Title of Invention

METHOD FOR PRODUCING AQUEOUS SUSPENSIONS OF MINERAL FILLERS AND AQUEOUS SUSPENSIONS OF MINERAL FILLERS THUS OBTAINED

Abstract

Claim: 1.A process for the preparation of aqueous suspensions of fluid mineral matter, which are able to be pumped and conveyed by the end user immediately after the filtration stage, possibly followed by a compression, with the use of small quantities of dispersant, and allowing the control of the quantities of dispersant present in the filtrate comprises a filtration in two separate stages that consist of a first stage in which a pre-layer is formed using no dispersant agent, followed by a second stage continuous with the first in the presence of one or more dispersant agents between 0.01% to 10%, preferably between 0.1% to 2%, by dry weight of dispersant relative to the dry weight of mineral matter to be filtered, during which the water of the pre-layer is replaced by the water of the second filtration stage containing one or more dispersant agents, wherein the quantity of dispersant agent present in the filtrate is controlled and limited by a continuous measurement of the electrical conductivity of the filtrate and in that the filtration stage is stopped as soon as the electrical conductivity of the filtrate increases.

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See Section 10, rule 13) TITLE OF INVENTION METHOD FOR PRODUCING AQUEOUS SUSPENSIONS OF MINERAL FILLERS AND AQUEOUS SUSPENSIONS OF MINERAL FILLERS THUS OBTAINED. 2. APPLICANT(S) (a) NAME : OMYA DEVELOPMENT AG, (b) NATIONALITY : SWISS Company (c) ADDRESS : BAGLESTRASSE 42, CH-4665 ORTRINGEN, SUISSE, SWITZERLAND 3. PREAMBLE TO THE DESCRIPTION The following specification particularly describes the nature of the invention and the manner in which it is to be performed : - PROCESS FOR PREPARATION OF AQUEOUS SUSPENSIONS OF MINERAL FILLERS. AQUEOUS SUSPENSIONS OF MINERAL FILLERS OBTAINED AND USES THEREOF. The present invention concerns the technical sector of mineral fillers, such as notably the paper field and in particular the coating of paper and the mass filling of paper, or the fields of paint, water treatment such as notably the field of purification muds, detergency, ceramics, cements or hydraulic binders, of public works, of inks and varnishes, of sizing of textiles, or all types of industry requiring the use of concentrated pigment suspensions, and it concerns more particularly the fields of paper, water treatment, paint and ceramics. In a more particular manner, the invention concerns a process for preparing aqueous suspensions of mineral fillers or pigments having a satisfactory rheology used in the abovementioned various fields. To produce the industrial applications in the above fields, it is necessary to produce suspensions of mineral fillers, notably calcium carbonates, having excellent rheology, i.e. having a weak viscosity during the storage period to facilitate handling and application, and also the highest possible mineral matter content, in order to reduce the quantity of water handled. During the manufacture of these aqueous suspensions of mineral fillers satisfying the abovementioned criteria, some processes lead to aqueous suspensions with weak concentrations of mineral or organic matter. It is then necessary to concentrate these suspensions in order to offer them to the end user who uses the said aqueous suspensions, or to eliminate the solvents present when these fillers are used in a powder form. One of the means known to date is to concentrate these suspensions by means of a filtration process but, until the present, these nitrations have produced cakes which are so compact that it is necessary firstly to add the dispersing agent after the filtration stage and secondly to use a large amount of mechanical energy to return them to suspension or convey the concentrated suspensions. Thus, patent application WO 00/39029 teaches the skilled man in the art that a process to prepare an aqueous suspension of calcium carbonate consists in continuing the filtration stage with a stage of thermal concentration and then by a stage involving the use of mechanical energy to return the mineral particles to suspension, with the addition of the dispersing agent after the filtration stage. Faced with this problem of additional use of dispersing agent or use of a large amount of mechanical energy, the Applicant has found in a surprising fashion that, according to the invention, the process for preparing aqueous suspensions of mineral matter characterised by a filtration in two separate stages enables the problem to be resolved and thus enables an aqueous suspension of mineral matter to be obtained which is directly usable after the filtration stage, possibly followed by a compression, without any obligation to implement an additional stage such as the addition of a dispersing agent after the concentration stage, or the use of mechanical energy to return the mineral matter to suspension. Thus, the filtering of suspensions not containing any dispersing agent is known (Solid-liquid filtration and separation technology, A. Rushton, A.S. Ward, R.G. Holdich, 1996; Filtration: Equipment selection Modelling and process simulation, RJ. Wakeman, E.S. Tarleton, 1999; Pratique de la filtration [Practice of filtration], J.P. Duroudier, 1999) but the disadvantage is that this produces cakes which are difficult to redisperse. The introduction, into an aqueous suspension of calcium carbonate, of half the quantity of dispersing agent before filtering the said suspension and adding the other half after the filtration stage to obtain a highly concentrated suspension of calcium carbonate, is also known (JP 53-025646). The skilled man in the art is also acquainted with another document (GB 1 482 258) which reveals a process for preparing aqueous suspensions of precipitated calcium carbonate (PCC) using a dispersing agent before the concentration stage by filtration in a single stage, but this process has two major disadvantages. The first consists in the need to use a pressure higher than 17 bars in order to be able to filter, and also in the need to use very particular dispersive apparatuses to disperse the cake obtained. The second disadvantage of the said method lies in the fact that large quantities of dispersing agent are found in the filtrate, causing environmental and ecological problems, and waste treatment problems, or problems with recirculating the used water in the remainder of the process, and also causing cost problems in the light of the large quantities of dispersing agent used. Similarly, patent GB 1 463 974 describes a method of filtration in a single stage leading to the same disadvantages as those mentioned above. Thus, the techniques known by the skilled man in the art lead him to use the dispersing agent either fully after the filtration or half before the filtration stage and the other half after the filtration stage, or to use the dispersing agent before the filtration stage but with the need to use firstly a large quantity of dispersing agent causing the abovementioned disadvantages, and secondly a very particular dispersive apparatus. Generally, all these techniques known until the present have the disadvantage that they cause great difficulty in returning the cake to suspension if one wishes to obtain highly concentrated suspensions of dry matter with a satisfactory rheology. Thus, one of the aims of the invention is to offer a process for preparing aqueous suspensions of fillers and/ or mineral pigments with a satisfactory rheology, i.e. to offer a process for preparing aqueous suspensions of fluid mineral matter, which is able to be pumped and conveyed by the end user immediately after the filtration stage, possibly followed by a compression, for small quantities of dispersing agent used and allowing control of the quantities of dispersing agent present in the filtrate with a view to obtain near-zero quantities of dispersing agent present in the filtrate. Near-zero quantities of dispersing agent present in the filtrate means that the end of the second stage corresponds to the appearance of the dispersing agent in the filtrate. This appearance of dispersing agent in the filtrate is quantified by an electrical conductivity measurement. This process of preparing, according to the invention, aqueous suspensions of fluid mineral matter, which are able to be pumped and conveyed by the end user immediately after the filtration stage, with small quantities of dispersing agent used and allowing control of the quantities of dispersing agent present in the filtrate, is characterised in that it comprises a filtration in two separate stages, possibly followed by a compression. In a more particular manner, these two separate filtration stages consist of a first stage in which a pre-layer is formed which uses no dispersing agent followed by a second stage following on from the first in the presence of one or more dispersing agents, and in an even more particular manner, followed by a second filtration stage containing 0.01% to 10%, and preferentially from 0.1% to 2%, by dry weight of dispersing agent relative to the dry weight of mineral matter for filtering. When this pre-layer has been formed, the water in the pre-layer is replaced, in the second stage, by the water in the second stage containing one or more dispersing agents such that the dispersing agent or agents are distributed in a homogeneous manner throughout the filtration cake. It should be noted that during the entire filtration period the pressure used has a value of the same magnitude as that commonly used in traditional filtration processes. In a still more particular manner, this process according to the invention is characterised in that the quantity of dispersing agent present in the filtrate is controlled and limited by a continuous measurement of the electrical conductivity of the filtrate, and in that the filtration stage is stopped as soon as the electrical conductivity of the filtrate increases. This stoppage of the filtration when the electrical conductivity increases corresponds to a near-zero quantity of dispersing agent present in the filtrate. Thus, the process according to the invention enables one to obtain directly aqueous suspensions of fluid mineral matter which are able to be pumped and conveyed immediately after the filtration stage, possibly followed by a compression, with small quantities of dispersing agent used and near-zero quantities of dispersing agent present in the filtrate. To accomplish this, the dispersing agent or agents used are chosen either from among the dispersing agents commonly used in the field of the suspension of mineral fillers such as, for example, polyphosphates, polyacrylates, whether or not functionalised, or any other polymer with a dispersant function, or from among the anionic, cationic, non- ionic or indeed zwitterionic surface active agents The process for preparing aqueous suspensions of mineral matter according to the invention is characterised in that the mineral matter can be chosen from among natural calcium carbonate, including notably the various chalks, calcites or marbles, or from synthetic calcium carbonate such as precipitated calcium carbonate at different stages of crystallisation, or from among the mixed carbonates of magnesium and calcium such as the dolomites, or from among magnesium carbonate, zinc carbonate, lime, magnesia, barium sulphate such as barita, calcium sulphate, silica, the magnesio-silicates such as talc, wollastonite, clays and other alumino-silicates such as kaolins, mica, metal or alkaline earth oxides or hydroxides such as magnesium hydroxide, iron oxides, zinc oxide, titanium oxide, titanium dioxide in its anatase or rutile forms, and mixtures of these such as, notably, mixtures of talc and calcium carbonate. In a preferential manner, the mineral matter is chosen from among natural calcium carbonate, synthetic calcium carbonate also called precipitated calcium carbonate, titanium dioxide in its anatase or rutile forms, kaolin, aluminium hydroxide, clays or mixtures of these. Finally, another aim of the invention concerns the use of aqueous suspensions according to the invention in the fields of paper, paint, treatment of water such as notably the field of purification muds, detergency, ceramics, cements or hydraulic binders, public works, inks and varnishes, sizing of textiles or again all types of industry requiring the use of concentrated pigment suspensions, and concerns more particularly the use of aqueous suspensions according to the invention in the fields of paper, water treatment, paint and ceramics. The scope and interest of the invention will be better appreciated through the following examples, which are by no means limitative. EXAMPLE 1 This example illustrates the invention and concerns the filtration of an aqueous suspension of natural calcium carbonate and more particularly of a Champagne chalk of median diameter equal to 2 micrometers. To accompUsh this, 286.8 grams of the chalk suspension with a dry matter concentration equal to 20.3% is used and, as the filtration device, an item of laboratory equipment from the company CHOQUENET consisting: - of a polypropylene frame with a chamber 2.2 cm wide and 25 cm2 in section, - of two steel plates, one of which fixed, with grooves on the inner face, in which the filtrate is collected, - of two joints providing the seal between the plates and the frame, - of two polypropylene filtrating membranes from the company SEFAR FYLTTS(ref.:F0149AN) The filtration chamber (CF) can be fed successively by a tank Rl containing the suspension of the pigment for concentration and then by a second tank R2 containing the same suspension as above, to which will be added a quantity of dispersing agent Co required to obtain a concentrated cake (ES2) and which can easily be removed, i.e. a cake with a sufficient consistency to be removed from the filtration chamber as a single element. Another alternative consists in having R2 contain only one dispersing agent solution. The filtration process itself is conducted in two separate stages (See diagram I): 1/ In a first stage, a pre-layer from suspension 1 is formed on the filtrating membranes, 2/ followed by a second stage in which the filtration is undertaken from suspension 2 containing the dispersing agent. In the second stage, the water contained in the pre-layer is replaced by the water loaded with the dispersing agent contained in suspension 2, such that at the end of the filtration stage the dispersing agent is distributed in a homogeneous manner throughout the filtration cake. Each of the filtration stage is accomplished at a pressure of 5 bars. The filtration stage is followed by a compression stage at a pressure of 15 bars, and enables a filtration cake of dryness ES2 to be obtained. The filtration cake is then subjected to a weak shearing in order to obtain a suspension also called a fluid "slurry". This stage is accomplished using a standard laboratory mechanical agitator of the RAYNERI type, fitted with an adapted blade. When the suspension is homogeneous we measure its viscosity (visco 2) using an RVT type Brookfield™ viscometer fitted with an adapted module. The suspension according to the invention, obtained by the process according to the invention described above, and using 0.2% by dry weight, relative to the dry weight of dry chalk, of an ammonium polyacrylate of molecular weight by weight of 4500g/mole, is then an aqueous suspension of chalk with a dry matter concentration of 76.8% and a Brookfield™ viscosity of 2900 mPa.s measured at 10 rpm and of 518 mPa.s measured at 100 rpm. The filtration stage is stopped when the electrical conductivity of the filtrate measured using a conductivity meter HI 8820N from Hanna Instruments (Portugal) increases, i.e. after 170.6 grams of filtrate have been collected. The dispersing agent content in the filtrate is then near-zero. EXAMPLE 2 This example illustrates the invention and concerns the filtration of an aqueous suspension of natural calcium carbonate and more particularly of a marble of median diameter equal to 0.75 micrometers. To accompKsh this, with the same operating method and the same equipment as in example 1, firstly 173.2 grams of the aqueous suspension of marble is used, the dry matter concentration of which is equal to 27.6%, and also equal to 0.5% by dry weight, relative to the dry weight of marble, of a sodium polyacrylate called Coatex DV 834, to obtain directly an aqueous suspension of marble the dry matter concentration of which is equal to 72.1%, and the Brookfield™ viscosity of which is equal to 635 mPa.s measured at 10 rpm and equal to 240 mPa.s measured at 100 rpm. The filtration stage is stopped when the electrical conductivity of the filtrate measured using a conductivity meter HI 8820N from Hanna Instruments (Portugal) increases, i.e. after 114.5 grams of filtrate have been collected. The dispersing agent content in the filtrate is then near-zero. EXAMPLE 3 This example illustrates the invention and concerns the filtration of an aqueous suspension of precipitated calcium carbonate (PCC) of median diameter equal to 0.9 micrometers. To accomplish this, with the same operating method and the same equipment as in example 1, firstly 156 grams of the aqueous suspension of PCC is used, the dry matter concentration of which is equal to 24%, and also equal to 1.0% by dry weight, relative to the dry weight of PCC, of a sodiun* polyacrylate of molecular weight by weight of 10,000 g/mole, to obtain directly an aqueous suspension of PCC the dry matter concentration of which is equal to 65.9%, and the ESrookfield™ viscosity of which is equal to 4570 mPa.s measured at 10 rpm and equal to 930 mPa.s measured at 100 rpm. The filtration stage is stopped when the electricle conductivity of the filtrate measureds using a conductivity meter HI 8820N from Hanna Instruments (Portugal) increases, i.e. after 123.7 grams of filtrate have been collected. The dispersing agent content in the filtrate is then near-zero, EXAMPLE 4 This example illustrates the invention and concerns the filtration of an aqueous suspension of natural calcium carbonate and more particularly of a marble of median diameter equal to 0.6 micrometers. To accomplish this, with the same operating method and the same equipment as in example 1, firstly 226.4 grams of the aqueous suspension of marble is used, the dry matter concentration of which is equal to 20.9%, and also equal to 1.0% by dry weight, relative to the dry weight of marble, of a sodium polyacrylate called Coatex DV 834, to obtain directly an aqueous suspension of marble the dry matter concentration of which is equal to 70.0%, and the Brookfield™ viscosity of which is equal to 1500 mPa.s measured at 10 rpm and equal to 670 mPa.s measured al 100 rpm. The filtration stage is stopped when the electrical conductivity of the filtrate measured using a conductivity meter HI 8820N from Hanna Instruments (Portugal) increases, i.e. after 177.7 grams of filtrate have been collected. The dispersing agent content in the filtrate is then near-zero. EXAMPLE 5 This example illustrates the invention and concerns the filtration of an aqueous suspension of titanium dioxide commercialised by the company Elementis under the name RHD2. To accomplish this, with the same operating method and the same equipment as in example 1, firstly 390.9 grams of the aqueous suspension of titanium dioxide is used, the dry matter concentration of which is equal to 24.2%, and also equal to 0.3% by dry weight, relative to the dry weight of titanium dioxide, of a copolymer commercialized by the company Coatex under the name Coatex BR3, to obtain directly an aqueous suspension of titanium dioxide the dry matter concentration of which is equal to 74.2%, and the Brookfield™ viscosity of which is equal to 1100 mPa.s measured at 10 rpm and equal to 460 mPa.s measured at 100 rpm. The filtration stage is stopped when the electrical conductivity of the filtrate measured using a conductivity meter HI 8820N from Hanna Instruments (Portugal) increases, i.e. after 288.5 grams of filtrate have been collected. The dispersing agent content in the filtrate is then near-zero. EXAMPLE 6 This example illustrates the invention and concerns the filtration of an aqueous suspension of kaolin commercialised by the company Imerys under the name SPS. To accomplish this, with the same operating method and the same equipment as in example 1, firstly 229.1 grams of the aqueous suspension of kaolin is used, the dry matter concentration of which is equal to 23.9%, and also equal to 0.2% by dry weight, relative to the dry weight of kaolin, of a sodium polyacrylate of molecular weight by weight of 4,500 g/mole, to obtain directly an aqueous suspension of kaolin the dry matter concentration of which is equal to 68.0%, and the Brookfield™ viscosity of which is equal to 1590 mPa.s measured at 10 rpm and equal to 655 mPa.s measured at 100 rpm. The filtration stage is stopped when the electrical conductivity of the filtrate measured using a conductivity meter HI 8820N from Hanna Instruments (Portugal) increases, i.e. after 167.7 grams of filtrate have been collected. The dispersing agent content in the filtrate is then near-zero. EXAMPLE 7 This example illustrates the invention and concerns the filtration of an aqueous suspension of aluminiurn hydroxide commercialised by the company Martinswerk under the name OL104. To accomplish this, with the same operating method and the same equipment as in example 1, firstly 201.0 grams of the aqueous suspension of aluminium hydroxide is used, the dry matter concentration of which is equal to 25.3%, and also equal to 0.25% by dry weight, relative to the dry weight of aluminium hydroxide, of a copolymer of molecular weight by weight of 3,500 g/mole, and consisting of acrylic acid and methoxy-polyethylene glycol methacrylate of molecular weight 2000, which has been totally neutralised using soda, to obtain directly an aqueous suspension of aluminium hydroxide the dry matter concentration of which is equal to 71.8%, and the Brookfield™ viscosity of which is equal to 230 mPa.s measured at 10 rpm and equal to 230 mPa.s measured at 100 rpm. The filtration stage is stopped when the electrical conductivity of the filtrate measured using a conductivity meter HI 8820N from Hanna Instruments (Portugal) increases, i.e. after 144.2 grams of filtrate have been collected. The dispersing agent content in the filtrate is then near-zero. Claim: 1. A process for the preparation of aqueous suspensions of fluid mineral matter, which are able to be pumped and conveyed by the end user immediately after the filtration stage, possibly followed by a compression, with the use of small quantities of dispersant, and allowing the control of the quantities of dispersant present in the filtrate comprises a filtration in two separate stages that consist of a first stage in which a pre-layer is formed using no dispersant agent, followed by a second stage continuous with the first in the presence of one or more dispersant agents between 0.01% to 10%, preferably between 0.1% to 2%, by dry weight of dispersant relative to the dry weight of mineral matter to be filtered, during which the water of the pre-layer is replaced by the water of the second filtration stage containing one or more dispersant agents, wherein the quantity of dispersant agent present in the filtrate is controlled and limited by a continuous measurement of the electrical conductivity of the filtrate and in that the filtration stage is stopped as soon as the electrical conductivity of the filtrate increases. 2. A process for the preparation of aqueous suspensions of mineral matter as claimed in claim 1, wherein the mineral matter is chosen from among natural calcium carbonate, such as the various chalks, calcites, marbles, or again chosen from the synthetic calcium carbonates such as the precipitated calcium carbonates at various stages of crystallisation, or again from the mixed carbonates of magnesium and calcium such as the dolomites, or from magnesium carbonate, zinc carbonate, lime, magnesia, barium sulphate such as barite, calcium sulphate, silica, the magnesio- silicates such as talc, wollastonite, clays and alumino-silicates such as the kaolins, mica, metal or alkaline-earth oxides or hydroxides such as magnesium hydroxide, iron oxides, zinc oxides, titanium oxide, titanium dioxides in anatase or rutile forms, and mixtures of them, and preferably chosen from natural calcium carbonate, synthetic calcium carbonate also called precipitated calcium carbonate, titanium dioxide in its anatase or rutile forms, kaolin, aluminium hydroxide, clays or mixtures of them. 3. An aqueous suspension of fluid mineral matter, which are able to be pumped and conveyed by the end user immediately after the filtration stage, possibly followed by a compression comprises 0.01% to 10%, preferably 0.1% to 2% by dry weight of dispersant relative to the dry weight of mineral matter to be filtered, and which is obtained by the process as claimed in claims 1 to 2, wherein the mineral matter is chosen from among natural calcium carbonate such as various chalks, calcites, marbles, or again chosen from synthetic calcium carbonates such as calcium carbonates precipitated at different stages of crystallisation, or from mixed carbonates of magnesium and calcium such as dolomites, or from magnesium carbonate, zinc carbonate, lime, magnesia, barium sulphate such as barite, calcium sulphate, silica, magnesio-silicates such as talc, wollastonite, clays and other alumino-silicates such as kaolins, mica, metal or alkaline-earth oxides or hydroxides such as magnesium hydroxide, iron oxides, zinc oxide, titanium oxide, titanium dioxides in anatase or rutile forms, and mixtures of them, and moreover mixtures of talc and calcium carbonate. Dated this 5th day of January, 2005.

Documents:

13-mumnp-2005 claims(granted)-(20-2-2006).doc

13-mumnp-2005 form 2(granted)-(20-2-2006).doc

13-mumnp-2005-cancelled pages(20-02-2006).pdf

13-mumnp-2005-claims(granted)-(20-02-2006).pdf

13-mumnp-2005-correspondence(20-02-2006).pdf

13-mumnp-2005-correspondence(ipo)-(03-10-2006).pdf

13-mumnp-2005-drawing(20-02-2006).pdf

13-mumnp-2005-form 1(20-02-2006).pdf

13-mumnp-2005-form 18(31-03-2005).pdf

13-mumnp-2005-form 2(granted)-(20-02-2006).pdf

13-mumnp-2005-form 3(07-01-2005).pdf

13-mumnp-2005-form 5(07-01-2005).pdf

13-mumnp-2005-other document(20-02-2006).pdf

13-mumnp-2005-power of attorney(16-02-2005).pdf

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