RU2169224C2 - Paper impregnation - Google Patents

Abstract

FIELD: papermaking. SUBSTANCE: invention provides aqueous dispersion of sizing agent containing sizing agent with chemical activity to cellulose and dispersing composition containing low-molecular cationic organic compound with molecular weight below 10000 and anionic stabilizer, in particular anionic polyelectrolyte. Acceptable anionic stabilizers include (i) anionic compounds functioning as stabilizers themselves and/or showing stabilizing effect in combination with cationic compounds and (ii) anionic compounds functioning as dispersants during preparation of sizing dispersions. Anionic compound is advantageously water-soluble or water-dispersible and can be either organic or inorganic, either naturally occurring or synthetic. EFFECT: increased stability and reduced viscosity of sizing dispersion resulting in improved quality of sizing. 23 cl, 7 tbl, 9 ex

Description

 The present invention relates to paper sizing and, in particular, to dispersions of cellulose-reactive sizing agents, the preparation of such dispersions and their use.

BACKGROUND OF THE INVENTION
Cellulose-reactive sizing agents, for example, those that are based on an alkyl ketene dimer (DAC) and alkenyl succinic anhydride (AAA), are widely used in papermaking, with a neutral or slightly alkaline pH in order to impart paper or paper cardboard has a certain resistance to wetting and penetration of aqueous liquids. Paper adhesives based on cellulose-reactive sizing agents are typically dispersions containing an aqueous phase and particles or droplets of a sizing agent finely dispersed therein. Dispersions are usually prepared using a dispersant composition consisting of an anionic compound, for example, sodium lignosulfonate, in combination with a high molecular weight amphoteric or cationic polymer, for example, cationic starch, polyamine, polyamide amine, or vinyl polymer. Depending on the total charge of the substances that make up the dispersing composition, the sizing dispersion will have a cationic or anionic character. However, dispersions of these types usually have very low stability and high viscosity, even with a relatively low solids content, which naturally causes certain difficulties in handling the dispersions, for example, during storage and use. An additional disadvantage is that such products are produced in the form of low-concentration dispersions, which leads to an increase in the cost of transportation per active component of the sizing agent.

 Cellulose-reactive sizing agents generally give good results at low dosages of the sizing agent. However, from experience with their use, it is known that the effectiveness of conventional sizing agents with respect to cellulose decreases when they are used together with processed raw materials, which have a high ability to absorb cations and contain a significant amount of lipophilic extractive substances of wood origin, such as, for example, tar acids, fatty acids, fatty acid esters, triglycerides, and others. Due to the anionic nature of lipophilic substances containing carboxylate or carboxylic acid groups, the processed feed contains a significant amount of lipophilic extractive substances, usually having a very high absorption capacity of cations. It was found that the presence of lipophilic substances adversely affects the adsorption of sizing agents by the fibers, which may cause poor sizing results. In order to improve the quality of the sizing when working with such feedstock, the paper manufacturer was forced to increase the dose of the sizing agent, which of course is undesirable for economic reasons and can lead to increased accumulation of the sizing agent in the white water that is recycled in the paper production process. These problems are of particular importance for paper mills, where white water is intensively recycled and fresh water is added only in small quantities; as a result, the ability of white water to absorb cations increases, and lipophilic extractive substances and an unabsorbed sizing agent accumulate both in white water and in paper pulp, which goes on to the water separation stage.

DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, it has been found that increased stability and improved sizing properties can be achieved in the case of aqueous dispersions of cellulose-reactive sizing agents in which the sizing agent is dispersed in the aqueous phase using a dispersant composition comprising a low molecular weight cationic compound and an anionic stabilizer. The dispersions for sizing according to this invention are characterized by excellent stability and low viscosity and are especially convenient when using raw materials for the manufacture of paper having a high absorption capacity of cations and / or containing large amounts of lipophilic substances. It was also found that better sizing results can be achieved by using such dispersions in paper manufacturing processes in which white water is intensively recycled. In particular, the present invention relates to an aqueous dispersion containing a cellulose-reactive sizing agent and a dispersing composition comprising a low molecular weight cationic compound and an anionic stabilizer, the preparation and use of such dispersions, as described in the claims below.

 The present sizing dispersions make it possible to produce paper with a higher sizing quality compared to conventional dispersions, with the same dosage of a sizing agent reactive with cellulose and using smaller doses of a sizing agent reactive with cellulose to obtain a similar sizing degree. The possibility of using smaller amounts of a sizing agent to provide the desired degree of sizing reduces the risk of accumulation of an unadsorbed sizing agent in the white water recycled in the system, thereby reducing the risk of aggregation and deposits of the sizing agent in a paper machine. The proposed invention, therefore, gives a significant economic effect and technical advantages.

The cellulose-reactive sizing agent in accordance with the invention may be selected from the group of currently known cellulose-reactive sizing agents. It is acceptable if the sizing agent is selected from the group consisting of hydrophobic ketene dimers, ketene oligomers, acid anhydrides, organic isocyanates, carbamoyl chlorides and mixtures thereof; preferably ketene dimers and acid anhydrides, most preferably ketene dimers. Suitable ketene dimers have the general formula (I) below, wherein R ¹ and R ² are saturated or unsaturated hydrocarbon groups, usually saturated hydrocarbon residues, acceptable hydrocarbon groups have 8 to 36 carbon atoms, are usually straight or branched alkyl groups having from 12 to 20 carbon atoms, such as hexadecyl or octadecyl groups. Suitable acid anhydrides may be described by formula (II) below, wherein R ³ and R ⁴ may be the same or different and may be saturated or unsaturated hydrocarbon groups, preferably containing from 8 to 30 carbon atoms or R ³ and R ⁴ , together with the -COC fragment, they can form a 5- or 6-membered ring, which, in turn, can have hydrocarbon groups containing up to 30 carbon atoms as substituents. Examples of acid anhydrides that are used on an industrial scale include alkyl or alkenyl succinic anhydrides and, especially, isooctadecenyl succinic anhydride.

Приемлемые димеры кетенов, ангидриды кислот и органические изоцианаты включают соединения, описанные в патенте США N 4522686, которые включаются в объем нашей заявки путем ссылки. Примеры приемлемых карбамоилхлоридов включают соединения, описанные в патенте США N 3887427, которые также включаются в объем нашей заявки путем ссылки.

Suitable ketene dimers, acid anhydrides, and organic isocyanates include the compounds described in US Pat. No. 4,522,686, which are hereby incorporated by reference. Examples of suitable carbamoyl chlorides include the compounds described in US patent N 3887427, which are also included in the scope of our application by reference.

 In addition to a sizing agent chemically active with respect to cellulose, the sizing dispersions may also contain a sizing agent that is chemically inactive with respect to cellulose. Examples of suitable sizing agents of this type include rosin, for example, enriched and / or esterified rosin, waxes, derivatives of fatty acids and resin acids, for example, fatty amides and fatty esters, for example, triglycerides of natural fatty acids.

 The dispersions of this invention comprise a dispersant or dispersant composition comprising a cationic organic compound and an anionic stabilizer. These compounds are preferably bonded together by electrostatic attraction, thus representing a hybrid dispersant. When used together, these compounds are effective as a dispersant of a sizing agent, although the cationic compound and / or anionic compound should not contribute to dispersion when used separately. A group of particularly preferred dispersions in accordance with this invention include those that contain a cationic surfactant and an anionic stabilizer, as will be described below. In a preferred embodiment, the dispersion is anionic in nature, i.e. the dispersing composition has a total anionic charge.

The cationic compound contains one or more cationic groups of the same or different types, and includes cationic compounds having one cationic group and cationic compounds having two or more cationic groups, i.e. cationic polyelectrolytes. Examples of suitable cationic groups include sulfonium groups, phosphonium groups, acid addition salts formed by primary, secondary or tertiary amines or amino groups and quaternary ammonium groups, for example, substances in which nitrogen was quaternized with methyl chloride, dimethyl sulfate or benzyl chloride, preferably salts acid additions formed by amines or amino groups and quaternary ammonium groups. Cationic polyelectrolytes can have a degree of substitution that varies over a wide range; the degree of substitution of cations (C3 _to ; DS _c ) can vary from 0.01 to 1.0, suitably from 0.1 to 0.8, and preferably from 0.2 to 0.6. Suitable cationic organic compounds for use within the scope of this invention include cationic compounds capable of acting as a surfactant and / or dispersant and / or retention agent between particles or droplets of a sizing agent and an anionic stabilizer. Preferably, the cationic compound is a surfactant. Preferred cationic surfactants include compounds having the general formula R ₄ N ⁺ X ^- , wherein each R group is independently selected from (i) hydrogen; (ii) hydrocarbon groups, for example aliphatic and, preferably, alkyl groups having from 1 to about 30 carbon atoms, preferably from 1 to 22 carbon atoms; and (iii) hydrocarbon groups, for example, aliphatic and, preferably, alkyl groups having up to about 30 carbon atoms, preferably 4 to 22 carbon atoms and which may contain 1 or more heteroatoms, for example, oxygen or nitrogen, and / or groups containing a heteroatom, for example carbonyl and acyloxy groups; where at least one, satisfactory, if not less than 3 and preferably all of these R-groups contain carbon atoms; satisfactory if at least one and preferably at least two of these R groups contain at least 7 carbon atoms, preferably at least 9 carbon atoms and most preferably at least 12 carbon atoms; and where X ^- is an anion, usually a halide like chloride, or an anionic group present in the anionic compound of the dispersant, for example, where the surfactant is a protonated amine of the formula R ₃ N, in which R and N are as defined above. Examples of suitable surfactants include dioktildimetilammony chloride, didecyldimethylammonium chloride, dikokodimetilammony chloride kokobenzildimetilammony chloride, coco (fractionated) - benzyldimethylammonium chloride, octadecyl trimethylammonium chloride, dioctadecyl dimethylammonium chloride, digeksadetsildimetilammony chloride, di (hydrogenated tallow) dimethylammonium chloride, di (hydrogenated tallow) benzylmethyl ammonium chloride, (hydrogenated fat) benzyl dimethyl ammonium chloride, dioleyl dimethyl ammonium chloride, and di (ethylene hexadecanecarboxylate) dimethylammonium chloride.

 Thus, a group of particularly preferred cationic surfactants includes those compounds that contain at least one hydrocarbon group having from 9 to 30 carbon atoms, and which are necessarily quaternary ammonium compounds.

 Further preferred cationic surfactants include quaternary di- and polyammonium compounds containing at least one hydrocarbon group, usually aliphatic and preferably alkyl, having from 9 to about 30 carbon atoms, preferably from 12 to 22 carbon atoms. Examples of suitable surfactants of this type include N-octadecyl-N-dimethyl-N'-trimethyl-propylene-diammonium dichloride.

 Preferred cationic polyelectrolytes further include low molecular weight cationic organic polymers, possibly partially cleaved, for example, obtained from polysaccharides such as starches and guar gums, cationic condensation products such as cationic polyurethanes, polyamidamines, for example polyamidamine-epichlorohydrin copolymers, polyamines, for example, epimel copolymers dimethylamine- ethylene diamine-epichlorohydrin copolymers, ammonia-dichloroethane copolymers, vinyl polymers formed from monomers with cationic groups, for example, homopolymers and copolymers of diallyldimethylammonium chloride, dialkylaminoalkyl acrylates, methacrylates and acrylamides (for example, dimethylaminoethyl acrylates and methacrylates), which are usually presented as acid addition salts or quaternary ammonium copolymers with, possibly, monomers, including acrylamide, alkyl acrylates, styrene and acrylonitrile and derivatives of these monomers, vinyl esters, and the like.

 The molecular weight of the cationic organic compound can generally be up to about 10,000, usually up to about 5,000, permissible up to about 3,000 and preferably up to about 800. The molecular weight is usually at least about 200. Suitable cationic surfactants can have a molecular weight of up to about 3000 and preferred cationic surfactants have a molecular weight of between about 200 and about 800.

Suitable anionic stabilizers used in this invention include anionic compounds that act as stabilizers and / or are effective in combination with a cationic compound to stabilize the sizing agent in the aqueous phase; it is also known that anionic compounds are convenient as dispersants in the preparation of sizing dispersions. Preferred is an anionic compound that is water soluble or dispersible in water. The anionic stabilizer can be selected from organic or inorganic compounds and it can come from natural or synthetic sources. The anionic stabilizer of the dispersant composition contains one or more anionic groups of the same or different types and includes anionic compounds having one anionic group and anionic compounds having two or more anionic groups, referred to herein as anionic polyelectrolytes. The term "anionic polyelectrolyte" also includes anionic compounds acting like a polyelectrolyte, for example, due to chemical non-ionic interaction or attraction. In a preferred embodiment, the anionic stabilizer is an anionic polyelectrolyte. Examples of acceptable anionic groups, i.e. groups that are anionic in nature or become anionic in water include phosphate, phosphonate, sulfate, sulfonate, acid residues of sulfonic and carboxylic acids and their salts, usually ammonium or alkali metal salts (mainly sodium). Anionic groups can be of natural origin or can be introduced by chemical modification by known methods. An anionic stabilizer can have anion substitution degree (C3 _a ; DS _a ), which varies over a wide range; Sz _a can be from 0.01 to 1.4, suitably from 0.1 to 1.2, and preferably from 0.2 to 1.0. Anionic polyelectrolytes can contain one or more cationic groups, but their number should not exceed the number of anionic groups and the total charge should be negative.

 In a preferred embodiment, the anionic stabilizer is selected from organic compounds. Suitable anionic stabilizers of this type include polymeric compounds, such as those based on polysaccharides such as starches, guar gums, celluloses, chitins, chitosans, glycans, galactans, glucans, xanthan gums, mannans, dextrins, etc., preferably phosphated, sulfated and carboxylated polysaccharides, as well as synthetic organic polymers such as condensation products, for example, anionic polyurethanes and polymer anionic compounds based on naphthalene, for example , condensation products of naphthalenesulfonates, as well as vinyl polymers formed from monomers having anionic groups, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid, vinyl sulfonic acid, sulfonated styrene and phosphates of hydroxyalkylated acrylates and methacrylates, possibly copolymers nonionic monomers, including acrylamide, alkyl acrylates, styrene and acrylonitrile along with derivatives of such monomers, vinyl esters, etc. Particularly preferred organic anionic stabilizers include anionic polysaccharides, for example, cellulose derivatives such as carboxymethyl cellulose, naphthalene sulfonate condensation products, anionic acrylamide-based polymers and polymers based on acrylic acid and related acid monomers.

 In a preferred embodiment, the anionic stabilizer is modified to render it hydrophobic and contains one or more hydrophobic groups, typically a polysaccharide, preferably carboxymethyl cellulose, modified to give hydrophobicity. Examples of suitable groups include hydrophobic substituents containing from 4 to about 30 carbon atoms, especially hydrophobic amide, ester and ether forming groups comprising a saturated or unsaturated hydrocarbon chain of at least 4 and preferably from 8 to 30 carbon atoms, possibly including one or more heteroatoms, for example, oxygen or nitrogen, and / or groups containing a heteroatom, for example, carbonyl or acyloxy. Suitable anionic polysaccharides, hydrophobized modified anionic polysaccharides and methods for introducing hydrophobic substituents into polysaccharides are described, for example, in US Pat. No. 4,687,519 and in International Patent No. WO 94/24169 (International Pat. Publ.), Which are included in the scope of our application. by reference to them.

 In another preferred embodiment, the anionic stabilizer is selected from inorganic anionic substances, preferably anionic inorganic polyelectrolytes, such as, for example, compounds containing silicon atoms, for example, various types of condensed or polymerized silicic acid, which has hydroxyl groups that dissociate to form a negatively charged ion, for example, oligomeric silicic acid, polysilicic acid, polysilicates and polyaluminosilicates.

 Anionic stabilizer can also be selected from the group of substances consisting of microparticles; this group includes both organic and inorganic anionic substances. Suitable materials of this type include highly crosslinked anionic vinyl polymers, for example, acrylamide and acrylate-based polymers, polymers obtained by condensation of anion-containing compounds, for example, melamine-sulfonic acid resin sols, inorganic substances based on silicon dioxide, for example, substances similar to those present in aqueous sols based on silicon dioxide, such as silicic acid sols, silicic acid sols with the addition of aluminum compounds, aluminosilicate sols, polysilicate microgels and polyaluminosilicate microgels as well as silicic acid gels and precipitated silica. Preferably, the microparticle materials are a colloid, i.e. particle size would be in the range characteristic of colloids. It is acceptable if such colloidal particles have a size of from about 1 nm to about 80 nm, preferably from 2 to 35 nm, and most preferably from 2 to 10 nm.

 The molecular weight of the anionic compound can vary over a wide range: from several hundred or thousands to several millions. Typically, the molecular weight is more than 200, most preferably above 500, while the upper limit is usually 10 million and preferably 2 million. In a preferred embodiment, the molecular weight reaches about 50,000.

 The amount of cationic and anionic compounds present in the dispersion of this invention can vary over a wide range of values, depending, inter alia, on the type of cationic and anionic compounds and their charge density, type of sizing agent, desired anionicity / cationicity and solid content in the final variance. Acceptable within the scope of this invention can be considered anionic dispersion, which means that the anionic charge of the anionic stabilizer is greater than the cationic charge of the cationic compound. The cationic compound may be present in the dispersion in an amount of up to 100% by weight, usually from 0.1 to 20% by weight, acceptable if from 1 to 10% by weight and preferably from 2 to 7% by weight, based on the sizing agent ; the anionic stabilizer may be present in an amount up to 100% by weight, usually from 0.1 to 20% by weight, acceptable if from 0.2 to 10% by weight and preferably from 0.3 to 6% by weight, based on a sizing agent, wherein the total charge of the cationic compound and the anionic stabilizer present in the dispersions is preferably anionic or negative.

 It was found that according to this invention it is possible to obtain dispersions having a high solids content, nevertheless having very good storage stability and low viscosity. Thus, this invention allows to obtain dispersion for impregnation, with increased storage stability, higher solids content and / or lower viscosity. Also, additional advantages of the proposed dispersions are that they are stable when diluted, which means less adhesion of particles or droplets of a sizing agent, resulting in smaller amounts of larger aggregates having a lower sizing ability, less deposition of a hydrophobic sizing agent on a paper machine and less sieve contamination resulting in reduced maintenance requirements for the paper machine. The proposed dispersions can mainly contain from about 0.1 to about 50% of a sizing agent and, more preferably, more than 20% by weight. Dispersions containing a ketene dimer as a sizing agent may contain it in an amount of from 5 to 50% by weight and preferably from about 10 to about 35% by weight. Dispersions or emulsions containing acid anhydride as the impregnating agent may contain it in an amount of from 0.1 to about 30% by weight and usually from 1 to about 20% by weight.

Sizing dispersions for, in accordance with the invention, can be obtained by mixing the aqueous phase with an anionic stabilizer, a cationic compound and a sizing agent, preferably at a temperature such that the sizing agent is a liquid, and then homogenizing the mixture thus obtained, preferably under pressure. Acceptable temperatures, if the sizing agent is a ketene dimer, are from about 55 ^° C to 95 ^° C, while temperatures for acid anhydrides may be lower. The resulting emulsion, which contains droplets of a sizing agent, usually having a size of 0.1 to 3.5 μm in diameter, is then cooled. In addition to the above components, other substances can also be added to the sizing dispersion, such as, for example, anionic and nonionic dispersants and stabilizers, fillers, for example, urea and its derivatives, and anticoagulants. It should be borne in mind that the negative and positive charges of compounds that are components of the dispersant composition can be formed in situ, for example, during the interaction of one of these compounds with another and / or as a result of mixing these compounds with the aqueous phase and / or lowering the pH water phase. For example, detachment of hydrogen from an acid group will lead to the formation of an anionic charge, and the main amine or amino group can become cationic by protonation or removal of hydrogen from the acid. Therefore, it is possible to start producing a dispersion having compounds that do not carry a charge, for example, an organic compound with basic amino groups or a basic amine of the formula R ₃ N can be used, and the corresponding ammonium derivative R ₄ N ⁺ X ^- can be formed during the process of producing the dispersion (values R, N and X are defined above).

 It was also found that the components of the proposed dispersions can easily be homogenized in the presence of an aqueous phase. Typically, less energy and less shear is required for homogenization compared to conventional dispersion processes, and thus simpler equipment can be used. Therefore, another method for preparing the present dispersions involves (i) mixing the cellulose-reactive sizing agents with a dispersant composition comprising an anionic stabilizer and a cationic compound as defined above to obtain an intermediate composition, and (ii) homogenizing the intermediate mixture in the presence of aqueous phase as described above. Preferably, the components are mixed in step (i). The sizing agent used in step (i) may be solid, although it is preferred that it be in a liquid state in order to facilitate mixing until homogenization. If desired, the intermediate composition can be removed after the mixing step (i) and, optionally, can be cooled to harden to form a practically anhydrous intermediate sizing composition, which makes transportation easier from an economic point of view. At the place of direct use, or in any other way, the sizing composition can be homogenized in the presence of water in the usual way. This method is especially convenient when preparing dispersions of ketene dimers and acid anhydrides, the latter of which is usually prepared in a paper mill just before use as a sizing agent in the paper manufacturing process. The storage stability property of the anhydrous sizing composition is economically and technically advantageous. The present invention thus relates to a substantially anhydrous sizing mixture comprising a cellulose-reactive sizing agent, a cationic organic compound and an anionic stabilizer, where the cationic and anionic compounds, when used together, are effective as a dispersing composition for the sizing agent in the aqueous phase, its preparation and use, as further defined in the claims.

 Preferably, such components as defined above are present in the composition of the present invention, i.e., a sizing agent, a cationic compound and an anionic stabilizer chemically active with respect to cellulose. The proposed composition is practically free of water, which means that small amounts of water may be present; the water content may be from 0 to 10% by weight, acceptable if less than 5% by weight and preferably less than 2%. Most preferably, if the composition is completely free of water. The composition preferably contains a sizing agent reactive with respect to cellulose in a predominant amount, based on weight, i.e. at least 50% by weight, acceptable if the content of the sizing agent in the mixture is in the range from 80 to 99.8% by weight, and preferably from 90 to 99.7% by weight. A cationic compound, preferably having surface-active properties, and an anionic stabilizer may be present in the impregnation composition in amounts as defined above for the dispersions, where percent concentrations are based on the weight of the sizing agent. Anionic stabilizer may be present in the mixture in an amount up to 100% by weight, usually from 0.1 to 20% by weight, acceptable if from 0.2 to 10% by weight and preferably from 0.3 to 6% by weight, calculated per sizing agent, and a cationic compound, for example, a surfactant, may be present in an amount up to 100% by weight, usually from 0.1 to 20% by weight, acceptable if from 1 to 10% by weight and preferably from 2 up to 7% by weight, based on the sizing agent, and the total charge of the cationic compound and the anionic stabilizer, which are present in Songs preferably is negative or anionic.

 The dispersions in accordance with the invention can be used in the usual way in the manufacture of paper when working with cellulose fibers of any type and they can be used both for surface treatment and for processing in bulk. The term "paper" here means not only paper as such, but also all types of products, which are based on cellulose, in the form of sheets or rolls, including, for example, cardboard and paper cardboard. The processed raw materials contain cellulosic fibers, if desired in combination with mineral fillers, and usually the content of cellulosic fibers is at least 50% by weight based on dry raw materials. Examples of conventional mineral fillers include kaolin, porcelain clay, titanium dioxide, gypsum, talc and natural or synthetic calcium carbonates such as chalk (loose limestone), marble and precipitated calcium carbonate. The presented invention also relates to a paper production method in which an aqueous dispersion, such as described above, is used as a substance for surface treatment or processing in bulk. The amount of sizing agent reactive with cellulose, usually either added to the pulp containing cellulosic fibers and possible fillers, which is then separated from the water on a sieve to form paper, or applied to the surface of the paper as a surface treatment agent, usually using size the press is from 0.01 to 1.0% by weight, based on the weight of dry cellulose fibers and possible fillers, preferably from 0.05 to 0.5% by weight, and the dosage depends mainly on th from weaving sizing paper or paper pulp of chemically active relative to cellulose-reactive sizing agent and the desired degree of sizing.

 The dispersions of this invention, in particular anionic dispersions, are especially suitable for sizing in bulk if the pulp has a high absorption capacity of cations and / or contains significant amounts of lipophilic substances, for example, pulps obtained from pulp containing wood pulp or recirculating pulp, for example when intensive recycling of white water is performed. Examples of lipophilic substances commonly found in paper pulp include anionic and non-ionic lipophilic substances, such as, for example, resin acids, fatty acids, fatty esters, triglycerides, etc. The amount of lipophilic substances may be at least 10 ppm (m etc.) and up to about 100 ppm, usually at least 20 ppm, acceptable if not less than 30 and preferably not less than 50 ppm, measured in dichloromethane (DCM) by extraction of DCM in a known manner. The ability to absorb cations should be at least 50, acceptable if not less than 100 and preferably 150 mEq / l, calculated on a liter of liquid filtered through a layer of pulp. The cation absorption capacity can be measured in the usual way, for example, using the Mutek Particle Charge Detector using a filtrate passing through a pulp layer obtained from a crude filtrate, additionally filtered through a filter with a pore size of 1.6 μm and poly (diallyldimethylammonium chloride) in as a titrant. Also, the proposed dispersions are preferably used in those paper production processes in which water is intensively recycled, i.e. when white water is almost completely used in a closed cycle, for example, from 0 to 30 tons of fresh water is used to produce one ton of dry paper, usually less than 20, acceptable if less than 15, preferably less than 10 and particularly preferably less than 5 tons of fresh water per ton paper. The return of white water to the process preferably occurs at the stage of mixing white water with cellulose fibers, which are preferably in the form of pulp or suspension, before or after the addition of a sizing dispersion, produced, for example, to form a suspension of fibers in water, which will then be separated. Fresh water can be introduced into the process at any stage; for example, it can be mixed with cellulosic fibers in order to form paper pulp, and it can be mixed with pulp containing cellulosic fibers to dilute and form a slurry, which will then be dehydrated on a sieve, before or after mixing the pulp with white water and before or after adding a sizing dispersion.

 Chemicals commonly added in the manufacture of paper to paper pulp, such as auxiliary binders, derivative compounds of aluminum, dyes, resins that increase the strength of paper in the wet state, optical brighteners, etc., of course, can be used in conjunction with the proposed dispersions. Examples of aluminum derivative compounds include alum, aluminates, and compounds containing several aluminum atoms, for example polyaluminium chlorides and sulfates. Examples of suitable auxiliary retention agents include cationic polymers, anionic inorganic substances in combination with organic polymers, for example, bentonite in combination with cationic polymers, based on silica in combination with cationic polymers, or cationic and anionic polymers. Particularly good mass sizing results can be achieved by using the dispersions of this invention in combination with auxiliary retention agents including cationic polymers. Suitable cationic polymers include cationic starch, guar gum, acrylate and acrylamide polymers, polyethyleneimine, dicyandiamide formaldehyde resins, polyamines, polyamidamines and poly (diallyldimethylammonium chloride), and combinations thereof. Preferably, cationic starch and cationic acrylamide-based polymers are used, both individually and in combination with each other or with other substances. In a preferred embodiment of the invention, the dispersions are used in combination with a retention composition comprising at least one cationic polymer and anionic particles based on silicon dioxide. The proposed dispersions can be added before, between, after or simultaneously with the introduction of a cationic polymer or polymers. It is also possible to pre-mix the sizing dispersion with auxiliary holding agents, for example, a cationic polymer such as cationic starch or a cationic polymer based on acrylamide, or a substance based on silicon dioxide, before the mixture thus obtained is introduced into the pulp to be processed. Accordingly, the dispersion can be obtained immediately before it is introduced into the pulp to be processed, by contacting a sizing dispersion containing a cationic compound, preferably a cationic surfactant and an anionic substance based on silicon dioxide, for example, as defined above .

 The invention is further illustrated by the following examples, which however do not exhaust its scope and are not intended to limit it. Fractions and% mean fractions by weight and% by weight, respectively, unless otherwise indicated.

Example 1
Anionic alkyl ketene dimer dispersions (DACs) according to the invention were prepared by mixing di (hydrogenated fat) dimethylammonium chloride, which is a cationic surfactant sold for sale by Akzo Nobel under the trade name Querton 442, with molten DAC at 70 ^° C. homogenizing the mixture using a homogenizer in the presence of an aqueous solution of an anionic stabilizer and then cooling the resulting dispersion. The pH of the dispersion was adjusted to about 5 by adding acid. The anionic stabilizer used in this example was carboxymethyl cellulose modified to form a substituted amide (MCMC) and containing a hydrophobic substituent derived from N- (hydrogenated fat) -1,3-diaminopropane obtained as described in WO 94/24169. MCMC had a degree of substitution in the carboxyl group of 0.6 and a degree of substitution of hydrophobic groups of 0.1. The dispersions contained DAC particles with an average particle size of about 1 μm, which were negatively charged, as shown by the negative zeta potential measured using ZetaMaster S Version PCS. The content of DAK in the dispersion was 30%. Dispersion No. 1 contained 3% cationic surfactant and 1% anionic stabilizer; percentages for both substances are calculated on the weight of DAK. Dispersion N 2 contained 7% cationic surfactant and 1% anionic stabilizer; percentages for both substances are calculated on the weight of DAK.

Example 2
The same procedure was repeated as in Example 1, but condensed sodium naphthalenesulfonate sold under the trade name Orotan ^TM SN for sale by Rohm & Haas Company was used as an anionic stabilizer, and the ratios between the dispersion components in this example were different. The dispersion N 3 obtained in this example contained 30% DAK, 6% anionic stabilizer and 4% cationic surfactant (the concentrations of the last two substances are indicated based on the weight of the DAK). The dispersion contained DAK in the form of particles with an average size of about 1 μm, which had a negative charge, which was determined as described above.

Example 3
The stability of the anionic dispersions obtained in examples 1 and 2 was verified in this way: the dispersion was diluted with water to a concentration of DAC of 40 ppm. In some tests, 10 ppm was added. stearic acid in order to increase the content of lipophilic substances and the ability to absorb cations. The diluted dispersion was placed in a vessel equipped with a device for measuring the turbidity of the medium, a circulation circuit, devices for circulation, heating and cooling. The studied volume of the diluted dispersion was circulated in a closed circulation circuit, at the same time, the turbidity of the medium was automatically recorded, and the dispersion was subjected to heating and cooling; the entire temperature cycle lasted 45 minutes. The temperature of the dispersion increased from 20 ^o C to 62 ^o C and then decreased again to 20 ^o C. The turbidity of the medium depends on the particle size, and the difference in turbidity of the dispersion before and after the cycle of temperature change is a measure of the ability of dispersed particles to resist growth by agglomeration and, thus is a measure of the dispersion stability. The change in the turbidity of the medium (ΔT) was calculated as follows: ΔT = (turbidity of the medium at the end / turbidity of the medium at the beginning) • 100. The higher ΔT, the higher the stability of the dispersion.

 Also, for comparison purposes, two standard dispersions were tested. Reference 1 was an anionic dispersion of DAA containing a dispersant composition comprising sodium lignosulfonate present in the ionic excess and cationic starch. Reference 2 was a cationic dispersion of DAK, also containing sodium lignosulfonate and cationic starch, but in this case, cationic starch was present in the ionic excess. Table 1 summarizes the results.

 As can be seen from table 1, the ΔT values for the dispersions of this invention were significantly higher than for standard dispersions, which indicates a higher stability during dilution.

Example 4
In this example, the sizing efficiency of the sizing dispersions obtained in accordance with Example 3 was determined. Sheets of paper were made according to the standard SCAN-C23X method for laboratory scale. The pulp used to make the paper contained 80% bleached pulp having a birch / pine ratio = 60:40 and 20% chalk, to which 0.3 g / l Na ₂ SO ₄ • 10H ₂ O was also added. Paper pulp had a density of 0.5 and a pH of 8.0. The sizing dispersion was used in conjunction with the Compozil ^™ industrial auxiliary composition to help remove water, including cationic starch and anionic silica modified with aluminum compounds, which were individually added to the paper pulp; cationic starch was added in an amount of 8 kg / t, calculated on the dry matter of the pulp, and a silica sol was added in an amount of 0.8 kg / t, calculated on the SiO ₂ and dry matter of the pulp.

 The values of the Cobb index, measured in accordance with the TAPPI T 441 OS-63 standard and obtained as a result of the tests, are shown in Table 2. The amount of DAC was calculated on the dry weight of the paper pulp.

 From the data of tables 2 it can be concluded about a higher sizing efficiency when using dispersions in accordance with this invention.

Example 5
The sizing ability was tested according to the same scheme as in example 4, except that the paper pulp did not contain chalk as a filler, but the precipitated calcium carbonate and the dosage of cationic starch was 12 kg / t, calculated on the dry matter of the mass. In some tests, 10 ppm was added to the pulp. stearic acid in order to increase the ability to absorb cations and increase the content of lipophilic substances. The test results are shown in table 3.

 As can be seen from table 3, the dispersion N 1 obtained in accordance with this invention, in most cases, gives a much better sizing than the dispersion Etalon 1, used for comparison; a significantly greater degree of sizing is also achieved when using paper pulp containing significant amounts of lipophilic compounds.

Example 6
An anhydrous sizing composition according to the invention was obtained by dry mixing 93 parts of granular DAK, 3 parts of cationic surfactant, the same as in example 1, and 4 parts of anionic stabilizer, the same as in example 2. The resulting dry mixture is then was added to hot water and the aqueous mixture thus obtained was heated to 80 ^° C, pumped using a pump creating a large shear force, and then cooled to room temperature. The resulting anionic dispersion. Dispersion No. 4 contained 20% DAA with an average particle size of about 1 μm. The sizing ability was tested in the same way as in example 4, but the amount of cationic starch was 12 kg / t, calculated on the dry weight of the paper pulp. The test results are shown in table 4.

 From table 4 it is seen that the dispersion for sizing obtained in accordance with the present invention, provides a higher quality sizing.

Example 7
In this series of tests, a dispersion of DAK, obtained in accordance with the invention and consisting of a dispersing composition comprising a cationic surfactant and an anionic stabilizer, which is an inorganic substance and consisting of microparticles, was tested.

The dispersion was obtained by pre-mixing at 75 ^° C. 0.2 g of cocoamine sold under the trade name Armeen C ^TM , which is a mixture of amines of the formula RNH ₂ , where R represents a hydrocarbon residue of C ₁₂ -C ₁₈ , and 1.0 g calculated as SiO ₂ , an aqueous silica sol modified with aluminum additives, of the type described in US Pat. No. 5,368,833, and then adding 25 g of DAC and an acid to pH 4.0. The aqueous mixture was homogenized with Ultra Turrax and then cooled. The resulting dispersion, Dispersion No. 5, contained a DAC of 25% by weight and an anionic dispersion composition.

 The sizing efficiency using this dispersion was evaluated using the same procedure as in Example 4, using a similar pulp at pH 8.1 and using the standard dispersion of DAK Etalon 2 for comparison. The test results are shown in Table 5, where the dosage of DAK is indicated in based on the weight of dry paper pulp.

Example 8
A DAC dispersion obtained in accordance with the invention was obtained and tested in the same manner as in Example 7, except that the anionic stabilizer used in this example was a melamine-sulfonic acid sol obtained in accordance with Int. Pat. Appl. Publ. N WO 96/34027. Dispersion No. 6 was obtained from 0.4 g of cocoamine, 2 g of melamine-sulfonic acid, 30 g of DAK and water in such an amount that the mass of the mixture was 100 g. The results of testing this dispersion are shown in table 6, in which the dosage of DAK is indicated in based on the dry weight of the pulp.

Example 9
The ease of obtaining dispersions in accordance with the invention was evaluated by preparing anionic dispersions of DAK containing different amounts of DAK. The dispersions of this invention were obtained by homogenizing a mixture of 0.8% by weight of di (hydrogenated fat) dimethylammonium chloride, 1.6% by weight of condensed sodium naphthalenesulfonate, 77.6% by weight of water and 20% by weight of DAK for a certain time, using Ultra Turrax mixer at 15,000 rpm and then the dispersion thus obtained was cooled for 2 hours. Similar dispersions were prepared in the same way, but with different contents of DAK: 10, 20, 30 and 40% by weight. Dispersions are indicated by the word "Invention", the following number then indicates the content of DAC in% by weight.

 Standard DAC dispersions were obtained for comparison in the same way and under the same conditions by homogenizing a mixture of 1.0% by weight of cationic starch, 0.25% by weight of sodium lignosulfonate, 89% by weight of water and 10% by weight of DAK. Thus, similar dispersions were obtained containing different amounts of DAK; standard dispersions contained 10, 20, 30 and 40% DAK by weight. These dispersions are designated "Reference 3", and the following number then indicates the content of DAC in% by weight.

 Particle size and viscosity were determined in the usual way. Table 7 summarizes the results.

 From table 3 it is seen that the dispersion according to this invention are easier; they have a lower viscosity with the same content of DAK and with the same energy consumption for dispersion have smaller particle sizes, which causes the formation of fewer deposits on the surfaces of the paper machine. Compared to reference dispersions, less energy and less shear are required to obtain dispersions with the same particle size. In addition, increasing the speed of the mixer to 25,000 rpm significantly reduces the particle size of the dispersions in accordance with the invention to values in the range from 1 to 2 μm.

Claims (23)

 1. An aqueous dispersion of a sizing agent containing a cellulose-reactive sizing agent and a dispersing composition, characterized in that the dispersing composition contains a low molecular weight cationic organic compound having a molecular weight of less than 10,000 and an anionic stabilizer, which is an anionic polyelectrolyte.  2. The aqueous dispersion according to claim 1, characterized in that the cationic organic compound is present in an amount of 0.1 to 20% by weight, based on a sizing agent, and the anionic stabilizer is present in an amount of 0.1 to 20% by weight, based on a sizing agent.  3. The aqueous dispersion according to claim 1 or 2, characterized in that the cationic organic compound is a cationic surfactant.  4. The aqueous dispersion according to claim 3, characterized in that the cationic surfactant has a molecular weight of 200 to 800.  5. The aqueous dispersion according to claim 3 or 4, characterized in that the cationic surfactant is selected from primary, secondary, tertiary and quaternary ammonium compounds containing at least one hydrocarbon group having from 9 to 30 carbon atoms.  6. The aqueous dispersion according to claims 3, 4 or 5, characterized in that the cationic surfactant is selected from dioctyl dimethyl ammonium chloride, didecyldimethyl ammonium chloride, dicocodimethyl ammonium chloride, cocobenzyl dimethyl ammonium chloride, coco (fractionated) benzyl dimethyl ammonium dimethyl ammonium chloride dimethyl ammonium chloride dihexadecyl dimethylammonium chloride, di (hydrogenated fat) dimethylammonium chloride, di (hydrogenated fat) benzylmethylammonium chloride, (hydrogenated fat) ben zyldimethylammonium chloride, dioleldimethylammonium chloride, di (ethylene hexadecanecarboxylate) dimethylammonium chloride and N-octadecyl-N-dimethyl-N'-trimethyl-propylene-diammonium dichloride.  7. The aqueous dispersion according to claim 1 or 2, characterized in that the cationic organic compound is a cationic polyelectrolyte.  8. Aqueous dispersion according to any one of the preceding paragraphs, characterized in that the anionic stabilizer is an organic compound.  9. The aqueous dispersion according to any one of claims 1 to 7, characterized in that the anionic stabilizer is an inorganic substance, which is based on silicon dioxide.  10. The aqueous dispersion according to claims 1, 2 or 8, characterized in that the anionic stabilizer is selected from anionic polyurethanes, condensed naphthalenesulfonates, polymer anionic compounds based on polysaccharides, vinyl polymers formed from monomers with anionic groups, optionally copolymerized with nonionic monomers, and anionic organic matter consisting of microparticles.  11. The aqueous dispersion according to any one of the preceding paragraphs, characterized in that the dispersion is anionic.  12. Aqueous dispersion according to any one of the preceding paragraphs, characterized in that the sizing agent is a ketene dimer or acid anhydride.  13. The aqueous dispersion according to one of claims 1 to 12, characterized in that it is used as a sizing agent for processing in bulk or as a sizing agent for surface treatment in the paper manufacturing process. 14. The aqueous dispersion according to claim 1, characterized in that the cationic organic compound is a cationic organic surfactant having the general formula R ₄ N ⁺ X ^- , in which each R group is selected from (i) hydrogen, (ii) hydrocarbon groups having from 1 to about 30 carbon atoms, and (iii) hydrocarbon groups having up to about 30 carbon atoms interrupted by one or more heteroatoms and / or groups containing a heteroatom; where X ^- represents an anion or anionic group present in the anionic compound of the dispersant, while at least one of these R groups contains at least 7 carbon atoms.  15. The aqueous dispersion according to 14, characterized in that at least one of these R groups contains at least 9 carbon atoms.  16. A method of obtaining an aqueous dispersion of a sizing agent chemically active in relation to cellulose, which is homogenized in the presence of an aqueous phase and a dispersing composition, characterized in that the dispersing composition contains a low molecular weight cationic organic compound having a molecular weight of less than 10000 and an anionic stabilizer, which is an anionic polyelectrolyte .  17. The method according to clause 16, wherein the cationic organic compound is formed from an organic non-ionized polymer with basic amino groups or from a basic amine, in which the corresponding cationic ammonium derivative is formed during the implementation of this method.  18. The method according to clause 16, characterized in that it includes obtaining a practically anhydrous composition containing a sizing agent chemically active with respect to cellulose, a cationic organic compound and an anionic stabilizer, and homogenizing the composition in the presence of an aqueous phase.  19. A method of producing paper by adding an aqueous dispersion of a sizing agent to a processed raw material containing cellulosic fibers and optionally fillers, separating water from the processed raw material on a sieve to produce paper and white water, characterized in that the dispersion is an aqueous dispersion according to any one of claims 1 - fifteen.  20. The method according to p. 19, characterized in that the white water is recycled in the process and optionally add fresh water to form a pulp containing cellulose fibers, followed by separation of the water, and fresh water is introduced in an amount of less than 30 tons per 1 ton of paper produced .  21. Almost anhydrous composition containing a cellulose-reactive sizing agent and a cationic organic compound, characterized in that the cationic organic compound has a molecular weight of less than 10,000, in addition. the composition contains an anionic stabilizer, which is an anionic polyelectrolyte.  22. The composition according to item 21, wherein the cationic organic compound is present in an amount of 0.1 to 20% by weight and the anionic stabilizer is present in an amount of 0.1 to 20% by weight, both based on the chemically active in relation to cellulose is a sizing agent in which the total charge of the cationic compound and the anionic stabilizer is negative.  23. The composition according to p. 21 or 22, characterized in that it is used to obtain an aqueous dispersion of a sizing agent chemically active in relation to cellulose according to any one of claims 1 to 15.

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