CA1074063A - Method of repairing punctured tubeless tires - Google Patents

Abstract

525?

Abstract of the Disclosure A punctured tubeless tire is repaired by applying to the puncture a repair material based on a mixture of a major proportion of a low molecular weight liquid elastomer with a high molecular weight solid elastomer, containing a crosslinking agent in amount sufficient to give at least a partial cure. An example of the repair composition is a blend of 60 parts of depolymerized natural rubber and 40 parts of cis-polyisoprene, contain-ing 6 parts of tetra-n-butyl titanate as a crosslinking agent.

Description

This invention relates to a method of repairing punctured tubeless tires, and to repaired tires resulting from such method.
The methods heretofore available for repairing punctures in tubeless tires have not been entirely satis-factory for a number of reasons. Particular difficulty has been experienced in trying ~o get consistently satis-factory results in repairing punctures in radial type tires by conventional methods.
In accordance with the invention it has now been found that punctures in tubeless tires, including radial tires, can be repaired in a convenient and reliably effective manner by applying to the puncture a composition based on a mixture of a major porportion of a low molecular weight liquid elastomer with a high molecular weight solid elastomer, containing a crosslinking agent in amount effect-ive to give a sufficient cure to prevent the composition from flowing at elevated temperatures and high centrifugal forces encountered under operating conditions. The composition is applied to the puncture to be repaired, and is thereafter cured in situ in the puncture.

...

The presently employed repair material contains major amounts, at least more than 50~, of a liquid elastomer which is an essential part of the repair mixture and is partially vulcanized with the high molecular weight solid elastomer. The resultant repair material is remarkable in that the high molecular weight partially vulcanized portion serves as a gelled matrix which restrains the low molecular weight p~rtion from flowing at elevated temperature and high centrifugal forces.
The invention will be described with reference to the accompanying drawing, wherein:
Fig. 1 is a largely diagrammatic sectional eleva- -tional view of a tubeless pneumatic tire, punctured by a nail;
Fig. 2 is a similar fragmentary view on a larger scale, showing the pu~ture being repaired by application of repair material by means of a syringe; and, Fig. 3 is a view similar to Fig. 1, showing a tire being repaired while mounted on a rim.
As indicated, the method of the invention involves applying a repair material to the puncture to be repaired and thereafter at least partially curing or cross-linking the material. In more detail, the repair material which is forced into the puncture to be repaired is a mixture of low molecular weight liquid elastomer with a high molecular weight solid elastomer, the low molecular weight liquid elastomer being present in amount greater than 50 based on the weight of the two polymers, containing sufficient curative to crosslink the

- 2 -.

., ...:.::

- . , .

;~
~3~

mixture to an extent, as measured by gel content and Mooney viscosity, to prevent it from flowing when subjected to the elevated temperatures and high centri-fugal forces encountered in a pneumatic tire under operating conditions. An additional quantity of repair material may be provided at the interior surface of the tire at the puncture to form an enlarged patch having an area greater than the cross sectional area of the puncture, said patch being integral with the repair material in the puncture, whereby in the final crosslinked repair structure the repair is maintained securely in place in the puncture. As will be explained in more detall here-inbelow, for this purpose an excess of repair material may be ~orced into the puncture ~rom the outside thus pro-viding addltional repair material at the inside of the tire at the puncture. Such excess deposited material therea~ter may be smeared or flattened against the inner sur~ace o~ the tlre surroundlng the puncture if an unmounted tire is being repaired. If the tire being repaired is mounted on a wheel, the elastic memory of the repalr ma-terial will automatically result in formation of an enlarged portion on the inside of the tire as the excess repair material emerges at the inside sur~ace of the tire, as will be set ~orth ln hereinbelow described detailed embodi-ment of the invention.
As the high molecular weight elastomeric component of the repair material employed in the invention there may be used any high molecular weight solid elastomer capable of being crosslinked. Ex~mples are the highly unsaturated rubbers such as those based on con~ugated

-3-- , ' ' '. ' . ' diolefins, whether homopolymers as in polyisoprene (particularly cis-polyisoprene, whether natural or synthetic), polybutadiene (including polybutadiene of high cis content), polychloroprene (neoprene), or co-polymers as exemplified by those having a major proportlon of such conjugated dienes as butadiene with a minor proportion of such monoethylenically unsaturated copoly-merizable monomers as styrene or acrylonitrile. Alternatlvely, elastomers of low unsaturation may be used, notably butyl type rubbers (copolymers of such isoolefins as isobutylene with small amounts of con~ugated dienes such as isoprene), or the EPDN types ~copolymers of at least two different monoolefins such as ethylene and propylene wlth a small amount oi a non-conjugated diene such as dicyclopentadiene, 1,4-hexadiene, 5-ethylidene-2-norbornene, etc.). Even saturated elastomers such as EPM or ethylene-vinyl acetate may be employed, using the proper cure syetem. The elastomer may be emulsion-prepared or solutlon-prepared, stero speci~ic or other-, .

-3A- :

- , , ~. ,. ~ .

~'7 wise. The molecular welght o~ the solld elastomPr is usually in excess of 50,000, ordinarily within the range o~ from 60,000 to 2 or 3 million or more. Ordinarily the solld elastomer~c component has a Mooney viscosity within the range of~rom 20 to 160 ML-4 at 212F.
The low molecular weight elastomer employed has a molecular weight less than 50,000, usually within the range ~rom 1,000 to 10,000, and is preierably of the "liquid" rubber type with a maximum Brookfield vlscosity at 150F. o~ 200,000 cps., ordinarlly wlthin the range o~ from 20,000 to 200,000 cps. Examples are: liquid cis-polyisoprene (e.g., heat depolymerlzed natural rubber, or cis-polylsoprene polymerized to low molecular weight), liquid polybutadiene, liquid polybutene, llquid EPDM, and liquid butyl rubber. The high molecular weight, elongation and film strength oP cis-polyisoprene (both natural and synthetic) and great tackiness oP depo~y-merized cis-polyisoprene give a comblnation of the~e two elastomersj when partially cured, a large degree of resistance to flow, coupled with efPiclent-sealing ability.
Other elastomer combinations, particularly the saturated ones, offer resistance to oxldation in service which makes them also highly desirable.
The repair material contains a maJor proportlon, th~t is, between more than 50~ and 90~ by welght, oP the low molecular weight elastomer based on the welght oP the two elastomers, dependlng mainly on the molecular weight of the hlgh molecular weight elastomer and other variables such as the particular elastomer involved, the amount and klnd o~ crosslinking agent, and the condltions oP the cross-linking treatment. Ordinarily the proportlon of the two

-4-~ t~

elastomeric components are cho~en so as to give an initial Mooney viscoslty at room temperature (the initial peak reading attained, which is usually wlthin the flr~t few seconds) of at least 30 (large rotor, ML) in the final crosslinked mixture, with a preferred value of at least 40. Below the aforementioned initial Mooney viscosity of 30, the repair composition will tend to flow out of the repair area and out of the puncture of the tire when it is run at high speed. Although there is no critical upper limlt to the degree of cure of the repair material, and the cure can if desired be as great as what would be regarded as substantially a full cure ln ordinary rubber compounding practice, nevertheless lt is not ordinarily necessary or desir~ble to use more curing agent than i~
required to pro~ide an initial Mooney of about 70-100 (ML
at room temperature) at the concluslon of the crossllnklng.
The Mooney viscosity of the final crosslinked mixture can also be controlled for a glven elastomerlc composl-tion by the amount of the mechanical shearing e~ployed in mixing the constituents. The net effect here, of course, ls to break down (i.e., lower) the molecular welght of the high molecular welght component, thereby lowerlng the Mooney vi8c081ty of the mlxture before cure.
As lndlcated, the repair material rurther lncludes a cro~slinklng agent. The cro~slink~ng agent may be any sultable ~ubstance or combination of substances c~pable of curlng or gelling the mlxture to the desired extent.
Examples are:
1) Sulfur curlng ~ystem~ ~uch as tho~e b~ed on sul~ur or sulfur-yleldlng materials (e.g., tebramethyl .

.. , .. , . . . . .. . . . . . . ~ . . ~ . .

thiuram disulfide) and conventional accelerators of sulfur vulcanization.
2) Quinoid curing systems such as p-quinone dioxime tGMF, trademark) with or without supplementary oxidant.
3) Organic peroxides (or hydroperoxides) such as dicumyl peroxide, cumene hydroperoxide, methyl ethyl ketone hydroperoxide or other radical generating cata-lysts such as azobisisobutyronitrile.
4) Polyisocyanates such as MDI (4,4'-methylene bis-phenyleneisocyanate), TDI (tolyene diisocyanate), and PAPI (polymethylene polyphenylisocyanate) as wel as dimers and trimers of MDI and TDI.

5) Tetrahydrocarbyl titanate esters.
The amount of crosslinking agent employed will vary with the particular elastomers employed and with their proportions, as well as with the particular cross-linking agent and the conditions of the crosslinking step. Ordinarily the amount used is that sufficient to prevent flow of the repair composition in a tire at temperatures up to 200F and speeds up to 50 mph, while still retaining su~ficient adhesiveness and conforma-bility to perform the described repair function. The amounts employed will vary depending on the proportion of high molecular weight elastomer in the mixture.
Hlgher proportions of high molecular weight elastomer will require less crosslinking agent and vice versa.
The amount of crosslinking agent will, of course, vary with t he nature of the elastomers themselves. Typically, for a depolymerized natural rubber (DPR)-natural rubber --6~
'`
,. .. . .

(NR) mixture, the amount of sulfur-containing or quinoid type curative will be in the range of from more than 0.5 to 2.0 phr (parts per 100 parts by weight of both elastomers added together)g ordinarlly from 0.7 to 1.5 phr. For this same mixture, with polyiæocyanate or hydrocarbyl titanate ester curati~es, the amounts required will ordinarily be ln the range from about 4 to 10 phr, preferably 5 to 8 phr. Similarly, the applicable range for peroxide or hydroperoxide cur-atives ~radical generating catalysts) would be 0.1 to 1.0 phr, preferably 0.2 to 0.7 phr.
The crosslinking of the repair mixture produces an increase in viscosity and an increase ln the gel content (content of insoluble material). It has been found that for the natural rubber, depolymerized natural rubber mixture, a gel content, as measured in toluene at room temperature, of at least 15%, preferably at least 20~, by welght, in the crosslinked blend 18 satisfactory.
Almo~t lnvariably the crosslinked repalr material will have a gel content within the range of from 20% to 80%
or higher (e.g. 95%), preferably 20~ to 60%. For other elastomer combinations the rRnge of gel content will vary depending on the molecular weight and proportion of the two elastomerlc components.
m e crosslinking ma~ be carr~ed out at ordinary amblent temperature or at elevated temperature, depend-ing on the temperature at which the particular cross-linking system selected is active in the particular elastomer combinati~n employed.
The repalr composition may further include~ if ... ... .

B ~7~
..
. . . -.
.
.

desired, varl~us appropr~ate additional compounding ingredients, lncluding pigments such as carbon black, fillers, extenders~ tacki~iers, stabilizers and anti-oxidants.
In practicing the invention the plastic repair material is prepared by mixing the described ingredients together uniformly, and thereafter applying the material to a tire to be repaired. Referring to the drawing, and particularly to Fig. 1, a typical tire to be repaired comprises a toroidal tubelesæ tire casing 10 of the radial ply type having the usual vulcanized rubber tread 11 and sidewall portions 12, 13 surmounting a vulcanized rubber carcass 14 reinforced with filamentary materlal, whlch terminates at bead areas 15, 16 containing the usual circumferential inextensible re~nforcement. The entlre lnside sur~ace of the carcass is covered by the usual air-impervious liner 17. The tire as shown in the drawing has been punctured by a nail 19 extendlng through the tread 11, carca~s 14 and liner 17 into the interior of the casing. To effect a repair of the tire in an unmounted condition, the nail is removed from the puncture 22, as shown in Fig. 2, and the repair material 23 is introduced into the hole by means of a syringe 24 or the like. The quantity of repair material in~ected, usually from about 50 to 200 grams, should be suff~cient to flll up the hole completely and to provide an excess. The excess material thus applied to the inside of the tire serves for the formation of an enlarged patch portion 25 which is formed by smearing or flattening the excess in~ected material against the lnner (liner) surface of the tire immediately surrounding the puncture. The repair material is then crossl~nked to render the repair permanent. In preferred practice, the ratio of the area of the patch portion to the cross sectional area of the hole should be from about 100 to about 400 to 1.
Additionally, in order to optimize the adhesion of the patch portion to the inner surface of the tire, the inner surface contact area surrounding the hole should be cleaned by methods such as washing with an aqueous soap ~olution, wiping with solvent and/or buffing. For optimum adhesion of the patch portion to the cleansed 10 area a thin layer of repair material may be laid down onto it from a solution in a suitable solvent. If the repair material requires heat to cure, the repair may be heated by any conventional means such as a radiant heating device~ a hot alr blower, a circulating hot air oven or 15 the like. If the repair material cures without heat, then heating ls of course unnecessary.
In the modification of the invention shown in Fig. 3, the repair is effected on the tire w~ le mounted on a rim 26. Again, as in the method described 20 above for repalring an unmounted tire, a quantity of repair material, usually from about 50 to 100 grams, is in~ected ~nto the tire irom a syringe 27 (Fig. 3). The quantity of the repair material should be an amount suffi-cient to fill up the hole completely to form a plug 29 25 and to provide an excess which remains attached to the ~ -plug on the inside of the tire as an enlarged lump 30.
The lump 30, thus provided at the in~ide of the tire at the hole, who~e cross sectional area is substantially larger than the cross sectional area of the hole (by 3 reason of the elastic memory of the repair material, which causes it to swell to a larger diameter as ~t issues from t.

the hole on the inside of the tire), acts as an anchor at the inside surface o~ ~he tire to immobolize the plug in the hole under operating conditions and prevent it from being blown out by the inflation pressure. The repair material is then crosslinked to render the repair permanent, as before.
An example of the repair material is a mixture of 6 lbs. of heat depolymerized natural rubber (DPR-400 [trademark~ Hardman Company, viscosity 80,000 cps at 150F), 45 grams o~ Antioxidant 2246 ~trademark, 2,2'-methylene bis (4-methyl-6-tert-butylphenol)~, 4 lbs of Hevea natural rubber (Standard Malaysian Rubber, Mooney viscosity 64 ML-4-212F) and 262 grams of tetra-n-butyl titanate. The mixture iB prepared by placing the DPR, antioxidant and 6 lbs. o~ creamed Hevea natural rubber latex (67~ total solids) in a double-arm sigma blade dough mixer and mixing at a shell temperature o~ 270F.
for 30 minutes. Vacuum is then applied and mixing con-tinued for 30 minutes at which time the moisture content i~ le~s than 0.2%. The tetra-n-butyl titanate is then added, the mixer tightly closed and mixing continued for an additional 30 minutes. As long as the resulting composition is kept con~ined under non-evaporative conditions, as in a tightly closed container, cros~linking will not take place, even at elevated temperature. However, when the mixture is exposed to evaporative conditions, crosslinking, with accompanying formation of gel and increase in viscosity, takes place, even at room temperature.
The material exemplified, cured by exposure to ambient atmospheric conditions ~or 5 days, has a gel content of 35% by weight (measured in toluene at roo~ temperature) and an initial ~.:
R -lo- ~

.

Mooney viscosity (ML, Large Rotor) at room temperature of 55. Heat speeds up the cure. A thin layer oi the material cures more rapidly than Q thick sectlon. Evldent-ly the cure is accompanled by evolutlon of alcohol cor-responding to the esterfying body of the titanate ester (in this case n-butyl alcohol). If the alcohol cannot evaporate (as when the material is in a tight~y closed container) cure will not take place. Once the alcohol is permitted to evaporate by exposing the material to the atmosphere, the cure goes forward.
For use, the repair composltlon may be loaded lnto a syringe, caulking gun, grease gun or the like, for application to a repair as described above. The materlal may be heated to an elevated temperature to facllltate 15 application by lncreasing the flowability or plastlclty but thls is not essential. The exemplifled formulatlon will not cure as long as the compo~ltion remains enclosed within the syrlnge or gun because the e~olution and escape of the hydrocarbyl alcohol, necesæary for the curing re-20 action, cannot take place. However, once the repair material is applie~ to the puncture, the alcohol has an opportunity to escape and the cure ad~anceæ. Typical `
repairs us~ng the exempliiled composition become cro~s-linked to the desired extent in about fl~e days at room 25 temperature or ln a shorter time li the repair 18 heated externally.
In one test an HR78-15 tlre was punctured by a 20-penny nail in the center groo~e and the inside ~urface surroundlng the hole was cleaned wlth n-hexane. U61ng 3o a grease gun filled wlth the ex~mplliied repalr mater~al .

- , . . .

which had been heated to 200F, a quantity, about 150 grams, o~ warm repair material was injected into the hole from the outer surface of the groove in the direction of the inner periphery of the tire. The excess repair material which emerged from the hole at the inside surface of the tire thus provided at such surface an addltional quantity of material which was then flattened to ~orm an enlarged retaining patch portion on the inside surface of the tire as described above~ The repaired tire was then placed in a circulating hot air oven and the repalr was cured for 24 hours at 200F; the patch and the materlal in the hole then formed an integral repalr. After cooling, the tire wa~ mounted on a standard automobile rim and inflated to a pressure of 40 psi. There was no loss of inflation pre~sure over a two week period. It should be noted that this two week period is not a necessary condition ~or the practice of this invention.
The repair i~ permanent immediately after the minimum cure is attained. At the end of the two week period the inflation pressure was ad~usted to 28 psi and the tire was run on a Getty wheel, ll-inch d~ameter with a 1000 pound load at 50 mph~ There was no loss of inflation pre3sure after 24 hours (1200 miles) at which point the run was di~continued.
The cure (crosslinking or gelling to an insoluble state) of unsaturated elastomer with an organo titanate ester takes place only when the mixture is exposed to the open atmosphere and can be prevented by maintalning the mix~ure in .. . . . .

a closed system. The unsaturated elastomers that may be cured with titanate ester include cis-polyisoprene (whether natural or synthetic), polybutadiene, notably cis-polybutadiene, butadiene-sytrene copolymer rubber, butadiene-acrylonitrile copolymer rubber, EPDM rubber (notably ethylene-propylene-5-ethylidene-2-norbornene terpolymer rubber having an iodine number greater than 8), polychloroprene rubber, butyl rubber (isoprene-isobutylene copolymer), and blends of such elastomers.
The organo titanate esters employed as curatives or crosslinking agents to gel the unsaturated elastomer are tetrahydrocarbyl titanates of the formula (RO)4Ti where R is hydrocarbyl group, such as an alkyl group, e.g., an alkyl group having 1 to 12 carbon atoms, pre-ferably 3 to 8 carbon atoms, or an aryl group having 6 to 10 carbon atoms, such as cresyl. In preparing the curable composition the mixing of the organo titanate ester crosslinking agent and unsaturated elastomer may be carried out under non-evaporative conditions in a closed system such as an internal mixer, e.g., a sigma blade mixer (such as a Baker-Perkins [trademark] or a closed Brebender mixer [trademark]). Alternatively, the organo titanate ester may be mixed with the unsaturated elastomer in solution in an inert volatile organic solvent for the elastomer (e.g., n-hexane), preferably in the presence of a small amount of volatile alcohol (e.g., ethyl alcohol) to suppress premature gellation. Gellation then occurs only after evaporation of the solvent and alcohol.
In the most typical practice the mixing is carried out under con-,, :

~7 ditions which suppress gellation (i.e., in a closed system under non-evaporative conditions, or in the presence o~ a volatile alcohol) and then, after the mixture has been shaped into the desired form (e.g., molded, extruded, coated, etc.), the mixture is permitted to gel simæly by exposing to evaporative conditions in the open atmosphere. Depending on the rubber and the amount o~ extraneous hydroxylic compounds such as antioxidants (hydroxylic compounds are inhiblt-ing substances in the cure) it contains, the amount and type of titanate ester used dictate the rate and extent o~ cure obtained.
The temperature and time required for titanate cure again depend on ~ne presence or &bsence of hydroxy-lic (inhibiting) additives and the type and level of titanate employed. Cure of the mixture ls accompanied by evaporation of alcohol, correspondlng to the alkoxy portion of the titanate ester. Hence, titanate esters of lower boiling alcohols effect cure more rapidly than titanate esters Or higher boiling alcohols, e.g., isopropyl titanate acts more rapldly than butyl titanate which in turn acts more rapidly than ethylhexyl titanate.
Elevated temperatures speed up the cure rate regardless of the type and level of titanate, although in the absence of added hydroxylic inhibitor and sol~ent cure is rapid at room temperature. In general, from 1 to 10 days are required ror cure at room temperature dependlng on such factors as the nature of the rubber, the amount of hydroxylic impurity, the surface to volume ratlo (the greater the surface exposed, the more rapid the cure), . .
- . . ~ .
~ , . . .. .

1~Ji7 as well as the level and type of tltanate ester. It is a remarkable feature of the cure that the curable mix-ture can be processed at elevated temperatures (under non-evaporative condltions) without premature cure, and yet cure can be accomplished at amblent temperature (under evaporative conditions).
As indicated, it has been observed that the titanate curing reaction is accompanied ~y the evolution of alcohol, that is, an alcohol ROH corresponding to the organic group oi the ester (RO)4Ti is generated dur-ing the cure. If the alcohol is prevented irom evaporat-ing, as in a closed container where non-evaporative condition~ prevall, the cure will not go iorward. How-ever, when the curable composition i8 placed in the open atmosphere where evaporatlve conditions prevail, and the evolved alcohol ROH can escape, the cure proceeds.
Thin sections such as coatings depo~ited irom a solu-tion, calendered or extruded iilms and sheets, and ; similar thin sections (e.g., 0.2 lnch thick or less) have higher surface to volume ratio than thicker sections (such as most molded ob~ects) and present greater oppor-tunity ior the generated alcohol ROH to escape. There-iore ~uch thin sections cure more rapidly than thick sections.
As the titanate cure proceeds the gel content -oi the rubber (that is, the iraction insoluble in organlc liquids that are normally solvents ior the uncured elastomer) increases, indicating that cros61inking is taking place, and evolution oi alcohol continues untll a plateau of gel content i~ reached.

As indicated, hydroxylic additives have an in-hibiting ef~ect on the titanate cure. For instance phenolic antioxidants have been found to slow down the cure rate. When such antioxidants are removed as ~oarly as possible solutions of the rubbers tend to gel quickly when titanate esters are added. Normally, appreciable gellation occurs slowly upon evaporatlon o~ solvent from the solution. Addition of small amounts of volatile alcohol to solutions of rubber inhibits any tendency to-ward premature gellation. In fact, the rate of cure can be controlled by the molecular welght of the added al-cohol. Low molecular weight alcohols such aæ ethyl al-cohol have a mild or temporary inhibiting effect whlle higher boiling alcohols such as dodecyl alcohol ha~e a more severe and lasting inhibiting effect. After gellation, the gelled rubber is lnsoluble to toluene and other organic solvents, but addltlon of acid 6uch as acetic acid reverses the process and the rubber be-comes soluble again. Addition of carboxylic acids llke-wise inhibits gel formation. It appears to be posslble that the crossllnking is a conæequence o~ titanate ester formation with the elastomer.
Preferred elastomers for use wlth t~e tltanate cure are those selected from the group consistlng of natural rubber, synthetlc cis-polylsoprene elaætomer, cis-polybutadiene elastomer and ethylene-propylene-5-ethylidene-2-norbornene terpolymer rubber having an iodine number of at least 1~, ln low molecular weight (liquid) or high molecular welght (solid) form.
It will be understood that the measurements of ~t7 gel content and Mooney viscosity set forth above for the cured repair material are obtainable on a separate sample of the repair material which has been sub~ected to curing conditions substantially equivalent to those to which the repaired tire is sub~ected; it is of course not practical to make these measurements on the actual repair in the tire itself.
In tires repaired by the present method the puncture is entirely filled with a material that is sufficientl~ plastic and oo~ormable in the uncured state to take the exact shape of the puncture and fill all intersticies there~f without setting up undesirable stresses. Such a repair, after at least partial cure in situ as described, tends to remain in place, unllke con-ventional repairs made with a preformed plug or the like, which tend to work loose. Conventional repalr plug5 are frequently cut through by working against the Rteel cords of belts used in radial ply tires (especially by frayed ends of broken cords at the puncture) whereas the present repair resists thls by reason of the nature of the repalr material and its manner of appllcatlon. Adheslon of the integral patch portion of the present repalr to the in-side surface of the tire iB good because o~ the manner ln which it is applied in the uncured state and cured ln situ on the tlre surface. Also, the llquid rubber com-ponent, which tends to acquire only a limited amount of vulcanlzation in the repalr process, ~erve~ to m~intain the tackiness and adhesivene~s of the repair, BO that it does not work loose.

Claims (14)

What is claimed is:

1. a method of repairing a puncture in a vulcanized rubber radial ply pneumatic tire casing of the tubeless type comprising injecting into the puncture a repair material comprising a blend of a low molecular weight liquid elastomer with a high molecular weight solid elastomer, and a crosslinking agent for the elastomers in an amount effective to partially crosslink the elastomers to an extent sufficient to prevent the blend from flowing at elevated temperatures and centrifugal forces encountered in the tire in use, and thereafter subjecting the applied material to curing conditions, the amount of low molecular weight elastomer in the said repair material being from more than 50% to 90% by weight and the amount of high molecular weight elastomer being correspondingly from less than 50%
to 10% by weight, based on the total weight of elastomers present, the amount of crosslinking agent in the said repair material being sufficient to provide in the blend, after crosslinklng, a gel content of from 15 to 95% by weight of the blend, as measured in toluene at room temperature and an initial Mooney viscosity of from 30 to 100 ML at room temperature, the said low molecular weight elastomer being a liquid rubber having a Brookfield viscosity at 150°F of from 20,000 to 200,000 cps., and the said high molecular weight elastomer having a Mooney viscosity of from 20 to 160 ML-4 at 212°F, the amount of said repair material injected being sufficient to fill the puncture and sufficient to provide an excess of repair material at the interior surface of the tire at the puncture to form an enlarged patch having an area greater than the cross sectional area of the puncture, said patch being integral with the repair in the puncture, whereby in the final crosslinked repair structure the repair is maintained securely in place in the puncture, the high molecular weight partially crosslinked elastomer serving as a gelled matrix which restrains the low molecular weight liquid elastomer from flowing at elevated temperature and high centrifugal force encountered in the tire under operating conditions, and the said low molecular weight liquid elastomer serving to maintain the tackiness and adhesiveness of the repair so that it does not work loose.

2. A method as in claim 1, in which the liquid rubber is heat depolymerized natural rubber.

3. A method as in claim 1, in which the high molecular weight elastomer is cis-polyisoprene.

4. A method as in claim 1 in which, in the said repair material, the low molecular weight elastomer is selected from the group consisting of liquid cis-polyisoprene, liquid polybutadiene, liquid polybutene, liquid ethylene-propylene-non-conjugated diene terpolymer rubber, and liquid isobutylene-isoprene copolymer rubber.

5. A method as in claim 1, in which, in the said repair material, the high molecular weight elastomer is selected from the group consisting of conjugated diolefin homopolymer rubbers, copolymers of a major proportion of a conjugated diolefin with a minor proportion of a copoly-merizable monoethylenically unsaturated monomer, copolymers of isobutylene with a small amount of isoprene, ethylene-propylene-non-conjugated diene terpolymers, ethylene-propylene copolymer and ethylene-vinyl acetate copolymer.

6. A method as in claim 1 in which, in the said repair material, the crosslinking agent is selected from the group consisting of sulfur or sulfur-yielding curative, quinoid curative, radical generating curative, polyisocyanate curative, and tetrahydrocarbyl titanate ester curative.

7. A method as in claim 1, in which, in the said repair material, the low molecular weight elastomer is liquid heat depolymerized natural rubber and the high molecular weight elastomer is solid cis-polyisoprene rubber.

8. A method as in claim 1, in which, in the said repair material, the crosslinking agent is selected from the following, present in the amounts recited:
from more than 0.5 to 4 parts of quinoid curative, from 0.1 to 1.5 part of radical generating curative;
from 4 to 25 parts of polyisocyanate curative; and from 4 to 25 parts of tetrahydrocarbyl titanate ester curative, the said parts being by weight based on 100 parts of the combined weight of the two elastomers.

9. A method of repairing a puncture in a vulcanized rubber radial ply pneumatic tire casing of the tubeless type comprising forcing into the puncture a plastic repair material to fill the puncture and to provide at the interior surface of the tire at the puncture a further quantity of the repair material to form an enlarged patch of repair material at the puncture in the interior of the tire integral with the repair material in the puncture, said repair material comprising a blend of from more than 50% to 90%
by weight of a low molecular weight liquid elastomer having a Brookfield viscosity at 150°F of from 20,000 to 200,000 cps. with correspondingly from less than 50% to 10% by weight of a high molecular weight solid elastomer having a Mooney viscosity of from 20 to 160 ML-4 at 212°F, the said percentages being based on the total weight of elastomers present, and from 4 to 25 parts, per 100 parts by weight of the two elastomers, of a tetraalkyl titanate ester crosslinking agent in which the alkyl groups have from 1 to 12 carbon atoms, and thereafter subjecting the applied repair material to curing conditions to partially crosslink the blend to a gel content of from 20% to 80% by weight based of the weight of the blend as measured in toluene at room temperature and an initial Mooney viscosity of from 40 to 100 ML at room temperature, the high molecular weight partially crosslinked elastomer serving as a gelled matrix which restrains the low molecular weight liquid elastomer from flowing at elevated temperature and high centrifugal force encountered in the tire under operating conditions, and the said low molecular weight liquid elastomer serving to maintain the tackiness and adhesiveness of the repair so that it does not work loose, whereby the puncture is effectively sealed against loss of air from the tire.

10. A method as in claim 9, in which the alkyl groups in the said tetraalkyl titanate ester crosslinking agent have from 3 to 8 carbon atoms and the amount of said titanate ester is from 5 to 15 parts per 100 parts by weight of the two elastomers.

11. A method of repairing a puncture in a tubeless vulcanized rubber pneumatic tire of the radial ply type com-prising forcing into the puncture a plastic repair material to fill the puncture and to provide at the interior surface of the tire at the puncture a further mass of the repair material to form an enlarged area of repair material at the puncture on the interior of the tire integral with the re-pair material in the puncture, said repair material com-prising a blend of from more than 50% to 90% by weight of liquid heat depolymerized natural rubber having a Brookfield viscosity at 150°F of from 20,000 to 200,000 cps. with correspondingly from less than 50% to 10% by weight of cis-polyisoprene elastomer having a Mooney viscosity of from 20 to 160 ML-4 at 212°F., the said percentages being based on the total weight of elastomers present, the said blend further containing a crosslinking agent for the said de-polymerized natural rubber and said cis-polyisoprene elas-tomer in an amount effective to partially crosslink the said blend to an extent specified hereinbelow, and there-after subjecting the thus applied repair material to curing conditions to crosslink the blend to an extent sufficient to provide in the blend a gel content of from 15 to 95% by weight of the blend as measured in toluene at room tempera-ture and an initial Mooney viscosity of from 30 to 100 ML
at room temperature, the thus-crosslinked cis-polyisoprene elastomer serving as a gelled matrix which restrains the de-polymerized natural rubber from flowing at elevated tempera-ture and high centrifugal force encountered in the tire under operating condition, and the depolymerized natural rubber serving to maintain the tackiness and adhesiveness of the repair so that it does not work loose, whereby the puncture is effectively sealed against loss of air from the tire.

12. A method of repairing a puncture in a vulcanized rubber radial ply pneumatic tire casing of the tubeless type comprising forcing into the puncture and to the interior of the tire at the puncture a plastic repair material which fills the puncture and provides an excess quantity of plastic repair material at the interior surface of the tire at the puncture, said excess quantity of plastic material constitu-ting an enlarged patch of repair material integral with the repair material in the puncture, said repair material com-prising a blend of from more than 50% to 90% by weight of liquid heat depolymerized natural rubber having a Brookfield viscosity at 150°F. of from 20,000 to 200,000 cps. with cor-respondingly from less than 50% to 10% by weight of cis-poly-isoprene elastomer having a Mooney viscosity of from 20 to 160 ML-4 at 212°F., the said percentages being based on the total weight of elastomers present, and from 4 to 25 parts, per 100 parts by weight of the elastomers, of a tetraalkyl titanate ester crosslinking agent in which the alkyl groups have from 1 to 12 carbon atoms, and thereafter subjecting the thus applied repair material to curing conditions to provide in the blend a gel content of 15% to 95% by weight based on the weight of the blend as measured in toluene at room temperature and an initial Mooney viscosity of at least 30 to 100 ML at room temperature, the thus-crosslinked cis-polyisoprene elastomer serving as a gelled matrix which re-strains the depolymerized natural rubber from flowing at elevated temperature and high centrifuged force encountered in the tire under operating conditions, and the depolymerized natural rubber serving to maintain the tackiness and ad-hesiveness of the repair so that it does not work loose, whereby the puncture is effectively sealed against loss of air from the tire.

13. A method as in claim 12, in which the gel con-tent of the blend after crosslinking is from 20 to 80% by weight based on the weight of the blend as measured in toluene at room temperature, the alkyl groups in the said tetraalkyl titanate ester crosslinking agent have from 3 to 8 carbon atoms, and the amount of tetraalkyl titanate cross-linking agent is from 5 to 15 parts per 100 parts by weight of the two elastomers.

14. A method as in claim 13, in which the tetra-alkyl titanate ester crosslinking agent is tetra-n-butyl titanate.