JPWO2018021545A1 - Separation membrane and method for producing the same - Google Patents

Abstract

The separation membrane of the present invention is mainly composed of a hydrophilic polymer, has a co-continuous structure with a structure period of a phase having a hydrophilic polymer and pores of 0.001 μm to 10 μm, and has a thickness of 10 μm to 500 μm. In the cross section in the thickness direction, the porosity of the region a at a depth of 1 to 4 μm from any one surface is Ha, and the porosity of the region b at a depth of 1 to 4 μm from the other surface is Hb, both Assuming that the porosity of the region c having a thickness of 3 μm at which the depth from the surface is the same is Hc, the following equations (1) and (2) are satisfied. (1) 1.00 ≦ Ha / Hc ≦ 1.50 (2) 1.05 ≦ Hb / Hc ≦ 1.50

Description

  The present invention relates to a separation membrane mainly composed of a hydrophilic polymer and a method for producing the same.

  The separation membrane removes suspended solids and ions from rivers, sea water, and lower wastewater, and produces membranes for water treatment to produce industrial water and drinking water, medical membranes such as artificial kidneys and plasma separation, foods, such as fruit juice concentrates, etc. It is used in a wide range of fields such as membranes for the beverage industry, gas separation membranes for separating carbon dioxide and the like.

  Most separation membranes are made of polymer. For example, in Patent Document 1, a hollow fiber membrane is obtained by discharging a membrane-forming solution (spinning stock solution) composed of cellulose triacetate, a solvent, and a nonsolvent into a coagulating solution composed of a solvent, a nonsolvent, and water to cause phase separation. Technology is disclosed.

  Patent Document 2 discloses a technique for obtaining a porous film by immersing a melt film-forming sheet of polymethyl methacrylate and polylactic acid in an aqueous solution of potassium hydroxide and hydrolyzing and removing polylactic acid.

  In patent document 3, after melt-kneading the resin composition which consists of a cellulose ester and a plasticizer, the technique which obtains a hollow fiber membrane by eluting a plasticizer from the hollow fiber which was discharged and taken up from the spinneret into air. Is disclosed.

Japan JP 2011-235204 Japanese Patent Application Laid-Open No. 2012-092318 International Publication No. 2016/52675

  According to the technique described in Patent Document 1, a so-called asymmetric film in which the hole diameter is largely different in the film thickness direction can be obtained. In the asymmetric membrane, a compact layer with a small pore diameter that exhibits separation performance is present near the surface layer of the membrane. In order to express high permeation performance, it is necessary to make the thickness of the dense layer sufficiently thin, and it is necessary to make the pore diameter sufficiently large except for the dense layer. The former is a cause of defects in the film during production and use, and the latter is a problem of low film strength. That is, it was not possible to obtain a separation membrane which simultaneously satisfies all of permeability, stability of membrane performance, and membrane strength.

  According to the technique described in Patent Document 2, a separation membrane having continuous holes uniformly controlled in the film thickness direction can be obtained. Due to its uniform structure, it becomes a separation membrane excellent in stability of membrane performance and membrane strength, but it has become a separation membrane with low permeability due to the large thickness of the uniform structure part that expresses separation performance .

  According to the technology described in Patent Document 3, a separation membrane with high membrane strength having a uniform structure in the film thickness direction can be obtained, but since it is a so-called reverse osmosis membrane, a very high pressure is required to express permeation performance. It is necessary to apply the same, and the transmission performance obtained is also low.

  In view of the background of the prior art, the present invention is intended to provide a separation membrane mainly composed of a hydrophilic polymer, which is excellent in permeability and stability of membrane performance and has high membrane strength, and a method for producing the same. is there.

  As a result of intensive investigations to solve the above problems, the present inventors have a hydrophilic polymer as a main component, and the phase having the hydrophilic polymer and the pore have a co-continuous structure with a structural period of a certain size. And, by setting the ratio of the porosity of the surface layer portion to the inner layer portion in a certain range in the cross section in the thickness direction, it has been found that a separation membrane capable of solving the problem can be provided, and the present invention has been completed. .

That is, the separation membrane of the present invention is a separation membrane containing a hydrophilic polymer as a main component, and
The structure cycle of the phase having the hydrophilic polymer and the pores has a co-continuous structure of 0.001 μm to 10 μm,
The thickness of the separation membrane is 10 μm or more and 500 μm or less,
In the cross section in the thickness direction, the porosity of the region a at a depth of 1 to 4 μm from any one surface (A surface) is Ha, and the porosity of the region b at a depth of 1 to 4 μm from the other surface (B surface) Hb, a separation membrane satisfying the following Formula (1) and Formula (2), where Hc is the porosity of a region c with a thickness of 3 μm where the depth from both surfaces is the same is Hc.
(1) 1.00 ≦ Ha / Hc ≦ 1.50
(2) 1.05 ≦ Hb / Hc ≦ 1.50

According to a preferred embodiment of the present invention, an average porosity calculated by a simple average of the porosity Ha, the porosity Hb and the porosity Hc is 20% or more and 80% or less.
Further, according to a further preferable aspect of the present invention, the hydrophilic polymer is at least one selected from the group consisting of polyester, polyamide and cellulose ester.
Further, according to a further preferred aspect of the present invention, the separation membrane is in the form of a hollow fiber.
Moreover, according to the further preferable form of this invention, the outer diameter of the said hollow fiber is 50 micrometers or more and 2500 micrometers or less.

Further, according to the present invention, there is provided a method for producing a separation membrane comprising a hydrophilic polymer as a main component, the method comprising at least the following steps 1 to 5 being carried out.
1. Melt-kneading step of obtaining a resin composition by melt-kneading a hydrophilic polymer of 20% to 80% by weight and a structure forming agent of 20% to 80% by weight. Film forming step of forming a film by discharging and cooling the resin composition from a die. Stretching step of stretching the film at a stretch ratio of 1.1 times to 5.0 times. A heat treatment step of heating the stretched film obtained in the stretching step at 50 ° C. or more and 300 ° C. or less; Elution process for eluting the structure forming agent from the film obtained in the heat treatment process

According to the present invention, a separation membrane having excellent permeability and stability of membrane performance and high membrane strength is provided. The separation membrane of the present invention can be preferably used in applications that require permeation performance and high membrane strength.
Specifically, membranes for water treatment to remove suspended solids from river water, seawater, brackish water, sewage, drainage, etc., medical membranes such as artificial kidneys and plasma separation, membranes for food and beverage industry such as juice concentration, It can be used as a gas separation membrane for separating exhaust gas, carbon dioxide gas, etc., a membrane for the electronic industry such as a fuel cell separator, etc. The type of the water treatment membrane can be preferably used for microfiltration, ultrafiltration and the like.

FIG. 1 is a cross-sectional view of the separation membrane and its enlarged view.

The separation membrane of the present embodiment is a separation membrane containing a hydrophilic polymer as a main component, and
The structure cycle of the phase having the hydrophilic polymer and the pores has a co-continuous structure of 0.001 μm to 10 μm,
The thickness of the separation membrane is 10 μm or more and 500 μm or less,
In the cross section in the thickness direction, the porosity of the region a at a depth of 1 to 4 μm from any one surface (A surface) is Ha, and the porosity of the region b at a depth of 1 to 4 μm from the other surface (B surface) And Hc, the following formula (1) and formula (2) are satisfied, where Hc is the porosity of the region c having a thickness of 3 μm where the depth from both surfaces is the same.
(1) 1.00 ≦ Ha / Hc ≦ 1.50
(2) 1.05 ≦ Hb / Hc ≦ 1.50
The separation membrane of the present invention may contain a liquid such as water therein to maintain its shape. However, in the following description, these liquids for retaining the shape are not considered as components of the separation membrane.

(Resin composition that constitutes separation membrane)
The separation membrane of the present invention can contain the components shown in the following (1) to (5).

(1) Hydrophilic Polymer It is important that the separation membrane of the present invention contains a hydrophilic polymer as a main component. The term "main component" as used herein refers to the component that is contained in the largest amount by weight among all the components of the resin composition that constitutes the separation membrane.

  In the present invention, the hydrophilic polymer refers to a polymer having a hydrophilic group as a constituent component of the polymer and having a contact angle with water of 60 ° or less with respect to the film of the polymer. Here, the hydrophilic group is a hydroxyl group, a carboxyl group, a carbonyl group, an amino group or an amide group.

  As specific examples of the hydrophilic polymer, polyester, polyamide, methyl polyacrylate, polyvinyl acetate, cellulose ester, polyester and the like can be used. Among these, at least one selected from the group consisting of polyester, polyamide and cellulose ester is preferable.

  Specific examples of polyamide include nylon 6, nylon 11 and the like.

  Specific examples of the cellulose ester include cellulose esters such as cellulose acetate, cellulose propionate and cellulose butyrate, and cellulose mixed esters such as cellulose acetate propionate and cellulose acetate butyrate.

  The weight average molecular weight (Mw) of the cellulose ester is preferably 50,000 to 250,000. When the Mw is 50,000 or more, the thermal decomposition of the cellulose ester at the time of melting at the time of manufacturing the separation membrane is suppressed, and the membrane strength of the separation membrane can reach a practical level. Since melt viscosity does not become high too much because Mw is 250,000 or less, stable melt film forming becomes possible.

  The Mw is more preferably 60,000 to 220,000, and still more preferably 80,000 to 200,000. The weight average molecular weight (Mw) is a value calculated by GPC measurement. The calculation method will be described in detail in an embodiment.

Each illustrated cellulose mixed ester has an acetyl group and other acyl groups (propionyl group, butyryl group, etc.). In the cellulose mixed ester contained in the separation membrane, the average degree of substitution of an acetyl group with another acyl group preferably satisfies the following formula.
1.0 ≦ (average degree of substitution of acetyl group + average degree of substitution of other acyl groups) ≦ 3.0
0.1 ≦ (average degree of substitution of acetyl group) ≦ 2.6
0.1 ≦ (average degree of substitution of other acyl groups) ≦ 2.6

  By satisfying the above equation, the permeation performance of the separation membrane and the good thermal fluidity when melting the resin composition constituting the separation membrane are realized. The average degree of substitution refers to the number of chemically bonded acyl groups (acetyl group + other acyl groups) among the three hydroxyl groups present per glucose unit of cellulose.

  Only one hydrophilic polymer may be contained, or two or more hydrophilic polymers may be contained.

  The content of the hydrophilic polymer in the resin composition constituting the separation membrane is preferably 70 to 100% by weight, and 80 to 100% by weight, based on 100% by weight of all the components of the resin composition constituting the separation membrane. % Is more preferable, and 90 to 100% by weight is particularly preferable.

  The hydrophilic polymer is preferably contained in an amount of 20% by weight or more and 80% by weight or less, based on 100% by weight of the components constituting the raw material for film formation.

  When the content is 20% by weight or more, the membrane strength of the separation membrane is good. When the content is 80% by weight or less, the thermoplasticity and permeability of the separation membrane become good. The content is more preferably 25% by weight or more, further preferably 30% by weight or more. The content is more preferably 70% by weight or less, still more preferably 60% by weight or less.

(2) Plasticizer of Hydrophilic Polymer The resin composition constituting the separation membrane of the present invention may contain a plasticizer of hydrophilic polymer.

  The plasticizer of the hydrophilic polymer is not particularly limited as long as it is a compound that thermoplasticizes the hydrophilic polymer. In addition to one type of plasticizer, two or more types of plasticizers may be used in combination.

  Specific examples of the plasticizer of the hydrophilic polymer include polyalkylene glycol compounds such as polyethylene glycol and polyethylene glycol fatty acid ester, glycerin compounds such as glycerin fatty acid ester and diglycerin fatty acid ester, citric acid ester compound, phosphoric acid ester Examples thereof include fatty acid ester-based compounds such as based compounds and adipates, caprolactone-based compounds, and derivatives thereof.

  Specific preferred examples of the polyalkylene glycol compound include polyethylene glycol, polypropylene glycol, and polybutylene glycol having a weight average molecular weight of 400 to 4,000.

  After forming the separation membrane, the plasticizer of the hydrophilic polymer may remain in the separation membrane or may be eluted from the separation membrane. In the case of elution, traces of plasticizer loss may sometimes become pores in the membrane, resulting in good permeation performance.

  The plasticizer of the hydrophilic polymer is preferably contained in an amount of 5% by weight or more and 40% by weight or less, based on 100% by weight of the components constituting the raw material for film formation.

  When the content is 5% by weight or more, the thermoplasticity of the hydrophilic polymer and the permeation performance of the separation membrane become good. By setting the content to 40% by weight or less, the membrane strength of the separation membrane becomes good. The content of the plasticizer of the hydrophilic polymer is more preferably 10 to 35% by weight, still more preferably 15 to 30% by weight.

(3) Antioxidant It is preferable that the resin composition which comprises the separation membrane of this invention contains antioxidant.

  As a specific example of an antioxidant, it is preferable to contain phosphorus antioxidant, and a pentaerythritol compound is more preferable. Specific examples of pentaerythritol compounds include bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite and the like. When the antioxidant is contained, the thermal decomposition at the time of melt film formation is suppressed, and as a result, the film strength can be improved and the coloring of the film can be prevented.

  The content of the antioxidant is preferably 0.005 to 0.500% by weight, based on 100% by weight of the components constituting the raw material for film formation.

(4) Structure Forming Agent The resin composition constituting the separation membrane of the present invention may contain a structure forming agent. In the present invention, the structure forming agent refers to a compound which is partially compatible with the mixture of the hydrophilic polymer and the plasticizer. Partial compatibility means that two or more substances are completely compatible under one condition but phase separate under another condition. The structure forming agent is a substance which is phase separated from the hydrophilic polymer when placed under specific conditions in the co-continuous structure forming process described later.

  The structure-forming agent in the present invention is preferably hydrophilic, and indicates a resin which is soluble in water or whose contact angle to water is smaller than that of the main component hydrophilic polymer.

  Specific examples of the structure forming agent include polyvinyl pyrrolidone (PVP), PVP / vinyl acetate copolymer, PVP-based copolymer such as PVP / methyl methacrylate copolymer, polyvinyl alcohol, polyester-based compound, etc. can give. These can be used alone or in combination.

  Since PVP becomes difficult to elute from the separation membrane when thermal crosslinking occurs, the weight average molecular weight is 20,000 from the viewpoint that intermolecular crosslinking is relatively difficult to progress and it is possible to elute even after crosslinking. It is preferable that it is the following. Moreover, it is also preferable to use the copolymer based on PVP described in the preceding paragraph in that thermal crosslinking is suppressed.

  The structure forming agent is eluted from the inside of the separation membrane after forming the separation membrane. By removing the structure-forming agent by elution, the trace of the structure-forming agent may sometimes become pores in the membrane, resulting in good permeability. In addition, although the said effect is acquired by removal of a structure formation agent, a structure formation agent may not be completely removed but may remain in a separation membrane.

  The content of the structure forming agent is preferably 20% by weight or more and 80% by weight or less, based on 100% by weight of the components constituting the raw material for film formation.

  When the content is 20% by weight or more, the permeation performance of the separation membrane becomes good. By setting the content to 80% by weight or less, the film strength becomes good. The content of the structure forming agent is more preferably 30% by weight or more, still more preferably 40% by weight. Further, the content of the structure forming agent is more preferably 75% by weight or less, still more preferably 70% by weight or less.

(5) Additive agent The resin composition which comprises the separation membrane of this invention may contain the additive except having described in (1)-(4) in the range which does not impair the effect of this invention.

  Specific examples of the additive include cellulose ether, polyacrylonitrile, polyolefin, polyvinyl compound, polycarbonate, poly (meth) acrylate, polysulfone, resin such as polyether sulfone, organic lubricant, crystal nucleating agent, organic particles, inorganic particles, terminal Blocking agents, chain extenders, UV absorbers, infrared absorbers, coloring inhibitors, matting agents, antibacterial agents, antistatic agents, deodorants, flame retardants, weathering agents, antistatic agents, antioxidants, ion exchange Agents, antifoam agents, color pigments, optical brighteners, dyes and the like.

(Film shape)
The shape of the separation membrane of the present invention is not particularly limited, but a hollow fiber-shaped separation membrane (hereinafter also referred to as a hollow fiber membrane) or a flat-shaped membrane (hereinafter also referred to as a flat membrane) is preferably employed. Among these, hollow fiber membranes are more preferable because they can be efficiently packed in a module and the effective membrane area per unit volume of the module can be increased. The hollow fiber membrane is a thread-like membrane having a hollow.

  The thickness of the separation membrane is preferably 10 μm or more and 500 μm or less from the viewpoint of achieving both permeability and membrane strength. The thickness of the separation membrane is more preferably 20 μm or more, still more preferably 30 μm or more, and particularly preferably 40 μm or more. The thickness of the separation membrane is more preferably 400 μm or less, still more preferably 300 μm or less, and particularly preferably 200 μm or less.

  In the case of the hollow fiber membrane, the outer diameter of the hollow fiber membrane is preferably 50 μm or more and 2500 μm or less from the viewpoint of achieving both the effective membrane area when filled in the module and the membrane strength. The outer diameter of the hollow fiber membrane is more preferably 100 μm or more, further preferably 200 μm or more, and particularly preferably 300 μm or more. The outer diameter of the hollow fiber membrane is more preferably 2000 μm or less, still more preferably 1500 μm or less, and particularly preferably 1000 μm or less.

  In the case of a hollow fiber membrane, the hollow ratio of the hollow fiber is preferably 15 to 70%, more preferably 20 to 65%, from the relationship between the pressure loss of the fluid flowing through the hollow portion and the buckling pressure. Preferably, it is 25 to 60%.

  The method for setting the outer diameter and the hollow ratio of the hollow fiber in the hollow fiber membrane to the above range is not particularly limited, but, for example, the shape of the discharge hole of the spinneret producing the hollow fiber or the draft ratio calculated by the winding speed / discharge speed. , Can be adjusted by changing as appropriate.

(Internal structure of membrane)
In the separation membrane of the present invention, it is important that the structural period of the phase having the hydrophilic polymer and the pores has a co-continuous structure of 0.001 μm to 10 μm. Here, the co-continuous structure means, for example, a phase and a pore having a hydrophilic polymer when a cross section obtained by applying stress to a separation membrane sufficiently cooled in liquid nitrogen and cutting it is observed by a scanning electron microscope (SEM) or the like. However, it says that a continuous structure is observed in the depth direction. In addition, the measuring method of a structure period is described in an Example. In the present invention, the width of the structural period may be simply referred to as the pore size.

  From the viewpoint of achieving both permeability and membrane strength, the structural period is preferably 0.005 μm or more, more preferably 0.010 μm or more, still more preferably 0.015 μm or more, and particularly preferably 0.020 μm or more. Similarly, the structural period is preferably 5.0 μm or less, more preferably 1.0 μm or less, still more preferably 0.5 μm or less, particularly preferably 0.3 μm or less or 0.2 μm or less, most preferably 0.1 μm or less .

  The method for setting the structural period to the above range is not particularly limited, but stretching may be performed under the conditions to be described later when the separation membrane is manufactured, and then heat treatment may be performed under the conditions to be described later.

(Porosity)
In the separation membrane of the present invention, referring to FIG. 1, in the cross section in the thickness direction of separation membrane 1, a region 1 to 4 μm deep from any one surface (surface A) (corresponding to symbol 2 in FIG. 1). a (corresponding to symbol 11 in FIG. 1) is Ha, and the other region (surface B) (corresponding to symbol 3 in FIG. 1) corresponds to a region b in a depth of 1 to 4 μm (symbol 12 in FIG. 1) Of H) and the depth from both surfaces is the same (that is, the distance 8 from the A-plane 2 and the distance 9 from the B-plane 3 are equal in FIG. 1) It is important that the following formulas (1) and (2) be satisfied, where Hc is the porosity of (corresponding to 13).
(1) 1.00 ≦ Ha / Hc ≦ 1.50
(2) 1.05 ≦ Hb / Hc ≦ 1.50

  From the viewpoint of achieving both permeability and membrane strength, Ha / Hc is preferably 1.05 or more, more preferably 1.10 or more, and still more preferably 1.15 or more. It is particularly preferable that it is 20 or more. Further, Ha / Hc is preferably 1.45 or less, more preferably 1.40 or less, still more preferably 1.35 or less, and particularly preferably 1.30 or less. Similarly, Hb / Hc is preferably 1.10 or more, more preferably 1.15 or more, still more preferably 1.20 or more, and particularly preferably 1.25 or more. . Further, Ha / Hc is preferably 1.45 or less, more preferably 1.40 or less, still more preferably 1.35 or less, and particularly preferably 1.30 or less.

  The method of setting Ha / Hc and Hb / Hc in the above range is not particularly limited, but stretching can be performed under the conditions described later during separation membrane production, and then heat treatment can be used under the conditions described later.

  In the separation membrane of the present invention, the average porosity calculated by the simple average of the porosity Ha, Hb, and Hc is preferably 20% or more and 80% or less. The average porosity is more preferably 25% or more, further preferably 30% or more, and particularly preferably 35% or more. Similarly, the average porosity is more preferably 75% or less, still more preferably 70% or less, and particularly preferably 65% or less.

  By setting the average porosity to 20% or more, the permeability becomes good, and by setting the average porosity to 80% or less, the film strength becomes good. Although the method to make an average porosity into the said range is not specifically limited, The method of making content of the structure formation agent in the whole component which comprises the raw material for film forming into the above-mentioned preferable range can be used.

  In addition, the measuring method of the porosity is described in an Example.

  By satisfying the structural period described above and the equations (1) and (2), the polymer phase and the pores have a bicontinuous structure having a structural period of a fixed size in the cross section in the thickness direction, and In the cross section in the film thickness direction, the porosity in the vicinity of at least one surface layer has a relationship such that the porosity in the central portion in the thickness direction is larger.

  In particular, the former co-continuous structure makes it possible to express high membrane strength. Moreover, it becomes possible to express high permeability and stability of membrane performance by the relationship of the porosity of the latter film thickness direction.

(Membrane permeation flux)
The separation membrane of the present invention preferably has a membrane permeation flux at 50 kPa and 25 ° C. of 0.1 m ³ / m ² / h or more and 10 m ³ / m ² / h or less. The membrane permeation flux is more preferably 0.3 m ³ / m ² / h or more, further preferably 0.5 m ³ / m ² / h or more. The measurement conditions of membrane permeation flux will be described in detail in Examples.

(Membrane strength)
The separation membrane of the present invention preferably has a tensile strength in the longitudinal direction of 30 MPa or more in order to develop the membrane strength against tensile in the longitudinal direction. The measurement conditions of tensile strength will be described in detail in Examples. The tensile strength is more preferably 50 MPa or more, still more preferably 70 MPa or more, and particularly preferably 90 MPa or more. The tensile strength is preferably high, but is preferably 300 MPa or less from the viewpoint of balance of elongation.

(Production method)
The method for producing the separation membrane of the present invention is
1. Melt-kneading step of obtaining a resin composition by melt-kneading a hydrophilic polymer of 20% to 80% by weight and a structure forming agent of 20% to 80% by weight. Film forming step of forming a film by discharging and cooling the resin composition from a die. Stretching step of stretching the film at a stretch ratio of 1.1 times to 5.0 times. A heat treatment step of heating the stretched film obtained in the stretching step at 50 ° C. or more and 300 ° C. or less; It has the elution process of eluting the said structure formation agent from the film | membrane obtained by the said heat processing process.

  Next, the method for producing the separation membrane of the present invention will be specifically described by way of example in which the separation membrane is a hollow fiber membrane, but the method is not limited thereto.

  In order to obtain the resin composition for forming a separation membrane of the present invention, a method of melt-kneading 20 wt% to 80 wt% of a hydrophilic polymer and 20 wt% to 80 wt% of a structure forming agent is used. Be If necessary, plasticizers, antioxidants and additives of the type and content described above can be contained in the hydrophilic polymer.

  The apparatus to be used is not particularly limited, and known mixers such as a kneader, roll mill, Banbury mixer, single screw or twin screw extruder can be used. Above all, the use of a twin-screw extruder is preferred from the viewpoint of improving the dispersibility of the structure forming agent and the plasticizer. From the viewpoint of being able to remove water and volatiles such as low molecular weight substances, use of a vented twin-screw extruder is more preferable.

  The obtained resin composition may be once pelletized and melted again to be used for melt film formation, or may be directly led to a die and used for melt film formation. When pelletizing once, it is preferable to dry the pellet and to use a resin composition having a water content of 200 ppm (by weight) or less.

  A hollow fiber membrane is formed by discharging the resin composition melted by the above method into air from a spinneret having a double annular nozzle in which a gas flow path is disposed at the center, and cooling by a cooling device. The draft ratio that can be calculated by the take-up speed / discharge speed is preferably 50 or more and 500 or less. The draft ratio is more preferably 400 or less, still more preferably 300 or less.

  The hollow fiber membrane thus formed may be taken up once and then taken out again to be used for drawing, or may be directly led to a drawing process for drawing. It is important to go through the stretching step not only in terms of improving the film strength by highly orientating the hydrophilic polymer, but also in terms of controlling the internal structure of the film formed by the subsequent heat treatment and the porosity within the above ranges. is there. Although the drawing method is not particularly limited, for example, the hollow fiber membrane before drawing may be heated to a temperature at which drawing is performed by being conveyed on a heating roll, and drawing may be performed using a circumferential speed difference between the rolls. The hollow fiber membrane before drawing may be conveyed in a dry heat oven to raise the temperature to the drawing temperature, and the drawing may be performed using the peripheral speed difference between the rolls. In addition, stretching may be performed in one stage, or may be performed in two or more stages.

  The preferable range of the temperature of the hollow fiber membrane in the drawing step is 40 to 180 ° C, more preferably 60 to 160 ° C, and still more preferably 80 to 140 ° C. The total draw ratio is preferably 1.2 times or more, more preferably 1.4 times or more, and still more preferably 1.6 times or more. Moreover, 5.0 times or less are preferable, as for the draw ratio of total, 4.5 times or less are more preferable, and 4.0 times or less are more preferable.

  Subsequently, the hollow fiber membrane (stretched membrane) is heat-treated by heating at 50 to 300 ° C. Through this heat treatment step, phase separation between the hydrophilic polymer and the structure forming agent is induced. The heat treatment may be carried by a method such as carrying on a heating roll, or by carrying it in a dry heat oven, or may be introduced into a dry heat oven in the form of a roll wound on a bobbin or paper tube. .

  As for heat processing temperature, 80-300 ° C is preferred, 100-250 ° C is more preferred, and 120-250 ° C is still more preferred. The heat treatment time is preferably 10 to 600 seconds, more preferably 20 to 480 seconds, and still more preferably 30 to 360 seconds.

  After passing through the step of eluting the structure forming agent by immersing the heat-treated hollow fiber membrane in water, an aqueous acid solution, an aqueous alkaline solution, an alcohol, or an aqueous alcohol solution, the separation membrane (hollow fiber membrane) of the present invention and Do. The present invention is a method of eluting a structure forming agent after inducing phase separation by heat treatment, and therefore, it is difficult to form a void exceeding 10 μm in the obtained separation membrane.

  The separation membrane thus obtained can be used as it is, but it is preferable to hydrophilize the surface of the membrane with, for example, an aqueous solution containing alcohol, an aqueous alkaline solution or the like before use.

  Thus, the separation membrane of the present invention containing a hydrophilic polymer as a main component can be produced.

(module)
The separation membrane of the present invention may be incorporated into the separation membrane module at the time of use. The separation membrane module includes, for example, a membrane bundle composed of a plurality of hollow fiber membranes, and a housing for housing the membrane bundle.

  Moreover, if it is a flat membrane, it will be fixed to a support body or an envelope-like membrane will be formed by sticking membranes together, and it will be modularized by mounting | wearing a water collection pipe etc. as needed.

  EXAMPLES The present invention will be more specifically described below with reference to examples, but the present invention is not limited thereby.

[Measurement and evaluation method]
Each characteristic value in the examples is obtained by the following method. In addition, in the following (3)-(7), it measured and evaluated in the state which vacuum-dried the separation membrane at 25 degreeC for 8 hours.

(1) Average degree of substitution of cellulose mixed ester The method of calculating the average degree of substitution of cellulose mixed ester in which an acetyl group and an acyl group are bonded to cellulose is as follows.
After 0.9 g of the cellulose mixed ester dried at 80 ° C. for 8 hours was weighed and dissolved by adding 35 ml of acetone and 15 ml of dimethyl sulfoxide, 50 ml of acetone was further added. While stirring, 30 ml of 0.5 N aqueous sodium hydroxide solution was added and saponified for 2 hours. After adding 50 ml of hot water and washing the side of the flask, it was titrated with 0.5 N sulfuric acid using phenolphthalein as an indicator. A blank test was conducted in the same manner as the sample. The supernatant of the solution after completion of the titration was diluted 100 times, and the composition of the organic acid was measured using an ion chromatograph. The degree of substitution was calculated from the measurement result and the result of acid composition analysis by ion chromatography according to the following equation.
TA = (B-A) x F / (1000 x W)
DSace = (162.14 × TA) / [{1- (Mwace− (16.00 + 1.01)) × TA} + {1- (Mwacy− (16.00 + 1.01)) × TA} × (Acy / Ace)]
DSacy = DSace × (Acy / Ace)
TA: Total organic acid content (ml)
A: Sample titer (ml)
B: Blank test titer (ml)
F: sulfuric acid titer W: sample weight (g)
DSace: Average degree of substitution of acetyl group DSacy: Average degree of substitution of other acyl groups Mwace: Molecular weight of acetic acid Mwacy: Molecular weight of other organic acid Acy / Ace: Molar of acetic acid (Ace) and other organic acid (Acy) Ratio 162.14: Molecular weight of repeating unit of cellulose 16.00: Atomic weight of oxygen 1.01: Atomic weight of hydrogen

(2) Weight average molecular weight (Mw) of cellulose ester
It was completely dissolved in tetrahydrofuran so that the concentration of cellulose ester was 0.15% by weight, and used as a sample for GPC measurement. Using this sample, under the following conditions, GPC measurement was performed with Waters 2690, and the weight average molecular weight (Mw) was determined by polystyrene conversion.
Column: Tosoh TSK gel GMHHR-H connected in a row Detector: Waters 2410 Differential Refractometer RI
Mobile phase solvent: tetrahydrofuran Flow rate: 1.0 ml / min Injection amount: 200 μl

(3) Structural period Measurement method 1
After freezing the separation membrane immersed in a 50% aqueous solution of glycerol for 1 hour with liquid nitrogen, it was cut by applying stress so that a cross section perpendicular to the longitudinal direction of the separation membrane and a thickness direction of the membrane were obtained. Under the present circumstances, when the longitudinal direction of a separation membrane is unknown, it shall cut in arbitrary directions. When cutting, use a razor or microtome, etc., as necessary. The separation membrane taken out of the cross section was vacuum dried at 25 ° C. for 8 hours, and the obtained cross section of the membrane was observed with a scanning electron microscope. At this time, the cross section of the film was observed with the center in the film thickness direction as the center of the microscopic field of view. The obtained scanning electron microscope image was subjected to Fourier transformation, and the presence or absence of the maximum peak when the wave number was plotted on the horizontal axis and the intensity on the vertical axis was confirmed. When the maximum peak exists, that is, when the plot result has the maximum value, the structural period λ (= 1 / q) is derived from the wave number q corresponding to the maximum value. At this time, the image size of the scanning electron microscope image was a square whose one side has a length of 10 times to 100 times the hole diameter. When the maximum value is indicated in the measurement method 1, the uniformity of the pore diameter is high, and higher membrane strength can be expressed, which is a preferable embodiment.
Measurement method 2
When the periodic structure is not measured by the above measurement method 1, the structural period is measured by the following method.
After freezing the separation membrane immersed in a 50% aqueous solution of glycerol for 1 hour with liquid nitrogen, it was cut by applying stress so that a cross section perpendicular to the longitudinal direction of the separation membrane and a thickness direction of the membrane were obtained. Under the present circumstances, when the longitudinal direction of a separation membrane is unknown, it shall cut in arbitrary directions. When cutting, use a razor or microtome, etc., as necessary. The separation membrane taken out of the cross section was vacuum dried at 25 ° C. for 8 hours, and the obtained cross section of the membrane was observed with a scanning electron microscope. At this time, the cross section of the film was observed with the center in the film thickness direction as the center of the microscopic field of view. In the obtained image, the diameters of the 20 pores were measured, and number average was made as the structure period. At this time, the image size of the scanning electron microscope image is a square whose one side has a length of 10 times to 100 times the hole diameter.

(4) Thickness of separation membrane (μm)
The cross section of the membrane produced in the above (3) was observed with an optical microscope and photographed, and the thickness (μm) of the separation membrane was calculated. In addition, the thickness of the separation membrane observed and calculated arbitrary ten places, and made it the average value.

(5) Porosity (Ha, Hb, Hc, average porosity) (%)
Regarding the cross section of the film prepared in (3), the region a at a depth of 1 to 4 μm from any one surface (A surface), the region b at a depth of 1 to 4 μm from the other surface (B surface), and both surfaces Region c having a thickness of 3 μm at which the depth from the same becomes the same was observed and photographed arbitrarily at five places with a scanning electron microscope. A transparent film or sheet was overlaid on the obtained photograph, and the portion corresponding to the void was filled with oil ink or the like. Next, an image analyzer is used to determine the ratio of the area corresponding to the void. The measurement was carried out at five locations where the measurement was taken, and by averaging, the porosity Ha (%), Hb (%), and Hc (%) of each region were determined.
The average porosity was calculated by simply averaging Ha, Hb and Hc.
At this time, the image size of the scanning electron microscope image is a square whose one side has a length of 10 times to 100 times the hole diameter.

(6) Outer diameter of hollow fiber membrane (μm)
The cross section of the membrane prepared in (3) was observed with an optical microscope and photographed to calculate the outer diameter (μm) of the hollow fiber membrane. In addition, the outer diameter of the hollow fiber membrane observed and calculated arbitrary ten places, and made it the average value.

(7) Tensile strength (MPa)
The tensile strength in the longitudinal direction of the separation membrane vacuum dried at 25 ° C. for 8 hours was measured using a tensile tester (Tensilon UCT-100 manufactured by Orientec Co., Ltd.) under an environment of temperature 20 ° C. and humidity 65%. . Specifically, measurement was performed under conditions of a sample length of 100 mm and a tensile speed of 100 mm / min, and a tensile strength (breaking strength) (MPa) was calculated from the tensile strength. The number of measurements was 5 and the average value was taken.

(8) Membrane permeation flux (m ³ / m ² / h)
When the separation membrane was a hollow fiber membrane, a small module having an effective length of 200 mm consisting of four hollow fiber membranes was produced. In this module, distilled water is fed for 30 minutes under conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa, and the amount of permeated water (m ³ ) obtained is measured, and unit time (h) and unit membrane area (m ²⁾ It converted into the numerical value per), and also pressure (50 kPa) was converted, and it was set as the permeation | transmission performance (unit = m < ³ > / m < ² > / h) of pure water.

(9) Stability of Membrane Performance Twenty small modules similar to (8) were produced, and membrane permeation flux was determined by the method described in (8). Standard deviations were calculated for the obtained 20 data. The standard deviation was used to evaluate based on the following criteria.
:: less than 0.02 ○: 0.02 or more and less than 0.05 △: 0.05 or more and less than 0.1 ×: 0.1 or more

[Hydrophilic Polymer (A)]
Cellulose ester (A1): Cellulose acetate propionate obtained by the following method: To 100 parts by weight of cellulose (Cotton Linter), 240 parts by weight of acetic acid and 67 parts by weight of propionic acid were added and mixed at 50 ° C for 30 minutes. After cooling the mixture to room temperature, 172 parts by weight of acetic anhydride and 168 parts by weight of propionic acid cooled in an ice bath are added as an esterification agent, 4 parts by weight of sulfuric acid is added as an esterification catalyst, and stirring is performed for 150 minutes. An esterification reaction was performed. In the esterification reaction, when it exceeded 40 ° C., it was cooled by a water bath.

  After the reaction, a mixed solution of 100 parts by weight of acetic acid and 33 parts by weight of water as a reaction terminator was added over 20 minutes to hydrolyze the excess anhydride. Thereafter, 333 parts by weight of acetic acid and 100 parts by weight of water were added, and the mixture was heated and stirred at 80 ° C. for 1 hour. After completion of the reaction, an aqueous solution containing 6 parts by weight of sodium carbonate was added, and the precipitated cellulose acetate propionate was separated by filtration, subsequently washed with water and then dried at 60 ° C. for 4 hours. The average degree of substitution of acetyl group and propionyl group of the obtained cellulose acetate propionate was 1.9 and 0.7, respectively, and the weight average molecular weight (Mw) was 178,000.

[Plasticizer of hydrophilic polymer (B)]
Plasticizer (B1): polyethylene glycol, weight average molecular weight 600

[Structure-forming agent (C)]
Structure-forming agent (C1): PVP / vinyl acetate copolymer (Kollidon VA 64 (BASF Japan Ltd.))
Structure-forming agent (C2): polyvinyl pyrrolidone (PVP K17)

[Antioxidant (D)]
Antioxidant (D1): bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite

[Production of separation membrane]
Example 1
45% by weight of hydrophilic polymer (A1), 24.9% by weight of plasticizer (B1), 30% by weight of structure-forming agent (C1) and 0.1% by weight of antioxidant (D1) in a twin-screw extruder The mixture was melt-kneaded at 220 ° C., homogenized and then pelletized to obtain a resin composition for melt spinning. The resin composition was vacuum dried at 80 ° C. for 8 hours.

  The dried resin composition is supplied to a twin-screw extruder, melted and kneaded at 220 ° C., and then introduced into a melt spinning pack at a spinning temperature of 220 ° C., and the die hole (2 The double circular tube type, with a discharge hole diameter of 8.3 mm, a slit width of 1.1 mm, was spun downward from the outer annular portion of a die having one hole. The spun hollow fiber was introduced into a cooling device, cooled by a cooling air at 25 ° C. and a wind speed of 1.5 m / sec, and wound by a winder so that the draft ratio was 60. The spun yarn was heated to 100 ° C. by passing it through a dry heat oven, and wound up with a draw ratio of 1.3 times using a peripheral speed difference between rolls. Subsequently, after heat treatment at 150 ° C. for 300 seconds, the separation membrane was immersed in a 50% aqueous ethanol solution for 12 hours to elute the plasticizer and the structure forming agent. Physical properties of the obtained separation membrane are shown in Table 1. In addition, the method as described in the above-mentioned measuring method 1 was used for the measurement of a structure period.

(Examples 2 to 13, Comparative Example 1)
A separation membrane was obtained in the same manner as in Example 1 except that the production conditions were as shown in Table 1, respectively. Physical properties of the obtained separation membrane are shown in Table 1. In addition, the measurement of a structure period used Example 2-10 and Example 13 used the method as described in the above-mentioned measuring method 1, and Example 11 and Example 12 used the method as described in the above-mentioned measuring method 2. .

From the results of Table 1, the separation membranes of Examples 1 to 13 have a membrane permeation flux of 0.1 m ³ / m ² / h or more, and a tensile strength of 30 MPa or more. And membrane strength was expressed. The separation membranes of Examples 1 to 10 and Example 13 had local maximum values in measurement method 1 of the structural cycle. This indicates that the uniformity of the pore size is high. The high uniformity of the pore diameter is considered to increase the strength of the separation membrane, and in fact, as shown in Table 1, the membranes of these Examples exhibited particularly high strength. The separation membranes of Examples 1 to 13 all had a co-continuous structure.
On the other hand, in the separation membrane of Comparative Example 1, both the membrane permeation flux and the stability of the membrane performance were insufficient.

  The present invention is a separation membrane mainly composed of a hydrophilic polymer, which is excellent in permeability, stability of membrane performance, and high membrane strength. The separation membrane of the present invention is a membrane for water treatment for producing industrial water, drinking water and the like from seawater, brackish water, sewage, drainage etc., medical membranes such as artificial kidney and plasma separation, foods and beverages such as fruit juice concentrate It can be used for industrial membranes, gas separation membranes for separating exhaust gas, carbon dioxide and the like, membranes for electronic industry such as fuel cell separators, and the like. The water treatment membrane can be preferably used as a microfiltration membrane, an ultrafiltration membrane, or the like.

  Although the invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application (Japanese Patent Application No. 2016-149351) filed on July 29, 2016, the contents of which are incorporated herein by reference.

1 separation film 2 A surface 3 B surface 8 distance from A surface 9 distance from B surface 11 region a
12 area b
13 area c

Claims (6)

A separation membrane comprising a hydrophilic polymer as a main component,
The structure cycle of the phase having the hydrophilic polymer and the pores has a co-continuous structure of 0.001 μm to 10 μm,
The thickness of the separation membrane is 10 μm or more and 500 μm or less,
In the cross section in the thickness direction, the void ratio of the region a at a depth of 1 to 4 μm from any one surface is Ha, and the void ratio of the region b at a depth of 1 to 4 μm from the other surface is Hb, the depth from both surfaces The separation membrane which satisfies the following formulas (1) and (2), where Hc is the porosity of the region c with a thickness of 3 μm where the same becomes the same.
(1) 1.00 ≦ Ha / Hc ≦ 1.50
(2) 1.05 ≦ Hb / Hc ≦ 1.50   The separation membrane according to claim 1, wherein an average porosity calculated by a simple average of the porosity Ha, the porosity Hb and the porosity Hc is 20% or more and 80% or less.   The separation membrane according to claim 1 or 2, wherein the hydrophilic polymer is at least one selected from the group consisting of polyester, polyamide and cellulose ester.   The separation membrane according to any one of claims 1 to 3, wherein the separation membrane is in the form of a hollow fiber.   The separation membrane according to claim 4, wherein the outer diameter of the hollow fiber is 50 μm or more and 2500 μm or less. A method for producing a separation membrane comprising a hydrophilic polymer as a main component, wherein at least the following steps 1 to 5 are carried out.
1. Melt-kneading step of obtaining a resin composition by melt-kneading a hydrophilic polymer of 20% to 80% by weight and a structure forming agent of 20% to 80% by weight. Film forming step of forming a film by discharging and cooling the resin composition from a die. Stretching step of stretching the film at a stretch ratio of 1.1 times to 5.0 times. A heat treatment step of heating the stretched film obtained in the stretching step at 50 ° C. or more and 300 ° C. or less; Elution process for eluting the structure forming agent from the film obtained in the heat treatment process

Images