Patent Application
20110146860
The present invention is directed to a cured pneumatic tire having a built-in innermost adhesive layer co-cured and thereby integral therewith and tire post cure applied polyurethane sealant thereon.
Pneumatic tires have been suggested which contain built-in polyurethane based sealant layers which can flow into a tire puncture hole for a purpose of resisting flow of tire inflation air through the tire puncture and to thereby promote a resistance of the pneumatic tire going flat by loss of tire inflation air. For example, see U.S. Patent Application No. 2009/0078352.
Other pneumatic tires have been proposed where a polyurethane sealant is not built into the tire but is applied to an already cured tire.
However, such application of a polyurethane sealant layer to an already cured tire typically involves one or more tedious and time consuming steps such as, for example:
(A) cleaning step for a portion of the cured tire inner liner—to remove mold release compounds and/or rubber processing oil which has migrated to the rubber surface;
(B) application and drying of solvent based adhesive;
(C) application of the polyurethane sealant layer.
Accordingly, is it a significant aspect of this invention to more conveniently provide adhesion of a polyurethane sealant layer to a cured tire.
In accordance with this invention, a pneumatic tire comprises:
(A) a sulfur cured assembly comprised of an outer circumferential rubber tread, a supporting carcass, innerliner rubber layer inwardly disposed on said supporting carcass and a built-in polymeric sulfur curable thermoplastic diene-based polyurethane (TPU) adhesive layer co-cured and thereby integral therewith and disposed on and inwardly of said rubber innerliner layer as an inner surface of said sulfur cured pneumatic tire, and
(B) a polyurethane sealant layer adhered to said built-in adhesive layer of said sulfur cured pneumatic tire which provides self-sealing properties to the pneumatic tire.
In further accordance with this invention a method of preparing a pneumatic tire is comprised of:
(A) applying a polymeric adhesive layer comprised of a sulfur curable diene-based thermoplastic polyurethane (TPU) circumferentially around a tire-building apparatus to which a protective removable polymeric film has been applied to the building drum which can later be removed from the adhesive layer after curing the tire assembly,
(B) building a remainder of tire components onto the adhesive layer including a sulfur curable rubber barrier layer overlaying said diene-based polyurethane adhesive layer, a sulfur curable inner liner layer overlaying said rubber barrier layer, a tire carcass and an outer a rubber tire tread onto the tire carcass to define an unvulcanized tire assembly and removing the unvulcanized tire assembly from said building drum,
(C) sulfur vulcanizing the unvulcanized tire assembly in a suitable mold at an elevated temperature to provide a co-cured and thereby integral, adhesive diene-based polyurethane layer on said inner liner rubber layer,
(D) removing said removable protective polymeric film from said diene-based polyurethane adhesive layer to provide a clean surface for said adhesive layer,
(E) applying and adhering a polyurethane based sealant layer to said clean surface of said integral adhesive layer to provide a self-sealant property for said pneumatic tire.
By virtue of the foregoing, there is provided a pneumatic tire that has an ability to seal against various puncturing objects.
The accompanying drawings are provided for a better understanding of the invention.
In the drawings,
In
Over the co-cured polymeric adhesive layer 23 of said sulfur cured pneumatic tire 10 is a post tire cure applied (applied after the tire is cured) crosslinked polyurethane based annular sealant layer 20 adhered to said adhesive layer 23 which has a property of sealing punctures caused by various puncturing objects.
In one embodiment, the polyurethane sealant layer 20 is a polyurethane composition applied to said adhesive layer of said sulfur cured tire as a pre-formed solid, self healing, puncture sealing polyurethane layer. The pre-formed solid polyurethane layer can be a seamless tubular polyurethane or a circumferential sheet with its ends abutted together.
In another embodiment, the polyurethane sealant layer 20 is applied to said adhesive layer of said sulfur cured tire as a liquid polyurethane precursor comprised of a polyurethane reaction mixture and said liquid reaction mixture allowed to react and form a self healing puncture sealing polyurethane layer adhered to said adhesive layer. Such liquid polyurethane reaction mixture may be applied to the built-in adhesive layer of said cured tire by spin casting procedure in which, for example, the tire is spun, or rotated, around a dispensing nozzle from which the liquid reaction mixture is dispensed, or sprayed, onto the adhesive layer.
In practice, the pre-formed polyurethane sealant layer may be substantially non-flowable in a sense that a sheet of the polyurethane, for example, may contact another sheet yet be pulled apart with relative ease and still substantially maintain its original form. Such polyurethane sealant may be, for example, a reaction product of methylene diphenyl 4,4′-diisocyanate (MDI) and poly(alkylene oxide) glycol. A suitable polyurethane composition for use as the precursor sealant layer may be obtained from Novex, Inc. of Wadsworth, Ohio. A self healing polyurethane as Tireliner™ by Silverstone, Inc. can also be used. It should be understood that formulations of polyurethane 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 polyurethanes.
In practice, said polymeric adhesive layer 23 may be a sulfur curable thermoplastic polyurethane elastomeric material (TPU) as a diene-based polyurethane as, for example, 7840 TPU™ from global specialty chemicals manufacturer Sartomer Company.
It is to be appreciated that upon vulcanization of the tire assembly at an elevated temperature, the sulfur curable diene-based polyurethane (TPU) adhesive layer becomes co-cured with and thereby integral with the tire inner liner rubber layer.
Because the diene-based polyurethane (TPU) is sulfur curable, for one embodiment of the invention, the said inner liner rubber composition may be comprised of a combination of sulfur curable rubber (e.g. at least one diene-based elastomer) and said sulfur curable diene-based polyurethane (TPU).
The tire inner liner rubber layer 22 may be comprised of a conventional sulfur curable rubber inner liner for use in pneumatic tires. In one example, the rubber innerliner 22 can be a sulfur curative-containing halobutyl rubber composition of a halobutyl rubber such as for example chlorobutyl rubber or bromobutyl rubber. Such halobutyl rubber based inner liner layer may also contain one or more sulfur curable diene-based elastomers such as, for example, c is 1,4-polyisoprene natural rubber, c is 1,4-polybutadiene rubber and styrene/butadiene rubber, or mixtures thereof. The inner liner 22 is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of appropriate width. When the tire 10 is cured, the inner liner 22 becomes co-cured and thereby integral with, the tire 10. Tire inner liner rubber layers and their methods of preparation are well known to those having skill in such art.
In practice, it is considered herein that said sulfur curable inner liner rubber layer (22) may:
(A) be comprised of a combination of sulfur curable rubber and at least one of sulfur curable diene-based polyurethane and millable non diene-based polyurethane, or
(B) have a layer of sulfur curable diene-based polyurethane on its sulfur curable rubber surface adjacent to said polyurethane sealant layer (20).
This is considered herein as being significant in a sense of promoting tack and adhesion between the polyurethane sealant layer (20) and inner liner rubber layer (22) within the tire.
A millable polyurethane is a low molecular weight polyurethane which can be blended with other materials. Exemplary millable polyurethanes are, for example, available from TSE Industries, Inc.
The tire carcass generally may be any conventional tire carcass for use in pneumatic tires 10. Generally, the tire carcass includes one or more layers of cord-containing carcass plies 17 and acts as a supporting structure for the tread portion 14 and sidewalls 12. The various tire components, for example the tire tread 14, sidewalls 12, and reinforcing beads 18 may generally may be selected from those well known in the art. Like the tire inner liner 22, the tire carcass, tire tread 14, and beads 18 and their methods of preparation are well known to those having skill in such art.
The thickness of the circumferential polyurethane sealant layer 20 can vary depending somewhat upon the degree of sealing ability desired as well as the tire itself, including the tire size and intended tire use. For example, the thickness of the polyurethane sealant layer may range from about 0.13 cm (0.05 inches) to about 1.9 cm (0.75 inches) depending somewhat upon the tire itself and its intended use. For example, in passenger tires, the precursor sealant layer 20 might, for example, have a thickness in a range of about 0.33 cm (0.125 inches) whereas for truck tires, the precursor sealant layer 20 might, for example, have a thickness in a range of about 0.76 cm (0.3 inches). The post cured tire applied built-on polyurethane sealant layer 20 is generally situated in the crown region of the tire 10, and, if desired, may include colorant so that it is of a non-black color that may contrast with the black colored inner liner, tread, or sidewall so that a tire puncture can be noticed.
Generally, the tire 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.
A laminate containing a polyurethane adhesive layer (TPU) similar to
For the layered test piece, the following layers were assembled on top of the other in the following order:
(1) a 7″×7″ (17.8×17.8 cm) calendared sulfur curable rubber tread strip of about 0.1″ (0.25 cm) thickness, similar to tread (14) of
(2) a 3″×3″ (7.6×7.6 cm) wire cord reinforced sulfur curable rubber of about 0.068″ (0.17 cm) thickness, similar to one of belt plies (16) of
(3) a 7″×7″ (17.8×17.8 cm) sulfur curable synthetic cord (such as, for example polyester cord) wire reinforced rubber belt layer (aligned with the above wire reinforced rubber) of about 0.026″ (0.066 cm) thickness, similar to carcass ply (17) of
(4) a 7″×7″ (17.8×17.8) sulfur curable rubber tire inner liner of thickness of about 0.03″ (0.08 cm), similar to inner liner (22) of
(5) a 5″×5″ (12.7×12.7 cm) thin sulfur curable diene-based thermoplastic polyurethane (TPU based adhesive layer, similar to adhesive layer (23) of
(6) a 6″×6″ (15.2×15.2 cm) removable undrawn nylon 6,6 film covering said TPU polyurethane adhesive layer (20), not shown in
The above laminated test piece was cured for about 35 minutes at about 50° C. under a pressure of about 200 psi (1378 kPa).
Because the diene-based TPU polyurethane adhesive layer is sulfur curable, it participates in the sulfur curing of the composite at the interface between the sulfur curable inner liner rubber layer and the adhesive layer and is thereby sulfur cured and integral with the inner liner rubber layer.
After cooling, the nylon film was removed and a 3″×3″ (7.6×7.6 cm) polyurethane sealant layer having a thickness of 0.125″ (0.32 cm) was applied and adhered to the exposed TPU adhesive layer, similar to adhesive layer (20) of
The test piece was tested to evaluate puncture sealing effectiveness. In the testing process, the test piece was secured lengthwise across an open chamber of a box, which defined a bench top nail hole tester, to generally seal the opening to the chamber. The test piece was situated so that the innermost 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. The 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 1 below.
From Table 1 it can be seen that the layered test piece which contained the post cured polyurethane sealant layer with accompanying built-in polyurethane adhesive (TPU) layer successively sealed against punctures caused by insertion of the respective nails completely through the test piece.
A pneumatic tire was prepared similar to
The ends of the applied polyurethane sealant layer were abutted together to form a splice and a 1 inch (2.54 cm) wide strip of the TPU polyurethane adhesive applied over the splice to therefore abridge the splice for which the splice was successfully prevented from separating.
The nail hole puncture sealing ability is reported in Table 2 by nails inserted completely through the tire from the tread through the sealant layer.
From Table 2 it can be seen that the nail induced puncture hole was successfully sealed in a sense of preventing loss of air pressure.
While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.
