Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Including strand or fiber material which is of specific...
Patent
1997-06-27
1999-03-30
Bell, James J.
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Including strand or fiber material which is of specific...
28104, 156 626, 1563082, 442361, 442364, 442408, 442409, D04H 100
Patent
active
058889167
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an improved wet-laid nonwoven fabric for a battery separator, a method for manufacturing the same, and a sealed type secondary battery using the same.
BACKGROUND ART
A nonwoven fabric for a battery separator has a function for separating an anode from a cathode, preventing electrode active material or electrode debris from migrating from one electrode to another to cause a short-circuit and for retaining an electrolyte therein. Also it must have a low internal resistance and/or a favorable chemical stability and durability against the electrolyte. Particularly, in a secondary battery such as a Ni-Cd storage battery, it is necessary that an oxygen gas generated upon overcharge due to a cathode reaction is smoothly consumed in an anode, and the electrolyte is prevented from being released from the separator due to the change in electrode thickness upon charging/discharging. A high gas-permeability and a high electrolyte holding capability are also required as a separator even after the compression is repeated. Also, a mechanical strength durable against a tension applied to the separator when the same is incorporated in a battery is one of the important requisites.
However, battery separators made of a conventional nonwoven fabric, such as a melt-blown type, a flash-spun type, a dry-laid type or a wet-laid type, have been unsatisfactory in the above requirement.
For example, Japanese Unexamined Patent Publication (Kokai) No. 1-157055 proposes the improvement in mechanical strength, electrolyte retention capability and short-circuit preventing ability, by heating a melt-blown type nonwoven fabric under a predetermined condition to form a compact structure on the surface thereof. However, the mechanical strength of the nonwoven fabric could not be improved by merely hot-pressing the same, but higher temperature and pressure are necessary for obtaining a desired mechanical strength, which results in a problem in that the electrolyte holding capability and gas-permeability deteriorate thereby. Japanese Unexamined Patent Publication (Kokai) No. 2-259189 discloses the improvement in mechanical strength and electrolyte retention capability of a nonwoven fabric by thermally bonding alkali-resistant fibers with hot-melt fibers in a wet-laid mixture fiber sheet. However, it is necessary to increase an amount of hot-melt fibers and increase the bonding temperature to obtain a higher mechanical strength, which results in a reduction in the number of voids in a fiber surface and a sheet to cause the deterioration of electrolyte retention capability. On the contrary, if a lower thermal bonding temperature is used, the mechanical strength becomes unsatisfactory for a battery separator and causes a problem in that the nonwoven fabric structure is liable to collapse upon compression, due to a poor interfiber entanglement, which results in the exhaustion of electrolyte in the separator; a so-called "dry-out"; and increases the electric resistance of the battery.
Japanese Unexamined Patent Publication (Kokai) No. 61-281454 discloses that a melt-blown type nonwoven fabric comprising fibers having a single fiber diameter in a range from 0.1 to 2 .mu.m is bonded with a sheet comprising fibers having a single fiber diameter of 5 .mu.m or more by highly pressurized water jets to result in a product suitably used for a battery separator, improved in air permeability and cathode/anode separation ability and capable of preventing short-circuit from occurring due to the migration of active material or debris from electrodes. However, the resultant nonwoven product has a plurality of through-holes on the surface thereof due to the highly pressurized water jets, which deteriorates the ability for preventing the active material from migrating. In Japanese Unexamined Patent Publication (Kokai) No. 5-89867, a method is disclosed wherein a nonwoven fabric is compressed with rolls having different peripheral speeds to contract the through-holes, but the through-holes, once formed on the sur
Goto Fumigo
Tadokoro Yoshiyuki
Takata Yoshinori
Uesaka Masaru
Asahi Kasei Kogyo Kabushiki Kaisha
Bell James J.
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