RUBBER COMPOSITION COMPRISING AN EPOXIDE RESIN AND A SPECIFIC AMINE HARDENER

Abstract

A rubber composition exhibiting an improved processability/stiffness compromise is based on at least a diene elastomer, a reinforcing filler, a crosslinking system, between 1 and 30 parts by weight per hundred parts by weight of elastomer, phr, of an epoxy resin and between 1 and 15 phr of a specific amine-comprising hardener comprising in particular at least two primary amine functional groups located on at least one six-membered aromatic ring and at least two Ri radicals, which are identical or different, selected from the group consisting of linear or branched C.sub.1-C.sub.6 alkyl radicals, halogens, and ethers, tertiary amines, thioethers, ketones, esters and amides, substituted by linear or branched C.sub.1-C.sub.6 alkyl radicals, the said ring not comprising a hydrogen atom located in the ortho position with respect to the primary amine functional groups.

Claims

1.-26. (canceled)

27. A rubber composition based on at least: a diene elastomer; a reinforcing filler; a crosslinking system; between 1 and 30 parts by weight, per hundred parts by weight of elastomer, phr, of an epoxy resin; between 1 and 15 phr of an amine-comprising hardener comprising at least a first primary amine functional group and a second primary amine functional group located on at least one six-membered aromatic ring, the at least one six-membered aromatic ring comprising: at least the first primary amine functional group, and at least two Ri radicals, which are identical or different, selected from the group consisting of linear or branched C.sub.1-C.sub.6 alkyl radicals, halogens, and ethers, tertiary amines, thioethers, ketones, esters and amides, substituted by linear or branched C.sub.1-C.sub.6 alkyl radicals, wherein the at least one six-membered aromatic ring does not comprise a hydrogen atom located in the ortho position with respect to the first or second primary amine functional groups, and wherein the second primary amine functional group is located on the at least one six-membered aromatic ring or on a second optional six-membered aromatic ring of the amine-comprising hardener.

28. The rubber composition according to claim 27, wherein the Ri radicals, which are identical or different, are selected from the group consisting of linear or branched C.sub.1-C.sub.6 alkyl radicals, halogens, and ethers, tertiary amines, and thioethers, substituted by linear or branched C.sub.1-C.sub.6 alkyl radicals.

29. The rubber composition according to claim 27, wherein the Ri radicals, which are identical or different, are selected from the group consisting of the linear or branched C.sub.1-C.sub.6 alkyl radicals.

30. The rubber composition according to claim 27, wherein the at least one six-membered aromatic ring of the amine-comprising hardener comprises at least two Ri radicals, which are identical or different, selected from the group consisting of halogens, and ethers, tertiary amines and thioethers, substituted by linear or branched C.sub.1-C.sub.6 alkyl radicals, and wherein at least one Ri radical is selected from the group consisting of linear or branched C.sub.1-C.sub.6 alkyl radicals.

31. The rubber composition according to claim 27, wherein the linear or branched C.sub.1-C.sub.6 alkyl radicals are selected from the group consisting of the methyl, ethyl, propyl, isopropyl, isobutyl and butyl radicals.

32. The rubber composition according to claim 31, wherein the linear or branched C.sub.1-C.sub.6 alkyl radicals are selected from the group consisting of methyl and ethyl radicals.

33. The rubber composition according to claim 27, wherein the at least one six-membered aromatic ring is an aromatic ring comprising six carbon atoms.

34. The rubber composition according to claim 27, wherein the amine-comprising hardener corresponds to formula (I): ##STR00007##

35. The rubber composition according to claim 27, wherein the amine-comprising hardener corresponds to formula (II): ##STR00008##

36. The rubber composition according to claim 27, wherein the amine-comprising hardener corresponds to formula (III): ##STR00009## in which: n represents an integer ranging from 0 to 4, and R.sub.1 and R.sub.2, which are identical or different, are selected from the group consisting of hydrogen atom, and methyl, ethyl, isobutyl and benzyl groups.

37. The rubber composition according to claim 36, wherein n represents an integer ranging from 1 to 3 and R1 and R2 both represent a hydrogen atom.

38. The rubber composition according to claim 27, wherein the amine-comprising hardener corresponds to formula (IV): ##STR00010## in which: n represents 1 or 2, and R1 and R2, which are identical or different, are selected from the group consisting of a hydrogen atom and methyl, ethyl, isobutyl and benzyl groups.

39. The rubber composition according to claim 38, wherein n is 1, and R1 and R2 both represent a hydrogen atom.

40. The rubber composition according to claim 27, wherein the amine-comprising hardener corresponds to formula (V): ##STR00011##

41. The rubber composition according to claim 27, wherein the amine-comprising hardener is selected from the group consisting of ##STR00012## and mixtures thereof.

42. The rubber composition according to claim 27, wherein the content of amine-comprising hardener is within a range extending from 5 to 10 phr.

43. The rubber composition according to claim 42, wherein the content of amine-comprising hardener is within a range extending from 2 to 8 phr.

44. The rubber composition according to claim 27, wherein the epoxy resin is selected from the group consisting of aromatic epoxy, alicyclic epoxy and aliphatic epoxy resins.

45. The rubber composition according to claim 27, wherein the epoxy resin is selected from the group consisting of 2,2-bis[4-(glycidyloxy)phenyl]propane, poly[(o-cresyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-(hydroxybenzaldehyde glycidyl ether)] and mixtures thereof.

46. The rubber composition according to claim 27, wherein the content of epoxy resin is between 10 and 25 phr.

47. The rubber composition according to claim 46, wherein the content of epoxy resin is between 15 and 20 phr.

48. The rubber composition according to claim 27, wherein an amount of reinforcing filler is between 20 and 200 phr.

49. The rubber composition according to claim 48, wherein the amount of reinforcing filler is between 30 and 150 phr.

50. The rubber composition according to claim 27, wherein the reinforcing filler comprises carbon black, a reinforcing inorganic filler or a mixture of carbon black and a reinforcing inorganic filler.

51. The rubber composition according to claim 50, wherein the reinforcing filler predominantly comprises carbon black.

52. The rubber composition according to claim 27, wherein the diene elastomer is selected from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, butadiene copolymers, isoprene copolymers and mixtures thereof.

53. The rubber composition according to claim 27 further comprising between 0.1 and 6 phr of cobalt salt.

54. The rubber composition according to claim 53, wherein the amine-comprising hardener comprises at least one Ri radical selected from the group consisting of halogens, and ethers, tertiary amines, thioethers, ketones, esters and amides, substituted by linear or branched C1-C6 alkyl radicals.

55. A finished or semi-finished rubber article comprising a rubber composition according to claim 27.

56. A tire comprising a rubber composition according to claim 27.

57. The tire according to claim 56, wherein the rubber composition is present in at least one layer chosen from the tread and an internal layer.

58. The tire according to claim 24, in which the internal layer is selected from the group consisting of carcass plies, crown plies, bead-wire fillings, crown feet, decoupling layers, tread underlayer and combinations thereof.

59. A process for preparing a rubber composition according to claim 27 comprising the following steps: (a) incorporating the reinforcing filler in the diene elastomer to form a mixture during a first non-productive stage by thermomechanically kneading until a maximum temperature of between 110 C. and 190 C. is reached; (b) cooling the mixture to a temperature of less than 100 C.; (c) then incorporating, during a second productive stage, a crosslinking system; (d) kneading the mixture up to a maximum temperature of less than 110 C.; and (e) incorporating the epoxy resin and the amine-comprising hardener independently of one another during step (a) or step (c).

Description

EXAMPLES

[0140] I. Measurements and Tests Used

[0141] I.1 Scorch Time

[0142] The measurements are carried out at 130 C. or 115 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, 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.

[0143] It should be remembered that, in a way well known to a person skilled in the art, the greater the consistometric index as a function of time, the more the crosslinking of the material will be delayed before curing.

[0144] 1.2 Mooney Plasticity

[0145] Use is made of an oscillating consistometer as described in French Standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the composition in the raw state (i.e., before curing) is moulded in a cylindrical chamber heated to 100 C. After preheating for one minute, the rotor rotates within the test specimen at 2 revolutions/minute and the working torque for maintaining this movement is measured after rotating for 4 minutes. The Mooney plasticity (ML 1+4) is expressed in Mooney unit (MU, with 1 MU=0.83 newton.Math.metre).

[0146] It should be remembered that, in a way well known to a person skilled in the art, the lower the Mooney plasticity, the easier the material is to work. Of course, beyond a certain value (e.g., 20 MU), the material becomes too liquid to be usable, in particular for manufacturing internal layers.

[0147] 1.3 Dynamic Properties

[0148] The dynamic properties G*(2%) are measured on a viscosity analyser (Metravib VA4000) 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, under standard temperature conditions (23 C.) according to Standard ASTM D 1349-99 or, as the case may be, at a different temperature, is recorded. A strain amplitude sweep is carried out from 0.1% to 50% (outward cycle) and then from 50% to 1% (return cycle). The result made use of is the complex dynamic shear modulus G*. For the return cycle, the complex dynamic shear modulus G*(2%) at 2% strain, at 40 C., is shown.

[0149] It should be remembered that the value of G*(2%) return at 40 C. is representative of the stiffness of the material: the greater G*(2%) at 40 C. is, the stiffer the material.

[0150] II. Preparation of the Compositions

[0151] The tests which follow are carried out in the following way: the diene elastomer, the reinforcing filler, between 1 and 30 phr of the epoxy resin, 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 60 C. Thermomechanical working is then carried out (non-productive phase) in one stage, which lasts in total approximately from 3 to 4 min, until a maximum dropping temperature of 165 C. is reached.

[0152] The mixture thus obtained is recovered and cooled and then sulfur, an accelerator of sulfenamide type and between 1 and 15 phr of the amine-comprising hardener are incorporated on a mixer (homofinisher) at 30 C., everything being mixed (productive phase) for an appropriate time (for example between 5 and 12 min).

[0153] The compositions thus obtained are subsequently calendered, either in the form of plaques (thickness of 2 to 3 mm) or of thin sheets of rubber, for the measurement of their physical or mechanical properties, or extruded in the form of a profiled element.

[0154] III. Tests on Rubber Compositions

[0155] Eleven rubber compositions were prepared as indicated above, seven in accordance with the invention (hereinafter denoted C.5 to C.11) and four not in accordance (control compositions, hereinafter denoted C.1 to C.4). Their formulations (in phr) and their properties have been summarized in Table 1 below.

[0156] With the exception of the control composition C.1, the compositions presented in this Table 1 do not result in the formation of formaldehyde during the curing.

[0157] The compositions C.2 to C.11 contain an epoxy resin (two different resins were tested) and a polyamine-comprising hardener as replacement for the phenol/formaldehyde resin/HMT hardener(s) pair present in the conventional control composition C.1. The compositions C.5 to C.11 in accordance with the present invention contain amine-comprising hardeners which are different from the amine-comprising hardeners of the control compositions C.2 to C.4.

[0158] The results, based on the scorch time and on G*(2%), are presented on base 100 with respect to the control composition C.1. The Mooney plasticity results are presented in absolute value.

TABLE-US-00001 TABLE 1 Constituent C.1 C.2 C.3 C.4 C.5 C.6 C.7 C.8 C.9 C.10 C.11 NR (1) 100 100 100 100 100 100 100 100 100 100 100 Carbon black (2) 70 70 70 70 70 70 70 70 70 70 70 ZnO (3) 3 3 3 3 3 3 3 3 3 3 3 6PPD (4) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Stearic acid (5) 2 2 2 2 2 2 2 2 2 2 2 Sulfur 3 3 3 3 3 3 3 3 3 3 3 CBS (6) 2 2 2 2 2 2 2 2 2 2 2 Phenol/formaldehyde 12 resin (7) HMT (8) 4 Epoxy resin (9) 12 12 12 12 16 12 12 Epoxy resin (10) 12 12 12 Control hardener (11) 4 4 Control hardener (12) 4 Hardener (13) 4 Hardener (14) 4 4 4 Hardener (15) 4 4 Hardener (16) 4 Scorch time 100 51 87 145 270 177 159 209 125 97 152 Mooney plasticity (MU) 46 77 79 62 47 39 26 38 31 39 38 G*(2%) return at 40 C. 100 109 103 101 116 102 104 102 98 101 86 (1) Natural rubber (2) Carbon black N326 (name according to Standard ASTM D-1765) (3) Zinc oxide (industrial grade - Umicore) (4) N-(1,3-Dimethylbuty1)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from Flexsys) (5) Stearin (Pristerene 4931 from Uniqema) (6) N-Cyclohexylbenzothiazolesulfenamide (Santocure CBS from Flexsys) (7) Phenol/formaldehyde novolac resin (Peracit 4536K from Perstorp) (8) Hexamethylenetetramine (from Degussa) (9) Epoxy resin (DEN 439 from Uniqema) (10) Epoxy resin (tris(4-hydroxyphenyl)methane triglycidyl ether from Sigma-Aldrich) (11) 1,3-Bis(aminomethyl)cyclohexane (from Sigma-Aldrich) (12) meta-Phenylenediamine from Sigma-Aldrich (13) Lonzacure DETDA from Lonza (14) Ethacure 300 from Albemarle (15) Lonzacure MDEA from Lonza (16) Lonzacure MCDEA from Lonza

[0159] It is noted that the use of an epoxy resin and a polyamine-comprising hardener in the compositions C.5 to C.11 in accordance with the present invention makes it possible to obtain an improved Mooney plasticity, with respect to the phenol/formaldehyde resin/HMT hardener(s) pair of the control composition C.1, but also with respect to the epoxy resin/polyamine-comprising hardener pair of the control compositions C.2 to C.4. Furthermore, the compositions in accordance with the present invention additionally make it possible to obtain a scorch time which is improved or at least equivalent to that of the control composition C.1, while retaining an equivalent stiffness to that of the control compositions C.1 to C.4.

[0160] To sum up, the results of these tests demonstrate that the use of an epoxy resin and of a specific polyamine-comprising hardener in the compositions of the invention makes it possible to obtain rubber compositions, the processability/stiffness compromise of which is far superior to that of a conventional composition, or of compositions comprising other amine-comprising hardeners, not in accordance with the present invention.

[0161] These tests illustrate rubber compositions which can be used especially in internal mixtures, such as carcass plies, crown plies, bead-wire fillings, crown feet, decoupling layers or the tread underlayer, in particular in carcass plies, crown plies, bead-wire fillings, crown feet, decoupling layers, regions requiring a high stiffness with low strain.