Resin film and water-resistant moisture-permeable membrane

Abstract

To provide a resin film capable of simultaneously realizing a high moisture permeability and a high water pressure resistance at a high level.SOLUTION: A resin film includes a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and has a water pressure resistance of 800 kPa or more and a moisture permeability of 1500 g / m2 day or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a resin film and a water-resistant, water-permeable membrane that have excellent water resistance and breathability and are used as clothing materials such as waterproof clothing and sportswear. [Background technology]

[0002] The water-resistant, breathable membrane containing fluororesin, marketed as "GORE-TEX" (registered trademark), is composed of a stretched polytetrafluoroethylene membrane (hereinafter also referred to as "ePTFE membrane"). For example, the ePTFE film "PoreFlon FP-010-60" (product name (PoreFlon is a registered trademark)) manufactured by Sumitomo Electric Fine Polymer Co., Ltd. has a thickness of 60 μm and a moisture permeability (Japanese Industrial Standard (hereinafter, "JIS") Z0208:1976) of 9415 g / m². 2 da y has a water pressure resistance of 375kPa. Also, the ePTFE membrane "PoreFlon FP-045-80" (product name) manufactured by Sumitomo Electric Fine Polymer Co., Ltd. has a thickness of 80μm and a moisture permeability (JIS Z0208) of 10438g / m². 2 The water pressure resistance is 200kPa. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-192749 [Patent Document 2] International Publication No. 2018 / 116517 [Patent Document 3] Japanese Patent Publication No. 2006-305937 [Patent Document 4] Japanese Patent Application Publication No. 9-255807 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] According to the inventors' research, commercially available ePTFE membranes still have room for improvement. Specifically, the moisture permeability and water pressure resistance of a water-resistant, moisture-permeable membrane are inversely related. Although the water pressure resistance of the ePTFE membrane described in Patent Document 1 is very high at over 800 kPa, the moisture permeability achieved is only 500 g / m². 2 It is less than one day. The moisture permeability of the ePTFE membrane described in Patent Document 2 is 13,000 g / m². 2 Although the water permeability is very high, the water pressure resistance achieved is an extremely low 25 kPa. Patent document 3 describes a composite material in which an elastic sheet is laminated onto an ePTFE membrane, but although the water permeability is high, the water pressure resistance achieved is still insufficient at 450 kPa. Furthermore, patent document 4 describes a porous membrane made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter also referred to as "PFA"), but the pore size is large and it was not a water-resistant and water-permeable membrane that could meet sufficient water pressure resistance. Therefore, one aspect of this disclosure aims to provide a resin film that can achieve both high moisture permeability and high water pressure resistance at a high level. Another aspect of this disclosure aims to provide a water-resistant and moisture-permeable film that can achieve both high moisture permeability and high water pressure resistance at a high level. [Means for solving the problem]

[0005] According to one aspect of this disclosure, a resin film comprising a resin, The resin comprises a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. The water pressure resistance of the resin film is 800 kPa or more. The moisture permeability of the resin film is 1500 g / m². 2 A resin film with a lifespan of 1 day or more is provided. According to other aspects of this disclosure, a resin film comprising a resin, The resin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. Including, The resin film has pores that open to a first surface and communicate with a second surface opposite to the first surface. When a first observation area measuring 8 μm in length and 11 μm in width is placed on the first surface, P1 is defined as the ratio of the total area of ​​the apertures observed within the first observation area to the area of ​​the first observation area. When a second observation area measuring 8 μm vertically and 11 μm horizontally is placed in the cross-section in the thickness direction of the resin film, and P2 is the ratio of the total area of ​​the pores observed within the second observation area to the area of ​​the second observation area, A resin film satisfying 1.3 ≤ (P2 / P1) is provided. A water-resistant, moisture-permeable membrane having the resin film described above is provided according to yet another aspect of this disclosure. [Effects of the Invention]

[0006] According to one aspect of this disclosure, a resin film can be obtained that can achieve both high moisture permeability and high water pressure resistance at a high level. Furthermore, according to another aspect of this disclosure, a water-resistant and moisture-permeable film can be obtained that can achieve both high moisture permeability and high water pressure resistance at a high level. [Brief explanation of the drawing]

[0007]

Figure 1

Figure 2

[0008] Unless otherwise specified, the notation "XX or greater and YY or less" or "XX~YY" which indicates a numerical range, means a numerical range that includes the endpoints, the lower limit and the upper limit. When numerical ranges are given in stages, the upper and lower limits of each range can be combined in any way.

[0009] The resin film according to the present disclosure contains a resin, and the resin includes a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter also referred to as "PFA") that can provide a flexible resin film. And the resin film has a water pressure resistance of 800 kPa or more. Preferably it is 840 kPa or more. The upper limit is not particularly limited, but preferably it is 1500 kPa or less, more preferably 1250 kPa or less. Also, the water vapor permeability of the resin film is 1500 g / m 2 ·day or more. Preferably it is 1800 g / m 2 ·day or more. The upper limit is not particularly limited, but preferably it is 8000 g / m 2 ·day or less, and more preferably 5500 g / m 2 ·day or less. More specifically, the resin film according to the present disclosure has a water pressure resistance of preferably 800 kPa or more and 1500 kPa or less, more preferably 840 kPa or more and 1250 kPa or less, and a water vapor permeability of preferably 1500 g / m 2 ·day or more and 8000 g / m 2 ·day or less, more preferably 1800 g / m 2 ·day or more and 5500 g / m 2 ·day or less.

[0010] The resin film according to one aspect of the present disclosure, which can achieve both the above-mentioned high water pressure resistance and high water vapor permeability, will be described below with reference to FIG. 1. Note that the present disclosure is not limited to this aspect. The resin film 1 has pores 3 inside the film between one surface 2A (hereinafter also referred to as "the first surface") and the surface 2B on the opposite side to the first surface (hereinafter also referred to as "the second surface"). The pores 3 are communication holes that open to the first surface and communicate with the second surface and also open to the second surface. And when a first observation region of a rectangle with a length of 8 μm and a width of 11 μm is set on the first surface, the ratio of the total area of the openings observed in the first observation region to the area of the first observation region is P<​​​​When a second observation area of ​​rectangle 8 μm in length and 11 μm in width is placed in the cross-section in the thickness direction of the resin film, and P2 is the ratio of the total area of ​​pores observed in the second observation area to the area of ​​the second observation area, it is preferable that 1.3 ≤ (P2 / P1), particularly 1.7 ≤ (P2 / P1), and even more preferably 5.0 ≤ (P2 / P1) are satisfied. There is no particular upper limit to P2 / P1, but it is preferably 20.0 or less, more preferably 15.0 or less, and even more preferably 10.0 or less. More specifically, P2 / P1 is preferably 1.3 to 20.0, more preferably 1.7 to 15.0, and particularly preferably 5.0 to 10.0.

[0012] By setting P1 and P2 to the above relationship, even if the diameter of the pores on the first surface is made small enough to prevent water from entering from the first surface, many pores still exist inside the resin film. Therefore, the entry of water vapor into the resin film from the second surface is not prevented. Furthermore, the water vapor inside the pores can be released through the openings on the first surface. As a result, the resin film achieves both high water pressure resistance and high moisture permeability.

[0013] P1 is calculated using the following method: Observe one surface of the resin film with a scanning electron microscope to obtain an SEM image (magnification 10,000x) of an observation area of ​​the first surface measuring 8 μm vertically and 11 μm horizontally. The resolution is set to a resolution that allows individual apertures to be recognized (for example, 717 pixels vertically and 986 pixels horizontally). The SEM image is converted to an 8-bit grayscale image using image processing software (product name: Image-J, manufactured by the National Institutes of Health (NIH)). After applying a median filter to the resulting grayscale image, a binarized image is obtained by further processing it using the same image processing software. The binarization process uses the YEN method to distinguish between the parts corresponding to apertures and the parts corresponding to PFAs in the SEM image. Then, the ratio of the number of pixels in the portion corresponding to the aperture in the obtained binarized image to the total number of pixels in the image is calculated. In this disclosure, observation areas are placed at 10 arbitrary locations on the first surface of the resin film, and the arithmetic mean of the ratios calculated from each observation area is defined as P1. The 10 locations where the observation areas are placed are such that they do not overlap with each other. The specific method will be explained in the embodiments described later.

[0014] P2 is calculated using the following method: A sample is cut from the resin film so that a cross-section encompassing the entire thickness of the resin film is exposed. A predetermined position on the cross-section of the cut sample is observed with a scanning electron microscope, and an SEM image of an observation area of ​​8 μm vertically × 11 μm horizontally is obtained. The resolution is set to a resolution that allows for the recognition of voids appearing in the cross-section (for example, 717 pixels vertically and 986 pixels horizontally). The SEM image is binarized using numerical calculation software (product name: MATLAB; manufactured by MathWorks Inc.) to obtain a binarized image. The binarization process uses Otsu's method to distinguish between the portion corresponding to the aperture and the portion corresponding to the PFA in the SEM image. Then, the ratio of the number of pixels in the portion corresponding to the void in the binarized image to the total number of pixels in the image is calculated. In this disclosure, the acquisition position of the SEM image in the thickness direction of the resin film in the cross-section is as follows. (1) The upper end of the observation area is 1 μm from the first surface side toward the second surface side of the cross-section, and the upper end of the observation area is at a position parallel to the first surface, (2) A position where the midpoint of the first surface and the second surface of the cross-section coincides with the centroid of the observation area, and where one side of the observation area is parallel to the first surface, (3) A position where 1 μm from the second surface toward the first surface marks the lower edge of the observation area, and the lower edge of the observation area is parallel to the second surface. Three acquisition points were set in the thickness direction of these cross-sections, and three points were set in the circumferential direction of the fixed rotating body, for a total of nine points. The arithmetic mean of the ratios calculated from each of the nine observation areas was defined as P2. A specific example will be explained later.

[0015] The P1 calculated by the above method is preferably 15.0% or less, and more preferably 12.0% or less, in order to prevent water from entering the resin film from the first surface and to give the resin film high water pressure resistance. On the other hand, in order to better release water vapor that has entered the pores of the resin film from the second surface from the first surface side, it is preferable that P1 be 1.0% or more, more preferably 1.5% or more, and even more preferably 3.0% or more. Specifically, P1 is preferably 1.0% to 15.0%, more preferably 1.5% to 12.0%, and most preferably 3.0% to 15.0%. Furthermore, P2 is preferably 20.0% or more, more preferably 25.0% or more. By setting P2 to 20.0% or more, the number of pathways for water vapor to pass through within the resin film can be increased, thereby improving moisture permeability. The upper limit of P2 is not particularly limited, but from the viewpoint of more reliably maintaining the strength of the resin film, it is preferably 60.0% or less, more preferably 50.0% or less. Specifically, P2 is preferably 20.0% to 60.0%, more preferably 25.0% to 50.0%.

[0016] The average aperture diameter of the openings on the first surface of the resin film is preferably 1 nm to 200 nm, and more preferably 50 nm to 140 nm. When the average aperture diameter is 1 nm or more, the diffusion paths for water vapor on the surface increase, which tends to improve moisture permeability. Furthermore, when the average aperture diameter is 200 nm or less, the penetration of water from the first surface into the interior of the resin film can be further suppressed, which contributes to improving the water pressure resistance of the resin film. The average aperture diameter of the openings on the first surface is the average value of the diameter of circles having the same area as the area corresponding to the opening, from the binarized image used to calculate P1 as described above. The specific method will be described later.

[0017] The resin film is preferably a single layer film. The resin film can be used as a water-resistant, moisture-permeable film. That is, it is preferable for the water-resistant, moisture-permeable film to have the resin film. The water-resistant, moisture-permeable film may consist only of the resin film, or it may have a configuration in which another resin film or fiber film is laminated on at least one of the first surface side and the second surface side of the resin film.

[0018] The thickness of the resin film is not particularly limited, but is preferably 12 μm or more, more preferably 15 μm or more, preferably 100 μm or less, more preferably 50 μm or less, and especially preferably 40 μm or less. Specifically, the thickness of the resin film is preferably 12 μm or more and 100 μm or less, more preferably 15 μm or more and 50 μm or less, and especially preferably 15 μm or more and 40 μm or less.

[0019] <pfa> The PFA contained in the resin film is a copolymer of perfluoroalkyl vinyl ether (hereinafter referred to as "PAVE") and tetrafluoroethylene (hereinafter referred to as "TFE"). The number of carbon atoms in the perfluoroalkyl chain in PAVE is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3. PAVE is preferably selected from perfluoromethyl vinyl ether (CF2=CF-O-CF3), perfluoroethyl vinyl ether (CF2=CF-O-CF2CF3), and perfluoropropyl vinyl ether (CF2=CF-O-CF2CF2CF3). The melting point of PFA is preferably 280°C to 320°C, and more preferably 290°C to 310°C.

[0020] Commercially available PFAs can be used, and specific examples are given below. • "451HP-J", "959HP-Plus", "350-J", "950HP-Plus" (all product names, manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.); • "P-66P", "P-66PT", "P-802UP" (all product names, AGC) Manufactured by the company; • "AP-230," "AP-231SH," etc. (all are product names, manufactured by Daikin Industries, Ltd.); • "6502N" (product name, manufactured by 3M).

[0021] <Method for manufacturing resin films> An example of a non-limiting method for manufacturing a resin film according to one aspect of the present disclosure described above is a method including the following steps (i) to (v).

[0022] (i) A step of preparing a resin film containing PFA (hereinafter also referred to as "unimpregnated resin film"), (ii) A step of masking one side surface of the unimpregnated resin film (hereinafter also referred to as the "first surface") (iii) A step of contacting the other surface of the unimpregnated resin film obtained in step (ii), which has the first surface masked (hereinafter also referred to as the "second surface"), with perfluoropolyether (PFPE) heated to a temperature near the melting point of PFA, thereby impregnating the unimpregnated resin film with PFPE from the second surface to obtain a resin film impregnated with PFPE (hereinafter also referred to as the "impregnated resin film"). (iv) A step of cooling the impregnated resin film to near room temperature (for example, 20 to 35°C, preferably 25 to 30°C), (v) A step of obtaining a resin film according to the present disclosure by removing at least a portion of the PFPE in the impregnated resin film, which has been cooled to near room temperature after step (iv), from the second surface side of the impregnated resin film, thereby forming voids that open to the second surface and communicate with the first surface (which are also voids that open to the first surface and communicate with the second surface).

[0023] The inventors speculate that the above method can be used to form a resin film according to one aspect of this disclosure as follows: In step (iii), the temperature near the melting point of the PFA contained in the unimpregnated resin film (temperature 300°C ± 50°C (preferably 290°C to 325°C)) ) So, Not containing invasion By bringing one surface of the resin film into contact with PFPE, the PFPE Not containing invasion Impregnated in the resin film , containing A resin-impregnated film is obtained.

[0024] In step (iii), the resin film impregnated with PFPE is at a high temperature, so following step (iii), in step (iv) , containing The resin film is cooled to room temperature, for example, 25°C. Then, in step (v), using a solvent Containing invasion By removing PFPE from the resin film, Containing invasion In the areas of the resin film where PFPE was present, voids are formed that open to the second surface of the resin film.

[0025] Furthermore, the resin film formed through the above steps (iv) to (v) has a pore area ratio P2 per unit area (8 μm × 11 μm) in its thickness-direction cross-section that is larger than the opening area ratio P1 per unit area (8 μm × 11 μm) on the second surface. This is because the resin expands due to the high temperature in step (iii). Containing invasion The resin film shrinks due to cooling in step (iv), Containing invasion The second surface of the resin film cools faster than the first surface, resulting in a greater degree of shrinkage. Containing invasion As the second surface of the resin film shrinks Containing invasion PFPE present near the second surface of the resin film is on the second surface or and others Containing invasion It is pushed out of the resin film. As a result, the opening on the second surface of the resin film shrinks in diameter. on the other hand, Containing invasion The PFPE that has penetrated to the first surface side of the resin film, Containing invasion Because the first surface of the resin film is masked, Containing invasion Also due to shrinkage of the resin film Containing invasion It is not released outside the resin film. Containing invasion It remains within the resin film. Therefore, the size of the aggregated PFPE portions that become voids after PFPE removal hardly decreases. As a result, the ratio of the void ratio P2 to the aperture ratio P1 (P2 / P1) on one side of the resin film formed through process (v) becomes large.

[0026] Here, the value of P2 / P1 is the impregnation step of step (iii) Not containing invasion This can be adjusted by the amount of PFPE impregnated into the resin film. That is, Not containing invasion Increasing the amount of PFPE impregnated into the resin film increases the number of voids within the resin film, thereby increasing the P2 value. Not containing invasion Increasing the amount of impregnation into the resin film increases the number of openings on the second surface of the resin film, thus increasing the value of P1. However, the reason for this is unclear. Not containing invasion The degree of increase in P1 due to the increase in the amount impregnated into the resin film is greater than the degree of increase in P2. Therefore, Not containing invasion By increasing the amount of PFPE impregnated into the resin film, the P2 / P1 ratio can be adjusted to decrease.

[0027] Not containing invasion The amount of PFPE impregnated into the resin film depends, for example, the temperature of the PFPE during impregnation, the viscosity of the PFPE, Not containing invasion This can be adjusted by the contact time between the resin film and the PFPE. Specifically, the higher the temperature within the PFA melting point range (250-350°C), the lower the viscosity of the PFPE, and the longer the contact time, the better the results. Not containing invasion This allows for an increase in the amount of PFPE impregnated into the resin film.

[0028] In order to achieve the preferred range of P2 as described above, in step (iii) , containing It is preferable to impregnate the resin film with PFPE such that the PFPE content ratio is preferably 25 to 60% by mass, and more preferably 30 to 45% by mass, based on the mass of the impregnated resin film.

[0029] Furthermore, the temperature of the PFPE in step (iii) is preferably 250°C to 350°C, and more preferably 290°C to 325°C, since the melting point (Tm) of PFA is in the range of 280°C to 320°C. Also, Resin film not containing invasion The contact time between the outer surface and the PFPE is as follows: Resin film not containing invasion The time required varies depending on the viscosity and amount of PFPE used for impregnation, but as a guideline, it is typically between 20 seconds and 5 minutes, and especially between 30 seconds and 2 minutes. Within this time range, Resin film not containing invasion It can be impregnated with a sufficient amount of PFPE to form voids inside.

[0030] Furthermore, the lower the viscosity of PFPE, the better. Resin film not containing invasion This can increase the amount of impregnation into the material. However, PFPE with too low viscosity may have a higher affinity for PFA, Resin film containing invasion Because aggregation and linkage within the material make it difficult to form PFPE regions, it can be difficult to obtain a high pore area ratio. Therefore, Not containing invasion The preferred viscosity of the PFPE to be impregnated into the resin film is 10 mPa·s to 400 mPa·s, and more particularly, 30 mPa·s to 350 mPa·s. Viscosity, as used here, is measured using a rheometer (TA Instruments: DHR-2) with a cone plate type measuring device having a cone angle of 1° and a cone radius of 20 mm, under a shear rate of 100 s. -1 This is the viscosity value after rotating for 60 seconds. The measurement temperature is 40°C.

[0031] Perfluoropolyethers preferably include PFPE having the structure shown in formula (1) below. The PFPE is preferably one that becomes oily at the melting point of PFA.

[0032] [ka]

[0033] In equation (1), a, b, c, d, e, and f are each independently 0 or a positive integer, satisfying 1 ≤ a + b + c + d + e + f ≤ 600, and at least one of a, b, c, and d is a positive integer. Furthermore, the order in which the repeating units in formula (1) may exist is not limited to the order described above. Moreover, each repeating unit in formula (1) may exist in multiple locations within the PFPE. In other words, the PFPE represented by formula (1) may be a block copolymer. It may also be a random copolymer.

[0034] Specifically, it is preferable that the perfluoropolyether has at least one structure selected from the group consisting of the following formulas (2) to (5).

[0035] [ka] (In equation (2), n is a positive number, and n is the number within the range of 30 mPa·s to 400 mPa·s for the viscosity of PFPE at a temperature of 40°C.)

[0036] [ka] (In equation (3), n' is a positive number, and n' is the number within the range of 10 mPa·s to 400 mPa·s for the viscosity of PFPE at a temperature of 40°C.)

[0037] [ka] (In equation (4), n'' and m are independent positive numbers, m / n'' is a number between 0.5 and 2, and n''+m is a number within the range that gives the viscosity of PFPE at 40°C a range of 20 mPa·s to 400 mPa·s.)

[0038] [ka]

[0039] (In equation (5), n'''' and m'' are independently positive numbers, m'' / n'''' is a number between 20 and 1000, and n'''' + m'' is a number within the range that gives the viscosity of PFPE at a temperature of 40°C to be between 20 mPa·s and 400 mPa·s.)

[0040] Examples of commercially available PFPEs within the preferred viscosity range described above include, for example, PFPEs having the structure shown in formula (2) (e.g., Demnum S-200, Demnum S-65 (both trade names); manufactured by Daikin Industries, Ltd.), PFPEs having the structure shown in formula (3) (e.g., Krytox GPL-105, Krytox GPL-104, Krytox GPL-103, Krytox GPL-102, Krytox GPL-101 (all trade names); manufactured by Chemours), PFPEs having the structure shown in formula (4) (e.g., Fomblin M07, Fomblin M15 (both trade names); manufactured by Solvay Specialty Polymers), and PFPEs represented by formula (5) (e.g., Fomblin Y15, Fomblin Y25 (both trade names); manufactured by Solvay Specialty Polymers).

[0041] For example, "Demnam S-200" has a viscosity of 377 mPa·s, "Krytox GPL-105" has a viscosity of 301 mPa·s, "Krytox GPL-104" has a viscosity of 111 mPa·s, "Krytox GPL-103" has a viscosity of 54 mPa·s, "Krytox GPL-102" has a viscosity of 26 mPa·s, and "Krytox GPL-101" has a viscosity of 12 mPa·s.

[0042] The thickness of the resin film is preferably 12 μm to 100 μm, and more preferably 15 μm to 40 μm.

[0043] In process (v) , containing The resin film is immersed in a solvent that can dissolve the PFPE in the resin film but does not dissolve the PFA, so that the first surface of the resin film is wet. Here, "solvents that dissolve PFPE" refer to solvents that, for example, dissolve 10g or more of PFPE per 100g of solvent at 25°C. On the other hand, "solvents that do not dissolve PFA" refer to solvents that, at 25°C, dissolve 1g or less of PFA per 100g of solvent. Examples of such solvents include hydrofluoroethers. Hydrofluoroethers that are commercially available, such as "Nove C7600" (trade name, manufactured by 3M), can be used. Furthermore, in process (v) , containing resin film らP FPE を To remove PFPE more efficiently, applying ultrasound or heating the fluorine solvent is effective. [Examples]

[0044] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples.

[0045] In this example, resin films were prepared using the following PFA resin and perfluoropolyether. (PFA) PFA-1: "959HP-Plus" (product name, manufactured by Mitsui Chemours Fluoroproducts) PFA-2: "451HP-J" (product name, manufactured by Mitsui Chemours Fluoroproducts) (Perfluoropolyether) PFPE-1: "Krytox GPL104" (product name, manufactured by Chemours, 111 mPa·s (40℃)) PFPE-2: "Krytox GPL105" (product name, manufactured by Chemours, 301 mPa·s (40℃))

[0046] (Example 1) (Preparation of PFA sheet) A 30 μm thick PFA sheet was produced by injection molding PFA-1. The entire surface of one side of the PFA sheet was masked by applying adhesive and then attaching a protective component.

[0047] (Impregnation process) Perfluoropolyether (PFPE-1) was placed in a borosilicate glass beaker. A heating wire covered with insulating material was wrapped around the entire beaker, and the PFPE was heated to a temperature of 310°C. A PFA sheet with one surface masked was attached to a dipping apparatus, and the PFA sheet was immersed in the heated PFPE so that the entire unmasked side of the PFA sheet was in contact with the PFPE. After 1 minute, the PFA sheet was removed from the beaker to obtain a PFPE-containing PFA sheet.

[0048] (Measurement of PFPE content in resin film) From the PFPE-containing PFA sheet produced by the above impregnation process, the protective material that masked one side of the PFA sheet was removed by dissolving the adhesive. The resulting PFPE-containing PFA sheet was analyzed using a thermogravimetric analyzer (TGA). The percentage of PFPE content (mass%) in the PFPE-containing PFA sheet was then calculated under the following measurement conditions. Equipment: TGA851 (manufactured by Mettler Toledo) Atmosphere: In the air Temperature: 425℃ In the measurement time-weight loss rate profile obtained by the above thermogravimetric analysis, a linear least-squares approximation formula was derived from the region where the slope was constant and only PFA was decreasing. The intercept of this linear least-squares approximation formula was taken as the amount of PFA (mass%), and the PFPE content (mass%) was calculated as 100 - amount of PFA.

[0049] (Vacancy formation process) The PFPE-containing PFA sheet prepared by the above impregnation process was immersed in a beaker containing a fluorine solvent (product name: Novec7300, manufactured by 3M) so that the unmasked side of the PFA sheet was completely submerged in the fluorine solvent. This beaker was placed in the water tank of an ultrasonic device (product name: Bransonic (model 2510J-DTH); manufactured by Emerson Japan Co., Ltd.) and ultrasonic waves were applied for 60 minutes. Subsequently, the PFA sheet was removed from the beaker and allowed to stand in an environment of 25°C for 60 minutes to dry. In this way, PFPE present on the surface and inside the PFPE-containing PFA sheet was removed. Furthermore, the protective material that had been masking one side of the PFA sheet was removed by dissolving the adhesive, and the resin film according to this embodiment was obtained. The resulting resin film had a visually white appearance, and the formation of pores within the resin film was confirmed. Two sets of this resin film were prepared. One set was subjected to the following water pressure resistance and moisture permeability tests. The other set was subjected to the following SEM image analysis (calculation of P1, P2, and surface aperture diameter).

[0050] <Rating> The following describes the evaluation method for resin films. <Water pressure resistance> For water pressure resistance, five evaluation samples were prepared, and the average value of the water pressure resistance (kPa) measured in accordance with the provisions of JIS L 1092:2009 "Water Resistance Test Method B (High Water Pressure Method)" was used as the water pressure resistance of the resin film. Specifically, the evaluation sample was mounted on a water resistance tester (product name: WP-1000K; manufactured by Daiei Chemical Machinery Co., Ltd.) so that water was applied to one surface of the evaluation sample. The water pressure was then increased at a rate of 100 kPa per minute, and the water pressure was measured when water was dispensed from three points on the opposite side of the evaluation sample. The arithmetic mean of the five samples was then calculated. This evaluation was performed on both surfaces of the resin film being measured. If the water pressure resistance values ​​differed on both sides, the higher value was adopted. The surface to which this value was assigned was designated as the first surface of the resin film.

[0051] <Moisture permeability> The moisture permeability was determined according to JIS Z 0208:1976, "Test method for moisture permeability of moisture-proof packaging materials (cup method)." Specifically, calcium chloride was placed inside a moisture-permeable cup made of aluminum. Then, the resin film was attached to the cup stand so that one side faced the moisture-permeable cup, and the periphery was sealed with a sealing agent to prepare the test specimen. The test specimen was placed in a constant temperature and humidity chamber (ESPEC PR-2KP) with an atmosphere of 40°C and 90% relative humidity, and the mass increase of the test specimen after 24 hours was measured using an electronic balance (Mettler Toledo AT201), over an area of ​​1 m². 2 The water vapor transmittance was calculated by converting it to a per-unit value. Furthermore, the water vapor permeability was calculated in the same manner as described above, except that the other side of the resin film was attached to the cup stand so that it faced the side of the moisture-permeable cup. If there was a difference in the obtained values, the value with the higher transmittance was adopted. The main test was then performed on three samples, and the arithmetic mean of these results was used as the water vapor permeability for this evaluation.

[0052] <Calculation of void ratio: P1, P2> (Measurement of P1) P1 was calculated as follows. As described above, the surface that was given a high water pressure resistance value was designated as the first surface of the resin film. The first surface of the resin film was observed with a scanning electron microscope, and an SEM image (magnification: 10,000x) of a region of 8 μm vertically and 11 μm horizontally on the first surface was obtained. The resolution of the SEM image was set to 717 pixels vertically and 986 pixels horizontally so that individual apertures of the first surface could be observed in the SEM image. A schematic diagram of the obtained SEM image is shown in Figure 2(A). In Figure 2, 201 indicates the aperture of the void 3 formed in the resin film on the first surface. Next, the acquired SEM images were converted to 8-bit grayscale images using image processing software (product name: Image-J, manufactured by the National Institutes of Health (NIH)). After applying a median filter to the resulting grayscale images, binarization was performed using the same image processing software to obtain binarized images. For binarization, the YEN method was used to distinguish between the parts corresponding to apertures and the parts corresponding to PFAs in the SEM images. Then, the ratio of the number of pixels in the area corresponding to the aperture in the obtained binarized image to the total number of pixels in the image was calculated. Here, the observation areas were set at 10 arbitrary locations on the first surface of the resin film, and the arithmetic mean of the ratios calculated from each observation area was defined as P1. The 10 observation areas were positioned so that their observation areas did not overlap with each other.

[0053] (Average aperture diameter of the first surface) The area of ​​the portion corresponding to the aperture in the binarized image created during the calculation of P1 above was approximated by a perfect circle of the same area, and the average of the diameters of these perfect circles (hereinafter referred to as the circle equivalent diameter) was calculated. Here, the arithmetic mean of the circle equivalent diameters of each aperture obtained from 10 binarized images was taken as the average aperture diameter of the first surface.

[0054] (Measurement of P2) P2 was calculated as follows: Three cross-sectional samples, each containing the entire thickness of the resin film, were cut from three locations using a cryomicrotome (Leica Microsystems). Each of the resulting cross-sections was observed with a scanning electron microscope, and an SEM image (magnification: 10,000x) of a rectangular observation area of ​​the cross-section, measuring 8 μm vertically and 11 μm horizontally, was obtained. The resolution was set to 717 pixels vertically and 986 pixels horizontally to allow recognition of voids appearing in the cross-section. A schematic diagram of the obtained SEM image is shown in Figure 2(B). The obtained SEM image was binarized using numerical calculation software (product name: MATLAB, manufactured by MathWorks Inc.) to obtain a binarized image. For the binarization process, Otsu's method was used to distinguish between the parts corresponding to voids and the parts corresponding to PFA in the SEM image. The ratio of the number of pixels in the parts corresponding to voids in the binarized image to the total number of pixels in the image was then calculated. The acquisition positions of the SEM image in the thickness direction of the cross-section of the cross-sectional sample were set to three locations as defined in (i) to (iii) below.

[0055] (1) From the first surface side of the cross-section toward the second surface side opposite to the first surface, the upper edge of the observation area is 1 μm, and the longer side of the observation area is parallel to the first surface. (2) A position where the midpoint of the first surface and the second surface of the cross-section coincides with the centroid of the observation area, and where the longer side of the observation area is parallel to the first surface, (3) A position where 1 μm from the second surface toward the first surface marks the lower edge of the observation area, and the longer side of the observation area is parallel to the second surface. In this way, a total of nine SEM images were obtained. The arithmetic mean of the above ratios calculated from each of the nine SEM images was then used as the P2 value of the resin film.

[0056] (Examples 2-5) The type of PFA, the thickness of the resin film, the type of PFPE to be impregnated in the impregnation process, and the temperature at which the PFA and PFPE come into contact were set as shown in Table 1. Except for these, the resin films according to Examples 2 to 5 were prepared in the same manner as in Example 1. For each of the obtained resin films, the PFPE content after the PFPE impregnation process, the porosity properties, and the water pressure resistance and moisture permeability were evaluated in the same manner as in Example 1.

[0057] (Comparative Example 1) Aqueous PFA dispersion (product name: 945HP, manufactured by Mitsui Chemours) was mixed with an acetone solution of tetrafluoroethylene-vinylidene fluoride copolymer resin (product name: Neoflon VDF, manufactured by Daikin Industries) (945HP:Neoflon VDF = 1:1 (mass ratio)) and gelled. The solid portion was removed by filtration, dried, and pelletized, and a 50 μm thick sheet was produced by extrusion molding. Subsequently, the tetrafluoroethylene-vinylidene fluoride copolymer resin was dissolved and removed by immersion in acetone to produce a PFA resin film with uniform porosity. The porosity properties, water pressure resistance, and moisture permeability of this resin film were evaluated in the same manner as in Example 1.

[0058] (Comparative Example 2) A solution of amorphous fluoropolymer (product name: Teflon AF2400, manufactured by Chemours) was dipped onto a stainless steel (SUS) sheet, dried, and then peeled off to create a resin film. The porosity, water pressure resistance, and moisture permeability were evaluated in the same manner as in Example 1.

[0059] (Comparative Example 3) A commercially available stretched polytetrafluoroethylene film (product name: Poaflon FP-010-60, manufactured by Sumitomo Electric Industries, Ltd. Fine Polymer Co., Ltd.) was prepared as the resin film (hereinafter also referred to as "ePTFE-1"). The porosity properties, water pressure resistance, and moisture permeability of this resin film were evaluated in the same manner as in Example 1.

[0060] (Comparative Example 4) A commercially available stretched polytetrafluoroethylene film (product name: Poaflon FP-045-80, manufactured by Sumitomo Electric Industries, Ltd. Fine Polymer Co., Ltd.) was prepared as the resin film (hereinafter also referred to as "ePTFE-2"). The porosity properties, water pressure resistance, and moisture permeability of this resin film were evaluated in the same manner as in Example 1.

[0061] Table 1 shows the evaluation results of the resin films prepared in Examples 1-5 and Comparative Examples 1-4.

[0062] [Table 1] * Water pressure when water comes out from one point on the opposite side of the evaluation sample.

[0063] The water pressure resistance and water permeability evaluation results shown in Table 1 indicate that the resin film according to this disclosure achieves high levels of both high water permeability and high water pressure resistance. This disclosure is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of this disclosure public. This application claims priority based on Japanese Patent Application No. 2020-217954, filed on December 25, 2020, and all of its contents are incorporated herein by reference. [Explanation of symbols]

[0064] 1: Resin film, 2A: One surface, 2B: The other surface, 3: Cavity< / pfa>

Claims

1. A resin film containing resin, The resin comprises a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. The water pressure resistance of the resin film is 800 kPa or more and 1500 kPa or less. The moisture permeability of the resin film is 1500 g / m². ２ - 8000g / m² or more per day - less than or equal to the day, A resin film characterized in that the thickness of the resin film is 25 μm or more and 50 μm or less.

2. The resin film has a void that opens to a first surface and communicates with a second surface opposite to the first surface. When a first observation area measuring 8 μm in length and 11 μm in width is placed on the first surface, P1 is defined as the ratio of the total area of ​​the openings observed within the first observation area to the area of ​​the first observation area. When a second observation area measuring 8 μm vertically and 11 μm horizontally is placed in the cross-section of the resin film in the thickness direction, and P2 is the ratio of the total area of ​​the pores observed within the second observation area to the area of ​​the second observation area, 1. The resin film according to claim 1, satisfying 3 ≤ (P2 / P1).

3. The above P1 is 1.0% or more and 15.0% or less. The resin film according to claim 2, wherein the P2 is 20.0% or more and 60.0% or less.

4. The resin film according to claim 2 or 3, wherein the average aperture diameter of the opening on the first surface of the resin film is 1 nm or more and 200 nm or less.

5. The resin film according to any one of claims 2 to 4, wherein the P2 / P1 ratio is 20.0 or less.

6. The resin film according to any one of claims 1 to 5, wherein the resin film is a single-layer film.

7. The water pressure resistance of the resin film is 800 kPa or more and 1250 kPa or less. The moisture permeability of the aforementioned resin film is 1500 g / m²·day or more and 5500 g / m². ２ ・Less than day The resin film according to any one of claims 1 to 6.

8. A water-resistant, moisture-permeable membrane characterized by having a resin film according to any one of claims 1 to 7.

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