AU783712B2

AU783712B2 - Product based on rubber, such as a tyre, and process for reducing the rolling resistance of the said tyre

Info

Publication number: AU783712B2
Application number: AU97186/01A
Authority: AU
Inventors: Emmanuelle Averty; Lucette Dumergue; Salvatore Pagano
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Priority date: 2000-12-12
Filing date: 2001-12-11
Publication date: 2005-12-01
Anticipated expiration: 2021-12-11
Also published as: ATE271093T1; AU9718601A; EP1215232B1; BR0106003B1; EP1215232A1; DE60104269T2; JP2002356622A; BR0106003A; DE60104269D1; JP4082902B2; CA2363211A1; ES2223711T3

Abstract

Rubber-based product with a buffer zone comprising an elastomer and an oxidation activator for trapping external oxygen and protecting a sensitive zone from oxidation, comprises a ferric salt of an aromatic monocarboxylic acid (I) as the oxidation activator. <??>Rubber-based product with a buffer zone comprising an elastomer and an oxidation activator for trapping external oxygen and protecting a sensitive zone from oxidation, comprises a ferric salt of an aromatic monocarboxylic acid of formula (I) as the oxidation activator. <??>Ar-COOH (I) <??>Ar = phenyl optionally substituted by 1-5 of 1-8C alkyl (optionally substituted), alkoxy or CN or fused with one or more optionally substituted 6-10C aryl groups.

Description

P/00/011 28/5/91 Regulaton 32(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: InventionTitle: Invention Title: PRODUCT BASED ON RUBBER, SUCH AS A TYRE, AND PROCESS FOR REDUCING THE ROLLING RESISTANCE OF THE SAID TYRE The following statement is a full description of this invention, including the best method of performing it known to us The present invention concerns a product based on rubber, the process for obtaining it, and a process for reducing the rolling resistance of a tyre made from the said product, such as a heavy-duty tyre.

One of the main concerns of tyre manufacturers is to increase the life of the tyres. In particular, it is important to improve the endurance in relation to oxidising processes of the rubber compositioris, the metallic or textile reinforcement and the interfaces between those mixes and reinforcements.

A known method of reducing these oxidation phenomena consists in restricting the amount of oxygen coming from the tyre inflation air or from the atmosphere outside the tyre, that gets to a zone of the tyre cover that is particularly sensitive to oxidation. For a very long time this has been done with an internal calendering rubber formed as a layer of butyl rubber, which is impermeable to oxygen, applied on the inside wall of the tyre S-covers. Unfortunately butyl rubber is not totally impermeable and the flow of oxygen into the body of the cover, though reduced, produces undesirable oxidation phenomena in the long term.

S Other materials even more impermeable than butyl rubber have been proposed for the same purpose, as described for example in the documents US-A-5 236 030, US-A-4 874 .:.ooi S670, US-A-5 036 113, EP-A-337 279, US-A-5 040 583 and US-A-5 156 921. These materials, however, are expensive and their use in tyre covers is associated with a number of problems.

Another way to avoid oxidation problems is to trap the oxygen chemically by the accelerated thermal oxidation of a rubber mix that acts as a buffer, located between a main source of oxygen and the zone to be protected against oxidation phenomena. For example, such a buffer composition may be located between the said internal calendering rubber layer and the carcass ply, to reduce the amount of oxygen that comes into contact 2 with the said ply from the inflation air, especially in tyre covers intended for fitting to heavy goods vehicles.

To accelerate the fixing of oxygen it is known to use in these buffer compositions a metallic salt that catalyses the oxidation, in particular a cobalt salt. The effect of the salt is to activate the homolytic decomposition of the hydroperoxides generated during the ageing brought about by the aforesaid oxidation phenomena. The salt is introduced into the buffer composition preferably in amounts of 0.2 to 0.3 parts by weight of cobalt equivalent per 100 parts by weight of the elastomer. This increases the amount of oxygen that can be trapped by the buffer composition by around 50 to 100% compared with the same composition containing no cobalt salt.

Unfortunately, experience shows that this improvement of the oxidation-related behaviour is accompanied by a substantial increase of the hysteresis losses of the buffer composition owing to the considerable quantity of cobalt salt introduced. This increase of the hysteresis losses leads on the one hand to self-heating of the composition and hence to shorter life, contrary to the purpose intended, and to an increase of the rolling resistance, which should also be avoided since manufacturers strive to limit the rolling resistance as much as possible in order to reduce fuel consumption.

For these reasons the use of buffer compositions, attractive as it may sound, has not developed as expected.

European patent document EP-A-507 207 describes a method for trapping oxygen by means of an elastomeric buffer composition contained in a wrapping layer. The buffer composition is characterised in particular by the presence of a transitional metal salt provided to activate the fixing of oxygen. As explained above, the metal salts described as preferred are cobalt salts. As subsidiaries, other metals such as manganese or even iron are also envisaged, but not in relation to specified salts.

3 The international patent documents WO-A-99/24502 and WO-A-00/68309 in the name of the applicant describe products based on rubber, such as tyre envelopes, each being of the type that comprises at least one buffer zone provided in order to trap oxygen from outside the product so as to protect from oxidation at least one sensitive zone of the said product, the said or each such buffer zone containing a composition based on at least one elastomer that comprises at least one specific iron (II) salt which is provided in order to activate oxidation in the said composition. Each product is obtained by incorporating the said salt by mechanical work into the elastomer contained in the said composition, to obtain the said buffer zone.

In document WO-A-99/24502 the said salt belongs to the group consisting of iron (III) acetylacetonate and the iron (III) salts of carboxylic acids having the formula Fe(C.H 2

,O

2 3 in which n may be from 6 to 23.

o..

In document WO-A-00/68309 the said salt is an iron (III) salt of a carboxylic acid having the formula Fe(C,H 2

,O

2 3 in which n may be from 2 to The rubber-based products described in these two documents are such that the specific Soiron (III) salts they contain enable oxygen to be trapped within the buffer zone with ooo.oi sufficient effectiveness to protect the sensitive zone, or each such zone, against oxidation to a greater extent compared with the known buffer zones containing an oxidation activator, in particular based on a cobalt salt.

In addition, the products described in these two documents allow a significant reduction of the hysteresis losses in the buffer zone compared with the aforesaid known buffer zones, and this thanks to the choice of the said specific iron (III) salts. When the said products are tyre envelopes, these show lower self-heating during rolling, and consequently longer life compared with tyre envelopes characterised by the said known buffer zones.

4 Unexpectedly, the applicant has found that the aforementioned benefits obtained by virtue of the said iron (II) salts are substantially retained by using new iron (II1) salts, also in order to obtain a rubber-based product of the type comprising at least one buffer zone provided in order to trap oxygen external to the said product so as to protect from oxidation at least one sensitive zone of the said product, the said or each such buffer zone containing a composition based on at least one elastomer which contains at least one specific iron (HI) salt according to the invention to activate oxidation in the said composition.

The product according to the invention is such that the said salt is an iron (HI) salt of an aromatic mono-carboxylic acid comprising one or more aromatic rings which may or may not be substituted, the said acid having one or other of the following general formulas: (R)n COOH B

COOH

R.(R)

COOH

i__,W ooooo\ in which n is an integer which may be from I to 5, and: in formulas A, B and C, R is a hydrogen atom, a substituted or unsubstituted alkyl group comprising from 1 to 8 carbon atoms, an alcoxyl group or a cyano group, and in formula D, R is a substituted or unsubstituted aryl group comprising from 6 to carbon atoms.

According to one example embodiment of the invention, the said acid is a cyanobenzoic acid such as p-cyanobenzoic acid.

According to another example embodiment of the invention, the said acid is benzoic acid or an alkylbenzoic acid such as p-butylbenzoic acid.

SAccording to another example embodiment of the invention, the said acid is a toluic acid such as p-toluic acid, m-toluic acid or o-toluic acid.

According to another example embodiment of the invention, the said acid is an alkoxybenzoic acid such as p-methoxybenzoic acid.

According to another example embodiment of the invention, the said acid is a naphthoic acid (with generic formula such as 1-naphthoic acid or 2-naphthoic acid.

If the said acid has the generic formula A, it is preferably p-cyanobenzoic acid, benzoic acid, a p-alkylbenzoic acid such as p-butylbenzoic acid, p-toluic acid, or a p-alkoxybenzoic acid such as p-methoxybenzoic acid.

If the said acid has the generic formula B, it is preferably m-toluic acid.

If the said acid has the generic formula C, it is preferably o-toluic acid.

Preferably, the quantity of the said iron (III) salt according to the invention present in the composition may range from 0.01 to 0.03 phr of equivalent iron, where the abbreviation "phr" means parts by weight per 100 parts by weight of the elastomer or totality of elastomers present in the composition. More preferably still, the quantity of iron (III) salt according to the invention ranges from 0.01 to 0.02 pbw of equivalent iron.

The composition according to the invention is based on natural or synthetic rubber, or a blend of two or more such rubbers. Examples of the synthetic rubbers suitable for use in the composition according to the invention are diene rubbers such as polyisoprene, polybutadiene, mono-olefin rubbers such as polychloroprene, polyisobutylene, the copolymers styrene-butadiene or styrene-butadiene-isoprene, the copolymers acrylonitrile-butadiene-styrene and the terpolymers ethylene-propylene-diene. Among the synthetic rubbers the diene rubbers are preferred, in particular any homopolymer obtained by polymerisation of a conjugated diene monomer having 4 to 12 carbon atoms, or any copolymer obtained by co-polymerisation of one or more dienes conjugated either between themselves or with one or more vinyl aromatic compounds having from 8 to carbon atoms.

Suitable conjugated dienes are, in particular, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3di(Cl to C5 alkoyl)-l,3-butadienes such as, for example, 2,3-dimethyl-1,3-butadiene, 2,3diethyl-1,3-butadiene, 2-methyl-3-ethyl- 1,3-butadiene, 2-methyl-3-isopropyl- 1,3butadiene, phenyl-1,3-butadiene, 1,3-pentadiene and 2,4-hexadiene.

Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta- and paramethylstyrene, the commercial mixture "vinyl-toluene", para-tertiobutylstyrene, the methoxy-styrenes, the chloro-styrenes, vinylmesitylene, divinyl benzene, vinyl naphthalene, etc.

The co-polymers may contain for example between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinyl aromatic units.

The polymers may have any microstructure that is a function of the polymerisation conditions used, in particular the presence or absence of a modifying and/or randomising agent and the quantities of modifying and/or randomising agent used. The polymers may for example be block, statistical, sequenced or micro-sequenced polymers, etc., and may be prepared in a dispersion or in solution.

Preferred diene synthetic rubbers are the polybutadienes and in particular those having a content of 1,2-units between 4% and 80% and those having a content of cis-1,4 bonds of more than 90%, the polyisoprenes, butadiene-styrene co-polymers and in particular those having a styrene content between 5% and 50% by weight and more particularly between 20% and 40% by weight, a content of 1,2-bonds of the butadiene part between 4% and 65%, and a content of trans-1,4 bonds between 30% and 80%, these having a total aromatic compound content between 5% and 50% and a glass transition temperature (Tg) between 0°C and -80 0 C, in particular those having a styrene content of between 25% and 30% by weight, a content of vinyl bonds of the butadiene part between 55% and 65%, a content of trans-1,4 bonds between 20% and 25% and a glass transition temperature between -20°C and -30 0

C.

In the case of butadiene-styrene-isoprene co-polymers, the suitable ones are those having a styrene content between 5% and 50% by weight and more particularly between and 40%, an isoprene content between 15% and 60% by weight and more particularly between 20% and 50% by weight, a butadiene content between 5% and 50% and more particularly between 20% and 40% by weight, a content of 1,2-units of the butadiene part between 4% and 85%, a content of trans-1,4 units of the butadiene part between 6% and a content of 1,2- plus 3,4-units of the isoprene part between 5% and 70%, and a content of trans-1,4 units of the isoprene part between 10% and The synthetic rubbers may be coupled and/or starred or alternatively functionalised with a coupling and/or starring or functionalising agent.

8 These rubbers may be vulcanised and or cross-linked by any of the known agents, such as sulphur, the peroxides, the bismaleimides, etc.

The composition according to the invention contains the usual fillers and additives such as carbon black, silica or any other reinforcing white filler, stearic acid, reinforcing resins, zinc oxide, activators, pigments, vulcanisation accelerators or retarders, anti-ageing agents such as anti-oxidants, anti-reversion agents, oils or various agents to facilitate use, tackiness promoting resins, metal adhesion promoters, anti-ozone waxes, silicon binding and/or covering agents, etc.

The compositions according to the invention can be used in a wide variety of applications and in particular for numerous rubber products, for example in tyre covers as buffer I compositions between a source of oxygen, in particular inflation air or the external atmosphere and a zone to be protected in the tyre cover. For example, these compositions may be used inside the internal calendering rubber, between this and the carcass ply, S; between the carcass ply and the crown plies, between the crown plies and the tread, between the carcass ply and the side walls, or even on the outside of the side walls.

e° A tyre cover according to the invention, the said cover being of the type comprising internal calendering rubber, a carcass ply extending from one bead wire to the other, crown plies, side walls ending in beads comprising at least one bead wire, and a tread, is characterised in that the said or each such buffer zone containing the said composition occupies at least one of the following positions: radially inside the said internal calendering rubber, between the said internal calendering rubber and the said carcass ply, between the said carcass ply and the said crown plies, between the said crown plies and the said tread, between the said carcass ply and the said side walls, inside or outside the said side walls, and inside or outside the said tread.

9 It is particularly preferable for the said tyre cover to be a heavy-duty tyre cover in which the said or each buffer zone containing the composition according to the invention is located within a reinforcing elastomer layer provided between the said internal calendering rubber and the said carcass ply.

This reinforcing layer acts in particular to protect the carcass ply from aggressions such as the diffusion of oxygen so that the said ply will preserve its original characteristics for as long as possible, and consequently increases the life of the heavy-duty tyre cover and if needs be the number of times it can be recapped.

The use of the iron compound according to the invention is very different from the known uses of iron compounds in the rubber industry, for example their known use as oxidising salts to promote the mastication of rubbers (peptising properties) or devulcanisation for recycling, these applications being described, for example, in the documents US-A-3 324 100, EP-A-157 079 and RU-A-2 014 339.

°o i As regards the process for obtaining a rubber-based product according to the present invention, this consists in incorporating the said iron (III) salt in the elastomer or elastomers contained in the buffer composition by working it in mechanically, to obtain the corresponding buffer zone.

According to another characteristic of the process, it consists in incorporating the said iron (III) salt in the said elastomer(s) at the same time as a filler intended to reinforce the said composition.

As regards the process according to the present invention for reducing the rolling resistance of a tyre cover, this consists in incorporating an iron (III) salt as defined above in an elastomer or in the elastomers constituting the said tyre cover, by working it in mechanically.

The invention will be easily understood with the help of the non-limiting examples given below.

These examples are either examples according to the invention, or ones not according to the invention that use compositions without any metallic derivative, or ones containing cobalt salts or even iron (III) salts that do not have the formula according to the invention specified earlier.

The oxidation-promoting efficacy of the iron or cobalt compounds is assessed by subjecting the compositions to ageing by thermal oxidation. The oxygen uptake is then measured by element analysis and the changes in mechanical properties such as the S modulus, hysteresis loss and rupture properties are determined.

o The tests are carried out under the following conditions: Vulcanisation Unless otherwise indicated, all the tests were carried out on specimens vulcanised by curing for 20 to 30 min at 150C.

*5 S Ageing by thermal oxidation i A ventilated stove at 85C is used. This temperature is regarded as representative of the temperatures encountered during the operation of tyre covers.

Hysteresis loss The hysteresis loss, or hysteresis (Ph) is measured by determining the energy lost at 60 0

C

on rebound compared with the energy put in, considering the sixth shock. The value, expressed as a percentage, is the difference between the energy supplied and the energy returned, referred to the energy supplied. The deformation for the losses measured is 11 Tensile tests These tests determine the elasticity stresses and rupture properties of the specimens tested. Unless otherwise indicated, they are carried out in accordance with the standard AFNOR-NFT-46002 of September 1988. During a second elongation after one cycle for accommodation purposes) the nominal secant modules (or apparent stresses, in MPa) are determined at 10% strain (M10) and at 100% strain (M100). The rupture stress Cr (in MPa) and the elongation Ar at rupture (in are also measured. All these tensile measurements are carried out under normal temperature and humidity conditions, in accordance with the standard AFNOR-NFT-40101 (December 1979).

In the examples below, the following basic composition (in phr) is used, this being prepared in a way known as such by using an internal mixer and then an external mixer.

***All the figures indicated are parts by weight (phr), and it is specified that the iron (III) is introduced into the internal mixer, for example a Banburry, at the same time as the carbon black, the ZnO, the stearic acid and the 6PPD.

Natural rubber 100 Carbon black N326 47 Sulphur DCBS 0.8 ZnO Stearic acid 0.9 6PPD in which: DCBS: N,N-dicyclohexyl-2-benzothiazolesulphenamide 6PPD: N-1,3-dimethylbutyl-N'-phenyl-paraphenylene diamine.

Starting with this basic composition, the following compositions are prepared.

Control compositions: o Composition TI: basic composition with no metallic derivative.

o Composition T2: o Composition T3: basic composition containing in addition 0.25 phr of cobalt equivalent in the form of cobalt acetylacetonate.

basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) acetylacetonate.

Preferred compositions according to the invention a Composition I1: U Composition 12: o Composition 13: basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) p-cyanobenzoate.

basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) p-butylbenzoate.

basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) p-toluiate.

basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) m-toluiate.

basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) p-methoxybenzoate.

basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) 2-naphthoate.

a Composition 14: o Composition 15: o Composition 16: o Composition 17: basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) benzoate.

o Composition 18: basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) o-toluiate.

o Composition 19: basic composition containing in addition 0.02 phr of iron equivalent in the form of iron (III) 1-naphthoate.

The iron (III) salts respectively included in compositions Il to 19 according to the invention (salts of p-cyanobenzoic, p-butylbenzoic, p-toluic, m-toluic, p-methoxybenzoic, 2-naphthoic, benzoic, o-toluic and 1-naphthoic acids) were all synthesised as described below which, as an example, relates to the synthesis of m-toluic acid (the quantity of acid varying according to the acid used).

In a 250-ml Erlenmeyer flask, 15 g (or 0.11 mole) of m-toluic acid are mixed with 10 ml of water, with stirring. Using a dropping funnel, a previously prepared solution of sodium hydroxide (4.41 g or 0.11 mole of sodium hydroxide dissolved in 100 ml of water) are added a drop at a time. The solution is stirred for 20 min.

A solution of FeCl 3 (5.95 g or 0.037 mole dissolved in 100 ml of water) is added in a single addition. A precipitate forms and the suspension obtained is filtered and washed three times in 500 ml of water each time, to eliminate the sodium chloride formed.

This yields 15.7 g of the product which, after drying in a stove at 50 0 C under vacuum, is obtained as a brown powder. Element analysis confirms the formation of the iron (III) salt of m-toluic acid.

14 As regards the aforementioned vulcanisation at 150 0 C of each composition obtained, it should be noted that this lasted 20 min for the said control composition T2, but 30 min for the other compositions.

a) Using these compositions, the strain moduli M10 and M100 and the hysteresis losses were determined. The results are shown in Table 1.

Table 1 Tl T2 T3 II 12 13 14 15 16 17 18 19 4.5 5.9 4.6 4.5 4.7 4.7 4.7 4.7 4.7 4.6 4.1 4.2 (MPa) M100 2.2 2.6 2.3 2.2 2.3 2.3 2.3 2.3 2.3 2.3 2.1 2.1 (MPa) Ph 17 21 18 17 18 17 18 18 18 17 16 16 Table 1 shows that the iron (III) salts of p-cyanobenzoic, p-butylbenzoic, p-toluic, mtoluic, p-methoxybenzoic, 2-naphthoic, benzoic, o-toluic and 1-naphthoic acids in the respective compositions II to 19 according to the invention, modify the characteristics of the basic composition less than does cobalt acetylacetonate in the control composition T2, and that the relative hysteresis loss of these compositions I1 to 19 is considerably lower than that of the said control composition T2.

b) Experiments were carried out to demonstrate the ability of compositions I1 to 19 according to the invention to fix oxygen after thermal oxidation for 2 weeks at comparing it with the control compositions TI, T2 and T3.

The results of these thermal oxidation tests are shown in Table 2 below, which gives the percentage by weight of oxygen fixed.

Table 2 Tl T2 T3 11 12 13 14 15 16 17 18 19 At 1.2 1.6 1.8 1.7 1.8 1.7 1.7 1.6 1.7 1.8 1.6 0

C,

2 weeks Table 2 shows that the iron (III) salt of p-cyanobenzoic, p-butylbenzoic, p-toluic, mtoluic, p-methoxybenzoic, 2-naphthoic, benzoic, o-toluic and 1-naphthoic acids enable composition I1 to 19 to fix an amount of oxygen that is essentially the same as or larger than that obtained with the control composition T2 containing cobalt acetylacetonate, the amount fixed being substantially larger compared with that of control composition T1 containing no iron or cobalt compound.

Basic compositions containing other metallic salts described as oxidation promoters in the literature, introduced in amounts such as to give an isomolar quantity of metal in relation to control composition T2, such as the salts of manganese (II) or (III) and in particular the carbonate, acetate or acetylacetonate of manganese manganese (III) acetylacetonate, the salts of molybdenum (IV) and in particular molybdenum (IV) sulphide and oxide, the salts of copper (II) and in particular copper (II) hydroxide, carbonate, stearate, acetate or acetylacetonate, the salts of chromium (III) and in particular chromium acetylacetonate, and cerium (IV) sulphate, lead to results similar to those obtained with control composition T1 which contains no metallic salt.

c) Experiments were also carried out to determine the moduli and rupture properties and the hysteresis of compositions I1 to 19 according to the invention compared with the control compositions T1, T2 and T3, after applying to each composition the aforesaid treatment of ageing by thermal oxidation (at 85°C for 2 weeks).

16 The results are given in Table 3 below, which shows, for each composition, the change in the values of the various parameters compared with those for the same composition before the thermal oxidation treatment.

Table 3 signifies that the specimen ruptured) Tl T2 T3 II 12 13 14 15 16 17 18 19 +59% +74% +109% +274% +86% +88% +73% +68% +68% +67% +51% M100 +138% +95% +100% Ph +30% +45% +67% +45% +40% +31% +38% +41% +50% +56% Ar -78% -92% -89% -90% -90% -89% -88% -90% -90% not not meas- measured ured Cr -71% -86% -86% -85% -86% -85% -83% -85% -81% not not meas- measured ured C 9 In relation to the results of paragraph b) above, this Table 3 shows that the compositions 11 to 19 according to the invention shows an ability to fix oxygen which is distinctly better compared with the said known composition T2, whereas following the treatment by thermal oxidation, they show mechanical elongation and rupture properties which have evolved almost analogously after the thermal oxidation treatment.

Claims

1. Product based on rubber, of the type comprising at least one buffer zone provided in order to trap oxygen external to the said product so as to protect from oxidation at least one sensitive zone of the said product, in which the said or each such buffer zone contains a basic composition based on at least one elastomer containing at least one iron (I1I) salt provided to activate oxidation in the said composition, characterised in that the said salt is an iron (III) salt of an aromatic mono-carboxylic acid, the said acid comprising one or more aromatic rings which may or may not be substituted, and having one or other of the following generic fonnulas: (R)n COOH COOH COOH and D: COOH (R)n *o 0(R)n n and D: in which n is an integer ranging from 1 to 5, and L. 18 in formulas A, B and C, R is a hydrogen atom, an alkyl group which may or may not be substituted having from 1 to 8 carbon atoms, an alkoxyl group or a cyano group, and in formula D, R is an aryl group which may or may not be substituted having from 6 to 10 carbon atoms.

2. Product based on rubber according to Claim 1, characterised in that the said acid is a cyanobenzoic acid such as p-cyanobenzoic acid.

3. Product based on rubber according to Claim 1, i characterised in that the said acid is benzoic acid or an alkylbenzoic acid such as p-butylbenzoic acid.

9. o 4. Product based on rubber according to Claim 1, characterised in that the said acid is a toluic acid such as p-toluic, m-toluic or o-toluic acid. g* Product based on rubber according to Claim 1, characterised in that the said acid is an alkoxybenzoic acid such as methoxybenzoic acid. 6. Product based on rubber according to Claim 1, characterised in that the said acid is a a naphthoic acid. 7. Product based on rubber according to Claim 1, characterised in that the quantity of the said iron (III) salt in the said composition ranges from 0.01 to 0.03 phr of iron equivalent. 19 8. Tyre cover, characterised in that it consists of a product based on rubber according to any one of the preceding claims. 9. Tyre cover according to Claim 8 the said tyre cover being of the type which comprises an internal calendering rubber, a carcass ply that extends from one bead wire to the other, crown plies, side walls that end in beads comprising at least one bead wire, and a tread, characterised in that the said or each such buffer zone containing the said composition occupies at least one of the following positions: radially inside the said internal calendering rubber, between the said calendering rubber and the said carcass ply, between the said carcass ply and the said crown plies, between the said crown plies and the said tread, between the said carcass ply and the said side walls, inside or outside the said side walls, and/or inside or outside the said tread. Heavy-duty tyre cover according to Claim 9, characterised in that the said or each said buffer zone containing the said composition is located within a reinforcing elastomer layer provided between the said internal calendering rubber and the said carcass ply.

11. Process for obtaining a product based on rubber according to any one of Claims 1 to 7, characterised in that it consists of incorporating by mechanical work the said iron (III) salt into the elastomer or elastomers contained in the said composition, to obtain the said or each such buffer zone.

12. Process for obtaining a product based on rubber according to Claim 11, the said product comprising a reinforcing filler, characterised in that it consists in incorporating the said iron (III) salt into the said elastomer or elastomers at the same time as a filler provided to reinforce the said composition.

14. Process for reducing the rolling resistance of a tyre cover, characterised in that it consists in incorporating by mechanical work, into an elastomer or elastomers constituting the said tyre cover, an iron (III) salt as defined in any one of Claims 1 to 7. DATED this 19th day of September 2005 SOCIETE DE TECHNOLOGIE MICHELIN and MICHELIN RECHERCHE ET TECHNIQUE S.A. WATERMARK PATENT TRADE MARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA P20607AU00