KR100853924B1 - Silica-based sols and their production and use - Google Patents

Abstract

The present invention relates to a process for preparing an aqueous silica-based sol comprising: (a) providing a cationic ion exchange resin having at least a portion of ion exchange capacity in hydrogen form; (b) contacting the ion exchange resin with an aqueous alkali metal silicate to form an aqueous slurry; (c) stirring the aqueous slurry until the pH of the aqueous phase is in the range from 5.0 to 11.5; And / or alternatively, stirring the aqueous slurry to enable particle agglomeration or microgel formation corresponding to an S value of 45% or less, thereby obtaining an aqueous phase pH of 5.0 or greater; (d) adjusting the pH of the aqueous phase to at least 9.0 using at least one material comprising at least one aluminum compound; And (e) separating the ion exchange resin from the aqueous phase after step (c) or step (d). The present invention also provides S values in the range of 15 to 25%, Si: Al molar ratio in the range 20: 1 to 50: 1, Si: X molar ratio in the range 5: 1 to 17: 1, wherein X = alkali metal, 5% by weight. A silica-based sol containing silica-based particles having a SiO ₂ content of at least and having a specific surface area of at least 300 m ² / g. The invention also relates to a papermaking method comprising: (i) providing an aqueous suspension comprising cellulose fibers; (j) adding to said suspension at least one drainage and retention agent comprising a silica-based sol according to the invention; And (k) dehydrating the suspension obtained to provide a paper sheet or paper web.

Description

Silica-based sol and its preparation and use {SILICA-BASED SOLS AND THEIR PRODUCTION AND USE}

Field of invention

The present invention generally relates to an aqueous silica-based sol suitable for use in papermaking. More particularly, the present invention relates to silica-based sol, their preparation and use in papermaking. The present invention provides an improved method for preparing silica-based sol having high stability and SiO ₂ content and improved drainage performance.

Background of the Invention

In the paper industry, an aqueous suspension containing cellulose fibers and optional fillers and additives is called a stock, which is fed into a headbox that discharges the stock over a forming wire. Water is drained from the stock to form a wet web of paper on the wire, which is further dehydrated and dried in the drying zone of the paper machine. Drainage and retention aids are traditionally introduced into the stock to facilitate drainage and increase the adsorption of fine particles on the cellulose fibers to retain with the fibers on the wire.

Sols of silica-based particles are widely used as drainage and retention agents in combination with charged organic polymers. Such additive systems are one of the most effective currently used in the paper industry. One of the variables affecting the properties and performance of silica-based sol is the specific surface area; A stable, high performance silica-based sol typically contains particles having a specific surface area of at least 300 m ² / g. Another variable is the S value, which indicates the degree of aggregation or microgel formation; Lower S-values indicate higher cohesion. High surface area and specific degree of aggregation or microgel formation may be beneficial in terms of performance, but very high surface areas and a wide range of particle aggregation or microgel formation result in significantly reduced stability of the silica-based sol. There is a need to dilute the sol extremely in order to avoid gel formation.

U.S. Patent 5,368,833 discloses a silica sol comprising silica particles having a specific surface area in the range of 750 to 1,000 m ² / g, wherein the silica particles are surface-modified with aluminum to a silicon atom substitution of 2 to 25%, Wherein the sol has an S value in the range of 8 to 45%. The patent also discloses a process for preparing silica sol, which method comprises acidifying a water glass solution to a pH in the range of 1-4; Alkalizing the acidic sol at a SiO ₂ content in the range of 7 to 4.5 wt%; Growing particles of the sol to a specific surface area in the range of 750 to 1,000 m ² / g; And causing the sol to be aluminum modified.

U.S. Patent 5,603,805 discloses a silica sol having an S value in the range of 15 to 40% and comprising anionic silica particles, wherein the silica particles are optionally aluminum modified and have a specific surface area in the range of 300 to 700 m ² / g. Has The patent further includes the step of acidifying the water glass solution to a pH within the range of 1 to 4; Alkalizing the acidic sol in SiO ₂ in the range of 7 to 5% by weight; Alternatively alkalizing the acidic sol to a pH value of 7-9; And growing particles of the sol to a specific surface area in the range of 300 to 700 m ² / g; And optionally involving an aluminum modification step.

WO 98/56715 discloses a process for preparing an aqueous polysilicate microgel, comprising mixing an aqueous phase of an alkali metal silicate with an aqueous phase of a silica-based material having a pH of 11 or less. Polysilicate microgels are used as coagulants in the manufacture of pulp and paper and in combination with one or more cationic or amphoteric polymers for water purification.

WO 00/66492 discloses a process for the preparation of an aqueous sol containing silica-based particles, which method comprises acidifying an aqueous silicate solution to a pH of 1 to 4 to form an acidic sol; Alkalizing the acidic sol in a first alkalizing step; Growing particles of the alkalized sol for at least 10 minutes and / or heat treating the alkalized sol at a temperature of at least 30 ° C .; Alkalizing the sol obtained in the second alkalizing step; And optionally, modifying the silica-based sol with, for example, aluminum.

U. S. Patent No. 6,372, 806 discloses a process for preparing stable colloidal silica having an S-value of 20-50, wherein the silica has a surface area of greater than 700 m ² / g, the method comprising the following steps: (a) filling a reaction vessel with a cationic ion exchange resin having at least 40% ion exchange capacity in hydrogen form, wherein the reaction vessel has means for separating the colloidal silica from the ion exchange resin; (b) filling the reaction vessel with an aqueous alkali metal silicate having a molar ratio of SiO ₂ to alkali metal oxide in the range of 15: 1 to 1: 1 and a pH of at least 10.0; (c) stirring the contents of the reaction vessel until the pH of the contents is in the range of 8.5 to 11.0; (d) adjusting the pH of the contents of the reaction vessel to at least 10.0 using the additional amount of alkali metal silicate; And (e) separating the colloidal silica produced from the ion exchange resin and removing the colloidal silica from the reaction vessel.

U.S. Pat.No. 5,176,891 discloses a process for the preparation of aqueous polyaluminosilicate microgels having a surface area of at least about 1,000 m ² / g, which process comprises: (a) an alkali metal containing from about 0.1 to 6% by weight of SiO ₂ ; Acidifying the dilute solution of silicate to a pH of 2 to 10.5 to produce polysilicic acid; Then (b) reacting the aqueous aluminate and the polysilic acid before the polysilic acid is gelled to obtain a product having an alumina / silica molar ratio of greater than about 1/100; Then (c) diluting the reaction mixture to about 2.0 wt.% Or less SiO ₂ equivalent before gelling occurs to stabilize the microgel.

It would be advantageous to be able to provide silica-based sol with high stability and SiO ₂ content as well as improved drainage performance. It would also be advantageous to be able to provide an improved method of preparing silica-based sol having improved drainage performance as well as stability and SiO 2 content. It would also be advantageous to be able to provide a papermaking method with improved drainage.

Summary of the Invention

The present invention generally relates directly to a process for the preparation of an aqueous silica-based sol comprising:

(a) providing a cationic ion exchange resin having at least a portion of ion exchange capacity in hydrogen form;

(b) contacting the ion exchange resin with an aqueous alkali metal silicate to form an aqueous slurry;

(c) stirring the aqueous slurry until the pH of the aqueous phase is in the range from 5.0 to 11.5; And / or alternatively, stirring the aqueous slurry to enable particle agglomeration or microgel formation corresponding to an S value of 45% or less, thereby obtaining an aqueous phase pH of 5.0 or greater;

(d) adjusting the pH of the aqueous phase to at least 9.0 using at least one material comprising at least one aluminum compound; And

(e) separating the ion exchange resin from the aqueous phase after step (c) or step (d).

The present invention also relates directly to a process for preparing an aqueous silica-based sol, generally comprising:

(a) providing a reaction vessel;

(b) forming an aqueous slurry by providing the reaction vessel with:

(i) a cationic ion exchange resin having at least some ion exchange capacity in the hydrogen form, and

(ii) aqueous alkali metal silicates;

(c) stirring the aqueous slurry until the pH of the aqueous phase is in the range from 5.0 to 11.5; Or, alternatively, stirring the aqueous slurry to enable particle agglomeration or microgel formation corresponding to an S value of 45% or less, thereby obtaining a pH of the aqueous phase of 5.0 or more;

(d) adding at least one material comprising at least one aluminum compound to the aqueous phase obtained after step (c) to form an aqueous phase having a pH of at least 9.0;

(e) separating the ion exchange resin from the aqueous phase after step (c) or step (d).

The invention also relates directly to the silica-based sol obtainable by the process. The present invention also generally relates to silica-based sol, in particular, an S value of 15 to 25%, a Si: Al molar ratio ranging from 20: 1 to 50: 1, a Si: X molar ratio ranging from 5: 1 to 17: 1, wherein X = alkali metal, directly related to silica-based sol containing silica-based particles having a SiO ₂ content of at least 5% by weight and having a specific surface area of at least 300 m ² / g.

The invention also relates directly to the use of the silica-based sol according to the invention, in particular as drainage and retention agent for the purification of paper and water.

The invention also generally relates directly to a papermaking method comprising the following steps

(a) providing an aqueous suspension comprising cellulose fibers;

(b) adding to the suspension one or more drainage and retention agents comprising a silica-based sol according to the invention as defined herein; And

(c) dehydrating the suspension obtained to provide a paper sheet or paper web.

Detailed description of the invention

According to the present invention there is provided a silica-based sol suitable for use as a coagulant in water purification and as a drainage and retention agent in papermaking. The silica-based sol of the present invention exhibits good stability, significantly high surface area stability and high stability that does not completely form a gel over extended periods of time. Silica-based sol also results in very good drainage and retention, especially with improved drainage when used in papermaking. This allows the present invention to use smaller amounts of additives to increase the speed of the paper machine and to provide a corresponding drainage effect, thereby leading to improved papermaking processes and economic advantages. The silica-based sol of the present invention is simple to control and control, and can be prepared by a fast and easy method, which makes it possible to use simple and less expensive manufacturing equipment. As such, the silica-sol of the present invention can be prepared by a simplified, improved and more economical method.

The ion exchange resins used in the process are cationic and have at least a portion of ion exchange capacity in the hydrogen form, ie acidic cationic ion exchange resins, preferably weakly acidic cationic ion exchange resins. Suitably, the ion exchange resin has at least 40% ion exchange capacity, preferably at least 50% ion exchange capacity in hydrogen form. Suitable ion exchange resins are available on the market by several manufacturers, for example Amberlite ^® IRC84SP from Rohm & Haas. Preferably, a reaction vessel equipped with means for mixing, such as, for example, a stirrer, is filled with an ion exchange resin. Preferably, the ion exchange resin is recycled, for example by adding sulfuric acid, preferably according to the manufacturer's instructions.

Step (b) of the process includes contacting the cationic ion exchange resin with an aqueous alkali metal silicate. Suitably, this contact is made by adding an ion exchange resin and an aqueous alkali metal silicate to the reaction vessel. Preferably, the reaction vessel containing the regenerated ion exchange resin is filled with an aqueous alkali metal silicate, whereby an aqueous slurry is formed. Usually, aqueous alkali metal silicate is calculated in minutes per ion and ion exchange resin in a reaction vessel containing an ion exchange resin having at least a portion of ion exchange capacity in the hydrogen form, as an ion exchange resin having 100% ion exchange capacity in the hydrogen form. It is added at a rate of 0.5 to 50, suitably 1 to 35, and preferably 2 to 20 g of SiO ₂ per kg. Alternatively, the reaction vessel containing the aqueous alkali metal silicate is filled with regenerated ion exchange or resin, whereby an aqueous slurry is formed. Examples of suitable aqueous alkali metal silicates or water glasses include traditional materials such as, for example, lithium silicate, sodium silicate and potassium silicate, preferably sodium silicate. The molar ratio of silica oxide to alkali metal oxides, such as SiO ₂ to Na ₂ O, K ₂ O or Li ₂ O, mixtures thereof, in the silicate solution ranges from 15: 1 to 1: 1, suitably from 4.5: 1 to It may be in the range of 1.5: 1, preferably in the range of 3.9: 1 to 2.5: 1. The aqueous alkali metal silicate used may have a SiO ₂ content of about 2 to about 35 weight percent, suitably about 5 to about 30 weight percent, preferably about 15 to about 25 weight percent. The pH of the aqueous alkali metal silicate is generally at least 11, typically at least 12.

Step (c) of the process includes stirring the aqueous slurry formed in step (b) until the pH of the aqueous phase is in the range from 5.0 to 11.5. Alternatively, or in addition, step (c) of the process may agitate the aqueous slurry to enable particle agglomeration or microgel formation corresponding to an S value of 45% or less, thereby increasing the pH of the aqueous phase at 5.0 or greater. To obtain. Suitably the stirring step is carried out until the pH of the aqueous phase is in the range of 6.0 to 11.0, preferably in the range of 6.5 to 10.0. In one preferred embodiment of the invention, the slurry is stirred until the pH of the aqueous phase is at most 8.0, suitably in the range from 6.0 to 8.0, preferably in the range from 6.5 to 7.5. In another preferred embodiment of the invention, the slurry is stirred until the pH of the aqueous phase is at least 8.0, suitably in the range from 8.0 to 11.0, preferably in the range from 9.0 to 10.0. Preferably, particle growth occurs while stirring the aqueous slurry. The formed silica-based particles usually have a specific surface area of at least 300 m ² / g, preferably at least 700 m ² / g. The specific surface area is suitably 1,500 m ² / g or less, preferably 1,000 m ² / g or less. Preferably, the slurry typically has agglomerates and microgels corresponding to S values in the range from 5 to 45%, suitably from 8 to 35%, preferably from 10 to 25% and most preferably from 15 to 23%. Stirring to form. Agitation usually takes place for a time of 5 to 240 minutes, preferably for a time of 15 to 120 minutes.

Step (c) of the method may be performed simultaneously with and / or after step (b). In a preferred embodiment, the aqueous alkali metal silicate is added with stirring to a reaction vessel containing an ion exchange resin having at least a portion of ion exchange capacity in hydrogen form, and after the addition is complete, stirring is continued to the pH and / or particles described above. Agglomeration or microgel formation is achieved. In another preferred embodiment, the aqueous alkali metal silicate is added under stirring to a reaction vessel containing an ion exchange resin having at least a portion of ion exchange capacity in hydrogen form to achieve pH and / or particle aggregation or microgel formation as described above. To achieve. Step (d) of the method includes adding at least one substance comprising at least one aluminum compound. Suitably, the pH of the aqueous phase is at least 9.0, preferably at least 10.0; Suitably in the range from 9.2 to 11.5, preferably in the range from 9.5 to 11.2, and most preferably in the range from 10.0 to 11.0. Preferably, the pH is adjusted by adding at least one substance comprising at least one aluminum compound, preferably the pH is raised by adding at least one alkaline substance comprising at least one aluminum compound. In a more preferred embodiment, an aluminum compound is added. In another preferred embodiment, alkaline materials and aluminum compounds are added. Examples of suitable aluminum compounds are alkaline aluminum salts and neutral and essentially neutral aluminum salts. Examples of suitable alkaline aluminum salts are aluminates, suitably aqueous aluminates such as sodium and potassium aluminate, preferably sodium aluminate. Examples of neutral and essentially neutral aluminum salts are aluminum nitrates. Examples of suitable alkaline materials include aqueous alkali metal silicates such as those defined above; Aqueous alkali metal hydroxides such as lithium hydroxide, sodium and potassium, preferably sodium hydroxide; Ammonium hydroxide; Suitably sodium silicate or sodium hydroxide, preferably sodium silicate. When using two or more materials comprising an alkaline material and an aluminum compound, the materials can be added in any order, preferably the alkaline material is added first, followed by the aluminum compound. In a preferred embodiment, aqueous alkali metal silicate is added first, followed by aqueous sodium aluminate. In another preferred embodiment, aqueous alkali metal hydroxide is added first, followed by aqueous sodium aluminate. The addition of aluminum compound provides an aluminated silica-based sol. Suitably, the addition of the aluminum compound results in aluminum modification of the silica-based particles, preferably the particles being surface-modified by aluminum. The amount of aluminum compound used can vary within wide limits. Usually the amount of aluminum compound added is from 10: 1 to 100: 1, suitably from 20: 1 to 50: 1, preferably from 25: 1 to 35: 1, and most preferably from 25: 1 to 30: 1. Corresponds to the molar ratio of Si: Al.

In step (d) of the process, when using an aqueous alkali metal silicate to adjust the pH of the aqueous phase, the weight ratio of the alkali metal silicate used in step (b) to the alkali metal silicate used in step (d) has a wide range of limits. Can change within; Usually the weight ratio is 99: 1 to 1: 9, suitably 19: 1 to 1: 2, preferably 4: 1 to 1: 1.

In step (e) of the process, the ion exchange resin is separated from the aqueous phase, for example by filtration. This step can be carried out after step (c), for example after step (c) but before step (d) or after step (d). It is also possible to separate the ion exchange resin from the aqueous phase during step (d). For example, the ion exchange resin can be separated after the addition of the alkaline material but before the addition of the aluminum compound. It is also possible to add a portion of the alkaline material, for example an aqueous alkali metal silicate, to separate the ion exchange resin from the aqueous phase and then add the remaining alkaline material. Preferably, the ion exchange resin is separated from the aqueous phase after step (d).

The concentration of the aqueous starting materials used in the process, for example aqueous alkali metal silicates, aqueous alkali metal hydroxides and aqueous sodium aluminates, is at least 3% by weight, suitably at least 5% by weight, preferably at least 6% by weight, Most preferably adjusted to provide a silica-based sol having a SiO ₂ content of at least 7.5% by weight, and suitably up to 20% by weight, preferably up to 15% by weight. The silica-based sol prepared by the process of the present invention may have the properties defined below.

Aqueous silica-sols according to the present invention are incorporated into silica-based particles, ie silica or SiO ₂ . Based particles, which are preferably in the range of anionic and colloidal, ie colloidal particle sizes. The particles may suitably be modified with aluminum, preferably surface modified with aluminum. The silica-based sol of the present invention is 10: 1 to 100: 1, suitably 20: 1 to 50: 1, preferably 25: 1 to 35: 1, most preferably 25: 1 to 30: 1 It may have a molar ratio of Si: Al.

The silica-based sol of the present invention may have an S value in the range of 10-50%, suitably 12-40%, preferably 15-25%, most preferably 17-24%. S-values are determined by J. Phys. Chem. Measured and calculated as disclosed by Her & Dalton at 60 (1956), 955-957. S-values indicate cohesion or microgel formation and low S-values indicate high cohesion.

The silica-based particles present in the sol may have a specific surface area of at least 300 m ² / g, suitably at least 700 m ² / g, preferably at least 750 m ² / g. The specific surface area is generally at most 1,000 m ² / g, suitably at most 950 m ² / g. The specific surface area is measured by titration with NaOH as disclosed by Sears in Analytical Chemistry 28 (1956): 12, 1981-1983, which titration is for example as disclosed by Sears and disclosed in US Pat. No. 5,176,891. This is done after appropriately removing or adjusting the compounds present in the sample, such as aluminum and boron compounds, which may interfere with the titration.

The silica-based sol of the present invention is generally at least 3: 1, suitably at least 4: 1, preferably at least 5: 1, most preferably at least 6: 1 of Si: X (where X = alkali metal) Has a molar ratio. The molar ratio of Si: X (where X = alkali metal) is generally at most 50: 1, suitably at most 20: 1, preferably at most 17: 1, more preferably at most 15: 1, most preferably 10: 1 maximum.

The silica-based sol of the present invention is preferably stable. Suitably, the sol maintains a specific surface area of at least 300 m ² / g, preferably at least 700 m ² / g, for at least three months of storage or aging at 20 ° C. in the dark and unstirred state. Suitably, the sol maintains an S value in the range of 10 to 50%, preferably 12 to 40%, for at least 3 months of storage or aging at 20 ° C. in the dark and unstirred state.

The silica-based sol of the invention is, for example, a coagulant in pulp and paper making, particularly in the field of water purification for both the purification of different kinds of wastewater and in particular for the purification of white water from the pulp and paper industry, especially in the drainage and retention It is appropriate as zero. Silica-based sol can be used as a coagulant, in particular drainage and retention agent, in combination with organic polymers which may be selected from anionic, amphoteric, non-ionic and cationic polymers and mixtures thereof. The use of such polymers as flocculants and drainage and retention agents is known in the art. The polymer may be derived from natural or synthetic raw materials, and the polymer may be linear, branched or crosslinked. In general, examples of suitable main polymers include anionic, amphoteric and cationic starches; Anionic, amphoteric and cationic acrylamide-based polymers including essentially linear, branched and crosslinked anionic and cationic acrylamide-based polymers; As well as cationic poly (diallyldimethyl ammonium chloride); Cationic polyethylene imine; Cationic polyamines; Cationic polyamideamine and vinylamide-based polymers, melamine-formaldehyde and urea-formaldehyde resins. Suitably, the silica-based sol is used in combination with one or more cationic or amphoteric polymers, preferably cationic polymers. Cationic starch and cationic polyacrylamides are particularly preferred polymers and they can be used alone or in conjunction with each other or with other polymers, such as other cationic and / or anionic polymers. Can be. The molecular weight of the polymer is suitably greater than 1,000,000, preferably greater than 2,000,000. The upper limit is not important; About 50,000,000, generally 30,000,000 and suitably about 25,000,000. However, the molecular weight of polymers derived from natural raw materials can be larger.

The silica-based sol herein can also be used in combination with cationic flocculants, with or without the aforementioned organic polymers. Examples of suitable cationic coagulants include water soluble organic polymeric coagulants and inorganic coagulants. The cationic coagulants may be used alone or together, i.e. the polymeric coagulant may be used in combination with the inorganic coagulant.

Examples of suitable aqueous organic polymeric cationic coagulants include cationic polyamines, polyamideamines, polyethyleneimines, dicyandiamide condensation polymers and water-soluble ethylenically unsaturated monomers or from 50 to 100 mole percent of cationic monomers and from 0 to 50 mole percent of Polymers of monomer mixtures formed of other monomers. The amount of cationic monomer is generally at least 80 mol%, suitably 100%. Examples of suitable ethylenically unsaturated cationic monomers are dialkylaminoalkyl (meth) -acrylates and -acrylamides, preferably in quaternised form, and diallyl dialkyl ammonium chlorides, for example diallyl Dimethyl ammonium chloride (DADMAC), preferably homopolymers and copolymers of DADMAC. Organic polymeric cationic flocculants generally have a molecular weight ranging from 1,000 to 700,000, suitably 10,000 to 500,000. Examples of suitable inorganic flocculants include aluminum compounds such as alum and polyaluminum compounds such as polyaluminium chloride, polyaluminum sulfate, polyaluminum silicate sulfates and mixtures thereof.

The components of the drainage and retention agents according to the invention can be added to the stock in any conventional manner and in any order. When using drainage and retention agents comprising a silica-based sol and an organic polymer, it can be used in the reverse order, but it is preferred that the organic polymer is added to the stock before the silica-based sol is added. More preferably, the organic polymer is added before the shearing step, which may be selected from pumping, mixing, cleaning, etc., and the silica-based sol is added after the shearing step. When using a cationic coagulant, a cationic coagulant is added to the cellulosic suspension, preferably before the addition of the silica-based sol and also preferably before the addition of the organic polymer.

The components of the drainage and retention agents according to the present invention, in particular, vary in a wide range depending on the type and number of components, the type of furnish, the filler content, the type of filler, the time of addition, and the like. It is added to and dehydrated. Generally, the ingredients are added in an amount that provides better drainage and retention than those obtained when no ingredients are added. Silica-based sol, calculated as SiO ₂ and based on dry furnish, ie dry cellulosic fibers and optional filler, is typically added in an amount of at least 0.001% by weight, often at least 0.005% by weight, with an upper limit of generally 1.0 % By weight and suitably 0.5% by weight. The organic polymer is generally added in an amount of at least 0.001% by weight, often at least 0.005% by weight, based on the dry finish and the upper limit is generally 3% by weight, preferably 1.5% by weight. When using a cationic polymeric coagulant, the cationic polymeric coagulant may be added in an amount of 0.05% or more based on the finish. Suitably, the amount is in the range of 0.07 to 0.5%, preferably in the range of 0.1 to 0.35%. When using an aluminum compound as the inorganic coagulant, the total amount added is calculated as Al ₂ O _{3 and} is generally at least 0.05% based on the dry finish. Suitably the amount is in the range of 0.1 to 3.0%, preferably 0.5 to 2.0%.

Traditional paper additives may be used in combination with additives according to the present invention in paper making, including, for example, dry strength agents, wet strength agents, optical brightening agents. , Sizing agents such as dyes, rosin-based sizing agents and cellulose-reactive sizing agents, for example alkyl and alkenyl ketene dimers and ketene multimers, alkyl and alkenyl succinic anhydrides and the like. Cellulose suspensions, or stocks, are for example natural and synthetic calcium such as kaolin, china clay, titanium dioxide, gypsum, talc and chalk, ground marble and precipitated calcium carbonate. It may contain traditional types of mineral fillers such as carbonates.

The method of the present invention is used for the manufacture of paper. The term "paper" as used herein includes paper and its products as well as cellulosic sheets or web-like products such as cardboard and paperboard, and their products. The method can be used to make paper from different types of cellulose-containing fiber suspensions, which suspension preferably contains at least 25% by weight, preferably at least 50% by weight, based on the precursor material. The suspensions are chemical pulp, such as sulphates from hardwood and softwood, sulphites and organosolve pulp, mechanical pulp such as thermomechanical pulp, chemistry -Based on fibers from chemo-thermomechanical pulp, refiner pulp and groundwood pulp, and also based on fibers from recycled fibers, optionally de-inked pulp And can be based on mixtures thereof. The pH of the suspension, ie the stock, may be in the range of about 3 to about 10. The pH is suitably above 3.5, preferably in the range of 4-9.

The invention is further illustrated in the following examples, but is not limited thereto. Unless otherwise indicated, parts and% are parts by weight and% by weight, respectively.

Example

The following equipment and starting materials were used throughout the examples:

(a) a reactor equipped with a stirrer;

(b) the ion exchange resin regenerated with sulfuric acid according to the manufacturer's instructions Amberiite ^® IRC84SP (Rohm & Haas can be purchased from, Inc.);

(c) an aqueous sodium silicate solution having a SiO ₂ content of about 21 wt% and a molar ratio of SiO ₂ to Na ₂ O 3.32.

(d) an aqueous sodium aluminate solution containing 2.44 wt% Al ₂ O ₃ ; And

(e) An aqueous sodium hydroxide solution having a concentration of 5 moles per kilo.

Example 1

This example presents the preparation of a silica-based sol according to the present invention: Regenerated ion exchange resin (471 g) and water (1,252 g) were charged to the reactor. The resulting slurry was vigorously stirred and heated to 30 ° C. Aqueous sodium silicate (298 g) was then added to the slurry at a rate of 5 g / min. After addition of sodium silicate, the pH of the slurry was about 7.3. The slurry was then stirred for 44 minutes, with the result that the pH of the aqueous phase was 6.9. Further aqueous sodium silicate (487 g) was then added to the slurry at a rate of 5 g / min, wherein the pH of the aqueous phase was 10.4. The silica-based sol obtained from the ion exchange resin was separated. Aqueous sodium aluminate (52 g) was added to the sol (527.4 g) under vigorous stirring for a period of 10 minutes.

The silica-based sol obtained had the following properties: SiO ₂ content = 7.7 wt%; Molar ratio of Si: Na = 7.5; Molar ratio of Si: Al = 26.2; pH = 10.7; Specific surface area = 790 m ² / g; And S-value = 18%.

Example  2

This example illustrates the preparation of another silica-based sol according to the present invention: a reactor was charged with regenerated ion exchange resin (1,165 g), and water (686 g), up to approximately 40% of ion exchange capacity. The aqueous slurry obtained was stirred vigorously. Aqueous sodium silicate (989 g) was then added to the slurry for a period of 10 minutes. After addition of sodium silicate, the pH of the aqueous slurry was about 10.7. The slurry was then stirred for 22 minutes, where the pH of the resulting aqueous slurry was 9.8. An additional aqueous sodium silicate (128 g) was then added to the slurry for 1 minute, at which time the pH of the aqueous slurry was 10.3. The aqueous phase was separated from the ion exchange resin. Aqueous sodium aluminate (57 g) was added to the aqueous phase (463 g) at 5.7 g / min under vigorous stirring.

The silica-based sol obtained had the following properties: SiO ₂ content = 10.3%; Si: Na molar ratio = 4.9; Si: Al molar ratio = 33.6; pH = 11.0; Specific surface area = 1,000 m ² / g; And S value = 23%.

Example  3

This example also describes the preparation of another silica-based sol according to the invention: Regenerated ion exchange resin (600 g) and water (1,600 g) were charged to the reactor. The aqueous slurry obtained was vigorously stirred and heated to a temperature of 30 ° C. Aqueous sodium silicate (764 g) was then added to the slurry at a rate of 6.8 g / min. After addition of sodium silicate, the pH of the aqueous slurry was about 8 at which time the ion exchange resin was separated from the aqueous phase. Aqueous sodium hydroxide (30 g) was added at the rate of 10 g / min at the aqueous phase with a pH of 10 at the aqueous phase. Aqueous sodium aluminate (83 g) was then added to the aqueous phase (776 g) for 10 minutes under vigorous stirring.

The silica-based sol obtained had the following properties: SiO ₂ content = 6.1 wt%; Si: Na molar ratio = 5.9; Si: Al molar ratio = 20.3; pH = 10.9; Specific surface area = 930 m ² / g; And S value = 22%.

Example  4

This example illustrates the preparation of another silica-based sol according to the present invention: The reactor was charged with regenerated ion exchange resin (1,785 g) and water (920 g) up to approximately 40% of ion exchange capacity. The aqueous slurry obtained was vigorously stirred. Aqueous sodium silicate (1,390 g) was then added to the slurry for 10 minutes. After addition of sodium silicate, the pH of the aqueous slurry was about 10.4. The slurry was then stirred for 24 minutes, at which time the pH of the aqueous slurry was 9.2. Ion exchange resin was separated from the aqueous phase. Aqueous sodium hydroxide (15.5 g) was added for about 2 minutes at which time the pH of the aqueous phase was 10. Aqueous sodium aluminate (56.7 g) was then added to the aqueous phase (483 g) at 5.7 g / min under vigorous stirring.

The silica-based sol obtained had the following properties: SiO ₂ content = 9.8 wt%; Si: Na molar ratio = 6.1; Si: Al molar ratio = 30.2; pH = 10.8; Specific surface area = 940 m ² / g; And S value = 22%.

Example  5

For comparison, the following silica-based sol of References 1-4 was prepared:

Reference 1 is a silica-based sol prepared according to the disclosure of Example 4 of US Pat. Nos. 6,372,089 and 6,372,806.

Reference 2 is a silica-based sol made according to the disclosure of US Pat. No. 5,368,833, having an S-value of about 25%, a Si: Al molar ratio of about 19, and having a SiO ₂ specific surface area of about 900 m ² / g. , Silica particles surface-modified with aluminum.

Reference 3 is a silica-based sol prepared according to the disclosure of US Pat. No. 5,603,805, containing silica particles having an S-value of 34% and a specific surface area of about 700 m ² / g.

Reference 4 is a silica-based sol prepared according to the disclosure of US Pat. No. 5,368,833, which has an S-value of 20%, a Si: Al molar ratio of about 18, and a specific surface area of about 820 m ² / g SiO ₂ . Silica particles surface-modified with aluminum.

Example  6

In the following tests, the drainage performance of the silica-based sol according to Examples 1 and 2 ("Example 1" and "Example 2", respectively) was tested for the drainage performance of the silica-based sol according to Example 5. Drainage performance was assessed using a Power Drain Analyzer (DDA), available from Akribi, Sweden, which installed a volume of stock when applying a vacuum to the wire side opposite the side where the stock was present. Measure the time while is drained through the wire.

The stock used was based on a standard fine paper finish consisting of 60% bleached birch sulfate and 40% bleached fine sulfate. 30% of ground calcium carbonate was added to the stock as a filler and 0.3 g / l Na ₂ SO ₄ .1OH ₂ O was added to increase conductivity. The pH of the stock was 8.1, the conductivity was 1.5 mS / cm, and the consistency was 0.5%. In the test, the silica-based sol was tested with cationic starch having a degree of substitution of about 0.042. The starch was added in an amount of 8 kg / tonne calculated as dry starch on the dry finish.

Throughout the test the stock was stirred in a baffled jar at a speed of 1,500 rpm and the chemical additives to the stock were prepared as follows:

i) stirring cationic starch for 30 seconds after addition;

Ii) stirring for 15 seconds after addition of the silica-based sol; And

Iii) draining the stock while automatically recording the drainage time.

Table 1 shows the results obtained using various doses (kg / tonne) of silica-based sol calculated as SiO ₂ based on the dry finish.

Test number Cationic Starch Dose [kg / t] Silica Dose [kg / t] Dehydration time [s] Example 1 Example 2 Comparison 1 Comparison 2 One 8 0 19.4 19.4 19.4 19.4 2 8 1.0 13.8 14.8 14.7 14.1 3 8 1.5 12.2 13.1 13.7 13.7 4 8 2.0 11.1 12.0 13.1 12.6

Example  7

The drainage performance of the silica-based sol according to Example 1 was further evaluated. The procedure of Example 6 was followed but cationic polyacrylamide (“PAM”) was used in place of cationic starch. Moreover, the stock was stirred in a baffled jar at a speed of 1,500 rpm during the test and the chemical additives to the stock were prepared as follows:

i) adding cationic polyacrylamide and stirring for 20 seconds;

Ii) stirring for 10 seconds after adding the silica-based sol; And

Iii) draining the stock while automatically recording the drainage time.

Table 2 shows the different capacities of cationic polyacrylamides (kg / tonne) calculated as dry starch based on dry finish, and the various capacities (kg) as silica-based sol calculated as SiO ₂ based on dry finish. / tonne) is used to show the result obtained.

Test number Cationic PAM Dose [kg / t] Silica Dose [kg / t] Dehydration time [s] Example 1 Comparison 1 Comparison 2 One 0.8 0 17.2 17.2 17.2 2 0.8 0.25 9.8 11.1 10.0 3 0.8 0.50 7.2 8.2 7.7 4 0.8 0.75 6.6 7.1 7.4

Example  8

The drainage performance of the silica-based sol according to Examples 3 and 4 was tested according to the procedure according to Example 6. Table 3 shows the results obtained using various doses (kg / tonne) of silica-based sol calculated as SiO ₂ based on the dry finish.

Test number Cationic Starch Dose [kg / t] Silica Dose [kg / t] Dehydration time [s] Example 3 Example 4 Comparison 1 Comparison 2 Comparison 3 One 8 0 20.6 20.6 20.6 20.6 20.6 2 8 1.0 13.9 14.8 15.5 14.7 15.1 3 8 1.5 12.8 13.5 14.1 13.6 14.4 4 8 2.0 12.5 12.8 13.6 13.5 13.4

Example  9

The drainage performance of the silica-based sol according to Examples 3 and 4 was tested according to the procedure according to Example 7. Table 4 shows the results obtained using various doses (kg / tonne) of silica-based sol calculated as SiO ₂ based on the dry finish.

Test number Cationic PAM Dose [kg / t] Silica Dose [kg / t] Dehydration time [s] Example 3 Example 4 Comparison 1 Comparison 2 Comparison 3 One 0.8 0 16.0 16.0 16.0 16.0 16.0 2 0.8 0.25 8.6 8.5 9.1 10.7 8.7 3 0.8 0.50 6.6 6.5 7.9 8.0 7.4 4 0.8 0.75 6.0 6.7 7.6 7.1 7.2

The present invention relates to a process for preparing an aqueous silica-based sol comprising: (a) providing a cationic ion exchange resin having at least a portion of ion exchange capacity in hydrogen form; (b) contacting the ion exchange resin with an aqueous alkali metal silicate to form an aqueous slurry; (c) stirring the aqueous slurry until the pH of the aqueous phase is in the range from 5.0 to 11.5; And / or alternatively, stirring the aqueous slurry to enable particle agglomeration or microgel formation corresponding to an S value of 45% or less, thereby obtaining an aqueous phase pH of 5.0 or greater; (d) adjusting the pH of the aqueous phase to at least 9.0 using at least one material comprising at least one aluminum compound; And (e) separating the ion exchange resin from the aqueous phase after step (c) or step (d). The present invention also provides S values in the range of 15 to 25%, Si: Al molar ratio in the range 20: 1 to 50: 1, Si: X molar ratio in the range 5: 1 to 17: 1, wherein X = alkali metal, 5% by weight. A silica-based sol containing silica-based particles having a SiO ₂ content of at least and having a specific surface area of at least 300 m ² / g. The invention also relates to a papermaking method comprising: (i) providing an aqueous suspension comprising cellulose fibers; (j) adding to said suspension at least one drainage and retention agent comprising a silica-based sol according to the invention; And (k) dehydrating the suspension obtained to provide a paper sheet or paper web.

Claims (33)

Aqueous silica-based sol preparation process comprising: (a) providing a cationic ion exchange resin having an ion exchange capacity of at least 40% in hydrogen form; (b) contacting the ion exchange resin with an aqueous alkali metal silicate to form an aqueous slurry; (c) stirring the aqueous slurry until the pH of the aqueous phase is in the range from 5.0 to 11.5; Or alternatively, stirring the aqueous slurry to enable particle agglomeration or microgel formation corresponding to an S value of 5 to 45% to obtain an aqueous phase pH of 5.0 to 11.5; (d) adjusting the pH of the aqueous phase to at least 9.2 to 11.5 using at least one material comprising at least one aluminum compound; And (e) separating the ion exchange resin from the aqueous phase after step (c) or step (d). Process for preparing an aqueous silica-based sol comprising the following steps: (a) providing a reaction vessel; (b) forming an aqueous slurry by providing the reaction vessel with: (i) a cationic ion exchange resin having an ion exchange capacity of at least 40% in hydrogen form, and (ii) aqueous alkali metal silicates; (c) stirring the aqueous slurry until the pH of the aqueous phase is in the range from 5.0 to 11.5; Or, alternatively, stirring the aqueous slurry to enable particle agglomeration or microgel formation corresponding to an S value of 5 to 45% to obtain a pH of an aqueous phase of 5.0 to 11.5; (d) adding at least one material comprising at least one aluminum compound to the aqueous phase obtained after step (c) to form an aqueous phase having a pH of 9.2 to 11.5; (e) separating the ion exchange resin from the aqueous phase after step (c) or step (d). The process according to claim 1 or 2, further comprising the step (f) of obtaining an aqueous silica-based sol having an S value of 10-50%. The process of claim 1 or 2, wherein the ion exchange resin is separated from the aqueous phase after step (c) but before step (d). The process according to claim 1 or 2, wherein the ion exchange resin is separated from the aqueous phase after step (d). The method of claim 1 or 2, wherein in step (d) said at least one substance comprises an alkaline substance. 7. The method of claim 6 wherein the alkaline material comprises an aqueous alkali metal silicate. 7. The method of claim 6, wherein the alkaline material comprises an aqueous alkali metal hydroxide. The aqueous phase pH of claim 1 or 2, wherein in step (c) the aqueous slurry is stirred to enable particle agglomeration or microgel formation corresponding to an S value of 8 to 35% to obtain an aqueous phase pH of 6.0 to 11.0. Characterized in that. The process according to claim 1 or 2, characterized in that in step (c) the aqueous slurry is stirred until the pH of the aqueous phase is in the range from 5.0 to 11.5. The process according to claim 1 or 2, characterized in that in step (c) the aqueous slurry is stirred until the pH of the aqueous phase is in the range of 6.0 to 8.0. The process according to claim 1 or 2, characterized in that in step (c) the aqueous slurry is stirred until the pH of the aqueous phase is in the range of 6.5 to 7.5. The process according to claim 1 or 2, characterized in that in step (c) the aqueous slurry is stirred until the pH of the aqueous phase is in the range of 9.0 to 10.0. The process according to claim 1 or 2, characterized in that in step (c) the slurry is stirred to enable particle agglomeration or microgel formation corresponding to an S-value in the range of 10-25%. The method of claim 1 or 2, wherein in step (d) the aluminum compound is sodium aluminate. The process according to claim 1 or 2, wherein in step (d) the pH of the aqueous phase is adjusted in the range of 9.5 to 11.2. The process of claim 1 or 2, wherein the pH of the aqueous phase in step (d) is adjusted by first adding aqueous sodium silicate and subsequently adding aqueous sodium aluminate. The aqueous phase according to claim 1 or 2, wherein in step (d) the pH of the aqueous phase is first added with an aqueous alkali metal silicate, after which the ion exchange resin is separated from the aqueous phase and the aqueous aluminum compound is subsequently followed. Controlled by addition. The process according to claim 1 or 2, wherein the pH of the aqueous phase in step (d) is adjusted by first adding aqueous sodium hydroxide and subsequently adding aqueous sodium aluminate. The process of claim 1 or 2, wherein the silica-based sol has a Si: X molar ratio in the range of 6: 1 to 10: 1, wherein X is an alkali metal. The method of claim 1 or 2, wherein the silica-based sol has an S-value in the range of 17 to 24%. The process of claim 1 or 2, wherein the silica-based sol contains silica-based particles having a specific surface area of 700 to 950 m ² / g. The process of claim 1 or 2, wherein the silica-based sol has a SiO ₂ content in the range of 6-15 wt%. S value in the range of 15 to 25%, Si: Al molar ratio in the range of 20: 1 to 50: 1, Si: X molar ratio in the range of 5: 1 to 17: 1, wherein X = alkali metal, 5 to 20% by weight of SiO It has a _second content having more than 300 m ² / g specific surface area of the silica-containing silica-based particles-based sol. The silica-based sol of claim 24, wherein the silica-based sol has a Si: X molar ratio in the range of 6: 1 to 10: 1. 26. The silica based sol of claim 24 or 25, wherein the silica-based sol has an S-value in the range of 17-24%. 26. The silica based sol of claim 24 or 25, wherein the silica-based sol contains silica-based particles having a specific surface area of 700 to 950 m ² / g. 26. The silica based sol of claim 24 or 25, wherein the silica-based sol has a SiO ₂ content in the range of 6-15 wt%. Paper manufacturing method including (i) providing an aqueous suspension comprising cellulose fibers; (ii) adding to the suspension one or more drainage and retention agents comprising a silica-based sol; And (iii) dehydrating the suspension obtained to provide a paper sheet or paper web; Wherein said sol is a silica-based sol according to claim 24. 30. The method of claim 29, wherein said drainage and retention agent comprises cationic starch. 30. The method of claim 29, wherein said drainage and retention agent comprises a cationic synthetic polymer. 30. The method of claim 29, wherein said drainage and retention agent comprises an anionic polymer. 30. The method of claim 29, comprising adding a cationic coagulant to the suspension.