JP2018001450A - Laminated porous film and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stretched porous film which has a structure with a large number of porosities having high air permeability and high porosity ratios, and is excellent in filtration performances such as filtration velocity, filtration accuracy and a filtration life, in particular to provide a filtration membrane which can be used for auto industry (electrodeposition paint-recovering-and-reusing system), semiconductor industry (ultrapure water production), pharmaceutical and food industry (disinfection, enzyme refining), etc.SOLUTION: A laminated porous film is provided which has an I layer and an II layer that satisfy the relation of formula (1): 2≤N/N≤50, and in which each of the I layer and the II layer is a porous layer composed of an olefin polymer (A) and a vinyl aromatic elastomer, respectively. (in the formula (1), Nand Nare each an abundance ratio of a porosity whose pore size in a major axis direction is 5-100 μm, in cross-sections of I layer and II layer).SELECTED DRAWING: None

Description

  The present invention relates to a laminated porous film, and the porous film can be used as a packaging product, sanitary product, livestock product, agricultural product, building product, medical product, light diffusing plate, reflective sheet, battery separator, or separation membrane, particularly food. It is suitably used as a filtration membrane used in related fields, pharmaceutical / cosmetic fields, chemical industry fields, and electronics industry fields. Furthermore, this invention relates to the manufacturing method of this laminated porous film.

Filtration with porous membranes such as microfiltration membranes and ultrafiltration membranes is used in the automobile industry (electrodeposition paint recovery and reuse system), semiconductor industry (ultra pure water production), pharmaceutical food industry (sanitization, enzyme purification), etc. It has been put to practical use in many fields. In particular, in recent years, it has been widely used as a method for producing river water and the like to turbidity and to produce drinking water and industrial water. A wide variety of materials such as cellulose, polyacrylonitrile, and polyolefin are used as the material of the membrane.
Among them, polyolefin polymers (polyethylene, polypropylene, polyvinylidene fluoride, etc.) are suitable as a material for aqueous filtration membranes because they are hydrophobic and have high water resistance, and are widely used.

Patent Document 1 discloses that a film obtained by melt extrusion molding a polyolefin resin composition containing a filler such as calcium carbonate and talc is uniaxially stretched for clothing, packaging, battery separator, and filter material. It is disclosed that a porous film excellent in flexibility suitable for use as a material for medical use or medical use, particularly as a packaging or medical use material can be obtained.
However, due to the non-uniform shape of the filler and poor compatibility with the resin, the porous film cannot be expected to have uniform physical properties, or the surface is not smooth, and irregularities occur. there were. In addition, these fillers have poor chemical resistance and may be eluted in an acid such as acetic acid, for example, so that there is a limit to applications.

In Patent Document 2, it is required for sterilization by stretching in a biaxial direction having a sea-island structure composed of a sea part containing polypropylene resin as a main component and an island part containing polyolefin / polystyrene elastomer as a main component. In blister packs and other packaging bodies that have uniform high-water-vapor-permeability holes with uniform appearance and have sufficient piercing strength to wrap sharp objects such as injection needles and catheters It is disclosed that a microporous film useful for a lid or the like can be obtained.
However, Patent Document 2 does not describe a usage method as a filtration membrane, and it is unclear how much performance is exhibited when used as a filtration membrane.

JP-A-60-229731 JP 2014-101445 A

  An object of the present invention is to provide a stretched porous film having a large number of porous structures with high air permeability and porosity, and excellent filtration performance such as filtration speed, filtration accuracy, and filtration life, particularly in the automobile industry (electrodeposition paint). The purpose of the present invention is to provide a filtration membrane that can be used in the collection and reuse system), the semiconductor industry (ultra pure water production), the pharmaceutical food industry (sanitization, enzyme purification), and the like.

  As a result of intensive 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 I layer and the II layer satisfying the relationship of the formula (1) are provided, and the I layer and the II layer are porous layers made of the olefin polymer (A) and the vinyl aromatic elastomer, respectively. There is provided a laminated porous film characterized in that: Formula (1): 2 ≦ N ₂ / N ₁ ≦ 50
(N ₁ and N ₂ represent the abundance ratio of holes having a major axis diameter of 5 to 100 μm in the cross sections of the I layer and the II layer, respectively)

  According to a second invention, there is provided a laminated porous film according to the first invention, which has a three-layer structure having the I layer as an intermediate layer and the II layer on the front and back surfaces.

  Furthermore, according to the third invention, there is provided a laminated porous film according to the first or second invention, wherein the thickness is 1 μm or more and 1000 μm or less, and the air permeability is 1-1000 seconds / 100 cc. Is done.

  Moreover, according to 4th invention, the laminated porous film characterized by being a biaxially stretched film in any one of 1st-3rd invention is provided.

  Furthermore, according to 5th invention, the layer which consists of an olefin polymer (A) and a styrene-olefin block copolymer (B), and an olefin polymer (A) and a styrene-olefin-styrene block copolymer ( An unstretched film having at least one layer composed of C) is prepared and stretched, and a method for producing a laminated porous film is provided.

  According to a sixth invention, in the fifth invention, the unstretched film is stretched 1.1 times or more and less than 3.0 times in the longitudinal direction at a temperature of 0 ° C. to 60 ° C. The film is stretched by 1.5 times or more and less than 6.0 times in the longitudinal direction at a temperature of 160 ° C, and is stretched by 1.1 to 10 times in the transverse direction at a temperature of 70 to 150 ° C. The manufacturing method of the laminated porous film of 5 is provided.

  Furthermore, according to the seventh invention, in the fifth or sixth invention, the styrene-olefin block copolymer (B) has a melt flow rate at 230 ° C. and a load of 2.16 kg of 1.0 g / 10 min or less. There is provided a method for producing a laminated porous film.

According to an eighth invention, in any of the fifth to seventh inventions, the styrene-olefin-styrene block copolymer (C) has a melt flow rate of 1.0 g at 230 ° C. and a load of 2.16 kg. The manufacturing method of the laminated porous film characterized by being / 10 minutes or less is provided.
According to 9th invention, the filter using the said laminated porous film in the invention in any one of 1-4 is provided.

  The stretched porous film of the present invention has a large number of porous structures having high air permeability and porosity, and is excellent in filtration performance such as filtration speed, filtration accuracy, and filtration life, especially in the automobile industry (recovery of electrodeposition paint). It is useful as a filtration membrane that can be used in the recycling system), semiconductor industry (ultra pure water production), pharmaceutical food industry (sanitization, enzyme purification) and the like.

It is an observation photograph of the cross section of the porous film produced in Example 1 by a scanning electron microscope.

  The present invention will be described in detail below. However, the contents of the present invention are not limited to the embodiments described below.

1. Laminated porous film A laminated porous film according to an example of an embodiment of the present invention (hereinafter sometimes referred to as “the present film”) has an I layer and an II layer satisfying the relationship of formula (1), Each of the II layers is a laminated porous film that is a porous layer having an olefin polymer and a vinyl aromatic elastomer.
Formula (1): 2 ≦ N ₂ / N ₁ ≦ 50
(N ₁ and N ₂ represent the abundance ratio of 5 to 100 μm holes in the cross sections of the I layer and the II layer, respectively)

This film has I layer and II layer which satisfy | fill Formula (1).
Formula (1): 2 ≦ N ₂ / N ₁ ≦ 50
(N ₁ and N ₂ represent the abundance ratio of 5 to 100 μm holes in the cross sections of the I layer and the II layer, respectively)

N ₂ / N ₁ is 2 or more, preferably 3 or more, more preferably 5 or more. On the other hand, the lower limit is 50 or less, preferably 40 or less, more preferably 20 or less. When N ₂ / N ₁ is 2 or more, excellent filtration accuracy can be imparted, and when it is 50 or less, excellent filtration rate and filtration life can be imparted.

The abundance ratio (N) of 5 to 100 μm pores is measured by the following method.
Using a scanning electron microscope (SEM) (“S-4500, manufactured by Hitachi High-Technologies Corporation”), it was visually confirmed from the cross-sectional image of the porous film that layers with different holes were formed, and the holes were different. When layers are formed, the length of each hole in the major axis direction is measured by image processing using image analysis software “SPIP (version 6.2.8)” manufactured by Image Metrology Co., Ltd. The abundance ratio of pores having a major axis diameter of 5 to 100 μm is calculated from the following formula.
Presence ratio [N] of holes having a hole diameter of 5 to 100 μm in the major axis direction in each layer =
(Number of 5-100 μm holes in each layer / number of 5-100 μm holes in all layers) × 100

(1) Thickness The thickness of the laminated porous film of the present invention is not particularly limited, but is preferably 25 μm or more, and more preferably 50 μm or more. On the other hand, the upper limit is preferably 500 μm or less, and more preferably 300 μm or less. If thickness is 25 micrometers or more, it can have sufficient intensity | strength. Moreover, if thickness is 500 micrometers or less, use is easy also for the use for which size reduction and weight reduction are calculated | required.

(2) Air permeability The air permeability of the laminated porous film of the present invention is preferably 1 second / 100 cc or more, more preferably 5 seconds / 100 cc or more, and further 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 further preferably 30 seconds / 100 cc or less. If the air permeability is in 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 at 25 ° C.

(3) Porosity The porosity is an important factor for defining the 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. Generally, it is 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, and more preferably 95% or less. When the porosity is 50% or more, a porous film having excellent porosity is obtained.
In addition, the porosity is measured based on the following formula based on the following formula 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. .
Porosity [%] = {(W0−W1) / W0} × 100

(4) Filtration rate The filtration rate of the stretched porous film of the present invention is preferably 23 ml / min · cm ² or more, more preferably 24 ml / min · cm ² or more, and further preferably 25 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 still more preferably 80 ml / min · cm ² or less. When the filtration rate is in the above range, a porous film having both strength and filtration efficiency is obtained.
The filtration rate is calculated based on the following equation by measuring the time t during which a predetermined volume V of acetone passes through a porous film having an effective filtration area A under a pressure of 0.07 MPa in an air atmosphere at 25 ° C. The
Filtration rate [ml / min · cm ² ] = (V × 60) / (t × A)

(5) Filtration accuracy The filtration accuracy of the laminated porous film of the present invention is preferably 0.50 or less, more preferably 0.25 or less, and still more preferably 0.20 or less. When the filtration accuracy is in the above range, a porous film with good filtration accuracy is obtained.
The filtration accuracy is 4% by weight with colloidal silica (product name: Snowtex MP-4540M), average particle size: 450 nm, solid content: 40% by weight, medium: water) manufactured by Nissan Chemical Co., Ltd. After diluting and dispersing sufficiently in an ultrasonic stirrer, the porous film is passed at a pressure of 0.07 MPa, the concentration of the liquid before and after passing is measured by the absorbance method, and the particle collection efficiency (%) is measured. Produced by seeking.

(6) Filtration life The filtration life of the laminated porous film of the present invention is preferably 1.0 g / cm ² or more, more preferably 1.1 g / cm ² or more, and further preferably 1.2 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 still more preferably 2.0 g / cm ² or less. When the filtration rate is in the above range, a porous film having good filtration efficiency is obtained.
The filtration life is 4% by weight with colloidal silica (product name: Snowtex MP-4540M), average particle size: 450 nm, solid content: 40% by weight, medium: water) manufactured by Nissan Chemical Co., Ltd. After diluting and sufficiently uniformly dispersing in an ultrasonic stirrer, the porous film is passed at a pressure of 0.09 MPa, and the weight W of the liquid that has passed before the filtration becomes impossible is measured. The filtration life (g / cm ² ) is calculated by dividing by.

The configuration of the laminated porous film of the present invention is not particularly limited, and may be not only a two-layer configuration but also a multilayer configuration of three layers, four layers, five layers, or more. In any layer configuration, if at least one layer corresponding to each of the I and II layers is provided, the filtration efficiency is excellent because the layered porous film has a large pore size distribution between the layers. Specifically, the laminated porous film satisfies the above filtration accuracy and filtration life range. Furthermore, if it is a porous film which not only has a layer corresponding to the I and II layers but also satisfies the above air permeability and / or porosity ranges, it will be a porous film having an excellent filtration rate.
By arranging the II layer having a large number of holes having a pore diameter of 5 to 100 μm in the major axis direction on the surface side of the I layer, while filtering, while capturing relatively large particles with the front and back layers, Since relatively small particles are captured by the intermediate layer, it is preferable because efficient filtration with excellent filtration speed, filtration accuracy, and filtration life can be performed.

In addition, a centrally symmetric structure that satisfies the relationship of II layer / I layer / II layer and I layer / II layer / I layer is preferable from the viewpoint of reducing the risk of environmental warping and twisting.
In particular, a layer having a small number of holes having a major axis direction diameter of 5 to 100 μm in the intermediate layer, such as II layer / I layer / II layer, and a major axis direction pore diameter of 5 to 100 μm in the front and back layers. By arranging a layer with a large number of pores, when filtration is performed, relatively large particles are captured by the front and back layers, while relatively small particles are captured by the intermediate layer. And efficient filtration can be performed.

The thickness ratio (laminate ratio) of each layer of the laminated porous film of the present invention is not particularly limited.
In particular, in the case of a two-layer / three-layer configuration of II layer / I layer / II layer, the lamination ratio of the I layer with respect to the total thickness is preferably 10% or more and 80% or less, more preferably 15% or more and 75% or less, More preferably, it is 20% or more and 70% or less. If the thickness ratio of the I layer is 10% or more, the film of the present invention preferably has good filtration accuracy. Moreover, it is preferable if the thickness of the I layer is 80% or less because it has a good filtration rate. Here, when a plurality of I layers are arranged, the total thickness of each layer is used for calculation.

  Since this film should just be equipped with the said structure, you may further provide the other layer.

  Hereinafter, the porous layer which comprises this film is demonstrated. Then, the formation method of the said laminated porous film as a manufacturing method is demonstrated.

2. Porous layer The porous layer constituting the laminated porous film of the present invention is a layer (I layer) having a small number of holes having a major axis direction diameter of 5 to 100 μm and a major axis direction pore diameter of 5 to 100 μm. It has at least two porous layers of a layer having a large number of pores (II layer). Each porous layer has an olefin polymer and a vinyl aromatic elastomer.

<Olefin polymer>
The olefin polymer is a polymer that forms a sea phase in the laminated porous film of the present invention. Examples of the component of the film imparted with porosity by stretching include one or two or more polymers selected from the group of olefin polymers from the viewpoints of cost, solvent resistance, and heat resistance.

The olefin polymer (A) is preferably a polymer composed of an aliphatic hydrocarbon monomer from the viewpoint of compatibility with the styrene-olefin block copolymer (B) described later.
Examples of the olefin polymer (A) include ethylene homopolymer (homopolyethylene); ethylene and 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene or 1-decene. An ethylene polymer such as a copolymer of propylene; a propylene homopolymer (homopolypropylene); propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene or 1-decene And a propylene polymer such as a propylene copolymer obtained by copolymerization. Among these, a propylene polymer is suitably 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%, and 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 defined by the upper limit that can be obtained industrially at present, but this is not the case when a more regular resin is developed in the industrial level in the future. is not. The isotactic pentad fraction is a three-dimensional structure in which five methyl groups that are side chains are located in the same direction with respect to the main chain of carbon-carbon bonds composed of arbitrary five consecutive propylene units. Or the ratio is meant.
Signal assignment of the methyl group region is as follows. Zambelliet at al. (Macromol. 8, 687 (1975)).

In the propylene 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 still 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 extrudability can be obtained and industrial mass production is possible. On the other hand, by setting Mw / Mn to 10.0 or less, sufficient mechanical strength can be ensured.
Mw / Mn is obtained by GPC (gel per emission 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, more preferably 1.0 or more. On the other hand, the upper limit is preferably 15 g / 10 min or less, and more preferably 10 g / 10 min or less. By setting the MFR to 0.5 g / 10 min or more, it has a sufficient melt viscosity at the time of molding and can ensure high productivity. On the other hand, when the MFR is 15 g / 10 min or less, sufficient strength can be obtained.
MFR is measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  Examples of the propylene polymer include “Novatech PP” “WINTEC” (manufactured by Nippon Polypro Co., Ltd.), “Notio” “Toughmer XR” (manufactured by Mitsui Chemicals), “Zeras” “Thermolan” (manufactured by Mitsubishi Chemical Corporation). “Sumitomo Noblen” “Tufselen” (manufactured by Sumitomo Chemical Co., Ltd.), “Prime PP” “Prime TPO” (manufactured by Prime Polymer), “Adflex” “Adsyl” “HMS-PP (PF814)” (manufactured by Sun Aroma), Commercially available products such as “Versify” and “Inspire” (Dow Chemical) can be used.

On the other hand, in the case of an ethylene polymer, Mw / Mn, which is a parameter indicating a 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 still 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 extrudability can be obtained and industrial mass production is possible. On the other hand, by setting Mw / Mn to 10.0 or less, sufficient mechanical strength can be ensured.
Mw / Mn is obtained by GPC (gel per emission chromatography) method.

Further, the melt flow rate (MFR) of the ethylene polymer is not particularly limited, but usually the MFR is preferably 0.5 or more, more preferably 1.0 or more. On the other hand, the upper limit is preferably 15 g / 10 min or less, and more preferably 10 g / 10 min or less. By setting the MFR to 0.5 g / 10 min or more, it has a sufficient melt viscosity at the time of molding and can ensure high productivity. On the other hand, when the MFR is 15 g / 10 min or less, sufficient strength can be obtained.
MFR is measured under the conditions of a temperature of 190 ° C. and a load of 2.16 kg in accordance with JIS K7210.
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 target porous structure can be satisfied. On the other hand, if the density exceeds 0.970, the crystallinity is too high and stretching unevenness is likely to occur.
The density is measured according to JIS K7112.

  Examples of the ethylene polymer include “Novatech LD”, “Novatech LL”, “Novatech HDPE” (manufactured by Nippon Polyethylene Co., Ltd.), “Hi-Zex”, “Evolu H” (manufactured by Prime Polymer), “Nipolon-L”, “Petrocene”. "" Nipolon Hard (manufactured by Tosoh Corporation) and other commercially available products can be used.

<Vinyl aromatic elastomer>
The vinyl aromatic elastomer is a polymer that forms an island phase in the laminated porous film of the present invention. The vinyl aromatic elastomer contained in the I layer and the II layer is not particularly limited, but the vinyl aromatic elastomer contained in the I layer is selected to have a relatively high compatibility with the olefin polymer and a small island phase. It is. On the other hand, the vinyl aromatic elastomer contained in the II layer is selected to have a relatively low compatibility with the olefin polymer and a large island phase.

  The vinyl aromatic elastomer constituting the I layer is preferably a styrene-olefin block copolymer (B) because of its relatively low compatibility with the olefin polymer. By selecting the styrene-olefin block copolymer (B) as the resin constituting the I layer, 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) used in the present invention is a kind of thermoplastic elastomer based on a styrene component, and a polystyrene block (hard segment) which is a hard component and a polyolefin structure which is a soft component. And a block copolymer having a hard segment at one end of the 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) at a temperature of 230 ° C. and a load of 2.16 kg, preferably 1.0 g / 10 min or less, more preferably 0.5 g. / 10 minutes or less, more preferably 0.1 g / 10 minutes or less. When formed into a sheet shape, the dispersed styrene-olefin block copolymer (B) changes its shape due to the difference in viscosity from the resin, but if it is of MFR within the above range, its shape is This is because it tends to be spherical. Unlike the domain having a large aspect ratio, the 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. Furthermore, when the MFR is within the above range, stress tends to concentrate on the matrix interface having a high modulus of elasticity and the domain interface of a low modulus of elasticity during the stretching process, so that an opening start point is likely to be generated and porosity is likely to occur. It has the characteristics.
MFR is measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  In the styrene-olefin block copolymer (B) in the present invention, the content of the styrene structural unit is preferably 1 to 40% by weight, and more preferably 10% to 35% by weight. When the styrene content in the styrene-olefin block copolymer (B) is 1% by weight or more, domains 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.

  Although the specific kind of the styrene-olefin block copolymer (B) is not particularly limited, the styrene-butadiene block copolymer (SBR); the hydrogenated styrene-butadiene block copolymer (SEB); the styrene-isoprene. Block copolymer (SIR); styrene- (ethylene / propylene) block copolymer (SEP) and the like.

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

  In the film concerning this invention, the 1 type (s) or 2 or more types of copolymer chosen from the group of a styrene olefin block copolymer (B) may be included.

  As the vinyl aromatic elastomer constituting the II layer, a styrene-olefin-styrene block copolymer (C) is selected because of its relatively high compatibility with the olefin polymer. Since the styrene-olefin block copolymer (B) and the styrene-olefin-styrene block copolymer (C) have different compatibility with each olefin polymer (A), an unstretched sheet having a large distribution of dispersion diameters is used. can get. As a result, by stretching the unstretched sheet, a porous film having a large aperture ratio and pore size 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 one kind of thermoplastic elastomer based on a styrene component, and a polystyrene block (hard segment) which is a hard component and a polyolefin structure which is a soft component. It is a copolymer having an elastomer block (soft segment) and a block polymer having hard segments at both ends of the polymer chain.

The styrene-olefin-styrene block copolymer (C) used in the present invention is preferably 1.0 g / 10 min or less, more preferably 0.5 g / 10 min or less, still more preferably 0.1 g / 10 min or less. It is preferable that This is because the shape of the styrene-olefin-styrene block copolymer (C) changes depending on the difference in viscosity from the resin, but if it is of MFR within the above range, the shape tends to be spherical. Unlike the domain having a large aspect ratio, the 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. Furthermore, when the MFR is within the above range, stress tends to concentrate on the matrix interface having a high modulus of elasticity and the domain interface of a low modulus of elasticity during the stretching process, so that an opening start point is likely to be generated and porosity is likely to occur. It has the characteristics.
MFR is measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  The styrene-olefin-styrene block copolymer (C) in the present invention preferably has a styrene content of 1 to 40% by weight, and more preferably 10% to 35% by weight. When the styrene content of the styrene-olefin-styrene block copolymer (C) is 1% by weight or more, domains can be effectively formed when molded into a sheet, and the styrene content is 40% by weight. By being below, it is preferable at the point which can suppress excessively big domain formation.

  The specific type of the styrene-olefin-styrene block copolymer (C) is not particularly limited, but styrene-butadiene-styrene block copolymer (SBS); styrene- (butadiene / butylene) -styrene block copolymer. 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.

  In order to efficiently disperse the styrene-olefin-styrene block copolymer (C) when formed into a sheet, among styrene-olefin-styrene block copolymers (C), styrene- (ethylene / propylene) -Styrene block copolymer (SEPS) and styrene- (ethylene / butadiene) -styrene block copolymer (SEBS) are preferred from the viewpoint of high compatibility with the olefin copolymer (A).

  In the film concerning this invention, the 1 type (s) or 2 or more types of copolymer chosen from the group of a styrene-olefin-styrene block copolymer (C) may be included.

3. Manufacturing method of laminated porous film The manufacturing method of the laminated porous film of the present invention will be described. The following description is an example of the method of manufacturing the laminated porous film of the present invention, and the laminated porous film of the present invention. Is not limited to the laminated resin porous film produced by such a production method.

  A method for producing a laminated porous film according to an example of an embodiment of the present invention (hereinafter sometimes referred to as the present film production method) comprises an olefin polymer (A) and a styrene-olefin block copolymer (B). An unstretched film having at least one layer and a layer composed of an olefin polymer (A) and a styrene-olefin-styrene block copolymer (C) is prepared (film forming process) and stretched (stretching process) ) A method for producing a laminated porous film.

  Since this film manufacturing method should just be equipped with the said process, it may be further equipped with the other process and process.

Hereinafter, the film forming process and the stretching process will be sequentially described.

<Film forming process>
The olefin polymer (A) and the styrene-olefin block copolymer (B), and the olefin polymer (A) and the styrene-olefin-styrene block copolymer (C) are mixed.
Olefin polymer (A) is mixed at a ratio of 55 to 85% by weight and vinyl aromatic elastomer at 15 to 45% by weight. Preferably, the proportion is 60 to 80% by weight of the olefin polymer (A) and 20 to 40% by weight of the vinyl aromatic elastomer.
When the olefin polymer is 85% by weight or less, porosity due to stretching tends to occur, and by forming a sufficient pore structure, an improvement in filtration performance can be expected. On the other hand, when the olefin polymer is 55% by weight or more, the subaromatic elastomers in the olefin polymer are less likely to agglomerate and easily 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, crystallization of the olefin polymer (A) is promoted, and the crystal structure is made uniform and dense. Therefore, the olefin polymer (A) in the unstretched sheet is composed of a crystal part that is densely homogenized and an amorphous part that exists between the crystal parts, and the vinyl aromatic elastomer is the olefin polymer (A). ) In the amorphous part. Therefore, the porosity that occurs at the interface between the dense crystalline portion of the olefin polymer (A) and the vinyl aromatic elastomer by stretching is facilitated by the improvement of the elastic modulus accompanying the crystallization of the matrix, and the crystalline density is increased. The uniform structure 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 β-crystal nucleating agent described below, but an α-crystal nucleating agent is preferable because a more uniform pore structure is formed.

  Examples of the α crystal nucleating agent include inorganic compounds such as talc, alum, silica, titanium oxide, calcium oxide, magnesium oxide, carbon black, clay mineral; malonic acid, succinic acid, adipic acid, maleic acid, azelaic acid, sebacin 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-cycl Aliphatic monocarboxylic acids such as hexane-1,2-dicarboxylic acid, benzoic acid, toluic acid, xylyl acid, ethyl benzoic acid, 4-t-butylbenzoic acid, salicylic acid, phthalic acid, trimellitic acid, pyromellitic acid Carboxylic acid to be removed; normal salt or basic salt of the non-aliphatic monocarboxylic acid such as lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, and aluminum; 1,2,3,4-dibenzylidene sorbitol, etc. Diphenylidene sorbitol compounds; aryl phosphate compounds such as lithium-bis (4-t-butylphenyl) phosphate; among the above-mentioned aryl phosphate compounds, cyclic polyvalent metal aryl phosphate compounds and acetic acid, lactic acid , Propionic acid, acrylic acid, octylic acid, Octylic 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, melicic acid Fatty acid monocarboxylic acid alkali metal salts such as lithium, sodium or potassium salts of fatty acid monocarboxylic acids such as stearoyl lactic acid, β-N-laurylaminopropionic acid, β-N-methyl-N-lauroylaminopropionic acid, or bases Mixtures with functional 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-di Methyl-1-pentene, poly-4,4-dimethyl-1-hexene, poly-4-ethyl-1-hexene, poly-3-ethyl-1-hexene, polyallylnaphthalene, polyallylnorbornane, atactic polystyrene, syndiotactic Examples thereof include high molecular compounds such as polystyrene, polydimethylstyrene, polyvinyl naphthalene, polyallylbenzene, polyallyltoluene, polyvinylcyclopentane, polyvinylcyclohexane, polyvinylcyclopeptane, polyvinyltrimethylsilane, and polyallyltrimethylsilane.

  Specific examples of commercially available α crystal nucleating agents include “Gelall D” series, “Gelall MD” series manufactured by Shin Nippon Rika Co., Ltd., “NA” series manufactured by ADEKA, “Millad” series manufactured by Milliken Chemical, “Hyperform”. ”Series,“ IRGACLEAR ”series manufactured by BASF, and the like.

  Examples of the β crystal nucleating agent include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, etc. Alkali or alkaline earth metal salts of carboxylic acids represented by: aromatic sulfonic acid compounds represented by sodium benzenesulfonate or sodium naphthalenesulfonate; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanine blue Phthalocyanine pigments typified by: a two-component compound comprising component A which is an organic dibasic acid and a component B which is an oxide, hydroxide or salt of a Group IIA metal of the periodic table; a cyclic phosphorus compound; Made of magnesium compound Such as the formation thereof.

  Specific examples of commercially available β crystal nucleating agents include β crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd., and specific examples of propylene polymers to which β crystal nucleating agents are added include Aristech. Examples include polypropylene “Bepol B-022SP”, Borealis polypropylene “Beta (β) -PP BE60-7032,” Mayzo polypropylene “BNX BETAPP-LN”, and the like.

In this invention, in the range which does not impair the effect of this invention, except said olefin polymer (A), styrene-olefin block copolymer (B), and styrene-olefin-styrene block copolymer (C). It is permissible to mix other components than the olefin polymer (A).
Other resins include polystyrene resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polyester resins, polycarbonate resins, polyamide resins, polyacetal resins, acrylic resins, ethylene acetate Vinyl copolymer, polymethylpentene resin, polyvinyl alcohol resin, cyclic olefin resin, polylactic acid resin, polybutylene succinate resin, polyacrylonitrile resin, polyethylene oxide resin, cellulose resin, polyimide resin , Polyurethane resin, polyphenylene sulfide resin, polyphenylene ether resin, polyvinyl acetal resin, polybutadiene resin, polybutene resin, polyamideimide resin, polyamide bismaleimide resin, Arylate resins, polyether imide resins, polyether ether ketone resin, polyether ketone resin, polyether sulfone resin, polyketone resin, polysulfone resin, aramid-based resin, fluorine-based resins.

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

  When mixing the olefin polymer (A) and the styrene-olefin block copolymer (B), the olefin polymer (A) and the styrene-olefin-styrene block copolymer (C), these raw materials are, for example, After pre-blending with a mixer such as a tumbler mixer or omni mixer, the resulting mixture can be prepared by extrusion kneading, if necessary.

  You may heat-dry each raw material with an oven, a vacuum dryer, etc. separately or in the mixed state, respectively. In drying, it is preferable to set the conditions such that the components do not deteriorate or melt.

  When kneading, the machine to be used 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 pressure reducer may be connected to the vent port to remove moisture and low molecular weight substances.

  Examples of methods for heating and melting the resin mixture kneaded as described above include a T-die method and an inflation method, and it is preferable to employ the T-die method. Practically, it is preferable that the material resin is melt-extruded from a T-die and cast by a cast roll.

  When a T-die method is adopted as a specific method for forming a film into a sheet, while laminating sheet-like molten resins respectively extruded from the T-die, and in close contact with a rotating cast roll (chill roll, cast drum) The method of shape | molding in a take-off sheet-like material can be mentioned.

  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 set to a low temperature, electrical contact 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 and 800 μm or less, and particularly preferably 100 μm or more or 600 μm or less.
If the thickness of the unstretched sheet is 30 μm or more, the sheet is too thin to prevent breakage during stretching. If the thickness of the unstretched sheet is 1000 μm or less, the sheet becomes too rigid. Thus, it is possible not only to prevent the stretching from becoming difficult, but also to reduce the thickness of the sheet after stretching.

  In the unstretched sheet, the ratio of the thickness of each layer (lamination ratio) is not particularly limited, but in the case of a two-layer / three-layer configuration of II layer / I layer / II layer, the total thickness The lamination ratio of the I layer is preferably 10% or more and 80% or less, more preferably 15% or more and 75% or less, and further preferably 20% or more and 70% or less. If the thickness ratio of the I layer is 10% or more, the film of the present invention preferably has good filtration accuracy. Moreover, it is preferable if the thickness of the I layer is 80% or less because it has a good filtration rate. Here, when a plurality of I layers are arranged, the total thickness of each layer is used for calculation.

<Extension process>
Hereafter, the process of extending | stretching the said unstretched sheet and obtaining a laminated porous film is explained in full detail.
The obtained unstretched sheet is uniaxially stretched or biaxially stretched. Uniaxial stretching may be longitudinal uniaxial stretching or transverse uniaxial stretching. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. It is one advantage of the present invention that the thickness, air permeability, and porosity of the laminated porous film to be produced can be adjusted by changing the composition, thickness, and draw ratio of the unstretched sheet. In the case of producing a laminated porous film which is the object of the present invention, it is more preferable to use sequential biaxial stretching in which stretching conditions can be selected in each stretching step and the porous structure can be easily controlled. In addition, extending | stretching to the flow direction (MD) of a film-like thing is called "longitudinal extending | stretching", and extending | stretching to a perpendicular | vertical direction (TD) with respect to a flow direction is called "lateral extending | stretching." The lateral stretching is preferably performed by utilizing the speed difference between a pair of drive rolls serving as stretching sections, but is not limited thereto. On the other hand, it is preferable to use a clip type tenter for the apparatus used for transverse stretching. However, the present invention is not limited to this.

The manufacturing method of the extending | stretching porous film which concerns on an example of embodiment of this invention extends | stretches the said unstretched sheet | seat by 1.1 times or more and less than 3.0 times in the vertical direction at the temperature of 0 to 60 degreeC, and 60 degreeC. It is a method of stretching at a temperature of ˜160 ° C. in the longitudinal direction at 1.5 times or more and less than 6.0 times, and stretching at a temperature of 70 to 150 ° C. in the transverse direction at 1.1 times or more and less than 10 times. Details will be described below.

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

  Next, the stretched sheet obtained above is preferably 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 a range of 1.5 times or more and less than 5.0 times. When stretched below 60 ° C, the film tends to break, and when stretched at a temperature exceeding 160 ° C, the resulting stretched film tends to have low porosity and high air permeability. Moreover, it is preferable to extend | stretch 2 steps or more on the above conditions from a viewpoint of the physical property requested | required of the porous film of this Embodiment, or an application. If the stretching process is one stage, the stretched film obtained 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 still more preferably 1 .5 times or more and less than 10 times. By setting the draw ratio per uniaxial drawing to 1.1 times or more, whitening has progressed, suggesting that porosity due to stretching has occurred sufficiently. Moreover, by making it less than 15 times, the deformation | transformation of a void | hole is suppressed and the fully whitened porous film can be obtained.

As described above, it is preferable to use a clip type tenter as an apparatus used when performing transverse stretching. The clip type tenter includes a clip traveling device for transverse stretching and an oven.
The clip traveling device grips and conveys both ends of the longitudinally stretched sheet with a pair of clips, and at the same time, the guide rail of the grip traveling device opens to extend 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 and heated to a temperature at which the longitudinally stretched sheet can be stretched, stretched in the stretching zone, and after stretching, a heat treatment zone is provided as necessary to perform heat treatment. A slow cooling zone is provided before exposure.

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

  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, and further preferably 2.0 times or more and 8.0 times. Is less than. By stretching at a prescribed transverse stretching ratio, it is possible to have a sufficient porosity without deforming 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 obtained efficiently, and the production cost can be suppressed. On the other hand, if it is 20000% / min or less, the occurrence of sheet breakage or the like can be suppressed. it can.

<Explanation of terms>
“Sheet” generally refers to a product that is thin by definition in JIS and generally has a thickness that is small and flat for the length and width. In general, “film” is compared to the length and width. A thin flat product with an extremely small thickness and an arbitrarily limited maximum thickness, usually supplied in the form of a roll (Japanese Industrial Standard JIS K6900). For example, in terms of thickness, in the narrow sense, a film having a thickness of 100 μm or more is sometimes referred to as a sheet, and a film having a thickness of less than 100 μm is sometimes referred to as a film. However, the boundary between the sheet and the film is not clear, and it is not necessary to distinguish the two in terms of the present invention. Therefore, in the present invention, even when the term “sheet” is used, the term “film” is included, and the term “film” is used. Even in this case, “sheet” is included.

In the present invention, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” and “preferably Y”, with the meaning of “X to Y” unless otherwise specified. It means “smaller”.
Further, in the present invention, when expressed as “X or more” (X is an arbitrary number), it means “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, although an Example and a comparative example are shown and this porous body is demonstrated in detail, this invention is not limited to these. In addition, as an embodiment of the present porous body, it was shaped into a film. In addition, the film take-up (flow) direction is described as “MD”, and the perpendicular direction thereof as “TD”.

(Olefin polymer (A))
A-1: Homopolypropylene (MFR: 1.9 g / 10 min, Mw / Mn = 3.2)

(Styrene-olefin block copolymer (B))
B-1: Styrenic thermoplastic elastomer (styrene- (ethylene / propylene) copolymer (SEP), MFR (230 ° C., 2.16 kg): 0.1 g / 10 min, styrene content: 35 mass%)

(Styrene-olefin-styrene block copolymer (C))
C-1: Styrenic thermoplastic elastomer (styrene- (ethylene / propylene) -styrene block copolymer (SEPS), MFR (230 ° C., 2.16 kg): not flowing, styrene content: 20% by mass)

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

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

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

(3) Porosity A substantial amount W1 of the obtained porous film is measured, and a mass W0 in the case of a porosity of 0% is calculated from the density and thickness of the resin composition, and calculated based on the following formula from those values. did.
Porosity [%] = {(W0−W1) / W0} × 100

(4) Filtration rate In an air atmosphere at 25 ° C., the time t during 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 was measured and calculated based on the following formula.
Filtration rate [ml / min · cm ² ] = (V × 60) / (t × A)

(5) Filtration accuracy test Colloidal silica (product name: Snowtex MP-4540M) manufactured by Nissan Chemical Co., Ltd., average particle size: 450 nm, solid content: 40% by mass, medium: water) with water so as to be 4% by mass. Dilute and disperse sufficiently in an ultrasonic stirrer, then pass through the porous film at a pressure of 0.07 MPa, measure the concentration of the liquid before and after passage by the absorbance method, and collect the particles (%) Was calculated.

(6) Filtration life Colloidal silica (product name: Snowtex MP-4540M) manufactured by Nissan Chemical Co., Ltd., average particle size: 450 nm, solid content: 40% by mass, medium: water) diluted with water to 4% by mass Then, after being sufficiently uniformly dispersed in an ultrasonic stirrer, the porous film is passed at a pressure of 0.09 MPa, and the mass W of the liquid that has passed before filtration becomes impossible is measured. The filtration life (g / cm ² ) was calculated by dividing.

(7) Calculation of the number of holes in each layer
With a scanning electron microscope (SEM) (“S-4500 manufactured by Hitachi High-Technologies Corporation”), it was visually confirmed that layers having different pores were formed from the cross-sectional image of the porous film. When layers with different holes are formed, after measuring the length in the long axis direction of each hole by image processing using Image Analysis Software “SPIP (version 6.2.8)” manufactured by Image Metrology The existence ratio of pores having a major axis direction pore diameter of 5 to 100 μm in each layer was calculated from the following equation.
Abundance ratio of pores having a major axis diameter of 5 to 100 μm in each layer =
(Number of 5-100 μm holes in each layer / number of 5-100 μm holes in all layers) × 100

[Example 1]
70% by mass of polypropylene (A-1), 30% by weight of styrene-olefin block copolymer (B-1), and the polypropylene (A-1) and the styrene-olefin block copolymer (B-1) The crystal nucleating agent (D-1) is blended at a ratio of 0.1 part by weight (0.14 part by weight with respect to 100 parts by weight of the polypropylene resin) with respect to 100 parts by weight of the mixed resin composition. The mixture is put into an extruder, melt-kneaded at a set temperature of 240 ° C., shaped into a strand with a strand die, cooled and solidified in a water bath, cut with a strand cutter, and pellets (hereinafter “pellet (I ) "). In the same manner, polypropylene (A-1) 70% by mass, styrene-olefin-styrene block copolymer (C-1) 30% by weight, and the propylene copolymer (A-1) and the styrene-olefin- 0.1 part by weight of the crystal nucleating agent (D-1) is added to 100 parts by weight of the mixed resin composition with the styrene block copolymer (C-1). By blending at a ratio of parts by weight, pellets (hereinafter referred to as “pellet (II)”) were produced.

  The prepared pellets were melt-mixed at 200 ° C. using a single screw extruder, and then the pellets (II) were put into the front and back layer side extruders and the pellets (I) were put into the middle layer side extruders with a lip opening of 1 mm. Using, co-extrusion molding at an extrusion temperature of 200 ° C. so that the thickness ratio of the lamination is surface layer / intermediate layer / back layer = 1/1/1, leading to a cast roll at 127 ° C. and unstretched lamination A sheet was obtained. Then, the obtained unstretched sheet is stretched at a low temperature by applying 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. went. Next, between the roll (P) set at 120 ° C. and the roll (Q) set at 120 ° C., a draw ratio of 50% (stretching ratio: 1.5 times) was applied to perform high-temperature stretching to obtain an MD stretched film. . Next, the obtained MD stretched porous film was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then stretched 3.0 times in the transverse direction at a stretching temperature of 145 ° C. Thereafter, 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. Moreover, the observation photograph of the film cross section by the scanning electron microscope of the obtained film is shown in FIG. From the film cross section, it can be seen that pores having different pore size distributions are generated between the surface layer and the intermediate layer and between the intermediate layer and the back layer.

(Example 2)
An unstretched sheet was obtained in the same manner as in Example 1 except that the thickness ratio of the laminated layers was set to surface layer / intermediate layer / back layer = 1/2/1. The obtained unstretched sheet was stretched at a low temperature by applying 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. . Next, between the roll (P) set at 120 ° C. and the roll (Q) set at 120 ° C., a draw ratio of 50% (stretching ratio: 1.5 times) was applied to perform high-temperature stretching to obtain an MD stretched film. . Next, the obtained MD stretched porous film was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then stretched 3.0 times in the transverse direction at a stretching temperature of 145 ° C. Thereafter, 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.

(Comparative Example 1)
Pellet (I) is put into a single screw extruder, melt kneaded at a set temperature of 200 ° C, shaped into a sheet with a T-die, cooled and solidified with a cast roll set at 127 ° C, and unstretched A sheet was obtained. Then, the obtained unstretched sheet is stretched at a low temperature by applying 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. went. Next, between the roll (P) set at 120 ° C. and the roll (Q) set at 120 ° C., a draw ratio of 50% (stretching ratio: 1.5 times) was applied to perform high-temperature stretching to obtain an MD stretched film. . Next, the obtained MD stretched porous film was preheated at a preheating temperature of 145 ° C. and a preheating time of 12 seconds in a film tenter facility manufactured by Kyoto Machine Co., Ltd., and then stretched 3.0 times in the transverse direction at a stretching temperature of 145 ° C. Thereafter, 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.

(Comparative Example 2)
Pellet (II) is put into a single screw extruder, melt kneaded at a set temperature of 200 ° C, shaped into a sheet with a T-die, cooled and solidified with a cast roll set at 127 ° C, and unstretched A sheet was obtained. Thereafter, the obtained unstretched sheet was stretched under the same conditions as in Comparative Example 1 to obtain a biaxially stretched porous film. The evaluation results of the obtained film are shown in Table 1.

In Examples 1 and 2, the abundance ratio of pores of 5 to 100 μm was surface layer / intermediate layer = 9, back layer / intermediate layer = 10 in Example 1, surface layer / intermediate layer = 8, back layer / intermediate in Example 2. Layer = 7, and it can be confirmed that layers having different pore sizes are clearly formed by each layer. In addition, a laminated porous film having a porosity of 60% or more and an air permeability of 30 sec / 100 cc or less and having a porous structure sufficient to obtain good air permeability is obtained. Recognize. As for filtration performance, the filtration rate is 25 ml / min · cm ² or more, the filtration accuracy is 0.00%, the filtration life is 1 g / cm ² or more, and particles are supplemented by the presence of large and small pore layers. On the other hand, a porous laminated film excellent in air permeability and filtration efficiency is obtained.

Comparative Example 1 cannot clearly confirm layers having different pore sizes and is not a laminated structure, but the air permeability is excellent as in the example and the filtration accuracy is 0.00%. Has been collected. However, since the filtration life is lower than that of the example, clogging is likely to occur when the filtration object is filtered, and the performance as a filtration filter is low.
In Comparative Example 2, layers having different hole sizes cannot be clearly confirmed, and the layered configuration is not achieved. Moreover, although the air permeation performance is superior to that of the examples, the filtration accuracy is 0.72%, and particles cannot be collected. Therefore, although the filtration speed and the filtration life are excellent, the filtration efficiency is inferior due to the collection leakage of particles.

  The laminated porous film of the present invention is an inexpensive porous film in which layers having a large number of pore structures having different pore diameters are laminated, and is excellent in air permeability performance and filtration performance. It is useful as a filtration membrane in the coating paint collection and reuse system), semiconductor industry (ultra pure water production), pharmaceutical food industry (sanitization, enzyme purification) and the like.

Claims (9)

A laminated porous film having an I layer and an II layer satisfying the relationship of formula (1), wherein each of the I layer and the II layer is a porous layer made of an olefin polymer (A) and a vinyl aromatic elastomer.
Formula (1): 2 ≦ N ₂ / N ₁ ≦ 50
(N ₁ and N ₂ represent the abundance ratio of holes having a major axis diameter of 5 to 100 μm in the cross sections of the I layer and the II layer, respectively)   The laminated porous film according to claim 1, which has a three-layer structure having the I layer as an intermediate layer and the II layer on the front and back surfaces.   3. The laminated porous film according to claim 1, wherein the laminated porous film has a thickness of 1 μm or more and 1000 μm or less and an air permeability of 1 to 1000 seconds / 100 cc. It is a biaxially stretched film, The laminated porous film in any one of Claims 1-3 characterized by the above-mentioned. At least one layer composed of an olefin polymer (A) and a styrene-olefin block copolymer (B), and a layer composed of an olefin polymer (A) and a styrene-olefin-styrene block copolymer (C). The manufacturing method of the laminated porous film characterized by producing the unstretched film which has each, and extending | stretching.   The unstretched film is stretched 1.1 times or more and less than 3.0 times in the machine direction at a temperature of 0 ° C. to 60 ° C., and 1.5 times or more and 6.0 in the machine direction at a temperature of 60 ° C. to 160 ° C. 6. The method for producing a laminated porous film according to claim 5, wherein the film is stretched at a temperature of 70 to 150 [deg.] C. and stretched at a temperature of 70 to 150 [deg.] C. in a transverse direction of 1.1 to 10 times.   The laminated porous film according to claim 5 or 6, wherein the styrene-olefin block copolymer (B) has a melt flow rate at 230 ° C and a load of 2.16 kg of 1.0 g / 10 min or less. Production method.   8. The melt flow rate at 230 ° C. and a load of 2.16 kg of the styrene-olefin-styrene block copolymer (C) is 1.0 g / 10 minutes or less. A method for producing a laminated porous film.   The filter using the microporous film in any one of Claims 1-4.

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