PRESS COVER, AND PROCESS FOR PRODUCTION OF SUCH A PRESS COVER

Abstract

A press cover has at least one polymer layer. The polymer layer includes, or is produced from, a polyurethane. The polyurethane has been formed from a prepolymer and a crosslinker. The prepolymer is a reaction product of phenylene 1,4-diisocyanate and at least one polyol. The crosslinker includes at least two components, namely, a first component having at least one diamine and a second component from the group of the carbonic esters.

Claims

1-16. (canceled)

17. A press cover, comprising: at least one polymer layer, said polymer layer containing a polyurethane or consisting of a polyurethane; said polyurethane having been formed from a prepolymer and a crosslinker; said prepolymer being a reaction product of phenylene 1,4-diisocyanate and at least one polyol; and said crosslinker including at least two components, namely, a first component with at least one diamine; and a second component from the group of the carbonic esters.

18. The press cover according to claim 17, wherein said first component is selected from the group consisting of 4,4-methylenebis, 4,4-diaminodicyclohexylmethane, and mixtures thereof.

19. The press cover according to claim 17, wherein said crosslinker contains between 25% and 95% by weight of said first component.

20. The press cover according to claim 19, wherein said crosslinker contains between 30% and 70% by weight of said first component.

21. The press cover according to claim 17, wherein said second component is or comprises propylene carbonate.

22. The press cover according to claim 17, wherein said crosslinker contains from 1% to 25% by weight of the second component.

23. The press cover according to claim 17, wherein said crosslinker further comprises a third component being a polyol.

24. The press cover according to claim 23, wherein said third component is a bifunctional polyol having a molecular weight of 1000 to 4000 g/mol.

25. The press cover according to claim 23, wherein said third component is selected from the group consisting of polyester polyol, polycaprolactone polyol, polyether polyols, polytetramethylene ether glycol, polypropylene glycol, polyethylene glycol, polyhexamethylene ether glycol, polycarbonate polyol, polyether carbonate polyol, polybutadiene polyol, perfluoropolyether polyol, silicone polyol, and mixtures thereof.

26. The press cover according to claim 23, wherein said crosslinker contains not more than 65% by weight of said third component.

27. The press cover according to claim 23, wherein said crosslinker includes a fourth component with a catalyst, and said fourth component is selected from tertiary amines, triethylamine, metal compounds, organometallic compounds, and mixtures thereof.

28. The press cover according to claim 27, wherein said fourth component is a 1,4-diazabicyclo octane, a triethylamine, a metallic or organometallic compound including or containing bismuth, mercury, aluminum, zirconium, iron, calcium, sodium, potassium, lead, tin, and/or titanium.

29. The press cover according to claim 27, wherein the crosslinker contains not more than 5% by weight of said fourth component.

30. The press cover according to claim 17, wherein said at least one polymer layer is a radially outermost polymer layer of the press cover.

31. The press cover according to claim 17, further comprising a reinforcing structure embedded into said at least one polymer layer.

32. The press cover according to claim 17, wherein said polyol in said prepolymer comprises a polyether polycarbonate polyol, a polycarbonate polyol, a polytetramethylene ether glycol, or mixtures thereof.

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

34. A shoe press for treatment of a fibrous material web, the shoe press comprising: a press roll and an opposing roll disposed to form a press nip therebetween, said press roll carrying a circumferential press cover according to claim 17.

35. A method of producing a press cover, the method comprising the following steps: a) providing at least one rotatably mounted winding mandrel; b) providing a crosslinker with at least two components, namely, a first component containing at least one diamine and a second component from the group of the carbonic esters; c) providing a reaction product of phenylene 1,4-diisocyanate and at least one polyol; d) mixing the reaction product and the crosslinker to prepare a polyurethane being a reaction product-crosslinker mixture; e) deploying the reaction product-crosslinker mixture on a surface of the winding mandrel to form at least one polymer layer of the press cover; f) curing the at least one polymer layer; and g) removing the press cover thus produced from the winding mandrel.

36. The method according to claim 35, which further comprises introducing of a reinforcing structure into the reaction product-crosslinker mixture before or after step e).

Description

[0040] The invention is elucidated in detail hereinafter with reference to the drawings without restriction of generality. The drawings show:

[0041] FIG. 1 a schematic side view as a partial section of a shoe press with a press cover in a working example of the present invention.

[0042] FIG. 2 a schematic diagram as an enlarged partial section of a working example of a press cover in a cross section through its longitudinal axis;

[0043] FIG. 3 a highly schematic diagram of the execution of the process of the invention in a side view of an apparatus for production of the press cover.

[0044] FIG. 1 shows a shoe press 10 which, in the present context, comprises a press roll of the invention, such as a shoe press roll 12, and an opposing roll 14. Shoe press roll 12 and opposing roll 14 are arranged parallel to one another with regard to their longitudinal axes. Together, they form or bound a nip 22.

[0045] While the opposing roll 14 here consists of a roll of cylindrical configuration that rotates about its longitudinal axis, the shoe press roll 12 is composed of a shoe 16, a stationary yoke 18 that bears it, and a press cover 20. Shoe 16 and yoke 18 are in a fixed arrangement in relation to the opposing roll 14 or the press cover 20. This means that they do not rotate. The shoe 16 is supported here by the yoke 18 and pressed onto the radially innermost surface of the press cover 20 that revolves relative thereto via hydraulic press elements (not shown). The press cover 20 that surrounds shoe 16 and yoke 18 in circumferential direction rotates here about its longitudinal axis in the opposite sense from the opposing roll 14. Owing to the concave configuration of the shoe 16 on its side facing the opposing roll 14, the result is a comparatively long nip 22.

[0046] The shoe press 10 is especially suitable for dewatering of fibrous material webs 24. In the operation of the shoe press, a fibrous material web 24 is guided through the press gap 22 with one or two press felts 26, 26. In the present case, there are exactly two press felts 26, 26 that accept the fibrous material web 24 between them in a sandwich-like manner. In the course of passage through the nip 22, the press felts 26, 26 exert a pressure indirectly on the fibrous material web 24 in the nip 22. This is accomplished in 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 into direct contact with the corresponding press felts 26, 26. The liquid exiting from the fibrous material web 24 is temporarily absorbed by the press felt(s) 26, 26 and any recesses provided in the press cover surface (not shown). After leaving the nip 22, the liquid absorbed by the depressions of the press cover 22 is spun off before the press cover 20 enters the press gap 22 again. In addition, the water absorbed by the press felt 26, 26 can be removed by suction elements after departure from the press gap 22.

[0047] FIG. 2 shows one possible embodiment of the invention in a cross section along the longitudinal axis 20 of the finished press cover 20 which is shown in part and not to scale. What can be seen is the (exactly) one polymer layer 20.1 of the press cover 20. As indicated by the dotted lines, it would be conceivable that the press cover 20 consists of multiple polymer layers arranged radially one on top of another. For example, exactly two polymer layers would be conceivable: a radially inner polymer layer (shown by dotted lines) 20.2 and a radially outermost polymer layer (shown by solid lines) 20.1. The multiple polymer layers could then be produced in accordance with the invention.

[0048] In the present case, a reinforcing structure 20 has been embedded into the at least one polymer layer 20.1. This is indicated by the hatched circles that may be textile fabrics or linear structures such as fibers. The reinforcing structure 20 has been completely embedded into the polymer layer 20.1. This means that the reinforcing structure 20 does not extend beyond the boundaries of the polymer layer 20.1 into which it has been embedded.

[0049] FIG. 3 shows, in a highly schematic side view, an apparatus for production of a press cover 20 of the invention. The apparatus is set up to execute the process of the invention for producing the press cover 20. The apparatus in the present context has exactly one cylindrical winding mandrel 4, with application here, for example, of a reinforcing structure 20 of a starting material 20 in spiral form to the radially outermost cover surface thereof.

[0050] The diagram shows an initial stage of the production process. In the present case, for this purpose, one end of the starting material 20 has been secured to a polymer disposed at the outer extent of the winding mandrel 4. Apart from the schematic diagram shown, it would also be possible for one end of the starting material 20 to lie on or have been applied to the winding mandrel 4, i.e. directly, without initial provision of a polymer between starting material 20 and winding mandrel 4. The starting material 20 here may be a textile fabric or linear structure.

[0051] The winding mandrel 4 is mounted so as to be rotatable about its longitudinal axis 20, which corresponds to the longitudinal axis of the press cover to be produced. Longitudinal axis 20 runs at right angles here into the plane of the drawing. A casting material, such as castable, curable elastomeric polymer, e.g. polyurethane, is applied via a conduit 5 through a casting nozzle 6 downward onto the radially outermost cover surface of the winding mandrel 4 or onto the starting material 20. Such a casting material may be chosen, for example, with respect to its pot life and viscosity such that it does not drip off the winding mandrel 4 in the course of casting. During this period, the winding mandrel 4 is rotated about its longitudinal axis in the direction of the arrow. Simultaneously with this rotation, the casting nozzle 6 is guided parallel to and along the longitudinal axis 20 relative to the winding mandrel 4 by means of a suitable guide (not shown in detail in FIG. 3). Simultaneously with the casting application of the casting material, the starting material 20 is unrolled and wound on the rotating winding mandrel 4 to give windings. It is possible here for the casting material to get through the starting material 20 through to the winding mandrel 4. The polymer in this example, after the curing step, forms a first, preferably elastomeric polymer layer 20.1 of the press cover, which is the radially innermost here, of which FIG. 3 shows just part.

[0052] The casting material exiting from the casting nozzle 6 is a mixture of a prepolymer and a crosslinker. The former is provided from a prepolymer vessel (not shown) in which it is stored or stirred up. The reaction product may comprise an isocyanate of the invention and a polyol. It may be present in the reaction product vessel (prepolymer vessel), for example, in the form of a prepolymer of the substances just mentioned.

[0053] The crosslinker may be provided in a crosslinker vessel. The crosslinker comprises at least one first component K1 of the invention and one second component K2 of the invention. The crosslinker may also comprise a third component K3 of the invention, comprising at least one polyol, and/or a fourth component of the invention, such as a catalyst. A fifth or further components would also be conceivable in principle. The crosslinker with its corresponding components may be stirred up directly in the crosslinker vessel. It is, however, also conceivable that the apparatus comprises a corresponding individual vessel for each of the components that is connected to the crosslinker vessel in a flow-conducting manner via conduits (not shown), in order to produce the crosslinker of the invention in the crosslinker vessel.

[0054] Prepolymer vessel and crosslinker vessel are assigned to the apparatus for production of a press cover 20. They are connected via conduits (likewise not shown) in a flow-conducting manner to a mixing chamber (not shown) connected upstream of the casting nozzle 6 in flow direction. The prepolymer/crosslinker mixture is thus produced upstream of and outside the casting nozzle 6, i.e. mixed in the mixing chamber. Irrespective of the production of the mixture, this is then applied to the surface of the winding mandrel 4 to form the at least one polymer layer 20.1 of the press cover 20.

[0055] By means of such a continuous casting operation, which is also known as rotary casting, a continuous press cover 20 that forms an intrinsically closed cylinder about its longitudinal axis 20 is thus gradually produced over the width of the winding mandrel 4, the internal circumference of which corresponds essentially to the outer circumference of the winding mandrel 4.

[0056] In principle, it would be conceivable to wind the starting material 20 onto more than one winding mandrel 4 shown in FIG. 3. For example, it would be possible to provide two winding mandrels that could be arranged in parallel at a distance from one another with regard to their longitudinal axes. Alternatively, it would also be conceivable to apply the polymer to the radially inner cover surface of the winding mandrel 4 as well, for example in the manner of spinning.

[0057] Irrespective of the embodiment addressed, the finished press cover 20 is finally removed from the at least one winding mandrel 4.

[0058] As shown in the figures, the press cover 20 takes the form according to the invention. This means that the single polymer layer shown therein has been produced (partly or completely) from a polyurethane. The polyurethane here has been formed from a prepolymer of the inventionwhich is a reaction product of at least one polyol with an isocyanateand a crosslinker. The crosslinker comprises, for example, the components mentioned at the outset. It may also include further components known to the person skilled in the art.

[0059] By means of the invention, a particularly high stability of the press cover 20 is achieved with regard to mechanical and dynamic properties such as stability, surface hardness, resistance to pressure, temperature and hydrolysis, and low swelling, and lead in operation to a prolonged lifetime thereof. At the same time, by means of the rotary casting process described in the figures, it is possible to produce virtually bubble-free press covers that enable polymer layers of thickness up to 40 mm in one coating pass.

[0060] Although this is not shown in the figures, the reinforcing structure 20 of the at least one polymer layer 20.1, 20.2 may also have been constructed from multiple starting materials 20 that have been placed one on top of another in radial direction and each run in longitudinal axis direction and in circumferential direction of the press cover 20.