Porous polyamide film and method for purifying chemical liquid

Abstract

Provided is a porous polyamide film in which the pore diameter and pore shape are controlled and which, when filtering a fluid, can satisfactorily remove impurities in the fluid. Also provided is a method for purifying a chemical liquid using the porous polyamide film.　The porous polyamide film has a plurality of spherical pores therein, and is configured such that: the plurality of spherical pores form connected pores with spherical pores that are adjacent thereto; the spherical pores have an average pore diameter of 10 nm to 200 nm; a pore diameter distribution indicates that the difference between the maximum value and the minimum value of pores is 1 nm to 15 nm; and the surface area of a region having an area of 1 m2 on a main surface of the porous polyamide film is 1000 m2 to 6000 m2.

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, which are membranes for separating gases or liquids.

[0003] Commonly used filter membranes for removing impurities from gases or liquids include nylon, polyethylene, polypropylene, and PTFE. For example, the use of filter membranes made of nylon is known (see, for example, Patent Document 1).

[0004] Japanese Unexamined Patent Publication No. 55-008887

[0005] The porous polyamide resin membrane described in Patent Document 1 is manufactured 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 the solvent, and chemical reactions such as polymerization. Therefore, there is a problem in that it is difficult to control the pore size and shape of the porous membrane. Furthermore, when filtering fluids using a porous polyamide resin membrane such as the one described in Patent Document 1, it is difficult to remove impurities such as metal impurities due to the lack of control over the pore size and shape.

[0006] The present invention has been made in view of the above-mentioned problems, and aims 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.

[0007] The inventors have created a porous polyamide film having a plurality of spherical pores inside, such that the plurality of spherical pores form connecting pores with adjacent spherical pores, the average pore diameter of the spherical pores is 10 nm to 200 nm, and the difference between the maximum and minimum pores in the pore diameter distribution is 1 nm to 15 nm, with the area of ​​the main surface of the porous polyamide film being 1 m². ２ The surface area of ​​the region is 1000 m ２ Over 6000m ２We have found that the above problems can be solved by doing the following, and have completed the present invention. 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 a connecting pore, the average pore diameter of the spherical pores is 10 nm or more and 200 nm or less, and the pore diameter distribution of the spherical pores in the porous polyamide film is such that, as measured by a porometer, the distribution of the volume-based ratio of pores of each size to the total pore volume is measured at 1 nm intervals within the range of pore diameters of 5 nm or more, and the difference between the maximum value of the pore diameter range in the fraction with the largest pore diameter where pores exist and the minimum value of the pore diameter range in the fraction with the smallest pore diameter where pores exist is 1 nm or more and 15 nm or less, and the area of ​​the main surface of the porous polyamide film is 1 m². ２ The surface area of ​​the region is 1000 m ２ Over 6000m ２ The following is a porous polyamide film.

[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>>The porous polyamide film has a plurality of spherical pores inside. The plurality of spherical pores are connected to adjacent spherical pores to form communication pores. The average pore diameter of the spherical pores is 10 nm or more and 200 nm or less. Regarding the pore size distribution of the spherical pores in the porous polyamide film, measured by a porosimeter, in the range of pore diameters of 5 nm or more, measured every 1 nm of pore diameter range, in the volume-based distribution of pores of each size with respect to the total pore volume, the maximum value of the pore diameter range of the fraction of the maximum pore diameter where pores exist and the minimum value of the pore diameter range of the fraction of the minimum pore diameter where pores exist have a difference of 1 nm or more and 15 nm or less. The surface area of the area of 1 m ２ on the main surface of the porous polyamide film is 1000 m ２ or more and 6000 m ２ or less.

[0012] In the above porous polyamide film, the pore diameter and the shape of the pores are controlled. Also, the width of the pore size distribution regarding the pore diameter is narrow, and the surface area per unit area is large. As a result, when filtering a fluid using the above porous polyamide film, impurities in the fluid can be removed well.

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

[0014] A preferred method for producing a porous polyamide film includes: obtaining a thermoplastic polyamide resin composition in which inorganic fine particles are dispersed in a thermoplastic polyamide resin by melt-kneading a thermoplastic polyamide resin and spherical inorganic fine particles; forming the thermoplastic polyamide resin composition into a film by melt processing to obtain a polyamide resin composition film; 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. Moreover, by using spherical inorganic microparticles with a narrow particle size distribution, a porous polyamide film with a narrow pore size distribution can be obtained.

[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 of melt-kneading a thermoplastic polyamide resin and inorganic fine particles is not particularly limited. Melt-kneading is usually carried out using an extruder such as a single-screw extruder or a twin-screw extruder.

[0020] When melt-kneading a thermoplastic polyamide resin and inorganic fine particles, a plasticizer, a mold release agent, and other additives may be used. However, when forming a thermoplastic polyamide resin composition into a film by the above method, it is preferable not to use a plasticizer, a mold release agent, and other additives. The porous polyamide film obtained by removing inorganic fine particles from the polyamide resin composition film can be used for filtering various fluids. When filtering a fluid containing an organic solvent using the porous polyamide film, if the porous polyamide film contains a plasticizer, a mold release agent, and other additives, there is a risk that the plasticizer, the mold release agent, and other additives will elute into the filtered fluid.

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

[0022] The thermoplastic polyamide resin composition in which inorganic fine particles are dispersed in the thermoplastic polyamide obtained by melt-kneading is typically extruded from an extruder in a strand shape. The strand-shaped polyamide resin composition is cut into a desired size and made into pellets while being solidified by cooling.

[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] In addition, specific examples of the thermoplastic polyamide resin 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, and various amorphous polyamides.

[0026] The thermoplastic polyamide resin described above may be subjected to various known modifications.

[0027] (Inorganic fine particles) The material of the inorganic fine particles is not particularly limited as long as it can be removed from the polyamide resin composition film when producing the porous polyamide film using the polyamide resin composition film. Suitable examples of the material of the inorganic fine particles include, for example, metal oxides such as silica (silicon dioxide), titanium oxide, and alumina (Al ２ O ３ ), and metals such as iron and iron-nickel alloy. For spherical fine particles made of metal, they 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.

[0028] The shape of the inorganic fine particles is spherical. Here, the spherical shape means not only a geometrically perfect spherical shape but also a shape that can be recognized as being close to a spherical shape when visually observing a microscopic image.

[0029] As the spherical inorganic fine particles, for example, colloidal silica fine particles are preferable. As the colloidal silica, monodisperse spherical silica particles are preferable because they can form uniform pores in the porous polyamide film.

[0030] In the porous polyamide film, the average pore size of the spherical pores is 10 nm to 200 nm. The average pore size of the spherical pores can be adjusted by adjusting the volume-average particle size of the inorganic fine particles. The volume-average particle size of the inorganic fine particles is preferably 0.03 μm to 1.0 μm, and more preferably 0.05 μm to 0.5 μm. The volume-average particle size of the inorganic fine particles is so-called D50. D50 refers to the particle size at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction and scattering.

[0031] Inorganic fine particles may be used individually or in combination of two or more types.

[0032] In a porous polyamide film, the pore size distribution for spherical pores is such that, as measured by a porometer, the volume-based distribution of pores of each size relative to the total pore volume, measured at 1 nm intervals within the range of pores 5 nm or larger, is such that the difference between the maximum value of the pore size range in the fraction with the largest pore size and the minimum value of the pore size range in the fraction with the smallest pore size is between 1 nm and 15 nm. The pore size distribution width, which is the difference between the maximum value of the pore size range in the fraction with the largest pore size and the minimum value of the pore size range in the fraction with the smallest pore size, can be adjusted by adjusting the width of the particle size distribution of the inorganic microparticles. Specifically, the above-mentioned pore size distribution width can be narrowed by using inorganic microparticles with a narrow particle size distribution width.

[0033] Therefore, the amount of inorganic fine particles melt-mixed with the thermoplastic polyamide resin is adjusted so that the pore size distribution width of the porous polyamide film is within the above range.

[0034] Area of ​​the main surface of a porous polyamide film: 1 m² ２ The surface area of ​​the region is 1000 m ２ Over 6000m ２ The following applies to the area of ​​the main surface of the porous polyamide film, 1 m². ２The surface area of ​​this region can be increased by increasing the ratio of the mass of inorganic fine particles to the mass in the polyamide resin composition, or by reducing the volume-average particle size of the inorganic fine particles. Therefore, the amount of inorganic fine particles used depends on the volume-average particle size of the inorganic fine particles and the area of ​​the main surface of the resulting porous polyamide film (1 m²). ２ It is determined appropriately, taking into account the surface area of ​​the region.

[0035] 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.

[0036] (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.

[0037] 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.

[0038] [Melting Film Formation Process] In the melting film formation process, the thermoplastic polyamide resin composition is formed into a film by melting to obtain a polyamide resin composition film.

[0039] Melting methods for obtaining film include the T-die method, the inflation method, and the calendering method. Among these methods, the T-die method is preferred because it allows for easy adjustment of the film thickness and offers excellent film productivity.

[0040] The melting temperature for film formation is determined appropriately, taking into account the type of melting method, the melting point and glass transition temperature of the thermoplastic polyamide, and the thickness of the film.

[0041] 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.

[0042] By the above method, a polyamide composition film is obtained, which consists of a thermoplastic polyamide resin composition in which inorganic particles are dispersed in a thermoplastic polyamide resin.

[0043] [Inorganic Fine Particle Removal Process] A porous polyamide film is obtained by removing inorganic fine particles from the polyamide resin composition film obtained by the above method. The thickness of the porous polyamide film obtained through the inorganic fine particle removal process is preferably 20 μm to 200 μm, more preferably 40 μm to 150 μm, and even more preferably 50 μm to 100 μm, similar to the thickness of the polyamide resin composition film.

[0044] The method for removing inorganic fine particles from a polyamide resin composition film is not particularly limited. A preferred method for removing inorganic fine particles from a polyamide resin composition film is to bring the polyamide resin composition film into contact with a liquid capable of dissolving inorganic fine particles. While the method for bringing the polyamide resin composition film into contact with a liquid capable of dissolving inorganic fine particles is not particularly limited, a preferred method is to immerse the polyamide resin composition film in a liquid capable of dissolving inorganic fine particles.

[0045] 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.

[0046] 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.

[0047] ≪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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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. 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.

[0052] 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.

[0053] 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.

[0054] The area of ​​the main surface of a porous polyamide film is calculated based on the specific surface area of ​​the porous polyamide film measured by the BET method, and is calculated per square meter. ２ The surface of the region is 1000m ２ Over 6000m ２The following is true, 1100m ２ Over 5500m ２ The following is preferable: 1 m of porous polyamide film ２ The surface area per square meter of porous polyamide film is ２ The mass per unit (g) and the specific surface area (m²) of the porous polyamide film. ２ It is calculated by multiplying by ( / g).

[0055] When a porous polyamide film having the average pore size and specific surface area within the above range is used as a filter membrane to filter a liquid containing minute impurities, the minute impurities can be effectively removed. This is presumed to be because the average pore size obtained by the BET method is within the above range, which provides pores such as interconnected pores with a pore size suitable for sieving to remove impurities. Furthermore, because the surface area of ​​the porous polyamide film is within the above range, the frequency of contact between minute impurities and the surface of the pores within the porous polyamide film can be increased, which is presumed to improve the efficiency of removing minute impurities by adsorption to the pore surface.

[0056] Here, the BET method is a method of measuring adsorption isotherms by adsorbing and desorbing adsorbed molecules (e.g., nitrogen) onto a porous material, and analyzing the measured data based on the BET equation shown in equation (1). Based on this method, the specific surface area A and the total pore volume V can be calculated. Specifically, first, adsorption isotherms are determined by adsorbing and desorbing adsorbed molecules onto a porous material. Then, from the obtained adsorption isotherms, the specific surface area A and the total pore volume V can be calculated based on the following equation (1): [P / {V ａ (P ０ Calculate the equilibrium relative pressure (P / P) ０ Plot the points against ). Then, treat this plot as a straight line and, based on the least squares method, determine the slope s(=[(C-1) / (V). ｍ • C) ) and intercept i (= [1 / (V ｍ - Calculate C). Then, based on equations (2-1) and (2-2), V is calculated from the obtained slope s and intercept i. ｍ And calculate C. Furthermore, V ｍFrom this, the specific surface area A can be calculated based on equation (3). Furthermore, the adsorption data of the obtained adsorption isotherms is linearly interpolated to determine the amount of adsorption at the relative pressure set in the relative pressure for pore volume calculation. From this amount of adsorption, the total pore volume V can be calculated. Note that this BET method is a measurement method in accordance with JIS R 1626-1996 "Method for measuring the specific surface area of ​​fine ceramic powder by gas adsorption BET method". There are no particular restrictions on the measurement device for the BET method, but examples include Micromeristics (manufactured by Shimadzu Corporation).

[0057] [P / {V ａ (P ０ -P)}] = [1 / (V ｍ ・C)]+[(C-1) / (V ｍ ・C) ] (P / P ０ ) (1) V ｍ =1 / (s+i) (2-1) C=(s / i)+1 (2-2) A=(V ｍ ・L・σ) / 22414 (3)

[0058] However, Va: adsorption amount, Vm: adsorption amount of monolayer, P: equilibrium pressure of adsorbed molecules, P0: saturated vapor pressure of adsorbed molecules, L: Avogadro's number, σ: adsorption cross-sectional area of ​​adsorbed molecules.

[0059] ≪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.

[0060] 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.

[0061] As described above, the present inventors provide the following [1] and [2].

[0062] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0063] [Examples 1-3] The amounts of nylon 6 and spherical silica fine particles listed in Table 1 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 is as shown in Table 1. The polyamide resin composition discharged from the extruder in strand form was cut while being cooled and solidified to obtain the polyamide resin composition of each example as pellets.

[0064] The polyamide resin compositions of each example obtained as described above were 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 films, thereby obtaining polyamide resin composition films of each example. The film thickness of the polyamide resin composition films was 100 μm.

[0065] 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 the porous polyamide film of each example. The thickness of the porous polyamide film was 100 μm. When the cross-sections of the porous polyamide films of each example obtained were 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 all of the porous polyamide films.

[0066] [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.

[0067] [Comparative Example 2] A porous polyamide film was obtained in the same manner as in Comparative Example 1, except that the resin concentration of nylon 6 was changed to 20% by mass. 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.

[0068] For the porous polyamide films obtained in Examples 1-3, Comparative Example 1, and Comparative Example 2, the average pore diameter and the difference between the maximum value of the pore diameter range in the fraction with the largest pore diameter and the minimum value of the pore diameter range in the fraction with the smallest pore diameter (pore diameter distribution width) in the volume-based distribution of pores of each size relative to the total pore volume were measured using a liquid porometer (manufactured by Porometer) according to the method described above. The measurement results for the average pore diameter and pore diameter distribution width are shown in Table 1.

[0069] Furthermore, regarding the porous polyamide films obtained in Examples 1 to 3, Comparative Example 1, and Comparative Example 2, N ２ Based on the specific surface area measured by the BET method using gas, the area of ​​the main surface of the porous polyamide film is 1 m². ２ The surface area of ​​the region was calculated. Area of ​​the main surface of the porous polyamide film 1 m² ２ The surface area of ​​the region is shown in Table 1.

[0070] Furthermore, the porous polyamide films obtained in Examples 1-3, Comparative Example 1, and Comparative Example 2 were used to filter the chemical solution, and the amount of metal impurities in the filtered chemical solution was evaluated as described below.

[0071] 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.

[0072] The porous polyamide films obtained in Examples 1-3, Comparative Example 1, or Comparative Example 2 were each cut into circles with a diameter of 47 mm and used as filters. After setting the filters in a perfluoroalkoxyalkane (PFA) filtration holder, 1000 mL of OK73 thinner was passed through the filters to wash them. The aforementioned chemical solution was passed through the washed filters while pressurizing with nitrogen to a pressure of 0.08 MPa (G), and the purified chemical solution obtained by filtration was obtained as the filtrate.

[0073] [Measurement of Metal Atom Content] The metal compounds contained in the chemical solution samples filtered through the porous polyamide film obtained in Examples 1-3, Comparative Example 1, or Comparative Example 2 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.

[0074] [Evaluation of Defect Count] A chemical solution filtered through a porous polyamide film obtained in Examples 1-3, Comparative Example 1, or Comparative Example 2 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 film 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 Examples 1-3, Comparative Example 1, or Comparative Example 2 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.

[0075]

[0076] According to Table 1, the porous polyamide film has an internal structure of interconnected spherical pores, an average pore diameter of 10 nm to 200 nm, a pore diameter distribution width of 1 nm to 15 nm, and a main surface area of ​​1 m². ２ The surface area of ​​the region is 1000 m ２ Over 6000m ２ As shown below, in porous polyamide films, the pore size and pore shape are controlled, and it can be seen that when a fluid is filtered using the aforementioned porous polyamide film, impurities in the fluid can be effectively removed.

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 average pore diameter of the spherical pores is 10 nm or more and 200 nm or less, and the pore diameter distribution of the spherical pores in the porous polyamide film is such that, as measured by a porometer, the distribution of the volume of each size of pore relative to the total volume, measured at 1 nm intervals in the range of pore diameters of 5 nm or more, the difference between the maximum value of the pore diameter range in the fraction with the largest pore diameter where the pores exist and the minimum value of the pore diameter range in the fraction with the smallest pore diameter where the pores exist is 1 nm or more and 15 nm or less, and the area of ​​the main surface of the porous polyamide film is 1 m² ２ The surface area of ​​the region is 1000 m ２ Over 6000m ２ The following is a porous polyamide film.

2. A method for purifying a chemical solution, comprising using the porous polyamide film described in claim 1 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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