KR20220112792A - Separator and its manufacturing method - Google Patents

Abstract

The present invention is a separation membrane containing a cellulose ester, wherein the separation membrane has a plurality of pores in a cross section parallel to the longitudinal direction and the film thickness direction of the membrane, and the average depth D of the plurality of pores is 0.7 to 20 μm; , wherein the average length L of the plurality of pores is 3 μm or more, and the average value (l/d) _a of the ratio of the length l to the depth d of each of the pores is 2 to 40.

Description

Separator and its manufacturing method

The present invention relates to a separation membrane and a method for manufacturing the same.

In recent years, separation membranes have been used in various fields such as water treatment membranes such as water purification and wastewater treatment, medical membranes such as blood purification, food industry membranes, battery separator membranes, charged membranes, or fuel cell electrolyte membranes.

Most separators are made of polymers. Among them, cellulosic resins, including cellulose esters, are widely used as materials for separation membranes, including membranes for water treatment, from the viewpoint of having permeation performance resulting from its hydrophilicity and chlorine resistance performance being strong against chlorine-based disinfectants.

For example, Patent Document 1 discloses a technique for obtaining a hollow fiber-shaped separation membrane by discharging a film forming stock solution containing cellulose triacetate into a coagulating solution containing a solvent, a nonsolvent, and water to perform phase separation.

In addition, Patent Document 2 discloses a hollow fiber-shaped separation membrane in which hydroxyalkyl cellulose is adhered to the surface in the state of fine particles.

Japanese Patent Laid-Open No. 2011-235204 Japanese Patent Laid-Open No. 2015-157278

Ind. Eng. Chem. Res. 2011, 50, 3798-3817.

However, in the conventional separation membrane using cellulose ester as a material, the size of the pores is reduced in order to improve the separation performance. It had the problem of being easy.

Therefore, an object of the present invention is to provide a separation membrane having both high separation performance and permeation performance, and a method for manufacturing the same.

As a result of intensive studies to solve the above problems, the present inventors found that it is possible to improve the permeability while maintaining high separation performance by having pores that satisfy specific conditions in the separation membrane containing cellulose ester, and the present invention came to completion.

That is, the present invention relates to the following [1] to [10].

[1] A separation membrane containing cellulose ester,

The separation membrane has a plurality of voids in a cross section parallel to the longitudinal direction and the film 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

The average value (l/d) _a of the ratio of the length l and the depth d of each pore is 2 to 40, the separator.

[2] The separation membrane according to the above [1], wherein the occupancy rate of the plurality of voids in the cross section is 15 to 55%.

[3] The separation membrane according to [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 [1] to [3], wherein, in at least one surface, the average pore diameter of the surface pores is 0.050 to 0.500 µm.

[5] In at least one surface, the average minor diameter X of the surface pores is 0.030 to 0.250 μm, the average major diameter Y of the surface pores is 0.060 to 0.450 μm, and the average value of the ratio of the major and minor diameters (y/ x) The separation membrane according to any one of [1] to [4], wherein the value of _a is 1.00 to 1.50.

[6] The separation membrane according to any one of [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 [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 [1] to [7], wherein the membrane has a hollow fiber shape.

[9] (1) melt-kneading 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 to obtain a resin composition; the preparation process;

(2) a molding step of discharging the resin composition from a discharge nozzle using a filter having a pore diameter of 40 to 200 μm to obtain a resin molding at a draft ratio of 30 to 200;

(3) A method for producing a separation membrane comprising an immersion step in which the resin molding is immersed in a solvent having a solubility parameter distance D _S with respect to a cellulose ester in the range of 10 to 25.

[10] The method for producing a separation membrane according to the above [9], wherein the temperature of the resin molded product in the immersion step is 50 to 80°C.

ADVANTAGE OF THE INVENTION According to this invention, provision of the separation membrane which has both high separation performance and permeation performance, and its manufacturing method becomes possible.

Fig. 1 (a) is a diagram schematically showing the cross section Z and the internal structure of the separation membrane, (b) is a side view of (a), (c) is a top view of (a).
2 : is an example of the image which imaged the cross section Z by SEM.
Fig. 3 is an image obtained by denoising and binarizing the image of Fig. 2 and extracting voids.
Fig. 4 is an image in which the outline of the void is further extracted from the image of Fig. 3 .

The separation membrane of the present invention is a separation membrane containing a cellulose ester, has a plurality of pores in a cross section parallel to the longitudinal direction and the thickness direction of the membrane, and an average depth D of the plurality of pores is 0.7 to 20 μm, It is characterized in that the average length L of the plurality of voids is 3 µm or more, and the average value (l/d) _a of the ratio of the length l to the depth d of each void is 2 to 40. In the present specification, the ratio by mass (percentage, parts, etc.) is the same as the ratio by weight (percentage, parts, etc.).

(resin composition constituting the separation membrane)

The resin composition constituting the separation membrane of the present invention contains the cellulose ester shown in (1) below. Moreover, other than (1), the component shown to the following (2) - (6) can be contained.

(1) Cellulose Ester

The separation membrane of the present invention needs to contain a cellulose ester. In addition, in order to further enhance the effect of the present invention, the separation membrane of the present invention preferably contains a cellulose ester as a main component. The main component as used herein refers to a component that is included the most on a mass basis among all the components of the resin composition constituting the separation membrane.

Examples of the cellulose ester include cellulose esters such as cellulose acetate, cellulose propionate or cellulose butyrate, or cellulose mixed esters such as cellulose acetate propionate or cellulose acetate butyrate. Among them, from the viewpoint of the processability of the resin molded product and the film strength of the obtained separation membrane, cellulose mixed ester is preferable, cellulose acetate propionate and/or cellulose acetate butyrate are more preferable, and cellulose acetate propionate is still more preferable. Cellulose acetate propionate here is a cellulose ester in which the average degree of substitution of an acetyl group and a propionyl group is 0.1 or more, respectively.

It is preferable that the weight average molecular weights (Mw) of a cellulose ester are 50,000-250,000. When the weight average molecular weight (Mw) is 50,000 or more, 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 be easily reached at a practical level. When a weight average molecular weight (Mw) is 250,000 or less, since melt viscosity does not become high too much, stable melt film forming is attained. In addition, a weight average molecular weight (Mw) is a value computed by GPC (gel permeation chromatography) measurement. The calculation method will be described in detail in Examples.

Each of the cellulose mixed esters illustrated has an acyl group (propionyl group, butyryl group, etc.) different from an acetyl group. In the cellulose mixed ester contained in the separation membrane, the average degree of substitution of the acetyl group and other acyl groups 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

When the above formula is satisfied, the permeation performance of the separation membrane and the thermal fluidity at the time of melting the resin composition constituting the separation membrane become good. In addition, the average degree of substitution means the number to which an acyl group (acetyl group + another acyl group) was chemically bonded among three hydroxyl groups which exist per glucose unit of a cellulose.

The separation membrane may contain only one type of cellulose ester, and may contain two or more types 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, when all components of the separation membrane are 100% by mass. When the content of the cellulose ester in the separation membrane is 70 mass% or more, the membrane strength of the separation membrane is sufficient.

Moreover, when content of the cellulose ester in the raw material which manufactures a separation membrane makes the whole component which comprises a raw material 100 mass %, 10-80 mass % is preferable. When the content is 10% by mass or more, the membrane strength of the separation membrane becomes good. On the other hand, when content is 80 mass % or less, the thermoplasticity and permeation|transmission performance of a separation membrane become favorable. As for content, it is more preferable that it is 15 mass % or more, and it is still more preferable that it is 20 mass % or more. Moreover, as for content, it is more preferable that it is 70 mass % or less, It is still more preferable that it is 60 mass % or less, It is especially preferable that it is 45 mass % or less.

(2) Cellulose ester plasticizer

The resin composition constituting the separation membrane of the present invention may contain a cellulose ester plasticizer.

The plasticizer of a cellulose ester will not be specifically limited if it is a compound which thermoplasticizes a cellulose ester. In addition, not only one type of plasticizer but two or more types of plasticizers may be used together.

Examples of the cellulose ester plasticizer include polyalkylene glycol compounds such as polyethylene glycol or polyethylene glycol fatty acid esters, glycerin compounds such as glycerin fatty acid esters or diglycerin fatty acid esters, citric acid ester compounds, phosphate ester compounds, or Fatty acid ester-type compounds, such as dipic acid ester, or caprolactone-type compound, or those derivatives, etc. are mentioned.

Examples of the polyalkylene glycol-based compound include polyethylene glycol, polypropylene glycol or polybutylene glycol having a weight average molecular weight (Mw) of 400 to 4,000.

After forming the separation membrane, the plasticizer of the cellulose ester may remain in the separation membrane or eluted from the separation membrane. Moreover, when the plasticizer content of a cellulose ester makes the whole component which comprises a raw material 100 mass %, 5-40 mass % is preferable.

When content is 5 mass % or more, the thermoplasticity of a cellulose ester becomes favorable. On the other hand, when content is 40 mass % or less, the film strength of a separation membrane becomes favorable. As for plasticizer content of a cellulose ester, 5-35 mass % is more preferable, and its 5-30 mass % is still more preferable.

(3) antioxidants

The resin composition constituting the separation membrane of the present invention preferably contains an antioxidant. When the resin composition contains the antioxidant, thermal decomposition at the time of melting the polymer during the production of the separation membrane is suppressed, and as a result, the membrane strength of the obtained separation membrane is improved, and the coloring of the separation membrane is suppressed.

As antioxidant, a phosphorus antioxidant is preferable, and a pentaerythritol-type compound is more preferable. Examples of the pentaerythritol-based compound include bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite.

When content of antioxidant makes the whole component which comprises a raw material 100 mass %, 0.005-0.500 mass % is preferable. When content of antioxidant exists in the said range, a preparation process WHEREIN: A uniform resin composition can be obtained.

(4) structure former

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 a cellulose ester or a mixture of a cellulose ester and a plasticizer, and can be eluted or decomposed by a solvent that does not dissolve the cellulose ester. The weight average molecular weight of the structure-forming agent is preferably 1000 or more from the viewpoint of appropriately controlling the values of L, D and (l/d) _a to be described later.

Partially compatible means that two or more types of substances are completely compatible under certain conditions, but phase-separate under other conditions. A structure forming agent is a substance phase-separated from a cellulose ester by contacting with the solvent which satisfy|fills specific conditions in the immersion process mentioned later. Specific conditions will be described later.

The structure-forming agent in the present invention is preferably a hydrophilic compound from the viewpoint of being easily eluted. Here, the hydrophilic compound refers to a compound that is dissolved in water or has a contact angle with respect to water smaller than that of a cellulose ester contained in the separation membrane. Among the hydrophilic compounds, a compound soluble in water is particularly preferable from the viewpoint of being easily eluted.

Examples of the structure-forming agent include PVP-based copolymers such as polyvinylpyrrolidone (hereinafter, “PVP”), PVP/vinyl acetate copolymer, PVP/methyl methacrylate copolymer, polyvinyl alcohol, Or a polyester compound etc. are mentioned.

When PVP is used as the structure-forming agent, it becomes difficult to elute from the separation membrane when thermal crosslinking occurs, so intermolecular crosslinking is relatively difficult to proceed, and from the viewpoint that eluting is possible even after crosslinking, the weight average molecular weight (Mw) is It is preferable that it is 20,000 or less. Moreover, it is also preferable to use the copolymer which has the said PVP as a base at the point which thermal crosslinking is suppressed.

In the step after the immersion step described later, by eluting at least a part of the structure-forming agent, the traces from which the structure-forming agent is removed (eluted) become voids in the film, and as a result, the permeation performance is improved.

It is preferable that content of a structure forming agent is 10-80 mass %, when the whole of the component which comprises a raw material makes 100 mass %.

When content is 10 mass % or more, the permeation|transmission performance of a separation membrane becomes favorable. On the other hand, when content is 80 mass % or less, film|membrane intensity|strength becomes favorable. As for content of a structure forming agent, 20 mass % or more is more preferable, and 25 mass % or more is still more preferable. Moreover, as for content of a structure forming agent, 75 mass % or less is more preferable, and its 70 mass % or less is still more preferable.

(5) pore former

The resin composition constituting the separation membrane of the present invention may contain a pore former. Here, the pore-forming agent refers to a compound that is not compatible with the cellulose ester and is plasticized or melted by heat. By eluting the pore former that is not compatible with the cellulose ester, voids are formed at the site where the pore former exists. Further, when the pore former is plasticized or melted by heat, it is possible to increase the value of (l/d) _a , which is an average value of the ratio of the length l to the depth d of the pores to be formed.

Examples of the pore-forming agent include phthalic acid ester compounds, trimellitic acid ester compounds, polyalkylene glycol compounds such as polyethylene glycol, polypropylene glycol or polybutylene glycol, and derivatives of these compounds. As for the weight average molecular weight (Mw) of these compounds, 100,000-1 million are preferable. Since it is easy to control the values of L, D, and (l/d) _a to be described later by exhibiting an appropriate viscosity during heating, the weight average molecular weight (Mw) of the pore former is preferably 100,000 to 1,000,000, and 100,000 500,000 to 500,000 are more preferable, and 100,000 to 300,000 are especially preferable.

It is preferable that content of a pore former is 2-20 mass %, when the whole component which comprises a raw material makes 100 mass %. When content is 2 mass % or more, the permeation|transmission performance of a separation membrane becomes favorable. On the other hand, when content is 20 mass % or less, separation performance becomes favorable. As for content of a pore former, 3 mass % or more is more preferable, 5 mass % or more is still more preferable, and 10 mass % or more is especially preferable. Moreover, 18 mass % or less is more preferable, and, as for content, 15 mass % or less is still more preferable.

(6) additives

The resin composition constituting the separation membrane of the present invention may contain additives other than those described in (2) to (5) as long as the effects of the present invention are not impaired.

Examples of the additive include resins such as cellulose ether, polyacrylonitrile, polyolefin, polyvinyl compound, polycarbonate, poly(meth)acrylate, polysulfone or polyethersulfone, organic lubricant, crystal nucleating agent, and organic particles. , inorganic particles, terminal blockers, chain extenders, ultraviolet absorbers, infrared absorbers, color inhibitors, matting agents, antibacterial agents, antistatic agents, deodorants, flame retardants, weathering agents, antistatic agents, antioxidants, ion exchangers, defoamers, colored pigments , a fluorescent whitening agent or dye.

(Shape of Separator)

Although the shape of the separation membrane of the present invention is not particularly limited, a hollow fiber-shaped separation membrane (hereinafter, “hollow fiber membrane”) or a planar membrane (hereinafter, “flat membrane”) is preferably employed. Among them, the hollow fiber membrane is more preferable because it can efficiently fill the module and the effective membrane area per unit volume of the module can be large.

It is preferable that the thickness of a separation membrane is 10-500 micrometers from a viewpoint of making permeation|transmission performance and membrane strength compatible. Moreover, 30 micrometers or more are more preferable, and, as for thickness, 50 micrometers or more are still more preferable. As for thickness, 400 micrometers or less are more preferable, and 300 micrometers or less are still more preferable.

In the case of a hollow fiber membrane, it is preferable that the outer diameter of a hollow fiber membrane is 50-2500 micrometers from a viewpoint of making compatible the effective membrane area and membrane strength when a module is filled. The outer shape of the hollow fiber membrane is more preferably 100 µm or more, still more preferably 200 µm or more, and particularly preferably 300 µm or more. Moreover, as for an outer shape, 2000 micrometers or less are more preferable, 1500 micrometers or less are still more preferable, and it is especially preferable that it is 1000 micrometers or less.

Moreover, in the case of a hollow fiber membrane, it is preferable that the hollow ratio of a hollow fiber is 15 to 70% from the relationship between the pressure loss of the fluid which flows through a hollow part, and a buckling pressure. The hollow ratio is more preferably 20% or more, and still more preferably 25% or more. Moreover, 65 % or less is more preferable, and, as for a hollow rate, 60 % or less is still more preferable.

The method for making the outer diameter and hollow ratio of the hollow fiber in the hollow fiber membrane into the above range is not particularly limited, but for example, the shape of the discharge hole of a spinneret for manufacturing the hollow fiber, or the winding speed/discharge rate, which can be calculated It can be adjusted by changing the draft ratio suitably.

(Cross-section structure of separator)

The separation membrane of the present invention has a plurality of pores in which the average depth D, the average length L, and the average value of l/d (l/d) _a , which is the ratio of the depth d and the length l of each pore, are within a specific range. The depth and length of the voids are values measured in a cross section (hereinafter, “intersection Z”) parallel to the longitudinal direction and the film thickness direction of the separation membrane to be measured. Here, the longitudinal direction of the membrane is a direction parallel to the central axis in a hollow fiber membrane, and is a machine direction at the time of manufacture in a flat membrane. FIG. 1A is a diagram schematically illustrating a cross-section Z and an internal structure of the separation membrane when the separation membrane has a hollow fiber shape. Fig. 1 (b) is a side view of (a), (c) is a top view of (a). 1 , C represents a central axis, and the central axis C is parallel to the longitudinal direction of the film. In addition, in FIG.1(c), the bidirectional arrow illustrates the film thickness direction of a hollow fiber membrane, and the dotted line shows the direction parallel to the said film thickness direction.

Here, "gap" refers to a concave portion having an area of 1 µm ² or more when the cross section Z is observed at a magnification of 2,000 times using a scanning electron microscope (hereinafter, "SEM"). The detailed observation method is described in Example (7) Measurement regarding a plurality of voids and wall portions. In addition, "concave part" as used herein refers to a dark part in an image observed with SEM, and the outline can be extracted by binarizing the image captured by SEM using image analysis software (Huang's binarization). have.

Specifically, first, using imageJ, which is an image analysis software, an image captured by SEM is converted into 8-bit, and all pixels are replaced with the median value of 3 × 3 pixels in the vicinity of the pixel to remove noise (Despeckle in ImageJ). ) is performed 10 times, and then Huang's binarization is performed. Subsequently, by processing the obtained image as Masks display by setting the Size to 0-Infinity and Circularity to 0-1 in the Analyze Particles command of ImageJ, the image from which the recesses are extracted can be acquired. Based on the image obtained in this way, the outline of the concave portion can be extracted. Specifically, in the Analyze Particles command of ImageJ, by setting the Size to 0-Infinity and Circularity to 0-1, and processing as Bare Outlines display, the outline of the concave portion can be extracted.

In addition, the extraction of the void can be performed by setting the lower limit of the Size so that the concave portion of 1 µm ² or more is included in the extraction of the above-described concave portion. For example, in an image of 1 µm ² =100 pixel ² , the void can be extracted by setting the lower limit to 100 pixel ² . In the thus-obtained image, the outline of the void can be extracted by processing similarly to the extraction of the outline of the concave portion described above. In addition, in this application, an outline may be called an outer edge.

An example of an image captured by SEM is shown in FIG. 2 , the image in FIG. 2 is denoised and binarized, and voids are extracted in FIG. 3 , and the outline of the voids is extracted from the image in FIG. 3 , respectively, in FIG. 4 , respectively. .

When the cross-section Z is observed at a magnification of 5,000 times using an SEM, when the ratio of the sum of the areas of all the recesses occupied in the entire observation range is defined as the "recess area ratio", the permeation flow rate and separation performance are further improved For this reason, the concave area ratio of the separation membrane of the present invention is preferably 50 to 85%, more preferably 60 to 80%. In addition, the recessed part here is not limited to a recessed part with an area of 1 micrometer ² or more, ie, a space|gap, A recessed part with an area of less than 1 micrometer ² , ie, a pore, is also made into object collectively. As for the concave portion here, the outline can be extracted by removing noise and binarizing the image captured by SEM using image analysis software such as ImageJ (Huang's binarization) similarly to the above.

The "depth d of the void" refers to the depth direction of the void 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 the depth direction. refers to the maximum length. In addition, "the length of the gap l" is the longest line that can directly connect two points on the outer edge of the space to be measured when the section Z is observed at a magnification of 2,000 times the same using the SEM. is the length of the straight line. Here, the straight line capable of directly connecting two points on the outer edge means a straight line in which the straight line connecting two points on the outer edge does not pass through the other outer edge. The average value (l/d) _a of l/d, which is the ratio of the length l to the depth d of each void, is a value obtained by calculating l/d for each void in 30 randomly selected voids and taking the arithmetic mean value.

The average depth D of the plurality of voids refers to a value calculated as the arithmetic mean by measuring the depths of 30 randomly selected voids when the cross section Z is observed at a magnification of 2,000 times using SEM. In addition, the average length L of a plurality of voids is a value calculated as the arithmetic mean by measuring the lengths of 30 randomly selected voids when the cross-section Z is similarly observed at a magnification of 2,000 times using an SEM. say

The value of the average value (l/d) _a of l/d which is the ratio of the length l and the depth d of each void|gap needs to be 2-40. When the value of (l/d) _a is within this range, it is presumed that the separation membrane exhibits excellent permeation performance and separation performance because the voids are appropriately dispersed while reducing the substantial thickness of the separation membrane. (l/d) As for the value of _a , it is preferable that it is 3-20, It is more preferable that it is 4-20, It is more preferable that it is 8-20. Especially, by setting it as 4-20, especially high permeation performance and high separation|separation performance can be made compatible, and by setting it as 8-20, very high permeability and high separation|separation performance can be made compatible.

The average depth D of the plurality of voids needs to be 0.7 to 20 μm in order to reduce the substantial thickness of the separation membrane while appropriately dispersing the voids. 0.8 micrometer or more is preferable and, as for the average depth D of some space|gap, 1.0 micrometer or more is more preferable. Moreover, 5.0 micrometers or less are preferable and, as for the average depth D of some space|gap, 2.0 micrometers or less are more preferable.

The average length L of the plurality of voids needs to be 3 µm or more in order to appropriately disperse the voids. 4 micrometers or more are preferable, as for the average length L of some space|gap, 5 micrometers or more are more preferable, It is still more preferable that it is 10 micrometers or more. Moreover, it is preferable that it is 50 micrometers or less, and, as for the average length L of several space|gap, it is more preferable that it is 30 micrometers or less.

The longitudinal direction of the plurality of pores is preferably along the longitudinal direction of the separation membrane. When the longitudinal directions of the plurality of pores are substantially parallel, even if the separation membrane is bent in the longitudinal direction of the plurality of pores, stress is easily dispersed, and the film strength of the separation membrane is increased. The cross section Z is observed at a magnification of 2,000 times using an SEM, and the angle between the length l of each pore and the longitudinal direction of the membrane in 30 randomly selected pores is calculated, and the arithmetic mean value (hereinafter, “ angle in the longitudinal direction of the plurality of pores”) is within 20°, it may be determined that the longitudinal direction of the plurality of pores is along the longitudinal direction of the separation membrane. The angle in the longitudinal direction of the plurality of gaps is preferably within 15°, more preferably within 10°.

In the separation membrane of the present invention, in the cross section parallel to the longitudinal direction and the film thickness direction, the occupancy of a plurality of voids is preferably 15 to 55% in order to appropriately disperse the voids while further suppressing the substantial thickness of the separation membrane. and more preferably 18 to 50%, still more preferably 20 to 50%, particularly preferably 30 to 50%, and most preferably 40 to 50%. Here, "occupancy rate of a plurality of voids" refers to the ratio of S ₁ which is the sum of the areas of all voids occupied by the area S ₀ of the entire observation range when the section Z is observed at a magnification of 2,000 times using SEM. .

In the cross section Z of the separation membrane, the average thickness of the wall portion is preferably 0.7 to 5.0 μm, more preferably 1.0 to 4.0 μm, in order to appropriately disperse the voids and obtain good separation performance while further suppressing the substantial thickness of the separation membrane. It is preferable, and 1.0-3.0 micrometers is more preferable. Especially, by setting it as 1.0-3.0 micrometers, especially excellent permeation|transmission performance and separation performance can be made compatible. Here, the "wall part" of a hollow fiber membrane refers to the site|part other than a space|gap in the case where the cross section Z is observed at the magnification of 2,000 times using SEM (FIG. 1). In the above observation, the "average thickness of the wall portion" means a straight line passing through the center of the observation image, in a direction perpendicular to the longitudinal direction of the separation membrane, and parallel to each other at an interval of 20 µm on both sides of the line In the case of drawing , it means the average value of the lengths of each wall portion on these straight lines.

(Shape of surface hole)

In the separation membrane of the present invention, in order to further improve separation performance and water permeability, it is preferable that the average pore diameter of the surface pores on at least one surface is 0.050 to 0.500 µm. 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. Moreover, as for the average pore diameter of a surface hole, 0.450 micrometer or less is more preferable, and its 0.400 micrometer or less is still more preferable. Here, a surface hole means the recessed part in the image which imaged the surface of the separation membrane at 10,000 times using SEM. In addition, the "concave part" here refers to the dark part in the image observed by SEM, and the image imaged by SEM is denoised and binarized (Huang's binarization) using image analysis software such as ImageJ. The outline can be extracted. A specific extraction method of the contour of the concave portion is as described above. A detailed observation method is described in (3) Shape of surface hole of an Example. In addition, the average pore diameter of a surface pore may be called a surface pore diameter.

In the separation membrane of the present invention, on at least one surface, it is preferable that the average minor diameter X of the surface pores, the average major diameter Y, and the average value (y/x) _a of the ratio of the major and minor diameters (y/x) a are within a specific range. . In addition, the average minor diameter X means the arithmetic mean of the minor diameter x when each surface hole is regarded as an ellipse. The average major diameter Y means the arithmetic mean of major major diameters when each surface hole is regarded as an ellipse. The average value (y/x) _a means the arithmetic mean of the value obtained by dividing the short diameter x of each surface hole by the long diameter y. The average minor diameter X of the surface pores, the average major diameter Y, and the average value (y/x) _a of the ratio of the major and minor diameters (y/x) a is an image obtained by imaging the surface of the separation membrane at a magnification of 10,000 using SEM, ImageJ, etc. It is obtained by analyzing using the image analysis software of Specifically, in the Set Measurements of ImageJ, after selecting Fit Ellipse, the Analyze Particles command of ImageJ is executed for the extracted recesses in the same manner as described above. Thereby, since the minor diameter x and the major diameter y of each surface hole are computed, the average minor diameter X and the average major diameter Y can be calculated|required by arithmetic average of each. Moreover, by calculating|requiring y/x about each surface hole and carrying out arithmetic average, the average value (y/x) _a of the ratio of a major diameter and a minor diameter can be calculated|required.

The average minor diameter X of the surface pores is preferably 0.030 to 0.250 µm in order to further improve the separation performance and the water permeability performance. It is more preferable that it is 0.040-0.160 micrometers, and it is still more preferable that it is 0.045-0.160 micrometers.

The average major diameter Y of the surface pores is preferably 0.060 to 0.450 μm, more preferably 0.070 to 0.240 μm, still more preferably 0.075 to 0.240 μm, and 0.085 in order to further improve separation performance and water permeability. to 0.240 μm is particularly preferred.

The average value (y/x) _a of the ratio of the major and minor diameters of the surface pores is preferably 1.00 to 1.50, more preferably 1.00 to 1.40, in order to further improve the separation performance and water permeability, It is more preferable that it is 1.00-1.35, and it is especially preferable that it is 1.30-1.35.

(Membrane permeation flow rate)

In the separation membrane of the present invention, the membrane permeation flow rate at 50 kPa and 25° C. is preferably 0.10 to 20 m ³ /m ² /h, more preferably 0.25 to 15 m ³ /m ² /h, and 0.30 to 10 m ³ It is more preferably /m ² /h, particularly preferably 0.50 to 7.00 m ³ /m ² /h. The calculation method will be described in detail in Examples.

(Separation Performance)

In the separation membrane of the present invention, the separation performance of polystyrene latex particles having an average particle diameter of 0.2 μm is preferably 50% or more, more preferably 90% or more, still more preferably 95% or more, and particularly preferably 99% or more. The calculation method will be described in detail in Examples.

(Method for manufacturing separator)

The separation membrane manufacturing method of the present invention includes the following (1) to (3).

(1) A preparation step in which a resin composition is obtained by melt-kneading a mixture containing 10 to 80% by mass or less of a cellulose ester, 10 to 80% by mass of a structure forming agent, and 2 to 20% by mass of a pore forming agent. .

(2) A molding process, wherein the resin composition is discharged from a discharge 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) The immersion process of immersing the said resin molding in the solvent whose solubility parameter distance D _S with respect to a cellulose ester is the range of 10-25.

Next, the method for manufacturing the separation membrane of the present invention will be described in detail by taking the case where the separation membrane is a hollow fiber membrane as an example.

In the preparation step of obtaining the resin composition for manufacturing the separation membrane of the present invention, a mixture comprising 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 This is melt-kneaded. The mixture preferably contains 15 to 75 mass% of a cellulose ester, 20 to 75 mass% of a structure forming agent, and 3 to 18 mass% of a pore forming agent, 20 to 60 mass% of a cellulose ester; It is more preferable to contain 25 to 70 mass % of a structuring agent and 5 to 15 mass % of a pore former, 20 to 60 mass % of a cellulose ester, 25 to 70 mass % of a structuring agent, 10 It is especially preferable to contain -15 mass % of a pore former.

There is no restriction|limiting in particular about the apparatus used for melt-kneading a mixture, A mixer, such as a kneader, a roll mill, a Banbury mixer, or a single screw or twin screw extruder, can be used. Among them, from the viewpoint of improving the dispersibility of the structure-forming agent and plasticizer, the use of a twin-screw extruder is preferable, and from the viewpoint of being able to remove volatile substances such as moisture and low molecular weight substances, a twin-screw extruder having a vent hole is used This is more preferable. Moreover, although you may use the twin screw extruder provided with the screw which has a flight part and a kneading disk part, in order to make the intensity|strength of kneading|mixing low, it is preferable to use the twin screw extruder provided with the screw comprised only with a flight part.

The resin composition obtained in the preparation step may be pelletized once, melted again, and used for melt film formation, or may be directly directed to a spinneret and used for melt film formation. When pelletizing once, it is preferable to dry a pellet and to use the resin composition which made the moisture content 200 ppm (mass basis) or less. When the moisture content is 200 ppm (based on mass) or less, deterioration of the resin can be suppressed.

A shaping|molding process is a process of forming a resin molding by discharging the resin composition obtained in the preparation process from a discharge nozzle. The molding step may be, for example, a step in which a resin molded product is formed by discharging into the air from a discharge nozzle having a double annular nozzle having a gas flow path arranged in the center portion, and cooling with a cooling device.

It is preferable to discharge the resin composition which passed the filter beforehand from the discharge nozzle. In order to increase the values of l, L and (l/d) _a and to suppress the bonding of the pores, the pore diameter of the filter is preferably 40 to 200 µm, more preferably 70 to 150 µm, It is more preferable that it is 70-120 micrometers. When the resin composition passes through the filter, the pore-forming agent contained in the resin composition expands, increases the values of l, L, and (l/d) _a , and it is estimated that the effect of suppressing bonding between the pores is obtained.

The resin molding cooled by the cooling device, that is, the hollow fiber, may be wound up by the winding device. In this case, the value of the draft ratio calculated as (winding speed)/(discharge speed from the discharge nozzle) by the winding device increases the values of l, L and (l/d) _a , and further increases the value of the separation membrane in the longitudinal direction of the separation membrane. In order to suppress that the average thickness of the wall part in this is suppressed from falling too much, it is preferable that it is 30-200, It is more preferable that it is 50-150, It is especially preferable that it is 100-150. When the resin composition discharged from the nozzle expands under the conditions of the draft ratio, the pore former contained in the resin composition expands, increases the values of l, L, and (l/d) _a , and also prevents bonding between the pores. It is estimated that the inhibitory effect is acquired. In solution film forming performed by mixing 50% by weight or more of a low molecular weight compound having a molecular weight of less than 1000 and a polymer, spinning at a high draft ratio as in the present invention is difficult and the pore former is not sufficiently expanded, so obtaining such an effect is difficult. difficult.

An immersion process is a process of impregnating the said resin molding in the solvent whose solubility parameter distance D _S with respect to the cellulose ester which is a raw material is 10-25. At this time, the extreme swelling and plasticization of resin can be suppressed by using the solvent or mixed solvent which has a cellulose ester and moderate affinity. Therefore, the solvent permeates into the resin molding while maintaining the shape of the resin. At this time, it is estimated that a plasticizer and a structure-forming agent are eluted while phase separation occurs in the resin molding. 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 the voids and pores in the cross section Z tend to be. In this invention, it is preferable to select the solvent which has a cellulose ester and affinity to some extent. The affinity of a cellulose ester and a solvent can be estimated by the three-dimensional Hansen solubility parameter (nonpatent literature 1). The affinity of a solvent with respect to a cellulose ester is high, so that the solubility parameter distance D _S calculated|required from following formula (1) specifically, is small.

However, δ _Ad , δ _Ap and δ _Ah are the dispersion terms, polar terms and hydrogen bonding terms of the solubility parameter of the cellulose ester, and δ _Bd , δ _Bp and δ _Bh are the dispersion terms and polar terms of the solubility parameter of the solvent or mixed solvent. and a hydrogen bond term. About the solubility parameter (delta _Mixture ) of a mixed solvent, it can calculate|require by following formula (2).

However, φ _i and δ _i are the volume fraction and solubility parameters of component i, and are each constituted by a dispersion term, a polarity term, and a hydrogen bonding term. Here, "volume fraction of component i" means the ratio of the volume of component i before mixing with respect to the sum of the volumes of all components before mixing. As the three-dimensional Hansen solubility parameter of the solvent, the value described in Non-Patent Document 1 was used. For solvent parameters not described, the values contained in the software "Hansen Solubility Parameter in Practice" developed by Charles Hansen et al. were used. The three-dimensional Hansen solubility parameter of a solvent or polymer without a description in the software can be calculated by the Hansen sphere method using the software.

The present inventors, by impregnating the resin molding in a solvent having the solubility parameter distance D _S of 10 to 25, the depth d of each void and the average depth D of the plurality of voids are increased, and a film having large d and D is obtained, I gained an unexpected knowledge. And it discovered that the effect of reducing a substantial film thickness was acquired more notably by this. Although it is not clear why such an effect is obtained, it is estimated as follows. That is, since the pore former is not compatible with the cellulose ester, the pore former is dispersed in the cellulose ester after the molding process and before the immersion process, and in the immersion process, the solubility parameter distance D _s for the cellulose ester is With a solvent of 10 to 25, it is presumed that the pore former swells to obtain a film having large d and D.

It is preferable that the temperature of the resin molding in the said immersion process is 50-80 degreeC. When the temperature of the resin molding in the immersion step is 50 to 80° C., surprisingly, the voids of the cross section Z are (l/d) _a is 2 to 40, but the average value of the ratio of the major and minor diameters of the surface pores (y /x) _a was found to be lowered to 1.0 to 1.5, that is, close to a circle. The reason for this is estimated as follows. That is, when the actual temperature of the resin molding is 50 to 80° C., the molecules become relatively mobile, but at this time, the surface becomes a state in which the molecules are particularly mobile compared to the inside. It is presumed that this is because, when plasticization is further promoted by immersion, the structure-forming agent that has been enlarged by the filter hole or draft returns to its original shape on the surface and approaches a circular shape.

In this invention, as a solvent in which a resin molding is immersed, the solvent used as DS of _13-25 is preferable. As such a solvent, a solvent in which _DS is 4 to 12, and a mixed solvent of water are preferable, for example, γ-butyrolactone (hereinafter, γ-BL), acetone, acetonitrile, 1,4-dioxane, and a mixed solvent of at least one selected from the group consisting of methyl acetate and tetrahydrofuran, and water. By using a mixed solvent of a solvent having D _S of 4 to 12 and water, the resulting separation membrane has good membrane strength.

Although the obtained separation membrane can be used as it is, it is preferable to hydrophilize the surface of the membrane with, for example, an alcohol-containing aqueous solution or an aqueous alkali solution before use.

It is preferable to provide the process of removing a space|gap former, when the space|gap former remains even if it passes through the process up to this. As a method of removing the pore-forming agent, for example, the cellulose ester does not dissolve or decompose, but is immersed in a solution that dissolves or decomposes the pore-forming agent.

Example

The present invention will be more specifically described below with reference to Examples, but the present invention is not limited thereto.

[Measurement and evaluation method]

Each characteristic value in an Example was calculated|required by the following method.

(1) Average degree of substitution of cellulose mixed ester

The calculation method of the average degree of substitution of the cellulose mixed ester in which an acetyl group and another acyl group are bonded to cellulose is as follows.

0.9 g of the cellulose mixed ester dried at 80 degreeC for 8 hours was weighed, and after adding and dissolving 35 mL of acetone and 15 mL of dimethyl sulfoxide, acetone 50mL was further added. While stirring, 30 mL of a 0.5N aqueous sodium hydroxide solution was added, followed by saponification for 2 hours. After adding 50 mL of hot water and washing the flask side, phenolphthalein was titrated with 0.5N-sulfuric acid as an indicator. Separately, a blank test was performed in the same manner as the sample. The supernatant of the solution after the titration was completed was diluted 100-fold, and the composition of the organic acid was measured using an ion chromatograph. From the measurement result and the acid composition analysis result by the ion chromatograph, 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 (mL)

A: Sample titer (mL)

B: blank test titer (mL)

F: titer of sulfuric acid

W: sample mass (g)

DSace: average degree of substitution of acetyl groups

DSacy: average degree of substitution of other acyl groups

Mwace: 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: repeat unit molecular weight 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 melt|dissolved in tetrahydrofuran so that the density|concentration of a cellulose ester might be set to 0.15 mass %, and it was set as the sample for GPC measurement. Using this sample, GPC measurement was performed using a GPC apparatus (Waters2690) under the following conditions, and the weight average molecular weight (Mw) was calculated|required by polystyrene conversion.

Column: Connect two TSK gel GMHHR-H paints

Detector: Waters2410 Differential Refractometer RI

Moving bed solvent: tetrahydrofuran

Flow rate: 1.0 mL/min

Injection volume: 200 μL

(3) the shape of the surface hole

The outer surface of the separation membrane sputtered with platinum was observed at a magnification of 10,000 times using an SEM, the pore diameters r of 50 randomly selected surface pores were measured, and the arithmetic mean value of the surface pore diameters in Tables 1 and 2 was obtained. r.

Here, the hole diameter r of each surface hole was computed from the following formula (6), assuming that the area of a surface hole was measured by image processing, a hole of the same area was assumed.

r=(4×A/π) ^0.5 … … (6)

A: Area of the hole

In addition, the observation conditions using sputtering and SEM are as follows.

(Sputtering conditions)

Apparatus: Hitachi High-Tech Co., Ltd. (E-1010)

Deposition time: 40 seconds

Current value: 20mA

(SEM conditions)

Device: Hitachi High-Tech Co., Ltd. (SU1510)

Acceleration voltage: 5kV

Probe Current: 30

In addition, the outer surface of the separation membrane was observed under the same observation conditions as above, and the average minor diameter X of the surface pores, the average major diameter Y, and the average value (y/x) of the ratio of the major and minor diameters of the surface pores by the above-described analysis method The value of _a was obtained.

(4) Thickness of hollow fiber membrane

After freezing the hollow fiber membrane with liquid nitrogen, stress was applied (using a razor or microtome as needed), and the diametric cross section was cut to expose. The obtained cross section was observed with the optical microscope, and the average value of the thickness of 10 places randomly selected was made into the thickness (film thickness) of a hollow fiber membrane.

(5) Outer diameter of hollow fiber membrane

The cross section of said (4) was observed with the optical microscope, and the average value of the outer diameters of ten randomly selected places was made into the outer diameter of a hollow fiber membrane, respectively.

(6) Membrane permeation flow rate of hollow fiber membrane

A small module with an effective length of 100 mm including one hollow fiber membrane was manufactured. Distilled water was fed to this small module by external pressure total filtration over 30 minutes under the conditions of a temperature of 25° C. and a filtration differential pressure of 16 kPa, and the obtained permeate amount (m ³ ) was measured, and this was measured in unit time (h) and unit membrane area. It was converted into a numerical value per (m ² ) and further converted to a pressure (50 kPa) to obtain the pure water permeation performance (unit = m ³ /m ² /h).

(7) Measurement of a plurality of voids and walls

After the separator was frozen with liquid nitrogen, stress was applied (using a razor or a microtome if necessary), and the separator was cut so as to expose a cross-section Z, which is a cross section parallel to the longitudinal direction and the thickness direction of the separator. Then, after sputtering with platinum and pretreating the cross section Z, the field of view was set so that the distances from both surfaces were equal in the center of the field of view using an SEM, and observation was performed at a magnification of 2,000 times. Similarly, after observing 5 fields of view, and randomly extracting 30 voids in each visual field, the average depth D (μm) and the average length L (μm) of the plurality of voids, and the average value of l/d of each void (l /d) _a was calculated, and the occupancy rate (%) of the plurality of voids, the average thickness (µm) of the wall portion, and the angle (°) in the longitudinal direction of the plurality of voids were calculated. In addition, the observation conditions using sputtering and SEM are as follows.

(Sputtering conditions)

Apparatus: Hitachi High-Tech Co., Ltd. (E-1010)

Deposition time: 40 seconds

Current value: 20mA

(SEM conditions)

Device: Hitachi High-Tech Co., Ltd. (SU1510)

Acceleration voltage: 5kV

Probe Current: 30

(8) Area ratio of the concave portion

The separation membrane was cut in the same manner as in (7) above, and the exposed cross-section Z was observed at a magnification of 5,000 times using an SEM, and the area ratio of the recesses (area ratio of the recesses) was calculated.

(9) Separation performance

In the same manner as in (6) above, a small module was produced. An aqueous solution containing 20 ppm of polystyrene latex particles (manufactured by Magsphere) with an average particle diameter of 0.2 μm as a suspension component was fed to this small module by external pressure total filtration over 30 minutes under conditions of a temperature of 25° C. and a filtration differential pressure of 16 kPa, and the feed water And the suspended matter component concentration of each of the permeated water was calculated from the ultraviolet absorption coefficient of wavelength 234 nm measured using a spectrophotometer (manufactured by Hitachi, Ltd.; U-3200), and calculated from the following formula (7).

Separation performance (%) = [1-2 x (concentration of suspended matter component in permeate water)/{(concentration of suspended matter component in feed water at the start of filtration) + (concentration of suspended matter component in feed water at the end of filtration)}] x 100 … … Equation (7)

[Cellulose Ester (A)]

As a cellulose ester, the following were prepared.

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 mixed at 50°C for 30 minutes. After cooling the mixture 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 esterifying agent and 4 parts by mass of sulfuric acid as an esterification catalyst, followed by stirring for 150 minutes, followed by esterification. . In the esterification reaction, when it exceeded 40 degreeC, it cooled in a water bath.

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 anhydride. Then, 333 mass parts of acetic acid and 100 mass parts of water were added, and it heat-stirred at 80 degreeC for 1 hour. After completion of the reaction, an aqueous solution containing 6 parts by mass of sodium carbonate was added, and the precipitated cellulose acetate propionate was separated by filtration and washed with water, followed by drying at 60°C for 4 hours. The average substitution degrees of the acetyl group and propionyl group of the obtained cellulose acetate propionate were 1.9 and 0.7, respectively, and the weight average molecular weight (Mw) was 178,000.

Cellulose ester (A2): 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): 185,000)

[Other raw materials]

As other raw materials, the following were prepared.

Cellulose ester plasticizer (B): 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) 300,000)

Antioxidant (E): bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite

(Example 1)

Cellulose ester (A1) 40 mass%, plasticizer (B) 26.9 mass%, structure forming agent (C) 30 mass%, pore forming agent (D) 3 mass%, antioxidant (E) 0.1 mass% After melt-kneading and homogenizing at 220 degreeC with a twin screw extruder, it pelletized and obtained the resin composition. This resin composition was vacuum-dried under the conditions of 80 degreeC and 8 hours.

The dried resin composition is supplied to a twin-screw extruder equipped with a screw composed of only the flight part, melt-kneaded at 220 ° C., and then introduced into a melt spinning pack at a spinning temperature of 220 ° C., at a discharge rate of 10 g/min. , discharged downward from the outer annular portion of the discharge nozzle having one hole (double cylindrical type, discharge hole diameter 2.6 mm, slit width 0.35 mm). The discharged hollow fiber was guided to a cooling device, cooled by a cooling wind at 25°C and a wind speed of 1.5 m/sec, and wound up with a winder so that the draft ratio was 30. Here, as the filter in the melt spinning pack, a metal filter having a pore diameter (filter diameter) of 200 μm was used. The wound hollow fiber (resin molding) is heated to 30° C., immersed in an aqueous acetone solution having a volume fraction of 40% for 1 hour, and further immersed in water for 1 hour or more, a plasticizer (B), a structure former (C) and The pore former (D) was eluted to obtain a separation membrane. Table 1 shows the physical properties of the obtained separation membrane.

(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 of the resin composition and the manufacturing conditions were changed as in Tables 1 and 2, respectively. The physical properties of the obtained separation membrane are shown in Tables 1 and 2. In addition, in Comparative Example 1, no voids were observed, and in Comparative Example 2, spinning was not possible due to yarn breakage.

All of the separation membranes obtained in Examples 1 to 9 had a membrane permeation flow rate of 0.1 m ³ /m ² /h or more and a separation performance of 50% or more, so that a high membrane permeation flow rate and separation performance were compatible. On the other hand, in Comparative Example 2, the yarn could not be spun due to breakage, and a separation membrane could not be obtained. In addition, the separation membranes of Comparative Examples 1 and 3 to 6 in which the shape of the plurality of pores do not satisfy the requirements of the present invention exhibited low values of at least one of the membrane permeation flow rate and separation performance, resulting in a high membrane permeation flow rate and separation performance. Reconciliation could not be realized.

Although this invention was detailed also demonstrated with reference to the specific embodiment, it is clear for those skilled in the art that various changes and correction can be added without deviating from the mind and range of this invention. This application is based on the Japanese patent application (Japanese Patent Application No. 2019-231579) of an application on December 23, 2019, The content is taken in here as a reference.

The separation membrane of the present invention is a water treatment membrane for producing industrial water or drinking water from seawater, brine, sewage or drainage, etc., a medical membrane for artificial kidney or plasma separation, etc., a food and beverage industry membrane for fruit juice concentration, etc.; It can be suitably used for a gas separation membrane for separating exhaust gas or carbon dioxide gas, or a membrane for electronic industry, such as a fuel cell separator.

Claims (10)

It is a separation membrane containing cellulose ester,
The separation membrane has a plurality of voids in a cross section parallel to the longitudinal direction and the film 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
The average value (l/d) _a of the ratio of the length l and the depth d of each pore is 2 to 40, the separator. The separation membrane according to claim 1, wherein an occupation rate of the plurality of voids in the cross section is 15 to 55%. The separation membrane according to claim 1 or 2, wherein the average thickness of the wall portion in the cross section is 0.7 to 5.0 µm. The separation membrane according to any one of claims 1 to 3, wherein, on at least one surface, the average pore diameter of the surface pores is 0.050 to 0.500 µm. 5. The elongate according to any one of claims 1 to 4, wherein in at least one surface, the average minor diameter X of the surface pores is 0.030 to 0.250 μm, the average major diameter Y of the surface pores is 0.060 to 0.450 μm, The average value (y/x) _a of the ratio of the diameter and the short diameter is 1.00 to 1.50, the separator. 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. The separation membrane according to any one of claims 1 to 6, wherein the cellulose ester contains cellulose acetate propionate and/or cellulose acetate butyrate. The separation membrane according to any one of claims 1 to 7, which has a hollow fiber shape. (1) a preparation step of melt-kneading 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 to obtain a resin composition; ,
(2) a molding step of discharging the resin composition from a discharge nozzle using a filter having a pore diameter of 40 to 200 μm to obtain a resin molding at a draft ratio of 30 to 200;
(3) A method for producing a separation membrane comprising an immersion step in which the resin molding is immersed in a solvent having a solubility parameter distance D _S with respect to a cellulose ester in the range of 10 to 25. The method of claim 9, wherein the temperature of the resin molded product in the immersion step is 50 to 80°C.

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