Transmission belt comprising a non-thermoplastic elastomeric matrix and thermoplastic bonding layers and method of manufacturing said belt

Abstract

A transmission belt (10) comprising an elastomeric body (11) made from a non-thermoplastic elastomeric matrix and comprising a main portion (12c) and two end portions (12a, 12b) each extending from one end of the main portion (12c), each end portion (12a, 12b) being delimited transversely by an inner surface (15a, 15b) and an outer surface (13a, 13b), said transmission belt (10) being configured to pass from an initial state, in which the end portions (12a, 12b) are free, to an assembled state in which the end portions (12a, 12b) are integral with one another.The inner surface (15a) of one of the end portions (12a) is coated at least in part with an inner bonding layer (17) of elastomeric thermoplastic crosslinked only locally at the interface with the elastomeric matrix (12) and the outer surface (13b) of the other of the end portions (12b) is coated at least in part with an outer bonding layer (18) of elastomeric thermoplastic crosslinked only locally at the interface with the elastomeric matrix (12). Figure for abstract: Fig 2.

Description

Title of the invention: Transmission belt comprising a non-thermoplastic elastomeric matrix and thermoplastic bonding layers and method of manufacturing said belt

[0001] The present invention relates to the field of transmission of drive forces, more particularly transmission belts, in particular synchronous belts.

[0002] The present invention may also relate to rubber tracks for agricultural, military, public works and leisure vehicles (snowmobiles, motorcycles, etc.)

[0003] A belt is presented, in a manner known per se, in the form of a closed band capable of transmitting the forces from a driving pulley to a driven pulley, preferably synchronously.

[0004] Installing a new belt is quite complex and usually requires dismantling different parts of the machine, which results in increased consumption of resources and time.

[0005] In order to overcome this drawback, it is known to produce an open belt which can be easily installed and closed at the installation site, for example by gluing using an adhesive, for example glue.

[0006] However, bonding requires the supply of material to the installation site.

[0007] Such belts are commonly referred to as "welding belts".

[0008] The aim of the invention is to provide an improved belt, or an improved track, which is easy to manufacture and to install on the installation site, without the need for additional material on the installation site.

[0009] The invention relates to a transmission belt or a track comprising an elastomeric body made from an elastomeric matrix and comprising a main portion and two end portions each extending from one end of the main portion.

[0010] Each end portion is delimited transversely by an internal surface and an external surface.

[0011] Said transmission belt is configured to pass from an initial, unassembled state in which the end portions are free to an assembled state in which the end portions are secured to one another.

[0012] The elastomeric matrix is ​​made of a first non-thermoplastic elastomeric material.

[0013] The inner surface of one of the end portions is coated at least in part with an internal bonding layer crosslinked only locally at the interface with the elastomeric matrix and the external surface of the other of the end portions is coated at least in part with an external bonding layer crosslinked only locally at the interface with the elastomeric matrix.

[0014] Said connecting layers are made of a second thermoplastic elastomer material, distinct from the first material, and configured to be secured or assembled to one another, in particular during a heat-sealing step, in the assembled state of the belt.

[0015] In other words, the transmission belt is a so-called "open" belt, that is to say that it is stored in an initial unassembled state and is configured to be installed in a complex mechanical environment requiring its assembly directly on the installation site.

[0016] Preferably, the bonding layers are located exclusively on each of the end portions of the transmission belt.

[0017] Thanks to the connecting layers, the transmission belt according to the invention is dimensional.

[0018] In other words, it is designed so that once in the closed or assembled state, the belt has a length adapted to the desired dimension.

[0019] Furthermore, the transmission belt is prepared upstream of the installation site to avoid any additional material being brought to the installation site.

[0020] In fact, the bonding system is directly included in the transmission belt, without the need to provide external glue or adhesive.

[0021] Such a connection of the free end portions of the transmission belt makes it possible to obtain good mechanical strength at a junction zone in the assembled state of the belt.

[0022] For example, the elastomeric body is delimited transversely by an external surface and an internal driving surface.

[0023] Advantageously, one of the end portions is offset transversely from the main portion of the elastomeric body and connected to said main portion by a connecting portion extending transversely outwards in an oblique direction.

[0024] The transverse offset of the end portions allows the inner bonding layer of the inner surface of one of the end portions to be brought into contact with the outer bonding layer of the outer surface of the other of the end portions.

[0025] However, such a transverse offset can cause a transverse offset of the neutral fiber of the reinforcing elements at the junction zone.

[0026] For example, each bonding layer has a transverse dimension, i.e. a thickness, of between 20 pm and 100 pm, preferably between 30 pm and 60 pm.

[0027] By "thickness" is meant the dimension of the belt in the transverse direction, perpendicular to the direction of longitudinal extension of the belt in the free state.

[0028] Preferably, the bonding layers have the same length in the direction of extension of the belt.

[0029] Advantageously, the end portions of the transmission belt in the free state are configured to be assembled at a junction zone, by bringing the bonding layers into contact together in the transverse direction which is perpendicular to the direction of extension of the belt, then by bonding between said bonding layers by applying a pressure of between 0.1 bar and 20 bar and heat, in particular a temperature of between 80°C and 200°C, preferably between 120°C and 200°C.

[0030] According to one embodiment, the mechanical drive surface is smooth, so as to form a contact surface by adhesion. This type of belt is known as a “flat” belt.

[0031] According to another embodiment, the mechanical drive surface comprises a plurality of ribs or teeth each extending in the direction perpendicular to the direction of extension of the transmission belt.

[0032] The teeth are advantageously intended to be engaged in grooves or grooves of complementary shape, for example provided on pulleys on which the belt is intended to be mounted.

[0033] When the transmission belt is in the initial state, before assembly, it extends along the longitudinal axis and its teeth extend along the transverse axis.

[0034] Each tooth has, in a non-limiting manner, a trapezoidal section along a plane perpendicular to the transverse axis. The general directions of the teeth are substantially parallel to each other.

[0035] Advantageously, the internal surface of one of the end portions coated with the internal bonding layer is devoid of teeth.

[0036] According to one embodiment, each connecting layer is coated with a removable protective film intended to be removed before assembly of the free end portions of the belt.

[0037] For example, each protective film is made of polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), polyamide or nylon (PA), polyethylene terephthalate (PET), polyester.

[0038] The protective films serve to protect the associated bonding layer during storage and handling of the transmission belt.

[0039] The protective films allow the transmission belt to be easily stored in its initial, unassembled state, without the risk of the end portions accidentally welding together. free. In addition, the films help to preserve the properties, particularly the welding capabilities, of the bonding layers.

[0040] Preferably, the first non-thermoplastic elastomer material of the elastomeric matrix comprises at least one elastomer chosen from the group consisting of a natural rubber (NR), a synthetic polyisoprene (IR), a butadiene-styrene copolymer (SBR).

[0041] In one embodiment, the elastomeric matrix comprises a so-called “reinforcing” filler.

[0042] When a reinforcing filler is used, any type of reinforcing filler known for its ability to reinforce an elastomeric matrix may be used, for example an organic filler, such as carbon (CB), a reinforcing inorganic or mineral filler such as silica, or a mixture of these two types of fillers.

[0043] The rubber compositions may also comprise all or part of the additives, which are usually used in elastomeric materials, such as plasticizing resins or extending oils, whether the latter are of an aromatic or non-aromatic nature, protective agents such as anti-ozone waxes, anti-oxidants, etc.

[0044] Preferably, the elastomeric matrix comprises a crosslinking system.

[0045] The crosslinking system advantageously comprises a co-crosslinking agent, preferably sulfur or triallylcyanurate. Advantageously, the level of the co-crosslinking agent is between 0.5 pce and 5 pce

[0046] For example, the second material of the bonding layers is composed of a thermoplastic elastomer comprising a block copolymer comprising at least one elastomer block and at least one thermoplastic block, and the total content of thermoplastic elastomer being within a range varying from 65 to 100 pce (parts by weight per hundred parts of elastomer).

[0047] For example, the second material composed of a thermoplastic elastomer is chosen from the following copolymers: a copolymer whose elastomer blocks are unsaturated, and which comprises styrene blocks and diene blocks, a copolymer whose elastomer blocks are unsaturated, and which comprises styrene blocks and diene blocks, and a linear or star copolymer whose elastomer blocks comprise a saturated part and an unsaturated part.

[0048] According to one embodiment, the belt comprises reinforcing elements embedded in the elastomeric body.

[0049] Advantageously, the reinforcing elements are parallel to each other in the vertical direction and extend in a single reinforcing layer.

[0050] The reinforcing elements have a transverse dimension, that is to say a thickness, of between 0.1 mm and 7 mm.

[0051] In one embodiment, each reinforcing element is metallic.

[0052] Alternatively, each reinforcing element could be made of a non-metallic material, for example polyethylene terephthalate (PET), polyamide or nylon (PA6), carbon, glass, rayon, etc.

[0053] For example, each reinforcing element is a wired reinforcing element. The reinforcing elements may be woven to form a woven web. Alternatively, the reinforcing elements may be fibers blended with the non-thermoplastic elastomeric material.

[0054] By "wire reinforcement element" is meant elongated elements of great length relative to their cross-section, whatever the shape of the latter, for example circular, oblong, rectangular, square or flat.

[0055] A wire reinforcement element can be rectilinear or non-rectilinear, for example twisted or corrugated.

[0056] A reinforcing element may comprise a plurality of elementary monofilaments assembled together.

[0057] The wire reinforcement elements may be arranged in the length direction of the transmission belt, possibly forming an angle of between 0° and 45° relative to the length direction of the belt.

[0058] According to another aspect, the invention relates to a method of manufacturing a transmission belt, or a track, comprising an elastomeric body comprising a main portion and two end portions each extending from one end of the main portion.

[0059] Each end portion is delimited transversely by an internal surface and an external surface, said transmission belt being configured to pass from an initial state, in which the end portions are free, to an assembled state in which the end portions are secured to one another.

[0060] According to the method:

[0061] - the body is shaped from an elastomeric matrix produced in a first non-thermoplastic elastomer material;

[0062] - an internal bonding layer and an external bonding layer are formed from a second thermoplastic elastomer material;

[0063] - the internal bonding layer is deposited on at least part of the internal surface of one of the end portions;

[0064] - the external bonding layer is deposited on at least part of the external surface from the other end portions.

[0065] The method further comprises a step of curing the belt comprising the non-thermoplastic elastomeric body optionally comprising the reinforcements, and comprising the bonding layers.

[0066] For example, the cooking of the belt 10 can be carried out in a mold, in an oven, for example at a temperature between 100°C and 200°C, preferably between 100°C and 150°C at a pressure between 0.1 bars and 20 bars, preferably at a temperature of 140°C to 2 bars.

[0067] During the curing step, although the bonding layers do not have a crosslinking system, the crosslinking system of the elastomeric matrix is ​​sufficient to bond the thermoplastic elastomer bonding layers with said non-thermoplastic elastomeric matrix by crosslinking. Indeed, the crosslinking system of the elastomeric matrix migrates during assembly of the belt, under the effect of pressure and thanks to the supply of heat, from the matrix to the bonding layers.

[0068] In other words, the bonding layers are crosslinked only locally at the interface with the non-thermoplastic elastomeric matrix during the assembly step.

[0069] This crosslinking bond between the elastomeric matrix and the bonding layers is robust over time.

[0070] Thus, the belt is prepared upstream in a production site, which may be separate from the installation site to avoid any additional material being brought to the installation site.

[0071] Advantageously, after the cooking step, the end portions of the transmission belt in the free state are assembled in a heat-sealing step at a junction zone, by bringing the bonding layers into contact with each other in a direction perpendicular to a direction of extension of the belt, then by bonding between said bonding layers by applying a pressure of between 0.1 bar and 20 bar and heat, in particular a temperature of between 80°C and 300°C, preferably between 120°C and 200°C.

[0072] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0073] [Fig.l] very schematically represents a general view of a transmission belt according to the invention;

[0074] [Fig.lB] illustrates in detail a flat portion of the transmission belt of [Fig.l];

[0075] [Fig.2] and [Fig.3] are detailed views of a transmission belt according to two embodiments before assembly of the end portions of said belt;

[0076] [Fig.4] and [Fig.5] are detailed views respectively of the belts of [Fig.2] and 3 after as- assembly of the end portions of said belt;

[0077] [Fig.6] illustrates the steps of a manufacturing process for the belt of [Fig.l]; and

[0078] [Fig.7] represents a tensile test carried out on a specimen of structure similar to the transmission belt of [Fig.4].

[0079] Figures 1 to 7 are described as relating to a transmission belt, and are to be understood as also being able to relate to a track.

[0080] In the following description, the terms "longitudinal", "transverse", "vertical", "front", "rear", "left" and "right" are defined according to the usual orthogonal reference of transmission belts, shown in the drawings, and which includes:

[0081] - a longitudinal axis X, horizontal and oriented from left to right on [Fig.lB] in the direction of travel of the transmission belt;

[0082] - a transverse axis Y, horizontal, perpendicular to the longitudinal axis X and oriented from bottom up on [Fig.lB];

[0083] - a vertical axis Z, orthogonal to the longitudinal and transverse axes X and Y and directed from front to back in [Fig.lB].

[0084] [Fig.l] illustrates an example of a transmission belt, referenced 10 as a whole, configured to transmit a rotational movement and / or mechanical power between two or more mechanical members, for example pulleys (not shown).

[0085] By “thickness” is meant the dimension of the belt 10 in the transverse direction Y visible in Figures 1B and 2 to 6.

[0086] By “length” is meant the dimension of the belt 10 in the longitudinal direction X visible in Figures 1B and 2 to 6.

[0087] By “width” is meant the dimension of the belt 10 in the vertical direction Z visible in Figures 1B and 2 to 6.

[0088] The transmission belt 10 is here in the closed or assembled state, ready to be used for the mechanical drive of the mechanical components.

[0089] The transmission belt 10 is a so-called "open" belt, that is to say that it is stored in an initial unassembled state and is configured to be installed in a complex mechanical environment requiring its assembly directly on the installation site.

[0090] The transmission belt 10 comprises an elastomeric body 11 made from an elastomeric matrix 12.

[0091] In the example illustrated and in a non-limiting manner, the transmission belt 10 comprises reinforcing elements 14 embedded in the elastomeric matrix 12. As a variant, it could be provided that the transmission belt 10 is devoid of reinforcing elements.

[0092] The elastomeric body 11 is delimited transversely by an external surface 13 and an internal surface 15.

[0093] The terms "external" and "internal" are defined in relation to the center C of the drive belt when closed, with the external surfaces being further apart than the internal surfaces.

[0094] The internal surface 15 of the elastomeric body 11 forms a mechanical drive surface configured to drive a mechanical member (not shown).

[0095] In the example illustrated in Figures 2 and 4, the mechanical drive surface 15 is smooth, so as to form a contact surface by adhesion. This type of belt is known as a “flat” belt.

[0096] Alternatively, in the example illustrated in Figures 3 and 5, the mechanical drive surface 15 comprises a plurality of ribs or teeth 16 each extending in the direction perpendicular to the direction of extension of the belt 10.

[0097] When the transmission belt 10 is in the initial state, before assembly, it extends along the longitudinal axis X and its teeth extend along the transverse axis Y.

[0098] Each tooth 16 has here, in a non-limiting manner, a trapezoidal section along a plane perpendicular to the transverse axis Y. The general directions of the teeth 16 are substantially parallel to each other.

[0099] The teeth 16 extend over the entire length of the belt 10, except the internal surface 15a of one of the end portions 12a.

[0100] The teeth 16 are intended to be engaged in grooves or grooves (not shown) of complementary shape, for example provided on pulleys on which the belt 10 is intended to be mounted.

[0101] In the initial, unassembled state, visible in Figures 2 and 3, the power transmission belt 10 is delimited along its longitudinal extension axis X by two free end portions 12a, 12b connected by a main portion 12c.

[0102] Each free end portion 12a, 12b is delimited transversely by an internal surface 15a, 15b and an external surface 13a, 13b.

[0103] The inner surface 15a of one of the end portions 12a and the outer surface 13b of the other of the end portions 12b form contact surfaces of the end portions 12a, 12b.

[0104] As illustrated in Figures 3 and 5, one of the free end portions 12a is offset transversely from the main portion 12c of the elastomeric body 11 and connected to said main portion 12c by a connecting portion 12d extending transversely outwards in an oblique direction.

[0105] The internal surface 15a of one of the free end portions 12a, here the right-hand portion, is partly coated with an internal bonding layer 17 and the external surface 13b of the other of the free end portions 12b, here the left portion, is partly coated with an external bonding layer 18.

[0106] The internal bonding layer 17 is crosslinked only locally at the interface with the elastomeric matrix 12 during the curing step described below with reference to [Fig.6].

[0107] The external bonding layer 18 is crosslinked only locally at the interface with the elastomeric matrix 12 during the curing step described below with reference to [Fig.6].

[0108] The internal surface 15a of one of the free end portions 12a is devoid of teeth 16.

[0109] The connecting layers 17, 18 here have the same length in the direction of extension of the belt 10.

[0110] The connecting layers 17, 18 are located exclusively on each of the end portions 12a, 12b of the transmission belt 10.

[0111] Thanks to the connecting layers 17, 18, the transmission belt 10 according to the invention is dimensional. In other words, it is designed so that once in the closed or assembled state, the belt has a length adapted to the desired dimension.

[0112] In the example illustrated in [Fig.2], each bonding layer 17, 18 is coated with a removable protective film 19, 20 intended to be removed before assembly of the free end portions 12a, 12b of the belt 10.

[0113] Each protective film 19, 20 is for example made of polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), polyamide or nylon (PA), polyethylene terephthalate (PET), polyester, etc.

[0114] The protective films 19, 20 have the function of protecting the associated bonding layer 17, 18 during storage and handling of the transmission belt 10.

[0115] The protective films 19, 20 make it possible to easily store the transmission belt 10 in its initial, unassembled state, without the risk of accidental welding of the free end portions 12a, 12b.

[0116] The free end portions 12a, 12b of the transmission belt 10 are assembled at a junction zone Zl, by bringing the connecting layers 17, 18 into contact together in a direction perpendicular to the direction of extension of the belt 10, then by bonding between said connecting layers 17, 18 by applying a pressure of between 0.1 bar and 20 bar and heat, in particular a temperature of between 80°C and 300°C, preferably between 120°C and 200°C.

[0117] Thus, the transmission belt 10 is prepared upstream of the installation site to avoid any additional material being brought to the installation site.

[0118] Indeed, the bonding system is directly included in the transmission belt 10, without the need to provide external glue or adhesive.

[0119] Such a connection of the free end portions of the transmission belt makes it possible to obtain good mechanical strength at the junction zone ZI in the assembled position, as will be explained with reference to [Fig.7].

[0120] In the assembled position, visible in Figures 4 and 5, one of the free end portions 12a is offset transversely from the other of the free end portions 12b, so that the internal bonding layer 17 of the internal surface 15a of one of the free end portions 12a is in contact with the external bonding layer 18 of the external surface 15b of the other of the free end portions 12b.

[0121] The transverse offset of the free end portions 12a, 12b causes a transverse offset of the neutral fiber of the reinforcing elements 14 at the junction zone Zl. Elastomeric matrix

[0122] By “elastomeric matrix” is meant a matrix with elastomeric behavior.

[0123] The elastomeric matrix 12 in which the reinforcing elements 14 are embedded comprises one or more elastomers.

[0124] The elastomeric matrix 12 is made from a first material.

[0125] Preferably, the first material comprises at least one elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprene (IR), butadiene-styrene copolymer (SBR).

[0126] Generally, the elastomeric matrix 12 does not comprise a thermoplastic block.

[0127] In other words, the elastomeric matrix 12 is made of diene rubber as a non-thermoplastic elastomer, this diene rubber being able to be used alone, or in a blend with at least one (i.e. one or more) other non-thermoplastic rubber or elastomer.

[0128] By “diene” elastomer or rubber, we mean one or more elastomers derived at least in part (i.e.; a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

[0129] In one embodiment, the elastomeric matrix 12 comprises a so-called “reinforcing” filler.

[0130] When a reinforcing filler is used, any type of reinforcing filler known for its ability to reinforce an elastomeric matrix may be used, for example an organic filler, such as carbon (CB), a reinforcing inorganic or mineral filler such as silica, or a mixture of these two types of fillers.

[0131] The rubber compositions may also comprise all or part of the usual additives usually used in elastomeric materials, such as plasticizing resins or extending oils, whether the latter are of a natural aromatic or non-aromatic, protective agents such as anti-ozone waxes, anti-oxidants etc.

[0132] Preferably, the elastomeric matrix 12 comprises a crosslinking system (not shown).

[0133] The crosslinking system advantageously comprises a co-crosslinking agent, preferably sulfur or triallylcyanurate. Advantageously, the level of the co-crosslinking agent is between 0.5 pce and 5 pce. Reinforcing elements

[0134] The reinforcing elements 14 are embedded in the elastomeric matrix 12.

[0135] The reinforcing elements 14 form the core of the transmission belt 10.

[0136] As illustrated, the reinforcing elements 14 are parallel to each other in the vertical direction Z and extend in a single reinforcing layer.

[0137] The reinforcing elements have a transverse dimension, that is to say a thickness, of between 0.1 mm and 7 mm.

[0138] In one embodiment, each reinforcing element 14 is metallic.

[0139] Alternatively, each reinforcing element 14 could be made of a non-metallic material, for example polyethylene terephthalate (PET), polyamide or nylon (PA6), carbon, glass, rayon, etc.

[0140] For example, each reinforcing element 14 is a wire reinforcing element. The reinforcing elements 14 may be woven to form a woven web. Alternatively, the reinforcing elements may be fibers blended with the non-thermoplastic elastomeric material.

[0141] By “wire reinforcement element” is meant elongated elements of great length relative to their cross-section, whatever the shape of the latter, for example circular, oblong, rectangular, square or flat.

[0142] A wire reinforcement element can be rectilinear or non-rectilinear, for example twisted or corrugated.

[0143] A reinforcing element may comprise a plurality of elementary metallic monofilaments assembled together.

[0144] The wire reinforcement elements may be arranged in the length direction of the transmission belt, possibly forming an angle of between 0° and + / -45° relative to the length direction of the belt. Bonding layers

[0145] Each bonding layer 17, 18 directly coats one of the free end portions 12a, 12b of the elastomeric matrix 12.

[0146] By layer “directly” coating an object, we mean that the layer is in contact with the object without any other object, in particular another layer, being interposed. between the two.

[0147] Each bonding layer 17, 18 has a transverse dimension, i.e. a thickness, of between 20 pm and 100 pm, preferably between 30 pm and 60 pm.

[0148] Each bonding layer 17, 18 is made of a second material distinct from the first material forming the elastomeric matrix 12.

[0149] The second material preferably comprises exclusively a thermoplastic elastomer, with the acronym “TPE”.

[0150] In particular, the second material, before being shaped to compose the bonding layers 17 and 18, does not comprise a co-crosslinking system agent. Thermoplastic elastomer

[0151] Said thermoplastic elastomer is a block copolymer comprising at least one elastomer block and at least one thermoplastic block, and the total content of thermoplastic elastomer being within a range varying from 65 to 100 pce (parts by weight per hundred parts of elastomer).

[0152] In other words, thermoplastic elastomers have an intermediate structure between thermoplastic polymers and elastomers. They are block copolymers, consisting of rigid, thermoplastic blocks, connected by flexible, elastomeric blocks.

[0153] The second material is distinct from the first material in that the first material does not comprise rigid, thermoplastic blocks.

[0154] The number-average molecular mass (denoted Mn) of the TPE is preferably between 30,000 and 500,000 g / mol, more preferably between 40,000 and 400,000 g / mol.

[0155] In the present application, when reference is made to the glass transition temperature of the TPE, this is the Tg relative to the elastomer block. The TPE preferably has a glass transition temperature ("Tg") which is preferably less than or equal to 25°C, more preferably less than or equal to 10°C. A Tg value higher than these minima can reduce the performance of the bonding layer during use at very low temperatures; for such use, the Tg of the TPE is more preferably still less than or equal to -10°C. Also preferably, the Tg of the TPE is greater than -100°C.

[0156] As is known, TPEs have two peaks of glass transition temperature (Tg, measured according to ASTM D3418-21), the lower temperature being relative to the elastomer part of the TPE, and the higher temperature being relative to the thermoplastic part of the TPE. Thus, the flexible blocks of TPEs are defined by a Tg lower than room temperature (25°C), while the rigid blocks have a Tg higher than 80°C.

[0157] Thermoplastic blocks having a Tg (or Tf, where appropriate) greater than or equal to 80°C can be made from polymerized monomers of various natures, in particular, they can constitute the following blocks or their mixtures: polyolefins (polyethylene, polypropylene); polyurethanes; polyamides; polyesters; polyacetals; polyethers (polyethylene oxide, polyphenylene ether); polyphenylene sulfides; polyfluorinated materials (FEP, PFA, ETFE); polystyrenes (detailed below); polycarbonates; polysulfones; polymethylmethacrylate; polyetherimide; thermoplastic copolymers such as acrylonitrile-butadiene-styrene copolymer (ABS).

[0158] Alternatively, other monomers could be provided.

[0159] For example, TPE is a copolymer whose elastomer blocks are saturated, and comprise styrene blocks and alkylene blocks. The alkylene blocks are preferably ethylene, propylene or butylene. More preferably, this TPE elastomer is chosen from the following group, consisting of linear or star diblock, triblock copolymers: styrene / ethylene / butylene (SEB), styrene / ethylene / propylene (SEP), styrene / ethylene / ethylene / propylene (SEEP), styrene / ethylene / butylene / styrene (SEBS), styrene / ethylene / propylene / styrene (SEPS), styrene / ethylene / ethylene / propylene / styrene (SEEPS), styrene / isobutylene (SIB), styrene / isobutylene / styrene (SIBS) and mixtures of these copolymers.

[0160] According to another example, the TPE is a copolymer whose elastomer blocks are unsaturated, and which comprises styrene blocks and diene blocks, these diene blocks being in particular isoprene or butadiene blocks. More preferably, this TPE elastomer is chosen from the following group, consisting of linear or star diblock or triblock copolymers: styrene / butadiene (SB), styrene / isoprene (SI), styrene / butadiene / isoprene (SBI), styrene / butadiene / styrene (SBS), styrene / isoprene / styrene (SIS), styrene / butadiene / isoprene / styrene (SBIS) and mixtures of these copolymers.

[0161] For example also, TPE is a linear or star copolymer whose elastomer blocks comprise a saturated part and an unsaturated part such as for example styrene / butadiene / butylene (SBB), styrene / butadiene / butylene / styrene (SBBS) and mixtures of these copolymers.

[0162] The addition of bonding layers 17, 18 to the end portions 12a, 12b of the transmission belt 10 facilitates the bonding of said end portions 12a, 12b and provides improved thermal resistance of the belt 10.

[0163] [Fig.6] illustrates the steps of a method 100 for manufacturing the transmission belt 10.

[0164] During a first step 101, the elastomeric body 11 of the belt is shaped, from a non-thermoplastic elastomeric matrix 12.

[0165] Shaping may be achieved by molding, extrusion, or other known techniques.

[0166] The elastomeric body 11 of the belt possibly contains the elements of reinforcements 14 which are embedded in the elastomeric matrix 12.

[0167] At the end of this step 101, the elastomeric body 11 is not yet crosslinked.

[0168] During a second step 102, each bonding layer 17, 18 is shaped at from the second material described above.

[0169] The shaping can be carried out for example by molding, extrusion or by other known techniques.

[0170] During a third step 103, the end portions 12a and 12b of the elastomeric body 11 are respectively coated with a bonding layer 17 and 18.

[0171] Then, during a fourth step 104, the belt comprising the non-thermoplastic elastomeric body, possibly comprising the reinforcements, and comprising the bonding layers 17 and 18, is cured.

[0172] For example, the cooking of the belt 10 can be carried out in a mold, in an oven, for example at a temperature between 100°C and 200°C, preferably between 100°C and 150°C at a pressure between 0.1 bars and 20 bars, preferably at a temperature of 140°C to 2 bars.

[0173] During the curing step, although the bonding layers 17, 18 do not have a crosslinking system, the crosslinking system of the elastomeric matrix 12 is sufficient to bond the bonding layers 17, 18 made of thermoplastic elastomer with said non-thermoplastic elastomeric matrix 12 by crosslinking. Indeed, the crosslinking system of the elastomeric matrix 12 migrates during the assembly of the belt 10, under the effect of pressure and thanks to the supply of heat, from the matrix 12 to the bonding layers 17 and 18.

[0174] In other words, the bonding layers 17, 18 are crosslinked only locally at the interface with the non-thermoplastic elastomeric matrix 12 during the assembly step 104.

[0175] This crosslinking connection between the elastomeric matrix 12 and the bonding layers 17, 18 is robust over time.

[0176] In polymer chemistry, crosslinking corresponds to the formation of one or more three-dimensional networks, by chemical or physical means. The crosslinking of polymers is well known and will not be described further.

[0177] Then, optionally, during a fifth step 105, the end portions 12a, 12b of the transmission belt 10 are assembled, during a heat-sealing step, in the free state at a junction zone ZI by bringing the connecting layers 17, 18 into contact together in a direction perpendicular to a direction of extension of the belt 10 and then by baking or heat-sealing the belt 10 comprising the non-thermoplastic elastomeric body 11, optionally comprising reinforcements 14, and comprising the connecting layers 17 and 18.

[0178] Heat sealing step 105 is performed by applying a pressure of between 0. Ibars and 20bars and heat, in particular a temperature between 80°C and 300°C, preferably between 120°C and 200°C.

[0179] [Fig.7] illustrates tests carried out on a test piece to determine the tensile strength of the thermoplastic elastomer bonding layers 17, 18 of a transmission belt according to the invention at the junction zone Zl.

[0180] To carry out the experiment, two elastomeric matrices 12a, 12b made of non-thermoplastic diene rubber were used, comprising reinforcing elements 14 made of nylon-type polyamide embedded in the corresponding elastomeric matrix.

[0181] A portion of the outer surface of one of the elastomeric matrices 12a has been crosslinked with an inner tie layer 17 and a portion of the inner surface of the other of the elastomeric matrices 12b has been crosslinked with an outer tie layer 18.

[0182] The thermoplastic elastomer bonding layers 17, 18 were bonded together by heat welding at a temperature of 140°C at 2 bars.

[0183] Each bonding layer 17, 18 has a transverse dimension, i.e. a thickness, of 0.4 mm.

[0184] Each bonding layer 17, 18 comprises a styrene / butadiene / styrene (SBS) and 10% expanded polypropylene (EPP).

[0185] A portion of the outer surface of one of the elastomeric matrices 12a is devoid of the inner bonding layer 17 and a portion of the inner surface of the other of the elastomeric matrices 12b is devoid of the outer bonding layer 18.

[0186] The parts without a bonding layer 17, 18 are pulled respectively according to a force F1, F2 along the transverse axis Y in two opposite directions, perpendicular to the bonding layers 17, 18.

[0187] The tensile forces measured before detachment of the bonding layers 17, 18 are greater than 10N per mm of width.

[0188] In the context of the invention, the carbon products mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass.

[0189] The term "pce" (in English "phr") means, within the meaning of the present patent application, part by weight per hundred parts of elastomer, thermoplastic and non-thermoplastic combined. Within the meaning of the present invention, thermoplastic elastomers (TPE) are part of the elastomers.

[0190] Thanks to the particular structure of the transmission belt comprising two layers of distinct materials, one comprising a thermoplastic and the other devoid of thermoplastic, we benefit from a bonding system directly included in the transmission belt, without the need for external glue or adhesive. Furthermore, such a connection of the free end portions of the transmission belt provides good mechanical strength at a junction area in the assembled state of the belt.

Claims

Claims

1. Transmission belt (10) or track comprising an elastomeric body (11) made from an elastomeric matrix (12) and comprising a main portion (12c) and two end portions (12a, 12b) each extending from one end of the main portion (12c), each end portion (12a, 12b) being delimited transversely by an internal surface (15a, 15b) and an external surface (13a, 13b), said transmission belt (10) being configured to pass from an initial state, in which the end portions (12a, 12b) are free to an assembled state in which the end portions (12a, 12b) are integral with one another, characterized in that: - the elastomeric matrix is made from a first non-thermoplastic elastomer material,and that: - the internal surface (15a) of one of the end portions (12a) is coated at least in part with an internal bonding layer (17) crosslinked only locally at the interface with the elastomeric matrix (12) and the external surface (13b) of the other of the end portions (12b) is coated at least in part with an external bonding layer (18) crosslinked only locally at the interface with the elastomeric matrix (12), said bonding layers (17, 18) being made of a second thermoplastic elastomer material and configured to be integral with one another in the assembled state of the belt (10).,

2. A transmission belt (10) according to claim 1, wherein one of the end portions (12a) is offset transversely from the main portion (12c) of the elastomeric body (11) and connected to said main portion (12c) by a connecting portion (12d) extending transversely outward in an oblique direction.

3. Transmission belt (10) according to claim 1 or 2, wherein each connecting layer (17, 18) has a transverse dimension of between 20 pm and 100 pm, preferably between 30 pm and 60 pm.

4. A transmission belt (10) according to any preceding claim, wherein the connecting layers (17, 18) have the same length in the direction of extension of the transmission belt (10).

5. A transmission belt (10) according to any preceding claim, wherein the end portions (12a, 12b) of the transmission belt (10) in the free state are configured to be assembled at a junction zone (Zl), by bringing the bonding layers (17, 18) into contact together in the transverse direction which is perpendicular to the direction of extension of the belt (10), then by bonding between said bonding layers (17, 18) by applying a pressure of between 0.1bars and 20bars and heat, in particular a temperature of between 80°C and 300°C, preferably between 120°C and 200°C.

6. A transmission belt (10) according to any preceding claim, wherein each connecting layer (17, 18) is coated with a removable protective film (19, 20) intended to be removed before assembly of the end portions (12a, 12b) of the transmission belt (10).

7. Transmission belt (10) according to claim 9, wherein each protective film (19, 20) is made of polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), polyamide or nylon (PA), polyethylene terephthalate (PET), polyester.

8. A transmission belt (10) according to any preceding claim, wherein the first non-thermoplastic elastomeric material of the elastomeric matrix (12) comprises at least one elastomer selected from the group consisting of a natural rubber (NR), a synthetic polyisoprene (IR), a butadiene-styrene copolymer (SBR).

9. A transmission belt (10) according to any preceding claim, wherein the second material of the connecting layers (17, 18) is composed of a thermoplastic elastomer comprising a block copolymer comprising at least one elastomer block and at least one thermoplastic block, and the total content of thermoplastic elastomer being within a range varying from 65 to 100 pce (parts by weight per hundred parts of elastomer).

10. Transmission belt (10) according to claim 9, in which the second material composed of a thermoplastic elastomer is chosen from the following copolymers: a copolymer whose elastomer blocks are unsaturated, and which comprises styrene blocks and diene blocks, a copolymer whose elastomer blocks are unsaturated, and which comprises styrene blocks and diene blocks, and a linear or star copolymer whose elastomer blocks comprise a saturated part and an unsaturated part.

11. A transmission belt (10) according to any one of the claims- preceding indications, comprising reinforcing elements (14) embedded in the elastomeric body (11).

12. A transmission belt (10) according to claim 11, wherein the reinforcing elements (14) are parallel to each other in the vertical direction (Z) and extend in a single reinforcing layer.

13. A method of manufacturing a transmission belt (10) comprising an elastomeric body (11) comprising a main portion (12c) and two end portions (12a, 12b) each extending from one end of the main portion (12c), each end portion (12a, 12b) being delimited transversely by an inner surface (15a, 15b) and an outer surface (13a, 13b), said transmission belt (10) being configured to pass from an initial state, in which the end portions (12a, 12b) are free, to an assembled state in which the end portions (12a, 12b) are integral with one another, in which: - the body (11) is shaped from an elastomeric matrix (12) made of a first non-thermoplastic elastomeric material; - an internal bonding layer (17) and an external bonding layer (18) are formed from a second thermoplastic elastomer material;- the internal bonding layer (17) is deposited on at least a portion of the internal surface (15a) of one of the end portions (12a); - the external bonding layer (18) is deposited on at least a portion of the external surface (13b) of the other of the end portions (12b); the manufacturing method comprising a step of curing (104) the belt comprising the non-thermoplastic elastomeric body.;

14. Manufacturing method according to claim 13, wherein, after the baking step (104), the end portions (12a, 12b) of the transmission belt (10) are assembled in the free state at a joining zone (Zl) during a heat-sealing step (105), by bringing the connecting layers (17, 18) into contact with each other in a direction perpendicular to a direction of extension of the belt (10), then by bonding said connecting layers (17, 18) by applying a pressure of between 0.1 bar and 20 bar and heat, in particular a temperature of between 80°C and 300°C, preferably between 120°C and 200°C.

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