Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-06-23
2002-04-23
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S265000, C524S269000, C524S496000, C524S508000
Reexamination Certificate
active
06376587
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a rubber composition for a tire tread which can reduce rolling resistance (RR) to improve the fuel consumption without impairing the braking performance and the turning performance of an automobile on a wet (WET) road surface, and a pneumatic tire using said rubber composition.
(2) Description of the Prior Art
Recently, the fuel consumption of automobiles has been highlighted as an environmental problem due to the exhaust gas control of automobiles.
To improve the fuel consumption, it is known that reduction of the rolling resistance is effective. A main factor of the rolling resistance is the internal friction of a material forming a tire, and the internal friction of respective parts such as a tread, a side wall, a carcass and an inner liner can be involved. Among them, a tread is most contributive. Therefore, it is most effective for the reduction of the rolling resistance to reduce a strain energy loss due to compression of the compounded rubber for a tread, bending shear and the like.
Since the rolling resistance correlates largely with a loss tangent (tan &dgr;) at 60° C., it is necessary to decrease this value of the rubber composition for improving the fuel consumption.
Heretofore, as the technique for decreasing tan &dgr; at 60° C., for example, attention is given to carbon black as a reinforcing agent which is blended in a rubber composition for a tread, and there have been known such methods that carbon black to be blended is simply reduced, or that the grade of carbon black to be used is lowered, that is, carbon black having a large particle diameter, for example, the one having a nitrogen absorption specific surface area (N
2
SA) of about 90 m
2
/g is used.
In addition to this, improvement of polymers has been tried. Considering other performance required for a tire, however, satisfactory effects have not always been obtained with these combinations.
Furthermore, there can be combined a method in which silica or a silane coupling agent are used together in the reinforcing agent to be blended and they are used in an amount of from 0 to 100% by weight relative to the total amount of the reinforcing agent. However, it is not a satisfactory level for all the required performance.
On the other hand, there has been conventionally known a rubber composition for a tire tread in which carbon black and silica are blended in a specific amount per 100 parts by weight of diene based rubber components containing styrene-butadiene rubber so that tan &dgr; (at 60° C.) is sufficiently lowered to reduce the rolling resistance, and tan &dgr; (at 0° C.) becomes adequately large to improve wettability. However, a recent higher level requirement for braking and turning performance cannot be satisfied with such formation. In this case, the problems are present in block rigidity and a contact area, and there is a problem that if they are not secured sufficiently, the braking and turning performance peculiar to the composition cannot be exerted.
To secure the block rigidity, the dynamic modulus (E′) has to be increased. To increase E′, the reinforcing agent is increased, or the crosslinking density is increased. However, the increase of the reinforcing agent has a problem that it unnecessarily increases tan &dgr; (60° C.) to make the rolling resistance worse. Moreover, the increase of the crosslinking density increases the tensile stress (M300, RT: under room temperature). As a result, there are such problems that a pressure at the contact surface between the tread and a road is not uniform and thus satisfactory braking and turning performance is not exerted.
SUMMARY OF THE INVENTION
With a view to solving the above problems, an object of the present invention is to provide a rubber composition for a tire tread which can reduce the rolling resistance (RR) to improve the fuel consumption without impairing the braking performance and the turning performance of an automobile on a wet road surface, and a pneumatic tire using said rubber composition.
The present inventor made an intensive investigation on the above described problems, and succeeded in obtaining the intended rubber composition for a tire tread and a pneumatic tire using said rubber composition, by blending a specific resin and the like as well as a specific rubber component, carbon black and silica in a specific amount to form a rubber composition and by specifying characteristic values of the rubber composition.
Namely, the present invention comprises the following constitutions (1) to (2):
(1) a rubber composition for a tire tread comprising: per 100 parts by weight of a diene based rubber component containing at least 50 parts by weight of styrene-butadiene rubber,
a) 5 to 50 parts by weight of carbon black having a nitrogen absorption surface area (N
2
SA) of from 90 to 180 m
2
/g and an oil-absorbing amount of dibutylphthalate (DBP) of from 100 to 170 ml/100 g;
b) 5 to 50 parts by weight of silica,
c) wherein the total amount of said carbon black and silica is from 30 to 90 parts by weight; and
d) 5 to 20% by weight of a silane coupling agent relative to the blended amount of silica;
e) 1 to 15 parts by weight of a thermoplastic (novolac type) phenol resin; and
f) 5 to 20% by weight of hexamethylenetetramine relative to the blended amount of resin, wherein tan &dgr; at 60° C., tan &dgr; at 0° C., dynamic modulus E′ at 30° C., and tensile stress at the time of extending 300% (M300) at 25° C. of the rubber composition are tan &dgr; (60° C.)≦0.14, tan &dgr; (0° C.)≧0.50, dynamic modulus E′ (30° C.)≧1.2×10
7
pa and tensile stress at the time of extending 300% (M300) (25° C.)≦9.5 Mpa, respectively;
(2) a rubber composition for a tire tread as described in the above item (1), wherein the styrene-butadiene rubber is a solution polymerized styrene-butadiene rubber;
(3) a rubber composition for a tire tread as described in the above item (1), wherein the nitrogen absorption surface area (N
2
SA) of carbon black is from 100 to 140 m
2
/g and the oil-absorbing amount of dibutylphthalate (DBP) is from 110 to 150 ml/100 g;
(4) a rubber composition for a tire tread as described in the above item (1), wherein the nitrogen absorption surface area (N
2
SA) of silica is from 100 to 300 m
2
/g;
(5) a rubber composition for a tire tread as described in the above item (1), wherein the thermoplastic (novolac type) phenol resin is an alkyl-substituted phenol resin;
(6) a rubber composition for a tire tread as described in the above item (1), wherein the thermoplastic (novolac type) phenol resin is an oil-modified phenol resin; and
(7) a pneumatic tire using the rubber composition for a tire tread as described in any of the above items (1) to (6) for at least a portion of the tread rubber which is brought into contact with the road surface.
According to the present invention, there are provided a rubber composition for a tire tread which can reduce rolling resistance (RR) to improve the fuel consumption without impairing the braking performance and the turning performance of an automobile on a wet road surface, and a pneumatic tire using the rubber composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will now be described in detail.
As the rubber component used for the rubber composition for a tire tread (hereinafter referred to as “rubber composition”) of the present invention, it has to be a diene based rubber component containing at least 50 parts by weight of styrene-butadiene rubber (SBR) per 100 parts by weight of the whole rubber component.
In the present invention, the reason why SBR is contained in an amount of at least 50 parts by weight per 100 parts by weight of the whole rubber component is to attain excellent WET braking performance and turning performance by obtaining desired grip force. If the SBR is outside the above-mentioned range, that is, less than 50 parts by weight, the desired grip force cannot be obtained, hence the WET braking performance and t
Ajiro Yukitoshi
Yagawa Kazuo
Bridgestone Corporation
Mulcahy Peter D.
Sughrue & Mion, PLLC
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