Porous film, ventilation member, and sheet for supplying member

Abstract

This porous film contains a fluorine-free thermoplastic resin as a primary component. The weight average molecular weight of the thermoplastic resin is 700,000 or more. This ventilation member comprises: the porous film; and an adhesive layer bonded to the porous film. This sheet for supplying a member comprises: a ventilation member disposed on a face of a target, the face having an opening therein; and a base material sheet having the ventilation member disposed on a surface thereof. The ventilation member comprises: a porous film having a shape that covers the opening when disposed on the face; and an adhesive layer bonded to the porous film.

Description

Porous film, ventilation member, and member supply sheet

[0001] The present invention relates to a porous film, a ventilation member, and a member-supplying sheet.

[0002] Fluorine resin porous films are used in various applications such as filters, sound-permeable membranes, air-permeable membranes, diaphragms, etc. Fluorine-free porous membranes have also been proposed for use in these applications.

[0003] For example, Patent Document 1 discloses a microporous biaxially stretched film for use as a separator for a lithium ion secondary battery, which has micropores, contains an olefin-based resin, has a puncture strength of 0.7 N or more, and has an air permeability of 75 to 400 s / 100 mL.

[0004] Japanese Patent Application Laid-Open No. 2017-095576

[0005] A porous film used to ensure ventilation through an opening in a housing or the like of a smartwatch while preventing the penetration of foreign matter through the opening is required to have high water resistance in addition to breathability. However, according to the studies of the present inventors, improving the water resistance of a porous film that does not contain fluorine is in conflict with ensuring breathability, and therefore, imparting practical water resistance to a porous film that does not contain fluorine results in a problem of reduced breathability.

[0006] Therefore, an object of the present invention is to provide a fluorine-free porous film, a ventilation member, and a member-supplying sheet that are suitable for improving water resistance while maintaining excellent breathability.

[0007] The present invention provides a porous film comprising a fluorine-free thermoplastic resin as a main component, wherein the thermoplastic resin has a weight average molecular weight of 700,000 or more.

[0008] From another aspect, the present invention provides a porous film containing a fluorine-free thermoplastic resin as a main component, wherein, when the surface of the porous film is observed with a scanning electron microscope, a plurality of island regions and a plurality of fibrils connecting the plurality of island regions are observed, and the proportion of pores having an equivalent circle diameter of 0.7 μm or less is 10% or more.

[0009] From another aspect, the present invention provides a ventilation member comprising: the porous film of the present invention; and an adhesive layer bonded to the porous film.

[0010] From yet another aspect, the present invention provides a member supply sheet comprising: a ventilation member to be placed on a surface of an object having an opening; and a base sheet with the ventilation member placed on a surface thereof, wherein the ventilation member comprises: a porous film having a shape that covers the opening when placed on the surface; and an adhesive layer bonded to the porous film, and the porous film is the porous film of the present invention described above.

[0011] According to the present invention, it is possible to provide a fluorine-free porous film, a ventilation member, and a member-supplying sheet that are suitable for improving water resistance while maintaining excellent breathability.

[0012] FIG. 1 is a cross-sectional view schematically showing an example of a porous film of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of a film member of the present invention. FIG. 3 is a cross-sectional view schematically showing a first modified example of the film member of FIG. 2. FIG. 4 is a cross-sectional view schematically showing a second modified example (rolled body) of the film member of FIG. 2. FIG. 5 is a cross-sectional view schematically showing an example of a ventilation member of the present invention. FIG. 6 is a cross-sectional view schematically showing a first modified example of the ventilation member of FIG. 5. FIG. 7 is a cross-sectional view schematically showing a second modified example of the ventilation member of FIG. 5. FIG. 8 is a cross-sectional view schematically showing a third modified example of the ventilation member of FIG. 5. FIG. 9 is a cross-sectional view schematically showing a fourth modified example of the ventilation member of FIG. 5. FIG. 10 is a cross-sectional view schematically showing a fifth modified example of the ventilation member of FIG. 5. FIG. 11 is a cross-sectional view schematically showing an example of a member supply sheet of the present invention. FIG. 12 is a cross-sectional view schematically showing a first modified example of the member supply sheet of FIG. 11. 13 is a cross-sectional view schematically showing a modified example 2 of the member supply sheet of FIG. 11. FIG. 14A is a view (5000x magnification) showing the results of observing the surface of the porous film of Example 1 with a scanning electron microscope (SEM). FIG. 14B is a view (5000x magnification) showing the results of observing the cross section of the porous film of Example 1 with an SEM. FIG. 15A is a view (5000x magnification) showing the results of observing the surface of the porous film of Example 2 with an SEM. FIG. 15B is a view (5000x magnification) showing the results of observing the cross section of the porous film of Example 2 with an SEM. FIG. 16A is a view (5000x magnification) showing the results of observing the surface of the porous film of Example 3 with an SEM. FIG. 16B is a view (5000x magnification) showing the results of observing the cross section of the porous film of Example 3 with an SEM. FIG. 17A is a view (5000x magnification) showing the results of observing the surface of the porous film of Comparative Example 1 with an SEM. Fig. 17B is a diagram (5000x magnification) showing the results of SEM observation of the cross section of the porous film of Comparative Example 1. Fig. 18 is a diagram (5000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 4. Fig. 19A is a diagram (5000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 5. Fig. 19B is a diagram (5000x magnification) showing the results of SEM observation of the cross section of the porous film of Comparative Example 5.

[0013] A porous film according to a first aspect of the present invention contains a fluorine-free thermoplastic resin as a main component, and the thermoplastic resin has a weight average molecular weight of 700,000 or more.

[0014] In a second aspect of the present invention, for example, in the porous film according to the first aspect, the thermoplastic resin is a polyolefin resin.

[0015] In the third aspect of the present invention, for example, the porous film according to the first or second aspect has a water pressure resistance of 500 kPa or more and an air permeability expressed in Gurley number of 60 seconds / 100 mL or less.

[0016] In a fourth aspect of the present invention, for example, the porous film according to the third aspect satisfies R≦0.09, where R is defined as the value obtained by dividing the air permeability by the water pressure resistance.

[0017] In a fifth aspect of the present invention, for example, in a porous film according to any one of the first to fourth aspects, when a cross section of the porous film is observed with a scanning electron microscope, the proportion of pores having a circle equivalent diameter of 0.7 μm or less is 10% or more.

[0018] In a sixth aspect of the present invention, for example, in the porous film according to any one of the first to fifth aspects, when the surface of the porous film is observed with a scanning electron microscope, the porosity is 40% or less.

[0019] In a seventh aspect of the present invention, for example, in the porous film according to any one of the first to sixth aspects, when a cross section of the porous film is observed with a scanning electron microscope, the porosity is 30% or more.

[0020] In an eighth aspect of the present invention, for example, the porous film according to any one of the first to seventh aspects has a thickness of 70 μm or less.

[0021] In a ninth aspect of the present invention, for example, the porous film according to any one of the first to eighth aspects is a stretched film.

[0022] A porous film according to a tenth aspect of the present invention is a porous film containing a fluorine-free thermoplastic resin as a main component, wherein, when the surface of the porous film is observed with a scanning electron microscope, a plurality of island regions and a plurality of fibrils connecting the plurality of island regions are observed, and the proportion of pores having a circle equivalent diameter of 0.7 μm or less is 10% or more.

[0023] In an eleventh aspect of the present invention, for example, in the porous film according to the tenth aspect, the thermoplastic resin is a polyolefin resin.

[0024] A ventilation member according to a twelfth aspect of the present invention includes, for example, the porous film according to any one of the first to eleventh aspects, and an adhesive layer bonded to the porous film.

[0025] A component supply sheet according to a thirteenth aspect of the present invention is a component supply sheet comprising a ventilation member to be placed on a surface of an object having an opening, and a base sheet having the ventilation member placed on its surface, wherein the ventilation member comprises: a porous film having a shape that covers the opening when placed on the surface; and an adhesive layer bonded to the porous film, and the porous film is, for example, a porous film according to any one of the first to eleventh aspects.

[0026] In a fourteenth aspect of the present invention, for example, in the member supplying sheet according to the thirteenth aspect, a plurality of the ventilation members are arranged on the surface of the base sheet.

[0027] A method for producing a porous film according to a fifteenth aspect of the present invention includes the steps of: kneading a composition containing a fluorine-free thermoplastic resin and a plasticizer to obtain a kneaded mixture; performing a pressing or extrusion process; performing a cooling process; performing a stretching process; and performing a plasticizer extraction process, wherein the thermoplastic resin has a weight average molecular weight of 700,000 or more.

[0028] In a sixteenth aspect of the present invention, for example, the method for producing a porous film according to the fifteenth aspect further comprises a step of carrying out an annealing treatment.

[0029] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, but is not limited to the following embodiments.

[0030] [Porous Film] An example of the porous film of the present invention is shown in Figure 1. The porous film 1 in Figure 1 contains a fluorine-free thermoplastic resin as a main component. The "main component" refers to the component that is contained in the porous film 1 in the largest amount by weight. With this configuration, the porous film 1 can be adhered to an object such as a smart watch housing by heat fusion without using an adhesive layer, for example.

[0031] The weight-average molecular weight of the fluorine-free thermoplastic resin (hereinafter sometimes simply referred to as thermoplastic resin) is 700,000 or more. The present inventors have discovered that by using a thermoplastic resin having a weight-average molecular weight of 700,000 or more, the porous film 1 can be improved in water resistance while maintaining excellent breathability.

[0032] The lower limit of the weight average molecular weight of the thermoplastic resin may be 750,000 or more, and the upper limit of the weight average molecular weight of the thermoplastic resin is, for example, 1,000,000 or less.

[0033] The porous film 1 can be made of a resin composition containing a thermoplastic resin. The weight ratio of the thermoplastic resin in the resin composition is preferably 20% by weight or more and less than 50% by weight. With such a composition, the characteristic cross-sectional structure and surface structure described below are easily formed during the manufacturing process, particularly during stretching.

[0034] The lower limit of the weight ratio of the thermoplastic resin in the resin composition is more preferably 25% by weight or more, and the upper limit of the weight ratio of the thermoplastic resin in the resin composition is more preferably 45% by weight or less.

[0035] The weight ratio of the thermoplastic resin in the resin composition can be determined, for example, from the charged amount.

[0036] The resin composition may contain additives such as a plasticizer and an antioxidant in addition to the thermoplastic resin.

[0037] The water pressure resistance of the porous film 1 is preferably 500 kPa or more as evaluated by the water resistance test method B (high water pressure method) specified in JIS L1092: 2009. The porous film 1 satisfying the above numerical range has high water resistance.

[0038] The lower limit of the water pressure resistance of the porous film 1 may be 600 kPa or more, 700 kPa or more, 800 kPa or more, 900 kPa or more, or even 1000 kPa or more. The upper limit of the water pressure resistance of the porous film 1 is, for example, 2000 kPa or less. The water pressure resistance of the porous film 1 may be 600 kPa or more and 2000 kPa or less, 700 kPa or more and 2000 kPa or less, 800 kPa or more and 2000 kPa or less, 900 kPa or more and 2000 kPa or less, or even 1000 kPa or more and 2000 kPa or less.

[0039] The water pressure resistance of the porous film 1 can be measured using a measuring jig in accordance with the above-mentioned water resistance test method as follows. An example of the measuring jig is a 47 mm diameter stainless steel (SUS) disk with a 1.0 mm diameter through-hole (having a circular cross section) in the center. This disk has a thickness that does not deform due to the water pressure applied when measuring the water pressure resistance. Measurement of the water pressure resistance using this measuring jig can be carried out as follows.

[0040] The porous film 1 to be evaluated is fixed to one side of the measuring jig so as to cover the opening of the through-hole. Fixation is performed so that water does not leak from the fixed portion of the membrane during water pressure resistance measurement. The porous film 1 can be fixed using double-sided adhesive tape with a water passage hole (1.6 mm diameter) punched in the center, whose shape matches the opening. The double-sided adhesive tape is simply placed between the measuring jig and the porous film 1 so that the periphery of the water passage hole coincides with the periphery of the opening. Next, the measuring jig with the porous film 1 fixed thereto is set in the testing device so that the surface opposite the fixed surface of the porous film 1 becomes the water pressure application surface during measurement, and the water pressure resistance is measured according to Water Resistance Test Method B (high water pressure method) specified in JIS L1092:2009. Note that the water pressure resistance is measured based on the water pressure when water is released from one point on the membrane surface of the porous film 1. The measured water pressure resistance can be used as the water pressure resistance of the porous film 1. The test device may have the same configuration as the water resistance test device exemplified in JIS L1092:2009 and have a test piece mounting structure on which the above-mentioned measuring jig can be set.

[0041] The air permeability in the thickness direction of the porous film 1, expressed as a Gurley number, is preferably 60 seconds / 100 mL or less. A porous film 1 satisfying the above numerical range has high air permeability. In this specification, the "Gurley number" refers to the air resistance (Gurley air permeability) measured in accordance with the Oken testing machine method specified in JIS P8117:2009.

[0042] The upper limit of the air permeability of the porous film 1, expressed in Gurley number, may be 50 seconds / 100 mL or less, or may be 40 seconds / 100 mL or less. The lower limit of the air permeability of the porous film 1, expressed in Gurley number, is, for example, 0.1 seconds / 100 mL or more. The lower limit of the air permeability of the porous film 1, expressed in Gurley number, may be 1 second / 100 mL or more, or may be 5 seconds / 100 mL or more. The air permeability of the porous film 1 may be 0.1 seconds / 100 mL or more and 50 seconds / 100 mL or less, or may be 0.1 seconds / 100 mL or more and 40 seconds / 100 mL or less.

[0043] Even if the size of the porous film 1 does not meet the recommended dimensions (50 mm x 50 mm) of the test piece for the Oken Testing Machine Method, it is possible to evaluate the air resistance (Gurley air permeability) in accordance with the Oken Testing Machine Method by using a measuring jig.

[0044] The measurement jig has a shape and size that can be placed in the air permeability measurement section of the Oken testing machine, and is made of a thickness and material that will not deform due to the differential pressure applied to the test piece during air permeability resistance measurement. An example of the measurement jig is a 2 mm thick, 47 mm diameter SUS disk. A through-hole with an opening smaller than the membrane to be evaluated is provided in the center of the surface of the measurement jig. The cross section of the through-hole is typically circular, and the diameter is such that the opening of the through-hole is completely covered by the membrane to be evaluated. The diameter of the through-hole can be, for example, 1 mm or 2 mm. Next, the porous film 1 to be evaluated is fixed to one side of the measurement jig so as to cover the opening. The fixation is performed so that during air permeability resistance measurement, air passes only through the opening and the effective test portion of the porous film 1 to be evaluated (the portion overlapping with the opening when viewed perpendicular to the main surface of the fixed porous film 1), and the fixed portion does not obstruct the passage of air through the effective test portion of the porous film 1. To fix the porous film 1, double-sided adhesive tape with a vent hole punched in the center, having a shape that matches the shape of the opening, can be used. The double-sided adhesive tape can be placed between the measurement jig and the porous film 1 so that the periphery of the vent hole matches the periphery of the opening. Next, the measurement jig with the porous film 1 fixed is set in the air permeability measurement section of the Oken tester so that the fixed surface of the porous film 1 is downstream of the air flow during measurement, and a test is performed using the Oken tester method, and the air permeability resistance indicated value t shown by the tester is recorded. Next, the recorded air permeability resistance indicated value t is measured using an effective test area of ​​6.452 [cm2] as specified in the Oken tester method. 2 ] per value t K In equation t K = {t × (area of ​​the effective test portion of the porous film 1 [cm 2 ]) / 6.452 [cm 2 ]}, and the resulting converted value t Kcan be regarded as the air resistance (Gurley air permeability) of the porous film 1 measured in accordance with the Oken type testing machine method. It has been confirmed that the air resistance measured without using a measuring jig for a porous film 1 that meets the recommended dimensions (50 mm x 50 mm) of the test piece for the Oken type testing machine method is in good agreement with the air resistance measured using a measuring jig after cutting the porous film 1 into small pieces, that is, the use of a measuring jig does not substantially affect the measured value of the air resistance.

[0045] The ratio R is defined as the value obtained by dividing the air permeability (seconds / 100 mL) of the porous film 1 by the water pressure resistance (kPa). The ratio R tends to decrease as the water resistance and breathability of the porous film 1 increase. Therefore, the ratio R can be an index for evaluating the water resistance and breathability of the porous film 1 together. The ratio R is preferably 0.09 or less (R≦0.09). A porous film 1 that satisfies the above numerical range can have excellent water resistance and breathability.

[0046] The upper limit of the ratio R may be 0.07 or less, 0.06 or less, 0.05 or less, or even 0.04 or less. The lower limit of the ratio R is, for example, 0.01 or more.

[0047] As described above, the porous film 1 contains a fluorine-free thermoplastic resin as a main component. The fluorine-free thermoplastic resin may be a polyolefin resin. When the thermoplastic resin is a polyolefin resin, it is easy to obtain a porous film 1 suitable for improving water resistance while maintaining excellent breathability.

[0048] The polyolefin resin includes polyethylene (PE) resin, polypropylene (PP) resin, and polymethylmenthene (PMP) resin.

[0049] The polyolefin resin may be a polymethylpentene resin. The polymethylpentene resin is a homopolymer or copolymer such as poly(4-methylpentene-1) resin or poly(3-methylpentene-1) resin. Examples of the copolymer include random copolymers and block copolymers. From the viewpoints of heat resistance and moldability, a homopolymer of poly(4-methylpentene-1) resin is preferred.

[0050] The polyolefin resin may be a poly(4-methylpentene-1) resin. Poly(4-methylpentene-1) resin refers to a homopolymer of 4-methylpentene-1 or a copolymer of 4-methylpentene-1 and at least one α-olefin. The composition ratio of 4-methylpentene-1 to the α-olefin contained in the copolymer can be adjusted so that the melting point is in the range of 180°C or higher.

[0051] The fluorine-free thermoplastic resin may be a thermoplastic resin having a melting point of 180° C. or higher and 300° C. or lower. When the melting point of the thermoplastic resin is 180° C. or higher, sufficient heat resistance can be ensured in the porous film 1. When the melting point of the thermoplastic resin is 300° C. or lower, the porous film 1 can be produced by melt molding, for example.

[0052] The melting point of the thermoplastic resin may be 200°C or higher and 280°C or lower, and may further be 220°C or higher and 260°C or lower.

[0053] The porous film 1 is in the form of a film or a sheet. The thickness of the porous film 1 is preferably 70 μm or less. When the thickness is within the above range, it is easy to achieve a water pressure resistance and an air permeability that satisfy the above range.

[0054] The thickness of the porous film 1 can be determined by measuring the thickness at any five points on the porous film 1 using, for example, a dial gauge, and calculating the average value of these measured values. The thickness of the porous film 1 can also be determined by measuring the thickness at any five points on an SEM image of the cross section of the porous film 1 and calculating the average value of these measured values.

[0055] The upper limit of the thickness of the porous film 1 may be 60 μm or less, 50 μm or less, 40 μm or less, or even 30 μm or less. The lower limit of the thickness of the porous film 1 is, for example, 20 μm or more.

[0056] The porous film 1 may have multiple nodes and multiple fibrils. The porous film 1 may have multiple island regions and multiple fibrils connecting the multiple island regions. The island regions may include multiple nodes. A porous film 1 having such a structure is suitable for achieving both water resistance and breathability. The above structure can be confirmed, for example, by observing the main surface of the porous film 1 vertically using a scanning electron microscope (SEM). In this disclosure, the term "main surface" refers to the surface of a film-like or sheet-like member having the largest area. In this disclosure, the terms "main surface," "surface," and "face" of the porous film 1 are used interchangeably.

[0057] When the surface of the porous film 1 is observed with an SEM, the boundaries between the multiple island regions and the multiple fibrils connecting the multiple island regions do not need to be clear. The shape of the island regions is not particularly limited. The island regions may have, for example, a polygonal shape. However, the polygonal region does not necessarily have to have an outer shape composed of only straight lines, and also includes an approximately polygonal region in which some sides are curved, such as an arc. Furthermore, the polygonal shape is not limited to a hexagon.

[0058] When the surface of the porous film 1 is observed with an SEM, cracks may be present on the surface of the island regions. The cracks on the surface of the island regions may be formed, for example, by the cleavage of massive nodes during stretching.

[0059] It is preferable that a plurality of fine through-holes are formed in the island regions when the surface of the porous film 1 is observed with an SEM. The porous film 1 having such a surface structure is particularly suitable for improving water resistance while maintaining excellent breathability.

[0060] For example, Figure 14A shows the results of SEM observation of the surface of the porous film of Example 1 (described later) (5000x magnification). As shown in Figure 14A, multiple island regions and multiple fibrils connecting the multiple island regions are observed in the porous film of Example 1. Furthermore, in the porous film of Example 1, cracks exist on the surface of the island regions, and multiple fine through-holes are formed in the island regions.

[0061] When the cross section of the porous film 1 is observed with an SEM, a plurality of nodes may be present along the thickness direction. The plurality of nodes may be present throughout the entire thickness direction of the porous film 1. The plurality of nodes may be uniformly present throughout the thickness direction of the porous film 1. Adjacent agglomerated nodes may be connected by a plurality of fibrils, or adjacent agglomerated nodes may be directly connected to each other without being connected by a plurality of fibrils.

[0062] When the cross section of the porous film 1 is observed with an SEM, it is preferable that the nodes or clusters of nodes are densely packed and that minute gaps (pores) are formed between the nodes or clusters of nodes. The porous film 1 having such a cross-sectional structure is particularly suitable for improving water resistance while maintaining excellent breathability.

[0063] For example, Figure 14B is a diagram (5000x magnification) showing the results of SEM observation of the cross section of the porous film of Example 1 described later. As shown in Figure 14B, in the cross section of the porous film of Example 1, the nodes or clustered nodes are densely packed, and minute gaps (pores) are formed between the nodes or clustered nodes.

[0064] As described above, the porous film 1 has a plurality of gaps (pores). When the cross section of the porous film 1 is observed with an SEM, it is preferable that the proportion Rc of pores having a circle-equivalent diameter of 0.7 μm or less is 10% or more. According to the studies of the present inventors, the water pressure resistance of the porous film 1 is related to the presence of pores having a circle-equivalent diameter of 0.7 μm or less in the cross section, and the larger the proportion Rc, the higher the water pressure resistance of the porous film 1 tends to be. When the proportion Rc satisfies the above numerical range, the porous film 1 has excellent water resistance.

[0065] The upper limit of the ratio Rc is, for example, 40% or less, or may be 35% or less, 30% or less, or 25% or less.

[0066] The percentage Rc of pores with a circle-equivalent diameter of 0.7 μm or less in the cross section of the porous film 1 can be determined by the method described below. First, the cross section of the porous film 1 is observed using an SEM (see, for example, FIG. 14B). Next, the obtained SEM observation image (or a portion thereof) is binarized using image analysis software. Pores are identified from the obtained binarized image, and the area of ​​each pore contained in the image is calculated. For each pore, the circle-equivalent diameter is calculated from the calculated area. The circle-equivalent diameter is the diameter of a perfect circle having the same area as the area of ​​the pore being measured. The average of the calculated circle-equivalent diameters can be considered as the circle-equivalent diameter of the pores in the cross section of the porous film 1. The percentage Rc can be determined by calculating the ratio of the total area of ​​pores with a circle-equivalent diameter of 0.7 μm or less to the area of ​​the image. The percentage Rc is determined by measuring 300 or more pores, for example, 300 to 5,000 pores. Note that when identifying pores, pores on the edges of the image are omitted from the analysis. As the image analysis software, for example, imageJ can be used.

[0067] When the surface of the porous film 1 is observed with an SEM, the proportion Rs of pores having a circle-equivalent diameter of 0.7 μm or less may be 20% or less.

[0068] The lower limit of the ratio Rs is, for example, 5% or more, and may be 8% or more.

[0069] The proportion Rs of pores with a circle-equivalent diameter of 0.7 μm or less on the surface of the porous film 1 can be determined by the same method as the method for determining the proportion Rc on the cross section of the porous film 1 described above, except that the surface of the porous film 1 is observed with an SEM (see, for example, FIG. 14A). The proportion Rs is determined by measuring 500 or more pores, for example, 500 to 26,000 pores.

[0070] When the surface of the porous film 1 is observed with an SEM, the porosity Ps of the porous film 1 is preferably 40% or less. When the surface porosity Ps satisfies the above numerical range, a water pressure resistance and an air permeability that satisfy the above numerical range are likely to be achieved.

[0071] The upper limit of the porosity Ps of the porous film 1 may be less than 40%, 35% or less, 30% or less, or even 25% or less. The lower limit of the porosity Ps of the porous film 1 is, for example, 10% or more. The lower limit of the porosity Ps of the porous film 1 may be 15% or more.

[0072] The porosity Ps of the surface of the porous film 1 can be determined by the method described below. First, the surface of the porous film 1 is observed with an SEM (see, for example, FIG. 14A). Next, the obtained SEM observation image (or a portion thereof) is binarized using image analysis software. Pores are identified from the obtained binarized image, and the area of ​​each pore contained in the image is calculated. The porosity Ps of the porous film 1 can be determined by calculating the ratio of the total area of ​​pores to the area of ​​the image. The porosity Ps is determined by measuring 700 or more pores, for example, 700 to 26,000 pores. Note that when identifying pores, pores on the edges of the image are omitted from the analysis. For example, ImageJ can be used as the image analysis software.

[0073] When the cross section of the porous film 1 is observed with an SEM, the porosity Pc of the porous film 1 is preferably 30% or more. When the porosity Pc of the cross section satisfies the above numerical range, a water pressure resistance and an air permeability that satisfy the above numerical range are likely to be achieved.

[0074] The upper limit of the porosity Pc of the porous film 1 is, for example, 60% or less. The upper limit of the porosity Pc of the porous film 1 may be 55% or less. The porosity Pc of the porous film 1 may be 30% or more and 60% or less, or 30% or more and 55% or less.

[0075] The porosity Pc in the cross section of the porous film 1 can be determined by the same method as the method for determining the porosity Ps in the surface of the porous film 1. However, the cross section of the porous film 1 is observed with an SEM (see, for example, FIG. 14B ). The porosity Pc is determined by measuring 600 or more pores, for example, 600 to 5,000 pores.

[0076] The porous film 1 may be a stretched film. When the porous film 1 is a stretched film, it is easy to control the water pressure resistance and air permeability. The stretched film may be a biaxially stretched film or a uniaxially stretched film.

[0077] At least one of the main surfaces of the porous film 1 may be subjected to a surface modification treatment. Examples of the surface modification treatment include an oil-repellent treatment, a chemical treatment, a sputter etching treatment, and a plasma treatment. The bonding property of the porous film 1 is improved in the area subjected to the surface modification treatment.

[0078] At least one of the main surfaces of the porous film 1 may be subjected to a liquid-repellent treatment. The liquid-repellent treatment is generally carried out by applying a liquid-repellent agent to the surface of the porous film 1 or by immersing the porous film 1 in the liquid-repellent agent. The liquid-repellent agent is not particularly limited, and may be a fluorine-based liquid-repellent agent, a silicone-based liquid-repellent agent, or an acrylic-based liquid-repellent agent. The fluorine-based liquid-repellent agent has, for example, a structure having an acrylic main chain and a hydrocarbon side chain saturated with fluorine (perfluoroalkyl group).

[0079] [Method for Producing Porous Film] The porous film 1 described above can be produced, for example, by the following method.

[0080] The method for producing the porous film 1 includes, for example, kneading a composition containing a fluorine-free thermoplastic resin and a plasticizer to obtain a kneaded mixture (step S1), pressing the kneaded mixture to obtain a pressed body (step S2), cooling the pressed body to obtain a molded body (step S3), stretching the molded body to obtain a sheet body (step S4), and extracting the plasticizer from the sheet body (step S5).

[0081] As another method, the method for producing the porous film 1 includes, for example, kneading a composition containing a fluorine-free thermoplastic resin and a plasticizer to obtain a kneaded mixture (step S1), extruding the kneaded mixture using a twin-screw extruder (step ST2), cooling the extruded kneaded mixture to obtain a molded body (step ST3), stretching the molded body to obtain a sheet body (step S4), and extracting the plasticizer from the sheet body (step S5).

[0082] Steps S1 to S3 correspond to a process for producing a precursor of the porous film 1. Steps S4 to S5 correspond to a process for growing a porous structure. Note that step S5 may be performed before step S4.

[0083] Step S1 is carried out, for example, at a temperature of 230° C. to 260° C. for 5 to 30 minutes.

[0084] As the fluorine-free thermoplastic resin, for example, polymethylpentene resin can be used.

[0085] The composition containing the thermoplastic resin and the plasticizer may be mixed with a resin such as polyethylene, polypropylene, poly-1-butene, or cyclic polyolefin, as long as the properties of the porous film 1 are not affected.

[0086] The plasticizer is a non-volatile solvent that, when mixed with a thermoplastic resin such as polymethylpentene resin, forms a mixture at or above the melting point of the resin, and that undergoes thermally induced phase separation when the mixture is cooled. The plasticizer may be in the form of a liquid or a solid at room temperature. The plasticizer may be used alone, or two or more types of plasticizers may be mixed and used.

[0087] The mixing ratio of the thermoplastic resin and the plasticizer is set so as to obtain a uniform kneaded product in step S1. Specifically, the weight ratio of the thermoplastic resin in the resin composition is preferably, for example, 20% by weight or more and less than 50% by weight. With this configuration, the characteristic cross-sectional structure and surface structure described above are more likely to be formed during stretching (step S4).

[0088] The composition containing the thermoplastic resin and the plasticizer may further contain additives such as antioxidants, crystal nucleating agents, antistatic agents, flame retardants, lubricants, ultraviolet absorbers, colorants, and inorganic fillers for improving strength, depending on the purpose.

[0089] Step S2 is carried out for 2 to 30 minutes at a temperature of 230 to 260° C., for example. The thickness of the pressed body obtained in step S2 is, for example, 0.1 mm.

[0090] In step S3, the pressed body obtained in step S2 is cooled to a temperature sufficiently lower than the crystallization temperature of the thermoplastic resin by contacting it with a thermal conductor, for example, and solidified. Examples of thermal conductors used for cooling include water, air, metal, and plasticizer.

[0091] The manufacturing method may include, instead of step S2, performing an extrusion process on the kneaded material using a twin-screw extruder (step ST2). In step ST2, the kneaded material may be extruded onto a metal roll whose surface temperature is controlled. A flat die (hanger coat die) may be used to extrude the kneaded material. By using a flat die, the kneaded material can be extruded in a wide width, so that a sheet-like molded product can be easily obtained in step ST2.

[0092] When step ST2 is included instead of step S2, the manufacturing method may include, instead of step S3, performing a cooling treatment on the extruded kneaded material to obtain a molded body (step ST3). In step ST3, for example, a metal roll with a controlled surface temperature may be used to roll out the kneaded material while cooling it to obtain a sheet-like molded body. The surface temperature of the metal roll is controlled to, for example, 120°C. A plurality of metal rolls may be used. A sheet-like molded body may be formed while cooling by passing the kneaded material through a plurality of metal rolls.

[0093] The cooled compact may be annealed (step S3') between steps S3 and S4. Step S3' is performed at a temperature of 180°C to 200°C for 30 to 60 minutes, for example.

[0094] In step S4, the cooled molded body is stretched at least once in at least one uniaxial direction. Stretching in at least one uniaxial direction includes uniaxial stretching in the longitudinal direction, uniaxial stretching in the transverse direction, simultaneous biaxial stretching, and sequential biaxial stretching. The molded body may be biaxially stretched sequentially, or simultaneously. Step S4 generates pores in the molded body. At this time, for example, cracks occur on the surface of the island-like regions of the molded body, and multiple fine through-holes are formed in the island-like regions. In the cross section of the molded body, for example, nodes or clustered nodes are densely packed, and fine gaps (voids) are formed between the nodes or clustered nodes.

[0095] The stretching temperature may be 20°C to 240°C, 50°C to 230°C, or even 100°C to 220°C in each of the longitudinal and transverse directions.

[0096] The stretching ratio in the longitudinal and / or transverse uniaxial directions may be 2.0 to 10.0 times, 2.0 to 8.0 times, or even 2.0 to 5.0 times.

[0097] The strain rate in the stretching may be 1% / sec to 10% / sec, 1% / sec to 8% / sec, or even 1% / sec to 5% / sec in the machine direction and / or the transverse direction. When the strain rate is within the above range, breakage is unlikely to occur during stretching, and productivity is improved.

[0098] In step S5, the plasticizer is extracted and removed from the sheet using, for example, an extraction solvent. After step S5, the sheet from which the plasticizer has been extracted and removed may be dried using a dryer or by natural drying. In this way, the porous film 1 is obtained.

[0099] The extraction solvent is preferably a poor solvent for thermoplastic resins such as polymethylpentene resins, but a good solvent for plasticizers, and has a boiling point lower than the melting point of the porous film 1. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and 2-butanone. Considering safety and other factors, alcohols and ketones are preferably used. Methyl ethyl ketone (MEK) may also be used as the extraction solvent.

[0100] Between step S4 and step S5, the sheet may be heat-set. Heat-set may be performed, for example, using a hot air circulating oven. Heat-set may reduce the thermal shrinkage of the sheet after stretching. The heat-set temperature is, for example, 50°C to 240°C. The heat-set temperature may be 100°C to 230°C, or may be 150°C to 220°C.

[0101] Heat setting may be performed after step S4, between steps S4 and S5, or both after steps S4 and S5. Examples of the heat setting method include fixing the film in the width direction with a tenter and continuously passing it through a heat treatment furnace, applying an appropriate tension and continuously passing it through a heat treatment furnace without fixing it in the width direction, and winding the film around a roll and feeding it into a heat treatment furnace in batches.

[0102] [Film member] An example of the film member of the present invention is shown in Figure 2. The film member 2 (2A) in Figure 2 includes a porous film 1. A first modified example of the film member in Figure 2 is shown in Figure 3. The film member 2 (2B) in Figure 3 further includes an air-permeable support material 3. The air-permeable support material 3 is laminated on the porous film 1. The air-permeable support material 3 can improve the strength and handleability of the film member 2.

[0103] The breathable support material 3 usually has higher breathability in the thickness direction than the porous film 1. Examples of the breathable support material 3 include woven fabric, nonwoven fabric, net, and mesh. Examples of materials constituting the breathable support material 3 include polyesters such as polyethylene terephthalate (PET), polyolefins such as polyethylene (PE) and polypropylene (PP), and aramid resin. The shape of the breathable support material 3, when viewed perpendicularly to the main surface of the film member 2, may be the same as or different from the shape of the porous film 1. The breathable support material 3 may have a peripheral edge corresponding to the peripheral edge of the porous film 1, when viewed perpendicularly to the main surface of the film member 2.

[0104] The film member 2B in Fig. 3 includes one breathable support material 3 arranged on one surface of the porous film 1. The film member 2 may include two or more breathable support materials 3. In the film member 2, the breathable support materials 3 may be arranged on both surfaces of the porous film 1. The porous film 1 and the breathable support material 3 may be joined by welding such as thermal welding or ultrasonic welding, an adhesive, or a pressure-sensitive adhesive.

[0105] The film member 2 may include any layers and / or members other than those described above.

[0106] The thickness of the film member 2 is, for example, 1 to 300 μm, and may be 50 to 200 μm.

[0107] The basis weight of the film member 2 is, for example, 1.0 to 200.0 g / m 2 The basis weight of the film member 2 is 10.0 to 100.0 g / m 2 may be.

[0108] The film member 2 can have the same properties as the porous film 1, for example, air permeability in the thickness direction and / or water pressure resistance.

[0109] The film member 2 may be subjected to a liquid-repellent treatment and / or a coloring treatment.

[0110] The film member 2 can be used as, for example, a filter member, but the uses of the film member 2 are not limited to the above example.

[0111] The shape of the film member 2, when viewed perpendicularly to the main surface of the film member 2, is, for example, a polygon including a square and a rectangle, a circle, an ellipse, or a strip. The corners of the polygon may be rounded. However, the shape of the film member 2 is not limited to the above examples. A strip-shaped film member 2 may be wound to form a wound body. Furthermore, if necessary, the film member 2 may be wound in a state where it is laminated with a release liner.

[0112] A second modification (roll) of the film member of Fig. 2 is shown in Fig. 4. The roll 10 shown in Fig. 4 includes the film member 2A and release liner 11 of Fig. 2. The film member 2A and the release liner 11 are bonded to each other by an adhesive layer 12. In the roll 10, a release surface 13 formed when the release liner 11 is peeled from the film member 2A is located between the film member 2A and the adhesive layer 12. That is, in the roll 10, when the release liner 11 is peeled off, the adhesive layer 12 is also peeled off from the film member 2A, resulting in a film member 2A that does not have the adhesive layer 12 formed on its surface.

[0113] The film member 2A supplied by the roll 10 and having no adhesive layer 12 formed on its surface can be bonded to the opening of the housing by any bonding method. That is, the film member 2A has a high degree of freedom in the method of bonding to the opening of the housing. Bonding methods include, for example, bonding using an adhesive layer newly disposed on the surface of the film member 2A, bonding by thermal welding, and bonding by ultrasonic welding.

[0114] The film member 2A supplied by the roll 10 can be processed into any shape as needed. That is, the film member 2A has a high degree of freedom in terms of shape. However, "shape" also includes "size." The above means that the roll 10 allows the film member 2A, which functions as a waterproof membrane, to be supplied with a high degree of freedom in terms of the joining method to the opening of the housing and / or the shape.

[0115] Furthermore, according to the wound body 10, misalignment between the film member 2A and the release liner 11 during winding is suppressed by the adhesive layer 12. The wound body 10 can suppress the occurrence of malfunctions (abnormal shape of the wound body) caused by tightness during winding, etc.

[0116] [Ventilation Member] An example of a ventilation member of the present invention is shown in FIG. 5. The ventilation member 4 (4A) in FIG. 5 has breathability in the thickness direction and includes the porous film 1 or film member 2 described above as a member that prevents the penetration of foreign matter in that direction. The ventilation member 4 is, for example, a member that is placed on a surface of an object having an opening, and ensures ventilation through the opening while preventing the penetration of foreign matter through the opening. In this case, the ventilation member 4 is typically placed so that the porous film 1 or film member 2 covers the opening of the object. The ventilation member 4A in FIG. 5 includes a porous film 1. Below, an example will be described in which the ventilation member 4 has breathability in the thickness direction and includes a porous film 1 as a member that prevents the penetration of foreign matter in that direction.

[0117] The ventilation member 4 (4A) has an adhesive layer 5 arranged on one side of the porous film 1. The porous film 1 and the adhesive layer 5 are directly bonded to each other. The ventilation member 4A can be placed on the surface of an object via the adhesive layer 5.

[0118] Examples of adhesives constituting the adhesive layer 5 include acrylic adhesives, silicone adhesives, urethane adhesives, epoxy adhesives, and rubber adhesives. When consideration must be given to using the ventilation member 4 at high temperatures, it is preferable to select an acrylic adhesive or a silicone adhesive, particularly a silicone adhesive, which have excellent heat resistance. The adhesive layer 5 may be a substrate-less double-sided adhesive tape. The adhesive may be a curable adhesive such as a phenolic resin, an epoxy resin, a urea resin, a polyurethane resin, a melamine resin, or a polyester resin.

[0119] The outer periphery of the porous film 1 and the outer periphery of the adhesive layer 5 coincide when viewed perpendicularly to the main surface of the porous film 1. The shape of the adhesive layer 5 corresponds to the peripheral edge of the porous film 1 when viewed perpendicularly to the main surface of the porous film 1. The region of the porous film 1 to which the adhesive layer 5 is not bonded can be used as the ventilation region of the ventilation member 4A. However, the shape of the adhesive layer 5 is not limited to the above example.

[0120] The area of ​​the ventilation area is, for example, 40 mm 2 The ventilation member 4 having a ventilation region area within this range is suitable for placement in an object having a small diameter opening, for example. The lower limit of the ventilation region area is, for example, 0.008 mm 2 However, the area of ​​the ventilation region may be larger depending on the type of object in which the ventilation member 4 is placed.

[0121] Fig. 6 shows a first modification of the ventilation member of Fig. 5. The ventilation member 4 (4B) of Fig. 6 has the same configuration as the ventilation member 4A of Fig. 5, except that it further includes an adhesive layer 5 (5B) arranged on the other surface of the porous film 1. The porous film 1 is sandwiched between a pair of adhesive layers 5 (5A, 5B).

[0122] As shown in Figure 6, the adhesive layer 5 may include a first adhesive layer 5A bonded to one surface (first main surface 1a) of the porous film 1 and a second adhesive layer 5B bonded to the other surface (second main surface 1b) of the porous film 1.

[0123] Fig. 7 shows a second variation of the ventilation member of Fig. 5. The ventilation member 4 (4C) of Fig. 7 further includes a base material layer 6 disposed on one side of the porous film 1, and has the same configuration as the ventilation member 4A of Fig. 5, except that the porous film 1 and the adhesive layer 5 are joined via the base material layer 6. The base material layer 6 can improve the strength and handleability of the ventilation member 4, and can prevent damage to the porous film 1 during handling or placement on an object.

[0124] Examples of materials constituting the base material layer 6 include polyolefins such as PE and PP, polyesters such as PET, silicone resins, polycarbonate, polyimide, polyamideimide, polyphenylene sulfide, polyether ether ketone (PEEK), polyvinyl chloride, fluororesins, and metals such as aluminum and stainless steel. Examples of fluororesins include PTFE, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-ethylene copolymer (ETFE). However, the materials constituting the base material layer 6 are not limited to the above examples.

[0125] The outer periphery of the porous film 1 and the outer periphery of the base material layer 6 coincide when viewed perpendicularly to the main surface of the porous film 1. The shape of the base material layer 6 corresponds to the peripheral edge of the porous film 1 when viewed perpendicularly to the main surface of the porous film 1. The region of the porous film 1 to which the base material layer 6 is not bonded can be used as the ventilation region of the ventilation member 4C. However, the shape of the base material layer 6 is not limited to the above example.

[0126] The porous film 1 and the base layer 6 may be joined by a pressure-sensitive adhesive or adhesive, or by welding such as thermal welding or ultrasonic welding. The porous film 1 and the base layer 6 may be joined by an adhesive layer. The adhesive layer may have the same structure as the adhesive layer 5. The base layer 6 may be a single-sided adhesive tape or a double-sided adhesive tape.

[0127] A third variation of the ventilation member of Fig. 5 is shown in Fig. 8. The ventilation member 4 (4D) of Fig. 8 has the same configuration as the ventilation member 4C of Fig. 5, except that it further includes a base material layer 6 (6B) arranged on the other side of the porous film 1. The porous film 1 is sandwiched between the pair of base material layers 6 (6A, 6B). This sandwiching structure can further improve the strength and handleability of the ventilation member 4.

[0128] As shown in Figure 8, the substrate layer 6 may include a first substrate layer 6A bonded to one surface (first main surface 1a) of the porous film 1 and a second substrate layer 6B bonded to the other surface (second main surface 1b) of the porous film 1.

[0129] Fig. 9 shows a fourth variation of the ventilation member of Fig. 5. The ventilation member 4 (4E) of Fig. 9 has the same configuration as the ventilation member 4B of Fig. 6, except that it further includes a release liner 7 and the porous film 1 and the release liner 7 are bonded via an adhesive layer 5 (5B).

[0130] As shown in Figure 9, the ventilation member 4 (4E) may further include a release liner 7, with a second adhesive layer 5B disposed between the release liner 7 and the porous film 1, and the second adhesive layer 5B bonded to the release liner 7.

[0131] The release liner 7 has a tab that protrudes outward beyond the outer periphery of the porous film 1 when viewed perpendicularly to the main surface of the porous film 1. The ventilation member 4E can be handled or placed on the surface of an object by grasping the tab. The release liner 7 is usually removed when the ventilation member 4E is used. The release liner 7 can be made of, for example, the same material as the material that makes up the base layer 6.

[0132] Fig. 10 shows a fifth variation of the ventilation member of Fig. 5. The ventilation member 4 (4F) of Fig. 10 further includes a release liner 7, and has the same configuration as the ventilation member 4D of Fig. 8, except that the release liner 7 is bonded to the base material layer 6 (6B) via an adhesive layer 5 (5B).

[0133] [Component supply sheet] The ventilation member 4 can be supplied by, for example, a component supply sheet. FIG. 11 shows an example of a component supply sheet that is a supply mode of the ventilation member 4. The component supply sheet 20 (20A) of FIG. 11 comprises a ventilation member 4 (4A) that is to be placed on the surface of an object having an opening, and a base sheet 9 on whose surface the ventilation member 4 (4A) is placed. The component supply sheet 20A comprises a ventilation member 4A as the ventilation member 4. The ventilation member 4A comprises a porous film 1 that has a shape that covers the opening when placed on the surface of the object, and an adhesive layer 5 bonded to the porous film 1.

[0134] The ventilation member 4 (4A) is disposed on the base sheet 9 via the pressure-sensitive adhesive layer 5. The member supply sheet 20 (20A) makes it possible to efficiently supply the ventilation member 4, for example, in the step of placing the ventilation member 4 on the surface of an object.

[0135] The ventilation member 4 may be placed on the base sheet 9 via an adhesive layer provided on the placement surface of the base sheet 9 on which the ventilation member 4 is placed. The adhesive layer on the placement surface preferably has weak adhesiveness.

[0136] Although not shown in the drawings, a plurality of ventilation members 4 may be arranged on the surface of the base sheet 9 .

[0137] Examples of materials constituting the base sheet 9 include paper, metal, resin, and composite materials thereof. Examples of metal include stainless steel and aluminum. Examples of resin include polyester such as PET, and polyolefins such as PE and PP. However, the materials constituting the base sheet 9 are not limited to the above examples. The base sheet 9 may be in the form of a sheet or a strip. When the base sheet 9 is in the form of a strip, the member supply sheet 20 may be rolled up to form a roll.

[0138] Examples of objects in which the ventilation member 4 is disposed include the housing of an electronic device and the housing of a vehicle electrical component. The ventilation member 4 can be disposed on the outer surface and / or inner surface of the housing. In this case, the opening may be an air vent and / or a sound vent provided in the housing. Examples of electronic devices include wearable devices such as smart watches and wristbands; various cameras including action cameras and security cameras; information and communication devices such as mobile phones, smartphones, and tablets; virtual reality (VR) devices; augmented reality (AR) devices; and sensor devices. Examples of vehicle electrical components include lamps and ECUs. However, the objects are not limited to the above examples.

[0139] The foreign matter that is prevented from passing through by the arrangement of the ventilation member 4 is, for example, particles such as dust, and liquid water such as water droplets.

[0140] Fig. 12 shows a first modification of the member supply sheet of Fig. 11. The member supply sheet 20 (20B) of Fig. 12 has the same configuration as the member supply sheet 20A of Fig. 11, except that it is provided with the ventilation member 4E of Fig. 9 as the ventilation member 4.

[0141] A second modification of the member supply sheet of Fig. 11 is shown in Fig. 13. The member supply sheet 20 (20C) of Fig. 13 has the same configuration as the member supply sheet 20A of Fig. 11, except that it is provided with the ventilation member 4F of Fig. 10 as the ventilation member 4.

[0142] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0143] [Example 1] Poly(4-methylpentene-1) resin (manufactured by Mitsui Chemicals, Inc., DX845, weight average molecular weight: 776,000) was used as the thermoplastic resin. 2Liquid paraffin (manufactured by MORESCO) with a viscosity of 1 / s was prepared. Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (manufactured by BASF Japan) was used as the antioxidant. A mixture was obtained by mixing 30.0 wt% of thermoplastic resin, 69.8 wt% of plasticizer, and 0.2 wt% of antioxidant. The mixture was kneaded at 260°C for 30 minutes using a Labo Plastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) to obtain a uniform kneaded product. 1.6 g of the kneaded product pellet was sandwiched between two polyimide plates (thickness 150 μm) and then sandwiched between a stainless steel plate (thickness 3.0 mm). The pellet was then hot-pressed at 1.0 kN for 5 minutes using a compression molding machine heated to 260°C to obtain a pressed body. The pressed body was cooled by contacting it with water at 18°C ​​while sandwiched between the polyimide plates to obtain a molded body. Next, using a biaxial stretching machine, the molded body was subjected to simultaneous biaxial stretching under the conditions of a stretching temperature of 100°C and a stretch ratio of 2x (longitudinal direction) x 2x (transverse direction). The strain rate during stretching was 1% / sec (0.655 mm / sec) in both the longitudinal and transverse directions. This resulted in a sheet body. Stretching was performed 5 minutes after the molded body was placed in a furnace set at the stretching temperature. Finally, an extraction operation was performed by immersing the sheet body in MEK at room temperature for 2 minutes using methyl ethyl ketone (MEK) as the extraction solvent. This resulted in the extraction and removal of the plasticizer from the sheet body. The extraction operation was performed while the sheet body was fixed to a stainless steel frame to suppress shrinkage. In this way, the porous film of Example 1 was obtained.

[0144] 14A is a diagram (5000x magnification) showing the results of SEM observation of the surface of the porous film of Example 1. FIG. 14B is a diagram (5000x magnification) showing the results of SEM observation of the cross section of the porous film of Example 1.

[0145] [Example 2] The plasticizer was extracted from the cooled molded body. After the plasticizer was extracted and removed, simultaneous biaxial stretching was performed. A porous film of Example 2 was obtained in the same manner as in Example 1, except for these steps.

[0146] 15A is a diagram (5000x magnification) showing the results of SEM observation of the surface of the porous film of Example 2. FIG. 15B is a diagram (5000x magnification) showing the results of SEM observation of the cross section of the porous film of Example 2.

[0147] [Example 3] The cooled molded body was annealed at 180°C for 30 minutes. The annealed molded body was subjected to a plasticizer extraction operation. After the annealing treatment, simultaneous biaxial stretching was performed. Except for these, the porous film of Example 3 was obtained by the same method as Example 1.

[0148] 16A is a diagram (5000x magnification) showing the results of SEM observation of the surface of the porous film of Example 3. FIG. 16B is a diagram (5000x magnification) showing the results of SEM observation of the cross section of the porous film of Example 3.

[0149] Comparative Example 1 Poly(4-methylpentene-1) resin (manufactured by Mitsui Chemicals, Inc., RT18, weight average molecular weight: 499,000) was used as the thermoplastic resin. 2 / s liquid paraffin (manufactured by MORESCO Corporation). Pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (manufactured by BASF Japan Ltd.) was used as the antioxidant. A mixture was obtained by mixing 50.0 wt% of thermoplastic resin, 49.8 wt% of plasticizer, and 0.2 wt% of antioxidant. Except for these, the porous film of Comparative Example 1 was obtained by the same method as in Example 1.

[0150] 17A is a diagram (5000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 1. FIG. 17B is a diagram (5000x magnification) showing the results of SEM observation of the cross section of the porous film of Comparative Example 1.

[0151] [Comparative Example 2] A mixture was obtained by mixing 30.0 wt% of a thermoplastic resin, 69.8 wt% of a plasticizer, and 0.2 wt% of an antioxidant. Except for this, a porous film of Comparative Example 2 was obtained in the same manner as in Comparative Example 1. In Comparative Example 2, the film broke during stretching.

[0152] [Comparative Example 3] Poly(4-methylpentene-1) resin (DX820, manufactured by Mitsui Chemicals, Inc., weight average molecular weight: 266,000) was used as the thermoplastic resin. Except for this, a porous film of Comparative Example 3 was obtained in the same manner as in Comparative Example 2. In Comparative Example 3, the film broke during stretching.

[0153] [Comparative Example 4] A poly(4-methylpentene-1) resin (MX002, manufactured by Mitsui Chemicals, Inc., weight average molecular weight: 600,000) was used as the thermoplastic resin. Except for this, a porous film of Comparative Example 4 was obtained in the same manner as in Comparative Example 2.

[0154] FIG. 18 is a diagram (5000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 4.

[0155] [Comparative Example 5] A mixture of poly(4-methylpentene-1) resin (manufactured by Mitsui Chemicals, Inc., DX470, weight average molecular weight: 493,000) and poly(4-methylpentene-1) resin (manufactured by Mitsui Chemicals, Inc., DX845, weight average molecular weight: 776,000) in a mass ratio of 30:70 (weight average molecular weight: 691,100) was used as the thermoplastic resin. 50.0 wt% of thermoplastic resin, 49.8 wt% of plasticizer, and 0.2 wt% of antioxidant were mixed to obtain a mixture. The plasticizer was extracted from the cooled molded body. After the plasticizer was extracted and removed, simultaneous biaxial stretching was performed. A porous film of Comparative Example 5 was obtained by the same method as in Example 1, except for the above.

[0156] 19A is a diagram (5000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 5. FIG. 19B is a diagram (5000x magnification) showing the results of SEM observation of the cross section of the porous film of Comparative Example 5.

[0157] The manufacturing conditions for the porous films of Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1.

[0158]

[0159] Using the methods described above for the porous film, the thickness, air permeability, water pressure resistance, etc. were evaluated for the porous films of Examples 1 to 3 and Comparative Examples 1 to 5. The evaluation results are shown in Table 2.

[0160]

[0161] Using the methods described above for the porous film, the surface porosity Ps, cross-sectional porosity Pc, etc. were determined for the porous films of Examples 1 to 3 and Comparative Examples 1 to 5. The results are shown in Table 3.

[0162]

[0163] As can be seen from Table 2, the porous films of Examples 1 to 3 using a thermoplastic resin having a weight average molecular weight of 700,000 or more had a water pressure resistance of 500 kPa or more and an air permeability expressed in Gurley number of 60 seconds / 100 mL or less, and thus had improved water resistance while maintaining excellent air permeability.

[0164] As can be seen from comparing Figures 14A, 15A, and 16A with Figures 17A, 18, and 19A, multiple island regions and multiple fibrils connecting the multiple island regions were observed in the porous films of Examples 1 to 3. As can be seen from comparing Figures 14B, 15B, and 16B with Figures 17B and 19B, in the porous films of Examples 1 to 3, nodes or clusters of nodes were densely packed, and fine gaps (voids) were observed between the nodes or clusters of nodes. Furthermore, as can be seen from Table 3, when the cross sections of the porous films of Examples 1 to 3 were observed with an SEM, the proportion Rc of voids with a circle equivalent diameter of 0.7 μm or less was 10% or more.

[0165] From these results, it is presumed that the porous films of Examples 1 to 3, which used a thermoplastic resin having a weight-average molecular weight of 700,000 or more, easily formed the characteristic cross-sectional structure and surface structure described above, thereby realizing high water resistance and high breathability.

[0166] From the above results, it can be seen that the porous films of Examples 1 to 3 are suitable for improving water resistance while maintaining excellent breathability.

[0167] The technology of the present invention can be applied to, for example, waterproof gas-permeable membranes, waterproof sound-permeable membranes, separators for electricity storage devices, and the like.

Claims

1. A porous film comprising a fluorine-free thermoplastic resin as a main component, wherein the weight average molecular weight of the thermoplastic resin is 700,000 or more.

2. The porous film according to claim 1, wherein the thermoplastic resin is a polyolefin resin.

3. The porous film according to claim 1, having a water pressure resistance of 500 kPa or more and an air permeability, expressed as a Gurley number, of 60 seconds / 100 mL or less.

4. The porous film according to claim 3, wherein when the value obtained by dividing the air permeability by the water pressure resistance is defined as a ratio R, the ratio R≦0.09 is satisfied.

5. The porous film according to claim 1, wherein, when a cross section of the porous film is observed under a scanning electron microscope, the proportion of pores having a circle equivalent diameter of 0.7 μm or less is 10% or more.

6. The porous film according to claim 1, wherein the porosity is 40% or less when the surface of the porous film is observed with a scanning electron microscope.

7. The porous film according to claim 6, wherein the porosity is 30% or more when the cross section of the porous film is observed with a scanning electron microscope.

8. The porous film according to claim 1, having a thickness of 70 μm or less.

9. The porous film according to claim 1, which is a stretched film.

10. A porous film containing a fluorine-free thermoplastic resin as a main component, wherein, when the surface of said porous film is observed with a scanning electron microscope, a plurality of island regions and a plurality of fibrils connecting said plurality of island regions are observed, and the proportion of pores having a circle equivalent diameter of 0.7 μm or less is 10% or more.

11. The porous film according to claim 10, wherein the thermoplastic resin is a polyolefin resin.

12. A ventilation member comprising: the porous film according to any one of claims 1 to 11; and an adhesive layer bonded to the porous film.

13. A component supply sheet comprising a ventilation member to be placed on a surface of an object having an opening, and a base sheet with the ventilation member placed on its surface, wherein the ventilation member comprises: a porous film having a shape that covers the opening when placed on the surface; and an adhesive layer bonded to the porous film, and the porous film is a porous film according to any one of claims 1 to 11.

14. The member supply sheet according to claim 13, wherein a plurality of the ventilation members are arranged on the surface of the base sheet.

15. A method for producing a porous film, comprising the steps of: kneading a composition containing a fluorine-free thermoplastic resin and a plasticizer to obtain a kneaded mixture; performing a pressing or extrusion process; performing a cooling process; performing a stretching process; and performing a plasticizer extraction process, wherein the thermoplastic resin has a weight average molecular weight of 700,000 or more.

16. The method for producing a porous film according to claim 15, further comprising the step of performing an annealing treatment.

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