METHOD FOR MANUFACTURED PAPER AND CARDBOARD

Abstract

The present invention relates to a method for 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 P1 in the form of solid particles, P1 being composed of at least one nonionic 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 solid particles of polymer P1 to an aqueous solution M1 of: (i) an alkali hydroxide and / or an alkali-earth hydroxide, (ii) an alkali hypohalide and / or a hypohalide of alkaline-earth 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 cardboard 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 solid particles 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 the paper or cardboard.

[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 injecting the product into the fibrous suspension to obtain paper or cardboard, only the reaction of the poly- acrylamide in solution with hydroxides and hypophalides of alkali or alkaline earth is carried out.

[0010] However, this need for polyacrylamide solutions involves transporting them to the paper mill or the need for equipment for dissolving the polymer in particle form 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 solid particles 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 the dissolution of the polymer takes place very quickly in the reaction mixture of hydroxide and alkali metal and / or alkaline earth metal hypohalide and since 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 the form of solid particles 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 for 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 an aqueous suspension of cellulose fibers), (b) formation of 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 solid particles, 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 solid particles of water-soluble polymer PI into an aqueous solution Ml comprising: (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 particles PI.

[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 solid particles of water-soluble polymer PI into 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 advantageously consists of cellulose fibers and fillers. The term "cellulose fibers" encompasses any cellulose 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 salts of anionic monomers of the polymer PI are salts of 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 consists of adding the solid particles 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.

[0038] Advantageously, the aqueous solution Ml is an aqueous solution of sodium hydroxide (sodium hydroxide) and sodium hypochlorite.

[0039] Advantageously, the reaction time of the polymer PI in the aqueous solution Ml of hypohalide and hydroxide is from 10 seconds to 180 minutes.

[0040] The reaction Re is advantageously carried out at a temperature between 10 and 30°C, more advantageously between 15 and 25°C.

[0041] 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.

[0042] The reaction Re is advantageously carried out by adding polymer PI in the form of solid particles in the aqueous solution Ml. Preferably, the solid particles of polymer PI are in the form of powder, microbeads, solid particles in oily suspension, or solid particles in aqueous suspension.

[0043] These different forms of solid particles are obtained by techniques known to those skilled in the art.

[0044] The powder form of the PI polymer can be obtained by gel polymerization, precipitation polymerization or spray drying of the inverse emulsion polymer.

[0045] The PI polymer microbeads are advantageously obtained by reverse suspension polymerization.

[0046] Oily suspensions of solid PI polymer particles may be obtained by distillation of the polymer in inverse emulsion or by suspending the polymer in an oil. The oily suspensions may contain between 10 and 60% by weight of PI polymer particles.

[0047] Aqueous suspensions of solid PI polymer particles are advantageously obtained by dispersion polymerization (in brine) or by suspending the polymer in brine. The aqueous suspension may contain between 10 and 50% by weight of PI polymer particles.

[0048] Even more preferably, the polymer PI is added to the reaction medium in the form of a powder resulting from gel polymerization or microbeads resulting from reverse suspension polymerization.

[0049] When the polymer PI is in powder form, it is preferably dispersed and solubilized in an aqueous solution Ml by means of a polymer dispersion and grinding device, in particular a PSU (Polymer Slicing Unit, document WO2011107683), supplied by a circuit of the aqueous solution Ml. Those skilled in the art know how to adapt the manufacturing materials of this type of device so that it resists the aqueous solution Ml of hydroxide and hypohalide.

[0050] For the reaction Re, preferably between 0.1 and 20% by weight of solid particles 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, the aqueous solution Ml is added.

[0051] 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.

[0052] 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.

[0053] 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).

[0054] Advantageously, the polymer P2 (or P3) can also be introduced into the papermaking process at the forming table, for example by spraying or in the form of foam, or at the size press (coater).

[0055] 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.

[0056] 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.

[0057] 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, hydrophobic, or associative.

[0058] The following examples illustrate the invention without, however, limiting its scope. Examples of embodiments of the invention

[0059] Procedures used in application tests: a) Types of pastes used

[0060] 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. b) Drainage Performance Assessment (DDA)

[0061] 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.

[0062] The pressure under the canvas 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 canvas 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.

[0063] cl Performance in DSR application (dry strength), grammage at 90 gm-2

[0064] The necessary quantity of paste is taken so as to obtain a sheet having a weight of 90 g.m2.

[0065] 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.

[0066] 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 and building the water wall. The treated pulp is distributed on the water wall to form the fibrous mat on the forming fabric.

[0067] 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 the sheets obtained by this procedure are then measured.

[0068] 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.

[0069] 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: PI Polymers

[0070] Synthesis of Polymer PI-A

[0071] 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. Pour 2, 0.48 g of 100% sodium persulfate and 48 g of water for 180 minutes. The polymer solution is kept at 80°C for 120 minutes after the end of casting.

[0072] 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.

[0073] Pl-B Polymer: Acrylamide homopolymer in the form of microbeads marketed by SNF under the name: Flobeads™ AB 300 H.

[0074] PI-C Polymer: Acrylamide homopolymer in commercial powder form by SNF under the name: Flopam™ FA 920 BPM.

[0075] The polymers Pl-A (in aqueous solution), Pl-B (microbeads) and Pl-C (powder) are acrylamide homopolymers which are distinguished only by their physical form. P2 Polymers

[0076] Polymer synthesis P2-A

[0077] Preparation of a 10% by weight solution of Pl-A in water, by diluting 20 g of a 20% by weight solution of Pl-A in water with 20 g of water. The polymer solution is heated to 50°C.

[0078] 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 alpha (0.5) and beta (2.0) coefficients 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. The polymer P2-A is obtained at a concentration of 2% by weight.

[0079] Synthesis of Polymers P2-B and P2-C

[0080] An aqueous solution Ml of 3.11 g of sodium hypochlorite (NaOCl) at 14.6% (by weight in water) and 1.63 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. 37.7 g of water are then added.

[0081] 0.87 g of polymer Pl-B or Pl-C are added to the aqueous solution Ml at tem room temperature and with stirring. The polymer in suspension form dissolves and reacts for 120 minutes in the aqueous solution of sodium hypochlorite and sodium hydroxide. The polymer solutions P2-B or P2-C are obtained respectively, with a final concentration by weight of polymer equal to 2%. Application testing Drainage performance (DDA)

[0082] [Tables 1] Drainage (s) l.7kg / T 3.4kg / T P2-A 21.04 15.65 P2-B 12.12 9.53 P2-( 11.47 9.17 White 34.39

[0083] Table 1: Drainage as a function of the polymer.

[0084] An improvement in drainage is observed with the use of P2-B polymers and P2-C (compared to polymer P2-A).

[0085] Performance in DSR application (dry strength)

[0086] [Tables2] % Burst index % DBL SM % DBL ST White ref. ref. ref. P2-A 17% 14% 27% P2-B 34% 23% 34% P2-C -..O 6X-Cl 16% 49¾

[0087] Table 2: Dry strength as a function of the polymer.

[0088] Burst performance is improved by using P2-B and P2-C 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 solid particles, 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 solid particles of water-soluble polymer PI to an aqueous solution Ml comprising: (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 reaction Re having a reaction time of 10 seconds to 5 hours after the addition of the water-soluble polymer particles PI, the dissolution of the polymer P2 taking place very quickly in the aqueous solution Ml.,

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

4. Process according to one of claims 1 to 3, 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.

5. Method according to one of claims 1 to 4, characterized in that the solid particles of water-soluble polymer PI are in the form of powder, microbeads, solid particles in oily suspension, or solid particles in aqueous suspension.

6. Method according to one of claims 1 to 5, characterized in that the solid particles of water-soluble polymer PI are in the form of a powder resulting from gel polymerization or microbeads resulting from reverse suspension polymerization.

7. Method according to claim 6, characterized in that when the solid particles of water-soluble polymer PI are in the form of powder which is dispersed in the aqueous solution Ml by means of a polymer dispersion and grinding device supplied by a circuit of the aqueous solution Ml.

8. Method according to one of claims 1 to 7, characterized in that between 0.1 and 20% by weight of solid particles of water-soluble polymer PI are added to the aqueous solution Ml.

9. Method according to one of claims 1 to 8, 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.

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

11. Method according to one of claims 1 to 8, 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.

12. Method according to one of claims 1 to 11, 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.