DE102023108256A1 - Press arrangement and method for pressing a fibrous web - Google Patents

Abstract

The invention relates to a press arrangement and a method for pressing a fibrous web, comprising a main press with an extended press nip, the press nip having a length of at least 150 mm, the main press being designed such that, when operated with a line load LL of less than 1,200 kN/m, a line load ratio LLR of at least 0.56 and at most 1.33 results, the line load ratio LLR being the quotient of a weighted line load WLL to the line load LL, the weighted line load being the result of an integration of the quadratic local pressure p(x) ² weighted with a weighting factor A over the press nip length x, the weighting factor A being one divided by ten megapascals, and the line load LL being the result of an integration of the local pressure p(x) over the press nip length x, so that the following formula results for the line load ratio LLR: $$LLR=\frac{WLL}{LL}=\frac{{\displaystyle \int A\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}=\frac{{\displaystyle \int \frac{1}{10MPa}\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}$$

Description

The present invention relates to a press arrangement for pressing a fibrous web, in particular a packaging paper web, comprising a main press with an extended press nip, wherein the press nip has a length of at least 150 mm, preferably at least 190 mm. Furthermore, the present invention relates to a method for pressing a fibrous web, in particular a packaging paper web, such as packaging testliner, wherein the fibrous web is guided through a main press with an extended press nip of at least 150 mm in length, preferably at least 190 mm in length. In addition, a further aspect of the present invention relates to a method for converting an existing press.

Such a press arrangement and such a pressing process are described, for example, in the publication WO2017207475A1 described, the disclosure of which is hereby incorporated by reference.

Machines for producing a fibrous web usually have a press arrangement in which the fibrous web is dewatered or dehumidified by mechanical pressure. The press arrangement is usually arranged between the forming and drying sections. A particularly efficient type of mechanical dewatering can be achieved using a so-called extended press nip. The advantages of an extended press nip are well known: the press nip is flat and not essentially linear as with conventional roller presses. This means that the pressure exerted on the fibrous web to be dewatered in the press nip in the running direction does not start suddenly, but can be increased continuously from a low value to a high value. This reduces the risk of the fibrous web to be dewatered being crushed in the press nip. In this way, the fibrous web can be dewatered very efficiently in an extended press nip on the one hand and in a way that preserves its volume on the other.

For example, the fibrous web can be guided through the extended press nip together with a felt or between two felts, whereby the extended press nip can be formed in a so-called shoe press between a shoe press roll and a counter roll. In contrast to the production of tissue webs, the thickness or so-called bulk is less important in the production of paper webs, especially packaging paper webs. For this reason and because of the considerably higher basis weight of paper webs, especially packaging paper webs, significantly higher line loads are used in the press, namely line loads of at least 500 kN/m.

The topics of “energy costs” and “ _CO2 footprint” are playing an increasingly important role in the production of fibrous webs. Energy consumption in the drying section, which is now almost exclusively gas-heated, is a key factor. In order to save energy or gas here, it would be very advantageous if the fibrous web coming from the upstream press arrangement already had as high a dry content as possible. An obvious idea could be to simply increase the line load in the press arrangement in order to achieve a higher dry content. However, this approach is only of limited practical use, as there is a risk that the fibrous web to be dewatered will be crushed in the press nip. In addition, energy consumption in the press arrangement also increases with increasing line load at the same machine speed, and investment costs increase with increasing line load, as a considerably more massive frame is required.

It is an object of the present invention to reduce the energy costs and/or the _CO2 footprint for the production of a fibrous web, in particular a packaging web.

This object is solved by the independent claims. The dependent claims relate to advantageous developments of the present invention.

Specifically, the task is solved by a generic press arrangement described at the beginning, which is particularly characterized in that the main press is designed in such a way that when it is operated with a line load LL of at least 500 kN/m and a maximum line load LL of less than 1,200 kN/m, a line load ratio LLR of at least 0.56 and at most 1.33 results, wherein the line load ratio LLR is the quotient of a weighted line load WLL to the line load LL, wherein the weighted line load WLL is the result of an integration of the quadratic local pressure p(x) ² weighted with a weighting factor A over the press gap length x, wherein the weighting factor A is one divided by ten megapascals, and wherein the line load LL is the result of an integration of the local pressure p(x) over the press gap length x, so that the following formula results for the line load ratio LLR: $$LLR=\frac{WLL}{LL}=\frac{{\displaystyle \int A\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}=\frac{{\displaystyle \int \frac{1}{10MPa}\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}$$

For a better understanding, please refer to the diagram in 3 which illustrates purely schematically how the line load ratio LLR can be easily determined and understood. Even if no real pressure curve can be seen in this schematic diagram, the diagram does illustrate the basic procedure well: First, the actual pressure profile p(x) is determined, i.e. the course of the pressure that acts over the length x of the extended press nip of the main press. In the example at hand, the main press has an extended press nip of 190 mm. Furthermore, for the sake of simplicity, it is assumed that the local pressure p(x) increases linearly along the extended press nip from 0 MPa at the beginning of the extended press nip at x=0 mm to approximately 11.5 MPa at the end of the extended press nip at x=190 mm, so that the pressure profile p(x) is a straight line. The determination of the local pressures, which together result in the pressure profile, can be carried out, for example, using a pressure film that is introduced into the extended press nip before pressure is applied to it by the main press. The printing film then measures, for example using the piezo effect, exactly where which local pressure is applied in the press nip. The pressure in the cross-machine direction is usually constant, so that only the pressure profile in the machine direction, i.e. along the length of the extended press nip, is important. At most, there may be a slight change in the pressure in the cross-machine direction in the side edge area, although these effects in the side edge area will be ignored here. Such printing films with various resolutions are offered commercially, for example by Fujifilm under the brand name "Prescale". Measurements are preferably taken before the press is started up, after installing a fresh felt, in particular a fresh and still dry felt, which is used to guide the fibrous web through the extended press nip. Measurements should preferably be taken with the press at its maximum operating line load.

If the pressure profile p(x) is integrated over the length of the extended press gap x, the line load LL results. In the present example according to 3 The line load LL corresponds to the triangular area under the straight line that represents the pressure profile p(x). Here it is 1,093 kN/m, which is within the scope of the present invention. In this way, the quality of the measurement taken can be checked very easily, namely by comparing the line load LL determined by integration with the value that was previously set as the line load LL of the main press. Basically, it should be noted at this point that the line load LL indicates the total force that the main press applies per meter of width in the cross-machine direction or orthogonal to the direction of movement of the fibrous web.

Dies ergibt die in 3 dargestellte gekrümmte Kurve, welche die Gerade des Druckprofils p(x) bei 10 MPa schneidet. Die Fläche unterhalb dieser gekrümmten Kurve entspricht dabei der gewichteten Linienlast WLL. Deutlich erkennt man in der Grafik der 3, dass lokale Drücke von weniger als 10 MPa zu einer geringeren Fläche und Drücke von über 10 MPa zu einer vergrößerten Fläche gegenüber der Dreiecksfläche, welche die Linienlast LL darstellt, führen. In dem vorliegenden Beispiel beträgt die gewichtete Linienlast WLL 838 kN/m. Hieraus ergibt sich ein Linienlastverhältnis LLR als Quotient aus gewichteter Linienlast WLL zu Linienlast LL von 0,77, was im Bereich der beanspruchten Erfindung liegt, nämlich im Bereich: $$\mathrm{0,56}\le \frac{WLL}{LL}\le \mathrm{1,33}$$

Based on the measured pressure profile p(x), the curve of the weighted quadratic local pressure can now be easily determined using the following formula: $\frac{1}{10Mpa}\ast p{\left(x\right)}^2.$

This results in the 3 The curved curve shown here intersects the straight line of the pressure profile p(x) at 10 MPa. The area below this curved curve corresponds to the weighted line load WLL. The graph clearly shows the 3 that local pressures of less than 10 MPa lead to a smaller area and pressures of more than 10 MPa lead to an increased area compared to the triangular area, which represents the line load LL. In the present example, the weighted line load WLL is 838 kN/m. This results in a line load ratio LLR as the quotient of weighted line load WLL to line load LL of 0.77, which is within the scope of the claimed invention, namely in the range: $$0.56\le \frac{WLL}{LL}\le 1.33$$

In practice, the pressure profile curve p(x) does not have to be a straight line. Instead, there is an almost inexhaustible variety of possible pressure profile curves p(x), even if the line load LL, i.e. the area under the curve, remains the same. The shape of the pressure profile curve p(x) depends largely on the geometric design of the press elements that form the extended press gap between them, in particular on the geometric design of any press shoe when using a shoe press.

Until now, only the line load LL was used to characterize the pressure curve in an extended press nip. However, the inventors have recognized that this parameter alone is not sufficient to accurately characterize the pressure curve and thus also the drainage behavior in the press nip.

Since a certain averaging takes place through integration, for example, a constant pressure curve p=10 MPa over the entire length of the press nip produces the same line load LL as a pressure curve of p=0 MPa in the first half and p=20 MPa in the second half of the shoe length. However, the effect of these two pressure curves on the drainage and on the sheet structure is very different.

This difference is made visible by the weighting in the weighted line load WLL. For the first case (p=10 MPa) this results in WLL = LL, or a line load ratio LLR of 1, and in the second case WLL = 1.5 LL, i.e. a line load ratio LLR of 1.5.

The ratio therefore makes it very easy and efficient to differentiate between pressure profiles with the same line load in terms of their effect, without having to analyse the course of the pressure curve in detail. In general, for the same line load, pressure profiles with strong pressure fluctuations and higher peak pressures tend to produce larger LLR values than balanced profiles with average pressure values.

It is to the credit of the inventors that they have discovered that particularly efficient dewatering of the fibrous web can be achieved if the line load ratio LLR is at least 0.56 and at most 1.33, with the boundary conditions being that the line load is at least 500 kN/m and a maximum of less than 1,200 kN/m and that the press nip has a length of at least 150 mm. If the extended press nip is provided by a shoe press, the counter roll to the shoe also preferably has a diameter that is less than 3,000 mm.

The line load ratio LLR thus indirectly describes the geometric design of the press elements, in particular of any press shoe. Since there is an unmanageable number of different geometric designs, all of which lead to a line load ratio LLR between 0.56 and 1.33, the choice of the line load ratio LLR is appropriate here to describe the solution according to the invention. It is important that the line load ratio LLR can be determined easily and clearly for a press arrangement with a fixed design of the press elements. It is also within the skill of the expert, with knowledge of the present invention, to design the press elements in such a way that the desired line load ratio LLR is achieved.

In known press arrangements, the line load ratio LLR for the above-mentioned boundary conditions is always below 0.56. In the press arrangement according to the invention, however, the press elements are designed such that a line load ratio LLR of between 0.56 and 1.33 results, preferably between 0.61 and 1.01, particularly preferably between 0.66 and 0.89. It has surprisingly been shown that such a line load ratio LLR leads to more efficient dewatering of the fibrous web, compared to known presses whose line load ratio LLR lies outside this value range, in particular below 0.56.

The inventors have also found that it is advantageous with regard to efficient dewatering of the fibrous web if the press arrangement also comprises a pre-press arranged in the running direction of the fibrous web, preferably immediately upstream of the main press. The pre-press serves to pre-consolidate and dehumidify the fibrous web to such an extent that it is not crushed despite a high peak pressure in the main press. The press arrangement according to the invention can also comprise one or more further presses if required. In particular, another press can be arranged upstream of the pre-press.

In particular, the pre-press can preferably also have an extended press nip, wherein the pre-press is designed such that its line load ratio LLR is less than 0.56, but at least less than 0.66.

The maximum operating line load with which the main press can be operated can only be 1,100 kN/m. Older press arrangements in particular are designed in such a way that they cannot achieve higher operating line loads. As mentioned above, changing the frame would lead to enormous investment costs.

Even if the peak pressure cannot be arbitrarily high for the reasons described above, it is preferably above 8 MPa, which, when using the line load ratio LLR according to the invention, still leads to a significant increase in dry matter content, but without unduly compressing the fibrous web.

A preferred embodiment of the invention provides that the pre-press is a shoe press which comprises a press shoe with a substantially concavely curved surface and a shoe press jacket rotatably mounted around the press shoe.

It has proven to be advantageous if the shoe press cover consists at least partially of polyurethane, which is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and/or at least one polycarbonate polyol, and wherein the crosslinking component contains a C _2-14 diol. It is further preferred if the polyol component of the prepolymer comprises polytetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol. Alternatively or additionally, the crosslinking component can comprise polytetramethylene ether glycol (PTMEG) and/or at least one polycarbonate polyol.

A press jacket with such a polyurethane layer has proven to be surprisingly resistant even at high peak pressures. Peak pressures of significantly more than 8 MPa are no problem. At the same time, this polyurethane mixture is capable of maintaining good adhesion to the reinforcement threads embedded in it, even after many alternating load cycles under high peak pressures.

According to a further aspect, the present invention relates to a machine for producing a fibrous web, preferably packaging testliner, comprising a previously described press arrangement according to the invention.

The invention further relates to a method for pressing a fibrous web, in particular packaging paper web, such as packaging testliner, preferably using a previously described press arrangement according to the invention, wherein the fibrous web is guided through a main press with an extended press nip of at least 150 mm in length, preferably at least 190 mm in length, wherein the main press is operated with a line load of at least 500 kN/m and a maximum line load LL of less than 1,200 kN/m, preferably at least 1,100 kN/m, wherein the main press is designed in such a way that a line load ratio LLR of at least 0.56 and at most 1.33 results, wherein the line load ratio LLR is the quotient of a weighted line load WLL to the line load LL, wherein the weighted line load WLL is the result of an integration of a quadratic local pressure p(x) ² weighted with a weighting factor A over the press nip length x, wherein the weighting factor A is one divided by ten megapascals, and where the line load LL is the result of an integration of the local pressure p(x) over the press gap length x, so that the line load ratio LLR is given by the following formula: $$LLR=\frac{WLL}{LL}=\frac{{\displaystyle \int A\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}=\frac{{\displaystyle \int \frac{1}{10MPa}\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}$$

The effects and advantages previously stated with regard to the press arrangement according to the invention also apply mutatis mutandis to the method according to the invention and vice versa.

Thus, in the method according to the invention, the line load ratio LLR is preferably at least 0.61 and at most 1.01, more preferably at least 0.66 and at most 0.89.

In addition, the fibrous web is preferably further guided through a pre-press which is arranged upstream of the main press in the running direction of the fibrous web, preferably immediately upstream, whereby the pre-press can also have an extended press nip, and whereby the pre-press can be designed such that the line load ratio LLR of the pre-press is less than 0.56, but in any case less than 0.66.

The method and device according to the invention are particularly suitable when the fibrous web is a graphic paper type or a type that is assigned to the board and packaging sector. It is particularly preferred when the fibrous web is a packaging paper web, such as packaging testliner. Tissue types, on the other hand, are of lesser or no importance.

The method according to the invention can be used particularly efficiently if the fibrous web consists of at least 20% by weight, preferably at least 50% by weight, of OCC fibers. OCC is an abbreviation known in the art and stands for "old corrugated containers". In other words, the press arrangement according to the invention and the method according to the invention are particularly well suited to efficiently dewatering fibrous webs that have a significant or even significant proportion of used fibers, i.e. no fresh fibers. This is related to the high resistance of the OCC fibers to high pressures. The remaining fibers of the fibrous web to be pressed can be selected, for example, from mechanical pulp or cellulose, such as TMP, CTMP and/or PGW.

wobei die Pressenanordnung derart umgebaut wird, dass sich nach dem Umbau ein Linienlastverhältnis LLR von mindestens 0,56 und höchstens 1,33 ergibt.A further aspect of the present invention relates to a method for converting an existing press arrangement for pressing a fibrous web, in particular a cardboard web, comprising a main press with an extended press nip, the press nip having a length of at least 150 mm, preferably of at least 190 mm, the main press being designed to be operated with a line load of more than 500 kN/m and a maximum line load LL of less than 1,200 kN/m, resulting in a line load ratio LLR of less than 0.56, the line load ratio LLR being the quotient of a weighted line load WLL to the line load LL, the weighted line load WLL being the result of an integration of the quadratic local pressure p(x) ² weighted with a weighting factor A over the press nip length x, the weighting factor A being one divided by ten megapascals, and the line load LL being the result of an integration of the local pressure p(x) over the press nip length x is over,
so that the following formula results for the line load ratio LLR: $$LLR=\frac{WLL}{LL}=\frac{{\displaystyle \int A\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}=\frac{{\displaystyle \int \frac{1}{10MPa}\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}$$

wherein the press arrangement is modified in such a way that after the modification a line load ratio LLR of at least 0.56 and at most 1.33 results.

By means of such a conversion, the dewatering efficiency of older press arrangements can also be subsequently increased without too much effort, in particular without having to reinforce the frame, as would be necessary if the maximum applicable line load LL were increased.

The present invention advantageously allows the conversion to be structurally limited essentially to the replacement of at least one press element of the main press, in particular to the replacement of a press shoe if the main press is a shoe press.

• 1: eine erfindungsgemäße Pressenanordnung, umfassend eine Hauptpresse und eine Vorpresse;
• 2: eine vergrößerte und detaillierte Darstellung der Hauptpresse der in 1 gezeigten Pressenanordnung,
• 3: eine beispielhafte Druckkurve im verlängerten Pressspalt der Hauptpresse, wobei die Druckkurve nur der Verdeutlichung dient.

The invention is explained in more detail below using an embodiment described with the aid of schematic figures.

• 1 : a press arrangement according to the invention, comprising a main press and a pre-press;
• 2 : an enlarged and detailed representation of the main press of the 1 shown press arrangement,
• 3 : an example pressure curve in the extended press nip of the main press, whereby the pressure curve is for illustrative purposes only.

1 shows a very schematic representation of a press arrangement according to the invention, comprising a main press 1 and a pre-press 11 arranged directly in front of it in the direction of movement BR of a fibrous web 8. In this exemplary embodiment, both the main press 1 and the pre-press 11 are designed as shoe presses and thus each have an extended press nip. Alternatively, however, the pre-press 11 could also have no extended press nip and/or the pre-press 11 and the main press 1 could share a common central roller. The central roller would then be a press element by means of which both the extended press nip of the pre-press 11 and the extended press nip of the main press 1 would be formed.

2 shows an enlarged and detailed illustration of the main press 1, which is of particular importance according to the invention. This is designed to be operated with a line load LL of at least 500 kN/m and a maximum of less than 1,200 kN/m. The extended press nip 7 of the main press 1 is provided by two press elements, namely a shoe press roll 2 and a counter roll 3. The shoe press roll 2 comprises a press shoe 5, which is supported on a stationary yoke 4, and a shoe press cover 6, which is arranged so as to be rotatable around the press shoe 5. The fibrous web 8 is preferably guided through the extended press nip 7 in a sandwich-like manner between two press felts 9. The press shoe 5 has a substantially concavely shaped surface over which the shoe press cover 6 runs, while the press shoe 5 presses it with a high compressive force F in the direction of the counter roll 3. The geometric design of the pressing elements, in particular of the press shoe 5, is selected such that a line load ratio LLR of at least 0.56 and at most 1.33 results.

The pressure force F is preferably selected to be so large that the peak pressure acting on the fibrous web 8 in the extended press nip 7 is at least 8 MPa. The length of the extended press nip of the main press 1 is at least 150 mm, preferably at least 190 mm.

It has proven to be particularly advantageous at such peak pressures if the shoe press cover 6 consists at least partially of polyurethane which is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and/or at least one polycarbonate polyol, and wherein the crosslinking component contains a C _2-14 diol. For example, the shoe press cover 6 can have a reinforcement structure made of threads embedded in the polyurethane layer, wherein the prepolymer of the polyurethane layer consists of 50 wt.% of a mixture of 1,4-phenylene diisocyanate (PPDI) and C _5-6 polycarbonate diol and 50 wt.% of a mixture of 1,4-phenylene diisocyanate (PPDI) and polytetramethylene ether glycol (PTMEG), and wherein the crosslinker comprises polytetramethylene ether glycol (PTMEG) and 1,6-hexanediol or is preferably formed substantially therefrom.

The in 1 The schematically shown pre-press 11 can and is preferably designed differently from the main press 1. In particular, unlike the main press 1, it can be designed such that the line load ratio LLR of the pre-press 11 is less than 0.56, but at least less than 0.66. The pre-press 11 serves in the press arrangement in particular to sufficiently pre-consolidate the fibrous web 8 for passage through the main press 1 so that it can be used despite a relatively high peak pressure in the second press 1 is not pressed too strongly.

The fibrous web 8 is preferably used to produce a packaging paper web or is such a packaging paper web. Furthermore, the fibrous web preferably consists of at least 20% by weight, more preferably at least 50% by weight, of OCC fibers, which are characterized by a particularly high resistance even to high peak pressures.

The press arrangement 1 according to the invention could theoretically also have more presses than just the pre-press 11 and the main press 1. However, the main press 1 is preferably the last press of the press arrangement, i.e. the last press before the fibrous web 8 is transferred to a drying section downstream of the press arrangement.

List of reference symbols

1

main press

2

shoe press roll

3

counter roller

4

standing yoke

5

press shoe

6

shoe press cover

7

extended press nip

8

fibrous web

9

press felt

10

press arrangement

11

pre-press

BR

direction of movement

F

compressive force

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• WO 2017207475 A1 [0002]

Claims (15)

Press arrangement (10) for pressing a fibrous web (8), in particular a packaging paper web, comprising a main press (1) with an extended press nip (7), the press nip (7) having a length of at least 150 mm, preferably of at least 190 mm, characterized in that the main press (1) is designed such that, when it is operated with a line load LL of at least 500 kN/m and a maximum line load LL of less than 1,200 kN/m, a line load ratio LLR of at least 0.56 and at most 1.33 results, the line load ratio LLR being the quotient of a weighted line load WLL to the line load LL, the weighted line load WLL being the result of an integration of the quadratic local pressure p(x) ² weighted with a weighting factor A over the press nip length x, the weighting factor A being one divided by ten megapascals, and the line load LL is the result of an integration of the local pressure p(x) over the press gap length x, so that the following formula results for the line load ratio LLR: $$LLR=\frac{WLL}{LL}=\frac{{\displaystyle \int A\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}=\frac{{\displaystyle \int \frac{1}{10MPa}\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}$$

Press arrangement (10) according to Claim 1 , characterized in that the line load ratio LLR is at least 0.61 and at most 1.01, preferably at least 0.66 and at most 0.89. Press arrangement (10) according to Claim 1 or 2 , characterized in that the press arrangement (10) further comprises a pre-press (11) arranged upstream of the main press (1) in the running direction of the fibrous web (8), preferably immediately upstream. Press arrangement (10) according to one of the preceding claims, characterized in that the main press (1) is designed to be operated with a line load LL of at most 1,100 kN/m. Press arrangement (10) according to one of the preceding claims, characterized in that the main press (1) is a shoe press which comprises a press shoe (5) with a substantially concavely curved surface and a shoe press jacket (6) rotatably mounted around the press shoe (5). Press arrangement (10) according to claim 5 , characterized in that the shoe press cover (6) consists at least partially of polyurethane which is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and/or at least one polycarbonate polyol, and wherein the crosslinking component contains a C _2-14 diol. Press arrangement (10) according to claim 6 , characterized in that the polyol component of the prepolymer comprises polytetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol. Press arrangement (10) according to claim 6 or 7 , characterized in that the crosslinking component comprises polytetramethylene ether glycol (PTMEG) and/or at least one polycarbonate polyol. Machine for producing a fibrous web (8), preferably packaging testliner, comprising a press arrangement (10) according to one of the preceding claims. Method for pressing a fibrous web (8), in particular packaging paper web, such as Packaging Testliner, preferably using a press arrangement (10) according to one of the Claims 1 until 8 , wherein the fibrous web (8) is guided through a main press (1) with an extended press nip (7) of at least 150 mm in length, preferably at least 190 mm in length, characterized in that the main press (1) is operated with a line load LL of at least 500 kN/m and a maximum line load LL of less than 1,200 kN/m, preferably less than 1,100 kN/m, wherein the main press (1) is designed in such a way that a line load ratio LLR of at least 0.56 and at most 1.33 results, wherein the line load ratio LLR is the quotient of a weighted line load WLL to the line load LL, wherein the weighted line load WLL is the result of an integration of a quadratic local pressure p(x) ² weighted with a weighting factor A over the press nip length x, wherein the weighting factor A is one divided by ten megapascals, and wherein the line load LL is the result of an integration of the local pressure p(x) over the press gap length x, so that the following formula results for the line load ratio LLR: $$LLR=\frac{WLL}{LL}=\frac{{\displaystyle \int A\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}=\frac{{\displaystyle \int \frac{1}{10MPa}\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}$$

procedure according to claim 10 , characterized in that the line load ratio LLR is at least 0.61 and at most 1.01, preferably at least 0.66 and at most 0.89. procedure according to claim 10 or 11 , characterized in that the fibrous web (8) is further guided through a pre-press (11) arranged upstream of the main press (1) in the running direction of the fibrous web (8), preferably immediately upstream. Method according to one of the Claims 10 until 12 , characterized in that the fibrous web (8) consists of at least 20 wt.%, preferably at least 50 wt.% OCC fibers. Method for converting an existing press arrangement (10) for pressing a fibrous web (8), in particular a packaging paper web, comprising a main press (1) with an extended press nip (7), the press nip (7) having a length of at least 150 mm, preferably of at least 190 mm, the main press (1) being designed to be operated with a line load of more than 500 kN/m and a maximum line load LL of less than 1,200 kN/m, resulting in a line load ratio LLR of less than 0.56, the line load ratio LLR being the quotient of a weighted line load WLL to the line load LL, the weighted line load WLL being the result of an integration of the quadratic local pressure p(x) ² weighted with a weighting factor A over the press nip length x, the weighting factor A being one divided by ten megapascals, and the line load LL being the result of an integration of the local pressure p(x) over the press gap length x, so that the following formula results for the line load ratio LLR: $$LLR=\frac{WLL}{LL}=\frac{{\displaystyle \int A\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}=\frac{{\displaystyle \int \frac{1}{10MPa}\ast p{\left(x\right)}^{2}dx}}{{\displaystyle \int p\left(x\right)dx}}$$

characterized in that the press arrangement (10) is converted such that after the conversion a line load ratio LLR of at least 0.56 and at most 1.33 results. procedure according to claim 14 , characterized in that the conversion is structurally essentially limited to the replacement of at least one pressing element of the main press (1), in particular to the replacement of a press shoe (5) if the main press (1) is a shoe press.

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