Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-03-26
2001-03-13
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S236000, C524S240000, C524S251000, C524S252000, C524S571000, C524S575500
Reexamination Certificate
active
06201049
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rubber composition for tire sidewall.
BACKGROUND ART
Hitherto, an antioxidant, a wax and the like have been contained in a rubber composition for tire sidewall to prevent cracking caused by ozone. As the antioxidant, an antioxidant containing N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD) or N-(1,3-dimethylbutyl)-N′-phenyl-phenylenediamine (6PPD) is employed in general and, as the wax, a petroleum wax which contains a component having about 20 to 50 carbon atoms and has an average number of carbon atoms of 30 to 35 is employed in general.
IPPD and 6PPD can provide tire sidewall with superior ozone resistance. However, there is the problem that the surface of the tire sidewall is discolored to a brown color, thereby causing a deterioration of in tire appearance.
Also, the wax is used for improving ozone resistance since the wax blooms to form a film on the surface of tire sidewall. There is a problem, however, that the surface of tire sidewall can be discolored to white when the wax blooms excessively.
For example, in JP-A-63-10646 and JP-A-63-162738, there is disclosed a technology to prevent such deterioration of tire appearance caused by brown discoloration with the use of, as an antioxidant, a compound represented by the general formula:
wherein R and R′ are independently a hydrogen atom or an alkyl, and the sum of carbon atoms of R and R′ is 8 to 19.
There is not disclosed, however, a technology to prevent white discoloration caused by excess bloom of the wax.
Considering the above-mentioned facts, an object of the present invention is to provide a rubber composition which is superior in ozone resistance and is resistant to brown and white coloration.
SUMMARY OF THE INVENTION
The present invention relates to a rubber composition for a tire sidewall obtained by blending 0.5 to 2.5 parts by weight of a wax which contains a component having 45 or more carbon atoms and has an average number of carbon atoms of 28 to 38, and 3.0 to 7.0 parts by weight of an antioxidant containing 30 to 100% by weight of N-(1-methylheptyl)-N′-phenyl-p-phenylenediamine per 100 parts by weight of a rubber component comprising a diene rubber.
In such a case, it is preferable that the rubber component contains 50 to 80% by weight of butadiene and the rubber composition is obtained by further blending therein 0.8 to 1.8 parts by weight of sulfur and an accelerator in an amount satisfying the equation of a weight ratio of sulfur/accelerator=1.5 to 6.0 per 100 parts by weight of the rubber component.
DETAILED DESCRIPTION
The present invention relates to a rubber composition for tire sidewall obtained by blending 0.5 to 2.5 parts by weight of a wax which contains a component having 45 or more carbon atoms and has an average number of carbon atoms of 28 to 38, and 3.0 to 7.0 parts by weight of an antioxidant (antiozonant) containing 30 to 100% by weight of N-(1-methylheptyl)-N′-phenyl-p-phenylenediamine per 100 parts by weight of a rubber component comprising a diene rubber.
The diene rubber constituting the rubber component in the present invention may be a diene rubber employed conventionally in the field of tire. As the diene rubber, there are, for example, natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR) and the like. The diene rubbers may be used alone or in optional admixture of two or more. Among them, combination use of NR and BR is particularly preferable from the viewpoint of cut growth resistance.
Particularly when BR is used, an amount thereof is preferably 50 to 80% by weight of the rubber component, further preferably 55 to 70% by weight of the rubber component from the viewpoint of compatibility between cut growth resistance and kneading and extruding processability.
In the present invention, a wax which contains 3 to 10% by weight of a component having 45 or more carbon atoms and has an average number of carbon atoms of 28 to 38 is used from the viewpoint of compatibility between cut growth resistance and prevention of white discoloration. Further, a wax which contains 5 to 10% by weight of a component having 45 or more carbon atoms and has an average number of carbon atoms of 34 to 37 is preferably used from the viewpoint of prevention of white discoloration during storage.
As such wax, there is, for example, OZOACE 0355 (component having 45 or more carbon atoms: 9% by weight, average number of carbon atoms: 36, commercially available from Nippoin Seiro Co., Ltd.).
Also, a plurality of different kinds of waxes may optionally be used in optional admixture. In this case, a total amount of components having 45 or more carbon atoms and an average number of carbon atoms with respect to the whole wax admixture are within the above-mentioned ranges.
The antioxidant of the present invention contains 30 to 100% by weight of N-(1-methylheptyl)-N′-phenyl-p-phenylenediamine (8PPD) from the viewpoint of compatibility between ozone crack resistance and prevention of brown discoloration, and preferably contains 30 to 60% by weight of 8PPD from the viewpoint of initial ozone crack resistance.
Also, as the component other than 8PPD which the antioxidant can contain, there are, for example, compounds described as PPD type antioxidants in JP-A-63-10646 and JP-A-63-162738. As 8PPD, for example, OZONONE 35 commercially available from SEIKO CHEMICAL CO., LTD. can be suitably used in the present invention.
A plurality of different kinds of antioxidants may be also optionally used, in admixture. In this case, the 8PPD content in the entire antioxidant admixture may be within the above-mentioned range.
The rubber composition for tire sidewall of the present invention is obtaind by blending together the above-mentioned rubber component, wax and the antioxidant. As the mixing ratio thereof, 0.5 to 2.5 parts by weight of the wax and 3.0 to 7.0 parts by weight of the antioxidant are blended with 100 parts by weight of the rubber component from the viewpoint of compatibility between ozone crack resistance and the prevention of white and brown discoloration. Preferably, 0.5 to 1.5 parts by weight of the wax and 3.0 to 6.0 parts by weight of the antioxidant are blended together from the viewpoint that white discoloration during storage is inhibited and brown discoloration during usage is prevented.
In the present invention, further to the above-mentioned components, sulfur and an accelerator are preferably blended therewith. Particularly when the rubber component contains 50 to 80% by weight of butadiene, sulfur is preferably blended in an amount of 0.8 to 1.8 parts by weight and the accelerator is preferably blended in an amount satisfying the equation of a weight ratio of sulfur/accelerator=1.5 to 6.0 per 100 parts by weight of the rubber component from the viewpoint of ozone crack resistance. In the case where the amount of sulfur is less than 0.8 parts by weight and a ratio of sulfur to the accelerator is less than 1.5, it is not preferable because the amount of the polysulfide bond which relaxes distortion of the tire caused by external force becomes lower, and it is disadvantageous for ozone resistance. On the other hand, when the amount of sulfur is higher than 1.8 parts by weight and the ratio of sulfur to the accelerator is higher than 6.0, it is not preferable because the crosslinking density becomes too high and the blooming rates of the antioxidant and the wax become extremely lower.
Further preferably, sulfur is blended in an amount of 0.8 to 1.3 parts by weight and the accelerator is blended in an amount satisfying the equation of a weight ratio of sulfur/accelerator=1.5 to 4.0 per 100 parts by weight of the rubber component from the viewpoint of stabilizing the ozone crack resistance during the use of the tire. In this case, if an amount of sulfur is not higher than 1.3 parts by weight and the ratio of sulfur to the accelerator is not higher than 4.0, changes in the physical properties of the tire after its use, which is caused by
Kawase Masato
Kotani Marina
Mizuno Yoichi
Sakamoto Shuichi
Tsumori Isamu
Birch & Stewart Kolasch & Birch, LLP
Sumitomo Rubber Industries Ltd.
Zitomer Fred
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