Double-layer multi-strand cord with a coated inner layer and improved permeability

Abstract

The present invention relates to a double-layered multi-strand cord (50) comprising: a cord inner layer (CI) consisting of K≥1 inner strands (TI), and a cord outer layer (CE) consisting of L>1 outer strands (TE) wound around the cord inner layer (CI) and having a spiral radius R2. The intermediate and outer layers (C2, C2', C3, C3') of each inner and outer strand (TI, TE) are unsaturated. The cord (50) is obtained by a method comprising the steps of: a step of manufacturing a coated inner layer (CIG) in which the inner layer (CI) is surrounded by an elastomeric composition having a thickness G, then by the outer layer (CE), G satisfying the range 1.02 to 1.25 of R2 / Rt, where Rt is the spiral radius of the theoretical outer layer (CET) obtained when the inner layer (CI) is in direct contact with the theoretical outer layer (CET); and a step of bringing the cord outer layer (CE) closer to the circle circumscribing the cord inner layer (CI) (400) so that the ratio R2 / Rt is in the range 1.00 to 1.10.

Description

Double-layer multi-strand cord with a covered inner layer and improved permeability. Technical Field

[0001] This invention relates to multi-strand cords, which can be used particularly for reinforcing tires, especially tires for heavy industrial vehicles. Background Technology

[0002] A tire with radial carcass reinforcement includes a tread, two non-stretchable bead sections, two sidewalls connecting the bead sections to the tread, and a belt layer or crown reinforcement arranged circumferentially between the carcass reinforcement and the tread. The crown reinforcement includes multiple ply layers made of an elastomeric composition, which may be reinforced by reinforcing elements, such as metal or fabric cords or monofilaments.

[0003] The tread reinforcement typically comprises at least two stacked tread plies (sometimes called working plies or cross plies), wherein the typically metallic reinforcing elements of the tread plies are arranged almost parallel to each other within the plies but cross from one ply to the other, that is, they are (symmetrically or asymmetrically) inclined at an angle typically between 10° and 45° relative to the circumferential midplane. The working plies typically include reinforcing elements exhibiting very low elongation in order to perform their function of guiding the tire.

[0004] The tread reinforcement may also include various other auxiliary ply or elastomeric composition layers, which have widths that can be varied depending on the situation, and may or may not contain reinforcing elements. For example, so-called protective ply or so-called hoop ply may be mentioned, which serves to protect the remainder of the belt layer from external impact or perforation. The hoop ply (referred to as the "zero-degree" ply) contains reinforcing elements oriented substantially circumferentially, whether radially outward or inward relative to the working ply layer. Protective ply layers typically include reinforcing elements exhibiting high elongation, allowing them to deform under stress imposed by concave bodies (such as stones).

[0005] A working fabric reinforcement element is known in the prior art, comprising a double-layer multi-strand metal cord having a structure 189.23. This cord includes an inner cord layer and an outer cord layer, the inner cord layer being composed of inner strands, and the outer cord layer being composed of six outer strands wound in a spiral around the inner cord layer. Application WO2019243691 also discloses a double-layer multi-strand metal cord having a structure 171.26, comprising an inner cord layer and an outer cord layer, the inner cord layer being composed of inner strands, and the outer cord layer being composed of six outer strands wound in a spiral around the inner cord layer.

[0006] Each strand of the inner and outer strands consists of an inner layer of three inner threads, a middle layer of nine threads, and an outer layer of fifteen outer threads. Each thread has a diameter of 0.23 mm.

[0007] Tires on heavy-duty industrial vehicles (especially those used on construction sites) suffer from numerous attacks. Specifically, these types of tires are often driven on uneven road surfaces, sometimes resulting in punctures in the tread. These punctures allow corrosive agents (such as air and water) to enter, oxidizing the metal reinforcing elements of the tread reinforcement (particularly the tread ply), thus significantly reducing tire life.

[0008] One solution to increase tire life is to increase the breaking strength of the cords. Typically, this is achieved by increasing the diameter of the filaments that make up the cord and / or by increasing the number of filaments and / or the individual strength of each filament. However, further increasing the filament diameter, for example, beyond 0.45 mm (as in application WO2016051669), inevitably leads to a decrease in the cord's flexibility, which is undesirable. Increasing the number of filaments generally reduces the ability of the elastomer composition to penetrate the strands. Finally, increasing the individual strength of each filament requires a significant investment in the equipment used to manufacture the filaments.

[0009] Another solution to increase tire life is to combat the spread of these corrosive agents.

[0010] Therefore, it is possible to configure the cord by covering each metal wire with an elastomer composition during the manufacturing process. During this process, the elastomer composition permeates the capillaries present between each layer of each strand, thereby preventing the diffusion of corrosive agents. Such cords are commonly referred to as in-situ rubberized cords and are well known in the prior art.

[0011] The spacing between the filaments in the intermediate and outer layers of the inner and / or outer strands can also be increased to promote the filling of capillaries by the elastomeric composition of the ply during tire curing. This can be achieved by removing one or more filaments from the layers, or by using filaments with reduced diameters in the layers of the strands. Reducing the number of filaments results in a decrease in the breaking strength of the cord, which is undesirable.

[0012] Finally, the spacing between the outer strands can be increased to allow the elastomer composition to better penetrate the inner strands. This can be achieved by using inner strands with a diameter larger than that of the outer strands. However, this solution results in the need to manage multiple different filament diameters during cord manufacturing, or in one or more inner strands having different constructions than the outer strands, which is undesirable. Summary of the Invention

[0013] The object of the present invention is a cord that, compared with cord 189.23, exhibits improved permeability of its outer strands and easier penetration of the elastomer composition into the inner strands, thereby reducing the intrusion and diffusion of corrosive agents into the cord without compromising the cord's breaking strength.

[0014] The cord according to the present invention

[0015] Therefore, one subject of the present invention is a double-layer multi-strand cord, which includes:

[0016] - An inner layer composed of Q = 2, 3, or 4 internal metal wires.

[0017] - An intermediate layer consisting of M intermediate metal wires with a diameter d2 wound around the inner layer, and

[0018] - An outer layer consisting of N outer metal wires with a diameter d3 wound around the middle layer.

[0019] - An outer layer of cord consisting of L>1 outer strands wound around the inner layer of the cord, the outer layer having a helical radius R2, each outer strand being a three-layered strand and comprising:

[0020] - An inner layer composed of 2, 3, or 4 internal metal wires,

[0021] - An intermediate layer consisting of M' intermediate metal wires with a diameter d2' wound around the inner layer, and

[0022] - An outer layer consisting of N' outer metal wires with a diameter d3' wound around the middle layer.

[0023] in:

[0024] - The inner strands or the middle layer of each inner strand are unsaturated, such that the sum SI2 of the wire spacing I2 of the inner strands or the middle layer of each inner strand is greater than or equal to the diameter d2.

[0025] - The inner strands or the outer layer of each inner strand are unsaturated, such that the sum SI3 of the spacing I3 of the inner strands or the outer layer of each inner strand is greater than or equal to the diameter d3.

[0026] - The outer strands or the intermediate layer of each outer strand are unsaturated, such that the sum of the wire spacing I2' of the intermediate layer of each outer strand (TE) is greater than or equal to the diameter d2'.

[0027] - The outer layer of each outer strand is unsaturated, such that the sum of the spacing I3' of the outer strands of each outer strand is greater than or equal to the diameter d3';

[0028] -The cord is obtained through a method including the following steps:

[0029] - The step of manufacturing a covered inner layer, wherein the inner layer is surrounded by an elastomeric composition having a thickness G, and then surrounded by an outer layer, wherein the thickness G of the elastomeric composition satisfies a ratio R2 / Rt ranging from 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer obtained when the inner layer is in direct contact with the theoretical outer layer; and - the step of bringing the outer layer of the cord closer to the circle circumscribed by the inner layer of the cord, such that the ratio R2 / Rt ranges from 1.00 to 1.10.

[0030] Any range of values ​​expressed as “between a and b” represents a range of values ​​from greater than a to less than b (i.e., excluding endpoints a and b), while any range of values ​​expressed as “from a to b” means a range of values ​​from endpoint “a” to endpoint “b”, i.e., including the strict endpoints “a” and “b”.

[0031] By definition, the helical radius R2 of the outer layer of the cord is the radius of the theoretical circle, which passes through the center of the outer strands of the outer layer in a plane perpendicular to the cord axis.

[0032] By definition, the diameter of a strand is the diameter of the smallest circle that can be circumscribed within it.

[0033] By definition, an unsaturated layer with filaments is a layer in which sufficient space is left between the filaments to allow the passage of an uncrosslinked elastomer composition. According to the invention, the outer layer of each strand is unsaturated, meaning that the outer filaments do not contact each other and there is sufficient space between two adjacent outer filaments to allow the elastomer composition to pass through; that is, the sum of the filament spacing is greater than or equal to the diameter of the filaments. On a cord cross-section perpendicular to the main axis of the cord, the filament spacing of the layer is defined as the shortest distance between two adjacent filaments in the average separating layer. Therefore, the filament spacing is calculated by dividing the sum of the filament spacings by the amount of space between the filaments in the layer. In other words, the layer can be unsaturated when the filament spacing is greater than or equal to 5 μm.

[0034] Preferably, the spacing I2 between the inner strands or the intermediate layer of each inner strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, even more preferably greater than or equal to 50 μm, and the height is preferably greater than or equal to 60 μm.

[0035] Preferably, the spacing I2' of the intermediate layer of each outer strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, even more preferably greater than or equal to 50 μm, and the height is preferably greater than or equal to 60 μm.

[0036] Preferably, the spacing I3 between the inner strands or the outer layer of each inner strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, even more preferably greater than or equal to 50 μm, and the height is preferably greater than or equal to 60 μm.

[0037] Preferably, the spacing I3' of the outer layer of each outer strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, even more preferably greater than or equal to 50 μm, and the height is preferably greater than or equal to 60 μm.

[0038] Preferably, the spacing between the outermost strands of each strand is less than or equal to 100 μm.

[0039] Conversely, a saturated layer with filaments ensures that there is insufficient space between the metal wires for the elastomer composition to pass through; that is, the sum of the wire spacing is strictly smaller than the wire diameter. In other words, a saturated layer with filaments can allow the wire spacing to be less than 5 μm.

[0040] In this invention, the cord has two layers with strands, which means that it comprises an assembly consisting of no more and no less than two layers with strands. This means that the assembly has two layers with strands, not one layer or three layers, but only two layers.

[0041] Direct contact with the theoretical outer layer means that there is no covering between the inner layer and the theoretical outer layer.

[0042] An elastomer composition or a composition of elastomers means that the composition contains at least one elastomer or a rubber (these two terms are synonymous) and at least one other component.

[0043] The inner layer of the cord is surrounded by an elastomer composition with a thickness G, and then surrounded by an outer layer.

[0044] Compared to cord 189.23 (which is unpermeable because there is no elastomeric composition between the inner and outer layers), the cord according to the invention provides improved permeability. The inventors of the invention propose that an initial ratio R2 / Rt ranging from 1.02 to 1.25 allows for a sufficiently thick elastomeric composition that can penetrate the inner strands and fill the gaps during tire curing. This is made possible by the unsaturation of the intermediate and outer layers of the inner and outer strands, allowing the elastomeric composition to permeate both between the outer strands and between the outer and inner strands, thereby allowing the elastomeric composition derived from the covering to enter one or more inner strands up to the central capillary. Therefore, by means of the final step of bringing the outer strands closer to the inner layer, the diameter of the cord can be reduced while the cord is well permeated.

[0045] Advantageously, the internal strands or each internal strand has a cylindrical layer.

[0046] Advantageously, each outer strand has a cylindrical layer.

[0047] Advantageously, the inner strands, or each inner strand and each outer strand, have cylindrical layers. It should be recalled that such cylindrical layers are obtained when the various layers of the strand are wound with different twist pitches and / or when the winding directions of these layers differ from one layer to another. Strands with cylindrical layers are extremely permeable, unlike the strands described below with compact layers, in which all layers have the same twist pitch and all layers have the same winding direction, thus exhibiting much lower permeability.

[0048] It should be recalled that, as is known, the twist pitch of a strand represents the length of that strand measured parallel to the axis of the cord, after which the strand with this twist pitch completes a full loop around the axis of the cord. Similarly, the twist pitch of a filament represents the length of that filament measured parallel to the axis of the strand in which the filament is located, after which the filament completes a full loop around the axis of the strand.

[0049] The winding direction of a layer with strands or threads refers to the direction in which the strands or threads are formed relative to the axis of the cord or strand. The winding direction is usually indicated by the letters Z or S.

[0050] Determine the twist pitch, winding direction, and diameter of the yarn and strands according to the 2014 standard ASTM D2969-04.

[0051] Preferably, the strands are not pre-formed.

[0052] Advantageously, the cord is made of metal. The term "metallic cord" is understood by definition to mean a cord formed of cords that are primarily (i.e., more than 50% of the cords) or entirely (100% of the cords) metallic. Such metallic cords are preferably made of steel cords, more preferably cords made of pearlitic (or ferritic-pearlitic) carbon steel (hereinafter referred to as "carbon steel"), or cords made of stainless steel (defined as steel containing at least 11% chromium and at least 50% iron). However, it is of course possible to use other steels or other alloys.

[0053] When carbon steel is used advantageously, its carbon content (by weight of steel) is preferably between 0.05% and 1.2%, particularly between 0.4% and 1.1%; these contents represent a good trade-off between the mechanical properties required for the tire and the availability of yarn.

[0054] The metal or steel used, whether particularly carbon steel or stainless steel, may be coated with a metal layer that, for example, improves the processability of the metal cord and / or its components, or improves the performance of the cord and / or tire itself, such as adhesion, corrosion resistance, or aging resistance. According to a preferred embodiment, the steel used is coated with a brass (Zn-Cu alloy) layer or a zinc layer.

[0055] Preferably, all the threads in the same layer of the predetermined (inner or outer) strands have substantially the same diameter. Advantageously, all the outer strands have substantially the same diameter. "Substantially the same diameter" means that the threads or strands have the same diameter within industrial tolerances.

[0056] Advantageously, the outer strands are wound in a spiral around the inner strands with a twist pitch of 40 mm to 100 mm, preferably 50 mm to 90 mm.

[0057] In a first embodiment of the invention, the outer layer of the cord is saturated such that the strand spacing E of the outer strands is strictly less than 20 μm. On the cross-section of the cord perpendicular to the main axis of the cord, the strand spacing E is defined as the shortest distance that evenly separates two adjacent outer strands inscribed in a circular envelope.

[0058] By definition, the saturated layer of the cord ensures that the spacing between the outer strands is strictly less than 20 μm. On a cross-section of the cord perpendicular to its main axis, the spacing between the outer strands of the outer layer is defined as the shortest distance between the average dividing circular envelope (where two adjacent outer strands are inscribed). Therefore, this construction of the cord ensures good structural stability of the outer layer, and the saturation of the outer layer ensures that it includes a relatively high number of outer strands and thus exhibits relatively high breaking strength.

[0059] Conversely, the unsaturated layer of the cord makes the spacing E between the outer strands greater than or equal to 20 μm.

[0060] In a second embodiment of the invention, L is less than or equal to the maximum number of outer strands Lmax that can be laid on a theoretical outer layer having a helical radius Rt, and L satisfies that the outer layer is not completely unsaturated.

[0061] By definition, a layer that is not entirely unsaturated means there is insufficient space within that layer to add at least one (P+1)th strand with the same diameter as the P strands of that layer. In this specific case, there is insufficient space in the outer layer to add at least one (L+1)th outer strand with the same diameter as the L outer strands of the outer layer. Therefore, this construction of the cord ensures good structural stability of the outer layer, and the incomplete unsaturation of the outer layer ensures that it includes a relatively high number of outer strands and thus exhibits relatively high breaking strength.

[0062] By definition, in contrast to a partially unsaturated layer, a fully unsaturated layer provides sufficient space within it to add at least one (P+1)th strand with the same diameter as the layer's P strands, such that multiple strands may or may not touch each other. In this specific case, there is sufficient space within the outer layer to add at least one (L+1)th strand with the same diameter as the outer layer's L outer strands.

[0063] Preferably, L is equal to the maximum number of outer strands Lmax that can be laid on the theoretical outer layer with a helical radius Rt, and L satisfies that the outer layer is not completely unsaturated. The outer layer includes a high number of outer strands and therefore exhibits relatively high breaking strength.

[0064] Advantageously, the thickness G of the coating of the elastomeric composition is strictly greater than 0 mm, preferably greater than or equal to 0.01 mm. The greater the thickness G of the elastomeric composition, the better its permeability in the inner layer.

[0065] Advantageously, the thickness G of the coating of the elastomer composition is less than or equal to 0.80 mm, preferably less than or equal to 0.60 mm, and more preferably less than or equal to 0.52 mm. This thickness allows for optimization of the permeability of the inner layer while limiting the outer diameter of the cord.

[0066] Advantageously, the elastomer composition comprises an elastomer selected from polybutadiene, natural rubber, synthetic polyisoprene, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers.

[0067] Preferably, the elastomer composition comprises an elastomer selected from natural rubber, synthetic polyisoprene, isoprene copolymers, and mixtures of these elastomers.

[0068] Preferably, the elastomer composition further comprises a vulcanization system and fillers. More preferably, the elastomer is a diene elastomer.

[0069] Preferably, the elastomer composition contains carbon black as a reinforcing filler.

[0070] Advantageously, K = 1, 2, 3 or 4, preferably K = 1, 2 or 3, more preferably K = 1 or 3.

[0071] Advantageously, L = 6, 7, 8, 9 or 10, preferably L = 6, 7, 8 or 9, more preferably L = 6 or 9.

[0072] In the first variant, K = 1 and L = 6. In the cord with K = 1, the presence of the elastomer composition ensures good permeability, and furthermore, due to the strong lateral load exerted on the inner strands by the outer strands, the presence of the elastomer composition reduces the contact pressure on the inner strands.

[0073] In the second variant, K = 2 and L = 7 or 8, preferably K = 2 and L = 8.

[0074] In the third variant, K = 3 and L = 7, 8 or 9, preferably K = 3 and L = 9.

[0075] In the fourth variant, K = 4 and L = 9 or 10, preferably K = 4 and L = 10.

[0076] In embodiments not according to the invention, particularly in those with K=3 or 4, there is a risk that corrosive agents can be observed to diffuse very noticeably between the K=3 or 4 inner strands when the cord is not sufficiently permeated. These K=3 or 4 inner strands define a central capillary, which greatly promotes the diffusion of corrosive agents along the cord. This disadvantage can be overcome by a coating surrounding the K inner strands that allows the inner strands to be permeated by an elastomeric composition, thus preventing corrosive agents from entering the central capillary, which itself is permeated, thereby preventing the diffusion of these corrosive agents along the cord.

[0077] In a cord with K > 1, the strongest lateral load applied to the cord when it is taut is the lateral load applied between the inner strands. Cords known from the prior art have a K > 1 configuration and include multiple outer strands, such that the outer layer of the cord is saturated to maximize breaking strength by adding the maximum number of outer strands. Here, because the outer layer of the strands is unsaturated, on the one hand, the cord has space between the outer strands that allows the elastomer composition to pass through, thus making the cord less sensitive to corrosion. On the other hand, although the number of outer strands is reduced, the unsaturation of the outer layer of the strands allows the elastomer composition to permeate between the outer strands and allows the elastomer composition of a coating to be extruded between the inner strands, thereby forming an elastomer composition buffer that at least partially absorbs the lateral load applied between the inner strands. Therefore, better corrosion resistance is achieved compared to similar cords with a saturated outer layer.

[0078] The internal strands of the cord according to the present invention

[0079] In a preferred embodiment, Q > 1, preferably Q = 2, 3, or 4. When Q equals 1, under repeated compressive loads applied to the cord, there is a risk that the inner threads of the inner strands may become visible radially detached from the inner strands or even the cord itself. This risk is reduced because there are several threads in the inner layer of the inner strands (Q > 1), and the compressive load is distributed across the multiple threads in the inner layer.

[0080] Advantageously, M = 7, 8, 9 or 10, preferably M = 7, 8 or 9.

[0081] Advantageously, N = 12, 13, 14, 15 or 16, preferably N = 12, 13 or 14.

[0082] Preferably, Q = 4, M = 9 and N = 14.

[0083] The outer strands of the cord according to the present invention

[0084] Advantageously, M' = 7, 8, 9 or 10, preferably M' = 7, 8 or 9.

[0085] Advantageously, N' = 12, 13, 14, 15 or 16, preferably N' = 12, 13 or 14.

[0086] Preferably, Q' = 3, M' = 9 and N' = 14.

[0087] Advantageously,

[0088] -Q = 4, M = 9 and N = 14.

[0089] - The diameter d1 of each inner wire in each inner strand is equal to the diameter d2 of each middle wire in each inner strand and equal to the diameter d3 of each outer wire in each inner strand.

[0090] -Q' = 3, M' = 9 and N' = 14.

[0091] - The diameter d2' of each intermediate wire in each outer strand is equal to the diameter d3' of each outer wire in each outer strand, and

[0092] -d1=d2=d3=d1'.

[0093] Advantageously, the corresponding diameters d1, d1', d2, d2', d3, d3' of each metal wire range from 0.10 mm to 0.60 mm, preferably from 0.12 mm to 0.50 mm, and more preferably from 0.15 mm to 0.42 mm.

[0094] Method for manufacturing the cord according to the invention

[0095] Another subject of the present invention is a method for manufacturing double-layer multi-strand cord, wherein:

[0096] - The following steps are performed, wherein K ≥ 1 internal strands are spirally assembled by cable twisting or twisting to form the inner layer of the cord; the internal strands or each internal strand is a three-layered strand and includes: an inner layer consisting of Q = 2, 3 or 4 internal metal wires; an intermediate layer consisting of M intermediate metal wires with diameter d2 wound around the inner layer, such that the sum SI2 of the wire spacing I2 of the internal strands or the intermediate layer of each internal strand is greater than or equal to the diameter d2; and an outer layer consisting of N outer metal wires with diameter d3 wound around the intermediate layer, such that the sum SI3 of the wire spacing I3 of the internal strands or the outer layer of each internal strand is greater than or equal to the diameter d3.

[0097] - Performing a step in which an inner layer is surrounded by an elastomeric composition having a thickness G, thereby forming a covered inner layer, wherein the thickness G of the elastomeric composition satisfies a ratio R2 / Rt ranging from 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer obtained when the inner layer is in direct contact with the theoretical outer layer;

[0098] - The steps are performed in which L>1 outer strands are spirally assembled around the inner layer of the cord by cable twisting or twisting; each outer strand is a double-layered strand and includes: an inner layer consisting of Q' = 2, 3 or 4 inner metal wires; an intermediate layer consisting of M' intermediate metal wires with diameter d2' wound around the inner layer, such that the sum SI2' of the wire spacing I2' of the intermediate layer of each outer strand is greater than or equal to the diameter d2'; and an outer layer consisting of N' outer metal wires with diameter d3' wound around the intermediate layer, such that the sum SI3' of the wire spacing I3' of the outer layer of each outer strand is greater than or equal to the diameter d3'.

[0099] - Performing a step in which a device is used to bring the outer layer of the cord closer to the circle circumscribed by the inner layer of the cord, such that the ratio R2 / Rt ranges from 1.00 to 1.10.

[0100] Advantageously, the steps of spirally assembling K≥1 inner strands and assembling L>1 outer strands around the inner layer of the cord are performed using a cable tie.

[0101] Advantageously, the device for bringing the outer layer of the cord closer to the circle circumscribed with the inner layer of the cord consists, for example, two rows of rollers mounted facing each other but offset from each other, allowing the cord to pass between them.

[0102] In one implementation, one row is movable and can be brought closer to the fixed row, causing the cord to undergo a series of bends.

[0103] In another implementation, rows of rollers are capable of moving around the axis of the cord.

[0104] Enhanced product according to the present invention

[0105] Another subject of the invention is a reinforced product comprising an elastomer matrix and at least one cord as defined above.

[0106] Advantageously, the reinforced product comprises one or more cords according to the invention embedded in an elastomer matrix, wherein in the case of multiple cords, the cords are arranged side by side along the main direction.

[0107] Tires according to the present invention

[0108] Another subject of the invention is a tire comprising at least one cord or a reinforced product as defined above.

[0109] Preferably, the tire has a carcass reinforcement anchored in two beads and radially covered by a crown reinforcement, which is itself covered by the tread and is bonded to the beads via two sidewalls and includes at least one cord as defined above.

[0110] In a preferred embodiment, the tread reinforcement includes a protective reinforcement and a working reinforcement, the working reinforcement including at least one cord as defined above, and the protective reinforcement being radially inserted between the tread and the working reinforcement.

[0111] Cords are most specifically designed for use in industrial vehicles, agricultural vehicles, or construction vehicles selected from heavy vehicles (e.g., “heavy-duty vehicles”, i.e., subways, buses, road transport vehicles (trucks, tractors, trailers), off-road vehicles), or other transport or handling vehicles.

[0112] Preferably, the tire is used on construction site type vehicles. Therefore, the tire has dimensions in which the base diameter of the rim intended to mount the tire is greater than or equal to 25 inches, preferably 39 to 63 inches.

[0113] The present invention also relates to rubber articles comprising components according to the invention or impregnated components according to the invention. Rubber articles are defined as any type of article made of rubber, such as balls, non-pneumatic objects (e.g., non-pneumatic tires), conveyor belts, or tracks. Attached Figure Description

[0114] The invention will be better understood by reading the following embodiments, which are given by way of non-limiting example only and with reference to the accompanying drawings, wherein:

[0115] - Figure 1 is a cross-sectional view perpendicular to the circumferential direction of the tire according to the present invention;

[0116] Figure 2 is a detailed view of region II in Figure 1;

[0117] Figure 3 is a cross-sectional view of the reinforced product according to the present invention;

[0118] - Figure 4 is a schematic diagram of a cross section perpendicular to the cord axis (assuming it is straight and stationary) of the cord (50) according to the invention;

[0119] - Figures 5 and 6 are schematic diagrams of an apparatus for manufacturing the cord (50) according to the present invention;

[0120] - Figure 7 is a schematic diagram of step 400, which moves the outer layer of the cord (50) according to the present invention closer to the inner layer;

[0121] Figure 8 shows photos of the EDT cord and comparison photos of cords C1 and C2; and...

[0122] Figure 9 is a photograph of cords 50, 51 and 70 according to the present invention. Detailed Implementation

[0123] Embodiments of tires according to the present invention

[0124] Reference frames X, Y, and Z are shown in Figures 1 and 2, which correspond to the tire's usual axial direction (X), radial direction (Y), and circumferential direction (Z), respectively.

[0125] The tire's "circumferential midplane" M is a plane that is perpendicular to the tire's axis of rotation and equidistant from the annular reinforcement structure of each bead.

[0126] Figures 1 and 2 show a tire according to the invention, indicated by the overall designation 10.

[0127] Tire 10 is used for heavy-duty vehicles of the construction site type, such as "dump truck" type heavy-duty vehicles. Therefore, tire 10 has a size of 53 / 80R63.

[0128] Tire 10 has a crown 12 reinforced by crown reinforcement 14, two sidewalls 16, and two beads 18, each of which is reinforced by an annular structure, in this case by bead lines 20. Crown reinforcement 14 is radially covered by tread 22 and connected to the beads 18 via the sidewalls 16. Carcass reinforcement 24 is anchored in the two beads 18, in this case wrapped around the two bead lines 20, and includes a flange 26 disposed towards the outer side of tire 20, which is shown here as being mounted on a wheel rim 28. Carcass reinforcement 24 is radially covered by crown reinforcement 14.

[0129] The carcass reinforcement 24 includes at least one carcass ply 30 reinforced by radial carcass cords (not shown). The carcass cords are arranged substantially parallel to each other and extend from one bead 18 to the other, thereby forming an angle between 80° and 90° with the circumferential midplane M (a plane perpendicular to the axis of rotation of the tire, located between the two beads 18 and passing through the center of the crown reinforcement 14).

[0130] The tire 10 also includes a sealing ply 32 (commonly referred to as the “liner”) made of an elastomer, which defines the radial inner surface 34 of the tire 10 and is designed to protect the carcass ply 30 from air diffusion from the interior space of the tire 10.

[0131] The tread reinforcement 14, radially extending from the outer side to the inner side of the tire 10, includes: a protective reinforcement 36 radially disposed within the tread 22; a working reinforcement 38 radially disposed within the protective reinforcement 36; and an additional reinforcement 40 radially disposed within the working reinforcement 38. Thus, the protective reinforcement 36 is radially inserted between the tread 22 and the working reinforcement 38. The working reinforcement 38 is radially inserted between the protective reinforcement 36 and the additional reinforcement 40.

[0132] The protective reinforcement 36 includes first and second protective ply layers 42 and 44, each comprising protective metal cords. The first ply layer 42 is radially disposed inside the second ply layer 44. Optionally, the protective metal cords form an angle of at least 10° with respect to the tire's circumferential direction Z, preferably between 10° and 35°, and more preferably between 15° and 30°.

[0133] The working reinforcement 38 includes first and second working ply layers 46, 48, with the first ply layer 46 arranged radially inside the second ply layer 48. Each ply layer 46, 48 includes at least one cord 50. Optionally, the working metal cord 50 crosses from one working ply layer to the other and forms an angle with the circumferential direction Z of the tire of up to 60°, preferably in the range of 15° to 40°.

[0134] The additional reinforcement 40, also known as a restraining block, is intended to partially absorb the mechanical stress of inflation. The additional reinforcement 40 includes, for example, additional metal reinforcement elements known per se (e.g., as described in FR 2 419 181 or FR 2 419 182), which form an angle with the circumferential direction Z of the tire 10 of at most 10°, preferably in the range of 5° to 10°.

[0135] Embodiments of the enhanced product according to the present invention

[0136] Figure 3 shows a reinforced product according to the invention, indicated by the overall designation 100. The reinforced product 100 includes at least one cord 50 embedded in an elastomeric matrix 102, in this case, a plurality of cords 50.

[0137] Figure 3 shows the elastomer matrix 102 and cords 50 in reference frames X, Y, and Z, where direction Y is the radial direction and directions X and Z are the axial and circumferential directions, respectively. In Figure 3, the reinforcing product 100 includes a plurality of cords 50 arranged side by side in the main direction X. These cords 50 extend parallel to each other within the reinforcing product 100 and are collectively embedded in the elastomer matrix 102.

[0138] The cord according to the present invention

[0139] Figure 4 shows the cord 50 according to the invention. The cord 50 is shown prior to step 400, which brings the outer cord layer CE closer to the circle circumscribed with the inner cord layer CI.

[0140] The cord 50 is made of metal and is a multi-strand type with two cylindrical layers. Therefore, it will be understood that there are exactly two layers with strands that make up the cord 50.

[0141] The cord 50 includes an inner cord layer CI composed of K ≥ 1 inner strand TI. In this particular case, K = 1, 2, 3, or 4, preferably K = 1, 2, or 3, more preferably K = 1 or 3; here, K = 1. The inner cord layer CI is surrounded by an elastomer composition having a thickness G, thereby forming a covered inner cord layer CIG. The outer cord layer CE is composed of L > 1 outer strand TE wound around the covered inner cord layer CIG and has a helical radius R2. In this particular case, L = 6, 7, 8, 9, or 10, preferably L = 6, 7, 8, or 9, more preferably L = 6 or 9, and in this particular case, L = 6. Here, R2 is equal to 1.69 mm.

[0142] The thickness G of the elastomer composition satisfies a ratio R2 / Rt ranging from 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer CET obtained when the inner layer CI is in direct contact with the theoretical outer layer CET. Here, R2 = 1.69 mm and R2 / Rt = 1.06.

[0143] Finally, the cord 50 is obtained by a method including the following step 500: making the outer cord layer CE closer to the circle circumscribed by the inner cord layer CI, such that the ratio R2 / Rt ranges from 1.00 to 1.10. Here, R2 = 1.67 mm and R2 / Rt = 1.05.

[0144] The cord 50 also includes a winding F (not shown) consisting of a single winding thread.

[0145] 50 internal strands of the cord TI

[0146] The internal strand TI is a three-layer strand, including an inner layer C1 composed of 2, 3 or 4 internal metal wires, an intermediate layer C2 composed of M intermediate metal wires wound around the inner layer C1, and an outer layer C3 composed of N external metal wires wound around the intermediate layer C2.

[0147] Here, Q = 4.

[0148] M = 7, 8, 9, or 10, preferably M = 7, 8, or 9. Here, M = 9.

[0149] N = 12, 13, 14, 15 or 16, preferably N = 12, 13 or 14. Here, N = 14.

[0150] The intermediate layer C2 of each internal strand TI is unsaturated and not completely unsaturated. Because it is unsaturated, the spacing between the outer strands of each internal strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, and here equal to 43 μm. The sum SI2 of the spacing I2 of the intermediate layers of each internal strand is greater than or equal to the diameter d2 of the intermediate strand of each internal strand. Here, the sum SI2 = 0.39 mm, which is greater than d2 = 0.26 mm.

[0151] The outer layer C3 of each inner strand TI is unsaturated and not completely unsaturated. Because it is unsaturated, the spacing between the outer strands of each inner strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, even more preferably greater than or equal to 50 μm, and here equal to 53 μm. The sum SI3 of the spacing between the outer strands I3 of each inner strand is greater than or equal to the diameter d3 of the outer strand of each inner strand. Here, the sum SI3 = 0.74 mm, which is greater than d3 = 0.26 mm.

[0152] Each internal wire, each intermediate wire, and each outer wire of each internal strand TI has diameters d1, d2, and d3, respectively. The diameters d1 of each internal wire, d2 of each intermediate wire, and d3 of each outer wire of each internal strand TI range from 0.10 mm to 0.60 mm, preferably from 0.12 mm to 0.50 mm, and more preferably from 0.14 mm to 0.42 mm. Here, d1 = d2 = d3 = 0.26 mm.

[0153] TE outer strand of cord 50

[0154] Each outer strand TE has three layers, including an inner layer C1' consisting of 2, 3 or 4 inner metal wires Q', an intermediate layer C2' consisting of M' middle metal wires wound around the inner layer C1', and an outer layer C3' consisting of N' outer metal wires wound around the intermediate layer C2'.

[0155] Here, Q' = 3.

[0156] M' = 7, 8, 9 or 10, preferably M' = 7, 8 or 9. Here, M' = 9.

[0157] N' = 12, 13, 14, 15 or 16, preferably N' = 12, 13 or 14. Here, N' = 14.

[0158] The intermediate layer C2' of each outer strand TE is unsaturated and not completely unsaturated. Because it is unsaturated, the spacing between the outer strands of each outer strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, and here equal to 43 μm. The sum SI2' of the spacing I2' of the intermediate layers of each outer strand is greater than or equal to the diameter d2' of the intermediate strand of each outer strand. Here, the sum SI2' = 0.39 mm, which is greater than d2' = 0.23 mm.

[0159] The outer layer C3 of each outer strand TE is unsaturated and not completely unsaturated. Because it is unsaturated, the spacing between the outer strands of each outer strand is greater than or equal to 15 μm, more preferably greater than or equal to 35 μm, even more preferably greater than or equal to 50 μm, and here equal to 50 μm. The sum SI3' of the spacing between the outer strands I3' of each outer strand is greater than or equal to the diameter d3' of the outer strand's outer strand. Here, the sum SI3' = 0.70 mm, which is greater than d3' = 0.23 mm.

[0160] Each inner wire, each intermediate wire, and each outer wire of each outer strand TE has diameters d1', d2', and d3', respectively. The diameters d1' of each inner wire, d2' of each intermediate wire, and d3' of each outer strand TE range from 0.10 mm to 0.60 mm, preferably from 0.12 mm to 0.50 mm, and more preferably from 0.14 mm to 0.42 mm. Here, d1' = 0.26 mm and d2' = d3' = 0.23 mm.

[0161] Cord 50 satisfies: -Q = 4, M = 9 and N = 14.

[0162] - The diameter d1 of each inner wire in each inner strand is equal to the diameter d2 of each middle wire in each inner strand and equal to the diameter d3 of each outer wire in each inner strand.

[0163] -Q' = 3, M' = 9 and N' = 14.

[0164] - The diameter d2' of each intermediate wire in each outer strand is equal to the diameter d3' of each outer wire in each outer strand, and

[0165] -d1=d2=d3=d1'.

[0166] The outer layer CE of the cord is unsaturated. Therefore, the average strand spacing E separating two adjacent outer strands TE is greater than or equal to 20 μm. Preferably, the average strand spacing E separating two adjacent outer strands TE is greater than or equal to 40 μm, more preferably greater than or equal to 50 μm. Here, the strand spacing E is equal to 170 μm.

[0167] Each wire has a breaking strength expressed as Rm, satisfying 2500 ≤ Rm ≤ 3100 MPa. The steel used for these wires is designated as SHT (“Extremely High Tensile”) grade. Other wires can be used, such as secondary wires like NT (“Normal Tensile”) or HT (“High Tensile”) grade wires, or even higher grade wires like UT (“Ultra-Tensile”) or MT (“Extra-Tensile”) grade wires.

[0168] Method for manufacturing the cord according to the invention

[0169] An embodiment of a method for manufacturing multi-strand cord 50 will now be described with reference to Figures 5 and 6.

[0170] Each of the aforementioned internal strands is produced according to a known method comprising the steps described below, which are preferably performed sequentially:

[0171] -The first step in assembly is to form the inner layer C1 at the first assembly point by cable-bundling the inner layer C1 with Q=2, 3, or 4 inner threads F1 in the Z direction with a twist pitch p1;

[0172] - Next is the second step of assembly, in which the intermediate layer C2 is formed at the second assembly point by weaving or twisting the Q inner threads F1 around the inner layer C1 in the Z direction with a twist pitch p2 or twisting the M intermediate threads F2.

[0173] - Next is the third step of assembly, where the outer layer C3 is formed at the third assembly point by cabling or twisting the M intermediate filaments F2 around the intermediate layer C2 in the Z direction with a twist pitch p3 to the outer layer C3.

[0174] -Preferred final twisting balance step.

[0175] In step 100, K≥1 internal strands TI are spirally assembled by cable bonding to form the inner layer CI of the cord.

[0176] In step 200, the inner layer CI is surrounded by an elastomer composition having a thickness G, thereby forming a covered inner layer CIG, wherein the thickness G of the elastomer composition satisfies a ratio R2 / Rt ranging from 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer CET obtained when the inner layer CI is in direct contact with the theoretical outer layer CET.

[0177] Each of the aforementioned outer strands is produced according to a known method comprising the steps described below, which are preferably performed sequentially:

[0178] -The first step in assembly is to form the inner layer C1' at the first assembly point by cable-bundling the inner layer C1' with Q' = 2, 3, or 4 inner filaments F1' in the Z direction with twist p1';

[0179] - Next is the second step of assembly, in which the intermediate layer C2' is formed at the second assembly point by cable or twisting M' intermediate threads F2' in the Z direction with a twist pitch p2' around the Q' inner threads F1' of the inner layer C1';

[0180] - Next is the third step of assembly, in which the outer layer C3' is formed at the third assembly point by cabling or twisting the M' intermediate filaments F2' around the intermediate layer C2' in the Z direction with a twist pitch p3' to the outer layer C3'.

[0181] -Preferred final twisting balance step.

[0182] As is known to those skilled in the art, “twist balance” here means the elimination of residual torque pairs (or elastic reset of twist) on each strand of the yarn in the intermediate layer, as applied in the outer layer.

[0183] After this final twisting and balancing step, the strand manufacturing is complete. Before the subsequent operation of assembling the basic strands by cable bonding to obtain multi-strand cord, each strand is wound onto one or more receiving spools for storage.

[0184] In step 300, L>1 outer strands TE are spirally assembled around the inner layer CI of the cord by cable bonding. In step 400, device 500 is used to bring the outer layer CE of the cord closer to the circle circumscribed by the inner layer CIG of the cord, such that the ratio R2 / Rt is in the range of 1.00 to 1.10.

[0185] The following description of step 400 is based on Figure 7.

[0186] An apparatus 500 for bringing the outer layer CE of a cord closer to the circle circumscribed by the inner layer CI of the cord, for example, consists of two rows of rollers mounted facing each other but offset by a certain distance, allowing the cord to pass between them. Each row contains between six and eight rollers. One row is movable and can be brought closer to the fixed row, causing the cord to undergo a series of bends. These rows of rollers can be fixed or movable about the axial direction of the cord.

[0187] Therefore, the cord undergoes a series of bending operations that reduce its diameter, as shown in Figure 7.

[0188] L equals the maximum number of outer strands TE that can be laid on the theoretical outer layer CET with a helical radius Rt, Lmax, and L satisfies that the outer layer CE is not completely unsaturated. Here, Lmax = 6 and L = Lmax = 6.

[0189] The thickness G of the coating of the elastomeric composition is strictly greater than 0 mm, preferably greater than or equal to 0.01 mm, and less than or equal to 0.80 mm, preferably less than or equal to 0.60 mm, more preferably less than or equal to 0.52 mm. Here, G = 0.08 mm.

[0190] The elastomer composition contains a vulcanization system, fillers, and diene elastomers.

[0191] The elastomer composition used is a conventional diene elastomer composition for tires, based on natural (gel-soluble) rubber and carbon black N330 (65 phr), and also contains the following commonly used additives: sulfur (7 phr), sulfenamide accelerator (1 phr), ZnO (8 phr), stearic acid (0.7 phr), antioxidant (1.5 phr), and cobalt naphthenate (1.5 phr) (phr means parts by weight per hundred parts elastomer); the E10 modulus of the coated elastomer composition is about 10 MPa.

[0192] Feasibly, in the final assembly step, the winding material F is wound around the previously obtained component in the S direction with a twist pitch pf.

[0193] The cords are then incorporated into a composite fabric formed by calendering from a known composition based on natural rubber and carbon black (as reinforcing filler), which is typically used to manufacture the crown reinforcement of radial tires. In addition to the elastomer and reinforcing filler (carbon black), the composition essentially contains antioxidants, stearic acid, extender oil, cobalt naphthenate as a adhesion promoter, and a final vulcanization system (sulfur, accelerator, and ZnO).

[0194] The composite fabric reinforced by these cords has an elastomeric composition matrix formed by two thin layers of elastomeric composition, each layer stacked on either side of the cord and having a thickness ranging from 1 mm to 4 mm. The calendering pitch (the spacing between the cords laid in the elastomeric composition fabric) ranges from 4 mm to 8 mm.

[0195] These composite fabrics are then used as working cord layers in the tread reinforcement during a method of manufacturing tires, the steps of which are otherwise known to those skilled in the art.

[0196] Table 1 below summarizes the characteristics of various cord types 50, 51, 60, and 70.

[0197] [Table 1]

[0198]

[0199] Comparative Test

[0200] Breathability test

[0201] This test allows the determination of the longitudinal air permeability of the tested cord by measuring the volume of air passing through the test specimen under constant pressure over a given time. As is known to those skilled in the art, the principle of this test is used to verify the effectiveness of treatments applied to the cord to make it airtight; these have been described, for example, in standard ASTM D2692-98.

[0202] This test is conducted on untreated, unaged cords. The untreated cords are pre-coated on the outside with an elastomer composition called the coating composition. For this purpose, a series of 10 parallel cords (distance between cords: 20 mm) are placed between two layers or “surfaces” (two 80 x 200 mm rectangles) of the untreated diene elastomer composition, each surface having a thickness of 5 mm; all materials are then fixed in a mold, using a clamping mold to hold each cord under sufficient tension (e.g., 3 daN) to ensure straight laying when placed in the mold; then vulcanized (cured) for approximately 8 hours at a temperature of approximately 110°C and a pressure of 15 bar (using an 80 x 200 mm rectangular piston). Afterward, the entire assembly is removed from the mold, and 10 test specimens of the coated cords are cut into parallelepiped shapes of 7 x 7 x 60 mm for characterization.

[0203] The composition used as the coating elastomer composition is a conventional diene elastomer composition for tires, based on natural (gel-soluble) rubber and carbon black N330 (65 phr), and also contains the following commonly used additives: sulfur (7 phr), sulfenamide accelerator (1 phr), ZnO (8 phr), stearic acid (0.7 phr), antioxidant (1.5 phr), and cobalt naphthenate (1.5 phr) (phr means parts by weight per hundred parts elastomer); the E10 modulus of the coating elastomer composition is about 10 MPa.

[0204] The cord is therefore coated with a cured elastomer composition (or coated with an elastomer composition), and the test is performed on a 6 cm length of the cord as follows: air is injected into the inlet end of the cord at a pressure of 1 bar, and a flow meter (calibrated, for example, from 0 to 500 cm) is used. 3The air volume at the outlet end is measured ( / min). During the measurement, a sample of the cord is fixed in a compressible airtight seal (e.g., a seal made of dense foam or rubber) so that only the amount of air passing through the cord from one end to the other along the longitudinal axis of the cord is considered in the measurement; the airtightness of the airtight seal itself is checked in advance using a solid elastomer composition test specimen (i.e., a test specimen without the cord).

[0205] The higher the longitudinal air tightness of the curtain, the lower the measured average airflow (the average of 10 test samples). This is because the measurement accuracy is ±0.2cm. 3 / min, less than or equal to 0.2cm 3 The measured value / min is considered to be zero; the measured value corresponds to a cord that can be called airtight (completely airtight) along the axis of the cord (i.e., in its longitudinal direction).

[0206] Table 2 summarizes the features of the comparative cords C1 and C2 as well as the prior art cord EDT (189.23).

[0207] [Table 2]

[0208]

[0209] Table 3 below summarizes the corresponding air permeability test results for prior art cords EDT, comparative cords C1 and C2, and cords 50, 60, and 70 according to the present invention. Comparative cord C1 is of the prior art cord type 189.23, wherein the layer with the yarns is unsaturated and the yarn diameters are different to improve permeability. Cord C2 is another type of prior art cord 189.23. The results of these tests are expressed in base 100. Therefore, for any of these tests, a result greater than 100 indicates that the tested cord exhibits greater air impermeability than the control cord (in this case, control cord C1 compared to cords C2, 50, 51, 60, and 70).

[0210] [Table 3]

[0211]

[0212] It can be noted that the cords 50, 51, 60, and 70 according to the invention exhibit significantly better permeability than cord EDT and significantly better permeability than comparative cords C1 and C2, solely due to the ratio R2 / Rt according to the invention. Further observation in Figure 9 reveals that in the case of cords 50, 51, and 70, the central capillary is almost completely permeated, whereas this is not the case for cord EDT and comparative cords C1 and C2 in Figure 8; the black areas represent regions lacking the elastomeric composition.

[0213] Therefore, Table 3 shows that, for different coating thicknesses, compared with prior art cords with R2 / Rt = 1 and types represented by control cords C1 and C2, the penetration of the elastomer composition into the cord is significantly improved by the ratio R2 / Rt according to the invention achieved through the presence of a coating with thickness G, and thus the ability of the elastomer composition to penetrate the internal strands is significantly improved.

[0214] Of course, the present invention is not limited to the exemplary embodiments described above.

[0215] For reasons of industrial feasibility, cost and overall performance, it is preferred to implement the present invention using linear threads with a conventional circular cross-section (i.e., straight threads).

[0216] Features of the various implementation schemes described or envisioned above can also be combined, provided that these features are compatible with each other.

Claims

1. A double-layer multi-strand cord (50), characterized in that, The cord (50) comprises: - an inner cord layer (CI) consisting of K ≥ 1 inner strand (TI), wherein each inner strand (TI) is a three-layered strand (C1, C2, C3) and includes: - an inner layer (C1) consisting of Q = 2, 3, or 4 inner metal wires (F1); - an intermediate layer (C2) consisting of M intermediate metal wires (F2) with diameter d2 wound around the inner layer (C1); - an outer layer (C3) consisting of N outer metal wires (F3) with diameter d3 wound around the intermediate layer (C2); and - an outer cord layer (CE) consisting of L > 1 outer strand (TE) wound around the inner cord layer (CI). The outer layer (CE) of the cord has a helical radius R2, and each outer strand (TE) is a three-layer (C1', C2', C3') strand comprising: - an inner layer (C1') consisting of Q' = 2, 3, or 4 inner metal wires (F1'); - an intermediate layer (C2') consisting of M' intermediate metal wires (F2') with diameter d2' wound around the inner layer (C1'); and - an outer layer (C3') consisting of N' outer metal wires (F3') with diameter d3' wound around the intermediate layer (C2'), wherein: - the inner strands or the intermediate layer (C2) of each inner strand (TI) are unsaturated, such that the inner strands or each inner strand The sum of the spacing I2 of the middle layer of (TI) is greater than or equal to the diameter d2; - the inner strands or the outer layer (C3) of each inner strand (TI) are unsaturated, such that the sum of the spacing I3 of the inner strands or the outer layer of each inner strand (TI) is greater than or equal to the diameter d3; - the middle layer (C2') of each outer strand (TE) is unsaturated, such that the sum of the spacing I2' of the middle layer (C2') of each outer strand (TE) is greater than or equal to the diameter d2; - the outer layer (C3') of each outer strand (TE) is unsaturated, such that the sum of the spacing I3' of the outer layer (C3') of each outer strand (TE) is greater than or equal to the diameter d2; The sum SI3' is greater than or equal to the diameter d3'; - The cord (50) is obtained by a method comprising the following steps: - A step of manufacturing a covered inner layer (CIG), in which the inner layer (CI) is surrounded by an elastomer composition having a thickness G and then surrounded by an outer layer (CE), the thickness G of the elastomer composition satisfying a ratio R2 / Rt ranging from 1.02 to 1.25, where Rt is the helical radius of the theoretical outer layer (CET) obtained when the inner layer (CI) is in direct contact with the theoretical outer layer (CET); and - A step (400) of bringing the outer layer (CE) of the cord closer to the circle circumscribed with the inner layer (CI) of the cord, such that the ratio R2 / Rt ranges from 1.00 to 1.

10.

2. The cord (50) according to claim 1, wherein, The outer layer (CE) of the cord is saturated, such that the spacing E between the outer strands is strictly less than 20 μm. On the cross-section of the cord perpendicular to the main axis of the cord (50), the spacing E is defined as the shortest distance that averages the distance between two adjacent outer strands (TE) inscribed in the circular envelope.

3. The cord (50) according to claim 1, wherein, L is equal to the maximum number of outer strands (TE) that can be laid on the theoretical outer layer (CET) with a helical radius Rt, Lmax, and L satisfies that the outer layer (CE) is not completely unsaturated.

4. The cord (50) according to claim 1, wherein, The thickness G of the coating of the elastomer composition is strictly greater than 0 mm.

5. The cord (50) according to claim 1, wherein, The thickness G of the coating of the elastomer composition is less than or equal to 0.80 mm.

6. The cord (50) according to claim 1, wherein, The elastomer composition comprises an elastomer selected from polybutadiene, natural rubber, synthetic polyisoprene, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers.

7. The cord (50) according to claim 1, wherein, K = 1, 2, 3 or 4.

8. The cord (50) according to claim 1, wherein, L = 6, 7, 8, 9 or 10.

9. The cord (50) according to claim 1, wherein, M = 7, 8, 9 or 10.

10. The cord (50) according to claim 1, wherein, M' = 7, 8, 9 or 10.

11. The cord (50) according to claim 1, wherein, N = 12, 13, 14, 15 or 16.

12. The cord (50) according to claim 1, wherein, N' = 12, 13, 14, 15 or 16.

13. A method for manufacturing double-layer multi-strand cord (50), characterized in that: - Perform the following step (100), wherein K ≥ 1 inner strand (TI) are spirally assembled by cable twisting or twisting to form the inner layer (CI) of the cord; the inner strand or each inner strand (TI) is a three-layer (C1, C2, C3) strand and includes: an inner layer (C1) consisting of Q = 2, 3 or 4 inner metal wires (F1); an intermediate layer (C2) consisting of M intermediate metal wires (F2) with diameter d2 wound around the inner layer (C1), such that the sum SI2 of the wire spacing I2 of the inner strand or the intermediate layer of each inner strand (TI) is greater than or equal to the diameter d2. Diameter d2; and an outer layer (C3) consisting of N outer metal wires (F3) with diameter d3 wound around the intermediate layer (C2), such that the sum SI3 of the wire spacing I3 of the inner strands or the outer layer of each inner strand (TI) is greater than or equal to the diameter d3; - performing a step (200) in which the inner layer (CI) is surrounded by an elastomeric composition having a thickness G, thereby forming a covered inner layer (CIG), the thickness G of which satisfies a ratio R2 / Rt ranging from 1.02 to 1.25, where Rt is the diameter of the inner layer (CI) and the theoretical outer layer (CET). The theoretical helical radius of the outer layer (CET) obtained upon contact; - performing a step (300) in which L>1 outer strands (TE) are spirally assembled around the inner layer (CI) of the cord by cable twisting or twisting; each outer strand (TE) is a three-layer (C1', C2', C3') strand and includes: an inner layer (C1') consisting of Q' = 2, 3 or 4 inner metal wires (F1'); an intermediate layer (C2') consisting of M' intermediate metal wires (F2') with diameter d2' wound around the inner layer (C1'), such that the intermediate of each outer strand (TE) The sum of the spacing I2' of the threads in the layer (C2') is greater than or equal to the diameter d2'; and the outer layer (C3') is composed of N' outer metal wires (F3') with diameter d3' wound around the intermediate layer (C2'), such that the sum of the spacing I3' of the threads in the outer layer (C3') of each outer strand (TE) is greater than or equal to the diameter d3'; - performing a step (400) in which a device (500) is used to bring the outer layer (CE) of the cord closer to the circle circumscribed with the inner layer (CI) of the cord, such that the ratio R2 / Rt is in the range of 1.00 to 1.

10.

14. An enhanced product (100), characterized in that, The reinforced product (100) includes an elastomer matrix (102) and at least one cord (50) according to claim 1.

15. A tire (10), characterized in that, The tire (10) includes at least one cord (50) as claimed in claim 1.

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