Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-03-29
2003-11-04
Lu, Caixia (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S191000, C525S241000
Reexamination Certificate
active
06642315
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a rubber composition and a cross-linked rubber, more specifically relates to a rubber composition and cross-linked rubber suitable for use for a tire tread having a superior wet grip and abrasion resistance.
BACKGROUND ART
In recent years, improvement in performance has been sought for the rubber compositions for tires for automobiles, etc. In particular, rubber compositions for tire treads superior in mechanical properties, abrasion resistance, grip on wet roads (i.e., wet grip properties), and low heat build-up have been sought.
In the past, large amounts of natural rubber have been used for tires. However, in many cases, it has been used mixed with the other rubbers in order to improve various aspects of performance. For example, polybutadiene rubber has been compounded to improve the abrasion resistance, while a styrene-butadiene polymer rubber has been compounded to improve the wet grip.
For example, Japanese Unexamined Patent Publication (Kokai) No. 8-231767 discloses a rubber composition superior in balance of abrasion resistance and wet grip by controlling the compatibility of the blend rubber.
However, if the abrasion resistance is improved, the wet grip is decreased, while if the wet grip is improved, the low heat build-up property is decreased. In this and other ways, there is often an antitomy in the relationship of various aspects of performance. It was difficult to obtain a rubber composition superior in all aspects of performance.
On the other hand, as the starting rubber, ordinarily one which does not have a gel structure has been strongly sought in consideration of the kneadability of the starting rubber and reinforcing material. However, in order to improve various aspects of performance, it has also been proposed to use rubber having a gel structure.
For example, Japanese Unexamined Patent Publication (Kokai) No. 3-37246 discloses a rubber composition containing a polychloroprene gel, while Japanese Unexamined Patent Publication (Kokai) No. 6-57038 discloses a rubber composition containing a polybutadiene gel. These rubber compositions are superior in low heat build-up property and abrasion resistance, but inferior in wet grip.
Japanese Unexamined Patent Publication (Kokai) No. 10-204217 discloses a rubber composition containing a styrene-butadiene copolymer rubber gel having a toluene swelling index of 1 to 15. Such a rubber composition is superior in low heat build-up property and wet grip, but sometimes suffers from the problems of an insufficient abrasion resistance, lower elongation at break and consequently lower mechanical properties, etc.
Further, Japanese Unexamined Patent Publication (Kokai) No. 11-80438 discloses a rubber composition comprising a pre-cross-linked rubber and an uncross-linked rubber latex. However, this kind of rubber composition gives a cross-linked rubber superior in mechanical properties, while not containing a reinforcing material, but suffers from the problems of lower mechanical properties or insufficient abrasion resistance or wet grip when containing a reinforcing material.
DISCLOSURE OF THE INVENTION
In consideration of the above situation, the object of the present invention is to provide a rubber composition superior in abrasion resistance and wet grip, without impairing the mechanical properties and low heat build-up property.
A further object of the present invention is to provide a cross-linked rubber superior in abrasion resistance and wet grip without impairing its mechanical properties and low heat build-up property.
In accordance with the present invention, there is provided a rubber composition comprising (A) a sulfur cross-linkable rubber and (B) a conjugated diene-based rubber gel, having a toluene swelling index of 16 to 70, comprising 40 to 75% by weight of conjugated diene monomer units and 60 to 25% by weight of aromatic vinyl monomer units.
In accordance with the present invention, there is also provided a cross-linked rubber produced by cross-linking the above rubber composition.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in further detail below.
The sulfur cross-linkable rubber (A) compounded into the rubber composition according to the present invention is not particularly limited so long as it is a rubber which can be cross-linked by sulfur, preferably it is one which includes double bonds corresponding to an iodine value of at least 2, more preferably 5 to 470, more preferably one containing conjugated diene monomer units and one having a Mooney viscosity(MLP
1+4
, 100° C.) of preferably 10 to 150, more preferably 20 to 120. Note that the “iodine value” is represented by the number of grams of iodine chemically bonding with 100 g of a substance (i.e., rubber) and, in general, can be found by adding and assaying iodine chloride into glacial acetic acid.
The sulfur cross-linkable rubber (A) is preferably one which substantially has no gel structure or which even if having some gel structure, has a toluene swelling index of more than 70.
Specific examples of the sulfur cross-linkable rubber ingredient (A) used in the present invention are, for example, natural rubber, synthetic polyisoprene, polybutadiene, an acrylic acid alkyl ester-butadiene copolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer, a styrene-isoprene-butadiene copolymer, an acrylonitrile-butadiene copolymer, a partial hydrogenate of an acrylonitrile-butadiene copolymer, an isobutylene-isoprene copolymer, an ethylene-propylene-diene copolymer, and any mixtures thereof. Further, these rubbers may be previously extended by an extender oil.
Among these specific examples of the rubber ingredient (A), natural rubber, a synthetic polyisoprene, a styrene-butadiene copolymer produced by emulsion polymerization or solution polymerization and having 1 to 60% by weight, preferably 10 to 45% by weight, more preferably 15 to 25% by weight of styrene units, a polybutadiene having a high cis-1,4 bond content, for example, a cis-1,4 bond content of at least 90% by weight, and mixtures thereof are preferable. Natural rubber, synthetic polyisoprene, a polybutadiene having a high cis-1,4 bond content, and mixtures thereof are particularly preferable.
The average glass transition temperature (Tg) of the sulfur cross-linkable rubber (A) is preferably −40° C. or less, more preferably is −100 to −50° C. If the value is in this range, the balance of the physical properties is more superior.
Here, the “average glass transition temperature” is given by the following formula I, when mixing n types of sulfur cross-linkable rubbers (A) and designating the glass transition temperature of a sulfur cross-linkable rubber
k
as Tgk and the weight percentage of the sulfur cross-linkable rubber
k
in the entire weight of the sulfur cross-linkable rubber (A) as &phgr;k. Note that “Tgk” is the value measured at a rate of temperature rise of 2° C./min using a DSC (differential scan calorimeter):
Average glass transition temperature=
n
&Sgr;Tgk·&phgr;k
(
I
)
The conjugated diene-based rubber gel (B) compounded in the rubber composition according to the present invention is a rubber containing conjugated diene monomer units and aromatic vinyl monomer units as essential ingredients and is composed of 40 to 75% by weight of conjugated diene monomer units, preferably 45 to 65% by weight, more preferably 50 to 60% by weight, and 60 to 25% by weight of aromatic vinyl monomer units, preferably 55 to 35% by weight, more preferably 50 to 40% by weight, and has a toluene swelling index of 16 to 70, preferably 20 to 65, more preferably 20 to 40.
If the amount of the conjugated diene monomer units of the conjugated diene-based rubber gel (B) is small, the low heat build-up property and abrasion resistance are inferior, while conversely if the amount of the conjugated diene monomer units is large, the wet grip is inferior.
If the amount of the aromatic vinyl monomer units of the conjugated diene-based rubber gel (B) is small, the wet grip is inferior, while
Amino Naoya
Endo Koichi
Nakamura Masao
Lu Caixia
Rader & Fishman & Grauer, PLLC
The Yokohama Rubber Co. Ltd.
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