JP2005116514A - Separator for battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for battery which is excellent in tensile strength, electrolytic solution retention property and short-circuit resistant property, capable of exerting a stable battery property. <P>SOLUTION: The separator for battery is made by integrally laminating a plurality of water flow interlaced nonwoven fabrics made of card webs containing a thermally adhesive fabric having fineness of 0.3-5.5 dtex by thermocompression bonding, so that the separator has a cavity appropriate in size and has holes having appropriate sizes and roughly uniform diameters, and furthermore, has fabric density roughly uniform as a whole. Accordingly, the separator obtains excellent tensile strength, holding the property of an electrolyte solution and resistance to a short circuit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a battery separator that can be suitably used for alkaline storage batteries such as nickel-cadmium batteries, nickel-zinc batteries, and nickel-hydrogen batteries, and a method for producing the same.

  Conventional battery separators include non-woven fabric made of nylon or polypropylene fibers (hereinafter referred to as “dry non-woven fabric”), non-woven fabric manufactured by wet papermaking (hereinafter referred to as “wet non-woven fabric”), synthetic Resin porous films are used.

  In general, wet nonwoven fabrics are dense and have excellent uniformity. Therefore, when wet nonwoven fabrics are used, battery separators with excellent short-circuit resistance can be obtained, while productivity is poor and the fiber length of the constituent fibers is low. Because it is short, it is inferior to dry nonwoven fabrics in terms of tensile strength, and there is a problem that it is easy to break when winding the electrode and separator firmly like a cylindrical alkaline storage battery, resulting in a decrease in short-circuit resistance. .

  Also, the dry nonwoven fabric is larger than the wet nonwoven fabric with the same tensile strength, and when this dry nonwoven fabric is used as a battery separator, it has excellent winding properties but is inferior to the nonwoven fabric, and the fiber. There was a problem that the density was high, the piercing strength was weak, and the short-circuit resistance was poor.

Therefore, as a battery separator having both tensile strength and short-circuit resistance, Patent Document 1 discloses that a melt blown nonwoven fabric having a basis weight of 10 g / m ² or more and a hydroentangled nonwoven fabric made of a short fiber web are laminated and integrated by thermocompression bonding. A battery separator has been proposed.

  However, the fibers constituting the melt-blown nonwoven fabric constituting the battery separator are blown with hot air and accumulated directly on the conveyor because the melt-spun fibers are blown away, so there is no stretching treatment, the degree of stretching is low, and there are many amorphous parts. doing. Accordingly, the puncture strength of the battery separator is not sufficient, and the battery separator does not have satisfactory short-circuit resistance. Furthermore, as described above, since the fibers constituting the meltblown nonwoven fabric have many amorphous parts, the processing temperature range when the meltblown nonwoven fabric and the hydroentangled nonwoven fabric are laminated and integrated by thermocompression bonding becomes narrower. . As a result, delamination between the meltblown nonwoven fabric and the hydroentangled nonwoven fabric is likely to occur, or the meltblown nonwoven fabric may melt excessively to form a film, resulting in poor battery separator productivity. .

  Furthermore, in Patent Document 2, a polyolefin-based split composite fiber having an average fiber length of 20 to 60 mm, a high-strength fiber having an average fiber length of 30 to 60 mm, and a fiber strength of 5 g / denier or more, There has been proposed a battery separator obtained by hydrophilizing a nonwoven fabric obtained by subjecting a polyolefin-based heat-bonding fiber having an average fiber length of 30 to 60 mm to heat fusion treatment and hydroentanglement treatment.

  However, card webs composed of fibers having a relatively long fiber length, in particular, unidirectional card webs (parallel card webs) tend to be inferior in formation and tend to be denser and denser, so that high-strength fibers are simply used. It was difficult to improve the short-circuit resistance of the battery separator only by the inclusion.

JP-A-5-182654 (Claims) JP-A-10-154502

  The present invention provides a battery separator that is excellent in productivity, excellent in tensile strength and short-circuit resistance, and can exhibit stable battery characteristics, and a method for producing the same.

  The battery separator of the present invention is formed by laminating and integrating a plurality of hydroentangled nonwoven fabrics made of card webs containing thermal adhesive fibers having a fineness of 0.3 to 5.5 dtex by thermocompression bonding.

  The separator for a battery according to the present invention is characterized in that a plurality of hydroentangled nonwoven fabrics made of card webs containing heat-adhesive fibers having a fineness of 0.3 to 5.5 dtex are laminated and integrated by thermocompression bonding. The fibers are bonded together in a state where the conductive fibers are crushed and deformed, and the pores having an appropriate size and a substantially uniform diameter are formed as well as having an appropriate size void. It also has electrolyte retention and short circuit resistance.

  Moreover, since the battery separator is formed by laminating and integrating a plurality of hydroentangled nonwoven fabrics made of card webs by thermocompression bonding, the battery separator is excellent in productivity and has a substantially uniform fiber density as a whole. It excels in strength and puncture strength, and there is almost no risk of damage or short-circuiting when it is incorporated in the battery or used in the battery, thereby impairing the battery performance.

  In the battery separator, when the heat-adhesive fiber is a core-sheath type composite fiber, the core component can maintain the fiber shape, so that the tensile strength and piercing strength of the obtained battery separator can be further increased. While being able to improve, it is easy to ensure the space | gap between fibers and it is excellent in electrolyte solution retainability.

  Further, in the battery separator, the card web is a polyolefin resin having a fineness of 0.3 to 5.5 dtex and a melting point higher by 5 ° C. or more than the melting point of the heat bonding component of the heat bonding fiber. When the fiber is included, the polyolefin fiber becomes a skeleton and is integrated by the heat-adhesive fiber, so that an appropriately sized void is formed in the battery separator, and the electrolyte retention is particularly excellent. Yes.

  In the battery separator, when the card web includes a heat-adhesive fiber having a fineness of 0.3 to 5.5 dtex and a polyolefin-based splitting composite fiber, the card-based splitting fiber is formed by splitting the polyolefin-based splitting composite fiber. Due to the ultrafine fibers formed, voids of an appropriate size are formed in the battery separator, and the electrolyte retainability is excellent.

  Furthermore, in the battery separator, when the fineness of the polyolefin-based split composite fiber after splitting is smaller than the fineness of the heat-adhesive fiber and the polyolefin-based fiber, fine voids are formed in the battery separator. Thus, the electrolytic solution retention can be improved.

  And in the said battery separator, a card web is a polyolefin fiber which has a melting point 5 degreeC or more higher than the melting | fusing point of the thermal-adhesion fiber of 0.3-5.5 dtex, and the thermal-adhesion component of this thermal-adhesive fiber. In the case of including the polyolefin-based split composite fiber, an appropriately sized void is formed in the battery separator, and the electrolytic solution retention is particularly excellent.

  In addition, the battery separator manufacturing method includes a step of laminating a plurality of card webs containing heat-adhesive fibers having a fineness of 0.3 to 5.5 dtex, and subjecting the card webs to hydroentanglement to obtain hydroentangled nonwoven fabrics. And a step of producing a laminated nonwoven fabric by laminating a plurality of hydroentangled nonwoven fabrics, and a temperature of 25 ° C. lower than the melting point of the thermal adhesive component of the thermal adhesive fiber and the melting point of the thermal adhesive component. A battery excellent in tensile strength, electrolytic solution retention and short-circuit resistance because it includes a step of integrating hydroentangled nonwoven fabrics by compressing in the thickness direction at a pressure of 15 to 10000 N / cm in a temperature range of less than Can be easily manufactured.

  In addition, the battery separator manufacturing method includes a plurality of hydroentangled nonwoven fabrics made of card webs having a predetermined fiber configuration, which are laminated and integrated by thermocompression bonding, and are excellent in manufacturing efficiency and low cost as described above. A battery separator having tensile strength, electrolytic solution retention and short-circuit resistance can be easily produced.

  The thermoadhesive fiber constituting the card web refers to a fiber having an action of adhering fibers constituting the battery separator. Such a heat-adhesive fiber is not particularly limited as long as the fineness is 0.3 to 5.5 dtex. As the heat-bonding fiber, it is preferable to use a staple fiber which has been conventionally used as a constituent fiber of a battery separator and has been melt-spun and subjected to a stretching process. Examples of the heat-adhesive fiber include polypropylene, ethylene-propylene copolymer, ethylene-butene-1-propylene copolymer, high-density polyethylene, low-density polyethylene, ethylene-vinyl alcohol copolymer, ethylene-acrylic acid copolymer. Single fibers such as polyolefin fibers such as polymers and ethylene-methyl acrylate copolymers; and composite fibers such as a core-sheath type, an eccentric core-sheath type, a parallel type, and a sea-island type. It is preferable that the heat-adhesive fiber is not divided.

  It is preferable to use a core-sheath type composite fiber as the heat-adhesive fiber. This is because the core component can maintain the fiber form, so that when the thermal bonding is performed, the tensile strength and piercing strength of the separator can be maintained high, and the inter-fiber voids can be easily secured. In addition, as a cross-sectional shape of a heat bondable fiber, any of circular shape, unusual shape, a hollow shape, etc. may be sufficient, for example.

  Examples of the core-sheath composite fiber include a core-sheath composite fiber in which the sheath component is an ethylene-propylene copolymer and the core component is polypropylene, and the sheath component is high-density polyethylene and the core component is polypropylene. Examples of the core-sheath type composite fiber include a core-sheath type composite fiber in which the sheath component is low-density polyethylene and the core component is polypropylene. The core-sheath type composite fiber includes a core-sheath type composite fiber in which the sheath component is high-density polyethylene and the core component is polypropylene, and a core sheath in which the sheath component is an ethylene-propylene copolymer and the core component is polypropylene. At least one core-sheath type composite fiber selected from the group consisting of type composite fibers is preferred. This is because the tensile strength and piercing strength of the battery separator can be improved.

  Furthermore, if the fineness of the heat-adhesive fiber is small, the card-passing property is lowered. On the other hand, if the fineness is large, spots are generated in the formation of the hydroentangled nonwoven fabric, so that it is limited to 0.3 to 5.5 dtex. . The preferred fineness of the heat-adhesive fiber is 0.5 dtex or more. The preferred fineness of the heat-adhesive fiber is 3.3 dtex or less. A more preferable fineness of the heat-bonding fiber is 2.2 dtex or less. Moreover, since the card | curd permeability will fall even if the fiber length of the said heat bondable fiber is short or long, 30-70 mm is preferable. A more preferable fiber length of the heat-adhesive fiber is 35 mm or more. A more preferable fiber length of the heat-adhesive fiber is 65 mm or less.

  And when a staple fiber having a length of 30 to 70 mm is used as the heat-adhesive fiber, the staple fiber is obtained because it has higher strength than an unstretched fiber such as a fiber constituting a melt blown nonwoven fabric. The puncture strength of the battery separator can be made excellent.

  Furthermore, when staple fibers are used as the heat-bonding fibers, the battery separator obtained is dense and uniform compared to a spunbond nonwoven fabric composed of continuous fibers, and therefore has excellent piercing strength.

  In addition, if the content of the heat-adhesive fiber in the card web is small, delamination occurs between hydroentangled nonwoven fabrics, or it becomes difficult to adjust the pore size of the battery separator, and the tensile strength and piercing strength of the battery separator are low. Since there exists a possibility that it may fall, 15 mass% or more is preferable. 100 mass% may be sufficient as the upper limit of content of a heat bondable fiber. If the amount is too large, it may be difficult to ensure the inter-fiber voids of the separator. Therefore, the more preferable content of the heat-adhesive fiber is 80% by mass or less. The content of the particularly preferable heat-adhesive fiber is 60% by mass or less. Further, the more preferable content of the heat-adhesive fiber is 20% by mass or more.

  The card web can be mixed with polyolefin fibers. The polyolefin fiber constituting the card web is not particularly limited. For example, polypropylene, ethylene-propylene copolymer, ethylene-butene-1-propylene copolymer, high-density polyethylene, low-density polyethylene, ethylene-vinyl alcohol. Examples thereof include fibers comprising a copolymer, an ethylene-acrylic acid copolymer, an ethylene-methyl acrylate copolymer, and the like. A polypropylene fiber, a sheath component is an ethylene-vinyl alcohol copolymer, and a core component is a polyolefin core. A sheath type composite fiber is preferred. For example, when enhancing the hydrophilicity of the battery separator, a core-sheath type composite fiber in which the sheath component is an ethylene-vinyl alcohol copolymer and the core component is polyolefin is preferable. Examples of the core component polyolefin include polyethylene and polypropylene.

  And if the melting point of the polyolefin-based fiber is low, it melts or softens in the process of manufacturing the battery separator, and the puncture strength of the resulting battery separator may decrease and the short circuit resistance may decrease. It is preferably 5 ° C. or more higher than the melting point of the heat bonding component of the heat bonding fiber. A more preferable lower limit of the melting point of the polyolefin fiber is (the melting point of the heat bonding component of the heat-bonding fiber + 10 ° C.). The upper limit of the melting point of the preferred polyolefin fiber is 250 ° C. In addition, melting | fusing point of the heat-bonding component of polyolefin fiber and a heat-bondable fiber means what was measured based on DSC method based on JISK7121.

  Furthermore, if the fineness of the polyolefin fiber is small, the puncture strength of the battery separator may be reduced and the short-circuit resistance may be reduced. On the other hand, if the fineness is large, the electrolyte solution retention of the battery separator may be reduced. Therefore, 0.3 to 5.5 dtex is preferable. The fineness of the polyolefin fiber is more preferably 0.5 dtex or more. More preferable fineness of the polyolefin fiber is 3.3 dtex or less.

  Also, if the fiber length of the polyolefin fiber is short, the puncture strength of the battery separator may be reduced and short-circuit resistance may be reduced. On the other hand, if the fiber length is long, the uniformity of the texture of the battery separator may be reduced. Since there exists, 30-70 mm is preferable. A more preferable fiber length of the polyolefin fiber is 35 mm or more. The fiber length of the polyolefin fiber is more preferably 65 mm or less.

  And if there is much content of the polyolefin-type fiber in a card web, since there exists a possibility that delamination may arise between hydroentangled nonwoven fabrics, or adjustment of the hole diameter of a battery separator may become difficult, 85 mass% or less is below. Preferably, if the amount is too small, it may be difficult to ensure the inter-fiber gap of the battery separator, and therefore the content of the polyolefin fiber is more preferably 20% by mass or more. The content of polyolefin fibers is more preferably 80% by mass or less.

  Further, the card web may contain a polyolefin-based split composite fiber, and by containing the polyolefin-based split composite fiber in this way, the electrolyte solution retention of the battery separator can be improved. It is possible to improve the battery life because the battery characteristics are not deteriorated even if charging and discharging are repeated for a long period of time.

  Such a polyolefin-type split composite fiber may be any fiber that does not melt during the manufacturing process of the battery separator. That is, if the melting point of each resin component constituting the polyolefin-based split composite fiber is low, it melts or softens in the process of manufacturing the battery separator, and the puncture strength of the obtained battery separator is reduced, resulting in short circuit resistance. Is lower than the melting point of the heat-bonding component of the heat-adhesive fiber. A more preferable lower limit of the melting point of each resin component constituting the polyolefin-based split conjugate fiber is (the melting point of the heat bonding component of the heat-bonding fiber + 10 ° C.). A more preferable upper limit of the melting point of each resin component constituting the polyolefin-based split conjugate fiber is 250 ° C. In addition, melting | fusing point of each resin component which comprises a polyolefin-type split type composite fiber means what was measured based on DSC method based on JISK7121. Examples of such a polyolefin-based split type composite fiber include a combination of polypropylene and an ethylene-vinyl alcohol copolymer, a combination of polypropylene and polymethylpentene, and a combination of polypropylene and polyethylene.

  The polyolefin-based split composite fiber is composed of a polyolefin-based split composite fiber composed of a combination of polypropylene and an ethylene-vinyl alcohol copolymer, and a polyolefin-based split composite fiber composed of a combination of polypropylene and polymethylpentene. At least one split-type conjugate fiber selected from the group is preferred. The combination of the polyolefin-based split composite fibers is appropriately selected according to the required performance of the battery separator and the hydrophilic treatment method of the battery separator.

  If the fineness of the polyolefin-based splitting composite fiber is small, the card passing property is deteriorated and the productivity is lowered. On the other hand, if the fineness is large, it is necessary to increase the number of divisions in order to obtain a desired fineness after splitting. In addition to a decrease in productivity, if the split-type composite fiber is made into a non-woven fabric, if it remains as an undivided fiber, sufficient electrolyte retention may not be obtained, so that 0.3 to 5.5 dtex is obtained. preferable. The fineness of the polyolefin-based split composite fibers is more preferably 1 dtex or more. The fineness of the polyolefin-based split composite fibers is more preferably 4 dtex or less.

  And, if the fineness after splitting of the above-mentioned polyolefin-based splitting composite fiber is large, the effect of improving the electrolyte solution retention may not be obtained. Therefore, it is preferably 0.3 dtex or less, and the heat-adhesive fiber and the polyolefin It is more preferable that it is smaller than the system fiber. The fineness after splitting of the polyolefin-based split composite fiber is preferably 0.01 dtex or more. The number of divisions of the polyolefin-based split composite fiber is not particularly limited as long as the fineness after splitting satisfies the above range, but it is preferably, for example, 4 to 24 in terms of fiber production. .

  Moreover, when the fiber length of the polyolefin-based split composite fiber is short, the splitting property is improved, but the productivity of the hydroentangled nonwoven fabric may be reduced, and the nonwoven fabric strength when the hydroentangled nonwoven fabric is reduced. On the other hand, if the length is long, the uniformity of the formation of the separator may be lowered, so 30 to 70 mm is preferable. The fiber length of the polyolefin-based split composite fiber is more preferably 35 mm or more. The fiber length of the polyolefin-based split composite fiber is more preferably 65 mm or less.

  If the content of the polyolefin-based split composite fiber in the card web is small, the electrolyte solution retention of the battery separator may be reduced. On the other hand, if the content is large, the separator becomes too dense and the interfiber gap Since securing may become difficult, 85 mass% or less is preferable. The content of the polyolefin-based split composite fiber is more preferably 5% by mass or more. The content of the polyolefin-based split composite fiber is particularly preferably 10% by mass or more. The content of the polyolefin-based split composite fiber is more preferably 80% by mass or less.

  In addition, when the heat-adhesive fiber, polyolefin-based fiber and polyolefin-based split composite fiber are used in combination as the fiber constituting the card web, the heat-adhesive fiber is 15 to 80% by mass, and the polyolefin fiber is 10 to 75% by mass. And 10 to 75% by mass of the polyolefin-based split composite fiber, more preferably 20 to 60% by mass of the heat-bonding fiber, 20 to 60% by mass of the polyolefin-based fiber, and 20 to 60% by mass of the polyolefin-based split composite fiber.

  The battery separator of the present invention comprises a plurality of hydroentangled nonwoven fabrics made of card webs including the above-mentioned thermoadhesive fibers and, if necessary, polyolefin fibers and polyolefin split composite fibers, laminated and integrated by thermocompression bonding. It becomes. Thus, by laminating a plurality of hydroentangled nonwoven fabrics and laminating them by thermocompression bonding, correcting the unevenness of the fiber density of each hydroentangled nonwoven fabric, the fiber density of the resulting battery separator is substantially uniform, Excellent battery strength can be exhibited by imparting excellent tensile strength and short circuit resistance.

  Moreover, since the battery separator of the present invention is formed by laminating and integrating a plurality of hydroentangled nonwoven fabrics, each hydroentangled nonwoven fabric can have a relatively low basis weight. Therefore, energy consumption can be reduced in the hydroentanglement process, and the formation of the hydroentangled nonwoven fabric can be improved.

  In addition, when a card web containing polyolefin-based split composite fibers is used, each hydroentangled nonwoven fabric can be produced with a relatively low basis weight, so that the polyolefin-based split composite fibers can be uniformly split in the web thickness direction. Thus, the ultrafine fibers can be uniformly dispersed in the hydroentangled nonwoven fabric. A battery separator obtained by laminating and integrating such hydroentangled nonwoven fabrics maintains a state in which ultrafine fibers are uniformly dispersed, and exhibits good battery characteristics.

  Next, the manufacturing method of the said battery separator is demonstrated. First, if necessary, polyolefin fibers and / or polyolefin-based split composite fibers are added to the heat-adhesive fibers, mixed, supplied to a plurality of card machines, and carded. The card web is continuously discharged. A laminated web is manufactured in a state in which a plurality of long card webs are stacked on top of each other. By laminating a plurality of card webs in this way, the density of the fiber density of each card web can be corrected. Further, by laminating a plurality of card webs to form a laminated web, the mixed fibers can be dispersed substantially uniformly in the thickness direction of the laminated web.

  The number of stacked card webs is preferably three. This is because when the three card webs are laminated, it is easy to adjust the basis weight of the battery separator to a desired value while effectively achieving the above-described effects.

The basis weight of each laminated web is preferably 10 to 45 g / m ² . The basis weight of each laminated web is more preferably 15 g / m ² or more. The basis weight of each laminated web is more preferably 40 g / m ² or less. This is because the formation of the laminated web is stabilized by setting the basis weight of each laminated web within the above range. In addition, when the polyolefin-based divided composite fiber is contained in the laminated web, the polyolefin-based divided composite fiber is uniformly divided in the web thickness direction by the hydroentanglement process described later. Weight per unit area of each card web, 5~25g / m ² is preferred. When a laminated web is manufactured by laminating three card webs, the basis weight of each card web is preferably 5 to 15 g / m ² for the same reason as described above.

  Thereafter, a laminated web formed by laminating a plurality of card webs is continuously fed onto the support member, and a high-pressure water stream is ejected from a plurality of orifice heads arranged in one or a plurality of rows. Examples of the form of the water flow include a columnar shape and a spray shape. A water flow is made to collide with the laminated web so that the laminated web is entangled over the entire surface substantially uniformly to obtain a hydroentangled nonwoven fabric (water entanglement treatment). In addition, although the water flow from an orifice head may be made to collide only with one side of a laminated web, after making a water flow collide with one surface of a laminated web, it is preferable to make a water flow collide with the other surface of a laminated web.

  Although it does not specifically limit as said hydroentanglement process conditions, It carries out on conditions milder than the hydroentanglement process conditions at the time of normal nonwoven fabric manufacture. This is because the card webs are entangled and integrated while holding the gap formed in the card web, and the electrolyte separator retainability of the battery separator is maintained.

  As specific conditions for the water flow entanglement treatment, the interval between adjacent orifice heads is preferably 0.3 mm or more, more preferably 0.5 mm or more. On the other hand, if wide, the entanglement by the water flow may be insufficient. 0.5 mm or less is preferable, and 1.3 mm or less is more preferable.

  In addition, when the water pressure during hydroentanglement treatment is low, fiber entanglement may be insufficient. Therefore, 1 MPa or more is preferable, and 2 MPa or more is more preferable. Therefore, the retention of the electrolytic solution may be reduced, so that it is preferably 10 MPa or less, and more preferably 6 MPa or less.

  In addition, when the card | curd web is made to contain the polyolefin division | segmentation type | mold composite fiber, it is necessary to adjust hydroentanglement process conditions so that a polyolefin type | system | group division | segmentation type | mold composite fiber may be divided | segmented.

The hydroentangled nonwoven fabric obtained by hydroentangling and integrating a plurality of card webs is dried with a hot air dryer or the like because it contains moisture. The drying temperature is preferably a temperature below the lowest melting point T ₀ among the melting points of the fibers constituting the hydroentangled nonwoven fabric, that is, the temperature at which all the fibers constituting the nonwoven fabric do not melt. A more preferable drying temperature is 5 ° C. or lower than the lowest melting point T ₀ , and a particularly preferable drying temperature is 8 ° C. or lower than the lowest melting point T ₀ . On the other hand, the drying temperature is not particularly limited as long as the hydroentangled nonwoven fabric can be completely dried, but 60 ° C. or higher is preferable in consideration of productivity.

  The reason why the hydroentangled nonwoven fabric is preferably dried under the above-described drying temperature condition is as follows. First, it is possible to easily adjust the thermal bonding state when the hydroentangled nonwoven fabrics are laminated and integrated, and to increase the delamination strength between the hydroentangled nonwoven fabrics. Secondly, when the polyolefin-based divided composite fiber is included, the polyolefin-based divided composite fiber is not unexpectedly melted and the pore size of the battery separator can be easily adjusted.

A plurality of hydroentangled nonwoven fabrics manufactured in this way are stacked to form a laminated nonwoven fabric. The laminated nonwoven fabric is compressed in the thickness direction from both sides at a pressure T of 15 to 10000 N / cm at a temperature T (° C.) satisfying the following formula 1, thereby producing a battery separator by integrating the hydroentangled nonwoven fabrics. be able to.
Melting point Tm−25 ° C. ≦ T of heat bonding component of heat bonding fiber
<The melting point Tm of the thermal adhesive component of the thermal adhesive fiber: Formula 1

  The method for integrating the hydroentangled nonwoven fabrics by compressing the laminated nonwoven fabric from both sides in the thickness direction is not particularly limited. For example, between the opposed surfaces of a pair of heat rolls facing each other with a predetermined interval. There is a method in which the laminated nonwoven fabric is sandwiched from both sides by the pair of heat rolls, and the hydroentangled nonwoven fabrics are integrated with each other by the thermal adhesive fibers.

And as temperature at the time of compressing the said laminated nonwoven fabric from both surfaces, it is limited to temperature T (degreeC) which satisfy | fills Formula 1, Temperature T (degreeC) which satisfy | fills Formula 2 is preferable, Temperature T (degreeC which satisfy | fills Formula 3) ) Is more preferable. This is because when the compression temperature is low, the hydroentangled nonwoven fabrics are not sufficiently integrated with each other, and the hydroentangled nonwoven fabrics may be separated from each other. On the other hand, when the compression temperature is high, melting of the thermoadhesive fibers proceeds. This is because a film is formed too much, or the pore size of the battery separator is reduced, so that gas permeability when used in a battery is lowered and the internal pressure of the battery tends to increase. In addition, when there are a plurality of heat-adhesive components of the heat-adhesive fiber, the melting point Tm of the heat-adhesive component of the heat-adhesive fiber means the lowest temperature.
Melting point Tm−25 ° C. ≦ T of heat bonding component of heat bonding fiber
<The melting point Tm of the thermal adhesive component of the thermal adhesive fiber: Formula 1
Melting point Tm−20 ° C. ≦ T of heat bonding component of heat bonding fiber
<The melting point Tm of the thermal adhesive component of the thermal adhesive fiber: Formula 2
Melting point Tm−20 ° C. ≦ T of heat bonding component of heat bonding fiber
<The melting point Tm-5 ° C. of the heat bonding component of the heat bonding fiber
... Formula 3

  Furthermore, as a pressure at the time of compressing the said laminated nonwoven fabric from the both surfaces in the thickness direction, it is limited to 15-10000 N / cm. As a pressure which compresses a laminated nonwoven fabric, 100 N / cm or more is preferable and 200 N / cm or more is more preferable. On the other hand, as a pressure which compresses a laminated nonwoven fabric, 700 N / cm or less is preferable and 600 N / cm or less is more preferable.

  This is because if the pressure for compressing the laminated nonwoven fabric is low, the hydroentangled nonwoven fabrics are not sufficiently integrated with each other, and the hydroentangled nonwoven fabrics may be delaminated or it may be difficult to adjust the pore size of the battery separator. On the other hand, if the pressure for compressing the laminated nonwoven fabric is high, the pore size of the battery separator becomes small, the gas permeability when used in a battery is lowered, and the internal pressure of the battery may be increased. It is.

  In this way, the laminated nonwoven fabric is compressed in the thickness direction from both sides within a predetermined temperature and a predetermined pressure range, and the hydroentangled nonwoven fabrics are integrated with each other, so that the surface portion of the obtained battery separator is constituted. The heat-adhesive fiber is crushed and deformed. Furthermore, the heat-bonding fibers constituting the surface portion of the battery separator are heat-bonded to each other while being crushed and deformed. In addition, when the fiber which comprises the battery separator contains the polypropylene fiber as a polyolefin fiber, the polypropylene fiber is also crushed and deformed. Therefore, the obtained battery separator has a large number of voids formed therein, and can sufficiently hold the electrolytic solution. It is preferable that the heat-adhesive fibers having a circular cross-section are crushed in the radial direction and the cross-section is deformed into an elliptical shape or a state close to an elliptical shape to bond the heat-adhesive fibers to each other.

  In particular, when the battery separator includes a heat-adhesive fiber, a polyolefin-based fiber having a melting point higher by 5 ° C. than the melting point of the heat-adhesive component of the heat-adhesive fiber, and a polyolefin-based split composite fiber, While maintaining the fiber form, the thermal adhesive fibers are crushed and bonded with the thermal adhesive fibers, so that the gap of the battery separator can be adjusted to an appropriate size and the hydroentangled nonwoven fabric They can be firmly integrated into a state in which appropriate gaps are formed between the nonwoven fabrics, and the electrolyte can be more sufficiently held.

  In the battery separator thus obtained, the thermal adhesive fiber constituting the surface portion is more crushed than the thermal adhesive fiber inside. Therefore, when the battery separator is wound between the current collectors, the burrs generated at the ends of the current collectors penetrate the battery separators, or foreign matter such as dendrites generated during the battery charge / discharge process. As a result, the battery separator can be effectively prevented from being short-circuited by being damaged. The surface portion of the battery separator refers to a portion between the surface of the battery separator and a portion that is inward by 25 μm in the thickness direction from the surface of the battery separator. Further, the inside of the battery separator refers to the remaining portion excluding the surface portion of the battery separator. Furthermore, the degree of crushing of the heat-adhesive fibers constituting the battery separator can be confirmed by enlarging and observing the cross section of the battery separator using an electron microscope (SEM) or the like.

  As described above, the laminated nonwoven fabric is compressed in the thickness direction from both sides within a predetermined temperature and a predetermined pressure range, and the hydroentangled nonwoven fabrics are integrated with each other. While being able to adjust to an appropriate size, the pore diameter can be made substantially uniform, and as a result, the electrolyte retention and gas permeability of the battery separator can be made favorable. Further, when the laminated nonwoven fabric is compressed in the thickness direction within a predetermined temperature and a predetermined pressure range, the battery separator can be adjusted to a desired thickness at the same time, and productivity can be improved.

  In addition, a plurality of card webs are superposed to produce a hydroentangled nonwoven fabric, and a plurality of hydroentangled nonwoven fabrics are laminated and integrated. The fiber has a high fiber density, has almost no sparse fiber density, and has an excellent tensile strength. Therefore, there is no possibility that the battery separator is broken even when the battery separator is incorporated in a wound state in the battery.

  And since a plurality of hydroentangled nonwoven fabrics obtained by overlapping a plurality of card webs are laminated and integrated, the fibers constituting each hydroentangled nonwoven fabric are substantially uniform in the thickness direction of the battery separator. The battery separator thus dispersed is excellent in mechanical strength and has high battery performance stability.

  In particular, since the battery separator has excellent tensile strength as described above, the battery separator is interposed between a pair of electrodes, and the cylinder is used by firmly winding the battery separator. It can be suitably used for a type alkaline storage battery.

  Furthermore, as described above, the battery separator has excellent mechanical strength because there are almost no parts with low fiber density. Therefore, when the battery separator is wound between the current collectors, the burrs generated at the ends of the current collectors penetrate the battery separators, or foreign matter such as dendrites generated during the battery charge / discharge process. As a result, the battery separator can be effectively prevented from being short-circuited (short-circuit resistance).

Further, the battery separator produced as described above may be subjected to a hydrophilic treatment. Examples of such hydrophilic treatment include hydrophilic surfactant treatment, vinyl monomer graft copolymerization treatment, fluorine gas treatment, sulfonation treatment, corona discharge treatment, plasma discharge treatment, and the like. Treatment and fluorine gas treatment are preferred. Specific examples of the sulfonation treatment include SO ₃ gas treatment, concentrated sulfuric acid treatment, fuming sulfuric acid treatment, and chlorosulfonic acid treatment. For example, the corona discharge treatment may be performed 1 to 20 times so that the total discharge amount is 0.05 to 5 kW · min / m ² on one side or both sides of the battery separator. Examples of the fluorine gas treatment include a method of treating a battery separator in a mixed gas of fluorine gas and sulfurous acid gas and / or oxygen gas.

If the basis weight of the battery separator is small, the tensile strength, short-circuit resistance and electrolyte retention of the battery separator may be reduced. On the other hand, if the basis weight is large, the battery using the battery separator is downsized. 30 to 90 g / m ² is preferable, and 30 to 70 g / m ² is more preferable.

  Furthermore, if the thickness of the battery separator is thin, the tensile strength, short-circuit resistance and electrolyte retention of the battery separator may be reduced. On the other hand, if the battery separator is thick, the battery using the battery separator is downsized. 50 to 250 μm is preferable, and 80 to 200 μm is more preferable.

  The difference between the maximum pore diameter (BUBBLE POINT PORE DIAMETER) and the minimum pore diameter (SMALLEST DETECTED PORE DIAMETER) measured by the bubble point method in accordance with ASTM F31686 in the battery separator of the present invention is 45 μm or less. It is preferable. For example, when a battery separator is used for a small battery represented by AA type and AAA type, the difference between the maximum pore diameter (BUBBLE POINT PORE DIAMETER) and the minimum pore diameter (SMALLEST DETECTED PORE DIAMETER) is 20 to 40 μm. It is preferable. When battery separators are used for large batteries typified by sub-C and D types, the difference between the maximum pore size (BUBBLE POINT PORE DIAMETER) and the minimum pore size (SMALLEST DETECTED PORE DIAMETER) is 30 to 45 μm Is preferred. In addition, when a battery separator is used for a rectangular battery, the difference between the maximum pore diameter (BUBBLE POINT PORE DIAMETER) and the minimum pore diameter (SMALLEST DETECTED PORE DIAMETER) is preferably 20 to 45 μm, more preferably 20 to 40 μm. preferable.

  The difference between the maximum pore size (BUBBLE POINT PORE DIAMETER) and the minimum pore size (SMALLEST DETECTED PORE DIAMETER) is an index indicating the uniformity of the pore size of the battery separator, and the smaller the difference, the more uniform the pore size. I can say that. In conventional battery separators that use a single layer of hydroentangled nonwoven fabric with card webs laminated and integrated, the spots on the card web itself are hydroentangled so that the spots become more noticeable. There was a tendency for the difference between the pore size and the minimum pore size to increase. According to the present invention, a plurality of hydroentangled nonwoven fabrics made of card webs are laminated and integrated by thermocompression bonding, and the unevenness of the card web is corrected. A separator is obtained.

(Example 1)
A core-sheath type composite heat-adhesive fiber having a sheath component of high-density polyethylene and a core component of polypropylene (melting point of high-density polyethylene: 135 ° C., fineness: 1 dtex, fiber length: 38 mm) and 50% by mass of polypropylene fiber (melting point: 165 ° C., fineness: 1.7 dtex, fiber length: 45 mm) mixed at a ratio of 50% by mass, supplied to three semi-random card machines and carded, and a card web with a basis weight of 8 g / m ² from each card machine Were continuously discharged. These three long card webs were stacked on top of each other, and a laminated web having a basis weight of 24 g / m ² was continuously produced.

  Thereafter, the laminated web was continuously fed onto the porous support member, and a water flow was ejected in a columnar shape from a plurality of orifice heads having a nozzle diameter of 0.08 mm at a pressure of 3 Mpa. This water flow was collided with one surface of the laminated web, and the card webs were laminated and integrated by interlacing the fibers of the superimposed card webs.

  Next, water flow jetted from a plurality of orifice heads was collided with the other surface of the laminated web in the same manner, and the fibers of the overlapped card web were entangled and integrated to produce a hydroentangled nonwoven fabric. Thereafter, the hydroentangled nonwoven fabric was heated to 125 ° C. and dried. The orifice heads in which water flow was jetted on both sides of the laminated web were arranged at intervals of 0.6 mm in the direction orthogonal to the feeding direction of the laminated web and arranged in three rows in the feeding direction of the laminated web. .

Subsequently, two hydroentangled non-woven fabrics obtained as described above were successively and successively laminated to form a laminated non-woven fabric. And this laminated nonwoven fabric is continuously supplied between the opposed surfaces of a pair of thermal rolls facing each other with a predetermined interval, and the laminated nonwoven fabric is 440 N / cm at 120 ° C. from both sides by this pair of thermal rolls. A separator for a battery was obtained by compressing in a thickness direction with pressure and laminating and integrating the hydroentangled nonwoven fabrics by thermocompression bonding. The battery separator had a basis weight of 51.7 g / m ² and a thickness of 128 μm. Moreover, the outer peripheral surface of the heat roll was formed in the smooth surface.

(Example 2)
A battery separator was produced in the same manner as in Example 1 except that the basis weight of the card web was adjusted to 10 g / m ² . Then, this battery separator is supplied into an SO ₃ gas treatment machine, and left in an SO ₃ gas atmosphere having a concentration of 8% by volume at 60 ° C. for 60 seconds to perform the sulfonation treatment of the battery separator. It was. Next, the battery separator subjected to the sulfonation treatment was neutralized with a 5% by mass aqueous sodium hydroxide solution, washed with warm water at 60 ° C., and then dried with a drum dryer at 70 ° C. A separator for battery was obtained. The battery separator had a basis weight of 61.7 g / m ² and a thickness of 155 μm.

  And the surface of the obtained battery separator was image | photographed by 200-times multiplication factor using the electron microscope (SEM), and the obtained enlarged photograph was shown in FIG. Furthermore, the obtained battery separator was cut in the thickness direction at an arbitrary location, and this cut surface was photographed at a magnification of 250 times using an electron microscope (SEM), and the obtained enlarged photograph is shown in FIG. It was.

  As can be seen from FIGS. 1 and 2, the heat-adhesive fibers and polypropylene fibers constituting the surface portion of the battery separator are crushed in the radial direction, and the cross section is deformed into an elliptical shape or a state close to an elliptical shape. I understand that. And the heat-adhesive fiber and polypropylene fiber which comprise the surface part of a battery separator are crushed in the radial direction more largely than the heat-adhesive fiber and polypropylene fiber inside a battery separator.

  Further, the heat-adhesive fibers constituting the surface portion of the battery separator maintain the fiber form, and the fibers are bonded together in a state where the cross-section is deformed into an elliptical shape or a state close to an elliptical shape. It can be seen that they are thermally bonded. Further, the fibers constituting the battery separator are dispersed substantially uniformly in the thickness direction of the battery separator, and the battery separator has a substantially uniform quality.

(Example 3)
A sulfonated battery separator was obtained in the same manner as in Example 2 except that the basis weight of the card web was adjusted to 12 g / m ² . The battery separator had a basis weight of 72.8 g / m ² and a thickness of 154 μm.

Example 4
A core-sheath type composite heat-bonding fiber whose sheath component is high-density polyethylene and whose core component is polypropylene (melting point of high-density polyethylene: 135 ° C., fineness: 1 dtex, fiber length: 38 mm), 25% by mass, polypropylene fiber (melting point: 165 ° C., fineness: 1.7 dtex, fiber length: 45 mm) 25% by mass, and a polyolefin-based splitting composite fiber (fineness) that is a combination of polypropylene and an ethylene-vinyl alcohol copolymer and is radially divided into 16 from the center : 3.3 dtex, fineness after splitting: approx. 0.2 dtex, fiber length: 45 mm) Mix at a ratio of 50% by weight, supply to three semi-random card machines, card, and 8 g per unit weight from each card machine / a m ² carded web continuously discharged was that the temperature at the time of compressing the laminated nonwoven fabric in the thickness direction is 125 ° C. To obtain a separator for a battery in the same manner as in Example 1 except that. The battery separator had a basis weight of 51.0 g / m ² and a thickness of 123 μm. Then, the corona discharge treatment was performed so that the total discharge amount was 0.24 kw · min / m ² four times on each of both surfaces of the battery separator.

  And the surface of the obtained battery separator was image | photographed by 250-times multiplication factor using the electron microscope (SEM), and the obtained enlarged photograph was shown in FIG. Further, the obtained battery separator was cut in the thickness direction at an arbitrary position, and this cut surface was photographed at 500 times magnification using an electron microscope (SEM), and the obtained enlarged photograph is shown in FIG. It was.

  As can be seen from FIGS. 3 and 4, the heat-adhesive fibers and polypropylene fibers constituting the surface portion of the battery separator are crushed in the radial direction, and the cross section is deformed into an elliptical shape or a state close to an elliptical shape. I understand that. And the heat-adhesive fiber and polypropylene fiber which comprise the surface part of a battery separator are crushed in the radial direction more largely than the heat-adhesive fiber and polypropylene fiber inside a battery separator.

  Further, the heat-adhesive fibers constituting the surface portion of the battery separator maintain the fiber form, and the fibers are bonded together in a state where the cross-section is deformed into an elliptical shape or a state close to an elliptical shape. It can be seen that they are thermally bonded. Further, the fibers constituting the battery separator are dispersed substantially uniformly in the thickness direction of the battery separator, and the battery separator has a substantially uniform quality. Further, the polyolefin-based split composite fibers were split to form ultrafine fibers having a wedge-shaped cross section. Furthermore, the ultrafine fibers constituting the surface portion of the battery separator were also crushed in a direction perpendicular to the length direction.

(Example 5)
A core-sheath type composite thermal adhesive fiber whose sheath component is high-density polyethylene and whose core component is polypropylene (melting point of high-density polyethylene: 135 ° C., fineness: 1 dtex, fiber length: 38 mm), 40% by mass, polypropylene fiber (melting point: 165 ° C., fineness: 1.7 dtex, fiber length: 45 mm), and a polyolefin-based splitting composite fiber (fineness) consisting of a combination of polypropylene and an ethylene-vinyl alcohol copolymer and radially dividing into 16 from the center : 3.3 dtex, fineness after splitting: about 0.2 dtex, fiber length: 45 mm, melting point of polypropylene: 165 ° C., melting point of ethylene-vinyl alcohol copolymer: 175 ° C.) carding is supplied to the base of the semi-random card machine, Kadou having a basis weight of 8g / m ² from each card machine Continuously discharged was that the blanking, except that the temperature at the time of compressing the laminated nonwoven fabric in the thickness direction and 125 ° C. in the same manner as in Example 1 to obtain a battery separator. The battery separator had a basis weight of 52.8 g / m ² and a thickness of 119 μm. Then, the corona discharge treatment was performed so that the total discharge amount was 0.24 kw · min / m ² four times on each of both surfaces of the battery separator.

(Example 6)
A battery separator was produced in the same manner as in Example 5. Then, this battery separator is supplied into a fluorine gas treatment machine and left in a mixed gas atmosphere consisting of 1% by volume of fluorine gas, 3% by volume of sulfurous acid gas and 96% by volume of nitrogen gas for 30 minutes. A mixed gas was reacted with the separator. Next, 50% by volume of the mixed gas in the fluorine gas processing machine was replaced with oxygen gas. Then, the battery separator was left in the fluorine gas treatment machine for 30 minutes, the mixed gas was reacted with the battery separator, and the battery separator was subjected to fluorine gas treatment. Next, the battery separator subjected to the fluorine gas treatment was neutralized with a 5% by mass aqueous sodium hydroxide solution, washed with hot water at 60 ° C., and then dried with a hot air dryer at 70 ° C. A gas-treated battery separator was obtained. The battery separator had a basis weight of 53.5 g / m ² and a thickness of 122 μm.

(Example 7)
Core-sheath composite heat-adhesive fiber (ethylene-propylene copolymer: 145 ° C., fineness: 1.8 dtex, fiber length: 51 mm) whose sheath component is an ethylene-propylene copolymer and whose core component is polypropylene 40% by mass And a polyolefin-based splitting composite fiber (fineness: 2.2 dtex, fineness after splitting: 0.25 dtex, fiber length: 45 mm) consisting of a combination of polypropylene and polymethylpentene and radially dividing into eight from the center 60 weight %, And supplied to three semi-random card machines for carding, and adjusted for a card web basis weight of 12 g / m ² for the battery in the same manner as in Example 1. A separator was produced.

Then, the battery separator is supplied to the SO ₃ gas treatment machine, concentration was carried out by reacting a sulfonated at a treatment machine for 60 seconds at 60 ° C. under SO ₃ gas atmosphere is 8% by volume. Next, the battery separator subjected to the sulfonation treatment was neutralized with a 5% by mass sodium hydroxide aqueous solution, washed with warm water at 60 ° C., and then dried with a drum dryer at 70 ° C. A separator for battery was obtained. The battery separator had a basis weight of 74.3 g / m ² and a thickness of 191 μm.

(Comparative Example 1)
A hydroentangled nonwoven fabric was produced in the same manner as in Example 1 except that the basis weight of the card web was adjusted to 13 g / m ² . Only one sheet of this hydroentangled nonwoven fabric is supplied between the opposed surfaces of a pair of thermal rolls facing each other with a predetermined interval, and the hydroentangled nonwoven fabric is 440 N / cm at 120 ° C. from both sides by this pair of thermal rolls. A battery separator having a basis weight of 39.3 g / m ² and a thickness of 120 μm was obtained by sandwiching with pressure. In addition, the outer peripheral surface of the heat roll was formed in the smooth surface.

(Comparative Example 2)
The basis weight of the card web was adjusted to 21 g / m ² , the drying temperature after the card web fibers were entangled and integrated with each other was set to 135 ° C., and the thermoadhesive fibers simultaneously with drying. In the same manner as in Comparative Example 1, except that the hydroentangled nonwoven fabric was not supplied between the pair of heat rolls, and the thickness was adjusted with a calender roll having a linear pressure of 9.8 N / cm. A separator was obtained. The battery separator had a basis weight of 64.2 g / m ² and a thickness of 152 μm. The obtained battery separator was sulfonated in the same manner as in Example 2.

  The thickness, air permeability, tensile strength, puncture strength and hole diameter of the obtained battery separator were measured as shown below, and the results are shown in Table 1.

(Thickness)
The thickness was measured at 10 different points of each of the three samples under a load of 175 kPa (measured with a micrometer according to JIS-B-7502), and the average value of 30 points in total was taken as the thickness of the battery separator.

(Air permeability)
The air permeability of the battery separator was measured according to JIS L1096 using a Frazier type tester.

(Tensile strength)
A flat rectangular test piece having a length of 5 cm and a width of 15 cm was cut out from the battery separator. The test piece is gripped in the MD direction at an interval of 10 cm, stretched at a tensile speed of 30 cm / min according to JIS L1096 using a constant speed extension type tensile tester, and the load value when the test piece is cut is determined. Tensile strength was assumed.

(Strong piercing)
A test piece having a plane rectangular shape of 30 mm in length and 100 in width was cut out from the battery separator. Using a compression tester (trade name “KES-G5 Handy Compression Tester” manufactured by Kato Tech Co., Ltd.), a circular through-hole with a diameter of 11 mm was formed in the center on the test piece, 46 mm long × 86 mm wide × A flat rectangular aluminum presser plate having a thickness of 7 mm was placed.

  After that, the tip portion of the needle whose tip portion is formed in a spherical shape with a diameter of 1 mm and whose shaft portion is formed in a conical shape (bottom surface: circular with a diameter of 2.2 mm, height is 18.7 mm) is inserted into the through hole of the presser plate. The test piece was stabbed perpendicularly to the surface at a speed of 2 mm / sec through the center of the test piece, and the maximum load at the time of stab was stabbed to make it strong.

(Pore diameter)
Using a Palm Porometer (manufactured by Porous Materials Inc. 16 S) for the minimum pore size (SMALLEST DETECTED PORE DIAMETER), maximum pore size (BUBBLE POINT PORE DIAMETER), and average pore size (MEAN FLOW PORE DIAMETER) of the battery separator, using the F. In accordance with the bubble point method.

  Since the battery separators of Examples 1 to 7 were formed by laminating and integrating two hydroentangled nonwoven fabrics by thermocompression bonding, they were excellent in tensile strength and piercing strength. In addition, the battery separators of Examples 1 to 7 are generally smaller in average pore diameter than Comparative Examples 1 and 2 composed of a single hydroentangled nonwoven fabric, and have a maximum pore diameter and a minimum pore diameter that are indicators of uniformity. Since the difference between the two was small, the uniformity was excellent.

  The battery separators of Examples 1 to 3 have a relatively large difference between the average hole diameter and the maximum hole diameter and the minimum hole diameter, and are suitably used for high-power secondary batteries such as electric tools. In addition, since the battery separators of Examples 4 to 7 include ultrafine fibers obtained by dividing the split type composite fiber, the average pore diameter and the difference between the maximum pore diameter and the minimum pore diameter are different for the batteries of Examples 1 to 3. It is smaller than the separator and is suitably used for secondary batteries for vehicles such as small secondary batteries, hybrid vehicles (HEV), and electric vehicles (PEV).

4 is an enlarged photograph showing the surface of the battery separator of Example 2. FIG. 4 is an enlarged photograph showing a cross section of the battery separator of Example 2. FIG. 4 is an enlarged photograph showing the surface of the battery separator of Example 4. FIG. 4 is an enlarged photograph showing a cross section of the battery separator of Example 4. FIG.

Claims (16)

A battery separator comprising a plurality of hydroentangled nonwoven fabrics made of a card web containing thermal adhesive fibers having a fineness of 0.3 to 5.5 dtex, laminated and integrated by thermocompression bonding. The battery separator according to claim 1, wherein the heat-adhesive fiber is a core-sheath type composite fiber. A core-sheath type composite fiber in which the heat-adhesive fiber is a high-density polyethylene sheath component and a core component is polypropylene, and a core-sheath type composite fiber in which the sheath component is an ethylene-propylene copolymer and the core component is polypropylene. The battery separator according to claim 1, wherein the battery separator is at least one core-sheath type composite fiber selected from the group consisting of: The card web includes heat-adhesive fibers having a fineness of 0.3 to 5.5 dtex, and polyolefin fibers having a melting point higher by 5 ° C. than the melting point of the heat-adhesive component of the heat-adhesive fibers. The battery separator according to claim 1. The battery separator according to claim 4, wherein the polyolefin fiber is a polypropylene fiber. 2. The battery separator according to claim 1, wherein the card web includes a heat-adhesive fiber having a fineness of 0.3 to 5.5 dtex and a polyolefin-based split composite fiber. The polyolefin-based split composite fiber was selected from the group consisting of split composite fibers composed of a combination of polypropylene and ethylene-vinyl alcohol copolymer, and split composite fibers composed of a combination of polypropylene and polymethylpentene. The battery separator according to claim 6, wherein the battery separator is at least one split-type composite fiber. The separator for a battery according to claim 6, wherein the fineness of the polyolefin-based split composite fiber after splitting is smaller than the fineness of the heat-adhesive fiber and the polyolefin-based fiber. The card web includes a heat-adhesive fiber having a fineness of 0.3 to 5.5 dtex, a polyolefin fiber having a melting point higher by 5 ° C. than the melting point of the heat-adhesive component of the heat-adhesive fiber, and a polyolefin-based split composite fiber. The battery separator according to claim 1, comprising: a battery separator; 10. The battery separator according to claim 9, wherein the thermal adhesive fiber contains 15 to 80% by mass, the polyolefin fiber contains 10 to 75% by mass, and the polyolefin split composite fiber contains 10 to 75% by mass. . The battery separator according to claim 1, which has been subjected to a hydrophilic treatment. The difference between the maximum pore size (BUBBLE POINT PORE DIAMETER) and the minimum pore size (SMALLEST DETECTED PORE DIAMETER) measured by a bubble point method in accordance with ASTM F 316 86 is 45 μm or less. Battery separator. The battery separator according to claim 1, wherein the heat-adhesive fibers constituting the surface portion are crushed and deformed. The heat-adhesive fibers constituting the surface portion and the interior are both crushed and deformed, and the degree of the heat-adhesive fibers constituting the surface portion being crushed is larger than the heat-adhesive fibers constituting the interior. The battery separator according to claim 1. A step of obtaining a laminated web by laminating a plurality of card webs containing thermal adhesive fibers having a fineness of 0.3 to 5.5 dtex, a step of obtaining a hydroentangled nonwoven fabric by subjecting the laminated web to hydroentanglement, and this water flow A process of manufacturing a laminated nonwoven fabric by laminating a plurality of entangled nonwoven fabrics, and hydroentangled nonwoven fabric by compressing the laminated nonwoven fabric in the thickness direction at a temperature T (° C.) satisfying the following formula at a pressure of 15 to 10000 N / cm. A process for producing a battery separator, comprising the step of integrating each other.
Melting point Tm−25 ° C. ≦ T of heat bonding component of heat bonding fiber
<Melting point Tm of heat bonding component of heat bonding fiber The method for producing a battery separator according to claim 15, wherein the pressure for compressing the laminated nonwoven fabric in the thickness direction is 15 to 700 N / cm.