JP2012216427A - Separator material, and battery comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator material having excellent fineness and a uniform texture, showing high resistance to shorts when used as a separator of an alkaline secondary battery, and achieving a long charge-discharge cycle life, and a battery comprising the same.SOLUTION: A separator material in accordance with an embodiment of the present invention is made of a nonwoven fabric containing high-strength composite fibers having a single-fiber strength of 4.0 cN/dtex or higher. In the nonwoven fabric, at least a portion of constituent fibers is thermally bonded together with the high-strength composite fibers, the extension percentage of the high-strength composite fibers is higher than 30% and equal to or lower than 60%, and the modulus of elasticity is equal to or higher than 3250 N/mmand lower than 4650 N/mm.

Description

  The present invention is used for alkaline secondary batteries represented by nickel-hydrogen batteries and nickel-cadmium batteries, lithium ion secondary batteries, electric double layer capacitors, electric elements such as capacitors, or ion exchange separators (ion catchers). The present invention relates to a separator material and a battery using the same.

  Conventionally, in order to improve the short-circuit resistance by increasing the piercing strength and tensile strength as separator materials, two different types of polyolefin resins are used as the structural unit, and two types in the fiber cross section are combined with each other. So-called core-sheath type composite fibers in which one resin component is disposed as a sheath component disposed on the fiber surface and the other resin component is disposed as a core component disposed near the center of the fiber cross section. A number of separator materials have been proposed in which the above-mentioned object is achieved by making the core-sheath type composite fiber into a fiber having a higher strength or a fiber having a finer fineness.

  For example, in Japanese Patent Application Laid-Open No. 2004-296355, in order to improve short-circuit resistance and productivity, it is composed of only a composite high-strength polypropylene fiber having a single fiber strength of 4.5 cN / dtex or more, and an average 5% modulus strength is 50 to 50%. A 120N / 5cm battery separator has been proposed. In JP 2002-180330 A, a crystalline propylene polymer that can be used as a battery separator material is used as a core material, and an olefin polymer other than the crystalline propylene polymer is used as a sheath material. It has been proposed to draw a drawn composite fiber having an A of greater than 5.74 cN / dtex, an elongation of 30% or less, and a Young's modulus of 43.1 cN / dtex or more.

JP 2004-296355 A JP 2002-180330 A

  However, the separator material has the following problems. For example, a separator composed only of a composite high-strength polypropylene-based composite fiber having a single fiber strength of 4.5 cN / dtex or more, which is proposed in Japanese Patent Application Laid-Open No. 2004-296355, is constituted only by a high-strength composite fiber. Mechanical properties such as the piercing strength and tensile strength of the separator are enhanced. However, considering only the strength of the single fiber, and using a composite fiber with increased strength, the strength of the separator material derived from the strength of the composite fiber itself can be increased, but the composite fiber has become a fiber with high single fiber strength. Thus, the flexibility of the separator material as a whole is lost, and the handleability may be reduced.

  In addition, a high strength, low elongation, high Young's modulus drawn composite fiber proposed in JP 2002-180330 A can be used as a battery separator material. There is room for study and improvement for use in separator materials. In addition, the drawn conjugate fiber described in this document is a conjugate fiber having a very low elongation. When such a fiber is used for the separator material, the stretched composite fiber itself has high strength, but the fiber is difficult to stretch and is not easily deformed. Therefore, the separator material using the fiber is not easily deformed and is not flexible. For battery separator applications, when pressure is applied in a very narrow area due to needle-like foreign matter such as dendrites, it becomes difficult to disperse the pressure, so pressure concentrates on the part in contact with the foreign matter. It may be added and may be easily broken from a portion other than the drawn composite fiber (for example, a heat-bonded portion between constituent fibers). In addition, the drawn composite fiber described in this patent document is manufactured by a drawing method using heated saturated steam, which not only makes the drawing process large, but also uses high-temperature heated steam. Because of rapid heating, fusion between fibers is likely to occur, and the dispersibility of the obtained stretched composite fiber in water may be deteriorated, or the fusion fiber in which fibers are fused may be mixed into the product. is there.

  In order to solve the above-described conventional problems, the present invention is excellent in the density and uniformity of the nonwoven fabric, and when used as a separator for various alkaline secondary batteries, The present invention relates to a separator material having high piercing strength and high short-circuit resistance, and a battery using the same.

  In order to overcome the above-described problems, the present inventors have focused on characteristics required for high-strength fibers used in separator materials. A separator material using high-strength composite fibers having a certain degree of elongation, that is, relatively high elongation, high single fiber strength, and Young's modulus within a predetermined range, was loaded inside the battery. At this time, even if it is in contact with foreign matter mixed in or needle-like foreign matter such as dendrites generated by repeated charge and discharge and pressure is applied so as to penetrate in the thickness direction, the separator material will be deformed appropriately, foreign matter etc. Has been found to be difficult to penetrate and to improve short-circuit resistance.

That is, the separator material of the present invention is composed of at least two types of thermoplastic resins, includes high-strength composite fibers having a single fiber strength of 4.0 cN / dtex or more, and at least part of the constituent fibers is formed by the high-strength composite fibers. It is a non-woven fabric that is heat-bonded, characterized in that the elongation of the high-strength composite fiber is greater than 30% and 60% or less, and the Young's modulus is 3250 N / mm ² or more and less than 4650 N / mm ² .

  The battery of the present invention is characterized by incorporating the separator material.

  When the separator material of the present invention is used as a separator material by using a predetermined high-strength composite fiber, the separator material comes into contact with foreign matters mixed in or needle-like foreign matters such as dendrites generated by repeated charge and discharge, and the thickness direction Even when pressure is applied so as to penetrate through, the separator material is appropriately deformed, so that foreign matter is difficult to penetrate and the short circuit resistance is high.

  Since the battery of the present invention incorporates a separator material that is difficult to penetrate even if pressure is applied so as to penetrate the thickness direction in contact with the needle-like foreign matter, the battery of the present invention has short circuit resistance. High and excellent in cycle life.

It is typical sectional drawing of the various split type composite fiber which can be used for the separator material of this invention.

The high-strength composite fiber used for the separator material of the present invention will be described. In the separator material according to the present invention, the high-strength composite fiber is thermally bonded between the constituent fibers of the separator material, and has a mechanical strength of the separator material, for example, maximum penetration force F (hereinafter also referred to as piercing strength), tensile strength. Contributes to improvement. High-strength composite fibers are particularly limited if the single fiber strength is 4.0 cN / dtex or more, the elongation is greater than 30% and 60% or less, and the Young's modulus is 3250 N / mm ² or more and less than 4650 N / mm ^2. Not. The high-strength composite fiber has a single fiber strength of 4.0 cN / dtex or more, which improves the mechanical properties of the separator material such as piercing strength and tensile strength. There is a tendency to improve the handleability. The upper limit of the single fiber strength of the high strength composite fiber is not particularly limited, but is preferably 8.0 cN / dtex or less. If the single fiber strength of the high-strength composite fiber is 8.0 cN / dtex or less, the separator material is not more rigid than necessary and the flexibility is not easily lost, and the elongation is less than 30%. Moreover, a high strength composite fiber can be produced efficiently. The single fiber strength of the high-strength conjugate fiber is preferably 4.2 cN / dtex or more and 7.5 cN / dtex or less, more preferably 4.5 cN / dtex or more and 7.0 cN / dtex or less. More preferably, it is 8 cN / dtex or more and 6.5 cN / dtex or less, and most preferably 5.0 cN / dtex or more and 6.2 cN / dtex or less. In the present invention, the single fiber strength is in accordance with JIS L 1015, a tensile tester is used, a tensile test is performed with the gripping interval of the sample being 20 mm, and the load value when broken is measured to obtain the single fiber strength. .

  The elongation of the high strength composite fiber is more than 30% and not more than 60%. When the elongation of the high-strength composite fiber satisfies this range, the high-strength composite fiber stretches or deforms appropriately with respect to pressure, particularly the pressure on the side of the fiber. Separator material that disperses or absorbs the pressure applied to the separator material when it comes into contact with needle-shaped foreign matter such as dents and dendrites, and is deformed by the foreign matter, but does not easily penetrate the foreign material It becomes. If the elongation of the high-strength composite fiber is 30% or less, the high-strength composite fiber is not easily stretched by the pressure applied by the foreign matter, so the pressure cannot be dispersed by the deformation of the fiber, and only in the part that is in contact with the foreign matter. A strong load comes to be applied, and it may break from the part or foreign matter may easily penetrate. When the elongation of the high-strength composite fiber exceeds 60%, the high-strength composite fiber becomes excessively stretched or deformed, and the piercing strength and tensile strength of the separator material may be reduced. The elongation of the high strength composite fiber is more preferably 32% or more and 60% or less, particularly preferably 32% or more and 55% or less, and most preferably 35% or more and 50% or less. The elongation referred to in the present invention is in accordance with JIS L 1015. A tensile tester is used and a tensile test is performed with the gripping interval of the sample being 20 mm. The elongation at break is the elongation of the fiber.

The Young's modulus of the high strength composite fiber is 3250 N / mm ² or more and less than 4650 N / mm ² . When the Young's modulus of the high-strength composite fiber is 3250 N / mm ² or more and less than 4650 N / mm ² , the high-strength composite fiber is relatively likely to be distorted in the fiber length direction and is moderate in the fiber cross-section direction. Therefore, the separator material including the high-strength composite fiber is compatible with mechanical properties such as piercing strength and tensile strength and flexibility in the thickness direction in particular. As a result, the pressure applied to the separator material by contact with foreign matter mixed in the battery or needle-like foreign matter such as dendrites and when the pressure is applied, the high-strength composite fiber will bend and deform appropriately. The fiber is dispersed or absorbed, and although it is deformed by a foreign substance, the foreign substance is difficult to penetrate and a separator material with high short-circuit resistance is obtained. When the Young's modulus of the high-strength composite fiber is less than 3250 N / mm ² , the high-strength composite fiber is easily deformed by an external force, so that the piercing strength and tensile strength of the separator material may be reduced. When the Young's modulus of the high-strength composite fiber is 4650 N / mm ² or more, the pressure cannot be dispersed due to the deformation of the fiber, and a strong load is applied only to the part in contact with the foreign substance. It may be easy to penetrate. Preferably the Young's modulus of the high-strength composite fibers are 3530N / mm ² or more 4460N / mm ² or less, more preferably 3720N / mm ² or more 4460N / mm ² or less. The Young's modulus refers to the value of the apparent Young's modulus calculated from the initial tensile resistance measured by the method defined in JIS L 1015. The initial tensile resistance is the value measured by a constant speed tension type tester. Say.

  The fineness of the high-strength composite fiber is not particularly limited, but the fineness is preferably 0.1 dtex or more and 4.4 dtex or less. This is because a separator material with uniform texture can be obtained when the fineness of the high-strength conjugate fiber satisfies the above range. The fineness of the high strength composite fiber is more preferably 0.2 dtex or more and 2.2 dtex or less, particularly preferably 0.4 dtex or more and 1.2 dtex or less, and most preferably 0.5 dtex or more and 0.9 dtex or less.

  The fiber length of the high-strength composite fiber is not particularly limited, but when using the wet papermaking method, the fiber length is preferably 0.5 mm or more and 25 mm or less. When the fiber length is 0.5 mm or more, the fiber does not fall off and the surface of the obtained separator material does not fluff. This is because when the fiber length is 25 mm or less, the dispersibility of the fibers in the slurry is not lowered when the nonwoven fabric is produced by the wet papermaking method, and a uniform nonwoven fabric is easily obtained. The fiber length of the high strength composite fiber is more preferably 1 mm or more and 20 mm or less, particularly preferably 3 mm or more and 10 mm or less, and most preferably 3 mm or more and 6 mm or less.

  The high-strength conjugate fiber is not particularly limited as long as it has thermal adhesiveness. However, the high-strength conjugate fiber is composed of at least two different thermoplastic resins, and has a higher melting point than a thermoplastic resin (high melting point resin) and a high melting point resin. It is preferable to include a thermoplastic resin having a low melting point (low melting point resin). More preferably, it is composed of two or more different thermoplastic resins, and among the thermoplastic resins, the thermoplastic resin having the lowest melting point is exposed on the fiber surface, and the exposed area is at least relative to the area of the entire fiber surface. It is a composite fiber occupying 20% or more. As such a composite fiber, a core-sheath type composite fiber in which two different resin components are arranged concentrically, an eccentric core-sheath type composite fiber in which a so-called core component is displaced from the center of the fiber. In addition, a parallel type composite fiber (also referred to as a side-by-side type composite fiber) in which two different resin components are bonded together, and a multilayer bimetal type composite fiber in which two different resin components are superposed. In particular, considering that the constituent fibers are thermally bonded mainly by the low melting point thermoplastic resin component constituting the high-strength composite fiber, concentric core-sheath type composite fibers and eccentric core-sheath type composites with high thermal adhesiveness are considered. A fiber and a parallel type composite fiber are preferable, and a concentric core-sheath type composite fiber or an eccentric core-sheath type composite fiber is particularly preferable. Hereinafter, the concentric core-sheath composite fiber and the eccentric core-sheath composite fiber are collectively referred to as a core-sheath composite fiber. The core-sheath type composite fiber preferably includes a thermoplastic resin having a melting point lower by 10 ° C. or more than the thermoplastic resin constituting the core component. More preferably, a resin whose melting point is 20 ° C. or more lower than that of the core component is used as the sheath component.

  When the high-strength conjugate fiber is a core-sheath conjugate fiber, the mechanical properties of the high-strength conjugate fiber depend on the core component present near the center of the high-strength conjugate fiber. A so-called sheath component located outside the core component covers the core component and covers the fiber surface. The sheath component melts moderately in thermal processing and has a function of thermally bonding the constituent fibers, and the gap between the constituent fibers is partially filled by thermal bonding, so that the separator material becomes denser. The component contributes to the improvement of mechanical properties resulting from thermal bonding between fibers. Accordingly, in the high-strength composite fiber, the volume ratio of the core component to the sheath component (also referred to as composite ratio or core-sheath ratio) is not particularly limited, but the mechanical properties of the high-strength composite fiber itself and the constituent fibers of the sheath component It is preferable that the thermal adhesive force of the glass be maximized. When the high-strength conjugate fiber is a core-sheath conjugate fiber, the conjugate ratio (core / sheath) is preferably 80/20 to 30/70 by volume. Since the composite ratio is 80/20 to 30/70, both the mechanical strength of the separator material resulting from the mechanical properties of the high-strength composite fiber and the mechanical properties of the separator resulting from thermal bonding between the constituent fibers are compatible. Thus, a separator material having high piercing strength and tensile strength can be obtained. If the composite ratio is more than 30/70, the constituent fibers are strongly thermally bonded, but the core component is reduced and the single fiber strength of the high-strength composite fiber itself is reduced. If the separator material is incorporated in the battery, the battery characteristics may be deteriorated due to the decrease in liquid retention and the air permeability. On the other hand, if the composite ratio is more than 80/20, the mechanical properties of the high-strength composite fiber itself are improved, but the constituent fibers of the separator material are not sufficiently thermally bonded, and the fibers are not thermally bonded. Not only the resulting mechanical properties are degraded, but also the constituent fibers are not sufficiently dense, so that the porosity is increased and the battery properties when the separator is incorporated into the battery may be degraded. The composite ratio (core / sheath) of the high-strength composite fiber is more preferably 80/20 to 50/50 by volume ratio, particularly preferably 75/25 to 60/40, and 75/25 to 65/35. Most preferred.

  As described above, the thermoplastic resin used for the high-strength conjugate fiber is not limited as long as it is two or more different thermoplastic resins, and a known thermoplastic resin can be used. For example, polyethylene terephthalate, polybutylene terephthalate, Polyester resins such as polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate; various polyethylenes such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, and ultra high molecular weight polyethylene Resin, various polypropylene resins such as isotactic, atactic and syndiotactic polymerized using ordinary Ziegler-Natta catalysts and metallocene catalysts; various polymethylpentene resins, ethylene-vinyl alcohol copolymer resins Ethylene - various polyolefin resins such as propylene copolymer resin; nylon 6, nylon 66, nylon 11, a polyamide resin such as nylon 12; polycarbonates, polyacetals, polystyrene, engineering plastics such as cyclic polyolefins can be used. These resins can be used for the high-strength composite fiber, but when the separator material is incorporated in a battery as a battery separator and used, the separator material is impregnated with a strong alkaline aqueous solution such as an aqueous potassium hydroxide solution as an electrolyte. The strength composite fiber is preferably used by selecting two or more different resins from polyolefin resin having high alkali resistance.

  In addition to the polyolefin-based resin, a known polyolefin resin can be used for the two resin components constituting the high-strength conjugate fiber, but mechanical properties such as productivity and single fiber strength of the high-strength conjugate fiber can be used. Considering the characteristics, when the high-strength conjugate fiber is a core-sheath type conjugate fiber, the core component / sheath component is a polypropylene resin / polyethylene resin as a combination of polyolefin resins constituting the high-strength conjugate fiber. Polypropylene resin / ethylene-propylene copolymer resin, polypropylene resin / ethylene-vinyl alcohol copolymer resin, polymethylpentene resin / polyethylene resin, polymethylpentene resin / polypropylene resin, polymethylpentene resin / Ethylene-propylene copolymer resin, polymethylpentene resin / ethylene A combination of polyolefin resin represented by ethylene-vinyl alcohol copolymer resin, ethylene-propylene copolymer resin / polyethylene resin, ethylene-propylene copolymer resin / ethylene-vinyl alcohol copolymer resin, and polypropylene resin / A combination of polyethylene resin, polypropylene resin / ethylene-propylene copolymer resin, polymethylpentene resin / polyethylene resin, polymethylpentene resin / polypropylene resin is particularly preferable, and polypropylene resin / polyethylene resin is most preferable. .

  In the present invention, the polypropylene-based resin is a homopolymer of propylene, a copolymer of propylene and one or two kinds of α-olefins having 2 to 20 carbon atoms, and a homopolymer of propylene and another thermoplastic resin. A mixture etc. are mentioned, The thing which contains 85 mol% or more of propylene in a resin component is called a polypropylene resin. The polypropylene resin is not particularly limited, but in consideration of spinnability, stretchability, and various physical properties of the resulting high-strength composite fiber, the polypropylene resin does not adversely affect spinnability and stretchability. Polypropylene resins having low fluidity are more preferred because the single fiber strength, elongation, and Young's modulus of high-strength conjugate fibers tend to satisfy the above ranges.

  In the present invention, the polyethylene-based resin is an ethylene homopolymer, a copolymer of ethylene and one or two kinds of α-olefin having 2 to 20 carbon atoms, and an ethylene homopolymer and another thermoplastic resin. A mixture etc. are mentioned, The thing which contains 85 mol% or more of ethylene in a resin component is called a polyethylene-type resin. Similarly to the polypropylene resin, the polyethylene resin is not particularly limited, but considering the spinnability, stretchability, and various physical properties of the resulting high strength composite fiber, the polyethylene resin does not adversely affect the spinnability and stretchability. Within the range, a polyethylene-based resin having low fluidity at the time of melting is preferable because a single fiber strength, elongation, and Young's modulus of the high-strength composite fiber tend to satisfy the above ranges.

  In the present invention, the ethylene-propylene copolymer resin includes a copolymer composed of ethylene and propylene, or a mixture of a copolymer composed of ethylene and propylene and another thermoplastic resin. A resin containing 50 mol% or more, preferably 85 mol% or more of ethylene and propylene is called an ethylene-propylene copolymer resin. The ethylene-propylene copolymer resin that can be used for the high-strength composite fiber is not particularly limited, and a commercially available ethylene-propylene copolymer resin can be used, but the ethylene content is 1 mol% or more and 20 mol% or less. preferable. When the ethylene content is less than 1 mol%, the melting point increases, and the physical properties of the homopolymer of propylene are close, so that the thermal adhesiveness may be lowered. If the ethylene content exceeds 20 mol%, interfiber fusion is likely to occur during melt spinning, and spinnability may be reduced. The melting point of the ethylene-propylene copolymer resin is not particularly limited, but is preferably 120 ° C. or higher and 150 ° C. or lower. Further, the melt flow rate (MFR; measuring temperature 230 ° C., load 2.16 kgf (21.2 N)) according to JIS K 7210 of the ethylene-propylene copolymer resin is not particularly limited, but is 1 g / 10 min or more and 100 g / It is preferable that it is 10 minutes or less.

  In the present invention, the polymethylpentene resin is a homopolymer of 4-methylpentene-1, 4-methylpentene-1, for example, ethylene, propylene, butene-1, hexene-1, octene-1, decane-1, Copolymers of one or two α-olefins having 2 to 20 carbon atoms such as tetradecane-1 and octadecane-1, and mixtures of 4-methylpentene-1 homopolymers with other thermoplastic resins, etc. A resin component containing 85 mol% or more of 4-methylpentene-1 is referred to as a polymethylpentene resin. The polymethylpentene resin is not particularly limited, but preferably has a melting point of 210 ° C. or more and 245 ° C. or less, and has a melt flow rate (MFR) according to ASTM D 1238 (measurement temperature 260 ° C., load 5.0 kgf (49. 0N), hereinafter also referred to as MFR 260.) is preferably 120 g / 10 min or more and 280 g / 10 min or less. Examples of the polymethylpentene resin that can be used in the separator material of the present invention include “TPX” (registered trademark) manufactured by Mitsui Chemicals, Inc.

  In the present invention, the ethylene-vinyl alcohol copolymer resin includes a copolymer composed of ethylene and vinyl alcohol, or a mixture of a copolymer composed of ethylene and vinyl alcohol and another thermoplastic resin. A resin component containing 50 mol% or more, preferably 85 mol% or more of ethylene and vinyl alcohol is called an ethylene-vinyl alcohol resin. The ethylene-vinyl alcohol copolymer resin preferably has an ethylene content of 20 mol% to 70 mol%. The ethylene-vinyl alcohol copolymer resin has a melt flow rate (MFR; measuring temperature 210 ° C., load 2.16 kgf (21.2 N), hereinafter also referred to as MFR210) according to ASTM D 1238 of 1 g / 10 min to 50 g. It is preferable to use a resin of / 10 minutes or less because of excellent spinnability. A more preferable lower limit of MFR210 is 10 g / 10 minutes or more. A more preferable upper limit of MFR210 is 30 g / min or less. As an ethylene-vinyl alcohol-based resin that can be used for the separator material of the present invention, there is “Soarnol” (registered trademark) manufactured by Nippon Synthetic Chemical Industry Co., Ltd.

  The high-strength conjugate fiber can be produced by the following method. First, a thermoplastic resin having a plurality of different components, preferably a two-component polyolefin-based resin, is prepared, and a desired composite nozzle (preferably a concentric core-sheath type composite nozzle or an eccentric core-sheath type is used) by a known melt spinning machine. Compound spinning) can be used for melt spinning. At this time, considering the fiber cross-sectional shape of the high-strength composite fiber, adjust the melt viscosity of each resin by adjusting the shearing force and spinning temperature of the extruder so that the sheath component uniformly covers the core component in the fiber cross-section. Is preferably adjusted. A spun filament (undrawn yarn) is obtained from the melted thermoplastic resin, and the fineness of the spun filament is preferably 2 dtex or more and 10 dtex or less.

  Next, the spinning filament is drawn as necessary, but is drawn under the conditions of a drawing temperature of 80 ° C. or more and 160 ° C. or less and a draw ratio of 1.5 times or more and 8 times or less. The stretching method is not particularly limited, and wet stretching is performed while being heated with a high-temperature liquid such as high-temperature hot water, dry stretching is performed while being heated in a high-temperature gas or a high-temperature metal roll, and 100 ° C. or higher. It is also possible to perform a known stretching process such as steam stretching in which stretching is performed while heating the fiber under normal pressure or pressurized condition. Conventional stretching equipment can be used, the stretching process is not complicated, and fusion between the spinning filaments is less likely to occur. Therefore, wet stretching or dry stretching is preferable, while leaving the elongation (relatively large elongation). ), And easy to obtain high strength composite fibers having high single fiber strength and high Young's modulus, dry stretching is more preferable. The stretching process can be performed in one stage, or a so-called multistage stretching process in which a stretching process by a known stretching method is performed in a plurality of times. Among these, it is preferable to perform one-stage or two-stage drawing because productivity, economy, and the whole unstretched fiber bundle can be easily and uniformly heated. The obtained drawn filament is provided with a fiber treatment agent as necessary, and is subjected to crimping treatment if necessary, and is cut into a predetermined fiber length and used as a high-strength composite fiber.

  The separator material of the present invention is not particularly limited as long as it contains the high-strength conjugate fiber, but it is preferable that the separator material contains an ultrafine fiber having a fineness of 0.5 dtex or less. When the separator material of the present invention contains the ultrafine fiber in addition to the high-strength composite fiber, a finer inter-fiber gap can be formed. As a result, the separator material obtained is dense and has a good texture, and can improve short-circuit resistance when incorporated in a battery. In addition, since the specific surface area of the separator material is increased, sufficient hydrophilicity can be obtained even in a relatively weak condition in a hydrophilic treatment such as a sulfonation treatment, a fluorine gas treatment or a corona discharge treatment. In addition to improving the cycle life, it is possible to suppress an increase in internal pressure and internal resistance, and it is possible to suppress strong deterioration of the nonwoven fabric due to the hydrophilization treatment. The ultrafine fiber preferably has a fineness of 0.005 dtex or more and 0.4 dtex, more preferably 0.01 dtex or more and 0.3 dtex or less, and particularly preferably 0.05 dtex or more and 0.15 dtex or less.

  The fiber length of the ultrafine fiber is not particularly limited, but when the wet papermaking method is used, the fiber length is preferably 0.5 mm or more and 25 mm or less. When the fiber length is 0.5 mm or more, the fiber does not fall off and the surface of the separator material obtained is not fuzzy. When the fiber length is 25 mm or less, when a nonwoven fabric is produced by a wet papermaking method, the dispersibility of the fibers in the slurry is not lowered, and a uniform nonwoven fabric is easily obtained. The fiber length of the ultrafine fibers used in the separator material of the present invention is more preferably 1 mm or more and 20 mm or less, particularly preferably 3 mm or more and 10 mm or less, and most preferably 3 mm or more and 6 mm or less.

  The manufacturing method of the ultrafine fiber is not limited as long as it satisfies the fineness range. The ultrafine fiber can be used as an ultrafine fiber obtained by leaching sea components from a composite fiber having a so-called sea-island cross section, and after producing an ultrafine fiber having a relatively long fiber length by a melt blown method or an electrospinning method, You may use what was cut | disconnected and selected so that it might become moderate fiber length, for example, the said fiber length. However, the ultrafine fiber is obtained by dividing a split type composite fiber composed of two kinds of resin components from the viewpoint that it can be produced relatively easily and an ultrafine fiber having a desired property is easy to produce. Is preferred. The fineness before splitting of the split-type composite fiber is not particularly limited as long as the ultrafine fiber generated by the splitting process satisfies the range of the fineness of the ultrafine fiber, but is preferably 0.1 dtex or more and 4 dtex or less, more preferably 0. It is 5 dtex or more and 3.3 dtex or less, and 0.8 dtex or more and 2.2 dtex or less is particularly preferable.

  The split-type composite fiber is not particularly limited as long as it generates a plurality of ultrafine fibers composed of different resin components by split processing, and may be a two-component split-type composite fiber, or a resin having three or more components A split type composite fiber that can be divided into components may be used. However, in consideration of the productivity and splitability of the split type composite fiber, split type composite fibers composed of two different types of resin components are preferable. The resin component used for the ultrafine fibers can be used without particular limitation as long as it is a thermoplastic resin, such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, polybutylene succinate, etc. Polyester resins: Low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-high-molecular-weight polyethylene, and other polyethylene resins, polymerized using ordinary Ziegler-Natta catalysts and metallocene catalysts Polyolefins such as various isotactic, atactic and syndiotactic polypropylene resins, various polymethylpentene resins, ethylene-vinyl alcohol copolymer resins, ethylene-propylene copolymer resins, etc. System resin; nylon 6, nylon 66, nylon 11, a polyamide resin such as nylon 12; polycarbonates, polyacetals, polystyrene, engineering plastics such as cyclic polyolefins can be used. Although these thermoplastic resins can be used for the ultrafine fibers, when the separator material is incorporated in a battery, the separator material is impregnated with a strong alkaline aqueous solution such as an aqueous potassium hydroxide solution as an electrolytic solution. Ultrafine fibers using a high polyolefin resin are preferred.

  In the case of using an ultrafine fiber obtained by dividing a split-type composite fiber as the ultrafine fiber, the cross-sectional shape of the split-type composite fiber is not limited, and an orange with a hollow portion shown in FIG. Section (hereinafter also referred to simply as a hollow orange section), a so-called solid orange section (hereinafter also referred to simply as a solid orange section) having no hollow portion as shown in FIG. In addition to the C-shaped orange cross section (hereinafter also simply referred to as C-type orange cross section) disclosed in JP-A-328348 and JP-A-2002-88580, FIG. A hollow composite split type in which one component shown is a core-sheath type composite fiber (hereinafter also simply referred to as a hollow composite split type orange cross section), or an orange cross section of a solid composite split type shown in FIG. Less than, Any cross-sectional shape of a known split-type composite fiber that can generate two or more types of ultrafine fibers by splitting, such as a solid composite split-type orange cross-section) or a multi-layer bimetal cross-sectional shape. It may be. Among these, taking into account the productivity and splitability of the split composite fiber, the hollow orange cross section, solid orange cross section, C type orange cross section, hollow composite split orange section, solid composite split orange section A hollow orange cross section, a C-type orange cross section, and a hollow composite split orange cross section are more preferable. The number of divisions is not particularly limited as long as it is a known number of divisions. However, 4-32 divisions are preferable, 4-24 divisions are preferable, and 8-16 divisions are particularly preferable.

  As described above, the split composite fiber is preferable because it is made of a polyolefin resin having a plurality of components different from each other, because a separator material obtained is highly resistant to electrolytes and alkalis. Examples of the polyolefin resin used for the split composite fiber include homopolymers and copolymers of various α-olefins and terpolymers (also referred to as terpolymers). Specific examples of polyolefin resins include poly (4-methylpentene-1), polymethylpentene resins such as 4-methylpentene-1 and other olefin copolymers, and polypropylene resins (Ziegler).・ In addition to polypropylene polymerized with Natta catalyst, also includes polypropylene polymerized with metallocene catalyst, polyethylene resin (high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density Polyethylene (LLDPE), including polyethylene polymerized with Ziegler-Natta catalyst, polyethylene polymerized with metallocene catalyst), polybutene-1, ethylene-propylene copolymer resin, ethylene-propylene-butene copolymer resin, ethylene- Vinyl alcohol copolymer resin It is below.

  In addition to the polyolefin-based resin, a known polyolefin resin can be used for each resin component of the split-type composite fiber. However, considering the productivity and splitability of the split-type composite fiber, the split-type composite fiber is configured. Polyolefin resin combinations include polypropylene resin / polyethylene resin, polypropylene resin / polymethylpentene resin, polypropylene resin / ethylene-vinyl alcohol copolymer resin, polypropylene resin / ethylene-propylene copolymer resin, poly Methylpentene resin / polyethylene resin, polymethylpentene resin / ethylene-propylene copolymer resin, polymethylpentene resin / ethylene-vinyl alcohol copolymer resin, ethylene-propylene copolymer resin / polyethylene resin, ethylene-propylene Copolymerization A combination of resin such as fat / ethylene-vinyl alcohol copolymer resin is preferable, and a combination of polypropylene resin / polyethylene resin, polypropylene resin / polymethylpentene resin, and polypropylene resin / ethylene-vinyl alcohol copolymer resin is more preferable. preferable.

  In the present invention, the polypropylene-based resin is a homopolymer of propylene, a copolymer resin of propylene and one or two kinds of α-olefin having 2 to 20 carbon atoms, and a homopolymer of propylene and another thermoplastic resin. A mixture etc. are mentioned, The thing which contains 85 mol% or more of propylene in a resin component is called a polypropylene resin. The polypropylene resin is not particularly limited, but considering the spinnability, stretchability, and splitability of the resulting split-type composite fiber, the polypropylene resin is within a range that does not adversely affect spinnability and stretchability. Polypropylene resin having a low fluidity is preferred because the splitability of the resulting split composite fiber tends to be high.

In the present invention, the polyethylene-based resin is an ethylene homopolymer, a copolymer of ethylene and one or two kinds of α-olefin having 2 to 20 carbon atoms, and an ethylene homopolymer and another thermoplastic resin. A mixture etc. are mentioned, The thing which contains 85 mol% or more of ethylene in a resin component is called a polyethylene-type resin. Similarly to the polypropylene resin, the polyethylene resin is not particularly limited, but considering the spinnability, stretchability, and splitability of the resulting split-type composite fiber, the polyethylene resin does not adversely affect spinnability and stretchability. Within the range, a polyethylene resin having a low fluidity at the time of melting is preferable because the splitability of the resulting split composite fiber tends to be high. As the polyethylene resin, as described above, various polyethylenes such as high density polyethylene, medium density polyethylene, low density polyethylene, and linear low density polyethylene can be used. Among the components, the higher the crystallinity of the polymer contained, the better the resolution, so the density of the polyethylene used is preferably 0.94 g / cm ³ or more.

  The polymethylpentene resin used for the split composite fiber is not particularly limited, but the melting point thereof is preferably 210 ° C. or higher and 245 ° C. or lower, and the melt flow rate (MFR) according to ASTM D 1238 (measurement temperature 260 ° C.). And a load of 5.0 kgf (49.0 N), hereinafter also referred to as MFR260) is preferably 120 g / 10 min or more and 280 g / 10 min or less. This is because when the melting point of the polymethylpentene resin is 210 ° C. or higher and 245 ° C. or lower, spinning becomes easy and the drawability is excellent. Further, when the MFR260 of the polymethylpentene resin is 120 g / 10 min or more and 280 g / 10 min or less, spinning becomes easy and the splitting property of the resulting split composite fiber is easily improved. As a preferable polymethylpentene resin that satisfies such properties and can be used for the split type composite fiber, for example, “TPX” (registered trademark) manufactured by Mitsui Chemicals, Inc. is available.

  The ethylene-vinyl alcohol copolymer resin used for the split type composite fiber preferably has an ethylene content of 20 mol% or more and 70 mol% or less. More preferable ethylene content is 25 mol% or more and 60% or less, and particularly preferable ethylene content is 35 mol% or more and 50% or less. This is because if the ethylene content is less than 30 mol%, the stretchability at the time of fiber production is poor, and if the ethylene content exceeds 70 mol%, the hydrophilicity of the fiber itself is poor. The ethylene-vinyl alcohol copolymer resin has a melt flow rate (MFR; measurement temperature 210 ° C., load 2.16 kgf (21.2 N), hereinafter also referred to as MFR210) according to ASTM D 1238 of 1 g / 10 min or more. Use of a resin of 50 g / 10 min or less is advantageous because of excellent spinnability. A preferred ethylene-vinyl alcohol copolymer resin that satisfies such properties and can be used for the split type composite fiber is “Soarnol” (registered trademark) manufactured by Nippon Synthetic Chemical Industry Co., Ltd.

  Two types of thermoplastic resins different from the above-mentioned various thermoplastic resins, preferably from the above-mentioned various polyolefin-based resins, can be combined to form a split type composite fiber used for the separator material of the present invention. As described above, the cross-sectional shape is not particularly limited. However, in the case of a split type composite fiber having a hollow, solid, or C-shaped orange cross section, the resin component composed of different thermoplastic resins is 30:70 by volume. A split type composite fiber having a weight ratio of ˜70: 30 is preferable. When the volume ratio of the resin components is 30:70 to 70:30, melt spinning can be performed when the split composite fiber is melt-spun without causing the fiber cross-sectional shape to become distorted or the cross-sectional shape to collapse. In addition, the fineness of the ultrafine fiber formed from one resin component of the divided ultrafine fiber is not extremely increased. The volume ratio of the resin component is preferably 40:60 to 60:40, most preferably 50:50, that is, melt spinning so that the resin component has the same volume.

  In the split type composite fiber, when the cross-sectional shape is a composite split type composite fiber having a hollow composite split type orange cross section or a solid composite split type orange cross section, the component B in FIGS. 1 (c) and 1 (d) As the core component (22, 32) of the resin component which is a core-sheath type composite fiber shown by the above, and the A component which becomes an ultrafine single fiber after splitting treatment, heat having a higher melting point among the two types of thermoplastic resins Two types of thermoplastic resins are used as the sheath portions (24, 34) of the resin component, which is a core-sheath type composite fiber shown in FIG. 1 (c) and FIG. Of these, melt spinning is preferably performed so that a thermoplastic resin having a lower melting point is disposed from the viewpoints of spinnability and thermal adhesiveness of the resulting split-type composite fiber. In this case, a thermoplastic resin having a high melting point and a thermoplastic resin having a low melting point are melt-spun so that the high melting point thermoplastic resin: the low melting point thermoplastic resin = 80: 20 to 40:60 (volume ratio). As a result, not only can the fiber cross-sectional shape become distorted or the cross-sectional shape does not collapse, but melt spinning can be performed, and the fineness of the ultrafine fiber made from one resin component is extremely fine. It is preferable because it does not increase. When the sectional shape of the split composite fiber is a composite split type such as a hollow composite split orange section or a solid composite split orange section, the volume ratio of each thermoplastic resin component is high melting point thermoplastic resin: low melting point heat. Plastic resin = 75: 25 to 45:55 is preferable, and it is particularly preferable to perform melt spinning so as to be 70:30 to 50:50.

  The split composite fiber may have a so-called solid cross section that does not have a continuous cavity portion in the fiber length direction in the fiber cross section, and may have a hollow cross section or a C-shaped cross section that has a continuous cavity portion. As described above, the split composite fiber used for the separator material of the present invention may have a fiber length direction in the fiber cross-section in consideration of spinnability, splitability of the split composite fiber, and the like. It is preferable that the fiber has a hollow cross-section having a continuous cavity portion. If the hollow part is hollow, the hollow part may not be located in the center (concentric) or may be eccentric. However, considering the productivity of the split-type conjugate fiber, the hollow part is preferably located concentrically. Further, the shape of the hollow portion may be circular, elliptical, or irregular. The hollow ratio of the hollow portion is preferably in the range of 5% to 40% of the fiber cross-sectional area. A more preferable range of the hollow ratio is 8% or more and 30% or less, and particularly preferably 10% or more and 25% or less. This is because it is difficult to expose each constituent component to the hollow portion when the hollow ratio is less than 5%, and when the hollow portion exceeds 40%, it tends to be difficult in terms of productivity.

  The split type composite fiber can be produced by the following method. First, a thermoplastic resin having a plurality of different components, preferably a two-component polyolefin resin, is prepared, and melt spinning using a desired split type composite nozzle (for example, a hollow split type composite nozzle) with a known melt spinning machine. it can. At this time, considering the cross-sectional structure of the split-type conjugate fiber, the fiber cross-sectional shape of the ultrafine fiber after splitting, and the splitting property, the melt viscosity of each resin is adjusted by adjusting the shearing force, spinning temperature, etc. of the extruder, and the fiber cross-section. It is preferable to adjust the section so that one component does not involve another component. A spun filament (undrawn yarn) is obtained from the molten thermoplastic resin, and the fineness of the spun filament is preferably 2 dtex or more and 12 dtex or less.

  Next, the spinning filament is drawn as necessary, but is drawn in a heating medium under conditions of 80 ° C. or higher and 160 ° C. or lower and a draw ratio of 1.5 times or higher and 8 times or lower. The stretching method is not particularly limited, and wet stretching is performed while being heated with a high-temperature liquid such as high-temperature hot water, dry stretching is performed while being heated in a high-temperature gas or a high-temperature metal roll, and 100 ° C. or higher. A known stretching process such as steam stretching, in which the steam is stretched while heating the fiber under normal pressure or a pressurized state, can be performed in one step, and a plurality of stretching processes by a known stretching method can be performed. A so-called multi-stage stretching process can be performed separately. Among these, it is preferable to perform dry stretching or wet stretching in one or two stages because productivity, economy, and the whole unstretched fiber bundle can be easily and uniformly heated. The obtained drawn filament is obtained by applying a fiber treatment agent as necessary, and applying a crimping treatment if necessary, and cutting it into a predetermined fiber length.

  As will be described later, the ultrafine fibers are formed from the split composite fibers by splitting the split composite fibers by applying an external force to the fibers in the process of manufacturing the fiber web and the nonwoven fabric. The fiber can be divided by, for example, jetting a high-pressure water stream or performing needle punching, or when producing a nonwoven fabric by a wet papermaking method, the fiber is subjected to a disaggregation process during papermaking. It can be implemented using impact.

  The content of the high-strength composite fiber in the separator material of the present invention is preferably 30% by mass or more. Specifically, only high-strength conjugate fibers, that is, 100% by mass, or 30% by mass to 95% by mass when other fibers are mixed is preferable. If the content of the high-strength composite fiber is less than 30% by mass, not only there is a possibility that sufficient piercing strength and tensile strength may not be obtained due to insufficient thermal bonding between the constituent fibers of the separator material. There are many voids between the fibers, and the performance of the separator may be reduced. When other fibers, specifically containing the ultrafine fibers, if the content of the high-strength composite fibers exceeds 95% by mass, it is difficult to obtain the effect of blending the ultrafine fibers even if blended with the ultrafine fibers, There is a possibility that a uniform separator material and a dense separator material cannot be obtained. In the separator material of the present invention, the content of the high-strength conjugate fiber is more preferably 50% by mass to 90% by mass, particularly preferably 65% by mass to 85% by mass, and 68% by mass. It is most preferably 78% by mass or less.

  The content of the ultrafine fiber in the separator material of the present invention is preferably 5% by mass or more and 50% by mass or less. When the content of the ultrafine fiber is 5% by mass or more, the average pore diameter of the nonwoven fabric formed by the inter-fiber voids is small inside the separator material, and the denseness of the nonwoven fabric is maintained, so that the short-circuit resistance of the separator material is reduced. There is nothing. When the content of the ultrafine fibers is 50% by mass or less, a fiber ball phenomenon in which the ultrafine fibers and the ultrafine fibers and other fibers are entangled with each other is not caused, so that a nonwoven fabric having a uniform texture can be obtained. Moreover, by using together with a high-strength composite fiber, both puncture resistance and denseness as a separator can be achieved. In the separator material of the present invention, the content of the ultrafine fibers is more preferably 10% by mass or more and 40% by mass or less, particularly preferably 15% by mass or more and 35% by mass or less, and more preferably 22% by mass or more and 32% by mass. % Or less is most preferable.

  The separator material of the present invention may contain fibers other than the ultrafine fibers and the high-strength composite fibers (hereinafter also referred to as other fibers) as long as the effects of the present invention are not lost. The type of the other fibers is not particularly limited. Ramie (linen), linen (flax), kenaf (marine), abaca (Manila hemp), Heneken (sisal hemp), jute (burlap), hemp (cannabis), Synthetic resins, which may be natural fibers such as palm, palm, mulberry, mitsumata, bagasse, and semi-synthetic fibers (also called regenerated fibers) such as viscose rayon, tencel (registered trademark), lyocell (registered trademark), and cupra. The fiber consisting of is preferred. Examples of the fibers made of a synthetic resin that can be used for the other fibers include, for example, a simple polyester resin such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate. Single fiber, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, single-fiber made of known polyethylene resin such as ultra-high molecular weight polyethylene, ordinary Ziegler-Natta catalyst or metallocene catalyst A single fiber made of a known polypropylene resin such as isotactic, atactic, syndiotactic, or a copolymer resin of these polyolefin monomers, or a polymer of these polyolefins. A single fiber made of a known polyolefin resin such as polyolefin using a metallocene catalyst (also called Kaminsky catalyst), a single fiber made of a known polyamide such as nylon 6, nylon 66, nylon 11 or nylon 12, acrylic Nitrile (poly) acrylic single fibers, polycarbonate, polyacetal, polystyrene, single fibers of engineering plastics such as cyclic polyolefins, polyesters, polyolefins, polyamides, different types of resins of engineering plastics, or the same type of A composite fiber in which resins made of different polymer components (for example, polyethylene terephthalate and polytrimethylene terephthalate) are combined is exemplified. When the other fiber is a composite fiber, the composite state is not particularly limited, and the cross-sectional shape in the fiber cross section is a core-sheath type composite fiber, an eccentric core-sheath type composite fiber, a parallel type composite fiber, or a citrus tufted shape. It may be a split type composite fiber or a sea-island type composite fiber in which resin components are alternately arranged. Since the separator material of the present invention is required to have durability against an alkaline aqueous solution, the other fiber is preferably a single fiber made of a polyolefin-based resin or a composite fiber made of a polyolefin-based resin. Polypropylene single fiber with a high (for example, 6.0 cN / dtex or more), low heat shrinkable composite fiber, and the like.

  When the other fiber is a composite fiber composed of a cross-sectional shape, a type of synthetic resin, a number, or a plurality of resin components, the combination of the synthetic resins and the composite form of the constituent resins are not particularly limited. However, the fineness of other fibers, fiber length, cross-sectional shape, and the composite ratio is not particularly limited when the other fibers are composite fibers. However, if the other fibers are significantly different from the preferred fineness range and preferred fiber length range of the high-strength composite fibers, the productivity may be reduced when producing wet fiber webs and wet nonwoven fabrics by the papermaking method. In addition, since the effects of the present invention may be impaired, the fineness of the other fibers is preferably 0.2 dtex or more and 5.6 dtex or less, more preferably 0.5 dtex or more and 3.3 dtex or less. preferable. Moreover, when producing a nonwoven fabric by a wet papermaking method, the fiber length of the other fibers is preferably 1 mm or more and 20 mm or less, and more preferably 3 mm or more and 10 mm or less.

  The said other fiber may be contained in the separator material in the ratio of less than 50 mass%. That is, it is preferable that 50 mass% or more of the ultrafine fiber and the high strength composite fiber are contained in the separator material. If the total content of ultrafine fibers and high-strength composite fibers is less than 50% by mass, the mechanical properties of the separator material may be deteriorated, or the air permeability and liquid retention may be reduced, leading to deterioration of battery properties. There is. The separator material of the present invention preferably contains 70% by mass or more of the ultrafine fiber and the high-strength composite fiber, more preferably 80% by mass or more, and the ultrafine fiber or ultrafine fiber. It is most preferable that it is composed of only two fibers, i.e., a fiber capable of generating a high-strength composite fiber.

The separator material of this invention is demonstrated according to the manufacturing method of a nonwoven fabric. The separator material of the present invention has a high-strength composite fiber having a single fiber strength of 4.0 cN / dtex or more, an elongation of 30% to 60% and a Young's modulus of 3250 N / mm ² or more and less than 4650 N / mm ^2. If necessary, fine fibers having a fineness of 0.5 dtex or less and / or fibers capable of generating the ultrafine fibers (including sea-island type composite fibers and split type composite fibers, hereinafter also referred to simply as ultrafine fiber generating fibers), Further, if necessary, the mixed fiber is prepared, and a fiber web in which these fibers are uniformly mixed is prepared. The fiber web can be produced by a known method, and examples thereof include a card method, an airlaid method, a wet papermaking method, a spunbond method, and a meltblown method. Among these, the wet papermaking method is preferable in that a uniform fiber web can be obtained. The fiber web is produced, for example, according to a known wet papermaking method, and the fiber web is Tm-10 ° C. or higher and Tm + 60 ° C. when the melting point of the low melting point resin contained in the high-strength composite fiber is Tm (° C.). By performing heat treatment at the following temperature, at least a part of the fibers constituted by a part of the resin contained in the high-strength composite fiber is thermally bonded to produce a nonwoven fabric. The nonwoven fabric after performing the fiber web or heat treatment may be subjected to fiber entanglement treatment if necessary, and if the generation of ultrafine fibers from the ultrafine fiber generating fibers is small, A dividing process (for example, a dividing process using a high-pressure water flow) may be performed.

  The separator material of the present invention is preferably a non-woven fabric obtained by a wet papermaking method (hereinafter referred to as “wet non-woven fabric”) in terms of denseness and uniformity. The wet nonwoven fabric can be produced by the following method. First, the high-strength composite fiber, if necessary, the ultrafine fiber having a fineness of 0.5 dtex or less and / or the ultrafine fiber generating fiber are mixed, and if necessary, the other fibers are mixed. A water-dispersed slurry that is uniformly dispersed in water so as to have a concentration of 0.005 to 0.6% by mass is prepared. At this time, an ultrafine fiber can be generated by dividing at least a part of the ultrafine fiber generating fiber using a disaggregator. Examples of the disaggregator include a pulper, a chest, and a refiner. Especially, since the generation condition of the ultrafine fiber from the said ultrafine fiber generation fiber can be adjusted by a pulper controlling with stirring time and rotation speed, it is preferable. The ratio of the generation of ultrafine fibers in the wet papermaking stage (if the ultrafine fiber-generating fiber is a split type composite fiber) is preferably 50% or more and 95% or less. If the ratio of the occurrence of ultrafine fibers is less than 50%, not only the denseness of the entire wet nonwoven fabric obtained may be impaired, but also uniform treatment may be difficult in the hydrophilization treatment described later. . If the proportion of ultrafine fibers generated exceeds 95% at the wet papermaking stage, fiber balls are likely to be generated, and a uniform wet nonwoven fabric may not be obtained. Next, wet papermaking is performed on the water-dispersed slurry to obtain a fiber web. As this wet papermaking method, any of the conventionally known methods such as a short net method, a circular net method, a long net method, or a known paper making method such as a long net / circular net combination method, a short net / circular net combination method, etc. A fiber web can be formed by a wet papermaking method in combination.

  Next, the fiber web obtained by each wet papermaking method described above is subjected to heat treatment, and the constituent fibers of the fiber web are thermally bonded. At this time, fibers composed of at least a part of the resin contained in the high-strength conjugate fiber are thermally bonded to obtain a thermally bonded nonwoven fabric. The conditions for the heat treatment are appropriately selected according to the basis weight of the fiber web, the thickness of the fiber web, and the type of resin constituting the fiber contained in the wet nonwoven fabric. As the heat treatment machine used for the heat treatment, a known heat treatment machine can be used, but a heat treatment machine capable of drying while thermally bonding the constituent fibers of the fiber web is preferable. For example, a cylinder dryer (Yankee dryer), A hot air spraying machine, a hot roll processing machine, a hot embossing machine, or the like can be used. In particular, the cylinder dryer (Yankee dryer) can perform thermal bonding treatment by bringing the fiber web into contact with a heating roll, so that it becomes surface bonding instead of mere point bonding at the entanglement point between the constituent fibers, and the thickness of the nonwoven fabric. The fibers can be effectively thermally bonded to each other while adjusting the thickness. The heat treatment is performed at a temperature of Tm-10 ° C. or higher and Tm + 60 ° C. or lower, where Tm (° C.) is the melting point of the low melting point component contained in the high strength composite fiber. For example, when the sheath component of the high-strength composite fiber is a polyethylene resin, the temperature is preferably 120 ° C. or higher and 160 ° C. or lower. In particular, when it is high-density polyethylene, the temperature is preferably 130 ° C. or higher and 150 ° C. or lower. In the case of the core-sheath type composite fiber, the upper limit of the heat treatment temperature is preferably 10 ° C. or lower than the melting point of the core component (high melting point component). If the sheath component of the high-strength composite fiber is an ethylene-vinyl alcohol copolymer resin, the temperature of the heat treatment is 130 ° C. or higher and 160 ° C. or lower, preferably 140 ° C. or higher and 150 ° C. or lower. Further, when the sheath component of the high-strength composite fiber is a polypropylene resin, the heat treatment temperature is 150 ° C. or higher and 200 ° C. or lower, preferably 160 ° C. or higher and 180 ° C. or lower.

The heat-bonded non-woven fabric subjected to the heat treatment is not particularly limited as long as at least part of the constituent fibers is thermally bonded by at least a low melting point resin component contained in the high-strength composite fiber, and the basis weight, thickness, average pore diameter, The tensile strength is not particularly limited. However, the basis weight of the heat-bonding nonwoven fabric is preferably in the range of 10 g / m ² or more and 100 g / m ² or less. A more preferable basis weight is in a range of 20 g / m ² or more and 90 g / m ² or less, particularly preferably in a range of 25 g / m ² or more and 80 g / m ² or less, and most preferably 30 g / m ² or more and 80 g / m ^2. The range is as follows. If the basis weight of the heat-bonding nonwoven fabric is less than 10 g / m ² , the nonwoven fabric may become dense and short-circuited when used as a separator. When the basis weight of the heat-bonding nonwoven fabric exceeds 100 g / m ² , the thickness of the separator increases, and the amount of the positive electrode and the negative electrode in the battery may be reduced accordingly.

  The thickness of the heat-bonding nonwoven fabric is preferably in the range of 150 μm or more and 350 μm or less. More preferably, it exists in the range of 200 micrometers or more and 300 micrometers or less, Most preferably, it exists in the range of 230 micrometers or more and 270 micrometers or less. When the thickness of the heat-bonding nonwoven fabric is within the above range, the thickness that absorbs / recovers against the pressure generated in the thickness direction when compression / release is repeated in the battery while the heat-bonding of fibers is strengthened. This is because it can be secured. If the thickness of the heat-bonding nonwoven fabric is less than 150 μm, uneven formation may occur or the piercing strength of the separator material may be reduced. When the thickness of the heat-bonding nonwoven fabric is larger than 350 μm, the separator thickness is increased, so that the amount of the positive electrode and the negative electrode in the battery decreases.

The heat bonding nonwoven fabric preferably has a specific volume of 3.5 cm ³ / g or more and 6.0 cm ³ / g. If the specific volume of the heat-bonding nonwoven fabric is less than 3.5 cm ³ / g, the heat-bonding nonwoven fabric will be too dense, and the resulting separator material will also be dense, reducing the electrolyte retention, In addition to an increase in internal resistance, the flexibility of the separator material is lost, and the processability as the separator material may be reduced. On the other hand, when the specific volume of the separator material exceeds 6.0 cm ³ / g, the bulk of the separator material becomes too large and it becomes difficult to reduce the pore diameter of the separator material, and as a result, a fine powder short circuit is likely to occur. There is a tendency. Preferred specific volume than in the separator material of the present invention, 3.7 cm ³ / g or more, or less 5.8 cm ³ / g, particularly preferably 4.0 cm ³ / g or more 5.5cm is ³ / g or less Most preferably, it is 4.2 cm ³ / g or more and 5.2 cm ³ / g or less.

  Next, the obtained heat-bonding nonwoven fabric can be subjected to a hydrophilic treatment as necessary. The separator material of the present invention preferably contains 70% by mass or more of ultrafine fibers and high-strength composite fibers made of polyolefin resin, but polyolefin resins other than ethylene-vinyl alcohol copolymer resins are generally hydrophobic. Therefore, the hydrophilicity required for the separator material is often not exhibited. Therefore, it is preferable to perform a hydrophilic treatment. The hydrophilization treatment may be performed using any method conventionally used in the production of separator materials. Specifically, the hydrophilization treatment includes various discharges such as treatment exposed to a fluorine atmosphere (hereinafter simply referred to as fluorine treatment), vinyl monomer graft polymerization treatment, sulfonation treatment, ozone gas treatment, corona discharge treatment and plasma discharge treatment. Examples thereof include a treatment, a surfactant treatment, a hydrophilic resin application treatment, a treatment for repeating these hydrophilic treatments, and a hydrophilic treatment performed in combination.

For example, in the case of corona discharge treatment, it may be treated 1 to 20 times on both sides of the heat-bonded nonwoven fabric, and the treated total discharge amount may be treated in the range of 0.05 to 10 kW · min / m ² . In the case of fluorine treatment, the thermal bonding nonwoven fabric is exposed to a mixed gas of fluorine gas diluted with an inert gas such as nitrogen, argon or helium, oxygen gas, sulfurous acid gas (also called sulfur dioxide gas), carbon dioxide gas, etc. By this, the method of introduce | transducing a hydrophilic group into the heat bonding nonwoven fabric surface is mentioned. In addition, after making sulfurous acid gas contact and react with the thermobonding nonwoven fabric surface, when making fluorine gas contact and react, permanent hydrophilicity can be provided more efficiently. When the fluorine treatment is performed, the heat-bonded nonwoven fabric after the treatment may be neutralized in an alkaline solution such as an aqueous potassium hydroxide solution, washed with warm water, and dried.

  If it is a graft polymerization treatment, a method of immersing a heat-bonded nonwoven fabric in a solution containing a vinyl monomer and a polymerization initiator and heating, a method of irradiating radiation after applying a vinyl monomer to the heat-bonded nonwoven fabric, etc. may be used. Furthermore, it is preferable that the surface of the heat-bonded nonwoven fabric is modified by ultraviolet irradiation, corona discharge, plasma discharge, or the like before the vinyl monomer solution and the heat-bonded nonwoven fabric are brought into contact with each other because efficient graft polymerization can be achieved.

  Examples of the sulfonation treatment include treatment with concentrated sulfuric acid, treatment with fuming sulfuric acid, treatment with chlorosulfonic acid, treatment with anhydrous sulfuric acid, and the like. Concentrated sulfuric acid, fuming sulfuric acid, sulfur trioxide, chloro Various sulfur oxides such as sulfur monoxide gas, sulfur dioxide gas or sulfur trioxide gas, or a method of introducing a sulfonic acid group into the surface of the heat-bonded nonwoven fabric by dipping the heat-bonded nonwoven fabric in a solution of sulfuric acid or sulfuryl chloride Examples thereof include a method of introducing a sulfonic acid group into the surface of the heat-bonded nonwoven fabric by applying a discharge treatment to the surface of the heat-bonded nonwoven fabric in a gas-containing atmosphere. When the sulfonation treatment is performed, the treated wet nonwoven fabric may be neutralized in an alkaline solution, washed with warm water and dried.

  In the case of a surfactant treatment, there is a method of immersing or applying a thermal bonding nonwoven fabric in a solution of an anionic surfactant or a nonionic surfactant having hydrophilic performance. The hydrophilic treatment method may be any method described above, or a combination of two or more. Moreover, it may be performed before the thickness adjusting step described later, or after the thickness adjusting step. However, when a hydrophilic treatment is performed after the thickness adjusting step, the components adhered to the inside of the heat-bonding nonwoven fabric or the surface of the heat-bonding nonwoven fabric Since it may be difficult for a component (for example, fluorine gas, sulfurous acid gas, fuming sulfuric acid, sulfur oxide gas, and the like) to react with the carbon atom of the gas, it is preferable to carry out before the thickness adjusting step.

  In the method for producing a separator material of the present invention, the obtained heat-bonding nonwoven fabric is subjected to a heat calendering process, and at least one thickness adjustment step is performed to adjust the thickness to be suitable for the separator material. When performing the thickness adjustment step on the thermobonding nonwoven fabric, using a pair of press machines (thermal calender rolls) having a temperature higher than 40 ° C. and 10 ° C. lower than the temperature at which the constituent fibers of the thermobonding nonwoven fabric are melted, It is preferable that the non-woven fabric is pressed so as to have a thickness of 50 μm to 300 μm. By performing such treatment, the thermobonding nonwoven fabric is adjusted to a desired thickness, and when there are fibers that can generate ultrafine fibers in which the ultrafine fibers are not sufficiently generated, the ultrafine fibers are generated. The ratio can be further increased. Examples of the pair of press machines include a roll type and a flat plate type, but it is preferable to use a flat roll type calendering machine in consideration of productivity. A more preferable lower limit of the processing temperature is a temperature higher than 45 ° C. A more preferable upper limit of the processing temperature is a temperature lower by 30 ° C. or more than a temperature at which the fibers constituting the nonwoven fabric melt, and an even more preferable lower limit of the processing temperature is a temperature higher than 50 ° C. An even more preferable upper limit of the processing temperature is a temperature that is 40 ° C. or more lower than the melting temperature of the fibers constituting the nonwoven fabric. If the processing temperature is too low, thickness unevenness may occur in the width direction of the nonwoven fabric, or the thickness of the nonwoven fabric may be restored (thickness recovery) after processing. When the processing temperature exceeds a temperature 10 ° C. lower than the melting temperature of the constituent fibers, not only the gap between the fibers on the nonwoven fabric surface is blocked, but the electrolyte and gas permeability may be lowered. In the case where the thickness adjustment step is performed after the hydrophilization treatment is performed, the hydrophilic group imparted by the hydrophilization treatment may deteriorate due to the temperature of the thickness adjustment step, and the hydrophilicity of the heat-bonded nonwoven fabric may be attenuated. .

  In the thickness adjusting step, the linear pressure in the press treatment is preferably 150 N / cm or more and 1500 N / cm or less. A more preferable lower limit of the linear pressure is 200 N / cm. A more preferable lower limit of the linear pressure is 300 N / cm. A more preferable upper limit of the linear pressure is 1000 N / cm. A more preferable upper limit of the linear pressure is 800 N / cm. If the linear pressure is less than 150 N / cm, the thickness adjustment process may become unstable. If the linear pressure exceeds 1500 N / cm, the nonwoven fabric surface tends to be easily formed into a film, which hinders gas and electrolyte permeability. There is a risk of causing.

The manufacturing method of the separator material of this invention can also be specified by the method shown below. A step of wet-making a slurry containing a high-strength composite fiber having a fiber strength of 4.0 cN / dtex or more and an elongation of greater than 30% but not more than 60% to obtain a fiber web, heat-treating the fiber web, A step of obtaining a heat-bonded nonwoven fabric in which fibers constituting the fiber web are thermally bonded to each other by a part of the resin contained in the high-strength composite fiber, and heat calendering the heat-bonded nonwoven fabric, and at least one thickness adjustment is performed. comprise conducting, T ₁ the non-woven fabric thickness of said thermal bonding nonwoven fabric, when the nonwoven fabric thickness after the thickness adjustment was T _2, the thickness adjusted to the thickness ratio (T ₂ / T ₁₎ is 0.65 or less It is characterized by doing. According to the above manufacturing method, in addition to the high-strength conjugate fiber appropriately extending or deforming with respect to the pressure in the length direction of the fiber, the fiber entanglement point obtained by thermal bonding of the high-strength conjugate fiber is surface bonded. Therefore, the strain of the fiber is relatively likely to occur between the fiber entanglement points, and the separator material containing this high-strength composite fiber has mechanical characteristics such as piercing strength and tensile strength. And particularly flexibility in the thickness direction. As a result, the pressure applied to the separator material by contact with foreign matter mixed in the battery or needle-like foreign matter such as dendrites and when the pressure is applied, the high-strength composite fiber will bend and deform appropriately. The fiber is dispersed or absorbed, and although it is deformed by a foreign substance, the foreign substance is difficult to penetrate and a separator material with high short-circuit resistance is obtained.

  In order for the thickness ratio to be 0.65 or less, it is preferable that the heat-bonded nonwoven fabric before the thickness adjustment step is relatively bulky. By performing the thickness adjustment step on such a bulky heat-bonded nonwoven fabric, it becomes a flexible separator material having a thickness suitable for the separator material while leaving voids therein and having a high bulk recovery property. . If the thickness ratio exceeds 0.65, the heat-bonded nonwoven fabric before the thickness adjustment step is already dense and the heat-bonded nonwoven fabric with few voids inside. Therefore, the resulting separator material tends to be highly rigid, and when it is loaded inside the battery, the effect of reducing the internal pressure may be reduced.

The said thickness ratio can be calculated | required from the thickness before and behind a thickness adjustment process, when performing a thickness adjustment process once. If a plurality of times the thickness adjusting process, the thickness prior to the first thickness adjusting step and T _1, the thickness after the final thickness adjustment step and T _2. In addition, the thickness before the thickness adjustment step may not be the thickness immediately before the thickness adjustment step if the thickness has not greatly changed, and after the heat treatment after wet papermaking is completed as the thickness before the thickness adjustment step. If the thickness of the heat-bonded nonwoven fabric is the thickness before the thickness adjustment step (T ₁ ) and the thickness after the thickness adjustment step does not vary greatly, the thickness of the separator material obtained is the thickness after the thickness adjustment step (T _2). ). A more preferred thickness ratio (T ₂ / T ₁ ) is 0.6 or less, and even more preferably 0.55 or less. The lower limit of the thickness ratio is not particularly limited, but if the thickness ratio is less than 0.15, it is excessively compressed in the thickness adjusting step, so the heat-bonded nonwoven fabric may become too dense or filmy, which is not preferable. . The lower limit of the thickness ratio is more preferably 0.3 or more, and even more preferably 0.4 or more.

  The separator material of the present invention preferably satisfies the following physical property values. When the following physical property values satisfy the respective ranges, the separator material is excellent in denseness and formation uniformity, and when used as a separator for various alkaline secondary batteries, even when subjected to pressure in contact with foreign matter, This is because the piercing strength is high, and in addition, since the separator is appropriately deformed, it is difficult for foreign matter to penetrate, and it is easy to become a separator material with high short-circuit resistance.

  The stress (maximum penetration force F) at the penetration point in the needle penetration force measurement of the separator material of the present invention is preferably 12 N or more. The piercing strength of the separator material is a substitute characteristic that represents the degree of short-circuit prevention (short-circuit resistance) caused by metallic foreign matter such as metal burrs and dendrites that are generated when secondary batteries are used repeatedly. A larger value indicates that a short circuit caused by a metal foreign object or a dendrite is less likely to occur. When the separator material has a piercing strength of less than 12N, a short circuit due to a metal foreign object or a dendrite is likely to occur when the separator material is used as a separator. A more preferable lower limit of the piercing strength of the separator material of the present invention is 12.5 N or more, and a particularly preferable lower limit is 13 N or more. The upper limit of the piercing strength is not particularly limited, but is preferably 30N or less, more preferably 27N or less, and particularly preferably 25N or less in consideration of the productivity and handling properties of the separator material.

  The piercing strength and the maximum displacement amount by the needle penetration force measurement are values measured by the following method. First, a separator material to be measured or a thermally bonded nonwoven fabric is prepared as a sample cut into a size of 30 mm in length and 100 mm in width. This sample was placed on a support having a cylindrical through-hole (diameter 11 mm) of a handy compression tester (KES-G5, manufactured by Kato Tech Co., Ltd.), and further, 46 mm long, 86 mm wide and 7 mm thick. A pressing plate having a hole with a diameter of 11 mm at the center of the aluminum plate was placed so that the hole coincided with the cylindrical through hole of the support. Next, a load when a needle of a cone shape having a height of 18.7 mm, a bottom surface diameter of 2.2 mm, and a tip shape of 1 mm in diameter is pierced vertically at the center of the holding plate at a speed of 2 mm / second, The sample is pushed by the conical needle and the length of the deformation is measured. Of the measured load, the stress at the penetration point where the conical needle penetrates the sample is the maximum penetration force F (piercing strength (N )), And the amount of displacement at the penetration point was defined as the maximum displacement S (mm). The piercing strength is measured by taking four samples from one separator material or a heat-bonding nonwoven fabric, measuring each sample at 15 different points, and averaging the values measured at a total of 60 points in the sample. Strength and maximum displacement.

  The separator material of the present invention has an F / S (N / mm) obtained by dividing the maximum load F (that is, the piercing strength (N)) when the piercing strength is measured by a maximum displacement S (mm) is 4.5 N / mm. It is preferable that it is not less than mm and not more than 10 N / mm. The F / S is an index indicating a penetration force required to deform the separator material by 1 mm when a pressure is applied so that the needle penetrates the separator material, and the penetration force (Force) -displacement amount ( Strain) Indicates the slope of the curve. When this inclination (F / S) is within a predetermined range, the separator material is deformed in the thickness direction with respect to the foreign matter, and the stress of the foreign matter can be absorbed. When the F / S is less than 4.5 N / mm, when pressure is applied so as to penetrate the separator material, the separator material is excessively deformed so that the piercing strength is reduced, and foreign matter is likely to penetrate. Short circuit resistance may be reduced. On the other hand, when the F / S is larger than 10 N / mm, the separator material is not easily deformed with respect to the pressure, and when the pressure is applied so as to penetrate the separator material, the separator material hardly deforms. The pressure applied from the foreign material or the like is concentrated at one point where the separator material and the foreign material are in contact with each other, and the foreign material is likely to pass through. It becomes difficult to bend, and productivity and handleability may decrease. The F / S (N / mm) is more preferably 4.5 N / mm or more and 8.0 N / mm or less, particularly preferably 4.75 N / mm or more and 7.8 N / mm or less. Most preferably, it is 0 N / mm or more and 7.5 N / mm or less.

  The separator material of the present invention preferably has a thickness of 50 μm or more and 300 μm or less. When the thickness of the separator material is less than 50 μm, the pore diameter of the separator material, particularly the maximum pore diameter, tends to increase, and the fine powder short-circuit prevention property and the dendrite short-circuit prevention property may deteriorate. On the other hand, when the thickness of the separator material exceeds 300 μm, the electrolyte permeability may deteriorate and the internal resistance of the battery may increase. In addition, since the number of electrode plates per battery volume is reduced, the battery performance tends to be inferior. The thickness of the separator material of the present invention is more preferably 70 μm or more and 200 μm or less, particularly preferably 100 μm or more and 150 μm or less, and most preferably 105 μm or more and 140 μm or less.

The separator material of the present invention preferably has a basis weight in the range of 10 g / m ² or more and 100 g / m ² or less. If the basis weight of the separator material is out of the above range, the thickness and pore diameter of the separator material of the present invention may not satisfy a predetermined range. Preferred mass per unit area than in the separator material of the present invention, 20 g / m ² or more 90 g / m ² or less, particularly preferable to be 25 g / m ² or more 80 g / m ² or less, 30 g / m ² or more 80 g / m ² or less Is most preferable.

The separator material of the present invention preferably has a specific volume in the range of 1.5 cm ³ / g or more and 3.5 cm ³ / g. If the specific volume of the separator material is less than 1.5 cm ³ / g, the separator material becomes too dense and the electrolyte retention (retention rate) decreases, resulting in an increase in the internal resistance of the battery. is there. On the other hand, when the specific volume of the separator material exceeds 3.5 cm ³ / g, the bulk of the separator material becomes too large, and it becomes difficult to reduce the pore diameter of the separator, and as a result, a tendency to easily generate a fine powder short circuit. It is in. Specific volume of the separator material of the present invention is more preferably 2.0 cm ³ / g or more 3.0cm is ³ / g or less, in particular be 2.2 cm ³ / g or more 2.7cm is ³ / g or less Preferably, it is 2.3 cm ³ / g or more and 2.5 cm ³ / g or less.

  The separator material of the present invention preferably has an average pore diameter in the range of 4 μm to 15 μm. When the average pore diameter is in the range of 4 μm or more and 15 μm or less, it is possible to obtain a separator material having excellent fine powder short circuit prevention and dendrite short circuit prevention. When the average pore diameter is less than 4 μm, the electrolyte solution retention tends to decrease and the internal resistance of the battery tends to increase. On the other hand, when the average pore diameter exceeds 15 μm, a fine powder short circuit and a dendrite short circuit tend to occur. The average pore diameter is preferably 4.5 μm or more and 14 μm or less, particularly preferably 4.8 μm or more and 12 μm, and most preferably 5.0 μm or more and 10 μm or less.

  The tensile strength of the separator material of the present invention is not particularly limited, but the tensile strength in at least one direction (for example, MD direction (also referred to as machine direction or longitudinal direction), CD direction (also referred to as width direction or lateral direction)) is 50 N / It may be 5 cm or more, may be 80 N / 5 cm or more, and may be 100 N / 5 cm or more. The upper limit of the tensile strength is not particularly limited and may be 350 N / 5 cm or less. When the tensile strength of the separator material is less than 50 N / 5 cm, the puncture strength, which is another mechanical property, may be lowered. In addition, when the separator material is produced or when the battery is manufactured, the handling and productivity of the separator material may be reduced.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these Examples. Various physical properties of the fibers used and various physical properties of the obtained heat-bonding nonwoven fabric and separator material were measured by the following methods.

[Single fiber fineness]
It measured according to JIS L1013.

[Single fiber strength / Single fiber elongation]
According to JIS L 1015, using a tensile tester, the holding interval of the sample was 20 mm, the load value when the fiber was cut was the single fiber strength, and the elongation when cut was the single fiber elongation.

[Single fiber Young's modulus]
In accordance with JIS L 1015, using a tensile tester, a tensile test was performed with the gripping interval of the sample being 20 mm, the initial tensile resistance P (N / tex) was obtained from the load-elongation curve, and the value calculated by the following equation Was defined as the single fiber Young's modulus. Where ρ is the fiber density (g / cm ³ ).
Single fiber Young's modulus (N / mm ² ) = 1000 × P × ρ

[Thickness]
Using a micrometer (Micrometer MDC-25MJ manufactured by Mitutoyo Corporation), the thickness of the heat-bonding nonwoven fabric and the separator material is 175 kPa at 10 different locations of the three samples according to JIS B 7502. Then, the thickness was measured, and the average value of a total of 30 locations was determined and used as the thickness of the sample.

[Tensile test]
According to JIS L 1096 6.12.1 A method (strip method), using a constant speed tension type tensile tester, tensile test under the conditions of 5 cm width of specimen, 10 cm of gripping distance and 30 ± 2 cm / min. The tensile strength (N / 5cm) was the load at the time of cutting, and the elongation (%) was the elongation at the time of cutting.

[Pore size distribution (average pore size)]
A palm porometer (manufactured by Porous Materials INC.) Was used, and measurement was performed by the bubble point method according to ASTM F31686.

[Constituent fibers of fiber web]
When manufacturing the separator material of an Example and a comparative example, the fiber shown below was used.

[Split type composite fiber]
Split type composite fiber 1: One resin component is made of ethylene-vinyl alcohol copolymer resin, the other resin component is made of polypropylene, and the composite ratio of ethylene-vinyl alcohol copolymer resin and polypropylene is 5/5 (volume ratio). ), Which is obtained by melt spinning so that the hollow ratio is 12%, and is a hollow 16-divided mold having a cross-sectional shape shown in FIG. 1A, having a fineness of 1.1 dtex and a fiber length of 3 mm. Composite fiber.
Split type composite fiber 2: A hollow 16 split type composite fiber obtained in the same manner as the split type composite fiber 1 except that the fineness is 2.2 dtex and the fiber length is 4 mm.
Split type composite fiber 3: one resin component is made of polymethylpentene and the other resin component is made of polypropylene, so that the composite ratio (volume ratio) of polymethylpentene and polypropylene is 5/5, and the hollow ratio is 12%. A hollow 8-split type composite fiber having a fineness of 1.8 dtex and a fiber length of 3 mm obtained by melt spinning.

[High strength composite fiber]
High-strength conjugate fiber 1: The core component is made of polypropylene and the sheath component is made of high-density polyethylene. The composite ratio (volume ratio) of the core component and the sheath component is (core / sheath) = 7/3, and the core component is not exposed. Each of the physical properties obtained by melt spinning so that the core component and the sheath component are concentric, producing an unstretched fiber bundle, and subjecting the unstretched fiber bundle to dry two-stage stretching A concentric core-sheath composite fiber having a fineness of 0.8 dtex and a fiber length of 5 mm with the following values.
・ Single fiber strength: 5.25 cN / dtex
Young's modulus: 4325.8 N / mm ²
・ Elongation: 41.0%
High-strength conjugate fiber 2: A concentric core-sheath conjugate fiber obtained in the same manner as the high-strength conjugate fiber 1 except that the draw ratio was changed to 1.1 dtex.
・ Single fiber strength: 4.87 cN / dtex
・ Elongation: 45.0%
High-strength conjugate fiber 3: A concentric core-sheath conjugate fiber obtained in the same manner as the high-strength conjugate fiber 1 except that the draw ratio was changed to 1.4 dtex.
・ Single fiber strength: 5.24 cN / dtex
・ Elongation: 58.9%
High-strength conjugate fiber 4: A concentric core-sheath conjugate fiber obtained in the same manner as the high-strength conjugate fiber 1 except that the draw ratio was changed to 1.7 dtex.
Single fiber strength: 5.38 cN / dtex
・ Elongation: 49.4%
High-strength conjugate fiber 5: A concentric core-sheath conjugate fiber obtained in the same manner as the high-strength conjugate fiber 1 except that the composite ratio was changed to (core / sheath) = (8/2).
・ Single fiber strength: 6.9 cN / dtex
・ Elongation: 28.4%
High-strength conjugate fiber 6: A concentric core-sheath conjugate fiber obtained in the same manner as the high-strength conjugate fiber 1 except that the composite ratio was changed to (core / sheath) = (6/4).
・ Single fiber strength: 5.69 cN / dtex
・ Elongation: 32.8%
Young's modulus: 4331.8 N / mm ²
High-strength conjugate fiber 7: A concentric core-sheath conjugate fiber obtained in the same manner as the high-strength conjugate fiber 1 except that the composite ratio was changed to (core / sheath) = (5/5).
・ Single fiber strength: 5.26 cN / dtex
・ Elongation: 30.2%
Young's modulus: 4018.8 N / mm ²

[Core-sheath type composite fiber]
Core-sheath type composite fiber 1: A concentric core-sheath type composite fiber obtained in the same manner as the high-strength composite fiber 7 except that the core component polypropylene and the sheath component high-density polyethylene were changed.
・ Single fiber strength: 3.94 cN / dtex
・ Elongation: 61.4%
Young's modulus: 3137.1 N / mm ²

[Examples 1 to 11 and Comparative Examples 1 to 3]
First, in order to examine the conditions of the wet nonwoven fabric optimal for the separator material, the split type composite fiber capable of generating ultrafine fibers, and the wet nonwoven fabric in which the physical properties and mixing ratio of the high-strength composite fiber are changed are Examples 1 to 11 and Comparative Examples. 1 to 3 were produced. A split type composite fiber, a high strength composite fiber, and other fibers were weighed so that the mixing ratios shown in Tables 1 and 2 were obtained, and an aqueous dispersion slurry was prepared so that the raw cotton used had a concentration of 0.01% by mass. . The prepared slurry is stirred for 1 minute at 2,000 revolutions per minute using a home mixer to divide the split composite fiber into resin components to generate ultrafine fibers and at the same time, each constituent fiber is uniformly dispersed. A slurry was obtained. The obtained slurry was subjected to wet paper making to prepare a fiber web having a basis weight of about 53 g / m ² . Contained at the same time that the fiber web is dried by transporting the fiber web with a carrier for transportation and heating the web for 45 seconds using a cylinder dryer (yankee dryer) heated to 140 ° C. The fibers were bonded to each other with a high-strength conjugate fiber and / or a core-sheath conjugate fiber to obtain a heat-bonded nonwoven fabric.

  Next, the thermobonding nonwoven fabric is subjected to thickness processing using a heat roll under the conditions of a temperature of 60 ° C. and a linear pressure of 320 N / cm. In Example 10, Comparative Examples 3 and 4, the thickness is about 160 μm, and the others are about 120 μm. The thickness was adjusted to produce a separator material. In order to evaluate the adaptability to the separator material for the heat-bonded nonwoven fabrics of Examples 1 to 11 and Comparative Examples 1 to 3, each item of basis weight, thickness, piercing strength, and tensile strength was measured. The results of measuring each item are shown in Tables 1 and 2.

The separator materials of Examples 1 to 11 obtained a separator material having a high piercing strength of 12 N or more, whereas the separator materials of Comparative Examples 1 and 3 both had a piercing strength of less than 12 N, and the piercing strength. That is, a separator material with sufficiently high short-circuit resistance could not be obtained. This is presumably because the separator materials of Comparative Examples 1 and 3 do not contain high-strength composite fibers having a single fiber strength of 4.0 cN / dtex or higher and a Young's modulus of 3250 N / mm ² or higher. Moreover, when the separator material of Examples 1-11 and the separator material of Comparative Example 2 are compared, the single fiber strength of the high strength fiber included in Comparative Example 2 is higher than that of the high strength composite fiber used in Examples 1-11. Although high, the piercing strength of the separator material is lower than that of the separator materials of Examples 1 to 11. This is because the elongation of the high-strength composite fiber used in Comparative Example 2 is less than 30%, and therefore pressure was not absorbed due to deformation of the fiber when pressure was applied to the separator material in a very narrow range. It is presumed that the piercing strength has decreased.

  Comparing Examples 1, 3, and 4, in order to obtain a separator material with high piercing strength and improved short-circuit resistance, the core-sheath ratio (core / sheath) has more core components than 5/5. 6/4 and 7/3 high-strength composite fibers are more preferable, and it is considered particularly preferable to use high-strength composite fibers of around 7/3.

  When Examples 1, 5, 6, and 7 are compared, it is considered that the fineness of the high-strength composite fiber is preferably smaller in order to obtain a separator material having high piercing strength and improved short-circuit resistance. It is considered that 1.2 dtex or less is preferable.

  Moreover, when Example 1 and Example 8, and Example 5 and Example 9 are compared, the separator material of Example 1 and 5 which is a separator material which uses the split type composite fiber of a finer fineness is pierced, and is a separator material with high strength. It has become. Therefore, in order to obtain a separator material with high piercing strength and short-circuit resistance in a separator material in which high-strength composite fiber and split-type composite fiber are mixed, use split-type composite fibers with smaller fineness. Is considered preferable.

[Examples 12 to 15, Comparative Example 4]
From the results of Examples 1 to 11 and Comparative Examples 1 to 3, the optimum high-strength conjugate fiber, ultrafine fiber, or the tendency of fibers capable of generating ultrafine fibers was grasped, so the split conjugate fiber 1 and the core-sheath conjugate fiber 1. The separator material was produced using the core-sheath composite fiber 8 as needed. First, each fiber was weighed so as to have a mixing ratio shown in Table 3, and an aqueous dispersion slurry was prepared so that the raw cotton used had a concentration of 0.5% by mass. With respect to the prepared slurry, the split type composite fiber contained in the water-dispersed slurry was subjected to split processing using a pulper. The resulting water-dispersed slurry is combined with a short net-type wet paper machine and a circular net paper machine to produce a wet paper-making web. The wet papermaking web is dried by heating at 140 ° C., and at least a part of the constituent fibers of the wet papermaking web is melted by melting the heat-bonding component of the high strength composite fiber and / or the core-sheath composite fiber. A heat bonded nonwoven fabric was obtained by heat bonding. The obtained heat-bonded nonwoven fabric was collected, and the basis weight, thickness (T ₁ ), and pore size distribution were measured.

  Next, the resulting heat-bonded nonwoven fabric was subjected to a hydrophilic treatment using a reactive gas such as fluorine gas, and hydrophilicity was imparted to the heat-bonded nonwoven fabric by introducing functional groups onto the surface of the heat-bonded nonwoven fabric. .

  In order to obtain the optimum thickness for the separator material of the present invention, the thickness processing (calendar processing) using a heat roll comprising a pair of plain rolls was performed on the fluorine-bonded heat-bonded nonwoven fabric. The thickness processing (calendar treatment) was carried out under the conditions of a processing speed of 15 m / min by heating a hot roll to 60 ° C. and applying a linear pressure of 500 N / cm to the thermobonded nonwoven fabric.

In order to further enhance the hydrophilicity of the heat-bonded nonwoven fabric after the thickness processing, corona discharge treatment was performed on both surfaces of the heat-bonded nonwoven fabric to obtain the separator material of the present invention. Corona discharge treatment was performed four times on each side of the heat-bonded nonwoven fabric with a discharge amount of 1.0 kW · min / m ² (total discharge amount of 8 kW · min / m ² ). After the corona discharge treatment was completed, the basis weight, thickness (T ₂ ), piercing test, and pore size distribution were measured by the measurement methods described above for the separator materials of Examples 11 to 14 and Comparative Examples 1 and ₂ . . The results are shown in Table 3 together with the fiber configurations of Examples 12 to 15 and Comparative Example 4, and various measurement results of the heat-bonded nonwoven fabric.

  The separator materials of Examples 12 to 15 have a high puncture strength of 12 N or higher because the separator material contains high-strength composite fibers having a single fiber strength of 4.0 cN / dtex or higher. In addition, the high-strength composite fiber not only has high single fiber strength but also a high-strength composite fiber with an elongation exceeding 30%. Therefore, a separator material using the high-strength composite fiber can balance strength and elongation against pressure. The F / S in the piercing test is in the range of 4.5 N / mm or more and 10 N / mm or less which is optimum as a separator material. Thereby, when the separator material of the present invention is used by being loaded inside a battery housing, for example, when subjected to pressure by a needle-like foreign material, the separator material exhibits high strength, and is appropriately bent and deformed. Thus, since the pressure is dispersed by being appropriately deformed while withstanding the applied pressure, the separator material is less likely to penetrate foreign matter and has excellent short-circuit resistance.

  On the other hand, the separator material of Comparative Example 4 does not include a high-strength composite fiber having a single fiber strength of 4.0 cN / dtex or more, and the constituent fibers are thermally bonded with a composite fiber having a low single fiber strength. Since this composite fiber has a high degree of elongation, the composite fiber stretches greatly during the piercing test, so the amount of displacement until it penetrates increases, but the strength of the fiber itself is insufficient, so the piercing strength is less than 12N. It is sufficient and the short circuit resistance is inferior to that of the separator material of the present invention.

  The separator material of the present invention is suitable as a separator used for an alkaline secondary battery, a lithium ion secondary battery, an electric element such as an electric double layer capacitor or a capacitor, or an ion exchange separator (ion catcher), and particularly nickel- It is suitable for alkaline secondary battery applications such as a cadmium battery, a nickel-zinc battery, and a nickel-hydrogen battery.

A component A
B component B
6 Hollow part 10 Hollow split type composite fiber 20 Solid split type composite fiber 22 Core component 24 Sheath component 30 Hollow composite split type composite fiber 32 Core component 34 Sheath component 40 Solid composite split type composite fiber

Claims (8)

A non-woven fabric comprising at least two types of thermoplastic resins, including a high-strength composite fiber having a single fiber strength of 4.0 cN / dtex or more, and at least a part of the constituent fibers being thermally bonded by the high-strength composite fiber;
A separator material in which the elongation of the high-strength composite fiber is greater than 30% and 60% or less, and the Young's modulus is 3250 N / mm ² or more and less than 4650 N / mm ² .   The nonwoven fabric has a stress (maximum penetration force F) at a penetration point in needle penetration force measurement of 12 N or more, and a value obtained by dividing the maximum penetration force F by the displacement amount (maximum displacement amount S) of the penetration point (F / The separator material according to claim 1, wherein S) is 4.5 N / mm or more. The high-strength conjugate fiber is a core-sheath type conjugate fiber comprising two different thermoplastic resins, a thermoplastic resin having a high melting point as a core component, and a thermoplastic resin having a melting point lower than the core component by 10 ° C. or more as a sheath component. And
The separator material according to claim 1 or 2, wherein the core component / sheath component is polypropylene resin / polyethylene resin or polypropylene resin / ethylene-propylene copolymer resin.   The separator material according to claim 3, wherein the high-strength conjugate fiber has a volume ratio (core / sheath) of a core component and a sheath component of 60/40 to 75/25.   The separator material according to any one of claims 1 to 4, wherein the nonwoven fabric contains 30 to 95% by mass of the high-strength conjugate fiber and 5 to 50% by mass of ultrafine fibers of 0.5 dtex or less. The ultrafine fiber is an ultrafine fiber obtained by dividing a split type composite fiber composed of at least two types of thermoplastic resins,
In the split type composite fiber, one thermoplastic resin is a polypropylene resin, and the other thermoplastic resin is a polymethylpentene resin, a polyethylene resin, an ethylene-propylene copolymer resin, and an ethylene-vinyl alcohol copolymer resin. The separator material according to claim 5, which is at least one resin selected from the group consisting of: A step of wet-making paper containing a high strength composite fiber having a fiber strength of 4.0 cN / dtex or more and an elongation of greater than 30% and less than 60% to obtain a fiber web;
Heat-treating the fiber web, and obtaining a heat-bonded nonwoven fabric in which fibers constituting the fiber web are thermally bonded to each other by at least a part of the resin contained in the high-strength composite fiber;
Applying a heat calendering process to the heat-bonding nonwoven fabric and performing at least one thickness adjustment;
T ₁ The nonwoven fabric thickness of said thermal bonding nonwoven fabric, when the nonwoven fabric thickness after the thickness adjustment was T _2, to a thickness adjusted such that the thickness ratio (T ₂ / T ₁₎ is 0.65 or less, the separator material Production method.   A battery incorporating the separator material according to claim 1.