CN107452927B

CN107452927B - Separator for alkaline battery and method for producing the same

Info

Publication number: CN107452927B
Application number: CN201710377819.3A
Authority: CN
Inventors: 伊藤康博; 村田修一; 川野明彦; 田中政尚
Original assignee: Japan Vilene Co Ltd
Current assignee: Japan Vilene Co Ltd
Priority date: 2016-05-31
Filing date: 2017-05-25
Publication date: 2021-07-23
Anticipated expiration: 2037-05-25
Also published as: JP2017216112A; JP6925784B2; CN107452927A; HK1244107A1

Abstract

The invention provides a separator for an alkaline battery and a manufacturing method thereof. The separator for an alkaline battery is used at a high temperature, and it is difficult to cause a short circuit caused by a dendrite, and the electrolyte is difficult to be exhausted, and a battery with a long service life can be produced. . The separator for an alkaline battery is composed of a non-woven fabric comprising quasi-ultrafine irregular short fibers with a non-circular cross-sectional shape, a fiber diameter of 3-5 μm, and a fiber length of 1-20 mm, and the non-woven fabric has a The apparent density is 0.33 g/cm ³ or less, and the mass reduction rate after friction is 5% or less. The separator for an alkaline battery can be produced by applying a water flow to a fiber web containing split-type composite short fibers to generate quasi-ultrafine irregular short fibers from the split-type composite short fibers, and the split-type composite short fibers It is composed of two or more kinds of resins, and can be divided by mechanical action to produce quasi-ultrafine irregular short fibers with a non-circular cross-sectional shape, a fiber diameter of 3 to 5 μm, and a fiber length of 1 to 20 mm.

Description

Separator for alkaline battery and method for producing same

Technical Field

The present invention relates to a separator for an alkaline battery and a method for manufacturing the same.

Background

Due to recent increases in environmental awareness, hybrid vehicles and electric vehicles tend to be preferred as automobiles. As a battery as a power source of such a hybrid vehicle and an electric vehicle, an alkaline battery such as a nickel-hydrogen secondary battery is used. Among such alkaline batteries in the automobile field, alkaline batteries for consumer use are increasing in number, and are required to have high reliability, particularly, high reliability for preventing short circuit due to dendrite. In addition, when an alkaline battery is used in the automobile field, the alkaline battery is frequently used in a high-temperature environment, and the battery life tends to be shortened due to exhaustion of an electrolyte.

In addition, although automotive applications are not being pursued, the applicant of the present application proposes the following as a separator that can be expected to prevent the occurrence of short circuits due to dendrites: "a separator for a battery, comprising a nonwoven fabric comprising: (1) superfine short fiber with fiber diameter below 3 μm; (2) a quasi-ultrafine irregularly shaped short fiber having a fiber diameter (round equivalent value) of 3 to 5 μm (not including 3 μm) and a non-round cross-sectional shape; and (3) a composite high-strength polypropylene fiber having a weld component on the surface thereof and having a tensile strength of 4.5cN/dtex or more, the weld component of the composite high-strength polypropylene fiber being welded. "(patent document 1).

As a method for producing such a battery separator, a method is disclosed in which a split type composite short fiber is split by a water flow to produce a pseudo-ultrafine irregularly shaped short fiber. As described above, in order to sufficiently divide the divided type composite short fibers by the water flow, a water flow of high water pressure is required, and as a result, only a battery separator having a small thickness and a high apparent density can be manufactured. When a separator having a small thickness and a high apparent density is applied to an alkaline battery used in a high-temperature environment in the field of automobiles, the amount of electrolyte retained is small, and therefore, the electrolyte is easily consumed, and the battery life tends to be short.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2006 and 236991

Disclosure of Invention

Technical problem to be solved by the invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a separator for an alkaline battery, which is less likely to cause short-circuiting due to dendrites even when used at high temperatures, and which is less likely to cause depletion of an electrolytic solution, and a method for manufacturing the same, and which can manufacture a battery having a long life.

Means for solving the problems

The invention is a separator for alkaline batteries comprisingA non-woven fabric comprising quasi-ultrafine profiled short fibers having a non-circular cross-sectional shape, a fiber diameter (converted from a circular value) of 3 to 5 μm, and a fiber length of 1 to 20mm, wherein the non-woven fabric has an apparent density of 0.33g/cm³The mass reduction rate after friction is 5% or less.

The present invention preferably further contains a high-strength composite binder staple fiber having a tensile strength of 5cN/dtex or more and a fiber length of 1 to 20 mm.

The present invention preferably further comprises a super-fine short fiber having a fiber diameter of less than 3 μm and a fiber length of 1 to 20 mm.

The present invention preferably contains a quasi-ultrafine irregularly shaped short fiber composed of a methylpentene-based resin.

The separator for alkaline batteries preferably has a thickness of 150 μm or more.

The invention relates to a method for manufacturing a separator for an alkaline battery, which comprises the steps of acting water flow on a fiber web containing split composite short fibers to generate quasi-ultra-fine profiled short fibers from the split composite short fibers, and enabling the quasi-ultra-fine profiled short fibers to contain the quasi-ultra-fine profiled short fibers and have an apparent density of 0.33g/cm³The non-woven fabric is characterized in that the split composite short fibers are composed of two or more resins, and are split by mechanical action to produce quasi-ultrafine profiled short fibers having a non-circular cross-sectional shape, a fiber diameter (equivalent to a circle) of 3 to 5 [ mu ] m, and a fiber length of 1 to 20mm, and the mass loss rate after the rubbing is 5% or less.

Effects of the invention

The present invention has excellent performance of preventing short circuit caused by dendrite because of containing quasi-superfine profiled short fiber and low mass reduction rate after friction. That is, since the quasi-ultrafine short fibers are contained, the path to the other pole is complicated and long, and the mass reduction rate after the rubbing is low means that entanglement between fibers is sufficient, and the path to the other pole is more complicated and long, and therefore, the performance of preventing the occurrence of short circuit due to dendrite is excellent. Further, when the apparent density is 0.33g/cm³Since a large amount of the electrolyte can be retained by the following voids, the electrolyte can be produced even at a high levelAn alkaline battery which is hardly exhausted even when used at a low temperature and has a long battery life.

When the present invention contains the high-strength composite binder short fibers, the fibers are less likely to be damaged by pressure, and therefore, the voids can be maintained. Therefore, when a battery using such an alkaline battery separator is used in a high-temperature environment, even if the electrolyte solution is somewhat volatilized and the amount of the electrolyte solution is reduced, since most of the electrolyte solution is retained, a stable electrification reaction can be exhibited for a long time. Namely, it is easy to manufacture an alkaline battery having a long life.

When the present invention contains the ultrafine short fibers, the retention of the electrolyte is excellent. That is, since the inclusion of the ultrafine short fibers forms more fine voids and the electrolyte solution retention capacity is enhanced by capillary action, even when an alkaline battery using such an alkaline battery separator is used in a high-temperature environment, the electrolyte solution is less likely to volatilize, and an alkaline battery having a longer life can be manufactured. Further, since the route to the other electrode is more complicated and long by containing the ultrafine short fibers, it is easy to manufacture an alkaline battery in which short circuit due to dendrite hardly occurs.

The present invention contains the pseudo-ultrafine irregularly shaped short fibers made of a methylpentene-based resin, since the heat resistance is excellent, it is easy to manufacture an alkaline battery that can be used even at high temperatures.

When the thickness of the separator for an alkaline battery of the present invention is 150 μm or more, the electrolyte can be retained in a large amount because many voids are available for retaining the electrolyte. Therefore, it is easy to manufacture an alkaline battery having a long battery life in which the electrolyte is hardly consumed even when used at high temperatures.

The manufacturing method of the present invention can manufacture the separator for alkaline batteries. That is, an alkaline battery having excellent performance of preventing short circuit due to dendrite, and having a long battery life can be manufactured, in which the electrolyte is less likely to be consumed even when used at high temperature.

Drawings

Fig. 1 is a schematic cross-sectional view of a split type composite short fiber that can be used for the production of a separator for an alkaline battery of the present invention.

Fig. 2 is a schematic cross-sectional view of another segmented composite short fiber that can be used for producing the separator for an alkaline battery of the present invention.

Fig. 3 is a schematic cross-sectional view of another segmented composite short fiber that can be used in the production of the separator for alkaline batteries of the present invention.

Fig. 4 is a schematic cross-sectional view of another alternative segmented composite staple fiber that can be used in the manufacture of the alkaline battery separator of the present invention.

Fig. 5 is a schematic cross-sectional view of another alternative segmented composite staple fiber that can be used in the manufacture of the alkaline battery separator of the present invention.

Fig. 6 is a schematic cross-sectional view of another alternative segmented composite staple fiber that can be used in the manufacture of the alkaline battery separator of the present invention.

Description of the reference numerals

1: a split type composite short fiber; 11: a resin component; 12: a resin component.

Detailed Description

The alkaline battery separator of the present invention (hereinafter, simply referred to as "separator") contains a quasi-ultrafine irregularly shaped short fiber in order to make the path to the other electrode complicated and long and to have excellent performance for preventing short circuit due to dendrite. In addition, the quasi-ultrafine short fibers have a non-circular cross-sectional shape, which also provides an effect that the quasi-ultrafine short fibers are less likely to be broken by pressure and the amount of electrolyte retained increases.

The shape of the cross section of the quasi-ultrafine short fibers is not particularly limited as long as it is non-circular, that is, not perfect circles, but may be, for example, oblong, elliptical, polygonal (for example, triangular, quadrangular such as rectangular, trapezoidal, pentagonal, hexagonal, etc.), and particularly, because the angle of the apex is small, the path to the other pole is easily complicated, and thus, a quadrangular such as triangular, trapezoidal, etc. is suitable.

In addition, the pseudo-ultrafine profiled short fibers of the present invention have a fiber diameter of 5 μm or less, preferably 4.5 μm or less, and more preferably 4.2 μm or less, in order to increase the surface area of the fibers in a predetermined volume and to improve the electrolyte retention. On the other hand, the pseudo-ultrafine profiled short fiber of the present invention has a fiber diameter of 3 μm or more, preferably 3.5 μm or more, in order to facilitate the complicated path to the other pole and to maintain the thickness against pressure. The term "fiber diameter" as used herein means a value obtained by calculation and measurement of an electron micrograph, and when the cross-sectional shape is non-circular like a quasi-ultrafine short fiber, the diameter of a circle having the same area as the cross-sectional area is defined as the fiber diameter.

Further, in order to uniformly disperse the quasi-ultrafine profiled short fibers and make the path to the other pole complicated and long, the length of the quasi-ultrafine profiled short fibers is 1-20 mm, preferably 2-15 mm, and more preferably 3-10 mm. The "fiber length" in the present invention means an average fiber length measured by a method specified in 8.4.1 (direct method (C method)) of JIS L1015-2010.

The resin constituting the quasi-ultrafine profiled short fiber of the present invention is not particularly limited, but in order to make the resistance to electrolyte excellent, the quasi-ultrafine profiled short fiber of the present invention preferably contains a polyolefin-based resin, and is preferably composed of only a polyolefin-based resin. Examples thereof include polyethylene resins [ ultra-high-molecular-weight polyethylene, high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene copolymers (e.g., ethylene-vinyl alcohol copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer), etc. ], polypropylene resins (e.g., polypropylene, propylene copolymer, etc.), and polymethylpentene resins (e.g., polymethylpentene, methylpentene copolymer, etc.). In particular, the pseudo-ultrafine short fibers made of a methylpentene-based resin are excellent in heat resistance and are suitable for the easy production of alkaline batteries that can be used even at high temperatures.

The quasi-ultrafine short fibers may be made of, for example, polyamide-based resins such as nylon 6, nylon 66, nylon 610, nylon 612, nylon 10, and nylon 12. In addition, the quasi-ultrafine profiled short fibers may include two or more quasi-ultrafine profiled short fibers different from each other in at least one of a cross-sectional shape, a fiber diameter, a fiber length, and a resin composition.

Further, in order to make the electrolyte resistance excellent, as described above, the quasi-ultrafine profiled short fibers preferably contain a polyolefin-based resin, but since the affinity of the polyolefin-based resin with the electrolyte is low and the retention of the electrolyte tends to be low, when the quasi-ultrafine profiled short fibers contain a polyolefin-based resin, particularly when the quasi-ultrafine profiled short fibers are composed of a polyolefin-based resin, it is preferable to have a hydrophilic group (for example, a sulfonic acid group, a carboxyl group, a carbonyl group, or the like) on the fiber surface.

Such a pseudo ultrafine shaped short fiber can be obtained by, for example, dividing a divided type composite short fiber made of two or more resins by a mechanical action. More specifically, the segmented composite short fiber 1 having an orange-type cross-sectional shape as shown in fig. 1 is segmented by a mechanical action, and a triangular quasi-ultrafine profiled short fiber composed of the resin component 11 and a triangular quasi-ultrafine profiled short fiber composed of the resin component 12 can be produced. By dividing the segmented composite short fiber 1 having an orange-type cross-sectional shape as shown in fig. 2 by a mechanical action, an elliptical quasi-ultrafine profiled short fiber composed of the resin component 11 and a triangular quasi-ultrafine profiled short fiber composed of the resin component 12 can be produced. The segmented composite short fiber 1 having an orange-type cross-sectional shape as shown in fig. 3 is segmented by a mechanical action, and a triangular pseudo-ultrafine profiled short fiber composed of the resin component 11, a triangular pseudo-ultrafine profiled short fiber composed of the resin component 12, and a round pseudo-ultrafine profiled short fiber composed of the resin component 12 can be produced. By mechanically dividing the segmented composite short fiber 1 having an orange-type cross-sectional shape as shown in fig. 4, an elliptical quasi-ultrafine profiled short fiber composed of the resin component 11, a triangular quasi-ultrafine profiled short fiber composed of the resin component 12, and a circular quasi-ultrafine profiled short fiber composed of the resin component 11 can be produced. By dividing the divided type composite short fiber 1 having the multi-bimetal cross-sectional shape shown in fig. 5 by a mechanical action, a trapezoidal quasi-ultrafine profiled short fiber composed of the resin component 11 or the resin component 12 and a semicircular quasi-ultrafine profiled short fiber composed of the resin component 11 or the resin component 12 can be generated. The segmented composite short fiber 1 having an orange-shaped cross-sectional shape and a hollow portion as shown in fig. 6 can be segmented by a mechanical action to produce a trapezoidal quasi-ultrafine irregularly shaped short fiber composed of the resin component 11 or the resin component 12. The quasi-ultrafine profiled short fibers can also be obtained by using a spinneret capable of spinning fibers having a profiled cross-sectional shape.

Further, as the mechanical action, for example, a fluid flow such as a water flow, a calender, a refiner, a pulper, a mixer, a beater and the like can be cited, but as described below, since the mass reduction rate after the friction is preferably 5% or less, it is preferable that the quasi-ultrafine irregularly shaped short fibers are generated by the fluid flow such as the water flow and entanglement occurs at the same time.

The quasi-ultrafine profiled short fibers of the present invention are preferably in a stretched state in order to make the separator excellent in strength and hard to break when manufacturing a battery. The "stretched state" in the present specification means a state in which the fibers are mechanically stretched after the fibers are formed, and for example, the fibers formed by the melt blowing method, which are in a stretched state at the time of fiber formation, are not in a stretched state. In addition, if the split type composite short fibers are in a stretched state at the stage, the produced quasi-ultrafine profiled short fibers are in a stretched state.

In order to easily exhibit the above-described effects, the pseudo-ultrafine irregularly shaped staple fibers are preferably contained in the nonwoven fabric in an amount of 20 mass% or more, more preferably 25 mass% or more, and still more preferably 30 mass% or more. On the other hand, since the high-strength conjugate staple fibers and/or the ultrafine staple fibers described below are preferably further contained, such quasi-ultrafine profiled staple fibers are preferably 80% by mass or less, more preferably 70% by mass or less, and further preferably 60% by mass or less in the nonwoven fabric.

In particular, although the pseudo-ultrafine profiled short fibers made of a methylpentene-based resin are suitable, the pseudo-ultrafine profiled short fibers made of a methylpentene-based resin are preferably contained in the nonwoven fabric in an amount of 10% by mass or more, more preferably 12.5% by mass or more, and still more preferably 15% by mass or more.

In order to make the separator of the present invention less likely to be damaged by pressure and maintain a gap, and to allow a battery using the separator of the present invention to be used in a high-temperature environment, even if the electrolyte solution is somewhat volatilized and the amount of the electrolyte solution is reduced, most of the electrolyte solution can be retained and a stable electrification reaction can be easily exerted over a long period of time, it is preferable that the separator further contains a high-strength composite binder short fiber having a tensile strength of 5cN/dtex or more and a fiber length of 1 to 20 mm.

Further, since a separator which is hard to break can be obtained by containing the high-strength composite binder short fibers, when the separator is arranged between electrodes and an electrode group is assembled, there is a problem that the separator is hardly cut by the projections of the electrodes, and the projections of the electrodes penetrate the separator to cause short-circuiting.

Further, when the splittable conjugate staple fiber is split by mechanical action to obtain the pseudo-ultrafine irregularly shaped staple fiber, the high-strength conjugate staple fiber has a high young's modulus and an appropriate rigidity, and therefore, when the splittable conjugate staple fiber is split, it can function as a support, and the splittability is improved, and a nonwoven fabric having an excellent texture can be obtained.

Since the higher the tensile strength, the more excellent the above performance, the tensile strength of the high-strength conjugate staple fiber is preferably 5.5cN/dtex or more, more preferably 6.0cN/dtex or more, and further preferably 6.2cN/dtex or more. Although the upper limit of the tensile strength is not particularly limited, about 50cN/dtex is preferable. The "tensile strength" in the present invention means a tensile strength in accordance with JIS L1015: 2010 "chemical short fiber test method" 8.7.1 (test under standard conditions), tensile strength was measured using a constant-speed tension type tensile tester under conditions of a nip interval of 20mm and a tensile speed of 20 mm/min.

In addition, in order to uniformly disperse the high-strength composite bonding short fibers and easily and uniformly retain the electrolyte, the fiber length of the high-strength composite bonding short fibers is 1-20 mm, preferably 2-15 mm, and more preferably 3-10 mm.

The high-strength composite binder staple fibers of the present invention may be composed of any resin component, but in order to achieve excellent electrolyte resistance, it is preferable to contain a polyolefin-based resin, preferably only a polyolefin-based resin, as in the case of the pseudo-ultrafine profiled staple fibers. For example, it is preferable that the adhesive is composed of two or more resins selected from polyethylene resins (for example, ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene copolymers, and the like), polypropylene resins (for example, polypropylene, propylene copolymers, and the like), and polymethylpentene resins (for example, polymethylpentene, methylpentene copolymers, and the like), and the adhesive component is exposed on the surface. Among these, when the segmented composite short fibers are segmented by mechanical action to produce pseudo-ultrafine profiled short fibers, the polypropylene-based resin is preferably contained so that the high-strength composite binder short fibers can have an appropriate rigidity to thereby obtain an action as a support.

The polypropylene resin may be a homopolymer of propylene or a copolymer of propylene and an α -olefin (e.g., ethylene, 1-butene, etc.). More specifically, there may be mentioned, for example, isotactic propylene homopolymers having crystallinity, ethylene-propylene random copolymers having a small ethylene unit content, propylene block copolymers comprising a homopolymeric moiety composed of a propylene homopolymer and a copolymeric moiety composed of an ethylene-propylene random copolymer having a relatively large ethylene unit content, and further crystalline propylene-ethylene- α -olefin copolymers comprising a product obtained by copolymerizing each of the homopolymeric moiety and the copolymeric moiety in the above-mentioned propylene block copolymer with an α -olefin such as 1-butene. Among them, isotactic polypropylene homopolymer is preferable from the viewpoint of strength, and in particular, Isotactic Pentad Fraction (IPF) is 90% or more, Q value (weight average molecular weight/number average molecular weight ═ Mw/Mn) as an index of molecular weight distribution is 6 or less, and melt index MI (temperature 230 ℃ c., load 2.16kg) is 3 to 50g/10 minutes. Such a polypropylene component can be obtained by homopolymerizing propylene or copolymerizing propylene and another α -olefin using a Ziegler-Natta catalyst (Ziegler-Natta catalyst) or a metallocene catalyst.

As described above, when the high-strength conjugate staple fibers contain a polypropylene resin, the melting point of the binder component is preferably 10 ℃ or higher, more preferably 20 ℃ or higher lower than that of the polypropylene resin so that the binder component does not affect the polypropylene resin during the binding and the fiber morphology can be maintained by the polypropylene resin. Specifically, examples of the binder component include ethylene polymers (e.g., high-density, medium-density, and low-density polyethylene, linear low-density polyethylene, and the like), copolymers of propylene and other α -olefins, and the like. Since the adhesive component preferably has a high melting point in order to maintain the adhesive effect even when used at high temperatures, it is preferably made of high-density polyethylene. Further, if the binder component is high-density polyethylene, a separator having a certain hardness, gloss, and elasticity can be obtained, and thus a separator having excellent handling properties can be obtained. Further, when the splittable conjugate short fiber is split by a mechanical action to produce the pseudo-ultrafine irregularly shaped short fiber, the binder component is preferably composed of high-density polyethylene in view of obtaining an action as a support by giving appropriate rigidity to the high-strength conjugate short fiber.

In the high-strength composite binder short fiber of the present invention, in order to enable bonding by the binder component, the binder component occupies at least a part of the fiber surface, but the higher the proportion of the binder component in the fiber surface, the more the binder component that can participate in bonding, and therefore, the binder component occupies preferably 50% or more (excluding both end portions), more preferably 70% or more (excluding both end portions), still more preferably 90% or more (excluding both end portions), and most preferably the entire fiber surface (excluding both end portions). Therefore, the arrangement state of each component in the cross section of the high-strength composite binder short fiber is preferably of a sheath-core type, an eccentric type, or a sea-island type.

As described above, the high-strength composite staple fibers of the present invention preferably contain a polyolefin-based resin in order to have excellent electrolyte resistance, but since the polyolefin-based resin has low affinity with the electrolyte and tends to have low retention of the electrolyte, it is preferable that the high-strength composite staple fibers have a hydrophilic group (e.g., a sulfonic acid group, a carboxyl group, a carbonyl group, etc.) on the fiber surface when they contain a polyolefin-based resin, particularly when they are composed of a polyolefin-based resin.

In order to obtain a separator which is less likely to be damaged by pressure, maintains voids, and has excellent electrolyte retention, the young's modulus of the high-strength composite binder staple fiber of the present invention is preferably 30cN/dtex or more, more preferably 35cN/dtex or more, and still more preferably 40cN/dtex or more. The upper limit of the Young's modulus is not particularly limited, but is preferably 110cN/dtex or less. The "young's modulus" is measured by a method defined by JIS L1015: 2010, 8.11, and a value of apparent Young's modulus calculated from the initial tensile resistance measured by the method defined in item(s). It should be noted that the initial tensile resistance is a value measured at a tensile rate of 20 mm/min using a constant-speed tension type tensile tester.

The heat shrinkage of the high-strength composite binder staple fiber of the present invention is preferably 10% or less. This is because, if the thermal shrinkage ratio is used, the shrinkage is difficult even when the battery is used in an alkaline battery used at high temperature, and the performance of preventing short circuit is excellent. The heat shrinkage is more preferably 9% or less. The heat shrinkage is measured in accordance with JIS L1015: 20108.15 (b) the rate of change in dry heat dimension was measured by heat treatment for 30 minutes using an oven dryer at a temperature of 120 ℃.

The fiber diameter of the high-strength composite binder staple fiber of the present invention is not particularly limited, but is preferably 5 to 32 μm, and more preferably 8 to 17 μm. This is because the high-strength composite binder short fibers tend to be easily broken by pressure and to be difficult to maintain a gap when the fiber diameter is less than 5 μm, and also tend to break through the separator by the protrusions of the electrode plate or to be easily torn by the edge of the electrode plate, and when the fiber diameter is more than 32 μm, the high-strength composite binder short fibers are difficult to uniformly disperse and the electrolyte solution tends to be difficult to uniformly remain.

Such a high-strength composite binder short fiber that can be used in the present invention can be produced, for example, by the method described in japanese patent application laid-open No. 2002-180330. Namely, it can be obtained by: a composite undrawn yarn having a binder component on the surface of a fiber is spun by a melt spinning method which is a common method, and then is drawn 4 to 15 times in pressurized saturated steam having a temperature of 100 ℃ or higher and lower than the melting point of the binder component, and cut into a desired fiber length.

The nonwoven fabric constituting the separator of the present invention may contain two or more kinds of high-strength conjugate staple fibers different from each other in fiber diameter, fiber length, resin composition, tensile strength, young's modulus, and/or heat shrinkage rate.

In order to obtain a separator which is less likely to be damaged by pressure, maintains voids, and has excellent electrolyte retention properties, the high-strength composite binder staple fibers are preferably included in the nonwoven fabric in an amount of 20 mass% or more, more preferably 30 mass% or more, and still more preferably 40 mass% or more. On the other hand, the content of such high-strength conjugate staple fibers in the nonwoven fabric is preferably 80 mass% or less, more preferably 70 mass% or less, and still more preferably 60 mass% or less, from the viewpoint of balance with the pseudo-ultrafine conjugate staple fibers, preferably with the ultrafine conjugate staple fibers described later.

The nonwoven fabric constituting the separator of the present invention preferably further contains ultrafine short fibers having a fiber diameter of less than 3 μm and a fiber length of 1 to 20mm, in addition to the quasi-ultrafine irregularly shaped short fibers. This is because the inclusion of the ultrafine short fibers can form finer voids, and the retention of the electrolyte solution is enhanced by capillary action, so that an alkaline battery having a longer life can be produced in which the electrolyte solution is less likely to volatilize even when the alkaline battery using the separator for an alkaline battery is used in a high-temperature environment. Further, since the route to the other electrode is further complicated and long by the inclusion of the ultrafine short fibers, an alkaline battery in which short circuit due to dendrite is more difficult to occur can be manufactured.

In order to easily exhibit the capillary action and to make the path to the other pole complicated and long, the fiber diameter of the ultrafine short fibers in the present invention is preferably 2.5 μm or less, more preferably 2 μm or less. On the other hand, the lower limit of the fiber diameter is not particularly limited, but is preferably 0.01 μm or more.

In order to uniformly disperse the ultrafine short fibers, uniformly retain the electrolyte due to capillary action, and uniformly complicate and lengthen the path to the other pole, the fiber length of the ultrafine short fibers of the present invention is 1 to 20mm, preferably 1 to 15mm, and more preferably 1 to 10 mm.

It is preferable that the ultra fine short fiber of the present invention has almost the same fiber diameter in the length direction. This is because, if the fiber diameters are almost the same as described above, the nonwoven fabric can have pores with a uniform pore diameter and a uniform internal space, and the electrolyte solution is uniformly distributed, and the ion permeability is excellent. The ultrafine short fibers having substantially the same fiber diameter may be ultrafine short fibers composed of island components remaining after removing the sea component of the sea-island type composite fiber. In particular, the ultrafine short fibers composed of the remaining island components, which are produced by removing the sea component from the sea-island type composite fibers produced by the composite spinning method, have substantially the same fiber diameter even among a plurality of ultrafine short fibers, and therefore the performance is more excellent, and therefore, the ultrafine short fibers are particularly preferable. Further, the ultrafine fibers produced by the melt blowing method are not ultrafine fibers having a fiber diameter almost the same in the longitudinal direction and ultrafine fibers having a fiber diameter almost the same even among a plurality of ultrafine fibers.

The island component of the sea-island type composite fiber is a base of the ultrafine short fiber and is composed of the same resin as the ultrafine short fiber, and the sea component of the sea-island type composite fiber is removed by a solvent or the like and is composed of a resin which can be removed faster than the island component. For example, a sea-island type composite fiber in which the island component is composed of a polyolefin resin and the sea component is composed of a polyester or a copolyester, and only the sea component is removed by an alkaline solution, thereby obtaining a super fine short fiber composed of the island component.

The shape of the cross section of the ultrafine short fibers of the present invention may be non-circular or circular, but is preferably circular. This is because, when the cross-sectional shape is circular, the nonwoven fabric has excellent texture and can uniformly retain the electrolyte.

Further, if bundles of the ultrafine short fibers are present, it is difficult for the nonwoven fabric to exhibit capillary action as a whole, and since a path to the other electrode tends to be simple and short in the nonwoven fabric as a whole, it is preferable that the ultrafine short fibers are not present in a bundle state and the respective ultrafine short fibers are dispersed.

In addition, in order to make the separator excellent in strength and difficult to break at the time of manufacturing a battery, it is preferable that the ultrafine short fibers be in a stretched state. In addition, if the sea-island type composite fiber is in a stretched state at the stage, the ultrafine short fibers composed of the island components are in a stretched state.

In order to provide excellent electrolyte resistance, the ultrafine short fibers preferably contain a polyolefin resin, and more preferably are composed of a polyolefin resin. For example, the resin composition may be composed of a polyethylene resin [ for example, ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, an ethylene copolymer (for example, an ethylene-vinyl alcohol copolymer, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer), or the like ], a polypropylene resin (for example, polypropylene, a propylene copolymer, or the like), or a polymethylpentene resin (for example, polymethylpentene, a methylpentene copolymer, or the like), and preferably a polypropylene resin or a polyethylene resin. Further, the resin may be composed of a polyamide resin such as nylon 6, nylon 66, nylon 610, nylon 612, nylon 10, or nylon 12.

Further, as described above, in order to make the electrolyte resistance excellent, the ultrafine short fibers preferably contain a polyolefin-based resin, but since the affinity of the polyolefin-based resin with the electrolyte is low and the retention of the electrolyte tends to be low, when the ultrafine short fibers contain a polyolefin-based resin, particularly when the ultrafine short fibers are composed of a polyolefin-based resin, it is preferable to have a hydrophilic group (for example, a sulfonic acid group, a carboxyl group, a carbonyl group, or the like) on the fiber surface.

Further, if the ultra-short fibers contain a resin component (hereinafter, sometimes referred to as "welding component") capable of participating in welding and the ultra-short fibers are in a welded state by the welding component, the ultra-short fibers are preferably hard to fall off and fluff. When the ultrafine short fibers are in a fused state, the ultrafine short fibers may be composed of only the fused component composed of the resin, or may be composed of two or more components, that is, a fused component and a component having a melting point higher than that of the fused component (hereinafter, sometimes referred to as "non-fused component"). As in the latter case, if the ultra-fine short fibers are composed of two or more components of a welding component and a non-welding component, even if the welding component is welded, the fiber form can be maintained by the non-welding component, and the capillary action is not impaired, which is preferable. The cross-sectional shape of such a super-fine short fiber is preferably a sheath-core type, an eccentric type, or a sea-island type, for example, in order to obtain excellent fusion strength. In order to maintain the fiber shape, the non-welding component preferably has a melting point higher by 10 ℃ or more than the melting point of the welding component, and more preferably has a melting point higher by 20 ℃ or more than the melting point of the welding component.

The "melting point" in the present specification means a temperature at which a maximum value is given to a dissolution endothermic curve obtained by heating from room temperature at a temperature rise temperature of 10 ℃/minute using a differential scanning calorimeter. When there are 2 maxima, the maximum temperature is defined as the melting point.

In order to easily exhibit the above-described effects, the nonwoven fabric preferably contains such ultrafine short fibers in an amount of 3 mass% or more, more preferably 5 mass% or more, and still more preferably 10 mass% or more. On the other hand, since the high-strength conjugate staple fibers are preferably contained in the nonwoven fabric from the viewpoint of the pseudo-ultrafine profiled staple fibers, the content of such ultrafine staple fibers is preferably 30% by mass or less, more preferably 25% by mass or less, and still more preferably 20% by mass or less.

The ultrafine short fibers may contain two or more types of ultrafine short fibers different from each other in fiber diameter, fiber length, cross-sectional shape, and/or resin composition.

The nonwoven fabric of the separator of the present invention contains the quasi-ultrafine profiled short fibers as described above, and preferably contains the high-strength conjugate staple fibers and/or the ultrafine profiled short fibers, but when the segmented conjugate short fibers are segmented to produce the quasi-ultrafine profiled short fibers, the segmented conjugate short fibers are not sufficiently segmented, and pulp fibers in which the quasi-ultrafine profiled short fibers are mutually bonded may be mixed.

The nonwoven fabric as the separator of the present invention contains the above-mentioned quasi-ultrafine irregularly shaped short fibers, but maintains its form by entanglement of the fibers and/or bonding of the high-strength composite binder short fibers when the nonwoven fabric contains the high-strength composite binder short fibers.

The nonwoven fabric used as the separator of the present invention has an apparent density of 0.33g/cm³Since the electrolyte solution is present in a large amount in the following cases, an alkaline battery having a long battery life can be manufactured in which the electrolyte solution is hardly consumed even when used at high temperatures. Since the lower the apparent density, the more voids and the larger the amount of electrolyte retained, 0.32g/cm is preferable³Hereinafter, more preferably 0.31g/cm³Hereinafter, more preferably 0.30g/cm³Hereinafter, more preferably 0.29g/cm³Hereinafter, more preferably 0.28g/cm³The following. On the other hand, if the apparent density is too low and the number of voids is too large, the morphological stability tends to be poor, and therefore, it is preferably 0.18g/cm³Above, more preferably 0.19g/cm³Above, more preferably 0.20g/cm³The above. The "apparent density" means a calculated value obtained by dividing "weight per unit area" by "thickness".

The thickness of the separator of the present invention is preferably 150 μm or more. This is because, as described above, even if the apparent density is low and the proportion of voids is high, the amount of electrolyte retained decreases if the absolute volume of the separator of voids is small, and when used at high temperatures, the electrolyte may run out, and the battery life may become short. When the thickness of the separator is large, the absolute volume of the separator becomes large, and therefore, it is more preferably 160 μm or more, still more preferably 170 μm or more, still more preferably 180 μm or more, and still more preferably 190 μm or more. On the other hand, if the thickness of the separator is too large, the volume occupied by the separator in the alkaline battery tends to increase and the active material content tends to decrease, and therefore, it is preferably 250 μm or less, more preferably 230 μm or less, and still more preferably 220 μm or less.

The "thickness" of the present invention means that when the load is 5N, the thickness is measured using JIS B7502: 199, an arithmetic average of the thicknesses of 10 points obtained by measuring 10 points selected at random with an outside micrometer (0 to 25 mm).

The weight per unit area of the separator of the present invention is not particularly limited, but if the weight per unit area is large, a separator having a large fiber amount, excellent texture, and high reliability can be obtained, and therefore, 30g/m is preferable²Above, more preferably 40g/m²Above, more preferably 50g/m²The above. On the other hand, when the weight per unit area is increased and the thickness is constant, the apparent density is increased and the number of voids is decreased, and therefore, it is preferably 80g/m²Hereinafter, more preferably 70g/m²Hereinafter, more preferably 60g/m²The following. The "weight per unit area" in the present invention means a weight per unit area as measured in accordance with JIS P8124: 2011 (determination of the weight per square meter of paper and board) obtained on the basis of the method specified.

In addition, since the nonwoven fabric constituting the separator of the present invention has a low mass reduction rate after rubbing of 5% or less and fibers are sufficiently entangled with each other, the path to the other electrode is complicated and long, and the nonwoven fabric has excellent performance of preventing short circuit due to dendrite. In particular, if the high-strength composite binder short fibers are in a bonded state, the high-strength composite binder short fibers are in a bonded state with many contact points between the fibers, and therefore a separator having excellent breaking strength can be obtained. As described above, since the route to the other electrode is complicated and long as the degree of entanglement between fibers is larger as the mass reduction rate is lower, the mass reduction rate is preferably 4% or less, more preferably 3% or less, further preferably 2% or less, and further preferably 1% or less.

In the present invention, the mass reduction rate of the nonwoven fabric (separator) after the rubbing is a value obtained by the following operation.

(1) From 3 points in the width direction of the nonwoven fabric, a rectangular test piece having a width direction of 25mm and a production direction of 180mm was taken.

(2) The test piece was mounted on a test piece stand in accordance with type II friction tester (vibration test type) described in JIS L0849-2013.

(3) A white cotton cloth for rubbing (No. 3 printed cloth) was attached to the tip of the rubbing roller, and the rubbing was performed 100 times in a reciprocating manner at a speed of 30 times per minute under a load of 2N and 10cm at the center of the test piece.

(4) At this time, the mass reduction rate (Re) after the rubbing of 3 test pieces was calculated from the mass (M0) of the test piece before the rubbing and the mass (M1) of the test piece after the rubbing using the following formula.

Re＝[(M0-M1)/M0]×100

(5) The mass reduction rate (Re) of the 3 test pieces was arithmetically averaged to obtain the mass reduction rate after the rubbing of the nonwoven fabric (separator).

The separator (nonwoven fabric) of the present invention has a breaking strength of preferably 60N/50mm or more, more preferably 80N/50mm or more, and even more preferably 100N/50mm or more, in order to sufficiently entangle fibers and to prevent short-circuiting due to dendrites, and to enable stable production without breaking during production of the separator (nonwoven fabric) and during production of a battery.

In addition, the breaking strength of the present invention is a value obtained by the following operation.

(1) A rectangular test piece having a width of 50mm and a production direction of 200mm was taken from 3 points in the width direction of the nonwoven fabric.

(2) Each test piece was pulled in the longitudinal direction under the conditions of a nip interval of 100mm and a tensile speed of 300mm/min by a belt method according to method 8.14.1JIS a) of JIS L1096-2010 using a constant tension type tensile tester, and the tensile load at the time of breaking was read.

(3) The arithmetic mean value of the tensile load was calculated as the breaking strength.

In addition, in order to arrange the separator between the electrodes and to prevent breakage due to the projections of the electrodes or short circuit due to the projections of the electrodes penetrating the separator when the electrode group is loaded, the average needle penetration resistance of the separator (nonwoven fabric) of the present invention is preferably 800gf or more, more preferably 900gf or more, and still more preferably 1000gf or more. The upper limit of the average needle penetration resistance is not particularly limited, but is actually 1800gf or less.

In addition, the average needle penetration resistance in the present invention is a value obtained by the following operation.

(1) A test piece having a width direction of 1050mm and a production direction of 50mm was taken from a nonwoven fabric.

(2) The test piece was placed on a sheet having an area of 1cm attached to a manual compression tester (KES-G5 manufactured by KATO TECH Co., Ltd.)²After the circular hole of (2) was set on the table, a circular hole having an area of 1cm was used²The clip of the circular hole of (2) fixes the test piece. Wherein the fixing is performed in a manner that the holes of the table and the holes of the clamp are consistent.

(3) From above the circular hole, a needle (tip shape: R: 0.5mm) having a diameter of 1mm was lowered at a speed of 1 mm/sec relative to the center portion of the hole, and a puncture was made perpendicularly to the test piece, and the force (gf) required for the penetration was measured at 10cm intervals in the width direction.

(4) The arithmetic mean of the forces required to achieve penetration in each test piece was calculated as the mean pin penetration resistance.

Further, the separator (nonwoven fabric) of the present invention is preferably excellent in texture in order to allow the electrolyte to be uniformly retained. Specifically, the average texture index is preferably 1.8% or less, more preferably 1.6% or less, and still more preferably 1.4% or less.

The average texture index can be measured using a texture meter (trade name: FPI MEAS, Toshiba Solutions Co., Ltd.). More specifically, an image (100mm × 100mm) of the nonwoven fabric (separator) was acquired using a scanner (e.g., EPSON co., Ltd, model GT-X970) having a resolution of 6400 dpi. The brightness in 0.8mm angle units was digitized from the collected images (255 gradations), and the texture index (Ui, unit:%) was calculated from the following formula.

Ui＝(Lsd/Lm)×100

In the formula, Lsd and Lm represent a standard deviation of luminance and an arithmetic average value of luminance, respectively.

The separator of the present invention can be manufactured, for example, in the following manner.

First, a split type composite short fiber is prepared, which is composed of two or more types of resins and can be split by a mechanical action to produce a quasi-ultrafine profiled short fiber having a non-circular cross-sectional shape, a fiber diameter (converted to a circular value) of 3 to 5 μm, and a fiber length of 1 to 20 mm. Examples of such a splittable conjugate staple fiber include the splittable conjugate staple fibers shown in fig. 1 to 6 as described above. Further, since the splittable conjugate staple fiber is a source of the quasi-ultrafine irregularly shaped staple fiber, the splittable conjugate staple fiber is preferably a fiber in which a methylpentene resin, a polypropylene resin, and a polyethylene resin are appropriately combined, and particularly preferably a splittable conjugate staple fiber which is low in compatibility, can be split by a water flow having a low pressure, and is constituted by a combination of a methylpentene resin and a polypropylene resin without excessively reducing the thickness of a fiber web.

Further, as described above, since the separator of the present invention preferably contains the high-strength composite binder short fibers, it is also preferable to prepare the high-strength composite binder short fibers. As the high-strength conjugate staple fibers, the fibers described above can be used, and particularly, a high-strength conjugate staple fiber which is composed of polypropylene and high-density polyethylene and has a core-sheath structure in which the high-density polyethylene occupies the entire fiber surface, and which can function as a support when a split type conjugate staple fiber is split is preferable.

Further, as described above, since the separator of the present invention preferably contains the ultrafine short fibers, the ultrafine short fibers are also preferably prepared. The above-mentioned fiber, particularly the ultrafine short fiber composed of the island component remaining after removing the sea component of the sea-island type composite fiber, can be preferably used because the ultrafine short fibers have substantially the same fiber diameter in the longitudinal direction, have pores with uniform pore diameters and uniform internal spaces, and can easily produce a separator having a uniform electrolyte distribution. In addition, when the high-strength conjugate staple fibers containing high-density polyethylene occupying the entire fiber surface are contained, it is preferable that the ultra-fine staple fibers be composed of polypropylene in order to maintain the fiber morphology even in a thermal environment when the high-strength conjugate staple fibers are bonded.

Subsequently, a web is formed using split type composite staple fibers, preferably high strength composite binder staple fibers and/or ultra-fine staple fibers. The blend ratio of these fibers is not particularly limited, but in order to prevent short-circuiting due to dendrites easily by the pseudo-ultrafine short fibers, it is preferable to contain 20 mass% or more of the segmented composite short fibers. In the invention, because the preferred separator contains the quasi-superfine profiled short fiber, the high-strength composite binding short fiber and the superfine short fiber, the weight ratio of the superfine profiled short fiber to the high-strength composite binding short fiber is preferably 20-77: 20-77: 3 to 30, more preferably 25 to 65: 30-65: 5 to 25, and more preferably 30 to 55: 35-55: 10-20 mass ratio of the composite short fiber comprises a split type composite short fiber, a high-strength composite bonding short fiber and an ultrafine short fiber.

The method of forming the fiber web is not particularly limited, but the fiber web is preferably formed by a wet method in order to uniformly disperse the fibers, to obtain a superior texture, and to uniformly retain the electrolyte solution. Examples of the suitable wet method include a horizontal fourdrinier system, an inclined wire type short wire system, a cylinder system, and a combined fourdrinier-cylinder system.

Thereafter, the water flow is applied to the fiber web (particularly, wet fiber web) to produce quasi-ultrafine conjugate staple fibers from the split conjugate staple fibers. Through the water flow effect, the cutting type composite short fibers can be cut to generate the quasi-superfine special-shaped short fibers, and the fibers can be entangled. As described above, the segmented composite short fibers composed of a combination of a methylpentene-based resin and a polypropylene-based resin are preferably segmented by a water flow under a relatively low pressure, and the thickness of the fiber web is not excessively reduced. In addition, when the high-strength composite binder short fiber is contained, it functions as a support, and the effect of easily dividing the divided composite short fiber to produce the pseudo-ultrafine irregularly shaped short fiber can be obtained.

The water flow is not particularly limited as long as the flow can divide the divided composite short fibers and sufficiently entangle the fibers to reduce the mass loss rate after the friction to 5% or less, and for example, the water flow having a pressure of 1 to 8MPa may be ejected to the web from a nozzle plate having 1 or 2 or more rows of nozzles arranged at a diameter of 0.05 to 0.3mm and a pitch of 0.2 to 3 mm. The fiber web may be sprayed with such water flow 1 or more times on one or both sides thereof. When the water stream is applied, if the non-perforated part of the support such as a net supporting the fiber web is thick, the resulting separator also has large pores and is likely to cause short circuits, and therefore, it is preferable to use a support having a wire diameter of 0.25mm or less.

In addition, in order to divide the divided type composite short fibers by a water flow having a lower pressure without making the thickness of the fiber web thin, it is preferable to fix the fibers constituting the fiber web before the flowing water is applied. For example, when the high-strength composite binder short fiber is contained, it is preferable to fix the split type composite short fiber by binding with the binder component of the high-strength composite binder short fiber. Even when the split type short composite fibers are fixed as described above, the split type short composite fibers are split by the action of the water flow to generate the pseudo-ultrafine irregularly shaped fibers and are entangled with each other.

In the case of bonding by the bonding component of the high-strength composite bonding short fibers as described above, the bonding may be performed under a pressureless condition, or the bonding component may be melted and then pressurized under a pressureless condition. Examples of devices capable of performing such bonding include a hot calender, a hot air penetration heat treatment device, and a cylinder contact heat treatment device.

Although the nonwoven fabric in which quasi-ultrafine foreign fibers are produced by applying a water flow as described above can be used as the separator, it is preferable to fix the fibers constituting the nonwoven fabric after applying a water flow in order to lower the mass reduction rate after rubbing. For example, when the high-strength composite binder short fiber is contained, it is preferable to fix the quasi-ultrafine profiled short fiber by binding with the binder component of the high-strength composite binder short fiber. As described above, when the high-strength composite binder short fibers are bonded after the water flow is applied, a separator having excellent breaking strength can be manufactured. The bonding by bonding the bonding component of the high-strength composite short fibers can be performed by the same method and conditions as the bonding of the fiber web before the water flow is applied, and when the bonding is performed without pressing with a solid such as a roll, a nonwoven fabric (separator) having a low apparent density and many voids can be easily produced, which is preferable.

In the separator of the present invention, in order to make the electrolyte resistance excellent, it is preferable that the pseudo-ultrafine irregularly shaped short fibers, the high-strength composite binder short fibers, and the ultrafine short fibers are each composed of a polyolefin-based resin, but since the polyolefin-based resin has low affinity with the electrolyte, it is preferable to apply a known hydrophilization treatment, such as sulfonation treatment, fluorine gas treatment, graft polymerization treatment of a vinyl monomer, discharge treatment, surfactant treatment, or hydrophilic resin application treatment, to impart or improve the retention of the electrolyte.

Further, the apparent density of the separator of the present invention is set to 0.33g/cm³Hereinafter, it is preferable to increase the number of voids, and to adjust the thickness with an extremely weak pressure (linear pressure of 20N/m or less) to press down the pile of the fiber without performing the thickness adjustment or even when performing the thickness adjustment. That is, in the conventional separator, since the segmented composite short fibers are segmented by the high-pressure water flow, the unevenness of the separator surface is remarkable, and it is difficult to uniformly retain the electrolyte, and therefore, only a separator having a high apparent density and few voids, which requires thickness adjustment by a high pressure, can be manufactured. That is, it is possible to manufacture a battery capable of retaining a large amount of electrolyte and hardly consuming the electrolyte even when used at high temperatureAn alkaline battery having a long life.

Further, for example, by sufficiently entangling the fibers with each other with a water flow and/or by bonding with high-strength composite binder short fibers, a separator excellent in breaking strength can be produced.

Further, a separator having a high average needle penetration resistance can be produced by, for example, incorporating high-strength composite binder staple fibers and/or improving the uniformity of a nonwoven fabric by blending ultra-fine staple fibers.

Further, a separator having excellent texture can be produced by forming a fiber web using a wet method, by reducing the water pressure of a water stream, and/or by blending ultra-fine short fibers, for example.

Since the separator of the present invention is less likely to cause short circuit due to dendrite and the electrolyte is less likely to be exhausted even when used at high temperature, the electrolyte is less likely to be exhausted and less likely to cause short circuit due to dendrite if the separator of the present invention is used, and thus an alkaline battery having a long life can be manufactured. Therefore, the battery can be suitably used as a power source for a hybrid vehicle and an electric vehicle used at high temperatures. However, an alkaline battery that exhibits superior performance to conventional batteries can be manufactured by the separator of the present invention even when used at ordinary temperatures.

The form of the battery may be, for example, a cylindrical, rectangular or button type, and the type of the battery may be, for example, a primary battery such as an alkaline manganese battery, a mercury battery, a silver oxide battery or an air battery, or a secondary battery such as a nickel-cadmium battery, a silver-zinc battery, a silver-cadmium battery, a nickel-zinc battery, a nickel-hydrogen battery or a lead storage battery, and particularly, a nickel-cadmium battery or a nickel-hydrogen battery.

Examples

Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

(Split type composite short fiber A)

A split type composite short fiber A having a fineness of 1.7dtex and a fiber length of 5mm and having an orange-type cross-sectional shape as shown in FIG. 1 was prepared, which comprises a polypropylene component (capable of forming a polypropylene quasi-ultrafine profiled short fiber (melting point: 160 ℃ C.) having a triangular-like cross-sectional shape and a fiber diameter of 3.8 μm as shown by reference numeral 11 in 8 figures) and a polymethylpentene component (capable of forming a polymethylpentene quasi-ultrafine profiled short fiber (melting point: 235 ℃ C.) having a triangular-like cross-sectional shape and a fiber diameter of 4.0 μm as shown by reference numeral 12 in 8 figures).

(Split type composite short fiber B)

A split type composite short fiber B having a fineness of 1.7dtex and a fiber length of 5mm and having an orange-type cross-sectional shape as shown in FIG. 1 was prepared, which comprises a polypropylene component (capable of forming a polypropylene quasi-ultrafine profiled short fiber (melting point: 160 ℃ C.) having a triangular-like cross-sectional shape and a fiber diameter of 3.8 μm as shown by the reference numeral 11 in 8 figures) and a high-density polyethylene component (capable of forming a high-density polyethylene quasi-ultrafine profiled short fiber (melting point: 130 ℃ C.) having a triangular-like cross-sectional shape and a fiber diameter of 3.7 μm as shown by the reference numeral 12 in 8 figures).

(high-Strength composite binding short fiber A)

A high-strength composite binder staple fiber A (fiber diameter: 10 μm, fiber length: 5mm, Young's modulus: 45cN/dtex, heat shrinkage: 7%) was prepared, which had a core-sheath type cross-section, a core component comprising isotactic polypropylene homopolymer (melting point: 168 ℃ C.), a sheath component comprising high-density polyethylene (melting point: 135 ℃ C.), and a tensile strength of 6.5 cN/dtex.

(composite binder staple fiber B)

Composite binder staple fibers B (fiber diameter: 10 μm, fiber length: 5mm, Young's modulus: 24cN/dtex, heat shrinkage: 10%) were prepared, and the cross section thereof was arranged in a core-sheath type, wherein the core component was polypropylene (melting point: 165 ℃ C.), the sheath component was low-density polyethylene (melting point: 110 ℃ C.), and the tensile strength was 4.0 cN/dtex.

(superfine short fiber)

A sea-island type composite undrawn fiber in which 61 island components made of polypropylene are present among sea components made of polyethylene terephthalate was spun by a composite spinning method, and the sea-island type composite fiber produced by drawing was immersed in an alkaline aqueous solution for 120 minutes to extract and remove the polyethylene terephthalate as the sea component, and then cut to produce polypropylene ultrafine short fibers having substantially the same fiber diameter in the longitudinal direction (fiber diameter: 2 μm, fiber length 3mm, melting point: 168 ℃, cross-sectional shape: circular, and substantially the same among a plurality of polypropylene ultrafine short fibers).

(examples 1 to 3 and comparative examples 1 to 5)

After forming a slurry mixed and dispersed in accordance with the blending method shown in table 1, a fiber web was formed by a wet method (horizontal fourdrinier system). When polypropylene ultrafine short fibers are contained, the polypropylene ultrafine short fibers are dispersed.

Thereafter, the web was dried under conditions of 140 ℃ (when containing high-strength composite binder staple fibers a) or 110 ℃ (when containing composite binder staple fibers B) without applying pressure, and bonded using the high-strength composite binder staple fibers a or the composite binder staple fibers B, thereby producing a bonded staple fiber web.

Thereafter, the web of the binder staple fibers was placed on a web having a wire diameter of 0.15mm, and a water stream having a pressure of 3.5 to 11MPa was discharged from a nozzle plate having a nozzle diameter of 0.13mm and a pitch of 0.6mm 2 times in a manner of alternating the two surfaces, thereby producing a water-entangled fiber web by dividing the divided composite staple fibers A, B and entangling the fibers.

Thereafter, the hydroentangled web was dried without applying pressure at a temperature of 140 ℃ (when containing the high-strength composite binder staple fibers a) or 110 ℃ (when containing the composite binder staple fibers B), and the high-strength composite binder staple fibers a or the composite binder staple fibers B were bonded again to produce a bonded hydroentangled nonwoven fabric.

Thereafter, the bonded hydroentangled nonwoven fabric was treated with a fuming sulfuric acid solution (15% SO) at a temperature of 60 deg.C₃Solution) for 2 minutes, then sufficiently washed with water, dried, and then introduced with sulfonic acid groups on the fiber surface, and the fiber was subjected to thickness adjustment at a linear pressure shown in Table 1 using a calender at room temperature, or without thickness adjustment, to produce a fiber having a basis weight of 55 to 75g/m²The separator of (1). In addition, inIn the case of polypropylene ultra-short fibers, the individual fibers are in a dispersed state.

(evaluation of physical Properties)

By the method, the breaking strength, the mass reduction rate after friction, the average pin penetration resistance, the texture index, the specific surface area, and the pressurized liquid retention rate of each separator were measured. These results are shown in table 1.

The "specific surface area" is an index indicating a path to the other pole, and a larger specific surface area means a longer path to the other pole, and is measured by the following procedure.

(measurement of specific surface area)

Each separator (sample) was treated in vacuum at 70 ℃ for 4 hours, cooled to room temperature, and then evacuated to 1X 10^-3And (5) Torr. Thereafter, about 0.5g of a sample was precisely weighed. Thereafter, a gas adsorption measuring apparatus [ BEL Japan, Inc., BELSORP 28A, manufactured by BEL Japan, Inc. ]]Measured by the BET method. Therein, krypton is used as the adsorption gas.

Further, the pressurized liquid retention rate is an index indicating the performance of retaining the electrolytic solution, and is measured by the following procedure.

(measurement of liquid holding Rate under pressure)

(1) A5 cm square test piece was taken from each separator, and the mass (A) was measured.

(2) Each test piece was immersed in an electrolyte solution (1.3g/mL aqueous potassium hydroxide solution) to fill the gap in the test piece with the electrolyte solution.

(3) The test piece was sandwiched between 3 sheets of filter paper (model: ADVANTEC-TYPE2) on both sides of the test piece, compressed at a pressure of 1.23MPa, and the electrolyte solution was sucked up by the filter paper.

(4) The mass (B) of each test piece having the electrolyte absorbed therein was measured, and the liquid retention ratio (R, unit:%) was calculated by the following formula.

R＝[(B-A)/A]×100

[ Table 1]

As is clear from comparison of examples 1 to 3 with comparative examples 1 and 2, since the mass reduction rate after the rubbing is 5% or less, not only fibers are in a sufficiently entangled state, but also the specific surface area is large, and the path to the other electrode is long and complicated, it is estimated that an alkaline battery in which short circuit due to dendrite is less likely to occur can be manufactured.

Further, as is clear from comparison between example 2 and comparative examples 3 to 5, the apparent density was 0.33g/m³Since the liquid retention under pressure is high, it is presumed that an alkaline battery having a long battery life, in which the electrolyte is hardly consumed even when used at high temperature, can be manufactured.

Further, in the separators of examples 1 to 3, since the mass reduction rate after the rubbing was 5% or less, the fibers were in a sufficiently entangled state, and the breaking strength and the average pin penetration resistance were high, it was estimated that the separators and the alkaline batteries could be stably manufactured.

Industrial applicability

The separator for an alkaline battery of the present invention can be suitably used for an alkaline secondary battery such as a nickel-metal hydride secondary battery. In particular, since it is a highly reliable separator for alkaline batteries, it can be suitably used as a separator for alkaline batteries for hybrid vehicles and electric vehicles.

Claims

1. A separator for an alkaline battery, comprising a nonwoven fabric on which a water flow has been applied, wherein the separator for an alkaline battery is formed by adjusting the pressure of the water flow so that the nonwoven fabric on which the water flow has been applied does not have a thickness or is adjusted so that the nonwoven fabric has a linear pressure of 20N/m or less, and wherein the nonwoven fabric has a weight per unit area of 40g/m²Above 60g/m²A thickness of 190 to 250 μm and an apparent density of 0.32g/cm³And a mass reduction rate after rubbing of 5% or less, the nonwoven fabric comprising:

a quasi-ultrafine profiled short fiber composed of a methylpentene resin and a quasi-ultrafine profiled short fiber composed of a polypropylene resin, which are produced by being split by applying a water flow to a split type composite short fiber composed of a combination of a methylpentene resin and a polypropylene resin, and which have a non-circular cross-sectional shape, a fiber diameter of 3 to 5 μm converted to a circular shape, and a fiber length of 1 to 20 mm;

high-strength composite bonding short fibers with tensile strength of more than 5cN/dtex and fiber length of 1-20 mm; and

and (3) superfine short fibers with the fiber diameter less than 3 mu m and the fiber length of 1-20 mm.

2. A method for producing a separator for alkaline batteries, characterized in that a nonwoven fabric is produced by applying a water flow to a web containing split composite short fibers comprising a methylpentene-based resin and a polypropylene-based resin, high-strength composite binder short fibers and ultrafine short fibers, and the split composite short fibers are split into quasi-ultrafine irregularly shaped short fibers comprising a methylpentene-based resin and quasi-ultrafine irregularly shaped short fibers comprising a polypropylene-based resin, and the non-woven fabric is used as a separator for alkaline batteries, wherein the split composite short fibers are split by a mechanical action to produce quasi-ultrafine irregularly shaped short fibers comprising a methylpentene-based resin and having a non-circular cross-sectional shape, a fiber diameter converted to a circular shape of 3 to 5 [ mu ] m, and a fiber length of 1 to 20mm, and the high-strength composite binder short fibers have a tensile strength of 5cN/dtex or more, and the quasi-ultrafine irregular short fibers comprising a polypropylene-based resin, And a fiber length of 1 to 20mm, the superfine short fibers have a fiber diameter of less than 3 [ mu ] m and a fiber length of 1 to 20mm, the nonwoven fabric contains quasi-superfine profiled short fibers composed of a methylpentene resin and quasi-superfine profiled short fibers composed of a polypropylene resin, and has a basis weight of 40g/m²Above 60g/m²A thickness of 190 to 250 μm and an apparent density of 0.32g/cm³The mass reduction rate after friction is 5% or less,

wherein the pressure of the water flow is such that the nonwoven fabric on which the water flow has acted is not subjected to thickness adjustment or is subjected to thickness adjustment at a pressure of not more than 20N/m, thereby constituting a separator for an alkaline battery.