EP4551481A1

EP4551481A1 - Belt with reinforcing polyolefin fabric

Info

Publication number: EP4551481A1
Application number: EP23736316.3A
Authority: EP
Inventors: Sebastian Seibold; Andrey MINKIN; Christel Bäuerle-Müller; Stavros Podias; Frank Kantorek; Mohamad Bachir; Donald Brown
Original assignee: Contitech Deutschland GmbH
Current assignee: Contitech Deutschland GmbH
Priority date: 2022-07-08
Filing date: 2023-06-29
Publication date: 2025-05-14
Also published as: WO2024008551A1

Abstract

The present invention is concerned with belts and comprising an upper thermoplastic elastomer layer, a composite reinforcing fabric and a lower thermoplastic elastomer layer, wherein the fabric is positioned between the upper and lower elastomer layers and comprises polyolefin yarns. In the composite fabric, the yarns in the length direction are essentially straight and have a tensile strength which is at least 10% higher that the tensile strength in the width direction to provide an optimal balance of strength in the length direction and costs. In addition, since the belt is prepared at least predominantly for thermoplastic material, the belt can be molten as a whole for simplified recycling. The present invention is further concerned with fabrics for use in such belts, and processes for the recycling of such belts and the refabrication of belts from the generated recyclate.

Description

Title: Belt with reinforcing polyolefin fabric

The present invention is concerned with belts comprising an upper thermoplastic elastomer layer, an in-between composite reinforcing fabric and a lower thermoplastic elastomer layer, wherein the fabric comprises polyolefin yarns, which in the length direction have a tensile strength which is at least 10% higher than the tensile strength in the width direction. The present invention is further concerned with fabrics for use in such belts, and processes for the recycling of such belts and the refabrication of belts from the generated recyclate.

State of the art

Conventional conveyor belts today are produced with bodies of an elastomeric material and reinforcing elements for tensile reinforcement in the length direction, where pulling forces are applied during use. In most cases, these elements are cords or fabrics on the basis of polyester or polyamide (including polyaramide) fibers or steel cables, onto which the elastomer is applied from both sides to provide the body and thereafter vulcanized to consolidate the construction. Obviously, such belts cannot easily be recycled as the different materials have to be separated and the vulcanized rubber cannot be recycled in the regular sense since the crosslinking effected by vulcanization is not reversible. This leads to a situation, where recycling is usually not economically feasible, so that the belts are only used as a feedstock in “thermal recycling”.

A possible means to avoid the problems of reusability of vulcanized materials is to use thermoplastic elastomers (“TPE”) for the carcass of the belt, as these materials can be remolten and thus more easily be separated from reinforcement materials. Such belts can e.g. be produced by extruding the thermoplastic elastomer onto the reinforcing element (or elements) followed by cooling to provide the respective reinforced belt.

As an alternative, non-reinforced belts are known (e.g. in the food industry), which avoid the problem of material separation altogether. These belts are mostly made of polyurethane, but due to the lack of reinforcement have a tendency to stretch while in use, which results in manufacturing shutdowns where the conveyor lines are stopped to allow for reworking the belt to take up excessive slack. In addition, such belts can only be used for applications, where the belting is not exposed to significant deforming forces.

WO 2021/188760 A1 describes a reinforced food grade belt, which is formed from an elastomeric belt body material and a plurality of thermoplastic synthetic filaments, which extend in the length direction of the belt. These belts are described as being beneficial both in terms of having reinforcement and complying with safety protocols for food grade compliance. In WO 2021/188760 A1 , the belt construction is such in that the thermoplastic synthetic filaments have a melting point, which is below the melting point of the thermoplastic elastomer. Due to this configuration, WO 2021/188760 A1 claims that the applied thermoplastic elastomer is melted into the belt when belt ends are connected together to form a continuous loop belt. However, in practice, this production of such belts is relatively complex, as it has to be ensured that the filaments do not completely melt or recrystallize, which would compromise the strength of the belt.

US application No. US 63/218,500 describes reinforced elastomer parts comprising a reinforcement member and a layer made of thermoplastic elastomer, where the materials of the reinforcement member and the thermoplastic elastomer are compatible to the extent that they can be processed to form a homogeneous single-phase or multi-phase mixture above the melting temperature of the materials. This construction allows for a uniform processing of the parts in a melting recycling process without the necessity for elaborate separation of different materials of the elastomer parts.

As is apparent for the above, there is a need for conveyor and other reinforced belts, which are easy to produce, and which have an improved recyclability compared to conventional belts prepared from vulcanized or thermoplastic elastomers. The present invention addresses these needs. Description of the invention

In the investigations underlying the present invention, it has unexpectedly been found that a thermoplastic elastomer can be compounded with a polyolefin reinforcement material without a relevant detrimental effect on the mechanical properties of the elastomer and that such belts provide the required characteristics for light to heavy duty applications (belt strength classes 400 N/m or more) as e.g. in paper or agricultural products. Accordingly, for the recycling of such belts it is not necessary to separate the reinforcement element from thermoplastic elastomer, which significantly simplifies the recycling process.

In addition, it has been found that in a belt, which is fabricated with a polyolefin reinforcement element, the tensile strength in the length direction is more critical, as the pulling force is applied in this direction. A reinforcement in the width direction of the belt, which provides the belt with the required transverse strength and strength against slitting, in this case can be provided by a less robust and more cost effective material than the reinforcement in the length direction. In such belt the material, which is used in the width direction, still ensures an optimal alignment and orientation of the reinforcement strands in the length direction and can even serve to tune the elasticity in the length direction via the construction of the fabric (e.g. via an alignment of reinforcement stands in zig-zag form).

Accordingly, in a first aspect, the present invention is directed to a reinforced belt, which comprises an upper thermoplastic elastomer layer, a reinforcing fabric and a lower thermoplastic elastomer layer, wherein the fabric is positioned between the upper and lower elastomer layers and comprises polyolefin yarns, wherein the yams in the length direction of the belt have a tensile strength which is higher than the tensile strength in the width direction by at least 10% and wherein preferably the yarns in the length direction are oriented such that they do not twist against the straight line of extension by an angle of more than 30°. Here the angle indicates the maximum of the twist of the yam towards the length direction. The thermoplastic elastomer and the polyolefin in the polyolefin yarns are sufficiently miscible and compatible so that on melting they can form a homogenous mixture and can be homogenized with one another in the melt to provide either a single-phase mixture or at least a sufficiently stable dispersion of one material in the other material, which may have several (= two or more) phases. The materials of the reinforcement and of the thermoplastic elastomer are preferably matched to one another in such a way, that only one phase forms in the melt.

The presence of a single phase in the mixture can be detected, for example, by means of DSC, where only one melting range without two distinguishable melting points is detected. Accordingly, the skilled person in the art is readily able to determine an appropriate combination of materials for the thermoplastic elastomer and the polyolefin in the yarns of the fabric using his or her background knowledge and, if necessary, some experimentation to determine the miscibility of the materials.

The belt according to the invention is preferably a belt with a strength of at least 400 N/mm and more preferably a belt with a strength of at least 1000 N/mm to about 4000 N/mm (according to DIN EN ISO 22102:2020).

The thermoplastic elastomer and the polyolefin (or polyolefins) of the reinforcement fabric suitably have melting points or differences between the mean value from the start and end point of the melting range which have a maximum temperature difference of 70°C, preferably a maximum of 50°C and particularly preferably a maximum of 40°C. The respective melting point for the purposes of this invention are determined by DSC.

In a preferred embodiment, the reinforced belt does not comprise constituents or elements, which maintain their integrity when the thermoplastic elastomer and the polyolefin yarns are molten, provided that these elements are opposed to the formation of a homogenous mixture. I.e. particulate and fiber fillers or other constituents, which can be homogeneously blended into a mixture of the molten thermoplastic elastomer and the polyolefin, may be present in the yarns or elastomeric body, as such elements can readily be recycled together with the thermoplastic elastomer and polyolefin yarns to provide a mixture, from which e.g. a new elastomeric body of a new belt could be prepared.

It is possible that the inventive reinforced belt comprises one or more additional layers with constituents or elements, which maintain their integrity when the thermoplastic elastomer and the polyolefin yarns are molten or which on melting have a detrimental impact on the mechanical properties of the resulting thermoplastic elastomer mixture. However, as such layers or elements would have to be separated from the polyolefin and thermoplastic elastomer constituents of the belt, it is preferred that the inventive reinforced belt does not comprise such layers or elements. Such detrimental effect in the context of the invention is understood as e.g. a decline in the tensile strength by more than 20%, preferably more than 15% and even more preferably more than 10%, when the mixture obtained from the melt at 23°C is compared to the virgin thermoplastic elastomer.

The reinforcement fabric preferably also has a tensile strength in the length direction of the belt, determined according to DIN EN ISO 13934-1 , of at least 100 N/mm, and more preferably in the range from 400 N/mm to 4000 N/mm. In addition, it is preferred that the tenacity of the yarns in the warp direction is higher by at least 10% than the tenacity of the yarns in the weft direction, where more preferably the difference in the tenacity is 100% or more and even more preferably 200% or more, where the tenacity is given in cN/tex as determined by DIN EN ISO 5079:2021. In one embodiment, the difference in the tenacity is 1000% or less. Concerning absolute values, in one embodiment the yarns in the warp direction have a tenacity of 15 cN/dtex or more, preferably of 20 to 50 cN/dtex and more preferably of from 25 to 40 cN/dtex and the yarns in the weft direction have a tenacity of 13.5 cN/dtex or less, preferably of 2 to 12 cN/dtex and more preferably of from 4 to 10 cN/dtex.

As noted above, the yarns in the reinforcing fabric which extend in the length direction of the belt (as designated as warp direction) are preferably based on a material which provides a higher tensile strength than the yams which are provided in the width direction (as designated as weft direction), where the difference between the two is at least 10%. For the comparison of the respective tensile strength, the tensile strength is determined according to DIN EN ISO 2062. In addition, it is preferred that the yams, which extend in the length direction of the belt, are substantially straight in the length direction, with a minimal level of crimp, preferably with a crimp level of less than 1 %. In this manner, it can be ensured that the fabric provides the strength in the length direction directly when it is stressed and there is no offset, which results from bringing the yam, which is twisted around a straight line of the direction of extension, into a straight line.

Preferably, the elongation of the belt at a working strength (which is 10% of the breaking strength) of equal to or less than 4.5%, more preferably at equal to or less than 3 % and even more preferably in the range of from 2.5 to 0.3 %. As the elongation in the belt is primarily determined by the fabric reinforcement, the elongation properties of the fabric are preferably in the same range.

The polyolefin yams can be made of any polyolefin, which is suitable for the production of fibers and/or yams. Preferably, the polyolefin yams are based on polyethylene and/or polypropylene, as these are the most readily available polyolefins and they can be blended into one another to provide a homogeneous or substantially homogeneous mixture. In one embodiment, the fabric has polyethylene yams in the length and width direction, where the yams in the width direction have a tensile strength which is at least 10% less than the tensile strength in the length direction. In another embodiment, the fabric has polypropylene yams in the length and width direction, where the yams in the width direction have a tensile strength which is at least 10% less than the tensile strength in the length direction. In a particularly preferred embodiment, the fabric has polyethylene yams in the length direction of the belt and polypropylene yams in the width direction of the belt.

The polyethylene in the polyethylene yams is preferably a polyethylene with a molecular weight of at least 1 ,000,000 g/mol and more preferably with a molecular weight Mw of from 2,000,000 to 6,000,000 g/mol. Such molecular weight is generally referred to as UHMWPE. The molecular weight Mw in this case is determined via the intrinsic viscosity (“IV”, as measured on solution in decalin at 135°C), which is a measure for the molecular weight, but can more easily be determined than actual molecular weight parameters like M_n and Mw. There are several empirical relations between IV and Mw. For the purposes of this invention, the molecular weight Mw is calculated from the intrinsic viscosity via the empirical equation Mw = 5.37 * 10⁴ [IV]^{1 37} (see EP 0504954 A1 ).

UHMWPE yams are particularly favorable as they provide a typical high tensile strength of 528 N to 636 N per single yam (at a linear density of 1760 dtex) when tested according to ISO 2062. Accordingly, UHMWPE yams are preferably used as yam in the length (or warp) direction of the belt.

Polypropylene yams for the use in this invention preferably provide a tensile strength of from 60 N to 300 N per single yam (at a linear density of 930 to 4400 dtex, respectively), which is sufficiently lower than the tensile strength of the UHMWPE yams. Accordingly, polypropylene yams are preferably used in the width (or weft) direction of the belt.

Alternatively or in addition, it is preferred that the polyethylene has a density of from 0.91 to 0.98 g/cm³ and more preferably of from 0.95 to 0.98 g/cm³. Moreover, alternatively or in addition the polyethylene has a crystallinity of from 30 to 90 % and more preferably 75 to 85%, wherein the %-age of crystallinity is determined by measuring the melting energy by DSC and comparing the energy with the melting energy released upon melting of a standard sample of polyethylene with known crystallization degree.

The linear density of the yams in the fabric, which is used for reinforcement in the reinforced belts of the invention is not subject to any relevant restrictions, as long as the yam provides the required strength to the fabric and belt, into which it is incorporated. Here, the linear density of the yams especially in the length (or warp) direction of the fabric can be varied over a broad rage, but preferably is from 220 to 3600 dtex and more preferably from 1760 to 3520 dtex. Likewise, the linear density of the yarns in the width (or weft) direction of the fabric in the belt can be varied in a broad range and preferably is within the range of 930 to 8500 dtex.

The yarns can be formed from one single yarn or a multitude of single yams, which are plied and twisted together. The single yarns in either case preferably have a linear density in the length direction of from 220 dtex to 3300 dtex and more preferably from 1760 to 2640 dtex. Irrespective of whether the yarns in the width direction are formed from a single yarn or a multitude of single yarns, the single yams in the width direction preferably have a linear density of from 930 dtex to 4400 dtex.

The yam in both the length and width direction can be a single yam or can be assembled from multiple single yams, which are cabled or twisted together to provide the yam. In one embodiment, the yams in the length and/or the width direction are constituted from 1 to 10 single yams and preferably from 1 to 5 single yams. In a particularly preferred embodiment the yams in the length and the width direction are constituted from 1 to 5 single yams. If the yam is constituted from more than one single yam, the yam can also be designated as a secondary yam, which is constituted form the primary single yams.

The thermoplastic elastomer, which is used in the upper and lower thermoplastic elastomer layer, is preferably based on thermoplastic elastomer which is miscible with the polyolefin. Accordingly, the thermoplastic usually is not based on a fluoropolymer or perfluorinated polymers, which do regularly not meet this requirement. Preferred thermoplastic elastomer in the respective upper and lower layers of the inventive belt comprise a non-fluoropolymer thermoplastic vulcanisate, a thermoplastic polyolefin or a thermoplastic polyurethane as base material.

Suitable materials for the thermoplastic elastomer include, for example, EPDM (ethylene propylene diene rubber) or mixtures thereof with polyolefins, preferably in the form of polypropylene. Such mixtures can be used as TPO (thermoplastic polyolefin) or TPV (thermoplastic vulcanisate = cross-linked “thermoplastic polyolefin”). A particularly suitable polypropylene which can be used in such blends is, for example, a polypropylene with a density of 0.90 to 0.91 g/cm³ Other suitable thermoplastic elastomer materials include ethylene acrylate rubber (AEM) and acrylate rubber (ACM), preferably in combination with polyamide, and also thermoplastic polyurethane elastomers (TPU).

An ethylene-propylene-diene rubber having an ethylene content in the range of 45 to 75% by weight and particularly 45 to 55% by weight is preferred as the EPDM. The diene content here is suitable in the range from 0.1 to 12% by weight, preferably in the range from 2 to 10% by weight and particularly preferably in the range from 3 to 9% by weight. Any dienes used in EPDM can be used here as dienes, with cyclopentadiene, ethylidene norbornene and 1 ,4-hexadiene being preferred dienes.

The thermoplastic elastomer in the inventive reinforced belt can form a layer on the polyolefin fabric, or the fabric can be penetrated by the thermoplastic elastomer, which fills the cavities within the reinforcing fabric so that the thermoplastic elastomer in the upper and lower layer directly contact each other. Regularly, the belt will be constituted such that the thermoplastic elastomer in the upper and lower layer directly contact each other.

As noted above, it is of importance for the reinforced belts of the present invention that they are constituted from materials, which can be molten to provide an at least substantially homogeneous mixture. Thus, it is possible that the reinforced belts of the invention comprise minor amounts of materials, which are other than polyolefins and thermoplastic elastomers. These materials can be present in the thermoplastic elastomer layers or in the polyolefin fabric. In one embodiment, the fabric comprises other materials in the form of one or more additional yams, which are preferably in the form of thermoplastic polyurethane, polyester or polyamide yams. These yams can be present as additional yams in the length, width or both in the length and width direction of the polyolefin fabric. The thermoplastic elastomer and/or the thermoplastic polymer can also contain conventional additives, such as fibers or fillers for reinforcement purposes, or formulation auxiliaries. However, the thermoplastic elastomer and/or the thermoplastic polymer preferably contain such components in a proportion of up to 40% by weight at most, for example in a proportion of 10 to 30% by weight. Furthermore, it is preferred that the reinforced belt does not contain any components that counteract an intimate mixing of the components of the thermoplastic elastomer and the thermoplastic polymer.

To be able to form a melt without relevant degradation of the components of the belt, it is further preferred that the belt disintegrates by melting when heated to a temperature of from 130°C to 250° and more preferably of from 140°C to 200°C. The indication, that the belts “disintegrates by melting” here means that the polymeric constituents of the belt melt at least at the upper limit of the indicated range, even if fillers or other additives, which do not hinder the formation of a homogeneous melt, are still present in non-molten form.

The fabric can be present in the reinforced belt as one or more layers. In a preferred embodiment, the fabric is present as a single layer. In another embodiment, the reinforced belt comprises two to four layers, wherein preferably the space between the layers is filled by a thermoplastic elastomer and preferably by the thermoplastic elastomer, which forms the upper and/or lower layer. In this way, the belt is further consolidated.

The belt can have any shape of a belt for force transmission, such as e.g. a toothed belt or a V-shaped belt, wherein the reinforcing fabric is sandwiched between upper and lower thermoplastic elastomer layers. The belt can be an endless belt, or a belt, where two ends of a belt strand are connected to one another, e.g. via clamps or other holding means. The belt can be formed e.g. as a power transmission, timing or conveyor belt and the like, and can be used accordingly. In a second aspect, the present invention concerns a fabric as specified herein above, i.e. a fabric, which has polyolefin yams in the length direction having a tensile strength which is at least 10% higher that the tensile strength of the polyolefin yarns in the width direction, and wherein preferably the yarns in the warp direction are essentially straight, i.e. the yarns are oriented that they do not twist against the straight line of extension by an angle of more than 30°. The length direction in this case is the direction of the warp yams, which regularly is longer than the extension of the fabric in the weft direction. Preferably, the fabric has polyethylene yams in the warp direction and polypropylene yams in the weft direction.

The fabric can have any suitable weaving pattern, as long as the yams having a higher tensile strength are predominantly oriented in the warp direction and the yams having a lower tensile strength are predominantly oriented in the weft direction. In one embodiment, the weaving pattern is a single layer, double layer or multiple layer pattern. In a preferred embodiment, the weaving pattern is a weaving pattern with a straight warp design or a 3D weaving design. Here 3D weaving indicates a fabric having substantially straight yams in the warp and weft direction, which further comprises yams designated as “Z-yarns”, which fix the crossed warp and weft yams on one another via a zig-zag weaving pattern.

The yams providing the fabric and especially the yams, which in the fabric provide the warp yams, can be twisted or non-twisted yams, where a twisting in the range of from 0 to 300 turns per meter (tpm) is preferred and a twisting of from 25 to 80 tpm is more preferable. When the yams are twisted yams, this has the effect of increasing the bundle integrity, especially for the weaving process. In addition, with an optimized twist of the single yams, the dynamic properties of fabrics can be increased. Multiple twisting arrangements for assembled yams are also possible.

As noted above, the yams in the warp direction in a preferred embodiment are yams of UHMWPE. In addition or in alternative thereto, it is preferred that the yams are oriented that they do not twist against the straight line of extension by an angle of more than 25°, more preferably not more than 20° and even more preferably not more than 10°. As noted above, this design ensures that the belt provides a high tensile strength and low elongation even at low tensile stresses of about 10% of the breaking strength.

Another factor, which may be used for the characterization of yams, is the twist factor, which is a measure of the degree of twisting of a yam. The twist factor K of the plied yam (or more precisely of the elementary filaments constituting said plied yam) is proportional to the twist angle and is expressed according to the following relation:

K = (twist in turns/meter) x [linear density of strand (unit: dtex) I (10000 ■ p)] ^1/2

Here, the twist is expressed as the number of turns per meter, the linear density is expressed as dtex (weight of 10000 meters of the strand in grams), and p is the density or mass per unit volume of the material from which the plied yam is made in units of g/cm³ (approximately 0.94 for UHMWPE and 0.91 for polypropylene).

The filaments constituting a multifilament yam made of UHMWPE, which is preferred for use in the inventive reinforced belt of fabric, are preferably twisted together with a twist factor between 5 and 90, more preferably between 10 and 50. Further, it is preferred that the yams have a twist level of between 25 turns/m and 150 turns/m, more preferably between 25 turns/m and 50 turns/m,

The filaments constituting a multifilament yam made of high tenacity polypropylene, which is preferred for use in the inventive reinforced belt of fabric, are preferably twisted together with a twist factor comprised between 10 and 100, preferably between 20 and 65. Further, it is preferred that the yams have a twist level of between 25 turns/m and 150 turns/m, preferably between 50 turns/m and 80 turns/m.

The yams can be S twisted or Z twisted. In some instances, a combination of alternating S and Z twist, or solely S or Z twisting can be used. In the fabric the surfaces of the respective yams can be modified to provide any desired properties such as activation of the surface (to promote adhesion of thermoplastic elastomer applied thereon), cleaning or protection of the yarns, e.g. by covering the yarns with a protective coating.

In one embodiment, the surface of the yarns is smoothened to provide a defined surface roughness Ra of 300 nm or less and preferably 250 nm or less. Here, the surface roughness Ra is determined with an optical profilometer (Veeco NT1100). Smoothing can e.g. be performed by washing with an organic liquid, in particular with an aliphatic organic liquid.

In another embodiment, the surface of the yarns has been activated. Suitable means for activation include in particular flame or corona discharge treatment, plasma treatment, atmospheric pressure plasma treatment and an oxidative treatment with a chemical oxidant, such as a hydroperoxide or organic peroxide, chromate or mixture thereof. Alternatively, the surface of the yarns has been activated by treatment with an organic or inorganic acid, wherein the organic acid is preferably acetic or trifluoroacetic acid.

In yet another embodiment, the yams have been modified with a surface finishing of a polymer film, wherein the film material is preferably selected from thermoplastic polyolefins, polyesters and polyurethanes.

The fabric of the invention, as well as the inventive reinforced belt comprising the same can comprise one or more additional yarns, which are formed from a different material than the majority of the warp and weft yarns. In a preferred embodiment, the additional yarn or yarns are included into the fabric in a proportion of 15 wt.-% or less, more preferably 10 wt.-% or less and even more preferably 1 to 6 wt.-% or less relative to the total weight of the fabric.

A particularly suitable material, on which additional yams in the inventive fabric can be based, is polyethylene terephthalate (PET), in particular PET, which has a melting point of from ± 30 °C of the melting point of the other yams in the fabric. In one embodiment, one or more PET yams are used in combination with polypropylene yarns in the weft direction. In another embodiment, the yams in the weft direction are hybrid yams, where polypropylene and PET strands are assembled or twisted in combination. In another embodiment, one or more PET yams are used in combination with polyethylene (in particular UHMWPE) yams in the warp direction. In a yet further embodiment, the yams in the warp direction are hybrid yams, where polyethylene (in particular UHMWPE) and PET strands are assembled or twisted in combination.

In a yet further aspect, the present invention concerns a process for the recycling of a reinforced belt as described above, wherein the process comprises the melting and internal intimate mixing of the reinforcing fabric and the thermoplastic elastomer and thereby obtaining a homogeneous mixture with one or more phases. Preferably, the homogeneous mixture has one phase only. The mixture, which has thus been prepared, can be used to manufacture new products, which can be elastomeric components such as conveyor belts or other products.

A yet further aspect of the invention concerns a process for the production of a reinforced belt comprising a reinforcing fabric and a thermoplastic elastomer, wherein the process comprises (i) melting a reinforced belt as described above and internal intimate mixing to thereby obtain a homogeneous mixture with one or more phases and (ii) forming a reinforced conveyor belt comprising a reinforcing fabric at least one thermoplastic elastomer layer, wherein the thermoplastic elastomer layer is formed from the homogeneous mixture in (i).

In this manner, the reinforced belt which is used as the starting material in the process and the reinforced belt produced within the process have a comparable structure, with the result that the reinforced belt, which is produced can itself be converted into a new reinforced belt via an analogous process.

For the reinforced belt and methods described above, it is preferred if the reinforcement fabric accounts for a proportion of 2 to 20 wt.-% and preferably 5 to 15 wt.-% of the total amount of reinforcement and thermoplastic elastomer in the reinforced belt, respectively in the starting materials used for preparing the reinforced belt. In this manner, it is easy to ensure in the process that the mechanical properties of the thermoplastic elastomer do not deteriorate in a critical manner as a result of the thermoplastic polymer being incorporated into the thermoplastic elastomer, without the necessity to compensate this by the addition of virgin thermoplastic elastomer.

In the context of the methods described here, the melting and intimate mixing of thermoplastic polymer and thermoplastic elastomer suitably takes place in an extrusion process, which can be carried out in any suitable extrusion device. It is particularly expedient if a twin-screw extruder is used as the extrusion device.

In addition, it is preferred if the upper and lower thermoplastic elastomer layers of the reinforced belt produced by the method described are formed from the mixture of the melted-in thermoplastic elastomer component and the reinforcement fabric. In a yet further aspect, the present invention relates to a reinforced belt which is prepared by the above indicated process.

A yet further aspect is directed to the use of a fabric as described above in combination with a thermoplastic elastomer for the provision or a simplified recyclability, wherein the material of the polyolefin yarns are adjusted to the thermoplastic elastomer in a manner that a homogeneous polymer mixture having one or more phases is formed when the polyolefin and the thermoplastic elastomer are molten together and are intimately mixed.

In the following, the present invention will be further illustrated in more detail using a few exemplary embodiments, which, however, should not be understood in any way as limiting the scope of protection of the application.

Examples:

Example 1 :

Several different belts with a TPE cover and lower layer and a mono layer fabric of different design were prepared and investigated for their mechanical characteristics.

For comparison, an all-PET fabric (comparative example 1 ) and mixed PET/polyamide fabric (comparative example 2) were used, which provide the intended target tension together with a low elongation at working strength of less than 2%. The respective characteristics of these belts are provided in the below table 1 . The respective belts were subjected to tension at a working strength of 10% of the breaking strength to simulate a working environment with proper running and power transmission from the pulleys to the belt. Due to the more dissimilar properties of the PET and polyamide fibers, the materials could not be melt-processed with the cover and lower layer material to provide a homogeneous mixture.

As further example 1 , a fabric with UHMWPE yarns in the warp direction and polypropylene yarns in the weft direction was prepared using a plain weave design. As is apparent from the below table 1 , the respective belt did not fully reach the intended target tension despite the warp yams theoretically provide the required tension. In addition, the belt exhibited a comparative high working elongation of about 5 %, which was higher than in the comparative examples (< 2%) and also significantly higher than in steel cables (elongation of approx. 0.5% or lower). In contrast to the convention belt designs, it was possible to meltprocess the belts with the fabric and cover and lower layer materials to provide a homogeneous mixture.

Table 1 : Properties in warp direction of Tension class 400 N/mm Example 2

A further sample set was prepared as indicated in Example 1 above, where different weave designs were tested and where the respective fabrics were based on UHMWPE and polypropylene yams. The respective belts were prepared to provide an intended target tension of 1000 N/mm.

Table 2:

As is apparent from the above, by adjusting the weave design, it is possible to provide belt properties in terms of target tension and elongation, which meet the requirements for use as transport belts.

Claims

1 . A reinforced belt comprising an upper thermoplastic elastomer layer, a reinforcing fabric and a lower thermoplastic elastomer layer, wherein the fabric is positioned between the upper and lower elastomer layers and comprises polyolefin yams, wherein the yarns in the length direction of the belt have a tensile strength which is higher than the tensile strength in the width direction by at least 10%, and wherein preferably the yarns in the length direction are oriented such that they do not twist against the straight line of extension by an angle of more than 30°.

2. Reinforced belt according to claim 1 , wherein the fabric has polyethylene yams in the length direction of the belt and polypropylene yams in the width direction of the belt.

3. Reinforced belt according to claim 2, wherein the polyethylene yams comprise polyethylene with a molecular weight Mw of from 2,000,000 to 6,000,000 g/mol.

4. Reinforced belt according to claim 2 or 3, wherein the polyethylene has a density of from 0.91 to 0.98 g/cm³ and preferably 0.95 to 0.98 g/cm³ and/or a crystallinity of from 30 to 90 % and preferably 75 to 85%.

5. Reinforced belt according to any one of claims 2 to 4, wherein the yams are constituted from 1 to 10 and preferably 1 to 5 single yams.

6. Reinforced belt according to any one of claims 2 to 5, wherein polyethylene single yams have a linear density of from 220 to 3300 dtex and preferably from 1760 to 2640 dtex and/or wherein polypropylene single yams have a linear density of from 930 to 4400 dtex.

7. Reinforced belt according to any one of claims 2 to 6, wherein the upper and lower thermoplastic elastomer layers comprise a non-fluoropolymer thermoplastic vulcanisate, a thermoplastic polyolefin or a thermoplastic polyurethane as base material.

8. Reinforced belt according to any one of claims 2 to 7, wherein the fabric further comprises at least one thermoplastic polyurethane, polyester or polyamide yam.

9. Reinforced belt according to any one of the preceding claims, which disintegrates by melting when heated to a temperature of from 130°C to 250° and preferably of from 140°C to 200°C.

10. Reinforced belt according to any one of the preceding claims, wherein the fabric is provided in one or more layers, and preferably in from 1 to 4 layers.

11 . Reinforced belt according to any one of the preceding claims, which is formed as a conveyor belt, a timing belt or a power transmission belt.

12. A fabric as specified in any one of claims 2 to 6 or 8, wherein the fabric preferably comprises yams with a surface roughness Ra of less than 300 nm and preferably less than 250 nm.

13. Fabric according to claim 12, wherein the yams of the fabric or fabric itself has been pre-stretched.

14. Process for the recycling of a reinforced belt according to any one of claims 1 to 11 , wherein the process comprises the melting and internal intimate mixing of the reinforcing fabric and the thermoplastic elastomer and thereby obtaining a homogenous mixture with one or more phases.

15. Process for the production of a reinforced belt comprising a reinforcing fabric and a thermoplastic elastomer, wherein the process comprises (i) melting a reinforced conveyor belt according to any one of claims 1 to 11 and internal intimate mixing to thereby obtain a homogenous mixture with one or more phases and (ii) forming a reinforced conveyor belt comprising a reinforcing fabric at least one thermoplastic elastomer layer, wherein the thermoplastic elastomer layer is formed from the homogenous mixture in (i).

16. Use of a fabric according to any one of claims 12 or 13 in combination with a thermoplastic elastomer for the provision or a simplified recyclability, wherein the material of the polyolefin yarns are adjusted to the thermoplastic elastomer in a manner that a homogeneous polymer mixture having one or more phases is formed when the polyolefin and the thermoplastic elastomer are molten together and are intimately mixed.