JP4291794B2 - Battery separator and battery using the same - Google Patents

Description

  The present invention relates to a battery separator suitable for alkaline storage batteries such as nickel-cadmium batteries, nickel-zinc batteries, nickel-hydrogen batteries, and a method for producing the same.

  In recent years, nonwoven fabrics made of polyolefin fibers such as polypropylene have been preferably used as battery separators, and battery separators in which nonwoven fabrics made of polyolefin ultrafine fibers have been hydrophilized have been proposed. For example, in the present applicant, Japanese Patent Application Laid-Open No. 5-186911 and Japanese Patent Application Laid-Open No. 5-186964 disclose sulfonation in which a sulfo group is introduced into a split type composite fiber comprising a combination of methylpentene polymer / polyolefin polymer. A fiber assembly containing 60% by weight or more of polyolefin fiber is proposed.

  Japanese Patent Application Laid-Open No. 7-147154 discloses a battery separator obtained by hydrophilizing a hydroentangled nonwoven fabric comprising 50% by weight or more of a polyolefin-based split composite fiber by graft polymerization or sulfonation of a vinyl monomer. ing. JP-A-8-273654 discloses a battery separator in which a hydroentangled non-woven fabric in which polyolefin ultrafine fibers are 50% by weight or more, and the ultrafine fibers are partially fused to each other is hydrophilized. ing.

  However, the battery separator has the following problems. For example, when the fiber assembly of JP-A-5-186911 and JP-A-5-186964 is used as a battery separator, the strength of the nonwoven fabric after the sulfonation treatment tends to be low, and the cost is high. I can't say that. In addition, the battery separator disclosed in Japanese Patent Application Laid-Open No. 7-147154 is mainly composed of split composite fibers made of polypropylene / polyethylene and thermally bonded by composite adhesive fibers made of a combination of polypropylene / low-density polyethylene. However, it is inferior in processability, for example, it cannot be efficiently hydrophilized. In order to solve this problem, the battery separator disclosed in Japanese Patent Laid-Open No. Hei 8-273654 is obtained by fusing together low melting point ultrafine fibers, which are one component of a split type composite fiber, and then splitting and intertwining them. Therefore, although the strength of the nonwoven fabric is improved, since the ultrafine fiber component itself is self-fused, it is difficult to secure voids, which is insufficient in terms of liquid retention.

  In view of these circumstances, the present invention has excellent liquid retention and sufficient non-woven fabric strength, battery separators that can contribute to the improvement of battery capacity without reducing battery life, and excellent self-discharge characteristics. It was made for the purpose of obtaining a battery having excellent battery characteristics.

The battery separator of the present invention comprises a poly (4-methylpentene-1) or a methylpentene polymer composed of a copolymer of 4-methylpentene-1 and another olefin as a first component, Is a split-type composite in which a different polyolefin polymer or a copolymer thereof is used as the second component, two components are alternately arranged adjacent to each other in the fiber cross section, and at least one of the two components is divided into two or more. A nonwoven fabric comprising at least two types of fibers and a polyolefin-based composite fiber composed of a high-melting-point component and a low-melting-point component, wherein each of the split-type composite fiber and the polyolefin-based composite fiber has a content of 60% by weight. The polyolefin is hydrophilized, the melting point of the second component of the split-type conjugate fiber is D _2m , and the polyolefin D _2m , B _1m, and B _2m satisfy a specific relational expression, where B _{1m is} the melting point of the high melting point component and B _2m is the melting point of the low melting point component . It has been found that by adopting such a configuration, a battery separator having excellent liquid retention and sufficient nonwoven fabric strength and excellent battery characteristics can be obtained.

  In the battery separator of the present invention, it is desirable that the content of the split composite fiber is 15 to 60% by weight, the content of the polyolefin-based composite fiber is 20 to 60% by weight, and 40% by weight of other synthetic fibers. You may make it contain in the range which does not exceed%.

  The nonwoven fabric is preferably heat-sealed with the low-melting-point component of the polyolefin-based conjugate fiber without substantially melting the two components constituting the split-type conjugate fiber.

  Moreover, when the fiber lengths of the split composite fiber, polyolefin composite fiber, and other synthetic fibers constituting the nonwoven fabric are 3 to 25 mm, a dense nonwoven fabric is obtained, which is advantageous in terms of liquid retention.

  The nonwoven fabric is desirably a composite nonwoven fabric obtained by laminating fiber webs having different fiber lengths from the viewpoint of improving the strength of the nonwoven fabric.

  A preferable embodiment of the battery separator of the present invention is a composite sheet obtained by laminating another sheet on at least a part of the nonwoven fabric, and the composite sheet is hydrophilized. This form is advantageous in terms of winding strength and short-circuit resistance because the nonwoven fabric strength is improved.

  In another preferred embodiment of the battery separator of the present invention, it is desirable that another sheet is laminated on at least a part of the hydrophilic treated nonwoven fabric.

  It is desirable that the split type composite fiber has a methylpentene polymer as a first component and a polypropylene polymer as a second component.

  The hydrophilization treatment is preferably a sulfonation treatment. When any one of the fuming treatment, fuming sulfuric acid treatment, chlorosulfonic acid treatment, or anhydrous sulfuric acid treatment is used, the battery is self-dischargeable. This is advantageous in that it can be improved. The sulfonation degree is preferably 0.4 to 2% by weight.

  Among the above, a battery incorporating any of the battery separators improves self-discharge and is particularly suitable for an electric vehicle (PEV) or a hybrid vehicle (HEV).

  The battery separator of the present invention is mainly composed of a split type composite fiber composed of a methylpentene polymer and a polyolefin polymer, and a polyolefin composite fiber composed of a high melting point component and a low melting point component, and is subjected to a hydrophilic treatment. In addition to heat resistance, it has excellent liquid retention and sufficient nonwoven fabric strength, and can improve battery capacity without reducing battery life. When the hydrophilization treatment is a sulfonation treatment, it contributes particularly to improvement of self-discharge properties.

BEST MODE FOR CARRYING OUT THE INVENTION

The contents of the present invention will be specifically described below.
The split-type composite fiber used in the present invention has, as a first component, a poly (4-methylpentene-1) or a methylpentene-based polymer composed of a copolymer of 4-methylpentene-1 and another olefin. A polyolefin-based polymer different from the component or a copolymer thereof is used as the second component, two components are alternately arranged adjacent to each other in the fiber cross section, and at least one of the two components is divided into two or more, The structural units are continuous in the length direction, and a part of all the structural units always has a cross-sectional shape exposed on the fiber surface. Specifically, the one in which the first component and the second component are arranged as shown in FIGS. 1 to 3 can be preferably used.

  Examples of the methylpentene polymer that is the first component of the split composite fiber include poly (4-methylpentene-1) or a copolymer of 4-methylpentene-1 and another olefin. Examples of other olefins include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, and 3-methyl-1-butene.

As the second component of the split type composite fiber, a polyolefin polymer different from the first component such as polyethylene, polypropylene, polybutene-1, or a copolymer thereof is used, and in particular, the melting point (D _2m ) is 130 ° C. As described above, a polyolefin polymer having a temperature of 150 ° C. or higher or a copolymer thereof may be used. The split-type composite fiber composed of the first component and the second component has excellent heat resistance and can sufficiently cope with an extreme reaction in the battery. Of these, a combination in which a methylpentene polymer is the first component and a polypropylene polymer is the second component is the most effective.

  The division number of both components in the split type composite fiber is preferably 5 to 20, and the composite ratio of both components is about 30:70 to 70:30 for the first component: second component from the viewpoint of easy spinning process. preferable. Further, the fineness of the split-type composite fiber may be appropriately determined by adjusting the number of splits and the composite ratio so that the fineness of each constituent unit after splitting is 0.1 to 0.5 dtex. When the fineness of each constituent unit after the division is less than 0.1 dtex, when the treatment with fuming sulfuric acid or chlorosulfonic acid is performed, rapid deterioration occurs, and the strength of the nonwoven fabric is lowered. This is because if it exceeds 0.5 dtex, the difference in fineness with a composite fiber or synthetic fiber described later is reduced, and a dense void cannot be secured.

  The proportion of the split composite fiber in the battery separator of the present invention is in a range not exceeding 60% by weight, and preferably 15 to 60% by weight. More preferably, it is 20 to 60% by weight. If the content of the split-type composite fiber is too small, the ratio of methylpentene polymer is too small, so it is impossible to introduce sufficient hydrophilic groups unless the conditions are strongly hydrophilic, leading to a decrease in the strength of the nonwoven fabric and high costs. It becomes. This is because if it exceeds 60% by weight, the strength of the nonwoven fabric after hydrophilization tends to be low, and the cost increases.

The polyolefin-based composite fiber composed of a high melting point component and a low melting point component used in the present invention is a polyolefin polymer such as polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1, ethylene-vinyl alcohol copolymer, or the like. The copolymer is used. Melting point B _{1 m} of high melting point component _and the melting point of the low melting point component and B _2m, low melting component satisfying the following relationships.
(1) B _1m > B _2m
(2) 120 ° C. <B _2m <D _2m
Examples of the polyolefin-based composite fibers satisfying the above relationship include high-density polyethylene / polypropylene, ethylene-propylene copolymer / polypropylene, and the like. It is preferable in that peeling is small and sufficient fusion strength is obtained.

  The fiber form of the conjugate fiber is not particularly limited, and examples thereof include concentric or eccentric sheath-core conjugate fibers, parallel conjugate fibers, or single fibers in which two or more of the above materials are mixed, and the cross-sectional shape is also circular or irregular. Any of these may be used.

  In the present invention, in particular, a concentric sheath / core composite fiber made of a combination of high density polyethylene / polypropylene has a wide processing temperature range during heat treatment of the nonwoven fabric, and the resulting nonwoven fabric has high strength, chemical resistance, and oxidation resistance. It is preferable at the point which is excellent in deterioration.

  And the said polyolefin-type composite fiber is the range which does not exceed 60 weight%, and it is preferable to contain 20 to 60 weight%. More preferably, it is 40 to 60% by weight. This is because if the content of the polyolefin-based composite fiber is too small, sufficient strength of the nonwoven fabric cannot be obtained, and if it exceeds 60% by weight, it is difficult to secure voids, which is insufficient in terms of liquid retention.

  Furthermore, you may mix the other synthetic fiber in the battery separator of this invention in the range which does not exceed 40 weight%. More preferably, it is 20 to 40% by weight. This is because if the content of other synthetic fibers exceeds 40% by weight, the effect of the hydrophilic treatment is reduced and the required performance cannot be obtained. For example, if the gap formed between the fibers is to be secured, the synthesis is greater than the fineness of each constituent unit after splitting formed by splitting the split-type composite fiber, and is equal to or smaller than the fineness of the polyolefin-based composite fiber. A fiber may be used, and if the hydrophilicity is further improved, a synthetic fiber in which a hydrophilizing agent or the like is premixed in a resin may be used. The other synthetic fibers are selected from those that do not substantially melt at the temperature at which the polyolefin-based composite fiber melts, and commonly used synthetic fibers such as polypropylene, polyester, and nylon can be used. Among these, a polypropylene fiber having a fineness of 0.5 to 5 dtex and a fiber strength of 6 to 15 cN / dtex is preferable in terms of high chemical resistance.

  The form of the fiber web containing the constituent fibers is a dry fiber obtained by a card method, an air lay method or the like, a wet web obtained by a wet method, or a long fiber obtained by a direct method such as a melt blow method or a spun bond method. The web. Among these, a wet web having a fiber length of 3 to 25 mm is preferable from the viewpoint of obtaining a homogeneous web. A more preferable fiber length is 5 to 15 mm. If the fiber length is less than 3 mm, the fibers are scattered during the high-pressure water flow treatment described later, resulting in insufficient entanglement between the fibers. This is not preferable in the process, and if the fiber length exceeds 25 mm, the fibers in the slurry are particularly produced by wet papermaking. This is because the dispersibility of the resin deteriorates and a uniform nonwoven fabric cannot be obtained.

  These fiber webs are treated by methods such as thermal calendaring, hot air processing, and high-pressure water flow. At this time, it is preferable that at least the two components constituting the split-type conjugate fiber are not melted substantially and are thermally fused by the low melting point component of the polyolefin-based conjugate fiber. The term “substantially melted” as used herein refers to a material in which a part of the fiber is completely melted, not softened and flattened by thermocompression bonding or the like, and the fibers are not in close contact with each other. When the constituent fibers are heat-sealed only with the low-melting-point component of the polyolefin-based composite fiber, the ultrafine fiber and other synthetic fibers obtained by dividing the split-type composite fiber ensure voids, and the high Since the melting point component maintains the fiber strength and is fused, there is little variation in the strength of the nonwoven fabric, and a dense void can be secured.

  And as another form of a nonwoven fabric, the composite nonwoven fabric which laminated | stacked by changing suitably the mixing rate within the range of the said structural fiber, or laminated | stacked the fiber web from which fiber length differs may be sufficient. For example, in the case of the latter, a fiber web made of a staple paper having a fiber length of more than 25 mm or a long fiber web is laminated on at least one surface of the fiber web by a wet papermaking method made of constituent fibers having a fiber length of 3 to 25 mm. be able to. When fiber webs with different fiber lengths are laminated, the fiber webs with short fiber lengths contribute to the denseness, and the fiber webs with long fiber lengths contribute to the improvement of nonwoven fabric strength, resulting in excellent productivity when incorporating batteries. convenient. These fiber webs are in any form, such as unbonded webs such as card webs, bonded nonwoven fabrics in which some of the constituent fibers are bonded by an adhesive or self-adhesion, or nonwoven fabrics entangled by needle punching or high-pressure water flow treatment. There may be. As a laminating method, fibers may be entangled after laminating unbonded webs, or at least one fiber web is previously woven with a non-woven fabric by the above bonding or entanglement method, and then the fibers are entangled. May be.

  Furthermore, as another form of the nonwoven fabric, another sheet may be laminated on at least a part of the layer of the nonwoven fabric. Here, another sheet may be laminated on at least a part of the nonwoven fabric in advance to prepare a composite sheet, and then a hydrophilic treatment may be performed, or the nonwoven fabric may be hydrophilized in advance. After the treatment, another sheet may be laminated on at least a part of the layers. The other sheet here is a wet nonwoven fabric composed of fibers having a fiber length of 3 to 25 mm, a bonded nonwoven fabric obtained by bonding a part of constituent fibers composed of fibers having a fiber length of more than 25 mm by an adhesive or self-adhesion, Non-woven fabric or porous film entangled by needle punching or high-pressure water flow treatment. When a wet nonwoven fabric made of fibers having a fiber length of 3 to 25 mm is used among the other sheets, a nonwoven fabric with a low basis weight and a small percentage of through-holes can be obtained, and the short-circuit rate in the battery can be reduced. . Further, if a fiber or a porous film having a fiber length exceeding 25 mm is used, the strength of the nonwoven fabric can be further improved.

  The material of the other sheet is not particularly limited, and may be any of polyolefin resin, polyamide resin, polyester resin, and the like. Further, the lamination method is not particularly limited as long as another sheet is laminated on at least a part of the layers, and another sheet may be laminated on one side or both sides of the nonwoven fabric of the present invention. Another sheet may be inserted into the sheet. Furthermore, the above laminate may be laminated in two or more layers. And the bonding method between each layer in the laminate is not particularly limited, for example, the nonwoven fabric of the present invention is prepared in advance by high-pressure water flow treatment and laminated with other sheets, and then hot air, a hot roll, etc. It may be bonded by heat treatment, or may be bonded by high-pressure water flow treatment after previously laminating the fiber web constituting the present invention and another sheet.

The basis weight of the non-woven fabric or composite sheet can be adjusted depending on the amount of fibers, but is preferably 30 to 100 g / m ² . Since the strength of the nonwoven fabric becomes low at less than 30 g / m ^2, short circuit easily occurs between the positive electrode and the negative electrode, exceeds 100 g / m ² breathable like is lowered.

  And it is preferable that the nonwoven fabric or composite sheet mentioned above is hydrophilized. Hydrophilic treatment includes vinyl monomer graft copolymerization treatment, fluorine gas treatment, sulfonation treatment, corona discharge treatment, plasma treatment, etc. Among them, sulfonation treatment improves the self-discharge property of the battery. Excellent sulfonation treatment includes concentrated sulfuric acid treatment, fuming sulfuric acid treatment, chlorosulfonic acid treatment, sulfuric anhydride treatment, etc. Among the sulfonation treatment, fuming sulfuric acid treatment, chlorosulfonic acid treatment, or sulfuric anhydride treatment Is preferable because of its high reactivity and relatively easy sulfonation treatment. Further, the degree of sulfonation is preferably 0.4 to 2% by weight, and more preferably 0.7 to 1.5% by weight. When the degree of sulfonation is less than 0.4% by weight, the improvement of the self-discharge property of the battery is insufficient, and when it exceeds 2% by weight, not only the treatment cost is increased, but also the strength of the nonwoven fabric is reduced. Because. The hydrophilization treatment is preferably performed after the formation of the nonwoven fabric in terms of productivity. However, when the nonwoven fabric is a laminate, it is sufficient that at least the nonwoven fabric containing the split-type conjugate fiber is hydrophilized.

  Next, an example of the manufacturing method of the battery separator of the present invention will be described. As a method for producing the nonwoven fabric used as the base material of the separator of the present invention, the wet papermaking method is desirable, and the wet papermaking may be performed by an ordinary method. First, 15 to 60% by weight of split-type composite fiber, 20 to 60% by weight of polyolefin-based composite fiber, and other synthetic fibers are mixed within a range not exceeding 40% by weight, and a concentration of 0.01 to 0.6% Disperse in water to prepare a slurry. At this time, a small amount of a dispersant may be added. The slurry is made using a short net type, a circular net type, or a paper machine using a combination of both. Next, it is preferable to melt the polyolefin-based composite fiber so that the fibers are lightly bonded to each other because the nonwoven fabric is easy to handle. The polyolefin-based composite fiber may be melted at the same time as drying during the drying process in the paper making process, or may be carried out by heat treatment after making the wet nonwoven fabric once.

Then, the fibers are lightly bonded by melting the polyolefin-based composite fiber and the form is stabilized, and then subjected to a high-pressure water flow treatment to divide the split-type composite fiber to form ultrafine fibers and between the fibers. It is good to entangle. In the high-pressure water flow treatment, a columnar water flow having a water pressure of 5 to 20 MPa is preferably sprayed once or more on the front and back of the nonwoven fabric from a nozzle in which orifices having a hole diameter of 0.05 to 0.5 mm are provided at intervals of 0.5 to 1.5 mm. . The obtained entangled nonwoven fabric may be dried at 120 to D _{2 m} ° C., preferably 130 to 145 ° C., and simultaneously heat-bonded the constituent fibers with the low melting point component of the polyolefin-based composite fiber.

  Thereafter, the nonwoven fabric is immersed in a fuming sulfuric acid reaction tank, a chlorosulfonic acid reaction tank, or a sulfuric anhydride reaction tank, and a sulfone group is introduced. The sulfonation treatment conditions may be set as appropriate so that the sulfonation degree is 0.4 to 2% by weight. For example, in the case of sulfuric anhydride treatment, the sulfur trioxide gas concentration is 10 to 80% by volume, the reaction The treatment may be performed at a temperature of 10 to 90 ° C. and a reaction time of 10 to 600 seconds. At this time, in order to promote sulfonation, the surface of the nonwoven fabric may be activated by ultraviolet rays or radiation and then subjected to sulfonation treatment.

  Furthermore, after a hydrophilic treatment is performed on the nonwoven fabric, a hydrophilic surfactant may be uniformly attached by a dipping method, a spray method, a roll touch method, or the like, or other hydrophilic treatment methods may be combined. Thereafter, it is heat calendered, adjusted to a predetermined thickness, and the battery separator of the present invention is obtained.

  Hereinafter, the contents of the present invention will be described with reference to examples. The tensile strength, liquid retention rate, short rate, capacity storage rate, cycle life, and degree of sulfonation were measured by the following methods.

(1) Vertical tensile strength In accordance with JIS L 1096, a sample piece having a width of 5 cm and a length of 15 cm is gripped at a spacing of 10 cm with respect to the vertical direction of the nonwoven fabric, and a tensile speed of 30 cm using a constant-speed extension type tensile tester. The tensile strength was taken as the load value at the time of cutting.

(2) Liquid retention rate The weight (W) of the test piece in a water equilibrium state is measured to 1 mg. Then the test piece was immersed in KOH solution having a specific gravity of 1.30, after standing KOH solution is pulled up from the later solution imbibed 1 hour 10 minutes, and weighed (W ₁₎ of the test specimen, holding The liquid retention rate was calculated from the formula: liquid ratio (%) = ((W ₁ −W) / W) × 100.

(3) Cylindrical sealed nickel metal hydride battery The negative electrode was prepared by adding water to a hydrogen storage alloy, carbonyl nickel, carboxymethylcellulose (CMC), and polytetrafluoroethylene (PTFE) and kneading to prepare a slurry. This slurry was dip-coated on nickel-plated punching metal, dried at 80 ° C., and pressure-molded to prepare a hydrogen storage alloy negative electrode. A known sintered nickel electrode was used as the positive electrode. Each separator was sandwiched between the negative electrode and the positive electrode, inserted into a battery case, and an electrolytic solution was injected to prepare a cylindrical sealed nickel metal hydride battery.

(4) Capacity Preservation Rate The produced cylindrical sealed nickel metal hydride battery was charged at a 0.1C rate for 12 hours, rested for 0.5 hour, discharged at a 0.1C rate and a final voltage of 1.0 V, and charged and discharged for 10 cycles. Repeatedly, the initial battery activity was performed.
After the initial activation, the charge 0.1 C rate for 12 hours, the rest 0.5 hour, the discharge 0.1 C rate and the final voltage 1.0 V, the same conditions for the discharge capacity after 5 cycles repeated The ratio of the remaining capacity (0.1 C rate discharge, final voltage 1.0 V) when left at 45 ° C. for 14 days after charging at (0.1 C rate) was defined as the capacity storage rate after self-discharge. Charging / discharging was performed at 25 degreeC.

(5) Short-circuit rate When 100 cylindrical sealed nickel-metal hydride batteries were assembled, the rate at which a short circuit occurred was defined as the short-circuit rate.

(6) Cycle life The theoretical capacity of a cylindrical sealed nickel-metal hydride battery that was initially activated was charged at a rate of 0.1 C, 10 hours, downtime 0.5 hours, and discharged at a rate of 0.1 C (end voltage 1.0 V). The number of cycles was obtained when the utilization ratio for the ratio was 90% or less. Charging / discharging was performed at 25 degreeC.

(7) Degree of sulfonation A test piece of 5 cm × 5 cm was taken from the sample and immersed in a 13% KOH aqueous solution for 30 minutes. Thereafter, the sample was washed with tap water for 30 minutes, and the sample washed with pure water for 30 minutes was dried at 60 ° C. for 1 hour to prepare a sample. And the sulfur element density | concentration in a nonwoven fabric was measured using the fluorescent X-ray-measurement apparatus, and what was remove | divided by the total element density | concentration and made 100 times was made into the sulfonation degree.

(8) Preparation of fibers The following fibers were prepared as raw materials.
[Fiber 1] The first component is a methylpentene copolymer having a melting point (D _1m ) of 240 ° C. (manufactured by Mitsui Chemicals), and the second component is polypropylene having a melting point (D _2m ) of 163 ° C. (Nippon Polychem Corporation) 1), a split type composite fiber having a composite ratio of 50:50, a fineness of 2.3 dtex having a fiber cross section shown in FIG. 1, and a fiber length of 6 mm.

[Fiber 2] The first component is a methylpentene copolymer having a melting point (D _1m ) of 240 ° C. (manufactured by Mitsui Chemicals), and the second component is polypropylene having a melting point (D _2m ) of 163 ° C. (Nippon Polychem Corporation) 1), a split type composite fiber having a composite ratio of 50:50, a fineness of 2.3 dtex having a fiber cross section shown in FIG. 1, and a fiber length of 45 mm.

[Fiber 3] The sheath component is a high-density polyethylene (manufactured by Nippon Polychem Co., Ltd.) having a melting point (B _2m ) of 132 ° C., and the core component is polypropylene (manufactured by Nippon Polychem Co., Ltd.) having a melting point (B _1m ) 163 ° C. A concentric sheath-core type composite fiber having a composite ratio of 50:50, a fineness of 1.7 dtex, and a fiber length of 10 mm.

[Fiber 4] The sheath component is a low density polyethylene (manufactured by Nippon Polychem Co., Ltd.) having a melting point (B _2m ) of 105 ° C., and the core component is polypropylene (manufactured by Nippon Polychem Co., Ltd.) having a melting point (B _1m ) of 163 ° C. A concentric sheath-core type composite fiber having a composite ratio of 50:50, a fineness of 1.7 dtex, and a fiber length of 10 mm.

[Fiber 5] The sheath component is a high-density polyethylene (manufactured by Nippon Polychem Co., Ltd.) having a melting point (B _2m ) of 132 ° C., and the core component is polypropylene (manufactured by Nippon Polychem Co., Ltd.) having a melting point (B _1m ) of 163 ° C. A concentric sheath-core type composite fiber having a composite ratio of 50:50, a fineness of 1.7 dtex, and a fiber length of 51 mm.

  [Fiber 6] Polypropylene fiber made of polypropylene (manufactured by Nippon Polychem Co., Ltd.) having a melting point of 163 ° C., having a fineness of 0.8 dtex and a fiber length of 10 mm.

  [Fiber 7] Polypropylene fiber made of polypropylene (manufactured by Nippon Polychem Co., Ltd.) having a melting point of 163 ° C., having a fineness of 0.8 dtex and a fiber length of 51 mm.

  [Fiber 8] 2. The first component is an ethylene-vinyl alcohol copolymer (ethylene content 38 mol%), the second component is polypropylene, the composite ratio is 50:50, and the fineness having the fiber cross section shown in FIG. Split composite fiber with 3dtex and 6mm fiber length.

[Example 1]
40% by weight of fiber 1, 40% by weight of fiber 3 and 20% by weight of fiber 6 are mixed to prepare a slurry to a concentration of 0.5%, and wet paper making is used to make a base paper having a basis weight of 80 g / m ² . Got. By spraying a high-pressure columnar water stream from the front and back surfaces of the base paper at a pressure of 10 MPa, the fibers 1 are divided to form ultrafine fibers, and the fibers are entangled and thermally fused simultaneously with drying at 135 ° C. to obtain a nonwoven fabric. It was.

The obtained non-woven fabric was immersed in a treatment bath at 40 ° C. mixed with 50% by weight of chlorosulfonic acid and 50% by weight of concentrated sulfuric acid for 1 hour, then immersed in dilute sulfuric acid for 10 minutes and then immersed in KOH solution for 1 hour. Neutralization. Thereafter, the plate was washed with water and dried, and then subjected to a heat calendar treatment to obtain a battery separator having a basis weight of 65 g / m ² and a thickness of 0.15 mm.

[Example 2]
A battery separator having a basis weight of 65 g / m ² and a thickness of 0.15 mm was obtained in the same manner as in Example 1 except that 100% chlorosulfonic acid was used as the treatment liquid.

[Example 3]
A battery separator having a basis weight of 65 g / m ² and a thickness of 0.15 mm was obtained in the same manner as in Example 1 except that the treatment liquid was a mixed liquid of fuming sulfuric acid 20% by weight and concentrated sulfuric acid 80% by weight.

[Example 4]
The fibers 1 40 wt%, the fiber 3 40 wt%, the fiber 6 to prepare a slurry to 0.5% concentration by mixing 20 wt%, a basis weight of 55 g / m ² by a wet paper making raw paper Got. By spraying a high-pressure columnar water stream from the front and back surfaces of the base paper at a pressure of 10 MPa, the fibers 1 are divided to form ultrafine fibers, and the fibers are entangled and thermally fused simultaneously with drying at 135 ° C. to obtain a nonwoven fabric. It was.

The obtained nonwoven fabric was immersed in an aqueous acrylic acid solution, and then irradiated with ultraviolet rays to graft copolymerize acrylic acid monomers. The nonwoven fabric was washed to remove unreacted acrylic acid, and then dried and subjected to a heat calendering process to obtain a battery separator having a basis weight of 65 g / m ² and a thickness of 0.15 mm.

[ Reference Example 1 ]
40% by weight of fiber 2, 40% by weight of fiber 4, and 20% by weight of fiber 7 were mixed to prepare a fiber web having a basis weight of 30 g / m ² using a semi-random card machine. Then, by spraying a high-pressure columnar water stream from the front and back surfaces of the fiber web at a pressure of 5 MPa, the fibers 2 are divided to form ultrafine fibers, and the fibers are entangled and thermally fused simultaneously with drying at 135 ° C. A dry nonwoven fabric having a basis weight of 30 g / m ² was obtained.

Next, in the wet paper machine, the non-woven fabric is installed on the entrance side of the Yankee dryer, and a slurry with a concentration of 0.5% composed of the constituent fibers of Example 1 is prepared, so that the basis weight is 50 g / m ^2. While making paper, laminated dry non-woven fabrics were laminated and heat-treated with a 135 ° C. Yankee dryer, and the heat-fusible fibers in both layers were fused to obtain a composite non-woven fabric.

The obtained non-woven fabric was immersed in a treatment bath at 40 ° C. mixed with 50% by weight of chlorosulfonic acid and 50% by weight of concentrated sulfuric acid for 1 hour, then immersed in dilute sulfuric acid for 10 minutes and then immersed in KOH solution for 1 hour. Neutralization. Thereafter, the plate was washed with water and dried, and then subjected to a heat calendar treatment to obtain a battery separator having a basis weight of 65 g / m ² and a thickness of 0.15 mm.

[ Reference Example 2 ]
A battery separator having a basis weight of 65 g / m ² and a thickness of 0.15 mm was obtained in the same manner as in Example 1 except that the fiber 4 was used instead of the fiber 3 as a raw material.

[Example 5 ]
A battery having a basis weight of 65 g / m ² and a thickness of 0.15 mm in the same manner as in Example 1 except that the mixing ratio of the fibers was 10% by weight for fiber 1, 50% by weight for fiber 3, and 40% by weight for fiber 6. A separator was obtained.

[Example 6 ]
The nonwoven fabric of Example 1 was treated in sulfur trioxide gas for 30 seconds, neutralized with sodium hydroxide, washed with ion-exchanged water, and dried at 60 ° C. A thermal calendar process was performed to obtain a battery separator having a basis weight of 65 g / m ² and a thickness of 0.15 mm.

[Comparative Example 1]
A battery separator having a basis weight of 65 g / m ² and a thickness of 0.15 mm was obtained in the same manner as in Example 1 except that the fiber 8 was used instead of the fiber 1 as a raw material.
The physical properties of Examples 1 to 6 , Reference Examples 1 and 2, and Comparative Example 1 are shown in Table 1.

Since Example 4 does not have a sulfone group, the cycle life is slightly short, and Example 5 has a small amount of mixed composite fibers composed of a methylpentene polymer and a polyolefin polymer, so that hydrophilic groups are introduced. Although not only the amount is small, the separator lacks the denseness, the capacity storage rate and the cycle life are slightly lowered, but in Examples 1 to 3 and 6 , the sufficient strength is retained even after the hydrophilic treatment, In addition, the capacity preservation rate when incorporated in a battery was maintained at about 80%, which contributed to the improvement of self-discharge. On the other hand, in Comparative Example 1, the fiber is damaged more than necessary due to the harsh hydrophilic treatment such as sulfonation treatment, the tensile strength in the vertical direction is extremely lowered, causing breakage during assembly, and the short-circuit rate is increased. Productivity was significantly reduced.

  A battery incorporating the battery separator of the present invention has improved self-discharge characteristics, and is particularly suitable for electric vehicles (PEV) and hybrid vehicles (HEV).

An example of fiber sectional drawing of the split type composite fiber used for this invention is shown. An example of fiber sectional drawing of the split type composite fiber used for this invention is shown. An example of fiber sectional drawing of the split type composite fiber used for this invention is shown.

Explanation of symbols

1. First component Second component

Claims (14)

A battery separator in which a non-woven fabric made of a fiber (excluding a resin having a molecular structure of syndiotactic poly (1,2-butadiene)) is hydrophilized, and the non-woven fabric is made of poly (4 -Methylpentene-1) or a polyolefin-based polymer different from the first component, or a copolymer thereof, comprising a methylpentene-based polymer comprising a copolymer of 4-methylpentene-1 and another olefin as the first component A split component composite fiber in which two components are alternately arranged adjacent to each other in the fiber cross section, and at least one of the two components is divided into two or more, and a high melting point component and a low melting point component A non-woven fabric containing at least two types of polyolefin-based composite fibers, wherein the split-type composite fibers and the content of the polyolefin-based composite fibers are Is in a range not exceeding 60 wt%, the nonwoven fabric has been subjected to a hydrophilic treatment,
When the melting point of the second component of the split-type conjugate fiber is D _2m , the melting point of the high melting point component of the polyolefin-based conjugate fiber is B _1m , and the melting point of the low melting point component is B _2m , D _2m , B _1m and B _2m Satisfies the following relational expressions (1) and (2) .
(1) B _1m > B _2m
(2) 120 ° C. <B _2m <D _2m The battery separator according to claim 1 , wherein the second component of the split-type composite fiber is a polyolefin polymer having a melting point (D _2m ) of 130 ° C. or higher. Content of 15 to 60 wt% of the splittable conjugate fiber, the battery separator according to claim 1 or 2 content of the polyolefin composite fibers are characterized in that 20 to 60% by weight. The battery separator according to any one of claims 1 to 3, further comprising other synthetic fibers in a range not exceeding 40% by weight. The other synthetic fiber is a synthetic fiber whose fineness is larger than the fineness of each constituent unit after splitting formed by splitting the splittable composite fiber, and is equal to or smaller than the fineness of the polyolefin-based composite fiber. The battery separator according to claim 4 . The battery separator according to claim 4 or 5 , wherein the other synthetic fibers are polypropylene fibers. Nonwoven, substantially without melting the two components constituting the splittable conjugate fiber, to any one of claims 1 to 6, characterized in that it is heat-sealed by a low melting point component of the polyolefin composite fibers The battery separator as described. The battery separator according to any one of claims 1 to 7 , wherein the fiber length of the split-type conjugate fiber, the polyolefin-based conjugate fiber, and the other synthetic fiber is 3 to 25 mm. The battery-type separator according to any one of claims 1 to 8 , wherein the split-type composite fiber comprises a methylpentene polymer as a first component and a polypropylene polymer as a second component. Hydrophilic treatment, a battery separator of any one of claims 1-9, characterized in that the sulfonation process. Sulfonation treatment, a battery separator according to claim 1 0, characterized in that fuming sulfuric acid treatment, chlorosulfonic acid process, or is any one of sulfuric anhydride process. The battery separator of claim 1 1, wherein the degree of sulfonation is 0.4 to 2 wt%. A methylpentene polymer comprising a copolymer of poly (4-methylpentene-1) or 4-methylpentene-1 and another olefin is used as a first component, and a polyolefin polymer different from the first component or its A split type composite fiber in which a copolymer is a second component, two components are alternately arranged adjacent to each other in the fiber cross section, and at least one of the two components is divided into two or more, a high melting point component and a low melting point component At least two types of polyolefin composite fibers composed of a melting point component, the melting point of the second component of the split type composite fiber is D _{2 m} , the melting point of the high melting point component of the polyolefin composite fiber is B _1m , and the low melting point component the melting point is taken as _{B 2m,} D _{2m, B 1m} and _{B 2m} relation formula (1) and (2):
(1) B _1m > B _2m
(2) 120 ° C. <B _2m <D _2m
A wet papermaking web (with a molecular structure of syndiotactic poly (1,2) in which the content of the split type composite fiber and the polyolefin type composite fiber does not exceed 60% by weight, respectively. -Butadiene), except those containing fibers made of resin of structure) ,
Melting the low melting point component of the polyolefin-based composite fiber, and subjecting the wet papermaking web to high-pressure water flow treatment to split the split-type composite fiber to form ultrafine fibers and entangle the fibers A method for producing a battery separator, comprising producing a non-woven fabric by the method, and hydrophilizing the non-woven fabric. Battery incorporating a battery separator according to any of claims 1 to 1 2.

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