SK102599A3 - Aqueous dispersions of hydrophobic material - Google Patents

Abstract

The invention relates to an aqueous dispersion containing a dispersant and a disperse phase containing a hydrophobic material, the dispersant comprising an anionic compound having a molecular weight less than 50,000 and being selected from carbon-containing compounds and silicon-containing compounds, and a cationic organic compound having a molecular weight less than 50,000. The invention further relates to the preparation and use of the dispersion in the production of paper. The invention also relates to a substantially water-free composition containing a hydrophobic material, an anionic compound having a molecular weight less than 50,000 and being selected from carbon-containing compounds and silicon-containing compounds, and a cationic organic compound having a molecular weight less than 50,000, as well as its use in the preparation of an aqueous dispersion.

Description

Technical field

The present invention relates to aqueous dispersions of hydrophobic material, and in particular to dispersions having a dispersion system comprising two counter-charged compounds, their preparation and use.

BACKGROUND OF THE INVENTION

Aqueous dispersions of hydrophobic materials are well known and used in a variety of applications. For example, in paper making, aqueous dispersions of hydrophobic material are used as glues to obtain paper and board with a degree of resistance to wetting and penetration by aqueous fluids. Examples of hydrophobic materials widely used for sizing include cellulose reactive sizing agents such as alkyl ketene dimers and substituted succinic anhydrides, and cellulose non-reactive sizing agents such as rosin-based and resin-based sizing agents.

Dispersions of the hydrophobic material typically comprise an aqueous phase and finely divided particles or droplets of the hydrophobic material dispersed therein. Dispersions are usually prepared by homogenizing a hydrophobic, water-insoluble material in an aqueous phase in the presence of a dispersant using high shear forces and fairly high temperatures. Commonly used dispersing agents include anionic, amphoteric and cationic high molecular weight polymers such as lignosulfonates, starches, polyamines, polyamidamines, and vinyl addition polymers. The polymers can be used singly, together or in combination with other compounds to form a dispersant. Depending on the overall charge of the dispersing agent components, the glue dispersions are anionic or cationic in nature.

Dispersions of hydrophobic material usually exhibit rather poor stability and high viscosity at relatively low solids content, which obviously leads to difficulties in processing dispersions, for example during storage and use. A further disadvantage is that the products are to be supplied as low-concentration dispersions, which further increases the cost of transporting the active hydrophobic material.

It is therefore an object of the present invention to provide aqueous dispersions of hydrophobic material with improved stability and viscosity properties. It is a further object of the present invention to provide improved aqueous dispersions of the glue, in particular cellulose-reactive glue. Other subjects will be explained below.

SUMMARY OF THE INVENTION

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

The present invention makes it possible to provide dispersions of hydrophobic material with improved storage stability, higher solids content and / or lower viscosity. Further, as a dispersion is used in applications involving a very high dilution of an initially highly concentrated dispersion, it has been found that the dispersion phase is more stable, i.e. the dispersions exhibited improved dilution stability. Examples of extremely high dilution applications include preparing the paper under wet conditions and storing or internal sizing comprising adding a dispersion of a 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 the hydrophobic size, thereby creating lower levels of larger aggregates with lower sizing efficiency, as well as less deposition of the hydrophobic size on the paper machine and less winding contamination, thereby reducing the need for paper machine maintenance. Other advantages to be expected with said dispersion include improved stability in the presence of interfering substances, such as anionic wastes derived from contaminated paper and / or recycled fibers, less accumulation of hydrophobic material in white water recirculated in the paper making process. Therefore, the dispersions of the invention are particularly suitable for processes where the white water is extensively recirculated and where the cellulosic suspension contains a substantial amount of waste. Further, the dispersions of the present invention allow to obtain improved sizing over conventional sizing dispersions at the appropriate sizing dosage and the use of a lower sizing dosage to obtain the appropriate sizing level. The possibility of using smaller amounts of sizing to achieve sizing in the description further reduces the risk of accumulating unadsorbed hydrophobic sizing in the white water recirculating in the process, further reducing the risk of aggregation and deposition of the hydrophobic material in the paper machine. Thus, the present invention offers substantial economic and technical advantages.

The hydrophobic material present in the dispersion is preferably water insoluble. Examples of suitable hydrophobic materials include sizing compounds in paper making, which can be derived from both natural and synthetic sources, such as cellulose-reactive hydrophobic materials and cellulose-non-reactive hydrophobic materials. In a preferred embodiment, the hydrophobic material has a melting point below about 100 ° C and in particular below about 75 ° C.

In a preferred embodiment of the present invention, the hydrophobic material is a cellulose-reactive sizing agent, which may be selected from any of the cellulose-reactive sizing agents known in the art. The sizing agent is preferably 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, even more preferably ketene dimers.

Preferred ketene dimers have the general formula (I) below, wherein R ¹ and R ² are saturated or unsaturated hydrocarbon groups, usually saturated hydrocarbons, hydrocarbon groups preferably having 8 to 36 carbon atoms, usually straight or branched alkyl chains of 12 to 20 carbon atoms. carbon atoms such as hexadecyl or octadecyl. Preferred acid anhydrides may be characterized by the general formula (II) below, wherein R ³ and R ⁴ may be the same or different and represent saturated or unsaturated hydrocarbon groups preferably containing 8 to 30 carbon atoms, or R ³ and R ⁴ together with the -COC moiety may form a 5- to 6-membered ring, which is preferably further substituted by a hydrocarbon group containing up to 30 carbon atoms. Examples of acid anhydrides that are commonly used include alkyl and alkenyl succinic anhydrides and especially isooctadecenyl succinic anhydride.

R ¹ -CH = C-CH-R ²

I I (I)

O-C = O

O O

II II (di)

R ³ - C - O - C - R ⁴

Preferred ketene dimers, acid anhydrides and organic isocyanates include the compounds described in U.S. Patent 4,522,686, which is incorporated herein by reference. Examples of suitable carbamoyl chlorides include those described in U.S. Patent 3,887,427, which is also incorporated herein by reference.

In another preferred embodiment of the invention, the hydrophobic material is a non-cellulose-reactive hydrophobic material which can be selected from any of the cellulose-non-reactive sizing agents known in the art. The preferred cellulose-non-reactive sizing agent is selected from the group consisting of hydrophobic rosins, such as rosin, disproportionated rosin, hydrogenated rosin, polymerized rosin, formaldehyde treated rosin, esterified rosin, fortified rosin, and mixtures thereof acids and their derivatives such as fatty acid esters and amides such as bis-stearamides, resins and their derivatives such as hydrocarbon resins, bitumen acids, bitumen esters and amides, waxes such as crude and refined paraffin waxes, synthetic waxes, naturally occurring waxes, etc.

The dispersions of the present invention comprise dispersants or a dispersing system comprising at least one anionic compound and at least one cationic organic compound, both of low molecular weight (hereinafter referred to as LMW). Preferably, the LMW compounds bind together by an electrostatic attraction force indicating coacervation of the dispersant. When used in combination, the LMW compounds are effective as dispersants for the hydrophobic amterial, although anionic and cationic compounds may not, and usually are, not effective as dispersants when used alone. In a preferred embodiment, at least one of the anionic and cationic compounds is a polyelectrolyte. The term "polyelectrolyte," as used herein, refers to a compound having two or more charged (anionic / or cationic) compounds acting as polyelectrolyte, i.e., by chemical non-ionic interaction or treatment.

The anionic dispersant compound comprises one or more anionic groups of the same or different types and including anionic compounds with one anionic group and anionic compounds with two or more anionic groups, referred to herein as anionic polyelectrolytes. The anionic polyelectrolytes may contain one or more cationic groups as long as they have a total anionic charge. Examples of suitable anionic groups include sulfate groups and carboxylic, sulfonic, phosphoric and phosphonic acid groups, which may be present as free acids or water-soluble ammonium or alkali metal (usually sodium) salts such as sodium carboxylates and sulfonates. The anionic polyelectrolytes may have a degree of substitution varying within a wide range; the degree of anionic substitution (DS _a ) may be from 0.01 to 1.4, preferably from 0.1 to 1.2, and more preferably from 0.2 to 1.0.

The anionic compound in the dispersant can be derived from synthetic and natural sources and is preferably water-soluble or water-dispersible. In a preferred embodiment, the anionic compound is an organic compound, i.e., contains carbon atoms. Preferred anionic compounds include anionic surfactants such as alkyl, aryl and alkylarylsulfates and ether sulfates, alkyl, aryl and alkylaryl carboxylates, alkyl, aryl and alkylarylsulfonates, alkyl, aryl and alkylaryl phosphates and ether and dialkyl sulfosuccinates, alkyl groups of 1 to 1 Cry-Cry a aryl, C až-Cry a aryl aryl and C až-C alky alky alkyl aryl groups. Examples of suitable anionic surfactants include sodium lauryl sulphate, sodium lauryl sulphonate and sodium dodecylbenzenesulphonate. Other examples of suitable anionic compounds include anionic polyelectrolytes, such as anionic organic polymers of LMW, preferably degraded, i.e., derived from phosphated, sulfonated and carboxylated polysaccharides such as starches, guar gums and celluloses, preferably cellulose derivatives and especially carboxymethylcelluloses, as well as condensation products, i.e., anionic polyurethanes and condensed naphthalenesulfonates, other vinyl addition polymers formed from monomers with anionic groups such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid, vinylsulfonic acid, sulfonated styrene, and hydroxyalkyl copolymer acrylate copolymer phosphates, monomers including acrylamide, alkyl acrylates, styrene and acrylonitrile, as well as derivatives of these monomers, vinyl esters and the like. The anionic compound may also be selected from inorganic LMW compounds containing silicon atoms, such as silicates and other forms of fused or polymerized silicas, such as oligomeric silicic acid, polysilicic acids, polyaluminosilicates, polyosilicate microgilites, polyosilicate microglials, , as in the form of silica soles having negative hydroxyl groups.

The cationic dispersant compound comprises one or more cationic groups of the same or different type and include the same or different types and includes cationic compounds with one cationic group and cationic compounds with two or more cationic groups, herein referred to as polyelectrolyte. The cationic polyelectrolytes may contain one or more anionic groups if it has a total cationic charge. Examples of suitable cationic groups include sulfonium groups, phosphonium groups, acid addition salts of primary, secondary and tertiary amines or amino groups and quaternary ammonium groups, e.g. The cationic polyelectrolytes may have a degree of substitution varying within a wide range; the degree of cationic substitution (DS _C ) may be from 0.01 to 1.0, preferably from 0.1 to 0.8, and even more preferably from 0.2 to 0.6.

The cationic compound of the dispersant may be derived from synthetic and natural sources and is preferably water-soluble or water-dispersible. The cationic new compound is preferably an organic compound. Examples of suitable cationic compounds include cationic surfactants, i.e. compounds of the type

R ₄ N ⁺ X, wherein each R is independently selected from (i) hydrogen;

(ii) hydrocarbon groups, preferably aliphatic and preferably alkyl groups having 1 to about 30 carbon atoms, preferably 1 to 22 carbon atoms; and (iii) hydrocarbon groups, preferably aliphatic and preferably alkyl groups having up to about 30 carbon atoms, preferably 4 to 22 carbon atoms, and which are interrupted by one or more heteroatoms such as oxygen or nitrogen and / or heteroatom containing groups such as carbonyl, and acyloxy; wherein at least one, preferably at least three, and preferably all, said R groups contain carbon atoms; preferably 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 even more preferably at least 12 carbon atoms; and where

X is an anion, typically a halogen such as a chloride, or an anionic group present in the anionic compound of the dispersant, i.e. where the surfactant is a protonated amine of formula

R ₃ N wherein R and N are as defined above.

Examples of suitable surfactants include dioctyldimethylammonium chloride, didecyldimethylammonium chloride, dicocodimethylammonium chloride, cocobenzyldimethylammonium, coco (fractionated) benzyldimethylammonium, oktadecyltrimetylamóniumchlorid, dieicosyl, dihexadecyl dimethylammonium chloride, di (hydrogenated tallow) dimethylammonium chloride, di (hydrogenated tallow) benzylamó4ο monium chloride, (hydrogenated tallow) benzyldimethylammonium chloride, dioleyldimethylammonium chloride, and di (etylénhexadekánkarboxylát) dimethylammonium chloride. Particularly preferred cationic surfactants thus include those containing at least one C 9 -C 30 hydrocarbon group, and in particular quaternary ammonium compounds. Other suitable cationic surfactants include quaternary di- and polyammonium compounds containing at least one hydrocarbon group, preferably aliphatic and preferably alkyl of 9 to 30 carbon atoms, preferably 12 to 22 carbon atoms. Examples of suitable surfactants of this type include N-octadecyl-N-dimethyl-N'-trimethylpropylenediammonium dichloride. Other examples of suitable cationic compounds include cationic polyelectrolytes such as cationic organic polymers of LMW, optionally degraded, i.e., those derived from polysaccharides such as starches and guar gums, cationic condensation products such as polyurethanes, polyamidamines such as polyamidamine epichlorohydrins, polyamines, polyamines, polyamines, polyamines, polyamines, polyamines, copolymers of dimethylamine-epichlorohydrin copolymers, dimethylamine-ethylenediamine-epichlorohydrin copolymers, dimethylamine-ethylenediamine-epichlorohydrin copolymers, ammonia-ethylene dichloride, vinyl addition polymers formed from monomers with cationic groups, e.g. homopolymers and copolymers of diallyldimethylammonium chloride, dialkylaminoalkyl acrylates, methacrylates and acrylamides (e.g. dimethylaminoethyl and methacrylates), which are usually present as acid addition salts or quaternary ammonium salts, optionally copolymerized with non-ionic monomers including acrylamide, alkyl acrylates, styrene and acrylonitrile and derivatives of these monomers, vinyl esters and the like.

The anionic LMW compound and the cationic LMW compound for use in the present invention have a molecular weight (hereinafter referred to as MW) of less than 50,000, preferably less than 30,000 and preferably less than 20,000. Other advantages are evident when the MW of the anionic compound and / or a cationic dispersant compound even lower, for example less than 15,000 and even less than 10,000. Normally, the anionic and cationic surfactants have a lower MW than the anionic and cationic polyelectrolytes; preferred surfactants have a MW of 200 to 800. When one of the dispersant compounds is a surfactant, the other dispersant compound may preferably be a polyelectrolyte having a MW as defined above.

The dispersions preferred according to the invention comprise a dispersant selected from the group consisting of a dispersant (i) comprising a cationic surfactant and an anionic polyelectrolyte, wherein the dispersant has an overall anionic charge; a dispersant (ii) comprising a cationic polyelectrolyte and an anionic polyelectrolyte, wherein the dispersant has an overall anionic charge; a dispersant (iii) comprising an anionic surfactant and a cationic polyelectrolyte, wherein the dispersant has an overall cationic charge; and a dispersant (iv) comprising an anionic polyelectrolyte and a cationic polyelectrolyte, wherein the dispersant has an overall cationic charge; anionic and cationic surfactants, anionic and cationic polyelectrolyte, and their molecular weight is as defined above.

The anionic and cationic dispersant compounds may be present in the dispersion in amounts varying over a wide range depending on, inter alia, the molecular weight of the compounds, the degree of ionic substitution of the compounds, i.e. the charge density, the desired overall 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, preferably from 0.1 to 20% by weight, and preferably from 1 to 10% by weight, based on the hydrophobic material.

It has been found that the dispersions of the present invention can be prepared with high solid contents and yields and exhibit very good storage stability and low viscosity. Thus, the present invention provides dispersions of hydrophobic material with improved storage stability and / or high solids contents. Particularly preferred dispersions in this regard include dispersions of cellulose-reactive glues, in particular dispersions with a dispersant having a total anionic charge. Generally, the cellulose-reactive sizing dispersions of the invention may have a sizing content of from about 0.1 to about 50% by weight and preferably about 20% by weight. Dispersions comprising a ketene dimer as the size according to the present invention should have a ketene dimer content of from 5 to 50% by weight and preferably from about 10 to about 35% by weight. The dispersion or emulsion containing the acid anhydride glue according to the invention is intended to have an acid anhydride content in the range of about 0.1 to about 30% by weight and usually about 1 to about 20% by weight. Dispersions of cellulose-non-reactive glues usually have a glucosity content of from 5 to 50% by weight and preferably from 10 to 35% by weight.

The dispersions of the invention may be prepared by mixing the aqueous phase with a dispersing system and a hydrophobic material, preferably at a temperature where the hydrophobic material is a liquid, and homogenizing the mixture thus obtained, preferably under pressure. The obtained aqueous emulsion, which contains drops of a hydrophobic substance, normally having a diameter of from 0.1 to 3.5 µm in diameter, is then cooled. Other materials, such as additional dispersants and stabilizers, such as non-ionic dispersants, diluents such as urea and urea derivatives, and preservatives, may also be incorporated into the sizing dispersion. It is contemplated that the negative and positive charges of the dispersant compounds may be formulated in situ, for example by contacting the compounds with each other and / or by mixing the compounds with the aqueous phase and / or lowering the pH of the aqueous phase. For example, the loss of hydrogen from the acidic group creates an anionic charge and the basic amine or amine group can be converted to cationic protonation or hydrogen removal. Therefore, it is possible to start with non-charged compounds when preparing the dispersion. For example, an organic compound with a basic amino group or a basic amine of the formula R 3 N may be used, wherein the corresponding ammonium moiety R ₄ N ⁺ X "may be formed during preparation, where R, N and X may be as defined above.

It has been found that the components of the present dispersions can be readily homogenized in the presence of an aqueous phase, especially when LMW dispersant compounds are used in combination with hydrophobic materials having a melting point below about 100 ° C and in particular below about 75 ° C. Usually, these processes require less energy and lower shear forces compared to processes for preparing conventional dispersions, and thus a simpler device can be used. Thus, a further process for preparing dispersions comprises (i) mixing the hydrophobic material with anionic and cationic dispersant compounds to obtain an intermediate composition, and (ii) homogenizing the intermediate composition in the presence of an aqueous phase as described above. Preferably, the components are homogeneously mixed in step (i). The hydrophobic materials used in step (i) may be solid, although it is preferred that they be liquid, as this will facilitate homogeneous mixing. If desired, the intermediate composition may be removed after mixing step (i) and optionally cooled to solidification to form a substantially anhydrous intermediate composition comprising a dispersant and a hydrophobic material (which will facilitate easier loading in an economically attractive manner). At the point of use or elsewhere, the intermediate hydrophobic composition can be homogenized in the presence of water by a conventional or simplified procedure, preferably at elevated temperature, such that the intermediate composition is transformed into a liquid form. This process is of particular interest when dispersions of ketene dimers and acid anhydrides are prepared, the latter usually being prepared in a direct bond paper mill using them as a sizing agent in papermaking. The condition of stable storage of the substantially anhydrous composition thus brings desirable economic and technical advantages. Accordingly, the present invention relates to a substantially anhydrous concentrated composition comprising a hydrophobic material, an anionic LMW compound selected from carbon-containing compounds and silicon-containing compounds, and a cationic organic LMW compound, wherein the anionic and cationic compounds when used in combination are effective as a dispersant a system for hydrophobic material in an aqueous phase, the preparation of this composition and the use as defined below in the claims.

The components that are present in the concentrated composition (composition) of the invention, i.e. the hydrophobic material and the anionic and cationic compounds, are preferably the same as defined above. The composition is substantially anhydrous, that is, it may contain a small amount of water; the water content may be from 0 to 10% by weight, preferably with a content of less than 5% by weight and preferably less than 2%. Most preferably, it contains no water. The composition preferably comprises a hydrophobic material in a predetermined amount by weight, i.e. at least 50% by weight, and preferably the composition has a hydrophobic material content ranging 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 compositions in an amount as defined above with respect to dispersions where the percentages are based on the hydrophobic material. Accordingly, both the anionic and cationic compounds may be present in the compositions in an amount of up to 100% by weight, preferably from 0.1 to 20% by weight, and preferably from 1 to 10% by weight, based on the hydrophobic material.

The dispersions of the invention can be used by conventional techniques such as sizing agents in papermaking using any type of cellulosic fiber and can be used for surface sizing as well as internal sizing or sizing of paper. The term "paper," as used herein, means that it includes not only paper but all types of cellulose-based products in sheet or strip form, including, for example, cardboard and paperboard. The pulp comprises cellulose fibers, optionally in combination with mineral fillers, and typically the cellulosic fiber content is at least 50% by weight relative to the dry stock. Examples of conventional mineral fillers include kaolin, aluminum silicate, titanium dioxide, gypsum, talc, and natural or synthetic calcium carbonates such as chalk, ground marble, and precipitated calcium carbonate. The amount of hydrophobic size added to the pulp may be from 0.01 to 5% by weight, preferably from 0.05 to 1.0% by weight, based on the dry weight of the cellulosic fibers and optionally the filler, where the dosage depends mainly on the quality of the pulp or paper. the size of the sizing used and the desired level of sizing.

In a preferred embodiment, dispersions are used in the sizing of cellulosic pulp pulp, where the pulp has high cationic requirements and / or contains substantial amounts of lipophilic substances, such as pulp prepared from some stages of wood-containing pulp and recycled, for example where white water recirculation is extensive. Particularly preferred dispersions in such applications include cellulose-reactive glue dispersions and dispersions having a total anionic dispersant. Typically, the cationic requirement is at least 50, preferably at least 100, and preferably at least 150 g / liter of pulp filtrate. The cationic collection can be measured by a conventional procedure, for example by means of a Particle Charge Detector using a pulp filtrate obtained from a raw pulp filtered through a 1.6 gm filter and with poly (dialyldimethylammonium chloride) as the titration agent. The content of lipophilic extracts may be at least 10 ppm, usually at least 20 ppm, preferably at least 30 ppm and preferably at least 50 ppm, measured as ppm of DCM by extraction and using DCM (dichloromethane) by a known method.

Further, the present dispersions are particularly suitable in paper making processes where extensive white water is recirculated extensively, for example with a high degree of white water capsule, for example where 0 to 30 tonnes of fresh water per tonne of dry paper produced, usually less than 20, preferably less than 15 are used. and preferably less than 10, and in particular less than 5 tons of fresh water per tonne of paper. The recirculation of the white water in the process preferably takes place by mixing the white water with the cellulosic fibers, preferably in the form of a pulp or suspension, before or after adding the sizing dispersion, thus forming a pulp to be dewatered. Fresh water can be fed to the process at any stage; for example, it may be blended with cellulosic fibers to form a pulp and may be blended with pulp containing cellulosic fibers to dilute it so as to form a pulp to be dewatered before or after mixing the pulp with white water and before or after the addition of the sizing dispersion.

Chemicals commonly added to paper pulp, such as retention aids, aluminum compounds, dyes, wet strength resins, optically brighteners, etc. they can of course be used together with the sizing dispersions present. With cellulose non-reactive sizing agents, aluminum compounds are typically used to fix the sizing agent to the cellulose fiber. Examples of aluminum compounds include alum, aluminates, and polyaluminium compounds such as polyaluminium chlorides, and sulfates. Examples of suitable retention aids include cationic polymers, anionic inorganic materials in combination with organic polymers such as bentonite in combination with cationic polymers, silica-based soles in combination with cationic polymers or cationic and anionic polymers. Particularly good paper size glue can be obtained when the dispersions of the invention are used in combination with retention aids containing cationic polymers. Suitable cationic polymers include cationic starch, guar gum, acrylate and polymers based on acrylamide, polyethyleneimine, dicyandiamide formaldehyde, polyamines, polyamidoamines and poly (dialyldimethylammonium chloride) and combinations thereof. Cationic starch and acrylamide-based cationic polymers are preferably used either alone or in combination with each other or with other materials. In a preferred embodiment of the invention, dispersions are used in combination with a retention system comprising at least one cationic polymer and anionic silica-based particles. Said dispersions may be added before, between, after or simultaneously with the addition of the cationic polymer or polymers. It is also possible to premix the size dispersion with a retention aid, i.e., a cationic polymer such as a cationic starch or an acrylamide-based cationic polymer, or an anionic silica-based material, before introducing the thus obtained mixture into the paper stock. Accordingly, a dispersion can be prepared just prior to being introduced into the paper by bringing a sizing dispersion containing a cationic compound, preferably a cationic surfactant, into contact with a silica-based anionic material, for example as defined above.

The invention will be further illustrated by the following non-limiting examples. Parts and% refer to parts and percentages by weight unless otherwise stated.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

A dispersion of hydrophobic alkyl ketene dimer (AKD) of this invention was prepared by mixing di (hydrogenated tallow) dimethylammonium chloride, which is a cationic surfactant with a MW of 340, commercially available under the trade name Querton 442, Akzo Nobel, with molten AKD at 70 ^e C, passing the mixture through a homogenizer in the presence of an aqueous solution of condensed sodium naphthalenesulfonate having a MW of about 6000, commercially available under the trade name Orotan ^TK SN, by the Rohm & Haas Company, and then cooling the dispersion thus obtained. The pH of the dispersion was adjusted to about 5 by the addition of acid. The dispersion, designated Dispersion 1, had an AKD content of 30% and contained 6% anionic compound and 4% cationic compound based on the weight of AKD. The dispersion contained particles of a cellulose-reactive hydrophobic substance with an average particle size of about 1 µm which were anionically charged, as evidenced by the negative zeta potential determined by the ZetaMaster S PCS version.

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 tests, 10 ppm of stearic acid was added to assess stability in the presence of a lipophilic anionic waste substance. The diluted dispersion was poured into a vessel equipped with a turbidity measuring device, a loop, circulation and heating and cooling means. The deposited volume of the diluted dispersion was circulated in the loop, while turbidity was automatically recorded and the dispersion was subjected to a heating and cooling cycle for a period of 45 minutes. The temperature of the dispersion was raised from 20 ° C to 62 ^e C and then lowered again to 20 ° C. Turbidity is influenced by particle size and the difference in turbidity of the dispersion before and after the temperature cycle is a measurement of the ability of the dispersed particles to resist agglomeration growth and thus measurement of the stability of the dispersion. The turbidity difference (..T) is calculated as follows:

ΔΤ - (final haze / initial haze) x 100

The higher the ΔΤ, the better the stability.

Two standard dispersions were also tested for comparative purposes:

Ref. 1 is an anionic dispersion AKD comprising a dispersion system comprising sodium lignosulfonate and a high molecular weight Lo (HMW) cationic starch, wherein the anionic lignosulfonate is present in an ionic excess;

Ref. 2 is an AKD cationic dispersion also containing sodium lignosulfonate and HMW cationic starch, but wherein the cationic starch is present in an ionic excess.

Table 1 shows the results obtained.

Table 1

Dispersion No._Stearic acid (ppm) _

- 72

10 55

Ref. 1 - 45

Ref. 32

Ref. 2 - 35

Ref. 2 10 6

As shown in Table 1, the dispersion ΔΤ values of this invention were significantly higher than those of the standard dispersions and accordingly indicate better dilution stability.

Example 3

The concentrated anhydrous composition of the invention was prepared by dry blending 93 parts of AKD pellets with 3 parts of cationic surfactant and 4 parts of anionic compound used in Example 1. This dry mixture was later added to hot water and the resulting aqueous mixture was heated to 80 ° C. was pumped through a high shear pump and then cooled to room temperature. The anionic dispersion obtained, number 2 dispersion, had an AKD content of 20% and an average particle size of 1 µm.

The sizing efficiency was evaluated in the preparation of paper sheets according to the standard SCAN-C23X method on a laboratory scale and using pulp containing 80% blend of birch / pine sulphate (60:40) and 20% chalk to which 0.3 g / l Na was added. ₂ SO ₄ .10H ₂ O consistency was 0.5% and pH 8.0. The dispersions were used in conjunction with the commercial retention and drainage system, Compozil ™, containing cationic starch and anionic aluminum modified silica sol, which were added to the pulp separately; cationic starch was added in an amount of 12 kg / tonne relative to the dry stock, and silica sol was added in an amount of 0.8 kg / tonne, calculated as SiO ₂ based on the dry stock.

The Cobb values, measured according to TAPPI standard T 441 OS63, obtained during testing are given in Table 2. The dosage of AKD refers to dry stock.

Table 2

Dispersion No_Dose AKD (kg / l) _ Cobb (g / m ² )

2 0, 30 58 2 0.40 30 Ref. 1 0.30 84 Ref. 1 0.40 65 Ref. 2 0.30 66 Ref. 2 0.40 40

Table 2 demonstrates the improved sizing of the paper obtained with the dispersion of the invention.

Example 4

The ease of manufacture of the dispersions of the invention was evaluated by preparing anionic AKD dispersions having different AKD contents. The dispersions according to the invention were prepared by homogenizing a mixture of 0.8 wt. di (hydrogenated tallow) dimethylammonium chloride,

1.6 wt. % condensed sodium naphthalenesulfonate, 77.6 wt. % water and 20 wt. AKD for a set time using an Ultra Turrax mixer at 15,000 rpm and then cooling the dispersion so obtained for 2 hours. Similar dispersions were prepared in the same manner with different values of AKD content to obtain dispersions with AKD contents of 10, 20, and 40 wt. Dispersions are labeled INV. Followed by an AKD content in% by weight.

Standard AKD dispersions were prepared for comparative purposes in the same manner and under the same conditions by homogenizing the 1.0 wt. % cationic starch, 0.25 wt. % sodium lignosulfate, 89 wt. % water and 10 wt. AKD. Similar dispersions were prepared with different AKD contents to obtain standard dispersions with AKD contents of 10, 20, 30 and 40 wt. Dispersions are labeled Ref. 3, followed by the AKD content in wt.

Particle size and viscosity were determined by conventional procedures. Table 3 shows the results obtained.

Table 3

AKD dispersion no. Particle size (μιη) viscosity Inv. -10% 2, 98 10 Inv. -20% 3.12 20 Inv. -30% 3.50 20 Inv. -40% 3.50 25 Ref.3-10% 4.31 15 Ref.3-20% 4.52 20 Ref.3-30% 5.20 25 Ref.3-40% 5.57 40

Table 3 shows that the dispersions of the invention were easier to process for production; a lower viscosity was obtained at the appropriate AKD content and a smaller particle size was obtained using the same amount of energy to treat the free surfaces. Thus, compared to standard dispersions, less energy and lower shear forces are required in the present invention to produce dispersions of the same particle size. Further, increasing the stirrer speed to 25,000 rpm suitably reduces the particle size of the dispersions of the invention, which is in the range of 1 to 2 µmη.

// MO 't ¹

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Claims (20)

PATENT CLAIMS An aqueous dispersion comprising a dispersant and a dispersion phase comprising a hydrophobic glue, characterized in that the dispersant comprises (a) an anionic compound having a molecular weight of less than 50,000 selected from carbon-containing compounds and silicon-containing compounds, and (b) cationic an organic compound having a molecular weight of less than 50,000, wherein at least one of the anionic and cationic compounds is a polyelectrolyte. Dispersion according to claim 1, characterized in that the anionic compound and the cationic compound have a molecular weight of less than 20,000. Dispersion according to claim 1 or 2, characterized in that the anionic compound is an organic compound. Dispersion according to claim 1, 2 or 3, characterized in that the dispersant is anionic and comprises a cationic surfactant and an anionic polyelectrolyte. Dispersion according to claim 1, 2 or 3, characterized in that the dispersant is anionic and comprises a cationic polyelectrolyte and an anionic polyelectrolyte. tr j * Dispersion according to claim 1, 2 or 3, characterized in that the dispersant is cationic and comprises an anionic surfactant and a cationic polyelectrolyte. Dispersion according to claim 1, 2 or 3, characterized in that the dispersant is cationic and comprises an anionic polyelectrolyte and a cationic polyelectrolyte. Dispersion according to any one of the preceding claims, characterized in that it has a hydrophobic size of at least 20% by weight. Dispersion according to any one of the preceding claims, characterized in that the hydrophobic size is a cellulose-reactive size. Dispersion according to any one of the preceding claims, characterized in that the glue is a ketene dimer or an acid anhydride. Dispersion according to any one of claims 1 to 8, characterized in that the hydrophobic glue is a glue non-reactive with cellulose. Dispersion according to any one of the preceding claims, characterized in that the hydrophobic size has a melting point below 75 ° C. A process for preparing an aqueous dispersion by homogenizing a hydrophobic size in the presence of an aqueous phase and a dispersant comprising an anionic compound having a molecular weight of less than 50,000 selected from carbon containing compounds and silicon containing compounds and a cationic organic compound having a molecular weight of less than 50,000. one of the anionic and cationic compounds is a polyelectrolyte. 14. The method of claim 13, wherein the anionic compound and the cationic compound have a molecular weight of less than 20,000. The method of claim 13 or 14, wherein the anionic organic compound is an organic compound. Use of the aqueous dispersion according to any one of claims 1 to 12 as a paper size glue or surface size glue in the manufacture of paper. A substantially anhydrous sizing composition comprising a hydrophobic material, an anionic compound having a molecular weight of less than 50,000 selected from carbon-containing and silicon-containing compounds, and cationic organic compounds having a molecular weight of less than 50,000, wherein at least one of the anionic and cationic of the compounds is a polyelectrolyte. 18. The composition of claim 17, wherein the anionic compound is an organic compound. The composition of claim 17 or 18, wherein the hydrophobic sizing material is ketene dimer or acid anhydride. Use of a composition according to claim 17, 18 or 19 for the preparation of an aqueous dispersion according to any one of claims 1 to 20