Patent Application
20070272336
The embodiments of the present invention shall be explained below in details.
The leg part rubber (numeral 8 shown in the drawing) of the supporter for a run-flat tire according to the present invention is characterized by comprising a rubber composition comprising a rubber component containing 60 mass parts or more of a conjugate diene base rubber per 100 mass parts of the rubber component.
In the production of the supporter according to the present invention, a metallic flat plate is molded into, for example, a form shown in
A material used for the metallic flat plate includes iron, high tension steel, stainless steel, aluminum and the like.
Synthetic resin base, phenol resin base and silicone base adhesives for rubber are preferably used as the adhesive used for adhering the supporting part and the leg part rubber.
When the leg part rubber comprises a rubber composition comprising a rubber component containing less than 60 mass parts of a conjugate diene base rubber per 100 mass parts of the rubber component, an effect (impact resistance) of absorbing impact coming from a run-flat supporter in run-flat running is inferior, and therefore it is not preferred. Accordingly, a compounding amount of the conjugate diene base rubber in the leg part rubber is preferably 60 mass parts or more, most preferably 100 mass parts per 100 mass parts of the rubber component. The leg part rubber comprising the rubber component containing 60 mass parts or more of the conjugate diene base rubber per 100 mass parts of the rubber component makes it possible to concurrently actualize improvement in adhesiveness to the metal-made run-flat supporting part and improvement in durability of the rubber.
A supporter having the leg part rubber described above is referred to as the first embodiment of the present invention.
To be more specific, the conjugate diene base rubber described above is preferably isoprene rubber or natural rubber. Performances which the leg part rubber of the supporter for a run-flat tire is endowed with include that it can stably support the supporter for a run-flat tire in run-flat running and that it has to be endurable against impact from the above supporter. Isoprene rubber and natural rubber are the principal constitutional elements of the leg part rubber of the supporter of the present invention because of the most excellent fracture resistance thereof, and the supporter having the leg part rubber is referred to as the second embodiment of the present invention.
When the leg part rubber of the supporter for a run-flat tire does not satisfy the second embodiment of the present invention, that is, when a leg part rubber does not comprise a rubber composition comprising a rubber component containing 60 mass parts or more of the conjugate diene base rubber per 100 mass parts of the rubber component, the effects (elastic modulus and tensile strength (TB)) of the present invention can not be exhibited. Natural rubber and isoprene base rubber have a large tensile strength (TB) and are excellent in low heat build-up, and therefore they are the most suitable material for the leg part rubber of the present invention. On the other hand, SBR which is a synthetic rubber has a large loss tangent (tan δ) and is inferior in low heat build-up, and as a result thereof, time spent until reaching a temperature limit is short. Further, BR has small TB as compared with those of natural rubber and isoprene base rubber, and therefore they are a little inferior in performances as a rubber component for the leg part rubber of the supporter of the present invention.
The rubber composition for leg part rubber in the first or second embodiment of the present invention described above may be blended with sulfur of less than 4 mass parts per 100 mass parts of the rubber component, and the above constitution is referred to as the third embodiment of the present invention. It is a matter of course that sulfur is blended for the purpose of vulcanization, and since a sulfur blending amount of 4 mass parts or more enhances an elastic modulus of the rubber composition, the leg part rubber is improved in an impact absorbing property, but reduction in the deterioration resistance which is indispensable to the leg part rubber is brought about. Accordingly, it is not preferred.
In the fourth embodiment of the present invention, the supporter is described in any of the first to third embodiments described above, and it is characterized by that the leg part rubber has a tensile strength (TB) of 18 MPa or more before commencement of use, that is, in an unused state. This is prescribed as a tensile strength (TB) which the leg part rubber of the supporter for a run-flat tire is expected to be provided with at least before starting run-flat running. If the tensile strength (TB) before commencement of use, that is, in an unused state is 18 MPa or more, safety and durability of the supporter of the present invention are secured. The tensile strength (TB) before commencement of use, that is, in an unused state is more preferably 19 MPa or more, further preferably 21 MPa or more. If the above tensile strength (TB) is less than 18 MPa, it is difficult to sufficiently endure severe run-flat running, and the rubber composition is not suited as the leg part rubber of the supporter of the present invention.
In the fifth embodiment, the supporter is described in any of the first to fourth embodiments described above, and it is the supporter characterized by that the leg part rubber has a tensile strength (TB) of 11 MPa or more after left standing at a temperature of 100° C. for 6 days in the air. The leg part rubber of the supporter for a run-flat tire is estimated to be heated at a temperature of 100° C. or higher at lowest by run-flat running, and therefore the above range is a requisite imposed to the leg part rubber as durability required in order to endure impact exerted from a road surface via the supporter at 100° C. which is assumed to be the lowest in the run-flat running. If the tensile strength (TB) after left standing at a temperature of 100° C. for 6 days in the air is 11 MPa or more, a safety performance of the leg part rubber of the supporter for a run-flat tire is high. If the above tensile strength (TB) is less than 11 MPa, cracks are produced in the rubber at an end stage of running to make it difficult to sufficiently endure severe run-flat running further longer distance, and therefore that is not suited as the leg part rubber of the supporter of the present invention. In the leg part rubber of the supporter of the present invention, the above tensile strength (TB) is more preferably 13 MPa or more, further preferably 15 MPa or more.
The sixth embodiment is the supporter described in any of the first to fourth embodiments described above, and it is the supporter characterized by that the leg part rubber has a dynamic modulus of elasticity (E′, in 1% distortion) of 5 MPa or more at 24° C. before commencement of use, that is, in an unused state and a dynamic modulus of elasticity (E′, in 1% distortion) of 4 MPa or more after left standing at a temperature of 100° C. for 6 days in the air. The leg part rubber of the supporter for a run-flat tire undergoes periodically impact from a road surface via the supporter in run-flat running, and the above range is prescribed in order to endure the impact. The above leg part rubber of the sixth embodiment secures the performances of the supporter of the present invention and can sufficiently endure severe run-flat running. The leg part rubber of the sixth embodiment has more preferably a dynamic modulus of elasticity (E′, in 1% distortion) of 13 MPa or more at 24° C. before commencement of use, that is, in an unused state and a dynamic modulus of elasticity (E′, in 1% distortion) of 8 MPa or more after left standing at a temperature of 100° C. for 6 days in the air.
The seventh embodiment is the supporter described in any of the first to sixth embodiments described above, and the leg part rubber is characterized by having a loss tangent (tan δ, in 1% distortion) of 0.30 or less at 24° C. before commencement of use, that is, in an unused state and a loss tangent (tan δ, in 1% distortion) of 0.30 or less after left standing at a temperature of 100° C. for 6 days in the air. The larger the loss tangent is, the higher the heat build-up grows, and the more quickly the rubber reaches a temperature limit, so that the durability is reduced. That is, the loss tangent is prescribed from the viewpoint of the low heat build-up which is expected to be endowed. The leg part rubber of the present invention has more preferably a loss tangent (tan δ, in 1% distortion) of 0.25 or less at 24° C. before commencement of use, that is, in an unused state and a loss tangent (tan δ, in 1% distortion) of 0.25 or less after left standing at a temperature of 100° C. for 6 days in the air, and the above values are further preferably 0.20 or less and 0.15 or less respectively.
The second invention is a run-flat tire comprising the supporter in the first to seventh embodiments described above. The run-flat tire of the present invention is a run-flat tire equipped with the supporter in the first to seventh embodiments described above, and therefore it is excellent in safety and a run-flat running property as a run-flat tire.
The natural rubber component constituting the leg part rubber of the supporter in the first to seventh embodiments described above shall not specifically be restricted, and NR RSS#4 can suitably be used. Further, the conjugate diene base rubber component other than natural rubber shall not specifically be restricted, and IR can suitably be used, and further SBR 1500, BR01 and the like can also be used.
The leg part rubber of the supporter of the present invention may be blended with carbon black. Carbon black which may be blended is particularly preferably FEF and/or HAF from the viewpoint of the reinforcing property and the elasticity (dynamic modulus of elasticity). However, blending of carbon black with the rubber composition leads to, on the other hand, bringing about reduction in workability and degradation in the heat build-up. Accordingly, a blending amount of carbon black is preferably 30 to 70 mass parts per 100 mass parts of the rubber component, and a blending amount of exceeding 90 mass parts is not preferred
The leg part rubber of the supporter of the present invention may further contain spindle oil, antioxidants and heat stabilizers, waxes, zinc oxide, stearic acid, vulcanization accelerators, DCPD resins and the like as optional compounding ingredients. In this case, the amounts (mass parts) of the above optional ingredients which may be contained in the rubber composition constituting the leg part rubber are preferably 0 to 5 mass parts for spindle oil, 0 to 3 mass parts for antioxidants and heat stabilizers, 0 to 5 mass parts for waxes, 3 to 5 mass parts for zinc oxide, 1 to 5 mass parts for stearic acid, 0.5 to 3 mass parts for vulcanization accelerators and 0 to 5 mass parts for DCPD resins each per 100 mass parts of the rubber component.
The constitutions and the effects of the present invention shall be specifically shown below with reference to examples. The present invention shall by no means be restricted to the following examples.
Rubber compositions having recipe ratios shown in the following Table 1 were prepared. NR RSS#4 as a natural rubber component, SBR1500, BR01 or IIR as a synthetic rubber component blended with the natural rubber component, FEF or HAF as carbon black, in addition thereto, spindle oil, a heat stabilizer (Nonflex RD), an antioxidant (Nocrac 6C), wax, zinc oxide, stearic acid, a vulcanization accelerator (Nocceler CZ), sulfur and a DCPD resin were kneaded by means of a Banbury mixer and vulcanized at 145° C. for 30 minutes. The rubber compositions A to F thus obtained were used to produce run-flat tires, and the following performances of the run-flat tires were evaluated. The respective rubber compositions A to F obtained were measured for a dynamic modulus of elasticity, a loss tangent and a tensile strength by methods shown below.
A sheet having a width of 150 mm and a length of 150 mm was cut out from a slab sheet having a thickness of 2 mm obtained by vulcanizing the rubber composition under the conditions of 160° C. and 15 minutes to prepare a measuring sample. This sample was measured for a dynamic modulus of elasticity (E′) and a loss tangent (tan δ) by means of a spectrometer manufactured by Ueshima Seisakusho Co., Ltd. under the conditions of a chuck to chuck distance of 10 mm, an initial distortion of 200 μm, a dynamic distortion of 1%, a frequency of 52 Hz, a measurement initiation temperature of 24° C., a heating speed of 3° C./minute and a measurement termination temperature of 250° C.
A tensile test was carried out based on JIS-K-6251 using a JIS No. 3 test piece to measure a tensile strength (TB) at break at 24° C.
The rubber composition described above was used for a leg part rubber of a supporter for a run-flat tire to produce a radial tire of a size 235/55R18 for passenger cars having the structure shown in
Each trial tire was mounted in a rim at an atmospheric pressure and charged with air to an inner pressure of 230 kPa, and then it was left standing at a room temperature of 38° C. for 24 hours. Thereafter, a core of the valve was drawn to reduce the inner pressure to an atmospheric pressure, and the tire was subjected to a drum running test under the conditions of a load of 4.17 kN (425 kg), a speed of 89 km/h and a room temperature of 38° C. In the above test, a distance traveled until troubles were caused was measured and shown by an index with a distance in Comparative Example 2 set to 100, and the index was set as a barometer of the run-flat durability. It is shown that the larger the index value is, the better the run-flat durability is. Results obtained by testing the run-flat durability of the run-flat tires are shown in the following Table 1.
As can be seen from the results shown in Table 1 described above, satisfactory evaluation of the run-flat durability could not be obtained from the run-flat tires using the leg part rubbers of a supporter in which the rubber component in the rubber composition does not contain the prescribed amount of the conjugate diene base rubber.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-143670 | May 2006 | JP | national |
