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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
  • D21H17/68—Water-insoluble compounds, e.g. fillers, pigments siliceous, e.g. clays
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic 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
  • D21H17/20—Macromolecular organic compounds
  • D21H17/21—Macromolecular organic compounds of natural origin; Derivatives thereof
  • D21H17/24—Polysaccharides
  • D21H17/28—Starch
  • D21H17/29—Starch cationic
• • 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
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/37—Polymers of unsaturated acids or derivatives thereof, e.g. polyacrylates
  • D21H17/375—Poly(meth)acrylamide
• • 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

Definitions

• Silica-based sols, preparation and use of the sols The present invention relates to silica-based sols con ⁇ taining silica-based anionic particles having a high specific surface area and silica-based anionic particles having a low specific surface area.
• the invention also relates to a method for producing the sols and to the use thereof as flocculating agents, in combination with amphoteric or cationic polymers, particularly in the production of paper and pulp but also for water purification.
• Silica-based sols, which term is used herein for silica- based hydrosols are aqueous systems with very small silica- based particles which can be used in several fields of appli ⁇ cation depending, inter alia, on the particle size.
• silica-based sols with anionic silica particles of small particle size have gained an increased use in the production of paper.
• the silica sols are here used as addi ⁇ tives to the stock in combination with amphoteric or cationic polymers, primarily to improve retention and dewatering.
• European Patent 41056 discloses, for example, the use of colloidal silica sols in combination with cationic starch in papermaking.
• European Patents 185068 and 218674 disclose com ⁇ binations of silica sols with particles where at least the surface groups contain aluminium, and cationic natural poly ⁇ mers and cationic polyacrylamides, respectively.
• the colloidal silica in these sols has a specific surface area of 50-1000 m 2 /g.
• Sols with colloidal particles of the above-mentioned order of size have resulted in good retention and dewatering and have high stability.
• silica sols which are to be used commercially that they are as monodisperse as possible, i.e. that they have as narrow a particle size distribution as possible.
• European Patent 491879 discloses silica sols having a degree of aggregate or microgel formation corresponding to an S-value of 8-45% containing silica-based particles with a spe ⁇ cific surface area of 750-1000 m 2 /g which are surface-modified with aluminium to a degree of 2-25%.
• the present invention relates to new silica-based sols containing silica-based anionic particles having a high speci ⁇ fic surface area and silica-based anionic particles having a low specific surface area. It has been found that the sols according to the invention, in combination with cationic poly ⁇ mers, surprisingly give improved retention and dewatering results at the production of paper and similar products. A higher effect can be achieved with these sols than what could be expected from the included amount of the respective types of particles. With the sols according to the invention, silica-based particles having a comparatively low specific surface area, from about 50 to 400 m 2 /g, i.e. a comparatively large average particle size, corresponding to from about 54 to about 7 nm, can also be used with good results. Silica-based sols with these larger particle sizes have themselves not given sufficiently good results to be used commercially within the field of retention and drainage.
• the present invention thus relates to silica-based sols as further defined in the claims.
• the invention also relates to a method for producing silica-based sols and to the use of the sols as further indicated in the appended claims.
• Silica-based particles i.e. particles based on Si0 2 , having a high specific surface area which can be used in the present sols include colloidal silica, colloidal aluminium- modified silica, aluminium silicate and different types of polysilicic acid.
• the particles can have a specific surface area within the range of from 425 to 1700 m 2 /g, corresponding to an average particle size within the range of from about 6.4 to about 1.0 nm.
• the given specific surface area can be measu ⁇ red by titration with NaOH according to the method described by Sears in .Analytical Chemistry 28(1956) :12, 1981-1983.
• the average particle size of discrete spherical particles can be calculated from the relation 2720 divided by the specific surface area indicated in m 2 /g, giving the average particle diameter in nm, as described by Her in The Chemistry of Silica, pp 346-347, John Wiley & Sons, 1979.
• the specific surface area of the silica-based particles is suitably higher than 450 m 2 /g and preferably higher than 475 m 2 /g.
• the upper limit for the specific surface area of the particles is suit ⁇ ably 1400 m 2 /g and preferably 1200 m 2 /g.
• An especially suitable range for the specific surface area is 750-1000 m 2 /g, in particular 800-950 m 2 /g.
• Suitable silica-based particles having a high specific surface area are such particles which in silica-based sols result in an S-value within the range of from 8 to 90%, and preferably within the range of from 8 to 60%.
• the indicated S-value can be measured and calculated in accordance with what is described by Her and Dalton in J. Phys. Chem. 60(1956), 955-957.
• the S-value indicates the degree of aggregate or microgel formation, where a low S-value indicates a higher microgel content, and can also be seen as a measure of the Si0 2 content, in % by weight, in the disperse phase.
• the silica-based particles having a high specific surface area may be such particles which are described in the above-mentioned European Patents 41056 and 185068, which are hereby incorporated herein by reference, provided that the specific surface area lies within the indicated limits.
• Suit- able particles described in these patents have a specific surface area of 425-1000 m 2 /g.
• Particularly suitable silica- based particles having a high specific surface area originate from silica-based sols having an S-value within the range of from 8 to 45% containing silica-based particles with a specific surface area within the range of from 750 to 1000 m 2 /g which are surface-modified with aluminium to a degree of from 2 to 25%.
• Silica-based anionic particles having a low specific surface area which can be used in the present sols include colloidal silica, colloidal aluminium-modified silica and aluminium silicate. These particles are suitably substantially spherical and preferably discrete, i.e non-aggregated, in con ⁇ trast to microgel and aggregates, which contain aggregated particles, e.g. in the form of straight or branched chain-like formations. These silica-based particles can have a specific surface area within the range of from 50 to 400 m 2 /g, suitably from 70 to 375 m 2 /g, and preferably from 80 to 250 m 2 /g.
• Sols with suitable silica-based particles having a low specific surface area can have an S-value within the range of from 25 to 95%, suitably at least 50%, and preferably from 60 to 95%.
• Sols with suitable silica-based particles having a low speci- fie surface area are commercially available under the trade- name BindzilTM, produced by Eka Nobel.
• the sols of silica-based particles according to the invention may include silica-based particles having the high specific surface area in an amount of at least 50% by weight, suitably at least 60%, and preferably at least 75%, based on the total amount of silica-based particles.
• the upper limit of the included amount of high specific surface area particles is 99%, suitably 98%, preferably 95% and more preferably 90% by weight, based on the total amount of silica-based particles.
• the silica-based sols according to the invention may include the low specific surface area particles in an amount of from 1%, suitably from 2%, preferably from 5% and more preferably from 10% by weight, up to 50%, suitably to 40% and preferably to 25% by weight, based on the total amount of silica-based particles.
• Sols according to the invention suitably have a dry solids content, calculated as Si0 2 , of from 0.1 to 30% by weight.
• the dry solids content suitably exceeds 1%, preferably exceeds 3% and more preferably exceeds 5% by weight.
• the upper limit is 25% and preferably 20% by weight.
• a major advantage of the present sols is that they can be prepared with higher dry solids contents and that an improved floccula- tion and dewatering effect can be obtained as compared with sols containing only silica-based particles having a specific surface area within the range of 425-1700 m 2 /g.
• the costs for storage and transportation can be significantly reduced.
• the improved dewatering obtained with the sols according to the invention means that the speed of the papermaking machine can be increased and, moreover, less water have to be removed in the press and drying sections of the machine, resulting in an substantially improved papermaking process.
• the silica-based sols according to the invention can be prepared by mixing, suitably under agitation, a sol containing silica-based anionic particles having a high specific surface area as defined above with a sol containing silica-based anio ⁇ nic particles having a low specific surface area as defined above.
• the sols according to the invention can contain a mixture of a sol containing silica-based anionic particles having a high specific surface area within the range of from 425, suitably from 450, preferably from 475 and most prefer ⁇ ably from 750 m 2 /g, to 1700, suitably to 1400, preferably to 1200 and most preferably to 1000 m 2 /g, and a sol containing silica-based anionic particles having a low specific surface area within the range of from 50 m 2 /g, suitably from 70 and preferably from 80 m 2 /g, to 400 m 2 /g, suitably to 375 and preferably to 250 m 2 /g.
• the sol containing silica-based particles having the high specific surface area can be included in an amount of from 50%, suitably from 60% and preferably from 75%, up to 99%, suitably to 98%, prefer ⁇ ably to 95% and more preferably to 90% by weight, and the sol containing silica-based particles having the low specific sur- face area can be included in an amount of from 1%, suitably from 2%, preferably from 5% and more preferably from 10%, up to 50%, suitably to 40% and preferably 25% by weight, calcu ⁇ lated on the total amount of silica-based particles.
• Sols of the respective types of particles within the defined specific surface area ranges that can be used in order to produce the sols according to the invention are known in the art and can be prepared by the skilled person.
• the sol with particles having the high specific surface area suitably has a dry solids content, calculated as Si0 2 , of 0.5-20% by weight, preferably 5-17% by weight, and the sol with particles having the low specific surface area may have a dry solids content of up to 60% by weight, suitably 3-60% and preferably 15-50% by weight.
• the silica-based sols according to the invention may also contain hydrated particles of clays which are expandable in water and which are of the smectite type.
• Clays of the smectite type are thin flake-like, layered silicate minerals and comprise both naturally occurring materials and synthetic ones. The materials may be chemically treated, for example alkali-treated. The clays should be dispersible in water and thereby expand so that particles having a high surface area are obtained.
• Examples of clays of smectite type which are expandable in water and which can be used in the present sols are montmorillonite, bentonite, hectorite, beidellite, nontro- nite and saponite.
• Bentonite is preferred, and a suitable ben ⁇ tonite is, for example, the one described in European Patent 235893, which after swelling preferably has a surface area of from 400 to 800 m 2 /g.
• the weight ratio of silica-based partic ⁇ les to clay particles can be from 20:1 to 1:10, based on dry matter. Suitably, the weight ratio ranges from 10:1 to 1:5, and preferably from 6:1 to 1:3.
• Aqueous mixtures of silica- based particles and clay particles according to the invention are stable and may have a dry solids content of from 1%, suitably from 5% and preferably from 8% by weight, up to 40%, suitably to 30% and preferably to 25% by weight
• Silica-based sols according to the invention containing hydrated particles of clays which are expandable in water may, for example, be prepared by first mixing the clay into water and then adding a silica-based sol before the clay has had time to expand in the water, whereupon the aqueous mixture is well dispersed. It is however preferred that these mixtures be prepared by mixing the clay into a sol of silica-based partic- les and dispersing it well therein, using high shear forces.
• the sols used in the above-mentioned methods may be a silica- based sol according to the invention or a sol intended for the preparation thereof, whereby the mixture of clay particles and silica-based particles after the dispersing process is mixed with additional silica-based sol in order to prepare the mix ⁇ ture according to the invention.
• Aqueous mixtures of silica- based particles and clay particles of the smectite type and the preparation thereof are disclosed in PCT Application WO 94/05595, which is hereby incorporated herein by reference.
• the present sols are suitable for use as flocculating agents, for example in the production of pulp and paper and within the field of water purification, both for purification of different types of waste water and for purification speci- fically of white water from pulp and paper industry.
• the sols are used as flocculating agents in combination with cationic or amphoteric polymers, which may be natural, i.e. based on carbohydrates, or be synthetic.
• suitable poly ⁇ mers can be mentioned cationic and amphoteric starch, cationic and amphoteric guar gum, cationic and amphoteric linear and branched acrylamide-based polymers, cationic polyethylene imines, polyamido amines and poly(diallyl dimethyl ammonium chloride) .
• the sols can be used with one or more polymers.
• the sols can also be used in combination with polymers of opposite charges, such as sol in combination with cationic polymers, especially cationic starch, and anionic acrylamide-based poly ⁇ mer. Even if an arbitrary order of addition can be used, it is preferred that the polymer or polymers be added to pulp, stock or water before the sol.
• a preferred field of use of the sols, in combination with polymer, is for improvement of retention and dewatering in papermaking.
• the terms "paper” and “papermaking” as used herein of course include not only paper and the production thereof but also other cellulose fibre containing sheets or web-like products, such as pulp sheets, board and paperboard and the production thereof.
• the sols are hereby suitably added to the stock in an amount of from 0.05 to 5 kg/ton, calculated as dry on dry stock system, i.e. fibres and optional fillers, and preferably in an amount of from 0.1 to 3 kg per ton.
• the dry solids content of the sols when added to the stock is suitably adjusted to 0.1-10% by weight.
• cationic or amphoteric polymers use is usually made of at least 0.01 kg of polymer, calculated as dry matter per ton of dry stock system, and amounts of from 0.01 to 3 are suitably used and preferably from 0.03 to 2 kg per ton.
• carbohydrate-based cationic or amphoteric polymers such as starch and guar gum
• these polymers use is made of amounts of from 0.5 to 30 kg/ton, preferably from 1 to 15 kg/ton.
• the invention further encompasses forming and dewatering the suspension in the pre ⁇ sence of cationic or amphoteric polymers, e.g. those mentioned above, and a silica-based sol according to the invention com ⁇ prising the mixture, in weight ratios as defined above, of a sol containing silica-based anionic particles having the high specific surface area as defined above, and a sol containing silica-based anionic particles having the low specific surface area as likewise defined above.
• the invention also encompasses separately adding to the stock the sol containing silica-based particles having the high specific surface area and the sol containing silica-based particles having the low specific surface area, . in arbitrary order and at the same or different points.
• the sols may, in combination with the polymers, be used in the production of paper from different types of stocks of cellulose-containing fibres such as stocks of fibres from chemical pulp, such as sulphate and sulphite pulp, chemo- thermomechanical pulp (CTMP) , thermomechanical pulp, refiner pulp or groundwood pulp from both hardwood and softwood, and can also be used for stocks based on recycled fibres.
• the stocks may contain mineral fillers of conventional types, such as kaolin, titanium dioxide, gypsum, talc and both natural and synthetic calcium carbonates. Good results have also been obtained for stocks which are normally considered difficult.
• Such stocks are those containing mecha- nical pulp such as groundwood pulp, stocks based on recycled fibre pulp and stocks which due to the white water system contain high amounts of anionic impurities, such as lignin and dissolved organic compounds and/or high contents of electroly- tes.
• mecha- nical pulp such as groundwood pulp
• stocks based on recycled fibre pulp stocks which due to the white water system contain high amounts of anionic impurities, such as lignin and dissolved organic compounds and/or high contents of electroly- tes.
• anionic impurities such as lignin and dissolved organic compounds and/or high contents of electroly- tes.
• aluminium com ⁇ pound any in paper production per se known aluminium com ⁇ pound can be used, such as alum, aluminates, aluminium chlo- ride, aluminium nitrate and polyaluminium compounds, such as polyaluminium chloride, polyaluminium sulphate and polyalumi ⁇ nium compounds containing both chloride and sulphate ions.
• the stock may of course also contain known hydrophobing agents, such as colophonium dispersions, or synthetic stock sizes, e.g. ketene dimer and alkenyl succinic anhydride dispersions.
• Example 1 Parts and percentages relate to parts by weight and per cent by weight, respectively, unless otherwise stated.
• silica-based sols according to the invention were prepared.
• sols with silica-based particles having a high specific surface area were used: A) A polysilicic acid of the type described in European Patent 348366 having a specific surface area of about 1400 m 2 /g and a dry solids content of 1% by weight.
• silica-based sols with particles having a low specific surface area were used: D) .An anionic silica sol having a specific surface area of 360 m 2 /g and a dry solids content of 30% by weight, sold by Eka Nobel under the tradename BindzilTM 30/360.
• To a beaker equipped with a magnetic stirrer and contain ⁇ ing 1.0 kg of sol with silica-based particles having a high specific surface area was added sol with silica-based partic ⁇ les having a low specific surface area in varying amounts, based on dry matter, as defined below.
• sols were agitated for 10 min.
• the following sols were prepared: Sol .AE 80% of sol A,. 20% of sol E, dry solids content 1.2% Sol AF 80% of sol A, 20% of sol F, dry solids content 1.2% Sol AG 80% of sol A, 20% of sol G, dry solids content 1.2% Sol AH 80% of sol A, 20% of sol H, dry solids content 1.2% Sol BE 80% of sol B, 20% of sol E, dry solids content 10.0% Sol BF 80% of sol B, 20% of sol F, dry solids content 9.9% Sol BG 80% of sol B, 20% of sol G, dry solids content 10.1% Sol BH 80% of sol B, 20% of sol H, dry solids content 9.9% Sol BI 80% of sol B, 20% of sol I, dry solids content 10.1% Sol BI90: 90% of sol B, 10% of sol I, dry solids content 9.4%
• Sol BI95 95% of sol B, 5% of sol I, dry solids content 8.8%
• Sol CD 80% of sol C, 20% of sol D, dry solids content 16.7%
• Sol CI 80% of sol C, 20% of sol I, dry solids content 17.4%
• a silica-based sol according to the invention containing bentonite was prepared.
• a bentonite-containing sol having a dry solids content of about 9.0% was prepared from sol B according to Example 1 and sodium bentonite.
• the bentonite-containing sol was prepared from 152.5 g of sol B, 6.4 g of bentonite and 54.0 g of water.
• the ratio of silica particles to bentonite particles in this sol was about 2:1.
• the bentonite was added to sol B, and dispersion was carried out by means of an Ultra-Turrax at 10,000 rpm for 10 min.
• sol I prepared as above was added sol I according to Example 1 in an amount of 7.9 g under agitation.
• the following sol was prepared in the indicated weight ratios, based on dry matter;
• Sol Bib 46.7% of sol B, 30.0% of sol I, 23.3% of bentonite, dry solids content 12.0% by weight
• the resulting sol was stored for 1 week before being eva- luated, and showed good stability. No bottom phase was formed, and the viscosity of the sol was substantially constant. Examples 3-5
• CSF Canadian Standard Freeness
• the stock was based on a CTMP pulp. 0.3 g/1 of Na 2 S0 4 - 10H 2 0 had been added to the stock having a pH of 7.5. The stock concentration was 5.0 g/1. The CSF-value when no chemi ⁇ cals had been added was 200 ml. In all the tests, alum was added to the stock in an amount of 1 kg/ton, based on dry fibres, before the addition of cationic starch and silica- based sol.
• the cationic starch employed was a conventional medium-high cationised starch, Raisamyl 142, having a degree of substitution of 0.042.
• the cationic starch was added to the stock in an amount of 8 kg/ton, based on dry fibres.
• the stock was agitated for 30 sec, whereupon silica-based sol was there ⁇ after added in an amount of 1.0, 2.0 and 4.0 kg/ton, respec ⁇ tively, calculated as dry on dry fibres. After another 15 sec, the stock was transferred to the freeness apparatus.
• Example 3 Comparative tests
• Table 1 shows the dewatering effect (ml CSF) for the sols added in different amounts (kg/ton) .
• the cationic polymer was a cationic starch of the same type as in Examples 3-5, which was added in an amount of 8.0 kg/ton of dry stock system.
• the stock was agitated for 25 sec, whereupon silica-based sol was added in amounts of from 0.5 to 1.0 kg/ton of dry stock system. After another 15 sec, the stock was transferred to the freeness apparatus.
• Example 6 In this Example, the dewatering effect was evaluated for reference sols B and I and inventive sols BI95, BI90 and BI prepared in Example 1. Alum was not used in this Example.
• Table 4 shows the dewatering effect (ml CSF) for the sols added in different amounts (kg/ton) . Table 4

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• Chemical & Material Sciences (AREA)
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Cited By (17)

Citations (2)

• 1994
  • 1994-02-28 SE SE9400690A patent/SE502464C2/sv not_active IP Right Cessation
• 1995
  • 1995-02-22 ZA ZA951466A patent/ZA951466B/xx unknown
  • 1995-02-23 TW TW084101674A patent/TW282504B/zh active
  • 1995-02-24 AU AU19062/95A patent/AU1906295A/en not_active Abandoned
  • 1995-02-24 WO PCT/SE1995/000200 patent/WO1995023021A1/en active Application Filing

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