Polyamide porous membrane and method for producing the same

Abstract

To provide a polyamide porous membrane having an excellent porous structure, and a method for producing a polyamide porous membrane, which can be produced without using organic solvent, acid or the like and has an excellent porous structure.SOLUTION: A polyamide porous membrane having a porous structure is provided, which comprises a nodes 10 that are the aggregate of polyamide resin, and fibrils 11 that connect the nodes and are made of polyamide resin. A method for producing a polyamide porous membrane includes applying width-constrained stretching to a polyamide film comprising polyamide resin, to form a porous structure that comprises nodes that are the aggregate of polyamide resin, and fibrils that connect the nodes and are made of polyamide resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a polyamide porous membrane and a method for making the same. [Background technology]

[0002] Polyamide resin is an engineering plastic with a high melting point. It contains a polar amide group (-CO-NH-) that forms hydrogen bonds with adsorbates containing highly electronegative atoms such as oxygen, sulfur, nitrogen, and halogens. Therefore, porous membranes containing polyamide resin are expected to be used as filters with excellent separation capabilities. For example, porous membranes containing polyamide resin are thought to be useful as filters for detecting and removing impurities such as metal particles from ultrapure water used for cleaning large-scale integrated circuits (LSIs).

[0003] Patent Document 1 discloses a polyamide porous membrane containing a polyamide resin, in which the surface layer has a honeycomb porous structure with a pore size of 5 to 50 μm, the interior is formed in a three-dimensional mesh shape, the pores inside the mesh have a continuous pore structure, and the honeycomb porous structure and the mesh structure are connected to each other. Patent Document 2 discloses a porous film containing an aromatic polyamide, the porous film having surfaces with different opening ratios, wherein the ratio Pa / Pb of the opening ratio Pa of the surface with the smaller opening ratio (small opening ratio surface) to the opening ratio Pb of the surface with the larger opening ratio (large opening ratio surface) is 0.05 or more and 0.90 or less, and the ratio of oxygen atoms to carbon atoms (O / C) of at least one surface is 0.05 or more and 0.40 or less. Patent Document 3 discloses a porous polyamide film for filters, which has a porous structure with fine through-holes, a porosity of 15 to 85%, a pore size of 0.01 to 5 μm, and a film thickness of 10 to 50 μm, and which has a structure in which a microporous layer and a layer with relatively large voids or openings are stacked in the cross-sectional direction of the film, and the above two layers are connected to each other by the through-holes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-106261 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-254577 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-113143 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have now found that there is room for further improvement in the porous structure of conventionally known porous films containing polyamide resins. Furthermore, the inventors have discovered a new problem that conventionally known porous membranes containing polyamide resins are manufactured by methods using organic solvents, acids, etc. (wet methods, methods using track etching), and when these porous membranes are used as filters, the organic solvents, acids, etc. remaining in the porous membrane may be mixed into ultrapure water, etc.

[0006] The problem to be solved by the present disclosure is to provide a polyamide porous membrane having a good porous structure. The problem to be solved by the present disclosure is to provide a method for producing a polyamide porous membrane having a good porous structure, which can be produced without using organic solvents, acids, etc. [Means for solving the problem]

[0007] <1> a node which is an aggregate of polyamide resin; Fibrils connecting the nodes and made of polyamide resin; A polyamide porous membrane having a porous structure comprising: <2> The fibrils extend in one direction. <1> The polyamide porous membrane according to claim 1. <3> the nodes extend in a direction different from that of the fibrils; <2> The polyamide porous membrane according to claim 1. <4> The breaking strength in the direction in which the fibrils extend is 50 MPa or more. <2> or <3> 1. The polyamide porous membrane according to any one of the above. <5> The nitrogen permeability coefficient measured at 25°C is 1 x 10 -13 mol m / (m 2 ·s·Pa) or more, <1> ~ <4> 1. The polyamide porous membrane according to any one of the above. <6> The polyamide resin contains polycaprolactam. <1> ~ <5> 1. The polyamide porous membrane according to any one of the above. <7> The content of the polycaprolactam relative to the total mass of the polyamide resin is 70 mass% or more. <6> The polyamide porous membrane according to claim 1. <8> The content of the polyamide resin relative to the total mass of the polyamide porous membrane is 50 mass% or more. <1> ~ <7> 1. The polyamide porous membrane according to any one of the above. <9> The average length of the fibrils is 1 μm to 500 μm. <1> ~ <8> 1. The polyamide porous membrane according to any one of the above. <10> The node has a width of 1 μm to 500 μm. <1> ~ <8> 1. The polyamide porous membrane according to any one of the above. <11> The area ratio of fibrils on the surface of the polyamide porous membrane is 10% to 90%. <1> ~ <10> 1. The polyamide porous membrane according to any one of the above. <12> The thickness is 1 μm to 500 μm. <1> ~ <11> 1. The polyamide porous membrane according to any one of the above. <13> A method for producing a polyamide porous membrane, comprising width-constraining and stretching a polyamide film containing a polyamide resin to form a porous structure including nodes, which are aggregates of the polyamide resin, and fibrils, which connect the nodes and are also made of the polyamide resin. <14> The polyamide resin contains polycaprolactam. <13> A method for producing the polyamide porous membrane described in [Effects of the Invention]

[0008] According to the present disclosure, a polyamide porous membrane having a good porous structure can be provided. According to the present disclosure, a method for producing a polyamide porous membrane having a good porous structure can be provided, which can be produced without using organic solvents, acids, etc. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 shows an SEM image of the surface of the porous polyamide membrane of Example 1. [Figure 2] FIG. 2 shows an enlarged SEM image of a portion of FIG. [Figure 3] FIG. 3 shows an SEM image of the surface of the porous polyamide membrane of Example 2. [Figure 4] FIG. 4 shows an enlarged SEM image of a portion of FIG. [Figure 5] FIG. 5 shows an SEM image of the surface of the stretched film of Comparative Example 2. [Figure 6] FIG. 6 shows an SEM image of the stretched film of Comparative Example 3 and an enlarged image of a part of the SEM image. [Figure 7] FIG. 7 is a schematic diagram for explaining one embodiment of the gas permeability evaluation. [Figure 8] FIG. 8 is a diagram showing the gas permeability coefficient of each block of the test piece of the porous polyamide membrane of Example 1. [Figure 9] FIG. 9 is a diagram showing the gas permeability coefficient of each block of the test piece of the porous polyamide membrane of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments for carrying out the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, components are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0011] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0012] In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content of each component means the total content of the multiple substances present in the composition, unless otherwise specified.

[0013] (Polyamide porous membrane) The polyamide porous membrane of the present disclosure has a porous structure including nodes, which are aggregates of polyamide resin, and fibrils, which connect the nodes and are also made of polyamide resin.

[0014] According to the present disclosure, a polyamide porous membrane having a good porous structure can be provided.

[0015] The reason for the above effect is presumed to be as follows, but is not limited to this. The polyamide porous membrane of the present disclosure has a structure including nodes, which are aggregates of polyamide resin, and fibrils, which connect the nodes and are made of polyamide resin. It is presumed that a good porous structure is formed because slit-like pores are formed in the fibrils formed between the nodes and the fibrils are held by the nodes.

[0016] The polyamide porous membrane of the present disclosure has a porous structure including nodes, which are aggregates of polyamide resin, and fibrils connecting the nodes. In the porous structure, the fibrils connecting the nodes form pores through which liquids and gases can pass. Therefore, the polyamide porous membrane of the present disclosure can be suitably used as a filter for removing impurities, etc.

[0017] The fibrils preferably extend in one direction. In the polyamide porous membrane of the present disclosure, the fibrils extend in one direction, which allows a good porous structure to be formed and maintained, thereby improving the impurity removal performance when used as a filter or the like. In one embodiment, the one direction is the stretching direction of width-constrained stretching carried out in the method for producing a porous polyamide membrane described below.

[0018] The nodes preferably extend in one direction, preferably in a direction different from that in which the fibrils extend. In the polyamide porous membrane of the present disclosure, the nodes extend in one direction, which allows a porous structure to be well formed and well maintained, thereby improving the impurity removal performance when used as a filter or the like. In one embodiment, the one direction is a direction perpendicular to the stretching direction of width-constrained stretching carried out in the method for producing a porous polyamide membrane described below.

[0019] When fibrils extend in one direction and in a direction different from the direction in which the nodes extend, the angle between the direction in which the nodes extend and the direction in which the fibrils extend is preferably 45° to 135°, more preferably 60° to 120°, and even more preferably 70° to 110°. By setting the angle between the direction in which the nodes extend and the direction in which the fibrils extend within the above range, a porous structure is well formed and maintained, and the impurity removal performance when used as a filter or the like can be improved.

[0020] The above angle is measured by the following method. First, a scanning electron microscope (SEM) is used to obtain an SEM image of the surface of the polyamide porous membrane. Next, in an observation area of ​​1000 μm×1000 μm, the average value of the angle formed between the extending direction of the node and the extending direction of the fibril is calculated and used as the above-mentioned angle.

[0021] From the viewpoint of improving the impurity removal performance when used as a filter or the like, the pore diameter of the pores possessed by the polyamide porous membrane of the present disclosure, as measured by mercury intrusion porosimetry, is preferably 500 nm or less, and more preferably 100 nm or less. The upper limit of the pore diameter is not particularly limited, and can be set to 1000 nm or more.

[0022] From the viewpoint of improving the impurity removal performance when used as a filter or the like, the specific surface area of ​​the pore diameter of the polyamide porous membrane of the present disclosure is 1 m 2 / g or more, and 2 / g or more is more preferable. In the present disclosure, the pore diameter specific surface area is measured by mercury intrusion porosimetry.

[0023] The average length of the fibrils is preferably 1 μm to 500 μm, and more preferably 5 μm to 100 μm. By setting the average fibril length within the above range, a good porous structure can be formed, and the impurity removal performance can be improved when used as a filter or the like.

[0024] The width of the node is preferably 1 μm to 500 μm, and more preferably 5 μm to 100 μm. By setting the node width within the above range, the porous structure is maintained in a good condition, and the impurity removal performance can be improved when the porous structure is used as a filter or the like.

[0025] In the present disclosure, the average fibril length and node width are measured by the following method. First, a scanning electron microscope (SEM) is used to obtain an SEM image of the surface of the polyamide porous membrane. Next, the lengths of all fibrils and widths of node bands included in an observation area of ​​1000 μm×1000 μm are measured, and the average values ​​are taken as the average fibril length and node width.

[0026] The area ratio of fibrils on the surface of the polyamide porous membrane is preferably 10% to 90%, more preferably 25% to 75%, and even more preferably 40% to 70%. By setting the area ratio of fibrils to 90% or less, a porous structure is formed well and maintained well, thereby improving the impurity removal performance when used as a filter, etc.

[0027] The area ratio of fibrils is measured by the following method. First, a scanning electron microscope (SEM) is used to obtain an SEM image of the surface of the polyamide porous membrane. Next, an observation area of ​​1000 μm×1000 μm is image-processed, and the area ratio of fibrils is measured by pixel ratio.

[0028] The polyamide porous membrane of the present disclosure comprises a polyamide resin. Polyamide resins include polycaprolactam (nylon 6), poly-ω-aminoheptanoic acid (nylon 7), poly-ω-aminononanoic acid (nylon 9), polyundecaneamide (nylon 11), polylaurinlactam (nylon 12), polyethylenediamineadipamide (nylon 2,6), polytetramethyleneadipamide (nylon 4,6), polyhexamethylenediadipamide (nylon 6,6), polyhexamethylenesebacamide (nylon 6,10), polyhexamethylenedecamide (nylon 6,12), polyoctamethyleneadipamide (nylon Nylon 8,6), polydecamethylene adipamide (nylon 10,6), polydecamethylene sebacamide (nylon 12,10), polydecamethylene dodecamide (nylon 10,12), metaxylenediamine 6 nylon, polyundecamethylene adipamide (nylon 11,6), polyundecanamide (nylon 11), polytetramethylene succinamide (nylon 4,4), polytetramethylene glutamide (nylon 4,5), polytetramethylene azelamide (nylon 4,9), polytetramethylene sebacamide (nylon 4,10), polytetramethylene Polypentamethylene dodecamide (Nylon 4,12), Polypentamethylene succinamide (Nylon 5,4), Polypentamethylene glutamide (Nylon 5,5), Polypentamethylene adipamide (Nylon 5,6), Polypentamethylene azelamide (Nylon 5,9), Polypentamethylene sebacamide (Nylon 5,10), Polypentamethylene dodecamide (Nylon 5,12), Polyhexamethylene succinamide (Nylon 6,4), Polyhexamethylene glutamide (Nylon 6,5), Polyhexamethylene azelamide (Nylon 6,9), Polynonamethylene Polydodecamethylene adipamide (Nylon 9,6), Polynonameethylene azelamide (Nylon 9,9), Polynonameethylene sebacamide (Nylon 9,10), Polynonameethylene dodecamide (Nylon 9,12), Polydecamethylene azelamide (Nylon 10,9), Polydodecamethylene adipamide (Nylon 12,6), Polydodecamethylene azelamide (Nylon 12,9), Polydodecamethylene sebacamide (Nylon 12,10), Polydodecamethylene dodecamide (Nylon 12,12), Nylon 9,2, Nylon 10,2, Nylon 12,2, Nylon 6,The nylon may include one or more nylons selected from the group consisting of nylon 2 and copolymers thereof. From the viewpoint of forming a good porous structure and improving the impurity removal performance when used as a filter or the like, the polyamide resin preferably contains one or more polyamides selected from the group consisting of polycaprolactam, polyethylenediamineadipamide, and copolymers thereof, and more preferably contains polycaprolactam.

[0029] The polyamide contained in the polyamide resin may be charge-modified. When the polyamide resin contains the charge-modified polyamide, the impurity removal performance can be improved when the polyamide resin is used as a filter, etc. In particular, the adsorption performance for metal particles and the like can be improved. Materials that can be used for charge modification of polyamides include conventionally known materials, such as a reaction product of epichlorohydrin and polydiallylmethylamine.

[0030] When the polyamide resin contains polycaprolactam, the content of polycaprolactam relative to the total mass of the polyamide resin is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, most preferably 95% by mass or more, and may be 100% by mass. By setting the content of polycaprolactam within the above range, a good porous structure can be formed, and the impurity removal performance can be improved when used as a filter or the like.

[0031] The content of the polyamide resin relative to the total mass of the polyamide porous membrane is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. By setting the content of the polyamide resin within the above range, a good porous structure can be formed, and the impurity removal performance can be improved when used as a filter or the like. The upper limit of the content of the polyamide resin is not particularly limited, and can be set to 95% by mass or less.

[0032] The polyamide porous membrane of the present disclosure preferably does not contain an organic solvent or an acid, or contains at least one of an organic solvent and an acid, and the total content of these organic solvents and acids relative to the mass of the polyamide porous membrane is preferably less than 5 mass%, and more preferably does not contain an organic solvent or an acid. The polyamide porous membrane has a low content of organic solvents and acids, and therefore when used as a filter, it can prevent the organic solvents and acids from being mixed into ultrapure water or the like. Examples of the organic solvent include alcohol solvents such as methanol, ethanol, isopropanol, 1-butanol, hexafluoroisopropanol, and trifluoroethanol; amide solvents such as N-methyl-2-pyrrolidone, dimethylacetamide, hexamethylene phosphoramide, dimethylformamide, and dimethylimidazolidinone; dimethyl sulfone, acetone, tetrahydrofuran, dioxane, 2-butanone, ethyl acetate, isopropyl acetate, benzene, and toluene. The acid includes formic acid, nitric acid, sulfuric acid, and the like.

[0033] The nitrogen permeability coefficient of the polyamide porous membrane of the present disclosure measured at 25°C is 1 × 10 -13 mol m / (m 2 ·s·Pa) or more, and -13 mol m / (m 2 s Pa) or more, and 1×10 -12 mol m / (m 2 It is more preferable that the viscosity is 1.0 s·Pa or more. By setting the nitrogen permeability coefficient of the polyamide porous membrane of the present disclosure within the above numerical range, the impurity removal performance can be improved when used as a filter or the like. The upper limit of the nitrogen permeability coefficient is not particularly limited, and is 1×10 -8 mol m / (m 2 ·s·Pa) or less.

[0034] In the present disclosure, the nitrogen permeability coefficient is measured as follows. First, the polyamide porous membrane of the present disclosure is cut into a circular shape with a diameter of 30 mm to prepare a test piece. Next, in an environment of 25°C, the circular test piece is set in the measurement cell of a membrane diffusion measurement device. Next, nitrogen gas is introduced into the high-pressure side gas reservoir, and the low-pressure side of the cell is evacuated. The high-pressure side valve of the cell is opened to introduce nitrogen gas, and gas permeation measurement is started. The time course of the voltage change at this time is recorded, and the nitrogen permeability coefficient is calculated according to the following formula (voltage on the low-pressure side and the high-pressure side (1 V = 1.6 KPa)). As the membrane diffusion measuring device, a K-315N-01 manufactured by Tsukubarika Seiki Co., Ltd. connected to a data logger GL20 manufactured by Graphtec Corporation or a device of the same level can be used. Q1=(V / (R×T×P×A))×(dp / dt) p1=Q1×L (In the formula, Q1: Nitrogen permeability (mol / (m 2 ·s·Pa)) p1 = nitrogen permeability coefficient (mol m / (m 2 ·s·Pa)) V: Cell low-pressure side volume (L) A: Transmission area (m 2 ) (Note that π=3.14) T: Test temperature (℃) P: Supply gas differential pressure (Pa) dp / dt: Change in pressure (p) on the low pressure side per unit time (t) (Pa / s) L: thickness of test piece)

[0035] The thickness of the polyamide porous membrane of the present disclosure is preferably 1 μm to 500 μm, more preferably 10 μm to 500 μm, and even more preferably 10 μm to 100 μm. By making the thickness of the polyamide porous membrane 1 μm or more, the strength of the polyamide porous membrane can be improved, and breakage during processing or the like can be suppressed. By setting the thickness of the polyamide porous membrane to 500 μm or less, the porous structure is well interconnected, and the impurity removal performance can be improved when used as a filter or the like. In the present disclosure, the thickness of a polyamide porous membrane is measured at any five points using a micrometer, and the average value is calculated. The micrometer may be, for example, an MDH-25MB manufactured by Mitutoyo Corporation or an equivalent device.

[0036] When fibrils extend in one direction, the breaking strength of the polyamide porous membrane of the present disclosure in the direction in which the fibrils extend is preferably 50 MPa or more, more preferably 100 MPa or more, from the viewpoint of preventing breakage during processing, etc. The upper limit of the breaking strength is not particularly limited, and can be 500 MPa or less.

[0037] When fibrils extend in one direction, the breaking strength of the polyamide porous membrane of the present disclosure in the direction perpendicular to the fibril extension direction is preferably 20 MPa or more, more preferably 30 MPa or more, from the viewpoint of suppressing breakage during processing, etc. The upper limit of the breaking strength is not particularly limited, and can be 500 MPa or less.

[0038] The ratio of the breaking strength in the direction perpendicular to the fibril extension direction to the breaking strength in the fibril extension direction of the polyamide porous membrane of the present disclosure (breaking strength in the direction perpendicular to the fibril extension direction / breaking strength in the fibril extension direction) is preferably 1 / 10 to 9 / 10, and more preferably 2 / 10 to 7 / 10. By setting the breaking strength ratio within the above range, a good porous structure can be formed and breakage during processing or the like can be suppressed.

[0039] In the present disclosure, the breaking strength of a porous polyamide membrane is measured by a tensile test. Specifically, a dumbbell-shaped piece (test piece) measuring 12 mm in length and 3 mm in width is cut out from the polyamide porous film. The test pieces are cut out so that the stretching direction of the porous polyamide membrane produced by width-constrained stretching is the longitudinal direction of the dumbbell piece, and the direction perpendicular to the stretching direction is the lateral direction of the dumbbell piece. The test piece is subjected to a tensile test using a tensile tester at a test speed of 20 mm / min and at 19.8° C. The maximum stress in the recorded stress chart is divided by the cross-sectional area of ​​the film to obtain the tensile breaking strength. As the tensile tester, a Tensilon universal testing machine RTC-1325A manufactured by ORIENTEC or a device of the same level can be used.

[0040] The polyamide porous membrane of the present disclosure has a porous structure including nodes, which are aggregates of polyamide resin, and fibrils that connect the nodes, and can be suitably used as an adsorption filter for removing impurities contained in liquids or gases in various fields. The polyamide porous membrane of the present disclosure can also be used as a filter for testing the quality of washing water (ultrapure water, etc.) used to wash LSIs and the like.

[0041] (Method of manufacturing a polyamide porous membrane) The method for producing a polyamide porous membrane of the present disclosure includes width-constraining and stretching a polyamide film to form a porous structure including nodes, which are aggregates of the polyamide resin, and fibrils, which connect the nodes and are composed of the polyamide resin. Width-constrained stretching refers to stretching in the longitudinal direction (machine direction (MD)) while restraining the film in the transverse direction (TD) to prevent stretching in the transverse direction. The lateral direction means a direction perpendicular to the longitudinal direction.

[0042] According to the present disclosure, it is possible to provide a polyamide porous membrane that can be produced without using organic solvents, acids, etc.

[0043] The reason for the above effect is presumed to be as follows, but is not limited to this. In the method for producing a polyamide porous membrane of the present disclosure, a film containing a polyamide resin is stretched under width constraint to form a porous structure including nodes, which are aggregates of polyamide resin extending in the width constraint direction, and fibrils extending in the stretching direction and connecting the nodes. Therefore, there is no need to use a wet method using an organic solvent or a track etching method using an acid to produce a porous membrane. Therefore, the polyamide porous membrane produced by the method of the present disclosure contains a small amount of organic solvent, acid, etc., and even when used as an adsorption filter, organic solvent, acid, etc. are less likely to be mixed into ultrapure water, etc. The polyamide porous membrane produced by the production method of the present disclosure has a structure including nodes, which are aggregates of polyamide resin, and fibrils connecting the nodes. It is presumed that a good porous structure is formed because slit-like pores are formed in the fibrils formed between the nodes and the fibrils are held by the nodes.

[0044] The fibrils preferably extend in the stretching direction, which allows a porous structure to be well formed and maintained, improving the impurity removal performance when used as a filter or the like.

[0045] The nodes preferably extend in a direction different from the stretching direction, which allows the porous structure to be well formed and well maintained, improving the impurity removal performance when used as a filter or the like.

[0046] The angle between the extending direction of the nodes and the extending direction of the fibrils is preferably 45° to 135°, more preferably 60° to 120°, and even more preferably 70° to 110°. By setting the angle between the extending direction of the nodes and the extending direction of the fibrils within the above range, a porous structure is well formed and maintained, and the impurity removal performance when used as a filter or the like can be improved.

[0047] The pore diameter of the pores, the specific surface area of ​​the pore diameter, the average fibril length, the node width, the area ratio of the fibrils, and the preferred numerical ranges of the thickness and breaking strength of the polyamide porous membrane produced by the polyamide porous membrane production method of the present disclosure are as described above, and therefore will not be described here.

[0048] When the temperature at which the polyamide film is stretched in a restricted width direction is designated as T, it is preferable that the following formula (1) is satisfied, and it is more preferable that the following formula (2) is satisfied. When the temperature at which the polyamide film is stretched in a widthwise constrained direction is T, satisfying the following formula (1) allows a good porous structure to be formed, thereby improving the impurity removal performance when used as a filter, etc. In the present disclosure, the melting point is the melting peak temperature determined by differential scanning calorimetry (DSC) in accordance with JIS K 7121 (1987). In the present disclosure, the melting point is measured using a differential scanning calorimeter (for example, DSC7200, manufactured by Hitachi High-Tech Science Corporation) at a temperature increase rate of 10° C. / min. T≧Melting point of polyamide resin -40℃ (1) T≧Melting point of polyamide resin -20℃ (2)

[0049] The temperature at which the width-constrained stretching of the polyamide film is carried out is preferably 185°C or higher, more preferably 190°C or higher, and even more preferably 200°C or higher. By performing width-constrained stretching of the polyamide film at a temperature of 185°C or higher, a good porous structure is formed, and the impurity removal performance can be improved when the film is used as a filter or the like. The upper limit of the temperature is not particularly limited, and can be set to the melting point of the polyamide resin + 50°C or less. The temperature at which width-constrained stretching is carried out refers to the temperature near the surface of the polyamide film during width-constrained stretching, and the surface temperature is measured by a thermocouple installed in the stretching machine.

[0050] In the width-constrained stretching of the polyamide film, the stretch ratio in the MD is preferably 1.1 times or more, more preferably 1.5 times or more, and even more preferably 1.8 times or more. In the width-constrained stretching, the stretch ratio in the TD is limited to 1. By setting the MD stretching ratio in width-constrained stretching of a polyamide film to 1.1 times or more, a good porous structure is formed, and the impurity removal performance when used as a filter, etc. can be improved. The stretching ratio in the MD during width-constrained stretching of the polyamide film is preferably 5 times or less, more preferably 4 times or less, and even more preferably 3.5 times or less. By setting the MD stretching ratio in width-constrained stretching of the polyamide film to 5 times or less, the strength of the polyamide porous membrane can be improved, and breakage during processing or the like can be suppressed. The stretching ratio is determined based on the length of the polyamide film immediately before the width-constrained stretching. In other words, when biaxial stretching is performed before the width-constrained stretching, the stretching ratio is determined based on the length of the polyamide film after the biaxial stretching.

[0051] When the length of the polyamide film in the width-constrained stretching direction is X (mm), the stretching speed in the width-constrained stretching of the polyamide film is preferably 0.1X / min to 10X / min, and more preferably 0.5X / min to 5X / min. By setting the stretching speed in the width-constrained stretching of the polyamide film within the above range, a good porous structure can be formed, and the impurity removal performance can be improved when the film is used as a filter or the like.

[0052] The width-constrained stretching of the polyamide film may be carried out two or more times, and the temperature, stretch ratio, and stretching speed in each width-constrained stretching may be the same or different.

[0053] The polyamide film may be biaxially stretched before being subjected to width-constrained stretching. By biaxially stretching the polyamide film before width-constrained stretching, a good porous structure is formed, and the impurity removal performance can be improved when the polyamide film is used as a filter or the like.

[0054] The temperature at which the polyamide film is biaxially stretched is preferably equal to or higher than the glass transition temperature of the polyamide resin. By setting the temperature for biaxial stretching to be equal to or higher than the glass transition temperature of the polyamide resin, a good porous structure is formed, and the impurity removal performance can be improved when the film is used as a filter or the like. The temperature at which the polyamide film is biaxially stretched is preferably 140°C or higher, more preferably 150°C or higher, and even more preferably 160°C or higher. The upper limit of the temperature is not particularly limited, and can be set to the melting point of the polyamide resin + 50°C or less. In the present disclosure, the glass transition temperature is the midpoint glass transition temperature determined by DSC in accordance with JIS K 7121 (1987). The temperature at which biaxial stretching is carried out refers to the temperature near the surface of the polyamide film during biaxial stretching, and the surface temperature is measured by a thermocouple installed in the stretching machine.

[0055] The stretching ratio in MD and TD during biaxial stretching of the polyamide film is preferably 1.1 times or more, more preferably 1.5 times or more, and even more preferably 1.8 times or more. By setting the stretching ratio during biaxial stretching of a polyamide film to 1.1 times or more, a good porous structure can be formed by width-constrained stretching following biaxial stretching, thereby improving the impurity removal performance when used as a filter, etc. The stretching ratio in MD and TD during biaxial stretching of the polyamide film is preferably 5 times or less, more preferably 4 times or less, and even more preferably 3.5 times or less. By setting the stretching ratio in biaxial stretching of the polyamide film to 5 times or less, the strength of the polyamide porous membrane can be improved, and breakage during processing or the like can be suppressed. The stretching ratios in MD and TD may be the same or different. In addition, simultaneous biaxial stretching, in which MD stretching is performed first and then TD stretching, may be used, or sequential biaxial stretching, in which MD stretching is performed first and then TD stretching may be used. The stretching ratio is determined based on the length of the polyamide film immediately before biaxial stretching.

[0056] When the lengths of the polyamide film in the biaxial stretching directions are Y (mm) and Z (mm), respectively, the stretching speed in biaxial stretching of the polyamide film is preferably 0.1Y(Z) / min to 10Y(Z) / min, and more preferably 0.5Y(Z) / min to 5Y(Z) / min. By setting the stretching speed in biaxial stretching of the polyamide film within the above numerical range, a porous structure can be formed well by width-constrained stretching following biaxial stretching, and the impurity removal performance can be improved when the film is used as a filter, etc.

[0057] The polyamide film used in the width-constrained stretching may be prepared by a conventionally known method, or a commercially available film may be used. For example, it can be produced by melt-press molding raw material pellets containing a polyamide resin. The preferred composition of the polyamide resin is as described above, and will not be described here. Furthermore, the raw material pellets preferably do not contain organic solvents or acids. Since the raw material pellets do not contain organic solvents or acids, when the produced polyamide porous membrane is used as a filter, it is possible to prevent the organic solvents and acids from being mixed into ultrapure water, etc. [Example]

[0058] The above embodiment will be specifically described below using examples, but the above embodiment is not limited to these examples.

[0059] Example 1 Raw material pellets of polycaprolactam (Toray Industries, Inc., Alamin CM1041LO, melting point 225°C) were dried in a vacuum oven at 80°C for 6 hours to thoroughly remove moisture. The dried raw material pellets were placed in a spacer and sandwiched between a polyimide sheet (Ube Industries, Ltd., Upilex (registered trademark) 125S) and a stainless steel plate. Using a vacuum press molding machine manufactured by Japan Baldwin Co., Ltd., the temperature was maintained at 250°C, which is above the melting point of polycaprolactam (225°C), for 7 minutes. After that, the air was evacuated several times at a pressure of 2 MPa for 2 minutes, and then melt press molding was performed at a pressure of 5 MPa. The mixture was then slowly cooled to room temperature to obtain a pressed film with a thickness of 150 μm. The resulting pressed film was stored in a desiccator to prevent water absorption.

[0060] The resulting pressed film was cut into 30 mm x 30 mm pieces and placed in a biaxial stretching machine equipped with an air chuck and a stress detector. The biaxial stretching machine allows for heating by blowing hot air from above and below the film using a blower. The raw film was then heated for 3 minutes at 160°C, above the glass transition temperature of polycaprolactam (47°C). After this, the film was simultaneously biaxially stretched at a stretching rate of 20 mm / min while maintaining the temperature, resulting in a 60 μm-thick biaxially stretched film. The stretching ratios in both the MD (longitudinal direction) and TD (transverse direction) were 2x.

[0061] The biaxially stretched film was set in the biaxial stretching machine. The transverse direction of the stretched film was fixed. The stretched film was held at 200°C, which is above the glass transition temperature (47°C) of polycaprolactam, for 3 minutes, and then stretched with width constraint at a stretching speed of 20 mm / min while maintaining the temperature, to obtain a 40 μm thick porous polyamide membrane. The stretching ratio in the MD was 2 times.

[0062] When the above-mentioned porous polyamide membrane was observed with a scanning electron microscope (SEM), a porous structure was observed having nodes 10, which are aggregates of polycaprolactam, and fibrils 11 connecting the nodes 10, as shown in Figure 1. The arrow in Figure 1 indicates the stretching direction during width-constrained stretching. 1, it can be seen that the nodes 10 and the fibrils 11 extend in different directions. The angle formed by the extending direction of the nodes and the extending direction of the fibrils was measured and found to be 90°. The area ratio of fibrils was 50%. The node width was measured to be 25 μm, and the average fibril length was 25 μm. FIG. 2 is an eight-times enlarged image of the area where fibrils 11 are formed in the porous polyamide membrane (the area surrounded by a square in FIG. 1).

[0063] <Example 2> The press film produced in Example 1 was set in the biaxial stretching machine. The raw film was held at 160°C, which is above the glass transition temperature of polycaprolactam (47°C), for 3 minutes, and then, while maintaining the temperature, it was stretched with width constraint at a stretching speed of 20 mm / min to obtain a width-constrained stretched film with a thickness of 90 μm. The stretching ratio in both MD directions was 2x.

[0064] The width-constrained stretched film was cut into a size of 30 mm x 30 mm and set in the biaxial stretching machine. The short-side direction of the set stretched film was fixed. The stretched film was held at 200°C, which is above the glass transition temperature of polycaprolactam (47°C), for 3 minutes, and then, while maintaining the temperature, it was stretched with width constraint at a stretching speed of 20 mm / min to obtain a polyamide porous membrane with a thickness of 70 μm. The stretching ratio in the MD was 2 times.

[0065] When the above-mentioned porous polyamide membrane was observed with a scanning electron microscope, a porous structure was observed having nodes 20, which are aggregates of polycaprolactam, and fibrils 21 connecting the nodes 20, as shown in Figure 3. The arrows in Figure 3 indicate the stretching direction during width-constrained stretching. 3, it can be seen that the nodes 20 and the fibrils 21 extend in different directions. The angle formed by the extending direction of the nodes and the extending direction of the fibrils was measured and found to be 65°. The area ratio of fibrils was 35%. The width of the nodes was measured to be 35 μm, and the length of the fibrils was 20 μm. FIG. 4 is an eight-times enlarged image of the area where fibrils 21 are formed in the porous polyamide membrane (the area surrounded by a square in FIG. 3).

[0066] <Comparative Example 1> The pressed film produced in Example 1 was prepared.

[0067] <Comparative Example 2> The biaxially stretched film produced in Example 1 was prepared. When the biaxially stretched film was observed with a scanning electron microscope, no porous structure having nodes and fibrils was observed, as shown in FIG.

[0068] <Comparative Example 3> The pressed film prepared in Example 1 was placed in a uniaxial stretching machine (Tensilon Universal Testing Machine RTC-1325A, manufactured by ORINTEC Corporation). In the uniaxial stretching machine, the film can be heated by blowing hot air from above and below the placed film using a blower. The raw film was held at 200°C, which is above the glass transition temperature of polycaprolactam (47°C), for 3 minutes, and then, while maintaining the temperature, it was uniaxially stretched at a stretching rate of 1 / min to obtain a stretched film with a thickness of 100 μm. The stretching ratio was 2x.

[0069] When the uniaxially stretched film was observed under a scanning electron microscope, only fibrils were observed, and no nodes were observed, as shown in FIG. FIG. 6 also shows an 8x magnified image of the area where fibrils are formed in the stretched film (area surrounded by a square in the SEM image).

[0070] <<Evaluation of porous structure>> The polyamide porous films of Examples 1 and 2, the pressed film of Comparative Example 1, the biaxially stretched film of Comparative Example 2, and the uniaxially stretched film of Comparative Example 3 were cut into circular pieces with a diameter of 30 mm to prepare test pieces. Next, in an environment of 25°C, the circular test piece was set in the measurement cell of a membrane diffusion measuring device (K-315N-01, manufactured by Tsukubarika Seiki Co., Ltd.) connected to a data logger GL20, manufactured by Graphtec Corporation. Next, nitrogen gas was introduced into the high-pressure side gas reservoir, and the low-pressure side of the cell was evacuated to a vacuum. The high pressure side valve of the cell was opened to introduce nitrogen gas, and gas permeation measurement was started. The time course of the voltage change was recorded, and the nitrogen permeability coefficient was calculated according to the following formula (voltage on the low-pressure side and the high-pressure side (1 V=1.6 KPa)). Q = (V / (R×T×P×A))×(dp / dt) p=Q×L (In the formula, Q: Gas permeability (mol / (m 2 ·s·Pa)) p = gas permeability coefficient (mol m / (m 2·s·Pa)) V: Cell low-pressure side volume (L) A: Transmission area (m 2 ) (Note that π=3.14) T: Test temperature (℃) P: Supply gas differential pressure (Pa) dp / dt: Change in pressure (p) on the low pressure side per unit time (t) (Pa / s) L: thickness of test piece

[0071] The gas permeability coefficient (nitrogen permeability coefficient) of the polyamide porous membrane of Example 1 was 2.9 × 10 -12 mol m / (m 2 ·s·Pa), which indicates that a good porous structure has been formed. The gas permeability coefficient (nitrogen permeability coefficient) of the polyamide porous membrane of Example 2 was 4.4 × 10 -11 mol m / (m 2 ·s·Pa), which indicates that a good porous structure has been formed. The gas permeability coefficient (nitrogen permeability coefficient) of the press film of Comparative Example 1 and the biaxially stretched film of Comparative Example 2 was both 5.0 × 10 -15 mol m / (m 2 s·Pa), and gas permeability could not be confirmed, which indicates that the porous structure was not well formed. The uniaxially stretched film of Comparative Example 3 did not have a porous structure, and the gas permeability coefficient could not be measured.

[0072] In order to demonstrate that the test pieces of the polyamide porous membranes produced in Examples 1 and 2 have a porous structure formed throughout, rather than only partially, the following test was conducted separately.

[0073] As shown in FIG. 6, the test piece 30 is formed by dividing the area of ​​each block into 7.07×10 -4 mm 2 The circle having a diameter of 30 mm was divided into four blocks so that the gas permeability coefficient of each block was measured in the same manner as above. The block of test piece 20 not used for the measurement had a gas permeability coefficient of 5.0×10 as shown in FIG. -15 mol m / (m 2 The pressure was reduced by sealing with tape 31 (less than 1.5 s·Pa).

[0074] The measurement results of the gas permeability coefficients of blocks 1 to 4 in the test piece of the polyamide porous membrane of Example 1 are shown in Figure 7. From Figure 7, it can be seen that blocks 1 to 4 all have a gas permeability coefficient of 1 x 10 -13 mol m / (m 2 ·s·Pa) or more, which indicates that a good porous structure is formed throughout. The measurement results of the gas permeability coefficients of blocks 1 to 4 in the test piece of the polyamide porous membrane of Example 2 are shown in Figure 8. From Figure 8, it can be seen that blocks 1 to 4 all have a gas permeability coefficient of 1 x 10 -13 mol m / (m 2 ·s·Pa) or more, which indicates that a good porous structure is formed throughout.

[0075] Example 3 Raw material pellets of polycaprolactam (Toray Industries, Inc., Alamin CM1041LO, melting point 225°C) were dried in a vacuum oven at 80°C for 6 hours to thoroughly remove moisture. The dried raw material pellets were placed in a spacer and sandwiched between a polyimide sheet (Ube Industries, Ltd., Upilex (registered trademark) 125S) and a stainless steel plate. Using a vacuum press molding machine manufactured by Japan Baldwin Co., Ltd., the mixture was held at 250°C, which is above the melting point of polycaprolactam (225°C), for 7 minutes, and then melt-press molded at a pressure of 30 MPa. The mixture was then slowly cooled to room temperature, yielding a pressed film with a thickness of 150 μm. The resulting pressed film was stored in a desiccator to prevent water absorption.

[0076] The resulting pressed film was cut into 30 mm x 30 mm pieces and placed in a biaxial stretching machine equipped with an air chuck and a stress detector. The biaxial stretching machine allows for heating by blowing hot air from above and below the film using a blower. The raw film was then heated for 3 minutes at 160°C, above the glass transition temperature of polycaprolactam (47°C). After this, the film was simultaneously biaxially stretched at a stretching rate of 20 mm / min while maintaining the temperature, resulting in a 60 μm-thick biaxially stretched film. The stretching ratios in both the MD (longitudinal direction) and TD (transverse direction) were 2x.

[0077] The biaxially stretched film was set in the biaxial stretching machine, and the transverse direction of the stretched film was fixed. After the stretched film was held at 200°C, which is above the glass transition temperature (47°C) of polycaprolactam, for 3 minutes, it was stretched at a stretching speed of 20 mm / min while maintaining the temperature, to obtain a 40 μm thick porous polyamide membrane. The stretching ratio in the MD was 2 times.

[0078] When the above-mentioned polyamide porous membrane was observed with a scanning electron microscope (SEM), a porous structure having nodes, which are aggregates of polycaprolactam, and fibrils connecting the nodes was observed (not shown). The nodes and fibrils extend in different directions, and the angle formed between the extending direction of the nodes and the extending direction of the fibrils was measured to be 80°. The area ratio of fibrils was 50%. The node width was measured to be 45 μm, and the fibril length was 45 μm.

[0079] <Comparative Example 4> The pressed film produced in Example 3 was prepared.

[0080] <Comparative Example 5> The biaxially stretched film produced in Example 3 was prepared. When the biaxially stretched film was observed under a scanning electron microscope, no porous structure having nodes and fibrils was observed (not shown).

[0081] <<Breaking strength measurement>> From the polyamide porous film of Example 3, the pressed film of Comparative Example 1, and the biaxially stretched film of Comparative Example 2, dumbbell-shaped specimens (test specimens) measuring 12 mm in length and 3 mm in width were cut out. Test pieces were cut out from the polyamide porous membrane of Example 3 so that the stretching direction of the polyamide porous membrane produced by width-constrained stretching was the longitudinal direction of the dumbbell piece and the direction perpendicular to the stretching direction was the short direction of the dumbbell piece.

[0082] The test piece was subjected to a tensile test using a tensile tester at a test speed of 20 mm / min at 25° C., and the maximum stress in the recorded stress chart was divided by the cross-sectional area of ​​the film to determine the tensile breaking strength. The tensile tester used was a Tensilon universal testing machine RTC-1325A manufactured by ORIENTEC.

[0083] The breaking strength was measured three times in each MD of the polyamide porous membrane of Example 3, and the average value was calculated to be 143.9 MPa. The breaking strengths of the pressed film of Comparative Example 1 and the biaxially stretched film of Comparative Example 2 were similarly measured and found to be 78.4 MPa and 109.8 MPa, respectively. The reason why the MD breaking strength of the polyamide porous film of Example 3 is superior to the breaking strength of the biaxially stretched film of Comparative Example 2 is presumably because fibrils were formed by width-constrained stretching in the MD.

[0084] The breaking strength was measured three times for each TD of the polyamide porous membrane of Example 3, and the average value was calculated to be 47.2 MPa. [Explanation of symbols]

[0085] 10, 20: Node, 11, 21: Fibril, 30: Test piece, 31: Tape

Claims

1. a node which is an aggregate of polyamide resin; fibrils connecting the nodes and made of polyamide resin; having a porous structure comprising The nodes are in the shape of strips.

2. A polyamide porous film as described in claim 1, wherein the width of the node band is 5 μm to 100 μm.

3. The polyamide porous membrane according to claim 1 or claim 2, wherein the fibrils extend in one direction.

4. The porous polyamide membrane of claim 3 , wherein the nodes extend in a direction different from the direction in which the fibrils extend.

5. A polyamide porous membrane as described in claim 4, wherein the angle between the extension direction of the nodes and the extension direction of the fibrils is 60° to 120°.

6. The polyamide porous membrane according to any one of claims 3 to 5, wherein the breaking strength in the direction in which the fibrils extend is 50 MPa or more.

7. The nitrogen permeability coefficient measured at 25°C is 1 x 10 －１３ mol m / (m ２ The polyamide porous membrane according to any one of claims 1 to 6, wherein the elastic modulus is 1.5 s. Pa or more.

8. The polyamide porous membrane according to any one of claims 1 to 7, wherein the polyamide resin contains polycaprolactam.

9. The polyamide porous membrane according to claim 8, wherein the content of the polycaprolactam relative to the total mass of the polyamide resin is 70 mass% or more.

10. The polyamide porous membrane according to any one of claims 1 to 9, wherein the content of the polyamide resin relative to the total mass of the polyamide porous membrane is 50 mass% or more.

11. The polyamide porous membrane according to any one of claims 1 to 10, wherein the average length of the fibrils is 1 µm to 500 µm.

12. The polyamide porous membrane according to any one of claims 1 to 11, wherein the area ratio of fibrils on the surface of the polyamide porous membrane is 10% to 90%.

13. The polyamide porous membrane according to any one of claims 1 to 12, having a thickness of 1 µm to 500 µm.

14. A method for producing a polyamide porous membrane, comprising width-constraining and stretching a polyamide film containing a polyamide resin to form a porous structure including nodes, which are aggregates of the polyamide resin, and fibrils, which connect the nodes and are also made of the polyamide resin.

15. The method for producing a porous polyamide membrane according to claim 14, wherein the polyamide resin comprises polycaprolactam.

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