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
1998-12-21
2001-01-23
Dawson, Robert (Department: 1712)
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...
C524S571000, C524S575500, C524S262000, C525S342000, C525S343000, C152S450000
Reexamination Certificate
active
06177503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber composition and to a pneumatic tire using said rubber composition, and more particularly, to a rubber composition showing improved workability due to suppressing an increase with time in Mooney viscosity of a mixed rubber and improving shrinkage of the mixed rubber, and to a pneumatic tire using said rubber composition and having excellent uniformity and abrasion resistance.
2. Description of the Related Art
Recently, because of social requirements to save energy and to save resources, and particularly to cut down fuel consumption of automobiles, much research has been carried out with respect to decreasing the rolling resistance of tires and many proposals have been made.
To further improve the low heat buildup property and the low rolling resistance of a rubber composition or a tire using the same, silica is generally used in the rubber composition and a silane coupling agent such as Si69 is also used in combination.
However, a rubber composition containing silica shows very large shrinkage, causing inferior workability. Generally in a process for producing a tire, an unvulcanized rubber composition is extruded to form a prescribed shape and the extruded composition is cut to lengths prescribed for various rubber parts of the tire in accordance with the tire size. However, a rubber composition containing silica shows large shrinkage causing changes in the length after being cut and workability in tire building deteriorates to a great degree. The shrinkage is larger in portions in the vicinity of the cut surfaces of the rubber parts. As the result, the rubber parts around joint portions have larger weights and this causes a decrease in the uniformity of the tire. A rubber composition containing silica has another drawback in that the abrasion resistance thereof is inferior.
A rubber composition containing silica and Si69 shows a large increase in Mooney viscosity with time after being prepared by mixing, and workability in the extrusion step is inferior.
As for the rubber composition containing silica and a silane coupling agent, it is disclosed in International Patent Application Laid-Open No. WO97/40095 that a rubber composition comprising a conventional rubber component, silica, a specific silane coupling agent and various types of silica dispersion improvers can suppress formation of blisters during extrusion at high temperatures, prevent formation of gel, improve dispersion of silica without decreasing workability and provide a tire having excellent abrasion resistance, low heat buildup property and low rolling resistance. However, it is desired that an increase with time in Mooney viscosity of a mixed rubber composition be suppressed and shrinkage be decreased, to improve the workability and uniformity of a tire. It is disclosed in International Patent Application Laid-Open No. WO97/40096 that a rubber composition comprising a conventional rubber component and a specific silane coupling agent shows an effect similar to that shown in International Patent Application Laid-Open No. WO97/40095. However, the same drawback as that described above remains. Similar rubber compositions are disclosed in Japanese Patent Application Laid-Open (hereinafter, referred to as JP-A) Nos. 9-3245, 8-337687 and 8-333482. However, improvement in the workability and uniformity of a tire by suppressing an increase with time in Mooney viscosity of a rubber composition and by improving shrinkage is not sufficiently disclosed, not disclosed at all or not even suggested.
SUMMARY OF THE INVENTION
In view of the above circumstances, an object of the present invention is to provide a rubber composition which shows improved workability due to suppressing an increase with time in Mooney viscosity of a mixed rubber and improving the shrinkage of the mixed rubber and which improves the uniformity and the abrasion resistance of a tire and to provide a pneumatic tire using this rubber composition.
As the result of extensive studies by the present inventors with attention particularly paid to the rubber component and compounding ingredients, it was found that the above object can be achieved by the following means. The present invention has been completed on the basis of this knowledge.
Accordingly, (1) the rubber composition of the present invention comprises:
a rubber component which is a blend rubber of a copolymer rubber and other diene based rubbers or the copolymer rubber alone, the copolymer rubber being obtained by copolymerization of 1,3-butadiene and styrene using an organolithium compound as an initiator, the copolymer rubber having a glass transition temperature of −60° C. or higher, a styrene content of 15 to 30% by weight and a vinyl content of 40 to 70% of a butadiene portion and the blend rubber comprising 55 parts by weight or more of the copolymer rubber and 45 parts by weight or less of the other diene based rubbers in 100 parts by weight of the rubber component;
20 to 100 parts by weight of silica per 100 parts by weight of the rubber component;
0 to 100 parts by weight of carbon black per 100 parts by weight of the rubber component, a ratio by weight of the amount of silica to the amount of carbon black being 1:1 to 1:0; and
in an amount of 1 to 20% by weight of the amount of silica, a silane coupling agent represented by following general formula (1):
(C
n
H
2n+1
O)
3
Si—(CH
2
)
m
—S
y
—(CH
2
)
m
—Si(OC
n
H
2n+1
)
3
(1)
(wherein n represents an integer of 1 to 3, m represents an integer of 1 to 9, y represents a positive number of 1 or more and has a distribution), and in which the content of trisulfide silane component, where y is 3, is 25% or more based on the entire amount of the silane coupling agent, and the content of high polysulfide components, where y is 5 or a number greater than 5, is 50% or less based on the entire amount of the silane coupling agent.
(2) In (1) described above, it is preferable that the amount of the silane coupling agents is 2 to 15% by weight based on the amount by weight of silica.
(3) In (1) described above, it is preferable that the content of the trisulfide silane component, where y is 3, in the sulfide silane coupling agent molecule represented by general formula (1) is 30% or more based on the entire amount of the silane coupling agent, and the content of the high polysulfide silane components, where y represents 5 or a number greater than 5, is 40% or less based on the entire amount of the silane coupling agent.
(4) In (1) described above, it is preferable that the copolymer rubber has been treated by coupling at ends of the copolymer chains with one coupling agent selected from the group consisting of coupling agents containing tin, coupling agents containing silicon and coupling agents containing alkoxysilanes.
(5) In (1) described above, it is preferable that the other diene based rubber is at least one rubber selected from the group consisting of natural rubber, polybutadiene rubber, polyisoprene rubber and styrene-butadiene copolymer rubbers produced by emulsion polymerization.
(6) In (1) described above, it is preferable that the silica has colloidal properties which are a nitrogen adsorption specific surface area of 100 m
2
/g or more and less than 300 m
2
/g and a dibutyl phthalate oil absorption of 100 ml/100 g or more and less than 400 ml/100 g.
(7) In (1) described above, it is preferable that the rubber composition comprising the rubber component, the silica, the carbon black and the coupling agents is treated by mixing at temperatures having a maximum at 150° C. to 180° C.
(8) In (1) described above, it is preferable that the rubber composition shows an increase in Mooney viscosity of 2 to 15% after being left standing at a room temperature for 48 hours before being vulcanized.
(9) In (1) described above, it is preferable that the carbon black is an electrically conductive carbon black.
(10) The pneumatic tire of the present invention has a rubber composition disposed at least in a portion of a tread that is in
Araki Shunji
Yanagisawa Kazuhiro
Bridgestone Corporation
Dawson Robert
Peng Kwo-Liang
Sughrue Mion Zinn Macpeak & Seas, PLLC
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