Porous membrane, method of manufacturing porous membrane, membrane distillation module, membrane distillation apparatus, and method of manufacturing purified liquid

Abstract

To provide a porous membrane which can be used for membrane distillation for purifying a liquid with low surface tension such as isopropyl alcohol and which is excellent in durability, a method of manufacturing the porous membrane, a membrane distillation module having the porous membrane as a membrane for the membrane distillation, a membrane distillation apparatus having the membrane distillation module, and a method of manufacturing the liquid purified by the membrane distillation using the porous membrane as the membrane distillation membrane.SOLUTION: A surface of a principal plane on the side of contact with a crude liquid has a liquid repellent layer. The arithmetic mean roughness Ra of the principal plane is 10 nm or more, and the surface tension of the principal plane is 15 mN / m or less. A porous membrane described above is used.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a porous membrane used in membrane distillation, a method for producing the porous membrane, a membrane distillation module including the porous membrane as a membrane for membrane distillation, a membrane distillation apparatus including the membrane distillation module, and a method for producing a purified liquid by membrane distillation using the porous membrane as a membrane for membrane distillation. [Background technology]

[0002] As semiconductors become increasingly miniaturized and multi-layered, pattern collapse during the drying process in semiconductor manufacturing has become a problem. To prevent pattern collapse, high-purity isopropyl alcohol is required as a liquid for use in cleaning and drying during semiconductor manufacturing.

[0003] As a technique for increasing the purity of isopropyl alcohol, for example, distillation is known (see Patent Document 1). However, distillation has the problem that it requires large-scale equipment.

[0004] Meanwhile, membrane distillation is also a method for purifying isopropyl alcohol (see Patent Document 2). Membrane distillation is a method for purifying a crude liquid by allowing vapor to permeate a porous membrane due to the vapor pressure generated by the temperature difference between two liquids separated by the porous membrane. Compared to distillation, membrane distillation can be made more compact. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2017 / 217279 [Patent Document 2] Japanese Patent Application Publication No. 2023-521918 Summary of the Invention [Problem to be solved by the invention]

[0006] Liquids with low surface tension (surface free energy), such as isopropyl alcohol, easily penetrate membranes. For this reason, when purifying (highly purifying) liquids with low surface tension, such as isopropyl alcohol, using membrane distillation, a porous membrane with high liquid repellency is required. Furthermore, in membrane distillation methods, conventional techniques such as those described in Patent Document 2 have a problem in that the durability of the porous membrane is insufficient and deteriorates over time, making it difficult to perform a high-purity treatment (refining treatment) on isopropyl alcohol and the like.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a porous membrane that can be used in a membrane distillation method for purifying a liquid with low surface tension, such as isopropyl alcohol, and that has excellent durability; a method for producing the porous membrane; a membrane distillation module that includes the porous membrane as a membrane for membrane distillation; a membrane distillation apparatus that includes the membrane distillation module; and a method for producing a liquid purified by membrane distillation using the porous membrane as a membrane distillation membrane. [Means for solving the problem]

[0008] The present inventors have found that the above-mentioned problems can be solved by using a porous membrane having a liquid-repellent layer on the main surface that comes into contact with a coarse liquid, and having an arithmetic mean roughness Ra of the main surface of 10 nm or more and a surface tension of 15 mN / m or less, and have arrived at the present invention. Specifically, the present invention provides the following.

[0009] [1] In a membrane distillation method, a porous membrane is used to obtain a purified liquid by passing vapor of the crude liquid to be purified, the porous membrane has a liquid-repellent layer on the main surface that comes into contact with the crude liquid, A porous film, wherein the principal surface has an arithmetic mean roughness Ra of 10 nm or more and a surface tension of 15 mN / m or less.

[0010] [2] The porous film according to [1] above, wherein the liquid-repellent layer is formed by plasma treatment using a gas containing a fluorinated hydrocarbon.

[0011] [3] The porous membrane according to [1] or [2] above, wherein the crude liquid is a liquid having a water content of 1% by mass or less.

[0012] [4] The porous membrane according to any one of the above [1] to [3], wherein the crude liquid contains isopropyl alcohol.

[0013] [5] The porous membrane according to any one of the above [1] to [4], wherein the thickness of the liquid-repellent layer is 1 μm or less.

[0014] [6] A method for producing a porous membrane according to any one of [1] to [5] above, a roughening treatment step of roughening the surface of an untreated porous membrane to obtain a roughened porous membrane; and a liquid-repellent treatment step of making the surface of the roughened porous membrane liquid-repellent by plasma treatment derived from a gas of a liquid-repellent agent.

[0015] [7] The method for producing a porous membrane according to [6] above, wherein in the surface roughening treatment step, the surface of the untreated porous membrane is roughened by plasma treatment.

[0016] [8] The method for producing a porous membrane according to [6] or [7] above, wherein the liquid repellent agent contains a fluorinated hydrocarbon.

[0017] [9] The method for producing a porous membrane according to any one of the above [6] to [8], wherein the rate of change in air permeability calculated by the following formula based on the Gurley air permeability GP1 of the untreated porous membrane before the surface roughening treatment step and the liquid repellency treatment step, and the Gurley air permeability GP2 of the porous membrane after the surface roughening treatment step and the liquid repellency treatment step, is 50% or less. Air permeability change rate (%) = (GP1 - GP2) / GP1 x 100

[0018]

[10] A membrane distillation module comprising the porous membrane according to any one of the above [1] to [5] as a membrane for membrane distillation.

[0019]

[11] A high-temperature tank into which a crude liquid to be purified is introduced and a liquid receiving tank for recovering the purified liquid; the high-temperature tank and the liquid-receiving tank are separated by the porous membrane, The membrane distillation module according to

[10] above, wherein the purified liquid obtained by condensing the vapor derived from the crude liquid while the vapor is permeating through the porous membrane or after the vapor has permeated through the porous membrane is recovered in the liquid receiving tank.

[0020]

[12] The membrane distillation module according to

[11] above; A membrane distillation apparatus comprising at least one of a heater that heats the crude liquid introduced into the high-temperature tank or the crude liquid introduced into the high-temperature tank, and a cooler that lowers the internal temperature of the receiving tank.

[0021]

[13] A method for producing a purified liquid, comprising membrane distilling the crude liquid using the membrane distillation apparatus described in

[12] above.

[0022]

[14] Contacting a crude liquid to be purified with the porous membrane according to any one of [1] to [5] above; A method for producing a purified liquid by membrane distillation, comprising condensing the vapor derived from the crude liquid during or after the vapor has permeated through the porous membrane to obtain a purified liquid. [Effects of the Invention]

[0023] According to the present invention, there can be provided a porous membrane that can be used in a membrane distillation method for purifying a liquid with low surface tension, such as isopropyl alcohol, and that has excellent durability; a method for producing the porous membrane; a membrane distillation module that includes the porous membrane as a membrane for membrane distillation; a membrane distillation apparatus that includes the membrane distillation module; and a method for producing a liquid purified by membrane distillation using the porous membrane as a membrane distillation membrane. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram showing an example of a membrane distillation apparatus using a porous membrane of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] ≪Porous membrane≫ Porous membranes are used in membrane distillation to allow vapor from a crude liquid to be purified to pass through, thereby obtaining a purified liquid. The porous membrane has a liquid-repellent layer on the main surface that comes into contact with the coarse liquid. The principal surface has an arithmetic mean roughness Ra of 10 nm or more, and a surface tension of 15 mN / m or less.

[0026] The crude liquid to be purified is not particularly limited, but preferably contains a liquid with low surface tension such as isopropyl alcohol. The crude liquid preferably has a water content of 1% by mass or less.

[0027] In the porous membrane, the liquid-repellent layer provided on the surface of the main surface that comes into contact with the crude liquid is not particularly limited as long as the liquid-repellent layer satisfies the above conditions, but it is preferably formed by plasma treatment using a gas containing a fluorinated hydrocarbon. Fluorinated hydrocarbons include CF4, C4F8 and C3F8.

[0028] The thickness of the liquid-repellent layer in the porous membrane is not limited, but is preferably a thin film of 1 μm or less. If the thickness is 1 μm or less, the pores of the porous membrane are less likely to be blocked and permeability during membrane distillation is less likely to be impaired. The thickness of the liquid-repellent layer can be determined, for example, by measuring the thickness at multiple locations with a micrometer and averaging the measurements, or by observing the cross section of the film with a scanning electron microscope (SEM) and averaging the measurements.

[0029] The porous membrane can be used in a membrane distillation method for purifying a liquid with low surface tension, such as isopropyl alcohol (IPA), and has excellent durability. For example, when isopropyl alcohol as a crude liquid is purified by membrane distillation using the porous membrane, the contact angle of isopropyl alcohol on the main surface of the porous membrane (the main surface having the liquid-repellent layer on its surface) can be maintained at 60° or more even after one hour has passed. Therefore, isopropyl alcohol does not easily permeate the porous membrane even after one hour has passed, and isopropyl alcohol can be successfully purified. The contact angle of isopropyl alcohol on the main surface of the porous membrane (the main surface having the liquid-repellent layer on its surface) before membrane distillation is 60° or more, preferably 70° or more or 80° or more.

[0030] The arithmetic mean roughness Ra of the principal surface is preferably 20 nm or more, more preferably 30 nm or more, and even more preferably 40 nm or more, and is preferably 350 nm or less, and more preferably 60 nm or less.

[0031] The surface tension of the main surface is preferably 10 mN / m or less. The surface tension of the main surface is also preferably 9.0 mN / m or less. There is no particular lower limit to the surface tension of the main surface, but it is, for example, 3.0 mN / m or more.

[0032] In this specification, the surface tension (surface free energy) of the principal surface is determined by measuring the contact angle of various liquid droplets on the surface of the principal surface. The surface tension ([mN / m]) of the principal surface is calculated based on the surface free energy [mJ / m 2 ]) has the same absolute value as In this specification, the arithmetic mean roughness Ra is a value defined by JIS B 0601 (1994). In this specification, the contact angle of a liquid (e.g., isopropyl alcohol) is a static contact angle. Unless otherwise specified, the static contact angle of a liquid can be measured using a contact angle meter ("Dropmaster 700" manufactured by Kyowa Interface Science Co., Ltd.) by dropping a 2.0 μL droplet of the liquid onto the surface of the porous membrane (the surface of the main surface) and measuring the contact angle 10 seconds after dropping.

[0033] The air permeability of the porous membrane is preferably 20 seconds or more and 150 seconds or less, more preferably 25 seconds or more and 100 seconds or less, and particularly preferably 30 seconds or more and 50 seconds or less. Here, the air permeability is the Gurley air permeability.

[0034] The shape of the pores in the porous membrane is not particularly limited as long as the porous membrane is permeable to the vapor of the crude liquid to be purified. As the porous membrane, a porous membrane manufactured by a known method, such as a phase separation method such as a water vapor absorption method or a thermally induced phase separation method, a stretching method, or a method of removing fine particles from a membrane containing fine particles, which will be described later, can be used. The pores in the porous membrane may be spherical or non-spherical. A plurality of pores in the porous membrane may form a structure in which the pores are interconnected (hereinafter referred to as interconnected pores). When the porous film is a laminate, the same applies to the porous layer included in the laminate.

[0035] The shape of the pores in the porous membrane may be spherical or non-spherical. The sphericity of the pore shape includes a perfect sphere, but is not necessarily limited to a perfect sphere. The sphericity may be essentially a perfect sphere, and also includes a shape that can be recognized as an approximately perfect sphere when visually observing an enlarged image of the pore. Specifically, in the case of a spherical hole, the surface defining the hole portion is a curved surface, and the curved surface may define a hole having a perfect sphere or a nearly perfect sphere. When the porous film is a laminate, the porosity and the pore size of the spherical pores may be the same or different for each porous layer constituting the laminate.

[0036] The diameter of the pores contained in the porous membrane is not particularly limited. Typically, the preferred range of pore diameter is adjusted appropriately within the range of 30 nm or more, preferably 30 nm or more and 2000 nm or less, depending on the type of material of the porous membrane, the surface treatment method performed on the porous membrane, the type of surface treatment method, etc. For example, when the material of the porous membrane is polyimide resin, the pore diameter is preferably 30 nm or more and 400 nm or less. When the material of the porous membrane is polyethersulfone, the pore diameter is also preferably more than 250 nm. When the cross-sectional shape of the hole is a shape other than a circle, the diameter of the hole can be the equivalent circle diameter of the cross-section of the hole.

[0037] When a porous membrane has interconnected pores consisting of spherical pores, the individual spherical pores are typically formed by removing individual particles present in a resin-particle composite membrane in a later step, as described below. Furthermore, the interconnected pores are formed by removing, in a later step, multiple particles present in contact with each other in the resin-particle composite membrane in the manufacturing method for a porous membrane, as described below. The locations where the interconnected spherical pores are present originate from the locations where multiple particles contact each other before being removed.

[0038] When a porous membrane has communicating holes that penetrate the porous membrane in the thickness direction and serve as fluid flow paths, the fluid can permeate from one main surface of the porous membrane to the other main surface.

[0039] The porous membrane may be a single-layer membrane consisting of only one type of membrane without a liquid-repellent layer (hereinafter also referred to as an "untreated porous membrane"), or a laminated membrane consisting of two or more types of membranes stacked in two or more layers.

[0040] When the untreated porous film is a laminated film, the laminated film can be formed by a conventional method such as lamination.In addition, the untreated porous film included in the laminated film can be formed sequentially on the untreated porous film constituting one of the outermost layers of the laminated film.In addition, the precursor film of the untreated porous film can be laminated by lamination, coating method, etc., and then the laminated film on which the precursor film is laminated can be made porous to form the untreated porous film that is a laminated film.As the precursor film, for example, a layer containing fine particles that can be removed by thermal decomposition or treatment with organic solvent, water, acid, alkali, etc. in a matrix made of resin can be mentioned.

[0041] The thickness of the porous membrane is not particularly limited. The thickness of the porous membrane is appropriately determined depending on the type of liquid to be purified by membrane distillation. Typically, the thickness of the porous membrane is preferably 20 μm or more, more preferably 20 μm or more and 200 μm or less, and even more preferably 30 μm or more and 150 μm or less.

[0042] The thickness of a porous film, or, if the porous film is a laminated film, the thickness of each porous film included in the laminated film, can be determined, for example, by measuring the thickness at multiple locations using a micrometer or the like and averaging the results, or by observing the cross section of the film using a scanning electron microscope (SEM) and averaging the results.

[0043] The material for forming the untreated porous membrane may be organic or inorganic. Polymeric materials are typically preferred due to their excellent processability and flexibility. Examples of polymeric materials include polyimide, polyethersulfone, polyamideimide, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), and nylon. Suitable examples of materials for forming untreated porous membranes include solutions of various resins, thermosetting resin compositions, and photosensitive resin compositions.Photosensitive resin compositions include positive-type photosensitive resin compositions in which the exposed part is soluble in the developer, and negative-type photosensitive resin compositions in which the exposed part is insoluble in the developer, and both can be used to form untreated porous membranes.As materials for forming untreated porous membranes, thermosetting resin compositions that are cured by heating are preferred because they can form thin films with excellent strength.

[0044] <Varnish for manufacturing untreated porous membranes> Hereinafter, a varnish for producing an untreated porous membrane, which is suitably used for producing an untreated porous membrane having continuous pores, will be described. For the production of the above-mentioned untreated porous membrane, it is preferable to use a varnish for producing an untreated porous membrane (hereinafter also simply referred to as "varnish") which contains predetermined fine particles, a resin material, and a solvent, and in which the resin material is dissolved in the solvent. The varnish is typically produced by a microparticle dispersion preparation step of dispersing microparticles in a solvent, a resin solution preparation step, and a kneading step of mixing the microparticle dispersion and the resin solution to adjust the concentration. The resin used in preparing the varnish is preferably at least one selected from the group consisting of polyethersulfone, polyamic acid, polyimide, polyamic acid that serves as a polyamideimide precursor, and polyamideimide.

[0045] For kneading the varnish, a rotation-revolution mixer (for example, trade name: Awatori Rentaro, manufactured by Thinky Corporation), a planetary mixer, a bead mill, or the like can be used.

[0046] [Resin material] As described above, the resin contained in the varnish is preferably at least one resin material selected from the group consisting of polyethersulfone, polyamic acid, polyimide, polyamideimide precursor, and polyamideimide. These resins are described below.

[0047] (Polyethersulfone) The polyethersulfone is not particularly limited as long as it is soluble in the solvent used to form the varnish. The polyethersulfone can be appropriately selected depending on the application of the porous membrane to be produced. It may be an aliphatic polyethersulfone or an aromatic polyethersulfone. The mass-average molecular weight of the polyethersulfone is not particularly limited as long as the desired effect is not impaired. The mass-average molecular weight is, for example, 5,000 to 1,000,000, and preferably 10,000 to 300,000.

[0048] (Polyamic acid) The polyamic acid may be any product obtained by polymerizing any tetracarboxylic dianhydride and diamine, and is not particularly limited. The amounts of tetracarboxylic dianhydride and diamine used are not particularly limited, but the amount of diamine used is preferably 0.50 mol to 1.50 mol, more preferably 0.60 mol to 1.30 mol, and particularly preferably 0.70 mol to 1.20 mol, per mol of tetracarboxylic dianhydride.

[0049] The tetracarboxylic dianhydride can be appropriately selected from tetracarboxylic dianhydrides that have conventionally been used as raw materials for synthesizing polyamic acids. The tetracarboxylic dianhydride may be an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride, but from the viewpoint of the heat resistance of the resulting polyimide resin, it is preferable to use an aromatic tetracarboxylic dianhydride. The tetracarboxylic dianhydride may be used alone or in combination of two or more.

[0050] 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 of two or more.

[0051] 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. These diamines may be used alone or in combination of two or more.

[0052] Examples of aromatic diamines include diamino compounds having one or about 2 to 10 phenyl groups bonded to one another, such as phenylenediamine and its derivatives, diaminobiphenyl compounds and their derivatives, diaminodiphenyl compounds and their derivatives, diaminotriphenyl compounds and their derivatives, diaminonaphthalene and its derivatives, aminophenylaminoindan and its derivatives, diaminotetraphenyl compounds and their derivatives, diaminohexaphenyl compounds and their derivatives, and cardo-type fluorenediamine derivatives.

[0053] Phenylenediamines include m-phenylenediamine and p-phenylenediamine, and phenylenediamine derivatives include diamines to which alkyl groups such as methyl groups and ethyl groups are bonded, such as 2,4-diaminotoluene and 2,4-triphenylenediamine.

[0054] Diaminobiphenyl compounds have two aminophenyl groups bonded together, such as 4,4'-diaminobiphenyl and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl.

[0055] Diaminodiphenyl compounds are compounds in which two aminophenyl groups are bonded to each other via another group. The 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 is approximately 1 to 6. The alkylene group derivative group is an alkylene group substituted with one or more halogen atoms, etc.

[0056] 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'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 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 ... bis(p-aminophenyl)-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.

[0057] Among these, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, and 4,4'-diaminodiphenyl ether are preferred in terms of price, availability, and the like.

[0058] A diaminotriphenyl compound is a compound in which two aminophenyl groups and one phenylene group are bonded via other groups. The other groups are selected from the same groups as in the diaminodiphenyl compounds. Examples of diaminotriphenyl compounds include 1,3-bis(m-aminophenoxy)benzene, 1,3-bis(p-aminophenoxy)benzene, and 1,4-bis(p-aminophenoxy)benzene.

[0059] Examples of diaminonaphthalenes include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene.

[0060] Examples of aminophenylaminoindan include 5 or 6-amino-1-(p-aminophenyl)-1,3,3-trimethylindan.

[0061] 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.

[0062] Examples of cardo-type fluorenediamine derivatives include 9,9-bisanilinefluorene.

[0063] The number of carbon atoms in the aliphatic diamine is preferably, for example, from about 2 to about 15. Specific examples of the aliphatic diamine include pentamethylenediamine, hexamethylenediamine, and heptamethylenediamine.

[0064] 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.

[0065] There are no particular limitations on the means for producing the polyamic acid, and any known method can be used, such as a method of reacting an acid and a diamine component in a solvent.

[0066] The reaction between tetracarboxylic dianhydride and diamine is usually carried out in a solvent. The solvent used for 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. One solvent may be used alone, or two or more solvents may be used in combination.

[0067] Examples of 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 phenol-based solvents such as cresols and xylene-based mixed solvents. These solvents may be used alone or in combination of two or more. There is no particular limitation on the amount of solvent used, but it is desirable that the content of the produced polyamic acid be 5 to 50 mass %.

[0068] Among these 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 in terms of the solubility of the polyamic acid produced.

[0069] The polymerization temperature is generally from −10° C. to 120° C., preferably from 5° C. to 30° C. The polymerization time varies depending on the composition of the raw materials used, but is usually from 3 hours to 24 hours (hours). The polyamic acid may be used alone or in combination of two or more kinds.

[0070] (Polyimide) The polyimide is not limited in structure or molecular weight, and known polyimides can be used. The polyimide may have a condensable functional group such as a carboxyl group or a functional group that promotes a crosslinking reaction during baking in its side chain. Furthermore, when the varnish contains a solvent, a soluble polyimide that can be dissolved in the solvent used is preferred.

[0071] To make the polyimide soluble in a solvent, it is effective to use a monomer for introducing a flexible, bent structure into the main chain, for example, an aliphatic diamine such as ethylenediamine, hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, or 4,4'-diaminodicyclohexylmethane; an aromatic diamine such as 2-methyl-1,4-phenylenediamine, o-tolidine, m-tolidine, 3,3'-dimethoxybenzidine, or 4,4'-diaminobenzanilide; a polyoxyalkylene diamine such as polyoxyethylenediamine, polyoxypropylenediamine, or polyoxybutylenediamine; a polysiloxane diamine; 2,3,3',4'-oxydiphthalic anhydride, 3,4,3',4'-oxydiphthalic anhydride, or 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 a solvent, for example, a fluorinated diamine such as 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl or 2-trifluoromethyl-1,4-phenylenediamine. Furthermore, in addition to the monomer for improving the solubility of the polyimide, the same monomer as the monomer described in the polyamic acid section above can also be used in combination, as long as the solubility is not impaired. The polyimide and the monomer thereof may be used singly or in combination of two or more kinds.

[0072] There are no particular limitations on the means for producing polyimides. For example, known methods such as chemical imidization or thermal imidization of polyamic acid can be used. Examples of such polyimides include aliphatic polyimides (fully aliphatic polyimides) and aromatic polyimides, with aromatic polyimides being preferred. Examples of aromatic polyimides include polyimides obtained by thermally or chemically ring-closing polyamic acids having repeating units represented by formula (1), or polyimides having repeating units represented by formula (2). In the formula, Ar represents an aryl group. When the varnish contains a solvent, these polyimides may then be dissolved in the solvent used. [ka] [ka]

[0073] (Polyamideimide and polyamideimide precursors) The polyamideimide is not limited in structure or molecular weight, and known polyamideimides can be used. The polyamideimide may have a condensable functional group such as a carboxyl group or a functional group that promotes a crosslinking reaction during baking in its side chain. Furthermore, when the varnish contains a solvent, a soluble polyamideimide that can be dissolved in the solvent used is preferred.

[0074] Polyamideimides that can be used are generally, without particular limitation, (i) resins obtained by reacting an acid having a carboxyl group and an acid anhydride group in one molecule, such as trimellitic anhydride, with a diisocyanate, or (ii) resins obtained by imidizing a precursor polymer (polyamideimide precursor) obtained by reacting a reactive derivative of the above acid, such as trimellitic anhydride chloride, with a diamine.

[0075] Examples of the above acid or its reactive derivative include trimellitic anhydride, trimellitic anhydride halides such as trimellitic anhydride chloride, and trimellitic anhydride esters.

[0076] Examples of the optional diamine include the diamines exemplified in the description of polyamic acid above. Diaminopyridine compounds can also be used.

[0077] The optional diisocyanate is not particularly limited, and examples thereof include diisocyanate compounds corresponding to the optional diamines. Specific examples thereof include 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'- ... Examples of suitable isocyanates include 2,4-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.

[0078] In addition to the above, compounds described as general formulas in JP-A-63-283705 and JP-A-2-198619 can also be used as raw material monomers for polyamideimides. Furthermore, the imidization in the above method (ii) can be either thermal imidization or chemical imidization. Chemical imidization can be achieved by immersing an unbaked composite film formed using a varnish containing a polyamideimide precursor or the like in acetic anhydride or a mixed solvent of acetic anhydride and isoquinoline. The polyamideimide precursor can also be referred to as a polyimide precursor from the perspective of a precursor before imidization.

[0079] The polyamideimide contained in the varnish may be (1) a polymer obtained by reacting an acid such as trimellitic anhydride with a diisocyanate, or (2) a polymer obtained by imidizing a precursor polymer obtained by reacting a reactive derivative of the above acid such as trimellitic anhydride chloride with a diamine. In this specification and claims, "polyamideimide precursor" means a polymer (precursor polymer) before imidization. The polyamideimide and polyamideimide precursor may each be used alone or in combination of two or more thereof.Furthermore, with respect to the polyamideimide, the polymer, raw material monomer, and oligomer may each be used alone or in combination of two or more thereof.

[0080] [Fine particles] The material of the particles is not particularly limited, and any known material can be used as long as it is insoluble in the solvent contained in the varnish and can be subsequently removed from the resin-particle composite film. For example, inorganic materials include metal oxides such as silica (silicon dioxide), titanium oxide, and alumina (Al2O3), and organic materials include organic polymer particles such as high-molecular-weight olefins (polypropylene, polyethylene, etc.), polystyrene, epoxy resins, cellulose, polyvinyl alcohol, polyvinyl butyral, polyester, and polyether.

[0081] Specific examples of fine particles include colloidal silica. Among them, monodispersed spherical silica particles are preferred because they can form uniform pores.

[0082] Furthermore, it is preferable that the microparticles have a high sphericity and a small particle size distribution index. Microparticles that meet these conditions have excellent dispersibility in the varnish and can be used without agglomerating together. The average particle size of the microparticles used is, for example, preferably 15 nm to 1800 nm, more preferably 20 nm to 1500 nm, and even more preferably 30 nm to 1200 nm. By satisfying these conditions, the pore size of the untreated porous membrane obtained by removing the microparticles can be made uniform. The average particle size of the microparticles is D50. D50 refers to the particle size at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction / scattering. The fine particles may be used alone or in combination of two or more kinds.

[0083] 〔solvent〕 The solvent is not particularly limited as long as it can dissolve the resin and does not dissolve the fine particles. Examples of the solvent include the 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. In the case of polyethersulfone, examples of the solvent include the nitrogen-containing polar solvents described above, as well as polar solvents such as diphenylsulfone, dimethylsulfone, dimethylsulfoxide, benzophenone, tetrahydrothiophene-1,1-dioxide, and 1,3-dimethyl-2-imidazolidinone.

[0084] [Dispersant] A dispersant may be added 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 in the varnish, and furthermore, allows the fine particles to be uniformly distributed in the film formed from the varnish. As a result, dense openings can be formed on the surface of the finally obtained untreated porous film, and the front and back surfaces can be efficiently connected, thereby improving the air permeability of the untreated porous film. Furthermore, adding a dispersant tends to improve the drying properties of the varnish and also tends to improve the peelability of the formed unfired composite film from the substrate, etc.

[0085] The dispersant is not particularly limited, and known dispersants can be used. For example, anionic surfactants such as coconut fatty acid salts, castor sulfated oil salts, lauryl sulfate salts, polyoxyalkylene allyl phenyl ether sulfate salts, alkyl benzene sulfonic acid, alkyl benzene sulfonate salts, alkyl diphenyl ether disulfonate salts, alkyl naphthalene sulfonate salts, 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; Nonionic surfactants of polyoxyalkylene primary alkyl ethers or polyoxyalkylene secondary alkyl ethers, such as ethylene 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, but are not limited to these.The above dispersants can also be used in combination of two or more.

[0086] In the varnish, the content of the dispersant is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less, relative to the mass of the microparticles, for example, from the viewpoint of film-forming properties.

[0087] <Suitable method for producing untreated porous membrane> A preferred example of a method for producing an untreated porous membrane using the above-mentioned varnish will be described below, but the method for producing an untreated porous membrane is not limited to the method described below.

[0088] [Unfired composite film formation process] In the green composite film forming step, for example, the green composite film can be formed by applying the above-mentioned varnish onto a substrate and drying it under normal pressure or in vacuum at a temperature of 0° C. to 100° C., preferably at normal pressure and 10° C. to 100° C. Examples of the substrate include a PET film, a SUS substrate, and a glass substrate.

[0089] Furthermore, when peeling the unfired composite film from the substrate, a substrate pre-formed with a release layer can be used to further enhance the film's releasability. When a release layer is pre-formed on the substrate, a release agent is applied to the substrate and dried or baked before applying the varnish. The release agent used here can be any known release agent, such as an alkyl ammonium phosphate salt, a fluorine-based agent, or a silicone-based agent, without any particular restrictions. When peeling the dried unfired composite film from the substrate, a small amount of release agent remains on the peeled surface of the unfired composite film, which can cause discoloration during firing and adversely affect the electrical properties, so it is preferable to remove it as much as possible. To remove the release agent, a cleaning step can be introduced in which the unfired composite film peeled from the substrate is washed with an organic solvent.

[0090] On the other hand, when the substrate is used as is without providing a release layer for forming the green composite film, the above-mentioned release layer forming step and the above-mentioned cleaning step can be omitted. Furthermore, in the production of the green composite film, the following optional steps may be provided before the firing step described below: a step of immersing in a solvent containing water, a pressing step, and a drying step after the immersion step.

[0091] [Firing process] The unsintered composite film is subjected to post-treatment (sintering) by heating to form a composite film (resin-particle composite film) consisting of resin and fine particles. The baking temperature in the baking step varies depending on the structure of the unsintered composite film and the presence or absence of a condensing agent, but is preferably 120°C to 450°C, more preferably 150°C to 400°C. Furthermore, when an organic material is used for the fine particles, the temperature must be set lower than their thermal decomposition temperature. It is preferable to complete the imidization in the baking step.

[0092] The firing conditions may include, for example, a method in which the temperature is raised from room temperature to 400°C over 3 hours and then held at 400°C for 20 minutes, or a stepwise drying-thermal imidization method in which the temperature is raised from room temperature to 400°C in 50°C increments (each step held for 20 minutes), and finally held at 400°C for 20 minutes.When an unfired composite film is formed on a substrate and then temporarily peeled off from the substrate, a method can be used in which the edges of the unfired composite film are fixed to a stainless steel mold or the like to prevent deformation.

[0093] [Particle removal process] By selecting an appropriate method to remove the particles from the resin-particle composite film formed as described above, an untreated porous film having a desired structure can be produced with good reproducibility. When silica is used as the material of the fine particles, for example, the silica can be dissolved and removed by treating the resin-fine particle composite film with low-concentration hydrogen fluoride water or the like. When the fine particles are organic fine particles, the fine particles can also be removed from the polyimide resin-fine particle composite film by thermally decomposing the organic fine particles. Furthermore, when the fine particles are organic fine particles, a treatment liquid that dissolves the fine particles but does not dissolve the resin is selected, and the organic fine particles can be removed by treatment with the treatment liquid. Typically, an organic solvent is used as the treatment liquid. When the organic fine particles are soluble in an acid or an alkali, an acidic aqueous solution or an alkaline aqueous solution can also be used as the treatment liquid.

[0094] [Resin removal process] The method for producing an untreated porous membrane may include a resin removal step of removing at least a portion of the resin portion of the resin-particle composite membrane before the particle removal step, or a resin removal step of removing at least a portion of the untreated porous membrane after the particle removal step. By removing at least a portion of the resin portion of the resin-particle composite membrane before the particle removal step, or by removing at least a portion of the untreated porous membrane after the particle removal step, it is possible to improve the porosity of the untreated porous membrane compared to when removal is not performed.

[0095] The step of removing at least a portion of the resin portion or the step of removing at least a portion of the untreated porous membrane can be carried out by a conventional chemical etching method or physical removal method, or a combination of these methods.

[0096] 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 containing alkali hydroxides, hydrazine, and 1,3-dimethyl-2-imidazolidinone as main components. 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.

[0097] The solvent for each of the above solutions can be selected appropriately from pure water or alcohols. Solvents containing an appropriate amount of surfactant can also be used. The alkali concentration is, for example, 0.01% by mass or more and 20% by mass or less.

[0098] Physical methods that can be used include, for example, dry etching using plasma (oxygen, argon, etc.) or corona discharge, and a surface treatment method in which an abrasive (e.g., alumina (hardness 9)) is dispersed in a liquid and irradiated onto the surface of the film at a speed of 30 m / s to 100 m / s.

[0099] The above-mentioned method is preferable because it can be applied to the resin removal step either before or after the fine particle removal step.

[0100] On the other hand, as a physical method applicable only to the resin removal process performed after the fine particle removal process, a method can be adopted in which the target surface is pressed onto a mount film (e.g., a polyester film such as a PET film) wetted with a liquid, and then the untreated porous membrane is peeled off from the mount film either without drying or after drying. Due to the surface tension or electrostatic adhesion of the liquid, the untreated porous membrane is peeled off from the mount film with only the surface layer of the untreated porous membrane remaining on the mount film.

[0101] <Method for manufacturing porous membrane> a roughening treatment step of roughening the surface of an untreated porous membrane to obtain a roughened porous membrane; The porous membrane can be produced by a method for producing a porous membrane, which includes a liquid-repellent treatment step of making the surface of the roughened porous membrane liquid-repellent by plasma treatment derived from a gas of a liquid-repellent agent. Each step will be explained below.

[0102] [Surface roughening process] In the surface-roughening treatment step, the surface of the untreated porous membrane is roughened to obtain a roughened porous membrane. It is believed that roughening the surface of the untreated porous membrane can increase the contact angle of the coarse liquid. The untreated porous membrane is as described above in the section "Porous membrane."

[0103] The method for roughening the surface of the untreated porous membrane is not particularly limited, as long as it can make the arithmetic mean roughness Ra of the main surface 10 nm or more and the surface tension 15 mN / m or less in the porous membrane produced through the surface roughening treatment step and the liquid repellency treatment step.The method for roughening the surface of the untreated porous membrane can be, for example, a method for roughening by blasting or sputtering, but it is preferable to roughen the surface of the untreated porous membrane by plasma treatment. It is difficult to obtain a porous film having an arithmetic mean roughness Ra of the main surface of 10 nm or more and a surface tension of 15 mN / m or less by the surface roughening treatment step alone.

[0104] As a method for roughening the surface of an untreated porous membrane by plasma treatment, for example, a plasma treatment derived from an oxygen-containing gas can be mentioned. The treatment conditions for the plasma treatment derived from an oxygen-containing gas are, for example, as follows. Pressure: 2~40Pa Flow rate: 100~300sccm Temperature: 20℃ Time: 10~20sec

[0105] [Liquid repellent treatment process] In the liquid-repellent treatment step, the surface of the roughened porous membrane is made liquid-repellent by plasma treatment using a gaseous liquid-repellent agent, forming a liquid-repellent layer on the surface of the main surface of the porous membrane. It is difficult to obtain a porous film having an arithmetic mean roughness Ra of the main surface of 10 nm or more and a surface tension of 15 mN / m or less by the liquid repellency treatment process alone.

[0106] The plasma treatment can be easily carried out in a plasma generating device using a liquid repellent gas as the process gas. Examples of liquid repellent agents include fluorinated hydrocarbons such as CF4, C4F8, and C3F8, and silicon-containing compounds such as polydimethylsiloxane and polymethylphenylsiloxane. The treatment conditions for the plasma treatment in the liquid repellency treatment step are, for example, as follows. Pressure: 3~40Pa Flow rate: 80~100sccm Temperature: 20℃ Time: 3 minutes

[0107] The air permeability change rate calculated by the following formula based on the Gurley air permeability GP1 of the untreated porous membrane before the surface roughening treatment step and the liquid repellency treatment step, and the Gurley air permeability GP2 of the porous membrane after the surface roughening treatment step and the liquid repellency treatment step, is, for example, 50% or less. Air permeability change rate (%) = (GP1 - GP2) / GP1 x 100

[0108] Here, if the liquid-repellent treatment is a coating process of a liquid-repellent agent rather than a plasma treatment derived from the liquid-repellent agent gas, the liquid-repellent agent may enter the pores of the roughened porous membrane to be treated for liquid repellency, and at least some of the pores may become blocked in the porous membrane produced. However, since the liquid-repellent treatment step is a plasma treatment using the liquid-repellent gas, the liquid-repellent layer formed can be a thin film, for example, 1 μm or less, and therefore, the pores of the porous film produced can be prevented from being at least partially blocked. Therefore, the rate of change in air permeability calculated by the above formula can be set to a low value (50% or less).

[0109] <<Uses of porous membranes>> <Membrane distillation module> The porous membrane can be used as a membrane for membrane distillation, and is preferably used as a membrane distillation module. The membrane distillation module includes a high-temperature vessel into which the crude liquid to be purified is introduced and a receiver vessel for collecting the purified liquid. The porous membrane is installed to separate the high-temperature vessel from the receiver vessel. In this case, the liquid-repellent layer of the porous membrane of the membrane distillation module is preferably installed so as to be in contact with the crude liquid. That is, the porous membrane of the membrane distillation module is preferably installed so that the main surface of the porous membrane having the liquid-repellent layer faces the high-temperature tank and the main surface opposite to the main surface having the liquid-repellent layer faces the liquid-receiving tank. In such a membrane distillation module, the purified liquid obtained by condensing the vapor derived from the crude liquid while it is passing through the porous membrane or after it has passed through is recovered in a receiving tank.

[0110] <Membrane distillation apparatus and method for producing purified liquid> The membrane distillation apparatus includes the above-mentioned membrane distillation module, and at least one of a heater that heats the crude liquid introduced into the high-temperature tank or the crude liquid introduced into the high-temperature tank, and a cooler that lowers the internal temperature of the receiving tank. A purified liquid can be produced by performing membrane distillation of the crude liquid using a membrane distillation apparatus.

[0111] Specifically, as shown in Figure 1, the membrane distillation apparatus 1 has a membrane distillation module 10, a heater 11 that heats the crude liquid to be introduced into the high-temperature tank or the crude liquid introduced into the high-temperature tank, and a cooler 12 that lowers the internal temperature of the receiving tank. 1, heater 11 is, for example, a water bath that heats containers 13 and 14 containing crude liquid. Also, in FIG. 1, cooler 12 is a cooling chiller that lowers the internal temperature of the liquid receiving tank by using cooling water. In Figure 1, vessels 13 and 14 containing the crude liquid are connected to the membrane distillation module 10 by piping 16 or the like via a pump 15 such as a diaphragm pump. The membrane distillation module 10 and vessels 13 and 14 are also connected by piping 18 and 19 via a three-way cock 17. In the membrane distillation apparatus 1, nitrogen or air is introduced, and as shown by the arrows in Figure 1, the crude liquid contained in containers 13 and 14 and heated by heater 11 is introduced into the high-temperature tank of the membrane distillation module 10. The crude liquid introduced into the high-temperature tank of the membrane distillation module 10 is cooled by the cooler 12 while or after passing through the porous membrane as vapor, condenses, and is collected in the receiving tank, thereby obtaining a purified liquid. In FIG. 1, the liquid that is not recovered in the receiver tank is received in a container 14 via a pipe 18, heated by a heater 11, and purified again in a membrane distillation module 10. The membrane distillation apparatus may be a vacuum apparatus operating under reduced pressure, but is preferably an atmospheric pressure apparatus operating under atmospheric pressure.

[0112] It is preferable to use a heater or cooler to maintain the temperature difference between the crude liquid and the internal temperature of the liquid receiving tank at 20°C or more. This allows the vapor that has permeated the porous membrane to be efficiently condensed, improving the recovery efficiency of the purified liquid.

[0113] The membrane distillation apparatus is relatively compact. Therefore, for example, when the purified liquid is used as a semiconductor cleaning liquid, it can be installed close to an existing semiconductor manufacturing device. This shortens the transfer distance to the semiconductor device containing the cleaning target, suppresses contamination by piping, containers, etc., and allows for the use of a more pure liquid as a semiconductor cleaning liquid.

[0114] <Membrane distillation method> The porous membranes described above can be used in any membrane distillation process, such as direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD), sweeping gas membrane distillation (SGMD), vacuum membrane distillation (VMD), and permeation gap membrane distillation (PGMD).

[0115] The permeation flux of membrane distillation using the porous membrane mentioned above is 4.0 kg / m 2 ·h or more is preferable, 8.0 kg / m 2 More than 10.0 kg / m 2 More than ·h is even more preferable.

[0116] The permeation flux can be calculated by the following formula by measuring the recovery amount of the purified liquid obtained by the membrane distillation method using an electronic balance. Permeation flux (kg / m 2 h) = Liquid recovery amount (kg) / (Membrane area (m 2 ) × collection time (h) [Example]

[0117] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0118] Comparative Example 1 As the porous membrane of Comparative Example 1, a porous membrane manufactured by Merck (product name: Durapore) whose resin material is PVDF was used.

[0119] Comparative Example 2 Slurry A containing 70 parts by mass of silica fine particles, 0.35 parts by mass of a nonionic surfactant as a dispersant, and 70 parts by mass of dimethylacetamide was stirred in a 200 mL container at 400 rpm with a stirring blade for 15 minutes. The stirred slurry A was then subjected to five dispersion treatments at 200 MPa using a dispersing device (Yoshida Kikai Kogyo Co., Ltd., NVL-S008). Silica with an average particle diameter of 100 nm was used as the silica fine particles.

[0120] The dispersed slurry A was mixed with 30 parts by mass of polyamic acid to obtain slurry B. The polyamic acid was used as a dimethylacetamide solution with a solids concentration of 20% by mass. The polyamic acid used was a polymer obtained by polymerizing equimolar amounts of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (hereinafter referred to as 6FDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (hereinafter referred to as HFBAPP)). Slurry B contained dimethylacetamide and gamma-butyrolactone as organic solvents so that the solid content concentration was 29 mass %. The mass ratio of dimethylacetamide to gamma-butyrolactone in Slurry B was 90:10 (dimethylacetamide:gamma-butyrolactone).

[0121] The obtained slurry B was dispersed in a 200 mL container by stirring with a stirring blade at 400 rpm for 30 minutes to prepare a varnish for producing a porous membrane. The varnish for producing a porous membrane was applied to a PET film, which was then heated at 90°C for 300 seconds to remove the solvent, forming a coating film with a thickness of approximately 40 μm.

[0122] The formed coating film was peeled off from the PET film and imidized by heat treatment (baking) at 380°C for 15 minutes to obtain a polyimide resin-particle composite film. The obtained polyimide resin-particle composite film was immersed in a 10% HF solution for 10 minutes to remove the silica particles contained in the film. After removing the silica particles, the film was washed with water and dried to obtain an untreated porous film with spherical pores and interconnected pores, which was designated as the porous film of Comparative Example 2. The pore size of the resulting untreated porous membrane was 300 nm.

[0123] Comparative Example 3 An untreated porous membrane obtained in the same manner as in Comparative Example 2 was subjected to oxygen plasma treatment on the main surface that was to come into contact with the crude liquid, to obtain a porous membrane of Comparative Example 3. The oxygen plasma treatment was performed using TCA3822 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 20°C, RF: 500 W, time: 10 seconds, pressure: 3.0 Pa, and flow rate: 100 sccm.

[0124] Comparative Example 4 An untreated porous membrane obtained in the same manner as in Comparative Example 2 was immersed in a fluororesin-based water repellent agent "FS1610" (polymer concentration 1.0 mass%) manufactured by Fluorotechnology Co., Ltd. for 1 minute, then air-dried for 5 minutes, and then dried at 100°C for 5 minutes to obtain a porous membrane of Comparative Example 4. The membrane obtained in Comparative Example 4 had filled pores and had an air permeability change rate of 103(%).

[0125] Comparative Example 5 An untreated porous membrane obtained in the same manner as in Comparative Example 2 was subjected to C4F8 plasma treatment on the main surface that was to come into contact with the crude liquid, to obtain a porous membrane of Comparative Example 5. The C4F8 plasma treatment was performed using TCA3822 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the conditions of temperature: 20°C, RF: 500 W, time: 180 seconds, pressure: 3.8 Pa, and flow rate: 82 sccm.

[0126] Example 1 The porous membrane obtained in the same manner as in Comparative Example 2 was subjected to oxygen plasma treatment on the liquid-contacting principal surface to obtain a roughened porous membrane (surface roughening treatment step). The oxygen plasma treatment was performed using TCA3822 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 20°C, RF (power): 500 W, time: 10 seconds, pressure: 3.0 Pa, and flow rate: 100 sccm. Next, the main surface of the roughened porous membrane that comes into contact with the liquid (the main surface that has been roughened) was subjected to C4F8 plasma treatment to obtain the porous membrane of Example 1. The C4F8 plasma treatment was performed using TCA3822 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 20°C, RF (power): 500 W, time: 180 seconds, pressure: 3.8 Pa, and flow rate: 82 sccm.

[0127] Example 2 The porous membrane obtained in the same manner as in Comparative Example 2 was subjected to oxygen plasma treatment on the liquid-contacting principal surface to obtain a surface-roughened porous membrane (surface-roughening treatment step). The oxygen plasma treatment was performed using TCA3822 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 20°C, RF (power): 500 W, time: 10 seconds, pressure: 2.0 Pa, and flow rate: 100 sccm. Next, the main surface of the roughened porous membrane that comes into contact with the liquid (the main surface that has been roughened) was subjected to C4F8 plasma treatment to obtain the porous membrane of Example 2. The C4F8 plasma treatment was performed using TCA3822 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 20°C, RF (power): 500 W, time: 180 seconds, pressure: 3.8 Pa, and flow rate: 82 sccm.

[0128] Example 3 The porous membrane obtained in the same manner as in Comparative Example 2 was subjected to oxygen plasma treatment on the liquid-contacting principal surface to obtain a roughened porous membrane (surface roughening treatment step). The oxygen plasma treatment was performed using TCA3822 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 20°C, RF (power): 500 W, time: 30 seconds, pressure: 13.5 Pa, and flow rate: 100 sccm. Next, the main surface of the roughened porous membrane that comes into contact with the liquid (the main surface that has been roughened) was subjected to C4F8 plasma treatment to obtain the porous membrane of Example 3. The C4F8 plasma treatment was performed using TCA3822 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) under the following conditions: temperature: 20°C, RF (power): 500 W, time: 180 seconds, pressure: 3.8 Pa, and flow rate: 82 sccm.

[0129] [Production of purified liquids using membrane distillation] Using a membrane distillation apparatus 1 (Fig. 1) equipped with a membrane distillation module having a high-temperature tank and a liquid receiving tank separated by the porous membranes obtained in Examples 1 to 3 and Comparative Examples 1 to 5, membrane distillation was carried out under the following conditions to obtain a purified liquid. As the crude liquid to be treated, isopropyl alcohol (IPA) or water was used. However, in Comparative Examples 1 to 3, although water could be subjected to membrane distillation, IPA membrane distillation could not be carried out because the contact angle of IPA on the porous membrane before membrane distillation was low. For Examples 1 to 3 and Comparative Examples 4 to 5, both IPA and water could be subjected to membrane distillation.

[0130] <Water treatment> Treatment time: 1 hour 〔High-temperature tank〕 · Temperature: 50°C · Circulation flow rate: 5.0 L / min 〔Liquid receiving tank (low-temperature tank)〕 · Refrigerant: Tap water · Temperature: 20°C <IPA treatment> Treatment time: 1 hour 〔High-temperature tank〕 · Temperature: 30 - 40°C · Circulation flow rate: 5.0 L / min 〔Liquid receiving tank (low-temperature tank)〕 · Refrigerant: Tap water · Temperature: 5 - 20°C

[0131] For the porous membranes of Examples 1 to 3 and Comparative Examples 1 to 5, the surface tension, arithmetic mean roughness Ra, thickness of the liquid repellent layer, contact angle of IPA, air permeability, and water permeation flux were measured. For the surface tension, arithmetic mean roughness Ra, thickness of the liquid repellent layer, and contact angle of IPA, measurements were made on the main surface on the side where the treatment (plasma treatment) was carried out. Also, for the porous membranes after membrane distillation of isopropyl alcohol under the above-mentioned conditions using the porous membranes of Examples 1 to 3 and Comparative Examples 1 to 5, the contact angle of IPA was measured on the main surface on the side where the treatment (plasma treatment) was carried out. The air permeability, arithmetic mean roughness Ra, and surface tension were measured according to the following methods. The water permeation flux was measured by the method described above. The results are shown in Table 1.

[0132] [Air permeability measurement] Using a 5 cm x 5 cm porous membrane sample, the time it took for 100 mL of air to pass through the sample was measured using a Gurley densometer (manufactured by Toyo Seiki Seisakusho) in accordance with JIS P 8117. The smaller the air permeability value, the shorter the time it took for 100 mL of air to pass through, and the faster the gas passed through the sample. The air permeability change rate calculated by the following formula from the air permeability of the porous membranes of Examples 1 to 3 (i.e., the Gurley air permeability GP2 of the porous membrane after the surface roughening treatment step and the liquid repellency treatment step) and the air permeability of the porous membrane of Comparative Example 2 (i.e., the Gurley air permeability GP1 of the untreated porous membrane before the surface roughening treatment step and the liquid repellency treatment step) is also shown in Table 1. Table 1 also shows the air permeability change rate when the air permeability of the porous membranes of Comparative Examples 4 and 5 is set to the Gurley air permeability GP2 in the formula below and the air permeability of the porous membrane of Comparative Example 2 is set to the Gurley air permeability GP1. Air permeability change rate (%) = (GP1 - GP2) / GP1 x 100

[0133] [Measurement of surface tension (surface free energy)] Using a contact angle meter ("Dropmaster 700" manufactured by Kyowa Interface Science Co., Ltd.), droplets of pure water and methylene iodide were dropped onto the surface of each porous membrane prepared in the examples and comparative examples under conditions of a temperature of 25°C and a relative humidity of 50%, and the contact angle was measured 1 second after the droplet adhered to the surface. The surface tension (surface free energy) was calculated from each contact angle obtained according to the Owens-Wendt method. The results are shown in Table 1.

[0134] [Measurement of arithmetic mean roughness Ra] The arithmetic mean roughness Ra of the porous films of the examples and comparative examples was measured using an AFM (apparatus name: Wide Range AFM AS-7B-μX, manufacturer: Takano) in accordance with JIS B 0601 (1994). The measurement range was 10 μm × 10 μm.

[0135] [Observation of IPA penetration into porous membrane after membrane distillation] Isopropyl alcohol was membrane distilled in the same manner as in the above [Production of purified liquid by membrane distillation], except that the treatment time was 1 hour and 40 minutes. After membrane distillation, isopropyl alcohol was dropped onto the main surface of the porous membrane that had been treated (plasma treated), and the presence or absence of isopropyl alcohol permeating into the porous membrane was visually observed. A case in which isopropyl alcohol had not permeated the porous membrane was evaluated as ◯, and a case in which isopropyl alcohol had permeated the porous membrane was evaluated as ×. The results are shown in Table 1.

[0136] [Table 1]

[0137] According to Table 1, the porous membranes of Examples 1 to 3, which have a liquid-repellent layer on the main surface that comes into contact with the crude liquid, and in which the arithmetic mean roughness Ra of the main surface is 10 nm or more and the surface tension of the main surface is 15 mN / m or less, can be used in membrane distillation to purify liquids with low surface tension such as isopropyl alcohol, and are excellent in durability, maintaining a contact angle of isopropyl alcohol of 60° or more even after one hour of membrane distillation. Furthermore, in Examples 1 to 3, the rate of change in air permeability before and after the surface roughening treatment step and the liquid repellency treatment step is 50% or less, and it is clear that the surface roughening treatment step and the liquid repellency treatment step are unlikely to clog the pores of the porous membrane. On the other hand, it can be seen that Comparative Examples 1 to 5, in which the arithmetic mean roughness Ra of the main surface is not 10 nm or more and the surface tension of the main surface is not 15 mN / m or less, are unable to perform membrane distillation to purify liquids with low surface tension such as isopropyl alcohol, or have poor durability. [Explanation of symbols]

[0138] 1. Membrane distillation apparatus 10. Membrane distillation module 11 Heater 12 Cooler 13, 14 container 15 Pump 16, 18, 19 Piping 17 Three-way cock

Claims

1. In a membrane distillation method, a porous membrane is used to obtain a purified liquid by allowing vapor of a crude liquid to pass through, the porous membrane has a liquid-repellent layer on the main surface that comes into contact with the crude liquid, A porous film, wherein the principal surface has an arithmetic mean roughness Ra of 10 nm or more and a surface tension of 15 mN / m or less.

2. The porous membrane according to claim 1 , wherein the liquid-repellent layer is formed by a plasma treatment using a gas containing a fluorinated hydrocarbon.

3. The porous membrane according to claim 1 , wherein the crude liquid is a liquid having a water content of 1% by mass or less.

4. The porous membrane of claim 3 , wherein the crude liquid comprises isopropyl alcohol.

5. The porous membrane according to claim 1 , wherein the liquid-repellent layer has a thickness of 1 μm or less.

6. A method for producing the porous membrane according to any one of claims 1 to 5, a roughening treatment step of roughening the surface of an untreated porous membrane to obtain a roughened porous membrane; and a liquid-repellent treatment step of making the surface of the roughened porous membrane liquid-repellent by plasma treatment derived from a gas of a liquid-repellent agent.

7. The method for producing a porous membrane according to claim 6 , wherein the surface of the untreated porous membrane is roughened by plasma treatment in the surface roughening treatment step.

8. The method for producing a porous membrane according to claim 6 , wherein the liquid repellent agent comprises a fluorinated hydrocarbon.

9. The method for producing porous membrane according to claim 6, wherein the Gurley air permeability GP1 of untreated porous membrane before described surface roughening treatment process and described liquid repellency treatment process, and the Gurley air permeability GP2 of porous membrane after described surface roughening treatment process and described liquid repellency treatment process are calculated by the following formula, and the air permeability change rate is below 50%: Air permeability change rate (%) = (GP1 - GP2) / GP1 x 100

10. A membrane distillation module comprising the porous membrane according to any one of claims 1 to 5 as a membrane for membrane distillation.

11. The system includes a high-temperature tank into which a crude liquid to be purified is introduced, and a liquid receiving tank for recovering the purified liquid, the high-temperature tank and the liquid-receiving tank are separated by the porous membrane, The purified liquid obtained by condensing the vapor derived from the crude liquid while the vapor is permeating through the porous membrane or after the vapor has permeated through the porous membrane is recovered in the liquid receiving tank. The membrane distillation module according to claim 10.

12. The membrane distillation module according to claim 11; A membrane distillation apparatus comprising at least one of a heater that heats the crude liquid introduced into the high-temperature tank or the crude liquid introduced into the high-temperature tank, and a cooler that lowers the internal temperature of the receiving tank.

13. A method for producing a purified liquid, comprising: performing membrane distillation on the crude liquid using the membrane distillation apparatus according to claim 12.

14. Contacting a crude liquid to be purified with the porous membrane according to any one of claims 1 to 5; A method for producing a purified liquid by membrane distillation, comprising condensing the vapor derived from the crude liquid during or after the vapor has permeated through the porous membrane to obtain a purified liquid.

Images