Separator for alkaline battery

Abstract

To provide an alkaline battery separator superior in the property of retaining an electrolyte solution.SOLUTION: The inventors of the present invention found that an alkaline battery separator comprising a porous base material and a zirconium oxide particle is superior in the property of retaining an electrolyte solution if at least one of the following requirements is satisfied: (1)a maximum-intensity peak arising in measurement on the alkaline battery separator by X-ray diffraction has a half value width of 0.40° or larger; (2)the zirconium oxide particle included in the alkaline battery separator has a peak in a range of 3200-3600 cm-1 in FT-IR measurement; and (3)the water content of the zirconium oxide particle included in the alkaline battery separator is 2.0% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a separator for an alkaline battery containing zirconium oxide particles.

Background Art

[0002] Conventionally, a separator has been used to separate the positive and negative electrodes of a battery to prevent short - circuiting and to hold an electrolytic solution so that an electromotive reaction can be smoothly carried out. Also, when the battery is charged and discharged, the electrodes expand and contract, and the expansion and contraction of the electrodes apply pressure to the separator. If the separator cannot hold a sufficient amount of electrolytic solution, the battery becomes unusable. Therefore, a separator with excellent electrolytic solution retention is required for extending the battery life.

[0003] As such a separator with excellent electrolytic solution retention, for example, Japanese Patent Application Laid - Open No. 11 - 315472 (Patent Document 1) discloses a non - woven fabric having a porous layer composed of fine particles of inorganic oxides such as titanium oxide and zirconium oxide on the surface of the fibers constituting the non - woven fabric, and it is disclosed that this non - woven fabric is preferably used as a separator for an alkaline secondary battery.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, although the separator for an alkaline battery described in Patent Document 1 was indeed a separator with excellent electrolytic solution retention, it was not sufficient.

[0006] The present invention has been made under such circumstances, and an object thereof is to provide a separator for an alkaline battery with even better electrolytic solution retention. [Means for Solving the Problems]

[0007] The invention according to claim 1 of the present invention is "a separator for an alkaline battery including a porous substrate and zirconium oxide particles, wherein when the separator for an alkaline battery is measured by X-ray diffraction, the half-value width of the peak with the highest intensity is 0.40° or more, a separator for an alkaline battery."

[0008] The invention according to claim 2 of the present invention is "a separator for an alkaline battery including a porous substrate and zirconium oxide particles, wherein when the zirconium oxide particles contained in the separator for an alkaline battery are measured by FT-IR, a peak is present in the range of 3200 to 3600 cm -1 , a separator for an alkaline battery."

[0009] The invention according to claim 3 of the present invention is "a separator for an alkaline battery including a porous substrate and zirconium oxide particles, wherein the water content of the zirconium oxide particles contained in the separator for an alkaline battery is 2.0% or more, a separator for an alkaline battery."

[0010] The invention according to claim 4 of the present invention is "the separator for an alkaline battery according to any one of claims 1 to 3, wherein the porous substrate and the zirconium oxide particles are bonded with a binder containing an acrylic resin."

[0011] The invention according to claim 5 of the present invention is "the separator for an alkaline battery according to any one of claims 1 to 4, wherein the content of zirconium oxide in the zirconium oxide particles is 95 mass% or more."

[0012] The invention according to claim 6 of the present invention is "the separator for an alkaline battery according to any one of claims 1 to 5, wherein the zirconium oxide particles contain zirconium oxide having a cubic or tetragonal crystal structure." [Advantages of the Invention]

[0013] The inventors of the present invention have found that in a separator for an alkaline battery including a porous substrate and zirconium oxide particles, (1) when measuring the separator for an alkaline battery by X-ray diffraction, the full width at half maximum of the peak with the highest intensity is 0.40° or more, (2) when measuring the zirconium oxide particles contained in the separator for an alkaline battery by FT-IR, there is a peak in the range of 3200 to 3600 cm -1 ; (3) the water content of the zirconium oxide particles contained in the separator for an alkaline battery is 2.0% or more, and if it meets at least one of the above, it is a separator for an alkaline battery having excellent electrolyte retention.

[0014] As a reason why a separator for an alkaline battery with excellent electrolyte retention can be realized by (1), since the full width at half maximum of the X-ray diffraction peak of zirconium oxide constituting the separator for an alkaline battery is large, the crystallite size of zirconium oxide is small. Because the crystallite size of zirconium oxide is small, there are many crystal ends of zirconium oxide, and thus there are many hydroxy groups on the crystal surface of zirconium oxide. It is considered that a large amount of water of hydration can be contained by the hydroxy groups on the crystal surface of zirconium oxide.

[0015] As a reason why a separator for an alkaline battery with excellent electrolyte retention can be realized by (2), in the zirconium oxide particles constituting the separator for an alkaline battery, the peak appearing in the range of 3200 to 3600 cm -1 is a peak derived from the hydroxy groups at the crystal ends of zirconium oxide, and it is considered that a large amount of water of hydration can be contained by the hydroxy groups on the crystal surface of zirconium oxide.

[0016] The reason why a separator for an alkaline battery excellent in electrolyte retention can be realized by (3) is that the high water content of 2.0% or more in the zirconium oxide particles constituting the separator for an alkaline battery means that a large number of hydroxy groups are present on the crystal surface of zirconium oxide, and it is considered that this is because a large amount of water of hydration is contained due to the presence of a large number of hydroxy groups on the crystal surface of zirconium oxide.

[0017] Since the invention according to claim 4 of the present invention is composed of an acrylic resin in which the binder is excellent in alkali resistance, the acrylic resin is excellent in electrolyte resistance and can stably fix zirconium oxide particles for a long time, so that the electrolyte retention of the separator for an alkaline battery can be maintained.

[0018] Since the invention according to claim 5 of the present invention has a zirconium oxide content of 95 mass% or more in the zirconium oxide particles, the purity of zirconium oxide in the zirconium oxide particles is high, the electrochemical stability and chemical stability are excellent, and the electrolyte retention of the separator for an alkaline battery is also more excellent.

[0019] Since the invention according to claim 6 of the present invention contains zirconium oxide having a cubic or tetragonal crystal structure in the zirconium oxide particles, the electrolyte retention of the separator for an alkaline battery is more excellent. The reason for this is considered to be that when zirconium oxide has a cubic or tetragonal crystal structure, it can contain more water of hydration.

Mode for Carrying Out the Invention

[0020] The separator for an alkaline battery of the present invention (hereinafter sometimes referred to as a separator) contains zirconium oxide particles. The zirconium oxide particles mainly play a role in increasing the specific surface area of the separator, the electrolyte retention property due to the water of hydration contained in zirconium oxide, and the electrolyte resistance property. The zirconium oxide particles of the present invention refer to particles whose main component is zirconium oxide. Since it is considered that the higher the content rate of zirconium oxide in the zirconium oxide particles, the better the electrolyte retention property of the separator, 95 mass% or more is preferable, 98 mass% or more is more preferable, and 99 mass% or more is still more preferable.

[0021] The separator of the present invention (1) When the separator is measured by X-ray diffraction measurement, the full width at half maximum of the peak with the highest intensity that appears is 0.40° or more, (2) When the zirconium oxide particles contained in the separator are measured by FT-IR, it has a peak in the range of 3200 to 3600 cm -1 ; (3) The water content rate of the zirconium oxide particles contained in the separator is 2.0% or more, and at least one of the above is satisfied, whereby the electrolyte retention property of the separator is excellent.

[0022] First, the reason why a separator with excellent electrolyte retention can be realized by meeting the requirement of (1) is as follows. When the separator is measured by X-ray diffraction, the highest peak that appears is a peak derived from the crystal of zirconium oxide contained in the zirconium oxide particles constituting the separator. According to Scherrer's formula, when the half-value width of the X-ray diffraction peak is large, it is known that the crystallite size is small. Therefore, the crystallite size of zirconium oxide is small, and due to the small crystallite size of zirconium oxide, there are many crystal ends of zirconium oxide. As a result, there are many hydroxy groups on the crystal surface of zirconium oxide, and it is considered that a large amount of water of hydration can be contained by the hydroxy groups on the crystal surface of zirconium oxide. The larger the half-value width of the peak with the highest intensity that appears when the separator is measured by X-ray diffraction measurement, the smaller the crystallite size of zirconium oxide, and the more hydroxy groups on the crystal surface of zirconium oxide are considered. Therefore, 0.60° or more is more preferable, and 0.70° or more is even more preferable. Although the upper limit is not particularly limited, 12° or less is realistic.

[0023] In the present invention, it is preferable that the zirconium oxide particles contain zirconium oxide having a cubic or tetragonal crystal structure because the electrolyte retention of the separator is more excellent. Although the reason for this is not completely clear, it is considered that when zirconium oxide has a cubic or tetragonal crystal structure, zirconium oxide can contain more water of hydration due to the difference in crystal structure.

[0024] Furthermore, the measurement by X-ray diffraction can be performed by a known X-ray diffractometer based on JIS K 0131 (1996) "General Rules for X-ray Diffraction Analysis", and the half-value width can be obtained from the width of the peak at half of the height of the peak in the X-ray diffraction measurement result.

[0025] Next, the reason why a separator with excellent electrolyte retention can be realized by meeting the requirement of (2) is as follows. In the zirconium oxide particles constituting the separator, in the range of 3200 to 3600 cm by FT-IR -1The peak appearing in the range is considered to be the peak derived from the hydroxy groups at the crystal ends of zirconium oxide, because the hydroxy groups on the crystal surface of zirconium oxide can contain a large amount of water of hydration.

[0026] In addition, the measurement of zirconium oxide particles in the present invention by FT-IR was performed by removing moisture by vacuum drying zirconium oxide particles at 105 °C for 24 hours and measuring with a known FT-IR apparatus by the ATR method based on JIS K 0117 (2017) "General Rules for Infrared Spectral Analysis".

[0027] Next, the reason why a separator excellent in electrolyte retention can be realized by corresponding to (3) is that the high moisture content of 2.0% or more of the zirconium oxide particles constituting the separator means that there are many hydroxy groups on the crystal surface of zirconium oxide, and it is considered that this is because a large amount of water of hydration is contained due to having many hydroxy groups on the crystal surface of zirconium oxide. The more the moisture content of the zirconium oxide particles constituting the separator, the more water of hydration zirconium oxide contains, and the more excellent the electrolyte retention of the separator. Therefore, 2.5% or more is more preferable, and 3.0% or more is even more preferable. Although there is no particular limitation on the upper limit, 15% or less is realistic.

[0028] In addition, the moisture content of zirconium oxide particles in the present invention is measured by the following method. (1) Leave zirconium oxide particles at a temperature of 25 °C and a humidity of 60% for 3 hours or more. (2) Measure the mass a (g) of zirconium oxide particles. (3) Vacuum-dry zirconium oxide particles at 105 °C for 24 hours. (4) Measure the mass b (g) of zirconium oxide particles after vacuum drying. (5) Calculate the moisture content W (%) of zirconium oxide particles by the following formula. W = {(a - b) / a} × 100

[0029] The shape of the zirconium oxide particles constituting the separator of the present invention can be appropriately selected from, for example, spherical (substantially spherical or true spherical), needle-like, plate-like, polygonal cubic, feather-like, etc.

[0030] The average particle diameter of the zirconium oxide particles of the present invention is appropriately adjusted. However, in order for the zirconium oxide particles to be uniformly present in the voids of the porous substrate, the distribution of the electrolytic solution in the separator becomes uniform and the electrolytic solution retention property is excellent. The average particle diameter of the zirconium oxide particles is preferably 10 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less. The lower limit of the average particle diameter of the zirconium oxide particles is not particularly limited, but 10 nm or more is realistic.

[0031] In addition, the average particle diameter of the zirconium oxide particles is obtained by subjecting the zirconium oxide particles to FPRA1000 manufactured by Otsuka Electronics Co., Ltd. (measurement range 3 nm to 5000 nm) and performing continuous measurement for 3 minutes by the dynamic light scattering method, and from the particle diameter measurement data obtained from the scattering intensity. That is, the particle diameter measurement is performed 5 times, and the obtained particle diameter measurement data is arranged in ascending order of the particle diameter distribution width. The particle diameter D at the cumulative value 50% point of the zirconium oxide particles in the data showing the value with the narrowest particle diameter distribution width at the 3rd position 50 (Hereinafter, abbreviated as D 50 is taken as the average particle diameter of the zirconium oxide particles. The dispersion liquid used for the measurement is adjusted to a temperature of 25 ° C, and water at 25 ° C is used as a blank for the scattering intensity.

[0032] Also, the particle diameter distribution of the zirconium oxide particles of the present invention is appropriately adjusted. However, when there are a large number of zirconium oxide particles with a large particle diameter, there is a risk that the zirconium oxide particles may fall off and pinholes may be easily formed. When there are a large number of zirconium oxide particles with a small particle diameter, there is a risk that the voids of the porous substrate may be blocked.

[0033] Therefore, the particle diameter distribution of the zirconium oxide particles is (D 50 / 2) or more (D 50It is preferably within the following range: (×2). The particle size distribution of the zirconium oxide particles is measured by the dynamic light scattering method described above, and is determined from the particle size measurement data obtained from the measurement intensity.

[0034] Furthermore, the higher the specific surface area of the zirconium oxide particles of the present invention, the better the electrolyte retention of the separator. Therefore, it is preferably 5 m 2 / g or more, more preferably 20 m 2 / g or more, and even more preferably 100 m 2 / g or more. If the specific surface area is too high, the zirconium oxide particles become brittle and there is a risk that the zirconium oxide particles will fall off from the separator. Therefore, it is realistic to be 500 m 2 / g or less.

[0035] In the present invention, the "specific surface area" means that after treating the zirconium oxide particles in a vacuum at a temperature of 70 °C for 4 hours, cooling to room temperature and evacuating to 1 × 10 -3 Torr, about 0.5 g of the sample is precisely weighed, and using a gas adsorption measurement device [manufactured by BEL Japan, Inc., BELSORP 28A], it is a value measured by the BET method. Note that krypton is used as the adsorption gas.

[0036] The higher the content rate of the zirconium oxide particles with respect to the separator of the present invention, the greater the specific surface area of the separator, the better the electrolyte retention, and it is possible to prevent internal short circuits from occurring in the alkaline battery. On the other hand, if the content rate of the zirconium oxide particles is too high, the voids of the porous substrate contained in the separator may be blocked by the zirconium oxide particles, and the internal resistance and internal pressure of the battery may increase. Therefore, 10 to 70 mass% is preferable, 20 to 60 mass% is more preferable, and 35 to 50 mass% is even more preferable.

[0037] The separator of the present invention contains a porous substrate in addition to the zirconium oxide particles. In the separator of the present invention, the porous substrate mainly plays a role in forming the skeleton of the separator.

[0038] The type of the porous substrate can be appropriately selected. For example, fibrous structures such as non-woven fabrics, woven fabrics, or knitted fabrics, single materials such as porous films or porous foams having air permeability and liquid permeability, those obtained by laminating a plurality of single types of materials, and those obtained by laminating a plurality of multiple types of materials can be used. Among these, a fibrous structure is preferable because of its excellent strength, and among the fibrous structures, a non-woven fabric capable of achieving a high porosity is more preferable.

[0039] The material constituting the porous substrate can be composed of, for example, polyolefin resins (such as polyethylene, polypropylene, polymethylpentene, polyolefin resins having a structure in which a part of hydrocarbons is substituted with a halogen such as a cyano group, fluorine, or chlorine), styrene resins, polyvinyl alcohol resins, polyether resins (such as polyether ether ketone, polyacetal, modified polyphenylene ether, aromatic polyether ketone, etc.), polyimide resins, polyamideimide resins, polyamide resins (such as aromatic polyamide resins, aromatic polyetheramide resins, etc.), nylon resins which are a kind of polyamide resins (such as nylon 6, nylon 66, etc.), urethane resins, epoxy resins, polysulfone resins (such as polysulfone, polyether sulfone, etc.), fluorine resins (such as polytetrafluoroethylene, polyvinylidene fluoride, etc.), cellulose resins, polybenzimidazole resins, acrylic resins (such as polyacrylate esters, polymethacrylate esters, polyacrylonitrile, polyacrylonitrile resins copolymerized with acrylate esters or methacrylate esters, modacrylic resins copolymerized with acrylonitrile and vinyl chloride or vinylidene chloride, etc.), etc., using known organic polymers. Among these, since it has excellent electrolytic solution resistance, it is preferable that the porous substrate is composed of a polyolefin resin or a nylon resin.

[0040] These organic polymers may be either linear polymers or branched polymers, and the organic polymers may be block copolymers or random copolymers, and the three-dimensional structure or the presence or absence of crystallinity of the organic polymers may be any. Further, a mixture of multi-component organic polymers may also be used.

[0041] When the porous substrate is a fibrous structure, the constituent fibers of the fibrous structure can be obtained by known methods such as, for example, a dry spinning method, a wet spinning method, a direct spinning method [for example, a melt blowing method, a spunbond method, an electrospinning method, a method of discharging a spinning dope and a gas stream in parallel to perform spinning (for example, the method disclosed in JP-A-2009-287138)], a method of extracting fibers having a small fiber diameter by removing one or more resin components from composite fibers, a method of obtaining fibers obtained by beating and splitting fibers, and the like.

[0042] The fibers constituting the fibrous structure may be composed of one type of organic polymer or may be composed of a plurality of types of organic polymers. As fibers composed of a plurality of types of organic polymers, those generally referred to as composite fibers, for example, can be in the form of a core-sheath type, a sea-island type, a side-by-side type, an orange type, a bimetal type, or the like.

[0043] The fibrous structure may contain adhesive fibers as constituent fibers. By including adhesive fibers, it is possible to improve the strength of the fibrous structure, which is preferable. The type of adhesive fiber is appropriately selected, and for example, core-sheath type adhesive fibers, side-by-side type adhesive fibers, or fully meltable adhesive fibers can be employed.

[0044] Further, the fibrous structure may contain fibers having a cross-sectional shape other than substantially circular fibers or elliptical fibers as constituent fibers. Examples of the non-circular cross-section fibers include fibers having a cross-section of a polygonal shape such as a triangular shape, an alphabetic character shape such as a Y shape, an irregular shape, a multi-leaf shape, a symbol shape such as an asterisk shape, or a shape in which a plurality of these shapes are combined.

[0045] The finer the average fiber diameter of the fibers constituting the fibrous structure, the denser the structure of the separator becomes, making it less likely for the alkaline battery to short-circuit. Also, there is a tendency to prevent the occurrence of internal short-circuits by making the size of the voids uniform and small. Therefore, the average fiber diameter of the fibers constituting the fibrous structure is preferably, for example, 15 μm or less, more preferably 10 μm or less, and most preferably 8 μm or less. Note that the lower limit of the average fiber diameter of the fibers is not particularly limited, but it is practical to be 0.01 μm or more.

[0046] Note that the "average fiber diameter" as referred to in the present invention is the arithmetic mean value of the fiber diameters of 100 randomly selected fibers analyzed from an electron micrograph of the cross-section of the fibrous structure or the separator containing the fibers, and the fiber diameter refers to the diameter of a circle having the same area as the cross-sectional area of the fiber.

[0047] Also, the fiber length can be appropriately selected, but it can be 0.5 to 150 mm, and depending on the manufacturing method of the fibers, it can also be continuous fibers. Note that two or more types of fibers different in terms of the average fiber diameter and / or the fiber length may be included.

[0048] Various configurations of the porous base material, such as the basis weight and thickness, can contain a sufficient amount of zirconium oxide, and can be appropriately adjusted so as to obtain a separator capable of preparing an alkaline battery in which internal short-circuits are less likely to occur.

[0049] Also, for the purpose of, for example, making it easier to apply the mixed liquid described later to the porous base material, the porous base material may be hydrophilized. The method of hydrophilizing the porous base material can be appropriately selected, and examples thereof include methods of subjecting it to plasma treatment, sulfonation treatment, fluorine gas treatment, or corona charging treatment.

[0050] The separator of the present invention contains a porous substrate and zirconium oxide particles, and it is preferable that the zirconium oxide particles are adhered to the porous substrate so as not to easily fall off from the separator. Examples of the adhesion between the porous substrate and the zirconium oxide particles include adhesion by a binder, adhesion by deforming a part of the porous substrate by melting and solidifying or softening it, and the like. Among these, adhesion by a binder is preferable because the porous substrate and the zirconium oxide particles are firmly adhered and the zirconium oxide particles are not easily detached from the separator.

[0051] Examples of the types of binders that can be used include polyolefin resins, acrylic resins (e.g., ethyl acrylate, methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylene-acrylate copolymers such as ethylene-ethyl acrylate copolymer, 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 resins, epoxy resins, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, and the like. Among these, it is preferable to use an acrylic resin that has excellent electrolyte resistance and can stably fix zirconium oxide particles for a long time, so that the electrolyte retention of the separator can be maintained. These may be used alone or in combination of two or more.

[0052] The mode of existence of zirconium oxide particles in the separator may be a mode in which they exist only on the surface of the porous substrate or a mode in which they exist on both the surface of the porous substrate and in the voids. However, when zirconium oxide particles exist on both the surface of the porous substrate and in the voids, compared with the case where they exist only on the surface of the porous substrate, it is difficult for the zirconium oxide particles to form a layered structure by depositing and aggregating on the surface of the porous substrate, and there is a tendency for the zirconium oxide particles to be dispersed and present inside the porous substrate. Since the surface of the zirconium oxide particles is exposed due to the non-aggregation of the zirconium oxide particles, it is suitable because it easily contributes to an increase in the specific surface area of the separator. Further, when there is a layer of zirconium oxide particles on the surface of the porous substrate, when the separator holds the electrolytic solution, the distribution of the electrolytic solution may be biased inside the separator, leading to an increase in the electrical resistance of the battery. Therefore, it is preferable that there is no layer of zirconium oxide particles on the surface of the porous substrate.

[0053] Also, the content ratio of the binder with respect to the zirconium oxide particles contained in the separator is appropriately adjusted. However, if the content ratio of the binder with respect to the zirconium oxide particles contained in the separator is too high, the binder may coat the zirconium oxide particles and inhibit the action of the zirconium oxide, and there is a possibility that the improvement in the electrolytic solution retention property may not be sufficient. On the other hand, if the content ratio of the binder with respect to the zirconium oxide particles contained in the separator is too low, there is a possibility that the zirconium oxide particles contained in the separator for alkaline batteries may fall off, and there is a possibility that the place where the zirconium oxide particles fall off may become a pinhole and cause an internal short circuit in the battery. Therefore, the content ratio of the binder with respect to the zirconium oxide particles contained in the separator is preferably 0.05 to 10 mass%, more preferably 0.1 to 5 mass%, and still more preferably 0.2 to 4 mass%.

[0054] The basis weight of the separator of the present invention is appropriately adjusted, but it can be 2 to 80 g / m 2 and can be 5 to 50 g / m 2 and can be 10 to 30 g / m 2 The "basis weight" referred to in the present invention means the basis weight per 1 m of the main surface, which is the widest surface. 2It refers to the mass per unit area.

[0055] Also, regarding the thickness of the separator of the present invention, although a thinner separator tends to reduce the internal resistance of the battery, if the thickness is too thin, there is a risk of poor internal short-circuit resistance. Therefore, it is preferably 5 to 100 μm, more preferably 10 to 70 μm, and even more preferably 30 to 60 μm. Here, the "thickness" referred to in the present invention means the average value of 10 randomly selected and measured points using an external micrometer (measurement range: 0 to 25 mm) defined in 3.1 of JIS B 7502 (2016) "Micrometer".

[0056] The separator of the present invention can be manufactured, for example, as follows.

[0057] First, a porous substrate is prepared. When the porous substrate is a porous film or a porous foam having air permeability and liquid permeability, the preparation method can be appropriately selected. For example, it can be prepared by a known method such as pouring a melted organic polymer into a mold for molding and performing a foaming treatment. When the porous substrate is a woven fabric or a knitted fabric, it can be prepared by weaving or knitting fibers.

[0058] When the porous substrate is a nonwoven fabric, first, a fiber web is formed from fibers by a dry method (e.g., carding method, air-laying method, etc.) or a wet method. Among these, it is preferable to form the fiber web by the wet method, which is easy to manufacture a separator with uniformly dispersed fibers and less fiber dispersion unevenness. As this wet method, a conventionally known method, for example, a horizontal long-mesh method, an inclined wire-type short-mesh method, a cylinder mesh method, or a long-mesh · cylinder mesh combination method can be used. When laminating two or more layers, it is preferable to laminate fiber webs having the same fiber composition so that a separator having a single-layer structure can be manufactured. Next, the fibers constituting the fiber web are bonded to prepare a nonwoven fabric. The method of bonding the fibers to each other can be appropriately selected. For example, a method of entangling the fibers with a needle or a water flow, a method of bonding the fibers with a binder, or a method of melting and solidifying the fiber surfaces of the adhesive fibers to bond the fibers by fusion can be mentioned. As the heat treatment method, for example, a method of heating and pressing with a calendar roll, a method of heating with a hot air dryer, a method of irradiating infrared rays under no pressure, etc. can be used. Alternatively, a nonwoven fabric may be prepared by collecting the fibers spun by the direct spinning method.

[0059] Also, for the purpose of making it easier for the porous substrate to contain the mixed liquid described later, the porous substrate may be hydrophilized by the above method.

[0060] Next, zirconium oxide particles are bonded to the porous substrate. As the method of bonding zirconium oxide particles to the porous substrate, for example, there are a method of bonding with a binder and a method of deforming and bonding a part of the porous substrate by melting and solidifying or softening. Among these, the method of bonding with a binder can be appropriately selected. For example, 1. Prepare a zirconium oxide mixed liquid (hereinafter sometimes referred to as a mixed liquid) obtained by mixing a binder and zirconium oxide particles in a solvent or a dispersion medium, and immerse the porous substrate in the mixed liquid. 2. Spray the mixed liquid onto the porous substrate. 3. Using a coating method such as the kiss coater method using a gravure roll, apply the mixed solution to one main surface or both main surfaces of the porous substrate. After performing this, it is possible to use a method of drying the porous substrate containing the mixed solution to remove the solvent or dispersion medium in the mixed solution.

[0061] In addition, when the binder exists as a solid such as particles in the mixed solution, it is preferable to bond the zirconium oxide particles to the porous substrate with the binder by melting and solidifying or softening and deforming the solid binder when performing the above drying. At this time, the shape of the binder particles present in the mixed solution is appropriately selected, and for example, it can be appropriately selected from spherical (substantially spherical or true spherical), needle-like, flat plate-like, polygonal cube-like, feather-like, etc. The type of the solvent or dispersion medium is appropriately selected, and for example, water, alcohols, ethers, etc. can be used alone or in combination.

[0062] Further, in order to prevent aggregation of the binder and zirconium oxide particles and improve the dispersibility in the mixed solution, for example, a surfactant (for example, a cationic surfactant, an anionic surfactant, a nonionic surfactant, etc.) may be added, and the addition amount is appropriately adjusted.

[0063] The method of drying the porous substrate containing the mixed solution is appropriately selected. For example, a method of removing the solvent or dispersion medium by subjecting it to heating means such as a near-infrared heater, a far-infrared heater, or a halogen heater, or a method of removing the solvent or dispersion medium by hot air or blowing can be used. Further, known methods such as a method of leaving the porous substrate containing the mixed solution at room temperature (25 ° C), a method of exposing it under reduced pressure conditions, or a method of exposing it in an atmosphere at a temperature above the temperature at which the solvent or dispersion medium can volatilize can be used.

Example

[0064] Hereinafter, the present invention will be specifically described by way of examples, but these do not limit the present invention.

[0065] (Preparation of Zirconium Oxide Particles and Yttrium Oxide Particles) Zirconium oxide particles A to D, yttrium-containing zirconium oxide particles, and yttrium oxide particles were prepared.

[0066] The zirconium oxide content (ZrO2 content), the average particle diameter of these particles, the specific surface area, and the presence or absence of peaks (IR peak presence or absence) appearing in the range of 3200 to 3600 cm -1 when measured by FT-IR by the above method, and the moisture content measured by the above method are shown in Table 1 below. The yttrium oxide particles were measured in the same manner as the zirconium oxide particles.

[0067] [Table 1]

[0068] (Example 1) (Method for Preparing Nonwoven Fabric) A core-sheath composite fiber with a core component of homopolypropylene and a sheath component of high-density polyethylene (volume ratio of core component to sheath component = 60:40, fineness: 0.8 dtex, fiber length: 5 mm) was prepared. Furthermore, 61 island components made of polypropylene were present in the sea component made of polyethylene terephthalate. The sea-island type composite undrawn fiber was spun by a composite spinning method and stretched. The sea-island type composite drawn fiber thus produced was immersed in an aqueous alkali solution for 120 minutes. After extracting and removing the polyethylene terephthalate, which is the sea component, it was cut to produce polypropylene ultra-fine fibers (fiber diameter: 2.0 μm, fiber length: 3 mm, melting point: 168 °C, cross-sectional shape: circular) with substantially the same fiber diameter in the longitudinal direction. These polypropylene ultra-fine fibers were not fibrillated and were stretched, and each fiber had the same fiber diameter. Next, 60 mass% of the core-sheath composite fiber and 40 mass% of the ultra-fine fiber were mixed, and a fiber web was prepared by a wet-laying method. Thereafter, the fiber web was treated with hot air at a temperature of 140°C for 10 seconds, and then fed to a calendar roll at 40°C while adjusting the roll pressure applied to the fiber web, to prepare a nonwoven fabric (basis weight: 13 g / m 2 , thickness: 50 μm) in which only the sheath component of the core-sheath composite fiber was fused. The nonwoven fabric was composed only of fibers. Furthermore, the prepared nonwoven fabric was subjected to plasma treatment to prepare a hydrophilized nonwoven fabric (basis weight: 13 g / m 2 , thickness: 50 μm).

[0069] (Preparation of Mixture A) As components of the mixture, 29.9 mass% of zirconium oxide particles A, 0.1 mass% of an acrylic resin, and 70 mass% of water were mixed to prepare a mixture A with a solid content concentration of 30 mass%. In the mixture A, the zirconium oxide particles A were uniformly dispersed without aggregation.

[0070] (Application of Mixture A to Nonwoven Fabric and Drying) Using a kiss coater method with a gravure roll, mixture A was applied to the entire one main surface of the hydrophilized nonwoven fabric so that the mass of the zirconium oxide particles A became 12 g / m 2 . Thereafter, the hydrophilized nonwoven fabric coated with mixture A was fed to a dryer equipped with a far-infrared heater to remove water from the mixture A applied to the hydrophilized nonwoven fabric, thereby preparing a separator (basis weight: 25 g / m , thickness: 50 μm, proportion of zirconium oxide particles A in the separator: 48 mass%). In the separator, the zirconium oxide particles A were present on the surface and in the voids of the nonwoven fabric, and no layer of zirconium oxide particles A was present on the surface of the nonwoven fabric. 2

[0071] (Example 2) First, the same hydrophilized nonwoven fabric as in Example 1 was prepared.

[0072] (Preparation of Mixture B) Next, 29.9 mass% of zirconium oxide particles B, 0.1 mass% of an acrylic resin, and 70 mass% of water were mixed as components of the mixed liquid to prepare a mixed liquid B with a solid content concentration of 30 mass%. In the mixed liquid B, the zirconium oxide particles B were uniformly dispersed without aggregation.

[0073] (Application and drying of the mixed liquid B to the nonwoven fabric) The mass of the zirconium oxide particles B was 12 g / m 2 Except for applying the mixed liquid B to the hydrophilized nonwoven fabric so that the mass became 12 g / m, the application and drying of the mixed liquid were carried out in the same manner as in Example 1, and a separator (basis weight: 25 g / m 2 , thickness: 50 μm, ratio of zirconium oxide particles B in the separator: 48 mass%) was prepared. In the separator, the zirconium oxide particles B were present on the surface and in the voids of the nonwoven fabric, and there was no layer of zirconium oxide particles B on the surface of the nonwoven fabric.

[0074] (Comparative Example 1) First, the same hydrophilized nonwoven fabric as in Example 1 was prepared.

[0075] (Preparation of the mixed liquid C) Next, 29.9 mass% of zirconium oxide particles C, 0.1 mass% of an acrylic resin, and 70 mass% of water were mixed as components of the mixed liquid to prepare a mixed liquid C with a solid content concentration of 30 mass%. In the mixed liquid C, the zirconium oxide particles C were uniformly dispersed without aggregation.

[0076] (Application and drying of the mixed liquid C to the nonwoven fabric) The mass of the zirconium oxide particles C was 12 g / m 2 Except for applying the mixed liquid C to the hydrophilized nonwoven fabric so that the mass became 12 g / m, the application and drying of the mixed liquid were carried out in the same manner as in Example 1, and a separator (basis weight: 25 g / m 2, thickness: 50 μm, ratio of zirconium oxide particles C in the separator: 48 mass%) was prepared. In the separator, zirconium oxide particles C were present on the surface and in the voids of the nonwoven fabric, and no layer of zirconium oxide particles C was present on the surface of the nonwoven fabric.

[0077] (Comparative Example 2) First, a nonwoven fabric subjected to the same hydrophilic treatment as in Example 1 was prepared.

[0078] (Preparation of Mixed Liquid D) Next, 29.9 mass% of zirconium oxide particles D, 0.1 mass% of an acrylic resin, and 70 mass% of water were mixed as components of the mixed liquid to prepare a mixed liquid D with a solid content concentration of 30 mass%. In the mixed liquid D, the zirconium oxide particles D were uniformly dispersed without aggregation.

[0079] (Application of Mixed Liquid D to Nonwoven Fabric and Drying) The mass of zirconium oxide particles D is 12 g / m 2 except that the mixed liquid D was applied to the hydrophilic-treated nonwoven fabric so that the coating and drying of the mixed liquid were carried out in the same manner as in Example 1, and a separator (basis weight: 25 g / m 2 , thickness: 50 μm, ratio of zirconium oxide particles D in the separator: 48 mass%) was prepared. In the separator, zirconium oxide particles D were present on the surface and in the voids of the nonwoven fabric, and no layer of zirconium oxide particles D was present on the surface of the nonwoven fabric.

[0080] (Comparative Example 3) First, a nonwoven fabric subjected to the same hydrophilic treatment as in Example 1 was prepared.

[0081] (Preparation of Mixed Liquid E) Next, 29.9 mass% of yttrium-containing zirconium oxide particles, 0.1 mass% of an acrylic resin, and 70 mass% of water were mixed as components of the mixed liquid to prepare a mixed liquid E with a solid content concentration of 30 mass%. In the mixed liquid E, the yttrium-containing zirconium oxide particles were uniformly dispersed without aggregation.

[0082] (Application and Drying of Mixed Liquid E to Nonwoven Fabric) The mass of yttrium oxide-containing zirconium oxide particles is 12 g / m 2 Except that the mixed liquid E was applied to the hydrophilized nonwoven fabric so that the mass of yttrium oxide-containing zirconium oxide particles became 12 g / m, the application and drying of the mixed liquid were carried out in the same manner as in Example 1, and a separator (basis weight: 25 g / m 2 , thickness: 50 μm, ratio of yttrium oxide-containing zirconium oxide particles in the separator: 48 mass%) was prepared. In the separator, yttrium oxide-containing zirconium oxide particles were present on the surface and in the voids of the nonwoven fabric, and a layer of yttrium oxide-containing zirconium oxide particles was not present on the surface of the nonwoven fabric.

[0083] (Comparative Example 4) First, the same hydrophilized nonwoven fabric as in Example 1 was prepared.

[0084] (Preparation of Mixed Liquid F) Next, 29.9 mass% of yttrium oxide particles, 0.1 mass% of an acrylic resin, and 70 mass% of water were mixed as components of the mixed liquid to prepare a mixed liquid F with a solid content concentration of 30 mass%. In the mixed liquid F, the yttrium oxide particles were uniformly dispersed without aggregation.

[0085] (Application and Drying of Mixed Liquid F to Nonwoven Fabric) The mass of yttrium oxide particles is 12 g / m 2 Except that the mixed liquid F was applied to the hydrophilized nonwoven fabric so that the mass of yttrium oxide particles became 12 g / m, the application and drying of the mixed liquid were carried out in the same manner as in Example 1, and a separator (basis weight: 25 g / m 2 , thickness: 50 μm, ratio of yttrium oxide particles in the separator: 48 mass%) was prepared. In the separator, yttrium oxide particles were present on the surface and in the voids of the nonwoven fabric, and a layer of yttrium oxide particles was not present on the surface of the nonwoven fabric.

[0086] Table 2 shows the inorganic particles contained in the separators of the examples and comparative examples, the basis weight of the separators, the content of the inorganic particles in the separators (inorganic particle content), the thickness of the separators, and the ratio of zirconium oxide particles or yttrium oxide particles in the separators (inorganic particle content ratio).

[0087]

Table 2

[0088] Next, the peak position with the highest intensity (X-ray diffraction measurement peak position) and the full width at half maximum of the peak with the highest intensity (X-ray diffraction measurement peak full width at half maximum) in the X-ray diffraction measurement of the separators of the examples and comparative examples were measured by the above method, and the KOH aqueous solution dropping absorption time, the pressure retention rate, and the electrical resistance were measured and evaluated by the following (Measurement of KOH aqueous solution dropping absorption time), (Measurement of pressure retention rate), and (Measurement of electrical resistance).

[0089] (Measurement of KOH aqueous solution dropping absorption time) (1) Five 5 cm square test pieces were taken from each separator. (2) 30 μl of an aqueous potassium hydroxide (KOH) solution with a density of 1.3 g / cm³ at 20°C was dropped onto the test piece, and the time until complete absorption was measured. 3 of potassium hydroxide (KOH) aqueous solution was dropped onto the test piece, and the time until complete absorption was measured. (3) The measurement in (2) was performed 5 times for each test piece, and the average value was taken as the KOH aqueous solution dropping absorption time. If the absorption of the KOH aqueous solution took 300 seconds or more even once in the 5 measurements, the KOH aqueous solution dropping absorption time was taken as 300 seconds or more. (Measurement of pressure retention rate)

[0090] (1) Three 5 cm square test pieces were taken from each separator, and their masses (a (unit: g)) were measured respectively. (2) Each test piece was immersed in an electrolytic solution (an aqueous potassium hydroxide solution with a density of 1.3 g / cm³ at 20°C) 3 to fill the voids in the test piece with the electrolytic solution. (3) On both sides of the test piece, the test piece was sandwiched between three pieces of filter paper (model number: ADVANTEC-TYPE2), compressed at a pressure of 1.23 MPa, and the filter paper absorbed the electrolyte. (4) The mass (b (unit: g)) of each test piece that had absorbed the electrolyte was measured, and the pressure retention rate R (%) was calculated using the following formula. This measurement was performed three times for each test piece, and the average value was taken as the pressure retention rate. R = [(b - a) / a] × 100

[0091] (Measurement of electrical resistance) (1) Three 5 cm square test pieces were taken from each separator and their masses were measured respectively. (2) After absorbing 50 mass% of an aqueous potassium hydroxide solution with a density of 1.3 g / cm³ at 20°C relative to the mass of each test piece, each test piece was sandwiched between 35 mm square nickel plates, and the electrical resistance (Ω) at a load of 49 N was measured. This measurement was performed three times for each test piece, and the average value was taken as the electrical resistance. 3 (3) After absorbing 50 mass% of an aqueous potassium hydroxide solution with a density of 1.3 g / cm³ at 20°C relative to the mass of each test piece, each test piece was sandwiched between 35 mm square nickel plates, and the electrical resistance (Ω) at a load of 49 N was measured. This measurement was performed three times for each test piece, and the average value was taken as the electrical resistance.

[0092] The evaluation results from the measurement of the separators of the examples and comparative examples are shown in Table 3 below.

[0093]

Table 3

[0094] From the comparison between the examples and the comparative examples, the separator that satisfies the configuration of the present invention is a separator that has a short KOH dropping absorption time and is easy to wet, and also has a high pressure retention rate and a low electrical resistance, and is a separator with excellent electrolyte retention.

Industrial applicability

[0095] The separator for an alkaline battery of the present invention can be suitably used as a separator for a primary battery using an alkaline electrolyte, or an alkaline secondary battery such as a nickel-metal hydride battery, a nickel-cadmium battery, or a nickel-zinc battery.

Claims

1. A separator for an alkaline battery comprising a porous substrate and zirconium oxide particles, wherein when the separator for an alkaline battery is measured by X-ray diffraction, the full width at half maximum of the peak with the highest intensity is 0.40° or more.

2. A separator for an alkaline battery comprising a porous substrate and zirconium oxide particles, When measuring zirconium oxide particles contained in a separator for an alkaline battery by FT-IR, a separator for an alkaline battery having a peak in the range of 3200 to 3600 cm －１ is obtained.

3. A separator for an alkaline battery comprising a porous substrate and zirconium oxide particles, wherein the water content of the zirconium oxide particles contained in the separator for an alkaline battery is 2.0% or more.

4. The separator for an alkaline battery according to any one of claims 1 to 3, wherein the porous substrate and the zirconium oxide particles are bonded with a binder containing an acrylic resin.

5. The separator for an alkaline battery according to any one of claims 1 to 4, wherein the content of zirconium oxide in the zirconium oxide particles is 95 mass% or more.

6. The separator for an alkaline battery according to any one of claims 1 to 5, wherein the zirconium oxide particles contain zirconium oxide having a cubic or tetragonal crystal structure.

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