Porous membrane, laminate, and method for producing porous membrane

Abstract

This porous membrane 1 contains a fluorine-free resin as a main component, and has a first surface 1a in which a plurality of holes are present and a second surface 1b on the opposite side from the first surface 1a. The arithmetic mean height Sa1 of the first surface 1a is 0.2 μm or greater. This method for producing a porous membrane 1 comprises, in the following order, a step for applying a solution that contains a fluorine-free resin and a solvent to a first surface 5a of a base material 5 to form a coating film, a step for immersing the coating film in water, a step for drying the coating film, and a step for detaching the coating film from the base material 5. The arithmetic mean height Sa3 of the first surface 5a of the base material 5 is 0.42 μm or greater.

Description

Porous membrane, laminate, and method for manufacturing a porous membrane

[0001] This invention relates to porous membranes, laminates, and methods for manufacturing porous membranes.

[0002] Porous membranes made of fluororesin are used in a variety of applications, including filters, sound-transmitting membranes, ventilation membranes, and diaphragms. For these applications, porous membranes that do not contain fluorine have also been proposed. For example, polyimide porous membranes are particularly suitable for use in semiconductor devices such as micro electro-mechanical systems (MEMS) that involve heat treatment such as solder reflow during manufacturing, due to their excellent heat resistance. For instance, Patent Document 1 describes a polyimide porous membrane manufactured using a predetermined reaction product as a raw material.

[0003] Porous membranes are manufactured, for example, according to phase separation methods. Examples of phase separation methods include non-solvent-induced phase separation (NIPS) and drying-induced phase separation (DIPS). For example, Patent Document 2 describes how a polyimide porous membrane with high porosity and a small average pore size was obtained by inducing phase separation by volatilizing the solvent contained in the coating film during the drying process.

[0004] In the NIPS method, a coating film of a polymer solution or polymer precursor solution formed on a substrate is immersed in a non-solvent such as water, which promotes phase separation and porosity formation. It is known that the coating film may peel off from the substrate during immersion in the non-solvent. If the coating film peels off from the substrate during immersion, shrinkage of the coating film occurs, which can reduce the permeability of the resulting porous film.

[0005] To prevent the coating from peeling off the substrate during immersion, it has been proposed to use a substrate with through-holes in the thickness direction, such as a nonwoven fabric, mesh, or porous membrane. However, when a substrate with through-holes is used, the polymer solution or polymer precursor solution penetrates into the through-holes. As a result, it becomes difficult to peel the porous membrane from the substrate after its formation, and in some cases, the membrane may be damaged. Therefore, porous membranes made using a substrate with through-holes are generally supplied not as a single membrane, but as a composite in which the substrate and the porous membrane are integrated.

[0006] Japanese Patent Publication No. 2015-71755, International Publication No. 2016 / 104309

[0007] Conventional technologies have made it difficult to realize a single-layer porous membrane that possesses sufficient air permeability on its own. Therefore, the present invention aims to provide a porous membrane suitable for achieving excellent air permeability despite being a single layer, and a method for manufacturing a porous membrane.

[0008] The present invention provides a porous membrane that mainly contains a fluorine-free resin, has a first surface with multiple pores and a second surface opposite to the first surface, and has an arithmetic mean height Sa1 of 0.2 μm or more on the first surface.

[0009] From another perspective, the present invention provides a laminate comprising: a substrate having a first surface and a second surface opposite to the first surface; and a porous membrane disposed on the first surface of the substrate, wherein the porous membrane is the porous membrane of the present invention, and the arithmetic mean height Sa3 of the first surface of the substrate is 0.42 μm or more.

[0010] From yet another perspective, the present invention provides a method for manufacturing a porous membrane, comprising the steps of: applying a solution containing a fluorine-free resin and a solvent to the first surface of a substrate having a first surface and a second surface opposite to the first surface to form a coating film; immersing the coating film in water; drying the coating film; and peeling the coating film from the substrate, in this order, wherein the arithmetic mean height Sa3 of the first surface of the substrate is 0.42 μm or more.

[0011] According to the present invention, it is possible to provide a porous membrane suitable for achieving excellent air permeability despite being a single membrane, and a method for manufacturing a porous membrane.

[0012] Figure 1 is a schematic cross-sectional view showing an example of a porous membrane according to the present invention. Figure 2 is a schematic cross-sectional view showing another example of a porous membrane according to the present invention. Figure 3 is a partially enlarged view of Figure 2. Figure 4 is a schematic cross-sectional view showing modification 1 of the porous membrane of Figure 2. Figure 5 is a schematic cross-sectional view showing modification 2 of the porous membrane of Figure 2. Figure 6 is a schematic cross-sectional view showing modification 3 of the porous membrane of Figure 2. Figure 7 is a schematic cross-sectional view showing an example of a laminate according to the present invention.

[0013] A porous membrane according to a first aspect of the present invention contains a fluorine-free resin as its main component, has a first surface having a plurality of pores and a second surface opposite to the first surface, and the arithmetic mean height Sa1 of the first surface is 0.2 μm or more.

[0014] In a second embodiment of the present invention, for example, in the porous membrane according to the first embodiment, the resin comprises at least one selected from the group consisting of polyimide resin, polysulfone resin, polyethersulfone resin, polyphenylsulfone resin, polystyrene resin, polyacrylonitrile resin, vinyl chloride resin, polycarbonate resin, polyamideimide resin, and polyetherimide resin.

[0015] In a third aspect of the present invention, for example, in a porous film according to the first or second aspect, the unfolded interface area ratio Sdr1 of the first surface is 10% or more.

[0016] In a fourth aspect of the present invention, for example, a porous membrane according to any one of the first to third aspects comprises a porous layer and a microporous layer disposed on one or both surfaces of the porous layer, wherein the surface of the microporous layer constitutes the first surface.

[0017] In a fifth aspect of the present invention, for example, in a porous membrane according to the fourth aspect, the microporous layer is arranged on both surfaces of the porous layer, and the microporous layer includes a first microporous layer arranged on one surface of the porous layer and a second microporous layer arranged on the other surface of the porous layer, wherein the surface of the first microporous layer constitutes the first surface.

[0018] In a sixth embodiment of the present invention, for example, in a porous membrane according to any one of the first to fifth embodiments, the ratio of the arithmetic mean height Sa2 of the second surface to the arithmetic mean height Sa1 of the first surface is in the range of 0.10 or more and 0.55 or less.

[0019] In a seventh aspect of the present invention, for example, in a porous membrane according to any one of the first to sixth aspects, the porous membrane has a thickness of 10 μm or more and 50 μm or less.

[0020] In the eighth aspect of the present invention, for example, in a porous membrane according to any one of the first to seventh aspects, the average pore diameter on the first surface is 0.01 μm or more and 5 μm or less.

[0021] In the ninth aspect of the present invention, for example, in a porous membrane according to any one of the first to eighth aspects, the average pore diameter on the second surface is 0.1 μm or more and 10 μm or less.

[0022] In the tenth aspect of the present invention, for example, in a porous membrane according to any one of the first to ninth aspects, the air permeability of the porous membrane is 15 seconds / 100 cm, expressed in Gurley numbers. 3 The following applies:

[0023] In the eleventh aspect of the present invention, for example, in a porous membrane according to any one of the first to tenth aspects, the water pressure resistance of the porous membrane, as measured according to the water resistance test method B (high water pressure method) specified in JIS L1092:2009, is 100 kPa or more.

[0024] In a twelfth aspect of the present invention, for example, in a porous membrane according to any one of the first to eleventh aspects, the fluorine content in the porous membrane is less than 0.1% by weight.

[0025] In a thirteenth aspect of the present invention, for example, a porous membrane according to any one of the first to twelfth aspects does not have a substrate arranged in contact with the first surface.

[0026] A laminate according to a fourteenth aspect of the present invention comprises a substrate having a first surface and a second surface opposite to the first surface, and a porous membrane disposed on the first surface of the substrate, wherein the porous membrane is the porous membrane described in any one of the first to thirteenth aspects, and the arithmetic mean height Sa3 of the first surface of the substrate is 0.42 μm or more.

[0027] In a 15th aspect of the present invention, for example, in the laminate according to the 14th aspect, the unfolded interface area ratio Sdr3 of the first surface of the substrate is 3% or more.

[0028] In the sixteenth aspect of the present invention, for example, in the laminate according to the fourteenth or fifteenth aspect, the substrate is a non-porous film.

[0029] In the seventeenth aspect of the present invention, for example, in a laminate according to any one of the fourteenth to sixteenth aspects, the substrate has a thickness of 30 μm or more and 150 μm or less.

[0030] In the eighteenth aspect of the present invention, for example, in a laminate according to any one of the fourteenth to seventeenth aspects, the fluorine content in the substrate is less than 0.1% by weight.

[0031] A method for manufacturing a porous film according to a 19th aspect of the present invention comprises, in this order: applying a solution containing a fluorine-free resin and a solvent to the first surface of a substrate having a first surface and a second surface opposite to the first surface to form a coating film; immersing the coating film in water; drying the coating film; and peeling the coating film from the substrate, wherein the arithmetic mean height Sa3 of the first surface of the substrate is 0.42 μm or more.

[0032] In the 20th embodiment of the present invention, for example, in the method for producing a porous film according to the 19th embodiment, the resin includes at least one selected from the group consisting of polyimide resin, polysulfone resin, polyethersulfone resin, polyphenylsulfone resin, polystyrene resin, polyacrylonitrile resin, vinyl chloride resin, polycarbonate resin, polyamideimide resin, and polyetherimide resin.

[0033] Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments.

[0034] [Porous Membrane] Figure 1 is a schematic cross-sectional view showing an example of a porous membrane according to the present invention. Figure 2 is a schematic cross-sectional view showing another example of a porous membrane according to the present invention. Figure 3 is an enlarged view of part III of Figure 2. As shown in Figures 1 and 2, the porous membrane 1A has a first surface 1a having a plurality of pores and a second surface 1b opposite to the first surface 1a. The first surface 1a has an uneven structure and an arithmetic mean height Sa1 of 0.2 μm or more. The porous membrane 1A mainly contains a fluorine-free resin.

[0035] In this embodiment, the porous membrane 1A does not have a substrate arranged in contact with the first surface 1a. That is, the porous membrane 1A can be supplied as a single membrane. In this specification, "the porous membrane 1A is a single membrane" means that the porous membrane 1A does not have a substrate arranged in contact with the first surface 1a, and does not mean that the porous membrane 1A itself may consist of multiple layers (for example, the porous layer 10 and microporous layer 20 described later).

[0036] Through diligent research, the inventors have discovered that a porous membrane 1A having the above configuration achieves excellent air permeability despite being a single membrane. The porous membrane 1A having the above configuration can be manufactured, for example, by using a substrate having a predetermined arithmetic mean height Sa in the NIPS method. By using the above substrate, the coating film is less likely to peel off from the substrate during immersion, and the occurrence of shrinkage of the coating film is suppressed. As a result, the decrease in the air permeability of the resulting porous membrane 1A is suppressed. The porous membrane 1A of this embodiment is suitable for achieving excellent air permeability despite being a single membrane.

[0037] As described above, the porous membrane 1A contains, as a main component, a resin that does not contain fluorine. "Main component" means the component that is most contained in the porous membrane 1A by weight ratio.

[0038] The resin that does not contain fluorine may contain at least one selected from the group consisting of polyimide-based resins and sulfone-based thermoplastic resins. The polyimide-based resin may contain at least one selected from the group consisting of polyimide resin, polyetherimide resin, and polyamideimide resin. The sulfone-based thermoplastic resin may contain at least one selected from the group consisting of polysulfone resin, polyethersulfone resin, and polyphenylsulfone resin.

[0039] The resin that does not contain fluorine may contain at least one selected from the group consisting of polyimide resin, polysulfone resin, polyethersulfone resin, polyphenylsulfone resin, polystyrene resin, polyacrylonitrile resin, vinyl chloride resin, polycarbonate resin, polyamideimide resin, and polyetherimide resin.

[0040] The resin that does not contain fluorine may contain at least one selected from the group consisting of polyimide resin and polysulfone resin.

[0041] The resin that does not contain fluorine may be polyimide resin. That is, the porous membrane 1A may contain polyimide as a main component. The porous membrane 1A containing polyimide resin as a main component is excellent in heat resistance, and thus can be particularly preferably used for applications of semiconductor elements such as MEMS that involve heat treatment such as solder flow during manufacturing.

[0042] The polyimide resin may be soluble polyimide. Soluble polyimide is a polyimide having the property of being soluble in an organic solvent. Examples of the organic solvent include solvents that can be used in the method for producing a porous membrane described later. As the soluble polyimide, for example, a soluble polyimide in which imidization is completed can be preferably used.

[0043] The fluorine-free resin may be a polysulfone resin. That is, the porous membrane 1A may contain a polysulfone resin as its main component.

[0044] The lower limit of the arithmetic mean height Sa1 of the first surface 1a may be 0.25 μm or 0.3 μm.

[0045] The upper limit of the arithmetic mean height Sa1 of the first surface 1a is, for example, 0.9 μm. The upper limit of the arithmetic mean height Sa1 of the first surface 1a may also be 0.8 μm, 0.7 μm, 0.6 μm, or even 0.5 μm.

[0046] In the porous membrane 1A, the arithmetic mean height Sa1 of the first surface 1a may be the same as or greater than the arithmetic mean height Sa2 of the second surface 1b.

[0047] The ratio of the arithmetic mean height Sa2 of the second surface 1b to the arithmetic mean height Sa1 of the first surface 1a (Sa2 / Sa1) may be in the range of 0.10 or more and 0.55 or less. A porous membrane 1A having such a configuration can achieve better air permeability.

[0048] The arithmetic mean height Sa2 of the second surface 1b may be less than 0.2 μm. The lower limit of the arithmetic mean height Sa2 of the second surface 1b may be, for example, 0.1 μm.

[0049] In the porous membrane 1A, the unfolded interface area ratio Sdr1 of the first surface 1a may be 10% or more. The unfolded interface area ratio Sdr is an index that shows how much the unfolded area (surface area) of the target region has increased relative to the area of ​​the target region. The porous membrane 1A having the above configuration can be manufactured, for example, by using a substrate having a predetermined unfolded interface area ratio Sdr in the NIPS method. By using the above substrate, the adhesion between the substrate and the coating film is maintained even during immersion, and the occurrence of shrinkage of the coating film is suppressed. As a result, the decrease in the air permeability of the resulting porous membrane 1A is suppressed.

[0050] The lower limit of the unfolded interface area ratio Sdr1 of the first surface 1a may be 11%, 12%, or even 13%.

[0051] The upper limit of the unfolded interface area ratio Sdr1 of the first surface 1a is, for example, 30%. The upper limit of the unfolded interface area ratio Sdr1 of the first surface 1a may be 29%, 28%, 27%, 26%, or even 25%.

[0052] In the porous membrane 1A, the unfolded interface area ratio Sdr1 of the first surface 1a may be the same as or greater than the unfolded interface area ratio Sdr2 of the second surface 1b.

[0053] The ratio of the unfolded interface area ratio Sdr2 of the second surface 1b to the unfolded interface area ratio Sdr1 of the first surface 1a (Sdr2 / Sdr1) may be in the range of 0.1 to 0.7. A porous membrane 1A having such a configuration can achieve better air permeability.

[0054] The unfolded interface area ratio Sdr2 of the second surface 1b may be less than 10%. The lower limit of the unfolded interface area ratio Sdr2 of the second surface 1b may be, for example, 5%.

[0055] (Method for measuring the arithmetic mean height Sa and unfolded interface area ratio Sdr of the surface of a porous membrane) The arithmetic mean height Sa1 and unfolded interface area ratio Sdr1 of the first surface 1a of the porous membrane 1A can be measured using a 3D measuring laser microscope (for example, OLS5000 manufactured by Olympus). Specifically, the arithmetic mean height Sa1 and unfolded interface area ratio Sdr1 of the first surface 1a can be measured using a 3D measuring laser microscope at a total observation magnification of 1121x. The arithmetic mean height Sa2 and unfolded interface area ratio Sdr2 of the second surface 1b of the porous membrane 1A can be measured in the same manner.

[0056] In this embodiment, the porous membrane 1A comprises a porous layer 10 and a microporous layer 20 disposed on one or both surfaces of the porous layer 10. The surface of the microporous layer 20 constitutes the first surface 1a. The average pore diameter on the surface of the microporous layer 20 is smaller than the average pore diameter in the porous layer 10.

[0057] As shown in Figure 1, the porous membrane 1A may comprise a porous layer 10 and a microporous layer 20 (first microporous layer 21) disposed on one surface of the porous layer 10. In the example of Figure 1, the surface 21s of the first microporous layer 21 corresponds to the first surface 1a of the porous membrane 1A. As shown in Figure 2, the porous membrane 1A may comprise a porous layer 10 and a microporous layer 20 disposed on both surfaces of the porous layer 10. That is, the microporous layer 20 may include a first microporous layer 21 disposed on one surface of the porous layer 10 and a second microporous layer 22 disposed on the other surface of the porous layer 10. In the example of Figure 2, the surface 21s of the first microporous layer 21 corresponds to the first surface 1a of the porous membrane 1A, and the surface 22s of the second microporous layer 22 corresponds to the second surface 1b of the porous membrane 1A. As shown in Figures 1 and 2, the surface 21s of the first microporous layer 21 may constitute the first surface 1a.

[0058] In the porous membrane 1A shown in Figures 1 and 2, the porous layer 10 has a plurality of rod-shaped voids 11 extending in the thickness direction TD of the porous membrane 1A. A porous membrane 1A having such a configuration is suitable for achieving both breathability and water resistance.

[0059] In this specification, "rod-shaped void" means a void having an elongated shape in the thickness direction TD in a cross-section of a porous membrane 1A parallel to the thickness direction TD, as shown in Figures 1 and 2. However, "rod-shaped void" does not necessarily mean that the void extends parallel to the thickness direction TD. Although not shown in the illustrations, "rod-shaped voids" may include, for example, those having a certain angle of inclination with respect to the thickness direction TD. Furthermore, "rod-shaped voids" does not necessarily mean that the void has a constant pore diameter in the surface direction SD perpendicular to the thickness direction TD. As will be described later, "rod-shaped voids" may include, for example, those in which the pore diameter decreases from the first surface 1a towards the second surface 1b.

[0060] The porous membrane 1A may be in the form of a sheet or a film. The porous membrane 1A may have a thickness T1 of 10 μm or more and 50 μm or less. A porous membrane 1A that satisfies the above numerical range is suitable because it achieves both breathability and water resistance.

[0061] The lower limit of the thickness T1 of the porous membrane 1A may be 12 μm, 15 μm, 17 μm, or even 20 μm. The upper limit of the thickness T1 of the porous membrane 1A may be 90 μm, 80 μm, 70 μm, or even 60 μm.

[0062] The thickness T1 of the porous membrane 1A can be determined, for example, based on a scanning electron microscope (SEM) image of a cross-section of the porous membrane 1A parallel to the thickness direction TD. The thickness T1 is measured at arbitrary locations (e.g., 6 locations) of the porous membrane 1A in the SEM image. The thickness T1 may be the average of these measured values.

[0063] The porous layer 10 may have a thickness T10 of 5 μm or more and 80 μm or less. The lower limit of the thickness T10 may be 10 μm. The upper limit of the thickness T10 may be 70 μm.

[0064] The thickness T10 of the porous layer 10 can be determined by the same method as described for the thickness T1 of the porous membrane 1A. However, if the boundary line B1 between the porous layer 10 and the first microporous layer 21 is unclear in the cross-sectional SEM image, as shown in Figure 3, a straight line b1 parallel to the planar direction SD, passing through the first end 11a on the first microporous layer 21 side of the rod-shaped void 11 closest to the first microporous layer 21, can be considered as the boundary line B1. Similarly, if the boundary line B2 between the porous layer 10 and the second microporous layer 22 is unclear in the cross-sectional SEM image, as shown in Figure 3, a straight line b2 parallel to the planar direction SD, passing through the second end 11b on the second microporous layer 22 side of the rod-shaped void 11 closest to the second microporous layer 22, can be considered as the boundary line B2. In this case, the first end 11a closest to the first microporous layer 21 and the second end 11b closest to the second microporous layer 22 do not have to be the first end 11a and second end 11b of the same rod-shaped void 11. Also, the rod-shaped void 11 having the first end 11a closest to the first microporous layer 21 and the rod-shaped void 11 having the second end 11b closest to the second microporous layer 22 do not have to be entirely included in the SEM image.

[0065] The first microporous layer 21 has a plurality of first pores 23. The second microporous layer 22 has a plurality of second pores 24.

[0066] In the porous membrane 1A shown in Figures 1 and 2, the rod-shaped voids 11 may be in communication with the first pores 23 of the first microporous layer 21.

[0067] In the porous membrane 1A shown in Figure 2, it is preferable that the rod-shaped voids 11 do not communicate with at least the second pores 24 of the second microporous layer 22. Specifically, the rod-shaped voids 11 may communicate with the first pores 23 of the first microporous layer 21, but it is preferable that they do not communicate with the second pores 24 of the second microporous layer 22.

[0068] As shown in Figure 2, it is more preferable that the rod-shaped void 11 does not communicate with either the first pore 23 of the first microporous layer 21 or the second pore 24 of the second microporous layer 22. In other words, it is preferable that the rod-shaped void 11 does not penetrate the porous layer 10. Having such a structure for the rod-shaped void 11 prevents the porous membrane 1A from becoming too permeable and reducing its water resistance.

[0069] To put it another way, it is preferable that the rod-shaped void 11 is closed at both ends (first end 11a, second end 11b) in the thickness direction TD of the porous layer 10. In this case, as shown in Figures 1 and 2, the porous layer 10 may have a first partition wall 12a located on the first surface 1a side and a second partition wall 12b located on the second surface 1b side. In the porous membrane 1A shown in Figure 1, the first partition wall 12a is in contact with the first microporous layer 21. In the porous membrane 1A shown in Figure 2, the first partition wall 12a is in contact with the first microporous layer 21, and the second partition wall 12b is in contact with the second microporous layer 22.

[0070] As shown in Figures 1 and 2, the porous layer 10 extends in the thickness direction TD and may further have a third partition wall 12c located between adjacent rod-shaped voids 11. The third partition wall 12c may be connected to the first partition wall 12a on the side of the first microporous layer 21. The third partition wall 12c may be connected to the second partition wall 12b on the side of the second microporous layer 22.

[0071] Although not shown in the figures, the first partition wall 12a, the second partition wall 12b, and the third partition wall 12c may contain pores with a diameter smaller than that of the rod-shaped voids 11. In a cross-section of the porous membrane 1A parallel to the thickness direction TD, the average pore diameter of the above pores may be in the range of 10 nm to 1000 nm. A porous layer 10 that satisfies the above numerical range makes it easier to maintain excellent permeability in the porous membrane 1A. In this specification, the average pore diameter is the number average pore diameter.

[0072] As described above, in this embodiment, multiple pores exist on the first surface 1a of the porous membrane 1A. The presence of multiple pores on the first surface 1a of the porous membrane 1A can be confirmed, for example, by an SEM image of the first surface 1a of the porous membrane 1A.

[0073] The average pore size D1 on the first surface 1a may be 0.01 μm or more and 5 μm or less.

[0074] The lower limit of the average pore size D1 may be 0.015 μm or 0.019 μm. The upper limit of the average pore size D1 may be 4 μm, 3 μm, 2 μm, 1 μm, 0.5 μm, or even 0.1 μm.

[0075] The average pore size D2 on the second surface 1b may be between 0.1 μm and 10 μm.

[0076] The lower limit of the average pore size D2 may be 0.5 μm or 1 μm. The upper limit of the average pore size D1 may be 9 μm, 8 μm, 7 μm, 6 μm, or even 5 μm.

[0077] As described above, in the porous membrane 1A shown in Figure 1, the surface 21s of the first microporous layer 21 corresponds to the first surface 1a. In the porous membrane 1A shown in Figure 1, the average pore diameter D1 on the first surface 1a is larger than the average pore diameter D2 on the second surface 1b. When this relationship is satisfied, the desired water resistance is easily achieved in the porous membrane 1A.

[0078] As described above, in the porous membrane 1A shown in Figure 2, the surface 21s of the first microporous layer 21 corresponds to the first surface 1a, and the surface 22s of the second microporous layer 22 corresponds to the second surface 1b. In the porous membrane 1A shown in Figure 2, the average pore diameter D1 on the first surface 1a is larger than the average pore diameter D2 on the second surface 1b. When this relationship is satisfied, the desired water resistance is easily achieved in the porous membrane 1A.

[0079] The average pore diameter D1 on the first surface 1a can be determined, for example, based on an SEM image of the first surface 1a of the porous membrane 1A. In the porous membrane 1A shown in Figures 1 and 2, the surface 21s of the first microporous layer 21 corresponds to the first surface 1a. The pore diameters of the six largest pores (first pores 23) in the SEM image are measured. However, if there are exceptionally large voids with a pore diameter exceeding 20 μm in the SEM image, such voids are excluded from the pore diameter measurement. The average pore diameter D1 can be calculated by averaging these measured values.

[0080] The average pore diameter D2 on the second surface 1b can be determined, for example, based on an SEM image of the second surface 1b of the porous membrane 1A. In the porous membrane 1A shown in Figure 2, the surface 22s of the second microporous layer 22 corresponds to the second surface 1b. The pore diameters of the six largest pores (second pores 24 in Figure 2) in the SEM image are measured. However, if there are exceptionally large voids with a pore diameter exceeding 20 μm in the SEM image, such voids are excluded from the pore diameter measurement. The average pore diameter D2 can be calculated by averaging these measurements.

[0081] In this embodiment, if the porous membrane 1A is used, for example, to prevent the penetration of foreign matter through an opening in the housing of a device while ensuring ventilation through the opening, the second surface 1b may face the side to which pressure such as water pressure is applied. With such an arrangement, the desired water resistance can be easily achieved in the porous membrane 1A. However, the first surface 1a may also face the side to which pressure such as water pressure is applied.

[0082] The first microporous layer 21 may have a thickness T21 of 50 nm or more and 8000 nm or less. The lower limit of the thickness T21 may be 100 nm. The upper limit of the thickness T21 may be 7500 nm.

[0083] The second microporous layer 22 may have a thickness T22 of 100 nm or more and 3000 nm or less. The upper limit of the thickness T22 may be 2750 nm, 2500 nm, 2250 nm, or even 2000 nm.

[0084] The thickness T21 of the first microporous layer 21 and the thickness T22 of the second microporous layer 22 can be obtained by the same method as that described for the thickness T1 of the porous membrane 1A and the thickness T10 of the porous layer 10.

[0085] The air permeability of the porous membrane 1A may be 15 seconds / 100 cm or less in terms of Gurley number. Thus, the porous membrane 1A has high air permeability. In this specification, the "Gurley number" is the air permeability resistance (Gurley air permeability) measured in accordance with the King Research type tester method defined in JIS P8117:2009. 3 The upper limit of the air permeability of the porous membrane 1A may be 14.6 seconds / 100 cm,

[0086] 14 seconds / 100 cm, 3 13 seconds / 100 cm, 3 12 seconds / 100 cm, 3 11 seconds / 100 cm, 3 10 seconds / 100 cm, 3 9 seconds / 100 cm, 3 or even 3 The lower limit of the air permeability of the porous membrane 1A is, for example, 1.5 seconds / 100 cm in terms of Gurley number. 3

[0087] Even when the size of the porous membrane 1A does not meet the recommended dimensions (50 mm × 50 mm) of the test piece of the King Research type tester method, it is possible to evaluate the air permeability resistance (Gurley air permeability) in accordance with the King Research type tester method by using a measuring jig.

[0088] The measuring jig has a shape and size that can be placed in the air permeability measuring section of the Wangyan type testing machine, and has a thickness and material that does not deform due to the differential pressure applied to the test piece when measuring air permeability resistance. An example of a measuring jig is a SUS disc with a thickness of 2 mm and a diameter of 47 mm. A through hole with an opening smaller in size than the membrane to be evaluated is provided at the center of the surface of the measuring jig. The cross-section of the through hole is typically circular, and its diameter is such that the opening of the through hole is completely covered by the membrane to be evaluated. For example, the diameter of the through hole can be 1 mm or 2 mm. Next, the porous membrane 1A to be evaluated is fixed so that the first surface 1a faces one surface of the measuring jig so as to cover the opening. The fixing is done so that during the measurement of air permeability resistance, air passes only through the opening and the effective test portion of the porous membrane 1A to be evaluated (the portion that overlaps with the opening when viewed from a direction perpendicular to the main surface of the fixed porous membrane 1A), and the fixing portion does not obstruct the passage of air in the effective test portion of the porous membrane 1A. To fix the porous membrane 1A, double-sided adhesive tape with a vent punched out in the center that matches the shape of the opening can be used. The double-sided adhesive tape should be placed between the measuring jig and the porous membrane 1A so that the circumference of the vent coincides with the circumference of the opening. Next, the measuring jig with the porous membrane 1A fixed to it is set in the air permeability measurement section of the Wang-Lan testing machine so that the fixed surface of the porous membrane 1A is on the downstream side of the airflow during measurement, and the test is performed according to the Wang-Lan testing machine method, and the air permeability resistance indicator value t shown by the testing machine is recorded. Next, the recorded air permeability resistance indicator value t is set to the effective test area of ​​6.452 [cm²] specified in the Wang-Lan testing machine method. 2 ] Value t K In equation t, K = {t × (area of ​​the effective test portion of porous membrane 1A [cm²] 2 ]) / 6.452 [cm 2 Converted using ]}, the obtained converted value t KThis can be considered the air permeability resistance (Gurley air permeability) of the porous membrane 1A measured in accordance with the Wang-Lan testing machine method. It has been confirmed that the air permeability resistance measured without using a measuring jig for a porous membrane 1A that meets the recommended dimensions of the test specimen for the Wang-Lan testing machine method (50 mm x 50 mm) agrees well with the air permeability resistance measured using a measuring jig after the porous membrane 1A has been cut into pieces, meaning that the use of a measuring jig does not substantially affect the measured value of air permeability resistance.

[0089] The water pressure resistance of porous membrane 1A, as measured according to the water resistance test method B (high water pressure method) specified in JIS L1092:2009, may be 100 kPa or more.

[0090] The lower limit of the water pressure resistance of the porous membrane 1A may be 110 kPa, 120 kPa, 130 kPa, 140 kPa, 150 kPa, 160 kPa, 170 kPa, 180 kPa, or even 190 kPa. The upper limit of the water pressure resistance of the porous membrane 1A is, for example, 500 kPa.

[0091] The above water pressure resistance can be measured using a measuring jig in accordance with the above water pressure resistance test method, as follows. An example of a measuring jig is a 47 mm diameter stainless steel (SUS) disc with a 1.0 mm diameter through hole (having a circular cross-section) in the center. This disc has a thickness that does not deform under the water pressure applied when measuring water pressure resistance. The measurement of water pressure resistance using this measuring jig can be carried out as follows.

[0092] The porous membrane 1A to be evaluated is fixed to one side of the measuring jig so that its first surface 1a faces the opening of the through-hole in the measuring jig. The fixing is done in a way that prevents water from leaking from the fixed part of the membrane during water pressure resistance measurement. For fixing the porous membrane 1A, double-sided adhesive tape with a water inlet punched out in the center that matches the shape of the opening can be used. The double-sided adhesive tape should be placed between the measuring jig and the porous membrane 1A so that the circumference of the water inlet coincides with the circumference of the opening. Next, the measuring jig with the porous membrane 1A fixed to it is set in the test apparatus so that the side of the porous membrane 1A opposite to the fixing surface becomes the water pressure application surface during measurement, and the water pressure resistance is measured according to the water pressure resistance test method B (high water pressure method) specified in JIS L1092:2009. However, the water pressure resistance is measured based on the water pressure when water is released from one point on the membrane surface of the porous membrane 1A. The measured water pressure resistance can be used as the water pressure resistance of the porous membrane 1A. The test apparatus can be one that has a configuration similar to the water resistance test apparatus exemplified in JIS L1092:2009, and also has a test specimen mounting structure that allows the above-mentioned measuring jig to be set.

[0093] In this embodiment, the porous membrane 1A is substantially fluorine-free. Specifically, the fluorine content in the porous membrane 1A is less than 0.1% by weight.

[0094] Methods for confirming that the fluorine content in the porous membrane 1A is less than 0.1% by weight include, for example, infrared absorption spectroscopy (IR), nuclear magnetic resonance analysis (NMR), gel permeation chromatography (GPC), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The fluorine content in the porous membrane 1A being less than 0.1% by weight may also be confirmed by MALDI-TOF-MS. The fluorine content in the porous membrane 1A being less than 0.1% by weight may also be confirmed by two or more methods selected from the above methods.

[0095] Surface modification treatment may be applied to at least one surface of the porous film 1A. Examples of surface modification treatments include chemical treatment, sputter etching, liquid repellency treatment, and plasma treatment. In the region where surface modification treatment has been applied, for example, the bonding properties and liquid repellency of the porous film 1A may be improved.

[0096] At least one surface of the porous membrane 1A may be treated with a liquid-repellent agent. The liquid-repellent agent is preferably substantially free of fluorine. For example, a liquid-repellent agent containing a silicone resin having alkoxy groups directly bonded to silicon atoms can be used. Such a liquid-repellent agent can impart excellent liquid repellency to the porous membrane 1A.

[0097] Examples of silicone resins having alkoxy groups directly bonded to silicon atoms include polydimethylsiloxane, polydimethyldiphenylsiloxane, polymethylphenylsiloxane, and their oligomers. Furthermore, the above-mentioned silicone resin may be a polymer containing the above-mentioned structural units, such as a copolymer.

[0098] In the examples in Figures 1 and 2, the rod-shaped voids 11 have a substantially cylindrical shape. However, the shape of the rod-shaped voids 11 is not limited to the examples in Figures 1 and 2. Also, in the examples in Figures 1 and 2, there is one rod-shaped void 11 located in the direction of the thickness T10 of the porous layer 10. However, the number of rod-shaped voids 11 located in the direction of the thickness T10 of the porous layer 10 is not limited to the examples in Figures 1 and 2. Furthermore, in the examples in Figures 1 and 2, the shape of the voids in the porous layer 10 is rod-shaped (rod-shaped voids 11). However, the shape of the voids in the porous layer 10 is not limited to the examples in Figures 1 and 2. Below, modifications 1 to 3 of the porous membrane according to the present invention will be described based on the example in Figure 2. In the following, the same reference numerals may be used to indicate the same configuration as the porous membrane 1A shown in Figures 1 and 2 described above, and the explanation may be omitted.

[0099] (Modification 1) Figure 4 is a schematic cross-sectional view of the porous membrane 1B of Modification 1. In the porous membrane 1B, the rod-shaped voids 11 have a substantially conical shape. Except for this point, the porous membrane 1B has the same structure as the porous membrane 1A shown in Figure 2 described above. The porous membrane 1B of Modification 1 can be obtained, for example, by controlling the speed of phase separation and the way in which phase separation proceeds in the manufacturing method by selecting a solvent, phase separation conditions, etc.

[0100] As can be seen from Figure 4, in a cross-section of the porous membrane 1B parallel to the thickness direction TD, the length of the rod-shaped voids 11 along the surface direction SD decreases from the first microporous layer 21 side to the second microporous layer 22 side. A porous membrane 1B having such a structure is also suitable for achieving both breathability and water resistance.

[0101] (Modification 2) Figure 5 is a schematic cross-sectional view of the porous membrane 1C of Modification 2. In the porous membrane 1C, the number of rod-shaped voids 11 existing in the thickness T10 direction of the porous layer 10 is not limited to one. Except for this point, the porous membrane 1C has the same structure as the porous membrane 1A shown in Figure 2 described above. The porous membrane 1C having such a structure is also suitable for achieving both air permeability and water resistance. The porous membrane 1C of Modification 2 can be obtained, for example, by controlling the speed of phase separation and the way in which phase separation proceeds in the manufacturing method by selecting a solvent, phase separation conditions, etc.

[0102] As shown in Figure 5, two or more rod-shaped voids 11 (11A, 11B) may exist in the thickness T10 direction of the porous layer 10.

[0103] As shown in Figure 5, the major axes 11L of two or more rod-shaped gaps 11 (11A, 11B) may be offset from each other in the planar direction SD.

[0104] As shown in Figure 5, in the porous membrane 1C, a fourth partition wall 12d may exist between two or more rod-shaped voids 11 (11A, 11B) located in the thickness T10 direction of the porous layer 10.

[0105] As illustrated in Figure 5, in porous membranes 1A, 1B, and 1C, the porous layer 10 may have other voids 15 having a short-axis length similar to that of the rod-shaped voids 11. The other voids 15 are distinguished from the rod-shaped voids 11 in that they do not have an elongated shape in the thickness direction TD.

[0106] (Modification 3) Figure 6 is a schematic cross-sectional view of the porous membrane 1D of Modification 3. The porous membrane 1D is composed of a porous layer 10. The porous layer 10 has third pores 16 dispersed in the thickness direction TD. The third pores 16 do not have an elongated shape in the thickness direction TD like the rod-shaped voids 11. A porous membrane 1D having such a structure is also suitable for achieving both air permeability and water resistance. As shown in Figure 6, the third pores 16 may have a uniform pore diameter. Although not shown, the third pores 16 may have different pore diameters in the thickness direction TD. The pore diameter of the third pores 16 on one side (e.g., the first surface 1a) may be larger than the pore diameter of the third pores 16 on the other side (e.g., the second surface 1b). The pore diameter of the third pores 16 may gradually increase from one side to the other. The porous membrane 1D of the modified example 3 can be obtained, for example, by controlling the rate of phase separation and the way in which phase separation proceeds in the manufacturing method, by selecting a solvent, determining phase separation conditions, etc.

[0107] [Laminate] The porous membrane 1 (1A, 1B, 1C, 1D) of this embodiment can be supplied, for example, as a laminate combined with a substrate.

[0108] An example of a laminate according to the present invention is shown in Figure 7. The laminate 40 shown in Figure 7 comprises a porous membrane 1 and a substrate 5 according to this embodiment. The substrate 5 has a first surface 5a and a second surface 5b opposite to the first surface 5a. The porous membrane 1 is arranged on the first surface 5a of the substrate 5 such that the first surface 1a is in contact with the substrate 5. The arithmetic mean height Sa3 of the first surface 5a of the substrate 5 is 0.42 μm or more.

[0109] In the example shown in Figure 7, the laminate 40 includes the porous membrane 1A shown in Figure 2 as the porous membrane 1. Although not shown, the laminate 40 may also include the porous membrane 1A shown in Figure 1, the porous membrane 1B shown in Figure 4, the porous membrane 1C shown in Figure 5, or the porous membrane 1D shown in Figure 6 as the porous membrane 1.

[0110] Through diligent research, the inventors have discovered that the adhesion between the substrate 5 and the porous film 1 is maintained when a laminate 40 having the above configuration is used. The laminate 40 having the above configuration can be manufactured, for example, by using a substrate 5 in which the arithmetic mean height Sa3 of the first surface 5a is 0.42 μm or more in the NIPS method. By using a substrate 5 that satisfies the above numerical range, the coating film is less likely to peel off from the substrate 5 during immersion. As a result, the decrease in adhesion in the resulting laminate 40 is suppressed. The laminate 40 of this embodiment is suitable for maintaining the adhesion between the substrate 5 and the porous film 1.

[0111] The upper limit of the arithmetic mean height Sa3 of the first surface 5a is, for example, 0.9 μm. The upper limit of the arithmetic mean height Sa3 of the first surface 5a may also be 0.85 μm or 0.8 μm.

[0112] In the laminate 40, the unfolded interface area ratio Sdr3 of the first surface 5a of the base material 5 may be 3% or more. The laminate 40 having the above configuration can be manufactured, for example, by using a base material 5 in which the unfolded interface area ratio Sdr3 of the first surface 5a is 3% or more in the NIPS method. By using a base material 5 that satisfies the above numerical range, the adhesion between the base material 5 and the coating film is maintained even during immersion. As a result, the decrease in adhesion in the resulting laminate 40 is suppressed.

[0113] The lower limit of the unfolded interface area ratio Sdr3 of the first surface 5a may be 4%, 5%, or even 6%.

[0114] The upper limit of the unfolded interface area ratio Sdr3 of the first surface 5a is, for example, 20%. The upper limit of the unfolded interface area ratio Sdr3 of the first surface 5a may be 19%, 18%, 17%, 16%, or even 15%.

[0115] (Method for measuring the arithmetic mean height Sa and unfolded interface area ratio Sdr of the substrate surface) The arithmetic mean height Sa3 and unfolded interface area ratio Sdr3 of the first surface 5a of the substrate 5 can be measured using a scanning white light interferometer (for example, a Newview 7300 manufactured by Zygo). Specifically, the substrate 5 is placed on a measurement stand with a vibration isolation table of the scanning white light interferometer, interference fringes are generated using a single white LED illumination, and an interference objective lens (1.4x) with a reference plane is scanned in the Z direction (thickness direction) to selectively acquire the smoothness (surface smoothness) of the first surface 5a of the substrate 5 in a field of view of 12.4 mm □. The substrate 5 is used by bonding it to a microslide glass (manufactured by Matsunami Glass Industry Co., Ltd., S200200) so that the first surface 5a is exposed. Based on this measurement, the arithmetic mean height Sa3 and unfolded interface area ratio Sdr3 of the first surface 5a of the substrate 5 can be calculated. However, if the substrate 5 is a transparent material such as a PET film or a glass plate, it can be measured using the same method as described above for the arithmetic mean height Sa1 and the unfolded interface area ratio Sdr1 of the first surface 1a of the porous membrane 1A.

[0116] The substrate 5 is preferably a non-porous membrane. In this embodiment, "non-porous" means that there are no pores connecting one main surface of the membrane to the other main surface, or that the number of pores is extremely small. For example, a membrane with an air permeability expressed in Gurley number greater than 10,000 seconds / 100 mL can be determined to be a non-porous membrane. Here, the Gurley number is a value obtained by measurement in accordance with JIS P8117:2009.

[0117] If the substrate 5 is a non-porous film, for example, the coating film does not easily penetrate into the interior of the substrate 5 in the NIPS method. Therefore, in the resulting laminate 40, the decrease in the peelability of the porous film 1 from the substrate 5 is suppressed. In other words, with the laminate 40 having the above configuration, it is possible to achieve both good adhesion between the substrate 5 and the porous film 1 and good peelability of the porous film 1 from the substrate 5.

[0118] The fact that the substrate 5 is a non-porous film can be confirmed, for example, by an SEM image of the first surface 5a of the substrate 5.

[0119] The base material 5 preferably contains a thermoplastic resin that does not contain fluorine as its main component. "Main component" means the component that is present in the largest amount by weight in the base material. Specifically, it is preferable that the fluorine content in the base material 5 is less than 0.1% by weight. If the base material 5 contains fluorine, for example, when manufacturing the laminate 40, the fluorine component contained in the base material 5 may be transferred to the porous film 1, which is undesirable.

[0120] As a method for confirming that the fluorine content in the substrate 5 is less than 0.1% by weight, the method described above as a method for confirming that the fluorine content in the porous membrane 1A is less than 0.1% by weight can be used.

[0121] Examples of fluorine-free thermoplastic resins include polyolefin resins, polyester resins, and polyimide resins. A fluorine-free thermoplastic resin may contain at least one selected from the group consisting of polyolefin resins, polyester resins, and polyimide resins.

[0122] A fluorine-free thermoplastic resin may contain at least one selected from the group consisting of polyolefin resins and polyester resins.

[0123] A thermoplastic resin that does not contain fluorine may also contain a polyolefin resin.

[0124] Examples of polyolefin resins include polyethylene (PE) resin, polymethylpentene (PMP) resin, and polypropylene (PP) resin.

[0125] Polyolefin resin may also be polyethylene (PE) resin.

[0126] The polyolefin resin may also be polymethylpentene (PMP) resin. The same polymethylpentene resin described above for the liquid repellent can be used.

[0127] A thermoplastic resin that does not contain fluorine may also contain polyester resin.

[0128] Examples of polyester resins include polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, polybutylene terephthalate (PBT) resin, polybutylene naphthalate (PBN) resin, polyethylene furanoate (PEF) resin, and polytrimethylene terephthalate resin.

[0129] The polyester resin may also be polyethylene terephthalate (PET) resin.

[0130] A fluorine-free thermoplastic resin may also contain polyimide (PI) resin.

[0131] The base material 5 is preferably in the form of a sheet or film. If the base material 5 is in the form of a sheet or film, it can be supplied, for example, as a wound body in which the laminate 40 is wound. Since it is difficult to supply it as a wound body, the base material 5 is preferably not a rigid member such as a glass plate or a stainless steel plate.

[0132] The substrate 5 may have a thickness of 30 μm or more and 150 μm or less. A substrate 5 that satisfies the above numerical range is suitable because it improves the peelability of the porous film 1 from the substrate 5.

[0133] The lower limit of the thickness of the base material 5 may be 40 μm, or even 50 μm. The upper limit of the thickness of the base material 5 may be 140 μm, 130 μm, 120 μm, 110 μm, or even 100 μm.

[0134] The thickness of the substrate 5 can be determined by the same method as described above for determining the thickness T1 of the porous membrane 1A.

[0135] Next, the manufacturing methods for the porous membrane 1 (1A, 1B, 1C, 1D) and the laminate 40 in this embodiment will be described.

[0136] [Method for Manufacturing Porous Membranes] The method for manufacturing the porous membranes 1 (1A, 1B, 1C, 1D) in this embodiment is not limited to a specific method. The porous membranes 1 can be manufactured, for example, according to a phase separation method. Examples of phase separation methods include non-solvent-induced phase separation (NIPS method) and drying-induced phase separation (DIPS method). The porous membranes 1 described above tend to achieve excellent air permeability even as single membranes, especially when manufactured using the NIPS method.

[0137] The following describes an example of a method for manufacturing the porous membrane 1A shown in Figure 2 using the NIPS method. The manufacturing method for the porous membrane 1A shown in Figure 2 includes, for example, the steps of forming a coating film by applying a solution containing a fluorine-free resin and a solvent to the first surface of a substrate having a first surface and a second surface opposite to the first surface (step 1), immersing the coating film in water (step 2), drying the coating film (step 3), and peeling the coating film off the substrate (step 4), in this order.

[0138] In step 1, the above solution is applied to the first surface of a predetermined substrate to form a coating film. The arithmetic mean height Sa of the first surface of the substrate is 0.42 μm or more. The unfolded interface area ratio Sdr of the first surface of the substrate may be 3% or more. As the substrate, the substrate described above for substrate 5 can be used. The substrate can be manufactured, for example, by sandblasting one side of the substrate body, which is a non-porous film, so that the arithmetic mean height Sa of the first surface is 0.42 μm or more.

[0139] As described above, the fluorine-free resin may include at least one selected from the group consisting of polyimide resin, polysulfone resin, polyethersulfone resin, polyphenylsulfone resin, polystyrene resin, polyacrylonitrile resin, vinyl chloride resin, polycarbonate resin, polyamideimide resin, and polyetherimide resin. The fluorine-free resin may also include at least one selected from the group consisting of polyimide resin and polysulfone resin. Examples of fluorine-free resins that can be used include soluble polyimide varnish (manufactured by Mitsubishi Gas Chemical Company, NeoPrim S101D (solids content: 20 wt%, DMAc solvent)) and polysulfone resin (manufactured by Synsqo, Udel P-3500LCD).

[0140] The above solvent includes, for example, at least one selected from the group consisting of lactone solvents, sulfone solvents, ketone solvents, cyclic ether solvents, and amide solvents. A lactone solvent includes, for example, γ-butyllactone. The lactone solvent may also be γ-butyllactone. A sulfone solvent includes, for example, sulfolane. A ketone solvent includes, for example, cyclopentanone. A cyclic ether solvent includes, for example, 1,3-dioxolane. An amide solvent includes, for example, dimethylformamide (DMF). The amide solvent may also be DMF.

[0141] In the production of the porous film 1A, a first microporous layer 21 can be formed in contact with the first surface of the substrate of the coating film of the above solution. By using a substrate in which the arithmetic mean height Sa of the first surface is 0.42 μm or more, it is easier to form a porous film 1A in which the arithmetic mean height Sa1 of the first surface 1a is 0.42 μm or more.

[0142] In step 2, the coating film of the above solution is immersed in water. This promotes phase separation in the coating film, accelerates porosity, and extracts the solvent from the coating film. At this time, because the arithmetic mean height Sa of the first surface of the substrate is 0.42 μm or more, the coating film is less likely to peel off the substrate. Therefore, the occurrence of shrinkage of the coating film due to peeling is suppressed.

[0143] The coating film of the above solution is immersed in a water bath at, for example, 20°C to 40°C. The water used in the water bath is typically pure water. The immersion time is, for example, 1 minute to 30 minutes. In step 2, the phase separation rate increases as you approach the outermost layer of the coating film, and the solvent is rapidly extracted. As a result, a second microporous layer 22 with a denser structure is formed on the surface side of the coating film, and the first microporous layer 21 is formed in contact with the surface of the coating film that is in contact with the substrate. Due to the formation of the first microporous layer 21 and the second microporous layer 22, the solvent is less likely to be extracted from the inside of the coating film, and as a result, a porous layer 10 having rod-shaped voids 11 is formed on the inside of the coating film.

[0144] In step 3, the porous coating is dried. The drying time is, for example, 1 minute to 30 minutes.

[0145] In step 4, the dried coating is peeled off the substrate. At this time, because the arithmetic mean height Sa of the first surface of the non-porous substrate is 0.42 μm or more, the coating is easier to peel off the substrate compared to when a substrate with through-pores such as nonwoven fabric, mesh, or porous membrane is used. Therefore, damage to the coating during peeling is suppressed. In this way, a single porous membrane 1A is obtained.

[0146] [Method for Manufacturing the Laminate] The laminate 40 in this embodiment can be manufactured, for example, by completing the method for manufacturing the porous membrane 1A described above in step 3. This makes it possible to obtain the laminate 40 shown in Figure 7.

[0147] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the examples shown below.

[0148] [Example 1] As a fluorine-free resin, a soluble polyimide varnish (NeoPrim S101D, manufactured by Mitsubishi Gas Chemical Company, solids content: 20 wt%, DMAC solvent) was prepared. As solvents, a sulfone-based solvent, sulfolane (Fujifilm Wako Pure Chemical Industries, Ltd.), and a cyclic ether-based solvent, 1,3-dioxolane (Tokyo Chemical Industries, Ltd.), were prepared. 3.5 g of soluble polyimide varnish was mixed with 2.0 g of sulfolane and 4.5 g of 1,3-dioxolane. This obtained the polyimide (PI) solution of Example 1. The polyimide concentration of the PI solution of Example 1 was 7 wt%.

[0149] In Example 1, a PET film (thickness: 50 μm) with one surface (first surface) sandblasted was used as the substrate (manufactured by Kaisei Kogyo Co., Ltd., Type A). The substrate in Example 1 had an uneven surface on the first surface.

[0150] Next, the PI solution of Example 1 was applied to the first surface of the substrate using an applicator to a wet thickness of 125 μm to form a coating film. Next, the coating film was immersed in a 20°C water bath for 10 minutes to allow porosity formation by phase separation and solvent extraction to proceed (immersion step). It is preferable to perform the immersion step before the diluting solvent evaporates, for example, within 30 seconds of the formation of the coating film. Next, the coating film was fixed to a square SUS member with a side length of 10 cm in a plan view and dried at 80°C for 10 minutes (drying step). In this way, a laminate of Example 1 was obtained, which had a porous film mainly composed of polyimide resin placed on the first surface of the substrate. The porous film was peeled off the substrate of the laminate (peeling step). In this way, the porous film of Example 1 was obtained. The porous film of Example 1 had the same configuration as the porous film 1A shown in Figure 2.

[0151] [Example 2] The PI solution prepared in Example 1 was used as the solution for Example 2. As the substrate for Example 2, a substrate (KIMOTO Co., Ltd., standard blasting) was used, in which one surface (first surface) of a PET film (Toray Industries, Ltd., Matt Lumirror 50, thickness: 50 μm) was sandblasted. The substrate for Example 2 had an uneven structure on the first surface. The laminate and porous membrane of Example 2 were obtained in the same manner as in Example 1. The porous membrane of Example 2 had the same configuration as porous membrane 1A shown in Figure 2.

[0152] [Example 3] The PI solution prepared in Example 1 was used as the solution for Example 3. As the substrate for Example 3, a substrate (KIMOTO Co., Ltd., standard blasting) was used, in which one surface (first surface) of a PET film (Toray Industries, Ltd., Matt Lumirror 100, thickness: 100 μm) was sandblasted. The substrate for Example 3 had an uneven structure on the first surface. The laminate and porous membrane of Example 3 were obtained in the same manner as in Example 1. The porous membrane of Example 3 had the same structure as porous membrane 1A shown in Figure 2.

[0153] [Example 4] The PI solution prepared in Example 1 was used as the solution for Example 4. As the substrate for Example 4, a substrate (KIMOTO Co., Ltd., deep blasting (double blasting)) was used, in which one surface (first surface) of a PET film (Toray Industries, Ltd., Matt Lumirror 100, thickness: 100 μm) was sandblasted. The substrate for Example 4 had an uneven structure on the first surface. The laminate and porous membrane of Example 4 were obtained in the same manner as in Example 1. The porous membrane of Example 4 had the same structure as porous membrane 1A shown in Figure 2.

[0154] [Example 5] The PI solution prepared in Example 1 was used as the solution for Example 5. As the substrate for Example 5, a substrate (Type D, manufactured by Kaisei Kogyo Co., Ltd.) was used, in which one surface (first surface) of a PET film (thickness: 50 μm) was sandblasted. The substrate for Example 5 had an uneven structure on the first surface. The laminate and porous membrane of Example 5 were obtained in the same manner as in Example 1. The porous membrane of Example 5 had the same configuration as the porous membrane 1A shown in Figure 2.

[0155] [Example 6] The PI solution prepared in Example 1 was used as the solution for Example 6. The same substrate used in Example 1 was used as the substrate for Example 6. The PI solution was applied to the first surface of the substrate with a wet thickness of 100 μm using an applicator to form a coating film. The laminate and porous film of Example 6 were obtained in the same manner as in Example 1. The porous film of Example 6 had the same structure as porous film 1A shown in Figure 2.

[0156] [Example 7] As with Example 4, the PI solution prepared in Example 1 was used as the solution in Example 7. The same substrate used in Example 4 was used as the substrate in Example 7. The PI solution was applied to the first surface of the substrate with a wet thickness of 200 μm using an applicator to form a coating film. The laminate and porous film of Example 7 were obtained in the same manner as in Example 4. The porous film of Example 7 had the same structure as porous film 1A shown in Figure 2.

[0157] [Example 8] As a fluorine-free resin, a soluble polyimide varnish (NeoPrim S101D, manufactured by Mitsubishi Gas Chemical Company, solid content: 20 wt%, DMAC solvent) was prepared. As solvents, a sulfone-based solvent, sulfolane (Fujifilm Wako Pure Chemical Industries, Ltd.), and a cyclic ether-based solvent, 1,3-dioxolane (Tokyo Chemical Industries, Ltd.), were prepared. 1.8 g of sulfolane and 4.2 g of 1,3-dioxolane were added to 4.0 g of soluble polyimide varnish and mixed uniformly. This obtained the polyimide (PI) solution of Example 8. The polyimide concentration of the PI solution of Example 8 was 8 wt%. The laminate and porous membrane of Example 8 were obtained in the same manner as in Example 4. The porous membrane of Example 8 had the same structure as porous membrane 1A shown in Figure 2.

[0158] [Example 9] A polysulfone resin (Syensqo, Udel P-3500LCD) was prepared as a fluorine-free resin. DMF (Tokyo Chemical Industries, Ltd.) was prepared as the solvent. 1.1 g of polysulfone resin was mixed with 8.9 g of DMF. This obtained the polysulfone (PSU) solution of Example 9. The polysulfone concentration of the PSU solution of Example 9 was 11 wt%.

[0159] In Example 9, the same PET film as in Example 4 was used as the substrate. A PSU solution was applied to the first surface of the substrate using an applicator to a wet thickness of 125 μm to form a coating film.

[0160] Next, the coating film was placed inside a constant temperature and humidity chamber adjusted to a temperature of 25°C and a relative humidity of 70% for 3 seconds to perform a humidification step. After that, the coating film was immersed in a 50°C water bath for 10 minutes to allow porosity formation by phase separation and solvent extraction to proceed. Next, the coating film was fixed to a square SUS component with sides of 10 cm in plan view and dried at 80°C for 10 minutes. This obtained the laminate of Example 9, which has a porous film mainly composed of polysulfone resin. The porous film was peeled off the substrate of the laminate (peeling step). In this way, the porous film of Example 9 was obtained. The porous film of Example 9 had the same structure as the porous film 1A shown in Figure 2.

[0161] [Example 10] The PSU solution prepared in Example 9 was used as the solution for Example 10. As the substrate for Example 10, a substrate (KIMOTO Co., Ltd., standard blasting) was used, in which one surface (first surface) of a PET film (Toray Industries, Ltd., Matt Lumirror 100, thickness: 100 μm) was sandblasted. The substrate for Example 10 had an uneven structure on the first surface. The laminate and porous membrane of Example 10 were obtained in the same manner as in Example 9. The porous membrane of Example 10 had the same structure as porous membrane 1A shown in Figure 2.

[0162] [Comparative Example 1] The PI solution prepared in Example 1 was used as the solution for Comparative Example 1. As the substrate for Comparative Example 1, a substrate (Toyo Cross Co., Ltd., Tokuromat Film (Type E), Single-Sided Matte (TMFS50 Series)) was used, in which one surface (first surface) of a PET film (thickness: 50 μm) was subjected to chemical etching. The substrate for Comparative Example 1 had an uneven structure on its first surface. The laminate and porous film of Comparative Example 1 were obtained in the same manner as in Example 1. The porous film of Comparative Example 1 had the same structure as the porous film 1A shown in Figure 2.

[0163] [Comparative Example 2] The PI solution prepared in Example 1 was used as the solution for Comparative Example 2. As the substrate for Comparative Example 2, a substrate (Toyo Cross Co., Ltd., Tokuromat Film (Type E), Single-Sided Matte (TMFS29 Series)) was used, in which one surface (first surface) of a PET film (thickness: 29 μm) was subjected to chemical etching. The substrate for Comparative Example 2 had an uneven structure on its first surface. The laminate and porous film of Comparative Example 2 were obtained in the same manner as in Example 1. The porous film of Comparative Example 2 had the same structure as porous film 1A shown in Figure 2.

[0164] [Comparative Example 3] The PI solution prepared in Example 1 was used as the solution for Comparative Example 3. A PET film (thickness: 50 μm) was used as the substrate for Comparative Example 3. The substrate for Comparative Example 3 did not have an uneven structure on one surface (first surface). The laminate and porous membrane of Comparative Example 3 were obtained in the same manner as in Example 1. The porous membrane of Comparative Example 3 had the same structure as porous membrane 1A shown in Figure 2.

[0165] [Comparative Example 4] The PI solution prepared in Example 1 was used as the solution for Comparative Example 4. A glass plate (thickness: 5 mm) was used as the substrate for Comparative Example 4. The substrate for Comparative Example 4 did not have an uneven structure on one surface (first surface). The laminate and porous membrane of Comparative Example 4 were obtained in the same manner as in Example 1. The porous membrane of Comparative Example 4 had the same structure as the porous membrane 1A shown in Figure 2.

[0166] [Comparative Example 5] The PSU solution prepared in Example 9 was used as the solution for Comparative Example 5. The same PET film as the substrate for Comparative Example 3 was used as the substrate for Comparative Example 5. The laminate and porous membrane of Comparative Example 5 were obtained in the same manner as in Example 1. The porous membrane of Comparative Example 5 had the same structure as porous membrane 1A shown in Figure 2.

[0167] (Method for evaluating adhesion in the immersion process) The adhesion in the immersion process was evaluated as follows: S: No lifting or peeling of the coating film from the substrate was observed, and the substrate and coating film were in perfect adhesion. A: There were some areas where the edges of the coating film were slightly peeling from the substrate, but the substrate and coating film were in good adhesion. C: The entire coating film was lifting or peeling from the substrate.

[0168] (Method for evaluating adhesion during the drying process) The adhesion during the drying process was evaluated as follows: S: No peeling of the coating film from the substrate was observed, and the substrate and coating film were in perfect adhesion. A: There were some areas where the edges of the coating film were slightly peeled from the substrate, but the substrate and coating film were in good adhesion. C: The entire coating film had peeled off the substrate.

[0169] (Method for evaluating peelability in the peeling process) The peelability in the peeling process was evaluated as follows: S: The porous film could be smoothly peeled from the substrate. A: There was slight resistance during peeling, but the porous film could be peeled from the substrate. C: It was difficult to peel the porous film from the substrate, and the porous film was damaged when it was forcibly peeled off.

[0170] In the preparation of the porous membranes in Examples 1 to 10 and Comparative Examples 1 to 5, the adhesion during the immersion process, the adhesion during the drying process, and the peelability during the peeling process were evaluated using the method described above. The evaluation results are shown in Tables 1 to 3.

[0171] The substrates and porous membranes of Examples 1 to 10 and Comparative Examples 1 to 5 were evaluated for the items listed in Tables 1 to 3 below, using the methods described above for the substrates and porous membranes. The evaluation results are shown in Tables 1 to 3.

[0172]

[0173]

[0174]

[0175] As can be seen from Tables 1 to 3, the porous membranes of Examples 1 to 10 achieved superior air permeability despite being single membranes, compared to the porous membranes of Comparative Examples 1 to 5. Specifically, the porous membranes of Examples 1 to 10, expressed in Gurley numbers, achieved 15 seconds / 100 cm. 3 The following air permeability was observed. Furthermore, the porous membranes of Examples 1 to 10 achieved excellent water resistance. Specifically, the water resistance of the porous membranes of Examples 1 to 10 was 100 kPa or higher. Thus, the porous membranes of Examples 1 to 10 achieved a balance between air permeability and water resistance.

[0176] As can be seen from Tables 1 to 3, compared to the laminates of Comparative Examples 1 to 5, the laminates of Examples 1 to 10 maintained adhesion between the substrate and the porous film while suppressing a decrease in the peelability of the porous film from the substrate. In other words, the laminates of Examples 1 to 10 achieved both adhesion between the substrate and the porous film and peelability of the porous film from the substrate.

[0177] For example, as can be seen from comparing the results of Example 6 and Example 7, increasing the thickness of the porous membrane tended to improve the water resistance of the porous membrane, although the adhesion between the substrate and the porous membrane decreased slightly. On the other hand, decreasing the thickness of the porous membrane tended to improve both the adhesion between the substrate and the porous membrane and the air permeability of the porous membrane. Furthermore, as can be seen from comparing the results of Example 4 and Example 8, for example, increasing the resin (PI) concentration in the solution tended to improve the water resistance of the porous membrane. This is thought to be because the density of the porous membrane increased due to the increase in the resin concentration in the solution.

[0178] The technology of the present invention can be applied, for example, to waterproof and breathable membranes, waterproof and sound-permeable membranes, separators for energy storage devices, and the like.

Claims

1. A porous membrane comprising a fluorine-free resin as the main component, having a first surface with multiple pores and a second surface opposite to the first surface, wherein the arithmetic mean height Sa1 of the first surface is 0.2 μm or more.

2. The porous membrane according to claim 1, wherein the resin comprises at least one selected from the group consisting of polyimide resin, polysulfone resin, polyethersulfone resin, polyphenylsulfone resin, polystyrene resin, polyacrylonitrile resin, vinyl chloride resin, polycarbonate resin, polyamideimide resin, and polyetherimide resin.

3. The porous membrane according to claim 1, wherein the unfolded interface area ratio Sdr1 of the first surface is 10% or more.

4. The porous membrane according to claim 1, comprising a porous layer and a microporous layer disposed on one or both surfaces of the porous layer, wherein the surface of the microporous layer constitutes the first surface.

5. The porous membrane according to claim 4, wherein the microporous layer is arranged on both surfaces of the porous layer, and the microporous layer includes a first microporous layer arranged on one surface of the porous layer and a second microporous layer arranged on the other surface of the porous layer, and the surface of the first microporous layer constitutes the first surface.

6. The porous membrane according to claim 1, wherein the ratio of the arithmetic mean height Sa2 of the second surface to the arithmetic mean height Sa1 of the first surface is in the range of 0.10 or more and 0.55 or less.

7. The porous membrane according to claim 1, wherein the porous membrane has a thickness of 10 μm or more and 50 μm or less.

8. The porous membrane according to claim 1, wherein the average pore size on the first surface is 0.01 μm or more and 5 μm or less.

9. The porous membrane according to claim 1, wherein the average pore size on the second surface is 0.1 μm or more and 10 μm or less.

10. The permeability of the porous membrane is expressed in Gurley numbers as 15 seconds / 100 cm. 3 The porous membrane according to claim 1, which is as follows:

11. The porous membrane according to claim 1, wherein the water pressure resistance of the porous membrane, as measured according to the water resistance test method B (high water pressure method) specified in JIS L1092:2009, is 100 kPa or more.

12. The porous membrane according to claim 1, wherein the fluorine content in the porous membrane is less than 0.1% by weight.

13. The porous membrane according to claim 1, which does not have a substrate arranged in contact with the first surface.

14. A laminate comprising a substrate having a first surface and a second surface opposite to the first surface, and a porous membrane disposed on the first surface of the substrate, wherein the porous membrane is the porous membrane described in any one of claims 1 to 13, and the arithmetic mean height Sa3 of the first surface of the substrate is 0.42 μm or more.

15. The laminate according to claim 14, wherein the unfolded interface area ratio Sdr3 of the first surface of the substrate is 3% or more.

16. The laminate according to claim 14, wherein the substrate is a non-porous film.

17. The laminate according to claim 14, wherein the substrate has a thickness of 30 μm or more and 150 μm or less.

18. The laminate according to claim 14, wherein the fluorine content in the substrate is less than 0.1% by weight.

19. A method for producing a porous film, comprising the steps of: applying a solution containing a fluorine-free resin and a solvent to the first surface of a substrate having a first surface and a second surface opposite to the first surface to form a coating film; immersing the coating film in water; drying the coating film; and peeling the coating film from the substrate, wherein the arithmetic mean height Sa3 of the first surface of the substrate is 0.42 μm or more.

20. The method for producing a porous membrane according to claim 19, wherein the resin comprises at least one selected from the group consisting of polyimide resin, polysulfone resin, polyethersulfone resin, polyphenylsulfone resin, polystyrene resin, polyacrylonitrile resin, vinyl chloride resin, polycarbonate resin, polyamideimide resin, and polyetherimide resin.

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