WO1999006480A1

WO1999006480A1 - Rubber composition for colour tyre

Info

Publication number: WO1999006480A1
Application number: PCT/EP1998/004601
Authority: WO
Inventors: Christophe Penot; Didier Vasseur
Original assignee: Compagnie Generale Des Etablissements Michelin-Michelin & Cie.
Priority date: 1997-08-01
Filing date: 1998-07-22
Publication date: 1999-02-11
Also published as: EP1000117A1; AU9254598A; JP2001512167A

Abstract

The invention concerns a white, light-coloured or coloured rubber composition, devoid of carbon black, usable for making colour tyres or rubber articles designed for such tyres, comprising at least (i) a diene elastomer, (ii) a reinforcing white or coloured filler, and (iii) an antidegradant, photostable and non-staining relative to said composition, consisting of a N-phenyl-maleimide derivative of formula (1) in which: R?1 and R2¿, identical or different, represent hydrogen or a halogen; Ph represents a phenyl group, substituted or not; Ar represents an aryl group, substituted or not, with 6 to 12 carbon atoms.

Description

RUBBER COMPOSITION FOR COLOR TIRE

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.

As is known, 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. Gummi Kunst., 47, No 4, 1994. 248-255; ref. [3]: "Antioxidants" in Encycl. Polym. Sci. and Eng .. 2nd Edition. Flight. 2, 73-91; ref. [4]: "Protection of rubber agaisnt ozone", RCT (Rubber Chem. Technol.) Vol 63, No 3, 1990, 426-450). These complex mechanisms lead, following ruptures of the double bonds and the oxidation of the sulfur bridges, different types of degradation: the oxidation results in a stiffening and weakening of the vulcanizates. whereas the attack on ozone results in the initiation of cracks or surface cracks which will widen and propagate more or less quickly depending on the nature and severity of the dynamic constraints imposed on these vulcanizates during their usage. The above degradation mechanisms are also accelerated under the combined action of heat by thermo-oxidation, or even that of light by photo-oxidation (see for example ref. [5]: "Photo-oxidation and stabilization of polymers ", Trends in Polym. Sci., Vol. 4, No 3, 1996, 92-98; or ref. [6]:" Dégradation mechanisms of ruhbers ", Int. Polym. Sci. and Technol .. Vol 22, No 12, 1995, 47-57).

All of the above aging phenomena could be gradually inhibited thanks to the development and marketing of various antidegradant, antioxidant or antiozonant agents. We have even found compounds capable of fulfilling these two functions simultaneously; the most effective, both as antioxidants and antiozonants, are known derivatives of quinoline, such as, for example, 2,2,4-trimethyl-1,2-dihydroquinoolein ("TMQ"), or derivatives of p-phenylenediamine ("PPD") even more active than the first, such as for example Nl, 3-dimethylbutyl-N'-phenyl-p-phenylenediamine ("6-PPD") or N-isopropyl- N'- phenyl-p-phenylenediamine ("I-PPD"). These TMQ and PPD type antidegradants, sometimes even associated, are today very widespread and used almost systematically (see for example ref. [1], [2] and [4] above) in conventional rubber compositions. loaded at least in part with carbon black giving them their characteristic black color. Since fuel savings and the need to protect the environment have become a priority, and in particular since the publication of European patent application EP-A-0 501 227, the interest in compositions reinforced with silica has been largely revived. This application EP-A-0 501 227 describes a sulfur vulcanizable rubber composition reinforced with a particular precipitated silica which makes it possible to manufacture a tire having a markedly improved rolling resistance, without affecting the other properties, in particular those of adhesion, endurance and resistance to wear.

The European patent application 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.

We can now consider the marketing of colored tires which, for aesthetic reasons, in particular in the field of passenger vehicles, correspond to a real expectation of users, while being able to offer them a substantial saving in fuel.

It turns out that the anti-degrading agents described above, developed and optimized after many years of research on conventional rubber compositions of black color, are not suitable for the protection of rubber compositions loaded exclusively with white fillers, in particular of silica or alumina. Indeed, most of them. and in particular the TMQ or PPD derivatives mentioned above are not light stable: under the effect of UN radiation. they exhibit a color change and stain the rubber compositions, which does not allow their use to be envisaged in white, clear or colored compositions. These well-known drawbacks have for example been described in FR-A-1 573 393. FR-A-1 577 770. FR-A-2 733 987. On the other hand, the absence of carbon black, which played up to 'here a role of absorber UN. very effective in conventional compositions, has the consequence of aggravating all the degradation processes described above, in particular those of photo-oxidation.

It was therefore necessary to develop for these colored tires new anti-aging protection systems presenting compromises of new properties, displaced with respect to those used for conventional black tires, and in particular more effective with respect to the UN., by developing complex, more or less synergistic combinations of different known products, such combinations using both antioxidants, antiozonants and anti-UN products, all of which must be sufficiently active in their respective function and compatible with the severe conditions of use of tires (temperature, fatigue due to dynamic stresses), while being stable in the light and non-staining with respect to the compositions which they protect.

However, such anti-aging systems, as efficient as they are, present, in addition to their difficulty of development, a certain number of drawbacks. - j - First of all, 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.

As for 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. 728-739: and ref. [8]:" Improve ent in the ozone resistance of elastomers with non staining aniioxidanis ". presented at" Rubbercon '95 ". Goteborg. Sweden. May 9-12, 1995), but these products are there still less active than the PPD or TMQ derivatives used in the black compositions.

Finally, 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). 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.

It was therefore entirely desirable, for the anti-aging protection of white, clear or colored rubber compositions intended for colored tires, to develop formulations which are simpler and less costly than the multi-product formulations described above. -above. Ideally, it was even more desirable to find a sufficiently effective anti-degrading agent which, on its own, could fulfill the various functions of antioxidant, chemical anti-zoning agent and anti-UV agent, while being not only photostable and non-marking with respect to protected compositions, but still compatible with use in tires and non-disturbing with regard to the vulcanization system. The Applicant has found during its research that a very specific family of compounds unexpectedly meets all of these requirements.

Consequently, 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 Ν-phenyl-maleimide derivative of formula -teneral:

in which:

- R ¹ and R ² , identical or different, represent hydrogen or a halogen; - Ph represents a phenyl group, substituted or unsubstituted, and Ar represents an aryl group, substituted or unsubstituted, having from 6 to 12 carbon atoms.

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.

By 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 invention as well as its advantages will be easily understood in the light of the description and of the exemplary embodiments which follow. I. MEASUREMENTS AND TESTS USED

The properties of the rubber compositions are evaluated as indicated below. During the photo-oxidation and colorimetry tests, 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) .

1-1. Toasting time

The measurements are carried out at 130 ° C. in accordance with standard AFNOR-NF-T43-005 of November 1980. The evolution of the consistometric index as a function of time makes it possible to determine the toasting time (also called safety to roasting) of the rubber compositions, assessed in accordance with the norm mentioned above by the parameter T5, expressed in minutes (min) and defined as being the time necessary to obtain an increase in the value of the consistometric index (expressed in "Mooney unit" (MU). with the relation 1 MU = 0 .S3 Newton. Meter) by 5 units above the minimum value measured for this index.

1-2. Tensile tests

These tests make it possible to determine the elasticity moduli and the breaking properties, in accordance with standard AFNOR-NF-T46-002 of September 1988. The secant modules are measured in second elongation (ie after an accomodation cycle) at 10% elongation (M 10). at 100% elongation (M 100) and 300% elongation (71300). Unless otherwise indicated in the text, all of these tensile measurements are carried out under normal temperature and hygrometry conditions according to the standard AFNOR-NF-T40-101 of December 1979.

1-3. Shore A hardness tests

These measurements make it possible to assess the hardness of the compositions after baking, in accordance with standard ASTM D 2240-86.

1-4. Photo-oxidation tests

The 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. In particular, the tensile tests after accelerated photoaging are carried out by extensometry of the test pieces at constraints of low elongations (10% and 25%). in first elongation. on an Instron 1122 machine, at low traction speed (10 mm / min). The measured stresses are noted F10 and F25. 1-5. Ozone resistance tests

These tests make it possible to evaluate the resistance of the materials tested to the aggression of an atmosphere of ozonized air for a variable duration, at constant temperature. The measurements are carried out within the framework of AFNOR standards NF-T-46-019 and NF-T-46-039 of December 1992, the tests being carried out in enclosures whose characteristics correspond to those of AFNOR standard NF-T- 46-038. The measurements are carried out either statically (test noted S 10) at 10% o elongation (duration 1 to 20 days), or dynamically (test noted D25 - frequency 0.5 Hz) at 25%) elongation (duration 48 hours), at a temperature of 27 ° C and under an atmosphere containing 40 ppcm (parts per 10 ⁸ ) of ozone.

The results are obtained by visual observation of the test pieces and notation of the latter according to the following scales:

- Note for test D25: from "0" (very good) to "10" (very bad);

- Notes to test S 10 (on each of the following parameters in this order: number, width and depth of cracks): from "0.0.0" (very good) to "5.5.5" (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.

1-6. Colorimetric tests

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.

These measurements are reported in the CIE LAB system of the 3 three-dimensional colorimetric coordinates L *. a *, b *. known system in which:

- 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);

-ΔE = [(ΔL *) - + (Δa *) ² + (Δb *) ² ] ^{, 2} represents the average overall color difference of each sample compared to an un aged control; the higher ΔE, the more the composition has lost its initial color. II. CONDITIONS FOR CARRYING OUT THE INVENTION

In addition to the usual additives and optionally at least one coloring agent, the 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).

II- 1. Diene elastomer

By 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).

In general, the term “essentially unsaturated” diene elastomer is understood here to mean 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).

Thus, for example, 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%>).

In the category of “essentially unsaturated” diene elastomers, 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%).

These definitions being given, the expression “diene elastomer capable of being used in the compositions according to the invention” is understood in particular to be:

(a) - any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

(b) - any copolymer obtained by copolymerization of one or more dienes conjugated together or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms:

(c) - a ternary copolymer obtained by copolymerization of ethylene, of an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having of 6 to 12 carbon atoms, such as for example the elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular hexadiene-1.4, ethylidene norbornene, dicyclopentadiene;

(d) - a copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated versions. in particular chlorinated or brominated, of this type of copolymer. Although it applies to any type of diene elastomer. a person skilled in the art of tires will understand that the present invention is first of all implemented with essentially unsaturated diene elastomers, in particular of the type (a) or (b) above.

By way of conjugated dienes, butadiene-1.3 is suitable in particular. 2-methyl-1,3-butadiene. 2.3-di (Cι-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.

Examples of vinyl aromatic compounds are 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.

Preferably, 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. 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.

In the case of 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%. a butadiene content of between 5%> and 50%> by weight and more particularly of between 20%> and 40%>, a content of units -1, 2 of the butadiene part of between 4%> and 85%>, a content of trans units -1, 4 of the butadiene part of between 6% and 80%>. a content of units -1, 2 plus -3.4 of the isoprenic part of between 5%> and 70%> and a content of trans units -1.4 of the isoprenic part of between 10% and 50%>, and more generally any butadiene-styrene-isoprene copolymer having a Tg between -20 ° C. and -70 ° C. Of course, 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.

Preferably, 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.

When the composition in accordance with the invention is intended for a tread for a colored tire, 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.

II-2. Reinforcing filler

By way of reinforcing filler, 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.

Preferably, 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.

Preferably, in particular when the composition of the invention relates to such a tire capable of traveling at high speed, silica (Si0 ₂ ) or alumina (AI2O3), or even the two associated, constitute (s) the majority c ' that is to say more than 50%> by weight of the total reinforcing filler. Even more preferably, the 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. Thus, it has been found that 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.

It has also been found that the use of titanium oxide (TiO2) 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.

Of course, 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 πr / 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. As 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 πr / g, more preferably from 80 to 250 πr / 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. As nonlimiting examples of such reinforcing aluminas, mention may in particular be made of aluminas A125, CR125, D65CR from the company Baikowski.

The physical state under which the reinforcing white charge is present is immaterial, whether in the form of powder, microbeads, granules, or even beads. Of course, the term 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 (Cι-C) silylpropyl) tetrasulphides), in particular of bis (trimethoxysilylpropyl) or bis (triethoxysilylpropyl), in particular the last of these compounds, of formula [(C2H5θ) 3Si (CH2) 3S2J2 _> sold for example by the company Degussa under the name Si69, or by the company Osi under the URC2 designation.

II-3. Anti-aging agent

As stated previously, 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:

In this formula (1). 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, and 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 _| -C ₄ , in particular methyl or ethyl, or C1-C ₄ alkoxyls, with straight or branched chain, in particular methoxyl or ethoxyl.

Compounds corresponding to the general formula (1) above had certainly already been described for their antioxidant or antiozonant properties, in conventional rubber compositions loaded with carbon black (see for example FR-A-1 350 428, FR- A-2 050 984 or US-A-3 767 628. US-A-5 244 028, requests JP 1987/124134, JP 1987/190237 or JP 1988/137938). However, they were reputed to belong to a family of products having insufficient anti-degrading properties in conventional black compositions, in any case clearly inferior to those of the usual anti-degrading agents such as TMQ or PPD derivatives previously described. For this reason, they have moreover, to the knowledge of the Applicant, never been marketed. It is therefore unexpectedly that it has been discovered that the compounds of formula (1) above can satisfactorily meet the specific and severe requirements of white, clear or colored rubber compositions intended for the manufacture of tires. color, in particular to the specific problems of photo-oxidation.

It is also known that a general problem posed by the anti-aging protection of diene elastomers is that the anti-degrading agents must not be extracted, or as little as possible, from the vulcanizates or tires which they protect by the action of water, detergents or other solvents (known problem of "leaching"). A notable advantage of the N-phenyl-maleimide derivatives of formula (1) above is that they are easily grafted, by themselves, on the diene elastomers, which further reinforces their effectiveness.

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.

The above 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.

However, the 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.

Those skilled in the art will know how to adjust the content of 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.

II-4. Coloring agent

One can of course not use a coloring agent, and choose to keep the color provided by the reinforcing filler itself, whether the latter is a so-called "white" filler (ie white or clear, translucent) or on the contrary colorful. For a colored composition (other than white or clear), 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. By way of example, mention may be made of 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. Mention may also be made of 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.

II-5. Miscellaneous additives

Of course, the 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.

The 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.

11-6. Preparation of the compositions

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.

According to the conventional one-step process, all the necessary constituents, with the exception of the vulcanization system, are introduced into a conventional internal mixer. The result of this first mixing step is then taken up on an external mixer, generally a roller mixer, and the vulcanization system is then added to it. A second step can be added to the internal mixer, essentially for the purpose of subjecting the mixture to an additional heat treatment. III. EXAMPLE OF EMBODIMENT OF THE INVENTION

The following tests are carried out as follows: 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).

Trial 1

We compare three rubber compositions based on silica, red in color, intended for the manufacture of treads for colored tires. These three compositions are identical except for the following differences:

- composition No 1 (control): no anti-aging protection;

- 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-phenylèιιe 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).

As a diene elastomer. an SBR / BR cut is used here; 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).

On reading these different results tables, the following observations can be made:

- the classic properties of rubber (Table 2). after cooking and before aging, are little different from one composition to another, whether they are protected or not by an anti-degrading agent; it is noted that the roasting times T5, for the protected compositions, are within a range of values satisfactory for the use of the compositions;

- after photo-oxidative aging (Table 2), the protected compositions (No2 and

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);

the use of the N-phenyl-maleimide derivative (composition No 3) makes it possible to very significantly increase the resistance to ozone (Table 3), in static and dynamic tests, compared with control composition No 1, even if the results obtained are less good than those observed with 6-PPD (composition No2), which was expected given the excellent antiozonant properties known from the conventional anti-degrading agent;

on the other hand, concerning the evolution of colorimetric properties (Table 4). it is found that the composition No2 protected by the PPD derivative degrades in a very significant and unacceptable manner. with in particular a pronounced blackening, while the composition No3 according to the invention shows excellent color stability (no visible staining after photo-oxidation), almost equivalent to that recorded on the control composition.

It is noted in particular that the parameter ΔE 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.

Trial 2

Here we compare four natural rubber compositions based on silica, white, intended for the manufacture of treads for colored tires. Unlike the previous test, no coloring agent is used; the white color is brought here by the addition of kaolin and titanium oxide, without which these compositions loaded with silica would be clear, that is to say more or less translucent (color due to the silica filler).

These four compositions are identical except for the following differences:

- composition No4 (control): no anti-aging protection; - composition No5: PPD type anti-degradant;

- Composition No6: antidegradant consisting of N- (4-anilinophenyl) -maleimide;

- composition No7: antidegradant consisting of N- (4-anilinophenyl) -bromomaleimide.

Only 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.

5 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).

10 The properties after cooking here 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).

15

On reading these different results tables, the same observations can be made as for the previous test 1, namely:

conventional rubber properties (Table 6), after curing and before aging, little different from one composition to another, in particular for protected compositions (ie containing an antidegradant);

after 4-day photo-oxidative aging (Table 6), the protected compositions (No5 to No7) are those whose mechanical properties (F 10. F25 and hardness

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);

on the other hand, concerning the evolution of the colorimetric properties (table 7), it can be seen that the composition No5 protected by the derivative I-PPD degrades very significantly (pronounced blackening illustrated by the evolution of ΔL), while the two compositions in accordance with the invention (No6 and No7) show excellent color stability (no visible staining after photo-oxidation), close to that recorded on the control composition No4.

It is noted in particular that the parameter ΔE 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.

40

In summary, the preceding tests demonstrate that the compositions in accordance with the invention make it possible to obtain a very good compromise in properties after aging, thus offering colored tires a satisfactory resistance to atmospheric aging due to the combined action of oxygen. , ozone and UN light, while guaranteeing excellent color stability. Table 1

(i) butadiene-styrene copolymer

(2) polybutadiene Europrene Cis (company Enichem) (3) Silica Zeosil 1,165 MP (company Rhône-Poulenc) (4) Si69 (company Degussa) (5) 6-PPD (6) 4-anilino-phenyl-maleimide (7 ) protective wax Redezon 500 (company Repsoi) (8) pigment Cromophtal Red BRN Cl - Red 144 (company Ciba-Geigy) (9) 1, 3-diphenylguanidine

(10): N-cyciohexyl-benzothiazyl-sulfenamide

Table 2

Initial properties

Before photo-oxidation:

After 12-day photo-oxidation:

Table 3

("R" means a rupture of the test piece)

Table 4

Composition No.

Initial properties:

L * 38.1 37.7 34.1 a * 36.4 34.4 26.4 b * 22.2 21.1 16.6

After photo-oxidation (12 days)

ΔL * -4.8 16 -6.0 Δa * -4.8 27 -6.4 Δb * -1.2 11 -1.7

ΔE +6.9 + 33 +8.9 Table 5

(3) Zeosil silica 1,165 MP (Rhône-Poulenc company) (4) Si69 (Degussa company) (6) 4-anilino-phenylI-maleimide (7) Redezon 500 protective wax (Repsoi company) (9) 1, 3 -diphenylguanidine (10) N-cyclohexyl-benzothiazyl-sulfenamide

(H) Titanium oxide "anatase" (company Thann and Mulhouse) (12) I-PPD

(13) 4-anilino-phenyl-bromomaleimide

Table 6

Initial properties

Before photo-oxidation:

After photo-oxidation 4 days

9? -

Table 7

Initial properties:

After 12-day photo-oxidation:

Claims

1. A white, clear or colored rubber composition, free of carbon black and usable for the manufacture of colored tires, comprising at least (i) a diene elastomer, (ii) a white or colored reinforcing filler and (iii) an agent anti-aging consisting of an N-phenyl-maleimide derivative of formula:

in which:

- R ¹ and R ² , identical or different, represent hydrogen or a halogen;

- Ph represents a phenyl group. substituted or unsubstituted, and Ar represents an aryl group. substituted or unsubstituted, having 6 to 12 carbon atoms.

2. Composition according to claim 1 in which the anti-aging agent is N- (4-anilinophenyl) -maleimide.

3. Composition according to claims 1 or 2 in which the diene elastomer is chosen from the group consisting of 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.

4. Composition according to claim 3, in which the diene elastomer is 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 15% and 75% and a glass transition temperature between -20 ° C and -55 ° C, this butadiene-styrene copolymer being optionally used in mixture with a polybutadiene preferably having more than 90%) of cis-1,4 bonds.

5. Composition according to any one of claims 1 to 4, in which the reinforcing filler consists mainly of silica and / or alumina.

6. Composition according to claim 5. in which is associated with silica and / or alumina, another white filler chosen from chalk, talc or kaolin, preferably at a rate of 2.5 to 12.5% ( % by weight relative to the weight of silica and / or alumina).

7. Composition according to claims 5 or 6, in which is associated with silica and / or alumina, titanium oxide preferably at a rate of 0.5 to 7% (% by weight relative to the weight silica and / or alumina).

8. Use of a rubber composition according to any one of claims 1 to 7, for the manufacture of colored tires or colored rubber articles intended for such tires, these articles being chosen in particular from group made up of treads, underlayments, sidewalls, heels, protectors, air chambers or internal rubber compounds for tubeless tires.

9. Colored tire or rubber article intended for this tire, comprising a rubber composition according to any one of claims 1 to 7.

10. Colored tire tread, comprising a composition according to claim 4.

1 1. Process for protecting against aging a white, clear or colored rubber composition, devoid of carbon black and usable for the manufacture of colored tires or of rubber articles intended for such tires, this process being characterized in that which is incorporated by mixing into said composition, before its vulcanization, an N-phenyl-maleimide derivative of formula:

in which:

- R ¹ and R ² . identical or different, represent hydrogen or halogen;

- Ph represents a phenyl group, substituted or unsubstituted, and Ar represents an aryl group. substituted or unsubstituted, having 6 to 12 carbon atoms.

12. The method of claim 1 1 wherein the antiaging agent is N- (4-anilinophenyl) -maleimide.

13. Use, for the anti-aging protection of white, clear or colored rubber compositions, devoid of carbon black and usable for the manufacture of color tires or of rubber articles intended for such color tires, of a derivative of N-phenyl-maleimide of formula:

in which:

- R ¹ and R ² . identical or different, represent hydrogen or halogen;

- Ph represents a phenyl group, substituted or unsubstituted, and Ar represents an aryl group, substituted or unsubstituted, having from 6 to 12 carbon atoms.

14. Use according to claim 13 wherein the anti-aging agent is N- (4-anilinophenyl) -maleimide.