CN118251268A - Separation membrane and method for producing same - Google Patents

Separation membrane and method for producing same Download PDF

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Publication number
CN118251268A
CN118251268A CN202280026655.9A CN202280026655A CN118251268A CN 118251268 A CN118251268 A CN 118251268A CN 202280026655 A CN202280026655 A CN 202280026655A CN 118251268 A CN118251268 A CN 118251268A
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separation membrane
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ratio
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orientation
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Inventor
田口万里奈
花川正行
山村刚平
高田皓一
荣村弘希
青山滋
阿久津美句
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Toray Industries Inc
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Toray Industries Inc
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Abstract

The present invention provides a separation membrane having high strength and low leakage while maintaining high gas permeability, using poly (4-methyl-1-pentene) excellent in chemical resistance and gas permeability. Provided is a separation membrane comprising poly (4-methyl-1-pentene) as a main component, wherein the fraction RA of the rigid amorphous poly (4-methyl-1-pentene) in the separation membrane is 43-60%, the void ratio is 30-70%, and a dense layer is provided on at least one surface.

Description

Separation membrane and method for producing same
Technical Field
The present invention relates to a separation membrane and a method for producing the same.
Background
As a degassing method for removing dissolved gas from a liquid and a gas exchange method for exchanging dissolved gas in a liquid with a gas component in a gas phase, there is a method using a hollow fiber membrane. Since hollow fiber membranes used in these applications require solvent resistance and high gas permeability with respect to the liquid to be treated, poly (4-methyl-1-pentene) having excellent properties is sometimes used as a membrane material. Among such hollow fiber membranes, a membrane having a thin dense layer of 2.0 μm or less in the surface layer is desirable in that the gas permeation flow rate can be improved as a whole.
On the other hand, such a separation membrane having a thin dense layer on the surface layer is unsuitable for production by stretching because a through-hole is formed in the thin dense layer by stretching, and solution leakage occurs with the hole as a starting point. Further, the support layer located on the inner side of the surface layer of the separation membrane has a plurality of voids, and the strength is low due to the high void ratio.
In recent years, a separation membrane having high permeability and high strength has been demanded. Various methods have been proposed so far for obtaining a gas permeable membrane having high permeability or high strength and low leakage. Low leakage refers to: and a difficult leakage degree of the liquid when the dissolved gas is removed from the liquid and when the dissolved gas in the liquid is exchanged with the gas component.
For example, patent document 1 discloses a dry-wet solution method using a polyolefin polymer. Specifically, in patent document 1, a polymer solution obtained by dissolving a polyolefin polymer in a good solvent is extruded from a ferrule at a temperature higher than the melting point of a polyolefin resin, and the polymer solution is brought into contact with a cooling solvent, whereby an asymmetric structure having a dense layer on one surface is formed by thermally induced phase separation. However, the film of patent document 1 has a problem that the strength is insufficient without stretching. Further, in order to prevent the pores of the dense layer from being significantly perforated by stretching, the stretching should not exceed 10%, and there is a disadvantage that only low-rate stretching is possible.
Patent document 2 discloses a hollow fiber membrane by a fusion method. Specifically, the polyolefin resin is extruded from the tube head at a temperature equal to or higher than the melting point, cooled and solidified, and then stretched to locally crack the tube head, thereby forming the internal pores and forming a structure having a dense surface layer and a porous interior. In this method, a film having high strength and low leakage can be obtained, but the film has a low void ratio, and therefore has a disadvantage of insufficient gas permeability.
Prior art literature
Patent literature
Patent document 1: international publication No. 2003/061812
Patent document 2: japanese patent laid-open No. 7-155569
Disclosure of Invention
Problems to be solved by the invention
The separation membrane of patent document 1 has difficulty in achieving high strength while maintaining practical gas permeability and low leakage. The separation membrane obtained in patent document 2 has high strength and low leakage, but has insufficient void fraction and insufficient gas permeability.
In view of the problems of the prior art described above, the present inventors have an object of providing a separation membrane having high strength and low leakage while maintaining high gas permeation performance, using poly (4-methyl-1-pentene) excellent in chemical resistance and gas permeation performance.
Means for solving the problems
The present inventors have conducted intensive studies to solve the above problems, and as a result, found that: the present invention has been accomplished by providing a separation membrane comprising poly (4-methyl-1-pentene) as a main component and having a dense layer on at least one surface, wherein the ratio RA of the rigid and amorphous poly (4-methyl-1-pentene) in the membrane is in a specific range, and wherein the porosity is in a specific range, thereby achieving high strength and low leakage while maintaining high gas permeability.
That is, the separation membrane is a separation membrane containing poly (4-methyl-1-pentene) as a main component, wherein the ratio RA of the rigid amorphous of poly (4-methyl-1-pentene) defined by formula 1 in the separation membrane is 43% or more and 60% or less, the void ratio of the whole separation membrane is 30% or more and 70% or less, and a dense layer is provided on at least one surface side of the separation membrane.
RA (%) =100- (ma+c) … formula 1
Wherein MA is the proportion of movable amorphous, and C is the crystallinity.
In the separation membrane, the temperature-loss elastic modulus (E ") curve of the separation membrane based on the dynamic viscoelasticity test has a peak in a range of 30.0 ℃ to 50.0 ℃.
Effects of the invention
According to the present invention, a separation membrane having high strength and low leakage while maintaining high gas permeation performance is provided by using poly (4-methyl-1-pentene) excellent in chemical resistance and gas permeation.
Drawings
Fig. 1 is an example of an image obtained by scanning a cross section cut along the thickness direction of a separation membrane by SEM.
Fig. 2 is an image obtained by binarizing the image of fig. 1 and removing noise.
Fig. 3 is a schematic diagram showing a method of obtaining a dense layer thickness from an image.
Fig. 4 is a two-dimensional diffraction image of wide-angle X-rays of the hollow fiber membrane.
Fig. 5 is a graph showing the azimuthal intensity distribution of the hollow fiber membrane at 2θ=9.7°.
Detailed Description
The separation membrane of the present invention is characterized in that the separation membrane comprises poly (4-methyl-1-pentene) as a main component, the ratio RA of the rigid amorphous poly (4-methyl-1-pentene) in the separation membrane is 43% to 60%, the void ratio is 30% to 70%, and a dense layer is provided on at least one surface side.
In the present specification, the mass-based ratio (percentage, part, etc.) is the same as the weight-based ratio (percentage, part, etc.). Hereinafter, a resin composition constituting the separation membrane will be described.
< Resin composition constituting separation Membrane >
The resin composition constituting the separation membrane of the present invention contains poly (4-methyl-1-pentene) as the main component shown in the following (1). In addition to (1), the composition may contain the following components (2) to (3).
(1) Poly (4-methyl-1-pentene) (hereinafter referred to as "PMP")
The separation membrane of the present invention needs to contain PMP as a main component. The main components mentioned here are: the content of the components in the separation membrane is 50 wt% or more based on the total components.
PMP is only required to have a repeating unit derived from 4-methyl-1-pentene. The PMP may be a homopolymer of 4-methyl-1-pentene or a copolymer with a monomer copolymerizable with 4-methyl-1-pentene other than 4-methyl-1-pentene. Specifically, examples of the monomer copolymerizable with the 4-methyl-1-pentene include olefins having 2 or more and 20 or less carbon atoms (hereinafter referred to as "olefins having 2 or more and 20 or less carbon atoms") other than 4-methyl-1-pentene.
Examples of the olefin having 2 or more carbon atoms and 20 or less carbon atoms copolymerized with 4-methyl-1-pentene include ethylene, propylene, 1-butene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene and the like.
The olefins having 2 or more and 20 or less carbon atoms copolymerized with 4-methyl-1-pentene may be one kind or two or more kinds may be combined.
The density of the PMP of the present invention is preferably 825kg/m 3 to 840kg/m 3, more preferably 830kg/m 3 to 835kg/m 3. If the density is less than the above range, there may be a problem that the mechanical strength of the separation membrane is lowered and defects are likely to occur. On the other hand, if the density is greater than the above range, the gas permeability tends to be low.
The Melt Flow Rate (MFR) of PMP measured at 260℃under a 5kg load is not particularly limited as long as it is in a range that can be easily mixed with a plasticizer to be described later and can be coextruded, and is preferably 1g/10min or more and 200g/10min or less, more preferably 5g/10min or more and 30g/10min or less. If the MFR is in the above range, extrusion molding is easy to achieve a relatively uniform film thickness.
PMP can be produced directly by polymerizing olefins or by thermally decomposing a high molecular weight 4-methyl-1-pentene polymer. The 4-methyl-1-pentene polymer may be purified by a method such as solvent separation by a difference in solubility in a solvent or molecular distillation by separation by a difference in boiling point. The PMP may be, for example, a commercially available polymer such as TPX manufactured by mitsunobu chemical company, in addition to the one produced by polymerizing olefins as described above.
When the total content of the separation membrane is 100% by mass, the PMP content in the separation membrane is preferably 70% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less, and still more preferably 90% by mass or more and 100% by mass or less. The PMP content in the separation membrane is 70 mass% or more, whereby the gas permeability is sufficient.
When the total content of the components constituting the raw material is 100% by mass, the PMP content in the raw material for producing the separation membrane is preferably 10% by mass or more and 50% by mass or less. When the content is 10 mass% or more, the membrane strength of the separation membrane is improved. On the other hand, when the content is 50 mass% or less, the permeation performance of the separation membrane is improved. The content is more preferably 15% by mass or more and 50% by mass or less, still more preferably 20% by mass or more and 45% by mass or less, particularly preferably 25% by mass or more and 40% by mass or less.
(2) Plasticizer(s)
The resin composition constituting the separation membrane of the present invention may contain a plasticizer of PMP. From the viewpoint of improving the permeability, the content of the plasticizer in the separation membrane is preferably 1000ppm (mass basis) or less, more preferably 500ppm (mass basis) or less, and particularly preferably 100ppm (mass basis) or less.
The plasticizer for PMP is not particularly limited as long as it is a compound that plasticizes PMP. The plasticizer of PMP may be 1 plasticizer alone, or 2 or more plasticizers may be used in combination.
Examples of the plasticizer for PMP include palm kernel oil, dibutyl phthalate, dioctyl phthalate, dibenzyl ether, coconut oil, and a mixture thereof. Among them, dibutyl phthalate and dibenzyl ether are preferably used from the viewpoints of compatibility and stringiness.
The plasticizer of the PMP is preferably dissolved out of the separation membrane after the separation membrane is formed. When the total content of the components constituting the raw material is 100% by mass, the content of the plasticizer of PMP in the raw material for producing the separation membrane is preferably 50% by mass or more and 90% by mass or less.
When the content is 90 mass% or less, the membrane strength of the separation membrane is improved. In addition, the content is 50 mass% or more, whereby the permeability of the separation membrane becomes good. The content is more preferably 50% by mass or more and 85% by mass or less, still more preferably 55% by mass or more and 80% by mass or less, particularly preferably 60% by mass or more and 75% by mass or less.
(3) Additive agent
The resin composition constituting the separation membrane of the present invention may contain additives other than those described in (2) as long as the effects of the present invention are not impaired.
Examples of the additives include resins such as cellulose ether, polyacrylonitrile, polyolefin, polyvinyl, polycarbonate, poly (meth) acrylate, polysulfone, and polyether sulfone, organic lubricants, crystallization nucleating agents, organic particles, inorganic particles, end-capping agents, chain extenders, ultraviolet absorbers, infrared absorbers, coloring resists, matting agents, antibacterial agents, antistatic agents, deodorizing agents, flame retardants, weather-proofing agents, antistatic agents, antioxidants, ion exchangers, antifoaming agents, coloring pigments, fluorescent brighteners, and dyes.
< Shape of separation Membrane >
The shape of the separation membrane of the present invention is preferably a hollow fiber-shaped separation membrane (hereinafter referred to as "hollow fiber membrane"). The hollow fiber membrane is preferably used because the hollow fiber membrane can be efficiently filled into the module and the effective membrane area per unit volume of the module can be increased.
The shape of the separation membrane in the present invention, that is, the thickness of the separation membrane, the outer diameter and inner diameter of the hollow fiber membrane, and the hollow ratio can be observed by using an optical microscope or a Scanning Electron Microscope (SEM), for example, with respect to a cross section (hereinafter, referred to as a "radial cross section") obtained by applying stress to the separation membrane sufficiently cooled in liquid nitrogen and cutting the separation membrane in the thickness direction of the membrane. With respect to specific methods, detailed descriptions are given in examples.
From the viewpoint of both the permeation performance and the membrane strength, the thickness of the separation membrane is preferably 10 μm or more and 500 μm or less. The thickness is more preferably 30 μm or more, and still more preferably 50 μm or more. The thickness is more preferably 200 μm or less, still more preferably 150 μm or less, particularly preferably 100 μm or less.
From the viewpoint of both the effective membrane area and the membrane strength at the time of filling into the module, the outer diameter of the hollow fiber membrane is preferably 50 μm to 2500 μm. The outer diameter 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. The outer diameter is more preferably 1000 μm or less, still more preferably 500 μm or less, particularly preferably 450 μm or less.
The inner diameter of the hollow fiber membrane is preferably 20 μm or more and 1000 μm or less from the viewpoint of the relation between the pressure loss and buckling pressure of the fluid flowing through the hollow portion. The inner diameter of the hollow fiber membrane is more preferably 50 μm or more, still more preferably 100 μm or more, and particularly preferably 150 μm or more. The inner diameter is more preferably 500 μm or less, still more preferably 300 μm or less, and particularly preferably 250 μm or less.
The hollow fiber membrane preferably has a hollow ratio of 15% to 70% in terms of the relationship between the pressure loss of the fluid flowing through the hollow portion and the buckling pressure. The hollow ratio is more preferably 20% or more, and still more preferably 25% or more. The hollow ratio is more preferably 60% or less, still more preferably 50% or less, and particularly preferably 40% or less.
The method of setting the outer diameter, inner diameter, and hollow ratio of the hollow fibers in the hollow fiber membrane to the above ranges is not particularly limited, and the hollow fiber membrane may be adjusted by, for example, appropriately changing the shape of the discharge hole of the spinning nozzle for producing the hollow fibers, or by calculating the draft ratio by the winding speed/discharge speed, or the air travel distance. The distance travelled in the air referred to herein is the distance from the nozzle tip to the cooling bath in the formation step described below.
As described later, the separation membrane of the present invention can be produced by forming a resin molded product from a membrane-forming stock solution containing a polymer and stretching the resin molded product. For convenience, the state before stretching is referred to as "resin molded product", and the state after stretching is referred to as "separation film".
The dense layer in the separation membrane of the present invention has a thickness of 0.1 μm or more and 2.0 μm or less. The compact layer refers to: when observed at a magnification of 10,000 times using a Scanning Electron Microscope (SEM), the layer of the separation film does not have a void, which means: for example, a hole portion having a diameter of 10nm or more when the radial cross section or the longitudinal cross section of the separation membrane is observed at a magnification of 2,000 times by using a scanning electron microscope (hereinafter referred to as "SEM"). When the hole is observed by the above operation, the hole may appear concave. That is, having a dense layer means: when the film surface is observed with a Scanning Electron Microscope (SEM) at a magnification of 2,000 to 10,000 times, 1 pore having a diameter of 10nm or more, that is, 1 void, is not observed. Here, voids having a diameter of less than 10nm are not easily observed in terms of resolution in SEM observation. It is also difficult to determine voids having a diameter of less than 10nm when observed at 10,000 times, but the dense layer of the separation membrane of the present invention may have pores having a diameter of less than 10nm, i.e., minute voids. From the viewpoint of gas permeability, the diameter of the voids of the dense layer is preferably small, and furthermore, the dense layer is more preferably free of voids.
In addition, the dense layer thickness refers to: when a line is drawn perpendicularly from an arbitrary point of a surface having no void (e.g., film surface 1 of fig. 1) toward the other surface, holes having a diameter exceeding 10nm, i.e., first reach the length of the void. The detailed description will be made with reference to the drawings. For the separation membrane to be observed, for example, a separation membrane sufficiently cooled in liquid nitrogen is subjected to stress (a blade, a microtome, or a wide ion beam is used as necessary), and a radial cross section or a cross section parallel to the longitudinal direction of the membrane and parallel to the thickness direction of the membrane (hereinafter referred to as a "longitudinal cross section") is used. A longitudinal section including the dense layer near the surface of the separation membrane was observed using a Scanning Electron Microscope (SEM). Using the image thus obtained, the size of the voids and the thickness of the dense layer can be obtained.
Fig. 1 (a) is an example of a cross-sectional SEM image including a dense layer near the surface of a separation membrane. Fig. 1 (a) shows the film surface 1 and the void portion 3. In fig. 1 (a), the void is a portion that appears darker than the surrounding area, and a symbol 3 marks the position of a representative void portion. The dense layer 2 is at the membrane surface and an inner layer 5 is shown as a support layer in the lower layer of the dense layer 2. Fig. 1 (b) is a schematic view schematically showing the relationship between the void portion 3 and the dense layer 2. The void 3 is a hole or recess having a diameter of 10nm or more, and is a portion that appears darker than the surrounding area in fig. 1 (a). As shown in fig. 1 (b), the shortest distance from the film surface 1 to each void 3 is obtained as the thickness 4 of the dense layer at each point. Although not shown, the inner layer 5 of the separation membrane is a porous layer, and large voids are further present in the lower layer of the dense layer.
The thickness of the dense layer is obtained as an average value of the imaginary curve 6 of the dense layer. At this time, the virtual curve 6 connects the shortest route points of the respective voids 3 as shown in fig. 1 (b). Specifically, in the vicinity of the film surface 1, a plurality of distances to the voids 3 observed in the form of holes or depressions having a diameter of 10nm or more can be measured, and the average value thereof can be used as the thickness of the dense layer. Further, the coefficient of variation in the thickness of the dense layer can be obtained from the variation of the virtual variation curve 6, specifically, the variation can be obtained by measuring a plurality of distances to the voids 3 observed in the form of holes or depressions having a diameter of 10nm or more in the vicinity of the film surface 1 and obtaining the variation thereof. The coefficient of variation can be calculated by dividing the standard deviation by the average value and converting it into a percentage based on the thickness measurement results of the plurality of dense layers.
FIGS. 2 and 3 show an example of a method for specifying voids having a diameter of 10nm or more. Can be obtained by extracting only pores larger than 10nm after binarizing the obtained cross-sectional SEM image in the image analysis software "ImageJ". In the processed image shown in fig. 2, the resin portion is white, and the void portion 3 is black. The film surface 1 is indicated by a dashed line. Fig. 3 is a processed image showing the boundary line of the void portion 3 having a diameter of 10nm or more (an area of 78.5nm 2 or more) extracted from the processed image of fig. 2. The thickness 4 of the dense layer is the shortest path from the film surface 1 at each location, in other words, the distance from the line representing the film surface 1 to the point at which the line segment falling vertically intersects the boundary line shown in fig. 3.
The longitudinal direction mentioned here means the mechanical direction at the time of manufacture, and in the case of a hollow fiber membrane, is the direction perpendicular to the radial direction. In the case of a hollow fiber membrane, the width direction is a direction parallel to the radial direction, that is, the in-plane direction of the hollow surface can be modified. On the other hand, in the case where the separation membrane is a flat membrane, it is difficult to determine the longitudinal direction from the appearance of the separation membrane. Thus, the longitudinal direction of the flat membrane in the present invention is the direction in which the separation membrane is oriented. That is, in the orientation degree measurement of polarized IR described later, the direction of highest intensity is defined as the longitudinal direction of the flat film. The method for measuring the dense layer thickness (for example, dense layer thickness 2 in fig. 3) is also described in detail in examples.
The leakage resistance is improved by setting the thickness of the dense layer to 0.10 μm or more, and the permeability is improved by setting the thickness to 2.0 μm or less. That is, the thickness of the dense layer is preferably 0.1 μm or more and 1.5 μm or less. The thickness of the dense layer is preferably 0.1 μm or more and 1.0 μm or less, more preferably 0.1 μm or more and 0.4 μm or less.
The dense layer in the separation membrane of the present invention is preferably at the outer surface. By providing the dense layer on the outer surface, the specific surface area during operation is increased, and the permeability is more easily improved.
In the separation membrane of the present invention, the coefficient of variation of the thickness of the dense layer is preferably 80% or less, more preferably 50% or less, further preferably 30% or less, and particularly preferably 10% or less. By setting the coefficient of variation within the above range, both the permeability and the separation performance can be easily achieved. The lower limit of the coefficient of variation in the thickness of the dense layer is not particularly limited, but is usually preferably smaller, and most preferably 0%. As a method for setting the coefficient of variation of the dense layer thickness to the above range, for example, a method in which the draft ratio at the time of ejecting the resin composition from the ejection tip is set to 1 to 10 is included, but the method is not limited thereto.
In the support layer of the separation membrane of the present invention, the number of voids larger than 10 μm is preferably 3 or less relative to the membrane area. The support layer is a layer of the separation membrane from which the dense layer is removed, and has a plurality of voids. The plurality of voids means: in the case where the supporting layer in the radial section or the longitudinal section is observed at a magnification of 2,000 times using SEM, 10 or more voids exist per 1 field of view. The strength of the separation membrane is improved by setting the number of voids larger than 10 μm in the support layer to 3 or less. The voids of 10 μm or more in the support layer can be obtained as follows: the separation membrane sufficiently cooled in, for example, liquid nitrogen is subjected to stress (using a blade or a microtome or a wide ion beam as required), a radial cross section or a longitudinal cross section is observed using a scanning electron microscope (hereinafter, referred to as SEM), and after binarizing the obtained image in image analysis software "ImageJ", only pores having an average diameter of more than 10 μm are extracted. The number of voids larger than 10 μm in the support layer is more preferably 2 or less, still more preferably 1 or less, and particularly preferably 0. The method for measuring voids larger than 10 μm in the support layer is described in detail with examples.
The average pore diameter of the support layer in the separation membrane of the present invention is preferably 100nm to 1000 nm. The support layer of the present invention means a porous membrane layer which is further inside than the dense layer on the surface of the separation membrane. The average pore size of the support layer can be obtained as follows: for example, after exposing a separation membrane sufficiently cooled in liquid nitrogen to a radial cross section by a microtome, the resultant image is observed by a Scanning Electron Microscope (SEM), and after binarizing the image in an image analysis software "ImageJ", only pores having an average diameter of more than 100nm are extracted. The average pore diameter of the support layer is set to 100nm or more, whereby the permeability is improved, and the strength of the separation membrane is improved to 1000nm or less. The average pore diameter of the support layer is preferably 100nm to 800nm, more preferably 100nm to 600nm, still more preferably 100nm to 570nm, particularly preferably 100nm to 500 nm. The method for measuring the average pore diameter of the support layer is described in detail in examples.
< Ratio of Condition of Rigid Amorphous (RA) >
In general, a polymer has a crystalline region and an amorphous region, wherein the amorphous region can be classified into a mobile amorphous that shows a stepwise endothermic peak accompanied by a change in specific heat capacity at a glass transition temperature and a rigid amorphous that does not undergo a change in specific heat capacity under normal conditions. The possibility of molecular orientation of the rigid amorphous or the existence of a so-called linking molecule that links crystals, etc. can be considered.
The ratio of the rigid amorphous is determined with high accuracy from the change in specific heat capacity before and after the glass transition on the TMDSC curve of the reversible component by the temperature-modulated differential scanning calorimeter (hereinafter referred to as "TMDSC") and the heat of fusion in the DSC curve by the differential scanning calorimeter (hereinafter referred to as "DSC").
In the separation membrane of the present invention, it is important that the ratio RA of the rigid amorphous form of poly (4-methyl-1-pentene) in the separation membrane (hereinafter referred to as "the ratio RA of rigid amorphous") is 43% or more and 60% or less. The ratio RA of the rigid amorphous was obtained by RA (%) =100- (ma+c). Here, MA is the proportion of mobile amorphous, and C is the crystallinity.
When the ratio RA of the rigid amorphous is 43% or more, the strength of the separation membrane is improved, and when the ratio RA is 60% or less, the flexibility of the separation membrane is improved. The ratio RA of the rigid amorphous is preferably 48% or more and 60% or less, more preferably 50% or more and 60% or less, and still more preferably 56% or more and 60% or less.
The method in which the ratio RA of the rigid amorphous is 43% or more and 60% or less includes a method in which the production conditions described in the production method of the separation membrane described later are set to a preferable range.
Preferable production conditions for producing a separation membrane by controlling the ratio RA of the rigid amorphous to 43% or more and 60% or less include the following production conditions: in the method for producing the separation film, the stretch ratio of the resin molded product having a predetermined structure described later at a predetermined stretching temperature and stretching speed is set to 2.0 times or more and 6.0 times or less. In addition, the heat setting temperature range and the heating time after stretching are set to the preferable ranges described below, respectively.
< Void fraction >
The separation membrane of the present invention has a void ratio of 30% to 70%. The void ratio is the ratio of voids when the whole film is PMP. The porosity is set to 30% or more, whereby the permeability is improved, and the porosity is set to 70% or less, whereby the film strength is improved. The void ratio is preferably 40% or more and 65% or less, more preferably 45% or more and 60% or less, and particularly preferably 53% or more and 60% or less. In order to obtain a void fraction in this range, a structure formation using thermally induced phase separation, which will be described later, is preferably employed. The method for measuring the void fraction is described in detail in examples.
Next, the characteristics of the separation membrane of the present invention will be described.
(Peak temperature of the temperature curve with respect to loss elastic modulus (E "))
The separation membrane of the present invention is preferably: in a loss elastic modulus (E ') -temperature curve obtained by performing a dynamic viscoelasticity test (temperature dependency test) on the film in the longitudinal direction, the loss elastic modulus (E') has a peak whose peak temperature is in the range of 30.0 ℃ to 50.0 ℃. It can be considered that: the peak of the loss elastic modulus (E') -temperature curve around this temperature region (above 30.0 ℃ and below 50.0 ℃) corresponds to the movement of the amorphous chains of the PMP bound by crystallites. Amorphous chains bound to crystallites hardly move at low temperatures outside this temperature region, but in the vicinity of this peak temperature, the mobility increases sharply.
The high peak temperature, that is, the difficulty in movement of the amorphous chain bound to the crystallites means that the degree of binding of the amorphous chain is large. It can be considered that: since the peak temperature of the loss elastic modulus (E ") -temperature curve of the separation membrane of the present invention is at a high temperature of 30.0 ℃ or higher, the degree of binding of the amorphous chain by the crystallites is large and the mobility is small, and as a result, it is considered that the strength of the membrane can be improved. It is preferable that the peak temperature is 50.0 ℃ or lower, since the decrease in transmittance due to excessive binding of the amorphous chain can be suppressed, and the excellent transmittance can be obtained.
In the loss elastic modulus (E ') -temperature curve, the peak temperature of the loss elastic modulus (E') is preferably in the range of 31.0 ℃ or higher and 40.0 ℃ or lower, more preferably in the range of 32.0 ℃ or higher and 36.0 ℃ or lower, and still more preferably in the range of 32.5 ℃ or higher and 35.0 ℃ or lower. In order to improve accuracy in the measurement of peak temperature, it is preferable that: the peak temperature of the loss elastic modulus (E') -temperature curve is determined for any 3 or more, preferably 5 or more, membrane fragments of the separation membrane, and the average value thereof is used. The measurement method for the dynamic viscoelasticity test is described in detail in examples.
The peak temperature of the loss elastic modulus (E ") -temperature curve is set to 30.0 ℃ or higher and 50.0 ℃ or lower, and the production conditions described in the production method of the separation membrane described later are set to a preferable range, but the method is not limited thereto. Preferable production conditions at the time of production include, for example, the following production conditions: in the method for producing the separation membrane, the stretch ratio of the resin molded product having a predetermined structure described below at a predetermined stretching temperature is set to 2.0 times or more and 6.0 times or less. In addition, the temperature range and the heating time of the heat-setting after stretching are set to the preferable ranges described below, respectively.
(5% Stress at elongation (F5 value))
The separation membrane of the present invention preferably exhibits an F5 value of 5.0MPa or more at 25 ℃ in the length direction of the membrane. The longitudinal direction mentioned in the present invention means the mechanical direction at the time of manufacture. The measurement conditions of the stress at 5% elongation are described in detail in examples.
In the separation membrane of the present invention, an F5 value within the above range means that the degree of orientation of the molecular chains of PMP is high. In other words, the molecular chain of PMP has high order and becomes rigid, and thus, as a result, high film strength can be obtained. The method for setting the stress at 5% elongation in the longitudinal direction to 5.0MPa or more includes a method in which the stretching conditions at the time of stretching are set to the preferable range described below. The stress at 5% elongation is more preferably 7.0MPa or more, still more preferably 8.0MPa or more, particularly preferably 9.0MPa or more, and most preferably 9.5MPa or more. The stress at 5% elongation in the longitudinal direction is preferably 20.0MPa or less, and from this point of view, it is preferable that the stress is 20.0MPa or less, so that the decrease in permeability due to excessive orientation of the molecular chains can be suppressed, and that good permeability can be obtained. The stress at 5% elongation is more preferably 18.0MPa or less, still more preferably 15.0MPa or less, particularly preferably 13.0MPa or less.
In order to improve the measurement accuracy, it is preferable that: the F5 value is obtained for any of 5 or more, preferably 10 or more, film fragments, and the average value thereof is used. The method for measuring the F5 value is described in detail in examples.
(Degree of crystal orientation. Pi.)
In the separation membrane of the present invention, the molecular chains of the polymer are preferably oriented in a certain direction. The predetermined direction is the longitudinal direction of the separation membrane. The molecular chain has a crystal orientation degree pi of 0.7 or more and less than 1.0. The crystal orientation degree pi is calculated from the half-value width H (°) obtained by wide-angle X-ray diffraction measurement according to the following formula 1.
Degree of crystal orientation pi= (180 ° -H)/180 ° … ° 2
Wherein H is the half-value width (°) of the diffraction intensity distribution in the circumferential direction of the wide-angle X-ray diffraction image.
The method for measuring the porous orientation of the molecular chain and the crystal orientation degree pi thereof will be described in detail below. To calculate the crystal orientation degree pi, the hollow fiber membrane was attached to the fiber sample stage so that the longitudinal direction of the hollow fiber membrane was perpendicular.
When X-ray diffraction is performed, a diffraction image in the form of a ring called Debye-Schlemen ring (Debye-SCHERRER RING) is obtained. In the unoriented sample, no significant change in diffraction intensity was observed along the debye-scherrer ring, but in the oriented sample, the intensity distribution on the debye-scherrer ring was biased. Thus, from this intensity distribution, the degree of orientation can be calculated based on the above equation 2.
More specifically, when the molecular chain is unoriented, a peak is observed between the diffraction angle 2θ=5 ° and 30 ° inclusive when 2θ/θ scanning is performed in the width direction (in other words, when a diffraction pattern representing the diffraction intensity distribution in the radial direction of the debye-scherrer ring is obtained). In this case, the horizontal axis of the obtained diffraction pattern represents the diffraction angle 2θ of the X-ray, and the vertical axis represents the diffraction intensity. In the diffraction pattern in which the obtained horizontal axis represents the diffraction angle 2θ of the X-ray and the vertical axis represents the diffraction intensity, the diffraction angle 2θ is fixed to the peak position where the diffraction intensity is high, and the sample is scanned along the azimuth angle β direction, whereby the diffraction pattern in which the horizontal axis represents the azimuth angle β and the vertical axis represents the diffraction intensity is obtained. In unoriented samples, the diffraction intensity was almost constant throughout 360 ° in the circumferential direction of the debye-scherrer ring. In a diffraction pattern having the X-ray diffraction angle 2θ on the horizontal axis and the diffraction intensity on the vertical axis, the peak position, that is, the value of the diffraction angle 2θ at which the peak is observed varies depending on the type, structure, and compound of the polymer. In the case of the α crystal of PMP, a diffraction peak originating from a plane parallel to the (200) plane, i.e., the molecular chain, was observed in the vicinity of 2θ=10°. In the present invention, in the case of the α -crystal of PMP, the value of 2θ when the sample is scanned in the azimuth β direction is set to the position of the diffraction peak originating from the (200) plane. The positions of diffraction peaks originating from the (200) plane are 10 °,20 °. Hereinafter, specifically, a method for measuring the crystal orientation degree pi is described below.
When the molecular chains are oriented in the longitudinal direction, strong diffraction intensity is observed at the debye-scherrer ring around 2θ=10°, which corresponds to the azimuth angle β in the width direction of the separation membrane (in other words, at the equator), and small diffraction intensity is obtained at other portions (for example, fig. 4). In other words, in the diffraction intensity distribution in the radial direction of the debye-scherrer ring of the orientation sample, a diffraction peak was observed near 2θ=10° similarly to the non-orientation sample, and in the distribution in the circumferential direction, unlike the non-orientation sample, a diffraction peak was observed at the azimuth angle β corresponding to the separation film width direction. For example, fig. 5 is a graph showing the intensity distribution in the azimuth β direction at 2θ=10° of the hollow fiber membrane of example 4, in which peaks are observed near β=90° and near 270 °.
As described above, the intensity distribution in the azimuth angle β direction is obtained by fixing the value of the diffraction angle 2θ and further measuring the intensity of 0 ° to 360 ° in the azimuth angle β direction (circumferential direction). The intensity distribution may be an intensity distribution obtained by scanning a crystal peak in a diffraction image along the circumferential direction thereof. Here, in the β scanning, when the intensity ratio of the maximum intensity to the minimum intensity is 0.80 or less or 1.25 or more, the peak is regarded as present, and the half-value width H at the half position of the peak height is found in the intensity distribution in the azimuth direction.
By substituting the half-value width H into the above formula 2, the crystal orientation degree pi is calculated. The separation membrane of the present invention has a crystal orientation degree pi in a range of 0.7 or more and less than 1.0, preferably 0.8 or more and less than 1.0, more preferably 0.9 or more and less than 1.0. By setting the crystal orientation degree pi to 0.7 or more, the mechanical strength of the separation membrane becomes large. In the case of measuring the degree of crystal orientation pi by wide-angle X-ray diffraction along the longitudinal direction of the separation film at measuring points spaced 1cm apart, it is preferable that 80% or more of the measuring points be 0.4 or more and less than 1.0.
In the intensity distribution obtained by scanning the crystal peak in the circumferential direction, it is considered that no peak exists when the ratio of the maximum intensity to the minimum intensity exceeds the range of 0.80 to less than 1.25. In other words, in this case, it is determined that the separation membrane is not oriented.
The half-value width H is preferably obtained from an intensity distribution obtained by scanning a crystal peak (2θ=10°) derived from the (200) plane of the α -crystal of PMP measured by wide-angle X-ray diffraction along the circumferential direction.
As means for setting the crystal orientation degree pi of the molecular chain to the above range, for example, the following methods are cited: in the method for producing the separation film, the draft ratio when the resin composition is ejected from the ejection tube head is set to be in the range of 1 to 10 inclusive, and the resin composition is stretched at a glass transition temperature of the thermoplastic resin of +10 ℃ to +100 ℃ to 3 to 6 times inclusive. The degree of crystal orientation pi of the molecular chain can be increased by, for example, increasing the stretching ratio.
< Degree of orientation of outer surface >
The degree of orientation of the outer surface of the separation membrane in the longitudinal direction of the present invention is preferably 1.3 to 3.0. The outer surface mentioned here means: in the radial cross section of the separation membrane, the longer surface of the two surfaces parallel to the film thickness direction. For example, the outer diameter side surface of the hollow fiber membrane. On the other hand, in the case of a flat film, the lengths of both surfaces are equal, and therefore, in the present invention, the surface having a high degree of orientation among the two surfaces parallel to the film thickness direction is set as the outer surface for convenience. In addition, the other surface parallel to the film thickness direction with respect to the outer surface in the radial cross section of the separation film is referred to as an inner surface. That is, the hollow fiber membrane has an inner diameter side surface as an inner surface, and a flat membrane has a surface having a low degree of orientation among two surfaces parallel to the film thickness direction as an inner surface. When the degree of orientation of the outer surface is 1.3 or more, the film strength is improved. When the degree of orientation of the outer surface of the separation membrane is 1.4 or more and 1.7 or more, a higher effect can be obtained.
On the other hand, the flexibility of the separation membrane is improved by setting the degree of orientation of the outer surface to 3.0 or less. The degree of orientation of the outer surface of the separation membrane is preferably 2.8 or less and 2.5 or less.
The degree of orientation can be obtained by orientation analysis based on polarized infrared spectroscopy (hereinafter referred to as "polarized IR"). With respect to a specific method, description is made in examples.
(Degree of orientation of outer surface/degree of orientation of inner surface ratio)
The ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface of the separation membrane of the present invention is preferably 1.0 or more and 1.5 or less. The CO 2/N2 selectivity is improved by setting the ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface to 1.5 or less. On the other hand, when the ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface is 1.0 or more, the strength of the separation membrane is improved. The ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface is preferably 1.0 to 1.4, more preferably 1.0 to 1.3. The method for measuring the degree of orientation will be described later in examples.
(Gas permeability)
The N 2 permeation performance of the separation membrane of the present invention at 100kPa and 37℃is preferably 5GPU or more. The N 2 transmission performance is more preferably 10GPU or more, further preferably 50GPU or more, particularly preferably 100GPU or more, further preferably 200GPU or more. The calculation method is described in detail in the examples.
(CO 2/N2 Selectivity)
By making the dense layer of the present application non-porous, it has a very long leak time, and, because it is non-porous, the permeation of gas takes place by means of a dissolution-diffusion mechanism. On the other hand, the porous structure has a short leak time because of the through holes, and allows gas permeation by knudsen diffusion. That is, the compactibility of the dense layer can be evaluated by the separation coefficient of the gas, and the film having high compactibility tends to have a longer leak time.
In general, the permeation in a polymer membrane depends on the pore size in the membrane. In a membrane having a dense layer with a maximum pore diameter of 3nm or less, gas permeates through the membrane by a dissolution-diffusion mechanism. In this case, the separation coefficient α, which represents the ratio of the transmission coefficient of the two gases or the gas flow rate Q, depends only on the polymer material and not on the thickness of the dense layer. Thus, for example, the gas separation coefficients α 0(CO2/N2 associated with CO 2 and N 2) may be shown as P 0(CO2)/P0(N2). The polymers typically used will yield at least 1 or more alpha 0(CO2/N2) values.
On the other hand, in a porous film having pores with a size of 3nm or more and 10 μm or less, gas permeation is mainly caused by "knoop diffusion". In this case, the gas separation coefficient α1 is obtained by the square root of the ratio of the molecular weights of the gases. Thus, α 1(CO2/N2) becomes ∈28/44=0.80. In the case of knoop diffusion, there is a risk of leakage, and in the case of α 1(CO2/N2) of 1 or more, the risk of leakage is low, which is preferable. In particular, in the case of a film having a dense layer thickness of 0.1 μm or more and 3.0 μm or less as described above, the selectivity of CO 2/N2 is 1.0 or more, and the low leakage is excellent. In the case of a membrane having a dense layer with a microporous support structure and defects, on the one hand, the apparent permeability coefficient increases, but on the other hand, the gas separation coefficient decreases.
The drawbacks mentioned here are: the surface of the dense layer has pores with a size of 3nm or more. Thus, no pores, defects in the dense layer of the films of the present invention can be read by the gas separation coefficient α (CO 2/N2) measured for CO 2 and N 2. In the case where the gas separation coefficient α (CO 2/N2) is less than 1, the dense layer of the film has a plurality of holes or defects therein. In the case of a plurality of holes or defects in the dense layer, too fast liquid leakage or plasma leakage occurs, and the membrane is not suitable for long-term use. As such, such membranes cannot be used in the field of gas separation. In contrast, when the gas separation coefficient α (CO 2/N2) is 1.0 or more, the film has low leakage. Therefore, the membrane of the present invention preferably has a gas separation coefficient α (CO 2/N2) of 1.0 or more, more preferably 1.5 or more, and even more preferably 2 or more.
(Tensile elastic modulus)
The tensile elastic modulus of the separation membrane of the present invention in the longitudinal direction is preferably 100MPa or more. By setting the tensile elastic modulus to 100MPa or more, good strength can be maintained during use. The tensile elastic modulus is more preferably 200MPa or more, still more preferably 250MPa or more, and particularly preferably 300MPa or more. The method for measuring the tensile elastic modulus of the separation membrane is described in detail in examples.
< Method for producing separation Membrane >
The method for producing a separation membrane of the present invention comprises the following (1) to (3).
(1) A preparation step of melt-kneading a mixture containing from 10 to 50 mass% of PMP and from 50 to 90 mass% of a plasticizer to obtain a resin composition.
(2) And a molding step of discharging the resin composition from a discharge nozzle, cooling the resin composition with a cooling bath, and winding the resin composition at a draft ratio of 1 to 10 to obtain a resin molded article having an external surface orientation degree of 1.0 to 1.5 and an external surface orientation degree/internal surface orientation degree ratio of 1.0 to 1.5.
(3) And a stretching step of stretching the resin molded article at a temperature of 60 ℃ to 120 ℃ at a ratio of 2 to 6 times.
Next, a method for producing a separation membrane according to the present invention will be specifically described by taking a case where the separation membrane is a hollow fiber membrane as an example.
(Preparation step)
In the production process for obtaining the resin composition for producing the separation membrane of the present invention, a mixture containing from 10 to 50 mass% of PMP and from 50 to 90 mass% of plasticizer is melt kneaded. The mixture preferably contains 15 to 50 mass% of PMP and 50 to 85 mass% of plasticizer, more preferably contains 20 to 45 mass% of PMP and 55 to 80 mass% of plasticizer, and particularly preferably contains 25 to 40 mass% of PMP and 60 to 75 mass% of plasticizer.
Examples of the apparatus used for melt kneading the mixture include a kneader, a roll mill, a Banbury mixer, and a mixer such as a single-screw extruder or a twin-screw extruder. Among them, a twin-screw extruder is preferably used in view of improving the uniform dispersibility of the plasticizer, and a twin-screw extruder with vent holes is more preferably used in view of removing volatile matters such as moisture and low molecular weight substances. Further, a twin-screw extruder having a screw with a kneading disc portion is preferably used from the viewpoint of improving kneading strength and improving uniform dispersibility of the plasticizer.
The resin composition obtained in the production step may be pelletized once and remelted for melt film formation, or may be directly introduced into a pipe head for melt film formation. In the case of once granulating, it is preferable to use a resin composition in which the granules are dried so that the moisture content is 200ppm (mass basis) or less. By setting the water content to 200ppm (mass basis) or less, deterioration of the resin can be suppressed.
(Formation step)
In the step of forming the separation film, a resin molded article is obtained from a molten mixture of PMP and plasticizer, that is, a resin composition by phase separation. Specifically, the method comprises the following steps: the resin composition obtained in the production step is discharged from a discharge nozzle having a double annular nozzle with a gas flow path arranged in the center, for example, into a gas atmosphere, and is introduced into a cooling bath, whereby the resin composition is phase-separated to obtain a resin molded article.
Specifically, the resin composition in a molten state is discharged from the outer tube of the double annular nozzle for spinning, and the hollow portion forming gas is discharged from the inner ring of the double tubular pipe head. The resin composition discharged in this manner is cooled and solidified in a cooling bath, whereby a resin molded article is obtained.
Here, a cooling bath for cooling the resin composition discharged from the discharge nozzle is described. The solvent of the cooling bath is preferably selected according to affinity with PMP and plasticizer. As the solvent of the cooling bath, a solvent having a three-dimensional hansen solubility parameter distance Ra of 5 to 13 inclusive and a three-dimensional hansen solubility parameter distance Rb of 4 to 10 inclusive with respect to the plasticizer is preferably used for the cooling bath, and a solvent having a Ra of 10 to 12 inclusive and a Rb of 4 to 6 inclusive is more preferably used for the cooling bath. By setting Ra and Rb in the above ranges, the dense layer can be thinned, and the permeability can be improved. When Ra is in the range of 10 to 12, rb is in the range of 4 to 6, the dense layer can be made particularly thin, and therefore, the permeability becomes good, and when the ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface of the resin molded product to be described later is in the range of 1.0 to 1.5, the degree of orientation of the outer surface is in the range of 1.0 to 1.5, the stretching can be performed particularly high. As a reason for this, it is assumed that Ra is set in a range of 10 to 12 inclusive, so that solidification is advanced as compared with crystallization of PMP, and Rb is set in a range of 4 to 6 inclusive, so that exchange of a solvent and a plasticizer is rapidly performed, and as a result, excessive crystallization is suppressed, and thinning is achieved. This can be considered as follows: the permeability becomes good and the stretching can be performed at high power.
The affinity of PMP for solvents can be estimated based on three-dimensional hansen solubility parameters. Three-dimensional hansen solubility parameters are described in gregoriy R. [ ind.eng.chem.res.2011,50,3798-3817 ]. Specifically, the smaller the solubility parameter distance (Ra) of the following formula 3, the higher the affinity of the solvent for PMP.
[ Number 1]
Here, δ Ad、δAp and δ Ah are dispersion terms, polar terms, and hydrogen bonding terms of solubility parameters of PMP, and δ Cd、δCp and δ Ch are dispersion terms, polar terms, and hydrogen bonding terms of solubility parameters of solvents.
The affinity of the plasticizer for the cooling solvent can also be estimated by the same procedure. Specifically, the smaller the solubility parameter distance (Rb) of the following formula 4, the higher the affinity of the solvent for the plasticizer.
[ Number 2]
Here, δ Bd、δBp and δ Bh are dispersion terms, polar terms, and hydrogen bonding terms of solubility parameters of PMP, and δ Cd、δCp and δ Ch are dispersion terms, polar terms, and hydrogen bonding terms of solubility parameters of solvents.
When the solvent is a mixed solvent, the solubility parameter (δ Mixture) of the mixed solvent can be obtained by using the following formula 5.
[ Number 3]
Delta Mixture＝∑Φiδi … … type 5
Here the number of the elements is the number,Δi is the volume fraction and solubility parameter of component i, and the dispersion term, the polar term and the hydrogen bond term are established respectively. Here, "volume fraction of component i" refers to the ratio of the volume of component i before mixing to the volume of all components before mixing. The three-dimensional hansen solubility parameter of the solvent is used when there is a description in gregoriy r. (ind. Eng. Chem. Res.2011,50, 3798-3817). For solvent parameters not described, the values reported in software "Hanse NSolubility PARAMETER INPRACTICE" developed by Charles hansen et al were used. The three-dimensional hansen solubility parameters of the solvent and polymer, which are not described in the above software, can be calculated by hansen ball method using the above software.
In the method for producing a separation membrane of the present application, when dibutyl phthalate is used as the solvent used in the cooling bath in the forming step, it is preferable to use triacetin or N-methylpyrrolidone, and among them, N-methylpyrrolidone is more preferable because Ra and Rb fall within the above-mentioned more preferable ranges.
The resin composition discharged from the discharge nozzle is preferably exposed to a gaseous atmosphere that promotes vaporization of the plasticizer, i.e., an atmosphere in which vaporization of the plasticizer can occur, before cooling, on at least one surface of the surface, preferably on the surface where the dense layer should be formed. The gas used for forming the gaseous atmosphere is not particularly limited, and air or nitrogen is preferably used. The gaseous atmosphere typically has a lower temperature than the spout head temperature. In this case, in order to evaporate a sufficient amount of the plasticizer, at least one surface of the molded body is preferably exposed to a gaseous atmosphere for a time of at least 0.5 milliseconds (ms).
In the step of forming the separation film of the present invention, the resin composition discharged from the discharge tube head is wound by a winding device. In this case, it is important that the value of the draft ratio calculated based on (winding speed)/(speed discharged from the discharge tube head) of the winding device is 1 to 10. The draft ratio is more preferably 1 to 8, still more preferably 1 to 6. When the draft ratio is 1 or more, winding is stabilized, and fluctuation in yarn shape is reduced. By setting the draft ratio to 10 or less, excessive extension of the resin composition discharged from the ferrule can be suppressed, and the orientation of the molecular chains on the outer surface can be suppressed, so that stretching can be performed at a high magnification in a stretching step described later.
Specifically, since the winding speed is faster than the ejection speed, the resin composition is elongated, and the molecular chains are oriented by the drawing, and when the resin composition is elongated, the outer surface side in direct contact with the cooling bath is solidified first if the resin composition is in the cooling bath, and therefore the outer surface side is elongated while being solidified, and the molecular chains are strongly oriented. On the other hand, the inner surface side of the separation membrane, which is not in contact with the cooling bath, is elongated before solidification, and therefore orientation is less likely to occur. As described above, if the draft ratio is large, the orientation of the outer surface side and the inner surface side of the resin molded article before stretching becomes uneven. When such a resin molded article is stretched, the outer surface side where orientation has already occurred cannot withstand high-power stretching, and causes defects.
The inventors found that: the present invention has been completed by making the ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface of the resin molded product before stretching to be in the range of 1.0 to 1.5, and making the degree of orientation of the outer surface to be in the range of 1.0 to 1.5, and thereby realizing high-power stretching. The ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface of the resin molded product before stretching is preferably 1.0 or more and 1.4 or less, more preferably 1.0 or more and 1.3 or less, and still more preferably 1.0 or more and 1.2 or less. By setting the ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface of the resin molded product before stretching to 1.5 or less, both the suppression of occurrence of surface defects and stretching by a factor of 2.0 or more can be achieved. On the other hand, by setting the ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface to 1.0 or more, yarn deformation during stretching can be suppressed. The degree of orientation of the outer surface of the resin molded article before stretching is preferably 1.0 to 1.4, more preferably 1.0 to 1.3, and still more preferably 1.0 to 1.2.
By setting the degree of orientation of the outer surface of the resin molded product before stretching to 1.5 or less, it is possible to achieve both suppression of occurrence of surface defects and stretching by 2.0 times or more. On the other hand, by setting the degree of orientation of the outer surface to 1.0 or more, yarn deformation at the time of stretching can be suppressed. The method for measuring the degree of orientation will be described later in examples.
As an example, the control of the rigid amorphous is achieved by stretching a resin molded article having a ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface of 1.5 or more, but uniform stretching is difficult, the rigid amorphous cannot be controlled, and the CO 2/N2 selectivity is lowered.
In general, when a separation membrane having a plurality of void portions, for example, a separation membrane having a void ratio of 30% or more is stretched, a tissue is broken starting from the void portions, and therefore, it is very difficult to stretch itself. In particular, when the separation membrane has a phase separation structure obtained by dry-wet spinning using the principle of non-solvent induced phase separation and thermally induced phase separation, there are many fine voids and the void ratio is high, and this tendency is remarkable.
In the case of a resin molded article having an external surface orientation degree/internal surface orientation degree ratio exceeding 1.5, stretching of not less than 2.0 times is difficult, and as a result of intensive studies for this reason, the winding speed is as high as 72 m/min, and as a result, the draft specific volume tends to become large, and as described above, the external and internal orientations of the resin molded article before stretching become uneven. Namely, found that: the ratio of the degree of orientation of the outer surface to the degree of orientation of the inner surface becomes large, and the oriented surface cannot withstand high-power stretching, and defects (i.e., CO 2/N2 selectivity of 1 or less) occur, and high-power stretching cannot be performed.
In contrast, the present inventors found that: if the resin molded product has an outer surface orientation degree/inner surface orientation degree ratio within a predetermined range and an outer surface orientation degree of 1.5 or less, the whole can be uniformly stretched, and a high-magnification stretching of 2.0 times or more can be realized. Further, the ratio of the rigid amorphous is successfully controlled by such uniform and high-magnification stretching, and the occurrence of defects is successfully suppressed and the strength is increased.
(Washing step)
The resin composition thus obtained is immersed in a solvent which does not dissolve the polymer but is miscible with the plasticizer, and the plasticizer is eluted, whereby a porous structure can be obtained inside. In this case, the solvent or the mixed solvent having an appropriate affinity for the plasticizer is used, thereby performing a good solvent exchange and improving the washing efficiency. The solvent is not particularly limited as long as it is a solvent in which the polymer is insoluble but miscible with the plasticizer, and methanol, ethanol, isopropanol, and acetone are preferably used as specific examples.
(Drying step)
The resin composition after the washing step is preferably subjected to a drying step for the purpose of removing the solvent adhering to the resin composition during the washing step. The drying is preferably performed at a temperature at which the solvent which does not dissolve the polymer but is miscible with the plasticizer is removed by vaporization, and specifically, is preferably performed at a temperature of not less than room temperature but not more than 150 ℃.
(Stretching step)
The formed resin molded article may be wound up once and wound out again and then used for stretching, or may be directly introduced into a stretching step to be stretched. The stretching step is important in controlling the ratio RA of the rigid amorphous to the above range. The stretching method is not particularly limited, and may be, for example, a method in which a resin molded article is conveyed on heated rolls to a temperature at which stretching is performed and a circumferential speed difference between the rolls is used, or a method in which a resin molded article is conveyed in a dry heat oven or in a liquid bath to a temperature at which stretching is performed and a circumferential speed difference between the rolls is used. Among them, from the viewpoint of suppressing collapse of the hollow portion and improving the hollow rate, it is preferable to transport the hollow portion in a dry heat oven or a liquid bath. The stretching may be performed before or after the plasticizer is dissolved, and is preferably performed after the plasticizer is dissolved, from the viewpoint of reducing the residue of the solvent in the separation membrane and improving the void ratio.
The stretching temperature in the stretching step is preferably in the range of 60 ℃ to 120 ℃, more preferably 70 ℃ to 110 ℃ inclusive, and even more preferably 75 ℃ to 90 ℃ inclusive. By stretching in an atmosphere of 60 ℃ or higher, stretching can be performed stably and uniformly. By stretching in an atmosphere of 120 ℃ or less, yarn deformation due to PMP softening can be suppressed, and a decrease in the void fraction can be suppressed. The stretching ratio is preferably 2.0 to 6.0 times, more preferably 3.0 to 6.0 times, still more preferably 3.5 to 6.0 times, particularly preferably 4.5 to 6.0 times. The inventors found that: by setting the stretching temperature to 60 ℃ or higher and 120 ℃ or lower and the stretching ratio to 2.0 times or higher and 6.0 times or lower, the Ratio (RA) of the rigid amorphous can be controlled within a preferable range, and a good film strength can be obtained. Further, by setting the stretch ratio to 6.0 times or less, the occurrence of through-holes in the dense layer can be suppressed.
(Heat treatment step)
Then, the separation membrane can be heat-treated by heating at 100 ℃ or higher and 200 ℃ or lower. By performing this heat treatment step, the crystallinity of PMP can be improved, and a separation membrane having more excellent strength can be obtained. The heat treatment may be carried on a heated roller, carried in a dry heat oven, or put into a dry heat oven in a state of being wound up into a roll such as a bobbin or a paper tube.
The heat treatment temperature is preferably 100 ℃ to 200 ℃, more preferably 110 ℃ to 180 ℃, still more preferably 120 ℃ to 160 ℃. The heat treatment time is preferably 1 second to 600 seconds, more preferably 5 seconds to 300 seconds, still more preferably 10 seconds to 60 seconds. The separation membrane of the present invention containing PMP as a main component can be produced by the steps described above.
Examples
The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples at all. The measurement and evaluation methods are shown below.
The characteristic values in the examples were obtained by the following methods.
(1) Outer diameter and inner diameter (μm) of hollow fiber membrane
The radial cross section exposed by applying stress (using a blade or a microtome as needed) after freezing the hollow fiber membrane with liquid nitrogen was observed by an optical microscope, and the average value of the outer diameter and the inner diameter of 10 randomly selected portions was taken as the outer diameter and the inner diameter of the hollow fiber membrane, respectively.
(2) Hollow fiber membrane void fraction (%)
Based on the outer diameter and the inner diameter obtained by the above (1), the hollow ratio of the hollow fiber membrane was calculated by the following formula.
Hollow ratio (%) =100× [ inner diameter (μm) ] 2/[ outer diameter (μm) ] 2
(3) Gas permeation performance (GPU)
A small module having an effective length of 100mm and formed of 1 hollow fiber membrane was produced. The gas permeation rate was measured using the small module. The carbon dioxide or nitrogen was used as a measurement gas for evaluation, and the pressure change on the permeation side of carbon dioxide or nitrogen per unit time was measured by external pressure at a measurement temperature of 37℃according to the pressure sensor method of JIS K7126-1 (2006). Here, the pressure difference between the supply side and the permeation side was set to 100kPa.
Next, the gas permeation rate Q is calculated by the following equation. The gas permeation rate ratio of each component is set to the separation coefficient α. Here, the membrane area is calculated from the outer diameter and length of the region contributing to gas permeation.
Permeation rate Q (GPU) =10 -6 [ permeation gas amount (cm 3) ]/[ membrane area (cm 2) ×time(s) ×pressure difference (cmHg) ]
(4) Thickness of dense layer (μm)
The separation membrane was frozen with liquid nitrogen in the same manner as the outer diameter and inner diameter (μm) of the hollow fiber membrane (1) above, and then subjected to stress (using a blade, a microtome, or a wide ion beam as necessary) to cut so that the radial cross section or the longitudinal cross section was exposed. Next, sputtering was performed with platinum under the following conditions, and after pretreatment was performed on the radial cross section or the longitudinal cross section, when a straight line was drawn perpendicularly to the outer surface from any point on the outer surface of the separation membrane toward the inner surface side when observed at a magnification of 10,000 times using SEM, the length up to the first hole reaching more than 10nm was set to the dense layer thickness. The extraction of wells is performed after binarization of the analysis image in the image analysis software "ImageJ". Binarization was performed as follows: when the horizontal axis represents the luminance in the analysis image and the vertical axis represents the pixel number distribution of the number of pixels at the luminance, the dot with the smaller luminance among the 2 luminances that are the number of 1/2A is implemented when the number of pixels at the highest luminance of the number of pixels is a. Further, denoising (corresponding to DESPECKLE in ImageJ) was performed on the obtained binarized image, in which all pixels were replaced with the central value of the 3×3 pixels in the vicinity of the pixel 1 time, and the image thus obtained was used as an analysis image. The extraction of the wells was performed by the Analyze Particles instructions of ImageJ and the dense layer thickness was determined from the resulting images. The measurement was performed for 10 arbitrary sites, and the average value thereof was used as the dense layer thickness. The coefficient of variation in the thickness of the dense layer was calculated by dividing the standard deviation by the average value and converting the standard deviation into a percentage for the thickness of the dense layer at any 10 points where the measurement was performed.
(Sputtering)
The device comprises: hitachi high science Co Ltd (E-1010)
Evaporation time: 40 seconds
Current value: 20mA
(SEM)
The device comprises: hitachi high science Co Ltd (SU 1510)
Acceleration voltage: 5kV (kV)
Probe current: 30
(5) Voids in the support layer greater than 10 μm
In the same manner as in (1) above, the separation membrane is frozen with liquid nitrogen, and then subjected to stress (a blade, a microtome, or a wide ion beam, as necessary), and cut so that the radial cross section or the longitudinal cross section is exposed. Then, sputtering was performed with platinum under the following conditions, and after pretreatment was performed on the radial cross section or the longitudinal cross section, observation was performed at a magnification of 2,000 times using SEM, and all holes having a diameter of more than 10 μm at this time, that is, holes having an area of more than 78.5 μm 2 were extracted, and the number thereof was calculated as the average pore diameter of the support layer. The wells were extracted by binarizing the analysis image (binarization of Huang) in image analysis software "ImageJ". Further, denoising (corresponding to DESPECKLE in ImageJ) was performed on the obtained binarized image, in which all pixels were replaced with the central value of the 3×3 pixels in the vicinity of the pixel 1 time, and the image thus obtained was used as an analysis image. The extraction of wells was performed using the Analyze Particles instruction of ImageJ, and the number of wells obtained was calculated. The measurement was performed for 5 arbitrary sites, and the average value thereof was used as voids larger than 10 μm in the support layer.
(Sputtering)
The device comprises: hitachi high science Co Ltd (E-1010)
Evaporation time: 40 seconds
Current value: 20mA
(SEM)
The device comprises: hitachi high science Co Ltd (SU 1510)
Acceleration voltage: 5kV (kV)
Probe current: 30
(6) Average pore diameter of support layer
In the same manner as in (1) above, the separation membrane was frozen with liquid nitrogen and then cut so that the radial cross section was exposed by using a microtome. Then, sputtering was performed with platinum under the following conditions, the radial cross section was subjected to pretreatment, and then observed with SEM at a magnification of 2,000 times, and all pores having a diameter of more than 100nm, that is, pores having an area of more than 7854nm 2 at this time were extracted, and the average pore diameter was calculated from the average area thereof, to thereby obtain an average pore diameter of the support layer. Regarding the observation field, from one surface of the separation film, the observation was performed with respect to the film thickness direction with a point of (film thickness/2) μm as the center, and regarding the film thickness, when the observation was performed with respect to the same sample with a magnification of 250 times using SEM, a straight line was drawn from an arbitrary point on one surface toward the other surface so as to become the minimum length, and the length at this time was set as the film thickness of the separation film. The wells were extracted by binarizing the analysis image (binarization of Huang) in image analysis software "ImageJ". For the obtained binarized image, noise removal (corresponding to DESPECKLE in ImageJ) was performed by replacing all pixels with the central value of the 3×3 pixels in the vicinity of the pixel 1 time, and the image thus obtained was used as an analysis image. Extraction of pores the pores with an area greater than 7854nm 2 were all extracted using the Analyze Particles instruction of ImageJ and the average pore diameter of the support layer was calculated from the average area of the pores obtained. The measurement was performed for 5 arbitrary sites, and the average value thereof was used as the average pore diameter of the support layer.
(Sputtering)
The device comprises: hitachi high science Co Ltd (E-1010)
Evaporation time: 40 seconds
Current value: 20mA
(SEM)
The device comprises: hitachi high science Co Ltd (SU 1510)
Acceleration voltage: 5kV (kV)
Probe current: 30
(7) Ratio of Congo amorphous (RA)
The measurement was performed by cutting out the separation membrane. Using a temperature modulated differential scanning calorimeter: q1000 manufactured by TA Instruments, inc., was measured on the separation membrane TMDSC under the following conditions. Universal Analysis 2000 manufactured by TAInstruments was used for data processing.
Atmosphere: nitrogen flow (50 mL/min)
Temperature/heat correction: high purity indium (tm= 156.61 ℃, Δhm=28.71J/g)
Temperature range: about-40 ℃ to 100 DEG C
Heating rate: 2 ℃/min
Sample amount: about 5mg
Sample container: aluminum standard container
The specific heat difference (Δcp) before and after the glass transition temperature of the separation membrane was obtained from the TMDSC curve of the reversible component, and the movable amorphous ratio (MA) was calculated from the following formula. The following formula is described in THERMAL ANALYSIS of Polymeric Materials, springer,2005, p780.
MA(％)＝ΔCp/ΔCp0×100
Here, Δcp0 is the specific heat difference before and after the completely amorphous glass transition of PMP.
Subsequently, using Q100 manufactured by TA Instruments, DSC measurement of the separation membrane was performed under the following conditions. For data processing, universal Analysis 2000,2000 manufactured by TA Instruments corporation was used.
Atmosphere: nitrogen flow (50 mL/min)
Temperature/heat correction: high purity indium (tm= 156.61 ℃, Δhm=28.71J/g)
Temperature range: about 20-300 DEG C
Heating rate: 10 ℃/min
Sample amount: about 5mg
Sample container: aluminum standard container
The heat of fusion (Δhm) of the separation membrane was obtained from the DSC curve, and the ratio of the crystallinity (C) was calculated from the following formula.
C(％)＝ΔHm/ΔHm0×100
Here Δhm 0 is the heat of fusion of the PMP, which is completely amorphous.
Using the ratio (MA) and crystallinity (C) of the obtained mobile amorphous, the Ratio (RA) of the rigid amorphous was calculated from the following formula 1.
RA (%) =100- (ma+c) … formula 1
(8) Peak temperature of loss elastic modulus (E ") -temperature curve
The loss elastic modulus of the separation membrane was determined by viscoelasticity measurement. The hollow fiber membrane was cut out in a length direction of 30mm to prepare a sample. The temperature dependence of the loss elastic modulus (E') was measured by using a dynamic viscoelasticity measuring apparatus (Rheogel-E4000, manufactured by UBM Co.) while heating at a temperature rise rate of 3 ℃/min in a temperature range of-100 ℃ to 200 ℃ inclusive under a nitrogen atmosphere. At this time, the measurement length was set to 10mm, the frequency was set to 10Hz, and the tensile strain was set to 0.05%. The temperature is plotted on the vertical axis and the temperature is plotted on the horizontal axis, the maximum value of the loss elastic modulus (E ") of 20 ℃ to 90 ℃ is set as a peak, and the corresponding temperature is set as the peak temperature (. Degree. C.) of the loss elastic modulus (E"). The samples were changed and measured 3 times to determine the average value.
(9) Tensile elastic modulus (MPa)
The tensile elastic modulus of the separation membrane was measured by a method defined in "JIS L1013:2010 chemical fiber filament yarn test method.8.10 initial tensile resistance" under conditions of a temperature of 20℃and a humidity of 65% using a tensile tester (TENSILON UCT-100 manufactured by ORIENTEC Co.) under conditions of a sample length of 100mm and a tensile speed of 100mm/min, and the apparent Young's modulus calculated from the initial tensile resistivity was defined as tensile elastic modulus (kgf/mm 2). The number of measurements was 5, and the average value was used.
(10) Void fraction (%)
The yarn length L (mm) and the mass M (g) of the hollow fiber membrane dried in vacuo at 25℃for 8 hours were measured. The density ρ 1 of the hollow fiber membrane was calculated according to the following formula using the values of the outer diameter (mm) and the inner diameter (mm) measured in the above (1).
Ρ 1 =m/[ pi× { (outer diameter/2) 2 - (inner diameter/2) 2 } ×l ]
The void ratio ε (%) is calculated by the following formula.
ε＝1-ρ1/ρ2
Here ρ 2 is the density of the polymer.
(11) Stress at 5% elongation (F5 value)
The tensile modulus of the separation membrane was obtained by dividing the tensile force of a sample at 5% elongation (when the distance between chucks reached 105 mm) by the cross-sectional area of the sample before measurement (excluding the hollow portion) using a tensile tester (TENSILON UCT-100 manufactured by orintec corporation) at a temperature of 25 ℃ and a humidity of 65% under conditions that the sample length was 100mm and the elongation rate was 100mm/min, and was set to an F5 value (MPa). The number of measurements was 5, and the average value was obtained.
(12) Degree of orientation of outer surface
The external surfaces of the resin molded article and the separation membrane were vacuum-dried at 25℃for 8 hours in the longitudinal direction (MD) and in the direction perpendicular to the longitudinal direction (radial direction) (TD) were measured by S-polarization ATR spectrometry using FTIR (FTS-55A) manufactured by BioRad DIGILAB company to which a primary reflection ATR attachment was attached. The ATR crystallization was performed by S polarization using a diamond prism, the incident angle was 45 °, the cumulative number was 64, and the polarizing plate was performed by using a wire grid. From the obtained ATR spectra, the band intensity ratio was calculated using 1 band in which the band intensities in MD and TD were changed as orientation parameters. For example, in the case of a resin molded article and a separation membrane of PMP, the strength of a band (-CH 3 base transverse shaking vibration) in the vicinity of 918cm-1 was measured in MD and TD of the resin molded article and the separation membrane, respectively.
When the vibration direction of the molecular chain matches the polarization direction of the incident light, the band intensity is strongly obtained, and therefore, the band intensity ratio changes in accordance with the degree of orientation, and therefore, the degree of orientation is obtained from the following equation.
The degree of orientation of the outer surface= [ band strength around 918cm -1 in MD ]/[ band strength around 918cm -1 in TD ]
The degree of orientation was normalized and measured in the same manner as the intensity of the band (-CH angular vibration) around 1465cm -1.
(13) Degree of orientation of inner surface
After freezing the resin molded product and the separation membrane with liquid nitrogen in the same manner as in (1) above, the resin molded product and the separation membrane were cut in parallel with the longitudinal direction by using a blade or a microtome so that the hollow portion of the membrane, i.e., the inner surface was exposed, and the alignment parameter of the hollow portion, i.e., the inner surface was measured by using FTIR (FTS-55A) manufactured by BioRadDIGILAB company with a primary reflection ATR attachment in the same manner as in (12) above. The separation membrane sample was vacuum-dried at 25℃for 8 hours, and the S-polarization ATR spectrum was measured on the inner surface of the separation membrane sample in the longitudinal direction (MD) and the direction perpendicular to the longitudinal direction (radial direction) (TD).
The ATR crystallization was performed by S polarization using a diamond prism, an incident angle of 45 °, and the cumulative number of times of 64 times, and a wire grid as a polarizing plate. From the obtained ATR spectra, the band intensity ratio was calculated as an orientation parameter using 1 band in which the band intensities in MD and TD were changed. For example, in the case of a resin molded article and a separation membrane of PMP, the strength of a band (-CH 3 -based transverse shaking vibration)) in the vicinity of 918cm -1 was measured in MD and TD of the resin molded article and separation membrane, respectively. When the vibration direction of the molecular chain matches the polarization direction of the incident light, the band intensity is strongly obtained, and therefore, the band intensity ratio changes in accordance with the degree of orientation, and therefore, the degree of orientation is obtained from the following equation.
Internal degree of orientation= [ band intensity near 918cm -1 in MD ]/[ band intensity near 918cm -1 in TD ]
The degree of orientation was normalized and measured in the same manner as the intensity of the band (-CH angular vibration) around 1465cm -1.
(14) Degree of crystal orientation: pi
In the case of a hollow fiber membrane, the hollow fiber membrane is mounted on a fiber sample stage so that the longitudinal direction of the separation membrane is vertical. In the case of a flat film, the film is mounted on a sample stage such that the direction of incidence of the X-rays is perpendicular to the film surface. X-ray diffraction measurements (2. Theta./. Theta. Scan, beta. Scan) were performed using an X-ray diffraction apparatus (SmartLab, cuK. Alpha. Rays for polymers, manufactured by Rigaku Co.). First, the existence of the peak top was confirmed by 2θ/θ scanning. In the diffraction pattern in which the obtained horizontal axis represents the diffraction angle 2θ of the X-ray and the vertical axis represents the diffraction intensity, the diffraction angle 2θ is fixed to the peak position where the diffraction intensity is high, and the sample is scanned along the azimuth angle β direction, whereby the diffraction pattern in which the horizontal axis represents the azimuth angle β and the vertical axis represents the diffraction intensity is obtained. In the case of the α -crystal of PMP, the value of 2θ fixed when the sample is scanned along the azimuth β direction is set to the position of the diffraction peak originating from the (200) plane. In the case of the α -crystal of PMP, the position of the diffraction peak originating from the (200) plane is around 10 °. Next, for the value of 2θ determined by the 2θ/θ scan, the intensity of 0 ° to 360 ° in the azimuth β direction is measured by β scan, and thus the intensity distribution in the azimuth β direction is obtained (fig. 5).
Here, when the intensity ratio of the maximum peak intensity to the minimum peak intensity is 0.80 or less or 1.25 or more, the existence of a peak is regarded as being present, and the width (half value width H) at half the peak height is obtained in the intensity distribution in the azimuth β direction, and the crystal orientation degree pi is calculated by the following formula (1). A straight line passing through two minima of the intensity in the β scan was used as a baseline.
Degree of crystal orientation pi= (180 ° -H)/180 ° … ° 2
[ PMP raw Material ]
As PMP, the following substances were prepared.
PMP: TPX DX845 (Density: 833kg/m 3, MFR:9.0g/10 min)
[ Other raw materials ]
And (3) a plasticizer: dibutyl phthalate.
Example 1]
PMP 35 mass% and dibutyl phthalate 65 mass% were fed to a twin screw extruder, melt kneaded at 290℃and then introduced into a melt-spinning pack having a spinning temperature of 245℃and spun downward from an outer annular portion of a nozzle tip having 1 tip hole (double round tube type, nozzle diameter of 4.6mm and slit width of 0.45 mm). The spun resin molded article was introduced into a cooling bath, and wound up by a winder so that the draft ratio became 5. At this time, the distance of travel in the air was set to 20 mm. Here, as a filter in the melt-spinning pack, a metal filter having a diameter of 200 μm was used. The wound resin molded article was immersed in isopropyl alcohol for 24 hours, and then dried under vacuum at room temperature to remove isopropyl alcohol. The obtained resin molded article was stretched at a speed of 500mm/min under an atmosphere at 80℃and a stretching ratio of 3 times to obtain a separation film.
Physical properties of the obtained separation membrane are shown in table 1. The obtained separation membrane had a ratio RA of rigid amorphous of 47%, a void ratio of 43%, a N 2 permeation performance of 48GPU, a tensile elastic modulus of 370mpa, a co 2/N2 separation coefficient α of 7.3, a high permeation performance and excellent strength, and also had a low leakage.
Example 2]
A separation film was obtained in the same manner as in example 1 except that the stretching ratio was set to 4 times. As a result, as shown in Table 1, the ratio RA of the rigid amorphous was 49% and the tensile elastic modulus was 395MPa.
Example 3 ]
A separation film was obtained in the same manner as in example 1 except that the stretching ratio was set to 5 times. As a result, as shown in table 1, the ratio RA of the rigid amorphous was 54%, and the tensile elastic modulus was 450MPa.
Example 4 ]
A separation membrane was obtained in the same manner as in example 1 except that the coagulation bath was changed to N-methylpyrrolidone and the stretching ratio was 6 times. As a result, as shown in table 1, the ratio RA of the rigid amorphous was 58%, and the tensile elastic modulus was increased to 465MPa. Further, the thickness of the dense layer was 0.18 μm, and the N 2 permeation performance was increased to 220GPU by thinning.
Example 5 ]
A separation membrane was obtained in the same manner as in example 1 except that the stretching ratio was set to 5 times and the stretching temperature was set to 60 ℃. As a result, as shown in table 1, the ratio RA of the rigid amorphous was 50%, and the tensile elastic modulus was increased to 410MPa.
Example 6]
A separation membrane was obtained in the same manner as in example 1 except that the stretching ratio was set to 5 times and the stretching temperature was set to 100 ℃. As a result, as shown in table 1, the ratio RA of the rigid amorphous was 52%, and the tensile elastic modulus was increased to 415MPa.
Example 7 ]
A separation membrane was obtained in the same manner as in example 1 except that PMP was 40 mass%, dibutyl phthalate was 60 mass%, and the draft ratio was 9. As a result, as shown in table 1, the ratio RA of the rigid amorphous was 46%, and the tensile elastic modulus was reduced to 360MPa.
Comparative example 1]
A separation membrane was obtained in the same manner as in example 1 except that the draft ratio was set to 231 and stretching was not performed. As a result, as shown in table 2, the ratio RA of the rigid amorphous was 39%, and the tensile elastic modulus was as low as 86 MPa.
Comparative example 2]
A separation membrane was obtained in the same manner as in example 1, except that stretching was not performed. As a result, as shown in table 2, the ratio RA of the rigid amorphous was 36%, and the tensile elastic modulus was as low as 92 MPa.
Comparative example 3 ]
A separation membrane was obtained in the same manner as in example 1, except that the PMP was set to 100 mass%, the draw ratio was set to 700, the spinning was performed, the stretching temperature was set to 130 ℃ after air cooling, the stretching magnification was set to 2.3 times, and the stretching was performed. As a result, as shown in table 2, the void fraction became 20%, and the N 2 transmission performance showed values as low as 3 GPUs.
Comparative example 4 ]
As a result of the same operation as in example 1 except that PMP was 8 mass% and dibutyl phthalate was 92 mass%, yarn breakage was caused, and spinning was not possible.
TABLE 1
TABLE 2
The separation membranes obtained in examples 1 to 7 satisfied the conditions of the present invention in all items of the ratio RA and the void ratio of the rigid amorphous, had N 2 permeation performance of 5GPU or more, had tensile elastic modulus of 100MPa or more, had CO 2/N2 separation coefficient α of 1 or more, had high permeation performance and excellent strength, and had low leakage. On the other hand, in the separation membranes of comparative examples 1 to 4, in which at least one of the ratio RA and the void ratio of the rigid amorphous was not satisfied the conditions of the present invention, at least one of the N 2 permeability, the tensile elastic modulus, and the CO 2/N2 separation coefficient α exhibited a low value.
Industrial applicability
The separation membrane of the present invention can be suitably used for separating a gas from a liquid or imparting a gas to a liquid. For example, the deaeration film can be suitably used for reducing the amount of dissolved gas in water, an aqueous solution, an organic solvent, a resist solution in a semiconductor production line, a liquid crystal color filter production line, ink production of an ink jet printer, and the like; the membrane is suitably used for a gas exchange membrane in an artificial lung for medical use. In particular, the film is useful for degassing photoresist solutions and developing solutions used for photolithography in a semiconductor production line.
Description of the reference numerals
1. Film surface
2. Compact layer
3. Void portion
4. Thickness of dense layer
5. Inner layer of separation membrane
6. Imaginary curve of variation of dense layer

Claims (18)

1. A separation membrane comprising poly (4-methyl-1-pentene) as a main component, wherein the poly (4-methyl-1-pentene) in the separation membrane has a ratio RA of rigid-amorphous defined by the following formula 1 of 43% to 60%, and wherein the void ratio of the whole separation membrane is 30% to 70%, and
A dense layer is provided on at least one surface side of the separation membrane,
RA (%) =100- (ma+c) … formula 1
Here, MA is the proportion of mobile amorphous, and C is the crystallinity.
2. The separation membrane according to claim 1, wherein in a dynamic viscoelasticity test-based loss elastic modulus (E ") -temperature curve of the separation membrane, the loss elastic modulus (E") has a peak in a range of 30.0 ℃ or more and 50.0 ℃ or less.
3. The separation membrane according to claim 1 or 2, wherein the separation membrane has a wide-angle X-ray-based crystal orientation degree pi calculated according to the following formula 2 of 0.70 or more and less than 1.00,
Degree of crystal orientation pi= (180 ° -H)/180 ° … ° 2
H is a half-value width (°) of the diffraction intensity distribution in the circumferential direction of the wide-angle X-ray diffraction image.
4. A separation membrane according to any one of claims 1 to 3, wherein the separation membrane is a gas permeable membrane for use in separating or dissolving a gas from or in a liquid.
5. The separation membrane according to any one of claims 1 to 4, wherein a thickness of the dense layer from a surface side of the separation membrane is 0.1 μm or more and 2.0 μm or less.
6. The separation membrane according to any one of claims 1 to 5, wherein the dense layer is a dense layer having voids with a diameter of less than 10 nm.
7. The separation membrane according to any one of claims 1 to 6, wherein the ratio RA of the rigid amorphous is 50% or more and 60% or less.
8. The separation membrane according to any one of claims 1 to 7, wherein in a temperature-loss elastic modulus (E ") curve of the separation membrane based on a dynamic viscoelasticity test, the loss elastic modulus (E") has a peak in a range of 31.0 ℃ or more and 40.0 ℃ or less.
9. The separation membrane according to any one of claims 1 to 8, wherein the separation membrane has a stress (F5 value) of 5% elongation in the longitudinal direction of 5.0MPa or more.
10. The separation membrane according to any one of claims 1 to 9, wherein the separation membrane is in the shape of hollow fibers.
11. The separation membrane according to any one of claims 1 to 10, wherein a ratio of a degree of orientation of an outer surface to a degree of orientation of an inner surface of the separation membrane based on polarized infrared spectroscopy is 1.0 or more and 1.5 or less.
12. The separation membrane according to any one of claims 1 to 11, wherein the degree of orientation of an outer surface of the separation membrane based on polarized infrared spectroscopy is 1.3 or more and 3.0 or less.
13. The separation membrane according to any one of claims 1 to 12, wherein the separation membrane has a ratio of CO 2 permeability to N 2 permeability (CO 2/N2 selectivity) of 1 or more at 100 kPa.
14. The separation membrane according to any one of claims 1 to 13, wherein the separation membrane has a N 2 permeability of 5GPU or more at 100 kPa.
15. The separation membrane according to any one of claims 1 to 14, wherein the separation membrane has a tensile elastic modulus in a longitudinal direction of 100MPa or more.
16. A separation membrane according to any one of claims 1 to 15, wherein in the separation membrane the dense layer is present on the outer surface.
17. A method for producing a separation membrane, which comprises the following steps (1) to (3):
(1) A production step in which a resin mixture containing 10 to 50 mass% of poly (4-methyl-1-pentene) and 50 to 90 mass% of a plasticizer is melt-kneaded to obtain a resin composition;
(2) A molding step in which the resin composition is melted, discharged from a discharge tube head, cooled by a cooling bath, and wound at a draft ratio of 1 to 10 to obtain a resin molded article having an outer surface orientation degree of 1.0 to 1.5 and an outer surface orientation degree/inner surface orientation degree ratio of 1.0 to 1.5;
(3) And a stretching step in which the resin molded article is stretched at 60 ℃ or more and 120 ℃ or less by 2 times or more and 6 times or less to obtain a stretched article.
18. The method according to claim 17, wherein in the molding step, a solvent having a three-dimensional hansen solubility parameter distance Ra of 5 to 13 with respect to poly (4-methyl-1-pentene) and a three-dimensional hansen solubility parameter distance Rb of 4 to 10 with respect to the plasticizer is used in the cooling bath.
CN202280026655.9A 2021-04-28 2022-04-27 Separation membrane and method for producing same Pending CN118251268A (en)

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JP2021-075671 2021-04-28
JP2021-075672 2021-04-28

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CN118251268A true CN118251268A (en) 2024-06-25

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