RUBBER COMPOSITION COMPRISING A HIGHLY SATURATED DIENE ELASTOMER

Abstract

A rubber composition is based on at least one elastomer matrix predominantly comprising a highly saturated diene elastomer, carbon black and an aliphatic diacid dialkyl ester, the highly saturated diene elastomer being a copolymer of ethylene and a 1,3-diene in which the ethylene units represent at least 50 mol % of the monomer units of the copolymer.

Claims

1.-14. (canceled)

15. A rubber composition based on at least one elastomer matrix predominantly comprising a highly saturated diene elastomer, carbon black and an aliphatic diacid dialkyl ester plasticizer and a crosslinking system, the highly saturated diene elastomer being a copolymer of ethylene and a 1,3-diene in which the ethylene units represent at least 50 mol % of the monomer units of the copolymer.

16. The rubber composition according to claim 15, wherein the ethylene units represent between 50 mol % and 95 mol % of the monomer units of the copolymer.

17. The rubber composition according to claim 15, wherein the ethylene units represent at least 65 mol % of the monomer units of the copolymer.

18. The rubber composition according to claim 15, wherein the 1,3-diene is 1,3-butadiene.

19. The rubber composition according to claim 15, wherein the copolymer is a random copolymer.

20. The rubber composition according to claim 15, wherein a content of highly saturated diene elastomer in the rubber composition varies within a range from 80 to 100 phr.

21. The rubber composition according to claim 15, wherein a content of aliphatic diacid dialkyl ester plasticizer is within a range from 5 to 50 phr.

22. The rubber composition according to claim 15, wherein the aliphatic diacid dialkyl ester plasticizer is a compound of formula ROOC(CH.sub.2).sub.nCOOR in which R is a linear or branched alkyl and n represents an integer from 4 to 20.

23. The rubber composition according to claim 22, wherein R is an alkyl comprising from 4 to 20 carbon atoms.

24. The rubber composition according to claim 22, wherein R is a branched alkyl.

25. The rubber composition according to claim 22, wherein n represents an integer from 4 to 12.

26. The rubber composition according to claim 15, wherein the aliphatic diacid dialkyl ester plasticizer is diisooctyl sebacate.

27. The rubber composition according to claim 15, wherein a carbon black content is between 15 and 65 phr.

28. A pneumatic or non-pneumatic tire casing which comprises the rubber composition according to claim 15.

Description

III. EXAMPLES OF IMPLEMENTATION OF THE INVENTION

III.1 Tests and Measurements:

III.1-1 Determination of the Microstructure of the Elastomers:

[0058] The microstructure of the elastomers is determined by .sup.1H NMR analysis, combined with .sup.13C NMR analysis when the resolution of the .sup.1H NMR spectra does not make it possible to assign and quantify all the entities. The measurements are performed using a Broker 500 MHz NMR spectrometer at frequencies of 500.43 MHz for proton observation and 125.83 MHz for carbon observation.

[0059] For the insoluble elastomers which have the capacity of swelling in a solvent, a 4 mm z-grad HRMAS probe is used for proton and carbon observation in proton-decoupled mode. The spectra are acquired at rotational speeds of from 4000 Hz to 5000 Hz.

[0060] For the measurements on soluble elastomers, a liquid NMR probe is used for proton and carbon observation in proton-decoupled mode.

[0061] 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 a person skilled in the art. The amounts of material used are adjusted so as to obtain spectra of sufficient sensitivity and resolution.

[0062] 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 a person skilled in the art.

[0063] In both cases (soluble sample or swollen sample):

[0064] 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.

[0065] 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.

[0066] The NMR measurements are performed at 25 C.

III.1-2 Measurement of the dynamic properties:

Dynamic Properties

[0067] The dynamic properties are measured on a viscosity analyser (Metravib V A4000) according to the standard ASTM D5992-96. 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, according to the standard ASTM D 1349-99, is recorded.

[0068] The following results are based on measurements using temperature scans at a given stress and strain scans at a stress frequency of 10 Hz.

[0069] Stiffness: the stiffness is determined at a strain of 50% return during a strain scan at 60 C. from 0.1% to 100% peak-to-peak strain.

[0070] Glass transition temperature: the glass transition is determined as the temperature at which the mixture has a maximum G value in imposed stress shear tests of 0.7 MPa.

III.2 Preparation of the Rubber Compositions:

[0071] The rubber compositions, the details of the formulation of which are given in Table 1, were prepared in the following manner:

[0072] The elastomer, the reinforcing filler and also the various other ingredients, with the exception of sulfur and vulcanization accelerators, are successively introduced into an internal mixer (final filling rate: approximately 70% by volume), whose initial tank temperature is approximately 90 C. The oils are introduced at 115 C. Thermomechanical working (non-productive phase) is then performed in one step, lasting a total of about 3 to 4 minutes, until a maximum drop temperature of 160 C. is reached. The mixture thus obtained is recovered, cooled and the sulfur and vulcanization accelerators are then incorporated on a mixer (homo-finisher) at 30 C., the whole being mixed (productive phase) for an appropriate time (for example about minutes).

[0073] The compositions thus obtained are subsequently calendered, either in the form of slabs (thickness of 2 to 3 mm) or of thin sheets of rubber, for measurement of their physical or mechanical properties, or extruded in the form of a tyre tread.

[0074] The elastomer (EBR) is prepared according to the following procedure:

[0075] 30 mg of metallocene [{Me2SiFlu2Nd(-BH4)2Li(THF)}2, the symbol Flu representing the fluorenyl group of formula C13H8], are introduced into a first Steinie bottle in a glovebox. The co-catalyst, butyloctylmagnesium dissolved beforehand in 300 ml of methylcyclohexane in a second Steinie bottle, is introduced into the first Steinie bottle containing the metallocene in the following proportions: 0.00007 mol/L of metallocene, 0.0004 mol/L of co-catalyst. After contact for 10 minutes at ambient temperature, a catalytic solution is obtained. The catalytic solution is then introduced into the polymerization reactor. The temperature in the reactor is then increased to 80 C. When this temperature is reached, the reaction starts by injection of a gaseous mixture of ethylene and 1,3-butadiene (80/20 mol %) into the reactor. The polymerization reaction proceeds at a pressure of 8 bar. The proportions of metallocene and of co-catalyst are, respectively, 0.00007 mol/L and 0.0004 mol/L. The polymerization reaction is stopped by cooling, degassing of the reactor and addition of ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in a vacuum oven. In a reactor containing, at 80 C., methylcyclohexane, ethylene and butadiene in proportions of 80/20 mol % ethylene/butadiene, butyloctylmagnesium (BOMAG) is added to neutralize the impurities in the reactor, then the catalytic system is added. At this time, the reaction temperature is regulated at 80 C. and the polymerization reaction starts. The polymerization reaction takes place at a constant pressure of 8 bar. The reactor is fed throughout the polymerization with ethylene and butadiene in proportions of 80/20 mol % (ethylene/butadiene). The polymerization reaction is stopped by cooling, degassing of the reactor and addition of ethanol. An antioxidant is added to the polymer solution. The copolymer is recovered by drying in an oven under vacuum to constant mass.

[0076] The catalytic system is a preformed catalytic system. It is prepared in methylcyclohexane from a metallocene, [Me2Si(Flu)2Nd(u-BH4)2Li(THF)], a co-catalyst, butyloctylmagnesium (BOMAG), and a preformation monomer, 1,3-butadiene, in the following contents: metallocene: 0.00007 mol/L, co-catalyst: 0.00036 mol/L. It is prepared according to a preparation method in accordance with paragraph II.1 of patent application WO 2017/093654 A1.

[0077] Rubber composition C3 is in accordance with the invention. The rubber compositions C1 and C2 are not in accordance with the invention because they do not comprise the specific plasticizing system required in the invention.

TABLE-US-00001 TABLE 1 Components C1 C2 C3 EBR (1) 100 100 100 Carbon black (2) 42 42 42 Oil 1 (3) 11 Oil 2 (4) 11 Wax (5) 1 1 1 Antioxidant (6) 2 2 2 Stearic acid 1.5 1.5 1.5 ZnO 2.5 2.5 2.5 Diphenylguanidine 0.5 0.5 0.5 Accelerators (7) 0.8 0.8 0.8 Sulfur 0.4 0.4 0.4 (1) EBR Mooney 85, ethylene content: 77%, (2) Carbon black, ASTM N234 from the company Cabot, (3) Extensoil 51 liquid paraffin from the company Repsol, (4) Plasthall DOS oil from the company Hallstar, (5) Ozone wax C32 ST, (6) Santoflex 6PPD from the company Flexsys, (7) Accelerators: cyclohexylbenzothiazylsulfenamide CBS and tetrabenzylthiuram disulfide TBzTD from the company Akrochem.

III.3 Results:

[0078] The results are given in Table 2.

TABLE-US-00002 TABLE 2 MDC measurements C1 C2 C3 Stiffness at 60 C. (G* 50% return) 1.25 0.92 1.24 Glass transition (T G max) 39.45 43.47 46.93

[0079] The results show that the composition in accordance with the invention makes it possible to simultaneously lower the glass transition of the mixture, while maintaining high levels of stiffness, suitable for use in tyre treads. Lowering of the glass transition temperature of the mixture allows this formulation to be used at lower temperatures and the lower reduction in stiffness makes it possible to maintain good tyre performance and also acceptable wear of the composition in the tread.