HK1078285B - Composite membrane - Google Patents

Description

Composite porous membrane

Technical Field

The present invention relates to a composite multi (micro) porous membrane used as a fine filtration membrane or an ultrafiltration membrane for water treatment and a manufacturing method thereof.

Background

In recent years, water treatment by a membrane filtration method using a filtration membrane having excellent separation completeness and a small size has been attracting attention due to an increase in concern about environmental pollution and a predetermined enhancement. For such water treatment applications, filtration membranes are required to have not only excellent separation characteristics and permeability but also higher mechanical properties than ever.

Conventionally, as a filtration membrane having excellent permeability, filtration membranes made of polysulfone, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, and the like, which are manufactured by a wet or dry-wet spinning method, have been known. These filtration membranes are formed by microphase separating a polymer solution and then solidifying the polymer solution in a non-solvent, and have a dense layer and a support layer, and have a high porosity and an asymmetric structure.

Among the above-mentioned filter membrane materials, polyvinylidene fluoride resin is suitable as a separation membrane material because of its excellent drug resistance and heat resistance. However, the filtration membrane made of the polyvinylidene fluoride hollow fiber membrane proposed so far has a problem of poor mechanical strength.

As a filtration membrane having improved strength, a porous membrane in which hollow strands are completely embedded in a porous semipermeable membrane has been proposed (see Japanese patent laid-open publication Nos. 52-081076, 52-082682, and 52-120288). However, this porous membrane has a problem of low water permeability because the string is completely embedded in the porous semipermeable membrane among the porous semipermeable membranes.

On the other hand, in order to improve water permeability, a separation membrane in which a porous membrane is provided on the surface of a hollow strand has been proposed (see U.S. Pat. No. 5472607). However, since the separation membrane is disposed only on the surface of the string, there is a problem that the porous membrane is easily peeled off from the string.

The present invention has been made in view of the above circumstances, and an object of the present invention is to: provided are a composite porous membrane having excellent mechanical properties, which has excellent mechanical properties, while having excellent permeability and excellent adhesion between a porous membrane and a string, and a method for producing the same.

Disclosure of Invention

That is, the present invention provides a composite multi- (micro) porous membrane having a string and a membrane material, wherein the membrane material has a first porous layer and a second porous layer, the first porous layer having a dense layer adjacent to the outer surface of the strand, the second porous layer has a dense layer adjacent to the first porous layer, the dense layer of the first porous layer has an average pore diameter in the range of 0.2 to 1 μm, the average pore diameter range of the dense layer of the second porous layer is 0.1-0.8 mu m, the dense layer of at least one of the first porous layer and the second porous layer is located at the inner side 0.1-50 mu m away from the outermost surface of the porous layer where the dense layer is located, the average pore diameter of the holes located at the outermost side of the first porous layer is 1-5 mu m, and the average pore diameter of the holes located at the outermost side of the second porous layer is 0.8-2 mu m.

The composite porous membrane of the present invention is preferably a porous hollow fiber membrane formed by coating a membrane material on a string. In water treatment applications, it is necessary to cause a liquid on the primary filtration side through which the membrane permeates to flow against the membrane surface. Since the membrane flows vibrate and pull the membrane, the composite porous membrane of the present invention needs to have sufficient mechanical strength. Since the cord bears the mechanical strength, the composite porous film of the present invention has excellent mechanical strength.

The composite porous membrane of the present invention has 2 or more dense layers, and therefore, the durability of the membrane can be improved.

The present invention also provides a method for producing a composite porous membrane, comprising applying a membrane forming solution to a string with an annular nozzle, solidifying the membrane forming solution in a solidifying solution to form a first porous layer, and then applying the membrane forming solution to the surface of the first porous layer with the annular nozzle, and solidifying the membrane forming solution in the solidifying solution to form a second porous layer.

Drawings

Fig. 1 is a cross-sectional view showing an example of an annular nozzle used for producing the composite porous membrane of the present invention.

Detailed Description

The preferred embodiments of the present invention will be described below.

The composite porous membrane of the present invention has a string and a membrane material, and is characterized in that the membrane material has a first porous layer and a second porous layer, the first porous layer has a dense layer adjacent to the outer surface of the string, and the second porous layer has a dense layer adjacent to the first porous layer.

First, the string used for the composite porous film of the present invention will be described.

The yarn used in the present invention is preferably a composite yarn, a monofilament yarn or a spun yarn. The cross-sectional shape of the wire is preferably any one of a circular cross-section, a hollow structure, and a deformed cross-section.

When the composite yarn is used as the cord, the composite yarn having a yarn number of 30 to 200 is preferably used because of its excellent strength and permeability. If the number of filaments is less than 30, the crush resistance is low, which is not preferable. If the number of filaments exceeds 200, the water permeability may be reduced due to the reduction of the inner diameter, which is not preferable.

As the raw material of the cord, synthetic fibers, semisynthetic fibers, regenerated fibers, natural fibers, or inorganic fibers may be used alone or in combination.

Examples of the synthetic fibers include various polyamide fibers such as nylon 6, nylon 66, and aromatic polyamide; various fibers of polyester type of polyethylene terephthalate, polybutylene terephthalate, polylactic acid, and polyglycolic acid; acrylic fibers such as polyacrylonitrile; polyolefin-based fibers such as polyethylene and polypropylene; various fibers of polyvinyl alcohol; various fibers of polyvinylidene chloride; polyvinyl chloride-based fibers; various fibers of polyurethane system; a phenol-based fiber; fluorine-based fibers made of polyvinylidene fluoride, polytetrafluoroethylene, or the like; and polyalkylene paraben-based fibers.

Examples of the semi-synthetic fibers include various cellulose derivative fibers as raw materials such as cellulose diacetate, cellulose triacetate, keratan, and chitosan (キトサン); and various protein fibers called "plemicks" (プロミツクス).

Examples of the regenerated fibers include: various cellulose-based regenerated fibers obtained by a viscose spinning method, a copper-ammonia spinning method or an organic solvent method include, specifically, rayon, cuprammonium short fiber, high wet modulus viscose fiber and the like.

Examples of natural fibers include flax and jute.

Examples of the inorganic fibers include glass fibers, carbon fibers, and various metal fibers.

Among these fibers, from the viewpoint of excellent drug resistance, fibers composed of at least one of polyester fibers, acrylic fibers, polyvinyl alcohol fibers, polyamide fibers, and polyolefin fibers are preferred. In addition, polyester fiber and acrylic fiber are particularly preferable.

From the viewpoint of improving the durability and adhesiveness of the film, the fineness of the cord is preferably in the range of 500-. When the fineness of the string is less than 500 dtex, the bursting strength of the film is reduced, which is not preferable. On the other hand, if the fineness of the cord is larger than 1200 dtex, the water permeability may be reduced by reducing the inner diameter, which is not preferable.

In addition, the number of threads of the cord is preferably 8 to 50 from the viewpoint of improving the durability and water permeability of the film. If the number of threads of the cord is less than 8, the crush resistance is undesirably low. Further, if the number of threads of the cord is more than 50, the inner diameter may be reduced to lower the water permeability, which is not preferable.

The number of cilia of the cord is preferably less than 15 per meter. If the number of cilia is more than 15 per meter, the coating failure portion is easily dispersed, and bacteria such as coliform bacteria and suspended matter are easily permeated through the coating failure portion, and the practicability is not satisfactory. The number of cilia is preferably 10 or less per meter, more preferably 5 or less.

Here, the cilia means a state in which fibers constituting the cord are thrown out of the cord by fiber breakage or breakage during the knitting process, and means a state in which fibrous or other foreign matter other than the fibers constituting the cord is attached to the cord and protrudes from the surface of the cord.

The hot water shrinkage of the cord is preferably 5% or less in view of increasing the impregnation rate of the resin contained in the film agent with respect to the cord. The hot water shrinkage is more preferably 4% or less, still more preferably 3% or less. If the hot water shrinkage rate exceeds 5%, the cord shrinks significantly in the hot water bath in the hot water washing step, which is one step of the production process. When the string contracts, the first porous layer impregnated (absorbed) in the string also contracts in the same manner. On the other hand, as described in detail below, the second porous layer does not completely adhere to the first porous layer, and therefore does not shrink greatly. This enlarges the gap between the first porous layer and the second porous layer, and the large gap makes it difficult for the resin to impregnate (soak) the porous layer.

The cord supply tension affects the stability of the film forming process and the impregnation property of the fixing resin. To improve this, the string supply tension is preferably set to 1kPa to 30 kPa. If the cord supply tension is less than 1kPa, a failure such as the cord being separated from the guide groove tends to occur easily in the manufacturing process. When the string supply tension exceeds 30kPa, the string and the first porous layer tend to be thinned, but the second porous layer is not deformed much. Therefore, the gap between the first porous layer and the second porous layer tends to be easily enlarged. The cord supply tension is preferably 3kPa to 25kPa, more preferably 5kPa to 20 kPa. The string supply tension may be obtained by measuring a pressure generated by the string at a portion where the string is introduced into the annular nozzle by using a tension meter or the like.

As the cord, for example, a cord prepared by knitting 96 monofilaments of 8.6 dtex (デシテツクス), that is, a total of 830 dtex (デシテツクス) and 16 monofilaments, into a hollow cord shape at a speed of 10 rpm in a braiding machine can be used.

Next, the film material will be explained.

The membrane material has a first porous layer having a dense layer adjacent to the outer surface of the strand and a second porous layer having a dense layer adjacent to the first porous layer.

From the viewpoint of achieving sufficient filtration performance or the like, the membrane material preferably has a plurality of holes communicating from one surface to the other surface. The holes provided in the film material may be holes that pass directly through or holes having a mesh structure that penetrate into the inside.

From the viewpoint of improving the drug resistance and heat resistance, the film material is preferably formed of a fluorine-based resin. Polyvinylidene fluoride is particularly preferred. Further, it is preferable that the polyvinylidene fluoride (A) having a weight average molecular weight of 100,000 to 1,000,000 and the polyvinylidene fluoride (B) having a weight average molecular weight of 10,000 to 500,000 are contained in a mass ratio of (A)/(B) of 0.5 to 10. (A) The mass ratio of (B) is preferably 1 to 3. By such a mass ratio, the pore diameter of the membrane can be easily adjusted.

If the thickness of the film is too large, the water permeability will be low, while if it is too small, there is a risk of breakage, so the outer surface of the cord, i.e., the thickness from the innermost surface of the film to the outermost surface of the film, is preferably in the range of 200 to 500 μm.

The first porous layer and the second porous layer have improved strength as a composite porous film when the outer surface of the first porous layer and the inner surface of the second porous layer are bonded together. However, when the bonding is completed, the water permeability is lowered, and therefore, it is preferable to bond 1 to 50% to 100% of the area of the interface between the both.

From the viewpoint of having both water permeability and aperture control for division into blocks (Japanese: control of division aperture), the first porous layer preferably has a dense layer having an average aperture in the range of 0.2 to 1 μm. Further, the second porous layer preferably has a dense layer having an average pore diameter in the range of 0.1 to 0.8. mu.m.

The thickness of the dense layer is preferably in the range of 50nm to 50 μm, more preferably in the range of 200nm to 30 μm, and most preferably in the range of 500nm to 10 μm.

In addition, from the viewpoint of having both water permeability and controlling the pore diameter for partitioning, it is preferable that either one or both of the first porous layer and the second porous layer have a dense layer on the inner side of 0.1 to 50 μm from the surface of the membrane. A membrane having a dense layer at a position less than 0.1 μm from the membrane surface is not preferable because it is easily damaged by external impact or by troublesome operations such as adhesion between membranes in a membrane forming process, but on the other hand, it is sufficient to have a dense layer at an inner side of 50 μm or more from the outermost position, although the membrane performance is not deteriorated.

In order to improve the water permeability, it is preferable that either or both of the first porous layer and the second porous layer have a support layer having a pore diameter gradually increasing from the dense layer side toward the cord. By adopting such an inclined structure, even if the thickness is increased, high water permeability can be ensured.

The support layer may contain large voids having a pore diameter of 50 to 150 μm. The pore diameter of the support layer other than the large voids is preferably in the range of 0.1 to 50 μm, more preferably in the range of 0.3 to 30 μm, and most preferably in the range of 0.5 to 20 μm.

The average pore diameter at the outermost position of each layer is preferably in the range of 1 to 5 μm in the first porous layer and 0.8 to 2 μm in the second porous layer.

Here, the position that becomes the outermost side of each porous layer as described herein means a position that becomes an interface between the first porous layer and the second porous layer; in the second porous layer, the position of the outermost surface of the second porous layer when the second porous layer is the outermost layer, and the position of the interface with another porous layer when the second porous layer is present around the second porous layer are referred to as the positions of the interfaces with the second porous layer.

Hereinafter, a composite porous film having the cord and the film material will be described.

The thickness of the entire composite porous membrane is preferably 600 to 1200 μm in consideration of water permeability and compressive crushing strength. When the thickness is too large, the membrane area per unit volume decreases, and when the thickness is too small, the diameter of the hollow portion becomes too small, and the water flow resistance increases, so that the outer diameter of the composite porous membrane is preferably 2000 to 5000 μm, and the inner diameter is preferably 700 to 3000 μm.

From the viewpoint of achieving sufficient filtration performance, the water permeability (WF) of the composite porous membrane is preferably 50 (m)³/m²h/MPa) or more. If the permeability is less than 50 (m)³/m²h/MPa) low filtration performance and difficult use. Although there is no upper limit to the filtration performance, it is practically 400 (m)³/m²/h/MPa) is sufficient.

The bubble pressure point (BP) of the composite porous membrane is preferably 50(kPa) or more. When the bubble pressure point is less than 50kPa, permeation of bacteria such as coliform bacteria and suspended matter occurs, and this is not preferable in terms of practicality.

From the viewpoint of having both water permeability and pore size control for partitioning, the water passage rupture pressure of the composite porous membrane is preferably 200kPa or more. When the pressure for water passage and rupture of the porous membrane is less than 200kPa, bacteria such as coliform bacteria and suspended matter are caused to permeate through the porous membrane, and this is not preferable in terms of practical use. Although there is no upper limit to the water passage cracking pressure, it is practically sufficient if 1000kPa is provided.

From the viewpoint of having both water permeability and pore size control for partitioning, when water is continuously passed through the composite porous membrane at 200kPa, the durability time is preferably 150 hours or more. If the duration is less than 150 hours, bacteria such as coliform bacteria and suspended matter permeate the film, and this is not practical. Although there is no upper limit to the duration, in practice, 10000 hours is sufficient. Here, the term "durability time" refers to a time period during which the performance of partitioning the porous composite membrane into blocks is maintained before water passes through the porous composite membrane.

Further, the number of times of durability when the pressure of 400kPa is repeatedly applied is preferably 100 or more. When the number of times of durability is less than 100 times at 400kPa, permeation of bacteria such as coliform bacteria and suspended matter occurs, and this is not preferable in terms of practicality. Although there is no upper limit to the number of times of endurance, in practice, 10,000 times are sufficient. The number of times of durability as used herein refers to the number of times that the performance of the composite porous film in dividing the blocks is maintained before the pressure is initially applied.

Hereinafter, a method for producing a composite porous film having the above characteristics will be described.

Preferably, a so-called dry-wet spinning method is used. That is, it is preferable that the membrane is left standing for a predetermined period of time after the membrane-forming solution is discharged from the annular nozzle (Japanese: empty), and then is impregnated with the coagulating liquid to form a porous membrane material. When the film is formed, the thread rope firstly passes through the annular nozzle and then the film-forming liquid is coated on the thread rope.

The method for producing a composite porous membrane of the present invention is a method in which a membrane forming solution is applied to a string by an annular nozzle to form a first porous layer by solidifying the membrane forming solution in a solidifying solution, and then the membrane forming solution is applied to the surface of the first porous layer by the annular nozzle to form a second porous layer by solidifying the membrane forming solution in the solidifying solution.

First, when a first porous layer is formed on a wire, a first film-forming solution that is thin and easily impregnated into the wire is applied to the wire, and then a second film-forming solution that is more concentrated than the first film-forming solution and is suitable for forming a porous layer is applied to the wire. By using the first deposition solution and the second deposition solution having different concentrations, the main portion of the cord can be impregnated with the first deposition solution and the second deposition solution, and peeling of the film material from the cord can be improved.

In consideration of the impregnation property into the strand, the concentration of the polymer forming the film material in the first film-forming solution is preferably 12% or less, more preferably 10% or less, and most preferably 7% or less. By making the concentration as such, the first film-forming solution is easily impregnated into the cord. In addition, since the polymer concentration of the film material occupying the gaps of the strands during film formation is about the same as the polymer concentration in the first deposition solution, the water permeability of the film during filtration can be maintained high. Further, the film material can be attached to the string with sufficient strength.

The second deposition solution is also a deposition solution obtained by dissolving a polymer as a film material in a solvent, as in the first deposition solution. In order to obtain mechanical strength with which a void layer is difficult to form when a composite porous film is formed, it is preferable to use a polymer solution having the same or higher polymer concentration than the first deposition solution. Specifically, the polymer concentration of the film material in the second deposition solution is set to be 12% or more, preferably 15% or more. In order to increase the permeation flux, the polymer concentration is preferably in the range of not more than 25%.

The solvent used for the first and second deposition solutions is preferably an organic solvent. As the organic solvent, N-dimethylformamide, dimethylacetamide (Japanese: ジメチルアセトアミド), dimethylsulfoxide and the like can be used. Among them, dimethylacetamide is more preferable in that the obtained porous body has a high water flow rate.

Further, as an additive for controlling the mutual separation, it is preferable to dissolve a hydrophilic polymer such as a monoalcohol, a diol, a triol, or polyvinylpyrrolidone represented by polyethylene glycol in the membrane-forming solution at the same time. The lower limit of the concentration of the hydrophilic polymer is preferably 1% by mass, more preferably 5% by mass. The upper limit of the concentration of the hydrophilic polymer is preferably 20% by mass, more preferably 12% by mass.

When the temperature of the deposition solution discharged from the nozzle is less than 20 ℃, the deposition solution may be gelled at a low temperature, which is not preferable. On the other hand, when the temperature of the film-forming solution is 40 ℃ or higher, it is difficult to control the pore diameter, and as a result, permeation of bacteria such as coliform bacteria and suspended matter occurs, and the practicability is not satisfactory. Therefore, the temperature of the film-forming solution is preferably 20 to 40 ℃.

Then, the film forming liquid applied to the wire is emptied, and then the first porous layer is formed by immersing the wire in a solidifying liquid.

If the standing time is 0.01 seconds or less, the filtration performance is lowered, which is not preferable. The standing time is not limited to an upper limit, but only 4 seconds are sufficient for practical use. Therefore, the standing time is preferably 0.01 to 4 seconds.

As the solidification solution, an aqueous solution containing a solvent used in the film-forming solution is preferably used. Although depending on the type of solvent used, when dimethylacetamide is used as a solvent for the deposition solution, the concentration of dimethylacetamide in the coagulation solution is preferably 1 to 50%.

The temperature of the solidification liquid is preferably low in view of improving mechanical strength. However, when the temperature of the coagulation liquid is excessively lowered, the water flow rate of the formed film is lowered, and therefore, the temperature is usually selected to be 90 ℃ or lower, more preferably 50 ℃ or higher and 85 ℃ or lower.

After solidification, the solvent is preferably washed in hot water at 60 ℃ to 100 ℃. The temperature of the cleaning tank is set to as high a temperature as possible within a range where thermal fusion does not occur between the first porous layers. From this viewpoint, the temperature of the cleaning tank is preferably 60 ℃ or higher.

After the hot water washing, it is preferable to perform chemical washing with hypochlorous acid or the like. When an aqueous solution of sodium hypochlorite is used, the concentration is preferably 10 to 120,000 mg/L. When the concentration of the sodium hypochlorite aqueous solution is less than 10mg/L, the permeation flux of the film to be formed is undesirably reduced. Although there is no upper limit to the concentration of the sodium hypochlorite aqueous solution, it is practically sufficient if the concentration is 120,000 mg/L.

Then, the film after the chemical cleaning is preferably cleaned in hot water at 60 to 100 ℃. Then, it is preferable to dry the sheet at a temperature of 60 ℃ or higher but less than 100 ℃ for 1 minute or more but less than 24 hours. When the temperature is not higher than 60 ℃, the drying treatment time is too long, and the production cost is increased, so that the method is unfavorable in industrial production. At 100 ℃ or higher, the film is excessively shrunk in the baking step, and minute cracks may occur on the film surface, which is not preferable.

The dried film is preferably wound on a bobbin or cartridge holder (Japanese: カセ). The single body (エレメント) is preferably rolled up on the cassette holder because it is easy to process.

As described above, since the water permeability is lowered when the first porous layer and the second porous layer are completely bonded, it is preferable to attach a solution that does not dissolve the film material to the surface of the first porous layer before the second porous layer is formed in order to prevent this.

As the solution not dissolving the film material, an aqueous solution containing a solvent for the film-forming solution is preferably used. For example, when dimethylacetamide is used as a solvent for the film-forming solution, the concentration of dimethylacetamide in a solution that does not dissolve the film material is preferably 1 to 50%. As another preferable solution not dissolving the film material, an organic solvent, a mixture of an organic solvent and water, or a solution obtained by adding an additive such as glycerin as a main component to the former solution is preferably used.

And then coating a second membrane-forming solution on the surface of the first porous layer to form a second membrane-forming solution. The first deposition solution having a low concentration is not required to be used for forming the second deposition solution.

In carrying out the above-described manufacturing method, it is preferable to use an annular nozzle having a structure shown in fig. 1, for example. The annular nozzle is composed of 3 members, i.e., a distribution plate 10, a first distribution nozzle 9 assembled adjacent to the distribution plate 10, and a second distribution nozzle 8 assembled adjacent to the first distribution nozzle 9 and constituting a tip portion of a tubular nozzle.

The distribution plate 10 is a disk-shaped member, and a line 1 through which a cord passes is formed at the center thereof. The distribution plate 10 has a first supply port 6 for supplying the first deposition solution and a second supply port 7 for supplying the second deposition solution around the pipe 1.

The first distribution nozzle 9 is a member having a substantially T-shaped cross section and a disk-shaped planar shape. In the center thereof, a projecting tubular portion 13 projecting into the second distribution nozzle 8 is formed. The interior of the projecting tubular portion 13 is a hollow portion which communicates with the above-mentioned pipe 1, forming a cord channel 100. If the first distribution nozzle 9 is overlapped concentrically with the distribution plate 10, the string passage 100 is formed in the center thereof.

The first distribution nozzle 9 has a hollow portion communicating with the first supply port 6 and a hollow portion communicating with the second supply port 7 around the string passage 100.

When the distribution plate 10 and the first distribution nozzle 9 are concentrically overlapped, grooves are formed in these to form a first pool portion 11 communicating with the first supply port 6. In addition, in the case where these are overlapped in a concentric shape, a ring-shaped slit is also formed so that the first discharge port 2 is formed over the entire peripheral wall of the string passage 100. The first discharge port 2 communicates with the first reservoir portion 11. The first reservoir portion 11 communicates with the first discharge port 2.

When the distribution plate 10 and the first distribution nozzle 9 are concentrically overlapped and the liquid is supplied to the first supply port 6, the supplied liquid can be stored in the first liquid pool portion 11 and then the liquid can be discharged from the first discharge port 2 to the string passage 100.

The second distribution nozzle 8 is also a disk-shaped member, and has a second liquid pool portion 12 formed at the center thereof, and a hollow portion communicating with the second liquid pool portion 12. This hollow portion communicates with the second supply port 7 through a hollow portion formed in the first distribution nozzle 9 and communicates with the second supply port 7. The second distribution nozzle 8 and the first distribution nozzle 9 are concentrically overlapped with each other, whereby the second pool portion 12 is formed around the first distribution nozzle 9. Specifically, the space formed by the projecting tubular portion 13 and the second distribution nozzle 8 on the end surface of the first distribution nozzle 9 on which the projecting annular portion 13 is provided serves as the second liquid pool portion 12. The second tank portion 12 is formed so that its cross-sectional area is reduced toward the front end of the projecting tubular portion 13 of the first distribution nozzle 9. That is, the inner wall of the second distribution nozzle 8 gradually bulges toward the projecting annular portion 13.

The second protrusion port 3 is formed at the front stage of the second tank section 12. That is, the second discharge port 3 is formed by the outer wall of the front end portion of the projecting tubular portion 13 and the inner wall of the second distribution nozzle 8.

In particular, the front end surface of the protruding annular portion 13, i.e. the front end surface 110 of the wire channel 100, is preferably located further inside the annular nozzle than the front end surface 5 of the second discharge opening 3, i.e. the front end surface 5 of the second distribution nozzle 8.

In other words, the distance 4 (hereinafter, referred to as a liquid seal length) between the tip end surface of the protruding annular portion 13, i.e., the string passage 100, and the tip end surface 5 of the second discharge port 3, i.e., the tip end surface 5 of the second distribution nozzle 8 is preferably 0.5 to 150 mm. The lower limit of the length of the liquid seal (Japanese: liquid シ - ル) is more preferably 0.6mm or more, still more preferably 0.8mm or more. When the liquid seal length is less than 0.5mm, the second deposition solution applied to the surface of the first porous layer is discharged almost without coating pressure. Therefore, even if the outer diameter of the film formed on the first porous layer is small, the second porous layer can be discharged with the same diameter. As a result, a large gap may be formed between the first porous layer and the second porous layer. From the viewpoint of coating pressure, the upper limit of the liquid seal length is not particularly limited, but if it is too long, it tends to be difficult to manufacture the annular nozzle. Therefore, the upper limit of the liquid seal length is preferably 150mm or less. The upper limit of the liquid seal length is preferably 100mm or less, more preferably 50mm or less.

In the case where the composite porous membrane of the present invention is actually used for water treatment, a fixing member such as a general synthetic resin is used to separate the primary filtration side from the secondary filtration side, but if such a gap is formed in the composite porous membrane, the possibility that the resin enters the gap and water to be treated is hardly impregnated in the entire composite porous membrane increases. When the liquid seal length is set to an appropriate length, the coating pressure of the discharged coating solution (Japanese patent No. コ - テイング) tends to increase. It is possible to prevent a situation where a large gap is formed in between the first porous layer and the second porous layer.

As described above, when the liquid is supplied to the second supply port 7 in a state where the distribution plate 10, the first distribution nozzle 9, and the second distribution nozzle 8 are concentrically overlapped, the supplied liquid can be stored in the second pool portion 12 through the hollow portion of the first distribution nozzle 9 and the hollow portion formed by the first distribution nozzle 9 and the second distribution nozzle 8, and then discharged from the second discharge port 3 to the string pathway 100.

To produce a composite porous membrane using the annular nozzle having such a structure, first, a cord is supplied from the pipe 1 to the cord channel 1. The first deposition solution is supplied from the first supply port 6 to the first reservoir portion 11. The second deposition solution is supplied from the second supply port 7 to the second cell portion 12.

The first deposition solution is discharged from the first discharge port 2 while the cord is supplied to the pipeline 1, that is, while the cord is moved in the cord passage 10, so as to be impregnated into the cord, and the second deposition solution is discharged from the second discharge port 3 so as to be impregnated into the cord.

Next, as described above, the strand impregnated with the first and second deposition solutions is immersed in the coagulating liquid, washed with hot water and a chemical solution, dried, and wound.

Then, a solution that does not dissolve the membrane material is supplied to the first supply port 6, and the solution that does not dissolve the membrane material is discharged from the first discharge port, and the solution is applied to the surface of the first porous layer.

Thereafter, the second deposition solution supplied from the second supply port 7 and stored in the second cell unit 12 is discharged again from the second discharge port 3, and applied to the surface of the first porous layer.

In the above description, the composite porous film in which the film material is composed of the first porous layer and the second porous layer has been described, but in the present invention, it does not matter if a plurality of porous layers are further provided on the upper surface of the second porous layer. In this case, the second porous layer may be formed on the first porous layer in the same order as the order in which the porous layers are formed.

Test examples

The present invention will be described in more detail below based on experimental examples.

The physical property values were measured by the methods shown below.

In addition, "%" used for the content and concentration marks represents mass%.

< maximum pore diameter (. mu.m) (bubble pressure point method) >

Ethanol was measured as a measurement medium in accordance with JIS K3832.

< Hot Water shrinkage >

The strand cut to a length of about 1m was immersed in hot water at 90 ℃ for 30 minutes, and the length before and after the treatment was measured, and obtained from the following formula.

Hot water shrinkage (%) (length of cord before treatment-length of cord after hot water treatment) ÷ length of cord before treatment × 100

Experimental example 1

Casting solutions 1 and 2 having the compositions shown in Table 1 were prepared using polyvinylidene fluoride A (product name カイナ -301F, manufactured by アトフイナジヤパン), polyvinylidene fluoride B (product name カイナ -9000 LD, manufactured by アトフイナジヤパン), polyvinylpyrrolidone (product name K-90, manufactured by ISP Co., Ltd.), and N, N-dimethylacetamide.

TABLE 1

Composition of	First film-forming liquid	Second film-forming liquid
			Polyvinylidene fluoride A	3% by mass	12% by mass
Polyvinylidene fluoride B	2% by mass	8% by mass
			Polyvinylpyrrolidone	2% by mass	10% by mass
N, N-dimethyl acetamide	93% by mass	70% by mass
			Temperature of liquid	50℃	60℃
Concentration of polyvinylidene fluoride in liquid	12% by mass	20% by mass

A polyester composite filament (composite filament; total decitex 830/96 monofilaments, 16 filaments (Japanese: dozen ち)) was introduced into a pipe 1 having an outer diameter of 2.5mm and an inner diameter of 2.4mm of a circular nozzle shown in FIG. 1, which was kept at 30 ℃, and the first deposition solution was discharged from a first discharge port 2 and the second deposition solution was discharged from a second discharge port 3. The strand coated with the first and second film-forming liquids was introduced into a coagulating liquid comprising 5 parts by mass of N, N-dimethylacetamide and 95 parts by mass of water, and kept at 80 ℃.

The strand having the first porous layer was desolventized in hot water at 98 ℃ for 1 minute, and then immersed in an aqueous solution of 50000mg/L sodium hypochlorite. Thereafter, the sheet was washed in hot water at 90 ℃ for 10 minutes and wound on a winder which was dried at 90 ℃ for 10 minutes. The number of cilia attached or embedded in the cord is one per meter. The hot water shrinkage of the cord was 1%. The supply tension of the cord was 9.8 kPa.

Then, a string having a first porous layer was introduced into a pipe line 1 of a circular nozzle having an outer diameter of 2.7mm and an inner diameter of 2.6mm shown in FIG. 1, which was kept at 30 ℃, and glycerol (and first grade of those manufactured by the photo-spring pharmaceutical industry) as an internal coagulation liquid was discharged from the first discharge port, and a second deposition solution was discharged from the second discharge port 3. Thereby coating the second deposition solution on the first porous layer. The obtained string was introduced into a coagulating liquid composed of 5 mass% of N, N-dimethylacetamide and 95 mass% of water and kept at 80 degrees to obtain a composite porous membrane. The composite porous membrane was desolvated in hot water at 98 ℃ for 1 minute, immersed in an aqueous solution of 50000mg/L sodium hypochlorite, washed in hot water at 90 ℃ for 10 minutes, and wound up with a winder which was dried at 90 ℃ for 10 minutes.

The obtained composite porous membrane had an outer diameter/inner diameter of about 2.8/1.1m, a membrane thickness of 900 μm,The permeability is 100m³/m²A water passage rupture pressure of 500kPa, a durability number of 1000 times at 400kPa, and a continuous water passage durability time of 2000 hours at 200 kPa.

Experimental example 2

After obtaining the composite porous membrane having the first porous layer, a composite porous membrane was obtained in the same manner as in experimental example 1 except that a ring-shaped nozzle having an outer diameter of 8mm, an inner diameter of 2.7mm and a liquid seal length of 1.0mm was used without washing and drying.

The obtained composite porous membrane had an outer diameter/inner diameter of about 2.8/1.2mm, a membrane thickness of 800 μm, a resin layer thickness from the strand to the surface of 400 μm, a bubble pressure point of 180kPa, and a permeability of 110m³/m²A water passage rupture pressure of 520kPa, a durability number of 1300 times at 400kPa, and a continuous water passage durability time of 3000 hours at 200 kPa.

Industrial applicability of the invention

The composite porous membrane of the present invention has mechanical properties such as adhesive strength between the filter material and the string, which have not been achieved so far. Therefore, the membrane filter can be used under severe conditions such as various water treatments which have been difficult to filter and separate by the conventional membrane filtration method, and the quality of the filtrate can be improved. Further, since the permeability is high, the membrane area to be used can be reduced, and the size of the device can be reduced.

In addition, according to the production method of the present invention, the composite porous film having the above-described excellent characteristics can be easily produced.

Claims (5)

1. A composite porous membrane having a strand and a membrane material, wherein the membrane material has a first porous layer having a dense layer adjacent to an outer surface of the strand and a second porous layer having a dense layer adjacent to the first porous layer,

the average pore diameter range of the dense layer of the first porous layer is 0.2-1 μm, the average pore diameter range of the dense layer of the second porous layer is 0.1-0.8 μm,

the dense layer of at least one of the first porous layer and the second porous layer is located at the inner side 0.1-50 μm away from the outermost surface of the porous layer where the dense layer is located,

the average pore diameter of the holes located on the outermost side of the first porous layer is within the range of 1-5 μm, and the average pore diameter of the holes located on the outermost side of the second porous layer is within the range of 0.8-2 μm.

2. The composite porous membrane of claim 1 having a water permeability of 50m³/m²A foaming pressure point of 50kPa or higher.

3. The composite porous film according to claim 1, wherein a water passage rupture pressure is 200kPa or more.

4. The composite porous film according to claim 1, wherein the durability time is 150 hours or more when water is continuously passed at 200 kPa.

5. The composite porous film according to claim 1, wherein the number of times of durability when a pressure of 400kPa is repeatedly applied is 100 or more.