Manufacturing process of TPE-belts with reinforcing polyolefin fabric

Abstract

The present invention relates to a process for manufacturing a reinforced belt comprising a first thermoplastic elastomer cover layer, a reinforcing fabric comprising polyolefin yarns, and a second thermoplastic elastomer cover layer in that order by assembling, wherein the reinforcing fabric is pre-stretched in the length direction of the belt by 0.01 to 1.5%, based on the initial length of the reinforcing fabric, during the assembling step, wherein the assembling step is preferably a laminating step or a co-extrusion, calendaring and cooling step. The present invention further relates to reinforced belts obtainable by such a process.

Description

[0001] MANUFACTURING PROCESS OF TPE-BELTS WITH REINFORCING

[0002] POLYOLEFIN FABRIC

[0003] The present invention relates to a process for manufacturing of reinforced belts comprising a first thermoplastic elastomer cover layer, a reinforcing fabric comprising polyolefin yams, and a second thermoplastic elastomer cover layer in that order. The present invention further relates to reinforced belts obtainable by such a process.

[0004] State of the art

[0005] Typical elastomer conveyor belts have top and bottom rubber covers and a carcass, which for steel cord belts is made of large number of steel cords and for fabric belts from one or several tensile reinforcements (“fabric plies”) using woven fabrics typically containing polyester, polyamide or aramid yams.

[0006] A typical manufacturing process of such elastomer conveyor belts consists of compounding, assembling and vulcanization. The assembling includes e.g. manufacturing of a fabric carcass with rubber covers by a calendaring process or assembling of steel cords with top and bottom covers containing bonding rubber. The vulcanization step can be realized for steel cord or fabric belts with a standard press discontinuously or for fabric belts also continuously using a double band press (DoBa).

[0007] The final product should comply with a technical (design) specification, where among many other technical parameters the nominal breaking strength and the reference elongation measured at 10% of the nominal breaking strength in the warp direction are the key values. Tested values of the belt warp tensile strength must be never less, and tested values of the elongation at reference load be never more than the designated values of the Nominal Breaking Strength and the Reference Elongation in the Warp direction in a technical specification. The maximum nominal breaking strength of fabric belts typically does not exceed 4000 N / mm, whereas for steel cord belts a nominal breaking strength of up to 10.000 N / mm is possible.

[0008] The elongation properties of a conveyor belt determine the size of a belt conveyor take-up (obligatory tensioning device), belt transitional lengths (from troughed idler stations to a pulley) and curve radii. Fabric conveyor belts have typical values of the total reference elongation in interval in the range of 1 .3 to 3.5% and steel cord conveyor belts in the range of 0.1 to 0.35%.

[0009] Consequently, fabric belts are commonly used for center distances of up to max. 500 m, “tight” curves with small curve radii and / or short transitional length trough- to-pulley, whereas steel cord belts are primary used for center distances of more than 500 m (long-distance conveyors) and everywhere, where a low belt elongation is required (e.g. as a part of special mining or construction machines) or in cases where fabric belts cannot be applied because of e.g. a limited nominal breaking strength due to a very long conveying distance, high elevation and / or high mass capacity of a conveyor system.

[0010] A rather new development are TPE-belts which include reinforcing polyolefin fabric, usually as a monolayer, which can substitute commonly used tension members of conveyor belts. The polyolefin reinforcing fabrics usually comprise high strength polyolefins such as polyethylene (PE, e.g. UHMW-PE) and / or polypropylene (PP) yarns. The elastomer compounds in the commonly used cover layers are replaced by thermoplastic elastomers such TPU and TPV which have much better mechanical properties. Such TPE-belts make a vulcanization obsolete and enable an easy recycling concept. Ideally, described above TPE-Belts should provide advantages of common fabric or a steel cord conveyor belts or at least constitute a compromise of both belt types.

[0011] Despite some similarities, the manufacturing process of these TPE-belts is different from typical manufacturing processes of common steel cord and fabric conveyor belts described above. In a manufacturing process of described TPE-belts, TPE-covers plates are assembled with a polyolefin fabric carcass using hot melt adhesive films or e.g. liquid reactive adhesives or other TPE-adhesives applied on both sides of the fabric and / the covers and laminated in a flatbed laminator or in a double band press. Alternatively, TPE-hot melt adhesive layers and TPE-covers can be coextruded on a fabric one after the other in two or several steps.

[0012] For the manufacturing process of TPE-belts, appropriate selection of time and temperature for a heating step to activate adhesives and a cooling step to prevent a ’’memory” effect and to maintain required adhesion level after the process is completed, as well as fabric tensile properties are important. An overheating due to a wrongly selected temperature, time or both can cause a strong deterioration of warp tensile properties of the TPE-belt.

[0013] A problem with the preparation of TPE-belts according to the prior art is that the industrial requirements with fabric warp tensile strength and fabric warp elongation at reference load are often not met. Thus, though polyolefin fabrics originally designed and supplied with so called tensile reserves (higher fabric warp tensile strength and lower fabric warp elongation at reference load as requested) are used, the resulting TPE-belts often do not fulfil the industrial requirements. In other words, after the manufacturing process is finished, the requirements defined by a technical specification value of the nominal breaking strength and the reference elongation in warp direction are not achieved.

[0014] As mentioned, various manufacturing processes for TPE-belts are known, with all processes having in common that the cover layers, the reinforcing fabric and, if necessary, an adhesive must be combined in an assembling step such as in a coextrusion step or in a laminating step. For the manufacturing process, a tuning of different process parameters during the assembling step, such as the temperature, tension of the reinforcing fabric and the duration (time) of the assembling process, have been considered. On the other hand, information on the effect of fabric or belt tensioning during an assembling process is not available. Description of the invention

[0015] Accordingly, there is a need for a process for the manufacturing of reinforced TPE- belts such as conveyor belts, which have an improved belt warp tensile strength compared to conventional belts prepared from thermoplastic elastomers. Thus, the object of the invention is to provide a manufacturing process for TPE-belts including a reinforcing polyolefin fabric with improved belt warp tensile strength that ensures that the belt warp tensile strength of the belt produced is equal or higher than the required specified belt warp nominal breaking strength. In particular, the belt produced should have a belt warp tensile strength, which is not significantly lower than and preferably at least as high as the fabric warp tensile strength of reinforcing fabric used therein.

[0016] Moreover, it should be possible to adjust the elongation at reference load (reference elongation) of the belt as desired with respect to the specific belt application and / or customers requirements by simple modification of the process.

[0017] The inventors found that the process for manufacturing conventional fabric belts produced by continuous vulcanization is not transferable to the production of TPE. In particular, the inventors unexpectedly found that in opposition to the common vulcanization process where the reinforcing fabric is incorporated in an unstretched state, pre-stretching of the reinforcing fabric can significantly improve the mechanical properties of TPE-belts.

[0018] Surprisingly, it was found that a certain degree of pre-stretching of the polyolefin fabric during the assembling step of TPE-belts can improve the mechanical properties, in particular the belt warp tensile strength and the reference elongation in length direction of the belt.

[0019] Accordingly, in a first aspect, the present invention is directed to a process for manufacturing a reinforced belt comprising a first thermoplastic elastomer cover layer, a reinforcing fabric comprising polyolefin yarns, and a second thermoplastic elastomer cover layer in that order, wherein the process comprises assembling on each side of the reinforcing fabric a thermoplastic elastomer layer by means of an adhesive, wherein the reinforcing fabric is pre-stretched in the length direction of the belt by 0.01 to 1 .5% based on the initial length of the reinforcing fabric during the assembling step, wherein the assembling step is preferably a laminating step or a co-extrusion, calendering and cooling step.

[0020] Accordingly, the reinforced belt according to the invention generally comprises a first thermoplastic elastomer cover layer, a first adhesive layer, a reinforcing fabric, preferably in the form of a monolayer, a second adhesive layer and a second thermoplastic elastomer cover layer in that order.

[0021] The inventive process provides a TPE-belt with improved belt warp tensile strength, which is similar or even better to the fabric warp tensile strength of the reinforcing fabric used so that it can be ensured that the belt warp tensile strength is equal or higher than the required specified belt warp nominal breaking strength. Moreover, the belt warp elongation at reference load can also be improved. In addition, the inventive process makes it possible to steer the elongation at reference load as desired with respect to the specific belt application and / or customers requirements by simple modification of the process.

[0022] The reinforcement fabric is pre-stretched by tensioning. Thus, tensioning of a polyolefin fabric resulting in a pre-stretch of 0.01 to 1.5% such as 0.5% during the assembling of said TPE-belts improves the belt warp tensile strength and the elongation at reference load and enables to achieve required / specified values of the Nominal Breaking strength and the Reference Elongation for a TPE-belt, which can be close to those of aramid DPP belts. By using different pre-stretch levels reference elongation values typical for fabric EP, PP, EPP-belts, aramide DPP belts or even for steel cord belts can be achieved. The higher the pre-tension in the manufacturing process of TPE-belts, the lower is the reference elongation. Furthermore, a reduction of a fabric stretch, e.g. from 0.5% to 0.25% or less, during a assembling (lamination, co-extrusion / calendering etc.) process allows to achieve the belt warp tensile strength equal or higher than the required belt warp nominal breaking strength and high values of elongation at reference load comparable or even higher than values of Reference Elongation of common fabric belts in warp direction, which enables to use such “stretchable” TPE-belts for “tight” curves with small curve radii and / or short transitional length trough-to-pulley.

[0023] Summarizing, the stretch level of a reinforcing fabric comprising polyolefins during an assembling process with TPE-cover layers not only helps to achieve specified nominal breaking strength in the warp direction, but also to “steer” the elongation at reference load in accordance with a desired belt application.

[0024] In the following, the invention is described in detail.

[0025] In the sense of the present application, pre-stretching means that a reinforcing fabric is pre-stretched by a certain value in the warp direction compared to the initial length of the fabric, i.e. in the unstretched state. Since the reinforcing fabric is located in the belt along its warp direction, the warp direction corresponds to the length direction of the belt. Accordingly, a pre-stretch of 0.01 to 1.5% means that the reinforcing fabric is stretched so that the length in the warp direction is 0.01 to 1.5% higher than the length of the reinforcing fabric in the unstretched state. For example, if a fabric has a length of 100 m in the unstretched state, a pre-stretch of 0.5% would result in a lengthening of the fabric to a length of 100.5 m.

[0026] In the process for manufacturing a reinforced belt according to the invention, the reinforcing fabric is pre-stretched by 0.01 to 1 .5%, preferably by 0.10 to 0.60%, particularly preferably by 0.20 to 0.55%, even more preferably by 0.45 to 0.55%, based on the initial length of the reinforcing fabric during the assembling step. A pre-stretch of about 0.5% or about 0.25% are particular preferred embodiments.

[0027] Belt warp tensile strength refers to the tensile strength of the belt in length direction. Belt warp elongation at reference load refers to the elongation of the belt in length direction. Belt warp tensile strength, belt warp elongation at break and belt warp elongation at reference load can be measured according to DIN EN ISO 283.

[0028] By the assembling step an assembly is formed. Assembling preferably refers to or comprises a) a laminating step or b) a co-extrusion step, a calendering step and a cooling step, in which the thermoplastic elastomer cover layers are bonded to the reinforcing fabric by means of an adhesive positioned therebetween. The assembling of the two thermoplastic elastomer layers on the reinforcing fabric can be carried out simultaneously or successively.

[0029] In one embodiment the assembling step is a laminating step. The laminating step usually involves a heating step and a cooling step. According to this embodiment, on each side of the reinforcing fabric a thermoplastic elastomer layer is laminated by means of an adhesive to form a laminated assembly. The assembly formed by applying the adhesive layer or layers and the thermoplastic elastomer layer or layers is generally heated and subsequently cooled to form a laminated assembly. The lamination of the two thermoplastic elastomer layers by an adhesive can be carried out simultaneously or subsequently, wherein simultaneously is preferred.

[0030] In an alternative embodiment the assembling step is a co-extrusion step, a calendering step and cooling step. According to this embodiment, on each side of the reinforcing fabric a thermoplastic elastomer layer and an adhesive layer are co-extruded and the reinforcing fabric with the thermoplastic elastomer layer(s) and adhesion layer(s) co-extruded thereon is calendered and subsequently cooled to form an assembly. The assembling of the two thermoplastic elastomer layers by an adhesive by co-extrusion, calendaring and cooling can be carried out simultaneously or subsequently.

[0031] The reinforcing fabric is tensioned throughout the assembling step so that reinforcing fabric is pre-stretched to the extent required by the present invention during the assembling step. Preferably, the reinforcing fabric is also tensioned before the formation of the assembly so that reinforcing fabric is also pre-stretched in the length direction of the belt by 0.01 to 1 .5% or the preferred ranges given above based on the initial length of the reinforcing fabric before the formation of the assembly, or the reinforcing fabric is tensioned during the entire process. The preferred ranges for the extent of stretch before the formation of the assembly or the entire process correspond to those mentioned above for the assembling step.

[0032] An advantage of the present method is that the material properties can be adjusted by setting the pre-stretch of the reinforcing fabric during the assembling step. At a pre-stretch of about 0.3 to 0.6 % belt warp tensile strength and elongation at break are improved to such an extent that the nominal breaking strength and the elongation at reference load are close to aramid belts.

[0033] With a pre-stretch in a range of 0.1 to 0.3 %, the belt warp tensile strength and elongation at the reference load of the TPE-belts are still equal to or higher than those of conventional fabric belts, whereas the extensibility could be increased, opening up further application possibilities.

[0034] The tensioning of the reinforcing fabric in the length direction of the belt to achieve the required pre-stretch of the reinforcing fabric can be accomplished and measured by common means well known by the skilled person.

[0035] Assembling of the first and second thermoplastic elastomer layers on the reinforcing fabric can be carried out simultaneously or subsequently, preferably simultaneously.

[0036] The process of the invention can be carried out as a continuous process or as a discontinuous process.

[0037] The assembling of the thermoplastic elastomer layer with the reinforcing fabric is carried by means of an adhesive to achieve a firm bond between the reinforcing fabric and each of the thermoplastic elastomer cover layers. The adhesive is applied between the respective thermoplastic elastomer layers and the central reinforcing fabric. For this purpose, an adhesive can be applied on both sides of the reinforcing fabric and / or the side of the thermoplastic elastomer layers facing the reinforcing fabric. The layered assembly obtained corresponds to the reinforced belt to be manufactured.

[0038] The assembling step can be carried out by conventional means and methods.

[0039] In a preferred embodiment assembling is carried out by lamination as described above. The lamination is effected on an assembly including the reinforcing fabric and one or both thermoplastic elastomer layers wherein the adhesive is positioned between the reinforcing fabric and the thermoplastic elastomer layer(s). It is generally preferred to apply pressure during the laminating step.

[0040] In a preferred embodiment, wherein the assembling step is a laminating step, the thermoplastic elastomer layer(s) in the assembly are solid thermoplastic elastomer layer(s), e.g. in form of a plate, a sheet or a film. In this embodiment, the thermoplastic elastomer layers are preferably laminated simultaneously. The thermoplastic elastomer layer can be prepared e.g. by extruding and / or calendering a thermoplastic elastomer material.

[0041] In this embodiment, laminating usually includes heating, preferably heating and subsequent cooling, of the assembly, wherein it is preferred that during the heating step and the cooling step, if used, pressure is applied. The heating step serves to activate the adhesive. The cooling step may serve to ensure that the TPE-belt retains its shape (memory effect), prevent a deterioration of tensile properties of a polyolefin reinforcing fabric and to maintain the required adhesion level after the process is completed.

[0042] The lamination step and the cooling step may be carried out for instance in a flatbed laminator including a heating and pressure zone, e.g. nip rolls, for laminating and a cooling zone for cooling. Process parameters (pressure, temperature and time) depend on a belt thickness, applied materials (TPE-type and type of polyolefin fabric) and on the used equipment. In the heating step, in particular for an assembly having a thickness of

[0043] 5 to 8 mm, the assembly is preferably heated to a temperature in the range of 100 to 160°C, preferably 120 to 140°C, preferably for a time in the range of 1 to 6 minutes, preferably 3 minutes and wherein preferably a pressure between 5 to 10 bar, preferably 6 bar is applied.

[0044] In the cooling step, the assembly is preferably cooled to a temperature in the range of 25 to 40°C, preferably 30 to 35C, wherein the cooling time is preferably in the range of 1 to 12 minutes, preferably 2 to 8 minutes.

[0045] Particularly preferably, the assembly is heated to a temperature in the range of 100 to 160°C, preferably 120 and 140°C, preferably for a time in the range of 1 to

[0046] 6 minutes, preferably 2 to 5 minutes, and then cooled to a temperature in the range of 25 to 40°C, preferably 30 to 35°C, preferably for a time in the range of 1 to 12 minutes, preferably 2 to 8 minutes.

[0047] In a preferred embodiment, the laminating step includes heating and subsequent cooling of an assembly of the first thermoplastic elastomer layer, the reinforcing fabric and the second thermoplastic elastomer layer in that order, wherein the adhesive is positioned between the reinforcing fabric and the thermoplastic elastomer layers. Reference is made to the preferred temperatures and durations for the heating step and cooling step mentioned above.

[0048] In a preferred embodiment, laminating is carried out by means of a flatbed laminator or a press, preferably a double belt press.

[0049] In an embodiment, mono or multilayers of an adhesive, preferably a granulate adhesive, are co-extruded and calendered onto the reinforcing fabric, resulting in a "coated" fabric. In the second step, thermoplastic elastomeric cover layers are coextruded and calendered in one or two steps. The cooling step can be realized by cooled rolls or preferably by a cooling double press to prevent a memory effect. In an alternative embodiment, the assembly is formed by applying the thermoplastic elastomer cover layer(s) together with the adhesive layers on the reinforcing fabric by co-extrusion and following calendering in one step. Thermoplastic elastomer cover layers and the adhesive layers applied are in a heated state due to the co-extrusion and after the co-extrusion step a subsequent calendering step is carried out during which pressure is preferably applied on the co-extruded adhesive layer or layers and thermoplastic elastomer cover layer or layers on the reinforcing fabric. Thereafter, the assembly is cooled to prevent a memory effect. The subsequent cooling step is preferably carried out by cooling rolls (also termed chill rolls) or with a double press (e.g. flatbed laminator).

[0050] In this embodiment, each of the first and second thermoplastic elastomer cover layers and each of the adhesive layers are applied on the reinforcing fabric by coextruding and calendering step-by-step, wherein after application the resulting assembly is subjected to cooling, preferably under slight pressure, using e.g. cooling rolls or a cooling double press.

[0051] In the cooling step after co-extrusion and calendering, the assembly is preferably cooled to a temperature in the range of 25 to 40°C, preferably 30 to 35C, wherein the cooling time is preferably in the range of 1 to 20 minutes.

[0052] In this embodiment, the thermoplastic elastomer layers are preferably assembled on the reinforcing fabric successively in two steps. In the first step, the one or both adhesive layers are applied to one or both sides of the reinforcing fabric by coextrusion and calendering and subsequently cooled. In the second step, one or both thermoplastic elastomer layers are applied to the reinforcing fabric by coextrusion and calendering and cooled again as in the first step. Preferably, the adhesive layers are applied on both sides of the reinforcing fabric in the first step, and both thermoplastic elastomer layers in the second step. Alternatively, in the first step the first thermoplastic elastomer layer and the one adhesive layer are applied to one side of the reinforcing fabric by coextrusion and calendering and subsequently cooled. In the second step, the second thermoplastic elastomer layer and adhesive layer are co-extruded, calendered to the opposite side of the reinforcing fabric, and cooled thus forming an assembled belt with the top and bottom covers and fabric reinforcement.

[0053] In case of thick thermoplastic elastomer layers (e.g. > 4mm) the 3rdstep of assembling can be required to build up the required product specification cover thickness, when one or both thermoplastic elastomer layers are applied in the coextrusion and calendaring process on an assembled belt from the step 1 and 2.

[0054] In general, it is preferred that pressure is applied during the laminating step or the calendering step of the assembling variant including a co-extrusion step and a calendering step. The pressure applied to the assembly may vary depending on the assembly technologies used, e.g. flatbed laminator, press, double belt press, co-extrusion, calendering, etc.

[0055] The adhesive is not restricted, although some adhesives may be more advantageous depending on process control and the type of assembling step. Proven adhesives include liquid reactive adhesives, which feature durable bonds between substrates and offer chemical, moisture and heat resistance.

[0056] The adhesive may be liquid or solid at room temperature (e.g. 23°C). A solid adhesive may be in form of a granulate or film (sheet) usually provided with a release substrate or applied by co-extrusion. A liquid adhesive may be applied by common means, e.g. coating, spraying or rolling using dozing- and coating slot die systems or a roll coater or spraying systems. A granulate adhesive may be applied on a fabric in a co-extrusion and calendaring process.

[0057] The adhesive is preferably a liquid reactive adhesive or a hot-melt adhesive, such as in form of a hot-melt adhesive granulate or hot melt adhesive film. These adhesive film types can be monolayer or multilayer films and are well known to the skilled person. A preferred example of a hot-melt adhesive is a hot-melt adhesive comprising thermoplastic polyurethane elastomer (TPU). A preferred example of a liquid reactive adhesive is a one-component polyurethane adhesive. If a one- component polyurethane adhesive is used, it is preferably applied to the fabric by spraying or slot die extrusion.

[0058] In preferred embodiments, adhesive granulate or mono or multilayer adhesive films or 1 K-PU-adhesive are applied on both sides of the reinforcing fabric to bond TPE-covers with the fabric on.

[0059] The reinforcing fabric used in the inventive process comprises polyolefin yams, preferably UHMWPE yams in the warp direction. The reinforcing fabric can be hybrid which means using a different polyolefin yam such as polypropylene in the weft direction.

[0060] The polyolefin reinforcing fabric used in the process according to the invention consists of one or more layers. Preferably, the reinforcing fabric is a monolayer. Alternatively, 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 first and / or second adhesive layer. In this way, the belt is further consolidated.

[0061] The reinforcing fabric preferably has a fabric warp 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 yams in the warp direction is higher by at least 10% than the tenacity of the yams 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.

[0062] Preferably, the yams 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 yams 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. Preferably, the elongation at reference load of the TPE-belt at a working strength (which is 10% of the breaking strength) is 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 at reference load in the TPE-belt is primarily determined by the reinforcing fabric, the elongation properties of the reinforcing fabric are preferably in the same range.

[0063] The polyolefin yarns can be made from any polyolefin suitable for manufacturing fibers and / or yams. Preferably, the polyolefin yarns are made of polyethylene and / or polypropylene, preferably polyethylene. The polyolefin yams are most preferably made of ultra-high molecular weight polyethylene (UHMWPE).

[0064] The polyethylene in the polyethylene yams has preferably 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. Polyethylene with such molecular weight is generally referred to as UHMWPE. The molecular weight Mw is determined by known methods such as Gel Permeation Chromatography and Light Diffusion or is calculated from the Intrinsic Viscosity (IV) as measured on solution in decalin at 135°C. There are several empirical relations between IV and Mw.

[0065] 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.

[0066] The reinforcement fabric may contain one or more types of yam. Thus, the yams in the length (warp) direction and in the width (weft) direction of the reinforcing fabric may be the same or different. In a particularly preferred embodiment, the reinforcing fabric has polyethylene yams and / or propylene yams, preferably polyethylene yams, more preferably UHMWPE yams, in the length direction of the belt. In a particularly preferred embodiment, the reinforcing fabric has polyethylene yams in the length direction of the belt and polypropylene yams in the width direction of the belt. Polypropylene yarns for the use in this invention preferably provide a tensile strength of from 60 N to 300 N per single yarn (at a linear density of 930 to 4400 dtex, respectively), which is sufficiently lower than the tensile strength of the UHMWPE yams. Accordingly, polypropylene yarns are preferably used in the width (or weft) direction of the belt.

[0067] Alternatively or in addition, it is preferred that the polyethylene has a density of from 0.91 to 0.98 g / cm3and 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.

[0068] The linear density of the yams in the fabric, which is used for reinforcement in the belts of the invention is not subject to any relevant restrictions, as long as the yam provides the required strength to the reinforcing fabric and belt, into which it is incorporated. Here, the linear density of the yams especially in the length (or warp) direction of the reinforcing 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 yams in the width (or weft) direction of the reinforcing fabric in the belt can be varied in a broad range and preferably is within the range of 930 to 8500 dtex.

[0069] The yams can be formed from one single yam or a multitude of single yams, which are plied and twisted together. The single yams 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 yams in the width direction are formed from a single yam or a multitude of single yams, the single yams in the width direction preferably have a linear density of from 930 dtex to 4400 dtex. The yarn in both the length and width direction can be a single yarn or can be assembled from multiple single yarns, which are cabled or twisted together to provide the yarn. In one embodiment, the yarns 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.

[0070] In the reinforcing 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 yams, e.g. by covering the yams with a protective coating.

[0071] It is possible to activate the surface of the yams. 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 yams has been activated by treatment with an organic or inorganic acid.

[0072] The yams of the reinforcing fabric can be modified with a surface finishing of a polymer film, wherein the film material is preferably selected from thermoplastic polyolefins, polyesters and polyurethanes.

[0073] The thermoplastic elastomer (TPE) layers used in the inventive process preferably comprise a thermoplastic vulcanizate (TPV), preferably a non-fluoropolymer TPV, a thermoplastic polyolefin (TPO) or a thermoplastic polyurethane (TPU) as base material.

[0074] Suitable materials for the thermoplastic elastomer of the thermoplastic elastomer layers 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 for the thermoplastic elastomer layers include ethylene acrylate rubber (AEM) and acrylate rubber (ACM), preferably in combination with polyamide, and thermoplastic polyurethane elastomers (TPU) as base material.

[0075] The thermoplastic elastomer layers 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.

[0076] The invention is also directed to a reinforced belt, obtainable by a process according to the invention as described above.

[0077] All aspects, proportions and embodiments described above for the inventive method, in particular with respect to the pre-stretch, the reinforcing fabric and the thermoplastic elastomer cover layers also apply to the inventive belt so that reference is made thereto.

[0078] The reinforced belt according to the invention is preferably a belt with a nominal breaking strength of at least 100 N / mm up to10000 N / mm or even more, but more preferably a belt with a strength of at least 400 N / mm to about 4000 N / mm (according to DIN EN ISO 22102:2020).

[0079] The reinforced belt according to the invention can have any shape of a belt for force transmission, such as e.g. a belt with patterned or cleated surfaces, 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 mechanical fasteners (clamps) of any types, a finger splice, or other holding means or splice technology.

[0080] The reinforced belt of the invention is preferably a conveyor belt, a timing belt or a power transmission belt, more preferably a conveyor belt.

[0081] The reinforced belt of the invention is preferably manufactured in part lengths, dispatched in belt reels and spliced on-site by a customer in an endless belt due to long center distances of conveyor systems and transport (dispatch) restrictions (weight and dimensions of a belt reel). In certain cases the reinforced belt can be manufactured as an endless belt, e.g. a baler belt or a belt for short conveyor systems.

[0082] In a preferred embodiment, the reinforcing fabric of the reinforced belt of the invention is stretched in the length direction of the belt by 0.01 to 1 .5% during a manufacturing process.

[0083] As already mentioned, it is possible to adjust the tensile properties of the reinforced belt according to the invention by adjusting the pre-stretch of the reinforcing fabric during the process according to the invention. In particular, a high belt warp tensile strength of a TPE-belt can be achieved while at the same time ensuring the necessary elongation, which is particularly advantageous for short center distances of conveyor belts.

[0084] Preferably, the reinforced belt according to the invention is used as a conveyor belt.

[0085] 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.

[0086] Figure 1 : Production of reinforced belt according to the invention with hot melt film as adhesive film The reinforcing fabric is let off a roll 1 A by means of a motor and held in place by a brake 2A. The fabric is spread and centered 3A before the hot-melt adhesive films are applied on both sides 4A and the cover sheets of the hot-melt adhesive films are winded up 5A. The reinforcing fabric with the hot-melt adhesive film on both sides is passed over a leader tape table 6A, then the TPE plates are laid on both sides of the reinforcing fabric with the hot-melt film 7A and the cover sheets of the TPE plates are also winded up 8A. The resulting assembly is laminated under pressure and passes through a heating and a cooling zone 9A. A corresponding pulling device 10A ensures that the pre-stretch of the reinforcing fabric as defined in the invention is maintained. The resulting reinforced TPE belt is winded up 11A.

[0087] Figure 2: Production of reinforced belt according to the invention with 1 component Pll liquid reactive adhesive as adhesive film

[0088] The reinforcing fabric is let off a roll 1 B by means of a motor and held in place by a brake 2B. The fabric is spread and centered (3B) before the 1 K-PU-adhesive is applied on both sides 4B. TPE plates are laid on both sides of the coated reinforcing fabric 5B and the cover sheets of the TPE plates are winded up 6B. The resulting assembly is passed over a leader tape table 7B and is laminated under pressure while passing through a heating and a cooling zone 8B. A corresponding pulling device 9B ensures that the pre-stretch of the reinforcing fabric as defined in the invention is maintained. The resulting reinforced TPE belt is winded up 10B.

[0089] Figure 3: Production of reinforced belt according to the invention by co-extrusion and calendering of a granulated adhesive TPE and cover TPE onto a reinforcing fabric

[0090] The reinforcing fabric is let off a roll 1 C by means of a motor and held in place by a brake 2C. The fabric is spread and centered 3C before the cover TPE and hot- melt adhesive are co-extruded on one side or both sides of the reinforcement fabric 4C. The resulting assembly is calendered 5C and then subjected to a cooling press or cooling (chill) rolls 6C. A corresponding pulling device 7C ensures that the pre-stretch of the reinforcing fabric according to the invention is maintained. The resulting reinforced TPE belt is winded up 8C. The co-extrusion and calendering process of TPEs onto the fabric can be also done in two steps - for the adhesive TPE on both sides first and then for the cover TPE onto the coated with adhesive TPE fabric.

[0091] Examples

[0092] In all following examples a single-layer reinforcing fabric with UHMWPE yams in the length direction of the belt (warp direction) and polypropylene yarns in the width direction of the belt (weft direction) and various TPE-belts with TPE-cover layers (Reference Examples 1-2 and Examples 1-5) and such single-layer reinforcing fabric (Test Examples 1-3) were manufactured and investigated for their mechanical properties.

[0093] The TPE-cover layers are made of TPU plates with a thickness of 2 mm.

[0094] In Reference Examples 1-2 and Examples 1-5, the thermoplastic elastomer cover layers and adhesive were applied to the reinforcing fabric to form an assembly, which was then laminated at a pressure of between 6 and 25 bar. During the assembling step, the assembly was first pressed and heated and then cooled, with the respective temperatures and times given in the tables below.

[0095] In some examples, the reinforcing fabric was pre-stretched prior to application of the thermoplastic elastomer cover layers and adhesive.

[0096] The fabric warp tensile strength of the reinforcing fabric was compared with the belt warp tensile strength of the manufactured TPE-belt. In Tables 1 and 2, the relative changes of the tensile strength are given as a percentage, with a negative value expressing that the TPE-belt shows a poorer tensile strength as the reinforcing fabric used. In an analogous manner, the relative change in elongation at the reference load was determined, with a positive value expressing that the TPE-belt is more stretchable than the reinforcing fabric used.

[0097] Belt warp tensile strength, belt warp elongation at break and belt warp elongation at reference load were measured according to DIN EN ISO 283.

[0098] Fabric warp tensile strength, fabric warp elongation at break and fabric warp elongation at reference load were measured according to DIN EN ISO 13934-1.

[0099] Reference Example 1 and Examples 1 to 4

[0100] All examples in Table 1 refer to preparation of TPE-belts with a minimum width of 300 mm, a minimum length of 750 cm and with single-layer reinforcement fabrics with a target warp tensile strength of 1000 N / mm also known as belt nominal breaking strength. The lamination of all TPE-belts was carried out by means of a press or of a flatbed laminator.

[0101] In the Examples in Table 1 , the adhesive films and the thermoplastic elastomer layers on each side of the reinforcing fabric were laminated in one step.

[0102] Table 1 : Properties of TPE-belts with different degrees of pre-stretched reinforcement fabric. Reference Example 2 and Example 5

[0103] Reference Example 2 in Table 2 refers to preparation of a TPE-belt with a minimum width of 340 mm, a minimum length of 800 cm and with single-layer reinforcement fabrics with a target warp tensile strength of 1000 N / mm.

[0104] Example 5 in Table 2 refers to preparation of a TPE-belt with a minimum width of about 300 mm, a minimum length of 100 cm and with single-layer reinforcement fabrics with a target warp tensile strength of 400 N / mm. The lamination of the TPE-belts of Reference Example 2 and Example 5 were both carried out by means of a flatbed laminator. The process parameters and results of these examples are given in Table 2. Table 2:

[0105] Test Examples 1 to 3

[0106] All examples in Table 3 refer to preparation of polyolefin single-layer reinforcement fabrics with a minimum width of 100 mm, a minimum length of 500 mm and with a target warp tensile strength of 1000 N / mm also known as belt nominal breaking strength. The fabrics were subjected to a heat treatment of 135°C for 180 seconds, wherein the fabric is not pre-stretched during the treatment (Test Example 1 ) or subjected to a pre-stretch of 1.0% or 1.5% in the warp direction (Test Examples 2 and 3). Table 3 is showing the effect of pre-stretch of the fabric on its warp elongation at reference load (Reference Elongation) at the same temperature and time and proof that with an increasing of the pre-stretch the reference elongation decreases. Table 3: Effect of pre-stretch on Fabric Reference Elongation for polyolefin reinforcing fabric sample with the nominal breaking strength of 1000 N / mm in the warp direction.

[0107] Conclusion

[0108] The objective was to investigate the influence of pre-stretching of the reinforcing fabric on the belt warp tensile strength and the belt warp elongation at reference load. Different degrees of pre-stretching applied to the reinforcing fabric were tested and compared to unstretched reinforcing fabric.

[0109] Table 3 shows that at the same temperature and time with an increasing of the pre-stretch from 0 to 1 .5% the reference elongation of the reinforcing fabric decreases without deterioration of the fabric warp tensile strength.

[0110] As is apparent from the Table 1 above, a pre-stretch of the reinforcing fabric in a belt manufacturing process enables to provide a TPE-belt with improved belt warp tensile strength and desired reference elongation. In particular, it was shown that pre-stretch of 0% results in a deterioration of the belt warp tensile strength, which becomes below minimal required by a specification nominal belt breaking strength. However a pre-stretch of 0.5% results in a TPE-belt with a belt warp tensile strength, which is higher as the required nominal breaking strength and the fabric warp tensile strength of reinforcing fabric used therein, which represents a significant improvement over TPE-belts with unstretched reinforcing fabric, and with the reference elongation values, which are typical for aramid belts and consequently take place between typical values of the reference elongation for steel cord belts and for fabric belts.

[0111] The reduction of the pre-stretch from 0.5% up to 0.25% provides the belt tensile strength, which is still higher than the fabric warp tensile strength, but with a significantly higher value of the reference elongation, typical for highly elastic fabric belts.

[0112] List of reference signs

[0113] I A. Let off of reinforcing fabric

[0114] 2A. Brake

[0115] 3A. Spreading and centering of reinforcing fabric

[0116] 4A. Let off hot melt film

[0117] 5A. Wind of cover sheets for hot melt film

[0118] 6A. Leader tape table

[0119] 7A. Let off TPE plate

[0120] 8A. Wind of cover sheets for TPE plate

[0121] 9A. Flatbed laminator

[0122] IOA. Pulling

[0123] I I A. Wind up of reinforced belt

[0124] I B. Let off of reinforcing fabric

[0125] 2B. Brake

[0126] 3B. Spreading and centering of reinforcing fabric

[0127] 4B. Two 1 K-PU-coating units for top and bottom sides of the reinforcing fabric

[0128] 5B. Let off TPU plate

[0129] 6B. Wind of cover sheets for TPU plate

[0130] 7B. Leader tape table

[0131] 8B. Flatbed laminator

[0132] 9B. Pulling

[0133] IOB. Wind up of reinforced belt

[0134] I C. Let off of reinforcing fabric

[0135] 2C. Brake

[0136] 3C. Spreading and centering of reinforcing fabric

[0137] 4C. Extruder

[0138] 5C. Calender rolls

[0139] 6C. Cooling double press (e.g. Flatbed laminator) or chill rolls

[0140] 7C. Pulling

[0141] 8C. Wind up of reinforced belt

Claims

Claims1. A process for manufacturing a reinforced belt comprising a first thermoplastic elastomer cover layer, a reinforcing fabric comprising polyolefin yarns, and a second thermoplastic elastomer cover layer in that order, wherein the process comprises assembling on each side of the reinforcing fabric a thermoplastic elastomer layer by means of an adhesive, wherein the reinforcing fabric is pre-stretched in the length direction of the belt by 0.01 to 1.5%, based on the initial length of the reinforcing fabric, during the assembling step.

2. The process according to claim 1 , wherein the assembling step is or comprises a) a laminating step or b) a co-extrusion step, a calendering step and a cooling step.

3. The process according to claim 1 or 2, wherein the reinforcing fabric is prestretched in the length direction of the belt by 0.10 to 0.60%, preferably by 0.20 to 0.55%, based on the initial length of the reinforcing fabric, during the assembling step.

4. The process according to any one of the preceding claims, wherein assembling of the first and second thermoplastic elastomer layers on the reinforcing fabric is carried out simultaneously or subsequently, and / or the process is a continuous process or a discontinuous process.

5. The process according to any one of the preceding claims, wherein the assembling step is a laminating step and laminating is carried out by means of a flatbed laminator or a press, preferably a double belt press.

6. The process according to any one of the preceding claims, wherein the assembling step is a laminating step which includes heating and subsequent cooling of an assembly of the first thermoplastic elastomer layer, the reinforcingfabric and the second thermoplastic elastomer layer in that order, wherein the adhesive is positioned between the reinforcing fabric and the first thermoplastic elastomer layer and between the reinforcing fabric and the second thermoplastic elastomer layer.

7. The process according to claim 6, wherein the assembly is heated to a temperature in the range of 100 to 160°C, preferably 120 to 140°C, preferably for a time in the range of 1 to 6 minutes, preferably 3 minutes and preferably a pressure between 5 to 10 bar, preferably 6 bar is applied.

8. The process according to any one of claims 1 to 4, wherein each of the first and second thermoplastic elastomer cover layers and each of the thermoplastic adhesive layers are applied on the reinforcing fabric by co-extruding and calendering step-by-step or simultaneous, wherein after application the resulting assembly is subjected to cooling, preferably in a double belt press or with cooling (chill) rolls.

9. The process according to any one of the preceding claims, wherein a pressure is applied during the laminating step or the calendering step.

10. The process according to any one of the preceding claims, wherein the adhesive is a liquid reactive adhesive, preferably a one-component polyurethane adhesive, or a hot-melt adhesive, preferably a hot-melt adhesive comprising thermoplastic polyurethane elastomer (TPU).11 . The process according to any one of the preceding claims, wherein the polyolefin yarns comprises polyethylene yams, wherein the polyethylene is preferably ultrahigh molecular weight polyethylene (UHMWPE), and / or polypropylene yarns, wherein polyethylene yams are preferred.

12. The process according to claims 11 , wherein the reinforcing fabric comprises polyethylene yams in the length direction of the belt, wherein the yams in the width direction of the belt are preferably polypropylene yams.

13. The process according to any one of the preceding claims, wherein the thermoplastic elastomer (TPE) layers comprise a non-fluoropolymer thermoplastic vulcanizate (TPV), preferably a non-fluoropolymer TPV, a thermoplastic polyolefin (TPO) or a thermoplastic polyurethane (TPU) as base material.

14. A reinforced belt obtainable by a process according to any one of the claims 1 to 13, wherein the reinforcing belt is preferably formed as a conveyor belt, a timing belt or a power transmission belt, preferably a conveyor belt.

15. The reinforced belt according to claim 14, wherein the reinforced belt is an endless belt, e.g. a baler belt, and / or the reinforcing fabric is stretched in the length direction of the belt by 0.01 to 1 .5% during the manufacturing process.

Images