METHOD FOR SEPARATING CELLULOSIC PARTICULATES OUT OF FIBER SUSPENSIONS AND/OR FILTRATES

Abstract

The invention relates to a method for separating particulates out of filtrates of a paper, cardboard, paperboard or pulp production plant and for reapplying the separated particulates to a surface of paper, cardboard or paperboard, comprising at least the following steps: a) separating the particulates out of the filtrates at a size of less than 1200 pm, b) coagulating the separated particulates of same, c) as applicable, mixing the separated particulates with further particulates from a paper, paperboard or pulp production, and/or microfibrillated cellulose (MFC), d) forming an aqueous suspension from the particulates, e) as applicable, adding to the suspension further additives for the surface treatment of paper or paperboard, selected from native and oxidatively degraded starch or calcium carbonate, f) homogenously applying the formed suspension to a paper or paperboard surface in a quantity between 0.5 and 30 g/m.sup.2, in particular 4 and 15 g/m.sup.2, and g) drying the paper or paperboard.

Claims

1. Method for separating particulates out of fibre suspensions and/or filtrates of a paper, cardboard, paperboard- or pulp production plant and for repeat application of the separated particulates to a surface of paper, cardboard or paperboard, wherein at least the following steps are carried out a) separation of cellulosic particulates out of the filtrates with a size less than 1200 m, (measured according to ISO 16065-1) and of further contained additives, b) coagulating the separated cellulosic particulates, c) mixing the separated cellulosic particulates with further particulates from paper, cardboard, paperboard or pulp production, and/or micro- or nanofibrillated cellulose (MFC or NFC), d) forming an aqueous suspension from the cellulosic particulates, or from the mixture of particulates originating from paper, cardboard, or paperboard production with additives, e) adding to the suspension of additives used in paper, cardboard, paperboard or pulp production selected from native, derivatized or oxidatively treated starch, sizing agents, wet strength agents or other chemical additives or from minerals selected from calcium carbonate or kaolin, f) homogeneous application of the suspension formed to the surface of a paper, cardboard or paperboard web in a quantity between 4 and 15 g abs. dry/m.sup.2 (abs. dry=absolutely dry) of the solids present in the suspension, wherein the particulate content in the suspension constitutes up to 100% of a dry mass contained in the suspension, and g) drying the paper, cardboard or paperboard and simultaneous or subsequent pressing, sanitizing, coating with additives in a film- or pond-style size press or a spraying process or other coating units used in paper, cardboard and paperboard production, h) repeating steps f) and g).

2. The method according to claim 1, wherein one or more of the fibre suspensions and/or the filtrates is/are introduced into a papermaking machine, cardboard or paperboard machine or pulp production plant after a pressure screening system selected from a curved screen or a belt washer, which are used in the separation step for separating particulates and other contained additives.

3. The method according to claim 1, wherein the separation of the particulates out of the fibre suspensions and/or filtrates is carried out in a single- or multistage filtration and flotation process with a disc filter or a flotation process.

4. The method according to claim 1, wherein the coagulation is performed until a total solid content comprising particulates and additives originating from paper, cardboard or paperboard production between 1 and 30% by weight is achieved.

5. The method according to claim 1, wherein at least one additive selected from the group consisting of calcium carbonate, talcum, clay, titanium dioxide, alkylated ketene dimers (AKD), alkenyl succinic acid anhydride (ASA), cationic or native/anionic resin sizes, fatty acids, cationic starch or native, enzymatically or oxidatively degraded starch and retention agents is/are added as further additives to the suspension formed from the particulates for surface treatment of paper, cardboard or paperboard.

6. The method according to claim 5, wherein a ratio of particulates to further additives between 1:100 and 100:1 is selected.

7. The method according to claim 5, wherein the particulates are used as particulates impregnated with the further additives originating from paper, cardboard or paperboard production selected from calcium carbonate, talcum, clay, titanium dioxide, alkylated ketene dimers (AKD), alkenyl succinic acid anhydride (ASA), cationic or native/anionic resin sizes, fatty acids, cationic starch or native, enzymatically or oxidatively degraded starch and retention agents, or as adducts of the further additives on the surface of the particulates.

8. The method according to claim 1, wherein a pH of the suspension to be applied to a paper, paperboard or pulp surface is chosen between pH 2 and pH 11.

9. The method according claim 1, wherein a surface coating of a paper web, cardboard or paperboard web having a dry content between 2% and 100% with a film press or pond-style size press or a spraying process is used as a surface coating process.

10. The method according to claim 1, wherein after the surface coating process a surface finishing process selected from sanitizing, pressing, drying on a polished machine smoothed Yankee cylinder, or a coating system selected from film- or pond-style size press, rolling or calendering is carried out.

11. A paper, cardboard or paperboard produced according to the method according to claim 1, wherein the paper, cardboard or paperboard has a surface coating which contains between at least 4 g abs. dry/m.sup.2 and 15 g abs. dry/m.sup.2 particulates and further additives.

12. A paper, cardboard or paperboard according to claim 11, wherein the surface coating includes a mixture of particulates selected from a mixture of particulates and additives originating in the filtrates from paper, cardboard, paperboard- or pulp production, selected from calcium carbonate, talcum, clay, titanium dioxide, alkylated ketene dimers (AKD), alkenyl succinic acid anhydride (ASA), cationic or native/anionic resin sizes, fatty acids, cationic starch or native, enzymatically or oxidatively degraded starch and retention agents.

13. The paper, cardboard or paperboard according to claim 11, wherein besides particulates, the mixture of particulates and the additives originating in the filtrates from paper, cardboard, paperboard- or pulp production, selected from calcium carbonate, talcum, clay, titanium dioxide, alkylated ketene dimers (AKD), alkenyl succinic acid anhydride (ASA), cationic or native/anionic resin sizes, fatty acids, cationic starch or native, enzymatically or oxidatively degraded starch and retention agents, the surface coating contains further additives selected from tensides, polyacrylic acid salts, wet strength agents or rheology additives, which are added before the coating.

14. A paper, cardboard or paperboard according to claim 11, wherein the further additives of the surface coating are contained in a quantity from 0.5% by weight to 99% by weight of the dry mass of the coating.

Description

DESCRIPTION OF THE DRAWINGS

[0068] In the following text, the invention will be explained in greater detail with reference to drawings and exemplary embodiments thereof. In the drawings

[0069] FIG. 1 is a schematic representation of a flowchart of an integrated pulp, paper, cardboard or paperboard factory, showing schematically the capability of separating particulates and the final application of same.

DETAILED DESCRIPTION OF THE INVENTION

[0070] In this representation, an integrated pulp, paper, cardboard or paperboard production site is indicated by the broken peripheral line 1, the integrated paper and pulp production facility being divided into two separate plants, like a pulp production plant that might also be a paper, cardboard or paperboard production facility, which is represented by another broken peripheral line 2, and will be referred to as a pulp production plant 2, and a paper, cardboard- or paperboard production facility, which is divided by a further broken peripheral line 3.

[0071] In the pulp production plant 2, in this case an unbleached fibre feedstock material or a fibrous material or also a filtrate is introduced at 5 into a separation apparatus 6, which may be for example a filtration system, a pressure screening unit, a disc filter, a flotation plant or also a sedimentation installation. In this separation apparatus 6, cellulosic particulates are extracted at 7 and subsequently as necessary undergo coagulation 8, for example by flotation. Clear filtrate drawn from the coagulation 8 and consisting substantially of water or water containing soluble chemicals is drawn off at 9.

[0072] In the separation apparatus 6 not only are cellulosic particulates of unbleached feedstock material drawn off, but in particular the unbleached feedstock material or fibrous material or the filtrate is cleansed of the unwanted cellulosic particulate from the pulp production; this is extracted from the feedstock material, which is thus cleansed thereof at 10, and may be fed for example to a bleaching step (not shown).

[0073] The suspension containing the particulates is either passed through the coagulation stage 8 and then drawn off from said coagulation stage 8 either supplied directly to the papermaking machine 4 via line 11 and used for surface finishing, or as applicable mixed at 12 with other cellulosic and/or fibrous particulates, additives and chemicals that may be contained from paper production and are supplied via line 18.

[0074] Alternatively, however, the method may also be arranged so as to bypass the coagulation stage 8, in which case the particulates drawn off at 7 undergo further treatment as described above via line 11.

[0075] The particulates recovered from the pulp, paper, cardboard or paperboard production plant can be applied to the fibrous material in the paper, cardboard or paperboard machine 4. The filtrate from the dewatering of the paper, cardboard or paperboard machine 4 is again forwarded to a separation stage 14 via line 13, at which separation 14 particulates are separated from the clear filtrate. This separation may in turn be performed by flotation or for example with disc filters. The clear filtrated recovered in this separation may in turn either be fed directly to the papermaking machine 4 via line 15 or as applicable again mixed with another clear filtrate 16, which may come from an optional coagulation stage 17, and then fed to the paper, cardboard or paperboard machine 4. The cellulosic particulates which are concentrated further in the additional coagulation stage 17 are mixed with the cellulosic particulates originating from the pulp production plant 2 at 12, and then supplied to the paper, cardboard or paperboard machine 4 via line 11.

[0076] With a method arrangement of such kind, it is possible to separate cellulosic and/or fibrous particulates contained in the filtrates and/or fibre suspensions from paper, cardboard, and/or pulp production from said filtration, to concentrate the material and apply it as a surface finishing material to a previously manufactured paper, cardboard or paperboard web, whereby it is then possible not only to significantly improve the surface properties of the paper, cardboard or paperboard, but in particular it is also possible to realise a considerable reduction of the dosage of retention agents, possibly even to dispense with them entirely, and moreover avoid the adverse effect of the particulates on dewatering in paper production.

[0077] In the following, the invention will be explained in greater detail with reference to exemplary embodiments.

Example 1: Mechanical Paper Properties

[0078] After application of the particulates recovered from paper production (solid content 0.3% mass fraction particulates in water) to the moist base paper, the effect on the mechanical paper properties was investigated. It is clearly evident that the application of particulatesregardless of the application processaffects the mechanical paper properties positively. The application of particulates brings about a densification of the fibre network and leads to more fibre-particulate bonds, which have positive effects on important mechanical properties such as tensile strength, rigidity, tensile energy absorption (TEA). An increase in the mechanical paper properties can be detected in application quantities greater than about 1 g/m.sup.2, wherein the improvements in the mechanical paper properties increase in line with the quantity of applied particulates.

[0079] The following examples (I) to (IV) were each carried out with a particulate application weight of 3 g abs. dry/m.sup.2 on a paper sheet with a mass per unit area of 100 g/m.sup.2.

[0080] In example (I), and improvement of about 10% in the mechanical paper properties was achieved with a particulate application weight of 3 g abs. dry/m.sup.2 on a paper sheet with a mass per unit area of 100 g/m.sup.2. [0081] A) Tensile strengthmeasured in accordance with ISO 1924-3-2005 [0082] a.) Unprocessed paperuntreated sample.fwdarw.7.5 kN/m [0083] b.) Paper+applied particulate.fwdarw.8.2 kN/m [0084] B) Tensile Energy Absorptionmeasured in accordance with ISO 1924-3-2005 [0085] a.) Unprocessed paperuntreated sample.fwdarw.165 J/m.sup.2 [0086] b.) Paper+applied particulate.fwdarw.180 J/m.sup.2 [0087] C) Stiffnessmeasured in accordance with ISO 1924-3-2005 [0088] a.) Unprocessed paperuntreated sample.fwdarw.775 kN/m [0089] b.) Paper+applied particulate.fwdarw.850 kN/m

[0090] Papers treated with particulates also have a high grease resistance. Depending on the type and application, a KIT value (test for grease resistance with KIT values from 1no grease barrier to 12excellent grease barrier) as high as 11 is possible.

[0091] In example (II), grease resistance was measured (KIT value measured based on T559-cm-2012) [0092] Unprocessed paperparticulate-free, untreated.fwdarw.KIT value=1 [0093] Paper surface-treated with particulate.fwdarw.KIT value=11

[0094] A further advantage is that with the application of the particulates it becomes possible to obtain a closed paper surface. This was characterized using Bendtsen air permeability (unit: millilitres of air per minute).

[0095] In example (III), air permeability was measured based on Bendtsen (DIN 53120-1-2018) [0096] Unprocessed paperparticulate-free, untreated.fwdarw.222 ml/min [0097] Paper treated with particulate.fwdarw.0 ml/min (impermeable)

[0098] Particulates also improve the water vapour transmission (WVT, unit: water vapour mass per m.sup.2 in 24 hours) of the paper and they can serve as a water vapour barrier or to improve the water vapour transmission of various paper types. A low WVT is of particular concern for packaging papers and can be influenced positively with the particulates.

[0099] In example (IV), the water vapour transmission was measured according to ISO 2528-2017. [0100] Unprocessed paperparticulate-free, untreated.fwdarw.WVT=425 g/m.sup.2*24 h [0101] Paper treated with particulate.fwdarw.WVT=170 g/m.sup.2*24 h

Example 2. Enhanced Effectiveness of Additives, Economies of Retention Agents

[0102] If particulates from a separation-/coagulation step are not returned back to the circuit as usual, i.e. return to the machine reservoir after grinding, where among other things the additives are also introduced in doses, advantages are realised of almost 100% retention and greater effectiveness of the dosed additives, for example of cationic starch for increasing mechanical strength. The mode of action is explained in that particulates have a large specific surface and anionic charge, which means they readily bind cationic starch, with the result that the increase in tensile strength of the end product is more modest. With the process arrangement according to the invention, the fraction of particulates in the machine reservoir falls, thus affording the ability to obtain comparable paper properties even with a lower dosage of starch or another cationic synthetic or natural polymer.

[0103] Particulates were removed from an industrially ground pulp (low consistency grinding to a freeness of 20 SR), so that the freeness could be lowered to 15 SR (measured according to ISO 5267-1:1999). The air resistance also fell noticeably (from 15 seconds to less than 10 seconds). Surprisingly, the tensile strength of laboratory sheets (according to ISO 1924-3:2005, laboratory sheets according to ISO 5269-2:2004, grammage according to ISO 536:2012) only fell slightly as a result of the reduced particulate content. The pulp was diluted with the filtrate from a papermaking machine to 0.5% material density or solid content, and the pH was adjusted to pH 6.8 with aluminium sulfate. Then, dosage series with cationised starch (2 similar types) were carried out, to the effect that 10 kg starch/t pulp, and 15 kg/t and 20 kg/t were dosed. Then, laboratory sheets with 80 g/m.sup.2 were produced. The laboratory sheets were acclimatised overnight at 23 C. and 50% rel. humidity, and then tested.

[0104] The results of the tests are presented in Table 1

TABLE-US-00001 Reduced particulate Reference with particulate Cationised starch type 2 Cationised starch type 1 Cationised starch type 2 Cationised starch type 1 Reference 0% 1% 1.5% 2% 1% 1.5% 2% 1% 1.5% 2% 1% 1.5% 2% Freeness 20 15 n.i. n.i.. n.i. n.i.. n.i. n.i.. n.i. n.i.. n.i. n.i.. n.i.. k.A. SR Grammage 79 79 81 78 77 77 78 79 78 79 81 81 81 81 g/m.sup.2 Air 15.6 4.92 3.65 3.39 3.26 3.18 3.35 3.40 10.3 9.18 8.69 9.47 9.08 9.64 resistance s/(l/(m.sup.2*s)) Tensile 84.57 82.70 98.51 102.59 105.69 101.77 105.84 106.56 101.09 104.33 103.10 98.33 100.86 107.475 strength N*m/g Elongation 2.80 2.78 3.35 3.39 3.47 3.46 3.50 3.51 3.33 3.36 3.42 3.33 3.35 3.53 at break % Stretching 692.8 678.7 697.9 683.0 673.3 637.8 680.6 684 682.2 710.9 712.8 703.4 699.6 718.7 stiffness kN/m Spec. tear 12.7 13.4 11.8 10.1 9.90 10.2 9.94 10.5 9.81 9.12 9.32 10.0 9.54 9.32 propagation resistance mN*m.sup.2/g Spec. 5.91 6.54 7.43 8.58 8.41 8.06 8.53 8.83 7.80 8.17 8.24 7.82 8.28 8.03 rupture angle kPa*m.sup.2/g Spec. 1.66 1.59 2.19 2.31 2.41 2.31 2.44 2.45 2.24 2.33 2.34 2.21 2.27 2.51 tensile energy absorption J/g Degree of 18.86 19.54 19.04 19.16 18.95 18.93 19.19 19.06 16.42 16.50 16.66 16.86 16.67 16.69 whiteness % ISO

Example 3

[0105] After the application or spreading of the particulates (application weight >1 g abs. dry/m.sup.2) on the dry paper sheet, a reduction of the air permeability (measured with Gurley ISO 5636-3-2013-11) and the Bendtsen roughness (measured according to ISO 8791-2-2013-9) was achieved. [0106] Pattern 1. Paper without particulatesLD according to Gurley=15 s (seconds) [0107] Paper treated with particulatesLD according to Gurley=126 s [0108] Pattern 2. Paper without particulatesRoughness according to Bendtsen=1575 ml/min [0109] Paper treated with particulatesRoughness according to Bendtsen=673 ml/min

[0110] From the ratio between the tensile strength and Gurley air resistance, which is significantly improved by the method arrangement compared with the state of the art, it is evident that the separation of the cellulosic particulates out of the filtrates and/or fibre suspensions of a paper, cardboard, paperboard or pulp production plant and the subsequent application of same to the paper surface has the effect of enabling the realisation of a substantial improvement in the properties of the paper, paperboard or cardboard.