Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-12-27
2003-06-03
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S495000
Reexamination Certificate
active
06573323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to aluminum hydroxide, and a tire tread rubber composition and a pneumatic tire employing the aluminum hydroxide. More particularly, the present invention relates to aluminum hydroxide having specific characteristics; a tire tread rubber composition having the aluminum hydroxide blended therein, which allows grip performance on a wet road surface (wet grip performance) and abrasion resistance to increase and allows rolling resistance to decrease to improve fuel efficiency; and a pneumatic tire employing the tire tread rubber composition.
2. Description of the Background Art
In recent years, in response to the demands for fuel-efficient automobiles, fuel-efficient tires with decreased rolling resistance have been developed. As a technique to decrease the rolling resistance, carbon black conventionally used as a reinforcing agent for tread rubber has been partially replaced with silica, in an effort to balance the antinomic properties of fuel efficiency and wet grip performance.
When compared to the conventional rubber composition with carbon black blended therein, however, the rubber composition with silica blended therein exhibits various problems in terms of processibility. Specifically, it easily decomposes because of high viscosity of unvulcanizate, and is poor in dimensional stability after extrusion. Thus, a tread rubber composition satisfying both the processibility and the performance has been desired.
Several techniques for improving the wet grip performance have also been proposed. One of such techniques is to increase a glass transition temperature (Tg) of a rubber component, or, to increase loss tangent (tan&dgr; value) at 0° C. Another technique is to blend carbon black of small particle size into a rubber composition with high loading. If the glass transition temperature (Tg) is increased, however, low temperature performance deteriorates and the rolling resistance increases. The rubber composition heavy-loaded with the carbon black of small particle size also suffers a disadvantage that its rolling resistance increases.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a filler for tire, and a tread rubber composition and a pneumatic tire employing the same filler, that can solve the above-described problems by allowing wet grip performance and abrasion resistance to increase, rolling resistance to decrease for improvement of fuel efficiency, and achieving superior processibility at the same time.
According to an aspect of the present invention, aluminum hydroxide is provided which has a loosed bulk density of not more than 0.60 g/cm
3
, a DOP oil absorption of at least 70 cm
3
/100 g and less than 250 cm
3
/100 g, and a BET specific surface area of at least 30 m
2
/g and not more than 350 m
2
/g. Particularly, the loosed bulk density of at least 0.10 g/cm
3
and not more than 0.35 g/cm
3
is preferable.
The aluminum hydroxide preferably has a crystal structure of boehmite type, having a crystal size of boehmite (002) plane of at least 5 nm and not more than 20 nm.
According to another aspect of the present invention, a tire tread rubber composition is provided which is obtained by blending and kneading 5-150 parts by weight of the aluminum hydroxide as described above with 100 parts by weight of a rubber component.
The rubber component is preferably composed of at least 20 parts by weight of styrene-butadiene rubber having a glass transition temperature (Tg) of not more than −27° C. and at least 20 parts by weight of diene type rubber including at least one kind of rubber selected from natural rubber, polyisoprene rubber and polybutadiene rubber. In the tire tread rubber composition, 5-60 parts by weight of carbon black having a BET specific surface area of at least 60 m
2
/g is preferably blended with respect to 100 parts by weight of the rubber component. Further, in the tire tread rubber composition, 2-20% by weight of silane coupling agent is preferably blended with respect to the weight of the aluminum hydroxide.
Alternatively, the tire tread rubber composition may employ a rubber component that includes at least 60 parts by weight of styrene-butadiene rubber having a styrene content of 20-60% by weight. 10-100 parts by weight of carbon black having a BET specific surface area of at least 60 m
2
/g may be added with respect to 100 parts by weight of this rubber component, and/or 2-20% by weight of silane coupling agent may be blended with respect to the weight of the aluminum hydroxide.
According to a further aspect of the present invention, a pneumatic tire is provided which employs the tire tread rubber composition as described above.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The aluminum hydroxide according to the present invention has a loosed bulk density, as measured conforming to JIS H1902, of not more than 0.60 g/cm
3
, and preferably at least 0.10 g/cm
3
and not more than 0.35 g/cm
3
. If it is greater than 0.60 g/cm
3
, abrasion resistance of the rubber composition considerably deteriorates. If it is too low, torque when kneading the aluminum hydroxide and the rubber increases, thereby degrading the workability.
Further, the aluminum hydroxide described above has a DOP oil absorption, as measure conforming to JIS K6221, of at least 70 cm
3
/100 g and less than 250 cm
3
/100 g, and preferably at least 90 cm
3
/100 g and not more than 150 cm
3
/100 g. If it is out of such a range, the rubber composition suffers degradation of its abrasion resistance.
Still further, for the purposes of achieving a rubber composition having an effect to decrease the rolling resistance and exhibiting sufficient grip performance, the aluminum hydroxide has a BET specific surface area, as measured by nitrogen adsorption, of at least 30 m
2
/g and not more than 350 m
2
/g, preferably at least 30 m
2
/g and not more than 200 m
2
/g, and more preferably more than 100 m
2
/g and not more than 200 m
2
/g. If it exceeds 350 m
2
/g, torque when kneading the aluminum hydroxide and the rubber may increase, thereby degrading the workability.
Moreover, for the purposes of further improving the grip performance, the abrasion resistance and the effect to decrease the rolling resistance of the rubber composition, the aluminum hydroxide of the present invention preferably has a crystal structure of boehmite type. More preferably, the crystal size of boehmite (020) plane is at least 5 nm and not more than 20 nm.
The crystal size was calculated as follows. Peaks of the boehmite (020) planes were measured from the profile obtained using an X-ray diffractometer. For these peaks of the crystal planes, fitting was conducted, based on the Gaussian distribution, using software for “multi-peak separation” of RINT 2100. Using the half-value width of the calculated result and the peak angle obtained by the barycentric method, the crystal size was calculated by the Scherrer's formula. The measurement conditions for the X-ray diffraction were as follows.
Measurement device: Rint-2100 V from Rigaku International Corporation.
Measurement conditions: Cu target; Voltage×Current=40 kV×40 mA; Slit: DS1°−SS1°−RS 0.3 mm; Scan mode: continuous; Scan speed=2°/min; Scan step=0.010°/step; Scan axis: 2 &thgr;/&thgr;; Scan range: 2-70°; and Rotation speed: 0 rpm.
A blended amount of the aluminum hydroxide described above is 5-150 parts by weight, preferably 5-80 parts by weight, and particularly 5-60 parts by weight, with respect to 100 parts by weight of the rubber component described above. If it is less than 5 parts by weight, the decrease of the rolling resistance by virtue of such addition is not adequate, and the grip performance against a wet road surface is improved only to a small extent. If the blended amount exceeds 150 parts by weight, viscosity of the rubber
Kikuchi Naohiko
Nippa Satoru
Ota Takeshi
Uchida Mamoru
Birch & Stewart Kolasch & Birch, LLP
Cain Edward J.
Sumitomo Rubber Industries Ltd.
Wyrozebski-Lee Katarzyna I
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