Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/06—Paper forming aids
  • D21H21/10—Retention agents or drainage improvers
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/16—Sizing or water-repelling agents
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/71—Mixtures of material ; Pulp or paper comprising several different materials not incorporated by special processes
  • D21H17/72—Mixtures of material ; Pulp or paper comprising several different materials not incorporated by special processes of organic material

Definitions

• the present invention refers to a process for sizing paper comprising adding to a cellulosic suspension an aqueous composition containing particles having a weight average diameter of at least 5 ⁇ m comprising a sizing agent, whereby the composition is formed by mixing in any order, a solution of a coagulation agent and an aqueous dispersion comprising a sizing agent.
• the invention also encompasses an aqueous sizing composition.
• sizing agents In order to obtain a paper which is suited for printing and other commercial applications different kinds of performance chemicals are added to the cellulosic suspensions in the paper mill.
• One type of compounds which are added serve the purpose of rendering the paper more resistant to the penetration of liquids such as aqueous solutions and are commonly referred to as sizing agents.
• These sizing agents often contain hydrophobic moieties, whereby the compounds are either covalently bound to the cellulosic fibres or alternatively only associated to the fibres.
• the performance of the sizing agents which are usually added to the suspension in from of a dispersion or emulsion is influenced by numerous factors such as the type of pulp in the suspension, i.e.
• Contaminants present in the suspension which have an effect on the retention of sizing agents are inter alia ionic compounds ranging from salts to polymers having a substantial molecular weight.
• the existence of charged polymeric compounds like xylanes in the suspension is often indicated by measuring the cationic demand of the suspension. A higher cationic demand signifies a higher concentration of charged polymeric compounds in the suspension.
• Suspensions with high cationic demands can originate from type of pulp used, i.e. recycled paper, diluting water used, and the degree of re-circulation of the white-water in the paper-mill.
• a paper-mill where the white-water is extensively recirculated tend to end up with a suspension having a high cationic demand. Accordingly, one objective with the present invention is to provide a process for sizing paper, where the paper is formed from a suspension containing cellulosic fibres having a high cationic demand and/or a high conductivity. A further objective is to improve the retention of the sizing agent, specifically the so called first pass retention.
• the sizing composition according to the present invention may even render paper which is sufficiently sized without the additional addition of retention agents. Further objectives will be apparent hereinafter.
• the sizing agent per se is a compound with a hydrophobic character, therefore, it is virtually impossible to disperse/emulsify the sizing agent in an aqueous solution without the presence of compounds which effect or facilitate the formation of a dispersion.
• further compounds may be required in order to stabilise the dispersion.
• the formation of a sizing dispersion prior to the addition of the sizing agent to the suspension is in principle a prerequisite in order to obtain a paper which is sufficiently sized.
• the particle size or the weight average particle size of the particles containing the sizing agent has an influence on the sizing efficiency. Better sizing according to common practice is achieved if the particles containing the sizing agent are as small as possible, suitable below 1 ⁇ m.
• the object with the present invention is to render a composition comprising particles containing the sizing agent which are substantially larger than sizing particles in conventional dispersions. It has surprisingly been shown that the process and composition according to the present invention renders a paper which is sufficiently sized, i.e. a cobb-value below 30, even without the use of retention agents. In addition, the process and composition significantly improves sizing when applied to cellulosic suspensions having a high cationic demand and/or high conductivity.
• a sizing dispersion which is stabilised by a cationic colloidal coacervate stabilising agent, where the coacervate agent contains an anionic component and a cationic component.
• the anionic and cationic components must be present in a proportion so that the zeta potential of the dispersion is at least 20 mV, though a zeta potential of at least 40 mV is more preferable.
• the objective with the coacervate agent is to stabilise the emulsified or dispersed sizing agent.
• the present invention refers to a process for sizing paper and a sizing composition according to the claims. More specifically, the present invention relates to a process for sizing paper comprising providing an aqueous suspension comprising cellulosic fibres, dewatering said aqueous suspension thereby forming a paper web, said process comprising adding to the cellulosic suspension an aqueous composition comprising particles comprising a sizing agent obtainable by mixing in any order prior to the addition to the aqueous suspension, (i) a solution comprising at least one coagulation agent, and (ii) an aqueous dispersion comprising a sizing agent, wherein the particles of the composition comprising a sizing agent have a weight average diameter of at least 5 ⁇ m.
• the invention also enclose an aqueous sizing composition as specified in the claims.
• the aqueous composition containing particles comprising having a weight average diameter of at least 5 ⁇ m is obtained by mixing in any order prior to the addition to the aqueous suspension (i) a solution comprises at least one charged coagulation agent, and (ii) a charged aqueous dispersion comprising a sizing agent, whereby the charge of the coagulating agent is opposite the charge of the dispersion.
• the present invention refers to a process for sizing paper comprising adding the composition containing particles comprising a sizing agent to the suspension without adding a retention agent or retention agents to said suspension.
• the coagulation agent of the solution can virtually be any compound or mixture of compounds provided that said coagulation agent effects flocculation/agglomeration of the sizing particles when mixing the solution of the coagulation agent and the sizing agent dispersion.
• the coagulation agent is selected from the group consisting of non-ionic polymers, polyelectrolytes, surfactants, silica-based particles, inorganic aluminium-containing compounds, and mixtures thereof. If charged coagulation agents are comprised in the aqueous solution then the aqueous sizing dispersion should preferably have the opposite charge.
• non-ionic polymers are polyalkylene oxides, also referred to as polyalkylene glycols, specifically polyethylene oxides and phenolic resins.
• the phenolic resins which can be selected are polycondensation products of phenols and aldehydes, preferably formaldehyde, commonly referred to as resols and novolacs, and phenolic resins modified by natural resins, i.e. rosin acids from e.g. gum rosin, wood rosin and tall-oil rosin.
• rosin acids e.g. gum rosin, wood rosin and tall-oil rosin.
• mixtures of polyalkylene oxides and phenolic resins are used as coagulating agent. It is favourable if the non-ionic polymers are water-soluble or water-dispersible.
• the present invention is directed to a process for sizing paper where an aqueous composition is formed by providing a charged aqueous dispersion or emulsion of a sizing agent (depending on the physical state of the sizing agent at ambient temperature), and an aqueous solution comprising a charged coagulation agent, wherein the charge of the coagulation agent is opposite the charge of the dispersion, mixing the dispersion and the solution thereby obtaining the aqueous composition comprising particles containing a sizing agent having a weight average diameter of at least 5 ⁇ m.
• charged aqueous dispersion of the claims is also meant a charged aqueous emulsion depending on the type of sizing agent present in the dispersion. If, for example, a sizing agent is present which is solid or mostly solid at ambient temperature a dispersion is formed, however, if the sizing agent is liquid at ambient temperature an emulsion is obtained.
• charged dispersion refers to the overall charge of the dispersing/stabiiising system of the dispersion.
• the charge is either positive or negative depending on the charge of the dispersion. Accordingly, the coagulation agent should not contain an equal amount of negative and positive charges. Accordingly, the charged coagulation agent is suitably anionic or cationic, i.e. the agent may have an anionic or cationic overall charge, whereby the coagulation agent can have only anionic groups, solely cationic groups or both anionic and cationic groups, the latter referred to as amphoteric coagulation agents.
• the order of mixing the solution with the dispersion does not seem to be of relevance.
• the solution comprising the coagulation agent is added to the aqueous dispersion. Any method of mixing the dispersion and the solution can be applied, though, suitably the addition of the solution is adjusted so that the zeta potential of the formed aqueous composition is up to at least about 20 mV thereby obtaining particles comprising the sizing agent having a weight average diameter of at least 5 ⁇ m provided a solution containing a charged coagulation agent is used.
• the zeta potential is around the iso-electric point of the composition, for example, from about -10 mV up to about 10mV, preferably from about -5 mV up to about 5 mV.
• zeta potential of the obtained composition after mixing may have an influence on the flocculation, thus, a zeta potential of the obtained composition suitably up to at least about 20 mV seems to be favourable. It is believed that a zeta potential of the composition after mixing of over 20 mV can be disadvantageous for preserving the size of the particles, i.e. the agglomerates; containing the sizing agent.
• the zeta potential of the composition may be up to about 18 mV, more preferably up to at least 15 mV, suitably up to about 10 mV.
• the zeta potential of the composition after mixing may even be as low as around the iso-electric point of the composition, i.e. from about -5 mV up to about +5 mV.
• the charge of the aqueous composition i.e. the dispersion/stabilising system is commonly verified by measuring the zeta potential.
• a positive value of the zeta potential indicates a cationic dispersion, whereas a negative zeta potential indicates an anionic dispersion.
• the zeta potential can be measured using particle micro electrophoresis as described in the text book "Introduction to colloid and surface chemistry", Shaw.
• the particles comprising the sizing agent are loosely packed agglomerates where the sizing agent is evenly distributed within the agglomerate.
• the particles comprise from 0.01 to 10 % by weight of the sizing agent based, preferably from 0.1 to 5.0, more preferably from 0.1 to 1.0, the rest mainly believed to constitute water, coagulation agent and optionally dispersing/stabilising agents from the aqueous sizing dispersion.
• sizing particles of dispersions which are larger or considerably larger that sizing particles in the micron range, around 1 ⁇ m, cause poor distribution of the sizing agent in the paper web, eventually leading to impaired sizing of the paper.
• the particles comprised in the composition of the present, having the sizing agent evenly distributed within the particles provide for effective spreading of the sizing agent at reasonable dosage of the composition over the fibre surface during the drying phase.
• a composition comprising particles of the sizing agent having a weight average diameter of at least about 5 ⁇ m, suitably at least about 10 ⁇ m, more preferably at least about 15 ⁇ m.
• the upper weight average diameter of the particles can vary significantly depending on process parameters such as type of cellulosic suspension and other performance chemicals added to the suspensions like dry strength agents, wet strength agents, etc.
• the weight average diameter of the particles is suitably below 250 ⁇ m, preferably below 100 ⁇ m, more preferably below 80 ⁇ m.
• Preferred ranges of the weight average diameter of the particles are from about 10 ⁇ m up to about 100 ⁇ m, suitably from about 15 ⁇ m up to about 60 ⁇ m, more preferably from about 15 ⁇ m up to about 50 ⁇ m.
• weight average diameter of the particles is measured using a Malvern Mastersizer Microplus (Malvern Instruments Ltd.) with a small volume cell top.
• weight average diameter in the claims is meant the particle size distribution presented as PSD D(v.0.5), representing a volume weighted particle size for which 50% of the particles is below the value given.
• the charged coagulation agent is preferably selected from the group consisting of polyelectrolytes, silica-based particles, inorganic aluminium-containing compounds, and mixtures thereof.
• the composition of the charged aqueous dispersion comprising a sizing agent is not critical as long as the overall charge is cationic or anionic.
• the dispersion suitably comprises compounds which facilitate the formation of dispersed sizing particles and stabilises the sizing particles.
• Such dispersing/stabilising agents are preferably naturally polymers such as polysaccharides like cellulose derivatives and starches, and synthetic polymers, i.e. vinyl addition polymers and condensation polymers.
• the particle size of the sizing agent of the dispersion may range from about 0.1 up to about 2 ⁇ m.
• the charged aqueous dispersion may further to the above mentioned stabilising/dispersion agents or instead of such agents contain any of the agents referred to as coagulation agents in this application.
• the type and amount of dispersion/stabilising agents and/or coagulation agents of the dispersion are so chosen that the dispersion is rendered anionic or cationic.
• the charge of the dispersion is suitably measured by particle micro electrophoresis.
• Preferred charged coagulation agents are polyelectrolytes which can be cationic or anionic, i.e. having an overall anionic or cationic charge.
• the polyelectrolyte comprised in the aqueous solution has suitably a weight average molecular weight of at least about 6,000, preferably at least about 10,000 and is commonly water-dispersible or water-soluble. Usually, the weight average molecular weight is below about 10,000,000 and more preferably from about 100,000 up to about 1,000,000.
• the polyelectrolyte may have a charge density of at least about 0.1 meq/g.
• Common charge densities range from about 0.1 up to about 18 meq/g, more preferably from about 0.1 up to about 12 meq/g, typically from about 0.5 up to about 6 meq/g.
• the cationic or anionic polyelectrolyte may also have charged groups of the opposite charge, commonly referred to as amphoteric polyelectrolytes.
• the charged polyelectrolyte is suitably selected from the group consisting of polysaccharides, vinyl addition polymers, condensation polymers, and mixtures thereof.
• cationic polyelectrolytes are present in the solution comprising the coagulation agent they may be of similar type or a mixture of different cationic polyelectrolytes.
• the cationic polyelectrolyte is suitably selected from the group consisting of polysaccharides, e.g. starches which can be derived from potato, corn, just to mention a few, suitably having tertiary anime groups, quaternary ammonium groups or reaction products of trimethylamine and epichlorohydrine; condensation polymers such as polyepihalohydrines, polyamideamines, poltethyleneimines, and the like, chain-reaction polymers exemplified by vinyladdition polymers, i.e. polyacrylamide, co-polymers of acrylates and acrylamide, diallyldimethylammonium chloride polymers referred to as poly-DADMAC.
• polysaccharides e.g. starches which can be derived from potato, corn, just to mention a
• anionic polyelectrolytes are comprised in the solution of the coagulation agent the anionic polyelectrolytes may constitute a mixture of different anionic polyelectrolytes or only a specific anionic polyelectrolyte.
• the anionic polyelectrolyte is suitably selected from the group consisting of polysaccahides, condesation polymers and chain-reaction polymers. Suitable anionic polyelectrolyte are carboxylated cellulose, e.g. carboxymethylcellulose; phosphate modified polysaccharides, e.g.
• polyacrylates such as polyacrylamides
• polysulfates exemplified by polyvinyl sulfate, polyethylene sulfate, etc
• polysulfonates like polyvinyl sulfonate, lignin sulfonate, condensated naphthalene sulfonate, anio.
• Coagulation agents from the group of silica-based particles include inter alia colloidal silica, colloidal borosilicates, aluminium-modified silica or aluminium silicates, polyaluminosilicate microgels, and mixtures thereof.
• the silica-based particles are often referred to as silica sols.
• the particles can be colloidal, i.e. in the colloidal range of particle size, or preferably amorphous or essentially amorphous.
• the silica-based sols can also be modified and contain other elements, e.g. aluminium and/or boron, which can be present in the aqueous phase and/or in the silica-based particles.
• Suitable silica-based particles of this type include colloidal aluminium-modified silica and aluminium silicates. Mixtures of such suitable silica-based particles can also be used.
• Anionic silica-based particles are suitably structured anionic silica sols, where the silica particles can have a specific surface area within the range from 30 to 1200 m 2 /g and an S-value of typically within the range of from 8 to 45 per cent, suitably from 10 to 35 per cent and preferably from 10 to 30.
• the specific surface area can be measured by means of titration with NaOH in known manner, e.g. as described by Sears in Analytical Chemistry 28(1956):12, 1981-1983 and in U.S. Patent No.
• the given S-value can be measured and calculated as described by Iler, R.K. & Dalton, R.L. i J. Phys. Chem. 60(1956), 955-957.
• the S-value can be said to be a measure of the degree of aggregate or microgel formation and a lower S-value indicates a higher microgel content and can be seen as a measure of the amount of SiO 2 , in per cent by weight, in the disperse phase.
• the silica particles of the structured sols are commonly surface modified with aluminium to a degree of 2 to 25 per cent, suitably from 3 to 20 per cent. With an aluminium surface modification degree is meant the number of aluminium atoms which has replaced silicon atoms in the particle surface.
• the degree of modification is given in per cent and is calculated on basis of 8 silanol groups per nm 2 . This is described by Iler, R.K. in Journal of Colloidal and Interface Science, 55(1976):1, 25-34.
• the S-value given for the sols is to a high degree correlated to the particle size distribution.
• Cationic silica-based particles i.e. sols of cationic silica-based particles
• the silica particles are coated with one polyvalent metal-oxygen compound, suitably with tri- and tetravalent metal-oxygen compound such as aluminium, chromium, gallium, titanium and zirconium, whereby aluminium is especially preferred.
• Suitable anionic counter ions include halides such as chloride, acetate or nitrate.
• the positively charged colloidal silica particles are inorganic silica particles which may be surface-modified, preferably with aluminium such as various oxides and hydroxides of aluminium.
• the positively charged silica particles can have a particle size less than about 500 nm and usually greater than 1.0 nm.
• the specific surface area of the silica particles can be in the range of about 5 to about 1800 m 2 /g, suitably in the range of from about 30 to about 1200 m 2 /g and more preferably from 50 to 1000 m 2 /g.
• the positively charged colloidal aluminium-modified silica particles preferably have a weight ratio of Al 2 O 3 to SiO 2 in the range from 1:20 up to 4:1, suitably from 1:10 up to 2:1 and most preferably in the range from 1:5 to 1:1.
• Suitable inorganic aluminium-containing compounds functioning as coagulating agents are salts comprising aluminium such as aluminium sulphate, commonly referred to as alum, aluminium chloride and various inorganic polyaluminium compounds like polyaluminium chloride, polyaluminium chloride compounds containing sulphate and polyaluminium hydroxy silicate sulphate compounds.
• Polyaluminium compounds are based on aluminium, hydroxy groups and anions, they are termed basic and in aqueous solutions they are polynuclear complexes.
• polyaluminium compounds can have the general formula Al n (OH) m X 3n-m wherein X is a negative ion such as chloride or acetate and both n and m are positive integers so that 3 n-m is greater than 0.
• Polyaluminium chlorides can also contain anions from sulphuric acid, phosphoric acid, polyphosphoric acid, chromic acid, di-chromic acid, silicic acid, citric acid, carboxylic acids or sulphonic acids.
• Commercially available inorganic aluminium-containing compounds are e.g.
• Ekoflock produced and sold by Eka Chemicals AB, Sachtoklar (R) , sold by Sachtleben Chemie in Germany, the sulphate-containing WAC sold by Atochem in France, the highly basic polyaluminium chloride compound Locron sold by Hoechst AG in Germany, poly(hydroxyaluminium)sulphate Omniklir, sold by OmniKem, USA, Niaproof, which is an aluminium hydroxy acetate, sold by Niacet in the USA and Alzofix which is based on polyaluminium chloride and dicyandiamide, sold by SKW Trostberg, Germany.
• the sizing agent may be flocculated by changing the pH of the dispersion with the addition of a suitable acid or base.
• sizing dispersions containing aluminium-containing compounds are acidic, i.e. the dispersions have a pH in the range from 2-5. Accordingly, by increasing the pH of acidic dispersion, suitably to neutral levels (pH from 6 to 7.5) or even to slightly alkaline levels (pH from 8 to10) flocculation of the sizing agent can be induced.
• the type of sizing agent comprised in the aqueous dispersion is not critical, thus, any sizing agent known to the skilled person may be used such as non-cellulose-reactive agents including rosins, e.g. fortified and/or esterified rosins, waxes, fatty acids and resin acid derivatives, e.g. fatty amides and fatty esters, e.g. glycerol triesters of natural fatty acids, and cellulose-reactive agents.
• the aqueous dispersion may be an anionic or cationic dispersion comprising a rosin sizing agent.
• preferred sizing agents comprised in the aqueous dispersion are non-rosin sizing agents, suitably selected from the group consisting of cellulose-reactive sizing agents.
• Suitable cellulose-reactive sizing agents are selected from the group consisting of hydrophobic ketene dimers, ketene dimer multimers, acid anhydrides, organic isocyanates, carbamoyl chlorides and mixtures thereof, preferably selected from the group consisting of ketene dimers and acid anhydrides, most preferably ketene dimers.
• Suitable ketene dimers have the general formula (I) below, wherein R 1 and R 2 represent saturated or unsaturated hydrocarbon groups, usually saturated hydrocarbons, the hydrocarbon groups suitably having from 8 to 36 carbon atoms, usually being straight or branched chain alkyl groups having 12 to 20 carbon atoms, such as hexadecyl and octadecyl groups.
• the ketene dimers may be liquid at ambient temperature, i.e. at 25 °C, suitably at 20 °C.
• acid anhydrides can be characterized by the general formula (II) below, wherein R 3 and R 4 can be identical or different and represent saturated or unsaturated hydrocarbon groups suitably containing from 8 to 30 carbon atoms, or R 3 and R 4 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.
• acid anhydrides which are used commercially include alkyl and alkenyl succinic anhydrides and particularly isooctadecenyl succinic anhydride.
• Suitable ketene dimers, acid anhydrides and organic isocyanates include the compounds disclosed in U.S. Pat. No. 4,522,686, which is hereby incorporated herein by reference.
• suitable carbamoyl chlorides include those disclosed in U.S. Pat. No. 3,887,427 which is also incorporated herein by reference.
• Another preferred embodiment of the present invention refers to a process for sizing paper comprising providing an aqueous suspension comprising cellulosic fibres, dewatering said aqueous suspension thereby forming a paper web, said process comprising adding to the cellulosic suspension an aqueous composition comprising particles comprising a sizing agent, the composition obtainable by mixing in any order prior to the addition to the aqueous suspension, (i) a solution comprising at least an anionic coagulating agent, and (ii) a cationic aqueous dispersion comprising a sizing agent, wherein the particles of the composition comprising a sizing agent have a weight average diameter of at least 5 ⁇ m.
• the anionic coagulation agent is an anionic polysaccharide, i.e. an anionic derivative of cellulose such as carboxymethylcellulose having a charge density commonly from about 0.5 up to about 18 meq/g, more preferably from about 1.0 up to about 6 meq/g.
• the cationic aqueous dispersion suitably comprises a cationic polyelectrolyte, suitably cationic condensation polymers exemplified by epihalohydrine-type polymers (i.e. polyamines), amideamine-type polymers and ethyleneimine-type polymers. Depending on the monomers used the cationic polymers can be branched or non-branched.
• the cationic polyelectrolyte has a charge density ranging from about 0.5 up to about 20 meq/g, typically from about 1.0 up to about 12 meq/g, and preferably from about 1.0 up to about 6 meq/g.
• Preferred cationic condensation polymers include polyamideamine like those formed from aliphatic amines and aliphatic dicarboxylic acids, e.g. condensation of adipic acid, ethylene diamine or hexamethylene diamine and diethylene triamine; polyamideamine epichlorohhydrine resins, polyethylene imine, vinylamine-type polymers. Generally, larger particles containing the sizing agent are formed (better flocculation) if the charge density of the cationic polymer(s) present in the dispersion and/or the charge density of the coagulation agent is/are increased.
• the aqueous composition comprising particles comprising a sizing agent is obtained by providing an charged aqueous dispersion comprising the sizing agent and an aqueous solution comprising a coagulating agent and mixing them.
• the aqueous dispersion is produced by applying known dispersion/emulsion techniques.
• the dispersion is suitably formed by providing the sizing agent in melted form and dispersing the liquid sizing agent in an aqueous solution comprising dispersing agents using a high pressure equipment. If sizing agents are used which are solid at ambient temperatures they are melted prior to emulsification.
• aqueous solution comprising the coagulation agent these are formed by simply mixing the water dispersible or water-soluble agent, optionally together with suitable dispersing agents, in the aqueous solution.
• the amount of coagulation agent present in the solution is not critical.
• the amount of coagulation agent present in the solution is from about 0.01 up to about 15 weight %.
• the sizing agent is suitably present in the composition of all embodiments in an amount of from about 0.01 up to about 10 % by weight based on total composition, preferably from about 0.07 up to about 5 % by weight, even more suitably from about 0.1 up to about 2 % by weight, whereas the coagulation agent typically is present in the composition in an amount ranging from about 0.1 to about 10 % by weight based on the sizing agent, preferably from 0.1 to 5% by weight.
• the aqueous sizing composition does suitably not contain any rosin sizing agents.
• the process of this invention is used for the production of paper.
• paper as used herein, of course include not only paper and the production thereof, but also other sheet or web-like products, such as for example board and paperboard, and the production thereof.
• the process can be used in the production of paper from different types of suspensions of cellulose-containing fibres and the suspensions should suitably contain at least 25% by weight and preferably at least 50% by weight of such fibres, based on dry substance.
• the suspensions can be based on fibres from chemical pulp such as sulphate, sulphite and organosolv pulps, mechanical pulp such as thermomechanical pulp, chemothermomechanical pulp, refiner pulp and groundwood pulp, from both hardwood and softwood, and can also be based on recycled fibres, optionally from de-inked pulps, and mixtures thereof.
• the invention is particularly useful in the manufacture of paper from suspensions based on pulps comprising recycled fibres and de-inked pulp, and the content of cellulosic fibres of such origin can be up to 100%, suitably from 20% to 100%.
• the process of the invention can be used for sizing paper from a suspension containing cellulosic fibers, and optional fillers, having a high cationic demand and/or a high conductivity.
• Sufficient sizing of the paper is obtained if the cationic demand of the suspension is above about 1000 meq/l, and even if the cationic demand of the suspension is above about 2000 meq/l, suitably above about 3000 meq/l, preferably above about 4000 meq/l.
• the conductivity of the stock can be at least 0.20 mS/cm, preferably at least 3.5 mS/cm.
• the cationic demand can be measured by polyelectrolyte titration (Mütec PC 02).
• the conductivity can be measured by standard equipment such as, for example a WTW LF 539 instrument supplied by Christian Berner.
• the values referred to above are suitably determined by measuring the cationic demand or conductivity of the cellulosic suspension that is fed into or present in the headbox of the paper machine or, alternatively, by measuring the cationic demand or conductivity of white water obtained by dewatering the suspension.
• High conductivity levels mean high contents of salts (electrolytes), where the various salts can be based on mono-, di- and multivalent cations like alkali metals, e.g. Na + and K + , alkaline earths, e.g. Ca 2+ and Mg 2+ , aluminium ions, e.g. Al 3+ , Al(OH) 2+ and polyaluminium ions, and mono-, di- and multivalent anions like halides, e.g., Cl - , sulfates, e.g. SO 4 2- and HSO 4 - , carbonates, e.g.
• alkali metals e.g. Na + and K +
• alkaline earths e.g. Ca 2+ and Mg 2+
• aluminium ions e.g. Al 3+ , Al(OH) 2+ and polyaluminium ions
• mono-, di- and multivalent anions like halides, e.g.
• the invention is particularly useful in the manufacture of paper from stocks having high contents of salts of di- and multivalent cations, and usually the cation content is at least 200 ppm, suitably at least 300 ppm and preferably at least 400 ppm.
• the salts can be derived from the cellulosic fibres and fillers used to form the stock, in particular in integrated mills where a concentrated aqueous fibre suspension from the pulp mill normally is mixed with water to form a dilute suspension suitable for paper manufacture in the paper mill.
• the salt may also be derived from various additives introduced into the stock, from the fresh water supplied to the process, or be added deliberately, etc. Further, the content of salts is usually higher in processes where white water is extensively recirculated, which may lead to considerable accumulation of salts in the water circulating in the process.
• the present invention further encompasses papermaking processes where white water is extensively recirculated (recycled), i.e. with a high degree of white water closure, for example where from 0 to 30 tons of fresh water are used per ton of dry paper produced, usually less than 20, suitably less than 15, preferably less than 10 and notably less than 5 tons of fresh water per ton of paper.
• Recirculation of white water obtained in the process suitably comprises mixing the white water with cellulosic fibres and/or optional fillers to form a suspension to be sized; preferably it comprises mixing the white water with a suspension containing cellulosic fibres, and optional fillers, before the suspension enters the forming wire for sizing.
• % refers to % by weight if not otherwise indicated.
• the weight average diameter of the particles comprising the sizing agent was measured using a Malvern Mastersizer Microplus (Malvern Instruments Ltd) with a small volume cell top.
• the relative particle refractive index for the ketene dimer (AKD) particles was set to 1.15, the imaginary refractive index was set to 0.1 and the refractive index for the dispersing medium (water) was set to 1.33.
• the data were analysed according to a polydisperse model, 5OHD.
• a pre-flocculated sizing composition according to the invention was produced by mixing to 100 ml of a potassium sulphate solution (0.3 g/l potassium sulphate) a) an aqueous solution containing 0.092 mg/l of carboxymethylcellulose (CMC) having a charge density of 3.6 meq/g and a weight average molecular weight of 250000, and b) a cationic sizing dispersion containing a standard ketene dimer (AKD), a cationic polyamine and naphthalene sulphonate.
• the CMC solution was added to the dispersion in an amount to effect charge neutralisation of the composition.
• the charge of the composition was measured using PCD (Particle Charge Detector, Mütec PC 02).
• the obtained sizing composition had an amount of 0.025 % of the ketene dimer.
• the weight average diameter of the particles of the composition comprising the ketene dimer sizing agent was around 30 ⁇ m.
• a non-flocculated cationic ketene dimer sizing dispersion was provided by using the same sizing dispersion which was pre-flocculated, however, without mixing the sizing dispersion with neither the CMC solution nor the potassium sulphate solution.
• the weight average diameter of the ketene dimer particles was 0.77 ⁇ m.
• the sizing efficiencies of the pre-flocculated composition and the non-flocculated dispersion were evaluated by adding the composition and the dispersion to a furnish in amount which are evident in the tables 1 and 2 containing hard wood (HW) and soft wood (SW) sulphate pulp in a weight ratio of 60:40, having a pH of 8.0, a conductivity of 480 ⁇ S/cm, a concentration of 0.511 % (w/w) based on dry fibres and 0.3 g/l of potassium sulphate. No retention agents were added to the suspensions.
• the paper sheets, having a grammage of 70 g/m 2 was formed using a Finnish Sheet former.
• ketene dimer sizing dispersion used example 1 was flocculated by adding a solution of an anionic aluminium modified silica sol (NP590).
• the pre-flocculated composition was manufactured according to the method outlined in example 1. Similar paper suspensions as in example 1 were used. Sizing evaluation of sizing dispersion pre-flocculated with NP590. Sheet No. Added pre-flocculated AKD, [kg /tonne dry fibres] COBB-60 1 0,4 90 2 0,5 78 3 0,6 54 4 0,7 46 5 0,8 32
• a cationic sizing dispersion containing 8.9 % of a standard ketene dimer sizing agent and 1.1 % of polyamideamine having a charge density of 640 ⁇ eq/g was flocculated by the addition of 0.120 g CMC/g total dispersion in a Britt Dynamic Drainage Jar (BDDJ), Paper research Materials Inc.. The resulting composition was stirred at 1000 rpm for 3 minutes. The same cationic dispersion containing polyamideamine, however not pre-flocculated, was used for comparative purpose. The weight average diameter of the particles containing the sizing agent was 20 ⁇ m (pre-flocculated composition) and 0.8 ⁇ m (non-flocculated dispersion).
• the sizing efficiency of the pre-flocculated composition and cationic dispersion were evaluated by measuring the 1-minute cobb (SCAN-P 12:64) of laboratory sheets made in a Formette Dynamique (Centre Technique du Textil, France). The sheets were formed by adding the pre-flocculated composition and the non-flocculated, respectively, to the stock based in amounts indicated by tables 4 or 5.
• the paper stock contained TCF (totally chlorine free) birch pulp and had a concentration of 0.15 % (w/w), a pH of 7.5-7.7 and a conductivity in the range of 1000-1200 ⁇ S/cm. Sizing evaluation pre-flocculated composition. Sheet No.

Priority Applications (11)

Applications Claiming Priority (1)

Publications (1)

Family

ID=8184898

Family Applications (2)

Family Applications After (1)

Country Status (9)

Cited By (5)

Families Citing this family (8)

Citations (7)

Family Cites Families (3)

• 2001
  • 2001-11-19 EP EP01850198A patent/EP1314822A1/de not_active Withdrawn
• 2002
  • 2002-11-15 JP JP2003545884A patent/JP3998638B2/ja not_active Expired - Fee Related
  • 2002-11-15 EP EP02786334A patent/EP1446527A1/de not_active Withdrawn
  • 2002-11-15 BR BR0214270-8A patent/BR0214270A/pt not_active IP Right Cessation
  • 2002-11-15 AU AU2002349853A patent/AU2002349853B2/en not_active Ceased
  • 2002-11-15 CA CA002473653A patent/CA2473653A1/en not_active Abandoned
  • 2002-11-15 CN CN 02822958 patent/CN1259481C/zh not_active Expired - Fee Related
  • 2002-11-15 WO PCT/SE2002/002095 patent/WO2003044274A1/en active IP Right Grant
  • 2002-11-15 RU RU2004118668/12A patent/RU2263172C2/ru not_active IP Right Cessation
  • 2002-11-15 PL PL02370323A patent/PL370323A1/xx not_active Application Discontinuation

Patent Citations (7)

Also Published As

Similar Documents

Legal Events