EP2831338B1 - Roll cover - Google Patents

Description

The invention relates to a roll cover, in particular for use in calenders and calenders, according to the preamble of claim 1.

The use of fiber reinforced and filled epoxy resins for calender covers and other abrasion resistant roll covers for use in the paper industry and similar applications has long been prior art.

For example, from the patent EP 1 612 329 B1 It is known that by using nanoparticles, in combination with larger particles, certain characteristics of the roll cover, such as the abrasion resistance and the printing modulus (for example, determined according to EN ISO 604: 2003 Point 3.6), can be adapted and modeled to the respective requirements in the selected roll position.

The proportions of fillers used are always a compromise between the various demands on the roll cover. To achieve the highest possible abrasion resistance and the desired high pressure module, the highest possible degree of filling is desirable.

However, the surface roughness which is obtained in use limits in particular the amount of hard, abrasion-resistant fillers in a grain size of> 0.5 μm, since otherwise a surface which is too rough and has a negative effect on the desired smoothing of the paper is formed.

Furthermore, an increasing filler content leads, starting from certain limits, to an increasing embrittlement of the material and thus an increasing risk of massive damage in case of selective overloading or occurring thermal stresses.

It is accordingly an object of the invention to overcome the known disadvantages of the prior art and to provide a roll cover, which shows both a high pressure modulus and good abrasion resistance with low surface roughness during operation and the lowest possible brittleness.

The object is achieved by the characterizing features of claim 1 in conjunction with the generic features.

According to the invention it is provided that at least three fillers are present, which each have different average particle sizes.

Due to the at least triple combination of different mineral fillers or synthetically produced hard materials with different average grain sizes, a high abrasion resistance is achieved with simultaneously low surface roughness in use and high mechanical and thermal resistance.

Further advantageous aspects and embodiments of the invention will become apparent from the dependent claims.

According to the invention, a first filler has an average particle size in the range from 5 to 50 nm, preferably from 10 to 30 nm. As a result, a high crack resistance and an increase of the pressure module are achieved.

A second filler has a mean grain size in the range of 100 to 500 nm, preferably 100 to 300 nm, and advantageously performs a bridging function between large and small fillers. It reduces the erosion of the resin matrix on the free surface between the large fillers.

A third filler has an average particle size in the range from 1 to 7 μm, preferably from 2 to 4 μm, and can thus bring about a further increase in the pressure modulus and an increase in the abrasion resistance.

According to a further advantageous aspect of the invention, at least two of the fillers, in particular three of the fillers, can be chemically identical.

Alternatively, the at least three fillers may be different. As a result, it is possible to choose from a wide selection of suitable fillers which are commercially available in the respective particle sizes required, and it is possible to use different properties (for example high hardness or good matrix connection) and morphologies (for example spherical particles with high abrasion resistance to achieve the same in operation resulting surface roughness or rod-shaped or fibrous fillers for structural reinforcement) can be used to optimize the overall system.

Preferably, at least the second and / or the filler may be selected from: oxides, carbides, nitrides, aluminum silicates, silicates of mineral or synthetic origin or mixtures thereof. These have a high hardness and abrasion resistance and are commercially available in a variety of forms.

According to an advantageous aspect of the invention, the first filler may further be selected from: oxides, carbides, nitrides, aluminum silicates, silicates, sulfates, carbonates, phosphates, titanates, carbonanotubes, carbonanofibres, metals of mineral or synthetic origin or mixtures thereof.

Particularly preferably, the fillers, in particular the first filler, can be surface-modified, which allows a better attachment to the resin matrix.

According to an advantageous aspect of the invention, the content of fillers in the matrix system may be between 0.5 and 30% by volume. This value represents a good middle ground for the maximum achievable abrasion resistance at the required elasticity.

Advantageously, the content of first filler 0.5 to 20 volume percent, preferably 1.5 to 15 volume percent, while the content of the second filler 0.5 to 5 volume percent, preferably 1 to 3 volume percent and the content of third filler 0.5 to 20% by volume, preferably 3 to 15% by volume.

The matrix system may preferably be a duroplastic, in particular an amine or anhydride crosslinked or a self-crosslinking epoxy resin or an isocyanate ester or mixtures thereof. Such resin systems are commercially available in a wide range and can be selected according to requirements.

The invention will be explained in more detail below.

Calenders or calenders for fibrous webs such as paper or board webs have the task of smoothing the fibrous web either directly after its production (online) or even later (offline). By this task, the roller covers of existing rollers in a calender highest demands are placed on the one hand in terms of their surface quality and on the other hand in terms of their resistance to thermal and mechanical stresses.

Usually, a plurality of rolls are arranged in a stack in a stack, wherein according to a common embodiment, a metallic heatable roll runs against an unheated elastic roll to form a nip. First In several consecutive nips a first side of the fibrous web is smoothed by pressure and heat. In a supercalender or multinip calender, a so-called alternating tip is usually provided approximately in the middle of the stack, after which the other side of the fibrous web comes into contact with the smoothing heating rollers. From this constellation arises immediately the need to make the roll surface of the unheated elastic rolls as smooth as possible, so that the previously achieved smoothness of the fibrous web is not nullified.

The roll covers of the unheated rolls usually consist of at least one, often also of several layers of various materials such as rubber, polyurethane or fiber-reinforced plastics, which are applied to a roll body. Fiber-reinforced plastics are usually the material of choice for use in the calender since they have high temperature resistance as well as high mechanical strength and good abrasion resistance.

Such plastics usually have a matrix system of a resin and embedded fiber reinforcement of glass, carbon or aramid fibers or similar other suitable fibers as a reinforcement. The production of such roll covers is well known, so that only a brief summary is given here.

The preparation can be carried out according to various known methods. On the one hand, it is possible to wrap the fibers dry and apply the matrix by a casting process. Another common method provides that fiber bundles, so-called rovings, are drawn through a resin bath containing the resin matrix and then wet-wound onto the roll body. Also, injection molding processes in which the matrix material is applied by axially movable nozzles on a rotating roller body, are known and suitable for producing a roll cover according to the invention.

In this case, the structure can take place in one or more layers, and it is also possible to provide further layers, such as, for example, a base layer, which serves for the bonding between roll core and roll cover, and additional bonding layers. The measures according to the invention relate to a functional layer of the roll cover, which comes into contact with the fibrous web.

Suitable matrix systems include amine, anhydride crosslinked but also self-crosslinking epoxy resins, isocyanate esters or other thermosets or mixtures thereof.

In all processes, it is possible and common to fill the resin matrix with fillers so as to improve their mechanical and thermal properties.

The prior art already knows the combination with two fillers having different average grain sizes in the resin matrix. The practice proves both the feasibility and the positive effects of such combinations, however, the performance of the thus designed roller covers is not sufficient.

According to the invention, it is thus provided to introduce at least one further filler into the resin matrix.

The combination of at least three different at least with respect to the mean grain size fillers with significantly different average grain sizes, the synergies between the individual fillers can be used optimally.

A hereinafter referred to as a first filler component having a particle size in the range between 5 to 50 nanometers, takes over an effect as a crack stopper and causes an associated increase in mechanical strength and an increase in the pressure module. Prerequisite for this is a good integration with the matrix and an even distribution of the Particles in the matrix. Due to the increased pressure modulus, the substantially pressure-induced wear mechanism of a calender results in a significant later onset of heavy wear, since the deformation and thus the occurring stresses are reduced.

A component referred to hereinafter as the third filler, which is also referred to as "large" hard materials, has an average grain size in the single-digit micrometer range, increases primarily the resistance to abrasive wear and leads to a further increase in the pressure modulus.

Furthermore, a component is provided, which is referred to as a second filler and has medium particle sizes of the order of 0.1 to 0.5 micrometers.

The second filler fulfills a bridging function between the other two fillers and, inter alia, reduces matrix erosion by means of indented particles originating from the fibrous web or the coating medium between the "large" hard materials.

A comparable effect is not or only very difficult to achieve reproducible by particularly broad particle size distributions of a filler, because particles with such broad particle size distributions almost always have significant fluctuations between the particle size distributions of individual batches.

Table 1 shows a summary of the mean particle sizes and the possible particle size distributions of the fillers and the respective degree of filling. Table 1 First filler Second filler Third filler Nanoscale fillers Sub-micrometer-scale fillers Micrometer-scale fillers Volumes in the epoxy matrix 0.5 - 20% 0,5 - 5% 0.5 - 20% Preferred Vol.% 1.5 - 15% 1-3% 3 - 15% mean grain size 5 - 50 nm 100-500 nm 1 - 7 μm preferred average grain size 10 - 30 nm 100-300 nm 2 - 4 μm

The materials for the third filler preferably originate from a first group comprising oxides, carbides, nitrides, aluminum silicates, silicates of mineral or synthetic origin or glasspheres or mixtures thereof. Suitable materials for the first filler are the materials from the first group, but also from a second group comprising sulfates, carbonates, phosphates, titanates, Carbonanotubes, Carbonanofibres, metals of mineral or synthetic origin or mixtures thereof in question.

The choice of material of the second filler can be made from two groups. Preferably, second and third fillers are selected from the same group, more preferably from the first group.

The first filler can be used with or without surface modification, eg with poly L-lactide coated SiO ₂ for better attachment to the matrix.

The optimum composition depends on the specific selected fillers, their particle size distribution and morphology as well as the desired hardness or the desired pressure modulus and the required surface roughness during operation.

The three fillers can be selected from a wide range of suitable commercially available components in the particular grain sizes required. Through the selection specifically different properties, such as a high hardness or a good matrix connection can be emphasized.

Regarding the morphologies of the three fillers can also be chosen from a wide range. For example, spherical particles such as glass spheres with high abrasion resistance to achieve high hardness at low operating surface roughness resulting useful and feasible. Rod-shaped or fibrous fillers such as carbonanotubes can be used for structural reinforcement and for optimizing the overall system.

The three fillers are preferably distributed as homogeneously as possible in one layer. However, it is also possible to achieve gradients within the layer or targeted stepwise changes by suitable modification of the above-described application methods.

Claims (10)

1. Roll cover, in particular for use in apparatus for producing or surface finishing a fibrous web such as a web of paper or of board, wherein the roll cover is formed of a fiber-reinforced plastic and includes a matrix system wherein fillers are provided, characterized in that the fillers provided are at least three in number and each have different median particle sizes, wherein a first filler has a median particle size in the range from 5 to 50 nm and preferably from 10 to 30 nm, a second filler has a median particle size in the range from 100 to 500 nm and preferably from 100 to 300 nm, a third filler has a median particle size in the range from 1 to 7 µm and preferably from 2 to 4 µm, wherein the three fillers are distributed in a layer of the roll cover.
2. Roll cover according to any of Claim 1, characterized in that at least two of the at least three fillers, especially three of the fillers are chemically identical.
3. Roll cover according to either of Claims 1 and 2, characterized in that at least the second and/or third filler is selected from: oxides, carbides, nitrides, aluminosilicates, silicates of mineral or synthetic origin or mixtures thereof.
4. Roll cover according to any of Claims 1 to 3, characterized in that the first filler is selected from: oxides, carbides, nitrides, aluminosilicates, silicates, sulfates, carbonates, phosphates, titanates, carbonanotubes, carbonanofibers, metals of mineral or synthetic origin or mixtures thereof.
5. Roll cover according to claim 4, characterized in that the first filler is a surface-modified filler.
6. Roll cover according to any preceding claim, characterized in that the level of fillers in the matrix system is between 0.5 and 30 volume percent.
7. Roll cover according to Claim 6, characterized in that the level of first filler is from 0.5 to 20 volume percent, preferably from 1.5 to 15 volume percent.
8. Roll cover according to Claim 6 or 7, characterized in that the level of second filler is from 0.5 to 5 volume percent, preferably from 1 to 3 volume percent.
9. Roll cover according to any of Claims 6 to 8, characterized in that the level of third filler is from 0.5 to 20 volume percent, preferably from 3 to 15 volume percent.
10. Roll cover according to any preceding claim, characterized in that the matrix system is a thermoset, in particular an amine- or anhydride-crosslinked or self-crosslinking epoxy resin or an isocyanate ester or a mixture thereof.