JP2006188770A - Nonwoven fabric, method for producing nonwoven fabric, separator for electric double layer capacitor by using nonwoven fabric, separator for lithium ion secondary battery, electric double layer capacitor or lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonwoven fabric capable of being applied in various uses by being excellent in mechanical strength in addition to its ion permeability, gas permeability or liquid permeability, and a method for producing the nonwoven fabric. <P>SOLUTION: This nonwoven fabric containing a thermoplastic resin fiber and a heat resistant fiber consisting of a resin having a melting point or carbonizing point higher than the melting point of the thermoplastic resin fiber is provided with that the nonwoven fabric-constituting fibers are fixed by melting the thermoplastic resin having the same composition with the thermoplastic resin fiber-constituting thermoplastic resin in a state of without forming a film. The nonwoven fabric is also produced by performing a heat-treatment on a fiber web obtained by using the thermoplastic fibers and heat resistant fibers and melting only a part of the thermoplastic resin fibers for melt-fixing. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a nonwoven fabric and a method for producing the nonwoven fabric, and a separator for an electric double layer capacitor, a separator for a lithium ion secondary battery, an electric double layer capacitor or a lithium ion secondary battery using the nonwoven fabric.

  Conventional non-woven fabrics have various properties by appropriately selecting and combining fiber types, fiber web forming methods, fiber web bonding methods, and post-processing, and thus have been applied to various applications. .

  For example, one application utilizing the electrical insulation performance, which is one of the characteristics of a nonwoven fabric, is an electrical double layer capacitor separator application. In other words, an electric double layer capacitor has a structure in which a pair of electrodes is immersed in an ionic solution. When a voltage is applied to the electrodes, ions of the opposite sign to the electrodes are distributed in the vicinity of the electrodes, and the layer of ions is formed. On the other hand, charges of opposite sign to ions are accumulated inside the electrode. Therefore, if a load is connected between the electrodes, the charge inside the electrodes is discharged, and the ions distributed in the vicinity of the electrodes are separated from the vicinity of the electrodes and return to the neutralized state. In such an electric double layer capacitor, if a pair of electrodes come into contact with each other, it is difficult to form an ion layer in the vicinity of the electrodes. Therefore, a separator is disposed between the pair of electrodes.

  As a separator for an electric double layer capacitor made of such a nonwoven fabric, “a liquid crystalline property having a melting point or a thermal decomposition temperature of 250 ° C. or more, an average fiber length of 0.3 mm to 2 mm, and at least a part of which is fibrillated to a fiber diameter of 1 μm or less. There has been proposed a separator for an electric double layer capacitor which is a nonwoven fabric containing polymer fibers and has a porosity of 68% to 85% (Patent Document 1). This separator for an electric double layer capacitor is actually manufactured by forming a wet fiber web containing a core-sheath composite fiber composed of a polyester core component and a modified polyester sheath component, and then bringing it into contact with a heating drum. Although this separator is excellent in electrical insulation performance, a film is formed by press-fusing the core-sheath composite fiber, so that the internal resistance is high and the ion permeability is poor.

With respect to the separator for an electric double layer capacitor made of such a nonwoven fabric, the applicant of the present application “has a fibril-containing fiber and a fine polyester fiber having a fineness of 0.45 dtex (decitex) or less, and an areal density of 20 to 40 g. in / ^{m 2,} a thickness of 30 to 50 [mu] m, apparent density exceeds the 0.5 g / cm ^3, was proposed an electric double layer separator for capacitor "consisting of 0.8 g / cm ³ or less of the nonwoven fabric (Patent Document 2). This separator for an electric double layer capacitor was actually manufactured by heating and pressurizing a wet fiber web with a thermal calendar having a temperature lower than the melting point of the fine polyester fiber. This separator for electric double layer capacitors has a low internal resistance and superior ion permeability compared to the electric double layer capacitor of Patent Document 1 because the fine polyester fiber is not melted and does not form a film. However, there has been a demand for a separator for an electric double layer capacitor that has a lower internal resistance and further improved ion permeability.

JP 2002-266281 A (Claim 1, Claim 7, Claim 12, Examples, etc.) JP 2002-270471 A (Claim 1, Claim 4, Examples, etc.)

  Therefore, the applicant of the present application stated that “a heat-resistant fiber made of a resin having a melting point or a carbonization temperature of 300 ° C. or higher is solidified in a non-fiber state at a fiber intersection, and is lower than the melting point or the carbonization temperature of the heat-resistant fiber. A separator for electric double layer capacitors consisting of a wet nonwoven fabric fixed with a thermoplastic resin having a melting point was proposed. This separator is excellent in ion permeability, gas permeability, liquid permeability, etc. because the thermoplastic resin solidified in a non-fiber state fixes the heat-resistant fiber at the fiber intersection, but the expansion of the electrode In addition, it may be torn by shrinkage and impair the originally required electrical insulation performance.

  As described above, there has been a long-awaited demand for a nonwoven fabric that is excellent in performance such as ion permeability, gas permeability, and liquid permeability and that has mechanical strength (particularly tear strength) that is not cut by an external force. Such non-woven fabrics are used for separators for lithium ion secondary batteries, for gas or liquid filter media, for separators for alkaline secondary batteries, for base materials for laminates, as well as for separators for electric double layer capacitors as described above. In addition, a nonwoven fabric satisfying the same performance as described above has been desired when applied to an electrode support material application, a wiping material application, a medical substrate application, and a fixing unit cleaning sheet application such as a copying machine.

  The present invention was made in order to solve such problems, and in addition to ion permeability, gas permeability, liquid permeability, etc., non-woven fabric that can be applied to various uses by being excellent in mechanical strength, An object of the present invention is to provide a non-woven fabric manufacturing method, an electric double layer capacitor separator made of the non-woven fabric, a lithium ion secondary battery separator, an electric double layer capacitor including the non-woven fabric, or a lithium ion secondary battery. .

  The invention according to claim 1 of the present invention is a nonwoven fabric comprising a thermoplastic resin fiber and a heat-resistant fiber made of a resin having a melting point or a carbonization temperature higher than the melting point of the thermoplastic resin fiber, and the nonwoven fabric configuration A nonwoven fabric characterized in that the fibers are fused and fixed in a state where no film is formed by a thermoplastic resin having the same composition as the thermoplastic resin constituting the thermoplastic resin.

  The invention according to claim 2 of the present invention states that “a fusion cross section in which two or more thermoplastic resin fibers are fused is observed when an electron micrograph of a cross section in the thickness direction at an arbitrary position of the nonwoven fabric is taken. The non-woven fabric according to claim 1, characterized by:

  The invention according to claim 3 of the present invention is “the nonwoven fabric according to claim 1 or 2, wherein the thermoplastic resin for fusion-fixing the nonwoven fabric constituting fiber is derived from the thermoplastic resin fiber”. It is.

  The invention according to claim 4 of the present invention is characterized in that “the thermoplastic resin fiber is made of a thermoplastic resin having a melting point of 200 ° C. or higher and lower than the melting point or carbonization temperature of the heat-resistant fiber. -The nonwoven fabric in any one of Claim 3. ".

  The invention according to claim 5 of the present invention is as follows: “The resin constituting the heat-resistant fiber is made of a resin having a melting point or a carbonization temperature of 300 ° C. or higher. The nonwoven fabric described.

  The invention according to claim 6 of the present invention is “the nonwoven fabric according to any one of claims 1 to 5, wherein the nonwoven fabric includes heat-resistant fibers having fibrils as heat-resistant fibers”. is there.

  The invention according to claim 7 of the present invention is the nonwoven fabric according to any one of claims 1 to 6, wherein a crystallization peak is not drawn on a DSC curve drawn by differential scanning calorimetry of the nonwoven fabric. . "

The invention according to claim 8 of the present invention is characterized in that “the basis weight of the nonwoven fabric is 5 to 30 g / m ² , the thickness is 17 to 55 μm, and the apparent density is 0.32 to 0.6 g / cm ^3. The nonwoven fabric according to any one of claims 1 to 7.

  The invention according to claim 9 of the present invention is “the nonwoven fabric according to claim 8, wherein the tear strength per unit weight in at least one direction of the nonwoven fabric is 0.02 N / g or more.” It is.

  The invention according to claim 10 of the present invention is “the nonwoven fabric according to claim 8 or 9, wherein the elongation in at least one direction of the nonwoven fabric is 3% or more”.

  The invention concerning Claim 11 of this invention is "the separator for electric double layer capacitors consisting of the nonwoven fabric in any one of Claims 1-10."

  The invention concerning Claim 12 of this invention is "the separator for lithium ion secondary batteries which consists of a nonwoven fabric in any one of Claims 1-10."

  The invention according to claim 13 of the present invention is "an electric double layer capacitor comprising the nonwoven fabric according to any one of claims 1 to 10 as a separator."

  The invention concerning Claim 14 of this invention is "the lithium ion secondary battery provided with the nonwoven fabric in any one of Claims 1-10 as a separator."

  The invention according to claim 15 of the present invention is “fibers that form a fiber web using thermoplastic resin fibers and heat-resistant fibers made of a resin having a melting point or carbonization temperature higher than the melting point of the thermoplastic resin fibers”. Web forming step, heat-treating the fiber web, melting a part of the thermoplastic resin fiber so that a part of the thermoplastic resin fiber remains in a fiber form, and aggregating the molten thermoplastic resin A non-woven fabric comprising a coagulation step of forming an aggregated fiber web, and a coagulation step of coagulating the aggregated thermoplastic resin under no pressure and fusion-bonding without forming a film. Manufacturing method. "

  The invention according to claim 16 of the present invention further comprises “a crystallization step of crystallizing the thermoplastic resin by heat treatment after the aggregation step”. Method. "

  The invention according to claim 17 of the present invention is the nonwoven fabric according to claim 15 or 16, wherein the heat treatment in the coagulation step is a heat treatment selected from hot air blowing, infrared irradiation, and laser irradiation. Manufacturing method. "

  The invention according to claim 18 of the present invention is “a method for producing a nonwoven fabric according to any one of claims 15 to 17, wherein the fineness of the thermoplastic resin fiber is 0.45 dtex or less.” It is.

  According to the first aspect of the present invention, the thermoplastic resin fiber includes the thermoplastic resin fiber, and the thermoplastic resin fiber has the same composition as the thermoplastic resin fiber-constituting thermoplastic resin (hereinafter, “the same composition thermoplastic resin”). ”), And the thermoplastic resin fiber and thermoplastic resin of the same composition have high compatibility and are firmly fused and fixed, so that mechanical strength such as tear strength is obtained. Is excellent. In addition, the non-woven fabric constituent fibers are fusion-fixed in a state where a film is not formed with the same composition thermoplastic resin, and since the film is not formed, ion permeability, gas permeability, liquid permeability, etc. Also excellent.

  According to the invention according to claim 2 of the present invention, the fact that a fusion cross section in which two or more thermoplastic resin fibers are fused at an arbitrary place is observed means that a fusion part between thermoplastic resin fibers is fused. This means that the nonwoven fabric is superior in mechanical strength (particularly tear strength).

  According to the invention of claim 3 of the present invention, the thermoplastic resin having the same composition is derived from the thermoplastic resin fiber, and the compatibility between the thermoplastic resin fiber and the thermoplastic resin having the same composition is extremely high. Since the fibers are firmly fused and fixed, mechanical strength such as tear strength is further improved.

  According to the invention of claim 4 of the present invention, since the thermoplastic resin fiber is excellent in heat resistance, it can be applied to various applications.

  According to the invention concerning Claim 5 of this invention, since heat resistant fiber is excellent in heat resistance, it can apply to various uses.

  According to the invention of claim 6 of the present invention, since the nonwoven fabric can have a dense structure by including heat-resistant fibers having fibrils, electrical insulation, separation performance, liquid retention performance, wiping Excellent in various performances such as safety and concealment.

  According to the invention of claim 7 of the present invention, the fact that no crystallization peak is drawn on the DSC curve means that the thermoplastic resin of the same composition is crystallized. Is excellent in thermal stability.

  According to the invention of claim 8 of the present invention, not only is it thin, but it has excellent ion permeability, gas permeability, liquid permeability, etc. due to the large number of voids.

  According to the invention of claim 9 of the present invention, although it has a relatively low basis weight and a relatively low apparent density, it has an excellent tear strength, and therefore can be applied to various applications.

  According to the invention of claim 10 of the present invention, although the basis weight is relatively low and the apparent density is relatively low, it has excellent elongation, and therefore can be applied to various applications. For example, when it is used as a separator for an electric double layer capacitor, it can follow the expansion and contraction of the electrode, so that it is less likely to be torn and electrical insulation performance can be maintained.

  According to the invention concerning Claim 11 of this invention, it is a separator for electric double layer capacitors with low internal resistance and excellent ion permeability. If this separator for electric double layer capacitors is used, an electric double layer capacitor that can be used for a long period of time without breakage during use can be produced.

  According to the invention concerning Claim 12 of this invention, it is a separator for lithium ion secondary batteries with low internal resistance and excellent ion permeability. By using this lithium ion secondary battery separator, it is possible to produce a lithium ion secondary battery that is difficult to break during use and can be used for a long period of time.

  According to the invention of claim 13 of the present invention, it is an electric double layer capacitor that is not easily broken during use and can be used for a long period of time.

  According to the fourteenth aspect of the present invention, there is provided a lithium ion secondary battery that is not easily broken during use and can be used for a long time.

  According to the invention of claim 15 of the present invention, the nonwoven fabric of claims 1 to 3, that is, excellent in mechanical strength such as tear strength, and has ion permeability, gas permeability, liquid permeability, etc. Can also produce excellent nonwoven fabrics.

  According to the invention of claim 16 of the present invention, the nonwoven fabric of claim 7, that is, the nonwoven fabric having excellent mechanical strength and excellent thermal stability even at high temperatures can be produced.

  According to the invention of claim 17 of the present invention, it is easy to manufacture a nonwoven fabric in which the nonwoven fabric constituting fibers are fused and fixed in a state where a film is not formed by the thermoplastic resin having the same composition.

  According to the invention of claim 18 of the present invention, the nonwoven fabric solidified uniformly over the entire nonwoven fabric without impairing the uniform dispersibility of the fibers by forming a space by melting a part of the thermoplastic resin fibers Can be manufactured.

  The nonwoven fabric of the present invention is higher than the melting point of the thermoplastic resin fiber as described later (preferably higher by 10 ° C., more preferably higher by 20 ° C. or higher) so that the fiber form can be maintained and mechanical strength can be imparted to the nonwoven fabric. ) It contains heat-resistant fibers made of a resin having a melting point or a carbonization temperature. This heat resistant fiber may have fibrils which are fine fibers branched from one fiber, or may not have fibrils. The heat-resistant fiber having the former fibril can be a non-woven fabric having a dense structure, and is excellent in various performances such as electrical insulation, separation performance, liquid retention performance, wiping performance, and concealment performance. On the other hand, if the heat-resistant fiber does not have the latter fibril, it can be a nonwoven fabric having excellent mechanical strength.

  The resin constituting the heat resistant fiber is not particularly limited because it is determined by the relationship with the thermoplastic resin fiber, but since it is preferably excellent in heat resistance, such as a nonwoven fabric excellent in versatility, the melting point or The carbonization temperature is preferably made of a resin having a temperature of 300 ° C. or higher. Examples of suitable heat-resistant fiber constituent resins include “resins having a melting point of 300 ° C. or higher”, such as polytetrafluoroethylene and polyphenylene sulfide, and “resins having a carbonization temperature of 300 ° C. or higher”. , Meta-type wholly aromatic polyamide, para-type wholly aromatic polyamide, polyamideimide, aromatic polyether amide, polybenzimidazole, wholly aromatic polyester, and the like. Among these, wholly aromatic polyamides (meta-type wholly aromatic polyamides, para-type wholly aromatic polyamides) or wholly aromatic polyesters are particularly suitable because they are particularly excellent in heat resistance.

  The preferred wholly aromatic polyamide heat-resistant fiber and / or wholly aromatic polyester heat-resistant fiber preferably occupies 50 mass% or more of the heat-resistant fiber so as to be excellent in heat resistance, and is 70 mass% or more. Is more preferable, more preferably 90% by mass or more, and most preferably 100% by mass.

  “Melting point” in the present invention refers to a melting temperature obtained from a differential thermal analysis curve (DTA curve) obtained by differential thermal analysis defined in JIS K 7121, and “carbonization temperature” is defined in JIS K 7120. The temperature at the time when the mass of the test piece is reduced by 5% is measured.

  In addition, when the heat-resistant fiber does not have fibrils, it is a nonwoven fabric with a dense structure, so that various performances such as electrical insulation, separation performance, liquid retention performance, wiping performance, and concealment performance are excellent. The fineness is preferably 1 dtex or less, more preferably 0.8 dtex or less. In addition, when the heat-resistant fiber does not have fibrils, it is a non-woven fabric with a dense structure, so that various performances such as electrical insulation, separation performance, liquid retention performance, wiping performance, and hiding performance are excellent. The fiber length is preferably 0.1 to 15 mm, more preferably 0.1 to 10 mm, and still more preferably 0.1 to 5 mm.

  In the present invention, “fineness” refers to a value obtained by Method A defined in JIS L 1015, and “fiber length” refers to a length obtained by Method B (corrected staple diagram method) of JIS L 1015.

  On the other hand, when the heat-resistant fiber has fibrils, it is a non-woven fabric having a dense structure, so that it is excellent in various properties such as electrical insulation, separation performance, liquid retention performance, wiping performance, and concealment performance. The degree is preferably 300 mlCSF or less, more preferably 200 mlCSF or less, and even more preferably 100 mlCSF or less. In addition, it is preferable that the freeness is 50 mlCSF or more. The heat-resistant fiber having fibrils having such freeness can be obtained by fibrillation with a refiner, pulper, beater, mill, high-pressure homogenizer, or the like, or by promoting fibrillation. The “freeness” in the present invention refers to a value measured by the JIS P8121 Canadian standard freeness test method.

  Such heat resistant fibers are preferably contained in the nonwoven fabric in an amount of 50 mass% or more, more preferably 60 mass% or more so that the nonwoven fabric can be provided with mechanical strength. On the other hand, it is preferably 80% by mass or less, more preferably 70% by mass or less, from the relationship with the thermoplastic resin fibers described later and the thermoplastic resin of the same composition.

  The heat-resistant fibers may include both heat-resistant fibers having fibrils and heat-resistant fibers not having fibrils. In that case, in the heat-resistant fibers, (heat-resistant fibers having fibrils) pair ( The heat resistant fiber having no fibrils is preferably 60 to 95: 5 to 40, and more preferably 80 to 90:10 to 20. Furthermore, even if it is a heat-resistant fiber which has a fibril, it may contain the heat-resistant fiber which has two or more types of fibrils which differ in the point of resin composition and / or freeness, and does not have a fibril. Even so, heat-resistant fibers that do not have two or more types of fibrils that differ in terms of resin composition, fineness, and / or fiber length may be included. In such a case, the total mass is preferably within the above range.

  The nonwoven fabric of the present invention contains thermoplastic resin fibers in addition to the heat-resistant fibers as described above. Since the above heat-resistant fibers are heat-resistant, it is difficult to fuse and fix the heat-resistant fibers to each other. Therefore, the heat-resistant fibers are fused and fixed with a thermoplastic resin having a lower melting point than the heat-resistant fibers. However, if only heat-resistant fibers are fusion-fixed, the mechanical strength such as tear strength tends to be inferior, and therefore thermoplastic resin fibers are included, and the thermoplastic resin fiber constituting thermoplastic resin and The thermoplastic resin fibers are also firmly fused and fixed by the same composition thermoplastic resin of the same composition, thereby increasing the mechanical strength such as tear strength.

  The thermoplastic resin fiber of the present invention may be composed of a resin having a melting point lower than the carbonization temperature or melting point of the heat-resistant fiber (preferably lower by 10 ° C., more preferably lower by 20 ° C.), and is particularly limited. Although not, for example, polyester resin (polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, etc.), polyamide resin (nylon 6, nylon 66, etc.), polyphenylene sulfide resin, polyvinyl chloride resin, polyurethane resin, polyolefin resin (polypropylene) , Polyethylene, poly-4-methylpentene-1, etc.), polyvinylidene chloride resin, and the like. Among these thermoplastic resin fibers, it is preferable that the thermoplastic resin fibers are made of a resin having a melting point of 200 ° C. or higher (preferably 210 ° C. or higher, more preferably 220 ° C. or higher) so as to be excellent in heat resistance. Examples of thermoplastic resins having a melting point of 200 ° C. or higher include polyester resins (polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, etc.), polyamide resins (nylon 6, nylon 66, etc.), polyphenylene sulfide resins, Polyvinyl chloride resin, polyurethane resin, poly-4-methylpentene-1, and the like can be mentioned, and among these, polyester resin excellent in heat resistance is preferable.

  The fineness of the thermoplastic resin fiber of the present invention is not particularly limited, but the fineness is 0.45 dtex so as to be excellent in various properties such as electrical insulation, separation performance, liquid retention performance, wiping performance, and concealment performance. Or less, more preferably 0.35 dtex or less, even more preferably 0.25 dtex or less, and even more preferably 0.15 dtex or less. Although the minimum of the fineness of a thermoplastic resin fiber is not specifically limited, It is preferable that it is about 0.00000001 dtex so that mechanical strength can be improved. In addition, the fiber length of the thermoplastic resin fiber is a non-woven fabric having a dense structure, and 0.1-15 mm so as to be excellent in various properties such as electrical insulation, separation performance, liquid retention performance, wiping performance, and concealment performance. It is preferable that it is 0.1-10 mm, it is more preferable that it is 0.1-5 mm.

  Such thermoplastic resin fibers preferably occupy 20 mass% or more of the nonwoven fabric, and more preferably occupy 30 mass% or more so that the nonwoven fabric has excellent mechanical strength. On the other hand, it is preferable to occupy 50 mass% or less, and more preferably 40 mass% or less from the relationship with the heat resistant fiber and the thermoplastic resin having the same composition. In addition, when increasing the elongation of the nonwoven fabric and increasing the tear strength, the thermoplastic resin fibers preferably occupy 35 to 50 mass% of the nonwoven fabric, and occupy 40 to 45 mass%. Is more preferable. Moreover, the thermoplastic resin fiber may contain two or more types of thermoplastic resin fibers that differ in terms of resin composition, fineness and / or fiber length. When two or more types of thermoplastic resin fibers are included, the total mass is preferably within the above range.

  As described above, the fineness of the thermoplastic resin fiber is preferably 0.45 dtex or less, but such a thermoplastic resin fiber is, for example, an island component manufactured by removing the sea component of the sea-island fiber. It can be comprised from the fiber, the melt blown fiber manufactured by the melt-blowing method, and the electrospun fiber manufactured by the electrospinning method.

  More specifically, the island component fiber produced by removing the sea component of the sea-island fiber can have a fineness of 0.1 dtex or less, and preferably 0.05 dtex or less. In addition, the lower limit of the fineness of the island component fibers is suitably about 0.0000001 dtex.

  Such island component fibers are prepared by using sea island-type fibers having the island component fiber as the island component and the sea component as a resin that can be removed by a solvent that cannot remove the island component. Can be produced by removing with a solvent. For example, a polyester suitable as a resin constituting a thermoplastic resin fiber, that is, an island component fiber made of polyester is, for example, a sea island type fiber having an island component made of polyester in a sea component made of polystyrene. After being produced by the spinning method, it is immersed in dimethylformamide (DMF), and the polystyrene, which is a sea component, is extracted and removed, whereby island component fibers made of polyester can be produced.

  The melt blown fiber, which can be another thermoplastic resin fiber, is manufactured by the melt blow method, that is, the diameter is reduced by blowing a gas such as air against the resin melt-extruded from the die. The fineness of the meltblown fiber has a relatively large variation. However, the average fineness of the meltblown fibers (arithmetic average value of 100 meltblown fibers) can be 0.3 dtex or less, preferably 0.05 dtex or less. The lower limit of the average fineness of the meltblown fiber is suitably about 0.0001 dtex.

  Such a meltblown fiber can be produced by a conventional meltblown method. In addition, when meltblown fibers produced by the meltblowing method are accumulated on a collecting body such as a conveyor, the meltblown fibers are likely to be in a fused state, so that they are accumulated and then poured into water, refiners, pulpers, beaters, mills, Or it is preferable to make it isolate | separate into each melt blown fiber with a high pressure homogenizer etc.

  Further, as another thermoplastic resin fiber, an electrospun fiber manufactured by an electrospinning method can be used. The fineness of the electrospun fiber can be 0.01 dtex or less, preferably 0.007 dtex or less. The lower limit of the fineness of the electrospun fiber is suitably about 0.00000001 dtex.

  Such an electrospun fiber can be produced by a conventional electrospinning method. Electrospun fibers produced by the electrospinning method are generally long fibers with continuous fibers, so that they can be a nonwoven fabric that is uniformly dispersed together with heat-resistant fiber fibers. It is preferable to cut after accumulating on the aggregate. In addition, if the electrospun fibers produced by the electrospinning method are accumulated on a collecting body such as a conveyor, the electrospun fibers are likely to be fused together, and after being accumulated (preferably after being cut), It is preferable to put it into water and separate it into individual electrospun fibers using a refiner, pulper, beater, mill, high-pressure homogenizer or the like. By using such a refiner, a pulper, a beater, a mill, or a high-pressure homogenizer, the electrospun fiber can be cut.

  In the nonwoven fabric of this invention, glass fiber can be included other than the above heat resistant fibers and thermoplastic resin fibers. By including such a glass fiber, it is difficult to be crushed by pressurization and can maintain a void, so that ion permeability, gas permeability, liquid permeability, and the like are excellent.

  The fiber diameter (value converted into a circular cross section) of such a glass fiber is not particularly limited, but can be a non-woven fabric having a dense structure, electrical insulation, separation performance, liquid retention performance, wiping performance. In order to be excellent in various performances such as concealing properties, it is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less. On the other hand, it is preferably 0.001 μm or more, and more preferably 0.01 μm or more. Further, the fiber length of the glass fiber is not particularly limited, but is preferably 0.1 to 15 mm, more preferably 0.1 to 10 mm so that it can be a dense nonwoven fabric. More preferably, it is 0.1-5 mm.

  Such a glass fiber having a small fiber diameter can be produced, for example, by an electrostatic spinning method. More specifically, it can be produced by the method disclosed in JP-A-2003-73964. That is, (1) a step of forming a sol solution mainly composed of tetraethoxysilane, (2) extruding the sol solution from a nozzle and making it thin by applying an electric field to the extruded sol solution. And (3) drying the accumulated gel-like fine fibers to form dry gel-like fine fibers; and (4) the dried gel. The glass fiber can be produced by a step of sintering the fine fiber. In addition, since the glass fiber manufactured by such an electrospinning method is generally a continuous continuous fiber, it can be mixed with a heat-resistant fiber or a thermoplastic resin fiber so that it can be mixed with a gel-like fine fiber or a dried gel-like fiber. It is preferable to cut fine fibers or glass fibers. In addition, when gel-like fine fibers produced by electrostatic spinning are accumulated on a support such as a conveyor, the gel-like fine fibers are likely to be in a bonded state, and are also likely to be in a bonded state by sintering. After sintering (preferably after cutting), it is preferably introduced into water and separated into individual glass fibers with a refiner, pulper, beater, mill, high-pressure homogenizer or the like. The glass fiber can be cut by using a refiner, a pulper, a beater, a mill, a high-pressure homogenizer, or the like.

  It is preferable that the mass ratio in the whole nonwoven fabric of such a glass fiber is 30 mass% or less from the relationship with a heat resistant fiber, a thermoplastic resin fiber, and the below-mentioned same composition thermoplastic resin.

  In the nonwoven fabric of the present invention, non-woven fabric constituent fibers such as heat-resistant fibers, thermoplastic resin fibers, and optionally including glass fibers are fused and fixed by the same composition thermoplastic resin having the same composition as the thermoplastic resin fiber constituent thermoplastic resin. Since there are many fusion-fixing points of heat-resistant fibers via thermoplastic resin fibers, the nonwoven fabric has excellent mechanical strength such as tear strength. In addition, since the thermoplastic resin having the same composition does not form a linear or curved film that extends long like a fiber, it is excellent in ion permeability, gas permeability, liquid permeability, and the like.

  In addition, it is preferable that the same composition thermoplastic resin originates in a thermoplastic resin fiber. When it is derived from the thermoplastic resin fiber in this way, not only is the thermoplastic resin fiber fusion-fixed by the thermoplastic resin of the same composition strong, but it is derived from the thermoplastic resin fiber. This means that the resin fibers become thinner, and thus various performances such as ion permeability, gas permeability, and liquid permeability are more excellent. Thus, it is preferable that the thermoplastic resin fiber is composed of a single resin component so that the thermoplastic resin fiber is firmly fused and fixed by the thermoplastic resin having the same composition.

  The thermoplastic resin having the same composition may be composed of a thermoplastic resin having the same composition as the thermoplastic resin fiber as described above. Such a thermoplastic resin having the same composition can be obtained by, for example, melting a part of the thermoplastic resin fiber as described above, or removing the solvent from a solution obtained by dissolving the thermoplastic resin fiber in an appropriate solvent. Can be formed.

  In addition, it is preferable that the same composition thermoplastic resin is not unevenly distributed in the thickness direction of a nonwoven fabric. This is because if the amount of the thermoplastic resin with the same composition is the same, it is excellent in ion permeability, gas permeability, liquid permeability, etc. because it is not unevenly distributed. Such a state is difficult when the heat resistant fiber and the thermoplastic resin fiber are bonded with an emulsion type adhesive or a solution type adhesive. That is, when drying is performed for bonding with an emulsion type adhesive or a solution type, the adhesive also moves (so-called migration) to the nonwoven fabric surface as the liquid volatilizes.

  The nonwoven fabric of the present invention is one in which the nonwoven fabric constituting fibers are fused and fixed without forming a film with the same composition thermoplastic resin, and this state is reflected in the air permeability. That is, when the film is formed, the air permeability is lowered. However, when the film is fused and fixed as in the present invention, the air permeability is increased. More specifically, the air permeability of the nonwoven fabric of the present invention is preferably 140 s / 100 ml or less, and more preferably 130 s / 100 ml or less. This “air permeability” refers to a value measured with a Gurley tester (type B) specified in JIS P8117 with an adapter having a diameter of 5 mm attached to the tip of the gasket.

  The nonwoven fabric of the present invention contains the above heat-resistant fibers and thermoplastic resin fibers, but when taking an electron micrograph of a cross section in the thickness direction at an arbitrary location of the nonwoven fabric, two or more thermoplastic resin fibers are It is preferable to observe a fusion cross-section in which is fused. The fact that a fusion cross section in which two or more thermoplastic resin fibers are fused together at an arbitrary location is observed means that there are many fusion parts between thermoplastic resin fibers, This is because the mechanical strength (particularly the tear strength) is more excellent. The number of fusions between the thermoplastic resin fibers may be two or more, and the number is not limited, and heat-resistant fibers may be mixed. The electron micrograph of the cross section in the thickness direction is taken at a magnification of 2000 times.

The nonwoven fabric of the present invention preferably has a basis weight of 5 to 30 g / m ² , a thickness of 17 to 55 μm, and an apparent density of 0.32 to 0.6 g / cm ³ . This is because if the nonwoven fabric satisfies such physical properties at the same time, it is excellent in ion permeability, gas permeability, liquid permeability, etc. due to being thin and having many voids. That is, if the basis weight of the nonwoven fabric is less than 5 g / m ² , the uniformity of the nonwoven fabric tends to be impaired, and if it exceeds 30 g / m ² , the thickness tends to increase, and the ion permeability, gas permeability, or There exists a tendency for liquid permeability etc. to worsen. Moreover, when the thickness of the nonwoven fabric is less than 17 μm, various performances such as electrical insulation performance, separation performance, liquid retention performance, wiping performance, and concealment performance, which are basic performances, tend to be deteriorated, and the thickness is 55 μm. If it exceeds, there is a tendency that the advantages of the non-woven fabric cannot be utilized, so a more preferable thickness is 20 to 50 μm. Furthermore, when the apparent density of the nonwoven fabric is less than 0.32 g / cm ³ , the mechanical strength tends to be weak and the handling tends to be difficult. When the apparent density exceeds 0.6 g / cm ³ , the dense structure As a result, the ion permeability, gas permeability, liquid permeability, etc. tend to deteriorate. The “weight per unit area” refers to the basis weight obtained based on the method specified in JIS P 8124 (paper and paperboard—basis weight measurement method), and the “thickness” is a measured value according to the method specified in JIS B 7502, that is, The value measured with an external micrometer at 5 N load is used. Furthermore, “apparent density (D, unit: g / cm ³ )” is the basis weight (W, unit: g / cm ² ) and thickness (T, unit: quotient divided by cm), that is, a value obtained from the following equation.
D = W / T

  The nonwoven fabric of the present invention has a basis weight, thickness, and apparent density as described above, has a relatively small basis weight, and has many voids, but has a tensile strength of at least 7 N / 15 mm width in at least one direction. It is preferable that the tensile strength is high (more preferably 9 N / 15 mm width or more) and the material is easy to handle. The direction having such tensile strength may be any direction, but since the nonwoven fabric is often handled while applying tension to the longitudinal direction, the tensile strength in the longitudinal direction of the nonwoven fabric is 7 N / 15 mm width. The above is preferable. In addition, “tensile strength” is obtained by collecting a rectangular sample (width: 15 mm, length: 200 mm) from a non-woven fabric, and then, according to JIS P-8113, a tensile tester (produced by Orientec Co., Ltd., UCT- 500), the grip interval is 100 mm, and the pulling speed is 50 mm / min. It refers to the tensile strength measured in.

  Further, the tensile strength per unit weight in at least one direction is 0.2 N / g or more (more preferably 0.3 N / g or more, more preferably 0.4 N / g or more), and the tensile strength is high and easy to handle. It is preferable. The direction having such tensile strength may be any direction, but since the nonwoven fabric is often handled while applying tension to the longitudinal direction, the tensile strength per unit weight in the longitudinal direction of the nonwoven fabric is low. It is preferably 0.2 N / g or more. “Tensile strength per unit basis weight” refers to a quotient obtained by dividing the tensile strength by basis weight.

For example, when the nonwoven fabric is used for an electric double layer capacitor separator, the nonwoven fabric of the present invention is not easily broken by an external force when the nonwoven fabric is used. The tear strength per unit weight in at least one direction is preferably 0.02 N / g or more, more preferably 0.03 N / g or more, so that it is difficult to break even under the pressure of 0.03 N / g. It is more preferably 04 N / g or more, and further preferably 0.05 N / g or more. The direction having such tear strength may be any direction, but since a long nonwoven fabric is often used, when the longitudinal direction of the test piece and the longitudinal direction of the nonwoven fabric match in the following test, It is preferable that the tear strength per unit weight of the test piece (nonwoven fabric) is 0.02 N / g or more.
(Tear strength per unit weight)
1. Five rectangular test pieces (width: 50 mm, length: 100 mm) are collected from the nonwoven fabric.
2. According to JIS L-1096 8.15.4 (Method C), the maximum load when tearing at a tensile speed of 200 mm / min is measured.
The tear strength is calculated by arithmetically averaging the maximum loads of the 3.5 test pieces.
4). Divide the tear strength by the basis weight of the nonwoven fabric to calculate the tear strength per unit basis weight.

For example, when the nonwoven fabric is used for an electric double layer capacitor separator, the nonwoven fabric of the present invention is not easily broken by an external force when the nonwoven fabric is used. The elongation in at least one direction is preferably 3% or more, more preferably 5% or more, still more preferably 7% or more, and more preferably 9% or more so that it is difficult to break even under the pressure of More preferably. The direction having such elongation may be any direction, but since a long nonwoven fabric is often used, the elongation in the longitudinal direction of the nonwoven fabric is preferably 3% or more. “Elongation” is obtained by collecting a rectangular sample (width: 15 mm, length: 200 mm) from a non-woven fabric, and then according to JIS P-8113, a tensile testing machine (manufactured by Orientec Co., Ltd., UCT-500). ) Using a gripping interval of 100 mm and a pulling speed of 50 mm / min. Elongation measured in. That is, the value obtained from the following equation.
L = (D / Li) × 100 = D
Here, L means elongation (%), D means elongation at break (mm), and Li means gripping distance (= 100 mm).

The nonwoven fabric of the present invention preferably has a basis weight of 5 to 30 g / m ² and an average flow pore size of 1.1 μm or less. As described above, the fact that the average flow pore size is small despite the low basis weight and the small amount of fiber means that the heat-resistant fiber and the thermoplastic resin fiber are uniformly dispersed, and the separation performance, liquid This is because it is excellent in various performances such as holding performance, wiping properties, and concealing properties and can be applied to various applications. More preferably, the basis weight is 10 to 30 g / m ² and the average flow pore size is 1 μm or less. The “average flow pore size” refers to a value obtained by a method defined in ASTM-F316, and can be measured by a bubble point method using, for example, a porometer (Polometer, manufactured by Coulter).

  The nonwoven fabric of the present invention contains the above heat-resistant fibers and thermoplastic resin fibers, but the nonwoven fabric of the present invention is excellent in mechanical strength even at high temperatures and excellent in thermal stability. Even if the DSC curve is drawn by differential scanning calorimetry of the nonwoven fabric, it is preferable that no crystallization peak is drawn. In other words, the fact that the crystallization peak is not drawn means that the thermoplastic resin having the same composition is sufficiently crystallized, so that the heat-resistant fiber and the thermoplastic resin fiber are fused to resist external force even at a high temperature. This is because it is excellent in thermal stability that can maintain a fixed state, suppress structural changes of the nonwoven fabric, and exhibit desired performance (such as tensile strength and tear strength).

The differential scanning calorimetry is performed under the following conditions in accordance with JIS K 7121 (heat flux differential scanning calorimetry) to draw a DSC curve.
1. Shape, size and mass of test piece (nonwoven fabric): A circular non-woven fabric having a diameter of 6.4 mm is used as the test piece. The test piece is weighed to the second decimal place using an electronic balance with 5 mg as a guide.
2. Inflow rate of nitrogen gas; 50 ml / min.
3. Heating rate: 10.0 deg / min.
4). Measurement start temperature; room temperature (25 ° C)

  The nonwoven fabric of the present invention is not only excellent in electrical insulation performance, separation performance, liquid retention performance, wiping performance, or concealment performance, which are basic performance of the nonwoven fabric, but also in contradictory performance, such as ion permeability, gas Since it has excellent permeability and liquid permeability, it can be used for various purposes. For example, separators for electric double layer capacitors, separators for lithium ion secondary batteries, separators for alkaline secondary batteries, gas or liquid filter materials, base materials for laminates, electrode support materials, wiping materials, It can be suitably used for medical substrate applications, fixing roll cleaning sheet applications in electrophotographic apparatuses, and the like.

  In particular, when the nonwoven fabric of the present invention is used as a separator for an electric double layer capacitor, (1) a stable electric double layer capacitor in which leakage current does not easily occur can be manufactured because of excellent electrical insulation. (2) Since mechanical strength is high, it is easy to handle when manufacturing electric double layer capacitors, and round type electric double layer capacitors are easy to manufacture. (3) Mechanical strength such as tear strength is high. High (especially when a fused fiber bundle is present) and can be a non-woven fabric having a high degree of elongation, so that it does not impair electrical insulation performance, such as breaking during charging / discharging of the electric double layer capacitor, (4) Heat-resistant fibers and thermoplastic resin fibers are fused and fixed without forming a film with the same composition thermoplastic resin, so there are many voids and excellent ion permeability. Therefore, it is possible to manufacture an electric double layer capacitor having a low internal resistance and a large capacity. (5) Since it can be made of a nonwoven fabric having a low basis weight and a small thickness, an electric double layer capacitor having a high energy density in a constant volume is manufactured. (6) When the heat resistant fiber is excellent in heat resistance such as wholly aromatic polyamide or wholly aromatic polyester, the temperature after the separator for the electric double layer capacitor, the collector electrode, and the electrode is assembled is 150. The non-woven fabric of the present invention has an electric double layer because it can be dried together at a high temperature of ℃ or higher, and it is easy to produce an electric double layer capacitor with a high withstand voltage and an electric double layer capacitor with a high energy density. It can be suitably used as a capacitor separator. In addition, when the nonwoven fabric containing glass fiber is used as a separator for an electric double layer capacitor, the affinity of the nonwoven fabric is high for both the aqueous electrolyte solution and the organic electrolyte solution, and the internal resistance is reduced. .

Moreover, when using the nonwoven fabric of this invention as a separator for electric double layer capacitors, it is preferable that an apparent density is 0.32-0.6 g / cm < ³ >. When the apparent density is less than 0.32 g / cm ³ , the mechanical strength tends to be weak and the handling tends to be difficult. When the apparent density exceeds 0.6 g / cm ³ , the structure becomes too dense, This is because the ion permeability tends to deteriorate and it becomes difficult to manufacture an electric double layer capacitor having a large capacity.

  When the nonwoven fabric of the present invention is used as a separator for a lithium ion secondary battery, the internal resistance is low and the ion permeability is excellent, so that a lithium ion secondary battery excellent in high rate characteristics can be produced. Therefore, this lithium ion secondary battery can be suitably used as a battery for applications that require power, such as an electric motorcycle or a tool. In addition, when the heat resistant fiber is excellent in heat resistance such as wholly aromatic polyamide or wholly aromatic polyester, even if the temperature exceeds 180 ° C., the separator (nonwoven fabric) has pores. A highly safe lithium ion secondary battery that does not open or shrink and is unlikely to cause a short circuit due to contact between electrodes can be manufactured.

In addition, when using the nonwoven fabric of this invention as a separator for lithium ion secondary batteries, it is preferable that an apparent density is 0.5-0.6 g / cm < ³ >. When the apparent density is less than 0.5 g / cm ³ , the electrode active material that has fallen out penetrates the separator, or the mechanical strength tends to be weak, and the handling tends to be difficult. On the other hand, when the apparent density exceeds 0.6 g / cm ³ , the structure becomes too dense, the ion permeability is deteriorated, and it tends to be difficult to manufacture a lithium ion secondary battery having excellent high rate characteristics. Because.

  The nonwoven fabric of the present invention is, for example, a fiber web forming step of forming a fiber web using thermoplastic resin fibers and heat-resistant fibers made of a resin having a melting point or carbonization temperature higher than the melting point of the thermoplastic resin fibers, Heat treatment is performed on the fiber web, and a part of the thermoplastic resin fiber is melted so that a part of the thermoplastic resin fiber remains in a fiber form, and the melted thermoplastic resin is aggregated to aggregate. It can be produced by a coagulation step for forming a fiber web, and a coagulation step for coagulating the agglomerated thermoplastic resin under no pressure and fusion-fixing it without forming a film.

  In the fiber web forming step, first, heat-resistant fibers and thermoplastic resin fibers as described above are prepared. In addition, it is preferable that the fineness of a thermoplastic resin fiber is 0.45 dtex or less. This is because part of the thermoplastic resin fiber melts, agglomerates and solidifies, but if the thermoplastic resin fiber is thin, the voids formed by the thin thermoplastic resin fiber are small, so the fiber dispersion is uniform. The fineness is more preferably 0.35 dtex or less, and the more preferred fineness is 0.25 dtex or less, and the most preferable. The fineness is 0.15 dtex or less. The lower limit of the fineness of the thermoplastic resin fiber is not particularly limited, but is preferably about 0.00000001 dtex.

  A fiber web is formed by mixing such heat-resistant fibers and thermoplastic resin fibers, but the mixing ratio of heat-resistant fibers and thermoplastic resin fibers is excellent in heat resistance, versatility, and heat It is preferably 50-80: 20-50, and more preferably 60-70: 30-40 so that it can be firmly fused and fixed with the same composition thermoplastic resin generated from the plastic resin fiber. Particularly when elongation is required, the mixing ratio of the heat resistant fiber and the thermoplastic resin fiber is preferably 50 to 65:35 to 50, and more preferably 55 to 60:40 to 45. .

  The method of forming a fiber web using such heat-resistant fibers and thermoplastic resin fibers is not particularly limited, and can be formed by a conventionally known method. For example, it can be formed by a dry method such as an air array method or a card method, or a wet method. In particular, a fiber web formed by a wet method is suitable because it can produce a non-woven fabric that is dense and excellent in uniform fiber dispersion. Examples of suitable wet methods include a horizontal long net method, an inclined wire type short net method, a circular net method, a forward flow net / reverse flow net combination method, a forward flow net / circular former combination method, and a reverse flow circle. Examples include a network / circle network former combination system, a short network / circle network combination system, a long network / circle network combination system, and the like.

  In addition, it is preferable to form a laminated fiber web (particularly, a laminated fiber web having different fiber orientations of adjacent fiber webs) in which two or more fiber webs having the same or different fiber orientations are laminated. This is because such a laminated fiber web can produce a nonwoven fabric that is further excellent in various properties such as electrical insulation performance, separation performance, liquid retention performance, wiping performance, and hiding performance. For example, when a fiber web is formed by a wet method, wet fiber webs made with the same type of net are stacked, or paper is made with different types of nets (eg, short net and circular net, long net and circular net). Laminated wet fiber webs can be produced by laminating the wet fiber webs, and when wet fiber webs made by different types of nets are laminated, laminated wet fiber webs having different fiber orientations can be formed. In addition, when drying the wet wet fiber web that has been made up, it is preferable to dry at a temperature at which the thermoplastic resin fibers do not melt.

  Next, an aggregation step is performed. In this agglomeration step, heat treatment is performed on the fiber web, and a part of the thermoplastic resin fiber is melted, and a part of the thermoplastic resin fiber is left to maintain the fiber form, and the melted same composition This is a step of aggregating a thermoplastic resin to form an agglomerated fiber web.

  In this step, it is preferable to melt the thermoplastic resin fibers under no pressure so that the thermoplastic resin having the same composition is likely to aggregate. Moreover, the film derived from the same composition thermoplastic resin is not formed by melting under no pressure in this way. In other words, if pressure is applied at this stage, aggregation of the thermoplastic resin of the same composition is hindered, and fusion is performed in a state close to the fiber state, that is, in a state where the thermoplastic resin of the same composition is continuous in a linear or curved shape. It is fixed or fused and fixed in the form of a film around the intersection of constituent fibers, and tends to deteriorate various performances such as ion permeability, gas permeability, or liquid permeability, but if pressure is not applied, A nonwoven fabric excellent in various performances such as ion permeability, gas permeability, or liquid permeability can be produced. Such melting of the thermoplastic resin fibers under no pressure can be performed by, for example, a method of irradiating infrared rays, a method of blowing hot air, or a method of irradiating a laser alone or in combination.

  For example, in the case of irradiating infrared rays (in particular, far infrared rays having a wavelength of 5.6 to 1000 μm are preferable), not only the surface and inside of the fibers (heat-resistant fibers and thermoplastic resin fibers) existing outside the fiber web. The surface and the inside of the fiber (heat-resistant fiber and thermoplastic resin fiber) existing inside the fiber web can also be heated, and a part of the thermoplastic resin fiber can be instantaneously melted. Can be agglomerated.

  When irradiating infrared rays, it heats on the conditions which only a part of thermoplastic resin fiber fuses. In other words, although the thermoplastic resin fiber is irradiated until the temperature becomes higher than the melting point of the thermoplastic resin fiber and lower than the melting point of the heat resistant fiber or the carbonization temperature, the irradiation time is shortened, the output is reduced, etc. No irradiation until the plastic resin fibers are completely melted. Such conditions are not particularly limited because they vary depending on the types of thermoplastic resin fibers and heat-resistant fibers. The infrared irradiation conditions can be appropriately set by repeating the experiment. In this way, the same composition thermoplastic resin in which a part of the thermoplastic resin fiber is melted is agglomerated, but if a pressure is applied at this stage, the aggregation of the thermoplastic resin of the same composition is prevented, that is, a state close to the fiber state, that is, In order to deteriorate the permeability such as ion permeability, gas permeability, or liquid permeability, the thermoplastic resin having the same composition is linearly or curvedly fused and fixed in a continuous film state. Is preferred. In addition, it is preferable that a part of the thermoplastic resin fiber in the fiber web is easily melted by blowing or circulating hot air having a temperature equal to or higher than the glass transition temperature of the thermoplastic resin fiber. When hot air is blown or circulated in this way, the thermoplastic resin with the same composition tends to aggregate at the intersections of the fiber web constituent fibers due to the wind pressure, so that the permeability such as ion permeability, gas permeability, or liquid permeability is further increased. improves. The “glass transition temperature” in the present invention refers to a value obtained by the method for determining the glass transition temperature defined in JIS K 7121-1987.

  Further, even if a portion of the thermoplastic resin fibers is melted by blowing hot air, the thermoplastic resin fibers can be aggregated without forming a film of the molten thermoplastic resin having the same composition. In this case, although a part of the thermoplastic resin fiber melts, hot air at a temperature at which the heat resistant fiber does not melt or carbonize is blown. In other words, although hot air is blown at a temperature higher than the melting point of the thermoplastic resin fiber and lower than the melting point of the heat resistant fiber or the carbonization temperature, the thermoplastic resin fiber is completely removed by shortening the blowing time or reducing the amount of blowing air. Do not spray until melted. The thermoplastic resin having the same composition in which a part of the thermoplastic resin fiber is melted by the action of hot air in this way also acts as a wind pressure when the hot air is blown, and easily aggregates at the intersection of the fiber web constituent fibers. When pressure is applied in addition to spraying hot air at the stage, the thermoplastic resin is fused and fixed in a state close to the fiber state, that is, in a linear or curved continuous film state, or at the intersection of the fiber web constituent fibers It is preferable that no pressure be applied other than spraying hot air, because it tends to deteriorate various performances such as ion permeability, gas permeability, or liquid permeability. In this agglomeration step, a part of the thermoplastic resin fiber in the fiber web is melted by blowing hot air, but a part of the thermoplastic resin fiber in the fiber web is also easily melted. Hot air is preferably blown so that the hot air passes through the fiber web so as to aggregate at the intersections of the constituent fibers and have excellent permeability such as ion permeability, gas permeability, or liquid permeability.

  In addition, by irradiating the fiber web with a laser, not only the surface and inside of the fiber existing outside the fiber web but also the surface and inside of the fiber existing inside the fiber web are heated uniformly, A part can be melted and agglomerated without forming a melted film of the same composition thermoplastic resin.

  This laser is not particularly limited as long as only a part of the thermoplastic resin fiber can be melted. For example, a gas laser (mainly carbon dioxide laser, He-Ne laser, Ar ion laser) or a solid laser is used. (Mainly ruby laser, Nd: YAG laser, Nd: glass laser) or liquid laser (mainly dye laser) can be used. Laser irradiation is performed so that only a part of the thermoplastic resin fiber melts, but the irradiation conditions (wavelength, output, irradiation time, etc.) vary depending on the type of thermoplastic resin fiber and heat resistant fiber. Repeat to set as appropriate. Further, the laser beam can be irradiated to the entire fiber web by, for example, branching with an optical fiber or using a combination of a diffusion lens (ZnSe lens or the like) and an optical fiber.

  When irradiating with laser, a part of the thermoplastic resin fiber is efficiently melted, and hot air is transmitted through the fiber web so that the molten thermoplastic resin having the same composition tends to aggregate at the intersection of the fibers. It is preferable to blow hot air. This is because it is more excellent in permeability such as ion permeability, gas permeability, or liquid permeability. The temperature of the hot air is not particularly limited, but is a temperature not lower than the glass transition temperature of the thermoplastic resin fiber and not lower than the melting point by not less than 10 ° C. so as not to prevent aggregation of the molten thermoplastic resin having the same composition. Is preferred.

  Next, the non-woven fabric of the present invention can be produced by carrying out a coagulation step, that is, a step of coagulating the aggregated thermoplastic resin of the same composition under no pressure and fusing and fixing it without forming a film. This coagulation step may be any method as long as the aggregated thermoplastic resin is coagulated, and is not particularly limited. For example, a gas having a temperature lower than the glass transition temperature of the thermoplastic resin is used. There are a method of spraying or circulating, or a method of leaving it in a gas having a temperature lower than the glass transition temperature of the thermoplastic resin having the same composition. Even in this solidification step, if a pressure is applied to the thermoplastic resin of the same composition that is still in a molten state, a film is formed over a wide range, although not in the form of fibers, and ion permeability, gas permeability, or liquid In order to deteriorate the permeability such as permeability, it is performed under no pressure. As understood from the above description, “under no pressure” in the present invention means that no pressure is applied other than the gas blowing pressure and the gas circulation pressure.

  The nonwoven fabric of the present invention can be produced as described above, but when a part of the thermoplastic resin fibers is instantaneously melted, the degree of crystallinity is low and the heat resistance tends to be inferior. Even if it is used for an application where external force is applied at high temperatures, a structural process hardly occurs and the desired performance can be exhibited, and the thermal stability is excellent. It is preferable to use a nonwoven fabric. In addition, this crystallization process may be implemented after implementing a solidification process, and can also be implemented simultaneously with a solidification process.

  The heat treatment for crystallizing the thermoplastic resin of the same composition is not particularly limited as long as the thermoplastic resin of the same composition is crystallized, but hot air having a temperature lower than the melting point of the thermoplastic resin of the same composition is blown. Or a method of circulating. The heat treatment temperature is not particularly limited as long as it is a heat treatment for crystallizing the thermoplastic resin of the same composition, and is appropriately set by experiment because it varies depending on the composition of the thermoplastic resin of the same composition. For example, when the thermoplastic resin having the same composition is made of a suitable polyester, the temperature is preferably 130 to 230 ° C. In the case of polyester, crystallization tends to be insufficient at less than 130 ° C., and when it exceeds 230 ° C., it approaches the extrapolated dissolution start temperature (temperature at which the resin begins to melt), and the polyester begins to remelt, This is because the solidification state of the polyester is changed, and the temperature is more preferably 150 to 220 ° C. Further, the heat treatment in this crystallization step is preferably performed under no pressure in any stage so that the thermoplastic resin having the same composition does not form a linear or curved continuous film. Note that “crystallize” means that a crystallization peak is not drawn on a DSC curve drawn by differential scanning calorimetry of the manufactured nonwoven fabric.

  In addition, when taking an electron micrograph of a cross section in the thickness direction at an arbitrary location, a nonwoven fabric in which a fusion cross section in which two or more thermoplastic resin fibers are fused together is observed is irradiated with infrared rays or a laser. It can be formed when a part of the thermoplastic resin fiber is melted instantaneously, such as irradiation, to generate the thermoplastic resin of the same composition, and in particular, an agglomeration process that melts a part of the thermoplastic resin fiber instantaneously. Before carrying out the above, if a densification step for increasing the adhesion of the fiber web constituent fibers (thermoplastic resin fibers, heat resistant fibers) is carried out, the degree of freedom of the thermoplastic resin of the same composition generated from the thermoplastic resin fibers is low, Since the compatibility with the nearby thermoplastic resin fibers may be high and the thermoplastic resin fibers tend to aggregate, the non-woven fabric is easy to manufacture. In the densification step, for example, at a temperature lower than the softening temperature of the thermoplastic resin fiber, pressure is applied (for example, by a calendar) so that the thickness of the fiber web is 95% or less of the original thickness. Pressure).

Moreover, when the non-woven fabric after the coagulation step has a thickness variation, when the apparent density is not within the range of 0.32 to 0.6 g / cm ³ , which is suitable, the tensile strength in at least one direction is 7 N / When there is no width of 15 mm or more, when the tensile strength per unit weight in at least one direction is not 0.2 N / g or more, or when the tear strength per unit weight in at least one direction is not 0.02 N / g or more In order to solve the above problem, it is preferable to perform a pressure treatment (for example, calendar treatment) at a temperature lower than the softening temperature of the thermoplastic resin fiber. Preferably, the pressure treatment (for example, calendar treatment) is performed at a temperature 20 ° C. or more lower than the softening temperature of the thermoplastic resin fiber. The pressure in the pressurizing process (for example, calendar process) is not particularly limited because it varies depending on the degree of thickness variation, desired apparent density, desired tensile strength, desired tear strength, and the like. This pressure can be appropriately set by repeating the experiment.

  A nonwoven fabric having an elongation of 3% or more in at least one direction is such that the amount of thermoplastic resin fibers is 35-50 mass% (preferably 40-45 mass%), and agglomerates that instantaneously melt part of the thermoplastic resin fibers Before carrying out the step, it can be produced by appropriately combining a densification step similar to that described above, optimizing the melting amount of the thermoplastic resin fibers, and the like.

  In addition, the nonwoven fabric whose average flow hole diameter is 1.1 micrometers or less forms a fiber web by a wet method, uses the heat resistant fiber which has a fibril as a heat resistant fiber, and the thermoplastic resin whose fineness is 0.05 dtex or less It can manufacture by using a fiber, performing a pressurization process (for example, calendar process) after a coagulation process, etc. individually or in combination.

  Moreover, when applying the nonwoven fabric of this invention to various uses, you may implement the post-processing which improves the adaptability to each use. For example, when used for separators for electric double layer capacitors, separators for lithium ion secondary batteries, separators for alkaline secondary batteries, to give affinity to electrolyte solution, impart affinity such as hydrophilization treatment In order to increase the affinity with varnish when used for treatment, gas or liquid filter media use or wiping use, electretization treatment to enhance the trapping properties of dust, etc. In order to suppress the permeation of contaminated liquid when used for an affinity imparting treatment, for electrode support materials, an affinity imparting treatment for improving adhesion to a metal film, or for a medical substrate use In the case of using for water / oil repellent treatment, and fixing sheet cleaning sheet application, a release agent such as silicone oil can be applied.

  As described above, the method for producing the nonwoven fabric in which the heat-resistant fiber and the thermoplastic resin fiber are fusion-fixed with the same composition thermoplastic resin has been described. However, the glass fiber is included and the glass fiber is also fusion-fixed with the same composition thermoplastic resin. The nonwoven fabric can be produced in the same manner as described above except that, in the process of forming the fiber web, in addition to the heat resistant fiber and the thermoplastic resin fiber similar to those described above, the fiber web is formed using glass fibers. it can.

  The electric double layer capacitor of the present invention can be exactly the same as the conventional electric double layer capacitor except that the nonwoven fabric as described above is used as a separator. The cell structure of the electric double layer capacitor is not particularly limited, and may be a multilayer type, a cylindrical type, a square type, a coin type, or the like.

  For example, as a collector electrode, for example, a metal thin plate such as an aluminum thin plate or a platinum thin plate can be used. As an electrode, for example, a granular activated carbon is mixed with a conductive agent and an adhesive, and a compacting method, a rolling method In addition, those produced by a coating method or a doctor blade method can be used. In addition, as the electrolytic solution, for example, an organic electrolytic solution in which tetraethylammonium tetrafluoroborate is dissolved in propylene carbonate, an organic electrolytic solution in which tetraethylphosphonium tetrafluoroborate is dissolved in propylene carbonate, or the like is used. Can do.

  The manufacturing method of this electric double layer capacitor will be briefly described. First, a separator made of the collector electrode as described above, an electrode, and the nonwoven fabric as described above is prepared. Next, for example, the stacking of the collector electrode, the electrode, the separator, the electrode, and the collector electrode is repeated, or the stacked body thus stacked is rolled up to form an electrode group.

  Next, after inserting the electrode group and the organic electrolyte as described above into the case, the case can be sealed to manufacture a capacitor. When the heat-resistant fiber constituting the nonwoven fabric as the separator is made of a resin having a melting point or a carbonization temperature of 300 ° C. or higher, the electrode group is formed at a temperature of 150 ° C. or higher after forming the electrode group. And the separator can be simultaneously dried and inserted into the case. When the heat-resistant fibers constituting the nonwoven fabric as the separator are made of a resin having a melting point or carbonization temperature of less than 300 ° C., the electrode group is formed after individually drying in advance.

The lithium ion secondary battery of the present invention can be exactly the same as the conventional lithium ion secondary battery except that the nonwoven fabric as described above is used as a separator. For example, a positive electrode having a lithium-containing metal compound paste supported on a current collector is used, and a negative electrode is a lithium metal or lithium alloy, and a carbon material containing carbon or graphite capable of inserting and extracting lithium (for example, Coke, carbon materials such as natural graphite and artificial graphite), those in which composite tin oxide is supported on a current collector, etc. are used, and LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate as an electrolyte. A water electrolyte or the like can be used. The cell structure of the lithium ion secondary battery is not particularly limited, and may be a stacked type, a cylindrical type, a square type, a coin type, or the like.

  Although the manufacturing method of a lithium ion secondary battery is not specifically limited, For example, an aluminum pack type lithium ion secondary battery can be manufactured with the following method.

  First, as a negative electrode, a negative electrode mixture paste formed by mixing a negative electrode active material with a solution such as Pvdf-NMP (polyvinylidene fluoride-N-methylpyrrolidone) is applied onto a copper foil, dried, and pressure-molded. After that, heat treatment is performed to prepare a negative electrode. Also, a positive electrode mixture paste formed by mixing a lithium composite oxide, a conductive agent, and a solution such as Pvdf-NMP as a positive electrode is applied onto an aluminum foil, dried, and subjected to pressure molding, followed by heat treatment. Thus, a positive electrode is prepared. Next, a plurality of units in which a separator made of the nonwoven fabric of the present invention is interposed between a negative electrode and a positive electrode, and a nonaqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent are loaded in an aluminum pack, sealed, An aluminum pack type lithium ion secondary battery can be manufactured.

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

Example 1
Heat-resistant fiber having fibrils made of para-type wholly aromatic polyamide (registered trademark: Twaron 1094, manufactured by Teijin, carbonization temperature: 500 ° C. or higher, freeness (CSF): 150 ml), and fineness of 0.1%. A polyester fiber (registered trademark: Tepyrus, manufactured by Teijin, melting point: 260 ° C., softening temperature: 253 ° C., glass transition temperature: 90 ° C.) having 11 dtex and a fiber length of 3 mm was prepared.

  Next, a slurry was formed in which the heat-resistant fiber having the fibrils and the heat-resistant fiber (freeness (CSF): 90 ml) whose fibrillation was promoted by a refiner and the polyester fiber were dispersed at a mass ratio of 65:35. .

  Thereafter, the slurry is supplied to each net to a paper machine equipped with a forward flow net, an inclined wire type short net, a forward flow net, and a Yankee dryer, and each wet fiber web is formed, and each wet fiber web is laminated. The laminated wet fiber web was formed, and then the laminated wet fiber web was dried by a Yankee dryer set at a temperature of 120 ° C. to form a three-layer wet fiber web in which the fiber orientation was unidirectional, random, and unidirectional. (Fabric web forming step). As shown in FIG. 1, an electron micrograph of the surface of the three-layer wet fiber web was in a state where heat-resistant fibers having fibrils and polyester fibers were mixed.

  Next, a distance of 30 m / min. Between the far infrared ceramic heaters of the far infrared irradiation apparatus provided with 12 far infrared ceramic heaters (manufactured by Ryoka) set at a temperature of 490 ° C., each of which is 12 in the vertical direction. Then, by passing the three-layer wet fiber web, only a part of the polyester fiber was melted and aggregated to form an aggregated fiber web. All the far infrared ceramic heaters were passed 50 mm apart. Further, hot air having a temperature of 220 ° C. was sprayed on the moving three-layer wet fiber web (the agglomeration step).

  Next, the coagulated fiber web was air-cooled at room temperature under no pressure to coagulate the coagulated polyester resin of the same composition to produce a coagulated nonwoven fabric (the coagulation step).

  Thereafter, the solidified nonwoven fabric was passed through a dryer heated to a temperature of 220 ° C. under no pressure for 3 seconds to crystallize the polyester resin of the same composition to produce a crystallized nonwoven fabric (the crystallization step).

Next, this crystallized nonwoven fabric was pressed with a calendar at room temperature (linear pressure: 180 N / cm) to produce a wet nonwoven fabric having a basis weight of 30 g / m ² , a thickness of 50 μm, and an apparent density of 0.6 g / cm ³ . An electron micrograph of the wet nonwoven fabric surface is shown in FIG. Thus, the polyester resin fiber and the heat-resistant fiber coexisted, and the polyester resin fiber was in a state of being fused and fixed without forming a film by the polyester resin having the same composition. Moreover, when the electron micrograph (2000 times) of the thickness direction cross section in 5 points | pieces chosen at random was each photographed and observed, the same composition polyester resin is not unevenly distributed in the thickness direction of a wet nonwoven fabric, and is uniform. Further, a fusion cross-section in which polyester resin fibers were fused to each other was observed in any electron micrograph. An electron micrograph of a typical cross section in the thickness direction is shown in FIG. Furthermore, when the differential scanning calorimetry of this wet nonwoven fabric was measured, a DSC curve as shown in FIG. 4 was drawn, and no crystallization peak was drawn.

(Example 2)
The heat resistance having fibrils is the same as in Example 1 except that the same fibrillation-promoted heat-resistant fiber and polyester fiber as in Example 1 were used in a slurry dispersed in a mass ratio of 55:45. A three-layer wet fiber web in which fibers and polyester fibers were mixed was formed (the fiber web forming step).

  Next, the three-layer wet fiber web is passed between calendar rolls at a temperature of 60 ° C. (linear pressure: 160 N / cm) to form a densified fiber web having 64% of the original thickness of the three-layer wet fiber web. (The densification step).

  Next, the distance between the far-infrared ceramic heaters of the far-infrared irradiation apparatus provided with twelve upper and lower far-infrared ceramic heaters (manufactured by Ryoka) set at a temperature of 450 ° C. is 20 m / min. By passing the densified fiber web through, only a part of the polyester fiber was melted and aggregated to form an aggregated fiber web. All the far infrared ceramic heaters were passed 50 mm apart. Further, hot air having a temperature of 220 ° C. was sprayed on the moving densified fiber web (the agglomeration step).

  Next, the coagulated fiber web was air-cooled at room temperature under no pressure to coagulate the coagulated polyester resin of the same composition to produce a coagulated nonwoven fabric (the coagulation step).

Thereafter, the coagulated non-woven fabric was passed through a dryer heated to a temperature of 220 ° C. under no pressure for 3 seconds to crystallize the same composition polyester resin, having a basis weight of 21 g / m ² , a thickness of 38 μm, and an apparent density of 0. A 55 g / cm ³ wet nonwoven fabric was produced (the crystallization step).

  In this wet nonwoven fabric, polyester resin fibers and heat resistant fibers coexisted, and were fused and fixed by the same composition polyester resin without forming a film. Moreover, when the electron micrograph (2000 times) of the thickness direction cross section in 5 points | pieces chosen at random was each photographed and observed, the same composition polyester resin is not unevenly distributed in the thickness direction of a wet nonwoven fabric, and is uniform. Further, a fusion cross-section in which polyester resin fibers were fused to each other was observed in any electron micrograph. Furthermore, when the differential scanning calorimetry of this wet nonwoven fabric was measured and a DSC curve was drawn, no crystallization peak was drawn.

(Example 3)
In the fiber web forming process, a slurry in which heat-resistant fibers and polyester fibers that promoted fibrillation were dispersed at a mass ratio of 60:40 was used, and in the densification process, the temperature of the calendar was 90 ° C. In the agglomeration step, the densified fiber web is made 16 m / min. A wet non-woven fabric having a basis weight of 28 g / m ² , a thickness of 47 μm, and an apparent density of 0.61 g / cm ³ was produced in the same manner as in Example 2 except that it was passed at a speed of. In this wet nonwoven fabric, polyester resin fibers and heat resistant fibers coexisted, and were fused and fixed by the same composition polyester resin without forming a film. Moreover, when the electron micrograph (2000 times) of the thickness direction cross section in 5 points | pieces chosen at random was each photographed and observed, the same composition polyester resin is not unevenly distributed in the thickness direction of a wet nonwoven fabric, and is uniform. Further, a fusion cross-section in which polyester resin fibers were fused to each other was observed in any electron micrograph. Furthermore, when the differential scanning calorimetry of this wet nonwoven fabric was measured and a DSC curve was drawn, no crystallization peak was drawn.

(Comparative Example 1)
Heat resistant fiber that promotes fibrillation as in Example 1, polyester fiber as in Example 1, and core-sheath type composite polyester fiber (registered trademark: Melty, manufactured by Unitika, melting point of core: 255 ° C., sheath Melting point: 110 ° C., fineness 1.1 dtex, fiber length: 3 mm).

  Next, a slurry in which heat-resistant fibers, polyester fibers, and core-sheath type composite polyester fibers were dispersed at a mass ratio of 50:20:30 was formed. Thereafter, the slurry is supplied to each net to a paper machine equipped with a forward flow net, an inclined wire type short net, a forward flow net, and a Yankee dryer, and each wet fiber web is formed, and each wet fiber web is laminated. Then, the laminated wet fiber web is dried by a Yankee dryer set at a temperature of 120 ° C. and the core-sheath type composite polyester fiber is fused, and the fiber orientation is unidirectional, random, and one. A three-layer wet fiber web in the direction was formed.

Subsequently, both surfaces of this three-layer wet fiber web were tempo 20 m / min. To produce a wet nonwoven fabric having a basis weight of 20 g / m ² , a thickness of 55 μm, and an apparent density of 0.36 g / cm ³ . In this wet nonwoven fabric, the core-sheath type composite polyester fiber was fused in a fiber state, and a film was formed in a linear or curved shape, and was in a surface fused state.

(Comparative Example 2)
The same heat resistant fiber and polyester fiber as in Example 1 were prepared. Next, a slurry in which heat-resistant fibers (freeness (CSF): 90 ml) whose polyester was promoted by a refiner and polyester fibers were dispersed at a mass ratio of 70:30 was formed. Thereafter, the slurry is supplied to each net to a paper machine equipped with a forward flow net, an inclined wire type short net, a forward flow net, and a Yankee dryer, and each wet fiber web is formed, and each wet fiber web is laminated. The laminated wet fiber web was formed, and then the laminated wet fiber web was dried by a Yankee dryer set at a temperature of 120 ° C. to form a three-layer wet fiber web in which the fiber orientation was unidirectional, random, and unidirectional. .

Next, this dried three-layer wet fiber web was pressed (linear pressure: 50 N / cm) with a pair of thermal calenders set at a temperature of 220 ° C., with a basis weight of 30 g / m ² , a thickness of 50 μm, and an apparent density of 0.6 g. A wet nonwoven fabric of / cm ³ was produced. This wet nonwoven fabric was in a state where it was pressure-bonded in a state of fibers in which the width of the polyester fiber was widened.

(Comparative Example 3)
The distance between the far-infrared ceramic heaters of the far-infrared irradiation apparatus provided with 12 each of the far-infrared ceramic heaters (manufactured by Ryoka) set at a temperature of 490 ° C. is 8 m / min. Thus, the polyester fiber was completely melted and aggregated by passing through a three-layer wet fiber web formed in the same manner as in Example 1 to form an aggregated fiber web. All the far infrared ceramic heaters were passed 50 mm apart. Further, hot air having a temperature of 220 ° C. was sprayed on the moving three-layer wet fiber web (the agglomeration step).

  Next, the aggregated fiber web was air-cooled at room temperature under no pressure to coagulate the aggregated polyester resin to produce a coagulated nonwoven fabric (the coagulation step).

  Thereafter, the solidified nonwoven fabric was passed through a dryer heated to a temperature of 220 ° C. under no pressure for 3 seconds to crystallize the polyester resin, thereby producing a crystallized nonwoven fabric (the crystallization step).

Next, this crystallized nonwoven fabric was pressed with a calendar at room temperature (linear pressure: 170 N / cm) to produce a wet nonwoven fabric having a basis weight of 30 g / m ² , a thickness of 50 μm, and an apparent density of 0.6 g / cm ³ . An electron micrograph of the wet nonwoven fabric surface is shown in FIG. Thus, the polyester resin was in a state of being fused and fixed in a state where no film was formed. Moreover, when the electron micrograph (2000 times) of the thickness direction cross section in 5 points | pieces chosen at random was each photographed and observed, the same composition polyester resin is not unevenly distributed in the thickness direction of a wet nonwoven fabric, and is uniform. However, polyester resin fibers were not present. A typical electron micrograph of the cross section in the thickness direction is shown in FIG. Furthermore, when the differential scanning calorimetry of this wet nonwoven fabric was measured, a DSC curve as shown in FIG. 7 was drawn, and no crystallization peak was drawn.

(Measurement of internal resistance)
As an electrode, granular activated carbon, carbon black, and polytetrafluoroethylene are mixed and kneaded, aluminum foil as a collecting electrode, wet nonwoven fabric of each example and each comparative example as a separator, and tetraethylammonium tetrafluoroborate as an electrolyte Was prepared by dissolving propylene carbonate in propylene carbonate.

  Subsequently, the electrode group which consists of a laminated body which repeated stacking in order of the collector electrode, an electrode, the separator of Examples 1-3, or Comparative Example 1- Comparative Example 3, the electrode, and the collector electrode was formed, respectively. Subsequently, this electrode group was dried at a temperature of 200 ° C. Next, the dried electrode group and the electrolyte solution were inserted into a case, and then the case was sealed to prepare 100 coin cell type capacitors.

  Thereafter, the internal resistance of each capacitor was obtained from a charge / discharge curve measured by a charge / discharge tester. That is, it was determined from a charge / discharge curve obtained by an operation of charging to 2.5 V for 2 minutes at a constant current of 1 A and then discharging for 2 minutes. The results are shown in Table 1. If this internal resistance is 2Ω or less, it can be judged that the ion permeability is excellent, but as is clear from Table 1, the separator made of the wet nonwoven fabric of the present invention has an excellent ion transmission of 1.8 to 1.9Ω. It showed sex. It was predicted that this was due to the wet nonwoven fabric having no film and having a structure with many voids.

(Evaluation of short circuit prevention)
When 100 coin cell type capacitors used in the above (measurement of internal resistance) were produced 100 pieces each, the percentage of capacitors that were short-circuited and became defective products (failure rate) was calculated. The results are shown in Table 1. When the separator made of the wet nonwoven fabric of the present invention was used, a defective capacitor was not produced, and the short circuit prevention property was excellent. This was presumed to be because the wet nonwoven fabric constituent fibers were uniformly dispersed and the mechanical strength such as tensile strength and tear strength was excellent.

(Measurement of tensile strength)
After collecting a rectangular sample (width: 15 mm, length (longitudinal direction): 200 mm) from the wet nonwoven fabric of each example and each comparative example, a tensile tester (Orientec Co., Ltd.) according to JIS P-8113. Manufactured by UCT-500), using a grip interval of 100 mm and a pulling speed of 50 mm / min. The tensile strength was measured at The results are shown in Table 1. If this tensile strength is 7 N / 15 mm width or more, it can be used without any trouble in both coin type and round type capacitors. As is clear from Table 1, the wet nonwoven fabric of the present invention had excellent tensile strength of 8.2 N / 15 mm or more and excellent handleability.

(Measurement of air permeability)
The air permeability of the wet nonwoven fabrics of each Example and each Comparative Example was measured in a state where an adapter having a diameter of 5 mm was attached to the tip of the gasket in a Gurley tester (B type) specified in JIS P8117. The results are shown in Table 1.

(Measurement of average flow hole diameter)
The average flow pore diameters of the wet nonwoven fabrics of each Example and each Comparative Example were measured by a bubble point method using a porometer (Polometer, manufactured by Coulter). The results are shown in Table 1.

(Measurement of tear strength per unit weight)
Five rectangular test pieces (width: 50 mm, length: 100 mm, the longitudinal direction of the test piece coincides with the longitudinal direction of the nonwoven fabric) were sampled from the wet nonwoven fabrics of each Example and each Comparative Example. Subsequently, according to JIS L-1096 8.15.4 (C method), the maximum load at the time of tearing at a tensile speed of 200 mm / min was measured. Thereafter, the maximum load of the five test pieces was arithmetically averaged to calculate the tear strength. Then, the tear strength was divided by the basis weight of the nonwoven fabric to calculate the tear strength per unit basis weight. As is apparent from Table 1, the wet nonwoven fabric of the present invention had an excellent tear strength of 0.029 N / g or more.

(Measurement of elongation)
After collecting a rectangular sample (width: 15 mm, length: 200 mm) from the wet nonwoven fabric of each example and each comparative example, a tensile tester (manufactured by Orientec Co., Ltd., UCT-) according to JIS P-8113. 500), the grip interval is 100 mm, and the pulling speed is 50 mm / min. The elongation was calculated from the following formula from the elongation at break and elongation at break.
L = (D / Li) × 100 = D
Here, L means elongation (%), D means elongation at break (mm), and Li means a holding interval (= 100 mm). As is apparent from Table 1, the wet nonwoven fabric of the present invention had an excellent elongation of 4.8% or more.

＊：括弧内は単位目付あたりの引張り強さ（Ｎ／ｇ）
＃：総合評価
◎：内部抵抗が低く、引張強さ、引裂強さ等の機械的強度に優れ、不良品を発生させない、特に良好な湿式不織布（セパレータ）
×１：内部抵抗が高く、また引裂き強さが弱く、不良率が比較的高いため使用できない
×２：内部抵抗が高く、しかも引張強さや引裂き強さ等の機械的強度に劣り、不良率が非常に高いため使用できない
△：内部抵抗がやや高く、引裂き強さがやや弱く、不良品を発生させるため使用しずらい

*: Tensile strength per unit weight (N / g) in parentheses
#: Overall evaluation A: Low internal resistance, excellent mechanical strength such as tensile strength, tear strength, etc., especially good wet nonwoven fabric (separator) that does not cause defective products
× 1: Internal resistance is high, tear strength is weak, and defect rate is relatively high, so it cannot be used. × 2: Internal resistance is high, and mechanical strength such as tensile strength and tear strength is inferior. Cannot be used because it is very high △: Internal resistance is slightly high, tear strength is slightly weak, and it is difficult to use because it causes defective products

Example 4
A wet nonwoven fabric having a basis weight of 20 g / m ² , a thickness of 33 μm, and an apparent density of 0.6 g / cm ³ was produced in exactly the same manner as in Example 1. In this wet nonwoven fabric, polyester resin fibers and heat resistant fibers coexisted, and were fused and fixed by the same composition polyester resin without forming a film. Moreover, when the electron micrograph (2000 times) of the thickness direction cross section in 5 points | pieces chosen at random was each photographed and observed, the same composition polyester resin is not unevenly distributed in the thickness direction of a wet nonwoven fabric, and is uniform. Further, a fusion cross-section in which polyester resin fibers were fused to each other was observed in any electron micrograph. Furthermore, when the differential scanning calorimetry of this wet nonwoven fabric was measured and a DSC curve was drawn, no crystallization peak was drawn.

(Comparative Example 4)
A commercially available polyethylene microporous membrane (manufactured by Celgard, basis weight: 15 g / m ² , thickness: 25 μm, apparent density: 0.6 g / cm ³ ) was prepared.

(Production of lithium ion secondary battery)
First, a paste obtained by mixing graphitized mesophase spherules and a Pvdf-NMP (polyvinylidene fluoride-N-methylpyrrolidone: 13% by weight) solution at a solid mass ratio of 90:10 is placed on a copper foil. Four negative electrodes were prepared by coating, drying, pressure molding, and heat treatment.

In addition, a paste prepared by mixing LiCoO ₂ : acetylene black: Pvdf-NMP solution (12 wt%) at a solid mass ratio of 85: 5: 10 was applied onto an aluminum foil, dried, pressure-molded, and then heated. Three positive electrodes were prepared by processing.

Subsequently, the wet nonwoven fabrics or microporous membranes of Example 4 and Comparative Example 4 were used as separators, respectively, and a plurality of units were formed by being interposed between the negative electrode and the positive electrode. On the other hand, a non-aqueous electrolyte solution in which 1 mol / L LiPF ₆ was dissolved in a solvent in which ethylene carbonate / diethyl carbonate was mixed at a volume ratio of 1: 1 was prepared. Thereafter, the plurality of units and the non-aqueous electrolyte were loaded into an aluminum pack to produce an aluminum pack type lithium ion secondary battery (cell size: 40 × 60 mm, battery capacity: 180 mAh).

(Evaluation of battery characteristics of lithium ion secondary battery)
The produced lithium ion battery was charged to 4.2 V at a constant current-constant voltage (0.5 C, 3 hours), and a constant current discharge was performed at a discharge end voltage of 3.0 V. Each discharge rate characteristic was calculated when the discharge capacity at a 0.2 C current value was 100%. The results are shown in Table 2. As is apparent from Table 2, the battery using the separator made of the wet nonwoven fabric of the present invention was excellent in discharge characteristics. It was predicted that this was due to the excellent ion permeability due to the structure having many voids and no film formed on the wet nonwoven fabric.

(Safety test)
After charging each of the produced lithium ion batteries until full charge, the laminate pack was pierced with nails, and the measurement and state of the battery surface maximum temperature were observed. The results are shown in Table 2. As is clear from Table 2, the battery using the separator made of the wet nonwoven fabric of the present invention does not shrink even if the separator (wet nonwoven fabric) has a hole and short-circuits, and can prevent a short circuit due to contact between electrodes. It was highly safe.

＃１：発火、発煙ともになし
＃２：発煙
＊：単位目付あたりの引張り強さ（Ｎ／ｇ）
◎：安全性が高く、放電レート特性（ハイレート）に優れている
×：安全性が低く、放電レート特性（ハイレート）にも劣る

# 1: Neither ignition nor smoke # 2: Smoke *: Tensile strength per unit weight (N / g)
A: High safety and excellent discharge rate characteristics (high rate) ×: Low safety and poor discharge rate characteristics (high rate)

(Measurement of tear strength per unit weight)
A rectangular test piece (width: 50 mm, length: 100 mm, the longitudinal direction of the test piece coincides with the longitudinal direction of the wet nonwoven fabric or microporous membrane) from the wet nonwoven fabric or microporous membrane of Example 4 and Comparative Example 4. Samples were collected one by one. Subsequently, according to JIS L-1096 8.15.4 (C method), the maximum load at the time of tearing at a tensile speed of 200 mm / min was measured. Thereafter, the maximum load of the five test pieces was arithmetically averaged to calculate the tear strength. Then, the tear strength per unit basis weight was calculated by dividing the tear strength by the basis weight. As is apparent from Table 2, the wet nonwoven fabric of the present invention was 0.025 N / g and had excellent tear strength.

(Measurement of various physical properties)
The tensile strength, air permeability, average flow pore size and elongation of the wet nonwoven fabric or microporous membrane of Example 4 and Comparative Example 4 were measured in the same manner as the wet nonwoven fabrics of Examples 1-3 and Comparative Examples 1-3. . These results are shown in Table 2.

Electron micrograph of the three-layer wet fiber web surface of Example 1 Electron micrograph of wet nonwoven fabric surface of Example 1 Electron micrograph of a representative cross section in the thickness direction of Example 1 DSC curve of wet nonwoven fabric of Example 1 Electron micrograph of wet nonwoven fabric surface of Comparative Example 3 Electron micrograph of representative cross section in thickness direction of Comparative Example 3 DSC curve of wet nonwoven fabric of Comparative Example 3

Explanation of symbols

1 Heat-resistant fiber 2 Polyester fiber 3 Fusion cross section

Claims (18)

A non-woven fabric comprising a thermoplastic resin fiber and a heat-resistant fiber made of a resin having a melting point or a carbonization temperature higher than the melting point of the thermoplastic resin fiber, and the non-woven fabric constituting fiber is the thermoplastic resin fiber constituting thermoplastic resin; A non-woven fabric characterized by being fused and fixed with a thermoplastic resin having the same composition without forming a film. The fusion cross section in which two or more thermoplastic resin fibers are fused together is observed when an electron micrograph of a thickness direction cross section at an arbitrary location of the nonwoven fabric is taken. Non-woven fabric. The nonwoven fabric according to claim 1 or 2, wherein the thermoplastic resin for fusing and fixing the nonwoven fabric constituting fibers is derived from the thermoplastic resin fibers. The nonwoven fabric according to any one of claims 1 to 3, wherein the thermoplastic resin fiber is made of a thermoplastic resin having a melting point of 200 ° C or higher and lower than the melting point or carbonization temperature of the heat-resistant fiber. The nonwoven fabric according to any one of claims 1 to 4, wherein the resin constituting the heat resistant fiber is a resin having a melting point or a carbonization temperature of 300 ° C or higher. The non-woven fabric according to any one of claims 1 to 5, wherein the non-woven fabric includes heat-resistant fibers having fibrils as the heat-resistant fibers. The nonwoven fabric according to any one of claims 1 to 6, wherein a crystallization peak is not drawn on a DSC curve drawn by differential scanning calorimetry of the nonwoven fabric. The basis weight of the nonwoven fabric is 5 to 30 g / m ² , the thickness is 17 to 55 µm, and the apparent density is 0.32 to 0.6 g / cm ^3. The nonwoven fabric described. The nonwoven fabric according to claim 8, wherein the tear strength per unit weight in at least one direction of the nonwoven fabric is 0.02 N / g or more. The nonwoven fabric according to claim 8 or 9, wherein the elongation in at least one direction of the nonwoven fabric is 3% or more. The separator for electric double layer capacitors which consists of a nonwoven fabric in any one of Claims 1-10. The separator for lithium ion secondary batteries which consists of a nonwoven fabric in any one of Claims 1-10. The electric double layer capacitor provided with the nonwoven fabric in any one of Claims 1-10 as a separator. The lithium ion secondary battery provided with the nonwoven fabric in any one of Claims 1-10 as a separator. A fiber web forming step of forming a fiber web using a thermoplastic resin fiber and a heat-resistant fiber made of a resin having a melting point or carbonization temperature higher than the melting point of the thermoplastic resin fiber;
Heat treatment is performed on the fiber web, and a part of the thermoplastic resin fiber is melted so that a part of the thermoplastic resin fiber remains in a fiber form, and the melted thermoplastic resin is aggregated to aggregate. An agglomeration step to form a fiber web;
A coagulation step in which the agglomerated thermoplastic resin is solidified under no pressure, and is fused and fixed in a state where no film is formed;
The manufacturing method of the nonwoven fabric characterized by comprising. The method for producing a nonwoven fabric according to claim 15, further comprising a crystallization step of crystallizing the thermoplastic resin by heat treatment after the aggregation step. The method for producing a nonwoven fabric according to claim 15 or 16, wherein the heat treatment in the coagulation step is a heat treatment selected from hot air blowing, infrared irradiation, and laser irradiation. The method for producing a nonwoven fabric according to any one of claims 15 to 17, wherein the fineness of the thermoplastic resin fiber is 0.45 dtex or less.

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