SIZING COMPOSITION

Abstract: The present invention relates to a substantially water-free sizing composition, an aqueous sizing dispersion, the use for sizing or surface sizing paper and board and a process for the production of paper and board. The substantially water-free sizing composition comprises a cellulose reactive sizing agent and an esterified copolymer which is obtainable from a mixture comprising aliphatic olefins and derivatives of unsaturated carboxylic acids. More specifically, the composition comprises an esterified copolymer obtainable form a mixture comprising alpha -olefins and derivatives of alpha , beta -unsaturated dicarboxylic acids.

Description: Sizing Composition Field of the invention The present invention relates to sizing of paper and paperboard products. More specifically, the invention relates to a substantially water-free sizing composition and an aqueous sizing dispersion comprising a cellulose reactive sizing agent and an esterified copolymer obtainable from a mixture comprising aliphatic olefins and derivatives of unsaturated carboxylic acids. Background of the invention Cellulose-reactive sizing agents have long been used in conjunction with paper and paperboard production in order to introduce water repellence. The cellulose-reactive sizing agents are hydrophobic in their character, hence, they are not easily soluble in polar solvents such as water. Thus, before the sizing agent is added to a paper wet stock the cellulose-reactive sizing agent is dispersed in an aqueous medium. In order to achieve proper sizing of paper or board the particle size of the cellulose-reactive agent contained in the dispersion must be under a specific value. A small particle size of the cellulose-reactive agent is obtained by introducing high shear forces while forming the dispersion by using a high pressure dispersing unit. Cellulose-reactive sizing agents in general and substituted succinic anhydrides in particular decompose in the presence of aqueous media, i.e. they lose their sizing ability. Accordingly, sizing dispersions comprising cellulose-reactive sizing agents must be used fairly quick subsequent to their preparation. Substituted succinic anhydrides are even so unstable in the presence of aqueous media that dispersion containing such sizing agents must be formulated close to the location of the intended use, i.e. at the paper mill. Thus, the objective of the present invention is to provide a storage stable sizing composition comprising a cellulose-reactive sizing agent which is easily emulsifiable. Another objective of the present invention is to simplify the preparation of dispersions/emulsions comprising cellulose-reactive agent by omitting the use of high pressure emusifying/dispersing equipment. Still another objective is to simplify the preparation of dispersions/emulsions by forming emulsions without the addition of any additional emulsification agent which are not comprised in the compositions of the present invention. A still further objective is the reduction of cost for transporting the compositions of the present invention. Further objectives of the present invention are apparent from the text below. US 5266165 discloses copolymers of long chain olefins and maleic anhydride or itaconic anhydride in the form of the semiamides with morpholine which are comprised in aqueous sizing dispersions. WO 9916973 refers to an aqueous dispersion comprising cellulose-reactive size and cellulose non-reactive size, wherein the cellulose non-reactive size are copolymers of styrene or substituted styrene with vinyl monomers containing carboxyl groups or ethylenically unsaturated carboxylic acid. US 4695401 and US 4915786 refer to an ASA composition containing an emulsifier formed by the reaction of ASA and a nonionic water soluble compound having from 1 to 3 reactive polar groups. The latter compounds are exemplified particularly by polyethylene glycols or polypropylene glycols which may be capped at one end by an alkyl group. The product formed are esters, where polyalkylene glycols are linked to 1 to 3 ASA compounds. Summary of the invention The present invention relates to a substantially water-free sizing composition, an aqueous sizing dispersion, the use of a substantially water-free sizing composition and an aqueous sizing dispersion/emulsion for sizing or surface sizing paper or board, and a process for the production of paper and paperboard according to the claims. More specifically, the invention relates to a substantially water-free sizing composition comprising a cellulose-reactive sizing agent and an esterified copolymer obtainable from a mixture comprising aliphatic olefins and derivatives of unsaturated carboxylic acids. By providing substantially water-free sizing compositions storage stability is obtained. Furthermore, substantially water-free compositions can be transported over longer distances not only due to improved stability but due to the exclusion of water. Substantially water-free sizing compositions comprising cellulose-reactive sizing agents are further more resistant to temperature changes than aqueous dispersions. Detailed description of the invention According to the present invention the cellulose-reactive sizing agent is selected among any cellulose-reactive sizing agents known in the art. The cellulose-reactive sizing agents are suitably 2-oxetanone sizing compounds or substituted succinic anhydrides, commonly referred to as ASA, or mixtures thereof, ASA being especially preferred. Preferred 2-oxetanone sizing agents are mixtures of 2-oxetanone sizing compounds having at least one reactive 2-oxetanone group and pendant hydrophobic hydrocarbon groups. The mixture of 2-oxetanone compounds is suitably not solid at 35 °C. Preferably, the mixture of 2-oxetanone compounds is not solid at 25 °C, more preferably even at 20 °C. Even more preferably, the sizing agent is liquid at 35 °C, more preferably at 25 °C, and most preferably at 20 °C. The term "liquid" apply to the sizing agent per se and not to a composition or a dispersion. The preferred structure of 2- oxetanone sizing agents is as follows: (I) R" - C — HC— C— R'— C = C — CH — R I I I I o — c=o O — C = 0 n wherein n can be from 0 to 6, more preferably 0 to 3, and most preferably 0. R and R", which may be the same or different, are selected from the group of straight or branched alkyl or alkenyl chains. If n=0, then suitably not all are straight alkyl chains. Preferably, at least 25% by weight of the sizing agent consists of the 2-oxetanone structure in which at least one of R and R" is not straight chain alkyl. R and R" can be substantially hydrophobic in nature, are suitably acyclic, and are preferably at least 6 carbon atoms in length, more preferably from 8 up to 36, most preferably from 12 up to 20 carbon atoms in length. When n>0 the sizing agents are termed 2-oxetanone multimers. R' is preferably straight chain alkyl, more preferably a straight chain alkyl containing from 6 to 16 carbon atoms, most preferably containing from 8 to 20 carbon atoms. Preferably, the 2-oxetanone sizing agent is made from fatty acids or fatty acid chlorides containing irregularities such as double bonds and chain branching. Preferred fatty acid are selected from the group comprising oleic, linoleic, linoleic, palmitoleic, dodecenoic, tetradecenoic (myristoleic), hexadecenoic (palmitoleic), .octadecadienoic (linoelaidic), octadecatrienoic (linolenic), eicosenoic (gadoleic), eicosatetraenoic (archidionic), docosenoic (erucic), docosenoic (brassidic) and docosapentaenoic (clupanodinic) acids or mixtures thereof. According to one preferred embodiment of the present invention the cellulose- reactive sizing agent is suitable acid anhydrides such as substituted succinic anhydrides which may be characterized by the general formula (II) below, wherein R A and R B can be identical or different and represent saturated or unsaturated hydrocarbon groups suitably containing from 8 to 30 carbon atoms, or R A and R B together with the -C-O-C- moiety can form a 5 to 6 membered ring, optionally being further substituted with hydrocarbon groups containing up to 30 carbon atoms. Examples of acid anhydrides which are used commercially include alkyl and alkenyl succinic anhydrides and particularly isooctadecenyl succinic anhydride. Further examples of substituted succinic anhydrides are: iso-octadecyl succininc anhydride, n-hexadecenyl succinic anhydride, dodecenyl succinic anhydride, decenyl succininc anhydride, octenyl succinic anhydride, triisobytenyl succinic anhydride, 1-octyl-2- decenyl-succinic anhydride and 1-hexyl-2-octenyl-succinic anhydride. (II) O O R Λ A — C II — O — I C' — R B B Suitable ketene dimers and acid anhydrides include the compounds disclosed in U.S. Pat. No. 4,522,686, US 3102064, US 3821069, US 3968005 which are hereby incorporated by reference. The esterified copolymer suitably functioning as an emulsifier in the present invention is preferably a copolymer obtainable from a reaction mixture comprising one or more aliphatic olefins and one or more derivatives of unsaturated carboxylic acids. Suitably the copolymer is prepared from a monomer mixture comprising one or more aliphatic olefins and one or more unsaturated carboxylic acids with the proviso that the mixture is free from alkyl acrylates. Suitable copolymers are disclosed in DE 3136931 A1 , which is hereby incorporated by reference. The aliphatic olefins used for obtaining the copolymer are preferably aliphatic α- olefins, usually containing from about 3 up to about 36 carbon atoms, preferably containing from about 8 up to about 30 carbon atoms, more preferably from about 12 up to about 26 carbon atoms and most preferably from 14 up to 24 carbon atoms. The aliphatic olefins are suitably linear or branched or mixtures of linear or branched olefins, although linear olefins are more preferred. According to one preferred embodiment of the invention the esterified copolymer is prepared from a mixture comprising aliphatic olefins and derivatives of unsaturated dicarboxylic acids. The term unsaturated dicarboxylic acids encompasses also unsaturated acid anhydrides. Suitably, the derivatives of unsaturated dicarboxylic acids are derivatives of α-β-unsaturated dicarboxylic acids, whereby the α-β-unsaturated dicarboxylic acids may be maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, aconitric acid and the like, whereby maleic acid and fumaric acid are preferred. The derivatives of unsaturated dicarboxylic acids, such as α-β-unsaturated dicarboxylic acids, are suitably esters of dicarboxylic acids, such as diesters or monoesters of unsaturated dicarboxylic acids, the monoesters being preferred. The derivatives of unsaturated dicarboxylic acids suitably comprise a compound comprising a hydrophilic moiety, said hydrophilic moiety being covalently linked to the unsaturated dicarboxylic acid by an ester function, i.e. the derivatives of unsaturated dicarboxylic acids are suitably esterified with a compound comprising a hydrophilic moiety such as a polyalkylene oxide alkyl ether. The polyalkylene oxide alkyl ether suitably comprises from 1 up to 45 alkylene oxide groups, more preferably from 5 up to 30 and most preferably from 7 up to 25 alkylene oxide groups. Suitable polyalkylene oxides are polyethylene oxides and polypropylene oxides, wherein polyethylene oxide alkyl ethers are preferred. The alkyl group of the polyalkylene oxide alkyl ether preferably comprises from 1 up to 36 carbon atoms, suitably from 1 up to 8 carbon atoms, and most preferably linear alkyl groups comprising from 1 up to 8 carbon atoms. The alkyl group may be linear or branched. The average molecular weight of the emulsifier is suitably from 1000 up to 100000, preferably from 10000 up to 50000. The copolymers are suitably accessible in two manners. According to one embodiment the copolymer is suitably obtainable by copolymerisation of an olefin and a derivative of an unsaturated dicarboxylic acid or anhydride followed by esterification with a compound comprising a hydrophilic moiety. The unsaturated dicarboxylic acids and olefins are preferably copolymerised at temperatures ranging from 70 °C up to 250 °C in the presence of a peroxide catalyst in an inert gas atmosphere. The molar ratio of unsaturated dicarboxylic acids to olefins can range from 0.5:1 up to 4:1 , more preferably from 0.8:1 up to 3:1. The molar ratio of compounds comprising a hydrophilic moiety to unsaturated dicarboxylic acids are suitably from 0.5:1 up to 3:1 more preferably from 1 :1 up to 2:1. According to this reaction path, the obtained copolymer (emulsifier) can have a molar ratio of olefins to unsaturated dicarboxylic acids around 1 :1. According to another embodiment the copolymer is accessible from already esterified unsaturated dicarboxylic acids which are copolymerised with olefins. This process can be characterised in that olefins and esterified unsaturated dicarboxylic acids are copolymerised at temperatures from about 120 °C up to 250 °C in the presence of a peroxide catalyst and an inert gas atmosphere. The molar ratio of esterified unsaturated dicarboxylic acids to olefins in the reaction mixture may vary from 1 :0.5 up to 1 :7. According to this embodiment copolymers are suitably obtained having a molar ratio of olefins to unsaturated dicarboxylic acids ranging from 0.5:1 up to 4:1. Furthermore, the copolymer suitably has a main chain consisting of carbon atoms. The present invention provides both a substantially water-free sizing composition and an aqueous sizing dispersion, wherein the dispersion comprises a cellulose-reactive sizing agent and an esterified copolymer obtainable from a mixture comprising aliphatic olefins and derivatives of unsaturated carboxylic acids. By substantially water-free is meant that a small amount of water can be present; the water content can be from 0 up to 10% by weight, suitably less than 5% by weight and preferably less than 2%. Most preferably the substantially water-free composition is free from water, i.e. the composition contains less than 0,1% water. The invention also encompasses a method for obtaining an aqueous sizing dispersion comprising dispersing a substantially water-free composition comprising a cellulose-reactive sizing agent and an esterified copolymer obtainable from a mixture comprising aliphatic olefins and derivatives of unsaturated carboxylic acids in the presence of an aqueous solution, wherein preferably low shear forces are used. The present invention refers also to the use of a substantially water-free composition or an aqueous sizing dispersion for sizing or surface sizing of paper or board. The substantially water-free composition suitably contains the emulsifier from about 0,1 up to 50 weight %, more preferably from 0,5 up to 20 weight % and most preferably from 5 up to 15 weight %, the rest in said compositions suitably being substantially cellulose-reactive sizing agent. The copolymer is preferably mixed with the cellulose-reactive sizing agent under gentle heating, suitably at a temperature from 30°C up to 100°C. The substantially water-free composition according to the present invention has excellent storage stability due to the absence of chemical moieties which reacts with the cellulose-reactive sizing agent. Hence, the sizing composition can be formulated at a location other than the location for intended use. The composition can be stored for extended periods of time at elevated temperatures without impairing the particle size and/or particle size distribution and/or loosing sizing performance subsequent disperion/emulsification. The substantially water-free composition is preferably emulsified immediately before being feed to the wet stock. However, the substantially water-free composition may be introduced directly into the wet stock provided that proper amount of shear forces are present in order to attain suitable particle size of the cellulose-reactive sizing agent. The composition is preferably emulsified in the presence of an aqueous phase. The present substantially water-free composition is preferably emulsified using low-shear forces. The distinction between high shear and low shear conditions is well known in the art. Low-shear forces are preferably introduced without the necessity of high shear turbine pumps or high pressure homogenisation, but merely by stirring, by using low- shear venturi system, by passing through a mixing valve, or by using agitation present in the paper stock preparation system. Moreover, shear forces can also be introduced by using an impeller stirrer. Regardless by which means the shear forced are applied the resulting aqueous emulsion has a narrow particle size distribution an appropriate particle size. The aqueous sizing dispersion preferably has at least about 0,5 weight % of cellulose-reactive sizing agent, more preferably from about 0,5 up to 20 weight %, and most preferably from 1 up to 5 weight %. According to yet another preferred embodiment of the invention the composition and/or dispersion can comprise common fixing agents, stabilising agents and/or activators, (hereinafter called additives) known to the person skilled in the art such as anionic compounds, cationic compounds or amphoteric compounds or mixtures thereof exemplified by cationic or amphoteric starch, polyamine, polyamideamine, or additional vinyl addition polymers. These additives are suitably added when preparing the aqueous dispersion more preferably they are added subsequent the emulsification. The composition/emulsion of this invention can be used as sizing agent in conventional manner in a process for the production of paper or board using any type of cellulosic fibres. Preferably, the present invention ' can be used in a process for the production of paper or board by the addition of the substantially water-free composition or the aqueous emulsion of a sizing agent to a stock containing cellulosic fibres and optional fillers, dewatering the stock on a wire to obtain paper or board and white water. Furthermore, the use of the emulsion is not limited to internal sizing, thus the emulsion is also used for surface or stock sizing. The term "paper" should be interpreted in a wide meaning including all types of cellulose-based products in sheet or web form such as board and paperboard. The stock comprises cellulosic fibres, optionally in combination with mineral fillers with a content of cellulosic fibres of at least 50 % by weight, based on dry stock. Examples of mineral fillers include kaolin, china clay, titanium oxide, gypsum, talc and natural and synthetic calcium carbonates such as chalk, ground marble and precipitated calcium carbonate. The amount of cellulose-reactive sizing agent added to the stock can vary from 0,01 up to 5 % by weight suitably from 0,05 up to 1 ,0 % by weight, based on dry weight of cellulosic fibres and optional fillers, where the dosage mainly is dependent on the quality of the pulp or paper, the sizing agent used and the level of sizing desired. Conventional chemicals added to the stock in papermaking such as retention aids, aluminium compounds, dyes, wet-strength resins, optical brightening agent can be used together with the present sizing composition/emulsion. Examples of suitable retention aids include cationic polymers or cationic inorganic materials in conjunction organic polymers, such as bentonite in combination with cationic polymers, silica-based sols in combination with cationic polymers or cationic and anionic polymers. Particularly good stock sizing can be achieved when using the composition/emulsion of the invention with retention aids comprising cationic polymers. Suitable cationic polymers include cationic starch, guar gum, acrylate and acrylamide-based polymers, polyethyleneimine, dicyanamide-formaldehyd, polyamines, polyamidoamines and poly(diallyldimethyl ammoniumchloride) and combinations thereof. Cationic starch and cationic acrylamide- based polymers are preferably used, either alone or in combination. In a preferred embodiment of the invention, the emulsions are used in combination with a retention system comprising at least one cationic polymer and anionic silica-based particles. The present emulsion can be added before, between, after or simultaneously with the addition of the cationic polymer or polymers. It is also possible to pre-mix the size emulsion with a retention aid, e.g. a cationic polymer or an anionic silica-based material, prior to introducing the mixture thus obtained into the stock. The invention is further illustrated in the following examples, which, however, are not intended to limit the same. Parts and % relate to parts by weight and % by weight, respectively, unless otherwise stated Example 1 Materials Alkenyl succinic anhydride The sizing agent used was the reaction product of maleic anhydride and straight-chain internal C 16/18 olefin. Emulsifier Different emulsifiers according to the invention were produced by the copolymerisation of an α-olefin and maleic anhydride esterified with 1 mol of methyl polyethylene glycolether (MPEG) per 1 mol of maleic anhydride. The emulsifier products are specified in the table below in terms of chain length of the starting α-olefin, molar ratio of α-olefin to esterified maleic anhydride and molecular weight of the methyl polyethylene glycol (MPEG). table Preparation of sizing compositions The emulsifier (A-F) was mixed in an appropriate amount with ASA, yielding a clear solution. This mixture was kept for at least 2 hour at 80 °C before the full emulsifying power was obtained. Each of the sizing compositions containing the emulsifiers were evaluated regarding particle size distribution subsequent emulsification. The emulsification in water was accomplished within a set period of time at low shear by means of an impeller stirrer. A beaker (250 ml) was charged with 100 ml of cold tap water. 3 g of the ASA/emulsifier composition was added under stirring (1600 rpm). The resulting compositions/emulsions were analysed for particle size distribution using a Mastersizer μ (Malvern Instruments). The results, which were obtained with different emulsifiers, are summarised in table II. 50% (90%) of all particles are not greater than the number given by Dv 50 (Dv 90). Small particles, in particular the 90% value is a prerequisite for good sizing performance. table II ASA and emulsifier blended at 80 °C during 2 hours. The emulsification was performed after 1 month storage time at 20 °C. Example 2 The emulsifiers of the present invention were compared with prior art emulsifiers. Emulsifier A, according to the invention, was compared to an emulsifier generated in-situ by reacting an appropriate amount of polyethylene glycol precursor (PEG) or methoxy polyethylene glycol precursor (MPEG) with ASA. The effective amount of emulsifier content is the sum of added PEG or MPEG and the equivalent of ASA that was esterified with the PEG or MPEG. It is taken into account that also the polymeric emulsifier of the present invention contains up to 2 weight % of MPEG, which reacts with ASA, thus yielding a higher effective emulsifier concentration. The ASA emulsifier compositions of the following examples were made by mixing into ASA an appropriate amount of PEG, MPEG or polymeric emulsifier of the present invention, respectively, so that the resulting composition was 200 g in total with an effective emulsifier concentration of 12 % by weight. The compositions were made at 80 °C under stirring with a magnetic stirrer and they were kept for additional 2 A hour in a sealed glass at 80 °C in an oven. table III * resulting in 12% effective emulsifier after reaction with ASA Table III show that the emulsifiability of a sizing composition of the present invention after storage is significantly improved compared to prior art emulsifiers. Example 3 Sizing tests were performed using a furnish of a 70/30 blend of hardwood/softwood (36 ° SR freeness). As filler was used 15 weight % calciumcarbonate (Albacar HO) and the retention system was Compozil S with 1 weight % cationic potato starch (Hi-Cat 142, Roquette) and 0,5 weight % silicasol BMA-0 (Eka Chemicals). Aluminium sulphate was used at an amount of 0,15 weight %, resulting in a pH of 7,8 in the headbox. The ASA emulsion used as sizing agent was prepared by emulsification of an ASA- emulsifier composition with 10 weight % of emulsifier A (Dapral GE202) according to example 1. The sizing results at different addition rates and the particle size distribution of the ASA emulsions are shown in table IV. table IV From table IV it is apparent, that the composition according to the invention shows excellent sizing properties.

Claims: Claims 1. A substantially waer-free sizing composition characterised in that the composition comprises a cellulose-reactive sizing agent and an esterified copolymer obtainable from a mixture comprising aliphatic olefins and derivatives of unsaturated carboxylic acids. 2. A sizing composition according to claim ^ ch aracterised in that the derivatives of the unsaturated carboxylic acids are derivatives of unsaturated dicarboxylic acids. 3. A sizing composition according to claim 2, ch a racterised in that the derivatives of the unsaturated dicarboxylic acids are esterified α-β unsaturated dicarboxylic acids. 4. A sizing composition according to claim 2, cha racterised in that the derivative of the unsaturated dicarboxylic acids are monoesters of unsaturated dicarboxylic acids. 5. A sizing composition according to claim 2, cha racterised in that the derivatives of the unsaturated dicarboxylic acids are diesters of unsaturated dicarboxylic acids. 6. A sizing composition according to claims 2-5, characterised in that the unsaturated dicarboxylic acids are esterified with a compound comprising a hydrophilic moiety. 7. A sizing composition according to claims 2-6, characte rised in that the unsaturated dicarboxylic acids are esterified with polyalkylene oxide alkyl ether. 8. A sizing composition according to claim 7, characterised in that the polyalkylene oxide alkyl ether contains from 1 up to 45 alkylene oxide groups. 9. A sizing composition according to claims 7-8, characterised in that the alkyl group of the polyalkylene oxide alkyl ether contains from 1 up to 36 carbon atoms. 10. A sizing composition according to any of the preceding claims ch a racterised in that the cellulose-reactive sizing agent is a substituted succinic anhydride or a 2-oxetanone compound. 11. A sizing composition according to any of the preceding claims cha racte ri sed in that the cellulose-reactive sizing agent is a substituted succinic anhydride. 12. Use of the substantially water-free composition defined by claims 1-11 for sizing or surface sizing paper or board. 13. A process for the production of paper or board by the addition of a substantially water-free sizing composition defined by claims 1-11 to a stock containing cellulosic fibres and optional fillers, dewatering the stock on a wire to obtain paper or board and white water. 14. An aqueous sizing dispersion, characterised in that dispersion comprises a cellulose-reactive sizing agent and an esterified copolymer obtainable from a mixture comprising aliphatic olefins and derivatives of unsaturated carboxylic acids. 15. An aqueous sizing dispersion according to claim 14, characterised in that the amount of cellulose-reactive sizing agent is at least 0,5 weight %. 16. Use of the aqueous sizing dispersion defined by claims 14 and 15 for sizing or surface sizing paper or board 17. A process for the production of paper or board by the addition of an aqueous sizing dispersion defined by claim 14 to a stock containing cellulosic fibres and optional fillers, dewatering the stock on a wire to obtain paper or board and white water. 18. A method for obtaining an aqueous sizing dispersion comprising dispersing a substantially water-free composition defined by claims 1-11 in the presence of an aqueous solution.

Inventors: HOFFMANN JOCHEN, KRUECKEL RALF, MILLS ROBERT J, VAN DE BERG ALBERT, HOFFMANN, JOCHEN, KRUECKEL, RALF, MILLS, ROBERT, J., VAN DE BERG, ALBERT
Applicants: AKZO NOBEL NV, BERG ALBERT VAN DE, EKA CHEMICALS AB, HOFFMANN JOCHEN, KRUECKEL RALF, MILLS ROBERT J, AKZO NOBEL N.V., HOFFMANN, JOCHEN, KRUECKEL, RALF, MILLS, ROBERT, J., VAN DE BERG, ALBERT
Application year: 2000
Main classification: D21H21
IPC codes: B01F17, D21H17, D21H21