Porous film, method for producing porous film, ventilation member, and sheet for supplying member

Abstract

This porous film contains a fluorine-free thermoplastic resin as a main component. In an observation image obtained by observing, with a scanning electron microscope, a cross section parallel to the thickness direction of the porous film, when a range from 1 / 3 to 2 / 3 along the thickness direction with one end of the porous film taken as a starting point is defined as a central portion of the porous film, the ratio of the porosity of the central portion to the porosity of the whole porous film is 90% or more. Alternatively, the porous film contains a fluorine-free thermoplastic resin as a main component, and the Gurley air permeability is 20 seconds or less per 100 mL.

Description

Porous film, method for producing porous film, ventilation member, and member supply sheet

[0001] The present invention relates to a porous film, a method for producing 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 films 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, and has a puncture strength of 0.7 N or more and an air permeability of 75 to 400 s / 100 mL.

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

[0005] Porous films used to ensure ventilation through openings in the housings of smartphones and the like while preventing the penetration of foreign matter through the openings are required to have high breathability in addition to water resistance. Studies by the present inventors have shown that fluorine-free porous films are prone to have their pores blocked during production, which reduces their breathability.

[0006] Therefore, an object of the present invention is to provide a fluorine-free porous film suitable for improving breathability, a method for producing the porous film, a ventilation member, and a member-supplying sheet.

[0007] The present invention provides a porous film containing a fluorine-free thermoplastic resin as a main component, wherein, in an image of a cross section of the porous film parallel to the thickness direction observed with a scanning electron microscope, when the central part of the porous film is defined as the range from 1 / 3 to 2 / 3 of the way along the thickness direction, starting from one end of the porous film, the ratio of the porosity of the central part to the porosity of the entire porous film is 90% or more.

[0008] From another aspect, the present invention provides a porous film containing a fluorine-free thermoplastic resin as a main component, the porous film having a Gurley air permeability of 20 seconds / 100 mL or less.

[0009] From another aspect, the present invention provides a method for producing a porous film, comprising: kneading a mixture containing a fluorine-free thermoplastic resin and a plasticizer using a twin-screw extruder, and then extruding the kneaded mixture; obtaining a molded body while cooling the extruded kneaded mixture; stretching the molded body to obtain a sheet body; and removing the plasticizer from the sheet body, wherein the specific energy of the twin-screw extruder is 0.5 kWh / kg or more.

[0010] From yet 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.

[0011] 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 a tacky adhesive layer bonded to the porous film, and the porous film is the porous film of the present invention described above.

[0012] According to the present invention, it is possible to provide a fluorine-free porous film suitable for improving breathability, a method for producing a porous film, a ventilation member, and a member-supplying sheet.

[0013] FIG. 1 is a cross-sectional view schematically showing an example of a porous film of the present invention. FIG. 2 is a view schematically showing an example of an observation image of a cross section of the porous film of FIG. 1 observed with a scanning electron microscope (SEM). FIG. 3 is a cross-sectional view schematically showing an example of a film member of the present invention. FIG. 4 is a cross-sectional view schematically showing a first modified example of the film member of FIG. 3. FIG. 5 is a cross-sectional view schematically showing a second modified example (rolled body) of the film member of FIG. 3. FIG. 6 is a cross-sectional view schematically showing an example of a ventilation member of the present invention. FIG. 7 is a cross-sectional view schematically showing a first modified example of the ventilation member of FIG. 6. FIG. 8 is a cross-sectional view schematically showing a second modified example of the ventilation member of FIG. 6. FIG. 9 is a cross-sectional view schematically showing a third modified example of the ventilation member of FIG. 6. FIG. 10 is a cross-sectional view schematically showing a fourth modified example of the ventilation member of FIG. 6. FIG. 11 is a cross-sectional view schematically showing a fifth modified example of the ventilation member of FIG. 6. FIG. 12 is a cross-sectional view schematically showing an example of a member supplying sheet of the present invention. 13 is a cross-sectional view schematically showing a first modified example of the member supply sheet of FIG. 12. FIG. 14 is a cross-sectional view schematically showing a second modified example of the member supply sheet of FIG. 12. FIG. 15A is a view (1000x magnification) showing the results of SEM observation of a cross section of a porous film of Example 1. FIG. 15B is a view (1000x magnification) showing the results of SEM observation of a surface of a porous film of Example 1. FIG. 16A is a view (1000x magnification) showing the results of SEM observation of a cross section of a porous film of Example 2. FIG. 16B is a view (1000x magnification) showing the results of SEM observation of a surface of a porous film of Example 2. FIG. 17A is a view (1000x magnification) showing the results of SEM observation of a cross section of a porous film of Example 3. FIG. 17B is a view (1000x magnification) showing the results of SEM observation of a surface of a porous film of Example 3. 18A is a diagram (1000x magnification) showing the results of SEM observation of the cross section of the porous film of Comparative Example 1. FIG. 18B is a diagram (1000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 1. FIG. 19A is a diagram (1000x magnification) showing the results of SEM observation of the cross section of the porous film of Comparative Example 2. FIG. 19B is a diagram (1000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 2. FIG. 20 is a diagram explaining how to determine the distance between nodes of the porous film of FIG. 1.

[0014] A porous film according to a first aspect of the present invention is a porous film containing a fluorine-free thermoplastic resin as a main component, wherein, in an image of a cross section of the porous film parallel to the thickness direction observed with a scanning electron microscope, when the central part of the porous film is defined as the range from 1 / 3 to 2 / 3 of the way along the thickness direction, starting from one end of the porous film, the ratio of the porosity of the central part to the porosity of the entire porous film is 90% or more.

[0015] In a second aspect of the present invention, for example, in the porous film according to the first aspect, the weight average molecular weight of the thermoplastic resin in the porous film is 330,000 or less.

[0016] In a third aspect of the present invention, for example, in the porous film according to the first or second aspect, the thermoplastic resin is a polyolefin resin.

[0017] In a fourth aspect of the present invention, for example, the porous film according to any one of the first to third aspects is a stretched film.

[0018] In a fifth aspect of the present invention, for example, in the porous film according to any one of the first to fourth aspects, the pores have an equivalent circle diameter of 1.5 μm or more.

[0019] In a sixth aspect of the present invention, for example, in the porous film according to any one of the first to fifth aspects, the Feret diameter of the pores is 2.1 μm or more.

[0020] A porous film according to a seventh aspect of the present invention contains a fluorine-free thermoplastic resin as a main component and has a Gurley air permeability of 20 seconds / 100 mL or less.

[0021] In an eighth aspect of the present invention, for example, in the porous film according to the seventh aspect, the water pressure resistance is 0.08 MPa or more.

[0022] A method for producing a porous film according to a ninth aspect of the present invention includes: kneading a mixture containing a fluorine-free thermoplastic resin and a plasticizer using a twin-screw extruder, and then extruding the kneaded mixture; obtaining a molded body while cooling the extruded kneaded mixture; stretching the molded body to obtain a sheet body; and removing the plasticizer from the sheet body, wherein the specific energy of the twin-screw extruder is 0.5 kWh / kg or more.

[0023] A ventilation member according to a tenth aspect of the present invention includes, for example, the porous film according to any one of the first to eighth aspects, and an adhesive layer bonded to the porous film.

[0024] A component supply sheet according to an eleventh 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 eighth aspects.

[0025] 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.

[0026] [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. In this specification, "main component" means the component that is contained in the largest amount by weight in the porous film 1. By containing a thermoplastic resin as a main component, the porous film 1 can be adhered to a smartphone housing or the like by heat fusion without using an adhesive or pressure-sensitive adhesive, for example.

[0027] The porous film 1 has a first main surface 1a and a second main surface 1b. Figure 2 is a diagram schematically showing an example of an observation image of a cross section of the porous film 1 parallel to the thickness direction T observed with a scanning electron microscope (SEM). As shown in Figure 2, in the cross-sectional observation image 100, the range from 1 / 3 to 2 / 3 of the way along the thickness direction T, starting from one end of the porous film 1, is defined as a central portion 100b of the porous film 1. In this case, the ratio R (Pb / Pa x 100) of the porosity Pb ​​of the central portion 100b to the porosity Pa of the entire porous film 1 is 90% or more. The porosity Pa of the entire porous film 1 is the porosity in the entire range 100a along the thickness direction T in the cross-sectional observation image 100.

[0028] As described above, fluorine-free porous films are prone to pore blockage during production, which reduces their breathability. The inventors have discovered that the pore blockage of fluorine-free porous films during production is caused by shrinkage in the thickness direction during the stretching process, particularly shrinkage of the central portion. In the porous film 1 of this embodiment, the porosity ratio R is 90% or more, and shrinkage of the central portion 100b is suppressed. Therefore, the porous film 1 is suitable for improving breathability because pore blockage in the thickness direction T is suppressed.

[0029] The lower limit of the porosity ratio R may be 92%, 95%, 97%, or even 100%. The upper limit of the porosity ratio R is, for example, 115%. The upper limit of the porosity ratio R may be 112% or 110%.

[0030] The porosity in an SEM image of a cross section of the porous film 1 parallel to the thickness direction T can be determined by the method described below. First, a cross section of the porous film 1 parallel to the thickness direction T is observed using an SEM (see, for example, FIG. 2). As shown in FIG. 2, the cross-sectional image is an image of a cross section perpendicular to the main surface (first main surface 1a or second main surface 1b) of the porous film 1, and includes the first main surface 1a and the second main surface 1b. The magnification of the image is, for example, 1000x. In the obtained image, the range from 1 / 3 to 2 / 3 of the way along the thickness direction T, starting from one end of the porous film 1, is defined as the central portion 100b. Next, the image is binarized using image analysis software. Pores are identified from the obtained binarized image, and the area of ​​each pore included in the image is calculated. The porosity Pa of the porous film 1 can be determined by calculating the ratio of the total area of ​​pores contained in the entire area 100a of the porous film 1 along the thickness direction T in the observed image to the area of ​​the entire area 100a of the porous film 1. The porosity Pb ​​of the central portion 100b of the porous film 1 can be determined by calculating the ratio of the total area of ​​pores contained in the central portion 100b of the porous film 1 to the area of ​​the central portion 100b in the observed image. The porosity Pa of the porous film 1 is determined by measuring 300 or more pores, for example, 300 to 5,000 pores. When identifying pores, pores on the edges of the image are omitted from the analysis. ImageJ, for example, can be used as image analysis software.

[0031] In an image of a cross section of the porous film 1 observed with an SEM, the porosity Pa of the porous film 1 is preferably 25% or more. When the porosity Pa satisfies the above numerical range, excellent breathability is likely to be achieved.

[0032] The upper limit of the porosity Pa of the porous film 1 is, for example, 45%. The upper limit of the porosity Pa of the porous film 1 may be 40%.

[0033] In an image of a cross section of the porous film 1 observed with an SEM, the porosity Pb ​​of the central portion 100b of the porous film 1 is preferably 25% or more. When the porosity Pb ​​satisfies the above numerical range, excellent breathability is likely to be achieved.

[0034] The upper limit of the porosity Pb ​​of the central portion 100b of the porous film 1 is, for example, 45%. The upper limit of the porosity Pb ​​of the central portion 100b of the porous film 1 may be 40%.

[0035] The weight-average molecular weight of the fluorine-free thermoplastic resin in the porous film 1 is preferably 330,000 or less. When the weight-average molecular weight of the thermoplastic resin in the porous film 1 is 330,000 or less, it is easy to achieve a porosity ratio R of 90% or more in the porous film 1.

[0036] According to the studies of the present inventors, when the weight-average molecular weight of the fluorine-free thermoplastic resin in the porous film 1 is 330,000 or less, the molecular chains are less entangled, and therefore shrinkage in the thickness direction during the stretching step is less likely to occur. Therefore, in the porous film 1 having such a configuration, pore blockage in the thickness direction T is more suppressed, and it is easy to achieve a porosity ratio R of 90% or more.

[0037] The upper limit of the weight average molecular weight of the fluorine-free thermoplastic resin in the porous film 1 may be 320,000, 310,000, 300,000, 299,000, or even 298,000. The lower limit of the weight average molecular weight of the fluorine-free thermoplastic resin in the porous film 1 is, for example, 200,000. The lower limit of the weight average molecular weight of the fluorine-free thermoplastic resin may be 230,000.

[0038] The weight-average molecular weight of the fluorine-free thermoplastic resin in the porous film 1 can be determined by the method described below. First, a sample is prepared for gel permeation chromatography (GPC) analysis. Specifically, 8 mg of the porous film 1 is added to a continuously flowing measurement solvent (mobile phase: o-dichlorobenzene containing 0.025 wt% BHT) in a GPC apparatus, and the mixture is shaken at 150°C under a nitrogen atmosphere to dissolve. Next, the solution is hot-filtered through an in-line filter with a pore size of 10 μm to obtain a filtrate. The weight-average molecular weight of the fluorine-free thermoplastic resin in the porous film 1 can be determined using the obtained filtrate under the following measurement conditions. GPC apparatus: GPC-IR type high temperature gel permeation chromatograph manufactured by Polymer Char (built-in detector: IR6 type MCT infrared detector) Column: TSKgel GMH6-HT (manufactured by Tosoh Corporation, 7.5 mm x 300 mm) x 2 + TSKgel GMH6-HTL (manufactured by Tosoh Corporation, 7.5 mm x 300 mm) x 2 Column temperature: 140°C Flow rate: 1.0 mL / min Injection volume: 0.4 mL Column calibration: monodisperse PS (manufactured by Tosoh Corporation, TSKgel standard polystyrene) Molecular weight calibration: relative calibration method (PS conversion) Analysis software: Empower3 manufactured by Nippon Waters K.K.

[0039] In this embodiment, the air permeability of the porous film 1 in the thickness direction T is 20 seconds / 100 mL or less, as expressed by the air permeability (Gurley air permeability) determined in accordance with the air permeability measurement method B (Gurley method) specified in JIS L1096: 2010. Thus, the porous film 1 has extremely excellent air permeability.

[0040] The upper limit of the Gurley air permeability of the porous film 1 may be 15 seconds / 100 mL, 10 seconds / 100 mL, 9 seconds / 100 mL, 8 seconds / 100 mL, 7 seconds / 100 mL, 6 seconds / 100 mL, or even 5 seconds / 100 mL. The lower limit of the Gurley air permeability of the porous film 1 is, for example, 0.1 seconds / 100 mL. The lower limit of the Gurley air permeability of the porous film 1 may be 0.5 seconds / 100 mL, 1 second / 100 mL, or even 1.5 seconds / 100 mL.

[0041] Even when the size of the porous film 1 is smaller than the size of the test piece in the Gurley method (approximately 50 mm x 50 mm), the Gurley air permeability can be evaluated by using a measuring jig. An example of the measuring jig is a stainless steel (SUS) disk having a thickness of 2 mm and a diameter of 47 mm and a through-hole (having a circular cross section with a diameter of 1 mm or 2 mm) at the center. Measurement of the Gurley air permeability using this measuring jig can be carried out as follows.

[0042] The porous film 1 to be evaluated is fixed to one surface of the measuring jig so as to cover the opening of the through-hole of the measuring jig. The fixation is performed so that during the measurement of the Gurley air permeability, 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 from a direction 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 matching the shape of the opening can be used. The double-sided adhesive tape can be placed between the measuring jig and the porous film 1 so that the periphery of the vent hole and the periphery of the opening coincide. Next, the measuring jig with the porous film 1 fixed thereto is set in a Gurley air permeability tester so that the fixed surface of the porous film 1 is downstream of the air flow during measurement, and the time t1 for 100 mL of air to pass through the porous film is measured. Next, the measured time t1 was calculated based on the effective test area of ​​642 [mm 2 ] as defined in the air permeability measurement method B (Gurley method) of JIS L1096:2010. 2 ], the value t per unit area is calculated by the formula t = {(t1) × (area of ​​the effective test part of the porous film [mm 2 ]) / 642 [mm 2 ]}, and the resulting converted value t can be used as the Gurley air permeability of the porous film 1. When the above-mentioned circular plate is used as the measuring jig, the area of ​​the effective test portion of the porous film 1 is the area of ​​the cross section of the through-hole. It has been confirmed that the Gurley air permeability measured without using a measuring jig for a porous film that meets the size of the above-mentioned test piece agrees well with the Gurley air permeability measured using the measuring jig after cutting the porous film 1 into small pieces, i.e., that the use of the measuring jig does not substantially affect the measured value of the Gurley air permeability.

[0043] The water pressure resistance of the porous film 1 can be 0.08 MPa or more as evaluated by the water resistance test method B (high water pressure method) specified in JIS L1092: 2009. In this way, the porous film 1 can have high water resistance.

[0044] The lower limit of the water pressure resistance of the porous film 1 may be 0.1 MPa. The upper limit of the water pressure resistance of the porous film 1 is, for example, 2.0 MPa.

[0045] The water pressure resistance of the porous film 1 can be evaluated in accordance with the above-mentioned water resistance test method using a measuring tool. An example of the measuring tool is a 2 mm thick, 47 mm diameter SUS disk with a 1.6 mm diameter through-hole (with 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 tool can be carried out as follows.

[0046] 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 porous film 1 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 a 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.

[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 having a porosity ratio R of 90% or more.

[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 may be 1 μm or more and 100 μm or less. When the thickness is in the above numerical range, it is easy to obtain a porous film 1 having a porosity ratio R of 90% or more.

[0054] The lower limit of the thickness of the porous film 1 may be 5 μm or 10 μm, and the upper limit of the thickness of the porous film 1 may be 90 μm or 80 μm.

[0055] 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 measurements. The thickness of the porous film 1 can also be determined by measuring the thickness at any five points on an observation image (see, for example, FIG. 2) obtained by observing the cross section of the porous film 1 with an SEM, and calculating the average value of these measurements.

[0056] The porous film 1 may have multiple nodes and multiple fibrils. When the cross section of the porous film 1 is observed with an SEM, multiple nodes may be present along the thickness direction. The multiple nodes may be present throughout the thickness direction T of the porous film 1. It is preferable that the multiple nodes are present uniformly throughout the thickness direction of the porous film 1. Such a cross-sectional structure is easily achieved when pore blockage in the thickness direction T is suppressed. For example, FIG. 15A is a diagram (1000x magnification) showing the results of SEM observation of the cross section of the porous film of Example 1 described below. As shown in FIG. 15A, when the cross section of the porous film of Example 1 is observed, multiple nodes are present uniformly throughout the thickness direction of the porous film 1.

[0057] When the cross section of the porous film 1 is observed with an SEM, adjacent agglomerated nodes may be connected by multiple fibrils, or adjacent agglomerated nodes may not be connected by multiple fibrils and the nodes may be directly connected to each other.

[0058] When the surface of the porous film 1 is observed with an SEM, the porous film 1 may have a hexagonal structure formed by a plurality of nodes and a plurality of fibrils. The hexagonal structure may exist throughout the entire porous film 1. A porous film 1 having such a structure is suitable for achieving both water resistance and breathability. The hexagonal structure can be confirmed, for example, by observing the main surface of the porous film 1 with an SEM from the vertical direction.

[0059] In the present disclosure, the term "hexagonal structure formed by multiple nodes and multiple fibrils" refers to a structure that can be confirmed by observing the surface of the porous film 1 with an SEM, in which island-like regions formed by multiple nodes are irregularly connected and these island-like regions are connected to each other by multiple fibrils. The island-like regions have, for example, a polygonal shape. Note that the polygonal-shaped region does not necessarily have to have an outer shape composed only of straight lines, and also includes approximately polygonal-shaped regions in which some sides are curved, such as circular arcs. Furthermore, the polygonal shape is not limited to a hexagon.

[0060] The island regions may vary in size. When the surface of the porous film 1 is observed with an SEM, island regions of different sizes may be present in random positions. The number of nodes forming relatively large island regions is greater than the number of nodes forming relatively small island regions. For example, FIG. 15B is a diagram (1000x magnification) showing the results of SEM observation of the surface of the porous film of Example 1 described below. As shown in FIG. 15B, the surface of the porous film of Example 1 has a tortoiseshell structure formed by multiple nodes and multiple fibrils, and island regions of different sizes formed by the multiple nodes are present in random positions.

[0061] When the surface of the porous film 1 is observed with an SEM, the equivalent circle diameter of the nodes of the porous film 1 is preferably 2.5 μm or more. When the equivalent circle diameter of the nodes is within the above numerical range, an air permeability that satisfies the above numerical range is easily achieved. In this disclosure, with regard to the "equivalent circle diameter of the node," "Feret diameter of the node," and "distance between nodes," "node" and "island region formed by multiple nodes" are used interchangeably.

[0062] The upper limit of the equivalent circle diameter of the node of the porous film 1 is, for example, 10.0 μm. The upper limit of the equivalent circle diameter of the node of the porous film 1 may be 9.0 μm, 8.0 μm, 7.0 μm, 6.0 μm, or even 5.0 μm.

[0063] When the surface of the porous film 1 is observed with an SEM, the Feret diameter of the nodes of the porous film 1 is preferably 2.5 μm or more. When the Feret diameter of the nodes is within the above numerical range, an air permeability that satisfies the above numerical range is easily achieved.

[0064] The lower limit of the Feret diameter of the nodes of the porous film 1 may be 3.0 μm. The upper limit of the Feret diameter of the nodes of the porous film 1 is, for example, 10.0 μm. The upper limit of the Feret diameter of the nodes of the porous film 1 may be 9.0 μm, 8.0 μm, 7.0 μm, 6.0 μm, or even 5.0 μm.

[0065] The circle-equivalent diameter and Feret diameter of the nodes of the porous film 1 can be determined by the method described below. First, the surface of the porous film 1 is observed using an SEM (see, for example, FIG. 15B). Next, the SEM observation image (or a portion thereof) obtained using image analysis software is binarized. Nodes are identified from the obtained binarized image, and the area of ​​each node included in the image is calculated. For each node, 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 node being measured. The average of the calculated circle-equivalent diameters can be considered as the circle-equivalent diameter of the nodes of the porous film 1. Furthermore, the Feret diameter of each node included in the binarized image is calculated. The Feret diameter is the maximum distance between parallel tangents to the contour line of the node. The circle-equivalent diameter and Feret diameter are determined by measuring 50 or more nodes, for example, 100 to 1000 nodes. Note that when identifying the nodes, nodes on the edge of the image are omitted from the analysis. As the image analysis software, for example, imageJ can be used.

[0066] When the surface of the porous film 1 is observed with an SEM, the distance between nodes of the porous film 1 is preferably 3.0 μm or more. When the distance between nodes is within the above numerical range, an air permeability that satisfies the above numerical range is easily achieved.

[0067] The lower limit of the distance between nodes of the porous film 1 may be 3.5 μm or 4.0 μm. The upper limit of the distance between nodes of the porous film 1 is, for example, 10.0 μm. The upper limit of the distance between nodes of the porous film 1 may be 9.0 μm, 8.0 μm, 7.0 μm, 6.0 μm, or 5.0 μm.

[0068] The distance between nodes of the porous film 1 can be determined by the method described below. Fig. 20 is a schematic diagram for explaining how to determine the distance between nodes of the porous film 1 in Fig. 1. First, a binarized image is obtained by the same method as that described for the circle equivalent diameter of the nodes of the porous film 1, and the nodes are identified from the binarized image (see Fig. 20). As shown in Fig. 20, the distance between nodes L between node A and node B isAB can be calculated as the distance between the center of gravity c of node A and the center of gravity c of node B minus the circle equivalent diameter x 1 / 2 of node A and the circle equivalent diameter x 1 / 2 of node B. In this way, the inter-node distance (L AB , L AC and L AD That is, the distance between node A and the fourth or subsequent node (node ​​E) is calculated. AE ) is not adopted. However, the node (node ​​F) that overlaps with node A in the image is excluded from the three nodes that are first to third closest in distance from node A. The average of the distances between the three nodes closest to node A obtained in this way is considered to be the distance between node A and the other nodes. The distance between nodes is obtained in the same manner for each node included in the image. The average of the obtained distances between nodes can be considered to be the distance between nodes of the porous film 1.

[0069] The porous film 1 has a plurality of pores. When the surface of the porous film 1 is observed with an SEM, it is preferable that the equivalent circle diameter of the pores in the porous film 1 is 1.5 μm or more. When the equivalent circle diameter of the pores satisfies the above numerical range, an air permeability that satisfies the above numerical range is easily achieved.

[0070] The upper limit of the equivalent circle diameter of the pores of the porous film 1 is, for example, 5.0 μm. The upper limit of the equivalent circle diameter of the pores of the porous film 1 may be 4.0 μm, 3.0 μm, or 2.0 μm.

[0071] When the surface of the porous film 1 is observed with an SEM, the Feret diameter of the pores of the porous film 1 is preferably 2.1 μm or more. When the Feret diameter of the pores satisfies the above numerical range, an air permeability that satisfies the above numerical range is easily achieved.

[0072] The lower limit of the Feret diameter of the pores of the porous film 1 may be 2.2 μm, 2.3 μm, 2.4 μm, or 2.5 μm. The upper limit of the Feret diameter of the pores of the porous film 1 is, for example, 5.0 μm. The upper limit of the Feret diameter of the pores of the porous film 1 may be 4.5 μm, 4.0 μm, 3.5 μm, or 3.0 μm.

[0073] The circle-equivalent diameter and Feret diameter of the pores in the porous film 1 can be determined by the same method as the method for determining the circle-equivalent diameter and Feret diameter of the nodes of the porous film 1 described above. However, the pores are identified from the obtained binarized image. Note that when identifying the pores, pores on the edges of the image are omitted from the analysis.

[0074] When the surface of the porous film 1 is observed with an SEM, the porosity Ps of the surface of the porous film 1 is preferably 25% or more. When the porosity Ps of the surface satisfies the above numerical range, an air permeability that satisfies the above numerical range is easily achieved.

[0075] The lower limit of the porosity Ps in the surface of the porous film 1 may be 26% or more, or may be 27% or more. The upper limit of the porosity Ps in the surface of the porous film 1 is, for example, 50%. The upper limit of the porosity Ps in the surface of the porous film 1 may be 45%, 40%, 35%, or 30%.

[0076] The porosity Ps of the surface of the porous film 1 can be determined by the same method as the method for determining the circle-equivalent diameter of the nodes of the porous film 1 described above. However, 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 surface 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 of the surface is determined by measuring 300 or more pores, for example, 500 to 3,000 pores.

[0077] The porous film 1 may be a stretched film. When the porous film 1 is a stretched film, properties such as breathability and water resistance can be easily controlled. The stretched film may be a biaxially stretched film or a uniaxially stretched film.

[0078] 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 a liquid-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.

[0079] 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).

[0080] [Method for Producing Porous Film] The porous film 1 described above can be produced, for example, by the following method.

[0081] The method for producing the porous film 1 includes, for example, using a twin-screw extruder to knead a mixture containing a fluorine-free thermoplastic resin and a plasticizer, followed by extruding the kneaded mixture (step S1), cooling the extruded mixture to obtain a molded body (step S2), stretching the molded body to obtain a sheet (step S3), and removing the plasticizer from the sheet (step S4). In step S1, the specific energy of the twin-screw extruder is 0.5 kWh / kg or more. This production method can produce a porous film 1 having a porosity ratio R of 90% or more, for example. The porous film 1 is suitable for improving breathability because pore blockage in the thickness direction T is suppressed.

[0082] Steps S1 and S2 correspond to a process for producing a precursor of the porous film 1. Steps S3 and S4 correspond to a process for growing a porous structure.

[0083] Step S1 is performed using a twin-screw extruder (e.g., TEX25αIII, manufactured by The Japan Steel Works, Ltd.). In step S1, the specific energy of the twin-screw extruder is 0.5 kWh / kg or more. The specific energy of the twin-screw extruder is the value obtained by dividing the work performed on the raw materials by the twin-screw extruder per unit extrusion mass, and can be used as an index of the degree of mixing. By making the specific energy of the twin-screw extruder 0.5 kWh / kg or more, it is easy to achieve a porous film 1 having a porosity ratio R of 90% or more.

[0084] In step S1, the specific energy of the twin-screw extruder may be 0.6 kWh / kg or more, or 0.7 kWh / kg or more.

[0085] In step S1, 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 S2.

[0086] The weight average molecular weight of the fluorine-free thermoplastic resin used as a raw material for the porous film 1 is, for example, 300,000 or more and 800,000 or less.

[0087] As the fluorine-free thermoplastic resin, for example, polymethylpentene resin can be used.

[0088] The mixture 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.

[0089] 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 exhibits 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. A single plasticizer may be used, or two or more types of plasticizers may be mixed and used. Examples of such plasticizers include plasticizers having a kinematic viscosity of 50 to 150 mm at 40°C. 2 / s can be used.

[0090] The mixing ratio of the thermoplastic resin and the plasticizer is set so that a uniform mixture can be obtained in step S1 and a molded body can be formed in step S2. Specifically, the weight ratio of the thermoplastic resin in the mixture containing the thermoplastic resin and the plasticizer is, for example, 20% by weight or more and 80% by weight or less, and preferably 30% by weight or more and 70% by weight. By setting the weight ratio of the thermoplastic resin to 20% by weight or more, it is possible to prevent the viscosity of the mixture from decreasing too much. By setting the weight ratio of the thermoplastic resin to 80% by weight or less, it is easy to obtain a good porous structure.

[0091] The mixture 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.

[0092] In step S2, for example, the kneaded mixture is cooled and rolled out using a metal roll having a controlled surface temperature to obtain a sheet-like compact. A plurality of metal rolls may be used. The sheet-like compact may be formed while being cooled by passing the mixture through a plurality of metal rolls.

[0093] In step S3, the molded body is stretched at least once in at least one axial direction. Step S3 is performed using a biaxial stretching machine. Stretching in at least one axial 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 may be biaxially stretched simultaneously. Step S3 generates pores in the molded body. Furthermore, a structure is formed in which island-like regions of different sizes formed by multiple nodes are present in random positions.

[0094] According to the manufacturing method of this embodiment, shrinkage in the thickness direction T, particularly shrinkage of the central portion 100b, can be suppressed in step S3. This suppresses clogging of pores in the thickness direction T, and makes it possible to manufacture a porous film 1 suitable for improving breathability.

[0095] When a porous film is produced using a thermoplastic resin with a low molecular weight (e.g., a weight-average molecular weight of 300,000 or less), the film is prone to breakage during the stretching process. For this reason, it has been thought that producing a porous film using a low-molecular-weight thermoplastic resin is difficult. However, according to the production method of this embodiment, the weight-average molecular weight of the thermoplastic resin in the produced porous film 1 can be achieved to be 330,000 or less. When the weight-average molecular weight of the thermoplastic resin in the porous film 1 is 330,000 or less, molecular chain entanglement is reduced, thereby further suppressing shrinkage in the thickness direction T, particularly in the central portion 100b, in step S3.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] In step S4, the plasticizer is removed from the sheet using, for example, an extraction solvent, thereby obtaining a porous film 1.

[0100] 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.

[0101] Between step S3 and step S4, 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.

[0102] Heat setting may be performed after step S3, between steps S3 and S4, or both after steps S3 and S4. 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.

[0103] [Film member] An example of the film member of the present invention is shown in Figure 3. The film member 2 (2A) in Figure 3 includes a porous film 1. A first modified example of the film member of Figure 3 is shown in Figure 4. The film member 2 (2B) in Figure 4 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.

[0104] 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.

[0105] The film member 2B in Fig. 4 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, a pressure-sensitive adhesive, or the like.

[0106] The film member 2 may include any layers and / or members other than those described above.

[0107] The thickness of the film member 2 is, for example, 1 to 300 μm, and may be 50 to 200 μm.

[0108] 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.

[0109] The film member 2 can have the same properties as the porous film 1, for example, the Gurley air permeability and / or water pressure resistance in the thickness direction.

[0110] The film member 2 may be subjected to a liquid-repellent treatment and / or a coloring treatment.

[0111] 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.

[0112] 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.

[0113]

[0033] Figure 5 shows a second modified example (roll) of the film member of Figure 3. The roll 10 shown in Figure 5 includes the film member 2A and release liner 11 of Figure 3. 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.

[0114] As used herein, "adhesive" means "sticking" or "adhesion." For example, "adhesive layer" means "sticking layer" or "adhesive layer."

[0115] As used herein, "pressure-sensitive adhesive," as defined by JIS, refers to a type of adhesion that is temporary and can bond with only slight pressure. It also refers to a property that, while possessing cohesive strength and elasticity, provides strong adhesion, it can also be peeled off from hard, smooth surfaces. Pressure-sensitive adhesives are soft solids and do not undergo state changes like adhesives. Pressure-sensitive adhesives wet to the adherend in their original state and resist peeling, so when adherends are bonded together, they instantly exhibit practical adhesive strength. In other words, pressure-sensitive adhesives possess both the liquid properties (fluidity) that allow them to wet to the adherend and the solid properties (cohesive strength) that resist peeling. Because pressure-sensitive adhesives are soft solids, the contact area with the adherend gradually increases with the application of pressure or over time. Furthermore, because they can maintain this softness for a long period of time, they have the property of being easily removable.

[0116] In this specification, "adhesive" refers to the property of bonding and integrating solid surfaces of the same or different types, as defined by JIS. An adhesive is a fluid substance that wets and blends with the adherends when bonding them together. It then transforms into a solid through heating or chemical reaction, firmly binding the adherends at their interfaces and exerting resistance to peeling. In other words, an adhesive wets the fluid substance and adheres as a solid.

[0117] The film member 2A supplied by the roll 10 and not having the 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 by an adhesive layer newly disposed on the surface of the film member 2A, bonding by thermal welding, and bonding by ultrasonic welding.

[0118] 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 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 the joining method to the opening of the housing and / or the shape.

[0119] 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.

[0120] [Ventilation Member] An example of a ventilation member of the present invention is shown in FIG. 6. The ventilation member 4 (4A) in FIG. 6 has air permeability 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. 6 includes a porous film 1. Below, an example will be described in which the ventilation member 4 has air permeability in the thickness direction and includes a porous film 1 as a member that prevents the penetration of foreign matter in that direction.

[0121] 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 the object via the adhesive layer 5.

[0122] 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.

[0123] The outer periphery of the porous film 1 and the outer periphery of the adhesive layer 5 are coincident 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. A region of the porous film 1 to which the adhesive layer 5 is not bonded can be used as a ventilation region of the ventilation member 4A. However, the shape of the adhesive layer 5 is not limited to the above example.

[0124] 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.

[0125] Fig. 7 shows a first modification of the ventilation member of Fig. 6. The ventilation member 4 (4B) of Fig. 7 has the same configuration as the ventilation member 4A of Fig. 6, 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).

[0126] As shown in Figure 7, 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.

[0127] Fig. 8 shows a second variation of the ventilation member of Fig. 6. The ventilation member 4 (4C) of Fig. 8 has the same configuration as the ventilation member 4A of Fig. 6, except that it further includes a base material layer 6 arranged on one side of the porous film 1, and 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.

[0128] 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.

[0129] 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.

[0130] The porous film 1 and the base layer 6 may be bonded together with a pressure-sensitive adhesive or adhesive, or may be bonded together by welding such as thermal welding or ultrasonic welding. The porous film 1 and the base layer 6 may be bonded together with 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.

[0131] A third variation of the ventilation member of Fig. 6 is shown in Fig. 9. The ventilation member 4 (4D) of Fig. 9 has the same configuration as the ventilation member 4C of Fig. 8, 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.

[0132] As shown in Figure 9, 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.

[0133] Fig. 10 shows a fourth variation of the ventilation member of Fig. 6. The ventilation member 4 (4E) of Fig. 10 has the same configuration as the ventilation member 4B of Fig. 7 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).

[0134] As shown in FIG. 10 , 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.

[0135] 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.

[0136] Fig. 11 shows a fifth variation of the ventilation member of Fig. 6. The ventilation member 4 (4F) of Fig. 11 further includes a release liner 7, and has the same configuration as the ventilation member 4D of Fig. 9 except that the release liner 7 is bonded to the base material layer 6 (6B) via an adhesive layer 5 (5B).

[0137] [Component supply sheet] The ventilation member 4 can be supplied by, for example, a component supply sheet. An example of a component supply sheet, which is a supply mode of the ventilation member 4, is shown in FIG. 12. The component supply sheet 20 (20A) of FIG. 12 comprises a ventilation member 4 (4A) 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 having 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.

[0138] The ventilation member 4 (4A) is disposed on the base sheet 9 via the 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.

[0139] The ventilation member 4 may be disposed on the base sheet 9 via an adhesive layer provided on the surface of the base sheet 9 on which the ventilation member 4 is disposed. The adhesive layer on the surface on which the ventilation member 4 is disposed preferably has weak adhesive properties.

[0140] Although not shown in the drawings, a plurality of ventilation members 4 may be arranged on the surface of the base sheet 9 .

[0141] 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.

[0142] 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.

[0143] 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.

[0144] Fig. 13 shows a first modification of the member supply sheet of Fig. 12. The member supply sheet 20 (20B) of Fig. 13 has the same configuration as the member supply sheet 20A of Fig. 12, except that it is provided with the ventilation member 4E of Fig. 10 as the ventilation member 4.

[0145] Fig. 14 shows a second modification of the member supply sheet of Fig. 12. The member supply sheet 20 (20C) of Fig. 14 has the same configuration as the member supply sheet 20A of Fig. 12, except that it is provided with the ventilation member 4F of Fig. 11 as the ventilation member 4.

[0146] 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.

[0147] [Example 1] Poly(4-methylpentene-1) resin (manufactured by Mitsui Chemicals, Inc., RT18, weight average molecular weight: 499,000) was used as a fluorine-free 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 Tokyo Chemical Industry Co., Ltd.) was used as an antioxidant. 0.15 parts by weight of the antioxidant was dry-blended with 100 parts by weight of the thermoplastic resin in a tumbler to obtain a mixture. 50 parts by weight of the mixture and 50 parts by weight of the plasticizer were kneaded using a twin-screw extruder (manufactured by The Japan Steel Works, Ltd., TEX25αIII), and the kneaded mixture was then extruded onto a metal roll with a controlled surface temperature using a hanger coat die. The specific energy of the twin-screw extruder was set to 0.71 kWh / kg. The extruder cylinder temperature of the twin-screw extruder was set to 235°C, and extrusion was carried out. The extruded mixture was stretched using a metal roll while being cooled, to obtain a sheet-like molded product with a thickness of 129.7 μm. Next, a biaxial stretching machine was used. The molded body was then subjected to simultaneous biaxial stretching under conditions of a stretching temperature of 100°C and a stretching 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 removed the plasticizer from the sheet body. The extraction operation was performed while the sheet body was fixed to a stainless steel frame to prevent shrinkage. In this way, the porous film of Example 1 was obtained. The thickness of the porous film of Example 1 was 80.0 μm, and the weight-average molecular weight of the fluorine-free thermoplastic resin in the porous film was 298,000.

[0148] 15A is a diagram (1000x magnification) showing the results of SEM observation of the cross section of the porous film of Example 1. FIG. 15B is a diagram (1000x magnification) showing the results of SEM observation of the surface of the porous film of Example 1.

[0149] [Example 2] By controlling the throughput of the twin-screw extruder and the take-up speed of the metal roll during extrusion, a sheet-like molded product with a thickness of 105.7 μm was obtained. The molded product was subjected to simultaneous biaxial stretching under the conditions of a stretching ratio of 1.75 times (longitudinal direction) x 1.75 times (transverse direction). Except for these, a porous film of Example 2 was obtained by the same method as in Example 1. The thickness of the porous film of Example 2 was 66.5 μm, and the weight average molecular weight of the fluorine-free thermoplastic resin in the porous film was 298,000.

[0150] 16A and 16B are SEM images (1000x magnification) showing the cross section of the porous film of Example 2. Fig. 16B is a SEM image (1000x magnification) showing the surface of the porous film of Example 2.

[0151] [Example 3] By controlling the throughput of the twin-screw extruder and the take-up speed of the metal roll during extrusion, a sheet-like molded product with a thickness of 108.0 μm was obtained. The molded product was subjected to simultaneous biaxial stretching under the conditions of a stretching ratio of 2.25 times (longitudinal direction) x 2.25 times (transverse direction). Except for these, a porous film of Example 3 was obtained by the same method as in Example 1. The thickness of the porous film of Example 3 was 58.1 μm, and the weight average molecular weight of the fluorine-free thermoplastic resin in the porous film was 298,000.

[0152] 17A and 17B are SEM images (1000x magnification) showing the cross section of the porous film of Example 3. Fig. 17B is a SEM image (1000x magnification) showing the surface of the porous film of Example 3.

[0153] [Comparative Example 1] The specific energy of the twin-screw extruder during extrusion was set to 0.41 kWh / kg. As a result, a sheet-like molded product having a thickness of 125.7 μm was obtained. Except for this, a porous film of Comparative Example 1 was obtained in the same manner as in Example 1. The thickness of the porous film of Comparative Example 1 was 53.0 μm, and the weight average molecular weight of the fluorine-free thermoplastic resin in the porous film was 332,000.

[0154] Fig. 18A is a diagram (1000x magnification) showing the results of SEM observation of the cross section of the porous film of Comparative Example 1. Fig. 18B is a diagram (1000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 1.

[0155] [Comparative Example 2] The specific energy of the twin-screw extruder during extrusion was set to 0.22 kWh / kg. As a result, a sheet-like molded product having a thickness of 126.7 μm was obtained. Except for this, a porous film of Comparative Example 2 was obtained in the same manner as in Example 1. The thickness of the porous film of Comparative Example 2 was 42.0 μm, and the weight average molecular weight of the fluorine-free thermoplastic resin in the porous film was 340,000.

[0156] 19A is a diagram (1000x magnification) showing the results of SEM observation of the cross section of the porous film of Comparative Example 2. Fig. 19B is a diagram (1000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 2.

[0157] Table 1 shows the manufacturing conditions of the porous films of Examples 1 to 3 and Comparative Examples 1 and 2.

[0158]

[0159] By the method described above for porous film, for the porous film of Examples 1 to 3 and Comparative Examples 1 to 2, evaluate the porosity Pa of the whole porous film in thickness direction, the porosity Pb ​​of the central part, the porosity ratio R, Gurley air permeability, water pressure resistance, and the weight average molecular weight of the thermoplastic resin in porous film.Evaluation results are shown in Table 2.

[0160]

[0161] Furthermore, for the porous films of Examples 1 to 3 and Comparative Examples 1 and 2, the porosity Ps on the surface, the circle equivalent diameter of the pores of the nodes, the circle equivalent diameter of the pores, etc. were determined by the method described above for the porous film. The evaluation results are shown in Table 3.

[0162]

[0163] As can be seen from Table 2, the porous films of Examples 1 to 3 had a porosity ratio R in the thickness direction of 90% or more, and pore blockage in the thickness direction was suppressed. As can be seen from Table 3, the porous films of Examples 1 to 3 had a pore equivalent circle diameter of 1.5 μm or more on the surface and a Feret diameter of pores on the surface of 2.1 μm or more. The porous films of Examples 1 to 3 had a Gurley air permeability of 20 seconds / 100 mL or less, and had extremely excellent air permeability.

[0164] 15A, 16A, and 17A compared with Fig. 18A and Fig. 19A, the porous films of Examples 1 to 3 were more suppressed in shrinkage in the thickness direction, particularly in the central portion, than the porous films of Comparative Examples 1 and 2. From these results, it is presumed that in the porous films of Examples 1 to 3, the specific energy of the twin-screw extruder was controlled to 0.5 kWh / kg or more during extrusion, thereby suppressing shrinkage in the thickness direction, particularly in the central portion, during the stretching process, thereby suppressing the blockage of pores in the thickness direction.

[0165] From the above results, it can be seen that the porous films of Examples 1 to 3 are suitable for improving breathability.

[0166] 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 containing a fluorine-free thermoplastic resin as a main component, wherein, in an image of a cross section of the porous film parallel to the thickness direction observed with a scanning electron microscope, when the range from 1 / 3 to 2 / 3 of the way from one end of the porous film along the thickness direction is defined as the central part of the porous film, the ratio of the porosity of the central part to the porosity of the entire porous film is 90% or more.

2. The porous film according to claim 1, wherein the weight average molecular weight of the thermoplastic resin in the porous film is 330,000 or less.

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

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

5. The porous film according to claim 1, wherein the pores have an equivalent circle diameter of 1.5 μm or more.

6. The porous film according to claim 1, wherein the Feret diameter of the pores is 2.1 μm or more.

7. A porous film containing a fluorine-free thermoplastic resin as its main component and having a Gurley air permeability of 20 seconds / 100 mL or less.

8. The porous film according to claim 7, having a water pressure resistance of 0.08 MPa or more.

9. A method for producing a porous film, comprising: kneading a mixture containing a fluorine-free thermoplastic resin and a plasticizer using a twin-screw extruder, and then extruding the kneaded mixture; obtaining a molded body while cooling the extruded kneaded mixture; stretching the molded body to obtain a sheet; and removing the plasticizer from the sheet, wherein the specific energy of the twin-screw extruder is 0.5 kWh / kg or more.

10. A ventilation member comprising the porous film according to any one of claims 1 to 8 and an adhesive layer bonded to the porous film.

11. 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 the porous film described in any one of claims 1 to 8.

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