SELF SEALING TIRE

Abstract

This invention reveals an uncured pneumatic tire which is comprised of 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 inwardly from the supporting carcass, and an innerliner which is disposed inwardly from the sealant layer, wherein said circumferential tread is adapted to be ground-contacting, and wherein the sealant layer is comprised of polyisobutylene or a butyl rubber, wherein the polyisobutylene or the butyl rubber has a number average molecular weight which is within the range of 30,000 to 100,000.

Claims

1. An uncured pneumatic tire which is comprised of 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 inwardly from the supporting carcass, and an innerliner which is disposed inwardly from the sealant layer, wherein said circumferential tread is adapted to be ground-contacting, and wherein the sealant layer is comprised of polyisobutylene or a butyl rubber, wherein the polyisobutylene or the butyl rubber has a number average molecular weight which is within the range of 30,000 to 100,000.

2. The uncured pneumatic tire as specified in claim 1 wherein the sealant layer has a storage modulus (G′) at 40° C., 1 Hz, and 5% strain which is within the range of 0.005 to 0.2 MPa as measured by RPA, wherein the sealant layer is further comprised of a reinforcing filler and a plasticizer, wherein the reinforcing filler is included at a level which is within the range of 10 phr to 50 phr, and wherein the plasticizer is included at a level which is within the range of about 2 phr to about 30 phr.

3. The uncured pneumatic tire as specified in claim 1 wherein the sealant layer is encapsulated by a material that does not interfere with the function of the surrounding tire components.

4. The uncured pneumatic tire as specified in claim 3 wherein the material that does not interfere with the function of the surrounding tire components is low molecular weight polyethylene.

5. The uncured pneumatic tire as specified in claim 3 wherein the material that does not interfere with the function of the surrounding tire components is a material that becomes a sealant.

6. The uncured pneumatic tire as specified in claim 2 wherein the reinforcing filler is polypropylene.

7. The uncured pneumatic tire as specified in claim 6 wherein the sealant composition is void of reinforcing fillers other than the polypropylene.

8. The uncured pneumatic tire as specified in claim 1 wherein said sealant composition is void of carbon black.

9. The uncured pneumatic tire as specified in claim 8 wherein said sealant layer is further comprised of a colorant.

10. The uncured pneumatic tire as specified in claim 9 wherein the colorant is a red, orange, yellow, green, or blue pigment or colorant.

11. The uncured pneumatic tire as specified in claim 1 wherein said sealant composition is void of 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.

12. The uncured pneumatic tire as specified in claim 1 wherein the sealant layer is further comprised of a peroxide.

13. The uncured pneumatic tire as specified in claim 12 wherein the peroxide is present at a level which is within the range of 1 phr to 5 phr.

14. The uncured pneumatic tire as specified in claim 13 wherein the peroxide has an active oxygen content of at least 2%.

15. A method of manufacturing a pneumatic rubber tire having a puncture sealing feature which comprises: (1) building an unvulcanized tire comprised of 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; and (2) 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; said method being characterized in that said sealant formulation layer is comprised of polyisobutylene or the butyl rubber, wherein the polyisobutylene or the butyl rubber has a number average molecular weight which is within the range of 30,000 to 100,000, wherein the sealant formulation layer is extruded onto the unvulcanized supporting carcass, and wherein the sealant layer of the pneumatic rubber tire has a storage modulus (G′) at 40° C., 1 Hz, and 5% strain which is within the range of 0.005 to 0.2 MPa as measured by RPA.

16. The method of manufacturing a pneumatic rubber tire having a puncture sealing feature as specified in claim 15 wherein the sealant formulation layer is extruded onto the unvulcanized supporting carcass.

17. The method of manufacturing a pneumatic rubber tire having a puncture sealing feature as specified in claim 15 wherein the sealant formulation layer is a solid material, and wherein the sealant formulation layer is further comprised of a peroxide.

18. The method of manufacturing a pneumatic rubber tire having a puncture sealing feature as specified in claim 15 wherein the sealant layer is further comprised of a reinforcing filler and a plasticizer, wherein the reinforcing filler is included at a level which is within the range of 10 phr to 50 phr, and wherein the plasticizer is included at a level which is within the range of about 2 phr to about 30 phr.

19. The method of manufacturing a pneumatic rubber tire having a puncture sealing feature as specified in claim 15 wherein the sealant layer is encapsulated by a material that becomes a sealant.

20. The method of manufacturing a pneumatic rubber tire having a puncture sealing feature as specified in claim 15 wherein the reinforcing filler is polypropylene, and wherein the sealant composition is void of reinforcing fillers other than the polypropylene.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention is further illustrated by the accompanying drawings. These drawings represent two preferred embodiments of the present invention.

[0028] FIG. 1 is a cross-sectional view of a tire of this invention wherein the sealant layer is sandwiched between the innerliner and carcass of the tire.

[0029] FIG. 2 is a cross-sectional view of a pneumatic rubber tire of this invention wherein the self-sealant layer of the tire is located between two layers of innerliner in the tire.

[0030] FIG. 3 is a cross-sectional view of a pneumatic rubber tire of this invention wherein the self-sealant layer of the tire is located inwardly from the carcass of the tire and is sandwiched between the carcass and a containment layer which is the innermost layer of the tire. In this embodiment of the invention the tire does not contain an innerliner.

DETAILED DESCRIPTION OF THE INVENTION

[0031] 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 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 another scenario, the sealant formulation can be sandwiched between a layer of innerliner and a layer of less expensive rubbery formulation.

[0032] 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. 1. 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 is typically comprised of 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. 2. 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. 3. 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.

[0033] 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 about 100° C. to about 200° C. However, it is generally preferred for the tires of this invention to be cured at a temperature ranging from about 130° C. to about 170° C. It is typically more preferred for the tires of this invention to reach a maximum temperature ranging from a 140° C. to 165° C. during vulcanization. For instance, it is typically optimal for the tire to reach a maximum curing temperature which is within the range of 160° C. to 165° C. It is generally preferable for the cure cycle used to vulcanize the uncured tires to have a duration which is within the range of about 4 minutes to about 240 minutes. In the practice of this invention the uncured tires with normally be cured for a period which is within the range of about 10 minutes to 25 minutes with the cure period preferably being from about 10 minutes to 17 minutes, and most preferably being within the range of about 11 minutes to 13 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.

[0034] Tires made in accordance with this invention are depicted in FIG. 1, FIG. 2, and FIG. 3. In FIG. 1 a self-sealing pneumatic rubber tire 2 of this invention is shown wherein the tire has sidewalls 3, a supporting carcass 4, inextensible beads 5, an innerliner (air barrier layer) 6, a sealant layer 7, and an outer circumferential tread (tread portion) 8. The individual sidewalls 3 extend radially inward from the axial outer edges of the tread portion 8 to join the respective inextensible beads 5. The supporting carcass 4 acts as a supporting structure for the tread portion 8 and sidewalls 3. The sealant layer 7 is disposed inwardly from said supporting carcass 4 and outwardly from said innerliner 6. The outer circumferential tread 8 is adapted to be ground contacting when the tire is in use. In this embodiment of the invention, the innerliner 6 is disposed inwardly from said supporting carcass 4.

[0035] In FIG. 2 a self-sealant pneumatic rubber tire 10 of another embodiment of this invention is depicted. This pneumatic tire of the tubeless type includes a tread portion 11, a crown area 12, sidewalls 13, a supporting carcass 14, inextensible beads 15, an innerliner 16, and sealant layer 17. In this embodiment of the present invention the sealant layer 17 is sandwiched between two layers of innerliner 16. This, sealant layer 17 is disposed inwardly from one layer of innerliner and outwardly from another layer of innerliner. Both layers of innerliner 16 and the sealant layer 17 are disposed inwardly from the supporting carcass 14.

[0036] A tire in accordance with this invention which is free of an innerliner layer is illustrated in FIG. 3. In this scenario the self-sealing pneumatic rubber tire 22 is shown wherein the tire has sidewalls 23, a supporting carcass 24, inextensible beads 25, a containment layer 26, a sealant layer 27, and an outer circumferential tread (tread portion) 28. The individual sidewalls 23 extend radially inward from the axial outer edges of the tread portion 28 to join the respective inextensible beads 25. The supporting carcass 24 acts as a supporting structure for the tread portion 28 and sidewalls 23. The sealant layer 27 is disposed inwardly from said supporting carcass 24 and outwardly from the containment layer 26. In other words, the sealant layer 25 is sandwiched between the supporting carcass 24 and the containment layer 26. The outer circumferential tread 28 is adapted to be ground contacting when the tire is in use. In this embodiment of the invention, the containment layer 26 is disposed inwardly from the sealant layer 27 and is the innermost layer of the tire 22.

[0037] The sealant layer formulation used in the practice of this invention is comprised of a polyisobutylene. The sealant layer formulation will typically 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.

[0038] The polyisobutylene (PIB) utilized in the practice of this invention is a low molecular weight homopolymer of isobutylene. It will typically have a weight average molecular weight which is within the range of 40,000 to 120,000, and it will more typically have a weight average molecular weight which is within the range of 50,000 to 110,000. For instance the polyisobutylene can have a weight average molecular weight which is within the range of 40,000 to 60,000, which is within the range of 60,000 to 80,000, or which is within the range 80,000 to 120,000. The polyisobutylene will typically have a viscosity average molecular weight which is within the range of 30,000 to 50,000, which is within the range of 50,000 to 70,000, or which is within the range 70,000 to 95,000. The polyisobutylene will also typically have a number average molecular weight which is within the range of 20,000 to 30,000, which is within the range of 30,000 to 50,000, or which is within the range 50,000 to 70,000. Additionally, the polyisobutylene will normally have a polydispersity (Mw/Mn) which is within the range of 1.6 to 3.4, and a glass transition temperature which is within the range of −55° C. to −70° C. The polyisobutylene will normally have a glass transition temperature which is within the range of −62° C. to −66° C. and which is more typically within the range of −63° C. to −65° C. The polyisobutylene rubber can optionally be stabilized with a small amount of an antioxidant, such as from about 100 ppm to 1,000 ppm of an antioxidant. Such antioxidants will typically be incorporated into the polyisobutylene rubber at a level of about 300 ppm to about 700 ppm. A wide variety of antioxidants can be employed with butylated hydroxytoluene (BHT) typically being used.

[0039] 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 40,000, a weight average molecular weight of 53,000 and a glass transition temperature (Tg) of −64° C.; Oppanol® B12 has a viscosity average molecular weight of 55,000, a weight average molecular weight of 70,000, and a glass transition temperature (Tg) of −64° C.; and Oppanol® B15 has a viscosity average molecular weight of 85,000, a weight average molecular weight of 108,000, and a glass transition temperature (Tg) of −64° C.

[0040] 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, 2:1 layered silicate clays, talc, diatomaceous earth, calcium carbonate (CaCO.sub.3), calcium silicate, starch, lignin, alumina, or polypropylene. The 2:1 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.

[0041] 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 2-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 H-bond that is oriented out of plane. The distance between adjacent carbon atoms in graphene is approximately 0.142 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. Typically, at least 50 percent, 60 percent, 70 percent, or 80 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 40 percent, 50 percent, or 60 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 40 percent, 50 percent, or 60 percent of the carbon-carbon bonds on the edges of the graphene structure will be in the armchair configuration. In another embodiment at least 40 percent, 50 percent, or 60 percent of the carbon-carbon bonds on the edges of the graphene structure will be in the bay configuration. Typically, less than 40 percent of the carbon-carbon bonds on the edges of the graphene structure will be in the cove configuration and more typically less than 30 percent of the carbon-carbon bonds on the edges of the graphene structure will be in the cove configuration. In another embodiment less than 40 percent of the carbon-carbon bonds on the edges of the graphene structure will be in the cove configuration and less than 30 percent or more typically less than 20 percent of the carbon-carbon bonds on the edges of the graphene structure will be in the fjord configuration.

[0042] 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 100 nanometers (nm) or smaller. Preferably, all length, width and thickness values are smaller than 100 nm. This NGP material can be produced by a process the method described in U.S. Pat. No. 7,071,258 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 U.S. Pat. No. 7,071,258 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).

[0043] The reinforcing filler is typically included at a level which is within the range of about 1 phr to about 75 phr and is more typically included at a level which is within the range of 5 phr to 50 phr. The reinforcing filler is normally included at a level which is within the range of about 10 phr to about 45 phr, is preferably included at a level which is within the range of 20 phr to 40 phr, and is more preferably included at a level which is within the range of 30 phr to 38 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 about 35 percent to 40 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. Low molecular weight polypropylene is preferred for use as a filler in the practice of this invention. Such low molecular weight polypropylene typically has a weight average molecular weight (M.sub.w) which is within the range of about 4,000 to about 40,000. The low molecular weight polypropylene will normally have a weight average molecular weight which is within the range of 6,000 to 25,000, will preferably have a weight average molecular weight which is within the range of 8,000 to 20,000, and will most preferably have a weight average molecular weight which is within the range of 10,000 to 15,000. 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.

[0044] 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 3 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 2000 Parts, 2003, 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 87 percent ricinoleic acid, 7 percent oleic acid, 3 percent linoleic acid, 2 percent palmitic acid, and 1 percent stearic acid. The processing oil will typically be employed at a level which is within the range of about 1 phr to about 20 phr and will more typically be employed at a level which is within the range of 1 phr to 10 phr. In most cases the processing oil will be included at a level which is within the range of about 2 phr to about 5 phr and will preferably be employed at a level which is within the range of 2 phr to 4 phr.

[0045] 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 12 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 about 1 phr to about 5 phr, and will preferably be used at a level which is within the range of 2 phr to 4 phr.

[0046] 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 1 (CAS No. 2512-29-0), Pigment Yellow 110 (CAS No. 5590-18-1), Pigment Yellow 12 (CAS No. 15541-56-7), Pigment Yellow 126 (CAS No. 90268-23-8), Pigment Yellow 127 (CAS No. 68610-86-6), Pigment Yellow 13 (CAS No. 5102-83-0), Pigment Yellow 138 (CAS No. 30125-47-4), Pigment Yellow 14 (CAS No. 5468-75-7), Pigment Yellow 150 (CAS No. 68511-62-6), Pigment Yellow 151 (CAS No. 31837-42-0), Pigment Yellow 154 (CAS No. 68134-22-5), Pigment Yellow 168 (CAS No. 71832-85-4), Pigment Yellow 17 (CAS No. 4531-49-1), Pigment Yellow 174 (CAS No. 78952-72-4), Pigment Yellow 180 (CAS No. 77804-81-0), Pigment Yellow 183 (CAS No. 65212-77-3), Pigment Yellow 191 (CAS No. 129423-54-7), Pigment Yellow 3 (CAS No. 6486-23-3), Pigment Yellow 34 (CAS No. 1344-37-2), Pigment Yellow 42 (CAS No. 51274-00-1), Pigment Yellow 65 (CAS No. 6528-34-3), Pigment Yellow 74 (CAS No. 6358-31-2), Pigment Yellow 75 (CAS No. 52320-66-8), Pigment Yellow 81 (CAS No. 22094-93-5), Pigment Yellow 83 (CAS No. 5567-15-7), C.I. Pigment Yellow 42 (iron oxide), C.I. Pigment Yellow 34 (lead chromates), C.I. Pigment Yellow 184 (bismuth vanadates), C.I. Pigment Yellow 53 (nickel antimony), C.I. Pigment Orange 20 (cadmium sulfide), C.I. Pigment Red 101 (iron oxide), C.I. Pigment Red 104, C.I. Pigment Red 29 (ultramarine pigment), C.I. Pigment Blue 29 (ultramarine pigment), C.I. Pigment Blue 28, C.I. Pigment Blue 36, C.I. Pigment Violet 15 (ultramarine pigment), C.I. Pigment Violet 16 (manganese violet), Pigment Green 17 (chrome oxide green), C.I. Pigment Green 19 (cobalt-based mixed metal oxides), C.I. Pigment Green 26 (cobalt-based mixed metal oxides), and C.I. Pigment Green 50 (cobalt-based mixed metal oxides).

[0047] Some additional inorganic pigments that can be used include Ultramarine blue, Persian blue, Cobalt blue (CAS No. 1345-16-0), Curlean blue, Egyptian blue, Han blue (BaCuSi.sub.4O.sub.10), Azurite blue (Cu.sub.3(CO.sub.3).sub.2(OH).sub.2, Prussian blue (CAS No. 14038-43-8), YInMn blue (Oregon blue), Realgar red (α-As.sub.4S.sub.4), cadmium red (Cd.sub.2SSe), Cerium sulfide red, Venetian red (Fe.sub.2O.sub.3), Red Ochre (anhydrous Fe.sub.2O.sub.3), Burnt sienna red, Red lead (Pb.sub.3O.sub.4), Vermilian red, Cinnabar red, Ultramarine violet, Han purple (BaCuSi.sub.2O.sub.6), Cobalt violet (CO.sub.3(PO.sub.4).sub.2), Manganese violet (NH.sub.4MnP.sub.2O.sub.7), Purple of Cassius, Primrose yellow (BiVO.sub.4), Cadmium yellow (CdS), Chrome yellow (PbCrO.sub.4), Aureolin yellow (K.sub.3Co(NO.sub.2).sub.6), Yellow Ochre (Fe.sub.2O.sub.3.H.sub.2O), Naples yellow, Titanium yellow (NiOSb.sub.2O.sub.3.20TiO.sub.2), Zinc yellow (ZnCrO.sub.4), and Chrome orange (PbCrO.sub.4PbO).

[0048] Polyethylene glycol can also optionally be included in the sealant formulations of this invention. The polyethylene glycol will typically have a molecular weight which is within the range of 500 to 12,000 and will more typically have a molecular weight which is within the range of 4,000 to 8,000. In cases where polyethylene glycol is utilized it will typically be included at a level which is within the range of about 0.1 phr to about 2 phr, preferably 0.2 phr to 1 phr, and most preferably 0.3 phr to 0.7 phr.

[0049] 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 about 100° C. 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); 2,5-bis(t-butyl peroxy)-2,5-dimethyl hexane; 1,1-di-t-butyl peroxy-3,3,5-trimethyl cyclohexane; 2,5-dimethyl-2,5-di(t-butyl peroxy) hexyne-3; p-chlorobenzyl peroxide; 2,4-dichlorobenzyl peroxide; 2,2-bis-(t-butyl peroxy)-butane; di-t-butyl peroxide; benzyl peroxide; 2,5-bis(t-butyl peroxy)-2,5-dimethyl hexane; and 2,5-dimethyl-2,5-di(t-butyl peroxy) hexane. Such peroxide vulcanizing agents can be added to the polymer composition layer in pure form (100 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 about 30 to 55 weight percent active peroxide and typically contain from 35 to 50 weight percent active peroxide. For instance, the peroxide carrier composition can contain from about 38 to about 43 weight percent active peroxide, such as dicumyl peroxide, on a mineral carrier, such as calcium carbonate. The peroxide will normally be included in the solid sealant layer formulation used in the practice of this invention at a level which is within the range of 0.5 phr to 7 phr (based upon active peroxide) and will typically be present at a level which is within the range of 2.5 phr to 5 phr. It is preferred for the peroxide to be present at a level which is within the range of 3 phr to 4.2 phr and is more preferably included at a level which is within the range of 3.5 phr to 4 phr. The term “phr” stands for parts by weight per 100 parts by weight of rubber.

[0050] In the practice of this invention, it is preferred to utilize a peroxide that has an active oxygen content (AOC) of at least 2. 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 16) and a total molecular weight of 208. Accordingly, the active oxygen content of t-butyl cumyl peroxide is 16/208 which is 0.077 or 7.7%. In any case, peroxides having active oxygen contents of greater than 7%, 8%, 9%, or even 10% 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 6.5), t-butyl cumyl peroxide (AOC of 7.7), and di-t-butyl peroxide (AOC of 11.0%) are preferred for use in the practice of this invention.

[0051] The puncture sealant formulation employed should extend from one shoulder of the tire to the other, in other words, it should cover 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 will range from about 0.2 mm to about 8.5 mm. It is generally preferred for the sealant composition layer to have a thickness of 3 mm to 6 mm and is typically most preferred for the sealant layer to have a thickness which is within the range of 4 mm to 5 mm. In passenger tires it is normally most preferred for the polymer composition layer to have a thickness of about 4.5 mm.

[0052] The following examples are included to further illustrate the method of manufacturing the self-sealing pneumatic rubber tires of this invention. These examples are intended to be representative of the present invention and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

Examples 1-3 and Comparative Example 4

[0053] 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 1. As can be seen in Table 1, Oppanol® 10 was used in Example 1, Oppanol® 12 was used in Example 2, Oppanol® 15 was used in Example 3, and a commercial sealant was evaluated in Comparative Example 4 after being cured (12/170° C. cure).

TABLE-US-00001 TABLE 1 Example 4 1 2 3 Conventional Formulation Oppanol 10 Oppanol 12 Oppanol 15 Sealant G′ 5%, 40° C., 0.022 MPa 0.054 MPa 0.099 MPa 0.028 MPa 1 Hz G″ 5%, 40° C., 0.032 MPa 0.047 MPa 0.053 MPa 0.040 MPa 1 Hz G′ 5%, 60° C., 0.005 MPa 0.022 MPa 0.057 MPa 0.013 MPa 1 Hz G″ 5%, 60° C., 0.013 MPa 0.029 MPa 0.044 MPa 0.020 MPa 1 Hz

[0054] As can be seen from Table 1, after being cured a satisfactory storage modulus of less than about 0.070 MPa can be attained in formulations that contain only low molecular weight polyisobutylene. In fact, a storage modulus within a highly desirable range of 0.030 MPa to 0.050 MPa could be attained. This experiment accordingly shows that commercially viable self-sealing tires can be made in accordance with this invention used a sealant layer which is made of low molecular weight polyisobutylene.

[0055] Variations in the present invention are possible in light of the description of it provided herein. The illustrations and corresponding descriptions are not intended to restrict or limit the scope of the appended claims in any way. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.