JP2002088182A - Porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film which has high moisture permeability and air permeability, produced with a conventional stretching ratio and the conventional contents of an inorganic filler. SOLUTION: This porous film comprising 25 to 55 wt.% of the mixture of a polyolefin-based resin with a thermoplastic elastomer having moisture permeability and 75 to 45 wt.% of an inorganic filler, characterized in that the content of the thermoplastic elastomer having moisture permeability is 0.5 to 10 vol.% in the mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a porous film containing a polyolefin resin containing a thermoplastic elastomer having moisture permeability and an inorganic filler.

[0002]

2. Description of the Related Art Conventionally, a porous film is prepared by adding an inorganic filler to a polyolefin resin, melt-forming the film, and then stretching the film to separate the interface between the polyolefin resin and the inorganic filler. Manufactured in such a way. Since these porous films have a large number of fine pores inside, they have high waterproofness while having high moisture permeability. Therefore, for example, when a porous film is used as a back film of a disposable diaper or a sanitary napkin, it is effective as a leak-proof material without stuffiness.

[0003] In recent years, in the use of such disposable diapers, attempts to improve the feel to the skin by laminating a nonwoven fabric on a porous film have become mainstream. However, since the pores of the porous film are partially closed by lamination with the nonwoven fabric, and the moisture permeability tends to decrease, it is required to improve the moisture permeability on the porous film side. Furthermore, the occurrence of stuffiness and rash especially in summertime, which is observed in disposable diapers and the like, has become a serious problem, and a demand for a highly moisture-permeable porous film has been increasing in order to further improve comfort.

Here, as a method of improving the moisture permeability of the porous film, a method of increasing the stretching ratio and a method of increasing the amount of the inorganic filler have been conventionally used. However, a method of increasing the stretching ratio is not preferable because the film tends to be broken at the time of stretching and the productivity is reduced. Further, even if stretching is possible, there is a limit because the moisture permeability tends to be not improved at a certain stretching ratio or more. On the other hand, the method of increasing the amount of the inorganic filler is not preferable because the amount of the resin is reduced, so that the strength is insufficient or the film is easily broken at the time of stretching.

On the other hand, a film using a thermoplastic elastomer having moisture permeability, which is different from a porous film,
It is known as a film having high moisture permeability. However, since the raw material cost is high, it is not suitable for applications such as disposable diapers and sanitary materials. As a method of reducing the raw material cost, a method of reducing the thickness of a film is also conceivable. However, since the film strength is reduced, it cannot be used for the above-mentioned applications. Furthermore, the film itself using a thermoplastic elastomer can provide moisture permeability but is not a porous film, and therefore cannot provide air permeability, and is insufficient in preventing stuffiness and rash.

[0006]

However, an object of the present invention is to provide a porous film having high moisture permeability and high air permeability while maintaining the same draw ratio and the content of an inorganic filler as a conventional porous film. To provide a functional film.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have added a required amount of an inorganic filler to a resin mixture of a polyolefin resin and a thermoplastic elastomer having moisture permeability to form a film, It has been found that a porous film obtained by stretching it has high moisture permeability and high air permeability, and has finally reached the present invention.

That is, the present invention relates to a mixture 2 of a polyolefin resin and a thermoplastic elastomer having moisture permeability.
A porous film containing 5 to 55% by weight and 75 to 45% by weight of an inorganic filler, wherein the content of the thermoplastic elastomer having moisture permeability in the mixture is 0.5 to 10% by volume. It is a characteristic porous film.

The porous film according to the present invention comprises a polyolefin resin containing 0.5 to 10% by volume of a moisture-permeable thermoplastic elastomer, 25 to 55% by weight of a mixture thereof, and 75 to 45% by weight of an inorganic filler. A film can be produced by molding a film from the resin composition containing the film, and then stretching the obtained film in at least a uniaxial direction.

A feature of the porous film provided by the present invention is that it has high moisture permeability while maintaining the same draw ratio and the content of the inorganic filler as the conventional one. A porous film having such properties can be produced by mixing a moisture-permeable thermoplastic elastomer with a polyolefin-based resin. The porous film according to the present invention has a high number of pore interfaces therein, and has high moisture permeability and air permeability because the thermoplastic resin has moisture permeability.

Therefore, the porous film according to the present invention can be suitably used for sanitary materials such as disposable diapers, packaging materials for foods, and clothing. still,
The moisture permeability and air permeability of the porous film in the present invention mean values obtained by a method described in Examples described later.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The porous film of the present invention is formed by melt-molding a resin composition containing a mixture of a polyolefin resin and a thermoplastic elastomer having moisture permeability at a specific ratio, and an inorganic filler to form a film. It can be manufactured by stretching in a uniaxial direction.

The polyolefin resin is mainly composed of a monoolefin polymer such as ethylene, propylene and butene and a copolymer thereof. Specifically, polyethylene resins such as low-density polyethylene, linear low-density polyethylene (ethylene-α-olefin copolymer), medium-density polyethylene, and high-density polyethylene, and polypropylene resins such as polypropylene and ethylene-polypropylene copolymer , Poly 4-methylpentene, polybutene,
Examples thereof include an ethylene-vinyl acetate copolymer and a mixture thereof.

These polyolefin-based resins may be resins produced using a multi-site catalyst such as a Ziegler catalyst, or resins produced using a single-site catalyst such as a metallocene catalyst. . Among these, ethylene-α is considered in consideration of the moldability into a film, heat resistance and stretchability of the obtained film.
-Linear low-density polyethylene resins, low-density polyethylene resins, polypropylene resins, and ethylene-propylene copolymers, which are olefin copolymers, are preferred. The above resins may be used alone or in combination of two or more.

The melt index (hereinafter referred to as MI) of the polyolefin resin affects the strength and productivity of the porous film. The MI of the polyolefin-based resin used in the present invention is 0.1 to 10 g / 10 min when used alone, or when used as a mixture of two or more kinds. Preferably it is 0.5 to 8 g / 10 min. More preferably, it is 1 to 5 g / 10 min. MI is 0.1 to 10 g /
The polyolefin resin for 10 minutes has high strength and productivity. Incidentally, even if the polyolefin resin alone falls outside the above range, it may be used in the present invention as long as the MI as a mixture is within the above range. Here, the melt index in the present invention is ASTM D-123.
8, a temperature of 190 ° C. and a load of 216
It was measured under the conditions of 0 g (for a polyethylene resin), 230 ° C., and a load of 2.16 kg (for a polypropylene resin).

The MI of the polyolefin resin is 0.1 g /
When the time is less than 10 minutes, the porous film has high strength, but the viscosity of the resin at the time of melting becomes high, and the productivity becomes poor, which is not preferable. M of polyolefin resin
When I is more than 10 g / 10 min, the viscosity of the resin at the time of melting is low, but the strength of the resin is lowered. Absent.

The density of the polyolefin resin affects the physical properties of the obtained film. Generally, 0.910
It is preferably in the range of 0.935 g / cm ³ . More preferably, it is 0.910 to 0.930 g / cm ³ . When the density is less than 0.910 g / cm ³ , the resulting film has an extremely low moisture permeability, which is not preferable. When the density exceeds 0.935 g / cm ³ , moisture permeability can be obtained, but uniform stretchability is poor, and the flexibility of the film is reduced, which is a problem when used as a back film of a disposable diaper.

The porous film of the present invention contains a specific proportion of a thermoplastic elastomer having moisture permeability in the polyolefin resin. The elastomer referred to here is a polymer substance and is an elastic material. At a high temperature, it is preferably a thermoplastic elastomer that can be molded in the same manner as a normal thermoplastic resin. Further, as the thermoplastic elastomer having moisture permeability, various thermoplastic elastomers having moisture permeability can be used.

Suitable thermoplastic elastomers having moisture permeability include urethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, and polyolefin-based ionomers. Thermoplastic urethane elastomers include polyurethane obtained by the reaction of a short-chain polyol (molecular weight 60 to 600) with diisocyanate, and a long-chain polyol (molecular weight 6).
And a polyurethane obtained by the reaction of diisocyanate with a polyurethane. As the diisocyanate, toluene diisocyanate,
And diphenylmethane diisocyanate.
Short-chain polyols include ethylene glycol, 1,3
-Propylene glycol, bisphenol A and the like.

As the urethane-based thermoplastic elastomer, a polycaprolactone ester polyol such as polycaprolactone glycol can be used in the presence of a short-chain polyol.
Diisocyanate addition polymerized (polyether polyurethane); poly (ethylene-1,4-adipate)
Glycol, poly (butylene-1,4, -adipate)
Addition of diisocyanate to adipic ester polyol such as glycol in the presence of short-chain polyol (polyester polyurethane); polyisocyanate in polytetramethylene glycol obtained by ring-opening of tetrahydrofuran in presence of short-chain polyol Examples thereof include those obtained by addition polymerization of a naat. Commercially available products include Vulcolan (trade name, manufactured by Bayer AG), Chemigum SL (trade name, manufactured by Goodyear), Adiprene (trade name, manufactured by DuPont), Harcaprene (trade name, manufactured by ICI), and the like.

The polyester elastomer is represented by the following general formula (1) derived from an aromatic polyester:

[0022]

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And a structural unit represented by the following general formula (2) derived from an aliphatic polyether:

[0024]

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(In the general formulas (1) and (2), D is a divalent residue obtained by removing two hydroxyl groups from a diol having a molecular weight of 14 to 250, and R is an aromatic dicarboxylic acid having a molecular weight of 78 to 300. G is a divalent aromatic residue obtained by removing two carboxyl groups from an acid, and G has an average molecular weight of 14 to 3500.
Is a divalent residue obtained by removing the hydroxyl groups at both terminals from poly (alkylene oxide) glycol of the formula (1).

Here, the amount of the ethylene oxide unit inserted into the structural unit represented by the general formula (2), which is a copolyetherester of poly (alkylene oxide) glycol, is 25 to the total weight of the copolyetherester. About 68% by weight. In the present invention, the aromatic polyester unit represented by the general formula (1) is a tetramethylene terephthalate unit, and the aliphatic polyether unit represented by the general formula (2) is an alkylene ether terephthalate unit. Is preferred.
Specific examples include a polybutylene terephthalate / polytetramethylene ether glycol block copolymer. Examples of the commercially available product include Hytrel (trade name, manufactured by DuPont).

Examples of the polyamide elastomer include a multiblock copolymer of a polyamide and a diol of a polyester or a polyol having a glass transition temperature of -100 ° C to 100 ° C. Here, as the polyamide component, nylon 6, 66, 610, 11,
12 and the like. Of these, nylon 6 and nylon 12 are preferred. Examples of the polyether diol include poly (oxytetramethylene) glycol and poly (oxypropylene) glycol.

Examples of the polyester diol include poly (ethylene-1,4-adipate) glycol, poly (butylene-1,4-adipate) glycol, polytetramethylene glycol and the like. Specific examples include a nylon 12-polytetramethylene glycol block copolymer. Examples of commercially available products include diamide (manufactured by Daicel Huls), PEBAX (manufactured by Atochem) [all are trade names].

As the polyolefin ionomer,
There are copolymer metal salts of ethylene, propylene, butene, etc. and unsaturated carboxylic acids. Examples of commercially available products include Himilan (trade name, manufactured by Du Pont-Mitsui Polychemicals) using methacrylic acid as an acid monomer. Among these, urethane-based elastomers and polyester-based elastomers are preferred because of their excellent moisture permeability.

The mixing ratio of the thermoplastic elastomer having moisture permeability to the polyolefin resin affects the moisture permeability, air permeability, and strength of the obtained porous film. If the amount of the thermoplastic elastomer having moisture permeability in the mixture of the polyolefin resin and the thermoplastic elastomer having moisture permeability is too large, high moisture permeability is easily obtained, but the film strength is insufficient, and the film at the time of molding is insufficient. It is not preferable because it may cause a pinhole which breaks or impairs waterproofness. Also, if the amount of the thermoplastic elastomer having moisture permeability is too small, there is no effect on the film strength,
It is not preferable because the effect of enhancing moisture permeability and air permeability is insufficient. From this viewpoint, the amount of the moisture-permeable thermoplastic elastomer in the mixture of the polyolefin-based resin and the moisture-permeable thermoplastic elastomer is 0.5 to 10%.
It is preferably volume%. More preferably, 1 to 8
% By volume.

The porous film of the present invention contains a polyolefin resin containing the above-mentioned thermoplastic elastomer having moisture permeability, and a predetermined amount of an inorganic filler. As an inorganic filler,
Examples include calcium carbonate, barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide, aluminum hydroxide, zinc oxide, magnesium oxide, titanium oxide, silica, talc and the like. Of these, calcium carbonate and barium sulfate are preferred. These inorganic fillers may be used alone or as a mixture of two or more.

The inorganic filler has an average particle size of 0.1 to 5
μm is preferred. More preferably 0.5 to 3
μm. More preferably, it is 0.7 to 2.5 μm. When the average particle size of the inorganic filler is less than 0.1 μm,
It is difficult to uniformly disperse the inorganic filler particles in the resin, which is not preferable. In addition, it is difficult to form the communication hole, and the moisture permeability is undesirably reduced. When the average particle size of the inorganic filler exceeds 5 μm, the dispersion of the inorganic filler in the resin becomes easy. In addition, communication holes are easily formed, and have high moisture permeability. However, it is not preferable because the particle size is extremely increased, which causes a problem such as film breakage during film formation.

These inorganic fillers are subjected to a surface treatment to improve the dispersibility with the polyolefin resin, promote the interfacial separation with the resin, and prevent the absorption of moisture from the outside. It may be done. As the surface treating agent, those capable of making the surface hydrophobic by coating the surface of the inorganic filler are preferable, and examples thereof include higher fatty acids such as stearic acid and lauric acid, and metal salts thereof.

The composition ratio of the polyolefin resin containing the thermoplastic elastomer having moisture permeability and the inorganic filler affects the moldability and stretchability of the film and the moisture permeability and air permeability of the resulting porous film. If the amount of the inorganic filler is less than 45% by weight, the number of internal pores decreases, and the moisture permeability decreases, which is not preferable. Further, when the amount of the inorganic filler is 7
If the content exceeds 5% by weight, internal pores increase and moisture permeability increases, but it is not preferable because the strength of the film is reduced or molding defects such as stretch breakage occur when the film is formed. From such a viewpoint, the composition ratio of the polyolefin-based resin containing the thermoplastic elastomer having moisture permeability and the inorganic filler is preferably 25 to 55% by weight of the polyolefin-based resin and 75 to 45% by weight of the inorganic filler. . More preferably, the polyolefin resin containing a thermoplastic elastomer having moisture permeability is 30 to 50% by weight, and the inorganic filler is 70 to 50% by weight.

In the porous film of the present invention, a drawing aid such as a fatty acid ester, a stabilizer, an antioxidant, a coloring agent, a light stabilizer, a flame retardant, an antistatic agent, etc. Other additives such as a deodorant and an antibacterial agent may be added.
Of these additives, it is desirable to add a drawing aid such as a fatty acid ester in order to improve the drawability.
If the amount is too large, the productivity of the film is reduced, and if the amount is too small, a sufficient effect cannot be obtained. 0.1 ~
3% by weight is preferred.

The porous film of the present invention is produced by the following method. After mixing the polyolefin-based resin and the thermoplastic elastomer having moisture permeability, and the inorganic filler, and other additives as necessary, mixed using a Henschel mixer, a super mixer, a tumbler type mixer or the like,
Thereafter, the mixture is kneaded by a usual single screw or twin screw extruder and pelletized. Next, the pellet is melted at a temperature equal to or higher than the melting point of the polyolefin resin,
At a temperature of 0 ° C. or higher and lower than the decomposition temperature, melting and film formation are performed using a known molding machine such as an extruder equipped with a T-die or the like or an inflation molding machine equipped with a circular die. In some cases, it is possible to form a film directly with a molding machine without pelletizing.

The formed film is heated at a temperature not lower than room temperature and lower than the softening point of the resin (a value measured by a method specified in JIS K-6760) by a known method such as a roll method or a tenter method. Stretching is performed at least in a uniaxial direction. Stretching may be performed in one step or may be performed in multiple steps. Further, after stretching, a heat setting treatment may be performed as needed to stabilize the form of the obtained aperture. As heat setting treatment, the softening point of the resin or higher,
A method of performing a heat treatment at a temperature lower than the melting point for 0.05 to 100 seconds.

The stretching ratio affects the physical properties and stretchability of the obtained porous film. If the stretching ratio is less than 1.1 times, pores are not sufficiently formed, and the moisture permeability is undesirably reduced. If the stretching ratio exceeds 7 times, pores are sufficiently formed, but on the contrary, stretching breakage frequently occurs and productivity is lowered, which is not preferable. From such a viewpoint, the stretching ratio of the porous film is preferably 1.1 to 7 times. More preferably, it is 1.2 to 5 times.

The thickness of the porous film is 10 to 100 μm.
m is preferred. If the thickness of the film is less than 10 μm, the film strength is undesirably reduced. On the other hand, if the film thickness exceeds 100 μm, it is not preferable because the texture becomes poor and the cost increases when used for applications such as disposable diapers.

The porous film obtained under the above composition and production conditions has a moisture permeability of at least 3000 g / m ² · 24.
hr, a porous film having an air permeability of less than 3000 seconds / 100 ml. For example, in order to use a porous film as a backside film for a disposable diaper, it is desired to have high moisture permeability and air permeability for the purpose of preventing diaper rash and pursuing comfort. The porous film according to the present invention has a large number of internal pores, and has high moisture permeability and air permeability because the thermoplastic elastomer has moisture permeability. The moisture permeability of the porous film is 30
Less than 00 g / m ² · 24 hr or air permeability of 3000
When the speed is at least 100 seconds / 100 ml, the wearer may suffer from stuffiness, rash and the like, which is not preferable.

[0041]

EXAMPLES The present invention will be described in more detail with reference to the following examples. Note that the present invention is not limited to these examples. The MI, moisture permeability, air permeability, and film thickness shown in the examples are values measured by the following methods.

(1) Melt index (g / 10 mi)
n) According to the method specified in ASTM D-1238-57T (E), at a temperature of 190 ° C., a load of 2160 g (for polyethylene resin), 230 ° C., and a load of 2.16 kg (for polypropylene resin). Measure.

(2) Moisture Permeability (g / m ² · 24 hr) Based on the method specified in ASTM E-96, a temperature of 4
It is measured under the conditions of 0 ° C., 60% relative humidity, and pure water method. Samples are randomly collected at 10 points, and the average value is calculated.
The measurement time is 24 hours.

(3) Air permeability (sec / 100 ml) According to the method specified in JIS P-8117, a sample was randomly collected at 10 points using an Oken-type air permeability meter, and the average value was taken. Is calculated.

(4) Film thickness (μm) From the porous film, a sample [MD: 10 cm, TD: 10
cm], and 5 points at 3 cm intervals per sheet,
For a total of 50 measurement points, a thickness measuring machine (PEAC
UPRIGHT DIAL GUAGE manufactured by OCK
NO. The thickness is measured using 25), and the average value is calculated.

Example 1 Linear low-density polyethylene (trade name, manufactured by Mitsui Chemicals, Inc.)
Evolu SP2040, density: 0.920 g / c
m ³ , MI: 4.0 g / 10 min) 37% by weight, polyester elastomer which is a thermoplastic elastomer (trade name: Hytrel 354, manufactured by Du Pont-Toray Co., Ltd.)
8 L, density: 1.15 g / cm ³ ) 3% by weight (6% by volume of the total amount of linear low-density polyethylene and thermoplastic elastomer, the same applies hereinafter) to calcium carbonate (trade name, manufactured by Dowa Calfine Co., Ltd.) : MD-2) 60% by weight and 1% by weight of calcium stearate were mixed by a tumbler mixer, and then uniformly kneaded at 230 ° C using a tandem type extruder to be processed into pellets. The pellet was melt-extruded at 230 ° C. using an extruder equipped with a T-die to obtain an unstretched film. The obtained unstretched film was uniaxially stretched in the machine direction at a stretching ratio of 2 between a preheating roll heated at 65 ° C. and a stretching roll to obtain a porous film 1 having a thickness of 20 μm. Porous film 1
Had good moisture permeability and air permeability.

Example 2 A porous film 2 was obtained in the same manner as in Example 1 except that the amount of the thermoplastic elastomer was changed as shown in Table 1. The porous film 2 had good moisture permeability and air permeability.

Examples 3 and 4 A porous film was produced in the same manner as in Example 1 except that the blending ratio of the mixture of the polyolefin resin and the thermoplastic elastomer and the inorganic filler and the stretching ratio were as shown in Table 1. 3 and 4 were obtained. The porous films 3 and 4 had good moisture permeability and air permeability.

Example 5 A porous film 5 was obtained in the same manner as in Example 1 except that the thickness of the porous film was as shown in Table 1. The porous film 5 had good moisture permeability and air permeability.

Example 6 The procedure of Example 1 was repeated except that a polypropylene resin (trade name: F103WH, density 0.910 g / cm 3, MI 2.4 g / 10 min, manufactured by Grand Polymer Co., Ltd.) was used as the polyolefin resin. A porous film 6 was obtained. The porous film 6 had good moisture permeability and air permeability.

Example 7 A porous film 7 was obtained in the same manner as in Example 1, except that sedimentable barium sulfate (trade name: HD, manufactured by Barite Industry Co., Ltd.) was used as an inorganic filler. Porous film 7
Had good moisture permeability and air permeability.

Example 8 A porous film 8 was obtained in the same manner as in Example 1 except that a polyurethane-based thermoplastic elastomer (trade name: Rezamin P210, manufactured by Dainichi Seika Kogyo KK) was used as the thermoplastic elastomer. . The porous film 8 had good moisture permeability and air permeability.

Comparative Examples 1-2 The same procedure as in Example 1 was repeated except that the mixing ratios of the thermoplastic elastomers were as shown in Table 2, respectively.
10 was obtained. The porous film 9 did not have sufficient moisture permeability. As for the porous film 10, a sample could not be obtained because the film could not be formed due to insufficient strength of the film.

Comparative Examples 3 and 4 Porous films 11 and 12 were obtained in the same manner as in Example 1 except that the mixing ratio of the mixture of the polyolefin resin and the thermoplastic elastomer and the inorganic filler was set as shown in Table 2. Was. As for the porous film 11, a sample could not be obtained because the film could not be formed due to insufficient strength of the film. Since the amount of the inorganic filler was small in the porous film 12, sufficient air permeability and moisture permeability could not be obtained.

Comparative Example 5 A porous film 13 was obtained in the same manner as in Example 1, except that the mixing ratio of the thermoplastic elastomer was as shown in Table 2.
The porous film had many pinholes during the film formation. Although the obtained film has good moisture permeability and air permeability, it has no waterproofness due to the presence of pinholes and cannot be used as a leakproof material.

[0056]

[Table 1]

[0057]

[Table 2]

<Explanation of Table Symbols> [Table 1] and [Table 2]
The symbols described in the above mean the following. LLDPE: linear low density polyethylene, CaCO ₃ : calcium carbonate, B
aSO ₄ : barium sulfate, the volume% of the thermoplastic elastomer indicates a value based on the total amount of the polyolefin resin and the thermoplastic elastomer. An asterisk means the presence of a large pinhole.

[0059]

The characteristics of the porous film provided by the present invention are that it has high moisture permeability and air permeability while maintaining the same stretching ratio and the content of the inorganic filler as the conventional porous film. It is in. A porous film having such properties can be produced by mixing a specific amount of a moisture-permeable thermoplastic elastomer with a polyolefin-based resin. The porous film according to the present invention,
Having a large number of pore interfaces inside, and having high moisture permeability and air permeability due to the thermoplastic resin having moisture permeability. Therefore, the porous film according to the present invention, for sanitary materials such as disposable diapers, for packaging materials such as food, for clothing,
It can be suitably used.

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Claims (5)

[Claims] 1. A porous film comprising 25 to 55% by weight of a mixture of a polyolefin resin and a thermoplastic elastomer having moisture permeability, and 75 to 45% by weight of an inorganic filler. A porous film having a thermoplastic elastomer content of 0.5 to 10% by volume. 2. The resin according to claim 1, wherein the thermoplastic elastomer having moisture permeability is at least one resin selected from urethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, and polyolefin-based ionomers. Porous film. 3. The porous film according to claim 1, wherein the thermoplastic elastomer having moisture permeability is at least one resin selected from a urethane elastomer and a polyester elastomer. 4. The porous film according to claim 1, wherein the film is stretched in at least one direction by 1.1 to 7 times. 5. A water vapor transmission rate of at least 3000 g / m ² ···
The porous film according to claim 1, wherein the porous film has an air permeability of less than 3000 seconds / 100 ml and a thickness of 10 to 100 µm for 24 hours.