Ventilation structure and porous film

Abstract

A ventilation structure (100) is provided with: a housing (20) in which an opening (21) is formed; and a porous film (10) that is ultrasonically welded to the housing (20) so as to close the opening (21). The porous film (10) has a first main surface (10a) facing the opening (21) and a second main surface (10b) facing the side opposite from the opening (21). Defining the weld strength of the porous film (10) to be the maximum stress when a push-in pin is pushed in from the side of the first main surface (10a) of the porous film (10), the weld strength of the porous film (10) is in the range of 1.5 N to 30 N. The housing (20) includes, for example, a housing of an on-vehicle component.

Description

Ventilated structure and porous membrane

[0001] The present invention relates to a vent structure and a porous membrane.

[0002] Conventionally, in in-vehicle parts, electronic devices, etc., breathable membranes have been used to eliminate the pressure difference between the inside and outside of a housing. The breathable membrane is attached to the housing so as to cover an opening provided in the housing, and is intended to provide dustproofness and waterproofness while ensuring ventilation. Porous membranes with good breathability are often used as such breathable membranes.

[0003] Porous membranes serving as breathable membranes are bonded to housings of in-vehicle components, electronic devices, etc. by adhesion using double-sided tape, adhesives, etc., or by welding, such as ultrasonic welding, heat welding, or laser welding. Adhesion is a simple method, but it does not provide sufficient chemical resistance. When used in housings of in-vehicle components, adhesion of oil, gasoline, etc. to the double-sided tape, adhesive, etc. can result in a decrease in adhesive strength. Therefore, it is desirable to bond porous membranes to housings of in-vehicle components by welding, which is less susceptible to the effects of oil, gasoline, etc. For example, Patent Document 1 describes a technique for welding a gas-permeable porous fluororesin membrane made of fluororesin to a housing (resin component) for housing electrical components in an automobile.

[0004] Japanese Patent Application Laid-Open No. 2015-205420

[0005] Although the technology described in Patent Document 1 is expected to improve the welding strength of the porous membrane to the housing, it requires a protrusion on the working surface of the welding horn of the welding device. There is a need for a technology that can achieve excellent welding strength by utilizing the characteristics of the porous membrane itself, without relying on the structure of the welding device.

[0006] Therefore, an object of the present invention is to provide a ventilation structure in which the welding strength of the porous membrane to the housing is improved, and a porous membrane in which the welding strength to the housing is improved.

[0007] The present invention provides a ventilation structure comprising: a housing having an opening formed therein; and a porous membrane ultrasonically welded to the housing so as to close the opening, wherein the porous membrane has a first main surface facing the opening and a second main surface facing the opposite side to the opening, and wherein, when the maximum stress when a push-in pin is pushed into the porous membrane from the first main surface side is defined as the welding strength of the porous membrane, the welding strength of the porous membrane is in the range of 1.5 N to 30 N.

[0008] From another aspect, the present invention provides a porous membrane, the weld strength of which, as determined by the following weld strength measurement test, is in the range of 1.5 N or more and 30 N or less. <Weld Strength Measurement Test> A sample body is prepared in which the porous membrane is ultrasonically welded to a housing having an opening so as to close the opening. In the sample body, the porous membrane has a first main surface facing the opening and a second main surface facing the opposite side to the opening. The maximum stress of the sample body is measured when a push-in pin is pressed into the porous membrane from the first main surface side. The measured value is the weld strength of the porous membrane.

[0009] According to the present invention, it is possible to provide a ventilation structure in which the welding strength of the porous membrane to the housing is improved, and a porous membrane in which the welding strength to the housing is improved.

[0010] Fig. 1A is a cross-sectional view schematically showing an example of the porous membrane of the present invention. Fig. 1B is a plan view schematically showing the porous membrane of Fig. 1A. Fig. 2A is a cross-sectional view schematically showing an example of the ventilation structure of the present invention. Fig. 2B is a plan view schematically showing the ventilation structure of Fig. 2A. Fig. 3 is a cross-sectional view schematically showing an example of a welding device. Fig. 4 is a schematic view for explaining a measurement test of welding strength. Fig. 5 is a scanning electron microscope (SEM) image of a cross section of the PTFE porous membrane of Example 3.

[0011] A ventilation structure according to a first aspect of the present invention comprises a housing having an opening formed therein, and a porous membrane ultrasonically welded to the housing so as to close the opening, wherein the porous membrane has a first main surface facing the opening and a second main surface facing the opposite side to the opening, and when the maximum stress when a push-in pin is pressed into the porous membrane from the first main surface side is defined as the welding strength of the porous membrane, the welding strength of the porous membrane is in the range of 1.5 N or more and 30 N or less.

[0012] In a second aspect of the present invention, for example, in the ventilation structure according to the first aspect, the porous membrane includes fibrils and nodes connected to the fibrils, and the average node area of ​​the porous membrane is 100 μm 2 Super 500μm 2 It is in the following range:

[0013] In a third aspect of the present invention, for example, the ventilation structure according to the first or second aspect has a first region where the housing and the porous membrane are present and which includes a weld formed between the housing and the porous membrane, and a second region where the housing is not present and the porous membrane is exposed, and the average thickness of the porous membrane in the second region is in the range of 120 μm or more and 350 μm or less.

[0014] In a fourth aspect of the present invention, for example, in the ventilation structure according to any one of the first to third aspects, the Gurley air permeability of the porous membrane is in the range of 3 seconds / 100 mL or more and 40 seconds / 100 mL or less.

[0015] In a fifth aspect of the present invention, for example, in the ventilation structure according to any one of the first to fourth aspects, the housing is formed from a thermoplastic resin.

[0016] In a sixth aspect of the present invention, for example, in the ventilation structure according to any one of the first to fifth aspects, the housing includes a housing for an in-vehicle component.

[0017] The porous membrane according to the seventh aspect of the present invention has a weld strength in the range of 1.5 N or more and 30 N or less, as determined by the following weld strength measurement test. <Weld Strength Measurement Test> A sample body is prepared in which the porous membrane is ultrasonically welded to a housing having an opening so as to close the opening. In the sample body, the porous membrane has a first main surface facing the opening and a second main surface facing the opposite side to the opening. The maximum stress when a push-in pin is pressed into the porous membrane from the first main surface side of the sample body is measured. The measured value is the weld strength of the porous membrane.

[0018] In an eighth aspect of the present invention, for example, the porous membrane according to the seventh aspect includes fibrils and nodes connected to the fibrils, and the average node area is 100 μm 2 Super 500μm 2 It is in the following range:

[0019] In a ninth aspect of the present invention, for example, the porous membrane according to the seventh or eighth aspect has an average thickness in the range of 120 μm or more and 350 μm or less.

[0020] In a tenth aspect of the present invention, for example, in the porous membrane according to any one of the seventh to ninth aspects, the Gurley air permeability is in the range of 3 seconds / 100 mL or more and 40 seconds / 100 mL or less.

[0021] In an eleventh aspect of the present invention, for example, the porous film according to any one of the seventh to tenth aspects is used as a breathable film for an on-vehicle part.

[0022] 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.

[0023] [Porous membrane] Fig. 1A is a cross-sectional view schematically showing an example of a porous membrane 10 of the present invention. Fig. 1B is a plan view schematically showing the porous membrane 10 of Fig. 1A. As shown in Fig. 1B, the porous membrane 10 has a circular shape in plan view. The porous membrane 10 of this embodiment has a welding strength S in the range of 1.5 N or more and 30 N or less.

[0024] In the technology described in Patent Document 1, a protrusion provided on the working surface of a welding horn provided in a welding device is essential to improve the welding strength of the porous membrane to the housing. In contrast, the porous membrane 10 of this embodiment has an excellent welding strength S in the range of 1.5 N to 30 N due to the characteristics of the porous membrane itself.

[0025] <Welding Strength Measurement Test> The welding strength S of the porous membrane 10 can be measured by the test described below. FIG. 3 is a cross-sectional view schematically showing an example of a welding device 50. FIG. 4 is a schematic diagram illustrating a measurement test for the welding strength S. First, as shown in FIG. 3, a circular porous membrane 10 having a diameter d10 of 10 mm is concentrically placed in a housing 20 having a circular opening 21 having a diameter d20 of 4.9 mm so as to close the opening 21. Next, using the welding device 50, the porous membrane 10 is ultrasonically welded to the housing 20 with a welding horn 51 to produce a sample body 101. The welding horn 51 has a circular ring shape in a plan view. The inner diameter d1 of the welding horn 51 is 6.6 mm, and the outer diameter d2 is 8.2 mm. The frequency for producing the sample body 101 was 35 kHz, the amplitude was 32.5 μm, the contact load (load of the welding horn 51 before ultrasonic vibration) was 25 N, the welding load (load of the welding horn 51 when ultrasonic vibration is applied) was 50 N, and the welding energy was 30 J. The stop mode was set to "energy." Next, as shown in FIG. 4, the sample body 101 was placed in a tensile tester. In the sample body 101, the porous membrane 10 has a first main surface 10a facing the opening 21 and a second main surface 10b facing the opposite side of the opening 21. For the sample body 101, the maximum stress σ was measured when a pusher pin 60 with a diameter of 4 mm and a tip diameter of 2 mm was pushed into the first main surface 10a of the porous membrane 10 at a speed of 1 mm / min. The measured maximum stress σ was taken as the welding strength S of the porous membrane 10. The welding strength S may be an average value of the maximum stress σ measured for a plurality of (e.g., five) sample bodies 101. In the present disclosure, the term "main surface" refers to the surface of a sheet-like or film-like member having the largest area.

[0026] The porous membrane 10 in this embodiment is used without being laminated with a support material such as a nonwoven fabric or mesh.

[0027] The lower limit of the welding strength S of the porous membrane 10 may be 2.5 N or more, 5 N or more, 7.5 N or more, or even 10 N or more. The upper limit of the welding strength S of the porous membrane 10 may be 29 N or less, 28 N or less, or even 27 N or less.

[0028] The porous membrane 10 may be a single-layer membrane, or may be a laminated membrane in which multiple layers are stacked.

[0029] The porous membrane 10 may be a porous fluororesin membrane. A porous fluororesin membrane is a porous membrane formed by stretching a fluororesin membrane to make it porous, typically by biaxial stretching. The porous fluororesin membrane may include countless fibrils formed during stretching and nodes connected to the fibrils. Nodes and fibrils are formed by stretching the fluororesin sheet. The configuration of the nodes and fibrils varies depending on, for example, the stretching conditions of the fluororesin sheet.

[0030] Examples of the fluororesin contained in the fluororesin porous membrane include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-ethylene copolymer.

[0031] The fluororesin may be PTFE. That is, the fluororesin porous membrane may be a PTFE porous membrane. A PTFE porous membrane has excellent water resistance and dustproof properties, and therefore has an excellent function of preventing foreign matter such as water and dust from entering the housing from the outside.

[0032] When the porous membrane 10 includes fibrils and nodes, the longitudinal length L1 of the node is preferably in the range of 5 μm to 80 μm, and the lateral length L2 of the node is preferably in the range of 1 μm to 30 μm. When the longitudinal length L1 and lateral length L2 of the node included in the porous membrane 10 are in the above-mentioned numerical ranges, the welding strength S is likely to be in the range of 1.5 N to 30 N.

[0033] The lower limit of the length L1 in the longitudinal direction of the node may be 10 μm or more. The upper limit of the length L1 in the longitudinal direction of the node may be 70 μm or less. The lower limit of the length L2 in the lateral direction of the node may be 5 μm or more. The upper limit of the length L2 in the lateral direction of the node may be 20 μm or less.

[0034] When the porous membrane 10 includes fibrils and nodes, the average node area An of the porous membrane 10 is 100 μm 2 Super 500μm 2 It is preferable that the average node area An of the porous membrane 10 is in the above numerical range. When the average node area An of the porous membrane 10 is in the above numerical range, the welding strength S is likely to be in the range of 1.5 N or more and 30 N or less.

[0035] The lower limit of the average node area An of the porous film 10 is 110 μm 2 It may be 120 μm or more. 2 It may be 130 μm or more, 2 The upper limit of the average node area An of the porous film 10 is 450 μm 2 It may be less than 400 μm 2 It may be less than 350 μm 2 It may be less than 300 μm, 2 It may be the following:

[0036] When the porous membrane 10 includes fibrils and nodes, the porous membrane 10 preferably has a structure in which the nodes are connected in the direction of extension of the fibrils. A porous membrane 10 having such a structure is likely to have a welding strength S in the range of 4.5 N or more.

[0037] The lower limit of the average node area An of the porous film 10 is 200 μm 2 It may be 250 μm or more, 2 When the lower limit of the average node area An of the porous membrane 10 is within the above numerical range, the porous membrane 10 is likely to have a structure in which the nodes are connected in the extension direction of the fibrils.

[0038] <Method for Measuring Node Length and Node Area> The longitudinal length L1, lateral length L2, and average node area An of the nodes contained in the porous membrane 10 can be determined by the measurement method described below. First, a cross section of the porous membrane 10 cut parallel to the thickness direction is observed with a scanning electron microscope (SEM). Next, using image software (e.g., ImageJ), the obtained SEM observation image (or a portion thereof) is binarized. Fibrils are removed from the obtained binarized image to create an image of only the nodes. In the fibril removal process, fibrils can be removed by enlarging the binarized image and filling in the fibril areas with black. For n nodes contained in the obtained image of only the nodes, the longitudinal length, lateral length, and area are calculated. For example, the longitudinal length, lateral length, and area of ​​the nodes can be calculated using an observation image containing at least 10 nodes (n = 10). The average of the calculated longitudinal lengths is taken as the longitudinal length L1 of the nodes. The average of the calculated short-side lengths is defined as the short-side length L2 of the node. The average of the calculated areas is defined as the average node area An. Note that, to obtain the longitudinal length, short-side length, and area of ​​the node, an observation image should be used that is sufficiently wide so that it can be determined that the entire cross section of the porous membrane 10 cut parallel to the thickness direction is being observed. The observation image preferably includes an area of ​​at least 120 μm × 90 μm.

[0039] When the porous membrane 10 includes fibrils and nodes, the longitudinal length L3 of the fibrils is preferably in the range of 8 μm to 30 μm. When the longitudinal length L3 of the fibrils contained in the porous membrane 10 is in the above numerical range, the welding strength S is likely to be in the range of 1.5 N to 30 N.

[0040] The longitudinal length L3 of the fibrils contained in the porous membrane 10 can be determined by the measurement method described below. In the above-mentioned method for measuring node length and node area, nodes are deleted from the obtained binarized image to create an image of only fibrils, and the longitudinal length of each of N fibrils contained in the obtained image of only fibrils is calculated. For example, the longitudinal length of the fibrils can be calculated using an observation image containing at least 100 fibrils (N = 100). The average of the calculated longitudinal lengths is taken as the longitudinal length L3 of the fibrils.

[0041] The porous membrane 10 preferably has an average thickness in the range of 120 μm to 350 μm. When the average thickness of the porous membrane 10 is in the above numerical range, the welding strength S is likely to be in the range of 1.5 N to 30 N.

[0042] The lower limit of the average thickness of the porous membrane 10 may be 125 μm or more, 135 μm or more, 150 μm or more, or even 175 μm or more. The upper limit of the average thickness of the porous membrane 10 may be 340 μm or less, 330 μm or less, or even 320 μm or less.

[0043] <Method of measuring thickness> The average thickness of the porous membrane 10 can be determined by measuring the thickness at any five points of the porous membrane 10 using, for example, a dial gauge, and averaging these measured values. The average thickness of the porous membrane 10 can also be determined by measuring the thickness at any five points in an SEM observation image of the cross section of the porous membrane 10 and averaging these measured values.

[0044] The porous film 10 has an average node area An of 100 μm 2 Super 500μm 2 It is more preferable that the average node area An of the porous membrane 10 is within the above range and the average thickness is within the above range, and the welding strength S is more likely to be within the range of 1.5 N to 30 N.

[0045] The porous membrane 10 preferably has a Gurley air permeability in the range of 3 seconds / 100 mL or more and 40 seconds / 100 mL or less.

[0046] The lower limit of the Gurley air permeability of the porous membrane 10 may be 5 seconds / 100 mL or more, 7.5 seconds / 100 mL or more, or even 10 seconds / 100 mL or more.

[0047] <Method for Measuring Gurley Air Permeability> The Gurley air permeability of the porous membrane 10 can be measured in accordance with the Gurley tester method defined in JIS P8117:2009.

[0048] As described above, it is desirable to join the porous membrane 10 to the housing 20 of the in-vehicle part by welding. The porous membrane 10 has an excellent welding strength S in the range of 1.5 N or more and 30 N or less, and is therefore particularly suitable for use as a breathable membrane for the in-vehicle part.

[0049] The porous membrane 10 may be supplied in the form of a tape-like member in which circular porous membranes 10 are attached in a row along the longitudinal direction of a tape-like base sheet, or in the form of a sheet-like member in which circular porous membranes 10 are attached at equal intervals over the entire surface of a single-sheet base sheet.

[0050] [Method for manufacturing porous membrane] Hereinafter, a method for manufacturing the porous membrane 10 will be described. The porous membrane 10 can be manufactured, for example, by the following method. The method described below is an example in which the porous membrane 10 is a PTFE porous membrane.

[0051] First, a liquid lubricant is uniformly mixed with PTFE fine powder. The mixture is compressed into a cylinder and then extruded using a ram extruder. This results in a sheet-like molded body stretched in a predetermined direction. The sheet-like molded body containing the liquid lubricant is passed through mill rolls and rolled. The liquid lubricant is removed by heating the sheet-like molded body, and then the sheet-like molded body is dried. Next, the sheet-like molded body is stretched once in the longitudinal direction only. This results in a porous PTFE membrane. The properties of the porous PTFE membrane, such as the average node area An and average thickness, can be adjusted by changing the stretching conditions.

[0052] [Ventilation Structure] Next, the ventilation structure of the present invention will be described. Fig. 2A is a cross-sectional view schematically showing an example of the ventilation structure 100 of the present invention. Fig. 2B is a plan view schematically showing the ventilation structure 100 of Fig. 2A. The ventilation structure 100 comprises a housing 20 and a porous membrane 10 having the above-described characteristics. As shown in Fig. 2B, the opening 21 of the housing 20 has a circular shape in a plan view. Below, the description of the porous membrane 10 described above may be omitted.

[0053] The ventilation structure 100 includes a housing 20 having an opening 21 formed therein, and a porous membrane 10 ultrasonically welded to the housing 20 so as to close the opening 21. The porous membrane 10 has a first main surface 10a facing the opening 21 and a second main surface 10b facing the opposite side of the opening 21. The maximum stress σ when a push-in pin 60 is pushed into the porous membrane 10 from the first main surface 10a side is defined as the weld strength S of the porous membrane 10. In this case, the weld strength S of the porous membrane 10 is in the range of 1.5 N or more and 30 N or less. The weld strength S of the porous membrane 10 can be measured by the weld strength measurement test described above.

[0054] In the ventilation structure 100, the welding strength S of the porous membrane 10 is in the range of 1.5 N or more and 30 N or less, which is higher than that of conventional ventilation structures using porous membranes.

[0055] The lower limit of the welding strength S of the porous membrane 10 in the ventilation structure 100 may be 2.5 N or more, 5 N or more, 7.5 N or more, or even 10 N or more. The upper limit of the welding strength S of the porous membrane 10 may be 29 N or less, 28 N or less, or even 27 N or less.

[0056] 2A and 4, a weld 30 is formed between the housing 20 and the porous membrane 10 by ultrasonic welding, whereby the material forming the housing 20 is melted and solidified. The weld 30 has a circular ring shape in plan view. For ease of understanding, the weld 30 is shown in a see-through manner in FIG. 2B.

[0057] As shown in Fig. 2A, the ventilation structure 100 has a first region 11 where the housing 20 and porous membrane 10 are present and include the welded portion 30, and a second region 12 where the housing 20 is not present and the porous membrane 10 is exposed. As shown in Fig. 2B, the first region 11 has an annular shape in plan view. The second region 12 has a circular shape in plan view. As long as the first region 11 includes the welded portion 30, the outer edge 11a of the first region 11 may or may not overlap the outer edge 30a of the welded portion 30. The inner edge 11b of the first region 11 may or may not overlap the inner edge 30b of the welded portion 30.

[0058] The width 30d (radial length) of the welded portion 30 may be set appropriately depending on, for example, the width 11d (radial length) of the first region 11. Alternatively, it may be set appropriately depending on the width (radial length: (d2-d1) / 2) of the working surface 51s of the welding horn 51 provided in the welding device 50 as shown in Fig. 3. The width 30d of the welded portion 30 may be, for example, in the range of 0.5 mm to 1.5 mm.

[0059] In the ventilation structure 100, the average thickness of the porous membrane 10 in the second region 12 is preferably in the range of 120 μm to 350 μm. The average thickness of the flat region 12 of the porous membrane 10 in the second region 12 is the same as the average thickness of the porous membrane 10 before ultrasonic welding to the housing 20.

[0060] The lower limit of the average thickness of the porous membrane 10 in the second region 12 may be 125 μm or more, 135 μm or more, 150 μm or more, or even 175 μm or more. The upper limit of the average thickness of the porous membrane 10 in the second region 12 may be 340 μm or less, 330 μm or less, or even 320 μm or less.

[0061] <Method for measuring thickness in second region> The average thickness of the porous membrane 10 in the second region 12 can be determined by measuring the thickness at any five points of the porous membrane 10 in the second region 12 using, for example, a dial gauge, and calculating the average value of these measured values. The average thickness of the porous membrane 10 in the second region 12 can also be determined by measuring the thickness at any five points in an SEM observation image of the cross section of the porous membrane 10 in the second region 12 and calculating the average value of these measured values.

[0062] The weld strength S of the porous membrane 10 can vary depending on the material forming the housing 20. The material forming the housing 20 is preferably a resin, and particularly preferably a thermoplastic resin. The housing 20 may be formed from a thermoplastic resin. If the housing 20 is formed from a thermoplastic resin, a weld 30 is likely to be formed between the housing 20 and the porous membrane 10 during ultrasonic welding, as the thermoplastic resin forming the housing 20 melts and solidifies.

[0063] The thermoplastic resin may contain an additive such as glass fiber. When the thermoplastic resin contains an additive, the content of the additive may be, for example, in the range of 15 to 45 mass %, or in the range of 20 to 40 mass %.

[0064] Examples of thermoplastic resins include polypropylene (PP), polybutylene terephthalate (PBT), polycarbonate (PC), polyamide 6 (PA6), polyamide 66 (PA66), ABS, and ASA.

[0065] The housing 20 may be made of PP or PBT. The housing 20 may be made of PP blended with glass fiber or PBT blended with glass fiber. For example, when the housing 20 is made of PP blended with glass fiber, the welding strength S of the porous membrane 10 may be in the range of 2.5 N or more and 30 N or less. For example, when the housing 20 is made of PBT blended with glass fiber, the welding strength S of the porous membrane 10 may be in the range of 1.5 N or more and 25 N or less.

[0066] The housing 20 includes a housing for an on-vehicle component. The housing 20 is preferably a housing for an on-vehicle component. As described above, in the case of a housing for an on-vehicle component, it is desirable to join the porous membrane 10 to the housing 20 by welding. The ventilation structure 100 can improve the welding strength of the porous membrane 10 to the housing 20 for the on-vehicle component.

[0067] [Method for manufacturing ventilation structure] The following describes a method for manufacturing the ventilation structure 100. The ventilation structure 100 can be manufactured, for example, by the following method.

[0068] First, a circular porous membrane 10 is placed in a housing 20 having a circular opening 21 so as to close the opening 21. Next, using a welding device 50 as shown in Fig. 3, the porous membrane 10 is ultrasonically welded to the housing 20 with a welding horn 51. In this way, a ventilation structure 100 can be obtained.

[0069] 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.

[0070] The average thickness, average node area, and Gurley air permeability of the porous membrane were determined by the methods described above.

[0071] [Preparation of Porous Membrane] (Example 1) 100 parts by weight of PTFE fine powder (Polyflon F-104, manufactured by Daikin Industries, Ltd.) was uniformly mixed with 20 parts by weight of a liquid lubricant (n-dodecane, manufactured by Japan Energy Corporation). The mixture was compressed into a cylinder and then extruded using a ram extruder. This resulted in a sheet-like molded body stretched in a predetermined direction. The sheet-like molded body, while still containing the liquid lubricant, was passed between metal rolling rolls and rolled to a thickness of 260 μm. The liquid lubricant was removed by heating the sheet-like molded body to 150°C, and the sheet-like molded body was then dried. Next, the sheet-like molded body was stretched 3.7 times in the longitudinal direction at 380°C. Stretching was performed once only in the longitudinal direction. This resulted in the PTFE porous membrane of Example 1. The PTFE porous membrane of Example 1 had the average thickness, average node area, and Gurley air permeability shown in Table 1.

[0072] [Example 2] The PTFE porous membrane of Example 2 is obtained by the same method as in Example 1, except that the sheet-shaped molding that is rolled to a thickness of 260 μm is stretched at 4.2 times in longitudinal direction at 380 ° C. The PTFE porous membrane of Example 2 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0073] [Example 3] The PTFE porous membrane of Example 3 is obtained by the same method as in Example 1, except that the sheet-shaped molding that is rolled to a thickness of 200 μm is stretched at 3.0 times in the longitudinal direction at 380 ° C. The PTFE porous membrane of Example 3 has the average thickness, average node area and Gurley air permeability shown in Table 1. Figure 5 shows the SEM image (magnification: 1000 times) of the cross section of the PTFE porous membrane of Example 3. As shown in Figure 5, the PTFE porous membrane of Example 3 has a structure in which nodes are connected in the elongation direction of fibril.

[0074] [Example 4] Except that the sheet-shaped molding that is rolled to a thickness of 240 μm is stretched at 3.0 times in longitudinal direction at 380 ° C, the PTFE porous membrane of Example 4 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 4 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0075] [Example 5] Except that the sheet-shaped molding that is rolled to a thickness of 240 μm is stretched at 4.0 times in longitudinal direction at 380°C, the PTFE porous membrane of Example 5 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 5 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0076] [Example 6] Except that the sheet-shaped molding that is rolled to a thickness of 240 μm is stretched at 5.0 times in longitudinal direction at 380 ° C, the PTFE porous membrane of Example 6 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 6 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0077] [Example 7] Except that the sheet-shaped molding that is rolled to a thickness of 240 μm is stretched at 6.0 times in longitudinal direction at 380 ° C, the PTFE porous membrane of Example 7 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 7 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0078] [Example 8] Except that the sheet-shaped molding that is rolled to a thickness of 300 μm is stretched at 380°C in longitudinal direction by 3.0 times, the PTFE porous membrane of Example 8 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 8 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0079] [Example 9] Except that the sheet-shaped molding that is rolled to a thickness of 300 μm is stretched at 6.0 times in longitudinal direction at 380 ° C, the PTFE porous membrane of Example 9 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 9 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0080] [Example 10] Except that the sheet-shaped molding that is rolled to a thickness of 280 μm is stretched at 5.2 times in longitudinal direction at 380 ° C, the PTFE porous membrane of Example 10 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 10 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0081] [Example 11] Except that the sheet-shaped molding that is rolled to a thickness of 450 μm is stretched at 5.0 times in longitudinal direction at 380 ° C, the PTFE porous membrane of Example 11 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 11 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0082] [Example 12] Except that the sheet-shaped molding that is rolled to a thickness of 400 μm is stretched at 380°C in longitudinal direction by 4.2 times, the PTFE porous membrane of Example 12 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 12 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0083] [Example 13] Except that the sheet-shaped molding that is rolled to a thickness of 280 μm is stretched at 380°C in longitudinal direction by 3.2 times, the PTFE porous membrane of Example 13 is obtained by the same method as in Example 1. The PTFE porous membrane of Example 13 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0084] [Comparative Example 1] The PTFE porous membrane of Comparative Example 1 is obtained by the same method as in Example 1, except that the sheet-shaped molding that is rolled to a thickness of 200 μm is stretched at 10 times in the longitudinal direction at 380° C. The PTFE porous membrane of Comparative Example 1 has the average thickness, average node area and Gurley air permeability shown in Table 1.

[0085] Using the above-described method, the porous membranes of Examples 1 to 13 and Comparative Example 1 were evaluated for weld strength to housing A made of PP containing 30% by mass of glass fiber, and for weld strength to housing B made of PBT containing 30% by mass of glass fiber. A Herrmann HiQ DIALOG (frequency: 35 kHz) was used as the welding device for ultrasonic welding. Shimadzu Corporation's Autograph AG-X plus, 5 kN, was used as the tensile tester for measuring weld strength. The evaluation results are shown in Table 1 below.

[0086]

[0087] As shown in Table 1, the porous membranes of Examples 1 to 13 exhibited high welding strengths in the range of 1.5 N or more and 30 N or less. The welding strengths of the porous membranes of Examples 1 to 13 to housing A were in the range of 2.5 N or more and 30 N or less. The welding strengths of the porous membranes of Examples 1 to 13 to housing B were in the range of 1.5 N or more and 25 N or less. In contrast, the welding strength of the porous membrane of Comparative Example 1 was low, at 0.8 N or less.

[0088] The porous membranes of Examples 1 to 13 have an average node area of ​​100 μm 2 Super 500μm 2 The average node area was within the range of 100 μm or more, and the average thickness was within the range of 120 μm or more and 350 μm or less.2 Super 500μm 2 When the thickness is within the range below and the average thickness is within the range of 120 μm or more and 350 μm or less, it is estimated that a welding strength S within the range of 1.5 N or more and 30 N or less can be easily achieved.

[0089] The technology disclosed in this specification can be applied to various electronic devices, such as in-vehicle components such as ECUs (electronic control units), lamps, motors, various sensors, pressure switches, and actuators; wearable devices such as smart watches; various cameras; communication devices such as mobile phones and smartphones; and sensor devices.

Claims

1. A ventilated structure comprising: a housing having an opening; and a porous membrane ultrasonically welded to the housing so as to close the opening, wherein the porous membrane has a first main surface facing the opening and a second main surface facing the opposite side to the opening, and wherein the welding strength of the porous membrane is defined as the maximum stress when a push-in pin is pressed into the porous membrane from the first main surface side, and the welding strength of the porous membrane is in the range of 1.5 N to 30 N.

2. The porous membrane includes fibrils and nodes connected to the fibrils, and the average node area of the porous membrane is 100 μm 2 Super 500μm 2 The ventilation structure according to claim 1, which is in the following range:

3. The ventilation structure according to claim 1 or 2, wherein the ventilation structure has a first region where the housing and the porous membrane are present and which includes a weld formed between the housing and the porous membrane, and a second region where the housing is not present and the porous membrane is exposed, and the average thickness of the porous membrane in the second region is in the range of 120 μm or more and 350 μm or less.

4. The ventilation structure according to claim 1 or 2, wherein the Gurley air permeability of the porous membrane is in the range of 3 seconds / 100 mL or more and 40 seconds / 100 mL or less.

5. The ventilation structure according to claim 1 or 2, wherein the housing is made of a thermoplastic resin.

6. The ventilation structure according to claim 1 or 2, wherein the housing includes a housing for an in-vehicle component.

7. A porous film whose weld strength, as determined by the following weld strength measurement test, is in the range of 1.5 N or more and 30 N or less. <Weld Strength Measurement Test> A sample body is prepared in which the porous film is ultrasonically welded to a housing having an opening so as to close the opening. In the sample body, the porous film has a first main surface facing the opening and a second main surface facing the opposite side to the opening. The maximum stress is measured for the sample body when a push-in pin is pressed into the porous film from the first main surface side. The measured value is the weld strength of the porous film.

8. A fiber comprising fibrils and nodes connected to the fibrils, the average node area being 100 μm 2 Super 500μm 2 8. The porous membrane of claim 7, wherein the porous membrane has a viscosity in the range of:

9. The porous membrane according to claim 7 or 8, having an average thickness in the range of 120 μm to 350 μm.

10. The porous membrane according to claim 7 or 8, having a Gurley air permeability in the range of 3 seconds / 100 mL or more and 40 seconds / 100 mL or less.

11. The porous film according to claim 7 or 8, which is used as a breathable film for an on-vehicle part.

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