Filtration treatment method, and porous film

Abstract

To provide a fluid filtration treatment method which prevents a failure of filtration and a remarkable decrease in filtration speed, even when filtration of fluid is performed at high temperature, and a porous film which is preferably used in the filtration treatment method.SOLUTION: In a filtration treatment method for filtering fluid at 25°C or higher by a porous film, a polyimide resin porous film which has a communication hole and an average pore size of 0.3 μm or more, or a polyamide-imide resin porous film is used as a porous film.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for filtering a fluid using a porous membrane, and to a porous membrane that is suitably used in the filtering method. [Background technology]

[0002] BACKGROUND ART Conventionally, organic solvents, resist compositions, varnishes, and the like used in the manufacture of semiconductor devices have been subjected to filtration using a filter for the purpose of removing impurities.

[0003] Common filter membranes capable of removing impurities from chemical solutions and resin materials used in semiconductor devices and the like are made of nylon, polyethylene, polypropylene, PTFE, and the like. For example, it is known that organic impurities can also be removed by using a filter membrane such as nylon (e.g., Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4637476 Summary of the Invention [Problem to be solved by the invention]

[0005] In the manufacture of semiconductor devices, heated organic solvents or relatively viscous varnishes are sometimes used. When filtering highly viscous varnishes, the varnishes are heated to reduce their viscosity. For these reasons, chemicals used in the manufacture of semiconductor devices are often filtered at high temperatures.

[0006] However, when a porous membrane made of nylon, polyethylene, polypropylene, PTFE, or the like as described in Patent Document 1 is used as a filter, filtration at high temperatures may result in a decrease in filtration rate due to shrinkage of the porous membrane.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a method for filtering a fluid, which does not fail to filter the fluid or does not result in a significant decrease in filtration speed, even when filtering the fluid at high temperatures, and a porous membrane that is suitably used in the filtering method. [Means for solving the problem]

[0008] The present inventors have found that the above-mentioned problems can be solved by using a porous polyimide resin membrane or a porous polyamide-imide resin membrane having continuous pores and an average pore size of 0.3 μm or more in a filtration treatment method for filtering a fluid at a temperature of 25° C. or higher through a porous membrane, and have completed the present invention. Specifically, the present invention provides the following.

[0009] A first aspect of the present invention is a method for filtering a fluid using a filter, comprising: The fluid temperature is 25°C or higher, The filter is a porous membrane having communicating holes, the porous membrane is a polyimide resin porous membrane or a polyamide-imide resin porous membrane, The method relates to a method in which the average pore size of the porous membrane is 0.3 μm or more.

[0010] A second aspect of the present invention provides a porous membrane for use in the method according to the first aspect, comprising: the porous membrane is a polyimide resin porous membrane or a polyamide-imide resin porous membrane, The porous membrane has an average pore size of 0.3 μm or more. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a method for filtering a fluid, which does not fail to filter the fluid or does not result in a significant decrease in filtration rate, even when the fluid is filtered at high temperatures, and a porous membrane that is preferably used in the filtering method. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Fluid filtration treatment method> In a method for filtering a fluid using a filter, a fluid having a temperature of 25° C. or higher is filtered. The filter is a porous membrane having continuous pores. The porous membrane is a polyimide resin porous membrane or a polyamide-imide resin porous membrane. The average pore size of the porous membrane is 0.3 μm or more.

[0013] <Porous membrane> The porous membrane used as a filter is a polyimide resin porous membrane or a polyamideimide resin porous membrane. Hereinafter, the polyimide resin porous membrane and the polyamideimide resin porous membrane may be collectively referred to as a "polyimide resin porous membrane."

[0014] The porous membrane has communicating pores. The communicating pores are formed by adjacent and connected individual pores (hereinafter sometimes simply referred to as "pores") that impart porosity to the porous membrane. The individual pores are preferably holes having a curved inner surface as described below, and more preferably spherical or nearly spherical pores as described below. In the porous membrane, the portions where such individual pores are formed adjacent to each other are communicating pores. The communicating pores have a structure in which such individual pores are interconnected. Usually, a plurality of such pores are connected together to form a flow path for the liquid to be purified. Usually, the "flow path" is formed by a series of individual "pores" and / or "communicating pores." It can also be said that the individual pores are formed by removing individual particles present in the polyimide resin-particle composite membrane in a subsequent process in the porous membrane manufacturing method described below. In addition, the communicating holes can also be said to be adjacent individual pores formed in the polyimide resin-particle composite film in the region where the individual particles present in the polyimide resin-particle composite film were in contact with each other in the manufacturing method of the polyimide resin porous film described below, by removing the particles in a subsequent process.

[0015] The porous membrane preferably has communicating holes that have openings on the outer surface of the porous membrane, which communicate the interior of the porous membrane and also have openings on the outer surface on the opposite side (back side) of the porous membrane, ensuring a flow path for a fluid to pass through the porous membrane.

[0016] The average pore size of the porous membrane is 0.3 μm or more, preferably 0.3 μm or more and 0.8 μm or less. The average pore size is the average value of the diameter of the openings shared by adjacent pores. The average pore size can be measured using a perm porometer (for example, manufactured by Porous Materials Co., Ltd.).

[0017] The porosity of the porous membrane is, for example, preferably 60% to 90%, more preferably 60% to 80%. The porosity is the ratio of the volume of pores to the volume of the entire porous membrane. The volume of the entire porous membrane includes the volume of pores.

[0018] When a fluid is passed through a porous membrane having interconnecting pores, the fluid can pass through the interior of the porous membrane. The porous membrane preferably has a flow path inside, where each pore has a curved surface on the inner surface and interconnecting pores are connected. Therefore, not only can the fluid pass through the interior of the porous membrane, but also, by passing through while contacting the curved surfaces of each pore, the contact area with the inner surface of the pore increases, and it is thought that minute substances such as metal particles present in the fluid are easily adsorbed into the pores in the porous membrane.

[0019] As described above, the porous membrane is preferably a porous membrane containing pores having a curved inner surface, and more preferably, most (preferably, substantially all) of the pores in the porous membrane are formed with a curved surface. In this specification, the phrase "having a curved inner surface" in relation to pores means that at least the inner surface of the pore that creates the porosity has a curved surface in at least a part of the inner surface.

[0020] It is preferable that the inner surfaces of the pores in the porous membrane are substantially entirely curved. Such pores are hereinafter sometimes referred to as "spherical or approximately spherical pores." In this specification, "spherical or approximately spherical pores" refers to pores whose inner surfaces form spherical or approximately spherical spaces. Spherical or approximately spherical pores can also be said to be pores formed when the microparticles used in the method for producing a polyimide-based resin porous membrane described below are spherical or approximately spherical. In this specification, "spherical or approximately spherical" refers to a concept that includes true spheres, but is not necessarily limited to true spheres, and includes particles that are substantially spherical. In this specification, "substantially spherical" refers to a particle with a sphericity of 1±0.3 or less, defined as the sphericity obtained by dividing the major axis by the minor axis. The sphericity of the spherical or approximately spherical pores in the porous membrane is preferably 0.9 to 1.1, more preferably 0.95 to 1.05.

[0021] By having the pores in the porous membrane have a curved inner surface, when a fluid is passed through the porous membrane, the fluid can be sufficiently distributed inside the pores in the porous membrane and can fully contact the inner surface of the pores. In some cases, it is possible that the fluid may undergo convection along the curved inner surface. For this reason, it is thought that minute substances such as metal particles present in the fluid are easily adsorbed into the pores in the porous membrane or into recesses that may exist on the inner surface of the pores. The spherical or approximately spherical pores may further have recesses on their inner surfaces. For example, the recesses may be formed by pores with a smaller pore diameter than the spherical or approximately spherical pores, which have openings on the inner surface of the spherical or approximately spherical pores.

[0022] The thickness of the porous membrane is preferably 15 μm or more and 100 μm or less, more preferably 20 μm or more and 40 μm or less, from the viewpoint of achieving both an excellent filtration rate and excellent membrane strength.

[0023] As described above, the porous membrane is a polyimide resin porous membrane or a polyamide-imide resin porous membrane. In this specification, polyimide resins and polyamide-imide resins may be collectively referred to as "polyimide-based resins."

[0024] The polyimide resin or polyamideimide resin contained in the porous film may have at least one selected from the group consisting of a carboxy group, a salt-type carboxy group, and an -NH- bond. The polyimide resin or polyamideimide resin preferably has the carboxy group, the salt-type carboxy group, and / or the -NH- bond at a position other than the terminal of the polyimide and / or polyamideimide main chain.

[0025] In this specification, the term "salt-type carboxy group" refers to a group in which a hydrogen atom in a carboxy group is substituted with a cationic moiety. In this specification, the term "cationic moiety" may refer to a cation itself in a completely ionized state, or a -COO - The cationic component may be an M ion component consisting of an n-valent metal M, and the cation itself may be M n+ The cation component is expressed as "-COOM 1 / n " is the element represented by "M".

[0026] The "cation component" includes a cation formed when the compounds listed as compounds contained in the chemical etching solution described below are ionically dissociated. Representative examples include an ion component or an organic alkali ion component. For example, when the alkali metal ion component is a sodium ion component, the cation itself is a sodium ion (Na + ) and the cationic component is the element represented by "Na" in "-COONa", and the cationic component with partial charge is Na δ+ The cationic component is not particularly limited, and may be an inorganic component or NH4 + , N(CH3)4 + The inorganic component may be, for example, an alkali metal such as Li, Na, or K, or an alkaline earth metal such as Mg or Ca. The organic component, particularly the organic alkali ion component, may be NH4+ , e.g. NR4 + (four R's may be the same or different and represent an organic group). The organic group represented by R is preferably an alkyl group, more preferably an alkyl group having 1 to 6 carbon atoms. Examples of quaternary ammonium cations include N(CH3)4 + etc.

[0027] The state of the "salt-type carboxy group" and the "cation component" is not particularly limited, and may generally depend on the environment in which the polyimide and / or polyamideimide exists, for example, whether it is in an aqueous solution, an organic solvent, or dry. When the cationic component is a sodium ion component, for example, in an aqueous solution, -COO - and Na + If the solution is in an organic solvent or is dry, it is highly likely that -COONa is not dissociated.

[0028] The polyimide resin or polyamideimide resin may have at least one selected from the group consisting of a carboxy group, a salt-type carboxy group, and an -NH- bond. When the polyimide resin or polyamideimide resin has at least one of these, the polyimide resin or polyamideimide resin usually has both a carboxy group and / or a salt-type carboxy group and an -NH- bond. The polyimide resin or polyamideimide resin may have only a carboxy group, only a salt-type carboxy group, or both a carboxy group and a salt-type carboxy group.

[0029] Specifically, the polyimide resin or polyamideimide resin preferably has at least one structural unit selected from the group consisting of structural units represented by the following formulas (3) to (6). The polyimide resin may have a structural unit represented by the following formula (3) and / or a structural unit represented by the following formula (4). The polyamideimide resin may have a structural unit represented by the following formula (5) and / or a structural unit represented by the following formula (6). [ka] [ka]

[0030] In the above formula, X may be the same or different and is a hydrogen atom or a cation component. Ar is an aryl group. Ar may be the same as the aryl group represented by Ar to which a carbonyl group is bonded in the repeating unit represented by formula (1) constituting the polyamic acid described below or the repeating unit represented by formula (2) constituting the aromatic polyimide described below. Y is a divalent residue obtained by removing the amino group of a diamine compound. Y may be the same as the aryl group represented by Ar to which N is bonded in the repeating unit represented by formula (1) constituting the polyamic acid described below or the repeating unit represented by formula (2) constituting the aromatic polyimide described below.

[0031] In the polyimide resin or polyamideimide resin, a portion of the imide bonds ([-C(=O)]2-N-) generally contained in the polyimide resin or polyamideimide resin may be ring-opened to form the constitutional unit represented by the above formula (3), the constitutional unit represented by the above formula (4), and the constitutional unit represented by the above formula (5).

[0032] <Method of manufacturing a porous polyimide resin membrane> In the method for producing a polyimide-based resin porous membrane made of a polyimide resin or a polyamideimide resin, (a) before the fine particle removal step, a composite membrane of polyimide and / or polyamideimide and fine particles may be subjected to an imide bond ring-opening step, or (b) after the fine particle removal step, a polyimide and / or polyamideimide formed membrane made porous by the fine particle removal step may be subjected to an imide bond ring-opening step. The latter method (b) is preferred because it can increase the degree of porosity in the resulting polyimide-based resin porous membrane.

[0033] The method for producing a porous polyimide resin membrane will be described in detail below, mainly taking as an example the case where the membrane is in the form of a porous membrane, which is a preferred embodiment. The membrane can be suitably produced using a varnish.

[0034] [Varnish manufacturing] Varnish can be produced by mixing polyamic acid, polyimide, or polyamideimide in any ratio with an organic solvent containing pre-dispersed microparticles, or by polymerizing tetracarboxylic dianhydride and diamine in an organic solvent containing pre-dispersed microparticles to form polyamic acid, or by further imidization to form polyimide. The final viscosity of the varnish is preferably 300 cP to 2000 cP (0.3 Pa·s to 2 Pa·s), more preferably 400 cP to 1800 cP (0.4 Pa·s to 1.8 Pa·s). A varnish viscosity within this range facilitates the formation of a uniform film.

[0035] In the varnish, the particles can be mixed with a resin selected from polyamic acid, polyimide resin, and polyamideimide resin so that when a polyimide resin-particle composite film is formed by baking (or drying if baking is optional), the ratio of particles to polyimide resin (by mass) is 1 to 4. The ratio of particles to polyimide resin is preferably 1.1 to 3.5 (by mass). It is also preferable to mix the particles with a resin selected from polyamic acid, polyimide resin, and polyamideimide resin so that the volume ratio of particles / polyimide resin in the polyimide resin-particle composite film is 1.1 or more and 5 or less. The volume ratio of particles to polyimide resin in the polyimide resin-particle composite film is more preferably 1.1 or more and 4.5 or less. When the mass ratio or volume ratio of the fine particles to the polyimide resin is within the above range, it is easy to form holes with an appropriate density as a porous film, and it is easy to stably form a film without problems such as an increase in viscosity or cracks in the film. In this specification, the volume percentages and volume ratios are values ​​at 25°C.

[0036] <Fine particles> The material of the fine particles to be incorporated into the varnish is not particularly limited as long as it is insoluble in the organic solvent used in the varnish and can be selectively removed after film formation. Examples of inorganic materials include silica (silicon dioxide), titanium oxide, alumina (Al2O3), and metal oxides such as calcium carbonate. Examples of organic materials include resin fine particles such as high-molecular-weight polyolefins (polypropylene, polyethylene, etc.), polystyrene, acrylic resins (polymethyl methacrylate (PMMA), polyisobutyl methacrylate, etc.), epoxy resins, cellulose, polyvinyl alcohol, polyvinyl butyral, polyesters, and polyethers.

[0037] As the fine particles, silica such as colloidal silica, which is an inorganic fine particle, and PMMA fine particles, which is an organic polymer fine particle, are preferable because they can easily form minute pores having curved inner surfaces.

[0038] The particle size of the fine particles is appropriately selected depending on the average pore size of the porous membrane to be finally formed.

[0039] A dispersant may be added to the varnish together with the fine particles to uniformly disperse the fine particles in the varnish. Adding a dispersant allows the fine particles to be mixed more uniformly with a resin selected from polyamic acid, polyimide resin, and polyamideimide resin. Furthermore, the fine particles can be uniformly distributed in the molded or formed precursor film. As a result, dense openings can be formed on the surface of the finally obtained porous film, and communicating pores can be formed that efficiently connect the front and back surfaces of the porous film to improve the air permeability of the porous film.

[0040] The dispersant is not particularly limited. Examples of the dispersant include anionic surfactants such as coconut fatty acid salts, castor sulfated oil salts, lauryl sulfate salts, polyoxyalkylene allyl phenyl ether sulfate salts, alkyl benzene sulfonic acids, alkyl benzene sulfonates, alkyl diphenyl ether disulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinate salts, isopropyl phosphate, polyoxyethylene alkyl ether phosphate salts, and polyoxyethylene allyl phenyl ether phosphate salts; cationic surfactants such as oleylamine acetate, lauryl pyridinium chloride, cetyl pyridinium chloride, lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, and didecyl dimethyl ammonium chloride; amphoteric surfactants such as coconut alkyl dimethyl amine oxide, fatty acid amidopropyl dimethyl amine oxide, alkyl polyaminoethyl glycine hydrochloride, amido betaine surfactants, alanine surfactants, and lauryliminodipropionic acid; Examples of suitable dispersants include, but are not limited to, nonionic surfactants of polyoxyalkylene primary alkyl ethers or polyoxyalkylene secondary alkyl ethers, such as polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene laurylamine, polyoxyethylene oleylamine, polyoxyethylene polystyrylphenyl ether, and polyoxyalkylene polystyrylphenyl ether; other polyoxyalkylene-based nonionic surfactants, such as polyoxyethylene dilaurate, polyoxyethylene laurate, polyoxyethylenated castor oil, polyoxyethylenated hydrogenated castor oil, sorbitan laurate, polyoxyethylene sorbitan laurate, and fatty acid diethanolamides; fatty acid alkyl esters, such as octyl stearate and trimethylolpropane tridecanoate; and polyether polyols, such as polyoxyalkylene butyl ether, polyoxyalkylene oleyl ether, and trimethylolpropane tris(polyoxyalkylene) ether. Furthermore, two or more of the above dispersants can also be used in combination.

[0041] <Polyamic acid> The polyamic acid may be any resin obtained by polymerizing any tetracarboxylic dianhydride and any diamine. The amounts of the tetracarboxylic dianhydride and diamine used are not particularly limited. The amount of diamine used per mole of tetracarboxylic dianhydride is preferably 0.50 moles or more and 1.50 moles or less, more preferably 0.60 moles or more and 1.30 moles or less, and particularly preferably 0.70 moles or more and 1.20 moles or less.

[0042] The tetracarboxylic dianhydride can be appropriately selected from tetracarboxylic dianhydrides conventionally used as raw materials for synthesizing polyamic acids. The tetracarboxylic dianhydride may be an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride. From the viewpoint of the heat resistance of the resulting polyimide resin, it is preferable to use an aromatic tetracarboxylic dianhydride. Two or more tetracarboxylic dianhydrides may be used in combination.

[0043] Specific preferred examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, and 2,2,6,6-biphenyltetracarboxylic dianhydride. Carboxylic acid dianhydrides, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3',4,4'-benzophenone tetraanhydride Carboxylic acid dianhydrides, bis(3,4-dicarboxyphenyl) ether dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, 2,2',3,3'-benzophenonetetracarboxylic acid dianhydride, 4,4-(p-phenylenedioxy)diphthalic dianhydride, 4,4-(m-phenylenedioxy)diphthalic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid Examples of suitable aliphatic tetracarboxylic dianhydrides include 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, 9,9-bisphthalic anhydride fluorene, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride. Examples of suitable aliphatic tetracarboxylic dianhydrides include ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and 1,2,3,4-cyclohexanetetracarboxylic dianhydride. Among these, 3,3',4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferred in terms of price, availability, and the like.These tetracarboxylic dianhydrides may be used alone or in combination.

[0044] The diamine can be appropriately selected from diamines conventionally used as raw materials for synthesizing polyamic acid. The diamine may be an aromatic diamine or an aliphatic diamine, but aromatic diamines are preferred from the viewpoint of the heat resistance of the resulting polyimide resin. Two or more of these diamines may be used in combination.

[0045] The aromatic diamine may be a diamine containing one benzene ring, or may be a polycyclic aromatic diamino compound in which two or more and ten or less benzene rings are condensed with each other or bonded via a single bond or any linking group. Specific examples of aromatic diamines include phenylenediamine and derivatives thereof, diaminobiphenyl compounds and derivatives thereof, diaminodiphenyl compounds and derivatives thereof, diaminotriphenyl compounds and derivatives thereof, diaminonaphthalene and derivatives thereof, aminophenylaminoindan and derivatives thereof, diaminotetraphenyl compounds and derivatives thereof, diaminohexaphenyl compounds and derivatives thereof, and cardo-type fluorenediamine derivatives.

[0046] Phenylenediamines include m-phenylenediamine and p-phenylenediamine. Phenylenediamine derivatives include phenylenediamines to which alkyl groups such as methyl and ethyl groups are bonded. Specific examples of phenylenediamine derivatives include 2,4-diaminotoluene and 2,4-triphenylenediamine.

[0047] Diaminobiphenyl compounds are compounds in which two aminophenyl groups are bonded together via the phenyl groups, such as 4,4'-diaminobiphenyl and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl.

[0048] A diaminodiphenyl compound is a compound in which two aminophenyl groups are bonded to each other via another group. The other group bond may be an ether bond, a sulfonyl bond, a thioether bond, a bond via an alkylene or its derivative group, an imino bond, an azo bond, a phosphine oxide bond, an amide bond, or a ureylene bond. The number of carbon atoms in the alkylene bond (alkylene group) is preferably 1 to 6. The derivative group is a group in which one or more hydrogen atoms of the alkylene group are substituted with a halogen atom or the like.

[0049] Examples of the diaminodiphenyl compound include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl methane, 3,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl ketone, 3,4'-diaminodiphenyl ketone, 2,2-bis(p-aminophenyl)propane, 2,2'-bis(p-aminophenyl)hexafluoropropane, 4-methyl-2,4-bis(p-aminophenyl)-1-pentene, 4-methyl-2,4-bis(p-aminophenyl) bis(4-aminophenoxy)phenyl]-2-pentene, iminodianiline, 4-methyl-2,4-bis(p-aminophenyl)pentane, bis(p-aminophenyl)phosphine oxide, 4,4'-diaminoazobenzene, 4,4'-diaminodiphenylurea, 4,4'-diaminodiphenylamide, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and the like.

[0050] Among these, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, and 4,4'-diaminodiphenyl ether are preferred in terms of price, availability, and the like.

[0051] A diaminotriphenyl compound is a compound in which two aminophenyl groups and one phenylene group are bonded via another group. The other group is selected from the same group as in the diaminodiphenyl compound. Examples of diaminotriphenyl compounds include 1,3-bis(m-aminophenoxy)benzene, 1,3-bis(p-aminophenoxy)benzene, and 1,4-bis(p-aminophenoxy)benzene.

[0052] Examples of diaminonaphthalenes include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene.

[0053] Examples of aminophenylaminoindan include 5 or 6-amino-1-(p-aminophenyl)-1,3,3-trimethylindan.

[0054] Examples of diaminotetraphenyl compounds include 4,4'-bis(p-aminophenoxy)biphenyl, 2,2'-bis[p-(p'-aminophenoxy)phenyl]propane, 2,2'-bis[p-(p'-aminophenoxy)biphenyl]propane, and 2,2'-bis[p-(m-aminophenoxy)phenyl]benzophenone.

[0055] Examples of cardo-type fluorenediamine derivatives include 9,9-bisanilinefluorene.

[0056] The number of carbon atoms in the aliphatic diamine is preferably, for example, from 2 to 15. Specific examples of suitable aliphatic diamines include pentamethylenediamine, hexamethylenediamine, and heptamethylenediamine.

[0057] The diamine may be a compound in which the hydrogen atom of the diamine is substituted with at least one substituent selected from the group consisting of a halogen atom, a methyl group, a methoxy group, a cyano group, a phenyl group, and the like.

[0058] There are no particular limitations on the means for producing polyamic acid, and for example, known methods such as a method of reacting a tetracarboxylic dianhydride and a diamine in an organic solvent can be used.

[0059] The reaction between tetracarboxylic dianhydride and diamine is usually carried out in an organic solvent. The organic solvent used in the reaction between tetracarboxylic dianhydride and diamine is not particularly limited as long as it can dissolve the tetracarboxylic dianhydride and diamine and does not react with the tetracarboxylic dianhydride and diamine. The organic solvent can be used alone or in combination of two or more.

[0060] Examples of organic solvents used in the reaction of tetracarboxylic dianhydride with diamine include nitrogen-containing polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea; lactone-based polar solvents such as β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, and ε-caprolactone; dimethyl sulfoxide; acetonitrile; fatty acid esters such as ethyl lactate and butyl lactate; ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methyl cellosolve acetate, and ethyl cellosolve acetate; and phenolic solvents such as cresols. These organic solvents can be used alone or in combination. Among these, a combination of a nitrogen-containing polar solvent and a lactone-based polar solvent is preferred.

[0061] There is no particular limitation on the amount of organic solvent used, but it is desirable to use the organic solvent in an amount such that the content of polyamic acid in the reaction liquid after completion of the reaction is 5% by mass or more and 50% by mass or less.

[0062] Among these organic solvents, nitrogen-containing polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea are preferred from the viewpoint of solubility of the resulting polyamic acid. Furthermore, from the viewpoint of film-forming properties, mixed solvents containing lactone-based polar solvents such as γ-butyrolactone are also preferred. The amount of the lactone-based polar solvent added to the mixed solvent is preferably 1% by mass to 20% by mass, more preferably 5% by mass to 15% by mass, based on the total amount of the mixed solvent.

[0063] The polymerization temperature is generally preferably −10° C. or higher and 120° C. or lower, more preferably 5° C. or higher and 30° C. or lower. The polymerization time varies depending on the composition of the raw materials used, but is usually preferably 3 hours or higher and 24 hours or lower. The intrinsic viscosity of the polyamic acid solution obtained under such conditions is preferably 1,000 cP or more and 100,000 cP or less, and more preferably 5,000 cP or more and 70,000 cP or less.

[0064] <Polyimide resin> The polyimide resin is not limited in structure or molecular weight as long as it is soluble in the organic solvent contained in the varnish. The polyimide resin may have a condensable functional group such as a carboxyl group in its side chain or a functional group that promotes a crosslinking reaction or the like during baking.

[0065] To produce organic solvent-soluble polyimide resins, it is effective to use a monomer that introduces a flexible, bent structure into the main chain. Examples of such monomers include aliphatic diamines such as ethylenediamine, hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, and 4,4'-diaminodicyclohexylmethane; aromatic diamines such as 2-methyl-1,4-phenylenediamine, o-tolidine, m-tolidine, 3,3'-dimethoxybenzidine, and 4,4'-diaminobenzanilide; polyoxyalkylene diamines such as polyoxyethylenediamine, polyoxypropylenediamine, and polyoxybutylenediamine; polysiloxane diamines; 2,3,3',4'-oxydiphthalic anhydride, 3,4,3',4'-oxydiphthalic anhydride, and 2,2-bis(4-hydroxyphenyl)propanedibenzoate-3,3',4,4'-tetracarboxylic dianhydride. It is also effective to use a monomer having a functional group that improves solubility in organic solvents, such as fluorinated diamines such as 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 2-trifluoromethyl-1,4-phenylenediamine. Furthermore, in addition to the monomer for improving the solubility of the polyimide resin, the same monomers as those described in the polyamic acid section above can also be used in combination, provided that the solubility is not impaired.

[0066] There are no particular limitations on the means for producing a polyimide resin soluble in an organic solvent. For example, known methods can be used, such as chemically imidizing or thermally imidizing a polyamic acid and then dissolving it in an organic solvent. Examples of polyimide resins soluble in organic solvents include aliphatic polyimide resins (all aliphatic polyimide resins) and aromatic polyimide resins, with aromatic polyimide resins being preferred. Examples of aromatic polyimide resins include polyamide resins obtained by thermally or chemically ring-closing a polyamic acid having a repeating unit represented by formula (1), or polyimide resins having a repeating unit represented by formula (2). In the formula, Ar represents an aryl group. [ka] [ka]

[0067] <Polyamide-imide resin> The polyamide-imide resin is not limited in structure or molecular weight, and any known soluble polyamide-imide resin can be used as long as it is soluble in the organic solvent contained in the varnish. The polyamide-imide may have a condensable functional group such as a carboxyl group or a functional group that promotes a crosslinking reaction or the like during baking in its side chain.

[0068] The polyamide-imide resin can be used without any particular limitation, and may be a resin obtained by reacting any trimellitic anhydride with a diisocyanate, or a resin obtained by imidizing a precursor polymer obtained by reacting any reactive derivative of trimellitic anhydride with a diamine.

[0069] Any trimellitic anhydride or reactive derivative thereof may be, for example, trimellitic anhydride, trimellitic anhydride halides such as trimellitic anhydride chloride, trimellitic anhydride esters, and the like.

[0070] The optional diisocyanate may, for example, be metaphenylene diisocyanate, p-phenylene diisocyanate, o-tolidine diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 4,4'-oxybis(phenylisocyanate), 4,4'-diisocyanatodiphenylmethane, bis[4-(4-isocyanatophenoxy)phenyl]sulfone, 2,2'-bis[4-(4-isocyanatophenoxy)phenyl]propane, 2,4- Examples of the isocyanate include tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, 3,3'-diethyldiphenyl-4,4'-diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, m-xylene diisocyanate, p-xylene diisocyanate, and naphthalene diisocyanate.

[0071] Examples of the optional diamine include the same diamines as those exemplified in the description of polyamic acid.

[0072] <Organic solvents> The varnish contains an organic solvent. The organic solvent is not particularly limited as long as it can dissolve polyamic acid and / or polyimide resin but does not dissolve fine particles. Examples of such organic solvents include the organic solvents exemplified as solvents used in the reaction between tetracarboxylic dianhydride and diamine. The solvents may be used alone or in combination of two or more.

[0073] Of all the components in the varnish, the content of the organic solvent is preferably 50% by mass to 95% by mass, more preferably 60% by mass to 85% by mass. The solid content concentration in the varnish is preferably 5% by mass to 50% by mass, more preferably 15% by mass to 40% by mass.

[0074] In addition to the above-mentioned components, the varnish may contain known components, such as antistatic agents, flame retardants, chemical imidizing agents, condensing agents, mold release agents, and surface conditioners, as needed, for the purposes of antistatic properties, imparting flame retardancy, low-temperature baking, mold releasability, coatability, and the like.

[0075] [Production of unsintered composite membrane] An unsintered composite film containing polyamic acid or polyimide resin and fine particles is formed by coating the varnish onto a substrate and drying it at atmospheric pressure or in a vacuum, preferably at 0° C. to 120° C., more preferably at 0° C. to 100° C. More preferably, the unsintered composite film is formed by drying at atmospheric pressure at 60° C. to 95° C., particularly preferably at atmospheric pressure at 65° C. to 90° C.

[0076] The thickness of the coating film is not particularly limited, and the coating thickness is appropriately selected depending on the desired thickness of the porous film. A release layer may be provided on the substrate as needed. In addition, in the production of the unsintered composite film, the following optional steps may be performed before the production (sintering step) of the polyimide resin-particle composite film described below: a step of immersing in a solvent containing water, a pressing step, and a drying step after the immersion step.

[0077] The release layer can be prepared by applying a release agent to the substrate and drying or baking it. As the release agent, any known release agent such as an alkyl ammonium phosphate release agent, a fluorine-based release agent, or a silicone-based release agent can be used without any particular limitation. When an unsintered composite film containing dried polyamic acid or polyimide resin and fine particles is peeled off from a substrate, a small amount of release agent remains on the peeled surface of the unsintered composite film. This remaining release agent can affect the wettability of the porous film surface and the inclusion of impurities, so it is preferable to remove it.

[0078] Therefore, it is preferable to wash the unsintered composite film peeled from the substrate using an organic solvent or the like. The washing method can be selected from known methods such as immersing the unsintered composite film in a washing solution and then removing it, or shower washing. Furthermore, the unsintered composite film after washing can be dried by known methods such as air drying at room temperature or heating to an appropriate set temperature in a thermostatic chamber. For example, a method can be used in which the edges of the unsintered composite film are fixed to a stainless steel mold or the like to prevent deformation.

[0079] On the other hand, when the substrate is used as it is without providing a release layer for forming the green composite film, the steps of forming the release layer and washing the green composite film can be omitted.

[0080] [Manufacturing polyimide resin-particle composite film (baking process)] The dried unbaked composite film is then subjected to post-treatment (baking) by heating to form a composite film (polyimide resin-particle composite film) consisting of a polyimide resin and fine particles. When the varnish contains polyamic acid, it is preferable to complete imidization in the baking step. The baking step is an optional step. In particular, when polyimide or polyamideimide is used in the varnish, the baking step may not be performed.

[0081] The baking temperature varies depending on the structure of the polyamic acid or polyimide resin contained in the unbaked composite film and the presence or absence of a condensing agent, but is preferably 120°C to 400°C, more preferably 150°C to 375°C.

[0082] The firing process and the drying process do not necessarily have to be clearly separated. For example, when firing at 375°C, a method of raising the temperature from room temperature to 375°C over 3 hours and then holding at 375°C for 20 minutes can be used, or a stepwise drying-thermal imidization method can be used in which the temperature is raised from room temperature to 375°C in 50°C increments (each step is held for 20 minutes) and finally held at 375°C for 20 minutes. In this case, a method of fixing the edges of the unfired composite film to a stainless steel mold or the like to prevent deformation can be used.

[0083] [Particle removal process (making the polyimide resin-particle composite film porous)] By selecting an appropriate method to remove the particles from a polyimide-based resin-particle composite film, a porous film with micropores can be produced with good reproducibility. For example, when silica is used as the particles, the polyimide-based resin-particle composite film can be made porous by dissolving and removing the silica using low-concentration hydrogen fluoride (HF) or the like. Furthermore, when the particles are resin particles, the film can be heated to a temperature above the thermal decomposition temperature of the resin particles but below the thermal decomposition temperature of the polyimide-based resin, as described above, to decompose the resin particles and remove them.

[0084] [Imide bond ring opening process] The method for producing a porous film may include the imide bond ring-opening step as described above. Specifically, (a) before the fine particle removal step, the polyimide resin-fine particle composite film may be subjected to the imide bond ring-opening step, or (b) after the fine particle removal step, the polyimide resin formed film made porous by the fine particle removal step may be subjected to the imide bond ring-opening step. As for the above-mentioned production method, even the former method (a) can open the imide bonds present on the outer surface of the polyimide resin formed film and in the vicinity thereof. The latter method (b) is preferred in that it can increase the degree of porosity of the resulting porous film.

[0085] The imide bond ring-opening step can be carried out by a chemical etching method, a physical removal method, or a combination of these. The chemical etching method is not particularly limited, and for example, a conventionally known method can be used.

[0086] Chemical etching methods include treatment with chemical etching solutions such as inorganic alkaline solutions or organic alkaline solutions. Inorganic alkaline solutions are preferred. Examples of inorganic alkaline solutions include hydrazine solutions containing hydrazine hydrate and ethylenediamine; solutions of alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, sodium carbonate, sodium silicate, and sodium metasilicate; ammonia solutions; and etching solutions mainly containing alkali hydroxides, hydrazine, and 1,3-dimethyl-2-imidazolidinone. Examples of organic alkaline solutions include alkaline solutions of primary amines such as ethylamine and n-propylamine; secondary amines such as diethylamine and di-n-butylamine; tertiary amines such as triethylamine and methyldiethylamine; alcohol amines such as dimethylethanolamine and triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; and cyclic amines such as pyrrole and piheridine.

[0087] The solvent for each of the above solutions can be selected appropriately from pure water or alcohols. A suitable amount of surfactant can also be added. The alkali concentration is, for example, 0.01% by mass or more and 20% by mass or less.

[0088] As a physical method, for example, dry etching using plasma (oxygen, argon, etc.) or corona discharge can be used.

[0089] The above-mentioned method is preferable because it can be applied to either the imide bond ring-opening step before or after the particle removal step. In addition, when a chemical etching method is performed after the particle removal step, it is easy to form continuous pores inside the porous film, and the opening rate can be improved.

[0090] When chemical etching is carried out as the imide bond ring-opening step, the porous membrane may be washed again to remove excess etching solution components. As for the cleaning after chemical etching, water washing alone may be used, but it is preferable to combine acid washing and / or water washing. The porous film may be re-baked to improve the wettability of the surface of the porous film to organic solvents and to remove residual organic matter. The baking conditions may be appropriately set similarly to those in [Production of polyimide-based resin-particle composite film (baking step)].

[0091] [Filtration method] The porous membrane described above is used to filter a fluid. The fluid may be a gas or a liquid. The purpose of the filtration is not particularly limited. Examples of the purpose of the filtration include separating solids contained in the fluid and purifying the fluid by removing solids contained in the fluid.

[0092] In the method for filtering a fluid, a fluid having a temperature of 25° C. or higher is filtered. The temperature of the fluid is preferably 50° C. or higher and 200° C. or lower, and more preferably 60° C. or higher and 80° C. or lower. When the porous membrane described above is used, the filtration rate is unlikely to decrease even when filtration is carried out at high temperatures.

[0093] In order to prevent the filtration rate from being excessively slowed, it is preferable to heat the casing or jacket of the filter device, which will be described later, during filtration. The heating temperature is determined taking into consideration the boiling point of the liquid component contained in the fluid to be filtered. The heating temperature is preferably lower than the boiling point of the liquid component contained in the fluid to be filtered, preferably 10°C or more lower than the boiling point of the liquid component, and more preferably 20°C or more lower than the boiling point of the liquid component. Note that the boiling point here is the boiling point under atmospheric pressure. As mentioned above, the preferred heating temperature is determined taking into consideration the boiling point of the liquid components contained in the fluid to be filtered, but typically the heating temperature is preferably 40°C or higher and 200°C or lower, more preferably 40°C or higher and 120°C or lower, and even more preferably 40°C or higher and 80°C or lower.

[0094] Furthermore, polyimide resins and polyamide-imide resins are widely known to have excellent chemical stability and heat resistance, so even when high-temperature fluids are filtered using the porous membranes, there is almost no elution of substances derived from the porous membrane into the fluid to be filtered.

[0095] The fluid to be filtered is not particularly limited. Preferred fluids include various chemicals used in semiconductor device manufacturing. Specific examples of chemicals include organic solvents, photoresist compositions, and polymer-containing varnishes. Examples of varnishes include varnishes containing photosensitive or non-photosensitive polyimides used in displays, protective films for semiconductors and electronic components, insulating films, etc., and varnishes containing dissolved novolac resins used in photoresists.

[0096] Varnishes containing polymers have high viscosities near room temperature, making filtration through a porous membrane difficult. In this case, it is preferable that the viscosity of the fluid at 20°C is 5.0 Pa·s or higher and the viscosity at the filtration temperature is 8.0 Pa·s or lower. The filtration temperature is 25°C or higher. The viscosity of the fluid at the filtration temperature is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less of the viscosity of the fluid at 20°C.

[0097] When performing filtration, the porous membrane can be attached to various filter devices. In this case, the porous membrane may be processed into various shapes. For example, the porous membrane may be folded to increase the surface area. The porous membrane may also be processed into a cylindrical or bag shape.

[0098] The filtration of the fluid is carried out appropriately by a method depending on the type of filter device in which the porous membrane is mounted. [Example]

[0099] The present invention will be explained in more detail below by showing examples, but the scope of the present invention is not limited to these examples.

[0100] [Example 1, Example 2, and Comparative Example 1] The following porous polyimide resin membranes were used in Examples 1 and 2 and Comparative Example 1. The following porous polyimide resin membranes were produced by forming a polyimide resin-particle composite membrane according to the above-mentioned method and then removing the particles from the composite membrane. The average pore size of the following polyimide resin porous membrane was adjusted by adjusting the average particle size of the spherical silica fine particles contained in the polyimide resin-fine particle composite membrane. The average pore size is the average value of the diameters of the openings shared by adjacent pores in the communicating pores contained in the porous membrane. The average pore size was measured according to the method described above. Example 1: Average pore size 0.8 μm, thickness 40 μm, porosity 70% Example 2: Average pore size 0.3 μm, thickness 40 μm, porosity 70% Comparative example 1: average pore diameter 0.01 μm, thickness 40 μm, porosity 70% Using the porous membrane, the filtration time of Brookfield silicone standard viscosity liquid (5000 cP) was measured according to the following method: Filtration time was measured using the silicone standard viscosity liquid at 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, and 80°C. Specifically, a porous membrane cut into a circular shape with a diameter of 47 mm was placed as a filter in a pressure vessel having a cylindrical internal space. The exterior of the pressure vessel containing the filter was covered with a jacket heater and heated to 60°C. 10 mL of the standard viscosity liquid was filled into the pressure vessel containing the filter. The pressure vessel was pressurized to 0.5 MPa (G), and the speed at which 10 mL of the standard viscosity liquid passed through the porous membrane was measured as the filtration time. The filtration time measurement results are shown in the table below.

[0101] [Table 1]

[0102] As shown in Table 1, in the methods of Examples 1 and 2 in which a fluid at 25°C or higher is filtered using a polyimide resin porous membrane with an average pore size of 0.3 μm or more, there was no decrease in the filtration rate even when filtering at high temperatures. On the other hand, in the method of Comparative Example 1 in which a fluid at 25° C. or higher was filtered using a polyimide resin porous membrane with an average pore size of less than 0.3 μm, the fluid could not be filtered even when the fluid temperature was increased. The method, wherein the porous membrane has an average pore size of 0.3 μm or more.

Claims

1. A method for filtering a fluid using a filter, comprising: The temperature of the fluid is 25°C or higher, The filter is a porous membrane having communicating holes, the porous membrane is a polyimide resin porous membrane or a polyamide-imide resin porous membrane, The method, wherein the porous membrane has an average pore size of 0.3 μm or more.

2. 2. The method for filtering a fluid according to claim 1, wherein the porous membrane has an average pore size of 0.3 μm or more and 0.8 μm or less.

3. The method for filtering a fluid according to claim 1, wherein the temperature of the fluid is 50°C or higher and 200°C or lower.

4. The method for filtering a fluid according to claim 2, wherein the temperature of the fluid is 60°C or higher and 80°C or lower.

5. 2. The filtration method according to claim 1, wherein the viscosity of the fluid at 20°C is 5.0 Pa·s or more and the viscosity of the fluid at the filtration temperature is 8.0 Pa·s or less.

6. The method of claim 1 , wherein the fluid is an organic solvent.

7. A porous membrane used in the method according to any one of claims 1 to 6, the porous membrane is a polyimide resin porous membrane or a polyamide-imide resin porous membrane, A porous membrane having an average pore size of 0.3 μm or more.

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