Forward osmosis membrane manufacturing method

Abstract

To provide a method for producing a forward osmosis membrane having an excellent balance between water permeability and a salt blocking rate.MEANS FOR SOLVING THE PROBLEM: A method for producing a forward osmosis membrane that is a self-supporting film includes a step of casting a varnish obtained by dissolving a resin (A) including a structure selected from an aromatic structure, a proton acid group, an ether structure (-O-) and a ketone structure (-CO-) in an organic compound (S) onto a film having a surface with a contact angle with the organic compound (S) of 10° to 60°, and drying the varnish.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a forward osmosis membrane.

Background Art

[0002] A semipermeable membrane is useful for selectively separating a predetermined component from a liquid mixture or a gas mixture, and is suitably used, for example, in the production of high-purity water or in separating a specific solute from a solution.

[0003] Among the reverse osmosis method and the forward osmosis method, which are membrane separation methods using a semipermeable membrane, in the conventionally mainstream reverse osmosis method, the reverse osmosis membrane is exposed to high pressure. Therefore, as the reverse osmosis membrane, in order to obtain high strength, a composite semipermeable membrane formed by laminating a porous support (for example, a nonwoven fabric), a porous polymer layer (for example, a polysulfone layer), and a layer that actually functions as a semipermeable membrane (also referred to as a skin layer, a separation layer, etc.) in this order is the mainstream.

[0004] On the other hand, in the forward osmosis method, water moves from the low-salt concentration feed solution side (for example, fresh water) to the high-salt concentration draw solution side (for example, seawater) using the osmotic pressure generated between aqueous solutions with different solute concentrations separated by a forward osmosis membrane as a driving force. Therefore, it is possible to expect advantages such as not requiring high pressure application or membrane strength to overcome the osmotic pressure as in the reverse osmosis method, being excellent in energy saving, and simplifying the structure of the osmosis membrane.

[0005] However, in the forward osmosis method, it is a problem that the permeation flux is small (for example, Patent Document 1), and when a large amount of water is treated using a forward osmosis membrane for agricultural water or water purification applications, further improvement of the permeation flux from the low-salt concentration side to the high-salt concentration side is required.

[0006] On the other hand, the present inventor has disclosed a forward osmosis membrane having excellent permeation flow rate using, for example, a semipermeable membrane having a polyether ketone structure (for example, Patent Document 2). Further, in the examples of Patent Document 2, a self-supporting membrane is obtained by a casting method using a varnish containing a polymer having the above-mentioned polyether ketone structure on a release film.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] According to the studies of the present inventors, in the forward osmosis membrane with a large water permeation flux from the feed solution as disclosed in the above Patent Document 2, the amount of reverse diffusion of salt from the draw solution tended to increase. Also, it has been found that the amount of reverse diffusion of salt per unit water permeation flux is not necessarily at a low level. From such a perspective, the present inventors have been developing a forward osmosis membrane capable of achieving both high water permeability and high salt rejection rate. The performance required for such a forward osmosis membrane needs to be further enhanced in the future.

Means for Solving the Problems

[0009] In view of the above problems, as a result of the studies by the present inventors, it has been found that in the above cast film, the surface on the peeled side may have relatively many irregularities in some cases. Also, in some cases, streaks visible to the naked eye or the like can be confirmed on the surface on the peeled side. It was also considered that such a shape might be the cause of the reverse diffusion of the above salt and the like.

[0010] As a result of the studies by the present inventors from the above perspective, it has been found that by manufacturing a forward osmosis membrane by a method using a specific release film, a membrane with a smooth surface can be obtained, and the reverse diffusion of the above salt can be more suppressed, leading to the completion of the present invention.

[0011] That is, the present invention relates to the following [1] to [4]. [1] An aromatic structure, and A protonic acid structure, and A structure selected from an ether structure (-O-) and a ketone structure (-CO-), and A varnish obtained by dissolving a resin (A) containing the same in an organic compound (S) is cast on a film having a surface with a contact angle of 10° to 60° of the organic compound (S), and then dried. A method for producing a forward osmosis membrane which is a self-supporting membrane.

[0012] [2] The method for producing a forward osmosis membrane according to [1], wherein the resin (A) has a structural unit (1) represented by the following formula (1) and a structural unit (2) represented by the following formula (2).

Chemical formula

[0013] [3] The method for producing a forward osmosis membrane according to [1], wherein the resin (A) contains a protonic acid group-containing resin (A1) and a resin (A2) having a molar fraction of protonic acid group-containing structural units different from that of the resin (A1).

[0014] [4] The method for producing a forward osmosis membrane according to [3], wherein the semipermeable membrane is a laminate including a layer containing the resin (A1) and a layer containing the resin (A2).

Advantages of the Invention

[0015] According to the present invention, a forward osmosis membrane excellent in the balance between water permeability and salt rejection rate can be produced, specifically, a forward osmosis membrane having high water permeability and high salt rejection rate can be produced.

Brief Description of the Drawings

[0016] [Figure 1] FIG. 1 is a schematic diagram of an apparatus used for evaluating the separation performance of a forward osmosis membrane in an example.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, the present invention will be specifically described. [Forward osmosis membrane] A preferred embodiment of the forward osmosis membrane of the present invention includes a semipermeable membrane and a porous substrate disposed on at least one surface thereof. Here, the semipermeable membrane contains a resin (A) (hereinafter, may be simply referred to as resin (A)) including an aromatic structure, a protonic acid group-containing structure, and a structure selected from an ether group and a ketone group.

[0018] The semipermeable membrane used in the forward osmosis membrane is often obtained as a self-supporting membrane. Preferably, regardless of whether it is a self-supporting membrane or not, it includes the porous substrate disposed on at least one of its surfaces, and can achieve high water permeability and high salt rejection rate.

[0019] (Method for manufacturing a semipermeable membrane) The semipermeable membrane contains a resin (A) having a protonic acid group-containing structural unit, an aromatic structure, and a structure selected from an ether group and a ketone group. For example, a protonic acid group-containing resin having a structural formula such as the formula (1), and a protonic acid group-containing resin having both the structural formulas of the formula (1) and the formula (2) can be cited. The latter is preferred.

[0020] A preferred embodiment of the resin (A) is a structure including at least a protonic acid group-containing resin (A1) and a resin (A2) having a higher molar fraction of protonic acid group-containing structural units than the resin (A1). From the viewpoint of the balance between water permeability and salt rejection rate, the absolute value of the difference between the molar fraction of the protonic acid groups contained in the resin (A1) and the molar fraction of the protonic acid groups of the resin (A2) is preferably 0.03 to 0.6. A more preferred lower limit value is 0.06, still more preferably 0.1, and particularly preferably 0.15. On the other hand, a more preferred upper limit value is 0.5, still more preferably 0.45, and particularly preferably 0.4.

[0021] Hereinafter, the resins (A), (A1), and (A2) are also simply referred to as "resin (A)", "resin (A1)", and "resin (A2)", respectively. Details of these resins will be described later.

[0022] In the present invention, the protonic acid group means a functional group that easily releases a proton or a group in which its hydrogen atom is substituted with Na or K. Examples thereof include a sulfonic acid group (-SO3H), a carboxylic acid group (-COOH), a phosphonic acid group (-PO3H2), an alkylsulfonic acid group (-(CH2) n SO3H), an alkylcarboxylic acid group (-(CH2) nCOOH), alkylphosphonic acid group (-(CH2) n PO3H2), hydroxyphenyl group (-C6H4OH), and those in which the terminal hydrogen atoms thereof are substituted with Na or K. n is an integer of 1 to 10.

[0023] The molar fraction of the protonic acid group-containing structural unit is the following ratio: the number of protonic acid group-containing structural units / the total number of structural units constituting the resin.

[0024] The resin (A) has excellent water permeability. When using at least two resins having different molar fractions of the protonic acid group-containing structural unit, that is, the resin (A1) and the resin (A2), the water permeability is improved by the resin (A2) having a large molar fraction of the protonic acid group-containing structural unit, and the reverse diffusion of salts can be suppressed by the resin (A1) having a small molar fraction of the protonic acid group-containing structural unit.

[0025] The method for producing the semipermeable membrane of the present invention is characterized by having a step of casting a varnish in which the resin (A) is dissolved in the organic compound (S) onto a film having a surface with a contact angle of 10° to 60° of the organic compound (S) and then drying.

[0026] (Varnish of resin (A)) The resin (A) has a basically linear molecular structure and has a crosslinked structure derived from the polyfunctional compound in a small amount, so it has excellent solvent solubility. Therefore, the resin (A) can be in the form of a varnish dissolved in a solvent.

[0027] Examples of the organic compound (S) used as the so-called solvent for forming the varnish are not particularly limited, and include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and butanol; hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methyl chloride and methylene chloride; ethers such as dichloroethyl ether, 1,4-dioxane, and tetrahydrofuran; fatty acid esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; cellosolves such as 2-methoxyethanol and 2-ethoxyethanol; and aprotic polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and dimethyl carbonate. These can be used alone or in combination of two or more. Among them, lower alcohols (such as methanol, ethanol, 1-propanol, 2-propanol, and t-butyl alcohol), tetrahydrofuran, N,N-dimethylformamide, N-methyl-2-pyrrolidone, etc. are preferred due to their water solubility, and a mixed solvent of these and water is also preferred. The resin concentration in the varnish can be selected depending on the method of using the varnish, but is preferably 1% by mass or more and 80% by mass or less.

[0028] (Film) The film (so-called release film) used in the casting method of the present invention is a film whose surface exhibits a contact angle of 10° to 60° with the organic compound (S). In addition, the film of the present invention includes modes called sheets and plates. When the organic compound (S) is a mixture of a plurality of compounds, the contact angle is preferably the contact angle of the mixture, but the contact angle of the most polar compound may be within the above angle range. The contact angle of the present invention is specified by the method shown in the examples.

[0029] In addition, the organic compound (S) used for measuring the contact angle is, of course, one component of the organic compound (S) contained in the varnish cast directly on the film.

[0030] The organic materials (resins) and inorganic materials such as glass that are film raw materials are not particularly limited as long as they meet the above requirements. Also, although the contact angle varies depending on the smoothness of the film surface and the surface material (a typical example is the so-called release layer), these are not limited as long as they meet the above contact angle range.

[0031] Specific examples of the film materials as described above include glass plates, polyester films such as PET films and PBT films. Other examples include polyolefin films such as polyethylene films, polypropylene films, and poly-4-methyl-1-pentene films (trade name: TPX (registered trademark)), halogen-containing films such as polyvinyl chloride films, polyvinylidene chloride films, and polyvinylidene fluoride films, poly(meth)acrylate-based films such as polyacrylic acid esters and polymethacrylic acid esters, polyamide films such as various nylon films, olefin-based films containing polar groups such as (meth)acrylic acid and (meth)acrylic acid esters and vinyl acetate, and films containing hydroxy groups such as polyvinyl alcohol.

[0032] Among the above, considering factors such as the ease of setting drying conditions at high temperatures and cost, polyester films and polyamide films are preferred, and particularly preferred is a polyester film. Also, its surface shape is preferably as smooth as possible. Also, a film having a release layer on the surface is preferred. As the raw material for the release layer, known materials such as silicone-based release agents can be used as long as they meet the requirements of the contact angle.

[0033] The contact angle range of 10 to 60° is the numerical range observed with the above organic compound (S). The preferred lower limit of the contact angle is 12°, more preferably 13°, still more preferably 14°, and particularly preferably 15°. On the other hand, the preferred upper limit is 50°, more preferably 45°, still more preferably 42°, and particularly preferably 40°.

[0034] By using the method for manufacturing the forward osmosis membrane (semipermeable membrane) of the present invention, the reverse diffusion of the above-mentioned salt can be effectively suppressed. Also, there is a tendency to easily obtain a membrane with high surface smoothness.

[0035] Although the reason why the above effects are manifested in the forward osmosis membrane (semipermeable membrane) obtained by the above method is not clear, the present inventors speculated as follows. Generally, it is preferable that the semipermeable membrane has few irregularities and the like and little thickness unevenness, but that was mainly from the viewpoint of strength and the like. The present inventors consider that the influence of the thickness unevenness of the semipermeable membrane on the reverse diffusion of salt may be unexpectedly large. That is, the present inventors consider that if there is a portion with a slightly thinner film thickness, salt moves to that portion and accumulates, causing structural changes in the membrane and making it easier for reverse diffusion of salt to occur.

[0036] The semipermeable membrane obtained by the manufacturing method of the present invention tends to have particularly excellent surface smoothness. Therefore, it is likely to exhibit the effect of suppressing the reverse diffusion of salt inherent in the semipermeable membrane.

[0037] Hereinafter, the resin (A) containing the proton acid group structure, the aromatic structure, and the structure selected from the ether structure and the ketone structure of the present invention, and the resin (A1) and the resin (A2) which are preferable embodiments thereof will be described.

[0038] The resin (A), resin (A1), and resin (A2) of the present invention preferably contain the structure of the following formula (1), or the structures of the following formula (1) and the following formula (2).

[0039]

Chemical formula

[0040] R 1 ~R 10 each independently represents H, Cl, F, CF3, or C m H 2m+1 (where m represents an integer from 1 to 10), and Cm H 2m+1 Examples of [H] include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group.

[0041] R 1 ~R 10 At least one of them is C m H 2m+1 (where m represents an integer from 1 to 10). Specifically, if i, j, k, and l and R 1 ~R 10 are selected such that the structural unit (1) and / or the structural unit (2) has at least one group represented by C m H 2m+1 That is, when i, j, k, and l are all 1, at least one of R 1 ~R 10 is C m H 2m+1 For example, when i = 0, j = 1, k = 0, and l = 1, at least one of R 1 ~R 3 , R 5 ~R 8 and R 10 ~R m H 2m+1 is C

[0042] R 1 ~R 10 may each be present in two or more on the aromatic ring, and when two or more C m H 2m+1 are present on one aromatic ring, each C m H 2m+1 may be the same as or different from each other.

[0043] X 1 ~X 5 Each is independently H, Cl, F, CF3, or a protic acid group.

[0044] X 1 ~X 5 At least one of them is a protic acid group. Specifically, i and j and X 1 ~X 5is selected such that the structural unit (1) has at least one protonic acid group. That is, when i = 1 and j = 1, X 1 ~X 5 at least one of which is a protonic acid group, but when j = 0, X 1 ~X 3 at least one of which is a protonic acid group, and when i = 0 and j = 1, X 1 ~X 3 and X 5 at least one of which is a protonic acid group.

[0045] X 1 ~X 5 may each be present in two or more on the aromatic ring. When two or more protonic acid groups are present on one aromatic ring, each protonic acid group may be the same as or different from each other.

[0046] A 1 ~A 6 are each independently a direct bond, -CH2-, -C(CH3)2-, -C(CF3)2-, -O- or -CO-, and at least one of A 1 ~A 6 is preferably -CO-.

[0047] The lines at both ends of formulas (1) and (2) indicate the bonds with adjacent structural units.

[0048] In the present invention, the protonic acid group means a functional group that easily releases a proton or a group in which its hydrogen atom is substituted with Na or K. Examples thereof include a sulfonic acid group (-SO3H), a carboxylic acid group (-COOH), a phosphonic acid group (-PO3H2), an alkylsulfonic acid group (-(CH2) n SO3H), an alkylcarboxylic acid group (-(CH2) n COOH), an alkylphosphonic acid group (-(CH2) n PO3H2), a hydroxyphenyl group (-C6H4OH) and those in which the terminal hydrogen atoms thereof are substituted with Na or K. n is an integer of 1 to 10. As the protonic acid group, -C n' H 2n'-SO3Y (where n' is an integer from 0 to 10, preferably 0, and Y is H, Na, or K) is preferred.

[0049] Examples of the structural unit (1) include structural units represented by the following formula (1-1) or formula (1-2). In these structures, A 1 is preferably -CO-.

[0050]

Chemical formula

[0051]

Chemical formula

[0052] Examples of the structural unit (2) include structural units represented by the following formula (2-1) or formula (2-2).

[0053]

Chemical formula

[0054]

Chemical formula

[0055] In the entire resin (A), the molar fraction of the structural unit (1) with respect to the total amount of the structural unit (1) and the structural unit (2) is preferably 0.1 or more, more preferably 0.2 or more, and still more preferably 0.25 or more because a semipermeable membrane with high water permeability can be formed; also, since a semipermeable membrane with high salt rejection rate and no gelation can be formed, it is preferably 0.9 or less, more preferably 0.7 or less, and still more preferably 0.6 or less.

[0056] In the molar fraction of the structural unit (1) with respect to the total amount of the structural unit (1) and the structural unit (2), from the viewpoint of the balance between water permeability and salt rejection rate, the absolute value of the difference between the molar fraction of the resin (A1) and the molar fraction of the resin (A2) is preferably 0.03 to 0.6, more preferably 0.1 to 0.4.

[0057] Note that in the above regulation of the difference in molar fraction, the resins contained in the resin (A) are not limited to two types. When the resin (A) contains three or more resins with different molar fractions of the structural unit (1), the above regulation of the difference in the molar fraction of the structural unit (1) only needs to be satisfied by at least one set of "two resins".

[0058] The resin (A) may further contain a structural unit derived from a polyfunctional compound described later. The resin (A) may be a crosslinked product or a non-crosslinked product.

[0059] The weight average molecular weight (Mw) of the resin (A) measured by the GPC (Gel Permeation Chromatography) method under the following conditions (1) to (6) is preferably 70,000 or more, more preferably 80,000 or more, and still more preferably 90,000 or more. When the molecular weight is in the above range, the obtained semipermeable membrane has high mechanical properties and is difficult to break during film formation or use. Also, from the viewpoint of the gel generation rate, the weight average molecular weight is preferably 180,000 or less.

[0060] (1) Measurement temperature: 40 °C (2) Developing solvent: N,N-dimethylformamide (DMF) (3) Flow rate: 1.0 ml / min (4) Injection volume: 500 μl (5) Detector: UV detector (6) Molecular weight standard substance: Standard polystyrene The weight average molecular weight can be controlled by adjusting the molar ratio of the raw material monomers and the amount of the end-capping agent when producing the resin (A).

[0061] The proton acid group equivalent of the resin (A), that is, the mass of the resin (A) per mole of the proton acid group, is preferably 200 g / mol or more because a semipermeable membrane with a small electrolyte membrane permeation amount, which is insoluble in water and methanol and has suppressed swelling, can be obtained. Also, since a semipermeable membrane with high water permeability and high economy can be obtained, it is preferably 5000 g / mol or less, more preferably 1000 g / mol or less.

[0062] In particular, if both the resin (A1) and the resin (A2) have the structure of the formula (1) or the structure of the formula (1) and the structure of the formula (2), the dispersion of these resins is considered to be good. For this reason, it is considered that a dense and multi-stage pseudo (A1) / (A2) unit continuous layer is formed, so that the water permeation characteristics and the effect of suppressing the reverse diffusion of salts can be efficiently exerted.

[0063] In one embodiment, it is preferable that the concentration of the proton acid group derived from the resin (A) in the semipermeable membrane has a gradient in the thickness direction of the semipermeable membrane. The concentration gradient may be a mode in which the concentration continuously increases or a mode in which the concentration increases stepwise. As an example, for example, the semipermeable membrane is a laminated membrane having a layer (L1) containing the resin (A1) and a layer (L2) containing the resin (A2). The ratio of the thickness of the layer (L1) to the layer (L2) (thickness of L1: thickness of L2) is usually 5:95 to 80:20, preferably 20:80 to 60:40. Such a multilayer structure can provide higher water permeability and salt rejection rate.

[0064] This embodiment can be said to be a preferred embodiment from the viewpoint of more surely achieving the effects of the above-described (A1) / (A2) unit configuration.

[0065] Here, the concentration gradient of the protonic acid group derived from the resin (A) means that the concentration of the protonic acid group contained in the resin (A) changes in the thickness direction of the semipermeable membrane. When the protonic acid group is a sulfonic acid group or a group in which the terminal hydrogen atom thereof is substituted with Na or K, the concentration gradient can be confirmed by analyzing the concentration distribution of sulfur atoms in the cross-section of the semipermeable membrane by elemental mapping.

[0066] Here, when using the forward osmosis membrane, it is preferable to arrange the forward osmosis membrane so that, in the semipermeable membrane, the side with a higher protonic acid group concentration faces the feed solution side and the side with a lower protonic acid group concentration faces the draw solution side. For example, it is preferable to arrange the forward osmosis membrane so that the layer (L2) containing the resin (A2) in the semipermeable membrane faces the feed solution side and the layer (L1) containing the resin (A1) faces the draw solution side. In such an embodiment, higher water permeability and salt rejection rate can be obtained.

[0067] In one embodiment, it is preferable that the semipermeable membrane is formed from a mixture containing at least the resin (A1) and the resin (A2). As an example thereof, the semipermeable membrane has a structure separated into at least two phases corresponding to the resin (A1) and the resin (A2), respectively. With this phase separation structure, higher water permeation flux and salt rejection rate can be obtained. In the mixture, the mass ratio (A1:A2) of the resin (A1) and the resin (A2) is usually 10:90 to 90:10, preferably 30:70 to 70:30.

[0068] Such a phase separation structure can be confirmed by observation with an electron microscope (TEM or SEM). As the phase separation structure, a sea-island structure, an interpenetrating structure, etc. can be considered, but from the viewpoint of preventing the reverse diffusion of salts from the dope solution, the interpenetrating structure is more preferable. In the case of the sea-island structure, it is preferable that the resin (A1) having a small molar fraction of the protonic acid group-containing structural unit forms the sea phase, and the resin (A2) having a large molar fraction forms the island phase.

[0069] In the present invention, a semipermeable membrane using the resin (A) as a raw material can be manufactured as a self-supporting membrane, and by laminating this semipermeable membrane and a porous substrate, a forward osmosis membrane having high water permeability and high salt rejection rate can be obtained.

[0070] The semipermeable membrane consists substantially only of the resin (A), but may contain other components in a small amount (for example, 1% by mass or less, or 0.1% by mass or less) to such an extent that the effects of the present invention are not impaired.

[0071] The thickness of the semipermeable membrane is usually 3.0 μm or less, preferably 0.01 to 3.0 μm, more preferably 0.01 to 1.5 μm. A forward osmosis membrane using a semipermeable membrane having a thickness within this range has sufficient membrane strength and exhibits sufficiently high water permeability in practical use. The thickness of the semipermeable membrane can be controlled by the manufacturing conditions of the semipermeable membrane, such as the temperature and pressure during press molding, the varnish concentration and coating thickness during casting, etc.

[0072] The semipermeable membrane preferably has as little thickness unevenness as possible. That is, it is preferable that the surface of the semipermeable membrane has few irregularities. Such irregularities can be specified by the surface roughness (SA value) measured by the method as shown in the examples. In the present invention, the surface roughness is preferably 10 nm or less. More preferably 8 nm or less, still more preferably 5 nm or less. The preferable lower limit is of course zero, but a practical preferable lower limit is about 0.5 nm.

[0073] Here, the structural units (1) in these resins (A1) and (A2) may be the same or different, and the structural units (2) in the resins (A1) and (A2) may be the same or different.

[0074] (Method for manufacturing resin (A)) The resin (A) can be obtained by condensation of a monomer having an aromatic ring according to a conventionally known method (for example, the method described in International Publication No. 2003 / 33566). For example, the following formulas (1a) and (2a)

[0075]

Chemical formula

[0076]

Chemical formula

[0077]

[0078] It is preferable to use a basic catalyst such as K2CO3 for the condensation.

[0079] As the monomer represented by the above formula (1a) (where at least one of X 1 ~X 2 is a protonic acid group), for example, protonic acid group-containing aromatic dihalide compounds such as 5,5'-carbonylbis(2-fluorobenzenesulfonic acid sodium) and 5,5'-carbonylbis(2-chlorobenzenesulfonic acid sodium) can be mentioned.

[0080] As the monomer represented by the above formula (2a), for example, Aromatic dihalide compounds such as 4,4'-difluorobenzophenone, 3,3'-difluorobenzophenone, 4,4'-dichlorobenzophenone, 3,3'-dichlorobenzophenone, 4,4'-difluorobiphenyl, 4,4'-difluorodiphenylmethane, 4,4'-dichlorodiphenylmethane, 4,4'-difluorodiphenylether; and Alkyl group-containing aromatic dihalide compounds such as 3,3'-dimethyl-4,4'-difluorobenzophenone, 3,3'-diethyl-4,4'-difluorobenzophenone, 3,3',5,5'-tetramethyl-4,4'-difluorobenzophenone, 3,3'-dimethyl-4,4'-dichlorobenzophenone, 3,3',4,4'-tetramethyl-5,5'-dichlorobenzophenone are mentioned.

[0081] As the monomer represented by the above formula (2b) (or the monomer represented by the above formula (1b) provided that X 3 ~X 5 are all hydrogen atoms.), for example, Aromatic dihydroxy compounds such as 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenylether, 4,4'-dihydroxybenzophenone, 2,2-bis(4-hydroxyphenyl)propane, 1,1,1,3,3,3-hexafluoro-2,2-bis(4-hydroxyphenyl)propane, 1,4-bis(4-hydroxyphenyl)benzene, α,α'-bis(4-hydroxyphenyl)-1,4-dimethylbenzene, α,α'-bis(4-hydroxyphenyl)-1,4-diisopropylbenzene, α,α'-bis(4-hydroxyphenyl)-1,3-diisopropylbenzene, 1,4-bis(4-hydroxybenzoyl)benzene, 3,3'-difluoro-4,4'-dihydroxybiphenyl; and 3,3'-dimethyl-4,4'-dihydroxybiphenyl, 3,3',5,5'-tetramethyl-4,4'-dihydroxybiphenyl, 3,3'-dimethyl-4,4'-dihydroxydiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-dihydroxydiphenylmethane (alias: bis(3,5-dimethyl-4-hydroxyphenyl)methane), 3,3',5,5'-tetraethyl-4,4'-dihydroxydiphenylmethane, 3,3'-dimethyl-4,4'-dihydroxydiphenyl ether, 3,3',5,5'-tetramethyl-4,4'-dihydroxydiphenyl ether, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3-ethyl-4-hydroxyphenyl)propane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, α,α'-bis(3-methyl-4-hydroxyphenyl)-1,4-diisopropylbenzene, α,α'-bis(3,5-dimethyl-4-hydroxyphenyl)-1,4-diisopropylbenzene, α,α'-bis(3-methyl-4-hydroxyphenyl)-1,3-diisopropylbenzene, α,α'-bis(3,5-dimethyl-4-hydroxyphenyl)-1,3-diisopropylbenzene and other alkyl group-containing aromatic dihydroxy compounds include

[0082] Within the range where the solvent solubility of the resin (A) is not impaired, a polyfunctional compound may be copolymerized with the monomer. By copolymerizing the polyfunctional compound, the resin (A) can adopt a micro-crosslinked structure. Examples of the polyfunctional compound include those having three or more hydroxyl groups in one molecule, such as (2,4-dihydroxyphenyl)(4-hydroxyphenyl)methane, 4-[1-(4-hydroxyphenyl)-1-methylethyl]-1,3-benzenediol, 4-[(2,3,5-trimethyl-4-hydroxyphenyl)methyl]-1,3-benzenediol, 4-[(4-hydroxyphenyl)methyl]-1,2,3-benzenetriol, (4-hydroxyphenyl)(2,3,4-trihydroxyphenyl)methane, 4-[(3,5-dimethyl-4-hydroxyphenyl)methyl]-1,2,3-benzenetriol, 4-[(2,3,5-trimethyl-4-hydroxyphenyl)methyl]-1,2,3-benzenetriol, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bis[benzene-1,2-diol], 5,5'-[1,4-phenylenebis(1-methylethylidene)]bis[benzene-1,2,3-triol], α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene, phloroglucinol, pyrogallol, and the like.

[0083] From the perspective of preventing a decrease in the solvent solubility of the resin (A), a decrease in the fluidity during film formation of the resin, and a decrease in the elongation rate of the semipermeable membrane, the copolymerization amount is preferably 0 to 8 mol% / total OH equivalent (that is, out of the total amount (100 mol%) of the OH groups possessed by the monomer of the above formula (1b), the monomer of the formula (2b), and the polyfunctional monomer, 0 to 8 mol% are OH groups derived from the polyfunctional monomer.), and more preferably 0 to 5 mol% / total OH equivalent.

[0084] 《Tensile modulus of elasticity, tensile breaking strength and elongation at break》 The tensile elastic modulus of the semipermeable membrane is preferably 0.8 to 2.0 GPa, more preferably 1.2 to 1.6 GPa. The tensile breaking strength of the semipermeable membrane is preferably 40 MPa or more, and its upper limit is, for example, 100 MPa. Further, the elongation rate of the semipermeable membrane is preferably 40% or more, and its upper limit is, for example, 200%. These tensile elastic modulus, tensile breaking strength, and elongation rate are those measured under the following conditions.

[0085] A test piece with a length × width × thickness of 100 mm × 10 mm × 5 μm is prepared, and it is pulled at a speed of 50 mm / min using a tensile testing machine. The strength (the value obtained by dividing the tensile load value by the cross-sectional area of the test piece) and the elongation rate are determined when the test piece is cut (broken).

[0086] The elongation rate is calculated by the following formula. Elongation rate (%) = 100 × (L - L0) / L0 (L0: Length of the test piece before the test, L: Length of the test piece at the time of breakage) Further, the tensile elastic modulus is taken as the value obtained by dividing the load at breakage by the cross-sectional area of the test piece and the amount of strain at breakage, that is, (L - L0) / L0.

[0087] The tensile breaking strength and the elongation rate can be increased, for example, by increasing the molecular weight of the resin (A).

[0088] 《Solubility and mass loss rate》 The solubility of the semipermeable membrane in dimethyl sulfoxide (hereinafter also referred to as "DMSO") and water can be evaluated by the following mass loss rates, respectively. The mass loss rate is preferably less than 2% by mass, more preferably 1.0% by mass or less, and particularly preferably 0.5% by mass or less.

[0089] The semipermeable membrane is allowed to stand and dry at 150°C for 4 hours in a nitrogen atmosphere and then weighed. The semipermeable membrane is immersed in DMSO or water and allowed to stand at 25°C for 24 hours. The semipermeable membrane is taken out from DMSO or water, allowed to stand and dry at 150°C for 4 hours in a nitrogen atmosphere, and then weighed. Based on the mass of the semipermeable membrane before and after immersion, the mass loss rate is calculated from the following formula.

[0090] Mass reduction rate = (Mass before immersion of the semipermeable membrane - Mass after immersion of the semipermeable membrane) / Mass before immersion of the semipermeable membrane × 100 The amount of dissolution can be reduced, for example, by crosslinking the resin (A). Therefore, even if the proton acid group equivalent is small, the amount of dissolution can be within the above range.

[0091] (Method for manufacturing a semipermeable membrane)

[0092] In the present invention, the semipermeable membrane is produced by a casting method from the aforementioned varnish. That is, the varnish is applied to the film, and the semipermeable membrane can be obtained by volatilizing and removing the solvent. Furthermore, the semipermeable membrane can be peeled off from the film to form a self-supporting film.

[0093] When organic solvents or the like during casting remain in the semipermeable membrane, the mechanical strength of the semipermeable membrane may decrease and it may be easily damaged. Therefore, it is preferable to subject the semipermeable membrane produced by the casting method to sufficient drying and / or washing with water, an aqueous sulfuric acid solution, hydrochloric acid, or the like.

[0094] In addition, when the proton acid group of the resin (A) used for producing the semipermeable membrane is one in which a hydrogen atom is substituted with Na or K in a functional group that easily releases a proton, a film of the resin (A) is formed, and then this film is brought into contact with hydrochloric acid, an aqueous sulfuric acid solution, or the like to substitute Na or K of the proton acid group with a hydrogen atom.

[0095] For a semipermeable membrane in which the concentration of the above-mentioned proton acid group has a gradient in the thickness direction of the semipermeable membrane, specifically, a laminated film, for example, can be obtained by forming a layer (L1) containing the resin (A1) and then forming a layer (L2) containing the resin (A2) on the layer (L1), and can also be obtained by forming a layer (L2) containing the resin (A2) and then forming a layer (L1) containing the resin (A1) on the layer (L2).

[0096] When forming the above L2 layer, the organic compound (S) contained in the varnish used is, of course, preferably a compound in which the L1 layer is insoluble or hardly soluble.

[0097] In the above lamination process, in any process thereof (for example, the process of forming the first film, the process of forming the second film to form a laminated structure, etc.), irradiation with light such as UV, plasma treatment, etc. can be performed. In particular, it is preferable to perform the above light irradiation on the layer containing the resin (A2).

[0098] In addition, the semipermeable membrane formed from a mixture containing at least the above-described resins (A1) and (A2) can adjust the dispersion diameter of the above phase separation structure, for example, according to the stirring speed of the above mixed resin or varnish.

[0099] (Porous substrate) It is preferable from the viewpoint of handling and the like that the semipermeable membrane of the present invention be used in combination with a layer such as a porous base material or a mesh material.

[0100] The air permeability of the above porous base material is preferably 100 to 400 cm 3 / cm 2 / s. This air permeability is measured as follows based on the A method (Frazyr method) described in JIS L 1096.

[0101] A 20 cm × 20 cm test piece is attached to a testing machine, the suction fan and air holes are adjusted so that the inclined barometer has a pressure of 125 Pa, and the pressure indicated by the vertical barometer is measured. The air volume passing through the test piece is obtained from the measured pressure and the type of air hole using a conversion table attached to the testing machine.

[0102] In addition, the thickness of the above porous base material is usually 50 to 700 μm, preferably 80 to 600 μm, and more preferably 100 to 500 μm.

[0103] Since the forward osmosis membrane preferably has such a high air permeability and a thin porous substrate, when using the forward osmosis membrane, the concentration polarization occurring inside the porous substrate can be suppressed, and the fluid resistance when water permeates through the forward osmosis membrane can be reduced. As a result, it is considered that the water permeability of the forward osmosis membrane can be increased. The air permeability and thickness of the porous substrate can be controlled by conventional methods.

[0104] Preferred materials constituting the porous substrate include synthetic resins and natural fibers.

[0105] Examples of the synthetic resin include thermoplastic resins and thermosetting resins, with thermoplastic resins being preferred. Specific examples of the thermoplastic resin include olefin polymers, polyester resins, polyamide resins, polyvinyl chloride, and (meth)acrylic resins. Among these, olefin polymers and polyester resins are preferred, and olefin polymers are particularly preferred.

[0106] Specifically, the olefin polymer is a homopolymer or copolymer of an α-olefin, or a copolymer of an α-olefin and another monomer. Examples of the α-olefin include α-olefins having 2 to 8 carbon atoms such as ethylene, propylene, and 1-butene. The olefin polymer includes polyolefin resins such as polypropylene, polyethylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-4-methyl-1-pentene copolymer, propylene-1-butene copolymer, and 4-methyl-1-pentene-1-decene copolymer, and copolymers of an α-olefin and another monomer such as ethylene-vinyl alcohol copolymer.

[0107] Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Examples of the polyamide resin include nylon 6 and nylon 66.

[0108] Examples of natural fibers include plant fibers such as cotton and hemp, and animal fibers such as silk and wool. Among them, cotton and silk are preferred.

[0109] Examples of the porous substrate include cloth substrates such as woven fabrics, non-woven fabrics, and knitted fabrics, and foamed sheets. Among them, cloth substrates are preferred, woven fabrics and non-woven fabrics are more preferred, and non-woven fabrics are particularly preferred.

[0110] Examples of non-woven fabrics include long fiber non-woven fabrics such as spunbond non-woven fabrics by the spunbond method, short fiber non-woven fabrics by the meltblown method, and flash spun non-woven fabrics, spunlace non-woven fabrics, airlaid non-woven fabrics, thermal bond non-woven fabrics, needle punch non-woven fabrics, chemical bond non-woven fabrics, etc. Among them, spunbond non-woven fabrics and meltblown non-woven fabrics are preferred. Among them, spunbond non-woven fabrics are preferred, and polyethylene terephthalate or polypropylene spunbond non-woven fabrics are particularly preferred.

[0111] The non-woven fabric may be a composite fiber made of different resins for the constituent fibers, and may be a core-sheath type or side-by-side type composite fiber with different resins arranged on the outer surface side of the fiber. Examples of composite fibers include core-sheath type or side-by-side type composite fibers of polyethylene / polypropylene.

[0112] The non-woven fabric may be a laminated non-woven fabric. Examples of laminated non-woven fabrics include laminated non-woven fabrics including spunbond non-woven fabrics and meltblown non-woven fabrics, such as those in which a spunbond non-woven fabric and a meltblown non-woven fabric are laminated (SM), and those in which a spunbond non-woven fabric, a meltblown non-woven fabric, and a spunbond non-woven fabric are laminated in this order (SMS).

[0113] To obtain such a laminated nonwoven fabric, a spunbond nonwoven fabric and a meltblown nonwoven fabric are laminated and integrated. Examples of the integration method include a method of overlapping and heating and pressing the spunbond nonwoven fabric and the meltblown nonwoven fabric, a method of bonding both with an adhesive such as a hot melt adhesive or a solvent-based adhesive, and a method of depositing fibers on the spunbond nonwoven fabric by the meltblown method and thermally fusing them.

[0114] The nonwoven fabric may be a laminated nonwoven fabric in which a porous film having micropores is sandwiched between nonwoven fabrics. Examples of such a laminated nonwoven fabric include those in which a polypropylene (PP) nonwoven fabric, a porous PP film, and a PP nonwoven fabric (SFS) are laminated in this order, and those in which a PP nonwoven fabric, a porous PP film, and a rayon PP nonwoven fabric (SFR) are laminated in this order.

[0115] The basis weight of the nonwoven fabric (in the case of a laminated nonwoven fabric, the basis weight as a laminated nonwoven fabric) is preferably about 10 to 80 g / m 2 and more preferably about 20 to 40 g / m 2 .

[0116] The forward osmosis membrane of the present invention may be provided with the porous substrate on both sides of the semipermeable membrane. In this aspect, the strength of the forward osmosis membrane is further improved.

[0117] The forward osmosis membrane of the present invention may include a layer other than the porous substrate on both sides or one side of the semipermeable membrane in the order of semipermeable membrane / layer other than porous substrate / porous substrate, but it is preferable not to include a layer other than the porous substrate from the viewpoint of obtaining good permeability. The layer other than the porous substrate may include a polyamide layer, but its thickness is preferably 100 μm or less.

[0118] (Method for manufacturing a forward osmosis membrane) The forward osmosis membrane can be produced, for example, by manufacturing the semipermeable membrane as a self-supporting membrane and sandwiching the semipermeable membrane between two of the porous substrates from both sides thereof.

[0119] The forward osmosis membrane can be specifically manufactured by the following procedure. For example, a dilute solution of resin (A) is applied onto a substrate made of PET or the like so that the thickness after drying becomes the target thickness, and after drying, the formed membrane is peeled off as a self-supporting membrane. In the process from this application to making it a self-supporting membrane, providing the above-described light irradiation step or plasma treatment step is one of the preferred embodiments of the present invention. Among these, it is also preferable to perform the above-described light irradiation after the drying step and before the step of peeling off as a self-supporting membrane.

[0120] The present invention is a method for manufacturing a forward osmosis membrane by installing one or two porous substrates such as non-woven fabric on one side or both sides of the self-supporting membrane. Further, the light irradiation step of the present invention may be provided in the step of making a forward osmosis membrane using this porous membrane and the semipermeable membrane in addition to the above-described film-forming step.

[0121] When the area of the forward osmosis membrane is large, in order to maintain the distance between the semipermeable membrane and the porous substrate, they may be adhered using an adhesive to such an extent that it does not affect the permeability.

[0122] Further, the forward osmosis membrane can also be manufactured by manufacturing the semipermeable membrane as a self-supporting membrane and laminating this on the porous substrate. At this time, the two may be bonded together using an adhesive.

[0123] According to the above manufacturing method, first, the semipermeable membrane described above is manufactured as a self-supporting membrane, and this is laminated on a porous substrate (such as non-woven fabric) or sandwiched between two porous substrates (such as non-woven fabric) to manufacture a forward osmosis membrane. Therefore, a forward osmosis membrane with a controlled thickness of the semipermeable membrane and showing high water permeability and high salt rejection rate can be easily manufactured.

[0124] [Applications of forward osmosis membrane] The forward osmosis membrane element of the present invention includes the forward osmosis membrane and the spacer of the present invention described above. In other words, the forward osmosis membrane element of the present invention is one in which the forward osmosis membrane of the present invention is used as the forward osmosis membrane in a conventional forward osmosis membrane element including a forward osmosis membrane and a spacer. As the spacer, a conventionally known spacer used for a forward osmosis membrane element can be used.

[0125] The forward osmosis membrane module of the present invention is formed by housing the forward osmosis membrane element of the present invention in a container. In other words, the forward osmosis membrane module of the present invention is one in which the forward osmosis membrane element of the present invention is used as the forward osmosis membrane element in a conventional forward osmosis membrane module formed by housing a forward osmosis membrane element in a container. As the container, a conventionally known container used for a forward osmosis membrane module can be used.

[0126] The system of the present invention has a drive pump for flowing a feed solution (FS) on one surface of the forward osmosis membrane of the present invention included in the forward osmosis membrane module of the present invention and a draw solution (DS) having a higher solute concentration such as salt than the feed solution on the other surface, and is configured to be able to move the water contained in the feed solution through the forward osmosis membrane to the draw solution.

[0127] With such a device, pressure can also be applied from the FS side to the DS side. In an embodiment of the present invention, it may be preferable to apply pressure from the FS side to the DS side. For example, it may be preferable to apply a pressure of preferably 15 kPa or less, more preferably 12 kPa or less, and even more preferably 10 kPa or less from the FS side to the DS side.

Examples

[0128] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereby. The contents of the abbreviations used in this example and the comparative example are shown.

[0129] (1) Solvent DMSO: Dimethyl Sulfoxide NMP: N-Methyl-2-pyrrolidone DMF: N,N-Dimethylformamide

[0130] (2) Constituents of Aromatic Polyether DFBP: 4,4'-Difluorobenzophenone DSDFBP: 5,5'-Carbonylbis(2-fluorobenzenesulfonic acid sodium salt) TMBPF: 3,3',5,5'-Tetramethyl-4,4'-dihydroxydiphenylmethane

[0131] Various measurement methods (Measurement of Contact Angle on Film Surface) The contact angles of the surfaces of each substrate used in the examples and comparative examples were measured using the following apparatus. With a syringe dedicated to the apparatus, 1 drop (about 0.5 ml) of the following test solvent (mixed solvent) was dropped onto the surface of the following sample (substrate), and left standing for 1 minute. Then, the contact angle between the surface of each substrate and the liquid droplet was measured to evaluate the wettability of the film surface. The results are shown in Table 2. Measuring Apparatus: DM500 type apparatus manufactured by KYOWA Test Solvent: Mixed solvent of DMF and toluene (weight ratio 55:45. The varnish solvent used in the examples and comparative examples) Sample: Film 1 used in the examples and Film 2 used in the comparative examples (described later)

[0132] (Measurement of Peel Strength) During the casting molding in the examples and comparative examples, the 180° peel strength when peeling the semipermeable membrane from the substrate film was measured. The measurement was carried out under the following apparatus and conditions. The results are shown in Table 3. Measuring Apparatus: StroGraph E-S type apparatus manufactured by TOYOSEIKI Measuring Speed: 50 mm / min Measuring Range: 2.5 N Sample Shape: Width 15 mm, length about 6 cm Number of Measurements N: 3 times (the average value was taken as the measured value.)

[0133] (Observation of the surface and measurement of roughness of the semi-permeable membrane peeling surface) The surface state of the peeling surface of the semi-permeable membrane peeled from the substrate was visually evaluated and the surface roughness was measured. The surface roughness was measured using a VS1800 type device manufactured by Hitachi High-Tech Corporation in Wave mode. The results are shown in Table 4.

[0134] (Method for measuring film thickness) Using a Nikon DigiMicro MH-15M type device (contact type film thickness measuring device: minimum reading value: 0.01 μm), the measurement was carried out by the following method. The results are shown in Table 5. At the stage of applying varnish on the substrate and drying it, that is, at the stage of the laminate of "substrate / coating film", a part was cut out as a sample for thickness measurement. The thickness was measured using the above device (thickness A (μm)). Next, after peeling the film at the measurement location from the substrate, the thickness of the substrate at that location was measured (thickness B (μm)).

[0135] From the above results, the value was calculated by the formula "film thickness = thickness A - thickness B". The measurement was carried out at 5 or more locations, and the average value was determined as the film thickness. In the case of a semi-permeable membrane with a two-layer or more laminated structure, the above operation was repeated every time a layer was formed (average value of 5 or more measurement locations). The film thickness of each layer was determined from the difference between the respective measured values.

[0136] (Performance evaluation of the forward osmosis membrane) Using the apparatus 10 as shown in Fig. 1, the performance of the forward osmosis membrane was evaluated by the following method. The apparatus 10 includes a feed solution tank 1, a flow path 2, a pump 3, a draw solution tank 11, a flow path 12, a pump 13, and an evaluation cell 21. The feed solution tank 1 is installed on a balance 4, and the draw solution tank 11 is equipped with an electrical conductivity meter 15. At the start of the evaluation, 500 g of Milli-Q water having an electrical conductivity of 50 μS / cm or less is stored in the feed solution tank 1 as a feed solution FS (Feed Solution), and 800 g of a 0.6 M aqueous ammonium sulfate solution is stored in the draw solution tank 11 as a draw solution DS (Draw Solution). The feed solution in the feed solution tank 1 flows through the flow path 2 at a rate of 0.6 L / min by using the pump 3, and the draw solution in the draw solution tank 11 flows through the flow path 12 at a rate of 0.6 L / min by using the pump 13. The feed solution flowing through the flow path 2 and the draw solution flowing through the flow path 12 are in contact with each other through a forward osmosis membrane 22 having an effective membrane area of 0.0042 m 2 2. A part of the feed solution moves to the draw solution through the forward osmosis membrane 22, and a part of the salt (NaCl) in the draw solution moves to the feed solution (reverse flow).

[0137] <Water permeation flux (Jw)> The balance 4 measures the weight reduction amount of the feed solution every minute, and the weight reduction amount per unit area of the forward osmosis membrane per unit time is taken as the water permeation flux (L / (m 2 ·h)). The results are shown in Table 5.

[0138] <Salt reverse diffusion permeability coefficient (SRSF)> The electrical conductivity meter 15 measures the change in the electrical conductivity of the draw solution every minute, converts this into the change in the weight of the draw solution, and the change in weight per unit area of the forward osmosis membrane per unit time is taken as the salt permeation amount (g / (m 2 ·h)). Further, by dividing this value by the water permeation flux (Jw), the SRSF value (g / L) is calculated. The results are shown in Table 5.

[0139] (Resin synthesis example 1) In a five-necked reactor equipped with a nitrogen inlet tube, a thermometer, a reflux condenser, and a stirring device 、D SDFBP 40.1 g (0.095 mol), DFBP 62.2 g (0.285 mol), TMBPF 97.4 g (0.380 mol) and potassium carbonate 65.7 g (0.475 mol) were weighed. To this, 783.4 g of DMSO and 261.1 g of toluene were added, stirred under a nitrogen atmosphere, heated at 130 °C for 12 hours, and after removing the generated water out of the system, toluene was distilled off.

[0140] Subsequently, the reaction was carried out at 160 °C for 12 hours to obtain a viscous polymer solution. After adding 570 g of toluene to the obtained solution for dilution, it was discharged into 2400 g of methanol, and the precipitated polymer powder was filtered, washed, and then dried at 150 °C for 4 hours to obtain 171.6 g of polyether ketone powder (resin 1). Resin (1) has, as the structural unit (1),

[0141]

Chemical formula

[0142]

Chemical formula

[0143] (Resin Synthesis Example 2) The raw materials and solvents of the resin were DSDFBP 48.1 g (0.114 mol), DFBP 58.0 g (0.265 mol), TMBPF 97.4 g (0.380 mol) and potassium carbonate 65.7 g (0.475 mol), and DMSO 814.4 g and toluene 271.5 g. Otherwise, in the same manner as in Example 1, 175.2 g of polymer powder (resin 2) was obtained. Resin 2 has a content of the structural unit (1) of 30 mol%.

[0144] (Resin Synthesis Example 3) The raw materials and solvents of the resin were DSDFBP 80.2 g (0.190 mol), DFBP 41.5 g (0.190 mol), TMBPF 97.4 g (0.380 mol), and potassium carbonate 65.7 g (0.475 mol), and DMSO 876.4 g and toluene 292.1 g. Otherwise, in the same manner as in Resin Synthesis Example 1, 174.6 g of polymer powder (Resin 3) was obtained. The content of the structural unit (1) in Resin 3 is 50 mol%.

[0145] (Resin Synthesis Example 4) The raw materials and solvents of the resin were DSDFBP 96.3 g (0.228 mol), DFBP 33.2 g (0.152 mol), TMBPF 97.4 g (0.380 mol), and potassium carbonate 65.7 g (0.475 mol), and DMSO 907.5 g and toluene 302.5 g. Otherwise, in the same manner as in Resin Synthesis Example 1, 173.6 g of polymer powder (Resin 4) was obtained. The content of the structural unit (1) in Resin 4 is 60 mol%.

[0146] The constituent raw materials and the sulfonic acid unit content of the polymers synthesized in Resin Synthesis Examples 1 to 4 are shown in Table 1.

[0147]

Table 1

[0148] [Example 1] The resin 1 produced in Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene (DMF / toluene = 55 / 45 (weight ratio)) to prepare a varnish. This varnish was cast onto a PET substrate having a release agent layer ("PLD38TH" manufactured by Lintec Corporation; Film 1), and dried at 110°C for 3 minutes to obtain a film of Resin 1. A part of this film was peeled off from Film 1, and the appearance and surface roughness of the peeled surface were measured. The results are shown in Table 4.

[0149] Next, Resin 3 produced in Resin Synthesis Example 3 was dissolved in a solvent of methyl cellosolve to prepare a varnish. This varnish was cast on the film of Resin 1 and dried at 160 °C for 3 minutes to obtain a two-layer film. Then, this was peeled off from Film 1 to obtain a self-supporting film, Film 1.

[0150] [Example 2] Resin 1 produced in Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene (DMF / toluene = 55 / 45 (weight ratio)) to prepare a varnish. This varnish was cast on Film 1 and dried at 110 °C for 3 minutes to obtain a film. A part of this film was peeled off from the said Film 1, and the appearance and surface roughness of the peeled surface were measured. The results are shown in Table 4.

[0151] Next, Resin 4 produced in Resin Synthesis Example 4 was dissolved in a solvent of methyl cellosolve to prepare a varnish. This varnish was cast on the film of Resin 1 and dried at 160 °C for 3 minutes to obtain a two-layer film. Then, this was peeled off from Film 1 to obtain a self-supporting film, Film 2.

[0152] [Example 3] Resin 2 produced in Resin Synthesis Example 2 was dissolved in a mixed solvent of DMF and toluene (DMF / toluene = 55 / 45 (weight ratio)) to prepare a varnish. This varnish was cast on Film 1 and dried at 110 °C for 3 minutes to obtain a film of Resin 2. A part of this film was peeled off from the said Film 1, and the appearance and surface roughness of the peeled surface were measured. The results are shown in Table 4.

[0153] Next, Resin 3 produced in Resin Synthesis Example 3 was dissolved in a solvent of methyl cellosolve to prepare a varnish. This varnish was cast on the film of Resin 2 and dried at 160 °C for 3 minutes to obtain a two-layer film. Then, this was peeled off from Film 1 to obtain a self-supporting film, Film 3.

[0154] [Example 4] The resin produced in Resin Synthesis Example 2 was dissolved in a mixed solvent of DMF and toluene (DMF / toluene = 55 / 45 (weight ratio)) to prepare a varnish. This varnish was cast onto Film 1 and dried at 110 °C for 3 minutes to obtain a film of Resin 2. A part of this film was peeled off from Film 1, and the appearance and surface roughness of the peeled surface were measured. The results are shown in Table 4.

[0155] Next, Resin 4 produced in Resin Synthesis Example 4 was dissolved in a solvent of methyl cellosolve to prepare a varnish. This varnish was cast onto the film of Resin 2 and dried at 160 °C for 3 minutes to obtain a two-layer film. Then, this was peeled off from Film 1 to obtain a free-standing film, Film 4.

[0156] [Preparation of Forward Osmosis Membrane] Two nonwoven fabrics with an air permeability of 300 m 3 / cm 2 / s, a thickness of 290 μm, and a material of polypropylene (manufactured by Mitsui Chemicals, Inc., "SyntheX (registered trademark) PS-105") were prepared. The films 1 to 4 were sandwiched between these two nonwoven fabrics and integrated to obtain forward osmosis membranes 1 to 4. The evaluation results of Examples 1 to 4 are shown in Table 5.

[0157] [Comparative Example 1] Similar to Example 1, Resin 1 produced in Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene (DMF / toluene = 55 / 45 (weight ratio)) to prepare a varnish. This varnish was cast onto a smooth PET substrate without a release layer (Film 2) and dried at 110 °C for 3 minutes to obtain a film. A part of this film was peeled off from Film 2, and the appearance and surface roughness of the peeled surface were measured. The results are shown in Table 4.

[0158] Next, Resin 3 produced in Resin Synthesis Example 3 was dissolved in a solvent of methyl cellosolve to prepare a varnish. This varnish was cast onto the above film and dried at 160 °C for 3 minutes to obtain a two-layer film. After that, this was peeled off from Film 2 to obtain a free-standing film, and further sandwiched between two nonwoven fabrics in the same manner as above to obtain forward osmosis membrane C1. The evaluation results are shown in Table 5.

[0159] The above-mentioned film 2 is the same as the release film used in the examples of the publications related to the invention of the forward osmosis membrane, such as International Publication No. 2017 / 079733, International Publication No. 2019 / 189547, International Publication No. 2019 / 189548, and International Publication No. 2020 / 032019.

[0160] [Comparative Example 2] Similar to Example 2, Resin 1 produced in Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene (DMF / toluene = 55 / 45 (weight ratio)) to prepare a varnish. This varnish was cast on Film 2 and dried at 110°C for 3 minutes to obtain a film. A part of this film was peeled off from the Film 2, and the appearance and surface roughness of the peeled surface were measured. The results are shown in Table 4.

[0161] Next, Resin 4 produced in Resin Synthesis Example 4 was dissolved in a solvent of methyl cellosolve to prepare a varnish. This varnish was cast on the above film and dried at 160°C for 3 minutes to obtain a two-layer film. After that, this was peeled off from Film 2 to form a self-supporting film, and further sandwiched between two non-woven fabrics in the same manner as above to obtain a forward osmosis membrane C2. The evaluation results are shown in Table 5.

[0162] [Comparative Example 3] Similar to Example 3, Resin 2 produced in Resin Synthesis Example 2 was dissolved in a mixed solvent of DMF and toluene (DMF / toluene = 55 / 45 (weight ratio)) to prepare a varnish. This varnish was cast on Film 2 and dried at 110°C for 3 minutes to obtain a film. A part of this film was peeled off from the Film 2, and the appearance and surface roughness of the peeled surface were measured. The results are shown in Table 4.

[0163] Next, Resin 3 produced in Resin Synthesis Example 3 was dissolved in a solvent of methyl cellosolve to prepare a varnish. This varnish was cast on the film and dried at 160°C for 3 minutes to obtain a two-layer film. After that, this was peeled off from Film 2 to form a self-supporting film, and further sandwiched between two non-woven fabrics in the same manner as above to obtain a forward osmosis membrane C3. The evaluation results are shown in Table 5.

[0164] [Comparative Example 4] In the same manner as in Example 4, Resin 2 produced in Resin Synthesis Example 2 was dissolved in a mixed solvent of DMF and toluene (DMF / toluene = 55 / 45 (weight ratio)) to prepare a varnish. This varnish was cast onto Film 2 and dried at 110°C for 3 minutes to obtain a film. A part of this film was peeled off from Film 2, and the appearance and surface roughness of the peeled surface were measured. The results are shown in Table 4.

[0165] Next, Resin 4 produced in Resin Synthesis Example 4 was dissolved in a solvent of methyl cellosolve to prepare a varnish. This varnish was cast onto the film and dried at 160°C for 3 minutes to obtain a two-layer film. Thereafter, this was peeled off from Film 2 to form a free-standing film, and further sandwiched between two nonwoven fabrics in the same manner as described above to obtain a forward osmosis membrane C4. The evaluation results are shown in Table 5.

[0166]

Table 2

[0167] From the measurement results in Table 2, while the contact angle of Film 2 used in Comparative Examples 1 to 4 with the solvent (mixed solvent of DMF and toluene) was less than 10°, the contact angle of Film 1 used in Examples 1 to 4 with the solvent (mixed solvent of DMF and toluene) was 10° or more.

[0168]

Table 3

[0169] From the measurement results in Table 3, compared with Comparative Examples 1 to 4, Examples 1 to 4 had a lower peel strength. This is considered to lead to less damage to the film when the film is peeled off and to the improvement of surface roughness and appearance described later.

[0170]

Table 4

[0171] From the results in Table 4, compared with Comparative Examples 1 to 4, the membranes in Examples 1 to 4 had a visually uniform surface. Also, the surface roughness (SA value) of the Examples was 10 nm or less, which was a lower value compared to the Comparative Examples (greater than 10 nm).

[0172]

Table 5

[0173] From the results in Table 5, it can be said that the forward osmosis membrane obtained by the method for producing a forward osmosis membrane of the present invention is excellent in the balance between the permeation flux and the suppression of reverse diffusion of salts.

Explanation of Signs

[0174] 1 Feed solution tank 2, 12 Flow path 3, 13 Pump 4, 14 Balance 10 Evaluation device 11 Draw solution tank 15 Conductivity meter 21 Evaluation cell 22 Forward osmosis membrane DS Draw solution FS Feed solution

Claims

1. an aromatic structure; a protonic acid structure; a structure selected from an ether structure (—O—) and a ketone structure (—CO—); a step of dissolving a resin (A) containing the formula (I) in an organic compound (S) to form a varnish, the varnish being cast on a film made of an organic material having a surface with a contact angle of the organic compound (S) of 10° to 40°, and then drying the film; The method for producing a forward osmosis membrane that is a self-supporting membrane, wherein the resin (A) has a structural unit (1) represented by the following formula (1) and a structural unit (2) represented by the following formula (2): 【Chemical 1】 [In formulas (1) and (2), R 1 to R 10 each independently represent H, Cl, F, CF 3 or C m H 2m+1 (m represents an integer of 1 to 10); At least one of R 1 to R 10 is C m H 2m+1 (m is an integer of 1 to 10), Two or more of each of R 1 to R 10 may be present in an aromatic ring, and when two or more C m H 2m+1 groups are present in one aromatic ring, the C m H 2m+1 groups may be the same as or different from each other. X 1 to X 5 are each independently H, Cl, F, CF 3 or a protonic acid group; At least one of X 1 to X 5 is a protonic acid group; Two or more of each of X 1 to X 5 may be present in an aromatic ring, and when two or more protonic acid groups are present in one aromatic ring, the respective protonic acid groups may be the same or different. A 1 to A 6 are each independently a direct bond, —CH 2 —, —C(CH 3 ) 2 —, —C(CF 3 ) 2 —, —O— or —CO—, and at least one of A 1 to A 6 is —O— or —CO—. i, j, k, and l each independently represent 0 or 1.

2. 2. The method for producing a forward osmosis membrane according to claim 1, wherein the resin (A) comprises a protonic acid group-containing resin (A1) and a resin (A2) having a molar fraction of protonic acid group-containing structural units different from that of the resin (A1).

3. 3. The method for producing a forward osmosis membrane according to claim 2, wherein the forward osmosis membrane is a laminate including a layer containing the resin (A1) and a layer containing the resin (A2).

Images