PROCESS FOR MANUFACTURING PAPER OR CARDBOARD

Abstract

This invention relates to a method for manufacturing a sheet of paper or cardboard, according to which, before forming said sheet, at least one N-vinylformamide polymer that is partially hydrolyzed in the form of an inverse emulsion is added, at one or more injection points, to a fibrous suspension in the presence of an anti-gelling agent, and having a cationic regain between 30 and 150%, the inverse emulsion having a weight ratio of partially hydrolyzed N-vinylformamide polymer to anti-gelling agent in the range between 1,000,000/5000 and 1,000,000/50,000.

Claims

1. A process for manufacturing a sheet of paper or cardboard, said process comprising, before said sheet is formed, adding at least one N-vinylformamide polymer, partially hydrolyzed in the form of an inverse emulsion in the presence of an anti-gelling agent, and having a cationic regain of between 30 and 150%, is to a fibrous suspension at one or more injection points, the inverse emulsion having a partially hydrolyzed N-vinylformamide polymer/anti-gelling agent weight ratio of between 1,000,000/5,000 and 1,000,000/50,000.

2. The process according to claim 1, wherein the inverse emulsion contains between 20 and 50% by weight of partially hydrolyzed N-vinylformamide polymer.

3. The process according to claim 1, wherein the N-vinylformamide polymer partially hydrolyzed in the form of an inverse emulsion has a cationic charge density between 1.4 and 5.4 meq.Math.g.sup.−1.

4. The process according to claim 1, wherein the partially hydrolyzed N-vinylformamide polymer has a Brookfield viscosity greater than 1.2 cps at a concentration of 0.1% by weight in a 1M aqueous solution of NaCl, at 23° C., with a UL modulus and at 60 rpm.sup.−1.

5. The process according to claim 1, wherein the N-vinylformamide polymer partially hydrolyzed in the form of an inverse emulsion is introduced into the fibrous suspension at a rate of 100 to 800 g.t.sup.−1 of dry pulp.

6. The process according to claim 1, wherein a secondary retention agent selected from organic polymers and/or inorganic microparticles is added to the fibrous suspension.

7. The process according to claim 1, wherein a secondary anionic retention agent is added to the fibrous suspension at a rate of 20 to 2500 g.t.sup.−1 of dry pulp.

8. The process according to claim 1, wherein the partially hydrolyzed N-vinylformamide polymer is in the form of a water-in-oil inverse emulsion comprising 12 to 26% by weight of oil and 35 to 48% by weight of water.

9. The process according to claim 1, wherein the partially hydrolyzed N-vinylformamide polymer comprises N-vinylformamide functions of which 10 to 60 mol % are hydrolyzed.

10. The process according to claim 1, wherein the anti-gelling agent is selected from the group consisting of alkali metal sulfites, alkaline-earth metal sulfites, alkali metal hydrogen sulfites, alkaline-earth metal hydrogen sulfites, alkali metal bisulfites, alkaline-earth metal bisulfites, hydroxylamine hydrochloride, hydroxylamine sulfate, alkali metal dithionite, alkaline-earth metal dithionite, alkali metal borohydride, alkaline-earth metal borohydride, alkali metal hydroxy methane sulfonate, alkaline-earth metal hydroxy methane sulfonate, and mixtures thereof.

11. The process according to claim 1, wherein the partially hydrolyzed N-vinylformamide polymer comprises between 0 and 50 mol % of at least one monomer selected from the group consisting of non-ionic monomers, anionic monomers, cationic monomers, zwitterionic monomers, and mixtures thereof.

12. The process according to claim 1, wherein the N-vinylformamide polymer partially hydrolyzed in the form of an inverse emulsion is a partially hydrolyzed N-vinylformamide homopolymer.

13. The process according to claim 1, wherein the partially hydrolyzed N-vinylformamide polymer is a partially hydrolyzed N-vinylformamide homopolymer in which 10 to 60 mol % of the N-vinylformamide functions are hydrolyzed, and wherein the anti-gelling agent is selected from the group consisting of alkali metal sulfites, alkaline-earth metal sulfites, alkali metal hydrogen sulfites, alkaline-earth metal hydrogen sulfites, alkali metal bisulfites, alkaline-earth metal bisulfites, hydroxylamine hydrochloride, hydroxylamine sulfate, alkali metal dithionite, alkaline-earth metal dithionite, alkali metal borohydride, alkaline-earth metal borohydride, alkali metal hydroxy methane sulfonate, alkaline earth-metal hydroxy methane sulfonate, and mixtures thereof.

14. The process according to claim 1, wherein the anti-gelling agent is sodium bisulfite.

15. The process according to claim 1, wherein the inverse emulsion has a partially hydrolyzed N-vinylformamide polymer/anti-gelling agent weight ratio of between 1,000,000/5,000 and 1,000,000/30,000.

16. The process according to claim 2, wherein the N-vinylformamide polymer partially hydrolyzed in the form of an inverse emulsion has a cationic charge density between 1.4 and 5.4 meq.Math.g.sup.−1.

17. The process according to claim 16, wherein the partially hydrolyzed N-vinylformamide polymer has a Brookfield viscosity greater than 1.2 cps at a concentration of 0.1% by weight in a 1M aqueous solution of NaCl, at 23° C., with a UL modulus and at 60 rpm.sup.−1.

18. The process according to claim 17, wherein: the partially hydrolyzed N-vinylformamide polymer is in the form of a water-in-oil inverse emulsion comprising 12 to 26% by weight of oil and 35 to 48% by weight of water; the partially hydrolyzed N-vinylformamide polymer comprises N-vinylformamide functions of which 10 to 60 mol % are hydrolyzed; and the anti-gelling agent is selected from the group consisting of alkali metal sulfites, alkaline-earth metal sulfites, alkali metal hydrogen sulfites, alkaline-earth metal hydrogen sulfites, alkali metal bisulfites, alkaline-earth metal bisulfites, hydroxylamine hydrochloride, hydroxylamine sulfate, alkali metal dithionite, alkaline-earth metal dithionite, alkali metal borohydride, alkaline-earth metal borohydride, alkali metal hydroxy methane sulfonate, alkaline earth-metal hydroxy methane sulfonate, and mixtures thereof.

19. The process according to claim 6, wherein the secondary anionic retention agent is added to the fibrous suspension at a rate of 20 to 2500 g.t.sup.−1 of dry pulp.

20. The process according to claim 9, wherein the partially hydrolyzed N-vinylformamide polymer comprises N-vinylformamide functions of which 10 to 40 mol % are hydrolyzed.

Description

EXAMPLES OF EMBODIMENTS OF THE INVENTION

[0069] Products Tested in the Examples:

[0070] The following products (Table 1) are polymers in the form of a water-in-oil inverse emulsion. The polymers in emulsions A to D (examples) and E to G (counter-examples) are partially hydrolyzed N-vinylformamide polymers. Emulsions H and I are anionic and amphoteric retention agents, respectively, used as secondary retention agents in combination with the above emulsions. All emulsions contain 34.5% by weight of the polymer. The weight ratio of the hydrophilic phase to the lipophilic phase is 72/28. The lyophilic phase is Exxsol D 100 (aliphatic hydrocarbons C12-C15).

TABLE-US-00001 TABLE 1 Drainage performance Charge UL Cationic Hydrolyzed N- Amount Vacuum Density Viscosity regain vinylformamide of Na drainage Emulsion (meq .Math. g.sup.−1 (cPs) (%) functions (mol %) bisulfite performance A 2.7 1.35 33% 20 1% Excellent B 2.7 1.35 115%  20 2% Excellent C 2.7 1.4 40% 20 2% Excellent D 5.4 1.35 96% 40 2% Excellent E 2.7 1.25 200%  20 0% Average F 2.7 1.8 13% 20 10%  Average G 5.4 1.1 220%  40 0% Average H 5.4 2 N/A N/A N/A N/A I 1.35 3 N/A N/A N/A N/A

[0071] The amount of anti-gelling agent (Na bisulfite) is expressed as a weight percentage, based on the weight of the partially hydrolyzed N-vinylformamide polymer (1%=10,000 ppm).

[0072] For emulsion H, the polymer is a copolymer of acrylamide and sodium acrylate (70/30% mol).

[0073] For Emulsion I, the polymer is a terpolymer of acrylamide, sodium acrylate, and dimethyl amino ethyl acrylate quaternized with methyl chloride (50/20/30 mol %).

[0074] UL viscosities are measured at a concentration of 0.1% by weight of the polymer in an aqueous solution with 1M NaCl, at 23° C., with a UL modulus, and at 60 rpm′.

[0075] Cationic regain is determined by colorimetric titration of a 5 g.Math.L.sup.−1 polymer solution after a shear rate of 8,000 rpm.sup.−1 over 10 minutes.

[0076] Procedures Used in the Examples: [0077] a) The different types of pulps used

[0078] Virgin fiber pulp (used in examples 1, 2, 3, 4, 5):

[0079] The wet paste is obtained by disintegrating the dry paste to obtain a final aqueous concentration of 1% by weight. It is a neutral pH pulp composed of 10% bleached virgin long fiber, 70% bleached virgin short fiber, and 20% mechanical fiber. This pulp also contains an additional 30% GCC (Hydrocal® 55 from Omya) in relation to the weight of the fibers (GCC being ground calcium carbonate).

[0080] Recycled fiber pulp (used in Example 6):

[0081] The wet paste is obtained by disintegrating the dry paste to obtain a final aqueous concentration of 1% by weight. It is a pH-neutral pulp made from 100% recycled cardboard fibers. [0082] b) Evaluation of total retention and filler retention

[0083] Different results are obtained using a “Britt Jar” type container with a stirring speed of 1,000 rpm.

[0084] The sequence for adding the different retention agents is as follows:

[0085] T=0s: 500 ml of paste at 0.5% by mass is stirred

[0086] T=10s: The cationic retention agent is added

[0087] T=20s: The secondary cationic retention agent is added

[0088] T=30s: The first 20 ml corresponding to the dead volume under the fabric is removed, then 100 mL of white water is recovered

[0089] The First Pass Retention in percentage (% FPR:First Pass Retention), corresponding to the total retention, is calculated according to the following formula:

°% FPR=(C.sub.HBC.sub.WW/C.sub.HB*100

[0090] The first pass retention of ash in percentage (% FPAR:First Pass Ash Retention) is calculated using the following formula:

FPAR=(A.sub.HB-A.sub.WW)/A.sub.HB* 100

With:

[0091] C.sub.HB: Headbox consistency [0092] C.sub.WW: White water consistency [0093] A.sub.HB: Consistency of the headbox ashes [0094] A.sub.WW: Consistency of the white water ashes [0095] c) Dynamic Drainage Analyzer (DDA)

[0096] The DDA (Dynamic Drainage Analyzer) automatically determines the time (in seconds) required to vacuum drain a fibrous suspension. The polymers are added to the wet paste (0.6 liter of paste at 1.0 wt %) in the DDA cylinder under agitation at 1,000 rpm: [0097] T=0s: pulp is stirred [0098] T=10s: cationic retention agent is added [0099] T=20s: secondary cationic retention agent is added [0100] T=30s: agitation and vacuum drainage at 200mBar for 70s ends

[0101] The pressure under the fabric is recorded as a function of time. When all the water is evacuated from the fibrous mats, the air passes through it, causing a break to appear in the slope on the curve representing the pressure under the fabric as a function of time. The time, expressed in seconds, taken when the slope breaks, corresponds to the drain time. The shorter the time, the better the vacuum drainage.

Example 1

[0102] Influence of the Cationic Regain on Drainage Performance.

TABLE-US-00002 TABLE 2 Influence of the cationic regain on drainage performance Emulsions Blank A B C D E F G Cationic regain N/A 33% 115% 40% 96% 200% 13% 220% DDA (750 g/T 28.9 14.5 13.9 13.2 13.2 19.8 16.7 21.3 Dry Pulp

[0103] Drainage performance (Table 2) is better for partially hydrolyzed N-vinylformamide polymers with a cationic regain between 30 and 150%, whether for a charge density of 2.7 meq.Math.g.sup.−1 (emulsions A to C, E, and F) or 5.4 meq.Math.g.sup.−1 (emulsions D and G).

Example 2

[0104] Influence of Cationic Regain on Total Retention and Filler Retention.

TABLE-US-00003 TABLE 3 Influence of cationic regain on retention Emulsions Blank A B C E F Cationic regain N/A 33% 115% 40% 200% 13% FPR (%) Retention 61 78.2 77.8 78.49 65.5 71.4 FPAR (%) Retention 11 47 40 52 11 26

[0105] Total retention and filler retention (Table 3) are improved for partially hydrolyzed N-vinylformamide polymers with cationic regain of between 30 and 150% (emulsions A to C).

Example 3

[0106] Drainage Performance when N-Vinylformamide Polymer Partially Hydrolyzed in the Form of an Inverse Emulsion is Used in Combination with a Secondary Retention Agent.

TABLE-US-00004 TABLE 4 Drainage performance Emulsions Blank C C + H C + I D D + H D + I E E + H E + I DDA(s) 28.9 13.2 12.1 12.3 13.2 11.5 11.8 18.8 16.5 14.3

[0107] For this example, the dosage for emulsions C, D, and E is 750 g/t dry pulp, and for the secondary retention agents (emulsions H and I) 150 g/t dry pulp (Table 4).

[0108] In combination, the drainage performance is better when the N-vinylformamide polymer in the form of an inverse emulsion has a cationic regain between 30 and 150%.