METHOD FOR MANUFACTURED PAPER AND CARDBOARD

Abstract

The present invention relates to a process for manufacturing a sheet of paper or cardboard from a fibrous suspension, comprising the following steps: a) injecting a polymer P2 into a suspension of cellulosic fibers, b) forming a sheet of paper or cardboard, c) drying the sheet of paper or cardboard, the polymer P2 being prepared, prior to step a), from a water-soluble polymer P1 in the form of an inverse emulsion, P1 being composed of at least one non-ionic monomer selected from acrylamide, methacrylamide, N,N-dimethylacrylamide, and acrylonitrile, the polymer P1 being subjected to a reaction Re to give a polymer P2, the reaction Re consisting of adding the polymer P1 in the form of an inverse emulsion to an aqueous solution M1 of: (i) an alkali hydroxide and / or an alkali-earth hydroxide,(ii) an alkali hypohalide and / or an alkali-earth hypohalide prior to a reaction time of 10 seconds to 5 hours.

Description

Title of the invention: METHOD FOR MANUFACTURING PAPER AND CARDBOARD Field of invention

[0001] The present invention relates to a process for the manufacture of paper or board having improved drainage and machinability properties. More specifically, the invention relates to a process involving the reaction of a water-soluble polymer in the form of an inverse emulsion in a mixture of alkali metal hydroxide and / or alkaline earth metal hydroxide and alkali metal hypohalide and / or alkaline earth metal hypohalide and then injecting it directly into the fibrous suspension used to manufacture the paper or board.

[0002] The present invention also relates to papers and cardboards with improved physical properties obtained by this process. Prior art

[0003] The paper industry is constantly seeking to optimize its paper and cardboard manufacturing processes, particularly in terms of yield, productivity, cost reduction and quality of finished products.

[0004] The use of polymers as dry strength, drainability and machinability agents is very widely described.

[0005] Drainage properties relate to the ability of the fiber mat to evacuate or drain the maximum amount of water before drying. Improved drainage properties imply energy savings and an increase in production capacity.

[0006] Machinability refers to the optimization of the operation of the paper machine by increasing productivity through better drainage on the table, better dryness in the press section, a reduction in breakages through greater cleanliness of the circuits and a reduction in deposits.

[0007] Polyvinylamines are known to improve drainage during paper formation.

[0008] Polyvinylamines can be obtained by reacting a solution of polyacrylamide in a mixture of alkali metal hydroxide and / or alkaline earth metal hydroxide and alkali metal hypohalide and / or alkaline earth metal hypohalide followed by treatment in an acid medium.

[0009] When the reaction is carried out directly before injection of the product into the fibrous suspension to obtain paper or cardboard, only the reaction of the polyacrylamide in solution with the hydroxides and hypohalides of alkali or of alkaline earth is carried out.

[0010] However, this need for polyacrylamide solutions involves transporting them to the paper mill or the need for polymer dissolution equipment in the paper mill. In both cases, the footprint of polymer solution stocks or dissolution equipment remains significant.

[0011] In addition, this reaction on polyacrylamide requires heating the reaction medium and also a need for an exchanger to regulate its temperature at the end of the reaction. Presentation of the invention

[0012] Unexpectedly, the Applicant has discovered that a process involving the reaction of a water-soluble polymer in the form of an inverse emulsion (water in oil) in a mixture of hydroxide (alkali metal hydroxide and / or alkaline earth metal hydroxide) and hypohalide (alkali metal hypohalide and / or alkaline earth metal hypohalide) and then injecting it directly into the fibrous suspension used to manufacture paper or cardboard makes it possible to improve the drainage and dry strength properties.

[0013] This process also makes it possible to avoid all the logistics (transport or installation of a dissolution unit) inherent in the handling of water-soluble polymer solutions.

[0014] Furthermore, the process is all the simpler since, upon addition of the polymer in the form of an inverse emulsion to the mixture of hydroxide and alkali metal and / or alkaline earth metal hypohalide, the reaction medium is homogeneous and it is not necessary to heat the reaction medium or to use heat exchangers.

[0015] By "alkali" is meant an alkali metal, advantageously lithium, sodium or potassium. An "alkali hydroxide" means a hydroxide (OH ) of at least one alkali metal, for example NaOH, KOH or NaOH+KOH. The same applies to alkaline earth hydroxide.

[0016] By “alkaline earth” is meant an alkaline earth metal, advantageously calcium or magnesium.

[0017] A hypohalide is an oxyanion, for example hypochlorite CIO .

[0018] An "alkaline hypohalide" means a hypohalide of at least one alkali metal and at least one hypohalide, for example NaOCl, KOBr or NaOCl+KOBr. The same applies to the alkaline earth hypohalide.

[0019] Finally, since the molecular weight range of water-soluble polymers in inverse emulsion form is wide, the process of the invention makes it possible to increase the range of current drainage and dry strength agents compared to a similar process using polyacrylamides in aqueous solution form.

[0020] More specifically, the invention relates to a method of manufacturing a sheet of paper or cardboard from a fibrous suspension, comprising the following steps: a) injection of a polymer P2 into a fibrous suspension (advantageously a suspension of cellulose fibers), b) forming a sheet of paper or cardboard, c) drying the sheet of paper or cardboard, the polymer P2 being prepared, prior to step a), from a water-soluble polymer PI in the form of an inverse emulsion, PI being a water-soluble polymer of at least one non-ionic monomer chosen from acrylamide, methacrylamide, N,N-dimethylacrylamide, and acrylonitrile, the polymer P2 being obtained by a reaction Re consisting of adding the water-soluble polymer PI in the form of an inverse emulsion in an aqueous solution Ml of: (i) an alkali metal hydroxide, or an alkaline-earth metal hydroxide, or their mixtures (ii) an alkali metal hypohalide, or an alkaline-earth metal hypohalide, or their mixtures the Re reaction having a reaction time of 10 seconds to 5 hours after the addition of the water-soluble polymer PI in the form of an inverse emulsion.

[0021] Advantageously, step a) is carried out within a period not exceeding 24 hours from the start of the reaction Re, i.e. from the addition of the water-soluble polymer PI in the form of an inverse emulsion in the aqueous solution Ml.

[0022] In the remainder of the description and in the claims, all polymer dosages expressed in g.t1 or kg.t1 are given as weight of polymer per tonne of dry matter. The dry matter corresponds to the dry extract obtained after evaporation of the water from the fibrous suspension used in a process for manufacturing a sheet of paper or cardboard. The dry matter is generally based on cellulose fibers and fillers, advantageously consisting of cellulose fibers and fillers. The term "cellulose fibers" encompasses any cellulosic entity, including fibers, fines, microfibrils or nanofibrils. By fibrous suspension, we mean the thick stock or the diluted stock which are based on water and cellulose fibers. The thick stock, having a mass concentration of dry matter generally greater than 1%, or even greater than 3%, is upstream of the mixing pump (fan-pump).The diluted paste (Thin Stock), having a mass concentration of dry matter generally less than 1%, is located downstream of the mixing pump.

[0023] The term “polymer” designates both homopolymers and copolymers of at least two distinct monomers.

[0024] An amphoteric polymer is a polymer comprising cationic charges and anionic charges, preferably as many anionic charges as cationic charges.

[0025] As used herein, the term "water-soluble polymer" means a polymer that gives an aqueous solution without insoluble particles when dissolved under stirring for 4 hours at 25°C and with a concentration of 20 gL 1 in deionized water.

[0026] The value ranges include the lower and upper bounds. Thus, the value ranges “between 0.1 and 1.0” and “from 0.1 to 1” include the values ​​0.1 and 1.0.

[0027] The water-soluble polymer PI is a polymer of at least one non-ionic monomer chosen from acrylamide, methacrylamide, N,N-dimethylacrylamide, and acrylonitrile. Preferably, the polymer PI contains at least 50 mol% of at least one of these non-ionic monomers.

[0028] The polymer PI may also contain anionic and / or cationic and / or zwitterionic monomers. The polymer PI is advantageously free of non-ionic monomer which is not chosen from acrylamide, methacrylamide, N,N-dimethylacrylamide, and acrylonitrile.

[0029] The anionic monomers are preferably chosen from the group comprising monomers having a carboxylic acid function and their salts, including acrylic acid, methacrylic acid, itaconic acid, maleic acid, monomers having a sulfonic acid function and their salts; including acrylamido tert-butyl sulfonic acid (ATBS), allyl sulfonic acid and methallyl sulfonic acid, and their salts, and monomers having a phosphonic acid function and their salts.

[0030] Generally, the anionic monomers of the PI polymer have as counterion an alkali metal, an alkaline earth metal or an ammonium (preferably a quaternary ammonium).

[0031] The cationic monomers are preferably chosen from the group comprising quaternized or salified dimethylaminoethyl acrylate (ADAME), quaternized or salified dimethylaminoethyl methacrylate (MADAME), diallyldimethylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC), and methacrylamidopropyltrimethylammonium chloride (MAPTAC).

[0032] Advantageously, the cationic monomers of the polymer PI have as counterion a halide, preferably a chloride ion.

[0033] The zwitterionic monomers are preferably chosen from the group comprising sulfobetaine monomers such as sulfopropyl dimethylammonium ethylmethacrylate, sulfopropyl dimethylammonium propylmethacrylamide, or sulfopropyl 2-vinylpyridinium; phosphobetaine monomers, such as phosphato ethyltrimethylammonium ethylmethacrylate; and carboxybetaine monomers.

[0034] Preferably, the water-soluble polymer PI is a homopolymer or a copolymer of acrylamide or methacrylamide.

[0035] The polymer PI can be linear, structured or crosslinked. The crosslinking agents allowing the structuring can in particular be chosen from sodium allyl sulfonate, sodium methallyl sulfonate, sodium methallyl disulfonate, methylenebisacrylamide, triallylamine, triallylammonium chloride.

[0036] The structuring of the polymer PI can also be obtained with at least one polyfunctional compound containing at least 3 heteroatoms chosen from N, S, O, P and each having at least one mobile hydrogen. This polyfunctional compound can in particular be a polyethyleneimine or a polyamine.

[0037] The reaction Re is carried out by adding an inverse emulsion of water-soluble polymer PI to the aqueous solution Ml. Preferably, the inverse emulsion (water-in-oil emulsion) comprises: - An aqueous phase comprising at least the polymer PI, - An oily phase, - At least one emulsifying agent and at least one inversion agent.

[0038] The oily phase may be a mineral oil, a vegetable oil, a synthetic oil or a mixture of several of these oils.

[0039] Examples of mineral oil are mineral oils containing saturated hydrocarbons of aliphatic, naphthenic, paraffinic, isoparaffinic, cycloparaffinic or naphthyl type.

[0040] Examples of synthetic oil are hydrogenated polydecene or hydrogenated polyisobutene, an ester such as octyl stearate or butyl oleate. Exxon's Exxsol® product line is ideally suited.

[0041] In general, the weight ratio of the aqueous phase to the oily phase in the inverse emulsion is preferably from 50 / 50 to 90 / 10. This ratio includes the weight of the various constituents of the emulsion, in particular the water-soluble polymer PI.

[0042] The water-in-oil emulsion preferably comprises from 15 to 40% by weight of oil, from 20 to 55% by weight of water, from 15 to 50% by weight of PI polymer, the percentages being expressed relative to the total weight of the inverse emulsion of the PI polymer.

[0043] In the present invention, the term "emulsifying agent" designates an agent capable of emulsifying water in an oil while an "inverting agent" is an agent capable of emulsifying an oil in water. More precisely, it is considered that an inverting agent is a surfactant having an HLB greater than or equal to 10, and that an emulsifying agent is a surfactant having an HLB strictly less than 10.

[0044] The hydrophilic-lipophilic balance (HLB) of a chemical compound is a measure of its degree of hydrophilicity or lipophilicity, determined by calculating the values ​​of the dif different regions of the molecule, as described by Griffin in 1949 (Griffin WC, Classification of Surf ace-Active Agents by HLB, Journal of the Society of Cosmetic Chemists, 1949, 1, pages 311-326).

[0045] In the present invention, we have adopted Griffin's method based on calculating a value based on the chemical groups of the molecule. Griffin has assigned a dimensionless number between 0 and 20 to give information on the solubility in water and oil. Substances having an HLB value of 10 are distributed between the two phases, so that the hydrophilic group (molecular mass Mh) projects completely into the water while the hydrophobic hydrocarbon group (molecular mass Mp) is adsorbed in the non-aqueous phase.

[0046] The HLB value of a substance of total molecular mass M whose hydrophilic part has a molecular mass Mh, is HLB = 20 (Mh / M).

[0047] The inverse emulsion containing the polymer PI advantageously contains from 0.1% to 10% by weight of at least one emulsifying agent, the percentages being expressed by weight relative to the weight of the emulsion. This emulsifying agent is advantageously chosen from sorbitan esters, polyethoxylated sorbitan esters, polyethoxylated fatty acids, polyethoxylated fatty alcohols, polyesters having an average molecular weight of between 1000 and 3000 daltons resulting from the condensation between a poly(isobutenyl) succinic acid or its anhydride and a polyethylene glycol, block copolymers having an average molecular weight of between 2500 and 3500 daltons resulting from the condensation between hydroxystearic acid and a polyethylene glycol, ethoxylated fatty amines, derivatives of di-alkanol amides, copolymers of stearyl methacrylate, and mixtures of these emulsifying agents.

[0048] The inverse emulsion containing the polymer PI advantageously contains between 0.1 and 10% by weight of at least one inverting agent, the percentages being expressed by weight relative to the weight of the emulsion. This inverting agent is advantageously chosen from ethoxylated nonylphenols, preferably having 4 to 10 ethoxylations; ethoxylated / propoxylated alcohols preferably having an ethoxylation / propoxylation comprising between 12 and 25 carbon atoms; ethoxylated tridecyl alcohols; polyethoxylated fatty acids; poly(ethoxylated / propoxylated) fatty alcohols; ethoxylated sorbitan esters; polyethoxylated sorbitan laurate; polyethoxylated castor oil; heptaoxyethylated lauryl alcohol; polyethoxylated sorbitan monostearate; alkyl phenol polyethoxylated cetyl ethers; polyethylene oxide alkyl aryl ethers; N-cetyl-N-ethyl morpholinium ethosulfate; sodium lauryl sulfate;condensation products of fatty alcohols with ethylene oxide; condensation products of alkylphenols and ethylene oxide; condensation products of fatty amines with 5 or more molar equivalents of ethylene oxide; ethoxylated tristyryl phenols; condensates of ethylene oxide with polyhydric alcohols; partially esterified with fatty chains as well as their anhydrous forms; amine oxides; alkyl polyglucosides; glucamide; phosphate esters; alkylbenzene sulfonic acids and their salts; water-soluble surfactant polymers; and mixtures of several of these reversing agents.

[0049] The water-in-oil emulsion according to the invention can be prepared according to any method known to those skilled in the art. Generally, an aqueous solution comprising the monomer(s) and the emulsifying agent(s) is emulsified in an oily phase. Then, the polymerization is carried out by adding a free radical initiator. Reference may be made to redox couples, with cumene hydroperoxide, tertiary butylhydroxyperoxide or persulfates among the oxidizing agents, sodium sulfite, sodium metabisulfite and Mohr's salt among the reducing agents. Azo compounds such as 2,2'-azobis (isobutyronitrile) hydrochloride and 2,2'-azobis (2-amidinopropane) hydrochloride may also be used.

[0050] Conventionally, the polymerization is generally carried out isothermally, adiabatically or at a controlled temperature. Thus, the temperature is advantageously kept constant, generally between 10 and 60 °C (isothermal), or the temperature is allowed to increase naturally (adiabatic) and in this case, the reaction is generally started at a temperature below 10 °C and the final temperature is generally above 50 °C or, finally, the increase in temperature is controlled so as to have a temperature curve between the isothermal curve and the adiabatic curve.

[0051] Generally, the reversing agent(s) are added at the end of the polymerization reaction, preferably at a temperature below 50°C.

[0052] The reaction Re consists of adding the inverse emulsion of polymer PI into an aqueous solution Ml of: (i) an alkali metal hydroxide and / or an alkaline earth metal hydroxide, (ii) an alkali metal hypohalide and / or an alkaline earth metal hypohalide, with a reaction time Re of 10 seconds to 5 hours to form the polymer P2.

[0053] Advantageously, the aqueous solution Ml is an aqueous solution of sodium hydroxide (sodium hydroxide) and sodium hypochlorite.

[0054] Advantageously, the reaction time of the polymer PI in the aqueous solution Ml of hypohalide and hydroxide is from 10 seconds to 180 minutes.

[0055] The reaction Re is advantageously carried out at a temperature between 10 and 30°C, more advantageously between 15 and 25°C.

[0056] Preferably, for the reaction Re, the coefficient Alpha = moles of hypohalide (alkaline and / or alkaline-earth) / moles of non-ionic monomer(s) (acrylamide, methacrylamide, N,N-dimethylacrylamide, acrylonitrile or their mixtures) of the polymer PI is between 0.1 and 1.0 and the coefficient Beta = moles of hydroxide (alkaline and / or alkaline earth) / moles of hypohalide (alkaline and / or alkaline earth) is between 0.5 and 4.0.

[0057] For the reaction Re, preferably between 0.1 and 20% by weight of polymer PI, relative to the weight of the aqueous solution Ml, more preferably between 0.3 and 10% and even more preferably between 0.5 and 3.0% by weight, are added to the aqueous solution Ml.

[0058] Advantageously, at the end of the reaction Re, and before its injection into the fibrous suspension, the polymer P2 can be functionalized with a compound comprising at least one aldehyde function to give a polymer P3, for example by adding a compound comprising at least one aldehyde function. Preferably, the compound comprising at least one aldehyde function is glyoxal.

[0059] Preferably, before injection into the fibrous suspension, the pH of the reaction mixture resulting from the reaction Re and containing the polymer P2 can be adjusted by adding acid between 0.5 and 7.5, more preferably between 1.0 and 3.0. Those skilled in the art know how to adjust the pH of this type of reaction medium. The pH adjustment is advantageously carried out in the absence of formation of the polymer P3.

[0060] According to a preferred embodiment, the polymer P2 (or P3) is introduced into the white water and / or the thick paste and / or the mixture formed by the white water and the thick paste after homogenization of the fibrous suspension in the dilution pump (fan pump).

[0061] Advantageously, the polymer P2 (or P3) can also be introduced into the papermaking process at the forming table, for example by spraying or application in the form of foam, or at the size press (coater).

[0062] Advantageously, between 0.1 and 10 kg.t', and preferably between 0.2 and 5.0 kg.t1 of polymer P2 (or P3) are added to the fibrous suspension.

[0063] The fibrous suspension encompasses the possible use of different cellulosic fibers: virgin fibers, recycled fibers, chemical pulp, mechanical pulp, micro-fibrillated cellulose or nano-fibrillated cellulose. The fibrous suspension also encompasses the use of these different cellulosic fibers with all types of fillers such as TiO2, CaCO3 (ground or precipitated), kaolin, organic fillers and their mixtures.

[0064] The polymer P2 or P3 can be used within the papermaking process in combination with other products such as mineral or organic coagulants, dry strength agents, wet strength agents, natural polymers such as starches or carboxymethylcellulose (CMC), inorganic microparticles such as bentonite microparticles and colloidal silica microparticles, organic polymers of any ionic nature (non-ionic, cationic, anionic, or amphoteric) and which can be (without being limiting) linear, branched, crosslinked, hy- drophobic, or associative.

[0065] The following examples illustrate the invention without, however, limiting its scope. Examples of embodiments of the invention

[0066] Procedures used in application testing:

[0067] a) Types of pasta used

[0068] Recycled fiber pulp: Wet pulp is obtained by disintegrating dry pulp to obtain a final aqueous concentration of 1% by weight. It is a neutral pH pulp composed of 100% recycled cardboard fibers.

[0069] b) Drainage Performance Assessment (PDA)

[0070] The DDA ("Dynamic Drainage Analyzer") makes it possible to automatically determine the time (in seconds) required to drain under vacuum a fibrous suspension deposited on a fabric. The polymers are added to the wet paste (0.6 liters of paste at 1.0% by weight) in the DDA cylinder while stirring at 1000 revolutions per minute: - T=0 s: stirring the dough - T=20 s: Addition of the polymer - T=30 s: stop stirring and drain under vacuum at 200 mbar (1 bar = 105 Pa) for 70 seconds.

[0071] The pressure under the fabric is recorded as a function of time. When all the water is evacuated from the fibrous mat, the air passes through it, causing a break in slope to appear on the curve representing the pressure under the fabric as a function of time. The time, expressed in seconds, recorded at this break in slope corresponds to the draining time. The shorter the time, the better the vacuum draining.

[0072] cl Performance in DSR application (dry strength), grammage at 90 gm

[0073] The necessary quantity of paste is taken so as to obtain a sheet having a weight of 90 g.m2.

[0074] The wet paste is introduced into the vat of the dynamic form and is kept stirring. The various components of the system are injected into this paste according to the predefined sequence. A contact time of 30 to 45 seconds is generally observed between each addition of polymer.

[0075] Paper forms are made with an automatic dynamic form: a blotter and the forming fabric are placed in the bowl of the dynamic form before starting the rotation of the bowl at 1000 rpm 1 and building the water wall. The treated pulp is distributed on the water wall to form the fibrous mat on the forming fabric.

[0076] Once the water is drained, the fibrous mat is recovered, pressed under a press delivering 4 bar, then dried at 117°C. The sheet obtained is conditioned overnight in a room with controlled humidity and temperature (50% relative humidity and 23°C). The dry strength properties of all sheets obtained by this procedure are then measured.

[0077] The burst index is measured with a Messmer Buchel M 405 burst tester according to TAPPI T403 om-02 standard. The result is expressed in kPa or as a percentage relative to a reference. The burst index, expressed in kPa.mVg, is determined by dividing this value by the weight of the sheet tested.

[0078] The dry breaking length is measured in the machine direction (DBL SM) and in the cross direction (DBL ST) with a Testometric AX tensile tester according to TAPPI T494 om-01 standard. The result is expressed in km or as a percentage relative to a reference. Products tested in application trials:

[0079] PI Polymers

[0080] Pl-A Polymer Synthesis

[0081] 310 g of water are introduced into a 1 liter reactor equipped with a mechanical stirrer, a thermometer, a condenser and a nitrogen gas immersion rod. The pH of the reaction medium is adjusted to 3.3 using a pH buffer (NaOH 30% by weight in water and H3PO4 75% by weight in water). The medium is heated and maintained at a temperature between 79 and 81°C using a water bath. Using two continuous pours, 400 g of 50% acrylamide, 237.8 g of water and 2.40 g of 100% sodium hypophosphite are incorporated (pour 1) for 180 minutes. Casting 2, 0.48 g of 100% sodium persulfate and 48 g of water for 180 minutes. The polymer solution is maintained at 80°C for 120 minutes after the end of casting.

[0082] The obtained Pl-A polymer solution has a pH of 5.7, a Pl-A polymer weight concentration of 20% and a viscosity of 6000 cps.

[0083] PolymerPl-B: Acrylamide homopolymer in the form of an inverse emulsion marketed by SNF under the name: Flopam™EM 230.

[0084] Polymers Pl-A (in aqueous solution) and Pl-B (inverse emulsion) are acrylamide homopolymers which are distinguished only by their physical form.

[0085] P2 Polymers

[0086] Polymer synthesis P2-A

[0087] Preparation of a 10% by weight Pl-A solution in water, by diluting 20 g of a 20% by weight Pl-A solution in water with 20 g of water. The polymer solution is heated to 50°C.

[0088] An aqueous solution of 14.29 g of sodium hypochlorite (NaOCl) at 14.6% (by weight in water) and 7.5 g of sodium hydroxide at 30% (by weight in water) is prepared according to the coefficients alpha (0.5) and beta (2.0) for the reaction Re. When the polymer solution Pl-A is at 50°C, the aqueous solution of sodium hypochlorite and sodium hydroxide is added to Pl-A. After 30 seconds of reaction, 138.20 g of water is added. obtains a solution of polymer P2-A at a concentration of 2% by weight.

[0089] Polymer Synthesis P2-B

[0090] An aqueous solution Ml of 3.66 g of sodium hypochlorite (NaOCl) at 14.6% (by weight in water) and 1.92 g of sodium hydroxide at 30% (by weight in water) is prepared according to the coefficients alpha (0.5) and beta (2.0) for the reaction Re. 93.60 g of water are then added.

[0091] 3.20 g of Pl-B polymer (in inverse emulsion) is added to the aqueous solution Ml at room temperature and with stirring. The polymer is stirred for 60 minutes in the Ml solution. A solution of polymer P2-B is obtained, with a final concentration by weight of polymer equal to 1%. Application testing

[0092] Drainage performance (PDA)

[0093] [Tables 1] Drainage (s) l.7kg / T 3.4kg / T P2-A 21.04 15.65 P2 B 11.83 7.42 White 34.39

[0094] Table 1: Drainage as a function of the polymer.

[0095] An improvement in drainage is observed with the use of polymer P2-B compared to polymer P2-A.

[0096] Performance in DSR application (dry strength)

[0097] [Tables2] % Burst index % DBL SM % DBL ST White ref. ref. ref. P2-A 17% 14% 27% P2-B 31% 19% 47%

[0098] Table 2: Dry strength as a function of the polymer.

[0099] Burst performance is improved by using the P2-B polymer. The same trend is observed for the measurement of burst length in the forward direction (DBL SM) and in the cross direction (DBL ST).

Claims

Claims

1. A method of manufacturing a sheet of paper or cardboard from a fibrous suspension, comprising the following steps: a) injecting a polymer P2 into a fibrous suspension, b) forming a sheet of paper or cardboard, c) drying the sheet of paper or cardboard, the polymer P2 being prepared, prior to step a), from a water-soluble polymer PI in the form of an inverse emulsion, PI being a water-soluble polymer of at least one non-ionic monomer chosen from acrylamide, methacrylamide, N,N-dimethylacrylamide, and acrylonitrile, the polymer P2 being obtained by a reaction Re consisting of adding the water-soluble polymer PI in the form of an inverse emulsion to an aqueous solution Ml of: (i) an alkali metal hydroxide, or an alkaline-earth metal hydroxide, or mixtures thereof (ii) an alkali metal hypohalide, or a metal hypohalide alkaline earth, or their mixtures,the Re reaction having a reaction time of 10 seconds to 5 hours after the addition of the water-soluble polymer PI in the form of an inverse emulsion.,

2. Method according to claim 1, characterized in that the polymer PI contains at least 50 mol% of at least one non-ionic monomer chosen from acrylamide, methacrylamide, N,N-dimethylacrylamide, and acrylonitrile.

3. Method according to claim 1 or 2, characterized in that the polymer PI is a homopolymer or a copolymer of acrylamide or methacrylamide.

4. Method according to claims 1 to 3, characterized in that the inverse emulsion comprises: - An aqueous phase comprising at least the polymer PI, - An oily phase, - At least one emulsifying agent and at least one inversion agent.

5. Method according to the preceding claim, characterized in that the inverse emulsion of the polymer PI comprises from 15 to 40% by weight of oil, from 20 to 55% by weight of water, from 15 and 50% by weight of polymer, the percentages being expressed relative to the total weight of the inverse emulsion of the polymer PI.

6. Process according to one of claims 1 to 5, characterized in that, for the reaction Re, the coefficient Alpha = moles of hypohalide / moles of non-ionic monomer of the water-soluble polymer PI is between 0.1 and 1.0 and the coefficient Beta = moles of hydroxide / moles of hypohalide is between 0.5 and 4.

0.

7. Method according to one of claims 1 to 6, characterized in that between 0.1 and 20% by weight of polymer PI, relative to the weight of the aqueous solution Ml, are added to the aqueous solution Ml.

8. Method according to one of claims 1 to 7, characterized in that at the end of the reaction Re, and before injection into the fibrous suspension, the polymer P2 is functionalized with a compound comprising at least one aldehyde function to give a polymer P3.

9. Method according to claim 8, characterized in that the compound comprising at least one aldehyde function is glyoxal.

10. Method according to one of claims 1 to 7, characterized in that before injection into the fibrous suspension, the pH of the reaction mixture resulting from the reaction Re and containing the polymer P2 is adjusted by adding acid between 0.5 and 7.

5.

11. Method according to one of claims 1 to 10, characterized in that the polymer P2 or P3 is introduced into the white water and / or into the thick paste and / or into the mixture formed by the white water and the thick paste after homogenization of the fibrous suspension in the dilution pump.