Patent Description:
Over the years better puncture sealing tires have been developed which allow for the tire to provide longer service after being punctured.

<CIT> describes a self-sealing composition for a tire based on crosslinked butyl rubber having a very high molecular weight. However, such butyl rubbers have the drawback of exhibiting a high level of hysteresis over a broad temperature range which increases the rolling resistance of tires and is detrimental of fuel economy.

As an alternative to butyl rubbers, self-sealing compositions for tires can also be made using unsaturated diene elastomers, including natural rubber. Such compositions are described in <CIT>, <CIT>, and <CIT>. These compositions are characterized by the combined presence of a high content of hydrocarbon resin as tackifier, always greater than <NUM> parts by weight per hundred parts. In addition, a large amount of liquid elastomer gives a high fluidity to the composition which is a source of other drawbacks, in particular a risk of the self-sealing composition flowing during use at relatively high temperature (typically above <NUM>) frequently encountered during the use of the tires in certain geographical regions.

<CIT> describes a method of manufacturing a pneumatic rubber tire having a puncture sealant layer positioned between said inner liner and said carcass.

Many additional methods, sealants and tire constructions have been suggested for puncture sealant pneumatic tires. However, all of these ideas have had certain drawbacks. For example, the use of fluid puncture sealant coatings which seal by flowing into the puncture hole are frequently unsuccessful primarily because sealant coatings may flow excessively and thus tend to cause the tire to become out of balance. In other cases, the sealant coating is not operable or effective over a wide temperature range extending from hot summer to cold winter conditions. Central cores of cellular material which will physically maintain the shape of the tire when punctured can place a restriction on the maximum speed of a vehicle on which they are used because of potential breakdown or destruction of the cells caused by the effects of heat and distortion. More complicated structures wherein the sealant material is encased in a vulcanized material are usually expensive to manufacture and can also create balance and suspension problems due to the additional weight required in the tire.

Puncture sealing tires can be built wherein a layer of degraded rubber which is tacky or gummy (of low viscosity) is assembled into the unvulcanized tire. This method of construction is usually only possible on a commercial basis when the degraded layer of rubber is laminated with another undegraded layer which permits its handling during the tire building procedure. This is because the tacky, sticky nature and lack of strength in degraded rubber make it very difficult to handle alone without additional support and a barrier to keep it from sticking to a tire building machine or curing apparatus. By laminating the degraded rubber layer between two or more undegraded rubber layers it is capable of retaining its structural integrity during the tire building and vulcanization process wherein high pressures are applied to the tire which would displace the degraded rubber layer from its desired location if not laminated. Such a lamination procedure adds greatly to the cost of building a tire. Thus, such lamination procedures have not been widely accepted on a commercial basis for building puncture sealing pneumatic tires.

The most common commercial approach currently being used in manufacturing self-sealing tires is to build a layer of degradable material which can be easily handled into the tire. This layer of degradable material is sandwiched between other layers of the tire. In many cases it will be positioned between two layers of innerliner or between the innerliner and the supporting carcass of the tire. In any case, this degradable material breaks down at the elevated temperatures which are employed during the vulcanization of the tire into a low viscosity, tacky material. This approach greatly facilitates tire manufacturing by eliminating the need to handle sticky materials during the tire building procedure.

Today, challenges still remain in the field of manufacturing highly effective self-sealing tires without compromising tire uniformity and performance characteristics. For instance, off-gassing results as the sealant material is degraded during vulcanization into a low viscosity material having the needed characteristics for a sealant. This off-gassing frequently results in an undesirable expansion of the innerliner in cases where the sealant layer is situated between the innerliner and the supporting carcass or between two layers of innerliner. This expansion of the innerliner causes it to bubble which in turn results in poor tire uniformity and balance issues. Accordingly, there is a continuing need for a better technique for manufacturing high quality puncture-sealing pneumatic tires by a simple, low cost method that can be easily implemented on a commercial basis.

<CIT> describes a tire in accordance with the preamble of claim <NUM>.

Further tire having sealant layers comprising polyisobutylene or butyl rubber are known from <CIT>, <CIT>, <CIT> and <CIT>.

The invention relates to a tire in accordance with claim <NUM> and to a method in accordance with claim <NUM>.

The method of this invention provides a simple and inexpensive method for manufacturing self-sealing pneumatic rubber tires of the tubeless type having a higher degree of uniformity than can be made utilizing conventional manufacturing procedures that are currently being practiced.

A preferred embodiment of this invention reveals a sealant composition which comprises (a) a polyisobutylene rubber, and (b) polypropylene. It is typically preferred for the polypropylene to be a relatively low molecular weight polypropylene which has a weight average molecular weight which is within the range of from <NUM> to <NUM>,<NUM> or from <NUM>,<NUM> to <NUM>,<NUM>.

In another preferred embodiment of this invention, the sealant composition in the tire contains up to <NUM> phr of a peroxide.

The present invention is further illustrated by the accompanying drawings. These drawings represent preferred embodiments of the present invention.

In the method of this invention a sealant layer formulation is extruded into an unvulcanized rubber tire. In building the unvulcanized tire the sealant layer formulation is normally extruded onto the supporting carcass of the tire. Then the sealant layer formulation is covered with an innerliner layer as the innermost layer of the unvulcanized tire. In another scenario the supporting carcass is covered with a layer of innerliner and the sealant layer formulation is extruded onto it. Then after the sealant layer formulation is covered with an additional layer of innerliner the sealant layer is sandwiched between the two layers of innerliner. In still another scenario, which is not according to the present invention, layers of innerliner can be totally eliminated in which case the sealant layer formulation is covered with a containment layer of a less expensive rubbery formulation, such as natural rubber, synthetic polyisoprene rubber, styrene-butadiene elastomer, or polybutadiene rubber compounds or their blends. In such a scenario the containment layer will be capable of retaining the sealant layer formulation between it and the carcass of the tire. Such tires retain air (gas) well by virtue of the fact that the polyisobutylene sealant layer used in the tires of this invention provide excellent gas barrier properties.

In any case, the sealant layer formulation is assembled into the uncured tire inwardly from the tire supporting carcass of the tire. In most cases it will be built into the tire between the supporting carcass and the innerliner of the tire as is illustrated in <FIG>. The innerliner is an air barrier layer that serves to keep air or another gas, such as nitrogen, which is used to inflate the tire, from escaping through the tire structure by diffusion. The innerliner typically comprises a halobutyl rubber or some other suitable material having a high degree of resistance to gas permeation. In another embodiment of this invention the sealant layer formulation is built into the tire between two layers of innerliner as is illustrated in <FIG>. In other words, it is sandwiched between two or more layers of innerliner or between one or more innerliner layers and the tire carcass. In a further embodiment, which is not according to the present invention, the tire does not include any innerliner layers and the sealant formulation is built (extruded) into the tire between the supporting carcass and a containment layer of the tire as is illustrated in <FIG>.

After an unvulcanized tire is built so as to include a layer of the sealant formulation it is vulcanized utilizing conventional techniques. More specifically, after the unvulcanized pneumatic rubber tires of this invention are assembled, they are vulcanized using a normal tire cure cycle. In the practice of this invention the unvulcanized tires can be cured over a wide temperature range, such as a temperature which is within the range of <NUM> to <NUM>. However, it is generally preferred for the tires of this invention to be cured at a temperature ranging from <NUM> to <NUM>. It is typically more preferred for the tires of this invention to reach a maximum temperature ranging from a <NUM> to <NUM> during vulcanization. For instance, it is typically optimal for the tire to reach a maximum curing temperature which is within the range of <NUM> to <NUM>. It is generally preferable for the cure cycle used to vulcanize the uncured tires to have a duration which is within the range of <NUM> minutes to <NUM> minutes. In the practice of this invention the uncured tires with normally be cured for a period which is within the range of <NUM> minutes to <NUM> minutes with the cure period preferably being from <NUM> minutes to <NUM> minutes, and most preferably being within the range of <NUM> minutes to <NUM> minutes. Any standard vulcanization process can be used such as heating in a press or mold and/or heating with superheated steam or hot air. In any case, the uncured tire can be built, shaped, molded and cured by various methods which are known and which are readily apparent to those having ordinary skill in the art.

Tires made in accordance with this invention are depicted in <FIG>. In <FIG> a self-sealing pneumatic rubber tire <NUM> of this invention is shown wherein the tire has sidewalls <NUM>, a supporting carcass <NUM>, inextensible beads <NUM>, an innerliner (air barrier layer) <NUM>, a sealant layer <NUM>, and an outer circumferential tread (tread portion) <NUM>. The individual sidewalls <NUM> extend radially inward from the axial outer edges of the tread portion <NUM> to join the respective inextensible beads <NUM>. The supporting carcass <NUM> acts as a supporting structure for the tread portion <NUM> and sidewalls <NUM>. The sealant layer <NUM> is disposed inwardly from said supporting carcass <NUM> and outwardly from said innerliner <NUM>. The outer circumferential tread <NUM> is adapted to be ground contacting when the tire is in use. In this embodiment of the invention, the innerliner <NUM> is disposed inwardly from said supporting carcass <NUM>.

In <FIG> a self-sealant pneumatic rubber tire <NUM> of another embodiment of this invention is depicted. This pneumatic tire of the tubeless type includes a tread portion <NUM>, a crown area <NUM>, sidewalls <NUM>, a supporting carcass <NUM>, inextensible beads <NUM>, <NUM>', an innerliner <NUM>, and sealant layer <NUM>. In this embodiment of the present invention the sealant layer <NUM> is sandwiched between two layers of innerliner <NUM>. This, sealant layer <NUM> is disposed inwardly from one layer of innerliner and outwardly from another layer of innerliner. Both layers of innerliner <NUM> and the sealant layer <NUM> are disposed inwardly from the supporting carcass <NUM>.

A tire which is not in accordance with this invention which is free of an innerliner layer is illustrated in <FIG>. In this scenario the self-sealing pneumatic rubber tire <NUM> is shown wherein the tire has sidewalls <NUM>, a supporting carcass <NUM>, inextensible beads <NUM>, a containment layer <NUM>, a sealant layer <NUM>, and an outer circumferential tread (tread portion) <NUM>. The individual sidewalls <NUM> extend radially inward from the axial outer edges of the tread portion <NUM> to join the respective inextensible beads <NUM>. The supporting carcass <NUM> acts as a supporting structure for the tread portion <NUM> and sidewalls <NUM>. The sealant layer <NUM> is disposed inwardly from said supporting carcass <NUM> and outwardly from the containment layer <NUM>. In other words, the sealant layer <NUM> is sandwiched between the supporting carcass <NUM> and the containment layer <NUM>. The outer circumferential tread <NUM> is adapted to be ground contacting when the tire is in use. In this embodiment, the containment layer <NUM> is disposed inwardly from the sealant layer <NUM> and is the innermost layer of the tire <NUM>.

In one aspect, the sealant layer formulation used in the practice of this invention comprises a polyisobutylene. The sealant layer formulation will preferably be void of butyl rubber, halogenated butyl rubbers, natural rubber, synthetic polyisoprene rubber, emulsion styrene-butadiene rubber, solution styrene-butadiene rubber, isoprene-butadiene rubber, styrene-isoprene-butadiene rubber, styrene/butadiene diblock polymers, styrene/butadiene/styrene triblock polymers, neoprene, nitrile rubber, ethylene-propylene rubbers, and ethylene-propylene-diene monomer rubbers.

The polyisobutylene (PIB) utilized in the practice of this invention is a relatively low molecular weight homopolymer of isobutylene. It has a weight average molecular weight which is within the range of from <NUM> to <NUM>. For instance, the polyisobutylene can have a weight average molecular weight which is within the range of <NUM>,<NUM> to <NUM>,<NUM> or which is within the range of <NUM>,<NUM> to <NUM>,<NUM>.

The polyisobutylene preferably has a viscosity average molecular weight which is within the range of <NUM>,<NUM> to <NUM>,<NUM>, which is within the range of <NUM>,<NUM> to <NUM>,<NUM>, or which is within the range <NUM>,<NUM> to <NUM>,<NUM>.

The polyisobutylene preferably has a number average molecular weight which is within the range of <NUM>,<NUM> to <NUM>,<NUM>, which is within the range of <NUM>,<NUM> to <NUM>,<NUM>, or which is within the range <NUM>,<NUM> to <NUM>,<NUM>.

Preferably, the polyisobutylene will normally have a polydispersity (Mw/Mn) which is within the range of <NUM> to <NUM>, and/or a glass transition temperature which is within the range of -<NUM> to -<NUM>.

Preferably, the polyisobutylene has a glass transition temperature which is within the range of -<NUM> to -<NUM> or within the range of -<NUM> to -<NUM>.

The polyisobutylene rubber can optionally be stabilized with a small amount of an antioxidant, such as from <NUM> ppm to <NUM>,<NUM> ppm of an antioxidant. Such antioxidants will preferably be incorporated into the polyisobutylene rubber at a level of <NUM> ppm to <NUM> ppm.

A wide variety of antioxidants can be employed with butylated hydroxytoluene (BHT) typically being used.

Relatively low molecular weight polyisobutylene which is suitable for use in the practice of this invention is commercially available from BASF as Oppanol® B10, Oppanol® B12, and Oppanol® B15.

Oppanol® B10 has a viscosity average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM> and a glass transition temperature (Tg) of -<NUM>.

Oppanol® B12 has a viscosity average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM>, and a glass transition temperature (Tg) of -<NUM>.

Oppanol® B15 has a viscosity average molecular weight of <NUM>,<NUM>, a weight average molecular weight of <NUM>,<NUM>, and a glass transition temperature (Tg) of -<NUM>.

In this application, the glass transition temperature Tg for polymers is determined as a peak midpoint by a differential scanning calorimeter (DSC) at a temperature rate of increase of <NUM> per minute, according to ASTM D3418 or equivalent.

In this application, molecular weight refers to the molecular weight in g/mol of a polymer (copolymer or block of a copolymer). It is measured with gel permeation chromatography (GPC) using polystyrene calibration standards according to ASTM <NUM>-<NUM> or equivalent. Mn (number average molecular weight), Mw (weight average molecular weight) and Mz (z average molecular weight) are determined together using said gel permeation chromatography (GPC) according to ASTM <NUM>-<NUM>. For further explanations, please see ASTM <NUM>-<NUM> and/or <NPL>, in particular and sections <NUM> and <NUM>.

A reinforcing filler can optionally be included in the sealant layer formulation. A wide variety of reinforcing fillers can be used. For example, the filler can be carbon black, graphite, graphene, carbon nanotubes, wollastonite, silica, crystalline silica, clay, <NUM>:<NUM> layered silicate clays, talc, diatomaceous earth, calcium carbonate (CaCOs), calcium silicate, starch, lignin, alumina, or polypropylene. The <NUM>:<NUM> layered silicate clays that are typically preferred include montmorillonite, bentonite, hectorite, saponite, nontronite, beidellite, fluorohectorite, stevensite, volkonskoite, sauconite laponite, related analogs thereof and their physical blends. Clays that have been chemically modified to make them compatible with organic materials are preferred and are generally referred to as "organophilic" clays or "organo-clays". The basic starting material used to make organophilic clay is an exchangeable clay of the smectite group and can include montmorillonite (commonly known and mined as bentonite), hectorite, saponite, attapulgite and sepolite. These clays include exchangeable cationic species such as sodium, potassium or calcium ions on their surface and between clay galleries or layers. In the course of manufacturing an organophilic clay, at least a portion of these exchangeable cationic species are substituted by an organic cation such as a quaternary amine, an organophosphorus ion, any other ion of the type known in the art as an onium ion, or the like.

The graphene that can be used in the solid sealant layer formulations of this invention is a one-atom-thick crystalline form of carbon in which carbon atoms are held together by sigma bonds that are arranged in a two-dimensional honeycomb lattice. More specifically graphene is a crystalline allotrope of carbon with <NUM>-dimensional properties. The carbon atoms in graphene are densely packed in a regular atomic-scale hexagonal (chicken wire) pattern. Each atom has four bonds, one σ bond with each of its three neighbors and one Π-bond that is oriented out of plane. The distance between adjacent carbon atoms in graphene is approximately <NUM> nanometers. The graphene that can be advantageously used as a reinforcing filler in the practice of this invention can have zigzag, armchair, K-region, gulf, bay, cove, and fjord edge topologies. Typically, at least <NUM> percent, <NUM> percent, <NUM> percent, or <NUM> percent of the carbon-carbon bonds on the edges of the graphene structure will be in the zig-zag configuration, the armchair configuration, or the bay configuration. In many cases, at least <NUM> percent, <NUM> percent, or <NUM> percent of the carbon-carbon bonds on the edges of the graphene structure will be in the zig-zag configuration. In one embodiment at least <NUM> percent, <NUM> percent, or <NUM> percent of the carbon-carbon bonds on the edges of the graphene structure will be in the armchair configuration. In another embodiment at least <NUM> percent, <NUM> percent, or <NUM> percent of the carbon-carbon bonds on the edges of the graphene structure will be in the bay configuration. Typically, less than <NUM> percent of the carbon-carbon bonds on the edges of the graphene structure will be in the cove configuration and more typically less than <NUM> percent of the carbon-carbon bonds on the edges of the graphene structure will be in the cove configuration. In another embodiment less than <NUM> percent of the carbon-carbon bonds on the edges of the graphene structure will be in the cove configuration and less than <NUM> percent or more typically less than <NUM> percent of the carbon-carbon bonds on the edges of the graphene structure will be in the fjord configuration.

The graphene that can optionally be used as a reinforcing filler in the practice of this invention is exfoliated into nano-scaled graphene plate (NGP) material that is essentially comprised of individual single sheets of graphene or a plurality of sheets of graphite planes. Each graphite plane, also referred to as a graphene plane or basal plane and is comprised of a two-dimensional hexagonal structure of carbon atoms. Each plane has a length and a width parallel to the graphite plane and a thickness orthogonal to the graphite plane characterized in that at least one of the values of length, width, and thickness is <NUM> nanometers (nm) or smaller. Preferably, all length, width and thickness values are smaller than <NUM>. This NGP material can be produced by a process the method described in <CIT> which comprising the steps of: (a) carbonization or graphitization to produce a polymeric carbon, (b) exfoliation or expansion of graphite crystallites in the polymeric carbon to delaminate or separate graphene planes, and (c) mechanical attrition of the exfoliated structure to nanometer-scaled plates. The teachings of <CIT> are incorporated herein by references for the purpose or describing graphene that can be utilized in the practice of this invention and methods for manufacturing such graphene. In the practice of this invention, it is preferred for the graphene to be comprised of individual single sheets of graphene (single graphene planes or single basal planes).

The reinforcing filler is preferably included at a level which is within the range of <NUM> phr to <NUM> phr and is more preferably included at a level which is within the range of <NUM> phr to <NUM> phr.

The reinforcing filler is normally included at a level which is within the range of <NUM> phr to <NUM> phr, is preferably included at a level which is within the range of <NUM> phr to <NUM> phr, and is more preferably included at a level which is within the range of <NUM> phr to <NUM> phr.

In cases where polypropylene is utilized as a filler lower levels are required since it has been found to be highly effective.

More specifically, in cases where polypropylene is used as a filler <NUM> percent to <NUM> percent less material is required than is the case with conventional fillers, such as carbon black and mineral fillers. The use of polypropylene as a filler also offers an additional advantage in that it breaks down during the curing of the tire to work in conjunction with the polyisobutylene rubber as a sealant. In other words, polypropylene offers a unique advantage in that it acts both as a filler in building the tire and subsequently as a sealant in the cured tire.

Relatively low molecular weight polypropylene is preferred for use as a filler in the practice of this invention. Such relatively low molecular weight polypropylene has a weight average molecular weight (Mw) which is within the range of from <NUM> to <NUM>,<NUM> or from <NUM>,<NUM> to <NUM>,<NUM>.

The relatively low molecular weight polypropylene preferably has a weight average molecular weight which is within the range of <NUM>,<NUM> to <NUM>,<NUM>, more preferably has a weight average molecular weight which is within the range of <NUM>,<NUM> to <NUM>,<NUM>, and most preferably has a weight average molecular weight which is within the range of <NUM>,<NUM> to <NUM>,<NUM>.

It should also be noted that polypropylene can also be beneficially utilized in conventional butyl rubber-based sealant formulations that include typically compounding ingredients as described herein.

The sealant layer formulation used in the practice of this invention can optionally include one or more processing oils. A wide variety of processing oils can be used. Suitable processing oils may include various oils as are known in the art, including aromatic, paraffinic, naphthenic, triglyceride oils, and low PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils. Suitable low PCA oils may include those having a polycyclic aromatic content of less than <NUM> percent by weight as determined by the IP346 method. Procedures for the IP346 method may be found in Standard Methods for Analysis & Testing of Petroleum and Related Products and British Standard <NUM> Parts, <NUM>, 62nd edition, published by the Institute of Petroleum, United Kingdom. The triglyceride oils that can be used include vegetable oils, including but not limited to vegetable oils, soybean oil, canola oil (Rapeseed oil), corn oil, cottonseed oil, olive oil, palm oil, safflower oil, sunflower oil, coconut oil, and peanut oil. Castor oil, soybean oil, and corn oil are preferred oils for use in the solid sealant layer formulations of this invention. Castor oil is a triglyceride oil that contains approximately <NUM> percent ricinoleic acid, <NUM> percent oleic acid, <NUM> percent linoleic acid, <NUM> percent palmitic acid, and <NUM> percent stearic acid. The processing oil will typically be employed at a level which is within the range of <NUM> phr to <NUM> phr and will more typically be employed at a level which is within the range of <NUM> phr to <NUM> phr. In most cases the processing oil will be included at a level which is within the range of <NUM> phr to <NUM> phr and will preferably be employed at a level which is within the range of <NUM> phr to <NUM> phr.

Various pigments or colorants can also optionally be included in the sealant formulations of this invention. By including one or more pigments or colorants in the sealant formulation the fact that the tire has in fact been punctured and the location of puncture can more readily be identified. A wide variety of colors can be used for this purpose with lights colors which stand out from the characteristic black color of tire treads being preferred. For example, white, red, orange, yellow, green, or blue pigments or colorants can optionally be included. Titanium dioxide can be utilized to impart a brilliant white color, red iron pigment can be used to impart a brilliant red color, or pigment yellow <NUM> can be used to impart a brilliant yellow color. The pigment or colorant will typically be utilized in a quantity that will make punctures in the tire more readily apparent and will normally be used at a level which is within the range <NUM> phr to <NUM> phr, and will preferably be used at a level which is within the range of <NUM> phr to <NUM> phr.

Both organic and inorganic pigments can be utilized. In most cases the pigment or colorant will be of a white, red, orange, yellow, green, or blue color. Some representative examples of pigments that can be utilized include, but are not limited to, Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), Pigment Yellow <NUM> (CAS No. <NUM>-<NUM>-<NUM>), C. Pigment Yellow <NUM> (iron oxide), C. Pigment Yellow <NUM> (lead chromates), C. Pigment Yellow <NUM> (bismuth vanadates), C. Pigment Yellow <NUM> (nickel antimony), C. Pigment Orange <NUM> (cadmium sulfide), C. Pigment Red <NUM> (iron oxide), C. Pigment Red <NUM>, C. Pigment Red <NUM> (ultramarine pigment), C. Pigment Blue <NUM> (ultramarine pigment), C. Pigment Blue <NUM>, C. Pigment Blue <NUM>, C. Pigment Violet <NUM> (ultramarine pigment), C. Pigment Violet <NUM> (manganese violet), Pigment Green <NUM> (chrome oxide green), C. Pigment Green <NUM> (cobalt-based mixed metal oxides), C. Pigment Green <NUM> (cobalt-based mixed metal oxides), and C. Pigment Green <NUM> (cobalt-based mixed metal oxides).

Some additional inorganic pigments that can be used include Ultramarine blue, Persian blue, Cobalt blue (CAS No. <NUM>-<NUM>-<NUM>), Curlean blue, Egyptian blue, Han blue (BaCuSi<NUM>O<NUM>), Azurite blue (Cu<NUM>(CO<NUM>)<NUM>(OH)<NUM>, Prussian blue (CAS No. <NUM>-<NUM>-<NUM>), YlnMn blue (Oregon blue), Realgar red (α-As<NUM>S<NUM>), cadmium red (Cd<NUM>SSe), Cerium sulfide red, Venetian red (Fe<NUM>O<NUM>), Red Ochre (anhydrous Fe<NUM>O<NUM>), Burnt sienna red, Red lead (Pb<NUM>O<NUM>), Vermilian red, Cinnabar red, Ultramarine violet, Han purple (BaCuSi<NUM>O<NUM>), Cobalt violet (CO<NUM>(PO<NUM>)<NUM>), Manganese violet (NH<NUM>MnP<NUM>O<NUM>), Purple of Cassius, Primrose yellow (BiVO<NUM>), Cadmium yellow (CdS), Chrome yellow (PbCrO<NUM>), Aureolin yellow (K<NUM>Co(NO<NUM>)<NUM>), Yellow Ochre (Fe<NUM>O<NUM>•H<NUM>O), Naples yellow, Titanium yellow (NiO•Sb<NUM>O<NUM>•20TiO<NUM>), Zinc yellow (ZnCrO4), and Chrome orange (PbCrO<NUM>•PbO).

Polyethylene glycol can also be included in the sealant formulations of this invention. The polyethylene glycol preferably has a weight average molecular weight which is within the range of <NUM> to <NUM>,<NUM> and more preferably has a weight average molecular weight which is within the range of <NUM>,<NUM> to <NUM>,<NUM>.

In cases where polyethylene glycol is utilized it is included at a level which is within the range of <NUM> phr to <NUM> phr, preferably <NUM> phr to <NUM> phr, and most preferably <NUM> phr to <NUM> phr.

In the embodiments of this invention where a peroxide is included in the sealant formulation the peroxide compounds utilized are those generally used for the crosslinkage of rubbery polymers. Preferably, peroxide compounds which disintegrate only at high temperatures, above <NUM> are utilized.

Some representative examples of such peroxides include tert-butyl perbenzoate and dialkyl peroxides with the same or different radicals, such as dialkylbenzene peroxides and alkyl peresters. Preferably the peroxide vulcanizing agent employed will contain two peroxide groups. Frequently the peroxide groups are attached to a tertiary-butyl group. The basic moiety on which the two peroxide groups are suspended can be aliphatic, cycloaliphatic, or aromatic radicals. Some representative examples of such peroxide include: bis(α,α-dimethylbenzyl) peroxide (more commonly known as dicumyl peroxide); <NUM>,<NUM>-bis(t-butyl peroxy)-<NUM>,<NUM>-dimethyl hexane; <NUM>,<NUM>-di-t-butyl peroxy-<NUM>,<NUM>,<NUM>-trimethyl cyclohexane; <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-di(t-butyl peroxy) hexyne-<NUM>; p-chlorobenzyl peroxide; <NUM>,<NUM>-dichlorobenzyl peroxide; <NUM>,<NUM>-bis-(t-butyl peroxy)-butane; di-t-butyl peroxide; benzyl peroxide; <NUM>,<NUM>-bis(t-butyl peroxy)-<NUM>,<NUM>-dimethyl hexane; and <NUM>,<NUM>-dimethyl-<NUM>,<NUM>-di(t-butyl peroxy) hexane. Such peroxide vulcanizing agents can be added to the polymer composition layer in pure form (<NUM> percent active peroxide), but are typically employed on an inert, free-flowing mineral carrier or an oil, such as silicon oil. Calcium carbonate is an inert mineral carrier which is frequently utilized for this purpose. Such peroxide carrier compositions normally containing from <NUM> to <NUM> weight percent active peroxide and typically contain from <NUM> to <NUM> weight percent active peroxide. For instance, the peroxide carrier composition can contain from <NUM> to <NUM> weight percent active peroxide, such as dicumyl peroxide, on a mineral carrier, such as calcium carbonate.

The peroxide will preferably be included in the solid sealant layer formulation used in the practice of this invention at a level which is within the range of <NUM> phr to <NUM> phr (based upon active peroxide) and will typically be present at a level which is within the range of <NUM> phr to <NUM> phr.

It is preferred for the peroxide to be present at a level which is within the range of <NUM> phr to <NUM> phr and is more preferably included at a level which is within the range of <NUM> phr to <NUM> phr. The term "phr" stands for parts by weight per <NUM> parts by weight of rubber.

In the practice of this invention, it is preferred to utilize a peroxide that has an active oxygen content (AOC) of at least <NUM>. Active oxygen content is determined by dividing the weight of active oxygen atoms in the compound by its total molecular weight (this is done on the basis of one active oxygen atom for each peroxide moiety (-O-O-) in the compound. For example, t-butyl cumyl peroxide has one active oxygen atom (molecular weight of <NUM>) and a total molecular weight of <NUM>. Accordingly, the active oxygen content of t-butyl cumyl peroxide is <NUM>/<NUM> which is <NUM> or <NUM>%. In any case, peroxides having active oxygen contents of greater than <NUM>%, <NUM>%, <NUM>%, or even <NUM>% are highly preferred. This is because they generate less during the tire curing process than do peroxides having lower active oxygen contents. For this reason, benzoyl peroxide (AOC of <NUM>), t-butyl cumyl peroxide (AOC of <NUM>), and di-t-butyl peroxide (AOC of <NUM>%) are preferred for use in the practice of this invention.

The puncture sealant formulation employed preferably extends from one shoulder of the tire to the other, in other words, it preferably covers the crown area of the tire.

The thickness of the sealant layer can vary greatly in an unvulcanized puncture sealant tire. Generally, the thickness of the polymer composition layer ranges from <NUM> to <NUM>. It is generally preferred for the sealant composition layer to have a thickness of <NUM> to <NUM> and is typically most preferred for the sealant layer to have a thickness which is within the range of <NUM> to <NUM>. In passenger tires it is normally most preferred for the polymer composition layer to have a thickness of <NUM>.

The following examples are included to further illustrate the method of manufacturing the self-sealing pneumatic rubber tires of this invention. Unless specifically indicated otherwise, parts and percentages are given by weight.

In this series of experiments sealant compositions which were made in accordance with this invention were evaluated and compared to a conventional cured sealant formulation. More specifically, the storage modulus of the samples prepared was determined and is reported in Table <NUM>. As can be seen in Table <NUM>, Oppanol® <NUM> was used in Example <NUM>, Oppanol® <NUM> was used in Example <NUM>, Oppanol® <NUM> was used in Comparative Example <NUM>, and a commercial sealant was evaluated in Comparative Example <NUM> after being cured (<NUM>/<NUM> cure).

As can be seen from Table <NUM>, after being cured a satisfactory storage modulus of less than <NUM> MPa can be attained in formulations that contain only relatively low molecular weight polyisobutylene. This experiment accordingly shows that commercially viable self-sealing tires can be made in accordance with this invention using a sealant layer which is made of relatively low molecular weight polyisobutylene.

Claim 1:
A pneumatic tire comprising a generally toroidal-shaped supporting carcass (<NUM>) with an outer circumferential tread (<NUM>), two spaced beads (<NUM>), at least one ply extending from bead to bead, sidewalls (<NUM>) extending radially from and connecting said tread (<NUM>) to said beads (<NUM>), a sealant layer (<NUM>, <NUM>) which is disposed inwardly from the supporting carcass (<NUM>), and an innerliner (<NUM>, <NUM>) which is disposed inwardly from the sealant layer (<NUM>,<NUM>), the innerliner (<NUM>, <NUM>) being an air barrier layer serving to keep air or another gas from escaping through the tire structure by diffusion, wherein said circumferential tread (<NUM>) is adapted to be ground-contacting, wherein said sealant layer (<NUM>, <NUM>) comprises a sealant composition comprising polyisobutylene, and wherein said polyisobutylene has a weight average molecular weight which is within the range of from <NUM>,<NUM> to <NUM>,<NUM>, characterized in that the sealant composition comprises <NUM> to <NUM> phr of, or is encapsulated by, a polyethylene, a polypropylene or a polyethylene glycol having a weight average molecular weight in a range of from <NUM> to <NUM>,<NUM>.