[001] The present invention relates to a roll of a fiber web machine according to the preamble of patent claim 1 , comprising a roll body via which the roll may be mounted rotatably in the fiber web machine, and a work coating provided in connection with the body.

[002] The invention also relates to a fiber web calender according to the preamble of patent claim 16.

[003] Various rolls are generally used in the treatment of the web and in the control of the running of the web in fiber web machines. The use of polymer coatings has recently increased remarkably due to their positive properties. For example the surface properties of a roll having a steel roll body may be influenced by means of the coating. The coating has a significant influence on for example the surface treatment such as calendaring of the fiber web. A multi-roll calender typically has several successive roll nips formed by the rolls in a roll stack, through which the web has been arranged to run. Typically pressure and often also heat is directed by means of the rolls to the web in the nip. Typically the successive rolls in the calender have different surface properties so that there is a roll having a hard surface and a roll having an elastic surface against each other in each nip. Especially a roll having an elastic surface is typically a coated steel-body roll.

[004] The rolls of a fiber web machine typically have a steel body coated for example with a polymer coating. There are known efforts to improve the durability and strength properties of polymer coatings by using in the matrix material suitable reinforcing materials such as glass fiber. Also filler may be used. Particularly in polymer-coated rolls in a nip contact, the coating is subjected to a remarkable dynamic load. This has a significant influence on the life of the coating and the need to improve the durability of polymer coatings specifically under dynamic load has become apparent.

[005] An example of a calender roll coating is presented in US patent no. 4324177. The coating comprises thermosetting or thermoplastic polymer which is suitable for calendering particularly in elevated pressure and also in elevated temperature. The glass transition temperature of the polymer material is 12O ⁰ C or more and the material may be for example epoxy. The coating may contain particle or fiber fillers to improve the heat resistance and hardness. Typical filler /reinforcing materials are for example glass and carbon fiber or inorganic particles of the size range of 5 - 10 μm.

[006] Today, the use of fillers of the size range of 0.1 μm or less, i.e. so- called nanofillers, has been suggested. For example EP 1612329 proposes using carbide-based or oxide-based fillers. US publication no. 4466164 discloses the use of fillers of the size range of 0.05 - 10 μm, for example silica powder or carbon black. Although nanoclass particles already contribute to an improved homogeneity of the coating, the filler particles still create "discontinuity" spots in the roll coating and may thus limit the durability of the coating particularly when the running speed, the load and/or the temperature are raised.

[007] The publication WO2006040398A1 describes generally a certain manufacturing method of a nanomaterial and the nanomaterial. The publication discloses among other things chemical bonding of nanofiber tubes to a polymer and applications of the material produced in this way.

[008] The object of the invention is to provide a roll, which works more reliably then before in a fiber web machine, especially in the so-called nip position. [009] It is also an object of the invention to provide a fiber web calender where the operation reliability of the calender rolls is improved compared with the prior art.

[0010] . The objects of the invention are mainly achieved in the way described in the patent claims 1 and 16.

[0011] The other additional characteristics of the invention are disclosed in the appended patent claims and the following description of the embodiments of the drawing.

[0012] According to a preferred embodiment of the invention the roll of a fiber web machine comprises a roll body mountable rotatably in the fiber web machine and a work coating provided in connection with the body. The work coating is a polymer coating at least partly containing polymer into which nanocarbon has been bonded, the molecule structure of which is such that it forms an inner space defined by a carbon frame wall.

[0013] An inner space of this kind defined by a carbon frame wall is present in fullerenes and according to a preferred embodiment, nanocarbon is composed of fullerene. Fullerenes are one of the allotropic forms of carbon. They resemble graphite but instead of mere hexagons their molecule structure contains also pentagons and even heptagons. This bends the plate-like structure to spheres, ellipses or tubes. Thus, a fullerene comprising an inner space defined by a carbon frame wall may thus preferably be spherical or tubular in form.

[0014] The bonding of nanocarbon to the polymer may be performed chemically or physically. Chemical bonding means that a chemical bond is created between the chemical chain and the nanocarbon, preferably a covalent bond. The generation of the bond may be influenced for example by means of heat, pressure, radiation or ultra sound, like in the publication WO 2006040398 A1. In order to perform the chemical bonding, the polymer and the nanocarbon material are brought together and treated as mentioned above. The chemically modified material produced in this way is used as the roll coating material or as part of it. The physical bonding is carried out simply by adding nanocarbon material to the polymer before curing of the polymer whereby the nanocarbon material, due to its small size and advantageous form, is enclosed inside the polymer mesh.

[0015] According to a preferred embodiment, the nanocarbon comprises chemically bonded nanocarbon tubes in order to even in the surface the dynamic forces directed to the surface. With the structure modified in this way with nanocarbon tubes, the forces are distributed to a larger area and the durability of the coating improves remarkably.

[0016] According to a preferred embodiment the work coating is preferably a polymer coating and essentially of a fiber reinforcement -free material. Then the effect of the nanocarbon bonded in the polymer is stronger than in fiber- reinforced polymers. Preferably the nanocarbon is a fullerene and the polymer is epoxy.

[0017] According to an embodiment the polymer coating is of epoxy resin.

According to another embodiment the polymer coating is of polyurethane.

[0018] According to an embodiment the work coating comprises a mixture of nanocarbon-modified and non-nanocarbon-modified polymers.

[0019] According to yet another embodiment, the work coating is formed of several coating layers, whereby the outermost layer of the work coating is made of a polymer coating, nanocarbon being bonded in the polymer.

[0020] In a fiber web calender according to an embodiment of the invention, there is a stack of rolls containing two or more rolls arrangable in nip contact with each other, the stack of rolls comprising at least one roll, which comprises a roll body rotatably mountable in the fiber web machine, and a work coating provided in connection with the body. The work coating is a polymer coating comprising at least partly polymer into which nanocarbon has been bonded, the molecule structure of the nanocarbon forming an inner space defined by a wall.

[0021] According to an embodiment, the coating comprises nanocarbon tubes chemically bonded to the polymer in order to even in the coating the dynamic forces directed to the coating. Then, when the forces are distributed to a larger area, the durability of the coating improves remarkably and the operation reliability of the calender increases.

[0022] According to an embodiment the nanocarbon comprises fullerenes to even in the coating the dynamic forces directed to the coating. With the polymer structure produced in this way the forces are distributed to a larger area and the durability of the work coating improves remarkably.

[0023] According to an embodiment the work coating is preferably a polymer coating and essentially of a fibre reinforcement-free material. Then the influence of the fullerenes of the polymer is stronger than in fiber-reinforced polymers.

[0024] According to a preferred embodiment the polymer coating is of epoxy resin.

[0025] According to yet another embodiment the work coating is formed of several coating layers, whereby the outermost layer of the work coating is made of a polymer coating, nanocarbon being bonded in its polymer.

[0026] The invention and it operation are described below with reference to the accompanying schematic drawing, in which Fig. I illustrates schematically a roll of a fiber web machine according to an embodiment of the invention, disposed in a multi-roll calender.

[0027] Figure 1 illustrates, by way of an example, a multi-roll calender 10 of a fiber web machine. The calender comprises a stack of rolls formed by a so- called top roll 16 and a bottom roll 14 and intermediate rolls 12, 12' of a first type and intermediate rolls 13 of a second type, arrangable in nip contact with each other and disposed between the top roll and the bottom roll. In the calender the web W has been guided to run through nips N between the rolls 12, 13. In Figure 1 , every second roll is a roll 12 provided with a work coating, and between these there is a conventional roll 13 having essentially a hard surface. Between the nips in the calender the web has been arranged to run via fly rolls 15 in a way know per se.

[0028] The rolls 12, 12' have been presented here so that the figure illustrates the rolls partly in cross section. The roll 12 comprises a body 18 having a work coating, preferably a polymer coating, at its outer surface. When the calender is running, the coating of the roll 12 is subjected to a remarkable dynamic stress due to, among other things, the nip loads and uneven spots in the wire and possibly also in the web W. The work coating of the roll is preferably a polymer coating 20 and it comprises at least partly a polymer into which nanocarbon 22, the molecule structure of which forms an inner space defined by a wall, has been bound chemically in order to even in the coating the dynamic forces directed to the coating.

[0029] According to an embodiment of the invention, the nanocarbon 22 is of fullerene, tubular and/or spherical in form. Due the structure of the fullerene, an inner space is formed inside its wall. The inner space defined by the wall is formed at least in one section plane, in which case a nanocarbon tube is concerned. The area per volume unit of a fullerene is large which remarkably spreads out energy under dynamic stress whereby the energy generated by the nip pressure is efficiently distributed in the coating and thus it reduces the risk of damage to the coating.

[0030] According to another embodiment of the invention, the nanocarbon 22 is formed of spherical fullerenes. An inner space is formed inside the spherical fullerene due to its spherical structure. Preferably the fullerene is Ceo fullerene or C ₇₀ fullerene, of which C ₆ o fullerene is more preferred. The fullerene may also be a mixture of Ceo and C ₇ o fullerenes. The area per volume unit of spherical fullerene also is large which remarkably spreads out energy under dynamic stress whereby the energy generated by the nip pressure is efficiently distributed in the coating and thus it reduces the risk of damage to the coating.

[0031] When the nanocarbon tubes and/or spherical fullerene is bound to the polymer material, preferably epoxy, no internal discontinuity points are formed in the coating, unlike when mixing with particle-form filler, but the coating is more homogenous. The coating is particularly homogenous when the nanocarbon tubes and/or spherical fullerene have been bound to the polymer chemically. The dynamic load is distributed evenly in the coating thus reducing local heat stress peaks which initiate so-called hot spots and coating damage and delamination at high pressure and temperature loads. Specifically it has been noticed that the viscosity of the coating has improved when Ceo fullerene or a mixture of Ceo and C7 ₀ fullerenes is used. The viscosity improvement compared with pure epoxy is 15 - 20 % (Charpy Impact test, unnotched).

[0032] The polymer coating is preferably of a fiber reinforcement -free material, in other words it does not contain at least to a remarkable extent macro-enforcement fibers. The percentage of reinforcing fibers is thus 0 - 2 %. The coating is then essentially a pure polymer structure modified with nanocarbon tubes and/or spherical fullerenes. The polymer coating may be formed for example of epoxy resin or polyurethane. Containing no reinforcing fibers the coating is more homogenous, and the advantages provided by the invention become more apparent.

[0033] The coating contains nanocarbon tubes 0.5 - 5 % by weight. According to an embodiment the percentage of the nanocarbon tubes is 0.5 - 2 %

[0034] The work coating according to the invention may comprise nanocarbon-modified polymer, completely or in part. The coating may comprise several layers. According to an embodiment the roll has been coated with several coating layer as illustrated in Figure 1 with roll 12'. The polymer coating 22 modified with nanocarbon tube and/or spherical fullerene is preferably used in the fiber reinforcement-free outermost coating layer of the roll. The coating layer/layers 23 under the surface layer preferably comprise fiber-reinforced polymer. The outermost or the only work coating may also comprise a mixture of nanocarbon-modified and non-nanocarbon- modified polymer. For example, a part of the epoxy in a calender roll epoxy coating may be replaced with a nanocarbon-modified epoxy. The mixture ratio modified:non-modified is for example 10:90 - 90:10, more preferably, however, at least about 40:60, to achieve the advantages of the invention.

[0035] The roll according to the invention is excellently applicable particularly in calender rolls, as a temperature rise is found to be advantageous in view of the function of the work coating. Thus, the roll according to the invention is preferably used at a temperature of >40°C.

[0036] It must be understood that only a few most preferred embodiments of the invention have been presented above. Depending on the matrix used the details of the manufacture of the composite structure may vary. Although the invention has been described above in connection with a multi-roll calender the invention is applicable also in a 1-nip calender, such as a so-called soft calender. Thus it is obvious that the invention is not limited to the embodiments disclosed above but it may be modified in many ways within the scope of protection defined by the appended patent claims. The features described may be combined within the basic idea of the invention to form various entities if so desired and if technical feasibility for this exists.