Patent Description:
Puncture sealing tires are designed to retard or prevent the loss of air and consequential deflation after the tire has been punctured with a sharp object, such as a nail, screw, or another object which is capable of piercing through the tire. Pneumatic tires with puncture sealing capabilities have been described in the literature since at least the first part of the twentieth century.

<CIT> discloses a laminated puncture sealing strip for pneumatic tires comprising a plurality of superposed sealing sheets that are not more than one-tenth inch (<NUM>) or less than one-twentieth inch (<NUM>) in thickness and that are composed of a soft sticky unvulcanized synthetic rubber sealing composition.

<CIT> describes a method of manufacturing a pneumatic rubber tire having an outer circumferential tread, a supporting carcass therefore, and an inner liner disposed inwardly from said supporting carcass, containing a puncture sealant layer positioned between said inner liner and said carcass, the steps of which comprise, based upon parts by weight per <NUM> parts by weight uncured butyl rubber (phr): (A) providing a butyl rubber-based rubber composition comprised of: (<NUM>) <NUM> phr of uncured star branched butyl rubber, (<NUM>) <NUM> to <NUM> phr of a particulate precured rubber, selected from resin-cured butyl rubber and/or sulfur-cured diene-based rubber, homogeneously dispersed in said uncured butyl rubber, and (<NUM>) <NUM> to <NUM> phr of organoperoxide; (B) assembling said butyl rubber based rubber composition as a layer into an unvulcanized rubber tire between said carcass and said innerliner during the tire building process; and (C) shaping and curing said rubber tire at a temperature in a range of 130ºC to 175ºC for a sufficient period time to partially depolymerize said uncured butyl rubber in said butyl rubber-based rubber composition layer, wherein said particulate precured rubber substantially remains in its precured condition as a particulate dispersion within said partially depolymerized butyl rubber.

<CIT> describes a tire sealant material composition comprising at least one non-halogenated butyl rubber, and <NUM>,<NUM>'-dibenzamido-diphenyldisulfide, the sealant material composition having a viscosity that permits the sealant material composition to be incorporated into a tire during a tire building process and to degrade to a lower viscosity that permits the resulting degraded sealant material composition to flow into and seal a puncture in a tire.

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.

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

The method in accordance with the 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. In the practice of this invention a relatively low viscosity sealant formulation, which would ordinarily be difficult to handle and build into an uncured tire, is encapsulated in a relatively stiff rubber formulation. This makes it relatively easy to build the sealant layer into the tire since the low viscosity sealant formulation is contained with the more rigid solid material. The low viscosity sealant material requires little depolymerization, i.e., preferably less than <NUM> percent or less than <NUM> percent depolymerization, and preferably no depolymerization to act effectively as a sealant. Accordingly, it does not need to be depolymerized with a peroxide which causes off-gassing and the resultant tire uniformity and balance issues normally associated with polymer break down.

In the practice of this invention, the relatively stiff solid material has the ability to depolymerize during the vulcanization of the tire to form more sealant material in addition to the quantity of sealant that it originally encapsulated. For instance, the relatively stiff material used to encapsulate the sealant can be a rubber formulation that is used conventionally in sealant formulations which are depolymerized during vulcanization to make conventional sealant layers. For instance, the stiff material can be a butyl rubber or a halogenated butyl rubber. Since it represents only a fraction of the total sealant material the amount of off-gassing is significantly reduced. The level of off-gassing can be further reduced by utilizing as the relatively stiff material a rubber formulation which comprises (a) polyisobutylene, (b) a peroxide, and (c) a reinforcing filler, wherein the polyisobutylene is present in the sealant layer at a level of at least <NUM> weight percent polyisobutylene, based upon the total weight of elastomers in the sealant layer.

This invention more specifically discloses an uncured pneumatic tire which comprises a generally toroidal-shaped supporting carcass with an outer circumferential tread, two spaced beads, at least one ply extending from bead to bead, sidewalls extending radially from and connecting said tread to said beads, a sealant layer which is disposed radially inwardly from the supporting carcass, and an innerliner which is disposed radially inwardly from the sealant layer, wherein said circumferential tread is adapted to be ground-contacting, wherein the sealant layer is encapsulated by a relatively stiff composition, wherein the relatively stiff composition breaks down at temperatures typically used for vulcanization and forms a sealant material, and wherein (i) the relatively stiff material does not interfere with the function of the surrounding tire components and the sealant layer comprises a relatively low viscosity material that requires little or no depolymerization to act as a sealant material; and/or (ii) the sealant layer comprises polyisobutylene or a butyl rubber, the polyisobutylene or the butyl rubber having a number average molecular weight which is preferably within the range of from <NUM>,<NUM> to <NUM>,<NUM>.

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

The invention further reveals a method of manufacturing a pneumatic rubber tire having a puncture sealing feature which comprises: (<NUM>) building an unvulcanized tire comprising a circumferential rubber tread, a supporting carcass therefor, two spaced beads, two rubber sidewalls connecting said beads, an inner liner and a sealant formulation layer disposed radially inwardly from said supporting carcass and radially outwardly from said inner liner, wherein said sealant formulation layer comprises a relatively low viscosity material that requires little or no depolymerization to act as a sealant material, wherein the sealant layer is encapsulated by a relatively stiff composition, wherein the relatively stiff composition breaks down at temperatures typically used for vulcanization and forms a sealant material, and wherein the relatively stiff material does not interfere with the function of the surrounding tire components; and (<NUM>) shaping and vulcanizing said tire in a tire mold and curing the unvulcanized tire under conditions of heat and pressure to produce the pneumatic rubber tire having the puncture sealing feature.

The present invention also discloses a method of manufacturing a pneumatic rubber tire having a puncture sealing feature which comprises: (<NUM>) building an unvulcanized tire comprising a circumferential rubber tread, a supporting carcass therefor, two spaced beads, two rubber sidewalls connecting said beads, an inner liner and a sealant formulation layer disposed inwardly from said supporting carcass and outwardly from said inner liner, wherein said sealant formulation layer comprises polyisobutylene or the butyl rubber, wherein the polyisobutylene or the butyl rubber has a number average molecular weight which is within the range of from <NUM>,<NUM> to <NUM>,<NUM>, wherein the sealant formulation layer is encapsulated by a relatively stiff composition, wherein the relatively stiff composition breaks down at temperatures typically used for vulcanization and forms a sealant material, and wherein the relatively stiff material does not interfere with the function of the surrounding tire components; and (<NUM>) shaping and vulcanizing said tire in a tire mold and curing the unvulcanized tire under conditions of heat and pressure to produce the pneumatic rubber tire having the puncture sealing feature.

In a preferred embodiment of this invention the relatively stiff composition comprises solid polyisobutylene or butyl rubber and a peroxide.

In a preferred embodiment of this invention the relatively stiff composition comprises (a) polyisobutylene, (b) a peroxide, and (c) a reinforcing filler, wherein the polyisobutylene is present in the sealant layer at a level of at least <NUM> weight percent polyisobutylene, based upon the total weight of elastomers in the sealant layer.

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

A sealant layer formulation is built into an unvulcanized rubber tire. In building the tire, the sealant layer formulation is encapsulated within a relatively stiff rubber which makes the handling of the sealant composition and building it into a tire relatively easy. In any case, the relatively stiff rubber acts as a containment layer which is capable of retaining the sealant layer formulation between it and the carcass of the tire. In the case of tires made utilizing polyisobutylene as the sealant layer, the tire will typically exhibit good gas barrier properties by virtue of the gas permeation resistance provided by the polyisobutylene. Accordingly, in some cases it is possible to eliminate innerliners totally from such tires.

In any case, the sealant layer formulation is assembled into the uncured tire radially 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 for 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 of this 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>. In another embodiment of this invention, the sealant layer formulation is built into the tire between two layers, one of them being the innerliner and another being a containment layer.

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 100ºC to 200ºC. However, it is generally preferred for the tires of this invention to be cured at a temperature ranging from 130ºC to 175ºC. It is typically more preferred for the tires of this invention to reach a maximum temperature ranging from a 140ºC to 165ºC during vulcanization. It is typically optimal for the tire to reach a maximum curing temperature which is within the range of 160ºC to 165ºC.

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>, and <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>, 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 in accordance with an embodiment of this invention is free of an innerliner layer and 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 of the invention, the containment layer <NUM> is disposed inwardly from the sealant layer <NUM> and is the innermost layer of the tire <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 10ºC per minute, according to ASTM D3418-<NUM> or equivalent.

In this application, the glass transition temperature Tg for resins is determined as a peak midpoint by a differential scanning calorimeter (DSC) at a temperature rate of increase of 10ºC per minute, according to ASTM D6604 or equivalent.

In this application, the glass transition temperature Tg for oils is determined as a peak midpoint by a differential scanning calorimeter (DSC) at a temperature rate of increase of 10ºC per minute, according to ASTM E1356 or equivalent.

In this application, G' and tan delta have been obtained with an RPA <NUM>™ Rubber Process Analyzer of the company Alpha Technologies, based on ASTM D5289.

In this application, molecular weight refers to the true 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 permeation chromatography (GPC) according to ASTM <NUM>-<NUM> using polystyrene calibration standards (for further explanations, please see ASTM <NUM>-<NUM> and/or <NPL>, in particular and sections <NUM> and <NUM>.

In this application, the polydispersity index or polydispersity is the ratio of Mw/Mn, i.e., the ratio of the weight average molecular weight to the number average molecular weight.

Gel permeation chromatography (GPC) is a well-known method wherein polymers are separated according to molecular size, the largest molecule eluting first. The chromatograph is calibrated using commercially available polystyrene molecular weight standards. The detector used is an ultraviolet detector. The fraction of chains existing as mono chains is determined as the ratio of the areas under the GPC curve, i.e., (mono chain peak area)/(total area).

The sealant layer formulation used in the practice of this invention preferably comprises a polyisobutylene or a butyl.

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

For instance, the polyisobutylene can have a weight 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>, which is within the range <NUM>,<NUM> to <NUM>,<NUM>, which is within the range of <NUM>,<NUM> to <NUM>,<NUM>, which is within the range of <NUM>,<NUM> to <NUM>,<NUM>, which is within the range <NUM>,<NUM> to <NUM>,<NUM>, 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, polyisobutylene has 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 from -55ºC to -70ºC.

The polyisobutylene preferably has a glass transition temperature which is within the range of from -62ºC to -66ºC or within the range of from -63ºC to -65ºC.

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. Preferably, such antioxidants are 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 preferably 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 weight average molecular weight of <NUM>,<NUM> and a glass transition temperature (Tg) of -64ºC; Oppanol® B12 has a weight average molecular weight of <NUM>,<NUM>, and a glass transition temperature (Tg) of -64ºC; and Oppanol® B15 has a weight average molecular weight of <NUM>,<NUM>, and a glass transition temperature (Tg) of -64ºC.

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 (CaCO<NUM>), 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 preferably 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 zig-zag, armchair, K-region, gulf, bay, cove, and fjord edge topologies. Preferably, 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 preferably exfoliated into nano-scaled graphene plate (NGP) material that essentially comprises 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, comprises 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> 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> can be utilized in the practice of this invention for manufacturing such graphene. In the practice of this invention, it is preferred for the graphene to comprise 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 preferably 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 may be sufficient 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 an 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>,<NUM> to <NUM>,<NUM>.

Preferably, the relatively low molecular weight polypropylene has a weight average molecular weight which is within the range of from <NUM>,<NUM> to <NUM>,<NUM>. More preferably, the weight average molecular weight is within the range of from <NUM>,<NUM> to <NUM>,<NUM>, and will most preferably have a weight average molecular weight which is within the range of from <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 <NPL>. 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 is preferably employed at a level which is within the range of from <NUM> phr to <NUM> phr and is more preferably employed at a level which is within the range of from <NUM> phr to <NUM> phr. In most cases, the processing oil is included at a level which is within the range of from <NUM> phr to <NUM> phr and will most preferably be employed at a level which is within the range of from <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> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), Pigment Yellow <NUM> (<NPL>), 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 (<NPL>), Curlean blue, Egyptian blue, Han blue (BaCuSi<NUM>O<NUM>), Azurite blue (Cu<NUM>(CO<NUM>)<NUM>(OH)<NUM>, Prussian blue (<NPL>), YInMn 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 optionally 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 from <NUM> to <NUM>,<NUM>, more preferably within the range of from <NUM>,<NUM> to <NUM>,<NUM>.

In cases where polyethylene glycol is utilized it is preferably included at a level which is within the range of from <NUM> phr to <NUM> phr, more preferably from <NUM> phr to <NUM> phr, and most preferably from <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 relatively high temperatures, i.e., above 80ºC, are utilized.

Some representative examples of suitable 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 contains 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 is preferably included in the solid sealant layer formulation used in the practice of this invention at a level which is within the range of from <NUM> phr to <NUM> phr (based upon active peroxide), and is more preferably present at a level which is within the range of from <NUM> phr to <NUM> phr. It is more preferred for the peroxide to be present at a level which is within the range of from <NUM> phr to <NUM> phr, and it is most preferably included at a level which is within the range of from <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. Preferably, the thickness of the polymer composition layer ranges from <NUM> to <NUM>. It is generally more preferred for the sealant composition layer to have a thickness of from <NUM> to <NUM> and it is typically most preferred for the sealant layer to have a thickness which is within the range of from <NUM> to <NUM>. In passenger tires, it is normally most preferred for the polymer composition layer to have a thickness of <NUM>.

The relatively stiff rubber formulation that can be used in the practice of this invention can be any formulation which is known in the art to depolymerized under condition of tire vulcanization to form sealant material.

However, the relatively stiff rubber formulation should be capable of containing the sealant formulation in a manner that facilitates it to be easily build into an uncured tire.

Additionally, the relatively stiff material must not interfere with the function of the surrounding tire components.

In a preferred embodiment of this invention, the relatively stiff material causes only a minimal level of off-gassing during its breakdown during the vulcanization of the tire.

Some preferred rubber formulation for this use are described in <CIT> and <CIT>.

A preferred rubber formulation for use as the relatively stiff composition comprises (a) polyisobutylene or a butyl rubber, (b) a peroxide, and (c) a reinforcing filler, wherein the polyisobutylene or butyl are present in the composition at a level of at least <NUM> weight percent, based upon the total weight of elastomers in the sealant layer.

One embodiment of this invention relates to a relatively stiff composition comprising (a) a polyisobutylene rubber and/or a butyl rubber, (b) a peroxide, and (c) a reinforcing filler, wherein the peroxide has an active oxygen content of at least <NUM>% and which is preferably greater than <NUM>%.

Another embodiment of this invention reveals a relatively stiff material comprising (a) a polyisobutylene rubber and/or a butyl rubber, (b) a peroxide, and (c) 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>,<NUM> to <NUM>,<NUM>.

The relatively stiff rubber formulation used in the practice of this invention preferably comprises of (a) polyisobutylene or butyl, (b) a peroxide, and (c) a reinforcing filler, wherein the polyisobutylene is present in the sealant layer at a level of at least <NUM> weight percent, based upon the total weight of elastomers in the sealant formulation. The polyisobutylene/butyl can represent at least <NUM> weight percent, at least <NUM> weight percent, at least <NUM> weight percent, at least <NUM> weight percent, at least <NUM> weight percent, or at least <NUM> weight percent, of the total weight of elastomers in the sealant formulation.

The relatively stiff formulation can be void of other elastomers.

The relatively stiff formulation preferably contains less than <NUM> weight percent butyl rubber, more preferably less than <NUM> weight percent butyl rubber, less than <NUM> weight percent butyl rubber, less than <NUM> percent butyl rubber, less than <NUM> percent butyl rubber, or less than <NUM> weight percent butyl rubber.

The polyisobutylene rubber (PIB) and butyl rubber utilized in the relatively stiff formulation in the practice of this invention is a relatively high molecular weight polymer. It preferably has a weight average molecular weight which is within the range of from <NUM>,<NUM> to <NUM>,<NUM>, more preferably a weight average molecular weight which is within the range of from <NUM>,<NUM> to <NUM>,<NUM>, which is with the range of from <NUM>,<NUM> to <NUM>,<NUM>, or which is within the range of from <NUM>,<NUM> to <NUM>,<NUM>.

The peroxide compounds included in the relatively stiff formulations in the practice of this invention are those generally used for the crosslinkage of rubbery polymers.

A sealant layer <NUM>, <NUM>, <NUM> is provided that is encapsulated by a relatively stiff composition.

The relatively stiff composition is preferably a relatively stiff rubber composition.

The rubber used in the relatively stiff rubber composition preferably has a weight average molecular weight which is within the range of from <NUM>,<NUM> to <NUM>,<NUM>, more preferably a weight average molecular weight which is within the range of from <NUM>,<NUM> to <NUM>,<NUM>, which is with the range of from <NUM>,<NUM> to <NUM>,<NUM>, or which is within the range of from <NUM>,<NUM> to <NUM>,<NUM> or from <NUM>,<NUM> to <NUM>,<NUM>. Preferably, polyisobutylene rubber (PIB) or butyl rubber may be utilized in the relatively stiff formulation having a relatively high molecular weight polymer specified above.

The relatively stiff composition is characterized by its storage modulus G' measured at <NUM> % strain and a temperature of 40ºC preferably being in a range of from <NUM> to <NUM> MP, more preferably in the range of from <NUM> MPa to <NUM> MPa and most preferably in the range of from <NUM> MPa to <NUM> MPa.

The relatively stiff composition is configured to break down at temperatures used for tire vulcanization, preferably in a range of from 130ºC to 175ºC or from 160ºC to 175ºC.

The sealant layer comprises a relatively low viscosity material. The relatively low viscosity material is preferably characterized by a weight average molecular weight that is within the range of from <NUM>,<NUM> to <NUM>,<NUM> or from <NUM>,<NUM> to <NUM>,<NUM>. Such a material requires only little or no depolymerization to act as a sealant material. Preferably, polyisobutylene or butyl may be utilized. In addition, polypropylene as a filler may be used. The polypropylene is preferably also a relatively low molecular weight polypropylene which has a weight average molecular weight which is within the range of from <NUM>,<NUM> to <NUM>,<NUM>.

The low viscosity sealant material requires only little depolymerization, i.e., preferably less than <NUM> percent or less than <NUM> percent or less than <NUM> percent of depolymerization, and preferably no depolymerization to act effectively as a sealant.

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, compositions were prepared and cured with dicumyl peroxide into test strips for evaluation. In the procedures used non-productive formulations were made first and then the dicumyl peroxide was added to make productive formulations. The composition of each of the formulations evaluated in this series of experiments is shown in Table <NUM> with all levels being designated in parts by weight. Comparative Example <NUM> which contained only butyl rubber and no polyisobutylene rubber was cured using <NUM> parts by weight of dicumyl peroxide. The formulations of Example <NUM> and Comparative Examples <NUM> and <NUM> included three different levels of dicumyl peroxide as shown in Table <NUM>. The levels of the various materials delineated in Table <NUM> are given in parts by <NUM> parts of rubber.

Table <NUM> shows the storage modulus of the cured samples at the three different levels of dicumyl peroxide used to cure the samples. It should be noted that in Comparative Example <NUM> (which used <NUM>% butyl rubber as its only rubber component) only the sample using the highest level of dicumyl peroxide was prepared, which was necessary to reduce the storage modulus to a sufficient level for utilization as a puncture sealant.

As can be seen from Table <NUM>, the storage modulus of the samples was reduced with increasing levels of peroxide. Table <NUM> also shows that the reduction in storage modulus attained also increased with increasing levels of polyisobutylene rubber in the formulations. Table <NUM> further shows that a satisfactory storage modulus of less than <NUM> MPa can be attained in formulations that contain a relatively high level of polyisobutylene rubber. In fact, a storage modulus of <NUM> MPa (within the range of <NUM> MPa to <NUM> MPa) was attained in Example <NUM>, which was cured utilizing only <NUM> phr of dicumyl peroxide.

These formulations were also evaluated to determine the level of innerliner expansion that resulted. This was accomplished by curing the sealant formulations between two layers of innerliner and measuring the level of expansion that occurred on curing. Expansion was measured immediately after the samples came out of the cure press. The results of this testing are reported in Table <NUM>. The reduction in expansion is reported as compared to the butyl rubber control (Comparative Example <NUM>).

As can be seen from Table <NUM>, the use of the puncture sealant formulation of this invention resulted in significantly lower levels of innerliner expansion as compared to conventional puncture sealant formulations. It can accordingly be used in manufacturing pneumatic tires having better uniformity and better balance characteristics. Additionally, it can be easily built into tires using standard techniques without compromising puncture sealing capabilities.

In this experiment, a polyisobutylene rubber-based formulation was made in accordance with this invention using relatively low molecular weight polypropylene as a filler and was compared to a similar sealant formulation which were made utilizing conventional fillers (synthetic amorphous silica and clay). These formulations are further described in Table <NUM>. It should be noted that the sealant formulation of Example <NUM> is identical to the formulation previously described in Example <NUM> at the <NUM> parts by weight level of dicumyl peroxide. The sealant composition of Example <NUM> was made so as to have the same equivalent volume fraction of polypropylene as the volume fraction of fillers in the sealant composition of Example <NUM>. It should be noted that the levels of all of the materials delineated in Table <NUM> are given in parts by weight.

The storage modulus G' of these formulations was determined at temperatures from 40ºC up to 100ºC as reported in Table <NUM>.

As can be seen from Table <NUM>, all of the formulations made utilizing the low molecular weight polypropylene exhibited a lower level of storage modulus at equivalent temperatures. At higher temperatures this difference became more pronounced. The formulation made with the polypropylene also appeared to handle and process better and more easily. In cases where low molecular weight polypropylene is used as a filler, it is also possible to employ a lower level of peroxide to attain the desired storage modulus. This accordingly makes it possible to employ a lower level of peroxide which will further reduce the level of gas generated during curing.

In this series of experiment, dicumyl peroxide, benzoyl peroxide, and t-butyl cumyl peroxide were evaluated for use in butyl rubber sealant formulations. These formulations are further described in Table <NUM>. It should be noted that dicumyl peroxide was evaluated as a control in Comparative Example <NUM>. The levels of benzoyl peroxide and t-butyl cumyl peroxide used in Examples <NUM> and <NUM> were adjusted as needed to attain a decrease in storage modulus which was equivalent to the reduction realized in the control. More specifically, the required quantity of peroxides was used to reduce the storage modulus of the sealant compositions to a level of approximately <NUM> MPa. In any case, the levels of the various materials delineated in Table <NUM> are given in parts by weight.

This series of experiments shows that a smaller degree of gas generation results in cases where peroxides having high active oxygen contents are used in making the sealant formulations. Such peroxides can accordingly be beneficially utilized in making the polyisobutylene based sealant formulations of this invention as well as in making conventional butyl rubber based sealant formulations. Such butyl rubber based sealant formulations can, of course, also include additional ingredients, such as the reinforcing fillers, oils, ethylene glycol, colorants, and pigments previously described herein.

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 Example <NUM>, and a commercial sealant was evaluated in Comparative Example <NUM> after being cured (<NUM>/170ºC cure).

Claim 1:
An uncured pneumatic tire comprising a generally toroidal-shaped supporting carcass (<NUM>, <NUM>, <NUM>) with an radially outer circumferential tread (<NUM>, <NUM>, <NUM>), two spaced beads (<NUM>, <NUM>, <NUM>), at least one ply extending from bead to bead, sidewalls (<NUM>, <NUM>, <NUM>) extending radially from and connecting said tread to said beads, and a sealant layer (<NUM>, <NUM>, <NUM>) which is disposed radially inwardly from the supporting carcass (<NUM>, <NUM>, <NUM>), wherein the sealant layer (<NUM>, <NUM>, <NUM>) is located (i) radially between two layers of an innerliner (<NUM>, <NUM>) or (ii) radially between said supporting carcass (<NUM>, <NUM>, <NUM>) and a radially inner containment layer (<NUM>) or (iii) radially between an innerliner layer (<NUM>, <NUM>) and a containment layer (<NUM>), wherein said circumferential tread (<NUM>, <NUM>, <NUM>) is adapted to be ground-contacting, characterized in that the sealant layer (<NUM>, <NUM>, <NUM>) is encapsulated by a relatively stiff composition, wherein the relatively stiff composition is configured to break down at temperatures used for tire vulcanization, preferably in a range of from <NUM> to <NUM>, and to form a sealant material, wherein the relatively stiff material does not interfere with the function of surrounding tire components, and wherein the sealant layer (<NUM>, <NUM>, <NUM>) comprises a relatively low viscosity material that requires only little or no depolymerization to act as a sealant material.