TREAD FOR AN AIRCRAFT TIRE

Abstract

An aircraft tire comprises a tread (2), having an axial width L, which comprises a middle portion (3) having an axial width L.sub.C at least equal to 50% and at most equal to 80% of the axial width L of the tread and consisting of a middle rubber composition, and two lateral portions (41, 42), positioned axially on either side of the middle portion (3), each having an axial width (L.sub.S1, L.sub.S2) at least equal to 10% and at most equal to 25% of the axial width L of the tread and each consisting of a lateral rubber composition. The middle rubber composition comprises in particular from 25 to 85 phr of a tin-functionalized butadiene and styrene copolymer and from 15 to 75 phr of isoprene elastomer, and at least one lateral rubber composition is different from the middle rubber composition.

Claims

1.-15. (canceled)

16. An aircraft tire comprising a tread having an axial width L, the tread comprising: a middle portion having an axial width L.sub.C at least equal to 50% and at most equal to 80% of the axial width L of the tread and consisting of a middle rubber composition; and two lateral portions positioned axially on either side of the middle portion, each having an axial width (L.sub.S1, L.sub.S2) at least equal to 10% and at most equal to 25% of the axial width L of the tread and each consisting of a lateral rubber composition, wherein the middle rubber composition comprises at least one elastomeric matrix, a reinforcing filler and a crosslinking system, the elastomeric matrix comprising from 25 to 85 parts by weight per hundred parts by weight of elastomer, phr, of a tin-functionalized butadiene and styrene copolymer and from 15 to 75 phr of isoprene elastomer, a total content of isoprene elastomer and of butadiene and of tin-functionalized butadiene and styrene copolymer in the middle rubber composition being within a range extending from 45 to 100 phr, and wherein at least one lateral rubber composition is different from the middle rubber composition.

17. The aircraft tire according to claim 16, wherein the content of the isoprene elastomer in the middle rubber composition is within a range extending from 20 to 65 phr.

18. The aircraft tire according to claim 16, wherein the content of tin-functionalized butadiene and styrene polymer in the middle rubber composition is within a range extending from 35 to 80 phr.

19. The aircraft tire according to claim 16, wherein the elastomeric matrix of the middle rubber composition comprises more than 0 to 55 phr of another diene elastomer.

20. The aircraft tire according to claim 19, wherein the other diene elastomer is selected from the group consisting of non-tin-functionalized butadiene and styrene copolymers, polybutadienes, and mixtures thereof.

21. The aircraft tire according to claim 16, wherein the reinforcing filler of the middle rubber composition comprises carbon black, a reinforcing inorganic filler, or both carbon black and a reinforcing inorganic filler.

22. The aircraft tire according to claim 16, wherein the content of reinforcing filler in the middle rubber composition is within a range extending from 20 to 100 phr.

23. The aircraft tire according to claim 16, wherein the middle rubber composition also comprises from 1 to 30 phr of at least one hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers.

24. The aircraft tire according to claim 23, wherein the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers is such that the cycloaliphatic monomers are selected from the group consisting of cyclopentadiene, dicyclopentadiene and mixtures thereof, and the aromatic monomers are selected from the group consisting of styrene, alpha-methylstyrene, vinyltoluene, indene and mixtures thereof.

25. The aircraft tire according to claim 23, wherein the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has an aromatic proton content of between 0 and 12%, an ethylenic proton content greater than 3%, a number-average molecular weight greater than 500 g/mol and a polydispersity index greater than 2.

26. The aircraft tire according to claim 16, wherein the at least one lateral rubber composition comprises at least one diene elastomer, a reinforcing filler and a crosslinking system, in which the diene elastomer predominantly comprises at least one isoprene elastomer.

27. The aircraft tire according to claim 26, wherein the at least one lateral rubber composition comprises more than 85 phr of the at least one isoprene elastomer.

28. The aircraft tire according to claim 16, wherein the lateral portion composition of each of the two lateral portions, positioned axially on either side of the middle portion, are different from the middle rubber composition.

29. The aircraft tire according to claim 16, wherein the two lateral portions, positioned axially on either side of the middle portion, are formed by identical lateral rubber compositions.

30. The aircraft tire according to claim 16, wherein the two lateral portions, positioned axially on either side of the middle portion, have identical axial widths (L.sub.S1, L.sub.S2).

Description

III—BRIEF DESCRIPTIONS OF THE FIGURES

[0164] FIG. 1, not shown to scale in order to facilitate the understanding thereof, presents a view in cross section in a meridian plane of the crown of an aircraft tyre according to the invention, comprising, radially from the outside to the inside, a tread 2, a crown reinforcement 5 and a carcass reinforcement 6. The tread 2, having an axial width L, comprises a middle portion 3 having an axial width L.sub.C at least equal to 50% and at most equal to 80% of the axial width L of the tread and consisting of a middle rubber composition, and two lateral portions 41, 42, positioned axially on either side of the middle portion 3, each having an axial width (L.sub.S1, L.sub.S2) at least equal to 10% and at most equal to 25% of the axial width L of the tread and each consisting of a lateral rubber composition.

[0165] FIG. 2 presents a view in cross section in a meridian plane of the crown of an aircraft tyre according to a particular embodiment of the invention, in which the tyre 1 also comprises an interlayer 7 consisting of a rubber composition, in contact by a radially outer face with the tread 2 and by a radially inner face with the crown reinforcement 5.

IV—PREFERRED EMBODIMENTS

[0166] In the light of the aforementioned, the preferred embodiments of the invention are described below: [0167] A. Aircraft tyre (1) comprising a tread (2) having an axial width L, the tread (2) comprising: [0168] a middle portion (3) having an axial width L.sub.C at least equal to 50% and at most equal to 80% of the axial width L of the tread and consisting of a middle rubber composition, [0169] and two lateral portions (41, 42) positioned axially on either side of the middle portion (3), each having an axial width (L.sub.S1, L.sub.S2) at least equal to 10% and at most equal to 25% of the axial width L of the tread and each consisting of a lateral rubber composition, [0170] characterized in that the middle rubber composition comprises at least one elastomeric matrix, a reinforcing filler and a crosslinking system, said elastomeric matrix comprising from 25 to 85 parts by weight per hundred parts by weight of elastomer, phr, of a tin-functionalized butadiene and styrene copolymer and from to 75 phr of isoprene elastomer, the total content of isoprene elastomer and of butadiene and of tin-functionalized butadiene and styrene copolymer in the middle rubber composition being within a range extending from 45 to 100 phr, [0171] and in that at least one lateral rubber composition is different from the middle rubber composition. [0172] B. Tyre (1) according to embodiment A, in which the content of the isoprene elastomer in the middle rubber composition is within a range extending from 20 to 65 phr, preferably from 25 to 60 phr. [0173] C. Tyre (1) according to either one of the preceding embodiments, in which the isoprene elastomer of the middle rubber composition is selected from the group comprising natural rubber, synthetic polyisoprene, and mixtures thereof. [0174] D. Tyre (1) according to any one of the preceding embodiments, in which the isoprene elastomer of the middle rubber composition is a natural rubber. [0175] E. Tyre (1) according to any one of the preceding embodiments, in which the content of tin-functionalized butadiene and styrene copolymer in the middle rubber composition is within a range extending from 35 to 80, preferably from 40 to 75 phr. [0176] F. Tyre (1) according to any one of the preceding embodiments, in which the tin-functionalized butadiene and styrene copolymer of the middle rubber composition is a tin-functional butadiene and styrene copolymer with a low styrene content, the styrene content being within a range extending from 5% to 25%, preferably from 5% to 20%, more preferably from 10% to 19%. [0177] G. Tyre (1) according to any one of the preceding embodiments, in which the tin-functionalized butadiene and styrene copolymer of the middle rubber composition has a glass transition temperature within a range extending from −70° C. to −30° C. [0178] H. Tyre (1) according to any one of the preceding embodiments, in which the total content of isoprene elastomer and of tin-functionalized butadiene and styrene copolymer in the middle rubber composition is 100 phr. [0179] I. Tyre (1) according to any one of embodiments A to G, in which the elastomeric matrix of the middle rubber composition comprises from more than 0 to 55 phr, preferably from more than 0 to 50 phr of another diene elastomer. [0180] J. Tyre (1) according to embodiment I, in which the other diene elastomer of the middle rubber composition is selected from the group consisting of non-tin-functionalized butadiene and styrene copolymers, polybutadienes, and mixtures thereof. [0181] K. Tyre (1) according to embodiment I or J, in which the other diene elastomer of the middle rubber composition predominantly comprises a polybutadiene, preferably comprising predominantly cis-1,4 bonds. [0182] L. Tyre (1) according to embodiment K, in which the content of the other diene elastomer in the middle rubber composition is within a range extending from 10 to 30 phr, preferably from 15 to 25 phr. [0183] M. Tyre (1) according to embodiment I or J, in which the other diene elastomer of the middle rubber composition predominantly comprises a polybutadiene a composite polybutadiene, which comprises from 5% to 25% of 1,2-syndiotactic polybutadiene in a matrix of cis-1,4-polybutadiene. [0184] N. Tyre (1) according to embodiment M, in which the content of the other diene elastomer is within a range extending from 10 to 55 phr, preferably from 40 to 55 phr. [0185] O. Tyre (1) according to any one of the preceding embodiments, in which the reinforcing filler of the middle rubber composition comprises carbon black and/or a reinforcing inorganic filler. [0186] P. Tyre (1) according to embodiment O, in which the inorganic filler is a silica. [0187] Q. Tyre (1) according to any one of the preceding embodiments, in which the reinforcing filler of the middle rubber composition comprises predominantly, preferably exclusively, carbon black. [0188] R. Tyre (1) according to any one of the preceding embodiments, in which the content of reinforcing filler, preferably of carbon black, in the middle rubber composition is within a range extending from 20 to 100 phr, preferably from 25 to 75 phr, more preferably from 30 to 70 phr. [0189] S. Tyre (1) according to any one of embodiments O to R, in which the content of reinforcing inorganic filler, preferably of silica, in the middle rubber composition is within a range extending from 0 to 20 phr, preferably from 1 to 15 phr. [0190] T. Tyre (1) according to any one of embodiments O to S, in which in which the carbon black of the middle rubber composition has a BET specific surface area of between 80 and 170 m.sup.2/g, preferably between 120 and 145 m.sup.2/g. [0191] U. Tyre (1) according to any one of the preceding embodiments, in which the middle rubber composition also comprises from 1 to 30 phr of at least one hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers. [0192] V. Tyre (1) according to embodiment U, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers is such that the cycloaliphatic monomers are selected from the group consisting of cyclopentadiene, dicyclopentadiene and mixtures thereof, and the aromatic monomers are selected from the group consisting of styrene, alpha-methylstyrene, vinyltoluene, indene and mixtures thereof. [0193] W. Tyre (1) according to embodiment U or V, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has a glass transition temperature within a range extending from 30° C. to 150° C., preferably from 30° C. to 120° C. [0194] X. Tyre according to any one of embodiments U to W, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has an average molecular weight Mn within a range extending from 300 g/mol to 3000 g/mol and preferably from 400 to 1500 g/mol. [0195] Y. Tyre according to any one of embodiments U to X, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has an aromatic proton content within a range extending from 3% to 40%, preferably from 5% to 30%. [0196] Z. Tyre according to any one of embodiments U to Y, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has an ethylenic proton content within a range extending from 2% to 15%, preferably from 3% to 10%. [0197] AA. Tyre according to any one of embodiments U to Z, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has a polydispersity index within a range extending from 1 to 4, preferentially from 1.5 to 3.5. [0198] BB. Tyre (1) according to any one of embodiments U to W, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has an aromatic proton content of between 0 and 12%, an ethylenic proton content of greater than 3%, a number-average molecular weight of greater than 500 g/mol and a polydispersity index of greater than 2. [0199] CC. Tyre (1) according to embodiment BB, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has an aromatic proton content within a range extending from 1% to 10%, preferably from 2% to 7%. [0200] DD. Tyre (1) according to embodiment BB or CC, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has an ethylenic proton content within a range extending from 3% to 7%. [0201] EE. Tyre (1) according to any one of embodiments BB to DD, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has an average molecular weight Mn within a range extending from 500 g/mol to 1500 g/mol and preferably from 500 to 1000 g/mol. [0202] FF. Tyre (1) according to any one of embodiments BB to EE, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers has a polydispersity index within a range extending from 2 to 5, preferentially from 3 to 4.5. [0203] GG. Tyre (1) according to any one of embodiments BB to FF, in which the hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers also comprises units originating from pine derivatives, preferentially selected from the group consisting of alpha-pinene, beta-pinene, rosin, turpentine, tall oil and mixtures thereof. [0204] HH. Tyre (1) according to any one of embodiments U to HH, in which the content of hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers, in the middle rubber composition, is within a range extending from 2 to 30 phr, more preferentially from 2 to 15 phr. [0205] II. Tyre (1) according to any one of the preceding embodiments, in which the middle rubber composition does not comprise liquid plasticizer or comprises less than 20 phr thereof, preferably less than 10 phr thereof. [0206] JJ. Tyre (1) according to any one of the preceding embodiments, in which the middle rubber composition does not comprise liquid plasticizer. [0207] KK. Tyre (1) according to any one of the preceding embodiments, in which the at least one lateral rubber composition comprises at least one diene elastomer, a reinforcing filler and a crosslinking system, which the diene elastomer predominantly comprises at least one isoprene elastomer. [0208] LL. Tyre (1) according to any one of the preceding embodiments, in which the lateral rubber composition comprises more than 85 phr, preferably at least 90 phr, of at least one isoprene elastomer. [0209] MM. Tyre (1) according to any one of the preceding embodiments, in which the lateral rubber composition comprises 100 phr of at least one isoprene elastomer. [0210] NN. Tyre (1) according to any one of embodiments KK to MM, in which the at least one isoprene elastomer of the lateral rubber composition is selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof, preferably the at least one isoprene elastomer of the lateral rubber composition is a natural rubber. [0211] OO. Tyre (1) according to any one of the preceding embodiments, in which the two lateral portions (41, 42), positioned axially on either side of the middle portion (3), are different from the middle rubber composition. [0212] PP. Tyre (1) according to any one of the preceding embodiments, in which the two lateral portions (41, 42), positioned axially on either side of the middle portion (3), consist of identical lateral rubber compositions. [0213] QQ. Tyre (1) according to any one of the preceding embodiments, in which the two lateral portions (41, 42), positioned axially on either side of the middle portion (3), have identical widths (L.sub.S1, L.sub.S2). [0214] RR. Tyre (1) according to any one of the preceding embodiments, the tyre comprising a crown reinforcement (5) radially inside the tread (2), in which the tyre (1) comprises an interlayer (7) consisting of at least one rubber composition in contact by a radially outer face with at least the middle portion (3) of the tread (2) and by a radially inner face with the crown reinforcement (5). [0215] SS. Tyre (1) according to embodiment RR, in which the interlayer (7) consists of a rubber composition comprising natural rubber. [0216] TT. Tyre (1) according to any one of the preceding embodiments, the tyre comprising a carcass reinforcement (6) consisting of from 2 to 12, preferably from 5 to 10 carcass layers. [0217] UU. Tyre (1) according to any one of the preceding embodiments, the dimension of which is greater than or equal to 18 inches, preferably from 20 to 23 inches.

V—EXAMPLES

[0218] V-1 Measurements and Tests Used

[0219] Tensile Tests (Examples 1 and 2)

[0220] These tensile tests make it possible to determine the moduli of elasticity and the properties at break and are based on Standard NF ISO 37 of December 2005 on a type-2 dumbbell test specimen. The elongation at break thus measured at 60° C. is expressed as % of elongation.

[0221] Tensile Tests (Examples 3 and 4)

[0222] These tests make it possible to determine the elasticity stresses and the properties at break; those performed on cured mixtures are performed in accordance with Standard AFNOR-NF-T46-002 of September 1988.

[0223] The elongations at break (in %) are measured at two temperatures: at 23° C. and at 100° C., under standard hygrometry conditions (50% relative humidity), according to French Standard NF T 40-101 (December 1979), the breaking stresses (in MPa) and the impact energy may also be measured, the impact energy (breaking energy) being the product of the breaking stress and the elongation at break. The results are given in base 100, i.e. the values are expressed relative to a control, the elongation at break of which is considered as the reference at 100.

[0224] Loss in Weight

[0225] This test makes it possible to determine the loss in weight of a sample of aircraft tyre tread composition when it is subjected to an abrasion test on a high-speed abrasion tester.

[0226] The high-speed abrasion test is carried out according to the principle described in the paper by S. K. Clark, “Touchdown dynamics”, Precision Measurement Company, Ann Arbor, Mich., NASA, 35 Langley Research Center, Computational Modeling of Tires, pages 9-19, published in August 1995. The tread material rubs over a surface, such as a Norton Vulcan A30S-BF42 disc. The linear speed during contact is 70 m/s with a mean contact pressure of 15 to 20 bar. An energy of 10 to 20 MJ/m.sup.2 of contact surface is brought into play during the experiment.

[0227] The components of the constant-energy tribometry device according to the abovementioned paper by S. K. Clark are a motor, a clutch, a rotating plate and a sample holder.

[0228] Components of the constant-energy tribometry device according to the abovementioned paper by S. K. Clark: [0229] small wheel (toroidal ring made of test material mounted on a grooved pulley) [0230] rotating plate, for example consisting of a Norton disc integral with the axis of an electric motor and of a flywheel.

[0231] The performance is evaluated on the basis of the loss in weight according to the following formula:

[Loss in weight performance=loss in weight control/loss in weight sample]

[0232] The results are expressed in base 100. A performance for the sample of greater than 100 is regarded as better than the control.

[0233] Dynamic Properties (after Curing)

[0234] The dynamic properties G* and tan(δ)max are measured on a viscosity analyser (Metravib V A4000) according to Standard ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical test specimen with a thickness of 4 mm and a cross section of 400 mm.sup.2), subjected to a simple alternating sinusoidal shear stress, at a frequency of 10 Hz, at 60° C., according to Standard ASTM D 1349-99, is recorded. A peak-to-peak strain amplitude sweep is performed from 0.1% to 50% (outward cycle) and then from 50% to 1% (return cycle). The results exploited are the complex dynamic shear modulus (G*) and the loss factor tan(δ). The maximum value of tan(δ) observed (tan(δ)max) and the difference in complex modulus (G*) between the values at 0.1% and at 50% strain (Payne effect) are shown for the return cycle. The lower the value for the values of tan(δ)max at 60° C., the lower will be the hysteresis of the composition and thus the lower will be the heating.

[0235] Tearability

[0236] The tearability indices are measured at two temperatures: at 23° C. and at 100° C. The force to be exerted in order to obtain breaking (FRD, in N/mm) is notably determined and the breaking strain (DRD, in %) is measured on a test specimen with dimensions of 10×85×2.5 mm notched at the centre of its length with three notches to a depth of 5 mm, in order to bring about breaking of the test specimen. Thus, the energy for bringing about breaking (energy) of the test specimen, which is the product of the FRD and DRD, can be determined. The results are given in base 100, i.e. the values are expressed relative to a control, the breaking strain (DRD) of which is considered as the reference at 100.

[0237] Scorch Time (or Fixing Time)

[0238] The measurements are taken at 130° C., in accordance with French Standard NF T 43-005. The change in the consistometric index as a function of time makes it possible to determine the scorch time of the rubber compositions, which is assessed in accordance with the abovementioned standard by the parameter T5 (case of a large rotor), expressed in minutes, and defined as being the time necessary to obtain an increase in the consistometric index (expressed in MU) of 5 units above the minimum value measured for this index.

[0239] Microstructure of the Elastomers

[0240] Regarding the composition of the elastomers, the microstructure is generally determined by .sup.1H NMR analysis, supplemented by .sup.13C NMR analysis when the resolution of the .sup.1H NMR spectra does not enable the attribution and quantification of all the species. The measurements are carried out using a Bruker 500 MHz NMR spectrometer at frequencies of 500.43 MHz for the observation of the proton and 125.83 MHz for the observation of carbon. For the measurements of mixtures or elastomers which are insoluble but which have the ability to swell in a solvent, an HRMAS z-grad 4 mm probe is used, making it possible to observe protons and carbons in proton-decoupled mode. The spectra are acquired at rotational speeds of 4000 Hz to 5000 Hz. For the measurements on soluble elastomers, a liquid NMR probe is used for proton and carbon observation in proton-decoupled mode. The preparation of the insoluble samples is performed in rotors filled with the analysed material and a deuterated solvent enabling swelling, generally deuterated chloroform (CDCl.sub.3). The solvent used must always be deuterated and its chemical nature may be adapted by those skilled in the art. The amounts of material used are adjusted so as to obtain spectra of sufficient sensitivity and resolution. The soluble samples are dissolved in a deuterated solvent (about 25 mg of elastomer in 1 ml), generally deuterated chloroform (CDCl.sub.3). The solvent or solvent blend used must always be deuterated and its chemical nature may be adapted by those skilled in the art. The sequences used for proton NMR and carbon NMR, respectively, are identical for a soluble sample and for a swelled sample. A 30° single pulse sequence is used for proton NMR. The spectral window is set to observe all of the resonance lines belonging to the analysed molecules. The number of accumulations is set so as to obtain a signal-to-noise ratio that is sufficient for quantification of each unit. The recycle delay between each pulse is adapted to obtain a quantitative measurement. A 30° single pulse sequence is used for carbon NMR, with proton decoupling only during the acquisition to avoid nuclear Overhauser effects (NOE) and to remain quantitative. The spectral window is set to observe all of the resonance lines belonging to the analysed molecules. The number of accumulations is set so as to obtain a signal-to-noise ratio that is sufficient for quantification of each unit. The recycle delay between each pulse is adapted to obtain a quantitative measurement. The NMR measurements are performed at 25° C.

[0241] V-2 Preparation of the Compositions

[0242] In the examples which follow, the rubber compositions were produced as described in point II-5 above. In particular, the diene elastomers, the reinforcing fillers and also the various other ingredients, with the exception of the vulcanization system, are successively introduced into an internal mixer (final degree of filling: approximately 70% by volume), the initial vessel temperature of which is approximately 80° C. Thermomechanical working (non-productive phase) is then performed in one step, which lasts in total approximately 3 to 4 min, until a maximum “dropping” temperature of 165° C. is reached. The mixture thus obtained is recovered and cooled, and sulfur and a sulfamide-type accelerator are then incorporated on a mixer (homofinisher) at 70° C., everything being mixed (productive phase) for an appropriate time (for example approximately ten minutes).

[0243] V-3 Tests on Rubber Compositions

Example 1

[0244] The purpose of this example is to show the influence of the rate of incorporation of tin-functionalized SBR in compositions of the middle portion of the tread of aircraft tyres on the performance compromise between wear resistance and the preservation of mechanical and thermal properties.

[0245] T1, T2 and T3 are control compositions. T1 corresponds to the composition of an aircraft tread conventionally used by those skilled in the art; it is based on natural rubber as sole elastomer. T2 corresponds to a tread composition in which the natural rubber has been replaced by a tin-functionalized SBR. T3 corresponds to a tread composition in which half of the natural rubber has been replaced by a polybutadiene.

[0246] The tests C1 to C3 are in accordance with the invention. The compositions C to C3 differ in the respective contents of natural rubber and of tin-functionalized SBR.

[0247] The performance results for loss in weight and for elongation at break at 60° C. are expressed as percentage, base 100, with respect to the control composition T1 corresponding to the ordinary tread compositions.

[0248] Table 2 shows the compositions tested (in phr), as well as the results obtained.

TABLE-US-00002 TABLE 2 T1 C1 C2 C3 T2 T3 NR (1) 100 70 50 25 — 50 SBR (2) — 30 50 75 100 — BR (3) — — — — — 50 Carbon black (4) 49 49 49 49 49 49 Antioxidant (5) 1.5 1.5 1.5 1.5 1.5 1.5 Anti-ozone wax 1 1 1 1 1 1 Stearic acid 2.5 2.5 2.5 2.5 2.5 2.5 Zinc oxide (6) 3 3 3 3 3 3 Accelerator (7) 0.85 0.85 0.85 0.85 0.85 0.85 Sulfur 1.6 1.6 1.6 1.6 1.6 1.6 Performance Loss in weight as % 100 105 114 126 157 102 base 100 relative to T1 Elongation at break at 60° C. as % 100 91 82 80 59 85 base 100 relative to T1 Tan(δ)max at 60° C. 0.19 0.18 0.18 0.17 0.17 0.17 (1) Natural rubber (2) Tin-functionalized solution SBR, with 24% of 1,2-polybutadiene units, 15.5% of styrene units − Tg =-65° C. (3) Neodymium polybutadiene, 98% 1,4-cis- − Tg = −108° C. (4) Carbon black of N234 grade according to Standard ASTM D-1765 (5) N-(1,3-Dimethylbutyl)-N-phenyl-para-phenylenediamine, Santoflex 6-PPD from Flexsys (6) Zinc oxide of industrial grade from Umicore (7) N-Cyclohexy1-2-benzothiazolesulfenamide, Santocure CBS from Flexsys

[0249] The results presented in Table 2 above show that the loss in weight performance, representative of a better wear resistance during the landing phase, of the compositions C1 to C3 is always significantly improved with respect to the control.

[0250] Furthermore, these compositions C1 to C3 exhibit an elongation at break at 60° C. which is lower by 20%, with respect to the control T1 (composition of an aircraft tread conventionally used by those skilled in the art to manufacture an aircraft tyre tread), which remains an acceptable level for the mechanical properties. Beyond a fall of 20% with respect to T1, it may be considered that the mechanical properties might no longer be regarded as sufficient for the tread composition to be used on aircraft tyres.

[0251] The above results also show that the thermal stability of the composition, represented by the tan(δ)max values at 60° C., is maintained, indeed even improved, with respect to the control T1.

[0252] As shown by the results for the composition T2, the absence of natural rubber in the composition brings about a strong fall in the mechanical properties. In addition, the composition T3, corresponding to a tread composition in which half of the natural rubber has been replaced by a polybutadiene, does not make it possible to significantly improve the wear resistance.

[0253] Thus, only the middle compositions in accordance with the invention have the advantage of allowing better wear resistance of the middle portion of the tread during the landing phase of the aircraft, while at the same time maintaining, or even improving, the thermal properties of the composition and keeping the mechanical properties at an acceptable level. It is observed that the use of 45 to 75 phr of tin-functionalized SBR in the composition results in a better performance compromise between the wear resistance and the maintenance of the thermal and mechanical properties.

Example 2

[0254] The purpose of this example is to show the influence of the incorporation of other diene elastomers in addition to the tin-functionalized SBR on the performance compromise between wear resistance and the preservation of the mechanical and thermal properties of the middle portion of the tread.

[0255] C2 corresponds to the composition C2 of Example 1. It corresponds to an embodiment of the invention in which only the tin-functionalized SBR is present in addition to the diene elastomer.

[0256] Tests C4 and C5 are also in accordance with the middle rubber composition according to the invention. The compositions C4 and C5 comprise additional synthetic elastomers different in nature, as shown in Table 3 below.

[0257] The performance results for loss in weight and for elongation at break at 60° C. are expressed as percentage, base 100, with respect to the control composition C1 of Example 1.

[0258] Table 3 shows the compositions tested (in phr), as well as the results obtained.

TABLE-US-00003 TABLE 3 C2 C4 C5 NR (1) 50 35 30 SBR (2) 50 45 — SBR (8) — — 20 BR (3) — 20 — VCR412 (9) — — 50 Carbon black (4) 49 49 49 Antioxidant (5) 1.5 1.5 1.5 Anti-ozone wax 1 1 1 Stearic acid 2.5 2.5 2.5 Zinc oxide (6) 3 3 3 Accelerator (7) 0.85 0.85 0.85 Sulfur 1.6 1.6 1.6 Performance Loss in weight 114 118 138 as % base 100 relative to T1 Elongation at break at 60° C. 82 108 95 as % base 100 relative to T1 Tan(δ) at 60° C. 0.18 0.18 0.20 (1) to (7): see Table 2 (8) Tin-functionalized solution SBR, with 24% of 1,2-polybutadiene units, 26.5% of styrene units − Tg = −48° C. (9) VCR412 Ubepol from Ube-composite polybutadiene: 12% of syndiotactic 1,2-polybutadiene in a cis-1,4-polybutadiene matrix

[0259] The results presented in Table 3 above show that the loss in weight performance, representative of a better wear resistance during the landing phase, of the compositions C4 and C5 is always significantly improved with respect to the control T1 and are comparable with, indeed even superior to, the composition C2 in accordance with the present invention.

[0260] Furthermore, these compositions exhibit an elongation at break at 60° C. which is much less than 20%, indeed even greater, relative to the control T1, and the thermal stability of the composition is also maintained, relative to the control T1. These results are comparable with, indeed even superior to, the composition C2 in accordance with the present invention.

[0261] Thus, the middle rubber compositions in accordance with the invention, whether they do or do not comprise another diene elastomer in addition to the isoprene elastomer and the tin-functionalized SBR, have the advantage of providing a better wear resistance during the landing phase of the aircraft, while maintaining, indeed even improving, the thermal properties of the composition and while retaining good mechanical properties.

Example 3

[0262] The aim of these examples is to show the influence of the incorporation of the hydrocarbon-based resin predominantly composed of dicyclopentadiene and aromatic units into aircraft tyre tread compositions on the performance compromise between the cut resistance and the scorch time. Three types of elastomer matrices were tested.

[0263] Tables 4 and 5 show all of the compositions tested (in phr), and also the results obtained.

[0264] T4 and T5 are control compositions. Compositions C6 to C12 are in accordance with the invention.

[0265] The performance results in terms of elongation at break at 23° C. and at 100° C. are expressed as base 100 percentages relative to the control composition, and similarly for the performance results in terms of tear strength at 23° C. and at 100° C. The increase in the scorch time is expressed in minutes relative to the control.

TABLE-US-00004 TABLE 4 T4 C6 C7 C8 C9 NR (1) 50 50 50 50 50 SBR (2) 50 50 50 50 50 Carbon black (10) 49 49 49 49 49 Silica (12) 5 5 5 5 5 Coupling agent (13) 1 1 1 1 1 Hydrocarbon-based resin (11) 0 2.5 5 7.5 10 Antioxidant (5) 1.5 1.5 1.5 1.5 1.5 Anti-ozone wax 1 1 1 1 1 Stearic acid 2.5 2.5 2.5 2.5 2.5 ZnO (6) 3 3 3 3 3 Accelerator (7) 0.8 0.8 0.8 0.8 0.8 Sulfur 1.5 1.5 1.5 1.5 1.5 Elongation at break at 23° C. (base 100) 100 104 116 121 123 Elongation at break at 100° C. (base 100 115 130 142 157 100) DRD at 23° C. (base 100) 100 113 143 177 189 DRD at 100° C. (base 100) 100 113 144 179 108 Increase in scorch time (minutes) 0 15 17 20 22 (1), (2), (5) to (7): see Table 2 (10) Carbon black of N115 grade according to Standard ASTM D-1765 (11) DCPD/Aromatic hydrocarbon-based resin Novares TC160 from Rütgers Mn = 710 g/mol; Mw = 2000 g/mol; PI = 2.8, Tg = 106° C. Aromatic protons: 13%, Ethylenic protons: 5.6%, Aliphatic protons: 81.4% (12) Silica, Zeosil 1165 MP from Solvay-Rhodia, HDS type (13) Silane

TABLE-US-00005 TABLE 5 T5 C10 C11 C12 NR (1) 35 35 35 35 SBR (2) 65 65 65 65 Carbon black (10) 49 49 49 49 Silica (12) 5 5 5 5 Coupling agent (13) 1 1 1 1 Hydrocarbon-based resin (11) 0 5 7.5 10 Antioxidant (5) 1.5 1.5 1.5 1.5 Anti-ozone wax 1 1 1 1 Stearic acid 2.5 2.5 2.5 2.5 ZnO (6) 3 3 3 3 Accelerator (7) 0.8 0.8 0.8 0.8 Sulfur 1.5 1.5 1.5 1.5 Elongation at break at 23° C. (base 100) 100 116 128 132 Elongation at break at 100° C. (base 100 101 102 99 100) DRD at 23° C. (base 100) 100 146 147 216 DRD at 100° C. (base 100) 100 131 149 162 Increase in scorch time (minutes) 0 18 20 22 (1), (2), (5) to (7): see Table 2 (10) to (13): see Table 4

[0266] These results show that the cut resistance performance as represented by the elongation at break and tearability measurements, both at 23° C. and 100° C., are very much improved by the invention. Similarly, the scorch time is substantially lengthened, making it possible to increase the industrial productivity during the manufacture of aircraft tyres.

Example 4

[0267] The aim of these examples is to show the influence of the incorporation of a specific hydrocarbon-based resin into middle rubber compositions of a tread of aircraft tyres on the performance compromise between cut resistance and processability. Two types of elastomeric matrices were tested.

[0268] Table 6 shows all of the compositions tested (in phr) and also the results obtained.

[0269] T6 is a control composition. Compositions C13 to C15 are in accordance with the invention.

[0270] The results of performance in elongation at break at 23° C. and at 100° C. are expressed as percentage base 100 relative to the control composition, as are the results of performance in tear strength at 23° C. and at 100° C. Processability is represented by Mooney viscosity values in Mooney units.

TABLE-US-00006 TABLE 6 T6 C13 C14 C15 NR (1) 50 50 50 50 SBR (2) 50 50 50 50 Carbon black (10) 49 49 49 49 Silica (12) 5 5 5 5 Coupling agent (13) 1 1 1 1 Hydrocarbon-based resin (14) 0 5 7.5 10 Antioxidant (5) 1.5 1.5 1.5 1.5 Anti-ozone wax 1 1 1 1 Stearic acid 2.5 2.5 2.5 2.5 ZnO (6) 3 3 3 3 Accelerator (7) 0.8 0.8 0.8 0.8 Sulfur 1.5 1.5 1.5 1.5 Elongation at break at 23° C. (base 100) 100 112 121 122 Elongation at break at 100° C. (base 100) 100 130 143 159 DRD at 23° C. (base 100) 100 152 185 190 DRD at 100° C. (base 100) 100 162 198 230 Mooney viscosity (MU) 94 89 87 87 (1), (2), (5) to (7): see Table 2 (10), (12) and (13): see Table 4 (14) DCPD/Aromatic Nevroz 1420 hydrocarbon-based resin from Neville Mn = 913 g/mol; Mw = 3540 g/mol; PI = 3.9, Tg = 90° C. Aromatic protons: 3%, Ethylenic protons: 5%, Aliphatic protons: 92%, also including further units derived from pine derivatives

[0271] All the results show that the performances in terms of cut resistance as represented by the elongation at break and tearability measurements, both at 23° C. and 100° C., are greatly improved by the embodiment of the invention according to which the middle rubber composition of the tread comprises at least one hydrocarbon-based resin predominantly composed of units derived from aromatic and cycloaliphatic monomers. At the same time, the Mooney viscosity is reduced in the compositions useful for the invention, making it possible to increase industrial productivity during the manufacture of aircraft tyres.

[0272] In summary, the middle rubber compositions in accordance with the invention, based on at least in particular from 25 to 85 phr of a tin-functionalized butadiene and styrene copolymer and from 15 to 75 phr of isoprene elastomer, constituting the middle portion of the tread of an aircraft tyre, give the tyre a greatly improved performance in terms of touch wear, during landing.

[0273] On the basis of these results, it is estimated that a tyre according to the invention, compared to the reference tyre, allows an overall gain in wear life over the entire cycle of use of the tyre comprising the landing, taxiing and braking phases.

[0274] This gain in wear life of the tyre according to the invention, obtained by virtue of a more regular wearing of the tread, also presents an advantage in terms of retreading the tyre, that is to say replacing the worn tread of the tyre at the end of life.

[0275] For a tyre of the prior art at the end of life, for which the tread has a wear differential between the middle portion and the lateral portions, the retreading operation commonly requires, aside from the removal of the worn tread, the removal of the radially outermost crown layer, generally consisting of metal reinforcers and referred to as protective layer, said protective layer often being damaged at the end of life of the tyre due to its proximity to the tread.

[0276] For a tyre according to the invention, due to a more regular wearing over the axial width of the tread, removal of the protective layer is no longer necessary due to its integrity at the end of life of the tyre, which gives rise to an economic gain in the retreading operation.