JP7135709B2 - porous film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a porous film, and more particularly to a porous film that prevents permeation of water vapor but is excellent in permeation of oxygen.

Porous films with a large number of fine pores are used in the production of ultrapure water, purification of chemicals, separation membranes used in water treatment, moisture-permeable and waterproof films used in clothing and sanitary materials, electronic equipment and housing, It is used in various fields such as heat insulating films used in building materials and battery separators used in batteries. In general, a porous film that exhibits communication in the thickness direction due to the presence of pores inside prevents liquid water from penetrating into the porous structure, as typified by moisture permeation and waterproofness. However, it is difficult to adjust the permeation behavior of specific gases such as water vapor and oxygen, and it is opaque because it has pores inside. It was difficult to use in applications.

For example, a film for packaging fruits and vegetables can be mentioned as a film whose water vapor permeability and oxygen permeability need to be adjusted. This film is used to preserve the freshness of fresh vegetables and fruits and vegetables.It suppresses water vapor permeation in order to reduce wilting due to water loss, which is a prominent deterioration of fruits and vegetables, and has sufficient oxygen permeability so as not to hinder the respiration of fruits and vegetables. have sex. Patent Literature 1 discloses a film in which holes are formed by a laser irradiation device.

As another example, wound dressings used in medical applications require low water vapor permeability to prevent evaporation of water from the wound to promote healing, while having sufficient oxygen permeability. For example, high oxygen permeability is necessary because cells may become hypoxic and compromise healing functions (eg, antibacterial activity of neutrophils, or collagen production by fibroblasts). Patent Document 2 discloses a film coated with silicone as an oxygen diffusing material.

As another example, the membrane aeration bioreactor (MABR), which is one of the water treatment methods, adheres and immobilizes microorganisms in the form of a biofilm on the outer surface of a porous substrate, and supplies oxygen directly from the inside of the membrane. , It is a method that promotes the decomposition of organic matter by microorganisms, but if the permeation of water vapor through the porous substrate is high, water droplets adhere to the air layer. It has been demanded. Patent Document 3 discloses a film using a non-porous oxygen-permeable membrane.

JP 2014-140349 A Japanese translation of PCT publication No. 2015-532147 JP 2018-47403 A

However, in the hole formation by the laser irradiation apparatus of Patent Document 1, the size of the hole is very large, ie, 20 μm or more and 2000 μm or less, while keeping the water vapor permeation amount and the oxygen permeation amount within a certain range. There is concern and risk of tearing from the hole. In Patent Document 2, silicone is applied as an oxygen diffusing material, and in Patent Document 3, a non-porous oxygen permeable membrane is used. Therefore, the oxygen permeability is not sufficient, and if it is non-porous, the amount of permeated oxygen is significantly reduced. As a method for improving such oxygen permeability, there is a method of making the film porous. There was a problem that the amount of permeating water vapor also increased.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a porous film that prevents water vapor permeation, has excellent oxygen permeability, has excellent puncture strength, and has transparency.

As a result of intensive studies, the present inventors succeeded in obtaining a porous film capable of solving the above-described problems of the prior art, and completed the present invention.

That is, the object of the present invention is to provide a porous film containing a propylene-based resin as a main component, having a porosity of 10 to 40%, an air permeability of 20,000 seconds/dL or more, and an average light transmittance of 30% or more. resolved.

The porous film of the present invention is excellent in puncture strength and has both low water vapor permeability and high oxygen permeability, so that it selectively permeates and can be used as a separation membrane. It is also a porous film having optical transparency. Furthermore, according to the method for producing a porous film of the present invention, it is not essential to use a foaming agent such as a gas during production, so that it is highly environmentally friendly.

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

<Porous film>
A porous film (hereinafter sometimes referred to as "the present film") according to an embodiment of the present invention contains a propylene-based resin as a main component, has a porosity of 10 to 40%, and an air permeability of 20,000. The porous film has a second/dL or more and an average light transmittance of 30% or more.

(1) Thickness The thickness of the present film is not particularly limited, but is preferably 5 to 100 μm. The lower limit is preferably 10 μm or more, more preferably 15 μm or more. On the other hand, the upper limit is preferably 90 µm or less, more preferably 75 µm or less, and particularly preferably 50 µm or less. If the thickness is 5 μm or more, sufficient strength can be maintained as a film. Also, if the thickness is 100 μm or less, low water vapor permeability and high oxygen permeability can be maintained.

(2) Porosity The porosity of the present film is a numerical value that indicates the proportion of space in the porous film, and it is important that it is 10 to 40%. As a lower limit, 12% or more is more preferable, 14% or more is still more preferable, and 16% or more is particularly preferable. On the other hand, the upper limit is more preferably 38% or less, even more preferably 36% or less, and particularly preferably 34% or less. If the porosity is 10% or more, a high oxygen permeability can be obtained. Further, if the porosity is 40% or less, the formation of continuous pores in the thickness direction due to the pores in the film can be prevented, and the water vapor permeability can be low.
Therefore, by setting the porosity in the range of 10 to 40%, a general method for adjusting the porosity that can achieve both low water vapor permeability and high oxygen permeability is the addition of a foaming agent or various fillers. It is possible to adjust the amount of material, such as the amount of solvent added on the premise of extraction later, and the adjustment of conditions such as temperature, pressure, time, and draw ratio when processing the material. The porosity can be adjusted by adjusting the working surfaces together.
The method for measuring the porosity is as follows.
The actual mass W1 of the measurement sample is measured, the mass W0 when the porosity is 0% is calculated based on the density of the resin composition, and the porosity is calculated from these values according to the following formula.
Porosity (%) = {(W0-W1)/W0} x 100

(3) Air permeability
The air permeability of the film is preferably 20,000 sec/dL or more, more preferably 40,000 sec/dL or more, and particularly preferably 60,000 sec/dL or more. By setting the air permeability of the porous film to 20,000 sec/dL or more, excessive water vapor permeability can be prevented, and a balance with oxygen permeability can be maintained.
The air permeability indicates how difficult it is for air to pass through the porous film in the thickness direction, and is specifically expressed by the number of seconds required for 100 ml of air to pass through the porous film. Therefore, the smaller the number, the easier it is to pass through, and the larger the number, the harder it is to pass through. That is, a smaller numerical value means that the continuity of the porous film in the thickness direction is better, and a greater numerical value means that the continuity of the porous film in the thickness direction is poorer. Continuity is the degree of connection of pores in the thickness direction of the porous film. The air permeability (sec/100 ml) can be measured according to JISP8117, specifically by the method described in Examples.

(4) Average light transmittance
The average light transmittance of the film is preferably 30% or more, more preferably 35% or more, still more preferably 40% or more, and particularly preferably 45% or more. By setting the average light transmittance of the present film to 30% or more, transparency can be imparted to the porous film. The average light transmittance of the porous film is due to the pore structure and porosity inside the film.
Although there is no particular upper limit, it is usually 98% or less.
The light transmittance can be measured with a spectrophotometer, specifically by the method described in Examples.
Although the light transmittance varies somewhat depending on the film thickness, in the present invention, the average light transmittance per 15 μm thickness is preferably within the above range.

(5) Puncture strength The puncture strength of the present film is preferably 20 gf/μm or more, more preferably 22 gf/μm or more, still more preferably 24 gf/μm or more, and 26 gf/μm or more. is particularly preferred.
If the pin puncture strength of the film is 20 gf/μm or more, it can be said that the porous film has sufficient strength for practical use. It is thought that the piercing strength will be high enough to be practical. Although there is no particular upper limit, it is usually 40 gf/μm or less.

(6) Oxygen permeability The oxygen permeability of the present film is preferably 1,000,000 cc/m ² ·24 hr·atm or more, and is preferably 5,000,000 cc/m ² ·24 hr·atm or more. More preferably, it is particularly preferably 10,000,000 cc/m ² ·24 hr·atm or more. When the oxygen permeability of the porous film is 1,000,000 cc/m ² ·24 hr·atm or more, it can be said that the porous film has sufficient oxygen permeability. Although the upper limit is not particularly defined, it is usually 1,000,000,000 cc/m ² ·24 hr·atm or less. The oxygen permeability can be measured based on JIS K7126-2:2006, and specifically by the method described in Examples.

(7) Water vapor permeability The water vapor permeability of the present film is preferably 1,000 g/m ² 24 hr or less, more preferably 750 g/m ² 24 hr or less, and 500 g/m ² 24 hr or less. is particularly preferred. It can be said that passage of water vapor is suppressed when the water vapor transmission rate is 1,000 g/m ² ·24 hr or less. Although the lower limit is not specified, it is usually 1 g/m ² ·24 hr or more. The water vapor transmission rate can be measured based on JIS K7129:2008, and specifically can be measured by the method described in Examples.

The layer structure of the present film is not limited to a single layer, and may be a multilayer structure of 2 layers, 3 layers, 4 layers, 5 layers, or more as long as it does not significantly impair the effects of the present invention. It may further comprise layers.

In general, gas permeation of polymeric materials is considered in terms of the dissolution diffusion mechanism. For gases such as oxygen and carbon dioxide, the interaction between the polymer chains and the gas molecules is small, so the diffusion coefficient is more dominant than the solubility coefficient. It has a similar tendency of transmission, depending on the primary structure of the polymer chain and the higher order structure such as the crystal structure. On the other hand, in water vapor, when hydrogen bonds that cause strong interaction occur with the polymer chain, the solubility coefficient and diffusion coefficient increase significantly, so the primary structure of the polymer chain shows different behavior from the permeation behavior of oxygen and carbon dioxide. .
The present invention found that a film containing a propylene-based resin as a main component, having an appropriate porosity, and having appropriate light transmittance and air permeability has low water vapor permeability and high oxygen permeability. It is. This mechanism is currently considered as follows.
In other words, since this film has a light transmittance of 30% or more and an air permeability of 20,000 sec/cc, it is a film having a large number of nano-order fine pores. Therefore, with respect to oxygen, diffusion of oxygen in the film is promoted, and high oxygen permeability is realized. On the other hand, since water vapor is rate-determining in dissolution, it is insoluble in polypropylene resin. Furthermore, since the film has fine pores and cannot move easily between the pores, it is difficult to permeate the film. be. As a result, we believe that this film has high oxygen permeation selectivity.
The present inventors have found that it is important to arrange the nano-order pores in a porosity range of 10 to 40% in order to achieve both high oxygen permeability and low water vapor permeability.

In general, the porous film adjusts the moisture permeability and communication property by adjusting the porosity of the film. For example, increasing the porosity facilitates the formation of continuous pores, resulting in a film with good air permeability. Generally, however, as the porosity increases, whitening occurs due to the difference in refractive index between the resin and the air layer, resulting in deterioration in light transmittance and puncture strength. According to the present invention, by strictly adjusting the porosity, air permeability, and light transmittance, a porous film with nano-order pores is formed, and has high puncture strength, high oxygen permeability, and low water vapor permeability. It has been found that a film having

The propylene-based resin constituting the present film will be described below. After that, a method for forming the present film as a manufacturing method will be described.
<Propylene resin>

As the propylene-based resin constituting the present film, homopolypropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene or 1 - Random copolymers or block copolymers with α-olefins such as decene. Among these, homopolypropylene is more preferably used from the viewpoint of mechanical strength.

Further, the propylene-based resin preferably has an isotactic pentad fraction of 80 to 99%, more preferably 83 to 98%, and still more preferably 85 to 97%. If the isotactic pentad fraction is 80% or more, the mechanical strength is good. On the other hand, the upper limit of the isotactic pentad fraction is defined as the upper limit that can be obtained industrially at present. is not. The isotactic pentad fraction is a three-dimensional structure in which all five side chain methyl groups are located in the same direction with respect to the main chain formed by a carbon-carbon bond composed of any five consecutive propylene units. Or it means the ratio. The assignment of the signal in the methyl group region is A. Zambelli et al. (Macromol. 8, 687 (1975)).

Further, the propylene-based resin preferably has a Mw/Mn, which is a parameter indicating molecular weight distribution, of 1.5 to 10.0. More preferably 2.0 to 8.0, still more preferably 2.0 to 6.0. A smaller Mw/Mn means a narrower molecular weight distribution, but by setting the Mw/Mn to 1.5 or more, sufficient extrudability can be obtained and industrial mass production is possible. On the other hand, by setting Mw/Mn to 10.0 or less, sufficient mechanical strength can be ensured. Mw/Mn is measured by the GPC (gel per emission chromatography) method.

Also, the melt flow rate (MFR) of the propylene-based resin is not particularly limited, but usually the MFR is preferably 0.5 to 15 g/10 min, more preferably 1.0 to 10 g/10 min. is more preferable. By setting the MFR to 0.5 g/10 minutes or more, it is possible to have a sufficient melt viscosity at the time of molding and to ensure high productivity. On the other hand, by setting the MFR to 15 g/10 minutes or less, sufficient strength can be secured. The MFR is measured under 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 propylene-based resin is not particularly limited, and a known polymerization method using a known polymerization catalyst, such as a multi-site catalyst represented by a Ziegler-Natta type catalyst or a metallocene-based catalyst. and a polymerization method using a single-site catalyst.

Propylene-based resins include, for example, trade names "Novatec PP", "WINTEC", "WAYMAX" (manufactured by Japan Polypropylene Corporation), "Versify", "Notio", "Tafmer XR" (manufactured by Mitsui Chemicals), "Zerath" and "Thermoran". (manufactured by Mitsubishi Chemical Co., Ltd.), "Sumitomo Noblen", "Tafselene" (manufactured by Sumitomo Chemical Co., Ltd.), "Prime Polypro", "Prime TPO" (manufactured by Prime Polymer Co., Ltd.), "Adflex", "Adsyl", "HMS-PP (PF814)" (manufactured by SunAllomer), "Inspire" (Dow Chemical) and other commercially available products can be used.

The present film can be obtained, for example, by stretching a nonporous film-like material made of a resin composition containing a large amount of β-crystal, which is one of the crystal forms. Formation of a porous structure using β-crystals is a process in which β-crystals in the propylene-based resin transition to α-crystals during the stretching process. Compared to making porosity by adding a compatible organic substance, it is advantageous for preparing a porous structure because it does not depend on the particle size or dispersion diameter.

In order to obtain a fine porous structure by the stretching process, the film preferably has β-crystal activity, and more preferably contains a β-crystal nucleating agent. The β-crystal nucleating agents used in the present invention include those shown below, but are not particularly limited as long as they increase the formation and growth of β-crystals of the propylene-based resin. may

As a method for obtaining the β-crystal activity of the film described above, there is a method in which no substance that promotes the formation of α-crystals of the propylene-based resin is added to the resin composition constituting the film, and a method described in Japanese Patent No. 3739481. A method of adding a propylene-based resin treated to generate peroxide radicals, and a method of adding a β-crystal nucleating agent to the resin composition constituting the present film. Above all, it is particularly preferable to add a β-crystal nucleating agent to the resin composition constituting the present film to obtain β-crystal activity. By adding a β-crystal nucleating agent, the formation of β-crystals of the propylene-based resin can be promoted more homogeneously and efficiently, and a film having β-crystal activity can be obtained.

The β-crystal activity of this film can be regarded as an index indicating that the propylene-based resin generated β-crystals in the nonporous film before stretching. If the propylene-based resin in the non-porous film-like material before stretching forms β crystals, many fine and uniform pores are formed by subsequent stretching, so that the film has excellent mechanical properties and transparency. A porous film can be obtained.

The presence or absence of β-crystal activity in this film is determined by performing differential thermal analysis of the porous layer using a differential scanning calorimeter and determining whether or not the crystal melting peak temperature derived from the β-crystal of the propylene-based resin is detected. be done. Specifically, with a differential scanning calorimeter, the film was heated from 25°C to 240°C at a heating rate of 10°C/min and held for 1 minute, and then cooled from 240°C to 25°C at a cooling rate of 10°C/min. After the temperature was lowered, the temperature was held for 1 minute, and when the temperature was raised again from 25°C to 240°C at a heating rate of 10°C/min, the crystal melting peak temperature (Tmβ) derived from the β crystals of the propylene-based resin during the reheating. If detected, it is determined to have β-crystal activity.

The presence or absence of β-crystal activity can also be determined from the diffraction profile obtained by X-ray diffraction measurement of the film subjected to a specific heat treatment. Specifically, this film is subjected to heat treatment at 170 to 190 ° C., which is a temperature exceeding the crystal melting peak temperature of propylene-based resin, and slowly cooled to generate and grow β crystals. If a diffraction peak derived from the (300) plane of the β-crystal of the resin is detected in the range of 2θ=16.0° to 16.5°, it is determined that the β-crystal activity is present. For details on the β-crystal structure of propylene-based resins 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 (1995), Macromol. Chem. 75, 134 (1964), and references cited therein.

Examples of β-crystal nucleating agents include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, and the like. alkali or alkaline earth metal salts of carboxylic acids represented by; aromatic sulfonic acid compounds represented by sodium benzenesulfonate or sodium naphthalenesulfonate; di- or tri-basic carboxylic acid di- or triesters; phthalocyanine-based pigments represented by such as; a two-component compound consisting of component A, which is an organic dibasic acid, and component B, which is an oxide, hydroxide or salt of a Group 2 metal of the periodic table; a cyclic phosphorus compound and magnesium A composition composed of a compound and the like can be mentioned.
Among these, one or more selected from the group consisting of amide compounds, tetraoxaspiro compounds, and quinacridones are preferred.

Specific examples of the commercially available β-crystal nucleating agent include the β-crystal nucleating agent “Enjestar NU-100” manufactured by Shin Nippon Rika Co., Ltd., and a specific example of the propylene-based resin to which the β-crystal nucleating agent is added is Aritech Co., Ltd. polypropylene “Bepol B-022SP” manufactured by Borealis, polypropylene “Beta (β)-PP BE60-7032” manufactured by Mayzo, and polypropylene “BNX BETAPP-LN” manufactured by mayzo.

The content of the β-crystal nucleating agent in the film can be appropriately adjusted depending on the type of β-crystal nucleating agent or the composition of the propylene-based resin. 0 parts by mass is preferable, 0.001 to 3.0 parts by mass is more preferable, and 0.01 to 1.0 parts by mass is even more preferable. If it is 0.0001 part by mass or more, the β-crystal of the propylene-based resin can be generated and grown sufficiently during production, and sufficient β-crystal activity can be secured, and sufficient β-crystal activity can be secured even when a porous film is formed. , to obtain the desired oxygen permeability. On the other hand, addition of 5.0 parts by mass or less is economically advantageous and is preferable because the β crystal nucleating agent does not bleed to the film surface.

The main component of the film is a propylene-based resin, and the content thereof is 50% by mass or more, preferably 70 to 99.9999% by mass, more preferably 80 to 99.999% by mass, further preferably 90 to 99.99% by mass. %.

<Manufacturing method of this film>
Hereinafter, the method for producing the porous film of the present invention will be described, but the following explanation is an example of the method for producing the porous film of the present invention, and the present film is limited to the porous film produced by such a manufacturing method. not something.

A method for producing a porous film according to an example of the embodiment of the present invention (hereinafter sometimes referred to as the present film production method) comprises preparing and stretching an unstretched film containing a propylene-based resin and a β crystal nucleating agent. It is a method for manufacturing a porous film characterized by the following.

Since the manufacturing method of the present film only needs to include the above steps, it may further include other steps and treatments.

Further, in the present invention, other resins than the propylene polymer can be allowed to be mixed as long as the effects of the present invention are not impaired.
Other resins include polystyrene resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polyester resins, polycarbonate resins, polyamide resins, polyacetal resins, acrylic resins, and ethylene acetate. Vinyl copolymer, polymethylpentene resin, polyvinyl alcohol resin, cyclic olefin resin, polylactic acid resin, polybutylene succinate resin, polyacrylonitrile resin, polyethylene oxide resin, cellulose resin, polyimide resin , polyurethane resins, polyphenylene sulfide resins, polyphenylene ether resins, polyvinyl acetal resins, polybutadiene resins, polybutene resins, polyamideimide resins, polyamide bismaleimide resins, polyarylate resins, polyetherimide resins, Examples include polyetheretherketone-based resins, polyetherketone-based resins, polyethersulfone-based resins, polyketone-based resins, polysulfone-based resins, aramid-based resins, fluorine-based resins, and the like.

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

The machine used for kneading is not particularly limited. For example, known extruders such as single-screw extruders, twin-screw extruders and multi-screw extruders can be used. In addition, depending on the facility structure and necessity, a pressure reducer may be connected to the vent port to remove moisture and other low-molecular-weight substances.

The film-forming process and the stretching process will be sequentially described below.

(1) Film Forming Process Examples of the method of heating and melting the material resin include a T-die method and an inflation method. Practically, it is preferable to melt-extrude the material resin from a T-die and cast it with a cast roll.

When the T-die method is used as a specific method for forming a film, the sheets of molten resin extruded from the T-die are laminated and brought into close contact with a rotating cast roll (chill roll, cast drum). A method of forming into a take-off sheet-like material can be mentioned.

A touch roll, an air knife, an electric contact device, or the like may be attached to the cast roll in order to adhere the film material to the cast roll.
When forming a film while cooling the kneaded material, the temperature of the cast rolls is preferably 100° C. or higher. It is more preferably 110° C. or higher, and still more preferably 120° C. or higher. In the present invention, it is possible to adjust the porosity by opening pores during the stretching process in the crystalline and amorphous portions of the propylene-based resin in the film. It is preferred to obtain a non-porous membrane of high molecular weight.

In the resulting unstretched film, the thickness of the effective portion excluding both ends is preferably 320 μm to 5400 μm, more preferably 430 μm or more or 4300 μm or less, and more preferably 540 μm or more or 3200 μm or less.
If the thickness of the unstretched film is 20 µm or more, it is possible to prevent the film from being too thin and break during stretching. Difficulty in stretching can be prevented.

Regarding the layer structure of the original film of the present invention, not only the layer structure described above but also a structure in which other layers are combined may be used. Alternatively, the film may be prepared by a wet method in which an additive such as a solvent is added to the resin to obtain a nonporous film, and then the solvent is extracted to make the film porous.

(2) Stretching Step Next, the obtained nonporous membrane is uniaxially stretched or biaxially stretched. The uniaxial stretching may be vertical uniaxial stretching or horizontal uniaxial stretching. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. When producing a porous film, which is the object of the present invention, the stretching conditions can be selected in each stretching step, but lateral uniaxial stretching is more preferable because the pore size is fine and the porosity does not excessively increase. The stretching of the film in the machine direction (MD) is called "longitudinal stretching", and the stretching in the direction perpendicular to the machine direction (TD) is called "transverse stretching".

When horizontal uniaxial stretching is used, formation of pores with fine and coarse pore diameters can be prevented, and an excessive increase in porosity can be suppressed.

The longitudinal stretching temperature is preferably 60 to 140°C, more preferably 80 to 120°C. A longitudinal stretching temperature of 140° C. or lower is preferable because stretching can be performed at a temperature not higher than the melting point of the propylene-based resin, which is the main component, without breakage. On the other hand, a temperature of 60° C. or higher is preferable because breakage during stretching can be suppressed.

The longitudinal draw ratio can be arbitrarily selected, but the draw ratio per uniaxial drawing is preferably 1.1 to 10 times, more preferably 1.5 to 8.0 times, still more preferably 1.5 to 6.0 times. 0 times. When the stretching ratio per uniaxial stretching is 1.1 times or more, whitening progresses and porosity is generated by stretching. Moreover, by making it 10 times or less, it is possible to make porous without causing breakage.

The transverse stretching temperature is preferably 80 to 160°C, more preferably 90 to 150°C. When the lateral stretching temperature is within the specified range, the porous layer can be formed without excessive pore formation.

The transverse draw ratio can be arbitrarily selected, but is preferably 1.0 to 10 times, more preferably 2.0 to 9.0 times, still more preferably 3.0 to 8.0 times. By stretching at a specified transverse draw ratio, a uniformly microporous porous film can be obtained.
Furthermore, the porous film of the present invention is formed into a laminate which is subjected to surface treatment such as corona treatment, plasma treatment, printing, coating, vapor deposition, etc., and perforation, etc., as necessary within the range not impairing the present invention. good too. It is also possible to stack several sheets of this film depending on the application.

<Uses of this film>
The porous film of the present invention can be used for packaging applications, medical applications, water treatment applications, and other applications where it is necessary to adjust the balance between water vapor permeability and oxygen permeability. It can be suitably used for applications aimed at promoting healing and percutaneous absorption of drugs. Specifically, the film can be used as a wound protection material by combining it with a non-woven fabric, a drug, or the like.

Examples and Comparative Examples are shown below to describe the porous film of the present invention in more detail, but the present invention is not limited in any way.

(Propylene resin)
・ 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)
(β crystal nucleating agent)
· B-1: 2,6-naphthalenedicarboxylic acid dicyclohexylamide; "NJester NU-100" (manufactured by Shin Nippon Rika Co., Ltd.)
(Antioxidant)
· C-1; tris (2,4-di-t-butylphenyl) phosphite and tetrakis [3-(3',5'-di-t-butyl-4'-hydroxyphenyl) propionic acid] pentaerythritol 1: 1 mixture of (IRGANOX-B225, manufactured by BASF)

(Example 1)
100 parts by mass of propylene resin (A-1), 0.2 parts by mass of β-crystal nucleating agent (B-1), and 0.1 part by mass of antioxidant (C-1) were mixed and fed into a twin-screw extruder. Mixture 1 was obtained by melt extruding at 280°C. The above mixture 1 was extruded with a T-die having a lip opening of 0.8 mm, and was guided to cast rolls to obtain a nonporous membrane. Then, after preheating at a preheating temperature of 100°C and a preheating time of 12 seconds in a film tenter facility (manufactured by Kyoto Kikai Co., Ltd.), the film is stretched 7.0 times in the transverse direction at a stretching temperature of 100°C, and then heat-treated at 100°C. , to obtain a porous film. Table 1 summarizes the evaluation results of the obtained porous film.

(Comparative example 1)
The above mixture 1 was extruded with a T-die having a lip opening of 0.8 mm, and was guided to cast rolls to obtain a nonporous membrane. Table 1 summarizes the evaluation results of the obtained films.

(Comparative example 2)
The above mixture 1 was extruded with a T-die having a lip opening of 0.8 mm, and was guided to cast rolls to obtain a nonporous membrane. After that, the film was longitudinally stretched between rolls set at 105° C. at a draw ratio of 65% in three stages (longitudinal stretching ratio of 4.5 times). Table 1 summarizes the evaluation results of the obtained porous films.

(Comparative Example 3)
The above mixture 1 was extruded with a T-die having a lip opening of 0.8 mm, and was guided to cast rolls to obtain a nonporous membrane. After that, the film was longitudinally stretched between rolls set at 105° C. at a draw ratio of 65% in three stages (longitudinal stretching ratio of 4.5 times). Then, after preheating at a preheating temperature of 150°C and a preheating time of 12 seconds in a film tenter facility (manufactured by Kyoto Kikai Co., Ltd.), the film was stretched 2.0 times in the transverse direction at a stretching temperature of 150°C, and then heat-treated at 150°C. , to obtain a porous film. Table 1 summarizes the evaluation results of the obtained porous films.

Regarding the films obtained in Examples and Comparative Examples, film thickness, porosity, air permeability, average light transmittance, water vapor permeability, oxygen permeability and average pore size were measured by the following methods.

(1) Film Thickness A sample piece with a diameter of 40 mm was cut out from the measurement sample, and the thickness was measured at any five points in the film plane using a dial gauge with a scale of 1/1000 mm, and the average value was obtained.

(2) Porosity The actual mass W1 of the sample to be measured is measured, and the mass W0 when the porosity is 0% is calculated based on the density of the resin composition. rate was calculated.
Porosity (%) = {(W0-W1)/W0} x 100

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

(4) Average Light Transmittance An integrating sphere was attached to a spectrophotometer ("U-4000", manufactured by Hitachi, Ltd.), and the transmittance for light with a wavelength of 300 to 800 nm was measured. Before the measurement, the spectrophotometer was set so that an alumina white plate was used and the reflectance was 100%. The average light transmittance was obtained by averaging the transmittances at each wavelength of 300 to 800 nm.

(5) Puncture strength A measurement sample prepared by thickness measurement is fixed to a holder (measurement part: circle with a diameter of 10 mm), and a metal (SUS440C) needle with a diameter of 1 mm and a tip curvature radius of 0.5 mm is inserted in the thickness direction at 300 mm / min. , and the maximum load at which a hole opens was measured and converted to a thickness of 1 μm.

(6) Oxygen Permeability Based on JIS K7126-2:2006, the oxygen permeability of the porous film was measured in an atmosphere of 23° C. and 50% RH using an OXY-TRAN100 type oxygen permeability measuring device manufactured by Modern Control. It was measured. For the film exceeding the upper limit range of measurement by the above method, the oxygen permeability of the porous film was measured by gas chromatography in accordance with JIS K7126-2:2006.

(7) Water vapor permeability Based on JIS K7129:2008, the water vapor permeability of the porous film was measured in an atmosphere of 40°C and 90% RH using a PERMATRAN manufactured by MOCON.
(8) Oxygen/water vapor separation ability Those with an oxygen permeability of 1,000,000 cc/m ² · 24 hr · atm or more and a water vapor permeability of 1,000 g / m ² · 24 hr or less were evaluated as "○". , and others were evaluated as "x".

Table 1 shows the evaluation results of Examples and Comparative Examples.

Example 1 has a high puncture strength and achieves both a low water vapor permeability and a high oxygen permeability.
On the other hand, in Comparative Example 1, the oxygen permeability of the film having no pores was lower than the lower limit of measurement, and sufficient oxygen permeability was not obtained. In Comparative Examples 2 and 3, although they have sufficient oxygen permeability, the permeation amount of water vapor permeation is higher than the upper limit of measurement, and low water vapor permeability is not developed.

The porous film of the present invention can be used in applications where it is necessary to adjust the balance between water vapor permeability and oxygen permeability such as packaging applications, medical applications, and water treatment applications, and is suitable as a wound protection material because it has transparency. can be used.

Claims (8)

A porous film containing a propylene-based resin as a main component, having a porosity of 10 to 40%, an air permeability of 20,000 sec/dL or more, and an average light transmittance of 30% or more. 2. The porous film according to claim 1, which has a thickness of 5 to 100 μm. 3. The porous film according to claim 1, which has β-crystal activity. The porous film according to any one of claims 1 to 3, which has a puncture strength of 20 gf/μm or more. The porous film according to any one of claims 1 to 4, which has an oxygen permeability of 1,000,000 cc/m ² ·24 hr·atm or more. The porous film according to any one of claims 1 to 5, which has a water vapor permeability of 1,000 g/m ² ·24 hr or less. A wound protector comprising the porous film according to any one of claims 1-6. 7. The method for producing a porous film according to any one of claims 1 to 6, wherein an unstretched film containing a propylene-based resin and a β crystal nucleating agent is prepared and stretched.