EP4225990A1

EP4225990A1 - Roller cover or roller with improved hydrophobicity

Info

Publication number: EP4225990A1
Application number: EP21755432.8A
Authority: EP
Inventors: Delphine DELMAS; Uwe Matuschczyk; Michael Wokurek
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2020-10-05
Filing date: 2021-08-03
Publication date: 2023-08-16
Also published as: WO2022073671A1; DE102020126003A1

Abstract

The invention relates to a roller cover for a roller. The roller cover comprises at least one polyurethane-containing layer, and the polyurethane can be obtained in one or more steps by reacting i) a polyol component, ii) an isocyanate component, and iii) a component containing at least one cross-linking agent, wherein at least 90% by weight of the polyol component of the polyurethane consists of one or more different structural units of the following general formula (I), -O-R¹-X-R²-O- (I), in which each R1 and R2 of the one or more different structural units according to the general formula (I) is the same or different independently of one another and is selected from linear C₁-C₂₀ alkylene groups and branched C₁-C₂₀ alkalene groups, and each of the groups X of the one or more different structural units is the same or different independently of one another and is selected from the bond O, C(O)-O, and O-C(O)-O. The invention is characterized in that at least 70% by weight of the structural units according to the general formula (I) satisfy the following criteria: a) at least 80% of the groups X are O-C(O)-O and the rest of the groups X are selected from O and C(O)-O, b) the average chain length of all of the groups R¹ and R² equals 8 or more than 8 carbon atoms, and c) at least 50% of the groups R¹ and R² are a linear or branched C₈-C₁₂ alkylene group independently of one another.

Description

Fabric cover or roller with improved hydrophobicity

The present invention relates to a roll cover for a roll, in particular for a machine for producing or treating a fibrous web according to the preamble of claim 1, and a roll with such a roll cover.

The invention also relates to a press cover for a press roll, in particular for a press roll of a shoe press for dewatering a fibrous web, in particular a paper, cardboard, tissue or cellulose web, or conveyor belt, in particular for a machine for producing or treating a fibrous web, in particular paper -, Cardboard or tissue machine, wherein the press cover or the conveyor belt comprises at least one layer containing polyurethane. Furthermore, the present invention relates to a method for producing such a press cover or conveyor belt, a corresponding press cover and a corresponding conveyor belt.

In the manufacture of paper, rolls and in particular rolls with an elastic surface are used in a large number of process steps. The latter are used, for example, in sheet formation in the wire section of the paper machine, in dewatering in the press section of the paper machine and in coating, drying and calendering in the end section of the paper machine. In such a case, the radially outermost surface of such a roll is in almost constant contact with the paper web in some positions in the paper machine. Such rolls are therefore exposed to high mechanical loads during operation of the paper machine. Apart from that, these must have a low susceptibility to cracking, high impact strength, good tear resistance, high tear propagation resistance, high compressive strength and sufficiently high hardness. At the same time, the rollers be sufficiently resistant to abrasion and wear in order to have the longest possible service life.

In order to give the surfaces of rollers the performance properties required for their use, rollers are usually provided on their surface with a roller cover arranged on a roller core, the material of which is formulated with regard to the required performance properties.

Such a roll cover often comprises one or more layers which comprise or consist of a polyurethane. An example of this is described in EP 3491 187.

Press rolls are used in a large number of presses and, for example, in the form of shoe rolls in shoe presses, which in turn are used in particular for dewatering fibrous webs, such as paper webs. Such shoe presses are constructed from a shoe roll and a backing roll with a press nip formed between them. Shoe rolls consist of a stationary, ie non-rotating, pressing element, namely the shoe, and a flexible press jacket running around the shoe. The shoe is usually supported by a yoke that carries it and is pressed against the press jacket running around it by means of hydraulic pressing elements. An oil film is usually built up between the shoe and the press sleeve for lubrication. Due to the concave design of the shoe on its side opposite the backing roll, there is a comparatively long press nip, which is about 20 times longer than that of conventional presses consisting of two rotating rolls. During the operation of the shoe press, a fibrous web is guided through the press nip together with one or two press felt(s), the fibrous web being pressed out of the fibrous web due to the pressure exerted on the fibrous web in the press nip escaping liquid, which, in addition to water, contains dissolved and undissolved compounds, such as fibers, fiber fragments, fillers and/or additives, is temporarily absorbed by the press felt and by depressions provided in the press jacket surface. After leaving the press nip, the liquid taken up by the press jacket is thrown off the press jacket before the press jacket re-enters the press nip. In addition, the water absorbed by the press felt is removed with suction elements after leaving the press nip. Due to the relatively long press nip due to the concave design of the shoe, much better dewatering of the fibrous web is achieved with such a shoe press compared to a press consisting of two rotating rollers, so that the subsequent thermal drying can be correspondingly shorter. In this way, a particularly gentle dewatering of the fibrous web is achieved.

A press cover of such a shoe press ideally has to meet a large number of requirements in order to achieve optimum results. On the one hand, such a press jacket must be flexible enough to be able to be guided around the shoe. At the same time, the press cover must be sufficiently stiff so that it is not deformed and deformed too much under the press load prevailing in the press nip. In addition, a press cover must have high wear resistance, good abrasion resistance, high crack resistance, good crack growth resistance and high resistance to chemicals, such as in particular water, oil, acids, bases and solvents. In particular, a press sleeve must be characterized by very high hydrophobicity on the paper side.

In paper, board or tissue machines in particular, conveyor belts are used which have to meet at least some of the aforementioned requirements and, in particular, have very high hydrophobicity on the paper side must have. For example, such conveyor belts are used in the press section of such machines in order to transport a fibrous web through the press nip and then to a transfer point where the fibrous web is transferred to the subsequent drying section. Such conveyor belts generally comprise at least one polymer coating which provides the paper side of the belt and in which a load-bearing textile fabric is embedded.

In order to at least partially meet these diverse requirements, such press sleeves are usually made of fiber-reinforced polyurethane, ie a composite material in which a fiber fabric or fiber fabric is embedded in a matrix of crosslinked polyurethane. Both single-layer and corresponding multi-layer press jackets are known.

A press jacket for a shoe press is known from EP 2 284 314 A1, which is composed of one or more layers of crosslinked polyurethane in which fiber fabric is embedded. The crosslinked polyurethane is the reaction product of a prepolymer which has been prepared from an isocyanate component containing 55 to 100 mol% p-phenylene diisocyanate and a polyol, and a crosslinking component which contains 65 to 100 mol% of one or more specific polyamines . The polyol is preferably polytetramethylene glycol.

A press cover for a shoe press or a conveyor belt is known from EP 2 737 124 B1, the press cover or the conveyor belt comprising at least one layer containing crosslinked polyurethane, the crosslinked polyurethane being obtainable by a process in which a prepolymer which is the reaction product of an isocyanate component containing methylenediphenyl diisocyanate and a polyol component containing a polycarbonate polyol, is reacted with a crosslinker component which contains at least one polyol with a weight average molecular weight of more than 1000 g/mol. Polycarbonate polyol based on hexanediol is used, for example, as the polycarbonate polyol.

Although the above roll covers and press covers have good mechanical properties and high resistance to water and chemicals, their hydrophobicity is in need of improvement, particularly on the paper side.

The object of the present invention is therefore to provide a roll cover and a press cover or a conveyor belt, wherein the roll cover or the press cover or the conveyor belt has improved hydrophobicity, but is nevertheless characterized by excellent wear resistance, excellent abrasion resistance, excellent resistance to cracking, excellent resistance to crack growth, low swelling, high resistance to chemicals, such as in particular water, oil, acids, bases and solvents, excellent flexibility and excellent rigidity.

According to the invention, this object is achieved by providing a roll cover for a roll, in particular for a machine for producing or treating a fibrous web, in particular a paper, board or tissue machine, the roll cover comprising at least one layer containing polyurethane, the polyurethane reacting in one or more steps i) a polyol component, ii) an isocyanate component and iii) a component containing at least one crosslinker is obtainable, the polyol component of the polyurethane being at least 90% by weight of one or is composed of several different structural units according to the following general formula (I),

-OR ¹ -XR ² -O- (I), wherein all R ¹ and R ² of one or more different structural units according to the general formula (I) are independently identical or different and are selected from linear Ci-C2o-alkylene groups and branched Ci-C2o-alkylene groups and all X groups of one or more different structural units are independently the same or different and are selected from bond, O, C(0)-0 and OC(O)-O, with at least 70% by weight % of the structural units according to the general formula (I) meet the following criteria: a) at least 80% of the groups X are 0-C(0)-0 and the remainder of the groups X are selected from 0 and C(0)-0 and b) the average chain length of all groups R ¹ and R ² is 8 or more than 8 carbon atoms and c) at least 50% of the groups R ¹ and R ² are each independently a linear or branched C8-Ci2-alkylene group.

With regard to the press cover or the conveyor belt, this object is achieved by providing a press cover for a press roll, in particular for a press roll of a shoe press for dewatering a fibrous web, in particular a paper, cardboard, tissue or cellulose web, or a conveyor belt, in particular for a machine for the production or treatment of a fibrous web, in particular a paper, board or tissue machine, wherein the press cover or the conveyor belt comprises at least one layer containing polyurethane, the polyurethane by reacting in one or more steps i) a polyol component, ii) a isocyanate component and iii) a component containing at least one crosslinker, wherein at least 90% by weight of the polyol component of the polyurethane is composed of one or more structural units of the following general formula (I), which differ from one another,

-OR ¹ -XR ² -O- (I), wherein all R ¹ and R ² of one or more different structural units according to the general formula (I) are independently identical or different and are selected from linear Ci-C2o-alkylene groups and branched Ci-C2o-alkylene groups and all X groups of one or more different structural units are independently the same or different and are selected from bond, 0, C(0)-0 and OC(O)-O, with at least 70% by weight % of the structural units according to the general formula (I) meet the following criteria: a) at least 80% of the groups X are 0-C(0)-0 and the remainder of the groups X are selected from 0 and C(0)-0 and b) the average chain length of all groups R ¹ and R ² is 8 or more than 8 carbon atoms and c) at least 50% of the groups R ¹ and R ² are each independently a linear or branched C8-Ci2-alkylene group.

Surprisingly, it was found in the context of the present invention that a layer made of polyurethane, the polyol component of which is composed of at least 90% by weight of one or more different structural units according to the general formula (I), i.e. of polyol groups, of which at least 70 Wt .-% meet the criteria a) to c), has an improved hydrophobicity in particular on their surfaces. In addition, it was surprising that such a layer of polyurethane nevertheless by a excellent wear resistance, excellent abrasion resistance, excellent crack resistance, excellent crack growth resistance, low swelling, high resistance to chemicals, such as in particular water, oil, acids, bases and solvents, excellent flexibility and excellent rigidity.

According to the present invention, “composed of one or more different” structural units according to the general formula (I) means that the polyol component of the polyurethane contains a large number of such structural units according to the general formula (I), the individual structural units being identical in each case may or may differ from each other. Consequently, this formulation also includes, in particular, polyurethanes which each contain a large number of, for example, three different structural units, each of the three different structural units having the general formula (I), but each of the three different structural units differing from each of the other two. For example, in one of the three different structural units according to the general formula (I), the group X can be a carbonate group, the group R ¹ can be a nonylene group and the group R ² can be a decylene group, in another of the three different structural units according to the general formula (I ) the group X is a carbonate group, the group R ¹ is a nonylene group and the group R ² is a dodecylene group and in the third of the three different structural units according to the general formula (I) the group X can be a carbonate group and the groups R ¹ and R ² each be a nonylene group. In addition, “composed of one or more mutually different structural units according to the general formula (I)” does not mean that the individual structural units are directly connected to one another. Rather, they can be separated from one another by one or more atoms in a molecular chain. In the context of the present invention, an alkylene group is understood to be a CnH2n hydrocarbon group, ie a hydrocarbon group with two terminal radicals.

For the purposes of the present invention, polyols are all alcohols which have at least two hydroxyl groups and preferably have a weight-average molecular weight of 500 to 10,000 g/mol. According to the present invention, preferred polyols are diols and in particular those with the aforementioned molecular weight, ie long-chain polyols, ie no short-chain polyols, such as 1,4-butanediol.

The polyol component of the polyurethane is composed to an extent of at least 90% by weight of one or more different structural units of the general formula (I), ie polyol groups. The polyol component of the polyurethane is preferably composed of 95 to 100% by weight of one or more different structural units of the general formula (I). The polyol groups therefore form a main component of the polyurethane and not just a small component.

The polyurethane according to the invention can, but does not have to, be a pourable polyurethane and/or a thermoplastic polyurethane. This can have been obtained, for example, from at least one prepolymer and at least one crosslinking agent or by reacting the polyol component, the isocyanate component and the crosslinking agent in one step. If the polyurethane has been obtained from at least one prepolymer and at least one crosslinker, then the polyol structural units in these polyurethanes are necessarily contained in the prepolymer part and can, but do not have to, also be contained in the crosslinker. According to the invention, at least 70% by weight of the structural units of the general formula (I) meet the three aforementioned criteria a) to c). It is therefore essential that the majority of the polyol structural units contained in the polyurethane according to the general formula (I) meet the three aforementioned criteria a) to c), it being harmless if a minor number of the polyol structural units do not or not fully meet these criteria . However, good results are obtained in particular if at least 80% by weight, more preferably at least 90% by weight, very preferably at least 95% by weight and most preferably all of the one or more different structural units of the general formula (I ) meet the criteria a) to c) respectively.

In a further development of the inventive concept, it is proposed that all groups R ¹ and R ² of at least 70% by weight of one or more different structural units according to the general formula (I) which meet criteria a) to c), and preferably also those optionally up to 30% by weight of other structural units according to the general formula (I) which do not or at least do not fully meet criteria a) to c), are independently identical or different and are selected from linear C4-Ci4- Alkylene groups and branched C4-Ci4-alkylene groups and particularly preferably from linear Ce-Cu-alkylene groups and branched Ce-Cu-alkylene groups. Preferably, at least 50%, preferably at least 80%, particularly preferably at least 90% of at least 70% by weight of the structural units according to the general formula (I) which meet criteria a) to c) are and most preferably all of the groups R ¹ and R ² are each independently a linear or branched C8-Ci2-alkylene group.

According to a particularly preferred embodiment of the present invention, at least 90%, more preferably at least 95%, most preferably at least 99% and most preferably all of the groups X at least 70% by weight of one or more different structural units according to general formula (I) which meet criteria a) to c), and preferably all inclusive of at most less than 30% by weight of one or more different structural units according to general formula (I) which do not or not fully meet the criteria a) to c), carbonate groups OC(O)-O. In this embodiment, the degree of hydrophobicity is determined in particular by the length of the groups R ¹ and R ² . In this embodiment, however, the degree of crystallinity can be comparatively high.

For applications in which a reduced degree of crystallinity is desired, it is proposed in a further development of the inventive idea that the polyurethane be used in addition to polycarbonate polyol groups, i.e. in addition to structural units according to general formula (I), in which the group X is 0-C(0)-0 , Contains other polyol groups, such as in particular polyether polyol groups, i.e. structural units according to the general formula (I), in which all the groups X are O, or polyether polycarbonate groups, i.e. structural units according to the general formula (I), in which some of the groups X are O and others of the groups X are 0-C(0)-0. Examples of suitable polyether polyols are, for example, polytetramethylene glycol and polypropylene glycol. In this embodiment, preferably 80% to 99% and preferably 85 to 95% of the groups X of the one or more different structural units according to the general formula (I) have as group X 0-C(0)-0 and the remainder to 100% of X groups of one or more different structural units according to the general formula (I) as X O group.

A further possibility of reducing the degree of crystallinity of the polyurethane is to provide at least some of the groups R ¹ and R ² in the structural units according to general formula (I) as branched alkylene groups and in particular as branched Cs-12-alkylene groups. In this embodiment, preferably more than 1 to 30% of the groups R ¹ and R ² are the Structural units according to the general formula (I) are branched alkylene groups, whereas the remainder to 100% of the groups R ¹ and R ² are linear alkylene groups.

In addition, it was recognized within the scope of the present invention that the degree of crystallinity of the polyurethane can be reduced if the structural units of the general formula (I) contain groups R ¹ which have a different carbon chain length than the groups R ² .

According to criterion b), the average chain length of all groups R ¹ and R ² in the at least 70% by weight of one or more different structural units according to the general formula (I) which meet criteria a) to c) is 8 or more than 8 carbon atoms. Average carbon chain length means the arithmetic mean, ie the sum of the carbon chain lengths of all groups R ¹ and R ² of these structural units divided by the total number of groups R ¹ and R ² of these structural units. However, the average chain length of all groups R ¹ and R ² should not be too great either. Good results are obtained in particular when the average chain length of all groups R ¹ and R ² of at least 70% by weight of one or more different structural units according to the general formula (I) which meet criteria a) to c) is 8 to 15 , more preferably more than 8 to 12 and most preferably 9 to 11.

The above conditions preferably apply not only to the at least 70% by weight of one or more different structural units of the general formula (I) which meet criteria a) to c), but preferably to all structural units of the general formula (I) , i.e. also for those at most less than 30% by weight, which do not or not fully meet criteria a) to c). Therefore it is preferred that the average Chain length of all groups R ¹ and R ² of all structural units according to the general formula (I) 8 or more than 8 carbon atoms, more preferably 8 to 15 or more than 8 to 15, particularly preferably more than 8 to 12 and very particularly preferably 9 to 11 amounts to.

According to criterion c), at least 50% of the groups R ¹ and R ² in the at least 70% by weight of one or more different structural units according to the general formula (I) which meet criteria a) to c) are independent of one another each a linear or branched C8-C12 alkylene group. Good results are obtained in particular when at least 70%, more preferably at least 80%, more preferably at least 90%, most preferably at least 95% and most preferably all of the groups R ¹ and R ² of the one or more different structural units according to the general formula (I) are each independently a linear or branched Ce-Cu alkylene group or a linear or branched C8-C12 alkylene group.

The above conditions preferably apply not only to the at least 70% by weight of one or more different structural units of the general formula (I) which meet criteria a) to c), but preferably to all structural units of the general formula (I) , i.e. also for those at most less than 30% by weight, which do not or not fully meet criteria a) to c). It is therefore preferred that at least 50%, more preferably at least 70%, even more preferably at least 80%, more preferably at least 90%, most preferably at least 95% and most preferably all of the groups R ¹ and R ² of all structural units according to general formula (I) are each independently a linear or branched Ce-Cu alkylene group or a linear or branched C8-C12 alkylene group. In a further development of the inventive idea, it is proposed that at least some of the structural units according to the general formula (I) are oligomers, specifically having the general formula (II):

-(OR ³ -OC(O))ni-O- (II) wherein the group R ³ is selected from C 1 -C 20 linear alkylene groups and C 1 -C 20 branched alkylene groups, and n ¹ is an integer of at least 3 . If at least 60% by weight of the structural units of the general formula (I) have the general formula (II), the group R ³ must be a C8-C12 alkylene group, since otherwise criterion c) would not be met.

Preferably m is an integer between 3 and 100 and preferably between 4 and 25.

Furthermore, it is preferred that the weight-average molecular weight of the structural units of the general formula (II) is 500 to 10,000 g/mol, particularly preferably 800 to 4000 g/mol and very particularly preferably 1000 to 3000 g/mol. Molecular weight can be determined by gel permeation chromatography against a polystyrene standard. However, it is preferred according to the present invention to determine the weight-average molecular weight of the structural units via the hydroxyl number, ie via the amount of potassium hydroxide in milligrams which is equivalent to the amount of acetic acid bound in the acetylation of 1 g of substance. The hydroxyl number can be determined by back titration in accordance with DIN 53240 and is given in mg KOH/g. The weight average molecular weight can be determined by dividing 112,200 by the hydroxyl number. Also in this embodiment it is preferred that the groups R ³ of the structural units according to the general formula (II) from linear Ce-Cu alkylene groups and branched Ce-Cu alkylene groups and preferably from linear C8-Ci2-alkylene groups and branched C8-Ci2 alkylene groups, such as is most preferably selected from linear C10 alkylene groups and branched C10 alkylene groups.

In a further development of the inventive concept, it is proposed that at least 50% by weight, more preferably at least 70% by weight, particularly preferably at least 80% by weight, particularly preferably at least 90% by weight, of all and most preferably all of the structural units of the general formula ( I) have the general formula (II). In particular when there is a very high proportion of structural units of the general formula (II), the degree of crystallinity of the polyurethane can be comparatively high.

For applications in which a reduced degree of crystallinity is desired, it is proposed in a further development of the inventive concept that the polyurethane contains other polyol groups in addition to polycarbonate polyol groups, i.e. in addition to structural units according to the general formula (II), such as in particular polyether polyol groups, i.e. structural units according to the general formula Formula (I) in which the group X is O, or polyetherpolycarbonate groups, i.e. structural units according to general formula (I), in which some of the group X is O and others of the group X is 0-C(0)-0. Suitable examples of such a polyether polyol are, for example, polytetramethylene glycol and polypropylene glycol. In this embodiment, preferably 80% to 99% and preferably 85 to 95% of the structural units according to the general formula (I) have the general formula (II), whereas the rest of the structural units have the general formula (I) in which the group XO is. As explained above, another possibility for reducing the degree of crystallinity of the polyurethane in this embodiment is to provide branched alkylene groups and in particular branched Cs-12-alkylene groups as groups R ³ in general formula (II).

According to a further particularly preferred embodiment of the present invention, at least some of the structural units of the general formula (I) have the general formula (III):

-(OR ⁴ -OC(O)-OR ⁵ -OC(O))n2-O- (III), wherein R ⁴ and R ⁵ are different from each other and are independently selected from linear C 1 -C 20 -alkylene groups and branched C 1 -C20- alkylene groups and n2 is an integer of at least 2. If at least ⁶⁰ ^wt .

Preferably n2 is an integer between 2 and 50 and preferably between 2 and 12.

Furthermore, it is preferred that the weight-average molecular weight of the structural units of the general formula (III) is 500 to 10 000 g/mol, particularly preferably 800 to 4000 g/mol and very particularly preferably 1000 to 3000 g/mol.

Good results are obtained in particular if all groups R ⁴ and R ⁵ of the structural units according to the general formula (III) are selected independently from linear C4-Ci4-alkylene groups and branched C4-Ci4-alkylene groups, particularly preferably from linear Ce-Ci4- alkylene groups and branched Ce-Ci4-alkylene groups and most preferably from linear C8-Ci2-alkylene groups and branched C8-Ci2-alkylene groups, provided that at least 50%, preferably at least 80% and particularly preferably at least 90% of all groups R ¹ , R ² , R ³ , R ⁴ and R ⁵ of all structural units with the general formulas (I), (II) and (III) are each a linear or branched C8-Ci2-alkylene group.

According to a preferred embodiment, one of the groups R ⁴ and R ⁵ is a linear or branched Cs-Cy-alkylene group, preferably Ce-alkylene group, and the other of R ⁴ and R ⁵ is a linear or branched Cg-Cn-alkylene group, preferably C- io-alkylene group.

As explained, it is also highly preferred in this embodiment that all of the groups R ⁴ and R ⁵ of the structural units according to the general formula (III) are independently linear Ce-Ci4-alkylene groups and branched Ce-Cu-alkylene groups or linear C8 -Ci2-alkylene groups and branched C8-Ci2-alkylene groups are selected.

In a further development of the inventive concept, it is proposed that at least 50% by weight, more preferably at least 70% by weight, particularly preferably at least 80% by weight, particularly preferably at least 90% by weight, of all and most preferably all of the structural units of the general formula ( I) have the general formula (III). In particular when there is a very high proportion of structural units of the general formula (II), the degree of crystallinity of the polyurethane can be comparatively high.

In particular, when a reduced degree of crystallinity of the polyurethane is desired, it is preferred to provide branched alkylene groups and in particular branched Cs-12 alkylene groups as groups R ⁴ and R ⁵ in general formula (III). In a further development of the inventive idea, it is proposed that the polyurethane of the roll cover or the press cover or conveyor belt has a mixture of different polyol structural units, some of which have the general formula (II) and some of which have the general formula (III). For example, of all structural units of the polyurethane according to the general formula (I), 10 to 90% can have the general formula (II) and 10 to 90% have the general formula (III). According to a further example, the polyol structural units according to the general formulas (II) and (III) can be distributed such that a total of 20 to 40% by weight (such as 25% by weight) of the radicals R ³ , R ⁴ and R ⁵ are linear or branched C4-C7 alkylene groups and the remainder to 100% by weight (such as about 75% by weight) of the radicals R ³ , R ⁴ and R ⁵ are linear or branched C8-Ci2 alkylene groups. It is more preferred in this embodiment that 20 to 40% by weight (such as about 25% by weight) of the radicals R ³ , R ⁴ and R ⁵ are linear or branched Cs-Cy-alkylene groups and the remainder to 100 % by weight (such as about 75% by weight) of the radicals R ³ , R ⁴ and R ⁵ are a linear or branched C9-C11 alkylene group, or that 20 to 40% by weight (such as about 25% by weight -%) of the radicals R ³ , R ⁴ and R ⁵ is a linear or branched Ce-alkylene group and the radical to 100% by weight (such as 75% by weight) of the radicals R ³ , R ⁴ and R ⁵ is a linear one or branched Cw alkylene group.

With regard to the type of isocyanate component ii) used, the present invention is not particularly restricted. Good results are obtained in particular when the isocyanate component ii) is one or more diisocyanate compounds selected from the group consisting of toluene-2,4-diisocyanates (TDI), methylenediphenyl isocyanates (MDI), hexamethylene diisocyanates (HDI), 1,5-naphthalene diisocyanates ( NDI), isophorone diisocyanates (IDI), cyclohexane diisocyanates (CHDI), phenylene diisocyanates (PPDI), o-tolidine diisocyanate (TODI), 3,3'-dimethyl-4,4'-biphenyl diisocyanate, xylylene diiso- cyanate (XDI), is(isocyanatomethyl)cyclohexane (H6XDI) and mixtures of two or more of the aforementioned compounds.

The present invention is also not particularly restricted with regard to the type of at least one crosslinker used in component iii). In particular, component iii) can contain at least one crosslinker for this purpose, which is selected from the group consisting of amines, polyols and any mixtures of two or more of the aforementioned compounds.

Suitable amine compounds are, for example, those selected from the group consisting of 4,4'-methylene-bis-(2,6-diethyl-3-chloroaniline), 4,4'-methylene-bis-(2-chloroaniline) , 4,4'-methylene-bis-(2-ethylbenzylamine), 4,4'-methylene-bis-(2,6-diethylaniline), 4,4'-methylene-bis-(cyclohexylamine), diethylmethylbenzenediamine, 4,4'-diaminodicyclohexylmethane, 4,4'-diamino-3,3'-dimethyldicyclohexylmethane, 4,4'-diaminodiphenylmethane, 3,5-dimethylthio-tolyl-diamine, 3,5-dimethyltolyl-2,4- diamine, 3,5-dimethyltolyl-2,6-diamine, polytetramethylene oxide di-p-aminobenzoate, poly(tetramethylene-3-methyltetramethylene ether) glycol bis(4-aminobenzoate), trimethylene bis(4-aminobenzoate), isobutyl 4-chloro-3,5-diaminobenzoate, tetramethylammonium bromide, ethylenediamine, hydrazine, hexamethylenediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 1,4-diaminocyclohexane, 1,2-diaminocyclohexane, isophoronediamine, Diethyltoluenediamine, 3,5-dimethylthio-2,4-toluenediamine, 3,5-dimethylthio-2,6-toluenedi amine and any mixtures of two or more of the aforementioned compounds.

Instead of or in addition to an amine compound, component iii) can contain at least one short-chain polyol, preferably short-chain diol, which is preferably selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, polybutylene glycol, 1,4-butanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, Polyethylene glycol, N-N'-bis-(2-hydroxypropylaniline), hydroquinone-bis-2-hydroxyethyl ether, 1,3-bis(2-hydroxyethyl)resorcinol, triols, polytetrahydrofurans and any mixtures of two or more of the aforementioned compounds consists. If these compounds have a structural unit of the general formula (I), these are among the aforementioned structural units and are therefore relevant to whether the polyurethane meets criteria a) to c) or not.

Apart from that, component iii) can also have a polycarbonate polyol according to the general formula (IV):

HO-R ⁶ -(O(O)COR ₇ )n3-OH (IV), in which R ⁶ and R ⁷ independently of one another, are an optionally OH-substituted, linear or branched Ciu-alkylene group and very particularly preferably particularly preferably one optionally OH groups are substituted, linear or branched C4-io-alkylene group and ns is an integer between 2 and 50. The molecular weight of this polycarbonate polyol is preferably from 1000 to 3000 g/mol. This polycarbonate polyol is one of the aforementioned structural units and is therefore relevant to whether the polyurethane meets criteria a) to c) or not.

To initiate the crosslinking reaction, it is further preferred that component iii) also contains at least one catalyst, the at least one catalyst preferably being an organometallic compound or a salt of Zn, Co, Bi, Hg, Cd, K or another metal and/or or a tertiary amine and is particularly preferably a compound selected from the group consisting of dibutyltin dilaurate, tin octoate, dioctyltin diacetate, dibutyltin mercaptide, dibutyltin oxide, dimethyltin mercaptide, dioctyltin mercaptide, dimethyltin carboxylate and any mixtures of two or more of the aforementioned compounds. Preferred examples of tertiary amines are bis(2-dimethylaminoethyl)ether, alkylmorpholines, 1N,N- alkylbenzylamine, 1,2-dimethylimidazole, N,N-dimethylcyclohexylamine and N,N,N',N'-tetramethylenediamine. Other suitable catalysts are described in Szycher's Handbook of Polyurethanes, Chapter 10, ISBN 0-8493-0602-7.

In a further development of the idea of the invention, it is proposed that at least in the at least one layer of the roll cover or press cover or conveyor belt according to the invention, which is formed from the polyurethane described above, the polyurethane forms the matrix in which a fiber fabric or a fiber fabric is embedded.

The roll cover according to the invention or the press cover can have a single-layer or multi-layer design. If the roll cover or the press cover is designed in multiple layers, it is preferred that at least the outer layer is composed as described above. Alternatively, it is also possible for the polyurethane described above to be contained only in individual areas of the roll cover or press cover, such as in the press zone or on the edge of the shoe.

Another object of the present invention is a method for producing a roll cover, press cover or conveyor belt as described above, which comprises the following steps:

1) providing a polyol component i), an isocyanate component ii) and a component iii) containing at least one crosslinker, wherein the polyol component i) contains at least one polyol which is composed of structural units according to the following general formula (I),

^-OR1 ^-XR2 -O- (I), wherein all R ¹ and R ² of one or more different structural units according to the general formula (I) are independently the same or different and are selected from linear Ci-C2o-alkylene groups and branched Ci-C2o-alkylene groups and all groups X of the one or more different structural units are independently the same or different and are selected from bond, O, C(O)-O and OC(O)-O, ) reacting at least part of the polyol component i), the isocyanate component ii) and of component iii) to form a polyurethane in such a way that at least 90% by weight of the polyurethane is composed of one or more different structural units of the general formula (I), with at least 70% by weight of the structural units of the general formula ( I) meet the following criteria: a) at least 80% of the groups X are 0-C(0)-0 and the remainder of the groups X are selected from 0 and C(0)-0; and b) the avg The chain length of all groups R ¹ and R ² is 8 or more than 8 carbon atoms and c) at least 50% of the groups R ¹ and R ² are each independently a linear or branched C8-C12 alkylene group, and ) forms a roll cover, press cover or conveyor belt using the polyurethane produced in step 2). A further aspect of the invention is a roll for a machine for producing or treating a fibrous web, in particular a paper, board or tissue machine, the roll having a roll cover according to an aspect of the invention.

Such rolls can be used at many points in the paper machine. For example as calender rollers or as rollers on coating units such as sizing units. Use as transport or deflection rollers can also be advantageous. A large number of other applications are conceivable.

A further object of the present invention is a shoe press for dewatering a fibrous web, in particular a paper, cardboard, tissue or cellulose web, which comprises a press jacket as described above.

Furthermore, the present invention relates to a machine for producing or treating a fibrous web, in particular a paper, board or tissue machine, which comprises a conveyor belt as described above or a roller as described above.

The present invention is described below purely by way of example using advantageous embodiments and with reference to the accompanying drawings.

show:

1: a schematic view of a shoe press with a press cover according to an embodiment of the present invention and 2: a schematic view of a press section of a paper machine comprising a shoe press and a conveyor belt according to an embodiment of the present invention.

3 shows a section of a roller with a roller cover according to one aspect of the present invention

1 shows a shoe press 10 which includes a shoe roll 12 and a counter roll 14 . While the counter-roller 14 consists of a rotating, cylindrically configured roller, the shoe roller 12 is composed of a shoe 16 , a standing yoke 18 carrying it, and a press cover 20 . The shoe 16 is supported by the yoke 18 and is pressed against the press cover 20 running around it via hydraulic press elements (not shown). Due to the concave design of the shoe 16 on its side opposite the counter-roller 14, a comparatively long press gap 22 results.

The shoe press 10 is particularly suitable for dewatering fibrous webs 24, such as paper webs. During operation of the shoe press, a fibrous web 24 with one or two press films 26, 26' is guided through the press nip 22, with the liquid emerging from the fibrous web 24 due to the pressure exerted on the fibrous web 24 in the press nip 22, which, in addition to water, is dissolved and undissolved compounds, such as fibers, fiber fragments, fillers and/or additives, is temporarily taken up by the press felt(s) 26, 26' and by indentations (not shown) provided in the press jacket surface. After leaving the press gap 22, the liquid taken up by the press jacket 20 is thrown off the press jacket 20 before the press jacket 20 enters the press gap 22 again. In addition, the Press felt 26, 26 'absorbed water removed after leaving the press nip 22 with suction elements.

Due to the concave design of the shoe 16 on the side opposite the counter-roller 14, the press nip 22 is comparatively long, such a shoe press 10 achieves considerably better dewatering of the fibrous web 24 compared to a press consisting of two rotating rollers, so that the subsequent thermal Drying can be correspondingly shorter. In this way, a particularly gentle dewatering of the fibrous web 24 is achieved.

FIG. 2 shows a section of a press section of a paper machine which includes a shoe press 10 . As in the embodiment shown in FIG. 1, the shoe press 10 comprises a shoe roll 12 having a press cover 20 and a pressing element or shoe 16, and a counter-roll 14, with a press nip being formed between the shoe 16 and the counter-roll 14 . In addition, this part of the paper machine comprises two suction rolls 28, 28' and two deflection rolls 30, 30'. During operation of the paper machine, a felt 26 which is guided through the suction rolls 28, 28' and which takes up the fibrous web 24 on the suction roll 28 is guided through the press nip. In addition, below the felt 26 guiding the fibrous web 24, a conveyor belt or transfer belt 32 guided by the deflection rollers 30, 30' is guided through the press nip, with the transfer belt 32 taking over the fibrous web 24 from the felt 26 in the press nip and out via the deflection roller 30' discharged from the press nip. Due to the pressure exerted on the fibrous web 24 in the press nip, liquid escapes from the fibrous web, which, in addition to water, contains dissolved and undissolved compounds, such as fibers, fiber fragments, fillers and/or additives, which come from the felt 26 and from in the press jacket surface provided wells is temporarily included. After leaving the press nip, the pressure from the press cover 20 picked up liquid thrown off the press jacket 20 before the press jacket 20 re-enters the press nip. In addition, the water taken up by the felt 26 is removed by suction elements provided on the suction roll 28' after leaving the press nip. Due to the relatively long press nip due to the concave design of the shoe 16, a significantly better dewatering of the fibrous web 24 is achieved with such a shoe press compared to a press consisting of two rotating rollers, so that the subsequent thermal drying can be correspondingly shorter. In this way, a particularly gentle dewatering of the fibrous web 24 is achieved.

FIG. 3 shows an embodiment of a roller 51 in cross section through its longitudinal axis, which in the present case runs perpendicularly to the plane of representation. The roller 51 has a cylindrical roller core 53 and a roller cover 54 covering the outer surface of the roller core 53. The roller cover 54 is made here by way of example from two layers and in the present case has an intermediate layer 56 and an outer functional layer 58. To improve the adhesion of the intermediate layer 56 or another substructure that is arranged directly on the roller core 53, an adhesive layer 55 can be provided, as shown in FIG. Depending on the application, either the functional layer 58, the intermediate layer 56 or both can comprise or consist of a polyurethane according to one aspect of the present invention.

The roller 51 shown in Figure 3 and the roller cover 54 shown are only intended to explain aspects of the invention in more detail and does not represent a restriction to the exemplary roller shown here.

Other rollers are also possible within the scope of the present invention, in particular roller covers made from a single layer, or also structured roller covers, which can have grooves and/or bores, for example. Reference character list

shoe press

shoe roll

counter roll

shoe standing yoke

press jacket

press nip

Fibrous web, 26' press felt, 28' suction rolls, 30' deflection rolls

T ransportband/T ransferband

roller

roller core

roll cover

adhesive layer

intermediate layer

functional layer

Claims

28

Claims Roll cover for a roll, in particular for a machine for producing or treating a fibrous web, in particular paper, board or tissue machine, wherein the roll cover comprises at least one layer containing polyurethane, the polyurethane being reacted in one or more steps i) a polyol component, ii) an isocyanate component and iii) a component containing at least one crosslinker, the polyol component of the polyurethane being composed to an extent of at least 90% by weight of one or more structural units of the following general formula (I), which are different from one another,

-OR ¹ -XR ² -O- (I), wherein all R ¹ and R ² of one or more different structural units according to the general formula (I) are independently identical or different and are selected from linear Ci-C2o-alkylene groups and branched Ci-C2o-alkylene groups and all X groups of one or more different structural units are independently the same or different and are selected from bond, 0, C(0)-0 and OC(O)-O, characterized in that at least 70 % by weight of the structural units according to the general formula (I) meet the following criteria: a) at least 80% of the groups X are 0-C(0)-0 and the remainder of the groups X are selected from O and C(0) -0 and b) the average chain length of all groups R ¹ and R ² is 8 or more than 8 carbon atoms and c) at least 50% of the groups R ¹ and R ² are each independently a linear or branched C8-C12 alkylene group.

2. Roll cover according to claim 1, characterized in that at least 80% by weight, preferably at least 90% by weight, particularly preferably at least 95% by weight and most preferably 100% by weight, of the one or more different structural units Polyol component according to the general formula (I) each meet the criteria a) to c).

3. Roll cover according to claim 1 or 2, characterized in that all groups R ¹ and R ² of one or more different structural units according to the general formula (I) are independently identical or different and are selected from linear C4-Ci4-alkylene groups and branched C4-Ci4 alkylene groups and preferably from linear Ce-Ci4 alkylene groups and branched C6-C14 alkylene groups.

4. Roll cover according to at least one of the preceding claims, characterized in that the polyol component of the polyurethane contains two, three or more different structural units according to the general formula (I), where the group R ¹ and / or the group R ² of each of the two, three or more different structural units according to the general formula (I) from each other of the two, three or more different structural units according to the general formula (I). Roll cover according to at least one of the preceding claims, characterized in that the average chain length of all groups R ¹ and R ² of one or more different structural units according to the general formula (I) is 8 to 15, preferably more than 8 to 15, particularly preferably more than 8 to 12 and most preferably 9 to 11. Roll cover according to at least one of the preceding claims, characterized in that at least 70%, preferably at least 80%, more preferably at least 90%, very preferably at least 95% and most preferably all of the groups R ¹ and R ² of one or more different structural units according to the general formula (I) are each independently a linear or branched C8-Ci2-alkylene group. Roll cover according to at least one of the preceding claims, characterized in that at least some of the structural units according to the general formula (I) have the general formula (II):

-(OR ³ -OC(O))ni-O- (II) wherein R ³ is selected from C 1 -C 20 linear alkylene groups and C 1 -C 20 branched alkylene groups, and n ¹ is an integer of at least 3. Roll cover according to Claim 7, characterized in that m is an integer between 3 and 100 and preferably between 4 and 25. Roll cover according to at least one of the preceding claims, characterized in that the weight-average molecular weight of the structural units according to the general formula (I) and/or the general formula (II) is 500 to 10,000 g/mol, preferably 800 to 4,000 g/mol and particularly preferably is 1,000 to 3,000 g/mol. Roll cover according to at least one of claims 7 to 9, characterized in that the group R ³ of the structural units according to the general formula (II) consists of linear Ce-Cu alkyl groups and branched Ce-Cu alkyl groups or linear C8-Ci2-alkyl groups and branched C8-Ci2-alkyl groups is selected. Roll cover according to at least one of Claims 7 to 10, characterized in that at least 50% by weight, preferably at least 70% by weight, particularly preferably at least 80% by weight, particularly preferably at least 90% by weight, of all and most preferably all of the structural units of the general formula (I) have the general formula (II). 32 roll cover according to at least one of claims 7 to 11, characterized in that

80% to 99% and preferably 85 to 95% of the structural units according to general formula (I) have general formula (II), whereas the remainder of the structural units have general formula (I) in which the group X is 0. Roll cover according to at least one of the preceding claims, characterized in that at least some of the structural units according to the general formula (I) have the general formula (III):

-(OR ⁴ -OC(O)-OR ⁵ -OC(O)) n 2 -O- (III), wherein R ⁴ and R ⁵ are different and are independently selected from linear C 1 -C 20 alkylene groups and branched C 1 -C2o-alkylene groups, and n2 is an integer of at least 2. Roll cover according to Claim 13, characterized in that n2 is an integer between 2 and 50 and preferably between 2 and 12. Roll cover according to Claim 13 or 14, characterized in that the weight-average molecular weight of the structural units of the general formula (III) is 500 to 10,000 g/mol, preferably 800 to 4000 g/mol and particularly preferably 1000 to 3000 g/mol. 33 Roll cover according to at least one of claims 13 to 15, characterized in that all groups R ⁴ and R ⁵ of the structural units according to the general formula (III) are selected from linear Ce-Cu alkyl groups and branched Ce-Ci4 alkyl groups or from linear and branched Cs-Ci2 alkylene groups or from linear and branched C8-C12 alkylene groups. Roller cover according to at least one of the preceding claims, characterized in that the isocyanate component ii) one or more diisocyanate compounds selected from the group consisting of toluene-2,4-diisocyanates, methylenediphenyl isocyanates, hexamethylene diisocyanates, 1,5-naphthalene diisocyanates, isophorone diisocyanates, cyclohexane diisocyanates, p -Phenylene diisocyanates, o-tolidine diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, xylylene diisocyanate, is(isocyanatomethyl)cyclohexane and mixtures of two or more of the aforementioned compounds, and component iii) contains at least one crosslinking agent which consists of is selected from the group consisting of amines, polyols and any mixtures of two or more of the aforementioned compounds. Roller for a machine for producing or treating a fibrous web, in particular a paper, cardboard, tissue or cellulose web, characterized in that the roller has a roller cover according to one of the preceding claims.