GB2137639A - Deflation-proof tire and elastomeric filling medium therefor - Google Patents

Abstract

A deflation-proof pneumatic tire comprises a casing and a void-free elastomeric filler formed from a water in oil urethane emulsion having the carbon dioxide which results from the polymerization reaction dissolved therein. The tire casing is injected with a combination comprising a polyol, an organic polyisocyanate, and water in a stoichiometric excess of the amount required by the polymerization reaction to form a polyurethane elastomeric emulsion having water in the disperse phase, thereby providing a substantially void-free filling material.

Description

SPECIFICATION Deflation-proof tire and elastomeric filling medium therefor Field of the Invention The field of art to which the invention pertains includes the field of polymer-filled pneumatic tire casings.

Background and Summary of the Invention The pneumatic tire, i.e. a reinforced rubber casing containing a gas at a proper pressure, provides distinct advantages in providing load support for automobiles, trucks and other on-road vehicles. However, a major disadvantage of pneumatic tires is presented with off-road vehicles or industrial vehicles such as forklift trucks due to the inconvenience and expense posed by the risk of the puncturing and deflation of the tire. For example, tractors or other off-road vehicles may encounter sharp rocks capable of puncturing a tire, and industrial forklift trucks may encounter scrap metal material to the same effect.

In many operations, e.g. the operation of farm tractors, it is advantageous to add ballast to a tire or tires of the vehicle to provide additional stability in certain types of terrain. In this regard, operators of such vehicles have added metallic weights to the wheels or wheel hubs of tractors, or have filled the pneumatic tire casings of the vehicles with water. While the water in the pneumatic tire casings adds considerable weight as desired, the water adds considerable inertia to the vehicle if the tire is not completely filled, and a puncture of the tire casing allows the water to flow out of the tire to the level of the puncture with resultant damage to crops. If a puncture occurs at a substantial distance from a source of water, pumping means and puncturesealing composition, repairs are difficult to effect.

A variety of alternatives have been presented which attempt to prevent or mitigate the disadvantages of pneumatic tire casings. For example, solid rubber tires have been used on industrial forklift trucks, but fail to provide the shock absorption and traction of the deflectable pneumatic tire. A more prevalent method for overcoming the foregoing problems is that of converting the pneumatic tires to deflectable solid or semi-solid composite tires. Such solid, deflation-proof tires have depended on the presence of a foamed elastomer filling, for example, Lambe U.S. Patent No. 3,022,810, describes a pneumatic tire filled entirely with an intrinsically-compressed resilient foam which is produced in situ, that is, directly within the tire.The disclosure is exemplified by a polyurethane foam in which carbon dioxide bubbles or evolved during the reaction in order to produce a rubberlike polymer foam within the casing. Altorfer U.S. Patent No. 3,112,785 adds a conventional foaming agent to liquid polyurethane foaming material as it is pumped into a tire casing with similar results. Altorfer then injects a liquid antifreeze solution into the tire to be dispersed along with air into the cellular structure. Talcott et al. U.S. Patent No. 3,381,735 describes a deflation-proof vehicle tire in which synthetic rubber filler material is foamed in place and then vulcanized. Lombardi et al. U.S. Patent No.

3,605,848 describes a tire having its casing filled with a microcellular, open cell urethane core.

Water is described as serving as a blowing agent in the production of carbon dioxide upon reaction with the isocyanate component of the polyurethane precursor liquids. When the precursor material is injected into the tire casing, it results in the formation of a polymer foamed in situ.

Due to the fact that the foam fillings in such tires are comprised of gas bubbles and are easily flexed, these tires have serious disadvantages which relate to excessive heat buildup within the tire and filler not only due to a hysteresis effect, but also results from the fact that deflection causes the gas-filled cells to collapse and allow the cell walls to frictionally engage, creating additional heat. In addition, the foam itself tends to be an insulating medium, which tends to retain the heat within the filler rather than conducting it to the tire casing. Often such heat causes filler breakdown which decreases or eliminates casing support.

In addition, as foam fillings are formed by generating gases in situ, volumes and pressures are unpredictable and in order to obtain sufficient uniformity, factory installation is required with expensive and inordinate controls to assure uniformity from tire to tire.

Gomberg U.S. Patent Reissue No. 29,890 describes a pneumatic tire casing filled with a void-free elastomeric material which is claimed to have superior heat buildup characteristics.

However, because the Gomberg elastomer entirely fills the tire casing without voids, the cost of filling the tire is substantially increased. Efforts to reduce the cost by diluting the filler material with an extender oil can result in a sharp decrease in desirable hardness.

The present invention provides an elastomeric filling material for a pneumatic tire casing, which comprises a water-in-oil urethane emulsion which polymerizes in a solid, elastomeric form. A substantial stoichiometric excess of water is dispersed in the urethane polyol, and the carbon dioxide produced by the polymerization reaction is dissolved in the elastomer and the water dispersed therethrough to produce a substantially void-free elastomeric filling material. As the dispersed water may constitute up to about sixty percent of the composition, it will be appreciated that the result is a large saving in the cost of filling a tire. In addition, as water is a superior conductor of heat, the heat that is produced within the polymer will be conducted to the tire casing, i.e. the water tends to compensate for the fact that the polymer itself is a relatively poor conductor of heat.In addition, the water-in-polymer also appears to have an extremely low hysteresis effect, and thus a low initial heat production.

The invention provides an internally-curing polyurethane elastomer formed from a polyol, an organic isocyanate and water in excess of that required to polymerize the organic isocyanateterminated polyol. While the stoichiometric excess of water generally absorbs the carbon dioxide, alkaline materials such as magnesium or calcium oxide may be added to assist in absorbing the carbon dioxide which is formed in this reaction.

As a result of the water reaction, a polyurea-containing polyurethane elastomer is obtained having superior hardness and heat transfer characteristics. Oil can be added to control cost and viscosity while maintaining substantial durometer hardness. In addition, while scrap rubber dust, a particularly desirable and cost effective filler, is difficult to add to existing oil-based urethanes due to the moisture and air entrained thereon, particulate fillers of this type can easily be added in the form of a water slurry.

The urethane is prepared by reacting a polyol with an organic polyisocyanate and water, as described above. In a particular embodiment, the polyol is a polyol oxypropylene glycol triol or a combination of triols and diols. Ethylene oxide-capped triols are particularly advantageous due to their greater affinity towards water, although straight oxypropylene glycol triols, triol-diol combinations or other polyols having poor water affinity may be used in combination with more effective emulsifiers or extra mixing. A particularly useful polyisocyanate is toluene diisocyanate.

Another useful polyisocyanate is polymethylene polyphenylisocyanate. As described, one can also incorporate a small amount, up to about five weight percent, of an absorbent of carbon dioxide, such as calcium oxide or hydroxide, aluminum trihydrate, magnesium oxide, zinc oxide or the like.

Detailed Description of the Preferred Embodiment While the invention will be exemplified by reference to a specific polyurethane elastomeric polymer formed from a water-in-oil emulsion, the invention is general and certain aspects in particular are broad in scope, for example, the concept of curing a water-in-oil urethane emulsion within a pneumatic tire casing to form a void-free elastomer having the carbon dioxide which results from the elastomer reaction dissolved therein. Consequently, specific details disciosed herein are merely representative and are deemed to afford the best embodiments known at this time to provide a basis for the claims which define the scope of the present invention. It is to be understood that the invention is useful with any pneumatic tire casing, from bike size to giant size, whether the tire is of the tubed or tubeless variety.

Brief Description of the Drawings The Figure is a cross-sectional view of a conventional tire casing mounted on a vehicle wheel rim and filled in accordance with the present invention.

As shown in the Figure, a conventional tire casing 10 having a road-engaging tread 12 thereon is mounted on a rim 14 of a vehicle wheel (not shown). The rim 14 has an opening 1 5 for a valve stem 1 6 through which the liquid polymer is pumped into the tire. In following the procedure of the present invention, the space confined by the rim 14 and casing 10 is filled with an elastomeric organic polymer material 1 8 formed from a water-in-oil polyol emulsion.

Methods for filling pneumatic tires with elastomeric filling material are well known; see for example, the detailed description given in the Gomberg Patent Re. 29,890, the teaching thereof being incorporated herein by reference. The liquid filling material is introduced through the valve stem of the tire when the tire is mounted firmly on the wheel. A small hole is punctured through the tire opposite the valve stem opening to provide a gas escape outlet while the liquid filling material is being injected into the inside of the casing. As usual, the filling material reactants are provided in two separate containers, usually referred to as an "A-side" and "Bside", although in the present invention, the reactive materials other than water can be provided from one container. From the point of view of ease of measurement, the A-side and B-side are usually formulated so as to require approximately equal volume for appropriate reaction, as will be described in more detail hereinafter.

The mixed liquid is pumped into the tire. After partial filling, entrapped air is released by puncturing the tire as described. When all air is displaced by the liquid, the puncture is sealed with a flat head metal screw. Final liquid pressure must be about the same as used with air to firmly secure the tire casing to the rim and prevent slippage. When fully pressurized, the tire liquid supply inlet is sealed and the urethane is allowed to cure to full hardness before use.

Continuous processes for tire filling can be used, simultaneously proportioning, mixing, pumping and pressurizing the liquid components. Metering, pumping, and pressurizing in continuous equipment for tire filling may be accomplished by coupling two identical double-ball pumps to a single air motor. The pumps cycle simultaneously and deliver identical volumes of the two liquid components. Mixing is accomplished with static mixers. Several types are available including Tah, Ross, Kennics, and Komax. These mixers function in a similar fashion, i.e., they all blend liquids by dividing and recombining liquid streams pumped therethrough.

Mixers of this type are described in U.S. Patent No. 4,093,188, and may be used alone or combinations of different types may be employed. Slow pumping speeds generally provide better mixing and a particularly homogeneous elastomer. The inclusion of small amounts of soap, detergent, or other emulsifier also improves mixing. Dynamic mixing also produces homogeneous elastomers, but static mixers are particularly advantageous as they allow the combination of the steps of proportioning, mixing, pumping, and pressurizing the pneumatic tire casing.

The elastomer cures sufficiently overnight at room temperature, thus offering significant advantages over known tire filling materials which require longer time periods or higher temperatures for proper cure. The tire may then be used for its intended purpose. As usual, with elastomeric tire filling materials, additional cure may take place for a period of up to two weeks during use.

Referring more particularly to the polymer forming materials, the precursors to a polyurethane elastomer are advantageously provided in two parts, an A-side and a B-side. The A-side may comprise the polyol component and the organic polyisocyanate component. In addition, in a preferred embodiment where extender oil is used, the extender oil is inclined on the A-side. The B-side contains the water as well as an absorbent for the carbon dioxide produced by the isocyanate-water reaction and various emulsifiers, thickeners, and defoamers such as are suited to the particular mixing technique or use of the product. Alternatively, all the components except the water can be located.on one side, in which case, streams coming from the two containers must be metered appropriately to provide the desired ratio of components.Another alternative is to provide all of the polyol and polyisocyanate components on one side, volumetrically balancing the other side with extender oil, so that the two streams are of equal volume. Generally, the components can be combined in any ratio to fit the convenient processing of any tire filling machine.

Any of the organic polyisocyanates used in the art to prepare polyurethanes and polyureacontaining polyurethanes can be used, for example, hexametylene diisocyanate; m-xylyene diisocyanate; toluene diisocyanate; polymethylene polyphenylisocyanate; 4,4'-diphenylmethane diisocyanate; m-phenylene diisocyanate; methylenebis (2-methyl-p-phenylene) diisocyanate; 3,3'dimethoxy-4,4'-biphenylene diisocyanate; 2,2', 4,4'-tetramethyl-4,4'-biphenylene diisocyanate; 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate; 4,4'-diphenyl-isopropylidene diisocyanate; 1,5'-naphthylene diisocyanate; and polymethylene polyphenylisocyanate. One group of especially preferred polyisocyanates are the toluene diisocyanate isomers, particularly 2,4-toluene diisocyanate. The commercially available blends of the 2,4- and 2,6-isomers are effective -- the 80:20 and 65:35 blends being most readily available.Another especially preferred polyisocyanate is polymethylene polyphenylisocyananate such as sold by Upjohn Company under the trademark PAPI 901. This has an average molecular weight of 260-300, an isocyanate equivalent of 133, an NCO content of 31.6 weight percent, an acidity of 0.05% as HCI and a viscosity at 25'C of 80 Ips.

The polyol can be chosen from a variety of OH terminated polyethers. Preferred are the polyoxyalkylene polyols having 2-4 hydroxyl groups and where the alkylene group has 2-6 carbon atoms. A large variety are available, obtained by polymerization of an alkylene oxide, such as ethylene oxide, propylene oxide, or butylene oxide, with a glycol. Polyethers having higher functionality may be obtained by reaction with a triol or higher polyol, such as glycerine, trimethylolpropane, and pentaerythritol. Polyols of the above types are available commercially, for example: Voranols (trademark) from Dow Chemical Company; Poly-G (trademark) from Olin Chemicals Division; Pluracols (trademark) from BASF Wyandotte Corporation and Carpol (trademark) from the Carpenter Chemical Company.In particular, an ethylene oxide-capped predominantly polypropylene-oxide diol or triol having a molecular weight of at least 1 ,000 is most suitable.

A portion of the polyisocyanate, i.e. the polyisocyanate on the A-side, can be reacted with the polyol as to form a prepolymer or quasi-prepolymer, in which essentially all the terminal groups are isocyanate groups. Because the reaction between water and the isocyanate group is desired, one would not ordinarily "block" the prepolymer terminal isocyanate group, as is commonly done and is described in the Gomberg patent. On the other hand, the present method does not preclude blocking of a certain proportion of the polyisocyanate groups.

It is preferred to add at least 10 volume percent, up to about 30 volume percent, of an extender oil to reduce the cost and the viscosity of the elastomer precursors. It has been found that such additions of extender oil do not substantially lower the Durometer hardness of the elastomer. One can use any of the processing oils commonly used in industry to extend polymers that would be compatible with the urethane elastomer. Preferably, the extender oil is of relatively low viscosity, is substantially aromatic and may contain polar compounds. A particularly effective oil is the aromatic extender oil sold under the trademark Califlux LP sold by the Witco Chemical Company. Califlux LP comprises about 78 percent aromatics and 9 percent polar compounds, the remainder being saturates.It has a specific gravity at 6"F of 0.9786, an API gravity of 13.1, a viscosity, SUS, at 100"F of 169, a flash point C0C of 320 F, and an aniline point of less than 59"F.

Colloidal hydrated silicates, e.g. clay or other optional fillers, may also be added to the B-side as fillers or thickeners and to assist in mixing or in slurry formation if such is desired, as may small amounts of surfactants or emulsifiers, e.g. approximately 1 % of the B-side composition.

Other thickeners include calcium carbonate, talc, carbon black, cabosil, ground walnut shells or rice hulls, water soluble amines, gelling agents or crosslinkers.

Scrap rubber strands, rubber buffing dust or other rubber particulate material are added to the B-side to form a slurry which may thereafter be easily mixed with the A-side to form the urethane emulsion tire filling material of the present invention. A wide range of natural or synthetic rubber materials may be used, from a very coarse strand-like material having a maximum dimension of from 1/4 to 1/2 an inch, to a very fine rubber dust passing a 40-mesh sieve such as that which is ground from tires before retreading. The particular size of rubber may be varied in accordance with the intended use of the tire casing, and where a denser product is desired, it is preferable to use varying sizes of rubber particles in order to decrease the voids therebetween.The addition of a small amount of surfactant allows the addition of a higher proportion of particles in relation to a given amount of water, and the surfactant in combination with colloidal substances such as clay provides a semi-thixotropic composition which suspends the particulate filler for an extended period of time.

Various emulsifiers, known in the art, may also be added to the A or the B-side to assist in the formation of the water-in-oil emulsion. Similarly, step addition of the water side has proven advantageous in the dispersion of the water in the continuous oil phase.

Depending upon the application, a portion or all of the B-component may be mixed immediately prior to use, or the B-side may be premixed at the factory. For example, the desired thickness, fillers, emulsifiers, and carbon dioxide absorbent could be prepackaged and shipped, along with the A-side, to the use site whereupon the water portion of the B-component could be added thereto to form the B-side, which is then added in the proper amount to the A-side as described. It will be recognized that substantial shipping costs will be saved by this technique.

Moreover, the B-component, in a dry state, has an unlimited shelf life and the A-components hereafter described have shown a shelf life of 7 to 8 years without degradation.

It is to be understood that the ingredients may be placed on either side as long as the isocyanate is not mixed with a stoichiometric excess of water in a pre-mix form.

By curing the water-in-oil emulsion under conditions whereby the carbon dioxide is dissolved in the resulting elastomer and remains dissolved, i.e. wherein water in a stoichiometric excess of that required for polymerization is contained as a disperse phase in the elastomer to absorb the carbon dioxide, the heat otherwise produced by intrncellular friction in foam-filled tire casings is eliminated and the heat formed by the hysteresis effect is conducted from the filling medium to the tire casing.

The following examples, in which all parts are by volume unless indicated otherwise, further illustrate the invention.

Example One The A side of a liquid polyurethane precursor was prepared by mixing 35 parts of a 6,000 molecular weight ethylene oxide-capped polypropylene glycol based triol (Carpol (trademark) 6500) with 5 parts of toluene diisocyanate and 60 parts of Califlux LP extender oil.

The B side of the precursor was a blend of 96 parts water, 1.8 parts magnesium oxide, 1.5 parts Methocell J5MS thickener (Dow Chemical Company), 0.25 parts soap flakes and 0.009 parts SAG 30 defoamer (Union Carbide Company). The A and B sides constituted a 1:1 weight or volume system, and were mixed to form a water-in-oil emulsion in a STATA-tube (trademark) motionless mixer, produced by Tah Industries, Inc.

The formulation of Example One produced a elastomer having a "7" Shore A hardness and a pot life of about fifteen minutes.

Example Two The A side of the polyurethane precursor was prepared by mixing 35 parts of a 4,800 molecular weight ethylene oxide-capped polyol oxypropylene glycol triol (Poly-G (trademark) 8536) with 5 parts of toluene diisocyanate and 60 parts of Califlux LP extender oil;-The B side of the precursor was a blend of 96 parts water, 1 part magnesium oxide, 2 parts clay and 1 part Methocell J5MS thickener. The clay and the thickener are included to provide a superior emulsion with the A side. The emulsion was mixed as described in Example One.

The above formulation provided a dry elastomer having a "O" Shore A hardness and a pot life of about fifteen to twenty minutes.

Example Three An additional elastomeric composition was prepared by providing an A side which included 35 parts of a 6,000 molecular weight triol (Poly-G (trademark) 8529), 5 parts of toluene diisocyanate and 60 parts of Califlux LP extender oil. The B side included 98 parts water, 1 part magnesium oxide and 1 part Methocell J5MS thickener. The emulsion was mixed as described in Example One.

This formulation provided a resilient elastomer having an "8" Shore A hardness and a working life of about twenty minutes.

Example Four It was found that the hardness of the elastomer does not depend upon molecular weight of the polyol, but rather upon the amount of the toluene diisocyanate in the polyurethane precursor. An A side was prepared containing 31 parts of the 6,500 molecular weight trio employed in Example Three, along with 9 parts of toluene diisocyanate and 60 parts of Califlux extender oil. The B side contains 95 parts water, 3 parts magnesium oxide and 2 part Methocell J5MS thickener. The emulsion was mixed as described in Example One.

This formulation gave a dry elastomer having a "22-25" Shore A hardness and a working life of about ten minutes.

Due to the fact that water is used as a carrier in each of the foregoing formulations, one can add moisture-containing diluents, which is not feasible in water-free formulations. In this regard, in the processing of tires, a large quantity of rubber dust is created which contains a small amount of moisture which can be added as a diluent to any of the described examples in an amount up to fifty-eight percent or more.

The hardness data regarding the elastomers of Examples One through Four is shown in Table One. It is seen that the hardness does not necessarily increase with an increase in the molecular weight of the polyol. To properly interpret these results, it should be noted that higher molecular weight polyols have substantially fewer hydroxyl groups to react with the TDI. Thus, the free TDI in the system is lower in Example Two as a larger portion of the total TDI has reacted with the polyol. Example Two is seen to have the lowest hardness on the durometer "A" scale as Examples One and Three have more available TDI. Example Four is consequently seen to have the highest hardness rating.

It is to be understood that an elastomer of the present invention of any hardness value will be useful, dependant upon its intended use. For example, an extremely rigid tire-filling material having a durometer "A" hardness of 35 was produced using the formulation of Example Four with 10 parts of TDI.

Table One Molecular Isocyanate Polyol Example Weight (parts) (parts) Hardness 1 6,000 5 35 7 2 4,800 5 35 0 3 6,000 5 35 8 4 6,000 9 31 22 Example Five The A and B components described in Example One were pumped through a system consisting of two identical double-ball Arrow (trademark) pumps, each driven by a single airdriven motor, and mixed in a Tah STATA-tube (trademark) motionless mixer. This system provided the described water in oil emulsion which was then pumped into four Goodyear Power Torque (trademark) tires (11.2 X 24 and 1 8.4 X 38) at a pressure of about 80 psi, and allowed to cure overnight. The next day, the tires were mounted on a Kobata four-wheel drive tractor, which was then used to field test the experimental product. After nine months of daily use in farming operations, the tires were removed and examined. The tires were worn approximately 50%, and one of the tires had been recapped (three hours at 300 F.) and no apparent damage to the tire filling medium was detected.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the invention and, without departing from the spirit and scope thereof, can adapt the invention to various usages and conditions. Changes in form and the substitution of equivalents are contemplated as circumstances may suggest or render expedient; and although specific terms have been employed herein, they are intended in a descriptive sense and not for purposes of limitation, the scope of the invention being delineated in the following claims.

Claims (27)

1. A method for obtaining a deflation-proof tire, comprising: curing a water-in-oil emulsion comprising a polyol and an organic polyisocyanate, and a substantial stoichiometric excess of water in the disperse phase, the water being present in an amount sufficient to produce carbon dioxide and to form a polyurethane elastomer having a portion of the water dispersed therethrough, the carbon dioxide being dissolved in the elastomer to produce a substantially void-free elastomeric filling medium within the casing.

2. The method of claim 1 in which the polyol is a polypropylene glycol diol or triol.

3. The method of claim 2 in which the emulsion additionally comprises at least 10% oil.

4. The method of claim 3 in which a major portion of the oil is aromatic.

5. The method of claim 4 in which the polyisocyanate is toluene diisocyanate.

6. The method of claim 1 in which the emulsion additionally comprises an inorganic absorbent for the carbon dioxide.

7. The method of claim 6 in which the absorbent is magnesium oxide.

8. The method of claim 1 in which the emulsion additionally includes powdered rubber.

9. A method for obtaining a deflation-proof tire, comprising injecting into a pneumatic tire casing a combination comprising a polyol, an organic polyisocyanate and a substantial stoichiometric excess of water, in amounts sufficient to produce carbon dioxide and form a polyurethane elastomer containing polyurea and having a portion of the water dispersed therethrough, the carbon dioxide being dissolved in the dispersed water to produce a substantially void-free elastomeric filling medium within said casing.

10. The method of claim 9 in which said polyol is a polypropylene glycol diol or triol.

11. The method of claim 10 in which the polyol is an ethylene oxide capped triol.

1 2. The method of claim 10 in which said combination additionally comprises at least 10 volume per cent oil.

1 3. The method of claim 1 2 in which a major portion of said oil is aromatic.

14. The method of claim 1 3 in which said polyisocyanate is toluene diisocyanate.

1 5. The method of claim 1 3 in which said polyisocyanate is polymethylene polyphenylisocyanate.

16. The method of claim 10 in which said combination additionally comprises an inorganic absorbent for the carbon dioxide.

1 7. The method of claim 16 in which the absorbent is magnesium oxide.

18. A method for obtaining a deflation-proof pneumatic tire comprising: injecting into a pneumatic tire casing a water-in-oil emulsion comprising a polypropylene glycol diol or triol and an organic polyisocyanate, and a disperse phase containing water in a stoichiometric excess of the amount sufficient to produce carbon dioxide and form a polyurethane elastomer having a durometer hardness of at least zero on the "A" scale; filling the tire casing prior to significant production of carbon dioxide to a desired tire pressure; and curing the elastomer whereby the carbon dioxide is dissolved in the elastomer to produce a urethane elastomeric emulsion as a substantially void-free filling material within the casing.

19. The method of claim 18 in which the water-in-oil emulsion additionally contains an inorganic absorbent for the carbon dioxide.

20. The method of claim 1 9 wherein the polyol is a polypropylene glycol diol or triol.

21. A flat-free pneumatic tire comprising a pneumatic tire casing and a substantially voidfree polyurethane elastomer filling material confined, at least in part, by the casing, the filling material being formed from a water-in-oil emulsion comprising a polyol and an organic polyisocyanate, and a disperse phase including water in a stoichiometric excess of the amount sufficient to produce the polyurethane elastomer.

22. The tire of claim 21 in which the condition comprises filling-the tire casing prior to significant production of carbon dioxide to a predetermined tire pressure.

23. The tire of claim 22 in which the polyol is a polypropylene glycol diol or triol.

24. The tire of claim 23 in which the polyisocyanate is toluene diisocyanate.

25. The tire of claim 23 in which the polyisocyanate is polyethylene polyphenylisocyanate.

26. The tire of claim 23 in which the emulsion additionally comprises an inorganic absorbent for the carbon dioxide.

27. A flat-free pneumatic tire, comprising a pneumatic tire casing and a substantially voidfree polyurea-containing, oil-containing polyurethane elastomeric filling material having a disperse phase including water, said material confined, at least in part, by the casing, the material being the product of the reaction of a polypropylene glycol diol or triol and an organic polyisocyanate in a continuous phase, and a disperse phase including water in a stoichiometric excess of the amount necessary to form an elastomeric polymer and carbon dioxide and under conditions sufficient to form an elastomeric filling material having a portion of the water dispersed therethrough.