CN114828992A - Separation membrane and method for producing same - Google Patents
Separation membrane and method for producing same Download PDFInfo
- Publication number
- CN114828992A CN114828992A CN202080089607.5A CN202080089607A CN114828992A CN 114828992 A CN114828992 A CN 114828992A CN 202080089607 A CN202080089607 A CN 202080089607A CN 114828992 A CN114828992 A CN 114828992A
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- China
- Prior art keywords
- separation membrane
- pores
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- mass
- cellulose ester
- Prior art date
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- Granted
Links
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- HEMHJVSKTPXQMS-UHFFFAOYSA-M sodium hydroxide Inorganic materials [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 2
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- SSADPHQCUURWSW-UHFFFAOYSA-N 3,9-bis(2,6-ditert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane Chemical compound CC(C)(C)C1=CC(C)=CC(C(C)(C)C)=C1OP1OCC2(COP(OC=3C(=CC(C)=CC=3C(C)(C)C)C(C)(C)C)OC2)CO1 SSADPHQCUURWSW-UHFFFAOYSA-N 0.000 description 1
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- FDBMBOYIVUGUSL-UHFFFAOYSA-N OP(O)OP(O)O.C(C)(C)(C)C1=C(C(=CC(=C1)C)C(C)(C)C)C(O)(C(CO)(CO)CO)C1=C(C=C(C=C1C(C)(C)C)C)C(C)(C)C Chemical compound OP(O)OP(O)O.C(C)(C)(C)C1=C(C(=CC(=C1)C)C(C)(C)C)C(O)(C(CO)(CO)CO)C1=C(C=C(C=C1C(C)(C)C)C)C(C)(C)C FDBMBOYIVUGUSL-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
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- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
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- D—TEXTILES; PAPER
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- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/15—Use of additives
- B01D2323/18—Pore-control agents or pore formers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/02—Details relating to pores or porosity of the membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/02—Details relating to pores or porosity of the membranes
- B01D2325/0283—Pore size
- B01D2325/02833—Pore size more than 10 and up to 100 nm
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/02—Details relating to pores or porosity of the membranes
- B01D2325/0283—Pore size
- B01D2325/02834—Pore size more than 0.1 and up to 1 µm
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/04—Characteristic thickness
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/20—Specific permeability or cut-off range
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- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The present invention provides a separation membrane comprising a cellulose ester, wherein the separation membrane has a plurality of pores in a cross section of the membrane parallel to a longitudinal direction and a thickness direction, an average depth D of the plurality of pores is 0.7 to 20 [ mu ] m, an average length L of the plurality of pores is 3 [ mu ] m or more, and an average value (L/D) of a ratio of a length L to a depth D of each pore a The value of (1) is 2 to 40.
Description
Technical Field
The present invention relates to a separation membrane and a method for producing the same.
Background
In recent years, separation membranes have been used in a wide variety of fields, such as membranes for water treatment such as water purification and drainage, membranes for medical treatment such as blood purification, membranes for food industry, separators for batteries, charged membranes, and electrolyte membranes for fuel cells.
Most separation membranes use polymers as raw materials. Among them, cellulose resins including cellulose esters are widely used as materials for separation membranes including membranes for water treatment because of their hydrophilic permeability and chlorine resistance which strongly resists chlorine-based fungicides.
For example, patent document 1 discloses a technique of ejecting a film-forming dope containing cellulose triacetate into a coagulating liquid containing a solvent, a non-solvent and water to perform phase separation, thereby obtaining a hollow-fiber separation membrane.
Patent document 2 discloses a hollow fiber-shaped separation membrane in which hydroxyalkyl cellulose is solidified in a fine particle state on the surface.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2011-235204
Patent document 2: japanese laid-open patent publication (JP 2015-157278)
Non-patent document
Non-patent document 1: ind, eng, chem, res, 2011,50, 3798-.
Disclosure of Invention
Problems to be solved by the invention
However, since the size of pores is reduced in order to improve the separation performance of a conventional separation membrane using cellulose ester as a raw material, it is necessary to reduce the thickness of a thin film in order to improve the permeation performance, and as a result, there is a problem that defects are likely to occur in the separation membrane.
Accordingly, an object of the present invention is to provide a separation membrane having both high separation performance and permeation performance, and a method for producing the same.
Means for solving the problems
As a result of intensive studies to solve the above problems, the present inventors have found that a separation membrane containing a cellulose ester has pores satisfying specific conditions, and can improve permeability while maintaining high separation performance, and have completed the present invention.
That is, the present invention relates to the following [1] to [10 ].
[1] A separation membrane comprising a cellulose ester,
the separation membrane has a plurality of pores in a cross section of the membrane parallel to the longitudinal direction and the thickness direction of the membrane,
the average depth D of the plurality of pores is 0.7 to 20 μm,
the average length L of the plurality of pores is 3 μm or more, and
average value of the ratio of length l to depth d of each pore (l/d) a The value of (1) is 2 to 40.
[2] The separation membrane according to the above [1], wherein an occupancy rate of the plurality of pores in the cross section is 15 to 55%.
[3] The separation membrane according to the above [1] or [2], wherein the average thickness of the wall portion in the cross section is 0.7 to 5.0 μm.
[4] The separation membrane according to any one of the above [1] to [3], wherein in at least one surface, an average pore diameter of the surface pores is 0.050 to 0.500. mu.m.
[5]According to the above [1]]~[4]The separation membrane according to any one of the above, wherein in at least one surface, the average minor axis X of the surface pores is 0.030 to 0.250. mu.m, the average major axis Y of the surface pores is 0.060 to 0.450. mu.m, and the average value (Y/X) of the ratio of the major axis to the minor axis a The value of (A) is 1.00 to 1.50.
[6] The separation membrane according to any one of the above [1] to [5], wherein a longitudinal direction of the plurality of pores is along a longitudinal direction of the separation membrane.
[7] The separation membrane according to any one of the above [1] to [6], wherein the cellulose ester contains cellulose acetate propionate and/or cellulose acetate butyrate.
[8] The separation membrane according to any one of the above [1] to [7], which has a hollow filament shape.
[9] A method for producing a separation membrane, comprising:
(1) a preparation step of melting and mixing a mixture containing 10-80 mass% of cellulose ester, 10-80 mass% of a structure forming agent and 2-20 mass% of a pore forming agent to obtain a resin composition;
(2) a molding step of ejecting the resin composition from a nozzle using a filter having a pore diameter of 40 to 200 μm to obtain a resin molded article at a draft ratio of 30 to 200; and
(3) an impregnation step of impregnating the resin molded article at a distance D of solubility parameter with respect to cellulose ester S 10 to 25 parts of solvent.
[10] The method of producing a separation membrane according to the above [9], wherein the temperature of the resin molded product in the dipping step is 50 to 80 ℃.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, a separation membrane having both high separation performance and high permeation performance and a method for producing the same can be provided.
Drawings
Fig. 1 (a) is a drawing schematically showing a section Z and the internal structure of a separation membrane, (b) is a side view of (a), and (c) is a top view of (a).
Fig. 2 is an example of an image of the cross section Z taken by SEM.
Fig. 3 is an image obtained by subjecting the image of fig. 2 to noise removal, binarization, and pore extraction.
Fig. 4 is an image of further extracting the outline of the pore from the image of fig. 3.
Detailed Description
Separation according to the inventionThe film contains cellulose ester, and is characterized in that the film has a plurality of pores in a cross section parallel to the longitudinal direction and the film thickness direction, the average depth D of the pores is 0.7-20 μm, the average length L of the pores is more than 3 μm, and the average value (L/D) of the ratio of the length L to the depth D of each pore a The value of (1) is 2 to 40. In the present specification, the mass-based ratio (percentage, part, etc.) is the same as the weight-based ratio (percentage, part, etc.).
(resin composition for constituting separation Membrane)
The resin composition constituting the separation membrane of the present invention contains the cellulose ester shown in the following (1). In addition to (1), the following components (2) to (6) may be contained.
(1) Cellulose esters
The separation membrane of the present invention needs to contain a cellulose ester. In order to further enhance the effect of the present invention, the separation membrane of the present invention preferably contains cellulose ester as a main component. The main component referred to herein means a component that is contained most by mass in all components of the resin composition constituting the separation membrane.
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. Among these, from the viewpoint of processability of the resin molded product and film strength of the obtained separation film, cellulose mixed ester is preferable, cellulose acetate propionate and/or cellulose acetate butyrate are more preferable, and cellulose acetate propionate is even more preferable. The cellulose acetate propionate herein refers to a cellulose ester having an average degree of substitution of acetyl group and propionyl group of 0.1 or more, respectively.
The weight average molecular weight (Mw) of the cellulose ester is preferably 5 to 25 ten thousand. The weight average molecular weight (Mw) is 5 ten thousand or more, whereby thermal decomposition of cellulose ester at the time of melting is suppressed at the time of production of the separation membrane, and the membrane strength of the separation membrane can easily be brought to a practical level. Since the weight average molecular weight (Mw) is 25 ten thousand or less, the melt viscosity is not excessively high, and thus stable melt film formation can be performed. The weight average molecular weight (Mw) is a value calculated by GPC (gel permeation chromatography) measurement. The method of calculating the same is explained in detail in examples.
Each of the cellulose mixed esters exemplified has an acetyl group and another acyl group (propionyl group, butyryl group, etc.). In the cellulose mixed ester contained in the separation membrane, the average degree of substitution of acetyl groups and other acyl groups preferably satisfies the following formula.
1.0. ltoreq. acetyl group average degree of substitution + other acyl group average degree of substitution 3.0
0.1-2.6% (average degree of substitution of acetyl group)
0.1-2.6 (average degree of substitution of other acyl groups).
By satisfying the above formula, the permeability of the separation membrane and the thermal fluidity when the resin composition constituting the separation membrane is melted are improved. The average degree of substitution is the number of chemically bonded acyl groups (acetyl groups + other acyl groups) among 3 hydroxyl groups present in each glucose unit of cellulose.
The separation membrane may contain only 1 kind of cellulose ester, or may contain 2 or more kinds of cellulose esters.
The content of the cellulose ester in the separation membrane is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and still more preferably 90 to 100% by mass, based on 100% by mass of the total components of the separation membrane. When the content of the cellulose ester in the separation membrane is 70% by mass or more, the membrane strength of the separation membrane becomes sufficient.
The content of the cellulose ester in the raw material for producing the separation membrane is preferably 10 to 80% by mass, based on 100% by mass of the total components constituting the raw material. When the content is 10% by mass or more, the membrane strength of the separation membrane becomes good. On the other hand, when the content is 80% by mass or less, the separation membrane has good thermoplasticity and permeability. The content is more preferably 15% by mass or more, and still more preferably 20% by mass or more. The content is more preferably 70% by mass or less, still more preferably 60% by mass or less, and particularly preferably 45% by mass or less.
(2) Plasticizer for cellulose esters
The resin composition constituting the separation membrane of the present invention may contain a plasticizer of cellulose ester.
The plasticizer for the cellulose ester is not particularly limited as long as it is a compound that thermally plasticizes the cellulose ester. In addition, only 1 kind of plasticizer may be used, or 2 or more kinds of plasticizers may be used in combination.
Examples of the plasticizer for cellulose ester include polyalkylene glycol compounds such as polyethylene glycol and polyethylene glycol fatty acid esters, glycerin compounds such as glycerin fatty acid esters and diglycerol fatty acid esters, citric acid ester compounds, fatty acid ester compounds such as phosphoric acid ester compounds and adipic acid esters, caprolactone compounds, and derivatives thereof.
Examples of the polyalkylene glycol-based compound include polyethylene glycol, polypropylene glycol, and polybutylene glycol having a weight average molecular weight (Mw) of 400 to 4,000.
The plasticizer of the cellulose ester may remain in the separation membrane after the formation of the separation membrane, or may be eluted from the separation membrane. The content of the plasticizer in the cellulose ester is preferably 5 to 40% by mass, based on 100% by mass of the total components constituting the raw material.
When the content is 5% by mass or more, the cellulose ester has good thermoplasticity. On the other hand, when the content is 40% by mass or less, the membrane strength of the separation membrane becomes good. The content of the plasticizer in the cellulose ester is more preferably 5 to 35% by mass, and still more preferably 5 to 30% by mass.
(3) Antioxidant agent
The resin composition constituting the separation membrane of the present invention preferably contains an antioxidant. The resin composition containing the antioxidant suppresses thermal decomposition of the polymer when the polymer is melted during production of the separation membrane, and as a result, the separation membrane obtained has improved membrane strength and suppresses coloration of the separation membrane.
The antioxidant is preferably a phosphorus antioxidant, and more preferably a pentaerythritol compound. Examples of the pentaerythritol-based compound include bis (2, 6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite and the like.
The content of the antioxidant is preferably 0.005 to 0.500% by mass, based on 100% by mass of the total components constituting the raw material. By having the content of the antioxidant in the above range, a uniform resin composition can be obtained in the formulation step.
(4) Structure forming agent
The resin composition constituting the separation membrane of the present invention may contain a structure-forming agent.
The structure-forming agent in the present invention is not particularly limited as long as it is partially compatible with the cellulose ester or the mixture of the cellulose ester and the plasticizer thereof and is capable of being eluted or decomposed by a solvent that does not dissolve the cellulose ester. The weight-average molecular weight of the structure-forming agent is appropriately controlled from L, D (l/d) a From the viewpoint of the value of (b), it is preferably 1000 or more.
Partially compatible means that more than 2 substances are completely compatible under one condition, but phase separate under another condition. The structure-forming agent is a substance that is brought into contact with a solvent satisfying specific conditions in an impregnation step described later, thereby causing phase separation from the cellulose ester. Specific conditions are as described below.
The structure-forming agent in the present invention is preferably a hydrophilic compound from the viewpoint of being easily eluted. Here, the hydrophilic compound means a compound that dissolves in water or has a smaller contact angle with water than the cellulose ester contained in the separation membrane. Among hydrophilic compounds, compounds that dissolve in water are particularly preferred from the viewpoint of being easily eluted.
Examples of the structure-forming agent include copolymers based on PVP, such as polyvinylpyrrolidone (hereinafter referred to as "PVP"), PVP/vinyl acetate copolymers, and PVP/methyl methacrylate copolymers, polyvinyl alcohol, and polyester compounds.
When PVP is used as a structure-forming agent, the PVP is preferably 2 ten thousand or less in weight average molecular weight (Mw) because thermal crosslinking is difficult to elute from the separation membrane, and thus intermolecular crosslinking is relatively difficult to progress and elution is possible even if crosslinked. In addition, the use of the above-mentioned PVP-based copolymer is also preferable in terms of suppression of thermal crosslinking.
In the steps after the impregnation step described later, at least a part of the structure forming agent is eluted, and the trace of the detachment (elution) of the structure forming agent becomes pores in the film, and as a result, the permeability is improved.
The content of the structure-forming agent is preferably 10 to 80% by mass, based on 100% by mass of the total of the components constituting the raw material.
The content is 10% by mass or more, whereby the permeability of the separation membrane becomes good. On the other hand, the content is 80 mass% or less, whereby the film strength becomes good. The content of the structure-forming agent is more preferably 20% by mass or more, and still more preferably 25% by mass or more. The content of the structure-forming agent is more preferably 75% by mass or less, and still more preferably 70% by mass or less.
(5) Pore forming agent
The resin composition constituting the separation membrane of the present invention may contain a pore former. By void formers are meant herein compounds that are incompatible with cellulose esters and are plasticized or melted by heat. By dissolving out the pore former incompatible with the cellulose ester, pores are formed at the site where the pore former is present. Further, by plasticizing or melting the pore forming agent with heat, the average value (l/d) of the ratio of the length l to the depth d of each pore formed can be increased a The value of (c).
Examples of the pore-forming agent include phthalate compounds, trimellitate compounds, polyalkylene glycol compounds such as polyethylene glycol, polypropylene glycol, and polybutylene glycol, and derivatives of these compounds. The weight average molecular weight (Mw) of these compounds is preferably 10 to 100 ten thousand. When heated, the composition shows a moderate viscosity, and L, D (l/d) described later can be easily controlled a Accordingly, the weight average molecular weight (Mw) of the pore former is preferably 10 to 100 ten thousand, more preferably 10 to 50 ten thousand, and particularly preferably 10 to 30 ten thousand.
The content of the pore former is preferably 2 to 20% by mass, based on 100% by mass of the total components constituting the raw material. The content is 2% by mass or more, whereby the permeability of the separation membrane becomes good. On the other hand, the content is 20% by mass or less, whereby the separation performance becomes good. The content of the pore former is more preferably 3% by mass or more, still more preferably 5% by mass or more, and particularly preferably 10% by mass or more. The content is more preferably 18% by mass or less, and still more preferably 15% by mass or less.
(6) Additive agent
The resin composition constituting the separation membrane of the present invention may contain additives other than those described in (2) to (5) within a range not impairing the effects of the present invention.
Examples of the additive include resins such as cellulose ether, polyacrylonitrile, polyolefin, polyvinyl compound, polycarbonate, poly (meth) acrylate, polysulfone, and polyethersulfone, organic lubricants, crystal nucleating agents, organic particles, inorganic particles, end-capping agents, chain extenders, ultraviolet absorbers, infrared absorbers, coloring inhibitors, matting agents, antibacterial agents, antistatic agents, deodorizing agents, flame retardants, weather resistant agents, antistatic agents, antioxidants, ion exchangers, defoaming agents, coloring pigments, fluorescent whitening agents, and dyes.
(shape of separation Membrane)
The shape of the separation membrane of the present invention is not particularly limited, and a hollow fiber-shaped separation membrane (hereinafter referred to as "hollow fiber membrane") or a flat membrane (hereinafter referred to as "flat membrane") is preferably used. Among these, the hollow fiber membranes are more preferable because they can be packed in the module with high efficiency and the effective membrane area per unit volume of the module can be increased.
The thickness of the separation membrane is preferably 10 to 500 μm from the viewpoint of satisfying both the permeability and the membrane strength. The thickness is more preferably 30 μm or more, and still more preferably 50 μm or more. The thickness is more preferably 400 μm or less, and still more preferably 300 μm or less.
In the case of the hollow fiber membrane, the outer diameter of the hollow fiber membrane is preferably 50 to 2500 μm from the viewpoint of satisfying both the effective membrane area and the membrane strength when packed in a module. The outer shape 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 shape 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% in terms of the relationship between the pressure loss and buckling pressure of the fluid flowing through the hollow portion. The hollow ratio is more preferably 20% or more, and still more preferably 25% or more. The hollow ratio is more preferably 65% or less, and still more preferably 60% or less.
The method of setting the outer diameter and the hollow ratio of the hollow fiber in the hollow fiber membrane to the above ranges is not particularly limited, and may be adjusted by appropriately changing the shape of the discharge hole of the spinning nozzle for producing the hollow fiber or the draft ratio which can be calculated from the winding speed and the discharge speed, for example.
(Cross-sectional Structure of separation Membrane)
The separation membrane of the present invention has an average value (L/D) of an average depth D, an average length L and a ratio L/D of the depth D to the length L of each pore a Up to a specific range of a plurality of pores. The depth and length of the pores are values measured in a cross section (hereinafter referred to as "cross section Z") of the separation membrane to be measured, the cross section being parallel to the longitudinal direction and the film thickness direction. Here, the longitudinal direction of the membrane means a direction parallel to the central axis in the hollow fiber membrane, and the mechanical direction in the production in the flat membrane. Fig. 1 (a) is a drawing schematically showing a cross section Z and an internal structure of a separation membrane in the case where the separation membrane has a hollow fiber shape. Fig. 1 (b) is a side view of (a), and (c) is a top view of (a). In fig. 1, C denotes a central axis, and the central axis C is parallel to the longitudinal direction of the film. In fig. 1 (c), the double-headed arrows indicate the film thickness direction of the hollow fiber membranes, and the broken lines indicate the direction parallel to the film thickness direction.
Here, the term "pore" means that the area of the cross section Z is 1 μm when observed at a magnification of 2,000 times using a scanning electron microscope (hereinafter referred to as "SEM") 2 The above concave portion. The detailed observation method is described in (7) of example for the measurement of a plurality of pores and wall portions. The "concave portion" referred to herein is a dark portion in an image observed by SEM, and the contour of the image captured by SEM can be extracted by binarizing the image with image analysis software (binarization by Huang).
Specifically, first, an image 8 bit taken by SEM is converted into a noise removal image using imageJ as image analysis software, and after removing noise (Despeckle in imageJ) by replacing the central value of 3 × 3 pixels in the vicinity of the pixel 10 times for all pixels, the binarization of Huang is performed. Then, the image obtained is processed as mask display with Size set to 0-Infinity and circulation set to 0-1 in the Analyze Particles command of ImageJ, whereby an image of the extracted recessed portion can be obtained. Based on the image obtained in this manner, the contour of the concave portion can be extracted. Specifically, in the Analyze partitions command of ImageJ, the outline of the recess can be extracted by processing as a rule Outlines display with Size set to 0-definition and circulation set to 0-1.
Further, the extraction of pores can be performed by including 1 μm in the extraction of the concave portion described above 2 The lower limit of Size is set in the above-described manner of the concave portion. For example, 1 μm 2 =100 pixels 2 By setting the lower limit to 100 pixels in the image of (2) 2 The pores can be extracted. In the image obtained in this manner, the contour of the void can be extracted by the same processing as the extraction of the contour of the concave portion described above. In the present application, the contour is sometimes referred to as an outer edge.
Fig. 2 shows an example of an image captured by SEM, fig. 3 shows an image obtained by performing noise removal, binarization, and pore extraction on the image of fig. 2, and fig. 4 shows an image obtained by extracting the outline of a pore from the image of fig. 3.
When the cross section Z is observed at a magnification of 5,000 times using an SEM, and the ratio of the sum of the areas of all the recesses to the total observation range is referred to as "recess area ratio", the recess area ratio of the separation membrane of the present invention is preferably 50 to 85%, more preferably 60 to 80%, in order to further improve the permeation flux and the separation performance. The concave portion is not limited to a1 μm area 2 The area of the above recesses, i.e., pores, is less than 1 μm 2 The concave portions, i.e., the pores, are also targeted. The concave portion here can extract the contour of the image captured by SEM by performing noise removal and binarization (binarization by Huang) using image analysis software such as ImageJ, as in the above-described case.
The "depth d of the pores" is the maximum length in the depth direction of the pores to be measured when the cross section Z is observed at a magnification of 2,000 times using an SEM, and the film thickness direction of the separation membrane is referred to as the depth direction. The "length l of the pore" refers to the length of the longest straight line among straight lines that can directly connect two points on the outer edge of the pore to be measured when the cross section Z is observed at a magnification of 2,000 times using the same SEM. Here, the straight line capable of directly connecting two points on the outer edge means that the straight line connecting two points on the outer edge does not pass through the straight line on the other outer edge. Average value of the ratio l/d of the length l to the depth d of each pore (l/d) a The value of l/d was obtained for each of 30 randomly selected cells, and the arithmetic mean value was obtained.
The average depth D of the plurality of pores is a value calculated as an arithmetic average value of the depths of 30 pores randomly selected when the cross section Z is observed at a magnification of 2,000 times using an SEM. The average length L of the plurality of pores is a value calculated as an arithmetic average value of lengths of 30 pores randomly selected when the cross section Z is observed at a magnification of 2,000 times using the same SEM.
Average value of the ratio l/d of the length l to the depth d of each pore (l/d) a The value of (b) is required to be 2 to 40. (l/d) a Is within this range, it is presumed that the separation membrane exhibits excellent permeation performance and separation performance because pores are moderately dispersed while the substantial thickness of the separation membrane is reduced. (l/d) a The value of (b) is preferably 3 to 20, more preferably 4 to 20, and further preferably 8 to 20. Among them, the use of 4 to 20 can achieve both particularly high permeability and high separation performance, and the use of 8 to 20 can achieve both very high permeability and high separation performance.
The average depth D of the plurality of pores is required to be 0.7 to 20 μm in order to reduce the substantial thickness of the separation membrane while appropriately dispersing the pores. The average depth D of the plurality of pores is preferably 0.8 μm or more, more preferably 1.0 μm or more. The average depth D of the plurality of pores is preferably 5.0 μm or less, and more preferably 2.0 μm or less.
The average length L of the plurality of pores needs to be 3 μm or more in order to disperse the pores appropriately. The average length L of the plurality of pores is preferably 4 μm or more, more preferably 5 μm or more, and still more preferably 10 μm or more. The average length L of the plurality of pores is preferably 50 μm or less, and more preferably 30 μm or less.
The length direction of the plurality of pores is preferably along the length direction of the separation membrane. The longitudinal directions of the plurality of pores are approximately parallel, and even if the separation membrane is bent in the longitudinal direction of the plurality of pores, stress is easily dispersed, and the membrane strength of the separation membrane becomes high. When the angle formed by the direction of the length l of each of the 30 randomly selected pores and the longitudinal direction of the membrane was calculated by observing the cross section Z at a magnification of 2,000 times using an SEM and the arithmetic average value thereof (hereinafter, sometimes referred to as "angle in the longitudinal direction of the plurality of pores") was 20 ° or less, it could be determined that the longitudinal direction of the plurality of pores was along the longitudinal direction of the separation membrane. The angle in the longitudinal direction of the plurality of pores is preferably within 15 °, more preferably within 10 °.
The occupancy rate of the plurality of pores in the cross section parallel to the longitudinal direction and the film thickness direction of the separation membrane of the present invention is preferably 15 to 55%, more preferably 18 to 50%, even more preferably 20 to 50%, particularly preferably 30 to 50%, and most preferably 40 to 50%, in order to appropriately disperse the pores while further suppressing the substantial thickness of the separation membrane. The term "occupancy of a plurality of pores" as used herein means that the sum S of the areas of all pores when the cross section Z is observed at a magnification of 2,000 times using an SEM 1 Area S of the whole observation range 0 The ratio of (A) to (B).
The average thickness of the wall portion in the cross section Z of the separation membrane is preferably 0.7 to 5.0 μm, more preferably 1.0 to 4.0 μm, and still more preferably 1.0 to 3.0 μm, in order to further suppress the substantial thickness of the separation membrane and to appropriately disperse pores to obtain good separation performance. Among them, by setting the thickness to 1.0 to 3.0 μm, it is possible to achieve both of particularly excellent permeability and separation performance. Here, the "wall portion" of the hollow fiber membrane refers to a portion other than the pores when the cross section Z is observed at a magnification of 2,000 times using an SEM (fig. 1). The term "average thickness of the wall portion" means an average value of the lengths of the wall portions on the straight lines passing through the center of the observed image in the direction perpendicular to the longitudinal direction of the separation membrane in the above observation, and further, when the straight lines parallel to each other at an interval of 20 μm are drawn on both adjacent sides of the observed image.
(shape of surface pore)
In order to further improve the separation performance and water permeability of the separation membrane of the present invention, the average pore diameter of the surface pores in at least one surface is preferably 0.050 to 0.500. mu.m. The average pore diameter of the surface pores is more preferably 0.080 μm or more, still more preferably 0.090 μm or more, particularly preferably 0.095 μm or more, and most preferably 0.100 μm or more. The average pore diameter of the surface pores is more preferably 0.450 μm or less, and still more preferably 0.400 μm or less. Here, the surface pores refer to recesses in an image of the surface of the separation membrane taken at 10,000 times using an SEM. The "concave portion" referred to herein is a dark portion in an image observed by SEM, and the contour of the image captured by SEM can be extracted by performing noise removal and binarization (binarization by Huang) on the image using image analysis software such as ImageJ. The specific extraction method of the contour of the concave portion is as described above. The detailed observation method is described in the shape of the surface pores in example (3). The average pore diameter of the surface pores is sometimes referred to as the surface pore diameter.
The separation membrane of the present invention has, in at least one surface, an average minor axis X, an average major axis Y, and an average value (Y/X) of the ratio of the major axis to the minor axis of the surface pores a The value of (b) is preferably in a specific range. The average minor axis X is an arithmetic average of minor axes X when each surface pore is regarded as an ellipse. The average major axis Y is an arithmetic average of major axes when each surface pore is regarded as an ellipse. Mean value (y/x) a The term "average" means the arithmetic mean of the values of the minor axis x divided by the major axis y of each surface pore. Average minor axis X, average major axis Y, and average of ratio of major axis to minor axis (Y/X) of surface pores a The value of (b) is determined by analyzing an image of the surface of the separation membrane, which is taken at a magnification of 10,000 times by using an SEM, by using image analysis software such as ImageJ. Specifically, in Set Measurements of ImageJ, upon selection of Fit Ellipse, for a well extracted in the same manner as described above,execute the Analyze partitions command of ImageJ. In this way, the short diameter X and the long diameter Y of each surface hole are calculated, and therefore the average short diameter X and the average long diameter Y can be obtained by performing arithmetic averaging of the short diameter X and the long diameter Y. Further, by obtaining y/x for each surface hole and performing arithmetic mean, the average value (y/x) of the ratio of the major axis to the minor axis can be obtained a 。
The average minor axis X of the surface pores is preferably 0.030 to 0.250. mu.m, in order to further improve the separation performance and the water permeability. More preferably 0.040 to 0.160. mu.m, still more preferably 0.045 to 0.160. mu.m.
The average major axis Y of the surface pores is preferably 0.060 to 0.450. mu.m, more preferably 0.070 to 0.240. mu.m, still more preferably 0.075 to 0.240. mu.m, and particularly preferably 0.085 to 0.240. mu.m, for further improving the separation performance and the water permeability.
The average value (y/x) of the ratio of the major axis to the minor axis of the surface hole a The value of (b) is preferably 1.00 to 1.50, more preferably 1.00 to 1.40, further preferably 1.00 to 1.35, and particularly preferably 1.30 to 1.35, in order to further improve the separation performance and the water permeability.
(Membrane permeation flux)
The separation membrane of the present invention preferably has a membrane permeation flux of 0.10 to 20m at 25 ℃ under 50kPa 3 /m 2 A, more preferably 0.25 to 15m 3 /m 2 A more preferable range is 0.30 to 10m 3 /m 2 H, particularly preferably 0.50 to 7.00m 3 /m 2 H is used as the reference value. The method of calculating the same is explained in detail in examples.
(separation Performance)
The separation performance of the polystyrene latex particles having an average particle diameter of 0.2 μm in the separation membrane of the present invention is preferably 50% or more, more preferably 90% or more, still more preferably 95% or more, and particularly preferably 99% or more. The method of calculating the same is explained in detail in examples.
(method for producing separation Membrane)
The method for producing a separation membrane of the present invention has the following (1) to (3).
(1) A preparation step of melt-kneading a mixture containing 10 to 80 mass% or less of a cellulose ester, 10 to 80 mass% of a structure-forming agent, and 2 to 20 mass% of a pore-forming agent to obtain a resin composition.
(2) A molding step of ejecting the resin composition from a nozzle using a filter having a diameter of 40 to 200 μm to obtain a resin molded product at a draft ratio of 30 to 200.
(3) An impregnation step of impregnating the resin molded article at a distance D of a solubility parameter with respect to cellulose ester S Dipping in 10-25 solvent.
Next, the method for producing a separation membrane of the present invention will be specifically described by taking a case where the separation membrane is a hollow fiber membrane as an example.
In the step of preparing the resin composition for producing the separation membrane of the present invention, a mixture containing 10 to 80 mass% of a cellulose ester, 10 to 80 mass% of a structure-forming agent and 2 to 20 mass% of a pore-forming agent is melt-kneaded. The mixture preferably contains 15 to 75 mass% of cellulose ester, 20 to 75 mass% of structure forming agent and 3 to 18 mass% of pore forming agent, more preferably contains 20 to 60 mass% of cellulose ester, 25 to 70 mass% of structure forming agent and 5 to 15 mass% of pore forming agent, and particularly preferably contains 20 to 60 mass% of cellulose ester, 25 to 70 mass% of structure forming agent and 10 to 15 mass% of pore forming agent.
The apparatus used for melt-kneading the mixture is not particularly limited, and a kneader, a roll mill, a banbury mixer, a single-screw or twin-screw extruder, or the like can be used. Among them, a twin-screw extruder is preferably used from the viewpoint of improving the dispersibility of the structure-forming agent and the plasticizer, and a twin-screw extruder with vent holes is more preferably used from the viewpoint of removing volatile substances such as moisture and low molecular weight substances. Further, a twin-screw extruder having a screw portion and a kneading disc portion may be used, and in order to reduce the kneading strength, a twin-screw extruder having a screw constituted only by a screw portion is preferably used.
The resin composition obtained in the preparation step may be once pelletized and remelted for melt film formation, or may be directly introduced into a nozzle for melt film formation. When the pellets are formed into pellets once, it is preferable to use a resin composition obtained by drying the pellets so that the moisture content is 200ppm (by mass) or less. By setting the water content to 200ppm (by mass) or less, deterioration of the resin can be suppressed.
The molding step is a step of forming a resin molded article by ejecting the resin composition obtained in the preparation step from a nozzle. The molding step may be a step of forming a resin molded product by, for example, ejecting the gas from a nozzle having a double ring-shaped nozzle in which a gas flow path is arranged in the center portion, into air, and cooling the gas by a cooling device.
The resin composition passed through the filter in advance is preferably discharged from a nozzle. To increase L, L and (L/d) a The pore diameter of the filter is preferably 40 to 200 μm, more preferably 70 to 150 μm, and still more preferably 70 to 120 μm. By passing the resin composition through the filter, it is presumed that the pore former contained in the resin composition is elongated to increase L, L and (L/d) a And an effect of suppressing bonding of pores to each other is obtained.
The hollow yarn, which is the resin molded product cooled by the cooling device, may be wound by a winding device. In this case, the values of the draft ratios calculated by (winding speed)/(discharge speed from the nozzle) of the winding device are increased by L, L and (L/d) a The value of (3) is preferably 30 to 200, more preferably 50 to 150, and particularly preferably 100 to 150, and the average thickness of the wall portion in the longitudinal direction of the separation membrane is suppressed from excessively decreasing. The resin composition discharged from the nozzle is elongated under the conditions of the above draft ratio, whereby the void former contained in the resin composition is presumed to be elongated to increase L, L and (L/d) a And an effect of suppressing bonding of pores to each other is obtained. In solution film formation using a polymer mixed with 50 wt% or more of a low-molecular compound having a molecular weight of less than 1000, spinning at a high draft ratio as in the present invention is difficult, and the pore former cannot be sufficiently drawn, so that such an effect is difficult to obtain.
The impregnation step is carried out at a distance D of a solubility parameter relative to the cellulose ester as the starting material S A step of impregnating the resin molded product with a solvent of 10 to 25. In this case, the cellulose ester has a moderate affinity for the cellulose esterThe solvent or the mixed solvent of (2) can suppress extreme swelling and plasticization of the resin. Therefore, the solvent permeates into the resin molded product while maintaining the shape of the resin. In this case, it is presumed that the plasticizer and the structure-forming agent are eluted while phase separation is caused in the resin molded product. The longer or higher the immersion time and temperature of the solvent, the larger the surface pore diameter, and the larger the proportion and size of pores and pores existing in the cross section Z tend to be. In the present invention, it is preferable to select a solvent having a certain degree of affinity with cellulose ester. The affinity of cellulose ester with a solvent can be estimated by a three-dimensional hansen solubility parameter (non-patent document 1). Specifically, the solubility parameter distance D obtained from the following formula (1) S The smaller the affinity of the solvent for the cellulose ester.
[ number 1]
Where, delta Ad 、δ Ap And delta Ah Is the dispersion, polarity and hydrogen bond term of the solubility parameter of the cellulose ester, delta Bd 、δ Bp And delta Bh Is the dispersion, polarity and hydrogen bonding terms of the solubility parameter of the solvent or solvent mixture. Solubility parameter (. delta.) for mixed solvents Mixture ) The value can be obtained by the following formula (2).
[ number 2]
Here, phi i 、δ i Is the volume fraction and solubility parameters of component i, and the dispersion term, the polarity term, and the hydrogen bond term each hold. The "volume fraction of the component i" herein means a ratio of the volume of the component i before mixing to the sum of the volumes of all the components before mixing. The three-dimensional hansen solubility parameter of the solvent uses the value described in non-patent document 1. For the solvent parameters not described, the values recorded in the software "Hansen Solubility Parameter in Practice" developed by Charles Hansen et al were used. The three-dimensional Hansen solubility parameters of the solvent and the polymer, which are not described in the software, can be calculated by the Hansen sphere method using the software.
The inventors have found that the above-mentioned solubility parameter distance D is an unexpected finding S And impregnating the resin molded product in a solvent of 10 to 25, wherein the larger the depth D of each pore and the average depth D of a plurality of pores is, the larger the depth D and the average depth D of the pores are, the larger the film D and D are. And it was found that the effect of reducing the substantial film thickness was thereby obtained more significantly. The reason why such an effect is obtained is not clear, and is estimated as follows. That is, since it is presumed that the pore former is incompatible with the cellulose ester, the pore former is dispersed in the cellulose ester in the stage after the molding step and before the impregnation step, and the distance D is determined by the solubility parameter relative to the cellulose ester in the impregnation step s 10 to 25, the pore former swells, and thus a film having a large D and a large D is obtained.
The temperature of the resin molding in the impregnation step is preferably 50 to 80 ℃. When the temperature of the resin molded article in the impregnation step is set to 50 to 80 ℃, surprisingly, voids (l/d) of the cross section Z are found a 2 to 40, but the average value (y/x) of the ratio of the major diameter to the minor diameter of the surface pores a As low as 1.0-1.5, i.e., nearly circular. The reason for this is estimated as follows. That is, it is presumed that the molecules of the resin molded article are easily moved at the yarn temperature of 50 to 80 ℃, and in this case, the molecules are particularly easily moved on the surface rather than inside, and therefore, if the resin molded article is immersed in the solvent in the immersion step to further promote plasticization, the structure-forming agent stretched by the filter holes and draft is restored in the surface and approaches a circular shape.
In the present invention, it is preferable that D is used as the solvent for impregnating the resin molded product S A solvent of 13 to 25. As such a solvent, D is preferably used S Examples of the mixed solvent of the solvent of 4 to 12 and water include a mixed solvent of water and at least 1 selected from the group consisting of γ -butyrolactone (hereinafter referred to as γ -BL), acetone, acetonitrile, 1, 4-dioxane, methyl acetate and tetrahydrofuran. By using D S Up to 4-12% solvent and waterThe membrane strength of the separation membrane obtained by mixing the solvents becomes good.
The separation membrane thus obtained can be used as it is, and preferably the surface of the membrane is hydrophilized by, for example, an aqueous solution containing an alcohol or an aqueous alkali solution before use.
Even when the pore former remains in the previous step, it is preferable to provide a step of removing the pore former. Examples of a method for removing the pore former include dipping in a solution in which cellulose ester is not dissolved or decomposed and the pore former is dissolved or decomposed.
Examples
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
[ measurement and evaluation methods ]
The characteristic values in the examples were obtained by the following methods.
(1) Average degree of substitution of cellulose Mixed esters
The method for calculating the average degree of substitution of cellulose mixed ester in which acetyl group and other acyl group are bonded to cellulose is as follows.
0.9g of cellulose mixed ester dried at 80 ℃ for 8 hours was weighed, 35mL of acetone and 15mL of dimethyl sulfoxide were added and dissolved, and 50mL of acetone was further added. While stirring, 30mL of a 0.5N-sodium hydroxide aqueous solution was added, and saponification was performed for 2 hours. 50mL of hot water was added, the side of the flask was washed, and then titrated with 0.5N-sulfuric acid using phenolphthalein as an indicator. Further, a blank test was carried out by the same method as the sample. The supernatant of the titrated solution was diluted 100-fold, and the composition of the organic acid was measured by ion chromatography. From the measurement results and the results of acid composition analysis by ion chromatography, the degree of substitution was calculated by the following formulas (3) to (5).
TA=(B-A)×F/(1000×W) ······(3)
DSace=(162.14×TA)/[{1-(Mwace-(16.00+1.01))×TA}+{1-(Mwacy-(16.00+1.01))×TA}×(Acy/Ace)] ······(4)
DSacy=DSace×(Acy/Ace) ······(5)
TA: total organic acid amount (mL)
A: sample titration amount (mL)
B: empty test titration amount (mL)
F: titre of sulfuric acid
W: sample quality (g)
DSace: average degree of substitution of acetyl groups
DSacy: average degree of substitution of other acyl groups
Mway: molecular weight of acetic acid
Mwacy: molecular weight of other organic acids
Acy/Ace: molar ratio of acetic acid (Ace) to other organic acids (Acy)
162.14: molecular weight of repeating units of cellulose
16.00: atomic weight of oxygen
1.01: atomic weight of hydrogen.
(2) Weight average molecular weight (Mw) of cellulose ester
The cellulose ester was completely dissolved in tetrahydrofuran so that the concentration thereof became 0.15 mass%, and a sample for GPC measurement was prepared. Using this sample, GPC measurement was performed using a GPC device (Waters2690) under the following conditions, and the weight average molecular weight (Mw) was determined in terms of polystyrene.
Column: connecting TSK gel GMHHR-H made by Tosoh with 2 roots
A detector: waters2410 differential refractometer RI
Mobile phase solvent: tetrahydrofuran (THF)
Flow rate: 1.0 mL/min
Injection amount: 200 μ L.
(3) Shape of surface pores
The outer surface of the separation membrane sputtered with platinum was observed at a magnification of 10,000 times by SEM, and the pore diameter r of 50 randomly selected surface pores was measured, and the arithmetic mean value thereof was written as the surface pore diameter r in tables 1 and 2.
The pore diameter r of each surface pore is calculated by the following equation (6) by measuring the surface pore area by image processing and assuming a true circle pore of the same area.
r=(4×A/π) 0.5 ······(6)
A: area of the hole
The sputtering and observation conditions using SEM are as follows.
(sputtering conditions)
The device comprises the following steps: hightech, Kyowa Kabushiki Kaisha (E-1010)
Evaporation time: 40 seconds
Current value: 20 mA.
(SEM Condition)
The device comprises the following steps: hightech, Hightech corporation (SU1510)
Acceleration voltage: 5kV
Probe current: 30.
further, the outer surface of the separation membrane was observed under the same observation conditions as described above, and the average value (Y/X) of the average minor axis X, the average major axis Y, and the ratio of the major axis to the minor axis of the surface pores was determined by the above analysis method a The value of (c).
(4) Thickness of hollow fiber membrane
After freezing the hollow fiber membrane with liquid nitrogen, the membrane was cut so that the radial cross section was exposed by applying stress (using a razor or microtome as needed). The obtained cross section was observed by an optical microscope, and the average of the thicknesses of 10 randomly selected portions was defined as the thickness (film thickness) of the hollow fiber membrane.
(5) Outer diameter of hollow fiber membrane
The cross section of (4) was observed by an optical microscope, and the average value of the outer diameters at 10 randomly selected positions was defined as the outer diameter of the hollow fiber membrane.
(6) Membrane permeation flux of hollow fiber membrane
A small module having an effective length of 100mm and containing 1 hollow fiber membrane was produced. In the small-sized module, distilled water was fed by external pressure total filtration for 30 minutes under conditions of a filtration differential pressure of 16kPa at a temperature of 25 ℃ and the amount of permeate (m) obtained was measured 3 ) It is converted into a unit time (h) and a unit membrane area (m) 2 ) The numerical value of (1) is further expressed as the permeability of pure water in terms of pressure (50kPa) (unit = m) 3 /m 2 /h)。
(7) Determination of multiple pores and walls
After freezing the separation membrane with liquid nitrogen, stress is applied (using a razor or microtome as required) to separate the membrane into sections parallel to the longitudinal direction and the thickness direction of the membraneThe surface, i.e., the cross section Z, is cut so as to be exposed. Next, after the cross section Z was pretreated by sputtering with platinum, the field of view was set so that the distances from both surfaces in the center of the field of view were equal using an SEM, and observation was performed at a magnification of 2,000 times. Similarly, 5 visual fields were observed, and after 30 pores were randomly extracted from each visual field, the average depth D (. mu.m) and the average length L (. mu.m) of the pores and the average value L/D of each pore (L/D) were calculated a The occupancy (%) of the plurality of pores, the average thickness (μm) of the wall portion, and the angle (°) in the longitudinal direction of the plurality of pores were further calculated. The sputtering and observation conditions using SEM are as follows.
(sputtering conditions)
The device comprises the following steps: hightech, Kyowa Kabushiki Kaisha (E-1010)
Evaporation time: 40 seconds
Current value: 20 mA.
(SEM Condition)
The device comprises the following steps: hightech, Kyoki Kaisha (SU1510)
Acceleration voltage: 5kV
Probe current: 30.
(8) area ratio of concave portion
The separation membrane was cut in the same manner as in (7) above, and the exposed cross section Z was observed with an SEM at a magnification of 5,000 times, and the area ratio of the concave portions (concave portion area ratio) was calculated.
(9) Separation Performance
The small module is manufactured in the same manner as in (6) above. In this small-sized module, an aqueous solution containing 20ppm of polystyrene latex particles (manufactured by Magsphere Co.) having an average particle diameter of 0.2 μm as a turbid component was subjected to external pressure whole filtration at a temperature of 25 ℃ under a filtration differential pressure of 16kPa for 30 minutes, and the turbid component concentrations of the feed water and the permeated water were calculated from the ultraviolet absorption coefficient at a wavelength of 234nm measured by a spectrophotometer (manufactured by Hitachi, Ltd.; U-3200) and calculated from the following formula (7).
Separation performance (%) = [1-2 × (turbidity component concentration of permeated water)/{ (turbidity component concentration of feed water at the start of filtration) + (turbidity component concentration of feed water at the end of filtration) } ] × 100 · · equation (7).
[ cellulose ester (A) ]
The following were prepared as cellulose esters.
Cellulose ester (A1)
To 100 parts by mass of cellulose (cotton linter), 240 parts by mass of acetic acid and 67 parts by mass of propionic acid were added, and the mixture was mixed at 50 ℃ for 30 minutes. After the mixture was cooled to room temperature, 172 parts by mass of acetic anhydride and 168 parts by mass of propionic anhydride cooled in an ice bath were added as an esterification agent and 4 parts by mass of sulfuric acid was added as an esterification catalyst, and the mixture was stirred for 150 minutes to perform an esterification reaction. Cooling with water bath at temperature higher than 40 deg.C during esterification reaction.
After the reaction, a mixed solution of 100 parts by mass of acetic acid and 33 parts by mass of water was added as a reaction terminator over 20 minutes to hydrolyze excess acid anhydride. Thereafter, 333 parts by mass of acetic acid and 100 parts by mass of water were added thereto, and the mixture was heated and stirred at 80 ℃ for 1 hour. After the reaction was completed, an aqueous solution containing 6 parts by mass of sodium carbonate was added, and the precipitated cellulose acetate propionate was filtered off, washed with water, and then dried at 60 ℃ for 4 hours. The cellulose acetate propionate thus obtained had average degrees of substitution of acetyl and propionyl of 1.9 and 0.7, respectively, and a weight-average molecular weight (Mw) of 17.8 ten thousand.
Cellulose ester (a 2): cellulose acetate propionate (average degree of substitution of acetyl group: 0.2, average degree of substitution of propionyl group: 2.5, weight average molecular weight (Mw): 18.5 ten thousand).
[ other raw materials ]
As other raw materials, the following were prepared.
Plasticizer (B) of cellulose ester: polyethylene glycol (weight average molecular weight (Mw)600)
Structure-forming agent (C): PVP/vinyl acetate copolymer (PVP/vinyl acetate =6/4 (molar ratio), weight average molecular weight 50,000)
Pore former (D): polyethylene glycol (weight average molecular weight (Mw)30 ten thousand)
Antioxidant (E): bis (2, 6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite.
(example 1)
40 mass% of cellulose ester (A1), 26.9 mass% of plasticizer (B), 30 mass% of structure-forming agent (C), 3 mass% of pore-forming agent (D), and 0.1 mass% of antioxidant (E) were melt-kneaded at 220 ℃ by a twin-screw extruder, homogenized, and pelletized to obtain a resin composition. The resin composition was dried under vacuum at 80 ℃ for 8 hours.
The dried resin composition was supplied to a twin-screw extruder equipped with a screw composed only of a helical portion, melt-kneaded at 220 ℃, introduced into a melt-spinning pack having a spinning temperature of 220 ℃, and spun downward from an outer annular portion of a nozzle having 1 nozzle hole (double circular tube type, discharge hole diameter of 2.6mm, slit width of 0.35mm) at a discharge amount of 10 g/min. The spun hollow yarn was introduced into a cooling device, cooled by cooling air at 25 ℃ and a wind speed of 1.5 m/sec, and wound up by a winder so that the draft ratio reached 30. Here, as the filter in the melt spinning pack, a metal filter having a pore size (filter diameter) of 200 μm was used. The wound hollow fiber (resin molded article) was heated to 30 ℃, immersed in an acetone aqueous solution having a volume fraction of 40% for 1 hour, and further immersed in water for 1 hour or more, to thereby elute the plasticizer (B), the structure-forming agent (C), and the pore-forming agent (D), thereby obtaining a separation membrane. The physical properties of the separation membrane are shown in table 1.
(examples 2 to 9 and comparative examples 1 to 6)
A separation membrane was obtained in the same manner as in example 1, except that the composition and production conditions of the resin composition were changed as shown in tables 1 and 2, respectively. The physical properties of the separation membrane thus obtained are shown in tables 1 and 2. In comparative example 1, no voids were observed, and comparative example 2 could not be spun due to yarn breakage.
[ Table 1]
[ Table 2]
Membrane permeation flux of the separation membranes obtained in examples 1 to 9Are all 0.1m 3 /m 2 More than h, separation performance of more than 50 percent, and high membrane permeation flux and separation performance. On the other hand, comparative example 2 could not be spun due to yarn breakage, and a separation membrane could not be obtained. In the separation membranes of comparative examples 1, 3 to 6 in which the shapes of the plurality of pores do not satisfy the requirements of the present invention, at least one of the membrane permeation flux and the separation performance is low, and a high membrane permeation flux and a high separation performance cannot be achieved at the same time.
The present invention has been described with reference to specific embodiments in detail, but it is apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. The present application is based on the japanese patent application filed on 23.12.2019 (japanese patent application 2019-231579), the contents of which are incorporated herein by reference.
Industrial applicability
The separation membrane of the present invention is suitable for a water treatment membrane for producing industrial water or drinking water from seawater, brine water, sewage, drainage, or the like, a medical membrane for artificial kidney, plasma separation, or the like, a food/beverage industrial membrane for fruit juice concentration, or the like, a gas separation membrane for separating exhaust gas, carbon dioxide gas, or the like, or an electronic industrial membrane such as a fuel cell separator, or the like.
Claims (10)
1. A separation membrane comprising a cellulose ester,
the separation membrane has a plurality of pores in a cross section of the membrane parallel to the longitudinal direction and the thickness direction of the membrane,
the average depth D of the plurality of pores is 0.7 to 20 μm,
the average length L of the plurality of pores is 3 μm or more, and
average value of the ratio of length l to depth d of each pore (l/d) a The value of (1) is 2 to 40.
2. The separation membrane according to claim 1, wherein an occupancy rate of the plurality of pores in the cross section is 15 to 55%.
3. The separation membrane according to claim 1 or 2, wherein the wall portion in the cross section has an average thickness of 0.7 to 5.0 μm.
4. A separation membrane according to any one of claims 1 to 3, wherein in at least one surface, the surface pores have an average pore diameter of 0.050 to 0.500. mu.m.
5. The separation membrane according to any one of claims 1 to 4, wherein in at least one surface, the average minor axis X of the surface pores is 0.030 to 0.250. mu.m, the average major axis Y of the surface pores is 0.060 to 0.450. mu.m, and the average value (Y/X) of the ratio of the major axis to the minor axis a The value of (A) is 1.00 to 1.50.
6. The separation membrane according to any one of claims 1 to 5, wherein the longitudinal direction of the plurality of pores is along the longitudinal direction of the separation membrane.
7. The separation membrane according to any one of claims 1 to 6, wherein the cellulose ester comprises cellulose acetate propionate and/or cellulose acetate butyrate.
8. A separation membrane according to any one of claims 1 to 7, which is in the form of a hollow filament.
9. A method for producing a separation membrane, comprising:
(1) a preparation step of melting and mixing a mixture containing 10-80 mass% of cellulose ester, 10-80 mass% of a structure forming agent and 2-20 mass% of a pore forming agent to obtain a resin composition;
(2) a molding step of ejecting the resin composition from a nozzle using a filter having a pore diameter of 40 to 200 μm to obtain a resin molded article at a draft ratio of 30 to 200; and
(3) an impregnation step of impregnating the resin molded article at a distance D of solubility parameter with respect to cellulose ester S In a solvent in the range of 10 to 25.
10. The method for producing a separation membrane according to claim 9, wherein the temperature of the resin molded product in the impregnation step is 50 to 80 ℃.
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| MX2016001715A (en) * | 2013-08-09 | 2016-07-26 | Toray Industries | Elastic monofilament. |
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| CN107530644A (en) * | 2015-03-31 | 2018-01-02 | 东丽株式会社 | Seperation film |
| CN108136341A (en) * | 2015-09-30 | 2018-06-08 | 东丽株式会社 | The manufacturing method of seperation film, cellulose resin compositions and seperation film |
| CN110475606A (en) * | 2017-03-30 | 2019-11-19 | 东丽株式会社 | Seperation film and its manufacturing method |
| JP2019111476A (en) * | 2017-12-22 | 2019-07-11 | 東レ株式会社 | Separation membrane, and manufacturing method of separation membrane |
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| JPWO2021132397A1 (en) | 2021-07-01 |
| JP7107429B2 (en) | 2022-07-27 |
| KR20220112792A (en) | 2022-08-11 |
| WO2021132397A1 (en) | 2021-07-01 |
| CN114828992B (en) | 2024-05-17 |
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