EP1529133B1 - Method for the production of paper, paperboard, and cardboard - Google Patents

Abstract

A process for preparation of paper, pasteboard, or cardboard involving cutting of the paper pulp, addition of microparticles of cationic polymer, and a finely divided inorganic component after the last cutting step and before pulp swelling, dewatering of the pulp, and sheet formation and drying of the sheets is new. A process for preparation of paper, pasteboard, or cardboard involving cutting of the paper pulp, addition of microparticles of cationic polymer, and a finely divided inorganic component after the last cutting step and before pulp swelling, dewatering of the pulp, and sheet formation and drying of the sheets. The cationic polymer of the microparticle system is cationic polyacrylamide, polymer containing vinylamine units, and/or polydiallyl dimethylammonium chloride containing polymer of mean mol.wt. 500,000 Dalton, and maximum charge density 4.0 meq/g, where the microparticle system free from polymers of charging density (sic) more than 4 meq/g is used as the retention agent.

Description

The invention relates to a process for the production of paper, paperboard and cardboard by shearing the pulp, adding a microparticle system of a cationic polymer and a finely divided inorganic component to the pulp after the last shear stage in front of the headbox, draining the stock under sheet formation and drying the sheets.

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 the pulp is successively admixed with 2 different water-soluble cationic polymers, subsequently 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, the mixture then subjected to the action of a shear field, then adding an activated bentonite dispersion and dewatering the resulting pulp.

From the EP-A 0 711 371 Another method for producing paper is known. In this process, a synthetic, cationic, high molecular weight polymer is added to a thick stock 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 cardboard, 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 one doses a cationic retention agent to the thick stock in papermaking. 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 dosing 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 with this method subject the stock to shear after addition of the polymers. After addition of the polymers and the bentonite, the pulp can be dewatered without further action of shearing forces.

In the known papermaking processes where a microparticle system is used as the retention agent, larger amounts of polymer and bentonite are needed. 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 present invention has for its object to provide a further method for the production of paper using a microparticle system, which requires in comparison to the known processes lower amounts of polymers and bentonite, at the same time achieves improved retention and drainage and obtains papers that are less prone to yellowing.

The object is achieved by a method for producing paper, cardboard and cardboard by shearing the pulp, 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, draining the stock under sheet formation and drying the leaves, if as cationic polymers of the microparticle system cationic polyacrylamides, vinylamine units containing polymers and / or polydiallyldimethylammonium chloride having an average molecular weight Mw of at least 500 000 daltons and a charge density of not more than 4.0 meq./g used, wherein the retention agent used microparticle system is free of polymers with a charge density of more than 4 meq./g.

By the method according to the invention, all paper grades can be produced, for example cardboard, single / multilayer carton, single / 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. Preferably wood-free grades produced by the process according to the invention, which yield high-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 microparticle system according to the invention consists of a cationic polymer and a finely divided anionic component. Suitable cationic polymers are cationic polyacrylamides, polymers containing vinylamine units, polydiallyldimethylammonium chlorides or mixtures thereof having an average molecular weight Mw of at least 500,000 daltons and a charge density of not more than 4.0 meq./g in each case. Particular preference is given to cationic polyacrylamides having an average molecular weight Mw 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, the degree of hydrolysis of the vinylformamide units being 20 to 100 mol% and the average molecular weight of the polyvinylamine is at least 2 million daltons. The polyvinylamines are preferably prepared by hydrolysis of homopolymers of vinylformamide, the degree of hydrolysis being, for example, 70 to 95%.

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, diethylaminoethyloacrylyl, dimethylaminopropyl methacrylate, dimethylaminopropyl acrylate, diethylaminopropyl methacrylate, diethylaminopropyl acrylate and / or dimethylaminoethylacrylamide. 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 prior art references US Patent No. 5,393,381 . WO-A-99/66130 and WO-A-99/63159 described.

Further suitable cationic polymers are polydiallyldimethylammonium chlorides (PolyDADMAC) with an average molecular weight of at least 500,000 daltons, preferably at least 1 million daltons. Polymers of this type are commercial products.

The cationic polymers of the microparticle system are added to the stock in an amount of 0.005 to 0.5% by weight, preferably in an amount of 0.01 to 0.2% by weight.

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 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 sodium hydroxide solution, potassium hydroxide solution, soda or potash. Bentonite in the form treated with sodium hydroxide solution is preferably used as the inorganic component of the microparticle system. The platelet diameter of the water-dispersed bentonite in the sodium hydroxide-treated mold is, for example, 1 to 2 μm, and the thickness of the platelets is about 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 of 50-1000 m ² / g and an average particle size distribution of 1-250 nm, normally in the range 40-100 nm. The preparation of such components is described, for example, in US Pat EP-A-0041056 . EP-A-0185068 and US-A-5176891 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 at least 50% less than 2 microns.

As carbonates, preferably calcium carbonate, natural calcium carbonate (ground calcium carbonate, GCC) or precipitated calcium carbonate (PCC) can be used. GCC is produced 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. PCC is made by passing carbon dioxide into calcium hydroxide solution. The average particle size is in the range of 0.03 - 0.6 microns, the specific surface area can be greatly influenced by the choice of precipitation conditions. It is in the range of 6 - 13 m ² / g.

The inorganic component of the microparticle system is added to the stock in an amount of 0.01 to 1.0% by weight, preferably in an amount of 0.1 to 0.5% by weight.

The consistency of the pulp is for example 1 to 100 g / l, preferably 4 to 30 g / l. The aqueous fiber slurry 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 can be done for example in a pulper, classifier or in a refiner. After the last shear stage and before the headbox onto the sieve, according to the invention, the microparticle system is metered. Particularly preferred is a procedure in which first dosed the cationic polymer and then the inorganic component of the microparticle system to the pulp, which was previously sheared. However, it is also possible first to meter in the inorganic component of the microparticle system and then the cationic polymer or to add both components to the paper stock at the same time. Thereafter, the dehydration of the pulp is carried out without further action of shear forces on a sieve under sheet formation. The paper sheets are then dried.

In addition to the microparticle system, it is possible to add to the pulp the process chemicals usually used in papermaking in the usual amounts, e.g. Fixing agents, dry and wet strength agents, engine sizes, biocides and / or dyes.

With the method according to the invention, an increase in the retention of fillers and fillers as well as process chemicals such as starch, dyes and wet strength agents, and an improvement in the dewatering rate is achieved over the known processes, without worsening the formation and paper properties. In addition, it achieves a significant improvement in fiber recovery and thus a relief of the sewage treatment plant.

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

The first pass retention (FP retention) 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.

FPA retention (first-pass ash retention) was determined analogously to FP retention, but only the ash content was considered.

example 1

A paper pulp made from a wood-free, bleached pulp having a pulp density of 7 g / l and a filler content of 30% calcium carbonate was processed on a Fourdrinier machine with hybrid former to a paper with writing and printing quality. The following arrangement of mixing and shearing devices was used: mixing vessel, dilution to 7 g / l, mixing pump, cleaner, headbox pump, screen and headbox. 32 tons of paper were produced per hour.

After the screen (last shear stage before the headbox), first 270 g / t of a commercially available high molecular weight, cationic polyacrylamide (Polymin PR 8140, average molecular weight Mw 7 million) and then 2500 g / t bentonite were metered. FP retention was 81.5%, FPA retention 60.2%.

Comparative Example 1

The example was repeated with the exceptions that dosed 410 g / t of the cationic polyacrylamide before screen and pump and 3000 g / t bentonite after screen before the headbox. These quantities were required to achieve an equally good formation as in the example. The FP retention was 79.9%, the FPA retention 59.1%.

As a comparison of the results of the example with the results of the comparative example shows, the saving of polymer was 30% and the saving of bentonite 17%. With equally good formation, an improvement in retention could be achieved in the example according to the invention. The improvement in the Siebentwässerung was about 10%.

Example 2

Wood pulp and wood pulp having a pulp consistency of 7 g / l and a filler content of 30% of a mixture of clay and calcium carbonate (1: 1) was processed on a paper machine with a gap former into a LWC grade paper. The following arrangement of mixing and shearing devices was used: mixing vessel, dilution, deculator, pump, screen, headbox. 30 tons of paper were produced per hour.

After the screen (last shear stage in front of the headbox), initially 200 g / t of a commercially available high molecular weight cationic polyacrylamide (Polymin KP 2520, average molecular weight Mw 5 million) and then 1400 g / l bentonite were metered. The FP retention was 69%, the FPA retention 40%.

Comparative Example 2

Example 2 was repeated with the exceptions that 280 g / t of the cationic polyacrylamide before the pump and the screen and 1400 g / t bentonite after the screen before the headbox dosed. This amount was required to achieve equally good retention. The FP retention was 69%, the FPA retention 40%.

As a comparison of the results of Example 2 with the results of Comparative Example 2 shows, the savings in polymer was about 30%. Although in Example 2, a smaller amount of retention agent was used as in Comparative Example 2, in Example 2 an equally good formation and paper properties could be achieved.

Claims (9)

1. A process for the production of paper, board and cardboard by shearing the paper stock, adding a microparticle system comprising a cationic polymer and a finely divided inorganic component to the paper stock after the last shearing stage before the head box, draining the paper stock with sheet formation and drying the sheets, wherein cationic polyacrylamides, polymers comprising vinylamine units and/or polydiallyldimethylammonium chloride having an average molar mass Mw of in each case at least 500 000 Dalton and a charge density of in each case not more than 4.0 meq/g are used as cationic polymers of the microparticle system, the microparticle system used as a retention aid being free of polymers having a charge density of more than 4 meq/g.
2. The process according to claim 1, wherein cationic polyacrylamides having an average molar mass Mw of at least 5 million Dalton and a charge density of from 0.1 to 3.5 meq/g are used as cationic polymers of the microparticle system.
3. The process according to claim 1, wherein polyvinylamines which are obtainable by hydrolysis of polymers comprising vinylformamide units, the degree of hydrolysis of the vinylformamide units being from 20 to 100 mol% and the average molar mass of the polyvinylamines being at least 2 million Dalton, are used as cationic polymers of the microparticle system.
4. The process according to any of claims 1 to 3, wherein the cationic polymer of the microparticle system is added to the paper stock in an amount of from 0.005 to 0.5% by weight, based on dry paper stock.
5. The process according to any of claims 1 to 4, wherein the cationic polymer of the microparticle system is added to the paper stock in an amount of from 0.01 to 0.2% by weight, based on dry paper stock.
6. The process according to any of claims 1 to 5, wherein at least one bentonite, colloidal silica, silicate and/or calcium carbonate is used as the inorganic component of the microparticle system.
7. The process according to any of claims 1 to 6, wherein the inorganic component of the microparticle system is added to the paper stock in an amount of from 0.01 to 1.0% by weight, based on dry paper stock.
8. The process according to any of claims 1 to 7, wherein the inorganic component of the microparticle system is added to the paper stock in an amount of from 0.1 to 0.5% by weight, based on dry paper stock.
9. The process according to any of claims 1 to 8, wherein first the cationic polymer and then the inorganic component of the microparticle system are metered into the paper stock.