Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/16—Nitrogen-containing compounds
  • C08K5/34—Heterocyclic compounds having nitrogen in the ring
  • C08K5/3412—Heterocyclic compounds having nitrogen in the ring having one nitrogen atom in the ring
  • C08K5/3415—Five-membered rings

Definitions

• the present invention relates to rubber compositions for tires, as well as to anti-degrading agents, also called anti-aging agents, intended to protect these compositions against atmospheric aging.
• It relates more particularly to the protection of white, clear or colored rubber compositions, devoid of carbon black and reinforced with at least one white or colored filler, in particular of silica, such compositions being usable for the manufacture of tires of color.
• vulcanizates of natural and synthetic diene rubbers due to the presence of double bonds on their molecular chains, are liable to deteriorate more or less rapidly after prolonged exposure to the atmosphere, if they are not not protected, due to known mechanisms of oxidation and ozonolysis.
• Such mechanisms have been described, for example, in the following documents: FR-A- 1 358 702; FR-A-1 508 861 or US-A-3 419 639; FR-A-2,553,782; ref. [1]: "Antidegradants for tire applications” in “Tire compounding", Education Symposium No 37 (ACS), Cleveland, Communication I, October 1995; ref. [2]: “Non-blooming high performance antidegradants", Kaut.
• EP-A-0810258 published recently disclosed for its new diene rubber composition reinforced by another special white filler, in this case alumina (Al2O3) of high dispersibility, which allows also obtaining tires or treads having an excellent compromise of conflicting properties.
• alumina Al2O3
• the non-staining antioxidants conventionally used in white, clear or colored rubber compositions are phenolic derivatives (see for example FR-A-2 553 782; ref. [1] and [3 ] supra); the latter have the disadvantage of being less effective, for diene elastomers. than their PPD or TMQ derivative counterparts used in black color compositions.
• non-staining antiozonants protective waxes of the paraffinic, macro- or microcrystalline type are certainly used in a known manner, but these waxes, without chemical action with respect to ozone, constitute only simple barriers or protective films to the elastomer surface. physical barriers which lose their effectiveness as soon as they are broken by external phenomena such as repeated mechanical stresses, for example during the rolling of tires.
• An antiozonant remaining active under the effect of dynamic constraints is therefore essential: such chemically active antiozonants have certainly been proposed, such as for example lactams (see for example FR-A-2 553 782) or cyclic acetals (see by eg ref. [7]: "The action of antiozonants in rubber. RCT vol. 58, No 4. 1985.
• anti-UV agents are known. non-staining, for example UN absorbers. (so-called “UVA” products) based on benzotriazoles or benzophenones. or compounds based on sterically hindered amines, known as “Hindered Amine Light Stabilizers" (“HALS”) which are capable of neutralizing the combined action of UNs. and oxygen by the formation of stable nitroxy radicals (see for example application JP 1996/25920. ref. [3] and [5] above).
• HALS Hindered Amine Light Stabilizers
• These UVA or HALS compounds usually used for the protection of saturated polymers such as polyethylene or polypropylene. have the disadvantage of being very expensive.
• a first subject of the invention consists of a white, clear or colored rubber composition, devoid of carbon black and usable for the manufacture of color tires, comprising at least (i) a diene elastomer, (ii) a white or colored reinforcing filler and (iii) an anti-aging, photostable and non-staining agent with respect to this composition, consisting of a ⁇ -phenyl-maleimide derivative of formula -teneral: in which:
• a subject of the invention is also the use of a rubber composition in accordance with the invention for the manufacture of colored tires or for the manufacture of colored rubber articles intended for such tires, these articles being chosen in particular in the group formed by the treads, the sub-layers intended, for example, to be placed under these treads, the sidewalls, the heels, the protectors, the inner tubes or the inner waterproof gums for tubeless tires.
• tires or colored articles in the present application is meant tires or articles of which at least part is of a color other than conventional black, including a white color.
• the subject of the invention is also these colored tires and these colored rubber articles themselves, when they comprise a rubber composition in accordance with the invention.
• the invention also relates to a process for protecting against aging the white, clear or colored rubber compositions which can be used for the manufacture of color tires or of rubber articles intended for such tires, this process being characterized in that an anti-aging agent corresponding to formula (1) above is incorporated by mixing into said composition, before its vulcanization.
• a subject of the invention is finally the use of an anti-aging agent corresponding to formula (1) above for the protection of white, clear or colored rubber compositions which can be used for the manufacture of colored tires or rubber articles intended for such tires.
• the properties of the rubber compositions are evaluated as indicated below.
• the test pieces used are non-standard test pieces consisting of rubber strips with dimensions (L x 1 xe) equal to 1 10 x 15 x 2.5 (length, width and thickness in mm) .
• the measurements are carried out at 130 ° C. in accordance with standard AFNOR-NF-T43-005 of November 1980.
• compositions are subjected after cooking to an accelerated photo-aging in the following manner: one face of the test pieces is exposed for a determined time (for example 4 or 12 days) under 4 high pressure mercury vapor lamps (MAZDA MA400) at 60 ° C in a SEPAP 12/24 (MPC) enclosure. The changes in mechanical and colorimetric properties are then measured.
• MAZDA MA400 high pressure mercury vapor lamps
• MPC SEPAP 12/24
• test D25 from "0" (very good) to "10" (very bad);
• Test pieces that broke before the end of the test are indicated by the letter “R” in the results tables, which is equivalent to an even worse performance than a note “10” in test D25 or "5.5.5" in test S 10.
• the colorimetric values are determined using a Microflash 200 D DATA COLOR spectrocolorimeter in configuration D65 / 10 (daylight; observation angle 10 °). The colorimetric properties are measured in a known manner, according to the colorimeter instruction manual (May 1995). by analysis of the reflectance spectrum of the test pieces.
• the axis a * represents the green-red chromaticity coordinate, with a scale going from -100 (green) to +100 (red);
• - the axis b * represents the coordinate of blue-yellow chromaticity, with a scale going from -100 (blue) to +100 (yellow);
• the axis L * represents the brightness coordinate, with a scale going from 0 (black) to 100 (white);
• compositions according to the invention comprise as basic constituents (i) at least one diene elastomer, (ii) at least one white or colored filler as reinforcing filler , and (iii) at least one anti-degrading, photostable and non-staining agent with respect to these compositions, consisting of an N-phenyl-maleimide derivative corresponding to the above general formula (1).
• elastomer or “diene” rubber is understood in known manner an elastomer derived at least in part (i.e. a homopolymer or a copolymer) of diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).
• diene elastomer a diene elastomer derived at least in part from conjugated diene monomers, having a rate of units or units of diene origin (conjugated dienes) which is greater than 15% (% in moles).
• diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not enter into the preceding definition and can be qualified in particular as "essentially saturated diene elastomers". "(rate of motifs of diene origin low or very low, always less than 15%>).
• the expression “highly unsaturated” diene elastomer is understood in particular to mean a diene elastomer having a rate of units of diene origin (conjugated dienes) which is greater than 50%).
• butadiene-1.3 is suitable in particular. 2-methyl-1,3-butadiene. 2.3-di (C ⁇ -C 5 alkyl) -1.3-butadienes such as for example 2,3-dimethyl-1, 3-butadiene. 2.3-diethyl-1.3-butadiene. 2-methyl-3-ethyl-1,3-butadiene. 2-methyl-3-isopropyl-1.3-butadiene. an aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene.
• vinyl aromatic compounds examples include styrene, ortho-, meta-, para-methylstyrene. the commercial "vinyl-toluene" mixture. para-tertiobutylstyrene. methoxystyrenes. chlorostyrenes. vinyl mesitylene, divinylbenzene, vinylnaphthalene.
• the copolymers can contain between 99%> and 20%> by weight of diene units and from 1% to 50% by weight of vinyl aromatic units.
• the elastomers can have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used.
• the elastomers can be, for example, block, statistics, sequences, microsequences. and be prepared in dispersion or in solution.
• polybutadienes are suitable and in particular those having a content of - 1.2 units between 4% and 80%> or those having a cis-1.4 content greater than 80%>, polyisoprenes. butadiene-styrene copolymers and in particular those having a styrene content of between 5%> and 50%> by weight and more particularly between 20% and 40%). a content of bonds - 1.2 of the butadienic part between 4%> and 65%). a content of trans-1.4 bonds of between 20% and 80%.
• butadiene-isoprene copolymers and in particular those having an isoprene content of between 5%> and 90%> by weight and a glass transition temperature (Tg) from -40 ° C to -80 ° C.
• Tg glass transition temperature
• isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50%> by weight and a Tg of between -25 ° C and -50 ° C.
• butadiene-styrene-isoprene copolymers are particularly suitable those having a styrene content of between 5%> and 50%> by weight and more particularly between ⁇ 0% and 40%>, an isoprene content of between 15 % and 60%> by weight and more particularly between 20%> and 50%.
• the elastomer can be coupled and / or star or even functionalized with a coupling and / or star-forming or functionalizing agent.
• the elastomer can also be natural rubber or a blend based on natural rubber with any elastomer, in particular diene, synthetic.
• the diene elastomer of the composition in accordance with the invention is chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes. polyisoprenes or natural rubber, butadiene-styrene copolymers. butadiene-isoprene copolymers, isoprene-styrene copolymers, butadiene-styrene-isoprene copolymers. or a mixture of two or more of these compounds.
• the diene elastomer is preferably a butadiene-styrene copolymer prepared in solution having a styrene content of between 20%> and 30%> by weight, a content of vinyl bonds in the butadiene part of between 15% and 65%>, a content of trans-1.4 bonds between between 15%> and 75% and a glass transition temperature of between -20 ° C and - 55 ° C, this butadiene-styrene copolymer being optionally used in admixture with a polybutadiene preferably having more than 90% of cis-1,4 bonds.
• all the white fillers (also called clear fillers) capable of reinforcing, alone or in mixture with one another, more or less depending on the intended applications, are suitable for a tire rubber composition, such as, for example, silica, alumina, clays, hydrates or oxides of aluminum and / or magnesium, bentonite. talc, chalk, kaolin, titanium oxide.
• the rate of reinforcing filler is within a range from 30 to 150 phr (parts by weight per hundred parts of elastomer). more preferably from 30 to 100 phr. the optimum being different depending on the intended applications: the level of reinforcement expected on a bicycle tire, for example, is of course much lower than that required on a tire capable of traveling at high speed in a sustained manner, for example a motorcycle tire, a tire for passenger vehicle or for commercial vehicle such as truck.
• silica (Si0 2 ) or alumina (AI2O3) constitute (s) the majority c ' that is to say more than 50%> by weight of the total reinforcing filler.
• silica and / or alumina constitute more than 80% by weight of this total reinforcing filler.
• Silica and / or alumina can constitute the whole of the reinforcing filler; however, other white fillers may, depending on the intended applications, advantageously represent a more or less significant fraction of the reinforcing filler.
• another white filler associated for example with silica or alumina can have the effect of opacifying the colors, in other words of reducing the clearness, that is to say say more or less translucent of compositions loaded with silica or alumina.
• This other white filler is preferably chosen from chalk, talc or kaolin, more preferably kaolin; it is preferably used at a rate of 2.5 to 12.5%), more preferably from 5 to 10% (%> by weight relative to the weight of silica and / or alumina), depending on the intended applications; for a rate lower than 2.5% the effect is generally not very visible whereas for rates higher than 12.5%> the mechanical properties of the vulcanizates can decrease.
• titanium oxide has the effect of giving a pastel tone, particularly aesthetic, to the colors chosen; the level of titanium oxide preferably varies from 0.5 to 7%, more preferably from 1 to 3% (% by weight relative to the weight of silica and / or alumina), depending on the intended applications. For a rate lower than 0.5%, the effect is generally not very visible whereas for rates higher than 7% there is a risk of brushing on the surface of the vulcanizates.
• the invention also applies to cases where a colored reinforcing filler is chosen, compatible with the desired color for the tire, this colored filler being able to be a naturally colored filler, or also obtained by a prior coloring operation. , for example a precolored silica or alumina.
• the silica used can be any reinforcing silica known to a person skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a CTAB specific surface, both less than 450 ⁇ r / g, even if the highly dispersible precipitated silicas are preferred, in particular when the invention relates to tires having a low rolling resistance.
• the term “highly dispersible silica” is understood to mean any silica having a very significant ability to disaggregate and to disperse in a polymer matrix, observable in known manner by electron or optical microscopy, on fine sections.
• Nonlimiting examples of such preferential highly dispersible silicas mention may be made of Perkasil KS 430 silica from Akzo, BV 3380 silica from Degussa, Zeosil 1,165 MP and 1,115 MP silica from Rhône-Poulenc , Hi-Sil 2000 silica from PPG, Zeopol 8741 or 8745 silica from Huber. treated precipitated silicas such as for example the silicas "doped" with aluminum described in application EP-A-0 735 088.
• the reinforcing alumina preferably used is a highly dispersible alumina having a BET surface area from 30 to 400 ⁇ r / g, more preferably from 80 to 250 ⁇ r / g, an average particle size at most equal to 500 nm, more preferably at most equal to 200 nm, a high level of reactive Al-OH surface functions, as described in the above-mentioned application EP-A-0 810 258.
• reinforcing white filler is generally understood to mean mixtures of different reinforcing white fillers, in particular silica and / or highly dispersible aluminas such as described above.
• any known coupling agent can be used to ensure the connection between the reinforcing white filler and the diene elastomer, such as organosilanes, in particular polysulphurized alkoxysilanes such as bis (trialkoxyl (C ⁇ -C) silylpropyl) tetrasulphides), in particular of bis (trimethoxysilylpropyl) or bis (triethoxysilylpropyl), in particular the last of these compounds, of formula [(C2H5 ⁇ ) 3Si (CH2) 3S2J2 > sold for example by the company Degussa under the name Si69, or by the company Osi under the URC2 designation.
• organosilanes such as bis (trialkoxyl (C ⁇ -C) silylpropyl) tetrasulphides), in particular of bis (trimethoxysilylpropyl) or bis (triethoxysilylpropyl), in particular the last of these compounds, of formula
• the rubber composition in accordance with the invention is protected against aging by a photostable and non-staining anti-degrading agent with respect to this composition; the latter consists of an N-phenyl-maleimide derivative corresponding to the general formula (1) which follows:
• R 1 and R 2 identical or different, represent hydrogen or a halogen, in particular bromine (derivative of N-phenyl-bromomaleimide). More preferably. R 1 and R 2 both represent hydrogen.
• Ph represents a phenyl group. substituted or unsubstituted
• Ar represents an aryl group. substituted or unsubstituted, having from 6 to 12 carbon atoms, preferably a phenyl group. substituted or unsubstituted; where one or more substituents are present on one and / or the other of these two Ph and Ar groups, these substituents are preferably selected from alkyl C] -C] 0, straight chain or branched, of preferably in C
• the derivative more particularly selected is N- (4-anilinophenyl) -maleimide, in which Ph and Ar of the above formula (1) each represent an unsubstituted phenyl group; such a compound as well as its production methods have been described in particular in FR-A-1 350 428. GB-A-1 533 068. FR-A-2 050 984 or US-A-3 767 628.
• N-phenyl-maleimide derivatives have been found to be sufficiently effective on their own for the anti-aging protection of the compositions according to the invention, while being photostable and non-staining with respect to these compositions; they can therefore advantageously constitute the only antidegradant (antioxidant, chemical antiozonant and anti-UV) present in these compositions of the invention, apart from the conventional film-forming waxes which it is preferable to keep for specific, static and superficial antiozone protection , that they bring.
• compositions in accordance with the invention could of course contain, in addition to the N-phenyl-maleimide derivatives defined above, other known non-staining anti-degrading agents, such as for example antioxidants from the family of phenolic derivatives. , phosphites. thioesters or thioethers. substituted non-staining diphenylamines, these antioxidants being taken alone or in combination, chemical antiozonants such as cyclic acetals, or anti-U.V. such as benzotriazoles and / or "HALS" amines.
• other known non-staining anti-degrading agents such as for example antioxidants from the family of phenolic derivatives. , phosphites. thioesters or thioethers. substituted non-staining diphenylamines, these antioxidants being taken alone or in combination, chemical antiozonants such as cyclic acetals, or anti-U.V. such as benzotriazoles and / or
• N-phenyl-maleimide derivatives in the compositions of the invention, depending on the intended application and the nature of the diene elastomer to be protected.
• This content is preferably within a range of 0.5 to 5 phr, more preferably from 1 to 3 phr; below the minimum rate indicated, the effect of the anti-degrading agent is insufficient, while beyond the maximum rate indicated, there is no longer any improvement in protection while the costs of the formulation continue to increase , and that there is a risk of penalizing the mechanical properties of the vulcanizates.
• any type of coloring agent known to a person skilled in the art can be used, this coloring agent possibly being organic or inorganic, soluble or not in the compositions according to the invention.
• mineral dyes such as, for example, powdered metals, in particular copper or aluminum powder, or various metal oxides, in particular silicates, aluminates, titanates.
• iron oxides or hydroxides mixed oxides of different metallic elements such as Co. Ni, Al. Zn.
• organic pigments such as indanthrones, diketo-pyrrolo-pyrroles or diazo condensates. organometallic pigments such as phthalocyanines.
• the color of the compositions in accordance with the invention can thus vary over a very wide range, for example in different shades of red, orange, green, yellow, blue or even brown or gray.
• compositions in accordance with the invention contain, in addition to the compounds described above, all or part of the constituents usually used in diene rubber compositions of tires, such as for example plasticizers, a crosslinking system based either on sulfur or on sulfur and / or peroxide donors, vulcanization accelerators, extension oils, of the aromatic, naphthenic or paraffinic type. or various anti-fatigue agents.
• compositions in accordance with the invention may contain coupling agents and / or of recovery of the reinforcing filler other than those mentioned above, in combination or in place of the latter, such as, for example, polyols, amines, alkoxysilanes.
• the rubber compositions are prepared by using the diene elastomers according to completely known techniques, by thermomechanical work in one or two stages in an internal paddle mixer, followed by mixing on an external mixer.
• the diene elastomer or the mixture of elastomers is introduced into an internal mixer, filled to 70% and the temperature of which is approximately 60 ° C., then after an appropriate time kneading, for example of the order of 1 minute, all the other ingredients except the vulcanization system are added; the thermomechanical mixing work is continued until a determined drop temperature (175 ° C for test 1 below. 165 ° C for test 2). The mixture thus obtained is recovered and then the vulcanization system is added on an external mixer (homo-finisher) at 30 ° C. Vulcanization is carried out at 150 ° C (45 min for test 1, approximately 15 min for test 2).
• composition No2 PPD type anti-degradant
• composition No3 antidegradant consisting of N- (4-anilinophenyl) -maleimide.
• Composition No 3 is therefore the only composition in accordance with the invention.
• N- (4-anilinophenyl) -maleimide is prepared by the action of maleic anhydride on N-phenyl-p-phenylè ⁇ e diamine, according to the process described in the document FR-A- 1 350 428 cited above, with the difference that one proceeds in a single step in a single solvent, NN-dimethylformamide (instead of dioxane and benzene).
• the SBR elastomer (styrene-butadiene copolymer) is prepared in solution, and comprises 25.6%> of styrene, 60% of polybutadiene units 1 -2 and 1 S% of trans polybutadiene units - 1.4 (Tg equal to -29 ° C ): the elastomer BR (polybutadiene) is a commercial product, having more than 90% (approximately 98%>) of cis-1, 4 bonds.
• Tables 1 to 4 successively give the formulation of the different compositions (Table 1 - rate of the different products expressed in phr), their properties after cooking and the evolution of their mechanical properties after photo-oxidation (Table 2), their resistance to 'ozone (Table 3), and finally the evolution of their colorimetric properties after photooxidation (Table 4).
• composition No3 are those whose mechanical properties (F 10, F25 and Shore A hardness) change less quickly compared to the control composition (Nol).
• the results obtained on the composition according to the invention (No3) being substantially identical to those obtained with the conventional anti-degrading agent (composition No2);
• composition No 3 N-phenyl-maleimide derivative
• parameter ⁇ E is less than 10 for the composition according to the invention as for the control composition, while it is greater than 30 for the composition protected by 6-PPD.
• compositions are identical except for the following differences:
• composition No4 control: no anti-aging protection
• - composition No5 PPD type anti-degradant
• antidegradant consisting of N- (4-anilinophenyl) -maleimide
• composition No7 antidegradant consisting of N- (4-anilinophenyl) -bromomaleimide.
• compositions No6 and No7 are therefore in accordance with the invention.
• the N- (4-anilinophenyl) -maleimide is prepared as indicated in test 1 above.
• the N- (4-anilinophenyl) -bromomaleimide is prepared in the same way, but this time by action of bromomaleic anhydride on N-phenyl-p-phenylene diamine; it is used in composition No7 at an isomolar rate relative to the N- (4-anilinophenyl) -maleimide of composition No6.
• Tables 5 to 7 successively give the formulation of the different compositions (Table 5 - rate of the different products expressed in phr), their properties after cooking and the evolution of their mechanical properties after photo-oxidation (Table 6), and finally l 'evolution of their colorimetric properties after photo-oxidation (table 7).
• the properties after cooking correspond to the "optimum cooking” (ie at T99), determined in known manner according to standard AFNOR-NF-T43-015 of August 1975, in which T99 corresponds to the time necessary to obtain 99 % of the maximum torque difference between the minimum torque before cooking and the maximum torque after cooking, at the cooking temperature (150 ° C in this case).
• the protected compositions (No5 to No7) are those whose mechanical properties (F 10. F25 and hardness
• composition No7 25 Shore A evolve more slowly compared to the control composition (No4); the results obtained on composition No7 are substantially identical to those obtained with the conventional anti-degrading agent of the I-PPD type (composition No5);
• parameter ⁇ E is less than 25 for the compositions in accordance with the invention, as for the control composition, while it is greater than 50 for the composition protected by I-PPD.

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