Self supporting tire

A self supporting tire having a nonstaining high modulus low hysteresis inner sidewall composition comprising: (a) 100 parts by weight of sulfur vulcanizable rubber of which from about 50 to about 95 parts by weight is natural rubber and/or cis-polyisoprene and from about 5 to about 50 parts by weight is at least one elastomer selected from the group consisting of styrene-butadiene and cis-polybutadiene; and (b) from about 25 to about 80 parts by weight of carbon black per 100 parts by weight of rubber, wherein said carbon black has a dibutyl phthalate absorption value greater than about 80 and a particle size less than about 50 milli-microns. The self supporting tire is capable of operating both as a pneumatic tire under ordinary inflated conditions and also has the capability of operating without inflation for limited distance.

BACKGROUND OF THE INVENTION 
A pneumatic tire has historically been sought which has a reliable means of 
supporting the load of a vehicle upon the loss of the tire's inflation 
gas. Such a tire would allow the motorist to continue operating his 
vehicle for a limited distance before being required to change the tire. A 
tire having this "run-flat" feature would reduce the frequency of tire 
changes on high speed highways, thereby resulting in increased safety for 
the motoring public. Many devices have been proposed which will prevent 
the collapse of the tire upon its deflation. These devices are usually 
nonintegral with the tire and therefore difficult to mount, cumbersome, 
and generally not completely successful. 
A more desirable approach to obtain a tire which will operate over short 
distances without the support of inflation gas is to construct the tire 
such that it will be self-supporting. The self supporting feature is 
achieved by employing relatively thick rubber reinforcement inward of the 
carcass ply in the middle sidewall area of the tire. The rubber 
reinforcement prevents the tire from collapsing completely and thus 
provides a limited driving range or run-flat capability after the loss of 
inflation. 
U.S. Pat. Nos. 3,983,918 and 3,954,131 disclose tires having this inner 
sidewall reinforcement. 
A requirement for successful performance of such a tire, both in the 
presence and absence of inflation gas, is that the inner sidewall 
material, which undergoes the most severe deflection, be made of an 
elastomeric material having a high modulus of elasticity and a low 
hysteresis. Natural rubber compositions have traditionally been preferred 
for applications requiring high modulus and low hysteresis. However, 
natural rubber, after prolonged exposure to heat, undergoes reversion, 
which means that the initial stiff high-modulus vulcanized material 
gradually softens and exhibits lower and lower modulus values approaching 
that of the original unvulcanized crude rubber, which ultimately are too 
low for satisfactory support of the weight by an uninflated tire. To 
prevent reversion of the natural rubber compound, large quantities of 
highly active antioxidants are used. These antioxidants, although 
effective, present other problems. The most effective antioxidants are 
staining and if a compound containing staining antioxidants is placed next 
to a white rubber compound, the antioxidant will migrate to the white 
rubber and cause discoloration. Since the inner sidewall compound is 
located directly under the white area of a white sidewall tire, staining 
is a serious problem. It is desirable to have a tire which will operate 
with and without inflation gas and not stain the white sidewall. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a self supporting tire 
which has the capability of operating both with and without inflation gas. 
It is a further object of the present invention to provide a self 
supporting tire which has an integral inner sidewall composition that will 
not discolor the white sidewall of the tire. 
These and other objects, which will become evident from the subsequent 
description, are achieved by employing as an inner sidewall an elastomeric 
composition comprising: (a) 100 parts by weight of sulfur vulcanizable 
rubber of which from about 50 to about 95 parts by weight is natural 
rubber and/or cis-polyisoprene and from about 5 to about 50 parts by 
weight is at least one elastomer selected from the group consisting of 
styrene-butadiene and cis-polybutadiene; (b) from about 25 to about 80 
parts by weight of carbon black per 100 parts by weight of rubber, wherein 
said carbon black has a dibutyl phthalate absorption value greater than 
about 80 and a particle size less than about 50 milli-microns; and 
sufficient curing agents to effect vulcanization. Said inner sidewall 
being further characterized as having a 300% modulus of at least 1800 
psi., a hardness of at least 60 Shore A durometer and a heat build-up 
value less than about 60.degree. F. as measured by the Goodrich 
Flexometer.

DETAILED DESCRIPTION 
This invention can be used in any type of pneumatic tire in which the 
weight of the vehicle is borne entirely on the sidewalls without total 
collapse of the tire such that the inner surface of the tire contacts 
itself, but is particularly intended to be used in radial passenger car 
pneumatic tires. 
Pneumatic tires generally consist of a flexible cord carcass or body to 
resist the pressure of the inflation gas, terminated at each side edge by 
a bead which engages the rim of a wheel. The cords are embedded in rubber, 
and are protected from abrasion by tread and sidewall rubber, and are made 
to hold air by preferably having an integral, essentially impervious liner 
on the interior of the carcass. 
In the drawing, which illustrates the presently preferred embodiment, the 
invention is shown as embodied in a passenger vehicle tire that comprises 
at least one ply 10 of carcass cords. These cords may be high-tenacity 
rayon, polyester, nylon, aromatic polyamide or steel cords, and the like, 
i.e. with the individually rubberized cords essentially in radial planes. 
The edges of the ply or plies are suitably wrapped around inextensible 
bead grommets 12 forming part of molded beads 13 shaped for engagement 
with a standard rim. 
The radial cord ply 10 in the crown of the tire, which is the region 
capable of engaging the road, is surrounded by a circumferential belt, 
which in this instance is shown as consisting of two strips or plies 15 
and 17 of steel cords but could be of other low-extensible material such 
as aromatic polyamide fibers also known as arimid fibers. More than two 
plies of low-extensible material may be used to form the circumferential 
belt if greater stiffness is desired. The steel cord belt plies 15 and 17 
are preferably prepared with the cords in each ply parallel to each other 
and at an angle to the circumferential central plane of the tire, the 
cords in one ply extending in a direction opposite to the cords in the 
other ply. This angle in the finished tire may be about 15.degree. to 
30.degree. relative to the circumferential central plane. The two crown 
plies form an essentially inextensible belt around the radial cord ply. 
A protective layer of rubber completely surrounds the tire outwardly of the 
reinforcing carcass. This is preferably composed of a moderate thickness 
of black sidewall rubber 19 in the zones where intense flexing occurs. At 
least one sidewall of the tire may have an outer layer of white sidewall 
rubber 20. The crown of the tire has a thick layer of tread rubber 21 for 
resisting road wear. The tread layer has a suitable nonskid pattern 22 of 
slits, slots, grooves and the like as is well understood in the art. 
On the inner face of the tire is a liner 25 composed of a rubber material 
having resistance to diffusion of air such as butyl rubber, or halogenated 
butyl rubber, and/or blends thereof. This liner extends from one bead 13 
to the other bead so as to seal against the rim and minimize the loss of 
inflation gas or its penetration into the body of the tire. 
In accordance with this invention, the improved tire has, in addition to 
the features just described which were known before this invention, an 
integral layer of inner sidewall rubber 30 disposed outwardly of the liner 
25 and inwardly of the carcass ply 10. The layer of inner sidewall rubber 
30 extends from just above the bead area 13 to just beyond the edges of 
belt plies 15 and 17 at the outside edges of the tread 21. The inner 
sidewall layer 30 is profiled such that its maximum thickness is in the 
mid-sidewall region M of the tire where intense compression occurs in the 
uninflated state. The inner sidewall layer 30 gradually decreases in 
thickness as it extends from either side of the mid-sidewall region M and 
terminates as a thin edge at a point just above the bead area 13 and at a 
point just beyond the edges of belt plies 15 and 17. 
In order for the tire to be self supporting, the inner sidewall compound 
30, must have a 300% modulus (tensile stress at 300% elongation) of at 
least 1800 psi and preferably at least 2200 psi as measured by ASTM D412. 
The inner sidewall compound must also be a low hysteresis composition, 
that is it must have a heat build-up value less than 60.degree. F. and 
preferably less than 50.degree. F., as measured by the Goodrich Flexometer 
at a 0.225 inch stroke and 195.degree. F. according to ASTM Test D623 
Method A. A low hysteresis composition is required to minimize the 
excessive heat generated while the tire is running in a deflated 
condition. The inner sidewall compound should have a hardness of at least 
60 and preferably at least 65 Shore A durometer as measured according to 
ASTM D2240. 
Since on one side of the tire, the inner sidewall layer 30 is located under 
the white sidewall rubber 20, the composition of the inner sidewall must 
be nonstaining. Materials which cause a rubber compound to be staining are 
normally staining oils and certain antioxidants and antiozonants. If 
present in a rubber compound, these staining ingredients will migrate to 
adjacent layers of rubber and cause discoloration. 
A natural rubber composition because of its initial high modulus and low 
hysteresis properties is ideal for meeting the above physical properties 
when first vulcanized. However, with aging and especially under severe 
heat such as is present when a self supporting tire is running without 
inflation, natural rubber undergoes reversion which results in lower 
modulus and softness, which ultimately are too low for satisfactory 
support of an uninflated tire. To protect an all natural rubber 
composition from reversion, highly efficient antioxidants, such as those 
disclosed in U.S. Pat. No. 3,983,919 are normally used. These antioxidants 
are staining which results in a discoloration of adjacent white rubber 
compounds. 
Quite unexpectedly, I have found that a self supporting tire can be made 
having an inner sidewall which meets the physical property requirements 
and also is nonstaining. The novel inner sidewall composition of this 
invention comprises: (a) 100 parts by weight of sulfur vulcanizable 
rubbers of which from about 50 to about 95 parts by weight is natural 
rubber and/or cis-polyisoprene and from about 5 to about 50 parts by 
weight is at least one elastomer selected from the group consisting of 
styrene butadiene and cis-polybutadiene; and (b) from about 25 to about 80 
parts by weight of carbon black per 100 parts by weight of rubber, wherein 
said carbon black has a dibutyl phthalate absorption value greater than 
about 80 and a particle size less than about 50 milli-microns. 
In the inner sidewall composition, natural rubber and/or cis-polyisoprene 
is used at a level of from about 50 to about 95 parts by weight and 
preferably from about 70 to about 85 parts by weight. Synthetic 
cis-polyisoprene is chemically identical with natural rubber and the two 
can be interchanged with each other or blends of the two can be used. For 
processing and building tack, natural rubber is normally preferred over 
synthetic cis-polyisoprene. 
The remainder of the rubber component of the inner sidewall composition 
contains from about 5 to about 50 parts by weight, preferably from about 
15 to about 30 parts by weight, of at least one elastomer selected from 
the group consisting of styrene-butadiene and cis-polybutadiene. The 
styrene-butadiene and/or cis-polybutadiene elastomer is necessary to 
maintain the modulus and hardness levels of the original vulcanizate. 
With severe heat aging, as occurs in the inner sidewall during tire 
operation without inflation, natural rubber alone would revert and become 
soft and exhibit lower modulus and therefore be unable to support the 
tire. Styrene-butadiene and/or cis-polybutadiene rubber alone would become 
hard and brittle with aging and therefore would be unsuitable for use as 
an inner sidewall compound. By blending the styrene-butadiene and/or 
cis-polybutadiene with natural rubber, the reversion problem associated 
with natural rubber is overcome and therefore the need for staining 
antioxidants is eliminated. 
In addition to the elastomers, the inner sidewall composition contains from 
about 25 to about 80 parts by weight, preferably from about 35 to about 50 
parts by weight of carbon black per 100 parts by weight of rubber. It is 
necessary to use a carbon black which has a high dibutyl phthalate 
absorption value and a small particle size in order to achieve the desired 
high modulus with a low heat build-up value. The carbon black used must 
have a dibutyl phthalate absorption value greater than 80, preferably 
greater than 120, and a particle size less than about 50 milli-microns, 
and preferably less than 30 milli-microns. Dibutyl phthalate (DBP) 
absorption value is measured by the method specified in ASTM D2414. The 
DBP absorption values are usually reported in cubic centimeter of DBP 
absorped per 100 grams of carbon black. The DBP absorption value of a 
carbon black is a function of its particle size and its structure. The 
smaller the particle size for a given structure, the higher the DBP 
absorption value and the higher the structure for a given particle size, 
the higher the DBP absorption value. Carbon blacks with high structure and 
small particle size produce a desirably high modulus without undue 
increase in hysteresis. One or a blend of more than one carbon black may 
be mixed with the elastomer. Examples of suitable carbon blacks for use in 
this invention are those with ASTM designation N110, N234, N303, N339, 
N351, N358 and the like. 
Ingredients which have a softening effect on the composition are normally 
avoided. Such ingredients are oils, fatty acids, fusible resins and the 
like. In some circumstances, it may be necessary to use small quantities 
of not greater than 5 parts by weight and preferably not greater than 3 
parts by weight per 100 parts by weight of rubber softeners to facilitate 
processing. Softeners tend to lower the necessary high modulus of the 
inner sidewall composition. 
The inner sidewall composition of this invention is vulcanized using 
conventional vulcanizing agents. Because of their excellent heat aging 
characteristics, sulfurless or low sulfur cure systems are preferred. A 
particularly desirable cure system is one employing 1.5 parts sulfur, 2 
parts of dithio dimorpholine, and 1.15 parts of cyclohexyl benzothiazyl 
sulfenamide. Another suitable cure system is one employing 1.5 parts 
sulfur and 2.5 parts of cyclohexyl benzothiazyl sulfenamide. Said parts 
are expressed as parts by weight per 100 parts by weight of rubber. 
Activators such as zinc ozide are also used in the composition. Zinc oxide 
is also beneficial in heat aging prevention. Small quantities of 
resorcinol and hexamethylene tetramine, which form a heat setting phenolic 
resin are advantageous in the composition. The resin formed tends to 
increase modulus while decreasing the detrimental effects of heat aging, 
which is a very desirable feature. 
Cobalt compounds such as cobalt stearate, cobalt naphthenate and the like, 
are beneficial in the inner sidewall composition because they tend to 
induce cross linking of the rubber. Cobalt stearate was found to be 
particularly desirable because it melts during processing thereby 
providing a lubricating effect on the compound and eliminating the need 
for using softeners. 
Staining oils and staining antioxidants such as diphenyl-phenylenediamine, 
diphenylamine, dimethyl butylphenyl p-phenylene diamine and the like must 
be avoided. These ingredients will cause discoloration in the adjacent 
white rubber compound. 
The inner sidewall composition as described above performs very well in a 
self supporting tire both in the inflated and uninflated condition. The 
unique properties of high modulus, low hysteresis and nonstaining allow a 
self supporting tire to be made with a white sidewall which will not 
discolor. 
The inner sidewall composition is prepared by mixing the ingredients in 
conventional mixing equipment such as Banbury mixers, mills, continuous 
mixers and the like. Standard mixing procedures are used which is normally 
to mix the rubber, carbon black, zinc oxide and other nonvulcanizing 
ingredients together first and then, as the last step in the mixing, the 
vulcanizing agents are added. 
The desired shape and size of the inner sidewall is preferably obtained by 
extruding through a die of the desired size and shape. The thickness of 
the inner sidewall will vary depending on the size of the tire and the 
load the tire is designed to support. For a typical passenger car tire, a 
thickness of from about 0.3 to about 0.6 inch is preferred. 
Self supporting tires of this invention can be manufactured with ordinary 
equipment without alteration, and with only a slight increase in raw 
materials and labor costs. The principal change from ordinary practice is 
to place a pair of inner sidewalls in the sidewall area between the 
impervious liner and the carcass ply. The remainder of the tire is built 
onto the drum as in a conventional tire. Once the tire is built, it is 
vulcanized in a press using standard tire curing procedures and conditions 
which are well known in the art. 
In order to further illustrate the present invention, the following example 
is presented. 
EXAMPLE 
This example is presented to show that the run-flat performance of a self 
supporting tire can be dramatically improved by using as an inner sidewall 
a composition containing a rubber mixture of 80/20 natural 
rubber/styrene-butadiene versus a composition containing an all natural 
rubber formulation. The compositions used are shown in Table I. Both 
compositions are nonstaining in order to enable their use in a tire having 
a white sidewall. Formulation 1 is an all natural rubber formulation while 
formulation 2 is an 80/20 natural rubber/styrene-butadiene formulation. 
TABLE I 
______________________________________ 
Formulation 
Ingredient (Parts by Weight) 
1 2 
______________________________________ 
Natural Rubber 100 80 
Styrene-Butadiene -- 20 
ASTM N358 Carbon Black 40 40 
Zinc Oxide 10 10 
Cobalt Stearate 6 6 
Peptizer 0.25 0.25 
Resorcinol 1.50 1.50 
Hexamethylene Tetramine 
2.10 2.10 
Methylene Bis Methylbutyl Phenol 
2.00 2.00 
Sulfur 1.50 1.50 
Dithio Dimorpholine 2.00 2.00 
Cyclohexyl Benzothiazyl Sulfen- 
1.15 1.15 
amide 
Retarder 0.30 0.30 
______________________________________ 
Two tires were made with each of the above formulations as the inner 
sidewall in a self supporting GR78-15 radial passenger tire. The four 
tires were built using standard radial tire building equipment and 
procedures and then molded in a press for about 21 minutes at a 
temperature of 350.degree. F. and an internal pressure of 400 psig. The 
tires were tested by mounting on a conventional rim and placed on the 
right rear position of an automobile. After placing on the automobile, the 
valve core was removed from the valve so as to allow all the internal 
pressure to escape. The tires were run at a speed of 25 mph and a load of 
1380 pounds until failure. The mileage to failure was determined as the 
point where the tire would no longer support the 1380 pound load as 
evidenced by the complete collapse of the tire such that the sidewall 
developes severe folds as it goes through the road contacting area. The 
run flat mileage and the physical properties of the two formulations are 
shown in Table II. 
TABLE II 
______________________________________ 
Formulation 
Test 1 2 
______________________________________ 
Tensile Strength (psi) 
3600 3650 
300% Modulus (psi) 2600 2600 
Elongation (%) 405 405 
Durometer (Shore A) 70 71 
Goodrich Flexometer 
Heat Build-up (.degree.F.) 
36 36 
Run Flat Mileage (Ave. of 
2 Tires) 26.95 66.85 
______________________________________ 
The data in Table II shows that although the initial physical properties of 
the two formulations are almost identical, the self supporting tires 
having an inner sidewall of formulation 2 have dramatically improved run 
flat performance. Quite unexpectedly, the tires having an inner sidewall 
of the 80/20 natural rubber/styrene-butadiene formulation have almost a 
two and one-half fold increase in run flat mileage over the all natural 
rubber formulation. 
Tires employing this invention are useful on any vehicle where pneumatic 
tires are now used. Because of the added safety associated with tires of 
this invention, they are particularly suited for use on passenger cars. 
Although this invention has been illustrated, by way of example, with an 
inner sidewall compound containing 20 parts by weight of styrene-butadiene 
and 80 parts by weight of natural rubber, the ratio of rubbers may vary 
from 5 parts by weight styrene-butadiene and 95 parts by weight of natural 
rubber to 50 parts by weight of styrene-butadiene and 50 parts by weight 
of natural rubber. It is preferred that natural rubber be present at a 
level of from about 70 parts by weight to about 85 parts by weight per 100 
parts by weight of rubber. 
Cis-polybutadiene may be substituted on an equal part basis for 
styrene-butadiene in this invention or blends of cis-polybutadiene and 
styrene-butadiene rubbers may be used as long as at least 50 parts by 
weight of the rubber consists of natural rubber and/or cis-polyisoprene. 
Cis-polyisoprene, the synthetic duplicate of natural rubber, may be 
substituted or blended with natural rubber in this invention. As is well 
known by those skilled in the art, it is sometimes desirable to blend 
rubbers together to achieve better processing characteristics depending on 
the particular type of equipment and conditions used. 
The composition in the above example used N358 carbon black. Other carbon 
blacks may be substituted for N358 or blends of more than one carbon black 
may be used. The important criterion is that the carbon black used must 
have a dibutyl phthalate absorption value greater than 80 and a particle 
size less than about 50 milli-microns. 
The cure system shown in the example is a preferred cure system for 
achieving vulcanization. There are many different combinations of curing 
agents which will become apparent to those skilled in the art. 
In practicing this invention, those skilled in the art may make minor 
variations in the disclosed novel composition in order to facilitate 
processing on their particular equipment. Therefore, it is intended that 
the scope of this invention be limited only by the following claims.