Method for producing paper, board or the like

Abstract

The invention relates to a method for producing paper, board or the like. The method comprises obtaining a fibre stock comprising lignocellulosic fibres and adding a retention agent system comprising a cationic synthetic polymer to the fibre stock and forming a fibrous web from the fibre stock and drying the web. Microfibrillated non-wood cellulose is added to the fibre stock as a component of the retention agent system and sequentially with the cationic synthetic polymer.

Claims

1. A method for producing a paper, a board or the like, comprising: obtaining a fibre stock comprising lignocellulosic fibres; adding a retention agent system comprising a cationic synthetic polymer to the fibre stock; and forming a fibrous web from the fibre stock and drying the web, wherein microfibrillated cellulose comprising microfibrillated non-wood cellulose is added to the fibre stock as a component of the retention agent system and sequentially with the cationic synthetic polymer.

2. The method according to claim 1, wherein the microfibrillated cellulose comprises microfibrillated cellulose originating from hardwood or softwood.

3. The method according to claim 1, wherein the microfibrillated cellulose originates from vegetables, such as sugar beet pulp, potato pulp, cassava pulp, sweet potato; fruits, such as citrus peel; cellulose pith, such as bagasse pith, corn pith, bamboo pith; and mixtures thereof.

4. The method according to claim 1, wherein at least a part of the microfibrillated cellulose is added to a thick stock having consistency of 2 weight- %, preferably 2-6 weight- %, more preferably 3-5 weight- %.

5. The method according to claim 1, wherein the microfibrillated cellulose is microfibrillated parenchymal cellulose.

6. The method according to claim 1, wherein the microfibrillated cellulose is obtained by fibrillating plant-based cellulose rich material comprising essentially primary cell wall structures.

7. The method according to claim 1, wherein the microfibrillated cellulose is added to the fibre stock in a total amount of 1-50 kg, preferably 1-30 kg, even more preferably 10-30 kg, given as dry material per ton of dry solids of the fibre stock.

8. The method according to claim 1. wherein the cationic synthetic polymer is selected from a group comprising of polyacrylamide, polyethylene oxide (PEO), homo- or copolymers of diallyldimethylammonium chloride (DADMAC), polyamine, polyethyleneimine (PEI), polyvinyl amine (PVAm) and polydicyandiamide polymer resin.

9. The method according to claim 1, wherein the cationic synthetic polymer is cationic polyacrylamide having an average molecular weight of 4 000 000-18 000 000 Da, preferably 4 000 000-12 000 000 Da, more preferably 7 000 000-14 000 000 Da, and/or having a charge density of 0.2-2.5 meq/g, preferably 0.5-1.5 meq/g, more preferably 0.7-1.2 meq/g.

10. The method according to claim 1, wherein at least a first part of the cationic synthetic polymer is added to a thick stock having a consistency of 2 weight- %, preferably 2-6 weight- %, more preferably 3-5 weight- %.

11. The method according to claim 10, wherein at least 45%, more preferably at least 60%, even more preferably at least 80%, of the total amount of the cationic synthetic polymer is added to the thick stock.

12. The method according to claim 10, wherein the first part of the cationic synthetic polymer is added to the thick stock having consistency of 2 weight- %, preferably 2-6 weight- %, more preferably 3-5 weight-% and a second part of the cationic synthetic polymer is added to the a thin stock having consistency of <2 weight- %, preferably 0.2-1,99 weight- %, more preferably 0.3-1.5 weight- %.

13. The method according to claim 12, wherein the microfibrillated cellulose and at least 50% of the total amount of the cationic synthetic polymer of the retention agent system are added to the thick stock, in this order, and the remaining amount of cationic synthetic polymer is added to the thin stock.

14. The method according to claim 1, wherein at least a part of the microfibrillated cellulose is added to the fibre stock before addition of the cationic synthetic polymer.

15. The method according to claim 1, wherein the cationic synthetic polymer is added in a total amount of 0.1-2 kg/t, preferably 0.2-1.5 kg/t.

16. The method according to claim 1, wherein the fibre stock comprises cellulosic fibres obtained by mechanical pulping, chemithermomechanical pulping or by repulping recycled fibres or recovered fibres.

17. The method according to claim 1, wherein the fibre stock after the addition of microfibrillated cellulose is subjected to a mechanical treatment step, where the fibre stock is subjected to a shear force supplied by a mechanical device.

18. The method according to claim 1, wherein the fibre stock is subjected to a mechanical treatment in amount in the range 5-350 kWhit, preferably 20-250 kWh/t, indicated by specific energy consumption (SEC).

Description

EXPERIMENTAL

[0055] Some embodiments of the invention are disclosed in the following non-limiting examples.

Retention Example 1

[0056] Performance of a retention agent systems comprising microfibrillated cellulose and a cationic synthetic polymer was tested in pilot paper machine using a dry paper grade on-roll manufactured from recycled fibre grades. The fibre stock was prepared batch-wise by slushing ca. 75 kg dry paper into 3 m.sup.3 local tap water, temperature 8-10 C.

[0057] The prepared fibre stock was subjected to mixing, pumping and a mild refining (resembling a deflaking step) at 2.25 weigh- % feed consistency in an Esser-Wysch 13A refiner, operating to provide ca. 4 kWhit to the fibre stock.

[0058] Targeted white water conditions were: conductivity 8000 mS/cm; calcium level 800 ppm Ca.sup.2+; charge level 1500 meq/l. The anionic trash levels were adjusted by addition of calcium propionate (Caldic, Espoo, Finland), Na.sub.2SO.sub.4 (Algol, Espoo, Finland) and anionic carboxymethyl cellulose Staflo Exlo (Akzo Nobel, Gothenburg, Sweden). These additions were made to the re-pulped papermaking fibre stock as follows: first 3.72 g/l of calcium propionate is added to reach conductivity of 3500 mS/cm, followed by addition of 4.67 g/l of Na.sub.2SO.sub.4 and 3.5 mg/l of carboxymethyl cellulose, in this order.

[0059] The prepared fibre stock was fed to a pilot paper machine and diluted to headbox consistency with white water. The volume of the white water was ca 8.5 m.sup.3 per pulped batch as follows: pulper 2 m.sup.3; four mixing chests 5 m.sup.3; white water circulation ca. 1.5 m.sup.3. The fibre stock was formed into a web on the wire, speed 30 m/min, while passing four vacuum boxes, one vacuum roll and two nips, 50 MPa and 70 MPa and 11 drying cylinders having average effect of 120 kW at a production rate of ca. 90 kg/h.

[0060] A schematic illustration of the pilot machine set-up is shown in FIG. R1. Possible chemical dosage locations are indicated in FIG. R1. Thick stock having consistency >2 weight- % was fed from machines chest 1, 2 to low consistency refiner 4. First dosing point D1 for a component of the retention agent system was located before pump 3 and the second dosing point D2 was located after refiner 4. First and second dosing points D1, D2 dosed components to the thick stock.

[0061] After the refiner 4 the thick stock was diluted with white water to thin stock by pumping white water from white water tank 5 and mixing it with thin stock. Thin stock is then pumped by pump 6 to the headbox 7. The consistency of the obtained thin stock was 0.45-0.55 weight- %. Further dosing points D8, D9 were located after dilution stage but before the headbox 7 and forming wire 8. Conventionally retention agents are added to the thin stock at dosing points D8 and D9 or their immediate vicinity.

[0062] The retention agent system in Retention Example 1 comprised sugar beet based microfibrillated cellulose (MFC), solid content 12 weight- %, as well as a cationic synthetic polymer (Fennopol K3400, Kemira Oyj). Furthermore, a retention/drainage agent: an anionic silica sol (ECA NP2180, AkzoNobel Ab) was added to the fibre stock.

[0063] The added amounts of microfibrillated cellulose and the cationic synthetic polymer, as well as their dosage locations, are given in Table 1.

[0064] Drainage rate of the fibre stock in Table 1 is given as drainage capacity, which is measured by using a modified CSF-device with the bottom nozzle plugged, unit [mL/10 s], as well as Schopper-Riegler value, which is measured straight from the fibre stock, by using 4-4.65 g/l stock, unit [SR]. Overall water retention level, FPR, was determined by using head box (HB) and wire water (WW) consistencies [weight- %].

TABLE-US-00001 TABLE 1 Amounts of used MFC and other chemicals, dosage locations and retention results. Synt. Fennozil MFC Polymer 2180 Drainage FPR # [kg/t] Pos. [kg/t] Pos. [kg/t] Pos. [ml/10 s] [ SR] [%] reference 0.0 0.2 8 2.0 9 260.0 85.5 87.4 19 10.0 1 0.2 8 2.0 9 210.0 87.0 87.4 20 20.0 1 0.2 8 2.0 9 200.0 87.0 86.7 21 30.0 1 0.2 8 2.0 9 200.0 87.5 86.9 27 20.0 1 0.3 & 0.2 2 & 8 2.0 9 250.0 81.5 93.5 28 20.0 1 0.6 & 0.2 2 & 8 2.0 9 280.0 76.0 94.6 35 20.0 1 0.3 2 2.0 9 230.0 83.0 92.8 36 20.0 1 0.6 2 2.0 9 250.0 74.5 92.8 Pos. = Position of addition, see FIG. 1

[0065] It is seen from Table 1 that in Tests 27 and 28 where microfibrillar cellulose was added in position 1 and the cationic synthetic polymer was added in both positions 2 and 8, the drainage and wire retention FPR increased significantly in comparison to Test 20 or to the reference. It is also seen that increase in added polymer dose causes a clear increase in drainage (Test 28). On the other hand, similar drainage and retention results can be obtained with smaller dose (Test 27 vs Test 36). This means that addition of cationic synthetic polymer to both thick and thin stock improves the retention and drainage simultaneously when the amount of added microfibrillar cellulose is constant.

[0066] When single additions of the synthetic polymer are compared with each other, it is seen that the addition in position 2, i.e. thick stock, yields better wire retention results.

Retention Example 2

[0067] Retention Example 2 was conducted in the similar manner than Retention Example 1, but different dry paper grade on-roll manufactured from recycled fibre grades was used. The fibre stock was otherwise prepared in the same way.

[0068] The prepared fibre stock was subjected to mixing, pumping and a mild refining (resembling a deflaking step) at 2.25 weigh- % feed consistency in an Esser-Wysch 13A refiner, operating to provide ca. 17 kWh/t to the fibre stock.

[0069] Targeted white water conditions were: conductivity 3500 mS/cm; calcium level 100 ppm Ca.sup.2+; charge level 200 meq/l. The anionic trash levels were adjusted by addition of calcium propionate (Caldic, Espoo, Finland), Na.sub.2SO.sub.4 (Algol, Espoo, Finland) and anionic carboxymethyl cellulose Staflo Exlo (Akzo Nobel, Gothenburg, Sweden). These additions were made to the repulped papermaking fibre stock as follows: first 0.46 g/l of calcium propionate is added to reach conductivity of 3500 mS/cm, followed by addition of 2.5 g/l of Na.sub.2SO.sub.4 and 3.5 mg/l of carboxymethyl cellulose, in this order.

[0070] The prepared fibre stock was fed to a pilot paper machine and diluted as described in Retention Example 1.

[0071] The retention agent system and other chemicals in Retention Example 2 were the same as in Retention Example 1.

[0072] The added amounts of microfibrillated cellulose and the cationic synthetic polymer, as well as their dosage locations, are given in Table 2. The retention results are defined in the same manner as in Retention Example 1.

[0073] It can be seen from Table 2 that Test 10 with addition of the cationic synthetic polymer at both positions 2 and 8 resulted higher wire retention FPR than Test 3 or the reference. Drainage seemed to remain at the same level in all test points, i.e. no significant impairment could be observed.

TABLE-US-00002 TABLE 2 Amounts of used MFC and other chemicals, dosage locations and retention results. Synt. Fennozil MFC Polymer 2180 Drainage FPR # [kg/t] Pos. [kg/t] Pos. [kg/t] Pos. [ml/10 s] [ SR] [%] reference 0.0 0.2 8 2.0 9 240.0 82.0 85.8 2 10.0 1 0.2 8 2.0 9 250.0 87.0 90.4 3 20.0 1 0.2 8 2.0 9 230.0 86.0 88.7 4 30.0 1 0.2 8 2.0 9 210.0 91.0 85.6 10 20.0 1 0.3 & 0.2 2 & 8 2.0 9 220.0 87.0 90.4 11 20.0 1 0.6 & 0.2 2 & 8 2.0 9 220.0 87.0 87.6 Pos. = Position of addition, see FIG. 1

Anti-dusting Example 1

[0074] Performance of an anti-dusting agent comprising microfibrillated cellulose was tested in pilot paper machine. The overall dry paper production rate was 90 kg/h.

[0075] In test experiments anti-dusting agent, which comprised sugar beet based microfibrillated cellulose (MFC) solid content 12 weight- %, was added in amount that resulted in addition of 30 kg/t of microfibrillated cellulose. In reference experiments no anti-dusting agent was added. Otherwise the conditions in the test experiments and the reference experiments were identical.

[0076] The experiments were conducted by using two different fibre stocks, A and B. Fibre stock A was a central European quality with fibre fine content of ca. 25%. Fibre stock B comprised a fraction of longer (Northern Pine) softwood fibres.

[0077] The size class data determined by dynamic light scattering method indicated reduction of the number/share of small particles in the dust released from the moist web on the metal scraper on the first drying cylinder. Results are shown in Table 3.

TABLE-US-00003 TABLE 3 Results of Anti-dusting Example 1 Particles, Particles, Particles, Particles, MFC dose <50 m, <100 m <150 m >1500 m [kg/t] [%] [%] [%] [%] reference 0 14.4 30.7 42.3 0.3 reference 0 16.8 35.8 47.8 0.1 test 1 30 12.1 26.5 38.7 n.a.

Anti-Dusting Example 2

[0078] The anti-dusting effect of the invention is visualised with the aid of following photographic figures:

[0079] FIG. 1 shows cleaned blade on a drying cylinder, first run.

[0080] FIG. 2 shows the blade of FIG. 1 after 15 min of the run when using fibre stock comprising recycled fibres, without anti-dusting agent comprising microfibrillated cellulose.

[0081] FIG. 3 shows cleaned blade on a drying cylinder, second run.

[0082] FIG. 4 shows the blade of FIG. 3 after 15 min of the second run when using fibre stock comprising recycled fibres, with anti-dusting agent comprising microfibrillated cellulose. The dosage of microfibrillated cellulose is 20 kg/t. The fibre stock comprises also 3 kg/t of cationic strength polymer.

[0083] FIG. 5 shows cleaned blade on a drying cylinder, third run.

[0084] FIG. 6 shows the blade of FIG. 5 after 15 min of the third run when using fibre stock comprising recycled fibres, with anti-dusting agent comprising microfibrillated cellulose. The dosage of microfibrillated cellulose is 30 kg/t, the fibre stock is different from the fibre stock used in first and second runs.

[0085] FIG. 7 shows cleaned blade on a drying cylinder, fourth run.

[0086] FIG. 8 shows the blade of FIG. 7 after 15 min of the fourth run when using fibre stock comprising recycled fibres, without anti-dusting agent comprising microfibrillated cellulose.

[0087] It is seen from the figures that the amount of fine dust on the blade is clearly reduced, when the stock comprised anti-dusting agent, which comprises microfibrillated cellulose.

[0088] Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.