WO2002096672A2

WO2002096672A2 - Runflat tire

Info

Publication number: WO2002096672A2
Application number: PCT/US2002/017174
Authority: WO
Inventors: Michael D. Grah
Original assignee: Societe De Technologie Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2001-05-29
Filing date: 2002-05-29
Publication date: 2002-12-05
Also published as: WO2002096677A1; AU2002316181A1; AU2002316181A8; WO2002096672A3

Abstract

The present invention comprises a tire with a support system comprising two adjacent crescent-shaped inserts (22, 24) interior to the sidewall (30). When the tire loses inflation pressure, perhaps due to sudden puncture, the inserts provide sufficient support for the tire to allow continued normal, comfortable operation of the vehicle until the tire can be repaired or replaced. The first crescent- shaped insert (24), which is nearer the exterior sidewall, has a lower modulus of elasticity (is less stiff) than the second crescent- shaped insert (22). The first insert (24) is made of an elastomer (i.e. rubber) cured with a sulfur system, whereas the second insert (22) is made of an elastomer cured with peroxide catalyst and metal salt of an unsaturated carboxylic acid, e.g., zinc dimethacrylate.

Description

RUNFLAT TIRE Field of the Invention

The invention is in the field of pneumatic tires, and specifically is in the field of pneumatic tires that function after losing all inflation pressure.

Background

There is an ongoing effort by automobile manufacturers to eliminate the spare tire in order to reduce vehicle curb weight, increase available space within the vehicle, and provide operator convenience. This is particularly true for vehicles having higher comfort specifications, such as conventional luxury, family or urban-economy-type vehicles. This is even true for the sports utility vehicle, and for the new generation of electrical and hybrid-type vehicles which have critical space and weight restrictions. Furthermore, with increased travel on multi-lane high-speed highways, safety becomes a major consideration in dealing with a flat tire. Even if a vehicle with a flat can be maneuvered to the roadside, changing a flat can be quite hazardous, and usually should not be attempted. Thus, the capability to readily reach the next exit is highly desirable should a flat occur. A promising product is the recently introduced "runflat" tire. This is a pneumatic tire that functions for a certain period to support a vehicle even after inflation pressure has been lost. This tire reduces the need for a spare tire and ancillary equipment. Therefore, in some cases it may achieve substantial savings in vehicle weight, and increase the space for other automotive systems and cargo. Numerous variations of runflat tires have been developed. These involve changes to the structure of the tire itself and modifications to the rim to hold and support the flat tire. Each variation is limited by restrictions on vehicle speed, length of travel, zero inflation pressure handling, and the magnitude of the lateral accelerations that force the bead of the tire off the rim seat. A number of general features of runflat tires have been disclosed that permit some degree of operation of a vehicle when tire pressure is lost. These features include thickened tire sidewalls, sidewall reinforcing plies, tire bead seat and vehicle rim configuration modifications, tire sidewall to rim flange contact, and tire belt package edge modifications. Each of these features can be used to help solve known runflat performance problems. As mentioned above, one feature of some runflat tires is thickened sidewalls to support the vehicle after loss of inflation pressure. Such a sidewall, as the tire is viewed in cross-section, presents a crescent-shaped mass of rubber on the inside of the tire's sidewalls. On complete deflation of the tire, the crescent-shaped mass is put into compression while the carcass cord reinforcement is in tension, thereby preventing total collapse of the sidewall. Hence the rolling radius of the tire is maintained at a relatively large percentage of the inflated rolling radius of the tire. An illustrative but not exhaustive list of patents that disclose a thick sidewall design is: U.S. Patent Nos. 6,022,434; 5,968,294; 5,868,190; 5,795,416; 5,511 ,599; 5427,166, all assigned to Michelin Recherche et Technique, S.A. (CH); U.S. Patent No. 4,067,374 assigned to B.F. Goodrich; U.S. Patent No. 4,779,658 assigned to Bridgestone Corp.; and French Patent No. 2,469,297 (FR).

U.S. Patent Nos. 3,994,329 and 4,287,924 both assigned to Pneumatiques, Caoutchouc Manufacture et Plastique, Japanese Patent No. 3- 4370 (JP), and French Patent Nos. 1 ,502,689 and 2,458,407 also disclose sidewall supports.

The extensive flexing of the runflat tire and the large deflections associated with the deflated rolling tire cause the various components within the runflat tire undergo gradual breakdown. High component temperatures also contribute to the breakdown of the materials in the runflat tire. Furthermore, presently available runflat constructions can alter the normal ride characteristics of a vehicle.

the vehicle during normal operation, but which after a significant influence after loss of tire inflation pressure comfortably preserves the load supporting and cornering capabilities of the vehicle. The tire should have less deflection when deflated, allow a trip to continue for longer periods, and permit the continuation of almost normal operation of the vehicle. This is particularly important for a luxury car, family or urban-economy vehicle, which may have relatively soft suspension system.

It is specifically an object of the present invention to increase the 5 distance a pneumatic tire may be run at zero inflation pressure.

It is also an object of the present invention to provide a novel rubber composite reinforcing structure for a run-flat pneumatic tire.

It is a further object of the invention to provide a pneumatic tire that provides a comfortable ride at zero inflation pressure, as well as at normal o inflation pressure.

It is a further object of the invention to provide a pneumatic tire that provides good handling and load support characteristics at zero inflation pressure.

5 Summary of the Invention

The invention is a pneumatic tire comprising at least one reinforced radial carcass layer having a crown portion and a pair of end portions each anchored in a respective spaced-apart bead; a tread outward of said crown portion of said carcass layer and a reinforced belt portion between said tread o and said carcass layer; a pair of sidewall portions each adjacent said carcass layer and extending radially from a respective bead to a respective lateral edge of said tread; an inner-liner interior to said carcass layer to retain air inside a cavity of the tire; each one of said pair of sidewalls having a crescent-shaped insert for providing continuous running with the loss of inflation pressure. Said 5 tire includes a first crescent-shaped insert placed to the interior of said at least one carcass layer, said first insert having a first compound which includes a sulfur-accelerated system for curing; a second crescent-shaped insert placed

crescent-shaped insert, said second insert having a second compound which o includes a peroxide catalyst and a metal salt of a carboxylic acid, preferably an acrylic acid, and wherein said second crescent-shaped insert has a higher modulus of elasticity than said first crescent-shaped insert.

In one embodiment of the invention, the metal salt of the acrylic acid comprises zinc dimethacrylate. In another embodiment of the invention, the tire is a bias-ply tire.

Description of the Drawings

Figure 1 is a cross-section of a runflat tire showing crescent-shaped reinforcing inserts according to one embodiment of the invention.

Detailed Description of the Invention

The present invention comprises a tire with a support system comprising a set of two inserts interior to each of the sidewalls. When the tire loses inflation pressure, perhaps due to sudden puncture, the inserts provide sufficient support for the tire to allow continued normal operation of the vehicle until the tire can be repaired or replaced. In some circumstances, the vehicle might have to be driven dozens of miles before service can be obtained. The first insert, which is next to the sidewall has a lower modulus of elasticity (is less stiff) than the second crescent-shaped insert. Placing a stiff insert next to the sidewall might lead to cracking of the sidewall. The first insert is made of an elastomer (i.e., rubber) cured with a sulfur system, whereas the second insert is made of an elastomer (i.e., rubber) cured with a peroxide co-agent system. The higher stiffness of the second insert means it will flex less as the tire rolls in the uninflated condition. Less flexure means less heat is generated, heat which could act to break down the structural components of the tire. Less flexure of the sidewall of the uninflated tire also improves the handling characteristics of the vehicle. The higher stiffness of the second insert also rn ariB :lτatart rm τ 4ηBeτt .arι-l3 -ns d as cumpared-tt ih -pτior^"aτtn^^~thiπner insert has less mass, and causes less hysteretic heat build-up when the tire is in the normally inflated condition.

The peroxide co-agent curing system contains a metal salt of an unsaturated carboxylic acid. In one embodiment of the invention, certain polymerizable metal salts of alpha, beta-ethylenically unsaturated carboxylic acids are employed. These include methacrylic acid, ethacrylic acid, acrylic acid, cinnamic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and the like. The metal may be selected from the group consisting of sodium, potassium, iron, magnesium, calcium, zinc, barium, aluminum, tin, zirconium, lithium, cadmium, and cobalt. Zinc is preferred. A particularly preferred monomer for this use is zinc dimethacrylate, which may also be referred to as a metal salt. Suitable zinc salts of acrylic acid are described in Sartomer Co., Inc., "New Metallic Coagents for Curing Elastomers", April 1998. Other suitable acrylates are disclosed in Sartomer Co., Inc., Sartomer Application Bulletin, May 1998, "Chemical Intermediates - Design Unique Polymers with Sartomer's Specialty Monomers," and Sartomer Co., Inc., Sartomer Application Bulletin, October 1999, "Glass Transition Temperatures of Sartomer Products." Both publications are incorporated by reference. In one embodiment of the invention, the metal salt of the carboxylic acid is present in an amount from 5 to 90 parts by weight per hundred parts by weight of rubber. In a more preferred embodiment of the invention, the metal salt is present in an amount from 10 to 60 parts by weight per hundred parts by weight of rubber. In a most preferred embodiment of the invention, the metal salt is present in an amount from 20 to 50 parts by weight per hundred parts by weight of rubber.

In the present invention, zinc dimethacrylate or other metal salt of a carboxylic acid, is combined with at least one of the rubber polymers disclosed above in a grafting reaction such that the polymer of the metal salt is grafted onto the polymeric backbone. Zinc dimethacrylate may be prepared by reacting with agitation zinc oxide and methacrylic acid in an amount of from about 0.5 to about 0.6 moles of zinc oxide per mole of methacrylic acid in a liquid—medium - (e.g. water or a volatile organic liquid such as a liquid hydrocarbon). The present inventors have found that the two inserts, though made with different curing systems, do not separate from one another during operation of the vehicle in the flat-tire mode. Furthermore, the second insert, cured with the metal salt/acrylic acid/peroxide system, has higher thermal stability, permitting longer operation of the tire in the uninflated condition. It has been found that more than two inserts can be used, but at least two inserts, as defined herein, work well. In another embodiment of the invention, a series of three or more adjacent inserts provides support for each of the sidewalls, the adjacent inserts having a gradient of elasticity. The insert having the lower modulus of elasticity would be next to the sidewall, with the modulus of elasticity increasing from that point toward the interior of the tire. In one embodiment of the invention, the inserts are crescent-shaped. When the tire is inflated, this support system contributes relatively negligible mass, rolling resistance, and stiffness (which affects comfort) to the tire. In the deflated mode, this support system exhibits high stiffness, low hysteresis, thermomechanical stability (at dynamic strain levels of greater than 10%), and enhanced thermo-oxidative stability. Figure 1 shows one embodiment of the present invention. Runflat tire 1 is shown in partial section having a rim contacting bead area 10, sidewall section 30, and crown tread 3. The bead area 10 includes bead wire 12, bead core 43 that anchors carcass-reinforcing ply 42. Underlying the tread 3 is the belt package 50 comprising reinforcing plies. In the sidewall 30 is the support that is comprised of a first crescent-shaped insert 24 and second crescent- shaped insert 22 contacting each other along interface 23. Innerliner 26 provides the pneumatic seal for the tire where under inflation. The respective thickness of insert 22 and 24 are designated as T1 and T2. Thicknesses T1 and T2 will vary depending upon the type of tire and the load it is expected to support. In some embodiments, T1 and T2 might be about one centimeter thick at their thickest points. Both inserts 22 and 24 are elastomeric, and in one embodiment the elastomer is a rubber compound. In one embodiment of the invention, each of inserts 22 and 24 have a major concave surface and a major convex surface. The convex surface of insert 22 lies adjacent to the concave surface of insert 24. First insert 24 is nearer the sidewall than second insert 22.

In otherwords, supposing the crescent shape of the inserts to be an arc with a radius drawn from an imaginary centerpoint, the radius drawn from the centerpoint to insert 22 is shorter than the radius drawn to insert 24. Inserts 22 and 24 are radially adjacent to one another.

Still referring to Figure 1 , elastomeric crescent-shaped second insert 22 in the sidewall is compounded to have a peroxide and co-agent cured system. Though the present invention is not bound by theory, it is thought that this obtains a three-dimensional covalently cross-linked elastomer network having carbon-carbon cross-links, instead of just sulfur-sulfur or sulfur-carbon crosslinks. The rubber employed in insert 22 may be a natural rubber or a synthetic rubber that is curable with a metal salt of a carboxylic acid and a peroxide cure system. Blends of such rubbers may also be employed. Such rubbers include, but are not limited to diene elastomers. "Diene" elastomer or rubber is understood to mean an elastomer resulting at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers bearing two double carbon- carbon bonds, whether conjugated or not). In general, "essentially unsaturated" diene elastomer is understood here to mean a diene elastomer resulting at least in part from conjugated diene monomers, having a content of members or units of diene origin (conjugated dienes) which is greater than 15% (mol %).

Thus, for example, diene elastomers such as butyl rubbers or copolymers of dienes and of alpha-olefins of the EPDM type do not fall within the preceding definition, and may in particular be described as "essentially saturated" diene elastomers (low or very low content of units of diene origin which is always less than 15%).

Within the category of "essentially unsaturated" diene elastomers, "highly unsaturated" diene elastomer is understood to mean in particular a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

These definitions being given, the following are understood more particularly to be meant by diene elastomer capable of being used in the compositions according to the invention:

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

(b) - any copolymer obtained by copolymerisation of one or more dienes conjugated together or with one or more vinyl aromatic compounds having

8 to 20 carbon atoms;

(c) - a ternary copolymer obtained by copolymerisation of ethylene, of an O- olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having 6 to 12 carbon atoms, such as, for example, the elastomers obtained from ethylene, from propylene with a non-conjugated diene monomer of the aforementioned type, such as in particular 1 ,4-hexadiene, ethylidene norbomene or dicyclopentadiene;

(d) - a copolymer of isobutene and isoprene (butyl rubber), and also the halogenated, in particular chlorinated or brominated, versions of this type of copolymer.

Suitable conjugated dienes include 1 ,3-butadiene, 2-methyl-1 ,3- butadiene, 2,3-di(Cι-C₅ alkyl)-1 ,3-butadienes such as, for instance, 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, for example, styrene, ortho-, meta- and para-methylstyrene, the commercial mixture "vinyltoluene", para-tert.-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene. The copolymers may contain 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 polymerisation 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, sequential or microsequential elastomers, and may be prepared in dispersion or in solution; they may be coupled and/or starred or alternatively functionalised with a coupling and/or starring or functionalising agent.

In summary, in one embodiment of the invention, the diene elastomer of the composition according to the invention is selected from the group of highly unsaturated diene elastomers which consists of polybutadienes (BR), polyisoprenes (IR), natural rubber (NR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

Such copolymers are more preferably selected from the group which consists of butadiene-styrene copolymers (SBR), butadiene-isoprene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene-butadiene- styrene copolymers (SBIR). As used herein, "rubber" and "elastomer" are synonymous.

[see also Sartomer Co., Inc., "Sartomer Application Bulletin: Basic Principles of Peroxide-Coagent Curing of Elastomers," April 1997, incorporated by reference.]

Peroxides which may be employed to catalyze the curing of the elastomer of crescent-shaped insert 22 include, but are not limited to: di-cumyl peroxide, bis-(tert-butyl peroxy)-diisopropyl benzene, t-butyl perbenzoate, di- tert-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxide hexane, etc. Amounts of peroxide curing agents included in the composition will depend upon the elastomer and coagent loading utilized. In general, such amounts may range from about 0.5 parts per hundred weight to about 5.0 parts per hundred weight of elastomer. Zinc dimethyl methacrylate may be formed from the combination of zinc oxide and methacrylic acid.

In one embodiment of the invention, insert (22) is composed of a blend of natural rubber and polybutadiene ranging from 100% (by weight) natural rubber to 20% natural rubber/80% polybutadiene (by weight). Insert (22) also may contain carbon black (up to 120 parts per hundred weight of elastomer) and/or precipitated silica (up to 90 parts per hundred weight of elastomer).

In one embodiment of the invention, insert 22 has a shore A hardness greater than 74, and preferably greater than 80, while insert 24 has a shore A hardness greater than 90 or 95. In one embodiment of the invention, insert 22 has an elastic modulus greater than 35 or 40 kg/(cm squared) when the elongation strain is 100 percent, and insert 22 has an elastic modulus greater than 65 or 70 kg/(cm squared) when the elongation strain is 100 percent.

The remaining portions of the tire include rubber components with conventional sulfur-accelerated vulcanization systems to obtain multiple carbon-sulfur and sulfur-sulfur links. Elastomers which may be employed to form crescent-shaped insert 24 include, but are not limited to those elastomers listed above for insert 22. As stated above, the elastomers would be employed in a sulfur-cured system for insert 24. In one embodiment of the invention, it is desirable that crescent-shaped insert 22 have a modulus of elasticity of between 10 — 50 MPa at 10% elongation, while crescent-shaped insert 24 has a modulus of elasticity of between 5-15 MPa at 10% elongation. One embodiment of the invention is a pneumatic tire having enhanced physical properties and run-flat endurance, where at least one reinforced radial carcass layer has a crown portion and a pair of end portions each anchored in a respective spaced apart bead; a tread outward of said crown portion of said carcass layer and a reinforced belt portion between said tread and said carcass layer; a pair of sidewall inserts each adjacent said carcass layer and extending radially from a respective bead to a respective lateral edge of said tread; and there is an innerliner interior to said carcass layer to retain air inside a cavity of the tire. The improvement in this tire is in that each one of said pair of sidewalls has inserts for providing continuous running with the loss of inflation pressure. The pair of sidewalls each includes a first insert inserted to the interior of said at least one carcass layer, the first insert comprising rubber having a sulfur-accelerated system for curing. The second insert is inserted to the interior of the first insert, and has a common interface with the first insert. The second insert comprises rubber and has a peroxide and a co-agent for curing. The second insert has a higher modulus of elasticity than the first insert.

The co-agent comprises a metal salt of a carboxylic acid. The metal salt may comprise a metal selected from the group consisting of sodium, potassium, iron, magnesium, calcium, zinc, barium, aluminum, tin, zirconium, lithium, cadmium, and cobalt and mixtures thereof. The carboxylic acid is selected from unsaturated carboxylic acids. In one embodiment of the invention, the carboxylic acids are selected from the group consisting of methacrylic acid, ethacrylic acid, acrylic acid, cinnamic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and mixtures thereof.

The peroxide may be selected from the group consisting of di-cumyl peroxide, bis-(tert-butyl peroxy)-diisopropyl benzene, t-butyl perbenzoate, di- tert-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxide hexane and mixtures thereof. The metal salt of the carboxylic acid is preferably zinc dimethacrylate. In one embodiment of the invention, the first insert has modulus of elasticity at ten percent unit strain in a range of about 5 mega Pascals to about 15 mega Pascals and the second insert has a modulus of elasticity at ten percent unit strain in a range of about 10 mega Pascals to about 50 mega Pascals.

Another embodiment of the invention is a pneumatic tire, the improvement comprising multiple sidewall stiffening inserts, where: (a) a first stiffening insert comprises a sulfur-curable rubber composition; and

(b) a second stiffening insert comprises a peroxide-curable rubber composition; and the first and second inserts are adjacent each other and in contact along a common interface. The first insert may be crescent-shaped. It may comprise a mixture of rubber, a metal salt of an acrylic acid, and a peroxide curing agent. The rubber is selected from the group consisting of natural rubbers and synthetic rubbers (see listing above).

In one embodiment of the invention, the metal salt carboxylate is selected from the group consisting of zinc diacrylate and zinc di-methacrylate. In one embodiment of the invention, the second insert comprises 5 to 90 parts of metal salt of a carboxylic acid per hundred parts by weight of rubber. In another embodiment of the invention, the first insert comprises 10 to 60 parts of metal salt of a carboxylic acid per hundred parts by weight of rubber. In another embodiment of the invention, the first insert comprises 20 to 50 parts of metal salt of a carboxylic acid per hundred parts by weight of rubber.

A tire according to the invention may be, for example, a bias-ply tire or a radial tire.

In one embodiment of the invention an insert is comprised of a blend of natural rubber and polybutadiene wherein the polybutadiene ranges from zero percent by weight to eighty percent by weight, and the natural rubber ranges from one hundred percent by weight to twenty percent by weight. The inserts may further comprise a filler such as carbon black and silica. In one embodiment, the filler comprises 0 to 120 parts by weight per hundred parts rubber. In another embodiment, the filler comprises 0 to 65 parts by weight per hundred weight of rubber. The inserts may also be crescent shaped. In another embodiment of the invention, a tire comprises a sidewall, where the sidewall includes at least two adjacent crescent-shaped inserts. Each insert has a major concave surface and a major convex surface, where the major concave surface of the first insert lies adjacent to the major convex surface of the second insert, and the first insert is substantially nearer the sidewall than the second insert. The second insert comprises a peroxide- curable rubber composition including a metal salt of a carboxylic acid, and the first insert comprises a sulphur-curable rubber composition. In one embodiment of the invention, the metal salt of the carboxylic acid is selected from zinc diacrylate and zinc dimethacrylate.

In another embodiment of the invention, a tire comprises a sidewall, where the sidewall includes at least two radially adjacent crescent-shaped inserts, wherein said radius is drawn from the centerpoint of the tire. The first insert is substantially nearer the sidewall than the first insert, the second insert comprises a peroxide-curable rubber composition including a metal salt of a carboxylic acid, and wherein said first insert comprises a sulphur-curable rubber composition.

In one embodiment of the invention, the first insert has a shore A hardness greater than 72, and an elastic modulus greater than 35 kg/cm² when the elongation strain is one hundred percent, and wherein the second insert has a shore A hardness greater than 90, and an elastic modulus greater than 65 kg/cm² when the elongation strain is one hundred percent. In another embodiment of the invention, the first insert has a shore A hardness greater than 75, and an elastic modulus greater than 40 kg/cm² when the elongation strain is one hundred percent, and wherein the second insert has a shore A hardness greater than 95, and an elastic modulus greater than 70 kg/cm² when the elongation strain is one hundred percent. In one embodiment of the invention, the second insert comprises 20 to 50 parts of metal salt of a carboxylic acid per hundred parts by weight of rubber. In another embodiment of the invention, the second insert further comprises a filler comprising 0 to 120 parts by weight per hundred parts rubber. In another embodiment of the invention, the second insert further comprises a filler comprising 0 to 65 parts by weight per hundred parts rubber.

In one embodiment of the invention, the second insert further comprises between 0 and 2.5 parts by weight sulfur per hundred parts by weight of rubber. The invention may be further understood by reference to the following non-limiting examples.

EXAMPLE 1 - Formulation of a sidewall insert

The rubber mix of crescent-shaped insert 22 was created by replacing the sulfur vulcanization system of the conventional sulfur-cured crescent-shaped insert 24 with dicumyl peroxide and portions of the carbon black with zinc dimethacrylate (ZDMA).

Mixing was conducted in a Banbury mixer (Farrel Corp., Ansonia, CT 06401) by the typical upside down mix process. The ZMDA was added along with the carbon black in a bag to minimize product dusting. Rotor speed was 55 RPM, and the initial temperature was 50°C. The control mix, and #1 were dropped from the Banbury mixer at 165°C, while mixes #2 through #6 were dropped from the mixer after 4 minutes at temperatures less than 165°C. All vulcanization curatives and the peroxide were added on a mill at temperatures less than 100°C. The compositions are shown in greater detail in Table 1. The proportions are given in parts per hundred weight of rubber. Table 1

(1) PB1208, Goodyear Chemical Corp., Akron, OH 44304

(2) SR634, Sartomer Corp., Exton, PA 19341

(3) SR633, Sartomer Corp.

(4) Flexsys America Akron, Ohio 44334

(5) Santocure CBS, Flexsys America

(6) Dicup 40C, Hercules Corp., Wilmington, DE 19894

[N650 carbon black is available from Engineered Carbons, Inc., Borger, Texas 79008, and other suppliers]

[6PPD is N- (1, 3-dimethylbutyl) -N' -phenyl-p-phenylenediamine. ] [TMQ is poly (1, 2-dihydro-2,2,4-trimethyl quinoline. It is also known and Vulcanox 4020, by Bayer]

The physical characteristics of the resulting compositions are shown in Table 2.

Table 2

Dynamic properties were measured on an MTS loading rig (MTS

Systems Corp., Eden Prairie, MN 55344) at 10 hertz under pure shear mode of deformation.

Under tensile loading, the force divided by the original area of the sample under duress is called the stress (shown above in units of mega Pascals). The displacement (movement or stretch) of the material is called the strain. Normally the strain is given as the change in length divided by the original length, and the units are dimensionless. The modulus is the slope of the curve of stress versus strain (stress in the ordinate, strain in the abscissa). The elastic shear modulus (G') of a material is the ratio of the elastic (in-phase) stress to strain and relates to the ability of a material to store energy elastically. The loss modulus (G") of a material is the ratio of the viscous (out of phase) component to the shear strain, and is related to the material's ability to dissipate stress through heat. The ratio of these moduli (G7G") is defined as tangent delta, and indicates the relative degree of viscous to elastic dissipation, or damping of the material. A low tan delta means higher resilience and less hysteresis.

In Table 2, G' represents the shear modulus in mega Pascals, and tan delta represents the relative hysteresis of the material. As demonstrated by the data in Table 1 and Table 2, in the normally- inflated mode, (25 degrees Celsius and 6% strain), samples #1 through #6 show significantly less hysteresis (Tan delta) than the control. Therefore, an insert made with the peroxide plus co-agent curing system generates less heat (and rolling resistance) when the tire is normally inflated. Furthermore, the data indicates that the second insert could be significantly thinner than in the prior art, and therefore reduce mass (mixes 2, 4, and 6).

When a tire is in the uninflated mode, corresponding to 100° Celsius and 25% strain, the hysteresis (tan delta) of samples #1 through #5 are equal to or lower than the control. However, samples #1 through #6 are again able to support a significantly higher load (see G' at 100° Celsius, 25% strain).

This combination of low hysteresis at normally inflated conditions, but equivalent or better hysteresis and high load capacity at deflated conditions is unique and valuable.

EXAMPLE 2 - Road Test of Tire with Insert System

The first insert 24 was formed from a control mixture with a sulfur curing system [a different control than that of Table 1]. The second insert 22 was formed from a peroxide co-agent curing system. Crescent-shaped inserts were formed with this composition having the respective general cross-sections shown in Figure 1. These inserts were positioned in a conventional mold after the other tire components were arranged. After the inner liner was put into place, the mold closed and heating began according to a predetermined schedule. Curing was terminated after the first insert was essentially cured. The tire of this invention was cured in a single curing operation. This did not degrade the endurance of the tire, but surprisingly enhanced the endurance of the tire (see below).

A tire with inserts compounded as above was compared with experimental control tires of the same size and architecture. The standard Tire and Rim Association (Copley, Ohio 44321) dimensions were 205/50 R17; with the tires having an architecture of the Michelin MXM4 ZP tire line (Michelin North America, Inc. Greenville, SC). These tires are illustrated in Fig. 1. Various tire and material performance parameters were measured to compare the experimental control tires with the tire of this invention. The control tires were made with the same components except the second crescent-shaped insert 22 was made with the same first compound as the first crescent shaped insert 24, being a sulfur-accelerated system. Two tires of each type were tested.

The tires were heated to a temperature of 160 degrees centigrade before terminating the cure at 17 minutes. The integrity of the cured tire of this invention was investigated by measuring Shore A hardness and modulus of elasticity (modulus) of the first and second crescent shaped inserts. The modulus at ten percent unit strain for the first crescent shaped insert 24 was nine (9) mega Pascals (MPa) and the modulus for second crescent shaped insert 22 was seventeen (17) MPa. Although the curing time to reach a given percent vulcanization for the peroxide co-agent cured system is longer than that of the sulfur-cured system to reach the same percent vulcanization, the strength of the peroxide co-agent cured system is realized by terminating the cure based on the cure law of the sulfur cured system. This is at least partially due to the location of second crescent-shaped insert 22 adjacent to the innerliner 26 to provide a higher level of input thermal energy during curing of the tire.

The Shore A hardness across the first crescent-shaped insert was constant at 74 and the Shore A hardness across the second crescent shaped insert was constant at 90. There was no point where the hardness at the interface 23 dropped below that of either crescent-shaped insert. Therefore, the degrading of the physical properties of either crescent-shaped insert by the other adjacent crescent-shaped insert which might be expected because of the proximity of the antioxidant (6PPD), sulphur and peroxide curing systems was not found. That is, a weakening or separation at the interface 23 between the crescent-shaped inserts did not occur. An important physical parameter of a run-flat tire is the amount of deflection under load with zero inflation pressure. The amount of deflection directly relates to the amount of strain the various tire components are subjected to with each rotation of the tire. Durability of the tire is greatly improved with small decreases in deflection of the loaded tire. The tire of this invention had a deflection of 25.9 millimeters under a load of 490 kilograms compared with an average of 28.1 millimeters for the control tires under the same load. This is an eight (8) percent reduction in the deflection. The radial stiffness of the tire was improved by 8.5 percent, as measured by vertical deflection on an STL machine. This reduction is a direct result of the higher modulus of the second crescent shaped insert, which results in less strain in the tire's components and the interfaces between components. Tire endurance for a run-flat tire is best measured by recording the number of miles traveled by a vehicle at a given speed, with zero pressure in the tires, without the tire being physically impaired. Typical failure modes for a pneumatic tire include cracking of the sidewall, and under high heat conditions, softening of the tire material. The run-flat tires of this invention were placed on a Bayerische Motor Werke (BMW) vehicle. One tire lasted for 173 miles until the car was stopped by the driver. Inspection of the tire showed some cracking in the support. The other tire went 200 miles, at which time the test was stopped and an inspection of the tire showed no evidence of extensive physical damage to the support system of the tires. The test run was performed at a variety of speeds not exceeding 55 miles per hour, on a winding test track that gave high lateral force loading. No failures were present at interface 23 between the first and second crescent shaped inserts for the tire of this invention.

As explained above, the higher modulus of elasticity of the innermost crescent-shaped insert allowed the runflat tire of this invention to operate with less deflection when running without an inflation pressure. Less deflection reduced the unit strains within the runflat tire, thereby decreasing heat build-up. Higher modulus also improved the handling of the tire in the zero inflation condition. The greater thermal stability of the elastomer cured with peroxides and the metal salt of an acrylic acid meant that longer operation of the tire was possible in the uninflated state before the support system broke down. It is therefore expected that a tire according to the present invention will be able to travel over 200 miles in the uninflated condition without breaking down.

While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the invention.

Claims

What is claimed is:

1. A pneumatic tire having enhanced physical properties and run-flat endurance, where:

5 at least one reinforced radial carcass layer having a crown portion and a pair of end portions each anchored in a respective spaced apart bead; a tread outward of said crown portion of said carcass layer and a reinforced belt portion between said tread and said carcass layer; a pair of sidewall inserts each adjacent said carcass layer and extending o radially from a respective bead to a respective lateral edge of said tread; an innerliner interior to said carcass layer to retain air inside a cavity of the tire; the improvement of which comprises: each one of said pair of sidewalls having inserts for providing s continuous running with the loss of inflation pressure, said pair of sidewalls each including: a first insert inserted to the interior of said at least one carcass layer, said first insert comprising rubber having a sulfur-accelerated system for curing; o a second insert inserted to the interior of said first insert, wherein said second insert has a common interface with said first insert, said second insert comprising rubber and having a peroxide and a co-agent for curing.

2. The tire of claim 1 , wherein said second insert has a higher modulus of 5 elasticity than said first insert.

3. The tire of claim 1 wherein said co-agent comprises a metal salt of a carboxylic acid.

4. The tire of claim 3, wherein the metal salt comprises a metal selected from the group consisting of sodium, potassium, iron, magnesium, calcium, zinc, barium, aluminum, tin, zirconium, lithium, cadmium, and cobalt and mixtures thereof.

5. The tire of claim 3, wherein the carboxylic acid is an unsaturated carboxylic acid.

6. The tire of claim 3, wherein the carboxylic acids are selected from the lo group consisting of methacrylic acid, ethacrylic acid, acrylic acid, cinnamic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and mixtures thereof.

7. The tire of claim 1 wherein the peroxide is selected from the group consisting of di-cumyl peroxide, bis-(tert-butyl peroxy)-diisopropyl benzene, t- i5 butyl perbenzoate, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxide hexane and mixtures thereof.

8. The tire of claim 3, wherein the metal salt of the carboxylic acid is zinc dimethacrylate.

20

9. The tire of claim 1 wherein said first insert has modulus of elasticity at ten percent unit strain in a range of about 5 mega Pascals to about 15 mega Pascals and said second insert has a modulus of elasticity at ten percent unit strain in a range of about 10 mega Pascals to about 50 mega Pascals.

25

10. In a pneumatic tire, the improvement comprising multiple sidewall stiffening inserts, wherein:

(a) a first stiffening insert comprises a sulfur-curable rubber composition; and (b) a second stiffening insert comprises a peroxide-curable rubber composition; and said first and second inserts are adjacent each other and in contact along a common interface.

11.The tire of claim 10 wherein an insert is crescent-shaped.

12. The tire of claim 10 wherein the second insert comprises a mixture of rubber, a metal salt of an acrylic acid, and a peroxide curing agent.

13. The tire of claim 10, wherein the rubber is selected from the group consisting of natural rubbers and synthetic rubbers.

14. The tire of claim 10, wherein the insert comprises a dienic rubber.

15. The tire of claim 14, wherein the dienic rubber is selected from the group consisting of: butadiene-styrene copolymers (SBR), butadiene-isoprene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene-butadiene- styrene copolymers (SBIR)

16. The tire of claim 10, wherein the metal salt carboxylate is selected from the group consisting of zinc diacrylate and zinc di-methacrylate.

17. The tire of claim 10 wherein the second insert comprises 5 to 90 parts of metal salt of a carboxylic acid per hundred parts by weight of rubber.

I δ.The tire of claim 10 wherein the second insert comprises 10 to 60 parts of metal salt of a carboxylic acid per hundred parts by weight of rubber.

19. The tire of claim 10, wherein the tire is selected from the group 5 consisting of bias-ply tires and radial tires.

20. The tire of claim 1 wherein said second insert is comprised of a blend of natural rubber and polybutadiene wherein the polybutadiene ranges from zero percent by weight to eighty percent by weight, and the natural rubber ranges o from one hundred percent by weight to twenty percent by weight.

21.The tire of claim 1 wherein the inserts further comprise a filler selected from the group consisting of carbon black and silica.

s 22. The tire of claim 1 wherein at least one of the inserts is crescent shaped.

23. A tire comprising a sidewall, wherein the sidewall includes at least two adjacent crescent-shaped inserts, each insert having a major concave surface and a major convex surface, wherein the major concave surface of the first o insert lies adjacent to the major convex surface of the second insert, and wherein the first insert is substantially nearer the sidewall than the second insert, and wherein the first insert comprises a sulfur-curable rubber composition including a metal salt of a carboxylic acid, and wherein said second insert comprises a peroxide-curable rubber composition. 5

24. The tire of claim 23, wherein the metal salt of the carboxylic acid is selected from the group consisting of zinc diacrylate and zinc dimethacrylate.

25. A tire comprising a sidewall, wherein the sidewall includes at least two radially adjacent crescent-shaped inserts, wherein said radius is drawn from the centerpoint of the tire, wherein the first insert is substantially nearer the sidewall than the second insert, and wherein the second insert comprises a 5 peroxide-curable rubber composition including a metal salt of a carboxylic acid, and wherein said first insert comprises a sulphur-curable rubber composition.

26. The tire of claim 25, wherein the first insert has a shore A hardness greater than 72, and an elastic modulus greater than 35 kg/cm² when the elongation o strain is one hundred percent, and wherein the second insert has a shore A hardness greater than 90, and an elastic modulus greater than 65 kg/cm² when the elongation strain is one hundred percent.

27. The tire of claim 25, wherein the first insert has a shore A hardness greater s than 75, and an elastic modulus greater than 40 kg/cm² when the elongation strain is one hundred percent, and wherein the second insert has a shore A hardness greater than 95, and an elastic modulus greater than 70 kg/cm² when the elongation strain is one hundred percent.

0 28. The tire of claim 10 wherein the second insert comprises 10 to 50 parts of metal salt of a carboxylic acid per hundred parts by weight of rubber.

29. The tire of claim 1 wherein the second insert further comprises a filler comprising 0 to 120 parts by weight per hundred parts rubber. 5

30. The tire of claim 1 wherein the second insert further comprises a filler comprising 0 to 65 parts by weight per hundred parts rubber.

31. The tire of claim 1 wherein the second insert further comprises between 0 o and 2.5 parts by weight sulfur per hundred parts by weight of rubber.