JP3974907B2 - Composite separation membrane and method for producing the same - Google Patents

Description

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

  Conventionally, porous separation membranes for microfiltration have been used for the removal of fine particles of 0.1 to 10 μm, particularly 0.1 to 5 μm, and the removal of bacteria in the fields of electronics industry and food.

  The porous separation membrane includes a symmetrical separation membrane in which the outer and inner pore diameters do not substantially change, and an asymmetric separation membrane in which the pore diameter changes continuously or discontinuously in the thickness direction, and the pore diameters are different on the front and back sides. The membrane is classified into an internal dense separation membrane having a microporous layer having a minimum pore size inside the membrane.

  The symmetrical separation membrane has a large resistance with respect to the flow rate of the fluid to be treated in the filtration operation, and thus it is difficult to filter the fluid to be treated at a large flow rate. In addition, if particles having a diameter larger than the pore size adhere to the surface of the target film, the particles are deposited and clogged to shorten the filtration life. Although attempts have been made to reduce the film thickness in order to reduce the resistance of such a symmetrical separation membrane, there arises a new problem that the strength is reduced and the film is easily damaged.

  The asymmetric separation membrane has a structure in which a large pore is formed on the surface in contact with the fluid to be processed and a microporous layer having a fine pore diameter on the back surface side. By controlling the thickness to be thinner, it is possible to reduce the resistance applied to the entire film even if the flow rate of the fluid to be processed is increased. Further, in the filtration of a fluid to be treated containing fine particles and the like, since relatively large pores exist on the surface, the fine particles can be captured inside the membrane, and the filtration life can be extended. However, the asymmetric separation membrane has a microporous layer on the back side that is vulnerable to external impact and is easily scratched. Therefore, when this membrane is stored in a cartridge such as a filter in a folded shape, Large pores were formed, and the original excellent function was reduced.

  The inner dense separation membrane compensates for the disadvantages of the asymmetric separation membrane and has strength to withstand external impacts. In addition, by controlling the thickness of the micropore layer with the smallest pore diameter and the pore diameter to reduce the difference between the largest and smallest pore diameters, the membrane resistance can be lowered against the flow rate of the fluid to be treated for various applications. It becomes possible.

  Patent Document 1 discloses that the above-mentioned internal dense separation membrane is manufactured by stacking two asymmetric separation membranes so that their microporous layers are in close contact with each other.

Patent Document 2 discloses a method for producing an internal dense separation membrane in which a microporous layer is formed inside the membrane. In this method, a swelling agent, a hydrophilic polymer, and a non-solvent are added to a polymer that is a membrane material, and these are dissolved in a good solvent to prepare a film-forming stock solution. Evaporate the solvent inside, cause local phase separation on the membrane surface with moisture in the air, and further immerse in a coagulating liquid such as water to remove the solvent from the inside of the membrane, then wash and dry This is a method for producing an internal dense separation membrane by peeling from a support.
JP 58-150402 A JP-A-63-141607

  The present invention provides a composite separation membrane having a filtration performance equivalent to that of a conventional internal dense separation membrane and capable of guaranteeing a decrease in mechanical strength due to a microporous layer, and a method for producing the same. For the purpose.

According to the present invention, a composite separation membrane consisting essentially of a porous membrane made of polyethersulfone and a nonwoven fabric,
The interface between the porous membrane and the non-woven fabric has a structure in which non-woven fabric fibers enter each other,
In the porous membrane, a fine pore layer having a fine pore diameter is formed on the surface portion on the nonwoven fabric side, and the pore diameter increases from the fine pore layer toward the surface opposite to the nonwoven fabric. A composite separation membrane characterized by having a distributed structure is provided.

  According to the present invention, a film-forming stock solution containing polyethersulfone, a swelling agent, a hydrophilic polymer, a good solvent and a non-solvent is cast on a support, and a non-woven fabric is stacked on the surface of the cast film, and then a coagulation liquid A method for producing a composite separation membrane is provided, which is immersed in the membrane.

  The present invention has a filtration performance equivalent to that of a conventional internal dense separation membrane, and guarantees a decrease in mechanical strength due to the microporous layer to prevent damage during transport and assembly, and a decrease in performance. It is possible to provide a high-performance, high-reliability composite separation membrane and a method for manufacturing the same.

  Hereinafter, the composite separation membrane and the production method thereof according to the present invention will be described in detail.

  The composite separation membrane according to this embodiment is composed of a porous membrane substantially made of polyethersulfone and a nonwoven fabric, and has a structure in which fibers of the nonwoven fabric enter each other at the interface between the porous membrane and the nonwoven fabric. In the porous membrane, a fine pore layer having a fine pore diameter is formed on the surface portion on the nonwoven fabric side, and the pore diameter increases from the fine pore layer toward the surface opposite to the nonwoven fabric. It has a distributed structure. The pores of the fine pore layer and the layer having a pore size distribution (pore gradient layer) are continuous pores.

  Although the said nonwoven fabric will not be specifically limited if it is made from a plastic fiber, For example, it is made from a polyethylene fiber or a polypropylene fiber.

The basis weight of the nonwoven fabric is preferably 20 to 60 g / m ² .
The thickness of the nonwoven fabric does not greatly affect the performance of the composite separation membrane. However, when the composite separation membrane is used as a filter cartridge, if the thickness of the nonwoven fabric is too thick, a restriction is imposed on the area to be folded and stored in the cartridge. There is a possibility that the water tightness may be reduced due to close contact with each other. For this reason, it is desirable that the thickness of the nonwoven fabric be 100 to 600 μm, more preferably 150 to 450 μm.

  The porous membrane desirably has a thickness of 100 to 200 μm, more preferably 130 to 160 μm.

The thickness at which the fibers constituting the nonwoven fabric enter each other at the interface between the porous membrane and the nonwoven fabric is preferably 5 to 20 μm.

  The pore diameter of the microporous layer of the porous membrane is preferably 0.005 to 0.5 μm, more preferably 0.01 to 0.2 μm. This fine pore layer preferably occupies 5 to 15% of the total thickness of the porous membrane.

  The pore diameter on the surface of the porous membrane opposite to the nonwoven fabric is desirably 5 to 20 μm, more preferably 8 to 15 μm.

  An example of the structure of the composite separation membrane according to this embodiment will be specifically described with reference to FIG.

  The composite separation membrane 1 is composed of a porous membrane 2 substantially made of polyethersulfone and a nonwoven fabric 3 and has a structure in which fibers 4 of the nonwoven fabric 3 enter each other at the interface between the porous membrane 2 and the nonwoven fabric 3. . The porous membrane 2 has a fine pore layer 5 having a fine pore diameter formed on the surface portion on the nonwoven fabric 3 side, and a pore diameter increases from the fine pore layer 5 toward the surface on the opposite side of the nonwoven fabric. And the inclined hole layer 6 formed so as to be distributed. The pores of the micropore layer 5 and the pore gradient layer 6 are continuous pores that are continuously connected. When the composite separation membrane 1 is applied to a filtration filter, the surface of the porous membrane 2 on the pore inclined layer 6 side is the inflow side of the fluid to be treated.

  Next, the manufacturing method of the above-mentioned composite separation membrane will be described.

(First step)
A film-forming stock solution containing polyethersulfone, a swelling agent, a hydrophilic polymer, a good solvent and a non-solvent is cast on a support.

  As the swelling agent, for example, one or a mixture of two or more selected from polyethylene glycol, polyvinyl pyrrolidone, hydroxypropyl cellulose, sodium chloride, lithium chloride, and magnesium bromide can be used. Among these swelling agents, polyethylene glycol is preferable, and polyethylene glycol having a weight average molecular weight of 400 to 800 is particularly preferable.

  The hydrophilic polymer is not particularly limited in its weight average molecular weight, but preferably has a weight average molecular weight of 30,000 to 50,000, for example. As the hydrophilic polymer, for example, polyvinylpyrrolidone or hydroxypropylcellulose can be used. Among the hydrophilic polymers, polyvinyl pyrrolidone is preferable, and polyvinyl pyrrolidone having the weight average molecular weight is particularly preferable.

  As the good solvent, for example, N-methyl-pyrrolidone, acetone, dimethylformamide and the like can be used.

  As the non-solvent, for example, water, monohydric alcohol, polyhydric alcohol, ethylene glycol, tetraethylene glycol or the like can be used.

  The blending ratio of the polyethersulfone, the swelling agent and the hydrophilic polymer in the stock solution for film formation is not particularly limited. (C) The hydrophilic polymer is preferably 5 to 20% by weight.

  When the blending ratio of the polyethersulfone is less than 10% by weight, when the obtained composite separation membrane is used for filtration and separation, the strength of the porous membrane is low and there is a risk of breakage. On the other hand, if the blending ratio of the polyether sulfone exceeds 20% by weight, the strength of the porous membrane of the obtained composite separation membrane becomes too strong and may be damaged when used for filtration and separation. A more preferable blending ratio of the polyethersulfone is 13 to 16% by weight.

  When the blending ratio of the swelling agent is less than 10% by weight, it becomes difficult to form a desired network structure on the porous membrane of the obtained composite separation membrane. On the other hand, when the blending ratio of the swelling agent exceeds 20% by weight, it becomes difficult to prepare a homogeneous and uniform film forming stock solution. A more preferable blending ratio of the swelling agent is 13 to 17% by weight.

  When the blending ratio of the hydrophilic polymer is less than 5% by weight, the pore size of the porous membrane of the obtained composite separation membrane becomes uniform as a whole, and the intended micropore layer and pore size distribution can be formed. It becomes difficult. On the other hand, when the blending ratio of the hydrophilic polymer exceeds 20% by weight, the hydrophilic polymer tends to remain in the porous membrane of the obtained composite separation membrane, and a small amount is eluted from the porous membrane. There is a risk of initial contamination. A preferable blending ratio of the hydrophilic polymer is 9 to 13% by weight.

  As the support, for example, a polyethylene phthalate (PET) film or the like can be used.

  The casting atmosphere is preferably set to a temperature of 15 to 23 ° C. and a humidity of 50 to 80%.

  If the atmospheric temperature during casting is less than 15 ° C., it is difficult to obtain a composite separation membrane having a porous membrane having a target network structure. On the other hand, if the atmospheric temperature during casting exceeds 23 ° C., the nonwoven fabric interface of the porous membrane in the composite separation membrane obtained by surface evaporation may become a skin layer having no fine pores. More preferable atmospheric temperature during casting is 15 to 20 ° C.

  When the atmospheric humidity at the time of casting is less than 50%, the cast film surface is hard to be cured, and when the non-woven fabrics are stacked, the polymer component of the film forming amount excessively penetrates into the non-woven fabric and includes a microporous layer It becomes difficult to form a porous film having a network structure. On the other hand, if the atmospheric humidity at the time of casting exceeds 80%, defects will occur on the surface of the cast membrane, making it difficult to produce a composite separation membrane having the desired thickness and network structure. Moreover, there is a possibility that the film-forming stability when casting the film-forming stock solution is also lowered. More preferable atmospheric humidity during casting is 50 to 75%.

  The film thickness during casting is desirably about 100 μm to about 200 μm, more preferably about 130 μm to about 160 μm.

(Second step)
After the nonwoven fabric is stacked on the surface of the cast film on the support, it is immersed in a coagulation liquid. At this time, a fine pore layer having a fine pore diameter is formed on the surface of the cast film in contact with the nonwoven fabric by the interaction between the coagulating liquid and the swelling agent, hydrophilic polymer, good solvent and non-solvent that are components of the cast film. In addition, a pore inclined layer is formed by being distributed so that the pore diameter increases from the fine pore layer toward the surface opposite to the nonwoven fabric. Subsequently, the composite separation membrane having the structure described above is manufactured by washing, drying, and peeling from the support.

  Although the said nonwoven fabric will not be specifically limited if it is made from a plastic fiber, For example, it is made from a polyethylene fiber or a polypropylene fiber. The thickness of this nonwoven fabric does not significantly affect the performance of the composite separation membrane. However, when the manufactured composite separation membrane is used as a filter cartridge, if the thickness of the nonwoven fabric is too thick, the area to be folded and stored in the cartridge is limited. At this time, the separation membranes may be brought into close contact with each other to reduce water permeability. For this reason, it is desirable that the thickness of the nonwoven fabric be 100 to 600 μm, more preferably 150 to 450 μm.

  The non-solvent (for example, water, monohydric alcohol, polyhydric alcohol, ethylene glycol, tetraethylene glycol, etc.) mentioned above can be used for the coagulation liquid.

  The atmosphere until the nonwoven fabric adheres to the surface of the casting film on the support and is subsequently immersed in the coagulation liquid is maintained at the casting atmosphere, preferably at a temperature of 17 to 19 ° C. and a humidity of 55 to 75%. Is desirable.

  The washing is preferably performed with hot water of 50 to 70 ° C.

  In the composite separation membrane according to the embodiment of the present invention described above, the porous membrane and the non-woven fabric have the non-woven fabric fibers interpenetrating at the interface between them, so that the high adhesion force (high bonding strength) between them. And can be handled as an integrated member by preventing delamination when stored in a folded shape in a cartridge such as a filter.

  The porous membrane has a fine pore layer having a fine pore diameter formed on the surface portion on the nonwoven fabric side, and the pore diameter increases from the fine pore layer toward the surface opposite to the nonwoven fabric. The pore gradient layer formed in a distributed manner in the porous membrane in which the pore gradient layer is formed by controlling the micropore layer to be thinner than the entire thickness of the membrane. When the fluid to be treated is introduced from the surface side, the resistance applied to the entire film can be reduced even if the flow velocity of the fluid to be treated is increased. In addition, when filtering the fluid to be treated containing fine particles, the pores in the porous membrane have relatively large pores on the inflow surface of the fluid to be treated, so that the fine particles can be trapped inside the membrane. It becomes possible to extend the life.

Further, since the microporous layer is integrally covered with a nonwoven fabric and is protected against impact from the outside, when the composite separation membrane is stored in a cartridge such as a filter in a folded shape, the microporous layer is protected. It is possible to prevent the pore layer from being scratched and form large pores, and to exhibit the excellent filtration function inherent to the porous membrane.
According to the method of the embodiment of the present invention, a composite separation membrane having the above-described characteristics can be manufactured easily and with good reproducibility.
Embodiments of the present invention will be described below with reference to the drawings described above.

Example 1
First, 14% by weight of polyethersulfone (trade name: Sumikaflex 4200P, manufactured by Sumitomo Chemical Co., Ltd.), 13% by weight of polyethylene glycol having a weight average molecular weight of 600, 9% by weight of polyvinylpyrrolidone having a weight average molecular weight of 50,000, 15% by weight of 1-butanol, 47% by weight of N-methyl-pyrrolidone and 2% by weight of water were weighed, each component except N-methyl-pyrrolidone was put in a tank, stirred, and further N-methyl-pyrrolidone was added to dissolve the polymer component. Thereafter, degassing was performed to prepare a membrane-forming stock solution in which polyethersulfone was uniformly dissolved.
Next, the film-forming stock solution was cast on a PET film as a support in an atmosphere of a temperature of 17 ± 2 ° C. and a humidity of 70 ± 5% to a thickness of about 200 μm, and then allowed to stand for 10 seconds. Subsequently, before the casting film was immersed in a treatment tank containing water as a coagulation liquid, a polypropylene nonwoven fabric having a thickness of 250 μm and a basis weight of 40 g / m ² was laminated on the surface of the casting film. Subsequently, the membrane overlaid with the polypropylene nonwoven fabric was washed with a PET film in a 60 ° C. hot water tank and dried, and then the composite separation membrane was peeled from the PET film.
The obtained composite separation membrane had the structure shown in FIG. That is, in this composite separation membrane, a porous membrane made of polyethersulfone and having a thickness of 140 μm was integrally bonded to the polypropylene nonwoven fabric. The porous membrane has a fine pore layer having a fine pore diameter of 0.07 μm and an average diameter of 0.07 μm formed on the polypropylene nonwoven fabric side, and the opposite side from the nonwoven fabric to the nonwoven fabric. And a hole gradient layer formed so as to be distributed so that the hole diameter increases toward the surface. The average diameter of the holes on the surface side of the hole inclined layer was about 8 μm.
The obtained composite separation membrane was subjected to an IPA bubble point test and a water permeability test according to ASTM-F316. The water permeability test is a test that measures the time required to allow 100 mL of water to flow from the primary side (porous membrane side) by reducing the pressure (−80 kPa) on the secondary side (nonwoven fabric side) of the composite separation membrane. is there. As a result, the bubble point value was 85 kPa, and the water permeability was 9 seconds / 100 mL · −80 kPa. In addition, the porous membrane of the composite separation membrane was wetted with water, and the water permeability was increased.
Furthermore, when the obtained composite separation membrane was folded for use as a filter cartridge, it showed filtration performance comparable to that before the folding.

Sectional drawing which shows a composite separation membrane from the section to embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Composite separation membrane, 2 ... Porous membrane, 3 ... Fiber, 4 ... Nonwoven fabric, 5 ... Micropore layer, 6 ... Hole inclination layer.

Claims (7)

A composite separation membrane consisting essentially of a porous membrane made of polyethersulfone and a nonwoven fabric,
The interface between the porous membrane and the non-woven fabric has a structure in which non-woven fabric fibers enter each other,
In the porous membrane, a fine pore layer having a fine pore diameter is formed on the surface portion on the nonwoven fabric side, and the pore diameter increases from the fine pore layer toward the surface opposite to the nonwoven fabric. A composite separation membrane characterized by having a distributed structure.   The composite separation membrane according to claim 1, wherein the microporous layer of the porous membrane has a pore size of 0.005 to 0.5 μm.   The composite separation membrane according to claim 1, wherein the nonwoven fabric is made of polyethylene fiber or polypropylene fiber.   A film-forming stock solution containing polyethersulfone, swelling agent, hydrophilic polymer, good solvent and non-solvent is cast on a support, a nonwoven fabric is layered on the surface of the cast film, and then immersed in a coagulation liquid. A method for producing a composite separation membrane.   The method for producing a composite separation membrane according to claim 4, wherein the swelling agent is polyethylene glycol.   The method for producing a composite separation membrane according to claim 4, wherein the hydrophilic polymer is polyvinylpyrrolidone or hydroxypropylcellulose.   5. The method for producing a composite separation membrane according to claim 4, wherein the coagulation liquid comprises at least one non-solvent selected from water, monohydric alcohol, polyhydric alcohol, ethylene glycol, and tetraethylene glycol.

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