Conveyor belts with low rolling resistance tpe bottom cover

Abstract

The present invention concerns conveyor belts with a cover layer on the carrying side and a cover layer on the pulley side, wherein the layers comprise an elastomeric material and the conveyor belt further comprises a belt carcass having one or more embedded reinforcement members, wherein the pulley side cover layer of the conveyor belt is fabricated from a thermoplastic elastomer. The present invention is further concerned with methods for the production of respective conveyor belts, the use of thermoplastic elastomer based layer on the pulley side of a conveyor belts for the reduction of rolling resistance and conveyor belt systems comprising respective conveyor belts.

Description

[0001] Description

[0002] Title

[0003] CONVEYOR BELTS WITH LOW ROLLING RESISTANCE TPE BOTTOM COVER

[0004] The present invention concerns conveyor belts with cover layer (top cover) on the carrying side and a cover layer (bottom cover) on the pulley side, wherein the covers layers comprise an elastomeric material and the conveyor belt further comprises a belt carcass having one or more embedded reinforcement members, wherein the pulley side cover layer of the conveyor belt is fabricated from a thermoplastic elastomer. The present invention is further concerned with methods for the production of respective conveyor belts, the use of thermoplastic elastomer based layers on the pulley side of a conveyor belts for the reduction of rolling resistance and conveyor belt systems comprising respective conveyor belts.

[0005] State of the art

[0006] To transport bulk goods of all kinds such as stones, ores or coal in mining applications or grains, groceries or waste, conveyor belts are often used, which are subject to a wide variety of requirements depending on the application.

[0007] The carrying side and pulley side cover layers of a conveyor belt as core components of a conveyor system usually consist of a vulcanized rubber mixture, which is prepared from at least one rubber component or a rubber component blend, at least one crosslinking agent or a crosslinking system comprising a crosslinking agent and an accelerator, and usually further ingredients, in particular in the form of fillers, processing aids, aging inhibitors, plasticizers and other additives including fibers and color pigments. By means of such cover layers, the conveyor belt is provided with the required elastic properties. However, these elastic properties, especially in the cover layer on the pulley side of a conveyor belt, cause indentation when the conveyor belt is running on the support rollers. As a result, a certain amount of energy is dissipated on each support roller, which increases the energy demand for the operation especially in long, horizontal or slightly inclined conveyor systems.

[0008] In the prior art, some attempts have been described in order to reduce the rolling resistance resulting from indentation when the conveyor belt is transported over the support idlers. For example, DE 102012111599 A1 describes the provision of a cover layer on the pulley side of a conveyor belts, which is prepared from a specific rubber mixture comprising natural or synthetic polyisoprene (NR or IR) and at least one butadiene rubber (BR) in a ratio of 30:70 (30 / 70) to 70:30 (70 / 30) in addition to at least two different carbon black grades in a ratio 30 to 70 (30 / 70) to 70 to 30 (70 / 30). According to DE 102012111599 A1 this mixture provides an increased rebound and a lower tan6 which were seen as the key indicators for a good energy dissipation.

[0009] US 2019225424 A1 describes conveyor belts with rolling resistance factors in the range of 0.05 to 0.06 (at a temperature of 25°C), which have a pulley side layer of a sulfur cured rubber mixture comprising of from 20 phr to 40 phr of an EPDM elastomer, from 1 phr to 40 phr of a polybutadiene rubber, and from 30 phr to 80 phr of a natural rubber.

[0010] EP 2792709 A1 describes rubber compositions for conveyor belts, which comprise 100 parts by mass of a dienic polymer, and 25 to 55 parts by mass of two types of carbon black, which have a specific nitrogen absorption surface and dibutyl phthalate oil absorption. The rubber in EP 2792709 A1 is constituted from 15 to 65 mass% of natural rubber and / or isoprene rubber, and from 85 to 35% by mass of butadiene rubber. Similarly, DE 112015002461 B4 also uses two different types of carbon black, which are characterized by specific nitrogen absorption surfaces and dibutylphthalate oil absorptions, wherein the rubber composition is based on natural rubber and butadiene rubber in a ratio of 40 to 90 mass% natural rubber and 10 to 60 mass% butadiene rubber. In both of EP 2792709 A1 and DE 112015002461 B4 the respective compositions were vulcanized with sulfur and a vulcanization accelerator. Further similar rubber compositions are described in EP 3483210 A1 , EP3677632 A1 or JP 2018009061 A. Despite of the improvements made in the prior art with optimized vulcanized rubber compositions, a major downside of these compositions is that they usually exhibit a significant increase in the rolling resistance when the temperature is close to or below 0°C. In this case, it is no uncommon that the rolling resistance, as indicated by the rolling resistance factor, at -25°C is 1 .5 to even 2 times higher than the rolling resistance at 25°C. Accordingly, when the conveyor belt is used in environments where it may be exposed to very low temperatures, the belts may need much more energy for operation at such temperatures than at ambient temperature.

[0011] Accordingly, there is a need for conveyor belts which avoid the significant increase of the rolling resistance at low temperatures and which have a more even profile of low rolling resistance over a broad temperature range including temperatures below 0°C. At the same time, the conveyor belts should not make relevant compromises to vulcanized rubber based conveyor belts in terms of their mechanical properties.

[0012] The present application addresses these needs.

[0013] Description of the invention

[0014] In the investigations, which are underlying the resent invention, it has unexpectedly been discovered that thermoplastic elastomers provide a low level of rolling resistance over a broad temperature range, which includes temperatures of down to -50°C. In addition, thermoplastic elastomers can provide improved wear resistance in the sense of mechanical wear including relevant properties such as abrasion resistance, which makes these materials particularly suitable for the fabrication of pulley side cover layers in conveyor belts.

[0015] Accordingly, in a first aspect, the present invention pertains to a conveyor belt with a cover layer on the carrying side and a cover layer on the pulley side, wherein the respective cover layers comprise an elastomeric material and the conveyor belt further comprises a belt carcass having one or more embedded reinforcement members, wherein the pulley side cover layer of the conveyor belt is fabricated from a thermoplastic elastomer.

[0016] In other words, in the inventive conveyor belt, both cover layers are constituted from an elastomeric material, but the material on the pulley side is based on a thermoplastic elastomer as this material provides for a favorable reduction of energy dissipation between the conveyor belts on the supporting idlers.

[0017] In contrast to the prior art approaches of optimizing the rolling resistance of vulcanized rubbers, the basic concept of the invention resides in the use of a thermoplastic elastomer. This provides the additional advantage of a more cost effective and efficient possibility to recycle the conveyor belt material after it has surpassed its lifetime, as thermoplastic elastomers can be remolten, reprocessed and then reused as a formable elastomeric material. This provides a significant advantage over vulcanized rubbers, which are much more difficult to recycle because vulcanization / crosslinking is permanent so that it is only possible to process the rubber into smaller particles by grinding or cutting. The particles can then be incorporated into new products by incorporation into a matrix, which, however, limits the content of recycled material in a new product.

[0018] Particularly suitable thermoplastic elastomers for use in the inventive conveyor belts are thermoplastic polyurethanes and thermoplastic vulcanisates (i.e. elastic material, which have crosslinks between individual polymer molecules, but which still can be formed at elevated temperatures). Accordingly, it is preferred if the thermoplastic elastomer in the inventive conveyor belt is selected from a thermoplastic polyurethane and a thermoplastic vulcanisate.

[0019] Particularly suitable thermoplastic polyurethanes are those which are based on a polyether polyol, preferably polytetramethylene glycol, or a polyester polyol as the polyol component. Particularly advantageous polyester polyols are for example adipate-based polyester polyols, in particular in the form of polybutylene adipate, or polycaprolactone-based polyester polyol. To provide the respective thermoplastic polyurethanes, the polyols are reacted with a polyisocyanate or a mixture of polyisocyanates, wherein the polyisocyanate preferably comprises and in one embodiment consists of aromatic polyisocyanates. Particularly preferred aromatic polyisocyanates for the production of thermoplastic polyurethanes for use in the invention include toluene diisocyanate (TDI), methylene diisocyanate (MDI) or mixtures thereof. In addition to polymeric polyols, the thermoplastic polyurethane may also comprise segments resulting from the incorporation of monomeric polyols, in particular a, o-diols such as 1 ,4-butane diol.

[0020] Particularly suitable thermoplastic polyurethanes are based on a polyester or polyether-based polyol, diisocyanate and a short chain diol as extender (in particular C1 -6 and especially C1 -4 a, o-diols), which have a shore A hardness in the range of from 60 to 95 (according to ISO 48-4) and a 100% modulus in the range of 4 to 9 MPa (according to ISO 37: 2017).

[0021] If the thermoplastic elastomer, which is used in the inventive conveyor belt, is a thermoplastic vulcanisate, it is preferred that the vulcanisate is formed form ethylene-propylene-diene rubber (EPDM) and polypropylene by dynamic vulcanisation of the respective mixture thereof. In such mixtures, the EPDM is preferably present in an amount to 30 to 70 parts and the polypropylene is preferably present in an amount of 20 to 60 parts.

[0022] For the thermoplastic vulcanisate it is furthermore preferred that it has a shore A hardness of at last 70 and in particular in the range of 75 to 95 (according to ISO 48-4) and a 100% modulus in the range of 3 to 9 MPa. Here, the 100% modulus is determined according to ISO 37: 2017.

[0023] The pulley side of the conveyor belt is particularly preferably a material having a rolling resistance factor (RRF), as determined according to DIN 53513 via RRF = tan(delta) / E’A(1 / 3), where tan(delta) is E” / E’, in the range of 0 to -50°C of 0.05 MPa’1 / 3or less, preferably of 0.04 MPa-1 / 3or less and more preferably of 0.03 MPa-1 / 3. For the purposes of this invention, the rolling resistance factor is determined as indicated in the examples section.

[0024] The cover layer on the pulley side of the inventive conveyor belt preferably has thickness of from 0.5 mm to 30 mm, more preferably from 0.5 mm to 10 mm, even more preferably from 1 mm to 8 mm, and even more preferably from 1 mm to 6 mm.

[0025] In the inventive conveyor belt, the carrying side cover layer can be prepared from any appropriate elastomeric material, where styrene-butadiene rubbers (SBR), natural rubber (NR), isoprene rubber (IR) and butadiene rubber (BR) and appropriate blend of these materials can be mentioned as suitable. Material of the carrying side cover layer thus include the materials and material mixtures which are known in the art and DIN-X, DIN-W, DIN-Y and DIN-Z rubber compound, where DIN is DIN 22102-01.

[0026] In one particularly preferred embodiment, the carrying side cover layer of the conveyor belt comprises a thermoplastic elastomer, where in particular the whole elastomeric material in the carrying side cover layer is thermoplastic elastomer. In one embodiment, the carrying side cover layer consists of thermoplastic elastomer. In another embodiment, the carrying side cover layer consists of thermoplastic elastomer as the elastomeric component and further contains conventional additives including fillers. In a most preferred embodiment, the inventive conveyor belt comprises the same thermoplastic elastomer in the load- und pulley side cover layers, which minimizes the complexity of the production process and allows for an effective recycling of both layers.

[0027] As noted above, in addition to the load- und pulley side cover layers the inventive conveyor belt comprises a belt carcass, which has one or more reinforcement members embedded therein. The material to provide the reinforcement members in the invention is not subject to any relevant restrictions, and includes steel cords, UHMWPE cords, fabric, preferably on the basis of yarns from polyolefins (specifically polyethylene (including UHMWPE) and / or polypropylene), polyesters, polyamides, polyaramide, polyoxadiazole and cotton. If the reinforcement members are a plurality of cords, the cords are regularly aligned parallel to one another cord in the belt carcass. If the reinforcement members are one or more fabrics, they can be arranged as a monolayer or in the form of multiple layers. As a second constituent, the belt carcass comprises a matrix material, into which the reinforcement member or members are embedded. The matrix material is most often also an elastomeric material and can be rubber elastomer, thermoplastic elastomer, combination of both or even combination of thermoplastic with thermoplastic elastomer. In addition, it is possible that the elastomeric material is as well as a thermoplastic elastomer, where, as in the belt carcass the resilience towards damage is primarily provided by the reinforcement member(s), a grade of a lower quality can be used.

[0028] It is possible that the matrix material in the belt carcass and the carrying side cover layer are prepared from the same material, in which case there may not be a “boundary” between the belt carcass and the carrying side cover layer. Thus, in such configuration the belt carcass and the carrying side cover layer may also be formed as one piece comparable to a conveyor belt, which has a higher thickness of rubber on the carrying side than on the side of the running layer. Embodiments, where the belt carcass and the carrying side cover layer are formed as one piece are also encompassed by the inventive conveyor belt having a belt carcass and at least a load-side and a pulley side cover layer applied thereon.

[0029] The inventive belts in addition to the layers as described above may comprise further layers to optimize the operation properties, which can be arranged between the belt carcass and the outer cover layers. Such additional layer include for example additional transverse reinforcement layers (also known as breakers), which may be applied between the belt carcass and the cover layers. In addition, it is possible that further elastomeric layers are arranged between the cover layers, which are formed from a thermoplastic elastomer, which is different from the thermoplastic elastomer in the pulley side cover layer, or from one or more different rubber materials.

[0030] A schematic build-up of an inventive conveyor belt 1 is shown in Figure 1 , where the belt has a belt carcass 11a with steel cords as reinforcement members 11 embedded therein. On one side, the belt carcass is covered by a carrying side cover layer 12 and on the other side, the belt carcass is covered by a pulley side cover layer 13, which according to the invention is fabricated from a thermoplastic elastomer. Figure 2 and Figure 3 show a respective conveyor belt 1, which in addition has transverse reinforcements (breakers) 14, which are positioned between the belt carcass and the cover layers. Figure 4 shows a schematic buildup of an inventive conveyor belt 1, where the belt has a belt carcass 11a with fabric plies as reinforcement members 11 embedded therein and intermediate carcass matrix material 11b (here shown as a layer), which are positioned between the fabric ply reinforcement members.

[0031] The conveyor belt of the invention preferably has a total thickness of from 2 mm to 100 mm, more preferably from 4 to 60 mm and even more preferably from 6 to 40 mm.

[0032] In a further aspect, the present invention pertains to a method for the production of a conveyor belt as described above, wherein the method comprises the steps of: i) providing one or more reinforcement members 11 ; ii) embedding the one or more reinforcement members in a belt carcass 11a; iii) applying a cover layer on one side of the belt carcass, which is formed as a carrying side 12; iv) applying a cover layer on the other side of the belt carcass, which is formed as a pulley side 13; wherein the cover layer applied in iv) is prepared from a thermoplastic elastomer or a combination of a rubber layer and a thermoplastic elastomer layer where the thermoplastic elastomer layer is the outer layer.

[0033] The indication in the above, that the respective layer is formed as a carrying side or pulley side is intended to mean that the respective side has a shape or surface structure which is adapted for use as a carrying side or pulley side. E.g. the carrying side can have a roughened shape, which may prevent the sliding of material transported thereon, whereas the pulley side may have a substantially flat and even shape to facilitate the smooth running of the pulley side over idlers of a conveyor belt system.

[0034] In a yet further aspect, the present invention pertains to a use of a thermoplastic elastomer as a cover material on the pulley side of a conveyor belt to reduce the rolling resistance of the conveyor belt. It is also envisioned, that thermoplastic elastomer may reduce the rolling resistance of other types of belts. Accordingly, present invention also pertains to a respective use of a thermoplastic elastomer as a cover material of belts including timing belts or power transmission belts. In this case, the thermoplastic elastomer is used as a cover layer for the side of the belt, which in operation comes into contact with the powered idlers of the belt system. E.g., when the belt is a toothed belt, the thermoplastic elastomer is used as a cover material for the toothed side and when the belt is a multi-v-ribbed belt, the thermoplastic elastomer is used as a cover material for the side having the multi-v- ribbed surface. Accordingly, the present invention also encompasses power transmission and / or timing belts, which have a cover layer on the carrying side and a cover layer on the pulley side, wherein the layers comprise an elastomeric material and the conveyor belt further comprises a belt carcass having one or more embedded reinforcement members, wherein the pulley side cover layer of the power transmission and / or timing belt is fabricated from a thermoplastic elastomer.

[0035] In a yet further aspect, the present invention pertains to a conveyor belt system, which comprises, at least one drive or driven (head) pulley with one motor and at least one deflection (tail) pulley a conveyor belt as described above.

[0036] In the following, the present invention will be further illustrated by means of Examples, which should however not be construed as being limiting to the scope of the invention.

[0037] Examples

[0038] Example 1

[0039] Two different rubber layer samples R1 and R2 were prepared in a laboratory vulcanizations press by vulcanization at optimum cure. Respective thermoplastic elastomer samples TPE1 and TPE2 were prepared by injection molding. The sample R1 is a reference rubber compound for standard conveyor applications and R2 is reference rubber compound energy optimized with reduced RRF according to Example E3 according to DE 102012111599 A1 . The compositions of the samples R1 , R2, TPE1 and TPE2 were as follows:

[0040] Rubber R1 : 55 parts NR TRS 10 type, 35 parts SBR 1500 type, 10 parts BR (high cis content), 50 phr carbon black N 234, 12.1 phr additives (stearic acid, zinc oxide, wax, antioxidants, tackifiers), 1 .4 phr sulfur, 1 .5 phr accelerator (mixture of n-cyclohexyl-2-benzothiazole sulfonamide (CBS), tert-butyl-benzothiazole sulfonamide (TBBS) and N-(cyclohexylthio) phthalimide (CTP)).

[0041] Rubber R2: 40 parts IR, 60 parts BR; 25 phr carbon black N 339, 25 phr carbon black N 550; 11 ,3 phr additives (stearic acid, zinc oxide, wax, antioxidants, tackifiers), 1 .8 phr sulfur, 1 .7 phr mixture of CBS, TBBS and CTP.

[0042] TPE1 : thermoplastic polyurethane based on ether type polyol, MDI and BDO, having a Shore A hardness of 92 and a 100% modulus of 8 MPa.

[0043] TPE2: thermoplastic vulcanizate consisting of a polypropylene and ethylene- propylene-diene terpolymer, dynamically vulcanized, having a shore A hardness of 92 and 100% modulus of 7,5 MPa.

[0044] The respective test specimen were investigated for their mechanical properties and the rolling resistance factor. In these tests the tensile strength, elongation at break, tear strength and abrasion resistance were taken as indicators for durability. The rolling resistance factor is an indicator for the energy loss by indentation rolling resistance on the idlers in a conveyor system. The rolling resistance factor RRF was calculated based on dynamic mechanical analysis measurements (according to DIN 53513) via the formula RRF = tan6 / E’1 / 3where tan6 is the ratio of loss modulus (E”) and storage modulus (E’), i.e. E7E’. The results of the test are provided in the following table 1 :

[0045] As can be seen in Table 1 , the comparative rubber samples exhibit either high rolling resistance factors over the whole Temperature range of 50°C to -50°C (R1 ), or only have a low rolling resistance factor (less than 0.05 MPa_1 / 3) in the range of 0°C to 50°C. In contrast thereto, the TPE samples 1 and 2 exhibited very low rolling resistance factors of less than 0.04 MPa-1 / 3over the entire temperature range. For the thermoplastic vulcanisate, the RRF’s were even below 0.03 MPa_1 / 3over the whole temperature range.

[0046] In addition, the mechanical properties of the TPE cover layers were in most instances comparable, if not better than for the conventional rubber mixtures. List of reference signs

[0047] I conveyor belt

[0048] I I reinforcement member 11a belt carcass

[0049] 11 b carcass matrix material

[0050] 12 carrying side cover layer

[0051] 13 pulley side cover layer

[0052] 14 transverse reinforcement (breaker)

Claims

Claims1. Conveyor belt (1 ), with a cover layer (12) on the carrying side and a cover layer (13) on the pulley side, wherein the layers (12,13) comprise an elastomeric material and the conveyor belt further comprises a belt carcass (11a) having one or more embedded reinforcement members (11 ), wherein the pulley side cover layer of the conveyor belt (1 ) is fabricated from a thermoplastic elastomer.

2. Conveyor belt (1 ) according to claim 1 , wherein the thermoplastic elastomer is selected from a thermoplastic polyurethane, a thermoplastic polyolefin or a thermoplastic vulcanisate.

3. Conveyor belt (1 ) according to claim 1 or 2, wherein the thermoplastic polyurethane is based on a polyether, preferably polytetramethylene glycol, or polyester polyol, preferably an adipate-based polyester polyol or a polycaprolactone-based polyester polyol, as the polyol component and / or wherein thermoplastic polyurethane is based on an aromatic polyisocyanate, preferably selected from toluene diisocyanate or methylene diisocyanate.

4. Conveyor belt (1 ) according to claim 2 or 3, wherein the thermoplastic polyurethane is based on a polyester or polyether-based polyol, diisocyanate and a C1-6 diol as extender, and the thermoplastic polyurethane has a shore A hardness (according to ISO 48-4) of from 60 to 95 (according to ISO 48-4) and a 100% modulus (according to ISO 37: 2017) of from 4 to 9 MPa.

5. Conveyor belt (1 ) according to claim 2, wherein the thermoplastic vulcanisate is based on a dynamically vulcanized mixture comprising ethylene-propylene-diene rubber and polypropylene.

6. Conveyor belt (1 ) according to claim 2 or 5, wherein the thermoplastic vulcanisate comprises from 20 to 60 parts of polypropylene, and 30 to 70parts of EPDM having hardness in the range of shore A between 75 to 95 and 100% modulus in the range of 3 to 9 MPa. Conveyor belt (1 ) according to any one of the preceding claims, wherein the pulley side cover layer has a rolling resistance factor, as determined according to DIN 53513, in the range of 0 to -50°C of 0.05 MPaA(-1 / 3) or less, preferably of 0.04 MPaA(-1 / 3) or less and more preferably of 0.03 MPaA(-1 / 3), and or wherein the pulley side cover layer has a shore A hardness according to ISO 48-4 of at least 60 and preferably at least 80. Conveyor belt (1 ) according to any one of the preceding claims, wherein the carrying side cover layer of the conveyor belt comprises a thermoplastic elastomer. Conveyor belt (1 ) according to any one of the preceding claims, wherein the reinforcement members in the conveyor belt are one or more selected form steel cables, fabric, preferably on the basis of yarns from polyesters and polyamides, polyethylene and polypropylene and wherein the reinforcement members are arranged as a monolayer or in the form of multiple plies. Conveyor belt (1 ) according to any one of the preceding claims, wherein the conveyor belt has a total thickness of from 2 mm to 100 mm, preferably from 4 to 60 mm and more preferably from 6 to 40 mm. Conveyor belt (1 ) according to any one of the preceding claims, wherein the cover layer on the pulley side of the belt has thickness of from 0.5 mm to 30 mm, preferably from 1 mm to 8 mm, and more preferably from 1 mm to 6 mm. Method for the production of a conveyor belt according to any one of claims 1 to 11 , wherein the method comprises the steps of: i) providing one or more reinforcement members (11 ); ii) embedding the one or more reinforcement members in a belt carcass;iii) applying a cover layer (12) on one side of the belt carcass; iv) applying a cover layer (13) on the other side of the belt carcass; wherein the cover layer is 13 is formed as a pulley side cover layer and is prepared from a thermoplastic elastomer or a combination of a rubber layer and a thermoplastic elastomer layer where the thermoplastic elastomer layer is the outer layer. Use of a thermoplastic elastomer as a cover on the pulley side of the conveyor belt to reduce the rolling resistance of the conveyor belt. Conveyor belt system comprising at least one motor, at least a driving pulley with one motor, at least one deflection pulley and a conveyor belt according to any one of claims 1 to 11. A power transmission belt and / or timing belt having a cover layer on the carrying side and a cover layer on the pulley side, wherein the layers comprise an elastomeric material and the conveyor belt further comprises a belt carcass having one or more embedded reinforcement members, wherein the pulley side cover layer of the power transmission and / or timing belt is fabricated from a thermoplastic elastomer.

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