Fluororesin film, fluororesin film member, and electronic device

Abstract

The provided film is a fluororesin film having a network structure of a fluororesin. The mesh structure includes a first rope-shaped body made of a fluororesin. The first rope-shaped body has a diameter of 200 nm or more and 750 nm or less when viewed from a direction perpendicular to the main surface of the fluororesin film. When viewed from the above direction, the fluororesin film has a region A on at least one surface, the region A has a rectangular shape having a size of 8.3 [mu] m * 6.2 [mu] m, and the number of the first rope-shaped bodies extending from one long side to the other long side of the rectangular shape is 1-5. The film can be used as a waterproof film, and is suitable for improving waterproof performance while suppressing sacrifice of air permeability.

Description

Technical Field

[0001] The present invention relates to a fluororesin film, a fluororesin film member including the fluororesin film, and an electronic device. Background Art

[0002] In the case of a housing of an electronic device represented by a smartphone or a smartwatch, an opening for adjusting the internal pressure or ensuring air permeability between the inside and the outside of the housing is sometimes provided. Usually, a waterproof film for preventing foreign matters such as water from entering the inside of the housing is attached to the opening. A waterproof film having air permeability and exhibiting high waterproof performance is disclosed in Patent Document 1.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-184270 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In recent years, the waterproof performance required for electronic devices has been continuously improved. In order to enhance the attractiveness of products, it is also required to cope with activities such as water sports and diving, in which the device is expected to be exposed to water and high water pressure for a long time. Depending on the required level, the performance of the waterproof film of Patent Document 1 is not necessarily sufficient. Further improvement of the waterproof film is desired. However, the waterproof performance and the air permeability of the waterproof film are in a trade-off relationship and are not easily improved. It is common technical knowledge for those skilled in the art to sacrifice the air permeability in order to improve the waterproof performance.

[0008] An object of the present invention is to provide a technique suitable for improving the waterproof performance while suppressing the sacrifice of the air permeability for a film that can be used as a waterproof film.

[0009] Means for Solving the Problems

[0010] The present invention provides a fluororesin film which is a fluororesin film having a network structure of a fluororesin,

[0011] the network structure including a first cord-like body of the fluororesin,

[0012] when observed from a direction perpendicular to the main surface of the fluororesin film, the first cord-like body has a diameter of 200 nm or more and 750 nm or less,

[0013] when observed from the direction, the fluororesin film has a region A on at least one side,

[0014] the region A has a rectangular shape with dimensions of 8.3 μm × 6.2 μm, and the number of the first cord-like bodies extending from one long side of the rectangle to the other long side is 1 or more and 5 or less.

[0015] On the other hand, the present invention provides a fluororesin film, which is a fluororesin film having a network structure of fluororesin,

[0016] wherein the network structure includes a first cord-like body and a second cord-like body of the fluororesin,

[0017] When observed from a direction perpendicular to the main surface of the fluororesin film, the first cord-like body has a diameter of 200 nm or more and 750 nm or less, and the second cord-like body has a diameter of less than 200 nm,

[0018] When observed from the above direction, the fluororesin film has a region B on at least one side,

[0019] The region B has a rectangular shape with a size of 8.3 μm × 6.2 μm, and an annular structure formed by the first cord-like body is observed,

[0020] When observed from the above direction, the number of the second cord-like bodies observed inside the largest annular structure existing in the region B is 6 or more.

[0021] On the other hand, the present invention provides a fluororesin film, which is a fluororesin film having a network structure of fluororesin,

[0022] The Gurley air permeability of the fluororesin film per 1 μm thickness is 5 seconds / 100 mL / μm or less,

[0023] The ultimate water pressure resistance of the fluororesin film is 1.6 MPa or more.

[0024] On the other hand, the present invention provides a fluororesin film, which is a fluororesin film having a network structure of fluororesin,

[0025] The Gurley air permeability of the fluororesin film per 1 μm thickness is 5 seconds / 100 mL / μm or less,

[0026] The fluororesin film has a water pressure holding resistance capable of withstanding a water pressure holding test in which a circular water pressure application surface with a set diameter of 1 mm is exposed to a water pressure of 1.0 MPa for 30 minutes.

[0027] On the other hand, the present invention provides a fluororesin film member, which includes the above-mentioned fluororesin film of the present invention and includes a support layer and / or an adhesive layer.

[0028] In another aspect, the present invention provides an electronic device, which includes: a housing having an opening; and

[0029] a waterproof film mounted on the housing so as to cover the opening,

[0030] The waterproof film includes the fluororesin film of the present invention described above.

[0031] Effects of the Invention

[0032] The fluororesin film of the present invention is a film that can be used for a waterproof film and is suitable for improving the waterproof performance while suppressing the sacrifice of air permeability. Description of the Drawings

[0033] Figure 1 A plan view schematically showing an example of the fluororesin film of the present invention and a partial enlarged view of a part thereof.

[0034] Figure 2 A plan view schematically showing an example of region A in the fluororesin film of the present invention.

[0035] Figure 3A A schematic diagram for explaining a method of calculating the number of first cord-like bodies.

[0036] Figure 3B A schematic diagram for explaining a method of calculating the number of first cord-like bodies.

[0037] Figure 3C A schematic diagram for explaining a method of calculating the number of first cord-like bodies.

[0038] Figure 3D A schematic diagram for explaining a method of calculating the number of first cord-like bodies.

[0039] Figure 4A A schematic diagram for explaining a method of calculating the number of second cord-like bodies observed inside a ring structure formed by the first cord-like bodies.

[0040] Figure 4B A schematic diagram for explaining a method of calculating the number of second cord-like bodies observed inside a ring structure formed by the first cord-like bodies.

[0041] Figure 4C A schematic diagram for explaining a method of calculating the number of second cord-like bodies observed inside a ring structure formed by the first cord-like bodies.

[0042] Figure 4D A schematic diagram for explaining a method of calculating the number of second cord-like bodies observed inside a ring structure formed by the first cord-like bodies.

[0043] Figure 4E A schematic diagram for explaining a method of calculating the number of second cord-like bodies observed inside a ring structure formed by the first cord-like bodies.

[0044] Figure 4F ​​​​​​​​​​​​Schematic diagram for explaining a method of calculating the number of second rope-like bodies observed inside a ring structure formed by a first rope-like body.

[0045] Figure 4G Schematic diagram for explaining a method of calculating the number of second rope-like bodies observed inside a ring structure formed by a first rope-like body.

[0046] Figure 4H Schematic diagram for explaining a method of calculating the number of second rope-like bodies observed inside a ring structure formed by a first rope-like body.

[0047] Figure 5 Top view schematically showing an example of the fluororesin film of the present invention.

[0048] Figure 6 Cross-sectional view schematically showing an example of the fluororesin film member of the present invention.

[0049] Figure 7A Cross-sectional view schematically showing an example of the fluororesin film member of the present invention.

[0050] Figure 7B Cross-sectional view schematically showing an example of the fluororesin film member of the present invention.

[0051] Figure 8A Cross-sectional view schematically showing an example of the electronic device of the present invention.

[0052] Figure 8B Cross-sectional view schematically showing an example of the electronic device of the present invention.

[0053] Figure 9 Magnified observation image of the surface of sample 2 produced in the example.

[0054] Figure 10 Magnified observation image of the surface of sample 10 produced in the example. Detailed implementation mode

[0055] The film of the first aspect of the present invention is a fluororesin film having a network structure of fluororesin,

[0056] wherein the network structure includes a first rope-like body of the fluororesin,

[0057] When observed from a direction perpendicular to the main surface of the fluororesin film, the first rope-like body has a diameter of 200 nm or more and 750 nm or less,

[0058] When observed from the said direction, the fluororesin film has region A on at least one side surface,

[0059] ​​​​​​​​​​The region A has a rectangular shape with dimensions of 8.3 μm × 6.2 μm, and the number of the first rope-like bodies extending from one long side of the rectangle to the other long side is 1 or more and 5 or less.

[0060] In a second aspect of the present invention, for example, according to the fluororesin film of the first aspect, wherein the network structure further includes a second rope-like body of the fluororesin, and when observed from a direction perpendicular to the main surface of the fluororesin film, the second rope-like body has a diameter of less than 200 nm.

[0061] In a third aspect of the present invention, for example, according to the fluororesin film of the first or second aspect, wherein a ring structure formed by the first rope-like bodies is observed in the region A.

[0062] In a fourth aspect of the present invention, for example, according to the fluororesin film of the third aspect, wherein the network structure further includes a second rope-like body of the fluororesin, and when observed from a direction perpendicular to the main surface of the fluororesin film, the second rope-like body has a diameter of less than 200 nm, and when observed from this direction, the number of the second rope-like bodies observed inside the largest ring structure present in the region A is 6 or more.

[0063] In a fifth aspect of the present invention, for example, according to the fluororesin film of the fourth aspect, wherein the number of the second rope-like bodies is 17 or less.

[0064] In a sixth aspect of the present invention, for example, according to the fluororesin film of any one of the first to fifth aspects, wherein the proportion of the area occupied by the rope-like bodies of the fluororesin in the region A is 60% or less.

[0065] In a seventh aspect of the present invention, for example, according to the fluororesin film of any one of the first to sixth aspects, wherein the Gurley air permeability of the fluororesin film per 1 μm thickness is 5 seconds / 100 mL / μm or less.

[0066] In an eighth aspect of the present invention, for example, the ultimate hydrostatic pressure resistance of the fluororesin film of any one of the first to seventh aspects is 1.6 MPa or more.

[0067] In a ninth aspect of the present invention, for example, the fluororesin film of any one of the first to eighth aspects has a water retention resistance capable of withstanding a water pressure retention test in which a circular water pressure application surface with a set diameter of 1 mm is exposed to a water pressure of 1.0 MPa for 30 minutes.

[0068] In a tenth aspect of the present invention, for example, according to the fluororesin film of any one of the first to ninth aspects, wherein the fluororesin is polytetrafluoroethylene.

[0069] The film according to the 11th aspect of the present invention is a fluororesin film having a network structure of fluororesin,

[0070] wherein the network structure includes a first cord-like body and a second cord-like body of the fluororesin,

[0071] When observed from a direction perpendicular to the main surface of the fluororesin film, the first cord-like body has a diameter of 200 nm or more and 750 nm or less, and the second cord-like body has a diameter of less than 200 nm,

[0072] When observed from the above direction, the fluororesin film has a region B on at least one side,

[0073] The region B has a rectangular shape with a size of 8.3 μm × 6.2 μm, and an annular structure formed by the first cord-like body is observed,

[0074] When observed from the above direction, the number of the second cord-like bodies observed inside the largest annular structure existing in the region B is 6 or more.

[0075] The film according to the 12th aspect of the present invention is a fluororesin film having a network structure of fluororesin, and the Gurley air permeability of the fluororesin film per 1 μm thickness is 5 seconds / 100 mL / μm or less, and the ultimate water pressure resistance of the fluororesin film is 1.6 MPa or more.

[0076] The film according to the 13th aspect of the present invention is a fluororesin film having a network structure of fluororesin,

[0077] The Gurley air permeability of the fluororesin film per 1 μm thickness is 5 seconds / 100 mL / μm or less,

[0078] The fluororesin film has a water pressure retention resistance capable of withstanding a water pressure retention test in which water pressure is applied to a circular water pressure application surface with a set diameter of 1 mm at a water pressure of 1.0 MPa for 30 minutes.

[0079] The fluororesin film member according to the 14th aspect of the present invention includes the fluororesin film according to any one of the 1st to 13th aspects, and includes a support layer and / or an adhesive layer.

[0080] The electronic device according to the 15th aspect of the present invention includes:

[0081] a housing having an opening; and

[0082] a waterproof film mounted on the housing so as to cover the opening,

[0083] The waterproof film includes the fluororesin film according to any one of the 1st to 13th aspects.

[0084] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the following embodiments.

[0085] [Fluororesin film]

[0086] (First Embodiment)

[0087] An example of the fluororesin film of this embodiment is shown in Figure 1 . Figure 1 A partial enlarged view of the surface of the fluororesin film 1 (1A) is also shown in. The fluororesin film 1A has a network structure 11 of fluororesin. The network structure 11 includes rope-like bodies 12 of fluororesin. The network structure 11 has voids 13 between the rope-like bodies 12, and air permeability in the thickness direction of the fluororesin film 1 is mainly ensured by the voids 13. Figure 1 The network structure 11 of includes a first rope-like body 12A having a diameter of 200 nm or more and 750 nm or less when observed from a direction perpendicular to the main surface of the fluororesin film 1 (hereinafter referred to as the vertical direction) and a second rope-like body 12B having a diameter of less than 200 nm when observed from the vertical direction as the rope-like body 12.

[0088] In this specification, the rope-like body 12 is classified according to its diameter. The rope-like body 12 having a diameter of 200 nm or more and 750 nm or less when observed from the vertical direction is the first rope-like body 12A. The rope-like body 12 having a diameter of less than 200 nm when observed from the vertical direction is the second rope-like body 12B. The rope-like body 12 having a diameter of more than 750 nm when observed from the vertical direction is the third rope-like body. However, the diameter of the rope-like body 12 may vary in the length direction. When there is a point where the diameter change exceeds the boundary values of 200 nm and / or 750 nm along the length direction of a certain rope-like body 12, for each of the intervals before and after the change in the rope-like body 12, it is determined to belong to the first, second, or third rope-like body based on their respective diameters. For example, when the rope-like body 12 has a first interval with a diameter of 200 nm or more and 750 nm or less and a second interval with a diameter of less than 200 nm, the first interval is the first rope-like body 12A, and the second interval is the second rope-like body 12B. The lower limit of the diameter of the second rope-like body 12B is, for example, 20 nm or more. The upper limit of the diameter of the third rope-like body is, for example, 4500 nm or less.

[0089] The diameter of the rope-like body 12 can be obtained from a magnified observation image of the fluororesin film 1 of the rope-like body 12 that can be confirmed from the vertical direction. Image analysis using image analysis software such as ImageJ can also be used. When evaluating the diameter of the rope-like body 12, regarding the histogram of brightness, it is preferable to maximize the gray level between the darkest point and the brightest point in the magnified observation image within the range of gray levels used for analysis. The magnified observation image is, for example, an observation image based on a scanning electron microscope (SEM). The magnification is, for example, 5000 to 25000 times, preferably 10000 to 20000 times, and more preferably 15000 times. The acceleration voltage is usually 1 kV. If the acceleration voltage is determined, the depth of the magnified observation image (the range of the depth from the film surface that can be observed in this image) is determined. The magnified observation image obtained by this method can also be used for the determination of the following number A and number B.

[0090] When observed from the vertical direction, the fluororesin film 1A includes a region A having the following characteristics (1) and (2).

[0091] (1) It has a rectangular shape with dimensions of 8.3 μm × 6.2 μm.

[0092] (2) The number of the first rope-like bodies 12A (hereinafter, this number is referred to as number A) observed to extend from one long side of the rectangle to the other long side is 1 or more and 5 or less.

[0093] Number A can be 2 or more, can be 4 or less, and can also be 1 or more and 3 or less. When number A is within the above range, it can help suppress the sacrifice of the air permeability of the fluororesin film 1 and improve the waterproof performance. Figure 2 This shows an example of the region A. Figure 2 Only the first rope-like body 12A among the rope-like bodies 12 observed in the region A is shown. Figure 2 Number A in the region A of is 2 corresponding to the two first rope-like bodies 12Aa and 12Ab. After the first rope-like body 12Ac extends from the long side 51A, it disappears at its end 17, or does not extend to the long side 51B because its diameter deviates from the range of 200 nm or more and 750 nm or less, etc. Therefore, it is excluded from the calculation of number A. In addition, the first rope-like body 12Ad does not extend from the long side 51A and is also excluded from the calculation of number A.

[0094] A more specific description of the method for calculating number A is given. In principle, the number of the first rope-like bodies 12A that are connected to one long side 51A of the region A and reach the other long side 51B along their length directions is calculated. Among them, the first rope-like body 12A can have branches. Refer to Figures 3A to 3D The case where the first rope-like body 12A has branches is described. In Figures 3A to 3DAmong them, the first string-like body 12A is represented by the center line in the width direction. Among two or more first string-like bodies 12A branched at the branch point 14, the first string-like body 12Af that does not reach the other long side 51B is excluded from the calculation of the number A (see Figure 3A ). In the example of Figure 3A , one first string-like body 12Ae reaches the other long side 51B. Therefore, the number A calculated in the example of Figure 3A is 1. Next, among two or more first string-like bodies 12A branched at the branch point 14, when multiple first string-like bodies 12Ag and 12Ah reach the long side 51B, only the first string-like body 12Ag with the smallest angle θ formed between the straight line 52 passing through the branch point 14 and perpendicular to the long sides 51A and 51B is traced (see Figure 3B ). In other words, the first string-like body 12Ah with a non-minimum angle θ is excluded from the calculation of the number A (see Figure 3B ). The number A calculated in the example of Figure 3B is 1. It should be noted that when multiple first string-like bodies 12A with the smallest and equal angles θ are observed, 1 before branching is calculated as the number A. This rule is consistent with the confluence rule illustrated by Figure 3C . Next, when two or more first string-like bodies 12Ai and 12Aj extending from the long side 51A merge into one first string-like body 12A and reach the long side 51B, the number of the first string-like bodies 12A that reach is calculated as 1 (see Figure 3C ). Figure 3D shows another example. According to the above rules, the number A calculated in the example of Figure 3D is 1.

[0095] In region A, it may also be observed that there is no first string-like body 12A extending from one short side 53A of the rectangle to the other short side 53B.

[0096] The extending directions of the long sides 51A and 51B and the short sides 53A and 53B of region A may be the MD direction and the TD direction of the fluororesin film 1, respectively. The MD direction and the TD direction of the fluororesin film 1 are, for example, the longitudinal stretching direction and the transverse stretching direction during the manufacture of the fluororesin film 1, respectively.

[0097] In region A, a ring structure formed by the first string-like body 12A may also be observed. In Figure 2In the illustrated region A, a ring structure 16 formed by the first string-like body 12Ab is observed. The observed ring structure 16 is formed by the first string-like bodies 15A and 15B, which branch at the branch point 14A and merge at the branch point 14B when tracing the first string-like body 12Ab in the direction from the long side 51A to the long side 51B. The fluororesin film 1 in which the ring structure 16 is observed in the region A is particularly suitable for improving the waterproof performance while sacrificing the air permeability. In the ring structure 16, there may also be branches of the first string-like body 12A, the second string-like body 12B, or the third string-like body extending to the outside or inside of the ring structure 16. However, there is no section formed by the second string-like body 12B or the third string-like body in the ring structure 16 itself. The ring structure 16 typically may have a bent portion at the branch point of the first string-like body 12A. It is necessary to observe the entire circumference of the ring structure 16 within the region A. A plurality of ring structures 16 may be observed in the region A, and in this case, adjacent ring structures 16 may share a part of the edge. Other ring structures 16 with a smaller area may also be observed inside the ring structure 16.

[0098] The area of the ring structure 16 observed from the vertical direction is, for example, 0.3 to 20 μm 2 . The lower limit of the area may be 0.5 μm 2 or more, 1 μm 2 or more, 1.5 μm 2 or more, 2 μm or more, and further 2.5 μm 2 or more. The upper limit of the area may be 15 μm 2 or less, 13 μm 2 or less, 10 μm 2 or less, 8 μm 2 or less, and further 5 μm 2 or less. The area of the ring structure 16 can be determined as the area of the region surrounded by the inner circumference of the ring structure 16. In the determination of the area, image analysis of the magnified observation image can be used.

[0099] As Figure 1As shown, the network structure 11 may include a second cord-like body 12B made of a fluororesin. In this case, when viewed from the vertical direction, the number of second cord-like bodies 12B (hereinafter referred to as number B) observed inside the largest annular structure 16 existing in region A may be 6 or more, and may also be 7 or more, 8 or more, 9 or more, and further 10 or more. The upper limit of number B is, for example, 30 or less, and may be 27 or less, 25 or less, 24 or less, 23 or less, 22 or less, 21 or less, 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, and further 15 or less. Number B may be 6 or more and 20 or less, 8 or more and 17 or less, and further 10 or more and 15 or less. The fluororesin film 1 in which number B is within the above range is particularly suitable for suppressing the sacrifice of gas permeability and improving water resistance.

[0100] A method for calculating the number B of the second cord-like bodies 12B observed inside the annular structure 16 will be described. In principle, for each second cord-like body 12B observed from the vertical direction and extending from the edge of the annular structure 16 into the annular structure 16, the interval up to the point where it merges, crosses, or branches with other cord-like bodies 12 is counted as 1, and the sum of the counted numbers is taken as number B. The other cord-like bodies 12 may be any one of the first cord-like body 12A, the second cord-like body 12B, and the third cord-like body. For example, Figures 4A to 4G The numbers B in the examples shown are 7, 6, 4, 6, 6, 4, and 7 respectively. It should be noted that, Figures 4A to 4G and Figure 4H only show the annular structure 16 and the second cord-like body 12B. In addition, in Figures 4A to 4G and Figure 4H the interval of the second cord-like body 12B from the edge of the annular structure 16 to the above point is indicated by a thick line. The number of intervals indicated by the thick line corresponds to number B. Among them, when the first cord-like body 12A that branches from the edge of the annular structure 16 and extends into the annular structure 16 is observed, the second cord-like body 12B observed in such a way as to extend from the first cord-like body 12A extending into the interior to the interior of the annular structure 16 is also considered when calculating number B. For example, Figure 4H the number B in the example of

[0101] In region A, the third string-like body may also not be observable. The third string-like body is a third string-like body of fluororesin having a diameter exceeding 750 nm when observed from the vertical direction and extends from one long side of region A to the other long side. In region A, the third string-like body may also not be observable. The third string-like body is a third string-like body of fluororesin having a diameter exceeding 750 nm when observed from the vertical direction and a length exceeding 1000 nm. Further, the network structure 11 may also not include the third string-like body. The third string-like body is a third string-like body of fluororesin having a diameter exceeding 750 nm when observed from the vertical direction and a length exceeding 1000 nm. These embodiments are particularly suitable for improving the waterproof performance while suppressing the sacrifice of air permeability. It should be noted that when observing the string-like body from the vertical direction, the length of the string-like body can be obtained by tracing the center in the width direction along the length direction.

[0102] The proportion of the area occupied by the string-like body 12 of fluororesin in region A is, for example, 60% or less, and can be 59% or less, 58% or less, 57% or less, 56% or less, 55% or less, 54% or less, 53% or less, 52% or less, 51% or less, 50% or less, and further 49% or less. The lower limit of the proportion of the area is, for example, 40% or more. The fluororesin film 1 with the proportion of the area within the above range is particularly suitable for improving the waterproof performance while suppressing the sacrifice of air permeability. The proportion of the area occupied by the string-like body 12 of fluororesin in region A can be evaluated by performing image processing including binarization on the magnified observation image. The binarization can be performed in such a way that the string-like body 12 and the void 13 can be distinguished.

[0103] In region A, fibrils formed by fibrillation of fluororesin may not be observable. Further, the network structure 11 may also not include the above-mentioned fibrils. The difference between the fibrils and the string-like body 12 is at least that the fibrils can have unique crystals generated by fibrillation. As an example, a typical PTFE porous membrane having a so-called node / fibril structure shows an endothermic peak peculiar to the above-mentioned crystals at 360 to 385 °C in differential scanning calorimetry (DSC) (refer to Japanese Patent Laid-Open No. 2021-54892). In other words, the fluororesin film 1 in which the fluororesin is PTFE may not have an endothermic peak at 360 to 385 °C in the DSC chart. The specific DSC measurement method can be referred to the above-mentioned publication. It should be noted that a typical PTFE porous membrane is formed by extruding a mixture of uncalcined PTFE molding powder and a liquid lubricant into a sheet, removing the liquid lubricant from the obtained uncalcined PTFE sheet, and then stretching it.

[0104] The fluororesin film 1 has region A on at least one side. The fluororesin film 1 may also have region A on both sides.

[0105] The thickness of the fluororesin film 1 is, for example, 5 to 100 μm. The upper limit of the thickness can be 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, and further 20 μm or less. The lower limit of the thickness can be 7 μm or more, 10 μm or more, 12 μm or more, 13 μm or more, 15 μm or more, 17 μm or more, 20 μm or more, 22 μm or more, 25 μm or more, 27 μm or more, and further 30 μm or more. The thickness can be 25 μm or more and 40 μm or less, 30 μm or more and 35 μm or less, 31 μm or more and 34 μm or less, 32 μm or more and 34 μm or less, and further 33 μm or more and 34 μm or less.

[0106] Regarding the fluororesin film 1, the number A can be 1 or more and 3 or less, the number B can be 10 or more and 15 or less, and the thickness can be 33 μm or more and 34 μm or less.

[0107] The Gurley air permeability in the thickness direction of the fluororesin film 1 is, for example, 150 seconds / 100 mL or less, and can be 120 seconds / 100 mL or less, 100 seconds / 100 mL or less, 95 seconds / 100 mL or less, 90 seconds / 100 mL or less, 85 seconds / 100 mL or less, 80 seconds / 100 mL or less, 75 seconds / 100 mL or less, 70 seconds / 100 mL or less, 65 seconds / 100 mL or less, 60 seconds / 100 mL or less, 55 seconds / 100 mL or less, 50 seconds / 100 mL or less, 45 seconds / 100 mL or less, and further 40 seconds / 100 mL or less. The lower limit of the Gurley air permeability is, for example, 10 seconds / 100 mL or more, and can be 20 seconds / 100 mL or more, 30 seconds / 100 mL or more, 35 seconds / 100 mL or more, 40 seconds / 100 mL or more, 45 seconds / 100 mL or more, 50 seconds / 100 mL or more, 55 seconds / 100 mL or more, 60 seconds / 100 mL or more, 65 seconds / 100 mL or more, 70 seconds / 100 mL or more, 75 seconds / 100 mL or more, and further 80 seconds / 100 mL or more. In this specification, the "Gurley air permeability" refers to the air permeability determined by the air permeability measurement B method (Gurley method) specified in Japanese Industrial Standard (hereinafter referred to as JIS) L1096:2010.

[0108] It should be noted that when the size of the fluororesin film 1 is smaller than the size of the test piece in the Gurley method (about 50 mm × 50 mm), the Gurley air permeability can also be evaluated by using a measuring jig. An example of the measuring jig is a polycarbonate circular plate with a thickness of 2 mm and a diameter of 47 mm, which has a through-hole (with a circular cross-section having a diameter of 1 mm or 2 mm) in the center. The measurement of the Gurley air permeability using this measuring jig can be carried out as follows.

[0109] The fluororesin film 1 to be evaluated is fixed to one surface of the measuring jig so as to cover the opening of the through-hole of the measuring jig. The fixing is carried out in the following manner: in the measurement of the Gurley air permeability, air only passes through the effective test portion of the fluororesin film 1 as the opening and the object of evaluation (the portion overlapping the opening when viewed from a direction perpendicular to the main surface of the fixed fluororesin film 1), and the fixed portion does not hinder the passage of air through the effective test portion of the fluororesin film 1. In the fixing of the fluororesin film 1, a double-sided adhesive tape can be used, and the double-sided adhesive tape is punched out with a vent hole having a shape consistent with the shape of the opening at the center. The double-sided adhesive tape can be arranged between the measuring jig and the fluororesin film 1 such that the edge of the vent hole coincides with the edge of the opening. Then, the measuring jig with the fluororesin film 1 fixed is set in the Gurley-type air permeability tester in such a manner that the fixed surface of the fluororesin film 1 becomes the downstream side of the air flow during measurement, and the time t1 for 100 mL of air to pass through the fluororesin film 1 is measured. Then, the measured time t1 is converted into the value t specified in Method B (Gurley method) for the measurement of air permeability in JIS L1096:2010 per effective test area of 642 [mm 2 ) / 642 [mm 2} according to the formula t = {(t1) × (the area of the effective test portion of the fluororesin film 1 [mm 2 ), and the obtained converted value t can be used as the Gurley air permeability of the fluororesin film 1. When the above-mentioned circular plate is used as the measuring jig, the area of the effective test portion of the fluororesin film 1 is the cross-sectional area of the through-hole. It should be noted that it has been confirmed that for the fluororesin film 1 that satisfies the size of the above-mentioned test piece, the Gurley air permeability measured without using the measuring jig is in good agreement with the Gurley air permeability measured using the measuring jig after the fluororesin film 1 is fragmented, that is, the use of the measuring jig does not substantially affect the measured value of the Gurley air permeability.

[0110] Regarding the fluororesin film 1, the Gurley air permeability per 1 μm thickness (unit: seconds / 100 mL / μm) is, for example, 5 or less, and can be 4.5 or less, 4 or less, 3.5 or less, 3.3 or less, 3.1 or less, 3 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, 2.5 or less, and further 2.4 or less. The lower limit of the Gurley air permeability per 1 μm thickness is, for example, 2 or more.

[0111] Regarding the fluororesin film 1, the ultimate hydrostatic pressure resistance, which is one of the indicators of waterproof performance, is, for example, 1.5 MPa or more, and can be 1.6 MPa or more, 1.7 MPa or more, 1.8 MPa or more, 1.9 MPa or more, and further 2 MPa or more. The upper limit of the ultimate hydrostatic pressure resistance is, for example, 4 MPa or less. The ultimate hydrostatic pressure resistance can be measured as follows using a measuring jig in accordance with Test Method B (High Hydrostatic Pressure Method) of Water Resistance of JIS L1092:2009. An example of the measuring jig is a stainless steel circular plate with a diameter of 47 mm having a through hole with a diameter of 1 mm (with a circular cross section) in the center. The circular plate has a thickness that does not deform due to the water pressure applied during the measurement of the ultimate hydrostatic pressure resistance. The measurement of the ultimate hydrostatic pressure resistance using this measuring jig can be carried out as follows.

[0112] The fluororesin film 1 to be evaluated is fixed to one surface of the measuring jig so as to cover the opening of the through hole of the measuring jig. The fixing is performed in such a way that water does not leak from the fixing part of the film during the measurement of the hydrostatic pressure resistance. In the fixing of the fluororesin film 1, a double-sided adhesive tape with a water passage punched out in the center can be used. The double-sided adhesive tape may be arranged between the measuring jig and the fluororesin film 1 so that, when viewed from the vertical direction, the part of the double-sided adhesive tape other than the water passage does not overlap with the inside of the above opening of the measuring jig. Next, the measuring jig with the fluororesin film 1 fixed is set in the test device with the fixed surface of the fluororesin film 1 being the water pressure application surface during the measurement, and the hydrostatic pressure resistance is measured in accordance with Test Method B (High Hydrostatic Pressure Method) of Water Resistance of JIS L1092:2009. Among them, the hydrostatic pressure resistance is measured based on the water pressure when water comes out from one place on the film surface of the fluororesin film 1. The measured hydrostatic pressure resistance can be used as the ultimate hydrostatic pressure resistance of the fluororesin film 1. As the test device, a device having the same structure as the water resistance test device exemplified in JIS L1092:2009 and having a test piece mounting structure capable of setting the above measuring jig can be used.

[0113] Regarding the fluororesin film 1, as other indicators of waterproof performance, it has water resistance retention. The ability to retain water resistance under a specified water pressure and water pressure application time can be evaluated by the fact that even when the specified water pressure is continuously applied to the fluororesin film 1 for a specified time, the fluororesin film 1 does not rupture or leak. The water pressure retention test is the same as the ultimate water pressure resistance, and it can be carried out using the measuring jig and the water resistance test device exemplified in JIS L1092:2009. The water pressure application surface is the fixing surface of the fluororesin film 1 in the measuring jig. The diameter of the through-hole of the measuring jig is 1 mm or 0.2 mm. The diameter of the through-hole being X mm means that a circular water pressure application surface with a diameter of X mm is set for the fluororesin film 1 in the water pressure retention test. It should be noted that according to the research of the present inventors, in order to ensure water resistance retention, a film structure with particularly good balance may be required. For example, even for films with the same ultimate water pressure resistance, the water resistance retention may be very different. The number A and / or the number B can contribute to achieving a well-balanced film structure.

[0114] The fluororesin film 1 may have water resistance retention that can withstand a water pressure retention test in which it is exposed to a water pressure of 1.0 MPa for 30 minutes when a circular water pressure application surface with a diameter of 1 mm is set. The fluororesin film 1 may have water resistance retention that can withstand a water pressure retention test in which it is exposed to a water pressure of 1.25 MPa for 30 minutes when a circular water pressure application surface with a diameter of 1 mm is set. The fluororesin film 1 may have water resistance retention that can withstand a water pressure retention test in which it is exposed to a water pressure of 1.5 MPa for 30 minutes when a circular water pressure application surface with a diameter of 0.2 mm is set.

[0115] The fluororesin film 1 may simultaneously have: a Gurley air permeability of each 1 μm thickness within the above range including the preferred range, and an ultimate water pressure resistance and / or water resistance retention within the above range including the preferred range.

[0116] The weight per unit area of the fluororesin film 1 is, for example, 5 to 40 g / m 2 . The upper limit of the weight per unit area may be 35 g / m 2 Hereinafter, 32 g / m 2 Hereinafter, 30 g / m 2 Hereinafter, 27 g / m 2 Hereinafter, 25 g / m 2 Hereinafter, 22 g / m 2 Hereinafter, 20 g / m 2 Hereinafter, and further 18 g / m 2 Hereinafter. The lower limit of the areal density may be 8 g / m 2 or more, 10 g / m 2 or more, 13 g / m 2 or more, 15 g / m 2 or more, 18 g / m2 Above, 20g / m 2 Above, 23g / m 2 Above, 25g / m 2 Above, 28g / m 2 Above, further 30g / m 2 The weight per unit area can be calculated by dividing the mass of the fluororesin film 1 by the area (the area of ​​the main surface).

[0117] The fluororesin film 1 may be a single-layer film or a laminate of two or more films.

[0118] The fluororesin film 1 may be a colored film. The fluororesin film 1 may be colored, for example, in gray or black. The gray or black fluororesin film 1 may be formed, for example, by mixing a gray or black colorant in a material forming the film. An example of a black colorant is carbon black. It should be noted that a color in the range of 1 to 4 represented by the "achromatic brightness NV" specified in JIS Z8721:1993 may be defined as "black", and a color in the range of 5 to 8 may be defined as "gray".

[0119] The fluororesin film 1 may be subjected to a water repellent treatment, an oil repellent treatment, or a liquid repellent treatment. The liquid repellent treatment is a treatment for imparting both water repellency and oil repellency to the fluororesin film 1.

[0120] When viewed from the vertical direction, the shape of the fluororesin film 1 is, for example, a polygon including a circle, an ellipse, a square, and a rectangle, and a strip. The corners of the polygon may be rounded. However, the shape of the fluororesin film 1 is not limited to the above examples.

[0121] The fluororesin film 1 may be circulated in a shape for actual use or in a wound body of a strip-shaped film. When circulated in a shape for actual use, it may be circulated in the form of a single sheet having one or more fluororesin films 1 having the shape disposed on a base film. The surface of the base film on which the fluororesin film 1 is disposed may also be an adhesive surface. The adhesiveness of the disposed surface may be weak adhesiveness or slight adhesiveness. The fluororesin film 1 as a wound body may be punched into a predetermined shape for use, for example.

[0122] The fluororesin contained in the fluororesin film 1, more specifically the fluororesin that can form the mesh structure 11, is, for example, polytetrafluoroethylene (hereinafter referred to as PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), perfluoroalkoxyalkane (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP). The fluororesin is preferably PTFE. The fluororesin film 1 containing PTFE has a particularly good balance between mass and strength, and has particularly excellent heat resistance. In addition, the fluororesin film 1 containing PTFE is particularly suitable for heat treatment in a state where it is installed in the housing of an electronic device, such as a reflow process.

[0123] The fluororesin film 1 may or may not contain materials other than the fluororesin. The fluororesin film 1 may or may not contain materials other than the fluororesin that form the network structure 11. In the case of not containing other materials, the fluororesin film 1 may have high insulation properties derived from the fluororesin. In other words, the fluororesin film 1 may be an insulating film. The insulating film can be confirmed, for example, by having a surface resistivity of 1×10 14 Ω / □ or more.

[0124] (Second Embodiment)

[0125] The fluororesin film 1 of the present invention can also be represented by the number B of the second string-like body 12B observed inside the ring structure 16. The fluororesin film 1 (1B) with the number B of 6 or more can be suitable for improving the waterproof performance while suppressing the sacrifice of the gas permeability.

[0126] From this aspect, the fluororesin film of the second embodiment is as follows:

[0127] A fluororesin film, which is a fluororesin film having a network structure of fluororesin,

[0128] wherein the network structure includes a first string-like body and a second string-like body of fluororesin,

[0129] When observed from the vertical direction, the first string-like body has a diameter of 200 nm or more and 750 nm or less, and the second string-like body has a diameter of less than 200 nm.

[0130] When observed from the vertical direction, the fluororesin film has a region B on at least one side,

[0131] The region B has a rectangular shape with a size of 8.3 μm × 6.2 μm, and a ring structure formed by the first string-like body is observed.

[0132] When observed from the vertical direction, the number of the second string-like bodies observed inside the largest ring structure existing in the region B is 6 or more.

[0133] Figure 5 An example of the fluororesin film 1B of the second embodiment is shown. For the first string-like body 12A and the second string-like body 12B, the fluororesin film 1B of the second embodiment may include the number B and / or the number A described in the description of the first embodiment within the preferred range. In addition, the fluororesin film 1B may include the characteristics and / or the film structure of the fluororesin film 1 described in the description of the first embodiment within the preferred range and manner.

[0134] (Third Embodiment)

[0135] The fluororesin film 1 of the present invention can simultaneously have high gas permeability and waterproof performance. From this aspect, the fluororesin film 1 of the third embodiment is a fluororesin film having a network structure of fluororesin, and is a fluororesin film with a Gurley air permeability of 5 seconds / 100 mL / μm or less per 1 μm thickness and an ultimate hydrostatic pressure resistance of 1.6 MPa or more. The fluororesin film 1 of the third embodiment may contain the number A and / or the number B described in the description of the first embodiment within a preferred range. In addition, the fluororesin film 1 of the third embodiment may have the characteristics and / or the film structure of the fluororesin film 1 described in the description of the first embodiment within a preferred range and manner.

[0136] (Fourth Embodiment)

[0137] The fluororesin film 1 of the present invention can simultaneously have high gas permeability and waterproof performance. From this aspect, the fluororesin film 1 of the fourth embodiment is: a fluororesin film having a network structure of fluororesin, with a Gurley air permeability of 5 seconds / 100 mL / μm or less per 1 μm thickness, and having a water retention resistance capable of withstanding a water pressure retention test in which it is exposed to a water pressure of 1.0 MPa for 30 minutes when a circular water pressure application surface with a set diameter of 1 mm is used. The water retention resistance of the fluororesin film 1 of the fourth embodiment may be a water retention resistance capable of withstanding a water pressure retention test in which it is exposed to a water pressure of 1.25 MPa for 30 minutes when a circular water pressure application surface with a set diameter of 1 mm is used. The water retention resistance of the fluororesin film 1 of the fourth embodiment may be a water retention resistance capable of withstanding a water pressure retention test in which it is exposed to a water pressure of 1.5 MPa for 30 minutes when a circular water pressure application surface with a set diameter of 0.2 mm is used.

[0138] The fluororesin film 1 of the fourth embodiment may contain the number A and / or the number B described in the description of the first embodiment within a preferred range. In addition, the fluororesin film 1 of the fourth embodiment may have the characteristics and / or the film structure of the fluororesin film 1 described in the description of the first embodiment within a preferred range and manner.

[0139] (Manufacturing Method)

[0140] Regarding the manufacturing method of the fluororesin film 1, the case where the fluororesin film 1 is a PTFE film will be described as an example.

[0141] A coating film is formed by coating a dispersion of PTFE powder (PTFE dispersion) on a substrate. The substrate can be formed of a heat-resistant material such as a heat-resistant resin, metal, or ceramic. Examples of the heat-resistant resin are polyimide and polyether ether ketone. The formation of the coating film can be carried out by methods such as dipping the substrate in the dispersion and lifting it, spraying the dispersion on the substrate, or brushing the dispersion on the substrate. In order to improve the wettability of the substrate surface, surfactants such as silicone-based surfactants and fluorine-based surfactants can be contained in the dispersion.

[0142] Next, the coating film is heated to remove the dispersion medium and bond the PTFE particles to each other. By heating, a PTFE sheet is formed on the substrate. The heating can be a two-stage heating in which the coating film is initially heated at 90 to 150 °C and then at 350 to 400 °C. The removal of the dispersion medium can be carried out by the heating in the first stage, and the baking of PTFE can be carried out by the heating in the second stage. It should be noted that the baking of PTFE means heating PTFE at a temperature above the melting point. The heating can also be a one-stage heating in which the coating film is initially heated at a temperature above the melting point of PTFE. In addition, the thickness of the PTFE sheet can be adjusted by repeatedly performing the process of coating the dispersion on the substrate to form a coating film and the process of heating the coating film. The thickness of the formed PTFE sheet is, for example, 20 to 100 μm, and can be 25 to 80 μm, 30 to 70 μm.

[0143] Next, a process of stretching the PTFE sheet peeled from the substrate in the MD direction (length direction) and a process of stretching it in the TD direction (width direction) are sequentially carried out. The stretching in the MD direction in the first stage (longitudinal stretching) is preferably carried out in such a way as not to hinder the shrinkage in the width direction of the PTFE sheet during stretching. The stretching in the MD direction can be carried out, for example, using a roll-type longitudinal stretching device. For the stretching in the MD direction, the stretching ratio and the stretching temperature are, for example, 1.5 to 6.0 times and 150 to 380 °C, respectively. The stretching in the TD direction in the second stage (transverse stretching) can be carried out, for example, using a tenter stretching machine. For the stretching in the TD direction, the stretching ratio and the stretching temperature are, for example, 2.0 to 6.0 times and 200 to 380 °C, respectively. Usually, calendering of the PTFE sheet peeled from the substrate is not carried out. Thus, the fluororesin film 1 can be manufactured.

[0144] [Fluororesin film member]

[0145] An example of the fluororesin film member of the present invention is shown in Figure 6 . Figure 6The fluororesin film member 21 (21A) includes a fluororesin film 1 and a support layer 22 disposed on the fluororesin film 1. The support layer 22 has the same shape as the fluororesin film 1 when viewed from the vertical direction. Among them, the shape of the support layer 22 is not limited to the above example. The support layer 22 may have the shape of the peripheral portion of the fluororesin film 1, such as a ring shape or a frame shape.

[0146] Examples of the support layer 22 are woven fabrics, non-woven fabrics, meshes, nets, sponges, foams, and porous bodies formed of metals, resins, or composites thereof. Examples of the resin are polyolefins, polyesters, polyamides, polyimides, aromatic polyamides, fluororesins, and ultra-high molecular weight polyethylene. The support layer 22 can also be joined to the fluororesin film 1 by thermal lamination, heat welding, ultrasonic welding, etc.

[0147] The support layer 22 generally has air permeability in the thickness direction. The air permeability of the support layer is generally higher than that of the fluororesin film 1.

[0148] The shapes of the fluororesin film member 21A, the fluororesin film 1, and the support layer 22 are, for example, a circle, an ellipse, a polygon including a square and a rectangle, and a strip shape when viewed from the vertical direction. Among them, these shapes are not limited to the above examples.

[0149] Another example of the fluororesin film member of the present invention is shown in Figure 7A . Figure 7A The fluororesin film member 21 (21B) includes a fluororesin film 1 and an adhesive layer 23 disposed on the fluororesin film 1. When viewed from the vertical direction, the shape of the adhesive layer 23 is the shape of the peripheral portion of the fluororesin film 1. Among them, the shape of the adhesive layer 23 is not limited to the above example. It should be noted that when the adhesive layer 23 does not have air permeability in the thickness direction, the area inside the adhesive layer 23 (the area where the adhesive layer 23 is not provided) becomes the main air-permeable area in the fluororesin film member 21.

[0150] The adhesive layer 23 is formed of, for example, a double-sided adhesive tape. The double-sided adhesive tape can be an adhesive tape with a substrate or an adhesive tape without a substrate. Examples of the materials that can form the substrate are the same as the examples of the materials that can form the support layer 22. The adhesive layer of the double-sided adhesive tape can use well-known adhesives such as acrylic, silicone, and epoxy adhesives. The adhesive can be thermosetting.

[0151] Another example of the fluororesin film member of the present invention is shown in Figure 7B . Figure 7B The fluororesin film member 21 (21C) includes a fluororesin film 1 and a pair of adhesive layers 23A and 23B disposed on the fluororesin film 1 so as to sandwich the fluororesin film 1.

[0152] In the fluororesin film member 21, the fluororesin film 1 can be in direct contact with the support layer 21 and the adhesive layer 23, or other layers can be disposed therebetween.

[0153] The fluororesin film member 21 can be circulated in the shape for actual use, or can be circulated as a wound body of a strip-shaped member. When circulated in the shape for actual use, it can be circulated in the form of a single sheet having one or more fluororesin film members 21 of the shape disposed on the base film. In the joining with the base film, the adhesive layer 23 can also be used. The surface of the base film on which the fluororesin film member 21 is disposed can also be a surface having adhesiveness. The adhesiveness of the disposed surface can be weak adhesiveness or micro adhesiveness. The fluororesin film member 21 as a wound body can be used, for example, after being blanked into a specified shape.

[0154] One surface of the fluororesin film 1 included in the fluororesin film member 21 can be heat-treated. An example of the heat treatment is hot press molding for disposing the support layer 22 and / or the adhesive layer 23 on the fluororesin film 1. It should be noted that in the surface of the fluororesin film 1 where the heat treatment is performed, for example, in the contact surface of the hot press head used in the hot press molding, the network structure 11 sometimes deforms. In other words, in the fluororesin film 1 included in the fluororesin film member 21, the surface opposite to the surface where the heat treatment is performed can have the region A.

[0155] [Electronic device]

[0156] An example of the electronic device of the present invention is shown in Figure 8A . Figure 8A The electronic device 31 includes a housing 32 having an opening 33 and a waterproof film 34 mounted on the housing 32 so as to cover the opening 33. The waterproof film 34 is formed of the fluororesin film 1. In the Figure 8A example, the waterproof film 34 is mounted inside the housing 32. However, the position where the waterproof film 34 is mounted is not limited to the above example. The waterproof film 34 can be mounted on the housing 32 by various known methods such as heat welding, ultrasonic welding, and laser welding. The waterproof film 34 can also be mounted on the housing 32 through an adhesive layer, and the adhesive layer can be the adhesive layer 23 that the fluororesin film member 21 can include (see Figure 8B ). When mounted through the adhesive layer 23, it can be considered that the fluororesin film member 21 is mounted.

[0157] The waterproof film 34 can also include members and / or layers other than the fluororesin film 1.

[0158] The opening 33 is typically a ventilation port or an internal pressure adjustment port of the electronic device 31. The opening 33 can also be a sound transmission port that can transmit sound. However, the opening 33 is not limited to the above examples.

[0159] Examples of the electronic device 31 are portable electronic devices (including wearable terminals) such as smartphones, smart watches, earphones, smart speakers, smart glasses, VR headsets, drones, and action cameras, pressure sensors, barometric pressure sensors, gas sensors, CO 2 sensors, acoustic sensors, etc. in the sensor category, LEDs, lamps with LEDs, etc. in the lamp category. Among them, the electronic device 31 is not limited to the above examples.

[0160] Embodiment

[0161] Hereinafter, the present invention will be described more specifically by way of embodiments. The present invention is not limited to the following embodiments.

[0162] First, a method for evaluating the characteristics of fluororesin films (Sample 1 to Sample 12) is shown.

[0163] [Thickness]

[0164] The thickness is obtained by measuring the thickness of the fluororesin film punched into a circle with a diameter of 47 mm using a micrometer.

[0165] [Weight per unit area]

[0166] The weight per unit area is obtained by measuring the mass of the fluororesin film punched into a circle with a diameter of 47 mm and converting it to the mass per 1 m 2 area of the main surface.

[0167] [Gurley air permeability]

[0168] The Gurley air permeability is evaluated according to the air permeability measurement Method B (Gurley method) specified in JIS L1096:2010.

[0169] [Ultimate hydrostatic pressure resistance]

[0170] The ultimate hydrostatic pressure resistance is evaluated by the above method in accordance with the water resistance test Method B (high hydrostatic pressure method) of JIS L1092. It should be noted that the shape of the water passage in the double-sided adhesive tape used to fix the fluororesin film to the measurement jig is a circle with a diameter of 1.6 mm when observed from a direction perpendicular to the main surface of the double-sided adhesive tape.

[0171] [Retention of water resistance]

[0172] The water resistance retention is evaluated by the above-described water pressure retention test. In the water pressure retention test, the case where the fluororesin film does not rupture or leak is evaluated as good (A), and the case where rupture or leakage occurs is evaluated as unacceptable (D). The water pressure retention test is carried out under three conditions I to III with different diameters of the water pressure application surface (circular), water pressure, and water pressure application time. The respective conditions are shown in Table 1 below. In the order of Condition I, Condition II, and Condition III, the required water resistance retention of the film becomes higher.

[0173] [Table 1]

[0174] Condition Diameter (mm) Water pressure (MPa) Water pressure application time (minutes) I 1 1.0 30 II 1 1.25 30 III 0.2 1.5 30

[0175] [Production of Fluororesin Film]

[0176] (Sample 1)

[0177] In a PTFE dispersion (PTFE powder concentration: 40% by mass, average particle size of PTFE powder: 0.2 μm, containing 6 parts by mass of a nonionic surfactant relative to 100 parts by mass of PTFE), 1 part by mass of a fluorine-based surfactant (manufactured by DIC Corporation, Megafac F-142D) is added relative to 100 parts by mass of PTFE. Then, a long polyimide film (thickness: 125 μm) is immersed in the PTFE dispersion and lifted, and a coating film of the PTFE dispersion is formed on the film. At this time, a metering rod is used to make the thickness of the coating film 20 μm. Then, the coating film is heated at 100 °C for 1 minute, and then heated at 390 °C for 1 minute, thereby evaporating and removing the water contained in the dispersion, and causing the remaining PTFE particles to bond to each other to obtain a PTFE film. After repeating the above immersion and heating many times, the PTFE film is peeled off from the polyimide film to obtain a PTFE sheet (thickness: 55 μm) as a blank.

[0178] Next, the obtained PTFE sheet is stretched in the MD direction using a longitudinal stretching machine. The stretching temperature in the MD direction is 280 °C, and the stretching ratio is 2 times. When stretching in the MD direction, the PTFE sheet is set in a state of being free in the width direction. Then, it is further stretched in the TD direction using a tenter stretching machine to obtain the fluororesin film of Sample 1. The stretching temperature in the TD direction is set to 300 °C, and the stretching ratio is set to 3.4 times.

[0179] (Samples 2 to 8)

[0180] The thickness of the blank as a film-forming condition, the stretching ratio in the MD direction, and the stretching temperature and stretching ratio in the TD direction are changed as shown in Table 2 below. Except for this, the fluororesin films of Samples 2 to 8 are produced in the same manner as Sample 1.

[0181] [Table 2]

[0182]

[0183] (Sample 9)

[0184] A PTFE sheet (thickness 25 μm) as a blank was produced in the same manner as in Sample 1. Subsequently, the produced PTFE sheet was calendered in the MD direction using a roller calender. The calendering temperature was 70°C, and the calendering ratio was 1.8 times. Subsequently, the calendered PTFE sheet was further stretched in the TD direction using a tenter, and a fluororesin film of Sample 9 was obtained. The stretching temperature in the TD direction was set to 300°C, and the stretching ratio was set to 2.2 times.

[0185] (Samples 10 - 12)

[0186] The thickness of the blank as a film-forming condition, the calendering ratio in the MD direction, and the stretching temperature and stretching ratio in the TD direction were changed as shown in Table 3 below. Other than that, fluororesin films of Samples 10 - 12 were produced in the same manner as in Sample 9.

[0187] [Table 3]

[0188]

[0189] The surface of the fluororesin film produced from each sample was observed using FE-SEM, and the following evaluations were performed for a rectangular region of 8.3 μm × 6.2 μm in size:

[0190] (i) The number of first string-like bodies extending from one long side of the region to the other long side

[0191] (ii) Whether a ring structure formed by the first string-like bodies was observed

[0192] (iii) When a ring structure was observed, the number of second string-like bodies observed inside the largest ring structure present in the region

[0193] (iv) Whether a third string-like body with a length of 1000 nm or more was observed.

[0194] JEOL JSM-7500 was used for FE-SEM, and the acceleration voltage was set to 1 kV.

[0195] For each sample, the observation results of the region based on FE-SEM and the evaluation results of the characteristics are shown in Table 4 below. In addition, the magnified observation images of the regions based on FE-SEM of Samples 2 and 10 are shown in Figure 9 、 Figure 10It should be noted that the "number of the first rope-like bodies" in Table 4 is the number based on the above evaluation (i), and the "number of the second rope-like bodies" is the number based on the above evaluation (iii). The conditions for maintaining water resistance are shown in Table 1.

[0196] [Table 4]

[0197]

[0198] ※ The ring structure of (ii) was observed in all samples.

[0199] It was confirmed that Samples 1 to 8 are more suitable for improving the waterproof performance while sacrificing the air permeability performance compared with Samples 9 to 12.

[0200] Industrial applicability

[0201] The fluororesin film of the present invention can be used in various electronic devices such as portable electronic devices, wearable terminals, and various sensors.

Claims

1. A fluororesin film, which is a fluororesin film having a network structure of fluororesin, wherein, the network structure includes a first cord-like body of the fluororesin, when observed from a direction perpendicular to the main surface of the fluororesin film, the first cord-like body has a diameter of 200 nm or more and 750 nm or less, when observed from the above direction, the fluororesin film has at least one surface with a region A, the region A has a rectangular shape with dimensions of 8.3 μm × 6.2 μm, and the number of the first cord-like bodies extending from one long side of the rectangle to the other long side is 1 or more and 5 or less.

2. The fluororesin film according to claim 1, wherein, the network structure further includes a second cord-like body of the fluororesin, and when observed from a direction perpendicular to the main surface of the fluororesin film, the second cord-like body has a diameter less than 200 nm.

3. The fluororesin film according to claim 1, wherein, a ring-like structure formed by the first cord-like body is observed in the region A.

4. The fluororesin film according to claim 3, wherein, the network structure further includes a second cord-like body of the fluororesin, when observed from a direction perpendicular to the main surface of the fluororesin film, the second cord-like body has a diameter less than 200 nm, when observed from the above direction, the number of the second cord-like bodies observed inside the largest ring-like structure existing in the region A is 6 or more.

5. The fluororesin film according to claim 4, wherein, the number of the second cord-like bodies is 17 or less.

6. The fluororesin film according to claim 1, wherein, the proportion of the area occupied by the cord-like bodies of the fluororesin in the region A is 60% or less.

7. The fluororesin film according to claim 1, wherein, the Gurley air permeability of the fluororesin film per 1 μm thickness is 5 seconds / 100 mL / μm or less.

8. The fluororesin film according to claim 1, wherein, the ultimate hydrostatic pressure resistance of the fluororesin film is 1.6 MPa or more.

9. The fluororesin film according to claim 1, wherein, the fluororesin film has a water retention resistance capable of withstanding a water pressure retention test in which a circular water pressure application surface with a set diameter of 1 mm is exposed to a water pressure of 1.0 MPa for 30 minutes.

10. The fluororesin film according to claim 1, wherein, the fluororesin is polytetrafluoroethylene.

11. A fluororesin film, which is a fluororesin film having a network structure of fluororesin, wherein, the network structure includes a first cord-like body and a second cord-like body of the fluororesin, when observed from a direction perpendicular to the main surface of the fluororesin film, the first cord-like body has a diameter of 200 nm or more and 750 nm or less, and the second cord-like body has a diameter less than 200 nm, when observed from the above direction, the fluororesin film has at least one surface with a region B, the region B has a rectangular shape with dimensions of 8.3 μm × 6.2 μm, and a ring-like structure formed by the first cord-like body is observed, when observed from the above direction, the number of the second cord-like bodies observed inside the largest ring-like structure existing in the region B is 6 or more.

12. A fluororesin film, which is a fluororesin film having a network structure of fluororesin, the Gurley air permeability of the fluororesin film per 1 μm thickness is 5 seconds / 100 mL / μm or less, and the ultimate water pressure resistance of the fluororesin film is 1.6 MPa or more.

13. A fluororesin film, which is a fluororesin film having a network structure of fluororesin, the Gurley air permeability of the fluororesin film per 1 μm thickness is 5 seconds / 100 mL / μm or less, and the fluororesin film has water retention resistance capable of withstanding a water pressure retention test in which a circular water pressure application surface with a set diameter of 1 mm is exposed to a water pressure of 1.0 MPa for 30 minutes.

14. A fluororesin film member, which includes the fluororesin film according to any one of claims 1 to 13, and includes a support layer and / or an adhesive layer.

15. An electronic device, which includes: a housing having an opening; and a waterproof film mounted on the housing so as to cover the opening, wherein the waterproof film includes the fluororesin film according to any one of claims 1 to 13.

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