Copolymer latex for carbon dioxide separation membrane, composition for carbon dioxide separation membrane, carbon dioxide separation membrane, and method for producing carbon dioxide separation membrane

Abstract

To provide a carbon dioxide separation membrane which exhibits excellent carbon dioxide selective permeability and sufficient carbon dioxide permeability while having excellent strength and flexibility, and to provide a copolymer latex for a carbon dioxide separation membrane, a composition for a carbon dioxide separation membrane, and a method for producing a carbon dioxide separation membrane.SOLUTION: A copolymer latex for a carbon dioxide separation membrane comprises a copolymer having an aliphatic conjugated diene monomer unit, wherein the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass%. The copolymer may further comprise monomer units such as a vinyl cyanide monomer unit, the copolymer may have a glass transition temperature of -60 to 60°C, and the copolymer may have a gel content of 20 to 95 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a copolymer latex for a carbon dioxide separation membrane, a composition for a carbon dioxide separation membrane, a carbon dioxide separation membrane, and a method for producing a carbon dioxide separation membrane. [Background technology]

[0002] In recent years, methods for separating and recovering greenhouse gases have been studied with the aim of reducing greenhouse gas emissions.

[0003] As a method for separating and capturing carbon dioxide, which is one of the representative greenhouse gases, separation using a separation membrane and separation using an adsorbent have been studied. More specifically, Patent Document 1 studies the separation of carbon dioxide using a resin membrane made of a resin composition containing a polyimide resin and an ionic liquid, and Patent Document 2 studies the absorption and desorption of carbon dioxide using an absorbent containing a polymer with a specific structure as the main component and having a plurality of pores. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-84155 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-77561 Summary of the Invention [Problem to be solved by the invention]

[0005] Although various carbon dioxide separation membranes have been studied in addition to the separation membrane described in Patent Document 1, there is still a demand for carbon dioxide separation membranes with excellent carbon dioxide permselectivity. Carbon dioxide separation membranes are also required to have excellent strength and flexibility.

[0006] An object of the present invention is to provide a carbon dioxide separation membrane that has excellent carbon dioxide permselectivity and sufficient carbon dioxide permeability, as well as excellent strength and flexibility. Another object of the present invention is to provide a copolymer latex for a carbon dioxide separation membrane, a composition for a carbon dioxide separation membrane, and a method for producing a carbon dioxide separation membrane. [Means for solving the problem]

[0007] The present inventors have found that a carbon dioxide separation membrane formed from a composition containing a copolymer latex having a specific content of aliphatic conjugated diene monomer units has excellent carbon dioxide selective permeability and sufficient carbon dioxide permeability, as well as excellent membrane strength and flexibility.

[0008] That is, the present invention provides the following [1] to

[14] . [1] A copolymer containing an aliphatic conjugated diene monomer unit, the copolymer further comprises at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds; the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, a copolymer latex for a carbon dioxide separation membrane, wherein the copolymer has a total content of the vinyl cyanide-based monomer units, the aromatic vinyl-based monomer units, the unsaturated carboxylic acid alkyl ester-based monomer units, the unsaturated monomer units containing a hydroxyalkyl group, the ethylenically unsaturated carboxylic acid monomer units, the unsaturated carboxylic acid amide-based monomer units, and the polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds of 20 to 85% by mass. [2] A copolymer containing an aliphatic conjugated diene monomer unit, the copolymer further comprises at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds; the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, a copolymer latex for a carbon dioxide separation membrane, wherein the copolymer has a total content of the aliphatic conjugated diene-based monomer units, the vinyl cyanide-based monomer units, the aromatic vinyl-based monomer units, the unsaturated carboxylic acid alkyl ester-based monomer units, the unsaturated monomer units containing a hydroxyalkyl group, the ethylenically unsaturated carboxylic acid monomer units, the unsaturated carboxylic acid amide-based monomer units, and the polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds of 40% by mass or more. [3] The copolymer further contains the ethylenically unsaturated carboxylic acid monomer unit, The copolymer latex for a carbon dioxide separation membrane according to [1] or [2], wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is 0.1 to 10% by mass. [4] A copolymer containing an aliphatic conjugated diene monomer unit, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, The copolymer latex for a carbon dioxide separation membrane has a glass transition temperature of -60 to 60°C. [5] A copolymer containing an aliphatic conjugated diene monomer unit, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, The copolymer latex for a carbon dioxide separation membrane, wherein the gel content of the copolymer is 20 to 95% by mass. [6] The copolymer further comprises an ethylenically unsaturated carboxylic acid monomer unit, The copolymer latex for a carbon dioxide separation membrane according to [4] or [5], wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is 0.1 to 10% by mass. [7] A composition for a carbon dioxide separation membrane, comprising the copolymer latex for a carbon dioxide separation membrane according to any one of [1] to [6]. [8] A copolymer containing an aliphatic conjugated diene monomer unit, the copolymer further comprises at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds; the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, a carbon dioxide separation membrane, wherein the copolymer contains 20 to 85 mass% of the vinyl cyanide-based monomer units, the aromatic vinyl-based monomer units, the unsaturated carboxylic acid alkyl ester-based monomer units, the unsaturated monomer units containing a hydroxyalkyl group, the ethylenically unsaturated carboxylic acid monomer units, the unsaturated carboxylic acid amide-based monomer units, and the polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds. [9] A copolymer containing an aliphatic conjugated diene monomer unit, the copolymer further comprises at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds; the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, a carbon dioxide separation membrane, wherein the copolymer contains 40% by mass or more of the aliphatic conjugated diene-based monomer units, the vinyl cyanide-based monomer units, the aromatic vinyl-based monomer units, the unsaturated carboxylic acid alkyl ester-based monomer units, the unsaturated monomer units containing a hydroxyalkyl group, the ethylenically unsaturated carboxylic acid monomer units, the unsaturated carboxylic acid amide-based monomer units, and the polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds.

[10] The copolymer further contains the ethylenically unsaturated carboxylic acid monomer unit, The carbon dioxide separation membrane according to [8] or [9], wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is 0.1 to 10 mass %.

[11] A copolymer containing an aliphatic conjugated diene monomer unit, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, The copolymer has a glass transition temperature of -60 to 60°C.

[12] A copolymer containing an aliphatic conjugated diene monomer unit, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, A carbon dioxide separation membrane, wherein the copolymer has a gel content of 20 to 95% by mass.

[13] The copolymer further comprises an ethylenically unsaturated carboxylic acid monomer unit, The carbon dioxide separation membrane according to

[11] or

[12] , wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is 0.1 to 10% by mass.

[14] A method for producing a carbon dioxide separation membrane, comprising a step of solidifying and / or drying the carbon dioxide separation membrane composition according to [7]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a carbon dioxide separation membrane having excellent carbon dioxide selective permeability and sufficient carbon dioxide permeability, as well as excellent strength and flexibility. Furthermore, according to the present invention, it is possible to provide a copolymer latex for a carbon dioxide separation membrane, a composition for a carbon dioxide separation membrane, and a method for producing a carbon dioxide separation membrane. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0011] [Copolymer latex for carbon dioxide separation membranes] The copolymer latex for a carbon dioxide separation membrane according to one embodiment of the present invention (hereinafter also simply referred to as "copolymer latex") contains a copolymer having an aliphatic conjugated diene monomer unit.

[0012] Examples of copolymers containing aliphatic conjugated diene monomer units include styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, and methyl methacrylate-butadiene copolymers. Due to their molecular mobility, these conjugated diene copolymers, when used to form membranes using copolymer latexes containing such copolymers or compositions for carbon dioxide separation membranes containing such copolymers, exhibit excellent flexibility and strength. Furthermore, although the exact mechanism is unclear, due to their molecular structure, membranes obtained using copolymer latexes containing such copolymers or compositions for carbon dioxide separation membranes containing such copolymers tend to have high selective permeability for carbon dioxide relative to nitrogen. This is demonstrated in the examples below. Even when other monomers copolymerizable with aliphatic conjugated diene monomers are used, the resulting membranes have excellent selective permeability for carbon dioxide and sufficient carbon dioxide permeability. On the other hand, if the content of aliphatic conjugated diene monomer units is less than 10% by mass, membrane formation becomes difficult, and even if membrane formation is possible, it is difficult to obtain a carbon dioxide separation membrane with excellent flexibility. Furthermore, if the content of aliphatic conjugated diene monomer units exceeds 80% by mass, it is difficult to obtain a carbon dioxide separation membrane that combines excellent carbon dioxide selective permeability, sufficient carbon dioxide permeability, strength, and flexibility.

[0013] Examples of aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, pentadienes (e.g., substituted linear conjugated pentadienes), and hexadienes (e.g., substituted and side-chain conjugated hexadienes). The copolymer may have one or more aliphatic conjugated diene monomer units. From the viewpoint of achieving superior strength and flexibility of the resulting carbon dioxide separation membrane, the copolymer preferably has a structural unit derived from 1,3-butadiene as the aliphatic conjugated diene monomer unit.

[0014] The content of the aliphatic conjugated diene monomer units in the copolymer is 10 to 80% by mass. When the content of the aliphatic conjugated diene monomer units is 10% by mass or more, it becomes easier to form a membrane from a composition containing the copolymer, and it becomes easier to produce a carbon dioxide separation membrane. When the content of the aliphatic conjugated diene monomer units is 80% by mass or less, it becomes easier to achieve excellent carbon dioxide selective permeability, sufficient carbon dioxide permeability, strength, and flexibility. From the viewpoint of achieving better carbon dioxide permeability in the resulting carbon dioxide separation membrane, the content of the aliphatic conjugated diene monomer units in the copolymer is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. From the viewpoint of achieving a better balance between strength and flexibility in the resulting carbon dioxide separation membrane, the content of the aliphatic conjugated diene monomer units in the copolymer is preferably 75% by mass or less, more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less. From these viewpoints, the content of the aliphatic conjugated diene monomer unit in the copolymer is preferably 20 to 75 mass %, more preferably 30 to 70 mass %, and even more preferably 40 to 65 mass %.

[0015] From the viewpoint of achieving superior strength and flexibility of the resulting carbon dioxide separation membrane, the copolymer may contain, in addition to aliphatic conjugated diene-based monomer units, vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds, etc. From the viewpoint of achieving superior strength and flexibility of the carbon dioxide separation membrane, the copolymer may contain ethylenically unsaturated carboxylic acid monomer units. The copolymer may contain one or more of these monomer units.

[0016] Examples of vinyl cyanide monomers include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-ethylacrylonitrile. The copolymer may contain one or more vinyl cyanide monomer units. The copolymer preferably contains a structural unit derived from acrylonitrile as the vinyl cyanide monomer unit.

[0017] The content of vinyl cyanide-based monomer units in the copolymer is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. The content of vinyl cyanide-based monomer units in the copolymer may be 1% by mass or more, 3% by mass or more, or 5% by mass or more. In this specification, when the copolymer has a plurality of vinyl cyanide-based monomer units, the content of the vinyl cyanide-based monomer units means the total content of the plurality of vinyl cyanide-based monomer units.

[0018] The ratio of the content of vinyl cyanide-based monomer units to the content of aliphatic conjugated diene-based monomer units in the copolymer (content of vinyl cyanide-based monomer units / content of aliphatic conjugated diene-based monomer units) may be 0.01 or more, 0.05 or more, or 0.1 or more, and may be 1.5 or less, 1 or less, or 0.5 or less.

[0019] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, methyl-α-methylstyrene, vinyltoluene, and divinylbenzene. The copolymer may contain one or more aromatic vinyl monomer units. The copolymer preferably contains a structural unit derived from styrene as the aromatic vinyl monomer unit.

[0020] The content of aromatic vinyl monomer units in the copolymer may be 80% by mass or less, 70% by mass or less, or 65% by mass or less, or may be 20% by mass or more, 25% by mass or more, or 30% by mass or more. In this specification, when the copolymer has a plurality of aromatic vinyl monomer units, the content of aromatic vinyl monomer units means the total content of the plurality of aromatic vinyl monomer units.

[0021] The ratio of the content of aromatic vinyl monomer units to the content of aliphatic conjugated diene monomer units in the copolymer (content of aromatic vinyl monomer units / content of aliphatic conjugated diene monomer units) may be 0.1 or more, 0.5 or more, or 0.7 or more, and may be 3 or less, 2.5 or less, or 2 or less.

[0022] Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate. The copolymer may contain one or more unsaturated carboxylic acid alkyl ester monomer units. The copolymer preferably contains a structural unit derived from methyl methacrylate as the unsaturated carboxylic acid alkyl ester monomer unit.

[0023] The content of unsaturated carboxylic acid alkyl ester-based monomer units in the copolymer may be 80% by mass or less, 70% by mass or less, or 60% by mass or less, or may be 1% by mass or more, 2% by mass or more, or 3% by mass or more. In this specification, when the copolymer has a plurality of unsaturated carboxylic acid alkyl ester-based monomer units, the content of the unsaturated carboxylic acid alkyl ester-based monomer units means the total content of the plurality of unsaturated carboxylic acid alkyl ester-based monomer units.

[0024] The ratio of the content of unsaturated carboxylic acid alkyl ester monomer to the content of aliphatic conjugated diene monomer units in the copolymer (content of unsaturated carboxylic acid alkyl ester monomer / aliphatic conjugated diene monomer units) may be 0.05 or more, 0.1 or more, or 0.5 or more, and may be 3 or less, 2 or less, or 1 or less.

[0025] Examples of unsaturated monomers containing a hydroxyalkyl group include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di-(ethylene glycol) maleate, di-(ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis(2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate. The copolymer may contain one or more unsaturated monomer units containing a hydroxyalkyl group. The copolymer preferably contains a structural unit derived from hydroxyethyl acrylate as the unsaturated monomer unit containing a hydroxyalkyl group.

[0026] The content of unsaturated monomer units containing a hydroxyalkyl group in the copolymer may be 10% by mass or less, 5% by mass or less, or 3% by mass or less, or may be 0.1% by mass or more, 0.5% by mass or more, or 1% by mass or more. In this specification, when the copolymer has a plurality of unsaturated monomer units containing a hydroxyalkyl group, the content of unsaturated monomer units containing a hydroxyalkyl group means the total content of the plurality of unsaturated monomer units containing a hydroxyalkyl group.

[0027] The ratio of the unsaturated monomer containing a hydroxyalkyl group to the content of the aliphatic conjugated diene monomer unit in the copolymer (content of unsaturated monomer containing a hydroxyalkyl group / content of aliphatic conjugated diene monomer unit) may be 0.005 or more, 0.01 or more, or 0.015 or more, or may be 1 or less, 0.5 or less, or 0.1 or less.

[0028] Examples of unsaturated carboxylic acid amide monomers include acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, and N,N-dimethylacrylamide. The copolymer may have one or more unsaturated carboxylic acid amide monomer units. The copolymer preferably has a structural unit derived from acrylamide as the unsaturated carboxylic acid amide monomer unit.

[0029] Examples of ethylenically unsaturated carboxylic acid monomers include monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; and dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid. The copolymer may have one or more ethylenically unsaturated carboxylic acid monomer units. The copolymer preferably has, as the ethylenically unsaturated carboxylic acid monomer unit, a structural unit derived from at least one selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, and fumaric acid.

[0030] The content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is preferably 0.1 to 10% by mass. When the content of the ethylenically unsaturated carboxylic acid monomer unit is 0.1% by mass or more, the copolymer can be stably polymerized, thereby suppressing the formation of aggregates and resulting in a carbon dioxide separation membrane with superior strength and flexibility. When the content of the ethylenically unsaturated carboxylic acid monomer unit is 10% by mass or less, the viscosity of the copolymer during synthesis can be prevented from becoming too high, allowing for sufficient stirring and stable polymerization of the copolymer. Furthermore, the resulting copolymer tends to be easily formed into a membrane. The content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. The content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is more preferably 8% by mass or less, and even more preferably 7% by mass or less. The content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is more preferably 0.5 to 8% by mass, and even more preferably 1 to 7% by mass. In this specification, when a copolymer has a plurality of ethylenically unsaturated carboxylic acid monomer units, the content of the ethylenically unsaturated carboxylic acid monomer units means the total content of the plurality of ethylenically unsaturated carboxylic acid monomer units.

[0031] The ratio of the content of ethylenically unsaturated carboxylic acid monomer units to the content of aliphatic conjugated diene monomer units in the copolymer (content of ethylenically unsaturated carboxylic acid monomer units / content of aliphatic conjugated diene monomer units) may be 0.001 or more, 0.005 or more, or 0.01 or more, or may be 1 or less, 0.5 or less, or 0.1 or less.

[0032] Examples of polyfunctional ethylenically unsaturated monomers containing two or more unsaturated double bonds include allyl methacrylate; polyethylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate; and divinyl compounds such as divinylbenzene. The copolymer may have one or more polyfunctional ethylenically unsaturated monomer units. The copolymer preferably has a structural unit derived from at least one polyfunctional ethylenically unsaturated monomer selected from the group consisting of allyl methacrylate, ethylene glycol dimethacrylate, and divinylbenzene.

[0033] In addition to the above-mentioned monomers, the copolymer may have structural units derived from any monomer commonly used in emulsion polymerization, such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, etc.

[0034] The copolymer preferably contains 20 to 85% by mass of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds. When the total content of the above monomer units is 20% by mass or more, the carbon dioxide separation membrane obtained has a better balance between strength and flexibility. When the total content of the above monomer units is 85% by mass or less, the carbon dioxide permeability of the carbon dioxide separation membrane obtained is better. That is, the copolymer latex for a carbon dioxide separation membrane according to one embodiment of the present invention contains a copolymer having an aliphatic conjugated diene-based monomer unit, and the copolymer further contains at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds, and the total content of the vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds in the copolymer is 20 to 85 mass%. Such a copolymer latex for a carbon dioxide separation membrane is referred to as "copolymer latex A for a carbon dioxide separation membrane" or "copolymer latex A," and such a copolymer is also referred to as "copolymer A." When the copolymer latex contains copolymer A, a carbon dioxide separation membrane having excellent carbon dioxide selective permeability and sufficient carbon dioxide permeability, as well as excellent strength and flexibility, can be obtained using the copolymer latex. The descriptions regarding the copolymer described above and below can be applied to copolymer A.

[0035] The total content of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds in the copolymer is more preferably 30% by mass or more, and even more preferably 40% by mass or more, from the viewpoint of achieving a better balance between strength and flexibility of the resulting carbon dioxide separation membrane. The total content of the above monomer units in the copolymer is more preferably 80% by mass or less, and even more preferably 70% by mass or less, from the viewpoint of achieving better carbon dioxide permeability of the resulting carbon dioxide separation membrane. From these viewpoints, the total content of the above monomer units in the copolymer is more preferably 30 to 80% by mass, and even more preferably 40 to 70% by mass.

[0036] Furthermore, the copolymer preferably contains 40% by mass or more of the aliphatic conjugated diene monomer units, vinyl cyanide monomer units, aromatic vinyl monomer units, unsaturated carboxylic acid alkyl ester monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds. A total content of the above monomer units of 40% by mass or more provides the obtained carbon dioxide separation membrane with an excellent balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility. That is, the copolymer latex for a carbon dioxide separation membrane according to one embodiment of the present invention contains a copolymer having an aliphatic conjugated diene-based monomer unit, and the copolymer further contains at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds, and the total content of the aliphatic conjugated diene-based monomer units, vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds in the copolymer is 40 mass% or more. Such a copolymer latex for a carbon dioxide separation membrane is referred to as "copolymer latex B for a carbon dioxide separation membrane" or "copolymer latex B," and such a copolymer is also referred to as "copolymer B." When the copolymer latex contains copolymer B, a carbon dioxide separation membrane having excellent carbon dioxide selective permeability and sufficient carbon dioxide permeability, as well as excellent strength and flexibility, can be obtained using the copolymer latex. The descriptions regarding the copolymer described above and below can be applied to copolymer B.

[0037] The total content of aliphatic conjugated diene monomer units, vinyl cyanide monomer units, aromatic vinyl monomer units, unsaturated carboxylic acid alkyl ester monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds in the copolymer is more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more, from the viewpoint of achieving a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility of the resulting carbon dioxide separation membrane. The total content of the above monomer units in the copolymer is more preferably 95% by mass or less, even more preferably 90% by mass or less, and particularly preferably 85% by mass or less, from the viewpoint of achieving a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility of the resulting carbon dioxide separation membrane. From these viewpoints, the total content of the above monomer units in the copolymer is more preferably 50 to 95% by mass, further preferably 60 to 90% by mass, and particularly preferably 70 to 85% by mass.

[0038] The total content of the vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, and unsaturated carboxylic acid alkyl ester-based monomer units in the copolymer is preferably 20 to 80% by mass. When the total content of the monomer units is 20% by mass or more, the resulting carbon dioxide separation membrane has a better balance between strength and flexibility. When the total content of the monomer units is 80% by mass or less, the resulting carbon dioxide separation membrane has better carbon dioxide permeability. From the viewpoint of a better balance between strength and flexibility of the resulting carbon dioxide separation membrane, the total content of the monomer units in the copolymer is more preferably 30% by mass or more, and even more preferably 40% by mass or more. From the viewpoint of a better carbon dioxide permeability of the resulting carbon dioxide separation membrane, the total content of the monomer units in the copolymer is more preferably 75% by mass or less, and even more preferably 70% by mass or less. From these viewpoints, the total content of the monomer units in the copolymer is more preferably 30 to 75% by mass, and even more preferably 40 to 70% by mass.

[0039] The total content of the aliphatic conjugated diene monomer units, vinyl cyanide monomer units, aromatic vinyl monomer units, and unsaturated carboxylic acid alkyl ester monomer units in the copolymer is preferably 40 to 95% by mass. When the total content of the monomer units is within the above range, the carbon dioxide separation membrane obtained has a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility. From the viewpoint of a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility, the total content of the monomer units in the copolymer is more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more. From the viewpoint of a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility, the total content of the monomer units in the copolymer is more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less. From these viewpoints, the total content of the above monomer units in the copolymer is more preferably 50 to 90% by mass or more, even more preferably 60 to 85% by mass or more, and particularly preferably 70 to 80% by mass or more.

[0040] The total content of the hydroxyalkyl group-containing unsaturated monomer units, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds in the copolymer is preferably 0.01 to 30% by mass. When the total content of the monomer units is 0.01% by mass or more, the copolymer can be stably polymerized, thereby suppressing the formation of aggregates and resulting in a carbon dioxide separation membrane with superior strength and flexibility. When the total content of the monomer units is 30% by mass or less, the viscosity during copolymer synthesis can be prevented from becoming too high, allowing for sufficient stirring, resulting in stable polymerization of the copolymer and easier membrane formation. The total content of the monomer units in the copolymer is more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, from the viewpoints of stable polymerization of the copolymer, suppressing the formation of aggregates, and resulting in a carbon dioxide separation membrane with superior strength and flexibility. The total content of the monomer units in the copolymer is more preferably 25% by mass or less, and even more preferably 20% by mass or less, from the viewpoints of preventing the viscosity of the copolymer from becoming too high during synthesis, allowing for sufficient stirring, enabling more stable polymerization of the copolymer, and facilitating film formation. From these viewpoints, the total content of the monomer units in the copolymer is more preferably 0.05 to 25% by mass or more, and even more preferably 0.1 to 20% by mass or more.

[0041] When the copolymer contains vinyl cyanide-based monomer units, the content of vinyl cyanide-based monomer units in the copolymer is preferably 10 to 50 mass%, more preferably 20 to 45 mass%, and even more preferably 30 to 40 mass%, from the viewpoint of achieving a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility of the resulting carbon dioxide separation membrane. Furthermore, when the copolymer contains vinyl cyanide-based monomer units, the total content of aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds is preferably 25 mass% or less, more preferably 5 to 20 mass%, and even more preferably 10 to 15 mass%, from the viewpoint of achieving a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility of the resulting carbon dioxide separation membrane.

[0042] When the copolymer contains aromatic vinyl monomer units, the content of aromatic vinyl monomer units in the copolymer is preferably 20 to 80% by mass, more preferably 25 to 75% by mass, and even more preferably 30 to 70% by mass, from the viewpoint of achieving a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility of the resulting carbon dioxide separation membrane. Furthermore, when the copolymer contains aromatic vinyl monomer units, the total content of vinyl cyanide monomer units, unsaturated carboxylic acid alkyl ester monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds is preferably 60% by mass or less, more preferably 10 to 50% by mass, and even more preferably 15 to 40% by mass, from the viewpoint of achieving a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility of the resulting carbon dioxide separation membrane.

[0043] When the copolymer contains an unsaturated carboxylic acid alkyl ester monomer, the content of unsaturated carboxylic acid alkyl ester monomer units in the copolymer is preferably 20 to 80 mass%, more preferably 25 to 75 mass%, and even more preferably 30 to 70 mass%, from the viewpoint of achieving a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility of the resulting carbon dioxide separation membrane. Furthermore, when the copolymer contains an unsaturated carboxylic acid alkyl ester monomer, the total content of vinyl cyanide monomer units, aromatic vinyl monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds is preferably 40 mass% or less, more preferably 5 to 30 mass%, and even more preferably 10 to 20 mass%, from the viewpoint of achieving a better balance of carbon dioxide selective permeability, carbon dioxide permeability, strength, and flexibility of the resulting carbon dioxide separation membrane.

[0044] Known emulsifiers and surfactants can be used in the polymerization of copolymers. Examples of surfactants that can be used include anionic surfactants such as sulfate salts of higher alcohols, alkylbenzenesulfonates (e.g., sodium dodecylbenzenesulfonate), alkyldiphenyletherdisulfonates (e.g., sodium alkyldiphenyletherdisulfonate), aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, formalin condensates of naphthalenesulfonic acid, and sulfate salts of nonionic surfactants; and nonionic surfactants such as alkyl esters of polyethylene glycol, alkylphenyl ethers (e.g., polyoxyethylene lauryl ether), and alkyl ethers. These emulsifiers and surfactants can be used alone or in combination of two or more.

[0045] A known chain transfer agent can be used for the polymerization of the copolymer. Examples of the chain transfer agent include alkyl mercaptan compounds such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan; xanthogen compounds such as dimethyl xanthogen disulfide and diisopropyl xanthogen disulfide; thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide; 2,6-di-t-butyl-4-methylthiuram; Examples of suitable phenolic compounds include phenolic compounds such as phenol and styrenated phenol; allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, and carbon tetrabromide; vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, and α-benzyloxyacrylamide; triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, terpinolene, and α-methylstyrene dimer. These may be used alone or in combination of two or more.

[0046] A known polymerization initiator can be used for copolymerization. Examples of the polymerization initiator include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate; and oil-soluble polymerization initiators such as cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide, acetyl peroxide, diisopropylbenzene hydroperoxide, and 1,1,3,3-tetramethylbutyl hydroperoxide. The polymerization initiator is preferably at least one selected from the group consisting of potassium persulfate, sodium persulfate, cumene hydroperoxide, and t-butyl hydroperoxide. The amount of the polymerization initiator used is not particularly limited and can be appropriately adjusted taking into account the monomer composition, the pH of the polymerization reaction system, and the combination with other additives.

[0047] Known reducing agents can be used in the polymerization of copolymers. Examples of reducing agents include reducing sugars such as dextrose and saccharose; amines such as dimethylaniline and triethanolamine; carboxylic acids and salts thereof such as L-ascorbic acid, erythorbic acid, tartaric acid, and citric acid; sulfites, bisulfites, pyrosulfites, dithionites, dithionates, thiosulfates, formaldehyde sulfonates, and benzaldehyde sulfonates. The reducing agent is preferably L-ascorbic acid or erythorbic acid. The amount of reducing agent used can be adjusted appropriately taking into account the monomer composition, the pH of the polymerization reaction system, and the combination with other additives.

[0048] Water and known organic solvents can be used for the polymerization of the copolymer. Examples of organic solvents that can be used include saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, and cycloheptane; unsaturated hydrocarbons such as pentene, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene, and 1-methylcyclohexene; and aromatic hydrocarbons such as benzene, toluene, and xylene. The organic solvent is preferably cyclohexene or toluene, because it has a suitably low boiling point, can be easily recovered and reused by steam distillation or the like after polymerization, and is environmentally friendly.

[0049] In the polymerization of the copolymer, known additives such as oxygen scavengers, chelating agents, dispersants, antifoaming agents, antioxidants, preservatives, antibacterial agents, flame retardants, ultraviolet absorbers, etc. These additives are not particularly limited in type or amount, and can be used as appropriate.

[0050] During polymerization of the copolymer, examples of a method for adding the above-mentioned monomer components and components other than the monomer components, such as additives, to the reaction system include a batch addition method, a divided addition method, a continuous addition method, and a power feed method.

[0051] The copolymer can be obtained by polymerizing the above-mentioned monomers by a known polymerization method such as emulsion polymerization, suspension polymerization, solution polymerization, or bulk polymerization.

[0052] The temperature of the polymerization reaction varies depending on the type of monomer component used, and may be, for example, 40 to 150° C. The reaction time of the polymerization reaction may be, for example, 5 to 25 hours.

[0053] The polymerization of the copolymer is preferably terminated after confirming that the polymer conversion rate at the end of the polymerization reaction of the monomer components added to the reaction system exceeds 97%. That is, the polymer conversion rate at the end of the polymerization reaction of the copolymer is preferably greater than 97%. The polymer conversion rate can be calculated from the mass of the solid content in the reaction system or the amount of heat used to cool the inside of the polymerization reactor.

[0054] A polymerization terminator may be used to terminate the polymerization reaction. After the polymerization reaction is completed, unreacted monomer components may be removed by distillation or the like.

[0055] It is preferable that unreacted monomer components and other low boiling point components are removed from the copolymer latex by a method such as heating under reduced pressure distillation or steam distillation.

[0056] From the viewpoint of dispersion stability, the pH of the copolymer latex may be adjusted by adding a pH adjuster such as ammonia, potassium hydroxide, sodium hydroxide, etc. The pH of the copolymer latex is preferably 5 to 9, more preferably 5.5 to 8.5.

[0057] The glass transition temperature of the copolymer is preferably -60 to 60°C. A glass transition temperature of -60°C or higher results in superior carbon dioxide selective permeability, superior handleability of a composition containing the copolymer, and superior strength of the resulting carbon dioxide separation membrane. A glass transition temperature of 60°C or lower results in superior membrane-forming and processability of a composition containing the copolymer, and superior flexibility of the resulting carbon dioxide separation membrane. That is, another embodiment of the present invention is a copolymer latex for a carbon dioxide separation membrane, which contains a copolymer having an aliphatic conjugated diene monomer unit, the copolymer having an aliphatic conjugated diene monomer unit content of 10 to 80% by mass, and the copolymer having a glass transition temperature of -60 to 60°C. Such a copolymer latex for a carbon dioxide separation membrane is referred to as "copolymer latex C for a carbon dioxide separation membrane" or "copolymer latex C," and such a copolymer is also referred to as "copolymer C." When the copolymer latex contains copolymer C, it is possible to obtain a carbon dioxide separation membrane having excellent carbon dioxide selective permeability, sufficient carbon dioxide permeability, and excellent strength and flexibility. Although the exact mechanism by which the copolymer latex containing copolymer C exhibits the above-mentioned effect is not clear, it is believed that when the glass transition temperature of the copolymer is within the above range, the molecular motion of the molecules constituting the carbon dioxide separation membrane becomes active, thereby improving the carbon dioxide permeability. Note that the descriptions regarding the copolymer described above and below can be applied to copolymer C, and the glass transition temperature of the copolymer can be measured by the method described in the examples described below.

[0058] The glass transition temperature of the copolymer is more preferably -55°C or higher, and even more preferably -50°C or higher, from the viewpoints of improving the carbon dioxide selective permeability, the handleability of a composition containing the copolymer, and the strength of the resulting carbon dioxide separation membrane. The glass transition temperature of the copolymer is more preferably 45°C or lower, and even more preferably 30°C or lower, from the viewpoints of improving the film-forming properties and processability of a composition containing the copolymer and the flexibility of the resulting carbon dioxide separation membrane. From these viewpoints, the glass transition temperature of the copolymer is more preferably -55 to 45°C, and even more preferably -50 to 30°C. The glass transition temperature of the copolymer can be adjusted by appropriately adjusting the type, amount used, and addition method of the monomers used during polymerization of the copolymer.

[0059] The gel content of the copolymer is preferably 20 to 95% by mass. A gel content of 95% by mass or less improves the membrane formability and processability of a composition containing the copolymer, and the flexibility of the resulting carbon dioxide separation membrane. A gel content of 20% by mass or more improves the selective carbon dioxide permeability, the handleability of a composition containing the copolymer, and the strength of the resulting carbon dioxide separation membrane. That is, another embodiment of the present invention is a copolymer latex for a carbon dioxide separation membrane, which contains a copolymer having an aliphatic conjugated diene monomer unit, the content of the aliphatic conjugated diene monomer unit in the copolymer being 10 to 80% by mass, and the gel content of the copolymer being 20 to 95% by mass. Such a copolymer latex for a carbon dioxide separation membrane is also referred to as "copolymer latex D for a carbon dioxide separation membrane" or "copolymer latex D," and such a copolymer is also referred to as "copolymer D." When the copolymer latex contains copolymer D, it is possible to obtain a carbon dioxide separation membrane having excellent selective carbon dioxide permeability and sufficient carbon dioxide permeability, as well as excellent strength and flexibility. Although the exact mechanism by which the copolymer latex containing copolymer D exhibits the above-mentioned effect is not clear, it is thought that when the gel content of the copolymer is within the above range, the molecular motion of the molecules constituting the carbon dioxide separation membrane becomes active, thereby improving the carbon dioxide permeability. The gel content of the copolymer can be measured by the method described in the Examples below.

[0060] The gel content of the copolymer is more preferably 25% by mass or more, and even more preferably 30% by mass or more, from the viewpoints of improving the carbon dioxide selective permeability, the handleability of the composition containing the copolymer, and the strength of the resulting carbon dioxide separation membrane.The gel content of the copolymer is more preferably 90% by mass or less, and even more preferably 85% by mass or less, from the viewpoints of improving the membrane-forming ability and processability of the composition containing the copolymer and the flexibility of the resulting carbon dioxide separation membrane.From these viewpoints, the gel content of the copolymer is more preferably 25 to 90% by mass, and even more preferably 30 to 85% by mass.The gel content of the copolymer can be adjusted by appropriately adjusting the types, amounts used, and addition method of the monomers and chain transfer agents used during polymerization of the copolymer.

[0061] The number average particle diameter of the copolymer latex is preferably 50 to 300 nm, more preferably 70 to 250 nm, from the viewpoint of the polymerization stability of the copolymer, etc. The number average particle diameter of the copolymer latex can be adjusted by appropriately adjusting the type, amount, and addition method of the emulsifier used during polymerization of the copolymer latex, as well as the proportion of water, etc. The number average particle diameter of the copolymer latex can be measured by the method described in the examples below.

[0062] The copolymer latex can be used, for example, as a carbon dioxide separation membrane as described below, and can be used in a method for separating carbon dioxide. That is, another embodiment of the present invention is the use of the copolymer latex as a carbon dioxide separation membrane. Another embodiment of the present invention is a method for separating carbon dioxide using the copolymer latex. That is, another embodiment of the present invention is a method for separating carbon dioxide using the copolymer latex, in which the copolymer latex is any one of the above-mentioned copolymer latexes A to D.

[0063] [Composition for carbon dioxide separation membrane] The above-described copolymer latexes A to D can be used as a composition for a carbon dioxide separation membrane. That is, another embodiment of the present invention is a composition for a carbon dioxide separation membrane containing any of the above-described copolymer latexes A to D. The composition for a carbon dioxide separation membrane contains any of the copolymers A to D. The content of any of the copolymers A to D in the composition for a carbon dioxide separation membrane may be, for example, 80 mass % or more, 85 mass % or more, 90 mass % or more, 93 mass % or more, or 95 mass % or more based on the total amount of solids in the composition for a carbon dioxide separation membrane.

[0064] The carbon dioxide separation membrane composition preferably further contains zinc oxide in addition to any one of the copolymer latexes A to D. When the carbon dioxide separation membrane composition further contains zinc oxide, it becomes easier to obtain a carbon dioxide separation membrane that has excellent carbon dioxide selective permeability, sufficient carbon dioxide permeability, and strength.

[0065] The content of zinc oxide is preferably 0.5 parts by mass or more, and may be 0.8 parts by mass or more, or 1 part by mass or more, relative to 100 parts by mass (solid content) of the copolymer latex (any of copolymer latexes A to D). The content of zinc oxide is preferably 5 parts by mass or less, and may be 4 parts by mass or less, 3 parts by mass or less, 2.5 parts by mass or less, 2 parts by mass or less, 1.8 parts by mass or less, or 1.5 parts by mass or less, relative to 100 parts by mass (solid content) of the copolymer latex.

[0066] The carbon dioxide separation membrane composition may further contain a rubber latex such as natural rubber latex, isoprene rubber latex, etc. That is, the above-mentioned copolymer latexes A to D may be mixed with other latexes depending on the intended use.

[0067] The carbon dioxide separation membrane composition may further contain a pH adjuster (potassium hydroxide, sodium hydroxide, aqueous ammonia, etc.), a vulcanizing agent (colloidal sulfur, thiuram disulfide, etc.), a vulcanization accelerator (dialkyldithiocarbamate, xanthogenate, etc.), a vulcanization accelerator aid (litharge (PbO), red lead (PbO), magnesium oxide, etc.), an antioxidant (styrenated phenol, imidazoles, paraphenylenediamine, etc.), a colorant (titanium dioxide, fast yellow, phthalocyanine blue, ultramarine, etc.), etc.

[0068] The carbon dioxide separation membrane composition can be used, for example, as a carbon dioxide separation membrane as described below, and can be used in a method for separating carbon dioxide. That is, another embodiment of the present invention is the use of the carbon dioxide separation membrane composition as a carbon dioxide separation membrane, in which the carbon dioxide separation membrane composition contains any one of the copolymer latexes A to D. Furthermore, another embodiment of the present invention is a method for separating carbon dioxide using the carbon dioxide separation membrane composition, in which the carbon dioxide separation membrane composition contains any one of the copolymer latexes A to D.

[0069] [Carbon dioxide separation membrane] A carbon dioxide separation membrane can be formed from the above-described composition for a carbon dioxide separation membrane. The carbon dioxide separation membrane can be produced from, for example, any of copolymer latexes A to D, and contains any of copolymers A to D. That is, another embodiment of the present invention is a carbon dioxide separation membrane containing any of copolymers A to D.

[0070] The carbon dioxide separation membrane may contain a component that can be contained in a composition for a carbon dioxide separation membrane (for example, zinc oxide or a latex other than the above-mentioned copolymer latex) in addition to any of the copolymers A to D. By containing zinc oxide, the carbon dioxide separation membrane can more easily achieve superior carbon dioxide selective permeability, carbon dioxide permeability, and strength.

[0071] The carbon dioxide permeability of the carbon dioxide separation membrane is set to 10 × 1011 cm 3 cm / cm 2 ·s·cmHg or more, 30×10 11 cm 3 cm / cm 2 ·s·cmHg or more, 60×10 11 cm 3 cm / cm 2 ·s·cmHg or more, 100×10 11 cm 3 cm / cm 2 ·s·cmHg or more, 150×10 11 cm 3 cm / cm 2 ·s·cmHg or more, 200×10 11 cm 3 cm / cm 2 ·s·cmHg or more, 250×10 11 cm 3 cm / cm 2 s cmHg or more, or 300 x 10 11 cm 3 cm / cm 2 The carbon dioxide permeability of the carbon dioxide separation membrane may be, for example, 500×10 11 cm 3 cm / cm 2 The carbon dioxide permeability of the carbon dioxide separation membrane can be measured by the method described in the Examples below.

[0072] The nitrogen permeability of the carbon dioxide separation membrane is, for example, 12 × 10 11 cm 3 cm / cm 2 ·s·cmHg or less, 9×10 11 cm 3 cm / cm 2 ·s·cmHg or less, 6×10 11 cm 3 cm / cm 2 ·s·cmHg or less, 3×10 11 cm 3 cm / cm 2 ·s·cmHg or less, or 1.5×10 11 cm 3 cm / cm 2The nitrogen permeability of the carbon dioxide separation membrane may be, for example, 0.1×10 11 cm 3 cm / cm 2 The nitrogen permeability of the carbon dioxide separation membrane can be measured by the method described in the Examples below.

[0073] From the viewpoint of achieving better carbon dioxide selective permeability, the carbon dioxide separation membrane may have a carbon dioxide selective permeability (carbon dioxide permeability / nitrogen permeability) of 25 or more, 30 or more, or 34 or more. The carbon dioxide selective permeability (carbon dioxide permeability / nitrogen permeability) of the carbon dioxide separation membrane may be, for example, 50 or less.

[0074] From the viewpoint of achieving better flexibility, the stress at 100% elongation of the carbon dioxide separation membrane may be 10 MPa or less, 8 MPa or less, 5 MPa or less, or 3 MPa or less. The stress at 100% elongation of the carbon dioxide separation membrane may be, for example, 1.0 MPa or more. The stress at 100% elongation of the carbon dioxide separation membrane can be measured by the method described in the Examples below.

[0075] From the viewpoint of achieving superior strength, the stress at rupture of the carbon dioxide separation membrane may be 5 MPa or more, 10 MPa or more, 15 MPa or more, 20 MPa or more, or 25 MPa or more. The stress at rupture of the carbon dioxide separation membrane may be, for example, 50 MPa or less. The stress at rupture of the carbon dioxide separation membrane can be measured by the method described in the examples below.

[0076] The thickness of the carbon dioxide separation membrane may be, for example, 1 nm or more, 10 nm or more, 100 nm or more, 1 μm or more, 5 μm or more, 50 μm or more, or 100 μm or more, or may be 1000 μm or less, 500 μm or less, or 300 μm or less.

[0077] The carbon dioxide separation membrane can be produced, for example, by a method including a step of coagulating the above-mentioned carbon dioxide separation membrane composition by a salt coagulation method. The carbon dioxide separation membrane can be produced, for example, by a method including a step of coagulating the carbon dioxide separation membrane composition containing any of the copolymer latexes A to D by a salt coagulation method. That is, another embodiment of the present invention is a method for producing a carbon dioxide separation membrane, comprising a step of coagulating the carbon dioxide separation membrane composition by a salt coagulation method, wherein the carbon dioxide separation membrane composition contains any of the copolymers A to D.

[0078] A method for coagulating a carbon dioxide separation membrane composition by the salt coagulation method will be described. First, a coagulation liquid is applied to the surface of a substrate. The coagulation liquid is prepared by dissolving a metal salt (coagulant) such as a calcium salt, such as calcium chloride, calcium nitrate, or calcium acetate; or a magnesium salt, such as magnesium chloride, in water or a hydrophilic organic solvent, such as alcohol or ketone. The concentration of the metal salt in the coagulation liquid may be 5 to 50 mass%, and preferably 10 to 30 mass%. The coagulation liquid may contain, as necessary, a surfactant, such as a nonionic surfactant or an anionic surfactant; or a filler, such as calcium carbonate, talc, or silica gel.

[0079] The coagulation liquid is applied to a substrate and then dried to form a coating film containing a coagulant on the surface of the substrate. Next, a carbon dioxide separation membrane composition is applied to the coating film containing the coagulant. At this time, the coagulant reacts with the copolymer latex to form a coating on the surface of the substrate. After removing excess copolymer latex (or the carbon dioxide separation membrane composition) that has not reacted with the coagulant, the coating formed on the surface of the substrate is washed with water, dried, and peeled off from the surface of the substrate to obtain a carbon dioxide separation membrane.

[0080] The carbon dioxide separation membrane can be produced, for example, by a method including a step of drying the above-mentioned carbon dioxide separation membrane composition. The carbon dioxide separation membrane can be produced, for example, by a method including a step of drying the carbon dioxide separation membrane composition containing any of the copolymer latexes A to D. That is, another embodiment of the present invention is a method for producing a carbon dioxide separation membrane, which includes a step of drying the carbon dioxide separation membrane composition, and the carbon dioxide separation membrane composition contains any of the copolymers A to D.

[0081] A method for drying a carbon dioxide separation membrane composition includes, for example, applying the carbon dioxide separation membrane composition to a substrate (e.g., a glass substrate) and then leaving it for 24 hours or more in an environment at or above the minimum film-forming temperature of the copolymer contained in the carbon dioxide separation membrane composition (e.g., at room temperature (20 to 25°C) if the minimum film-forming temperature of the copolymer is 20°C or lower). The minimum film-forming temperature of the copolymer can be measured in accordance with JIS K6828-20:2003. To shorten the drying time, the carbon dioxide separation membrane composition may be dried by heating at 40 to 150°C for 1 to 8 hours. After drying at room temperature, the carbon dioxide separation membrane composition may be further dried by heating. After drying, the coating formed on the substrate is peeled off to obtain a carbon dioxide separation membrane.

[0082] The membrane (carbon dioxide separation membrane) obtained by drying the composition for a carbon dioxide separation membrane can be used in a method for separating carbon dioxide. That is, another embodiment of the present invention is a method for separating carbon dioxide using a carbon dioxide separation membrane, in which the carbon dioxide separation membrane contains any one of copolymers A to D.

[0083] The membrane obtained by drying the composition for a carbon dioxide separation membrane can be used as a carbon dioxide separation membrane. That is, another embodiment of the present invention is the use of the membrane as a carbon dioxide separation membrane, wherein the membrane contains any one of the copolymers A to D. [Example]

[0084] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0085] <Preparation of Copolymer Latex 1 (Polymerization Example 1)> A pressure-resistant polymerization reactor was charged with 90 parts by weight of pure water as a solvent, 0.6 parts by weight of sodium dodecylbenzenesulfonate as a surfactant, and 0.6 parts by weight of potassium persulfate as a polymerization initiator, and the mixture was stirred. The monomer components (unit: parts by weight) and other compounds (unit: parts by weight) shown in Table 1 were then added to the polymerization reactor, and the temperature was raised to 70°C (polymerization temperature), followed by polymerization for 8 hours (polymerization time). After confirming that the polymer conversion rate of the added monomer components exceeded 97%, a polymerization terminator was added to terminate the polymerization, and the temperature inside the polymerization reactor was cooled to below 35°C. Next, 0.4 parts by weight (solid content) of aqueous sodium hydroxide solution was added as a pH adjuster, and the mixture was maintained for 30 minutes. After this, unreacted monomer components were removed by heated vacuum distillation to obtain Copolymer Latex 1 (Polymerization Example 1).

[0086] <Preparation of Copolymer Latexes 2 to 18 (Polymerization Examples 2 to 18)> A copolymer latex was obtained in the same manner as in Copolymer Latex 1 (Polymerization Example 1), except that the components (unit: parts by mass) used in the polymerization and the polymerization conditions were changed to those shown in Tables 1 and 2.

[0087] [Table 1]

[0088] [Table 2]

[0089] <Measurement of glass transition temperature> Each copolymer latex prepared was cast onto a glass plate and dried at 70°C for 4 hours to produce a film. This film was then placed in an aluminum pan and placed in a differential scanning calorimeter (DSC6200, manufactured by Seiko Instruments Inc.). The apparatus was cooled to a temperature approximately 50°C lower than the expected glass transition temperature, and then the temperature was increased at a heating rate of 10°C / min to obtain a DSC curve. A differential curve was then obtained from the obtained DSC curve. The peak-top temperature of the obtained differential curve was taken as the glass transition temperature of the copolymer contained in each copolymer latex. If the peak shape of the differential curve was broad and no part recognized as a peak top was present, the temperature at the center of the peak instead of the peak-top temperature was taken as the glass transition temperature. If the differential curve had two or more peaks, the peak-top temperature of the peak with the largest area was taken as the glass transition temperature. Alternatively, if the peak shape of the differential curve was broad, the temperature at the center of the peak with the largest area was taken as the glass transition temperature. The measurement results are shown in Tables 1 and 2.

[0090] <Measurement of gel content (toluene insoluble matter)> Using each prepared copolymer latex, a film was produced in an atmosphere of 80°C and 85% humidity. Approximately 1 g of the produced film was weighed (weight: X (g)), placed in 400 mL of toluene, and left for 48 hours to swell and dissolve. The film was then filtered through a 300-mesh wire netting, and the toluene-insoluble matter captured on the wire netting was dried and then weighed (weight: Y (g)). The gel content of the copolymer was calculated from the percentage of the weight of the toluene-insoluble matter, Y, relative to the weight of the produced film, X. The measurement results are shown in Tables 1 and 2. Gel content (mass%) = (Y / X) x 100

[0091] <Measurement of number average particle size> The number average particle size (μm) of each copolymer latex prepared was measured by dynamic light scattering using a photon correlation method. The number average particle size was measured using FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.). The measurement results are shown in Tables 1 and 2.

[0092] <Preparation of carbon dioxide separation membrane composition> (Examples 1 to 9, 20 to 21, Comparative Examples 1 to 3) The following components were added to each of the prepared copolymer latexes to obtain a composition for a carbon dioxide separation membrane (solid content: 32% by mass). <Composition for carbon dioxide separation membrane> (Solid content) Copolymer latex 100.0 parts by mass Zinc oxide 1.5 parts by mass Colloidal sulfur 0.6 parts by mass Zinc diethyldithiocarbamate 0.6 parts by mass Titanium dioxide 1.5 parts by mass Potassium hydroxide 0.7 parts by mass

[0093] (Examples 10 to 19, 22 to 25) A composition for a carbon dioxide separation membrane was obtained in the same manner as in Example 1, except that the type of copolymer latex used and the amount of zinc oxide blended per 100 parts by mass of copolymer latex were changed to the conditions shown in Table 3.

[0094] <Manufacturing carbon dioxide separation membranes (salt coagulation method)> (Examples 1 to 9, 16 to 19, Comparative Examples 1 to 3) A calcium nitrate aqueous solution with a concentration of 15% by mass was prepared as the coagulation liquid and applied to the surface of a coated paperboard (substrate) using Wirebar #12. The substrate was then dried for 1 minute in a hot air circulation dryer at 120°C. A box-shaped substrate was formed with the surface of the substrate coated with the coagulation liquid facing inward. A sufficient amount of a carbon dioxide separation membrane composition was cast onto the box-shaped substrate and allowed to stand for 30 seconds. After removing the uncoagulated composition, the substrate was allowed to stand for another 40 seconds to form a coating on the surface of the box-shaped substrate coated with the coagulation liquid. Next, a sufficient amount of hot water at 45°C was cast onto the box-shaped substrate on which the coating had been formed, and the substrate was washed with hot water for 60 seconds. The coating formed on the box-shaped substrate was dried at room temperature for 2 hours and then heat-treated at 120°C for 15 minutes. The dried coating was then peeled off from the substrate to obtain a carbon dioxide separation membrane with a thickness of approximately 100 μm.

[0095] <Production of carbon dioxide separation membrane (drying method)> (Examples 10 to 15, 20 to 25) A coating solution was obtained by adding a 2% by mass aqueous solution of carboxymethylcellulose (Cellogen EP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) to 100 parts by mass of the carbon dioxide separation membrane composition so that the solid content was 2 parts by mass. The resulting coating solution was applied to a glass plate using an applicator with a clearance of 500 μm, dried at room temperature for 24 hours, and then heat-treated at 120°C for 15 minutes. The dried coating was then peeled off from the glass plate to obtain a carbon dioxide separation membrane with a thickness of approximately 100 μm.

[0096] <Gas permeability measurement> The gas permeability of each of the produced carbon dioxide separation membranes for carbon dioxide alone and nitrogen alone was measured under the following measurement conditions. The measurement results are shown in Table 3. Measuring equipment: Gas permeability measuring device GTR-10XACT (manufactured by GTR Tech Co., Ltd.) Detector: Gas chromatograph G2700 (Yanaco Technical Science Co., Ltd.) Measurement temperature: 22℃ Measurement area: 15.2cm 2 Sample gas pressure: 76cmHg

[0097] <Calculation of carbon dioxide selective permeability> Using the above-mentioned gas permeability measurement results, the carbon dioxide selective permeability was calculated according to the following formula. The measurement results are shown in Table 3. Carbon dioxide selective permeability = (carbon dioxide gas permeability) / (nitrogen gas permeability)

[0098] <Strength and flexibility evaluation> Tensile tests were performed on each of the produced carbon dioxide separation membranes in accordance with JIS K6251 to measure the stress at 100% elongation and the stress at break. The measurement results are shown in Table 3.

[0099] [Table 3] [Industrial Applicability]

[0100] As described above, by using a copolymer latex for a carbon dioxide separation membrane, which contains a copolymer having an aliphatic conjugated diene monomer unit, and the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass%, a carbon dioxide separation membrane having excellent carbon dioxide selective permeability and sufficient carbon dioxide permeability, as well as excellent strength and flexibility, can be obtained.

[0101] The carbon dioxide separation membrane described above can be suitably used, for example, in air conditioning (ventilation) systems. Examples of places where air conditioning (ventilation) systems using carbon dioxide separation membranes are installed include buildings such as ordinary homes and office buildings; and transportation equipment such as automobiles, trains, aircraft, and ships. The carbon dioxide separation membrane according to one embodiment of the present invention has excellent strength and flexibility, and can therefore be formed into even complex shapes. Furthermore, the carbon dioxide separation membrane according to one embodiment of the present invention has excellent carbon dioxide selective permeability and sufficient carbon dioxide permeability, and can therefore be suitably used in air conditioning (ventilation) systems installed in narrow spaces (for example, transportation equipment such as automobiles).

[0102] Furthermore, because people take in oxygen from the air through breathing and exhale air containing a lot of carbon dioxide, carbon dioxide concentrations increase in enclosed spaces. In particular, the smaller the space and the higher the density of people, the more likely the carbon dioxide concentration to increase significantly. It is known that increased carbon dioxide concentrations have effects on the human body, such as increased fatigue, decreased alertness, and drowsiness. Carbon dioxide concentrations can be reduced by introducing outside air through ventilation. However, when air conditioning or heating is in operation, ventilation cannot maintain a comfortable room temperature, so a lot of energy must be consumed to return the room to a comfortable temperature, resulting in low energy efficiency. On the other hand, an air conditioning (ventilation) system using a carbon dioxide separation membrane according to one embodiment of the present invention can reduce carbon dioxide concentrations without introducing outside air into the room, thereby reducing energy consumption for air conditioning and heating and improving energy efficiency.

Claims

1. Contains a copolymer having an aliphatic conjugated diene monomer unit, the copolymer further comprises at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, a copolymer latex for a carbon dioxide separation membrane, wherein the copolymer has a total content of the vinyl cyanide-based monomer units, the aromatic vinyl-based monomer units, the unsaturated carboxylic acid alkyl ester-based monomer units, the unsaturated monomer units containing a hydroxyalkyl group, the ethylenically unsaturated carboxylic acid monomer units, the unsaturated carboxylic acid amide-based monomer units, and the polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds of 20 to 85% by mass.

2. Contains a copolymer having an aliphatic conjugated diene monomer unit, the copolymer further comprises at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, a copolymer latex for a carbon dioxide separation membrane, wherein the copolymer has a total content of the aliphatic conjugated diene-based monomer units, the vinyl cyanide-based monomer units, the aromatic vinyl-based monomer units, the unsaturated carboxylic acid alkyl ester-based monomer units, the unsaturated monomer units containing a hydroxyalkyl group, the ethylenically unsaturated carboxylic acid monomer units, the unsaturated carboxylic acid amide-based monomer units, and the polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds of 40% by mass or more.

3. the copolymer further comprises the ethylenically unsaturated carboxylic acid monomer unit, 3. The copolymer latex for a carbon dioxide separation membrane according to claim 1, wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is 0.1 to 10 mass%.

4. Contains a copolymer having an aliphatic conjugated diene monomer unit, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, The copolymer latex for a carbon dioxide separation membrane has a glass transition temperature of -60 to 60°C.

5. Contains a copolymer having an aliphatic conjugated diene monomer unit, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, The copolymer latex for a carbon dioxide separation membrane has a gel content of 20 to 95 mass %.

6. the copolymer further comprises an ethylenically unsaturated carboxylic acid monomer unit, The copolymer latex for a carbon dioxide separation membrane according to claim 4 or 5, wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is 0.1 to 10 mass%.

7. A composition for a carbon dioxide separation membrane, comprising the copolymer latex for a carbon dioxide separation membrane according to claim 1 .

8. Contains a copolymer having an aliphatic conjugated diene monomer unit, the copolymer further comprises at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, a total content of the vinyl cyanide-based monomer units, the aromatic vinyl-based monomer units, the unsaturated carboxylic acid alkyl ester-based monomer units, the unsaturated monomer units containing a hydroxyalkyl group, the ethylenically unsaturated carboxylic acid monomer units, the unsaturated carboxylic acid amide-based monomer units, and the polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds in the copolymer is 20 to 85% by mass.

9. Contains a copolymer having an aliphatic conjugated diene monomer unit, the copolymer further comprises at least one monomer unit selected from the group consisting of vinyl cyanide-based monomer units, aromatic vinyl-based monomer units, unsaturated carboxylic acid alkyl ester-based monomer units, unsaturated monomer units containing a hydroxyalkyl group, ethylenically unsaturated carboxylic acid monomer units, unsaturated carboxylic acid amide-based monomer units, and polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, a total content of the aliphatic conjugated diene-based monomer units, the vinyl cyanide-based monomer units, the aromatic vinyl-based monomer units, the unsaturated carboxylic acid alkyl ester-based monomer units, the unsaturated monomer units containing a hydroxyalkyl group, the ethylenically unsaturated carboxylic acid monomer units, the unsaturated carboxylic acid amide-based monomer units, and the polyfunctional ethylenically unsaturated monomer units containing two or more unsaturated double bonds in the copolymer is 40% by mass or more.

10. the copolymer further comprises the ethylenically unsaturated carboxylic acid monomer unit, The carbon dioxide separation membrane according to claim 8 or 9, wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is 0.1 to 10 mass%.

11. Contains a copolymer having an aliphatic conjugated diene monomer unit, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, The glass transition temperature of the copolymer is −60 to 60° C.

12. Contains a copolymer having an aliphatic conjugated diene monomer unit, the content of the aliphatic conjugated diene monomer unit in the copolymer is 10 to 80 mass %, The copolymer has a gel content of 20 to 95 mass %.

13. the copolymer further comprises an ethylenically unsaturated carboxylic acid monomer unit, The carbon dioxide separation membrane according to claim 11 or 12, wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the copolymer is 0.1 to 10 mass%.

14. A method for producing a carbon dioxide separation membrane, comprising a step of solidifying and / or drying the composition for a carbon dioxide separation membrane according to claim 7 .

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