JP6651997B2 - Laminated porous film and method for producing the same - Google Patents

Description

  The present invention relates to a laminated porous film, and the porous film can be used as a packaging product, a sanitary product, a livestock product, an agricultural product, a construction product, a medical product, a light diffusion plate, a reflection sheet, a separator for a battery, or a separator, particularly a food product. It is suitably used as a filtration membrane used in the related fields, the pharmaceutical / cosmetic field, the chemical industry field, and the electronics industry field. Further, the present invention relates to a method for producing the laminated porous film.

Filtration operations using porous membranes such as microfiltration membranes and ultrafiltration membranes are used in the automobile industry (electrodeposition paint recovery and reuse system), the semiconductor industry (ultra pure water production), the pharmaceutical food industry (sterilization, enzyme purification), etc. It has been put to practical use in many fields. Particularly in recent years, it has been widely used as a method for producing drinking water and industrial water by turbidizing river water and the like. As the material of the membrane, various materials such as cellulose, polyacrylonitrile, and polyolefin are used.
Above all, polyolefin-based polymers (polyethylene, polypropylene, polyvinylidene fluoride, etc.) are suitable as a material for aqueous filtration membranes because they have high water resistance due to hydrophobicity and are widely used.

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

In Patent Document 2, it is required for sterilization by being stretched in a biaxial direction having a sea-island structure composed of a sea portion containing a polypropylene resin as a main component and an island portion containing a polyolefin / polystyrene-based elastomer as a main component. In a package such as a blister package or the like, which has a uniform communication hole having high water vapor permeability without unevenness in appearance, and has a sufficient piercing strength for packaging sharp objects such as injection needles and catheters. It is disclosed that a microporous film useful as a lid material or the like can be obtained.
However, Patent Literature 2 does not describe a method of using the membrane as a filtration membrane, and it is unclear to what extent the membrane shows performance 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 having high air permeability and porosity and having excellent filtration performance such as filtration speed, filtration accuracy, and filtration life, especially in the automotive industry (electrocoating paint). It is an object of the present invention to provide a filtration membrane which can be used in a semiconductor industry (production of ultrapure water), a pharmaceutical food industry (sterilization, enzyme purification), and the like.

  The present inventors have conducted intensive studies in view of the above-described circumstances, and as a result, have found that the above-mentioned problems can be solved, and have completed the present invention.

That is, according to the first invention, there are an I layer and an II layer satisfying the relationship of the formula (1), and the I layer and the II layer are each a porous layer made of the olefin polymer (A) and the vinyl aromatic elastomer. There is provided a laminated porous film characterized by the following formula (1): 2 ≦ N ₂ / N ₁ ≦ 50
(N ₁ and N ₂ represent the abundance ratio of pores having a pore diameter in the major axis direction 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 the laminated porous film according to the first invention, which has a three-layer structure having the I layer on the intermediate layer and the II layer on the front and back surfaces.

  Further, according to the third invention, there is provided the 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 to 1000 sec / 100 cc. Is done.

  According to a fourth invention, there is provided the laminated porous film according to any one of the first to third inventions, which is a biaxially stretched film.

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

  According to a sixth aspect, in the fifth aspect, the unstretched film is stretched in a longitudinal direction at a temperature of 0 ° C. to 60 ° C. by 1.1 times or more and less than 3.0 times, and The film is stretched at a temperature of 160 [deg.] C. in the longitudinal direction by 1.5 times or more and less than 6.0 times, and at a temperature of 70-150 [deg.] C. by a stretch of 1.1 times or more and less than 10 times. 5. A method for producing a laminated porous film according to item 5 is provided.

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

According to an eighth aspect, in any one of the fifth to seventh aspects, the styrene-olefin-styrene block copolymer (C) has a melt flow rate of 1.0 g at 230 ° C. under a load of 2.16 kg. / 10 minutes or less, a method for producing a laminated porous film is provided.
According to a ninth aspect, there is provided a filter using the laminated porous film according to any one of the first to fourth aspects.

  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. It is useful as a filtration membrane which can be used in the semiconductor industry (production of ultrapure water), the pharmaceutical food industry (sterilization, enzyme purification), and the like.

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

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

1. Laminated porous film The laminated porous film according to an example of the embodiment of the present invention (hereinafter, may be referred to as “the present film”) includes an I layer and a II layer satisfying the relationship of the formula (1), and Layer II is a laminated porous film which is a porous layer having an olefin polymer and a vinyl aromatic elastomer, respectively.
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 an I layer and a II layer satisfying the 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 provided, and when N ₂ / N ₁ is 50 or less, excellent filtration speed and filtration life can be provided.

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

(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, more preferably 300 μm or less. When the thickness is 25 μm or more, sufficient strength can be obtained. Further, if the thickness is 500 μm or less, it can be easily used for applications requiring miniaturization and weight reduction.

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

(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. In general, it is known that the higher the porosity, the better the filtration rate, and in the stretched porous film obtained by the production method of the present invention, the porosity is preferably 50% or more, more preferably. Is at least 60%, more preferably at least 65%. On the other hand, the upper limit is preferably 98% or less, more preferably 95% or less. When the porosity is 50% or more, a porous film having excellent porosity is obtained.
The porosity is measured by measuring the actual weight W1 of the porous film, calculating the weight W0 when the porosity is 0% from the density and the thickness of the resin composition, and calculating from these values based on the following equation. .
Porosity [%] = {(W0−W1) / W0} × 100

(4) Filtration speed The filtration speed 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 still more 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 speed is in the above range, a porous film having both strength and filtration efficiency is obtained.
The filtration speed is calculated based on the following equation by measuring the time t at which acetone having a predetermined volume V 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. You.
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 even more preferably 0.20 or less. When the filtration accuracy is in the above range, a porous film having good filtration accuracy is obtained.
The filtration accuracy was determined by using colloidal silica manufactured by Nissan Chemical Co., Ltd. (product name: Snowtex MP-4540M), average particle diameter: 450 nm, solid content: 40% by weight, medium: water) so as to become 4% by weight with water. After dilution and uniform dispersion in an ultrasonic stirrer, the mixture is passed through a porous film at a pressure of 0.07 MPa, and the concentration of the liquid before and after the passage is measured by an absorbance method. Produced by asking.

(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 still more 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 was determined by using 4% by weight of colloidal silica (product name: Snowtex MP-4540M, manufactured by Nissan Chemical Industries, Inc., average particle diameter: 450 nm, solid content: 40% by weight, medium: water) so as to be 4% by weight. After diluting and sufficiently dispersing uniformly in an ultrasonic stirrer, the mixture was passed through a porous film at a pressure of 0.09 MPa, and the weight W of the liquid that had passed until filtration became impossible was 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 three-layer, four-layer, five-layer or more multilayer configuration. Regardless of the layer configuration, if at least one layer corresponding to the I and II layers is provided, the filtration efficiency is excellent because the laminated porous film has a large pore size distribution between the layers. Specifically, it becomes a laminated porous film that satisfies the above-mentioned ranges of filtration accuracy and filtration life. Furthermore, a porous film which not only has the layers corresponding to the I and II layers but also satisfies the above-mentioned air permeability and / or porosity range is a porous film having an excellent filtration rate.
By arranging the II layer having a large number of pores having a long axis direction pore diameter of 5 to 100 μm on the surface side than the I layer, when filtering, while supplementing 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 can be performed with excellent filtration speed, filtration accuracy, and filtration life.

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

The ratio of the thickness of each layer (lamination ratio) of the laminated porous film of the present invention is not particularly limited.
In particular, in the case of a two-layer three-layer structure of II layer / I layer / II layer, the lamination ratio of the I layer to the total thickness is preferably 10% or more and 80% or less, more preferably 15% or more and 75% or less, 20% or more and 70% or less are more preferable. When the thickness ratio of the I layer is 10% or more, the film of the present invention has good filtration accuracy, which is preferable. Further, when the thickness of the I layer is 80% or less, it is preferable because a good filtration rate is obtained. Here, when a plurality of I layers are arranged, calculation is performed using the total thickness of each layer.

  The present film only needs to have the above configuration, and may further include another layer.

  Hereinafter, the porous layer constituting the present film will be described. Thereafter, a method for forming the laminated porous film as a production method will be described.

2. Porous layer The porous layer constituting the laminated porous film of the present invention has a layer (I layer) having a small number of pores having a long axis direction pore diameter of 5 to 100 μm in the film cross section and a long 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 (layer II). 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. As a component of the present film to which porosity has been imparted by stretching, one or two or more polymers selected from the group of olefin polymers from the viewpoint of cost, solvent resistance and heat resistance can be mentioned.

The olefin polymer (A) is preferably a polymer composed of an aliphatic hydrocarbon monomer in view of the 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. 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 with the like. Among them, a propylene polymer is preferably used from the viewpoint of heat resistance.

As the propylene polymer, one having an isotactic pentad fraction exhibiting stereoregularity of preferably 80 to 99%, more preferably 83 to 98%, and still more preferably 85 to 97% is used. . If the isotactic pentad fraction is too low, the mechanical strength may decrease. On the other hand, the upper limit of the isotactic pentad fraction is specified at the present time by the upper limit obtained industrially, but in the case where a resin with higher regularity is developed at the industrial level in the future, this limit is not. The isotactic pentad fraction is a steric structure in which all five methyl groups which are side chains with respect to the main chain formed by carbon-carbon bonds composed of any five consecutive propylene units are located in the same direction. Or it means the ratio.
Assignment of signals in the methyl group region is described in A. Zambelliet at al. (Based on Macromol. 8, 687 (1975).

The propylene polymer preferably has Mw / Mn, which is a parameter indicating a molecular weight distribution, of 1.5 or more, more preferably 2.0 or more. On the other hand, the upper limit is preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 6.0 or less. The smaller the Mw / Mn, the narrower the molecular weight distribution. However, by setting the Mw / Mn to 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 permeation chromatography).

The melt flow rate (MFR) of the propylene polymer is not particularly limited, but usually, the MFR is preferably 0.5 or more, and more preferably 1.0 or more. On the other hand, the upper limit is preferably 15 g / 10 minutes or less, more preferably 10 g / 10 minutes or less. When the MFR is 0.5 g / 10 minutes or more, a sufficient melt viscosity can be obtained at the time of molding and high productivity can be secured. On the other hand, when the MFR is 15 g / 10 minutes or less, sufficient strength can be obtained.
The 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 “Novatec PP” and “WINTEC” (manufactured by Nippon Polypropylene), “Natio” and “Tuffmer XR” (manufactured by Mitsui Chemicals), “Zeras” and “Thermolan” (manufactured by Mitsubishi Chemical). , "Sumitomo Noblen", "Tafselen" (Sumitomo Chemical), "Prime PP", "Prime TPO" (Prime Polymer), "Adflex", "Adsyl", "HMS-PP (PF814)" (Sun Allomer), 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, more preferably 2.0 or more. On the other hand, the upper limit is preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 6.0 or less. The smaller the Mw / Mn, the narrower the molecular weight distribution. However, by setting the Mw / Mn to 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 permeation chromatography).

Further, the melt flow rate (MFR) of the ethylene polymer is not particularly limited, but usually, the MFR is preferably 0.5 or more, and more preferably 1.0 or more. On the other hand, the upper limit is preferably 15 g / 10 minutes or less, more preferably 10 g / 10 minutes or less. When the MFR is 0.5 g / 10 minutes or more, a sufficient melt viscosity can be obtained at the time of molding and high productivity can be secured. On the other hand, when the MFR is 15 g / 10 minutes or less, sufficient strength can be obtained.
The MFR is measured at 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, more preferably 0.970 or less. When the density is 0.955 or more, the crystallinity of the porous film is increased, and the desired formation of the porous structure can be satisfied. On the other hand, if the density exceeds 0.970, the crystallinity is too high and stretching unevenness tends 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), “HIZEX”, “Evolu H” (manufactured by Prime Polymer), “Nipolon-L”, and “Petrocene”. Commercially available products such as Nipolon Hard (manufactured by Tosoh Corporation) 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 from those having relatively high compatibility with the olefin polymer and having a small island phase. It is. On the other hand, the vinyl aromatic elastomer contained in the layer II is selected to have 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 having a styrene component as a base material, and has a polystyrene block (hard segment) as a hard component and a polyolefin structure as a soft component. Is a block copolymer having a hard segment at one end of a polymer chain and a soft segment at the other end of the polymer chain.

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 of preferably 1.0 g / 10 min or less, more preferably 0.5 g or less. / 10 minutes or less, more preferably 0.1 g / 10 minutes or less. When molded into a sheet, the dispersed styrene-olefin block copolymer (B) changes its shape due to the difference in viscosity with the resin, but if it has an MFR within the above range, the shape is changed. This is because they tend to be spherical. Spherically dispersed domains are different from domains having a large aspect ratio, because the uniformity of the porous structure obtained by the subsequent stretching step is likely to be high and the physical properties are excellent in stability. Furthermore, when the MFR is within the above range, stress tends to concentrate on the interface between the matrix having a high elastic modulus and the domain having a low elastic modulus during the stretching step, so that the starting point of the hole is likely to occur and the porous body is easily formed. It has the feature of.
The MFR is measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

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

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

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

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

  As the vinyl aromatic elastomer constituting the II layer, a styrene-olefin-styrene block copolymer (C) is selected because it has 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 the respective olefin polymers (A), an unstretched sheet having a large distribution of the dispersion diameter can be obtained. can get. As a result, by stretching the unstretched sheet, a porous membrane having a large distribution of aperture ratio and pore diameter in the thickness direction can be obtained, and filtration efficiency can be improved.

  The styrene-olefin-styrene block copolymer (C) in the present invention is one kind of a thermoplastic elastomer having a styrene component as a base material, and has a polystyrene block (hard segment) as a hard component and a polyolefin structure as a soft component. Is a block polymer having hard segments at both ends of a polymer chain.

The styrene-olefin-styrene block copolymer (C) used in the present invention is preferably at most 1.0 g / 10 min, more preferably at most 0.5 g / 10 min, even more preferably at most 0.1 g / 10 min. It is preferred that This is because the shape of the styrene-olefin-styrene block copolymer (C) changes depending on the difference in viscosity with the resin, but if the styrene-olefin-styrene block copolymer has an MFR within the above range, the shape tends to be spherical. Spherically dispersed domains are different from domains having a large aspect ratio, because the uniformity of the porous structure obtained by the subsequent stretching step is likely to be high and the physical properties are excellent in stability. Furthermore, when the MFR is within the above range, stress tends to concentrate on the interface between the matrix having a high elastic modulus and the domain having a low elastic modulus during the stretching step, so that the starting point of the hole is likely to occur and the porous body is easily formed. It has the feature of.
The MFR is measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

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

  Although the specific type of the styrene-olefin-styrene block copolymer (C) is not particularly limited, 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, styrene- (ethylene / propylene) is preferred among the styrene-olefin-styrene block copolymers (C). Styrene block copolymer (SEPS) and styrene- (ethylene / butadiene) -styrene block copolymer (SEBS) are preferred because of high compatibility with olefin copolymer (A).

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

3. The method for producing the laminated porous film of the present invention will be described. The following description is an example of the method for producing the laminated porous film of the present invention, and the laminated porous film of the present invention is described below. 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 embodiment of the present invention (hereinafter, sometimes referred to as the present film production method) includes an olefin polymer (A) and a styrene-olefin block copolymer (B). A non-stretched film having at least one layer and at least one layer each composed of an olefin polymer (A) and a styrene-olefin-styrene block copolymer (C) is prepared (film-forming step) and stretched (stretching step) A) A method for producing a laminated porous film.

  The present film manufacturing method may include the above steps, and may further include other steps and processes.

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

<Film forming process>
The olefin polymer (A) and the styrene-olefin block copolymer (B), and further, the olefin polymer (A) and the styrene-olefin-styrene block copolymer (C) are mixed.
55-85% by weight of the olefin polymer (A) and 15-45% by weight of the vinyl aromatic elastomer are mixed. Preferably, the ratio 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 content is 85% by weight or less, porosity tends to be easily generated by stretching, and an improvement in filtration performance can be expected by forming a sufficient pore structure. On the other hand, when the content of the olefin polymer is 55% by weight or more, it is difficult for the vinyl aromatic elastomers in the olefin polymer to agglomerate with each other, so that the olefin polymer tends to be porous by stretching.

  In the present invention, it is preferable to further mix a nucleating agent (D). By mixing the crystal nucleating agent, the crystallization of the olefin polymer (A) is promoted, and the crystal structure becomes dense and uniform. Therefore, the olefin polymer (A) in the sheet before stretching is composed of dense and uniform crystal parts and an amorphous part existing between the crystal parts, and the vinyl aromatic elastomer is the olefin polymer (A). Many are present in the amorphous part of ()). Therefore, the porosity generated at the interface between the dense crystal part 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, By uniform homogenization, the resulting porous structure can easily form 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 based on 100 parts by weight of the olefin polymer (A).

  Examples of the crystal nucleating agent include the α crystal nucleating agent and the β crystal nucleating agent described below, but the α crystal nucleating agent is preferable because 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, and clay minerals; malonic acid, succinic acid, adipic acid, maleic acid, azelaic acid, sebacin Acid, dodecane diacid, 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 Aliphatic monocarboxylic acids such as hexane-1,2-dicarboxylic acid, benzoic acid, toluic acid, xylic acid, ethylbenzoic acid, 4-t-butylbenzoic acid, salicylic acid, phthalic acid, trimellitic acid, and pyromellitic acid. Excluding carboxylic acids; Normal or basic salts of the above-mentioned non-aliphatic monocarboxylic acids such as lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, and aluminum; 1,2,3,4-dibenzylidenesorbitol and the like A dibenzylidene sorbitol compound; an aryl phosphate compound such as lithium-bis (4-t-butylphenyl) phosphate; among the aryl phosphate compounds, a cyclic polyvalent metal aryl phosphate compound and acetic acid or 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 3-methyl-1-butene, poly-3-methyl-1-pentene, poly-3-ethyl-1-pentene, poly-4-methyl-1-pentene; mixtures with neutral aluminum lithium hydroxycarbonate hydrate , 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 Polymer 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 “Nippon Rika's“ Gelall D ”series,“ Gelall MD ”series, ADEKA's“ NA ”series, Milliken Chemical's“ Millad ”series, and“ Hyperform ”. "Series and" IRGACLEAR "series manufactured by BASF.

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

  Specific examples of commercially available β crystal nucleating agents include Nippon Rika's β crystal nucleating agent “NJESTA NU-100”, and specific examples of β crystal nucleating agent-added propylene polymers include Aristech Co., Ltd. Polypropylene "Bepol B-022SP", Borealis polypropylene "Beta (β) -PP BE60-7032", Mayzo polypropylene "BNX BETAPP-LN", and the like.

In the present invention, other than the olefin polymer (A), the styrene-olefin block copolymer (B), and the styrene-olefin-styrene block copolymer (C) as long as the effects of the present invention are not impaired. , For example, a resin other than the olefin polymer (A).
Other resins include polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride resin, chlorinated polyethylene resin, polyester resin, polycarbonate resin, polyamide resin, polyacetal resin, acrylic resin, and ethylene acetic acid. Vinyl copolymer, polymethylpentene resin, polyvinyl alcohol resin, cyclic olefin resin, polylactic acid resin, polybutylene succinate resin, polyacrylonitrile resin, polyethylene oxide resin, cellulose resin, polyimide resin , Polyurethane resin, polyphenylene sulfide resin, polyphenylene ether resin, polyvinyl acetal resin, polybutadiene resin, polybutene resin, polyamide imide 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 addition, in the present invention, in addition to the above-mentioned components, additives which are generally blended can be appropriately added as long as the effects of the present invention are not significantly impaired. Examples of the additives include recycled resin generated from trimming loss of ears and the like, silica, talc, kaolin, and calcium carbonate, 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 titanium oxide, pigments such as carbon black, flame retardants, weather resistance stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers, antioxidants, Additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, coloring agents and the like can be mentioned.

  When each of 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, these raw materials are used, for example. After pre-blending with a mixer such as a tumbler mixer or an omni mixer, the resulting mixture can be extruded and kneaded, if necessary, to prepare the mixture.

  Each raw material may be heated and dried separately or in a mixed state by using an oven, a vacuum dryer, or the like. It is preferable that the drying is performed under conditions that do not cause deterioration or fusion of the components.

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

  As a method of heating and melting the resin mixture kneaded as described above, for example, a T-die method, an inflation method and the like can be mentioned, and among them, the T-die method is preferable. 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, the sheet-shaped molten resin extruded from the T-die is laminated, and is adhered onto a rotating cast roll (chill roll, cast drum). A method of forming the sheet into a take-off sheet may be used.

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

In the obtained unstretched sheet, the thickness of the effective portion excluding both end portions 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 and 600 μm or less.
If the thickness of the unstretched sheet is 30 μm or more, it is possible to prevent breakage during stretching because the sheet is too thin, and if the thickness of the unstretched sheet is 1000 μm or less, the sheet becomes too rigid. In addition to preventing the stretching from becoming difficult, the thickness of the sheet after stretching can be reduced.

  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 structure of II layer / I layer / II layer, The lamination ratio of the I layer is preferably from 10% to 80%, more preferably from 15% to 75%, even more preferably from 20% to 70%. When the thickness ratio of the I layer is 10% or more, the film of the present invention has good filtration accuracy, which is preferable. Further, when the thickness of the I layer is 80% or less, it is preferable because a good filtration rate is obtained. Here, when a plurality of I layers are arranged, calculation is performed using the total thickness of each layer.

<Stretching process>
Hereinafter, the step of stretching the unstretched sheet to obtain a laminated porous film will be described in detail.
The obtained unstretched sheet is subjected to uniaxial stretching or biaxial stretching. The uniaxial stretching may be longitudinal uniaxial stretching or horizontal uniaxial stretching. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. One of the advantages of the present invention is that the thickness, air permeability, and porosity of the formed laminated porous film can be adjusted by changing the composition, thickness, and stretching ratio of the unstretched sheet. When producing a laminated porous film as the object of the present invention, stretching conditions can be selected in each stretching step, and sequential biaxial stretching in which the porous structure can be easily controlled is more preferable. The stretching of the film in the machine direction (MD) is referred to as “longitudinal stretching”, and the stretching in the direction perpendicular to the machine direction (TD) is referred to as “horizontal stretching”. The transverse stretching is preferably performed using a speed difference between a pair of drive rolls serving as a stretching section, but is not limited thereto. On the other hand, it is preferable to use a clip type tenter as an apparatus used for the transverse stretching. However, it is not limited to this.

In the method for producing a stretched porous film according to an example of the embodiment of the present invention, the unstretched sheet is stretched in a longitudinal direction at a temperature of 0 ° C to 60 ° C by 1.1 times or more and less than 3.0 times; This is a method in which the film is stretched in a longitudinal direction at a temperature of up to 160 ° C. by 1.5 times or more and less than 6.0 times, and at a temperature of 70 ° C. to 150 ° C. in a transverse direction by 1.1 times or more and less than 10 times. The details will be described below.

When performing longitudinal stretching, it is preferable to perform the following low-temperature longitudinal stretching step 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 10 ° C to 40 ° C, and preferably 1.1 times or more and less than 3.0 times in the longitudinal direction, more preferably 1.2 times or more. It is stretched 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 higher than 60 ° C., the resulting stretched film tends to have low porosity and high air permeability. Further, 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 time in a certain temperature range before performing the above-mentioned stretching step. .

  Next, the stretched sheet obtained above is preferably at a temperature of 60 ° C to 160 ° C, more preferably 70 ° C to 130 ° C, and 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 the film is stretched at a temperature lower than 60 ° C., the film tends to break, and when the film is stretched at a temperature higher than 160 ° C., the porosity of the obtained stretched film tends to be low and the air permeability tends to be high. In addition, from the viewpoint of physical properties and applications required for the porous film of the present embodiment, it is preferable to perform stretching in two or more steps under the above-described conditions. When the stretching process is performed in one stage, the obtained stretched film may not satisfy the required physical properties.

  The longitudinal stretching ratio can be arbitrarily selected, but the stretching ratio per uniaxial stretching is preferably 1.1 times or more and less than 15 times, more preferably 1.5 times or more and less than 12 times, and further preferably 1 time or less. 0.5 times or more and less than 10 times. By setting the stretching ratio per uniaxial stretching to 1.1 times or more, whitening progresses, suggesting that sufficient porosity due to stretching has occurred. Further, when the ratio is less than 15 times, deformation of the 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 an apparatus used for performing the transverse stretching. The clip type tenter includes a clip traveling device for transverse stretching and an oven.
The clip travel device stretches the longitudinally stretched sheet by grasping both ends of the stretched sheet with a pair of clips and simultaneously opening the guide rails of the grip travel device to increase 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 the longitudinally stretched sheet is heated to a temperature at which it can be stretched, stretched in the stretching zone, and after stretching, a heat treatment zone is provided as necessary, and heat treatment is performed. A slow cooling zone before exposure to water.

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

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

  The stretching speed is preferably in the range of 10 to 20,000% / min, more preferably in the range of 100 to 10,000% / min. When the rate is 10% / min or more, a sufficient stretching ratio can be efficiently obtained, and the production cost can be suppressed. On the other hand, when the rate is 20,000% / min or less, the occurrence of sheet breakage or the like can be suppressed. it can.

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

In the present invention, when expressed as "X to Y" (X and Y are arbitrary numbers), "preferably larger than X" and "preferably Y" together with "X or more and Y or less" unless otherwise specified. "Smaller".
In the present invention, the expression “X or more” (X is an arbitrary number) includes “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, the present porous body will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In addition, as an embodiment of the present porous body, the porous body was shaped into a film. Further, the direction of taking (flow) of the film is referred to as “MD”, and the direction perpendicular thereto is referred to as “TD”.

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

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

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

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

(1) Thickness The obtained porous film was measured indefinitely at five places with a 1/1000 mm dial gauge, and the average was defined as the thickness.

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

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

(4) Filtration speed In an air atmosphere at 25 ° C., a time t at which a predetermined volume V of acetone 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 equation.
Filtration rate [ml / min · cm ² ] = (V × 60) / (t × A)

(5) Filtration accuracy test Colloidal silica manufactured by Nissan Chemical Co., Ltd. (product name: Snowtex MP-4540M), average particle size: 450 nm, solid content: 40% by mass, medium: water so as to be 4% by mass with water. After dilution and sufficient uniform dispersion in an ultrasonic stirrer, the solution is passed through a porous film at a pressure of 0.07 MPa, and the concentration of the liquid before and after the passage is measured by an absorbance method, and the particle collection efficiency (%) Was calculated.

(6) Filtration life Nissan Chemical's colloidal silica (product name: Snowtex MP-4540M), average particle diameter: 450 nm, solid content: 40% by mass, medium: water diluted with water to 4% by mass. Then, after sufficiently uniformly dispersed in an ultrasonic stirrer, passed through a porous film at a pressure of 0.09 MPa, the mass W of the liquid that passed until filtration became impossible was measured, and the effective filtration area A 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 from the cross-sectional image of the porous film that layers having different holes were formed. In the case where layers having different holes 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. The abundance ratio of pores having a pore diameter in the major axis direction of 5 to 100 μm in each layer was calculated by the following formula.
Existence ratio of pores having a pore diameter in the long axis direction 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) 0.1 parts by weight of the crystal nucleating agent (D-1) with respect to 100 parts by weight of the mixed resin composition (0.14 parts by weight with respect to 100 parts by weight of the polypropylene-based resin); It is put into an extruder, melt-kneaded at a set temperature of 240 ° C., shaped into a strand by a strand die, cooled and solidified in a water tank, cut with a strand cutter, and pelletized (hereinafter referred to as “pellet (I ) "). In a similar manner, 70% by mass of polypropylene (A-1), 30% by weight of styrene-olefin-styrene block copolymer (C-1), and the propylene copolymer (A-1) and the styrene-olefin- 0.1 part by weight of the crystal nucleating agent (D-1) per 100 parts by weight of the mixed resin composition with the styrene block copolymer (C-1) (0.14 parts by weight based on 100 parts by weight of the polypropylene resin) Parts by weight) to produce pellets (hereinafter, referred to as “pellets (II)”).

  The prepared pellets were melt-mixed at 200 ° C. using a single-screw extruder, and then, using a T-die having a lip opening of 1 mm, pellets (II) were applied to the front and back layer side extruders and pellets (I) were applied to the middle layer extruders. The co-extrusion molding is performed at an extrusion temperature of 200 ° C. so that the thickness ratio of the laminate becomes the surface layer / intermediate layer / back layer = 1/1/1. I got a sheet. Thereafter, the obtained unstretched sheet is subjected to low-temperature stretching between a roll (X) set at 20 ° C. and a roll (Y) set at 20 ° C. by applying a draw ratio of 100% (drawing ratio 2.0 times). went. Next, between the roll (P) set at 120 ° C. and the roll (Q) set at 120 ° C., a draw ratio of 50% (a draw ratio of 1.5) 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 device manufactured by Kyoto Machinery Co., 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. Table 1 shows the evaluation results of the obtained films. FIG. 1 shows an observation photograph of a cross section of the obtained film by a scanning electron microscope. From the cross section of the film, 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 lamination was changed 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 of 2.0) between a roll (X) set at 20 ° C. and a 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% (a draw ratio of 1.5) 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 manufactured by Kyoto Machinery Co., 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. Table 1 shows the evaluation results of the obtained films.

(Comparative Example 1)
The pellet (I) is put into a single screw extruder, melt-kneaded at a set temperature of 200 ° C., shaped into a sheet by a T-die, cooled and solidified by a cast roll set at 127 ° C., and undrawn. I got a sheet. Thereafter, the obtained unstretched sheet is subjected to low-temperature stretching between a roll (X) set at 20 ° C. and a roll (Y) set at 20 ° C. by applying a draw ratio of 100% (stretching ratio of 2.0). went. Next, between the roll (P) set at 120 ° C. and the roll (Q) set at 120 ° C., a draw ratio of 50% (a draw ratio of 1.5) 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 manufactured by Kyoto Machinery Co., 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. Table 1 shows the evaluation results of the obtained films.

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

In Examples 1 and 2, the abundance ratio of pores having a size of 5 to 100 μm was as follows: surface layer / intermediate layer = 9, back layer / intermediate layer = 10 in Example 1, surface layer / intermediate layer = 8, back layer / middle Layer = 7, and it can be confirmed that layers having different pore sizes are clearly formed by each layer. Moreover, the porosity is not less than 60% and the air permeability is not more than 30 sec / 100 cc, respectively, and a laminated porous film having a sufficient porous structure for obtaining good air permeability can be obtained. Understand. Regarding the 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 the particles are captured by the presence of a layer having a large pore and a layer having a small pore. Meanwhile, a porous laminated film having excellent air permeability and filtration efficiency has been obtained.

In Comparative Example 1, particles having different pore sizes could not be clearly confirmed, and the structure was not a laminated structure. However, the air permeability was excellent as in the example, and the filtration accuracy was 0.00%. Have been collected. However, since the filtration life is shorter than that of the example, when the filtration target is filtered, clogging is likely to occur, and the performance as a filtration filter is low.
In Comparative Example 2, layers having different hole sizes could not be clearly confirmed, and the structure was not a laminated structure. In addition, the air permeability is higher than that of the embodiment and is excellent, but the filtration accuracy is 0.72%, and the particles cannot be collected. For this reason, although the filtration speed and the filtration life are excellent, the filtration efficiency is inferior due to the trapping 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 which is excellent in air permeability and filtration performance. It is useful as a filtration membrane in the coating industry for collecting and reusing paint, the semiconductor industry (production of ultrapure water), and the pharmaceutical food industry (sterilization and enzyme purification).

Claims (9)

A laminated porous film having an I layer and an II layer satisfying the relationship of the formula (1), wherein the I layer and the II layer are each 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 pores having a pore diameter in the major axis direction 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, wherein the laminated porous film has a three-layer structure having the I layer as an intermediate layer and the II layer on the front and back surfaces.   The laminated porous film according to claim 1, wherein the thickness is 1 μm or more and 1000 μm or less, and the air permeability is 1 to 1000 sec / 100 cc. The laminated porous film according to any one of claims 1 to 3, which is a biaxially stretched film. At least one layer comprising an olefin polymer (A) and a styrene-olefin block copolymer (B), and at least one layer comprising an olefin polymer (A) and a styrene-olefin-styrene block copolymer (C). A method for producing a laminated porous film, comprising: preparing an unstretched film having each film, and stretching the film.   The unstretched film is stretched in the longitudinal direction at a temperature of 0 ° C to 60 ° C by 1.1 times or more and less than 3.0 times, and at a temperature of 60 ° C to 160 ° C, 1.5 times or more by 6.0 times. The method for producing a laminated porous film according to claim 5, wherein the film is stretched at a temperature of 70 to 150C in a width direction of 1.1 to 10 times.   The melt flow rate of the styrene-olefin block copolymer (B) at 230 ° C. and a load of 2.16 kg is 1.0 g / 10 minutes or less, and the laminated porous film according to claim 5 or 6, wherein Production method.   8. The melt flow rate of the styrene-olefin-styrene block copolymer (C) at 230 ° C. and a load of 2.16 kg is 1.0 g / 10 minutes or less, 8. A method for producing a laminated porous film.   A filter using the microporous film according to claim 1.

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