Porous film

Abstract

To provide a porous film which achieves both thinness and air permeability.SOLUTION: A porous film contains a polyolefin-based resin (A) and a styrenic thermoplastic elastomer (B), wherein a melt flow rate (MFR (A)) at a temperature of 230°C and a load of 2.16 kg of the polyolefin-based resin (A) is 8 g / 10 min or more, and a difference (MFR(A)-MFR(B)) between a melt flow rate (MFR (A)) of the polyolefin-based resin (A) and a melt flow rate (MFR (B)) at a temperature of 200°C and a load of 10 kg of the styrenic thermoplastic elastomer (B) is 6 g / 10 min or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a porous film.

Background Art

[0002] Polymeric porous films having a large number of fine communication holes are used in various fields such as separation membranes used in the production of ultrapure water, purification of chemical solutions, water treatment, etc., waterproof and moisture-permeable films used in clothing and sanitary materials, or separators used in electronic components such as capacitors, batteries, electrolytic capacitors, etc.

[0003] Among them, porous films made of polyolefin-based resins are made by controlling the crystallization of polyolefin-based resins in the cooling and solidification process from melt extrusion, and stretching the film-like material of the crystallized polyolefin-based resin to make it porous, or by applying strain such as stretching to a polyolefin molded body in which different solids are microdispersed to generate pores between the different solids to make it porous, or by microdispersing fine powders such as different polymers, paraffins, waxes, etc. in a polyolefin-based resin and then solvent-extracting them.

[0004] Patent Documents 1 to 3 propose a technique for obtaining a stretched porous film by using a polypropylene-based resin as a matrix, blending a styrene-based thermoplastic elastomer showing partial compatibility with the matrix as a domain, melt-extruding from a T-die and melt-solidifying with a casting roll, and then biaxially stretching the obtained sheet-like material. With these techniques, the porous structure can be adjusted depending on the type of styrene-based thermoplastic elastomer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] In recent years, there has been a demand for thinning and improving the air permeability of porous films. However, the film thickness and air permeability are in an inverse relationship, and the air permeability tends to deteriorate as the thickness is reduced. The techniques described in Patent Documents 1 to 3 above do not provide sufficient air permeability, and there is a need for a porous film that is thin and yet has better air permeability.

[0007] Therefore, an object of the present invention is to provide a porous film that achieves both thinness and air permeability.

MEANS FOR SOLVING THE PROBLEMS

[0008] As a result of intensive studies in view of the above problems, the present inventors have found that a porous film containing a polyolefin resin (A) and a styrene-based thermoplastic elastomer (B) and having a melt flow rate (MFR(A)) of 8 g / 10 min or more at a temperature of 230°C and a load of 2.16 kg, and a difference (MFR(A) - MFR(B)) between the melt flow rate (MFR(A)) of the polyolefin resin (A) and the melt flow rate (MFR(B)) of the styrene-based thermoplastic elastomer (B) at a temperature of 200°C and a load of 10 kg of 6 g / 10 min or more can solve the present problem.

[0009] The present invention relates to the following. [1] A porous film containing a polyolefin resin (A) and a styrene-based thermoplastic elastomer (B), wherein the melt flow rate (MFR(A)) of the polyolefin resin (A) at a temperature of 230°C and a load of 2.16 kg is 8 g / 10 min or more, The difference (MFR(A) - MFR(B)) between the melt flow rate (MFR(A)) of the polyolefin resin (A) and the melt flow rate (MFR(B)) of the styrene-based thermoplastic elastomer (B) at a temperature of 200°C and a load of 10 kg is 6 g / 10 min or more, a porous film. [2] The porous film according to [1], wherein the melt flow rate (MFR(B)) of the styrene-based thermoplastic elastomer (B) at a temperature of 200°C and a load of 10 kg is 2.0 g / 10 min or less. [3] The porous film according to [1] or [2], wherein the air permeability (S) is 10 seconds / 100 cc or less, and the ratio (S / T) of the air permeability (S) (seconds / 100 cc) to the thickness (T) (μm) of the porous film is 0.5 or less. [4] The porous film according to any one of [1] to [3], wherein the wetting tension is 43 mN / m or more. [5] The porous film according to any one of [1] to [4], wherein the thickness (T) is 50 μm or less. [6] The porous film according to any one of [1] to [5], wherein the styrene content of the styrene-based thermoplastic elastomer (B) is 10% by mass or more and 50% by mass or less. [7] The porous film according to any one of [1] to [6], further containing a nucleating agent (C). [8] An ion exchange membrane support comprising the porous film according to any one of [1] to [7]. [9] A power storage device comprising the ion exchange membrane support according to [8]. [Effect of the Invention]

[0010] According to the present invention, a porous film having both thinness and air permeability characteristics can be obtained. In addition, since the porous film of the present invention is excellent in air permeability characteristics while being a thin film, it can be suitably used as an ion exchange membrane support, particularly an ion exchange membrane support for a power storage device. [Embodiments for Carrying Out the Invention]

[0011] Hereinafter, a porous film and a method for manufacturing the same as an example of an embodiment of the present invention will be described in detail, but the scope of the present invention is not limited to the embodiments described below. In the present invention, the term "film" conceptually includes sheets and films.

[0012] In the present invention, when described as "x to y" (where x and y are arbitrary numbers), unless otherwise specified, it includes the meaning of "x or more and y or less", and also includes the meaning of "preferably greater than x" or "preferably less than y". Further, when described as "x or more" (where x is an arbitrary number), unless otherwise specified, it includes the meaning of "preferably greater than x", and when described as "y or less" (where y is an arbitrary number), unless otherwise specified, it also includes the meaning of "preferably less than y". Furthermore, "x and / or y" (where x and y are arbitrary components) means at least one of x and y, and includes three cases: only x, only y, and both x and y.

[0013] <Resin composition> The porous film of the present invention (hereinafter also referred to as "the present film") is preferably formed from a resin composition (hereinafter also referred to as "the present composition") containing at least a polyolefin resin and a styrene-based thermoplastic elastomer.

[0014] Hereinafter, the components constituting the present composition will be described in detail.

[0015] 1. Polyolefin resin (A) Examples of the polyolefin resin (A) include homopolypropylene (propylene homopolymer), or a polyolefin resin such as a random copolymer or block copolymer of propylene and an α-olefin such as ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, or 1-decene. The polyolefin resin (A) exemplified above may be used alone or in combination of two or more. Among these, homopolypropylene is preferable from the viewpoint of mechanical strength.

[0016] When the polyolefin resin (A) is a polypropylene resin, the isotactic pentad fraction is not particularly limited, but is preferably 80 mol% or more and 99 mol% or less, more preferably 83 mol% or more and 98 mol% or less, and still more preferably 85 mol% or more and 97 mol% or less. The isotactic pentad fraction indicates stereoregularity. If the isotactic pentad fraction is too low, sufficient porosification may not be achieved by stretching. On the other hand, the upper limit of the isotactic pentad fraction is defined by the upper limit value that can be industrially obtained at present, but this is not the case when resins with higher regularity are developed at the industrial level in the future. The isotactic pentad fraction means a three-dimensional structure in which all five methyl groups that are side chains with respect to the main chain formed by carbon-carbon bonds composed of any five consecutive propylene units are located in the same direction, or the ratio thereof. The assignment of signals in the methyl group region conforms to A. Zambelli et al., Macromol., 8, 687 (1975).

[0017] The Mw / Mn of the polyolefin resin (A) is not particularly limited, but is preferably 1.5 or more and 10.0 or less, more preferably 2.0 or more and 8.0 or less, and even more preferably 2.0 or more and 6.0 or less. Mw / Mn is a parameter indicating the molecular weight distribution, and the smaller the Mw / Mn, the narrower the molecular weight distribution. By setting Mw / Mn to be equal to or higher than the above lower limit value, sufficient extrusion moldability can be obtained, and industrial mass production is possible. On the other hand, by setting Mw / Mn to be equal to or lower than the above upper limit value, sufficient mechanical strength can be ensured. In addition, the Mw / Mn in the present invention is a value measured by the GPC (gel permeation chromatography) method.

[0018] The melt flow rate (MFR(A)) of the polyolefin resin (A) in the present composition at a temperature of 230 °C and a load of 2.16 kg is 8 g / 10 min or more. When the styrene-based elastomer (B) described later is dispersed in the polyolefin resin (A) with the melt flow rate (MFR(A)) of 8 g / 10 min or more, the orientation of the styrene-based elastomer (B) in the plane direction can be suppressed, and the dispersion diameter of the styrene-based elastomer (B) becomes larger, so the connectivity in the thickness direction is increased. As a result, the air permeability of the present film can be improved. From this viewpoint, the melt flow rate (MFR(A)) is preferably 9 g / 10 min or more, more preferably 10 g / 10 min or more, and even more preferably 11 g / 10 min or more. On the other hand, the upper limit is preferably 20 g / 10 min or less, more preferably 18 g / 10 min or less, and even more preferably 16 g / 10 min or less. By setting the MFR to be equal to or lower than the above upper limit value, the strength of the present film can be sufficiently provided. When two or more polyolefin resins (A) are used in combination, at least one polyolefin resin (A) may have the above MFR value. In addition, the MFR of the polyolefin resin (A) in the present invention is a value measured under the conditions of a temperature of 230 °C and a load of 2.16 kg in accordance with JIS K7210-1 (2014).

[0019] As the polyolefin resin (A), for example, commercially available products such as the trade names "Novatec PP", "WINTEC" (manufactured by Japan Polypropylene Corporation); "Natio", "Tafmer XR" (manufactured by Mitsui Chemicals, Inc.); "Zealus", "Thermolan" (manufactured by Mitsubishi Chemical Corporation); "Sumitomo Noblen", "Tafsellen" (manufactured by Sumitomo Chemical Company, Limited); "Prime PP", "Prime TPO" (manufactured by Prime Polymer Co., Ltd.); "Adflex", "Adsyl", "HMS-PP(PF814)" (manufactured by San Aroma Co., Ltd.); "Versify", "Inspire" (manufactured by The Dow Chemical Company) can be used.

[0020] The content of the polyolefin resin (A) in the present composition is preferably 50% by mass or more and 95% by mass or less, more preferably 55% by mass or more and 90% by mass or less, and still more preferably 60% by mass or more and 85% by mass or less. When the content of the polyolefin resin (A) is within the above range, a sea-island structure in which the polyolefin resin (A) is used as a matrix and the styrenic thermoplastic elastomer (B) forms domains can be formed, and a porous structure is likely to be formed when stretching is performed.

[0021] 2. Styrenic thermoplastic elastomer (B) This film can efficiently obtain a porous film having a fine and highly uniform porous structure by adding a styrenic thermoplastic elastomer (B) to a polyolefin resin (A) and forming a sea-island structure in which the styrenic thermoplastic elastomer (B) forms domains in the matrix of the polyolefin resin (A), and it becomes easy to control the shape and pore diameter of the pores.

[0022] The styrenic thermoplastic elastomer (B) is a type of thermoplastic elastomer resin based on a styrene component, and is a copolymer composed of a continuum of a soft component (for example, a butadiene component) and a hard component (for example, a styrene component). Specifically, there is one that is hydrogenated to convert the carbon double bond of the copolymer into a single bond.

[0023] Examples of the type of copolymer include random copolymers, block copolymers, and graft copolymers. Examples of block copolymers include linear block structures and radial branched block structures, etc. In the present invention, any structure may be used.

[0024] Examples of the styrenic thermoplastic elastomer (B) include styrene-olefin-styrene copolymers (B1) and styrene-olefin copolymers (B2). Examples of the styrene-olefin-styrene copolymer (B1) include styrene-butadiene-styrene copolymers (SBS), styrene-butadiene-butylene-styrene copolymers (SBBS), styrene-ethylene-butadiene-styrene copolymers (SEBS), styrene-isoprene-styrene copolymers (SIS), styrene-ethylene-propylene-styrene copolymers (SEPS), styrene-ethylene-ethylene-propylene-styrene copolymers (SEEPS), etc. Examples of the styrene-olefin copolymer (B2) include styrene-butadiene copolymers (SBR), hydrogenated styrene-butadiene copolymers (SEB), styrene-isoprene copolymers (SIR), styrene-ethylene-propylene copolymers (SEP), etc. The styrenic thermoplastic elastomer (B) exemplified above may be used alone or in combination of two or more.

[0025] Among them, since a porous structure is likely to be formed when the compatibility with the polyolefin resin (A) is low, from the viewpoint of the formability of the porous structure, it is preferable to use, as the main component, a resin having a structure in which both ends are styrene polymers. On the other hand, in order to efficiently disperse the styrenic thermoplastic elastomer (B) in the present composition, it is preferable to use, as the main component, a resin containing an ethylene component (hydrogenated butadiene component), an ethylene-propylene component (hydrogenated isoprene component), or a butylene component, which has high compatibility with the polyolefin resin (A). That is, from the viewpoint of the formability of the porous structure, it is preferable to use a styrene-olefin-styrene copolymer (B1) as the main component, and from the viewpoint of the dispersibility of the styrenic thermoplastic elastomer (B), it is preferable to use SEP, SEPS, SEBS, or SEEPS as the main component. From both of the above viewpoints, it is more preferable to use SEPS or SEEPS as the main component, and among them, it is particularly preferable to use SEEPS as the main component. The "main component" in the styrenic thermoplastic elastomer (B) refers to the resin having the largest content as the styrenic thermoplastic elastomer (B) contained in the present composition. More specifically, when the total amount of the styrenic thermoplastic elastomer (B) is 100% by mass, it refers to a resin that occupies, with 100% by mass as the upper limit, preferably 50% by mass or more, more preferably 55% by mass or more, and still more preferably 60% by mass or more.

[0026] Among them, from the viewpoint of achieving both high air permeability and mechanical properties at a higher level, it is preferable that the styrenic thermoplastic elastomer (B) contained in the present composition includes a styrene-olefin-styrene copolymer (B1) and a styrene-olefin copolymer (B2). By combining two or more styrenic thermoplastic elastomers (B), the uniformity of the porous structure obtained by the stretching step can be enhanced.

[0027] In the porous film of the present invention, voids are formed starting from cracks generated during stretching inside the domains of the styrenic thermoplastic elastomer (B). The structure of the domains is closely related to the porous structure. The larger the domains, the larger the voids and the better the air permeability. Among the styrenic thermoplastic elastomers (B), styrene-olefin-styrene copolymer (B1) is preferred in that large domains are easily obtained. Further, the uneven distribution of the styrene-olefin copolymer (B2) on the surface of the domains improves the dispersibility of the domains and can enhance the uniformity of the porous structure. Furthermore, inside the domains, pores formed by the styrene-olefin copolymer (B2) are formed between the large voids formed by the styrene-olefin-styrene copolymer (B1), improving the connectivity of the voids and further enhancing the air permeability.

[0028] The styrene content of the styrenic thermoplastic elastomer (B) is preferably 10% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 45% by mass or less. If the styrene content is at least the above lower limit, domains can be effectively formed in the polyolefin resin (A), and if the styrene content is at most the above upper limit, excessive large domain formation can be suppressed. When there are two or more styrenic thermoplastic elastomers (B) contained in the present composition, the above styrene content refers to the total amount of the styrenic thermoplastic elastomers (B).

[0029] The weight average molecular weight (Mw) of the resin that is the main component among the styrenic thermoplastic elastomers (B) contained in the present composition is not particularly limited, but is preferably 100,000 or more, more preferably 150,000 or more and 1,000,000 or less, more preferably 150,000 or more and 800,000 or less, even more preferably 150,000 or more and 600,000 or less, even more preferably 150,000 or more and 500,000 or less, even more preferably 150,000 or more and 400,000 or less, even more preferably 150,000 or more and 350,000 or less, and particularly preferably 150,000 or more and 300,000 or less. In addition, although the Mw / Mn of the resin that is the main component among the styrenic thermoplastic elastomers (B) contained in this composition is not particularly limited, it is preferably 1.00 or more and 1.50 or less, more preferably 1.00 or more and 1.40 or less, and even more preferably 1.05 or more and 1.20 or less.

[0030] When the film made of this composition is stretched and porousified in at least one axial direction, the morphology of the polyolefin resin (A) and the styrenic thermoplastic elastomer (B) in the resin composition before stretching is an important factor in the formation of the porous structure. Specifically, it is important that the styrenic thermoplastic elastomer (B) present as a domain exists in a spherical shape with respect to the matrix mainly composed of the polyolefin resin (A).

[0031] Generally, when a resin composition having a matrix / domain sea-island structure is melt-extruded and cooled and solidified, the resin composition flowing out from a shaping facility such as a die or a nozzle is cooled and solidified by a cooling and solidifying facility such as a cast roll (cooling roll), air cooling, or water cooling. At this time, since the resin composition melts and elongates in the gap (clearance) between the shaping facility and the cooling and solidifying facility, when the weight average molecular weight of the styrenic thermoplastic elastomer (B) that is the domain is small, a resin composition in which the domain has elongated in the flow direction (extrusion direction) is obtained. And when the domain has elongated in the flow direction (extrusion direction), the area of the domain particles in the flow direction becomes large, so cleavage inside the domain hardly occurs with respect to the stress in the flow direction (extrusion direction), and there may be a case where a porous structure is not sufficiently formed.

[0032] On the other hand, when the weight average molecular weight of the styrenic thermoplastic elastomer (B) that is the domain is large, the domain is hardly affected by melt elongation, and the domain in the resin composition before stretching that is obtained is likely to maintain a spherical shape. When the domain is spherical, cleavage inside the domain is likely to occur with respect to the stress in the flow direction (extrusion direction), so it is considered that a porous structure is sufficiently formed.

[0033] Therefore, it is preferable that the weight average molecular weight (Mw) of the resin which is the main component of the styrenic thermoplastic elastomer (B) is within the above range. Further, when the ratio (molecular weight distribution) Mw / Mn of the number average molecular weight Mn and the weight average molecular weight (Mw) of the resin which is the main component of the styrenic thermoplastic elastomer (B) is within the above range, the dispersion diameter of the formed domain is likely to be uniform, which is more preferable.

[0034] The melt flow rate (MFR(B)) of the styrenic thermoplastic elastomer (B) contained in the present composition, measured at a temperature of 200°C and a load of 10 kg, is preferably 2.0 g / 10 min or less. The shape of the styrenic thermoplastic elastomer (B) dispersed in the resin composition changes due to the viscosity difference with the polyolefin resin (A). However, for a styrenic thermoplastic elastomer with an MFR below the above upper limit, it is easy to increase the viscosity difference with the polyolefin resin (A), and its shape is likely to become spherical. A spherically dispersed domain is more likely to have a higher uniformity of the porous structure obtained by the subsequent stretching process than a domain with a large aspect ratio, and a porous film excellent in physical property stability can be obtained while being a thin film. From such a viewpoint, the melt flow rate (MFR(B)) is preferably 1.0 g / 10 min or less, more preferably 0.5 g / 10 min or less, and even more preferably 0.1 g / 10 min or less. The lower limit is not particularly limited, but is usually 0 g / 10 min, that is, in a non-flowing state. When using two or more kinds of styrenic thermoplastic elastomers (B), at least one kind of styrenic thermoplastic elastomer (B) may have the above MFR value. Among them, if the styrenic thermoplastic elastomer with an MFR within the above range is the main component, during the stretching process, stress is likely to concentrate inside the domain, so that an opening starting point is likely to occur and it is easy to be porous, which is preferable. In addition, the MFR of the styrenic thermoplastic elastomer (B) in the present invention is a value measured under the conditions of a temperature of 200°C and a load of 10 kg in accordance with JIS K7210-1 (2014).

[0035] The content of the styrenic thermoplastic elastomer in the composition is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 45% by mass or less, and still more preferably 15% by mass or more and 40% by mass or less. When the content of the styrenic thermoplastic elastomer (B) is within the above range, a sea-island structure with a polyolefin resin (A) as the matrix and a styrenic thermoplastic elastomer (B) as the domain can be formed, and a porous structure is likely to be formed when stretching is performed.

[0036] The difference (MFR(A) - MFR(B)) between the melt flow rate (MFR(A)) of the polyolefin resin (A) in the composition at a temperature of 230 °C and a load of 2.16 kg and the melt flow rate (MFR(B)) of the styrenic thermoplastic elastomer (B) at a temperature of 200 °C and a load of 10 kg is 6 g / 10 min or more. In recent years, there has been a demand for thinning and improving the air permeability of porous films. However, thinning and air permeability are conflicting properties, and there has been a problem that the air permeability deteriorates as the thickness is reduced. More specifically, when obtaining a porous film with a thickness of 30 μm or less, it has been difficult to make the air permeability 10 seconds / 100 mL or less. As a result of intensive studies in view of the above problems, the inventors of the present invention have found that, in adjusting the combination of polyolefin resin and styrenic thermoplastic elastomer and film-forming conditions, particularly in a formulation in which the melt flow rates (MFR) of the polyolefin resin and the styrenic thermoplastic elastomer are widely separated, extremely good air permeability can be maintained even when the thickness is reduced. When the difference in the melt flow rate (MFR) between the polyolefin resin and the styrenic thermoplastic elastomer is large, the dispersion diameter of the styrenic elastomer domain that serves as the starting point of the opening increases, and the deformation of the domain in the in-plane direction is suppressed. As a result, it is considered that the connectivity in the thickness direction is improved. From the above viewpoints, the difference (MFR(A) - MFR(B)) between the melt flow rate (MFR(A)) of the polyolefin resin (A) and the melt flow rate (MFR(B)) of the styrenic thermoplastic elastomer (B) is preferably 7 g / 10 min or more, more preferably 8 g / 10 min or more, and even more preferably 10 g / 10 min or more. Also, from the viewpoint of film formability, the difference (MFR(A) - MFR(B)) is preferably 20 g / 10 min or less, and more preferably 15 g / 10 min or less. When the composition contains two or more polyolefin resins (A) and / or two or more styrenic thermoplastic elastomers (B), it is the difference between the polyolefin resin (A) with the highest MFR(A) value and the styrenic thermoplastic elastomer (B) with the lowest MFR(B) value.

[0037] 3. Nucleating agent (C) When the composition is made porous by stretching between the polyolefin resin (A) and the styrenic thermoplastic elastomer (B), it is considered effective for void formation to increase the rigidity of the polyolefin resin (A). Therefore, the composition may contain a nucleating agent (C). As the nucleating agent (C), an α-nucleating agent and a β-nucleating agent are preferred, and from the viewpoint of excellent heat resistance, an α-nucleating agent is preferred. On the other hand, from the viewpoint of heat fusion properties, a β-nucleating agent is preferred. Examples of the α-nucleating agent include dibenzylidene sorbitol (manufactured by Shin Nippon Rika Co., Ltd., trade name "Gelol MD"), "Adekastab NA-11", "Adekastab NA-27", "Adekastab NA-902", "Adekastab NA-21", "Adekastab NA-71" (all of the above five are manufactured by ADEKA Corporation), a masterbatch containing a mixture of magnesium stearate and silica (manufactured by Dainichi Seiko Kogyo Co., Ltd., trade name "Hi Cycle Master"), a masterbatch containing the sodium salt of 2-hydroxy-2-oxo-4,6,10,12-tetra-tert-butyl-1,3,2-dibenzo[d,g]perhydrodioxaphosphorosin (manufactured by ADEKA Corporation, trade name "Adekastab M-701"), etc. can be used.

[0038] In addition, examples of the α-nucleating agent include silica, talc, and calcium carbonate as inorganic nucleating agents. Examples of the organic type (carboxylic acid metal salt type) include calcium stearate, sodium benzoate, aluminum benzoate, aluminum dibenzoate, potassium benzoate, lithium benzoate, sodium β-naphthalate, sodium cyclohexanecarboxylate, metal pimelate, metal rosinate, and the like. There are also benzylidene sorbitol and its derivative types, and metal phosphate esters. Furthermore, examples of the polymer type include poly-3-methylbutene-1, polyvinylcycloalkane, polyvinyltrialkylsilane, EPR, Kevlar (registered trademark) fiber, sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl) phosphate, and the like. The content of the α-nucleating agent in the present composition is preferably 0.001 part by mass or more and 10 parts by mass or less, more preferably 0.005 part by mass or more and 5 parts by mass or less, still more preferably 0.01 part by mass or more and 2 parts by mass or less, and even more preferably 0.05 part by mass or more and 1.5 parts by mass or less, based on 100 parts by mass of the resin component in the present composition. If the content of the α-nucleating agent is 0.001 part by mass or more, the formation of α-crystals can be sufficient. On the other hand, if the content of the α-nucleating agent is 10 parts by mass or less, there is no risk of bleeding, plate-out, powder falling, etc. of the α-nucleating agent in the film-forming process, secondary processing process, etc., which is preferable in terms of cost reduction.

[0039] Examples of β nucleating agents include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; alkali or alkaline earth metal salts of carboxylic acids typified by potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, etc.; aromatic sulfonic acid compounds typified by sodium benzenesulfonate or sodium naphthalenesulfonate; diesters or triesters of tribasic carboxylic acids; phthalocyanine-based pigments typified by phthalocyanine blue; two-component compounds composed of component A which is an organic dibasic acid and component B which is an oxide, hydroxide or salt of a Group IIA metal of the periodic table; compositions composed of cyclic phosphorus compounds and magnesium compounds, etc. In addition, specific types of nucleating agents are described in JP-A-2003-306585, JP-A-06-289566, and JP-A-09-194650.

[0040] Examples of commercially available β nucleating agents include, for example, the β nucleating agent "Nujester NU-100" manufactured by Shin Nippon Rika Co., Ltd. Specific examples of polypropylene added with a β nucleating agent include polypropylene "Bepol B-022SP" manufactured by Aristech, polypropylene "Beta(β)-PPBE60-7032" manufactured by Borealis, polypropylene "BNXBETAPP-LN" manufactured by Mayzo, etc.

[0041] The β nucleating agent is preferably compounded with the polyolefin resin (A). At this time, the ratio of the β nucleating agent to the polyolefin resin (A) is preferably adjusted as appropriate according to the type of the β nucleating agent or the composition of the polyolefin resin (A). From such a viewpoint, the content of the β nucleating agent is preferably 0.0001 to 5.0 parts by mass with respect to 100 parts by mass of the polyolefin resin (A), more preferably 0.001 parts by mass or more or 3.0 parts by mass or less, and still more preferably 0.01 parts by mass or more or 1.0 parts by mass or less. If it is 0.0001 parts by mass or more, β crystals of the polyolefin resin (A) can be sufficiently generated and grown during production, and sufficient β crystal activity can be ensured, and desired air permeability can also be obtained when used as an ion exchange membrane support. Further, if it is 5.0 parts by mass or less, it is economically advantageous, and in addition, there is no bleeding of the β nucleating agent on the surface of the present porous film, which is preferable. Further, when a layer containing a polyolefin or the like is laminated in addition to the resin layer made of the polyolefin resin (A), the addition amounts of the β nucleating agent in each layer may be the same or different. By changing the addition amount of the β nucleating agent, the porous structure of each layer can be appropriately adjusted.

[0042] 4. Other components In the present composition, various additives such as heat stabilizers, antioxidants, ultraviolet absorbers, light stabilizers, colorants, antistatic agents, hydrolysis inhibitors, lubricants, and flame retardants may be appropriately blended to the extent that the properties are not impaired. Further, other resins may be contained to the extent that the properties are not impaired. Furthermore, the present composition can be subjected to surface treatments such as corona treatment, plasma treatment, printing, coating, vapor deposition, etc., and further perforation treatment, etc., as necessary within the range not impairing the present invention, and it is also possible to use several sheets of the porous film of the present invention stacked according to the application.

[0043] <Porous film> This film may be formed only of the porous layer made of the above resin composition, or other layers may be laminated within the range not inhibiting the features of the present invention. In the present invention, the "porous film" means that the porosity of the film is 50% or more, preferably 55% or more, more preferably 60% or more. The upper limit is not particularly limited, but it is practical that it is 90% or less. When this film has a layer other than the porous layer, it is sufficient that the porosity of only the porous layer is within the above range. The porosity can be calculated from the density of the resin composition by the method described in the examples.

[0044] The thickness (T) of this film is preferably 1 to 50 μm. When this film is used as an ion exchange membrane support in an energy storage device, a thickness (T) of 50 μm or less can contribute to thinning and high integration of the cell stack. On the other hand, the lower limit of the thickness (T) of this film is preferably 1 μm or more in terms of being able to maintain sufficient strength as a film. From such a viewpoint, the thickness (T) of this film is preferably 1 μm or more and 50 μm or less, more preferably 2 μm or more and 30 μm or less, and even more preferably 5 μm or more and 25 μm or less.

[0045] The average tensile strength of this film is not particularly limited, but preferably 2 MPa or more. When the average tensile strength of this film is 5 MPa or more, excellent mechanical properties can be obtained. From such a viewpoint, the average tensile strength of this film is preferably 4 MPa or more, particularly preferably 6 MPa or more, more preferably 8 MPa or more, and even more preferably 10 MPa or more. The upper limit is not particularly limited, and for example, it may be 400 MPa or less, 300 MPa or less, 200 MPa or less, or 100 MPa or less. When the average tensile strength of this film is below the upper limit, it is preferable in terms of excellent handleability. In the present invention, the average tensile strength is the average value of the tensile strengths in the MD and TD measured by the method described in the examples. When the MD and TD are unknown, it may also be the average value of the tensile strengths in an arbitrary length direction and the width direction perpendicular thereto.

[0046] In addition, the average tensile elongation at break of this film is not particularly limited, but is preferably 1% or more, more preferably 10% or more, still more preferably 20% or more, and even more preferably 30% or more. The upper limit is not particularly limited, but may be, for example, 200% or less. When the average tensile elongation at break of this film is within the above range, excellent mechanical properties can be obtained. The average tensile elongation at break in the present invention is the average value of the tensile elongation at break in the MD and TD measured by the method described in the examples. When the MD and TD are unknown, it may also be the average value of the tensile elongation at break in an arbitrary length direction and the width direction perpendicular thereto.

[0047] The average tensile strength and the average tensile elongation at break can be adjusted by the chemical structure, molecular weight, MFR, content, casting temperature during film formation, draw ratio, etc. of the polyolefin resin (A) and the styrene-based thermoplastic elastomer (B). For example, using a styrene-based thermoplastic elastomer (B) having low compatibility with the polyolefin resin (A) as the main component; using a resin having a high weight average molecular weight (Mw) as the main component of the styrene-based thermoplastic elastomer (B); using a resin having a low MFR (i.e., high viscosity) as the styrene-based thermoplastic elastomer (B); adjusting the content ratio of the polyolefin resin (A) and the styrene-based thermoplastic elastomer (B) to the above preferred range; in the production method described later, adjusting the temperature of the casting roll during film formation to the preferred range; when biaxially stretching, adjusting the longitudinal and transverse draw ratios and draw ratios to the preferred range, etc., the average tensile strength and the average tensile elongation at break can be adjusted. Applying the means exemplified above is considered to lead to the formation of a porous structure and an improvement in air permeability because it leads to the control of the morphology of the polyolefin resin (A) and the styrene-based thermoplastic elastomer (B), as well as the formation of a pore structure and the control of the film thickness.

[0048] The air permeability (S) of this film is not particularly limited, but it is preferably 10 seconds / 100 cc or less, more preferably 9 seconds / 100 cc or less, even more preferably 8 seconds / 100 cc or less, and still more preferably 7 seconds / 100 cc or less, with a lower limit of 0.25 seconds / 100 cc. Note that the air permeability (S) in the present invention is measured under the condition of 25 °C in accordance with JIS P8117:2009.

[0049] The ratio (S / T) of the air permeability (S) (seconds / 100 cc) to the thickness (T) (μm) of this film is preferably 0.01 or more and 0.5 or less. When the ratio (S / T) of the air permeability (S) to the thickness (T) is within the above range, a porous film excellent in air permeability characteristics can be obtained while being a thin film (for example, 50 μm or less). From such a viewpoint, the value of (S / T) is preferably 0.02 or more and 0.45 or less, more preferably 0.03 or more and 0.40 or less, even more preferably 0.04 or more and 0.35 or less, and particularly preferably 0.05 or more and 0.30 or less. The value of (S / T) can be adjusted by the chemical structure, molecular weight, MFR, content, casting temperature during film formation, draw ratio, etc. of the polyolefin resin (A) and the styrene-based thermoplastic elastomer (B).

[0050] This film preferably has a wetting tension of 43 mN / m or more. When the wetting tension is equal to or higher than the above lower limit value, the wettability and impregnation property of the liquid can be improved. Since polyolefin resins have a low wetting tension, when using a polyolefin-based porous film for applications where liquids are impregnated and permeated, the porous film may repel the liquid, which may have an adverse effect on practical properties such as the impregnation property of the liquid. As a result of intensive studies in view of the above problems, the inventors of the present invention have found that, in adjusting the combination of polyolefin-based resin and styrene-based thermoplastic elastomer and film-forming conditions, etc., in a formulation in which the melt flow rate (MFR) of the polyolefin-based resin and the styrene-based thermoplastic elastomer is greatly different, in particular, the connectivity of pores in the thickness direction is improved, and as a result, liquid efficiently penetrates into the pores of the porous film, so that the wetting tension can be increased, and the wettability and impregnation properties of the liquid are also improved. From the viewpoint of improving the wettability and impregnation properties of the liquid, the wetting tension is more preferably 44 mN / m or more, and even more preferably 46 mN / m or more. The upper limit is not particularly limited, but is usually 70 mN / m or less. The wetting tension can be determined by the method described in the examples.

[0051] <Method for producing porous film> The method for producing a porous film of the present invention (hereinafter, also referred to as "the present production method") preferably includes a step (I) of melt-extruding a resin composition containing a polyolefin-based resin (A) and a styrene-based thermoplastic elastomer (B) to obtain a pre-stretched sheet, and a step (II) of stretching the pre-stretched sheet to obtain a porous film.

[0052] <Step (I)> First, in step (I), the polyolefin-based resin (A), the styrene-based thermoplastic elastomer (B), and the crystal nucleating agent (C) are melt-kneaded using an extruder or the like under temperature conditions equal to or higher than the melting point and lower than the decomposition temperature of the polyolefin-based resin (A), and then formed to obtain a non-porous sheet before stretching. Examples of the forming method of the non-porous sheet include T-die forming.

[0053] Also, when forming the kneaded mixture into a sheet while cooling it, the temperature of the casting roll is preferably 60°C or higher and 150°C or lower, more preferably 70°C or higher and 140°C or lower, still more preferably 80°C or higher and 130°C or lower, and even more preferably 90°C or higher and 120°C or lower. When the temperature of the casting roll is at or above the above lower limit value, the crystallization of the polyolefin resin (A) proceeds sufficiently, so that a porous structure is sufficiently formed. On the other hand, when the temperature of the casting roll is at or below the above upper limit value, problems such as the pre-stretched sheet fusing to the roll and breaking the film are less likely to occur.

[0054] The speed of the casting roll is preferably 1.0 m / min or more and 5.0 m / min or less, more preferably 1.2 m / min or more and 4.0 m / min or less, and still more preferably 1.5 m / min or more and 3.0 m / min or less. By setting the speed of the casting roll at or above the above lower limit value, the productivity is improved. On the other hand, by setting the speed of the casting roll at or below the above upper limit value, it becomes easier to keep the domains in the pre-stretched sheet spherical, and a porous structure is more likely to be sufficiently formed after stretching.

[0055] <Process (I-a)> Further, in this production method, in the step (I), when the resin composition is melt-extruded into a sheet and adhered to the casting roll, a step (I-a) of adhering the sheet to the casting roll may be included. Specifically, a touch roll, pinning, touch rollers at both ends in the sheet width direction, etc. may be mentioned.

[0056] By adhering the sheet to the casting roll, uneven adhesion is less likely to occur, so unevenness in pore formation of the stretched film can be suppressed, and a porous film with uniform properties can be obtained.

[0057] <Process (II)> Next, the obtained pre-stretched sheet is uniaxially stretched or biaxially stretched. The uniaxial stretching may be longitudinal uniaxial stretching or transverse uniaxial stretching. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching.

[0058] To produce the present film having air permeability, the stretching conditions may be selected in each stretching step, and it is more preferable to adopt sequential biaxial stretching which is easy to control the porous structure. Note that the stretching in the machine direction (MD) of the sheet is referred to as "longitudinal stretching", and the stretching in the direction perpendicular to the machine direction (TD) is referred to as "transverse stretching".

[0059] When sequential biaxial stretching is used, it is relatively easy to control the porous structure, and it is easy to balance with other physical properties such as mechanical strength and shrinkage rate. Also, the stretching temperature may be appropriately selected according to the composition of the resin composition used, the crystal melting peak temperature, the crystallinity, etc.

[0060] It is desirable to perform the longitudinal stretching at a low temperature. The specific stretching temperature is preferably 0 to 50°C, more preferably 5 to 40°C. If the longitudinal stretching temperature is below the above upper limit value, stress is likely to concentrate inside the domain during stretching, and pores are likely to be formed. On the other hand, if the longitudinal stretching temperature is above the above lower limit value, breakage during stretching can be suppressed, which is preferable.

[0061] The longitudinal stretching ratio at a low temperature is preferably 1.1 to 5.0 times, more preferably 1.2 to 4.0 times, and still more preferably 1.3 to 3.0 times. By setting the stretching ratio at a low temperature to be above the above lower limit value, it is suggested that pore formation progresses and sufficient pore formation by stretching occurs. Also, by setting the stretching ratio at a low temperature to be below the above upper limit value, breakage during stretching can be suppressed.

[0062] Also, the longitudinal stretching may be a two-step stretching process in which stretching is performed at a high temperature following the stretching at the above low temperature. The specific stretching temperature at a high temperature is preferably 60 to 155°C, more preferably 70 to 140°C, and still more preferably 80 to 130°C. By setting the longitudinal stretching temperature at a high temperature to be above the above lower limit value, film breakage during stretching can be suppressed. On the other hand, by setting the longitudinal stretching temperature at a high temperature to be below the above upper limit value, it is possible to suppress the closing of the pores formed by the stretching at a low temperature.

[0063] The longitudinal stretching ratio at high temperature is preferably 1.1 to 5.0 times, more preferably 1.2 to 4.5 times, still more preferably 1.3 to 4.0 times, and even more preferably 1.3 to 3.0 times. By setting the stretching ratio at high temperature to be not less than the above lower limit value, the pores formed by longitudinal stretching at low temperature can be enlarged. Also, by setting the stretching ratio at high temperature to be not more than the above upper limit value, the properties of the film (thickness, air permeability and mechanical properties) can be adjusted to a suitable range, and film breakage during stretching can also be suppressed.

[0064] Next, the temperature for transverse stretching is preferably 100 to 155 °C, more preferably 110 to 150 °C. When the transverse stretching temperature is within the above range, the pores generated during longitudinal stretching can be enlarged, increasing the porosity of the porous layer, and sufficient air permeability and mechanical properties can be obtained.

[0065] The transverse stretching ratio can be arbitrarily selected, but is preferably 1.1 to 10 times, more preferably 1.5 to 8.0 times, and still more preferably 1.5 to 5.0 times. By stretching at the above transverse stretching ratio, sufficient porosity can be obtained without deforming the pores generated during longitudinal stretching.

[0066] Also, when producing this film by biaxial stretching, it is preferable that the stretching ratio of longitudinal stretching to transverse stretching is 0.5 to 1.5:1, and more preferably 0.7 to 1.2:1. When the stretching ratio is within the above range, the properties of the film (thickness, air permeability and mechanical properties) can be adjusted to a suitable range. In addition, when longitudinal stretching is performed in two stages of low temperature and high temperature, it is sufficient that (longitudinal stretching ratio at low temperature × longitudinal stretching ratio at high temperature):transverse stretching ratio is within the above range.

[0067] <Ion exchange membrane support> The porous film of the present invention is useful as an ion exchange membrane support. That is, the ion exchange membrane support of the present invention is composed of the porous film of the present invention. The preferred embodiments and preferred properties of the ion exchange membrane support of the present invention are the same as those described in the above porous film.

[0068] <Power storage device> The power storage device of the present invention includes the ion exchange membrane support of the present invention. Examples of the power storage device include redox flow batteries, nickel-hydrogen batteries, lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, and lithium ion polymer secondary batteries, such as lithium secondary batteries, aluminum electrolytic capacitors, electric double layer capacitors, and capacitor-based devices such as lithium ion capacitors. Among these, redox flow batteries and lithium secondary batteries are preferred.

Examples

[0069] Examples and comparative examples are shown below to explain the porous film of the present invention in more detail, but the present invention is not limited in any way.

[0070] <Measurement method> (1) Melt flow rate (MFR) For the polyolefin resin (A), in accordance with JIS K7210-1 (2014), MFR(A) was measured under the conditions of a temperature of 230°C and a load of 2.16 kg. Also, for the styrene-based thermoplastic elastomer (B), in accordance with JIS K7210-1 (2014), MFR(B) was measured under the conditions of a temperature of 200°C and a load of 10 kg. From the obtained MFR(A) value and MFR(B) value, the difference (MFR(A) - MFR(B)) was determined. For those that did not flow during the above MFR measurement, the MFR value was calculated as 0.

[0071] (2) Thickness (film thickness) (T) This film was cut into a 10 cm square, and measured at 9 points using a dial gauge with a scale of 1 / 1000 mm, and the average value was taken as the thickness.

[0072] (3) Air permeability resistance (air permeability (S)) at 25°C Under an air atmosphere of 25°C, the air permeability resistance was measured in accordance with JIS P8117:2009. As the measuring instrument, a digital type Ono Sokki air permeability dedicated machine (manufactured by Asahi Seiko Co., Ltd.) was used.

[0073] (4) Porosity This film was cut into a 10 cm square, the density ρ1 (apparent density) was measured, the density ρ0 (true density) in the case of 0% porosity was calculated, and the porosity was calculated from these values based on the following formula. Porosity (%) = (1 - ρ1 / ρ0) × 100

[0074] (5) Tensile strength, elongation at break A tensile testing machine (AG-1kNXplus tensile testing machine manufactured by Shimadzu Corporation) was used as the measuring device. As the test piece, a rectangle cut from this film with a length of 60 mm and a width of 10 mm in the measuring direction was used. Both ends of the test piece in the length direction were chucked with a chuck distance of 20 mm, pulled at a crosshead speed of 200 mm / min, the strength at the maximum point from the start of the test to breakage was defined as the tensile strength, and the elongation at breakage was defined as the elongation at break. Measurements were taken 3 times, and the average value was obtained. The above tensile test was carried out for both the MD tensile test and the TD tensile test of the film. Also, the average tensile strength and average elongation at break were obtained by averaging the MD and TD values of the tensile strength and elongation at break, respectively. The measurement was carried out at room temperature (25°C).

[0075] (6) Wetting tension A tension checker (film wetting tension check pen) manufactured by Pacific Chemical Co., Ltd. was used as the measuring instrument. Measurement dyn levels (wetting tensions) of 36, 38, 40, 42, 44, 46, 50, and 54 (mN / m) were used. The pen tip was applied horizontally to the surface of the object and moved in one direction for uniform application. After application, if the ink was retained after 2 seconds, it was determined that the object was above the dyn level of the pen. If the ink of the dyn pen shrank or disappeared after 2 seconds, it was determined that the object was below the dyn level of the pen. By testing pens with multiple dyn levels, the maximum dyn level at which the ink was retained on the film, that is, the wetting tension (mN / m), was specified. The measurement was carried out at room temperature (25°C).

[0076] <Material> (Polyolefin resin (A)) ·(A-1) Homopolypropylene (weight-average molecular weight (Mw): 365,000, molecular weight distribution (Mw / Mn): 3.46, MFR (230 °C, 2.16 kg): 11 g / 10 min) ·(A-2) Homopolypropylene (weight-average molecular weight (Mw): 254,300, molecular weight distribution (Mw / Mn): 5.03, MFR (230 °C, 2.16 kg): 10 g / 10 min) ·(a-1) Homopolypropylene (weight-average molecular weight (Mw): 538,000, molecular weight distribution (Mw / Mn): 3.22, MFR (230 °C, 2.16 kg): 1.9 g / 10 min) ·(a-2) Homopolypropylene (weight-average molecular weight (Mw): 403,000, molecular weight distribution (Mw / Mn): 3.96, MFR (230 °C, 2.16 kg): 5.0 g / 10 min) Note that (a-1) and (a-2) are polyolefin resins with a melt flow rate (MFR(A)) of less than 8 g / 10 min at a temperature of 230 °C and a load of 2.16 kg.

[0077] (Styrenic thermoplastic elastomer (B)) ·(B-1) Styrene-ethylene-propylene-styrene block copolymer (SEPS) (weight-average molecular weight (Mw): 271,000, molecular weight distribution (Mw / Mn): 1.09, MFR (230 °C, 2.16 kg): does not flow, MFR (200 °C, 10 kg): does not flow, styrene content: 20 mass%) ·(B-2) Styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) (weight-average molecular weight (Mw): 196,000, molecular weight distribution (Mw / Mn): 1.07, MFR (230 °C, 2.16 kg): does not flow, MFR (200 °C, 10 kg): does not flow, styrene content: 32 mass%) ·(B-3) Styrene-ethylene-propylene block copolymer (SEP) (weight-average molecular weight (Mw): 148,000, molecular weight distribution (Mw / Mn): 1.04, MFR (230 °C, 2.16 kg): does not flow, MFR (200 °C, 10 kg): 1.8 g / 10 min, styrene content: 36 mass%)

[0078] (Nucleating agent (C)) ·(C-1) α-Nucleating agent (1,3:2,4-bis-O-(4-methylbenzylidene)-D-sorbitol) ·(C-2) β-Nucleating agent (3,6-bis[4-(N-cyclohexylcarbamoyl)phenyl]-2,4,8,10-tetraoxaspiro[5.5]undecane)

[0079] <Preparation of porous film> Example 1 A material in which 60% by mass of polyolefin resin (A-1), 20% by mass of styrene-based thermoplastic elastomer (B-1), and 20% by mass of styrene-based thermoplastic elastomer (B-3) are blended, and a nucleating agent (C-1) is blended at a ratio of 0.1 part by mass per 100 parts by mass of the resin component is charged into a φ40 mm twin-screw extruder, melt-kneaded at a set temperature of 205 °C, formed into a sheet shape with a T-die, and then the sheet is landed on a casting roll set at 95 °C for cooling and solidification to obtain a pre-stretched sheet with a thickness of 100 μm. Thereafter, the obtained pre-stretched sheet was subjected to low-temperature stretching at the magnification shown in the table between a roll (X) set at 20 °C and a roll (Y) set at 20 °C. Next, high-temperature stretching was performed at the magnification shown in the table between a roll (P) set at 120 °C and a roll (Q) set at 120 °C to obtain an MD-stretched porous film. Next, the obtained MD-stretched porous film was preheated at a preheating temperature of 145 °C for 12 seconds using a film tenter facility manufactured by Kyoto Machinery Co., Ltd., then stretched in the transverse direction at a magnification shown in the table at a stretching temperature of 145 °C, and then heat-treated at 155 °C to obtain a biaxially stretched porous film. The evaluation results of the obtained film are summarized in Table 1.

[0080] Example 2 The contents of the polyolefin resin (A-1), styrene-based thermoplastic elastomers (B-1), (B-3), and crystal nucleating agent (C-1) were as described in Table 1, and a pre-stretching sheet with a thickness of 90 μm was obtained in the same manner as in Example 1. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretching sheet was stretched at the stretching ratio described in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0081] Example 3 The contents of the polyolefin resin (A-1), styrene-based thermoplastic elastomers (B-1), (B-3), and crystal nucleating agent (C-2) were as described in Table 1, and a pre-stretching sheet with a thickness of 101 μm was obtained in the same manner as in Example 1. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretching sheet was stretched at the stretching ratio described in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0082] Example 4 The contents of the polyolefin resin (A-1), styrene-based thermoplastic elastomers (B-1), (B-3), and crystal nucleating agent (C-2) were as described in Table 1, and a pre-stretching sheet with a thickness of 89 μm was obtained in the same manner as in Example 1. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretching sheet was stretched at the stretching ratio described in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0083] Example 5 The contents of the polyolefin resin (A-1), styrene-based thermoplastic elastomers (B-1), (B-3), and crystal nucleating agent (C-2) were as described in Table 1, and a pre-stretching sheet with a thickness of 88 μm was obtained in the same manner as in Example 1. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretching sheet was stretched at the stretching ratio described in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0084] Example 6 The contents of the polyolefin resin (A-1), styrene-based thermoplastic elastomers (B-1), (B-3), and crystal nucleating agent (C-2) were made as shown in Table 1, and a pre-stretching sheet with a thickness of 89 μm was obtained in the same manner as in Example 1. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretching sheet was stretched at the stretching ratio shown in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0085] Example 7 The contents of the polyolefin resin (A-2), styrene-based thermoplastic elastomers (B-1), (B-3), and crystal nucleating agent (C-2) were made as shown in Table 1, and a pre-stretching sheet with a thickness of 109 μm was obtained in the same manner as in Example 1. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretching sheet was stretched at the stretching ratio shown in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0086] Example 8 The contents of the polyolefin resin (A-2), styrene-based thermoplastic elastomer (B-2), and crystal nucleating agent (C-2) were made as shown in Table 1, and a pre-stretching sheet with a thickness of 109 μm was obtained in the same manner as in Example 1. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretching sheet was stretched at the stretching ratio shown in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0087] Comparative Example 1 The contents of the polyolefin resin (a-1), styrene-based thermoplastic elastomer (B-1), and crystal nucleating agent (C-1) were made as shown in Table 1. After melt-kneading at a set temperature of 200°C and forming into a sheet shape using a T-die, the sheet was landed on a casting roll set at 105°C for cooling and solidification to obtain a pre-stretching sheet with a thickness of 100 μm. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretching sheet was stretched at the stretching ratio shown in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0088] Comparative Example 2 The contents of the polyolefin resin (a-1), styrenic thermoplastic elastomer (B-1), and crystal nucleating agent (C-1) were as described in Table 1. The sheet was landed on a cast roll set at 127°C for cooling and solidification to obtain a pre-stretched sheet with a thickness of 420 μm. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretched sheet was stretched at the stretching ratio described in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0089] Comparative Example 3 The contents of the polyolefin resin (a-1), styrenic thermoplastic elastomers (B-1) and (B-3), and crystal nucleating agent (C-1) were as described in Table 1. The sheet was landed on a cast roll set at 97°C for cooling and solidification to obtain a pre-stretched sheet with a thickness of 100 μm. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretched sheet was stretched at the stretching ratio described in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0090] Comparative Example 4 The contents of the polyolefin resin (a-1), styrenic thermoplastic elastomers (B-1) and (B-3), and crystal nucleating agent (C-1) were as described in Table 1. A pre-stretched sheet with a thickness of 90 μm was obtained in the same manner as in Example 1. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretched sheet was stretched at the stretching ratio described in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0091] Comparative Example 5 The contents of the polyolefin resin (a-1), styrenic thermoplastic elastomers (B-1) and (B-3), and crystal nucleating agent (C-1) were as described in Table 1. The sheet was landed on a cast roll set at 105°C for cooling and solidification to obtain a pre-stretched sheet with a thickness of 100 μm. Thereafter, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretched sheet was stretched at the stretching ratio described in Table 1. The evaluation results of the obtained film were summarized in Table 1.

[0092] Comparative Example 6 The contents of the polyolefin resin (a-2), styrene-based thermoplastic elastomer (B-1), (B-3) and crystal nucleating agent (C-1) were as described in Table 1, and a pre-stretched sheet with a thickness of 82 μm was obtained in the same manner as in Example 1. Then, a biaxially stretched porous film was obtained in the same manner as in Example 1, except that the obtained pre-stretched sheet was stretched at the stretching ratio as described in Table 1. The evaluation results of the obtained film are summarized in Table 1.

[0093]

Table 1

[0094]

Table 2

[0095] As described in Table 1, in Examples 1 to 8, a porous film that achieved both a thin film and air permeability could be obtained. No uneven adhesion or film breakage occurred during film formation for these films. On the other hand, a porous film of a comparative example that did not contain a polyolefin resin (A) with an MFR (A) value of 8 g / 10 min or more and whose difference between MFR (A) and MFR (B) did not satisfy the present application could not achieve both thinning and air permeability.

Claims

1. A porous film containing a polyolefin resin (A) and a styrene-based thermoplastic elastomer (B), wherein the melt flow rate (MFR(A)) of the polyolefin resin (A) at a temperature of 230°C and a load of 2.16 kg is 8 g / 10 min or more, and the difference (MFR(A) - MFR(B)) between the melt flow rate (MFR(A)) of the polyolefin resin (A) and the melt flow rate (MFR(B)) of the styrene-based thermoplastic elastomer (B) at a temperature of 200°C and a load of 10 kg is 6 g / 10 min or more. A porous film.

2. The porous film according to Claim 1, wherein the melt flow rate (MFR(B)) of the styrene-based thermoplastic elastomer (B) at a temperature of 200°C and a load of 10 kg is 2.0 g / 10 min or less.

3. The porous film according to Claim 1, wherein the air permeability (S) is 10 seconds / 100 cc or less, and the ratio (S / T) of the air permeability (S) (seconds / 100 cc) to the thickness (T) (μm) of the porous film is 0.5 or less.

4. The porous film according to Claim 1, wherein the wetting tension is 43 mN / m or more.

5. The porous film according to Claim 1, wherein the thickness (T) is 50 μm or less.

6. The porous film according to Claim 1, wherein the styrene content of the styrene-based thermoplastic elastomer (B) is 10% by mass or more and 50% by mass or less.

7. The porous film according to Claim 1, further containing a nucleating agent (C).

8. An ion exchange membrane support comprising the porous film according to any one of Claims 1 to 7.

9. A power storage device comprising the ion exchange membrane support according to Claim 8.

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