RU2168579C2 - Aqueous dispersions of hydrophobic material - Google Patents

Abstract

FIELD: paper-and-pulp industry. SUBSTANCE: aqueous dispersion contains disperser and dispersed phase with hydrophobic sizing compound. Disperser is constituted by anionic carbon-containing or silicon-containing compound with molecular weight below 50000, and cationic organic compound with molecular weight below 50000. Dispersion is intended for sizing cellulose fibers. EFFECT: improved stability and increased viscosity of dispersion. 18 cl, 3 tbl, 4 ex

Description

 The present invention relates to aqueous dispersions of a hydrophobic material, and more particularly, to dispersions having a dispersant system containing two oppositely charged compounds, their preparation and use.

BACKGROUND OF THE INVENTION
Aqueous dispersions of hydrophobic material are well known and are used in numerous applications. For example, in the manufacture of paper, aqueous dispersions of a hydrophobic material are used as a sizing agent in order to give paper and paperboard some degree of resistance to wetting and penetration of aqueous liquids. Examples of hydrophobic materials that are widely used as sizing agents include cellulose-reactive sizing agents, e.g. alkyl ketene dimers and substituted succinic anhydrides, and cellulose-free sizing agents, such as rosin and resin based sizing agents.

 Dispersions of a hydrophobic material typically comprise an aqueous phase and finely divided particles or drops of hydrophobic material distributed therein. Dispersions are usually prepared by homogenizing a hydrophobic, water-insoluble material in the aqueous phase in the presence of a dispersant using high shear forces and fairly high temperatures. Traditionally used dispersants include anionic, amphoteric and cationic polymers with high molecular weights, for example lignosulfonates, starches, polyamines, polyamidamines and polymers with the addition of vinyl groups. The polymers can be used singly, together or in combination with other compounds in order to form a dispersant system. Depending on the total charge of the components of the dispersant system, the sizing dispersions will be anionic or cationic in nature.

 Dispersions of a hydrophobic material usually show rather poor stability and high viscosity, even with a relatively low solids content, which obviously leads to difficulties in handling dispersions, for example during storage or use. A further disadvantage is that the products must be supplied in the form of dispersions with a low concentration, which further increases the cost of transporting the active hydrophobic material.

 Accordingly, an object of the present invention is to provide aqueous dispersions of a hydrophobic material with improved stability and viscosity properties. Another objective of this invention is the provision of improved aqueous dispersions of a sizing agent, especially sizing agents, reactive with respect to cellulose. Further goals will be outlined below.

Description of the invention
In accordance with the present invention, it has been found that improved stability and viscosity properties can be obtained from aqueous dispersions of a hydrophobic material in which a hydrophobic material is dispersed in the aqueous phase using a dispersant comprising two oppositely charged compounds having relatively low molecular weights. More specifically, the present invention relates to an aqueous dispersion containing a dispersed phase comprising a hydrophobic material and a dispersant comprising an anionic compound having a molecular weight of less than 50,000 and selected from organic compounds and silicon-containing compounds, and a cationic organic compound having a molecular weight less than 50,000. The present invention, therefore, relates to an aqueous dispersion, its preparation and use, as defined further in the claims.

 The present invention makes it possible to provide dispersions of a hydrophobic material with improved storage stability, a higher solids content and / or lower viscosity. In addition, when using dispersions in cases involving very strong dilution of the dispersion with an initially high concentration, it was found that the dispersed phase is more stable, i.e. dispersions show improved dilution stability. Examples of applications with extremely high dilution include final stage wetting conditions for papermaking and storage, or internal sizing, which include adding a dispersion of hydrophobic material to an aqueous suspension containing cellulose fibers and optionally a filler. In this context, improved dilution stability means less aggregation of particles or drops of hydrophobic sizing agent, whereby lower levels of larger aggregates with lower sizing efficiency are formed, as well as less deposition of hydrophobic sizing agent on the paper machine and less wire contamination by which reduces the need for paper machine maintenance. Further benefits associated with this dispersion include improved stability in the presence of interfering substances, for example anionic impurities obtained from impurities of pulp and / or fibers returned for recycling, and less accumulation of hydrophobic material in white water recycled in the paper manufacturing process. Accordingly, the dispersions of the present invention are particularly useful in processes where white water is extensively recycled and where the cellulose suspension contains a significant amount of impurity. Moreover, the dispersions of this invention also make it possible to obtain improved sizing compared to conventional size dispersions with an appropriate dosage of sizing agent and to use lower dosages of the sizing agent to achieve an appropriate sizing level. The ability to use smaller amounts of sizing agent to achieve a sizing that meets the specifications further reduces the risk of accumulation of non-adsorbable hydrophobic sizing agents in the white water recycled in the process, thereby further reducing the risk of aggregation and deposition of hydrophobic material on a paper machine. The present invention thus offers significant economic and technical advantages.

The hydrophobic material present in the dispersion is preferably substantially insoluble in water. Examples of suitable hydrophobic materials include compounds useful as sizing agents in the manufacture of paper, which can be obtained from natural and synthetic sources, for example hydrophobic substances that are reactive with cellulose, and hydrophobic materials that are not reactive with cellulose. In a preferred embodiment, the hydrophobic material has a melting point below about 100 ^° C and especially below about 75 ^° C.

In a preferred embodiment of the present invention, the hydrophobic material is cellulose-reactive sizing agents that can be selected from any known cellulose-reactive sizing agent. Suitable sizing agents are selected from the group consisting of hydrophobic ketene dimers, ketene multimers, acid anhydrides, organic isocyanates, carbamoyl chlorides and mixtures thereof, preferably ketene dimers and acid anhydrides, most preferably from ketene dimers. Suitable ketene dimers have the general formula (I) shown below, where R ¹ and R ² are saturated or unsaturated hydrocarbon groups, usually saturated hydrocarbons, hydrocarbon groups having from 8 to 36 carbon atoms, usually straight or branched alkyl groups a chain having from 12 to 20 carbon atoms, such as, for example, hexadecyl or octadecyl groups. Suitable acid anhydrides can be described by the general formula (II) shown below, where R ³ and R ⁴ may be identical or different and represent saturated or unsaturated hydrocarbon groups, respectively containing from 8 to 30 carbon atoms, or R ³ and R ⁴ together with the —COC group, they can form from 5 to 6 membered rings, optionally being additionally substituted hydrocarbon groups containing up to 30 carbon atoms. Examples of acid anhydrides that are used on an industrial scale include alkyl and alkenyl succinic anhydrides and, in particular, isooctadecanoic succinic anhydride.

Подходящие димеры кетена, ангидриды кислот и органические изоцианаты включают соединения, описанные в патенте США N 4522686, который включен в описание в качестве ссылки. Примеры подходящих хлоридов карбамоила включают соединения, описанные в патенте США N 3887427, который также включен в качестве ссылки.

Suitable ketene dimers, acid anhydrides, and organic isocyanates include the compounds described in US Pat. No. 4,522,686, which is incorporated herein by reference. Examples of suitable carbamoyl chlorides include the compounds described in US Pat. No. 3,887,427, which is also incorporated by reference.

 In another preferred embodiment of the present invention, the hydrophobic material is a hydrophobic substance that is not reactive with respect to cellulose, which can be selected from any known sizing agent that is not reactive with respect to cellulose. Accordingly, a sizing agent that is not reactive with cellulose is selected from the group consisting of hydrophobic substances based on rosin, for example rosin, disproportionate rosin, hydrogenated rosin, polymerized rosin, formaldehyde-treated rosin, esterified rosin, enriched rosin and mixture and rosins, fatty acids and derivatives thereof thus treated, for example esters of fatty acids and amides, like bis-stearic amide, resins and e derivatives, for example hydrocarbon resins, acidic resins, resin acid esters and amides, waxes, e.g. crude and refined paraffin, synthetic waxes, naturally occurring waxes, etc.

 The dispersions of the present invention comprise a dispersant or dispersant system comprising at least one anionic compound and at least one cationic compound, both of which have a low molecular weight (hereinafter HMB). NMB compounds are preferably bonded to each other by electrostatic attraction, forming a coacervate dispersant. When used in combination, HMB compounds are effective as a dispersant of a hydrophobic material, although anionic and cationic compounds are not required to be, and usually are not, effective as a dispersant when used alone. In a preferred embodiment, at least one of the anionic and cationic compounds is a polyelectrolyte. The term "polyelectrolyte", as used here, refers to a compound having two or more charged (anionic / cationic) groups and charged (anionic / cationic) compounds acting as a polyelectrolyte, for example by chemical non-ionic interaction or attraction.

The anionic dispersant compound 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, which are referred to herein as anionic polyelectrolytes. Anionic polyelectrolytes may contain one or more cationic groups, provided that they have a common negative charge. Examples of suitable anionic groups include sulfate groups and carbonyl, sulfonic, phosphoric and phosphonic acid groups which may be present as free acids or water-soluble salts of ammonium or an alkali metal (typically sodium), for example sodium carboxylates and sulfonates. Anionic polyelectrolytes can have a degree of substitution that varies over a wide range; the degree of anionic substitution (DS _A ) may be from 0.01 to 1.4, suitably from 0.1 to 1.2, and preferably from 0.2 to 1.0.

 The anionic dispersant compound can be obtained from synthetic and natural sources and is preferably soluble in water or capable of forming a dispersion in water. In a preferred embodiment, the anionic compound is an organic compound, i.e. containing carbon atoms. Suitable anionic compounds include anionic surfactants like alkyl, aryl and alkylaryl sulfates and ethersulfates, alkyl, aryl and alkylaryl carboxylates, alkyl, aryl and alkylaryl sulfonates, alkyl, aryl and alkylaryl phosphates and etherphosphates and dialkyl sulfosuccinates having from 1 to 18 alkyl groups carbon atoms, aryl groups having from 6 to 12 carbon atoms and alkylaryl groups having from 7 to 30 carbon atoms. Examples of suitable anionic surfactants include sodium lauryl sulfate, sodium lauryl sulfonate and sodium dodecylbenzenesulfonate. Further examples of suitable anionic compounds include anionic polyelectrolytes, such as, for example, anionic organic HMB polymers, optionally cleaved, for example, compounds derived from phosphoric acid, sulfonated and carboxylated polysaccharides, such as starches, guar gum and cellulose, preferably from cellulose derivatives and especially carboxymethylated cellulose, as well as condensation products, for example anionic polyurethanes and condensed naphthalenesulfonates, and further vinyl-linked oligomers formed from anionic monomers, for example acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid, vinyl sulfonic acid, sulfonated styrene and phosphates of hydroxyalkyl acrylates and methacrylates, optionally copolymerized with non-ionic acrylamides, , styrene and acrylonitrile, as well as derivatives of such monomers, vinyl esters and the like. The anionic compound can also be selected from HMB inorganic compounds containing silicon atoms, such as, for example, silicates and various forms of condensed or polymerized silicic acids, for example oligomeric silicic acid, polysilicic acids, polysilicates, polyaluminosilicates, microgels of polysilicates, microgels of polyaluminosilicosilicates silicon-based, for example, in the form of a silica sol, which has negatively charged hydroxyl groups.

The cationic dispersant 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, which here refers to cationic polyelectrolytes. Cationic polyelectrolytes may contain one or more anionic groups, provided that it has a common positive charge. Examples of suitable cationic groups include sulfonium groups, phosphonium groups, acid addition salts to primary, secondary and tertiary amines or amino groups and quaternary ammonium groups, for example, where nitrogen is quaternized with methyl chloride, dimethyl sulfate or benzyl chloride, preferably acid addition salts to amines / amine amino groups and to groups. Cationic polyelectrolytes can have a degree of substitution that varies over a wide range; the degree of cationic substitution (DS _C ) may be from 0.01 to 1.0, suitably from 0.1 to 0.8, and preferably from 0.2 to 0.6.

The cationic dispersant compound can be obtained from synthetic and natural sources and is preferably water soluble or capable of forming a dispersion in water. The cationic compound is preferably an organic compound. Examples of suitable cationic compounds include cationic surfactants, for example, compounds of the type R ₄ N ⁺ X ^- , wherein each R group is independently selected from (i) hydrogen; (ii) hydrocarbon groups, suitably aliphatic and preferably alkyl groups having from 1 to about 30 carbon atoms, preferably from 1 to 22 carbon atoms; and (iii) hydrocarbon groups, suitably aliphatic and preferably alkyl groups having up to about 30 carbon atoms, preferably from 4 to 22 carbon atoms, and being broken by one or more heteroatoms, for example oxygen or nitrogen, and / or groups containing a heteroatom, for example, carbonyl or acyloxy groups; where at least one, suitably at least three, and preferably all of the above R groups contain carbon atoms; suitably at least one and preferably at least two of said 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, typically a halogen like chlorine, or an anionic group present in the anionic dispersant compound, for example where the surfactant is a protonated amine of the formula R ₃ N, where R and N are as defined above. Examples of suitable surfactants include dioktildimetilammoniya chloride, didecyldimethylammonium chloride, dikokodimetilammoniya chloride kokobenzildimetilammoniya chloride, coco chloride (fractionated) benzyldimethylammonium octadecyl trimethylammonium chloride, dioctadecyldimethylammonium chloride, digeksadetsildimetilammoniya chloride, di (hydrogenated tallow) dimethylammonium chloride, di (hydrogenated tallow) benzylmethylammonium, (hydrogenated tall oil chloride) benzyldimethylammonium, dioleyl dimethylammonium chloride I chloride and di (etilengeksadekankarboksilat) dimethylammonium. Particularly preferred cationic surfactants thus include substances containing at least one hydrocarbon group with from 9 to 30 carbon atoms and especially quaternary ammonium compounds. Further suitable cationic surfactants include quaternary di- and polyammonium compounds containing at least one hydrocarbon group, suitably aliphatic and preferably alkyl, with 9 to 30 carbon atoms, preferably 12 to 22 carbon atoms. Examples of suitable surfactants of this type include N-octadecyl-N-dimethyl-N'-trimethyl-propylene-diammonium dichloride. Further examples of suitable surfactants include cationic polyelectrolytes, such as, for example, cationic organic HMB polymers, optionally cleaved, for example, derived from polysaccharides like starches and guar gum, cationic condensation products like polyurethanes, polyamidamines, for example polyamide amine dichlorohydrins, e.g. copolymers of dimethylamine-epichlorohydrin, copolymers of dimethylamine ethylene diamine-epichlorohydrin, copolymers of ammonium-ethylene dichloride, polymers with addition vinyl formed from monomers with cationic groups, for example, diallyldimethylammonium chloride homopolymers and copolymers, dialkylaminoalkyl acrylates, methacrylates and acrylamides (e.g. dimethylaminoethyl acrylates and methacrylates), which are usually present in the form of salts with addition of acid or quaternary non-ionic monomers, including acrylamide, alkyl acrylates, styrene and acrylonitrile and derivatives of such monomers, vinyl esters and the like.

 Both the anionic HMB compound and the cationic HMB compound for use in the present invention have a molecular weight (hereinafter MV) of less than 50,000, suitably less than 30,000 and preferably less than 20,000. Further benefits may be seen where the MV of the anionic compound and / or the cationic compounds of the dispersant are even lower, for example, less than 15,000 and especially less than 10,000. Typically, anionic and cationic compounds have an MB above 200 and suitably above 500. Typically, anionic and cationic surfactants have an MV lower than that of anionic and cationic polyelectrolytes; preferred surfactants have an MB of 200 to 800. When one of the dispersant compounds is a surfactant, the other dispersant compound should preferably be an electrolyte that can have an MV such as defined above.

 Preferred dispersions of the present invention comprise a dispersant selected from the group consisting of a dispersant (i) comprising a cationic surfactant and an anionic polyelectrolyte, where the dispersant has a total anionic charge; a dispersant (ii) comprising a cationic polyelectrolyte and an anionic polyelectrolyte, where the dispersant has a total negative charge; a dispersant (iii) comprising an anionic surfactant and a cationic polyelectrolyte, where the dispersant has a total cationic charge, and a dispersant (iv) including an anionic polyelectrolyte and a cationic polyelectrolyte, where the dispersant has a total cationic charge; moreover, anionic and cationic polyelectrolytes and their molecular weights are as defined above.

 The anionic and cationic compounds of the dispersant can be present in the dispersion in amounts that vary within wide limits, and depend, inter alia, on the molecular weight of these compounds, the degree of ionic substitution of these compounds, i.e. charge density, the desired total charge of the dispersion and the hydrophobic material used. Both the anionic compound and the cationic compound may be present in an amount of up to 100% by weight, suitably from 0.1 to 20% by weight and preferably from 1 to 10% by weight, based on the weight of the hydrophobic material.

 It was found that the dispersions of the present invention can be prepared with a high solids content and despite this show very good storage stability and low viscosity. This invention provides dispersions of a hydrophobic material with improved storage stability and / or high solids content. Particularly preferred dispersions in this regard include dispersions of a sizing agent reactive with cellulose, especially dispersions having a fully negative charge dispersant. Dispersions of sizing agents reactive with the cellulose of the present invention typically have a sizing agent content of from about 0.1 to about 50% by weight, suitably above 20% by weight. Dispersions containing a sizing agent comprising a ketene dimer of the present invention have a ketene dimer content within the range of 5 to 50% by weight and preferably about 10 to about 35% by weight. Dispersions, or emulsions, containing the acid anhydride sizing agent of the present invention have an acid anhydride content within the range of from 0.1 to about 30% by weight and usually from about 1 to about 20% by weight. Dispersions of a sizing agent that is not reactive with cellulose can typically have a sizing agent content of 5 to 50% by weight and preferably 10 to 35% by weight.

The dispersions of the present invention can be produced by mixing the aqueous phase with a dispersant system and a hydrophobic material, preferably at a temperature at which the hydrophobic material is a liquid, and homogenizing the mixture thus obtained is suitably under pressure. The resulting aqueous emulsion, which contains droplets of a hydrophobic substance, typically having a size of 0.1 to 3.5 microns in diameter, is then cooled. In addition to the aforementioned components, other materials can also be incorporated into the sizing dispersions, such as, for example, additional dispersants and stabilizers, for example non-ionic dispersants, fillers, for example urea and urea derivatives, and dispersion stabilizers. It will be appreciated that the negative and positive charges of the dispersant compounds can be formed in situ, for example, by contacting the compounds with one another and / or mixing the compounds with the aqueous phase and / or by lowering the pH of the aqueous phase. For example, the loss of hydrogen from an acid group will lead to the formation of a negative charge, and the main amine or amino group may be cationic by protonation or separation of hydrogen. Accordingly, it is possible to start with uncharged compounds in the preparation of the dispersion. For example, an organic compound with basic amino groups or a basic amine of the formula R ₃ N can be used, wherein the corresponding ammonium group R ₄ N ⁺ X ^{- is} formed in a preparation method, where R, N and X can be as defined above.

It has been found that the components of the present dispersions can be easily homogenized in the presence of an aqueous phase, in particular where HMB dispersant compounds are used in combination with hydrophobic materials having a melting point below about 100 ^° C and especially below about 75 ^° C. Less energy is usually required. and lower mixing forces in this method compared to methods for preparing conventional dispersions and whereby simpler equipment can be used. Therefore, the further method for producing dispersions includes (i) mixing the hydrophobic material with the anionic and cationic compounds of the dispersant to obtain an intermediate composition, and (ii) homogenizing the intermediate composition in the presence of an aqueous phase, as described above. It is preferred that the components be homogeneously mixed in step (i). The hydrophobic substance used in step (i) may be solid, although it is preferred that it is a liquid to facilitate homogeneous mixing. If desired, the intermediate composition can be removed after mixing step (i) and optionally cooled to cure to obtain a substantially anhydrous intermediate composition containing a dispersant and a hydrophobic material, which makes it possible to simplify the shipment in an economically attractive manner. In the place where it is going to be used, or somewhere else, the intermediate hydrophobic composition can be homogenized in the presence of water in the traditional or simplified way, optionally at elevated temperatures so as to provide a liquid of the intermediate composition. This method is especially attractive in the preparation of dispersions of ketene dimers and acid anhydrides, the latter of which are usually prepared in mills for grinding paper in direct connection with their use as a sizing agent in paper production. Ensuring storage stability of a largely anhydrous composition thus offers significant economic and technical benefits. The present invention thus also relates to a composition of a substantially anhydrous concentrate comprising a hydrophobic material, an anionic HMW compound selected from carbon-containing compounds and silicon-containing compounds, and a cationic organic HMB compound, where the anionic and cationic compounds, when used in combination, are effective as a dispersant system for a hydrophobic material in the aqueous phase, its preparation and use, as defined further in the claims.

 The components that are present in the concentrate of the present invention, i.e., the hydrophobic material and the anionic and cationic compounds, are preferably as defined above. The composition is largely anhydrous and the present means that small amounts of water may be present; the water content may be from 0 to 10% by weight, suitably less than 5% by weight and preferably less than 2%. Most preferably, it does not contain water. The composition preferably contains a hydrophobic material in a predominant amount, by weight, i.e. at least 50% by weight, and suitably the composition has a hydrophobic substance content within the range of from 80 to 99.9% by weight and preferably from 90 to 99.7% by weight. The anionic and cationic compounds may be present in the composition in amounts as defined above for dispersions, where percentages are based on a hydrophobic material. Accordingly, both the anionic compound and the cationic compound can be present in the composition in amounts of up to 100% by weight, suitably from 0.1 to 20% by weight and preferably from 1 to 10% by weight, based on the weight of the hydrophobic material.

 The dispersions of this invention can be used as sizing agents in the traditional way in the manufacture of paper using any type of cellulose fiber and this can be used both for surface sizing and for internal sizing or sizing of raw materials. The term "paper", as used here, means that it includes not only paper, but all types of cellulose-based products in the form of sheets and rolls, including, for example, cardboard and paper board. The feed contains cellulose fibers optionally in combination with mineral fillers, and typically the cellulose fiber content is at least 50% by weight based on the weight of the dry feed. Examples of conventional types of mineral fillers include kaolin, porcelain clay, titanium dioxide, gypsum, talc and natural and synthetic calcium carbonates such as chalk, ground marble and precipitated calcium carbonate. The amount of hydrophobic sizing agent added to the feedstock may be from 0.01 to 5% by weight, suitably from 0.05 to 1% by weight, based on the dry weight of cellulose fibers and optional fillers, where the dosage mainly depends on on the quality of the pulp or paper to be glued, the sizing agent used and the level of sizing desired.

 In a preferred embodiment, the dispersions are used for sizing pulp feedstocks, where the feedstock has a high cationic demand and / or contains significant amounts of lipophilic substances, for example, feedstock made from certain varieties of wood-containing pulps or pulp returned to processing, for example, where there is a lot of recycling white water. Particularly preferred dispersions in such applications include dispersions of a sizing agent reactive with cellulose and dispersions having a dispersant with a total negative charge. Typically, the cationic requirement is at least 50, suitably at least 100, and preferably at least 150 mEq. / liter of feedstock filtrate. The cationic demand can be measured in a conventional manner, for example, using a Mutec particle charge detector, using a feedstock filtrate obtained from a feed filtered through a 1.6 micron filter and poly (diallyldimethylammonium chloride) as a titrant. The amount of lipophilic extracts may be at least 10 ppm, usually at least 20 ppm, suitably at least 30 ppm, and preferably at least 50 ppm, measured as ppm of DCM by extraction using DCM ( dichloromethane) in a known manner. Further, the present dispersions are preferably used in papermaking processes where white water is extensively recycled, i.e. with a high degree of closure of the white water cycle, for example, where from 0 to 30 tons of fresh water, usually less than 20, suitably less than 15, preferably less than 10 and especially less than 5 tons of fresh water per ton are used per ton of dry paper produced paper. The recycling of white water in the process preferably takes place by mixing white water with cellulose fibers, preferably in the form of a feedstock or suspension, before or after adding a sizing dispersion, for example to form a feedstock that needs to be dehydrated. Fresh water can be introduced into the process at any stage; for example, it can be mixed with cellulose fibers in order to obtain a feedstock, and it can be mixed with a feedstock containing cellulose fibers to dilute it in order to obtain a feedstock that needs to be dehydrated before or after mixing the feedstock raw materials with white water and before or after adding a dispersion of a sizing agent.

 Chemicals commonly added to feedstock in paper production, such as auxiliary retention agents, dyes, moisture resistant resins, optical brighteners, etc., of course, can be used in conjunction with the present sizing dispersions. Sizing agents that are not reactive with respect to cellulose are typically used with an aluminum compound to fix the sizing agent to the cellulose fiber. Examples of aluminum compounds include alum, aluminates and polyaluminium compounds, for example, polyaluminium chlorides and sulfates. Examples of suitable auxiliary retention agents include cationic polymers, anionic inorganic materials in combination with organic polymers, for example bentonite in combination with cationic polymers, silicic acid sols in combination with cationic polymers or cationic and anionic polymers. Particularly good sizing of the feedstock can be obtained using the dispersions of the present invention in combination with auxiliary retention agents including cationic polymers. Suitable cationic polymers include cationic starch, guar gum, polymers based on acrylate or acrylamide, polyethyleneimine, dicyandiamide formaldehyde, polyamines, polyamidamines and poly (diallyldimethylammonium chloride) and combinations thereof. Cationic starch and cationic acrylamide-based polymers are preferably used individually or in combination with each other or with other materials. In a preferred embodiment of the invention, the dispersions are used in combination with retention systems comprising at least one cationic polymer and silica-based anion particles. The present dispersions can be added before, between, after or simultaneously with the addition of a cationic polymer or polymers. It is also possible to pre-mix the sizing dispersion with an auxiliary retention agent, for example a cationic polymer like cationic starch or a cationic polymer based on acrylamide, or an anionic material based on silicon dioxide, before introducing the mixture thus obtained into the feedstock. Accordingly, a dispersion can be prepared immediately before it is introduced into the starting material by contacting a sizing dispersion containing a cationic compound, preferably a cationic surfactant, with an anionic material based on silicon dioxide, for example, as defined above.

 The present invention is further illustrated in the following examples, which, however, are not intended to limit the invention. Parts and% refer to parts by weight and% by weight, respectively, unless otherwise specified.

Example 1
The dispersion of the hydrophobic alkyl ketene dimer (AKD) of the present invention was prepared by mixing dimethylammonium di (hydrogenated tall oil) chloride, which is a cationic surfactant with a MV of 340, sold under the trade name Querton 442, Akzo Nobel, melted at 70 ^o C AKD, passing the mixture through a homogenizer in the presence of an aqueous solution of condensed sodium naphthalenesulfonate with an estimated MV of about 6000 sold under the trade name Orotan ^TM SN, Rohm & Haas Company, and then m of cooling of the dispersion thus obtained. The pH of the dispersion was adjusted to about 5 by adding acid. The dispersion, designated dispersion No. 1, had an AKD content of 30% and contained 6% anionic compound and 4% cationic compound, the content of both compounds based on the weight of AKD. The dispersions contained particles of a cellulose-reactive hydrophobic compound with an average particle size of about 1 μm, which were negatively charged, as shown by the negative zeta potential determined by ZetaMaster S Version PCS.

Example 2
The stability of the dispersion of Example 1 was tested as follows: the dispersion was diluted with water to give a dispersion containing 40 ppm AKD. In some of the tests, 10 ppm of stearic acid was added to evaluate stability in the presence of a lipophilic, anionic impurity compound. The diluted dispersion was placed in a jar equipped with a turbidity meter, loop, circulation means, and heating and cooling means. The established volume of the diluted dispersion was circulated in the loop, at the same time, turbidity was automatically recorded and the dispersion was subjected to a heating and cooling cycle for a set period of time equal to 45 minutes. The temperature of the dispersion was raised from 20 ^o C to 62 ^o C and then lowered again to 20 ^o C. The turbidity is affected by particle size, and the difference in turbidity of the dispersion before and after the temperature cycle is a measure of the ability of the distributed particles to resist growth by adhesion and thus measure of dispersion stability. The difference in turbidity (DT) is calculated as follows:
Δ T = (final turbidity / initial turbidity) • 100.

 The higher Δ T, the better stability.

 Two standard dispersions were also tested for comparison purposes. Reference. 1 is an anionic AKD dispersion containing a dispersant system consisting of sodium lignosulfanate and high molecular weight cationic starch (IUD), where the anionic lignosulfanate is present in an ionic excess. Reference 2 is a cationic AKD dispersion, also containing sodium lignosulfonate and IUD, cationic starch, but where cationic starch is present in excess of ion. Table 1 gives the results.

 As shown in table 1, the ΔT values of the dispersions of the present invention were significantly higher than the values of standard dispersions, which, respectively, is an indicator of better stability in the diluted state.

Example 3
The composition of the anhydrous concentrate according to the present invention was prepared by dry mixing 93 parts of AKD granules with three parts of the cationic surfactant and 4 parts of the anionic compound used in Example 1. This dry mixture was later added to hot water and the aqueous mixture thus obtained was heated to 80 ^o C, pumped through a pump with a strong shift and then cooled to room temperature. The resulting anionic dispersion, dispersion N 2, had an AKD content of 20% and an average particle size of about 1 μm.

The sizing efficiency was evaluated by preparing sheets of paper according to the standard SCAN-C23X method for laboratory scale and using raw materials for paper production containing 80% 60:40 bleached birch / pine sulfate and 20% chalk, to which 0.3 g / l Na was added ₂ SO ₄ • 10H ₂ O. The viscosity of the starting material was 0.5% and pH 8.0. Dispersions were used in conjunction with the Compozil ^™ commercial containment and dewatering system, including cationic starch and anionic silica sol modified with aluminum, which were added to the feed separately; cationic starch was added in an amount of 12 kg / t based on the dry feedstock and a silica sol was added in an amount of 0.8 kg / t calculated as SiO ₂ and based on the dry feedstock.

 The Cobb values measured according to the TAPPI T 441 OS-63 standard obtained in the tests are presented in Table 2. The AKD dosages are based on dry feedstock.

 Table 2 shows the improvement in the sizing of paper obtained with the dispersion of the present invention.

Example 4
The ease of production of the dispersions of the present invention was evaluated by preparing anionic AKD dispersions at various AKD contents. Dispersions according to the invention were prepared by homogenizing a mixture of 0.8% by weight dimethylammonium chloride (hydrogenated tall oil), 1.6% by weight of condensed sodium naphthalene sulfonate, 77.6% by weight of water and 20% by weight of AKD for a set time, using an Ultra Turrax stirrer at 15,000 rpm, and then cooling the dispersion thus obtained for 2 hours. Similar dispersions were prepared in the same way at different AKD contents to provide dispersions with AKD contents of 10, 20, 30 and 40% by weight. The dispersions indicated by the Invention are followed by the AKD content in weight%.

 Standard AKD dispersions were made for comparison purposes 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 AKD. Similar dispersions were prepared with different AKD contents in order to provide standard dispersions with AKD contents of 10, 20, 30 and 40% by weight. For the variances indicated by the Standard. 3, the AKD content in weight% follows.

 Particle size and viscosity were determined in the traditional way. Table 3 shows the results.

 Table 3 demonstrates that the dispersions of the present invention were easier to produce; lower viscosity was obtained with the corresponding AKD content and lower particle size was obtained using the same amount of energy to set the surface free. Compared to standard dispersion, thus, the present invention requires less energy and lower shear forces in order to produce dispersions with equal particle sizes. In addition, increasing the stirrer speed to 25,000 rpm significantly reduced the particle size of the dispersion of the present invention, which is within the range of 1 to 2 μm.

Claims (18)

1. An aqueous dispersion containing a dispersant and a dispersed phase containing a hydrophobic sizing agent, wherein the dispersant includes
a) an anionic compound having a molecular weight of less than 50,000 and selected from carbon-containing compounds and silicon-containing compounds, and
b) a cationic organic compound having a molecular weight of less than 50,000, where at least one of the anionic and cationic compounds is a polyelectrolyte.  2. The dispersion according to claim 1, in which the anionic compound and the cationic compound have a molecular weight of less than 20,000.  3. The dispersion according to claim 1 or 2, in which the anionic compound is an organic substance.  4. The dispersion according to claims 1, 2 or 3, in which the dispersant is anionic and includes a cationic surfactant and an anionic polyelectrolyte.  5. The dispersion according to claims 1, 2 or 3, in which the dispersant is anionic and includes a cationic polyelectrolyte and an anionic polyelectrolyte.  6. The dispersion according to claims 1, 2 or 3, in which the dispersant is cationic and includes an anionic surfactant and a cationic polyelectrolyte.  7. The dispersion according to claims 1, 2 or 3, in which the dispersant is cationic and includes an anionic polyelectrolyte and a cationic polyelectrolyte.  8. The dispersion according to any one of the preceding paragraphs, in which the content of the hydrophobic sizing agent is at least 20% by weight.  9. The dispersion according to any one of the preceding paragraphs, in which the hydrophobic sizing agent is a cellulose-reactive sizing agent.  10. The dispersion according to any one of the preceding paragraphs, in which the sizing agent is a ketene dimer or acid anhydride.  11. The dispersion according to any one of claims 1 to 8, in which the hydrophobic sizing agent is a sizing agent that is not reactive with respect to cellulose. 12. The dispersion according to any one of the preceding paragraphs, in which the hydrophobic sizing agent has a melting point below 75 ^o C.  13. A method of producing an aqueous dispersion by homogenizing a hydrophobic sizing agent in the presence of an aqueous phase and a dispersant comprising an anionic compound having a molecular weight below 50,000 and selected from carbon-containing compounds and silicon-containing compounds, and a cationic organic compound having a molecular weight below 50,000, where at least one of the anionic and cationic compounds is a polyelectrolyte.  14. The method according to item 13, in which the anionic compound and the cationic compound have a molecular weight of less than 20,000.  15. The method according to item 13 or 14, in which the anionic organic compound is an organic substance.  16. A substantially anhydrous sizing composition comprising a hydrophobic sizing agent, an anionic compound having a molecular weight of less than 50,000 and selected from carbon-containing compounds and silicon-containing compounds, and a cationic organic compound having a molecular weight of less than 50,000, where at least one of anionic and cationic compounds is a polyelectrolyte.  17. The composition according to clause 16, in which the anionic compound is an organic substance.  18. The composition according to clause 16 or 17, in which the hydrophobic sizing agent is a ketene dimer or acid anhydride.

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