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
1999-12-03
2002-04-09
Lipman, Bernard (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...
C525S332800, C525S332900, C525S333100, C525S333200
Reexamination Certificate
active
06369167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for making a polymer, in which fracture characteristics, wear resistance, and low exothermicity are maintained simultaneously at a very favorable level, the polymer obtained by the process, and a rubber composition using the polymer. More specifically, the present invention relates to a process for making a modified diene polymer in which a terminal of a polymer obtained by an anionic polymerization is modified so that the interaction with silica or carbon black is strengthened, a polymer obtained by the process, and a rubber composition using the polymer.
2. Description of the Related Art
In connection with the movement to regulate carbon dioxide emission on a worldwide level because of growing concerns about environmental problems, a demand for automobiles with lower fuel consumption is becoming more urgent. In order to comply with such a demand, reduction of rolling resistance is required in terms of the performance of tires. As for means to reduce the rolling resistance of tires, although the optimization of tire structure has been researched, the most commonly adopted means is to utilize a rubber composition having low exothermicity.
In order to obtain a rubber composition having low exothermicity, many technical developments have been made so as to increase the dispersibility of fillers for use in rubber compositions. Among these technologies, the most common is the method wherein a terminal of a polymer obtained by an anionic polymerization using an alkyllithium is modified with a functional group capable of having an interaction with a filler.
The most typical method known as the above-mentioned means is a method wherein carbon black is used as the filler and a polymer terminal is modified with a tin compound (Japanese Patent Application Publication (JP-B) No. 5-87,530). Also known is a method wherein carbon black is used as a filler and an amino group is introduced into a polymer terminal (Japanese Patent Application Laid-Open (JP-A) No. 62-207,342).
Further, with the recent increase in interest in the safety of automobiles, demands regarding performance on a wet road (hereinafter referred to as wet performance), breaking performance in particular, are growing, in addition to the demand for low fuel consumption. Therefore, what is required of a rubber composition for a tire tread is not only the reduction of the rolling resistance but also the realization of achieving high levels of wet property and low fuel consumption simultaneously, at a high level.
As a method for obtaining a rubber composition capable of imparting satisfactory low fuel consumption and wet performance simultaneously to tires, a method wherein silica is used as a reinforcing filler in place of traditionally used carbon black has already been put into practice.
It has become clear, however, that the use of silica as a reinforcing filler significantly lowers the breaking strength and wear resistance of a rubber composition in comparison with the use of carbon black. Furthermore, because of the poor dispersibility of silica, kneading processability, when silica is used, presents a serious problem during the actual production of tires.
Accordingly, in order to obtain a rubber composition that has low exothermicity and provides good productivity, it is required to use a combination of silica and carbon black instead of using carbon black or silica separately, and to provide a terminal modified polymer which exhibits an interaction with a wide variety of such fillers, thereby providing good dispersibility of the fillers and good wear resistance of the rubber composition.
However, since attempts have been mostly made to develop a modifier aiming at the use of a single filler in the above-described means, the availability of a terminal modified polymer that exhibits a sufficient interaction with a filler regardless of the type of the filler is extremely limited.
For example, the tin compound, which has been mentioned above, demonstrates a large dispersing effect with carbon black, but with respect to silica, demonstrates only a minimal dispersing effect and no reinforcing effect at all.
Methods using an alkoxysilane, which is effective in the improvement of dispersibility and reinforcing property of silica, are described, for example, in JP-A Nos. 1-188,501, 8-53,5153, and 8-53,576. It is clear however, that these methods are not effective when carbon black is used as a filler, because the alkoxysilyl group exhibits no interaction with a carbon black at all. The same can be said of other modified polymers for use with silica. For example, methods that use aminoacrylamide, described in JP-A Nos. 9-71,687 and 9-208,633, have neglible effects in the improvement of the dispersion of carbon black, although these methods have a certain effect in the improvement of the dispersion of silica. An additional problem associated with these methods is that, when these methods are applied to a rubber composition comprising a combination of carbon black and silica or to a rubber composition comprising carbon black, the hysteresis of the composition becomes larger.
A method, in which a terminal of a polymer, which is obtained by a polymerization reaction using a lithium amide initiator, is modified with an alkoxysilane, has been employed recently in order to enhance the effect of modification (JP-A No. 9-208,621). However, this method requires a fairly expensive initiator and is known to be not perfectly free from the problems with regard to processability of rubber compositions, despite its effectiveness in improving dispersion and reinforcement.
A modified polymer that is prepared by using a modifier composed of an alkoxysilane having a dialkylamino group introduced thereinto has been reported (JP-B Nos. 6-53,763 and 6-57,767). This method brings about good processability and a reinforcing effect when silica is used, and a certain level of dispersing effect for both silica and carbon black. However, the disadvantage of this method is that, since the amino group is a dialkyl group which is less effective with carbon black, the effect of this method is not sufficiently exhibited in a rubber composition, in particular in a rubber composition containing a large proportion of carbon black, in comparison with methods utilizing a tin-based modifier.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a modified diene polymer which exhibits good reinforcing characteristics and filler dispersing effect regardless of the kinds of the fillers, a method for making the diene polymer, and a rubber composition having good fracture characteristics, wear resistance, and low exothermicity, without the impairment of the wet performance, by upgrading the interactions with both carbon black and silica of the modified diene polymer in a simultaneous manner which has been difficult to obtain by methods hitherto known.
After extensive studies to obtain a polymer having excellent interaction with the above-mentioned various fillers, the present inventors have found that the use, as a terminal modifier of a polymer, of a compound having an imino group
exhibiting a specifically good interaction with both carbon black and silica makes it possible to obtain a very good effect in comparison with the polymers obtainable by known techniques.
Accordingly, the present invention has the following constitution among others.
(1) A process for manufacturing a polymer, said process comprising steps of polymerizing or copolymerizing a conjugated diene monomer by using an organolithium compound as an initiator in a hydrocarbon solvent, and thereafter allowing the active terminal of the polymer to react with a compound having an imino group represented by the following formula 1;
wherein R, R′, R″, and R′″ each independently represents a group having 1 to 18 carbon atoms selected from the group consisting of: an alkyl group, an allyl group, and an aryl group; m and n are integers of from 1 to 20 and from
Kondo Hajime
Morita Koichi
Bridgestone Corporation
Lipman Bernard
Sughrue MIon, PLLC
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