Power transmission belt exhibiting two-modulus elastic behavior during operation

Abstract

The object of the present invention is to obtain a belt which is easy to install but which is durable and exhibits good performance in terms of torque transmission. The invention relates to a power transmission belt (P) comprising one or more reinforcing elements (R) embedded in a polymeric composition (20), which has: a ratio MP2 / MP1 between the maximum tangent modulus MP2 in the range of 1-10% elongation exhibited by the belt (P) and the tangent modulus MP1 at 1% elongation exhibited by the belt (P) is equal to or greater than 2.00; and a force at 2% elongation exhibited by the belt (P) across the width of the belt (P) is equal to or less than 120.0 daN / cm. The belt (P) is obtained by a process comprising a step of embedding one or more reinforcing elements (R) in a polymeric composition (20), followed by curing to form the belt (P), in which the reinforcing element (R) has: a ratio MR2 / MR1 between the maximum tangent modulus MR2 in the range of 1-10% elongation exhibited by the reinforcing element (R) and the tangent modulus MR1 ​​at 1% elongation exhibited by the reinforcing element (R) is equal to or greater than 2.00; and a force at 2% elongation exhibited by the reinforcing element (R) over its diameter is strictly less than 11.0 daN / mm.

Description

Technical Field

[0001] The field of the invention is that of power transmission belts, in particular power transmission belts driven by friction.

Background Art

[0002] A power transmission belt comprising a belt ply comprising a reinforcement element comprising an assembly of three 168 tex multifilament strands of aramid known under the trade name Twaron 2100 and one 94 tex multifilament strand of nylon 6,6 known under the trade name Enka Nylon is known from the prior art, in particular from WO 97 / 06297. The diameter of this reinforcement element is 0.85 mm and the force at 2% elongation developed by the belt ply over the diameter of the reinforcement element is 12.0 daN / mm. However, having a belt ply that is easy to install, i.e., exhibits sufficient elongation under low loads, is desirable for being able to be installed on a belt, and when the ply is in operation, it is desirable to exhibit good performance in terms of torque transmission with low slippage and reduced creep. U.S. Patent Application Publication No. 20030171181, which describes a belt having an elastic behavior due to a low initial modulus of elasticity and comprising a stack of angled belt plies, is also known in the prior art. These have the following drawbacks: the belt ply has to be cut, oriented and stacked during manufacture, and once manufactured, the cut reinforcement elements are in the same plane as the ends of the belt, giving rise to problems with the operating durability of the belt.

Summary of the Invention

[0003] The object of the invention is to obtain a belt that is easy to install but exhibits good performance in terms of torque transmission in terms of durability. The subject of the invention is a power transmission belt comprising one or more reinforcement elements embedded in a polymeric composition. The belt is - The ratio of the maximum tangent coefficient MP2 within the range of 1-10% elongation exhibited by the belt to the tangent coefficient MP1 at 1% elongation exhibited by the belt, MP2 / MP1, is 2.00 or greater. - The force exerted by the belt at a 2% elongation across the width of the belt is 120.0 daN / cm or less. [Modes for carrying out the invention]

[0004] Power transmission belts are understood as closed or open belts. Belts are preferably used with pulleys and sometimes with tension adjustment systems, such as tensioner rollers or pulley substitutes. Closed, i.e., continuous belts can be used in pulley systems with substantially fixed sizes, while open belts (i.e., endless belts) can be used by cutting and fitting them to the size of the system, and by welding and reattaching them by the effect of heat and / or the addition of connectors. Flat friction power transmission belts exist with square, trapezoidal ("V-belts"), hexagonal or annular cross-sections, and there are also trapezoidal friction power transmission belts ("ribbed V-belts") which are paired or have ribs along the length, thereby greatly increasing the contact area between the pulley and the belt, and functioning by the teeth gripping the pulley. There are also friction power transmission belts with ribs along the lateral direction, thereby limiting energy dissipation due to the bending of the belt ("cogged belts"). Belts may also be toothed. A toothed belt is a belt with teeth that ensures power transmission through interlocking rather than gripping. Preferably, the power transmission belt is an elastic belt, and therefore has a low initial modulus of elasticity. These belts are easy to install, sometimes even manually. These belts often do not have a tension adjustment system, and therefore their implementation is relatively simple. Depending on the length of the belt and the complexity of the tension adjustment system, it is necessary to stretch the elastic belt by only 0.5 to 6%, and in most cases between 1 and 3%. The tension exhibited by the belt at a 2% stretch is representative of its ability to easily position the belt in the pulley groove.

[0005] While not limited to this use, these belts are particularly relevant to drive systems having pulleys positioned at a fixed distance. A reinforcing element is understood to be an element that mechanically reinforces the matrix in which it is intended to be embedded. In the description of this invention, unless otherwise explicitly indicated, any range of values ​​expressed by the expression "between a and b" means a range of values ​​greater than "a" but less than "b" (i.e., the limits a and b are excluded), while any range of values ​​expressed by the expression "a to b" means a range of values ​​from "a" to "b" (i.e., the exact limits a and b are included). The compounds referred to herein may be fossil-derived or bio-based. In the latter case, they may be derived in part or whole from biomass, or obtained from renewable raw materials derived from biomass. Similarly, the compounds referred to may be derived from the reuse of already used materials, in which case the compounds may be derived in part or whole from a reuse process, or themselves may be obtained from raw materials derived from a reuse process. Strands, filaments, polymers, plasticizers, fillers, etc., are particularly relevant.

[0006] Figure 5 shows the force / width-elongation curve of the belt according to the present invention, applying the 2016 standard ASTM D 378. The following modifications are applied to this standard: the testing machine is equipped with two pulleys having a diameter of 25.4 mm, which are suitable for the belt to be tested, without inserting the belt's meshing portion, and the tensile speed used is 50.8 mm / min. The maximum tangent coefficient MP2, which is expressed by the reinforcing element in the range of 1-10% elongation, is understood to be the maximum tangent coefficient obtained by calculating the derivative of the force-elongation curve at 1-10% elongation, which is obtained by applying the 2016 standard ASTM D 378. The tangent coefficient MP1 at 1% elongation, which is manifested by the reinforcing element, is understood to be the tangent coefficient obtained by calculating the derivative at 1% elongation of the force / width-elongation curve obtained by applying the 2016 standard ASTM D 378. The force exerted by the belt at 2% elongation is understood to be the force measured at 2% from the force / width-elongation curve, and is obtained by applying the 2016 standard ASTM D 378 to the 2% transverse coordinate point of this same curve.

[0007] The range of the ratio of the maximum tangential coefficient MP2 in the range of 1-10% elongation exhibited by the belt to the tangential coefficient MP1 at 1% elongation exhibited by the belt, according to the present invention, corresponds to the operating domain during belt stretching that enables the transmission of driving torque. When power transmission increases, a decrease in transmission efficiency occurs due to slippage between the belt and the pulley. The applicant has observed that with the two-modulus behavior defined within this range, there is less slippage with the same power transmission. Furthermore, over time, elastic belts of the prior art tend to creep, that is, they irreversibly plastically stretch and become unusable. The applicant has observed that with the significant two-modulus behavior within the range defined above, creep is very limited, thereby ensuring a longer operating life for the belt. Over time, this creep can cause tension loss in the elastic belt. This two-modulus behavior within the range defined above, represented by a ratio MP2 / MP1 of 2.0 or more, can reduce creep in belt plies with high torque transmission. The force exerted by the belt at a 2% elongation across its width is the force necessary for good installation. Advantageously, the force exerted by the belt at a 2% elongation across the width of the belt is 100.0 daN / cm or less, preferably 80.0 daN / cm or less.

[0008] According to the present invention, a power transmission belt comprises the steps of embedding one or more reinforcing elements in a polymeric composition, and subsequently curing to form a belt, wherein the reinforcing elements are - The ratio of the maximum tangent coefficient MR2 in the range of 1-10% elongation exhibited by the reinforcing element to the tangent coefficient MR1 at 1% elongation exhibited by the reinforcing element, MR2 / MR1, is 2.00 or greater. - The force exerted by the reinforcing element at 2% elongation across the diameter of the reinforcing element is strictly less than 11.0 daN / mm. It is obtained by method. Figure 4 shows the force-extension curves for the prior art reinforcing element and the reinforcing element according to the present invention. These curves represent what happens to the belt when subjected to a slight load during installation, i.e., small deformation (extension between 0 and 2%), and when subjected to the maximum load during operation, i.e., extension between 1 and 10%.

[0009] The maximum tangent coefficient MR2 exhibited by the reinforcing element in the range of 1-10% elongation is understood to be the maximum tangent coefficient obtained by calculating the derivative of the force-elongation curve at 1-10% elongation, which is obtained from the force-elongation curve obtained by applying the 2014 standard ASTM D 885 / D 885M-10a after a standard tensile preload of 0.5 cN / tex to the reinforcing element. The tangent coefficient MR1 at 1% elongation exhibited by the reinforcing element is understood to be the tangent coefficient obtained by calculating the derivative of the force-elongation curve at 1% elongation, which is obtained by applying the 2014 standard ASTM D 885 / D 885M-10a to the reinforcing element after a standard tensile preload of 0.5 cN / tex. In the case of reinforcing elements, the tangential coefficient is measured directly before the step of embedding the reinforcing element in the belt ply, i.e., without any other steps that alter the properties of the tangential coefficient performed between the final forming step (twisting or heat treatment) and the step of embedding in the polymeric composition. The force at 2% elongation exerted by the reinforcing element is obtained from the force-elongation curve obtained under the standard ASTM D 885 / D 885M-10a conditions of 2014, at the 2% transverse point of this same curve, and is understood to be the force measured at 2% immediately after a standard tensile preload of 0.5 cN / tex on the reinforcing element.

[0010] By definition, the diameter of a reinforcing element is the diameter of the smallest circle that circumscribes the reinforcing element on its inside. The range of the ratio of the maximum tangential coefficient MR2 in the range of 1-10% elongation exhibited by the reinforcing element to the tangential coefficient MR1 at 1% elongation exhibited by the reinforcing element, according to the present invention, corresponds to the operating domain during the stretching of the belt strands, enabling the transmission of driving torque. When power transmission increases, a decrease in transmission efficiency occurs due to slippage between the belt and the pulley. The applicant has observed that with the two-modulus behavior defined within this range, there was less slippage with the same power transmission. Furthermore, over time, prior art elastic belts tend to creep, i.e., irreversibly plastically stretch and become unusable. The applicant has observed that with the significant two-modulus behavior within the range defined above, creep is very limited, thereby ensuring a longer operating life for the belt. Over time, this creep can cause tension loss in the elastic belt. This two-modulus behavior within the range defined above, represented by a ratio MR2 / MR1 of 2 or more, can reduce creep in belt plies with high torque transmission. The force exerted by the reinforcing element across its width at a 2% elongation is the force necessary for good belt attachment.

[0011] Advantageously, the belt includes a single belt ply composed of a polymer 20 containing multiple reinforcing elements. The reinforcing elements are arranged parallel to each other in the longitudinal direction X, substantially perpendicular to the overall direction Y in which the reinforcing elements of the belt ply extend. Therefore, the manufacture of the belt is made easier by using a single belt ply and a reinforcing material that has two different elastic behaviors at substantially 0 degrees. Advantageously, each reinforcing element comprises an assembly including at least one multifilament strand of aromatic polyamide or aromatic copolyamide and at least one multifilament strand of aliphatic polyamide or polyester. One effect of using a hybrid reinforcing element comprising an assembly of at least one multifilament strand of aromatic polyamide or aromatic copolyamide and at least one multifilament strand of aliphatic polyamide or polyester is that a two-modulus curve is obtained, i.e., a curve with a relatively low modulus of elasticity at small deformations and a relatively high modulus of elasticity at large deformations. Specifically, the belt ply has a relatively low modulus of elasticity at small deformations, controlled by the modulus of elasticity of the aliphatic polyamide strand in this example, allowing for good installation. Furthermore, the belt reinforcing element exhibits a relatively high modulus of elasticity at large deformations, controlled by the modulus of elasticity of the aromatic polyamide or aromatic copolyamide strand in this example, making it possible to avoid slippage and transmit torque well under high loads.

[0012] Regarding multifilament strands of aromatic polyamides or aromatic copolyamides, it is well known that these are filaments of fibers composed of linear polymers, more specifically poly(p-phenylene terephthalamide) (or PPTA), in which at least 85% are aromatic groups linked by amide bonds directly connected to two aromatic rings, and it is recalled that for a very long time they have been manufactured from optically anisotropic spinning compositions. Among aromatic polyamides or aromatic copolyamides, examples include polyarylamides (or PAA, particularly known by Solvay's trade name lxef), poly(metaxylylene adipamide), polyphthalamides (or PPA, particularly known by Solvay's trade name Amodel), or para-aramids (or poly(paraphenylene terephthalamide or PA PPD-T, particularly known by Du Pont de Nemours' trade name Kevlar or Teijin's trade name Twaron). Aliphatic polyamide multifilament strands are understood to be linear polymer filaments of polymers or copolymers that contain amide functional groups, lack aromatic rings, and can be synthesized by condensation polymerization between carboxylic acids and amines. Among aliphatic polyamides, examples include nylon PA4.6, PA6, PA6.6, or PA6.10, particularly Zytel from DuPont, Technyl from Solvay, or Rilsamid from Arkema.

[0013] Regarding polyester multifilament strands, it is thought that these are linear polymer filaments formed by groups linked by ester bonds. Polyesters are produced by condensation polymerization through esterification between a dicarboxylic acid or one of its derivatives and a diol. For example, polyethylene terephthalate can be produced by condensation polymerization of terephthalic acid and ethylene glycol. Among the known polyesters, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene naphthalate (PBN), polypropylene terephthalate (PPT), or polypropylene naphthalate (PPN) can be mentioned. Advantageously, the ratio MR2 / MR1 is 2.50 or higher, preferably 3.00 or higher. Advantageously, the ratio MR2 / MR1 is 20.00 or less, preferably 15.00 or less. Advantageously, the force exerted by the reinforcing element (R) over the diameter of the reinforcing element (R) at a 2% elongation is 8.0 daN / mm or less.

[0014] Advantageously, the force exerted by the reinforcing element (R) over the diameter of the reinforcing element (R) at 2% elongation is 0.50 daN / mm or more, preferably 1.00 daN / mm or more. Advantageously, the belt is a friction-type power transmission belt. Advantageously, the diameter of the reinforcing element is 2.00 mm or less, preferably 1.00 mm or less, and more preferably 0.50 mm or less. In the first embodiment, each reinforcing element comprises an assembly consisting of a single multifilament strand of aromatic polyamide or aromatic copolyamide and a single multifilament strand of aliphatic polyamide or polyester, the strands being helically wound together around each other. Advantageously, each carcass reinforcing element is in twist equilibrium. The multifilament strands of aromatic polyamide or aromatic copolyamide and the multifilament strands of aliphatic polyamide or polyester are assembled together and are helically wound around each other.

[0015] In a second embodiment, each reinforcing element includes an assembly composed of two multifilament strands of aromatic polyamide or aromatic copolyamide and a single multifilament strand of aliphatic polyamide or polyester, and the strands are helically wound together to form a layer. The expression "composed assembly" is understood to mean that the assembly does not include multifilament strands other than two multifilament strands of aromatic polyamide or aromatic copolyamide and the multifilament strand of aliphatic polyamide. Advantageously, each carcass reinforcing element is twist balanced. The following features apply to the two above-described embodiments. The expression "composed assembly" is understood to mean that the assembly does not include multifilament strands other than two multifilament strands of aromatic polyamide or aromatic copolyamide or the multifilament strand of polyester.

[0016] The expression "twist balance" in two embodiments of the present invention is understood to mean that the multifilament strands are wound with substantially the same twist and the twist of the monofilaments of each multifilament strand in the final assembly is substantially zero. Specifically, the method for manufacturing these carcass reinforcing elements is well known in the prior art and each spun yarn of the monofilament (more appropriately referred to as "yarn") is first twisted individually in a given direction D’ = D1’ = D2’ = D3’ (which, according to the recognized terminology, is the S or Z direction respectively, representing the direction of rotation compared to the crossbar of S or Z), having initial twists R1’, R2’, R3’ where R1’ = R2’ = R3’, and the monofilament is deformed to form a strand or twist ply (more appropriately referred to as "strand") that is helical around the axis of the strand, including a first step. Next, during the second step, in order to obtain a reinforcing element (more appropriately referred to as "cord"), the strands are subsequently twisted together in a direction D4 that is opposite to the direction D’ = D1’ = D2’ = D3’ (Z or S direction respectively), with a final twist R4 such that R4 = R1’ = R2’ = R3’. This reinforcing element is then said to be in twist balance. Since R4 = R1’ = R2’ = R3’ and the direction D’ = D1’ = D2’ = D3’ is opposite to the direction D4, and since R1’ = R2’ = R3’ and this residual twist is zero or substantially zero, the monofilaments of the strand exhibit the same residual twist in the final reinforcing element. The expression "substantially zero residual twist" is understood to mean that the residual twist is less than 2.5% of the twist R4 exactly.

[0017] Preferably, the count of the multifilament strands of aromatic polyamide or aromatic copolyamide is 10 tex or more, preferably 20 tex or more. Preferably, the count of the multifilament strands of aromatic polyamide or aromatic copolyamide is 100 tex or less, preferably 80 tex or less, more preferably 60 tex or less. Preferably, the count of the aliphatic polyamide or polyester multifilament strand is 10 tex or higher, preferably 20 tex or higher. Preferably, the yarn count of the aliphatic polyamide or polyester multifilament strand is 100 tex or less, preferably 80 tex or less, and more preferably 60 tex or less. The thread count (or linear density) of each strand is determined in accordance with the standard ASTM D1423. The thread count is given in tex (for reference, a mass of 1000m of the product in grams: 0.111 tex is equal to 1 denier). Advantageously, the twist of each multifilament strand of the reinforcing element is in the range of 200 to 700 turns per meter, preferably 250 to 650 turns per meter.

[0018] The twist of the reinforcing elements can be determined using any method known to those skilled in the art, for example, in accordance with the 2014 standard ASTM D 885 / D 885M-10a. Advantageously, the density of reinforcing elements in the belt is in the range of 96 to 250 reinforcing elements per decimeter of belt, preferably 140 to 220 reinforcing elements per decimeter of belt. The density of reinforcing elements in a belt ply is the number of reinforcing elements contained in one decimeter of belt ply in a direction (X) perpendicular to the direction (Y) in which the reinforcing elements extend parallel to each other. To enable the manufacture of belt plies and to efficiently utilize reinforcing materials, the end-to-end distance between reinforcing elements typically represents a value of 10-50% of the diameter of the reinforcing elements. At a typical value of 30% of the diameter, if the diameter of the reinforcing elements is in the range of 0.3-0.8 mm, the belt plies can be manufactured with a density of 96-250 threads per decimeter and used in power transmission belts. Those skilled in the art can set this value in accordance with manufacturing constraints (viscosity of the polymeric composition) or usage conditions. Preferably, the polymeric composition is a polyurethane-type composition.

[0019] As is well known to those skilled in the art, polyurethane-type compositions consist of diisocyanate-terminated prepolymers cured with diamines or diols, and can be increased with other polymeric diols or diamines. Other additives, including curing catalysts, plasticizers, antistatic agents, colorants, and fillers, may be included to impart various properties, and this list is not limited. Advantageously, the reinforcing elements are arranged alternately in the final Z-twist and S-twist in the direction (X) perpendicular to the belt direction (Y). In the first alternative form, the belt has a continuous shape, with an outer surface shape that is trapezoidal, circular, semicircular, oval, square, or a combination of these shapes, having longitudinal or transverse lines or ribs. In the second alternative form, the belt has a welded, endless shape with an outer surface shape that is square, trapezoidal, trapezoidal with longitudinal or transverse lines or ribs, circular, semicircular, oval, or a combination thereof. The power transmission belt according to the present invention, having a semicircular or square shape, is particularly depicted as shown in Figure 6. The present invention will be better understood by considering the following description and referring to the drawings, but the following description is given solely as a non-limiting example. [Brief explanation of the drawing]

[0020] [Figure 1] This is a diagram illustrating the power transmission belt P according to the present invention. [Figure 2] Figure 1 shows a diagram illustrating polymer 20. [Figure 3] This is a diagram illustrating a tensile test. [Figure 4] This graph illustrates the force-extension curves of the belt reinforcing element EC of the prior art, and the belt reinforcing elements R1, R3, R4, and R5 of the present invention. [Figure 5] This is a graph illustrating the force-extension curve of belt P4 according to the present invention. [Figure 6] This is a diagram illustrating another power transmission belt according to the present invention. [Examples]

[0021] Example of belt P4 according to the present invention Figure 1 shows a continuous power transmission belt P according to the present invention having a trapezoidal outer shape. The power transmission belt P is intended to drive any member in rotation. The power transmission belt P comprises a polymer 20 made from a polyurethane matrix, in which reinforcing elements R are embedded for forming belt plies. The power transmission belt P also comprises a mechanical drive layer 22, similarly made of polyurethane, in contact with the polymer 20. The mechanical drive layer 22 comprises a plurality of ribs 24, each extending in an overall direction Y substantially perpendicular to the longitudinal direction X of the belt P. Each rib 24 has a trapezoidal shape in cross-section. The overall directions of the ribs 24 are substantially equilibrium with each other. The ribs 24 extend over the entire length of the belt P. These ribs 24 are intended to engage with complementary grooves or slots, for example, in a pulley to which the belt is intended to be mounted. In this case, belt P is belt P4 having a reinforcing element R4. The polymer 20 from Figure 1 is described here with reference to Figure 2. Belt P includes a single belt ply N4 composed of polymer 20 containing multiple reinforcing elements R4, as illustrated in Figure 2.

[0022] The polymer 20 includes a plurality of reinforcing elements R4. The reinforcing elements are arranged parallel to each other in the longitudinal direction X, substantially perpendicular to the overall direction Y in which these reinforcing elements extend over the belt ply. The power transmission belt P4 has a ratio, MP2 / MP1, of the maximum tangential coefficient MP2 in the range of 1-10% elongation exhibited by the belt P4 to the tangential coefficient MP1 at 1% elongation exhibited by the belt P4, which is 2.00 or more, in which case MP2 / MP1 = 3.5, and the force at 2% elongation exhibited by the belt P4 across the width of the belt P4 is 120.0 daN / cm or less, preferably 100.0 daN / cm or less, and more preferably 80.0 daN / cm or less, in which case F at 2% elongation = 74.7 daN / cm. The belt reinforcement element R4 and its corresponding set are described below.

[0023] Properties of the strands of the reinforcing element As schematically shown in Figure 2, the reinforcing element R4 includes an assembly composed of a multifilament strand of aromatic polyamide or aromatic copolyamide and a multifilament strand of aliphatic polyamide, with the two strands helically wound together. The belt reinforcing element P4 is in a twisted equilibrium state. The selected aromatic polyamide is, in this case, preferably a para-aramid known by Teijin's trade names Twaron 1000 or Twaron 2040. Aliphatic polyamide is nylon, known by the trade name TYP632 470f68 from Nexis.

[0024] Reinforcement element R4 number In the reinforcing element, the yarn count of the aromatic polyamide or aromatic copolyamide strands is 10 tex or higher, preferably 20 tex or higher, and 100 tex or lower, preferably 80 tex or lower, and more preferably 60 tex or lower. In this case, the yarn count of the aramid strands is equal to 55 tex. In the reinforcing element, the count of the aliphatic polyamide strand is 20 tex or higher, preferably 30 tex or higher, more preferably 40 tex or higher, and 100 tex or lower, preferably 80 tex or lower, more preferably 60 tex or lower. In this case, the count of the nylon strand is equal to 47 tex. Twist of reinforcing element R4 In the reinforcing element R4, the twist of each multifilament strand of the reinforcing element is in the range of 240 to 700 turns per meter, preferably 250 to 650 turns per meter. In this example, the twist of each multifilament strand of the reinforcing element R4 is equal to 350 turns per meter. The diameter of the reinforcing element R4 is 2.00 mm or less, preferably 1.00 mm or less, and more preferably 0.60 mm or less. In this case, the reinforcing element R4 has a diameter of D = 0.43 mm.

[0025] Force-elongation curve of reinforcing material R4 The ratio MP2 / MP1 between the maximum tangent coefficient MP2 in the range of 1-10% elongation exhibited by the reinforcing element R4 and the tangent coefficient MP1 at 1% elongation exhibited by the reinforcing element R4 is 2.00 or more, preferably 2.50 or more, and more preferably 3.00 or more. This ratio MP2 / MP1 is 20.00 or less, preferably 15.00 or less. In this case, MP2 / MP1 = 9.3. The force exerted by reinforcing element R4 at 2% elongation across the diameter of the reinforcing element is strictly less than 11.00 daN / mm, preferably 8.00 daN / mm or less, and this force is 0.50 daN / mm or more, preferably 1.00 daN / mm or more. In this case, the force exerted by reinforcing element R4 at 2% elongation across the diameter of the reinforcing element is equal to 2.3 daN / mm. Features of the external shape of Beltply N4 The density of reinforcing elements R4 in belt P4 is in the range of 96 to 250 reinforcing elements per decimeter of belt P4, preferably 140 to 220 reinforcing elements per decimeter of belt P4. In this case, the density of reinforcing elements R4 is equal to 179 reinforcing elements R4 per decimeter of belt P4.

[0026] Method for manufacturing reinforcing element R4 As described above, the reinforcing element R4 is in twist equilibrium, that is, the two multifilament strands are wound with substantially the same twist, and the twist of the monofilaments in each multifilament strand is substantially zero. In one embodiment, in the first step, each spun monofilament yarn (more appropriately referred to as "yarn") is first twisted individually by itself in a given direction, in this case the Z direction, with an initial twist equal to 350 twists per meter, to form a strand or twist strength (more appropriately referred to as "strand"). Next, in the second step, in order to obtain a set of reinforcing elements (more appropriately referred to as "cord"), the two strands are subsequently twisted together in the S direction to a final twist equal to 350 turns per meter. In another embodiment, in the first step, each spun monofilament yarn is first twisted individually by itself in a given direction, in this case the S direction, with an initial twist equal to 350 turns per meter, to form a strand or twist strength. Then, in the second step, two strands are subsequently twisted together in the Z direction to a final twist equal to 350 turns per meter in order to obtain a collection of reinforcing elements.

[0027] Method for manufacturing a belt according to the present invention The method for manufacturing the belt is a method conventionally used by those skilled in the art. Belt P4 is manufactured by embedding a plurality of reinforcing elements R4 in a polymeric composition, with the interposition of reinforcing elements assembled in the S and Z directions within a mold as described above. During the embedding step, the reinforcing elements are embedded in the polymeric composition, for example, polyurethane. Finally, in order to obtain belt P4, the untreated product thus obtained is crosslinked. Measurement and comparative testing For comparative examples, two types of prior art belts, denoted as PEDT and PC respectively, were used. Three control belts, C1, C2, and C3, were also used. The external features of the control belts C1, C2, and C3, the prior art belts (PEDT and PC), and the belts P1 to P6 according to the present invention are summarized in Tables 1 and 2 below.

[0028] Tables 1 and 2 below show the results of the belt's mountability, i.e., elongation under low load, so that the belt can be attached to the pulley. The term NC means that no measurements were obtained for these various belts. [Table 1]

[0029] [Table 2]

[0030] Belt comparison To perform a comparative analysis of the belts, tensile tests were conducted on the machine as shown in Figure 3. The principle of these tests is to drive the belt through two pulleys, one with driving torque and the other with braking torque. The transmitted torque is the difference between these two torques, and the slip is the difference in rotational speed between these two pulleys. Different tests were performed at a rotational speed of 1750 rpm. Three types of deformation were performed in the tensile test. - The first deformation involves allowing the pulleys to move freely relative to each other, while keeping the applied tensile preload PT of 22.7 kg fixed during the test. In this case, the change in the position of the pulleys over time, and therefore the elongation (%) of the belt, can be monitored by applying a torque of 2.71 Nm for 100 hours. - First, a tensile preload PT of 22.7 kg is applied, and the pulley is fixed to a fixed distance for a second deformation. As a result, by applying a fixed torque of 2.71 Nm to the belt for 100 hours, the decrease in tension over time in the belt compared to the tensile preload PT (%) can be monitored. - In a pulley configuration where the pulleys move freely relative to each other, a third modification was performed last. A tensile preload of 22.7 kg was applied, and a torque variation between 2.71 Nm and 7.45 Nm was applied. Slip, i.e., variation in rotational speed between the drive pulley and the braking pulley, was measured. Under conventional operating conditions, slip is less than 5%, preferably less than 3%.

[0031] The results are summarized in Table 3 below. Table 3 shows the resistance of the tested belts to tension loss during testing, using a fixed pulley. Good resistance to tension loss is indicated by the lowest possible value at a given point in time, measured by the percentage of tension loss between 100 seconds and 400,000 seconds. The resistance to creep, or elongation, during testing, using the tension applied between 10,000 seconds and 400,000 seconds, and the movable pulley, is also shown in this table. Similarly, the maximum allowable torques for achieving slip of less than 5% and 10% are indicated, respectively, and good torque transmission between the drive pulley and the braking pulley is indicated by the highest possible value.

[0032] [Table 3]

[0033] These results demonstrate that belts P4 and P5 according to the present invention exhibit both greater resistance to tension reduction than the prior art belt NC and control belt C3, and significantly better resistance to creep compared to the prior art belt NC. Belts P4 and P5 also exhibit a higher capacity to transmit significant torque for a given level of slip (5% or 10%). Therefore, the belt according to the present invention exhibits excellent resistance to tension reduction, improved resistance to creep, and improved ability to transmit mechanical torque.

[0034] Therefore, as the above results show, the present invention clearly relates to a power transmission belt comprising one or more reinforcing elements embedded in a polymeric composition. The belt is - The ratio of the maximum tangent coefficient MP2 within the range of 1-10% elongation exhibited by the belt to the tangent coefficient MP1 at 1% elongation exhibited by the belt, MP2 / MP1, is 2.00 or greater. - The force exerted by the belt (P) across the width of the belt at a 2% elongation is 120.0 daN / cm or less. The present invention is not limited to the embodiments described above. Different embodiments and the features of variations assumed above or above can be combined, insofar as they are compatible with each other and conform to the present invention.

Claims

1. In a power transmission belt (P) comprising a plurality of reinforcing elements (R) embedded in a polymeric composition (20), The ratio of the maximum tangent coefficient MP2 in the range of 1-10% elongation exhibited by the belt (P) to the tangent coefficient MP1 at 1% elongation exhibited by the belt (P), MP2 / MP1, is 2.00 or greater. The force exerted by the belt (P) across the width of the belt (P) at a 2% elongation is 120.0 daN / cm or less. The process for forming a belt (P) includes the steps of embedding one or more reinforcing elements (R) in a polymeric composition (20), and subsequently curing to form a belt (P), wherein the reinforcing elements (R) The ratio of the maximum tangent coefficient MR2 in the range of 1-10% elongation exhibited by the reinforcing element (R) to the tangent coefficient MR1 at 1% elongation exhibited by the reinforcing element (R), MR2 / MR1, is 2.00 or greater. The force exerted by the reinforcing element (R) across the diameter of the reinforcing element at 2% elongation is strictly less than 11.0 daN / mm. A belt (P) characterized by being obtained by a method, A belt (P) in which multiple reinforcing elements (R) are arranged parallel to each other along the longitudinal direction of the belt (P) within a single belt ply.

2. The belt (P) according to claim 1, wherein the force exerted by the belt (P) at a 2% elongation across the width of the belt (P) is 100.0 daN / cm or less.

3. The belt (P) according to claim 2, wherein each reinforcing element (R) comprises an assembly comprising at least one multifilament strand of aromatic polyamide or aromatic copolyamide and at least one multifilament strand of aliphatic polyamide or polyester.

4. The belt (P) according to claim 1, wherein the ratio MR2 / MR1 is 2.50 or greater.

5. The belt (P) according to claim 1, wherein the ratio MR2 / MR1 is 20.00 or less.

6. The belt (P) according to claim 1, wherein the force exerted by the reinforcing element (R) over the diameter of the reinforcing element (R) at a 2% elongation is 8.0 daN / mm or less.

7. The belt (P) according to claim 1, wherein the diameter of the reinforcing element (R) is 2.00 mm or less.

8. The belt (P) according to claim 1, wherein each reinforcing element (R) comprises an assembly composed of a single multifilament strand of aromatic polyamide or aromatic copolyamide and a single multifilament strand of aliphatic polyamide or polyester, the strands being helically wound together around each other.

9. The belt (P) according to claim 1, wherein each reinforcing element (R) comprises an assembly composed of two multifilament strands of aromatic polyamide or aromatic copolyamide and a single multifilament strand of aliphatic polyamide or polyester, the strands being helically wound together to form layers.

10. The belt (P) according to claim 1, wherein the reinforcing elements (R) are arranged alternately in a direction (X) perpendicular to the direction (Y) of the belt (P) with final Z twists and S twists.

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