Pressing device and method for pressing fibrous web

Abstract

The invention relates to an extrusion device and a method for extruding a fibrous web, comprising a main press having an extended extrusion gap, the extrusion gap having a length of at least 150 mm, the main press (1) being designed to produce a linear load ratio LLR of at least 0.69 and at most 1.52 when operated at a linear load LL of at least 1200 kN / m, the linear load ratio LLR being at least 0.69 and at most 1.52, the linear load ratio LLR being at least 0.69, and the linear load ratio LLR being at least 0.69. The linear load ratio LLR is the quotient of a weighted linear load WLL and a linear load LL, where the weighted linear load WLL is the result of integration of a square local pressure p (x) weighted with a weighting factor A over the extrusion gap length x, where the weighting factor A is one tenth megaPascals, and where the linear load LL is the result of integration of the local pressure p (x) over the extrusion gap length x, where the weighting factor A is one tenth megaPascals. The linear load ratio LLR is given by the following formula (I).

Description

[0001] This invention relates to an extrusion apparatus for extruding fiber webs, particularly packaging paper webs, the extrusion apparatus comprising a main press having an extended extrusion gap, wherein the extrusion gap has a length of at least 150 mm, preferably at least 190 mm. Furthermore, this invention relates to a method for extruding fiber webs, particularly packaging paper webs, such as packaging kraft paper webs, wherein the fiber web is guided through a main press having an extended extrusion gap with a length of at least 150 mm, preferably at least 190 mm.

[0002] Such extrusion apparatus and such extrusion method are described, for example, in document WO2017207475A1, the contents of which are incorporated herein by reference.

[0003] Machines used for manufacturing fiber webs typically have an extrusion unit, in which the fiber web is dehydrated or desiccated by mechanical pressure. The extrusion unit is usually located between the forming section and the drying section. A particularly efficient method of mechanical dehydration can be achieved through a so-called extended extrusion gap. The advantages of an extended extrusion gap are known: the extrusion gap is planar, rather than essentially linear as in a conventional roller press. This allows the pressure applied to the fiber web to be dehydrated in the extrusion gap to increase continuously from a low value to a high value, rather than being applied abruptly in the direction of travel. This reduces the risk of the fiber web being wrinkled in the extrusion gap. Therefore, the fiber web can be dehydrated very efficiently and volumetrically in an extended extrusion gap.

[0004] The fiber web can be guided, for example, along with a felt or between two felts through an extended extrusion gap, which can be formed between the shoe roll and the counter roll in a so-called shoe press. Unlike the production of thin paper webs, thickness or so-called volume is less important in the production of paper webs, especially packaging paper webs. For this reason, and due to the significantly greater weight per unit area of ​​paper webs, especially packaging paper webs, a significantly higher linear load is also used here, i.e., a linear load of at least 500 kN / m.

[0005] The themes of "energy cost" and "CO2 footprint" are playing an increasingly important role in the manufacture of fiber webs. Energy consumption, particularly in the drying section which is still almost entirely heated by gas, is a significant factor. To save energy or gas, it is highly advantageous if the fiber web from the upstream extrusion unit already has the highest possible dryness. An obvious idea might be to simply increase the linear load in the extrusion unit to achieve higher dryness. However, the feasibility of this approach is limited because there is a risk that the fiber web awaiting dehydration will be wrinkled in the extrusion gap. Furthermore, at the same machine speed, energy consumption in the extrusion unit increases with increasing linear load, and with increasing linear load, investment costs also increase due to the need for significantly more robust frames.

[0006] The technical problem to be solved by this invention is to reduce the energy cost and / or carbon dioxide footprint used in the manufacture of fiber webs, especially packaging paper webs.

[0007] The technical problem described herein is addressed by the independent claims. The dependent claims relate to advantageous improvements of the invention.

[0008] Specifically, the technical problem is solved by an extrusion apparatus of the type described in the opening paragraph according to the invention, characterized in particular by the fact that the main press is designed to produce a line load ratio LLR of at least 0.69 and at most 1.52 when operating at a line load LL of at least 1200 kN / m, wherein the line load ratio LLR is the quotient of the weighted line load WLL and the line load LL, wherein the weighted line load WLL is the result of integrating the squared local pressure p(x)² with a weighting factor A over the extrusion gap length x, wherein the weighting factor A is one-tenth of a megapascal, and wherein the line load LL is the result of integrating the local pressure p(x) over the extrusion gap length x, thereby the line load ratio LLR is given by the following formula:

[0009] For better understanding, please refer to Figure 3The diagram in the figure illustrates, purely schematically, how to simply determine and understand the line load ratio (LLR). First, the actual pressure distribution p(x) is determined, i.e., the curve of pressure variation acting along the length x of the extended extrusion gap of the main press. In this example, the main press has an extended extrusion gap of 260 mm. Furthermore, for simplicity, it is assumed that the local pressure p(x) increases linearly along the extended extrusion gap from 0 MPa at the beginning of the extended extrusion gap (x = 0 mm) to 12 MPa at the end of the extended extrusion gap (x = 260 mm), thus the pressure distribution p(x) is linear. The determination of the local pressures that sum to form the pressure distribution can be achieved, for example, by a pressure diaphragm introduced into the extended extrusion gap before pressure is applied by the main press. The pressure diaphragm measures, for example, the exact location and type of local pressure within the extrusion gap using the piezoelectric effect. The pressure along the transverse direction of the machine is generally constant here, so the pressure distribution only along the machine direction, i.e., along the length of the extended extrusion gap, is important. At most, slight variations in pressure along the transverse direction of the machine may occur only in the edge regions, where this effect should be ignored. Such pressure diaphragms with different resolutions are commercially available, for example, by Fujifilm under the trademark "Prescale". Preferably, measurements are taken before press start-up, after the installation of new felt, especially new and still-dry felt (used to guide the fiber web through the extended extrusion gap). Measurements should preferably be taken at the press's maximum operating line load.

[0010] Integrating the pressure distribution p(x) along the extended extrusion gap length x yields the line load LL. Based on... Figure 3 In the current example, the line load LL therefore corresponds to the area of ​​the triangle under the straight line representing the pressure distribution p(x). It is 1560 kN / m here. This makes it very easy to check the quality of the measurement performed, i.e., by comparing the integral-determined line load LL with the value of the line load LL previously set for the main press. It should be noted here that the line load LL gives the total force applied by the main press per meter of width along the machine's transverse or perpendicular direction of fiber web movement.

[0011] Based on the measured pressure distribution p(x), the curve of the weighted squared local pressure can be easily determined by the following formula. This is obtained. Figure 3 The curved curve shown intersects the straight line of the pressure distribution p(x) at 10 MPa. The area under this curved curve corresponds to the weighted linear load WLL. Figure 3As can be clearly seen in the graph, local pressures below 10 MPa result in a smaller area than the triangle representing the line load LL, while pressures exceeding 10 MPa result in a larger area than the triangle representing the line load LL. In the current example, the weighted line load WLL is 1250 kN / m. Therefore, the line load ratio LLR, which is the quotient of the weighted line load WLL and the line load LL, is 0.8, which falls within the scope of the claimed invention, i.e., within the range: .

[0012] In practice, the pressure distribution curve p(x) is certainly not a straight line. On the contrary, there are almost infinitely many possible pressure distribution curves p(x), even if the linear load LL, i.e., the area under the curve, remains constant. The shape of the pressure distribution curve p(x) depends primarily on the geometry of the press elements that form the extended extrusion gap therebetween, especially the geometry of the pressure shoe when using a shoe press.

[0013] To date, only the linear load LL has been used to characterize the pressure profile in an extended extrusion gap. However, the inventors recognized that this parameter alone is insufficient to accurately characterize the pressure profile, and therefore also insufficient to accurately characterize the dehydration behavior in the extrusion gap.

[0014] Because the integration involves averaging, for example, a pressure curve of p=10MPa maintained over the entire extrusion gap length produces the same linear load LL as a pressure curve of p=0MPa in the first half of the extrusion shoe length and p=20MPa in the second half. However, these two pressure curves have drastically different effects on dehydration and sheet structure.

[0015] This difference becomes apparent through the weighting of the weighted line load WLL. Thus, for the first case (p=10MPa), WLL=LL, or the line load ratio LLR is 1, while in the second case, WLL=1.5LL, or the line load ratio LLR is 1.5.

[0016] Therefore, this ratio value makes it very simple and efficient to distinguish the effects of pressure distributions with the same linear load without needing detailed analysis of the pressure curve's trend. Generally, under the same linear load, pressure distributions with strong pressure fluctuations and higher peak pressures tend to produce larger LLR values ​​than balanced distributions with moderate pressure values. The inventors' contribution lies in discovering that particularly effective dewatering of the fiber width can be achieved when the linear load to LLR is at least 0.69 and at most 1.52, wherein the boundary conditions are a linear load of at least 1200 kN / m and a squeeze gap length of at least 150 mm. If the extended squeeze gap is provided by a shoe press, the diameter of the rollers used for the shoe is preferably less than 3000 mm.

[0017] Therefore, the line load ratio (LLR) indirectly describes the geometry of the press elements, particularly the possible pressure shoe. Since there are numerous different geometries, all of which result in an LLR between 0.69 and 1.52, the LLR is chosen here to describe the solution according to the invention. Importantly, for extrusion devices with press elements of a fixed design, the LLR can be determined simply and clearly. Furthermore, those skilled in the art, knowing the invention, can design the press elements such that adjustments produce the desired LLR.

[0018] In known extrusion apparatuses, for the aforementioned boundary conditions, the linear load ratio (LLR) is consistently below 0.69. However, in the extrusion apparatus according to the invention, the press elements are designed such that the LLR is between 0.69 and 1.52, preferably between 0.71 and 1.35, and particularly preferably between 0.73 and 1.14. Unexpectedly, such a LLR produces more efficient fiber web dewatering than known presses, whose LLRs are outside this range, especially below 0.69.

[0019] The subranges of interest are those with LLR values ​​less than 1, specifically between 0.69 and 0.99, or between 0.71 and 0.97, or between 0.73 and 0.95.

[0020] The inventors have also discovered that, advantageous for effective dehydration of the fiber web, the extrusion apparatus further includes a pre-press located before, and preferably immediately adjacent to, the main press along the direction of fiber web movement. The pre-press serves to pre-consolidate and dehydrate the fiber web to such an extent that the fiber web is not wrinkled despite relatively high peak pressures in the main press. The extrusion apparatus according to the invention may include one or more additional presses when necessary. In particular, additional presses may be located before the pre-press.

[0021] The extrusion device using a pre-compressor can be implemented in a variety of different ways.

[0022] In particular, the pre-compressor can preferably also have an extended extrusion gap, wherein the pre-compressor is designed or can be designed such that the linear load ratio LLR of the pre-compressor is less than 0.69.

[0023] Alternatively or additionally, the pre-compactor can also have the classic roll gap.

[0024] A highly advantageous embodiment is a type of press sold by the applicant under the name "DuoCentri NipCo Flex" press. Here, two extrusion gaps are provided at the center roll. The first extrusion gap is the classic roll gap, which functions as a pre-press.

[0025] The main press is represented by a shoe-type extrusion gap, which is formed by a shoe-type pressure roller and a center roller that acts as a pair of rollers.

[0026] Another alternative design consists of three shoe presses arranged sequentially. The main press can be formed by the second or third shoe press among these shoe presses.

[0027] The linear load that the main press can operate at can also be higher than 1200 kN / m, i.e., at least 1300 kN / m, or significantly higher. As mentioned above, there are practical limitations to increasing the linear load because the risk of fiber web wrinkling increases, the drive energy increases, and, especially for designs with more robust frames, the investment cost increases.

[0028] Although the peak pressure cannot be arbitrarily high for the reasons mentioned above, it is preferably 10 MPa or higher, which results in a significant increase in dryness when using the linear load ratio LLR according to the invention, without unduly wrinkling the fiber width.

[0029] In a preferred embodiment of the invention, the pre-press is a shoe press comprising a shoe having a substantially concave curved surface and a shoe sleeve rotatably supported around the shoe.

[0030] Advantageously, the boot sleeve is at least partially composed of polyurethane, which is formed by the reaction of a prepolymer and a crosslinking agent component, wherein the prepolymer is a reaction product of 1,4-phenyl diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and / or at least one polycarbonate polyol, and wherein the crosslinking agent component contains C 2-14 - Diol. More preferably, the polyol component of the prepolymer comprises polytetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol. Alternatively or additionally, the crosslinking agent component may comprise polytetramethylene ether glycol (PTMEG) and / or at least one polycarbonate polyol.

[0031] The compression sleeve with this polyurethane layer has proven to be surprisingly durable even under high peak pressures. Peak pressures significantly exceeding 10 MPa pose no problem. Furthermore, this polyurethane blend is well-suited to maintain good adhesion to the embedded reinforcing wires even after multiple alternating load cycles under high peak pressures.

[0032] According to another aspect, the present invention relates to a machine for manufacturing fiber webs, preferably for packaging imitation kraft paper, comprising the extrusion device according to the invention as described above.

[0033] Furthermore, the present invention relates to a method for extruding fiber webs, particularly packaging paper webs, such as packaging kraft paper webs, preferably using the extrusion device according to the invention as described above, wherein the fiber web is guided through a main press having an extended extrusion gap of at least 150 mm, preferably at least 190 mm, wherein the main press operates with a line load of at least 1200 kN / m, preferably at least 1300 kN / m, wherein the main press is designed to produce a line load ratio LLR of at least 0.69 and at most 1.52, wherein the line load ratio LLR is the quotient of the weighted line load WLL and the line load LL, wherein the weighted line load WLL is the result of integrating the squared local pressure p(x)² with a weighting factor A over the extrusion gap length x, wherein the weighting factor A is one-tenth of a megapascal, and wherein the line load LL is the result of integrating the local pressure p(x) over the extrusion gap length x, thereby the line load ratio LLR is given by the following formula:

[0034] The previous description of the function and advantages of the extrusion device according to the invention applies accordingly to the method according to the invention, and vice versa.

[0035] Therefore, in the method according to the invention, the line load ratio LLR is preferably at least 0.71 and at most 1.35, more preferably at least 0.73 and at most 1.14.

[0036] Furthermore, the fiber width is preferably guided by a pre-press located before the main press, preferably adjacent to the main press, along the running direction of the fiber width. The pre-press may also have an extended extrusion gap. The pre-press may be designed such that the linear load ratio (LLR) of the pre-press is less than 0.69.

[0037] The method and apparatus according to the invention are particularly suitable when the fiber web is a graphic paper type or a paper type belonging to the paperboard and packaging fields. Particularly preferred is that the fiber web is a packaging paper web, such as a test liner. Conversely, the type of tissue paper is less relevant or irrelevant.

[0038] The method according to the invention can be used particularly effectively when the fiber web is composed of at least 20% by weight, preferably at least 50% by weight, of OCC fibers. OCC is an abbreviation known in the field for “used corrugated cardboard boxes.” In other words, the extrusion apparatus and method according to the invention are particularly suitable for effectively dewatering fiber webs with a large proportion or even a major proportion of recycled fibers, i.e., non-virgin fibers. This is related to the high resistance of OCC fibers to high pressure. The remaining fibers of the fiber web to be extruded can be selected, for example, from wood pulp or cellulose pulp, such as TMP, CTMP, and / or PGW.

[0039] The extrusion apparatus according to various aspects of the invention is advantageous also because it can operate at high production speeds. Therefore, speeds exceeding 1000 m / min, especially exceeding 1200 m / min or even exceeding 1400 m / min, are feasible. Here, the provision of a pre-compressor is generally considered advantageous, as it typically increases the production speed.

[0040] The present invention will now be described in detail with reference to embodiments illustrated in the schematic diagrams. Wherein:

[0041] Figure 1 An extrusion apparatus according to the present invention is shown, comprising a main press and a pre-press;

[0042] Figure 2 It shows Figure 1 The enlarged view and detailed view of the main press of the extrusion unit shown.

[0043] Figure 3 An exemplary pressure profile is shown in the extended extrusion gap of the main press.

[0044] Figure 1 A pressing device according to the invention is shown schematically, comprising a main press 1 and a pre-press 11 arranged adjacent to and upstream of the main press along the direction of movement BR of the fiber web 8. In this embodiment, both the main press 1 and the pre-press 11 are designed as shoe presses and therefore each has an extended pressing gap. Alternatively, however, the pre-press 11 may not have an extended pressing gap, and / or the pre-press 11 and the main press 1 may share a common center roller. The center roller will be the press element by which the extended pressing gap of both the pre-press 11 and the main press 1 is formed.

[0045] Figure 2 Enlarged and detailed views of the main press 1, which is particularly important according to the invention, are shown. This main press is designed to operate at a linear load LL of at least 1200 kN / m, preferably at least 1300 kN / m. The extended extrusion gap 7 of the main press 1 is provided by two press elements, namely a shoe roller 2 and a counterroller 3. The shoe roller 2 includes a shoe 5 supported on a stationary yoke 4, and a shoe sleeve 6 rotatably arranged around the shoe 5. Preferably, the fiber web 8 is guided in a sandwich manner between two press felts 9 through the extended extrusion gap 7. The shoe 5 has a substantially concave surface on which the shoe sleeve 6 runs, while the shoe 5 presses the shoe sleeve against the counterroller 3 at a high pressure F. The geometry of the press elements, especially the shoe 5, is chosen such that a linear load ratio LLR of at least 0.69 and at most 1.52 is produced.

[0046] The pressure F is preferably chosen to be sufficiently large such that the peak pressure acting on the fiber web 8 in the extended extrusion gap 7 is at least 10 MPa. The length of the extended extrusion gap of the main press 1 is at least 150 mm, preferably at least 190 mm.

[0047] What proves particularly advantageous for this peak pressure is that the shoe sleeve 6 is at least partially composed of polyurethane, which is formed by the reaction of a prepolymer and a crosslinking agent component, wherein the prepolymer is the reaction product of 1,4-phenyl diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and / or at least one polycarbonate polyol, and wherein the crosslinking agent component contains C 2-14 -diol. The shoe sleeve 6 may, for example, have a reinforcing structure consisting of a polyurethane layer embedded in a wire, wherein the prepolymer of the polyurethane layer is composed of 50% by weight of 1,4-phenylene diisocyanate (PPDI) and C 5-6 The mixture comprises a mixture of polycarbonate diol and 50% by weight of a mixture of 1,4-phenylene diisocyanate (PPDI) and polytetramethylene ether diol (PTMEG), wherein the crosslinking agent comprises or is preferably composed of polytetramethylene ether diol (PTMEG) and 1,6-hexanediol.

[0048] Figure 1 The pre-press 11, schematically shown, can and preferably is designed differently from the main press 1. In particular, unlike the main press 1, the pre-press 11 can be designed such that the linear load ratio (LLR) of the pre-press 11 is less than 0.69. The pre-press 11 is used in the extrusion apparatus, especially for pre-consolidating the fiber web 8 before passing it through the main press 1, so that the fiber web is not unacceptably wrinkled despite the relatively high peak pressure in the second press 1.

[0049] The fiber web 8 is preferably used for manufacturing packaging paper webs and / or such packaging paper webs. Furthermore, the fiber web is preferably composed of at least 20% by weight, more preferably at least 50% by weight, of OCC fibers, which are characterized by particularly high resistance to peak pressure.

[0050] The extrusion apparatus 1 according to the invention may theoretically include more presses in addition to the pre-press 11 and the main press 1. However, it is preferred that the main press 1 be the last press of the extrusion apparatus, that is, the last press before the fiber web 8 is transferred to the drying section located downstream of the extrusion apparatus.

[0051] List of reference numerals

[0052] 1 Main Press

[0053] 2 Shoe-type pressure rollers

[0054] 3 pairs of rollers

[0055] 4. The stationary yoke

[0056] 5. Press Boots

[0057] 6-shoe press sleeve

[0058] 7. Extended extrusion gap

[0059] 8 fiber width

[0060] 9 Pressed Felt

[0061] 10 Extrusion Unit

[0062] 11 Pre-compressor

[0063] BR movement direction

[0064] F pressure

Claims

1. An extrusion apparatus (10) for extruding fiber webs (8), particularly packaging paper webs, said extrusion apparatus comprising a main press (1) having an extended extrusion gap (7), wherein, The extrusion gap (7) has a length of at least 150 mm, preferably at least 190 mm, characterized in that the main press (1) is designed to produce a line load ratio LLR of at least 0.69 and at most 1.52 when operating at a line load LL of at least 1200 kN / m. Wherein, the line load ratio LLR is the quotient of the weighted line load WLL and the line load LL. The weighted linear load WLL is the result of integrating the squared local pressure p(x)², weighted by a weighting factor A, over the extrusion gap length x. The weighting factor A is one-tenth of a megapascal. Here, the line load LL is the result of integrating the local pressure p(x) over the extrusion gap length x. Therefore, the line load ratio LLR is given by the following formula: 。 2. The extrusion device (10) according to claim 1, characterized in that, The line load ratio (LLR) is at least 0.71 and at most 1.35, preferably at least 0.73 and at most 1.

14.

3. The extrusion device (10) according to claim 1 or 2, characterized in that, The extrusion device (10) further includes a pre-press (11) located upstream of the main press (1) and preferably adjacent to it, along the running direction of the fiber web (8).

4. The extrusion device (10) according to claim 3, characterized in that, The pre-press (11) also has an extended extrusion gap, wherein the pre-press (11) is designed such that the line load ratio of the pre-press is less than 0.

69.

5. The extrusion device (10) according to any one of the preceding claims, characterized in that, The main press (1) is designed to operate with a line load of at least 1300 kN / m LL.

6. The extrusion device (10) according to any one of the preceding claims, characterized in that, The main press (1) is a shoe press, which includes a shoe (5) having a substantially concave curved surface and a shoe sleeve (6) rotatably supported around the shoe (5).

7. The extrusion device (10) according to claim 6, characterized in that, The boot sleeve (10) is at least partially composed of polyurethane, which is formed by the reaction of a prepolymer and a crosslinking agent component, wherein the prepolymer is a reaction product of 1,4-phenyl diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and / or at least one polycarbonate polyol, and wherein the crosslinking agent component contains C 2-14 -Diol.

8. The extrusion device (10) according to claim 7, characterized in that, The polyol component of the prepolymer includes polytetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol.

9. The extrusion device (10) according to claim 7 or 8, characterized in that, The crosslinking agent component comprises polytetramethylene ether glycol (PTMEG) and / or at least one polycarbonate polyol.

10. A machine for manufacturing fiber webs (8), preferably for packaging imitation kraft paper, said machine comprising an extrusion device (10) according to any one of the preceding claims.

11. A method for extruding a fiber web (8), particularly a packaging paper web, for example, a packaging imitation kraft paper web, preferably using an extrusion device (10) according to any one of claims 1 to 9, wherein, The fiber web (8) is guided through a main press (1) having an extended extrusion gap (7) with a length of at least 150 mm, preferably at least 190 mm. The main press (1) is characterized by operating with a line load LL of at least 1200 kN / m, preferably at least 1300 kN / m, wherein the main press (1) is designed to produce a line load ratio LLR of at least 0.69 and at most 1.

52. Wherein, the line load ratio LLR is the quotient of the weighted line load WLL and the line load LL. The weighted linear load WLL is the result of integrating the squared local pressure p(x)², weighted by a weighting factor A, over the extrusion gap length x. The weighting factor A is one-tenth of a megapascal. Here, the line load LL is the result of integrating the local pressure p(x) over the extrusion gap length x. Therefore, the line load ratio LLR is given by the following formula: 。 12. The method according to claim 11, characterized in that, The line load ratio (LLR) is at least 0.71 and at most 1.35, preferably at least 0.73 and at most 1.

14.

13. The method according to claim 11 or 12, characterized in that, The fiber web (8) also guides a pre-press (11) located upstream of the main press (1) and preferably adjacent to it, along the running direction of the fiber web (8).

14. The method according to any one of claims 11 to 13, characterized in that, The method is carried out at a speed of at least 1000 m / min, preferably at least 1200 m / min, and especially more than 1400 m / min.

15. The method according to any one of claims 11 to 14, characterized in that, The fiber width (8) is composed of at least 20% by weight, preferably at least 50% by weight, of OCC fiber.

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