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
1999-08-19
2002-04-16
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...
C525S327600, C525S333700, C525S333900, C525S374000, C525S376000, C525S377000, C525S384000, C525S385000
Reexamination Certificate
active
06372855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a modified polybutene or polyisobutylene polymer and a rubber composition containing the same. More specifically, it relates to a modified polybutene or polyisobutylene having the improved tan &dgr; balance of a rubber composition when compounded into a rubber composition (i.e., the tan &dgr; at 0° C. is increased and the tan &dgr; at 60° C. is decreased), having the improved reinforcing effect of a filler such as carbon black, and having the improved abrasion resistance and also relates to a rubber composition containing the same, in particular a rubber composition useful as a tire tread of a pneumatic tire.
2. Description of the Related Art
A polymer containing isobutylene as a monomer, in particular, a so-called butyl rubber, exhibits a high grip property since the tan &dgr; is higher over a broad range of a temperature and is believed to improve the wet braking performance since the tan &dgr; at 0° C. is high. However, polymers containing isobutylene as a monomer have a small amount of double bonds in the molecule, and therefore the reinforcement with the carbon black is not sufficient and, as a result, the abrasion resistance is inferior.
On the other hand, these polymers have been developed as rubber compositions for pneumatic tires, in particular, tire treads. Under these circumstances, it is known in the art that an oil such as an aromatic oil is added to the rubber composition at the time of compounding the rubber for the purposes of reducing costs, improving the processability (i.e., reducing the viscosity of the composition), improving the physical properties (i.e., reducing the modulus and raising the elongation), etc. However, the addition of an oil has the problem that the compounded oil easily bleeds out from the vulcanized product and decreases the vulcanized rubber properties (e.g., tan &dgr; balance and abrasion resistance).
SUMMARY OF INVENTION
Accordingly, an object of the present invention is to eliminate the problems of a polymer containing isobutylene as a monomer, such as the above-mentioned conventional butyl rubber, and to provide a modified polybutene(polyisobutylene) which is useful for a rubber composition, having a high tan &dgr; at 0° C. (i.e., is superior in wet braking property) and has a low tan &dgr; at 60° C. (i.e., is superior in fuel consumption) and which is superior in the balance of the tan &dgr;, without substantially reducing the abrasion resistance, and to a rubber composition containing the same.
Another object of the present invention is to provide a rubber composition which is capable of solving the problems of the above-mentioned conventional oil-formulated rubber composition, is capable of improving the processability of the rubber composition due to the softening effect thereof, and has the superior tan &dgr; balance and the improved abrasion resistance.
A further object of the present invention is to provide a modified polybutene(polyisobutylene) which is useful for a tire, having the improved reinforcing properties, viscoelastic properties and abrasion resistance, and to provide a rubber composition containing the same.
In accordance with the present invention, there is provided a polymer comprising isobutylene repeating units and having backbone, at the ends, and/or at the side chains of the molecule thereof, at least one free radical selected from the group consisting of nitroxide radicals, hydrazyl radicals, aryloxy radicals, and trityl radicals stably present at a room temperature and in the presence of oxygen.
In accordance with the present invention, there is also provided a modified polybutene(polyisobutylene) comprising isobutylene as repeating units and having, in the backbone, at the ends, and/or at the side chains of the molecule thereof, at least one structure selected from the group consisting of (A) a half-ester structure, (B) an amic acid structure, (C) an onium salt structure, and (D) an imide structure, and a rubber composition containing said modified polymer.
In accordance with the present invention, there is further provided a rubber composition comprising 100 parts by weight of at least one starting diene rubber, at least 20 parts by weight of at least one filler, and 0.1 to 80 parts by weight of at least one acid anhydride-modified polybutene containing 50 mol % or more of isobutylene unit and having an alkenyl group.
In accordance with the present invention, there is further provided a polymer comprising isobutylene, as at least one monomer, and having an alkoxysilane and at least one hydrogen bondable moiety selected from the group consisting of a carboxylic acid, amide, ester, hydroxyl group and amino group in the molecule thereof.
DESCRIPTION OF PREFERRED EMBODIMENT
According to the first aspect of the present invention, as explained above, by introducing into the polybutene(polyisobutylene), preferably the end of the polymer thereof, a free radical compound stable at a room temperature and in the presence of oxygen, when the main chain of the starting rubber is radically cut, the cut radicals of the rubber are trapped with the free radicals and a block copolymer is produced in the system. This block copolymer has a high double bond content, and therefore interacts with the carbon black and, as a result, the reinforcing effect of the carbon black is increased. Therefore it is possible to increase the tan &dgr; at 0° C. and to decrease the tan &dgr; at 60° C., without substantially decreasing the abrasion resistance.
According to the present invention, preferably free radicals stably present at a room temperature and in the presence of oxygen are introduced into the polymer having the isobutylene as repeating units, preferably into the chain ends. Examples of such free radicals are nitroxide radicals, hydrazyl radicals, aryloxy radicals, and trityl radicals. Further, as the polymer having the isobutylene as repeating units, that is, the polymer obtained from the polymerization of isobutylene as a monomer, polyisobutylene, polybutene, butyl rubber, brominated butyl rubber, isobutylene maleate anhidride copolymer, isobutylene-p-methyl styrene-p-bromomethyl styrene copolymer, etc. are known. Of course, the polymer of the present invention is not intended to limit to these polymers.
According to the present invention, as shown in the Production Examples I-1 to I-3 below, it is possible to obtain the desired polymer by reading a polymer having isobutylene as repeating units with a compound having the free radicals. In the reaction, it is preferable to react the polymer having the isobutylene as repeating units with the free radical compound at a desired position, for example, at the end of the polymer chain, and modify the same with any reactive group so as to cause the bonding of the free radicals. Examples of such reactive groups are an alkoxysilyl group, acid anhydride group, ester group etc. These may be appropriately determined by a person skilled in the art. Further, the reaction conditions are not particularly limited.
The polybutene(polyisobutylene) according to the present invention is compounded into 100 parts by weight of a rubber generally used as a rubber composition in the past, especially, a starting diene rubber, in an amount of 0.1 to 100 parts by weight, preferably 1 to 30 parts by weight. If the content is too small, there is a tendency for no substantial additional effect, whereas if too large, the mixablility and rollability tend to be poor and the bleeding is caused, after vulcanization, to thereby remain a tack.
When mixing the silica into the rubber composition according to the present invention, in the same way as in the prior art, for example, it is possible to use a silane coupling agent in an amount of 5 to 30% by weight of the content of silica. Further, in this case, it is possible to mix a silanol condensation catalyst in an amount of 0.05 to 50% by weight of the content of the silane coupling agent. As the silane coupling agent usable for the silica-containing rubber composition according
Chino Keisuke
Ikawa Masahiro
Onoi Hidekazu
Arent Fox Kintner & Plotkin & Kahn, PLLC
Lipman Bernard
The Yokohama Rubber Co. Ltd.
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