Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-04-30
2003-05-06
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C525S210000
Reexamination Certificate
active
06559195
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a microporous film. More particularly, the present invention relates to a microporous film which is used for separators for batteries.
BACKGROUND ART
Non-aqueous electrolytic batteries in which a light metal such as lithium is used as an electrode have high energy density and little self-discharge. Therefore, the application range of these batteries has broadened and has played a part in the trend towards high performance and miniaturization in electronic devices. As electrodes for the non-aqueous electrolytic batteries described above, there have been used spirally wound group in which the battery is constituted by laminating and winding a cathode, an anode and a separator in ribbon-shapes, whereby a wide effective electrode area is secured. In the separator, the short-circuiting of both electrodes is basically prevented, and at the same time the battery reaction can be carried out by transmitting ions owing to its microporous structure. However, those having a so-called “shut-down” function (SD function), wherein a resin is thermally deformed with an increase in the internal temperature of the battery when abnormal electric current is generated due to an improper connection at the external of the battery or the like, so that the resin is prevented from having microporous structure, thereby stopping the battery reaction, have been employed, from the viewpoint of improving the safety.
As the separators having the SD function described above, there have been known, for instance, microporous films made of polyethylenes, and microporous films having a multi-layered structure made of polyethylenes and polypropylenes.
However, with the recent progress in the lithium ion secondary batteries and the like, it is desired not only that the separator has the SD function described above, but also that the separator has heat resistance even at higher temperatures, because when the temperature is further raised after being shut-down, the separator itself is subjected to film-breaking upon melting (melt-down), or plasticization to be in a breakable state, so that there arise some risks of ignition and explosion. Especially, as the developments in the battery having high capacity and the reduction of the internal resistance of the battery progress, factors such as increasing heat generation arise, thereby making it increasingly important.
In view of the problems mentioned above, there have been known a separator for a battery in which the greater the difference between the shut-down temperature (SD temperature) and the film-breaking temperature, and the higher the film-breaking temperature, the better the high-temperature properties and the higher the safety. For instance, Japanese Patent Laid-Open No. Sho 63-308866 discloses a microporous film having high strength and excellent high-temperature property by laminating a single film made of a low-melting point polyethylene and a high-melting point polypropylene. However, the internal resistance of the separator becomes high by the lamination, so that it is inappropriate as a separator for high-performance batteries with the applications requiring high-outputs. In addition, Japanese Patent Laid-Open No. Hei 10-298325 discloses a microporous film made of a high-molecular weight polyethylene composition comprising a polyethylene and a polypropylene each having a low molecular weight. However, when the composition is subjected to a drastic temperature increase, the polyethylene material constituting a majority of the microporous film easily melts and becomes easily breakable, so that its risk is greater. In addition, in the future high-performance battery for such applications requiring high-outputs, there has been desired to have a heat resistance surpassing those of separators comprising polypropylene, which are conventional high heat resistance types.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a microporous film having excellent permeability and mechanical strength, and also having excellent SD function at low temperatures and film-breaking resistance at high temperatures.
Another object of the present invention is to provide a separator for a battery comprising the microporous film of the present invention.
Still another object of the present invention is to provide a battery comprising the separator for a battery of the present invention.
As a result of intensive studies in view of accomplishing the above objects, the present inventors have found that a microporous film, which is made of at least a ring-opening polymer of an unsaturated condensed alicyclic compound, and a polyolefin having a weight-average molecular weight of 500,000 or less, a thermoplastic elastomer, or a graft copolymer, has the excellent features of a low SD temperature and a high film-breaking temperature. The present invention has been accomplished thereby.
Specifically, the present invention relates to:
(1) a microporous film made of a resin composition at least comprising 1 to 50% by weight of a ring-opening polymer of an unsaturated condensed alicyclic compound and 1 to 50% by weight of one or more resin components selected from the group consisting of polyolefins having a weight-average molecular weight of 500000 or less, thermoplastic elastomers and graft copolymers;
(2) a separator for a battery comprising the microporous film of item (1) above; and
(3) a battery comprising the separator for a battery of item (2) above.
BEST MODE FOR CARRYING OUT THE INVENTION
The ring-opening polymer of the unsaturated condensed alicyclic compound usable in the present invention (hereinafter also referred to as “first resin component”) has an aliphatic ring and a double bond derived from its monomer units as the main component. In addition, a part of the double bond may be hydrogenated in the ring-opening polymer.
The above-mentioned unsaturated condensed alicyclic compounds are roughly classified into the following three series of compounds. A first series of compounds include, among those classified as the condensed alicyclic compounds in a narrow sense, unsaturated compounds one of which rings has a double bond incorporated into the main chain after the ring opening polymerization. In addition, derivatives in which some of hydrogen atoms of these unsaturated compounds are substituted with other substituents can be also used as unsaturated condensed alicyclic compounds. Concrete examples thereof include bicyclo[3.2.0]hept-6-ene, bicyclo[4.2.0]oct-7-ene, and derivatives thereof, and the like.
A second series of compounds include, among those classified as the bridge-ring cyclic compounds, unsaturated compounds one of which rings has a double bond incorporated into the main chain after the ring opening polymerization. In addition, derivatives in which some of hydrogen atoms of these unsaturated compounds are substituted with other substituents can be also used as unsaturated condensed alicyclic compounds. Concrete examples thereof include bicyclo[2.2.1]hept-5-ene (also referred in the present specification as norbornene); norbornene derivatives such as bicyclo[2.2.1]hept-5-ene-2,3-dicarboxymethyl esters; bicyclo[2.2.2]oct-2-ene and derivatives thereof, and the like.
A third series of compounds include, compounds having bridge ring and condensed aliphatic ring, each of which compounds has an aliphatic ring and a double bond in its main chain after the ring opening polymerization. Concrete examples thereof include tricyclo[5.2.1.0
2.6
]deca-3,8-diene (dicyclopentadiene), tetracyclododecene, and derivatives thereof, and the like.
Among these unsaturated condensed alicyclic compounds, norbornene and norbornene derivatives are preferable, from the viewpoints of feeding raw materials and the like. In addition, these unsaturated condensed alicyclic compounds can be used alone, or in admixture of two or more kinds, or they can be sequentially subjected to ring opening polymerization.
As the ring-opening polymer of the unsaturated condensed alicyclic
Emori Hideyuki
Fujita Shigeru
Noumi Shunsuke
Uetani Yoshihiro
Yamamoto Kazushige
Birch & Stewart Kolasch & Birch, LLP
Foelak Morton
Nitto Denko Corporation
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