PRESS ARRANGEMENT AND METHOD FOR PRESSING A FIBROUS WEB

Abstract

A press arrangement for pressing a web of fibrous material includes at least two presses which are arranged one behind the other in a direction of travel of the web of fibrous material, the at least two presses including a first press and a second press following the first press, the first press including a first press nip, the second press including a second press nip which is an extended press nip, the second press being configured for being operated at a linear load of at least 500 kN/m, the second press being configured such that a quotient of an average pressure and a peak pressure in the second press nip is less than 0.5, the second press being configured for applying the peak pressure of at least 12 MPa onto the web of fibrous material.

Claims

1. A press arrangement for pressing a web of fibrous material, the press arrangement comprising: at least two presses which are arranged one behind the other in a direction of travel of the web of fibrous material, the at least two presses including a first press and a second press following the first press, the first press including a first press nip, the second press including a second press nip which is an extended press nip, the second press being configured for being operated at a linear load of at least 500 kN/m, the second press being configured such that a quotient of an average pressure and a peak pressure in the second press nip is less than 0.5, the second press being configured for applying the peak pressure of at least 12 MPa onto the web of fibrous material.

2. The press arrangement according to claim 1, wherein the quotient of the average pressure and the peak pressure is at least one of less than 0.46 and greater than 0.3.

3. The press arrangement according to claim 1, wherein the second press is configured for being operated at the linear load of at least 1,000 kN/m.

4. The press arrangement according to claim 1, wherein the first press is configured such that at least one of the following applies: a) a quotient of an average pressure and a peak pressure in the first press nip is greater than 0.5; b) a maximum linear load with which the first press is configured for being operated is less than a maximum linear load with which the second press is configured for being operated; and c) a peak pressure that can be applied to the web of fibrous material in the first press nip is less than the peak pressure that can be applied to the web of fibrous material in the second press nip.

5. The press arrangement according to claim 1, wherein the second press is a shoe press, which includes a press shoe, with a concavely curved surface, and a shoe press shell rotatably mounted around the press shoe.

6. The press arrangement according to claim 5, wherein the shoe press shell includes polyurethane, which is configured for being 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 of at least one polyether polyol and at least one polycarbonate polyol, and wherein the crosslinking component contains a C.sub.2-14 diol.

7. The press arrangement according to claim 6, wherein the polyol component of the prepolymer includes a poly-tetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol.

8. The press arrangement according to claim 6, wherein the crosslinking component includes at least one of poly-tetramethylene ether glycol (PTMEG) and at least one polycarbonate polyol.

9. A machine for producing of a web of fibrous material, the machine comprising: a press arrangement configured for pressing the web of fibrous material, the press arrangement including at least two presses which are arranged one behind the other in a direction of travel of the web of fibrous material, the at least two presses including a first press and a second press following the first press, the first press including a first press nip, the second press including a second press nip which is an extended press nip, the second press being configured for being operated at a linear load of at least 500 kN/m, the second press being configured such that a quotient of an average pressure and a peak pressure in the second press nip is less than 0.5, the second press being configured for applying the peak pressure of at least 12 MPa onto the web of fibrous material.

10. A method for pressing a web of fibrous material, the method comprising the steps of: guiding the web of fibrous material through at least two presses consecutively, the at least two presses including a first press and a second press following the first press, the first press including a first press nip, the second press including a second press nip which is an extended press nip; and pressing the web of fibrous material in the second press with a linear load of at least 500 kN/m, the web of fibrous material being pressed in the second press such that a quotient of an average pressure and a peak pressure in the second press nip is less than 0.5, the web of fibrous material being pressed in the second press with the peak pressure of at least 12 Mpa.

11. The method according to claim 10, wherein the quotient of the average pressure and the peak pressure is at least one of less than 0.46 and greater than 0.3.

12. The method according to claim 10, wherein the web of fibrous material is pressed in the second press with a linear load of at least 1,000 kN/m.

13. The method according to claim 10, wherein the web of fibrous material is pressed in the second press with a linear load of at least 1,300 kN/m.

14. The method according to claim 10, wherein the first press is operated such that at least one of the following applies: a) a quotient of an average pressure and a peak pressure in the first press nip is greater than 0.5; b) a maximum linear load with which the first press is operated is less than a maximum linear load with which the second press is operated; and c) a peak pressure that is applied to the web of fibrous material in the first press nip is less than the peak pressure that is applied to the web of fibrous material in the second press nip.

15. The method according to claim 10, wherein the web of fibrous material includes at least 20 wt. % of OCC (old corrugated containers) fibers.

16. The method according to claim 10, wherein the web of fibrous material includes at least 50 wt. % of OCC (old corrugated containers) fibers.

17. The method according to claim 10, wherein the web of fibrous material is a packaging paper web.

18. The method according to claim 10, wherein the method of pressing the web of fibrous material is carried out using a press arrangement, wherein the press arrangement includes the at least two presses which include the first press and the second press which is arranged behind the first press in the direction of travel of the web of fibrous material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0036] FIG. 1 is a press arrangement according to the present invention, including a first press and a second press; and

[0037] FIG. 2 is an enlarged and detailed presentation of the second press of the press arrangement shown in FIG. 1.

[0038] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0039] In an entirely schematic representation, FIG. 1 shows a press arrangement according to the invention, including a first press 11 and a second press 1 arranged directly behind it in the direction of travel BR of a fibrous web 8. In this exemplary design example, first press 11 as well as second press 1 are designed as shoe presses and thus each have an extended press nip. Alternatively, however, it would be possible for first press 11 to not have an extended press nip, and/or first press 11 and second press 1 could share a common central roll. The central roll would then be a press element by way of which both the first press nip of first press 11 and the second press nip of second press 1 would be formed.

[0040] FIG. 2 shows an enlarged and detailed representation of second press 1, which is of particular importance according to the invention. It is designed to be operated with a linear load of at least 500 kN/m. Second press nip 7 features two press elements, namely a shoe press roll 2 and a mating roll 3. Shoe press roll 2 includes a press shoe 5, which is supported by a standing yoke 4, and a shoe press shell 6, which is arranged rotatably around press shoe 5. Fibrous web 8 is optionally guided through second extended press nip 7 in a sandwich-like manner between two press felts 9. Press shoe 5 has an essentially concave surface covered by shoe press shell 6 while press shoe 5 presses the latter with a high compressive force F in the direction of mating roll 3. The geometric design of the press elements, in particular of press shoe 5, is selected in such a way that a quotient of average pressure and peak pressure in second press nip 7 is less than 0.5 according to the invention. Said quotient can optionally be between 0.3 and 0.46.

[0041] The compressive force F is optionally selected to be strong enough that the peak pressure acting on fibrous web 8 in the second, extended press nip 7 is at least 9 MPa, optionally at least 10 MPa, optionally at least 12 MPa. In order to achieve a quotient of average pressure and peak pressure in second press nip 7 that-according to the invention-is less than 0.5, with such a high peak pressure and a line load of at least 500 kN/m, press shoe 5 must be relatively long in order to provide a correspondingly large press zone length for fibrous web 8 in second press nip 7.

[0042] It turned out to be especially advantageous at such high peak pressures if shoe press shell 6 consists at least partially of polyurethane which is formed by the reaction of a prepolymer and a crosslinker 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 crosslinker component contains a C.sub.2-14 diol. For example, shoe press shell 6 can have a reinforcement structure consisting 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.sub.5-6 polycarbonate diol and 50 wt. % of a mixture of 1,4-phenylene diisocyanate (PPDI) and poly-tetramethylene ether glycol (PTMEG), and wherein the crosslinker includes poly-tetramethylene ether glycol (PTMEG) and 1,6-hexanediol or is optionally formed substantially therefrom.

[0043] First press 11, shown schematically in FIG. 1, can be and optionally is designed differently than second press 1. In particular, unlike second press 1, it can be designed such that a quotient of average pressure and peak pressure in the first press nip is greater than 0.5, and/or that the maximum linear load with which the first press can be operated is less than the maximum linear load with which the second press can be operated, and/or that the peak pressure that can be applied to the fibrous web in the first press nip is less than the peak pressure that can be applied to the fibrous web in the second press nip. Optionally, all three statements apply. In the press arrangement according to the invention, first press 11 serves in particular to sufficiently pre-solidify fibrous web 8 for traveling through second press 1 so that it is not crushed to an unacceptable state in spite of a high peak pressure in second press 1.

[0044] Fibrous web 8 optionally serves for the production of a packaging paper web or is such a packaging paper web. Moreover, the fibrous web consists of at least 20 wt. %, optionally at least 50 wt. %, of OCC fibers, which are characterized by an especially high resistance even to high peak pressures.

[0045] Press arrangement 1 according to the invention could theoretically also have more presses than only first press 11 and second press 1. However, second press 1 is optionally the last press in the press arrangement, that is, the last press before fibrous web 8 is transferred to a dryer section located downstream of the press arrangement. Only in exceptional cases may there be a smoothing press arranged after first press 1 and a downstream dryer section, however, said smoothing press does not have an extended press nip.

Component Identification Listing

[0046] 1 second press [0047] 2 shoe press roll [0048] 3 mating roll [0049] 4 standing yoke [0050] 5 press shoe [0051] 6 shoe press shell [0052] 7 second (extended) press nip [0053] 8 fibrous web [0054] 9 press felt [0055] 10 press arrangement [0056] 11 first press [0057] BR direction of travel [0058] F compressive force

[0059] While this invention has been described with respect to at least one embodiment, the

[0060] present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.