JP2003144869A - Separation membrane and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separation membrane which has high water permeability, whose impurity-blocking rate is hardly lowered even when the surface of a separation-functional layer is scratched, whose porous resin layer is hardly peeled off from a porous base material and from which the clogged impurities can be easily removed. SOLUTION: The separation membrane has the porous resin layer formed on the surface of the porous base material and a combined layer formed by integrating a part of a resin forming the porous resin layer with the porous base material. Pores satisfying the inequality: 2dB<=dA (wherein dA is the average pore diameter on the surface of the side of the liquid to be treated; dB is the average pore diameter on the surface of the side of the permeated liquid) are formed on both surfaces of the porous resin layer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to purification of sewage (domestic wastewater generated from cooking, laundry, bath, toilet, and other living environments) and wastewater generated from production plants, restaurants, fish processing plants, food processing plants, and the like. The present invention relates to a separation membrane used in, a method for producing the separation membrane, a separation membrane element having the separation membrane, and a wastewater treatment device.

[0002]

2. Description of the Related Art In recent years, separation membranes have been used for purification of sewage and wastewater. There are various kinds and forms of such separation membranes, but a resin solution containing a pore-opening agent is applied to the surface of a porous base material such as woven cloth or non-woven cloth, or a porous base material is used. Attention has been paid to a flat membrane, which is a so-called microfiltration membrane, which is obtained by solidifying a resin after being impregnated into a substrate and forming a porous resin layer on the surface of a porous substrate. The porous resin layer acts as a separation function layer,
In such a flat membrane, it is difficult to obtain a large effective membrane area per unit volume as compared to other forms of separation membrane, for example, a hollow fiber membrane, and therefore, it is possible to maintain the pore diameter according to the filtration target while permeating water. Larger quantities are required. However, if the porosity is increased in order to increase the water permeability, the pore size becomes too large or the surface is cracked, and the blocking rate decreases. On the other hand, if the pore size is reduced in order to increase the blocking rate, the amount of water permeation will decrease. That is, there is a contradictory relationship between the improvement of the blocking rate and the improvement of the water permeation amount, and it is difficult to provide both in a well-balanced manner.

Further, in the conventional separation membrane for sewage water, when inorganic substances such as sand, sludge, and other solid substances collide violently during use, the surface of the separation functional layer is scraped off, and the inside of which has a pore diameter larger than that of the surface. However, there is a problem in that the blocking rate is reduced due to exposure.

In addition, in the separation membrane for lower wastewater, air bubbles due to aeration operation for supplying oxygen to the activated sludge and preventing clogging may violently collide with the membrane surface, so that even such shocks may occur. It is required to have sufficient strength to endure. This strength is mainly borne by the porous base material, but in the case of the conventional separation membrane, in a significant case, the porous resin layer may be separated from the porous base material during the filtration operation or the aeration operation. There is also.

In addition, it is inevitable that activated sludge and other solids will be clogged in the porous resin layer and the amount of water permeation will decrease despite the aeration operation. In order to recover this amount of water permeation, contrary to the case of treating wastewater, clean water is poured from the permeate side to the treated water side to push out the clogged substance, so-called backwashing is performed. There is. However, in the conventional separation membrane, since the treated water side has an asymmetric membrane structure in which the pore size is smaller than the permeated water side, there is a problem that the once clogged substance is very difficult to wash and remove. .

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the prior art, to have a high water permeability and to prevent the blocking rate from being lowered even if the surface of the separation functional layer is scraped, In addition, the porous resin layer is difficult to peel from the porous substrate,
Furthermore, a separation membrane that can easily remove the substance once it is clogged, and a method for easily manufacturing such a separation membrane,
Another object of the present invention is to provide a separation membrane element using the separation membrane and a wastewater treatment device.

[0007]

In order to achieve the above-mentioned object, the present invention comprises a porous resin layer formed on the surface of a porous substrate, and a part of the resin forming the porous resin layer. forms a composite layer with the porous substrate enters the porous substrate, the porous resin layer, the average pore size of the liquid to be treated surface d _a, the average pore size of the permeate side surface d _B Is characterized by the separation membrane satisfying the inequality 2d _B ≦ d _A. However, the average pore diameter is 9.2 μm × 10.4 μ in a scanning electron microscope observation at a magnification of 10,000 times.
It is the average of the diameters of all the pores that can be observed within the range of m.

Further, the present invention provides a method for producing the above-mentioned separation membrane, in which a coating film of a stock solution containing a resin and a solvent is formed on the surface of a porous base material, and the stock solution is applied to a porous base material. Impregnate and then contact only the coating-side surface of the porous substrate having the coating with a coagulation bath containing a solvent and a non-solvent to coagulate the resin and form a porous resin layer on the surface of the porous substrate. A method for producing a separation membrane is provided.

Furthermore, the present invention provides a separation membrane element and a sewage treatment apparatus using the above-mentioned separation membrane.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The separation membrane of the present invention has a porous resin layer acting as a separation functional layer on the surface of a porous substrate.

The porous substrate supports the porous resin layer and gives strength to the separation membrane. Organic material,
Inorganic materials and the like are not particularly limited, but organic fibers are preferable from the viewpoint of easy weight reduction. More preferably, it is a woven or knitted fabric or a non-woven fabric made of organic fibers such as cellulose fibers, cellulose triacetate fibers, polyester fibers, polypropylene fibers and polyethylene fibers. Among them, a non-woven fabric which is relatively easy to control the density, easy to manufacture and inexpensive is preferable.

If the thickness of such a porous substrate is too thin, it becomes difficult to maintain the strength as a separation membrane, and if it is extremely thick, the amount of water permeation tends to decrease, so 50 μm to 1 m.
It is preferably in the range of m. Most preferred is 70
˜500 μm.

The density of the porous substrate is 0.7 g / c.
m ³ or less, preferably 0.6 g / cm ³ or less. This density range is suitable for receiving the resin forming the porous resin layer and forming the composite layer of the porous base material and the resin in the manufacturing process described later. However, if the density is extremely low, the strength of the separation membrane tends to decrease, so 0.3 g / cm ³ or more is preferable. The density here is an apparent density and can be determined from the area, thickness and weight of the porous substrate.

The porous resin layer functions as a separating function layer as described above, and is made of polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyvinylidene fluoride resin, polysulfone resin, polyether sulfone resin, polyimide resin, poly It is made of ether imide resin. A resin containing these resins as a main component may be used. Here, the main component means that the content is 50% by weight or more, preferably 60% by weight or more. Among them, polyvinyl chloride resin, polyvinylidene fluoride resin, polysulfone resin, and polyether sulfone resin, which are easy to form a film by a solution and have excellent physical durability and chemical resistance, are preferable. Most preferred is polyvinylidene fluoride resin or one containing it as a main component.

If the thickness of the porous resin layer is too thin, defects such as cracks may occur in the porous resin layer, and the filtration performance may deteriorate. If it is too thick, the water permeability may decrease, so it is usually 1 to 500 μm, preferably 5 to 20 μm.
It is preferable to select in the range of 0 μm.

Part of the resin forming the porous resin layer enters the porous base material to form a composite layer. When the resin enters the porous base material, the porous resin layer is firmly fixed to the porous base material by the so-called anchor effect, and the porous resin layer can be prevented from peeling from the porous base material. The porous resin layer may be present on one side of the porous base material in a biased manner, or may be present on both sides. The porous resin layer may have a symmetrical structure or an asymmetric structure with respect to the porous substrate. Further, when the porous resin layer is present on both sides of the porous substrate, the porous resin layers on both sides are continuous through the composite layer of the porous substrate and the porous resin layer. Or may be discontinuous.

[0017] Now, the separation membrane of the present invention, the porous resin layer, when the average pore size of the liquid to be treated surface d _A, the average pore size of the permeate surface and the d _B, inequality, 2d _B ≦ d Satisfied with _A. The separation membrane for sewage is a separation membrane used for purification of sewage and wastewater, but it is usually treated by bringing the wastewater to be treated into contact with the separation membrane, pressurizing and filtering. You are getting clear water. At this time, the side of the separation membrane that comes into contact with the lower waste water is called the treated liquid side, and the opposite side of the treated water that comes out is called the permeate side.

The surface of the porous resin layer on the side of the liquid to be treated of the separation membrane for lower wastewater is sometimes scraped during use due to violent collision of inorganic substances such as sand, sludge and other solid matter contained in the lower wastewater. , The internal holes may be exposed. When d _A becomes smaller than d _B , the internal pore diameter appearing on the surface becomes larger than d _{A, and the} more the surface of the porous resin layer on the liquid to be treated is shaved, the more the rejection rate becomes. Is decreased, which is not preferable. More preferably, d _A will be greater than twice d _B.

Further, since the sewage and wastewater enter the inside of the porous resin layer under pressure in the holes on the surface of the liquid to be treated of the porous resin layer, bacteria and sludge contained in the sewage and wastewater Easy to get clogged with dirt. If these contaminants become clogged, the amount of treatment liquid obtained will decrease, or the pressure applied will need to be increased in order to obtain the same amount of treatment liquid, and energy loss will increase, leading to membrane loss. Performance will be reduced. Therefore, it is necessary to remove the dirt clogging these holes. In order to remove this clogged dirt, normally, clear water is passed backward from the permeate side of the separation membrane to the liquid to be treated side, and the dirt clogged in the holes is pushed out to the liquid side to be treated and removed. Backwashing is done. d _A is d _B
If it is smaller than twice, the backwash efficiency is high because the dirt clogging the holes of the separation membrane is more likely to receive resistance from the wall surface of the holes when the backwashing is performed. Is bad and not preferable. More preferably, the inequality 3d _B ≦ d _A is satisfied. Here, the average pore diameter is the average of the diameters of all the pores that can be observed within the range of 9.2 μm × 10.4 μm in the observation with a scanning electron microscope at a magnification of 10,000 times.

The separation membrane of the present invention preferably has an exclusion rate of fine particles having an average particle size of 0.9 μm of 90% or more. When this exclusion rate is less than 90%, bacteria and sludge leak, clogging by bacteria and sludge occurs, filtration differential pressure rises, and life becomes extremely short. To do. Here, the rejection rate is polystyrene latex fine particles having an average particle size of 0.9 μm in purified water by a reverse osmosis membrane (nominal particle size 0.940 μm, standard deviation 0.0796).
Is used to obtain a concentration of 10 ppm, and while the stock solution is being stirred, the separation membrane is allowed to permeate under conditions of a temperature of 25 ° C. and a head pressure of 1 m. The absorbance is calculated from the following formula.

Exclusion rate = [(absorbance of stock solution−absorbance of permeate) / absorbance of stock solution] × 100 The separation membrane of the present invention can be used as a separation membrane element by combining it with a support.

A separation membrane element in which a support plate is used as a support and the separation membrane of the present invention is arranged on at least one surface of the support plate is one of the preferred forms of the separation membrane element of the present invention. The element of this form can be suitably used for the wastewater treatment application as described below. In this mode, since it is difficult to increase the membrane area, it is preferable to dispose the separation membranes on both sides of the support plate in order to increase the amount of water permeation.

The form of the element is not particularly limited,
An example of a suitable form will be described below with reference to the drawings.

The element is, as shown in FIGS.
The channel material 2 and the separation membrane 3 are arranged in this order on both surfaces of the support plate 1 having rigidity. The support plate 1 has a convex portion 4 and a concave portion 5 on both sides. The separation membrane 3 filters impurities in the liquid. The flow path member 2 is for efficiently flowing the filtered water filtered by the separation membrane 3 to the support plate 1. The filtered water that has flowed to the support plate 1 is taken out through the recess of the support plate 1.

The support plate 1 is not particularly limited as long as it has a structure having a plurality of irregularities on both sides of the plate-like body, but the distance to the filtered water outlet and the flow path resistance are made uniform to be treated. It is preferable that the concave portions are provided so as to form a plurality of grooves arranged in parallel at regular intervals so that the water flows evenly with respect to the film surface. At this time, the width of each recess 5 is in the range of 1 to 20 mm, further 1.5 to 10 mm in order to prevent the flow path member 2 and the separation membrane 3 from falling under severe aeration conditions while keeping the amount of filtered water high. It is preferably within the range of 5 mm. The depth of the recess 5 is preferably selected within a range of about 1 to 10 mm in order to secure the filtered water flow path while suppressing the thickness of the element. Furthermore, while maintaining the strength of the support plate,
In order to secure a sufficient flow path for the filtered water and suppress the flow resistance when the filtered water flows, the porosity of the support plate due to the recess is 15 to
It is preferably within the range of 85%. This shows the volume ratio of the voids formed by the recesses when the solid rectangular parallelepiped support plate is 100%, and the void ratio is 15%.
If it is less than 85%, the flow resistance becomes large, and the filtered water cannot be efficiently taken in. If it exceeds 85%, the strength of the support plate is remarkably reduced.

The material of the support plate 1 is ASTM
A material having a rigidity such that the tensile strength in D638 of the test method is about 15 MPa or more is preferable. It is preferable to use metals such as stainless steel, acrylonitrile-butadiene-styrene copolymer (ABS resin), resins such as polyethylene, polypropylene and vinyl chloride, composite materials such as fiber reinforced resin (FRP), and other materials. it can.

In order to secure the flow passage and reduce the thickness of the element, the thickness of the flow passage material is preferably in the range of 0.1 to 5 mm. Further, in order to reduce the pressure loss, it is preferable to use a material having a high porosity such as a plastic net. A channel material having a porosity of 40% to 96% is particularly preferable.

In addition, in the element of the present invention, it is also preferable to install the frame body 6 on the peripheral portion of the support plate 1. In this case, the separation membrane 3 may be fitted between the support plate 1 and the frame body 6 or may be adhered to the outer surface of the frame body 6. Here, "adhesion" means to wear in a state of being in contact with each other, and it may be adhered by using a separate resin or the like, or the separation membrane itself may be welded, or may be adhered by various other methods. . The cost can be reduced by fitting the frame body 6 manufactured by injection molding, extrusion molding or the like into the peripheral portion of the support plate 1 manufactured by an inexpensive manufacturing method such as extrusion molding. In order to make it easy to fit the support plate 1, it is preferable that the frame body 6 be formed so as to have a U-shaped cross section.

In the element configured as described above, the filtered water filtered by the separation membrane 3 flows into the flow path member 2 and the recess 5 of the support plate 1, and finally from the filtered water outlet 7. It is discharged to the outside of the element.

Furthermore, the separation membrane of the present invention can be preferably used in a lower wastewater treatment apparatus. The method of use is not particularly limited, but a suitable method of use will be described below.

A plurality of the elements 9 are housed in a housing in parallel with each other and with a space between the membrane surfaces of the separation membrane 3 to form a separation membrane module 10.
This separation membrane module is, for example, as shown in FIG.
It is used by being immersed in water to be treated such as organic wastewater stored in the water to be treated 11. Inside the separation membrane module 10, a plurality of vertically mounted elements 9 are provided.
And an air diffuser 12 for supplying the gas from the blower 13 to the membrane surface of the separation membrane, and a pump 14 for sucking filtered water downstream of the separation membrane module 10 is provided. .

In the lower wastewater treatment apparatus thus constructed, the water to be treated such as wastewater passes through the separation membrane 3 by the suction force of the pump 14. At this time, suspended substances such as microbial particles and inorganic particles contained in the water to be treated are filtered.
Then, the water that has passed through the separation membrane 3 passes through the filtered water flow path formed by the flow path member 2, passes through the water collecting portion 8 formed in the frame 6 from the recess 5 of the support plate 1, and passes through the filtered water. Exit 7
And is taken out of the water tank 11 to be treated. on the other hand,
The air diffuser 12 generates air bubbles in parallel with the filtration, and an upward flow parallel to the film surface of the element 9 caused by the air lift action of the air bubbles separates the filtered material accumulated on the film surface.

The separation membrane of the present invention described above is typically
It can be manufactured by a method as described below.

That is, first, a coating film of an undiluted solution containing the above-mentioned resin and a solvent is formed on the surface of the above-mentioned porous substrate, and the undiluted solution is impregnated into the porous substrate.
Then, only the coating-side surface of the porous base material having the coating is brought into contact with a coagulation bath containing a non-solvent to coagulate the resin and form a porous resin layer on the surface of the porous base material.
The stock solution may further contain a non-solvent. From the viewpoint of film-forming property, it is generally preferable to select the temperature of the stock solution within the range of 15 to 120 ° C.

Here, a pore opening agent may be added to the stock solution. The opening agent has a function of being extracted when immersed in the coagulation bath to make the resin layer porous. The pore-forming agent preferably has a high solubility in the coagulation bath. For example, an inorganic salt such as calcium chloride or calcium carbonate can be used. Further, polyoxyalkylenes such as polyethylene glycol and polypropylene glycol, water-soluble polymers such as polyvinyl alcohol, polyvinyl butyral and polyacrylic acid, and glycerin can be used.

The solvent dissolves the resin. The solvent acts on the resin and the opener to help them form a porous resin layer. As the solvent, N-methylpyrrolidinone (NMP), N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (D
MF), dimethyl sulfoxide (DMSO), acetone, methyl ethyl ketone and the like can be used. Above all, NMP, DMAc, DM with high solubility of resin
F and DMSO can be preferably used.

Further, a non-solvent can be added to the stock solution. A non-solvent is a liquid that does not dissolve the resin. The non-solvent acts to control the rate of solidification of the resin to control the size of the pores. As the non-solvent, water and alcohols such as methanol and ethanol can be used. Of these, water and methanol are preferable from the viewpoint of ease of wastewater treatment and price. It may be a mixture of these.

In the undiluted solution, the resin content is preferably 5 to 30% by weight and the solvent content is preferably 40 to 95% by weight.
If the amount of resin is extremely low, the strength of the porous resin layer will decrease,
If it is too large, the water permeability may decrease. It is more preferably within the range of 8 to 20% by weight. On the other hand, if the amount of the solvent is too small, the stock solution tends to gel, and if it is too large, the strength of the porous resin layer may be reduced. More preferably, it is in the range of 60 to 90% by weight.

In this case, the solvent is 40% in the coagulation bath.
˜90% by weight, preferably containing at least 10% by weight of non-solvent. If the solvent content is less than 40% by weight, the solidification rate of the resin will be high and the pore size will be small.
Further, if the solvent exceeds 90% by weight, the resin does not solidify,
It becomes difficult to form the porous resin layer. More preferably, it is in the range of 50 to 85% by weight. If the temperature of the coagulation bath is too high, the coagulation rate will be too fast, and if it is too low, the coagulation rate will be too slow.
Usually, it is preferable to select within the range of 15 to 80 ° C. A more preferable temperature range is 20 to 60 ° C.

The method of contacting only the coating-side surface of the coating-containing porous base material with the coagulation bath is not particularly limited, but, for example, the coating-side surface of the coating-containing porous base material may be on the lower side. And contacting the surface of the coagulation bath,
The surface opposite to the coating side is contacted with a smooth plate such as a glass plate or a metal plate and attached so that the coagulation bath does not go around to the back side, and the porous substrate having the coating is immersed in the coagulation bath with the plate. There are ways. In the latter method, the coating of the undiluted solution may be formed after the porous substrate is attached to the plate, or the undiluted solution may be formed on the porous substrate and then attached to the plate.

The coating of the undiluted solution on the porous substrate can be formed by applying the undiluted solution to the porous substrate or by immersing the porous substrate in the undiluted solution. When the stock solution is applied, it may be applied on one side or both sides of the porous substrate. At this time, although depending on the composition of the stock solution, when a porous substrate having a density of 0.7 g / cm ³ or less is used, the stock solution is appropriately impregnated into the porous substrate.

In the separation membrane manufactured in the above description, the average pore diameter of the side surface of the porous resin layer which is in contact with the coagulation bath is at least twice the average pore diameter of the other surface. This is because the coagulation bath contains 40 to 90% by weight of the solvent, so that the replacement speed between the stock solution and the coagulation bath is relatively slow, and the growth of holes on the side surface in contact with the coagulation bath proceeds in the porous resin layer. This is because the pore size becomes large, whereas the surface on the opposite side does not come into contact with the coagulation bath, so that holes are formed only by phase separation of the stock solution, and the pore size becomes relatively small. Therefore, in the separation membrane of the present invention, the side in contact with the coagulation bath may be the treated liquid side and the other may be the permeated liquid side.

In addition to the above, a pore-forming agent may be added to the undiluted solution, and the product can be produced by the method described below.

That is, as the above-mentioned stock solution, a resin,
A stock solution containing a pore opening agent and a solvent is used. A non-solvent may be further added to the stock solution.

The pore-forming agent has a function of being extracted when immersed in the coagulation bath to make the resin layer porous. The pore-forming agent preferably has a high solubility in the coagulation bath. For example, an inorganic salt such as calcium chloride or calcium carbonate can be used. Further, polyoxyalkylenes such as polyethylene glycol and polypropylene glycol, water-soluble polymers such as polyvinyl alcohol, polyvinyl butyral and polyacrylic acid, and glycerin can be used.

As the solvent and non-solvent, the same ones as described above can be used.

In the undiluted solution, the resin is in the range of 5 to 30% by weight, the opening agent is in the range of 0.1 to 15% by weight, the solvent is in the range of 40 to 94.9% by weight, and the non-solvent is in the range of 0 to 20% by weight. Is preferred. If the amount of resin is extremely small, the strength of the porous resin layer will be low, and if it is too large, the water permeability may be reduced. The resin content in the stock solution is more preferably in the range of 8 to 20% by weight. If the pore-opening agent is too small, the water permeability may decrease, and if it is too large, the strength of the porous resin layer may decrease. Further, if it is extremely large, it may remain in the porous resin and be eluted during use, and the water quality of the permeated water may deteriorate or the water permeability may fluctuate. Of the pore-forming agent content in the stock solution,
A more preferable range is 0.5 to 10% by weight. Furthermore, if the solvent is too small, the stock solution will easily gel,
If it is too large, the strength of the porous resin layer may decrease.
When no non-solvent is used, the solvent content in the stock solution is 55
To 94.9% by weight, and more preferably,
It is in the range of 60 to 90% by weight. If the amount of non-solvent is too large, gelation of the stock solution is likely to occur, and if it is extremely small, it becomes difficult to control the size of pores. The solvent content in the stock solution is more preferably in the range of 0.5 to 15% by weight.

It is preferable to add a non-solvent to the stock solution because the size of the pores on the surface of the porous resin layer tends to be uniform. In addition, it becomes easy to control the size of the macro void.
However, if the amount is too large, gelation of the stock solution easily occurs. In this case, the solvent content is preferably 40 to 94.8% by weight, and the non-solvent content is preferably 0.1 to 20% by weight. More preferably, the solvent is 40 to 94.4 wt% and the non-solvent is
It is in the range of 0.5 to 15% by weight.

For the coagulation bath, a non-solvent or a mixed liquid containing a non-solvent and a solvent can be used. In the coagulation bath,
When a non-solvent is used for the stock solution, the non-solvent is preferably at least 80% by weight. If it is too small, the solidification rate of the resin becomes slow and the pore size becomes large. A more preferred range is 85 to 100% by weight. In addition, when a non-solvent is not used in the stock solution, at least 60
It is preferably set to wt%. When the amount of the non-solvent is too large, the solidification rate of the resin is high and the surface of the porous resin layer becomes dense, but fine cracks may occur on the surface of the porous resin layer. A more preferable range is 60 to 99% by weight. If the temperature of the coagulation bath is too high, the coagulation rate will be too fast, and conversely, if it is too low, the coagulation rate will be too slow. Therefore, it is usually selected within the range of 15 to 80 ° C. preferable. A more preferable temperature range is 20
~ 60 ° C.

The coating of the stock solution on the porous substrate can be formed by applying the stock solution to the porous substrate. Although it depends on the composition of the stock solution, since the porous base material having a density of 0.7 g / cm ³ or less is used, the porous base material is appropriately impregnated with the stock solution.

The separation membrane manufactured in the above description has a structure in which the porous resin layer is exposed on the surface on which the coating film of the undiluted solution is formed and the porous substrate is exposed on the other surface. However, in the porous resin layer, the average pore diameter on the side surface on which the undiluted film is formed is 1/2 of the average pore diameter on the other surface.
It is as small as: This is because the side surface on which the coating film of the stock solution is formed comes into contact with the coagulation bath faster than the other surface, so that the replacement speed of the stock solution with the coagulation bath is fast and the pore size is small. Therefore, in the separation membrane of the present invention, the side of the stock solution on which the coating film is formed may be used as the permeate side and the other side may be used as the liquid to be treated side.

[0052]

EXAMPLES Example 1 Polyvinylidene fluoride (PVDF) resin as a resin,
N, N-dimethylacetamide (DMAc) as a solvent
Were sufficiently stirred at a temperature of 90 ° C. to obtain a stock solution having the following composition.

PVDF: 13.0% by weight DMAc: 87.0% by weight Next, after cooling the above stock solution to 25 ° C., it was placed on a glass plate in advance and the density was 0.48 g / c.
m ³ and a thickness of 220 μm applied to a polyester fiber non-woven fabric, and immediately put in a coagulation bath at 25 ° C. having the following composition:
It was immersed for a minute to obtain a porous base material on which a porous resin layer was formed.

Water: 30.0% by weight DMAc: 70.0% by weight This porous substrate was peeled from the glass plate and immersed in hot water at 80 ° C. three times to wash out DMAc to obtain a separation membrane. .
On the side of the separation membrane in contact with the coagulation bath, the surface area of the porous resin layer was within a range of 9.2 μm × 10.4 μm at a magnification of 1
When scanning electron microscope observation was performed at a magnification of 10,000,
The average diameter of all observable pores is 2.0 μm, and 9.2 μm of the surface of the porous resin layer on the opposite side ×
When a scanning electron microscope observation was performed at a magnification of 10,000 times in the range of 10.4 μm, the average diameter of all the observable pores was 0.1 μm.

Next, with respect to the above-mentioned separation membrane, an average particle diameter of 0.
The exclusion rate of 9 μm fine particles was measured and found to be 95%. The water permeability is 50 × 10 ^-9 m ³ / m ² · s · Pa.
Met. The amount of water permeation was measured at a head height of 1 m using purified water at 25 ° C. with a reverse osmosis membrane.

A forced abrasion test was conducted on this separation membrane. In the forced abrasion test, the separation membrane was fixed in water with the side in contact with the coagulation bath facing upward, and an emery paper (# 1,000) was cut onto it with a size of 7 cm x 15 cm and placed on it to give a surface thickness of 470 Pa. It was carried out by moving at a speed of 0.5 cm / s in the long-side direction while applying. Regarding the separation membrane that was subjected to this forced abrasion test, the average particle size was 0.9 μm.
When the rejection rate of fine particles of m was measured, it was 95%,
No change was seen.

On the other hand, as shown in FIG. 1, using the above-mentioned separation membrane which has not been subjected to the forced abrasion test, a support frame having a length of 320 mm in length, 220 mm in width, and 5 mm in thickness and having a permeated water outlet 4 in the upper portion is made of plastic. The separation membranes 1 and 1 were attached via the nets 2 and 2 so that the side in contact with the coagulation bath of the separation membrane was the side opposite to the support frame side, to obtain the element. This element is 500 mm long and 150 m wide
m, height 700 mm, having an air nozzle at the bottom and containing activated sludge having a concentration of 3,000 mg / liter, the air was supplied at a rate of 20 liters / minute from the air nozzle, and the filtration linear velocity was 0. A permeation test was performed at 4 m / day. In the porous resin layer of this separation membrane, the average pore size d _A on the surface of the liquid to be treated is 2.0 μm and the average pore size d _B on the surface of the permeate is 0.2 μm, so 2d _B = 0.4 μm ≦ d
It becomes _A. In this permeation test, the initial filtration differential pressure converted to 25 ° C. was 0.4 kPa, and it was 1.2 kPa after 1,000 hours had passed. Pure water was supplied from the permeate side of this element at a filtration linear velocity of 0.4 m / day for 1 hour, and then backwashing was performed. Then, a permeation test was conducted again in the same manner as above. The filtration differential pressure was 0.5 kPa. Recovered.

Comparative Example 1 The same stock solution as in Example 1 was cooled to 25 ° C., applied to the same nonwoven fabric as in Example 1, immediately immersed in the same coagulation bath at 25 ° C. as in Example 1 for 5 minutes, and further 80 DMAc and PEG were washed out by immersing in hot water at ℃ 3 times to obtain a separation membrane.
On the side of this separation membrane on which the undiluted solution is applied, the surface area of the porous resin layer is within a range of 9.2 μm × 10.4 μm at a magnification of 1
When scanning electron microscope observation was performed at a magnification of 10,000,
The average diameter of all observable pores is 2.0 μm, and 9.2 μm of the surface of the porous resin layer on the opposite side ×
When scanning electron microscope observation was carried out at a magnification of 10,000 times within the range of 10.4 μm, the average of the diameters of all the observable pores was 10.0 μm.

Next, with respect to the above-mentioned separation membrane, an average particle diameter of 0.
The rejection rate of 9 μm particles was 5%,
It was worse than Example 1.

The separation membrane was subjected to a forced rubbing test in the same manner as in Example 1 except that the side coated with the undiluted solution was brought into contact with emery paper, and the exclusion rate of fine particles having an average particle diameter of 0.9 μm was measured. It decreased to 2% and the scratch resistance was worse than that of Example 1.

On the other hand, an element was prepared in the same manner as in Example 1 except that the separation membrane which had not been subjected to the forced abrasion test was used so that the side coated with the stock solution was the side opposite to the support frame side. A permeation test was performed. In the porous resin layer of this separation membrane, the average pore diameter d _A on the surface of the liquid to be treated was 2.0.
μm, and the average pore diameter d _B of the permeate side surface is 10.0 μm, so 2d _B = 20.0 μm ≧ d _A. The initial filtration differential pressure converted to 25 ° C. in this permeation test was 0.2 k.
Pa, 0.8 kPa after 1,000 hours
Met. When pure water was supplied from the permeate side of this element at a filtration linear velocity of 0.4 m / day for 1 hour and backwashing was performed, a permeation test was again conducted in the same manner as above, and the filtration differential pressure was 0.8 kPa. It did not recover, and the backwash efficiency was worse than that of Example 1.

Example 2 Polyvinylidene fluoride (PVDF) resin as a resin,
Polyethylene glycol (PEG) having a molecular weight of about 20,000 was used as the opening agent, N, N-dimethylacetamide (DMAc) was used as the solvent, and pure water was used as the non-solvent. After stirring, a stock solution having the following composition was obtained.

PVDF: 13.0 wt% PEG: 5.5 wt% DMAc: 78.0 wt% Pure water: 3.5 wt% Next, after cooling the above stock solution to 25 ° C., the density was 0.48.
It is applied to a polyester fiber non-woven fabric of g / cm ³ and a thickness of 220 μm, and immediately after the application, it is immersed in pure water at 25 ° C. for 5 minutes, and further immersed in hot water at 80 ° C. three times to wash out DMAc and PEG. , A separation membrane was obtained. 9.2μ of the surface of the porous resin layer on the side of the separation membrane coated with the stock solution.
When a scanning electron microscope observation was performed at a magnification of 10,000 times in the range of m × 10.4 μm, the average diameter of all observable pores was 0.07 μm, and the porous resin layer on the opposite side was formed. When a scanning electron microscope observation was carried out at a magnification of 10,000 times within a range of 9.2 μm × 10.4 μm on the surface, the average diameter of all observable pores was 0.35 μm.

Next, with respect to the above-mentioned separation membrane, an average particle size of 0.
The exclusion rate of 9 μm fine particles was measured and found to be 98%. The water permeability is 37 × 10 ^-9 m ³ / m ² · s · Pa.
Met. The amount of water permeation was measured at a head height of 1 m using purified water at 25 ° C. with a reverse osmosis membrane.

About this separation membrane, Example 1 was repeated except that the side opposite to the side coated with the stock solution was brought into contact with emery paper.
Perform a forced rubbing test in the same manner as above, but average particle size is 0.9 μm.
The exclusion rate of the fine particles was measured to be 95%, and no change was observed.

On the other hand, an element was prepared and a permeation test was conducted in the same manner as in Example 1 except that the separation membrane which had not been subjected to the forced abrasion test was used so that the side coated with the stock solution was the support frame side. went. In the porous resin layer of this separation membrane, the average pore diameter d _A on the surface of the liquid to be treated is 0.35 μm,
Since the average pore diameter d _B of the permeate side surface is 0.07 μm, 2d _B = 0.14 μm ≦ d _A. The initial filtration differential pressure converted to 25 ° C. in this permeation test was 0.5 kPa.
The value was 1.2 kPa after 1,000 hours had passed. Pure water was supplied from the permeate side of this element at a filtration linear velocity of 0.4 m / day for 1 hour, and backwashing was performed. Then, a permeation test was conducted again in the same manner as above.
Recovered to 6 kPa.

Comparative Example 2 A separation membrane was obtained in the same manner as in Example 2. The separation membrane was subjected to a forced rubbing test in the same manner as in Example 2 except that the side coated with the stock solution was brought into contact with emery paper, and the exclusion rate of fine particles having an average particle diameter of 0.9 μm was measured.
%, And the scratch resistance was worse than that in Example 2.

On the other hand, an element was prepared in the same manner as in Example 2, except that the separation membrane on which the forced abrasion test was not conducted was used so that the side coated with the stock solution was the side opposite to the support frame side. A permeation test was performed. In the porous resin layer of this separation membrane, the average pore diameter d _A on the surface of the liquid to be treated was 0.07.
μm, and the average pore diameter d _B on the permeate side surface is 0.35 μm, so 2d _B = 0.70 μm ≧ d _A. The initial filtration differential pressure converted to 25 ° C. in this permeation test was 0.5 k.
Pa, 0.8 kPa after 1,000 hours
Met. When pure water was supplied from the permeate side of this element at a filtration linear velocity of 0.4 m / day for 1 hour and backwashing was performed, a permeation test was again conducted in the same manner as above, and the filtration differential pressure was 0.8 kPa. It did not recover, and the backwash efficiency was worse than that in Example 2.

Comparative Example 3 A separation membrane was obtained in the same manner as in Example 2 except that the stock solution having the composition shown below was used.

PVDF: 13.0% by weight PEG: 5.5% by weight DMAc: 81.5% by weight Range of 9.2 μm × 10.4 μm of the surface of the porous resin layer on the side of this separation membrane on which the stock solution was applied. Inside, magnification 1
When scanning electron microscope observation was performed at a magnification of 10,000,
The average diameter of all observable pores is 0.15 μm, and 9.2 μm of the surface of the porous resin layer on the opposite side ×
When scanning electron microscope observation was performed at a magnification of 10,000 times within the range of 10.4 μm, the average of the diameters of all the observable pores was 0.15 μm.

Next, with respect to the above-mentioned separation membrane, an average particle diameter of 0.
When the rejection of 9 μm fine particles was measured, it was 60%, which was worse than that in Example 2.

Comparative Example 4 A separation membrane was obtained in the same manner as in Example 2 except that a polyester fiber nonwoven fabric having a density of 0.90 g / cm ³ and a thickness of 101 μm was used as the porous substrate.

On the side of the separation membrane to which the stock solution is applied,
When a scanning electron microscope observation was performed at a magnification of 10,000 times within a range of 9.2 μm × 10.4 μm on the surface of the porous resin layer, the average diameter of all observable pores was 0.0.
7 μm, and the magnification on the opposite side within the range of 9.2 μm × 10.4 μm on the surface of the porous resin layer was 10,000.
When a scanning electron microscope observation was performed at 0 times, the average diameter of all the observable pores was 0.7 μm.

Next, with respect to the above-mentioned separation membrane, an average particle diameter of 0.
When the rejection of 9 μm fine particles was measured, it was 98%, which was the same as in Example 2. However, the water permeability is 10 × 10 ^-9
m ³ / m ² · s · Pa, which was worse than that in Example 2. The amount of water permeation was measured at a head height of 1 m using purified water at 25 ° C. with a reverse osmosis membrane.

[0075]

The separation membrane of the present invention has high water permeability, and the blocking rate is unlikely to decrease even if the surface of the separation functional layer is scraped off, as is clear from the comparison between Examples and Comparative Examples. It is difficult for the porous resin layer to peel from the porous substrate, and
Once clogged, the substance is easy to remove.

According to the method for producing a separation membrane of the present invention, the separation membrane of the present invention can be easily produced.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a separation membrane element using a separation membrane according to the present invention.

2 is a partial cross-sectional view of the element shown in FIG.

3 is a BB cross-sectional view of the element shown in FIG.

FIG. 4 is a schematic flow chart of the water production method of the present invention.

[Explanation of symbols]

1: Support plate 2: Flow path material 3: Separation membrane 4: convex part 5: recess 6: frame 7: Filtration water outlet 8: Water catchment section 9: Element 10: Separation membrane module 11: Water tank to be treated 12: Air diffuser 13: Blower 14: Pump

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08J 9/28 101 C08J 9/28 101 CER CER CEZ CEZ // C08L 101: 00 C08L 101: 00 F term ( (Reference) 4D006 GA07 HA41 JA05A JA05B JA05C JA07A JA07C JA25A JA53A KA43 KC03 LA06 MA22 MA31 MB01 MB02 MC11 MC18 MC22 MC23 MC27 MC29 MC29X MC48 MC58 MC59 MC61 MC62 NA05 NA10 NA13 NA16 NA17 NA18 NA19 PA01 PB08 A61 PCA APCA24 A61 AA74 AA87 AA97 CB14 CB17 CB34 CB43 CC10X CC29Y DA59

Claims (20)

[Claims] 1. A porous base material having a porous resin layer on the surface thereof, wherein a part of the resin forming the porous resin layer forms a composite layer with the porous base material, in the porous resin layer, when the average pore size of the liquid to be treated surface was d _a, the average pore size of the permeate surface and d _B, separation, characterized in that it satisfies the inequality, the 2d _B ≦ d _a film. 2. The separation membrane according to claim 1, wherein the density of the porous substrate is 0.7 g / cm ³ or less. 3. The separation membrane according to claim 1, wherein the exclusion rate of fine particles having an average particle diameter of 0.9 μm is at least 90%. 4. The porous substrate comprises organic fibers.
The separation membrane according to any one of 3 above. 5. The separation membrane according to claim 1, wherein the porous substrate is a non-woven fabric. 6. The separation membrane according to claim 1, wherein the resin is a resin containing polyvinylidene fluoride as a main component. 7. A separation membrane element having the separation membrane according to claim 1. 8. The separation membrane element according to claim 7, wherein a separation membrane is provided on at least one surface of the support plate. 9. The separation membrane element according to claim 7, which is a lower wastewater separation membrane element. 10. A method for treating lower wastewater, which comprises filtering the lower wastewater using the separation membrane according to claim 1. 11. A sewage treatment system comprising the separation membrane according to claim 1. 12. A porous base material is formed on its surface with a coating solution of a stock solution containing a resin and a solvent, and the stock solution is impregnated into the coating solution. A method for producing a separation membrane, which comprises contacting only a film-side surface with a coagulation bath containing a solvent and a non-solvent to coagulate a resin and form a porous resin layer on the surface of a porous substrate. 13. A resin containing 5 to 30% by weight and a solvent containing 40% by weight.
~ 95% by weight of the stock solution containing 40% solvent.
The method for producing a separation membrane according to claim 12, wherein a coagulation bath containing 90% by weight and at least 10% by weight of a non-solvent is used. 14. The method for producing a separation membrane according to claim 12, wherein the undiluted solution contains a resin, a pore opening agent, and a solvent. 15. A resin is 5 to 30% by weight, and a pore-forming agent is 0.1.
15. A coagulation bath comprising ˜15 wt% and a solvent in the range of 55 to 94.9 wt% and a coagulation bath comprising 1 to 40 wt% solvent and at least 60 wt% non-solvent. Method for manufacturing separation membrane. 16. The method for producing a separation membrane according to claim 12, wherein the stock solution contains a resin, a pore opening agent, a solvent, and a non-solvent. 17. A resin is 5 to 30% by weight, and a pore opening agent is 0.1.
17. A coagulation bath containing ~ 15 wt%, 40-94.8 wt% solvent and 0.1-20 wt% non-solvent and a coagulation bath containing at least 80 wt% non-solvent. The method for producing a separation membrane according to 1. 18. The separation membrane according to claim 12, wherein a stock solution having a temperature in the range of 15 to 120 ° C. is used and a coagulation bath having a temperature in the range of 15 to 80 ° C. is used. Production method. 19. The method for producing a separation membrane according to claim 12, wherein a nonwoven fabric is used as the porous substrate. 20. The method for producing a separation membrane according to claim 12, wherein a resin containing polyvinylidene fluoride as a main component is used as the resin.