PRESS COVER FOR A SHOE PRESS OR TRANSPORT BELT WITH IMPROVED HYDROPHOBICITY

Abstract

A press cover for a press roll or a transport belt has at least one polyurethane-containing layer. The polyurethane is obtainable by reaction of i) a polyol component, ii) an isocyanate component, and iii) a component containing at least one crosslinker. The polyol component is composed of mutually different structural units having the general formula —O—R.sup.1—X—R.sup.2—O— in which all of R.sup.1 and R.sup.2 independently of one another are identical or different and are linear or branched C.sub.1-C.sub.20 alkylene groups. Groups X are identical or different and are selected from bond, O, C(O)—O, and O—C(O)—O. At least 70 wt % of the structural units meet the following criteria: a) at least 80% of X are O—C(O)—O and the remainder are O or C(O)—O, and b) the average chain length of R.sup.1 and R.sup.2 is 8 or more carbon atoms, and c) at least 50% of R.sup.1 and R.sup.2 are independently of one another a linear or branched C.sub.8-C.sub.12 alkylene group.

Claims

1-19. (canceled)

20. A press cover for a press roll or a transport belt, the press cover or the transport belt comprising: at least one polyurethane-containing layer, the polyurethane being obtained by a reaction, in one or more steps, of i) a polyol component; ii) an isocyanate component; and iii) a component containing at least one crosslinker; wherein said polyol component is composed to an extent of at least 90 wt % of one or more mutually different structural units according to the following general formula (I):
—O—R.sup.1—X—R.sup.2—O—  (I); wherein all R.sup.1 and R.sup.2 in the one or more different structural units according to the general formula (I) independently of one another are identical or different and are selected from linear C.sub.1-C.sub.20 alkylene groups and branched C.sub.1-C.sub.20 alkylene groups, and all of groups X in the one or more different structural units independently of one another are identical or different and are selected from the group consisting of bond, O, C(O)—O, and O—C(O)—O; and at least 70 wt % of the structural units according to the general formula (I) meet the following criteria: a) at least 80% of the groups X are O—C(O)—O and a remainder of the groups X are selected from O and C(O)—O; and b) an average chain length of all the groups R.sup.1 and R.sup.2 is 8 or more than 8 carbon atoms; and c) at least 50% of the groups R.sup.1 and R.sup.2 are independently of one another each a linear or branched C.sub.8-C.sub.12 alkylene group.

21. The press cover or transport belt according to claim 20, wherein the press roll is configured for a shoe press for dewatering a fibrous web, and the transport belt is configured for a machine for producing or treating a fibrous web.

22. The press cover or transport belt according to claim 20, wherein at least 80 wt % of the one or more mutually different structural units of the polyol component according to the general formula (I) meet in each case the criteria a) to c). at least 90 wt % and most preferably 95 wt % of the one or more . . . .

23. The press cover or transport belt according to claim 20, wherein all of the one or more mutually different structural units of the polyol component according to the general formula (I) meet the criteria a) to c).

24. The press cover or transport belt according to claim 20, wherein all the groups R.sup.1 and R.sup.2 of the one or more different structural units according to the general formula (I) independently of one another are identical or different and are selected from linear C.sub.4-C.sub.14 alkylene groups and branched C.sub.4-C.sub.14 alkylene groups. selected preferably from linear C.sub.6-C.sub.14 alkylene groups and branched C.sub.6-C.sub.14 alkylene groups.

25. The press cover or transport belt according to claim 20, wherein the polyol component of the polyurethane contains two, three or more mutually different structural units according to the general formula (I), where the group R.sup.1 and/or the group R.sup.2 of each of the two, three or more mutually different structural units according to the general formula (I) are different from every other of the two, three or more mutually different structural units according to the general formula (I).

26. The press cover or transport belt according to claim 20, wherein the average chain length of all the groups R.sup.1 and R.sup.2 of the one or more different structural units according to the general formula (I) is 8 to 15 carbon atoms. chain length is more than 8 to 15, preferably more than 8 to 12, and very preferably 9 to 11 carbon atoms.

27. The press cover or transport belt according to claim 20, wherein at least 70% of the groups R.sup.1 and R.sup.2 of the one or more different structural units according to the general formula (I) independently of one another are each a linear or branched C.sub.8-C.sub.12 alkylene group. at least 80%, preferably at least 90%, more preferably at least 95% of the one or more different structural units

28. The press cover or transport belt according to claim 27, wherein all of the groups R.sup.1 and R.sup.2 of the one or more different structural units according to the general formula (I) independently of one another are each a linear or branched C.sub.8-C.sub.12 alkylene group.

29. The press cover or transport belt according to claim 20, wherein at least a portion of the structural units according to the general formula (I) have the general formula (II):
—(O—R.sup.3—O—C(O))n.sup.1-O—  (II); wherein R.sup.3 is selected from linear C.sub.1-C.sub.20 alkylene groups and branched C.sub.1-C.sub.20 alkylene groups, and n.sup.1 is an integer of at least 3. n.sup.1 is an integer between 3 and 100

30. The press cover or transport belt according to claim 29, wherein n.sup.1 is an integer between 4 and 25.

31. The press cover or transport belt according to claim 29, wherein a weight-averaged molecular weight of the structural units according to the general formula (I) and/or of the general formula (II) is 500 to 10,000 g/mol. the molecular weight is preferably 800 to 4000 g/mol, and more preferably 1000 to 3000 g/mol

32. The press cover or transport belt according to claim 29, wherein the group R.sup.3 of the structural units according to the general formula (II) is selected from linear C.sub.6-C.sub.14 alkyl groups and branched C.sub.6-C.sub.14 alkyl groups or from linear C.sub.8-C.sub.12 alkyl groups and branched C.sub.8-C.sub.12 alkyl groups.

33. The press cover or transport belt according to claim 29, wherein at least 50 wt % of the structural units according to the general formula (I) have the general formula (II). preferably at least 70 wt %, more preferably at least 80 wt %, more preferably at least 90 wt %, of the structural units according to the general formula (I) have the general formula (II).

34. The press cover or transport belt according to claim 29, wherein all of the structural units according to the general formula (I) have the general formula (II).

35. The press cover or transport belt according to claim 29, wherein 80% to 99% of the structural units according to the general formula (I) have the general formula (II), while a remainder of the structural units have the general formula (I) in which the group X is O. preferably 85% to 95% of the structural units have the general formula (II)

36. The press cover or transport belt according to claim 20, wherein at least a portion of the structural units according to the general formula (I) have the general formula (III):
—(O—R.sup.4—O—C(O)—O—R.sup.5—O—C(O))n.sup.2-O—  (III); where R.sup.4 and R.sup.5 are different from one another and independently of one another are selected from linear C.sub.1-C.sub.20 alkylene groups and branched C.sub.1-C.sub.20 alkylene groups, and n.sup.2 is an integer of at least 2.

37. The press cover or transport belt according to claim 36, wherein n.sup.2 is an integer between 2 and 50. n.sup.2 is between 2 and 12.

38. The press cover or transport belt according to claim 36, wherein a weight-averaged molecular weight of the structural units according to the general formula (III) is 500 to 10,000 g/mol. the molecular weight is preferably 800 to 4,000 g/mol, and more preferably 1,000 to 3,000 g/mol.

39. The press cover or transport belt according to claim 36, wherein all of the groups R.sup.4 and R.sup.5 of the structural units according to the general formula (III) are selected from linear C.sub.6-C.sub.14 alkyl groups and branched C.sub.6-C.sub.14 alkyl groups or from linear and branched C.sub.8-C.sub.12 alkylene groups or from linear and branched C.sub.8-C.sub.12 alkylene groups.

40. The press cover or transport belt according to claim 20, wherein: said isocyanate component (ii) comprises one or more diisocyanate compounds selected from the group consisting of toluene 2,4 diisocyanates, methylenediphenyl isocyanates, hexamethylene diisocyanates, naphthalene 1,5-diisocyanates, isophorone diisocyanates, cyclohexane diisocyanates, p-phenylene diisocyanates, o-tolidine diisocyanate, 3,3′-dimethyl-4,4′-biphenyl diisocyanate, xylylene diisocyanate, bis(isocyanatomethyl)cyclohexane, and mixtures of two or more thereof; and said component containing the at least one crosslinker (iii) contains at least one crosslinker selected from the group consisting of amines, polyols, and any desired mixtures of two or more of the aforesaid compounds.

41. A shoe press for dewatering a fibrous web, the shoe press comprising a press roll configured for dewatering paper web, cardboard web, tissue web, or pulp web, said press roll having a press cover according to claim 20.

42. A machine for producing or treating a fibrous web, the machine comprising a transport belt according to claim 20.

Description

[0070] In these drawings

[0071] FIG. 1 shows a schematic view of a shoe press having a press cover according to one exemplary embodiment of the present invention, and

[0072] FIG. 2 shows a schematic view of a press section of a paper machine, comprising a shoe press and a transport belt, according to one exemplary embodiment of the present invention.

[0073] Represented in FIG. 1 is a shoe press 10 which comprises a shoe roll 12 and an opposing roll 14. While the opposing roll 14 consists of a rotating, cylindrical roll, the shoe roll 12 is composed of a shoe 16, a stationary yoke 18 carrying said shoe, and a press cover 20. The shoe 16 here is supported by the yoke 18 and pressed via hydraulic press elements (not represented) against the press cover 20 running around these elements. Because of the concave architecture of the shoe 16, a comparatively long press nip 22 is produced at its side opposite the opposing roll 14.

[0074] The shoe press 10 is suitable especially for dewatering fibrous webs 24, such as paper webs. In the operation of the shoe press, a fibrous web 24 is passed with one or two press felts 26, 26′ through the press nip 22, and the liquid which emerges from the fibrous web 24, owing to the pressure exerted on the fibrous web 24 in the press nip 22, said liquid containing not only water but also dissolved and undissolved compounds, such as fibers, fiber fragments, fillers and/or additives, for example, is temporarily taken up by the press felt or press felts 26, 26′ and by indentations (not represented) provided in the press cover surface. After having left the press nip 22, the liquid taken up by the press cover 20 is spun off from the press cover 20, after which the press cover 20 enters the press nip 22 again. Moreover, after leaving the press nip 22, the water taken up by the press felt 26, 26′ is removed with suction elements.

[0075] Owing to the press nip 22, which is comparatively long because of the concave architecture of the shoe 16 on its side opposite the opposing roll 14, the dewatering of the fibrous web 24 that is achieved with a shoe press 10 of this kind, in comparison to a press consisting of two rotating rolls, is considerably better, and so the subsequent thermal drying can be made shorter correspondingly. In this way the dewatering of the fibrous web 24 that is achieved is particularly gentle.

[0076] FIG. 2 shows a detail of a press portion of a paper machine, comprising a shoe press 10. In this case the shoe press 10, as in the case of the embodiment represented in FIG. 1 as well, comprises a shoe roll 12, having a press cover 20 and a press element or shoe 16, and an opposing roll 14, with a press nip being formed between the shoe 16 and the opposing roll 14. Moreover, this part of the paper machine comprises two suction rolls 28, 28′ and two deflection rolls 30, 30′. In the operation of the paper machine, a felt 26 guided through the suction rolls 28, 28′, and picking up the fibrous web 24 at the suction roll 28, is passed through the press nip. Moreover, below the felt 26 carrying the fibrous web 24, a transport belt or transfer belt 32, carried by the deflection rolls 30, 30′, is passed through the press nip, and in the press nip the fibrous web 24 is taken over from the felt 26 by the transfer belt 32 and is taken off out of the press nip via the deflection roll 30′. Because of the pressure exerted on the fibrous web 24 in the press nip, liquid emerges from the fibrous web, and contains not only water but also dissolved and undissolved compounds, such as fibers, fiber fragments, fillers, and/or additives, for example, and which is taken up temporarily by the felt 26 and by indentations present in the press cover surface. After having left the press nip, the liquid taken up by the press cover 20 is spun off from the press cover 20, after which the press cover 20 enters the press nip again. Moreover, after having left the press nip, the water taken up by the felt 26 is removed with suction elements provided on the suction roll 28′. Because of the press nip, which is comparatively long owing to the concave architecture of the shoe 16, a shoe press of this kind, in comparison to a press consisting of two rotating rolls, achieves substantially better dewatering of the fibrous web 24, and so the subsequent thermal drying can be made shorter correspondingly. In this way the dewatering of the fibrous web 24 that is achieved is particularly gentle.

LIST OF REFERENCE NUMERALS

[0077] 10 shoe press [0078] 12 shoe roll [0079] 14 opposing roll [0080] 16 shoe [0081] 18 stationary yoke [0082] 20 press cover [0083] 22 press nip [0084] 24 fibrous web [0085] 26, 26′ press felt [0086] 28, 28′ suction rolls [0087] 30, 30′ deflection rolls [0088] 32 transport belt/transfer belt