WO2004031479A1

WO2004031479A1 - Method for producing paper, board and cardboard

Info

Publication number: WO2004031479A1
Application number: PCT/EP2003/010152
Authority: WO
Inventors: Friedrich Linhart; Klaus Bohlmann
Original assignee: Basf Aktiengesellschaft
Priority date: 2002-09-25
Filing date: 2003-09-12
Publication date: 2004-04-15
Also published as: DE10244926A1; AU2003266385A1

Abstract

The invention relates to a method for producing paper, board and cardboard from unbleached wood pulp by adding at least one water-soluble, non-ionic polymer containing N-acrylic acid amide units to the paper stock as a strengthening agent and draining the paper stock on a wire.

Description

Process for the production of paper, cardboard and cardboard

description

The invention relates to a process for the production of paper, cardboard and cardboard by adding a hardener to the paper stock and dewatering the paper stock on a sieve.

It is common knowledge that paper consists essentially of fibers consisting of wood and / or cellulose and optionally mineral fillers, and that the essential process in papermaking consists in separating these fibers and fillers from a dilute aqueous solution Suspension of these substances with the help of at least one sieve. It is also known that certain chemicals are added to the suspension of fiber and fillers in water both to improve this separation process and to achieve or improve certain properties of the paper. A very current overview of the commonly used paper chemicals and their application can be found in - Paper Chemistry, JC Roberts ed., Blackie Academic & Professional, London, Second edition 1996 (ISBN 0 7514 0236 2) - and in - Applications of Wet-End Paper Chemistry, C O. Au and I. Thorn eds. , Blackie Academic & Professional, London, 1995 (ISBN 0 7514 0034 3).

As can be seen from the literature cited, many of the paper chemicals used are cationic water-soluble polymers or, in other words, cationic polyelectrolytes or polycations with a preferably medium or high molecular mass. The positive charge of the polymers is necessary to fix the polymers to the negatively charged fibers. Otherwise they remain ineffective in the water phase of the paper pulp and are separated from the pulp on the sieve. In some cases, anionic polymers are also used to achieve certain effects, but these in turn have to be fixed to the fibers with polycations. These products are added to the very thin paper pulp before the paper sheet is formed on the sieve. Depending on their composition, they cause z. B. more fine material remains on the sieve or that the separation of the water on the sieve takes place faster or that certain substances are fixed on the paper fibers and thus do not get into the white water, with the latter property the cleanliness of the white water can be in the foreground, as well as the effect of the fixed substances, such as dyes or sizing agents, on the properties of the finished paper. Polycations can also increase the strength of the paper or also give the paper an improved residual strength when wet.

If, with the help of a cationic polyelectrolyte, more fine material is retained on the sieve and the separation of the water on the sieve is to be accelerated, it is called a retention aid. If the cationic polyelectrolyte undesirable or desired substances such. B. anionic oligomers and polymers, resins, adhesive contaminants, dyes, sizing agents, strengthening agents, etc., bind to the fibers, this is called a fixing agent. If the cationic polyelectrolyte improves the strength-relevant property of the paper, then it is a hardener.

Papers, boxes and cardboards intended for packaging purposes are subject to particularly high demands with regard to their strength properties, depending on their application. For these papers, but also for some other applications, strength is the most important quality criterion. Waste paper is mainly used as the raw material for the majority of packaging paper, and with the help of papermaking experience and strength-enhancing chemicals, paper products with sufficient strength can also be obtained for products based on this less efficient raw material. Unbleached cellulose is used as the raw material for particularly high-quality packaging papers that have a very high strength, or for papers that cannot be made from waste paper for hygienic or other reasons. Since there is a certain amount of fiber damage with every pulp bleach, unbleached sulfate pulp provides papers with the highest strength and is therefore also called kraft pulp or simply "Kraft" in English. Therefore, the top layer of a particularly hard-wearing corrugated cardboard can consist of "Kraftliner" Unlike using the "testliner" on the basis of waste paper. papers of high strength of unbleached pulp z. B. for the production of paper sacks, carrier bags, envelopes, grocery bags ( "brown bags"), ^{'Lebensmitteleinwickelpapier,} vacuum cleaner bags, wrapping paper, the mentioned force the liner, of technical papers and even coffee filters.

However, since pulp is very expensive in contrast to other pulps used in papermaking, it is the aim of the papermaker to save this pulp and to replace it with other pulps in combination with strength-increasing chemicals. As is known from the prior art, certain types of those mentioned above can be used as the solidifier use cationic polyelectrolytes. For example, the addition of cationized starch to the pulp is very common, but the addition of cationic polyacrylamides to the pulp has also been practiced for many years. However, the use of these 5 cationic polymers is often not sufficient or often even has disadvantages. For example, starch is a good nutrient for bacteria and fungi and can therefore contribute to slimeiness in the water cycle of the paper machine and to increase deposit problems and, in particular

10 if it is insufficiently fixed, difficulties with

Cause wastewater treatment. Cationic polyacrylamides can convert the usually weakly negative zeta potential of the paper stock into a positive zeta potential due to their relatively high positive charge and the high amounts required.

15 cause and experience has shown great difficulties in the manufacturing process and in the quality of the paper.

On the other hand, a large number of paper materials and water circuits in paper machines can contain large amounts of anionic oligomers and 20 polymers, which are unnecessary or even undesirable, but at the same time neutralize cationic polyelectrolytes and render them ineffective for the desired consolidation effects, so that an increased consumption of consolidators is required.

25 The addition of water-soluble homopolymers and copolymers of N-vinylcarboxamides, in particular of N-vinylformamide or polyvinylpyrrolidone, to the paper stock is known from US Pat. No. 4,772,359. With the help of these additives, an increase in retention and drainage speed in paper manufacture is achieved.

30 position. Characteristic of this application is the use of very small amounts of polymer, e.g. B. 0.002 to 0.1, preferably 0.005 to 0.05% by weight, based on dry paper stock and the use of polymers with a high molecular weight, e.g. the polymers described there have a K value of more than

35 130, preferably K values from 160 to 250.

The invention has for its object to provide an improved method for producing paper, cardboard and cardboard with increased strength.

40

The object is achieved according to the invention with a process for the production of paper, cardboard and cardboard by adding a hardener to the pulp and dewatering the pulp on a sieve if the pulp is unbleached and

45 as a solidifier, at least one water-soluble, nonionic, Polymer used containing N-vinylcarboxamide units in copolymerized form.

The invention also relates to the use of water-soluble, nonionic, polymers containing N-vinylcarboxamide units as strengthening agents in the production of paper, cardboard and cardboard from unbleached cellulose by adding such a strengthening agent to the pulp and dewatering the pulp on a sieve.

10

Suitable unbleached pulps which are used in the process according to the invention are, for example, sulfate pulps, sodium pulp and sulfite pulps. The unbleached pulps are preferably the only fiber in the

15 Production of paper consolidated according to the invention. However, they can also be processed together with other fibrous materials to form papers with high strength. However, the proportion of the other fibrous materials in the paper stock should not exceed an amount of 80% by weight and preferably not more than

20 50 wt .-%, each based on the dry fiber mixture.

Examples of suitable water-soluble, nonionic polymers containing N-vinylcarboxamide units are homo- or copoly-

25 merisate into consideration, which can be obtained by polymerizing straight-chain or cyclic N-vinylcarboxamides alone or in combination with at least one other copolymerizable nonionic monomer. As straight-chain or cyclic N-vinylcarboxamides which are incorporated into the non-ionic water

30 soluble polymers are polymerized in, for example N-vinylformamide, N-vinyl acetamide, N-methyl-N-vinylformamide, N-ethyl-N-vinylformamide, N-methyl-N-vinyl acetamide, N-ethyl-N- vinyl acetamide, N-vinyl propionamide, N-vinyl pyrrolidone, N-vinyl piperidone, N-vinyl caprolactam and N-vinyl oxazolidone. Out

35 of this group of monomers, N-vinylformamide and N-vinylpyrrolidone are preferably used for the preparation of the polymers to be used according to the invention as hardeners. Homopolymers of N-vinylformamide are used with particular advantage.

40 For the preparation of copolymers of N-vinylcarboxamides for use according to the invention as solidifiers, for example mixtures of at least two different N-vinylcarboxamides are polymerized or at least one N-vinylcarboxamide, preferably N-vinylforma-

45 mid, with at least one other nonionic vinyl monomer, e.g. B. N-vinylpiperidone, N-vinylcaprolactam, N-vinyloxazoϊidon, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, acrylic nitrile, or an ester of acrylic acid or methacrylic acid with preferably Cl to C4 alcohols. The proportion of the N-vinylcarboxamide units in the homopolymers and copolymers is, for example, 20 to 100% by weight, preferably 50 to 100% by weight. If water-insoluble monomers are used in the copolymerization, they are preferably used in an amount such that the resulting polymers remain water-soluble. Preferred copolymers contain, for example, 20 to 99% by weight of N-vinylformamide units and as comonomers at least one compound from the group N-vinyl acetamide, N-methyl-N-vinylformamide, N-ethyl-N-vinylformamide, N-methyl-N -vinylacetamide, N-ethyl-N-vinylacetamide, N-vinylpropionamide, N-vinylpyrrolidone, N- vinylpiperidone, N-vinylcaprolactam, N-vinyloxazolidone, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, acrylonitrile, esters of acrylic acid or methacrylic acid with preferably Cl to C4 alcohols in a poly erized form.

The preparation of the water-soluble nonionic homopolymers and copolymers of straight-chain or cyclic N-vinylcarboxamides has been known for a long time, cf. EP-A-0 249 891, page 3, lines 1 to 49 and ÜS-A-4,421,602 mentioned in the prior art.

The average molecular weight Mw of the polymers containing the N-vinylcarboxylic acid amide units can be varied within a wide range. If the K value according to H. Fikentscher is used to characterize the molecular weight of the polymers, the K value (measured in 5% aqueous saline solution at a temperature of 25 ° C, a polymer concentration of 0.5% by weight) and a pH of 7) at least 40 and is, for example, in the range from 40 to 200, preferably 40 to 160.

Since the polymer is intended to act as a hardener, it is advisable to add it at a point which is customary for the addition of hardeners, eg. B. in the mixing chest or machine chest, but also before the material grinding or in the Dünnεtoffbereich. For all applications, the optimal dosing parts must be determined in every single case through practical tests. The dosing amounts of the polymers required for sufficient consolidation effects are, for example, based on the dry paper stock, 0.5 kg / t to 100 kg / t, preferably from 1 kg / t to 10 kg / t.

The method according to the invention makes it easier for the person skilled in the art to carry out the difficult task of producing papers, cardboards and cardboard boxes based on unbleached cellulose of a higher quality using relatively simple means and with a high degree of flexibility. The strengthening agents to be used according to the invention can be combined with other paper Position over1icher process chemicals such as sizing agents, fixing agents, retention aids or drainage agents and dyes are processed. In contrast to the process of US Pat. No. 4,772,359, the solidifiers are used in the process according to the invention in a higher dosage, based on dry paper stock, and in the absence of phenolic compounds such as synthetic phenolic resins or natural oligomers and / or polymers containing phenolic groups ,

The parts given in the examples are parts by weight. The K values of the polymers were determined according to H. Fikentscher, Cellulose-Chemie, Vol. 13, 58-63 and 71-74 (1932) in 5% strength by weight aqueous saline solution at a temperature of 25.degree pH of 7 and a polymer concentration of 0.1 wt .-%.

The tear length was after. DIN EN ISO 1924 and the burst pressure determined according to DIN ISO 2758.

example 1

In a paper technology laboratory, paper sheets with a basis weight of approx. 80 g / m ² (or 60 g / m ² for unbleached sulfate pulp) were made using a Rapid-Köthen sheet former with various commercially available fibrous materials using the usual and well-known methods. manufactured. The following were used as fibers: bleached birch sulfate pulp, wood pulp, thermomechanical pulp (TMP), semi-bleached sulfate pulp and an unbleached pine sulfate pulp with the kappa number 27. For comparison, paper sheets were produced from the pulps given in Table 1. These paper stocks were also mixed with 0.25% by weight (= kg / t, based on the fiber) of a polyvinylformamide with a K value of 90 before the final dilution and sheet formation. The tear length of the sheets was determined according to the state of the art in test technology according to DIN EN ISO 1924 and the bursting pressure according to DIN ISO 2758. The test results are summarized in Table 1. Table 1

Example 2

Example 1 was repeated with the only exception that double the amount of polyvinylformamide was used as the solidifier. The results are shown in Table 2. Table 2

Example 3

Example 1 was repeated with the only exception that 1% by weight of the polyvinylformamide, based on dry paper stock, was used as the solidifier. The results are shown in Table 3. Table 3

As Examples 1 to 3 show, the water-soluble nonionic polymers used in the process according to the invention are only suitable when using unbleached cellulose

35 Paper raw material effective.

Example 4

From an unbleached spruce sulfate pulp with the Kappa number

40 42 and the degree of grinding 22 ° SR, as described in Example 1, paper sheets were formed. Before the final dilution, various amounts of a polyvinylformamide with a K value of 90 were added to the substance. When the tear length of the paper sheets produced was determined, the values listed in Table 4 were obtained.

45 The example shows that the effectiveness of the water-soluble nonionic polymers is not limited to a single type of unbleached pulp.

5 Table 4

10

15

Example 5

From an unbleached pine sulfate pulp with the Kappa number

20 27 and the degree of grinding 22 ° SR, as described in Example 1, paper sheets ^{' were} formed. Before the final dilution, various amounts of a polyvinylformamide with a K value of 90, a copolymer of 50 parts of N-vinylformamide (= VFA) and 50 parts of acrylamide (= AM) with a K value of 101 and a polyacrylic acid were added.

25 mids with a K value of 108 for the fabric. When determining the breaking length of the paper sheets produced the belle in the Ta _^ 5 values listed were obtained.

The example shows that copolymers of N-vinyl¬

30 formamide and acrylamide gets an increase in the strength of the paper, but not with the homopolymer of acrylamide that is isomeric to polyvinylformamide.

35

40

45 Table 5

Example 6

Since it is actually incomprehensible that polyvinylformamide and polyacrylamide with approximately the same molecular weight, despite their structural isomerism, have different effects, Example 5 was repeated with an unbleached sulfate pulp of another origin and was repeated with only one addition. Table 6 again shows the ineffectiveness of the polyacrylamide.

Table 6

Example 7

Paper sheets with a basis weight of 80 g / m ^{2 were} formed from an unbleached pine sulfate pulp with a kappa number of 27 and a freeness of 22 ° SR, as described in Example 1. Before the final dilution, various amounts of polyvinylformamides with different K values, polyvinylpyrrolidone with a K value of 90 and various amounts of a copolymer of 50 parts of N-vinylformamide and 50 parts of acrylamide were added. The tear length and the The burst pressure of the papers produced therewith can be seen in Table 7. The person skilled in the art will recognize from this that the polymers tested are effective according to the invention. The results also show that the effectiveness of polymers containing N-vinylformamide in particular increases with increasing molecular weight.

Table 7

Claims

claims

1. Process for the production of paper, cardboard and cardboard by adding a reinforcing agent to the paper stock and dewatering the

Paper pulp on a sieve, characterized in that unbleached pulp is used as the fibrous material and at least one water-soluble, nonionic polymer containing N-vinylcarboxamide units in copolymerized form is used as the solidifier.

2. ^' Process according to claim 1, characterized in that a homopolymer of N-vinylformamide with a K value of at least 40 is used as the water-soluble nonionic polymer.

3. The method according to claim 1 or 2, characterized in that the polymer is water-soluble, nonionic copolymers of N-vinylformamide and at least one monomer from the group N-vinyl acetamide, N-methyl-N-vinylformamide, N-ethyl-N-vinylformamide , N-methyl-N-vinyl acetamide, N-ethyl-N-vinyl acetate, N-vinyl propionamide, N-vinyl pyrrolidone, N-vinyl piperidone, N-vinyl caprolactam, N-vinyl oxazolidone, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, acrylonitrile, ester the acrylic acid or the methacrylic acid with preferably a -C ~ to C ₄ alcohol.

4. The method according to any one of claims 1 to 3, characterized in that water-soluble, nonionic copolymer is used which contain 20 to 99% by weight of copolymerized N-vinylformamide units.

5. The method according to claim 1, characterized in that a homopolymer or copolymer of N-vinylpyrrolidone is used as the water-soluble nonionic polymer.

6. The method according to any one of claims 1 to 5, characterized in that the water-soluble nonionic N-vinyl carboxamide units containing polymers in an amount of 0.5 to 100 kg / t, preferably 1 to 10 kg / t, based on dry Uses paper stock.

7. Use of water-soluble, nonionic, polymers containing N-vinylcarboxamide units as strengthening agents in the production of paper, cardboard and cardboard from non- bleached pulp by adding such a hardener to the pulp and dewatering the pulp on a sieve.