Porous polyamide film and method for purifying chemical solution

Abstract

Provided are: a porous polyamide film in which pore diameter and pore shape are controlled and which is capable of satisfactorily removing impurities in a fluid while the fluid is being filtered; and a method for purifying a chemical solution by using the porous polyamide film.　In the porous polyamide film having a plurality of spherical pores therein, the plurality of spherical pores are configured to form connection pores connected with the adjacent spherical pores, the porosity of the porous polyamide film is 50-70%, and the flatness of the spherical pores is 0-0.2.

Description

Porous polyamide film and method for purifying chemical solution

[0001] The present invention relates to a porous polyamide film and a method for purifying a chemical solution using the porous polyamide film.

[0002] Conventionally, various porous membranes have been used in applications such as filters that are membranes for separating gases or liquids.

[0003] As filter membranes capable of removing impurities from gases or liquids, nylon, polyethylene, polypropylene, PTFE, etc. are common. For example, it is known to use a filter membrane such as nylon (for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 55-008887

[0005] The polyamide resin porous membrane described in Patent Document 1 is produced by a phase separation method. The phase separation method is a method that utilizes external stimuli such as cooling, contact with a non-solvent, evaporation of a solvent, and chemical reactions such as polymerization. Therefore, there is a problem that it is difficult to control the pore diameter and the shape of the pores of the porous membrane. Further, when performing fluid filtration using a polyamide resin porous membrane as described in Patent Document 1, it is difficult to remove impurities such as metal impurities due to the lack of control of the pore diameter and the shape of the pores.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a porous polyamide film in which the pore diameter and the shape of the pores are controlled and impurities in a fluid can be favorably removed when performing fluid filtration, and a method for purifying a chemical solution using the porous polyamide film.

[0007] The inventors of the present invention have found that in a porous polyamide film having a plurality of spherical pores inside, the plurality of spherical pores are formed so as to form communication holes continuous with adjacent spherical pores, the porosity of the porous polyamide film is set to 50% or more and 70% or less, and the flatness ratio of the spherical pores is set to 0 or more and 0.2 or less, whereby the above problems can be solved, and the present invention has been completed. More specifically, the present invention provides the following.

[0008] A first aspect of the present invention is a porous polyamide film having a plurality of spherical pores inside, wherein the plurality of spherical pores are connected to adjacent spherical pores to form communicating pores, the porosity of the porous polyamide film is 50% or more and 70% or less, and the flattening ratio of the spherical pores, calculated by the following formula: Flattening ratio = (a - b) / a (wherein a is the average value of the major radii of the spherical pores, and b is the average value of the minor radii of the spherical pores), is 0 or more and 0.2 or less.

[0009] A second aspect of the present invention is a method for purifying a chemical solution, which involves using a porous polyamide film according to the first aspect as a filter to filter the chemical solution containing metal impurities, thereby removing at least a portion of the metal impurities contained in the chemical solution.

[0010] According to the present invention, it is possible to provide a porous polyamide film in which the pore diameter and pore shape are controlled, and which can effectively remove impurities from a fluid when filtering the fluid, and a method for purifying a chemical solution using the porous polyamide film.

[0011] ≪Porous Polyamide Film≫ A porous polyamide film has multiple spherical pores inside. These multiple spherical pores are connected to adjacent spherical pores to form connecting pores. The porosity of the porous polyamide film is 50% or more and 70% or less. In a porous polyamide film, the flattening ratio of the spherical pores is 0 or more and 0.2 or less. The flattening ratio of the spherical pores can be calculated using the following formula: Flattening ratio = (a - b) / a (where a is the average value of the major radii of the spherical pores, and b is the average value of the minor radii of the spherical pores.)

[0012] In the porous polyamide film described above, the pore size and pore shape are controlled. Furthermore, when using the porous polyamide film described above for fluid filtration, impurities in the fluid can be effectively removed.

[0013] <Method for producing porous polyamide film> The method for producing porous polyamide film is not particularly limited as long as it can produce a porous polyamide film that satisfies the above-mentioned predetermined conditions.

[0014] A preferred method for producing a porous polyamide film includes: melt-kneading a thermoplastic polyamide resin and spherical inorganic fine particles to obtain a thermoplastic polyamide resin composition in which inorganic fine particles are dispersed in the thermoplastic polyamide resin; forming the thermoplastic polyamide resin composition into a film by melt processing to obtain a polyamide resin composition film; and removing the inorganic fine particles from the polyamide resin composition film.

[0015] The shape of the inorganic microparticles is spherical. The spherical pores in the porous polyamide film are formed when spherical inorganic microparticles are removed from the thermoplastic polyamide resin composition. Therefore, the spherical pores have the same shape and size as the inorganic microparticles. In other words, the shape of the pores in the porous polyamide film is controlled to be spherical by using spherical inorganic microparticles. Furthermore, the pore diameter in the porous polyamide film can be controlled by appropriately selecting the particle size of the spherical inorganic microparticles.

[0016] Hereinafter, the process of melt-kneading a thermoplastic polyamide resin with inorganic fine particles to obtain a thermoplastic polyamide resin composition in which inorganic fine particles are dispersed within the thermoplastic polyamide resin will also be referred to as the melt-kneading process. The process of forming the thermoplastic polyamide resin composition into a film by melt processing to obtain a polyamide resin composition film will also be referred to as the melt-film formation process. The process of removing inorganic fine particles from the polyamide resin composition film will also be referred to as the inorganic fine particle removal process.

[0017] [Melting and kneading process] In the melting and kneading process, a thermoplastic polyamide resin and inorganic fine particles are melted and kneaded to obtain a thermoplastic polyamide resin composition in which inorganic fine particles are dispersed in the thermoplastic polyamide resin.

[0018] The temperature at which melt mixing is performed is not particularly limited, as long as it is the temperature at which the thermoplastic polyamide resin melts. For example, melt mixing is performed at a temperature 5°C to 100°C higher than the melting point of the thermoplastic polyamide resin. When multiple thermoplastic polyamide resins are used in a mixture, melt mixing is performed at a temperature 5°C to 100°C higher than the melting point of the thermoplastic polyamide resin with the highest melting point among the multiple types of thermoplastic polyamide resins. Here, the melting point of the polyamide resin is measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

[0019] The method for melt-mixing thermoplastic polyamide resin and inorganic fine particles is not particularly limited. Melt-mixing is usually carried out using an extruder such as a single-screw extruder or a twin-screw extruder.

[0020] When thermoplastic polyamide resin and inorganic fine particles are melt-kneaded, plasticizers, release agents, and other additives may be used. However, when forming a film from a thermoplastic polyamide resin composition using the above method, it is preferable that plasticizers, release agents, and other additives are not used. A porous polyamide film obtained by removing inorganic fine particles from a polyamide resin composition film can be used for filtering various fluids. When filtering a fluid containing an organic solvent using a porous polyamide film, if the porous polyamide film contains plasticizers, release agents, or other additives, there is a risk that the plasticizers, release agents, and other additives may leach into the filtered fluid.

[0021] The form of the thermoplastic polyamide resin composition obtained by melt-mixing, in which inorganic fine particles are dispersed in a thermoplastic polyamide, is not particularly limited. Examples of forms of thermoplastic polyamide resin compositions include flakes, powders, and pellets.

[0022] A thermoplastic polyamide resin composition, obtained by melt-mixing, in which inorganic fine particles are dispersed in thermoplastic polyamide, is typically extruded from an extruder in the form of strands. The stranded polyamide resin composition solidifies as it cools and is then cut into the desired size to form pellets.

[0023] (Thermoplastic Polyamide Resin) Any known thermoplastic polyamide resin can be used without particular limitation as the thermoplastic polyamide resin. The thermoplastic polyamide resin may be a ring-opening polymer of lactam or a condensed polymer of hydroxycarboxylic acid. The ring-opening polymer of lactam and the condensed polymer of hydroxycarboxylic acid may be a homopolymer or a copolymer. The thermoplastic polyamide resin may also be a condensed polymer obtained by the condensation polymerization of a diamine component and a dicarboxylic acid component. The condensed polymer obtained by the condensation polymerization of a diamine component and a dicarboxylic acid component may contain two or more constituent units derived from the diamine component and may contain two or more constituent units derived from the dicarboxylic acid component. The thermoplastic polyamide resin may be a polymer obtained by polymerization of lactam and / or hydroxycarboxylic acid, and a diamine component and a dicarboxylic acid component. Two or more lactams, hydroxycarboxylic acids, diamine components, and dicarboxylic acid components may each be used in combination.

[0024] Specific examples of thermoplastic polyamide resins include aliphatic polyamides such as nylon 6, nylon 7, nylon 9, nylon 11, nylon 12, nylon 26, nylon 46, nylon 66, nylon 610, nylon 612, nylon 86, nylon 108, nylon 6 / 12, nylon 6 / 9, nylon 6 / 66, nylon 12 / 66, nylon 26 / 66, nylon 66 / 610, and nylon 6 / 66 / 610). The names of these nylons are based on JIS K 6920-1. Furthermore, the raw materials for the above nylons are not particularly limited. For example, nylon 6 is generally produced by ring-opening polymerization of caprolactam. However, nylon 6 is not limited to ring-opening polymers of caprolactam, but may also be a condensation polymer of 6-aminohexanoic acid.

[0025] Other specific examples of thermoplastic polyamide resins include aromatic polyamides such as polyhexamethylene isophthalamide, polyhexamethylene terephthalamide, polymetaxylylene adipamide, hexamethylene isophthalamide / terephthalamide copolymer, poly-p-phenylene terephthalamide, and poly-p-phenylene-3,4'-oxydiphenylene terephthalamide, as well as various amorphous polyamides.

[0026] The thermoplastic polyamide resin described above may undergo various known modifications.

[0027] (Inorganic fine particles) In a porous polyamide film, the flatness ratio of the spherical pores is 0 or more and 0.2 or less. The flatness ratio of the spherical pores can be calculated using the following formula: Flatness ratio = (a - b) / a (where a is the average value of the semi-major radii of the spherical pores, and b is the average value of the semi-minor radii of the spherical pores).

[0028] Therefore, the flatness ratio of inorganic fine particles is between 0 and 0.2. The flatness ratio of inorganic fine particles can be calculated using the following formula: Flatness ratio = (A - B) / A (wherein A is the average value of the semi-major radii of the inorganic fine particles, and B is the average value of the semi-minor radii of the inorganic fine particles).

[0029] The major radii a and minor radii b of spherical pores in porous polyamide films, and the major radii A and minor radii B of inorganic fine particles are measured by the following method. For spherical pores, first, a sample with an exposed cross-section in the thickness direction is obtained by cutting a porous polyimide film in the thickness direction. Next, the cross-section in the thickness direction of the sample for measurement is observed using a scanning electron microscope (SEM) and a microscopic image of the cross-section is obtained. In the obtained image, the major radii a and major radii b of each of 10 arbitrary spherical pores are measured using image analysis software. The average value of major radii a and the average value of minor radii b for 10 spherical pores are adopted as the average value of major radii a and minor radii b for calculating the flattening ratio. For inorganic fine particles, a sample with an exposed cross-section in the thickness direction is obtained by cutting a polyamide resin composition film, as described later, in the thickness direction. Next, the cross-section in the thickness direction of the sample for measurement is observed using a scanning electron microscope (SEM) and a microscopic image of the cross-section is obtained. For each of the 10 arbitrary inorganic microparticles in the obtained image, the major axis A and major axis B are measured using image analysis software. The average values ​​of major axis A and minor axis B for the 10 spherical pores are adopted as the average values ​​of major axis A and minor axis B for calculating the flattening ratio.

[0030] The flattening ratio of spherical pores in a porous polyamide film can be adjusted by changing the flattening ratio of inorganic microparticles.

[0031] The material of the inorganic fine particles is not particularly limited, as long as it is a material that can be removed from the polyamide resin composition film when manufacturing a porous polyamide film using the polyamide resin composition film. Suitable examples of materials for inorganic fine particles include, for example, silica (silicon dioxide), titanium dioxide, and alumina (Al ２ O ３ Examples include metal oxides such as ) and metals such as iron and iron-nickel alloys. Spherical fine particles made of metal can be produced, for example, by the method described in Journal of Alloys and Compounds, Volume 480, Issue 2, 8 July 2009, Pages 529-533.

[0032] The shape of inorganic particles is spherical. Here, "spherical" does not mean a geometrically perfect sphere, but rather a shape that can be perceived as close to a perfect sphere when viewed under a microscope.

[0033] As spherical inorganic fine particles, colloidal silica fine particles are preferred, for example. As colloidal silica, monodisperse spherical silica particles are preferred because they can form uniform pores in a porous polyamide film.

[0034] Furthermore, for inorganic fine particles, it is preferable that the flattening ratio is close to 0, and that the particle size distribution index is small. Inorganic fine particles that meet these conditions exhibit excellent dispersibility in thermoplastic polyamide resin compositions. The volume-average particle diameter of the inorganic fine particles is preferably 0.03 μm or more and 1.0 μm or less, and more preferably 0.05 μm or more and 0.5 μm or less. The volume-average particle diameter of the inorganic fine particles is so-called D50. D50 refers to the particle diameter at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction and scattering.

[0035] Inorganic fine particles may be used individually or in combination of two or more types.

[0036] The porosity of a porous polyamide film is between 50% and 70%. The porosity of a porous polyamide film is calculated using the following formula: Porosity = (1 - apparent density / true density) Here, true density is the density of the polyamide resin at 20°C. Apparent density is the density of the porous polyamide film at 20°C.

[0037] Therefore, the amount of inorganic fine particles melt-mixed with the thermoplastic polyamide resin is adjusted so that the porosity of the porous polyamide film is within the above range.

[0038] The amount of inorganic fine particles used is preferably, for example, 50% to 70% by mass, more preferably 55% to 70% by mass, and even more preferably 60% to 70% by mass, relative to the mass of the thermoplastic polyamide resin composition. Accordingly, in the polyamide resin composition film, the inorganic fine particle content is preferably 50% to 70% by mass, more preferably 55% to 70% by mass, and even more preferably 60% to 70% by mass, relative to the mass of the thermoplastic polyamide resin composition. By using an amount of inorganic fine particles within the above range, it is easy to obtain a non-brittle and uniform polyamide resin composition, and when obtaining a porous polyamide film by the method described later, it is easy to obtain a porous polyamide film having the desired porous structure. The amount of inorganic fine particles used is adjusted appropriately considering the density of the inorganic fine particles and the porosity of the porous polyamide film.

[0039] (Other components) The thermoplastic polyamide resin composition may optionally contain, along with the thermoplastic polyamide resin and inorganic fine particles, other thermoplastic resins other than the thermoplastic polyamide resin and various additives. When the thermoplastic polyamide resin composition contains other thermoplastic polyamide resins along with the thermoplastic polyamide resin, the ratio of the mass of the other thermoplastic resins to the mass of the resin components contained in the thermoplastic polyamide resin composition is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. Examples of additives include colorants, antioxidants, ultraviolet absorbers, surfactants, and silane coupling agents.

[0040] When forming a thermoplastic polyamide resin composition into a film using the method described above, it is preferable that the above-mentioned additives are not used. A porous polyamide film obtained by removing inorganic fine particles from a polyamide resin composition film can be used for filtering various fluids. When filtering a fluid containing an organic solvent using a porous polyamide film, if the porous polyamide film contains the above-mentioned additives, there is a risk that the additives may leach into the filtered fluid.

[0041] [Melting Film Formation Step] In the melting film formation step, the thermoplastic polyamide resin composition is formed into a film by melt processing to obtain a polyamide resin composition film.

[0042] As the melt processing method for obtaining the film, the T-die method, the inflation method, the calendar method, etc. can be mentioned. Among these methods, the T-die method is preferred because it is easy to adjust the film thickness and has excellent film productivity.

[0043] The melt processing temperature for film formation is appropriately determined in consideration of the type of melt processing method, the melting point and glass transition point of the thermoplastic polyamide, the film thickness, etc.

[0044] The thickness of the polyamide resin composition film is preferably 20 μm or more and 200 μm or less, more preferably 40 μm or more and 150 μm or less, and even more preferably 50 μm or more and 100 μm or less.

[0045] By the above method, a polyamide composition film made of a thermoplastic polyamide resin composition in which inorganic particles are dispersed is obtained.

[0046] [Inorganic Fine Particle Removal Step] By removing inorganic fine particles from the polyamide resin composition film obtained by the above method, a porous polyamide film is obtained. The thickness of the porous polyamide film obtained through the inorganic fine particle removal step is preferably 20 μm or more and 200 μm or less, more preferably 40 μm or more and 150 μm or less, and even more preferably 50 μm or more and 100 μm or less, similar to the thickness of the polyamide resin composition film.

[0047] The method for removing inorganic fine particles from the polyamide resin composition film is not particularly limited. As the method for removing inorganic fine particles from the polyamide resin composition film, a method of bringing the polyamide resin composition film into contact with a liquid capable of dissolving the inorganic fine particles is preferred. The method of bringing the polyamide resin composition film into contact with a liquid capable of dissolving the inorganic fine particles is not particularly limited, but a method of immersing the polyamide resin composition film in a liquid capable of dissolving the inorganic fine particles is preferred.

[0048] For example, if the inorganic fine particles are silica fine particles, the silica fine particles can be removed from the polyamide resin composition film by contacting the film with an aqueous solution of hydrogen fluoride (hydrofluoric acid). Furthermore, if the inorganic fine particles are metal fine particles such as iron fine particles or iron-nickel alloy fine particles, the metal fine particles can be removed from the polyamide resin composition film by contacting the film with hydrochloric acid solution.

[0049] A porous polyamide film is obtained by removing inorganic fine particles from a polyamide resin composition film using the method described above, and then washing and drying the resulting film as needed. The washing method is not particularly limited. Typically, washing is performed using water or organic solvents such as methanol and ethanol. The drying method is not particularly limited. Drying can be performed by methods such as heating, vacuum drying, or standing in the air.

[0050] ≪Porous Polyamide Film≫ The porous polyamide film obtained by the above method contains a structure in which spherical pores are interconnected (hereinafter abbreviated as "connecting pores"). An opening in a porous polyamide film is a portion on the surface of the porous polyamide film where the above-mentioned connecting pores open.

[0051] The term "spherical" in relation to the shape of a hole includes a perfect sphere, but is not necessarily limited to a perfect sphere. A spherical shape is defined as being substantially spherical; a shape that can be visually recognized as approximately spherical when a magnified image of the hole is observed is also included in the definition of a spherical shape. Specifically, in a spherical hole, the surface defining the hole is curved, and the hole is defined as either perfectly spherical or approximately spherical by this curved surface.

[0052] Individual spherical pores are typically formed by the removal of individual inorganic microparticles present in the aforementioned polyamide resin composition film. Connecting pores are formed by the removal of multiple inorganic microparticles that are in contact with each other within the polyamide resin composition film. The locations where the spherical pores connect in the connecting pores originate from the locations where the multiple inorganic microparticles were in contact with each other before removal.

[0053] The average pore size of the spherical pores is preferably 10 nm to 200 nm, more preferably 15 nm to 150 nm, and particularly preferably 15 nm to 130 nm. The average pore size is the average pore size measured by a porometer.

[0054] The pore size distribution is the pore size distribution measured by a porometer. The pore size distribution of a porous polyamide film is the distribution of the volume of each pore size relative to the total volume of pores, measured at 1 nm intervals within the range of pore sizes of 5 nm or larger. The upper limit of the range of the pore size distribution is not particularly limited, but may be 150 nm or less, or 120 nm or less. In the pore size distribution of a porous polyamide film, the difference between the maximum value of the pore size range in the fraction with the largest pore size where pores exist and the minimum value of the pore size range in the fraction with the smallest pore size where pores exist is preferably 1 nm or more and 15 nm or less, more preferably 1 nm or more and 13 nm or less, and particularly preferably 1 nm or more and 11 nm or less.

[0055] The average pore size measured by a porometer is the average flow rate pore size due to liquid-liquid phase displacement. The average pore size can be measured, for example, using a liquid porometer LLP-1500A (ultra-low pressure, pore size distribution, and permeability performance measuring device) manufactured by PMI, according to the pore size distribution measurement test method [half-dry method (ASTM E1294-89)]. Perfluoropolyester (trade name Galwick) and isopropyl alcohol (interfacial tension value: 4.6 dyne / cm) are used as reagents for measuring the average pore size. After filling the pores of a porous polyamide film with isopropyl alcohol, one main surface of the porous polyamide film is filled with perfluoropolyester. Pressure is applied to the main surface of the porous polyamide film filled with perfluoropolyester, gradually increasing the pressure using compressed air. The measurement temperature is 25°C, and the measurement pressure is in the range of 50 to 500 psi.

[0056] The diameter of the openings in the porous polyamide film is, for example, in the range of 10 nm to 200 nm. The diameter of the openings in the porous polyamide film can be appropriately changed depending on the application of the porous polyamide film. The interconnected pores, which are composed of a series of spherical pores of this diameter, allow fluid to pass through the porous polyamide film well. The porous polyamide film has interconnected pores that penetrate the film in the thickness direction, serving as fluid channels. This allows the fluid to permeate from one main surface of the porous polyamide film to the other main surface. The fluid also passes through the interior of the porous polyamide film while in contact with the curved surfaces that define the individual spherical pores. The contact area of ​​the fluid inside the porous polyamide film is quite large due to the presence of interconnected pores made up of spherical holes. Therefore, when fluid passes through the porous polyamide film, it is thought that minute substances present in the fluid are easily adsorbed onto the spherical pores within the porous polyamide film.

[0057] The porosity of the porous polyamide film is as described above. A porous polyamide film having the aforementioned porosity exhibits excellent fluid permeability and strength.

[0058] ≪Method for purifying the chemical solution≫ By using the aforementioned porous polyamide film as a filter to filter the chemical solution containing metal impurities, at least a portion of the metal impurities contained in the chemical solution can be removed, thereby purifying the chemical solution.

[0059] The aforementioned porous polyamide film can be applied to the manufacture of electronic materials requiring very precise impurity removal, particularly to the purification of chemical solutions used in semiconductor manufacturing by filtration. Semiconductor manufacturing includes the manufacture of semiconductor substrates, the processing of semiconductor substrates, and the manufacture of semiconductor devices. The aforementioned porous polyamide film can be suitably applied, for example, to the purification of chemical solutions used in semiconductor manufacturing. Such chemical solutions are not particularly limited. Examples of chemical solutions include chemical solutions for forming protective films to modify substrates, chemical solutions for cleaning silicon wafers, chemical solutions containing photosensitive materials such as resist compositions, and raw material chemical solutions for photosensitive materials such as resin solutions. By filtering these chemical solutions using the aforementioned porous polyamide film, metallic impurities, such as iron and zinc, can be removed with a very high removal rate. Impurities contained in chemical solutions typically include metallic elements, metalloid elements, and some nonmetallic elements. Examples of metallic elements include alkali metals such as Li, Na, and K; alkaline earth metals such as Be, Mg, Ca, and Ba; transition metals belonging to groups 3 to 11 of the periodic table such as Cr, Mn, Fe, Co, Ni, Cu, and Zn; and metals belonging to groups 12 to 15 of the periodic table such as Zn, Al, Ga, and Sn. Examples of metalloid elements include B, Si, Ge, As, Sb, Te, and Po. Examples of nonmetallic elements include C, P, S, and I.

[0060] As described above, the present inventors provide the following [1] to [3]. [1] A porous polyamide film having a plurality of spherical pores inside, wherein the plurality of spherical pores are connected to adjacent spherical pores to form communicating pores, the porosity of the porous polyamide film is 50% or more and 70% or less, and the flatness of the spherical pores, as determined by the following formula: Flatness = (a - b) / a (wherein a is the average value of the major radii of the spherical pores, and b is the average value of the minor radii of the spherical pores), is 0 or more and 0.2 or less. [2] The porous polyamide film according to [1], wherein the average pore diameter of the spherical pores is 10 nm or more and 200 nm or less. [3] A method for purifying a chemical solution, wherein at least a portion of the metal impurities contained in the chemical solution is removed by filtering the chemical solution containing metal impurities using the porous polyamide film according to [1] or [2] as a filter.

[0061] The present invention will be described in detail below with reference to examples. The scope of the present invention is not limited to these examples.

[0062] [Example 1] 30 parts by mass of nylon 6 and 70 parts by mass of spherical silica fine particles were melt-kneaded using a twin-screw extruder (HK-25D, Parker Corporation) at a cylinder temperature of 270°C and a rotation speed of 200 rpm. The volume-average particle size of the spherical silica fine particles was 50 nm. The flattening ratio of the spherical silica fine particles was 0.05. The polyamide resin composition discharged from the extruder in strand form was cut while being cooled and solidified to obtain the polyamide resin composition as pellets.

[0063] The polyamide resin composition obtained as described above was extruded using a T-die extruder (Laboplastmill, Toyo Seiki Seisakusho Co., Ltd.) with the polyamide resin composition temperature set to 270°C and the die lip temperature to 280°C, and extruded at a rotation speed of 50 rpm to form a film, thereby obtaining a polyamide resin composition film. The film thickness of the polyamide resin composition film was 100 μm.

[0064] The polyamide resin composition film obtained as described above was immersed in 10% by mass hydrofluoric acid at 25°C (room temperature) for 5 minutes to remove silica particles from the polyamide resin composition film. After the removal of the silica particles, the film was removed from the hydrofluoric acid, washed with pure water, and then dried to obtain a porous polyamide film. The thickness of the porous polyamide film was 100 μm. When the cross-section of the obtained porous polyamide film was observed with a scanning electron microscope (SEM), it was found that interconnected pores, in which spherical pores are connected to each other, were formed inside the porous polyamide film.

[0065] [Comparative Example 1] A formic acid solution of nylon 6 containing nylon 6 at a concentration of 10% by mass was applied to a PET (polyethylene terephthalate) substrate using an applicator to form a coating film. The PET substrate with the coating film was immersed in pure water at 25°C for 5 minutes to induce phase separation in the nylon 6. After immersion for a predetermined time, the PET substrate with the porous polyamide film formed by the phase separation was removed from the pure water. The porous polyamide film on the PET substrate removed from the pure water was washed with pure water, dried, and then peeled off from the PET substrate to obtain the porous polyamide film of Comparative Example 1. The thickness of the porous polyamide film was 100 μm. When the cross-section of the obtained porous polyamide film was observed with a scanning electron microscope (SEM), a structure in which irregularly shaped pores were interconnected was observed inside the porous polyamide film.

[0066] The porosity, flattening ratio, and average pore diameter of the porous polyamide films produced in Example 1 and Comparative Example 1 were measured according to the method described above. These measurement results are shown in Table 1.

[0067] Furthermore, the porous polyamide films obtained in Example 1 and Comparative Example 1 were used to filter the chemical solution, and the amount of metal impurities in the filtered chemical solution was evaluated as described below.

[0068] A solution containing metal impurities was prepared by adding iron and zinc to 1000 mL of a solution containing polyhydroxystyrene (PHS) homopolymer at a concentration of 5% by weight in propylene glycol monomethyl ether (PGMEA) to a metal concentration of 10 ppb by mass.

[0069] The porous polyamide film obtained in Example 1 or Comparative Example 1 was cut into a circle with a diameter of 47 mm and used as a filter. After setting the filter in a perfluoroalkoxyalkane (PFA) filtration holder, 1000 mL of OK73 thinner was passed through the filter to wash it. The aforementioned chemical solution was passed through the washed filter while pressurizing it with nitrogen to a pressure of 0.08 MPa (G), and the purified chemical solution obtained by filtration was obtained as the filtrate.

[0070] [Measurement of Metal Atom Content] The metal compounds contained in the chemical solution samples filtered through the porous polyamide film obtained in Example 1 or Comparative Example 1 were heated at 600°C. After heating, the content of the metal compounds was determined from the mass of the remaining metal oxides. From the content of the metal compounds in the chemical solution samples, the content of metal atoms (mass ppb) relative to the total mass of the chemical solution purified by filtration was calculated. The metal atom content is shown in Table 1.

[0071] [Evaluation of Defect Count] A chemical solution filtered through a porous polyamide film obtained in Example 1 or Comparative Example 1 was applied to a 12-inch silicon substrate treated with hexamethyldisilazane (HMDS) using a spinner. The silicon substrate with the formed coating was pre-baked (PAB) on a hot plate at 80°C for 60 seconds to form a resin film with a thickness of 40 nm. In addition, a resin film with a thickness of 40 nm was formed on a 12-inch silicon substrate treated with HMDS using an unfiltered chemical solution according to the above method. The number of defects greater than 40 nm was measured on the obtained resin films using a surface defect observation device (SurfScanSP5 instrument, KLA-Tencor). The number of defects in the resin film formed using the chemical solution filtered through a porous polyamide film obtained in Example 1 or Comparative Example 1 was determined as a relative value, with the number of defects in the resin film formed using the unfiltered chemical solution set to 1. The number of defects is shown in Table 1.

[0072]

[0073] Table 1 shows that in porous polyamide films having an internal interconnected pore structure with multiple spherical pores, a porosity of 50% to 70%, and a spherical pore flattening ratio of 0 to 0.2, the pore diameter and pore shape are controlled, and impurities in the fluid can be effectively removed when using the aforementioned porous polyamide film for fluid filtration.

Claims

1. A porous polyamide film having a plurality of spherical pores inside, wherein the plurality of spherical pores are connected to adjacent spherical pores to form a connecting pore, the porosity of the porous polyamide film is 50% or more and 70% or less, and the flatness of the spherical pores, calculated by the following formula: Flatness = (a - b) / a (wherein a is the average value of the major radii of the spherical pores, and b is the average value of the minor radii of the spherical pores), is 0 or more and 0.2 or less.

2. The porous polyamide film according to claim 1, wherein the average pore diameter of the spherical pores is 10 nm or more and 200 nm or less.

3. A method for purifying a chemical solution, comprising using the porous polyamide film described in claim 1 or claim 2 as a filter to filter the chemical solution containing metal impurities, thereby removing at least a portion of the metal impurities contained in the chemical solution.

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