JP2015034194A - Fluorine-based resin porous body, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluorine-based resin porous body having a uniform porous structure and high gas permeability, and especially excellent in affinity to an electrolytic solution and degradation resistance against gaseous hydrogen fluoride when used as a separator for a battery at high productivity.SOLUTION: There is provided a fluorine-based resin porous body having at least one porous layer consisting of: a resin composition containing a fluorine-based resin (A) as a main component; and 1 mass% to 45 mass% of a thermoplastic elastomer (B) having a melt flow rate (MFR) of 30 g/10 minutes or less at a temperature of 230°C and a load of 2.16 kg. The porous layer is a layer made porous by drawing in at least one axis direction.

Description

The present invention relates to a fluororesin porous body and a method for producing the same. More specifically, it can be used as a packaging, sanitary, livestock, agricultural, architectural, medical, separation membrane, water treatment membrane, light diffusion plate, battery separator, in particular, a battery separator, and The present invention relates to a fluororesin porous body that can be suitably used for a battery using a battery separator and a method for producing the same.
The present invention also relates to a battery separator and a battery using the porous fluororesin.

  The polymer porous body with many fine communication holes is used for separation membranes used for the production of ultrapure water, purification of chemicals, water treatment, waterproof and moisture-permeable films used for clothing and sanitary materials, and batteries. It is used in various fields such as separators.

Among them, the secondary battery is widely used as a power source for portable equipment such as OA, FA, household electric appliances or communication equipment. In particular, portable devices using lithium ion secondary batteries, which are a type of non-aqueous electrolyte secondary battery, are increasing because they have a high volumetric efficiency and are reduced in size and weight when installed in equipment.
On the other hand, large-sized secondary batteries are being researched and developed in many fields related to energy / environmental issues, including road leveling, UPS, and electric vehicles, and are excellent in large capacity, high output, high voltage and long-term storage. Therefore, the use of lithium ion secondary batteries is expanding.

  The working voltage of a lithium ion secondary battery is usually designed with an upper limit of 4.1V to 4.2V. At such a high voltage, the aqueous solution causes electrolysis and cannot be used as an electrolyte. Therefore, so-called non-aqueous electrolytes using organic solvents are used as electrolytes that can withstand high voltages. As the solvent for the non-aqueous electrolyte, a high dielectric constant organic solvent capable of allowing more lithium ions to be present is used, and organic carbonate compounds such as propylene carbonate and ethylene carbonate are mainly used as the high dielectric constant organic solvent. It is used. As a supporting electrolyte that becomes a lithium ion source in the solvent, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in the solvent and used.

  In the lithium ion secondary battery, a separator is interposed between the positive electrode and the negative electrode from the viewpoint of preventing an internal short circuit. Of course, the separator is required to have insulating properties due to its role. Moreover, it is necessary to have a microporous structure in order to provide air permeability as a lithium ion passage and a function of diffusing and holding the electrolyte. In order to satisfy these requirements, a porous film is used as the separator.

  On the other hand, an electrolyte such as lithium hexafluorophosphate reacts with a small amount of moisture in the battery and easily generates hydrogen fluoride. For this reason, when the charge / discharge cycle is repeated, the separator interposed between the positive electrode and the negative electrode may be oxidized and deteriorated by hydrogen fluoride, thereby reducing the cycle characteristics of the battery. In particular, since the surface of the separator is in contact with the electrode, it is easily affected by deterioration due to hydrogen fluoride. In addition, hydrogen fluoride generated in the battery may cause additional gas to be generated due to a chain reaction with the electrolyte and the separator, which may cause the battery to swell. .

  Examples of separators include polyethylene and polypropylene porous films, two-layer films in which polyethylene and polypropylene are laminated, and three-layer films in which polyethylene is sandwiched between polypropylenes. Like this, it is easily affected by deterioration due to hydrogen fluoride and the like, and there are concerns about safety such as deterioration of the cycle characteristics of the battery and swelling of the battery. Further, these polyolefin-based porous membranes have a problem that the wettability with respect to the electrolytic solution is poor.

  In order to solve such a problem, it has been studied to use a fluororesin having a good affinity for an electrolytic solution as a separator.

  As a method for making the fluororesin porous, for example, a method in which polyvinylidene fluoride is dissolved in a solvent to form a wet film, and then the solvent is removed to make a porous body (Patent Document 1). Inorganic particles are mixed in the fluororesin. The method of removing inorganic particles after film formation (Patent Documents 2 to 4), the method of adding an extractable resin to a fluororesin and extracting the resin after film formation (Patent Document 5), polyvinylidene fluoride Numerous methods such as a method (Patent Document 6) in which a filler capable of eluting is mixed and sintered by molding and then the filler is eluted (Patent Document 6) have been proposed.

  In addition, a porous film made of polyvinylidene fluoride resin (Patent Document 7) or a terpolymer of vinylidene fluoride, hexafluoropropylene and chlorotrifluoroethylene is used by making these fluororesins porous. A polymer film (Patent Document 8) on which an electrolytic solution is supported has been proposed. In addition, a separator (Patent Document 9) in which a polymer that swells in an organic electrolyte such as polyvinylidene fluoride is added to an elastomer polymer is also proposed.

  Furthermore, a method of producing a porous body made of a thermoplastic fluorine-based resin containing at least 90% by weight of a vinylidene fluoride structural unit by melt extrusion and cold drawing (Patent Document 10), or a poorly compatible resin in polyvinylidene fluoride. There has also been proposed a method (Patent Document 11) in which, after blending and forming a film, it is stretched to cause cracks at the interface between the hardly compatible resin and the matrix resin to make it porous.

Japanese Patent Publication No.59-12691 Japanese Examined Patent Publication No. 62-17614 Japanese Patent Laid-Open No. 61-242602 JP-A-3-215535 Japanese Patent Publication No.57-10888 Japanese Patent Laid-Open No. 51-134761 JP 2000-309672-A JP 2001-332307 A JP-A-11-102686 Japanese Patent Laid-Open No. 9-328566 Japanese Patent Publication No. 52-26788

  However, the wet porosification methods such as Patent Documents 1 to 6 use a large amount of solvent and include a step of removing other components. Therefore, facilities for recovering the solvent and additives are required, and productivity is increased. Is significantly reduced.

  In addition, the polyvinylidene fluoride resin as used in Patent Documents 7 and 8 has a crystal density because a bulky molecule such as fluorine is bonded to the side chain of the molecule as compared with a crystalline resin such as polyolefin. Is low. Therefore, it is not easy to adopt a so-called dry-type porosity method, which is seen as a method for making a polyolefin or the like, which is made by cleaving between crystal lamellas.

  In addition, in the separator as in Patent Document 9, since the elastomer polymer is the base, heat resistance may be remarkably lowered, and, as described above, the wet porosity method is employed, and there is a problem from the viewpoint of productivity. is there.

  Further, in the production of a porous body as in Patent Document 10, when the melt is subjected to heat treatment as described in the Patent Document and then stretched, a uniform porosity is partially realized. However, as described above, the crystal density of the polyvinylidene fluoride resin is low, and it is still difficult to uniformly make the entire film porous by a dry porous method.

  Furthermore, in the method for making porous according to Patent Document 11, unless an appropriate poorly compatible resin is selected, not only a poor appearance occurs in the porous film, but also stress due to stretching deformation is caused by the poorly compatible resin and the polyvinylidene fluoride system. It is difficult to make the entire film uniformly porous because it is difficult to be transmitted to the interface of the resin, or the resin does not crack at all in the first place.

The present invention has been made in view of the above problems, and has a uniform porous structure, high air permeability, and heat resistance. Also, when used as a battery separator, the affinity for an electrolyte and hydrogen fluoride. An object of the present invention is to provide a fluororesin porous body having excellent resistance to gas deterioration, and a battery separator and battery using the same.
Furthermore, it aims at providing the manufacturing method which can obtain the said fluororesin porous body under high productivity.

  As a result of diligent investigation in view of the above-mentioned problems, the present inventor has obtained a porous layer comprising a resin composition containing a fluororesin as a main component and containing a specific ratio of a thermoplastic elastomer having a specific melt flow rate (MFR). In order to complete the present invention, it is found that a fluororesin porous body that has at least one layer and the porous layer is a layer that is made porous by stretching in at least a uniaxial direction can solve the above problems. It came.

  Furthermore, the present inventor has also found that the fluororesin porous body can be obtained with high productivity by a predetermined production method.

That is, the gist of the present invention is as follows.
[1] 1% by mass or more of a thermoplastic elastomer (B) having a fluororesin (A) as a main component and having a melt flow rate (MFR) of 30 g / 10 min or less at a temperature of 230 ° C. and a load of 2.16 kg, A fluororesin porous body comprising at least one porous layer made of a resin composition containing 45% by mass or less, wherein the porous layer is a layer made porous by stretching in at least a uniaxial direction. .
[2] The fluororesin porous body according to [1], wherein the fluororesin (A) is a polyvinylidene fluoride resin, a polytetrafluoroethylene resin, or a mixture thereof.
[3] The fluororesin porous body according to [1] or [2], wherein the thermoplastic elastomer (B) is a styrene thermoplastic elastomer.
[4] A battery separator using the porous fluororesin according to any one of [1] to [3].
[5] A battery comprising the battery separator according to [4].
[6] Thermoplastic elastomer (B) having a fluorine resin (A) as a main component and a melt flow rate (MFR) of 30 g / 10 min or less at a temperature of 230 ° C. and a load of 2.16 kg is 1% by mass or more, A resin composition containing 45% by mass or less,
(A) melt-extruding, cooling and solidifying into a sheet-like product having at least one layer made of the resin composition, or a fibrous product, or a hollow product; and
(B) a step of stretching the sheet-like product, the fibrous product, or the hollow product formed in the step (a) at a temperature of -20 ° C or higher and 90 ° C or lower;
(C) including a step of further stretching the sheet-like material, the fibrous material, or the hollow material stretched in the step (b) at a temperature of 100 ° C. or higher and 160 ° C. or lower.
A method for producing a fluororesin porous body.

  According to the present invention, it has a uniform porous structure, high air permeability, and heat resistance. In particular, when used as a battery separator, it has excellent affinity for an electrolyte and deterioration resistance to hydrogen fluoride gas. A fluororesin porous body can be provided with high productivity.

It is a schematic sectional drawing of the battery which accommodates the battery separator using the fluororesin porous body of this invention.

  Hereinafter, a fluororesin porous body (hereinafter also referred to as “the present porous body”) as an example of an embodiment of the present invention, a manufacturing method thereof, and a mode of application to a battery as a battery separator will be described in detail. . However, the scope of the present invention is not limited to the embodiments described below.

  Below, each component which comprises this porous body is demonstrated.

<Fluorine resin (A)>
It is important that the resin composition constituting the porous body is mainly composed of the fluororesin (A). Here, the main component means a component occupying 50% by mass or more of the resin composition constituting the porous body, more preferably 60% by mass or more, and further preferably 70% by mass or more.

  The fluororesin (A) used in the present invention is a synthetic polymer containing a fluorine atom in the molecule, for example, tetrafluoroethylene, trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, vinylidene fluoride, A polymer composed of one type of fluorine atom-containing vinyl monomer such as vinyl fluoride, or a copolymer composed of two or more types of these fluorine atom-containing vinyl monomers is used. These fluorine atom-containing vinyl monomers include ethylene, α-olefins such as propylene and butene, and fluoroolefins having a fluoroalkyl group such as perfluorobutylethylene (wherein the alkyl group of the fluoroalkyl group has 1 to 21 carbon atoms. The degree of carbon is preferably about 1 to 21), vinyl ethers such as alkyl vinyl ether, fluoroalkyl vinyl ether, and perfluoroalkyl vinyl ether (wherein the alkyl group of alkyl vinyl ether preferably has about 1 to 21 carbon atoms), fluoroalkyl methacrylate and fluoroalkyl acrylate (Meth) acrylates such as vinyl chloride, vinylidene chloride, hexafluoroisobutylene, and copolymers with vinyl monomers such as pentafluoropropylene. Moreover, you may blend 2 or more types of fluororesins. Further, a modified product of a fluororesin modified with a functional group such as an acid anhydride can also be used.

  Among them, from the viewpoint of processability and heat resistance, polytetrafluoroethylene, polyhexafluoropropylene, tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer, tetrafluoro Ethylene / ethylene copolymer, tetrafluoroethylene / ethylene / perfluoroalkylethylene copolymer, polychlorotrifluoroethylene, chlorotrifluoroethylene / ethylene copolymer, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, polyfluoroethylene Vinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, vinylidene fluoride / hexafluoropropylene / chlorotrifluoroethylene copolymer, Vinyl and the like are preferred, and in particular, polyvinylidene fluoride resins such as polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, vinylidene fluoride / hexafluoropropylene / chlorotrifluoroethylene copolymer, and polytetrafluoroethylene. Tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / ethylene copolymer, tetrafluoroethylene / ethylene / perfluoroalkylethylene copolymer Polytetrafluoroethylene resins such as tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers are preferred.

When the fluororesin (A) is a polyvinylidene fluoride resin, that is, a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride and another monomer, a structural unit derived from vinylidene fluoride is used. In addition, it is preferable to contain 70 mol% or more (including 100 mol%) in all the structural units.
When the fluororesin (A) is a polytetrafluoroethylene resin, that is, a tetrafluoroethylene homopolymer or a copolymer of tetrafluoroethylene and another monomer, the fluororesin (A) is derived from tetrafluoroethylene. It is preferable to contain 20 mol% or more of structural units (including 100 mol%) in all the structural units.

  When the fluororesin (A) is a polyvinylidene fluoride resin, the melt flow rate (MFR) of the polyvinylidene fluoride resin is not particularly limited, but usually at a temperature of 230 ° C. and a load of 2.16 kg. The MFR is preferably 0.03 to 60 g / 10 minutes, and more preferably 0.3 to 30 g / 10 minutes. If the MFR is in the above range, the back pressure of the extruder does not become too high during the molding process and the productivity is excellent.

  When the fluororesin (A) is a polytetrafluoroethylene resin, the melt flow rate (MFR) of the polytetrafluoroethylene resin is not particularly limited. Polymer, tetrafluoroethylene / ethylene / perfluoroalkylethylene copolymer, etc. at a temperature of 297 ° C., polytetrafluoroethylene / tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer Etc., the MFR at a temperature of 372 ° C. and a load of 49 N is preferably 0.03 to 60 g / 10 min, and more preferably 0.3 to 30 g / 10 min. If the MFR is in the above range, the back pressure of the extruder does not become too high during the molding process and the productivity is excellent.

  From the viewpoint of heat resistance, the melting point of the fluororesin (A) is preferably 130 ° C or higher, more preferably 140 ° C or higher, and further preferably 150 ° C or higher. On the other hand, from the viewpoint of moldability, 350 ° C. or lower is preferable, 320 ° C. or lower is more preferable, and 300 ° C. or lower is further preferable.

<Thermoplastic elastomer (B)>
It is important that the resin composition constituting the porous body contains a thermoplastic elastomer (B) having a melt flow rate (MFR) of 30 g / 10 min or less at a temperature of 230 ° C. and a load of 2.16 kg. The MFR of the thermoplastic elastomer (B) at a temperature of 230 ° C. and a load of 2.16 kg is preferably 10 g / 10 minutes or less, more preferably 5 g / 10 minutes or less, further preferably 1 g / 10 minutes or less, and it does not flow. Most preferred.

The most important point in the present invention is to select the MFR of the thermoplastic elastomer (B) within the range defined by the present invention. This is because, when the layer composed of the resin composition containing the fluororesin (A) and the thermoplastic elastomer (B) is stretched at least uniaxially to make it porous, the fluororesin in the resin composition before stretching. This is because the morphology of (A) and the thermoplastic elastomer (B) is an important factor in obtaining a good porous body.
Specifically, it is important that the thermoplastic elastomer (B) existing as a domain is present in the form of particles with respect to the matrix mainly composed of the fluororesin (A).

Generally, when a resin composition having a matrix / domain sea-island structure is melt-extruded and cooled and solidified, the resin composition that is extruded from a shaping equipment such as a die or a nozzle is flown into a cast roll (cooling roll) or air-cooled, Cool and solidify with cooling and solidification equipment such as water cooling. At that time, since the resin composition melts and expands in the gap (gap) between the shaping equipment and the cooling and solidification equipment, when the melt viscosity of the thermoplastic elastomer (B) that is the domain is low, the domain moves in the flow direction (extrusion direction). ) Is obtained.
When stretching a resin composition in which the domains are elongated in the flow direction (extrusion direction), the stress imparted by the deformation is easily applied to the entire resin composition, thereby preventing stress concentration at the matrix / domain interface. . This is because the cross-sectional area of the interface that receives the stress is small because the domain has been previously extended.

  On the other hand, when the melt viscosity of the domain is high, the domain is not easily affected by the melt elongation, and the domain in the obtained resin composition before stretching is easily maintained in the form of particles. Therefore, when the obtained resin composition is stretched, stress applied by deformation tends to concentrate on the interface of the matrix / domain, and the cross-sectional area of the interface that receives the stress also increases, so that interface peeling is likely to occur. As a result, a uniform porous structure can be formed. Therefore, it is most important in the present invention to select the MFR of the thermoplastic elastomer (B) within the range defined by the present invention.

The thermoplastic elastomer (B) used in the present invention is a polyamide-based thermoplastic elastomer, an ester-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, a styrene-based thermoplastic elastomer, a urethane-based thermoplastic elastomer, or a dynamic vulcanized thermoplastic. Elastomers, vinyl chloride thermoplastic elastomers, acrylic thermoplastic elastomers, polylactic acid thermoplastic elastomers, fluorine thermoplastic elastomers, silicone thermoplastic elastomers, ionomers, and their blends, alloys, modified products, dynamics It is a cross-linked product, and includes a block copolymer, a graft copolymer, a random copolymer, a core-shell type multilayered rubber, and the like.
Of these, olefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, and acrylic-based thermoplastic elastomers are preferable, and styrene-based thermoplastic elastomers are particularly preferable from the viewpoint of viscosity.

  When the thermoplastic elastomer (B) is a styrenic thermoplastic elastomer, a styrene-butadiene-styrene copolymer, a styrene-ethylene-butylene-styrene copolymer, a styrene-ethylene-propylene-styrene copolymer, styrene -Ethylene-propylene copolymer, styrene-isoprene-styrene copolymer, styrene-ethylene- (ethylene-propylene) -styrene copolymer, graft copolymer having styrene structure in side chain, and styrene structure in shell A core-shell multilayer rubber or the like can be suitably used, and two or more kinds of blends may be used. Of these, a styrene-ethylene-butylene-styrene copolymer, a styrene-ethylene-propylene-styrene copolymer, and a styrene-ethylene- (ethylene-propylene) -styrene copolymer are preferable.

  In the resin composition which comprises this porous body, only 1 type of said thermoplastic elastomer (B) may be contained, and 2 or more types may be contained.

In the resin composition containing the fluororesin (A) and the thermoplastic elastomer (B), it is important that the thermoplastic elastomer (B) is contained in an amount of 1% by mass to 45% by mass.
Generally, since the density of the fluororesin is as large as 1.5 g / cm ³ or more, when the content of the thermoplastic elastomer (B) in the resin composition exceeds 45% by mass, the fluororesin The volume of the thermoplastic elastomer (B) is larger than the volume of (A), the matrix of the resin composition to be formed becomes a thermoplastic elastomer, and it becomes difficult to form a porous structure, and the heat resistance is significantly reduced. There is a risk.
In addition, when the content of the thermoplastic elastomer (B) in the resin composition is less than 1% by mass, porosity is formed at the interface between the fluororesin (A) and the thermoplastic elastomer (B). May be difficult.
Therefore, the content of the thermoplastic elastomer (B) in the resin composition is preferably 5% by mass or more and 43% by mass or less, more preferably 10% by mass or more and 41% by mass or less, and more preferably 15% by mass or more. 39 mass% or less is further more preferable, and 20 mass% or more and 37 mass% or less are especially preferable.

<Other ingredients>
In the resin composition constituting the porous body, components other than the fluororesin (A) and the thermoplastic elastomer (B), for example, other than the fluororesin (A), as long as the effects of the present invention are not impaired. It can be allowed to contain other resins. Other resins include polyolefin resins, polystyrene resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polyester resins, polycarbonate resins, polyamide resins, polyacetal resins, ethylene acetate Vinyl copolymer, polymethylpentene resin, polyvinyl alcohol resin, cyclic olefin resin, polylactic acid resin, polybutylene succinate resin, polyacrylonitrile resin, polyethylene oxide resin, cellulose resin, polyimide resin , Polyurethane resin, polyphenylene sulfide resin, polyphenylene ether resin, polyvinyl acetal resin, polybutadiene resin, polybutene resin, polyamideimide resin, polyamide bismaleimide resin , Polyarylate resins, polyether imide resins, polyether ether ketone resin, polyether ketone resin, polyether sulfone resin, polyketone resin, polysulfone resin, aramid-based resin and the like. Among these, when a polyvinylidene fluoride resin is used as the fluorine resin (A), an acrylic resin and a polybutylene succinate resin are preferable from the viewpoint of compatibility.

  In addition to the components described above, additives generally blended in the resin composition can be appropriately added to the resin composition as long as the effects of the present invention are not significantly impaired. Examples of the additive include recycled resin generated from trimming loss of ears and the like, silica, talc, kaolin, carbonic acid, which are added for the purpose of improving / adjusting moldability, productivity and various physical properties of the porous film. Inorganic particles such as calcium, pigments such as titanium oxide and carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents , Antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, colorants and the like.

<This porous body>
This porous body is mainly composed of a fluororesin (A), and a thermoplastic elastomer (B) having a melt flow rate (MFR) of 30 g / 10 min or less at a temperature of 230 ° C. and a load of 2.16 kg is 1% by mass or more, It has at least one porous layer made of a resin composition containing 45% by mass or less, and the porous layer is a layer made porous by stretching in at least a uniaxial direction.

  Although there is no restriction | limiting in particular as a shape of this porous body, A sheet-like thing, a fibrous thing, or a hollow thing is mentioned. “Sheet” includes from thick (mm order) plates to thin (μm order) films, and “fibrous” includes from thick rods to thin threads, and “hollow” The term “thick pipe” means “thin tube”, “hollow fiber”, “inflation film” and the like. Of course, it goes without saying that a sheet-like material obtained by cutting an inflation film is included.

This porous body should just have at least one porous layer which consists of the said resin composition. That is, the present porous body may be formed only by a porous layer made of the resin composition, or may be formed by laminating with another porous layer as long as the characteristics of the present porous body are not impaired.
Further, when the porous body is a sheet-like material, a laminated sheet-like porous body laminated in the thickness direction of the sheet-like material may be used, and when the porous material is a fibrous material, a so-called core-sheath structure-like porous body may be used. In this case, a porous body laminated in the radial direction of the hollow body may be used.
In particular, when the porous body is used as a battery separator, a sheet-like material is preferable. Furthermore, the porous layer may be formed by laminating a porous layer made of the resin composition with a polyolefin resin porous film generally used as a battery separator. In this case, from the resin composition, The porous layer to be formed is preferably disposed on the outermost layer of the porous body.

  Furthermore, it is important that the layer made of the resin composition in the porous body is stretched at least in a uniaxial direction. When the layer made of the resin composition is stretched in at least a uniaxial direction, preferably in a biaxial direction, the layer becomes porous, and the porous body has excellent air permeability.

When this porous body is used as a battery separator, the thickness of the porous body as a sheet-like material is preferably 1 μm to 50 μm, and more preferably 1 μm to 30 μm. When used as a battery separator, if the thickness is 1 μm or more, substantially necessary electrical insulation can be obtained. For example, even when a large voltage is applied, short-circuiting is difficult and excellent safety is achieved.
Further, if the thickness is 50 μm or less, preferably 30 μm or less, the electrical resistance of the porous film can be reduced, so that the battery performance can be sufficiently secured.

The air permeability of the porous body is preferably 15000 seconds / 100 mL or less, more preferably 2000 seconds / 100 mL or less, and even more preferably 500 seconds / 100 mL or less. If the air permeability is 15000 seconds / 100 mL or less, it is preferable because the porous body can be communicated and can exhibit excellent air permeability.
The air permeability represents the difficulty in passing through the air in the thickness direction, and is specifically expressed in seconds required for 100 mL of air to pass through the porous body. Therefore, it means that the smaller the numerical value is, the easier it is to pass through, and the higher numerical value is, the more difficult it is to pass. That is, the smaller the value means the better in the thickness direction, and the larger the value means the less in the thickness direction. Communication is the degree of connection of holes in the thickness direction. If the air permeability of the porous body is low, it can be used for various purposes. For example, when used as a battery separator, a low air permeability means that lithium ions can be easily transferred, which is preferable because battery performance is excellent.
In addition, although there is no restriction | limiting in particular in the minimum of the air permeability of this porous body, Usually, it is about 1 second / 100mL.
A method for measuring the air permeability is described in the section of Examples described later.

The porosity of the porous body is preferably 30% or more, more preferably 35% or more, and still more preferably 40% or more. If the porosity is 30% or more, it is possible to obtain a porous film that ensures communication and has excellent air permeability.
On the other hand, the upper limit of the porosity is preferably 80% or less, more preferably 75% or less, and still more preferably 70% or less. If the porosity is 80% or less, there is no problem that the fine pores are excessively increased and the strength of the porous body is lowered, which is preferable from the viewpoint of handling.
In addition, the measuring method is described in the term of the below-mentioned Example for the porosity.

<Method for producing the present porous body>
Next, the manufacturing method of this porous body is demonstrated. As described above, in this porous body, a thermoplastic elastomer (B) having a fluororesin (A) as a main component and having a melt flow rate (MFR) of 30 g / 10 min or less at a temperature of 230 ° C. and a load of 2.16 kg. It is important that the layer made of the resin composition containing 1% by mass or more and 45% by mass or less) be made porous by stretching in at least a uniaxial direction.
More specifically, in the porous body, the resin composition is (a) melt-extruded and cooled and solidified into a sheet-like material, a fibrous material, or a hollow material having at least one layer made of the resin composition. And (b) a step of stretching the sheet-like material, the fibrous material, or the hollow material formed in the step (a) at a temperature of −20 ° C. or higher and 90 ° C. or lower, and (c ) The method for producing the porous body of the present invention, further comprising the step of stretching the sheet-like material, the fibrous material, or the hollow material stretched in the step (b) at a temperature of 100 ° C. or higher and 160 ° C. or lower. It is preferable to manufacture by.

[Step (a)]
Especially as a method of melt-extrusion of the resin composition, cooling and solidifying into a sheet-like material, a fibrous material, or a hollow material having at least one substantially non-porous layer made of the resin composition. Although it is not limited, a known method may be used. For example, the resin composition is melt-extruded using an extruder, extruded from shaping equipment such as a T die, a round die, a nozzle, and a hollow nozzle, and cast roll (cooling roll) ), And cooling and solidifying with air-cooling or water-cooling equipment. Moreover, the method of cutting open the film-like thing manufactured by the inflation method and the tubular method, and making it planar can also be applied.
The “substantially non-porous layer” means that in the step of melt-extruding the resin composition, cooling and solidifying, and forming the void intentionally in the layer, It means that it includes the case where a fine pinhole is unintentionally generated due to an unexpected factor.

In the melt extrusion of the resin composition, the extrusion processing temperature is appropriately adjusted depending on the flow characteristics and moldability of the resin composition. When the fluororesin (A) is a polyvinylidene fluoride resin, the extrusion temperature is generally 180 to 250 degreeC is preferable, 190-240 degreeC is more preferable, and 200-230 degreeC is still more preferable. When the fluororesin (A) is a polytetrafluoroethylene resin, the temperature is generally preferably 240 to 400 ° C, more preferably 250 to 390 ° C, and still more preferably 250 to 380 ° C. When the extrusion temperature is equal to or higher than the above lower limit, it is preferable because the viscosity of the molten resin is sufficiently low and the moldability is excellent and the productivity is improved. On the other hand, by setting the extrusion temperature to the above upper limit or less, it is possible to suppress the deterioration of the resin composition, and hence the mechanical strength of the obtained porous body.
Moreover, the cooling solidification temperature, for example, the cooling solidification temperature of the cast roll is preferably 20 to 160 ° C, more preferably 40 to 140 ° C, and still more preferably 50 to 130 ° C. By setting the cooling and solidification temperature to the above lower limit or more, crystallization of the fluororesin (A) is promoted, and a difference in elastic modulus from the thermoplastic elastomer (B) is likely to occur, and a porous body is formed during stretching. It is preferable because it is easy. Moreover, it is preferable to make the extruded resin below the above upper limit because troubles such as the extruded molten resin sticking to and wrapping around the cast roll are unlikely to occur, and the molding can be efficiently performed.

[Step (b)]
In the step (b), the sheet-like material, the fibrous material, or the hollow material obtained in the step (a) is stretched at a temperature of −20 ° C. or more and 90 ° C. or less (hereinafter, this step (b) is referred to as “ Sometimes referred to as “low-temperature stretching step”). Examples of the stretching method in the step (b) include methods such as a roll stretching method, a rolling method, a tenter stretching method, and a simultaneous biaxial stretching method, and these may be performed alone or in combination of two or more. Among these, from the viewpoint of productivity, stretching in the flow direction in the step (a) (that is, the extrusion direction or the take-off direction, hereinafter may be referred to as “longitudinal direction” or “MD”) is preferable, and the resin composition From the viewpoint of concentration of stress on the thermoplastic elastomer (B), a roll stretching method that facilitates increasing the stretching speed is preferred.

  Here, by stretching at a temperature of −20 ° C. or higher, a special facility for making the stretching atmosphere at a temperature lower than −20 ° C. is unnecessary, which is preferable in production. In addition, the elastic modulus of the fluororesin (A) in the stretching atmosphere does not become too high, deformation can follow the stretching, and the possibility of breakage is small. On the other hand, by stretching at a temperature of 90 ° C. or less, the elastic modulus of the fluororesin (A) does not become too low, stress concentration on the thermoplastic elastomer (B) is moderately expressed, and the resin composition is formed. The layer can be easily made porous. The temperature in the low temperature stretching step is particularly preferably 0 ° C. or higher and 70 ° C. or lower.

  The draw ratio in this low temperature drawing step is not particularly limited, but is preferably 1.15 times or more and 4.00 times or less, particularly preferably 1.25 times or more and 3.00 times or less. When the draw ratio is not less than the above lower limit, stress concentrates at the interface of the matrix / domain, and it is easy to form a porous structure by peeling of the interface accompanying deformation, and when the draw ratio is not more than the above upper limit, the formed porous structure is excessive. Since it is not obstruct | occluded by the deformation | transformation of, it is preferable.

[Step (c)]
In the step (c), the porous layer made of the resin composition obtained in the step (b) is further stretched at a temperature of 100 ° C. or higher and 160 ° C. or lower (hereinafter, this step (c) is referred to as a “high temperature stretching step”. Sometimes called). About the extending | stretching method in a process (c), although the same method as the above-mentioned process (b) can be employ | adopted, a roll extending | stretching method and a tenter extending | stretching method are preferable especially, and it forms by the process (b). From the viewpoint of expanding the pores, it is preferable to further stretch in the flow direction (longitudinal direction) by a roll stretching method.
Here, by extending | stretching at the temperature of 100 degreeC or more, the hole formed at the process (b) can be expanded | stretched and a hole diameter can be expanded. On the other hand, by stretching at a temperature of 160 ° C. or lower, the blockage of the holes formed in the step (b) can be suppressed. The temperature in the high temperature stretching step is particularly preferably 110 ° C. or higher and 150 ° C. or lower.

  Further, the draw ratio in this high temperature drawing step is not particularly limited, but is preferably 1.25 times or more and 6.00 times or less, particularly 1.40 times or more and 5.00 times or less. Furthermore, the stretching ratio of the low temperature stretching step and the high temperature stretching step is preferably 1.4 times or more and 24 times or less, particularly 1.75 times or more and 15 times or less. When the draw ratio is not less than the above lower limit, it is easy to expand the pore diameter and maintain the porous structure, and when it is not more than the above upper limit, blockage of the pores can be suppressed.

  In the method for producing a porous body, the steps are continuous in the order of (a), (b), and (c), in particular, by performing step (c) after step (b), The layer made of the resin composition can be easily made porous without the plastic elastomer (B) extending too much during stretching. If the process sequence is performed in the order of (a), (c), and (b), the thermoplastic elastomer (B) is stretched by the process (c) and is subjected to stress. Since the cross-sectional area is small, it is difficult to obtain a porous structure. This is the same as the state in which the domain extends in the flow direction in the step (a) described above. In addition, the manufacturing method of this porous body should just perform each process in order of (a), (b), (c), and other than that between each process of (a), (b), (c) A process may be included. Moreover, you may include a process other than that after a process (c).

  Specifically, it is preferable to perform heat treatment after the step (c) from the viewpoint of improving dimensional stability. Further, for the purpose of further expanding the pores, after step (c), the film is stretched in the direction (hereinafter sometimes referred to as “lateral direction” or “TD”) perpendicular to the longitudinal direction by a tenter stretching method or the like (transverse direction). It is also preferable to stretch) Furthermore, it is also preferable to perform heat treatment from the viewpoint of improving dimensional stability after transverse stretching by a tenter stretching method or the like. In addition, from the viewpoint of further dimensional stability, the obtained porous body may be cross-linked by electron beam cross-linking, etc., and from the viewpoint of improving adhesion when laminated with other porous layers as described later, The obtained porous body may be subjected to surface treatment by performing corona discharge treatment, plasma treatment or the like.

When lateral stretching is performed after step (c), the temperature in the lateral stretching step is 100 ° C. or higher and 160 ° C. or lower, particularly 110 ° C. or higher and 150 ° C. or lower. Is preferable. In addition, the draw ratio at that time is 1.25 times or more and 6.00 times or less, particularly 1.40 times or more and 5.00 times or less in terms of further expansion of the pore diameter and suppression of blockage of the pores. Is preferred.
Moreover, when performing heat processing after a process (c), it is preferable in terms of dimensional stability that the temperature in a heat processing process is 120 to 200 degreeC, especially 140 to 180 degreeC.

  Moreover, when setting it as this porous body which has other porous layers other than the porous layer which consists of the said resin composition, in the said process (a), the said fluororesin (A) and the said thermoplastic elastomer (B) are contained. The layer of the resin composition and the layer of the composition constituting the other porous layer are laminated by a co-extrusion method or a lamination method to produce a substantially non-porous laminate, and then the step (b) And this porous body may be produced by stretching and making it porous in the step (c), and a layer comprising a resin composition containing the fluororesin (A) and the thermoplastic elastomer (B), After making porous through the steps (a) to (c), the porous body may be produced by laminating with another porous layer by a laminating method or a coating method.

<Battery>
Next, a non-aqueous electrolyte secondary battery containing the porous body as a battery separator will be described with reference to FIG.
Both electrodes of the positive electrode plate 21 and the negative electrode plate 22 are wound in a spiral shape so as to overlap each other via the battery separator 10, and the outside is stopped with a winding tape to form a wound body.
The winding process will be described in detail. One end of the battery separator is passed between the slit portions of the pin, and the pin is slightly rotated to wind one end of the battery separator around the pin. At this time, the surface of the pin is in contact with the coating layer of the battery separator. Thereafter, the positive electrode and the negative electrode are arranged so as to sandwich the battery separator, and the pins are rotated by a winding machine to wind the positive and negative electrodes and the battery separator. After winding, the pin is pulled out of the wound object.

  A wound body in which the positive electrode plate 21, the battery separator 10 and the negative electrode plate 22 are integrally wound is housed in a bottomed cylindrical battery case and welded to the positive and negative electrode lead bodies 24 and 25. Next, the electrolyte is injected into the battery can, and after the electrolyte has sufficiently penetrated into the battery separator 10 or the like, the positive electrode lid 27 is sealed around the opening periphery of the battery can via the gasket 26, and precharging and aging are performed. A cylindrical non-aqueous electrolyte secondary battery is produced.

As the electrolytic solution, an electrolytic solution in which a lithium salt is used as an electrolytic solution and is dissolved in an organic solvent is used. The organic solvent is not particularly limited, but for example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, esters such as dimethyl carbonate, methyl propionate or butyl acetate, and nitriles such as acetonitrile. 1,2-dimethoxyethane, 1,2-dimethoxymethane, dimethoxypropane, 1,3-dioxolane, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran or 4-methyl-1,3-dioxolane, or sulfolane These may be used alone or in combination of two or more. Among them, an electrolytic solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆₎ at a rate of 1.0 mol / L in a solvent obtained by mixing 2 parts by mass of methyl ethyl carbonate relative to ethylene carbonate 1 part by weight is preferred.

  As the negative electrode, an alkali metal or a compound containing an alkali metal integrated with a current collecting material such as a stainless steel net is used. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the compound containing an alkali metal include an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin or magnesium, a compound of an alkali metal and a carbon material, a low potential alkali metal and a metal oxide, and the like. Or a compound with a sulfide or the like. When a carbon material is used for the negative electrode, the carbon material may be any material that can be doped and dedoped with lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Mesocarbon microbeads, carbon fibers, activated carbon and the like can be used.

  As the positive electrode, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, metal oxide such as vanadium pentoxide or chromium oxide, metal sulfide such as molybdenum disulfide, etc. are used as active materials. , These positive electrode active materials are combined with conductive additives and binders such as polytetrafluoroethylene as appropriate, and finished with a current collector material such as a stainless steel mesh as a core material. It is done.

  Next, although an Example and a comparative example are shown and this porous body is demonstrated in detail, this invention is not limited to these. In addition, as an embodiment of the present porous body, it was shaped into a sheet. Hereinafter, this porous body is called a porous film. Moreover, the take-up (flow) direction of a porous film is described as "MD" direction, and the perpendicular direction is described as "TD" direction.

(1) MFR
For the raw materials used in the examples and comparative examples, MFR was measured under conditions of a temperature of 230 ° C. and a load of 2.16 kg. However, for the tetrafluoroethylene / ethylene / perfluorobutylethylene copolymer used in the examples, MFR was measured under conditions of a temperature of 297 ° C. and a load of 49 N.

(2) Thickness The surface of the obtained porous film was measured unspecified in five places with a 1/1000 mm dial gauge, and the average was taken as the thickness.

(3) Air permeability A sample was cut out from the obtained porous film with a diameter of 40 mm, and the air permeability (second / 100 mL) was measured according to JIS P8117.

(4) Porosity was measured substantial amount W ₁ of the resulting porous film, to calculate the mass W ₀ if the density and the thickness porosity of 0% of the resin composition, the following formulas these values Calculated based on
Porosity (%) = {(W ₀ −W ₁ ) / W ₀ } × 100

  The raw materials used in Examples and Comparative Examples are as follows.

(Fluorine resin)
A-1: polyvinylidene fluoride (grade name: KYNAR710, manufactured by Arkema, melting point: 170 ° C., MFR; 9 g / 10 min)
A-2: tetrafluoroethylene / ethylene / perfluorobutylethylene copolymer (grade name: FluonETFE C88AXP, manufactured by Asahi Glass Co., Ltd., melting point: 256 ° C., MFR: 11 g / 10 min)
A-3: tetrafluoroethylene / ethylene / perfluorobutylethylene copolymer (grade name: FluonETFE LM740AP, manufactured by Asahi Glass Co., Ltd., melting point: 228 ° C., MFR; 32 g / 10 min)
A-4; tetrafluoroethylene / ethylene / perfluorobutylethylene copolymer (grade name: FluonETFE LM730AP, manufactured by Asahi Glass Co., Ltd., melting point: 228 ° C., MFR: 25 g / 10 min)
A-5: tetrafluoroethylene / ethylene / perfluorobutylethylene copolymer (grade name: FluonETFE LM720AP, manufactured by Asahi Glass Co., Ltd., melting point: 227 ° C., MFR; 13 g / 10 min)

(Thermoplastic elastomer)
B-1: Styrenic elastomer (styrene-ethylene-propylene-styrene copolymer, grade name: SEPTON 2005, manufactured by Kuraray Co., Ltd., MFR; not flowing)
B-2: Styrenic elastomer (styrene-ethylene-propylene-styrene copolymer, grade name: SEPTON 2006, manufactured by Kuraray Co., Ltd., MFR; not flowing)
B-3: Styrenic elastomer (styrene-ethylene-butylene-styrene copolymer, grade name: SEPTON 8006, manufactured by Kuraray Co., Ltd., MFR: non-flowing)
B-4: Styrenic elastomer (styrene-ethylene- (ethylene-propylene) -styrene copolymer, grade name: SEPTON 4044, manufactured by Kuraray Co., Ltd., MFR; not flowing)
B-5: Styrenic elastomer (styrene-ethylene- (ethylene-propylene) -styrene copolymer, grade name: SEPTON 4055, manufactured by Kuraray Co., Ltd., MFR; not flowing)
B-6: Styrenic elastomer (styrene-ethylene-propylene-styrene copolymer, grade name: SEPTON 2002, manufactured by Kuraray Co., Ltd., MFR; 70 g / 10 min)
B-7: Styrenic elastomer (styrene-ethylene-butylene-styrene copolymer, grade name: SEPTON 8076, manufactured by Kuraray Co., Ltd., MFR: 65 g / 10 min)
B-8; acrylic elastomer (methyl methacrylate-butyl acrylate-methyl methacrylate copolymer, grade name: Clarity LA2330, manufactured by Kuraray Co., Ltd., MFR; 42 g / 10 min)
B-9; acrylic elastomer (methyl methacrylate-butyl acrylate-methyl methacrylate copolymer, grade name: Clarity LA3270, manufactured by Kuraray Co., Ltd., MFR: 66 g / 10 min)
B-10; acrylic elastomer (methyl methacrylate-butyl acrylate-methyl methacrylate copolymer, grade name: Clarity LA4285, manufactured by Kuraray Co., Ltd., MFR; 31 g / 10 min)

Example 1
70% by mass of fluororesin (A-1) and 30% by mass of thermoplastic elastomer (B-1) are mixed and charged into a twin screw extruder (screw diameter 25 mmφ), and melted at a set temperature of 200 ° C. After kneading, it was shaped into a sheet with a T-die and then cooled and solidified with a cast roll set at 100 ° C. to obtain an unstretched sheet having a thickness of 100 μm. Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Subsequently, between the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C., a draw ratio of 100% (stretching ratio: 2.00 times) is applied to perform high temperature stretching to obtain an MD stretched porous film. It was. The evaluation results of the obtained film are summarized in Table 1.

(Example 2)
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer in Example 1 was changed to the thermoplastic elastomer (B-2). Thereafter, the obtained unstretched sheet-like material was subjected to a draw ratio of 52% (stretching ratio 1.52 times) between the roll (X) set at 20 ° C. and the roll (Y) set at 40 ° C. Stretching was performed. Next, the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. are stretched at a high temperature by applying a draw ratio of 163% (stretching ratio 2.63 times) to obtain an MD stretched porous film. It was. The evaluation results of the obtained film are summarized in Table 1.

Example 3
The MD stretched porous film obtained in Example 2 was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then the stretching temperature was 145 ° C. and the stretching time was 2.1 seconds. After stretching in the transverse direction, heat treatment was performed at 160 ° C. for 18 seconds to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

Example 4
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer in Example 1 was changed to the thermoplastic elastomer (B-3). Thereafter, the obtained unstretched sheet-like material was subjected to a draw ratio of 52% (stretching ratio 1.52 times) between the roll (X) set at 20 ° C. and the roll (Y) set at 40 ° C. Stretching was performed. Next, the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. are stretched at a high temperature by applying a draw ratio of 163% (stretching ratio 2.63 times) to obtain an MD stretched porous film. It was. The evaluation results of the obtained film are summarized in Table 1.

(Example 5)
The MD stretched porous film obtained in Example 4 was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then the stretching temperature was 145 ° C. and the stretching time was 2.1 seconds. After stretching in the transverse direction, heat treatment was performed at 160 ° C. for 18 seconds to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

(Example 6)
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer of Example 1 was changed to the thermoplastic elastomer (B-4). Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Subsequently, between the roll (P) set to 115 ° C. and the roll (Q) set to 115 ° C., a draw ratio of 50% (stretching ratio: 1.50 times) is applied to perform high temperature stretching to obtain an MD stretched porous film. It was. The evaluation results of the obtained film are summarized in Table 1.

(Example 7)
The MD stretched porous film obtained in Example 6 was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then the stretching temperature was 145 ° C. and the stretching time was 2.1 seconds. After stretching in the transverse direction, heat treatment was performed at 160 ° C. for 18 seconds to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

(Example 8)
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer in Example 1 was changed to the thermoplastic elastomer (B-5). Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Subsequently, between the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C., a draw ratio of 100% (stretching ratio: 2.00 times) is applied to perform high temperature stretching to obtain an MD stretched porous film. It was. The evaluation results of the obtained film are summarized in Table 1.

Example 9
The MD stretched porous film obtained in Example 8 was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then the stretching temperature was 145 ° C. and the stretching time was 2.1 seconds. After stretching in the transverse direction, heat treatment was performed at 160 ° C. for 18 seconds to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

(Example 10)
An unstretched sheet material having a thickness of 100 μm under the same conditions as in Example 1 except that 85% by mass of the fluororesin (A-1) and 15% by mass of the thermoplastic elastomer (B-2) were blended. Got. Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Subsequently, between the roll (P) set to 115 ° C. and the roll (Q) set to 115 ° C., a draw ratio of 50% (stretching ratio: 1.50 times) is applied to perform high temperature stretching to obtain an MD stretched porous film. It was. Next, the obtained MD stretched porous film was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then stretched 2.1 times in a stretching temperature of 145 ° C. and a stretching time of 6 seconds. After stretching in the direction, heat treatment was performed at 160 ° C. for 18 seconds to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

(Example 11)
70% by mass of fluororesin (A-2) and 30% by mass of thermoplastic elastomer (B-2) are blended and charged into a twin screw extruder (screw diameter: 25 mmφ) and melted at a set temperature of 280 ° C. After kneading, it was shaped into a sheet with a T die, and then cooled and solidified with a cast roll set at 100 ° C. to obtain an unstretched sheet having a thickness of 130 μm. Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Subsequently, between the roll (P) set to 115 ° C. and the roll (Q) set to 115 ° C., a draw ratio of 50% (stretching ratio: 1.50 times) is applied to perform high temperature stretching to obtain an MD stretched porous film. It was. Next, the obtained MD stretched porous film was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then stretched 2.1 times in a stretching temperature of 145 ° C. and a stretching time of 6 seconds. After stretching in the direction, heat treatment was performed at 160 ° C. for 18 seconds to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

(Example 12)
70% by mass of fluororesin (A-3) and 30% by mass of thermoplastic elastomer (B-2) are blended and charged into a twin-screw extruder (screw diameter 25 mmφ) and melted at a set temperature of 250 ° C. After kneading, it was shaped into a sheet with a T die, and then cooled and solidified with a cast roll set at 100 ° C. to obtain an unstretched sheet having a thickness of 130 μm. Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Subsequently, between the roll (P) set to 115 ° C. and the roll (Q) set to 115 ° C., a draw ratio of 50% (stretching ratio: 1.50 times) is applied to perform high temperature stretching to obtain an MD stretched porous film. It was. Next, the obtained MD stretched porous film was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then stretched 2.1 times in a stretching temperature of 145 ° C. and a stretching time of 6 seconds. After stretching in the direction, heat treatment was performed at 160 ° C. for 18 seconds to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

(Example 13)
70% by mass of fluororesin (A-4) and 30% by mass of thermoplastic elastomer (B-2) are blended and charged into a twin screw extruder (screw diameter 25 mmφ) and melted at a set temperature of 260 ° C. After kneading, it was shaped into a sheet with a T die, and then cooled and solidified with a cast roll set at 100 ° C. to obtain an unstretched sheet having a thickness of 130 μm. Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Subsequently, between the roll (P) set to 115 ° C. and the roll (Q) set to 115 ° C., a draw ratio of 50% (stretching ratio: 1.50 times) is applied to perform high temperature stretching to obtain an MD stretched porous film. It was. Next, the obtained MD stretched porous film was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then stretched 2.1 times in a stretching temperature of 145 ° C. and a stretching time of 6 seconds. After stretching in the direction, heat treatment was performed at 160 ° C. for 18 seconds to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

(Example 14)
70% by mass of fluororesin (A-5) and 30% by mass of thermoplastic elastomer (B-2) are blended and charged into a twin screw extruder (screw diameter: 25 mmφ), and melted at a set temperature of 280 ° C. After kneading, it was shaped into a sheet with a T die, and then cooled and solidified with a cast roll set at 100 ° C. to obtain an unstretched sheet having a thickness of 130 μm. Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Subsequently, between the roll (P) set to 115 ° C. and the roll (Q) set to 115 ° C., a draw ratio of 50% (stretching ratio: 1.50 times) is applied to perform high temperature stretching to obtain an MD stretched porous film. It was. Next, the obtained MD stretched porous film was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then stretched 2.1 times in a stretching temperature of 145 ° C. and a stretching time of 6 seconds. After stretching in the direction, heat treatment was performed at 160 ° C. for 18 seconds to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

(Comparative Example 1)
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer of Example 1 was changed to the thermoplastic elastomer (B-6). Thereafter, the obtained unstretched sheet-like material was subjected to a draw ratio of 25% (stretch ratio: 1.25 times) between the roll (X) set to 20 ° C. and the roll (Y) set to 40 ° C. When the film was stretched, the film was broken as described in Table 2.

(Comparative Example 2)
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer of Example 1 was changed to the thermoplastic elastomer (B-7). Thereafter, the obtained unstretched sheet-like material was subjected to a draw ratio of 25% (stretch ratio: 1.25 times) between the roll (X) set to 20 ° C. and the roll (Y) set to 40 ° C. When the film was stretched, the film was broken as described in Table 2.

(Comparative Example 3)
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer of Example 1 was changed to the thermoplastic elastomer (B-8). Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Subsequently, between the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C., a draw ratio of 100% (stretching ratio: 2.00 times) is applied to perform high-temperature stretching, and a whitened MD stretched film is obtained. Obtained. The evaluation results of the obtained film are summarized in Table 2.

(Comparative Example 4)
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer in Example 1 was changed to the thermoplastic elastomer (B-9). Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Next, the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. were stretched at a high temperature by applying a draw ratio of 100% (stretching ratio: 2.00 times). The stretched film was transparent. The evaluation results of the obtained film are summarized in Table 2.

(Comparative Example 5)
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer of Example 1 was changed to the thermoplastic elastomer (B-10). Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. Stretching was performed. Next, the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. were stretched at a high temperature by applying a draw ratio of 100% (stretching ratio: 2.00 times). The stretched film was transparent. The evaluation results of the obtained film are summarized in Table 2.

(Comparative Example 6)
An unstretched sheet material having a thickness of 100 μm was obtained under the same conditions as in Example 1 except that the thermoplastic elastomer was not added and the fluororesin (A-1) was used alone. Thereafter, the unstretched sheet-like material obtained was subjected to a draw ratio of 50% (stretching ratio: 1.50 times) between a roll (X) set at 20 ° C. and a roll (Y) set at 40 ° C. When the film was stretched, the film was broken as described in Table 2.

(Comparative Example 7)
The unstretched sheet-like material obtained in Comparative Example 6 was multiplied by a draw ratio of 25% (stretch ratio: 1.25 times) between the roll (X) set at 20 ° C. and the roll (Y) set at 40 ° C. The film was stretched at a low temperature. Next, the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. were stretched at a high temperature by applying a draw ratio of 100% (stretching ratio: 2.00 times). The stretched film showed scale-like unevenness. The evaluation results of the obtained film are summarized in Table 2.

(Comparative Example 8)
50% by mass of fluororesin (A-1) and 50% by mass of thermoplastic elastomer (B-2) are blended and charged into a twin-screw extruder (screw diameter 25 mmφ) and melted at a set temperature of 200 ° C. After kneading, an attempt was made to shape the sheet with a T-die. However, the molten resin discharged from the T-die was difficult to flow, and the sheet was torn when being picked up by a cast roll. A stretched sheet was not obtained.

From Table 1, it turns out that the fluororesin porous body of this invention obtained in Examples 1-14 has the outstanding air permeability and high porosity.
On the other hand, from Table 2, among Comparative Examples 1 to 5 using a thermoplastic elastomer that is outside the range of MFR defined by the present invention, in Comparative Examples 1 and 2, the film was broken and a porous film was not obtained. . This is because the MFR of the thermoplastic elastomer used departs from the scope of the present invention, so that when the cast sheet is formed, the thermoplastic elastomer forming the domain extends in the flow direction of the sheet and enters the matrix / domain interface. It was thought that the film was broken because the stress concentration was hindered. In Comparative Example 3, although the film was whitened, the porosity was low and no air permeability was exhibited. In Comparative Examples 4 and 5, the film was not whitened, and no porous body was formed. Further, in Comparative Example 6 in which the thermoplastic elastomer was not used, the film was broken, and in Comparative Example 7, a part that was partially whitened was observed, but scale-like unevenness occurred. That is, it has been found that the fluororesin alone has problems in the low-temperature stretching characteristics and the homogenization of the porous body. In Comparative Example 8, an unstretched sheet-like material was not obtained because the weight ratio of the thermoplastic elastomer specified by the present invention was deviated. This is thought to be because the thermoplastic elastomer is formed as a matrix having a sea-island structure because the weight ratio of the thermoplastic elastomer exceeds 40% by mass.

(Example 15)
The unstretched sheet-like material obtained in Example 2 was multiplied by a draw ratio of 52% (stretching ratio: 1.52 times) between the roll (X) set at 40 ° C. and the roll (Y) set at 40 ° C. The film was stretched at a low temperature. Next, the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. are stretched at a high temperature by applying a draw ratio of 163% (stretching ratio 2.63 times) to obtain an MD stretched porous film. It was. The evaluation results of the obtained film are summarized in Table 3.

(Example 16)
The unstretched sheet-like material obtained in Example 2 was multiplied by a draw ratio of 52% (stretching ratio: 1.52 times) between the roll (X) set at 60 ° C. and the roll (Y) set at 60 ° C. The film was stretched at a low temperature. Next, the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. are stretched at a high temperature by applying a draw ratio of 163% (stretching ratio 2.63 times) to obtain an MD stretched porous film. It was. The evaluation results of the obtained film are summarized in Table 3.

(Example 17)
The unstretched sheet-like material obtained in Example 2 was multiplied by a draw ratio of 52% (stretching ratio 1.52 times) between the roll (X) set at 80 ° C. and the roll (Y) set at 80 ° C. The film was stretched at a low temperature. Next, the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. are stretched at a high temperature by applying a draw ratio of 163% (stretching ratio 2.63 times) to obtain an MD stretched porous film. It was. The evaluation results of the obtained film are summarized in Table 3.

(Comparative Example 9)
The unstretched sheet-like material obtained in Example 2 was passed between the roll (X) set at 20 ° C. and the roll (Y) set at 40 ° C. with a draw ratio of 0% (unstretched). Subsequently, when the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. were stretched at a high temperature with a draw ratio of 163% (stretch ratio 2.63 times), transparent stretching was performed. A film was obtained. The evaluation results of the obtained film are summarized in Table 4.

(Comparative Example 10)
The unstretched sheet-like material obtained in Example 2 was multiplied by a draw ratio of 163% (stretching ratio 2.63 times) between the roll (X) set at 60 ° C. and the roll (Y) set at 60 ° C. The film was stretched at a low temperature. Next, when the sheet was passed between a roll (P) set at 115 ° C. and a roll (Q) set at 115 ° C. with a draw ratio of 0% (unstretched), a whitened stretched film was obtained. The evaluation results of the obtained film are summarized in Table 4.

(Comparative Example 11)
The unstretched sheet-like material obtained in Example 2 was multiplied by a draw ratio of 163% (stretching ratio 2.63 times) between the roll (X) set at 80 ° C. and the roll (Y) set at 80 ° C. The film was stretched at a low temperature. Next, when the sheet was passed between a roll (P) set at 115 ° C. and a roll (Q) set at 115 ° C. with a draw ratio of 0% (unstretched), a whitened stretched film was obtained. The evaluation results of the obtained film are summarized in Table 4.

(Comparative Example 12)
The unstretched sheet-like material obtained in Example 2 was multiplied by a draw ratio of 163% (stretching ratio 2.63 times) between the roll (X) set at 105 ° C. and the roll (Y) set at 105 ° C. The film was stretched at a low temperature. Next, when the sheet was passed between a roll (P) set at 115 ° C. and a roll (Q) set at 115 ° C. with a draw ratio of 0% (unstretched), a transparent stretched film was obtained. The evaluation results of the obtained film are summarized in Table 4.

(Comparative Example 13)
The unstretched sheet-like material obtained in Example 2 was multiplied by a draw ratio of 52% (stretching ratio 1.52 times) between the roll (X) set at 105 ° C. and the roll (Y) set at 105 ° C. The film was stretched at a low temperature. Next, a hot stretched film was applied at a draw ratio of 163% (stretching ratio 2.63 times) between the roll (P) set at 115 ° C. and the roll (Q) set at 115 ° C. to obtain a transparent stretched film. Got. The evaluation results of the obtained film are summarized in Table 4.

From Table 1 and Table 3, it turns out that the fluororesin porous body obtained by the Example has the outstanding air permeability.
On the other hand, from Table 4, in Comparative Example 9 using a method (method not passing through step (b)) that is outside the scope of the production method defined by the present invention, the film was transparent and not made porous. Further, in Comparative Examples 10 and 11 using the method (method not passing through the step (c)) which is outside the scope of the manufacturing method defined by the present invention, although whitening occurs, the air permeability characteristics are not expressed and the material is made porous. There wasn't. Moreover, in Comparative Examples 12 and 13 using a method that is outside the scope of the production method defined by the present invention (a method that does not substantially pass through step (b)), the film became transparent and was not made porous.

  The porous fluororesin of the present invention can be applied to various uses that require air permeability. Separators for lithium batteries; sanitary materials such as disposable paper diapers and pads for absorbing body fluids such as sanitary items or bed sheets; medical materials such as surgical clothing or base materials for hot compresses; for clothing such as jumpers, sportswear or rainwear Materials: Hollow fiber membranes for water treatment; Building materials such as wallpaper, roof waterproofing materials, heat insulating materials, sound absorbing materials; desiccants; moisture-proofing agents; oxygen scavengers; disposable warmers; packaging materials such as freshness-keeping packaging or food packaging It can be used very suitably as a material for the above.

DESCRIPTION OF SYMBOLS 10 Battery separator 20 Secondary battery 21 Positive electrode plate 22 Negative electrode plate 24 Positive electrode lead body 25 Negative electrode lead body 26 Gasket 27 Positive electrode cover

Claims (6)

  1% by mass or more and 45% by mass of thermoplastic elastomer (B) mainly composed of fluororesin (A) and having a melt flow rate (MFR) of 30 g / 10 min or less at a temperature of 230 ° C. and a load of 2.16 kg. A fluororesin porous body comprising at least one porous layer comprising a resin composition contained below, wherein the porous layer is a layer that has been made porous by stretching in at least a uniaxial direction.   The fluororesin porous body according to claim 1, wherein the fluororesin (A) is a polyvinylidene fluoride resin, a polytetrafluoroethylene resin, or a mixture thereof.   The fluororesin porous body according to claim 1 or 2, wherein the thermoplastic elastomer (B) is a styrene-based thermoplastic elastomer.   The battery separator which uses the fluororesin porous body of any one of Claims 1-3.   A battery comprising the battery separator according to claim 4. 1% by mass or more and 45% by mass of thermoplastic elastomer (B) mainly composed of fluororesin (A) and having a melt flow rate (MFR) of 30 g / 10 min or less at a temperature of 230 ° C. and a load of 2.16 kg. A resin composition containing:
(A) melt-extruding, cooling and solidifying into a sheet-like product having at least one layer made of the resin composition, or a fibrous product, or a hollow product; and
(B) a step of stretching the sheet-like product, the fibrous product, or the hollow product formed in the step (a) at a temperature of -20 ° C or higher and 90 ° C or lower;
(C) including a step of further stretching the sheet-like material, the fibrous material, or the hollow material stretched in the step (b) at a temperature of 100 ° C. or higher and 160 ° C. or lower.
A method for producing a fluororesin porous body.

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