PL214002B1 - Process for manufacturing paper - Google Patents

Abstract

The invention relates to a process for manufacturing paper and board comprising providing a suspension comprising cellulosic fibres and at least a sizing agent, dewatering said suspension thereby forming a paper-web, whereby an aromatic-containing cationic vinyl addition polymer, and an anionic polymer having a weight average molecular weight in the range of from 6,000 up to about 100,000 selected from the group consisting of vinyl addition polymers and condensation polymers is added to the suspension.

Description

Description of the invention

The invention relates to a method of making paper and board comprising preparing a slurry containing cellulosic fibers and at least an adhesive selected from the group consisting of ketene dimers and acid anhydrides, and dehydrating the slurry to form a paper web.

Internal adhesives are typically added to the papermaking process in a wet operation, thereby reducing the ability of the paper to adsorb liquids. Internal sizing agents based on rosin derivatives and cellulose reactive sizing agents, particularly ketene dimers and acid anhydrides, are commonly used. Universal office paper requires rather strong sizing in order to function properly in today's high speed copying machines. One method for producing paper, which is completely sealed with, ie., Has a cobb ₈ of less than 30, or the measurement result of the contact angle for a drop of water on the paper is greater than 80 degrees after 10 seconds, indicating a good sizing, it is to add a larger amount of adhesive agent to the slurry. However, then the probability of problems with the operation of the paper mill increases as well as the production costs.

In addition to adding the sizing agent, drainage and retention agents are also added to the pulp slurry. As their name implies, such agents increase both dehydration and pulp retention. It has surprisingly been found that the sizing performance is improved by adding at least two different types of polymers to the pulp slurry, which polymers simultaneously act as drainage and retention aids.

The invention relates to a process for the production of paper and board comprising preparing a slurry containing cellulosic fibers and at least an adhesive selected from the group consisting of ketene dimers and acid anhydrides, and dehydrating the slurry to form a paper web, the process being characterized by an aromatic cationic addition vinyl polymer and an anionic addition vinyl polymer having a weight average molecular weight ranging from about 6,000 to about 100,000 are added. In one preferred embodiment of the process of the invention, the anionic polymer has a weight average molecular weight ranging from about 100,000. 6,000 to about 80,000. In another preferred embodiment of the process of the invention, the anionic addition vinyl polymer comprises aromatic units. In a particularly preferred case, the aromatic units contain at least one sulfo group.

In a further preferred embodiment of the process according to the invention, the anionic vinyl addition polymer is polystyrene sulfonate. In a further preferred embodiment of the process of the invention, the anionic polymer is added to the slurry in an amount from about 0.005% by weight to about 1.0% by weight, based on the dry pulp. In a further preferred embodiment of the inventive process, the aromatic cationic vinyl addition polymer has a weight average molecular weight of at least about 500,000. In another preferred embodiment of the inventive process, the cationic vinyl addition polymer is made from a reaction mixture containing from about 1 to 99 mole% of a cationic monomer containing an aromatic moiety. In a particularly preferred case, the cationic aromatic monomer is represented by formula (I)

r ₂ (I)

O ₌ C — A, —Bt —N ⁺ —QX

R2 where Rt is H or CH ₃ ; R ₂ and R _3, independently of one another represent hydrogen or an alkyl group containing from 1 to 3 carbon atoms; At is O or NH; is an alkylene group having from 2 to 8 carbon atoms; Q is a substituent containing an aromatic moiety; and X is an anionic counterion.

In another preferred embodiment of the process of the invention, the aromatic cationic vinyl addition polymer is added in an amount of from about 0.002% by weight to about 1% by weight based on the dry pulp. In yet another preferred

In an embodiment of the process according to the invention, the suspension containing cellulose fibers has a conductivity of at least about 1.0 mS / cm.

The use of the method according to the present invention has a positive effect on both sticking and drainage and retention. This effect is also observed in the case of highly conductive suspensions.

The scope of the process of the invention is not limited to specific types of cellulose suspensions, but can be applied to cellulose suspensions containing primary or secondary pulp and various fillers such as calcium carbonate. The pH of the slurry may also vary from the acidic, which occurs when rosin-derived tackifiers are used, to neutral or alkaline. When cellulose-reactive tackifiers are used, the pH of the cellulose slurry is neutral to alkaline, i.e. in the range of about 5 to about 10, which also allows mineral fillers, e.g., precipitated calcium carbonate and clay, to be added to the slurry. Said two different polymers are suitably added to a significantly diluted slurry containing lignocellulose, commonly referred to as dilute raw material, with a concentration of 0.1 to 3.0% by weight based on dry fibers.

Moreover, the method does not depend on the type of tackifier added, so any tackifier or mixture of tackifiers may be present in the cellulose suspension. Preferably, the cellulose suspension comprises cellulose-reactive tackifiers, typically present in an amount of from 0.01 to 5% by weight, based on dry fibers, and has a pH suitable to ensure proper operation of the cellulose-reactive adhesive, i.e. a pH in the range from 5 to 10. Suitable cellulose-reactive sizing agents include ketene dimers, ketene multimers, acid anhydrides, organic isocyanates, carbamoyl chlorides, and mixtures thereof, with ketene dimers and acid anhydrides being preferred.

As mentioned above, in the process of the present invention, a cationic vinyl addition polymer containing aromatic moieties and an anionic vinyl addition polymer having a weight average molecular weight ranging from about 6,000 to about 100,000 are added to the cellulose slurry. Typically, the cationic polymer is added to the slurry before adding an anionic polymer. Accordingly, the addition of the cationic polymer is followed by the high shear step or steps, while the anionic polymer is added after any high shear stress step but prior to paper web formation.

Cationic aromatic vinyl addition polymer The cationic aromatic addition vinyl polymer may be linear or branched and include units containing anionic or potentially anionic groups, as long as the overall charge of the polymer is cationic. However, the cationic polymer is preferably polymerized from a reaction mixture substantially free of monomers having anionic groups or groups capable of being converted to anionic groups in aqueous compositions. The cationic polymer may be a homopolymer or a copolymer made up of cationic aromatic monomers, cationic non-aromatic monomers and non-ionic, also non-aromatic monomers. Suitably, the cationic addition vinyl polymer comprises units derived from cationic aromatic monomers selected from the group consisting of acrylamide, (meth) acrylamide, acrylate and (meth) acrylate, the cationic monomers preferably containing at least one aromatic group covalently bonded to a nitrogen atom or directly or via hydrocarbyl groups which may contain heteroatoms. Preferably, the cationic aromatic addition vinyl polymer is composed of aromatic (meth) acrylamide and / or (meth) acrylate units which are present in the polymer in an amount of from about 2 mole% to about 97 mole%. The cationic addition vinyl polymer containing aromatic moieties is suitably obtained by polymerizing a cationic monomer or a reaction mixture containing a monomer mixture containing a cationic monomer of general formula (I):

CH ₂ = C - Rt R ₂ (I)

O = C — A, - Βτ - N — Q X

R3

PL 214 002 Β1 wherein is H or CH ₃ ; R ₂ and R ₃ independently of one another are hydrogen or alkyl having from 1 to 3 carbon atoms, usually from 1 to 2 carbon atoms; At is O or NH; B, is alkylene of 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms, hydroxypropylene or hydroxyethylene; Q is a substituent containing an aromatic group, preferably - phenyl or substituted phenyl which can be attached to the nitrogen atom via alkylene group having generally from 1 to 3 carbon atoms, preferably from 1 to 2 carbon atoms, and preferably Q is a benzyl (-CH ₂ - C ₆ H ₅ ); and X is an anionic counterion, typically a halide such as chloride. Examples of suitable monomers of general formula (I) include quaternary monomers obtained by treating dialkylaminoalkyl (meth) acrylates e.g. Dimethylaminoethyl (meth) acrylamide, diethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide and diethylaminopropyl (meth) acrylamide by treatment with benzyl chloride. Preferred cationic monomers of general formula (I) include the quaternary salt of benzyl dimethylaminoethyl acrylate chloride, the quaternary salt of benzyl dimethylaminoethyl methacrylate chloride and the quaternary salt of benzyl dimethylaminopropyl (meth) acrylamide.

The cationic addition vinyl polymer may be a homopolymer obtained from a cationic monomer containing an aromatic group or a copolymer prepared from a mixture of monomers including cationic monomers containing aromatic groups and one or more copolymerizable monomers. Suitable copolymerizable nonionic monomers include the monomers of general formula (II):

_CH , = C - R «Rs (»)

I and

O = s O— - M

AND

D ίΛβ wherein R ₄ is H or CH ₃ , each of R ₅ and R ₈ is H, or a hydrocarbon, suitably an alkyl containing from 1 to 6, preferably from 1 to 4, and usually from 1 to 2 carbon atoms; A ₂ is O or NH; B ₂ is alkylene having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms, or hydroxypropylene or, alternatively, both A and B are absent, then there is a single bond between C and N (O = C-NR ₅ R ₆ ). Examples of suitable copolymerizable monomers of this type include (meth) acrylamide; acrylamide-based monomers such as N-alkyl (meth) acryl amides and Ν, Ν-dialkyl (meth) acrylamides, e.g. Nn-propyl acrylamide, N-isopropyl acrylamide, Nn-butyl acrylamide, N-isobutyl acrylamide and Nt acrylamide -butyl; and dialkylaminoalkyl (meth) acrylamides, e.g. dimethylaminoethyl (meth) acrylamide, diethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide and diethylaminopropyl (meth) acrylamide; acrylate monomers such as dialkylaminoalkyl (meth) acrylates, e.g. dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate and dimethylaminohydroxypropyl acrylate; and also vinylamides, e.g., N-vinylformamide and N-vinylacetamide. Preferred copolymerizable nonionic monomers include acrylamide and methacrylamide, ie (meth) acrylamide, and the host polymer is preferably an acrylamide based polymer.

Suitable copolymerizable cationic monomers include the monomers of general formula (III):

CH ₂ = C - R ₇ R _s (III)

I and

O ace 0— A3-Bg —N Ri, o X

AND

R "wherein R ₇ is H or CH ₃ ; R ₈ and R _g are preferably hydrocarbon, suitably alkyl having from 1 to 3 carbon atoms; R ₁₀ may be hydrogen or preferably a hydrocarbon, suitably alkyl of 1 to 8 carbon atoms, more typically 1 to 2 carbon atoms;

PL 214 002 Β1

A ₃ is O or NH; B ₃ is alkylene of 2 to 4 carbon atoms or hydroxypropylene and X is an anionic counterion, typically methyl sulfate or a halide such as chloride. Examples of suitable copolymerizable cationic monomers include acid addition and quaternary ammonium salts of dialkylaminoalkyl (meth) acrylates and dialkylaminoalkyl (meth) acrylamides mentioned above, typically obtained with acids such as HCl, H ₂ SO ₄ etc., or quaternizing agents. such as methyl chloride, dimethyl sulfate and the like; and diallyldimethylammonium chloride. Preferred copolymerizable cationic monomers include the quaternary salt of methyl chloride and dimethylaminoethyl (meth) acrylate, the quaternary salt of diallildimethylammonium chloride and the quaternary salt of benzyl chloride and dimethylaminopropyl (meth) acrylamide. Also, copolymerizable anionic monomers such as acrylic acid, methacrylic acid, itaconic acid, various sulfonate vinyl addition monomers and the like can be used, preferably in small amounts.

The cationic addition vinyl polymer can be prepared from a monomer mixture generally containing from 1 to 99 mol%, suitably from 2 to 50 mol% and preferably from 5 to 20 mol% of cationic monomers containing an aromatic group, preferably of general formula (I) and also from 99 to 1 mole%, suitably from 98 to 50 mole% and preferably from 95 to 65 mole% of other copolymerizable monomers which preferably include acrylamide or methacrylamide [(meth) acrylamide], the mixture being of monomers suitably comprises 98 to 50 mol%, preferably 95 to 80 mol% of (meth) acrylamide and the remainder up to 100% preferably compounds of general formula I and II.

Alternatively, the cationic polymer may include an aromatically modified polymer with an aromatic group-containing agent. Suitable modifying agents of this type include benzyl chloride, benzyl bromide, N- (3-chloro-2-hydroxypropyl) -N-benzyl-Ν, Ν-dimethylammonium chloride, and N- (5-chloro-2-hydroxypropyl) pyridinium chloride. Suitable polymers for such aromatic modifications include vinyl addition polymers. When the polymer contains a tertiary nitrogen atom that can be quaternized with a modifying agent, the use of such agents typically results in cationic polymers. Alternatively, a cationic polymer, e.g. a cationic vinyl addition polymer, can be subjected to aromatic modification.

Typically, the charge density of the cationic polymer ranges from 0.1 to 6.0 mole equivalents / g of dry polymer, suitably from 0.2 to 4.0, and preferably from 0.5 to 3.0. The weight average molecular weight of the cationic polymer is typically at least about 500,000, suitably greater than about 1,000,000, and preferably greater than about 2,000,000. The upper limit is not critical; the mass may be around 30,000,000, typically 20,000,000 and suitably 10,000,000.

The cationic vinyl addition polymer may be added to the slurry in amounts which may vary widely depending upon, but not limited to, the type of slurry, salt content, salt type, filler content, filler type, point of addition, etc. Generally, the cationic addition vinyl polymer is added. is in an amount which allows for better sizing, drainage and retention than would be obtained when not added and only the anionic vinyl addition polymer is added. The cationic polymer is usually added in an amount of at least 0.002%, often at least 0.005% by weight, based on the dry pulp, while the upper limit is usually 1.0% and suitably 0.5% by weight.

Anionic addition vinyl polymer

In addition to the aromatic-containing cationic vinyl addition polymer described above, an anionic polymer having a weight average molecular weight ranging from about 6,000 to about 100,000, selected from the group consisting of vinyl addition polymers and condensation polymers, is added to the cellulose slurry. The anionic polymer may be linear, branched or cross-linked, suitably substantially linear, typically water-soluble or water-dispersible. The anionic polymer may furthermore be a homopolymer or a copolymer of at least two different types of units. Preferably, the anionic polymer is a vinyl addition polymer having a weight average molecular weight ranging from about 6,000 to about 100,000. Suitable anionic vinyl addition polymers include polymers prepared from a reaction mixture containing vinyl unsaturated monomers, preferably vinyl unsaturated monomers containing an aromatic group having one or more anionic groups or anionic groups in aqueous solutions, suitably at least one sulfonate group. Examples of anionic groups attached to vinyl unsaturated monomers

PL 214 002 Β1 include phosphate, phosphonate, sulfate, acid sulfonate groups, sulfonate groups, acid carboxyl groups, carboxylate groups such as acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, itaconic acid, maleic acid or their salts, alcoholates , maleic acid groups, and phenolic groups, ie, hydroxy-substituted phenyl and naphthyl groups. Anionic charge-transfer groups typically include alkali metal, alkaline earth metal, or ammonia salts. The anionic vinyl addition polymer may also contain cationic groups to some extent, such as units containing cationic groups, although preferably only anionic groups are present in the vinyl addition polymer. Preferably, the anionic groups are bonded to aromatic vinyl (ethylenically) unsaturated monomers such as styrene, i.e. styrene sulfonate. When the anionic vinyl addition polymer is a copolymer, the polymer can be prepared from a reaction mixture containing non-ionic vinyl unsaturated monomers, e.g. acrylamide, (meth) acrylic amide. The anionic vinyl addition polymer may contain from about 20 mole% to about 100 mole% anionic units that carry at least one unit anionic charge.

Suitable anionic condensation polymers having a weight average molecular weight in the range of about 6,000 to about 100,000 include condensates of an aldehyde such as formaldehyde with one or more aromatic compounds containing one or more anionic groups, and optionally with other comonomers useful in the condensation polymerization such as urea and melamine. Examples of suitable aromatic compounds containing anionic groups include benzene and naphthalene derivatives containing anionic groups such as phenolic and naphthol compounds, e.g. phenol, naphthol, resorcinol and their derivatives, aromatic acids and their salts, e.g. phenyl, phenolic, naphthyl acids and salts and naphthol, typically sulfonic acids and sulfonates, e.g., benzenesulfonic acid and benzenesulfonates, xylene sulfonic acid and xylene sulfonates, naphthalenesulfonic acid and naphthalene sulfonates, phenolsulfonic acid and phenyl sulfonates. Examples of suitable anionic condensation polymers include benzene-based and naphthalene-based anionic condensation polymers, preferably naphthalenesulfonic acid based, and naphthalene sulfonate-based condensation polymers.

The weight average molecular weight of the anionic vinyl addition polymer and the condensation polymer ranges from about 6,000 to about 100,000. The lower limit is suitably from about 7,000, preferably from about 8,000, preferably from about 15,000, preferably from about 25,000. , while the upper limit is suitably up to about 80,000, preferably up to about 75,000, preferably up to 45,000, preferably up to about 40,000. The preferred range is any combination of the lower and upper limits. When the anionic polymer is a vinyl addition polymer, preferred weight average molecular weight ranges are from about 10,000 to about 100,000, more preferably from about 15,000 to about 75,000, and most preferably from about 25,000 to about 45,000.

The anionic polymer may vary widely in the degree of anionic substitution (DSa) depending, inter alia, on the type of polymer used; DS _A is typically from 0.01 to 2.0, suitably from 0.02 to 1.8, and preferably from 0.025 to 1.5; and the degree of aromatic substitution (DS _q ) may be from 0.001 to 1.0, typically from 0.01 to 1.0, suitably from 0.02 to 0.7, and preferably from 0.025 to 0.5. In the case of an anionic polymer containing cationic groups, the degree of cationic substitution (DS _C ) may be, for example, from 0 to 0.2, suitably from 0 to 0.1, preferably from 0 to 0.05, with the anionic polymer having an overall anionic charge. . Typically, the anionic charge density of the polymer ranges from 0.1 to 6.0 meq / g of dry polymer, suitably from 0.5 to 5.0, and preferably from 1.0 to 5.0.

The anionic polymer may be added to the slurry in amounts which can vary over a wide range depending, inter alia, on the type of workpiece, salt content, salt type, filler content, filler type, point of addition, etc. Generally, the anionic polymer is added in an amount which results in better sticking, drainage and retention than would be obtained when no anionic polymer is added but only the cationic vinyl addition polymer is added. The anionic polymer is usually added in an amount of at least 0.001%, often at least 0.005% by weight, based on the dry pulp, the upper limit being generally 3.0% and suitably 1.0% by weight.

According to one preferred embodiment of the present invention, the cationic addition vinyl polymer containing aromatic groups can be obtained in the form of an aqueous composition, suitably an aqueous solution, preferably containing additional cationic polymers, e.g. synthetic cationic polymers and naturally occurring polymers. Suitable cationic

PL 214 002 Β1 synthetic polymers include vinyl addition polymers such as acrylamide based polymers or acrylate based polymers. Other synthetic cationic polymers include cationic condensation polymers such as epihalohydrin type polymers, e.g. polymers made by reaction of aliphatic amines and epichlorohydrins, polyamidoamine polymers, polyethyleneimine polymers. Preferred naturally occurring cationic polymers include cationic polysaccharides, especially cationic starch and aromatically substituted cationic starch. The aqueous solution preferably comprises a predominant amount of cationic vinyl addition polymer containing aromatic moieties, i.e. at least 50% by weight, although the effects occur at much lower levels, up to an amount of at least 10% by weight. The additional cationic polymers described in this section can also be added separately.

According to yet another preferred embodiment of the present invention, inorganic anionic microparticulates such as anionic silica-based particles, poly (silicic acid) and smectite clays are added to the slurry. The inorganic anionic microparticulate material may be added to the slurry separately or preferably in an aqueous composition also containing the anionic polymer.

Moreover, the method can also be useful for the production of paper and board from a cellulosic suspension with a high conductivity. In such cases, the conductivity of the wire slurry is typically at least 1.0 mS / cm, suitably at least 2.0 mS / cm, and preferably at least 3.5 mS / cm. The conductivity can be measured using standard equipment such as the WTW LF 539 instrument supplied by Christian Bemer. The values given above have been determined respectively by the method of measuring the conductivity of the cellulosic suspension which is fed to or which is present in the headbox of the papermaking machine or, alternatively, by the method of measuring the conductivity of the white water obtained after dewatering the suspension. High conductivity means a high content of salts (electrolytes) that can come from the substances used to obtain the workpiece, from various additives introduced into the workpiece, from fresh water supplied to the process, etc. Moreover, the salt content is usually higher in processes such as whose sieve water is largely recycled into the process, which can lead to a significant accumulation of salt in the circulating water.

The invention is illustrated below by means of examples which, however, do not limit its scope. Parts and% refer to parts by weight and% by weight, respectively, based on dry fibers, unless otherwise indicated. The amounts of all compounds added to the system were converted to dry substance, unless otherwise indicated. In the examples, a measure of good retention was a low turbidity value of the white water, which means that most of the fine particles and filler remained in the formed sheet. A value for haze of less than 120 is acceptable and a value of less than 90 in the examples provided is excellent. The drainage value should also be small. The sizing of the paper was measured by measuring the contact angle of the water droplet on the paper. Contact angle values greater than 80 degrees after 10 seconds indicate good sealing.

Example 1

The cellulose pulp (3% level) was used, consisting of a mixture of 80/20 hardwood / softwood. The milled filler, calcium carbonate (GCC), was added to the pulp to a filler concentration of 40% on a dry solids basis. The resulting mixture was diluted to 0.3% before adding additional chemicals. The amounts of chemicals are given as% based on the dry weight of the solids in the mixture.

In this example, two mixtures were used, one having a low conductivity of 500 pS / cm (mixture I) and the other having a high conductivity of 4.0 LiS / cm (mixture II). The conductivity was adjusted by adding sodium sulfate. To the mixtures was added a dispersion containing a conventional sizing agent - ketene dimer and 1% cationic starch. Then either 0.1% of an aromatic cationic polyacrylamide containing benzyldimethylammonium groups (A-PAM) or 0.1% of a conventional non-aromatic cationic polyacrylamide (C-PAM) was added, prior to adding either 0.1% silica sol or 0.1% anionic poly ( styrene sulfonate) with a weight average molecular weight of 70,000 (PSS). The amounts of added compounds are given in Tables 1 and 2. The retention and drainage properties of the formed mixtures were estimated by measuring the drainage time using a Dynamie Drainage Analyzer (DDA-unit). The lower the value in this test, the better the dehydration performance. Retention was assessed by the turbidity measurement of white water using a nephelometer called Nephelometer 156 from Novasine. The lower the haze value means

PL 214 002 Β1 greater solids retention in the DDA-unit. In addition, the sizing of the formed, dried and cured paper was assessed by measuring the contact angle with water after 10 seconds using a Dynamie Absoption apparatus and a contact angle tester from Fibro Systems (DAT). The greater the contact angle, the better the sizing performance.

Table 1.

Mixture II (high specific conductivity)

Test Amount of added ketene dimer / [kg / t dry pulp] Type polyacrylamide cationic Type relationship anionic Cloudy- no Dehydration / [s] Contact angle (10 s / [degrees) Blind attempt* 0.2 no no 390 7.8 under 10 1 0.2 C-PAM silica sol 91 8.92 29.6 2 0.2 A-PAM PSS 47 4.54 44.6 3 0.3 C-PAM silica sol 90 6.64 80.6 4 0.3 A-PAM PSS 43 4.47 84.6 5 0.4 C-PAM silica sol 90 6.77 89.9 6 0.4 A-PAM PSS 47 4.47 94.4

As shown in Table 1, the addition of an aromatic modified cationic vinyl addition polymer and an anionic vinyl addition polymer greatly enhances not only drainage and retention but also sizing performance.

* No cationic polyacrylamide or anionic compound was added, other conditions were the same as in tests 1 and 2.

Table 2.

Mixture I (low specific conductivity)

Test Amount of added ketene dimer / / [kg / t dry pulp] Type polyacrylamide cationic Type of anionic compound Cloudy Dehydration/ / [s] Contact angle (10 s / [degrees) Blind Trial * 0.3 lack lack 420 5.6 35 1 0.3 C-PAM sol silica 100 4.8 83.3 2 0.3 A-PAM PSS 76 3.5 87.8

* Neither the cationic polyacrylamide nor the anionic compound was used in this test, other parameters were the same as in tests 1 and 2.

Example 2

The same mixture was used as in example 1, however in this example the conductivity of the mixture was adjusted to 400 pS / cm.

The sizing dispersion used in Example 1 was added to the mixture, followed by the addition of the cationic starch. The amount of tackifier was 0.03% (calculated as the active ketene dimer content in the dry mixture) and the cationic starch content was 1.0%. Upon completion of this addition, 0.1% of the aromatic cationic polyacrylamide having benzyldimethylammonium groups was added, prior to addition of 0.07% of the respective anionic styrene sulfonate of various weight average molecular weights as indicated in Table 3 and the anionic naphthalenesulfonate. The amounts of compounds added are given in Table 3. The retention and drainage properties of the formed mixtures were estimated by measuring the drainage time using a DDA-unit. Retention was assessed by the turbidity measurement of white water using a nephelometer called Nephelometer 156 from Novasine. In addition, the sizing of the formed, dried and cured paper was evaluated by measuring the contact angle with water after 10 seconds using a DAT machine.

PL 214 002 Β1

Table 3

Test The weight average molecular weight of the anionic polymer Cloudy Dehydration / [s] Contact angle (10s / [degrees) blind trial * no 125 5.4 under 30 1 8,000 ² 78 5.05 91 2 20,000 ² 75 4.95 94 3 35,000 ¹ 56 4.89 92.7 4 75,000 ¹ 50 4.03 88 5 100 OOO ¹ 47 3.82 85 6 780,000 ¹ thirty 3.17 69.2

^1: poly (styrene sulfonate), ² : naphthalene sulfonate * Neither cationic polyacrylamide nor anionic compound was added, other parameters were the same as in tests 1 to 6.

Tests 1 through 5 are mixtures of the present invention, ie, containing anionic polymers having a weight average molecular weight in the range of from about 6,000 to about 100,000.

As can be seen from Table 3, the sizing performance has increased significantly, while in the same case the turbidity and dehydration values remain high, with respect to tests 1 to 5, compared to the blank. Moreover, comparing Test 6 with Tests 1 to 5 (i.e. the compositions of the invention) shows that the sizing performance is much higher, while at the same time the haze value still indicates good retention. In addition, the contact angle of 69.2, as measured in Test 6, is not an acceptable degree of sizing. Thus, the overall properties of the composition in tests 1 to 5 in terms of retention, drainage as well as sticking clearly outweigh the composition in test 6.

Claims (11)

A method of making paper and board comprising preparing a slurry containing cellulosic fibers and at least a tackifier selected from the group consisting of ketene dimers and acid anhydrides, and dehydrating the slurry to form a paper web, characterized in that said slurry is added with aromatic moieties a cationic addition vinyl polymer and an anionic addition vinyl polymer having a weight average molecular weight in the range of from about 6,000 to about 100,000. 2. The method according to p. The method of claim 1, wherein the anionic polymer has a weight average molecular weight ranging from about 6,000 to about 80,000. 3. The method according to p. The process of claim 1, wherein the anionic vinyl addition polymer comprises aromatic units. 4. The method according to p. The process of claim 3, wherein the aromatic units contain at least one sulfo group. 5. The method according to p. The process of claim 1, wherein the anionic vinyl addition polymer is polystyrene sulfonate. 6. The method according to p. The method of claim 1, wherein the anionic polymer is added to the slurry in an amount from about 0.005 wt% to about 1.0 wt% based on the dry pulp. 7. The method according to p. The method of claim 1, wherein the aromatic cationic addition vinyl polymer has a weight average molecular weight of at least about 500,000. 8. The method according to p. The method of claim 1, wherein the cationic vinyl addition polymer is formed from a reaction mixture containing from about 1 to 99 mole% of a cationic monomer containing an aromatic moiety. PL 214 002 Β1 9. The method according to p. The process of claim 8, wherein the cationic aromatic monomer is represented by formula (I) r ₂ ABOUT) O ₌ C — A, —Bt —N ⁺ —QX R2 where Ri is H or CH ₃ ; R ₂ and R _3, independently of one another represent hydrogen or an alkyl group containing from 1 to 3 carbon atoms; At is O or NH; Bt is an alkylene group having 2 to 8 carbon atoms; Q is a substituent containing an aromatic moiety; and X is an anionic counterion. 10. The method according to p. The method of claim 1, wherein the aromatic cationic addition vinyl polymer is added in an amount from about 0.002% by weight to about 1% by weight based on the dry pulp. 11. The method according to p. The process of claim 1, wherein the cellulosic fiber suspension has a conductivity of at least about 1.0 mS / cm.