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
2000-12-13
2002-11-26
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S232000, C525S238000, C525S241000, C526S335000
Reexamination Certificate
active
06486258
ABSTRACT:
TECHNICAL FIELD
This invention relates to a novel conjugated diene rubber composition for tires having excellent rebound resilience, and a tire comprising the same.
BACKGROUND ART
In recent years, as protection of the environment and energy-saving have gained importance because of the global warming problem, there are increasing demands for low fuel consumption by automobiles. To achieve low fuel consumption by automobiles, low rolling resistance of tires is demanded. To enhance low rolling resistance of tires, it is generally effective to use a rubber material capable of providing a cured rubber having a low hysteresis loss. Conventionally, diene rubbers such as natural rubber(NR), polybutadiene(BR), polyisoprene(IR), styrene-butadiene copolymer rubber are used as a rubber material for tires. These diene rubbers are selected and used singly or in combination, depending on the type of a tire and a part where the rubber material is used. Of these diene rubbers, 1,4-polybutadiene having a high cis-bond content is capable of providing a cured rubber having the highest rolling resistance, i.e., the smallest hysteresis loss; however, conventional 1,4-polybutadiene having a high cis-bond content has a problem in that the hysteresis loss is increased owing to the low molecular weight portion present in its wide molecular weight distribution. It is known that high cis 1,4-polybutadiene having a cis-1,4 bond content of at least 90% is produced by polymerization using a typical coordinated polymerization catalyst which is a combination of an organic aluminum compound with a transition metal compound, i.e., Co-, Ni-, Ti- or Nd-compound, or a rare earth metal compound. When these catalysts are used, however, high-cis 1,4-polybutadiene having narrow molecular weight distribution is not obtained, because as the weight average molecular weight (Mw) increases, the molecular weight distribution (Mw/Mn) becomes wider. Hence, it is known that polybutadiene having a high strength has an undesirably high hysteresis loss.
On the other hand, polybutadiene having a high molecular weight and a narrow molecular weight distribution can be obtained by using an organic lithium catalyst; however, the thus-obtained polybutadiene has a cis-1,4-bond content of not larger than 40% and a low rebound resilience.
As a catalyst for polymerization of olefins, a combination of methylaluminoxane with metallocene type catalyst of a transition metal such as Ti, Zr and Hf has been developed and attracted attention. It is known that, by using these catalysts, &agr;-olefin such as ethylene and propylene can be polymerized with high efficiency to yield a polymer having a narrow molecular weight distribution as well as a narrow composition distribution in the case of copolymers. On the other hand, although there have been attempts to polymerize a conjugated diene such as butadiene and isoprene by using metallocene catalysts, stereo-regulation of a polymer thus obtained has been insufficient.
For example, copolymerization of ethylene or &agr;-olefin with butadiene is disclosed in
Macromol. Chem., Macromol. Symp
., 1986, vol. 4, page 103-118
; Macromol. Chem
., 1991, vol. 192, page 2591-2601; and Japanese Patent Publication (Tokuhyou, publication of a translated version of international application) No. H1-501633. In Japanese Unexamined Patent Publication (hereinafter abbreviated to “JP-A”) No. H7-112986, a rare earth metal-toluene complex is disclosed as a component of a catalyst, however, the catalyst does not exhibit a high activity for polymerization of a conjugated diene monomer such as butadiene or isoprene, and stereo-regulation of a polymer is difficult.
A catalyst comprising a combination of methylaluminoxane with a metallocene compound selected from (C
5
H
5
)TiCl
3
, (C
5
H
5
)Ti(OBu)
3
, (C
5
H
5
)TiCl
3
.2THF and [(C
5
H
5
)TiCl
2
]n for polymerization of 1,3-dienes is described in
Makromol. Chem., Macromol. Symp
., 1995, vol.89, p383-392. A catalyst comprising a combination of an aluminoxane with a transition metal compound for polymerization of 1,3-dienes is described in JP-A H1-254713, JP-A H3-188109 and JP-A H4-331213. When butadiene is polymerized by these catalysts, a polymer having a relatively high cis-bond content is obtained, but, the molecular weight of the polymer thus obtained is relatively low.
A catalyst for polymerization of a conjugated diene comprising a combination of aluminoxane with a transition metal compound of group IV of the periodic table is described in JP-A H9-77818, which has a high activity and gives a polymer with controlled stereoregularity. It is described that, when butadiene was polymerized with this catalyst, the polymerization proceeded at a high activity and a polymer having a cis-bond content of 96% was obtained. However, this patent publication is silent on the molecular weight of the polymer and regulation of the molecular weight distribution.
As stated above, by using conventional methods, it has been difficult to polymerize a conjugated diene monomer with high efficiency to a polymer having a high molecular weight, a narrow molecular weight distribution and a high cis-bond content.
Incidentally, a metallocene catalyst represented by the following formula: CH
3
O(CO)CH
2
(C
5
H
5
)TiCl
3
is described in
Makromol. Chem., Macromol. Symp
., 1997, vol.118, p55-60. But, this catalyst is not known to be used for polymerization of a conjugated diene monomer.
Further, in Japanese Examined Patent Publication H6-43517, main-chain modified high-cis poly butadiene is described as preferable from the aspect of rolling resistance and abrasion resistance of tires, but any specific example is not disclosed. In
Makromol. Chem., Macromol. Symp
., 1997, vol.118, p55-60, a process for preparing a high cis poly butadiene by using a new catalyst is disclosed, but little is reported about the properties of polymer thus obtained, hence it is not known if thus-obtained polymer is usable for tires.
DISCLOSURE OF THE INVENTION
Objects of the present invention are to provide a novel conjugated diene rubber composition for tires having an improved rebound resilience and a tire comprising the same, wherein said conjugated diene rubber composition has a high cis-bond content and a low ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn).
Thus, according to the present invention, there is provided a conjugated diene rubber composition for tires comprising:
(I) 2 to 100 percent by weight of a conjugated diene polymer rubber having a high cis-bond content, which is a polymer of conjugated diene monomer or monomers alone or a copolymer of a conjugated diene monomer with a monomer copolymerizable therewith, and characterized in that the content of units having a cis-bond in the total units derived from the conjugated diene monomer is at least 40%; the weight average molecular weight (Mw) is in the range of 20,000 to 10,000,000; and the ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) and the weight average molecular weight (Mw) satisfy the following formula (1):
log(Mw/Mn)<0.162×log(Mw)−0.682 (1)
and
(II) 0 to 98 percent by weight of other polymer rubber.
Further, according to the present invention, there is provided a tire comprising at least a tread which is composed of the above-mentioned conjugated diene rubber composition.
BEST MODE FOR CARRYING OUT THE INVENTION
Conjugated Diene Polymer Having a High Cis-Bond Content (High-Cis Conjugated Diene Polymer)
A high-cis conjugated diene polymer rubber used in the present invention is a polymer of conjugated diene monomer or monomers alone, i.e., a homopolymer of a conjugated diene monomer or a copolymer among conjugated diene monomers, or a copolymer of a conjugated diene monomer with a monomer copolymerizable therewith, and characterized in that the content of units having a cis-bond in the total units derived from the conjugated diene monomer is at least 40%; the weight average molecular weight (Mw) is in the range of 20,000 to 10
Fukahori Takahiko
Nakamura Masao
Noguchi Koukichi
Armstrong Westerman & Hattori, LLP
Nutter Nathan M.
Zeon Corporation
LandOfFree
Conjugated diene rubber composition for tire use and tire does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Conjugated diene rubber composition for tire use and tire, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Conjugated diene rubber composition for tire use and tire will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2922892