EP0910701A1

EP0910701A1 - Process for producing paper and cardboard

Info

Publication number: EP0910701A1
Application number: EP97930506A
Authority: EP
Inventors: Rainer Dyllick-Brenzinger; Hubert Meixner; Friedrich Linhart; Dietmar MÖNCH; Klaus-Dieter Gerber; Bernd Dirks; Peter Baumann
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1996-07-09
Filing date: 1997-07-07
Publication date: 1999-04-28
Anticipated expiration: 2017-07-07
Also published as: ES2151736T3; DE59702462D1; CA2258569A1; US6132558A; WO1998001623A1; CA2258569C; EP0910701B1; NO990078D0; JP2000514144A; NO990078L; ATE196937T1; DE19627553A1

Abstract

The invention relates to a process for producing paper and cardboard by dehydration of pulps, forming sheets and drying said sheets. Polyethylene imines of a molar mass Mw of greater than 500 000 or polymers containing vinyl amine units and having a molar mass of 5000 to 3 million are added to the pulps and subsequently, polymers containing cationic polyacrylic amides or vinyl amine units are added to said pulps, the molar masses Mw of the polymers being at least 4 million in each case. The pulp is then subjected to at least one shearing stage and flocculates by addition of bentonite, colloidal silicic acid or clay.

Description

Process for the production of paper and cardboard

description

The invention relates to a process for the production of paper and cardboard by dewatering pulps, with sheet formation and drying the leaves, the pulps being successively mixed with two different water-soluble, cationic polymers, then subjected to at least one shear stage and then by adding bentomite, colloidal silica or clay can be flocked.

The method described at the outset is known from EP-A 0 335 575. In this process, the pulp is first mixed with a low molecular weight, water-soluble, cationic polymer and then with a high molecular weight, water-soluble cationic polymer. The low molecular weight water-soluble cationic polymers have a molar mass below 500,000. Suitable low molecular weight cationic polymers are, for example, polyethylene resin, polyammine, polycyanediamide, formaldehyde condensates and polymers of diallyldimethylammonium chloride, dialkylaminoalkyl (meth) acrylates and dialkylammoalkyl (meth) acrylamides Cular cationic polymers have molar masses of more than 500,000. These polymers are the high molecular weight retention agents commonly used in papermaking, such as cationic polyacrylamides. After the cationic polymers have been added, the flocked fiber suspension is subjected to a shear step, e.g. in a pulper, refmer, sieve or sifter, whereby the so-called hard giant flakes contained in the paper stock are destroyed. Bentom, colloidal silica or clay are then added, as a result of which the destroyed flake constituents are aαsorptively collected into a "soft" microfloc. After that, the pulp is dewatered with the formation of leaves on a sieve and the leaves are dried.

The object of the invention is to further increase the dewatering speed and thus the production speed in papermaking.

The object is achieved according to the invention with a process for the production of paper and cardboard by dewatering pulps, with sheet formation and drying of the sheets, the pulps being successively mixed with two different water-soluble, cationic polymers, then subjected to at least one shear stage and then by adding bentomite , colloidal pebble acidic or clay can be flocculated when you first use water-soluble cat ionic polymers

a) Polyethylenimme a molar mass M _w of more than 500,000 or polymers containing vinylamine units with a molecular weight M _w from 5000 to 3 million, thereafter

b) uses cationic polyacrylamides, polymers containing cationic starch or vinylamine units, the molecular weights M _{w of} the polymers each being at least 4 million.

Unexpectedly, the use of polyethyleneimines with a molecular weight M _w of more than 500,000 or of vinyl-containing polymers with a molecular weight M _w of 5000 to

3 million as cationic polymers of group a), which is first added to the paper stock, compared to the prior art, according to which polyethylemme with a molecular weight of less than 500,000 is used, to increase the dehydration rate.

According to the invention, polymers of group a) with a molecular weight M _w of more than 500,000, preferably more than 700,000, are suitable. The polymers can be used in the manufacture of paper in the form of the free bases or as salts with organic or inorganic acids. Polyethylene blocks of such a high molecular weight are prepared by known processes by polymerizing ethyleneimine in aqueous solution in the presence of acidic catalysts. Products of this type are commercially available. They usually have a broad molar mass distribution. Particularly effective are those polyethylene resins which can be obtained as retentate by ultrafiltration of the polyethylene resin in question. In the case of ultrafiltration on membranes with exclusion limits of at least 500,000, for example 5 to 40% by weight of the polyethylene imm used is separated off as permeate.

Other suitable polymers of group a) are vinylamine unit-containing polymers having a molecular weight M _w of 5000 to 3 million polymers of this type are obtainable by polymerizing N -vinylformamide, if appropriate in the presence of other monomers copolymerizable therewith, and the Then partially or completely hydrolyzed polymers by splitting off the formyl group from the polymerized vinylformamide units to form vinylamine units. Partially hydrolyzed homopolymers of N-vinylformamide are known, for example, from EP-B-0 071 050. The partial described therein hydrolyzed homopolymers of N-vinylformamide contain V ylamm and N-Vinylformamid units in empolymerized form. In addition to the partially hydrolyzed poly-N-vinylformamides described in the cited literature reference, according to the invention, as component a), polymers are also suitable in which the degree of hydrolysis is up to 100%.

Other suitable polymers of component a) containing vinylamine units are the hydrolyzed copolymers of N vinyl ormamide known from EP-B-0 216 387. They are obtainable by, for example, copolymerizing N vinylformamide with other monoethyl unsaturated monomers and then partially or completely hydrolyzing the copolymers. The hydrolysis takes place in the presence of acids, bases or also enzymatically. During the hydrolysis, the n-Vmylformamide units which have been polymerized in form hydrolysis units by splitting off formyl groups. Suitable comonomers are, for example, vinyl formate, vinyl acetate, vinyl propiona, C - to Cg alkyl vinyl ether, monoethyl-unsaturated C ₃ to C ₈ carboxylic acids, their esters, nitriles, amides and, if available, also the anhydrides, N-Vmylurea, N-Vmylimidazoles and N-vinylimidazolines. If the copolymers contain carboxylic acids in a polymerized form, the hydrolysis of the N-vinylformamide groups gives rise to amphoteric copolymers whose content of vinyl amine units is greater than that of empolymerized units of ethylenically unsaturated carboxylic acids, so that these copolymers carry a cationic excess charge.

Examples of ethylenically unsaturated carboxylic acids are acrylic acid, methacrylic acid, dimethylacrylic acid, ethacrylic acid, crotonic acid, vylacetic acid, allylic acetic acid, maleic acid, fumaric acid, citraconic acid and itaconic acid and their respective esters, anhydrides, amides and nitriles. Anhydrides which are preferably used are, for example, maleic anhydride, ci raconic anhydride and itaconic anhydride.

Suitable comonomers for the copolymerization with N-vinylformamide are esters which are preferably derived from alcohols having 1 to 6 carbon atoms, such as methyl acrylate, methyl ethacrylate, ethyl acrylate, ethyl methacrylate, isobutyl acrylate, hexyl acrylate or

Glycols or polyalkylene glycols, where only one OH group of the glycols or polyglycols is esterified with a monoethyl-unsaturated carboxylic acid, for example hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate and hydroxybutyl methacrylate. Also suitable as comonomers are esters of ethylenically unsaturated carboxylic acids with amino alcohols, for example dimethyl on ethyl acrylate, dimethylammoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl ethacrylate, dimethylammopropyl acrylate and diethylaminopropyl methacrylate. Acrylamide and methacrylamide are preferred amides. The basic acrylates are used in the form of the free bases, the salts with mineral acids or carboxylic acids or also quaternary in the copolymerization with N-vinylformamide. Also suitable as comonomers are acrylonitrile, methacrylonitrile, N-vinyl imidazole and substituted N-vinylimidazoles such as N-vinyl -2-methylimidazole and N vinyl -2-ethylimidazole, N-vinylimidazoline and substituted N-vinylimidazoles such as N- Vmyl -2-methyl-imidazole. Monomers containing sulfo groups, such as vinylsulfonic acid, allylsulfonic acid, styrene sulfonic acid and 3-sulfopropyl acrylate, are also suitable as comonomers as other monoethyl-unsaturated monomers. The monomers containing acid groups can be used in the form of the free acids or as alkane or ammonium salts in the copolymerization with N-vinylformamide.

In order to produce low molecular weight polymers, the polymerization is expediently carried out in the presence of regulators. Suitable regulators are, for example, organic compounds containing sulfur in bound form. These include, for example, mercapto compounds such as mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptoacetic acid, mercaptopropionic acid, butyl mercaptan and dodecyl mercaptan. Also suitable as regulators are allyl compounds such as allyl alcohol, aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde and isobutyraldehyde, formic acid, ammonium formia, propionic acid, hydrazine sulfate and butenols. If the polymerization is carried out in the presence of regulators, preference is given to 0.05 up to 20% by weight, based on the monomers used in the polymerization.

The monomers are usually polymerized in an inert gas atmosphere with the exclusion of atmospheric oxygen. During the polymerization, good mixing of the reactants is generally ensured. In the case of smaller batches in which a reliable removal of the heat of polymerization is ensured, the monomers can be copolymerized discontinuously by heating the reaction mixture to the polymerization temperature and then allowing the reaction to proceed. These temperatures are, for example, in the range from 40 to 180 ° C., it being possible to work under normal pressure, reduced or else increased pressure. Polymers with a high molecular weight are obtained if the polymerization is carried out in water. This can be used, for example, for the production of water-soluble polymers in aqueous solution, as water-oil emulsions. sion or by the process of reverse suspension polymerization. In order to avoid hydrolysis of N-vinylformamide during the polymerization in aqueous solution, the polymerization is preferably carried out in a pH range from 4 to 9, in particular 5 to 8. In many cases it is advisable to also work in the presence of buffers, for example using primary res or secondary sodium phosphate as a buffer.

The homo- and copolymers of N-vinylformamide are subjected to a second stage in a polymer-analogous reaction of hydrolysis with acids, bases or enzymes. Suitable acids are, for example, mineral acids such as hydrogen halide (gaseous or in aqueous solution), sulfuric acid, nitric acid, phosphoric acid and organic acids such as Ci to C ₅ carboxylic acids, eg. B. formic acid, acetic acid and propionic acid or the aliphatic or aromatic sulfonic acids such as methanesulfonic acid, benzenesulfonic acid or toluenesulfonic acid. Hydrochloric acid or sulfuric acid is preferably used for the hydrolysis. In the case of hydrolysis with acids, the pH is 0 to 5. Per formyl group equivalent in the polymer, for example, 0.05 to 1.5 equivalents of an acid, preferably 0.4 to 1.2, are required.

In the hydrolysis with bases, metal hydroxides of metals of the first and second main groups of the periodic table can be used, for example lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide and barium hydroxide. However, ammonia and alkyl derivatives of ammonia can also be used, e.g. Alkyl- or arylamines such as tπethylamine, monoethanolam,

Diethanolamine, triethanolamine, morphol or aniline. In the case of hydrolysis with bases, the pH is 8 to 14. The bases can be used in solid, liquid or, if appropriate, also in the gaseous state, diluted or undiluted. Ammonia, sodium hydroxide solution or potassium hydroxide solution are preferably used as bases for the hydrolysis. The hydrolysis in the alkaline and in the acidic pH range usually takes place at temperatures of, for example, 30 to 170, preferably 50 to 120 ° C. It is complete after about 2 to 8, preferably 3 to 5 hours. After the hydrolysis, the reaction mixture is preferably neutralized so that the pH of the hydrolyzed polymer solution is 2 to 8, preferably 3 to 7. Neutralization is particularly necessary if the progress of the hydrolysis is to be avoided or delayed. In the hydrolysis of copolymers of N vinylformamide, a further modification of the polymers may occur in that the empolymeπsized comonomers are also hydrolyzed. Thus, for example, 5-unit units of vinyl esters form vinyl alcohol units. Depending on the hydrolysis conditions, the 3-polymer units can be completely or partially hydrolyzed. In the case of partial hydrolysis of vinyl acetate units, copolymers of N-vinylformamide containing polymerized

10 holds the hydrolyzed copolymeπsat in addition to unchanged vinyl acetate units, vinyl alcohol units and vinylamm and N-vinylformamide units. Units of monoethyl-unsaturated carboxylic acid anhydrides are used in the hydrolysis to produce carbon-acid units. E polymerized monoethyl unsaturated

15 carboxylic acids are not chemically changed during hydrolysis. In contrast, ester and amide units saponify to carboxylic acid units. Units of amides or carboxylic acids are formed from empolymerized monoethyl-unsaturated nitriles. Vmylamm- can also be made from

20 units are formed. The degree of hydrolysis of the copolymerized comonomers can easily be determined analytically.

Polymers of component a) which contain vinylamm units are preferably polymers which

25

1) Vinylamm units and

2) N- vinyl formamide, vinyl formate, vinyl acetate, vinyl propionate, vinyl alcohol and / or N-vinyl urea units

30 polymerized included. Polymer seeds to be used preferably contain

1) 10 to 100, preferably 20 to 100 mol% of methylamine units 35 and

2) 0 to 90, preferably 0 to 80 mol% of N-vinylformamide Emhei th.

40 These copolymers are either partially or fully hydrolyzed homopolymers of N-Vmylformamids. Hydrolysed copolymers of N-V contain nylformamide, for example

45 10 to 90, preferably 20 to 70 mol% vinylamm units and 10 to 90, preferably 30 to 80 mol of other monoethyl-unsaturated monomers.

The polymers containing vinylamm units have a molar mass M _{w of} from 5000 to 3 million, preferably from 20,000 to 2 million. The partially or fully hydrolyzed polymers of N-methylformamide have a charge density of 4 to 18, preferably 8 to 18 meq / g (determined at pH 7). The polymers of group a) are used in amounts of 0.01 to 0.8% by weight, preferably 0.01 to 0.5% by weight, in the process according to the invention.

Polymers of group b) are, for example, cationic polyacrylamides with molecular weights M _w of at least 4 million polymers of this type are described in EP-A-335 575 cited in the prior art. They are commercially available. The high molecular weight cationic polyacrylamides are produced by polymerizing acrylamide with cationic monomers. Suitable cationic monomers are, for example, the esters of ethylenically unsaturated C ₃ to C ₅ carboxylic acids with amino alcohols, such as dimethylammoethyl acrylate, diethylaminoethyl acrylate, dimethylamethylethyl methacrylate, diethylammoethyl methacrylate and di n-propylammoethylacrylate. Other suitable cationic monomers that can be copolymerized with acrylamide are N vinylimidazole, N-Vmylimidazolm and basic

Acrylamides such as D methylammoethylacrylamide. The basic monomers can be used in the form of the free bases, as salts or in quaternized form in the copolymerization. The catalytic polyacrylamides contain, for example, 5 to 40, preferably 10 to 40, cationic monomers in an empolymerized form. The molecular weights M _{w of} the cationic polyacrylamides are at least 4,000,000 and in most cases are above 5,000,000, for example in the range from 5,000,000 to 1,500,000.

Other suitable cationic polymers of group b) are polymers containing vinylamine units and having molecular weights of at least 4000000. Polymers containing vinylamine units have already been described above. The polymers containing vinylamine units which are suitable here as component b) differ from those of group a) in that they have a higher molar mass. These polymers are preferably completely or partially hydrolyzed homopolymers of N vinylformamide. In addition, hydrolyzed copolymers of N-vinylformamide with vinyl formate, vinyl acetate, vinyl propionate, acrylic acid, methacrylic acid, N-methylpyrrolidone and NV yicaprolactam are suitable. Copolymers of N-vinylformamide and ethyl-unsaturated carboxylic acids are according to the Hydro amphoteric lysis, but always have an excess of cationic charge. The polymers preferably contain up to a maximum of 40% by weight of polymerized vinylamine units. Those polymers which contain 10 to 35% by weight of vinylamine units are particularly preferably used. The polymers of group b) containing vinylamine units preferably have a charge density at pH 7 of, for example, 0.5 to 7 milliaquivalents per gram. They are added to the paper stock in amounts of 0.005 to 0.5, preferably 0.01 to 0.2% by weight.

All paper qualities and cardboard can be produced according to the method according to the invention, for example papers for newspaper printing, so-called medium-fine writing and printing papers, natural gravure papers and also lightweight coating base papers. For example, wood pulp, thermo-mechanical material (TMP), chemo-thermo-mechanical material (CTMP), pressure sanding (PGW) and sulfite and sulfate pulp can be used. Pulp and wood pulp can also be used as raw materials for the production of the pulp. Above all, these so-called integrated factories are further processed into paper in more or less moist form without paper thickening or drying. Due to the impurities that have not been completely removed from them, these fiber materials still contain substances which severely disrupt the normal paper production process. However, pulps containing contaminants can also be easily processed by the method according to the invention.

Both filler-free and filler-containing paper can be produced by the process according to the invention. The full peat content in paper can be up to a maximum of 40% by weight and is preferably in the range from 5 to 25% by weight. Suitable fillers are, for example, clay, kaolin, native and precipitated chalk, titanium dioxide, talc, calcium sulfate, barium sulfate, aluminum oxide, satin white or mixtures of the fillers mentioned.

The consistency of the pulp is, for example, 0.1 to

15% by weight. At least one cationic polymer from group a) is first added to the fiber slurry and then at least one cationic polymer from group b) is added. This additive causes a strong flocculation of the paper stock. In at least one subsequent shear step, the z. B. in one or more cleaning, mixing and pumping stages or a pulper, sifter or also in a refiner or sieve through which the pre-flocked paper stock is passed, the so-called "hard giant" present in the flocked system will lure "destroyed. After the shear step you sit Bentomt, colloidal silica or clay too, whereby so-called soft microflakes are formed. The amounts of bentome, colloidal silica or clay are 0.01 to 2, preferably 0.05 to 0.5% by weight, based on dry paper stock. Bentomt is an aluminum layer silicate based on Montmorillomt, which occurs in nature. It is mostly used after the calcium ions have been replaced by sodium ions. For example, Bentomt is treated in an aqueous slurry with sodium hydroxide solution. This makes it fully swellable in water and forms highly viscous tixotropic gel structures. The plate diameter of the bentome is, for example, 1 to 2 μm, the plate thickness is approximately 10 Å. Depending on the type and activation, the bentome has a specific surface area of 60 to 800 m ² / g. Due to the large inner surface and the outward negative excess charges on the surface, such inorganic polyamons can be used for adsorptive collection effects of catalytically reloaded and sheared paper materials. This results in optimal flocculation in the paper stock. With the cationic monomers of groups a) and b) used in accordance with the invention, surprisingly, compared to the prior art, a further improvement in the dewatering rate of paper stocks, in particular of those paper stocks containing storages, such as humic acids, wood extract or lignosulfonates, is obtained.

The percentages in the examples mean percent by weight, unless the context indicates otherwise. The molecular weights M _w were determined using the static light scattering method. Paper sheets are produced in a Rapid Kothen sheet former. The optical permeability of the white water was checked with a Dr. Long spectrometer determined at 588 nm. The drainage times, which are given in the examples, were determined for 500 ml of filtrate in a Schopper-Riegler test device.

Examples

The following polymers were used

Table 1

0 modified polyethylene m

Example 1 5

A pulp with a consistency of 5.9 g / l was produced from 40% TMP (thermo-mechanical material), 40% bleached pine sulfate with a degree of grinding of 40 degrees SR (Schopper-Riegler) and 20% coated scrap (coating waste). The pH of the pulp was 7.6. The paper stock was divided into several samples which were mixed with the polymers indicated in Table 2 in accordance with Examples a) to d). After polymers 2 to 5 had been added to the paper stock, the mixture was stirred and then the amounts of cationic polymer 6 likewise given in table 2 were added. Thereafter, the pulp was sheared for 1 min by stirring at a speed of 1500 revolutions / mm. Subsequently, 0.2%, based on dry paper stock, of bentomite was added and the dewatering time for each 500 ml of filtrate in the Schopper-Riegler - 0 test device and the optical permeability of the white water were determined from each sample. The results are shown in Table 2.

For comparison, the paper stock in the absence of polymers (comparative example 1.1) and in the presence of polymer 6 and 5 bentonite (comparative example 1.2) and according to the teaching of

EP-A-0 335 575 tested in the presence of polymer 5 (comparative example 1.3). The results are summarized in Table 2.

0

5 Table 2

Example 2

A pulp with a consistency of 6.1 g / 1 and a freeness of 50 ° SR was produced from 100 parts of unprinted newsprint with a filler content of approx. 10% and 10 parts of Chinaclay (Type XI from ECC). The pH of the pulp was 7.6. The paper stock was divided into several samples and dewatered under the conditions given in Table 3 in a Schopper-Riegler test device. First the polymers a) were metered in and then the polymers (b). The paper stock was then subjected to a shear step by stirring it 1 mm at 1500 revolutions / mm. Then the dome was dosed and the drainage time and optical permeability were determined. The results are shown in Table 3.

For comparison, a sample of the paper stock described above was dewatered without any addition (comparative example 2.1). In Comparative Examples 2.2 and 2.3, the paper stock was sheared after the polymers had been added in the order of polymer type a) and then polymer type b) for one minute at 1500 revolutions / mm, then bentomite was added, and the Schopper-Riegler test device was dewatered. The results are shown in Table 3.

Table 3

Example 3

A pulp with a consistency of 6 g / l and a freeness of 50 ° SR was produced from 100 parts of printed newsprint. The pH of the pulp was 7.6. The pulp was divided into several samples. In the examples according to the invention, the cationic polymer of type a) was metered in first and then the catalytic polymer in accordance with b). The pulps were then stirred for 1 min each with a stirrer at a speed of 1500 revolutions / mm. Then 0.2% bentomite, based on dry paper stock, was added and the dewatering time was determined in a Schopper-Riegler test device. The optical permeability of the white water was also determined.

In comparative example 3.1, the dewatering time and the optical permeability of the white water of the pulp were determined without any further addition. In Comparative Example 3.2, the pulp was subjected to a shear step after addition of polymer 6, then bentomite was added and dewatered. In Comparative Example 3.3, the polymers specified there were added as in Example 3a). After the pulp was sheared, bentomite was added and the drainage time and optical transmission were determined. The results obtained in the examples and comparative examples are shown in Table 4.

Table 4

Claims

claims

1. A process for the production of paper and cardboard by dewatering pulps, with sheet formation and drying of the leaves, the pulps being successively mixed with two different water-soluble, cationic polymers, then subjected to at least one shear stage and then by adding bentomite, colloidal silica or clay are flaked, characterized in that the water-soluble cationic polymers are initially

(a) Polyethylene group with a molecular weight M _w of more than 500,000 or polymers containing vinylamine units with a molecular weight M _w of 5,000 to 3 million and thereafter

(b) uses cationic polyacrylamides, polymers containing cationic starch or vinylamine units, where the molecular weights M _{w of} the polymers are each at least 4 million.

2. The method according to claim 1, characterized in that one as a water-soluble, cationic polymers

(a) Polyethylene with a molecular weight of more than 700,000 or polymers containing vinylamine units with molecular weights of 20,000 b 2 million and

(b) using cationic polyacrylamides or vinylamine units containing polymers which contain 10 to 35% by weight

Contain vinylamine units, the molecular weights M _{w of} the polymers being at least 5 million.

3. The method according to claim 1 or 2, characterized in that the water-soluble cationic polymers, each based on the weight of the dry pulp, in amounts of

(a) 0.001 to 0.8% by weight, preferably 0.01 to 0.5% by weight and (b) 0.001 to 0.8% by weight, preferably 0.01 to 0.2% by weight %

starts.

4. The method according to any one of claims 1 to 3, characterized in that the water-soluble cationic polymers (a) partially or completely hydrolyzed polymers of N- Vinylformamids with a charge density of 4 to 18 meq / g (determined at pH 7).

5. The method according to claim 4, characterized in that the water-soluble cationic polymers (a) partially or fully hydrolyzed homopolymers of N-Vmylforma - mids with a charge density of 8 to 18 meq / g (determined at pH 7).

6. The method according to any one of claims 1 to 5, characterized in that as water-soluble, cationic polymers (b) vinyl amine-containing polymers are used which contain at most 40 wt .-% vinyl amine units and a charge density of 0.5 to 7 meq / g (determined at pH 7).