IE43664B1 - Puncture sealing composition and tire - Google Patents

Description

Thisittventiop relates to a puncture sealing composition, to a pneumatic tire of the tubeless type embodying a layer of puncture sealant composition, and a method of repairing punctures in tubeless tires.

Our copending Application No. 42487 discloses the crosslinking of elastomers with alkyl titanate esters.

Puncture sealing tubeless tires having previously been proposed, containing, in the area of the tire normally most subject to punctures (that is, the undertread or : the area extending across the crown of the tire at least from one shoulder to the other ), a layer of sealant composition which has plastic and adhesive qualities such that the composition tends to stick to a puncturing object, and, when the puncturing object is withdrawn, tends to flow into the opening or puncture, forming a plug which seals the opening against loss of air from the tires. Unfortunately, it has proven difficult to provide a composition which would flow into the puncture hole and yet have sufficient viscosity to prevent it from flowing at elevated temperatures, up to 250°F, and higher, such as exist'in pneumatic tires under operating conditions.

The problem is complicated by the extreme centrifugal force Co which the composition is subjected as the tyre rotates at high speed, since such centrifugal force tends to cause the composition to flow into the central crown area, leaving the areas near the shoulders unprotected. Furthermore, it has proven difficult to provide a sealant composition which would retain this desired balance of viscosity, plasticity, adhesion and conformability over an extended period of service.

Furthermore, the methods heretofore available for repairing punctures in tubeless tires have not been entirely satisfactory for a number of reasons. Particular difficulty has been experienced in trying to get consistently satisfactory results in repairing punctures in radial type tires by conventional methods.

According to the present invention there is provided an elastomeric composition 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 2,000,000 cps^with correspondingly 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, and a crosslinking agent for the elastomers in an amount effective partially to crosslink the elastomers to an extent that the blend, after crosslinking, has a gel content of from 15 to 95% by weight of the blend as measured in toluene at room temperature and a peak Mooney viscosity of above -330 ML at 150°F, the blend having in the partially crosslinked state, sufficient adhesion and conformability to function as a sealant in a tire and whereby the blend is prevented from flowing at elevated temperatures and centrifugal forces encountered in a tire in use.

Preferably, the mixture contains one or more tackifying or plasticising substances which may allow a reduction of the amount of low molecular weight elastomer, but the total of tackifying or'plasticizing substance plus low molecular weight elastomer is more than 50$ of the mixture.

In a composition in accordance with the present invention, the high molecular weight partially vulcanized portion serves as a gelled matrix which restrains .the low molecular weight portion from flowing at elevated temperature and high i centrifugal forces and yet permits sufficient conformability for the composition to function effectively as a puncture sealant.

Furthermore, punctures in tubeless tires, including radial tires, can be repaired in a convenient and reliably effective manner by applying to the puncture a composition in accordance with the present invention. The composition is applied to the puncture to be repaired, and is thereafter cured in situ in the puncture. -443664 A composition in accordance with the present invention and in the form of a puncture sealing composition for a pneumatic tire preferably includes from 2 to 10 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, said blend being partially crosslinked by the said crosslinking agent to provide in the blend a gel content of from 20½ to 50% by weight, based on the weight of the blend,as measured in toluene at room temperature and a peak Mooney viscosity of from 40 to 50 ML at 150°F. Preferably the alkyl groups in the said tetraalkyl titanate ester crosslinking agent have from 3 to 8 carbon atoms, the amount of said titanate ester is from 3 toS parts per 100 parts by weight of the two elastomers, and the composition is devoid of fibrous filler.

The present invention also provides a puncture sealing tubeless pneumatic tire having a vulcanized rubber tread portion surmounting a vulcanized rubber carcass portion reinforced with filamentary material, said carcass portion having a crown area underlying the tread, and having sidewall portions extending from shoulder areas at the edges of the crown area to bead areas containing inextensible circumferential reinforcement, the interior surface of the -5£3864 tire being covered with an air-impervious liner, and a puncture sealing layer inside the tire disposed across the crown area of the tire and extending at least from one shoulder area to the other, said puncture sealing layer comprising a fiber-free composition of the invention wherein the crosslinking agent is selected from the following, present in the amounts recited: from more than 0.5 to 2.0 parts of sulfur or sulfuryielding curative; from more than 0.5 to 2.0 parts of quinoid curative; from 0.1 to 1.0 part of radical generating curative; from 2 to 10 p.arts of polyisocyanate curative; and from 2 to 10 parts of tetrahydrocarbyl titanate ester curative; the said parts of crosslinking agent being by weight based on 100 parts of the combined weight of the two elastomers, the gel content of the blend in the partially crosslinked state being from 15 to 60% by weight of the blend, as measured in toluene at room temperature, and the peak Mooney -643684 viscosity of the blend in the partially crosslinked state being from 30 to 55 ML at 150°F.

The present invention further provides a puncture sealing tubeless pneumatic tire having a vulcanized rubber tread portion surmounting a vulcanized rubber carcass portion reinforced with filamentary material, said carcass portion having a crown area underlying the tread, and having sidewall portions extending from shoulder areas at the edges of the crown area to bead areas containing inextensible circumferential reinforcement, the interior surface of the tire being covered with an air-impervious liner, and a puncture sealing layer inside the tire disposed across the crown area of the tire and extending at least from one shoulder area to the other, said puncture sealing layer comprising a composition of the invention wherein the ge) content in the blend is from 20% to 50% by weight,based on the weight of the blend;as measured in toluene at room temperature and a peak Mooney viscosity of from 40 to 55 ML at 150°F.

Preferably the alkyl groups in the said tetraalkyl titanate ester crosslinking agent have from 3 to 8 carbon atoms, the amount of said titanate ester is from 3 to 8 parts per 100 parts by weight of the two elastomers, and the composition -736 6 4 is devoid of fibrous filler.

Also provided by the present invention is a method of repairing a puncture in a tire casing of the tubeless tire comprising forcing into the puncture a plastic repair material to fill the puncture and depositing on 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 2,000,000 cps^with correspondingly from less than 50$ to 10$ by weight of a high molecular weight, solid j elastomer having, a Mooney viscosity of from 20 to 160 ML -4 at 212°F, 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 ι applied repair material to curing conditions at least partially to crosslink the blend to a gel content of from 20$ to 80$ by weightjbased on the weight of the blend^as measured in toluehe at room temperature and a peak Mooney viscosity of above 30 ML at 150°F, whereby the blend is prevented from flowing at elevated temperatures and -843664 centrifugal forces encountered in the tire in use and the puncture is effectively sealed against loss of air from the tire. Preferably 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 wieght of the two elastomers.

We have found that a mixture of high and low molecular weight elastomer, the latter being present in amount of more than 50% by weight, cured to a limited extent, sufficient to prevent flow under conditions of use, offers novel and unique advantages. The high molecular weight elastomer furnishes rigidity and strength. The low molecular weight elastomer furnishes the adhesion and conformability necessary in a puncture sealant. Preferably, the adhesion and conformability is enhanced by the inclusion of a tackifier and/or plasticizer. The tendency to flow is, of course, greatest in the low molecular weight component. By increasing the proportion of high molecular weight component, this tendency can be decreased, but not completely removed, In partially curing the mixture, the crosslinks are more effective in the high molecular weight elastomer, or skeleton to retard flow, without crosslinking the low -93684 molecular weight elastomer to the point where its ability to function as sealant would be significantly impaired.

The use of the composition as a repair material is remarkable in that the high molecular weight partially vulcanized portion serves as a gelled matrix which restrains the low molecular weight portion 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 elevation'al view of a pneumatic tire embodying a puncture ''sealant layer in accordance with the invention; Figs.2 and 3 are enlarged fragmentary views similar to Figure 1 illustrating the sealing action of the puncture sealant layer; and Fig. 4 is a view similar to Figure 1 showing a modification of the invention; -1043664 Fig. 5 is a largely diagrammatic sectional elevational view of a tubeless pneumatic tire, punctured by a nail; Fig. 5 is a similar fragmentary view on a 5 larger scale, showing a puncture being repaired by application of repair material by means of a syringe; and Fig. 7 is a view similar to Fig. 5 showing a tire being repaired while mounted on a rim.

As indicated, the invention is a puncture sealant composition which 1s a mixture of low molecular weight liquid elastomer with a high molecular weight elastomer being present in amount greater than 50% based on the weight of the two polymers, crosslinked to an extent, as measured by gel and Mooney viscosity, which will prevent it from flowing at elevated temperature, yet still possess sufficient adhesion and conformability to function as a sealant and repair composition. Preferably, a tackifier may be substituted for a portion of the low molecular weight rubber to enhance the adhesion and conformability of the resultant composition.

Furthermore, the method of the invention involves applying -1143SS4 a repair material to the puncture to be repaired and thereafter at least partially curing orcrosslinking the material.

As the high molecular weight elastomeric component of the sealant composition of the invention there may be employed any high molecular weight solid elastomer capable of being crosslinked. Examples are the highly unsaturated rubbers such as those based on conjugated diolefins, whether homopolymers as in polyisoprene (particularly cis-oolvisoprene, whether natural or synthetic), polybutadiene (including polybutadiene of high cis content), polychloroprene (neoprene), or copolymers as exemplified by those having a major proportion of such conjugated dienes as butadiene with a minor proportion of such monoethylenically unsaturated copolymerizable monomers as styrene or acrylonitrile. Alternatively, elastomers of low unsaturation may be used, notably butyl rubbers (copolymers of such isoolefins as isobutylene with small amounts of conjugated dienes such as isoprene) , or the EPDM types (copolymers of at least two different 0 monoolefins such as ethylene and propylene with a small amount of a non-conjugated diene such as dicyclopentadiene, 1,4-hexadiene and 5-ethylidene -2-norbornene). Even saturated elastomers such as EPM or ethylene-vinyl acetate may be -1243084 employed, using the proper cure system. The elastomer may be emulsion-prepared or solution-prepared, stereospecific or otherwise. The molecular weight of the solid elastomer is usually in excess of 50,000 ordinarily within the range of from 60,000 to 2 or 3 million or more.

Ordinarily the solid elastomeric component has a Mooney viscosity within the range of from 20 to 160 ML-4 at 212°F.

Examples of low molecular weight elastomers are: liquid cis-polyisoprene (e.g., heat depolymerized natural rubber, or cis-ool.yisoprene polymerized to low molecular weight), liquid polybutadiene, liquid polybutene, liquid EPDM, and liquid butyl rubber. The high molecular weight, elongation and film strength of ci.spolyisoprene (both natural and synthetic) and great tackiness of depolymerized cis15 polyisoprene give a combination of these two elastomers, when partially cured, according to the present invention,a large degree of resistance to flow, coupled with efficient sealing ability. Other elastomer combinations of the present invention, particularly the saturated ones, offer resistance to oxidation in service which makes them also highly desirable.

The tackifying or plasticising substances which are preferably -134 3 6 3 4 included in the composition are low molecular weight materials such as rosin esters (e.g. Staybelite (Trade Mark) Ester 10); aliphatic petroleum hydrocarbon resins (e.g. Piccopa'le (Trade Mark) A-70); polyterpene resins derived alpha-pinene (e.g. Piccolyte (Trade Mark) A-10), beta-pinene (e.g. Piccolyte S-25); resins made from styrene and related mon,omers (e.g. Piccolastic A-5); resins made from dicyclopentadiene (e.g. Piccodiene 2215); and resins made from the reaction of a mineral oil purification residue with formaldehyde and with nitric acid catalyst according to West German Patent 1,292,396, solid under the tradename of Struktol.

The novel composition of the invention contains a major proportion, that is, between more than 50% and 90% by I weight of total low molecular weight material (i.e. low molecular weight elastomer plus low molecular weight tackifier or plasticizer). The amount of the tackifier or plasticizer may range up to 70% based on the weight of low molecular weight elastomer plus tackifier of plasticizer.

The ratio of high to low molecular weight components, depends mainly on the molecular weight of the high molecular weight elastomer and other variables such as the particular elastomer involved, the amount and kind of crosslinking agent, and the conditions of the crosslinking -1443664 treatment. The proportion of the two elastomeric components are chosen so as to give a peak Mooney viscosity at 150°F (the maximum reading attained, which is usually at about 90 second of the 4 minute Mooney curve) of at least 30 (large rotor, ML) in the final crosslinked mixture, with a preferred range of from 30 to 55, more preferably from 40 to 50. Below the aforementioned peak Mooney viscosity of 30, the composition will tend to flow down from the shoulder and sidewall areas of the tire when it is run at high speed as well as out of the hole when the tire is punctured. Above the said peak Mooney' viscosity of 55, the sealant capability of the composition is sufficiently impaired to render it unusable for practical purposes. However, this maximum limitation does not apply when used as a repair material. Although there is no critical upper limit 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 in ordinary rubber compounding practice, nevertheless it is not ordinarily necessary or desirable to use more curing agent than is required to provide an initial Mooney of about 70-100 (ML at room temperature) at the conclusion of the crosslinking. The Mooney viscosity of the mixture can also be controlled for -1543 6 6 4 a given elastomeric composition of the present invention by the amount of the mechanical shearing employed in mixing the constituents. The net effect here, of course, is to break down (i.e. lower) the molecular weight of the high molecular weight component, thereby lowering the Mooney viscosity before cure.

As indicated, for purposes of the invention the mixture further includes a crosslinking agent. The crosslinking agent may be any suitable substance or combination of substance capable of curing or gelling the mixture to the desired extent. Examples are: 1) Sulfur curing systems such as those based on sulfur or sulfur-yielding materials (e.g., tetramethyl thiuram disulfide) and conventional accelerators of sulfur vulcanization. 2) Quinoid curing systems such as p-quinone dioxime (GMF, trademark, Uniroyal Chemical) with or without supplementary oxidant. 3) Organic peroxides (or hydroperoxides) such as dicumyl peroxide, cumene hydroperoxide, methyl ethyl ketone hydroperoxide or other radical generating catalysts such -1643664 as azoblsisobutyronitrile. 4) Polyisocyanates such as MDI (4,4'-methylene bisphenyl enei socyanate) , TDI (tolylene di isocyanate), and PAPI (polymethylene polypheny!isocyanate) as well as dimers and trimers of MDI and TDI.

) Tetrahydrocarbyl titanate esters as described in copending application No. 356/76 referred to above.

The amount of crosslinking agent employed will vary with the particular elastomers employed and with their proportions, as well as with the particular crosslinking agent and the conditions of the cross!inking step. Ordinarily the amount used is that sufficient to prevent flow of the composition in a tire at temperaturesup to 200°F and speeds up to 70 mph, while still retaining sufficient adhesiveness and conformability to perform the described sealant function. The amounts employed will vary depending on the proportion of high molecular weight elastomer in the mixture. Higher proportions of high molecular weight elastomer will require less crosslinking agent and vice-versa to maintain the desired combination of resistance to flow and sealing ability. The amount of 3 6 6 4 crosslinking agent will, of course, vary with the nature of the elastomers themselves. For a depolymerized natural rubber (DPR)- natural rubber (NR) mixture, used as a puncture sealing composition, the amount of sulfur5 containing or qijinoid type curative will be in the range of from more than 0.5 to 2.0 phr (parts per 100 parts by weight of bpth elastomers added together), ordinarily from 0.7 to 1.5 phr. For this same mixture, with polyisocyanate or hydrocarbyl titanate ester curatives the ) amounts required will ordinarily be in the range from 2 to 10 phr, preferably 2.5 to 8 phr. Similarly, the applicable range for peroxide or hydroperoxide curatives (radical generating catalysts) would be 0.1 to 1.0 phr, preferably 0.2 to 0.7 phr. ί Typically, for a depolymerized natural rubber (DPR)-natural rubber (NR) mixture, used as a repair material, the amount of sulfur-containing or quinoid type curative will be in the range of from more than 0.5 to 4 phr (part per 100 parts by weight of both elastomers added together), ordinarily from 0.7 to 2 phr. For this same mixture, with polyisocyanate or hydrocarbyl titanate ester curatives, the amounts required will ordinarily be in the range from 4 to 25 phr, preferably 5 to 15 phr. Similarly, the applicable range for peroxide or hydroperoxide curatives (radical generating catalysts) would be 0.1 to 1.5 phr, preferably 0.2 to 1 phr. -1843664 The crosslinking of the sealant mixture is accompanied by an Increase in viscosity and an increase in 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 between 15 to 60% preferably 20 to 50% by weight, in the crosslinked blend correlates with the desirable combination of sealing ability and lack of flow properties. For use as a repair material the gel content should be within the range of from 20% to 80% or higher (e.g. 95%), preferably 20% to 60%. For other elastomer combinations the range of optimum gel content will vary depending on the molecular weight and proportion of the two elastomeric components. As described previously an initial Mooney viscosity (ML at room temperature) of the ranges indicated of the final cured mixture has been found to correlate with the aforementioned desired combination of properties.

The crosslinking may be carried out at ordinary ambient temperature or at elevated temperature, depending on the temperature at which the particular crosslinking system selected is active in the particular elastomer combination employed. -19ΐ <3§06<4 The composition may further include, if desired, various appropriate additional compounding ingredients such as pigments such as carbon black, particulate inorganic fillers, extenders, tackifiers, stabilizers and antioxidants It is not necessary nor desirable to add fibrous fillers to the present compositions.

In practising the invention, using the composition as a puncture sealant composition, the ingredients are mixed together uniformly and the resulting mixture is incorporated in the tire in the form of a relatively thin (e.g, 0.1 inch) sealant layer. Referring to the drawing, and particularly to Fig. 1 a typical embodiment of the invention comprises a toroidal tubeless tire casing 10 having the usual vulcanized rubber tread 11 and sidewall portions 12, 13 surmounting a vulcanized rubber case 14 reinforced with filamentary material, which terminates at bead areas 15, 16 containing the usual circumferential inextensible reinforcement. The entire inside surface Of the carcass is covered by the usual air-impervious liner 17. A layer 18 of sealant material of the invention extends across the interior crown surface of the liner from one shoulder area of the tire to the other, and extends at least part way into each interior side wall area. -2043664 The sealing action of the layer 18 is represented in Fig. 2 and 3, wherein Fig. 2 shows a nail 19 puncturing the tire through the tread 11, carcass 14, liner 17 and sealant layer 18. The sealant composition tends to adhere to the nail and prevents loss of air pressure while the nail is in place. When the nail is withdrawn, as shown in Figure 3, it tends to pull a plug 20 of the sealant composition into the puncture 21, thereby sealing the puncture against loss of air.

In a modification of the invention, as shown in Fig. 4 the puncture sealant layer 23 of the invention is disposed in between the inner surface of the carcass 24, and the liner 25. In such cases where the sealant layer is incorporated in the tire, it may be crosslinked before or after said incorporation. Similarly, the tire may be cured before or after incorporation of the sealant layer.

In order to apply a sealant layer to the interior surface of a tire, the composition may be prepared as a solvent cement, for example as a solution in n-hexane or other suitable volatile organic solvent. This cement may be applied (e.g. sprayed or brushed) over the desired area of the inner surface of the tire liner, using as many -21coats as required to build up a desired thickness. Using the hydrocarbyl titanate curative system, the thus-applied sealant layer will become sufficiently crosslinked to perfdrm the sealant function in about five days at room temperature, although the cure time may be shortened if desired by storing the tire in a warm place, e.g. at 50 to 100°C.

Another method is to extrude the heated sealant composition into a tire at elevated temperature in the form of a layer or strip having the desired thickness. Conveniently the composition may be extruded directly onto the liner surface from a suitably shaped die extending into the tire carcass, while rotating the tire. For extrusion at elevated temperatures, a curative system must be selected which will not react prematurely at the temperature of extrusion, but which will subsequently cure the composition at some temperature higher than the extrusion temperature. The tetrahydrocarbyl titanate ester cure of the puncture sealant represents a particularly advantageous practice of !0 the invention in that with the tetrahydrocarbyl titanate ester curative it is possible to extrude the sealant at an elevated temperature without premature cure, and yet the cure of the applied sealant layer can be accomplished at a lower temperature (e.g. room temperature). The reason for this is that the titanate ester cure of the blend of -2243664 elastomers will not take place unless hydrocarbyl alcohol (apparently forrted as a by-product of the curing reaction) can escape from the composition. If the material is confined under non-evaporative conditions (e.g. in the barrel of an extruder) the cure will not take place, even at elevated temperature. However, after the blend is applied to the tire, the said hydrocarbyl alcohol is free to evaporate from the sealant layer, and the cure proceeds, even without any necessity for heating.

Alternatively, a previously prepared strip (e.g. an extruded strip) of sealant composition of suitable width and thickness may be applied by any suitable means to the interior of a tire.

The puncture sealing layer may if desired cover the entire interior surface of the tire from one bead or rim area to the other, in which case the liner may be omitted and the puncture sealing layer may serve as a liner.

In some cases it may be desirable to incorporate the sealant strip in the tire assembly as the tire is being manufactured, for example by laying down a strip of the sealant material 3 6 6 4 on a tire building drum, and then superimposing the liner and other carcass components. The sealant layer may be prevented from adhering to the building drum by first placing a layer of flexible material on the drum followed by the sealant layer and then the remaining components of the tire. Thus the liner may first be placed on the tire building drum followed by the sealant layer and carcass plies, to provide the type of construction shown in Fig. 4.

The puncture sealant ability and resistance to flow of the composition of the invention may be tested in an inflated tire. For this purpose the sealant is placed in the tire which is run at 75 to 90 mph and a load sufficient to generate an internal temperature of 250°F or higher.

After running at high spaed; the tire is then observed to determine whether the sealant has flowed out of the shoulders of the tire and into the crown area or whether it has formed a puddle in the bottom of the tire after the tire was stopped. The ability to resist flow at at least 50 mph at an internal air temperature of at least 200°F is an important criterion of performance for the present invention. To evaluate puncture sealant ability, the tire is punctured with nails of various sizes, which are subsequently removed from the tire, and the loss of air pressure within the tire measured. Another important advantage of the present invention is the ability of the sealant composition to seal holes of at least 0.125 inch in diameter.

In practising 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. 5, a typical tire to be repaired comprises a toroidal tubeless 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 material, which terminates at bead areas 15, 16 containing the usual circumferential inextensible reinforcement. The entire inside surface 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 extending through the tread 11, carcass 14 and liner 17 into the interior of t,he casing.

To effect a repair of the tire in an unmounted condition, the nail is removed from the puncture 22, as shown in Fig. 6, and the repair material 23 is introduced into the hole by means of a syringe 24 or the like. The quantity of repair material injected, usually from about 50 to 200 grams, should be sufficient to fill up the hole completely and to provide an excess for the formation of an enlarged patch -254 3 6 6 4 portion 25 which is formed by smearing or flattening the excess material against the inner (liner) surface of the tire immediately surrounding the puncture. The repair material is then crosslinked 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 solution, wiping with solvent and/or buffing. For optimum adhesion of the patch portion to the cleansed 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 air blower, a circulating hot air oven or the like. If the repair material cures without heat, then heating is of course unnecessary.

In the modification of the invention shown in Fig. 7, the repair is effected on the tire while mounted on a rim 26. Again, as in the method described above for repairing an unmounted tire, a quantity of repair material, usually from about 50 to 100 grams, is injected into the tire from -2643664 a syringe 27 (Fig.7·,) The quantity of the repair material should be an amount sufficient to fill up the hole completely to form a plug 29 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, whose cross sectional area is substantially larger than the cross sectional area of the hole (by reason of the elastic memory of the repair material, which causes it to swell to a larger diameter as it issues from the hole on the inside of the tire), acts as an anchor to immobilize 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.

The following examples will serve to illustrate the practice of the invention in more detail.

EXAMPLE I 480 grams of natural rubber (Standard Malaysian Rubber, Mooney viscosity 64 ML-4-212°F., weight average molecular β weight 4.7 x 10 ) was dissolved in 4 gallons of n-hexane.

To this solution was added 960 grams of depolymerized natural rubber (DPR-400 [trademarkf , Hardman Company, viscosity 80,000 cps@150°F.) and the mixture stirred until -2743 it is uniform. 100.8 grams of tetra-n-butyl titanate was added and the cement stirred once more. 24 grams of Antioxidant 2246 ^trademark, American Cyanamid, 2,2‘methylene-bis (4-Methyl-6-tert-butylphenoI)]was added at this point. The resulting cement had a solids content of about 14%.

The cement was then coated onto the inside air-retaining liner of a HR 78-15 radial tire for a distance of 4 inches on either side of the center point up the inner side walls of the tire. The liner had first been cleaned by washing with soap and water, and then dried. The cement was laid down by painting thin successive layers until a weight of 1200 grams of dry solids was reached around the complete circumference of the tire. The solvent was allowed to evaporate overnight at room temperature and cure was completed by allowing the tire to sit at room temperature for 5 days. This process can be accelerated so that an equivalent cure can be attained by heating the tire for 24 hours at 200°F. After the cure the gel content of the sealant composition was 35% as.measured in toluene at room temperature>compared to about 5% before cure.

The modified tire was tested by mounting it on a standard -2843664 automobile rim, inflating it to 28 psi and running it on a Getty wheel, Π-inch diameter, for one hour at 50 miles per hour in order to thermally equilibrate the tire. Eight 20-penny nails (about 0.185 inch shank diameter) were then driven into each of the 6 grooves of the tire tread, from edge to edge, one through each groove and two others between lugs, so that the head of the nail could not be driven flush into the groove through a rib. The tire was then run an additional 20 hours at 50 miles per hour without an adjustment of the inflation pressure. During this period, there was little or no loss of air from the tire. All the nails were then removed and it was observed that there were holes in the tread of about the same siameter as the shanks of the nails. Most importantly, it was observed that during the removal and immediately thereafter, there was only a slight loss of inflation pressure (less than 4 psi) followed by complete sealing of all holes by the puncture sealant. The tire was then run an additional 10,000 miles (200 hours at 50 mph) during which period no further loss in inflation pressure was observed.

A similar tire containing no puncture sealant coating lost complete inflation pressure when subjected to the foregoing test, immediately after removal of the nails.

EXAMPLE II A tire, in which the sealant, comprising 60% DRP-400 and 40% natural rubber, as applied by extrusion at 250°F as a 0.100 inch layer to the inner liner of the tire, gave a result similar to the tire in which the sealant was applied from a solution. For extrusion, a mixture of 6 lbs. of DPR-400, 45 gms. Antioxidant 2245 and 5 lbs. of creamed Hevea natural rubber latex (67% total solids) were mixed in a double-arm sigma blade dough mixer at a shell temp. of 27O°F for 30 minutes. Vacuum was then applied and mixing continued for 30 minutes at which time the moisture content of the blend was less than 0.2%.. The mixture was cooled at about 170°F and 272 gms. of tetra-n-butyl titanate was added. The mixer was tightly closed and mixing continued for an additional 30 minutes. The resultant composition was then extruded at 250°F as a 0.10 inch layer to the inner liner of a tire. The peak Mooney viscosity at 150°F (large rotor, .ML) of the fully cured sealant was 45.

EXAMPLE III The composition of Example II is used as a repair composition. For use, the repair composition may be loaded into syringe, caulking gun, grease gun or the like, for application to a repair as described above. The material may be heated to an elevated temperature to facilitate application by -3043664 increasing the flowability or plasticity but this is not essential. The exemplified formulation will not cure as long as the composition remains enclosed within the syringe or gun because the evolution and escape of the hydrocarbyl alcohol, necessary for the curing reaction, cannot take place. However, once the repair material is applied to the puncture, the alcohol has an opportunity to escape and the cure advanced. Typical repairs using the exemplified composition become crosslinked to the desired extent in about five days at room temperature or in a shorter time if the repair is heated externally.

In one test an HR78-15 tire was punctureiby a 20-penny nail in the center groove and the inside surface surrounding the hole was cleaned with n-hexane. Using a grease gun filled with the exemplified repair material which has been heated to 200°F, a quantity, about 150 grams?of warm repair material was injected into the hole from the outer surface of the groove in the direction of the inner periphery of t.he tire. The excess repair material was then flattened to form an enlarged retaining patch portion as described above. The repaired tire was then placed in a circulating hot air oven and the repair was cured for 24 hours at 200°F; the patch and the material in the hole then formed an integral repair. After cooling, the tire -3163684 was mounted on a standard automobile rim and inflated to a pressure of 40 psi. There was no loss of inflatic pressure over a two-week period. It should be noted th this two-week period is not a necessary condition for the practice of this invention. The repair is permanen immediately after the minimum cure is attained. At the end of the two-week period the inflation pressure was adjusted to 28 psi and the tire was run on a Getty wheel, inch diameter with a 1000 pound load at 50 mph. There w no loss of inflation pressure after 24 hours (1200 miles at which point the run was discontinued.

EXAMPLE IV A sealant containing equal parts of natural rubber, DPR400 and Struktol 30, along with 8% tetraisopropyl titanat and Π Antioxidant 2246 (both based on total rubber) was mixed according to the procedure of the second example.

It was then extruded onto the liner of a tire as a 0,125 layer at 240°F and cured by heating for 7 days at 150°F. The peak Mooney viscosity at 150°F of the cured sealant we and its gel content was 33.1% measured in toluene at 50°C for 24 hours.

The tire was mounted on a rim and inflated. As a measure of sealing efficiency, four 20d nails, 2 1/2 long were -3243664 driven into the tire, one in the outer rib, one in the outer groove and two in inner positions. The tire was then run on the Getty wheel, starting at 50 mph, for one hour periods at speed increments of 5 mph, until all the nails were ejected from the tire. All the holes, which in this test were the same diameter as the shank of the nail,sealed and no inflation was lost. A tire containing no sealant went flat within 1 minute after the first nail was ejected in this test.

EXAMPLE V A sealant indentical to that of Example IV, except that it contained 10% tetraisopropyl titanate (based on total rubber) was extruded into each of four tires as a 0.125 strip and cured as above. The cured sealant had ML peak values at 150°F ranging from 35 to 45 and gel contents of 18 to 25%. The tires were then mounted on a car, each with a 20d nail driven into an outside or inside tread position, and the car driven in 100 mile cycles at the following speeds, until the nails were ejected. 22.5 miles at 30 mph 37.5 miles at 50 mph miles at 80 mph For each tire, when the nail was ejected the hole sealed with little or no loss of inflation and the car was able to continue running. Uncoated tires, when tested similarly, lost inflation rapidly and went flat within one minute.

EXAMPLE VI A sealant containing 50 parts of natural rubber, 50 parts of DPR-400 and 70 parts of Piccadiene 2215 (a tackifying resin made from polymerized dicyclopentadiene, manufactured by Hercules, Inc.), plus 8% tetra-isopropyl titanate and % Antioxidant 2246 (based on total rubber) was mixed according to the procedure of the second example. It was then extruded at 250°F as a 0.125 thick strip onto a tire and cured. The puncture sealing efficiency of this material measured in the .nail ejection test of Example IV, shows an average sealing efficiency of 75% (3 out of 4 nail holes sealed).

EXAMPLE VII A sealant·composition containing 50 parts each of natural rubber and DPR-400, plus 50 parts of Piccopale 100 (a hydrocarbon polymer tackifying resin, Hercules. Inc), 16% tetra-isopropyl titanate and 10% Antioxidant 2246 (based on the total rubber) was mixed and extruded into a tire at 250°F as a 0.125 strip. Its sealing efficiency in the nail ejection test of Example IV was greater than 75%. -3443664 EXAMPLE VIII A sealant mixture of 50 parts by weight each of natural rubber, DPR-400 and Struktol 30, plus 10 parts by weight of Antioxidant 2246 was extruded at 250°F as a flat strip 0.250 thick and 8 wide. It was then irradiated in a 1.4 million volt electron beam at a dosage of 20 megarads. The irradiated sample showed a gel content of 29.6% and an ML peak at 150°F of 35. The strip was then incorporated on top of the layer in an uncured steel-belted radial tire which was cured in a conventional tire press. The tire gave 100% sealing efficiency in the nail ejection test of Example IV.

EXAMPLE IX A sealant composition containing 40 parts by weight of natural rubber, 30 parts by weight of DPR-400 and 30 parts by weight of Struktol 30, along with 4.2 parts by weight of tetra-isopropyl titanate and 0.7 parts by weight of Antioxidant 2246 was mixed according to the procedure of the second example. It was then extruded into a tire at 240°F as a 0.125 strip, cured and tested in the nail ejection test of Example IV. Its average sealing efficiency was 70%. -35EXAMPLE X Two parts of Butyl LM 430 (Enjay liquid polyisobutylene, viscosity average molecular weight 32,000,about 4 mole percent unsaturation) and one part Royalene 505 (Uniroyal, Inc., ethylene-propylene-ethylidene norbornene terpolymer 58/42 ethylene - propylene ratio, iodine number 20, ML-4=50 at 257°F) were dissolved in hexane to yield a concentration of about 10%«8 phr (based on the total rubber content) of tetra-n-butyl titanate was added and the mixture painted into the inside of a tire in an 8 inch width. Sufficient solution was used to leave a layer 0.125 in thickness when the solvent had completely evaporated. The sealant was allowed to cure by storage for at least 24 hours at room temperature after complete removal of solvent. The tire was inflated on a rim and then punctured in the tread with four nails of 0.125 daimeter. The tire was then run 1000 miles at 50 mph on a Getty wheel and the nails then removed.

There was less than 4 psi loss of inflation and the holes all sealed. on EXAMPLE XI A sealant'Composition containing equal parts of Butyl LM 430, Royalene 505 and Piccolyte A 100 43684 (a polyterpene resin derived from alpha-pinene, softening point 100°C)iplus 6% tetra-n-butyl titanate (based on total rubber) was made up in hexane solution and painted into a tire to yield a strip 8 wide and 0.125 thick after evaporation. After curing at room temperature, the sealing efficiency of the coating was tested in the same manner as in Example X, using 0.125 nails. Complete sealing after the nails were removed, with little or no loss of inflation, was found.

EXAMPLE XII A sealant composition containing equal parts of Royalene 505, Butyl LM 430 and Piccodiene 2215, plus 10% tetra-nbutyl titanate (based on the total rubber) was dissolved in hexane and painted into a tire to yield a strip 8 wide and 0.125 thick after evaporation. After being allowed to cure at room temperature, the tire was tested for /1 sealing efficiency as in Example X. Two nails of 0.125 diameter were used and when removed after 1000 miles, there was no loss of inflation.

EXAMPLE XIII A sealant composition containing equal parts of Royalene -3743664 525 (ethylene - propylene ethylidene norbornene terpolymer, iodine number 20, ML-4=55 at 257°F), Butyl LM 430 and Struktol 30, plus 10% tetraisopropyl titanate (based on the total rubber content) was dissolved in hexane and painted into a tire to yield a strip 8 wide and 0.125 thick when evaporated. The sealant was allowed to cure at room temperature, after which the tire was mounted on a rim and inflated to 28 psi. It was then punctured with two 20d nails and run at 50 mph for 20 hours. The nails were then pulled out with no loss of inflation being noted.

As is. described in more detail in the above-mentioned copending application No. 42487 the cure (crossl.ining or gelling to an isoluble 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 maintaining the mixture in a closed system. The unsaturated elastomers that may be cured with titanate ester include cis-polvisoprene (whether natural or synthetic), polybutadiene, notably cis polybutadiene, butadiene - styrene 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 -3843664 (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 (ROj^Tiwhere R is hydrocarbyl group, such as an alkyl group, e.g., an alkyl group having 1 to 12 carbon atoms, preferably 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 suc.h as an internal mixer, e.g., a sigma blade mixer (such as a Baker-Perkins [trademark] or a closed Brabender 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 conditions which suppress gellation (i.e., in a closed system under non-evaporative conditions, or in the presence of a volatile alcohol) and then, after the -3943684 mixture has been .shaped into the desired form (e.g. molded, extruded, coated, etc,), the mixture is permitted to gel simply by exposing to evaporative conditions in the open atmosphere. Depending on the rubber and the amount of extraneous hydroxylic compounds such as anti-oxidants (hydroxylic compounds are inhibiting substances in the cure) it contains, the amount and type of titanate ester used dictate the rate and extent of cure obtained.

The temperature and time required for titanate cure again depend on the presence or absence of hydroxylic (inhibiting) additives and the type and level of titanate employed.

Cure of the mixture is accompanied by evaporation of alcohol, corresponding to the alkoxy portion of the titanate ester.

Hence, titanate esters of lower boiling alcohols effect cure more readily than titanate esters of higher boiling alcohols, e.g., isopropyl titanate acts more rapidly than butyl titanate which in turn acts more rapidly than ethyhexyl 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 solventjcure. is rapid at room temperature. In general, from 1 to 10 days are required for cure at room temperature depending on such factors as the nature of the rubber, the amount of hydroxylic impurity, the surface to volume ratio -4043664 (the greater the surface exposed, the more rapid the cure), as well as the level and type of titanate ester. It is a remarkable feature of the cure that the curable mixture can be processed at elevated temperatures (under non5 evaporative conditions) without premature cure,and yet cure can be accomplished at ambient temperature (under evaporative conditions).

As indicated, it has been observed that the titanate curing reaction is accompanied by the evolution of alcohol, that is, an alcohol ROH corresponding to the organic group of the ester fR0)^Ti is generated during the cure. If the alcohol is prevented from evaporating, as in a closed container where non-evaporative conditions prevail, the cure will not go forward. However, when the curable composition is placed in the open atmosphere where evaporative conditions prevail, and the evolved alcohol ROH can escape, the cure proceeds. Thin sections such as coating deposited from a solution, calendered or extruded films and sheets, and similar thin sections (e.g.,0.2 inch thick or less) haye higher surface to volume ratio than thicker sections (such as most molded objects) and present greater opportunity for the generated alcohol ROH to escape. Therefore, such thin sections cure more rapidly than thick sections, -4143664 As the titanate cure proceeds the gel content of the rubber (that is, the fraction insoluble in organic liquids that are normally solvents for the uncured elastomer) increases indicating that crosslinking is taking place, and evolution of alcohol continues until a plateau of gel content is reached.

As indicated,, hydroxylic additives have an inhibiting effect on the titanate cure. For instance phenolic antioxidants have been found to slow down the cure rate.

When such antioxidants are removed as nearly as possible, solutions of the rubbers tend to gel quickly when titanate esters are addled, Normally, appreciable gellation occurs slowly upon evaporation of solvent from the solution. •Addition of small amounts of volatile alcohol to solutions of rubber inhibits any tendency toward premature gellation. In fact, the rate of cure can be controlled by the molecular weight of the added alcohol. Low molecular weight alcohols such as ethyl alcohol have a mild or temporary inhibiting effect while higher boiling alcohols such as dodecyl alcohol have a more severe and lasting inhibiting effect. After gellation, thegelled rubber is insoluble to toluene and other organic solvents, but addition of acid such as acetic acid reverses the process and the rubber becomes soluble again. Addition of carboxylic acids likewise -42436G4 inhibits gel formation. It appears to be possible that the crosslinking is a consequence of titanate ester formation with the elastomer.

Preferred elastomers for use with the titanate cure are 5 those selected from the group consisting of natural rubber, synthetic ci s-pol.visoprene elastomer, sis polybutadiene elastomer and ethylene - propylene - 5 ethylidene - 2 - norbornene terpolymer rubber having an iodine number of at least 12, in low molecular weight (liquid) or high molecular weight (solid) form.

It will be understood that the measurements of gel content and Mooney viscosity set forth above for the final cured sealant material are obtainable on a separate sample of the sealant composition which has been subjected to curing IS conditions substantially equivalent to those to which the final sealant material is subjected; it is of course not practical to make these measurements on an actual material in use in the tire itself.

In tires repaired by the present method the puncture is entirely filled with a material that is sufficiently plastic and conformable in the uncured state to take the exact shape of the puncture and fill all interstices thereof without setting up undesirable stresses. Such a -4343664 repair, after at least partial cure in situ as described, tends to remain in place, unlike conventional repairs made with a preformed plug or the like, which tend to work loose. Conventional repair plugs are frequently cut through by working against the steel cords of belts used in radial ply tires (especially by frayed ends of broken cords at the puncture) whereas the present repair resists this by reason of the nature of the repair material and its manner of application. Adhesion of the integral patch portion of the present repair to the inside surface of the tire.is good because of the manner in which it is applied in the uncured state and cured in situ on the tire surface. Also, the liquid rubber component, which tends to acquire only a limited amount of vulcanization in the repair process, serves to maintain the tackiness and adhesiveness of the repair, so that it does not work loose.

Claims (39)

1. An elastomeric composition comprising a blend of from more than 50% to 90% by weight of a low molecular weight liquid elastomer having a Brookfield viscosity 5 at 150°F of from 20,000 to 2,000,000 cps,with correspondingly 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 ? and a crosslinking agent for the elastomers in an amount effective partially to crosslink 10 the elastomers to an extent that the blend, after cross-linking, has a gel content 'of from 15 to 95% by weight of the blend as measured in toluene at room temperature and a peak Mooney viscosity of above 30MLat 150°F, the blend having in the partially crosslinked state sufficient 15 adhesion and conformability to function as a sealant in a tire and whereby the blend is prevented from flowing at elevated temperatures and centrifugal forces encountered in a tire in use.

2. A composition according to claim 1 wherein after 20 crosslinking the gel content is from 15 to 50% and the peak Mooney viscosity is from 30 to 55.

3. A composition according to claim 1 wherein after crosslinking the gel content is from 20 to 95%,

4. A composition according to any of the preceding 25 claims wherein the low molecular weight elastomer is heat depolymerized natural rubber. - 45 6 6 4

5. A composition according to any of claims 1 to 3 wherein the low molecular weight elastomer is liquid cis polyisoprene, liquid polybutadiene, liquid polybutene, liquid ethylenepropylene - non - conjugated diene terpolymer 5 rubber,or liquid isobutylene - isoprene copolymer rubber.

6. A composition according to any of the preceding claims whereih the high mo.lecular weight elastomer is a conjugated diolefin homopolymer rubber, a copolymer of a major proportion of a conjugated diolefin with a minor proportion 10 of a copolymerizable monoethylenically unsaturated monomer, a copolymer of isobutylene with a small amount of isoprene, an ethylene - propylene - non - conjugated diene terpolymer, or a saturated elastomer.

7. A composition according to any of the preceding 15 claims wherein the crosslinking agent is a sulfur or sulfur-yielding curative, a quihoid curative, a radical generating curative, a polyisocyanate curative, or a tetrahydrocarbyl titanate ester curative.

8. A composition according to any of the preceding 20 claims wherein the high molecular weight elastomer is solid cis-polvisoprene rubber.

9. A composition according to claim 1 or claim 2 and any of claims 4 to 8 when directly or indirectly dependent 25 on claim 1 or claim 2 wherein the blend is a depolymerised 4643664 * natural rubber-natural rubber mixture and the crosslinking agent is selected from the following, present in the amounts recited: from more than 0.5 to 2.0 parts of sulfur or sulfur yielding curative; from more than 0.5 to 2.0 parts of quinoid curative; from 0.1 to 1Ό parts of radical generating curative; from 2 to 10 parts of polyisocyanate curative; and from 2 to 10 parts of tetrahydrocarbyl titanate ester curative, the said parts being by weight based on 100 parts of the combined weight of the two elastomers.

10. A composition according to any of claims 1 to 8 wherein the crosslinking agent is selected from the following, present in the amounts: from more than 0.5 to 4 parts of quinoid curative; from 0.1 to 1.5 part of radical generative curative; from 4 to 25 parts of cpolyisocyanate 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. - 47 Ο

11. A composition according to any of the preceding . claims and in the form of a puncture sealing composition for a pneumatic tire wherein the composition includes from 2 to 10 parts, per 100 parts by weight of the two 5 elastomers, of a tetraalkyl titanate ester crosslinking agent in which the alkyl groups having from 1 to 12 carbon atoms, said blend being partially crosslinked by the aid crosslinking agent to provide in the blend a gel content of from 20% to 50% by weight based on the weight 10 of the blend as measured in toluene at room temperature and a peak Mooney viscosity of from 40 to 50 ML at 150°F.

12. A composition accordinq to claim 11, wherein the alkyl groups in the said tetraalkyl titanate ester crosslinking agent have from 3 to 8 carbon atoms, the 15 amount of said titanate ester is from 3 to 8 parts per 100 parts by weight of the two elastomers, and the composition is devoid of fibrous filler.

13. A puncture sealing composition according to claim 12 wherein the tetraalkyl titanate ester crosslinking agent 20 is tetra'ributyl titanate.

14. A modification of a composition according to any of the preceding claims wherein part of the low molecular weight liquid elastomer is replaced by a tackifying or plasticizing substance. 48 43664

15. A composition according to claim 14 wherein the tackifying or plasticizing substance is a rosin ester, an aliphatic petroleum hydrocarbon resin, a polyterpene resin, a styrene resin, a dicyclopentadiene resin, or a 5 resin prepared from the reaction of a mineral oil purification residue with formaldehyde and with a nitric acid catalyst.

16. A puncture sealing tubuless pneumatic tire having a vulcanized rubber tread portion surmounting a vulcanized 10 rubber carcass portion reinforced with filamentary material, said carcass portion having a crown area underlying the tread, and having sidewall portions extending from shoulder areas at the edges of the crown area to bead areas containing inextensible circumferential reinforcement,the interior 15 surface of the tire being covered with an air-impervious liner, and a puncture sealing layer inside the tire disposed across the crown area of the tire and extending at least from one shoulder area to the other, said puncture sealing layer comprising a fiber-free composition as claimed 20 in claim 1 wherein the crosslinking agent is selected from the following present in the amounts recited: from more than 0.5 to 2.0 parts of sulfur or sulfuryielding curative; from more than 0.5 to 2.0 parts of quinoid curative; 25 from 0.1 to 1.0 part of radical generating curative; from 2 to 10 parts of polyisocyanate curative; and from 2 to 10 parts of tetrahydrocarbyl titanate ester curative; the said parts of crosslinking agent being by weight based on 100 parts of the combined weight of the two elastomers, the gel content of the blend in the partially crosslinked state being from 15 to 60$ by 5 weight of the blend, as measured in toluene at room temperature, and the peak Mooney viscosity of the blend in the partially crosslinked state being from 30 to 55 ML at 150°F. i

17. A tire according to claim 16, wherein the said 10 puncture sealing layer is disposed on the inside surface of the said liner.

18. A tire according to claim 16, wherein the said sealing layer is sandwiched between the liner and the inside surface of the carcass. 15

19. A tire according to any of claims 16 to 18 wherein the liquid rubber is heat depolymerized natural rubber.

20. A tire according to any of claims 16 to 19 wherein the low molecular weight elastomer is liquid cis20 polyisoprene, liquid polybutadiene, liquid polybutene, liquid ethylene-propylene-non-conjugated diene terpolymer rubber,or liquid isobutylene-isoprene copolymer rubber.

21. A tire according to any of claims 16 to 19 wherein the high molecular weight elastomer is a conjugated 50 43664 diolefin homopolymer rubber, a copolymer of a major proportion of a conjugated diolefin with a minor proportion of a copolymerizable monoethylenically unsaturated monomer, a copolymer of isobutylene with a small amount of isoprene,an ethylene - propylene - non - conjugated diene terpolymer,or a saturated elastomer.

22. A modification of a tire according to any claims 16 to 21 wherein part of the low molecular weight liquid elastomer is replaced by a tackifying or plasticising substance,

23. A puncture sealing tubeless pneumatic tire having a vulcanized rubber tread portion surmounting a vulcanized rubber carcass portion reinforced with filamentary material, said carcass portion having a crown area underlying the tread, and having sidewall portions extending from shoulder areas at the edges of the crown area to bead areas containing inextensible circumferential reinforcement, the interior surface of the tire being covered with an air-impervious liner, and a puncture sealing layer inside the tire disposed across the crown area of the tire and extending at least from one shoulder area to the other, said puncture sealing layer comprising a composition as claimed in claim 1 wherein the gel content in the blend is from 20% to 50% by weight based on the weight of the blend as measured in toluene at room temperature and a peak Mooney viscosity of from 40 to 55 ML at 150°F.

24. A tire according to claim 23 wherein the alkyl groups in the said tetraalkyl titanate ester crosslinking agent have from 3 to 8 carbon atoms, the amount of said titanate ester is from 3 to- 8 parts per 100 parts by weight of the two elastomers, and the composition is devoid of fibrous filler.

25. A tire according to claim 23 or claim 24 wherein the tetraalkyl titanate ester crosslinking agent is tetra l - n - butyl titanate.

26. A method of repairing a puncture in a pneumatic tire casing of the tubeless type comprising applying to the puncture- a composition according to any of claims I to 15, and thereafter curing the composition to effect partial crosslinking thereof.

27. A method according to claim 26 wherein an additional quantity of repair material is applied to 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, sai'd patch being integral with the repair material in the puncture, whereby in the final crosslinked repair structure the repair is maintained securedly in place in the structure. 43684

28. A method of repairing a puncture in a tire casing of the tubeless type comprising forcing into the puncture a plastic repair material to fill the puncture and depositing on 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 repiar 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 2,000,000 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, 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 at least partially to crosslink the blend to a gel content of from 20% to 80% by weight,based on the weight of the blend,as measured in toluene at room temperature and a peak Mooney viscosity of above 30 ML at 150°F, whereby the blend is prevented from flowing at elevated temperatures·and centrifugal forces encountered in the tire in use and the puncture is effectively sealed against loss of air from the tire.

29. A method according to claim 28 wherein the alkyl groups in the said tetralkyl titanate ester crosslinking agent y»y V yy , 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.

30. A method according to any of claims 26 to 29 5 wherein the tire is of the radial ply type.

31. A composition according to claim 1 and substantially as herein described.

32. An elastomeric composition substantially as described in any of the specific Examples. 10

33. A pneumatic tire according to claim 16 and substantially as herein described.

34. A pneumatic tire substantially as described with reference to Figures 1 to 3 or Figure 4 of the accompanying drawings. 15

35. A pneumatic tire having a puncture sealing layer including a composition as claimed in claim 1 or having applied thereto a repair composition, including a composition as claimed in claim 1, and said tire being substantially as described in any of the specific Examples. , 0

36. A method according to claim 26 and substantially as herein described.

37. A method of repairing a tire substantially as described with reference to Figures 5 and 6 or Figure 7 of the accompanying drawings.

38. A method of repairing a puncture in a pneumatic tire 5 substantially as described in Example III.

39. A tire wherever repaired by a method as claimed in any of claims 26 to 30, or 36 to 38.