. The distance between the center of the dosing points of the retention agent is preferably at least 50 cm and the distance between the center of a dosing point for retention agent and the center of a dosing point for the finely divided inorganic component at least 50 cm. The distance between the center of the dosing points of the retention agent is in most cases, for example in the range of 50 cm to 15 m, wherein the distance between the center of a dosing agent for retention agent and the center of a dosing point for the finely divided inorganic component, for. at least 50 cm. The location of the addition points is preferably such that the distance between the center of the dosing points of the retention agent is 50 cm to 10 m and the distance between the center of a dosing point for retention agent and the center of a dosing point for the finely divided inorganic component 50 cm to 5 m.

For example, if one has two dosing agents for retention aids, one can dose the same retention agent, for example, a cationic polyacrylamide or a polyvinylamine, or use two different retention agents, e.g. a cationic polyacrylamide and diallyldimethylammonium chloride or a polyvinylamine and a poly (N-vinylformamide) or a polyvinylamine and a cationic polyacrylamide. The retention agents can also be metered into the paper stock stream at 3 to 5 positions arranged one behind the other. Likewise, it is possible to meter the finely divided inorganic component of the retention agent system into the stock stream at at least two successive locations.

In addition to the microparticle system, it is possible to add to the paper stock the customary amounts of process chemicals customarily used in papermaking, for example fixatives, dry and wet strength agents, engine sizes, biocides and / or dyes. The paper stock is dewatered on a sieve with formation of sheets. The leaves thus produced are dried. Dehydrating the pulp and Drying of the sheets are part of the papermaking process and are carried out continuously in the art.

The process according to the invention gives papers having a surprisingly good formation and, compared to known microparticle processes, has an improved filler and fines retention.

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

The First Pass Retention (FPR) was determined by determining the ratio of the solids content in the white water to the solids content in the headbox. The information is given in percent.

The first pass ash retention (FPAR) was determined analogously to the FPR, but only the ash content was considered.

The formation was measured with a TECHPAP 2D Lab Formation Sensor from Tecpap). The dimensionless FX value is given in the table. The lower this value, the better the formation of the tested paper.

Polymin® 215:

lineares, kationisches Acrylamidcopolymerisat einer mittleren Mol-masse M_w von 8 Millionen, einer Ladungsdichte von 1,7 meq/g und einem Feststoffgehalt von 46 %

Polymin® PR 8186:

verzweigtes, kationisches Acrylamidcopolymerisat mit einer mittleren Molmasse M_w von 7 Millionen, einer Ladungsdichte von 1,7 meq/g und einem Polymergehalt von 46%.

The following retention agents were used for the microparticle system:

Polymin® 215:

linear, cationic acrylamide copolymer having an average molecular weight M _w of 8 million, a charge density of 1.7 meq / g and a solids content of 46%

Polymin® PR 8186:

branched, cationic acrylamide copolymer having an average molecular weight M _w of 7 million, a charge density of 1.7 meq / g and a polymer content of 46%.

As an inorganic component of the microparticle system, Mikroflocc® XFB was used. Mikrofloc® XFB is a bentonite powder activated by treatment with aqueous caustic soda. It is usually converted on site in a 3-5% suspension.

Examples

The following examples and comparative examples were carried out on a GAP Former test paper machine. From a wood-free, bleached pulp was first prepared a pulp with a consistency of 8 g / l and 20% calcium carbonate as a filler, which in the examples and in the comparative examples in each case to a wood-free writing and printing paper having a basis weight of 80 g / m ^{2 was} processed. The paper machine contained the following arrangement of mixing and shearing units: mixing vessel, dilution, deaerator, screen and headbox. One ton of paper was produced per hour. The addition (amount and metering point) of retention aid and finely divided inorganic component was varied as indicated in the examples and comparative examples. The results obtained in each case are given in the table.

example 1

650 g / t Polymin 215 (the term "650 g / t" means that 650 g Polymin® 215 were used per ton of produced paper) were added in 2 doses to 350 g / t and 300 g / t with a distance of the dosing of 300 cm in each case before screen and then 2500 g / t of Microfloc® XFB after screen fed to the paper stock described above.

Comparative Example 1

Example 1 was repeated with the sole exception that the retention agent (650 g / t Polymin 215) was metered in at a single site 400 cm before screen.

Example 2

450 g / t Polymin 215 were continuously added to the stock in 2 doses at 250 g / t and 200 g / t at a distance of the dosing of 200 cm after each screen and then 2500 g / t Microfloc XFB also after Screen.

Comparative Example 2

Example 2 was repeated with the sole exception that the retention agent (450 g / t Polymin 215) was metered in at a single point.

Example 3

Per ton of the dry paper produced, 500 g of polyacrylamide in 2 doses were continuously added to the paper stock stream at a distance of the metering points of 2 m, initially 250 g of Polymin® 215, then 250 g, Polymin® PR 8186 and then 2500 g Microfloc® XFB (also screened).

Example 4

Per ton of dry paper produced, 500 g of Polymin® 215 in 2 doses were added to the stock stream, first 250 g of Polymin® 215 before screen, then 250 g of Polymin® 215 on screen and then 2500 g of Microfloc XFB (also according to Screen ) dosed. The distance of the 1st metering point for the retention agent was 4 m in front of the screen, the distance of the second metering point to the screen was 2 m, the distance between the metering point for Microfloc® XFB and the screen was 5 m. table FPR (%) FPAR (%) Formation / Tech Pap Example 1 79.1 54.2 97.6 See 1 78.0 52.1 122.3 Ex. 2 81.5 58.3 81.7 See 2 80.7 56.4 99.6 Example 3 81.0 58.1 75.3 Example 4 82.1 59.7 98.3

Claims (19)

1. A process for producing paper, board or cardboard by adding a microparticle system consisting of at least one cationic polymeric retention aid having a molar mass M_w of at least 2 million and a finely divided inorganic component to a paper stock having a density of not more than 20 g/l and draining the paper stock, the paper stock being subjected, before or after the addition of the cationic polymeric retention aid, to at least one shear stage, which comprises metering the cationic polymeric retention aid into the paper stock at at least two places and metering the finely divided inorganic component before or after the addition of the retention aid, wherein said finely divided inorganic component of the microparticle system comprises at least one bentonite, colloidal silica, silicates, calcium carbonate or mixtures thereof.
2. The process according to claim 1, wherein the retention aid is added after the last shear stage at at least two successive places and thereafter the finely divided inorganic component is metered.
3. The process according to claim 1, wherein the retention aid is added after the last shear stage at at least two places which are at equal distance from the shear stage, and thereafter the finely divided inorganic component is metered.
4. The process according to claim 1, wherein the retention aid is added before the last shear stage at at least two places which are disposed in a plane perpendicular to the paper stock flow or successively, and the finely divided inorganic component is metered after the last shear stage.
5. The process according to claim 1, wherein 25% to 75% by weight of the total retention aid is metered before the last shear stage and the remaining fraction of the retention aid thereafter, and subsequently the finely divided inorganic component is added.
6. The process according to claim 1, wherein before the last shear stage first the finely divided inorganic component and 25% to 75% by weight of the retention aid and after the last shear stage the remaining fraction of the retention aid are metered in.
7. The process according to claim 1, wherein before the last shear stage in each case first the finely divided inorganic component and the retention aid are metered in at at least two places disposed in a plane perpendicular to the paper stock flow or at places disposed successively.
8. The process according to any one of claims 1 to 7, wherein the distance between the center point of the retention aid metering places is at least 20 cm and wherein the distance between the center point of a metering place for retention aid and the center point of a metering place for the finely divided inorganic component is at least 20 cm.
9. The process according to any one of claims 1 to 8, wherein the distance between the center point of the retention aid metering places is at least 50 cm and wherein the distance between the center point of a metering place for retention aid and the center point of a metering place for the finely divided inorganic component is at least 50 cm.
10. The process according to any one of claims 1 to 9, wherein the distance between the center point of the retention aid metering places is 50 cm to 15 m and wherein the distance between the center point of a metering place for retention aid and the center point of a metering place for the finely divided inorganic component is at least 50 cm.
11. The process according to any one of claims 1 to 10, wherein the distance between the center point of the retention aid metering places is 50 cm to 10 m and wherein the distance between the center point of a metering place for retention aid and the center point of a metering place for the finely divided inorganic component is 50 cm to 5 m.
12. The process according to any one of claims 1 to 11, wherein said retention aid comprises at least one polymer from the group of nonionic polyacrylamides, cationic polyacrylamides, anionic polyacrylamides, poly(N-vinylformamides), polymers comprising vinylamine units, and diallyldimethylammonium chlorides.
13. The process according to any one of claims 1 to 12, wherein said retention aid comprises at least one cationic polymer having a charge density of not more than 4 meq/g.
14. The process according to any one of claims 1 to 13, wherein said retention aid comprises at least one polymer having a molar mass M_w of at least 3 million.
15. The process according to any one of claims 1 to 14, wherein said retention aid comprises at least one polyvinylamine obtainable by hydrolyzing polymers comprising vinylformamide units, the degree of hydrolysis of the vinylformamide units being 5 to 100 mol%.
16. The process according to any one of claims 1 to 15, wherein the retention aid is used in an amount of 0.005% to 0.5% by weight, based on dry paper stock.
17. The process according to any one of claims 1 to 16, wherein the retention aid is used in an amount of 0.001% to 0.25% by weight, based on dry paper stock.
18. The process according to any one of claims 1 to 17, wherein the finely divided inorganic component of the microparticle system is used in an amount of 0.01% to 2.0%, preferably 0.1% to 1.0% by weight, based on dry paper stock, and is metered into the paper stock flow at at least two places disposed consecutively.
19. The process according to any one of claims 1 to 18, wherein the retention aid is metered into the pulp flow at 3 to 5 places disposed successively.