JP2021154586A - Porous film - Google Patents

Abstract

To provide a porous film which has good heat sealability in processing, prevents edge breakage after heat seal, and is excellent in such bacteria barrier property as to maintain a sterilization state after sterilization treatment.SOLUTION: A porous film has at least a porous layer (I) and a porous layer (II), in which the porous layer (I) contains a polyolefin-based resin and a vinyl aromatic elastomer, the vinyl aromatic elastomer has such a sea-island structure as to form a domain in a matrix of the polyolefin-based resin, the porous layer (II) has β-crystal activity and constitutes a surface layer on at least one surface side of the porous film, and an average pore diameter of the porous film measured by a perm porometer is 0.050 μm or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a porous film having at least two porous layers.

Perforated films with a large number of fine pores are moisture-permeable and waterproof films used for clothing and sanitary materials, various filters used for water treatment, heat insulating materials for electronic devices, heat insulating films used for housing and building materials, etc. It is widely used in various fields such as battery separators used for batteries.
Further, in the field of medical packaging materials, since sterilization treatment with high-pressure steam or ethylene oxide gas may be involved, a porous film or non-woven fabric having air permeability inside and outside is used even after packaging.

Conventionally, medical devices such as disposable syringes and injection needles are stored in a package such as a blister package and then sterilized by high-pressure steam, ethylene oxide gas, or irradiation. As described above, since the medical packaging material undergoes the sterilization treatment, sufficient air permeability is required especially in highly versatile high-pressure steam and ethylene oxide gas sterilization. Specifically, it is required to have air permeability to allow gas required for sterilization treatment and water vapor having a diameter of 0.0004 μm to permeate, and a porous film or non-woven fabric is useful as a medical packaging material.
Further, in medical packaging materials, since it is necessary to have a bacterial barrier property to prevent various bacteria from invading the inside of the packaging material after sterilization treatment, the porous structure of the porous film or non-woven fabric is preferably fine, and various bacteria. It is desirable that there is no coarse pore size that allows the passage of.

By the way, when a porous film or a non-woven fabric is used as a medical packaging material, the medical device is mainly wrapped with a heat seal. Therefore, the porous film and the non-woven fabric have problems such as edge breakage in which the film tears at the boundary between the heat-sealed portion and the non-heat-sealed portion at the time of peeling, and fiber tearing in which the fiber tears at the boundary between the heat-sealed portion and the non-heat-sealed portion.

As a medical member using such a porous film, for example, in Patent Document 1, the outer material, the first adhesive layer, the microporous polytetrafluoroethylene film having moisture permeability, the second adhesive layer, and the lining are in this order. In the laminated fabric which is laminated and integrated, the outer material and the lining are mainly composed of polyester fibers, and the first and second adhesive layers contain a polycarbonate-based polyurethane resin which does not have moisture permeability. It is composed of a resin composition to be formed, and one of the first and second adhesive layers is formed on the entire surface and the other is formed on the non-overall surface. An excellent blood / virus barrier laminated fabric is disclosed.

Further, Patent Document 2 describes a porous laminate containing a polyolefin-based porous film and a polyolefin-based fiber layer, and has a moisture permeability of 150 g / m ² · h or more after being heat-treated at 121 ° C. for 30 minutes. , A porous laminate having a heat shrinkage rate of 5% or less in both the longitudinal direction and the width direction after heat treatment at 121 ° C. for 30 minutes is disclosed.
As described above, Patent Documents 1 and 2 state that excellent strength and bacterial barrier property can be achieved at the same time by compounding a fiber member with a porous film.

Further, for example, in Patent Document 3, a sea portion formed of a thermoplastic resin composition containing 25 to 75 parts by mass of a polyolefin / polystyrene-based elastomer with respect to 100 parts by mass of a polypropylene-based resin and containing the polypropylene resin as a main component. A microporous film having a sea-island structure composed of islands containing the polyolefin-polypropylene-based elastomer as a main component, and the melt flow rate of the polyolefin-polypropylene-based elastomer at 230 ° C. and a load of 2.16 kg is 0 to 0. A biaxially stretched microporous film characterized by being 0.1 g / 10 minutes is disclosed, and a uniform porous structure can be formed by adding a specific elastomer to a propylene resin and making it porous. It is said that it can be suitably used as a medical member.

On the other hand, as a method for preventing fiber tearing during peeling after heat sealing, for example, Patent Document 4 describes a gas permeable sheet material containing at least one porous non-woven web, which is a flash-spun net-like filament non-woven fabric sheet. A gas permeable sheet material selected from the group consisting of spunbond-film-spunbond composite sheets, spunbond-melt blown-spunbond composite sheets, spunlaced polyester / wood pulp composite sheets, and paper, and at least one thereof. A coated porous sheet material comprising a surface-coating polymer coating, wherein the gas permeability of the coated sheet material is substantially equal to the gas permeability of an equivalent sheet material without a coating. A coated porous sheet material is disclosed, and a composite member of a non-woven fabric and a coated porous sheet prevents fiber tearing during peeling after heat sealing.

Further, Patent Document 5 describes at least a linear low-density polyethylene, ^{an olefin-based copolymer having a Vicat softening point of 20 to 50 ° C. and a density of less than 0.900 g / cm 3} , and an inorganic filler. A porous film for a bag constituent member, which is formed from a raw material containing the same material and is made porous by stretching an unstretched film, is disclosed, and the density of the resin used for the porous film is disclosed. By adjusting, the edge breakage at the time of peeling after heat sealing is improved.

Japanese Unexamined Patent Publication No. 2015-224405 JP 2015-163465 Japanese Unexamined Patent Publication No. 2016-216726 Japanese Unexamined Patent Publication No. 2009-196362 Japanese Unexamined Patent Publication No. 2013-1435

The present invention has been made in view of the above problems, and has good heat-sealing properties during processing, prevents edge breakage after heat-sealing, and also has a bacterial barrier property that maintains a sterilized state after sterilization. It provides an excellent perforated film.

The present invention relates to the following [1] to [10].
[1] A porous film having at least a porous layer (I) and a porous layer (II), wherein the porous layer (I) contains a polyolefin resin and a vinyl aromatic elastomer, and the vinyl aromatic elastomer is the said. It has a sea-island structure that forms a domain in a matrix of polyolefin resin, and the porous layer (II) has β-crystal activity and constitutes a surface layer on at least one surface side of the porous film. A porous film having an average pore diameter of 0.050 μm or less as measured by a meter.

[2] The above-mentioned [1], wherein the difference between the average pore diameter of the porous layer (I) and the average pore diameter of the porous layer (II) measured in the cross section of the porous film is 1.0 μm or more. Perforated film.
[3] The porous film according to the above [1] or [2], wherein the melt flow rate of the vinyl aromatic elastomer measured at a temperature of 230 ° C. and a load of 2.16 kg is 1.0 g / 10 minutes or less.
[4] The porous film according to any one of [1] to [3] above, wherein the porous layer (II) contains a β-crystal nucleating agent.

[5] The porous film according to any one of [1] to [4] above, wherein the maximum pore diameter is 0.80 μm or less.
[6] The porous film according to any one of [1] to [5] above, wherein the thickness is 50 to 300 μm and the air permeability is 300 seconds / dL or less.
[7] The porous film according to any one of [1] to [6] above, which is a stretched film stretched at least in the uniaxial direction.

[8] The porous film according to any one of [1] to [7] above, wherein the porous layer (I) is a middle layer.
[9] The above [1] to the above, wherein the porous layer (II) constitutes a surface layer on both sides of the porous film, and the porous layer (I) has a structure of at least two types and three layers in which the porous layer (I) is a middle layer. The porous film according to any one of [8].
[10] A medical packaging material using the porous film according to any one of the above [1] to [9].

According to the present invention, it is possible to provide a porous film having good heat-sealing property during processing, preventing edge breakage after heat-sealing, and having excellent bacterial barrier property for maintaining a sterilized state after sterilization treatment. Can be done.

6 is a cross-sectional image of the perforated film of Example 3 taken in the TD direction with a scanning electron microscope.

Hereinafter, embodiments for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be appropriately modified and implemented within the scope of the gist thereof.
In addition, in this specification, the term "AB" regarding the description of a numerical value means "A or more and B or less" (in the case of A <B) or "A or less and B or more" (in the case of A> B). .. In the present invention, the combination of preferred embodiments is a more preferred embodiment.

[Perforated film]
The porous film according to an example of the present embodiment (hereinafter, also referred to as “film of the present invention”) is a porous film having at least a porous layer (I) and a porous layer (II).
The porous layer (I) contains a polyolefin resin and a vinyl aromatic elastomer, and has a sea-island structure in which the vinyl aromatic elastomer forms a domain in the matrix of the polyolefin resin, and the porous layer (II). ) Consulates a surface layer on at least one surface side of the porous film and has β-crystal activity, and the average pore diameter of the porous film measured by a palm poromometer is 0.050 μm or less.
The film of the present invention includes a porous layer (I) having a sea-island structure formed of a specific resin material and a porous layer (II) having β-crystal activity, and has an average pore diameter measured by a palm poromometer. Is adjusted to 0.050 μm or less, so that it has excellent heat-sealing property, edge cutting prevention property at the time of peeling after heat-sealing, and bacterial barrier property.
Further, the porous film of the present invention is highly environmentally compatible because a porous layer can be formed by porosity accompanying stretching without using a foaming agent such as gas.

<Average pore size of porous film>
The average pore diameter of the film of the present invention (hereinafter, the average pore diameter is also referred to as “MFP diameter”) is 0.050 μm or less. In the present invention, by setting the average pore diameter of the porous film to 0.050 μm or less, a fine porous structure can be formed and the bacterial barrier property against viruses and bacteria can be improved. In addition, the ability to prevent edge breakage during peeling after heat sealing can be improved. From the above viewpoint, the MFP diameter of the film of the present invention is preferably 0.001 to 0.050 μm, more preferably 0.005 to 0.045 μm, and further preferably 0.010 to 0.040 μm.

<Maximum pore diameter of porous film>
The maximum pore diameter of the film of the present invention (hereinafter, the maximum pore diameter is also referred to as “BP diameter”) is preferably 0.80 μm or less, more preferably 0.65 μm or less, still more preferably 0.50 μm or less. .. By setting the maximum pore diameter of the film of the present invention to 0.80 μm or less, the bacterial barrier property against various bacteria can be improved, and water droplets can be prevented from invading inside even during high-pressure steam sterilization. From the above viewpoint, the BP diameter of the film of the present invention is preferably 0.10 to 0.80 μm, more preferably 0.15 to 0.65 μm, and further preferably 0.25 to 0.50 μm.

The MFP diameter and BP diameter of the film of the present invention can be measured by a bubble point method based on JIS K3832: 1990 using a palm porometer (manufactured by PMI, 500 PSI type). It can be measured by the method described in the example.
The MFP diameter and BP diameter of the film of the present invention can be adjusted within the above ranges by providing the porous layer (I) and the porous layer (II) described later.

<Perforated layer (I)>
The porous layer (I) contains a polyolefin resin and a vinyl aromatic elastomer, and has a sea-island structure in which the vinyl aromatic elastomer forms a domain in the matrix of the polyolefin resin. In the present invention, the diameter of the pores formed in the porous layer (I) is set to be larger than that of the porous layer (II) by forming a sea-island structure made of a polyolefin resin and a vinyl aromatic elastomer and making the pores porous. can do.
The pore size of the porous layer (I) can be controlled by selecting the type and content of the polyolefin resin and the vinyl aromatic elastomer, selecting the stretching conditions of the porous film, and the like.

[Resin composition for forming porous layer (I)]
The porous layer (I) is formed from a resin composition containing a polyolefin-based resin and a vinyl aromatic elastomer (hereinafter, also referred to as “resin composition for forming the porous layer (I)”).
(Polyolefin resin)
The polyolefin-based resin includes, for example, a single weight obtained by polymerizing an α-olefin such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonen or 1-decene. Examples thereof include coalescing or copolymers. Among these, polypropylene-based resin or polyethylene-based resin is preferably used, and polypropylene-based resin is more preferable from the viewpoint of heat resistance of the porous film.
In addition, in this invention, 2 or more kinds of said homopolymers or copolymers may be mixed and used as a polyolefin resin.

(Polyethylene resin)
Examples of the polyethylene-based resin include high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and low-density polyethylene (LDPE).

(Polypropylene resin)
Examples of the polypropylene-based resin include homopolypropylene (propylene copolymer) or propylene, ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonen or 1-decene. Random copolymers with α-olefins such as, block copolymers, and the like can be mentioned.
Among these, as the polypropylene-based resin, homopolypropylene is preferable from the viewpoint of improving mechanical strength.

The polypropylene-based resin has an isotactic pentad fraction exhibiting stereoregularity, preferably 80 to 99%, more preferably 83 to 98%, and even more preferably 85 to 97%. When the isotactic pentad fraction is 80% or more, the mechanical strength of the film of the present invention is good.
On the other hand, the upper limit of the isotactic pentad fraction is specified by the upper limit value that can be obtained industrially at present, but this is limited to the case where a resin with higher regularity at the industrial level is developed in the future. is not it. The isotactic pentad fraction is a three-dimensional structure in which all five methyl groups, which are side chains, are located in the same direction as the main chain formed by a carbon-carbon bond composed of five consecutive propylene units. Or it means the ratio. Attribution of signals in the methyl group region is based on A. Zambelli et al. (Macromol. 8,687 (1975)).

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

The melt flow rate (MFR) of the polypropylene-based resin is not particularly limited, but is usually preferably 0.5 to 15 g / 10 minutes, more preferably 1.0 to 10 g / 10 minutes. By setting the MFR of the polypropylene resin to 0.5 g / 10 minutes or more, it is possible to have a sufficient melt viscosity at the time of molding and secure high productivity. On the other hand, by setting the MFR to 15 g / 10 minutes or less, sufficient strength can be secured.
In the present invention, MFR refers to a value measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210-1: 2014.

The method for producing the polypropylene-based resin is not particularly limited, and is represented by a known polymerization method using a known polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. Examples thereof include a polymerization method using a single-site catalyst.

Examples of the polypropylene-based resin include trade names "Novatec PP", "WINTEC" (manufactured by Japan Polypropylene Corporation), "Versify", "Notio", "Toughmer XR" (manufactured by Mitsui Chemicals, Inc.), "Zeras", etc. "Thermoran" (manufactured by Mitsubishi Chemical Co., Ltd.), "Sumitomo Noblen", "Tough Serene" (manufactured by Sumitomo Chemical Co., Ltd.), "Prime Polypropylene", "Prime TPO" (manufactured by Prime Polymer Co., Ltd.), "Adflex", "Adsyl" , "HMS-PP (PF814)" (manufactured by Sun Aroma Co., Ltd.), "Inspire" (Dow Chemicals Japan Co., Ltd.) and other commercially available products can be used.

The content of the polyolefin-based resin in the resin composition for forming the porous layer (I) is preferably 55% by mass or more, more preferably 60% by mass or more, still more preferably 65% by mass or more, and usually 90% by mass. It is as follows. When the content of the polyolefin-based resin in the resin composition for forming the porous layer (I) is within the above range, it becomes easy to obtain a sea-island structure in which the vinyl aromatic elastomer forms a domain in the matrix of the polyolefin-based resin. The mechanical strength of the film of the present invention is improved.

(Vinyl aromatic elastomer)
The vinyl aromatic elastomer is a kind of thermoplastic elastomer based on a styrene component, and is a copolymer composed of a continuum of a soft component (for example, a butadiene component) and a hard component (for example, a styrene component).
Examples of the copolymer constituting the vinyl aromatic elastomer include random copolymers, block copolymers, and graft copolymers. Various block copolymers such as a linear block structure and a radial branched block structure are known, but in the present invention, a copolymer having any structure may be used.

The vinyl aromatic elastomer that can be used in the present invention is not particularly limited, but includes styrene-butadiene block copolymer (SBR), hydrogenated styrene-butadiene block copolymer (SEB), and styrene-butadiene-styrene block. Polymer (SBS), styrene-butadiene-butylene-styrene block copolymer (SBBS), styrene-ethylene-butadiene-styrene block copolymer (SEBS), styrene-isoprene block copolymer (SIR), styrene-ethylene -Propylene block copolymer (SEP), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymer weight Examples include coalescence (SEEPS).

Among the vinyl aromatic polymers, an ethylene component having high compatibility with a polyolefin resin, particularly a polypropylene resin, from the viewpoint of efficiently dispersing the vinyl aromatic elastomer in the resin composition for forming the porous layer (I). , Butylene component is preferable, among them, styrene-ethylene-propylene block copolymer (SEP), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-butylene-styrene block. Copolymer (SEBS) is more preferred.

The melt flow rate (MFR) of the vinyl aromatic elastomer measured at a temperature of 230 ° C. and a load of 2.16 kg is preferably 1.0 g / 10 minutes or less, more preferably 0.8 g / 10 minutes or less, still more preferably. 0.5 g / 10 minutes or less. Normally, the shape of the vinyl aromatic elastomer dispersed in the resin composition for forming the porous layer (I) changes depending on the difference in viscosity with the resin, but if the MFR is within the above range, the shape becomes spherical. Easy to become. Unlike a domain having a large aspect ratio, a spherically dispersed domain is preferable because the uniformity of the porous structure obtained by the subsequent stretching step tends to be high and the physical property stability is excellent. Further, when the MFR of the vinyl aromatic elastomer is within the above range, stress is likely to be concentrated on the domain interface portion between the matrix having a high elastic modulus and the domain having a low elastic modulus during the stretching step, so that the opening starting point is set. It has the characteristics that it is easy to occur and it is easy to make it porous.

The styrene content of the vinyl aromatic elastomer is preferably 10 to 40% by mass, more preferably 10 to 35% by mass. When the styrene content in the vinyl aromatic elastomer is 10% by mass or more, the domain can be effectively formed in the resin composition for forming the porous layer (I), and the styrene content is 40% by mass. By the following, the formation of an excessively large domain can be suppressed.

The content of the vinyl aromatic elastomer in the total amount of the resin composition for forming the porous layer (I) is preferably 10 to 50% by mass, more preferably 15 to 40% by mass, and further preferably 20 to 35% by mass. .. When the content of the vinyl aromatic elastomer in the resin composition for forming the porous layer (I) is 10% by mass or more, porosity is likely to occur due to stretching, and an increase in pore size can be expected, which is preferable. On the other hand, when the content of the vinyl aromatic elastomer is 40% by mass or less, it is possible to prevent excessive coarsening of the porous structure due to stretching and improve mechanical properties.

(Other materials)
The resin composition for forming the porous layer (I) may be mixed with, for example, a resin other than the polyolefin-based resin as a component other than the polyolefin-based resin and the vinyl aromatic elastomer.

Examples of the other resins include polystyrene-based resins, polyvinyl chloride-based resins, polyvinylidene chloride-based resins, chlorinated polyethylene-based resins, polyester-based resins, polycarbonate-based resins, polyamide-based resins, polyacetal-based resins, and acrylic-based resins. Ethylene vinyl acetate copolymer, polymethylpentene resin, polyvinyl alcohol resin, cyclic olefin resin, polylactic acid resin, polybutylene succinate resin, polyacrylonitrile resin, polyethylene oxide resin, cellulose resin, polyimide Based resin, polyurethane resin, polyphenylene sulfide resin, polyphenylene ether resin, polyvinyl acetal resin, polybutadiene resin, polybutene resin, polyamideimide resin, polyamide bismaleimide resin, polyarylate resin, polyetherimide resin Examples thereof include resins, polyether ether ketone resins, polyether ketone resins, polyether sulfone resins, polyketone resins, polysulfone resins, aramid resins, and fluorine resins.

Further, in addition to the above-mentioned components, generally blended additives can be appropriately added.
The additives include recycled resins generated from trimming loss of ears and the like, pigments, flame retardants, and weather resistance, which are added for the purpose of improving and adjusting molding processability, productivity, and various physical properties of the film of the present invention. Sex stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, cross-linking agents, lubricants, nucleating agents, plasticizers, antiaging agents, antibacterial agents, antioxidants, light stabilizers, UV absorbers, neutralizing agents , Anti-fog agents, anti-blocking agents, slip agents, colorants and other additives.

Among the additives, the film of the present invention preferably contains an antibacterial agent composed of inorganic metal particles in any of the porous layers. Copper, zinc, and silver are known as the metal particles having antibacterial properties, and among these metal particles, silver particles are particularly preferable from the viewpoint of antibacterial properties.

The average particle size of the metal particles used as the antibacterial agent is preferably 1.0 μm or less, more preferably 0.9 μm or less, still more preferably 0.8 μm or less. When the average particle size is 1.0 μm or less, it is possible to prevent the occurrence of coarse pore size and to have a specific surface area of particles sufficient for exhibiting antibacterial properties. In the present invention, the average particle size of the metal particles is the average value calculated from 10 particle sizes measured from the cross-sectional SEM image of the porous film, or a laser diffraction / scattering type particle size distribution measuring device is used. Refers to the value measured in

When the resin composition for forming the porous layer (I) contains an additive such as the antibacterial agent, the content thereof is preferably 0.001 to 100 parts by mass with respect to 100 parts by mass of the resin for forming the porous layer (I). It is 3 parts by mass, more preferably 0.01 to 1.5 parts by mass. When the content of the additive such as an antibacterial agent is within the above range, it becomes possible to impart properties such as antibacterial property to the film while maintaining the strength and the like of the film.

<Perforated layer (II)>
The porous layer (II) in the porous film of the present invention has β-crystal activity and constitutes a surface layer on at least one surface side of the porous film. In the present invention, since the porous layer (II) has β crystal activity, it is possible to form a fine porous structure.
More specifically, if the resin composition forming the porous layer (II) before stretching (hereinafter, also referred to as “resin composition for forming the porous layer (II)”) produces β crystals, the resin composition is subsequently stretched. Since many fine and uniform pores are formed by applying the above, it is possible to secure the bacterial barrier property to prevent the invasion of various bacteria and the appropriateness of heat sealing. Further, in the present invention, by providing the porous layer (II) having a fine porous structure, it is possible to suppress the occurrence of edge breakage at the time of peeling after the processing treatment to the packaging member by heat.
In the present invention, by providing the above-mentioned large pore size porous layer (I), water vapor and gas can easily reach the inside during the sterilization treatment with high-pressure steam or ethylene oxide gas, and the sterilization treatment becomes easy. Furthermore, it is possible to impart a bacterial barrier property that maintains the sterilized state inside the package from various bacteria after the sterilization treatment.

As a method for imparting β-crystal activity to the porous layer (II), for example, a polypropylene-based resin is used as the resin composition for forming the porous layer (II), and a substance that promotes the formation of α-crystals of the polypropylene-based resin is not added. Method, a method of adding a polypropylene-based resin treated to generate a peroxide radical as described in Japanese Patent No. 3739481, a method of adding a β crystal nucleating agent to a resin composition for forming a porous layer (II). Among these, the method of adding the β crystal nucleating agent to the resin composition for forming the porous layer (II) is preferable.

[Resin composition for forming porous layer (II)]
As the resin composition for forming the porous layer (II) constituting the film of the present invention, that is, the resin composition for forming the porous layer (II), the formed porous layer (II) has β crystal activity. If there is any, the present invention is not particularly limited, and examples thereof include a resin composition containing a polyolefin-based resin as the resin for forming the porous layer (II) and having β-crystal activity.
As the resin for forming the porous layer (II), a polyolefin-based resin is preferable, and among them, a polypropylene-based resin containing a large amount of β crystals, which is one of the crystal forms, is particularly preferable. If the polypropylene-based resin in the non-porous film-like material before stretching produces β crystals, then stretching is performed to form many fine and uniform pores, which is also excellent in heat resistance. It can be a porous membrane.

The content of the resin for forming the porous layer (II) contained in the resin composition for forming the porous layer (II) is preferably 50% by mass or more, more preferably 70 to 99.9999% by mass, and further preferably. It is 80 to 99.999% by mass, more preferably 90 to 99.99% by mass. When a polypropylene-based resin containing a large amount of β crystals is used as the resin for forming the porous layer (II), a porous film having excellent heat resistance and having fine pores can be obtained by setting the content in the above range. ..

The β-crystal activity of the porous layer (II) can be regarded as an index indicating that the resin for forming the porous layer (II) (for example, polypropylene-based resin) produced β-crystals in the film-like material before stretching. ..
The presence or absence of β-crystal activity in the porous layer (II) is determined by performing differential thermal analysis of the film of the present invention using a differential scanning calorimeter, and melting crystals derived from β-crystals in the resin for forming the porous layer (II). It can be judged by whether or not the peak temperature is detected. Specifically, the film of the present invention is held at a heating rate of 10 ° C./min at a heating rate of 10 ° C./min for 1 minute with a differential scanning calorimeter, and then held at a cooling rate of 10 ° C./min from 240 ° C. to 25 ° C. Crystals derived from β crystals of the resin for forming a porous layer (II) when the temperature is lowered again for 1 minute and then reheated from 25 ° C. to 240 ° C. at a heating rate of 10 ° C./min. When the melting peak temperature (Tmβ) is detected, it is judged to have β crystal activity.

The β crystal activity of the porous layer (II) is determined by the amount of heat of crystal melting (ΔHmα) derived from α crystals of the detected porous layer (II) forming resin (for example, polypropylene resin) and the crystal melting derived from β crystals. It is obtained by calculating with the following formula using the amount of heat (ΔHmβ).
β crystal activity (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100
Specifically, in the case of homopolypropylene, the amount of heat of crystal melting (ΔHmβ) derived from β crystals detected mainly in the range of 145 ° C. or higher and lower than 160 ° C. and the α crystals mainly detected in the range of 160 ° C. or higher and 175 ° C. or lower. It can be calculated from the amount of heat of crystal fusion (ΔHmα) derived.
Further, for example, in the case of random polypropylene in which 1 to 4 mol% of ethylene is copolymerized, the amount of heat of crystal melting (ΔHmβ) derived from β crystals mainly detected in the range of 120 ° C. or higher and lower than 140 ° C. and mainly 140. It can be calculated from the amount of heat of crystal melting (ΔHmα) derived from α crystals detected in the range of ° C. or higher and 165 ° C. or lower.

The β-crystal activity of the porous layer (II) is preferably large, and the β-crystal activity is preferably 20% or more, more preferably 40% or more, still more preferably 60% or more. If the porous layer (II) has a β crystal activity of 20% or more, it is shown that a large amount of β crystals of the resin for forming the porous layer (II) are generated even in the film before stretching, and the film is finely formed by stretching. Moreover, many uniform pores are formed, and as a result, a porous film having excellent air permeability can be obtained. The upper limit of the β crystal activity is not particularly limited, but the higher the β crystal activity, the more effective the effect can be obtained, and the closer it is to 100%, the more preferable.

When the β crystal activity of the porous layer (II) is measured by DSC as it is for the porous film, the amount of heat of crystal melting (ΔHmβ) derived from β crystals derived from the layer (II) and the amount of heat of crystal melting (ΔHmα) are obtained. It may not be estimated accurately. Therefore, only the layer (II) portion of the present invention is peeled off, DSC is measured, and β crystal activity is calculated.
If peeling is difficult, the ΔHmβ derived from the layer (II) in the entire laminate is calculated by DSC measurement, and the lamination ratio of the porous layer (II) in the entire laminate is calculated as follows. From the calculation formula, the β crystal activity defined by the present invention can be calculated.
The stacking ratio is not particularly limited, but can be calculated by observing a cross section with an optical microscope, an electron microscope, or the like.
β crystal activity (%) = [ΔHmβ / (ΔHmβ + (ΔHmα * lamination ratio (%) of the porous layer (II) in the entire laminate))] × 100
The β-crystal activity of Examples and Comparative Examples described later was calculated based on the above formula.

The presence or absence of β-crystal activity can also be determined by the diffraction profile obtained by X-ray diffraction measurement of the film of the present invention subjected to a specific heat treatment. Specifically, the porous layer (II) forming resin (for example, polypropylene resin) was heat-treated at 170 to 190 ° C., which is a temperature exceeding the crystal melting peak temperature, and slowly cooled to generate and grow β crystals. When X-ray diffraction measurement is performed on the porous film and a diffraction peak derived from the (300) plane of the β crystal of the resin for forming the porous layer (II) is detected in the range of 2θ = 16.0 ° to 16.5 °. , It can be judged that there is β crystal activity.
For details on the β crystal structure of polypropylene resin and X-ray diffraction measurement, see Macromol.Chem.187,643-652 (1986), Prog.Polym.Sci.Vol.16,361-404 (1991), Macromol.Symp.89,499-511 (1991). 1995), Macromol. Chem. 75,134 (1964), and the references listed in these documents can be referred to.

(Β crystal nucleating agent)
In the present invention, the porous layer (II) preferably contains a β-crystal nucleating agent. That is, as a method for imparting β-crystal activity to the porous layer (II), a method of adding a β-crystal nucleating agent to the resin composition for forming the porous layer (II) as described above to obtain β-crystal activity is preferable. By adding the β crystal nucleating agent, the formation of β crystals of the resin for forming the porous layer (II) can be promoted more homogeneously and efficiently.
The β crystal nucleating agent is not particularly limited as long as it increases the formation and growth of β crystals of a polypropylene resin, but for example, an amide compound (for example, N, N'-dicyclohexyl-2, 6-naphthalenedicarboxyamide); tetraoxaspiro compounds (eg, 3,9-bis [4- (N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane) Kinacridones; Iron oxide having nanoscale size; Alkali or alkaline earth metal salts of carboxylic acids typified by potassium 1,2-hydroxystearate, magnesium benzoate, magnesium succinate, magnesium phthalate, etc.; benzene Aromatic sulfonic acid compounds typified by sodium sulfonate or sodium naphthalene sulfonate; di or triesters of di- or tribasic carboxylic acid; phthalocyanine pigments typified by phthalocyanine blue; components that are organic dibasic acids Examples thereof include a two-component compound composed of A and a component B which is an oxide, hydroxide or salt of a Group IIA metal of the periodic table; a composition composed of a cyclic phosphorus compound and a magnesium compound. One of these β crystal nucleating agents may be used alone, or two or more thereof may be used in combination.

Specific examples of commercially available β crystal nucleating agents include the β crystal nucleating agent “Ngester NU-100” manufactured by Shin Nihon Rika Co., Ltd.
Specific examples of polypropylene-based resin to which β-crystal nucleating agent is added include polypropylene "Bepol B-022SP" manufactured by Aristech, polypropylene "Beta (β) -PP BE60-7032" manufactured by Borealis, and polypropylene manufactured by mayzo. Examples include "BNX BE TAPP-LN".

The content of the β crystal nucleating agent added to the porous layer (II) forming resin composition is appropriately determined depending on the type of β crystal nucleating agent, the composition of the porous layer (II) forming resin (for example, polypropylene resin), and the like. Although it can be adjusted, it is preferably 0.0001 to 5.0 parts by mass, more preferably 0.001 to 3.0 parts by mass, and further preferably 0, based on 100 parts by mass of the resin for forming the porous layer (II). It is 0.01 to 1.0 parts by mass. When the content of the β crystal nucleating agent is 0.0001 parts by mass or more, β crystals of the resin for forming the porous layer (II) can be sufficiently generated and grown at the time of production, and sufficient β crystal activity can be ensured to form a film. Sufficient β-crystal activity can be ensured even when the film is used, and the desired air permeability can be obtained. On the other hand, when the content of the β-crystal nucleating agent is 5.0 parts by mass or less, the balance between the production cost and the obtained effect is improved, and the bleeding of the β-crystal nucleating agent on the film surface is eliminated, which is preferable. ..

(Other materials)
The resin composition for forming the porous layer (II) may be mixed with, for example, a resin other than the polyolefin-based resin in the same manner as the resin composition for forming the porous layer (I), or the above-mentioned components may be mixed. In addition, commonly blended additives can be added as appropriate.
As described above, since the porous layer (II) constitutes the surface layer on at least one surface side of the film of the present invention, it easily comes into contact with the outside air and bacteria, and therefore contains an antibacterial agent and an antioxidant among the other materials. Is preferable. When the resin composition for forming the porous layer (II) contains an antibacterial agent, in addition to the bacterial barrier property associated with the fine pore size of the porous layer (II), if bacteria adhere to or invade the surface or the inside of the membrane, , The growth of bacteria can be prevented by the effect of antibacterial agents. Further, by using an antibacterial agent composed of metal particles, it can be expected that fine pores are formed due to the stress difference between the resin and the particles from the periphery of the metal particles when the drawing is porous.

As the antibacterial agent, the compounds exemplified in the resin composition for forming the porous layer (I) can be preferably used. Specifically, an antibacterial agent composed of inorganic metal particles is preferable, and copper, zinc, and silver are preferable. Particles are preferred.

Further, the antioxidant is not particularly limited, and examples thereof include a hindered phenolic antioxidant, a phosphorus-based antioxidant, and the like. Among these, a hindered phenolic antioxidant and a phosphoric acid-based antioxidant are used. It is preferable to use in combination with.
The hindered phenolic antioxidant is not particularly limited, but is pentaerythritol-tetrakis (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate) and thiodiethylene-bis (3-( 3,5-Di-tert-butyl-4-hydroxyphenyl) propionate), octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, N, N'-hexane-1,6 -Diylbis (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamide), diethyl ((3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl) methyl) phosphate, etc. Can be mentioned. These may be used alone or in combination of two or more.

The phosphorus-based antioxidant is not particularly limited, but is tris (2,4-di-tert-butylphenyl) phosphite, bis (2,4-bis (1,1-dimethylethyl) -6-methylphenyl). Ethyl ester phosphite, tetrakis (2,4-di-tert-butylphenyl) (1,1-biphenyl) -4,4'-diylbisphosphonite, bis (2,4-di-tert-butylphenyl) ) Pentaerythritol diphosphite, bis (2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol-diphosphite and the like. These may be used alone or in combination of two or more.

When the resin composition for forming the porous layer (II) contains the antibacterial agent or the antioxidant, the content thereof is preferably 0, respectively, with respect to 100 parts by mass of the resin for forming the porous layer (II). It is 001 to 3 parts by mass, more preferably 0.01 to 1.5 parts by mass. When the content of the antibacterial agent or the antioxidant is within the above range, it is possible to impart antibacterial property and antioxidant property to the film while maintaining the strength of the film and the like.

<Layer structure of porous film>
The film of the present invention is not particularly limited as long as the surface layer on at least one surface side of the porous film is the porous layer (II), and is not limited to a two-layer structure having the porous layer (I) and the porous layer (II). It may have a multi-layer structure of three layers, four layers, five layers, or more. Among them, the porous layer (II) is a surface layer on at least one surface side, and the porous layer (I) is a middle layer. More preferably, the porous layer (II) is a surface layer on both sides of the porous film, and the porous layer (I) is a middle layer. (I) / porous layer (II)] is more preferable. When the film of the present invention has the layer structure, the bacterial barrier property and the heat seal property of the film of the present invention are further improved. In the present invention, a layer other than the porous layer (I) and the porous layer (II) may be provided.

<Difference in average pore size and average pore size between the porous layer (I) and the porous layer (II)>
The film of the present invention has a porous layer (I) and a porous layer (II) having different porous structures, but the average pore size of the porous layer (I) and the porous layer (the porous layer) measured in the cross section of the porous film. The difference from the average pore size of II) is preferably 1.0 μm or more.
As described above, since the porous layer (II) has β-crystal activity, a fine porous structure is formed, while the porous layer (I) is formed by forming a sea-island structure with a polyolefin resin and a vinyl aromatic elastomer to form a porous layer (II). ), A porous structure having a larger pore size than that of) is formed. At this time, the difference between the average pore diameter of the porous layer (I) and the average pore diameter of the porous layer (II) is 1.0 μm or more. Then, it can be provided with particularly excellent heat-sealing property, edge cutting prevention property after heat-sealing, and bacterial barrier property. From these viewpoints and from the viewpoint of ensuring the ventilation characteristics, the difference between the average pore size of the porous layer (I) and the average pore size of the porous layer (II) is preferably 1.5 to 10.0 μm, more preferably 1. It is 7 to 7.0 μm, more preferably 1.8 to 6.5 μm, and even more preferably 2.0 to 6.0 μm.

The average pore size of the porous layer (I) is preferably 3.0 to 10.0 μm, more preferably 3.5 to 8.0 μm, and even more preferably 4 from the viewpoint of ensuring the air permeability of the film of the present invention. It is .0 to 7.0 μm.
On the other hand, the average pore size of the porous layer (II) is preferably 0.01 to 3.0 μm, more preferably 0.05 to 2.0 μm, and even more preferably 0.01 to 3.0 μm, from the viewpoint of improving the bacterial barrier property of the film of the present invention. It is 0.1 to 1.0 μm.

The average pore diameter is obtained by photographing a cross section of the film of the present invention cut in the TD direction with a scanning electron microscope, measuring the maximum value of the pore diameter of each pore at 10 points, and calculating the average value. Specifically, it can be obtained by the method described in the examples. In the present specification, stretching of the film-like material in the flow direction (MD) is referred to as "longitudinal stretching", and stretching in the direction perpendicular to the flow direction (TD) is referred to as "transverse stretching".
As a method for adjusting the average pore diameter and the average pore diameter difference between the porous layer (I) and the porous layer (II) within the above range, the type and content of the resin composition forming the porous layer (I) and the porous layer (II) , A method of selecting the stretching conditions of the film of the present invention, and the like.

<Thickness of porous film, porous layer (I) and porous layer (II)>
The thickness of the film of the present invention is preferably 50 to 300 μm, more preferably 60 to 275 μm, and even more preferably 65 to 250 μm. When the thickness is 50 μm or more, the handleability is excellent and sufficient strength can be secured, and when the thickness is 300 μm or less, sufficient ventilation characteristics can be secured.

The ratio of the thickness of each layer (lamination ratio) of the pre-stretched film of the present invention is not particularly limited, and the thickness ratio of the porous layer (I) and the porous layer (II) is appropriately adjusted according to the application and purpose. can do. The thickness ratio [(I) :( II)] of the porous layer (I) to the porous layer (II) is preferably 1: 1 to 1: 0.025, more preferably 1: 0.5 to 1. : 0.05. The "thickness of the porous layer (I)" when there are two or more porous layers (I) means the total thickness of the plurality of porous layers (I), and the porous layer (II) is two or more layers. The "thickness of the porous layer (II)" in a certain case means the total thickness of a plurality of porous layers (II).
When the thickness ratio of the porous layer (I) to the porous layer (II) is within the above range, the balance between air permeability and mechanical properties is good, and a porous film suitable as a medical packaging material can be obtained. can.
The thickness and thickness ratio of the porous layer (I) and the porous layer (II) can be adjusted by changing the thickness of the non-porous film-like material before stretching, stretching conditions, and the like.

The thickness of the porous layer (I) in the film (film after stretching) of the present invention is preferably 5 to 290 μm, more preferably 10 to 280 μm. The film of the present invention can have the above-mentioned air permeability as long as the thickness ratio of the porous layer (I) and the thickness of the porous layer (I) in the film of the present invention are within the above ranges.

The thickness ratio of the porous layer (I) to the total thickness of the film of the present invention is preferably 50 to 97%, more preferably 55 to 96%, still more preferably 60 to 95%.

On the other hand, the thickness of the porous layer (II) in the film of the present invention is preferably 1 to 100 μm, more preferably 2 to 50 μm. The thickness ratio of the porous layer (II) to the total thickness of the film of the present invention is preferably 3 to 50%, more preferably 4 to 45%, still more preferably 5 to 40%.
When the thickness ratio of the porous layer (II) and the thickness of the porous layer (II) in the film of the present invention are within the above ranges, deterioration of air permeability can be prevented, and sterilization treatment with high-pressure steam or ethylene oxide gas can be performed. It will be easy.

<Porosity of porous film>
The porosity of the film of the present invention is an element that defines the porous structure, and is a numerical value indicating the ratio of the space portion of the porous layer in the film of the present invention. The porosity of the film of the present invention is preferably 55% or more, more preferably 57% or more, still more preferably 60% or more, and the upper limit is not particularly defined, but from the viewpoint of the strength of the film of the present invention. Usually 80%. When the porosity is 55% or more, sufficient ventilation characteristics can be ensured.

The method for measuring the porosity is as follows.
The actual amount W _{1 of the measurement sample is measured, the mass W 0} when the porosity is 0% is calculated based on the density of the resin composition, and the porosity is calculated from these values based on the following formula. ..
Porosity (%) = {(W ₀ − W ₁ ) / W ₀ } × 100

<Air permeability of porous film>
The air permeability of the film of the present invention is preferably 300 seconds / dL or less, more preferably 280 seconds / dL or less, still more preferably 260 seconds / dL or less. When the air permeability of the film of the present invention is 300 seconds / dL or less, water vapor or gas easily reaches the inside during the sterilization treatment with high-pressure steam or ethylene oxide gas, and the sterilization treatment becomes easy. In the present invention, in addition to the porous layer (II) having a fine porous structure, the porous layer (I) having a larger pore size than the layer (II) is provided, so that the air permeability is set to 300 seconds / dL or less. be able to. Since the air permeability changes depending on the thickness of the film, in the present invention, the film thickness is preferably 50 to 300 μm, and the air permeability is preferably 300 seconds / dL or less, 280 seconds. It is more preferably less than / dL, and even more preferably less than 260 seconds / dL.

The air permeability represents the difficulty of passing air in the thickness direction of the film of the present invention, and specifically, it is expressed by the number of seconds required for 1 dL of air to pass through the film of the present invention. Therefore, the smaller the value, the easier it is to pass through, and the larger the value, the more difficult it is to pass through. That is, a smaller value means better communication in the thickness direction of the film of the present invention, and a larger value means poor communication in the thickness direction of the film of the present invention.
The communication property is the degree of connection of holes in the thickness direction of the film of the present invention. The air permeability (seconds / dL) can be measured according to JIS P 8117: 2009, and specifically, can be measured by the method described in Examples.

<Film manufacturing method>
Hereinafter, the method for producing the film of the present invention will be described, but the following description is an example of the method for producing the porous film of the present invention, and the film of the present invention is limited to the porous film produced by such a production method. It is not something that is done.
In the method for producing a porous film according to an example of the present embodiment (hereinafter, also referred to as “the film production method of the present invention”), for example, a resin composition forming a porous layer (I) and a porous layer (II) is kneaded. Examples thereof include a step of forming a film of the composition obtained by kneading in multiple layers, and a method of producing by a manufacturing method including a step of stretching an unstretched film formed in multiple layers. In addition, other steps and treatments other than the said step may be further performed.

[Kneading process]
In the kneading step, the porous layer (I) and the porous layer (II) are formed by kneading using an extruder or the like under temperature conditions above the melting point of each resin composition and below the decomposition temperature. be. The machine used for kneading is not particularly limited, and known extruders 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 water and low molecular weight substances.
The temperature at the time of kneading is not particularly limited as long as it is a temperature equal to or higher than the melting point of each resin composition and lower than the decomposition temperature, but is preferably 180 to 300 ° C.

[Film formation process]
In the film-forming step, the resin composition for forming a porous layer obtained by the kneading step is heated and melted, and then a multi-layered film is formed.
Examples of the method for heating and melting the resin composition for forming a porous layer include a T-die method and an inflation method, and among them, the T-die method is preferably adopted. Practically, it is preferable to melt-extrude a resin for forming a porous layer from a T-die and cast-mold it with a cast roll.

When the T-die method is adopted as a specific method for forming a film, the sheet-shaped molten resins extruded from the T-dies are laminated and adhered to a rotating cast roll (chill roll, cast drum). Examples thereof include a method of picking up the product while allowing it to be formed into a sheet-like material. 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 film-like material into close contact with the cast roll.

When molding the kneaded product into a film while cooling it, the temperature of the cast roll is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, still more preferably 120 ° C. or higher. Since the porosity can be increased by opening the crystalline portion and the amorphous portion of the resin for forming the porous layer (I) and the porous layer (II) during the stretching step, the porosity can be increased, so that the temperature of the cast roll is set to 100 ° C. With the above, it is preferable to obtain a laminated non-porous film-like product having a high crystallinity.

The thickness of the obtained laminated non-porous film (unstretched film) (thickness of the effective portion excluding both ends) is preferably 100 to 700 μm, more preferably 150 to 600 μm, and further preferably 200 to 500 μm.
If the thickness of the unstretched film is 100 μm or more, breakage during stretching due to the film being too thin is unlikely to occur. On the other hand, when the thickness of the unstretched film is 700 μm or less, it is possible to prevent the film from becoming too rigid and difficult to stretch. The unstretched film may have a structure in which other layers are combined in addition to the above-mentioned layer structure (porous layers (I) and (II)).

[Stretching process]
In the stretching step, the laminated non-porous film-like material obtained in the film forming step is uniaxially stretched or biaxially stretched. The film of the present invention is preferably a stretched film stretched at least in the uniaxial direction, and more preferably a stretched film in the biaxial direction from the viewpoint of easily adjusting the pore size of the film of the present invention.
In the present invention, the stretching in the uniaxial direction may be a longitudinal uniaxial stretching or a horizontal uniaxial stretching. Further, the biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching.
When producing the film of the present invention, sequential biaxial stretching is particularly preferable from the viewpoint that stretching conditions can be selected in each stretching step and the porous structure can be easily controlled.
The stretching of the film-like material in the flow direction (MD) is referred to as "longitudinal stretching", and the stretching in the direction perpendicular to the flow direction (TD) is referred to as "transverse stretching".

Further, when sequential biaxial stretching is used, the stretching temperature can be appropriately adjusted according to the composition of the resin composition used, the crystal melting peak temperature, the crystallinity, etc., so that the porous structure can be relatively easily controlled. It is preferable because it is easy to balance with other physical properties such as mechanical strength and shrinkage rate.

The stretching temperature in longitudinal stretching is preferably 10 to 140 ° C, more preferably 15 to 130 ° C, and even more preferably 20 to 120 ° C. When the stretching temperature in the longitudinal stretching is 10 ° C. or higher, breakage during stretching is suppressed and uniform stretching can be performed, which is preferable. On the other hand, if the stretching temperature in longitudinal stretching is 140 ° C. or lower, pores can be efficiently formed.

The longitudinal stretching ratio can be arbitrarily selected, but the stretching ratio per uniaxial stretching is preferably 1.1 to 10 times, more preferably 1.5 to 8.0 times, still more preferably 1.5 to 6.0 times. Is. When the stretching ratio per uniaxial stretching is 1.1 times or more, whitening proceeds and porosity due to stretching is sufficiently generated. On the other hand, when the ratio is 10 times or less, breakage of the film is suppressed and a porous film can be stably obtained.

The transverse stretching temperature is preferably 100 to 160 ° C, more preferably 110 to 150 ° C. When the transverse stretching temperature is within the above range, it is possible to have a sufficient porosity without deforming the pores generated during the longitudinal stretching.

The transverse stretching ratio can be arbitrarily selected, but is preferably 1.1 to 10 times, more preferably 1.5 to 9.0 times, and further preferably 1.5 to 8.0 times. By stretching at a specified transverse stretching ratio, the pores generated during longitudinal stretching can be expanded to increase the porosity of the porous layer, and sufficient air permeability can be obtained.
Further, the film of the present invention can be subjected to surface processing such as corona treatment, plasma treatment, printing, coating, vapor deposition, etc., as well as perforation processing, etc., as necessary, as long as the present invention is not impaired. It is also possible to stack several films of the present invention accordingly.

<Medical packaging material>
The medical packaging material of the present invention (hereinafter, also referred to as "packaging material of the present invention") uses the film of the present invention. More specifically, the packaging material preferably has a base material layer and a sealant layer, and it is preferable that at least one layer of the base material layer and the sealant layer is composed of the film of the present invention.

Specific examples of the packaging material of the present invention include medical packaging materials for accommodating medical instruments such as syringes, catheters and lid materials for various chemicals, which are subjected to steam sterilization treatment at a high temperature exceeding 100 ° C. Although sterilization treatment is performed with ethylene oxide gas, the packaging material of the present invention can be sterilized after packaging by using the film of the present invention having a porous structure, and the sterilized state can be maintained for a long time. be able to.

Examples and comparative examples are shown below, and the film of the present invention will be described in more detail. However, the present invention is not limited by these examples and comparative examples.

<Polypropylene resin (A)>
A-1; Homopolypropylene (Novatec PP FY6HA, MFR: 2.4 g / 10 minutes [230 ° C, 2.16 kg load], Mw / Mn = 3.2, manufactured by Japan Polypropylene Corporation)

<Vinyl Aromatic Elastomer (B)>
B-1; styrene-ethylene-propylene block copolymer (grade name: SEPTON1001, styrene content: 35% by mass, MFR: 0.1 g / 10 minutes [230 ° C, 2.16 kg load] manufactured by Kuraray Co., Ltd.)
B-2; styrene-ethylene-propylene block copolymer (grade name: SEPTON1020, styrene content: 36% by mass, MFR: <0.1 g / 10 minutes [230 ° C, 2.16 kg load] manufactured by Kuraray Co., Ltd. )
B-3; Styrene-ethylene-butylene-styrene block copolymer (SEPTON8004, number average molecular weight: 118,000, weight average molecular weight: 125,000, styrene content: 31% by mass, MFR: <0.1 g / 10 minutes [230 ° C, 2.16 kg load], manufactured by Kuraray Co., Ltd.)

<β crystal nucleating agent (C)>
C-1: 3,9-bis [4- (N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5,5] undecane C-2: N, N'-dicyclohexyl -2,6-Naphthalene carboxamide (NU-100, manufactured by Shin Nihon Rika Co., Ltd.)

<Antioxidant (D)>
D-1; tris (2,4-di-t-butylphenyl) phosphite and tetrakis [3- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionic acid] pentaerythritol 1: 1 mixture (IRGANOX-B225, manufactured by BASF Japan Ltd.)

<Antibacterial agent (E)>
E-1: Polyethylene with added silver particles (MB-PP003, MFR: 7 [230 ° C, 2.16 kg load], average particle size: 0.01 μm, manufactured by Tokan Material Technology Co., Ltd.)

<Example 1>
70 parts by mass of polypropylene resin (A-1), 30 parts by mass of vinyl aromatic elastomer (B-1), and 1 part by mass of antibacterial agent (E-1) are mixed and melted at 230 ° C. with a twin-screw extruder. Mixture 1 was obtained by extrusion.
Further, 100 parts by mass of polypropylene resin (A-1), 0.2 parts by mass of β crystal nucleating agent (C-1), and 0.1 parts by mass of antioxidant (D-1) are mixed and extruded biaxially. Mixture 2 was obtained by melt extrusion at 280 ° C. in a machine.

Then, using a T-die with a lip opening of 1 mm, molding was performed using the mixture 1 in the intermediate layer side extruder and the mixture 2 in the front and back layer side extruders, and the two types were guided by a cast roll (set temperature 127 ° C.). A three-layer laminated non-porous film-like product was obtained.
Next, the obtained laminated non-porous film-like material was multiplied by a draw ratio of 50% between rolls set at 20 ° C. using a longitudinal stretching machine, and then a draw ratio of 100% was applied between rolls set at 120 ° C. (Total longitudinal stretching ratio 3.0 times) was multiplied to perform longitudinal stretching.
The film after longitudinal stretching is preheated in a film tenter facility (manufactured by Kyoto Machinery Co., Ltd.) at a preheating temperature of 150 ° C. and a preheating time of 12 seconds, then stretched 3.0 times in the transverse direction at a stretching temperature of 150 ° C. Heat treatment was performed at 155 ° C. to obtain a porous film. The obtained porous film was evaluated as follows, and the results are shown in Table 1. The β crystal activity of the porous layer (II) in Example 1 was 84%.

<Example 2>
100 parts by mass of polypropylene resin (A-1), 0.2 parts by mass of β crystal nucleating agent (C-2), 0.1 parts by mass of antioxidant (D-1), 1 part by mass of antibacterial agent (E-1) The parts were mixed and melt-extruded at 280 ° C. with a twin-screw extruder to obtain a mixture 3. Next, longitudinal stretching and transverse stretching were carried out in the same manner as in Example 1 except that a laminated non-porous film product of 2 types and 3 layers was obtained by using the mixture 3 in the front and back layer side extruders during melt extrusion. This was performed to obtain a porous film. The obtained porous film was evaluated as follows, and the results are shown in Table 1. The β crystal activity of the porous layer (II) in Example 2 was 88%.

<Example 3>
70 parts by mass of polypropylene resin (A-1), 15 parts by mass of vinyl aromatic elastomer (B-2), 15 parts by mass of vinyl aromatic elastomer (B-3), and 1 part by mass of antibacterial agent (E-1) are mixed. Then, the mixture 4 was obtained by melt extrusion at 230 ° C. with a twin-screw extruder.
Further, 100 parts by mass of polypropylene resin (A-1), 0.2 parts by mass of β crystal nucleating agent (C-1), 0.1 parts by mass of antioxidant (D-1), antibacterial agent (E-1). 1 part by mass was mixed and melt-extruded at 280 ° C. with a twin-screw extruder to obtain a mixture 5.

Then, using a T-die with a lip opening of 1 mm, the mixture 4 was used for the intermediate layer side extruder and the mixture 5 was used for the front and back layer side extruders, and the mixture was guided by a cast roll to form two types and three layers without holes. A film-like substance was obtained.
Next, the obtained laminated non-porous film-like material was multiplied by a draw ratio of 50% between rolls set at 20 ° C. using a longitudinal stretching machine, and a draw ratio of 150% (total) between rolls set at 120 ° C. Longitudinal stretching was performed by multiplying the longitudinal stretching ratio (3.8 times).
The film after longitudinal stretching was laterally stretched in the same manner as in Example 1 to obtain a porous film. The obtained porous film was evaluated as follows, and the results are shown in Table 1. The β crystal activity of the porous layer (II) in Example 3 was 87%.
FIG. 1 shows a cross-sectional image of the cross-section of the porous film obtained in Example 3 in the TD direction taken with a scanning electron microscope. In FIG. 1, the surface layer is the porous layer (II), and the middle layer is the porous layer (I).

<Comparative Examples 1 to 5>
A mixture was prepared according to the raw material mixing ratios shown in Table 1, and a laminated non-porous film-like product was obtained in the same manner as in Example 1. Then, the obtained laminated non-porous film-like material was subjected to longitudinal stretching and transverse stretching at a predetermined magnification in the same manner as in Example 1 to obtain a porous film. The obtained porous film was evaluated as follows, and the results are shown in Table 1. The β-crystal activity of the porous layer (II) in Comparative Example 4 was 88%, and the β-crystal activity of the porous layer (II) in Comparative Example 5 was 85%.

<Evaluation>
With respect to the porous films obtained in Examples and Comparative Examples, the film thickness, average pore size, average pore size, maximum pore size, porosity, air permeability, and heat sealability were measured by the following methods.

(1) Film thickness 10 points were randomly measured using a dial gauge of 1/1000 mm, and the average value was taken as the thickness.

(2) Average pore size The cross section of the obtained porous film cut in the TD direction was photographed with a scanning electron microscope (SEM). With respect to the porous layer (I) and the porous layer (II), the maximum value of the pore diameter of each pore projected by the SEM photograph taken was measured at 10 points, and the average value calculated for each was taken as the average pore diameter. The difference in the average pore diameters calculated for each of the porous layer (I) and the porous layer (II) was defined as the average pore diameter difference.

(3) Average pore diameter (MFP diameter), maximum pore diameter (BP diameter)
The MFP diameter and BP diameter of the porous film were measured by a bubble point method based on JIS K3832: 1990 using a palm poromometer (manufactured by PMI, 500 PSI type).

(4) Porosity measurement The actual amount W _{1 of the sample is measured, the mass W 0} when the porosity is 0% is calculated based on the density of the resin composition, and the mass W 0 is calculated from this value based on the following formula. The porosity was calculated.
Porosity (%) = {(W ₀ − W ₁ ) / W ₀ } × 100

(5) Air permeability at 25 ° C. The air permeability was measured in accordance with JIS P8117: 2009 under an air atmosphere of 25 ° C. As a measuring device, a digital type Oken type air permeability dedicated machine (manufactured by Asahi Seiko Co., Ltd.) was used.

(6) Evaluation of heat sealability A porous film was placed on a resin wide-mouthed bottle (material: high-density polyethylene, 100 mL, AS ONE) with the lid removed, and contacted with a hot plate set at 160 ° C for 10 seconds under a load of 500 g. Heat-sealing was performed by letting it. After heat sealing, the heat sealing property was judged by the following evaluation method at the time of peeling.
G (Good): After heat sealing, the film does not have edge breakage during peeling.
B (Bad): After heat sealing, the film is cut off at the time of peeling.

The porous films of Examples 1 to 3 have a predetermined porous layer (I) and a porous layer (II), and the average pore diameter is adjusted to a specific range, so that they have heat-sealing properties and bacterial barrier properties. It was excellent in quality and showed good processing characteristics without edge breakage even during peeling after heat sealing.
Further, since the porous layer (I) and the porous layer (II) are formed of a predetermined material or have a predetermined property, the film of the present invention is porous having different average pore diameters. It has a structure.
More specifically, the film of the present invention has heat-sealing property, bacterial barrier property, and edge cutting prevention property at the time of peeling after heat-sealing due to the fine porous structure of the porous layer (II). Due to the large pore size of the porous layer (I), it is possible to have excellent air permeability and communication, and it is possible to obtain an excellent sterilization treatment effect.
Further, in the porous films of Examples 1 to 3, the average pore diameter and the maximum pore diameter are adjusted within a predetermined range to prevent the invasion of bacteria into the inside, and the moisture permeable and waterproof property allows water droplets to enter the inside. Since it can prevent invasion and sufficiently permeate water vapor and various gases, it can be expected to have an excellent sterilization treatment effect and further excellent bacterial barrier property against various bacteria and viruses.
On the other hand, in the porous films of Comparative Examples 1 to 3 and 5, since the heat-sealed surface had a coarse porous structure, edge breakage occurred at the time of peeling after heat-sealing.
Further, since the porous film of Comparative Example 4 has only a layer having a fine pore diameter, the air permeability property may be deteriorated, which may cause a problem that water vapor or gas due to high-pressure vapor or ethylene oxide gas cannot be sufficiently permeated. Not suitable for sterilization.

The film of the present invention can be suitably used for moisture-permeable and waterproof films used for clothing, sanitary materials, etc., and for medical packaging applications involving sterilization treatment with high-pressure steam or ethylene oxide gas.

Claims (10)

A porous film having at least a porous layer (I) and a porous layer (II).
The porous layer (I) contains a polyolefin resin and a vinyl aromatic elastomer, and has a sea-island structure in which the vinyl aromatic elastomer forms a domain in the matrix of the polyolefin resin.
The porous layer (II) has β-crystal activity and constitutes a surface layer on at least one surface side of the porous film.
A porous film having an average pore diameter of 0.050 μm or less as measured by a palm poromometer. The porous film according to claim 1, wherein the difference between the average pore diameter of the porous layer (I) and the average pore diameter of the porous layer (II) measured in the cross section of the porous film is 1.0 μm or more. The porous film according to claim 1 or 2, wherein the melt flow rate of the vinyl aromatic elastomer measured at a temperature of 230 ° C. and a load of 2.16 kg is 1.0 g / 10 minutes or less. The porous film according to any one of claims 1 to 3, wherein the porous layer (II) contains a β-crystal nucleating agent. The porous film according to any one of claims 1 to 4, wherein the maximum pore diameter is 0.80 μm or less. The porous film according to any one of claims 1 to 5, which has a thickness of 50 to 300 μm and an air permeability of 300 seconds / dL or less. The porous film according to any one of claims 1 to 6, which is a stretched film stretched at least in the uniaxial direction. The porous film according to any one of claims 1 to 7, wherein the porous layer (I) is a middle layer. Any of claims 1 to 8, wherein the porous layer (II) constitutes a surface layer on both sides of the porous film, and the porous layer (I) has a structure of at least two types and three layers in which the porous layer (I) is a middle layer. The porous film according to item 1. A medical packaging material using the porous film according to any one of claims 1 to 9.

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