JP4585791B2 - Separator for organic electrolyte battery - Google Patents

Description

  The present invention relates to a separator for an organic electrolyte battery composed of a nonwoven fabric that can be suitably used for an organic electrolyte battery, particularly a lithium ion secondary battery.

  Secondary batteries represented by alkaline secondary batteries and organic electrolyte secondary batteries have been actively developed because of recent IT (information technology) and problems with resources and the environment. In particular, lithium ion secondary batteries that use organic electrolytes have a large market in response to demands such as reduction in size and weight of products because they have high voltage, high capacity, and high output but are light in mass. Furthermore, the development of batteries for hybrid vehicles (HEV) and electric vehicles (PEV) is also in progress. The lithium ion secondary battery includes a positive electrode made of a composite metal oxide capable of occluding and releasing lithium ions, a negative electrode made of a carbon material capable of occluding and releasing lithium ions, a separator, an organic material It consists of electrolyte solution. In particular, in a lithium ion secondary battery, an electrode obtained by electrochemically alloying lithium and another metal in the presence of an electrolytic solution may be used in order to improve battery performance. However, in this alloyed electrode, the lithium alloy is pulverized during alloying, and the pulverized alloy passes through the separator and reaches the other electrode to cause a short circuit (hereinafter referred to as a fine powder short circuit). There is a problem. For this reason, in order to prevent a fine powder short circuit, the separator with especially small hole diameter is requested | required. On the other hand, as the battery is repeatedly charged and discharged, the fine powder grows in a needle shape on the electrode, and finally breaks through the separator to cause a short circuit (hereinafter referred to as a dendrite short circuit). Therefore, the separator is required to have a sheet having a high strength against piercing (hereinafter referred to as piercing strength).

  Further, as one of the factors determining the battery life of the secondary battery, there is the number of electrodes or the total area of the electrodes per battery volume, and the number of electrodes or the total area of the electrodes is reduced by reducing the thickness of the electrode and the separator. To increase the battery life. Therefore, a thin separator is also required.

  A microporous membrane is currently used to satisfy these requirements simultaneously. However, the microporous membrane is complicated in manufacturing process and expensive. For this reason, an inexpensive non-woven fabric that can replace the microporous membrane and simultaneously satisfies the piercing strength and thickness has been studied.

  Various studies have been made on nonwoven fabrics used in separators for organic electrolyte batteries. For example, as a separator for an organic electrolyte battery using a wet nonwoven fabric containing split-type composite fibers, Patent Document 1 listed below discloses split-type composite fibers containing at least one component of ethylene-vinyl alcohol copolymer, and heat. A non-aqueous electrolyte battery separator has been proposed in which a polyalkylene-modified polysiloxane is supported by a chemical bond on a wet nonwoven fabric obtained by mixing fused fibers and dividing divided composite fibers. Patent Document 2 below proposes a separator for a non-aqueous electrolyte battery made of a wet nonwoven fabric mainly composed of plate-like ultrafine fibers obtained by dividing a split type composite fiber.

On the other hand, the following patent documents 3 to 6 propose a separator made of a nonwoven fabric obtained by wet-heat bonding an ethylene-vinyl alcohol copolymer.
JP 2000-285895 A JP 2001-283821 A JP-A-3-257755 JP 63-235558 A Japanese Patent Laid-Open No. 5-109397 Japanese Patent Laid-Open No. 8-138645

The separator of Patent Document 1 is prepared by once preparing a wet nonwoven fabric having a constant basis weight of 12 to 14 g / m ² containing split composite fibers, and then impregnating it with an aqueous polyalkylene-modified polysiloxane solution. An attempt is made to reduce the pore size. However, it is difficult to make the average pore diameter and the maximum pore diameter of the nonwoven fabric uniform, and the nonwoven fabric has a large variation in the pore diameter, and thus a stable piercing strength cannot be obtained. Furthermore, using a split type composite fiber containing at least one component of an ethylene-vinyl alcohol copolymer and a wet nonwoven fabric mixed with a heat fusion fiber, the processing temperature is raised to a temperature at which the heat fusion fiber exhibits adhesive force. Since the heat calender treatment is performed in a dry manner, it depends on the adhesive strength of only the heat-sealing fibers, and the piercing strength is insufficient. In the separator of Patent Document 2, after splitting a split type composite fiber composed of two components of polypropylene / polyester, nylon 66 / polyester, and polypropylene / polyethylene to express a plate-like ultrafine fiber, the melting point of the low melting point component is exceeded. Only a heat calender treatment was applied dry at a low temperature. Therefore, it is difficult to make the average pore diameter and the maximum pore diameter of the nonwoven fabric uniform, and since the nonwoven fabric has a large variation in pore diameter, a stable piercing strength cannot be obtained. In addition, a split-type composite fiber having a layered cross-sectional structure is divided into two plate-like ultrafine fibers having parallel long sides, but the layered cross-section is flatter than the radial cross-section. Since the surface area of the plate-like portion is different between the vicinity of the center and the surface of the fiber cross section before the division, the average pore diameter and the maximum pore diameter vary. In order to obtain finer ultrafine fibers from a split type composite fiber having a layered cross-sectional structure, the number of layers (number of splits) may be increased. However, since the thickness of each layer becomes thin, spinning becomes difficult, and eight splits or 11 Only a divisional degree can be obtained, and there is a limit to fineness. In addition, the maximum pore diameter is about 14 to 18 μm, which is not sufficient as an organic electrolyte battery separator.

  Patent Documents 3 to 6 disclose separators using wet-heat adhesive fibers, but all are intended for alkaline battery separators and have a small pore size as required for organic electrolyte batteries. It is difficult to get.

  The present invention has been made in view of such circumstances, and provides a separator for an organic electrolyte battery that can reduce the average pore diameter and the maximum pore diameter of the nonwoven fabric, and is uniform, yield, and battery defect rate. To do.

The separator for an organic electrolyte battery of the present invention is composed of two or more components of a wet heat gelled resin component that can be gelled by heating in the presence of moisture and another resin component, and each component is radially divided into a plurality of components. A separator for an organic electrolyte battery comprising a nonwoven fabric containing a wet heat gelled ultrafine fiber and other ultrafine fibers into which the split composite fiber is split, wherein the wet heat gelled ultrafine fiber and the other ultrafine fibers are are Wari繊radially 20 or more composite fiber total per one, the wet heat gelling ultrafine fibers are formed into a film-like gel products which are pushed open by wet heat gelling, and fix the fibers constituting the nonwoven fabric It is characterized by that.

  In the present invention, a desired average pore diameter and maximum pore diameter are obtained by fixing the constituent fibers of a nonwoven fabric with a film-like gelation product formed by wet-heat gelation of a resin having a property that can be gelled by heating in the presence of moisture. It is possible to obtain an organic electrolyte battery that is excellent in safety, has few short circuits, and has excellent battery characteristics. Furthermore, the present invention uses a split type composite fiber that is radially divided into 20 or more as a starting material, and when used with a split nonwoven fabric, when a substantially wedge-shaped ultrafine fiber is gelled, it easily spreads into a film, The average pore size and the maximum pore size can be optimized. In addition, from the wet papermaking stage, substantially wedge-shaped ultrafine fibers are accumulated in parallel along the surface direction of the nonwoven fabric, and the average pore diameter and the maximum pore diameter are easily uniformized. Further, since the surface area of the substantially wedge-shaped ultrafine fiber after splitting is uniform, the average pore diameter and the maximum pore diameter can be easily uniformized.

  As a result of diligent research, the present inventors have obtained a separator made of a non-woven fabric that is difficult to short-powder fine powder, not only by simply reducing the pore diameter, but also by optimizing the respective ranges of the average pore diameter and the maximum pore diameter. Inspired by good things. For this purpose, it has been found that the shrinkage when the non-woven fabric is heat-processed to reduce the pore size is small, and the binder resin is fixed substantially uniformly in the thickness direction of the non-woven fabric. In order to obtain such a nonwoven fabric, by using a specific heat processing method, gelling the wet heat gelled resin and fixing other fibers, the basis weight and thickness unevenness are reduced, and the piercing strength is increased, It has been clarified that a separator with excellent yield in separator production, a low defective product rate of battery, and particularly excellent dendrite short-circuit prevention property can be obtained because the variation in piercing strength is suppressed, and further, conventional microporous It has been found that an inexpensive separator can be obtained compared to a membrane. Hereinafter, the separator for an organic electrolyte battery of the present invention will be described in detail.

  In order to obtain a non-woven fabric having a small pore diameter, a method is used in which a resin softened or melted by applying heat is expanded by a thermocompression bonding means such as a hot roll at a certain pressure or more to fill the interfiber spaces. However, the conventional heat-meltable resin needs to be heated to a temperature higher than the melting point of the heat-meltable resin, and the dimensional change of the nonwoven fabric becomes large due to heat shrinkage accompanying the melting of the heat-meltable resin. As a result, the yield deteriorates, or the variation in the basis weight, thickness, hole diameter, piercing strength, etc. increases, so the defective product rate of the battery, in particular, the short-circuit prevention property is poor. In addition, when a hot roll is used, the surface of the nonwoven fabric is in a dense state with many fusions, the inside tends to be in a rough state with little fusion, and the electrolyte retention is difficult to be uniform. It was easy to contribute to worsening the rate.

  Therefore, in the present invention, instead of the conventional heat-meltable resin, a wet heat gelled resin that gels and swells in the presence of moisture is used, and the wet heat gelled resin component is one component, and each component is radially divided into a plurality of components. A membrane-like gel that is spread when wet-heat gelled by forming a wet-heat gelled ultrafine fiber having a substantially wedge-shaped cross-sectional shape obtained by radially dividing a segmented composite fiber into 20 or more. It is easy to form a compound. And the constituent fiber of the nonwoven fabric was fixed with the expanded gel-like gel, and the range of the average pore diameter and the maximum pore diameter was optimized. By fixing the constituent fibers of the nonwoven fabric with a gelled product, the piercing strength of the separator is increased, the separator is not easily broken during battery assembly, and the dendrite short-circuit prevention property is excellent. Furthermore, by optimizing the range of the average pore diameter and the maximum pore diameter, the fine powder short circuit prevention property is excellent. The gelled product in the present invention refers to a resin (solidified product) that has been solidified after the wet heat gelled resin is gelled by wet heat, and the separator of the organic electrolyte battery of the present invention is composed of the fibers constituting the separator. It is fixed with gelled material. In the present invention, the “substantially wedge-shaped cross-sectional shape” refers to a cross-sectional shape obtained by radially dividing a split type composite fiber in which each component is radially divided into a plurality of pieces into 20 or more, and deformation is also allowed. Means that

  The resin that can be gelled by heating in the presence of moisture (wet heat gelling resin) used in the separator for an organic electrolyte battery of the present invention is a gel that swells and gels at a temperature of 60 ° C. or higher in the presence of moisture. A resin capable of fixing a constituent fiber of a non-woven fabric as a compound. Since the battery is used in various environments, if it is gelled at less than 60 ° C., the stability of the battery is deteriorated. Any resin may be used as long as it has such properties. Among them, an ethylene-vinyl alcohol copolymer having a specific composition is suitable for wet heat gel processability, water resistance, and dimensional stability during nonwoven fabric processing. Is particularly preferable.

  An ethylene-vinyl alcohol copolymer is a copolymer obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree is preferably 95% or more. A more preferable lower limit of the degree of saponification is 98%. If the degree of saponification is less than 95%, the spinnability tends to deteriorate during fiber formation. Moreover, since it becomes easy to gelatinize also at low temperature, it becomes easy to generate | occur | produce a trouble in a fiber manufacture and a nonwoven fabric processing process. Furthermore, when incorporated in a battery, the chemical stability in the electrolyte is poor, or the stability at high temperatures is poor.

  The ethylene content in the ethylene-vinyl alcohol copolymer is preferably in the range of 20 mol% to 50 mol%. A more preferable lower limit of the ethylene content is 25 mol%. The upper limit of more preferable ethylene content is 45 mol%. If the ethylene content is less than 20 mol%, the spinnability is poor and softening tends to occur, and troubles are likely to occur in the fiber production and nonwoven fabric processing steps. Furthermore, when incorporated in a battery, the chemical stability in the electrolyte is poor, or the stability at high temperatures is poor. On the other hand, if the ethylene content exceeds 50 mol%, the wet heat gelation temperature becomes high, and in order to obtain the desired average pore diameter and maximum pore diameter, the processing temperature must be increased to the vicinity of the melting point, resulting in the dimensions of the nonwoven fabric. May have a negative impact on stability.

  The wet heat gelled resin used in the present invention is composed of two or more components of the wet heat gelled resin component and other resin components other than the wet heat gelled resin, and each component is divided into a plurality of pieces in a radial manner. Takes the form of mold composite fiber. A split type composite fiber in which each component is radially divided into a plurality of fibers can be split to obtain wet heat gelled ultrafine fibers and other ultrafine fibers having a substantially wedge-shaped cross-sectional shape. Since the obtained ultrafine fibers are substantially wedge-shaped, the surface area is uniform and the wedge-shaped ultrafine fibers accumulated in parallel along the surface direction of the non-woven fabric are gelled by heat and moisture, so that the expanded film shape The gelled product can be easily formed, and the average pore size and the maximum pore size of the nonwoven fabric can be easily optimized.

  The split type composite fiber is radially divided into 20 or more in total per one composite fiber. A preferable split fiber number is 22 or more. When the number of split fibers of the composite fiber is increased, the substantially wedge-shaped shape is further flattened, the fineness can be reduced, and a film-like gelled product tends to be easily formed. The upper limit of the number of split fibers of the composite fiber is 40 or less in consideration of fiber productivity.

  It is preferable that the fineness of the wet heat gelled ultrafine fiber and the other ultrafine fiber into which the split composite fiber is split is in a range of 0.01 dtex or more and 0.08 dtex or less. A more preferable ultrafine fiber is 0.02 dtex or more. A more preferable ultrafine fiber is 0.06 dtex or less. By setting the fineness of the ultrafine fiber within the above range, when the wet heat gelled ultrafine fiber becomes a gelled product, the other fiber is fixed by expanding it into a film without closing the gap between the fibers more than necessary. be able to. Furthermore, since the other ultrafine fibers remain without being subjected to wet heat gelation, voids can be maintained in the nonwoven fabric. For example, a split type composite fiber of 0.5 to 1.5 dtex is obtained using a split type spinning nozzle of about 20 to 30 splits, preferably about 22 to 26 splits, and this is split and expressed.

  Moreover, it is preferable that the short axis thickness (maximum thickness of a wedge-shaped cross section) of the wet heat gelled ultrafine fiber and other ultrafine fibers is in a range of 0.7 μm or more and 2.2 μm or less. This is because the flat direction of the fibers is oriented in the surface direction of the nonwoven fabric when formed on the nonwoven fabric. For the same reason, the length of the wedge-shaped section is preferably at least twice the maximum thickness of the wedge-shaped section.

  The wet heat gelled resin is preferably contained within a range of 10 mass% to 50 mass% with respect to the entire separator. Here, the content of the wet heat gelled resin is not limited to the case where the split type composite fiber remains completely unbroken except the wet heat gelled ultrafine fiber that is completely split. This is because even if it is not fine, it is possible to obtain a gelled product by wet heat gelation. The content of the wet heat gelling resin is more preferably 15 mass% or more, and still more preferably 20 mass% or more. The content of the wet heat gelling resin is more preferably 45 mass% or less, and still more preferably 40 mass% or less. If the content of the wet heat gelled resin is less than 10 mass%, even if the wet heat gelation is performed, the gelled product spreads uniformly in the nonwoven fabric, and it becomes difficult to sufficiently penetrate between the constituent fibers. As a result, it becomes difficult to optimize the range of the average hole diameter and the maximum hole diameter, and the piercing strength tends to vary easily. In particular, it is difficult to reduce the maximum hole diameter. Furthermore, since the fixed part of the fiber which comprises a nonwoven fabric decreases, a piercing strength may also become small. On the other hand, when the content of the wet heat gelled resin exceeds 50 mass%, the surface of the nonwoven fabric is easily formed into a film, the electrolytic solution holding ability is lowered, and the internal resistance of the battery may be increased. Furthermore, during the gel processing, the wet heat gelled resin tends to adhere to a roll or the like, and the nonwoven fabric production process tends to deteriorate.

  The other resin in the split type composite fiber may be compatible with the wet heat gelled resin, but incompatible resin is preferred in consideration of splitting property. As the resin incompatible with the wet heat gelled resin, for example, polypropylene, polyethylene, polymethylpentene, and copolymers thereof are preferable, and polypropylene is particularly preferable from the viewpoint of fiber production and stability to the battery electrolyte.

  The other ultrafine fibers are preferably contained within a range of 10 mass% to 50 mass% with respect to the entire separator. More preferably, the content of other ultrafine fibers is 15 mass% or more, and even more preferably, 20 mass% or more. More preferably, the content of other ultrafine fibers is 45 mass% or less, and even more preferably, 40 mass% or less. If the content of the other ultrafine fibers is less than 10 mass%, the fineness of the nonwoven fabric other than the wet heat gelled ultrafine fibers is increased, and an appropriate average pore size and maximum pore size may not be obtained. When the content of other ultrafine fibers exceeds 50 mass%, the content of the wet heat gelled resin decreases, and an appropriate average pore size and maximum pore size may not be obtained.

  The split type composite fiber is preferably contained within a range of 30 mass% to 100 mass% with respect to the entire separator. The content of the more preferable split type composite fiber is 40 mass% or more. By setting the content of the split-type conjugate fiber in the above range, the contents of the wet heat gelled ultrafine fiber and other ultrafine fibers can be set in a desired range.

  Moreover, it is preferable that the composite ratio (volume ratio) of the wet heat gelling resin component and the other resin components in the split type composite fiber is 30:70 to 70:30.

  The fibers other than the split-type composite fibers constituting the nonwoven fabric used in the present invention preferably have a fineness of 0.1 dtex or more and 1.1 dtex or less. More preferable fineness of other fibers is 1 dtex or less. If the fineness of the other fibers is less than 0.1 dtex, the piercing strength of the nonwoven fabric may be reduced, and the fine powder short circuit and the dendrite short circuit may not be suppressed. When the fineness of other fibers exceeds 1.1 dtex, it becomes difficult to optimize the average pore size and maximum pore size of the nonwoven fabric even when gelled with a wet heat gelled resin, and as a result, a tendency to easily generate a fine powder short circuit. It is in.

  As the other fibers, since the fibers constituting the nonwoven fabric are fixed by the gelled product, other heat-meltable fibers that do not gel by wet heat may not be included, but simplification of the nonwoven fabric manufacturing process, or It may be added for the purpose of improving the tensile strength and piercing strength of the nonwoven fabric. The content of the heat-meltable fiber is preferably 70 mass% or less with respect to the entire separator. A more preferable content is 60 mass% or less. When the content of the heat-meltable fiber exceeds 70 mass%, the ratio of the wet heat gelled ultrafine fiber and other ultrafine fibers decreases, so it becomes difficult to reduce the pore diameter of the nonwoven fabric, and as a result, a fine powder short circuit is likely to occur. There is a tendency.

  The heat-meltable fiber refers to a fiber that does not gel in the presence of moisture and melts in the vicinity of the melting point (melting peak temperature) and serves to bond the fibers, and is distinguished from a wet heat gelled resin. And it is preferable that it is a fiber which does not shrink | contract substantially at the temperature (henceforth gel processing temperature) which wet-heat gelled resin gelatinizes and becomes a gelled material. Here, “not substantially shrinking” means a fiber having a nonwoven fabric area shrinkage rate of 7% or less during gel processing. It should be noted that the hot-melt fiber is defined as described above when the non-woven sheet containing moisture is gel processed and the actual temperature is lower than the set temperature when the set temperature of the heat treatment machine is set to 100 ° C. or higher. This is because it may be difficult to accurately measure the actual temperature (gel processing temperature), and is expressed separately from the gel processing temperature, and it is assumed that the gel processing temperature does not substantially shrink.

  The resin used for the hot-melt fiber is not particularly limited, but a polyolefin-based resin is preferably used from the viewpoint of the stability of the electrolyte. Examples of the fiber form of the heat-meltable fiber include a single fiber and a composite fiber. Particularly, the sheath component is a low-melting resin whose sheath component is a low melting point resin and the core component is a resin having a higher melting point than the sheath resin. Is preferably used. Examples thereof include polyethylene / polypropylene, propylene-based copolymer / polypropylene, ethylene-methyl acrylate copolymer / polypropylene, and ethylene-vinyl acetate copolymer / polypropylene. A preferred ratio of the sheath component to the core component is preferably about sheath component: core component = 30: 70 to 70:30 (volume ratio). The fiber cross-sectional shape may be any one of a concentric sheath core type, an eccentric sheath core type, a parallel type, a sea island type, etc., but a concentric sheath core type is particularly preferable.

  When the polypropylene resin is used for the other ultrafine fibers, the heat-meltable fiber is a propylene copolymer resin having a fineness of 1.1 dtex or less in consideration of adhesiveness with the polypropylene resin and piercing strength after adhesion. It is preferable to use a concentric sheath-core type composite fiber made of a combination of / polypropylene. Examples of the propylene-based copolymer resin include an ethylene-propylene copolymer and an ethylene-butene-1-propylene copolymer resin. In particular, in order to stably obtain a fiber having a fineness of 1.1 dtex or less, it is preferable to use an ethylene-propylene copolymer polymerized with a metallocene catalyst as a sheath component. According to the ethylene-propylene copolymer polymerized with a metallocene catalyst, the thermal processing temperature range is wide, not only is the handleability high when it is made into a non-woven fabric, but there are few rubber properties peculiar to ethylene-propylene copolymers, This is because there is little generation of fused yarns or adhesive yarns during melt spinning, and finer fineness is possible.

  The other fibers preferably include high-strength fibers having a single fiber strength of 4.5 cN / dtex or more for the purpose of increasing the puncture strength of the nonwoven fabric and further improving the dendrite short-circuit preventing property. The single fiber strength of the high-strength fiber is more preferably 5 cN / dtex or more, and still more preferably 5.5 cN / dtex or more. When the single fiber strength is less than 4.5 cN / dtex, it becomes difficult to contribute to the improvement of the piercing strength, and a dendrite short circuit tends to occur. The melting point of the high strength fiber is preferably 20 ° C. or higher than the melting point of the wet heat gelled resin. A more preferable melting point of the high-strength fiber is equal to or higher than a temperature 15 ° C. lower than the melting point of the wet heat gelled resin. The upper limit of the melting point of the high strength fiber is not particularly limited. For example, when the high strength fiber is a polyolefin fiber, the temperature is preferably 250 ° C. or lower. If the melting point of the high strength fiber is less than 20 ° C. lower than the melting point of the wet heat gelled resin, it tends to easily cause shrinkage due to softening or melting of the resin constituting the high strength fiber during gel processing. Yes, unevenness such as basis weight, thickness, and hole diameter of the nonwoven fabric is likely to occur. As a result, the yield of the separator may decrease, or a fine powder short circuit and a dendrite short circuit may occur.

  The resin constituting the high-strength fiber is selected from those having the above properties, and may be any of polypropylene, polyethylene, ultrahigh molecular weight polyethylene, polyester, nylon, polyparaphenylene benzbisoxazole, carbon, and the like. Of the above resins, polyolefin resins are preferable in that when an ethylene-vinyl alcohol copolymer is used as the wet heat gelling resin, the handleability is excellent and desired battery characteristics are obtained. In particular, polypropylene is preferable from the viewpoints of fiber production, electrolytic solution stability, cost, and the like. The fiber form of the high-strength fiber may be either a single fiber or a composite fiber. The cross-sectional shape is not particular about circular, hollow, atypical, elliptical, star, flat, etc. In view of ease of fiber production, the cross-sectional shape is preferably circular. When the high-strength fiber is in the form of a composite fiber, the cross-sectional shape may be any of concentric circular sheath core type, eccentric sheath core type, parallel type, sea island type, split type, and the like.

  The content of the high-strength fiber is preferably 70 mass% or less with respect to the entire separator. A more preferable content is 60 mass% or less. When the content of the high-strength fiber exceeds 70 mass%, the ratio of the wet heat gelled ultrafine fiber and other ultrafine fibers decreases, so that it is difficult to reduce the pore diameter of the nonwoven fabric, and as a result, a fine powder short circuit tends to occur. It is in.

  The non-woven fabric may contain other fibers in addition to the split type composite fibers, and in this case, the other fibers are at least one fiber selected from a hot-melt fiber having a fineness of 1.1 dtex or less and a high-strength fiber. It is preferable. According to such a configuration, the other fibers can form the skeleton portion of the nonwoven fabric, and the nonwoven fabric can be densified, so that the piercing strength is improved.

  Moreover, the nonwoven fabric used for this invention may also contain fibers other than the fiber described above. The fiber form in this case is also not particularly limited. For example, synthetic pulp may be included in order to reduce the average pore size and the maximum pore size of the nonwoven fabric in addition to the split composite fibers and other fibers that constitute the nonwoven fabric. Synthetic pulp is a fibrous material made of a so-called fibrillated natural pulp-like synthetic resin with many branched fiber surfaces, and in the present invention, it is expressed separately from the other fibers. To do. Examples of the resin constituting the synthetic pulp include polyethylene and polypropylene. The average fiber length of the synthetic pulp is preferably in the range of 0.5 mm to 2 mm. The average fiber length of the synthetic pulp is used as an index representing the form of the synthetic pulp. When the average fiber length is less than 0.5 mm, when the nonwoven sheet is produced by the wet papermaking method, it is dropped in the papermaking process. There is a possibility that the amount of synthetic pulp to be increased. If the average fiber length exceeds 2 mm, the dispersibility during wet papermaking may be reduced. Examples of synthetic pulp that satisfies the above include trade names “SWP” EST-8 and E400 manufactured by Mitsui Chemicals.

  In addition, for the fibers constituting the nonwoven fabric, an antioxidant, a light stabilizer, an ultraviolet absorber, a neutralizer, a nucleating agent, a lubricant, and an antistatic agent, as necessary, within a range that does not interfere with the effects of the present invention. Additives such as additives, pigments, plasticizers, hydrophilizing agents may be added as appropriate.

  It is important that the separator for an organic electrolyte battery of the present invention has an average pore diameter in the range of 0.3 to 5 μm and a maximum pore diameter in the range of 3 to 20 μm. A more preferable average pore diameter is 0.4 μm or more, and still more preferably 0.5 μm or more. A more preferable average pore diameter is 4 μm or less, and even more preferable is 3 μm or less. On the other hand, a more preferable maximum pore diameter is 4 μm or more. A more preferable maximum pore size is 15 μm or less, and even more preferable is 10 μm or less. By satisfying these simultaneously, it is possible to obtain a separator excellent in fine powder short circuit prevention and dendrite short circuit prevention. When the average pore diameter is less than 0.3 μm, or the maximum pore diameter is less than 3 μm, the electrolyte solution retainability tends to deteriorate and the internal resistance of the battery tends to increase. On the other hand, when the average pore diameter exceeds 5 μm or the maximum pore diameter exceeds 20 μm, a fine powder short circuit and a dendrite short circuit tend to occur.

In the separator for an organic electrolyte battery of the present invention, when the average pore diameter of the nonwoven fabric after processing by gel processing of the wet heat gelled resin is X _B and the average pore diameter of the nonwoven sheet before gel processing is X, When the obtained value is defined as the average pore size reduction rate (%), the average pore size reduction rate is preferably 60% or more.

Average pore diameter reduction rate (%) = {(X−X _B ) / X} × 100
The average pore size reduction rate is the extent to which the wet heat gelled resin is expanded to form a gelled product when the non-woven sheet containing the wet heat gelled resin (starting material before gel processing) is gel processed. It is an index of the degree of gelation. A more preferable lower limit of the average pore diameter reduction rate is 70%. The upper limit of the average pore diameter reduction rate is preferably 95%. If the average pore diameter reduction rate is less than 60%, the wet heat gelled resin is not sufficiently and substantially uniformly gelled, and the desired piercing strength may not be obtained. When the average pore diameter reduction rate exceeds 95%, the gaps in the separator are reduced, and as a result, the electrolyte permeability may be reduced, and the internal resistance of the battery may be increased.

  The separator for an organic electrolyte battery of the present invention is a film-like gelled product that is fixed while other fibers are fixed while the wet heat-gelled ultrafine fibers are spread while being gelled by wet heat to fill between the fibers constituting the nonwoven fabric. . At that time, the film-like gelled product may partially cover the surface of the nonwoven fabric. The ratio of the film-form gelled product to the entire surface of the nonwoven fabric (film form degree) is preferably in the range of 50% to 95%. A more preferable filminess is 60% or more. This filminess is an index representing the degree of spreading of the gelled product, that is, the degree of penetration between fibers, and the larger this value, the more the gelled product spreads substantially uniformly on the nonwoven fabric surface and inside. If the membrane degree is less than 50%, the average pore diameter and the maximum pore diameter range are difficult to optimize because of insufficient penetration of the gelled material between the fibers, and in particular, the maximum pore diameter tends to increase. There is a possibility that a fine powder short circuit is likely to occur. On the other hand, if the degree of filminess exceeds 95%, the non-woven fabric is filmed and the area where no pores are present is likely to be large. As a result, the electrolyte permeability is deteriorated and the internal resistance of the battery may be increased. .

  The puncture strength of the separator for an organic electrolyte battery of the present invention is preferably 2N or more. More preferable piercing strength is 4N or more, and even more preferable is 5N or more. This piercing strength is a substitute characteristic that represents the degree of dendrite short-circuit prevention, and a larger value indicates that a dendrite short-circuit is less likely to occur. And if this piercing strength is less than 2N, a dendrite short circuit is likely to occur. The standard deviation of the piercing strength is preferably 1.1 N or less. More preferably, it is 0.8 N or less, More preferably, it is 0.5 N or less. The standard deviation of the piercing strength is an index representing the variation in the piercing strength. The larger the value, the more the portion of the piercing strength is partially present, and the dendrite short circuit is likely to occur. And when this standard deviation exceeds 1.1 N, it exists in the tendency for a dendrite short circuit to occur easily as mentioned above.

  The thickness of the organic electrolyte battery separator of the present invention is preferably in the range of 15 μm or more and 70 μm or less. A more preferred thickness is 60 μm or less, and even more preferred is 35 μm or less. When the thickness of the separator is less than 15 μm, the pore diameter of the separator, particularly the maximum pore diameter, tends to increase, and the fine powder short-circuit prevention property and the dendrite short-circuit prevention property may decrease. On the other hand, when the thickness of the separator exceeds 70 μm, the electrolyte solution permeability is deteriorated, and the internal resistance of the battery may be increased. In addition, since the number of electrode plates per battery volume decreases, battery performance tends to be inferior.

The specific volume of the nonwoven fabric in the organic electrolyte battery separator of the present invention is preferably in a 1.05 cm ³ / g or more 1.5 cm ³ / g in the range. A more preferable specific volume is 1.1 cm ³ / g. A more preferable specific volume is 1.3 cm ³ / g. If the specific volume is less than 1.05 cm ³ / g, the non-woven fabric becomes too dense and the electrolyte solution retainability deteriorates. As a result, the internal resistance of the battery may increase. On the other hand, if the specific volume exceeds 1.5 cm ³ / g, the bulk of the nonwoven fabric becomes too large, and it becomes difficult to reduce the pore diameter of the separator, and as a result, a fine powder short circuit tends to occur.

The basis weight of the nonwoven fabric in the organic electrolyte battery separator of the present invention is preferably in the range of 10 g / m ^{2 to} 50 g / m ² . More preferably, the nonwoven fabric has a basis weight of 15 g / m ² or more. More preferably, the nonwoven fabric has a basis weight of 35 g / m ² or less. This is because if the basis weight of the nonwoven fabric is out of the above range, it is difficult to obtain the desired separator thickness and pore diameter.

  Next, the organic electrolyte battery separator of the present invention will be described with reference to a production method.

  When the separator for an organic electrolyte battery of the present invention is produced, the range of the average pore diameter and the maximum pore diameter is easily optimized by uniformly dispersing the wet heat gelled resin in the nonwoven sheet. In addition, by maintaining moisture uniformly in the nonwoven sheet before gel processing, it becomes possible to gel the wet heat gelled resin present in the nonwoven sheet substantially uniformly, more uniformly, It becomes possible to fix between the constituent fibers with a gelled product. Therefore, it becomes easy to optimize the range of the average pore diameter and the maximum pore diameter. Furthermore, by performing gel processing in the presence of moisture at a temperature not lower than the gelling temperature of the wet heat gelled resin and not higher than the [melting point−20 ° C.] of the wet heat gelled resin, the wet heat gelled resin and It becomes possible to process at a temperature at which the constituent fibers do not substantially contract, and the shrinkage phenomenon associated with the melting of the wet heat gelled resin and the constituent fibers is less likely to occur. Therefore, it is possible to obtain a separator with a small dimensional change during processing of the nonwoven fabric, small variations in basis weight and thickness, and excellent yield, and a low defective product rate of batteries.

  In particular, when a wet heat gelled resin having such properties is used and pressed under high pressure with a hot roll or the like, the wet heat gelled resin of the entire nonwoven sheet is instantly gelled and expanded by wet heat. It can penetrate into the woven sheet. Therefore, it is possible to fix the fibers constituting the nonwoven fabric substantially uniformly in the planar direction and the thickness direction of the nonwoven fabric with a gelled product. As a result, the tensile strength and piercing strength are large, the range of the average pore size and the maximum pore size of the nonwoven fabric is optimized, and a separator with small variation in piercing strength can be obtained.

  In addition, by using a wet nonwoven fabric formed by a wet papermaking method as a non-woven sheet, wet-heat gelled ultrafine fibers and other ultrafine fibers having a substantially wedge-shaped cross-section split from the split composite fiber, Since the flat direction of the fiber is oriented in the plane direction of the nonwoven fabric, it is a film that is spread in the plane direction of the nonwoven fabric when it is accumulated in parallel along the nonwoven fabric surface direction to wet-heat gelled ultrafine fibers. It is easy to form the gelled product, and the other fine fibers can adjust the pore diameter in the surface direction of the nonwoven fabric to optimize the average pore diameter and the maximum pore diameter of the nonwoven fabric.

  In addition, a nonwoven sheet here shows a web and a nonwoven fabric, and shows the form until it gel-processes. The web refers to a web in which constituent fibers such as a card web, an air lay web, and a wet papermaking web are not joined. The non-woven fabric refers to a fabric in which constituent fibers are bonded to each other by subjecting the web to an adhesive treatment such as thermal bonding, hydroentanglement, entanglement treatment such as needle punching, or the like. The same applies to the following.

  The nonwoven sheet is prepared by preparing the above-described split type composite fiber and other fibers and using a known method. As the form of the nonwoven sheet, a wet papermaking web or a wet nonwoven fabric (hereinafter referred to as a wet nonwoven sheet) by a wet papermaking method is preferable because a more uniform nonwoven fabric is obtained.

  The fiber length of the fibers used for the wet nonwoven sheet is preferably in the range of 1 mm or more and 20 mm or less. A more preferable fiber length is 2 mm or more, and still more preferably 3 mm or more. A more preferable fiber length is 15 mm or less, and even more preferable is 12 mm or less. If the fiber length is less than 1 mm, the piercing strength is inferior, and as a result, a dendrite short circuit tends to occur. On the other hand, when the fiber length exceeds 20 mm, the dispersibility of the fibers in the slurry is deteriorated, and it is difficult to obtain a nonwoven fabric with uniform formation. As a result, the maximum pore diameter tends to increase, and a fine powder short circuit tends to occur.

  In the case of a wet non-woven sheet, it may be performed by a normal method, each fiber is mixed so as to be in a desired range, and dispersed in water so as to have a concentration of 0.01 to 0.6 mass%. Adjust the slurry. At this time, a small amount of a dispersant may be added. In the split type composite fiber, when the fiber is split and expressed at the time of slurry disaggregation and beating, the fine fibers split when paper is made are dispersed more uniformly in the nonwoven fabric, and the flat direction of the fibers is the nonwoven fabric. Since it is oriented in the plane direction and accumulated in parallel along the plane direction of the non-woven fabric, the gelled product is spread almost uniformly when gel processing is performed, and the average pore size and maximum pore size are optimized more precisely. It is possible to obtain a separator with a small variation in piercing strength. In particular, by using a split-type composite fiber containing a wet heat gelled resin and separating and expressing the fiber at the time of slurry disaggregation and beating, the wet heat gelled fiber that has become ultrafine fibers when paper is made is more concentrated in the nonwoven fabric. It can be uniformly dispersed. As a result, when the wet heat gelled fiber is gelled, the fibers that penetrate between the fibers while being spread and become a gelled product can be fixed substantially uniformly, and the average pore size and maximum pore size are optimized. Thus, it is easy to obtain a separator having a high piercing strength and a small variation in the piercing strength. As a result, it is possible to obtain a separator that is more excellent in the prevention of short-circuiting of fine powder and the prevention of dendritic short-circuiting. The slurry is made into paper with a desired basis weight using a short net type, a circular net type, a long net type, or a paper machine combining them.

  Moreover, you may perform a hydroentanglement process to a web or a nonwoven fabric in the range which does not prevent the effect of this invention as needed. By performing the hydroentanglement treatment, the splitting of the split composite fibers can be promoted and the degree of entanglement between the fibers can be increased.

  In order to obtain a separator in which the range of the average pore diameter and the maximum pore diameter is optimized as in the present invention, it is important to gel the wet heat gelled resin present in the entire nonwoven sheet more uniformly during the gel processing. is there. For that purpose, it is important to uniformly apply moisture to the entire nonwoven sheet before gel processing, and it is important that the nonwoven sheet has more uniform water wettability.

  An example of the index representing the water wettability described above is a contact angle with demineralized water. Since the smaller the contact angle, the easier it is to get wet with water, water can be uniformly applied by the nonwoven sheet. Specifically, it is preferable that the contact angle of the non-woven sheet surface with the desalted water before the gel processing is 60 degrees or less after 5 seconds from the dropping of the desalted water. A more preferable contact angle is 55 degrees or less. An even more preferable contact angle is 50 degrees or less. This is because when the contact angle of the non-woven sheet surface with demineralized water exceeds 60 degrees, this water wettability tends to be insufficient, and it becomes difficult to uniformly apply moisture.

  In the case where a hydrophobic fiber such as a polyolefin resin is used for the separator of the present invention, this water wettability tends to be insufficient, and it becomes difficult to uniformly apply moisture. Therefore, it is preferable to subject the nonwoven sheet to a hydrophilic treatment. It is good to produce the hydrophilic nonwoven sheet which satisfies the said contact angle by giving a hydrophilic treatment. Examples of the hydrophilic treatment include corona discharge treatment, plasma treatment, electron beam treatment, treatment exposed to a fluorine atmosphere (hereinafter referred to as fluorine treatment), graft treatment, sulfonation treatment, and surfactant treatment.

For example, in the case of corona discharge treatment, the treatment may be performed 1 to 20 times on both sides of the nonwoven sheet, and the treatment may be performed in the range of 0.05 to 10 kW · min / m ² . In the case of fluorine treatment, a method of introducing a hydrophilic group by bringing the nonwoven sheet into contact with a mixed gas of fluorine gas diluted with an inert gas and oxygen gas, sulfurous acid gas or the like can be mentioned. If it is a graft polymerization treatment, a method of immersing a nonwoven sheet in a solution containing a vinyl monomer and a polymerization initiator and heating, a method of irradiating radiation after applying the vinyl monomer to the nonwoven sheet, etc. may be used. Furthermore, it is preferable that the surface of the nonwoven sheet is modified by ultraviolet irradiation, corona discharge, plasma discharge, or the like before the vinyl monomer solution is brought into contact with the nonwoven sheet, so that the graft polymerization can be efficiently performed. Examples of the sulfonation treatment include concentrated sulfuric acid treatment, fuming sulfuric acid treatment, chlorosulfonic acid treatment, and sulfuric anhydride treatment. In the case of the surfactant treatment, there is a method of immersing or applying a nonwoven sheet in a solution of an anionic surfactant or a nonionic surfactant having hydrophilic performance. In addition, you may give the hydrophilic process mentioned above to the nonwoven fabric after gel processing at all. The processing method may be any method described above, or a combination of two or more.

  Among the hydrophilic treatments, the fluorine treatment is particularly preferable because moisture can be more evenly applied to the inside of the nonwoven sheet during gel processing. Furthermore, the fluorine treatment can introduce hydrophilic groups deeper into the resin surface, so that the decrease in hydrophilicity is small even after gel processing, and the hydrophilicity of the nonwoven fabric can be maintained even after gel processing. As specific conditions for the fluorine treatment, the fluorine concentration in the mixed gas in the fluorine treatment is preferably in the range of 0.01 to 80% by volume. A more preferable lower limit of the fluorine concentration is 0.1% by volume. An even more preferable lower limit of the fluorine concentration is 0.5% by volume. A more preferable upper limit of the fluorine concentration is 30% by volume. An even more preferable upper limit of the fluorine concentration is 10% by volume. Moreover, it is preferable that reaction temperature exists in the range of 10 to 50 degreeC. The reaction time is not particularly limited, but is preferably in the range of 1 second to 30 minutes.

  In the separator for an organic electrolyte battery obtained in the present invention, the contact angle of the non-woven fabric surface with desalted water is also preferably 60 degrees or less after 5 seconds of dropping of desalted water. A more preferable contact angle is 55 degrees or less. A more preferable contact angle is 50 degrees or less. This contact angle is an index representing the degree of wettability reduction due to gel processing. Hydrophilic treatment that can maintain the contact angle after gel processing at 60 degrees or less is preferable because moisture can be uniformly applied to the inside of the nonwoven sheet before gel processing of the present invention. Such a hydrophilic treatment that can maintain the contact angle after gel processing at 60 degrees or less includes fluorine treatment as described above, but any treatment method having the same effect can be used. It doesn't matter.

  Next, moisture is applied to the nonwoven sheet or the hydrophilic nonwoven sheet to produce a water-containing sheet. In order to obtain the separator of the present invention, it is not necessary to absorb moisture up to the inside of the wet heat gelled resin, as long as moisture is attached to the periphery thereof. If the water-containing sheet in such a state is sandwiched between the heated body by the following method, the instantaneously generated water vapor is enclosed in the nonwoven sheet by the heated body, and the moist heat gelled resin is instantaneously contained inside the nonwoven sheet. Can be gelled.

  It is preferable that the moisture content given to the said nonwoven sheet or the said hydrophilic nonwoven sheet exists in the range of 20 mass% or more and 300 mass% or less. A more preferable lower limit of the moisture content is 50 mass%. An even more preferable lower limit of the moisture content is 80 mass%. A more preferable upper limit of the moisture content is 200 mass%. An even more preferable upper limit of the moisture content is 150 mass%. When the moisture content is less than 20 mass%, the gelation of the wet heat gelled ultrafine fibers does not occur sufficiently, and it tends to be difficult to form a film-like gelled product, contributing to optimization of the average pore size and the maximum pore size range. May be difficult to do. On the other hand, when the moisture content exceeds 300 mass%, it tends to be difficult to uniformly apply heat to the nonwoven sheet surface and the inside during gel processing, and only the nonwoven fabric surface may be formed into a film. As a result, the degree of gelation in the thickness direction of the obtained separator is not uniform, the constituent fibers are not fixed uniformly, and the pore diameter unevenness in the thickness direction may increase. As a method for applying moisture, any method such as spraying or dipping in a water tank may be used.

  And the said water-containing sheet | seat is wet-heat-treated (gel processing) with the heat processing machine set to the temperature which is in the range more than the temperature which the said heat-and-humidity gelled resin gelatinizes, and below the [melting point-20 degreeC] of the said heat-and-heat gelled resin ), The wet heat gelled resin is gelled, and other fibers are fixed by the gelled wet heat gelled resin, so that a separator for an organic electrolyte battery can be obtained. The set temperature during the gel processing is preferably 60 ° C. or higher and the melting point of the wet heat gelled resin −20 ° C. or lower. A more preferable lower limit of the set temperature is 80 ° C. An even more preferable lower limit of the set temperature is 85 ° C. A more preferable upper limit of the set temperature is 140 ° C. An even more preferable upper limit of the set temperature is 135 ° C. When the set temperature of the gel processing is less than 80 ° C., it is difficult to sufficiently gel, the constituent fibers are not sufficiently fixed, or it is difficult to optimize the range of the average pore diameter and the maximum pore diameter. There is sex. On the other hand, when the set temperature of the gel processing exceeds the melting point of the wet heat gelled resin −20 ° C., when the hot roll is used for the gel processing, the wet heat gelled resin tends to adhere to the roll or the nonwoven fabric shrinks. As the dimensional stability deteriorates, the yield tends to decrease, and the defective product rate of the battery tends to increase. The gel processing temperature was set to the preset temperature when the non-woven sheet containing moisture was gel processed, and when the set temperature of the heat treatment machine was set to 100 ° C. or higher, the moisture in the nonwoven sheet first evaporates. . At that time, since the gelation of the wet heat gelled resin proceeds, the actual temperature of the gel processing tends to be lower than the set temperature. Therefore, it may be difficult to specify the gel processing temperature strictly. Therefore, even when the melting point of the other fiber is lower than the set temperature of the heat treatment machine, it may not melt or shrink substantially, and the gel processing temperature is a temperature at which the other fiber does not substantially shrink. It is preferable to process.

  The gel processing is preferably pressure processing such as a hot roll or a hot press. According to the pressure processing, when the wet heat gelled resin is turned into wet heat gel, the stretched membrane-like gelled material easily penetrates between the fibers, and the average pore size and the maximum pore size can be optimized. In particular, it is more preferable that the pressing process is a pressing process using a hot roll because the productivity is excellent.

  The linear pressure of the hot roll is preferably in the range of 350 N / cm to 15000 N / cm. A more preferable lower limit of the linear pressure is 400 N / cm. A more preferable upper limit of the linear pressure is 10,000 N / cm. When the linear pressure is less than 350 N / cm, it is difficult to sufficiently penetrate the wet heat gelled resin into the nonwoven fabric, and it is difficult to form a film-like gelled product. As a result, it is difficult to contribute to optimizing the range of the average pore diameter and the maximum pore diameter, and a fine powder short circuit tends to occur. On the other hand, when the linear pressure exceeds 15000 N / cm, the pressure is too high, so that the fiber is likely to be cut and the through hole is easily formed. there's a possibility that. The pressurizing with the hot roll may be performed once or may be performed twice or more. Moreover, when adhesion | attachment by the wet heat gelling resin to the heat roll at the time of gel processing generate | occur | produces, you may use mold release agents, such as surfactant, as needed. Moreover, you may add an oil agent, a paste, etc. to the nonwoven fabric after gel processing in the range which does not impair the effect of this invention.

  In addition, the nonwoven fabric used for this invention can be laminated | stacked and used for another sheet | seat, for example, a microporous film, another nonwoven fabric, etc. as needed other than using alone.

  The separator for an organic electrolyte battery according to the present invention has a non-woven sheet containing the wet heat gelled resin and other fibers so that the wet heat gelled resin has a temperature equal to or higher than a temperature at which the wet heat gelled resin gels. A separator satisfying the desired average pore size and maximum pore size can be obtained by adopting a production method in which gel processing is performed within the following range. By performing a hydrophilic treatment on the nonwoven sheet containing the wet heat gelled resin and other fibers before the gel processing, the entire nonwoven sheet can retain moisture uniformly. It can be gelled. Furthermore, by adopting heat and pressure processing as gel processing, the wet heat gelled resin dispersed substantially uniformly is gelled and expanded, and becomes a film-like gelled product, fixing the constituent fibers substantially uniformly to the inside of the nonwoven fabric. be able to.

  FIG. 1 shows a composite fiber according to an embodiment of the present invention. This composite fiber 10 is composed of a wet heat gelled ultrafine fiber 11 and another ultrafine fiber 12, and is a fiber that can be divided into 24 sections. Splitting radially from the center point is possible. FIG. 2 shows a cross-sectional view of the wet heat gelled ultrafine fiber 11, wherein the short axis thickness (maximum thickness of the wedge-shaped cross section) D is preferably 0.7 μm or more and 2.2 μm or less, and the length L is the maximum thickness D of the wedge-shaped cross section. It is preferable that it is 2 times or more.

[Example]
Hereinafter, the present invention will be specifically described with reference to examples. The melting point, the single fiber fineness, the single fiber strength, the thickness, the piercing strength, the standard deviation of the piercing strength, the average pore diameter, the maximum pore diameter, the film degree of the nonwoven fabric surface, the contact angle of the nonwoven fabric surface, and the nonwoven fabric area shrinkage (hereinafter referred to as “ The “shrinkage rate during processing” was measured by the following method.
(1) Melting point: Measured according to JIS K 7121 (DSC method).
(2) Single fiber fineness: Measured according to JIS L 1013.
(3) Single fiber strength: According to JIS L 1015, using a tensile tester, the gripping interval of the sample was 20 mm, and the load value when the fiber was cut was measured to obtain the single fiber strength.
(4) Thickness: 175 kPa load (measured with a micrometer according to JIS-B-7502) was used to measure the thickness at 10 different points of each of the three samples, and the average value was obtained at a total of 30 points.
(5) Puncture strength: Using a “KES-G5 Handy Compression Tester” manufactured by Kato Tech Co., Ltd., a non-woven fabric cut to a size of 30 mm in length and 100 mm in width was prepared, and 46 mm in length, 86 mm in width, and thickness on the sample. After a holding plate having a hole of 11 mm in diameter is placed in the center of a 7 mm aluminum plate, the tip is a 1 mmφ spherical part, the shaft part is a conical shape with a bottom diameter of 2.2 mm and a height of 18.7 mm. The maximum load (N) when the needle was stabbed perpendicularly into the center of the hole of the press plate at a speed of 2 mm / second was measured, and the puncture strength was obtained. In addition, this piercing strength measured thickness in 15 different places of four samples, respectively, and made it the average value of a total of 60 places.
(6) Standard deviation of piercing strength: The standard deviation of n = 60 measured above was determined.
(7) Average pore diameter / maximum pore diameter: measured by a bubble point method using a palm porometer (manufactured by Porous Materials Inc.) according to ASTM F31686.
(8) Film degree on the surface of the nonwoven fabric: The surface of any 10 locations of the nonwoven fabric is photographed with an electron microscope at a magnification of 200 times. On the surface of the nonwoven fabric, the percentage of the area where the fibers adjacent to each other are continuously fixed to the total area of the nonwoven fabric was calculated.
(9) Nonwoven sheet surface contact angle: manufactured by Kyowa Interface Chemical Co., Ltd., contact angle meter (cleaning degree evaluation system), model: CA-X150, as shown in FIG. A sample 2 measuring 1 cm in length and 5 cm in width is placed and fixed with tape. Next, 2 microliters of pure water 3 is accurately dropped onto the sample 2 with a microsyringe. After leaving for 5 seconds, the diameter a and height h of the water droplet shown in FIG. 3 are measured. From the diameter a and the height h, the contact angle θ is obtained using the following formula.
tan (θ / 2) = h / (a / 2)
(10) Shrinkage rate during processing (%): Calculated according to the following formula.
[1- (Nonwoven fabric area after gel processing / Nonwoven sheet area before gel processing)] × 100

  The fiber raw material used for an Example and a comparative example was prepared as follows.

[Fiber 1]
The first component is a wet heat gelling resin, and an ethylene-vinyl alcohol copolymer (EVOH, manufactured by Nippon Synthetic Chemical Co., Ltd., Soarnol K3835BN, melting point 170 ° C.) having an ethylene content of 38 mol% and a saponification degree of 99% is used. The two components are polypropylene (PP, manufactured by Nippon Polychem Co., Ltd., SAO3B, melting point 163 ° C.) and have a divided sectional shape radially divided into 24, the area ratio of the first component / second component is 50/50, the fineness A split type composite fiber having a fiber length of 1.2 dtex and a fiber length of 4 mm was prepared.
[Fiber 2]
The first component is a wet heat gelling resin, and an ethylene-vinyl alcohol copolymer (EVOH, manufactured by Nippon Synthetic Chemical Co., Ltd., Soarnol K3835BN, melting point 170 ° C.) having an ethylene content of 38 mol% and a saponification degree of 99% is used. The two components are polypropylene (PP, manufactured by Nippon Polypro, SA03B, melting point 163 ° C.), melt-spun by a known method, and stretched three times in air at 150 ° C. A split type composite fiber having a first component / second component area ratio of 50/50, a fineness of 1.4 dtex, and a fiber length of 6 mm was prepared.
[Fiber 3]
The first component is high density polyethylene (HDPE, Nippon Polypro, HE490, melting point 132 ° C.), and the second component is polypropylene (Nihon Polypro, SA 03B, melting point 163 ° C.), which is melt-spun by a known method. , Having a radial 16-divided cross-sectional shape stretched 5 times in 90 ° C. warm water, having a first component / second component area ratio of 50/50, a fineness of 1.4 dtex, and a fiber length of 6 mm A mold composite fiber was prepared.
[Fiber 4]
An ethylene-propylene copolymer (EP, manufactured by Nippon Polypro Co., Ltd., OX1066A, melting point 136 ° C.) obtained by polymerizing a sheath component (thermal adhesive component) with a metallocene catalyst, and a core component made of polypropylene (SAO 3A manufactured by Nippon Polypro Co., Ltd., melting point 163 ° C. The core / sheath component has an area ratio of 50/50 and a fineness of 0.9 dtex and a fiber length of 4 mm.
[Fiber 5]
A concentric circular sheath core type composite fiber having a fiber length of 10 mm was prepared.
[Fiber 6]
The sheath component is high-density polyethylene (manufactured by Nippon Polypro, HE490, melting point 132 ° C.), the core component is polypropylene (manufactured by Nippon Polypro, SA03B, melting point 163 ° C.), melt-spun by a known method, and warm water at 90 ° C. A core-sheath core-type composite fiber having a core component / sheath component area ratio of 50/50 and a fiber length of 10 mm was prepared.
[Fiber 7]
Polypropylene (manufactured by Nippon Polypro Co., Ltd., SA03B, melting point 163 ° C.) is melt-spun by a known method and stretched three times in air at 150 ° C., single fiber strength 5.8 cN / dtex, round section with fiber length 10 mm Polypropylene single fiber was prepared.

[Example 1]
50 mass% of fiber 1 and 50 mass% of fiber 4 were mixed, and disperse and beaten so as to obtain a concentration of 0.5 mass% to prepare an aqueous dispersion slurry. The obtained water-dispersed slurries were each made by making wet paper webs having a basis weight of 12.5 g / m ² from a circular mesh wet paper machine and a short mesh wet paper machine. Next, it is heat-treated at 137 ° C. using a cylinder dryer, dried and temporarily bonded with the wet heat gelled resin of the fiber 1 and the sheath component of the fiber 4, and a wet non-woven sheet having a basis weight of about 25 g / m ² is obtained with a roll Winded up. In the obtained wet nonwoven sheet, the fiber 1 was divided almost 100% and was dispersed substantially uniformly in the nonwoven fabric. The minor axis thickness of the ultrafine fiber after the splitting of the fiber 1 was about 1.6 μm. The dividing rate is calculated by calculating the ratio of divided fibers by bundling so that the longitudinal direction of the nonwoven fabric is a cross section, passing through a metal plate with a 1 mm diameter hole, and expanding by 400 times using an electron microscope. Asked.

  Next, the wet nonwoven sheet was treated at room temperature (25 ° C.) for 1 minute by introducing a mixed gas having a gas composition of 1 vol% fluorine, 73 vol% oxygen, and 26 vol% nitrogen into a processor. Then, it wash | cleaned with 60 degreeC hot water, and it dried at 70 degreeC with the hot air dryer, and was set as the hydrophilic nonwoven sheet. The contact angle of the obtained hydrophilic nonwoven sheet with demineralized water was 0 degree.

  The hydrophilic nonwoven sheet is impregnated with 180 mass% of water by spraying the sheet and heated at 120 ° C. with a hot roll consisting of a pair of plain rolls under a linear pressure of 8000 N / cm and a processing speed of 7 m / min. The gel processing was performed, and the thickness was adjusted under the same conditions as above to obtain the separator for an organic electrolyte battery of the present invention.

  FIG. 4 is a cross-sectional SEM photograph (300 times) of the wet nonwoven sheet before gel processing of this example. A split type conjugate fiber and a heat-meltable fiber are included, and the split type conjugate fiber is split to form a substantially wedge-shaped ultrafine fiber. (Equivalent to Example 1) The substantially wedge-shaped ultrafine fibers are accumulated with the flat direction of the fibers oriented in the plane direction of the nonwoven fabric to form a sheet.

  FIG. 5 is a surface SEM photograph (300 times) of the separator after the gel processing of this example. Wet heat gelled ultrafine fibers are formed into a gelled product that is formed by wet heat gelation.

  FIG. 6 is a cross-sectional SEM photograph (1000 times) of the separator after gel processing. It can be seen that the wet heat gelled ultrafine fibers are wet heat gelled and expanded to form a film-like gelled product and fix the constituent fibers.

[Example 2]
Wet paper webs having a basis weight of 9 g / m ² were produced from a circular net type wet paper machine and a short net type wet paper machine. Next, it was heat treated at 137 ° C. using a cylinder dryer and dried, and was temporarily bonded with a wet heat gelled resin of fiber 1 and a sheath component of fiber 4 to obtain a wet nonwoven sheet having a basis weight of about 18 g / m ^2. The same treatment as in Example 1 was performed to obtain an organic electrolyte battery separator.

[Example 3]
An organic electrolyte battery separator was obtained in the same manner as in Example 1, except that the fiber 5 was used instead of the fiber 4 and the temperature of the cylinder dryer after wet papermaking was set to 141 ° C.

[Example 4]
A separator for an organic electrolyte battery was obtained in the same manner as in Example 1 except that 100 mass% of fiber 1 was used and the temperature of the cylinder dryer machine after wet papermaking was set to 135 ° C.

  FIG. 7 is a cross-sectional SEM photograph (500 times) of the wet nonwoven sheet before gel processing of this example. 100 mass% of split-type composite fibers are split to form a substantially wedge-shaped ultrafine fiber. Substantially wedge-shaped ultrafine fibers are accumulated with the flat direction of the fibers oriented in the surface direction of the nonwoven fabric.

  FIG. 8 is a surface SEM photograph (300 times) of the separator after gel processing in this example. Wet heat gelled ultrafine fibers are formed into a gelled product that is formed by wet heat gelation.

  FIG. 9 is a cross-sectional SEM photograph (1000 times) of the separator after the gel processing of this example. It can be seen that the wet heat gelled ultrafine fibers are wet heat gelled and expanded to form a film-like gelled product and fix the constituent fibers.

[Comparative Example 1]
50 mass% of fiber 2, 30 mass% of fiber 6 of 0.8 dtex, and 20 mass% of fiber 7 of 0.6 dtex were mixed to prepare an aqueous dispersion slurry to a concentration of 0.5 mass%. The obtained water-dispersed slurries were each made by making wet paper webs having a basis weight of 15 g / m ² from a circular net type wet paper machine and a short net type wet paper machine. Next, it is heat-treated at 135 ° C. using a cylinder dryer, dried, and temporarily bonded with the wet heat gelled resin of the fiber 2 and the sheath component of the fiber 6 , and a wet nonwoven sheet having a basis weight of 30 g / m ² is wound with a roll. I took it. In the obtained wet nonwoven sheet, the fibers 2 were divided almost 100% and were dispersed substantially uniformly in the nonwoven fabric. The minor axis thickness of the ultrafine fiber after the splitting of the fiber 2 was about 2.6 μm.

  Next, the wet nonwoven sheet was treated at room temperature (25 ° C.) for 1 minute by introducing a mixed gas having a gas composition of 1 vol% fluorine, 73 vol% oxygen, and 26 vol% nitrogen into a processor. Then, it wash | cleaned with 60 degreeC hot water, and it dried at 70 degreeC with the hot air dryer, and was set as the hydrophilic nonwoven sheet. The contact angle of the obtained hydrophilic nonwoven sheet with demineralized water was 0 degree.

  Then, the hydrophilic nonwoven sheet is impregnated with water and subjected to pressure processing under conditions of a linear pressure of 500 N / cm and a processing speed of 3.3 m / min with a heat roll made of a pair of plain rolls heated to 130 ° C. Although a nonwoven fabric for application separator was obtained, it was difficult to roll up due to shrinkage during thickness processing.

[Comparative Example 2]
A wet nonwoven sheet was prepared in the same manner as in Comparative Example 1 except that the fiber 6 was 2.0 dtex and the fiber 7 was 2.0 dtex.

  Next, the wet nonwoven sheet was treated at room temperature (25 ° C.) for 1 minute by introducing a mixed gas having a gas composition of 1 vol% fluorine, 73 vol% oxygen, and 26 vol% nitrogen into a processor. Then, it wash | cleaned with 60 degreeC hot water, and it dried at 70 degreeC with the hot air dryer, and was set as the hydrophilic nonwoven sheet. The contact angle of the obtained hydrophilic nonwoven sheet with demineralized water was 0 degree.

  The hydrophilic nonwoven sheet is impregnated with 100 mass% of water by spraying the sheet, and a linear roll of 500 N / cm and a processing speed of 3.3 m / min with a hot roll made of a pair of plain rolls heated to 130 ° C. Gel processing was performed under conditions to obtain a nonwoven fabric for separator.

[Comparative Example 3]
A separator non-woven fabric was obtained in the same manner as in Comparative Example 2 except that the fiber 2 was 20 mass%, the 0.8 dtex fiber 6 was 50 mass%, and the 0.6 dtex fiber 7 was 30 mass%.

[Comparative Example 4]
The wet nonwoven sheet produced in Comparative Example 1 was impregnated with 100 mass% of moisture by spraying the sheet without applying a hydrophilic treatment, and heated with a pair of plain rolls heated to 130 ° C. Gel processing was performed under conditions of a linear pressure of 500 N / cm and a processing speed of 3.3 m / min to obtain a nonwoven fabric for a separator. However, since the contact angle with demineralized water before the gel processing was 105 degrees, moisture was evenly distributed. It did not permeate and could not be uniformly gelled.

[Comparative Example 5]
The same treatment as in Comparative Example 1 was performed except that the fiber 3 was used instead of the fiber 2, but the shrinkage of the nonwoven fabric during the thickness processing was large and roll winding was impossible.

  Tables 1 and 2 below summarize the conditions and results of Example 1-4 and Comparative Example 1-5.

  As is clear from Tables 1-2, in any of Examples 1-4, while maintaining good gel processability, the pore diameter is small, the average pore diameter and the maximum pore diameter range are optimized, and the standard deviation of the piercing strength In addition, it was confirmed that a nonwoven fabric in which the ratio of the film form degree of the gelled product was in a desired range was obtained. The separator using this had a low defective product rate of the battery, and no short circuit occurred. In particular, the thickness of the nonwoven fabric could be reduced to 20 to 30 μm by using split-type composite fibers that were radially divided into 24 as a starting material, and splitting to include a substantially wedge-shaped ultrafine fiber.

  On the other hand, in Comparative Example 1, the wet heat gelled resin did not gel because moisture was not impregnated, and the pore diameter and thickness of the separator could not be reduced. Moreover, since the water | moisture content was not provided, the temperature of a heat roll applied directly to the nonwoven fabric, As a result, since it became more than melting | fusing point of the sheath resin of the fiber 6, the shrinkage | contraction of the nonwoven fabric was also large. When this was used as a separator, a fine powder short circuit occurred. In Comparative Example 2, since the fiber diameter was large and the hole diameter was not reduced, a fine powder short circuit occurred when used as a separator. In Comparative Example 3, since the content of the wet heat gelled resin was small, the wet heat gelled resin did not sufficiently spread between the fibers, and the pore diameter, particularly the maximum pore diameter, did not decrease. When this was used as a separator, a fine powder short circuit occurred. Further, in Comparative Example 4, since the hydrophilic treatment was not performed before the gel thickness processing, moisture could not be uniformly applied to the nonwoven fabric, the maximum pore diameter was not reduced, and the piercing strength variation was increased. When this was used as a separator, a fine powder short circuit occurred. In Comparative Example 5, since the wet heat gelled resin was not used, the nonwoven fabric contracted greatly during the thickness processing, and it was impossible to wind it onto a roll.

The separator for an organic electrolyte battery of the present invention can be suitably used for an organic electrolyte battery, particularly a lithium ion secondary battery. Also, electric double layer capacitor, Ru is used in the electrochemical element such as a capacitor. Et al is, separators of the present invention is an improved self-discharge performance of the battery, commonly used consumer batteries such as is suitable in particular for electric vehicles (PEV) and hybrid vehicles (HEV).

It is a perspective view of the composite fiber in one Example of this invention. It is sectional drawing of a wet heat gelled microfiber. It is explanatory drawing which measures the contact angle on the surface of a nonwoven fabric similarly. It is a cross-sectional SEM photograph (300 times) of the wet nonwoven sheet before the gel process in Example 1 of this invention. It is the surface SEM photograph (300 times) of the separator after gel processing same as the above. It is a cross-sectional SEM photograph (1000 times) of the separator after gel processing same as the above. It is a cross-sectional SEM photograph (500 times) of the wet nonwoven sheet before the gel process in Example 4 of this invention. It is the surface SEM photograph (300 times) of the separator after gel processing same as the above. It is a cross-sectional SEM photograph (1000 times) of the separator after gel processing same as the above.

Explanation of symbols

10 Composite fiber 11 Wet heat gelled ultrafine fiber 12 Other ultrafine fiber

Claims (4)

A split type composite fiber composed of two or more components of a wet heat gelled resin component that can be gelled by heating in the presence of moisture and another resin component, each component being radially divided into a plurality of fibers, was split. A separator for an organic electrolyte battery comprising a nonwoven fabric containing wet heat gelled ultrafine fibers and other ultrafine fibers,
The wet heat gelled ultrafine fiber and other ultrafine fibers are radially split into a total of 20 or more per one of the conjugate fibers ,
The separator for an organic electrolyte battery, wherein the wet heat gelled ultrafine fiber is formed into a film-like gelled product that is formed by wet heat gelation and is expanded, and the constituent fibers of the nonwoven fabric are fixed.   2. The separator for an organic electrolyte battery according to claim 1, wherein the wet heat gelled ultrafine fiber and the other ultrafine fibers have a fineness in a range of 0.01 dtex or more and 0.08 dtex or less, respectively. 3. The separator for an organic electrolyte battery according to claim 1, wherein the wet heat gelled ultrafine fiber and the other ultrafine fibers have a thickness of 0.7 μm or more and 2.2 μm or less, respectively.   2. The non-woven fabric includes other fibers in addition to the split-type composite fibers, and the other fibers are at least one fiber selected from a heat-melt fiber and a high-strength fiber having a fineness of 1.1 dtex or less. Separator for organic electrolyte battery.