JP7195763B2 - Alkaline battery separator - Google Patents

Description

The present invention relates to a separator for alkaline batteries.

2. Description of the Related Art Conventionally, a separator has been used to separate the positive electrode and the negative electrode of a battery to prevent a short circuit, and to retain an electrolytic solution to facilitate an electromotive reaction.

In addition, the electrode expands and contracts due to charging and discharging of the battery, and the expansion and contraction of the electrode puts pressure on the separator, making it impossible for the separator to retain a sufficient amount of electrolyte, making the battery unusable. Therefore, there is a demand for a separator that is excellent in electrolyte retention.

For example, Japanese Patent Laid-Open No. 2002-124244 (Patent Document 1) describes separators having excellent electrolyte retention properties, such as "calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), manganese oxide (MnO , Mn ₂ O ₃ , Mn ₃ O ₄ , MnO ₂ , Mn ₂ O ₇ ), magnesium oxide (MnO), tin oxide (SnO, SnO ₂ ), nickel oxide (NiO), cobalt oxide (CoO, Co ₃ O ₄ ), yttrium oxide (Y ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ , YbO), zinc oxide (ZnO), vanadium oxide and at least one inorganic oxide selected from the group consisting of silicon dioxide (SiO ₂ ) A separator for an alkaline secondary battery in which a substance is present." is disclosed. Further, Patent Document 1 discloses that the content of the inorganic oxide is preferably 0.1 to 50% by weight.

The separator of Patent Document 1 is indeed a separator excellent in electrolyte retention, but in recent years, as electronic devices have become smaller and lighter, there has been a demand for thinner separators. There is a problem that the amount of electrolyte retained in the battery is reduced, shortening the life of the battery.

JP 2002-124244 A

SUMMARY OF THE INVENTION It is an object of the present invention to provide an alkaline battery separator that is thin but has excellent electrolyte retention.

The invention according to claim 1 of the present invention is "a separator for an alkaline battery (excluding one containing polyvinyl alcohol) comprising a porous substrate, inorganic oxide particles and a binder and having a thickness of 70 μm or less, ,
The content of the inorganic oxide particles with respect to the alkaline battery separator is greater than 50% by weight,
An alkaline battery separator, wherein the alkaline battery separator has a porosity of 60% or more. ”.

The invention according to claim 2 of the present invention is "the alkaline battery separator according to claim 1, wherein the porous base material is composed of a polyolefin-based resin or a nylon-based resin." .

According to claim 3 of the present invention, there is provided "the alkaline battery separator according to claim 1 or 2, wherein the binder is composed of an acrylic resin."

The invention according to claim 4 of the present invention is "the alkaline battery separator according to any one of claims 1 to 3, wherein the inorganic oxide is yttrium oxide."

The invention according to claim 5 of the present invention is "the alkaline battery separator according to any one of claims 1 to 4, wherein the specific surface area of the alkaline battery separator is 4 m ² /g or more. separator."

In the invention according to claim 1 of the present invention, although the thickness is 70 μm or less, the content of inorganic oxide particles in the separator for alkaline batteries is more than 50% by weight, so that the specific surface area of the separator is large and the electrolyte can be retained. Excellent in nature. In addition, when the porosity of the separator for alkaline batteries is 60% or more, the electrolyte solution holding property of the separator is excellent, and an increase in internal resistance and internal pressure of the battery can be suppressed.

In the invention according to claim 2 of the present invention, since the porous substrate is composed of a polyolefin resin or nylon resin having alkali resistance, it has excellent electrolyte resistance and maintains the electrolyte retention property of the separator. can be done.

In the invention according to claim 3 of the present invention, since the binder is made of an acrylic resin, it is excellent in electrolytic solution resistance and can stably fix the inorganic oxide particles for a long period of time. can keep.

In the invention according to claim 4 of the present invention, the inorganic oxide is yttrium oxide, so that the electrolyte solution resistance is excellent, and the electrolyte solution holding property of the separator can be maintained.

In the invention according to claim 5 of the present invention, since the alkaline battery separator has a large specific surface area of 4 m ² /g or more, it is excellent in electrolyte retention.

In the alkaline battery separator of the present invention, the porous substrate mainly plays a role of forming the skeleton of the alkaline battery separator.

The type of porous substrate can be selected as appropriate. can be used. Among these, fabrics are preferable because they are excellent in strength, and among fabrics, nonwoven fabrics, which easily realize a high porosity, are more preferable.

The material constituting the porous substrate is, for example, a polyolefin resin (e.g., polyethylene, polypropylene, polymethylpentene, polyolefin resin having a structure in which part of the hydrocarbon is substituted with a cyano group or a halogen such as fluorine or chlorine). , styrene resins, polyvinyl alcohol resins, polyether resins (e.g., polyether ether ketone, polyacetal, modified polyphenylene ether, aromatic polyether ketone, etc.), polyester resins (e.g., polyethylene terephthalate, polytrimethylene terephthalate, Polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycarbonate, polyarylate, wholly aromatic polyester resin, etc.), polyimide resin, polyamideimide resin, polyamide resin (e.g., aromatic polyamide resin, aromatic polyether amide resin, etc.), a type of polyamide resin, nylon resin (e.g., nylon 6, nylon 66, etc.), a nitrile group-containing resin (e.g., polyacrylonitrile, etc.), urethane resin, epoxy resin, polysulfone resin ( polysulfone, polyethersulfone, etc.), fluorine-based resins (e.g., polytetrafluoroethylene, polyvinylidene fluoride, etc.), cellulose-based resins, polybenzimidazole resins, acrylic resins (e.g., acrylic acid esters, methacrylic acid esters, etc.) polyacrylonitrile-based resins copolymerized with, modacrylic resins copolymerized with acrylonitrile and vinyl chloride or vinylidene chloride, etc.). Among these, the porous substrate is preferably composed of polyolefin-based resin or nylon-based resin because of its excellent alkali resistance.

These organic polymers may be straight-chain polymers or branched polymers, and the organic polymers may be block copolymers or random copolymers. It can be of any gender. Furthermore, a mixture of multi-component organic polymers may be used.

When the porous substrate is a fabric, the constituent fibers of the fabric are, for example, dry spinning, wet spinning, direct spinning [for example, meltblowing, spunbonding, electrostatic spinning, spinning stock solution and gas flow parallel (for example, the method disclosed in Japanese Patent Laid-Open No. 2009-287138)], a method of extracting fibers with a small fiber diameter by removing one or more resin components from the composite fiber, a method of extracting a fiber It can be obtained by a known method such as a method of obtaining split fibers by beating.

The fibers constituting the fabric may be composed of one type of organic polymer, or may be composed of a plurality of types of organic polymers. Fibers composed of a plurality of types of organic polymers may be generally referred to as composite fibers, for example, core-sheath type, sea-island type, side-by-side type, orange type, bimetal type, and the like.

The fabric may contain bonding fibers as constituent fibers. By including adhesive fibers, the strength of the fabric can be improved, which is preferable. The type of bonding fiber is appropriately selected, and for example, sheath-core type bonding fiber, side-by-side type bonding fiber, or all-melting type bonding fiber can be adopted.

In addition, the fabric may contain irregular cross-section fibers as constituent fibers in addition to fibers having substantially circular cross-sections and fibers having elliptical cross-sections. The modified cross-section fiber may be a polygonal shape such as a triangular shape, an alphabetical shape such as a Y shape, a symbolic shape such as an irregular shape, a multi-leaf shape, an asterisk shape, or a shape in which a plurality of these shapes are combined. A fiber having a fiber cross section such as can be exemplified.

When the fabric is woven or knitted, it can be prepared by weaving or knitting the fibers prepared as described above.

When the fabric is a nonwoven fabric, the nonwoven fabric may be, for example, a dry nonwoven fabric in which fibers are entangled by being supplied to a carding device or an air laying device to form a nonwoven fabric, or a nonwoven fabric in which the fibers are dispersed in a liquid and made into a sheet. Wet nonwoven fabric, direct spinning method (e.g., melt blow method, spunbond method, electrostatic spinning method, method of spinning by discharging spinning stock solution and gas flow in parallel (e.g., method disclosed in JP 2009-287138) etc.) are used to spin the fibers, and a non-woven fabric and the like obtained by collecting the fibers are exemplified.

A method for entangling and/or integrating fibers constituting a fabric can be selected as appropriate. When fibers containing resin are included, a method of melting the thermoplastic resin by heat treatment to integrate the fibers can be used. As the heat treatment method, for example, a method of applying heat and pressure using a calender roll, a method of applying heat using a hot air dryer, a method of applying infrared rays under no pressure, and the like can be used.
Alternatively, nonwoven fabrics may be prepared by collecting spun fibers using direct spinning methods.

As the average fiber diameter of the fibers constituting the fabric is smaller, the strength of the porous substrate can be improved to prevent breakage of the alkaline battery separator, and the size of the pores can be made uniform and small to prevent internal short circuits. tend to be preventable. Therefore, the average fiber diameter of the fibers constituting the fabric is, for example, preferably 15 μm or less, more preferably 10 μm or less, and most preferably 8 μm or less. Although the lower limit of the average fiber diameter of the fibers is not particularly limited, it is practically 0.01 μm or more.
The "average fiber diameter" referred to in the present invention is the arithmetic mean value of the fiber diameters of 100 fibers randomly selected by analyzing cross-sectional electron micrographs of alkaline battery separators containing fabrics and fibers. , and the fiber diameter is the diameter of a circle having the same area as the cross-sectional area of the fiber.

Also, the fiber length is appropriately selected, but it can be 0.5 to 150 mm, and depending on the manufacturing method of the fiber, it can be a continuous fiber. It should be noted that two or more types of fibers having different average fiber diameters and/or fiber lengths may be included.

When the porous substrate is a porous film or porous foam having air permeability or liquid permeability, the preparation method can be appropriately selected. It can be prepared by a known method.

In addition, for example, the porous substrate may be hydrophilized for the purpose of facilitating application of the coating liquid described below to the porous substrate. A method for hydrophilizing the porous substrate is appropriately selected, and examples thereof include plasma treatment, sulfonation treatment, fluorine treatment, corona electrification treatment, and the like.

Various constitutions of the porous substrate, such as basis weight and thickness, are appropriately adjusted so as to obtain an alkaline battery separator that is excellent in various characteristics such as discharge characteristics and less likely to cause an internal short circuit. do.

The porosity of the porous substrate of the present invention is appropriately adjusted so that the porosity of the alkaline battery separator, which is composed of inorganic oxide particles and a binder in addition to the porous substrate, is 60 to 90%. .
The "porosity (P)" (unit: %) referred to in the present invention is a value obtained from the following formula.

P=100−(Fr ₁ +Fr ₂ + . . . +Fr _n )
Here, Fr _n indicates the filling rate (unit: %) of the n component constituting the separator, and is a value obtained from the following formula.

_Frn = {(M x Prn)/(T x _SGn ) _} x 100
Here, M is the basis weight of the separator (unit: g/cm ² ), T is the thickness of the separator (unit: cm), Pr _n is the mass ratio of component n in the separator, SG _n is the specific gravity of component n (unit: : g/cm ³ ) respectively.

In the alkaline battery separator of the present invention, the inorganic oxide particles play a role of mainly contributing to increasing the specific surface area of the alkaline battery separator.

Types of inorganic oxide particles include, for example, silicon oxide (silica), aluminum oxide (alumina), alumina-silica composite oxide, calcium oxide, titanium oxide, tin oxide, yttrium oxide, zirconium oxide, barium titanate, tin- Indium oxide etc. are mentioned. Among these, it is preferable to use yttrium oxide because it has excellent electrolyte resistance and electrolyte retention when used as a separator for alkaline batteries.

The shape of the inorganic oxide particles to be used can be appropriately selected from, for example, spherical (substantially spherical or true spherical), fibrous, needle-like, flat plate-like, polygonal cube-like, feather-like, and the like.

The average particle size of the inorganic oxide particles that can be used in the present invention is adjusted as appropriate, and the uniform presence of the inorganic oxide particles in the pores of the porous substrate results in a uniform distribution of the electrolytic solution in the separator, thereby holding the electrolytic solution. The average particle size of the inorganic oxide particles is preferably 10 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less so as to have excellent properties.

The average particle size of the inorganic oxide particles is determined by subjecting the inorganic oxide particles to FPRA1000 (measurement range 3 nm to 5000 nm) manufactured by Otsuka Electronics Co., Ltd., and performing continuous measurement for 3 minutes by a dynamic light scattering method. Determined from particle size measurement data obtained from intensity. That is, the particle size measurement is performed five times, and the particle size measurement data obtained by the measurement is arranged in order of the narrowest particle size distribution width, and the inorganic oxide in the data showing the third narrowest value of the particle size distribution width The particle diameter D ₅₀ (hereinafter abbreviated as D ₅₀ ) at the cumulative 50% point of the particles is defined as the average particle diameter of the inorganic oxide particles. The temperature of the dispersion liquid used for measurement is adjusted to 25° C., and water at 25° C. is used as a blank for scattering intensity.

In addition, the particle size distribution of the inorganic oxide particles is appropriately adjusted, but if there are many inorganic oxide particles with a large particle size, the inorganic oxide particles may drop off and pinholes may easily form. When a large number of inorganic oxide particles with a small particle size are present, there is a risk of clogging the pores of the porous substrate.

Therefore, the particle size distribution of the inorganic oxide particles is preferably in the range of (D ₅₀ /2) to (D ₅₀ ×2). The particle size distribution of the inorganic oxide particles is measured by the dynamic light scattering method described above, and obtained from the particle size measurement data obtained from the measured intensity.

In the alkaline battery separator of the present invention, the binder mainly serves to adhere the inorganic oxide particles to the porous substrate. It is preferable that the inorganic oxide particles are adhered and fixed to the porous substrate only by the binder so that the inorganic oxide particles are less likely to fall off from the alkaline battery separator.

Types of binders that can be used include, for example, polyolefin resins, acrylic resins (e.g., ethyl acrylate, methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, methyl methacrylate, butyl methacrylate, methacrylic acid 2-ethylhexyl, etc.), ethylene-acrylate copolymers such as ethylene-ethyl acrylate copolymers, various rubbers and their derivatives [e.g., styrene-butadiene rubber (SBR), fluororubber, urethane rubber, ethylene-propylene-diene rubber (EPDM), etc.], polyethylene glycol (PEG), cellulose derivatives [e.g., carboxymethyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose, etc.], polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyurethane-based resins, epoxy-based Resin, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, and the like can be used. Among these, it is preferable to use an acrylic resin that is excellent in electrolyte resistance and can stably fix the inorganic oxide particles for a long period of time, and thus can maintain the electrolyte retaining property of the alkaline battery separator. In addition, these may be used individually by 1 type, or 2 or more types may be used together.

In the alkaline battery separator of the present invention, inorganic oxide particles are adhered to a porous substrate by a binder. The mode of existence of the inorganic oxide particles in the alkaline battery separator is a mode of existing on the surface of the porous substrate, a mode of existing in the pores of the porous substrate, and a mode of existing both on the surface and in the pores of the porous substrate. However, when the inorganic oxide particles are present at least in the pores of the porous substrate, the inorganic oxide particles tend to contribute to an increase in the specific surface area of the alkaline battery separator, and the alkaline battery separator retains the electrolyte. It is preferable that the inorganic oxide particles are present at least in the voids of the porous substrate, since the properties are excellent.

A method for bonding and fixing the inorganic oxide particles to the porous substrate with a binder can be selected as appropriate.
1. A coating solution (hereinafter sometimes referred to as coating solution) is prepared by mixing a binder and inorganic oxide particles in a solvent or dispersion medium, and the porous substrate is immersed in the coating solution.
2. spraying the coating liquid on the porous substrate,
3. Using a coating method such as a kiss coater method using a gravure roll, apply a coating liquid to one main surface or both main surfaces of the porous substrate;
After performing the above steps, the porous substrate containing the coating liquid is dried to remove the solvent and dispersion medium in the coating liquid. In addition, in this invention, a main surface means the surface of a part with the largest area.

A method for drying the porous substrate containing the coating liquid may be selected as appropriate. Alternatively, a method of removing the solvent or dispersion medium by hot air or blowing air can be used. In addition, the porous substrate containing the coating liquid, for example, a method of leaving at room temperature (25 ° C.), a method of exposing under reduced pressure conditions, a method of exposing to an atmosphere at a temperature above which the solvent or dispersion medium can volatilize, etc. , a known method can be used.

In addition, when the binder is present in the form of particles or the like in the coating liquid, the solid binder is melted or softened during the above-described drying, so that the inorganic oxide particles are attached to the porous substrate by the binder. is preferably fixed by adhesive. At this time, the shape of the binder particles present in the coating liquid is appropriately selected, for example, spherical (substantially spherical or true spherical), fibrous, needle-like, flat plate-like, polygonal cube-like, feather-like, etc. can be selected.

The type of solvent or dispersion medium is appropriately selected, and for example, water, alcohols, ethers and the like can be used singly or in combination.

In addition, in order to prevent aggregation of binders and inorganic oxide particles and improve dispersibility in the coating liquid, surfactants (e.g., cationic surfactants, anionic surfactants, nonionic surfactants, etc.) etc.) may be added, and the amount to be added is appropriately adjusted.

The alkaline battery separator of the present invention is characterized in that the content of inorganic oxide particles in the alkaline battery separator is greater than 50% by weight. The higher the content of the inorganic oxide particles, the greater the specific surface area of the separator and the better the retention of the electrolyte solution, and the more internal short circuits can be prevented in alkaline batteries. If the ratio is too high, the pores of the porous substrate may be clogged with the inorganic oxide particles, and the internal resistance and internal pressure of the battery may increase. % is more preferred.

In addition, the content of the binder relative to the inorganic oxide particles contained in the alkaline battery separator is adjusted as appropriate. The voids may be closed by the binder, increasing the internal resistance and internal pressure of the battery. On the other hand, if the content of the binder with respect to the inorganic oxide particles contained in the alkaline battery separator is too low, the inorganic oxide particles contained in the alkaline battery separator may fall off, and the portions where the inorganic oxide particles fall off may be large. There is a risk of pinholes and internal short circuits in the battery.

Therefore, the content of the binder with respect to the inorganic oxide particles contained in the alkaline battery separator is preferably 0.05 to 10% by weight, more preferably 1 to 5% by weight, and 2 to 4% by weight. is more preferable.

The alkaline battery separator of the present invention is characterized by having a porosity of 60% or more. The higher the porosity of the alkaline battery separator, the more electrolyte it can hold. If is too high, internal short circuit may occur in the battery.

The specific surface area of the alkaline battery separator is preferably 4 m ² /g or more, more preferably 5 m ² /g or more, and more preferably 6 m ² /g or more, because the larger the specific surface area, the better the electrolyte retention. is more preferred.

The "specific surface area" in the present invention means that the separator (sample) is treated in vacuum at a temperature of 70° C. for 4 hours, cooled to room temperature and evacuated to 1×10 ⁻³ Torr. It is a value measured by the BET method using a gas adsorption measurement device [BELSORP 28A manufactured by Bell Japan Co., Ltd.] after accurately weighing 5 g. Krypton is used as the adsorption gas.

The alkaline battery separator of the present invention is characterized by having a thickness of 70 μm or less. A thin alkaline battery separator tends to reduce the internal resistance of the battery, but if the thickness is too thin, the internal short-circuit resistance tends to be poor. Therefore, the thickness of the alkaline battery separator is preferably 10 to 70 μm, more preferably 20 to 60 μm, even more preferably 30 to 50 μm.

In addition, the "thickness" as used in the present invention is a measurement method of JIS C 2111 5.1 (1) using an outer micrometer (0 to 25 mm) specified in JIS B 7502: 1994, randomly The average value of 10 points selected and measured.

The basis weight of the alkaline battery separator is appropriately adjusted, and may be 2 to 40 g/m ² , 5 to 30 g/m ² , or 10 to 20 g/m ² .

The term "basis weight" as used in the present invention refers to the mass per ^square meter on the main surface.

EXAMPLES The present invention will be specifically described below with reference to Examples, but these are not intended to limit the scope of the present invention.

(Example 1)
1. Preparation method of non-woven fabric A core-sheath type composite fiber (volume ratio of core component to sheath component = 50:50, fineness: 0.4 dtex, fiber length: 6 mm) having a core component of homopolypropylene and a sheath component of high-density polyethylene was prepared. .

Furthermore, a sea-island composite undrawn fiber having 61 island components made of polypropylene in a sea component made of polyethylene terephthalate was spun by a composite spinning method and drawn to produce a drawn sea-island composite fiber in an alkaline aqueous solution. After immersing it in water for 120 minutes to extract and remove the polyethylene terephthalate, which is a sea component, it is cut into polypropylene ultrafine fibers with approximately the same fiber diameter in the length direction (fiber diameter: 1.5 μm, fiber length: 2 mm, melting point: 168 ° C. , cross-sectional shape: circular). The microfibers were not fibrillated, drawn, and each fiber had the same fiber diameter.

Next, 50 mass % of the core-sheath type composite fibers and 50 mass % of the ultrafine fibers were mixed to prepare a fiber web by a wet papermaking method.

After that, the fiber web was treated with hot air at a temperature of 140°C for 10 seconds, and then subjected to a calender roll at 40° ^C . thickness: 30 μm) was prepared.

Further, the prepared nonwoven fabric was subjected to plasma treatment to prepare a hydrophilized nonwoven fabric A (basis weight: 5.0 g/m ² , thickness: 30 µm).
The nonwoven fabric A was composed only of fibers.

2. Preparation method of coating liquid As coating components, 97 parts by mass of yttrium oxide particles (Y ₂ O ₃ , average particle diameter (D50): 600 nm) and 3 parts by mass of acrylic resin were mixed with water to obtain a solid content concentration of 25 masses. A coating liquid was prepared.
The yttrium oxide particles were uniformly dispersed in the coating liquid without agglomeration.

3. Application method of coating liquid The coating liquid was applied to the entire one main surface of the hydrophilized nonwoven fabric A using a kiss coater method using a gravure roll so that the weight of yttrium oxide was 11 g/m ² . .

4. Drying Method The hydrophilized nonwoven fabric A coated with the coating liquid is subjected to a dryer equipped with a far-infrared heater to remove water from the coating liquid applied to the hydrophilized nonwoven fabric A. , an alkaline battery separator (basis weight: 16.0 g/m ² , thickness: 33 μm) was prepared. In the alkaline battery separator, yttrium oxide particles were present in the pores of the alkaline battery separator.

(Example 2)
First, a hydrophilized nonwoven fabric B (basis weight: 7.3 g/m ² , thickness: 30 µm) was prepared in the same manner as in "1. Method for preparing nonwoven fabric" in Example 1. After that, 3. Example 1, except that the entire one main surface of the hydrophilized nonwoven fabric B was coated with the coating liquid so that the weight of the yttrium oxide was 8.2 g/m ² in the method of applying the coating liquid. An alkaline battery separator (basis weight: 15.5 g/m ² , thickness: 33 μm) was prepared in the same manner. In the alkaline battery separator, yttrium oxide particles were present in the pores of the alkaline battery separator.

(Comparative example 1)
First, nonwoven fabric B subjected to hydrophilic treatment in Example 2 was prepared. After that, 3. Example 1, except that the entire one main surface of the hydrophilized nonwoven fabric B was coated with the coating liquid so that the weight of the yttrium oxide was 5.0 g/m ² in the method of applying the coating liquid. A separator for an alkaline battery (basis weight: 12.3 g/m ² , thickness: 30 μm) was similarly prepared. In the alkaline battery separator, the yttrium oxide particles were present in the pores of the alkaline battery separator.

(Comparative example 2)
First, a hydrophilized nonwoven fabric C (basis weight: 12 g/m ² , thickness: 30 µm) was prepared in the same manner as in "1. Method for preparing nonwoven fabric" in Example 1. After that, 3. The method of applying the coating liquid was the same as in Example 1, except that the coating liquid was applied to the entire one main surface of the hydrophilized nonwoven fabric C so that the weight of yttrium oxide was 0.8 g/m ² . An alkaline battery separator (basis weight: 12.8 g/m ² , thickness: 30 μm) was prepared in the same manner. In the alkaline battery separator, yttrium oxide particles were present in the pores of the alkaline battery separator.

Table 1 summarizes the physical properties of the alkaline battery separators of Examples and Comparative Examples manufactured as described above. The yttrium oxide content (mass%) in the alkaline battery separator and the porosity (%) of the alkaline battery separator were rounded off to the nearest whole number.

Next, the specific surface areas of the alkaline battery separators of Examples and Comparative Examples were measured by the method described above, and the pressurized liquid retention rate and electrical resistance were determined as follows (measurement of pressurized liquid retention rate) and (measurement of electrical resistance). It was measured and evaluated by

(Measurement of pressure retention rate)
(1) A 5 cm square test piece was taken from each alkaline battery separator, and the weight (A) of each was measured.
(2) Each test piece was immersed in an electrolytic solution (1.3 g/mL potassium hydroxide aqueous solution) to fill the voids in the test piece with the electrolytic solution.
(3) Both sides of the test piece were sandwiched between three pieces of filter paper (model number: ADVANTEC-TYPE2), compressed at a pressure of 1.23 MPa, and the filter papers absorbed the electrolytic solution.
(4) The weight (B) of each test piece that absorbed the electrolytic solution was measured, and the liquid retention rate (R, unit: %) was calculated by the following formula.
R = [(B - A) / A] x 100

(Measurement of electrical resistance)
(1) A 5 cm square test piece was taken from each alkaline battery separator, and the weight of each piece was measured.
(2) After absorbing 50% by weight of a 1.3 g/mL potassium hydroxide aqueous solution with respect to the weight of each test piece, the test piece was sandwiched between 35 mm square nickel plates, and the electrical resistance was measured under a load of 5 kgf.
(3) Expressed as a ratio with the resistance value of Comparative Example 2 as a reference (100).

The evaluation results of the alkaline battery separators of Examples and Comparative Examples are shown in Table 2 below.

From the comparison between Examples and Comparative Examples, it was found that the higher the content of yttrium oxide particles in the alkaline battery separator, the larger the specific surface area of the alkaline battery separator.

In addition, when the content of yttrium oxide particles in the alkaline battery separator is greater than 50% by weight and the porosity of the separator is 60% or more, the pressurized liquid retention rate of the alkaline battery separator increases. It was found that the electrolytic solution retention was excellent and the electrical resistance was lowered. This is because the higher content of yttrium oxide particles makes it easier for the electrolyte to be held uniformly in the alkaline battery separator, and the high porosity allows the alkaline battery separator to hold more electrolyte. This is thought to be due to the fact that

The alkaline battery separator of the present invention can be suitably used as a separator for alkaline secondary batteries such as nickel-hydrogen secondary batteries.

Claims (4)

An alkaline battery separator (excluding polyvinyl alcohol) comprising a porous substrate, yttrium oxide particles , and a binder and having a thickness of 70 μm or less,
The content of the yttrium oxide particles in the alkaline battery separator is greater than 50% by weight,
An alkaline battery separator, wherein the alkaline battery separator has a porosity of 60% or more. 2. The alkaline battery separator according to claim 1, wherein said porous substrate is composed of a polyolefin resin or a nylon resin. 3. The alkaline battery separator according to claim 1, wherein said binder is made of an acrylic resin. 4. The alkaline battery separator according to claim 1, wherein the alkaline battery separator has a specific surface area of 4 m ² /g or more.