Process for manufacturing paper and board

Abstract

The present invention relates to a process for manufacturing a sheet of paper and/or board from a fibrous suspension, according to which, before the formation of said sheet, added to the fibrous suspension, at one or more injection points, are at least two retention aids respectively: (a) at least one water-soluble organic cationic polymer P1 having a cationicity greater than 2 meq.Math.g.sup.1, and (b) at least one water-soluble amphoteric polymer P2 of at least one anionic monomer and of at least one cationic monomer. The polymer P2 is added to the fibrous suspension after dissolving, in aqueous solution, the polymer P2 previously obtained by one of the following polymerization techniques: gel polymerization, suspension polymerization, inverse emulsion polymerization, dispersion polymerization. The polymer P2 has a factor F>2, said factor F being defined by the formula: F=UL.sup.2[(100A)/(100C)] with UL: Brookfield viscosity of the polymer P2 at 0.1% by weight in a 1M aqueous solution of NaCl, at 23 C., with a UL module and at 60 rev.Math.min.sup.1, A and C corresponding respectively to the molar percentages of the anionic and cationic monomers of the polymer P2.

Claims

1. A process for manufacturing a sheet of paper and/or board from a fibrous suspension, the process comprising, before formation of said sheet, adding to the fibrous suspension, at one or more injection points, at least two retention aids respectively: (a) at least one water-soluble organic cationic polymer P1 with a cationicity greater than 2 meq.Math.g.sup.1, and (b) at least one water-soluble amphoteric polymer P2 of at least one anionic monomer and of at least one cationic monomer, wherein the polymer P2 is added to the fibrous suspension after dissolving, in aqueous solution, the polymer P2 previously obtained by one of the following polymerization techniques: gel polymerization, suspension polymerization, inverse emulsion polymerization, dispersion polymerization, and in that polymer P2 has a factor F>2, said factor F being defined by the formula: F=UL.sup.2[(100A)/(100C)] with UL: Brookfield viscosity of the polymer P2 at 0.1% by weight in a 1M aqueous solution of NaCl, at 23 C., with a UL module and at 60 rev.Math.min.sup.1 A and C corresponding respectively to the molar percentages of the anionic and cationic monomers of the polymer P2.

2. A process according to claim 1, wherein the polymer P1 is introduced into the fibrous suspension at a rate of 100 to 1500 g.Math.t.sup.1 of dry paper and/or board.

3. A process according to claim 1, wherein the polymer P2 is introduced into the fibrous suspension at a rate of 100 to 1500 g.Math.t.sup.1 of dry paper and/or board.

4. A process according to claim 1, wherein the polymer P1 is selected from: (i) polyvinylamines and/or (ii) polyethyleneimines, and/or, (iii) polyamines, and/or, (iv) poly(diallyldimethylammonium chloride), and/or, (v) poly(amidoamine-epihalohydrin).

5. A process according to claim 1, wherein the polymer P1 results from the degradation reaction known as Hofmann, in aqueous solution, in the presence of an alkaline earth and/or alkali hydroxide and an alkaline earth and/or alkali hypo-halide, on a (co)polymer based on at least: a non-ionic monomer selected from the group comprising acrylamide, methacrylamide, N,N-dimethylacrylamide, t-butylacrylamide, octylacrylamide, optionally another monomer containing at least one unsaturated bond.

6. A process according to claim 1, wherein the polymer P1 is a fully or partially hydrolyzed N-vinylformamide (co)polymer.

7. A process according to claim 1, wherein the polymer P1 is a polyamine.

8. A process according to claim 1, wherein the polymer P1 is a poly(diallyldimethylammonium chloride).

9. A process according to claim 1, wherein the polymer P1 is a poly(amidoamine-epihalohydrin).

10. A process according to claim 1, wherein the polymer P1 has a cationic charge density greater than 4 meq.Math.g.sup.1.

11. A process according to claim 1, wherein the polymer P2 is a polymer of: a/ at least one cationic monomer selected from the group comprising dimethylaminoethyl acrylate (ADAME) quaternized or salified, and/or dimethylaminoethyl methacrylate (MADAME) quaternized or salified, and/or dimethyldiallylammonium chloride (DADMAC), and/or acrylamido propyltrimethyl ammonium chloride (APTAC) and/or methacrylamido propyltrimethyl ammonium chloride (MAPTAC), and/or fully or partially hydrolyzed N-vinyl formamide, b/ at least one anionic monomer having at least one carboxylic, and/or sulfonic, and/or phosphoric function, c/ and/or at least one monomer of a non-ionic nature, d/ optionally at least one monomer with a zwitterionic nature, e/ optionally at least one monomer with a hydrophobic nature, f/ optionally at least one monomer containing at least two unsaturated bonds.

12. A process according to claim 1, wherein the polymer P2 has a Brookfield viscosity greater than 2 cps.

13. A process according to claim 1, wherein the mass ratio between the polymer P1 and the polymer P2 is between 1/10 and 10/1.

14. A process according to claim 1, wherein a tertiary anionic retention aid selected from the organic polymers and/or inorganic microparticles is added to the fibrous suspension.

15. A process according to claim 14, wherein the tertiary anionic retention aid is introduced into the fibrous suspension at a rate of 20 to 2500 g.Math.t.sup.1 of dry paper and/or board.

16. A process according to claim 1, wherein the polymer P1 and the polymer P2 are independently introduced into the fibrous suspension at a rate of 100 to 1500 g.Math.t.sup.1 of dry paper and/or board.

17. A process according to claim 16, wherein the polymer P1 results from the degradation reaction known as Hofmann, in aqueous solution, in the presence of an alkaline earth and/or alkali hydroxide and an alkaline earth and/or alkali hypo-halide, on a (co)polymer based on at least: a non-ionic monomer selected from the group comprising acrylamide, methacrylamide, N,N-dimethylacrylamide, t-butylacrylamide, octylacrylamide, optionally another monomer containing at least one unsaturated bond.

18. A process according to claim 16, wherein the polymer P1 is: a fully or partially hydrolyzed N-vinylformamide (co)polymer; a polyamine; a poly(diallyldimethylammonium chloride); or a poly(amidoamine-epihalohydrin).

19. A process according to claim 18, wherein the polymer P1 has a cationic charge density greater than 4 meq.Math.g.sup.1.

20. A process according to claim 19, wherein the polymer P2 has a Brookfield viscosity greater than 2 cps, and is a polymer of: a/ at least one cationic monomer selected from the group comprising dimethylaminoethyl acrylate (ADAME) quaternized or salified, and/or dimethylaminoethyl methacrylate (MADAME) quaternized or salified, and/or dimethyldiallylammonium chloride (DADMAC), and/or acrylamido propyltrimethyl ammonium chloride (APTAC) and/or methacrylamido propyltrimethyl ammonium chloride (MAPTAC), and/or fully or partially hydrolyzed N-vinyl formamide, b/ at least one anionic monomer having at least one carboxylic, and/or sulfonic, and/or phosphoric function, c/ and/or at least one monomer of a non-ionic nature, d/ optionally at least one monomer with a zwitterionic nature, e/ optionally at least one monomer with a hydrophobic nature, f/ optionally at least one monomer containing at least two unsaturated bonds.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1 shows the burst index of a sheet of paper as a function of filler content.

(2) FIG. 2 shows the breaking length of a sheet of paper as a function of filler content.

EXAMPLE EMBODIMENTS OF THE INVENTION

(3) Products Tested in the Examples:

(4) In the following list, products of type A are anionic, type B amphoteric and type C cationic. These 3 classes of products conform to the retention aids described in the method of the invention.

(5) Products of type X are salts of trivalent cations, as described in the processes in the prior art.

(6) Products of type Z are amphoteric but do not have the characteristics of the polymers P2 described in the method of the invention. A1: Anionic polymer 40 mol %, in the form of a water-in-oil emulsion with a Brookfield viscosity of 2.5 cps (Module UL, 0.1%, NaCl 1M, 60 rev.Math.min.sup.1, 23 C. A2: Bentonite sold under the name Opazil AOG by Sd Chemie. B1: Water-soluble amphoteric polymer, in the form of a powder, with a Brookfield viscosity of 2.7 cps (Module UL, 0.1%, NaCl 1M, 60 rev.Math.min.sup.1, 23 C.) and a factor F of 7.78. B2: Water-soluble amphoteric polymer, in the form of a powder, with a Brookfield viscosity of 2.8 cps (Module UL, 0.1%, NaCl 1M, 60 rev.Math.min.sup.1, 23 C.) and a factor F of 8.88. B3: Water-soluble amphoteric polymer, in the form of microbeads, with a Brookfield viscosity of 2.6 cps (Module UL, 0.1%, NaCl 1M, 60 rev.Math.min.sup.1, 23 C.) and a factor F of 7.23. B4: Water-soluble amphoteric polymer, in the form of a water-in-water dispersion, with a Brookfield viscosity of 2.0 cps (Module UL, 0.1%, NaCl 1M, 60 rev.Math.min.sup.1, 23 C.) and a factor F of 3.72. C1: Cationic polymer obtained by Hofmann degradation reaction, Brookfield viscosity of 100 cps (Module LV1, 30 rev.Math.min.sup.1, 23 C.) and active material 10.5%. C2: Cationic polymer obtained by partial hydrolysis of poly(vinylformamide). The hydrolysis rate is 30 mol %, molecular weight 350,000 daltons and active material 16.4%. This is Xelorex RS 1100 from BASF. C3: Cationic polymer obtained by partial hydrolysis of poly(vinylformamide). The hydrolysis rate is 50 mol %, molecular weight 300,000 daltons and active material 13.4%. This is Hercobond 6350 from Solenis. C4: Cationic polymer of polyethylenimine type with molecular weight of 1,000,000 daltons and active material 21%. This is Polymin SK from BASF. C5: Polyamine with Brookfield viscosity 5,000 cps (Module LV3, 12 rev.Math.min.sup.1, 23 C.) at 50% active material. C6: Poly(DADMAC) with Brookfield viscosity 2,000 cps (Module LV3, 12 rev.Math.min.sup.1, 23 C.) at 40% active material. C7: PAE with Brookfield viscosity 50 cps (Module LV1, 60 rev.Math.min.sup.1, 23 C.) at 12.5% active material. X1: Aluminum polychloride (PAC) containing 18% alumina (Al.sub.2O.sub.3) X2: Technical aluminum sulfate (Alum) in powder form (Al.sub.2(SO.sub.4).sub.3.14H.sub.2O) Z1: Amphoteric polyacrylamide, in liquid form with Brookfield viscosity of 3,000 cps (Module LV3, 12 rev.Math.min.sup.1, 23 C.) at 19.8%, with a factor F of 1.60. Product used in the prior art U.S. Pat. No. 8,926,797 under the name Harmide RB217 from Harima. Z2: Amphoteric polyacrylamide, in liquid form with Brookfield viscosity of 7,000 cps (Module LV3, 12 rev.Math.min.sup.1, 23 C.) at 20.1%, with a factor F of 1.42. Product used in the prior art US 2011/0155339 under the name Hercobond 1205 from Solenis.
Procedures Used in the Examples:
a) The Various Types of Pulp Used Virgin fiber pulp (used in examples 1, 2, 3, 4, 5): Wet pulp is obtained by pulping dry pulp in order to obtain a final aqueous concentration of 1% by mass. This is a pulp with neutral pH composed of 90% long virgin bleached fibers, 10% short virgin bleached fibers, and 30% additional GCC (Hydrocal 55 from Omya) Recycled fiber pulp (used in example 6): Wet pulp is obtained by pulping dry pulp in order to obtain a final aqueous concentration of 1% by mass. This is a pulp with neutral pH composed of 100% recycled board fibers.
b) Evaluation of the Total Retention and Filler Retention

(7) The various results are obtained using a Britt Jar type container, with a stirring speed of 1000 rpm.

(8) The sequence of adding the various retention aids being as follows: T=0 s: Stirring 500 ml of pulp at 0.5% by mass T=10 s: Addition of cationic retention aid T=20 s: Addition of amphoteric retention aid T=25 s: Optional addition of tertiary retention aid T=30 s: Removal of the first 20 ml corresponding to the dead volume under the wire, then recovery of 100 mL white waters.

(9) First pass retention as a percentage (% FPR: First Pass Retention), corresponding to the total retention being calculated according to the following formula:
% FPR=(C.sub.HBC.sub.WW)/C.sub.HB*100

(10) First pass ash retention as a percentage (% FPAR: being calculated according to the following formula:
% FPAR=(A.sub.HBA.sub.WW)/A.sub.HB*100

(11) Where: C.sub.HB: Consistency of the headbox C.sub.WW: Consistency of the white water A.sub.HB: Consistency of the headbox ash A.sub.WW: Consistency of the white water ash
c) Evaluation of the Gravity Dewatering Performance Using Canadian Standard Freeness (CSF)

(12) In a beaker, the pulp is treated, subjected to a stirring speed of 1000 rpm. The sequence of adding the various retention aids being as follows: T=0 s: Stirring 500 ml of pulp at 0.6% by mass T=10 s: Addition of cationic retention aid T=20 s: Addition of amphoteric retention aid T=25 s: Optional addition of tertiary retention aid T=30 s: Stirring stopped and addition of the quantity of water necessary to obtain 1 liter.

(13) This liter of pulp is transferred into the Canadian Standard Freeness Tester and the TAPPI T227om-99 procedure is performed.

(14) The volume, expressed in mL, collected by the lateral tube gives a measure of the gravitational dewatering. The higher this value, the better the gravitational dewatering.

(15) d) Evaluation of the DDA Dewatering Performance

(16) The DDA (Dynamic Drainage Analyzer) makes it possible to automatically determine the amount of time (in seconds) necessary to drain a fibrous suspension under vacuum. The polymers are added to the wet pulp (0.6 liter of pulp at 1.0% by mass) in the DDA cylinder under stirring at 1000 rpm: T=0 s: pulp stirring T=10 s: addition of cationic retention aid T=20 s: Addition of amphoteric retention aid T=25 s: Optional addition of tertiary retention aid T=30 s: stirring stopped and dewatering under vacuum at 200 mBar for 70 s

(17) The pressure under the wire is recorded as a function of time. When all the water is evacuated from the fibrous web, air passes through it causing a break in the slope of the curve showing the pressure under the wire as a function of time. The time, expressed in seconds, at this break in the slope, corresponds to the dewatering time. The lower the time, the better the dewatering under vacuum.

(18) e) Dry Strength Resistance (DSR) Performance, Grammage 90 g.Math.m.sup.2

(19) The quantity of pulp necessary is sampled so as to obtain a sheet with a grammage of 90 g.Math.m.sup.2.

(20) The wet pulp is introduced into the dynamic handsheet former and is maintained under stirring. The various components of the system are injected into this pulp according to the predefined sequence. Generally, a contact time of 30 to 45 seconds between each addition of polymer is maintained.

(21) Paper handsheets are made with an automatic handsheet former: a blotter and the forming wire are placed in the jar of the dynamic handsheet former before starting rotation of the jar at 1000 rev.Math.min.sup.1 and constructing the water wall. The treated pulp is distributed over the water wall to form the fibrous sheet on the forming wire.

(22) Once the water has been drained, the fibrous sheet is collected, pressed under a press delivering 4 bars, then dried at 117 C. The sheet obtained is conditioned overnight in a controlled temperature and humidity room (50% relative humidity and 23 C.). The dry strength properties of all the sheets obtained by this method are then measured.

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

(24) The breaking length is measured in the machine direction with a Testometric AX traction device according to standard TAPPI T494 om-01 The result is expressed in km.

(25) To illustrate the fact that the increase in filler levels in the sheet, without any treatment, is detrimental to the mechanical properties of the paper obtained, a series of sheets has been produced using a pulp at neutral pH, composed of 90% by mass long virgin bleached fibers and 10% by mass of short virgin bleached fibers, with different quantities of additional fillers.

(26) The levels of fillers contained in these sheets as well as the mechanical properties (burst index and breaking length in the machine direction) have been measured.

(27) By plotting the mechanical performance as a function of the filler levels in the sheet, the graphs in FIGS. 1 and 2 are obtained.

(28) From these graphs, it is perfectly clear that the increase in filler levels in a sheet has a detrimental effect, by strongly decreasing the mechanical properties of the sheet itself.

Example 1: Combination, from the Invention, Between a Cationic Product and an Amphoteric Product (on a Virgin Fiber Pulp)

(29) TABLE-US-00001 TABLE 1 Properties obtained in the presence (invention) or not (blank) of a cationic product and an amphoteric product Breaking Filler Dosage FPAR DDA Burst index length content Products (kg/t) FPR (%) (%) (s) (kPa .Math. m.sup.2/g) (km) (% mass) Blank 0 72.6 8.6 33.6 1.48 4.09 20 C1 0.25 81.5 40.3 20.6 1.58 4.23 22.6 B1 0.25 C1 0.5 86.2 58.2 13.8 1.57 4.33 23.9 B1 0.5 C1 0.75 87.9 66.7 11.9 1.69 4.44 24.9 B1 0.75 C1 1 89.2 69.0 11.3 1.89 4.62 25.2 B1 1 C1 1.5 90.7 71.1 11.1 19.5 4.72 25.4 B1 1.5 The blank corresponds to a test without additive.

(30) By combining a Hofmann degradation product with an amphoteric product in the form of a powder, as described in the invention, at various dosages, it can be seen from Table 1 that it is possible, on the one hand, to drastically improve the retention, filler retention and dewatering performances, and on the other hand, to increase the level of filler in the sheet without negatively affecting the mechanical characteristics thereof (burst index and breaking length).

(31) It is also observed that there are no inverse effects by increasing the dosages of C1 and B2 and that all properties improve with the dosages applied, including the physical characteristics of the paper.

(32) Clearly, the formation of the sheet is not affected.

Example 2: Combination, from the Invention, Between a Cationic Product, an Amphoteric Product and an Anionic Product (on a Virgin Fiber Pulp)

(33) TABLE-US-00002 TABLE 2 Properties obtained in the presence (invention) or not (blank) of a cationic product, an amphoteric product and an anionic product Breaking Filler Dosage FPAR Burst index length content Products (kg/t) FPR (%) (%) DDA (s) (kPa .Math. m.sup.2/g) (km) (%) Blank 0 72.6 8.6 33.6 1.48 4.09 20 C1 0.25 87.5 64.6 11.9 1.5 4.01 23.8 B1 0.25 A1 0.15 C1 0.5 90.5 72.3 9.4 1.51 4.13 25.2 B1 0.5 A1 0.15 C1 0.75 92.2 78.3 7.7 1.61 4.21 26.2 B1 0.75 A1 0.15 C1 1 92.6 81.1 7.7 1.73 4.37 26.8 B1 1 A1 0.15 C1 0.5 89.7 71.7 8.5 1.50 4.10 25.1 B1 0.5 A2 1.5 The blank corresponds to a test without additive.

(34) With the three-component system previously described in the invention, it can be seen in Table 2 behavior identical to Example 1. Furthermore, the retention, filler retention and dewatering performances are even better with the use of the tertiary aid, notably at low dosage.

(35) The filler levels in the sheet are higher, without however compromising the mechanical properties.

(36) The fact that the mechanical characteristics of the sheet are not negatively impacted at the highest dosages clearly shows that the formation of the sheet has not been affected.

(37) The use of bentonite as tertiary anionic retention aid enables high retention, filler retention and dewatering performance levels to be obtained, comparable to an anionic organic polymer.

Example 3: Variation of the Cationic Component on the Retention, Filler Retention and Dewatering Under Vacuum Performances (on a Virgin Fiber Pulp)

(38) TABLE-US-00003 TABLE 3 Properties obtained in the presence (invention and counter-examples) or (not) of at least one cationic product and an amphoteric product Dosage FPR FPAR DDA Products (kg/t) (%) (%) (s) Blank 0 72.0 4.9 34.7 CE B1 0.5 79.6 29.8 17.7 C1 0.5 87.5 63.2 16.2 B1 0.5 C2 0.5 87.9 62.8 16.6 B1 0.5 C3 0.5 88.5 64.8 15.2 B1 0.5 C4 0.5 86.5 61.8 16.6 B1 0.5 C5 0.5 86.0 57.3 17.7 B1 0.5 C6 0.5 84.4 51.4 18.4 B1 0.5 C7 0.5 84.3 50.6 21 B1 0.5 X1 0.5 87.7 63.4 16.1 CE C1 0.5 B1 0.5 X1 0.5 79.7 30.0 17.5 CE B1 0.5 CE: counter-example, combination non-compliant with the method of the invention. The blank corresponds to a test without additive.

(39) From the results in Table 3, it can be seen that the combination, described in the invention, of the various cationic products of type Ci with the amphoteric product B1 presents a real synergy and enables the retention, filler retention and dewatering properties to be improved in a surprising way.

(40) The best performances are nevertheless obtained by combining a cationic polymer containing primary amine functions with an amphoteric polymer.

(41) Furthermore, the use of a mineral coagulant of type X1 (X1/B1 vs B1, or X1/C1/B1 vs C1/B1) does not offer any improvement in terms of retention, filler retention or dewatering performances, which clearly differentiates this invention from the BASF prior art (U.S. Pat. No. 8,926,797).

Example 4: Variation of the Nature of the Amphoteric Polymer on the Retention, Filler Retention and Dewatering Under Vacuum Performances (on a Virgin Fiber Pulp)

(42) TABLE-US-00004 TABLE 4 Properties obtained in the presence (invention and counter-examples) or not (blank) of a cationic product and an amphoteric product. Dosage FPR FPAR DDA Products (kg/t) (%) (%) (s) Blank 0 72.0 4.9 34.7 CE C1 0.5 78.1 29.7 25.5 C1 0.5 87.5 63.2 16.2 B1 0.5 C1 0.5 86.7 61.2 16.3 B2 0.5 C1 0.5 85.3 56.3 16.4 B3 0.5 C1 0.5 86.6 61.0 16.2 B4 0.5 C1 0.5 78.9 31.1 24.1 CE Z1 0.5 C1 0.5 78.2 30.3 26.5 CE Z2 0.5 CE: counter-example, combination non-compliant with the method of the invention. The blank corresponds to a test without additive.

(43) It clearly appears in Table 4 that the amphoteric products obtained by gel polymerization, suspension polymerization, inverse emulsion polymerization or dispersion polymerization are of real interest in terms of simultaneous retention, filler retention and dewatering performances vis--vis the amphoteric products obtained by solution polymerization used in the prior art.

(44) Indeed, by referring to products Z1 and Z2 (respectively the amphoteric products shown in prior art documents U.S. Pat. No. 8,926,797 and US 2011/0155339) in Table 4, this invention shows improvements, in terms of performance, in the order of 9 points for retention, 35 points for filler retention and 9 seconds for dewatering under vacuum.

Example 5: Comparison of the Method of the Invention/Prior Art Methods on Dewatering Under Vacuum Performances (on a Virgin Fiber Pulp

(45) TABLE-US-00005 TABLE 5 Properties obtained according to the invention or according to the prior art Dosages FPR FPAR DDA Products (kg/t) (%) (%) (s) Blank 0 72.0 4.9 36.8 CE C1 0.5 87.5 63.2 15.6 B1 0.5 C2 0.5 87.9 62.8 16.9 B1 0.5 C3 0.5 88.5 64.8 13.8 B1 0.5 C4 0.5 86.5 61.8 17.1 B1 0.5 X2 5 79.5 32.8 22.2 AA1 C2 0.5 Z1 0.5 X2 5 78.9 31.1 25.6 AA1 C1 0.5 Z1 0.5 X2 5 78.1 30.5 22.5 AA1 C4 0.5 Z1 0.5 C1 0.5 78.2 30.3 27.5 AA2 Z2 0.5 C3 0.5 78.9 31.2 26.5 AA2 Z2 0.5 AA1: described in document U.S. Pat. No. 8,926,797. AA2: described in document US 2011/0155339. The blank corresponds to a test without additive.

(46) In Table 5, it can be clearly seen that the retention, filler retention and dewatering performances delivered by the combination described in the invention are clearly better than those of the prior art.

Example 6: Combination, from the Invention, Between a Cationic Product and an Amphoteric Product (on Recycled Board Fiber Pulp)

(47) TABLE-US-00006 TABLE 6 Properties obtained according to the invention or not (blank) from a recycled fiber pulp Ash Dosage FPR FPAR DDA CSF Burst DBL Content (kg/t) (%) (%) (s) (ml) Index MD (%) Blank 0 76.5 31.7 44.1 308 1.60 2.16 6.2 C1 0.25 80.3 37.2 31.3 327 1.67 2.17 7.8 B1 0.25 C1 0.5 85.4 55.2 24 362 1.68 2.20 8.5 B1 0.5 C1 0.75 89.4 68.9 16.6 426 1.69 2.27 9.9 B1 0.75 C1 1 91.2 74.9 11.4 481 1.71 2.31 10.2 B1 1 C1 1.5 96.1 88.8 10.1 568 1.73 2.35 10.3 B1 1.5 The blank corresponds to a test without additive.

(48) According to Table 6, on a recycled board pulp, it is possible, on the one hand, to drastically improve the retention, filler retention and dewatering performances, and on the other hand, to increase the level of filler in the sheet without negatively affecting the mechanical characteristics thereof (burst index and breaking length).

(49) It is also observed that the dewatering performances, whether measured under vacuum or by gravity are in the two most improved cases.

(50) By referring to Example 1 (virgin fiber pulp), it can be concluded that the benefits of this invention are valid regardless of the type of fibers used, and the papers produced.