Rubber compositions and methods for producing the same

Details Rubber compositions and methods for producing the same Rubber compositions and methods for producing the same

2001-10-25

2004-05-25

Niland, Patrick D. (Department: 1714)

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...

C524S401000, C524S432000, C524S493000, C524S495000, C524S496000, C524S499000

Reexamination Certificate

active

06740700

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for producing a rubber composition by incorporating a silica as a reinforcing agent into a conjugated diene-based rubber, which can raise the temperature at which the rubber and the silica are kneaded and which can reduce the frequency of the kneading, whereby reducing the time period required for the production. The invention also relates to a method for producing a rubber composition capable of reducing the time period required for producing a composition and also capable of improving the physical properties of the rubber for a tire especially when the conjugated diene-based rubber has a specific functional group.
DESCRIPTION OF THE RELATED ART
In response to a recent demand for a low gas mileage of an automobile, a rubber composition for a tire having a sufficient hardness, a low rolling resistance, an excellent wearing resistance and a wet skid resistance, as a representative index of the steering stability, which is satisfactorily high is demanded. In order to reduce the rolling resistance of a tire, the hysteresis loss of a vulcanized rubber should be reduced. This hysteresis loss can evaluate variety of physical properties such as tan&dgr; at the temperature of 50 to 80° C. as an index. A raw rubber having a low hysteresis loss may for example be a natural rubber, an isoprene rubber or a butadiene rubber, which has a problematically low wet skid resistance.
On the other hand, a method in which a silica or a combination of a silica and a carbon black was used as a reinforcing agent in a rubber composition for a tire was proposed recently. A tire tread in which a silica or a combination of a silica and a carbon black is incorporated is excellent in the steering stability which is reflected mainly on the wet skid resistance and also has a low rolling resistance. Nevertheless, it involves a problem which is a poor wearing resistance of the vulcanized rubber. One of the reasons for such problem is considered to be a difficulty in obtaining a sufficient reinforcing effect due to a poor dispersion of the silica resulting from a lower compatibility with a conjugated diene-based rubber when compared with a carbon black.
In order to increase the compatibility between a silica and a conjugated diene-based rubber and to disperse the silica sufficiently, a silane coupling agent is employed generally. It is also suggested to employ a conjugated diene-based rubber into which a functional group having an affinity with a silica is introduced, and conjugated diene-based rubbers into which an alkoxysilyl group, an amino group, a hydroxyl group and the like are introduced are proposed.
Nevertheless, the dispersion of a silica, when the silica and a silane coupling agent are incorporated simultaneously into a conjugated diene-based rubber and then kneaded, is not always satisfactory because of the limitation in the kneading temperature and the like, and the physical properties of a vulcanized rubber is not improved. Also when a conjugated diene-based rubber into which a specific functional group described above is introduced is employed, it allows, upon being combined simultaneously with a conjugated diene-based rubber, a silica and a silane coupling agent and then kneaded, the reaction between the rubber and the silica to be inhibited by the silane coupling agent, resulting in a poor dispersion of the silica, and also allows a heat to be generated during a processing, resulting in a poor processability.
SUMMARY OF THE INVENTION
The invention is intended to solve the problems described above, and thus to provide a method for producing a rubber composition which is capable of increasing the kneading temperature of the formulation, reducing the kneading frequency and reducing the required time period when incorporating a silica as a reinforcing agent into a rubber composition containing a conjugated diene-based rubber, as well as a rubber composition obtained by the same. This invention also is intended to provide a method for producing a rubber composition capable of reducing time as well as dispersing the silica sufficiently and increasing the reinforcing effect especially when the conjugated dien-based rubber has a specific functional group, resulting in improving the physical properties of the rubber for a tire.
When a silica and a silane coupling agent are incorporated simultaneously into a conjugated diene-based rubber and then kneaded, the silane coupling agent employed customarily in this technical field which contains a sulfur atom in its molecular structure undergoes a cleavage, resulting in a crosslinking of the rubber molecules which leads to a gelation. Accordingly, in a conventional manner, the kneaded material is taken out from a kneader when its temperature reached 140 to 150° C. However, this manner can not disperse a silica in a conjugated diene-based rubber sufficiently, and requires 4 to 5 cycles of a procedure, each cycle involving a step in which a kneaded material is cooled once to about room temperature, loaded in the kneader again and then discharged from the kneader when it is heated to 140 to 150° C. Accordingly, the procedure is complicated and a long time is required for producing a rubber composition.
Now we found that by incorporating a rubber component containing a conjugated diene-based rubber and a silica, and kneading to form a rubber formulation followed by incorporating a silane coupling agent and kneading again to form a rubber formulation, it is possible to raise the temperature at which the rubber component containing the conjugated diene-based rubber and the silica are kneaded to a temperature as high as 170 to 180° C. Accordingly, this first kneading step is found to be enough to disperse the silica satisfactorily, resulting in a reduced kneading frequency which leads to a reduced time period required for producing a rubber composition. In addition, it was also discovered that when the conjugated diene-based rubber has a specific functional group capable of reacting with a silica the reinforcement by the silica is sufficient and the physical properties of a vulcanized rubber is further improved.
The present invention is based on the findings described above and can be described as follows.
1. A method for producing a rubber composition comprising:
a step for preparing a first rubber formulation [P1] by kneading a formulation (A1) comprising a rubber component containing a conjugated diene-based rubber and a silica;
a step for preparing a second rubber formulation [P2] by kneading a formulation (B1) comprising a mixed auxiliary material containing a silane coupling agent and said first rubber formulation [P1]; and
a step for kneading a formulation (C) comprising said second rubber formulation [P2], a zinc oxide and a vulcanizing agent.
2 The method for producing a rubber composition according to 1 above, wherein terminal temperature for kneading said formulation (A1) is 150 to 190° C., and terminal temperature for kneading said formulation (B1) is 130 to 170° C.
3. The method for producing a rubber composition according to 2 above, wherein 30 to 100 parts by mass of said conjugated diene-based rubber based on 100 parts by mass of said conjugated diene-based rubber, is a conjugated diene-based rubber having at least one selected from the group consisting of an alkoxysilyl, an amino, a hydroxyl and an epoxy groups.
4. The method for producing a rubber composition according to 3 above, further comprising an extending oil in said formulation (A1).
5. A method for producing a rubber composition comprising:
a step for preparing a first rubber formulation [Q1] by kneading a formulation (A2) comprising a rubber component containing a conjugated diene-based rubber and a silica;
a step for preparing a second rubber formulation [Q2] by kneading a formulation (B2) comprising a mixed auxiliary material containing a silane coupling agent and said first rubber formulation [Q1] and by continuing kneading a formulation (D) incorporatin

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