Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2000-05-09
2004-01-13
Ball, Michael W. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S537000, C152S510000, C152S525000, C524S394000, C524S398000
Reexamination Certificate
active
06675851
ABSTRACT:
BACKGROUND
The present invention relates to a rubber-based product, a method for producing the product and to a method for reducing the rolling resistance of a tire formed from said product.
One of the main concerns of tire manufacturers is to increase the life of tires. In particular, it is important to increase endurance, with regard to oxidation of the rubber compositions, the metal or textile reinforcements and the interfaces between the rubber compositions and these reinforcements in tires.
One known process for reducing such oxidation phenomena involves restricting the quantity of oxygen, which arrives in a zone of the tire which is particularly sensitive to oxidation, whether in the inflation air or the outside air. Thus, a butyl rubber layer, which is impermeable to oxygen, has, for a long time, been used against the inner wall of tires by manufacturers. Unfortunately, the butyl rubber is not totally oxygen-impermeable, and cannot prevent oxidation of the tire even from reduced oxygen flow during long term use.
Other materials which are more airtight than butyl rubber have been proposed to reduce tire oxidation as described, for example, in U.S. Pat. No. 5,236,030, U.S. Pat. No. 4,874,670, U.S. Pat. No. 5, 036,113, EP-A-337 279, U.S. Pat. No. 5,040,583 and U.S. Pat. No. 5,156,921. However, these materials are expensive and their use in tires causes many problems.
Another process for avoiding the problems of oxidation involves chemically trapping the oxygen by accelerated thermo-oxidation of a rubber composition which acts as a buffer, arranged between a main oxygen source and the zone which it is desired to protect from oxidation. By way of example, such a buffer composition may be located between the inner face of the tire, which may possibly be covered with butyl rubber, and the carcass ply, in order to reduce the quantity of oxygen which comes into contact with this ply from the inflation air. Such an arrangement is seen, in particular, in tires intended to be mounted on heavy vehicles. In order to accelerate the fixing of the oxygen, these buffer compositions comprise a metal salt which catalyzes oxidation, in particular a cobalt salt. The effect of this salt is to activate homolytic decomposition of the hydroperbxides produced upon aging resulting from the afore-mentioned oxidation phenomena. The metal salt is preferably introduced in an amount of 0.2 to 0.3 parts by weight (“phr”) in equivalent of cobalt to 100 parts by weight of the elastomer in the buffer composition. The amount of oxygen which can be trapped by this buffer composition is increased by about 50 to 100%, compared to the same composition without cobalt salt. Unfortunately, however, this improvement with regard to oxidation has been shown to be accompanied by a major increase in hysteresis losses of the buffer composition resulting from the significant quantity of cobalt salt introduced in the elastomer. This increase in hysteresis losses results, first, in an undesired self-heating of the composition, which results in a shortened life. Second, there is an undesired increase in the rolling resistance, which is contrary to the aim of tire manufacturers to restrict rolling resistance as far as possible in order to reduce fuel consumption.
For these reasons, the use of buffer compositions, no matter how attractive, has not been developed as much as expected.
European Patent application EP-A-507 207 describes a method for trapping oxygen by means of a buffer elastomeric composition, which is contained in a layer of a package. This buffer composition is in particular characterized by the presence of a transition metal salt designed to activate oxygen fixation. As above mentioned, the metal salts that are preferably described therein are cobalt salts. Other metals such as manganese or even iron are contemplated, but not in relation to specified salts.
SUMMARY
The present invention is based on the unexpected finding that the above described disadvantages can be greatly reduced by using specific iron salts, instead of cobalt salts, in antioxidation buffer compositions, to produce a rubber-based product for use in tires. The buffer compositions comprising such iron salts are used to provide a buffer zone to trap the oxygen external to said product in order to protect at least one sensitive zone of the rubber based product from oxidation. The buffer compositions comprise a composition containing at least one elastomer which comprises at least one iron (III) salt intended to activate the oxidation in said composition. More precisely, the elastomer composition comprises an iron salt selected from iron (III) acetylacetonate and an iron (III) salt of a carboxylic acid having the formula
Fe(C
n
H
2n
O
2
)
3
in which
n
is between 6 and 23.
Iron (III) salts of carboxylic acids which correspond to this formula include salts of hexanoic, 2-ethylhexanoic, lauric, tridecanoic, myristic, pentadecanoic, palmitic, heptadecanoic, stearic, nonadecanoic, eicosanoic, heneicosanoic, docosanoic and tricosanoic acids. Preferred salts include iron (III) acetylacetonate, iron (III) hexanoate, iron (III) 2-ethylhexanoate, or iron (III) laurate.
According to a further embodiment of the invention, the iron salt is an iron (III) salt of a fatty acid having the formula
Fe(C
n
H
2n
O
2
)
3
in which
n
is between 13 and 23.
Preferably, said iron (III) salt is iron (III) stearate or iron (III) palmitate.
Preferably, the quantity of the iron (III) compound in the composition comprises from 0.01 to 0.02 phr of equivalent in iron, wherein “phr” means parts by weight of iron (or other metal) equivalent to 100 parts by weight of the elastomer or of all the elastomers present in the composition.
DETAILED DESCRIPTION
The composition according to the invention is based on natural or synthetic rubber, or a blend of two or more of these rubbers. Synthetic rubbers capable of being used in the composition according to the invention include diene rubbers such as polyisoprene, polybutadiene, mono-olefinic rubbers such as polychloroprene, polyisobutylene, styrene-butadiene or styrene-butadiene-isoprene copolymers, acrylonitrile-butadiene-styrene copolymers and ethylene-propylene-diene/terpolymers.
Preferred synthetic rubbers include the diene rubbers, in particular any homopolymer obtained by polymerization of a conjugated diene monomer having 4 to 12 carbon atoms, any copolymer obtained by copolymerization of one or more conjugated dienes with one another or with one or more vinyl aromatic compounds having 8 to 20 carbon atoms.
Suitable conjugated dienes are, in particular, 1,3-butadiene, 2-methyl-1,3-butadiene, the 2,3-di(C
1
to 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 and 2,4-hexadiene.
Suitable vinyl aromatic compounds are, in particular, styrene, ortho-, meta-and para-methylstyrene, the commercial mixture “vinyl-toluene”, para-tertiobutylstyrene, the methoxy-styrenes, the chloro-styrenes, vinyl mesitylene, divinyl benzene and vinyl naphthalene.
The copolymers comprise between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinyl aromatic units. The elastomers may have any microstructure, which is a function of the polymerization conditions used, in particular of the presence or absence of a modifying and/or randomizing agent and the quantities of modifying
and/or randomizing agent used. The elastomers may, for example, be block, statistical, sequenced or microsequenced elastomers, and may be prepared in dispersion or in solution.
Preferred synthetic diene rubbers are polybutadienes, particularly those having a 1,2 bond content of between 4% and 80% and those having a content of cis-1,4 bonds of more than 90%, 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% by weight, a 1,2 bond content of the butadiene part of between 4% and 65%, a
Masson Francois
Renault Francis
Baker & Botts L.L.P.
Ball Michael W.
Fischer Justin
Michelin & Cie
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