EP2855134A1

EP2855134A1 - Reinforcing element having polyester layers

Info

Publication number: EP2855134A1
Application number: EP13725628.5A
Authority: EP
Inventors: Hélène DECORPS; David DOISNEAU; Eve-Anne FILIOL; Lina HENAO; Jérôme PULPYTEL; Xavier CALLIES; Farzaneh AREFI-KHONSERI; Olivier CARTON
Original assignee: Michelin Recherche et Technique SA Switzerland; Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Current assignee: Michelin Recherche et Technique SA Switzerland; Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2012-06-01
Filing date: 2013-05-24
Publication date: 2015-04-08
Also published as: JP2015521241A; CN104364071A; US20150141578A1; JP2015525259A; CN104411479A; KR20150016981A; US20150151578A1; WO2013178538A1; WO2013178539A1; JP6082876B2; EP2855133A1

Abstract

The invention relates to a reinforcing element (R), which includes a surface layer (C1, C2) having a degree of crystallinity Tc and an atomic percentage of an oxygen element Pc, as well as an inner layer (C3) having a degree of crystallinity Ti and an atomic percentage of an oxygen element Pi, such that Ti/Tc ≥ 1.10, and Pi/Pc < 1. Both the surface layer (C1, C2) and the inner layer (C3) is made of polyester.

Description

Reinforcement element with polyester layers

[001] The invention relates to reinforcing elements for tires, particularly tires for passenger vehicles, two wheels or for aircraft.

A radial carcass reinforcement tire comprises a tread, two beads each comprising a rod, two flanks connecting the beads to the tread and a belt, or crown reinforcement, arranged circumferentially between the carcass reinforcement. and the tread. The carcass and crown reinforcement may comprise reinforcing elements comprising textile fibers, for example polyester. These textile fibers generally take the form of a twist or a fabric. The fibers are embedded in a rubber matrix to form a reinforcing ply.

[003] In the case of a plied yarn, a yarn made of textile monofilament fibers is overworked so as to form a surtors. Then, several surtors are twisted together to form a twist.

In the case of a fabric, a number of plies are assembled using one or more weft threads by weaving so as to form a fabric.

It is known from the state of the art a method of chemical treatment of such twists.

During this process, the reinforcing element is first coated with an adhesion primer. The adhesion primer generally comprises an aqueous solution based on epoxy and isocyanates.

[007] Next, the reinforcing element coated with the adhesion primer is coated with an adhesive comprising resorcinol, formaldehyde and a latex, also called RFL glue.

[008] The adhesion primer improves the quality of the bond between the reinforcing element and the RFL glue whereas the RFL glue ensures adhesion between the reinforcing element and the rubber matrix in the crosslinked state.

[009] This method therefore comprises two chemical coating steps of the reinforcing element, which makes it relatively tedious and expensive.

[010] In addition, the use of epoxy and / or isocyanate requires to take certain toxicological and environmental safety measures expensive. Indeed, it is not uncommon for impurities to be present in the bath comprising the adhesion primer, especially epichlorohydrin, products which must be protected or must be removed appropriately.

The present invention aims a reinforcing element without adhesion primer. [012] For this purpose, the subject of the invention is a reinforcing element comprising a surface layer having a degree of crystallinity Te and an atomic percentage of oxygen element Pc and an inner layer having a degree of crystallinity Ti and an atomic percentage of oxygen element Pi satisfying Ti / Tc≥ 1, 10, Pi / Pc <1, each surface and inner layer being polyester.

[013] The surface layer of the reinforcing element has physical and chemical properties to obtain excellent adhesion between the rubber matrix and the reinforcing element while avoiding the use of an adhesion primer.

[014] The surface layer designates a portion of the material of the reinforcing element located under the outer surface of the polyester. The thickness of the surface layer is measured from the outer surface of the polyester.

[015] The surface layer has a relatively high polarity, that is to say an atomic percentage oxygen element greater than that of the inner layer. Thus, the surface layer is relatively hydrophilic which improves the wettability and diffusion of the adhesion adhesive in the reinforcing element. In addition, the surface layer is likely to carry polar groups that can react chemically with the adhesive adhesion.

[016] The surface layer has a relatively low degree of crystallinity. Thus, the surface layer being relatively unorganized, it allows a better diffusion of the adhesive in the reinforcing element.

[017] The layered structure of the reinforcing element according to the invention makes it possible to separate the functions of each surface and internal layer. Thus, the surface layer has an adhesion function while the inner layer has a reinforcing function thanks to its intrinsic mechanical properties.

[018] The polyester is generally semi-crystalline and therefore comprises, on the one hand, crystalline zones and, on the other hand, amorphous zones.

By polyester layer is meant that each layer comprises at least 50% by weight of polyester, preferably 75% and more preferably 90%. Each polyester layer may thus comprise, in addition to the polyester, additives, especially at the moment of shaping of the latter, these additives possibly being, for example, anti-aging agents, plasticizers, fillers such as silica, clays, talc, kaolin according to the specific nature of the reinforcing element.

[020] Advantageously, Ti / Tc ≥ 1, 20, preferably Ti / Tc ≥ 1, 45, more preferably Ti / Tc ≥ 1, 60 and even more preferably Ti / Tc ≥ 1.80. [021] Advantageously, P1 / Pc <0.95, preferably P1 / Pc <0.85 and more preferably Pi / Pc <0.75.

[022] Thus, by reducing the degree of crystallinity of the surface layer and increasing its atomic percentage oxygen element, it promotes more adhesion between the reinforcing element and the rubber matrix.

[023] In one embodiment, the thickness of the surface layer is greater than or equal to 0.5 μηι. Advantageously, the thickness is less than or equal to 10 μηη, preferably 5 μηη and more preferably 1 μηη.

[024] In another embodiment, the thickness is greater than or equal to 1 μηη. Advantageously, the thickness is less than or equal to 10 μηη, preferably 5 μηι.

[025] In yet another embodiment, the thickness is greater than or equal to 1.5 μηη. Advantageously, the thickness is less than or equal to 10 μηη.

[026] According to other preferred characteristics of the superficial layer:

Te <30%, preferably Te <25% and more preferably Te <21%.

- Pc≥27%, preferably Pc≥30% and more preferably Pc≥32%.

[027] Such values allow excellent adhesion of the reinforcing element to the gum matrix.

[028] According to other preferred features of the inner layer:

Ti <50%, preferably Ti <45% and more preferably Ti <40%.

Pi <27%, preferably Pi <26% and more preferably Pi <25%.

[029] The lower the degree of crystallinity of the inner layer, the easier it is to obtain a surface layer having a low degree of crystallinity by means of suitable treatment methods, for example by a method of treatment with a plasma torch. .

[030] Similarly, the higher the atomic percentage oxygen element of the inner layer, the easier it is to obtain a surface layer having a high oxygen atomic percentage by means of suitable treatment processes, for example by a method of treatment with a plasma torch.

[031] In one embodiment, the reinforcing element is a monofilament or elementary filament. Each monofilament preferably has a diameter of less than or equal to 30 μηη.

[032] In one embodiment, the reinforcing element comprises one or more multifilament fibers.

[033] A multifilament fiber consists of several monofilaments or elementary filaments possibly intermingled with each other. Each fiber comprises between 50 and 2000 monofilaments.

[034] In a variant, the reinforcing element comprises one or more multifilament fiber twists. The twist is obtained by twisting several surtors, each surtors being obtained by over-wrapping a multifilament fiber.

[035] In another variant, the reinforcing element comprises a surtors of a multifilament fiber.

[036] In one embodiment, the reinforcing member comprises a fiber fabric. Such a fabric preferably comprises a plurality of plies of fibers assembled together by weaving by means of one or more weft threads. Alternatively, the fiber fabric comprises two fiber layers, the fibers of each layer extending in different directions from one layer to another.

[037] In another embodiment, the reinforcing member comprises a film. In particular, a film designates any thin layer whose ratio of the thickness to the smallest of the other dimensions is less than 0.1. Preferably, the thickness of the film is preferably between 0.05 and 1 mm, more preferably between 0.1 and 0.7 mm. For example, film thicknesses of 0.20 to 0.60 mm have been found to be quite satisfactory for most uses.

[038] In one embodiment, the multifilament fiber, the fiber fabric, the film or the monofilament is integrally made of a material chosen from polyethylene terephthalate and polyethylene naphthalate, and preferably is entirely of polyethylene terephthalate.

[039] In another embodiment, the multifilament fiber, the fiber fabric, the film or the monofilament comprises a first portion of polyester and a second portion of a material different from that of the first part.

By different material is meant a non-identical material to that of the first part. Thus, for example, a polyester of a different nature, in particular having a degree of crystallinity different from that of the first part, is a different material.

[041] Preferably, the material of the first part is chosen from polyethylene terephthalate and polyethylene naphthalate, preferably polyethylene terephthalate

[042] Preferably, the material of the second part is chosen from a polyester, for example polyethylene terephthalate (PET) polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene naphthalate (PBN), polypropylene terephthalate (PPT) or polypropylene naphthalate (PPN), a polyamide, for example an aromatic polyamide, a polyketone, a cellulose or a mixture of these materials.

[043] Optionally, the reinforcing element comprises a layer of adhesion adhesive directly coating the surface layer.

[044] The glue allows the adhesion of the reinforcing element to the rubber matrix. By directly, it is meant that no layer is interposed between the surface layer and the adhesion adhesive layer. In particular, the reinforcing element does not comprise any layer of adhesion primer, in particular a primer comprising an epoxy resin.

[045] Preferably, the adhesion adhesive is of the thermosetting type. Alternatively, other types of glues may be used, for example thermoplastic glues.

[046] Among the thermosetting glues include those comprising at least one phenol, for example resorcinol, and at least one aldehyde, for example formaldehyde.

[047] Preferably, the adhesion adhesive comprises at least one diene elastomer. Such an elastomer makes it possible to improve the raw tack and / or bake glue with the rubber matrix.

[048] Advantageously, the diene elastomer is chosen from natural rubber, a copolymer of styrene and butadiene, a terpolymer of vinylpyridine, styrene and butadiene and a mixture of these diene elastomers.

[049] Other types of glue can be used to adhere the reinforcing element to the rubber matrix. Another object of the invention is a reinforcing ply comprising at least one reinforcement element as defined above, embedded in a rubber matrix.

[051] The rubber matrix comprises at least one diene elastomer, a reinforcing filler, a vulcanization system and various additives.

By diene elastomer of the rubber matrix is generally meant an elastomer derived at least in part (ie a homopolymer or a copolymer) of monomers dienes (monomers bearing two carbon-carbon double bonds, conjugated or not) .

[053] In a particularly preferred manner, the diene elastomer of the rubber matrix is chosen from the group of diene elastomers (essentially unsaturated) consisting of polybutadienes (BR), synthetic polyisoprenes (IR) and natural rubber (NR). ), butadiene copolymers, copolymers isoprene and mixtures of these elastomers. Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-copolymers butadiene-styrene (SBIR) and mixtures of such copolymers.

[054] The rubber matrix may contain a single diene elastomer or a mixture of several diene elastomers, the diene elastomer or elastomers may be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers for example thermoplastic polymers.

As a reinforcing filler, preferentially carbon black or an inorganic filler is used. More particularly, carbon blacks are suitable for all carbon blacks, especially blacks of the HAF, ISAF, SAF type conventionally used in tires. By way of nonlimiting examples of such blacks, mention may be made of N115, N134, N234, N330, N339, N347 and N375 blacks. However, the carbon black can of course be used in cutting with reinforcing fillers and in particular other inorganic fillers. Such inorganic fillers comprise silica, in particular highly dispersible silicas, for example the "Ultrasil" 7000 and "Ultrasil" 7005 silicas from Degussa.

[056] By way of other examples of inorganic filler that may be used in the rubber matrix, mention may also be made of aluminum (oxide) hydroxides, aluminosilicates, titanium oxides, silicon carbides or nitrides all of the reinforcing type as described in WO 99/28376 (or US 6,610,261), WO 00/73372 (or US 6,747,087), WO 02/053634 (or US2004- 0030017), WO 2004/003067, WO 2004 / 056,915.

[057] Finally, one skilled in the art will understand that as an equivalent load of the reinforcing inorganic filler described in this paragraph, could be used a reinforcing filler of another nature, in particular organic, since this reinforcing filler would be covered with an inorganic layer such as silica, or would comprise on its surface functional sites, especially hydroxyl, requiring the use of a coupling agent to establish the bond between the filler and the elastomer.

[058] To the reinforcing filler may also be added, according to the intended application, inert (non-reinforcing) fillers such as clay particles, bentonite, talc, chalk, kaolin, usable for example in flanks or strips of colored tire bearing. [059] The rubber matrix may also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of tires, for example plasticizers or extension oils, which are of aromatic nature. or non-aromatic, pigments, protective agents such as anti-ozone waxes, chemical antiozonants, anti-oxidants, anti-fatigue agents, reinforcing resins, acceptors (eg novalaque phenolic resin) or donors methylene (eg HMT or H3M).

[060] The rubber matrix also comprises a vulcanization system based on either sulfur, or sulfur and / or peroxide and / or bismaleimide, vulcanization accelerators, vulcanization activators and possibly vulcanization retarders. .

[061] Another object of the invention is a finished rubber article comprising at least one reinforcing element as defined above.

[062] Preferably, the finished article is a tire.

[063] The invention will be better understood on reading the description which follows, given solely by way of non-limiting example and with reference to the drawings in which:

Figure 1 is a sectional view of a finished article, here a tire, according to the invention;

Figure 2 is a detail view of a longitudinal section of a reinforcing ply of the tire of Figure 1 comprising a reinforcing element according to the invention;

Figure 3 illustrates an X-ray photoelectron spectrum of a PET material showing the theoretical peaks (in solid line) and measured (in dashed lines) associated with the oxygen atoms;

FIG. 4 illustrates an X-ray photoelectron spectrum of a PET material showing the theoretical peaks (in solid line) and measured (in broken lines) associated with the carbon atoms;

FIG. 5 illustrates an infrared spectrum of a surface layer (in solid line) and of an inner layer (in broken lines) of the element of FIG. 2; Figure 6 is a diagram of a treatment plant of a reinforcing element;

FIG. 7 is a diagram of a device for generating a plasma flow, and Figure 8 is a diagram illustrating steps of the processing method for obtaining the reinforcing element according to the invention.

[064] There is shown in Figure 1 a tire according to the invention and designated by the general reference 1.

[065] The tire 1 is intended for motor vehicles of the tourism type, 4x4, "SUV" (Sport Utility Vehicles), but also to two-wheeled vehicles such as motorcycles or bicycles, or industrial vehicles chosen from vans , "Heavy goods vehicles" - ie, metro, bus, road transport vehicles (trucks, tractors, trailers), off-the-road vehicles -, agricultural or civil engineering machinery, aircraft, other transport or handling vehicles.

[066] The tire 1 comprises a crown 2 surmounted by a tread 3, two sidewalls 4 and two beads 5, each of these beads 5 being reinforced with a bead wire 6. A carcass reinforcement 7 is wrapped around the two rods 6 in each bead 4, the upturn 8 of the armature 7 being for example disposed towards the outside of the tire 1 which is here shown mounted on its rim 9. The top 2 is here reinforced by a crown reinforcement or belt 10 consisting of at least one reinforcing ply 10. The reinforcing ply 10 is disposed radially between the tread 3 and the carcass reinforcement 7.

[067] In the tire 1 illustrated in Figure 1, it will be understood that the tread 3, the reinforcing ply 10 and the carcass reinforcement 7 may or may not be in contact with each other, even if these parts have were deliberately separated in Figure 1, schematic, for reasons of simplification and clarity of the drawing. They could be physically separated, at least for a part of them, for example by bonding gums, well known to those skilled in the art, for optimizing the cohesion of the assembly after firing.

[068] There is shown in Figure 2 the reinforcing ply 10.

[069] The reinforcing ply 10 comprises two masses of rubber M1, M2 forming a rubber matrix between which is interposed a reinforcing element R. The reinforcing element R is thus embedded in the rubber matrix.

The element R can be obtained by the method described below. The element R is textile, that is to say non-metallic. The element R comprises, in this example, a film made entirely of polyester, here polyethylene terephthalate (PET) sold under the names "Mylar" and "Melinex" (DuPont Teijin Films company) and is preferably in accordance with the film described in WO2010115861. The element R has a thickness equal to 0.35 mm. The element R comprises a layer of adhesion adhesive of the RFL type (not shown). Layer RFL glue directly affixes the element R, that is to say that it is in contact with the element R.

[071] The PET element comprises two outer surfaces S1, S2 in each of which is disposed a surface layer C1, C2. The element R also comprises an inner layer C3 interposed between the surface layers C1, C2. The adhesion adhesive layer directly covers each outer surface S1, S2.

[072] Each surface layer C1, C2 and internal C3 is made of PET.

[073] Each surface layer C1, C2 has a thickness E greater than or equal to 0.5 μιτι. The thickness E of each surface layer C1, C2 is, for example, less than or equal to 10 μηη, preferably 5 μηη and more preferably 1 μηη.

[074] In another embodiment, the thickness E of each surface layer C1, C2 is greater than or equal to 1 μιτι. The thickness E of each surface layer C1, C2 is for example less than or equal to 10 μιτι, preferably 5 μιτι.

[075] In yet another embodiment, the thickness E of each surface layer C1, C2 is for example greater than or equal to 1, 5 μιτι. The thickness E of each surface layer C1, C2 is, for example, less than or equal to 10 μιτι.

[076] Measurement of atomic percentage in oxygen element

[077] The atomic percentage in oxygen element is measured by X-ray photoelectron spectrometry (XPS).

[078] The atomic percentage oxygen element of the surface layer is measured directly on the element according to the invention.

[079] The atomic percentage oxygen element of the inner layer is measured on an element integrally in a material identical to that of the inner layer. In a variant, the atomic percentage of the inner layer is measured on the element according to the invention having previously removed the surface layer, for example having removed a material thickness greater than or equal to 5 μηη and preferably at 10 μιτι.

In a manner known to those skilled in the art, in a molecule, here PET, the energy of the electrons of an atom being influenced by its neighbors, one can differentiate different atoms belonging to the same element but not involved not in the same chemical function. Thus, the following documents are known for the energies corresponding to the different atoms of the PET, which makes it possible, from XPS spectra, to measure the atomic percentages of the various elements (S. Petit-Boileau, Ph.D. thesis of Université Pierre et Marie Curie (2003); Asandulesa, I. Topala, V. Pohoata, N. Dumitrascu. J. Appl. Phys. 108 (2010) 093310; NK Cuong, N. Saeki, S. Kataoka, S. Yoshikawa. Hyomen Kagaru (J. of The Surface Science Society of Japan) 23 (2002) 202-208; H. Krump, I. Hudec, M. Jasso, E. Dayss, AS Luyt. Applied Surface Science 252 (2006) 4264-4278 and M. Lejeune, F. Brétagnol, G. Ceccone, P. Colpo, F. Rossi. Surface & Coatings Technology 200 (2006) 5902-5907).

[081] Thus, the area of the peaks associated with the two types of oxygen atom of a PET unit (C = O and C-O of the ester function) is measured. These peaks associated with the oxygen atoms are between 530 and 536 eV and illustrated in FIG. 3. The peak P01 is associated with the oxygen atom of the C-0 bond and the peak P02 is associated with the atom. of oxygen of the bond C = 0.

[082] The area of the peaks associated with the other elements present in the PET is also measured. In particular, the area of the peaks corresponding to the three types of carbon atoms of a PET unit (benzene carbons, C = O and carbon of the ester chain) is measured. These peaks associated with the carbon atoms are between 280 and 292 eV and illustrated in FIG. 4. The peak PC1 is associated with the carbon atom of the bond O = C-0, the peak PC2 is associated with the atom of the C-O bond and the peak PC3 is associated with the carbon atoms of the CC and CH bonds.

[083] Other elements may be present, for example nitrogen following treatment with a plasma stream in which the gas comprises air or nitrogen. The area of each peak corresponds to the atomic percentage of each atom associated with it.

[084] The atomic percentage of the peaks associated with the oxygen atoms is calculated by making the ratio of the area of the peaks associated with the oxygen atoms to the area of the peaks associated with the oxygen and carbon atoms of the spectrum, and where appropriate, on the area of the peaks associated with the oxygen, carbon and nitrogen atoms. The areas used for the ratio calculation are Scofield cross sections. Baselines used for numerical simulation are Shirley type. After acquisition, the curves are preferably rectified.

[085] The atomic percentage Pc oxygen element of the surface layer C1, C2 is greater than or equal to 27%, preferably 30% and more preferably 32%, and is in this example equal to 35%.

[086] The atomic percentage Pi oxygen element of the spectrum of the inner layer C3 (or of an element integrally of a material identical to that of the inner layer), is less than or equal to 27%, preferably to 26% and more preferably 25%, and is in this example equal to 25%. [087] The ratio Pi / Pc of the atomic percentage Pi oxygen element of the inner layer (or of an element integrally of a material identical to that of the inner layer) on the atomic percentage Pc oxygen element of the surface layer is strictly less than 1, even less than or equal to 0.95, preferably 0.85 and more preferably 0.75. Indeed, in the case described above, Pi / Pc = 25/35 = 0.71.

[088] Thus, each surface layer C1, C2 has an atomic percentage Pc oxygen element strictly greater than the atomic percentage Pi oxygen element of the inner layer C3 (or an element integrally in a material identical to that of the inner layer ).

[089] Measurement of crystallinity

[090] The degree of crystallinity Te of the surface layer of the reinforcing element is measured by infrared spectroscopy, for example ATR (Attenuated Total Reflectance) infrared spectroscopy, a spectrum of which is illustrated in FIG. 5.

[091] The degree of crystallinity Te of the surface layer is measured directly on the element according to the invention.

[092] The degree of crystallinity Ti of the inner layer of the reinforcing element is measured by differential enthalpy analysis or, alternatively, by infrared spectroscopy, for example ATR (Attenuated Total Reflectance) infrared spectroscopy.

[093] The degree of crystallinity Ti of the inner layer is measured on an element integrally in a material identical to that of the inner layer. Alternatively, the degree of crystallinity Ti of the inner layer is measured on the element according to the invention having previously removed the surface layer, for example by having removed a material thickness greater than or equal to 5 μηι and preferably to 10 μηι.

[094] In the case of a differential scanning calorimetric measurement, spectrum acquisition is performed according to ASTM D3418. Then, we measure the area A1, A2 respectively of each peak of crystallization and melting. The degree of crystallinity T is given by the equation Τ = (Α2-Α1) / (ΔΗ ^* .Θ) in which ΔΗ ^* is the specific heat of fusion of the 100% crystalline polyester expressed in Jg ^-1 and G the temperature gradient. during differential enthalpy analysis expressed in Ks ^"1 .

[095] In the case of infrared spectroscopic measurement, a Bruker Vertex 70-2 Fourier Transform Spectrometer and a germanium crystal are used to limit the depth of penetration of the infrared beam into the sample and to perform measuring on an outer layer of the reinforcing element, this layer external having a thickness less than the thickness of the surface layer.

[096] The maximum intensity 11 of the peak, that is to say the height of the peak with respect to zero, is measured between 1090 and 1110 cm ^-1 (peak corresponding to the bond C = 0 "ester stretching left At 1102 cm ^-1 in theory), preferably without spectrum correction. This peak is characteristic of the amorphous part of PET.

[097] The maximum intensity of the peak 12, that is to say the height of the peak with respect to zero, is measured between 1115 and 1130 cm ^-1 (peak corresponding to the C bond = 0 "trans stretch ester At 1123 cm- ¹ in theory), preferably without spectrum correction. This peak is characteristic of the crystalline part of PET.

[098] The degree of crystallinity Ti, here Ti = 38%, of the inner layer C3 (or of an element integrally in a material identical to that of the inner layer) is known elsewhere. Indeed, it can be absolutely measured by differential enthalpy analysis as described above.

[099] The ratio 11/12 of the spectrum of the layer C3 (or of an element integrally of a material identical to that of the inner layer) makes it possible to obtain a reference ratio 11/12, here 11/12 = 107 for the degree of crystallinity Ti = 38%. Thus, to measure the degree of crystallinity of a sample, the 11/12 ratio of the sample is measured, in this example 11/12 = 57.7, and Te is calculated from the ratio 11/12 of reference above, this ratio 11/12 being proportional to the degree of crystallinity of the sample. In this example, Tc = 38 ^* 57.7 / 107 = 20% is obtained.

Thus, in this example, the degree of crystallinity Te of the surface layer C1, C2 is less than or equal to 30%, preferably 25% and more preferably 21%, and is here equal to 20%. The degree of crystallinity Ti of the inner layer C3 (or of an element integrally of a material identical to that of the inner layer) is less than or equal to 50%, preferably 45% and more preferably 40%, and is here equal to 38%.

The ratio Ti / Tc of the degree of crystallinity of the inner layer (or of an element integrally of a material identical to that of the inner layer) on the crystallinity rate Te of the surface layer is greater than or equal to 1 , 20, preferably at 1.45, preferentially at 1.60, and even more preferably at 1.80. Indeed, in the case described above, Ti / Tc = 38/20 = 1, 9.

Thus, each surface layer C1, C2 has a degree of crystallinity Te and the inner layer C3 (or an element integrally of a material identical to that of the inner layer) has a degree of crystallinity Ti satisfying Ti / Tc≥1 10.

FIG. 6 shows a processing facility for the element R making it possible to implement a plasma treatment method, in particular by plasma torch, for obtaining the reinforcing element according to the invention. The installation is designated by the general reference 20

The installation 20 comprises two devices 22a, 22b for generating a plasma stream and a device 24 for coating the reinforcing element R.

A plasma makes it possible to generate, from a gas subjected to an electrical voltage, a heat flux comprising molecules in the gaseous state, ions and electrons. Advantageously, the plasma is of the cold plasma type. Such a plasma, also called non-equilibrium plasma is such that the temperature comes mainly from the movement of electrons. A cold plasma must be distinguished from a hot plasma, also called thermal plasma in which the electrons, but also the ions confer on this plasma certain properties, in particular thermal, different from those of the cold plasma.

Each device 22a, 22b comprises a plasma torch 26 illustrated in detail in FIG. 7. Each device 22a, 22b is intended to respectively treat each surface S1, S2. The device 24 comprises a bath 28 containing the adhesion adhesive, here an RFL type adhesive.

The adhesion glue of the RFL type is produced according to a conventional method known to those skilled in the art, in particular from document DE4439031. The RFL glue thus manufactured is stored between 10 ° C and 20 ° C and must be used within 10 days after its manufacture.

The installation 20 also comprises two upstream and downstream storage rollers respectively designated by the references 30, 32. The upstream roll 30 carries the untreated reinforcement element R while the roll 32 carries the reinforcement element R plasma-treated by the devices 22a, 22b and coated with adhesion adhesive by means of the device 24. The devices 22a, 22b and 24 are arranged in this order between the rollers 30, 32 in the direction of travel of the reinforcing element R. The devices 22a, 22b are located upstream with respect to the device 24 in the direction of travel of the reinforcing element R.

There is shown in Figure 7 the device 22a for generating a plasma stream, here the plasma torch 26 sold by Plasmatreat GmbH. The device 22b is identical to the device 22a. The device 22a is powered by an alternating current with a voltage of less than 360 V and a frequency of between 15 and 25 kHz.

The device 22a comprises means 34 for supplying gas to a plasma generation chamber 36 and plasma output means 38 generated in the chamber 36 in the form of a plasma stream 42, here a jet of plasma. The device 22a also comprises means 44 for generating a rotating electric arc 46 in the chamber 36.

The supply means 34 comprise a conduit 48 for entering the gas into the chamber 36. The generating means 44 of the electric arc comprise an electrode 50. The output means 38 comprise an outlet orifice 52 of the flow of the plasma stream 42.

FIG. 8 is a diagram illustrating the main steps 100 to 300 of the plasma treatment method making it possible to manufacture the reinforcing element R according to the invention.

During a step 100, the surface S1 is exposed to the flow 42 generated by means of the plasma torch 26. During this step 100, the element R is processed continuously. The treatment process is at atmospheric pressure.

The use of a plasma at atmospheric pressure allows the establishment of a relatively simple and inexpensive industrial installation unlike a process requiring the use of a plasma under reduced pressure associated with the establishment of a depressurized room.

The stream 42 is obtained from a gas comprising at least one oxidizing component. By oxidizing component is meant any component capable of increasing the degree of oxidation of the chemical functions present in the polyester.

Advantageously, the oxidizing component is chosen from carbon dioxide (C0 ₂ ), carbon monoxide (CO), hydrogen sulphide (H ₂ S), carbon disulfide (CS ₂ ), dioxygen (0 ₂ ), nitrogen (N ₂ ), chlorine (Cl ₂ ), ammonia (NH ₃ ) and a mixture of these components. Preferably, the oxidizing component is chosen from oxygen (0 ₂ ), nitrogen (N ₂ ) and a mixture of these components. More preferably, the oxidizing component is air.

Here, the stream 42 is obtained from a mixture of air and nitrogen at a rate of 2400 L / h.

The orifice 52 is arranged opposite the element R to be treated, here facing the surface S1. The orifice 52 is located at a constant distance D from the surface S1. For example, this distance is less than or equal to 40 mm, preferably to 20 mm and more preferably to 10 mm. Preferably, the distance D is greater than or equal to 3 mm.

The element R is scrolled with respect to the plasma stream at an average speed V less than or equal to 100 meters per minute, preferably at 50 meters per minute and more preferably at 30 meters per minute. The average speed V is equal to the ratio of the distance traveled by the plasma stream 42 relative to the surface to be exposed for a predetermined period of time to travel this distance, in this case 30s. Movement of the flow with respect to the R element may be rectilinear or curved or a mixture of both. In this case, the plasma flow has a boustrophedon movement with respect to the element R so as to expose the entire surface S1.

Preferably, the average speed V and the distance D are such that V <-5.D + 110, D being expressed in mm and V in m. min ^"1. The conditions on V D and allow to improve the efficiency of the process. In order to improve the process efficiency, can be varied a great number of parameters other than the velocity V and the distance D , for example the plasma activation time ("PCT" for Plasma Cycle Time), the nature of the gas or even the pulse frequency of the plasma torch.

Here, D = 6 mm and V = 70 m. min ^"1 .

Then, during a step 200, the surface S2 is exposed to a flux of a plasma generated by means of the device 22b in a similar manner to step 100.

Then, in a step 300, subsequent to the steps 100 and 200, the reinforcing element R, here each surface S1, S2, is coated with the adhesion adhesive of the bath 28. reinforcing element R treated in steps 100 and 200 of the adhesion adhesive.

[0124] Other subsequent steps not shown can also be implemented. By way of example, it will be possible to carry out a spinning step (for example by blowing, calibrating) in order to eliminate the excess of glue; then a drying step for example by passing through an oven (for example for 30 s at 180 ° C) and finally a heat treatment step (for example for 30 s at 230 ° C).

Those skilled in the art will readily understand that the definitive adhesion between the reinforcing element R and the rubber matrix in which it is embedded is definitely ensured during the final firing of the tire of the invention.

[0126] COMPARATIVE TESTS

[0127] Preparation of test specimens

Specimens comprising reinforcing elements compliant and non-compliant with the invention were compared.

As a reinforcing element, a PET film marketed under the name "Mylar A190" by the company DuPont Teijin Films and having a degree of crystallinity equal to 38% and an atomic percentage in oxygen element equal to 26%.

The test gum used for the different plies and the rubber matrix in contact with the reinforcing element comprises one or more elastomers diene, here natural rubber, carbon black, a plasticizing oil, a tackifying resin, N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine (6-PPD), stearic acid N-cyclohexyl-2-benzothiazyl sulfenamide (CBS) and soluble sulfur.

Each test specimen comprises, in this order, a test mat, a test fabric, a test rubber matrix and the PET film conforming or not to the invention.

The test ply is obtained from two strips of rubber made in the test gum described above between which is interposed a cross-nylon textile fabric glued with a conventional RFL glue, as described in DE4439031 for example . Nylon textile fabric is marketed by Milliken under the reference Milliken Europe-Nylon cross-Z19, Canvas-N-094/1 -72-N-094/1 -72.

The textile test fabric is a nylon fabric 140/2 250/250 glued with a conventional RFL glue, as described in DE4439031 for example, and having a son density equal to 98 f / dm.

The test web, the test fabric, the test rubber matrix and the PET film are placed in a mold and in this order. The specimen is assembled so that the surface of the PET possibly exposed to the plasma is in contact with the test rubber matrix. An edge of the test specimen is interspersed with a Milar strip between the test rubber matrix and the PET film to create a peel primer.

Each test piece is cooked in a press at a temperature of 160 ° C. for 15 min at a pressure of 1.5 bar. After cooking, each test piece is cooled for 10 minutes. Γ0136Ί Performing peel tests

The peel test is carried out in accordance with ASTM D-4393-98. The PET film is thus progressively moved away from the rest of the test piece at a constant transverse speed of 100 mm / min.

A score representative of the peel facies is then assigned in accordance with Table 1 below. Thus, the better the adhesion, the less the film is stripped (the more it is covered with rubber), the higher the grade of facies. Table 1

[0139] First comparative test

In a first comparative test, a specimen (specimen A) comprising a PET film coated with an adhesion primer and an RFL adhesive and a test specimen (specimen B) comprising a PET film coated only RFL glue without adhesion primer. In each test piece A and B not according to the invention, Ti = Tc = 38% and Pi = Pc = 26%.

The primer comprises water, 49% sodium hydroxide, polyglycerol polyglycidyl ether marketed under the name "DENACOL EX-512" by the company Nagase Chemicals) and a surfactant, here dioctyl sodium sulfosuccinate in solution at 5% in the water marketed under the name "AOT" by Cyanamid.

The RFL glue is as described above.

In this first test, the PET film is coated with the adhesion primer and the RFL adhesive (test specimen A) or only RFL adhesive without adhesion primer (specimen B). Each film is removed from the corresponding bath after a few seconds and is, after each bath, hooked by means of a flat gripper over its width in an oven at 215 ° C for 2 minutes 20 seconds.

The specimen A has a facies score equal to 5 while the specimen B has a facies score equal to 0. The adhesion primer layer is therefore necessary for the good adhesion between the reinforcing element. R and the test gum mass of the test piece.

Second comparative test

In a second comparative test, several test specimens prepared were compared using a PET film whose surfaces were exposed to a plasma torch or a dielectric barrier discharge device (DBD). The DBD device comprises two electrodes covered with a dielectric material so as to form homogeneous glow discharges. The power delivered in the plasma flux generated by the DBD device, of the order of a few watts (P = Ulcos (p with U = 20 kV and 1 = 1 mA), is about a hundred times lower than that delivered in the plasma flow generated by the plasma torch The PET film is deposited on a moving glass plate with respect to an electrode at a maximum speed of 0.18 m / min The temperature of the plasma flow remains close to ambient temperature.

The plasma torch is sold by the company Plasmatreat GmbH and the atmospheric plasma stream is obtained from a gas comprising at least one oxidizing component, here a mixture of air and nitrogen.

The atomic percentage Pc in oxygen element of the surface layer is determined by XPS analysis according to the procedure described above. The results are collated in Table 2 below.

Table 2

The degree of crystallinity Te of the surface layer is determined by infrared spectroscopy, in particular by infrared spectroscopy ATR, according to the procedure described above. The results are summarized in Table 3 below. Table 3

From these results it can be deduced that only a surface layer having a relatively high percentage Pc of oxygen element, ie for which Pi / Pc <1, and a relatively low crystallinity level Te, is that is, for which Ti / Tc≥1, 1 promotes the adhesion of the reinforcing element to the test rubber matrix. Under conditions 3 and 4, a surface layer is obtained which does not have a sufficiently low degree of crystallinity to adhere properly to the test rubber matrix, even though it has an atomic percentage of oxygen element Pc greater than that of the inner layer ( or an element integrally of a material identical to that of the inner layer).

Third comparative test

In a third comparative test, a test specimen (specimen I) comprising a PET film having a 100% amorphization ratio and coated with an adhesion primer and with an RFL adhesive and a test specimen is compared (FIG. test piece II) comprising a PET film having a 100% amorphization ratio and coated solely with RFL glue without adhesion primer.

After the peel test, the specimen I has a facies score equal to 5 while the specimen II has a facies score equal to 0. Thus, the amorphization, even total, of the surface layer does not not sufficient to allow good adhesion between the reinforcing member and the test rubber matrix.

[0155] Conclusion of Comparative Tests

Thus, a low degree of crystallinity or a percentage of high oxygen element is not sufficient to allow good adhesion between the reinforcing element and the rubber matrix and thus the removal of the adhesion primer. On the other hand, the combination of a relatively low crystallinity level and a relatively high oxygen atomic percentage allows for excellent adhesion between the reinforcing element and the rubber matrix and thus the removal of the adhesion primer.

The invention is not limited to the previously described embodiments.

It will be noted that in order to measure the degree of crystallinity Ti and the atomic percentage of oxygen element Pi in the inner layer, it is possible, in the case where the chemical and physical modification of the surface layer originates from a surface treatment. , to measure this rate and this percentage on a reinforcing element not subject to this surface treatment, that is to say on an element integrally made of a material identical to that of the inner layer.

It may be provided to implement the invention with a multifilament fiber, a monofilament or a fabric of these fibers.

In the case of a multifilament fiber, the surface layer comprises one or more monofilaments, this or these monofilaments being those outermost with respect to the internal monofilaments forming the inner layer.

In the case of a fabric, it can be assembled from fibers treated according to the invention subsequently to the step of exposing the fibers to the plasma stream. Alternatively, the tissue can be assembled from untreated plasma fibers. The fabric comprising the assembled fibers is exposed to the plasma stream.

It may also be envisaged that the multifilament fiber, the fiber fabric, the film or the monofilament comprises a first portion of polyester and a second portion of a material different from that of the first part. For example, it will be possible to use a twist comprising a first surtors of one or more multifilament fibers made of polyester and a second surtors of one or more multifilament fibers made of aramid or polyester of a different nature from that of the first surtors.

There may be more than two plasma flow generating devices, for example four, so, especially in the case of a multifilament fiber, to treat the entire circumference of the fiber. As a variant, it will be possible to provide a single device for generating plasma flux that is movable along a circular path around the direction of displacement of the fiber.

It will also be possible to rotate the fiber on itself between two flow generating devices arranged so as to expose two portions. different circumferences of the fiber at each plasma flow.

In the case of a film, it will also be possible to simultaneously expose the two surfaces of the film or to expose only one surface of the film.

It is also possible to combine the characteristics of the different embodiments and variants described or envisaged above provided that they are compatible with each other.

Claims

1. Reinforcing element (R), characterized in that it comprises a surface layer (C1, C2) having a degree of crystallinity Te and an atomic percentage of oxygen element Pc and an inner layer (C3) having a degree of crystallinity Ti and an atomic percentage of oxygen element Pi satisfying Ti / Tc> 1, 10 and Pi / Pc <1, each surface layer (C1, C2) and inner layer (C3) being polyester.

2. Element (R) according to the preceding claim, wherein Ti / Tc ≥ 1, 20, preferably Ti / Tc≥ 1, 45 and more preferably Ti / Tc≥ 1, 60 and even more preferably Ti / Tc≥ 1, 80.

3. Element (R) according to any preceding claim, wherein Pi / Pc <0.95, preferably Pi / Pc <0.85 and more preferably Pi / Pc <0.75.

4. Element (R) according to any one of the preceding claims, wherein the thickness (E) of the surface layer (C1, C2) is greater than or equal to 0.5 μηι, preferably 1 μηη and more preferably 1 μηη. , 5 μηι.

5. Element (R) according to any one of the preceding claims, in which Te <30%, preferably Te <25% and more preferably Te <21%.

6. Element (R) according to any one of the preceding claims, wherein Pc 27 27%, preferably Pc 30 30% and more preferably Pc 32 32%.

7. Element (R) according to any one of the preceding claims, wherein Ti <50%, preferably Ti <45% and more preferably Ti <40%.

8. Element (R) according to any one of the preceding claims, wherein Pi <27%, preferably Pi <26% and more preferably Pi <25%.

9. Element (R) according to any one of the preceding claims, comprising at least one element selected from a multifilament fiber, a fiber fabric, a film and a monofilament.

10. Element (R) according to claim 9, wherein the multifilament fiber, the fiber fabric, the film or the monofilament is integrally made of a material selected from polyethylene terephthalate and polyethylene naphthalate, preferably is integrally polyethylene terephthalate.

1 1. An element (R) according to claim 9, wherein the multifilament fiber, fiber fabric, film or monofilament comprises a first polyester portion and a second portion of a different material from that of the first portion.

12. Element (R) according to any one of the preceding claims, comprising a layer of adhesion adhesive directly coating the surface layer (C1, C2).

13. Element (R) according to claim 12, wherein the adhesion adhesive is of the thermosetting type.

14. Element (R) according to claim 12 or 13, wherein the adhesion adhesive comprises at least one diene elastomer.

15. reinforcement web (10), characterized in that it comprises at least one reinforcing element (R) according to any one of claims 1 to 14 embedded in a rubber matrix (M1, M2).

16. Finished article (1) rubber, characterized in that it comprises at least one reinforcing element (R) according to any one of claims 1 to 14.

17. Finished article (1) according to the preceding claim, forming a tire (1).