BELTS WITH ANTISTATIC PROPERTIES

Description

[0001] The invention relates to a belt with a drive side and a back side opposite the drive side, comprising a belt body, wherein the belt body is made of an electrically conductive polymeric material. A plurality of tensile members are arranged longitudinally in the belt body and enclosed by the polymeric material of the belt body. The belt has a coating on a drive side that forms a strong adhesive bond with the belt body. The coating comprises an electrically conductive film layer and a fabric layer arranged between the belt body and the film layer. The fabric layer has voids, is electrically insulating, and is at least partially filled with the electrically conductive polymeric material, such that the belt has continuous electrical conductivity from the drive side to the back side of the belt. State of the art

[0002] In drive technology, belts are used for power transmission in various technical fields. For example, in an internal combustion engine, a belt can be a flexible, endless closed band. However, belts can also have two open ends, for example in elevator systems, to move an elevator car vertically.

[0003] Today, such belts are typically manufactured from a flexible material, such as an elastomer or a thermoplastic material, such as polyurethane (PU), into which tension members, such as steel cables or textile tension members, are embedded in the direction of power transmission, i.e., in the direction of movement. The belt has at least one profiled side, which, when in use, is in contact with at least one drive pulley or roller and at least one deflection pulley or idler, or a driven pulley or roller. This allows the belt to be driven and guided simultaneously. Depending on the application, the profile can be designed transversely to the direction of movement, e.g., as teeth, or in the direction of movement, e.g., as wedges or V-ribs.

[0004] To protect the belt body material from abrasion and the like, it is known to provide at least the profiled side of the belt with a coating. For example, a fabric can be used, one side of which is applied flat to the corresponding side of the belt body.

[0005] The production of such a belt typically involves manufacturing the coating separately as a laminate and then bonding it to the belt body. In this case, the fabric is doubled with a film to form a laminate. The laminate is then pre-formed to conform to the contour of the belt's profile. The film is plasticized, deformed, and then hardened again by cooling. This process also causes the fabric to take on the predetermined shape of the profile. The pre-formed laminate is then used in the belt manufacturing process so that the film forms the outer surface of the belt's profile.

[0006] Especially when belts are used in high-explosion environments, it is essential that electrostatic charges can be dissipated via the belt. Therefore, an electrically conductive connection must exist between the belt and at least one grounded pulley or back roller. Alternatively, electrostatic charges can also be dissipated via abrasive brushes in contact with the belt.

[0007] Various designs of conductive and therefore antistatic belts are known from the prior art.

[0008] US Patent 2010 / 0197435 A1 discloses a drive belt with a belt body made of elastomeric material and an antistatic and wear-resistant fabric coating. The antistatic properties of the fabric coating are achieved by electrically conductive fibers. The coating can be arranged on both the drive side and the opposite back side of the belt. In addition to the conductive fabric coating, the elastomeric material of the belt can also be electrically conductive.

[0009] Unfortunately, this embodiment of an antistatic fabric is only suitable for belts manufactured using the injection molding process and not for use with belts manufactured using the casting process, as this requires pre-forming of the fabric with an additional film preparation.

[0010] US Patent 6,770,004 B1 also discloses an electrically conductive drive belt with an electrically conductive coating made of thermoplastic polyethylene and an adjacent fabric layer. In this case, the belt's electrical conductivity is achieved via an electrically conductive film coating on the toothed side of the belt. Dissipation of electrostatic charge is disadvantageously limited to the areas coated with the conductive film, which in this case corresponds to the drive side of the timing belt. Additional dissipation of electrostatic charge via the belt's back and the rollers in contact with it is not possible due to the electrically insulating properties of the elastomeric material of the belt body. Electrical conductivity between the drive side and the back side of the belt is not achievable with the solution disclosed here.

[0011] US 2015 / 0285334 A1 discloses a belt with an electrically conductive tensile cord, an outer layer of electrically conductive thermoplastic material, and an electrically conductive fabric arranged between the outer layer and the tensile cord. This achieves conductivity of the belt between the belt surface and the tensile cord via the intervening conductive fabric. For improved mechanical bonding, the fabric can be at least partially filled with the elastomeric material, which can also be electrically conductive. A disadvantage is that fabric preparation is required to achieve the electrically conductive properties of the fabric. This necessitates additional process steps, resulting in increased manufacturing costs and effort.Furthermore, the electrically conductive tissue preparation may contain substances that adversely affect the mechanical bond between the elastomeric material and the tissue. Task

[0012] The invention is based on the objective of providing an electrically conductive belt with improved antistatic properties for transmitting high power, whereby the mechanical properties of the fabric coating should not be adversely affected. Furthermore, the belt should exhibit continuous electrical conductivity across its entire cross-section, so that electrostatic charges can be dissipated both via the belt backing and via the drive side opposite the belt backing. Solution to the task

[0013] The solution to this problem is achieved by a belt with the features of the main claim.

[0014] Further advantageous embodiments are disclosed in the dependent claims. Claim 10 also discloses a method for manufacturing a belt according to the invention. Advantages of the invention

[0015] The belt according to the invention, as disclosed in claim 1, comprises a belt body with a drive side and a back side opposite the drive side, the belt body being made of an electrically conductive polymeric material. A plurality of tensile members are arranged longitudinally in the belt body and enclosed by the polymeric material of the belt body, the belt having a coating on a drive side that forms a strong adhesive bond with the belt body. The coating comprises a film layer and a fabric layer arranged between the belt body and the film layer, the fabric layer having voids. The fabric layer is electrically insulating, being at least partially filled with the electrically conductive polymeric material, such that the belt has continuous electrical conductivity from the drive side to the back side of the belt.According to the invention, the foil layer comprises electrically conductive carbon blacks or carbon nanotubes.

[0016] Even small amounts of electrically conductive carbon black can give the foil layer electrical conductivity while maintaining good mechanical resistance. Typical mechanical stresses when using a foil layer on drive belts include alternating tensile and bending loads.

[0017] By using carbon nanotubes as an alternative, a higher electrical conductivity can be achieved compared to electrically conductive soot.

[0018] In other words, the invention relates to an electrically conductive drive belt in which the electrical conductivity can be achieved via an electrically conductive polymer. Elastomers based on vulcanizable rubber compounds, comprising at least one rubber component (e.g., EPM, EPDM, HNBR, FKM) and compound ingredients, can be used. In principle, all elastomers known to a person skilled in the art can be used.In a preferred embodiment, the elastomer is selected from the group consisting of ethylene propylene copolymer (EPM) or ethylene propylene diene copolymer (EPDM) or nitrile rubber (NBR) or (partially) hydrogenated nitrile rubber (HNBR) or fluororubber (FKM) or chloroprene rubber (CR) or natural rubber (NR) or styrene-butadiene rubber (SBR) or isoprene rubber (IR) or butyl rubber (IIR) or bromobutyl rubber (BIIR) or chlorobutyl rubber (CIIR) or butadiene rubber (BR) or chlorinated polyethylene (CM) or chlorosulfonated polyethylene (CSM) or polyepichlorohydrin (ECO) or ethylene vinyl acetate rubber (EVA) or acrylate rubber (ACM) or Ethylene acrylate rubber (AEM) or silicone rubber (MQ, VMQ, PVMQ, FVMQ) or fluorinated methyl silicone rubber (MFQ) or perfluorinated propylene rubber (FFPM) or perfluorocarbon rubber (FFKM) or polyurethane (PU).The aforementioned rubbers can be used alone or in blends.

[0019] Especially in applications involving belts in explosion-proof environments, the antistatic properties of the belt are of paramount importance. Relative movements between the belt and the pulleys it encircles can cause the belt to become electrostatically charged. This electrostatic charge can be dissipated via an electrically conductive belt and at least one grounded pulley, which is essentially metallic, also conductive, and engaged with the drive side of the belt. Depending on the application, the pulley can be grounded, for example, via the frame of a machine tool or the body of a vehicle. Electrostatic charge dissipation can also be achieved via any back rollers that may be present.

[0020] To protect the belt from wear and to optimize its friction properties and acoustics, the belt can be coated. This coating can be a woven and film composite, with the woven layer sandwiched between the film and the belt body. The electrically conductive polymer can penetrate the spaces within the non-conductive woven fabric, creating an electrically conductive connection between the conductive film layer and the polymer. Advantageously, despite the non-conductive woven fabric, electrical conductivity of the belt can be achieved across its entire cross-section, from the toothed side to the opposite back side. By eliminating the need for an electrically conductive coating, the woven fabric retains optimal mechanical properties.Since no elaborate fabric preparation is required to achieve antistatic properties of the belt, manufacturing costs can be reduced compared to belts with a conductive fabric.

[0021] A further advantageous embodiment of the belt according to the invention provides that the voids in the fabric layer are filled to at least 80% by the polymeric material. In other words, for optimal antistatic properties, it is particularly advantageous that 80% of the gaps in the fabric are filled with the polymeric material. This allows for a particularly advantageous implementation of electrical conductivity across the entire cross-section of the belt. This reduces electrical resistance and improves the dissipation of electrostatic charges across the belt.

[0022] According to a further aspect of the present invention, the polymeric material of the belt body comprises polyurethane or preferably consists of polyurethane. Polyurethane belts are characterized by particularly high performance and can be especially wear-resistant compared to belts made of rubber materials. The polyurethane can, in particular, be in the form of a multi-component, castable reaction mixture.

[0023] According to a further aspect of the present invention, the film layer comprises polyethylene, preferably the film layer consists of polyethylene. This allows the mechanically advantageous properties of polyethylene to be used for a belt according to the invention.

[0024] According to a further aspect of the present invention, the polymeric material contains carbon black in a proportion of 1 to 6 percent by weight. This allows good electrical conductivity of the polymeric material to be achieved without negatively affecting its mechanical properties.

[0025] According to a further aspect of the present invention, the polymeric material contains carbon black in a proportion of 2.5 to 3.5 percent by weight. It is particularly advantageous that this achieves a sufficiently high electrical conductivity for dissipating electrostatic charges, while simultaneously fulfilling the requirements for the polymeric material for a belt with particularly high power transmission.

[0026] According to a further aspect of the present invention, the drive side of the belt has a profile, preferably teeth oriented in the transverse direction. This improves mechanical contact with a pulley via the drive side of the belt, enabling the transmission of higher forces in the longitudinal direction of the belt. This can be achieved particularly effectively with teeth oriented in the transverse direction, i.e., when the belt according to the invention is designed as a toothed belt.

[0027] According to a further aspect of the present invention, the tension members are designed to be electrically conductive. This allows the conductivity of the belt to be increased particularly effectively.

[0028] According to a further aspect of the present invention, conductive tension members can be made, for example, of steel or carbon fibers. This is particularly advantageous because these materials exhibit high electrical conductivity and can also withstand extremely high mechanical loads. Due to their high modulus of elasticity, tension members made of steel or carbon fibers can impart particularly high longitudinal stiffness to the belt, enabling it to transmit exceptionally high power.

[0029] Another embodiment of the present invention provides a method for manufacturing a belt according to the invention, wherein the coating is pre-formed in a first process step and the belt is bonded to the coating in a casting process in a second process step. In other words, the coating is produced separately as a laminate consisting of a fabric and a film and then bonded to the belt body. The fabric is doubled with a film to form a laminate. The laminate is then pre-formed so that it assumes the contour of the belt's profile. The film is plasticized, deformed, and then solidified again by cooling. This also causes the fabric to assume the predetermined shape of the profile. Subsequently, the pre-formed laminate is used in the belt manufacturing process such that the film forms the outer surface of the belt's profile. Explanation of figures

[0030] An embodiment of the invention will be explained in more detail below with reference to the following figures. Fig. 1 shows a schematic longitudinal section through a belt. Fig. 2 shows a detailed view of the Fig. 1 Fig. 3 shows a two-layer structure of a belt.

[0031] The above figures are described in Cartesian coordinates with a longitudinal direction X, a transverse direction (not shown) perpendicular to the longitudinal direction X, and a vertical direction Z perpendicular to both the longitudinal direction X and the transverse direction. The longitudinal direction X can also be referred to as depth X, the transverse direction as width, and the vertical direction Z as height Z.

[0032] Fig. 1 shows a schematic longitudinal section through a belt 1. Fig. 2 shows a detailed representation of the Fig. 1 .

[0033] The belt 1 is a generally known belt 1, designed as a toothed belt 1. The toothed belt 1 has a belt body 10 made of electrically conductive polyurethane (PU). The toothed belt 1 has a first belt side 11, which is designed as the drive side 11, to interact with drive rollers, guide rollers, and idler rollers (not shown) of a drive system and to transmit forces. For this purpose, the drive side 11 has a profile 15 in the form of teeth 15. Opposite the drive side 11 at height Z, the toothed belt 1 has a second belt side 12. Within the belt body 10, several tension members 13 in the form of steel cables 13 are arranged in the longitudinal direction X, which is formed from individual steel strands. The steel cables 13 serve to transmit the tensile forces in the longitudinal direction X as the direction of movement of the toothed belt 1.

[0034] The outer surface of the drive side 11 of the timing belt 1 is formed by a coating 14, which is produced separately as a laminate and pre-formed with the profile 15. The laminated and pre-formed coating 14, together with the steel cables 13, is encapsulated with liquid polyurethane and cured, resulting in a metallurgical bond between the laminated coating 14 and the belt body 10, forming a one-piece timing belt 1, see e.g. Fig. 2 .

[0035] Fig. 3Figure 1 shows a two-layer structure of a belt 1, similar to the previously described toothed belt 1. A fabric layer 14b and a film 14c (the outer film 14c) are used. These are manufactured separately and joined together by layering them on top of each other to form a two-layer structure. The two-layer structure is then formed into the desired shape, which corresponds to the arrangement of the profile 15. The fabric layer 14b is electrically insulating. The film 14c forms the surface of the drive side 11 of the belt 1 and is electrically conductive due to the presence of electrically conductive carbon black or carbon nanotubes. Since the fabric layer 14b has a fiber mesh with intervening voids, the polyurethane of the belt body 10 fills these voids, thus forming an electrically conductive connection between the belt body 10 and the film 14c.In this way, the belt 1 acquires a continuous electrical conductivity across its entire cross-section, so that electrostatic charges can be dissipated via both the first belt side 11 and the second belt side 12. Reference symbol list

[0036] XL (longitudinal direction), Y (transverse direction); width, C (vertical direction); height 1 Belt; Timing belt 10 Belt body 11 First belt side; Drive side 12 Second belt side; Back side 13 Tension member 14 Coating 14b Fabric layer 14c Foil layer 15 Profiling or teeth of the first belt side 11

Claims

1.

1. belt (1) with one drive side (11) and one back side (12) opposite the drive side (11), comprising a belt body (10), wherein the belt body (10) has an electrically conductive polymer material, wherein in the belt body (10) a plurality of tension members (13) is arranged in a longitudinal direction (X) and enclosed by the polymer material of the belt body (10), wherein the belt (1) has a coating (14) on one side of the drive (11) which forms a firm adhesive bond with the belt body (10), wherein the coating (14) has an electrically conductive film layer (14c) and a fabric layer (14b) arranged between the belt body (10) and the film layer (14c), wherein the fabric layer (14b) has free spaces, wherein the fabric layer (14b) is electrically insulating, the fabric layer (14b) is at least partially filled by the electrically conductive polymer material, so that the belt (1) has a continuous electrical conductivity from the drive side (11) to the back side (12) of the belt (1), characterized in that the film layer (14c) has electrically conductive carbon blacks, or the film layer (14c) has carbon nanotubes.

2. Belt (1) according to claim 1, characterized by the fact that the free spaces of the tissue layer (14b) are at least 80% filled by the polymer material.

3. belt (1) according to any of the previous claims, characterized by the fact that the polymeric material of the belt body (10) has polyurethane, preferably consists of polyurethane.

4. Belt (1) according to any one of claims 1 to 3, characterized by the fact that the film layer (14c) has polyethylene, preferably consists of polyethylene.

5. a belt (1) according to any of the preceding claims, characterized by the fact that the polymer material has carbon black with a proportion of 1 to 6 percent by weight.

6. a belt (1) according to any of the preceding claims, characterized by the fact that the polymer material has carbon black with a proportion of 2.5 to 3.5 percent by weight.

7. belt (1) according to any of the previous claims, characterized by the fact that the drive side (11) of the belt (1) has a profile (15), preferably in the transverse direction.

8. belt (1) according to any of the previous claims, characterized by the fact that the tension members (13) are electrically conductive.

9. a belt (1) according to any of the preceding claims, characterized by the fact that the tension members (13) are made of steel or carbon fibre.

10. The method of producing a belt (1) according to any one of claims 1 to 9, characterized by the fact that the coating (14) is pre-formed in a first process step and the belt (1) is connected to the coating (14) in a second process step in a casting process.