METHOD AND TREATMENT SYSTEM FOR MAKING OF PAPER

Abstract

The invention relates to a method and treatment system for making of paper or surface ply of a multi-ply board from a fibre suspension, where at least 90 weight-% of fibres originate from chemical pulping process, chemi-thereto mechanical pulping process and/or office waste deinking pulping process. The fibre suspension further comprises inorganic mineral particles and cationic starch. A cationic copolymer of acrylamide and cationic monomers is incorporated to the fibre suspension and it is allowed to interact by flocculation with at least some of the said components of the fibre suspension. An anionic copolymer of acrylamide and more than 30 mol-% of anionic monomers is added to the fibre suspension, and fibre suspension is formed into a fibre web and drying the web to a dryness of at least 80%. An aqueous surface composition comprising polymeric binder is applied on the surface of the web.

Claims

1. A method for making of paper or surface ply of a multi-ply board from a fibre suspension, where at least 90 weight-% of fibres originate from chemical pulping process, chemi-thermo mechanical pulping process and/or office waste deinking pulping process, the fibre suspension further comprising inorganic mineral particles and cationic starch, said method comprising: incorporating a cationic copolymer of acrylamide and cationic monomers to the fibre suspension and allowing it to interact by flocculation with at least some of the said components of the fibre suspension, adding an anionic copolymer of acrylamide and more than 30 mol-% of anionic monomers to the fibre suspension, forming fibre suspension into a fibre web and drying the web to a dryness of at least 80%, and applying an aqueous surface composition comprising polymeric binder on the surface of the web.

2. The method according to claim 1, wherein the amount of inorganic mineral particles in the fibre suspension provides an ash content of at least 8 weight-%, preferably at least 15 weight-%, more preferably at least 22 weight-%.

3. The method according to claim 1, wherein in the inorganic mineral particles comprises calcium carbonate, more preferably precipitated calcium carbonate.

4. The method according to claim 1, further comprising: adding cationic starch in amount of 1-20 kg/ton, preferably 3-13 kg/ton, more preferably 5-10 kg/ton, and/or adding cationic copolymer of acrylamide in amount of 30-1000 g/ton, preferably 100-500 g/ton, more preferably 150-250 g/ton, and/or adding anionic copolymer of acrylamide in amount of 20-500 g/ton, preferably 30-100 g/ton, more preferably 50-75 g/ton.

5. The method according to claim 1, wherein incorporating cationic starch, cationic copolymer of acrylamide and anionic copolymer of acrylamide in the fibre suspension separately and individually from each other, preferably at different process locations.

6. The method according to claim 1, wherein adding bentonite microparticles to the fibre suspension, preferably in amount of 1.5-4 kg/ton, preferably 2-3 kg/ton.

7. The method according to claim 1, wherein adding bentonite microparticles to the fibre suspension simultaneously but separately with the anionic copolymer of acrylamide, preferably after the last stage of mechanical shear before a headbox.

8. The method according to claim 1, wherein adding cationic copolymer of acrylamide to the fibre suspension after the incorporation of cationic starch and before the addition of an anionic copolymer of acrylamide and optional bentonite microparticles,

9. A treatment system for making of paper or surface ply of a multi-ply board from a fibre suspension, wherein at least 90 weight-% of fibres originate from chemical, chemi-thermo mechanical pulping process and/or office waste deinking pulping process, the system comprising: a suspension component, which is incorporated into the fibre suspension and which comprises at least the following: (a) cationic starch, which is incorporated into the fibre suspension, (b) a cationic copolymer of acrylamide and cationic monomers, (c) an anionic copolymer of acrylamide and more than 30 mol-% of anionic monomers, and a surface component, which is applied on the surface of the paper and which comprises an aqueous surface composition comprising a polymeric binder.

10. The treatment system according to claim 9, wherein the cationic copolymer of acrylamide is a copolymer of acrylamide and at least one cationic monomer selected from 2-(dimethylamino)ethylacrylate (ADAM), [2-(acryloyloxy)ethyl] trimethylammonium chloride (ADAM-CI), 2-(dimethylamino)ethyl acrylate benzylchloride, 2-(dimethylamino)ethyl acrylate dimethylsulphate, 2-dimethylaminoethyl methacrylate (MADAM), [2-(methacryloyloxy)ethyl] trimethylammonium chloride (MADAM-CI), 2-dimethylaminoethyl methacrylate dimethylsulphate, [3-(acryloylamino)propyl]trimethylammonium chloride (APTAC) and [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC).

11. The treatment system according to claim 9, wherein the cationic copolymer is a cationic copolymer of acrylamide and at least 4 mol-%, more preferably 4-15 mol-%, even more preferably 5-11 mol-%, of cationic monomers.

12. The treatment system according to claim 9, wherein the anionic copolymer of acrylamide comprises more than 40 mol-%, preferably 45-70 mol-%, of anionic monomers.

13. The treatment system according to claim 9 wherein the anionic copolymer of acrylamide has an intrinsic viscosity in the range of 1.3-3.5 dl/g.

14. The treatment system according to claim 9, wherein the anionic copolymer of acrylamide has an intrinsic viscosity in the range of 5-10 dl/g.

15. The treatment system according to claim 9, wherein the anionic copolymer of acrylamide has a tan() value in the range of 0.5-2.5, preferably 0.8-1.8.

16. The treatment system according to claim 9, wherein the anionic copolymer of acrylamide is cross-linked anionic copolymer.

17. The treatment system according to claim 9, wherein the suspension component comprises further a synthetic internal size stabilized with a cationic polymer, the synthetic internal size being preferably alkyl succinic anhydride.

18. The treatment system according to claim 9, wherein the surface composition is a surface size composition comprising degraded starch as polymeric binder.

19. The treatment system according to claim 9, wherein the suspension composition further comprises bentonite microparticles.

20. A use of a treatment system according to claim claim 9 for making of paper or board, preferably uncoated surface sized paper, or surface ply of a multi-ply board.

Description

EXPERIMENTAL

[0054] Some embodiments of the invention are disclosed in the following non-limiting examples.

[0055] Chemicals used in Examples 1-3 are given in Table 1. The chemicals may be further diluted before dosage, e.g. by 5 times, to improve mixing

TABLE-US-00001 TABLE 1 Chemicals used in Examples 1-3. Name and Dissolving Abbreviation supplier/description Composition Concentration % Starch Raisamyl 50021, Chemigate Cationic potato starch 2.5 ASA FennoSize AS 1000, Kemira ASA emulsified to 2 parts 1.25 of starch above Starch2 Raisamyl 70021, Chemigate Cationic corn starch 2.5 AKD FennoSize KD 360M, AKD emulsion containing 1.25 Kemira cationic degraded starch PCC Syncarb S 270 NY, Omya Precipitated calcium 35 carbonate CPAM 10 mol-% cationic; Cationic polyacrylamide 0.5 MW about 10M Da Bentonite FennoLite UK, Kemira Montmorollonite clay, 3 sieved APAM-CR 35 mol-% anionic, Anionic cross-linked 0.5 intrinsic viscosity 11 dl/g, polyacrylamide tan() 0.7 at 0.02 Hz APAM-CR0 75 mol-% anionic, Anionic cross-linked 0.5 intrinsic viscosity 3.9 dl/g polyacrylamide tan() 0.7 at 0.02 Hz APAM-CR1 60 mol-% anionic, Anionic cross-linked 0.5 tan() 1.4 at 0.02 Hz polyacrylamide intrinsic viscosity 8 dl/g APAM-CR2 60 mol-% anionic, Anionic cross-linked 0.5 tan() 1.3 at 0.02 Hz polyacrylamide intrinsic viscosity 1.5 dl/g APAM-LIN 60 mol-% anionic, Anionic linear 0.5 intrinsic viscosity 11 dl/g polyacrylamide

Example 1

[0056] Pulp used in of Example 1 for the fibre suspension was mixing chest pulp from an uncoated fine paper mill using 90% bleached hardwood kraft pulp and 10% bleached soft wood kraft pulp. 20% dry dosage of precipitated calcium carbonate PCC (defined in Table 1) was added to the mixing chest pulp. The final fibre suspension for Example 1 was made by adding enough dilution water to this pulp and PCC mixture to reach a consistency of 9.2 g/l. Dilution water was blend of white water and clear filtrate in 50:50 ratio. Pulp and water properties are presented in Table 2.

TABLE-US-00002 TABLE 2 Pulp and water properties Mixing chest White Clear Final fibre pulp water filtrate suspension pH 8.0 7.9 7.8 8.2 Turbidity, NTU 132 1 1 44 Conductivity, mS/cm 1.06 0.94 0.93 0.96 Charge, ekv/l 21.3 25.6 31.1 NA Zeta potential, mV 18.2 NA NA 16.5 Consistency, g/l 41.0 1.3 0.0 9.2 Ash content, % 21.5 NA NA NA

[0057] Dynamic drainage jar DDJ (Paper Research Materials Inc.) was used to test retention. Mixer speed in DDJ was 1200 rpm. Wire type was 40M in DDJ. At the drainage moment filtrate hose was opened and consistency was determined form the first 100 ml. Retention was calculated as 100%(test pulp consistencyfiltrate consistency)/test pulp consistency.

[0058] A Dynamic Drainage Analyzer, DDA, (AB Akribi Kemikonsulter, Sweden) was used to measure drainage. DDA's vacuum and stirrer were calibrated and necessary adjustments to the settings were made. DDA was connected to a computer for measuring the time between an application of vacuum and the vacuum break point. A change of the vacuum expresses the forming time of a wet fibre web until air breaks through the thickening web indicating the drainage time. A drainage time limit was set to 30 seconds for the measurements.

[0059] In drainage measurements, 500 ml of the fibre suspension sample was measured into the reaction jar. The drainage test was performed by mixing the sample suspension with the stirrer at 1200 rpm for 40 seconds while the chemicals to be tested were added in predetermined order. Test chemical addition times are indicated in Table 3 as negative time before the start of the drainage. Drainage test was using a wire with 0.25 mm openings. 300 mbar vacuum for 30 s after drainage was used. The sheets were dried in vacuum dryers for 10 minutes at 92 C. and at 1000 mbar. Before testing the DDA sheets were pre-conditioned for 24 h at 23 C. in 50% relative humidity, according to ISO 187. Cobb60 value was measured from the DDA sheets with 5 cm diameter Cobb device. Cobb60 measurement is based on ISO 535 Paper and boardDetermination of water absorptivenessCobb method, measurement with 60 s absorption time. Cobb60 value is compared to Cobb60 value of 0-test without chemicals (test 23) to calculate reduction.

[0060] Test program for DDA and DDJ test is given in Table 3. Time is the dosing time of chemical before the drainage moment. The chemical dosages are given in kg/ton dry.

TABLE-US-00003 TABLE 3 Test program for DDA and DDJ test. Time, s 40 40 20 10 10 10 10 10 Chemical test no. Starch ASA CPAM Bentonite APAM-CR2 APAM-CR1 APAM-CR APAM-CR0 1-1 7 1.2 0.2 2.2 1-2 7 1.2 0.2 2.2 0.03 1-3 7 1.2 0.2 2.2 0.06 1-4 7 1.2 0.2 2.2 0.09 1-5 7 1.2 0.2 2.2 0.03 1-6 7 1.2 0.2 2.2 0.06 1-7 7 1.2 0.2 2.2 0.09 1-8 7 1.2 0.2 2.2 0.03 1-9 7 1.2 0.2 2.2 0.06 1-10 7 1.2 0.2 2.2 0.09 1-11 7 1.2 0.2 2.2 0.03 1-12 7 1.2 0.2 2.2 0.06 1-13 7 1.2 0.2 2.2 0.09 1-14 7 0.2 2.2 0.06 1-15 7 0.2 2.2 0.06 1-16 7 0.2 2.2 1-17 7 0.2 2.2 0.06 1-18 7 0.2 2.2 0.06 1-19 7 1.2 0.2 1-20 7 1.2 0.2 0.03 1-21 7 1.2 0.2 0.06 1-22 7 1.2 0.2 0.09 1-23 0 (0-test)

[0061] Table 4 shows the sizing, drainage and retention results for treatment systems based on invention and for references. APAM-CR1 and APAM-CR2 have more anionic charge and they will give at least 89% Cobb60 reduction with all dosages 0.03, 0.06 and 0.09 kg/t, where reference products APAM-CR0 and APAM-CR give required Cobb60 reduction only with one dosage level. Invented system allows to control dosage level for drainage and retention. Short drainage time and high retention are achieved when APAM is used with CPAM. Drainage time and retention are further improved when bentonite is added to the system.

TABLE-US-00004 TABLE 4 Sizing, drainage and retention results. Device DDA DDA DDJ Measurement Cobb60 Drainage Retention test no. reduction % times % 1-1 NA 4 78 1-2 93 4 79 1-3 90 4 81 1-4 90 4 84 1-5 89 4 80 1-6 93 4 81 1-7 91 4 80 1-8 92 4 78 1-9 85 4 82 1-10 85 4 83 1-11 82 4 80 1-12 90 4 80 1-13 87 4 84 1-14 0 4 82 1-15 0 4 82 1-16 0 4 82 1-17 0 4 83 1-18 0 4 83 1-19 80 8 67 1-20 82 7 72 1-21 80 6 75 1-22 83 6 77 1-23 0 9 58

Example 2

[0062] Test pulp was made by refining 90% bleached eucalyptus hardwood pulp and 10% bleached pine kraft pulp in Voith Sulzer laboratory refiner to Canadian Standard Freeness of 370 ml. After refining the pulp was diluted to obtain fibre suspension having a consistency of 5.07 g/l with tap water. The conductivity of tap water was adjusted to 1175 S/cm with CaCl.sub.22H.sub.2O 0.1 g/l+Na.sub.2SO.sub.4. pH of the fibre suspension was 7. 9. Consistency was measured according to ISO 4119 and conductivity with Knick Portamess 911 device.

[0063] Dynamic hand sheets were prepared by the equipment from Techpap. Drum was operated with 1400 rpm, mixer for pulp 400 rpm, pulp pump 800 rpm/min, number of sweeps 100 and scoop time was 60 s. Produced sheets were pressed in a Techpap roll press at 6 bar between blotting papers and dried restrained in a STFI plate dryer, 8 minutes at 140 C.

[0064] Chemical dosages, as kg/ton dry, to the fibre suspension are given in Table 5.

[0065] ASA-emulsion was prepared by mixing 2 parts of Starch2 to 1 part of ASA with an Osterizer household mixer equipped with a steel beaker to form a stable emulsion for 24 hours. ASA was dosed to the fibre suspension as emulsion. Active ASA dosages are given in Table 5.

[0066] Amount of Starch2 in Table 5 is the sum of Starch2 included in ASA emulsion and Starch2 added separately.

TABLE-US-00005 TABLE 5 Dosages and dosing times of chemicals in the Example 2. Time, s 80 65 45 35 20 10 10 10 Chemical test no. Starch2 ASA PCC CPAM Bentonite APAM-CR-2 APAM-CR1 APAM-LIN 2-1 7.4 0.7 350 0.2 2.2 (reference) 2-2 7.4 0.7 350 0.2 2.2 0.05 2-3 7.4 0.7 350 0.2 2.2 0.10 2-4 7.4 0.7 350 0.2 2.2 0.05 2-5 7.4 0.7 350 0.2 2.2 0.10 2-6 7.4 0.7 350 0.2 2.2 0.05 2-7 7.4 0.7 350 0.2 (reference) 2-8 7.4 0.7 350 0.2 0.05

[0067] Dynamic hand sheets were surface sized. Surface sizing composition comprised: [0068] Degraded nonionic starch 96.2% as dry: C*film 07311 cooked at 16% solids at 97 C. for 30 min; [0069] Optical brightener agent 1.8% as product: Neucoblanc PSP by lgcar, [0070] Sizing agent 2.0% as product: Impress 918 ST by Solenis; [0071] Deionized water to dilute composition to 10% dry solids.

[0072] Surface size was applied on the hand sheets by using a size press. Size press manufacturer: Werner Mathis AG, CH 8155 Niederhasli/Zrich; Size press model: HF 47693 Type 350; Operation speed: 2 m/min; Operation pressure: 1 bar; Operation temperature: 60 C.; Sizing solution volume: 115 ml/test.

[0073] Drying of the surface sized sheets was made in one-cylinder felted steam heated dryer drum at 92 C. for 1 min. Shrinkage was restricted in dryer. Paper passed the dryer once. Size curing was made in oven: 105 C., 15 min.

[0074] Surface size pick-up was given as percentage increase of air conditioned basis weight of base paper and surface sized paper. Basis weight was measured with Mettler Toledo according to ISO 536.

[0075] Internal bond of surface sized hand sheets was measured by using Scott Bond value of Huygen equipment according to Tappi T 569.

[0076] Ash content of the hand sheets without surface sizing was measured according to ISO 1762, temperature 525 C., and tensile index for the hand sheets without surface sizing was calculated from machine direction tensile strength measurement, according to ISO 1924-3, indexed to sheet basis weight.

[0077] Results for Example 2 are presented in Table 6.

TABLE-US-00006 TABLE 6 Properties of hand sheets (tensile index, sheet ash) and surface sized hand sheets (Scott bond, pick-up) Tensile index Sheet Ash Scott bond Pick-up Test no Nm/g % J/m.sup.2 % 2-1 44 35 187 9.5 2-2 46 35 208 9.8 2-3 47 36 203 9.6 2-4 47 35 197 10.2 2-5 47 36 224 9.2 2-6 48 34 221 10.2 2-7 44 34 167 9.5 2-8 47 34 184 9.9

[0078] It can be seen from Table 6 that anionic copolymer of acrylamide (APAM) which was added to the fibre suspension improved tensile strength compared to references without APAM addition. Use of APAM together with microparticles of bentonite improved Scott bond strength compared to reference 2-1, comprising bentonite but no APAM. Addition of APAM without bentonite (test 2-8) improved Scott bond strength after surface sizing compared to reference 2-7. A higher dosage of APAM increased ash retention, which is indicated by higher sheet ash content in test 2-3 and test 2-5. Higher intrinsic viscosity of APAM (see test 2-4, 2-6) may influence the surface size pick-up. Further, APAMs may influence to sheet porosity and ASA retention, which further influences surface sizing.

[0079] SEM pictures of sheet cross section were taken from resin embedded handsheets made with a gap former according to surface sized recipe of Test no 2-3 using anionic cross-linked polyacrylamide APAM-CR2 (FIG. 1a) and APAM-CR0 (FIG. 1b). From FIG. 1a it can be seen that the anionic cross-linked polyacrylamide APAM-CR2 provides flocs, which are relatively small, and the filler which is seen as white in the figure is well distributed throughout the sheet. From FIG. 1b it can be seen that the anionic cross-linked polyacrylamide APAM-CR0 provides flocs which are slightly bigger, and the filler is more concentrated in the centre of the sheet.

Example 3

[0080] Hand sheets were prepared and surface sized in the same manner as in Example 2. Dosages and dosing times for hand sheet preparation are expressed in Table 7. The chemical dosages are given in kg/ton dry, except PCC, which is given as dry.

TABLE-US-00007 TABLE 7 Dosages and dosing times of chemicals in Example 3. Time, s 80 65 65 45 35 20 10 10 10 Chemical Test no. Starch2 ASA AKD PCC CPAM Bentonite APAM-CR2 APAM-CR1 APAM-LIN 3-1 7.4 0.7 35 0.2 3-2 7.4 0.7 35 0.2 0.05 3-3 7.4 0.7 35 0.2 2.2 0.05 3-4 7.4 0.7 35 0.2 2.2 0.10 3-5 7.4 0.7 35 0.2 2.2 0.05 3-6 7.4 0.7 35 0.2 2.2 0.10 3-7 7.4 0.7 35 0.2 2.2 0.05 3-8 7.4 1.2 35 0.2 2.2 0.05 3-9 7.4 1.2 35 0.2 2.2 0.05 3-10 7.4 1.2 35 0.2 2.2 0.05 3-11 7.4 0.18 35 0.2 2.2 0.05 3-12 7.4 0.45 35 0.2 2.2 0.05

[0081] Penetration tests PDA for measuring the handsheets in contact with water were made with Surface & Sizing Tester Mtec EST 12 (Emtec Electronic GMbH), according to operating instructions of the equipment. Transmittance was recorded at 0.2 s.

[0082] Cobb60 measurement was based on ISO 535 Paper and boardDetermination of water absorptivenessCobb method, measurement with 60 s absorption time.

[0083] Contact angle (FibroDat 1100, Goniometer PG3) was determined according to Tappi T 558 om-97. Contact angle was recorded at 1 s.

[0084] Fluorescence was measured with Elrepho spectrophotometer of Lorenzen & Wettre according to ISO 11475 based on fluorescence component of CIE Whiteness D65 from top side.

[0085] Results are presented in Table 8. Results are shown both for surface sized handsheet samples (according to the invention) and for handsheet samples without surface sizing (Base paper) in order to show that the obtained effect originates not only from the application of surface sizing, but also from the addition of the suspension composition chemicals to the fibre suspension. It can be seen that Cobb60 value is clearly improved after surface sizing. Further, PDA transmittance is improved by addition of bentonite microparticles and APAM-CR2 to the fibre suspension and application of a surface size (Test 3-3 vs. test 3-1). Contact angle of at least 90 deg was achieved for surface sized paper in tests 3-3 and 3-6 even with low dosage of ASA. Test 3-3 generally indicates good sizing performance even with low dosage of ASA and low dosage of low IV cross-linked APAM. AKD made good internal sizing based on Cobb60, but sized paper PDA value is lower even when pick-up is higher. Therefore ASA as internal size may be preferable in some embodiments of the invention. Fluorescence is higher in tests 3-3 and 3-5 compared to test 3-4 as well as in test 3-8 compared to test 3-9. This indicates that pick-up and fluorescence can be increased with low IV cross-linked APAM.

[0086] 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.

TABLE-US-00008 TABLE 8 Properties of hand sheets. Base Surface Base Surface Base Surface Paper Sized Surface Surface Paper Sized Paper Sized Contact Contact Sized Sized Cobb60 Cobb60 PDA PDA angle angle Pick-up Fluorescence Test no. g/m.sup.2 g/m.sup.2 % % deg deg % % 3-1* 90 78 28 22 40 73 9.5 17.5 3-2 92 77 38 20 41 78 9.9 17.8 3-3 90 72 27 85 57 93 9.8 18.4 3-4 90 75 27 26 46 79 9.6 16.8 3-5 88 76 32 31 53 82 10.2 17.4 3-6 79 73 23 28 72 90 9.2 16.5 3-7 84 73 26 28 58 82 10.2 18.1 3-8 69 65 27 65 91 103 8.1 15.2 3-9 71 66 26 65 87 98 7.7 14.6 3-10 71 65 29 63 90 100 8.0 15.1 3-11 104 86 22 17 26 42 10.1 16.6 3-12 92 78 17 56 43 78 11.2 16.4 *Reference test point without anionic copolymer of acrylamide