The present invention relates to a rubber composition and tire made
from this rubber composition. More specifically, it concerns a rubber composition
for a tire tread, with superior balance in tire processability, rolling resistance,
and wet skid performance, and a tire with a tread made from this rubber composition.
In recent years, global consciousness regarding resource and energy
conservation has risen, and in the automobile industry, research is actively being
conducted on a low fuel consumption tire with reduced rolling resistance in order
to economize fuel consumption. One effective method of reducing the rolling resistance
of a tire is the method of replacing some or all of the carbon black which has conventionally
been used as a reinforcing agent, with silica. However, as demands toward tires
rise, corresponding simply by the method of using silica is no longer satisfactory,
and there is a need for further improvement in performance.
Besides low fuel consumption, a wide range of properties is requested
in an automobile tire, such as wet skid performance, abrasion resistance, and processability,
and various ingenious attempts are being made.
For example, for the purpose of improving wet skid performance, there
is a prior art of compounding metal silicicate with the rubber composition (JP-A-2001-40143).
However, this stops short of fulfilling various other functions such as abrasion
resistance, rolling resistance and processability.
The object of the present invention is to provide a rubber composition
with superior balance in processability, rolling resistance, and wet skid performance,
and a tire made from this rubber composition.
The present invention relates to a rubber composition comprising at
least one rubber selected from the group consisting of diene rubbers and natural
rubber, and per 100 parts by weight of said rubber, 30 to 120 parts by weight of
silica, and 5 to 40 parts by weight of zirconium silicate having an average particle
diameter of at most 10 µm.
The invention also concerns a tire with a tread made from the aforesaid
The present invention is explained in detail below.
The rubber composition of the present invention comprises a rubber
component, silica, and zirconium silicate.
The aforesaid rubber component is diene rubber and/or a natural rubber.
Examples of diene rubber are for example, styrenebutadiene rubber, butadiene rubber,
isoprene rubber and the like, and mixtures of these may also be used.
Though there are no limitations as to the silica, dry process silica
(silicic anhydride), wet process silica (silicic hydrate) and the like may be used.
Of these, wet process silica is preferred. Preferable examples of wet process silica
are Ultrasil VN3 (product name) available from Degussa Co., Nipsil VN3 AQ (product
name) available from Nippon Silica Industrial Co., Ltd.
As the silica, for example, silica with a nitrogen adsorption specific
surface area (N2SA) of 50 to 300 m2 /g can be used in the
composition. When the N2SA of silica is less than 50 m2 /g,
the dispersion modifying and reinforcing effects tend to diminish, and when the
N2SA of silica exceeds 300 m2 /g, dispersion becomes poor
and the heat build-up tends to increase.
The amount of silica to be compounded is 30 to 120 parts by weight,
more preferably 40 to 90 parts by weight, most preferably 45 to 80 parts by weight,
based on 100 parts by weight of the rubber component. When the amount of silica
is less than 30 parts by weight, wet skid performance and reinforcing property diminish,
and when the amount of silica is greater than 120 parts by weight, viscosity becomes
high when kneading, and workability decreases.
It is preferable that the zirconium silicate is fine powder and the
average particle diameter is at most 10 µm, preferably at most 2 µm. When the average
particle diameter of zirconium silicate is greater than 10 µm, abrasion resistance
and cut chipping performance diminish.
The amount of zirconium silicate to be compounded is 5 to 40 parts
by weight, preferably 8 to 30 parts by weight, more preferably 10 to 20 parts by
weight, based on 100 parts by weight of the rubber component. When the amount of
zirconium silicate is less than 5 parts by weight, sufficient effects cannot be
attained, and when the amount of zirconium silicate is greater than 40 parts by
weight, abrasion resistance decreases.
In the present invention, by using silica and zirconium silicate together,
in comparison to using them alone, the effect of improved balance between abrasion
resistance, rolling resistance and wet skid performance can be attained.
In the rubber composition of the present invention, a silane coupling
agent may also be compounded in joint use with silica.
Examples of silane coupling agents include bis(triethoxysilylpropyl)tetrasulfide,
bis(triethoxysilylpropyl)disulfide, triethoxysilylpropylisocyanate, vinyltriethoxysilane,
vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacyloxypropylmethyldimethoxysilane,
γ-(polyethylene amino)-propyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane,
N'-vinylbenzyl-N-trimethoxysilylpropylethylene diamine salt and the like. Among
them, bis(triethoxysilylpropyl)tetrasulfide, bis(triethoxysilylpropyl)disulfide,
triethoxysilylpropylisocyanate and γ-mercaptopropyltrimethoxysilane are preferable.
And bis(triethoxysilylpropyl)disulfide is more preferable.
The amount of the silane coupling agent to be compounded is preferably
4 to 14 % by weight, more preferably 6 to 10 % by weight, based on the amount of
silica. When the amount of the silane coupling agent is less than 4 % by weight,
abrasion resistance and wet skid performance tend to decrease, and when the amount
of the silane coupling agent is greater than 14 % by weight, the improvement of
physical properties is small despite an increase in costs.
Furthermore, aside from the rubber component, silica, zirconium silicate
and silane coupling agent, a compounding agent which is generally used in the rubber
composition, such as carbon black, process oil, zinc oxide, wax, antioxidant, vulcanizing
agent, or vulcanization accelerator may be compounded accordingly to the rubber
composition of the present invention.
The rubber composition of the present invention is obtained by mixing
the rubber component, silica, zirconium silicate, and any other compounding agents,
as the need arises, by using the usual processing machine, such as a roll, Banbury
mixer, kneader and the like.
The tire of the present invention is prepared by using the aforesaid
rubber composition as a tire tread, according to the conventional method. Specifically,
the rubber composition, when still unvulcanized, is processed by extrusion into
the form of the tire tread, each tire part being laminated together on the tire
making machine in the conventional method, to form an unvulcanized tire. A tire
is then obtained by heating and pressurizing these unvulcanized tires in the vulcanizer.
The tire obtained in this way has an excellent balance of processability, rolling
resistance, and wet skid performance.
The present invention is explained in detail based on Examples below,
but not limited thereto. In Examples and Comparative Examples, the following materials
EXAMPLES 1 to 2 and COMPARATIVE EXAMPLES 1 to 3
Natural rubber: RSS #3
S-SBR: Nipol NS116R available from Zeon Corporation. (amount of styrene unit: 20
% by weight, amount of 1,2-diene unit: 60 % by weight)
Silica: Zeosil 1165MP available from Rhoia Co., Ltd.
Zirconium silicate: Micropacks SS available from Hakusui Tech Co., Ltd. (average
particle size: 2 µm or less in 100 %)
Silane coupling agent: Si69 available from Degussa Co.
Process oil: Diana Process AH 40 available from Idemitsu Kosan Co., Ltd.
Zinc oxide: Zinc Oxide No. 2 available from Mitsui Mining and Smelting Co., Ltd.
Wax: SUN NOC wax available from Ohuchi Shinko Kagaku Kogyo Co., Ltd.
Stearic acid: KIRI available from NOF Corporation
Antioxidant: Santoflex 13 ((N-1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine)
available from FLEXSYS CO.
Sulfur: sulfur available from Karuizawa Seirensho Kabushiki Kaisha.
Vulcanization accelerator CBS: Nocceler CZ-G (N-cyclohexyl-2-benzothiazolylsulfenamide)
available from Ohuchi Shinko Kagaku Kogyo Co. Ltd.
Vulcanization accelerator DPG: Soxinol D (diphenyl guanidine) available from Sumitomo
Chemical Co., Ltd.
The raw material rubber and materials to be compounded except for
sulfur and vulcanization accelerator were mixed by using a Banbury internal mixer,
based on the compounding recipe shown in Tables 1 and 2. Sulfur and vulcanization
accelerator were then added to the obtained masterbatch on an open roll to prepare
the rubber composition for the tire tread. Subsequently, the respective rubber compositions
of Examples 1-2 and Comparative Examples 1-3 were used as the tread of pneumatic
tires, and the following property evaluations were carried out.
The rolling resistance was measured according to the usual method
under the conditions of a load of 4.66 kN, an inner pressure of 200 kPa and a speed
of 80 km/hour. The rolling resistance was represented as an index to the value of
Comparative Example 1 as 100 according to the following equation (rolling resistance
index). The larger the index, the smaller the rolling resistance is and the better
the property is.
(rolling resistance index) = (rolling resistance value of Comparative Example
1) ÷ (rolling resistance value of Example or Comparative Example) × 100
(Wet skid performance)
The braking distance from the initial running speed of 64 km/h was
measured on a wet asphalt road. In the test, a Japanese front engine/front wheel
drive automobile with a tire size of 185/65R14 was used. The wet skid performance
was represented as an index to the value of Comparative Example 1 as 100 according
to the following equation (wet skid index). The larger the index, the more excellent
the wet skid performance is.
(wet skid index) = (braking distance value of Comparative Example 1) ÷ (braking
distance value of Example or Comparative Example) × 100
A tire with the obtained tread was installed on a Japanese front engine/front
wheel drive automobile. After the automobile was run for 15,000 km on a paved road,
the driven distance at which the tire tread is worn out by 1 mm was compared, and
the value was represented as an index to the value of Comparative Example 1 as 100
according to the following equation (abrasion resistance index). The larger the
index, the more excellent the abrasion resistance is.
(abrasion resistance index) = ( value of distance driven in Example or Comparative
Example) ÷ (value of distance driven in Comparative Example 1) × 100
The results are shown in Table 2.
In comparison to Comparative Example 1, in which zirconium silicate
was not compounded into the silica compounded rubber composition, and Comparative
Example 2, in which a small amount of zirconium silicate was compounded, the balance
between abrasion resistance, processability, wet skid performance and rolling resistance
was improved in Examples 1-2, in which the appropriate amount of zirconium silicate
On the other hand, in Comparative Example 3, in which a great deal
of zirconium silicate was compounded, although rolling resistance and wet skid performance
increased, abrasion resistance and processability diminished considerably.
Part by weight
Silane coupling agent
Vulcanization accelerator CBS
Vulcanization accelerator DPG
Wet skid performance
According to the present invention, by compounding a specific amount
of silica and zirconium silicate to the rubber composition, the balance between
tire processability, abrasion resistance, rolling resistance, and wet skid performance
can be improved compared to prior technology.