Alkaline-battery separator, method for producing same, and alkaline battery

Abstract

Provided is an alkaline-battery separator that has excellent compression resistance when retaining liquid and has excellent liquid retention when compressed. The alkaline-battery separator is formed from a nonwoven fabric containing alkali-resistant fibers and polyvinyl alcohol-based binder fibers. The alkali-resistant fibers include polyvinyl alcohol-based fibers, and the fiber width of the polyvinyl alcohol-based binder fibers which are stained by iodine is 13 to 130 μm.

Description

Separator for alkaline batteries and method for manufacturing the same, and alkaline battery Related applications

[0001] This application claims priority to Japanese Patent Application No. 2024-165887, filed in Japan on September 25, 2024, which is incorporated herein by reference as forming part of this application.

[0002] The present invention relates to an alkaline battery separator that can be suitably used in alkaline batteries, a method for manufacturing the same, and an alkaline battery using this separator.

[0003] Generally, in alkaline batteries, negatively charged anions move from the positive electrode to the negative electrode and positively charged cations move from the negative electrode to the positive electrode through an alkaline electrolyte. A separator is used between the positive and negative electrodes to separate them and isolate the positive electrode active material from the negative electrode active material. To improve battery performance, alkaline battery separators are required to have various properties such as preventing internal short circuits, high alkali resistance, electrolyte absorption, and shielding properties.

[0004] For example, Patent Document 1 (Japanese Patent No. 2938315) discloses a separator for alkaline batteries characterized in that at least a portion of the main fibers are fibrilized cellulose fibers obtained by dissolving cellulose in a solvent and directly precipitating the cellulose. Patent Document 1 states that it is excellent in both separating properties and electrolyte absorption properties, and also states that by using a fibrous binder as a polyvinyl alcohol-based binder and reducing the moisture content before drying or lowering the drying temperature, the binder fibers are not completely dissolved, and point adhesion is made only at the intersections between the binder fibers and the main fibers while retaining their fibrous shape, thereby increasing the strength of the separator without causing a decrease in electrolyte absorption properties or an increase in the internal resistance of the battery.

[0005] Furthermore, Patent Document 2 (Japanese Patent No. 3770748) discloses a nonwoven fabric for alkaline battery separators comprising at least one type of split-type composite fiber with an average fiber diameter of 1 to 6 μm after splitting, in which two or more types of polyolefin resin components are alternately arranged adjacent to the fiber cross-section, and polyolefin fibers with a fiber diameter of 10 to 25 μm, and a heat-sealed composite fiber of 16 to 25 μm. The nonwoven fabric for alkaline battery separators described in Patent Document 2 is described as having excellent leak resistance and compression resistance, and surface strength that can prevent minute short circuits and liquid depletion phenomena.

[0006] Patent No. 2938315 Patent No. 3770748

[0007] However, in the embodiment of Patent Document 1, a separator for alkaline batteries is manufactured using fibrilized solvent-spun cellulose fibers and polyvinyl alcohol-based fibers as the main fibers, and a polyvinyl alcohol-based fibrous binder with a fineness of 1.0 denier is used to retain the fiber shape. However, such a separator does not have sufficient compressive resistance when considering the improvement of high-rate characteristics when discharged at high current values ​​and middle-rate characteristics when discharged at medium current values ​​(medium and high-rate discharge performance).

[0008] Furthermore, while Patent Document 2 describes a nonwoven fabric for alkaline battery separators that contains a split-type composite fiber, a polyolefin fiber, and a heat-fusible composite fiber with two or more polyolefin resin components, and applies a hydrophilic treatment to the nonwoven fabric, simply applying a hydrophilic treatment to the polyolefin fiber sometimes resulted in insufficient electrolyte absorption. Patent Document 2 also describes that repeated charging and discharging causes the positive electrode to gradually swell, compressing the nonwoven fabric for alkaline battery separators and the negative electrode. It also describes excellent electrolyte retention (measured as electrolyte depletion) and compression resistance (measured as thickness reduction) after repeated charging and discharging cycles. However, there is a need for greater electrolyte retention and compression resistance under more severe conditions, such as high-load compression of the nonwoven fabric in an electrolyte-retaining state.

[0009] Therefore, in view of the above problems, the present invention aims to provide an alkaline battery separator that is excellent in compression resistance in a liquid-retaining state and excellent in liquid retention when compressed, a method for manufacturing the same, and an alkaline battery.

[0010] The inventors of this invention have diligently studied and conducted research to solve the above problems, and as a result have completed the present invention. Specifically, the present invention includes the following aspects.

[0011] [Aspect 1] A separator for alkaline batteries comprising a nonwoven fabric containing alkali-resistant fibers and polyvinyl alcohol-based binder fibers, wherein the alkali-resistant fibers include polyvinyl alcohol-based fibers, and the fiber width of the polyvinyl alcohol-based binder fibers dyed with iodine is 13 to 130 μm (preferably 20 to 120 μm, more preferably 30 to 100 μm, even more preferably 35 to 90 μm, and even more preferably 40 to 85 μm).

[0012] [Aspect 2] A separator for alkaline batteries according to Aspect 1, wherein the polyvinyl alcohol-based binder fiber contains a vinyl alcohol-based polymer containing 50 mol% or more (preferably 70 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or more) of constituent units derived from vinyl alcohol.

[0013] [Aspect 3] A separator for alkaline batteries according to aspect 1 or 2, wherein the polyvinyl alcohol-based binder fiber is a non-composite fiber.

[0014] [Aspect 4] A separator for alkaline batteries according to any one of aspects 1 to 3, wherein the hot water dissolution temperature of the polyvinyl alcohol-based binder fibers is in the range of 65 to 100°C (preferably 76 to 100°C, more preferably 76 to 99°C, even more preferably 78 to 98°C, and even more preferably 78 to 95°C).

[0015] [Aspect 5] A separator for an alkaline battery according to any one of Aspects 1 to 4, wherein the content of the polyvinyl alcohol-based fibers, which are alkali-resistant fibers in the separator, is 30% by weight or more (preferably 30 to 70% by weight, more preferably 33 to 70% by weight, still more preferably 35 to 60% by weight, and even more preferably 43 to 50% by weight).

[0016] [Aspect 6] A separator for an alkaline battery according to any one of Aspects 1 to 5, wherein the content of the polyvinyl alcohol-based binder fibers in the separator is 16 to 30% by weight (preferably 16 to 28% by weight, more preferably 18 to 25% by weight).

[0017] [Aspect 7] A separator for an alkaline battery according to any one of Aspects 1 to 6, wherein the alkali-resistant fibers further include cellulose-based fibers.

[0018] [Aspect 8] A separator for an alkaline battery according to Aspect 7, wherein the cellulose-based fibers are fibrillated products.

[0019] [Aspect 9] A separator for an alkaline battery according to Aspect 8, wherein the CSF value of the fibrillated product is 5 to 600 ml (preferably 6 to 400 ml, more preferably 7 to 100 ml, still more preferably 8 to 19 ml).

[0020] [Aspect 10] A separator for an alkaline battery according to any one of Aspects 1 to 9, having a thickness of 40 to 120 μm (preferably 45 to 100 μm, more preferably 50 to 90 μm, still more preferably 50 to 85 μm).

[0021] [Aspect 11] A separator for an alkaline battery according to any one of Aspects 1 to 10, having a density of 0.34 g / cm ３ or more (preferably 0.34 to 0.50 g / cm ３ (for example, 0.34 to 0.43 g / cm ３ or 0.34 to 0.40 g / cm３ ), more preferably 0.35 to 0.47 g / cm ３ (for example, 0.35 to 0.43 g / cm ３ ), still more preferably 0.36 to 0.45 g / cm ３ (for example, 0.36 to 0.40 g / cm ３ ), a separator for an alkaline battery.

[0022] [Aspect 12] A separator for an alkaline battery according to any one of Aspects 1 to 11, wherein the total content rate of fibers containing a vinyl alcohol-based polymer is 40% by weight or more (preferably 40 to 80% by weight, more preferably 48 to 75% by weight, still more preferably 55 to 70% by weight, even more preferably 61 to 70% by weight), a separator for an alkaline battery.

[0023] [Aspect 13] An alkaline battery including the separator for an alkaline battery according to any one of Aspects 1 to 12.

[0024] [Aspect 14] A method for manufacturing a separator for an alkaline battery, comprising: a slurry preparation step of preparing a slurry containing an alkali-resistant fiber containing a polyvinyl alcohol-based fiber, a polyvinyl alcohol-based binder fiber having a fineness of 0.5 to 5.0 dtex (preferably 1.0 to 5.0 dtex, more preferably 1.5 to 5.0 dtex, still more preferably 1.7 to 4.7 dtex, even more preferably 1.9 to 4.4 dtex, particularly preferably 2.1 to 4.0 dtex), and water; a papermaking step of obtaining wet paper from the obtained slurry by a papermaking method; and a drying step of drying the obtained wet paper while maintaining the fiber shape of the polyvinyl alcohol-based binder fiber. In the slurry preparation step, the fineness of the polyvinyl alcohol-based binder fiber is Adtex, the hot water dissolution temperature of the polyvinyl alcohol-based binder fiber is B°C, the blending ratio of the fiber containing a vinyl alcohol-based polymer is C% by weight, in the drying step, the carry-in moisture rate of the wet paper is D% by weight, the drying temperature is E°C, the drying time is F seconds, and the basis weight of the separator paper obtained after drying is G g / cm ２ When it is, D×(E + 273.15)×F / {(A) １／２A method for manufacturing an alkaline battery separator, wherein {B + 273.15} × C × G} is 4.0 or less (preferably 0.1 to 4.0, more preferably 0.2 to 3.0, even more preferably 0.4 to 2.0, and even more preferably 0.6 to 1.5).

[0025] In this specification, "polyvinyl alcohol-based fiber" refers to a fiber containing a vinyl alcohol-based polymer as an alkali-resistant fiber, and "polyvinyl alcohol-based binder fiber" refers to a fiber containing a vinyl alcohol-based polymer as a binder fiber. Furthermore, "fiber containing a vinyl alcohol-based polymer" encompasses both polyvinyl alcohol-based fibers and polyvinyl alcohol-based binder fibers.

[0026] As used herein, the singular forms, “a,” “an,” and “the,” are intended to include the plural form, including “at least one,” unless the context explicitly indicates otherwise. As used herein, the terms “and / or,” “at least one,” and “one or more” include any and all combinations of the related enumerated items.

[0027] Furthermore, any combination of at least two components disclosed in the claims and / or specification is included in the present invention. In particular, any combination of two or more claims described in the claims is included in the present invention.

[0028] According to the present invention, it is possible to provide a separator for alkaline batteries that has excellent compressibility in a liquid-retaining state and excellent liquid retention when compressed.

[0029] [Separator for Alkaline Batteries] The alkaline battery separator of the present invention is an alkaline battery separator made of a nonwoven fabric containing alkali-resistant fibers and polyvinyl alcohol-based binder fibers. In this specification, alkali-resistant fibers mean fibers that can be used in alkaline batteries and exhibit chemical durability to alkaline electrolytes.

[0030] (Alkali-resistant fibers) In the alkaline battery separator of the present invention, the alkali-resistant fibers include polyvinyl alcohol-based fibers. Polyvinyl alcohol-based fibers not only have high resistance to alkaline electrolytes, but also have excellent electrolyte absorption properties due to their hydrophilicity. Therefore, by including polyvinyl alcohol-based fibers as alkali-resistant fibers, the alkali resistance and electrolyte retention properties of the separator can be improved. Furthermore, because polyvinyl alcohol-based fibers have rigidity, the compressive resistance of the separator can be improved.

[0031] Polyvinyl alcohol-based fibers are alkali-resistant fibers containing a vinyl alcohol-based polymer, and may contain components other than the vinyl alcohol-based polymer. For example, polyvinyl alcohol-based fibers may be non-composite fibers containing a vinyl alcohol-based polymer, or they may be composite fibers such as core-sheath type fibers or sea-island type fibers with other polymers. In this specification, composite fibers mean fibers obtained by composite spinning and having a composite cross-section continuously in the fiber axis direction. Non-composite fibers mean fibers that are not composite fibers and include mixed-spun fibers obtained by mixing and spinning other components. From the viewpoint of improving liquid retention by impregnating the electrolyte into the fiber interior due to the hydrophilicity of the vinyl alcohol-based polymer, polyvinyl alcohol-based fibers are preferably non-composite fibers.

[0032] From the viewpoint of electrolyte retention and mechanical performance, the polyvinyl alcohol fiber may contain 50% by weight or more of vinyl alcohol polymer based on its total weight, preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 98% by weight or more.

[0033] Vinyl alcohol polymers are polymers that mainly contain constituent units derived from vinyl alcohol (hereinafter sometimes referred to as vinyl alcohol units). For example, they may contain 50 mol% or more of vinyl alcohol units in total constituent units, preferably 70 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or more. Vinyl alcohol polymers may also contain constituent units other than vinyl alcohol units, such as ethylene units and vinyl ester units. Vinyl ester units may be constituent units remaining when vinyl alcohol units are formed by saponification of vinyl acetate units, etc., or they may be constituent units formed by modifying and esterifying vinyl alcohol units. For example, they may be subjected to treatments such as acetalization, and the hydroxyl groups of vinyl alcohol units in polyvinyl alcohol fibers may be chemically crosslinked.

[0034] The fineness of the polyvinyl alcohol-based fiber may be 0.1 to 1.0 dtex, preferably 0.2 to 0.8 dtex, and more preferably 0.2 to 0.6 dtex, from the viewpoint of improving rigidity and improving the shielding performance and thinning of the separator. In this specification, fineness refers to the fineness of a single fiber and can be measured in accordance with JIS L 1015:2021 8.5.1.

[0035] Furthermore, the average fiber length of the polyvinyl alcohol-based fibers can be appropriately set according to the type and fineness of the nonwoven fabric. For example, it can be selected from a wide range of about 0.1 to 70 mm, but from the viewpoint of papermaking properties, an average fiber length of 0.1 to 10 mm is preferred, and 1 to 6 mm is more preferred. Multiple polyvinyl alcohol-based fibers with different fineness and / or fiber lengths may be used in combination, thereby controlling the thickness of the resulting nonwoven fabric and ensuring the thickness required for use as a separator. In this specification, the average fiber length can be measured in accordance with JIS L 1015:2021 8.4.1.

[0036] The content of polyvinyl alcohol-based fibers, which are alkali-resistant fibers in the alkaline battery separator, may be 30% by weight or more, preferably 33% by weight or more, more preferably 35% by weight or more, and even more preferably 43% by weight or more. Polyvinyl alcohol-based fibers have relatively high rigidity, and the higher their content, the more stiffness can be given to the entire nonwoven fabric of the alkaline battery separator, thereby improving compression resistance, and because they have excellent hydrophilicity, the electrolyte retention capacity can be improved. In addition, the content of polyvinyl alcohol-based fibers, which are alkali-resistant fibers in the alkaline battery separator, may be 70% by weight or less, preferably 60% by weight or less, and even more preferably 50% by weight or less. The content of polyvinyl alcohol-based fibers, which are alkali-resistant fibers in the alkaline battery separator, may be, for example, 30 to 70% by weight, preferably 33 to 70% by weight, more preferably 35 to 60% by weight, and even more preferably 43 to 50% by weight. In this specification, the content of polyvinyl alcohol-based fibers, which are alkali-resistant fibers in alkaline battery separators, refers to the weight ratio of polyvinyl alcohol-based fibers based on the total weight of the separator.

[0037] The alkali-resistant fibers in the separator for alkaline batteries may include fibers other than polyvinyl alcohol-based fibers. Generally, examples of alkali-resistant fibers include alkali-resistant synthetic fibers, alkali-resistant organic fibers such as alkali-resistant cellulose fibers, and alkali-resistant inorganic fibers such as alkali-resistant glass fibers. Compared to inorganic fibers such as glass fibers, alkali-resistant organic fibers are preferred as alkali-resistant fibers constituting the separator because they have a lower elution rate into alkaline electrolytes.

[0038] Examples of alkali-resistant synthetic fibers other than polyvinyl alcohol-based fibers that can constitute a separator for alkaline batteries include polyolefin-based fibers (e.g., polypropylene fibers, polyethylene fibers, polypropylene-polyethylene composite fibers, etc.), polyamide-based fibers (e.g., polyamide 6 fibers, polyamide 66 fibers, polyamide 11 fibers, polyamide 610 fibers, polyamide 612 fibers, polyamide 9T fibers, polyamide 6T fibers, aramid fibers, polyamide-modified polyamide composite fibers, etc.). These fibers may be used individually or in combination of two or more types.

[0039] In the alkaline battery separator of the present invention, it is preferable that the alkali-resistant fibers further contain cellulosic fibers. Examples of cellulosic fibers include natural cellulose fibers (cotton, hemp, silk, wool, wood, etc.), regenerated cellulose fibers (rayon, polynosic, cupro, lyocell, etc.), and semi-synthetic cellulose fibers (acetate, triacetate, Promix, etc.). Furthermore, the cellulosic fibers may be cellulose fibers obtained by mercerizing natural cellulose fibers (e.g., natural wood fibers, cotton linter pulp, hemp pulp, etc.) (e.g., mercerized pulp, etc.) or cellulose fibers obtained by beating. These cellulosic fibers may be used alone or in combination of two or more types.

[0040] Among these cellulosic fibers, regenerated cellulose fibers are preferred. When regenerated cellulose fibers are included as alkali-resistant fibers, it is easier to achieve the desired paper thickness after papermaking, and it becomes easier to control the final thickness of the nonwoven fabric in the nonwoven fabric manufacturing process. Furthermore, among the regenerated cellulose fibers, it is preferable to use organic solvent-based cellulose fibers. Organic solvent-based cellulose fibers refer to regenerated fibers obtained by directly precipitating cellulose from a solution obtained by dissolving cellulose in an organic solvent without chemically altering it. For example, they can be produced by a method in which a spinning stock solution in which cellulose is dissolved in amine oxide is wet-dry spun in water to precipitate cellulose and obtain fibers, and then the obtained fibers are further stretched. A typical example of organic solvent-spun cellulose fiber is lyocell, which is sold by Lenzing AG in Austria under the trade name "Tencel" (registered trademark). Organic solvent-based cellulose fibers are suitable for use because fibrils are developed throughout the fiber, and good fibrillated products can be obtained by beating treatment.

[0041] Furthermore, mercerized cellulose fibers may be used as the cellulose fibers, for example, mercerized pulp may be used. Examples of mercerized pulp include mercerized pulps of hardwood pulp, softwood pulp, eucalyptus pulp, esparto pulp, cotton linter pulp, pineapple pulp, Manila hemp pulp, and sisal hemp pulp. Of these, mercerized pulps of natural wood fibers such as hardwood pulp and softwood pulp are preferred because they can provide a superior swelling suppression effect and are relatively inexpensive to obtain. The mercerized cellulose fibers may also be used as fibrillated products obtained by beating (for example, fibrillated products of mercerized pulp).

[0042] In the alkaline battery separator of the present invention, the alkali-resistant fibers may further contain fibrillated cellulose fibers. Fibrillated cellulose fibers can be obtained by beating unfibrillated fibers to a desired CSF value using a papermaking beating machine such as a beater, refiner, or high-speed beating machine. Among these, beating with a refiner is advantageous because, compared to beating with a beater or high-speed disintegrator, the mechanical structure allows for better capture and beating of the fibers, enabling efficient beating to the target CSF value in a short time. Furthermore, it is advantageous because it is less likely that the fibers will become too fine or, conversely, that thick fibers will remain, allowing for uniform finening of the entire fiber. Alternatively, fibrillated cellulose fibers may be obtained by subjecting a formed nonwoven fabric to a water entanglement treatment. The fibrillated cellulose fibers are preferably fibrillated regenerated cellulose fibers, and more preferably fibrillated organic solvent-based cellulose fibers.

[0043] The CSF value (Canadian Standard Freeness) of the fibrillated cellulosic fiber (preferably regenerated cellulose fiber, more preferably organic solvent-based cellulose fiber) may be, for example, 5 to 600 ml, preferably 6 to 400 ml, more preferably 7 to 100 ml, and even more preferably 8 to 19 ml. Since a smaller CSF value indicates a greater degree of beating, from the viewpoint of further improving shielding performance, it is preferable that the CSF value of the fibrillated cellulosic fiber be 19 ml or less. The CSF value is measured in accordance with JIS P 8121-2:2012 "Pulp - Methods for testing freeness - Part 2: Canadian Standard Freeness Method". Furthermore, the fibrillated cellulose fiber only needs to be fibrillated as a whole. For example, multiple types of fibers with different CSF values ​​(e.g., 2 to 4 types) may be combined to exhibit the predetermined CSF value mentioned above as a whole. In particular, by including fibrillated cellulose fibers as alkali-resistant fibers, for example, the fibrillated cellulose fibers, which have been finely subdivided by beating, become entangled in a support formed by polyvinyl alcohol fibers and polyvinyl alcohol binder fibers, thereby obtaining a separator with excellent shielding properties.

[0044] The content of cellulose fibers in the alkaline battery separator may be 20% by weight or more, preferably 25% by weight or more, and more preferably 30% by weight or more. Alternatively, the content of cellulose fibers in the alkaline battery separator may be 70% by weight or less, preferably 60% by weight or less, more preferably 50% by weight or less, and even more preferably 40% by weight or less. For example, the content of cellulose fibers in the alkaline battery separator may be 20 to 70% by weight, preferably 25 to 60% by weight, more preferably 30 to 50% by weight, and even more preferably 30 to 40% by weight. In this specification, the content of cellulose fibers in the alkaline battery separator means the weight ratio of cellulose fibers based on the total weight of the separator.

[0045] In the present invention, each alkali-resistant fiber constituting the separator can be appropriately selected and combined from the fibers exemplified above according to the desired physical properties, etc. The alkali-resistant fibers may include polyvinyl alcohol-based fibers and cellulose-based fibers. For example, by including polyvinyl alcohol-based fibers and cellulose-based fibers (preferably fibrillated cellulose-based fibers) as the main fibers constituting the separator, a nonwoven fabric with excellent shielding properties is obtained. In this specification, "main fibers" means fibers that do not have a binder function, that is, fibers other than binder fibers. When the separator contains polyvinyl alcohol-based fibers and cellulose-based fibers, the weight ratio of polyvinyl alcohol-based fibers to cellulose-based fibers may be, for example, 20 / 80 to 75 / 25 as polyvinyl alcohol-based fibers / cellulose-based fibers, preferably 25 / 75 to 70 / 30, and more preferably 30 / 70 to 60 / 40. By keeping the weight ratio of polyvinyl alcohol-based fibers to cellulose-based fibers within the above range, the nonwoven fabric can be made stiffer and its shielding properties can be improved.

[0046] The alkali-resistant fiber content in the alkaline battery separator may be 70% by weight or more, preferably 72% by weight or more, more preferably 75% by weight or more, and may also be 90% by weight or less, preferably 86% by weight or less, and more preferably 84% by weight or less, based on the total weight of the nonwoven fabric. The alkali-resistant fiber content in the alkaline battery separator may be, for example, 70 to 90% by weight, preferably 72 to 86% by weight, and more preferably 75 to 84% by weight. When the alkali-resistant fiber content is within the above range, the nonwoven fabric can be made stiffer and its alkali resistance can be improved. In this specification, the alkali-resistant fiber content in the alkaline battery separator means the ratio of the total weight of alkali-resistant fibers based on the total weight of the separator.

[0047] The total content of polyvinyl alcohol-based fibers and cellulose-based fibers in alkali-resistant fibers may be 90% by weight or more, preferably 95% by weight or more, more preferably 99% by weight or more, and even more preferably 100% by weight. When the total content of polyvinyl alcohol-based fibers and cellulose-based fibers in alkali-resistant fibers is within the above range, their hydrophilicity can further improve the electrolyte retention capacity. In this specification, the total content of polyvinyl alcohol-based fibers and cellulose-based fibers in alkali-resistant fibers means the ratio of the total weight of polyvinyl alcohol-based fibers and cellulose-based fibers that correspond to alkali-resistant fibers, based on the total weight of alkali-resistant fibers.

[0048] (Polyvinyl alcohol-based binder fibers) The alkaline battery separator of the present invention contains polyvinyl alcohol-based binder fibers, and the fiber width of the polyvinyl alcohol-based binder fibers, which are dyed with iodine, is 13 to 130 μm. In the present invention, it has been found that by bonding the polyvinyl alcohol-based binder fibers at the intersection with alkali-resistant fibers while keeping their fiber width within a specific range, the stiffness of the nonwoven fabric can be maintained, thereby improving the compressibility in the liquid-retaining state and the liquid retention when compressed. The fiber width of the polyvinyl alcohol-based binder fibers refers to the distance in the direction perpendicular to the fiber axis in the polyvinyl alcohol-based binder fibers while they are maintaining their fiber shape, and specifically refers to the value measured by the method described in the examples below. The nonwoven fabric constituting the separator contains not only polyvinyl alcohol-based binder fibers but also polyvinyl alcohol-based fibers as alkali-resistant fibers. However, due to differences in their crystallinity, only the polyvinyl alcohol-based binder fibers can be dyed with iodine. Therefore, polyvinyl alcohol-based binder fibers can be distinguished from polyvinyl alcohol-based fibers by whether or not they are dyed with iodine. In this invention, by measuring the fiber width of the polyvinyl alcohol-based binder fibers, it is possible to determine to what extent the flow of the vinyl alcohol-based polymer is suppressed during bonding and the fiber shape is maintained.

[0049] The fiber width of the polyvinyl alcohol-based binder fiber dyed with iodine may preferably be 20 to 120 μm, more preferably 30 to 100 μm, even more preferably 35 to 90 μm, and even more preferably 40 to 85 μm, from the viewpoint of further improving compressibility in a liquid-retaining state and further improving liquid retention during compression.

[0050] Polyvinyl alcohol-based binder fibers are binder fibers containing a vinyl alcohol-based polymer, and may also contain components other than the vinyl alcohol-based polymer. From the viewpoint of electrolyte retention and mechanical performance, polyvinyl alcohol-based binder fibers may contain 50% by weight or more of the vinyl alcohol-based polymer based on their total weight, preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 98% by weight or more.

[0051] In polyvinyl alcohol-based binder fibers, the vinyl alcohol-based polymer may contain constituent units other than vinyl alcohol units (e.g., ethylene units, vinyl ester units, etc.), but it is preferable that vinyl alcohol units make up 50 mol% or more of the total constituent units, more preferably 70 mol% or more, even more preferably 90 mol% or more, and even more preferably 95 mol% or more. For example, the vinyl alcohol-based polymer in polyvinyl alcohol-based binder fibers may consist only of vinyl alcohol units and optionally included vinyl ester units such as vinyl acetate units.

[0052] Polyvinyl alcohol-based binder fibers may be non-composite fibers, or they may be composite fibers such as core-sheath type fibers or sea-island type fibers that contain adhesive components as sheath or marine components. From the viewpoint of improving liquid retention by impregnating the electrolyte into the fiber interior due to the hydrophilicity of the vinyl alcohol-based polymer, non-composite fibers are preferable for polyvinyl alcohol-based binder fibers.

[0053] The fineness of the polyvinyl alcohol-based binder fibers is preferably 0.5 to 5.0 dtex, more preferably 1.0 to 5.0 dtex, even more preferably 1.5 to 5.0 dtex, even more preferably 1.7 to 4.7 dtex, particularly preferably 1.9 to 4.4 dtex, and particularly preferably 2.1 to 4.0 dtex. By using polyvinyl alcohol-based binder fibers having a specific fineness, it is possible to suppress the flow of the vinyl alcohol-based polymer during bonding, thereby making it possible to maintain the fiber width within a specific range.

[0054] The polyvinyl alcohol-based binder fibers may have an average fiber diameter of 6 to 23 μm, preferably 9 to 22 μm, more preferably 12 to 21 μm, even more preferably 13 to 20 μm, and even more preferably 15 to 20 μm. In this specification, the average fiber diameter of the polyvinyl alcohol-based binder fibers is the average value obtained by measuring the cross-sectional area of ​​the fiber cross-section perpendicular to the fiber axis and converting the diameter of that circle, assuming the fiber cross-section is a perfect circle, as the fiber diameter. Specifically, 100 polyvinyl alcohol-based binder fibers can be arbitrarily selected, measured using an optical microscope, and the average value obtained can be calculated as the average fiber diameter.

[0055] The average fiber length of the polyvinyl alcohol-based binder fibers can be appropriately set according to the type and fineness of the nonwoven fabric. For example, it can be selected from a wide range of about 0.1 to 70 mm, but from the viewpoint of water dispersibility during wet nonwoven fabric production, adhesion to alkali-resistant fibers, and the pore size of the resulting nonwoven fabric, it may be about 0.1 to 10 mm, and preferably about 1 to 6 mm.

[0056] The hot water dissolution temperature of the polyvinyl alcohol-based binder fiber may be in the range of 65 to 100°C, preferably 76 to 100°C, more preferably 76 to 99°C, even more preferably 78 to 98°C, and even more preferably 78 to 95°C. By using polyvinyl alcohol-based binder fibers having a hot water dissolution temperature within the above range, it becomes easier to adjust the adhesion of alkali-resistant fibers while maintaining the fiber width within a specific range. The hot water dissolution temperature of the polyvinyl alcohol-based binder fiber can be adjusted by the constituent units and degree of polymerization of the vinyl alcohol-based polymer contained. In this specification, the hot water dissolution temperature of the polyvinyl alcohol-based binder fiber is the value measured by the method described in the examples below.

[0057] It is believed that by increasing the fineness of the polyvinyl alcohol-based binder fibers within a specific range, raising its hot water dissolution temperature, reducing the moisture content before drying, lowering the drying temperature, or shortening the drying time, it is possible to prevent the polyvinyl alcohol-based binder fibers from completely dissolving, maintain the fiber width within a specific range, and point-bond only the intersections of the alkali-resistant fibers constituting the separator. This improves the compressive resistance in the liquid-retaining state and the liquid retention during compression. In particular, when adjusting the fiber width, it is preferable to set the fineness of the polyvinyl alcohol-based binder fibers within the specific range mentioned above.

[0058] The content of polyvinyl alcohol-based binder fibers in the separator for alkaline batteries may be 16 to 30% by weight, preferably 16 to 28% by weight, and more preferably 18 to 25% by weight. When the content of polyvinyl alcohol-based binder fibers is within the above range, the alkali-resistant fibers that constitute the main fibers of the separator can be sufficiently bonded to each other, thereby improving the mechanical strength of the separator and further improving its compressive strength. In addition, the hydrophilicity of the separator can be ensured, thereby improving its liquid retention. In this specification, the content of polyvinyl alcohol-based binder fibers in the separator for alkaline batteries refers to the weight ratio of polyvinyl alcohol-based binder fibers based on the total weight of the separator.

[0059] In alkaline battery separators, the total content of fibers containing vinyl alcohol-based polymer may be 40% by weight or more, preferably 48% by weight or more, and more preferably 55% by weight or more. In particular, from the viewpoint of further improving compressibility in the liquid-retaining state and further improving liquid retention during compression, it is preferable that it be 61% by weight or more. Also, the total content of fibers containing vinyl alcohol-based polymer in alkaline battery separators may be 80% by weight or less, preferably 75% by weight or less, and more preferably 70% by weight or less. For example, the total content of fibers containing vinyl alcohol-based polymer in alkaline battery separators may be 40 to 80% by weight, preferably 48 to 75% by weight, more preferably 55 to 70% by weight, and even more preferably 61 to 70% by weight. Fibers containing vinyl alcohol-based polymer include both polyvinyl alcohol-based fibers as alkali-resistant fibers and polyvinyl alcohol-based binder fibers as binder fibers. In this specification, the total content of fibers containing vinyl alcohol-based polymers in an alkaline battery separator refers to the ratio of the total weight of polyvinyl alcohol-based fibers and polyvinyl alcohol-based binder fibers based on the total weight of the separator.

[0060] (Nonwoven Fabric) The nonwoven fabric constituting the separator for alkaline batteries of the present invention includes the alkali-resistant fibers and binder fibers described above. The nonwoven fabric may also contain components that are neither alkali-resistant fibers nor binder fibers, to the extent that they do not impede the effects of the present invention. Examples of nonwoven fabrics include wet-laid nonwoven fabrics and dry-laid nonwoven fabrics. Of these nonwoven fabrics, wet-laid nonwoven fabrics are preferred, and paper is more preferred, because they can be made thin and can ensure strength and shielding properties.

[0061] The thickness of the nonwoven fabric (separator thickness) may be 40 to 120 μm, and from the viewpoint of thinning, it may be preferably 45 to 100 μm, more preferably 50 to 90 μm, and even more preferably 50 to 85 μm. In this specification, the thickness of the nonwoven fabric is the value measured by the method described in the examples below.

[0062] In a separator for alkaline batteries, the ratio of the fiber width (μm) of the polyvinyl alcohol-based binder fiber to the thickness (μm) of the nonwoven fabric (fiber width / thickness) may be 0.30 to 2.0, preferably 0.50 to 1.6, more preferably 0.60 to 1.4, and even more preferably 0.70 to 1.1.

[0063] The basis weight of the nonwoven fabric (separator basis weight) should be set appropriately according to the type of battery to be incorporated, for example, 10 to 50 g / m². ２ It may be, preferably 15 to 45 g / m² ２ More preferably 20 to 40 g / m ２ This may also be the case. In this specification, the basis weight of the nonwoven fabric is the value measured by the method described in the examples below.

[0064] The density of the nonwoven fabric (density of the separator) is 0.34 g / cm³. ３ It may be greater than or equal to 0.34 to 0.50 g / cm³, preferably 0.34 to 0.50 g / cm³. ３ (For example, 0.34 to 0.43 g / cm³) ３ , or 0.34-0.40 g / cm³ ３ ), more preferably 0.35 to 0.47 g / cm³ ３ (For example, 0.35 to 0.43 g / cm³) ３), more preferably 0.36 to 0.45 g / cm³ ３ (For example, 0.36 to 0.40 g / cm³) ３ ) may also be used. In this specification, the density of the nonwoven fabric is calculated by dividing the basis weight by the thickness, and specifically, it is the value measured by the method described in the examples below.

[0065] The air permeability of the nonwoven fabric (the air permeability of the separator) is 15 cc / cm². ２ It may be less than / sec. The air permeability of the nonwoven fabric represents its density and serves as an indicator of the separator's shielding ability. The air permeability of the nonwoven fabric can be controlled by adjusting the type and fineness of alkali-resistant fibers, the CSF value of cellulose fibers if they are included, the fiber width of polyvinyl alcohol fibers, the combination of each fiber and their ratios, etc. From the viewpoint of improving the separator's shielding ability, 10 cc / cm is preferable. ２ / sec or less, more preferably 5.0 cc / cm³ ２ Less than or equal to / sec, more preferably 1.5 cc / cm ２ It may be less than / sec. The lower limit of the air permeability of the nonwoven fabric is not particularly limited, but for example, 0.10 cc / cm ２ It may be greater than or equal to / sec. In this specification, the air permeability of the nonwoven fabric is a value measured by the method described in the examples below.

[0066] The separator for alkaline batteries may have a compression-resistant thickness of 15.0% or more, preferably 16.0% or more, more preferably 17.0% or more, even more preferably 18.0% or more, and even more preferably 20.0% or more, as determined by the method described in the examples below. There is no particular upper limit to the compression-resistant thickness, but for example, it may be 50.0% or less.

[0067] The separator for alkaline batteries may have an electrolyte (35% potassium hydroxide aqueous solution) absorption amount of 3.5 g / g or more, preferably 4.0 g / g or more, and more preferably 4.5 g / g or more, by the method described in the examples below. The upper limit of the electrolyte (35% potassium hydroxide aqueous solution) absorption amount is not particularly limited, but for example, it may be 10.0 g / g or less.

[0068] The separator for alkaline batteries may have a liquid retention rate of 28.0% or more when compressed by the method described in the examples below, preferably 35.0% or more. The upper limit of the liquid retention rate when compressed is not particularly limited, but for example, it may be 50.0% or less.

[0069] The separator for alkaline batteries may have a load resistance of 0.200 Ω or less, preferably 0.180 Ω or less, and more preferably 0.160 Ω or less, as determined by the method described in the embodiments below. The lower limit of the load resistance is not particularly limited, but may be, for example, 0.020 Ω or more.

[0070] [Method for Manufacturing Separators for Alkaline Batteries] The method for manufacturing separators for alkaline batteries of the present invention may include a slurry preparation step of preparing a slurry containing alkali-resistant fibers including polyvinyl alcohol fibers, polyvinyl alcohol binder fibers having a fineness of 0.5 to 5.0 dtex, and water; a papermaking step of obtaining wet paper from the obtained slurry by a papermaking method; and a drying step of drying the obtained wet paper while maintaining the fiber shape of the polyvinyl alcohol binder fibers.

[0071] In the method for manufacturing a separator for alkaline batteries, from the viewpoint of maintaining the fiber width of the polyvinyl alcohol-based binder fibers within a specific range, in the slurry preparation step, the fineness of the polyvinyl alcohol-based binder fibers is set to Adtex, the hot water dissolution temperature of the polyvinyl alcohol-based binder fibers is set to B°C, and the blending ratio of fibers containing vinyl alcohol-based polymer is set to C by weight. In the drying step, the moisture content of the wet paper is set to D by weight, the drying temperature is set to E°C, and the drying time is set to F seconds. The basis weight of the separator paper obtained after drying is set to G g / cm². ２ In that case, D × (E + 273.15) × F / { (A} １／２It is preferable that {B + 273.15} × C × G} is 4.0 or less. In the present invention, it has been found that by adjusting various conditions from the slurry preparation step to the drying step, the polyvinyl alcohol-based binder fibers can be melted to some extent in order to sufficiently bond the alkali-resistant fibers together, while the flow can be suppressed, thereby adjusting the fiber width of the polyvinyl alcohol-based binder fibers in the resulting separator paper. That is, as shown in the formula above, the finer the polyvinyl alcohol-based fibers are, and the higher the hot water dissolution temperature, the more their flow can be suppressed. Also, the higher the blending ratio of fibers containing vinyl alcohol-based polymers, and the higher the basis weight of the resulting separator paper, the more difficult it is to dry the wet paper, so the fiber width of the polyvinyl alcohol-based binder fibers tends to decrease. On the other hand, the lower the moisture content carried into the wet paper, the lower the drying temperature, and the shorter the drying time, the more difficult it is to dry the wet paper, so the fiber width of the polyvinyl alcohol-based binder fibers tends to decrease.

[0072] Furthermore, from the viewpoint of maintaining the fiber width of the polyvinyl alcohol-based binder fiber within a specific range, D × (E + 273.15) × F / { (A} １／２ D × (B + 273.15) × C × G} may preferably be 3.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less. Furthermore, from the viewpoint of improving the mechanical strength of the separator and further improving the compressive strength by fusing polyvinyl alcohol-based binder fibers and sufficiently bonding the alkali-resistant fibers together, D × (E + 273.15) × F / { (A １／２ {(B + 273.15) × C × G} may be, for example, 0.1 or more, preferably 0.2 or more, more preferably 0.4 or more, and even more preferably 0.6 or more. D × (E + 273.15) × F / {(A) １／２ The value of {×(B + 273.15) × C × G} may be 0.1 to 4.0, preferably 0.2 to 3.0, more preferably 0.4 to 2.0, and even more preferably 0.6 to 1.5.

[0073] The fineness of the polyvinyl alcohol-based binder fibers may be 0.5 to 5.0 dtex, preferably 1.0 to 5.0 dtex. Furthermore, a higher fineness of the polyvinyl alcohol-based binder fibers is preferable because it can suppress the flow of the vinyl alcohol-based polymer during bonding, making it easier to maintain the fiber width within a specific range. For example, the fineness of the polyvinyl alcohol-based binder fibers may more preferably be 1.5 to 5.0 dtex, even more preferably 1.7 to 4.7 dtex, even more preferably 1.9 to 4.4 dtex, and particularly preferably 2.1 to 4.0 dtex.

[0074] In the slurry preparation process, the above-mentioned alkali-resistant fibers and polyvinyl alcohol-based binder fibers can be used, and the amount of each can be adjusted according to the above-mentioned content ratios. For example, the blending ratio of fibers containing vinyl alcohol-based polymer in the slurry may be 40 to 80% by weight, preferably 48 to 75% by weight, more preferably 55 to 70% by weight, and even more preferably 61 to 70% by weight. Here, the blending ratio of fibers containing vinyl alcohol-based polymer refers to the ratio of the total weight of fibers containing vinyl alcohol-based polymer (polyvinyl alcohol-based fibers and polyvinyl alcohol-based binder fibers) based on the total weight of solids in the slurry. The slurry may be prepared by simultaneously dispersing the various fibers, such as alkali-resistant fibers and polyvinyl alcohol-based binder fibers, in water after mixing, or by mixing dispersions that have been separately dispersed in water.

[0075] In the papermaking process, wet paper can be obtained by known papermaking methods. For example, the slurry can be used to make paper using a general wet papermaking machine. Examples of screens used in the papermaking machine include circular screens, short screens, and long screens. These screens may be used individually to make single-layer paper, or they may be used individually or in combination of two or more to make multi-layer paper. Furthermore, if necessary, hydrophilization treatment using surfactants or the like may be performed to improve electrolyte absorption.

[0076] In the drying process, separator paper can be obtained by drying the resulting wet paper, and drying may be performed by contact drying using, for example, a Yankee-type dryer or a multi-cylinder dryer. In order to maintain the fiber shape of the polyvinyl alcohol-based binder fibers, in addition to the fineness mentioned above, it is also possible to control the fluidity of the vinyl alcohol-based polymer by adjusting the hot water dissolution temperature of the polyvinyl alcohol-based binder fibers. Furthermore, although it varies depending on the fineness and hot water dissolution temperature of the polyvinyl alcohol-based binder fibers, for example, methods such as adjusting the moisture content of the wet paper brought into the drying process, or adjusting the drying temperature and drying time in the drying process can be used. In this specification, the state in which the polyvinyl alcohol-based binder fibers maintain their fiber shape refers to a state in which the polyvinyl alcohol-based binder fibers are not completely dissolved, only the intersections of the alkali-resistant fibers constituting the separator are point-bonded, and the fiber width can be measured when the polyvinyl alcohol-based binder fibers are dyed.

[0077] For example, the moisture content of the wet paper brought into the drying process may be 50 to 90% by weight, preferably 55 to 85% by weight, and more preferably 60 to 80% by weight. The moisture content of the wet paper can be adjusted by, for example, installing a vacuum suction device during the process of transporting the wet paper obtained in the papermaking process to the dryer to absorb moisture from the wet paper until the desired moisture content is reached, squeezing out moisture from the wet paper using a press roll or the like until the desired moisture content is reached, controlling the moisture content of the felt that transports the wet paper, or using suction in the papermaking screen during the papermaking process.

[0078] The drying temperature and drying time in the drying process can be appropriately determined according to the type and structure of the dryer used, the moisture content of the wet paper, the type of binder fiber constituting the wet paper, its hot water dissolution temperature, and its content. For example, when polyvinyl alcohol-based binder fiber is used as the binder fiber constituting the wet paper, the drying temperature in contact drying using a Yankee-type dryer or the like may be 80 to 170°C, preferably 90 to 160°C, and more preferably 100 to 150°C. The drying time in contact drying using a Yankee-type dryer or the like may be, for example, 5 to 120 seconds, preferably 10 to 90 seconds, and more preferably 15 to 60 seconds. The drying time refers to the time the wet paper is in contact with the contact dryer.

[0079] [Alkaline Battery] The alkaline battery of the present invention (for example, a primary battery such as an alkaline manganese battery) is an alkaline battery comprising at least a positive electrode, a negative electrode, the above-described alkaline battery separator of the present invention disposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode may contain, for example, manganese dioxide as the positive electrode active material, and the negative electrode may contain, for example, zinc, zinc oxide, etc. as the negative electrode active material.

[0080] The alkaline battery of the present invention can be manufactured by various known or conventional manufacturing methods, as long as it is equipped with the alkaline battery separator of the present invention described above. Examples of the shape of the separator inside the alkaline battery include cross strip (cross-shaped cylindrical separator with a closed bottom), round strip (cylindrical separator with a wound core), and spiral (spirally wound separator).

[0081] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. In the following examples and comparative examples, various physical properties were measured by the methods described below.

[0082] [Fiber Fineness (dtex)] The single fiber fineness (dtex) was measured in accordance with JIS L 1015:2021 "Test Method for Chemical Fiber Staples" 8.5.1.

[0083] [Hot water dissolution temperature (°C)] A polyvinyl alcohol-based binder fiber with a test length of 5 cm was used as a sample, with a weight of 0.9 gf / 500 dtex attached to the tow. The sample was suspended in 500 cc of water (20°C), and the temperature was increased at a heating rate of 1°C / min until the fiber melted. The temperature at which the fiber broke was measured as the hot water dissolution temperature (°C).

[0084] [CSF value (ml)] The CSF value (ml) of cellulose fibers was measured in accordance with JIS P 8121-2:2012 "Pulp - Drainage test method - Part 2: Canadian standard drainage method".

[0085] [Moisture content of wet paper] For wet paper before drying, approximately 10 g of the sample was placed in a weighing bottle of known weight, and the lid was closed. The weight of the sample before drying (a) was measured. The sample, still in the weighing bottle, was placed in a drying oven adjusted to 105 ± 2°C. The lid of the weighing bottle was removed, and it was dried for 3 hours. After drying, the lid was closed in the drying oven, and it was placed in a desiccator to cool for 45 minutes. After cooling, the weight of the weighing bottle was measured, and the weight of the dried sample (b) was determined by the difference between the weight of the weighing bottle and the sample. The moisture content of the wet paper was calculated using the following formula: Moisture content (%) = (a - b) / a × 100

[0086] [Basal weight (g / m ２ )] In accordance with JIS P 8124:2011 "Paper and cardboard - Method for measuring basis weight", the basis weight (g / m²) of the obtained paper is calculated. ２ ) was measured.

[0087] [Thickness (μm) and density (g / cm³)] ３ )] In accordance with JIS P 8118:2014 "Paper and cardboard - Test methods for thickness, density and specific volume", the thickness (μm) and density (g / cm³) of the obtained paper were determined. ３ ) was measured.

[0088] [Fiber width (μm)] Each separator sample (30 mm x 30 mm) for measurement was immersed in a 0.05 mol / l iodine solution for 10 seconds. After that, the surface water of the sample was wiped off with a paper wiper, and it was air-dried for 1 hour. A plan view of the stained separator sample was photographed using a DIGITAL MICROSCOPE (Keyence Corporation). The width of the stained polyvinyl alcohol-based binder fibers was measured by measuring the distance between two points. Ten fibers were measured per field of view, and the average value of 10 fields of view (100 fibers in total) was calculated as the fiber width (μm).

[0089] [Permeability (cc / cm²)] ２ ( / sec)) Measurements were taken using a Fragile type tester in accordance with JIS L 1096 6.27 "General Textile Test Methods: Permeability". As an evaluation of the shielding performance of each separator sample, the permeability was set to 10 cc / cm². ２ If less than / sec, use A, 10cc / cm ２ If the value is greater than or equal to / sec, it is classified as B.

[0090] [Compression resistance thickness (%)] With five 40mm x 40mm separator samples stacked, the thickness was measured using a thickness measuring instrument (load 236g / cm²). ２ The thickness (original thickness) of the laminated sample was measured using a dial thickness gauge (H-type). After immersing the laminated sample in pure water adjusted to 20°C for 30 minutes, the laminated sample was removed from the pure water, and the thickness (thickness after swelling) of the laminated sample was measured using a thickness measuring instrument. The compression resistance thickness (%) was calculated using the following formula. Note that a higher compression resistance thickness indicates better compression resistance in the liquid-retaining state. As an evaluation of compression resistance in the liquid-retaining state, a compression resistance thickness of 18.0% or more was rated A, 15.0% or more and less than 18.0% was rated B, and less than 15.0% was rated C. Compression resistance thickness (%) = (thickness after swelling - original thickness) / original thickness × 100

[0091] [Electrolyte absorption amount (g / g)] A 50 mm x 50 mm separator sample, whose weight had been measured in advance, was immersed in a 35% potassium hydroxide (KOH) aqueous solution at a bath ratio of 1 / 100 for 30 minutes. The sample was removed from the KOH aqueous solution, and its weight was measured after 30 seconds of natural liquid drainage. The electrolyte absorption amount (g / g) was calculated by subtracting the sample weight before immersion from the sample weight after immersion, and then dividing the resulting weight of the retained liquid by the sample weight before immersion.

[0092] [Amount of liquid retained under pressure (g / g)] Five 50 mm x 50 mm separator samples, whose weights had been measured beforehand, were stacked and immersed in a 35% KOH aqueous solution at a bath ratio of 1 / 100 for 30 minutes. The stacked samples were removed from the KOH aqueous solution, sandwiched between filter paper on both sides, and then sandwiched between vinyl chloride plates on top of the filter paper. The stacked samples were then placed on a horizontal surface, and a 100 g weight was placed on the vinyl chloride plates and left for 1 minute. After that, the weight of the stacked samples was measured after removing the weight, vinyl chloride plates, and filter paper. The amount of liquid retained under pressure (g / g) was calculated by subtracting the weight of the stacked samples before immersion from the weight of the stacked samples after liquid retention, and then dividing the weight of the stacked samples before immersion by the weight of the stacked samples before immersion.

[0093] [Liquid Retention Rate under Compression (%)] Using the above electrolyte retention volume and compression volume, the liquid retention rate under compression (%) was calculated using the following formula. A higher liquid retention rate under compression indicates better liquid retention under compression. As an evaluation of liquid retention under compression, a liquid retention rate of 35.0% or higher was rated A, a rate of 28.0% or higher but less than 35.0% was rated B, and a rate of less than 28.0% was rated C. Liquid Retention Rate under Compression (%) = Compression Volume (g / g) / Electrolyte Absorption Volume (g / g) × 100

[0094] [Resistance under load] Five φ25 mm separator samples were immersed in a 35% KOH aqueous solution at a bath ratio of 1 / 100 for 30 minutes. After removing the samples from the KOH solution and allowing them to air dry for 30 seconds, the five samples were stacked and clamped with a fixing device, and the adapter terminal of an impedance meter was attached to the stacked sample. After compressing the stacked sample until the total thickness was 400 μm, the resistance value (Ω) of the separator stack was measured. This measurement was performed five times with different separator samples, and the average value of the obtained resistance values ​​was calculated as the resistance under load (Ω). Note that a smaller resistance under load means that the separator has better liquid retention when compressed, which prevents an increase in the internal resistance of the battery and contributes to improving the medium and high rate discharge performance. For the evaluation of compression resistance, a resistance under load of 0.180 Ω or less was designated as A, a resistance between 0.180 Ω and 0.200 Ω was designated as B, and a resistance above 0.200 Ω was designated as C.

[0095] (Example 1) (1) Preparation of slurry 1.7 dtex × 3 mm organic solvent-based cellulose fibers (Lyocell; Lenzing's "Tencel") were treated with a refiner and adjusted to 10 ml of CSF. 35% by weight of the fibrilized organic solvent-based cellulose fibers, 45% by weight of 0.39 dtex × 3 mm polyvinyl alcohol-based fibers (PVA; Kuraray Co., Ltd., Vinylon: VN30300), and 20% by weight of 2.7 dtex × 4 mm polyvinyl alcohol-based binder fibers (PVA; Kuraray Co., Ltd., Vinylon binder: VPB101×4) were dispersed in water to produce a slurry.

[0096] (2) Preparation of separator paper Using the slurry described above, papermaking was performed using a paper machine in a two-layer method to obtain wet paper. After adjusting the moisture content of the obtained wet paper to 71% by weight using a vacuum suction device and press rolls, it was dried in a Yankee-type dryer at a drying temperature of 130°C for 40 seconds, and then the thickness was adjusted between elastic rolls and metal rolls to obtain a basis weight of 29.8 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 82 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0097] (Example 2) 1. 7 dtex × 3 mm organic solvent-based cellulose fiber (Lyocell; Lenzing's "Tencel") was treated with a refiner to adjust the amount of CSF to 10 ml. The fibrillated content of the organic solvent-based cellulose fiber was changed to 39% by weight. 2. 7 dtex × 4 mm polyvinyl alcohol-based binder fiber (PVA; Kuraray, Vinylon Binder: VPB101 × 4) was changed to 16% by weight. Papermaking was carried out in the same manner as in Example 1 to obtain wet paper. After adjusting the moisture content of the obtained wet paper to 71% by weight, it was dried in a Yankee-type dryer at a drying temperature of 130°C for 40 seconds. Then, the thickness was adjusted between elastic rolls and metal rolls to obtain a basis weight of 29.7 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 82 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0098] (Example 3) 1. 7 dtex × 3 mm organic solvent-based cellulose fiber (Lyocell; Lenzing's "Tencel") was treated with a refiner to adjust the amount of CSF to 10 ml. The content of the fibrilized organic solvent-based cellulose fiber was changed to 50% by weight, the content of 0.39 dtex × 3 mm polyvinyl alcohol-based fiber (PVA; Kuraray Co., Ltd., Vinylon: VN30300) was changed to 34% by weight, and the content of 2.7 dtex × 4 mm polyvinyl alcohol-based binder fiber (PVA; Kuraray Co., Ltd., Vinylon binder: VPB101×4) was changed to 16% by weight. Papermaking was carried out in the same manner as in Example 1 to obtain wet paper. After adjusting the moisture content of the obtained wet paper to 72% by weight, it was dried in a Yankee-type dryer at a drying temperature of 130°C for 40 seconds, and then the thickness was adjusted between elastic rolls and metal rolls to obtain a basis weight of 30.4 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 82 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0099] (Example 4) 1. 7 dtex × 3 mm organic solvent-based cellulose fiber (Lyocell; Lenzing's "Tencel") was treated with a refiner to adjust the amount of CSF to 10 ml. The content of the fibrilized organic solvent-based cellulose fiber was changed to 55% by weight, the content of 0.39 dtex × 3 mm polyvinyl alcohol-based fiber (PVA; Kuraray Co., Ltd., Vinylon: VN30300) was changed to 25% by weight, and the content of 2.7 dtex × 4 mm polyvinyl alcohol-based binder fiber (PVA; Kuraray Co., Ltd., Vinylon binder: VPB101×4) was changed to 20% by weight. Papermaking was carried out in the same manner as in Example 1 to obtain wet paper. After adjusting the moisture content of the obtained wet paper to 71% by weight, it was dried in a Yankee-type dryer at a drying temperature of 130°C for 40 seconds. Then, the thickness was adjusted between elastic rolls and metal rolls to obtain a basis weight of 30.3 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 81 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0100] (Example 5) Except that 1.7 dtex × 3 mm organic solvent-based cellulose fiber (Lyocell; Lenzing's "Tencel") was treated with a refiner to change it into a fibrilized organic solvent-based cellulose fiber adjusted to 300 ml of CSF, papermaking was carried out in the same manner as in Example 1 to obtain wet paper. After adjusting the moisture content of the obtained wet paper to 71% by weight, it was dried in a Yankee-type dryer at a drying temperature of 130°C for 40 seconds, and then the thickness was adjusted between elastic rolls and metal rolls to obtain a basis weight of 32.2 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 86 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0101] (Example 6) Papermaking was carried out using the same composition and method as in Example 1 to obtain wet paper. The moisture content of the obtained wet paper was adjusted to 71% by weight, and after drying in a Yankee-type dryer at a drying temperature of 145°C for 40 seconds, the thickness was adjusted between elastic rolls and metal rolls to a basis weight of 30.8 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 82 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0102] (Example 7) Papermaking was carried out in the same manner as in Example 1, except that the polyvinyl alcohol-based binder fibers (PVA; manufactured by Kuraray Co., Ltd., vinylon binder: VPB105-1x3) were changed to 1.1 dtex x 3 mm, and wet paper was obtained. After adjusting the moisture content of the obtained wet paper to 65% by weight, it was dried in a Yankee-type dryer at a drying temperature of 140°C for 20 seconds, and then the thickness was adjusted between elastic rolls and metal rolls to a basis weight of 30.3 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 79 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0103] (Example 8) Papermaking was carried out using the same composition and method as in Example 7 to obtain wet paper. The moisture content of the obtained wet paper was adjusted to 60% by weight, and after drying in a Yankee-type dryer at a drying temperature of 130°C for 40 seconds, the thickness was adjusted between elastic rolls and metal rolls to a basis weight of 30.5 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 80 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0104] (Example 9) Papermaking was carried out in the same manner as in Example 1, except that the polyvinyl alcohol-based binder fibers (PVA; manufactured by Kuraray Co., Ltd., vinylon binder: VPB102 x 5) were changed to 1.1 dtex x 5 mm, and wet paper was obtained. After adjusting the moisture content of the obtained wet paper to 80% by weight, it was dried in a Yankee-type dryer at a drying temperature of 140°C for 80 seconds, and then the thickness was adjusted between elastic rolls and metal rolls to a basis weight of 30.7 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 80 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0105] (Comparative Example 1) (1) Preparation of Slurry 1.7 dtex × 3 mm organic solvent-based cellulose fibers (Lyocell; Lenzing's "Tencel") were treated with a refiner and adjusted to 10 ml of CSF. 35% by weight of the fibrilized organic solvent-based cellulose fibers, 45% by weight of 0.6 dtex × 3 mm polypropylene fibers (PP; Yamato Spinning Co., Ltd., PolyPro), and 20% by weight of 2.7 dtex × 4 mm polyvinyl alcohol-based binder fibers (PVA; Kuraray Co., Ltd., Vinylon Binder: VPB101×4) were dispersed in water to produce a slurry.

[0106] (2) Preparation of separator paper Using the slurry described above, papermaking was performed using a paper machine in a two-layer method to obtain wet paper. After adjusting the moisture content of the obtained wet paper to 76% by weight using a vacuum suction device and press rolls, it was dried in a Yankee-type dryer at a drying temperature of 130°C for 40 seconds, and then the thickness was adjusted between elastic rolls and metal rolls to obtain a basis weight of 26.8 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 81 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0107] (Comparative Example 2) (1) Preparation of Slurry 1.7 dtex × 3 mm organic solvent-based cellulose fibers (Lyocell; Lenzing's "Tencel") were treated with a refiner and adjusted to 10 ml of CSF. 35% by weight of the fibrilized organic solvent-based cellulose fibers, 45% by weight of 0.39 dtex × 3 mm polyvinyl alcohol-based fibers (PVA; Kuraray Co., Ltd., Vinylon: VN30300), and 20% by weight of 1.1 dtex × 3 mm polyvinyl alcohol-based binder fibers (PVA; Kuraray Co., Ltd., Vinylon Binder: VPB105-1×3) were dispersed in water to produce a slurry.

[0108] (2) Preparation of separator paper Using the slurry described above, papermaking was performed using a paper machine in a two-layer method to obtain wet paper. After adjusting the moisture content of the obtained wet paper to 71% by weight using a vacuum suction device and press rolls, it was dried in a Yankee-type dryer at a drying temperature of 130°C for 40 seconds, and then the thickness was adjusted between elastic rolls and metal rolls to obtain a basis weight of 29.9 g / m². ２A separator for alkaline batteries made of paper with a thickness of 82 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0109] (Comparative Example 3) (1) Preparation of Slurry 1.7 dtex × 3 mm organic solvent-based cellulose fibers (Lyocell; Lenzing's "Tencel") were treated with a refiner and adjusted to 10 ml of CSF. 35% by weight of the fibrilized organic solvent-based cellulose fibers, 45% by weight of 0.39 dtex × 3 mm polyvinyl alcohol-based fibers (PVA; Kuraray Co., Ltd., Vinylon: VN30300), and 20% by weight of 1.1 dtex × 4 mm polyvinyl alcohol-based binder fibers (PVA; Kuraray Co., Ltd., Vinylon Binder: VPB105-2×4) were dispersed in water to produce a slurry.

[0110] (2) Preparation of separator paper Using the slurry described above, papermaking was performed in two layers using a paper machine to obtain wet paper. After adjusting the moisture content of the obtained wet paper to 69% by weight using a vacuum suction device and press rolls, it was dried in a Yankee-type dryer at a drying temperature of 130°C for 40 seconds, and then the thickness was adjusted between elastic rolls and metal rolls to a basis weight of 29.5 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 82 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0111] (Comparative Example 4) Papermaking was carried out using the same composition and method as in Comparative Example 2 to obtain wet paper. The moisture content of the obtained wet paper was adjusted to 71% by weight, and after drying in a Yankee-type dryer at a drying temperature of 110°C for 120 seconds, the thickness was adjusted between elastic rolls and metal rolls to a basis weight of 30.1 g / m². ２ A separator for alkaline batteries made of paper with a thickness of 80 μm was obtained. The results of various measurements and evaluations of the obtained alkaline battery separator are shown in Table 1.

[0112]

[0113] As shown in Table 1, the alkaline battery separators of Examples 1 to 8 contain polyvinyl alcohol-based fibers as alkali-resistant fibers and polyvinyl alcohol-based binder fibers as binder fibers, and because the fiber width of the polyvinyl alcohol-based binder fibers is within a specific range, they have excellent compressibility in a liquid-retaining state and liquid retention under pressure.

[0114] In particular, the alkaline battery separators of Examples 1-4 and 6-8 contain fibrilized cellulose fibers with lower CSF values, resulting in superior liquid retention under compression and excellent shielding properties. Furthermore, the alkaline battery separators of Examples 1-3 and 5-8 have a high content of polyvinyl alcohol-based fibers as alkali-resistant fibers, which gives the entire nonwoven fabric stiffness, resulting in superior compression resistance in a liquid-retaining state.

[0115] Furthermore, the alkaline battery separators of Examples 1, 2, and 5-8 have a more precise control over the fiber width of the polyvinyl alcohol-based binder fibers, allowing them to maintain their fiber shape. Due to the high content of fibers containing vinyl alcohol-based polymers (polyvinyl alcohol-based fibers and polyvinyl alcohol-based binder fibers), they exhibit excellent compression resistance and can contribute to improved medium- and high-rate discharge performance.

[0116] On the other hand, the alkaline battery separator of Comparative Example 1 does not use polyvinyl alcohol-based fibers as alkali-resistant fibers, but rather polypropylene fibers, and therefore has poor liquid retention under compression and poor compression resistance.

[0117] Furthermore, the alkaline battery separators of Comparative Examples 2 and 3 use low-fiber polyvinyl alcohol-based binder fibers, and because the moisture content is high relative to the low fineness, the fiber width of the polyvinyl alcohol-based binder fibers becomes too large to be measured, and the fiber shape cannot be maintained. As a result, the compression resistance is poor, and the liquid retention during compression is insufficient.

[0118] In Comparative Example 4, the alkaline battery separator is dried at a relatively low temperature, allowing the polyvinyl alcohol-based binder fibers to maintain their shape. However, the long drying time results in excessively large fiber widths. Consequently, it exhibits poor compression resistance and insufficient liquid retention under compression.

[0119] The alkaline battery separator of the present invention is considered to have excellent medium- and high-rate discharge performance because it exhibits superior compressibility in the liquid-retaining state and liquid retention under pressure. Alkaline batteries equipped with such a separator can achieve good discharge characteristics.

[0120] As described above, preferred embodiments of the present invention have been explained, but those skilled in the art will readily anticipate various changes and modifications within the obvious scope by reviewing this specification. Therefore, such changes and modifications will be interpreted as falling within the scope of the invention as defined by the claims.

Claims

1. A separator for alkaline batteries comprising a nonwoven fabric containing alkali-resistant fibers and polyvinyl alcohol-based binder fibers, wherein the alkali-resistant fibers include polyvinyl alcohol-based fibers, and the fiber width of the polyvinyl alcohol-based binder fibers, which are dyed with iodine, is 13 to 130 μm.

2. A separator for alkaline batteries according to claim 1, wherein the polyvinyl alcohol-based binder fiber comprises a vinyl alcohol-based polymer containing 70 mol% or more of constituent units derived from vinyl alcohol.

3. A separator for alkaline batteries according to claim 1, wherein the polyvinyl alcohol-based binder fiber is a non-composite fiber.

4. A separator for alkaline batteries according to claim 1, wherein the hot water dissolution temperature of the polyvinyl alcohol-based binder fiber is in the range of 76 to 100°C.

5. A separator for alkaline batteries according to claim 1, wherein the content of the polyvinyl alcohol-based fiber, which is an alkali-resistant fiber in the separator, is 30% by weight or more.

6. A separator for alkaline batteries according to claim 1, wherein the content of the polyvinyl alcohol-based binder fibers in the separator is 16 to 30% by weight.

7. A separator for alkaline batteries according to claim 1, wherein the alkali-resistant fibers further comprise cellulose fibers.

8. A separator for alkaline batteries according to claim 7, wherein the cellulose fiber is a fibrillated product.

9. A separator for alkaline batteries according to claim 8, wherein the CSF value of the fibrilized material is 5 to 600 ml.

10. A separator for alkaline batteries according to claim 1, wherein the thickness is 40 to 120 μm.

11. A separator for alkaline batteries according to claim 1, wherein the density is 0.34 g / cm³. ３ That concludes the explanation of the separator for alkaline batteries.

12. A separator for alkaline batteries according to claim 1, wherein the total content of fibers containing a vinyl alcohol-based polymer is 40% by weight or more.

13. A separator for alkaline batteries according to claim 1, wherein the compression resistance thickness is 15.0% or more.

14. An alkaline battery comprising the separator for alkaline batteries described in any one of claims 1 to 13.

15. A method for manufacturing a separator for alkaline batteries, comprising: a slurry preparation step of preparing a slurry containing alkali-resistant fibers including polyvinyl alcohol fibers, polyvinyl alcohol binder fibers having a fineness of 0.5 to 5.0 dtex, and water; a papermaking step of obtaining wet paper from the obtained slurry by a papermaking method; and a drying step of drying the obtained wet paper while maintaining the fiber shape of the polyvinyl alcohol binder fibers, wherein in the slurry preparation step, the fineness of the polyvinyl alcohol binder fibers is Adtex, the hot water dissolution temperature of the polyvinyl alcohol binder fibers is B°C, and the blending ratio of fibers containing vinyl alcohol polymer is C by weight; in the drying step, the moisture content of the wet paper is D by weight, the drying temperature is E°C, and the drying time is F seconds; and the basis weight of the separator paper obtained after drying is G g / cm². ２ In that case, D × (E + 273.15) × F / { (A} １／２ A method for manufacturing an alkaline battery separator, wherein {B + 273.15} × C × G} is 4.0 or less.

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