Porous film, ventilation member, and member supply sheet

Abstract

This porous film contains a fluorine-free thermoplastic resin as a main component, and has a breaking strain of 15% or less as determined by a tensile test in an environment at a temperature of 25°C. This ventilation member comprises a porous film and an adhesive layer that is bonded to the porous film. This member supply sheet comprises: a ventilation member which is disposed on a surface of an object, the surface having an opening; and a base material sheet that has a surface on which the ventilation member is disposed. The ventilation member comprises: a porous film which has a shape that covers the opening when disposed on the surface; and an adhesive layer which is 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] Porous films are used in a variety of applications, such as filters, sound-permeable membranes, air-permeable membranes, and diaphragms.

[0003] Conventionally, a porous membrane containing a fluororesin has been proposed as a porous film (see, for example, Patent Document 1). An example of the porous membrane containing a fluororesin is a polytetrafluoroethylene (PTFE) porous membrane.

[0004] Japanese Patent Application Laid-Open No. 2003-503991

[0005] Porous films are sometimes provided in the form of a rolled body. If the porous film has a stretchable property, such as a PTFE porous membrane, the porous film may be stretched when unwound from the roll, and its properties may change. Therefore, for porous films that have a stretchable property, it is necessary to design them taking into account the change in properties during the manufacturing process.

[0006] Therefore, an object of the present invention is to provide a porous film, a ventilation member, and a member supply sheet that are suitable for suppressing changes in properties.

[0007] The present invention provides a porous film containing a fluorine-free thermoplastic resin as a main component, the porous film having a breaking strain of 15% or less in a tensile test at a temperature of 25°C.

[0008] 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.

[0009] From 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.

[0010] 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 suppressing changes in properties.

[0011] FIG. 1 is a cross-sectional view schematically showing an example of a porous film of the present invention. FIG. 2 is a schematic view showing a method of a T-peel test for measuring the cohesive strength of the porous film of FIG. 1. FIG. 3 is a view explaining how to determine the distance between nodes of the porous film of FIG. 1. FIG. 4 is a cross-sectional view schematically showing an example of a film member of the present invention. FIG. 5 is a cross-sectional view schematically showing a first modified example of the film member of FIG. 4. FIG. 6 is a cross-sectional view schematically showing a second modified example (rolled body) of the film member of FIG. 4. FIG. 7 is a cross-sectional view schematically showing an example of a ventilation member of the present invention. FIG. 8 is a cross-sectional view schematically showing a first modified example of the ventilation member of FIG. 7. FIG. 9 is a cross-sectional view schematically showing a second modified example of the ventilation member of FIG. 7. FIG. 10 is a cross-sectional view schematically showing a third modified example of the ventilation member of FIG. 7. FIG. 11 is a cross-sectional view schematically showing a fourth modified example of the ventilation member of FIG. 7. FIG. 12 is a cross-sectional view schematically showing a fifth modified example of the ventilation member of FIG. 7. FIG. 13 is a cross-sectional view schematically showing an example of the member supply sheet of the present invention. FIG. 14 is a cross-sectional view schematically showing a first modified example of the member supply sheet of FIG. 13. FIG. 15 is a cross-sectional view schematically showing a second modified example of the member supply sheet of FIG. 13. FIG. 16A is a diagram (1000x) showing the results of scanning electron microscope (SEM) observation of the surface of the porous film of Example 1. FIG. 16B is a partial enlarged view (2000x) of FIG. 16A. FIG. 16C is a diagram (1000x) showing the results of SEM observation of the cross section of the porous film of Example 1. FIG. 17A is a diagram (2000x) showing the results of SEM observation of the surface of the porous film of Comparative Example 1. FIG. 17B is a diagram (1000x) showing the results of SEM observation of the cross section of the porous film of Comparative Example 1. Fig. 18 is a graph showing the change (R1-R2) in the value obtained by dividing the air permeability by the water pressure resistance of the porous films of Examples 1 to 5 and Comparative Examples 1 to 7 before and after the heat resistance test. Fig. 19 is the SS curves of the porous films of Examples 1 to 5 and Comparative Examples 1 to 4.

[0012] The porous film according to the first aspect of the present invention contains a fluorine-free thermoplastic resin as a main component, and has a breaking strain of 15% or less in a tensile test at a temperature of 25°C.

[0013] In the second aspect of the present invention, for example, the porous film according to the first aspect does not exhibit a yield point in the stress-strain curve obtained by the tensile test.

[0014] 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.

[0015] In a fourth aspect of the present invention, for example, the porous film according to any one of the first to third aspects has a cohesive strength of 0.1 N / 10 mm or more.

[0016] In a fifth aspect of the present invention, for example, the porous film according to any one of the first to fourth aspects has a water pressure resistance of more than 140 kPa and an air permeability expressed as a Gurley number of 50 seconds / 100 mL or less.

[0017] In a sixth aspect of the present invention, for example, the porous film according to any one of the first to fifth aspects has a plurality of nodes and a plurality of fibrils, and the equivalent circle diameter of the nodes is 3.5 μm or more.

[0018] In a seventh aspect of the present invention, for example, in the porous film according to the sixth aspect, the distance between the nodes is 1.5 μm or more.

[0019] In an eighth aspect of the present invention, for example, in the porous film according to any one of the first to seventh aspects, the pores have an equivalent circle diameter of 0.8 μm or more.

[0020] In a ninth aspect of the present invention, for example, the porous film according to any one of the fifth to eighth aspects satisfies R1-R2≧-0.015, where R1 is defined as a ratio of the air permeability divided by the water pressure resistance, and R2 is defined as a ratio of the air permeability of the porous film after a heat resistance test in which the film is heated at 200°C for 5 minutes divided by the water pressure resistance.

[0021] In a tenth aspect of the present invention, for example, the porous film according to any one of the first to ninth aspects has a porosity of 30% or more when the surface of the porous film is observed with a scanning electron microscope.

[0022] In an eleventh aspect of the present invention, for example, the porous film according to any one of the first to tenth aspects is a stretched film.

[0023] 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.

[0024] A ventilation member according to a thirteenth aspect of the present invention is 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, for example, a porous film according to any one of the first to eleventh 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. 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 smartphone housing by heat fusion without using an adhesive layer, for example.

[0027] The porous film 1 has a breaking strain of 15% or less in a tensile test in an environment at a temperature of 25° C. The porous film 1 satisfying the above numerical range is unlikely to stretch when unwound from a roll, for example, and its properties are unlikely to change.

[0028] The upper limit of the breaking strain of the porous film 1 may be 14% or less. The lower limit of the breaking strain of the porous film 1 is, for example, 4% or more. The lower limit of the breaking strain of the porous film 1 may be 5% or more. The breaking strain of the porous film 1 may be 4% or more and 14% or less.

[0029] The porous film 1 has a maximum stress of 12 N / mm in a tensile test at a temperature of 25°C. 2 It may be the following:

[0030] The upper limit of the maximum stress of the porous film 1 is 11 N / mm 2 It may be 10 N / mm or less 2 The lower limit of the maximum stress of the porous film 1 may be, for example, 3 N / mm 2 The lower limit of the maximum stress of the porous film 1 is 4 N / mm 2 The maximum stress of the porous film 1 may be 3 N / mm 2 11N / mm or more 2 It may be 3 N / mm or less 2 10N / mm or more 2 It may be the following:

[0031] The breaking strain and maximum stress of the porous film 1 can be determined by a tensile test in an environment at a temperature of 25°C as described below in accordance with JIS K7127:1999. First, the porous film 1 is punched out with a tensile dumbbell-shaped test piece punching blade to obtain a test piece. A tensile test of the tensile dumbbell-shaped test piece is performed using a tensile tester (for example, a desktop precision universal testing machine, Autograph AGS-X, manufactured by Shimadzu Corporation) under conditions of a chuck distance of 25 mm and a tensile speed of 50 mm / min, and a stress-strain curve (SS curve) is obtained. From the SS curve, the tensile stress (maximum stress) and strain (breaking strain) at the time of breaking of the test piece can be measured.

[0032] The porous film 1 may not have a yield point in the S-S curve obtained by the tensile test. The porous film 1 having such a configuration is unlikely to stretch when unwound from a roll, and its properties are unlikely to change.

[0033] For example, Fig. 19 shows the SS curves of the porous films of Examples 1 to 5 and Comparative Examples 1 to 4 described below. As shown in Fig. 19, the porous films of Examples 1 to 5 do not show a yield point in the SS curves, and the plastic region and the elastic region cannot be distinguished.

[0034] As shown in FIG. 18, the porous film 1 may exhibit a monotonically increasing stress-strain behavior in the SS curve obtained in the tensile test.

[0035] The cohesive strength of the porous film 1 is preferably 0.1 N / 10 mm or more. The porous film 1 having such a configuration is prevented from undergoing cohesive failure when attached to, for example, the housing of a smartphone.

[0036] The upper limit of the cohesive strength of the porous film 1 is, for example, 2.0 N / 10 mm or less. The upper limit of the cohesive strength of the porous film 1 may be 1.0 N / 10 mm or less.

[0037] The cohesive strength of the porous film 1 can be measured in accordance with JIS Z0237:2009 by the method described below.

[0038] FIG. 2 is a schematic diagram showing a method of a T-peel test for measuring the cohesive strength of a porous film 1. First, the porous film 1 is cut to a size of 100 mm long x 10 mm wide. Next, two pieces of double-sided adhesive tape 51 (manufactured by Nitto Denko Corporation, No. 5610) having the same shape as the cut porous film 1 are prepared. Each double-sided adhesive tape 51 is bonded to one side and the other side of the porous film 1, respectively, with the outer peripheries aligned. Next, two pieces of PET film 52 (25 μm thick) having a length of 150 mm x width of 10 mm are prepared. Each PET film 52 is bonded to one side and the other side of the porous film 1, respectively, with the double-sided adhesive tape 51. The PET films 52 are bonded together so that both widthwise ends of each PET film 52 coincide with both widthwise ends of the porous film 1, and so that both longitudinal ends of each PET film 52 do not overlap the porous film 1 or the double-sided adhesive tape 51 when viewed perpendicular to the main surface of the PET film 52. However, the length (longitudinal direction) of the free end of each PET film 52 must be long enough (e.g., 25 mm) to allow the chuck of the tensile tester to stably grip the PET film 52. Next, a roller is moved back and forth once while applying a load of 2 kg so that a pressure is applied in the thickness direction of the laminate 50 of PET film 52 / double-sided adhesive tape 51 / porous film 1 / double-sided adhesive tape 51 / PET film 52. The laminate is then aged at room temperature for 24 hours. The aged laminate is used as the test piece 50.

[0039] Next, a tensile tester (for example, a desktop precision universal testing machine, Autograph AGS-X, manufactured by Shimadzu Corporation) is prepared. The free end of one PET film 52 at one end in the longitudinal direction of the test piece 50 is fixed to the upper chuck 61 of the tensile tester. The free end of the other PET film 52 at the other end in the longitudinal direction of the test piece 50 is attached to the lower chuck 62. Next, a tensile test is performed in which the upper end of one PET film 52 is pulled upward under conditions of a measurement temperature of 25 ° C. and a tensile speed of 300 mm / min, causing cohesive failure in the porous film 1. After the start of the measurement, the stress between the chucks measured during the initial 25 mm displacement is ignored, and the average value of the measured stress values ​​(N) recorded continuously during the subsequent 50 mm displacement is taken as the cohesive strength (N / 10 mm) of the porous film 1.

[0040] The water pressure resistance of the porous film 1 is preferably greater than 140 kPa as evaluated by 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.

[0041] The lower limit of the water pressure resistance of the porous film 1 may be 150 kPa or more, or 160 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 150 kPa or more and 2000 kPa or less, or 160 kPa or more and 2000 kPa or less.

[0042] 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.

[0043] 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.

[0044] The air permeability in the thickness direction of the porous film 1, expressed as a Gurley number, is 50 seconds / 100 mL or less. Thus, the porous film 1 has high breathability. 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.

[0045] The upper limit of the air permeability of the porous film 1, expressed in Gurley number, may be 40 seconds / 100 mL or less, 35 seconds / 100 mL or less, 30 seconds / 100 mL or less, or even 25 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 40 seconds / 100 mL or less, 0.1 seconds / 100 mL or more and 35 seconds / 100 mL or less, 0.1 seconds / 100 mL or more and 30 seconds / 100 mL or less, or even 0.1 seconds / 100 mL or more and 25 seconds / 100 mL or less.

[0046] 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.

[0047] 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.

[0048] The ratio R1 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 R1 tends to decrease as the air permeability and water resistance of the porous film 1 increase. Therefore, the ratio R1 can be used as an index for evaluating the air permeability and water resistance of the porous film 1 together. The ratio R1 is preferably 0.2 or less, and more preferably 0.15 or less. A porous film 1 that satisfies the above numerical range can have excellent air permeability and water resistance. The lower limit of the ratio R1 is, for example, 0.01 or more.

[0049] The ratio R2 is defined as the value obtained by dividing the air permeability (seconds / 100 mL) of porous film 1 by the water pressure resistance (kPa) after a heat resistance test in which the film is heated at 200°C for 5 minutes. The higher the heat resistance of porous film 1, the smaller the difference between ratios R1 and R2. Therefore, the change (R1-R2) in the value obtained by dividing the air permeability (seconds / 100 mL) by the water pressure resistance (kPa) before and after the heat resistance test can be an index for evaluating the heat resistance of porous film 1. It is preferable that porous film 1 satisfies the following formula: R1-R2≧-0.015

[0050] The porous film 1 satisfying the above numerical range has high heat resistance.

[0051] The porous film 1 may satisfy R1-R2≧-0.014, R1-R2≧-0.012, or R1-R2≧-0.010.

[0052] 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 that is suitable for achieving both water resistance and breathability.

[0053] The polyolefin resin includes polyethylene (PE) resin, polypropylene (PP) resin, and polymethylmenthene (PMP) resin.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] The porous film 1 is in the form of a film or a sheet. The thickness of the porous film 1 may be 20 μm or more and 100 μm or less. When the thickness is in the above numerical range, it is easy to achieve a water pressure resistance and an air permeability that satisfy the above numerical range.

[0059] 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.

[0060] The upper limit of the thickness of the porous film 1 may be 90 μm or less, or may be 80 μm or less.

[0061] The porous film 1 may have multiple nodes and multiple fibrils. The porous film 1 may have a hexagonal structure formed by multiple nodes and multiple fibrils. The hexagonal structure may exist throughout the entire porous film 1. A porous film 1 having such a structure is suitable for suppressing changes in properties. The hexagonal structure can be confirmed, for example, by observing the main surface of the porous film 1 from the vertical direction 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.

[0062] 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.

[0063] 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 at random positions. The number of nodes forming relatively large island regions is greater than the number of nodes forming relatively small island regions.

[0064] For example, Fig. 16A is a diagram (1000x magnification) showing the results of SEM observation of the surface of the porous film of Example 1 described below. Fig. 16B is a partial enlargement (2000x magnification) of Fig. 16A. As shown in Fig. 16A and Fig. 16B, the surface of the porous film of Example 1 has a tortoiseshell structure formed by multiple nodes and multiple fibrils, and island-like regions of different sizes formed by the multiple nodes are present in random positions.

[0065] 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.

[0066] It is preferable that there are many connection points between nodes or clusters of nodes in the thickness direction of the porous film 1. When there are many connection points between nodes or clusters of nodes, gaps (pores) formed between them tend to be concentrated. When the porous film has such a cross-sectional structure, the pore diameter tends to be large, and therefore, an air permeability that satisfies the above-mentioned numerical range is easily achieved.

[0067] For example, Figure 16C is a diagram (1000x magnification) showing the results of SEM observation of the cross section of the porous film of Example 1 described later. As shown in Figure 16C, when observing the cross section of the porous film of Example 1, it is found that there are many connections between the clustered nodes, resulting in the presence of a cluster of gaps (voids).

[0068] 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 3.5 μm or more. When the equivalent circle diameter of the nodes is within the above numerical range, it is easy to achieve a water pressure resistance and an air permeability that satisfy the above numerical range. In this disclosure, with regard to the "equivalent circle diameter of a node," "maximum diameter of a node," and "distance between nodes," the terms "node" and "island region formed by multiple nodes" are used interchangeably.

[0069] The lower limit of the equivalent circle diameter of the node of the porous film 1 may be 4.0 μm or more. The upper limit of the equivalent circle diameter of the node of the porous film 1 is, for example, 12.0 μm or less. The upper limit of the equivalent circle diameter of the node of the porous film 1 may be 11.0 μm or less, 10.0 μm or less, 9.0 μm or less, or even 8.0 μm or less. The equivalent circle diameter of the node of the porous film 1 may be 4.0 μm or more and 12.0 μm or less.

[0070] When the surface of the porous film 1 is observed with an SEM, the maximum diameter of the nodes of the porous film 1 is preferably greater than 4.5 μm. When the maximum diameter of the nodes is within the above numerical range, a water pressure resistance and an air permeability that satisfy the above numerical ranges are likely to be achieved.

[0071] The lower limit of the maximum diameter of the nodes of the porous film 1 may be 4.6 μm or more, 5.0 μm or more, 5.5 μm or more, or even 6.0 μm or more. The upper limit of the maximum diameter of the nodes of the porous film 1 is, for example, 15.0 μm or less. The upper limit of the maximum diameter of the nodes of the porous film 1 may be 14.0 μm or less, 13.0 μm or less, or even 12.0 μm or less. The maximum diameter of the nodes of the porous film 1 may be 4.6 μm or more and 15.0 μm or less, 5.0 μm or more and 15.0 μm or less, 5.5 μm or more and 15.0 μm or less, or even 6.0 μm or more and 15.0 μm or less.

[0072] The maximum diameter and the circle-equivalent 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 with an SEM (see, for example, FIG. 16A). Next, the obtained SEM observation image (or a portion thereof) is binarized using image analysis software. 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. Next, the nodes classified by circle-equivalent diameter are histogrammed based on the number to obtain a circle-equivalent diameter distribution (number basis). The number used as the calculation basis for the circle-equivalent diameter distribution is determined by counting the number of nodes present in the image. In the obtained circle-equivalent diameter distribution, the particle diameter corresponding to 100% cumulative volume from the small particle diameter side is considered as the maximum particle diameter of the nodes of the porous film 1. The circle equivalent diameter and maximum diameter are determined by measuring 30 or more nodes, for example, 50 to 200 nodes. When identifying nodes, nodes on the edge of the image are omitted from the analysis. ImageJ, for example, can be used as image analysis software.

[0073] When the surface of the porous film 1 is observed with an SEM, the distance between nodes of the porous film 1 is preferably 1.5 μm or more. When the distance between nodes is within 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 lower limit of the distance between nodes of the porous film 1 may be 1.6 μm or more, or 1.7 μm or more. The upper limit of the distance between nodes of the porous film 1 is, for example, 8.0 μm or less. The upper limit of the distance between nodes of the porous film 1 may be 7.0 μm or less, 6.0 μm or less, or 5.0 μm or less. The distance between nodes of the porous film 1 may be 1.6 μm or more and 8.0 μm or less, or 1.7 μm or more and 8.0 μm or less.

[0075] The distance between nodes of the porous film 1 can be determined by the method described below. Fig. 3 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 and the maximum diameter of the node of the porous film 1, and the nodes are identified from the binarized image (see Fig. 3). As shown in Fig. 3, the distance between nodes L between node A and node B is AB 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.

[0076] As described above, the porous film 1 has a plurality of gaps (pores). When the surface of the porous film 1 is observed with an SEM, it is preferable that the circle-equivalent diameter of the pores in the porous film 1 is 0.8 μm or more. When the circle-equivalent diameter of the pores satisfies the above-mentioned numerical range, a water pressure resistance and an air permeability that satisfy the above-mentioned numerical range are easily achieved.

[0077] The lower limit of the circle-equivalent diameter of the pores of the porous film 1 may be 1.0 μm or more, or 1.5 μm or more. The upper limit of the circle-equivalent diameter of the pores of the porous film 1 is, for example, 5.0 μm or less. The upper limit of the circle-equivalent diameter of the pores of the porous film 1 may be 4.0 μm or less, or 3.0 μm or less. The circle-equivalent diameter of the pores of the porous film 1 may be 1.0 μm or more and 5.0 μm or less, or 1.5 μm or more and 5.0 μm or less.

[0078] When the surface of the porous film 1 is observed with an SEM, the maximum diameter of the pores of the porous film 1 is preferably 1.4 μm or more. When the maximum diameter of the pores satisfies the above numerical range, a water pressure resistance and an air permeability that satisfy the above numerical range are likely to be achieved.

[0079] The lower limit of the maximum diameter of the pores of the porous film 1 may be 1.5 μm or more, or may be 2.0 μm or more. The upper limit of the maximum diameter of the pores of the porous film 1 is, for example, 7.0 μm or less. The upper limit of the maximum diameter of the pores of the porous film 1 may be 6.0 μm or less, or may be 5.0 μm or less. The maximum diameter of the pores of the porous film 1 may be 1.5 μm or more and 7.0 μm or less, or may be 2.0 μm or more and 7.0 μm or less.

[0080] The circle-equivalent diameter and maximum 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 maximum 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.

[0081] When the surface of the porous film 1 is observed with an SEM, the porosity of the porous film 1 is preferably 30% or more. When the porosity satisfies the above numerical range, a water pressure resistance and an air permeability that satisfy the above numerical range are likely to be achieved.

[0082] The lower limit of the porosity of the porous film 1 may be 32% or more, 35% or more, or 40% or more. The upper limit of the porosity of the porous film 1 is, for example, 95% or less. The upper limit of the porosity of the porous film 1 may be 90% or less. The porosity of the porous film 1 may be 32% or more and 95% or less, 35% or more and 95% or less, or 40% or more and 95% or less.

[0083] The porosity of the porous film 1 can be determined by the same method as the method for determining the maximum diameter and the equivalent circle 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 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 is determined by measuring 30 or more pores, for example, 50 to 200 pores.

[0084] 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.

[0085] A surface modification treatment may be applied to at least one of the main surfaces of the porous film 1. Examples of the surface modification treatment include oil-repellent treatment, chemical treatment, sputter etching treatment, and plasma treatment. In the area where the surface modification treatment is applied, the bonding property of the porous film 1 is improved.

[0086] 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).

[0087] [Method for Producing Porous Film] The porous film 1 described above can be produced, for example, by the following method.

[0088] 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), annealing the molded body (step S4), stretching the annealed molded body to obtain a sheet body (step S5), and extracting the plasticizer from the sheet body (step S6).

[0089] 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), annealing the molded body (step S4), stretching the annealed molded body to obtain a sheet body (step S5), and extracting the plasticizer from the sheet body (step S6).

[0090] Steps S1 to S4 correspond to a process for producing a precursor of the porous film 1. Steps S5 to S6 correspond to a process for growing a porous structure. Note that, instead of step S3, the production method may include a step of pressing the kneaded material to form a molded body, and cooling the pressed material on a metal plate to obtain a molded body, or a step of cooling the kneaded material with a metal roll to obtain a molded body (step S3').

[0091] Step S1 is carried out, for example, at a temperature of 230° C. to 260° C. for 5 to 30 minutes.

[0092] As the fluorine-free thermoplastic resin, for example, polymethylpentene resin can be used.

[0093] 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.

[0094] 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.

[0095] The mixing ratio of the thermoplastic resin and the plasticizer is set so that a uniform kneaded product can be obtained in step S1 and a molded body can be formed in step S3 (or step S2-3). Specifically, the weight ratio of the thermoplastic resin in the composition 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. When the weight ratio of the thermoplastic resin is 20% by weight or more, excessive reduction in the viscosity of the composition is avoided. When the weight ratio of the thermoplastic resin is 80% by weight or less, a good porous structure is easily obtained.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Step S4 is performed, for example, at a temperature of 180°C to 200°C for 30 to 60 minutes. In step S4, annealing is performed at a temperature near the crystallization peak temperature of the fluorine-free thermoplastic resin (e.g., polymethylpentene resin), which facilitates aggregation of highly crystalline portions that can become nodes and less crystalline portions that can become fibrils. As a result, during the subsequent stretching in step S5, large island regions are likely to be formed, and the distance between the island regions is likely to increase.

[0102] In step S5, the annealed molded body is stretched at least once in at least one direction. Stretching in at least one direction includes uniaxial stretching in the machine 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 S5 generates pores in the molded body, and forms a structure in which island-like regions of different sizes formed by multiple nodes are present in random positions.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] In step S6, the plasticizer is extracted and removed from the sheet using, for example, an extraction solvent. After step S6, 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.

[0107] 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.

[0108] Between step S5 and step S6, 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.

[0109] Heat setting may be performed after step S5, between steps S5 and S6, or both after steps S5 and S6. 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.

[0110] [Film member] An example of the film member of the present invention is shown in Figure 4. The film member 2 (2A) in Figure 4 includes a porous film 1. A first modified example of the film member in Figure 4 is shown in Figure 5. The film member 2 (2B) in Figure 5 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.

[0111] 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.

[0112] The film member 2B in Fig. 5 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.

[0113] The film member 2 may include any layers and / or members other than those described above.

[0114] The thickness of the film member 2 is, for example, 1 to 300 μm, and may be 50 to 200 μm.

[0115] 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.

[0116] 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.

[0117] The film member 2 may be subjected to a liquid-repellent treatment and / or a coloring treatment.

[0118] 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.

[0119] 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.

[0120] A second modification (roll) of the film member of Fig. 4 is shown in Fig. 6. The roll 10 shown in Fig. 6 includes the film member 2A and release liner 11 of Fig. 4. 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] [Ventilation Member] An example of a ventilation member of the present invention is shown in FIG. 7. The ventilation member 4 (4A) in FIG. 7 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. 7 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] The area of ​​the ventilation area is, for example, 40 mm 2The 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.

[0129] Fig. 8 shows a first modification of the ventilation member of Fig. 7. The ventilation member 4 (4B) of Fig. 8 has the same configuration as the ventilation member 4A of Fig. 7, 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).

[0130] As shown in Figure 8, 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.

[0131] A second variation of the ventilation member of Fig. 7 is shown in Fig. 9. The ventilation member 4 (4C) of Fig. 9 has the same configuration as the ventilation member 4A of Fig. 7, 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] A third variation of the ventilation member of Fig. 7 is shown in Fig. 10. The ventilation member 4 (4D) of Fig. 10 has the same configuration as the ventilation member 4C of Fig. 9, 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 a pair of base material layers 6 (6A, 6B). This sandwiching structure can further improve the strength and handleability of the ventilation member 4.

[0136] As shown in Figure 10, 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.

[0137] Fig. 11 shows a fourth variation of the ventilation member of Fig. 7. The ventilation member 4 (4E) of Fig. 11 further includes a release liner 7, and has the same configuration as the ventilation member 4B of Fig. 8, except that the porous film 1 and the release liner 7 are bonded via an adhesive layer 5 (5B).

[0138] As shown in Figure 11, 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.

[0139] 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.

[0140] Fig. 12 shows a fifth variation of the ventilation member of Fig. 7. The ventilation member 4 (4F) of Fig. 12 further includes a release liner 7, and has the same configuration as the ventilation member 4D of Fig. 10, except that the release liner 7 is bonded to the base material layer 6 (6B) via an adhesive layer 5 (5B).

[0141] [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. 13. The component supply sheet 20 (20A) of FIG. 13 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.

[0142] 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.

[0143] 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.

[0144] Although not shown in the drawings, a plurality of ventilation members 4 may be arranged on the surface of the base sheet 9 .

[0145] 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.

[0146] 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.

[0147] 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.

[0148] Fig. 14 shows a first modification of the member supply sheet of Fig. 13. The member supply sheet 20 (20B) of Fig. 14 has the same configuration as the member supply sheet 20A of Fig. 13, except that it is provided with the ventilation member 4E of Fig. 11 as the ventilation member 4.

[0149] Fig. 15 shows a second modification of the member supply sheet of Fig. 13. The member supply sheet 20 (20C) of Fig. 15 has the same configuration as the member supply sheet 20A of Fig. 13, except that it is provided with the ventilation member 4F of Fig. 12 as the ventilation member 4.

[0150] 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.

[0151] [Example 1] Poly(4-methylpentene-1) resin (RT18, manufactured by Mitsui Chemicals, Inc.) was used as the thermoplastic resin. 2 Liquid paraffin (manufactured by MORESCO) with a 1000-milliliter capacity (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 50.0 wt% thermoplastic resin, 49.8 wt% plasticizer, and 0.2 wt% 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. A 1.6 g pellet of the kneaded product was sandwiched between two polyimide plates (150 μm thick) and then sandwiched between two stainless steel plates (3.0 mm thick). The pellets were 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 on a metal plate at 120°C to obtain a molded body. The molded product was annealed at 200°C for 60 minutes. Next, using a biaxial stretching machine, the annealed molded product was simultaneously biaxially stretched at 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. Stretching was performed 5 minutes after the molded product was placed in a furnace set at the stretching temperature. Finally, an extraction operation was performed by immersing the sheet in methyl ethyl ketone (MEK) at room temperature for 2 minutes using MEK as the extraction solvent. This allowed the plasticizer to be extracted and removed from the sheet. The extraction operation was performed while the sheet was fixed to a stainless steel frame to prevent shrinkage. In this way, the porous film of Example 1 was obtained.

[0152] Figure 16A is a diagram (1000x magnification) showing the results of SEM observation of the surface of the porous film of Example 1. Figure 16B is a partially enlarged diagram (2000x magnification) of Figure 16A. Figure 16C is a diagram (1000x magnification) showing the results of SEM observation of the cross section of the porous film of Example 1.

[0153] [Example 2] The pressed body was cooled on a metal plate at 120°C, and the resulting molded body was annealed at 200°C for 30 minutes. Except for this, a porous film of Example 2 was obtained in the same manner as in Example 1.

[0154] [Example 3] After obtaining the kneaded product, 1.6 g of the kneaded product pellet was sandwiched between two polyimide plates (thickness 150 μm), and then sandwiched between two stainless steel plates (thickness 3.0 mm). Then, using a compression molding machine heated to 260 ° C, the pellet was hot pressed under the conditions of 1.0 kN and 5 minutes to obtain a pressed body. While sandwiched between polyimide plates, the pressed body was cooled by contacting it with water at 18 ° C to obtain a molded body. The molded body was subjected to annealing treatment at a temperature of 200 ° C for 60 minutes. Except for these, the porous film of Example 3 was obtained by the same method as in Example 1.

[0155] [Example 4] Poly(4-methylpentene-1) resin (DX845, manufactured by Mitsui Chemicals, Inc.) was used as the thermoplastic resin. After cooling, the molded body was subjected to an annealing treatment at a temperature of 180°C for 30 minutes. Except for these, the porous film of Example 4 was obtained by the same method as in Example 3.

[0156] [Example 5] As the thermoplastic resin, a mixture of poly(4-methylpentene-1) resin (DX845 manufactured by Mitsui Chemicals, Inc.) and poly(4-methylpentene-1) resin (DX820 manufactured by Mitsui Chemicals, Inc.) in a mass ratio of 50:50 was used. Except for this, the porous film of Example 5 was obtained by the same method as in Example 4.

[0157] [Comparative Example 1] A porous film of Comparative Example 1 was obtained by the same method as in Example 1, except that the pressed body was cooled on a metal plate at 120°C and the molded body was not subjected to annealing treatment but was subjected to coaxial biaxial stretching.

[0158] 17A is a diagram (2000x magnification) showing the results of SEM observation of the surface of the porous film of Comparative Example 1. FIG. 17B is a diagram (1000x magnification) showing the results of SEM observation of the cross section of the porous film of Comparative Example 1.

[0159] [Comparative Example 2] A porous film of Comparative Example 2 was obtained in the same manner as in Example 4, except that the cooled molded body was not subjected to an annealing treatment but was subjected to coaxial biaxial stretching.

[0160] [Comparative Example 3] The pressed body was cooled on a metal plate at 120°C to obtain a molded body, which was then annealed at 100°C for 60 minutes. Except for this, a porous film of Comparative Example 3 was obtained in the same manner as in Example 1.

[0161] Comparative Example 4 A porous film of Comparative Example 4 was obtained in the same manner as in Example 3, except that the cooled molded body was not subjected to an annealing treatment but was subjected to coaxial biaxial stretching.

[0162] Comparative Example 5: Poly(4-methylpentene-1) resin (MX002, manufactured by Mitsui Chemicals, Inc.) was used as the thermoplastic resin. 2Liquid paraffin (manufactured by MORESCO) with a viscosity of 1 / s was used. 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 35.0 wt% thermoplastic resin, 64.7 wt% plasticizer, and 0.3 wt% antioxidant. The mixture was kneaded using a Labo Plastomill at 260°C for 30 minutes 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. The molded body was annealed at 150°C for 30 minutes. Next, the annealed molded body was immersed in MEK at room temperature for 5 minutes to perform an extraction operation, and the plasticizer was extracted and removed from the molded body. Next, using a biaxial stretching machine, the molded body after the plasticizer extraction and removal was subjected to simultaneous biaxial stretching under the conditions of a stretching temperature of 150°C and a stretching ratio of 3 times (longitudinal direction) x 3 times (transverse direction). The strain rate in the stretching was 1% / sec (0.655 mm / sec) in both the longitudinal and transverse directions. This resulted in a sheet body. In this way, the porous film of Comparative Example 5 was obtained.

[0163] [Comparative Example 6] The porous film of Comparative Example 5 was subjected to annealing treatment at a temperature of 165°C for 5 minutes. Except for this, the porous film of Comparative Example 6 was obtained in the same manner as in Comparative Example 5.

[0164] Comparative Example 7 Poly(4-methylpentene-1) resin (DX845, manufactured by Mitsui Chemicals, Inc.) was used as the thermoplastic resin. 2Liquid paraffin (MORESCO) with a viscosity of 1 / s was used. Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (BASF Japan) was used as the antioxidant. A mixture was obtained by mixing 55 wt% thermoplastic resin, 44.5 wt% plasticizer, and 0.5 wt% antioxidant. The mixture was kneaded using a Labo Plastomill at 260°C for 30 minutes to obtain a uniform kneaded product. 1.6 g of the kneaded product pellet was sandwiched between two polyimide plates (150 μm thick) and then sandwiched between a stainless steel plate (3.0 mm thick). 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, the cooled molded body was immersed in MEK at room temperature for 5 minutes to perform an extraction operation, and the plasticizer was extracted and removed from the molded body. Next, using a biaxial stretching machine, the molded body after the plasticizer was extracted and removed was subjected to simultaneous biaxial stretching under the conditions of a stretching temperature of 180 ° C and a stretching ratio of 3 times (longitudinal direction) × 3 times (transverse direction). The strain rate in the stretching was 1% / sec (0.655 mm / sec) in both the longitudinal and transverse directions. This resulted in a sheet body. The sheet body was subjected to an annealing treatment at a temperature of 170 ° C for 5 minutes. In this way, the porous film of Comparative Example 7 was obtained.

[0165] [Comparative Example 8] The pressed body sandwiched between polyimide plates was air-cooled to obtain a molded body. Except for this, a porous film of Comparative Example 8 was obtained in the same manner as in Comparative Example 7. In Comparative Example 8, cracks occurred in the film during stretching.

[0166] [Comparative Example 9] Using a biaxial stretching machine, the molded body after extracting and removing the plasticizer was subjected to simultaneous biaxial stretching under the conditions of a stretching temperature of 170 ° C and a stretching ratio of 3 times (longitudinal direction) × 3 times (transverse direction). The strain rate in stretching was 1% / sec (0.655 mm / sec) in both the longitudinal and transverse directions. This resulted in a sheet body. In Comparative Example 9, annealing treatment was not performed because cracks occurred in the film during stretching. Except for these, the porous film of Comparative Example 9 was obtained by the same method as Comparative Example 7.

[0167] [Comparative Example 10] The pressed body sandwiched between polyimide plates was air-cooled to obtain a molded body. Except for this, a porous film of Comparative Example 10 was obtained in the same manner as in Comparative Example 9. In Comparative Example 10, cracks occurred in the film during stretching.

[0168] The conditions for producing the porous films of Examples 1 to 5 and Comparative Examples 1 to 10 are shown in Table 1.

[0169]

[0170] Using the methods described above for the porous film, the thickness, air permeability, water pressure resistance, cohesive strength, etc. were evaluated for the porous films of Examples 1 to 5 and Comparative Examples 1 to 10. The evaluation results are shown in Table 2.

[0171] FIG. 18 shows the change (R1-R2) in the value obtained by dividing the air permeability by the water pressure resistance of the porous films of Examples 1 to 5 and Comparative Examples 1 to 7 before and after the heat resistance test.

[0172] In addition, by the method described above for the porous film, the porous films of Examples 1 to 5 and Comparative Examples 1 to 10 were subjected to a tensile test at a temperature of 25°C to obtain S-S curves, and the breaking strain and maximum stress were measured. The results are shown in Table 2.

[0173] FIG. 19 shows the SS curves of the porous films of Examples 1 to 5 and Comparative Examples 1 to 4.

[0174]

[0175] Using the method described above for the porous film, the equivalent circle diameter of the nodes, the equivalent circle diameter of the pores, etc. were determined for the porous films of Examples 1 to 5 and Comparative Examples 1, 2, and 7. The results are shown in Table 3.

[0176]

[0177] As can be seen from Table 2, the porous films of Examples 1 to 5 had a breaking strain of 15% or less, and exhibited a property of being difficult to stretch. As can be seen from Figure 19, the porous films of Examples 1 to 5 did not show a yield point in the S-S curve.

[0178] As can be seen from Table 2 and FIG. 18, the porous films of Examples 1 to 5 satisfied R1-R2≧-0.015 and exhibited high heat resistance.

[0179] As can be seen from a comparison of Figures 16C and 17B, the porous film of Example (Example 1) had more connections between nodes or clusters of nodes in the thickness direction than the porous film of Comparative Example (Comparative Example 1), and the pores were more concentrated. From these results, it can be inferred that in the porous film of Example (Example 1), the annealing treatment (Step S4) was performed on the molded body at a temperature of 180 ° C to 200 ° C for 30 to 60 minutes before stretching (Step S5), which made it easier for the highly crystalline parts that could become nodes and the parts that could become low-crystalline fibrils to aggregate. As a result, stretching resulted in the formation of a structure with many connections between nodes or clusters of nodes, as shown in Figure 16C, and a concentration of pores, thereby achieving a resistance to stretching. Furthermore, it can be inferred that the porous films of Examples 1 to 5 achieved a cohesive force of 0.1 N / 10 mm or more due to the cross-sectional structure shown in Figure 16C.

[0180] Furthermore, as can be seen from a comparison of Figures 16A-16B with Figure 17A, the surfaces of both the porous film of Example 1 and the porous film of Comparative Example 1 had a tortoiseshell structure formed by multiple nodes and multiple fibrils. However, in the porous film of Example 1, island-like regions of different sizes formed by multiple nodes were present in random positions. From these results, it can be inferred that in the porous film of Example 1, the annealing treatment (Step S4) was performed on the molded body at a temperature of 180°C to 200°C for 30 to 60 minutes before stretching (Step S5), which made it easier for the highly crystalline portions that could become nodes and the less crystalline portions that could become fibrils to aggregate. As a result, stretching formed a structure in which island-like regions of different sizes formed by multiple nodes were present in random positions, as shown in Figures 16A-16B, which is believed to have achieved high water resistance and high breathability.

[0181] From the above results, it can be seen that the porous films of Examples 1 to 5 are suitable for suppressing changes in properties.

[0182] 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 its main component, with a breaking strain of 15% or less in a tensile test at a temperature of 25°C.

2. The porous film according to claim 1, wherein no yield point is observed in the stress-strain curve obtained in the tensile test.

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

4. The porous film according to claim 1, having a cohesive strength of 0.1 N / 10 mm or more.

5. The porous film according to claim 1, which has a water pressure resistance of more than 140 kPa and an air permeability, expressed as a Gurley number, of 50 seconds / 100 mL or less.

6. The porous film according to claim 1, having a plurality of nodes and a plurality of fibrils, the nodes having a circular equivalent diameter of 3.5 μm or more.

7. The porous film according to claim 6, wherein the distance between the nodes is 1.5 μm or more.

8. The porous film according to claim 1, wherein the pores have an equivalent circle diameter of 0.8 μm or more.

9. The porous film according to claim 5, wherein the ratio R1 is defined as the value obtained by dividing the air permeability by the water pressure resistance, and the ratio R2 is defined as the value obtained by dividing the air permeability of the porous film after a heat resistance test in which the film is heated at 200°C for 5 minutes by the water pressure resistance, and the ratio R1 - R2 is satisfied.

10. The porous film according to claim 1, wherein the porosity is 30% or more when the surface of the porous film is observed with a scanning electron microscope.

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

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.

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