Heat treatment of reinforcement elements

Abstract

The present invention relates to a method for producing a reinforcement sheet (6=) comprising an elastomer composition and at least one metallic reinforcing element (30), wherein the reinforcement (30) is subjected to a specific heat treatment: the reinforcement obtained by the unwinding step is heat treated under temperature and duration conditions such that T+13.7×ln(t)>175, where T represents the treatment temperature in °C and t represents the duration in seconds over which the reinforcement is maintained at temperature T.

Description

[Technical Field]

[0001] The present invention relates to the field of methods for treating metal reinforcements, in particular those used in reinforcing plies of tires, and to the reinforcements obtained by such methods. [Background technology]

[0002] The tire is obtained by assembling and then curing a green tire, which comprises a plurality of uncured elastomeric components in the form of plies, longitudinal portions of which are circumferentially positioned on the green tire being manufactured, and then the ends of the plies are butted together.

[0003] The ply is optionally reinforced by metal reinforcements, the majority of which are fibrous elements composed of monofilaments or assemblies of monofilaments. Hereinafter, the terms "reinforced ply" and "elastomeric composite" will be used interchangeably. The metal reinforcements are generally positioned inside the ply, parallel to each other and equally spaced in a single plane when the ply is laid flat. They can also be inclined so that they form a given angle with the longitudinal direction of the ply.

[0004] The manufacture of the reinforcing ply in particular comprises a step of winding and storing a plurality of metal reinforcements on a plurality of reels. One pass of the monofilament wound on a reel is known as a turn. A set of windings is known as a winding. The manufacture of the reinforcing ply then comprises a step of unwinding this plurality of metal reinforcements from the reels. The metal reinforcements are then positioned parallel to the longitudinal direction of the ply being manufactured, as described above, and then embedded in a layer of uncured rubber using a calendering or extrusion method. A reinforcing ply with metal reinforcements forming a given angle with the longitudinal direction is obtained by cutting the ply obtained at the end of the embedding step with a bevel at the given angle and at regular intervals, and then assembling the cut sections by their uncut edges.

[0005] Storing the metal reinforcement on a reel causes deformation of the metal reinforcement. The path formed by the metal reinforcement when unwound from the reel at the end of storage and without any external stress is slightly curved. The straightness defect measured by the method described in the following description is known as bending.

[0006] Bending of the metal reinforcements can result in shape defects in the ply where the fibrous elements are positioned, such as undulations, twists, curls, cutting into imprecise sections of the ply, or difficult positioning and abutment of portions of the ply on the green tire.

[0007] Although it is possible to manually lay plies with shape defects, this can only be envisaged for the production of a limited number of tires due to its poor industrial productivity. When automated, laying plies with shape defects exceeding a certain threshold proves difficult, if not impossible.

[0008] To solve this problem, WO2018 / 141566 proposes using a correction device comprising a cylinder to correct flatness defects in the reinforcing ply by applying a plastic deformation to it.

[0009] However, the closer the metal reinforcement is wound to the hub of the reel, the greater the bending resulting from retraction of the metal reinforcement. In other words, the bending resulting from retraction is not constant along the metal reinforcement due to the packing of the reel, while the reverse bending imparts a constant radius of curvature on the thread, albeit with an opposite sign. As a result, while the reverse bending does indeed make it possible to reduce the average bending of the metal reinforcement and the bending of the metal reinforcement closer to the hub of the reel, it may increase the bending of the metal reinforcement further away from the hub.

[0010] WO2019 / 081862 proposes a storage reel with a larger hub diameter in order to reduce the difference in the radius of curvature of the reinforcing elements between the parts of the elements stored near the hub and those stored around it. Although it gives good results, this solution requires the use of a non-standard reel.

[0011] EP 3 620 543 describes a cord obtained by a method comprising the steps of wire drawing, heat treatment, and winding onto a storage means, the cord having a deviation from the vertical of less than or equal to 30 mm for a 400 mm section after winding for between six months and one year. The heat treatment specifically satisfies condition (A): T + 13.67.ln(t) + 2.7τ ≥ 425, where T is the heating temperature in K, t is the heating time in seconds, and τ is the tensile force applied to the cord in kgf. The heat treatment is specifically applied to the cord between the wire drawing and winding steps. However, as shown in the examples, some cords that have undergone a heat treatment satisfying condition (A) have a deviation from the vertical (or straightness) much greater than 30 mm after seven months of winding. The relationship between condition (A) and the reduction in bending is therefore not very clear. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] WO2018 / 141566 [Patent Document 2] WO2019 / 081862 [Patent Document 3] EP 3 620 543 [Patent Document 4] WO2005 / 071157 Summary of the Invention [Problem to be solved by the invention]

[0013] Consequently, there remains a need for a simple solution that can be applied to the reinforcement before it is incorporated into the reinforcing ply by calendering or extrusion, ensuring a satisfactory flatness of the ply, i.e. making it possible to facilitate its industrial processing, in particular for tire manufacturing. [Means for solving the problem]

[0014] During its research, the Applicant discovered a treatment that can be applied to the metal reinforcement between its storage means and the step of incorporation into the elastomeric composition, making it possible to guarantee bending that is small enough to guarantee a satisfactory flatness of the plies, without having to measure the bending that the reinforcement undergoes during storage, whether this bending is due to the storage means or the storage time.The invention allows the use of reinforcing elements coming from different sources without distinguishing whether they have undergone an anti-bending treatment before storage or not.

[0015] The present invention relates to a method for manufacturing a reinforcing ply comprising an elastomeric composition and at least one metallic reinforcing element, said reinforcement being subjected to at least the following successive steps: a. the reinforcement is unwound from a storage means on which the reinforcement is wound; b. The reinforcement resulting from the unwinding step is heat treated under temperature and time conditions such that T + 13.7.ln(t) > 175, where T is the treatment temperature (°C) and t is the time (seconds) during which the reinforcement is kept at temperature T; c. The reinforcement obtained from the heat treatment step may be subjected to a step of embedding in an elastomer composition.

[0016] definition The carbon-containing compounds referred to herein can be of fossil or bio-origin. In the latter case, they can be derived partly or entirely from biomass or obtained from renewable raw materials derived from biomass. This is particularly relevant for polymers, plasticizers, fillers, etc.

[0017] Step a) of unwinding the reinforcement The storage means is typically a storage reel with a hub and two flanges. The dimensions of the reel depend on the reinforcement to be stored and are a compromise between the amount of reinforcement desired and the constraints associated with the use or transport of the method. Dimensions are standardized to facilitate their use. Reels particularly useful for the purposes of the present invention have a hub diameter of 100 mm to 200 mm.

[0018] The reinforcement is a metallic reinforcement. The metallic reinforcement can be a single metallic filamentary element, i.e., a metallic elementary filament. Such a metallic elementary filament has a steel core and is optionally coated with one or more coating layers, which can be metallic and / or based on a non-metallic adhesive composition.

[0019] The metal coating comprises a metal selected from zinc, copper, tin, cobalt, and alloys of these metals. Examples of alloys of these metals include brass and bronze. The core steel is a carbon steel containing between 0.1 and 1.2% by weight carbon, up to 11% by weight chromium, and less than 1% by weight of the following elements: manganese, silicon, aluminum, boron, cobalt, copper, molybdenum, nickel, niobium, titanium, tungsten, vanadium, zirconium, phosphorus, sulfur, and nitrogen, with the remainder being iron and unavoidable impurities resulting from processing. The steel can have a pearlitic, ferritic, austenitic, bainite, or martensite microstructure, or a mixture of these microstructures.

[0020] The metal elementary monofilaments have a mechanical strength ranging from 1,000 MPa to 5,000 MPa, which corresponds to the steel grades commonly found in the field of tires, namely NT (normal tensile), HT (high tensile), ST (super tensile), SHT (super high tensile), UT (ultra tensile), UHT (ultra high tensile) and MT (mega tensile), and their use allows, if necessary, to improve the reinforcement of the matrix in which the reinforcing elements are embedded and to reduce the weight of the matrix reinforced in this way.

[0021] When the metal elementary filaments have a circular cross section, the diameter of said metal elementary filaments is preferentially in the range 0.05 mm to 0.60 mm. Very preferably, the diameter of the metal fibrous elements is in the range 0.18 mm to 0.45 mm.

[0022] The metal reinforcement can be a plurality of metal filamentary elements, i.e. an assembly of a plurality of metal elementary filaments as described above, assembled together in a spiral, for example by twisting or plying the metal elementary filaments, so as to form a layered or twisted cord comprising a plurality of concentric layers of metal elementary filaments, each strand comprising said twisted cord comprising a plurality of concentric layers of metal elementary filaments. Optionally, as described in WO 2005 / 071157, such metal elementary elements comprise a composition-based layer comprising a polymer composition, preferably an elastomer, positioned between two layers of metal elementary filaments comprising the strands of the layered or twisted cord.

[0023] Preferably, the plurality of reinforcements are payed out from a plurality of storage means.

[0024] Heat treatment step b) According to the invention, the reinforcement obtained from the unwinding step is heat treated in a heat treatment step b) under temperature and time conditions such that T+13.7.ln(t)>175, where T is the treatment temperature (°C) and t is the time (seconds) during which the reinforcement is kept at temperature T.

[0025] By applying this heat treatment to the reinforcement, the bending due to storage of the reinforcement can be reduced to a value close to or even identical to the bending value of the reinforcement measured at the end of its manufacturing process, i.e. at the end of the wire drawing or assembly process, which is typically less than 20 mm.

[0026] Preferably, step b) is carried out using temperature and time conditions such that T+28.4.ln(t)<398.

[0027] Preferably, the heat treatment time is in the interval extending from greater than 0 seconds to less than 5 seconds, and the temperature is in the interval extending from greater than 200° C. to 400° C. Preferably, the treatment time of step b) is in the interval extending from greater than 0 seconds to less than 60 seconds, preferentially from greater than 0 seconds to less than 20 seconds, very preferentially from greater than 0 seconds to less than 5 seconds, preferably in the interval extending from 0 seconds to 2 seconds.

[0028] Preferably, the temperature is in the interval extending from 130°C to 400°C.

[0029] Highly preferably, the treatment time of step b) is in an interval extending from greater than 0 seconds to less than 20 seconds, in which case T is less than or equal to 300°C if the treatment time is less than 2 seconds, and T-23.8.ln(t)<315 if the treatment time ranges from 2 seconds to less than 20 seconds. These conditions maintain the mechanical strength of the reinforcement.

[0030] The heat treatment can be carried out by any means known to those skilled in the art: the reinforced product can be heated by conduction, convection or induction, preferentially by induction.

[0031] During the heat treatment, the reinforcement preferentially moves through a chamber in which a heating means is applied, the dimensions of the chamber and the speed of travel determining the duration of the heat treatment.

[0032] The duration of the heat treatment of the method according to the invention makes it possible to maintain the calendering speeds typically used in industrial processes, in particular in processes for manufacturing tires.

[0033] In the case of multiple reinforcements, each reinforcement can be treated individually or multiple reinforcements can be treated collectively. Preferably, multiple reinforcements are treated collectively. This particularly preferred configuration allows efficient industrial implementation by treating multiple reinforcements of different origins and with various curvatures collectively, and reduces processing costs by minimizing the amount of heat treatment equipment.

[0034] Step c) of feeding into a calendering step At the end of the heat treatment step, the reinforcement is subjected to a step in which it is embedded in an elastomer composition to obtain a reinforcing ply.

[0035] Preferably, the metal reinforcement elements are not coated with the polymer composition before step c).

[0036] Preferably, the elastomeric composition is based on a composition comprising at least one elastomer and at least one filler.

[0037] Preferably, the composition comprises an elastomer, preferably a diene elastomer. A "diene" elastomer (or, indifferently, rubber) is given the meaning of an elastomer (i.e., a homopolymer or copolymer) composed at least in part of diene monomer units (monomers carrying two conjugated or non-conjugated carbon-carbon double bonds), whether natural or synthetic, as is known. An "isoprene elastomer" is given the meaning of an isoprene homopolymer or copolymer, in other words, a diene elastomer selected from the group consisting of natural rubber (NR), synthetic polyisoprene (IR), various isoprene copolymers, and mixtures of these elastomers.

[0038] The diene elastomer is preferentially chosen from the group consisting of polybutadiene (BR), natural rubber (NR), synthetic polyisoprene (IR), styrene-butadiene copolymer (SBR), butadiene-isoprene copolymer (BIR), styrene-isoprene copolymer (SIR), styrene-butadiene-isoprene copolymer (SBIR) and mixtures of these elastomers, and very preferentially chosen from natural rubber and synthetic cis-1,4-polyisoprene.

[0039] Preferably, the elastomer composition used in step c) comprises primarily a diene elastomer selected from the group consisting of natural rubber, synthetic polyisoprene, or mixtures thereof.

[0040] The composition may also comprise all or part of one or more diene elastomers and additives typically employed in matrices intended for the manufacture of tires, such as fillers such as carbon black or silica, coupling agents, anti-aging agents, antioxidants, plasticizers or extending oils, the latter whether essentially aromatic or non-aromatic (in particular very slightly aromatic or non-aromatic oils, such as MES or TDAE oils of naphthenic or paraffinic type and with high or preferably low viscosity), plasticizing resins with a high glass transition temperature (higher than 30°C), agents improving the processability of the composition in the uncured state, tackifying resins, antireversible agents, methylene acceptors and donors, such as HMT (hexamethylenetetramine) or HMM (hexamethoxymethylmelamine), reinforcing resins (such as resorcinol or bismaleimides), known adhesion promoter systems of the metal salt type, such as, in particular, salts of cobalt, nickel or lanthanides, and crosslinking or vulcanizing systems.

[0041] Preferably, the system for crosslinking the elastomer composition is a so-called vulcanization system, i.e., based on sulfur (or sulfur on a sulfur donor) and a primary vulcanization accelerator. Various known secondary vulcanization accelerators or vulcanization activators can be added to this basic vulcanization system. Sulfur is used in a preferred content of between 0.5 and 10 phr, and primary vulcanization accelerators, such as sulfenamides, are used in a preferred content of between 0.5 and 10 phr. The content of reinforcing fillers, such as carbon black and / or silica, is preferably greater than 30 phr, particularly between 30 and 100 phr.

[0042] All carbon blacks conventionally used in tires are suitable, in particular of the HAF, ISAF, or SAF type ("tire-grade" carbon blacks). These more particularly comprise carbon blacks of the 300, 600, or 700 (ASTM) grade (e.g., N326, N330, N347, N375, N683, or N772). 2 / g, preferably 30 to 400m2 Precipitated or fumed silicas with a BET specific surface area of ​​1000 .mu.m / g are particularly suitable as silicas.

[0043] Those skilled in the art will know how to adjust the formulation of the rubber composition in light of this specification to achieve the desired level of properties (especially modulus of elasticity) and how to adapt the formulation to suit the particular application envisaged.

[0044] Preferably, each polymer matrix, in the crosslinked state, has a secant modulus at 10% elongation of between 4 and 25 MPa, more preferably between 4 and 20 MPa, with values ​​between 5 and 15 MPa having been found to be particularly suitable. Modulus measurements are carried out in tension according to ASTM D 412 (1998) (specimen "C") unless otherwise indicated: the "true" secant modulus (i.e., relative to the actual cross section of the specimen) is measured at 10% elongation at the second elongation (i.e., after the adaptation cycle), and is herein designated Ms and expressed in MPa (under standard temperature and relative humidity conditions according to ASTM D 1349 (1999)).

[0045] Preferably, when several reinforcements are present, they are positioned parallel to one another upstream or downstream of the heat treatment step b), and the reinforcements thus positioned are then embedded in the elastomer composition.

[0046] Embedding the reinforcement or reinforcements in the elastomeric composition can be done by any method known to those skilled in the art, for example by extrusion or calendering.

[0047] The step of embedding the reinforcement or reinforcements in the elastomeric composition may comprise the steps of: - making two layers of an elastomeric composition, - sandwiching the reinforcement between the two layers by placing the reinforcement between the two layers, - Curing the reinforcing plies if necessary.

[0048] Alternatively, the reinforcement is embedded in the elastomeric composition by placing the reinforcement on a portion of the elastomeric composition layer and then folding that layer over the reinforcement, thus sandwiching it over all or part of its length.

[0049] Preferably, steps a) to c) are carried out continuously and step b) is carried out on a continuously advancing portion of the reinforcement, the reinforcement advancing at a speed of 5 to 120 m / min, preferentially 10 to 80 m / min.

[0050] The method according to the invention makes it possible to include in the ply reinforcements of different origin, which may have been subjected to different degrees of bending during production and / or storage on the reels, thus greatly facilitating the control over the supply of reinforcements and the production of the reinforcing ply. The obtained reinforcing ply, comprising at least one reinforcing element, has a flatness that makes it compatible with its incorporation into the method for manufacturing a green tire.

[0051] The production of a green tire comprises a step of producing at least one reinforcing ply according to the method of the invention, which then comprises at least one step in which the reinforcing ply is wound onto a tire building drum to obtain a green tire. More specifically, the reinforcing ply is positioned in a circular shape on the green tire being produced and then both ends of the ply are butted against each other. [Brief explanation of the drawings]

[0052] [Figure 1] FIG. 10 shows the measurement of bending C of reinforcement sample 33. [Figure 2] 1 shows a schematic representation of a method according to the invention in which a plurality of reinforcements (30) are unwound from a plurality of storage means, here reels (20), and the reinforcements of the plurality are positioned parallel to one another before being treated in a heat treatment step (40), and then the plurality of reinforcements are supplied to a step (50) in which they are embedded in an elastomeric composition to obtain a reinforcing ply (60). DETAILED DESCRIPTION OF THE INVENTION

[0053] Example Measurement and comparison tests To measure the bending of the reinforcement after storage and after treatment in step b) of the method according to the invention, the height of the arc formed by a sample of the reinforcement was measured as follows: - a reinforcement sample (33) of 60 mm in length is cut; The bending C of the reinforcement sample (33) is measured as shown in Figure 1, where the reinforcement sample (33) when placed on a horizontal surface essentially forms an arc, which arc is characterized by its height, in other words the maximum distance perpendicular to the chord between the arc and the underlying chord (62).

[0054] Three bending measurements were performed: After wire extraction or assembly just before winding the reinforcement onto the "B80" reel for storage, The reinforcement sample taken from the hub of the reel, i.e., the sample that was subjected to the greatest bending during winding, was stored. After heat treatment (if necessary) to evaluate the reduction in bending before embedding the cord in the elastomer matrix.

[0055] Two reinforcements were evaluated: the first, designated "1.32," is a 0.32 mm diameter metal monofilament; the second, designated "9.35," is a two-layer assembly of 0.35 mm diameter metal monofilaments, with a 2+7 construction and a pitch of 7.7 / 15.4.

[0056] These two reinforcements are commonly used to reinforce the plies of tires.

[0057] The storage reel "B80" is a standard reel with a hub diameter of 118mm.

[0058] "Ply curl" is qualitatively rated on the output of the embedding step in the elastomer matrix. A width of ply is cut and positioned on a flat surface to evaluate how the ply corners curl. A "-" rating indicates the ply can be assembled into a tire subject to tire building machine setting adjustments or manual intervention; a "--" rating indicates the ply cannot be assembled into a tire; and a "+" rating indicates the ply can be assembled into a tire without building machine setting adjustments.

[0059] Table 1 summarizes the tests performed.

[0060] [Table 1] TIFF0007814372000001.tif82159

[0061] It should be noted that carrying out the method according to the invention makes it possible to obtain a reinforcing ply that can be incorporated into a rubber article, here a tire, without the need to adjust the settings of the building machine. In particular, applying a heat treatment makes it possible to return to the initial bending obtained at the end of the manufacturing method of the reinforcement (wire drawing or assembly).

Claims

1. 1. A method for manufacturing a reinforced ply comprising an elastomeric composition and at least one metal reinforcement, the method comprising: The metal reinforcement is subjected to at least the following successive steps: a. the metal reinforcement is unwound from a storage means on which the metal reinforcement is wound; b) the metal reinforcement resulting from the unwinding step is heat treated under temperature and time conditions such that T + 13.7 ln(t) > 175, where T is the treatment temperature in °C and t is the time in seconds over which the metal reinforcement is held at temperature T; c) the metal reinforcement resulting from the heat treatment step is subjected to a step in which it is embedded in an elastomer composition to obtain a reinforcing ply; the duration of said heat treatment of step b) is within an interval ranging from greater than 0 to less than 5 seconds, the temperature of the heat treatment is in the interval ranging from 200°C to 400°C; A method characterized by:

2. Step b) is carried out under temperature and time conditions such that T+28.4.ln(t)<398; The method of claim 1.

3. Steps a) to c) are performed continuously, and step b) is carried out on successively progressing portions of the metal reinforcement.

3. The method according to claim 1 or 2.

4. The metal reinforcement is a single metal fibrous element.

4. The method according to any one of claims 1 to 3.

5. the metal reinforcement is an assembly of a plurality of metal fibrous elements braided together in a spiral; 5. The method according to any one of claims 1 to 4.

6. the metal reinforcement is not coated with a polymer composition prior to step c).

6. The method according to any one of claims 1 to 5.

7. a. a plurality of metal reinforcements are unwound from a plurality of storage means on which the metal reinforcements are wound; b. the plurality of metal reinforcements are collectively heat treated; c) the plurality of metal reinforcements resulting from the heat treatment step are subjected to a step in which the plurality of metal reinforcements are embedded in an elastomer composition to obtain a reinforcing ply; 7. The method according to any one of claims 1 to 6.

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