METHOD FOR MANUFACTURING PAPER AND CARDBOARD

Abstract

This invention relates to a process for making a paper or cardboard sheet from a fibrous suspension, comprising the following steps: a) injecting a P3 polymer into a suspension of cellulosic fibers, b) forming a paper or cardboard sheet, c) drying the paper or cardboard sheet, the P3 polymer being prepared, prior to step a), from a water-soluble P1 polymer of at least one nonionic monomer selected from acrylamide, methacrylamide, N,N-dimethylacrylamide and acrylonitrile, the P1 polymer being subjected to an Rel reaction to give a P2 polymer, which is then subjected to an Re2 reaction to give the P3 polymer, which is injected into the fibrous suspension within 24 hours of the start of the Re1 reaction, the Re1 reaction comprises preparing a P2 polymer comprising isocyanate functions by reaction for 10 seconds to 60 minutes between (i) an alkali hydroxide and/or an alkaline earth hydroxide, (ii) an alkali hypohalite and/or an alkaline earth hypohalite and (iii) the P1 polymer, the Re2 reaction comprises preparing a P3 polymer by reaction between (iv) a micro-cellulose compound and (v) the P2 polymer comprising isocyanate functions.

Claims

1. A process for manufacturing a paper or cardboard sheet from a fibrous suspension, comprising the following steps: a) injecting a P3 polymer into a fibrous suspension, b) forming a paper or cardboard sheet, c) drying the paper or cardboard sheet, polymer P3 being prepared before step a) from a water-soluble polymer P1 of at least one nonionic monomer selected from acrylamide, methacrylamide, N,N-dimethylacrylamide, and acrylonitrile, polymer P1 being subjected to an Re1 reaction to give a polymer P2, which is then subjected to an Re2 reaction to give a P3 polymer, which is injected into the fibrous suspension within 24 hours from the start of the Re1 reaction, wherein the Re1 reaction comprises preparing a P2 polymer comprising isocyanate functions by reaction for 10 seconds to 60 minutes between (i) an alkali hydroxide and/or an alkaline earth hydroxide, (ii) an alkali metal hypohalite and/or an alkaline earth metal hypohalite, and (iii) the P1 polymer, wherein the Re2 reaction comprises preparing a P3 polymer by reaction between (iv) a micro-cellulose compound and (v) the P2 polymer comprising isocyanate functions.

2. The process according to claim 1, wherein polymer P1 is nonionic.

3. The process according to claim 1, wherein polymer P1 is a homopolymer of acrylamide or methacrylamide.

4. The process according to claim 1, wherein, for the Re1 reaction, the coefficient Alpha=moles of hypohalite/moles of nonionic monomer of the water-soluble P1 polymer is between 0.1 and 1.0 and the coefficient Beta=moles of hydroxide/moles of hypo-halide is between 0.5 and 4.0.

5. The process according to claim 1, wherein, for the Re2 reaction, the micro-cellulose compound is selected from nano-fibrillated cellulose, micro-fibrillated cellulose, nano-crystalline cellulose, nano-cellulose.

6. The process according to claim 1, wherein, for the Re2 reaction, between 10% and 100% of micro-cellulose compound is added to polymer P2, % by weight relative to the weight of polymer P2.

7. The process according to claim 1, wherein polymer P3 is introduced into the white water and/or into the thick stock and/or into the mixture formed by the white water and the thick stock after homogenization of the fibrous suspension in the dilution pump.

8. The process according to claim 1, wherein during the Re2 reaction, the micro-cellulose compound is in the form of a suspension in water.

9. The process according to claim 1, wherein the Re2 reaction is carried out in the absence of compounds having at least one aldehyde function or of compounds capable of generating at least one aldehyde function.

10. The process according to claim 1, wherein the Re1 reaction is carried out from an aqueous solution having a mass concentration of polymer P1 of between 0.5 and 20%, at a temperature between 30? C. and 60? C. and in the presence of an Alpha coefficient between 0.1 and 1.0, the Alpha coefficient being the ratio between the number of hypo-halide moles and the number of non-ionic polymer monomer moles P1; the Re2 reaction is carried out in the presence of polymer P2 and from 10 to 100% of micro-cellulose compound, by weight relative to polymer P2.

11. The process according to claim 1, wherein the process is free of any decarboxylation step after reaction Re1 and before reaction Re2.

12. The process according to claim 1, wherein the process is free of any decarboxylation step after reaction Re2.

13. The process according to claim 1, wherein, for the Re2 reaction, between 10% and 50% of micro-cellulose compound is added to polymer P2, % by weight relative to the weight of polymer P2.

14. The process according to claim 1, wherein between 0.1 and 10 kg, preferably between 0.2 and 5.0 kg, of polymer P3 are added to the fibrous suspension, per ton of dry matter of the fibrous suspension, wherein the fibrous suspension is a suspension of cellulosic fibers and fillers in water.

15. The process according to claim 1, wherein: for the Re1 reaction, the coefficient Alpha=moles of hypohalite/moles of nonionic monomer of the water-soluble P1 polymer is between 0.1 and 1.0 and the coefficient Beta=moles of hydroxide/moles of hypo-halide is between 0.5 and 4.0, for the Re2 reaction, the micro-cellulose compound is selected from nano-fibrillated cellulose, micro-fibrillated cellulose, nano-crystalline cellulose, nano-cellulose, for the Re2 reaction, between 10% and 100% of micro-cellulose compound is added to polymer P2, % by weight relative to the weight of polymer P2, the Re1 reaction is carried out from an aqueous solution having a mass concentration of polymer P1 of between 0.5 and 20%, at a temperature between 30? C. and 60? C.

16. The process according to claim 2, wherein polymer P1 is a homopolymer of acrylamide or methacrylamide.

17. The process according to claim 16, wherein: for the Re1 reaction, the coefficient Alpha=moles of hypohalite/moles of nonionic monomer of the water-soluble P1 polymer is between 0.1 and 1.0 and the coefficient Beta=moles of hydroxide/moles of hypo-halide is between 0.5 and 4.0; and for the Re2 reaction, the micro-cellulose compound is selected from nano-fibrillated cellulose, micro-fibrillated cellulose, nano-crystalline cellulose, nano-cellulose.

18. The process according to claim 17, wherein, for the Re2 reaction, between 10% and 100% of micro-cellulose compound is added to polymer P2, % by weight relative to the weight of polymer P2.

19. The process according to claim 18, wherein polymer P3 is introduced into the white water and/or into the thick stock and/or into the mixture formed by the white water and the thick stock after homogenization of the fibrous suspension in the dilution pump.

20. The process according to claim 18, wherein: the Re2 reaction is carried out in the absence of compounds having at least one aldehyde function or of compounds capable of generating at least one aldehyde function; the Re1 reaction is carried out from an aqueous solution having a mass concentration of polymer P1 of between 0.5 and 20%, at a temperature between 30? C. and 60? C.; the Re2 reaction is carried out in the presence of polymer P2 and from 10 to 50% of micro-cellulose compound, by weight relative to polymer P2. the process is free of any decarboxylation step after reaction Re1 and before reaction Re2; the process is free of any decarboxylation step after reaction Re2; and between 0.1 and 10 kg, preferably between 0.2 and 5.0 kg, of polymer P3 are added to the fibrous suspension, per ton of dry matter of the fibrous suspension, wherein the fibrous suspension is a suspension of cellulosic fibers and fillers in water.

Description

EXAMPLES OF EMBODIMENTS OF THE INVENTION

Procedures Used in Application Testing:

a) Types of Pulps Used

Recycled Fiber Pulp:

[0071] Wet pulp is obtained by disintegrating dry pulp to obtain a final aqueous concentration of 1% by weight. It is a pH-neutral pulp made from 100% recycled cardboard fibers.

b) Evaluation of the Drainage Performance (DDA)

[0072] The DDA (Dynamic Drainage Analyzer) makes it possible to automatically determine the time (in seconds) required to drain a fibrous suspension under vacuum. The polymers are added to the wet pulp (0.6 liters of pulp at 1.0% by weight) in the DDA cylinder with stirring at 1000 rpm: [0073] T=0s: pulp stirring [0074] T=20s: Add the additive [0075] T=30s: stop stirring and drain under vacuum at 200 mbar (1 bar=10.sup.5 Pa) for 70 s.

[0076] The pressure under the sheet 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 the slope to appear on the curve representing the pressure under the sheet as a function of time. The time, expressed in seconds, recorded at this break in slope corresponds to the drainage time. The shorter the time, the better the vacuum drainage.

c) Performance in the DSR Application (Dry Strength), Weight at 90 gm.sup.?2

[0077] The necessary amount of pulp is removed so as to obtain a sheet having a basis weight of 90 gm.sup.?2.

[0078] The wet pulp is introduced into the vat of the dynamic molder and is kept under agitation. The different components of the system are injected into this pulp according to the predefined sequence. A contact time of 30 to 45 seconds is generally observed between each addition of polymer.

[0079] Paper formers are made with an automatic dynamic former: a blotter and the forming sheet are placed in the bowl of the dynamic former before starting the rotation of the bowl at 1000 rpm.sup.?1 and building the water wall. The treated pulp is spread over the water wall to form the fibrous mat on the forming sheet.

[0080] 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.

[0081] The burst is measured with a Messmer Buchel M 405 burst meter according to TAPPI T403 om-02. The result is expressed in kPa. The bursting index, expressed in kPa.Math.m.sup.2/g, is determined by dividing this value by the weight of the sheet tested.

Products Tested in Application Trials:

P1 Polymers

[0082] 310 g of water are introduced into a 1 liter reactor equipped with a mechanical stirrer, a thermometer, a condenser, and a nitrogen gas plunger. The pH of the reaction medium is adjusted to 3.3 using a pH buffer (30% NaOH and H.sub.3PO.sub.4 75%). The medium is heated and maintained at a temperature of between 79 and 81? C. using a water bath. By means of two continuous castings, 400 g of 50% acrylamide, 0.28 g of 100% N,N-methylene-bis-acrylamide, 237.8 g of water, and 2.40 g of 100% sodium methallyl sulfonate are incorporated (casting 1) for 180 minutes. Casting 2, 0.48 g of 100% sodium persulfate and 48 g of water for 180 minutes. The polymer is left at 80? C. for 120 minutes after the end of casting.

[0083] The P1 polymer obtained has a pH of 5.7, a concentration of 20% and a viscosity of 6000 cps.

P2 Polymers

[0084] Preparation of a 10% P1 solution, 20 g of P1 and 20 g of water. The polymer is heated to 50? C.

[0085] A mixture of 14.6% sodium hypochlorite and 30% sodium hydroxide is prepared with an alpha coefficient equal to 0.5 and a beta coefficient equal to 2 for the Re1 reaction. When polymer P1 is at 50? C., the mixture of sodium hypochlorite and sodium hydroxide is added to P1. After 30 seconds of reaction, water (room temperature) is added. The P2 polymer is obtained.

P3 Polymers

[0086] 3 minutes after obtaining polymer P2, 17.7 g of micro-fibrillated cellulose (3% by weight in water at 30? C.) and 15 g of water (room temperature) are added to perform the Re2 reaction, i.e., 15% mass with respect to polymer P2. The P3-A polymer is obtained. [0087] 3 minutes after obtaining polymer P2, 41.3 g of micro-fibrillated cellulose (3% by weight in water at 30? C.) and 30 g of water (room temperature) are added to perform the Re2 reaction, i.e., 35% by weight of polymer P2. Polymer P3-B is obtained. [0088] 3 minutes after obtaining polymer P2, 4.7 g of micro-fibrillated cellulose (3% by weight in water at 30? C.) and 5 g of water (room temperature) are added to perform the Re2 reaction, i.e., 4% by weight of polymer P2. Polymer P3-C is obtained.

Application Tests:

[0089] Below, MFC means micro-fibrillated cellulose

TABLE-US-00001 TABLE 1 Drainage and dry strength depending on the measurements in micro-fibrillated cellulose or P3 polymers in the pulp. Sample Drainage Burst Index Blank 25 2.35 P3-A (1.5 kg/t) 18 2.9 P3-B (1.5 kg/t) 22 2.8 P3-C 1.5 kg/t 17 2.65 MFC (0.150 kg/t) 26 2.4 MFC (0.350 kg/t) 27 2.45 MFC (20 kg/t) 32 2.95

[0090] The addition of micro-fibrillated cellulose in the pulp causes a decrease in drainage. This is even more apparent with a micro-fibrillated cellulose measurement of 20 kg/t when this measurement gives the greatest improvement in bursting.

[0091] The process of the invention which consists in adding polymers P3-A, P3-B or P3-C to the pulp makes it possible to obtain equivalent results in terms of improved bursting, while allowing a marked improvement in drainage combined with a decrease in the consumption of micro-fibrillated cellulose. For P3-C, for which MFC weight % added for Re2 is below 10%, (by weight relative to the weight of polymer P2), the improvement in bursting is lower than for P3-A and P3-B.