JPS61201097A - Production of paper having high dry strength - Google Patents

Abstract

1. A process for making paper having a high dry strength by adding (A) a water-soluble cationic polymer and (B) a water-soluble anionic polymer in succession to the paper stock and draining the latter with sheet formation by using component (A) in an amount of from 0.01 to 3% by weight and component (B) in an amount of from 0.05 to 3% by weight, based on dry paper stock in each case, component (B) being a homopolymer of an ethylenically unsaturated C3 -C5 -carboxylic acid or a copolymer having a K value of from 50 to 250 (determined according to H. Fikentscher at 20 degrees C in 5% strength aqueous sodium chloride solution and at a polymer concentration of 0.5% by weight) and having been formed from (a) from 35 to 99% by weight of an ethylenically unsaturated C3 -C5 -carboxylic acid, (b) from 65 to 1% by weight of an amide, nitrile and/or ester of an ethylenically unsaturated C3 -C5 -carboxylic acid and (c) from 0 to 15% by weight of styrene or of a C1 -C4 -alkyl vinyl ether, the sum of the percentages by weight in the copolymer being 100 in each case.

Description

[Detailed description of the invention] The present invention relates to a method for producing paper with excellent dry strength.

In order to produce paper with high dry strength and low wet strength, it is known to apply an aqueous solution of a synthetic polymer, which acts as a dry strength agent, to the paper surface and dry the impregnated paper. .

The amount of dry strength agent to be uniformly applied to the surface of the paper is usually 0.1 to 4% by weight, based on the dry paper. Suitable dry strength agents are described, for example, in German patent no. It is known from the specifications of No. 16969 and No. 66995.

Since the dry strength agent is applied as a dilute aqueous polymer solution (generally the polymer concentration of the prepared solution is 1 to 10% by weight), a large amount of water must be evaporated in the subsequent drying step. This drying process therefore requires a large amount of energy. However, the capacity of conventional drying equipment in paper machines is not large enough to produce paper with improved dry strength by application of aqueous polymer solutions at the highest production rates possible for the paper machine. In order to dry a sufficient amount of paper, the production speed of the paper machine must be rather reduced.

The possibility of increasing production rates in papermaking lies in applying highly concentrated aqueous polymer solutions to the paper surface.

However, in this case too the paper contains large amounts of polymer, which do not significantly improve the properties of the paper. This method for producing high dry strength paper is therefore not practicable for economic reasons. Another possibility consists in foaming the aqueous polymer solution, then applying the foam to the surface of the paper and carrying out the usual drying process. However, this method of operation requires additional operating steps and results in a paper in which the polymer is not sufficiently homogeneously distributed and thus does not have the optimum strength to be achieved with a particular amount of polymer.

According to Canadian Patent No. 1,110,019, a water-soluble cationic polymer, such as polyethyleneimine, is first added to the stock, and then a water-soluble anionic polymer, such as hydrolyzed polyacrylamide, is added to the paper stock, and A manufacturing method with high dry strength is known, in which paper stock is dehydrated while forming paper sheets. The anionic polymer contains up to 30 mol% of acrylic acid. Since the paper stock already has a drying strength agent added to it, there is no need for surface application, and of course the anionic polymer degrades the dewatering of the paper stock suspension after a period of time, making the paper machine felt sticky. I will let you do it.

It is an object of the present invention to obtain a paper with improved dry strength compared to the process known from Canadian Patent No. 1,110,019, and with high whitening when bleached pulp is used. The object was to provide a method for producing paper with dry strength and wet strength as low as possible.

The present invention solves this problem, and includes as component (B) a homopolymer of ethylenically unsaturated C1-C3-carboxylic acid and/or (a) an ethylenically unsaturated C1-C5-carboxylic acid.
65-99% by weight of carboxylic acids, (b) 65-1% by weight of amides, nitriles and/or esters of ethylenically unsaturated C8-C3-carboxylic acids, and VC(c) styrene or C,% C4-alkyl vinyl ethers. Water-soluble cationic polymer (A) and water-soluble anionic polymer (B) characterized in that a copolymer of 0 to 15% by weight (both have a -value of 50 to 250) is used. This is a method for producing paper with high dry strength by sequentially adding the following to the paper stock and forming paper sheets while dewatering the paper stock. The K-values were determined at 20 DEG C. in a 5% saline solution and a polymer concentration of 0.5% by weight by the Quikencher method.

Cationic polymers are added to the stock for charge conversion of negatively charged cellulose fibers. Water-soluble cationic polymer (A
), the following compound groups are used, for example. 10%
As an aqueous solution at pH 7, 5 to 100, preferably 10 to 4
Viscosity of 0 mPa5 (20 rpm by rotational viscometer,
polyethyleneimine with a temperature of 20° C.). The polymers may be neutralized with organic acids such as formic acid, acetic acid or propionic acid or with inorganic acids such as hydrochloric acid, sulfuric acid or phosphoric acid.

In addition, partially to completely hydrolyzed homopolymers and copolymers of N-vinylbormamide are suitable as component (A). The degree of hydrolysis of N-vinylformamide in these polymers is at least 30 mol%
Preferably it is 50 to 100 mol%. For example, starting from a homopolymer of N-vinylformamide and hydrolyzing it to 100%, polyvinylamine is obtained. Copolymers of N-vinylformamide with other monomers such as vinyl acetate, acrylonitrile, memethrylnitrile, acrylamide or methacrylamide can likewise be hydrolyzed by the action of acids or bases. In the case of copolymers of N-vinylformamide, the degree of hydrolysis mentioned always relates to the amount of N-vinylformamide in the copolymer. When a copolymer of N-vinylformamide and vinyl acetate is saponified, a copolymer containing units of vinylamine and vinyl alcohol in addition to the monomer units forming the basis of the copolymer is obtained. Suitable N-
A homopolymer of vinylformamide/a copolymer of other ethylenically unsaturated monomers and N-vinylformamide may be used in a proportion of 50 to 250%, preferably 100 to 150% (
(based on Kuykencher's method). unsaponified N-
Part of the vinylformamide copolymer and part of the saponified version agree within error.

In addition, homopolymers and copolymers of N-vinylimidazole, N-vinylimidacillin, and derivatives thereof are suitable as component (A).

The copolymer may be N-vinylimidazole or, for example, acrylamide, methacrylamide, acrylonitrile, methacrylnitrile, vinyl propionate, vinyl acetate and vinyl-〇, ~C4-alkyl ethers (such as vinyl methyl ether or vinyl ethyl ether). ) is suitable.

As the derivatives of N-vinylimidazole and N-vinylimidacilline, for example, compounds substituted with an 01-C1-alkyl group or a phenyl group are used, respectively.

The polymer of N-vinylimidazole and the polymer of N-vinylimidacilline have a molecular weight of 50 to 250, preferably 100 to 1
It has a fraction of 50% (measured by the Quikencher method).

Another water-soluble cationic polymer (A) is a polyamide amine crosslinked with epichlorohydrin.

Suitable products of this type are for example US Pat. No. 2,926,111
It is known from the specification No. 6. It is produced by condensing a dicarboxylic acid such as adipic acid with a polyamine such as diethylenetriamine or tetraethylenepentamine and crosslinking the resulting resin with epichlorohydrin to the extent that a water-soluble reaction product is obtained. This polymer has a temperature of 20 to 200% at 20°C in a 10% by weight aqueous solution.
Viscosity of mPa5 (measured with a rotational viscometer at 20 rpm)
has.

Also included in this group of cationic copolymers are polyamidoamines grafted with ethyleneimine, which are copolymerized with epichlorohydrin or with German Patent No. 246
Crosslinked with a reaction product obtained by reacting the terminal hydroxyl groups of a polyalkylene oxide (preferably polyethylene oxide) having 8 to 100 alkylene oxide units with at least an equivalent amount of epichlorohydrin as described in No. 4816. It is something. The viscosity of the water-soluble product graft-copolymerized and crosslinked with ethyleneimine is 300-2500 mPa5, measured with a rotational viscometer at 20 rpm and 20'C.

In addition, as the cationic polymer (A), diallyl-
Homopolymers of />-C,%-C,-alkylammonium compounds and diallylmono-cl-C5-amines are also suitable. Both free bases and halides, particularly chlorides, can be used.

Homopolymers of diallyldimethylammonium chloride and diallyldiethylammonium chloride are particularly suitable. This group of polymers has a fraction of 5 to 15 degrees, preferably 1 oa to 15 degrees, as measured by the Eichencher method.

Among the compounds of component (A), it is preferable to hydrolyze a homopolymer of polyethyleneimide/N-vinylformamide or a copolymer of N-vinylformamide and vinyl acetate, acrylamide or acrylonitrile. Polyvinylamine (the degree of hydrolysis thereof is 5 to 100 mol % based on the N-vinylformamide contained in the polymer) and polyvinylimidazole are used. The cationic compound (A) is 0.01 to 3% by weight, preferably 0.1 to 0.0% by weight, based on the dry paper stock.
It is used in an amount of 5% by weight.

It is of course also possible to use mixtures of two or six cationic compounds in the process of the invention. If the cationic compound (A) is strongly basic, it may be used partially or completely neutralized with an acid. pH of the solution
The value is 6 to 8, preferably 7 to Z5.

As the water-soluble anionic polymer (component B), for example, a homopolymer of ethylenically unsaturated C3-C6-carboxylic acid is used. These include, for example, homopolymers of acrylic acid, methacrylic acid or maleic acid or hydrolyzed homopolymers of maleic anhydride and itaconic acid. This ethylenically unsaturated carboxylic acid may be copolymerized with other monomers. That is, the following components (Bl) are suitable: ethylenically unsaturated C3-C6
- 65-99% by weight of carboxylic acids (a), 65-1% by weight of amides, nitriles and/or esters of ethylenically unsaturated c3-C5-carboxylic acids (b), oak and styrene or 01-c4-alkyl vinyl ethers ~15% by weight (copolymer from C1).

This copolymer preferably comprises (a) ethylenically unsaturated C
3~C,-/F7/I/H:y acid 40~70% by weight
, (b) 60-60% by weight of amides, nitriles and/or esters of -m tyrenically unsaturated carboxylic acids, and (C) 0-15% by weight of styrene or 01-c4-alkyl vinyl ethers. The total weight percent in each copolymer is 100.

Ethylenically unsaturated C3-C5- of component (b) of the copolymer
Carbo/acid esters are preferably derived from alcohols having 1 to 4 carbon atoms. Particularly suitable as component (B) are terpolymers of (a) 40-7% by weight of acrylic acid, (bl) 10-50% by weight of acrylamide and (b2) 10-50% by weight of acrylonitrile. . The anionic water-soluble polymer CB+ has a molecular weight of 50 to 250, preferably 100 to 1500, according to the Eichencher method.
has some parts. A portion of the copolymer is measured at 20° C. in a 5% saline solution and at a polymer concentration of 0.5% by weight. The pH value in determining the K value is 7.

The anionic component CB+ is 0°05 relative to the dry solid substance.
It is used in an amount of ~6% by weight, preferably 0.1-1.0% by weight. The weight ratio of components (A) to (B) is from 1:0.5 to
10 preferably 1:2-4. The anionic component is
It can be used in the free acid form or partially or completely neutralized with a base.

In this case, it is only important that the partially or completely neutralized polymer is water-soluble. As bases used are caustic and alkaline earth hydroxide solutions as well as ammonia and amines, such as caustic soda solution, caustic potash solution, calcium hydroxide, barium hydroxide, ammonia, trimethylamine, ethanolamine and morpholine.

With the method of the invention it is possible to produce all known qualities of paper and paperboard, such as writing paper, printing paper and packaging paper. These papers are made from a variety of fibrous materials, such as bleached or unbleached sulphite pulp or kraft pulp;
Can be manufactured from ground wood pulp or waste paper. Paper making is 4.5-8
Preferably it is carried out at a pH value of 6-7. To adjust the pH value of the stock suspension, sulfuric acid or aluminum sulfate can be used. The process of the invention is preferably carried out in the presence of very small amounts of aluminum sulfate. According to the invention, the paper stock is first added with a cationic compound necessary for charge conversion of the cellulose fibers. Component (A) is fixed onto the fibers very quickly. Immediately thereafter or after a residence time of, for example, 1 to 10 minutes, one or more compounds according to (B) are added to the paper stock, the mixture is homogenized and optionally further customary auxiliaries such as retention agents, dewatering agents, etc. agents, fillers, sizing agents, optical brighteners, antifoaming agents, dyes, starches, polyvinyl alcohol, carboxymethylcellulose or mannogalactan, and then forming sheets on a paper machine.

When using the anionic component (B), an improvement in the retention of stock and filler as well as common auxiliaries such as flour or carboxymethyl cellulose is observed in all paper varieties compared to known processes. Another advantage of the addition of the anionic component (B) is that it improves the dewatering of the paper-resistant suspension, so that the paper machine felt does not stick even over long periods of time. These advantageous properties make the process of the invention particularly important for the production of paper from wastepaper. When producing bleached paper, a significantly higher whitening of the paper is observed compared to state-of-the-art methods.

The parts mentioned in the examples below are by weight and the percentages are by weight of the stock. A portion of the polymer was prepared at a pH of 7 and a polymer concentration of 0.5 according to the Quikencher method described in Ferrose Hemi, Vol. 13 (1932), pp. 58-64 and pp. 71-74.
%, measured at 20°C in 55 saline, where -4
・Means 103.

In laboratory tests, paper sheets were produced by a Ravid Kooten experimental paper sheet forming machine. Dry breaking length is DIN 531
12, the wet breaking length is DIN 53112
It was measured using two instruments. The leaves of the paper turn white. Measurements were made with a reflectance photometer according to DIN 56145 (Elrefo equipment). CMT-value is DIN56
143, the dry breaking pressure was determined according to DIN 55141.

Example 1 A 0.5% stock aqueous suspension is prepared from 10'0% mixed waste paper. The pH value of the suspension is Z2 and the freeness of the stock is 50° according to Schopper φ Riegler (SR). The stock suspension was then divided into five equal parts and 120,9/77
Process it into paper sheets with a basis weight of 12.

a) Control Paper sheets are made from this stock suspension without any other additives.

b) Comparison To a sample of the stock suspension described above, polyethyleneimine is added in an amount of 0.25%, based on the dry stock. The viscosity in a 10% aqueous solution is 5 Q mPa5. After 5 minutes, 0.5% of a copolymer of 80% acrylamide and 20% acrylic acid is added to the dry stock. The copolymer is in the form of a sodium salt.

It has a K-value of 120. Mix well and make one paper sheet after a residence time of 5 minutes.

C) Comparison To a sample of the above paper stock suspension, 3% of the same polyethyleneimine as in (b) was added to the dry paper stock, and after a residence time of 5 minutes, anionic polyacrylamide was added in the same manner as in (b). 1
．． Add 0%. The mixture is stirred for 5 minutes and then formed into paper sheets while being dehydrated.

d) Example To a sample of the above-mentioned paper stock suspension, the same polyethyleneimine as in (b) was added in an amount of 0.25% based on the dry paper stock.

After a residence time of 5 minutes, a copolymer of 50% acrylic acid and 50% acrylonitrile in the form of the sodium salt is
Add 0.5% to dry paper stock. A portion of this copolymer is 120%. After mixing for 5 minutes, one paper sheet is made.

e) Example To a sample of the above paper stock suspension, the same polyethyleneimine as in (b) was added in an amount of 0.5% based on the dry paper stock.

After a residence time of 5 minutes, 1.0% of a copolymer of 50% acrylic acid and 50% acrylonitrile is added. After mixing for 5 minutes, the resulting stock suspension is dehydrated to form paper sheets.

Table 1 shows the results of the tests conducted on each paper sheet.

Table 1 a) Control 120 140 5
0b) Comparison 0.5 160 150 6
50d) Example 0.5 165 16
0 450C) Comparison 1.0 185
180 870e) Example 1.0 1
90 190 550 Example 2 70% bleached groundwood pulp and 60% bleached beech sulfite pulp
A 0.5% aqueous stock suspension having a pH of 15 and a freeness of 45° SR is prepared from. This suspension was divided into five equal parts and processed into paper sheets having a basis weight of K 10097 m2 under the following conditions.

a) control The stock suspension described above is directly processed into paper sheets.

b) Comparison A sample of the stock suspension described above is mixed with a viscosity of 5 Q mPa5. This causes a charge conversion of the cellulose fibers. After a residence time of 1 minute, 0.9% of a copolymer of 90% acrylamide and 10% acrylic acid is added. This copolymer is in the form of an ammonium salt and has a K-value of 90.
has.

After the stock suspension has been stirred for another 10 minutes, sheets are formed while being dehydrated.

C) Comparison To a sample of the paper stock suspension described above, a homopolymer of part 9 from dimethyldiallylammonium chloride was added in an amount of 0.3% based on the dry stock, and after a residence time of 1 minute, The same anionic polymer as (b) from 90% acrylamide and 10% acrylic acid is added at 0.9% to the dry stock. After a residence time of 10 minutes, the stock liquor thus treated is formed into paper sheets while being dehydrated.

d) Example To a sample of the above paper stock suspension, the same polyethyleneimine as in (b) was added at 0.6% based on the dry paper stock, and after a residence time of 1 minute, 50% acrylic acid and 30% acrylamide were added. % and 0.9% of a copolymer from acrylonitrile 20%. The copolymer is in the form of an ammonium salt, with a value of 9
It is 0.

After mixing for 10 minutes, the stock liquid thus treated is formed into paper sheets while being dehydrated.

e) Example The same dimethyldiallylammonium chloride polymer as in (C) was added to a sample of the above paper stock suspension.

The same copolymer as (d) from 50% acrylic acid, 30% acrylamide and 20% acrylonitrile was added to the dry stock after adding 0.3% to the dry stock and after a residence time of 1 minute. Add 0.9% to the total amount. Then add the mixture to 1
After stirring for 0 minutes, form paper sheets while dehydrating.

The strength of each paper sheet was measured and the results are shown in Table 2.

Table 2 Dry fracture Dry fracture Wet fracture Example 2
Length Pressure Length m) (K
pa) (m)a) control 2630
130 100b) Comparison 5650
170 770C) Comparison 3050
150 240d) Example 3580
180 540e) Example 310
0 155 11 Example 3 From 70% bleached pine kraft pulp and 30% bleached white birch kraft pulp, a 0.5% paperstock aqueous suspension with a pH value of 6.5 and a freeness of 30°SR was prepared. Prepare a suspension. This suspension was divided into three equal parts and processed into paper sheets having a basis weight of 8097 m'' as described below.

a) A control stock suspension is formed into sheets while dewatering without other additives.

b) Comparison A sample of the paper stock suspension described above was injected with a resin obtained by condensation of adipic acid with diethylenetriamine and crosslinking of the resulting polyamidoamine with epichlorohydrin according to Example 1 of U.S. Pat. No. 2,926,116 on dry paper. Add 0.25% to the total amount. After a residence time of 2 minutes, 0.5% of a copolymer of 80% acrylamide, 10% acrylonitrile and 10% acrylic acid is added. The copolymer has a portion of 1300 in the form of the sodium salt. After an action time of 2 minutes, the stock suspension is dehydrated into paper sheets.

C) Comparison To a sample of the aqueous paper stock suspension described above, polyvinylamine having a proportion of 140% was added at 0.25%, based on the dry stock, and after an action time of 2 minutes, a further addition of acrylamide 80% was added.
%, 10% acrylonitrile and 10% acrylic acid, the same polymer as (b) is added at 0.5% based on the dry stock.

After an action time of 2 minutes, the stock suspension is dehydrated into paper sheets.

d) Example To a sample of the above paper stock aqueous suspension, the same epichlorohydrin resin as in (b) was added in an amount of 0.25% based on the dry stock,
After a residence time of 2 minutes, a further 0.5% of a copolymer of 60% acrylic acid, 15% acrylonitrile and 15% acrylamide, based on the dry stock, is added. The copolymer has a portion of 1600 in the form of its sodium salt. After an action time of 2 minutes, the stock suspension is dehydrated into paper sheets.

e) Example To a sample of the above paper stock aqueous suspension, 0.25% of the same polyvinylamine as in (C) was added to the dry paper stock, and after a residence time of 2 minutes, 60% of acrylic acid, The same copolymer as (d) of 15% acrylonitrile and 15% acrylamide is added at 0.5% based on the dry stock. After 2 minutes of action, it is dehydrated and made into paper sheets.

Table 3 shows the results of testing each paper sheet.

Table 6 (7FL) (m) (%) a) Control 6180 0 86.6b) Comparison 6950 1250 82.6C) Comparison 7
540 86077.2d) Example 7130
970 86.2e) Example 7
650 690 83.5 Example 4 A 0.5% stock aqueous suspension with a pH value of 15 and a freeness of 45° SR is prepared from mixed waste paper. This paper stock aqueous suspension was divided into three equal parts, and under the conditions described below, 120,! 9/m2
Processed into paper sheets with a basis weight of

a) control Paper sheets are formed from the stock suspension without other additives.

b) Comparison To a sample of the aqueous paper stock suspension described above, first a homopolymer of vinylimidazole containing a portion of 900% was added at 0.5% based on the dry paper stock, and the mixture was heated for a residence time of 5 minutes. Thereafter, a copolymer of 85% acrylamide and 15% acrylic acid is added at 1.0% based on the dry stock. This copolymer is a sodium salt and has a portion of 1600. After an action time of 1 minute, the stock mixture is dehydrated into paper sheets.

C) Comparison To a sample of the above paper stock suspension, 0.5% of polyvinylamine having a proportion of 1100% based on the dry stock was added, and after a residence time of 5 minutes, the same acrylamide 85% as in (b) was added. and a copolymer of 15% acrylic acid is added at 1.0% based on the dry stock.

After a working time of 1 minute, the stock is dehydrated and made into paper sheets.

d) Example After a residence time of 5 minutes, 1.0% of a copolymer of 60% acrylic acid and 40% acrylonitrile is added. This copolymer has a portion of 1300 in the form of its sodium salt. After an action time of 1 minute, the stock thus treated is dehydrated and formed into paper sheets.

e) Example A sample of the paper stock suspension described above was treated with 0.5% of the same polyvinylamine as in C) on the dry stock and, after an action time of 5 minutes, 60% of the same acrylic acid as in (d). % and 40% of acrylonitrile are added and after an action time of 1 minute, the paper stock suspension is dewatered while being processed.

Table 4 shows the results of testing the paper sheets manufactured by (a) to (e).

Table 4

Claims (1)

[Claims] As component (B), ethylenically unsaturated C_3 to C_5
- homopolymers of carboxylic acids and/or (a) 35-99% by weight of ethylenically unsaturated C_3-C_5-carboxylic acids;
, (b) 65-1% by weight of amides, nitriles and/or esters of ethylenically unsaturated C_3-C_5-carboxylic acids, and (C) copolymerization from 0-15% by weight of styrene or C_1-C_4-alkyl vinyl ethers. thing(
A water-soluble cationic polymer (A) and a water-soluble anionic polymer (B), each having a K-value of 50 to 250, are sequentially added to the paper stock, and A method of manufacturing paper with high dry strength by forming paper sheets while dehydrating the material.