JP7214978B2 - Stretched porous film - Google Patents

Description

The present invention relates to a stretched porous film, and the stretched porous film can be used as packaging products, sanitary products, livestock products, agricultural products, building products, medical products, light diffusion plates, reflective sheets, battery separators or separation membranes, particularly It is suitably used as a filter used in the food-related field, the pharmaceutical/cosmetics field, the chemical industry field, and the electronic industry field.

Filtration operations using porous membranes such as microfiltration membranes and ultrafiltration membranes are widely used in the automobile industry (electrodeposition paint recovery and reuse system), the semiconductor industry (superpure water production), the pharmaceutical and food industry (sterilization, enzyme purification), etc. It has been put to practical use in many ways. Especially in recent years, it has been widely used as a technique for producing drinking water and industrial water by removing turbidity from river water and the like. Various materials such as cellulose-based, polyacrylonitrile-based, and polyolefin-based materials are used as materials for membranes.
Among them, polyolefin-based polymers (polyethylene, polypropylene, polyvinylidene fluoride, etc.) are suitable as materials for aqueous filtration membranes and are widely used because of their hydrophobicity and high water resistance.

In addition, when used for applications such as filters, there is a problem that low molecular weight substances such as oligomers and stabilizers such as antioxidants may be mixed in the filtered liquid. A filter with less agent elution is strongly desired.

Various techniques described below have been proposed as techniques for forming a large number of fine through-holes in this type of polymer.
For example, Patent Document 1 discloses obtaining a porous membrane by biaxially stretching a sheet containing a polyolefin/polystyrene elastomer in a polypropylene resin.

Patent Document 2 discloses a method of obtaining a porous film by stretching a film made of a resin composition containing high-molecular-weight polyethylene, high-density polyethylene, and a filler.

Further, in Patent Document 3, after extruding and stretching a mixture containing a composition made of ultra-high molecular weight polyethylene and high-density polyethylene and a membrane-forming solvent, the membrane-forming solvent is extracted and dried to form a microporous membrane. Disclosed is a method for causing

JP 2014-101445 A JP 2007-297583 A JP 2013-108045 A

Patent Literature 1 discloses a porous membrane using a polypropylene-based resin, but a porous membrane with an even better filtration rate is desired.

In Patent Document 2, a porous membrane of a polyethylene resin is produced by stretching, but the air permeability of the obtained porous membrane is low, and there is a high possibility that the performance as a filtration membrane is insufficient.

Patent Document 3 has a problem that the cost required for extraction processing is high. Since the plasticizer is removed by extraction using an organic solvent, a large amount of the organic solvent is required, and there is concern about the impact on the environment.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive polypropylene porous film that has excellent air permeability and excellent filtration speed by having a large number of pore structures.

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

That is, according to the first invention, a stretched porous film containing polypropylene (A) and a vinyl aromatic elastomer (B), wherein the polypropylene (A) has a storage elastic modulus of 1.70×10 ⁹ Pa or more and 3.00×10 ⁹ Pa or less, a melt flow rate (MFR) at a temperature of 230° C. and a load of 2.16 kg of 3.0 g/10 min or more and 40 g/10 min or less, and an average pore diameter of 0.1 g/10 min or less. A stretched porous film having a thickness of 20 μm or more and 1.00 μm or less is provided.

According to a second invention, there is provided the stretched porous film according to the first invention, wherein the polypropylene (A) is a metallocene polypropylene.

Furthermore, according to a third invention, in the first or second invention, there is provided a stretched porous film having a filtration rate of 20 ml/min·cm ² or more and 200 ml/min·cm ² or less.

According to a fourth invention, in any one of the first to third inventions, the vinyl aromatic elastomer (B) has a melt flow rate (MFR) of 2.0 g at a temperature of 230° C. and a load of 2.16 kg. /10 minutes or less is provided.

Furthermore, according to a fifth invention, there is provided a stretched porous film according to any one of the first to fourth inventions, which has a porosity of 50% or more.

Further, according to a sixth invention, there is provided the stretched porous film according to any one of the first to fifth inventions, which has an air permeability of 50 seconds/100 cc or less.

A seventh invention provides a filter comprising the porous film according to any one of the first to sixth inventions.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the inexpensive polypropylene porous film which has the air permeability performance excellent by having many pore structures, and was excellent also in the filtration rate. This porous film is useful as a filtration membrane in the automobile industry (electrodeposition paint recovery and reuse system), the semiconductor industry (superpure water production), the pharmaceutical and food industry (sterilization, enzyme purification), and the like.

The present invention will be described in detail below.
It should be noted that the upper and lower limits of the numerical range in the present invention, even if it slightly deviates from the numerical range characterized by the present invention, as long as it has the same effect as within the numerical range of the present invention. It is included in the equivalent range. Further, the main component in the present invention means that it contains 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more.

1. Present film The stretched porous film of the present invention (hereinafter sometimes referred to as "this film") is a stretched porous film containing polypropylene (A) and a vinyl aromatic elastomer (B), wherein the polypropylene ( A) has a storage modulus of 1.70×10 ⁹ Pa or more and 3.00×10 ⁹ Pa or less, and a melt flow rate (MFR) of 3.0 g/10 minutes or more at a temperature of 230° C. and a load of 2.16 kg. It is a stretched porous film having a weight of 40 g/10 minutes or less and an average pore size of 0.20 μm or more and 1.00 μm or less.
The stretched porous film of the present invention is described below.

(1) Average pore size The average pore size of the present film is preferably 0.20 µm or more, more preferably 0.25 µm or more, still more preferably 0.30 µm or more, and particularly preferably 0.40 µm or more. . On the other hand, the upper limit is preferably 1.00 μm or less, more preferably 0.95 μm or less, and even more preferably 0.90 μm or less. When the thickness is 0.20 μm or more, the filtration rate of the present film is excellent. When the thickness is 1.00 μm or less, a film with high filtration accuracy can be obtained.
The average pore diameter can be adjusted by the type of resin used and stretching conditions, as described later.
Here, the average pore diameter is measured using a perm porometer (manufactured by Porous Materials), and the test solution is a polyhexafluoropropene-based liquid "GALWICK" (manufactured by Porous Materials, surface tension: 15.6 dynes/cm ) and measured according to ASTM F316-86.

(2) Thickness The thickness of the present film is not particularly limited, but is preferably 50 µm or more, more preferably 100 µm or more. On the other hand, the upper limit is preferably 300 µm or less, more preferably 200 µm or less. If the thickness is 50 μm or more, it can have sufficient strength. In addition, if the thickness is 300 mm or less, it is easy to use even in applications where miniaturization and weight reduction are required.

(3) Porosity
The porosity is an important factor for defining the porous structure, and indicates the ratio of the space portion of the porous layer in the present film. It is generally known that the higher the porosity, the better the filtration rate, and the present film has a porosity of 50% or more, preferably 60% or more, more preferably 65% or more. The upper limit is preferably 98% or less, more preferably 95% or less. If the porosity is 50% or more, a porous film having the desired porous function can be obtained.
The porosity can be adjusted by the type of resin used and stretching conditions.
Here, the porosity is measured by measuring the actual weight W1 of the stretched porous film obtained, and calculating the weight W0 at a porosity of 0% from the density and thickness of the composition constituting the film. It is calculated based on the following formula from W1.
Porosity (%) = {(W0-W1)/W0} x 100

(4) Air Permeability The air permeability of the present film is preferably 50 sec/100 cc or less, more preferably 45 sec/100 cc or less, still more preferably 40 sec/100 cc or less. If the air permeability is within the above range, a porous film having both strength and porosity can be obtained, which is preferable. On the other hand, the lower limit of air permeability is not particularly limited, but is usually 1 second/100 cc or more.

(5) Elution amount of antioxidant
In this film, the elution amount of the antioxidant is preferably 1450 ppm or less, more preferably 1400 ppm or less, and still more preferably 1350 ppm. When it is 1300 ppm or less, the filtrate after filtration is less contaminated, and a filtration membrane that can be used for filter applications can be obtained. The amount of elution can be adjusted depending on the type of material used.

(6) Filtration rate The filtration rate of the present film is preferably 20 ml/min·cm ² or more and 200 ml/min·cm ² or less. The lower limit is more preferably 40 ml/min·cm ² or more, and even more preferably 60 ml/min·cm ² or more. The upper limit is more preferably 180 ml/min·cm ² or less, and even more preferably 160 ml/min·cm ² or less. A filtration rate of 20 ml/min·cm ² or more provides a filtration rate that can be put to practical use in filter applications. On the other hand, when it is 200 ml/min·cm ² or less, a film with high filtration accuracy can be obtained.
Filtration rate can be adjusted by the average pore size.
Here, the filtration rate is defined as an effective filtration area (A) of 9.6 cm ² in an air atmosphere at 25°C, and a predetermined volume (V) of 100 cc of acetone passes through the porous film at a reduced pressure of 0.07 MPa. It is calculated based on the following formula by measuring the time (t) to the point.
Filtration rate = V x 60/t x A

Hereinafter, the raw material of the present film will be described in detail, and then the manufacturing method of the present film will be described in detail.

2. Raw material of this film (polypropylene (A))
The polypropylene (A) in the present invention includes homopolypropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene or 1- Examples include random copolymers and block copolymers with α-olefins such as decene.
The polypropylene (A) used in the present invention is preferably homopolypropylene. By selecting homopolypropylene, sufficient mechanical strength for filter applications can be ensured.

The storage elastic modulus of polypropylene (A) is 1.70×10 ⁹ Pa or more and 3.00×10 ⁹ Pa or less. The lower limit is 1.70×10 ⁹ Pa or more, more preferably 1.80×10 ⁹ Pa or more, and further preferably 1.90×10 ⁹ Pa or more. The upper limit is 3.00×10 ⁹ Pa or less, preferably 2.90×10 ⁹ Pa or less, and even more preferably 2.80×10 ⁹ Pa or less. When the viscosity is 1.70×10 ⁹ Pa or more, when a composition having a sea-island structure of polypropylene (A) and vinyl aromatic elastomer (B) is stretched, the interface between the two tends to become porous. On the other hand, when it is 3.00×10 ⁹ Pa or less, a film having excellent air permeability and filtration rate can be obtained.
The elastic modulus can be adjusted depending on the type of resin used.
Here, the storage elastic modulus is determined by dynamic viscoelasticity temperature dispersion measurement (JIS K7198A dynamic viscoelasticity measurement) under the conditions of strain 0.1%, frequency 10 Hz, heating rate 3°C/min, and 20°C. It is what you get.

Mixing polypropylene with a vinyl aromatic elastomer results in a composition having an islands-in-the-sea structure. Furthermore, when this composition is formed into a sheet and stretched, a film having holes is obtained by breaking the interface portion of the sea-island structure. Here, when a polypropylene having a high storage modulus is used, the stretching stress during stretching concentrates on the interface portion, so that the interface portion is broken efficiently and a porous film is obtained.
In the present invention, it has been found that a porous film having a large average pore diameter and excellent filtration rate can be obtained by using a polypropylene having a large MFR. That is, even if the storage elastic modulus is about the same, a porous film having a large average pore size and an excellent filtration rate can be obtained by using a polypropylene having a high MFR.
This effect is surprising because it was expected that when a polypropylene having a large MFR is used, the stretching stress during stretching would be relatively concentrated in the polypropylene portion, making it difficult for the interfacial portion to break.

Moreover, the polypropylene (A) is preferably a metallocene-based polypropylene synthesized with a metallocene catalyst from the viewpoint of easily satisfying the above storage modulus. Polypropylene is known to be able to control structural characteristics such as molecular weight, molecular weight distribution, and branched structure by selecting a catalyst, and those skilled in the art can distinguish between types of polymers according to the type of catalyst. For example, polypropylene polymerized with a metallocene catalyst may be called metallocene polypropylene, and polypropylene polymerized with a catalyst other than a metallocene catalyst may be called non-metallocene polypropylene.
Metallocene-based polypropylene contains less low-molecular-weight components and generates less foreign matter, so it is suitable for use in filter-related applications.

Further, the polypropylene (A) preferably has a melt flow rate (MFR) of 3.0 to 40 g/10 minutes or less at a temperature of 230 ° C. and a load of 2.16 kg, and is 5.0 to 40 g/10 minutes. is more preferred. When the MFR is 3.0 g/10 minutes or more, a sea-island structure having large island portions is formed, and the composition tends to become porous when stretched. On the other hand, when the MFR is 40 g/10 minutes or less, the film can have sufficient strength.
The MFR of polypropylene (A) was measured in accordance with JIS K7210 under conditions of a temperature of 230° C. and a load of 2.16 kg.

Polypropylene (A) contains one or more types of polypropylene (A), and when it consists of two or more components, it satisfies the above range of storage modulus and MFR as a blend of two or more components. is preferred.

In the stretched porous film of the present invention, the storage elastic modulus and MFR should satisfy the ranges described above when the polypropylene (A) is taken out by a separation operation such as solvent extraction.

(Vinyl aromatic elastomer (B))
It is important that the stretched porous film of the present invention contains a vinyl aromatic elastomer (B). By containing the vinyl aromatic elastomer (B), a fine and highly uniform porous structure can be efficiently obtained, and the shape and diameter of the pores can be easily controlled.

The vinyl aromatic elastomer (B) in the present invention is a type of thermoplastic elastomer having a styrene component as a base material, and is composed of a continuum of a soft component (e.g., butadiene component) and a hard component (e.g., styrene component). It is a polymer.

Moreover, random copolymers, block copolymers, and graft copolymers are mentioned as the types of the copolymer. Generally, various block copolymers such as linear block structures and radially branched block structures are known. Either structure may be used in the present invention.

The vinyl aromatic elastomer (B) used in the present invention preferably has a melt flow rate (MFR) of 2.0 g/10 minutes or less at a temperature of 230° C. and a load of 2.16 kg, and preferably 1.0 or less. is more preferred, and those that do not flow are particularly preferred. When mixed with polypropylene, the vinyl aromatic elastomer (B) dispersed in the composition changes its shape due to the difference in viscosity from the resin. This is because it tends to be spherical. Unlike domains with a large aspect ratio, spherically dispersed domains are preferable because the uniformity of the porous structure obtained by the subsequent drawing process is likely to be high and the physical properties are stable. Furthermore, when the MFR is within the above range, stress is likely to concentrate at the interface between the matrix having a high elastic modulus and the domain having a low elastic modulus during the stretching process, so opening starting points are likely to occur and porosity is likely to occur. It has the characteristics of
Here, the MFR of the vinyl aromatic elastomer (B) is measured according to JIS K7210 under conditions of a temperature of 230° C. and a load of 2.16 kg.

Also, the vinyl aromatic elastomer (B) in the present invention preferably has a styrene content of 10% by mass to 40% by mass, more preferably 10% by mass to 35% by mass. When the styrene content in the vinyl aromatic elastomer (B) is 10% by mass or more, domains can be effectively formed in the composition, and when the styrene content is 40% by mass or less, Excessively large domain formation can be suppressed.

In addition, regarding the amount of polypropylene (A) and vinyl aromatic elastomer in the film, 55 to 85 parts by mass of polypropylene (A) and 15 to 85 parts by mass of the vinyl aromatic elastomer (B) are used for 100 parts by mass of the film. It is preferably 45 parts by mass. More preferably, 60 to 80 parts by mass of polypropylene (A) and 20 to 40 parts by mass of vinyl aromatic elastomer (B) are used with respect to 100 parts by mass of the present film.
When the polypropylene (A) is 85 parts by mass or less and the vinyl aromatic elastomer (B) is 15 mass% or more, when a film in which the polypropylene (A) and the vinyl aromatic elastomer (B) are mixed is stretched, Pores are more likely to occur. On the other hand, when the polypropylene (A) is 55 parts by mass or more and the vinyl aromatic elastomer (B) is 45 parts by mass or less, when the polypropylene (A) and the vinyl aromatic elastomer (B) are mixed, the vinyl The aromatic elastomer (B) is appropriately dispersed, and the stretching facilitates the formation of many porous portions.

Specific types of the vinyl aromatic elastomer (B) are not particularly limited, but styrene-butadiene block copolymer (SBR), hydrogenated styrene-butadiene block copolymer (SEB), styrene-butadiene-styrene block. copolymer (SBS), styrene-butadiene-butylene-styrene block copolymer (SBBS), styrene-ethylene-butadiene-styrene block copolymer (SEBS), styrene-isoprene block copolymer (SIR), styrene- Ethylene-propylene block copolymer (SEP), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymer polymer (SEEPS) and the like.

In order to efficiently disperse the vinyl aromatic elastomer (B) in the film, among the vinyl aromatic elastomer (B), an ethylene component and a butylene component, which are highly compatible with the polypropylene (A), are contained. Among them, styrene-ethylene/propylene block copolymer (SEP), styrene-ethylene/propylene-styrene block copolymer (SEPS), styrene-ethylene/butylene-styrene block copolymer (SEBS) is more preferred.

The stretched porous film constituting the present invention may contain only one type of vinyl aromatic elastomer (B), or may contain two or more types.

(Crystal nucleating agent (C))
In the present invention, it is preferable that the polypropylene (A) further contains a crystal nucleating agent (C). By containing the crystal nucleating agent (C), the crystallization of the polypropylene (A) is promoted, and the crystal structure becomes dense and uniform. Therefore, the polypropylene (A) in the composition before stretching consists of a densely homogenized crystal part and an amorphous part existing between the crystal parts, and the styrene-based thermoplastic elastomer (B) is the polypropylene Many of them are present in the amorphous part of (A). Therefore, the porous formation caused by stretching at the interface between the dense crystal part of the polypropylene (A) and the styrene-based thermoplastic elastomer (B) is facilitated by the improvement in the elastic modulus accompanying the crystallization of the matrix, and The dense uniformity of crystals facilitates the formation of a dense and uniform porous structure.

As the crystal nucleating agent (C) used for obtaining a dense crystal structure of polypropylene (A), an α crystal nucleating agent or a β crystal nucleating agent is preferable. By containing the α-crystal nucleating agent, the obtained polypropylene (A) has a fine spherulite size. Therefore, the uniformity of the porous structure obtained during the stretching process is increased. Further, by containing the β-crystal nucleating agent, not only the above effects but also craze formation due to dislocation to α-crystals in the stretching step of the generated β-crystals becomes possible. By enlarging these crazes by biaxial stretching, even better air permeability can be obtained.

The content of the crystal nucleating agent (C) is preferably 0.001 to 5.0 parts by mass with respect to 100 parts by mass of the polypropylene (A).

Examples of α crystal nucleating agents include inorganic compounds such as talc, alum, silica, titanium oxide, calcium oxide, magnesium oxide, carbon black, and clay minerals; malonic acid, succinic acid, adipic acid, maleic acid, azelaic acid, and sebacine. acid, dodecanedioic 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 acid, toluic acid, xylyl acid, ethylbenzoic acid, 4-t-butylbenzoic acid, salicylic acid, phthalic acid, trimellitic acid, pyromellitic acid; normal or basic salts of lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, aluminum, etc. of group monocarboxylic acids; dibenzylidene sorbitol compounds such as 1,2,3,4-dibenzylidene sorbitol; Aryl phosphate compounds such as lithium-bis(4-t-butylphenyl) phosphate; Octylic acid, isooctyl acid, nonanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, 12-hydroxystearic acid, ricinoleic acid, behenic acid, erucic acid, montanic acid , melissic acid, stearoyl lactic acid, β-N-laurylaminopropionic acid, β-N-methyl-N-lauroylaminopropionic acid, etc. Lithium, sodium or potassium salts of fatty acid monocarboxylic acid alkali metal salts , or mixtures with basic aluminum lithium hydroxy carbonate hydrate; poly 3-methyl-1-butene, poly 3-methyl-1-pentene, poly 3-ethyl-1-pentene, poly 4-methyl- 1-pentene, poly 4-methyl-1-hexene, poly 4,4-dimethyl-1-pentene, poly-4,4-dimethyl-1-hexene, poly-4-ethyl-1-hexene, poly-3-ethyl-1-hexene, polyallylnaphthalene, polyallylnorbornane, atactic polystyrene , polymer compounds such as syndiotactic polystyrene, polydimethylstyrene, polyvinylnaphthalene, polyallylbenzene, polyallyltoluene, polyvinylcyclopentane, polyvinylcyclohexane, polyvinylcycloheptane, polyvinyltrimethylsilane, polyallyltrimethylsilane, etc. be done.

(other ingredients)
The raw material constituting the present film contains components other than the polypropylene (A) and the vinyl aromatic elastomer (B), such as resins other than polypropylene (A), as long as the effects of the present invention are not impaired. be allowed to do so.
Other resins include polyolefin resins, polystyrene resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polyester resins, polycarbonate resins, polyamide resins, polyacetal resins, and acrylic resins. Resin, ethylene vinyl acetate copolymer, polymethylpentene resin, polyvinyl alcohol resin, cyclic olefin resin, polylactic acid resin, polybutylene succinate resin, polyacrylonitrile resin, polyethylene oxide resin, cellulose resin , polyimide resin, polyurethane resin, polyphenylene sulfide resin, polyphenylene ether resin, polyvinyl acetal resin, polybutadiene resin, polybutene resin, polyamideimide resin, polyamide bismaleimide resin, polyarylate resin, polyether Examples include imide-based resins, polyetheretherketone-based resins, polyetherketone-based resins, polyethersulfone-based resins, polyketone-based resins, polysulfone-based resins, aramid-based resins, fluorine-based resins, and the like.

Moreover, in addition to the components described above, additives that are generally blended in films can be appropriately added to the present film within a range that does not significantly impair the effects of the present invention. Examples of the additives include recycled resin generated from trimming loss such as selvage, silica, talc, kaolin, and carbonic acid, which are added for the purpose of improving and adjusting molding processability, productivity, and various physical properties of the porous film. Inorganic particles such as calcium, pigments such as titanium oxide and carbon black, flame retardants, weather stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, cross-linking agents, lubricants, nucleating agents, plasticizers, anti-aging agents , antioxidants, light stabilizers, UV absorbers, neutralizers, anti-fogging agents, anti-blocking agents, slip agents, colorants and other additives.

Furthermore, in the present invention, corona treatment, plasma treatment, printing, coating, surface treatment such as vapor deposition, perforation, etc., can be applied as necessary within a range that does not impair the present invention. It is also possible to stack several porous sheets of the present invention.

3. Production Method of Present Film The film of the present invention is produced by first mixing raw materials and producing a substantially unstretched sheet by an extrusion method.
Various known methods such as single-screw or twin-screw extruders, Banbury mixers, mills, kneader blenders, etc. can be employed for mixing the raw materials. may be used for extrusion molding, or may be melt-mixed and directly extruded.
As the extrusion method, various molding methods such as T-die extrusion molding, inflation molding, calender molding, and scaife method can be employed. Molding is preferred.

The substantially unstretched film made by the extrusion method is then stretched to obtain the film of the present invention. As the stretching method, various methods such as roll, tenter, tubular, and autograph can be employed. It is preferred to employ sequential biaxial stretching.

The process of obtaining the present film by stretching the unstretched film so that the porosity is 50% or more will be described in detail below.
The obtained unstretched film is uniaxially stretched or biaxially stretched. The uniaxial stretching may be vertical uniaxial stretching or horizontal uniaxial stretching. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. One advantage of the present invention is that the thickness and porosity of the produced laminated porous film can be adjusted by changing the composition, thickness, and draw ratio of the unstretched film. When producing the present 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 in the machine direction (MD) is called "longitudinal stretching", and the stretching in the direction perpendicular to the machine direction (TD) is called "transverse stretching". The transverse stretching is preferably carried out by using a speed difference between a pair of drive rolls that form a stretching section, but the method is not limited to this. On the other hand, it is preferable to use a clip-type tenter as a device used for lateral stretching. However, it is not limited to this.

In the method for producing the present film according to an example of the embodiment of the present invention, the unstretched film is stretched 1.1 times or more and less than 5.0 times in the longitudinal direction at a temperature of 0 ° C. to 60 ° C., In this method, the film is longitudinally stretched at a temperature of 160° C. by 1.1 times or more and less than 3.0 times, and is biaxially stretched in the transverse direction at a temperature of 70 to 150° C. by 1.1 times or more and less than 10 times. Details are described below.

When performing longitudinal stretching, it is preferable to carry out the following low-temperature longitudinal stretching process molding before high-temperature longitudinal stretching for the reason of facilitating opening by stretching.
The unstretched film is preferably stretched at a temperature of 0° C. to 60° C., more preferably 10 to 40° C., preferably 1.1 times or more and less than 4.5 times, more preferably 1.2 times or more4. It is stretched in the range of less than 0 times. When the film is stretched at 0°C or lower, the film tends to break, and when the film is stretched at a temperature exceeding 60°C, the resulting stretched film tends to have a low porosity. In addition, since the permeability of the porous film obtained in the present embodiment is improved, the film obtained in the film forming step may be heat-treated within a certain temperature range for a certain period of time before the stretching step. .

Next, the stretched film obtained above is preferably 60° C. to 160° C., more preferably at a temperature of 70° C. to 130° C., preferably 1.1 times or more and less than 6.0 times in the machine direction, more preferably High-temperature longitudinal stretching is performed in the range of 1.2 times or more and less than 5.0 times. When the film is stretched at a temperature of less than 60°C, the film tends to break, and when the film is stretched at a temperature of over 160°C, the resulting stretched film tends to have a low porosity. Moreover, 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 stages under the conditions as described above. If the stretching process is performed in one step, the resulting stretched film may not satisfy the required physical properties.

The longitudinal draw ratio can be arbitrarily selected. .5 times or more and less than 10 times. This suggests that whitening progresses when the stretching ratio per uniaxial stretching is 1.1 times or more, and sufficient porosity is generated by stretching. Further, when the ratio is less than 15 times, deformation of pores is suppressed, and a sufficiently whitened porous film can be obtained.

As described above, it is preferable to use a clip-type tenter as a device used for lateral stretching. A clip-type tenter is composed of a clip traveling device for lateral stretching and an oven.
The clip traveling device grips both ends of the longitudinally stretched film with a pair of clips and conveys the film, and at the same time, stretches the film by opening the guide rails of the grip traveling device 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 amount of hot air can be changed for each zone. From the upstream side, a preheating zone is provided to heat the longitudinally stretched film to a temperature at which it can be stretched, the film is stretched in the stretching zone, a heat treatment zone is provided as necessary after stretching, heat treatment is performed, and the film comes out of the oven and returns to room temperature. A slow cooling zone is provided prior to exposure to

Regarding the temperature at which the film is laterally stretched, the film is preferably laterally stretched at 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 enlarged to increase the porosity and provide sufficient porosity.

The transverse draw 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, still more preferably 2.0 times or more and 8.0 times. is less than By stretching at a specified transverse draw ratio, the film can have a sufficient porosity without deforming the pores generated during longitudinal stretching.

The stretching speed is preferably in the range of 10-20000%/min, more preferably in the range of 100-10000%/min. If it is 10%/min or more, a sufficient draw ratio can be efficiently obtained, and production costs can be suppressed. can.

4. Filter The filter of the present invention comprises the present film of the present invention as described above. The filter of the present invention may have a structure of only the laminated porous film of the present invention, or may have a structure in which other layers are combined. The filter of the present invention is a filter for producing water-based solvents such as water or acetone, and petroleum-based solvents such as halides, esters, ethers, benzene, and toluene. system), semiconductor industry (superpure water production), pharmaceutical and food industry (sterilization, enzyme purification), etc.

When a porous film is incorporated into a filtration system, it can be wound concentrically (wind type), or it can be pleated and housed in a cylindrical container (cartridge filter). The filter can be conveniently incorporated into the filtration system.

Next, examples and comparative examples are shown to describe the present film in more detail, but the present invention is not limited to these. In addition, the drawing (flow) direction of the porous film is described as "MD", and the direction perpendicular thereto is described as "TD".

(Polypropylene (A))
· A-1; polypropylene (MFR (230°C, 2.16 kg): 20 g/10 minutes, 20°C storage modulus: 2.05 × 10 ⁹ Pa, density: 0.9 g/cm ³
· A-2; polypropylene (MFR (230°C, 2.16 kg): 3.5 g/10 minutes, 20°C storage modulus: 1.67 × 10 ⁹ Pa, density: 0.9 g/cm ³
· A-3; polypropylene (MFR (230°C, 2.16 kg): 2.4 g/10 minutes, 20°C storage modulus: 2.03 × 10 ⁸ Pa, density: 0.9 g/cm ³
(Vinyl aromatic elastomer (B))
・B-1; styrene-based thermoplastic elastomer (styrene-(ethylene/propylene)-styrene block copolymer (SEPS), MFR (230°C, 2.16 kg): does not flow during stretching, styrene content: 20 mass %).
・B-2; styrene-based thermoplastic elastomer (styrene-(ethylene/propylene) copolymer (SEP), MFR (230°C, 2.16 kg): 0.1 g/10 min, styrene content: 35% by mass) .
(Crystal nucleating agent (C))
・ C-1; α crystal nucleating agent (sorbitol compound, grade name: Gelol MD-LM30G, manufactured by Shin Nippon Rika Co., Ltd.)

(1) The average pore size was measured using a perm porometer (manufactured by Porous Materials). A polyhexafluoropropene-based liquid "GALWICK" (manufactured by Porous Materials, surface tension: 15.6 dynes/cm) was used as a test solution, and the measurement was performed according to ASTM F316-86.

(2) Thickness A 1/1000 mm dial gauge was used to measure the thickness of the obtained stretched film at five unspecified points in the plane, and the average thickness was taken as the thickness.

(3) Porosity The actual mass W1 of the obtained stretched film is measured, and the mass W0 when the porosity is 0% is calculated from the density and thickness of the composition constituting the film. calculated based on
Porosity (%) = {(W0-W1)/W0} x 100

(4) Antioxidant elution amount
300 cm ² of the resulting stretched film was immersed in butyl acetate (25 ml) at 50°C and allowed to stand for 72 hours. The mass was converted into a quantitative value.

(5) Air permeability Air permeability was measured in accordance with JIS P8117 in an air atmosphere at 25°C. As a measuring instrument, a digital Oken type air permeability machine (manufactured by Asahi Seiko Co., Ltd.) was used.
(6) Filtration rate Effective filtration area (A) of 9.6 cm ² in an air atmosphere at 25 ° C., and acetone of a predetermined volume (V) of 100 cc passes through the stretched porous film at a reduced pressure of 0.07 MPa. time (t) was measured. From these values, the filtration rate was calculated based on the following formula.
Filtration rate = V x 60/t x A

(Example 1)
70% by mass of polypropylene (A-1), 30% by mass of styrenic thermoplastic elastomer (B-1), mixed resin composition of polypropylene (A-1) and styrenic thermoplastic elastomer (B-1) The crystal nucleating agent (C-1) is blended at a ratio of 0.1 part by mass with respect to 100 parts by mass of the product, charged into a twin-screw extruder, melted and kneaded at a set temperature of 230 ° C., and then formed into a strand with a strand die. After shaping into , it was cut with a strand cutter and pelletized.
The obtained pellets are put into a single screw extruder, melted and kneaded at a set temperature of 200 ° C., formed into a sheet with a T-die, and then cooled and solidified with a cast roll set at 127 ° C. to a thickness of 230 μm. An unstretched sheet material was obtained. Thereafter, the obtained unstretched sheet-like material was placed between the roll (X) set at 20°C and the roll (Y) set at 20°C at a low temperature with a draw ratio of 100% (stretch ratio of 2.0). Stretched. Then, high-temperature stretching was performed at a draw ratio of 50% (stretch ratio of 1.5 times) between the roll (P) set at 120°C and the roll (Q) set at 120°C to obtain an MD stretched film. . Next, the obtained MD stretched film was preheated at a preheating temperature of 130°C for a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Kikai Co., Ltd., and then stretched 3.5 times in the transverse direction at a stretching temperature of 130°C. A heat treatment was performed at 140° C. to obtain a biaxially stretched porous film. Table 1 shows the evaluation results of the obtained film.

(Example 2)
70% by mass of polypropylene (A-1), 30% by mass of styrenic thermoplastic elastomer (B-2), mixed resin composition of polypropylene (A-1) and styrenic thermoplastic elastomer (B-1) The crystal nucleating agent (C-1) is blended at a rate of 0.1 part by mass with respect to 100 parts by mass of the product, charged into a Φ25 mm twin-screw extruder, melted and kneaded at a set temperature of 200 ° C., and then filmed from inside the T die. The material was extruded as a solid and was quenched in close contact with a cast roll at 115° C. to obtain an unstretched sheet having a thickness of 230 μm. The obtained unstretched sheet-like material is stretched at a low temperature by applying a draw ratio of 100% (stretch ratio of 2.0 times) between the roll (X) set at 20°C and the roll (Y) set at 20°C. gone. Then, high-temperature stretching was performed at a draw ratio of 50% (stretch ratio of 1.5 times) between the roll (P) set at 120°C and the roll (Q) set at 120°C to obtain an MD stretched film. . Next, the obtained MD stretched film was preheated at a preheating temperature of 130°C for a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Kikai Co., Ltd., then stretched 3 times in the horizontal direction at a stretching temperature of 130°C, and then stretched at 140°C. to obtain a biaxially stretched porous film. Table 1 shows the evaluation results of the obtained film.

(Comparative example 1)
70% by mass of polypropylene (A-2), 30% by mass of styrenic thermoplastic elastomer (B-2), mixed resin composition of polypropylene (A-1) and styrenic thermoplastic elastomer (B-1) The crystal nucleating agent (C-1) is blended at a rate of 0.1 part by mass with respect to 100 parts by mass of the product, charged into a Φ25 mm twin-screw extruder, melted and kneaded at a set temperature of 200 ° C., and then filmed from inside the T die. It was then extruded as a solid and rapidly cooled in close contact with a cast roll at 95° C. to obtain an unstretched sheet having a thickness of 230 μm. The obtained unstretched sheet-like material is stretched at a low temperature by applying a draw ratio of 100% (stretch ratio of 2.0 times) between the roll (X) set at 20°C and the roll (Y) set at 20°C. gone. Then, high-temperature stretching was performed at a draw ratio of 50% (stretch ratio of 1.5 times) between the roll (P) set at 120°C and the roll (Q) set at 120°C to obtain an MD stretched film. . Next, the obtained MD stretched film was preheated at a preheating temperature of 115°C for a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Kikai Co., Ltd., then stretched 3 times in the horizontal direction at a stretching temperature of 115°C, and then stretched at 125°C. to obtain a biaxially stretched porous film. Table 1 shows the evaluation results of the obtained film.

(Comparative example 2)
An unstretched sheet having a thickness of 230 μm was obtained in the same manner as in Example 1 except that 70% by mass of polypropylene (A-3) and 30% by mass of styrene-based thermoplastic elastomer (B-1) were used. The obtained unstretched sheet-like material is stretched at a low temperature by applying a draw ratio of 100% (stretch ratio of 2.0 times) between the roll (X) set at 20°C and the roll (Y) set at 20°C. gone. Then, high-temperature stretching was performed at a draw ratio of 50% (stretch ratio of 1.5 times) between the roll (P) set at 120°C and the roll (Q) set at 120°C to obtain an MD stretched film. . Next, the obtained MD stretched film was preheated at a preheating temperature of 145°C for a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Kikai Co., Ltd., then stretched 3 times in the horizontal direction at a stretching temperature of 145°C, and then stretched at 155°C. to obtain a biaxially stretched porous film. Table 1 shows the evaluation results of the obtained film.

(Comparative Example 3)
A biaxially stretched porous film was obtained in the same manner as in Comparative Example 2, except that 70% by mass of the polypropylene resin (A-3) and 30% by mass of the styrene-based thermoplastic elastomer (B-2) were used. Table 1 shows the evaluation results of the obtained film.

In Examples 1 and 2, since the filtration rate is 20 ml/min·cm ² or more and the air permeability is 50 sec/100 cc or less, a porous film having excellent air permeability and excellent filtration rate is obtained. I know there is.

In Comparative Example 1, the air permeability and porosity were significantly higher than those of Examples, and the filtration performance was considered to be inferior. rice field. This is probably because polypropylene has a low storage elastic modulus, which results in poor pore formation during stretching and a low percentage of pore formation.

Comparative Example 2 was inferior in air permeability and filtration speed as compared with Example 1 using the same vinyl aromatic elastomer (B-1).

Comparative Example 3 was inferior in air permeability and filtration rate as compared with Example 2 using the same vinyl aromatic elastomer (B-2).

INDUSTRIAL APPLICABILITY The stretched porous film of the present invention has a large number of pore structures, and is therefore excellent in air permeability and filtration performance. It is useful as a filtration membrane in the paint recovery and reuse system), the semiconductor industry (superpure water production), the pharmaceutical and food industry (sterilization, enzyme purification), etc.

Claims (9)

A stretched porous film containing polypropylene (A) and a vinyl aromatic elastomer (B),
The polypropylene (A) has a storage modulus of 1.70×10 ⁹ Pa or more and 3.00×10 ⁹ Pa or less, and a melt flow rate (MFR) of 20 g/10 at a temperature of 230° C. and a load of 2.16 kg. minutes or more and 40 g/10 minutes or less,
A stretched porous film having an average pore size of 0.20 μm or more and 1.00 μm or less. The stretched porous film according to claim 1, wherein the polypropylene (A) is a metallocene polypropylene. The stretched porous film according to claim 1 or 2, having a filtration rate of 20 ml/min·cm ² or more and 200 ml/min·cm ² or less. The stretched porous structure according to any one of claims 1 to 3, wherein the vinyl aromatic elastomer (B) has a melt flow rate (MFR) of 2.0 g/10 minutes or less at a temperature of 230°C and a load of 2.16 kg. the film. The stretched porous film according to any one of claims 1 to 3, wherein the vinyl aromatic elastomer (B) does not flow when measured for melt flow rate (MFR) at a temperature of 230°C and a load of 2.16 kg. The stretched porous film according to any one of claims 1 to 5 , which has a porosity of 50% or more. The stretched porous film according to any one of claims 1 to 6 , which has an air permeability of 50 sec/100 cc or less. The stretched porous film according to any one of claims 1 to 7, wherein the elution amount of the antioxidant is 1450 ppm or less. A filter comprising the stretched porous film according to any one of claims 1 to 8 .