FR2900410A1 - Treating talc useful to reduce the amount of unwanted colloids in paper manufacture, by contacting with an amphoteric polymer, comprises mixing talc with-, and forming an aqueous suspension, grinding dry/wet talc, drying and graining - Google Patents

Abstract

Treatment of talc by contacting with a polymer, comprises mixing the talc optionally containing the pulp of mechanical, thermomechanical, chemical and/or recycled nature, with aqueous suspension, forming aqueous suspension of talc i.e. initially in the form of dry powder, grinding the dry/wet talc, drying the aqueous suspensions of talc, and/or graining the talc, where the polymer is an amphoteric polymer comprising an anionic monomer, a cationic monomer and optionally a non-ionic monomer. Independent claims are included for: (1) talc treated with the amphoteric polymer; and (2) dry powder, granules and aqueous suspension of the treated talc.

Description

PROCESS FOR TREATING TALC WITH AMPHOTERIC POLYMERS, TALC

  OBTAINED, USE OF SAID TALC AS A REDUCING AGENT OF THE QUANTITY OF COLLOIDS IN THE MANUFACTURE OF AQUEOUS SYSTEMS The invention relates first of all to a novel process for treating talc, by means of at least one amphoteric polymer, in order to render this talc effective as an agent for decreasing the amount of natural and organic colloids in the process of making the paper sheet.

  A second object of the invention is a talc thus treated obtained from the process according to the invention.

  The third, fourth and fifth subjects of the invention consist of dry powders, aqueous suspensions and treated talc granules obtained from the process according to the invention.

  A final object of the invention is the use of the treated talc from the process according to the invention as a reducing agent for the amount of natural and organic colloids in the papermaking process.

  The method of manufacturing a paper sheet (still referred to herein as "the papermaking process") generates a large number of colloidal species consisting of hydrophobic particles wholly or partially insoluble in water. These colloids are either of natural origin and consist of a large variety of long-chain hydrophobic macromolecules (based on fatty acids, esters, alcohols, etc.) commonly called "pitch" according to the English term. well known to those skilled in the art, or of synthetic origin and consisting of sticky polymers that are frequently encountered in the paper industry and commonly called "stickies" according to the other well-known English term of the invention. skilled person. Both are equally undesirable, since they stick on the various equipment of the paper process (such as for example rollers) which requires frequent stops for cleaning, and that there is also the risk of them. find in the final product where they create surface imperfections that will affect the properties of the paper sheet, such as its whiteness, its mechanical properties or its surface appearance. In the present Application, they will be referred to as "undesirable colloids". Such undesirable colloids are found in the pulp, with the fibers or in the white waters of the papermaking process.

  There are two types of methods for reducing the amount of undesirable colloids: those involving, by introduction as an additive in the papermaking process, before the manufacture of the sheet of paper, an organic polymer and those that involve the same conditions an inorganic material (optionally treated with a polymer).

  In the first category, the skilled person knows a number of documents, which teach him the use of cationic polymers, anionic, nonionic or amphoteric.

  Thus, US Pat. No. 5,989,392 discloses the use of cationic polymers which are quaternary polyammoniums consisting of a cationic monomer and a crosslinking monomer, in order to reduce the amount of undesirable colloids in the paper pulp. .

  Those skilled in the art also know the document WO 01/88 264, which describes the use of nonionic polymers based on acrylamide and vinyl acetate, to reduce the deposition of sticky materials on the equipment of a paper machine.

  It also discloses US 6,051,160, which discloses a liquid composition based on guai gum and an anionic copolymer of styrene and maleic anhydride having a molecular weight of between 500 and 10,000 g / mol; this composition is used as an agent making it possible to limit the presence of undesirable colloids in the manufacturing process of the paper sheet. Those skilled in the art also know documents which use amphoteric polymers to reduce the proportion of these undesirable colloids. Thus, EP 0 464 993 teaches him the use of copolymers of (meth) acrylic acid and diallydimethyl ammonium chloride (DADMAC), as a pitch control agent in the manufacturing process of the piece of paper.

  As for the document US 2006 000 570, it teaches him, in order to reduce the amount of undesirable colloids, the use of copolymers of acrylic acid and / or acrylamide with DADMAC. However, these solutions which consist of the implementation of organic polymers directly in the paper process, do not satisfy the skilled person: in fact, such polymers do not prove effective enough to significantly reduce the amount of unwanted colloids. The second route which makes it possible to limit the amount of undesirable colloids consists in the use of an optionally processed mineral additive.

  As such, the skilled person has known for many years that talc is the preferred mineral material for this purpose, as indicated in the document "Talc as a pitch control agent in the paper industry" (Kam Pa Gikyoshi, 53 ( 9), 1999, pp. 1133-1142).

  In order to improve the properties of talc as an agent for reducing the amount of undesirable colloids, those skilled in the art will know a number of documents which employ polymers as talc treatment agents.

  He thus knows the document WO 89/06429 which describes a method for reducing the amount of undesirable colloids, by using a talc on which a cationic polymer is adsorbed, the resulting particle having a zeta potential of greater than or equal to + 30 mV. . The authors of this document have already noticed that the talc particles thus treated with cationic polymers, prove to be more effective than: the cationic polymers themselves, as agents reducing the amount of undesirable colloids (page 15 , lines 19-23). The examples indicate that the adsorption of the cationic polymer on the talc particle takes place during a simple mixing process.

  Those skilled in the art also know the document US 2003/096 143, which describes a method for improving the wettability of talc and its affinity vis-à-vis cellulose fibers, thus reducing unwanted colloids. This method is based on the dual treatment of talc with a metal hydroxide and a cationic polymer such as polyDADMAC, polyamines, polyethylenimines and cationic starch. This double treatment takes place by mixing between an aqueous suspension of talc and the aforementioned treatment agents.

  Finally, one skilled in the art knows the document US 2003/143 144, which describes a method for modifying the talc surface, the talc thus modified being able to be used as a reducing agent for the quantity of undesirable colloids. This modification takes place by bringing into contact, by simple mixing, an aqueous suspension of talc and a cationic polymer functionalized with a quaternary amine.

  Even if the processes described in the documents WO 89/06294, US 2003/096143 and US 2003/143 144 constitute an advance in terms of effectiveness of the particles of treated talc, as agents which reduce the amount of undesirable colloids, compared to other solutions that are content to implement a simple organic polymer as an additive introduced in the process of manufacturing the paper sheet, these solutions however represent a significant drawback for the skilled person: they are based on the implementation of cationic polymer. However, these cationic polymers are generally expensive on the one hand, and toxic vis-à-vis aquatic fauna when they are released into the water with wastewater resulting from the paper process. It is well known that products of a cationic nature will adsorb more easily on the anionic sites found on the gills of fish. As such, the document "Wastewater treatment polymers identified as the toxic component of a diamond mine effluent" (Environmental Toxicology and Chemistry, 23 (9), 2004, pp. 2234-2242) recalls the dangerousness of cationic polymers vis-à- live underwater wildlife.

  Therefore, there is a lack in terms of technical solution allowing the skilled person to have a method of reducing unwanted colloids, in the process of manufacturing the paper sheet, said method to be more effective than the methods employing polymers as simple additives, and said process should not have the drawbacks inherent in the use of cationic polymers.

  Also, pursuing its research with a view to providing the skilled person with such a technical solution, the Applicant has developed a method for treating talc with polymers, said polymers being brought into contact with talc:

  during a step of mixing with an aqueous suspension of talc, optionally containing pulp, of a mechanical and / or thermomechanical and / or chemical nature and / or recycled pulp, and / or during an aqueous suspension stage talc, initially present in the form of a dry powder, and / or during a step of grinding the talc, in a dry medium or in an aqueous medium, and / or during a step of drying an aqueous suspension of talc, and / or or during a talc granulation step,

  characterized in that the polymers are amphoteric polymers, consisting of:

  a) at least one anionic monomer, b) at least one cationic monomer, c) and optionally at least one nonionic monomer.

  In this way, a treated talc is obtained, which proves to be an effective agent in terms of reduction of undesirable colloids in the paper-making process, which was not the case with the solutions of the state of the art which did not only a single polymer or mixture of polymers (this property will be illustrated in the examples of the present Application). On the other hand, the solution thus proposed is less expensive and less dangerous (in terms of ecotoxicology) than the solutions based on the use of a cationic polymer as a talc treatment agent.

  In addition, the Applicant has noted that the amphoteric polymers used in the present invention allow, for any talc (that is to say in particular regardless of its particle size and its specific surface), to treat it in order to improve its reducing agent properties of undesirable colloids: in this sense, the amphoteric polymers used according to the present invention make it possible to boost the reducing agent properties of the undesirable colloids for any talc.

  Finally, the process developed by the Applicant has the advantage of being extremely flexible for the skilled person. Indeed, the technical solutions consisting in using a talc treated with a cationic polymer rely exclusively on treatment processes by simply mixing talc in aqueous suspension with said cationic polymers. However, the skilled person must also meet a number of requirements on the part of the end user that is the paper manufacturer. These requirements can be translated through the different unit processing steps that talc can undergo, before being sent to the end user. As such, said talc can undergo one or more of the following operations:

  a mixing step, when the talc is already present in the form of an aqueous suspension optionally containing pulp, the objective here being to allow the end user to treat an aqueous suspension of talc directly during the papermaking process, a suspension stage, when the talc is in the form of a dry powder, the objective being to deliver to the user a liquid product, a grinding stage, in a dry medium or in an aqueous medium, the objective being to to provide the end user with a reduced particle size talc with a higher specific surface area; - a drying step, when the talc was in aqueous suspension, the objective being to deliver to the end user a product in the form of of dry powder, 7 a granulation step, the objective being to deliver to the end user products in the form of granules.

  However, none of the solutions proposed by the state of the art allows the skilled person to treat talc, in order to make it effective to reduce the amount of undesirable colloids, by introducing an amphoteric polymer during Any of the above-mentioned steps: the simple case of mixing is extremely limiting for those skilled in the art. Thus, a first object of the invention is a method of treating talc with at least one polymer, said polymer being brought into contact with talc:

  during a mixing step with an aqueous suspension of talc, optionally containing pulp of mechanical and / or thermomechanical and / or chemical nature and / or recycled pulp, and / or during an aqueous suspending step of talc, initially present in the form of a dry powder, and / or during a step of grinding talc, in a dry medium or in an aqueous medium, and / or during a step of drying an aqueous suspension of talc, and / or during a talc granulation step, characterized in that said polymer is an amphoteric polymer, consisting of: a) at least one anionic monomer, b) at least one cationic monomer, c) and optionally at least one monomer nonionic. The process according to the invention is also characterized in that the amphoteric polymer consists of:

  a) at least one anionic monomer which is an anionic monomer with ethylenic unsaturation and monocarboxylic functional group in the acid or salified state, chosen from monomers with ethylenic unsaturation and monocarboxylic function, and preferably from acrylic acid, methacrylic, crotonic, isocrotonic, cinnamic or else the half-esters of diacids such as the C 1 -C 4 monoesters of maleic or itaconic acids, or chosen from ethylenically unsaturated monomers and dicarboxylic functional groups in the acidic or salified state, and preferentially among itaconic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid or anhydrides of carboxylic acids, such as maleic anhydride or chosen from ethylenically unsaturated monomers with a sulphonic function in the acidic or salified state, and preferentially among acrylamido-2-methyl-2-propanesulfonic acid, sodium methallylsulphonate, vinyl sulfonic acid and styrene sulphonic acid or else chosen from ethylenically unsaturated monomers and phosphoric function in the acid or salified state, and preferably from vinyl phosphoric acid, ethylene glycol methacrylate phosphate; , propylene glycol methacrylate phosphate, ethylene glycol acrylate phosphate, propylene glycol acrylate phosphate and their ethoxylates or else chosen from ethylenically unsaturated monomers and phosphonic function in the acid state or salified, and is preferably vinylphosphonic acid, or mixtures thereof,

  b) at least one cationic monomer chosen from quaternary ammoniums, and preferably from [2- (methacryloyloxy) ethyl] trimethyl ammonium chloride or sulphate, [2- (acryloyloxy) ethyl] trimethyl chloride or sulphate; ammonium, [3- (acrylamido) propyl] trimethyl ammonium chloride or sulphate, dimethyl diallyl ammonium chloride or sulphate, [3- (methacrylamido) propyl] trimethyl ammonium chloride or sulphate, or mixtures thereof, c) optionally at least one nonionic monomer chosen from N- [3- (dimethylamino) propyl] acrylamide or N- [3- (dimethylamino) propyl] methacrylamide, unsaturated esters such as N-methacrylate; [2- (dimethylamino) ethyl], or N- [2- (dimethylamino) ethyl] acrylate, or from acrylamide or methacrylamide and mixtures thereof, alkyl acrylates or methacrylates, vinyls, and preferentially vinyl acetate, vinylpyrrolidone, styrene, alphamé thylstyrene and their derivatives, or the monomers of formula (I): in which: m and p represent a number of alkylene oxide units of less than or equal to 150, n represents a number of ethylene oxide units less than or equal to 150, q represents an integer at least equal to 1 and such that 5 (m + n + p) q <150, and preferentially such that 15 <_ (m + n + p) q <120, RI represents hydrogen or the methyl or ethyl radical, R2 represents hydrogen or the methyl or ethyl radical, R represents a radical containing a polymerizable unsaturated functional group, preferentially belonging to the vinyl group as well as to the acrylic, methacrylic, maleic, itaconic, crotonic and vinylphthalic esters, as well as unsaturated urethanes such as acrylurethane, methacrylurethane, dimethylisopropenylbenzylurethane, allylurethane and the group of allyl or vinyl ethers Whether or not it is in the group of ethylenically unsaturated amides or imides, R 'represents hydrogen or a hydrocarbon radical having 1 to 40 carbon atoms,

  The process according to the invention is also characterized in that the said amphoteric polymers consist of:

  a) from 10% to 90%, preferably from 25% to 75%, very preferably from 40% to 60% by moles of at least one anionic monomer, b) from 10% to 90%, preferably from 25% to 75%; %, very preferably from 40% to 60% by moles of at least one cationic monomer, R 1 RO nr 9 10c) and from 0% to 30%, preferably from 0% to 20% by moles of at least one monomer nonionic, the sum of the molar percentages of each monomer constituting said amphoteric polymer being equal to 100%.

  The process according to the invention is also characterized in that the amphoteric polymers are obtained by known methods of radical polymerization in solution, in direct or inverse emulsion, in suspension or precipitation in appropriate solvents, in the presence of catalytic systems and known transfer agents, or by controlled radical polymerization processes and preferentially by controlled polymerization with nitroxides (NMP) or by cobaloxymes, radical atom transfer polymerization (ATRP), derivative-controlled radical polymerization sulfur, selected from carbamates, dithioesters or trithiocarbonates (RAFT) or xanthates.

  The process according to the invention is also characterized in that the amphoteric polymers are totally acidic, or totally or partially neutralized with a neutralization agent chosen from hydroxides of sodium, of potassium, hydroxides and / or oxides of calcium and magnesium. , ammonia, or mixtures thereof, preferably with a neutralizing agent selected from sodium hydroxide, potassium hydroxide, ammonia, or mixtures thereof, very preferably with a neutralizing agent which is ammonia.

  The method according to the invention is also characterized in that the amphoteric polymers may be optionally before or after their total or partial neutralization, be treated and separated into several phases, according to static or dynamic methods known to those skilled in the art, by one or more polar solvents preferentially belonging to the group consisting of water, methanol, ethanol, propanol, isopropanol, butanols, acetone, tetrahydrofuran or their mixtures. One of the two phases then corresponds to the polymers used according to the invention.

  The process according to the invention is also characterized in that the amphoteric polymers can be dried. A second object of the invention is constituted by a treated talc, characterized in that the talc treatment agent is an amphoteric polymer, consisting of:

  a) at least one anionic monomer, b) at least one cationic monomer, c) and optionally at least one nonionic monomer.

  The treated talc is also characterized in that the said amphoteric polymer consists of: a) at least one anionic monomer which is an anionic monomer with ethylenic unsaturation and with a monocarboxylic functional group in the acid or salified state, chosen from unsaturated monomers and ethylenic and monocarboxylic function, and preferably among acrylic acid, methacrylic, crotonic, isocrotonic, cinnamic or the half esters of diacids such as monoesters C1 to C4 maleic or itaconic acids, or selected from ethylenically unsaturated monomers and dicarboxylic function in the acid or salified state, and preferably among itaconic, maleic, fumaric, mesaconic, citraconic acid or carboxylic acid anhydrides, such as maleic anhydride or selected from ethylenically unsaturated monomers and sulfonic function in the acid or salified state, and preferentially acrylamido-2-methyl-2-propanesulfonic acid, sodium methallyl sulphonate, vinyl sulphonic acid and styrene sulphonic acid, or else chosen from monomers with ethylenic unsaturation and with phosphoric function in the state. acid or salified, and preferably from vinyl phosphoric acid, ethylene glycol methacrylate phosphate, propylene glycol methacrylate phosphate, ethylene glycol acrylate phosphate, propylene glycol acrylate phosphate, and the like. ethoxylates or else chosen from ethylenically unsaturated monomers and phosphonic function in the acid or salified state, and is preferably vinylphosphonic acid, or mixtures thereof,

  b) at least one cationic monomer chosen from quaternary ammoniums, and preferably from [2-12 (methacryloyloxy) ethyl] trimethyl ammonium chloride or sulphate, [2- (acryloyloxy) ethyl] chloride or sulphate trimethylammonium, [3- (acrylamido) propyl] trimethylammonium chloride or sulphate, dimethyl diallyl ammonium chloride or sulphate, [3- (methacrylamido) propyl] trimethyl ammonium chloride or sulphate or mixtures thereof ,

  c) optionally at least one nonionic monomer chosen from N- [3- (dimethylamino) propyl] acrylamide or N- [3- (dimethylamino) propyl] methacrylamide, unsaturated esters such as N-methacrylate; [2- (dimethylamino) ethyl], or N- [2- (dimethylamino) ethyl] acrylate, or from acrylamide or methacrylamide and mixtures thereof, alkyl acrylates or methacrylates, vinyls, and preferentially vinyl acetate, vinylpyrrolidone, styrene, alphamethylstyrene and their derivatives, or the monomers of formula (I): embedded image in which:

  m and p represent a number of alkylene oxide units less than or equal to 150, n represents a number of ethylene oxide units of less than or equal to 150, q represents an integer at least equal to 1 and such that 5 (m + n + p) q <150., and preferably such that 15 5 (m + n + p) q <120, 25 - R 1 represents hydrogen or the methyl or ethyl radical, R2 represents hydrogen or the methyl or ethyl radical, R represents a radical containing a polymerizable unsaturated functional group, preferably belonging to the vinyl group as well as to the group of acrylic, methacrylic, maleic, itaconic, crotonic and vinylphthalic esters, and also to the group of unsaturated urethanes such as acrylurethane, methacrylurethane, α-dimethylisopropenylbenzylurethane, allylurethane, as well as to the group of substituted or unsubstituted allylic or vinyl ethers, or else to the group of ethylenically unsaturated amides or imides. R 'represents hydrogen or a hydrocarbon radical having 1 to 40 carbon atoms,

  The treated talc is also characterized in that said amphoteric polymer consists of: a) from 10% to 90%, preferably from 25% to 75%, very preferably from 40% to 60% by moles of at least one anionic monomer, b) from 10% to 90%, preferably from 25% to 75%, very preferably from 40% to 60% by moles of at least one cationic monomer, c) and from 0% to 30%, preferentially from 0% to 20 mol% of at least one nonionic monomer,

  the sum of the molar percentages of each monomer constituting said amphoteric polymer being equal to 100%.

  The treated talc is also characterized in that the amphoteric polymers are obtained by known methods of solution radical polymerization, in direct or inverse emulsion, in suspension or precipitation in appropriate solvents, in the presence of catalytic systems and agents. known transfer or by controlled radical polymerization processes and preferably by controlled polymerization with nitroxides (NMP) or by cobaloxymes, free radical transfer polymerization (ATRP), controlled radical polymerization with sulfur derivatives , selected from carbamates, dithioesters or trithiocarbonates (RAFT) or xanthates. The treated talc is also characterized in that the amphoteric polymers are completely acidic or totally or partially neutralized by a neutralizing agent selected from hydroxides of sodium, of potassium, hydroxides and / or oxides of calcium, magnesium, ammonia, or mixtures thereof, preferably with a neutralizing agent selected from sodium hydroxide, potassium hydroxide, ammonia, or mixtures thereof, very preferably with a neutralizing agent which is ammonia.

  The treated talc is also characterized in that the amphoteric polymers may be optionally before or after their total or partial neutralization, treated and separated into several phases, according to static or dynamic processes known to those skilled in the art, by one or more solvents. polar preferentially belonging to the group consisting of water, methanol, ethanol, propanol, isopropanol, butanols, acetone, tetrahydrofuran or mixtures thereof. One of the two phases then corresponds to the polymers used according to the invention. The treated talc is also characterized in that the amphoteric polymers can be dried.

  A third subject of the invention is a treated talc dry powder, characterized in that the treated talc is that of the present invention. A fourth object of the invention is a treated talc granule, characterized in that the treated talc is that of the present invention.

  A fifth object of the invention is an aqueous suspension of treated talc, optionally containing pulp of a mechanical and / or thermomechanical and / or chemical nature and / or recycled pulp, characterized in that the treated talc is that of the present invention.

  A sixth and final subject of the invention is the use as a reducing agent of the amount of undesirable colloids, in the process for producing a sheet of paper, a talc treated according to the invention, a powder talc powder treated according to the invention, a talc granule treated according to the invention and an aqueous suspension of talc treated according to the invention. 20 EXAMPLES

  In all the examples, the polymolecularity indices and the average molecular weights of the polymers (when they were measured) are determined according to the method explained below.

  The average molecular weights and the polymolecularity index are determined by a size exclusion chromatography (CES) method. A test portion of the polymer solution corresponding to 90 mg of dry matter is introduced into a 10 ml flask. The mobile phase, added with 0.04% THF, is added to a total mass of 10 g. The composition of this mobile phase is as follows: NaNO3: 0.2 mol / L, CH3COOH: 0.5 mol / L, acetonitrile 5% volume. The CES chain is composed of a WatersTM 510 isocratic pump, the flow rate is set at 0.8 mL / min, a Waters 717+ sample changer, an oven containing a "Guard Column" precolumn Ultrahydrogel WatersTM ", followed by a set of columns 7.8 mm in internal diameter and 30 cm in length of type" Ultrahydrogel WatersTM ", whose nominal porosities are, in the order of their connection: 2000, 1000, 500 and 250À. The detection is ensured by a differential refractometer of the WatersTM 410 type. The temperature of the oven and the detector is regulated at 35 C. The acquisition and treatment of the chromatogram are carried out using the PSS WinGPC Scientific v 4.02 software. The CES is calibrated by a series of poly (DADMAC) standards provided by Polymer Standards ServiceTM. The calibration curve is of linear type and takes into account the correction obtained thanks to the flow rate marker (THF).

Example 1

  This example illustrates the process according to the invention in which an amphoteric polymer is used to treat a talc, during a stage of aqueous suspension of said talc (this suspension step being carried out according to the well known techniques of the invention. skilled person). The talc used is Finntal ™ P05 marketed by the company MONDO MINERALS, with a median diameter equal to 2.2 gm (as determined from a SedigraphTM 5100 device sold by the company MICROMERITICSTM) and BET specific surface area. equal to 10.0 m 2 / g (as measured from a FlowsorbTM II device sold by the company MICROMERITICSTM).

  Test No. 1 This test constitutes a reference. Pulp of mechanical nature, obtained from La Papeterie de Lancey (France) is filtered through a filter whose pore diameter is equal to 2 m. ~ o This wood pulp has a dry extract equal to 12 g / L and a particle concentration equal to 65 x 106 particles per cm3 measured by a counting cell marketed by the company NEUBAUERTM. A liquor is thus obtained. 200 g of water are added to 200 g of said liquor. The liquid phase is then centrifuged at 3000 rpm for 15 minutes, and its turbidity is measured from a MettlerTM DL 70 apparatus equipped with PhototrodeTM DP 660, both of which are marketed by METTLER TOLEDOTM. The phototrode is previously calibrated at a value of 1000 mV in bi-permuted water.

  Test No. 2 This test illustrates the prior art. An aqueous suspension of talc, containing 40% by dry weight of untreated talc with respect to the total weight of said suspension, is produced. 10 g of the suspension obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left stirring for 2 hours. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 apparatus equipped with PhototrodeTM DP 660, both of which are sold by the company METTLER TOLEDOTM The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water. Test No. 3 This test illustrates the invention. An aqueous dispersion of talc containing 40% by dry weight of talc is prepared in the presence of 1% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 50% by mole of MAPTAC (chloride [3- (methacrylamido) propyl] trimethylammonium) and 50 mol% acrylic acid. Its weight-average molecular weight is 44,200 g / mol and its polymolecularity index is equal to 1.95. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left to act for 2 hours with stirring. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipments being marketed. by METTLER TOLEDOTM The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water.

  Test No. 4 This test illustrates the invention.

  An aqueous dispersion of talc containing 40% by dry weight of talc is prepared in the presence of 1% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 60% by mole of MADQUAT (sodium chloride). [2- (methacryloyloxy) ethyl] trimethyl ammonium) and 40 mol% acrylic acid. Its weight-average molecular weight is 78,000 g / mol and its polymolecularity index is equal to 2,65. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left to act for 2 hours with stirring. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipments being marketed. by METTLER TOLEDOTM. The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water. The set of characteristics and results corresponding to the tests 1 to 4 are reported in Table 1.

  For each test, the difference between the 1000 mV value (the phototrode calibration value when immersed in the bi-permuted water) and the measured turbidity value for each sample is calculated: the lower the difference. the lower the amount of undesirable colloids remaining in the sample. Test No. 1 2 3 4 Reference / Prior Art / Invention Reference Art Invention Invention Previous Pulp (g) 200 200 200 200 Water added to the pulp (g) 20 10 10 10 Aqueous suspension containing 40% by weight of talc (g) Amphoteric polymer (% by dry weight / dry weight of talc) 1000 - turbidity value (mV) 690 150 60 Table 1 These results demonstrate that the talc used in test no. 2 can significantly reduce the amount (1000 - value of turbidity).

  The best results are, however, obtained for the tests n 3 and 4 which implement according to the invention an amphoteric polymer as a treatment agent of said talc, and which allow to exacerbate the effectiveness of said talc.

  These results therefore demonstrate the effectiveness of the polymers according to the invention as talc treatment agents, in order to make it effective in decreasing the amount of undesirable colloids in a papermaking process.

Example 2

  This example illustrates the process according to the invention in which an amphoteric polymer is used to treat a talc, during a step of aqueous suspension of said talc. The talc used is FinntalcTM P15 marketed by the company MONDO 5 19 MINERALS, with a median diameter equal to 5.5 gm (as determined from a SedigraphTM 5100 device marketed by MICROMERITICSTM) and BET specific surface area. equal to 6.0 m2 / g (as measured from a FlowsorbTM II device marketed by MICROMERITICSTM) For this series of tests, test No. 1 is still the reference.

  In addition to the turbidimetric measurement made during test n 1, a Chemical Oxygen Demand (COD) measurement is also carried out which represents the concentration (mg / L) of oxygen equivalent to the quantity of dichromate consumed. dissolved and suspended materials (1 mole of K 2 Cr 2 O 7 corresponds to 1 mole of oxygen). The measurement of COD is carried out according to the ISO 6060 standard, by implementing a Spectroquant Nova 60 photometer marketed by MERCKTM. This measurement is representative of the amount of undesirable colloids remaining in the liquid phase: the higher this value, the greater the amount of undesirable colloids remaining in suspension.

  Test No. 5 This test illustrates the prior art. An aqueous suspension of talc containing 40% by dry weight of talc with respect to the total weight of said suspension is produced. 10 g of the suspension obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left stirring for 2 hours. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipments being marketed. by METTLER TOLEDOTM The phototrode was previously calibrated to a value of 1000 mV in bipermuted water. A measurement of COD is also carried out on the liquid phase, according to the method previously described. Test No. 6 This test illustrates the invention. An aqueous dispersion of talc containing 40% by dry weight of talc is prepared in the presence of 1% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 50% by mole of MAPTAC and of 50 mol% acrylic acid. Its weight-average molecular weight is 44,200 g / mol and its polymolecularity index is equal to 1.95. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left to act for 2 hours with stirring. The liquid phase is then separated from the phase solid by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipments being sold by the company METTLER TOLEDOTM The phototrode is calibrated beforehand to a value of 1000 mV in bipermuted water. A measurement of COD is also carried out on the liquid phase, according to the method previously described.

  Test No. 7 This test illustrates the invention. An aqueous dispersion of talc containing 40% by dry weight of talc is prepared in the presence of 1% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 60% by mole of MADQUAT and 40% by weight. mole% acrylic acid. Its weight-average molecular weight is 78,000 g / mol and its polymolecularity index is equal to 2,65. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left to act for 2 hours with stirring. The liquid phase is then separated from the phase solid by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both equipment being marketed by METTLER TOLEDOTM.

  The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water. A measurement of COD is also carried out on the liquid phase, according to the method previously described.

  Test No. 8 This test illustrates the invention. An aqueous dispersion of talc containing 40% by dry weight of talc is prepared in the presence of 1% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 60% by mole of MADQUAT and 40 mol% acrylic acid. Its weight-average molecular weight is 121,000 g / mol and its polymolecularity index is equal to 2.20. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left to act for 2 hours with stirring. The liquid phase is then separated from the phase solid by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both equipment being marketed by METTLER TOLEDOTM.

  The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water. A measurement of COD is also carried out on the liquid phase, according to the method previously described.

  Test No. 9 This test illustrates the invention. An aqueous dispersion of talc containing 40% by dry weight of talc is prepared in the presence of 10% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 60% by mole of MADQUAT and 40 mol% acrylic acid. Its weight-average molecular weight is 54,500 g / mol and its polymolecularity index is equal to 2.45. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and 10 g of water, and allowed to stir for 2 hours with stirring. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipments being marketed. by METTLER TOLEDOTM The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water. A measurement of COD on the liquid phase is also carried out, according to the method previously described.

  The set of characteristics and results corresponding to tests Nos. 1 and 5 to 9 is reported in Table 2. Test No 1 5 6 7 8 9 Reference / Reference Art Invention Invention Invention Invention Art Anterior / Invention Anterior Pulp (g) 200 200 200 200 200 200 Water added to the pulp (g) 10 10 10 10 10 10 10 10 10 10 10 containing 40% by dry weight of talc (g) Amphoteric polymer (% 0 0 1 1 1 1 by weight dry / dry weight of talc) 1000 - value of 690 180 70 55 50 60 turbidity (mV) COD (mg / L) 3400 3050 2375 2680 2680 2680 Table 2 These results demonstrate that the talc used in test n 5 already makes it possible to substantially reduce the quantity (1000 ° turbidity value) while decreasing the COD value.

  The best results, however, are obtained for tests Nos. 6 to 9 which, according to the invention, implement an amphoteric polymer as a treatment agent for said talc, and which make it possible to exacerbate the effectiveness of said talc, both in terms of decrease in quantity (1000 - turbidity value) and decrease in COD. These results, therefore, demonstrate the effectiveness of the polymers according to the invention as talc treatment agents, in order to make it effective in decreasing the amount of undesirable colloids in a papermaking process.

Example 3

  This example illustrates the process according to the invention in which an amphoteric polymer is used to treat a talc, during a step of aqueous suspension of said talc.

  The talc used is a Finnish talc with a median diameter of 30 gm (as determined from a SedigraphTM 5100 device marketed by MICROMERIT ICSTM) and a BET specific surface area of 3.4 m2 / g ( as measured from a FlowsorbTM II device marketed by MICROMERIT ICSTM)

  For this series of tests, test No. 1 is still the reference.

  Test No. 10 This test illustrates the prior art. An aqueous suspension of talc containing 40% by dry weight of talc with respect to the total weight of said suspension is produced. 10 g of the suspension obtained are mixed with 200 g of the liquor as described in test 1, as well as with 10 g of water, and the mixture is left to act for 2 hours with stirring. solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipment being marketed by METTLER TOLEDOTM. The phototrode is calibrated beforehand at a value of 1000 mV in bi-permutated water.

  Test No. 11 This test illustrates the invention.

  An aqueous dispersion of talc, containing 40% by dry weight of talc, is produced in the presence of 19% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 50% by mole of MADQUAT. and 50 mol% acrylic acid.

  Its weight-average molecular weight is 84,400 g / mol and its polymolecularity index is equal to 3.1. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left to act for 2 hours with stirring. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipments being marketed. by METTLER TOLEDOTM. The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water.

  Test No. 12 This test illustrates the invention. An aqueous dispersion of talc containing 40% by dry weight of talc is prepared in the presence of 1% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 50% by mole of MAPTAC and 50% by weight. mole% acrylic acid. Its weight-average molecular weight is 44,200 g / mol and its polymolecularity index is equal to 1.95. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left to act for 2 hours with stirring. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipments being marketed. by METTLER TOLEDOTM.

  The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water.

  Test No. 13 This test illustrates the invention. An aqueous dispersion of talc containing 40% by dry weight of talc is prepared in the presence of 1% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 60% by mole of MADQUAT and 40% by weight. mole% acrylic acid. Its weight-average molecular weight is 78,000 g / mol and its polymolecularity index is equal to 2.55. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left to act for 2 hours with stirring. The liquid phase is then separated from the phase solid by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both equipment being marketed by METTLER TOLEDOTM. The phototrode is calibrated beforehand at a value of 1000 mV in bi-permutated water.

  Test No. 14 This test illustrates the invention.

  An aqueous dispersion of talc containing 40% by dry weight of talc is prepared in the presence of 1% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 10% by mole of MAPTAC, 40% by weight of mole% of MADQUAT, and 50 mol% of acrylic acid. Its weight-average molecular weight is 56,000 g / mol and its polymolecularity index is equal to 2.55. 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and with 10 g of water, and the mixture is left to act for 2 hours with stirring. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipments being marketed. by METTLER TOLEDOTM The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water.

  The set of characteristics and results corresponding to the tests n ° 10 to 14 is reported in table 3. Test n 1 10 11 12 13 14 Reference / Art Anterior / Reference Art Invention Invention Invention Invention Invention Anterior Mechanical pulp (g) 200 200 200 200 200 200 Water added to the pulp (g) 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 containing 10% dry weight of talc (g) Amphoteric polymer (% 0 0 1 1 1 1 in dry weight / dry weight of talc) 1000 to 690 680 250 70 30 225 turbidity (mV) Table 3 These results demonstrate that the talc used in test No. 10 makes it possible to reduce the value of the quantity only slightly ( 1000 - turbidity value): such untreated talc does not prove to be an effective agent for reducing the amount of undesirable colloids in the paper process. On the other hand, all the results obtained by the use of the amphoteric polymers according to the invention as a treatment agent for said talc, lead to much lower values of the quantity (1000 - turbidity value), with respect to the reference: these results therefore demonstrate that the talc thus treated with said amphoteric polymers is a very effective agent for reducing the amount of undesirable colloids in the paper process.

  EXAMPLE 4 This example illustrates the process according to the invention in which an amphoteric polymer is used to treat a talc during an aqueous milling step of said talc. The talc used is the ComitalTM GR45 marketed by the company of the same name, with a median diameter equal to 14.6 m (as determined from a SedigraphTM 5100 device sold by the company MICROMERITICSTM) and a BET specific surface area equal to at 3.22 m 2 / g (as measured from a FlowsorbTM II device sold by the company MICROMERITICSTM).

  For this series of tests, test No. 1 is still the reference.

  Test No. 15 This test illustrates the prior art.

  Grinding is carried out with a DynomillTM apparatus marketed by WABTM in the aqueous talc phase, containing 40% by dry weight of talc with respect to the total weight of said ground suspension. At the end of grinding, the value of the median diameter is 9 m (as determined from a SedigraphTM 5100 device marketed by the company MICROMERITICSTM).

  10 g of water and 10 g of the suspension obtained are mixed with 200 g of the liquor as described in test 1 and allowed to act for 2 hours with stirring. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 device equipped with PhototrodeTM DP 660, both of these equipments being marketed. by METTLER TOLEDOTM The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water.

  Test No. 16 This test illustrates the invention. Grinding is carried out with a DynomillTM apparatus marketed by the company WABTM Aqueous talc containing 40% by dry weight of talc, in the presence of 2% by dry weight (measured with respect to the dry weight of talc) of an amphoteric polymer consisting of 50% by mole of MAPTAC and 50% by mole of acrylic acid. Its weight-average molecular weight is 44,200 g / mole and its polymolecularity index is equal to 1.95. At the end of grinding, the value of the median diameter is 9 gm (as determined from a SedigraphTM 5100 device marketed by MICROMERITICSTM). 10 g of water and 10 g of the dispersion obtained are mixed with 200 g of the liquor as described in test 1 and allowed to act for 2 hours with stirring. The liquid phase is then separated from the solid phase by centrifugation at 3000 rpm for 15 minutes, and the turbidity of the liquid phase is measured from a MettlerTM DL 70 apparatus equipped with PhototrodeTM DP 660, both of which are marketed by METTLER TOLEDOTM. The phototrode is calibrated beforehand at a value of 1000 mV in bipermuted water. The set of characteristics and results corresponding to the tests n 15 and 16 is reported in table 4. Test n 1 15 16 Reference / Reference Art Invention Art Anterior / Invention Invention Pulp (g) 200 200 200 Water added to the pulp ( g) 20 0 0 Aqueous suspension obtained by grinding containing 40 0 10 10% by dry weight of talc (g) Water added to the suspension obtained by grinding (g) 10 10 Polymer amphoteric (% dry weight / dry weight 0 0 2 talc) 1000 ù turbidity value (mV) 690 220 40 10 Table 4 These results demonstrate that the talc used in test No. 15 makes it possible to reduce the value of the quantity (1000 - turbidity value) .

  Nevertheless, the best result is obtained with the polymer according to test No. 16: this result therefore clearly demonstrates that the talc thus treated with the said amphoteric polymer during a grinding step constitutes a very effective agent for reducing the amount of undesirable colloids in the paper process.

Claims (18)

  1 - Process for treating talc with at least one polymer, said polymer being brought into contact with talc: during a mixing step with an aqueous suspension of talc, optionally containing pulp, of a mechanical and / or thermomechanical nature and / or chemical and / or recycled pulp, and / or during an aqueous talc suspension step, initially present as a dry powder, and / or during a step of grinding talc, in dry medium or in medium and / or during a step of drying an aqueous talc suspension, and / or during a step of talc granulation, characterized in that said polymer is an amphoteric polymer, consisting of: a) at least one monomer anionic, b) at least one cationic monomer, c) and optionally at least one nonionic monomer.   2 - Process according to claim 1, characterized in that the amphoteric polymer consists of: a) at least one anionic monomer which is an anionic monomer with ethylenic unsaturation and with a monocarboxylic functional group in the acidic or salified state, chosen from monomers with ethylenic unsaturation and monocarboxylic function, and preferably from acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, cinnamic acid, or else semiesters of diacids such as the C 1 to C 4 monoesters of maleic or itaconic acids, or chosen from ethylenically unsaturated monomers and dicarboxylic function in the acid or salified state, and preferably among itaconic, maleic, fumaric, mesaconic, citraconic acid or carboxylic acid anhydrides, such as maleic anhydride or chosen from among the monomers with ethylenic unsaturation and sulphonic function in the acidic or salified state, and preferably essentially acrylamido-2-methyl-2-propanesulfonic acid, sodium methallyl sulphonate, vinyl sulphonic acid and styrene sulphonic acid, or else chosen from ethylenically unsaturated monomers with a phosphoric function. acid or salified state, and preferentially among vinyl phosphoric acid, ethylene glycol methacrylate phosphate, propylene glycol methacrylate phosphate, ethylene glycol acrylate phosphate, propylene glycol acrylate phosphate and their ethoxylates or else chosen from 10 ethylenically unsaturated monomers and phosphonic function in the acid or salified state, and is preferably vinylphosphonic acid, or mixtures thereof, b) at least one cationic monomer chosen from quaternary ammonium, and preferentially from [2- (methacryloyloxy) ethyl] trimethyl ammonium chloride or sulfate, [2- (a) cryloyloxy) ethyl] trimethyl ammonium, [3- (acrylamido) propyl] trimethyl ammonium chloride or sulfate, dimethyl diallyl ammonium chloride or sulfate, [3- (methacrylamido) propyl] trimethyl chloride or sulfate ammonium, or mixtures thereof, c) optionally at least one nonionic monomer selected from N- [3- (dimethylamino) propyl] acrylamide or N- [3- (dimethylamino) propyl] methacrylamide, unsaturated esters such as that N- [2 (dimethylamino) ethyl] methacrylate, or N- [2- (dimethylamino) ethyl] acrylate, or from acrylamide or methacrylamide and mixtures thereof, alkyl acrylates or methacrylates, vinyl, and preferably vinyl acetate, vinylpyrrolidone, styrene, alphamethylstyrene and their derivatives, or the monomers of formula (I): (I) in which: m and p represent a number of units of alkylene oxide less than or equal to 150, n represents a number of oxy of ethylene less than or equal to 150, q represents an integer at least equal to 1 and such that 5 (m + n + p) q 150, and preferentially such that 15 (m + n + p) q <120, R 1 represents hydrogen or the methyl or ethyl radical, R 2 represents hydrogen or the methyl or ethyl radical, R represents a radical containing a polymerizable unsaturated functional group, preferably belonging to the vinyl group as well as to the acrylic ester group, methacrylic, maleic, itaconic, crotonic, vinylphthalic and urethane unsaturated group such as acrylurethane, methacrylurethane, dimethylisopropenylbenzylurethane, allylurethane, as well as the group of substituted or unsubstituted allylic or vinyl ethers, or to the group of ethylenically unsaturated amides or imides, R 'represents hydrogen or a hydrocarbon radical having 1 to 40 carbon atoms,   3 - Process according to one of claims 1 or 2, characterized in that the amphoteric polymers consist of: a) from 10% to 90%, preferably from 25% to 75%, very preferably from 40% to 60% by moles at least one anionic monomer, b) from 10% to 90%, preferably from 25% to 75%, very preferably from 40% to 60% by moles of at least one cationic monomer, R 'rq 25 32 c) and from 0% to 30%, preferably from 0% to 20% by moles of at least one nonionic monomer, the sum of the molar percentages of each monomer constituting said amphoteric polymer being equal to 100%.   4 - Process according to one of claims 1 to 3, characterized in that the amphoteric polymers are obtained by radical polymerization processes in solution, in direct or inverse emulsion, in suspension or precipitation in solvents, in the presence of catalytic systems and transfer agents, or by controlled radical polymerization processes and preferentially by controlled polymerization with nitroxides (NMP) or by cobaloxymes, radical atom transfer polymerization (ATRP), radical polymerization controlled by sulfur derivatives, selected from carbamates, dithioesters or trithiocarbonates (RAFT) or xanthates.   5 - Process according to one of claims 1 to 4, characterized in that the amphoteric polymers are totally acidic or totally or partially neutralized, with a neutralization agent selected from hydroxides of sodium, potassium, hydroxides and / or oxides calcium, magnesium, ammonia, or mixtures thereof, preferably with a neutralizing agent selected from sodium hydroxide, potassium hydroxide, ammonia, or mixtures thereof, very preferably with a neutralizing agent which is ammonia.   6 - Process according to one of claims 1 to 5, characterized in that the amphoteric polymers can be optionally before or after their total or partial neutralization, treated and separated into several phases, according to static or dynamic processes, by one or more polar solvents preferentially belonging to the group consisting of water, methanol, ethanol, propanol, isopropanol, butanols, acetone, tetrahydrofuran or their mixtures.   7 - Process according to one of claims 1 to 6, characterized in that the amphoteric polymers are dried. 33   8 - Talc treated, characterized in that the talc treatment agent is an amphoteric polymer, consisting of: a) at least one anionic monomer, b) at least one cationic monomer, c) and optionally from less a nonionic monomer.   9 - Talc treated according to claim 8, characterized in that the amphoteric polymer consists of: a) at least one anionic monomer which is an anionic monomer with ethylenic unsaturation and monocarboxylic function in the acid or salified state, selected from monomers containing ethylenic unsaturation and monocarboxylic function, and preferably among acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, cinnamic acid, or else semiesters of diacids such as the C 1 to C 4 monoesters of maleic or itaconic acids, or chosen from monomers with ethylenic unsaturation and dicarboxylic function in the acid or salified state, and preferably among itaconic, maleic, fumaric, mesaconic, citraconic acid or carboxylic acid anhydrides, such as maleic anhydride or selected from the monomers to ethylenic and sulphonic unsaturation in the acidic or salified state, and prefer among acrylamido-2-methyl-2-propanesulfonic acid, sodium methallyl sulphonate, vinyl sulphonic acid and styrene sulphonic acid, or else chosen from ethylenically unsaturated monomers with phosphoric function. acid or salified state, and preferentially among vinyl phosphoric acid, ethylene glycol methacrylate phosphate, propylene glycol methacrylate phosphate, ethylene glycol acrylate phosphate, propylene glycol acrylate phosphate and their ethoxylates or else chosen from ethylenically unsaturated monomers and phosphonic function in the acid or salified state, and is preferably vinylphosphonic acid, or mixtures thereof, b) at least one cationic monomer selected from ammonium quaternaries, 34 and preferentially from [2- (methacryloyloxy) ethyl] trimethyl ammonium chloride or sulphate, [2- (acryloyl) xy) ethyl] trimethyl ammonium, [3- (acrylamido) propyl] trimethyl ammonium chloride or sulfate, dimethyl diallyl ammonium chloride or sulphate, [3- (methacrylamido) propyl] trimethyl ammonium chloride or sulphate or mixtures thereof, c) optionally at least one nonionic monomer selected from N- [3-10 (dimethylamino) propyl] acrylamide or N- [3- (dimethylamino) propyl] methacrylamide, unsaturated esters such as N- [2- (dimethylamino) ethyl] methacrylate, or N- [2- (dimethylamino) ethyl] acrylate, or from acrylamide or methacrylamide and mixtures thereof, acrylates or methacrylates thereof. alkyl, vinyls, and preferentially vinyl acetate, vinylpyrrolidone, styrene, alphamethylstyrene and their derivatives, or the monomers of formula (I): (1) in which: m and p represent a number of units of alkylene oxide less than or equal to 150, n represents a number of oxide units of ethylene less than or equal to 150, q represents an integer at least equal to 1 and such that 5 (m + n + p) q <150, and preferentially such that 15 5 (m + n + p) q <120, R 1 represents hydrogen or the methyl or ethyl radical, R 2 represents hydrogen or the methyl or ethyl radical, W q R represents a radical containing a polymerizable unsaturated functional group, preferably belonging to the group of vinyls as well as to the group of acrylic esters, methacrylic, maleic, itaconic, crotonic, vinylphthalic and urethane unsaturated group such as acrylurethane, methacrylurethane, dimethylisopropenylbenzylurethane, allylurethane, as well as the group of substituted or unsubstituted allylic or vinyl ethers, or group of amides or ethylenically unsaturated imides, R 'represents hydrogen or a hydrocarbon radical having 1 to 40 carbon atoms,   10 - Talc treated according to one of claims 8 or 9, characterized in that said amphoteric polymer consists of: a) from 10 / D to 90%, preferably from 25% to 75%, very preferably from 40% to 60% mol% of at least one anionic monomer, b) from 10% to 90%, preferably from 25% to 75%, very preferably from 40% to 60% by moles of at least one cationic monomer, c) and from 0% to 30%, preferably from 0% to 20% by moles of at least one nonionic monomer, the sum of the molar percentages of each monomer constituting said amphoteric polymer being equal to 100%. 25   11 - Talc treated according to one of claims 8 to 10, characterized in that the amphoteric polymers are obtained by radical polymerization processes in solution, in direct or inverse emulsion, in suspension or precipitation in solvents, in the presence of systems. Catalysts and transfer agents, or by controlled radical polymerization processes and preferentially by controlled polymerization with nitroxides (NMP) or by cobaloxymes, radical atom transfer polymerization (ATRP), radical polymerization controlled by sulfur derivatives, selected from carbamates, dithioesters or trithiocarbonates (RAFT) or xanthates. 10   12 - Talc treated according to one of claims 8 to 11, characterized in that the amphoteric polymers are completely acidic, or totally or partially neutralized with a neutralizing agent selected from hydroxides of sodium, potassium, hydroxides and / or oxides of calcium, magnesium, ammonia, or mixtures thereof, preferably with a neutralizing agent selected from sodium hydroxide, potassium hydroxide, ammonia, or mixtures thereof, very preferably with a neutralizing agent which is 'ammonia.   13 - Talc treated according to one of claims 8 to 12, characterized in that the amphoteric polymers may be optionally before or after their total or partial neutralization, treated and separated into several phases, according to static or dynamic processes, by one or several polar solvents preferentially belonging to the group consisting of water, methanol, ethanol, propanol, isopropanol, butanols, acetone, tetrahydrofuran or their mixtures.   14 - Talc treated according to one of claims 8 to 13, characterized in that the amphoteric polymers are dried.   15 - treated talc powder, characterized in that said treated talc is that according to one of claims 8 to 14.   Characterized in that said treated talc is that according to one of claims 8 to 14.   17 - An aqueous suspension of treated talc, characterized in that said treated talc is that according to one of claims 8 to 14.   18 - Use, in the method of manufacturing a sheet of paper as a reducing agent of the amount of undesirable colloids, a treated talc according to one of claims 8 to 14, a dry talc powder treated according to claim 15, a treated talc granulate according to claim 16 and an aqueous treated talc suspension according to claim 17.