PRESS COVER, USE THEREOF, AND PRESS ROLL, SHOE PRESS AND USE OF A REINFORCING THREAD IN A PRESS COVER

Abstract

A press cover contains at least one polymer layer in which a reinforcing structure is embedded. The reinforcing structure contains at least one reinforcing thread, wherein the material of the reinforcing structure and that of the at least one polymer layer are selected such that the visible light transmittances thereof differ from each other.

Claims

1-16. (canceled)

17. A press cover, comprising: at least one polymer layer; and a reinforcing structure embedded in said at least one polymer layer, said reinforcing structure having at least one reinforcing thread, wherein a material of said reinforcing structure and that of said at least one polymer layer are chosen in such a way that visible light transmittances thereof differ from one another.

18. The press cover according to claim 17, wherein a transmittance of said material of said at least one polymer layer is higher than a transmittance of said reinforcing structure.

19. The press cover according to claim 17, wherein a transmittance of said material of said at least one polymer layer is between 50% and 90%.

20. The press cover according to claim 17, wherein: said at least one polymer layer is produced from polyurethane or contains said polyurethane; and said at least one reinforcing thread is produced from a polymer or contains said polymer, said polymer is selected from the group consisting of a polyester, polyethylene naphthalate and polyamide.

21. The press cover according to claim 17, wherein said at least one polymer layer is uncolored.

22. The press cover according to claim 17, wherein said at least one reinforcing thread is provided as a longitudinal thread, which extends in a longitudinal direction of the press cover.

23. The press cover according to claim 22, wherein said at least one reinforcing thread is one of a plurality of reinforcing threads provided as longitudinal threads which, extend in the longitudinal direction of the press cover, and are disposed parallel to one another at a distance over a circumference of the press cover.

24. The press cover according to claim 23, further comprising at least one further reinforcing thread as a circumferential thread.

25. The press cover according to claim 24, wherein said reinforcing threads configured as said longitudinal threads and said at least one further reinforcing thread configured as said circumferential thread form a laid fabric with one another.

26. The press cover according to claim 25, wherein as viewed in a radial direction of the press cover, said longitudinal threads are spaced apart in the radial direction relative to said circumferential thread at crossing points.

27. The press cover according to claim 17, wherein said at least one polymer layer is one of a plurality of polymer layers, said at least one polymer layer, viewed in relation to a longitudinal axis of the press cover, is a radially inner or innermost polymer layer and, a further polymer layer of said polymer layers is a radially outermost polymer layer of said polymer layers, viewed in relation to the longitudinal axis of the press cover.

28. The press cover according to claim 27, wherein said plurality of polymer layers is exactly two polymer layers, and said radially inner polymer layer is at a same time the radially innermost polymer layer of the press cover.

29. The press cover according to claim 18, wherein the transmittance of said material of said at least one polymer layer is 1.1. to 1.5 times higher than the transmittance of said reinforcing structure.

30. The press cover according to claim 19, wherein the transmittance of said material of said at least one polymer layer is between 50% and 75%.

31. The press cover according to claim 24, wherein said circumferential thread extends in a form of a helix in a circumferential direction of the press cover within the at least one polymer layer.

32. The press cover according to claim 25, wherein said reinforcing threads configured as said longitudinal threads and said at least one further reinforcing thread configured as said circumferential thread form said laid fabric in such a way that said longitudinal threads are disposed radially within said circumferential thread, viewed in relation to a longitudinal axis of the press cover.

33. A press roll for a shoe press for treating a fibrous web, the press roll comprising: at least one press cover according to claim 17.

34. A shoe press for treating a fibrous web, the shoe press comprising: a press roll and an opposing roll which together form or delimit a nip, wherein said press roll containing a circulating press cover, said circulating press cover being formed according to claim 17.

35. A method of using a press cover, which comprises the steps of: providing the press cover according to claim 17 for a press for treating a fibrous web.

36. A method of building a structure, which comprises the steps of: disposing at least one reinforcing thread, functioning as a reinforcing structure, in a press cover, the press cover having at least one polymer layer in which the reinforcing structure is embedded, wherein a material of the reinforcing structure and that of the at least one polymer layer are chosen in such a way that visible light transmittances thereof differ from one another.

Description

[0033] The invention will be explained in more detail below with reference to the drawings without restricting the generality. In the drawings:

[0034] FIG. 1 shows a partly sectioned, schematic side according to an exemplary embodiment of the present invention;

[0035] FIGS. 2a & 2b show embodiments of a press cover, each in a section viewed through its longitudinal axis;

[0036] FIG. 3 shows a highly schematic illustration of a device for producing the press cover in a side view.

[0037] FIG. 1 illustrates a partly sectioned schematic side view of a shoe press 10 which, in the present case, comprises a press roll according to the invention, such as a shoe press roll 12, and an opposing roll 14. The shoe press roll 12 and opposing roll 14 are arranged parallel to each other with respect to their longitudinal axes. Together they form a nip 22 or delimit such a one.

[0038] While the opposing roll 14 here comprises a cylindrically configured roll rotating about its longitudinal axis, the shoe press roll 12 is assembled from a shoe 16, a stationary yoke 18 carrying the latter and a press cover 20. The shoe 16 and yoke 18 are arranged to be stationary in relation to the opposing roll 14 and the press cover 20. This means that they do not rotate. The shoe 16 is supported by the yoke 18 and, via hydraulic press elements not illustrated, is pressed against the radially innermost surface of the press cover 20 circulating relative thereto. The press cover 20, surrounds the shoe 16 and the yoke 18 in the circumferential direction and in the process rotates about its longitudinal axis in the opposite direction of rotation to the opposing roll 14. Because of the concave configuration of the shoe 16 on its side facing the opposing roll 14, the result is a comparatively long nip 22.

[0039] The shoe press 10 is suitable in particular for dewatering fibrous webs 24. During the operation of the shoe press, a fibrous web 24 is guided through the press nip 22 with one or two press felts 26, 26′. In the present case, there are exactly two press felts 26, 26′, which accommodate the fibrous web 24 between them in the manner of a sandwich. During the passage through the nip 22, a pressure is exerted indirectly on the fibrous web 24 by the press felts 26, 26′ in the nip 22. This takes place as a result of the fact that the radially outermost surface of the opposing roll 14, on the one hand, and the radially outermost surface of the press cover 20 come directly into contact with the corresponding press felts 26, 26′. The liquid escaping from the fibrous web 24 is picked up temporarily by the press felt or press felts 26, 26′ and any depressions (not illustrated) provided in the press cover surface. After leaving the nip 22, the liquid picked up by the depressions of the press cover 20 is thrown off before the press cover 20 enters the press nip 22 again. In addition, the water picked up by the press felt 26, 26′ can be removed by suction elements after leaving the press nip 22.

[0040] In a further embodiment of the invention, not illustrated in the figures, the press felts 26, 26′ can be omitted. In such a case, the fibrous web 24 is in direct contact on one side with the press cover 20 and on the other side with the opposing roll 14, which together form a press nip. Said opposing roll 14 can be designed as a heated drying cylinder.

[0041] As illustrated in the following figures, the press cover illustrated in FIG. 1 can be designed according to the invention.

[0042] In FIGS. 2a and 2b, different embodiments of the invention are illustrated in a cross section, not to scale and partly illustrated, through the longitudinal axis 20′ of the finished press cover 20. The distance of the longitudinal axis 20′ to the radially innermost surface of the corresponding polymer layer of the press cover 20 is likewise illustrated not to scale.

[0043] According to FIG. 2a, exactly two polymer layers are provided, namely a first 20.1 and a second 20.2. In the present case, the first polymer layer 20.1 is at the same time the radially outermost polymer layer of the press cover 20. The two polymer layers 20.1, 20.2 adjoin each other directly as viewed in the radial direction, that is to say there is no intermediate layer between these two.

[0044] As illustrated, a reinforcing structure 20″ can be provided in the second polymer layer 20.2. In the present case, this is embedded completely in the polymer layer 20.2. This is indicated by the hatched circles, which can be textile two-dimensional or linear structures such as fibers. This means that the reinforcing structure 20″ does not extend beyond the limits of the polymer layer 20.2.

[0045] Here, the reinforcing structure 20″ comprises a plurality of reinforcing threads 21 serving as longitudinal threads 21.1. These are arranged in the longitudinal direction of the press cover 20, extending parallel to one another at a distance over its circumference. In addition, here at least one further reinforcing thread 21 is provided as a circumferential thread 21.2, which preferably extends in the form of a helix in the circumferential direction of the press cover within the same polymer layer 20.1, 20.2, 20.3 in which the longitudinal threads 21.1 are also arranged. The longitudinal threads 21.1 and the circumferential thread 21.2 form a laid fabric with one another, specifically in such a way that the longitudinal threads 21.1 are arranged radially within the at least one circumferential thread 21.2—viewed in relation to the longitudinal axis 20′ of the press cover 20.

[0046] In the present case, the first and a second polymer layer 20.1, 20.2 are produced from a polyurethane. This can be obtained, for example, from a prepolymer and a cross-linker. The respective prepolymer itself can be obtained by reacting an isocyanate with a polyol.

[0047] FIG. 2b shows, in a modification relative to FIG. 2a, a three-layer press cover. This comprises a—here radially outermost—first polymer layer 20.1, a radially innermost, third polymer layer 20.3 and a second polymer layer 20.2 arranged between these two in the manner of a sandwich. The arrangement relates—as also in the illustration of FIG. 2a—starting from the longitudinal axis 20′ of the press cover 20 viewed in its radial direction. In the present case, a (single) reinforcing structure 20″ is provided only in the second polymer layer 20.2. Of course, this could also be different, so that, alternatively or additionally, such a reinforcing structure 20″ could also be arranged in the first polymer layer 20.1 and/or the third polymer layer 20.3. That which was explained in relation to the reinforcing structure 20″ in FIG. 2a also applies analogously.

[0048] It has transpired that the advantages according to the invention can be implemented particularly well if the polyurethane of the at least one polymer layer 20.1, 20.2, 20.3 or all the polymer layers is chosen in such a way that it is more transparent than the material of the reinforcing structure 20″. Therefore, in other words, that the material of the reinforcing structure 20″ and that of the at least one polymer layer 20.1, 20.2, 20.3 are chosen in such a way that their respective transmittance for visible light differs from one another and, preferably, the transmittance of the material of the at least one polymer layer 20.1, 20.2 exceeds the transmittance of the material of the reinforcing structure 20″.

[0049] FIG. 3 shows a highly schematic side view of a device for producing a press cover 20 according to the invention. In the present case, the device has exactly one cylindrical mandrel 4, wherein here, for example, a starting material 20″′ is applied spirally to its radially outermost lateral surface. After it has been embedded in the polymer, the starting material 20″′ forms the reinforcing structure 20″ of the finished press cover 20 according to the invention.

[0050] The illustration shows a starting stage of the production process. In the present case, for this purpose one end of the starting material 20″′ is fixed to a polymer, which is arranged on the outer circumference of the mandrel 4. Apart from the schematic illustration shown, one end of the starting material 20″′ could also be laid or applied directly to the mandrel 4 without a polymer initially being provided between the starting material 20″′ and the mandrel 4. The starting material 20″′ can be a textile two-dimensional structure or linear structure.

[0051] The mandrel 4 is mounted such that it can rotate about its longitudinal axis 20′, which corresponds to the longitudinal axis of the press cover to be produced. The longitudinal axis 20′ here extends perpendicularly into the drawing plane. Via a line 5, a casting material, such as castable, curable elastomeric polymer, for example polyurethane, is discharged through a casting nozzle 6 from above onto the radially outermost lateral surface of the mandrel 4 or onto the starting material 20″′. Such a casting material can be chosen, for example with regard to its pot time and viscosity, in such a way that it does not drip off the mandrel 4 during the casting. During this, the mandrel 4 is rotated about its longitudinal axis in the direction of the arrow. At the same time as this rotation, the casting nozzle 6 is guided along on the mandrel 4 along the longitudinal axis 20′ and parallel to the latter via a suitable guide, not further illustrated in FIG. 3. At the same time as the casting material is poured on, the starting material 20″′ is rolled onto the rotating mandrel 4 to form spirals. In the process, casting material can pass through the starting material 20″′ as far as the mandrel 4. In this example, after the curing step the polymer forms a radially innermost and preferably elastomeric polymer layer, which corresponds to the polymer layer 20.2 of the press cover from FIG. 2a, of which only part is shown in FIG. 3.

[0052] The casting material emerging from the casting nozzle 6 in the present case is a mixture of a prepolymer and a cross-linker. The first is provided from a prepolymer container, not shown, in which it is stored or stirred. The prepolymer is the reaction product of an isocyanate according to the invention and a polyol. In the prepolymer container, it can be present, for example, in the form of a prepolymer made of the materials just mentioned.

[0053] The cross-linker can be provided in a cross-linker container.

[0054] The prepolymer container and cross-linker container are assigned to the device for producing a press cover 20. They are connected in a flow-conducting manner to a mixing chamber (not illustrated) connected upstream of the casting nozzle 6 in the flow direction via lines, likewise not illustrated. The prepolymer-cross-linker mixture is therefore produced upstream and outside the casting nozzle 6, that is to say mixed in the mixing chamber. Irrespective of the production of the mixture, this is then applied to the surface of the mandrel 4 to form the at least one polymer layer of the press cover 20.

[0055] In principle, it would be conceivable that two or more casting nozzles 6 could be provided. These could be connected via appropriate lines to separate prepolymer and cross-linker containers, in order also to supply different polymers to the plurality of casting nozzles 6 independently of one another. The casting nozzles 6 could then be arranged along the longitudinal axis of the press cover 20 at a distance from one another in order to produce a plurality of polymer layers 20.1, 20.2, 20.3 simultaneously in one casting by the simultaneous discharge of the polymer out of the casting nozzle 6.

[0056] By means of such a continuous casting operation, which is also known as rotational casting, an endless, intrinsically closed cylindrical press cover 20, the inner circumference of which corresponds closely to the outer circumference of the mandrel 4, is therefore produced gradually over the width of the mandrel 4.

[0057] In principle, it would be conceivable to wind the starting material 20″′ onto more than the one mandrel 4 shown in FIG. 3. For example, two mandrels could be provided, which could be arranged parallel to one another at a distance with regard to their longitudinal axes. Alternatively, it would also be conceivable to apply the polymer also to the radially inner lateral surface of the mandrel 4, for example in the manner of centrifuging. Irrespective of the embodiment mentioned, the finished press cover 20 is finally taken off the at least one mandrel 4.

[0058] As illustrated in FIG. 3, the press cover 20 is designed according to the invention.

[0059] Although this is not illustrated in the figures, the reinforcing structure 20″ of the at least one polymer layer 20.1, 20.2 could also be built up from a plurality of starting materials 20″′ laid over one another in the radial direction, each extending in the longitudinal axial direction and in the circumferential direction of the press cover 20.