Tire with sidewall carcass reinforcement

A tire having at least one crescent-shaped rubber composition as an insert in its sidewall region which is comprised of at least one diene-based elastomer, carbon black and, optionally, silica and at least one of dithiodipropionic acid, benzoic acid and salicylic acid.

FIELD
 This invention relates to a tire and more particularly to a pneumatic tire
 designed for optional use without internal air pressure.
 BACKGROUND
 Tire constructions have been suggested for pneumatic tires which are
 designed to be run without internal pneumatic pressure, other than ambient
 atmospheric pressure.
 For example, tires have been suggested which have special sidewall inserts
 designed to improve sidewall stiffness, thereby reducing, or inhibiting,
 the tire's tendency to go flat without internal air pressure. (see, for
 example, U.S. Pat. No. 5,368,082). Also, tires have been suggested which
 have additional plies, such as tires having a total of three plies in
 their sidewalls, to enhance, or substantially maintain, the tire's
 performance when running without internal air pressure. (see, for example,
 U.S. Pat. Nos., 5,427,166 and 5,511,599).
 For this invention, it is desired to provide a tire with inserts in its
 sidewall portion(s) which have enhanced stiffness related properties.
 In the description of this invention, the term "phr" where used, relates to
 parts by weight of specified material, or ingredient, per 100 parts by
 weight rubber, in a rubber based composition. Such term is well known to
 those having skill in such art.
 Such terms as "compound" or "rubber compound" or "rubber composition" are
 used interchangeably. The term "compounding ingredient" refers to
 ingredients, usually including the elastomers themselves, that are blended
 to form a rubber compound. Such terms are well known to those having skill
 in such art.
 In the description of this invention, the viscoelastic properties E' and
 Tangent (Tan.) delta values art determined by a Rheovibron instrument at
 11 hz at a one tenth percent strain. A Rheovibron instrument from the
 Tmass company is used. It is understood that use of a Rheovibron
 instrument and such method of measurement of E' and Tan.Delta is
 understood by one having skill in the art. The E' and Tan.Delta values are
 to be determined at 60.degree. C.
 The term "runflat" tire, where used, relates to a pneumatic tire which is
 designed to run without internal air pressure, under ambient conditions,
 for limited periods of time and speeds.
 SUMMARY AND PRACTICE OF THE INVENTION
 In accordance with this invention, a tire is provided comprised of a
 toroidally-shaped carcass and an outer, circumferential tread designed to
 be ground-contacting, wherein said carcass is comprised of two spaced
 apart inextensible bead portions, two spaced apart sidewalls each
 individually extending radially inward from and connecting said tread to
 said bead potions, and at least one cord reinforced ply extending from
 bead to bead and through the sidewalls; an improvement in which a
 substantially crescent shaped rubber insert is juxtapositioned to and
 axially inward of at least one of said carcass plies in each of said
 sidewalls or the tire; wherein the rubber composition of said insert has a
 Shore A hardness at 100.degree. C. in a range of about 65 to about 85, a
 100 percent Modulus in a range of about 3.5 to about 10 MPa, a Hot Rebound
 at 100.degree. C. in a range of about 60 to about 80, an E' value in a
 range of about 2 to about 20 MPa at 60.degree. C. and a Tan.Delta value at
 60.degree. C. in a range of about 0.03 to about 0.15; and wherein said
 rubber composition of said insert is comprised of, based on 100 parts by
 weight rubber, (A) at least one diene-based elastomer, (B) about 30 to
 about 100 phr of particulate reinforcement as carbon black and,
 optionally, silica, and (C) about 0.5 to about 10 phr of at least one of
 dithiodipropionic acid, benzoic acid and salicylic acid.
 Preferably, the material (C) is 3,3' dithiodipropionic acid, although it is
 understood that it may exist in a 2,2' isomeric form.
 It is to be appreciated that the insert is sulfur co-cured with the tire
 assembly of said tread and carcass as a whole.
 Preferably, the insert(s) have a maximum thickness at a location about
 midway between the bead portions and the tread in the sidewall region of
 the tire.
 In one aspect of the invention, said dithiodipropionic acid, benzoic acid
 and/or salicylic acid are added by either (i) adding in-situ with
 ingredients for the said rubber composition or (ii) with the rubber
 composition as a composite of carbon black and/or silica pre-treated with
 at least one of said acids such as, for example, by organic solvent
 deposition or melt dispersion methods. For example, at least one of said
 acids may be adsorbed, absorbed, coated or melted, such as, for example,
 melt-spraying of molten material, onto the surface of said carbon black
 and/or silica filler.
 By blending one or more of said acids, preferably the dithiodipropionic
 acid, in-situ with ingredients of the rubber composition, it is meant that
 it is added to and mixed with the rubber composition as an individual
 ingredient.
 By pre-blending one or more of such acids, preferably the dithiodipropionic
 acid, with at least a portion of the carbon black and/or silica it is
 meant that it is pre mixed with the carbon black and/or silica prior to
 form a composite thereof and such composite is added to and mixed with
 ingredients for the rubber composition as an individual ingredient.
 By mixing with ingredients for the rubber composition, it is meant that one
 or more of the said acids, or said composite, as the case may be, is
 blended with the elastomer(s) as well as conventional compounding
 ingredients used for the rubber composition for the insert, conventionally
 in an internal rubber mixer. It is preferred the said acid, preferably the
 dithiodipropionic acid, or said composite, as the case may be, is mixed
 with the compounding ingredients in the absence of curatives such as
 sulfur and vulcanization accelerators, and that such curatives are
 subsequently blended with the rubber composition after said acid or
 composite addition.
 Alternatively, although not generally preferred, a portion of or all of the
 acid, or composite, may be added to the rubber composition with the
 curatives.
 The dithiodipropionic acid may typically be characterized by having a
 melting point in the range of about 153 to about 159.degree. C. Such
 melting point can conveniently be determined by a differential scanning
 calorimeter (DSC) at a heating rate of 10.degree. C. per minute.
 It is considered herein that the utilization of the said acids,
 particularly the 3,3'-dithiodipropionic acid, for the rubber filler
 composition is significant in order to enhance the stiffness of the sulfur
 vulcanized rubber composition of the insert as well as to endeavor to
 substantially maintain a relatively low hysteresis.
 In the practice of this invention, a significant function of the rubber
 composition based fillers in the sidewall portion of the tire is to
 stiffen/support the sidewall structure when the tire is operated without
 inflation pressure.
 The rubber composition based inserts are elastomeric in nature having a
 substantially crescent cross-sectional shape and material properties
 selected to enhance inflated ride performance while promoting the tire's
 run-flat durability. The inserts, if desired, may also be individually
 reinforced with cords or short fibers. Thus, one or more of such inserts
 may be so-reinforced.
 The shape of the fillers is described as being substantially crescent in
 shape. This is intended to also include an entrunkated crescent shape,
 particularly where the entrunkated portion of the crescent shaped filler
 is juxtapositioned to the tire's bead portion.
 In further practice of the invention, said tire carcass may have from one
 to three plies comprised of a first axially inner ply and optionally one
 or two additional plies as a second ply and third ply, respectively, each
 additional ply positioned sequentially axially outward from said first ply
 in the sidewall region of the tire.
 Accordingly, in accordance with this invention said tire contains one ply
 in its carcass wherein said insert is juxtapositioned to and axially
 inward of said ply in the sidewall region of the tire.
 In further accordance with this invention, said tire contains, in its
 carcass, an axially inner first ply and a second ply axially outward from
 the first ply; wherein said insert is juxtapositioned to and axially
 inward of said first ply, in the sidewall region of the tire.
 In additional accordance with this invention, said tire contains, in its
 carcass, an axially inner first ply and an axially outer second ply;
 wherein said insert is juxtapositioned to and interposed between said
 first and second ply, in the sidewall region of the tire.
 In further accordance with this invention, said tire contains, in its
 carcass, an axially inner first ply and an axially outer second ply;
 wherein one of said inserts is juxtapositioned to and interposed between
 said first and second ply, in the sidewall region of the tire, and another
 of said inserts is juxtapositioned to and axially inward of said first
 ply, in the sidewall region of the tire.
 In further accordance with this invention, said tire contains, in its
 carcass, an axially inner first ply, a second ply axially outward from
 said first ply and a third ply axially outward from said second ply;
 wherein said insert is juxtapositioned to and axially inward of said first
 ply, in the sidewall region of the tire.
 In additional accordance with this invention, said tire contains, in its
 carcass, an axially inner first ply, a second ply axially outward from
 said first ply and a third ply axially outward from said second ply;
 wherein said insert is juxtapositioned to and interposed between (a) said
 first and second plies and/or (b) said second and third plies, in the
 sidewall region of the tire.
 In further accordance with this invention, said tire contains, in its
 carcass, an axially inner first ply, a second ply axially outward from
 said first ply and a third ply axially outward from said second ply;
 wherein said insert is juxtapositioned to and interposed between (a) said
 first and second plies and/or (b) said second and third plies, in the
 sidewall region of the tire and, also, an insert juxtapositioned to and
 axially inward of the innermost of said plies.
 In one embodiment, the innermost ply, or plies, has synthetic or textile
 cord reinforcement of polyester, nylon, rayon or aramid, preferably nylon;
 while the outermost ply preferably has aramid, carbon fiber, fiberglass or
 metal cord reinforcement, preferably brass and/or zinc coated steel cords.
 Thus, in a preferred embodiment, the first ply has reinforcing cords of
 nylon, an aramid fiber, and the second and additional plies are steel
 cords.
 The term "ply" is contemplated to include cord reinforced inserts which do
 not extend entirely from one bead core to the opposite bead core. It is,
 however, contemplated that at least one ply must extend from bead core to
 the opposite bead core, preferably a radial ply. A second ply can extend
 from a bead core to just laterally under one or more of the reinforcing
 belts of the belt structure.
 In one aspect, the outermost ply preferably has cords of a higher modulus
 (i.e.: steel cords) and the innermost ply, or plies, have cords of a lower
 modulus (i.e.: nylon or rayon).
 At least one ply, preferably the innermost ply, extended from bead core to
 bead cord and wraps around the bead core. Alternatively, where two or more
 plies are used, at least one of the additional plies, while extending from
 bead core to bead core, does not actually wrap around the bead core.

DEFINITIONS
 "Axial" and "axially", where used, means directions that are parallel to
 the axis of rotation of the tire.
 "Bead portion" means generally that part of the tire comprising an annular
 inextensible tensile member such as a multiplicity of annular wires
 surrounded by an elastomer composition(s), and is associated with holding
 the tire to the rim being wrapped by ply cords and shaped, with or without
 other reinforcement elements such as flippers, chippers, apexes or
 fillers, toe guards and chaffers. The bead core usually refers to the wire
 beads of the bead portion but sometimes may refer to the bead portion
 itself.
 "Belt Structure" or "Reinforcing Belts", where used, means at least two
 annular layers or plies of parallel cords, woven or unwoven, underlying
 the tread, unanchored to the bead, and having both left and right cord
 angles in the range from 17.degree. to 27.degree. with respect to the
 equatorial plane of the tire.
 "Circumferential" may be used in the description to relate to a direction
 extending along (around) the outer perimeter of the surface of the tire
 carcass such as, for example, the circumferential tread on the carcass.
 "Carcass" means the tire structure apart from the tread but including
 supporting plies, sidewalls and the beads or bead portions.
 "Chafers", where used herein, refers to narrow strips of material placed
 around the outside of the bead to protect cord plies from the rim,
 distribute flexing above the rim.
 "Cord" means one of the reinforcement strands of which the plies in the
 tire are comprised. "Innerliner", where used herein, means the layer or
 layers of elastomer or other material that form the inside surface of a
 tubeless tire and that contain the inflating fluid within the tire.
 "Ply" means a layer of rubber-coated parallel cords.
 "Radial" and "radially" mean directions radially toward or away from the
 axis of rotation of the tire.
 "Radial Ply Tire", if used herein, means a belted or
 circumferentially-restricted pneumatic tire in which at least one ply has
 cords which extend from bead to bead are laid at cord angles between
 65.degree. and 90.degree. with respect to the equatorial plane of the
 tire.
 "Shoulder", if used herein, means the upper portion of sidewall just below
 the tread edge.
 "Sidewall" means that portion of a tire between the tread and the bead.
 DETAILED DESCRIPTION
 Referring to the drawings FIGS. 1, 2 and 3 show the fragmentary
 cross-section of a tire (1), its tread (2), bead portion (3), sidewall or
 sidewall region (4), inextensible wire bead core (5), rubber chafer (6),
 rubber toeguard (7), rubber composition innerliner (8), belt structure (9)
 underlying a portion of the tread (2), carcass ply (10), carcass ply
 turn-up (11), insert (12) and apex (13).
 The cords for use in the carcass plies may comprise from one (monofilament)
 to multiple twisted filaments. The number of total filaments in the cord
 may range from 1 to 13.
 The cords, particularly metallic cords, of the carcass ply are generally
 oriented such that the tire according to the present invention is what is
 commonly referred to as a radial.
 The steel cord of the carcass ply intersect the equatorial plane (EP) of
 the tire at an angle in the range of from 75.degree. to 105.degree..
 Preferably, the steel cords intersect at an angle of from 82.degree. to
 98.degree.. A more preferred range is from 89.degree. to 91.degree..
 The first and second reinforcing ply structure each may comprise a single
 ply layer, however, any number of carcass plies may be used.
 As further illustrated in the Figures, the first ply structure has a pair
 of turn-up ends respectively which wrap about each bead core 5 of the bead
 portion 3 of the carcass. The ends 11 of the second ply 10 are in
 proximity to the bead core 5 and terminate radially adjacent on either
 side of the bead core 5, above the bead core 5 or can be wrapped around
 the bead core 5 and terminates radially below the turn-up end 11 of the
 first ply 10 as shown. The turn-up ends 11 of the first ply 10 wrap about
 the second ply ends and the bead core 5. The turn-up ends of the first ply
 11 terminates radially a distance above the nominal rim diameter of the
 tire 1 in proximity to the radial location of the maximum section width of
 the tire. In a preferred embodiment, the turn-up ends are located within
 20% of the section height of the tire from the radial location of the
 maximum section width, most preferably terminating at the radial location
 of the maximum section width.
 The bead core 5 is preferably constructed of a single or monofilament steel
 wire continuously wrapped.
 Located within the bead region 3 and the radially inner portions of the
 sidewall portions 4 are high modulus elastomeric apex inserts disposed
 between carcass reinforcing structure 11 and the turn-up ends 11,
 respectively. The elastomeric apex inserts 13 extend from the radially
 outer portion of bead portions respectively, up into the sidewall portion
 gradually decreasing in cross-sectional width. The elastomeric apex
 inserts 13 terminate at a radially outer end.
 The inserts 12 may extend from each bead region radially to the edge of the
 tread, usually to just beneath the reinforcing belt structures 9. As
 illustrated in the Figures, the sidewall portions may each include a first
 insert 12 and a second insert 12 and even a third insert 12. The first
 inserts 12 are positioned as described above. The second inserts 12 are
 located (interposed) between the first and the second plies 10
 respectively. The second insert 12 extends from each bead region 3, or
 portion, radially outward to the edge of the tread 2, namely to just
 beneath the reinforcing belt structure 9.
 In one embodiment, the first inserts 10 each have a thickness at its
 maximum thickness of at least three percent of the maximum section height
 "SH" at a location approximately radially aligned the maximum section
 width of the tire.
 The second insert, and third insert, if used, has a thickness at its
 maximum thickness of at least one and one-half percent (1.5%) of the
 maximum section height of the tire at the location radially above the
 maximum section width of the tire. In a preferred embodiment the
 elastomeric second inserts, and third insert, if used, each have a
 thickness of approximately one and one-half percent (1.5%) of the maximum
 section height SH of the tire at a radial location of about 75% of the
 section height SH. For example, in a P275/40ZR17 size high performance
 tire this thickness of the second insert of the tire equals 0.08 inches (2
 mm). At the location approximately radially aligned with the location of
 the maximum section width of the tire, the thickness of the second insert
 is 0.05 inches (1.3 mm).
 The overall cross-sectional thickness of the combination of elastomeric
 inserts preceding from the bead portions to the radial location of the
 maximum section width (SW) is preferably of constant thickness. The
 overall sidewall and carcass thickness is at least 0.45 inches (11.5 mm)
 at the maximum section width location and increases to an overall
 thickness in the region where it merges into the shoulder near the lateral
 tread edges. Preferably, the overall thickness of the sidewall in the
 shoulder region of the tire is at least one hundred percent (100%) of the
 overall sidewall thickness at the maximum section width (SW). This ratio
 means that the sidewall can be made substantially thinner than the
 predecessor type runflat tires.
 As previously discussed, the tire of the present invention has at least one
 ply having a turn-up end 11 (wrapped around the bead core 5) while another
 ply can simply be terminated adjacent to the bead core 5 without actually
 wrapping around the bead core 5.
 The first insert 12 is preferably made of elastomeric material. The first
 insert 12 is designed to prevent the tire's sidewall from collapsing when
 operating under no inflation pressure. The insert 12 can be of a wide
 range of shore A hardnesses from a relative soft shore A of about 50 to
 very hard 85, the material shape and cross-sectional profile is modified
 accordingly to insure the ride performance and sidewall spring rate is
 acceptable. The stiffer the material the thinner the cross-section
 generally.
 The second insert 12, and third insert 12, if used, can be of the same or
 different material physical properties relative to the first insert. This
 means that the combination of a hard second insert 12, and/or third insert
 12 if used, with a softer first insert 12 is contemplated as well as the
 combination of a hard first insert 12 with a softer second and/or third
 insert 12. The elastomeric materials of the second insert may similarly be
 in the 50 to 85 shore A range.
 The second insert 12 and third insert 12, if used, as shown in the Figures,
 is made of elastomeric material. These inserts 12 can be used in multiples
 of inserts interposed between adjacent plies when more than two plies are
 used in the carcass structure.
 The second inserts 12, and third inserts 12, when used, when unreinforced
 with fibers, act as a spacer between the adjacent plies. The cords of the
 plies particularly the radially outer ply is placed in tension when the
 tire is operated uninflated.
 In practice, the rubber compositions for the inserts 12 utilized in this
 invention for the aforesaid pneumatic tire construction are preferably
 characterized by physical properties which enhance their utilization in
 the invention which are, collectively, believed to be a departure from
 properties of rubber compositions normally used in pneumatic tire
 sidewalls, particularly the combination of inserts 12 and with plies 10
 having a combination of either dissimilar or similar high stiffness yet
 essentially low hysteresis properties.
 In particular, for the purposes of this invention, the aforesaid inserts 12
 are designed to have a high degree of stiffness yet also having a
 relatively low hysteresis for such a degree of stiffness. This enabled the
 benefits of the change in moduli of the reinforcing cords to be fully
 appreciated.
 The stiffness of the rubber composition for inserts 12 is desirable for
 stiffness and dimensional stability of the tire sidewall 4.
 A similar stiffness of the rubber composition for the ply coat for one or
 more of plies is desirable for overall dimensional stability of the tire
 carcass, including its sidewalls, since it extends through both sidewalls
 and across the crown portion of the tire.
 However, it is to be appreciated that rubbers with a high degree of
 stiffness in pneumatic tires normally be expected to generate excessive
 internal heat during service conditions (operating as tires on a vehicle
 running under load and/or without internal inflation pressure),
 particularly when the rubber's stiffness is achieved by a rather
 conventional method of simply increasing its carbon black content. Such
 internal heat generation within the rubber composition typically results
 in a temperature increase of the stiff rubber and associated tire
 structures which can potentially be detrimental to the useful life of the
 tire 1.
 The hysteresis of the rubber composition is a measure of its tendency to
 generate internal heat under service conditions. Relatively speaking, a
 rubber with a lower hysteresis property generates less internal heat under
 service conditions than an otherwise comparable rubber composition with a
 substantially higher hysteresis. Thus, in one aspect, a relatively low
 hysteresis is desired for the rubber composition for the fillers and the
 plycoat(s) for one or more of the plies 10.
 Hysteresis is a term for heat energy expended in a material (e.g.: cured
 rubber composition) by applied work and low hysteresis of a rubber
 composition is indicated by a relatively high rebound and relatively low
 tangent delta (Tan. Delta) property values.
 Accordingly, it is important that the rubber compositions for one or more
 of the inserts 12 and plycoats for one or more of plies 10 have the
 properties of both relatively high stiffness and low hysteresis.
 The following selected desirable properties of the rubber compositions for
 the inserts 12 are summarized in the following Table A.
 TABLE A
 Properties Filler
 Hardness 100.degree. C. (Shore A).sup.1 65-85
 Modulus (100%) MPa.sup.2 3.5-10
 Hot Rebound (100.degree. C.).sup.3 60-80
 E' at 60.degree. C. (MPa).sup.4 2-20
 Tan.Delta 60.degree. C..sup.4 0.03-0.15
 .sup.1 Shore Hardness Test-ASTM Test No. D2240.
 .sup.2 Tension Modulus Test-ASTM Test No. D412.
 .sup.3 Zwick Rebound Test-DIN 53512.
 .sup.4 Rheovibron at 11 Hz, one tenth percent strain.
 Alternatively, where two or more inserts are used, the first insert may
 have properties the same as or different from the second or third inserts,
 if used, within the above stated ranges.
 For example, the innermost insert may have a Shore A hardness in a range of
 about 65 to about 75, a 100 percent modulus in a range of about 3.5 to
 about 8 MPa, and E' in a range of about 2 to about 15 MPa at 60.degree. C.
 and a Tan.Delta at 60.degree. C. in a range of about 0.03 to about 0.1 and
 said outward insert(s) may have a Shore A hardness in a range of about 70
 to about 85, a 100 percent modulus in a range of about 5 to about 10 MPa,
 and E' in a range of about 5 to about 20 MPa at 60.degree. C. and a Tan
 Delta at 60.degree. C. in a range of about 0.05 to about 0.15.
 The indicated hardness property is considered to be an expanded range of
 moderate rubber hardness permitted by the use of the unique ply cord
 structure.
 The indicated modulus property at 100% modulus is utilized instead of a
 300% modulus because the cured rubber has a relatively low ultimate
 elongation at its breaking point. Such a cured rubber is considered stiff.
 The indicated E' property is a coefficient of the storage or elastic moduli
 component of the viscoelastic property which is an indication of the
 material (e.g.: cured rubber composition) stiffness where a higher E'
 value indicates a higher stiffness.
 The indicated Tan. Delta property is a measure of the rubber composition's
 heat build up which is an indication of the hysteretic nature of the
 material (e.g.: cured rubber composition) with a relatively low Tan Delta
 value at 100.degree. C. being indicative of a relatively low hysteresis
 and a relatively low heat build up quality.
 The utilization of both the E' and Tan.Delta properties to characterize
 stiffness and hysteresis of rubber compositions is well known to those
 having skill in such characterizations of rubber.
 The indicated hot rebound test property at about 100.degree. C. is measured
 by Zwick Rebound Test (DIN 53512) test and is indicative of the material's
 (e.g.: cured rubber composition) resilience.
 Thus, the properties illustrated in the previous Table A indicate a cured
 rubber composition with a relatively high stiffness, moderate hardness and
 a relatively low hysteresis for a rubber with such a high stiffness.
 The low hysteresis is demonstrated by the relatively low Tan.Delta, and
 high rebound properties and is considered necessary for a rubber
 composition desired to have a relatively low internal heat buildup in
 service.
 In the compounding of the various tire components, various rubbers may be
 used which are, preferably, relatively high unsaturation diene-based
 rubbers. Representative examples of such rubbers are, although they may
 not be so limited, are: styrene-butadiene rubber, natural rubber, cis 1,4
 and trans 1,4-polyisoprene rubbers, cis 1,4, vinyl 1,2-and trans
 1,4-polybutadiene rubbers, styrene-isoprene-butadiene rubber,
 styrene-isoprene rubber and isoprene-butadiene rubber.
 Various of the preferred rubbers for the rubber compositions for the
 fillers and for the plycoat(s) for one or more of the plies are natural
 cis 1,4-polyisoprene rubber, isoprene/butadiene rubber, and cis
 1,4-polybutadiene rubber.
 Preferred combinations, or blends, of rubbers are natural and synthetic cis
 1,4-polyisoprene rubber and cis 1,4-polybutadiene rubber for the fillers
 and natural cis 1,4-polyisoprene rubber, cis 1,4-polybutadiene rubber and
 isoprene/butadiene copolymer rubber for the plycoat(s).
 In a preferred practice, based on 100 parts by weight rubber, (A) the
 fillers are comprised of about 60 to 100, preferably about 60 to 90, parts
 natural rubber and, correspondingly, up to about 40, preferably about 40
 to about 10, parts of at least one of cis 1,4 polybutadiene rubber and
 isoprene/butadiene rubber preferably cis 1,4-polybutadiene rubber, where
 said isoprene/butadiene rubber, if used, is present in a maximum of 20
 parts, and (B) the said plycoat(s) are comprised of up to 100, preferably
 about 80 to about 100 and more preferably about 80 to about 95, parts
 natural rubber and, correspondingly, up to about 100, preferably up to
 about 20 and more preferably about 20 to about 5, parts of at least one of
 isoprene/butadiene copolymer rubber and cis 1,4 polybutadiene rubber,
 preferably an isoprene/butadiene rubber; wherein the ratio of isoprene to
 butadiene in said isoprene/butadiene copolymer rubber is in a range of
 about 20/80 to about 80/20.
 It is further contemplated, and is considered to be within the intent and
 scope of this invention that a small amount, such as about 5 to about 15
 parts, of one or more organic solution polymerization prepared rubbers may
 be included with the aforesaid natural rubber, and cis 1,4-polybutadiene
 rubber and/or isoprene/butadiene rubber composition(s) for the said
 fillers and/or plycoat(s), of which the option and selection of such
 additional rubber(s) can be made by one having skill in the rubber
 compounding art without undue experimentation.
 Thus, in such circumstance, the description of the filler and plycoat
 rubbers is set forth in a "comprising" manner with the intent that small
 amounts of such solution polymerization prepared elastomers can be added
 so long as the aforesaid physical property parameters of the cured rubber
 compositions are met. It is considered that such rubber compounding is
 within the skill of those with experience in the rubber compounding art
 without undue experimentation.
 While not necessarily limited thereto, such other contemplated solution
 prepared rubbers are styrene/butadiene, and polymers of one or more of
 isoprene and butadiene such as trans 1,4-polyisoprene, trans
 1,4-polybutadiene, styrene/isoprene/butadiene terpolymers and medium vinyl
 polybutadiene.
 It should readily be understood by one having skill in the art that rubber
 compositions for components of the pneumatic tire, including the first and
 second fillers can be compounded by methods generally known in the rubber
 compounding art, such as mixing the various sulfur-vulcanizable
 constituent rubbers with various commonly used additive materials such as,
 for example, curing aids, such as sulfur, activators, retarders and
 accelerators, processing additives, such as rubber processing oils, resins
 including tackifying resins, silicas, and plasticizers, fillers, pigments,
 stearic acid or other materials such as tall oil resins, zinc oxide,
 waxes, antioxidants and antiozonants, peptizing agents and reinforcing
 materials such as, for example, carbon black. As known to those skilled in
 the art, depending on the intended use of the sulfur vulcanizable and
 sulfur vulcanized materials (rubbers), the certain additives mentioned
 above are selected and commonly used in conventional amounts.
 Typical additions of carbon black comprise about 30 to about 100 parts by
 weight, of diene rubber (phr), although about 40 to about a maximum of
 about 70 phr of carbon black is desirable for the high stiffness rubbers
 desired for the indicated fillers and plycoat(s) used in this invention.
 Typical amounts of resins, if used, including tackifier resins and
 stiffness resins, if used, including unreactive phenol formaldehyde
 tackifying resins and, also stiffener resins of reactive phenol
 formaldehyde resins and resorcinol or resorcinol and hexamethylene
 tetramine may collectively comprise about 1 to 10 phr, with a minimum
 tackifier resin, if used, being 1 phr and a minimum stiffener resin, if
 used, being 3 phr. Such resins may sometimes be referred to as phenol
 formaldehyde type resins. Typical amounts of processing aids comprise
 about 4 to about 10.0 phr. Typical amounts of silica, if used, comprise
 about 5 to about 50, although 5 to about 15 phr is desirable and amounts
 of silica coupling agent, if used, comprise about 0.05 to about 0.25 parts
 per part of silica, by weight. Representative silicas may be, for example,
 hydrated amorphous silicas. A representative coupling agent may be, for
 example, a bifunctional sulfur containing organo silane such as, for
 example, bis-(3-triethoxy-silylpropyl) tetrasulfide,
 bis-(3-trimethoxy-silylpropyl) tetrasulfide and
 bis-(3-trimethoxy-silylpropyl) tetrasulfide grafted silica from DeGussa,
 AG. Typical amounts of antioxidants comprise 1 to about 5 phr.
 Representative antioxidants may be, for example,
 diphenyl-p-phenylenediamine and others, such as those disclosed in The
 Vanderbilt Rubber Handbook (1978), pages 344-346. Suitable antiozonant(s)
 and waxes, particularly microcrystalline waxes, may be of the type shown
 in The Vanderbilt Rubber Handbook (1978), pages 346-347. Typical amounts
 of antiozonants comprise 1 to about 5 phr. Typical amounts of stearic acid
 and/or tall oil fatty acid may comprise about 1 to about 3 phr. Typical
 amounts of zinc oxide comprise about 2 up to about 8 or 10 phr. Typical
 amounts of waxes comprise 1 to about 5 phr. Typical amounts of peptizers
 comprise 0.1 to about 1 phr. The presence and relative amounts of the
 above additives are not an aspect of the present invention, so long as the
 hardness and modulus value requirements of the filler(s) used in the tire
 sidewalls in the practice of this invention.
 The vulcanization of the rubber composition(s) is/are conducted in the
 presence of a sulfur vulcanizing agent. Examples of suitable sulfur
 vulcanizing agents include elemental sulfur (free sulfur) or sulfur
 donating vulcanizing agents, for example, an amine disulfide, polymeric
 polysulfide or sulfur olefin adducts. Preferably, the sulfur vulcanizing
 agent is elemental sulfur. As known to those skilled in the art, sulfur
 vulcanizing agents are used in an amount ranging from about 0.5 to about 8
 phr with a range of from 3 to about 5 being preferred for the stiff
 rubbers desired for use in this invention.
 Accelerators are used to control the time and/or temperature required for
 vulcanization and to improve the properties of the vulcanizate. In one
 embodiment, a single accelerator system may be used, i.e., primary
 accelerator. Conventionally, a primary accelerator is used in amounts
 ranging from about 0.5 to about 3 phr. In another embodiment, combinations
 of two or more accelerators in which a primary accelerator is generally
 used in the larger amount (0.5 to about 2 phr), and a secondary
 accelerator which is generally used in smaller amounts (0.05-.50 phr) in
 order to activate and to improve the properties of the vulcanizate.
 Combinations of such accelerators have historically been known to produce
 a synergistic effect of the final properties of sulfur cured rubbers and
 are often somewhat better than those produced by use of either accelerator
 alone. In addition, delayed action accelerators may be used which are less
 affected by normal processing temperatures but produce satisfactory cures
 at ordinary vulcanization temperatures. Representative examples of
 accelerators include amines, disulfides, guanidines, thioureas, thiazoles,
 thiurams, sulfenamides, dithiocarbamates and xanthates. Preferably, the
 primary accelerator is a sulfenamide. If a second accelerator is used, the
 secondary accelerator is preferably a guanidine, dithiocarbamate or
 thiuram compound, although a second sulfenamide accelerator may be used.
 In the practice of this invention, one and sometimes two or more
 accelerators are preferred for the high stiffness rubbers.
 The tire can be built, shaped, molded and cured by various methods which
 will be readily apparent to those having skill in the art.
 EXAMPLE I
 Pre-treated carbon black and pre-treated silica reinforcing fillers are
 prepared by pre-treating the fillers with 3,3'-dithiodipropionic acid.
 The fillers were individually pre-treated by first dissolving the
 dithiodipropionic acid in acetone (20 ml/g) under reflux conditions. The
 solution was cooled slightly and mixed with a stirred suspension of the
 selected particulate filler in acetone. The pre-treated filler was
 recovered by removing the acetone via a Roto-vac instrument which utilizes
 a combination of heat and vacuum to remove the acetone solvent while
 rotating the mixture in a flask.
 The following Table 1 summarizes the pre-treated filler showing the amounts
 of dithiodipropionic acid per 100 parts of filler.
 Fillers M and N are carbon black pre-treated with 3,3'-dithiodipropionic
 acid. Fillers X and Y are silica pre-treated with 3,3'-dithiodipropionic
 acid.
 TABLE 1
 Pre-Treated Fillers
 Parts by Weight
 Material Filler M Filler N Filler X Filler Y
 Carbon Black.sup.1 100 100 0 0
 Silica.sup.2 0 0 100 100
 DTDP.sup.3 4 8 4 8
 .sup.1 N299 carbon black.
 .sup.2 HiSil-210 from PPG Industries, Inc.
 .sup.3 3,3'-dithiodipropionic acid.
 EXAMPLE II
 Rubber compositions were prepared using the pre-treated fillers of Example
 I, namely the carbon black and silica reinforcing fillers which had been
 pre-treated with dithiodipropionic acid. Formulations for the rubber
 compositions are shown in Table 2.
 The Control rubber composition Sample A contained both carbon black and
 silica reinforcing fillers which had not been pre-treated with
 dithiodipropionic acid.
 Sample B is identical to the control with the exception of the in-situ
 addition of 2 phr dithiodipropionic acid during the Banbury mixing step.
 In other words, for Sample B while 3,3'-dithiodipropionic acid is used,
 the carbon black and silica were not pre-treated with such material.
 Samples C, D and E contain dithiodipropionic acid pre-treated carbon black
 and/or silica Samples M, N, X and Y of Example 1.
 Thus, rubber compositions B, C, D and E contain 2 phr dithiodipropionic
 which was added (1) individually during the rubber composition mixing step
 (Sample B) or (2) as pre-treated filler during the rubber composition
 mixing step (Samples C, D and E).
 Samples A-E all contain silica coupling agent added during the
 non-productive stage of mixing.
 Rubber compositions represented by samples F and G compare the in-situ
 addition of the dithiodipropionic acid (Sample F) with the addition of
 pre-treated carbon black and pre-treated silica (Sample G), all in the
 absence of coupling agent.
 For this Example, the rubber compositions were prepared by first blending
 the rubber and ingredients, except for the sulfur curatives and
 accelerators in a non-productive mixing stage in an internal rubber mixer
 to a temperature of about 160.degree. C. for about 4 minutes.
 To the rubber composition was then mixed the sulfur and accelerators in a
 final productive mix stage in an internal rubber mixer to a temperature of
 about 105.degree. C. for about 2 minutes.
 The terms "non-productive" and "final productive" mixing stages are well
 known to those having skill in the rubber mixing art.
 TABLE 2
 Silica and CB Filled Compounds
 C D E G
 Sample # A B Pretreated Pretreated Pretreated F
 Pretreated
 Pretreated/In-situ Control In-situ Silica CB Silica/CB In-situ
 Silica/CB
 Non-Productive
 Polyisoprene.sup.1 100 100 100 100 100 100
 100
 Carbon Black.sup.2 25 25 25 0 0 25 0
 Silica.sup.3 25 25 0 25 0 25 0
 Oil.sup.4 5 5 5 5 5 5 5
 Zinc Oxide 5 5 5 5 5 5 5
 Stearic Acid 2 2 2 2 2 2 2
 Coupler.sup.5 5 5 5 5 5 0 0
 Filler M (CB) 0 0 0 0 26 0 26
 Filler N (CB) 0 0 0 27 0 0 0
 Filler X (Silica) 0 0 0 0 26 0 26
 Filler Y (Silica) 0 0 27 0 0 0 0
 DTDP 0 2 0 0 0 2 0
 Productive
 Accelerators 2.5 2.5 2.5 2.5 2.5 2.5 2.5
 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5
 Conventional amounts of rubber processing oil (five parts), stearic acid
 (two parts) and zinc oxide (5 parts), therefore, were used with two
 accelerators.
 1. Cis 1,4-polyisoprene NATSYN.RTM. 2200 from The Goodyear Tire & Rubber
 Company.
 2. N299 carbon black.
 3. Silica obtained as HiSil 210 from PPG.
 4. 3,3'-dithiodipropionic acid.
 5. A 50/50 composition of bis-3-(triethoxysilylpropyl) tetrasulfide carbon
 black obtainable as X50S from Degussa AG.
 The rubber compositions of Table 2 were cured at a temperature of about
 150.degree. C. for about 36 minutes.
 Cure behavior and cured physical properties for the rubber compositions are
 shown in Table 3.
 TABLE 3
 Sample # A B C D E F G
 Rheometer
 Max Torque 49 52 52.8 52.7 51.2 46 48.2
 Min Torque 5 4.8 5*3 5.5 6.2 5.3 7.7
 delta Torque 44 47.2 47.5 47.2 45 40.7 40.5
 T.sub.90 15.2 26.7 22.8 23.8 19 19.3 16.7
 T.sub.2 5.1 6.9 5.3 5.7 5.9 9.3 7.4
 Physicals
 100% Mod, MPa 3.6 4.2 4.1 4.2 4.0 2.9 3
 300% Mod, MPa 16.2 16.3 13.1 17.1 16.9 11.2 11.5
 Tensile, MPa 22.0 21.3 19.2 20.2 20.1 19.5 21.1
 Elongation % 422 414 368 381 381 477 502
 Hardness
 23.degree. C. 69.0 73.5 75.4 74.4 74.3 69.5 71.6
 100.degree. C. 66.7 70.5 70.5 70.0 69.5 65.7 67.4
 E', MPa 1.9 2.52 2.64 2.57 2.15 1.99 2.15
 Tan.delta 60.degree. C. 0.050 0.051 0.048 0.045 0.048 0.048
 0.050
 Rebound, %
 23.degree. C. 57.6 56.5 56.8 57.9 57.5 59.6 57.8
 100.degree. C. 71.8 64.9 65.4 66.1 66.2 68.3 66.6
 As shown in Table 3, the addition of the 2 phr of dithiodipropionic acid by
 in-situ or by pre-treated reinforcing filler resulted in an increased
 stiffness as evidenced by the rubber compositions 100% modulus, hardness
 and Rheovibron E' properties.
 Further, samples F and G illustrate comparative physical properties for
 in-situ verses pre-addition in the absence of silica coupling agent. Thus,
 the stiffness related physical properties were similar.
 EXAMPLE III
 Rubber compositions were prepared containing silica filler reinforcement as
 shown in Table 4. They were prepared in a manner similar to Example II.
 Sample H is the Control without the dithiodipropionic acid whereas Sample
 I contains the pre-treated silica of Example I and Sample J contains an
 in-situ addition of the dithiodipropionic acid.
 TABLE 4
 All Silica Filled Compounds
 Compound # Control H Pre-mix (I) In Situ (J)
 Non-Productive
 Polyisoprene.sup.1 100 100 100
 Treated Silica.sup.2 0 52 0
 Silica.sup.3 50 0 50
 Oil.sup.4 5 5 5
 Zinc Oxide 5 5 5
 Stearic Acid 2 2 2
 Coupler.sup.5 10 10 10
 DTDP.sup.6 0 0 2
 Productive
 Accelerators.sup.7 2.5 2.5 2.5
 Sulfur 1.5 1.5 1.5
 .sup.1 Synthetic cis 1,4-polyisoprene rubber obtained as NATSYN .RTM. 2200
 from The Goodyear Tire & Rubber Company.
 .sup.2 Pre-treated Filler X silica of Example I.
 .sup.3 HiSil-210 from PPG Industries, Inc.
 .sup.4 Naphthenic/paraffinic rubber processing oil.
 .sup.5 X50S as in Example II, Table 2.
 .sup.6 3,3'-dithiodipropionic acid.
 .sup.7 Of the sulfenamide type.
 The rubber compositions of Table 4 were cured for about 36 minutes at about
 150.degree. C. Cure behavior and cured properties are shown in Table 5.
 TABLE 5
 Sample # H Pre-mix (I) In-Situ (J)
 Rheometer
 Max Torque 48 56.9 56.5
 Min Torque 6.9 8.2 7.4
 delta Torque 41.1 48.7 49.1
 T.sub.90 17.5 24.4 29.9
 T.sub.2 7 8.3 9.5
 Physicals
 100% Mod, MPa 3.1 4.3 4.0
 300% Mod, MPa 12.9 16.1 15.0
 Tensile, MPa 21.9 21.4 21.5
 Elongation % 491 419 443
 Hardness
 23.degree. 69.5 76.6 75.7
 100.degree. C. 67.6 72.9 71.7
 E', MPa 1.60 2.56 2.75
 Tan D 60.degree. C. 0.051 0.035 0.034
 Rebound, %
 23.degree. 56.9 58.9 57.1
 100.degree. C. 71.3 66.9 65.2
 Inspection of the physical properties shown in Table 5 clearly indicates
 that the experimental samples I and J which contain dithiodipropionic acid
 exhibit higher stiffening properties such as 100 percent modulus, hardness
 and E' than the Control H sample.
 EXAMPLE IV
 Rubber compositions were prepared in which 3,3'-dithiodipropionic acid and
 benzoic acid are blended in-situ with a carbon black reinforced rubber
 composition.
 For the experimental (K) rubber composition dithiodipropionic acid was
 added in-situ in the non-productive mix stage.
 For the experimental (L) rubber composition benzoic acid was added in the
 productive mix stage.
 The rubber compositions were prepared and mixed by conventional rubber
 mixing processes and comprised of the materials shown in Table 6.
 The rubber compositions were mixed by first blending the rubber and
 ingredients, except for the sulfur curatives and accelerators in an
 nonproductive mixing stage in an internal rubber mixer to a temperature of
 about 160.degree. C. for about 4 minutes.
 Sulfur and accelerators were then added in a final productive mix stage in
 an internal rubber mixer to a temperature of about 105.degree. C. for
 about 2 minutes.
 TABLE 6
 Sample # K L
 1.sup.st Non-Productive
 Natural Rubber 80 80
 Cis 1,4-Polybutadiene.sup.1 20 20
 Carbon Black 60 60
 Processing Oil 4 4
 Antidegradants.sup.2 1.8 1.8
 Zinc Oxide 6 6
 Fatty Acid 1 1
 Dithiodipropionic Acid 1.5 0
 2.sup.nd Non-Productive
 Silica.sup.3 5 5
 Bis-(3- 1 1
 triethoxysilylpropyl
 tetrasulfide (50% active)
 Productive
 Benzoic Acid 0 1.5
 Sulfur 3.2 3.2
 Accelerators.sup.4 2.5 2.5
 Zinc Oxide 2 2
 .sup.1 High cis 1,4-polybutadiene (BUDENE .RTM. 1207) from The Goodyear
 Tire & Rubber Company;
 .sup.2 Amine types;
 .sup.3 Hi-Sil 210 from PPG Industries, Inc;
 .sup.4 Sulfenamide type.
 The rubber compositions were cured for about 36 minutes to a temperature of
 about 150.degree. C.
 The physical properties are shown in Table 7.
 TABLE 7
 Sample # K L
 Rheometer (150.degree. C.)
 Max. Torque, dNm 56.0 56.9
 Min. Torque 6.0 6.4
 Delta Torque 50.0 50.5
 T.sub.90, minutes 12.9 9.8
 Stress-Strain
 Tensile Strength, MPa 16.2 15.2
 Elongation @ Break, % 249 228
 100% Modulus, MPa 5.9 6.3
 Rebound
 100.degree. C. 64.8 62.0
 Hardness
 Shore A, 100.degree. C. 72 73
 The cured physical properties show that the addition of dithiodipropionic
 acid or benzoic acid to the rubber composition resulted in a rubber
 composition having a relatively high hardness value of about 72.
 EXAMPLE V
 Rubber compositions were prepared in which salicylic acid was blended with
 a carbon black reinforced natural rubber composition.
 The formulation (M) was a control without salicylic acid being added.
 For the experimental (N) rubber composition salicylic acid was added in the
 non-productive mix stage.
 The rubber compositions were prepared and mixed by conventional rubber
 mixing processes and comprised of the materials shown in Table 8.
 The rubber compositions were mixed by first blending the rubber and
 ingredients, except for the sulfur curatives and accelerators in an
 nonproductive mixing stage in an internal rubber mixer to a temperature of
 about 160.degree. C. for about 4 minutes.
 Sulfur and accelerators were then added in a final productive mix stage in
 an internal rubber mixer to a temperature of about 105.degree. C. for
 about 2 minutes.
 TABLE 8
 Sample # M (Ctrl) N
 Non-Productive
 Natural Rubber.sup.1 100 100
 Carbon Black, N299 50 50
 Processing Oil 5 5
 Antidegradants.sup.2 2 2
 Zinc Oxide 5 5
 Fatty Acid 2 2
 Salicylic Acid 0 2
 Productive
 Sulfur 1.4 1.4
 Accelerators.sup.3 1 1
 .sup.1 Cis 1,4-polyisoprene;
 .sup.2 Amine types;
 .sup.3 Sulfenamide type.
 The rubber compositions were cured for about 36 minutes to a temperature of
 about 150.degree. C.
 The physical properties are shown in Table 9.
 TABLE 9
 Sample # M (Ctrl) N
 Rheometer (150.degree. C.)
 Max. Torque, dNm 37.7 40.2
 Min. Torque, dNm 6.2 6.2
 Delta Torque 31.5 34.0
 T.sub.90, minutes 18.8 24.5
 Stress-Strain
 Tensile Strength, MPa 21.3 23.1
 Elongation @ Break, % 539 468
 100% Modulus, MPa 1.58 2.89
 Rebound
 100.degree. C. 61.1 59.5
 Hardness
 Shore A, 100.degree. C. 48.0 65.2
 The cured physical properties show that the addition of salicylic acid to
 the rubber composition resulted in a rubber composition having relatively
 high modulus and hardness values.
 In the practice of this invention, it is considered important that the
 rubber compositions for one or more of the inserts are relatively very
 stiff, moderately hard, and have a low hysteresis.
 It is important to appreciate that the indicated physical properties of the
 rubber compositions in Table 5 and 7 are for samples thereof and that the
 dimensions, including thickness, of the resulting tire components (inserts
 and plies) need be taken into account as factors contributing to the
 overall stiffness and dimensional stability of the tire sidewall and
 carcass.
 The hysteresis or Tan Delta values for the rubber composition for the
 aforesaid fillers is desirably somewhat lower than that for the rubber
 composition for the aforesaid ply coat(s) because of the bulk of the
 inserts versus the thin dimensions of the plycoat.
 In the practice of this invention, it is considered important that the
 rubber compositions for one or more of the inserts 12 are relatively very
 stiff, moderately hard, and have a low hysteresis.
 Chafing of the tire in the lower bead region radially outward of the
 carcass structure adjacent the rim flange may be minimized, especially
 during use of the tire in the uninflated condition, by providing hard
 rubber chafer portion 7.
 In one embodiment of the invention, a fabric overlay having cords at about
 zero degrees in relation to the centerplane of the tire is placed over the
 belt reinforcing structure 9.
 While certain representative embodiments and details have been shown for
 the purpose of illustrating the invention, it will be apparent to those
 skilled in this art that various changes and modifications may be made
 therein without departing from the spirit or scope of the invention.