Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1998-06-24
2000-04-25
Cooney, Jr., John M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521142, 521143, 429247, 526352, C08J 928
Patent
active
060544988
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a polyethylene microporous film, a separator comprising the film, and a battery made using the separator.
BACKGROUND ART
Polyethylene microporous films are used as microfiltration membranes, separators for batteries, separators for condensers, etc. Among these uses, when polyethylene microporous films are used as battery separators, especially as separators for lithium ion batteries, they are required to have a so-called "fuse effect" which is a property that when the insides of the batteries are overheated, the separator becomes molten and forms a coat which covers the electrode to break the current, thereby securing the safety of batteries. In addition, general properties such as mechanical strength and permeability are necessary.
It is known that the fuse temperature of polyethylene microporous films, namely, the temperature at which the fuse effect is developed, is about 130-150.degree. C. Even if the inside of battery is overheated for some reason, when the temperature reaches the fuse temperature, the microporous film melts to form a coating which covers the electrodes, and, hence, the ionic flow is interrupted to stop the battery reaction. However, when the temperature very abruptly rises, the temperature inside the battery further rises even after the fuse occurs, and consequently said coat is broken, which causes a short in the battery. Separators having such a high short resistance, which can surely continue to break the current even under the above-mentioned circumstances, are in demand.
The object of the present invention is to provide a polyethylene microporous film excellent in mechanical strength, permeability and productivity, and high in short resistance.
As a result of intensive research conducted by the inventors, it has been found that a polyethylene microporous film comprising a specific high-density polyethylene or linear copolymer polyethylene has a high short resistance, and the present invention has been accomplished.
DISCLOSURE OF INVENTION
A first embodiment of the present invention is a microporous film comprising a high-density polyethylene or linear copolymer polyethylene having a terminal vinyl group concentration of 2 or more per 10,000 carbon atoms in the polyethylene as determined by an infrared spectroscopic method. A preferred first embodiment of the present invention is a microporous film comprising a high-density polyethylene or linear copolymer polyethylene having a terminal vinyl group concentration of preferably 5 or more, more preferably 6 or more per 10,000 carbon atoms in the polyethylene as determined by an infrared spectroscopic method.
A second embodiment of the present invention is the microporous film of the first embodiment in which the weight-average molecular weight of the high-density polyethylene or linear copolymer polyethylene is 200,000-1,000,000.
A third embodiment of the present invention is a separator comprising the above microporous film.
A fourth embodiment of the present invention is a battery made using the above separator.
BEST MODE FOR CARRYING OUT THE INVENTION
The polyethylene used in the present invention (hereinafter referred to as "P-HDPE") can be fixed by the concentration of terminal vinyl group. The terminal vinyl group concentration of P-HDPE is 2 or more, preferably 5 or more, more preferably 6 or more per 10,000 carbon atoms in the polyethylene. Such a polyethylene can be produced by carrying out suspension polymerization, solution polymerization or gas phase polymerization using a chromium compound-supporting catalyst in combination with an organo-metallic compound disclosed, for example, in JP-B-1-12777.
It is not clear why P-HDPE has a high short resistance, but it is considered that short resistance, as evaluated by an overcharge test or washer test, can be greatly improved by using P-HDPE in place of ordinary HDPE having a terminal vinyl group concentration of less than 2 per 10,000 carbon atoms in the polyethylene (hereinafter referred to as "Z-HDPE"). The term "was
REFERENCES:
patent: 4959396 (1990-09-01), Yankov et al.
patent: 5340840 (1994-08-01), Park et al.
patent: 5422377 (1995-06-01), Aubert
patent: 5667911 (1997-09-01), Yu et al.
Hasegawa Takuya
Kondo Takahiko
Asahi Kasei Kogyo Kabushiki Kaisha
Cooney Jr. John M.
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