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
2000-02-15
2003-02-11
Henderson, Christopher (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...
C525S331800, C525S343000
Reexamination Certificate
active
06518367
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vulcanized rubber composition, more particularly relates to a vulcanized rubber composition balanced in heat aging characteristics, fatigue resistance, and heat buildup property by using a sulfur compound having a specific structure and optionally sulfur, to control the sulfur cross-linking structure of the rubber.
The present invention also relates to a rubber composition for a heavy duty tire tread, more particularly relates to a rubber composition for a heavy duty tire tread in which a diene rubber is compounded with a reinforcing filler, rosin base and/or cyclopentadiene base resin, sulfur compound having a specific tetrasulfide or benzothiazole structure so as to improve the abrasion resistance, heat aging characteristics, and appearance after use while maintaining the heat buildup property of the tire and the cut resistance when new.
2. Description of the Related Art
In the past, mainly sulfur has been used as a vulcanization agent for vulcanization of rubber, but rubber compositions comprising blends of rubber compositions with polysulfide polymers are known. For example, Japanese Unexamined Patent Publication (Kokai) No. 10-120788 describes a polysulfide polymer used as a rubber vulcanization agent,.Japanese Unexamined Patent Publication (Kokai) No. 10-139939 describes a cross-linkable rubber composition containing a polysulfide rubber, and Japanese Unexamined Patent Publication (Kokai) No. 10-251514 also describes a rubber composition containing a polysulfide polymer. Further, Japanese Unexamined Patent Publication (Kokai) No. 62-48739 describes a high grip tread rubber composition suitable for high speed driving.
The sulfur cross-linking structures of rubber are roughly classified into monosulfide bridges, disulfide bridges, and polysulfide bridges, but in general it is said that the greater the monosulfide bridges in vulcanized rubber, the better the heat aging characteristics become. If there are many monosulfide bridges, however, there is the problem that the strength and elongation at break and the fatigue failure characteristics fall. On the other hand, if there are many polysulfide bridges in the vulcanized rubber, while the strength and elongation at break and the fatigue failure characteristics are superior, there is the problem that the heat aging characteristics fall.
In addition, a general diene-base rubber suffers from the phenomenon of reversion where the various physical properties fall upon high temperature vulcanization in the case of a sulfur/vulcanization accelerator vulcanization system. Improvement of this is sought. To improve this, it is desirable to add a polysulfide polymer having 2 to 5 sulfur atoms, but there is the problem that if this is not suitably blended in, it causes a remarkable change in other physical properties and in particular causes a deterioration of the heat buildup property.
Furthermore, in heavy duty tires such as tires for construction machinery which are used on bad roads and under heavy duty conditions, improvement in the heat buildup property, the abrasion resistance, and other properties is sought. At the same time, in recent years, there have been rising demands for prevention of a decline in physical properties due to use and securing a good appearance due to the same. In order to meet these demands, for example, Japanese Unexamined Patent Publication (Kokai) No. 10-219034 proposes a specific ratio of formulation of specific carbon black and silica. Further, from the same viewpoint as the present invention, in the sense of prevention of heat degradation, it has been proposed to use a sulfur compound such as polyalkylene tetrasulfide (condensed product of sodium tetrasulfide and an alkylene dihalide) in order to obtain a thermally stable cross-linking state (see 1967 Synthetic Rubber Handbook (enlarged new edition), p. 309), but control of the molecular weight for securing the compatibility with rubber and handling is difficult and this is not preferred from the viewpoints of scorch resistance and safety.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a vulcanized rubber composition balanced in heat aging characteristics, fatigue resistance, and heat buildup property.
Another object of the present invention is to provide a vulcanized rubber composition improved in reversion resistance without changing the other physical properties.
A further object of the present invention is to provide a rubber composition for a heavy duty tire tread which enables improvement of the abrasion resistance, heat aging characteristics, and appearance after use while maintaining the heat buildup property, cut resistance when new, and other properties.
Other objects and advantages of the present invention will be apparent from the following description.
In accordance with the first aspect of the present invention, there is provided a vulcanized rubber composition comprising a vulcanizable rubber, a reinforcing filler, and a sulfur compound (1) having the formula (I):
—(S
x
R
1
)
n
— (I)
wherein R
1
represents an organic group, x is an average number of 3 to 5, and n is an integer of 1 to 100,
wherein a ratio (VM/VD) is not more than 0.4, in which:
a value VM is obtained from the degree of change before and after toluene swelling of the vulcanized rubber composition treated in a lithium aluminum hydride saturated tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution using the formula (A):
VM
=
-
1
Vs
·
[
ln
(
1
-
vr
M
)
+
vr
M
+
μ
·
vr
M
2
vr
M
1
/
3
-
vr
M
/
2
]
wherein
vr
M
=
1
-
φ
X
M
-
φ
(
A
)
wherein X
M
is the degree of change.before and after toluene swelling (volume after toluene swelling/volume before toluene swelling)after treatment in a lithium aluminum hydride saturated tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution,
&phgr; is the volume percentage of the reinforcing filler in the rubber composition,
V
s
is the molecular volume of toluene,
&mgr; is the rubber.toluene interaction coefficient, and
vr
M
is the volume percentage of rubber in the swelled rubber after treatment in a lithium aluminum hydride saturated tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution and
a value VD is obtained from the degree of change before and after toluene swelling of the vulcanized rubber composition treated.in a propane-2-thiol (0.4 mol/l)/piperidine (0.4 mol/l) added tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution using the formula (B):
VD
=
-
1
Vs
·
[
ln
(
1
-
vr
D
+
M
)
+
vr
D
+
M
+
μ
·
vr
D
+
M
2
vr
D
+
M
1
/
3
-
vr
D
+
M
/
2
-
ln
(
1
-
vr
M
)
+
vr
M
+
μ
·
vr
M
2
vr
M
1
/
3
-
vr
M
/
2
]
wherein
vr
D
+
M
=
1
-
φ
X
D
+
M
-
φ
(
B
)
wherein X
D+M
is the degree of change before and after toluene swelling (volume after toluene swelling/volume before toluene swelling)after treatment in a propane-2-thiol (0.4 mol/l)/piperidine (0.4 mol/l) added tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution and
vr
D+M
is the.volume percentage of rubber in the swelled rubber after treatment in a propane-2-thiol (0.4 mol/l)/piperidine (0.4 mol/l) added tetrahydrofuran/toluene (ratio by volume 1/1) mixed solution).
A vulcanized rubber composition according to the preferable embodiment of the first aspect of the present invention further has a ratio (VM/VT) is not more than 0.15, in which:
VT found from the degree of change before and after toluene swelling of the untreated vulcanized rubber composition using formula (C):
V
T
=
-
1
Vs
·
[
ln
(
1
-
vr
T
)
+
vr
T
+
μ
·
vr
T
2
vr
T
1
/
3
-
vr
T
/
2
]
wherein
vr
T
=
1
-
φ
X
T
-
φ
(
C
)
where X
T
is the degree of change before and after toluene swelling when untreated (volume after toluene swelling/volume before toluene swelling) and vr
T
is the
Fukutani Shuichi
Ishikawa Kazunori
Yatsuyanagi Fumito
Arent Fox Kintner & Plotkin & Kahn, PLLC
Henderson Christopher
The Yokohama Rubber Co. Ltd.
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