Patent Application
20090078353
The present invention is directed to a pneumatic tire having a built-in sealant layer and its preparation.
Various methods, sealants and tire constructions have been suggested for pneumatic tires that relate to use of liquid sealant coatings in which the sealant flows into the puncture hole. However, such liquid sealants can flow excessively at elevated temperatures and cause the tire to become out of balance. Also, the liquid sealant may not be entirely operable or effective over a wide temperature range extending from summer to winter conditions. More complicated tire structures which encase a liquid sealant in a vulcanized rubber material can be expensive to manufacture and can also create balance and suspension problems due to the additional weight required in the tire.
Puncture sealing tires also have been further proposed wherein a sealant layer of degradable rubber, for example, is assembled between unvulcanized tire layers to provide a built-in sealant. The method of construction, however, is generally only reasonably possible when, for example, the sealant layer is laminated with another non-degraded layer of rubber, e.g., a tire inner liner, which permits handling during the tire building procedure. This is because the degradable rubber tends to be tacky or sticky in nature and lacks strength making it very difficult to handle alone without additional support. The inner liner also keeps the sealant layer from sticking to a tire-building apparatus. By finally laminating the sealant layer between two or more non-degraded rubber layers, e.g., the tire inner liner and a tire carcass, the sealant layer retains structural integrity during the vulcanization operation wherein high pressures are applied to the tire, which would otherwise displace the degraded rubber layer from its desired location. Accordingly, the resulting puncture sealing tire typically has a sealant layer between the inner liner and tire carcass.
Such a lamination procedure significantly increases the cost of manufacturing a tire. In addition, the compounds in the built-in sealant, e.g., organic peroxide depolymerized butyl based rubber, may generate gases at higher temperature, such as during the cure or during the tire use, which can result in aesthetically unappealing inner liner blister formation. Aside from being unappealing, such blister formation may allow the sealant to unfavorably migrate away from its intended location.
Accordingly, there is a need for a simple and practical method of preparing a self-sealing tire that eliminates or reduces blister formation in the tire inner liner.
The present invention is directed to a pneumatic tire having a built-in sealant layer and a method of manufacturing such a tire.
In one embodiment, a pneumatic tire includes an outer circumferential rubber tread and a supporting carcass. A rubber inner liner is disposed inwardly from the supporting carcass. A built-in sealant layer is situated adjacent to an innermost gas permeable layer and disposed inwardly from the rubber inner liner. The sealant layer provides self-sealing properties to the pneumatic tire. The tire, with its innermost gas permeable layer, allows for elimination or reduction in blister formation in the tire.
The pneumatic tire, in one embodiment, can be prepared by positioning a gas permeable layer on a tire-building apparatus. Next, a precursor sealant layer is positioned directly on the gas permeable layer. A rubber inner liner is disposed outwardly of the precursor sealant layer followed by a tire carcass then a rubber tire tread on the tire carcass to form an unvulcanized tire assembly. Then, the unvulcanized tire assembly is vulcanized under conditions of heat and pressure such that the precursor sealant layer provides the pneumatic tire with self-sealing properties.
In another embodiment, a method of preparing a pneumatic tire includes positioning a non-woven sheet of polyester, nylon, or aramid on a tire-building apparatus. Next, a precursor sealant layer is positioned directly on the non-woven sheet. The precursor sealant layer may include an uncured butyl rubber-based rubber composition or a polyurethane based composition. A rubber inner liner is positioned directly on the precursor sealant layer followed by a tire carcass then a rubber tire tread on the tire carcass to define an unvulcanized tire assembly. The precursor sealant layer provides the pneumatic tire with self-sealing properties after vulcanization.
By virtue of the foregoing, there is provided a pneumatic tire that has an ability to seal against various puncturing objects and can eliminate or reduce inner liner blister formation in the tire, for example.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description of the invention given above, and detailed description given below, serve to explain the invention.
The innermost gas permeable layer 24 of the tire 10 defines a non-woven sheet of polymeric material. In one example, the gas permeable layer 24 includes a non-woven sheet of polyester, nylon, or aramid. The non-woven sheet may be prepared by a melt blown process, spun bond, or point bonding process, as is known in the art. Such polyester and nylon non-woven sheets, for example, are available from 3M of St. Paul, Minn. or Nolar Industries Limited of Ontario, Canada. The gas permeable layer 24 permits gas from the built-in sealant layer 22 to escape or become part of the tire's inflation air, such as when the tire 10 is at its running temperature.
The built-in sealant layer 22, prior to vulcanization of the pneumatic tire 10, is referred to herein as a precursor sealant layer 23. The precursor sealant layer 23 can generally include any non-flowing sealant material known in the art.
In one embodiment, the precursor sealant layer 23 can include a self-healing polyurethane composition. In one example, such polyurethane composition may define a non-flowing, or non-liquid, polyurethane composition that is neither gel-like nor substantially tacky and that provides a self-supporting precursor sealant layer 23. Concerning self-supporting, the polyurethane composition of the precursor sealant layer 23 maintains its own form, e.g., as a sheet or layer, without the need to be laminated to one or more supporting structures. The polyurethane composition is substantially non-tacky in that a sheet of the polyurethane composition, for example, may contact another sheet yet be pulled apart with relative ease and still substantially maintain its original form. The non-flowing polyurethane composition can include a self-healing polyurethane elastomeric material, which may contain, for example, methylene diphenyl 4,4′-diisocyanate (MDI) and poly(alkylene oxide) glycol. In another example, the self-healing polyurethane composition is gel-like and tacky. One such suitable polyurethane composition is Tyrlyner® available from VITA Industrial Inc. of Thomasville, Ga. It should be understood that formulations of urethane materials that can be used for the self-healing polyurethane composition may be readily produced by persons having ordinary skill in the art from known chemistry techniques in the production of urethanes.
After vulcanization, the polyurethane composition provides a gel-like and tacky polyurethane composition, such as by way of thermal degradation, which provides the pneumatic tire 10 with self-sealing properties and defines the built-in sealant layer 22.
In another example, the sealant layer 22, before vulcanization, can include an uncured butyl rubber-based rubber composition. One such suitable uncured butyl rubber-based rubber composition is disclosed in U.S. Pat. No. 6,962,181 which is expressly incorporated by reference herein in its entirety.
In one embodiment, the uncured butyl rubber-based rubber composition may include a peroxide and a dispersion therein of a particulate precured rubber selected from pre resin-cured butyl rubber. In one example, based upon parts by weight per 100 parts by weight of said butyl rubber, the butyl rubber-based rubber composition can include a copolymer of isobutylene and isoprene, wherein the copolymer contains from about 0.5 units to about 5 units derived from isoprene, and correspondingly from about 95 weight percent to about 99.5 weight percent units derived from isobutylene. The butyl rubber that can be employed may typically have a number average molecular weight, for example, in the range of 200,000 to 500,000. Such butyl rubber and its preparation is well known to those having skill in such art.
The uncured butyl rubber composition further includes a sufficient amount of organoperoxide to cause the butyl rubber to partially depolymerize, usually in a range of from about 0.5 to about 10 phr of the active organoperoxide depending somewhat upon the time and temperature of the tire curing operation and the degree of depolymerization desired.
Various organoperoxides may be used such as those that become active (e.g. generate peroxide free radicals) at high temperatures, that is, above about 100° C. Such organoperoxides are referred to herein as active peroxides. Examples of such organoperoxides are, for example, tertbutyl perbenzoate and dialkyl peroxides with the same or different radicals, such as dialkylbenzene peroxides and alkyl pre-esters. In one example, the active organoperoxide will contain two peroxide groups. In another example, 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 active organoperoxides are, for example, 2,5-bis(t-butyl peroxy)-2,5-dimethyl hexane; 1,1-di-t-butyl peroxi-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 peroxi)-butane; di-t-butyl peroxide; benzyl peroxide; 2,5-bis(t-butyl peroxy)-2,5-dimethyl hexane, dicumyl peroxide; and 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane. Other suitable organoperoxides may be found in P. R. Dluzneski, “Peroxide vulcanization of elastomers”, Rubber Chemistry and Technology, Vol. 74, 451 (2001), which is expressly incorporated by reference herein in its entirety.
The peroxide can be added to the uncured butyl rubber composition in pure form (100 percent active peroxide) or on an inert, free-flowing mineral carrier such as calcium carbonate. Silicon oil is an inert mineral carrier often utilized for this purpose. Such carrier composition containing from about 35 weight percent to 60 weight percent active ingredient (peroxide) can be employed. For example, 40 percent by weight dicumylperoxide on an inert carrier can be employed as the peroxide vulcanizing agent in the butyl rubber composition layer.
The uncured butyl rubber-based rubber composition may further include particulate filler including about 5 phr to about 90 phr of at least one of rubber reinforcing carbon black and coal dust, or mixtures thereof, and, optionally from zero phr to 6 phr of short fibers, and/or from zero phr to about 20 phr of hollow glass microspheres. It is also to be understood that other known fillers and/or reinforcing agents, such as silica and calcium carbonate, can be substituted for part of the carbon black in this composition.
For the carbon black, various particulate rubber reinforcing carbon blacks are, for example, carbon black referenced in The Vanderbilt Rubber Handbook, 1978, Pages 408 through 417, which are characterized by iodine adsorption (ASTM D1510) and dibutylphthalate absorption (ASTM D 2414) values which are prepared by deposition from a vapor phase at very high temperatures as a result of thermal decomposition of hydrocarbons, rather than a carbonization of organic substances. Such carbon black may have an Iodine adsorption value ranging from 20 mg/g to 270 mg/g and a dibutylphthalate absorption value ranging from 60 cc/100 gms to 180 cc/100 gms. Such carbon black is composed of aggregates of elemental carbon particles of colloidal dimensions, which have a high surface area.
Coal dust, or coal fines, is carbonaceous dust from naturally occurring coal. Coal dust is of significantly greater size than rubber reinforcing carbon black, is not rubber reinforcing in the sense of rubber reinforcing carbon black, and represents a significantly lower cost filler than rubber reinforcing carbon black. The coal dust can be used in greater quantities (concentration) in the butyl rubber composition without significantly adversely affecting the processing of the composition, yet being beneficial to aid in the efficiency of the puncture sealing ability of the resultant built-in sealant layer 22. Further, the coal dust is considered herein useful in promoting adjustment of the storage modulus (G′) property of the sealant.
The short fibers may be selected from, for example, cotton fibers and from synthetic fibers selected from rayon, aramid, nylon and polyester fibers, or mixtures thereof. Such cotton short fibers may have an average length, for example, in a range of up to about 200 microns (e.g. an average length of about 150 microns) and the synthetic (e.g. the polyester and nylon fibers) may have an average length, for example, of up to a maximum of about 2,500 microns. The short fibers are considered herein to promote adjustment of a G′ property of the sealant composition as well as, in relatively low concentrations, not significantly interfering with the processing of the sealant precursor composition and enhancing the efficiency of the resultant built-in sealant layer 22 and its puncture sealing ability.
Representative of the hollow glass microspheres are, for example, Scotchlite Glass Bubbles™ (S60/10000 series), having an average spherical diameter of about 30 microns, from the 3M Company. The hollow glass microspheres are considered herein to promote adjustment of a G′ property of the sealant composition as well as enhancing the puncture sealing efficiency and capability of the built-in sealant and, in relatively low concentrations, not significantly adversely affecting the processing of the sealant precursor composition.
The uncured butyl rubber-based rubber composition composition may further include from zero phr to about 20 phr of rubber processing oil, such as one having a maximum aromatic content of about 15 weight percent with a naphthenic content in a range of from about 35 weight percent to about 45 weight percent and a paraffinic content in a range of about 45 weight percent to about 55 weight percent.
The various rubber processing oils are known to those having skill in such art. In one example, the rubber processing oil has a low aromaticity content, such as less than about 15 weight percent. Such a rubber processing oil may be composed of, for example, about 35 weight percent to about 45 weight percent naphthenic content, about 45 weight percent to about 55 weight percent paraffinic content, and an aromatic content of less than about 15 weight percent (e.g. from about 10 to about 14 weight percent). It is considered herein that a representative of such rubber processing oil is Flexon 641™ from the ExxonMobil company.
The uncured butyl rubber-based rubber composition may further include from zero phr to about 10 phr of liquid conjugated diene-based polymer having a weight average molecular weight of less than 80,000 provided however, where the particulate filler is exclusively rubber reinforcing carbon black, the partially composition contains at least 1 phr of liquid diene-based polymer.
The liquid conjugated diene-based liquid polymer may be, for example, a liquid cis 1,4-polyisoprene polymer and/or liquid cis 1,4-polybutadiene polymer. It is to be appreciated that such liquid polymers for the butyl rubber precursor composition are therefore polymers that contain olefinic unsaturation and therefore are not intended to include polyisobutylene that does not contain olefinic unsaturation. A commercial liquid cis 1,4-polyisoprene polymer may be, for example, LIR 50™ from the Kuraray Company of Osaki, Japan. A liquid cis 1,4-polybutadiene polymer (absorbed on a particulate filler) may be, for example, Karasol PS-01™ from the Drobny Polymer Association.
It is considered herein that the liquid polyisoprene polymer in the butyl rubber acts to aid in regulating the storage modulus G′ of the partially depolymerized butyl rubber. For example, addition of the liquid polyisoprene polymer has been observed to provide the partially depolymerized butyl rubber composition with a somewhat increased loss modulus G′ which may be desirable for some applications.
In one example, the uncured butyl based composition can include 100 parts of a butyl rubber copolymer, about 10 to 40 parts of carbon black, about 5 to 35 parts of polyisobutylene, about 5 to 35 parts of an oil extender, about 0 to 1 part of sulfur, and from about 1 to 8 parts of a peroxide vulcanizing agent.
The polyurethane compositions for use in the resulting sealant layer 22 (and precursor sealant layer 23) may further include one or more of the additional components as discussed above, such as reinforcing filler, e.g., carbon black, silica, coal dust, fibers, or microspheres, processing oil, and other diene-based liquid polymers, for example, such as in conventional amounts. It should be understood by one having ordinary skill in the art that additional components may be included in the sealant layer 22 as desired, such as antidegradants, accelerators, etc., in conventional amounts.
The resulting built-in sealant layer 22 (and precursor sealant layer 23) may further include a colorant to provide a non-black colored built-in sealant layer having the capability of visibly identifying a puncture wound. That puncture wound may extend through a black colored rubber inner liner layer, black colored rubber tire tread, and/or black colored sidewall layer to the built-in sealant layer by a physical flow of a portion of the non-black colored built-in sealant layer through the puncture wound to form a contrastingly non-black colored sealant on a visible surface of the black colored inner liner, tread, or sidewall.
The colorant may include titanium dioxide. For example, the colorant of the sealant layer 22 may be titanium dioxide where a white colored sealant layer is desired. Also, such colorant may include titanium dioxide as a color brightener together with at least one non-black organic pigment and/or non-black inorganic pigment or dye. Various colorants may be used to provide a non-black color to the sealant layer 22. Representative of such colorants are, for example, yellow colored colorants as Diarylide Yellow™ pigment from Polyone Corporation and Akrosperse E-6837™ yellow EPMB pigment masterbatch with an EPR (ethylene/propylene rubber) from the Akrochem Company.
The various components of the precursor sealant layer 23, prior to building the tire 10, can be mixed together using conventional rubber mixing equipment, particularly an internal rubber mixer. The butyl rubber and polyurethane composition used in the precursor sealant layer 23 generally has sufficient viscosity and enough unvulcanized tack to enable its incorporation into an unvulcanized tire without substantially departing from standard tire building techniques and without the use of complicated, expensive tire building equipment.
Material permitting, the precursor sealant layer 23, prior to building of the tire 10, may be formed into sheet stock that can be cut into strips and then positioned on a tire building apparatus 30, such as a tire drum, during the tire build-up process. The tire building process is described in detail further below.
The rubber tire inner liner 20 may be any known rubber inner liner for use in pneumatic tires 10. In one example, the rubber inner liner 20 can be a sulfur curative-containing halobutyl rubber composition of a halobutyl rubber such as for example chlorobutyl rubber or bromobutyl rubber. Such tire halobutyl rubber based inner liner layer may also contain one or more sulfur curable diene-based elastomers such as, for example, cis 1,4-polyisoprene natural rubber, cis 1,4-polybutadiene rubber and styrene/butadiene rubber, or mixtures thereof. The inner liner 20 is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of appropriate width, which is sometimes referred to as a gum strip. When the tire 10 is cured, the inner liner 20 becomes an integral, co-cured, part of the tire 10. Tire inner liners and their methods of preparation are well known to those having skill in such art.
The tire carcass 16 generally may be any conventional tire carcass for use in pneumatic tires 10. Generally, the tire carcass 16 includes one or more layers of plies and/or cords to act as a supporting structure for the tread portion 14 and sidewalls 12. The remainder of the tire components, e.g., tire tread 14, sidewalls 12, and reinforcing beads 18, also generally may be selected from those conventionally known in the art. Like the tire inner liner 20, the tire carcass 16, tire tread 14, and beads 18 and their methods of preparation are well known to those having skill in such art.
The pneumatic tire of
With continuing reference to
The rubber inner liner 20 is then positioned on the precursor sealant layer 23, which is followed by the tire carcass 16. Finally, the rubber tire tread 14 is positioned on the tire carcass 16 thereby defining unvulcanized tire assembly 10a.
After the unvulcanized pneumatic tire 10a is assembled, the tire 10a is shaped and cured using a normal tire cure cycle. After curing, the composition of the precursor sealant layer 23 is gel-like and tacky which provides the pneumatic tire 10 with self-sealing properties and defines the built-in sealant layer 22.
Generally, the tire 10a can be cured over a wide temperature range. For example, passenger tires might be cured at a temperature ranging from about 130° C. to about 170° C. and truck tires might be cured at a temperature ranging from about 150° C. to about 180° C. Thus, a cure temperature may range, for example, from about 130° C. to about 180° C. and for a desired period of time. In one example, the tire assembly 10a is cured in a suitable mold at a temperature in a range of from about 150° C. to about 175° C. for a sufficient period of time such as to partially depolymerize the butyl rubber or thermally degrade non-flowing polyurethane that is neither gel-like nor substantially tacky, for example, thereby forming the built-in sealant layer 22 which has puncture sealing properties. After curing, the gas permeable layer 24 is securely attached to the built-in sealant 22.
Non-limiting examples of test pieces of the pneumatic tire 10 with built-in sealant 22 in accordance with the detailed description are now disclosed below. These examples are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Other examples will be appreciated by a person having ordinary skill in the art.
Three pneumatic tire test pieces were prepared for testing. Each test piece is described below.
Test Piece No. 1
Test Piece No. 2
Test Piece No. 3
Control Test Piece
Concerning test piece nos. 1 and 2, the non-woven polyester and nylon sheets were obtained from 3M of St. Paul. Minn. Each sheet was prepared by a melt blown process. The butyl based composition used for the precursor sealant layer in test piece nos. 1 and 2, and in the control is set forth below in Table I. The composition was prepared in a two-step process with the butyl rubber and the specified ingredients being mixed in a first non-productive step. In a second step, peroxide was mixed into the butyl rubber mixture. Concerning test piece no. 3, the non-woven polyester sheet was obtained from Nolar Industries Limited of Ontario, Canada, and the polyurethane based precursor sealant layer was Tyrlyner®, a gel-like and tacky polyurethane composition, obtained from Hyperlast North America of Chattanooga, Tenn.
1Yellow pigment, Akrochem E-6837
2Link-Cup ® NBV40C available from GEO Specialty Chemicals of Gibbstown, NJ; chemical name: n-butyl-4,4-di(tert-butylperoxy)valerate, 40% supported on calcium carbonate
The cured test pieces were tested to evaluate puncture sealing effectiveness. In the testing process, each test piece was secured lengthwise across an open chamber of a box, which defined a benchtop nail hole tester, to generally seal the opening to the chamber. Test piece nos. 1, 2, and 3 were situated so that the innermost gas permeable layer faced the open chamber and the tire tread faced outwardly. The control was situated so that the inner liner faced the open chamber and the tire tread faced outwardly. In the chamber, air pressure could be established via an inlet valve, maintained, and monitored to simulate a pressurized pneumatic tire. A nail was used to manually puncture the test piece. Each test piece was subjected to puncturing by nails of varying and increasing diameter to evaluate air pressure loss after nail insertion, removal, and reinflation (if needed). Air pressure readings at each step were taken after a two-minute period. The results of the puncture sealing testing are set out in Table 11 below.
Based upon the test results, the puncture sealing properties of test pieces nos. 1-3 are at least as good as the control. Specifically, the test results showed that test pieces 1 and 2, and the control could seal nail holes up to 0.176″ in diameter by maintaining air pressure after reinflation to the initial starting air pressure. Test piece no. 3, which utilized the polyurethane composition Tyrlyner®, could seal nail holes up to at least 0.235″ in diameter by maintaining initial air pressure after nail removal. In other words, reinflation of test piece no. 3 was not required.
Test piece nos. 1, 2, and 3, and the control were also placed in an oven at 150° C. for 15 minutes to test for blister formation. Each test piece was then removed from the oven and visually observed. Blister formation was not detected in test piece nos. 1, 2, and 3. However, the control showed heavy blister formation in the innermost inner liner. This suggested that the non-woven materials could bleed therethrough volatile material formed from thermal degradation of the butyl rubber based sealant and polyurethane composition thus preventing blister formation.
Accordingly, there is provided a pneumatic tire 10 that has an ability to seal against various puncturing objects and can eliminate or reduce inner liner blister formation in the tire 10.
While the present invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative product and method and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.
