JP2008173573A - Composite hollow fiber membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite hollow fiber membrane for gas separation which is made of a thermoplastic resin having particularly high chemical resistance and hydrophobicity and is provided with high gas permeability, high rupture elongation, and high heat resistance in addition to high gas separation property. <P>SOLUTION: The composite hollow fiber membrane comprising a support layer having a spherical structure of a thermoplastic resin and a separation layer made of a non-porous material is produced. The composite hollow fiber membrane has the size of 2 μm or smaller in the voids at the point of 5 μm depth in the support layer direction from the interface in the separation layer side of the support layer in a longitudinal cross-sectional photograph of the composite hollow fiber membrane. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a composite hollow fiber membrane for selectively separating components of a gas mixture. More specifically, separation of air from oxygen and nitrogen, separation and recovery of hydrogen from off-gas of the platform method, separation and recovery of hydrogen during ammonia synthesis, recovery of carbon dioxide from exhaust gas from thermal power generation and garbage incineration, and nitrogen oxidation Removal of substances and sulfur oxides, recovery of carbon dioxide from oilfield off-gas, removal of acidic gases such as hydrogen sulfide and carbon dioxide from natural gas mainly composed of methane, separation and recovery of helium, precision machinery and ozone It is applied to many fields such as air dehumidification for generators and dehydration from organic solvents.

  All polymer materials are more or less gas permeable, and their permeability varies greatly depending on the type of material and the type of gas. Therefore, a polymer membrane is used to separate and concentrate specific components from a gas mixture. It has been known for a long time. Gas separation by a membrane is actively applied in various industrial fields because it is advantageous in terms of energy as compared with other separation methods, and has features such as a small and light apparatus, a simple mechanism, and maintenance-free characteristics. In particular, in recent years, it has attracted attention from the viewpoints of resource saving, energy saving, and recovery of useful gas.

  Such a gas separation membrane is required to have high performance for selectively separating a target gas component from a mixed gas and high performance for efficiently transmitting the target gas component. That is, it is important that both gas separation property and gas permeability are high. In general, gas separability is an inherent characteristic of a membrane material in the case of a dense membrane. In contrast, gas permeability is inversely proportional to film thickness in the case of a homogeneous film. Therefore, in the production of gas separation membranes, how to produce a thin and dense membrane is an important issue, but on the other hand, the mechanical strength decreases as the film thickness decreases, so the film thickness that can be put to practical use. There were limits.

  Further, as described above, there are various uses and various usage environments. Therefore, when a compressor is used to pressurize the mixed gas, or when a warm mixed gas is used as it is, heat resistance at high temperatures is required. However, when the conventional polymer membrane is used at a high temperature, there is a problem that the separation performance is lowered.

  In view of the above background, a separation membrane having gas permeability, mechanical strength, and heat resistance is required in addition to the gas separation property inherent to the membrane material, and various proposals have been made.

  As one of them, a so-called thin dense layer having a high gas separation property and a relatively thick porous layer having both mechanical strength and gas permeability are integrally formed on a polymer membrane. There is an asymmetric separation membrane. For example, in Patent Document 1, using a solution of a polymer mixture containing at least one polymer of polyester, polyether, polycarbonate, polyamide, and polyimide having a fluorene skeleton, the surface layer is dense by a conventional wet spinning method, A hollow fiber membrane having a substantially sponge structure over the entire membrane has been reported. However, due to the necessity of increasing the gas permeability of the dense layer to some extent, the polymer concentration of the solution cannot be increased, and since it has a sponge structure, its mechanical strength is not sufficient and heat resistance is also low. .

Therefore, as another method, there is a so-called composite film formation in which a dense thin film of a polymer is laminated on a porous support substrate. For example, in Patent Documents 2 and 3, polyacetylene or silicone polymer having high gas permeability in a support layer made of polyvinylidene fluoride, which is suitable for gas separation membranes because of high chemical resistance and high hydrophobicity. A hollow fiber membrane in which a thin dense layer made of is laminated has been reported. However, in any case, since the support layer is formed by non-solvent induced phase separation, it has a sponge structure having defects called macrovoids, and its mechanical strength is not always sufficient. Moreover, the heat resistance of such a composite membrane is low. As a cause of this, a dense thin film may be thermally deformed or deteriorated. However, it is known that the influence of the heat deformation of the support layer is greater than that.
Japanese Patent Laid-Open No. 06-091145 JP-A-63-315104 Japanese Patent Application Laid-Open No. 09-066224

  In the present invention, in view of the above problems, it is made of a thermoplastic resin having high chemical resistance and high hydrophobicity. In addition to high gas separation properties, it has high gas permeability, high breaking strength, and high heat resistance. Another object is to provide a composite hollow fiber membrane for gas separation.

The present invention for solving the above problems is as follows.
(1) A composite hollow fiber membrane composed of a support layer composed of a spherical structure of a thermoplastic resin and a separation layer composed of a non-porous material, in a cross-sectional photograph perpendicular to the longitudinal direction of the composite hollow fiber membrane A composite hollow fiber membrane, wherein the size of a void at a depth of 5 µm in the direction of the support layer from the interface on the separation layer side of the layer is 2 µm or less.
(2) The composite hollow fiber membrane according to claim 1, wherein the spherical structure forming the opposite side of the support layer from the separation layer has an average diameter D2 of 0.1 μm or more and 2 μm or less.
(3) The composite hollow fiber membrane according to claim 2, wherein the average diameter D1 of the spherical structure forming the separation layer side of the support layer and the average diameter D2 satisfy a relationship of D1 <D2.
(4) The composite hollow fiber membrane according to claim 1 or 2, wherein the separation layer side of the support layer has a three-dimensional network structure, and the opposite side of the support layer to the separation layer has a spherical structure.
(5) The composite hollow fiber membrane according to any one of claims 1 to 4, wherein the thermoplastic resin is a polyvinylidene fluoride resin.
Consists of.

  According to the present invention, in addition to gas separability, a hollow fiber membrane having high gas permeability, breaking strength, heat resistance, and chemical resistance can be provided, and can be used for a wide range of gas separation applications.

  The composite hollow fiber membrane of the present invention is a composite hollow fiber membrane composed of a support layer composed of a spherical structure of a thermoplastic resin and a separation layer composed of a non-porous material, and is perpendicular to the longitudinal direction of the composite hollow fiber membrane. In a cross-sectional photograph, the void size at a depth of 5 μm in the direction of the support layer from the interface on the separation layer side of the support layer is 2 μm or less, so that high breaking strength, high gas permeability, and high heat resistance It is characterized by having. That is, the structure of the support layer is very important for the composite hollow fiber membrane to exhibit high performance. The support layer of the present invention has high breaking strength, high gas permeability, and high heat resistance, and the separation layer formed thereon is uniformly formed, and the adhesiveness with the separation layer is increased. Can do. As a result, the separation layer can be thinly and uniformly formed on the support layer and can exhibit high gas permeability.

  The structure of the support layer, which is important in the present invention, needs to consist mainly of a spherical structure of a thermoplastic resin.

  Here, the thermoplastic resin refers to a resin that is made of a chain polymer substance and that exhibits a property of being deformed / flowed by an external force when heated. Examples of this thermoplastic resin include polyethylene resin, polypropylene resin, acrylic resin, polyacrylonitrile resin, acrylonitrile-butadiene-styrene (ABS) resin, polystyrene resin, acrylonitrile-styrene (AS) resin, vinyl chloride resin, polyethylene terephthalate resin. , Polyamide resin, polyacetal resin, polycarbonate resin, modified polyphenylene ether resin, polyphenylene sulfide resin, polyvinylidene fluoride resin, polyamideimide resin, polyetherimide resin, polysulfone resin, polyethersulfone resin, and mixtures and copolymers thereof. It is done. Other resins miscible with these and polyhydric alcohols or surfactants may be contained in an amount of 50% by weight or less.

  Among these, in the present invention, a polyvinylidene fluoride resin that is hydrophobic, has high chemical resistance, and high physical strength is more preferably used. The polyvinylidene fluoride resin means a resin containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer, and may contain a plurality of types of vinylidene fluoride copolymers. The vinylidene fluoride copolymer is a polymer having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and other fluorine-based monomers. Examples of the copolymer include a copolymer of vinylidene fluoride and at least one selected from vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and trifluoroethylene chloride. Further, a monomer such as ethylene other than the fluorine-based monomer may be copolymerized to such an extent that the effects of the present invention are not impaired.

  Next, the spherical structure is a structure in which spherical solid portions, which are seen in a cross section perpendicular to the longitudinal direction of the support layer, are connected by sharing a part thereof. Since the relatively large solid part is connected to share many parts, the physical strength is high, and at the same time, the voids are large, so that the gas permeability is also high.

  The average diameter of the spherical structure is preferably 0.1 μm or more and 2 μm or less. Here, the average diameter of the spherical structure is the average diameter (average value of the major axis and the minor axis) of the spherical solid part. If the average diameter is less than 0.1 μm, the gaps between the spherical structures are also reduced and the gas permeability is lowered. On the other hand, when the thickness exceeds 2 μm, the connection between the spherical solid parts is reduced, the physical strength is lowered, and the heat shrinkage rate at high temperature is increased, so that the heat resistance is lowered. In addition, since the gas permeability of the composite hollow fiber membrane is more affected by the separation layer than the support layer, it is more effective as a gas separation membrane to lower the gas permeability of the support layer and increase the breaking strength and heat resistance. Therefore, the average diameter of the spherical structure of the support layer is more preferably 0.1 μm or more and 1.5 μm or less, and further preferably 0.1 μm or more and 0.7 μm or less.

  In the present invention, it is necessary to have a spherical structure, but other structures such as a three-dimensional network structure may be included.

  In the support layer of the present invention, in the cross-sectional photograph perpendicular to the longitudinal direction of the composite hollow fiber membrane, the size of the void at a depth of 5 μm in the support layer direction from the interface on the separation layer side of the support layer is 2 μm or less. It is necessary. This void is a hole in the support layer, and may be a communication hole from the interface on the separation layer side of the support layer or an isolated hole. If there is a hole larger than 2 μm at this position, if it is a communicating hole from the interface, the separation layer will enter the hole, causing a defect that is not formed uniformly on the support layer. A thin solid portion exists on the separation layer side, and the portion has low physical durability, and is destroyed by pressure during gas permeation.

  In other words, in order to firmly form a uniform thin separation layer on the support layer, the interface on the separation layer side of the support layer must have a dense structure with as few pores as possible so as not to significantly impair gas permeability. Is desirable. Here, the size of the void at a depth of 5 μm in the direction of the support layer from the interface on the separation layer side of the support layer is measured as described in the examples.

  Even if the 20 μm square photographed by chance does not exceed 2 μm, it does not satisfy the requirements of the present invention. In the case where the size of all the gaps in the part is 2 μm or less, the requirement of the present invention is satisfied. Conversely, even if the size of the gap exceeds 2 μm with a very low probability, It does not impair the essence of the invention. Therefore, it is sufficient that the size of all voids is 2 μm or less by measuring 12 points.

  In this way, in order to make the interface on the separation layer side of the support layer mainly composed of a spherical structure, the average diameter of the spherical structure is reduced, or the solidification rate of the surface when the support layer is solidified. It is preferably employed to increase the density and promote densification.

  Furthermore, as a more preferable method, the support layer has an average diameter D1 of the spherical structure forming the separation layer side of the support layer and an average diameter D2 of the spherical structure forming the side opposite to the separation layer of the support layer, where D1 <D2. It is a method to make the structure satisfying the relationship.

  That is, the separation layer side of the support layer has a dense structure with small pores by reducing the average diameter of the spherical structure as much as possible so that the gas permeability is not significantly impaired in order to form a uniformly thin separation layer on the support layer. In order to provide high gas permeability on the other side, it is preferable to make the average diameter of the spherical structure as large as possible to make the structure sparse with large pores so that the physical strength is not significantly impaired. The dense structure with small holes and the sparse structure with large holes may be formed stepwise or continuously.

  Specifically, both D1 and D2 are preferably 0.1 μm or more and 2 μm or less, more preferably D1 is 0.1 μm or more and 1.5 μm or less, D2 is 0.8 μm or more and 2 μm or less, and more preferably D1 is 0.1 μm or more and 0.7 μm or less, and D2 is 1.2 μm or more and 2 μm or less.

  Here, the measurement methods of the average diameter D1 of the spherical structure forming the separation layer side of the support layer and the average diameter D2 of the spherical structure forming the side opposite to the separation layer of the support layer are as in the examples.

  In addition to the spherical structure, a three-dimensional network structure may be formed on the separation layer side of the support layer. Here, the three-dimensional network structure refers to a structure in which the solid part is three-dimensionally spread in a network. In this case, it is necessary to form a dense structure at the interface on the separation layer side of the three-dimensional network structure. In addition, since the solid part is thin and the density is small, the three-dimensional network structure has a low breaking strength and elongation. Therefore, the average diameter of the spherical structure is preferably 0.1 μm or more and 2 μm or less in order to have a high breaking strength and elongation. More preferably, they are 0.1 micrometer or more and 1.5 micrometers or less, More preferably, they are 0.1 micrometer or more and 0.7 micrometers or less.

  The thickness of the support layer is preferably 20 to 1000 μm, more preferably 30 to 500 μm, and still more preferably 50 to 350 μm in consideration of physical strength and gas permeability.

  Next, the separation layer needs to be formed on the support layer and made of a non-porous material. The term “non-porous” as used herein refers to a structure having no pores having a diameter of 10 nm or more, in which pores are not confirmed on the cross section or surface by an electron microscope. The separation layer may be formed on either the outer surface side or the inner surface side of the hollow fiber membrane that is the support layer, and is preferably determined in consideration of the application, operability, and film forming property.

  As the material for the separation layer, various organic polymers, inorganic substances, mixtures thereof, and the like can be used according to the type of gas to be separated, the required gas permeability, gas separation properties, and the like. Examples of organic polymers include polysiloxanes such as polydimethylsiloxane, polymethylvinylsiloxane, polymethylphenylsiloxane, and polyimidesiloxane, poly-1-trimethylsilyl-2-propyne, poly-1-trimethylsilyl-3-propyne, and poly-p-trimethylsilyl. Polyacetylene and organosilicon compounds such as phenylacetylene and polyvinyltrimethylsilane, poly-4-methylpentene-1, polyethylene, polypropylene, polybutene-1, polyvinyl chloride, polyvinyl fluoride, polyvinyl chloride, polyvinylidene fluoride, polyvinyl alcohol, Polyvinyl ester, polyvinyl acetate, polyvinyl propionate, polyvinyl pyridine, polyvinyl pyrrolidone, polyvinyl ether, polyvinyl chloride Luketone, polyvinyl aldehyde, polyvinyl formal, polyvinyl butyral, polyvinyl amide, polyvinyl amine, polyvinyl urethane, polyvinyl urea, polyvinyl phosphate, polyvinyl sulfate, polyisoprene, polyacrylic acid and its ester derivatives, polymethacrylic acid and its ester derivatives Polyolefins such as polyolefin, polyphenylene oxide, polyxylene oxide, polystyrene and its derivatives, hydrocarbon resins such as methyl cellulose, cellulose acetate, nitrocellulose, polycarbonate, polysulfone, aryl polyamide, polyamide including aryl polyimide, polyimide, etc. These homopolymers, copolymers or mixtures may be used.

  The thickness of the separation layer is preferably 0.05 to 100 μm, more preferably 0.1 to 50 μm, and further preferably 0.5 to 20 μm in consideration of the integrity of the layer having no defect and gas permeability.

  Next, a method for producing the composite hollow fiber membrane of the present invention will be described.

  Although the support layer of the composite hollow fiber membrane of the present invention needs to have a spherical structure, the spherical structure can be formed by utilizing a thermally induced phase separation method. Here, thermally induced phase separation is phase separation in which a resin solution dissolved at high temperature is solidified by cooling.

  There are mainly two types of phase separation mechanisms in the thermally induced phase separation method. One is a liquid-liquid type in which a resin solution that is uniformly dissolved at a high temperature is separated into a dense phase and a dilute phase due to a decrease in the dissolving ability of the solution when the temperature is lowered, and the other is a resin solution that is uniformly dissolved at a high temperature. In the solid-liquid type, the resin crystallizes when the temperature is lowered, and the phase is separated into a polymer solid phase and a polymer dilute solution phase. Since the former mechanism mainly forms a three-dimensional network structure and the latter mechanism forms a spherical structure, the latter mechanism is used when forming the support layer. In order to induce solid-liquid thermally induced phase separation, it is necessary to select an appropriate solvent and resin concentration.

  The solvent is preferably a poor solvent of polyvinylidene fluoride resin, preferably a poor solvent having relatively high solubility of the resin, such as alkyl ketone, ester such as cyclohexanone, γ-butyrolactone, isophorone, dimethyl sulfoxide, and more preferably γ- Butyrolactone and dimethyl sulfoxide.

  As the resin concentration in the resin solution is higher, primary nuclei are more likely to be formed, and as a result, the average diameter of the spherical structure tends to be smaller. In order to make the average diameter of the spherical structure 0.1 μm or more and 2.0 μm or less, it is preferably 30 to 60% by weight.

  The resin solution charged with such a composition and melted at a high temperature is discharged from the annular port of the double-tube type die, and then cooled to below the crystallization temperature Tc of the resin solution and solidified before Tc + 20 ° C. or more and Tc + 55 ° C. or less It is necessary to hold at a temperature of 0.5 to 10 minutes. By maintaining at a low temperature for a long time, the number of primary nuclei generated in the spherical structure increases, and as a result, the average diameter of the spherical structure decreases. Here, the crystallization temperature Tc of the resin solution means that a mixture having the same composition as the resin solution, such as resin and solvent, is sealed in a sealed DSC container using a differential scanning calorimetry (DSC measurement) device, and the temperature rising rate is 10 ° C. The temperature is raised to the dissolution temperature at / min and held for 30 minutes to dissolve uniformly, and then set to the rising temperature of the crystallization peak observed in the process of lowering the temperature at a temperature drop rate of 10 ° C./min.

  When the temperature is higher than Tc + 55 ° C. or less than 0.5 minutes, the diameter of the spherical structure is difficult to be 2 μm or less, and when the temperature is lower than Tc + 20 ° C. or more than 10 minutes, the viscosity of the resin solution becomes too high, and the spinnability The hollow fiber membrane cannot be formed.

  Next, when cooling the discharged solution, it is preferable to use a cooling bath, and a mixed solvent of a solvent of the resin solution of the support layer and a non-solvent of the resin of the support layer is preferable. In this case, when the separation layer is formed on the outer surface side of the support layer, the non-solvent concentration of the resin of the support layer in the mixed solvent of the cooling bath may be increased in order to make the outer surface of the support layer a dense structure. preferable.

  For example, as a non-solvent for polyvinylidene fluoride resin, water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, Aliphatic hydrocarbons such as butylene glycol, pentanediol, hexanediol, low molecular weight polyethylene glycol, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinated organic liquids And mixed solvents thereof.

  Further, it is preferable that a mixed solvent of the solvent of the support layer solution and the non-solvent of the resin of the support layer is also discharged from the central tube of the double tube type die. At this time, as with the cooling bath, when the separation layer is formed on the inner surface side of the support layer, the non-solvent concentration of the resin of the support layer in the mixed solvent is increased in order to make the inner surface of the support layer a dense structure. It is preferable to do.

  As a method of making the structure in which the average diameter D1 of the spherical structure forming the separation layer side of the support layer and the average diameter D2 of the spherical structure forming the opposite side of the separation layer of the support layer satisfy the relationship of D1 <D2, 2 A method of using two resin solutions and making the support layer into a two-layer structure is preferable. At this time, there are a method of simultaneously forming a two-layer structure and a method of sequentially forming them.

  The former is a compound spinning method using a triple tube type die, the latter is a method in which a hollow fiber membrane is formed with one resin solution and then immersed in the other resin solution and then scraped through a nozzle or the like, or For example, the other resin solution may be spray coated. From the viewpoint of increasing the viscosity of both the resin solutions forming the two layers and improving the adhesion between the two layers, a method of forming simultaneously such as a composite spinning method using a triple tube die is more preferably used. That is, it is a method of discharging two resin solutions from the two annular ports on the outer side and the inner side of the triple tube type die.

  As described above, the average diameter of the spherical structure can be controlled mainly by the resin concentration in the resin solution, the holding temperature and the holding time before the resin solution is solidified, so the two resin solutions should be set to appropriate conditions for each. is required.

  Similarly, when the separation layer side of the support layer has a three-dimensional network structure and the opposite side of the support layer has a spherical structure, similarly, a method of using two resin solutions and making the support layer a two-layer structure Is preferred. Since the resin solution that forms the three-dimensional network structure has a relatively low resin concentration, both the method of forming the two layers simultaneously and the method of forming them in order are preferably employed. In order to form a three-dimensional network structure having a dense structure on the surface on the separation layer side, a non-solvent induced phase separation method can be used. Here, the non-solvent induced phase separation is phase separation in which a resin solution is solidified by contacting with a non-solvent.

  When the non-solvent induced phase separation method is used, the resin solvent is preferably a resin good solvent. For example, the polyvinylidene fluoride resin good solvent includes N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, Examples thereof include lower alkyl ketones such as methyl ethyl ketone, acetone and tetrahydrofuran, esters, amides and the like, and mixed solvents thereof. Thus, the three-dimensional network structure and the spherical structure are different in the phase separation mechanism used when forming, so in the method of forming at the same time, the non-solvent of the resin in the solvent discharged from the cooling bath and the central tube of the base The concentration or the thickness of the two layers of the three-dimensional network structure and the spherical structure are adjusted appropriately.

  The support layer thus produced may be stretched in order to enlarge the gap between the spherical structures, improve the gas permeability and strengthen the breaking strength. Furthermore, since it is wet with a solvent or a non-solvent, it is preferably employed after washing with a non-solvent of a low boiling point resin such as water and then drying.

  Thereafter, in the present invention, the support layer is preferably heat-treated at a temperature of 100 ° C. or higher and lower than the melting point of the support layer, and contracted in the length direction of the support layer at a contraction rate of 10% or more and 30% or less. Here, the melting point of the support layer is the peak top temperature of the lowest endothermic peak that appears when the dried support layer is heated at a rate of 10 ° C./min using a DSC measuring apparatus. In the case of a hollow fiber membrane made of polyvinylidene fluoride, the temperature is around 170 ° C. By carrying out such a treatment on the support layer having a spherical structure, the spherical solid portions shrink preferentially, and the large gaps between the solid portions hardly shrink, so that the gas permeability of the support layer is maintained. Further, the breaking strength and elongation are remarkably improved, and the heat shrinkage below the processing temperature is remarkably suppressed.

  Next, a method for forming the separation layer will be described.

  The separation layer is formed on the outer surface side or the inner surface side of the support membrane. As a method for forming on the outer surface side, a method in which the support layer is immersed in a solution of a resin or a monomer for forming a separation layer and then dried, crosslinked, polymerized, or plasma deposition and a related method can be used. The method of forming on the inner surface side is that after forming a hollow fiber membrane module of a support layer according to a normal example, and then injecting a solution of a resin or monomer that forms a separation layer from one end side to the other end side of the module A method of drying, crosslinking, polymerizing, or the like can be used.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples. Here, parameters related to the present invention were measured by the following methods.

(1) The size of the void at a depth of 5 μm from the interface on the separation layer side of the support layer in the direction of the support layer. Using a electron microscope, the cross section perpendicular to the longitudinal direction of the support layer 2 is 3000 times, and a 20 μm square photograph is included so that the interface 3 on the separation layer 1 side of the support layer 2 is included in each of the opposite sides of the photograph. Take a picture. Next, in the photograph, both ends of the photograph of the interface 3 on the separation layer 1 side of the support layer 2, that is, two points (A, C) on both ends of the photograph of the solid portion forming the interface 3, respectively, in the depth direction (separation layer). Take two points (B, D) at a distance of 5 μm in the direction opposite to 1) and draw a straight line connecting the two points (B, D). The length of the portion (line segment) passing through the gap 4 in the straight line is the size 5 of the gap at a depth of 5 μm from the interface 3 on the separation layer 1 side of the support layer 2. Here, when two solid parts overlap in the depth direction of the photograph, the solid part at the back of the photograph is ignored. In any 12 photographs, the size of the void is measured in the same manner, and it is determined whether the size of all the voids in all the locations is 2 μm or less (◯) or not (×).

(2) The average diameter D1 of the spherical structure forming the separation layer side of the support layer and the average diameter D2 of the spherical structure forming the opposite side of the support layer from the separation layer
The cross section perpendicular to the longitudinal direction of the support layer is 3000 to 6000 times using an electron microscope, and the distance of 10 μm from the interface of the support layer on the separation layer side to the depth in the support layer direction (the direction opposite to the separation layer) A photograph of 10 μm square is taken centering on an arbitrary point in the area. The average diameter of the spherical structure in the photograph is D1. Next, the cross section perpendicular to the longitudinal direction of the support layer is 3000 to 6000 times using an electron microscope, and is deep from the surface of the support layer on the side opposite to the separation layer (or an interface if further layers are provided). A photograph of 10 μm square is taken around an arbitrary point at a distance of 10 μm in the vertical direction (direction of the separation layer). The average diameter of the spherical structure in the photograph is D2.

(3) Breaking strength and breaking elongation of hollow fiber membrane Using a tensile tester (TENSILON / RTM100 manufactured by Toyo Baldwin Co., Ltd.), the hollow fiber membrane was tested with a test length of 50 mm and a full-scale load of 5 kg and a crosshead speed of 50 mm / Measured in minutes.

(4) Gas permeability of hollow fiber membrane Four hollow fiber membranes having a length of about 20 cm were bundled and inserted into a glass mini-module, and both ends were potted with an epoxy resin to prepare a test membrane module. When oxygen gas is used as the gas and a high pressure is applied from the separation layer side of the hollow fiber membrane, the volume of the gas permeating to the support layer side of the hollow fiber membrane (unit is cm ³ , the permeation amount is 25 ° C. 1 atmospheric pressure as a standard) is obtained by standardizing the measurement time (sec), the pressure difference (cmHg) of the gas on both sides of the hollow fiber membrane, the membrane surface area (cm ² ), and the membrane thickness (cm). It was.

(5) Heat Shrinkage Ratio of Hollow Fiber Membrane The dried hollow fiber membrane is held (heat treated) for 10 minutes in a dryer at 100 ° C. in a tensionless state, and the heat shrinkage rate is obtained according to the following formula.

Thermal shrinkage (%) = (initial sample length−sample length after heat treatment) / initial sample length × 100
(Example 1)
36% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 64% by weight of dimethyl sulfoxide were dissolved at 130 ° C. This resin solution (Tc: 32 ° C.) was held at 63 ° C. for 1.9 minutes, and then discharged from the outer annular port of the double-tube die. At the same time, an aqueous solution of 60% by weight of dimethyl sulfoxide was added to the double-tube die. The mixture was discharged from the central tube, solidified in a bath composed of an aqueous solution of 85% by weight of dimethyl sulfoxide, and then washed with water. The obtained support layer had a spherical structure, and the melting point of the support layer was 170 ° C. After that, it is passed between two drive rolls with rotational speeds of 8 m / min and 7.6 m / min through a dry heat atmosphere in which the atmosphere is 120 ° C. with hot air, and the shrinkage rate is 5 in the length direction of the hollow fiber membrane. %.

  The obtained eight support layers were bundled and inserted into a glass mini-module, and both ends were potted with an epoxy resin. After passing a 10% by weight cyclohexane solution of a room temperature curable silicone polymer containing polydimethylsiloxane as a main component into the hollow portion of the support layer, the excess silicone polymer was removed by ventilating the air. A cured thin film was formed on the inner surface side.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

(Example 2)
38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone were dissolved at 150 ° C. After this resin solution (Tc: 51 ° C.) was held at 97 ° C. for 0.7 minutes, it was discharged from the outer annular port of the double tube die, and at the same time, an aqueous solution of 75% by weight of γ-butyrolactone was added to the double tube die. The mixture was discharged from the center tube, solidified in a 5 ° C. bath composed of an 85% by weight aqueous solution of γ-butyrolactone, washed with water, and stretched 1.4 times in 90 ° C. water. The obtained support layer had a spherical structure, and the melting point of the support layer was 173 ° C. After that, it is passed between two drive rolls with rotational speeds of 8 m / min and 6.6 m / min through a dry heat atmosphere with an atmosphere of 160 ° C. by hot air, and the shrinkage rate is 17 in the length direction of the hollow fiber membrane. %.

  The thin film was formed in the same manner as in Example 1.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

(Example 3)
40% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 60% by weight of γ-butyrolactone were dissolved at 150 ° C. After holding this resin solution (Tc: 55 ° C.) at 90 ° C. for 2.3 minutes, the resin solution (Tc: 55 ° C.) is discharged from the outer annular port of the double tube die, and at the same time, an aqueous solution of 85% by weight of γ-butyrolactone is added to the double tube die. After being discharged from the central tube of the tube and solidified in a bath at a temperature of 5 ° C. consisting of an aqueous solution of 85% by weight of γ-butyrolactone, it was washed with water and stretched 1.2 times in 90 ° C. water. The obtained support layer had a spherical structure, and the melting point of the support layer was 173 ° C. After that, it is passed between two drive rolls with rotational speeds of 8 m / min and 7.4 m / min through a dry heat atmosphere in which the atmosphere is 120 ° C. with hot air, and the shrinkage rate is 7 in the length direction of the hollow fiber membrane. %.

  The thin film was formed in the same manner as in Example 1.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

Example 4
A resin solution 1 was prepared by dissolving 34% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 66% by weight of dimethyl sulfoxide at 130 ° C. Further, 37% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 63% by weight of dimethyl sulfoxide were dissolved at 130 ° C. to obtain Resin Solution 2. After this resin solution 1 (Tc: 28 ° C.) was held at 58 ° C. for 1.6 minutes, it was discharged from the outer annular port of the triple tube die, and at the same time, the resin solution 2 (Tc: 34 ° C.) was 2 at 62 ° C. After holding for 1 minute, it is discharged from the inner ring opening of the triple tube type die, and further 60% by weight of dimethyl sulfoxide aqueous solution is discharged from the central tube of the triple tube type die, and consists of 85% by weight aqueous solution of dimethyl sulfoxide. After solidifying in a bath at a temperature of 10 ° C., it was washed with water. The obtained support layer had a spherical structure, and the melting point of the support layer was 170 ° C. After that, it is passed between two drive rolls with rotational speeds of 8 m / min and 7.6 m / min through a dry heat atmosphere in which the atmosphere is 120 ° C. with hot air, and the shrinkage rate is 5 in the length direction of the hollow fiber membrane. %.

  The thin film was formed in the same manner as in Example 1.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

(Example 5)
A resin solution 1 was prepared by dissolving 38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone at 150 ° C. Further, 40% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 60% by weight of γ-butyrolactone were dissolved at 150 ° C. to obtain a resin solution 2. After this resin solution 1 (Tc: 51 ° C.) was held at 99 ° C. for 0.6 minutes, it was discharged from the annular port outside the triple tube die, and at the same time, the resin solution 2 (Tc: 55 ° C.) was 1 at 94 ° C. After holding for 5 minutes, it was discharged from the inner annular port of the triple tube type die, and an aqueous solution of 85% by weight of γ-butyrolactone was further discharged from the tube at the center of the triple tube type die to obtain an aqueous solution of 85% by weight of γ-butyrolactone. After solidifying in a bath at a temperature of 5 ° C., it was washed with water and stretched 1.4 times in 90 ° C. water. The obtained support layer had a spherical structure, and the melting point of the support layer was 170 ° C. After that, it is passed between two drive rolls with a rotational speed of 8 m / min and 6.9 m / min through a dry heat atmosphere in which the atmosphere is set to 150 ° C. with hot air, and the shrinkage ratio is 14 in the length direction of the hollow fiber membrane. %.

  The thin film was formed in the same manner as in Example 1.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

(Example 6)
A resin solution 1 was prepared by dissolving 38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 62% by weight of γ-butyrolactone at 150 ° C. Further, 40% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 60% by weight of γ-butyrolactone were dissolved at 150 ° C. to obtain a resin solution 2. The resin solution 1 (Tc: 51 ° C.) was held at 96 ° C. for 1.1 minutes, and then discharged from the annular port outside the triple tube die. At the same time, the resin solution 2 (Tc: 55 ° C.) was added at 90 ° C. for 3 minutes. After holding for 2 minutes, it was discharged from the inner annular port of the triple tube die, and an 85% by weight aqueous solution of γ-butyrolactone was discharged from the tube at the center of the triple tube die, and an 85% by weight aqueous solution of γ-butyrolactone was discharged. After solidifying in a bath at a temperature of 5 ° C., it was washed with water and stretched 1.1 times in water at 90 ° C. The obtained support layer had a spherical structure, and the melting point of the support layer was 172 ° C. After that, it is passed between two drive rolls with rotational speeds of 8 m / min and 7.4 m / min through a dry heat atmosphere in which the atmosphere is 120 ° C. with hot air, and the shrinkage rate is 7 in the length direction of the hollow fiber membrane. %.

  The thin film was formed in the same manner as in Example 1.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

(Example 7)
A support layer having a spherical structure was obtained in Example 1 by discharging an aqueous solution of 85% by weight of dimethyl sulfoxide from the central tube of the triple tube die.

  The support layer was immersed in a solution in which 13% by weight of a vinylidene fluoride homopolymer having a weight average molecular weight of 2840, 5% by weight of polyethylene glycol having a weight average molecular weight of 20,000, and 82% by weight of dimethylformamide were dissolved. The excess solution was scraped off using a resin nozzle, water-coagulated and dried. The obtained support layer had a three-dimensional network structure and a spherical structure, and the melting point of the support layer was 168 ° C.

  The obtained support layer was immersed in a 10% by weight cyclohexane solution of a room temperature curable silicone polymer mainly composed of polydimethylsiloxane, and the excess solution was scraped off using a silicone resin nozzle and dried. A cured thin film was formed on the outer surface side of the film.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

(Example 8)
The support layer is three-dimensional in the same manner as in Example 7, except that a support layer having a spherical structure was obtained in Example 2 by discharging an aqueous solution of 85% by weight of γ-butyrolactone from the tube at the center of the triple tube die. A composite hollow fiber membrane having a network structure and a spherical structure was obtained.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

Example 9
A composite hollow fiber membrane in which the support layer has a three-dimensional network structure and a spherical structure was obtained in the same manner as in Example 7, except that the support layer having a spherical structure was obtained in the same manner as in Example 3.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

(Comparative Example 1)
32% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 68% by weight of dimethyl sulfoxide were dissolved at 130 ° C. After holding this resin solution (Tc: 26 ° C.) at 85 ° C. for 0.2 minutes, the resin solution was discharged from the outer annular port of the double tube die, and at the same time, an aqueous solution of 85% by weight of dimethyl sulfoxide was added to the double tube die. The mixture was discharged from the central tube, solidified in a bath composed of an aqueous solution of 85% by weight of dimethyl sulfoxide at a temperature of 10 ° C., washed with water and dried. The obtained support layer had a spherical structure.

  The thin film was formed in the same manner as in Example 1.

  Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

  Since the holding temperature before discharging the resin solution from the outer annular port of the double-tube type die was high and the holding time was short, the average diameter of the spherical structure of the support layer was larger than 2 μm, and the elongation at break was high. The thin film was not formed uniformly on the inner surface of the hollow fiber membrane, and the exposed portion of the spherical structure was observed.

(Comparative Example 2)
Resin solution 1 was prepared by dissolving 40% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 60% by weight of γ-butyrolactone at 150 ° C. Further, 36% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and 64% by weight of γ-butyrolactone were dissolved at 150 ° C. to obtain a resin solution 2. The resin solution 1 (Tc: 55 ° C.) was held at 90 ° C. for 2.3 minutes, and then discharged from the outer annular port of the triple tube die. At the same time, the resin solution 2 (Tc: 48 ° C.) was 0 ° C. at 115 ° C. After holding for 1 minute, it was discharged from the inner annular port of the triple tube type die, and an aqueous solution of 85% by weight of γ-butyrolactone was further discharged from the tube at the center of the triple tube type die to obtain an aqueous solution of 85% by weight of γ-butyrolactone. After solidifying in a bath at a temperature of 5 ° C., it was washed with water, stretched 1.4 times in water at 90 ° C. and dried. The obtained support layer had a spherical structure.

The thin film was formed in the same manner as in Example 1. Table 1 shows the structure and performance of the obtained composite hollow fiber membrane.

  Since the holding temperature was high and the holding time was short before discharging the resin solution 2 from the inner annular port of the double tube type die, the average diameter of the spherical structure forming the separation layer side of the support layer was larger than 2 μm. Thus, a thin film was not uniformly formed on the inner surface of the hollow fiber membrane, and an exposed portion of the spherical structure was observed.

It is a schematic diagram showing the measuring method of the magnitude | size of the space | gap of the position of a depth of 5 micrometers in the support layer direction from the interface by the side of the separated layer of the support layer prescribed | regulated by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Separation layer 2 Support layer 3 Separation layer side interface 4 of support layer Void 5 Void size at a depth of 5 μm from support layer separation layer side interface toward support layer

Claims (5)

A composite hollow fiber membrane composed of a support layer composed of a spherical structure of a thermoplastic resin and a separation layer composed of a non-porous material, and the separation of the support layer in a cross-sectional photograph perpendicular to the longitudinal direction of the composite hollow fiber membrane A composite hollow fiber membrane, wherein the size of a void at a depth of 5 µm in the direction of the support layer from the layer side interface is 2 µm or less. The composite hollow fiber membrane according to claim 1, wherein an average diameter D2 of a spherical structure forming the side opposite to the separation layer of the support layer is 0.1 µm or more and 2 µm or less. The composite hollow fiber membrane according to claim 2, wherein the average diameter D1 of the spherical structure forming the separation layer side of the support layer and the average diameter D2 satisfy a relationship of D1 <D2. The composite hollow fiber membrane according to claim 1 or 2, wherein the separation layer side of the support layer has a three-dimensional network structure, and the opposite side of the support layer to the separation layer has a spherical structure. The composite hollow fiber membrane according to any one of claims 1 to 4, wherein the thermoplastic resin is a polyvinylidene fluoride resin.

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