Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
1998-08-14
2001-09-18
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
C429S250000
Reexamination Certificate
active
06291105
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a battery separator suitable for alkaline storage batteries such as nickel-cadmium batteries, nickel-zinc batteries, and nickel-hydrogen batteries, a method for manufacturing the same, and a battery using the same.
BACKGROUND OF THE INVENTION
For battery separators, non-woven fabrics comprising nylon and polypropylene fibers are generally used. Some non-woven fabrics called dry laid type non-woven fabrics are manufactured by a dry laid process, while other non-woven fabrics manufactured by a wet laid process are called wet laid type non-woven fabrics. As non-woven fabrics comprising nylon fibers have poor alkaline resistance, non-woven fabrics comprising polyolefin-based fibers such as polypropylene are preferably used.
Such non-woven fabrics comprising polyolefin-based fibers are, however, hydrophobic, and thus, they have poor wettability when used for battery separators. Therefore, various methods for providing hydrophilicity to polyolefin-based non-woven fabrics have been proposed. One of the well-known examples is a treatment of applying hydrophilic surfactants to non-woven fabrics for hydrophilicity. Tokko-Hei (Published Examined Japanese Patent Application) No. 1-36231 discloses a non-woven fabric comprising sheath-core type bi-component fibers of polypropylene/polyethylene with which vinyl monomer is graft-copolymerized. Tokko-Hei 5-46056 discloses a polypropylene non-woven fabric with which fluorine gas is contact-reacted, and Tokkai-Hei (Published Unexamined Japanese patent Application) No. 7-142047 discloses that splittable bi-component fibers comprising polyolefin/ethylene vinyl alcohol copolymer and polyolefin-based fibers are mixed and processed, entangled by using high-pressure water flow, and treated with corona surface discharge.
The above-mentioned battery separators, however, have several problems. For instance, a battery separator manufactured by providing a hydrophilic surfactant to a non-woven fabric for hydrophilicity is superior in the initial alkaline absorption and alkaline retaining property, but the surfactant adhered to the surface of the non-woven fabric will be washed away because of the repeated charge and discharge of the battery. As a result, the wettability of the alkaline electrolyte will be greatly lowered, and the battery life will be shortened.
The battery separators disclosed in Tokko-Hei 1-36231 and Tokko-Hei 5-46056 have non-woven fabrics having surfaces modified to provide hydrophilicity in order to improve durable hydrophilicity. These separators, however, require special work and the processability and productivity are poor, resulting in increased cost. Therefore, the separators are not practical.
Tokkai-Hei 7-142047 discloses a battery separator comprising 75-100 weight % of splittable bi-component fibers comprising hydrophobic polyolefin polymer and hydrophilic ethylene vinyl alcohol copolymer. Although the durable hydrophilicity of the fibers is improved by treating with corona charge for providing hydrophilic groups, the air permeability of the non-woven fabric is low due to the excessively small fiber gaps, and thus, the gas permeability required for a sealed battery is inferior.
SUMMARY OF THE INVENTION
This invention aims to provide a battery separator that has great alkaline absorption, alkaline retaining property and proper air permeability, which will improve the battery capacity without reducing the battery life, and also provide a battery with superior battery properties.
In order to achieve the purpose, a battery separator of this invention comprises a mixture of staple fibers comprising at least:
15-75 weight % of splittable bi-component fibers comprising polyolefin polymer (component A) and polyolefin polymer containing oxygen atoms (component B) that are arranged adjacent to each other when viewed in fiber cross-section;
20-60 weight % of thermal bonding fibers; and
0-50 weight % of synthetic fibers having greater fineness (i.e. the fibers are thicker) than that of ultra fine fibers formed by splitting the above-identified splittable bi-component fibers;
wherein the splittable bi-component fibers are split to form ultra fine fibers as the fibers are entangled and partially bonded to each other; and functional groups are present in the fibers on the surface of the non-woven fabric, and the percentage of the functional groups or the bonds to all the carbon atoms on the non-woven fabric is within the following range.
(1) Aldehyde groups (—CHO) or aldehyde bonds (—C
+
H—O
−
): 10-40%
(2) Carbonyl groups or carbonyl bonds (—CO—): 3-30%
(3) Carboxyl groups (—COO
+
)or ester bonds (—COO—): 0-15%
(4) Residual carbon atoms: 15-87%
It is preferable in the battery separator of the invention that the fiber length of the splittable bi-component fibers, thermal bonding fibers and the synthetic fibers ranges from 3 to 25 mm, and the fineness of the synthetic fibers is preferably the same or smaller than that of the thermal bonding fibers.
It is also preferable in the battery separator that the air permeability ranges from 5 to 50 ccs.
It is also preferable in the battery separator that the alkaline absorption height (durable alkaline absorption) at a third time is no less than 5 mm.
It is also preferable in the battery separator that the thermal bonding fibers are sheath-core type bi-component fibers whose sheath is polyethylene and whose core is polypropylene.
It is also preferable in the battery separator that the non-woven fabric is a composite non-woven fabric manufactured by laminating fiber webs of various fiber lengths.
It is also preferable in the battery separator that at least one sheet is laminated on at least one layer of the non-woven fabric.
It is also preferable in the battery separator that the component B is at least one polymer selected from the group consisting of ethylene vinyl alcohol copolymer, ethylene-(meth)acrylate copolymer, ethylene-(meth)acrylic acid copolymer and ethylene-vinyl acetate copolymer.
A method for manufacturing a battery separator of this invention comprises the steps of:
mixing and wet laid processing 15-75 weight % of splittable bi-component fibers 3-25 mm in length comprising polyolefin polymer (component A) and polyolefin polymer containing oxygen atoms (component B) that are arranged adjacent to each other when viewed in fiber cross-section, 20-60 weight % of thermal bonding fibers 3-25 mm in length, and 0-50 weight % of synthetic fibers 3-25 mm in length whose fineness is greater than that of ultra fine fibers formed by splitting the splittable bi-component fibers and is the same or smaller than that of the thermal bonding fibers in order to form a wet laid type non-woven fabric;
splitting the splittable bi-component fibers to form ultra fine fibers and to entangle the fibers in at least one step selected from the group consisting of wet laid process and a step following the formation of the wet laid type non-woven fabric; and
treating both the surfaces of the non-woven fabric with corona surface discharge and calendering by heated rollers.
It is preferable in the method that the splittable bi-component fibers are split by the impact provided by the stirring in the wet laid process.
It is preferable in the method that the splittable bi-component fibers are split by high-pressure water flow treatment.
It is preferable in the method that the split-formed ultra fine fibers are entangled by high-pressure water flow treatment.
It is preferable in the method that the split of the splittable bi-component fibers and the entanglement of the then-formed ultra fine fibers are conducted simultaneously by high-pressure water flow treatment.
It is preferable in the method that the total discharge amount to treat both the surfaces of the non-woven fabric with the corona surface discharge ranges from 0.05 to 5 kW·minute/m
2
.
It is also preferable in the method that a hydrophilic surfactant is applied to the non-woven fabric after the corona surface discharge treatment.
It is also preferable in the method that the component B is at least
Hori Shuuji
Kida Tatsunori
Sano Toyohiko
Tanaka Tomofumi
Yamamoto Hiroyuki
Brouillette Gabrielle
Daiwabo Co., Ltd.
Merchant & Gould P.C.
Ruthkosky Mark
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