JPH09313905A - Polysulfone porous separation membrane - Google Patents

Abstract

(57) Abstract: The surface of a separation membrane (22) has a minimum pore diameter layer with an average pore diameter in the range of 0.01-0.05 μm, has an asymmetric structure, and the membrane (22) is anchored to the porous reinforcing sheet (21). By being joined and reinforced, it effectively separates and removes submicron-order bacterial cells and fine particles and polymer substances with a molecular weight of 1 million order, and has a long membrane life and excellent back pressure strength. Provided is a flat membrane type porous separation membrane 20 to which pressure washing can be applied. SOLUTION: Polysulfone is heated and dissolved in a mixed solvent of N-methyl-2pyrrolidone, diethylene glycol and formamide to obtain a uniform film-forming solution, which is applied to a polyester non-woven fabric by a roll coater to obtain a relative humidity of 25%,
After the micro-phase separation is generated by changing the film forming speed in the atmosphere at a temperature of 30 ° C, it is immersed in a coagulation water tank at 35 ° C for desolvation and coagulation, and then the residual solvent is washed off in a water washing tank. To obtain a polysulfone porous separation membrane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous separation membrane, for sterilization, turbidity removal and protein removal of alcoholic beverages and fruit juice beverages in the food industry, ultrapure water production in the semiconductor manufacturing industry, pharmaceutical industry. It is used for the production of aseptic water, various industrial wastewater, wastewater for buildings such as buildings, sewage turbidity, pretreatment for desalination by reverse osmosis of river water, brine, seawater, etc. Efficiently separates order bacterial cells, fine particles, and polymeric substances
The present invention relates to a porous separation membrane for microfiltration or ultrafiltration that has been removed and is excellent in mechanical strength.

[0002]

2. Description of the Related Art Conventionally, as a porous separation membrane used in various industrial fields, polymers such as cellulose ester, polyamide, polyimide, polysulfone, polyfluorocarbon, polyethylene, polypropylene, polyvinyl alcohol and polyacrylonitrile are used as raw materials. And the like (for example, JP-A-48-32166, JP-A-58-146408, JP-A-61-161).
222505, JP 56-154051, JP 57-66114, and JP 52-15.
627, JP-A-58-45239, JP-A-48-86163). Among these, polysulfone is most preferably used as the material for the porous separation membrane in terms of heat resistance, chemical resistance, and cost.

Such a porous separation membrane has a so-called symmetrical membrane having a homogeneous structure in which the pore diameters on the surface and inside of the membrane do not substantially change, and the pore diameter changes continuously or discontinuously in the film thickness direction,
It is classified into a so-called asymmetric membrane having a minimum pore size layer on one or both surfaces of the membrane. Both membranes have advantages and disadvantages, and in general, symmetric membranes tend to be clogged and often have a short filtration life.On the other hand, asymmetric membranes have a minimum pore size layer on the surface, so the membrane surface is not suitable for modularization such as pleating. However, there is a problem that it is easily scratched and the separation / removal performance deteriorates.

As a solution to these problems, a film having an asymmetric structure in which a layer having the smallest pore size exists inside in the film thickness direction has been proposed. For example, according to Japanese Patent Application Laid-Open No. 62-27006, this membrane is a membrane forming method to which a dry-wet method generally used as a method for producing a hollow fiber membrane is applied. It is disclosed that it is obtained by appropriately controlling the evaporation of the solvent in the air and the absorption amount of the non-solvent from the atmosphere until the liquid is immersed in the liquid, by controlling the temperature, the humidity and the air flow. This membrane has a long filtration life, and its separation performance does not easily deteriorate even when the membrane surface is defective, and it can be said that this membrane is excellent as a microfiltration membrane used in a so-called total filtration system such as a pleated module.

[0005]

However, when the above-mentioned membrane is used in a cross-flow filtration system in which the liquid to be treated (stock solution) is flowed at a right angle to the filtration direction, there is no minimum pore size layer on the surface of the membrane, so that cross-flow The effect of suppressing clogging and the effect of reducing the so-called concentration polarization layer are not sufficiently obtained, and it is not necessarily an efficient membrane having a long filtration life.

Further, in a flat membrane without a reinforcing support as disclosed in Japanese Patent Laid-Open No. 62-27006, a rotary disc type module in which flat membranes are attached to both sides of a disc-shaped support plate or frame. It is difficult to apply to a module type in which the mechanical strength of the membrane itself is particularly required, such as an immersion type flat membrane module. Furthermore, the membrane used in the above module form has
In recent years, there has been a strong demand for a flat membrane excellent in back pressure strength that can be back-pressure washed, which is often used as one of effective cleaning methods for hollow fiber membranes.

In order to solve the above-mentioned conventional problems, the present invention has submicron-order bacterial cells and fine particles and a molecular weight of 1.
Efficiently separates and removes polymer substances of the order of, 000,000,
A first object is to provide a porous separation membrane having a long membrane life. A second object of the present invention is to provide a flat membrane type porous separation membrane having excellent back pressure strength and capable of applying back pressure washing.

[0008]

In order to achieve the above object, the polysulfone porous separation membrane of the present invention is a polysulfone porous separation membrane in which a membrane having substantially a separating function is present on the surface of a porous reinforcing sheet. The surface of the membrane has a minimum pore diameter layer having an average pore diameter in the range of 0.01 to 0.05 μm, has an asymmetric structure in which the pore diameter continuously expands in the thickness direction from the surface, and the membrane has porous reinforcement. It is characterized by being joined to the seat in an anchored state and reinforced. With this configuration, submicron-order cells and particles and molecular weight of 1
Efficiently separates and removes polymer substances of the order of, 000,000,
A porous separation membrane having a long membrane life can be realized. Further, it is possible to realize a flat membrane type porous separation membrane having excellent back pressure strength and capable of applying back pressure washing.

In the polysulfone porous separation membrane of the present invention, the porous reinforcing sheet is a nonwoven fabric, the thickness is in the range of 0.08 to 0.15 mm, and the density is 0.
It is preferably in the range of ^{5 to} 0.8 g / cm ³ .

In the polysulfone porous separation membrane of the present invention, the back pressure strength of the polysulfone porous separation membrane is preferably ² kg / cm ² or more.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view illustrating a polysulfone porous separation membrane according to an embodiment of the present invention. In FIG. 1, the membrane 22 having a substantially separating function is present in close contact with the surface of the porous reinforcing sheet 21. Further, a part of the resin component forming the film 22 is joined to the porous reinforcing sheet 21 in an anchored state to be reinforced. This polysulfone porous separation membrane 20 has a minimum pore diameter layer on the membrane surface, and its average pore diameter is in the range of 0.01 to 0.05 μm, which is one order smaller than that of an ordinary microfiltration membrane, and is close to an ultrafiltration membrane. It has a surface pore size. Therefore, submicron-order bacterial cells and fine particles can be almost completely blocked on the membrane surface, and clogging is less likely to occur in the cross-flow filtration method, and stable filtration performance can be maintained.

Further, even when the surface of the film is scratched or scratched, the pore size of the film is continuously and gradually expanded from the surface in the thickness direction,
Even in the middle part of the membrane, since the pore size is sufficient to capture fine particles of submicron order, there is no leakage of fine particles.

The porous reinforcing sheet used in the present invention includes polyester, polypropylene, polyethylene,
Examples of the material include woven fabrics, nonwoven fabrics, mesh nets, foamed sintered sheets, and the like made of polyamide or the like, and nonwoven fabrics are preferably used from the viewpoint of film-forming property and cost described later.

The nonwoven fabric used in the present invention has a thickness of 0.08 to 0.15 mm and a density of 0.5.
It is preferably 0.8 g / cm ³ . The thickness is 0.
Thinner than 08 mm and / or a density of 0.5 g / cm ³
If it is smaller, the strength as a reinforcing sheet cannot be obtained, and it is difficult to maintain a back pressure strength of 2 g / cm ² or more. On the other hand, when the thickness is thicker than 0.15 mm or the density is higher than 0.8 g / cm ³ , the reinforcing resistance of the membrane is high and the anchoring effect of the membrane on the nonwoven fabric is small, so that the membrane and the nonwoven fabric are small. It is not preferable because peeling easily occurs at the interface with.

Next, the method for producing the polysulfone porous separation membrane of the present invention will be described below. A solvent, a non-solvent, and a swelling agent are added to polysulfone and dissolved by heating to prepare a uniform film-forming solution. The polysulfone-based resin used in the present invention is not particularly limited as long as it has at least one (—SO ₂ —) site in the molecular structure as shown in the following formula (Formula 1).

[0016]

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(However, R represents a divalent aromatic, alicyclic or aliphatic hydrocarbon group, or a divalent organic group in which these hydrocarbon groups are bonded by a divalent organic bonding group.) Is a polysulfone represented by the structural formulas (Formula 2) to (Formula 4) below.

[0018]

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[0019]

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[0020]

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The polysulfone resin used in the present invention may be used alone, but may also be used as a mixture of two or more kinds. Further, if it is 50 mol% or less, it may be a copolymer with a polymer such as polyimide or a fluorine-containing polyimide resin, or a mixture thereof.

As the solvent for the polysulfone, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide and the like are preferably used. As the non-solvent, aliphatic polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol and glycerin, lower aliphatic alcohols such as methanol, ethanol and isopropyl alcohol, lower aliphatic ketones such as methyl ethyl ketone are preferable. Used.

The content of the non-solvent in the mixed solvent of the solvent and the non-solvent is not particularly limited as long as the obtained mixed solvent is uniform, but is usually 5 to 50% by weight, preferably 20 to 45.
% By weight.

Examples of the swelling agent used for promoting or controlling the formation of the porous structure include metal salts such as lithium chloride, sodium chloride and lithium nitrate, water-soluble agents such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone and polyacrylic acid. Polymer or its metal salt,
Formamide or the like is used. The content of the swelling agent in the mixed solvent is not particularly limited as long as the film forming solution is uniform, but is usually 1 to 50% by weight.

The concentration of polysulfone in the membrane forming solution is usually preferably 10 to 30% by weight. When it exceeds 30% by weight, the water permeability of the obtained porous separation membrane is poor in practicality,
On the other hand, when it is less than 10% by weight, the mechanical strength of the obtained porous separation membrane is poor and sufficient back pressure strength cannot be obtained.

Next, the above film forming solution is formed into a film on the nonwoven fabric support by a continuous film forming apparatus as shown in FIG. That is, the support sheet 2 such as a nonwoven fabric is delivered from the delivery machine 1 and the film-forming solution is applied to the surface thereof. The coating method is to coat the nonwoven fabric support with the film-forming solution using a gap coater such as a knife coater or a roll coater. In the present embodiment, the roll coater 4 is used, the film-forming solution 3 is accumulated between two rolls, and while being applied onto the nonwoven fabric support 2, the inside of the nonwoven fabric is sufficiently impregnated. A minute amount of water in the atmosphere is absorbed from the surface of the liquid film 5 applied to the surface of the liquid film 5 to cause microphase separation in the surface layer of the liquid film 5. 6 is a phase separation zone. Then, the polysulfone porous separation membrane 8 of the present invention is obtained by immersing it in the coagulating water tank 7, phase-separating and coagulating the whole liquid film, and washing and removing the solvent in the water washing tank 9, and winding it with the winder 10. take.

The above-mentioned film-forming method is a kind of so-called dry-wet method, but the micro-phase separation on the surface of the liquid film is not the phase separation by evaporation of the solvent from the surface of the liquid film, but rather the phase separation by absorption of moisture from the atmosphere. Is more dominant, and control of atmospheric humidity and moisture absorption time is important. Depending on the characteristics of the film forming solution, the atmosphere that causes microphase separation is usually
Temperature 20-40 ° C, relative humidity 40% or less, preferably 1
0 to 30%, and the phase separation time, that is, the moisture absorption time is 4 to 10
Seconds are preferred. Further, it is preferable that the atmosphere is substantially windless.

When air is blown onto the surface of the liquid film to forcibly absorb the moisture or the moisture absorption time is lengthened, the above-mentioned JP-A-62-2 is used.
The structure has a minimum pore size layer inside the membrane as disclosed in Japanese Patent No. 7006, which is different from the membrane structure of the present invention in which the minimum pore size layer exists on the membrane surface, which is not preferable. Further, if the relative humidity is increased or the temperature is increased to 40 ° C. or higher, the average pore diameter on the surface becomes larger than 0.05 μm and the minimum pore diameter layer is formed inside the membrane, which is not preferable. on the other hand,
On the other hand, when the relative humidity is low and the moisture absorption time is short, microphase separation becomes insufficient, and a discontinuous dense layer called a skin layer is formed on the film surface, which is not preferable.

As described above, in order to produce the polysulfone porous separation membrane of the present invention, it is important to control the atmosphere of microphase separation. However, a film or the like is formed around the lower part of the coater of the film forming apparatus shown in FIG. By shutting off the supply of moisture from the outside by surrounding it with a box, and further by covering the coagulation water tank to suppress the inflow of water vapor from the surface of the water, it is balanced with the absorption of moisture from the surface of the liquid film. It can be controlled to low humidity of less than%.

[0030]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

[0031]

Examples 1 to 3 and Comparative Examples 1 and 2 16.5 parts by weight of polysulfone (P-3500, manufactured by Amoco), N-methyl-2
Pyrrolidone 58 parts by weight, diethylene glycol 24.5
By weight, 1 part by weight of formamide and 1 part by weight of formamide were dissolved by heating to obtain a uniform film-forming solution. Thickness 0.1 mm, density 0.8 g / c
using a polyester nonwoven fabric of m ^3.

The above film-forming solution was impregnated and coated on the above-mentioned non-woven fabric with a roll coater having a coater gap adjusted to 0.13 mm using the film-forming apparatus shown in FIG. Then, by changing the film forming speed in an atmosphere of relative humidity 25% and temperature 30 ° C., 1 second, 4.5 seconds, 6 seconds, 9 seconds, 2 seconds.
After passing each for 0 seconds to cause microphase separation,
The polysulfone porous separation membrane was obtained by immersing in a coagulation water tank at 35 ° C. for solvent removal and coagulation, and then washing and removing the residual solvent in a water rinsing tank.

For each of the obtained membranes, the average pore diameter of the membrane surface, the amount of water permeation, observed by a scanning electron microscope,
The inhibition rate of polyethylene oxide having an average molecular weight of 1,000,000 and the back pressure strength were measured and are shown in Table 1. FIG. 3 shows an electron microscope (SE for the surface layer of the separation membrane obtained in Example 1).
M) A photograph (magnification: 4,000) is shown.

Here, the rejection rate of polyethylene oxide was obtained by the following equation (Equation 1) from the concentrations of the stock solution and the permeated solution after permeating a polyethylene oxide solution having a concentration of 500 ppm at a pressure of 1 kgf / cm ² .

[0035]

[Formula 1] Rejection rate (%) = [1- (permeate concentration / stock solution concentration)] × 100

As for the back pressure strength, a membrane having a diameter of 47 mm is set in a back pressure strength holder (effective diameter of 23 mm), and water pressure is applied from the back surface of the porous separation membrane formed on the porous reinforcing sheet, that is, the nonwoven fabric side. The pressure at which the film is peeled off from the nonwoven fabric or the membrane and the nonwoven fabric burst at the same time by gradually adding. The results are shown in Table 1.

[0037]

[Table 1] As shown in Table 1, each of the polysulfone porous separation membranes of the present invention obtained in Examples 1 to 3 has an average pore diameter of the surface of 0.01 to 0.05 μm and a polyethylene oxide blocking rate of 90%. The above shows excellent separation performance. Further, the back pressure strength was ² kgf / cm ² or more, which was an excellent mechanical strength. When the cross-sectional structure of the film was observed with an electron microscope (SEM), the films of Examples 1 to 3 all had an asymmetric structure in which the pore diameter continuously increased from the surface in the film thickness direction. FIG. 3 shows an electron microscope (SEM) photograph (magnification: 4,000) obtained in Example 1. Further, the voids of the non-woven fabric were impregnated with the film-forming solution and a part thereof reached the back surface of the non-woven fabric, and the film was united with the non-woven fabric and bonded to the non-woven fabric in an anchored state.

On the other hand, the porous separation membrane formed on the porous reinforcing sheet obtained in Comparative Example 1 has a discontinuous dense layer on the surface and has a typical finger-shaped cavity inside. The structure of the ultrafiltration membrane was different from that of the polysulfone porous separation membrane of the present invention.

Further, in the porous separation membrane formed on the porous reinforcing sheet of Comparative Example 2, the minimum pore size layer was present near the interface between the membrane and the nonwoven fabric, and voids were observed at the interface. This cavity is considered to have been generated by shrinkage during solidification due to microphase separation occurring near the interface of the nonwoven fabric, and it is presumed that the back pressure strength was reduced due to this.

[0040]

Example 4 A polysulfone porous separation membrane was obtained in the same manner as in Example 2 except that a polypropylene nonwoven fabric having a thickness of 0.14 mm and a density of 0.5 g / cm ³ was used. The back pressure strength of this membrane was measured to be 3.5k.
It had excellent mechanical strength of gf / cm ² or more. .

[0041]

Comparative Example 3 A porous film formed on a porous reinforcing sheet in the same manner as in Example 2 except that a polyester non-woven fabric having a thickness of 0.06 mm and a density of 0.4 g / cm ³ was used. A separation membrane was obtained. When the back pressure strength of this membrane was measured, the membrane ruptured together with the nonwoven fabric at 1 kgf / cm ² ,
It was extremely poor in mechanical strength.

[0042]

Comparative Example 4 A porous film formed on a porous reinforcing sheet in the same manner as in Example 2 except that a polyester nonwoven fabric having a thickness of 0.17 mm and a density of 0.85 g / cm ³ was used. A separation membrane was obtained. When the back pressure strength of this film was measured, the film peeled off at 1.5 kgf / cm ² . It is presumed that the anchoring property of the film on the non-woven fabric is insufficient because the non-woven fabric is dense.

[0043]

Example 5 was set on a holder for the back pressure strength measured using a porous separation membrane which is formed into a film porous reinforcing sheet obtained in Example 2, the back of 0kgf / cm ² -2kgf / cm ² When a back pressure fatigue test in which the pressure was repeated in a cycle of 6 seconds was carried out, no peeling of the film occurred even after 100,000 tests.

[0044]

INDUSTRIAL APPLICABILITY As described above, the polysulfone porous separation membrane of the present invention is a flat membrane having extremely excellent mechanical strength, and the back pressure cleaning can be applied to the flat membrane module which has been difficult to apply conventionally. It is possible, and it has become possible to apply it to the field of highly turbid liquids, which had a short membrane life due to clogging of the membrane and was considered difficult to apply.

Further, the polysulfone porous separation membrane of the present invention is capable of separating and removing submicron-order bacterial cells and fine particles with high accuracy, and is also capable of separating a high molecular weight substance having a molecular weight of about 1,000,000. Therefore, it can be applied to an intermediate field between conventional microfiltration and ultrafiltration.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a polysulfone porous separation membrane according to an embodiment of the present invention.

FIG. 2 is a process diagram illustrating a continuous film forming method according to an embodiment of the present invention.

FIG. 3 shows an electron microscope (SEM) photograph (magnification: 4,000) of the surface layer portion of the separation membrane obtained in Example 1 of the present invention.

[Explanation of symbols]

 1 Feeder 2 Support 3 Membrane forming solution 4 Roll coater 5 Liquid membrane 6 Phase separation zone 7 Coagulation water tank 8 Porous separation membrane 9 Washing tank 10 Winder 20 Polysulfone porous separation membrane 21 Porous reinforcement sheet 22 Separation function Film with

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[Procedure amendment]

[Submission date] September 3, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 3

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

In the polysulfone porous separation membrane of the present invention, the back pressure strength of the polysulfone porous separation membrane is preferably ² kg f / cm ² or more.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

The nonwoven fabric used in the present invention has a thickness
Is 0.08 to 0.15 mm and the density is 0.5
~ 0.8 g / cm^ThreeIt is preferred that The thickness is 0.
Thinner than 08mm and / or density 0.5g / cm^Three
If it is smaller, strength as a reinforcing sheet is obtained.
No, 2kgf/ Cm^TwoIt is possible to maintain the above back pressure strength
Have difficulty. On the other hand, if the thickness is greater than 0.15 mm or
Density 0.8g / cm ^ThreeIf it is larger,
The filtration resistance becomes large and the anchoring effect of the membrane on the non-woven fabric
Since it becomes smaller, peeling may occur at the interface between the membrane and the non-woven fabric.
It is not preferable because it becomes faster.

Claims (3)

[Claims] 1. A polysulfone porous separation membrane in which a membrane having a substantially separating function is present on the surface of a porous reinforcing sheet, wherein the surface of the membrane has an average pore diameter of 0.01 to 0.05.
It has a minimum pore size layer in the range of μm, has an asymmetric structure in which the pore size continuously expands from the surface in the thickness direction, and the membrane is joined to a porous reinforcing sheet in an anchored state and reinforced, A polysulfone porous separation membrane. 2. The porous reinforcing sheet is a non-woven fabric, the thickness is in the range of 0.08 to 0.15 mm, and the density is in the range of 0.5 to 0.8 g / cm ^3. The polysulfone porous separation membrane described. 3. The polysulfone porous separation membrane according to claim 1, wherein the back pressure strength of the polysulfone porous separation membrane is 2 kg / cm ² or more.