IE42487B1 - Puncture sealing composition and tire - Google Patents

Description

This invention 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. 356/76 discloses the crosslinking of elastomers with alkyl titanate esters.

Puncture sealing tubeless tires have 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adhesive qualities such that the composition tends to stick to a puncturing object, and, when the puncturing object is withdrawn tends to flow into the opening or puncture, forming a plug which seals the opening against loss of air from the tires.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 proved 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 43487 - 3 force to which the composition is subjected as the tire 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 molecular weight less than 50,000rwith 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-4at 212°F,and a cross-linking agent for the elastomers in an amount effective partially to cross-link the elastomers to an extent that the blend, after cross-linking, has a 4248 7 gel content of from 15 to 95% by weight of the blend as measured in toluene at room temperature, sufficient adhesion and conformability to function as a sealant in a tire and sufficient viscosity to prevent flow at elevated temperatures and centrifugal forces encountered in a tire in use.

Preferably, the blend after cross-linking, has an initial Mooney viscosity of above 30 ML at room temperature.

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

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 a high centrifugal forces,and yet permits sufficient conform20 ability for the composition to function effectively as a puncture sealant.

Furthermore, punctures in tubeless tires, including radial 43487 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.

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 conformabi1ity necessary in a puncture sealant. Preferably the adhesion and conformabi1ity 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 cross-links are more effective in the high molecular weight elastomer, thus allowing it to act as a supporting structure or skeleton to retard flow, without cross-linking the low molecular weight elastomer to the point where its ability to function as sealant would be significantly impaired. 43487 - 6 -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 drawings, wherein: Figure 1 is a largely diagrammatic sectional IQ elevational view of a pneumatic tire embodying a puncture sealant layer in accordance with the invention; Figures 2 and 3 are enlarged fragmentary views similar to Figure 1 illustrating the sealing action of the puncture sealant layer; and Figure 4 is a view similar to Figure 1 showing a modification of the invention: Figure 5 is a largely diagrammatic sectional elevational view of a tubeless pneumatic tire, punctured by a nai 1; 2o Figure. 6 is a similar fragmentary view on a larger scale, showing a puncture being repaired by application 43487 of repair material by means of a syringe; and Figure 7 is a view similar to Figure 5, showing a tire being repaired while mounted on a rim.

As indicated, the invention is a puncture sealant 5 composition which is a mixture of low molecular weight liquid elastomer with a high molecular weight solid elastomer, the liquid elastomer being present in amount greater than 50% based on the weight of the two polymers, cross-linked 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 a repair material to the puncture to be repaired and thereafter at least partially curing or cross20 linking 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 cross-linked. Examples are the highly 43487 - 8 unsaturated rubbers such as those based on conjugated diolefins, whether homopolymers as in polyisoprene (particularly cis-polyisoprene, 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 type 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 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 EPH or ethylene-vinyl acetate may be employed, using the proper cure system. The elastomer may be emulsion-prepared or solution-prepared, stereo specific 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. 48 7 - 9 The low molecular weight elastomer employed has a molecular weight less than 50,000, usually within the range from 1,000 and 10,000, and is preferably of the liquid rubber type with a maximum Brookfield viscosity of 150°F. of 2,000,000 cps., ordinarily within the range of from 20,000 to 1,000,000 cps.

Examples are: liquid cis-polyisoprene (e.g., heat depolymerized natural rubber, or cis-polyisoprene polymerized to low molecular weight), liquid polybutadiene, liquid polybutene, liquid EPDM, and liquid butyl rubber. The high molecular weight, elongation and film strength of cis-polyisoprene (both natural and synthetic) and great tackiness of depolymerized cis-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 plasticizing substances which are preferably included in the composition are low molecular weight materials such as rosin esters (e.g., - 10 Staybelite®Ester 10); aliphatic petroleum hydrocarbon resins (e.g., Piccopale ® A-70); polyterpene resins (5) derived alpha-pinene (e.g. Piccolyte w A-10), beta-pinene (e.g., Piccolyte ® S-25); resins made from styrene and related monomers (e.g., Piccolastic® A—5); resins made from dicyclopentadiene (e.g., Piccodiene w 2215); and resins from the reaction of a mineral oil purification residue with formaldehyde and with nitric acid catalyst according to West German Patent 1,292,396, sold under the tradename of Struktol® The novel composition of the invention contains a major proportion, that is, between more than 50% and 90% by weight bf total low molecular weight material (i.e., low molecular weight elastomer plus low molecular weight tackifier or plasticizer). The amount of tackifier or plasticizer may range up to 70% based on the weight of low molecular weight elastomer plus tackifier or 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 arid kind of crosslinking agent, and the condition·, of the cross-linking treatment. Ordinarily the proportion of the two 43487 - 11 elastomeric components are chosensoasto give an initial Mooney viscosity at room temperature (the initial peak reading attained, which is usually within the first few seconds) of between 30 and 70 (large rotor, ML) in the final cross-linked mixture, with a preferred range of 40 to 50. Below the aforementioned initial 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 initial Mooney viscosity of 70, 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 desi.red 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 cross-linking. The Mooney viscosity of the mixture can also be controlled for a given elastomeric composition of the present invention by 43487 - 12 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 Tower the Mooney viscosity before cure.

As indicated, for purposes of the invention the mixture further includes a cross-linking agent. The crosslinking agent may be any suitable substance or comination of substances 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 as azobisisobutyronitrile. 4) Polyisocyanates such as MDI (4,4'- methylene bisphenyleneisocyanate), TDI (tolylene di isocyanate), and 48487 - 12a PAPI (polymethylene polyphenyl 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 cross-linking 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 composition in a tire at temperatures up to 200°F and speeds up to 50 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 cross-linking agent and vice-versa to maintain the desired combination of resistance to flow and sealing ability. The amount of cross-linking agent wi11 - of course, vary with the nature of the elastomers themselves. Preferred amountsof curatives in the case of a puncture sealing 43487 - 13 composition, particularly for depolymerized natural rubber (DPR)-natural rubber (NR) mixture, are as follows:- an amount of sulfur-containing or quinoid type curative in the range of from more than 0.5 to 2.0 phr (parts per 100 parts by weight of both elastomers added together), ordinarily from 0.7 to 1.5 phr; an amount of polyisocyanate or hydrocarbyl titanate ester curativesintherange from 2 to 10 phr. preferably 2.5 to 8 phr; an amount of peroxide or hydroperoxide curatives (radical generating catalysts) of from 0.1 to 1.0 phr, preferably 0.2 to 0.7 phr.

A preferred puncture sealing composition is one in which the cross-linking agent is a tetraalkyl titanate ester in which the alkyl groupshave from 1 to 12 carbon atoms, the amount of the tetraalkyl titanate being sufficient to provide in the blend a gel content of from 20% to 50% by weight based on the weight of the blend as measured in toluene at room temperature,and an initial Mooney viscosity of from 40 to 60 ML at room temperature. More preferably the alkyl groups in the said tetraalkyl titanate ester cross-linking agent have from 3 to 8 carbon atoms, the amount of said titanate is from 3 to 8 parts per - 14 424S7 100 parts by weight of the two elastomers, and the composition is devoid of fibrous filler. A particularly preferred cross-linking agent is tetra-nibutyl titanate.

Preferred amounts of curatives in the case of a repair composition, again particularly for a depolymerized natural rubber (DPR)-natural rubber (NR) mixture, are as follows:- an amount of sulfur-containing or quinoid type curative in the range of from more than 0.5 to 4 phr (parts per 100 parts by weight of both elastomers added together), ordinarily from 0.7 to 2 phr; an amount of polyisocyanate or hydrocarbyl titanate ester curative in the range from 4 to 25 phr, preferably 5 to 15 phr; an amount of peroxide or hydroperoxide curative (radical generating catalysts) of from 0.1 to 1.5 phr, preferably 0,2 to 1 phr.

The cross-linking 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 cross-linked blend, correlates with the desirable combination of sealing - 15 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 cross-linking may be carried out at ordinary ambient temperature pr at elevated temperature, depending on the temperature at which the particular cross-linking system selected is active in the particular elastomer combination employed.

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. - 16 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. Accordingly, 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 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 blend of a major proportion by weight of a low molecular weight liquid elastomer with a minor proportion by weight of a high molecular weight solid elastomer, partially cross-linked to an extent sufficient to prevent the blend from flowing at elevated temperatures and centrifugal forces encountered in the tire in use, the partially cross-linked blend having sufficient 43487 - 17 adhesion and conformability to function as a sealant in the tire, the amount of said low molecular weight elastomer being from more than 50$ to 90$ by weight and the amount of said high molecular weight elastomer being correspondingly from less than 50$ to 10$ by weight, based on the combined weights of the two elastomers, the said low molecular weight elastomer being a liquid rubber having a molecular weight less than 50,000 ahd the said high molecular weight elastomer having a Mooney viscosity of from 20 to 160 ML-4 at 212°F., the said composition containing a cross-linking agent selected from the following, present in the amounts recited; from more than 0.5 to 2.0 parts of sulfur or sulfur15 yielding 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 parts of polyisocyanate curative; and from 2 to Ϊ0 parts of tetrahydrocarbyl titanate ester curative, the said parts of cross-linking agent being by weight - 18 based on 100 parts of the combined weight of the two elastomers, the gel content of the blend in the partially cross-linked state being from 15 to 60% by weight of the blend, as measured in toluene at room temperature, and the initial Mooney viscosity of the blend in the partially cross-linked state being from 30 to 70 ML at room temperature. Preferably the composition contains from 4 to 10 parts, per 100 parts by weight of the two elastomers, of a tetraalkyl titanate ester cross-linking agent in which the alkyl groups have from 1 to 12 carbon atoms, said blend being partially cross-linked by the said cross-linking agent to provide in the blend a gel content of from 20% to 50% by weight based on the weight of the blend as measured in toluene at room temperature and an initial Mooney viscosity of from 40 to 60 ML at room temperature. More preferably, the alkyl groups in the said tetraalkyl titanate ester cross-1 inking agent have from 3 to 8 carbon atoms, the amount of said titanate ester is from 3 to 8parts per 100 parts by weight of the two elastomers and the composition is devoid of fibrous filler. A particularly preferred cross-linking agent is tetra-n-butyl titanate.

Referring to the drawings, and particularly to Figure 1, a typical embodiment of the invention comprises a - 19 toroidal tubeless tire casing 10 having the usual vulcanized rubber tread 11 and sidewall portions 12, 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. 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.

The sealing action of the layer 18 is represented in Figures 2 and 3, wherein Figure 2 shows a nail 19 puncturing the tire through the tread 11, carcass 14, liner 17 and sealant layer 18. The sealing 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 Figure 4, the puncture sealant layer 23 of the invention is disposed in between the inner surface of the 43487 - 20 carcass 24 and the liner 25. In such cases where the sealant layer is incorporated in the tire, it may be cross-linked 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 coats as required to build up a desired thickness. Using the hydrocarbyl titanate curative system the thus-applied sealant layer will become sufficiently cross-linked to perform 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 348 7 - 21 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 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 elastomers will not take place unless hydrocarbyl alcohol (apparently formed 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 43487 - 22 width and thickness may be applied by any suitable mbans 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 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 Figure 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 424S7 - 23 of 250°F or higher. After running at high speed 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 least at 5O 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.

Thus, the present invention includes a method of repairing a puncture in a pneumatic tire casing of the tubeless type comprising applying to the puncture a composition of the invention. Preferably the initial Mooney viscosity is from 30 to 100 ML at room temperature.

It is preferred that an additional quantity of repair material is applied to the interior surface of the 424S7 - 24 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 cross5 linked repair structure the repair is maintained securely, in place in the puncture.

It is also preferred that the repair composition contains from 4 to 25 parts, per 100 parts by weight of the two elastomers, of a tetraalkyl titanate ester cross10 linking agent in which the alkyl groups have from to 12 carbon atoms, and the applied repair material is subjected to curing conditions at least partially to cross-link 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 an initial Mooney viscosity of from 40 to 100 ML. More preferably the alkyl groups in the said tetraalkyl titanate ester cross-linking 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.

In practising the invention the plastic repair material is prepared by mixing the described ingredients together uniformly, and thereafter applying the material 248 7 - 25 to a tire to be repaired. Referring to the drawing., and in particdlar to Figure 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 the casing. To effect a repair of the tire in an unmounted condition, the nail is removed from the puncture 22, as shown in Figure' 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 portion 25 which is formed by smearing or flattening the excess material againstthe inner (liner) surface of the tire immediately surrounding the puncture, the repair material is then cross-linked to render the repair permanent. In - 26 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 Figure 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 a syringe 27 (Figure 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 •42487 - 27 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 cross-linked to render the repair permanent, as before.

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

EXAMPLE 1 480 grams of natural rubber (Standard Malaysian Rubber, Mooney viscosity 64, ML-4-212°F., weight average molecular weight 4.7 χ 106) was dissolved in 4 gallons of n-hexane.

To this solution was added 960 grams of depolymerized natural rubber (DPR-400 [trademark^, Hardman Company, viscosity 80,000 cps @ 150°F.) and the mixture stirred until it is uniform. 100.8 grams of tetra-n-butyl titanate was added and the cement stirred once more. 2’4 grams of Antioxidant 2246 ^trademark, American Cyanamid, 2,2'-methylene-bis^- methyl-6-tert-butylphenol was added at this point. The resulting cement had a solids content of about 14$. 434 87 - 28 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 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 automobile rim, inflating it to 28 psi and running it on a Getty Wheel, 11-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 diameter as the shanks of the nails. Most importantly, it was observed that during the removal and immediately there·· after, 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% DPR-400 and 40% natural rubber, was 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, - 30 42467 a mixture of 6 lbs. of DPR-400, 45 gms. Antioxidant 2246 and 61bs of creamed Hevea natural rubber latex (67% total solids) were mixed in a double-arm sigma blade dough mixer at a shell temp, of 270°F for 30 minutes. Vacuum was then applied and mixingcontinued for 30 minutes at which time the moisture content of the blend was less then 0.2% . The mixture was cooled to about 17O°F and 272 gms. of tetra-n-butyl titanate was added.

The mixture was tightly enclosed 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 initial Mooney viscosity at room temperature (large rotor, ML) of the fully cured sealant was 55.

EXAMPLE III The composition of Example II is used as a repair composition.

For use, the repair composition may be loaded into a 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 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 - 31 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 cross-linked 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 punctured by 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 had been heated to 200°F, a quantity, about 150 grams,cf 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 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 was mounted on a standard automobile rim and inflated to a pressure of 40 psi. There was no loss of inflation pressure over a two week period. It should be noted that this two week period is not a necessary condition for the practice of this invention. The repair - 32 is permanent 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, 11-inch diameter with a 1000 pound load at 50 mpg. There was 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, DPR-400 and Struktol 30, along with 8% tetraisopropyl titanate and 1% 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 ML-j of the cured sealant at room temperature was 45 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 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, 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 - 33 after the first nail was ejected in this test.

EXAMPLE V A sealant identical to that of Example IVexcept that it contained 10% tetra-isopropyl titanate (based on total rubber) was extruded in to each of four tires as a 0.125“ strip and cured as above The cured sealant had ML^ values at room temperature ranging from 45 to 55 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 40 miles at 80 mph 15 For each ti re , , when the nail was ejected the hole sealed with' little or no Toss 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 containingSO parts of natural rubber, 50 parts of DPR-400 and 70 parts of Piccadiene 2215 (a tackifying resin 43487 - 34 made frcm polymerized dicyclopentadiene, manufactured by Hercules, Inc.), plus 8% tetra-isopropyl titanate and 10% 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 into a tire and cured. The puncture sealing efficiency of this material measured in the nail ejection test of Example IV, showed an average sealing efficiency 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%.

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 irradicated in a 1.4 million volt electron beam at a dosage of 20 - 35 megarads. Th4 irradiated sample showed a gel content of 29.6% and anML-j?at room temperature, of 43. The strip was theh incorporated on top of the liner 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%.

EXAMPLE 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 - 36 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 fournails of 0.125 diameter. The tire was then run 1000 miles at 50 mph on a Getty wheel and the nails then removed. There was less than 4psi loss of inflation and the holes all sealed.

EXAMPLE XI A sealant composition containing equal parts of Butyl LM 430, Royalene 505 and Piccolyte Al00 (a polyterpene resin derived from alpha-pinene, softening point 100°C.), plus 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 43487 - 37 505, Butyl LM 430 and Piccodiene 2215, plus 10% tetran-butyl 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 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 525 (ethylene -propylene-ethylidene norbornene terpolymer, iodine number 20, ML-4=55 at 257°F.), Butyl LM 430, and Struktol 30, plus 10% tetra-isopropyl 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 co-pending application No. 356/76 the cure (crosslinking or gelling to an insoluble state) of unsaturated - 38 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 cispolyisoprene (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 (isoprene-isobutylene copolymer), and blends of such elastomers, the organo-titanate esters employed as curatives or cross-linking agents to gel the unsaturated elastomer are tetrahydrocarbyl titanates of the formula (RO)^Ti where 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 cross-linking agent and unsaturated elastomer may be carried out under nonevaporative 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 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 mixture 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 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 antioxidants (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 - 40 Of lower boiling alcohols effect cure more rapidly than titanate esters of higher boi1ing alcohols, e.g., isopropyl titanate acts mors rapidly 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 vent,cure 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 (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 non-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 (RO)^Ti is generated during the cure. If the alcohol is prevented from evaporating, as in a closed container where non-evaoorative conditions 424S7 - 41 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 coatings deposited from a solution, calendered or extruded films and sheets, and similar thin sections (e.g., 0.2. inch thick or less) have 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.

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 cross-linking 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 added. Normally, appreciable gellation - 42 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, the gelled 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 inhibits gel formation. It appears to be possible that the cross-linking is a consequence of titanate ester formation with the elastomer.

Preferred elastomers for use with the titanate cure are those selected from the group consisting of natural rubber, synthetic cis-polyisoprene elastomer, cis-poly20 butadiene elastomer and ethylenepropylene - 5 - ethylidene - 2-norborene 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 . 43487 - 43 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 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 intersticies thereof without setting up undesirable stresses. Such a 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, 43487 - 44 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. 43487

Claims (41)

1. WHAT WE CLAIM IS: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 molecular weight less than 50,000, with correspondingly less than 50% to 10% 5 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 cross-linking agent for the elastomers in an amount effective partially to cross-link the elastomers to an extent that^the'blend, after cross10 linking, has a gel content of from 15 to 95% by weight of the blend as measured in toluene at room temperature, sufficient adhesion and conformability to function as a sealant in a tire and sufficient viscosity to prevent flow at elevated temperatures and 15 centrifugal forces encountered in a tire in use.

2. A composition according to Claim 1, wherein the blend, after cross-linking, has an initial Mooney viscosity of above 30 ML At room temperature.

3. A composition according to Claim 2, wherein after 20 cross-linking the gel content is from 15 to 60% and the initial Mooney viscosity is from 30 to 70.

4. A composition according to any of claims 1 to 3, - 46 wherein the cross-linking 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; 10 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 parts of polyisocyanate curative; and 15 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.

5. A composition according to Claim 1 or Claim 2, 20 wherein after cross-linking the gel content is from 20 to 95%.

6. , A composition according to Claim 5, wherein the cross-linking agent is selected from the following, 43487 - 47 present in the amounts recited: from more than 0.5 to 4 parts of sulfur or sulfuryie'lding or quinoid curative; from 0.1. to 1.5 part of radical generating curative; 5 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. 10

7. A composition according to any of the preceding claims, wherein the low molecular weight elastomer is heat depolymerized natural rubber.

8. A composition according to any of Claims 1 to 6, wherein the low molecular weight elastomer is liquid 15 cis-poly-isoprene, liquid polybutadiene, liquid polybutene, liquid ethylene-propylene-non-conjugated diene terpolymer rubber or liquid isobutylene-isoprene copolymer rubber.

9. A composition according to any of the preceding claims, wherein the high molecular weight elastomer is a conjugated diolefin homopolymer rubber, a copolymer of a major proportion of a conjugated diene with a minor proportion of a copolymerizable monoethylenically 5 unsaturated monomer, a copolymer of isobutylene with a small amount of isoprene, an ethylene-propylene-nonconjugated diene terpolymer or a saturated elastomer.

10. A composition according to any of the preceding claims, wherein the cross-linking agent is a sulfur or 10 sulfur-yielding curative, a quinoid curative, a radical generating curative, a polyisocyanate curative, or a tetrahydrocarbyl titanate ester curative.

11. A composition according to any of the preceding claims, wherein the high molecular weight elastomer is solid 15 cis-polyisoprene rubber.

12. A composition according to Claim 4, wherein the cross-linking agent is a tetraalkyl titanate ester cross-linking agent in which the alkyl groups have from 1 to 12 carbon atoms, the amount of the tetraalkyl 20 titanate being sufficient to provide in the blend a gel content of from 20% to 50% by weight based on the weight of the blend as measured in toluene at room temperature,sand an initial Mooney viscosity of from ·’ 43487 - 49 40 to 60 ML at room temperature.

13. A puncture sealing composition according to Claim 12, wherein the alkyl groups in the said tetraalkyl titanate ester cross-linking agent have from 3 to 8 carbon 5 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,

14. A puncture sealing composition according to Claim 13, wherein the tetraalkyl titanate ester cross-linking 10 agent is tetra-n-butyl titanate.

15. 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. 15

16. A composition according to Claim 15, 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 resin prepared from the reaction of a mineral oil 20 purification residue with formaldehyde and with a nitric acid catalyst. - 50 424G7

17. 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 fiberfree blend of a major proportion by weight of a low molecular weight liquid elastomer with a minor proportion by weight of a high molecular weight solid elastomer, partially cross-linked to an extent sufficient to prevent the blend from flowing at elevated temperatures and centrifugal forces encountered in the tire in use, the partially cross-linked blend having sufficient adhesion and conformabi1ity to function as a sealant in the tire, the amount of said low molecular weight elastomer being from more than 50% to ^0% by weight and the amount of said high molecular weight elastomer being correspondingly from less than 50% to 10% by weight, based on the combined weights of the two elastomers, the said low molecular weight elastomer being a liquid 43487 - 51 rubber having a molecular weight less than 50,000 and the said high molecular weight elastomer having a Mooney viscosity of from 20 to 160 ML-4 at 212°F., the said composition containing a cross-linking agent selected 5 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 1.0 part of radical generating curative; 10 from 2 to 10 parts of polyisocyanate curative; and from 2.to 10 parts Of tetrahydrocarbyl titanate ester curative, the said parts of cross-linking agent being by weight based on 100 parts of the combined weight of the two elastomers, 15 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 initial Mooney· viscosity of the blend in the partially cross-linked state being from 30 to 70 ML at room temperature. 43487 - 52

18. Λ tire according to Claim 17, wherein the said puncture sealing layer is disposed on the inside surface of the said liner.

19. A tire according to Claim 17, wherein the said 5 sealing layer is sandwiched between the liner and the inside surface of the carcass.

20. A tire according to any of Claims 17 to 19, wherein the liquid rubber is heat depolymerized natural rubber.

21. A tire according to any of Claims 17 to 20, wherein 10 the low molecular weight elastomer is liquid cis-polyisoprene, liquid polybutadiene, liquid polybutene, liquid ethylene-propylene-non-conjugated diene terpolymer rubber or liquid isobutylene-isoprene copolymer rubber.

22. A tire according to any of Claims 17 to 21, wherein 15 the high molecular weight elastomer is a conjugated 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 20 of isoprene, an ethylene-propylene-non-conjugated diene terpolymer,or a saturated elastomer. 43487 - 53

23. A modification of a tire according to any of Claims 17 to 22, wherein part of the low molecular weight liquid elastomer is replaced by a tackifying or plasticizing substance. 5

24. A tire according to any of Claims 17 to 23, wherein the composition contains from 4 to 10 parts, per 100 parts by weight of the two elastomers, of a tetraalkyl titanate ester cross-linking agent in which the alkyl groups have from 1 to 12 carbon atoms, said 10 blend being partially cross-linked by the said crosslinking agent to provide in the blend a gel content of from 20% to 50% by wei ght,-based on the weight of the blend,as measured in toluene at room temperature, and an initial Mooney viscosity of from 40 to 60 ML 15 at room temperature,

25. A tire according to Claim 24, 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 20 parts by height of the two elastomers, and the composition is devoid of' fibrous filler.

26. A tire according to Claim 24 or Claim 25, wherein the tetraalkyl titanate ester cross-linking agent is - 54 tetra-n-butyl titanate.

27. 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 5 1 to 16.

28. A method according to Claim 27, wherein the initial Mooney viscosity is from 30 to 100 ML at room temperature.

29. A method according to Claim 27 or Claim 28, wherein an additional quantity of repair material is applied to 10 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 cross-linked repair structure 15 the repair is maintained securely in place in the puncture.

30. A method according to any of Claims 27 to 29, wherein the composition contains from 4 to 25 parts, per 100 parts by weight of the two elastomers, of a tetraalkyl titanate ester cross-linking agent in which the alkyl 20 groups have from 1 to 12 carbon atoms, and the applied repair material is subjected to curing conditions at least - 55 partially to cross-link 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 an initial Mooney viscosity of from 40 to 100 ML. 5

31. A method according to Claim 30, wherein the alkyl groups in the said tetraalkyl titanate ester cross-linking 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. 10

32. A method according to any of Claims 27 to 31, wherein the tire is of the radial ply type.

33. A composition according to Claim 1 and substantially as herein described.

34. An elastomer composition substantially as described 15 in any of the specific Examples.

35. A pneumatic tire according to Claim 17 and substantially as herein described.

36. A pneumatic tire substantially as described with reference to Figures 1 to 3 or Figure 4 of the accompanying 20 drawings. - 56

37. A pneumatic tire substantially as described in any of the specific Examples.

38. A method according to Claim 27 and substantially as herein described.

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

40. A method of repairing a puncture in a pneumatic tire substantially as described in any appropriate one of the specific Examples.

41. A tire whenever repaired by a method as claimed in any of Claims 27 to 32 and 38 to 40.