United States Patent [191 [11] 4,340,104 Kuan [45] Jul. 20, 1982

3,739,829 6/1973 Powell et a1...... 152/330 R [54] DEFLATED TIRE LUBRICANT 3,850,217 11/1974 Edwards et a1. 152/330 RF [75] Inventor: Tiong H. Kuan, Stow, Ohio 3,931,843 l/ 1976 Edwards et al. .. 4,045,362 8/1977 Kuan et a1. [73] Assignee: The General Tire & Rubber Company, 4,057,092 11/1977 Tracy ...... l52/379.l Akron, Ohio 4,096,898 6/1978 Mosserly et a1...... [21] Appl. No.: 134,832 Primary Examiner—John E. Kittle [22] Filed: Mar. 28, 1980 [57] ABSTRACT . Related US. Application Data To facilitate relative movement between thelinternal surfaces of a pneumatic tire which come into contact [63] Continuation of Ser. No. 920,673, Jun. 30, 1978, aban when the tire is run in a de?ated condition, the interior doned. of the tire is coated with a lubricant which does not [51] Int. Cl.3 ...... B60C 17/00; B60C 5/12 ?ow at normal tire operating temperatures. The matrix [52] US. Cl...... 152/330 L; 152/347; of the lubricant is a polyester, polyurea or polyurethane ' 252/51.5 A; 252/56 R; 252/56 S which does not begin to flow until the tire reaches a [58] Field of Search ...... 152/152, 330 R, 330 L, temperature of from 65° C. to 150° C. If the lubricant 152/330 RF, 347, 374; 156/115; 252/51.5 A, 56 were allowed to flow at operating temperatures, it S, 56 R would adversely effect the balance and performance of p [56] References Cited the tire. The high tire temperature indicates that the tire is flat and reduces the viscosity of (liqui?es) the lubri U.S. PATENT DOCUMENTS cant causing it to flow. The lubricant then reduces rub-v 2,040,645 5/1936 Dickinson ...... 152/330 R bing friction and temperature rise which would ‘other; ' ' 3,299,934 l/l967 Pace 152/354 wise occur by rubber-to-rubber contact. The lubricated ’ ' 3,392,772 7/1968 Powers . . 152/1'58 tire can be run ?at to a service station. 3,394,751 7/1968 Sidles ct a1. . 152/330 R 3,421,566 1/1969 Sidles ct a1. 152/330 R 3,610,308 10/1971 McDonald ...... 152/158 4 Claims, 2 Drawing Figures US. Patent Jul. 20, 1982 4,340,104

7/////////// ////////

\ STEEL CHAMBER / F/G: Z \\ \\\ ZsbZ-sTQS §§\// 4,340,104 1 2 should include viscosity (hence mobility) and the ability DEFLATED TIRE LUBRICANT to transfer heat. For the heat sensitive lubricants, the temperature at which drastic reduction in viscosity This is a continuation of application Ser. No. 920,673 starts to occur is also an important factor. ?led June 30, 1978, now abandoned. An alternative to lubricants is one which behaves like a ?exible solid at ordinary service temperatures but BACKGROUND OF THE INVENTION melts into a liquid when heated above a certain critical 1. Field of the Invention temperature. The advantages of such a “phase”-change This invention relates to lubricants for pneumatic able lubricant are numerous. Foremost of all, its pres tires for vehicles and speci?cally to a lubricant for a tire ence in the tire maintains tire balance if distributed running while de?ated or underinflated. properly. The lubricant is stable dimensionally so that 2. Description of the Prior Art its presence in the tire does not pose any undue diffi A basic problem with all pneumatic tires is that they culty in handling, either-during mounting, shipping or occasionally become underin?ated or completely de storage. ?ated and when this occurs, the tire must be changed 5 Although a chemically cross-linked network gener and a spare tire put on. In some cases, a blowout can ally implies a three-dimensional structure which does cause the vehicle to go out of control. not melt or ?ow on heating, it is possible to make one A tire which can be run ?at has, for some time, been which does. The latter should not be confused with a desirable objective in the tire-making art. If a tire thermoplastic materials. Most thermoplastic materials could be run ?at for an appreciable distance, the driver are linear in structure and can be made to soften and could run on the ?at tire until a replacement tire was take on new shapes by the application of heat and pres obtained or the tire repaired. This would eliminate sure. changing tires on the road and dependence on a spare. The formation of a reversible network depends very A driver could also run on the suddenly deflated tire much on the type of materials used. Suitable materials until a safe place to stop the car is found, thus avoiding are polymers whose molecular chains are held together sudden stopping on crowded streets and highways. either by strong but thermo-labile van der Waals forces There are many problems associated with running a including hydrogen bonds, temperature dissociable conventional tire ?at. A ?at tire is unstable, making chemical cross-links or combination of these. The mo steering difficult. The lack of in?ation pressure causes lecular weight of the linear chains should be above the the tire beads to unseat, and eventually the tire may v30 critical level in which entanglements (physical cross come off the wheel rim. In addition, riding with a ?at - links) become important. tire can be an uncomfortable experience since there is Polyurethanes are examples. A reversible network practically no cushion between the wheel rim and the can be made of the appropriate urethane materials in road surface. which all of the three molecular forces or bonds are A number of designs have been proposed to increase 35 known to exist. The temperature dissociable and re the stability and rideability of the tire when de?ated or formable chemical cross-links are the biuret and allo ?at. Some of these proposals, such as U.S. Pat. Nos. phonate linkages. Another desirable feature of a poly 3,394,751 and 3,421,566 relate to movable sidewalls so urethane based network is the inherent lubricity of the that the tire tread force is communicated directly to the chemical intermediates (e.g. polypropylene glycol and rim. U.S. Pat. No. 4,057,092 relates to a circumferential 40 other diols) used for the polymerization. When melted, locking lug. Other proposals, such as U.S. Pat. Nos. a typical polyurethane based on polypropylene glycol 2,040,645; 3,392,772 and 3,610,308 have special units in will act as a natural lubricant. The temperature at which the interior of the tire. Other proposals include liquid the network breaks down can be controlled primarily lubricants within the tire, (U.S. Pat. No. 4,045,362) and by the types of urethane intermediates and chain exten solid lubricants which liquify on the addition of chemi 45 ders used. cals (U.S. Pat. No. 3,931,843). The lubricant of the present invention is essentially A problem generated by tires running ?at is the fric non-?owable at normal tire operating temperatures so tion which develops from the upper and lower portions that it does not adversely effect tire operation, but be of the deflated sidewall rubbing against each other. The comes liquid-like at ?at tire temperature and lubricates _ friction produces excess heat and causes the sidewalls to 50 the ?at tire to allow the tire to be driven twenty-?ve wear excessively. To reduce this friction, the inclusion miles or so for service. The lubricant which is used as a of either liquid or solid lubricants on the tire interiors coating or matrix on the interior surface of the tire is has been proposed. U.S. Pat. No. 2,040,645, for instance selected from the group consisting of polyether poly suggests a graphite lubricant, U.S. Pat. No. 3,610,308 urethane, polyester polyurethanes, polyesters and mentions the use of liquid silicone, and U.S. Pat. Nos. 55 polyureas (polyether and polyesters). The coating ma 3,739,829; 3,850,217 and 4,045,362 describe the use of trix does not begin to ?ow on the surface of the tire until polyalkylene glycols, glycerol, propylene glycol, sili the tire reaches a temperature between 65° C. to 150° C. cone and other lubricants. The liquid lubricants, how Preferably the coating matrix does not begin to ?ow ever, are not evenly distributed in the operating tire and until the tire reaches a temperature of from 80° C. to can adversely effect balance and tire performance. Solid 60 120° C. lubricants which liquify at ?at tire temperature are also The preferable coating matrix from the standpoint of known but they require a chemical reagent for liqui?ca non-flowability at normal service conditions and lubric tion (U.S. Pat. No. 3,931,843). ity is the polyurethane, either based on polyether or polyester. SUMMARY OF THE INVENTION 65 The coating matrix may be used alone or can contain Friction reducing capability is not the only important additional liquid lubricants such as polyglycols or can characteristic to be considered in designing a lubricant contain solid lubricants such as polyethylene or graph for use in run-?at tires. Other important parameters ite forming a mixture. The coating matrix can also con 4,340,104 3 4 tain rolling microbeads which is the subject of co-pend lubricant matrix 16 is also stable and remains in place in ing application Ser. No. 33,652 the tire when operated for long periods of time. The solid lubricant matrices 16 preferred for use in BRIEF DESCRIPTION OF THE DRAWINGS the present invention have excellent lubricity, are com FIG. 1 is a sectional view of a tire of the present patible with the rubber of the inner liner of the tire, are invention. stable and operable over a wide range of temperatures FIG. 2 is a sectional view of a test device to measure and shear rates, have a non-?ow property such that the friction and temperature rise. lubricant matrices remain uniformly distributed during normal use of the tire, have puncture-sealing capability, DESCRIPTION OF THE PREFERRED particularly when ?brous materials are added, and aid EMBODIMENT in air retention of the tire in normal use, particularly Referring to FIG. 1, there is shown a pneumatic tire. when the entire inner surface of the tire is coated with The tire has a thick tread portion 11 which extends a lubricant matrix. circumferentially around the tire, and sidewalls 12 Prior to this invention, there were no solid lubricants which extend from the tread portion along the sides of 5 which remained in place during normal tire use, but the tire. The tire is designed to be mounted on a conven which liqui?ed due to heat when needed and ade tional wheel rim 13 which has at its outer edges out quately lubricated the tire. The lubricant matrices as wardly flared ?anges 14 also of conventional design. disclosed hereinafter meet all of the requirements set Wire bead rings 15 are provided in the bead portion 16 forth in the previous paragraph. of the tire where the sidewall meets the rim 13. In ac 20 The lubricant matrices of this invention comprises cordance with conventional tire construction, the beads high molecular weight polymeric materials which are are designed to keep the tire on the rim when the tire is non-?owable, high viscosity, solid-like materials at nor in?ated. The in?ation pressure of the tire forces the mal tire operating temperatures but which become liq beads 15 against the ?ange 14, keeping the tire on the uid-like at the elevated temperatures generated by flat 25 rim and maintaining tire in?ation. tires. The solid-like state of the matrices is probably due The tire shown in the drawing may be of the conven to hydrogen bonding intermolecular interactions in tional bias/belted but is preferably of the belted radial cluding chemical reaction between adjacent polymer type. These tires have two bias or radial plies 17 and 18 molecules, physical cross-links or entanglements and/ or extending around the interior of the tire. The plies ex the combined. For example, the polyurethane lubricant tend from bead-to-bead and are folded around the bead matrix probably both forms hydrogen bonds between rings 15 so that the ends 19 and 20 of the plies are lo adjacent molecules and also chemically reacts to form cated in the sidewall region. There are also two steel or allophonate cross-links between the isocyanate and the fabric belts 21 and 22 extending circumferentially urethane linkages. Both the hydrogen bonds and the around the interior of the tire and located directly inte 35 allophonate cross-links are relatively weak and break rior to the tread portion 11. Conventional rubber com down at elevated temperatures generated in a ?at tire positions are used to form the tread and sidewall por resulting in the lubricant matrix forming a liquid lubri tions of the tire and the air-retaining inner liner. cant. A feature of this particular tire is the combination of Polyurethane actually covers a wide variety of mate the circumferential locking lug 24 and machine screws rials with polyethers and polyesters being the most 26. The lug results from a specially designed increase in commonly used. Strictly speaking, polyurethane applies the thickness of the sidewall at the end of the rim ?ange only to the reaction product formed between an isocya as shown. The locking lug 24 does not interfere with the nate-containing material and a hydroxyl-containing normal characteristics of the tire when in?ated. Upon material. Polyureas, on the other hand, are formed from de?ation, however, the locking lug 24 wraps around the 45 the reaction between an isocyanate-containing material ?ange 14 to secure the tire to the rim 13. Machine and an amine-containing material. The functionality of screws 26 also prevent the tire head from falling into the the latter reacting species should be at least two or rim well. Thus, the de?ated or ?at tire is secured to the greater in order for polymerization, chain extension rim allowing the tire to be driven ?at for a period of and/or cross-linking to occur. The isocyanate-contain’ time. ing material can be either in the form of a polyether The drawing illustrates a size BR78-l3 SBR tubeless based prepolymer such as duPont’s Adiprene LW-SlO tire mounted on a standard rim, and it will be under (a hexamethylene diisocyanate terminated polytetrahy stood that a larger tire, such as size HR78-l5 could have drofuran) or a polyester-based prepolymer such as Uni about the same shape. The rubber used in the tire can be royal’s Vibrathane system (a diphenylmethane diisocya the same as used in conventional tires, in which case the nate-terminated polyester) or simply a low molecular rubber of the sidewall portions could be an SBR with a weight diisocyanate. Shore A durometer hardness in the range of 40 to 80. The hydroxy-containing materials can likewise be Butyl rubber can be used in the inner liner to provide either a low molecular weight diol such as butanediol, maximum resistance to gas permeation. or a high molecular weight polyether polyol (e. g. It is preferable to provide the lubricant matrix 16 on 60 Dow’s Polyglycol 2000 and 4000) or polyester polyol the interior surface of the sidewall portions 28, particu (e.g. like that used in Mobay’s Multrathane system). larly at 47 to reduce the friction and heat generated by Examples of trifunctional polyols include trimethylol the rubbing of the upper and lower halves of the side propane and Dow’s Voranol 3000. walls when they are in contact during operation of the The more commonly used amines are difunctional de?ated collapsed tire. The liqui?ed solid lubricant 65 and have low molecular weight. Examples include du matrix 16 employed has excellent lubricity when hot. Pont’s MOCA (2,2’-dichloro-4,4’-diamino diphenyl The lubricant matrix has a non?ow stability which is methane) and MT Chemicals’ Apocure 601E (l,2-bis(2 maintained as the temperature is increased to 65° C. The aminophenyl)thioethane). 4, 340, ‘104 5 6 The type of chemical cross-links formed depends on The above components are mixed and heated to about the nature of the secondary reactions. Thegreaction 100° C. for one hour._ between an isocyanate and a urethane linkage results in X2-3107 is a non-reactive silanol terminated dimethyl an allophonate cross-link. The reaction between an siloxane containing 8% xylene. Polyglycols P4000 and isocyanate and a urea linkage, on the other hand, forms‘ P2000 are difunctional polypropylene glycols of molec a biuret cross-link. . , . . . .' ular weight 4000 and 2000, respectively. Plurafac D-25 The polyester lubricant matrix is solid containing is‘ a polyethylene oxide-polypropylene oxide copolymer crystalline particles which turns to a liquid whenthe surfactant. The above lubricant is‘a high viscosity, ?exi melting temperature of the crystalline particles is ble solid over a temperature range from room to about reached and therefore causes more lubricant matrix 75° C. Upon heating above 50° C., the lubricant will ?ow problems. Due to this flow problem, it is not con undergo gradual reduction in viscosity until it becomes templated that the polyester matrix will be the preferred a mobile fluid at temperatures above 100°C. Run ?at material where non-?ow is a criteria. The polyester mileage exceeding the minimum requirement (25 miles matrix, it is contemplated, is a superior lubricant to the at 25 mph) has been obtained with the use of this lubri polyurethane and in those situations where 50 to 100 cant- . run ?at miles are contemplatedis the preferred lubri The melting point should be more appropriately re cant. Higher melting crystalline materials are available ferred to as the temperature of liquefaction. It is the which can be usedto achieve the non-flow require temperatureat which the network lubricant is trans ments of the polyester lubricant during normal service forming into a highly mobile liquid. Most of the lubri conditions. ' Y 20 cants examined started to soften at the least 20° below The lubricant matrices can also contain very small the lique?cation temperature. The present melting point amounts of antioxidants, polyole?n lubricants, poly measuring device (Fisher Jones Co.) does not permit an ether lubricants, hydrocarbon wax lubricants, graphite, exact softening and liquifying temperature to be mea and other liquid and solid lubricants and small amounts sured. Hence, the liquifying temperatures listed are only of other ingredients commonly employed in run-?at 25 approximate, to perhaps :10” C. tires. They preferably contain cellulose ?bers or other The prepolymer used in this development work is suitable ?ller in an amount such as 3 to 8% by weight chosen by convenience and availability. The polyols are and preferably 4 to 6% by weight. The ?brous ?ller chosen because of their known lubricity. X2-3l07 is a may comprise ?bers with a length from 20 to 400 mi non-reactive silicone ?uid containing about 8% xylene. crons. 30 It is added in the lubricant to improve flow and lubric Solka Floc ?bers are made by Brown Company and ity. CAB-O-SIL fumed silica in formulation, imparts comprise cellulose ?bers. One type of ?ber is about 100 thixotropy to. the lubricant and thus, facilitates coating. microns long and about 16 microns thick. Another type of ?ber is about 50 microns long and about 17 microns thick. ’ " 35 EXAMPLE I(A) In addition to favorably affecting the rheological An example of a basic polyurethane lubricant behavior of the lubricant, the addition of the ?bers is shown below. imparts puncture-sealing capability to the lubricant. Trade Name The ?ber containing lubricant can, in some instances, Ingredients Manufacturer Parts successfully seal a puncture in a tire resulting from a 40 Polyether containing 4.25% Adiprene LWSlO 100 available NCO (duPont) nail. Leakage of air can,>in other instances, occur'upon Difunctional polypropylene Polyglycol puncturing with nails; however, the puncture sites be MW 4000 P4000 (Dow) 105 come covered with small amounts of the vlubricant, and MW 2000 P2000 (Dow) 55 leakage is reduced. - ' ' ' Silicone X2-3l07 (Dow 45 ‘ Corning) 5 Dibutyltin dilaurate T -l2 (M&T) 0.2 v EXAMPLE I ' catalyst Polyurethane Matrix Based Lubricant 2,6 Di-t-butyl-4-methyl Ionol (Harwick) 0.5 phenol Polyurethanes can be made to cross-link by either Total 265.7 allophonate or biuret branching or by the use of multi ' functional chain extender. The allophonate and biuret cross-links can dissociate on heating which leads to a This particular lubricant starts to soften at around reduction of viscosity. A typical polyurethane-paraf?n 150° F. (65° C.) but it does not become a mobile liquid wax lubricant is shown below in Table I. ‘ until the temperature reaches about 250° F. (125° C.). When this lubricant was added in the interface between TABLE I 55 two sliding rubber surfaces, friction was signi?cantly Heat Sensitive Polyurethane reduced as evidenced by the results shown below: Lubricant LubeI

. M - Parts By Weight Adiprene LWSlO 100 Apparent Ionol antioxidant 0.5 60 , Frictional Approx. Coef?cient X2-3l07 silicone 1.0 ~ Sliding , Force‘ Contact of Sliding Polyglycol P4000 ’ 106.7 Components (grams) Stress mPa Friction Polyglycol P2000 55.2 Rubber-on T-l2 catalyst 0.2 rubber (dry) (20210) 0.74 1.8 Paraf?n wax, ~70° C. MP 10.0 Rubber-on Paraf?n wax, ~l05° C. MP 100 65 rubber in the Plurafac D-25 ~- > 10.0 ‘presence of the Total 383.6 lubricant (Ex. IA) (a) thin ?lm (11285) 1.0 4,340,104 8 -continued TABLE II-continued Apparent HEAT SENSITIVE Frictional Approx. Coefficient POLYESTER-BASED LUBRICANT Sliding Force* Contact of Sliding Lubricant Components (grams) Stress mPa Friction Examples ‘ II III IV V VI (boundary) TX619 1.0 1.0 1.0 1.0 2.5 (b) thick ?lm Pluronics L61 0.5 0.5 0.5 0.5 1.5 (hydro- (8660) 0.8 Pluronics L81 2.5 2.5 2.5 2.5 5.0 dynamic) Pluronics L101 1.0 1.0 1.0 1.0 3.5 ‘Calculated from the torque required to maintain sliding of one rubber substrate on X2-3107 2.0 2.0 2.0 2.0 1.5 top of the other. The modi?ed Brabender plasticorder was used for the above Cab-O-Si] 4 friction measurement. Other conditions of the test follow: sliding speed = 115 rpm Total 340.2 360.2 360.2 360.2 159.5 (23 cm/sec); nonnal load = 10980 gm.

Over more than two hours of continuous sliding, the TABLE III temperature of the dry rubber substrates increased by at MATERIALS FOR least 39° C. while the lubricated rubber substrates in POLYESTER-BASED LUBRICANT creased only by about 14° C. The presence of the lubri Materials Description ( cant prevented abrasion of the rubber surfaces. Without PPG 2025 Polypropylene glycol of molecu the lubricant, abrasion was excessive. lar weight 2025 Other unique properties, aside from lubricity, that the 20 Emolein 2901A Polycarboxylic acid based on a lubricant possesses include non-volatility, dimensional C13 fatty acid stability and inertness toward the tire materials. Due to R-45 HT Hydroxyl-terminated polybutadiene with an approximate molecular its dimensional stability, a run flat tire which is coated weight of 2000 with the lubricant can be mounted in the conventional Vistanex LMMS Low molecular weight liquid way. The coated lubricant has no adverse effect on the 25 polyisobutylene running characteristics of the in?ated tire, i.e., minimal Ionol 2,6 Di-t-butylA-methylphenol, MP = 70° C. vibration during running. The viscosity and slight tacki TX619 Low molecular weight paraffin ness of the lubricant also imparts puncture sealing capa wax MP = 83.7-98.7” C. bility of the tire. Pluronics L61, L81, Copolymers of 10/90 poly(oxy Radial tires whose innerliner surfaces were coated L101 ethylene)-poly(oxypropylene) 30 with total molecular weight with the lubricant have been run-flat tested. The run of approximately 2000, 2500 ?at test results show a capability of 29.5 run-?at miles*. and 3600, respectively ‘Test Conditions X2-3 107 Non-reactive silicone contain Method=pulley wheel ing 8% xylene AFAX LR285 “Amorphous” polypropylene, Speed=25 mph 35 Load=35.6 kg (80% rated) MP = l2_4.6—164.8 Rim width: 11.4 cm Bead lock=rim well band In the synthesis of the polyester-based lubricant, the waxes were ?rst pre-melted in separate containers and EXAMPLE II then added together with the Pluronics and silicones to Polyester Matrix Based Lubricant the partially esteri?ed PPG 2025/Emolein 2901A. The Synthesis and Thermal Analysis PPG 2025/Emolein (2:1 molar ratio) esteri?cation pro ,cess was carried out at temperatures above 150° C. for This lubricant is prepared by blending paraf?n waxes half an hour or more. After the wax and the ester had of different melting points into an esteri?cation product i been thoroughly blended, the calcium stearate/mineral of a polycarboxylic acid and a polypropylene glycol oil mixture was then ?nally added with vigorous stir diol. Calcium stearate, mineral oil, and certain low mo ring to form a thick paste lubricant. Cab-O-Sil fumed lecular weight liquid polyole?ns (e.g., polyisobutylene silica, when needed, was added last. Results of the ther rubber, hydroxyl terminated polybutadiene) are added mal analysis (DTA) of the lubricants are shown in Table for viscosity and rheological modi?cations. To improve IV. The analysis was done on duPont’s Macrocell Ther mixing between the paraf?ns and the various polar mal Analyzer using glass beads as the reference. Mea materials, surfactants (e.g., Pluronics, silicones) are surements were done ?rst by heating the sample to as used. Typical formulations and a description of the high as 160° C. at a rate of 20° C./min. followed by materials used are shown in Tables II and III, respec quenching at the same rate. The melting temperatures tively. 55 given in Table IV represent the average values taken TABLE II from both the heating and cooling cycles. HEAT SENSITIVE TABLE IV POLYESTER-BASED LUBRICANT DIFFERENTIAL THERMAL ANALYSIS Lubricant OF POLYESTER-BASED LUBRICANTS Examples II III IV V ,VI 60 Tm (°C.) PPG 2025 100 100 100 100 25 Lubricant Peak Range Emolein 2901A - 91.2 91.2 91.2 91.2 22.8 AFAX LR285 — 20 —- —— -— 11 110.8 105.0-l18.7

R-45 HT —- — 20 — - III 112.5 l01.8—l22.0

Vistanex LM—MS — -— — 20 — IV 111.9 105.4~122.0 Ionol 0.5 0.5 0.5 0.5 0.2 65 V 112.0 l09.4-ll9.5 Mineral Oil 60 60 60 60 40 Calcium stearate 45 45 45 45 25 Paraffin wax MP 215 35 35 35 35 30 When a ?at occurs, the temperature of the tire can Carnauba wax 1.5 1.5 1.5 1.5 2.5 easily rise above 100° C. within 10 minutes at 25 mph. It 4,340,104 10 is therefore desirable for the lubricant to melt to a low The conversion (FIG. 2) of the commercial Bra viscosity ?uid at about 100°C. for effective lubrication. bender Plasticorder into a friction measuring device A lubricant with a relatively low melting temperature involved the following modi?cations. would flow and affect the dynamic balance of the tire (1) The two cam‘type rotors were replaced with a adversely. On the other hand, a lubricant having too single flat surface rotor 50. The rubber specimen 51 high a melting temperature would not function prop whose friction coef?cient is to be measured is molded erly when needed. Lubricants II through V started to on a metal ring 52. The ring, 2.54 cm ID><2.54 cm melt at around 100° C. which appears to be a desirable wide><0.635 cm thick (half of which consists of the region. rubber), ?ts snugly onto the rotor. (2) The center-jacketed mixing chamber was replaced VISCOSITY MEASUREMENT with a non-jacketed asbestos insulated steel chamber 54 The viscosities of the lubricants above their melting of different con?guration. The temperature of the points were determined using a Haake/Rotating vis chamber can be controlled. Besides, the chamber serves cometer. The results showing the effect of shear rate on as a reservoir for the lubricant. viscosity at 125° C. are summarized in Table V. (3) The conventional ram and loading chute assembly was replaced by one supported by linear bearings to TABLE V minimize friction. EFFECT OF SHEAR RATE ON VISCOSITY The slider, added to the Brabender, ?ts onto and OF POLYESTER~BASED LUBRICANT 20 pivots freely around the left supporting rod 58 used to Lubricant II III IV V VI‘ hold the conventional mixing chamber. The slider con Shear Rate sec‘1 Viscosity, centipoises tains a 6.35 cm>< 1.27 cm><0.635 cm groove 60 which 88.2 22.7 18.1 18.1 40.8 294.8 holds the flat rubber specimen 62. 176.3 20.4 18.6 17.0 32.2 238.1 264.5 19.4 18.1 16.6 30.2 176.9 The damping device on the plasticorder is discon 529.0 22.5 18.9 20.4 32.9 88.5 25 nected when friction measurements are made to obtain ‘Measured at 140° C. faster response. The modi?cations were made in such a way that changing from conventional Brabender torque All the above measurements were done using an measurements to rubber friction measurement can be MV-2 rotor. MV-2 designates a particular type of rotor completed in less than 10 minutes. ‘ and beaker set-up used in conjunction with the Haake When a ?at tire occurs, the bead wrap comes into viscometer. This particular rotor has a hollow bottom contact with the crown portion of the sidewall. The and its diameter and height dimensions are 36.8 mm and bead wrap is much stiffer due to the presence of the 60 mm, respectively. With the exception of lubricant beads and the higher hardness of the bead compound. In VI, the constancy of viscosity over the shear rate range order to approximate this condition in the laboratory, studied is rather surprising and resembles that of a New two compounds of different hardnesses were used for tonian liquid. friction measurements. The two compounds are essen tially identical except in the amount of carbon black VOLATILITY STUDY used, as shown in Table VII. The volatility of the polyester-based lubricants was TABLE VII measured in terms of the percent weight loss on heat RUBBER COMPOUNDS“ USED aging at 105° C. up to a period of one week. Results of FOR FRICTION STUDY the aging study are summarized in Table VI. Compound I II ~ Ingredients phr phr TABLE VI 45 Chlorobutyl HT1068 60 60 VOLATILITY OF RSS #1 10 10 POLYESTER-BASED LUBRICANTS SBR 1502 3D 30 Lubricant II III IV V VI Maglite D 0.5 0.5 Time of aging (days) Cumulative Weight Loss (%) HAF Black 40 113.3 Soft clay 40 40 l 5.9 5.8 2.5 7.8 5.8 50 Flexon 840 10 10 3 9.3 15.9 8.9 11.5 15.8 Amberol ST137 4 4 5 12.3 17.7 11.6 17.7 24.3 Stearic acid 1 1 7 16.8 23.2 15.2 22.1 30.5 Zinc Oxide 5.0 5.0 MBTS 1.25 1.25 Vultac 3 1.25 1.25 Lubricant IV is the least volatile. Close examination 55 Totals 203.0 276.3 of this aged sample shows that a layer of ?lm was depos 'Enjay Chlorobutyl formulary #25004 ited on top of the lubricant. The ?lm is relatively tough and is probably formed from the oxidation of the liquid The materials used in Table VII are: polybutadiene. The formation of the ?lm probably mini Chlorobutyl HT-l068: contains 1.2% by weight of mizes further volatilization. 60 chlorine in an isobutylene/isoprene rubber; the FRICTION MEASUREMENTS level of unsaturation is about 1.4%, ML 1+8 @100° 0:50, speci?c gravity=0.92 (Exxon Co.). An effective lubricant should signi?cantly reduce RSS #1: natural rubber as smoked sheet sliding friction between rubber surfaces inside the run SBR 1502: a styrene-butadiene rubber with 23.5% ?at tire. The ability of the lubricants to reduce friction 65 bound styrene and ML 1+4 @100° C.=52 (Gen was characterized using a modi?ed Brabender Plas eral Tire) ticorder. The device, shown in FIG. 2, has reproduc Maglite D: magnesium oxide, used as vulcanizer and ibility to within :tl5%. activator (C.P. Hall). 4,340,104 111 12 Flexon 840: a paraf?nic based petroleum oil (Exxon speed. The results for the temperature effect are some Chemical) what scattered. Amberol ST 137: a phenol formaldehyde resin used primarily as cross-linker for the chlorobutyl rubber LUBRICATED FRICTION (Rohm and Haas) The friction coef?cient increases with normal load in the lubricated case. At increasing load, the lubricant film is probably partially squeezed out so that direct mm contact between rubbers and, hence increasing friction 1 II coef?cient occurred. Shore A 62 86 10 The friction coef?cient between the hard and the soft 5% Modulus, psi (MPa) 25 (0.19) 130 (0.96) rubbers using various lubricants is summarized in Table 10% Modulus, psi (MPa) 50 (0.38) 185 (1.3) 100% Modulus, psi (MPa) 280 (1.9) 965 (6.7) IX. All measurements were done under the following 300% Modulus, psi (MPa) 840 (5.8) - conditions. Tensile, psi (MPa) 1690 (11.6) 1315 (9.1) Temperature: 100° C. % Elongation 550 150 15 Sliding Speed = 20 cm/sec. Tear Trouser, pli (kN/m) 31 (5.5) 19 (3.3) Normal load: 19.5 kg TABLE IX Compounds I and II are hereby referred to as soft and hard compounds, respectively. Although friction mea COEFFICIENT OF SLIDING FRICTION BETWEEN RUBBERS surements have been done using various combinations 20 Friction Force Friction of rubber pairing (i.e. hard/soft, soft/hard, hard/hard, Lubricant (Newtons) Coef?cient soft/soft), only the results showing the sliding of the None 1 19. 1 0.65 hard rubber on the soft rubber will be presented and II 10.6 0.056 discussed. The friction between a hard rubber slider and III 9.8 0.051 a soft rubber track best resembles the conditions en IV 10.0 0.054 ‘V 1 1.0 0.056 countered in a flat tire. The results of friction coef?cient VI 10.6 0.056 measurements between the non-lubricated rubber sur faces are shown in Table VIII. The results show the effectiveness of the polyester TABLE VIII 30 based lubricants in reducing sliding friction between NON-LUBRICATED FRICTION rubbers. A tenfold reduction in friction coef?cient is Sliding Friction Coefficient Between observed in all the lubricants examined. Hard and Soft Rubbers (Modi?ed Brabender) Network gels having melting points ranging from 70° Sliding Speed Friction Coefficient C. to 170° C. have been developed. Examples of various cm/sec. Normal Load kg (Modi?ed Brabender) network lubricants having a range of melting points are 0.85 15.3 1.40 shown in Table X. The lower melting gels are generally 0.85 19.5 1.18 0.85 24.4 0.91 slightly tacky on touching while the higher melting gels 2.1 15 15.3 1.21 are stiff and rubbery. Most of the gels started to soften 2.115 19.5 1.08 at some temperature which is quite distant from the 2.115 24.4 0.92 40 melting temperature. TABLE X All tests were run at room temperature. In the absence of a lubricant, sliding between rubbers EXAMPLES OF NETWORK LUBRICANTS resulted in an abrupt rise in temperature of the rubbers, Lubricant (Examples) VII VIII IX X XI 45 regardless of the load applied. This leads to severe wear Adiprene LWSlO 100 100 100 100 I00 Polyglycol P4000 105 — 71.2 — 102 of the rubbers. In order to avoid complications arising Polyglycol P2000 55 — 36.8 95.6 52.8 from heat build-up and wear, all the test measurements Voranol 3000 -— 100 — -— — were completed before noticeable heat build-up started Propylene glycol — - 1.3 —- — to occur. This usually took less than 5 minutes. In most DC203 — 5.0 -- — — 50 X2-3l07 5.0 — 2.5 2.0 2.5 cases, an equilibrium torque would have been reached CAB-O-SIL fumed after two minutes of sliding. The phenomenon of stick silica #MS — — — -— 125.0 slip was prevalent in all cases. Ionol 0.5 0.2 0.5 0.5 0.5 The friction torque was taken as the average of the T-12 0.2 0.2 0.2 0.2 0.2 BD/TP440 (95/5) — 4.24 — — — minimum and maximum values over the entire time Totals 265.7 209.64 212.5 198.3 183.0 scale. This averaging technique is valid as long as slid Approx. Liquifying ing speed is greater than 1 cm/sec. Results obtained this Temp. 85 110 120 175 220 way are reproducible to within 15%. As expected, the friction force is not directly proportional to normal The materials used are: load. There is a pronounced non-linearity especially at 60 Voranol 3000: a trifunctional polypropylene glycol the low load range. In another experiment involving (Dow Chemical). hard rubber sliding on the soft rubber at 11 cm/sec. at DC 203: a silicone based material used for flow modi 70° C., the coef?cient of friction decreases from 3.1 at ?cation (Dow Corning). about 1 kg normal load to 0.9 to about 18.2 kg load. BD/TP 440 (95/5): stands for a mixture of butanediol Reference to FIG. 2 shows the actual normal load is and Pluracol TP 440 (95:5 weight ratio). Pluracol related to the apparent normal load by a factor of Cos TP 440 (BASF Wyandotte) is a trifunctional 6. For a given applied normal load, frictional force and polyol. coef?cient decrease with increasing temperature and I claim: 4,340, 104 13 14 1. A pneumatic tire having an interior surface the heat generated by the tire running flat causes mounted on a rim to de?ne an in?ation chamber, the the tire to reach a temperature of between 65 de rim having means to prevent the tire beads from becom- grees C. and 150 degrees C. and liquify the matrix. ing dislodged from the rim when the tire is operated in 2. The tire of claim 1 wherein the coating matrix does a de?ated condition, wherein the improvement com- 5 not begin to flow until the tire reaches a temperature of prises: from 80° C. to 120° C. I a solid coating matrix on the interior surface of the 3. The tire of claim 2 wherein the coating matrix is a tire selected from the group consisting of polyes- polyurethane. ' ters, polyureas, and polyurethanes which coating 4. The tire of claim 2 wherein the coating matrix is a matrix does not begin to ?ow on the surface of the 10 polyester. tire and adversely effect the balance of the tire until * * * * *

15

2O

25

3O

35

40

45

50

55

60

65