JP6922161B2 - Method for manufacturing stretched porous film - Google Patents

Description

The present invention relates to a method for producing a stretched porous film obtained from a specific resin, and the stretched porous film is used for packaging products, sanitary products, livestock products, agricultural products, building products, medical products, light diffusers, reflective sheets, and batteries. It can be used as a separator or a separation film, and is particularly preferably used as a filter film used in the food-related field, the pharmaceutical / cosmetics field, the chemical industry product field, and the electronic industry field.

Conventionally, filtration operations using microfiltration membranes such as microfiltration membranes and ultrafiltration membranes have been used in the automobile industry (electrodeposition paint recovery and reuse system), semiconductor industry (ultrapure water production), and pharmaceutical food industry (sterilization, enzyme purification). It has been put to practical use in many fields such as. In particular, in recent years, it has been widely used as a method for producing drinking water and industrial water by deturbing river water and the like. As the material of the membrane, a wide variety of materials such as cellulosic, polyacrylonitrile, and polyolefin are used.
Among them, polyolefin-based materials (polyethylene, polypropylene, polyvinylidene fluoride, etc.) are suitable as materials for water-based filtration membranes because of their high water resistance due to their hydrophobicity, and are widely used.

It is known that when the size of the object to be filtered varies, the filtration filter can efficiently filter by using a filter having a change in pore diameter in the thickness direction. The following examples can be given as examples of improving the efficiency of the filter by changing the pore diameter in the thickness direction.

For example, in Patent Document 1, a plasticizer is added to a polyvinylidene fluoride resin, melt-kneaded, extruded into a hollow thread, cooled and solidified in a water bath, the plasticizer is extracted and removed with a solvent, and then dried to form a hollow thread. It is described that microporous films having different porosity in the thickness direction of the above can be obtained.

In Patent Document 2, by changing the addition ratio of the polyethylene resin, the plasticizer, and the filler (silica particles), two kinds of mixed raw materials adjusted to have different pore opening ratios are formed into a laminated structure of an outer layer and an inner layer. A laminated porous body having a pore diameter gradient in the thickness direction is described by extracting a plasticizer and a filler from the obtained sheet-like material by co-extruding each mixed raw material. There is.

JP-A-2014-101445 JP 2013-108045

In order to improve the efficiency of filtration, it is necessary to form a porous membrane having a change in aperture ratio and pore size in the thickness direction. However, the methods described in Patent Documents 1 and 2 have a problem that the cost required for the extraction treatment of the used plasticizer is high. Since the extraction and removal of the plasticizer is performed using an organic solvent, a large amount of the organic solvent is required, which may cause a concern about residual solvent and an impact on the environment.

Therefore, the present invention proposes a method for producing a stretched porous film which is inexpensive, has good productivity, has excellent filtration speed, filtration accuracy, and filtration life, and has good filtration efficiency without using a large amount of organic solvent. be.

As a result of diligent studies in view of the above circumstances, the present inventors have found that the above problems can be solved, and have completed the present invention.

That is, according to the first invention, the olefin polymer (A) is 55 to 85% by weight, the styrene-olefin block copolymer (B) is 1 to 44% by weight, and the styrene-olefin-styrene block copolymer (Styrene-olefin-styrene block copolymer). Provided is a method for producing a stretched porous film, which comprises producing an unstretched sheet obtained by mixing C) at a ratio of 1 to 44% by weight and stretching the unstretched sheet.

Further, according to the second invention, in the first invention, the melt flow rate of the styrene-olefin block copolymer (B) at 230 ° C. and a load of 2.16 kg is 1.0 g / 10 minutes or less. A method for producing a stretched porous film characterized by the above is provided.

Further, according to the third invention, in the first or second invention, the melt flow rate of the styrene-olefin-styrene block copolymer (C) at 230 ° C. and a load of 2.16 kg is 1.0 g / 10. Provided is a method for producing a stretched porous film, which is characterized by a minute or less.

Further, according to the fourth invention, in any one of the first to third inventions, there is provided a method for producing a stretched porous film, which comprises further mixing the crystal nucleating agent (D) in the mixing. ..

Further, according to the fifth invention, in any one of the first to fourth inventions, the thickness of the obtained stretched porous film is 25 μm or more and 500 μm or less, the air permeability is 1 second / 100 cc or more and 1000 seconds / 100 cc or less, and the air is empty. A method for producing a stretched porous film having a porosity of 50% or more and 98% or less is provided.

Further, according to the sixth invention, in any one of the first to fifth inventions, the unstretched sheet is stretched at a temperature of 0 ° C. to 60 ° C. in the longitudinal direction by 1.1 times or more and less than 3.0 times. Then, at a temperature of 60 ° C. to 160 ° C., it is stretched 1.5 times or more and less than 6.0 times in the vertical direction, and at a temperature of 70 to 150 ° C., it is stretched 1.1 times or more and less than 10 times in the horizontal direction. Provided is a method for producing a stretched porous film, which is characterized in that.

According to the present invention, since a large amount of organic solvent is not used, it is possible to provide a stretched porous film that is inexpensive and has good productivity. In addition, this stretched porous film has excellent air permeability and filtration performance, and is a filtration film for the automobile industry (electrodeposition paint recovery and reuse system), semiconductor industry (ultrapure water production), pharmaceutical food industry (sterilization, enzyme purification), etc. It is useful as.

Hereinafter, embodiments of the present invention will be described in detail. However, the content of the present invention is not limited to the embodiments described below.

<Manufacturing method of stretched porous film>
The method for producing a stretched porous film according to an example of the embodiment of the present invention (hereinafter, may be referred to as "the present film production method") contains 55 to 85% by weight of the olefin polymer (A) and a styrene-olefin block. An unstretched sheet prepared by mixing the polymer (B) at a ratio of 1 to 44% by weight and the styrene-olefin-styrene block copolymer (C) at a ratio of 1 to 44% by weight was prepared (film forming step). It is a method for producing a stretched porous film, which is characterized by stretching (stretching step).

Since the present film manufacturing method may include the above steps, it may further include other steps and treatments.

Hereinafter, the olefin polymer (A), the styrene-olefin block copolymer (B), and the styrene-olefin-styrene block copolymer (C) will be described, and then the film forming step and the stretching step will be described in order.

<Olefin polymer (A)>
Examples of the components of this film that are stretched to impart porosity include one or more polymers selected from the group of olefin polymers from the viewpoints of cost, solvent resistance, and heat resistance.

Examples of the olefin polymer (A) include ethylene homopolymers (homopolyethylene), ethylene and 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonen or 1-decene. Ethylene polymers such as polymers; propylene homopolymers, propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonen or 1-decene, etc. Examples thereof include propylene polymers such as propylene copolymers obtained by copolymerization. Among these, a propylene polymer is preferably used from the viewpoint of heat resistance.

As the propylene polymer, an isotactic pentad fraction exhibiting stereoregularity is preferably 80 to 99%, more preferably 83 to 98%, still more preferably 85 to 97%. .. If the isotactic pentad fraction is too low, the mechanical strength may decrease. On the other hand, the upper limit of the isotactic pentad fraction is specified by the upper limit value that can be obtained industrially at present, but this is limited to the case where a resin with higher regularity at the industrial level is developed in the future. is not it. The isotactic pentad fraction is a three-dimensional structure in which all five methyl groups, which are side chains, are located in the same direction as the main chain formed by a carbon-carbon bond composed of five consecutive propylene units. Or it means the ratio.
The attribution of the signal in the methyl group region is described in A.I. Zambelliet at al. (Macromol. 8, 687 (1975).

Further, the propylene polymer preferably has Mw / Mn, which is a parameter indicating the molecular weight distribution, of 1.5 or more, and more preferably 2.0 or more. On the other hand, the upper limit is preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 6.0 or less. The smaller the Mw / Mn, the narrower the molecular weight distribution. However, when the Mw / Mn is 1.5 or more, sufficient extrusion moldability can be obtained, and mass production is possible industrially. On the other hand, by setting Mw / Mn to 10.0 or less, sufficient mechanical strength can be secured.
Mw / Mn is obtained by the GPC (Gel Permeation Chromatography) method.

The melt flow rate (MFR) of the propylene polymer is not particularly limited, but usually, the MFR is preferably 0.5 or more, and more preferably 1.0 or more. On the other hand, the upper limit is preferably 15 g / 10 minutes or less, and more preferably 10 g / 10 minutes or less. When the MFR is 0.5 g / 10 minutes or more, it has a sufficient melt viscosity at the time of molding and can secure high productivity. On the other hand, when the MFR is 15 g / 10 minutes or less, sufficient strength can be obtained.
The MFR is measured in accordance with JIS K7210 under the conditions of a temperature of 230 ° C. and a load of 2.16 kg.

Examples of propylene polymers include trade names "Novatec PP" and "WINTEC" (manufactured by Japan Polypropylene Corporation), "Notio" and "Toughmer XR" (manufactured by Mitsui Chemicals), "Zeras" and "Thermoran" (manufactured by Mitsubishi Chemicals). , "Sumitomo Noblen" "Tough Serene" (manufactured by Sumitomo Chemicals), "Prime PP" "Prime TPO" (manufactured by Prime Polymer), "Adflex" "Adsil" "HMS-PP (PF814)" (manufactured by Sun Aromar), Commercially available products such as "Versify" and "Inspire" (Dow Chemicals) can be used.

On the other hand, in the case of an ethylene polymer, Mw / Mn, which is a parameter indicating the molecular weight distribution, is preferably 1.5 or more, and more preferably 2.0 or more. On the other hand, the upper limit is preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 6.0 or less. The smaller the Mw / Mn, the narrower the molecular weight distribution. However, when the Mw / Mn is 1.5 or more, sufficient extrusion moldability can be obtained, and mass production is possible industrially. On the other hand, by setting Mw / Mn to 10.0 or less, sufficient mechanical strength can be secured.
Mw / Mn is obtained by the GPC (Gel Permeation Chromatography) method.

The melt flow rate (MFR) of the ethylene polymer is not particularly limited, but usually, the MFR is preferably 0.5 or more, and more preferably 1.0 or more. On the other hand, the upper limit is preferably 15 g / 10 minutes or less, and more preferably 10 g / 10 minutes or less. When the MFR is 0.5 g / 10 minutes or more, it has a sufficient melt viscosity at the time of molding and can secure high productivity. On the other hand, when the MFR is 15 g / 10 minutes or less, sufficient strength can be obtained.
The MFR was measured in accordance with JIS K7210 under the conditions of a temperature of 190 ° C. and a load of 2.16 kg.
The density of the ethylene polymer is not particularly limited, but usually, the density is preferably 0.955 or more, and more preferably 0.957 or more. On the other hand, the upper limit is preferably 0.965 or less, and more preferably 0.970 or less. When the density is 0.955 or more, the crystallinity of the porous film becomes high and the formation of the desired porous structure can be satisfied. On the other hand, when the density exceeds 0.970, the crystallinity is too high and uneven stretching is likely to occur.
The density is measured according to JIS K7112.

Examples of ethylene polymers include the trade names "Novatec LD", "Novatec LL", "Novatec HDPE" (manufactured by Japan Polyethylene Corporation), "Hi-Zex", "Evolu H" (manufactured by Prime Polymer Co., Ltd.), "Nipolon-L" and "Petrosen". "Commercially available products such as Nipolon Hard (manufactured by Tosoh) can be used.

<Styrene-olefin block copolymer (B)>
In the present invention, it is important to add the styrene-olefin block copolymer (B) to the olefin polymer (A). By adding the styrene-olefin block copolymer (B), a fine porous structure can be efficiently obtained, and the shape and diameter of the pores can be easily controlled.

The styrene-olefin block copolymer (B) in the present invention is a kind of thermoplastic elastomer based on a styrene component, and is an elastomer having a polystyrene block (hard segment) as a hard component and a polyolefin structure as a soft component. It is a copolymer having a block (soft segment), and is a block copolymer having a hard segment at one end of a polymer chain and a soft segment at the other end.

The styrene-olefin block copolymer (B) used in the present invention has a melt flow rate (MFR) of preferably 1.0 g / 10 minutes or less, more preferably 0.5 g, at a temperature of 230 ° C. and a load of 2.16 kg. It is preferably less than / 10 minutes, more preferably 0.1 g / 10 minutes or less. When molded into a sheet, the dispersed styrene-olefin block copolymer (B) changes its shape due to the difference in viscosity with the resin, but if it is of MFR within the above range, the shape is This is because it tends to be spherical. Unlike a domain having a large aspect ratio, a spherically dispersed domain is preferable because the uniformity of the porous structure obtained by the subsequent stretching step tends to be high and the physical property stability is excellent. Further, when the MFR is within the above range, stress is likely to be concentrated on the domain interface portion between the matrix having a high elastic modulus and the domain having a low elastic modulus during the stretching step, so that an opening starting point is likely to occur and the porosity is likely to occur. It has the feature.
The MFR is measured in accordance with JIS K7210 under the conditions of a temperature of 230 ° C. and a load of 2.16 kg.

Further, the styrene-olefin block copolymer (B) in the present invention preferably has a styrene structural unit content of 1 to 40% by weight, more preferably 10% by weight to 35% by weight. When the styrene content in the styrene-olefin block copolymer (B) is 1% by weight or more, the domain can be effectively formed when molded into a sheet, and the styrene content is 40% by weight or less. Therefore, excessively large domain formation can be suppressed.

The specific type of the styrene-olefin block copolymer (B) is not particularly limited, but is limited to styrene-butadiene block copolymer (SBR); hydrogenated styrene-butadiene block copolymer (SEB); styrene-isoprene. Block copolymer (SIR); styrene- (ethylene / propylene) block copolymer (SEP) and the like can be mentioned.

In order to efficiently disperse the styrene-olefin block copolymer (B) when molded into a sheet, the compatibility of the styrene-olefin block copolymer (B) with the olefin polymer (A) is high. Those containing a high ethylene component and butylene component are preferable, and among them, styrene- (ethylene / propylene) block copolymer (SEP) is preferable.

The film according to the present invention may contain one or more copolymers selected from the group of styrene-olefin block copolymers (B).

<Styrene-olefin-styrene block copolymer (C)>
In the present invention, it is important to add not only the styrene-olefin block copolymer (B) but also the styrene-olefin-styrene block copolymer (C) to the olefin polymer (A). By adding the styrene-olefin block copolymer (B) and the styrene-olefin-styrene block copolymer (C), the distribution of the dispersion diameter is large due to the difference in compatibility with each olefin polymer (A). An unstretched sheet is obtained. As a result, by stretching the unstretched sheet, a porous membrane having a large aperture ratio and pore diameter distribution in the thickness direction can be obtained, and the filtration efficiency can be improved.

The styrene-olefin-styrene block copolymer (C) in the present invention is a kind of thermoplastic elastomer based on a styrene component, and has a polystyrene block (hard segment) which is a hard component and a polyolefin structure which is a soft component. It is a block polymer having an elastomer block (soft segment) of the above, and is a block polymer having hard segments at both ends of a polymer chain.

The styrene-olefin-styrene block copolymer (C) used in the present invention is preferably 1.0 g / 10 minutes or less, more preferably 0.5 g / 10 minutes or less, still more preferably 0.1 g / 10 minutes or less. Is preferable. The shape of the styrene-olefin-styrene block copolymer (C) changes depending on the difference in viscosity with the resin, but if it is MFR within the above range, the shape tends to be spherical. Unlike a domain having a large aspect ratio, a spherically dispersed domain is preferable because the uniformity of the porous structure obtained by the subsequent stretching step tends to be high and the physical property stability is excellent. Further, when the MFR is within the above range, stress is likely to be concentrated on the domain interface portion between the matrix having a high elastic modulus and the domain having a low elastic modulus during the stretching step, so that an opening starting point is likely to occur and the porosity is likely to occur. It has the feature.
The MFR is measured in accordance with JIS K7210 under the conditions of a temperature of 230 ° C. and a load of 2.16 kg.

The styrene-olefin-styrene block copolymer (C) in the present invention preferably has a styrene content of 1 to 40% by weight, more preferably 10% by weight to 35% by weight. When the styrene content of the styrene-olefin-styrene block copolymer (C) is 1% by weight or more, the domain can be effectively formed when molded into a sheet, and the styrene content is 40% by weight. The following is preferable in that excessively large domain formation can be suppressed.

The specific type of the styrene-olefin-styrene block copolymer (C) is not particularly limited, but is styrene-butadiene-styrene block copolymer (SBS); styrene- (butadiene / butylene) -styrene block common weight. Combined (SBBS); Styrene- (ethylene / butadiene) -Styrene block copolymer (SEBS); Styrene-Isoprene-Styrene block copolymer (SIS); Styrene- (ethylene / propylene) -Styrene block copolymer (SEPS) ); Styrene-ethylene- (ethylene / propylene) -styrene block copolymer (SEEPS) and the like.

Among the styrene-olefin-styrene block copolymers (C), styrene- (ethylene / propylene) is used to efficiently disperse the styrene-olefin-styrene block copolymer (C) when molded into a sheet. -Styrene block copolymer (SEPS) and styrene- (ethylene / butadiene) -styrene block copolymer (SEBS) are preferable because they have high compatibility with the olefin copolymer (A).

The film according to the present invention may contain one or more copolymers selected from the group of styrene-olefin-styrene block copolymers (C).

<Film formation process>
Hereinafter, an example of a method of mixing an olefin polymer (A), a styrene-olefin block copolymer (B), and a styrene-olefin-styrene block copolymer (C) and heating and melting them to produce an unstretched sheet. Will be described.

55-85% by weight of the above olefin polymer (A), 1-44% by weight of the styrene-olefin block copolymer (B), and 1-44% by weight of the styrene-olefin-styrene block copolymer (C). Mix at the ratio of. Preferably, it is 55 to 85% by weight, the styrene-olefin block copolymer (B) is 1 to 40% by weight, and the styrene-olefin-styrene block copolymer (C) is 1 to 40% by weight. More preferably, the olefin polymer (A) is 60 to 80% by weight, the styrene-olefin block copolymer (B) is 20 to 40% by weight, and the styrene-olefin-styrene block copolymer (C) is 20 to 40% by weight. By weight%.
When the olefin polymer (A) is 85% by weight or less, porosity is likely to occur due to stretching, and by securing a sufficient air layer, improvement in heat insulating properties can be expected. On the other hand, when the olefin polymer (A) is 55% by weight or more, the styrene-olefin block copolymer (B) and / or the styrene-olefin-styrene block copolymer (C) in the propylene polymer are used with each other. Is less likely to agglomerate and is more likely to become porous due to stretching.

In the present invention, it is preferable to further mix the crystal nucleating agent (D). By mixing the crystal nucleating agent, the crystallization of the olefin polymer (A) is promoted, and the crystal structure becomes densely uniform. Therefore, the olefin polymer (A) in the sheet before stretching is composed of a densely homogenized crystal portion and an amorphous portion existing between the crystal portions, and is composed of the styrene-olefin block copolymer (B) and the styrene-olefin block copolymer (B). A large amount of the styrene-olefin-styrene block copolymer (C) is present in the amorphous portion of the olefin polymer (A). Therefore, the porosity that occurs at the interface between the dense crystal portion of the olefin polymer (A) and the styrene-olefin block copolymer (B) or the styrene-olefin-styrene block copolymer (C) due to stretching is The improvement of the elastic modulus accompanying the crystallization of the matrix facilitates the formation of a dense and uniform porous structure, and the dense homogenization of the crystals facilitates the formation of a dense and uniform porous structure.

^{The content of the crystal nucleating agent (D) is preferably 1.0 × 10 -3 to} 5.0 parts by weight with respect to 100 parts by weight of the olefin polymer (A).

Examples of the crystal nucleating agent include the α crystal nucleating agent and the β crystal nucleating agent described below, but the α crystal nucleating agent is preferable because the crystals are more densely homogenized.

Examples of α-crystal nucleating agents include inorganic compounds such as talc, myoban, silica, titanium oxide, calcium oxide, magnesium oxide, carbon black, and clay minerals; malonic acid, succinic acid, adipic acid, maleic acid, azelaic acid, and sebacine. Acids, dodecandic acid, citric acid, butanetricarboxylic acid, butanetetracarboxylic acid, naphthenic acid, cyclopentanecarboxylic acid, 1-methylcyclopentanecarboxylic acid, 2-methylcyclopentanecarboxylic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, 1-Methylcyclohexanecarboxylic acid, 4-methylcyclohexanecarboxylic acid, 3,5-dimethylcyclohexanecarboxylic acid, 4-butylcyclohexanecarboxylic acid, 4-octylcyclohexanecarboxylic acid, cyclohexanecarboxylic acid, 4-cyclohexane-1,2-dicarboxylic acid Carboxylic acids excluding aliphatic monocarboxylic acids such as acids, benzoic acids, toluic acids, xylyl acids, ethyl benzoic acids, 4-t-butyl benzoic acids, salicylic acids, phthalic acids, trimellitic acids, pyromellitic acids; Positive or basic salts of group monocarboxylic acids such as lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, aluminum; divendilidene sorbitol compounds such as 1,2,3,4-dibenzylene sorbitol; Aryl phosphate-based compounds such as lithium-bis (4-t-butylphenyl) phosphate; among the aryl phosphate-based compounds, cyclic polyvalent metal aryl phosphate-based compounds and acetic acid, lactic acid, propionic acid, acrylic acid, Octylic acid, isooctylic acid, nonanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, 12-hydroxystearic acid, ricinolic acid, behenic acid, erucic acid, montanoic acid , Melicic acid, stearoyl lactic acid, β-N-laurylaminopropionic acid, β-N-methyl-N-lauroylaminopropionic acid and other fatty acid group monocarboxylic acids such as lithium, sodium or potassium salt and other fatty acid monocarboxylic acid alkali metal salts Or a mixture with basic aluminum, lithium, hydroxy, carbonate, hydride; poly-3-methyl-1-butene, poly3-methyl-1-pentene, poly3-ethyl-1-pentene, poly4-methyl- 1-pentene, poly 4-methyl-1-hexene, poly 4,4-Dimethyl-1-pentene, poly 4,4-dimethyl-1-hexene, poly4-ethyl-1-hexene, poly3-ethyl-1-hexene, polyallylnaphthalene, polyallylnorbornane, tactic polystyrene , Syndiotactic polystyrene, polydimethylstyrene, polyvinylnaphthalene, polyallylbenzene, polyallyltoluene, polyvinylcyclopentane, polyvinylcyclohexane, polyvinylcyclopeptane, polyvinyltrimethylsilane, polyallyltrimethylsilane and other high molecular compounds. Be done.

Specific examples of commercially available α-crystal nucleating agents include "Gelall D" series manufactured by Shin Nihon Rika Co., Ltd., "Gelall MD" series, "NA" series manufactured by ADEKA Corporation, "Millad" series manufactured by Milliken Chemical Co., Ltd., and "Hyperform". Series, BASF's "IRGACLEAR" series, etc.

Examples of the β crystal nucleating agent include amide compounds; tetraoxaspirones; quinacridones; iron oxide having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate and the like. Alkaline or alkaline earth metal salt of carboxylic acid typified by; Aromatic sulfonic acid compound typified by sodium benzenesulfonate or sodium naphthalene sulfonate; Di or triesters of di or tribasic carboxylic acid; Phthalocyanine blue Phthalocyanin-based pigments typified by such as; a two-component compound composed of a component A which is an organic dibasic acid and a component B which is an oxide, a hydroxide or a salt of a group IIA metal of the periodic table; a cyclic phosphorus compound and the like. Examples thereof include a composition composed of a magnesium compound.

As a specific example of a commercially available β crystal nucleating agent, a β crystal nucleating agent “Ngester NU-100” manufactured by Shin Nihon Rika Co., Ltd., and as a specific example of a polypropylene polymer to which a β crystal nucleating agent is added, Aristech Co., Ltd. Examples thereof include polypropylene "Bepol B-022SP" manufactured by Borealis, polypropylene "Beta (β) -PP BE60-7032" manufactured by Borealis, and polypropylene "BNX BETAPP-LN" manufactured by mayo.

In the present invention, components other than the above-mentioned olefin polymer (A), styrene-olefin block copolymer (B) and styrene-olefin-styrene block copolymer (C) are used as long as the effects of the present invention are not impaired. For example, it is acceptable to mix a resin other than the olefin polymer (A).
Other resins include polystyrene-based resins, polyvinyl chloride-based resins, polyvinylidene chloride-based resins, chlorinated polyethylene-based resins, polyester-based resins, polycarbonate-based resins, polyamide-based resins, polyacetal-based resins, acrylic resins, and ethylene acetic acid. 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, Polypolyacetal resin, Polybutadiene resin, Polybutene resin, Polyamideimide resin, Polyamide bismaleimide resin, Polyarylate resin, Polyetherimide resin, Examples thereof include polyether ether ketone-based resins, polyether ketone-based resins, polyether sulfone-based resins, polyketone-based resins, polysulfone-based resins, aramid-based resins, and fluorine-based resins.

Further, in the present invention, in addition to the above-mentioned components, additives generally blended can be appropriately added as long as the effects of the present invention are not significantly impaired. The additives include recycled resins generated from trimming loss of ears and the like, which are added for the purpose of improving and adjusting molding processability, productivity and various physical properties of porous films, silica, talc, kaolin and calcium carbonate. Inorganic particles such as titanium oxide, pigments such as carbon black, flame retardant, weather resistance stabilizer, heat stabilizer, antistatic agent, melt viscosity improver, cross-linking agent, talc, nucleating agent, plasticizer, anti-aging agent, etc. Additives such as antioxidants, light stabilizers, UV absorbers, neutralizers, anti-fog agents, anti-blocking agents, slip agents, colorants and the like can be mentioned.

When mixing the olefin polymer (A), the styrene-olefin block copolymer (B), and the styrene-olefin-styrene block copolymer (C), these raw materials are used, for example, in a tumbler mixer, an omni mixer, or the like. After pre-blending in a mixer, the resulting mixture can be extruded and kneaded, if desired.

Each raw material may be heat-dried in an oven, a vacuum dryer, or the like in a state of being separated or mixed. It is preferable that the conditions are such that the components do not deteriorate or fuse during drying.

The machine used for kneading is not particularly limited. For example, a known extruder such as a single-screw extruder, a twin-screw extruder, or a multi-screw extruder can be used. Further, depending on the equipment structure and necessity, a decompressor may be connected to the vent port to remove water and low molecular weight substances.

Examples of the method for heating and melting the resin mixture kneaded as described above include the T-die method and the inflation method, and among them, the T-die method is preferably adopted. Practically, it is preferable to melt-extrude the material resin from the T-die and cast-mold it with a cast roll.

When the T-die method is adopted as a specific method for forming a film into a sheet, the sheet-shaped molten resins extruded from the T-die are laminated and adhered to a rotating cast roll (chill roll, cast drum). Examples thereof include a method of molding into a take-back sheet.

A touch roll, an air knife, an electric contact device, or the like may be attached to the cast roll in order to bring the sheet-like material into close contact with the cast roll. In particular, when the cast roll is cooled to a low temperature, electrical adhesion is effective.

In the obtained unstretched sheet, the thickness of the effective portion excluding both ends is preferably 30 μm to 1000 μm, more preferably 50 μm or more or 800 μm or less, and more preferably 100 μm or more or 600 μm or less.
If the thickness of the unstretched sheet is 30 μm or more, it is possible to prevent the sheet from breaking due to being too thin, and if the thickness of the unstretched sheet is 1000 μm or less, the sheet becomes too rigid. Not only can it be prevented from becoming difficult to perform stretching, but also the thickness of the sheet after stretching can be reduced.

<Stretching process>
Hereinafter, the step of stretching the unstretched sheet to obtain a stretched porous film will be described in detail.
The obtained unstretched sheet is uniaxially stretched or biaxially stretched. The uniaxial stretching may be a longitudinal uniaxial stretching or a horizontal uniaxial stretching. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. One of the advantages of the present invention is that the thickness, air permeability, and porosity of the produced porous film can be adjusted by changing the composition, thickness, and draw ratio of the non-porous sheet-like material. be. When producing a porous film, which is the object of the present invention, sequential biaxial stretching is more preferable because the stretching conditions can be selected in each stretching step and the porous structure can be easily controlled. The stretching of the film-like material in the flow direction (MD) is referred to as "longitudinal stretching", and the stretching in the direction perpendicular to the flow direction (TD) is referred to as "horizontal stretching". The transverse stretching is preferably performed by utilizing the speed difference between the pair of drive rolls serving as the stretching section, but the transverse stretching is not limited to this. On the other hand, it is preferable to use a clip-type tenter as the device used for lateral stretching. However, it is not limited to this.

In the method for producing a stretched porous film according to an example of the embodiment of the present invention, the unstretched sheet is stretched at a temperature of 0 ° C. to 60 ° C. in the longitudinal direction at a temperature of 1.1 times or more and less than 3.0 times at 60 ° C. It is a method of stretching at a temperature of ~ 160 ° C. in the vertical direction at 1.5 times or more and less than 6.0 times, and at a temperature of 70 to 150 ° C. in the horizontal direction at 1.1 times or more and less than 10 times. Details will be described below.

When the longitudinal stretching is performed, it is preferable to perform the following low-temperature longitudinal stretching step molding before the high-temperature longitudinal stretching for the reason of facilitating the opening of holes by the stretching.
The unstretched sheet is preferably at a temperature of 0 ° C. to 60 ° C., more preferably 10 to 40 ° C., preferably 1.1 times or more and less than 3.0 times in the longitudinal direction, and more preferably 1.2 times or more. Stretch in the range of less than 0 times. When stretched at 0 ° C. or lower, the film tends to break, and when stretched at a temperature exceeding 60 ° C., the obtained stretched film tends to have a low porosity and a high air permeability. Further, since the permeability of the porous film obtained in the present embodiment is improved, the sheet obtained in the sheet molding step may be heat-treated in a certain temperature range for a certain period of time before the stretching step is carried out. ..

Next, the stretched sheet obtained above is preferably at a temperature of 60 ° C. to 160 ° C., more preferably 70 ° C. to 130 ° C., preferably 1.5 times or more and less than 6.0 times in the longitudinal direction, more preferably. High temperature longitudinal stretching is performed in the range of 1.5 times or more and less than 5.0 times. When stretched at 60 ° C. or lower, the film tends to break, and when stretched at 160 ° C. or higher, the obtained stretched film tends to have a low porosity and a high air permeability. Further, from the viewpoint of physical properties and applications required for the porous film of the present embodiment, it is preferable to stretch the film in two or more steps under the above-mentioned conditions. If the stretching step is one step, the obtained stretched film may not satisfy the required physical properties.

The longitudinal stretching ratio can be arbitrarily selected, but the stretching ratio per uniaxial stretching is preferably 1.1 times or more and less than 15 times, more preferably 1.5 times or more and less than 12 times, and further preferably 1. .5 times or more and less than 10 times. By setting the stretching ratio per uniaxial stretching to 1.1 times or more, whitening progresses, suggesting that perforation due to stretching has sufficiently occurred. Further, when the content is less than 15 times, deformation of the pores is suppressed, and a sufficiently whitened porous film can be obtained.

As described above, as a device used for lateral stretching, it is preferable to use a clip-type tenter. The clip-type tenter is composed of a clip traveling device for lateral stretching and an oven.
The clip traveling device stretches the sheet by grasping both ends of the vertically stretched sheet with a pair of clips and transporting the sheet, and at the same time, the guide rail of the grip traveling device is opened to widen the distance between the two rows of grips.
The oven is divided into several zones in the flow direction, and it is desirable that the set temperature or the air volume of hot air can be changed for each zone. From the upstream side, a preheating zone is provided to heat the vertically stretched sheet to a temperature at which it can be stretched, the stretched sheet is stretched in the stretched zone, and after stretching, a heat treatment zone is provided as necessary for heat treatment. A slow cooling zone is provided before exposure to.

Regarding the temperature at the time of lateral stretching, the sheet is preferably stretched in the lateral direction in a temperature range of 70 to 150 ° C., more preferably 80 to 140 ° C. When the transverse stretching temperature is within the specified range, the pores generated during the longitudinal stretching can be expanded to increase the porosity, and sufficient porosity can be obtained.

The transverse stretching ratio can be arbitrarily selected, but is preferably 1.1 times or more and less than 10 times, more preferably 1.5 times or more and less than 9.0 times, and further preferably 2.0 times or more and 8.0 times. Is less than. By stretching at a specified transverse stretching ratio, it is possible to have a sufficient porosity without deforming the pores generated during longitudinal stretching.

The stretching rate is preferably in the range of 10 to 20000% / min, more preferably in the range of 100 to 10000% / min. If it is 10% / min or more, a sufficient draw ratio can be efficiently obtained and the manufacturing cost can be suppressed, while if it is 20000% / min or less, it is possible to suppress the occurrence of sheet breakage or the like. can.

The stretched porous film obtained by the production method of the present invention is a porous film formed by mixing an olefin polymer (A), a styrene-olefin block copolymer (B), and a styrene-olefin-styrene block copolymer (C). Is. Hereinafter, this stretched porous film will be described.

(1) Thickness The thickness of the stretched porous film obtained by the production method of the present invention is not particularly limited, but is preferably 25 μm or more, more preferably 50 μm or more. On the other hand, the upper limit is preferably 500 μm or less, more preferably 300 μm or less. When the thickness is 25 μm or more, it can have sufficient strength. Further, if the thickness is 500 μm or less, it can be easily used for applications requiring miniaturization and weight reduction.

(2) Air permeability The air permeability of the stretched porous film obtained by the production method of the present invention is preferably 1 second / 100 cc or more, more preferably 5 seconds / 100 cc or more, still more preferably 10 seconds / 100 cc or more. On the other hand, the upper limit is preferably 1000 seconds / 100 cc or less, more preferably 100 seconds / 100 cc or less, and even more preferably 30 seconds / 100 cc or less. When the air permeability is within the above range, it is preferable because it is a porous film having both strength and porosity.
The air permeability is measured in accordance with JIS P8117 in an air atmosphere of 25 ° C.

(3) Porosity The porosity is an important factor for defining a porous structure, and is a numerical value indicating the ratio of the space portion of the porous layer in the porous film of the present invention. It is generally known that the higher the porosity, the better the filtration rate. In the stretched porous film obtained by the production method of the present invention, the porosity is preferably 50% or more, more preferably. Is 60% or more, more preferably 65% or more. On the other hand, the upper limit is preferably 98% or less, more preferably 95% or less. When the porosity is 50% or more, the porous film has excellent porosity.
The porosity is calculated by measuring the actual weight W1 of the porous film, calculating the weight W0 when the porosity is 0% from the density and thickness of the resin composition, and calculating from those values based on the following formula. ..
Porosity (%) = {(W0-W1) / W0} x 100

(4) Filtration rate The filtration rate of the stretched porous film obtained by the production method of the present invention is preferably 10 ml / min · cm ² or more, more preferably 20 ml / min · cm ² or more, still more preferably 23 ml / min · cm. ² or more. On the other hand, the upper limit is preferably 100 ml / min · cm ² or less, more preferably 90 ml / min · cm ² or less, and further preferably 80 ml / min · cm ² or less. If the filtration rate is within the above range, a porous film having both strength and filtration efficiency can be obtained.
The filtration rate is calculated based on the following formula by measuring the time t through which acetone having a predetermined volume V passes through a porous film having an effective filtration area A at a pressure of 0.07 MPa in an air atmosphere of 25 ° C. NS.
Filtration rate (ml / min · cm ² ) = (V × 60) / (t × A)

(5) Filtration accuracy The filtration accuracy of the stretched porous film obtained by the production method of the present invention is preferably 0.50 or less, more preferably 0.25 or less, still more preferably 0.20 or less. If the filtration accuracy is within the above range, the porous film has good filtration accuracy.
The filtration accuracy is as follows: Colloidal silica manufactured by Nissan Chemical Co., Ltd. (product name: Snowtex MP-4540M), average particle size: 450 nm, solid content: 40% by weight, medium: water) with water so as to be 4% by weight. After diluting and sufficiently uniformly dispersing in an ultrasonic stirrer, the particles are passed through a porous film at a pressure of 0.07 MPa, and the concentration of the liquid before and after the passage is measured by the absorbance method to determine the particle collection efficiency (%). Produced by asking.
(6) Filtration Life The filtration life of the stretched porous film obtained by the production method of the present invention is preferably 0.10 g / cm ² or more, more preferably 0.50 g / cm ² or more, still more preferably 1.0 g / cm. ² or more. On the other hand, the upper limit is preferably 10 g / cm ² or less, more preferably 5.0 g / cm ² or less, and further preferably 2.0 g / cm ² or less. If the filtration rate is within the above range, the porous film has good filtration efficiency.
The filtration life is 4% by weight of colloidal silica (product name: Snowtex MP-4540M) manufactured by Nissan Chemical Co., Ltd., average particle size: 450 nm, solid content: 40% by weight, medium: water). After diluting and sufficiently uniformly dispersing in an ultrasonic stirrer, the mixture is passed through a porous film at a pressure of 0.09 MPa, the weight W of the liquid passed until filtration becomes impossible is measured, and the effective filtration area A is measured. The filtration life (g / cm ² ) is calculated by dividing by.

The stretched porous film obtained by the production method of the present invention contains a styrene-olefin block copolymer and a styrene-olefin-styrene block copolymer, and is a porous film having a large pore size distribution, so that the filtration efficiency is excellent. Specifically, by the production method of the present invention, a stretched porous film satisfying the above-mentioned filtration speed, filtration accuracy, and filtration life range can be obtained.

<Explanation of terms>
Generally, a "sheet" is a thin product according to the definition in JIS, and its thickness is generally small for its length and width, and is flat. Generally, a "film" is compared to its length and width. A thin flat product with an extremely small thickness and an arbitrarily limited maximum thickness, which is usually supplied in the form of a roll (Japanese Industrial Standards JIS K6900). For example, in terms of thickness, in a narrow sense, a film having a thickness of 100 μm or more may be referred to as a sheet, and a film having a thickness of less than 100 μm may be referred to as a film. However, the boundary between the sheet and the film is not clear, and it is not necessary to distinguish between the two in the present invention. Therefore, in the present invention, even when the term "sheet" is used, the term "film" is included and is referred to as "film". Even in the case, the "sheet" shall be included.

In the present invention, when expressed as "X to Y" (X, Y are arbitrary numbers), unless otherwise specified, it means "X or more and Y or less", and "preferably larger than X" and "preferably Y". Includes the meaning of "smaller".
Further, in the present invention, when expressed as "X or more" (X is an arbitrary number), it includes the meaning of "preferably larger than X" unless otherwise specified, and "Y or less" (Y is an arbitrary number). ) Includes the meaning of "preferably smaller than Y" unless otherwise specified.

Next, Examples and Comparative Examples will be shown and the porous body will be described in more detail, but the present invention is not limited thereto. In addition, as an embodiment of this porous body, it was shaped into a film-like material. Further, the take-back (flow) direction of the film is described as "MD", and the direction perpendicular to the direction is described as "TD".

(Olefin polymer (A))
A-1; homopolypropylene (MFR: 1.9 g / 10 minutes, Mw / Mn = 3.2)

(Styrene-olefin block copolymer (B))
B-1; Styrene-based thermoplastic elastomer (styrene- (ethylene / propylene) copolymer (SEP), MFR (230 ° C., 2.16 kg): 0.1 g / 10 minutes, styrene content: 35% by weight, )

(Styrene-olefin-styrene block copolymer (C))
C-1; Styrene-based thermoplastic elastomer (styrene- (ethylene / propylene) -styrene block copolymer (SEPS), MFR (230 ° C., 2.16 kg): does not flow during MFR measurement, styrene content: 20 weight%)

(Crystal Nucleating Agent (D))
-D-1; α crystal nucleating agent (sorbitol compound, grade name: Gelol MD-LM30G, manufactured by Shin Nihon Rika Co., Ltd.)

(1) Thickness The obtained porous film was measured at 5 unspecified points in the plane with a 1/1000 mm dial gauge, and the average thereof was taken as the thickness.

(2) Air permeability The air permeability was measured in accordance with JIS P8117 in an air atmosphere of 25 ° C. As a measuring device, a digital type Oken type air permeability dedicated machine (manufactured by Asahi Seiko Co., Ltd.) was used.

(3) Porosity The actual weight W1 of the obtained porous film is measured, the weight W0 when the porosity is 0% is calculated from the density and thickness of the resin composition, and the weight W0 is calculated from those values based on the following formula. bottom.
Porosity (%) = {(W0-W1) / W0} x 100

(4) Filtration rate In an air atmosphere of 25 ° C., the time t for passing acetone of a predetermined volume V through the porous film having an effective filtration area A at a pressure of 0.07 MPa was measured and calculated based on the following formula.
Filtration rate (ml / min · cm ² ) = (V × 60) / (t × A)

(5) Filtration accuracy test Nissan Chemical Co., Ltd. colloidal silica (product name: Snowtex MP-4540M), average particle size: 450 nm, solid content: 40% by weight, medium: water) with water so as to be 4% by weight. After diluting and sufficiently uniformly dispersing in an ultrasonic stirrer, the particles are passed through a porous film at a pressure of 0.07 MPa, and the concentration of the liquid before and after the passage is measured by the absorbance method to determine the particle collection efficiency (%). Calculated.

(6) Filtration life Nissan Chemical Co., Ltd. colloidal silica (product name: Snowtex MP-4540M), average particle size: 450 nm, solid content: 40% by weight, medium: water) diluted with water to 4% by weight. Then, after sufficiently uniformly dispersing in an ultrasonic stirrer, the porous film was passed at a pressure of 0.09 MPa, the weight W of the liquid passed until filtration became impossible was measured, and the effective filtration area A was measured. The filtration life (g / cm ² ) was calculated by dividing.

<Example 1>
70% by weight of olefin polymer (A-1), 22.5% by weight of styrene-olefin block copolymer (B-1), 7.5% by weight of styrene-olefin-styrene block copolymer (C-1). 2 It was put into a shaft extruder, melt-kneaded at a set temperature of 240 ° C., shaped into a strand shape with a strand die, cooled and solidified in a water tank, and cut with a strand cutter to prepare pellets.

The produced pellets are put into a single-screw extruder, melt-kneaded at a set temperature of 200 ° C., shaped into a sheet with a T-die, and then cooled and solidified with a cast roll set at 127 ° C. without stacking. A porous sheet-like material was obtained. Then, the obtained non-porous sheet-like material was subjected to a draw ratio of 100% (stretching ratio 2.0 times) between the roll (X) set at 20 ° C. and the roll (Y) set at 20 ° C. Low temperature stretching was performed. Next, a draw ratio of 50% (stretching ratio 1.5 times) was applied between the roll (P) set at 120 ° C. and the roll (Q) set at 120 ° C. to perform high-temperature stretching to obtain an MD stretched film. .. Next, the obtained MD stretched porous film was preheated in a film tenter facility manufactured by Kyoto Machinery Co., Ltd. at a preheating temperature of 145 ° C. and a preheating time of 12 seconds, and then stretched 3.0 times in the lateral direction at a stretching temperature of 145 ° C. After that, heat treatment was performed at 155 ° C. to obtain a biaxially stretched porous film. The evaluation results of the obtained film are shown in Table 1.

<Example 2>
Regarding the blending ratio of pellets, 70% by weight of olefin polymer (A-1), 15% by weight of styrene-olefin block copolymer (B-1), and 15% by weight of styrene-olefin-styrene block copolymer (C-1). Except that the amount of the crystal nucleating agent (D-1) was 0.1 parts by weight (0.14 parts by weight with respect to 100 parts by weight of the olefin polymer) with respect to 100 parts by weight of the resin composition in which% was mixed. A non-porous sheet-like material was obtained in the same manner as in Example 1. The obtained non-porous sheet-like material was stretched in the same manner as in Example 1 to obtain a biaxially stretched porous film. The evaluation results of the obtained film are shown in Table 1.

(Example 3)
Regarding the blending ratio of the pellets, 70% by weight of the olefin polymer (A-1), 7.5% by weight of the styrene-olefin block copolymer (B-1), and the styrene-olefin-styrene block copolymer (C-1). 0.1 parts by weight of the crystal nucleating agent (D-1) was added to 100 parts by weight of the resin composition in which 22.5% by weight was mixed (0.14 parts by weight with respect to 100 parts by weight of the olefin polymer). A non-porous sheet-like material was obtained in the same manner as in Example 1. The obtained non-porous sheet-like material was stretched in the same manner as in Example 1 to obtain a biaxially stretched porous film. The evaluation results of the obtained film are shown in Table 1.

(Comparative Example 1)
Regarding the blending ratio of the pellets, the crystal nucleating agent (D) was added to 100 parts by weight of the resin composition obtained by mixing 70% by weight of the olefin polymer (A-1) and 30% by weight of the styrene-olefin block copolymer (B-1). A non-porous sheet-like material was obtained in the same manner as in Example 1 except that -1) was made 0.1 parts by weight (0.14 parts by weight with respect to 100 parts by weight of the olefin polymer). The obtained non-porous sheet-like material was stretched in the same manner as in Example 1 to obtain a biaxially stretched porous film. The evaluation results of the obtained film are shown in Table 1.

(Comparative Example 2)
Regarding the blending ratio of the pellets, the crystal nucleating agent was added to 100 parts by weight of the resin composition obtained by mixing 70% by weight of the olefin polymer (A-1) and 30% by weight of the styrene-olefin-styrene block copolymer (C-1). A non-porous sheet-like material was obtained in the same manner as in Example 1 except that (D-1) was 0.1 parts by weight (0.14 parts by weight with respect to 100 parts by weight of the olefin polymer). The obtained non-porous sheet-like material was stretched in the same manner as in Example 1 to obtain a biaxially stretched porous film. The evaluation results of the obtained film are shown in Table 1.

The porous films obtained in Examples 1 to 3 have a porosity of 60% or more and an air permeability of 30 seconds / 100 cc or less, and obtain better air permeability as compared with the porous films of Comparative Examples 1 and 2. Therefore, it can be seen that a porous film having a sufficiently porous structure is obtained. Regarding the filtration performance, the filtration rate is 23 ml / min · cm ² or more, the filtration accuracy is 0.00%, and the filtration life is 1.0 g / cm ² or more. The film is obtained. It is presumed that this is because the pore structure is controlled in a state suitable for filtering the object to be filtered by the present invention.

The perforated film obtained in Comparative Example 1 has lower air permeability than Examples 1 to 3. The filtration accuracy is 0.00%, and particles can be collected, but since the filtration life is lower than that of the examples, clogging is likely to occur when the object to be filtered is filtered, and the filter can be used as a filtration filter. Performance is low. It is presumed that this is because the pore diameter is smaller than that of the example, and small pores are concentrated on the object to be filtered.
The perforated film obtained in Comparative Example 2 has higher air permeability than Examples 1 to 3. However, the filtration accuracy was 0.72%, and the particles could not be collected. Although the filtration rate and air permeability are superior to those of Examples 1 to 3, the performance as a filtration filter is low due to the leakage of particles. It is presumed that this is because the pores to be formed have a large pore diameter and large pores are concentrated on the object to be filtered.

The stretched porous film obtained by the production method of the present invention is an inexpensive porous film having a large number of porous structures having high air permeability and porosity and excellent filtration performance, and this porous film is an automobile. It is useful as a filter membrane for industry (electrodeposition paint recovery and reuse system), semiconductor industry (ultra-pure water production), pharmaceutical food industry (sterilization, enzyme purification), etc.

Claims (7)

The proportion of the olefin polymer (A) is 55 to 85% by weight, the proportion of the styrene-olefin block copolymer (B) is 1 to 44% by weight, and the proportion of the styrene-olefin-styrene block copolymer (C) is 1 to 44% by weight. An unstretched sheet formed by mixing with each other is prepared and stretched .
A method for producing a stretched porous film for a filtration membrane, wherein the filtration accuracy of the obtained stretched porous film for a filtration membrane is 0.50 or less, and the filtration life is 1.0 g / cm ² or more . The stretched porous film for a filtration membrane according to claim 1, wherein the melt flow rate of the styrene-olefin block copolymer (B) at 230 ° C. and a load of 2.16 kg is 1.0 g / 10 minutes or less. Manufacturing method. The invention according to claim 1 or 2, wherein the melt flow rate of the styrene-olefin-styrene block copolymer (C) at 230 ° C. and a load of 2.16 kg is 1.0 g / 10 minutes or less. A method for producing a stretched porous film for a filtration membrane. The method for producing a stretched porous film for a filtration membrane according to any one of claims 1 to 3, wherein the crystal nucleating agent (D) is further mixed in the mixing. 7. A method for producing a stretched porous film for a filtration membrane. The proportion of the styrene-olefin block copolymer (B) is 7.5-44% by weight, and the proportion of the styrene-olefin-styrene block copolymer (C) is 7.5-44 wt%. The method for producing a stretched porous film for a filter film according to any one of claims 1 to 5. The unstretched sheet is stretched 1.1 times or more and less than 3.0 times in the vertical direction at a temperature of 0 ° C. to 60 ° C., and 1.5 times or more and 6.0 times or more in the vertical direction at a temperature of 60 ° C. to 160 ° C. The filtration membrane according to any one of claims 1 to 6, characterized in that it is stretched less than twice and stretched at a temperature of 70 to 150 ° C. in the lateral direction at a ratio of 1.1 times or more and less than 10 times. A method for producing a stretched porous film for use.