CA1098432A - Deflated tire lubricant - Google Patents

Abstract

Abstract of the Disclosure To facilitate relative movement between the internal surface of a pneumatic tire which come into contact when the tire is run in a deflated condition, the interior of the tire is coated with a lubricant which does not flow at normal tire operating temp-eratures. The matrix of the lubricant is a polyester, polyurea or polyurethane which does not begin to flow until the tire reaches a temperature of from 65°C
to 150°C. If the lubricant were allowed to flow at operating temperature, it would adversely effect the balance and performance of the tire. The high tire temperature indicates that the tire is flat and reduces the viscosity of (liquifies) the lubricant causing it to flow. the lubricant then reduces rubbing friction and temperature rise which would otherwise occur by rubber-to-rubber contact. The lubricant tire can be run flat to a service station.

Description

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BACKGROUND OF THE INVENTION
~ield of the Inventlon This invention relates to lubricants for pneu-matic tires for vehicles and specifically to a lubricant for a tire running while deflated or underinflated.

DESCRIPTION OF THE PRIOR ART
A basic problem with all pneumatic tires is that they occasionally become underinflated or completely deflated and when this occurs, the tire must be changed and a spare tire put on. In some cases, a blowout can cause the vehicle to go out of control.
A tire which can be run flat has, for some time, been a desirable ob~ective in the tire-making art.
If a tire could be run flat for an appreciable distance, the driver could run on the flat tire until a replacement t~re was obtained or the tire repaired. This would eliminate changing tires on the road and dependence on a spare. A driver could also run on the suddenly deflated tire until a safe place to stop the car is found, thus avoiding sudden stopping on crowded streets and hlghways.
There are many problems associated with running a conventional tire flat. A flat tire is unstable, making steering difficult. The lack of inflation pressure causes the tire beads to unseat, and eventually the tire .
may come off the wheel rim. In addition, rlding with a flat tire can be an uncomfortable experience since there r is practically no cushion between the wheel rim and the : .

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road surface.
A number of designs have been proposed to in-crease the stability and rideability of the tire when deflated or flat. Some of these proposals, such as U.S. Patent Nos. 3,394,751 and 3,421,566 relate to movable sidewalls so that the tire tread force is communlcated directly to the rim. U.S. Patent 4,057,092 relates to a circumferential locking lug. Other proposals, such as U.S. Patent Nos. 2,040,645; 3,392,722 and 3,610,308 have special units in the interior of the tire. Other proposals include liquid lubricants within the tire, (U.S. Patent 4,045,362) and solid lubricants which liquify on the addition of chemicals (U.S. Patent 3,931,843).
A problem generated by tires running flat is the friction which develops from the upper and lower por-tions of the deflated sidewall rubbing against each other. The friction produces excess heat and causes the sidewalls to wear excessively. To reduce this fric-tion, the inclusion of either liquid or solid lubricants on the tire interiors has been proposed. U.S. Patent No. 2,o40,645, for instance suggests a graphite lubricant, U.S. Patent No. 3,610,308 mentions the use of liquid silicone, and U.S. Patent Nos. 3~739,829; 3,850,217 and 4,045,362 describe the use of polyalkylene glycols, ~lycerol, propylene glycol, silicone and other lubri-cants. The liquid lubricants, however, are not evenly distributed in the operating tire and can adversely effect balance and tire performance. Solid lubricants 3~

which liquify at flat tire temperature are also known but they require a chemical reagent for liquification (U.S. Patent 3,931,843).

SUMMARY OF THE INVENTION
Friction reducing capability is not the only important characteristic to be considered in deslgning a lubricant for use in run-flat tires. Other important parameters should include viscosity (hence mobility) and the ability to transfer heat. For the heat sensi-tive lubricants, the temperature at which drastic re-duction in viscosity starts to occur is also an impor-tant factor.
An alternative to lubricants is one which behaves like a flexible solid at ordinary service temp-eratures but melts into a liquid when heated above a certain critical temperature. The advantages of such a "phase"-changeable lubricant are numerous. Foremost of all, its presence in the tire maintains tire balance lf distributed properly. The lubricant is stable dimen-sionally so that its presence ln the tire does not pose any undue difficulty in handling, either during mountlng, shipping or storage.
Although a chemically cross-linked network generally lmplies a three-dimensional structure which does not melt or flow on heating, it is possible to make one which does. The latter should not be confused with thermoplastlc materials. Most thermoplastic materials are linear ln structure and can be made to soften and 3`1~

take on new shapes by the application of heat and pres-sure.
The formation of a reversible network depends very much on the type of materials used. Suitable materials are polymers whose molecular chains are held together either by strong but thermo-lablle van der Waals forces including hydrogen bonds, temperature dis-sociable chemical cross-links or combination of these.
The molecular weight of the linear chains should be above the critical level in which entanglements (phy-sical cross-links) become important.
Polyurethanes are examples. A reversible net-work can be made of the appropriate urethane materials in which all of the three molecular forces or bonds are known to exist. The temperature dissociable and re-formable chemical cross-links are the biuret and allo-phonate linkages. Another desirable feature of a poly-urethane based network is the inherent lubricity of the chemical intermediates (e.g. polypropylene glycol and other diols) used for the polymerization. When melted, a typical polyurethane based on polypropylene glycol will act as a natural lubricant. The temperature at which the network breaks down can be controlled prl-- marily by the types of urethane intermedlates and chain ~ 25 extenders used.

1C~'a~34;~2 According to the invention there is provided a pneumatic tire having an interior surface and mounted on a rim to define an inflation chamber, the rim having means to prevent the tire beads from becoming dislodged from the rim when the tire is operated in a deflated condition, a phase changea~le solid lubrlcant consisting of a solid coating on the interior of the tire which becomes liquified by the heat generated when the tire runs flat, the liquified lubricant reducing friction caused by sldewall rubbing against the interior bead area, wherein the improvement comprises:
the solid coating on the interior surface of the tire selected from the group consisting of polyesters, poly-ureas, and pol~urethanes which coating begins to flow on the surface of the tire when heat generated by the tire running flat liquifies the coating at a temperature of between 65C
and 150C.
Thus, the lubricant of the present invention is essentially non-flo~able at normal tire operating temperatures so that it does not adversely effect tire operation, but becomes liquid-like at flat tire temperature and lubricates the flat tire to allow the t~re to be driven twenty-five mlles or so for service. The lubricant which ls used as a coating or matrix on the interior surface of the tire is selected from the group consisting of polyether polyurethane, polyester polyurethanes, polyesters and polyureas (polyether and polyesters~, The solid coating or coating matrix does not begin to flow on the surface of the tire until the tire reaches a temperature between 65C
to 150C. Pre~erably the coating matrix does not begin to flow until the tire reaches a temperature of from 80C to 120C.
The preferable coating matrix from the standpoint of non-flowability at normal service conditions and lubricity 1098~32 is the polyurethane, either based on polyether or polyester.
The coating matrix may be used alone or can contain additional liquid lu~ricants such as polyglycols or can contain solid lubricants such as polyethylene or graphite forming a mixture. The coating matrix can also contain rolling micro-beads.

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~ Q ~L~3 2 BRIEF ~ESCRIPTION O~ THE DRAWINGS

Figure 1 is a sectional view of a tlre of the present invention.
Flgure 2 is a sectional view of a test de-vice to measure friction and temperature rise.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referr~ng to Figure 1, there is shown a pneu-matic tire. The tire has a thick tread portion 11 which extends circumferentially around the tire, and sidewalls 12 which extend from the tread portion along the sldes of the tire. The tire is designed to be mounted on a conventional wheel rim 13 whlch has at its outer edges outwardly flared flanges 14 also of con-ventional design. Wire bead rings 15 are provided in the bead portion 16 of the tire where the sidewall meets the rim 13. In accordance with conventional tire construction, the beads are designed to keep the tire on the rim when the tire is inflated. The infla-tion pressure of the tire forces the beads 15 against the flange 14, keeping the tire on the rim and maintain-; ing tire inflation.
The tire shown in the drawing may be of theconventlonal bias/belted but is preferably of the belted radial type. These tires have two bias or radial plies 17 and 18 extending around the interior of the tlre.
The plies extend from bead-to-bead and are folded around the bead rings 15 so that the ends 19 and 20 of the , ~ . , . ,. ~ . ~ .

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plies are located in the sldewall region. There are also two steel or fabric belts 21 and 22 extending clr-cumferentially around the interior of the tire and lo-cated directly interior to the tread portion 11. Con-ventional rubber compositions are used to form the tread and sidewall portions of the tire and the air-retaining inner liner.
A feature of this particular tire i9 the com-bination of the circumferential locking lug 24 and ma-chine screws 26. The lug results from a speclally de-signed increase in the thickness of the sidewall at the end of the rim flange as shown. The locking lug 24 does not interfere with the normal characteristics of the tire when inflated. Upon deflation, however, the locking lug 24 wraps around the flange 14 to secure the tire to the rim 13. Machine screws 26 also prevent the tire bead from falling into the rim well. Thus, the deflated or flat tire is secured to the rim allowing the tire to be driven ~lat for a period of time.
The drawing illustrates a size BR78-13 SBR
tubeless tire mounted on a standard rim, and it will be understood that a larger tire, such as size HR78-15 could have about the same shape. The rubber used in the tire can be the same as used in conventional tires, in which case the rubber of the sidewall portions could be an SBR with a Shore A durometer hardness in the range of 40 to 80. Butyl rubber can be used in the inner liner to provide maximum resistance to gas permeation.

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It is preferable to provlde the lubrlcant matrix 16 on the interior surface of the sidewall por-tions 2~, particularly at 47 to reduce the frictlon and heat generated by the rubbing of the upper and lower halves of the sldewalls when they are in contact during operation of the deflated collapsed tire. The liqui-fied solid lubricant matrix 16 employed has excellent lubricity when hot. The lubricant matrix has a non-flow stability which is maintained as the temperature is increased to 65C. The lubricant matrix 16 is also stable and remains in place in the tire when operated for long periods of tlme.
The solid lubricant matrices 16 preferred for use in the present invention have excellent lubri-city, are compatible with the rubber of the inner liner of the tire, are stable and operable over a wide range of temperatures and shear rates, have a non-flow pro-perty such that the lubricant matrices remain uniformly distributed during normal use of the tire, have punc-ture-sealing capability, particularly when fibrous ma-terials are added, and aid in air retention of the tire in normal use, particularly when the entire lnner sur-face of the tire is coated wlth a lubricant matrix.
Prior to this invention, there were no solld lubricants which remained in place during normal tlre use, but which liquified due to heat when needed a~d adequately lubricated the tire. The lubricant matrices as disclosed hereinafter meet all of the requlrements set forth in the prevlous paragraph.

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The lubrlcant matrices of this invention compxises high molecular weight polymeric materials which are non-flowable, high viscosity, solid-like materials at normal tire operating temperatures but which become liquid-like at the elevated temperatures generated by flat tires. The solid-like state of the matrices is probably due to hydrogen bonding inter-molecular interactions including chemical reaction be-tween ad~acent polymer molecules, physical cross-links or entanglements and/or the combined. For example, the polyurethane lubricant matrix probably both forms hydrogen bonds between ad~acent molecules and also chemically reacts to form allophonate cross-links be-tween the isocyanate and the urethane linkages. Both the hydrogen bonds and the allophonate cross-links are relatively weak and break down at elevated temperatures generated in a flat tire resulting in the lubricant matrix forming a liquid lubricant.
Polyurethane actually covers a wide variety of materials with polyethers and polyesters being the most commonly used. Strictly speaking, polyurethane applies only to the reaction product formed between an isocyanate-containing materlal and a hydroxyl-contain-ing material. Polyureas, on the other hand, are formed from the reaction between an isocyanate-containing material and an amine-containing material. The func-tionality of the latter reacting specles should be at least two or greater in order for polymerization, chain 10 .

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extension and/or cross-linking to occur. The isocyanate-containing mater~al can be either ln the form of a polyether-based prepolymer such as duPont's Adiprene~
LW-510 (a hexamethylene diisocyanate terminated poly-tetrahydrofuran) or a polyester-based prepolymer such as Uniroyal's Vibrathane system (a diphenylmethane diisocya-nate-terminated PolYester) or simply a low molecular weight diisocyanate.
The hydroxyl-containing materials can likewise be either a low molecular weight diol such as butanediol, or a high molecular weight polyether polyol (e.g. Dow's Polyglycol 2000 and 4000) or polyester polyol (e.g.
llke that used in Mobay's Multrathane system). Examples of trifunctional polyols include trimethylol propane and Dow's Voranol 3000.
The more commonly used amines are difunctional and have low molecular weight. Examples include duPont's MOCA (2,2'-dichloro-4,4'-diamino diphenylmethane) and M&T Chemicals' Apocure 601E (1,2-bis(2-aminophenyl)-thioethane).
The type of chemical cross-links formed de-pends on the nature of the secondary reactlons. The reaction between an isocyanate and a urethane linkage results in an allophonate cross-link. The reactlon be-tween an isocyanate and a urea linkage, on the otherhand, forms a biuret cross-link.
The polyester lubricant matrix is solid con-taining crystalline particles which turns to a liquid 1> 6 ~ ~ ~lC5 .

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when the melting temperature of the crystalline particles is reached and therefore causes more lubricant matrlx flow problems. Due to this flow problem, it is not con-templated that the polyester matrlx will be the pre-ferred material where non-flow is a criteria. The poly-ester matrix, it is contemplated, is a superlor lubri-cant to the polyurethane and in those situations where 50 to 100 run fla~ miles are contemplated ls the pre-ferred lubricant. Higher meltlng crystalllne materlals are avallable which can be used to achieve the non-flow requirements of the polyester lubricant during normal service conditions.
The lubricant matrices can also contain very small amounts of antioxidants, polyolefin lubricants, polyether lubricants, hydrocarbon wax lubricants, graphite, and other liquid and solid lubricants and small amounts of other ingredients commonly employed in run-flat tires.
They preferably contain cellulose fibers or other suit-able filler in an amount such as 3 to 8% by weight and preferably 4 to 6% by weight. The fibrous filler may comprise fibers with a length from 20 to 400 microns.
Solka Floc~ ~lbers are made by Brown Company and comprise cellulose fibers. One type of fiber is about 100 microns long and about 16 microns thick.
Another type of fiber is about 50 microns long and about 17 microns thick.
In addition to favorably affecting the rheolo-gical behavior of the lubricant, the addition of the ~Rk 12.

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f~beJ`S ln~arts puncture-sealing capabllity to the lubri-cant. The fiber containing lubricant can, in some in-stances, successfully seal a puncture in a tire re-sultin~; from a nail. Leakage of air can, in other in-stances, occur upon puncturing with nails; however, thepuncture sites become covered with small amounts of the lubricant, and leakage is reduced.

EXAMPLE I
POLYIJRETHANE MATRIX BASED LUBRICANT

10 Polyurethanes can be made to cross-link by either allophonate or biuret branching or by the use of multifunctional chain extender. The allophonate and biuret cross-links can dissociate on heatlng which leads to a reduction of viscosity. A typical polyurethane-paraffin wax lubricant is shown below in Table I.

TABLE I

Heat Sensitive Polyurethane Lubricant tLube I) Parts By Wei~ht Adiprene LW510 100 - Ionol antioxidant 0.5 X2-310~ silicone 1.0 Polyglyco~ P4000 106.7 Polyglycol P2000 ~ 55-2 T-12~catalyst 0.2 Paraffin wax, ~70C MP 10.0 Paraffin wax, ~105C MP 100 Plurafac D-25 10.0 Total 383.6 a6 r~ S
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The above components are mixed and heated to about 100C ~or one hour.
X2-3107 is a non-reactive silanol terminated dimethyl siloxane containing 8% xylene. Polyglycols P4000 and P2000 are difunctional polypropylene glycols of molecular weight 4000 and 2000, respectively.
Plurafac D-25 is a polyethylene oxlde-polypropylene oxide copolymer surfactant. The above lubricant is a high viscosity, flexible solid over a temperature range from room to about 75C. Upon heating above 50C, the lubricant will undergo gradual reduction in viscos-ity until it becomes a mobile fluid at temperatures above 100C. Run flat mileage exceeding the minlmum re-quirement (25 miles at 25 mph) has been obtained with the use of this lubricant.
The melting point should be more appropriately ; referred to as the temperature of liquefaction. It is the temperature at which the network lubricant is transforming into a highly mobile liquid. Most of the lubricants examined started to soften at the least 20 below the liquefication temperature. The present melting point measuring device (Fisher Jones Co.) does not per-mit an exact softening and liqu~fying temperature to be measured. Hence, the liquifying temperatures listed are only approximate, to perhaps +10C.
The prepolymer used in this development work is chosen by convenience and availability. The polyols are chosen because of their known lubricity. X2-3107 is a 14.

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non-reactive silicone fluid containlng about 8% xylene.
It is added in the lubricant to lmprove flow and lubrl-city. CAB-O-SIL fumed silica in formulation, imparts thixotropy to the lubricant and thus, facilitates coating.

EXAMPLE I(A) An example of a basic polyurethane lubrlcant is shown below.

Trade Name Ingredients Manufacturer Parts Polyether containing 4.25% Adiprene LW510 100 available NCO (duPont) Difunctional polypropylene Polyglycol MW 4000 P4000 (Dow) 105 MW 2000 P2000 (Dow) 55 Silicone X2-3107 (Dow Corning) 5 Dibutyltin dilaurate T-12 (M&T) 0.2 catalyst

2,6 Di-t-butyl-4-methyl Ionol (Harwick) 0.5 phenol Total 265.7 This particular lubricant starts to so~ten at around 150F (65C) but it does not become a mobile liquid until the temperature reaches about 250F (125C).
When this lubricant was added in the interface between two sliding rubber surfaces, friction was signiflcantly reduced as evidenced by the results shown below:

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Apparent Frictional Approx. Coerficient Sliding Force* Contact of Sliding Components tgram9) Stress mPa Friction ._ ___ Rubber-on-rubber (dry) t20210) 0.74 1.8 Rubber-on~
rubber in the presence of the lubricant (Ex. IA ) a) thin film ~11285) 1.0 (boundary) b) thiçk film (hydro_ ( 8660) o.8 dynamic) *Calculated from the torque required to maintain slidin~ of one rubber substrate on top of the other. The modlfied Brabender plasticorder was used for the above frictlon measurement. Other conditlons of the test follow: sliding speed = 115 rpm (23 cm/sec); normal load = 10980 gm.
Over more than two hours of contlnuous sliding, the temperature of the dry rubber substrates increased by at least 39C while the lubricated rubber substrates lncreased only by about 14C. The presence of the lu-; bricant prevented abrasion of the rubber surfaces.
Without the lubricant, abrasion was excessive.
Other unique properties, aside from lubricity, that the lubricant possesses lnclude non-volatll~ty, dimenslonal stability and inertness toward the tire materials. Due to its dimensional stability, a run flat tire which ls coated with the lubricant can be 16.

mounted in the conventional way. The coated lubrl-cant has no adverse effect on the running character-istics of the inflated tire, i.e., minimal vibration during running. The viscosity and slight tackiness of the lubrlcant also imparts puncture sealing capability of the tlre.
Radial tires whose innerliner surfaces were coated with the lubricant have been run-flat tested.
The run-flat test results show a capabillty of 29.5 run-flat miles~.
*Test Conditions Method = pulley wheel Speed = 25 mph Load = 35.6kg (80% rated) Rim width= 11.4cm Bead lock= rim well band ; EXAMPLE II
POLYESTER MATRIX BASED LUBRICANT
Synthesis and Thermal Analysis This lubricant is prepared by blending paraffln waxes of different melting points into an esteriflca-tion product of a polycarboxylic acid and a polypropy-lene glycol diol. Calclum stearate, mineral oil, and certain low molecular weight liquid polyolefins (e.g., polyisobutylene rubber, hydroxyl terminated polybutadiene) are added for viscosity and rheological modifications.
To improve mixing between the paraffins and the various polar materials, surfactants (e.g., Pluronics, sillcones) are used. Typical formulations and a description of the materials used are shown in Tables II and III, respec-tively.

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TABLE II
HEAT SENSITIVE
POLYESTER-BASED LUBRICANT

Lubricant Examples II III IV V VI
PPG 2025 ~ 100 100 100 100 25 Emolein 2901A 91.2 91.2 91.2 91.2 22.8 ~ .

R-45 HT ~ - - 20 - -Vistanex LM-MS - - - 20 Ionol ~ 0.5 0.5 0.5 -5 0.2 Mineral Oil 60 60 60 60 40 Calcium stearate 45 45 45 45 25 Paraffln wax MP 215 35 35 35 35 3O
Carnauba wax 1.5 1.5 1.5 1.5 2.5 TX619 ~ 1.0 1.0 1.0 1.0 2.5 Pluronics L61 0.5 0.5 0.5 0.5 1.5 Pluronics L81 2.5 2.5 2.5 2.5 5.0 Pluronics L101 1.0 1.0 1.0 1.0 3.5 X2-3107 ~ 2.0 2.0 2.0 2.0 1.5 Cab-O-Sil ~ 4 Total 340.2 360.2 360.2 360.2 159.5 ~*

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TABLE III

MATE~IALS FOR
POLYESTER-BASED LUBRICANT

Materials Description PPG 2025 Polypropylene glycol of molecu-lar weight 2025 Emolein 2901A Polycarboxylic acid based on a Cl8.fatty acid R-45 HT Hydroxyl-terminated polybutadiene with an approximate molecular weight of 2000 Vistanex LMMS Low molecular weight liquid polylsobutylene Ionol 2,6 Di-t-butyl-4-methylphenol, MP = 70C

TX619 Low molecular weight paraffin wax MP - 83.7 - 98.7C

Pluronics L61, L81, Copolymers of 10/90 poly(oxy-L101 ethylene)-poly(oxypropylene) ; 20 with total molecular weight of approximately 2000, 2500 and 3600, respectively X2-3107 Non-reactive silicone contain-ing 8% xylene AFAX LR285 "Amorphous" polypropylene, MP = 124.6 - 164.8 In the synthesis of the polyester-based lubri-cant, the waxes were first pre-melted in separate con-tainers and then added together with the Plùronics and silicones to the partially esterified PPG 2025/Emoleln 2901A. The PPG 2025/Emolein (2:1 molar ratio) ester-ification process was carried out at temperatures above 150C for half an hour or more. After the wax and the ester had been thoroughly blended, the calcium 19 .

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stearate/mineral oil mixture was then finally added with vigorous stirring to form a thick paste lubrl-cant. Cab-O-Sil fumed silica, when needed, was added last. Results of the thermal analysis (DTA) of the lubricants are shown in Table IV. The analysis was done on duPont's Macrocell Thermal Analyzer using glass beads as the reference. Measurements were done first by heating the sample to as high as 160C at a rate of 20C/min. followed by quenching at the same rate. The melting temperatures given in Table IV
represent the average values taken from both the heat-ing and cooling cycles.

TABLE IV
DIFFERENTIAL THERMAL ANALYSIS
OF POLYES~ER-BASED LUBRICANTS

~ . ( C ) Lubricant PeakRange II 110.8105.0 - 118.7 III 112.5101.8 - 122.0 IV 111.9105.4 - 122.0 V 112.0109.4 - 119.5 When a flat occurs, the temperature Or the tire can easily rise above 100C within 10 minutes at 25 mph.
It is therefore desirable for the lubricant to melt to a low viscosity fluid at about 100C for effective lubrication. A lubricant with a relatively low melting temperature would flow and affect the dynamic balance .~

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of the tire adversely. On the other hand, a lubri-cant having too high a melting temperature would not function properly when needed. Lubrlcants II through V started to melt at around 100C which appears to be a deslrable region.

VISCOSIT~ MEASUREMENT
The viscosities of the lubricants above their melting points were determined using a Haake/Rotating viscometer. The results showing the effect of shear rate on viscosity at 125C are summarized in Table V.

TABLE V
EFFECT OF SHEAR RATE ON VISCOSITY
OF POLYESTER-BASED LUBRICANT
Lubricant IIIII IV V VI*
Shear Rate sec~l Viscosity, centipoises 88.2 22.7 18.1 18.1 40.8 294.8 176.3 20.4 18.6 17.0 32.2 238.1 264.5 19.4 18.1 16.6 30.2 176.9 529.0 22.5 18.9 20.4 32.9 88.5 *Measured at 140C

All the above measurements were done using an MV-2 rotor. MV-2 designates a particular type of rotor and beaker set-up used in con~unction with the Haake viscometer. This particular rotor has a hollow bottom and its diameter and height dimensions are 36.8mm and 60mm, respectively. With the exception of lubricant 21.

VI, the constancy of viscosity over the shear rate range studied is rather surprising and resembles that of a Newtonian liquid.

VOLATILITY STUDY
The volatility of the polyester-based lubri-cants was measured in terms of the percent welght loss on heat aging at 105C up to a period of one week. Results of the againg study are summarized in Table VI.

TABLE VI

VOLATILITY OF
POLYESTER-BASED LUBRICANTS

Lubricant II III IV V VI
Tlme of aging (days) Cumulatlve Welght Loss (%) 1 5.9 5.8 2.5 7.8 5.8 3 9.3 15.9 8.9 11.5 15.8 5 12.3 17.7 11.6 17.7 24.3 7 16.8 23.2 15.2 22.1 30.5 Lubricant IV is the least volatile. Close examlnation of this aged sample shows that a layer Or fllm was deposited on top of the lubricant. The film is re-latively tough and is probably formed from the oxidation of the liquid polybutadiene. The formation of the film probably minimizes further volatilization.

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~6~9~432 FRICTION MEASUREMENTS
An effective lubricant should slgnificantly reduce sliding friction between rubber surfaces inside the run-flat tire. The ability of the lubricants to re-duce friction was characterized using a modified Brabender Plasticorder. The device, shown in Figure 2, has repro-duclbility to within _15%.
The conversion (Figure 2) of the commercial Brabender Plasticorder into a frictlon measuring device involved the following modifications.
1) The two cam-type rotors were replaced wlth a single flat surface rotor 50. The rubber specimen 51 whose friction coefficient is to be measured is molded on a metal ring 52. The ring, 2.54cm ID x 2.54cm wide x 0.635cm thick (half of which consists of the rubber), fits snugly onto the rotor.
2) The center-~acketed mixing chamber was replaced with a non-~acketed asbestos insulated steel chamber 54 of different configuration. The temperature of the chamber can be controlled. Besldes, the chamber serves as a reservoir for the lubricant.
3) The conventional ram and loading chute assembly was replaced by one supported by linear bearings to minimize friction.
The slider, added to the Brabender, fits onto and pivots freely around the left supporting rod 58 used to hold the conventional mixing chamber. The slider 23.

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contains a 6.35cm x 1.27cm x 0.635cm groove 60 which holds the flat rubber specimen 62.
The damping device on the plasticorder is dls-connected when friction measurements are made to obtain faster response. The modifications were made in such a way that changing from conventional Brabender torque measurements to rubber friction measurement can be com-pleted in less than lO minutes.
When a flat tire occurs, the bead wrap comes into contact with the crown portion of the sidewall.
The bead wrap is much stiffer due to the presence of the beads and the higher hardness of the bead compound. In order to approximate this condition in the laboratory, two compounds of different hardnesses were used for frlc-tlon measurements. The two compounds are essentially identical except in the amount of carbon black used, as shown in Table VII.

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~Q~3432 TABLE VII
RUBBER COMPOUNDS* USED
FOR FRICTION STUDY

Compound I II
Ingredients phr phr ~' Chlorobutyl HT1068 60 60 RSS #1 10 10 SBR 1502 ~4 30 30 Maglite D ~ o, 5 o,5 HAF Black 40 113.3 Soft clay 40 40 Flexon 840 10 10 Amberol ST137 4 4 Stearic acid Zinc Oxide 5.0 5.0 MBTS 1.25 1.25 Vultac 3 1.25 1.25 Totals 203.0 276.3 -':
~ The materials used in Table VII are:
-~ 20 Chlorobutyl HT-1068 - contains 1.2% by welght of chlorine in an isobutylene/isoprene rubber; the level of unsaturation is about 1.4%, ML 1+8 @100C ~ 50, specific gravity = 0.92 tExxon Co. ) .
-;. RSS #l - natural rubber as smoked sheet ~ , SBR 1502 - a styrene-butadiene rubber with 23.5% bound styrene and ML 1+4 @100C = 52 tGeneral Tlre) : Maglite D - magnesium oxide, used as vul-canizer and activator (C.P. Hall).
*En;ay Chlorobutyl formulary #25. oo4 6~ks 25.

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Flexon 840 - a paraffinic based petroleum oil (Exxon Chemical) Amberol ST 137 - a phenol formaldehyde resin used primarily as cross-linker for the chlorobutyl rubber (Rohm & Haas) Propertles I II
Shore A 62 86 5% Modulus, psi (MPa) 25 (0.19) 130 (o.96) 10% Modulus, psi (MPa) 50 (0.38) 185 (1.3) 100% Modulus, psi (MPa) 280 (1.9) 965 (6.7) 300% Modulus, psi (MPa) 840 (5.8) Tensile, psi (MPa) 1690 (11.6) 1315 (9.1) % Elongation 550 150 Tear Trouser, pli (kN/m) 31 (5.5) 19 (3.3) Compounds I and II are hereby referred to as soft and hard compounds, respectively. Although friction ~; measurements have been done using various combinations of rubber palrlng (l.e. hard/soft, soft~hard, hard/hard, soft/soft), only the results showlng the slidlng of the hard rubber on the soft rubber will be presented and dls-cussed. The friction between a hard rubber slider and a soft rubber track best resembles the conditions encount-ered in a flat tire. The results of friction coefficient measurements between the non-lubricated rubber surfaces are shown in Table VIII.

26.

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~ABLE VIII
NON-I~UBRICATED FRICTION

Sliding Friction Coefficient Between Hard and Soft Rubbers ~Modified Brabender) Sliding Speed Frlction Coefficient cm/sec. _ Normal Load kg(Modified Brabender) 0.85 15.3 1.40 0.85 19.5 1.18 0.85 24.4 0.91 2.115 15.3 1.21 2.115 19.5 1.08 2.115 24.4 0.92 All tests were run at room temperature.

In the absence of a lubricant, sliding between rubbers resulted in an abrupt rise in temperature of the rubbers, regardless of the load applied. This leads to severe wear of the rubbers. In order to avoid compli-cations arising from heat build-up and wear, all the test measurements were completed before noticeable heat build-up started to occur. This usually took less than 5 ; minutes. In most cases, an equilibrium torque would have been reached after two minutes of sliding. The phenomenon of stick-slip was prevalent in all cases.

The friction torque was taken as the average of the minimum and maximum values over the entire time scale. This averaging technique is valid as long as sliding speed is greater than 1 cm/sec. Results obtained 27.

this way are reproducible to within 15%. As expected, the friction force is not directly proportional to normal load. There is a pronounced non-linearity especially at the low load range. In another experiment involving hard rubber sliding on the soft rubber at 11 cm/sec. at 70C, the coefficient of friction decreases from 3.1 at about lkg normal load to 0.9 at about 18.2kg load.
Reference to Figure 2 shows the actual normal load is related to the apparent normal load by a factor o~ CosO.
For a given applied normal load, frictlonal force and co-efficient decrease with increasing temperature and speed.
The results for the temperature effect are somewhat scattered.

LUBRICATED FRICTION

The friction coefficient increases with nor-mal load in the lubricated case. At increasing load, the lubricant film is probably partially squeezed out so that direct contact between rubbers and, hence in-creasing friction coefficient occurred.

The friction coefficient between the hard and the soft rubbers using various lubricants ls sum-mariæed in Table IX. All measurements were done under the following conditions.

Temperature = 100C
Sliding Speed= 20 cm/sec~

Normal load = 19.5kg TABLE IX
COEFFICIENT OF SLIDING FRICTION
BETWEEN RUBBERS

Friction Force Friction Lubrlcant (Newtons) Coefficient None 119.1 0.65 II 10.6 0.056 III 9.8 0.051 IV 10.0 0.054 V 11.0 o.o56 VI 10.6 o.o56 ' The results show the effectiveness of the polyester-based lubricants in reducing sliding friction ' between rubbers. A tenfold reduction in friction co-! efficient is observed in all the lubricants examined.
Network gels having melting points ranging from 70C to 170C have been developed. Examples of various network lubricants having a range of melting points are shown in Table X. The lower melting gels are generally slightly tacky on touching whlle the higher melting gels are sbif~ and rubbery. Most of the gels ~' started to soften at some temperature which is qulte distant from the melting temperature.

29.

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30 .

1~8432 l'~e materials used are:
Voranol 3000 - a trlfunctional polypropylene glycol (Dow Chemical).
DC 203 - a silicone based material used for flow modiflcation (Dow Corning).
BD/TP 440 (95/5) - stands for a mixture of butanediol and Pluracol TP 440 (95:5 welght ratlo).
Pluracol TP 440 tB~SF Wyandotte) 1s a trl~unotlonal polyol.

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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A pneumatic tire having an interior surface and mounted on a rim to define an inflation chamber, the rim having means to prevent the tire beads from becoming dislodged from the rim when the tire is operated in a deflated condition, a phase changeable solid lubricant consisting of a solid coating on the interior of the tire which becomes liquified by the heat generated when the tire runs flat, the liquified lubricant reducing friction caused by sidewall rubbing against the interior bead area, wherein the improvement comprises:
the solid coating on the interior surface of the tire selected from the group consisting of polyesters, poly-ureas, and polyurethanes which coating begins to flow on the surface of the tire when heat generated by the tire running flat liquifies the coating at a temperature of between 65°C
and 150°C

2. The tire of claim 1 wherein the solid coating does not begin to flow until the tire reaches a temperature of from 80°C to 120°C.

3. The tire of claim 2 wherein the solid coating is a polyurethane.

4. The tire of claim 2 wherein the solid coating is a polyester.