FI59445B - FOERFARANDE FOER FOERBAETTRANDE AV TORRSTYRKAN HOS ETT KORRUGERINGSMEDIUM MED EN POLYMER - Google Patents

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USA (US) 735578 (71) American Cyanamid Company, Wayne, New Jersey, USA (US) (72) John Andrew Sedlak, Stamford, Conn., USA (US) (TM Oy Kolster Ab (5 ^) Method for improving the dry strength of a corrugating medium Polymer - a method for förbattrande of torrstyrkan hos a korrugeringsmedium with a polymer the present invention relates to quaternized, dialkyyliaminometyloituja acrylamide polymers as reinforcing agents in the preparation of aallotusväliaineen More particularly, this invention relates to quaternized, dimetyyliaminometyloituja acrylamide strengthened as aallotusväliaineessa paper manufacture very anieni lashing raw materials, which contain large quantities. used cooking liquor.

The production of corrugated media with improved dry strength from pulps composed of unbleached fibers, especially when the pulp contains highly anionic raw materials or large amounts of cooking liquor, has posed a particular problem in the papermaking industry. Most dry strength improving polymers (both anionic and cationic) do not sufficiently improve the dry strength and dewatering of such pulps.

2 59445

Since most naturally occurring cellulosic fibers are normally anionic, the presence of cationic bonds in the polymers improves the strength of the polymers used in the cellulose. Likewise, the incorporation of a hydrophobic comonomer, e.g., styrene, makes the polymer stronger in some applications because it tends to precipitate on cellulosic fibers.

Quaternary cationic polymers have been used as dry strength improvers. In general, however, dry strength agents have not been used with the corrugating medium.

Cationic polymers have been used in the art as drying aids in corrugating media. But the amounts required are so large that they are uneconomical. See. e.g., Water-Soluble Polymers, N. Bikales, Ed., Plenum Press, N.Y. 1973, page 16.

The usefulness of quaternized polymers is generally pH independent. Thus, the quaternized polymer can improve dry strength and can be used as a dewatering aid for a corrugation medium normally treated in an alkaline pH range.

Wet strength resins are difficult to re-fiberize. It is common practice in the art to re-defiber the corrugating medium. Therefore, pulp and paper mills generally do not want a corrugating medium with good wet strength properties. The quaternary polymers of this invention do not improve wet strength.

The corrugating medium is generally treated by neutral, semi-chemical sulfite or soda liquor cooking processes.

It has now been found that the quaternized polymer improves the dry strength of the corrugation medium. It has also been found that the dry strength of the corrugating medium can be improved without substantially impairing dewatering. In fact, the addition of a quaternary polymer in a certain proportion improves the dewatering of the corrugating medium. Because the polymer is quaternized, it can retain more of its cationic charge at higher ρΗ values than non-quaternized cationic polymers. Therefore, its use at higher ρΗ values is more economical than the use of non-quaternized cationic polymers found in corrugated media masses.

The invention relates to a process for improving the dry strength of a corrugating medium with a polymer, which is added to a fiber suspension of said corrugating medium from 0.1 to 3% by weight based on the dry weight of fiber 59445, characterized in that the polymer contains at least 10% by weight of acrylamide bonds and 5 to 60 moles. -% of quaternized dialkylaminomethylated acrylamide bonds, wherein the pH of the fiber suspension is 6-10, and that a fibrous mat is formed from said corrugating medium and said mat is dried.

Excellent results have been obtained with dimethylaminomethylated acrylamide polymers quaternized with dialkyl sulfate. Therefore, a quaternized, dimethylaminomethylated acrylamide polymer is recommended. Other polymers, e.g., diethylaminomethylated acrylamide or dipropylaminomethylated acrylamide polymer quaternized with dialkyl sulfate, may also be preferred.

The quaternized polymer contains about 5-60 mole percent quaternized, dialkylaminomethylated acrylamide bonds and at least about 10 weight percent acrylamide bonds. In another preferred embodiment, the quaternized polymer may contain about 0-30% by weight of styrene bonds. In another preferred embodiment, the quaternized polymer may contain about 0-20% by weight of acrylonitrile bonds.

When the quaternized polymers described above are added to the fiber suspension of the corrugation medium in an amount of about 0.10 to 3% by weight based on the dry weight of the fiber in the fiber suspension, the dry strength of the corrugation medium is improved. In most applications, the dry strength of the corrugating medium is improved when the quaternized polymers described above are added to the fiber suspension of the corrugating medium in an amount of about 0.15 to 1% by weight based on the dry weight of the fiber. In certain cases, the quaternized polymers described above can improve the dry strength and drying of the corrugation medium. Effective compounds for quaternizing polymers of dimethylaminomethylated acrylamide, diethylaminomethylated acrylamide and dipropylaminomethylated acrylamide include dialkyl sulfate and alkyl chloride; preferred compounds are dimethyl sulfate and methyl chloride.

The particular superiority of quaternized polymers as dry strength enhancers in the manufacture of corrugated media from unbleached pulp is due to their ability to strengthen cellulose fibers at pH values above about 6.

The quaternized polymers used in the process of the invention can be prepared by mixing formaldehyde and (59445 di (C1-3) alkyl) amine and a polymer containing acrylamide bonds in an aqueous medium and allowing the mixture to stand at an alkaline pH (e.g. pH 10-12). and at about 10-40 ° C until the polymer has become sufficiently cationic to be adsorbed by the cellulosic fibers in the aqueous suspension.

This polymer is then treated at about 25 ° C with an amount of dimethyl sulfate equimolar in the Mannich reaction, initially with dimethylamine. Suitable conditions for carrying out the Mannich reaction are disclosed in U.S. Patent 3,323,979. The quaternization reaction may take several hours. According to the following chemical equation: -ch2-ch- + (ch3o) 2so2-) -ch2-ch- C = 0 C = 0

I I

NH NH

I I

fH2 fH2 N (CH3) 2 + N (CH3) 3 -CH3SO4

In addition to the quaternization of the polymeric amine, dimethyl sulfate can react with any free dimethylamine in the polymer.

The molecular weight is preferably about 200,000 to 15,000,000.

In the quaternized polymer of this invention, unsubstituted amide bonds provide dry strength once the polymers have been precipitated on the fibers. These bonds are therefore usually present in as large a number as possible. Hydrophobic vinyl bonds, when present, and quaternized, dialkylaminomethylated acrylamide bonds contribute to the precipitation of the polymer on the fibers at a pH above about 6 and in the highly anionic fiber composition range. A pH above about 6 and a highly anionic fibrous composition are common in pulps used to make corrugated media. Hydrophilic anionic bonds may be present as a result of hydrolysis of amide bonds. It is to be understood, however, that hydrophilic anionic bonds need not be present to practice the invention.

A corrugated medium having improved dry strength and dewatering can be prepared in accordance with the present invention by forming an aqueous suspension of cellulose-based corrugating medium fiber at a normal pH in the range of about 7-9, adding a sufficient amount of quaternized polymer to provide the desired reinforcing and dewatering effect, and then forming a dry mat. s 59445 racket mat. It is to be understood, however, that the invention may be practiced in any pH range used to prepare the corrugating medium. This pH range should generally be about 6-10.

The fibers can be any of the fibers commonly used to make corrugated media. However, it is recommended to use neutral, semi-chemical sulphite pulps or soda liquor pulps.

In general, the quaternized polymer can be added at any stage of the process after the refiners. For example, the polymer can be added in a control box or in a vane pump. The corrugating medium can be made in a multi-cylinder machine or a flat wire machine.

Preferably, the quaternized polymer is added after refining at a point at a sufficient distance upstream of the pressure box to provide good mixing.

Usually, the papermaker experiments with different items to determine which one works best. Because the following items provide easy access and inherent mixing, they could be used: the outlet side of the centrifugal screens and the inlet side of the vane pump.

The amount of quaternized polymer added to the corrugating medium mass is that which is sufficient to provide the desired strength improvement to the paper. In general, a sufficient amount is that which represents an effective amount of the purpose, usually between n.

0.01 to 3 per cent, calculated on the dry weight of the fibers.

The polymers of this invention have a reinforcing effect when the paper is air-dried, but this reinforcing effect is not significantly damaged when the paper is dried at elevated temperatures. Thus, the paper can be dried on steam-heated drying rollers having surface temperatures in the range of about 88-121 °, as is customary.

The invention is further illustrated by the following examples. These examples are preferred embodiments of the invention and should not be construed as limiting the scope of the claims to a clear, referenced or obvious scope.

Example 1

The following describes the preparation of the corrugating medium of the present invention. A Noble-Wood laboratory hand-held machine was used to mimic the circulating water conditions found in paper mills producing corrugated medium. The first circulating water is prepared by adding 150 ml of brown liquor containing 9.6 g of brown liquor solids and 3.6 g of sodium sulphate to 12 liters of e 59445 deionized water, followed by adjustment to pH 7.3 with sulfuric acid. This solution contains 0.08% brown liquor solids and 200 ppm sulfate ion. The solution is placed in the well of a hand-held sheet machine for use in subsequent dilutions of concentrated fiber suspensions.

The concentrated fiber suspension is prepared with a consistency of 2.5% from a neutral semi-chemical sulphite pulp ground to a Canadian Standard grinding degree of 401 ml, to which 2.8% of the brown liquor solids (calculated on the dry weight of the fibers) are added. The pH of the suspension is adjusted to 7.3 with sulfuric acid and then 200 ppm of sulphate ion (based on the whole suspension, added as sodium sulphate) are added. Six 880 g fractions of a 2.5% fiber suspension at pH 7.3 are taken to form six sets of hand sheets with a basis weight of 45 kg (63.5 cm x 101.6 cm / 500 rice). All circulating water is stored in the recess of the hand-held sheet machine and all dilutions to sheeting consistency (approximately 0.06%) are performed with this circulating water. Only the last three sets of sheets (three sheets each) are used for testing, as the first three sets do not represent circulating water equilibrium conditions. For each set of hand sheets, a 1 000 ml fraction at a consistency of 0,5% is used to measure the degree of grinding using a Canadian Standard Freeness tester.

The polymer is prepared by quaternizing with dimethyl sulfate a copolymer of 85% by weight of acrylamide and 15% by weight of styrene and containing 5 mol% of Mannich substitution in acrylamide. The viscosity of the acrylamide-styrene copolymer at 10% dry matter is 67,000 cP at 27 ° C as measured by Brookfield-Viscosity.

Polymer-treated sheets are prepared by the same procedure as reference sheets except that the polymer dispersion is added to a 2.5% fiber suspension.

The test sheets are standardized by storage for 24 hours at 23 ° C and 50% relative humidity and their Concora crumb strengths are determined. The results are as follows:

Run No. Added polymer- Grinding degree Concora crushing- 3 2 _nprosentt l_tuma_

Comparison 0 493 143.3 1_0_j_2_535_ 161> 5_

Measured at 0.5% consistency with Canadian Standar Freeness tester 7 59445 2 TAPPI Standard test procedure T 809 os-71; N, average of a series of three sheets 3

Calculated from the dry weight of the fiber Example 2

The following describes a process using a quaternized polymer in a concentrated fiber suspension.

A resin was prepared by quaternizing with dimethyl sulfate a copolymer of 85% by weight acrylamide and 15% by weight styrene copolymer containing 5 mol% Mannich substitution in acrylamide. The viscosity of the product as a solution containing 5% polymer solids was approximately 800 cP at 25 ° C as measured by a Brookfield viscometer.

The resin was tested with a corrugating medium prepared on a small scale flat wire paper machine at the Herty Foundation, Savannah, Georgia. The machine produced a 91.4 cm wide sheet at a speed of 25.3 m / min with a basis weight of 43-45 kg (63.5 cm x 101.6 cm / rice).

The raw material was soda-liquor pulp, which contained a total of 85 percent brown liquor solids from the fiber. The quaternized polymer latex of Example 1 was fed to a 3% thick pulp stream at the outlet of the Jordan refiner. The pH of the trough water was adjusted to 7.3. The results were as follows:

Run No. Added polymer- Average Average 2 1 rip percent drying ml / s Concora bruise-__inucle3_

Comparison 0 165 247.4 1 0.15 162 268.8 2 _0.30_ 1 76_293.3_ 1. ...

Measured by collecting drying water in a trough less than 13 x 30 cm of a seventh cone roller 2 ...

Calculated on the dry weight of the fiber

3PAPPI Standard Test Procedure T 809 os-71, M

Examples 3-6 describe preferred embodiments for the preparation of water-soluble, quaternized, dimethylaminomethylated acrylamide dipolymers (Polymers Nos. 1-3 in Example 5 and Polymer No. 4 in Example 6 are water dispersible) and a process for their use in a fiber suspension of a corrugating medium.

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Example 3 (A) Preparation of polymers

For each polymer preparation, the starting material is an aqueous solution of polyacrylamide. The Mannich reaction to provide dimethylaminomethyl substituents is performed by adding a formaldehyde solution and a dimethylamine solution to the polymer solution; the molar ratio of dimethylamine to formaldehyde is 2: 1. After standing for 18 hours at room temperature, an equimolar amount of dimethyl sulfate relative to dimethylamine is added and the mixture is allowed to stand for 18 hours at room temperature.

The results are as follows:

Polymer No. Starting Polycrylamide Moles CH 2 O.

_molecular weight_Moles of acrylamide 1 12-14 MM1 15 2 12-14 MM 30 3 12-14 MM 60 4 2 MM 15 5 2 MM 30 6 2 MM 60 7 250 M2 15 8 250 M 30 9 250 M 60 MM = 103 2 M = 104 5 6 3 as rune sulphate). Four aliquots of 850 ml are taken and one hand sheet with a basis weight of 45 kg (63.5 cm x 101.6 cm / 500 rice) forms 4 (B) Preparation of corrugating medium 5

Prepare a fiber suspension of 0,65% consistency from a neutral semi-chemical sulphite pulp ground to a Canadian Standard grinding degree of 377 ml. The pH of the suspension is adjusted to pH 9,0 with sulfuric acid and then 1 000 ppm of sulphate ion is added - 9 59445 of each fraction is made by standard laboratory procedures using a Noble-Wood hand-held machine, dilutions in sheet mold to sheet-making consistency (approximately 0.06%) are made with deionized water, and wet nonwovens are dried for 1 1/2 minutes in a laboratory tumble drier The sheets are standardized by storage for 24 hours at 23 ° C and 50% relative humidity and their Concora crush strengths and internal bonds are determined, taking a 770 ml fraction for each set of hand sheets and diluting to 1 000 ml with deionized water to 0,5%. consistency and degree of grinding are measured using the Canadian Standar d grinding stage tester.

The polymer-treated sheets are prepared by the same procedure as the reference sheets except that the polymer solution is added to a 0.65% fiber suspension. For grinding degree measurements, the polymer solution is added to 1,000 ml of pulp diluted to 0.5% consistency with deionized water.

The results are as follows:

Driving Polymer Added po- Grinding- Concora- Internal 1 2 .34 No. No._limer -% _ degree_Chrumbling bond

Comparison - 0 350 249.2 0.155 1 1 0.25 610 280.4 0.277 2 2 0.25 555 304.8 0.274 3 3 0.25 520 258.1 0.235 4 4 0.25 400 313.7 0.292 5 5 0.25 425 318.6 0.308 6 6 0.25 410 301.3 0.265 7 7 0.25 370 291.0 0.219 8 8 0.25 405 298.2 0.212 9 9 0.25 380 304.4 0.230 1. ..

Calculated from the dry weight of the fiber in ml, measured with a consistency of 0.5% on a Canadian Standard Grinding Degree Tester ^ TAPPI Standard Test Procedure T 809 os-71 \ N, Four-Sheet Average J / 2.5 cm x 2.5 cm, Four-Sheet Average 10 59445

Example 4 (A) Preparation of polymers Polymers 1, 4 and 7 described in Example 3 are used.

(B) Preparation of corrugating medium

A concentrated fiber suspension is prepared at 2.6% consistency from a neutral, semi-chemical sulfite pulp ground to a Canadian Standard grinding degree of 420 ml. One thousand ppm of sulfate ion is added (based on the total suspension, added as sodium sulfate) and the suspension is divided into five portions. One part is left untreated and four parts are treated with a sufficient amount of brown liquor to give a dry matter content of 1,0%, 3,0%, 5,0% and 10,0% brown liquor, calculated on the dry weight of the fiber. The pH of the five fiber suspensions is adjusted to 9.0.

Take a 925 g aliquot of each 2.6% fiber suspension and dilute to 0.5% fiber consistency with 3,875 ml of water containing brown liquor solids and 1,000 ppm sulphate ion. The brown liquor content of the dilution water is adjusted to obtain an added total brown liquor solids content (calculated on the dry weight of the fiber) of 0%, 6%, 17%, 28% and 55% in suspensions originally containing 1%, 3%, 5% and 10% brown liquors.

Take three 1 100 ml aliquots of each 0,5% fiber suspension and form one hand sheet at 45 kg basis weight (63.5 cm x 101.6 cm, 500 rice) by standard laboratory procedures using Noble-Wood - hand sheet items. Dilutions in the sheet mold to a sheet-making consistency (approximately 0.06%) are performed with water at pH 9.0 containing 1,000 ppm sulfate ion and brown liquor solids at approximately the same concentration as the 1,100 ml fraction. The sheets are tumble dried and conditioned by storage for 24 hours at 23 ° C and 50% relative humidity and their Concora shrinkage strengths and internal strengths are determined. For each set of hand sheets, a fraction of 1 000 ml of a 0,5% fiber suspension is taken and the degree of grinding is measured using a Canadian Standard degree of grinding tester.

U 59445

The polymer-treated sheets are prepared by the same procedure as the reference sheets except that the polymer is added to a 2.6% fiber suspension.

The results are as follows:

Driving Added rus- Polymer- Added Grinding- Concora- Internal 1 3.5 No. coli%% ri No. polymer- degree of crushing 4 _r, %_inucleus_

Comparison - 0 425 208.3 0.149 1 0 1 0.25 670 274.1 0.274 20 4 0.25 480 288.4 0.308 30 7 0.25 455 278.6 0.274

Comparison 1 - 0 452 205.6 0.177 4 1 1 0.25 620 272.34 0.294 5 1 4 0.25 455 313.7 0.316 6 1 7 0.25 405 262.6 0.219

Comparison 3 - 0 405 210.0 0.184 7 3 1 0.25 580 284.8 0.279 83 4 0.25 420 316.4 0.306 93 7 0.25 395 249.6 0.180

Comparison 5 - 0 430 202.0 0.163 10 5 1 0.25 565 267.0 0.288 11 5 4 0.25 405 302.6 0.278 12 5 7 0.25 390 254.5 0.200

Comparison 10 - 0 420 201.1 0.153 13 10 1 0.25 530 296.4 0.269 14 10 4 0.25 385 277.2 0.200 15 10 7 0.25 395 235.4 0.193 1. .

Lignite dry solids added to a 2.6 per cent fiber suspension, calculated on the dry weight of the fiber 2 ...

Calculated from the dry weight of the fiber in ml, measured with a consistency of 0,5% on a Canadian Standard Grinding Tester 3 i2 59445 ^ TAPPI Standard Test Procedure T 809 os-71; N, average of four sheets J / 2.5 cm x 2.5 cm, average of four sheets Example 5 (A) Preparation of polymers

The polymers are prepared as described in Example 3, with the exceptions shown in the table below:

Polymer Starting Polymer Starting Polymer No. Mole of Polymer Vis- Mole Activity of Rylamide _cP_ 1 85 Acrylamide / 15 Styrene ^ 300 ^ 5 2 85 Acrylamide / 15 Styrene ^ 67 000 ^ 5 3 85 Acrylamide / 15 Styrene ^ 1 300 ^ 5 · + Polyacrylamide, Mol.

weight 2MM4-5 5 Polyacrylamide, Mol.

weight 2MM - 10 6 Polyacrylamide, Mol.

weight 2MM - 20 7 Polyacrylamide, Mol.

weight 2MM - 40 ^ Measured at 5.3% dry matter, 25 ° C, Brookfield viscometer ^ Measured at 10% dry matter, 27 ° C, Brookfield viscometer 3

Weight percent "mm = 106. Y" 13. _ 59445 (B) Preparation of corrugating medium

A concentrated fiber suspension is prepared at a consistency of 2.5% from a corrugated medium pulp (75% soda liquor pulp and 25% unbleached sulphate pulp) ground to a Canadian Standard grinding degree of 194 ml. The suspension contains sufficient spent soda ash to provide a dry matter content of 12% soda ash based on the dry weight of the fiber. The pH of the suspension is adjusted to 8.5.

Take an aliquot of 880 g of a 2.5% fiber suspension and dilute to 0.5% fiber consistency with water at pH 8.5 containing 200 ppm sulphate ion (calculated from the whole suspension, added as sodium sulphate). Three 1 100 ml fractions are taken and one hand sheet is formed. At 45 kg basis weight (63.5 cm x 101.6 cm, 500 rice) for each fraction by standard laboratory procedures using a Noble-Wood hand sheet machine. Dilutions to sheet consistency (approximately 0.06%) are made with water having a pH of 8.5 and containing 200 ppm sulfate ion. The sheets are tumble dried and conditioned by storage for 24 hours at 23 ° C and 50% relative humidity and their Concora crush strengths are determined. For each set of hand sheets, take one 1 000 ml fraction of the 0,5% fiber suspension and measure the degree of grinding using a Canadian Standard degree of grinding.

Polymer-treated sheets are prepared by the same procedure as reference sheets except that the polymer solution is added to a 2.6% fiber suspension.

The results are as follows: 59445 - · 2 Driving Polymer Polymer Grinding rate Concora- • 1 3 No. No._added,% _crumbling

Comparison - 0 238 237.2 1 1 0.3 255 290.1 2 2 0.3 255 283.1 3 3 0.3 250 281.2 4 4 0.3 235 254.5 5 5 0.3 300 275 , 9 6 6 0.3 290 278.6 7 7 0.3 250. 247.9

Calculated on the dry weight of fiber 2 ml, measured at a consistency of 0,5% on a Canadian Standard Grinding Grade Tester 3 TAPPI Standard Test Procedure T 809 os-71; N, the average of three sheets

Example 6 (A) Preparation of polymers

The polymers are made as described in Example 3 except that equimolar amounts of formaldehyde and dimethylamine are used to prepare polymers 1, 2 and 3.

The results are as follows:

Poly- Starting Polymer Starting Poly- Mole CI ^ O

meri meri Moles of ac no. viscosylamide, cP____ 1 80 acrylamide / 20 acrylonitrile - 5 2 80 acrylamide / 20 acrylonitrile2 - 10 3 80 acrylamide / 20 acrylonitrile2 - 20. 2 1 4 85 acrylamide / 15 styrene 500 10 is 59445 1 ...

Measured at a dry matter content of 5.2 per cent, 25 per cent

Brookfield viscometer ^ Weight% (B) Preparation of corrugation medium

A concentrated fiber suspension is prepared at a consistency of 2.6% from a corrugated medium pulp (75% soda liquor pulp and 25% unbleached sulphate pulp) ground to a Canadian Standard grinding degree of 163 ml. The fiber suspension is divided into several portions of 840 g and the soda-liquor used is added to obtain batches with a lye dry matter content of 3 g / l, 4 g / l, 5 g / l, 6 g / l, 7 g / l and 8 g / l, which means 12%, 15%, 19%, 23%, 27% and 31% soda-dry solids, respectively, based on the dry weight of the fiber. The pH of the fiber suspensions is adjusted to 8.5.

A 840 g portion of a 2.6% fiber suspension is diluted to 0.5% with water having a pH of 8.5 and containing 200 ppm of sulfate ion (calculated from the total mixture, added as sodium sulfate). Take three aliquots of a 0.5% fiber suspension and form one hand sheet at 45 kg basis weight (63.5 cm x 101.6 cm / 500 rice) from each fraction by standard laboratory procedures using a Noble Wood hand sheet machine. Dilutions in the sheet mold to sheet-making consistencies (approximately 0.6%) are made with water having a pH of 8.5 and containing 200 ppm of sulfate ion. The sheets are tumble dried and conditioned for 24 hours at 23 ° C and 50% relative humidity and their Concora shatter strengths are determined. For each set of hand sheets, a 1 000 ml fraction of a 0,5% fiber suspension is used to measure the degree of grinding using a Canadian Standard degree of grinding tester.

The polymer-treated sheets are prepared by the same procedure as the reference sheets except that the polymer solution is added to the 2.6% fiber suspension.

The results are as follows:, \.

16 59445

Driving Added soo- Polymer Added Grinding- Concora- no dalipe,% 1 no polymer- degree1 crumbling2 _ri,% 2_

Comparison 12 0 230 237.6 1 12 1 0.3 300 294.1 2 12 2 0.3 290 282.6 3 12 3 0.3 265 288.8 * 4 1 5 2 0.3 380 269.2 5 19 2 0.3 370 276.8 6 23 2 0.3 360 286.6 7 27 2 0.3 335 250.5 8 31 2 0.3 335 269.2 9 12 4 0.3 280 287.9 10 15 4 0.3 285 283.0 11 19 4 0.3 285 262.6 12 23 4 0.3 270 259.4 13 27 4 0.3 295 261.2 14 31 4 0.3 270 239.0 1 . .

Soda-lye solids added in a 2.6% fiber suspension, calculated on the dry weight of the fiber 2 ...

Calculated on the dry weight of fiber in ml, measured with a consistency of 0,5% on a Canadian Standard Grinding Tester 2 TAPPI Standard Test Procedure T 809 os-71; N, the average of three sheets

Claims (9)

17 59445 A method for improving the dry strength of a corrugating medium with a polymer, comprising adding 0.1 to 3% by weight based on the dry weight of the fiber to a fiber suspension of said corrugating medium, characterized in that the polymer contains at least 10% by weight of acrylamide bonds and 5-60 mol% of quaternized dialkylaminomethylated acrylamides. , wherein the pH of the fiber suspension is 6 to 10, and that a nonwoven mat is formed from said corrugating medium and said mat is dried. Process according to claim 1, characterized in that said polymer contains about 0-30% by weight of styrene bonds. Process according to Claim 1, characterized in that the polymer contains about 0 to 20% by weight of acrylonitrile bonds. A method according to claim 1, characterized in that said fiber suspension is a neutral, semi-chemical sulfite pulp. A method according to claim 1, characterized in that the pH of said fiber suspension is about 7-9. Process according to claim 1, characterized in that said polymer is quaternized with dialkyl sulfate. Process according to claim 6, characterized in that said dialkyl sulphate is dimethyl sulphate. A method according to claim 1, characterized in that said polymer is quaternized with alkyl chloride. Process according to claim 8, characterized in that said alkyl chloride is methyl chloride.