JPH02160026A - Hydrophilic separation membrane - Google Patents

Abstract

PURPOSE:To obtain a separation membrane having superior performance by producing a membrane from a soln. contg. a hydrophobic polymer, a hydrophilic polymer and a hydrophilic-hydrophobic copolymer. CONSTITUTION:A hydrophobic polymer such as polysulfone or polyether sulfone, a hydrophilic polymer such as a cellulose polymer or aliphatic polyimide and a copolymer having repeating units of the hydrophobic polymer and repeating units of the hydrophilic polymer are dissolved in a solvent such as N-N- dimethylacetamide and a separation membrane is produced from the resulting soln. by a phase transformation method. This membrane has a microscopically ununiform hydrophilic-hydrophohic phase separated structure, high porosity and superior performance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hydrophilic separation membrane, and more specifically, it relates to a hydrophilic separation membrane. The present invention relates to a hydrophilic separation membrane manufactured by a phase conversion method from a solution containing .

[Prior art and problems to be solved by the invention] Membrane separation technology has attracted attention for its energy saving and compactness, and has made remarkable progress. Many types of polymers have been researched and developed as membrane materials for permselective separation membranes used in such systems, including cellulose-based, polyamide-based, polyacrylonitrile-based, polycarbonate-based, polyphenylene oxide-based, and polysulfone-based polymers. has been done.

Among them, hydrophobic polymers such as polysulfone, polycarbonate, polyphenylene oxide, and fluorine-containing polymers are originally used as engineering plastics, but they have excellent heat resistance and mechanical properties. Because of this, it is also being used as a material for separation membranes.

However, compared to hydrophilic resins such as cellulose acetate, hydrophobic resins such as borisulfone resins are extremely hydrophobic, so separation membranes made of such resins do not become wet with water after being dried. '', ``poor water permeability'', and ``hydrophobic solutes adhere to the membrane surface, making it susceptible to contamination''.

In order to solve these problems, various methods have been proposed to improve hydrophobic resin films.

Hereinafter, the hydrophilization methods that have been proposed so far will be outlined, taking as an example a separation membrane made of polysulfone resin, which has particularly excellent heat resistance among hydrophobic resins.

As a method for providing a hydrophilic polysulfone membrane by introducing a hydrophilic group or a hydrophilic polymer into an aromatic polysulfone polymer, for example, Japanese Patent Publication No. 53-13679 and Japanese Patent Application Laid-open No. 59-19
6322, etc., a sulfonic acid group is introduced into the polymer main chain, and JP-A-57-174104 is a polymer backbone polymer made from an aromatic polysulfone polymer that has been made hydrophilic by introducing or grafting a polyethyleneimine polymer ti to the polymer main chain. We are proposing a method of providing a permeable membrane. All of these methods are modification methods in which hydrophilic groups or hydrophilic polymers are randomly and uniformly bonded to the aromatic rings of the main chain of aromatic polysulfone polymers through covalent bonds, so they are made of unmodified polymers. It is inevitable that physical properties such as heat resistance will be lower than that of membranes.

Furthermore, if the ratio of hydrophilic groups introduced to the cough polymer is high, the resulting membrane will swell with water, which can be said to be a modification method that involves significant changes in the physical properties of the membrane.

On the other hand, various hydrophilized polysulfone membranes made of mixed polymers in which a hydrophilic polymer is blended with an aromatic polysulfone polymer have also been proposed. For example, JP-A-57-5
No. 0507 discloses that cellulose derivatives are
Publication No. 206404 proposes a hydrophilized polysulfone membrane made of a mixed polymer in which ethylene-vinyl alcohol copolymers are blended. However, in order to obtain a substantially hydrophilized polysulfone membrane, a significant amount of different polymers must be blended, and it is difficult to obtain a homogeneous blend with polymers with high molecular cohesion, such as aromatic polysulfone polymers. was difficult. especially,
When attempting to produce the above-mentioned hydrophilized polysulfone membrane by bringing a membrane-forming solution containing a polar organic solvent and a polymer into contact with a non-solvent of a polymer whose main component is water and coagulating the polymer, a uniform In addition to being difficult to obtain membrane-forming solutions, there are problems with the stability of the solutions, such as gelation and phase separation when left standing, and separation from different types of polymers when the polymer solidifies due to contact with non-solvents. There was also the possibility that this would cause the film structure to become non-uniform. In this way, the addition of different polymers not only has the effect of adding polymers with inferior physical properties, but also
It was thought that the formation of a non-uniform film structure also caused deterioration of the film's physical properties such as heat resistance and chemical resistance.

In response to the above proposal, as a method for making the membrane surface hydrophilic without impairing the physical properties of the polysulfone polymer, for example, JP-A-60-87803 proposes forming a polysulfone membrane, and then adding chlorosulfonic acid to the membrane while maintaining the membrane shape. JP-A No. 59-186604 proposes a method of sulfonating a polymer by subjecting a polynalfone film to a positive column plasma treatment. However, such methods are only applicable to products or semi-finished products that have undergone film formation.
It was a complicated method that required special methods and equipment, and was not common.

The purpose of the present invention is to develop a new hydrophilic membrane as a separation membrane with excellent physical properties and good permeability without substantially impairing the physical properties such as the excellent heat resistance and mechanical strength that hydrophobic resin membranes have. Our goal is to provide the following.

[Means to solve the problem]

As a result of intensive research in view of the above, the present inventors found that by forming a film by a phase conversion method from a solution containing three types of polymers: a hydrophobic polymer, a hydrophilic polymer, and a hydrophilic/hydrophobic copolymer. They discovered that a separation membrane with excellent performance can be obtained and completed the present invention.

That is, the present invention provides a hydrophobic polymer (A), a hydrophilic polymer (
B), and a copolymer (C) having at least one repeating unit of the hydrophobic polymer (A) and at least one repeating unit of the hydrophilic polymer (B). The present invention relates to a hydrophilic separation membrane characterized by being formed by a method.

As the hydrophobic polymer (A) in the present invention, a heat-resistant polymer having a water absorption rate of 5% or less when immersed in water (23° C. for 124 hours) according to ASTM 0570 is particularly preferably used. Such hydrophobic polymers have a molecular weight of 5.
000-1.000.000, and specific examples include polysulfone, polyethersulfone, polyphenylene oxide, polyacetal, triacetate, and Teflon. When these are used in the present invention, a tough hydrophilic separation membrane particularly excellent in chemical resistance, heat resistance, mechanical strength, etc. can be obtained. In addition to the above-mentioned polymers, a polymer having a lower water absorption rate or a larger contact angle with water than the hydrophilic polymer (B) may be used. for example,
Acrylic polymers, polyester polymers, polyolefin polymers, and the like can also be used as the hydrophobic polymer (A) in the present invention.

On the other hand, the hydrophilic polymer (B) in the present invention preferably has a molecular weight of t, ooo-t, ooo, ooo, and specific examples include cellulose polymers, aliphatic and aromatic polyamides, and the following formula: A hydrophilic polymer having one or more repeating units represented by (1) can be used.

CR, -C11□-...(1) (Here, R1 is hydrogen or a methyl group. Also, h is OOM (M is hydrogen, or an alkali metal or basic substance that ionically bonds with a carboxylic acid ion) .

0ORs (Ri is an aliphatic hydrocarbon group having 1 to 20 carbon atoms).

C0NR4R5 (Ra, Rs are each hydrogen or an aliphatic hydrocarbon group having 1 to 20 carbon atoms).

(R9 is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, n is an integer of 4 to 6, and xO is a halogen ion)
.

(n is an integer from O (valence bond) to 10; H is hydrogen, or an alkali metal or basic substance that ionically bonds with the sulfonate ion).

(R, , R1 and R3 are each an aliphatic hydrocarbon group having 1 to 20 carbon atoms, and X is a halogen ion).

(R1° is an aliphatic hydrocarbon group containing 1 to 20 carbon atoms, and xO is a halogen ion). ) In addition to the above, a sulfonated version of the hydrophobic polymer (A) described above can also be used as the hydrophilic polymer (8).

Next, the hydrophilic-hydrophobic copolymer (C) of the present invention has at least one repeating unit of the hydrophobic polymer (A) and at least one repeating unit of the hydrophilic polymer (B). Copolymers are used. The role of this copolymer (C) is explained later in that the copolymer (^) and polymer (I)
It also includes the function of promoting compatibilization (I), that is, making it easier to mix with each other. Therefore, among the repeating units of polymer (^) or polymer (B), copolymer (C) has a repeating unit that accounts for 70 mol% or more of heptad units in each polymer. is preferable, and the ratio of repeating units of polymer (A) and repeating units of polymer (B) in copolymer (C) is 80:2 in molar ratio.
It is desirable to be in the range of 0 to 20:80. Furthermore, the molecular structure of the copolymer (C) is a random copolymer,
Examples include graft copolymers and block copolymers, preferably graft copolymers and block copolymers.

The molecular weight of the copolymer (C) is io, ooo~1
,000,000 is preferred.

Polymers (A), (B), (
C) is made into a suitable solution and the amount N of the present invention is obtained by a phase conversion method.
The membrane is formed. At this time, the polymer (A) in the solution, (
The content of B) and (C) is 5 to 30% of the hydrophobic polymer (A).
The preferable range is 1 to 20% by weight of the hydrophilic polymer (B) and 0.5 to 20% by weight of the copolymer (C).

Examples of solvents that can be used include water-soluble solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, 2-pyrrolidone, dimethylsulfoxide, sulfolane, and tetrahydrofuran. are the first group of solvents) and water-insoluble halogenated hydrocarbon solvents such as methylene chloride and chloroform (these are the first group of solvents). There is no particular limitation as long as it can dissolve all of n) and (c). When using the first group of solvents, the above-mentioned polymer mixture is dissolved therein, and if necessary, an electrolyte or a water-soluble solvent (for example, water, alcohols, ketones, etc.) is simultaneously dissolved and mixed to form a film. A solution (this is called a dope) is prepared.

In order to form a T1 film in the form of a sheet or a tube, the dope is placed on a suitable support (for example, a glass plate or tube, non-woven fabric, cloth, etc.) in the form of a sheet or tube to a thickness of several tens to several hundreds. µ by an appropriate method, and if necessary, left in an atmosphere under certain conditions (for example, air containing vapor of a poor solvent) for a certain period of time, and then placed in a coagulation bath consisting of a poor solvent (mainly water). Wet or dry-wet film formation is performed by immersing the material in water and performing sol-gel phase conversion. Further, a hollow fiber membrane can be manufactured by spinning the dope through a hollow molding nozzle using a known method.

In addition, when using the solvent of Group Ⅰ, the dope prepared in the same manner as in Group 1 is cast or discharged in the form of a sheet, a tube, or a hollow system in the same manner as in Group 1, By exposing the membrane to an atmosphere under certain conditions for a certain period of time to cause liquid-liquid phase separation (phase conversion) and further evaporating the solvent, a relatively porous separation membrane can finally be obtained. This method is almost the same as the dry film forming method for cellulose acetate membrane filters.

When a film is formed by the method described above, a part of the above-mentioned polymer (B) may be eluted during immersion in a coagulation bath or during a washing process. For example, elution of the polymer (B) occurs when water is used in the coagulation bath or washing liquid and the polymer (B) is a water-soluble polymer. However, due to the action of the above-mentioned copolymer (C), the polymer (
A part of B) remains in the film. When the polymer (B) remains in the membrane, the pore surfaces of the membrane are effectively made hydrophilic. In addition, the porosity of the membrane also increases due to the elution of a portion of the polymer (B). In addition, when the copolymer (C) is a block or graft copolymer, the interior of the polymer aggregate that forms the network structure of the membrane due to the action of microphase separation is rich in hydrophobic polymer (A), and the surface of the aggregate can be expected to have a microphase-separated structure covered with the hydrophilic polymer (B). Due to this structure, the membrane of the present invention exhibits high water permeability and stain resistance without significantly impairing the high mechanical strength and heat resistance of the hydrophobic polymer. However, it is not preferable that the hydrophilic component in the membrane is too large, and the combined weight of the hydrophilic components of the polymer (B) and copolymer (C) in the membrane should be 60% or less of the total weight of the membrane. It is desirable that there be.

〔Effect of the invention〕

The hydrophilic separation membrane of the present invention differs from conventional microscopically uniform hydrophilic separation membranes (e.g., cellulose acetate membranes or hydrophilic polysulfone membranes used in conventional methods) to allow microscopically heterogeneous hydrophilic-hydrophobic phase separation. The membrane has a structure and has a high porosity.

To explain in more detail, (1) the deterioration of the membrane structure due to macroscopic phase separation that may occur when forming a membrane from a blended solution of a hydrophobic polymer (A) and a hydrophilic polymer (B) by a phase conversion method; Union (A
) and at least one repeating unit of polymer (B). At the same time, when the polymer (B) is a water-soluble polymer, , is expected to have the effect of preventing gradual elution and loss from the membrane during use.

■Next, the amphiphilic copolymer (C) is a block or graft copolymer, and when a membrane with a hydrophobic skeleton and a hydrophilic surface is formed by microphase separation, the copolymer (C) Hydrophobic polymer (A) and copolymer (C) with hydrophobic components
The coexistence of the hydrophilic polymer ([l) having a hydrophilic component is expected to have the effect of promoting microphase separation of the copolymer (C). By changing the mixing ratio of C), the pore size and porosity can be changed, making it possible to create a membrane with high water permeability.

As a result, the membrane of the present invention has a high water permeation rate and is resistant to leakage, while its mechanical strength and heat resistance are comparable to those of hydrophobic separation membranes (for example, polysulfone membranes). It has excellent performance. Therefore, it can be effectively used in fields where conventional hydrophilic separation membranes and hydrophobic separation membranes have not yielded satisfactory results.

〔Example〕

EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Polyethersulfone (P
Abbreviated as ES, Victrex 5003P+ IcI
15g of dimethyl sulfoxide (abbreviated as DMSO) was dissolved in 7.0-g of dimethyl sulfoxide (abbreviated as DMSO), 15g of vinylpyrrolidone was added, and N2 gas was blown in for 10 minutes while stirring. After heating this solution to 70°C, Abvis Isobutyronitrile 0,3
8 g was added and stirred for 4 hours. After returning to room temperature and adding 0.2 g of hydroquinone, 50 g of solution was collected. In this solution, as a hydrophobic polymer (A), a high molecular weight type PE5 (Vict
rex 5200P, manufactured by IC1) lOg.

DMSo 30g, acetone 10. The solutions were mixed and stirred overnight to obtain a homogeneous solution. After filtering and degassing this solution, it was cast onto a polyester nonwoven fabric (MP-80K, manufactured by Nippon Vilene Co., Ltd.) to a thickness of 150 ta, exposed to a certain volume of air for a certain period of time, and then immersed in water at 10'C. By doing so, an asymmetric separation membrane was obtained.

Furthermore, after washing with hot water at 90'C for 15 minutes, the pure water permeability coefficient (LP), the rate of decrease in Lp over time (β), and the rejection rate of ovalbumin (Ro) were measured.

The definition of each parameter is as follows.

(However, 1 hour after filtration, glue, 1, and 3 hours after filtration.

Let be LP3. ), and the result LP' = 8.7m27m"-day kg/cm
2. It had excellent performance of β=4.0% and Ro=90%.

In addition, this separation membrane is dried and the membrane material polymer is dissolved in DMSO.
di (deuterium-substituted DMSO), HNMR (10
When analyzed with 0MH2), polyvinylpyrrolidone (P
VP) component was found to be present in an amount of 28% by weight.

When this was further extracted with an aqueous acetone solution, the PvP component was reduced to 16% by weight, and it was found that the PvP homopolymer (ie, hydrophilic polymer (B)) was contained at 12% by weight.

In addition, the remainder of the reaction mixture was reprecipitated with water, further Soxhlet-extracted with water, dried, and analyzed by 270 MHz H-NMR and organic solvent-based GPC. (C)).

-(-C1hCII +-TrCHICIIO Comparative Example 1 High molecular weight type Pu5 (Victr
EX5200P) was used to form a #i membrane in the same manner as in Example 1. This separation membrane beam, ' = 9.6
m"/l12・day・kg/cra", but β=20%
Therefore, the pure water permeation rate is significantly reduced.

Example 2 Pus (Victrex 5003['
) 200g to D? ISO600- and chlorobenzene 30
It was dissolved in 0 ml of a mixed solvent at room temperature, and 0.5N NaOH aqueous solution 50- was added dropwise thereto and stirred at room temperature for 2 hours to obtain a solution of PES with sodium ferulate terminals.

After adding 4 g of benzyl chloride to this, it was kept in the chamber for 7 hours.
Stirring at 0''C for 2 hours changed one end of PI!S to benzyl ether type. 0.5N Na0115 was added to this solution.
0ml was added dropwise, and after stirring for 1 hour, chloromethylstyrene 6
g was added dropwise and reacted at room temperature for 1 hour and at 70°C for 3 hours to introduce a vinyl group into one end of PES. This reaction mixture was reprecipitated with a mixed solution of methanol/water (8:2 (volume ratio)), and the polymer was collected by filtration and dried. When this polymer was analyzed by I-NMR (270 MIIz), it was confirmed that it was a PES macromer having a benzyl ether group introduced at one end and a vinyl group (styryl group) introduced at the other end.

170g of this PES macromer and 17g of vinylpyrrolidone
0g was dissolved in DNSO800f, and N2 gas was blown into the solution. This solution was heated to 70"C, 2.1g of abbisisobutyronitrile was added as a polymerization initiator, and polymerized for 5 hours. After returning to room temperature and adding 2g of hydroquinone,
A solution of g was collected and placed in the same Victrex 5
The mixture was mixed with 50 g of a solution of 200P (hydrophobic polymer (A)) to obtain an asymmetric separation membrane in the same manner as in Example 1. This film has a LF′=12113/l112·day·kg/cm”.

β=1.2%, and the water permeability was excellent. Further, the Ro of this separation membrane was 90%, and this performance remained unchanged even after being immersed in hot water at 80°C for 30 days.

Furthermore, when the composition of this separation membrane was analyzed in the same manner as in Example 1, the PvP component was 28% by weight, of which 19% by weight was a graft copolymer (copolymer (C)) having the following properties. )), 9% by weight of the pvp was PvP homopolymer (hydrophilic polymer (B)).

PE5-PVP graft copolymer: M-2 140.000 MN = 70,000 MW/MN = 2.0 pvp content 37% by weight Trunk poly? -: PVP, MN=26,000 Polymer: PEs, MN=15,000 Number of branches=3 Example 3 25 g of the block copolymer of Example 1 (copolymer (C))
, PVP homopolymer (hydrophilic polymer (B)) (molecule ff 110,000, manufactured by Aldrich) 25 g
, Victrex 5200P (hydrophobic polymer (A)
) was dissolved in a mixed solvent of 600 g of DNSo and 200 g of polyethylene glycol (abbreviated as PEG) having a molecular weight of 200 to obtain a uniform film-forming solution (dope).

After filtering and defoaming, this dope is extruded from an annular nozzle for manufacturing hollow fibers, and DMSO/water - 1:1 (weight ratio) is sent inside the hollow fibers to coagulate it, and water is supplied from the outside as a coagulation liquid. It solidified.

The inner diameter of the obtained hollow membrane was 470 urB, and the thickness was 155 mm.
-, LP' = 22 m'/m"-day kg/cm",
It had excellent performance of β=1.0% and Re'''70%.

The content of PvP homopolymer in the film was 10% by weight (14% by weight when combined with PvP in the block copolymer).

Comparative Example 2 A hollow membrane was produced in the same manner as in Example 3 except that the block copolymer was not added. LP' of this film = 10
m3/m”・day・kg/cI112.β=10%, and the performance was inferior to the first model of Example 3.

The content of pvp homopolymer in the film was as low as 3% by weight.

Procedure Nefu Seisho (self-motivated) December 22, 1999 ■, Incident display Patent Application No. 63-315704 2. Name of the invention Hydrophilic separation membrane 3. Person making the amendment Relationship to the case Patent applicant (290) Daicel Chemical Industries, Ltd. 4. Agent

Claims (1)

[Scope of Claims] 1. At least one of the hydrophobic polymer (A), the hydrophilic polymer (B), and the repeating unit of the hydrophobic polymer (A) and the repeating unit of the hydrophilic polymer (B) A hydrophilic separation membrane characterized in that it is formed by a phase conversion method from a solution containing a copolymer (C) having at least one of the above. 2. The hydrophilic separation membrane according to claim 1, wherein the copolymer (C) is a block or graft copolymer. 3. The hydrophilic separation membrane according to claim 1, wherein the combined weight of the hydrophilic components of the hydrophilic polymer (B) and copolymer (C) in the membrane is 60% or less of the total weight of the membrane.