JP2000005576A - Separation membrane for water treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a separation membrane for treating water made of a nonwoven sheet, in place of a high molecular porous membrane, excellent in mechanical strength, having a sufficient water permeability, excellent in a separating property of particulates and producable at low cost. SOLUTION: A this film consisting of high molecular porous layer whose at least one part is buried in a dense layer is provided on a surface of the nonwoven sheet having an unsymmetrial multilayered structure consisting of a sheet-shaped supporting layer in which fibers are intersected and integrated each other and also confounded and/or bonded and the dense layer supported to the supporting layer and formed integrally on the other surface of the supporting layer and in which the fibers are arranged densely than that of the supporting layer and bonded each other and an average pore size is smaller than that of the supporting layer, moreover, on the surface of the dense layer of the nonwoven sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separation membrane for water treatment, and more particularly, to a solid-liquid separation of liquid containing suspended solids and sludge, treated wastewater, and river water, and having a strength capable of backwashing air. The present invention also relates to a separation membrane for water treatment which can maintain a high permeation flux and has excellent separation performance.

[0002]

2. Description of the Related Art Conventionally, water treatment using a non-woven fabric has been attempted in the separation treatment of liquids including suspended matter and sludge, and the filtration performance has been improved. Some measures have been taken to ensure stability. For example, Japanese Unexamined Patent Publication (Kokai) No. 61-174912 discloses a filter cloth having a nap portion made of synthetic fiber and having a directional index of 1.2 to 1.2.
10. Disclosed is a filter cloth for solid-liquid separation, characterized in that the unevenness index is 0.5 or less and the specific surface area of the raised synthetic fibers is 9 × 10 ³ cm ² / g or more.

Japanese Patent Application Laid-Open No. Sho 61-174913 discloses a method for producing a nonwoven fabric having excellent reinforcing properties and abrasion resistance by interposing a sheet made of a low-melting polymer in the above nonwoven fabric and heat-sealing the sheet. A method is disclosed. In addition, "The 34th Sewerage Research Presentation Lectures" by Daido et al.
In "Dynamic membrane filtration of 7-89 activated sludge mixture" described on pages 647 to 649, filtration of the activated sludge mixture is attempted using a nonwoven fabric.

However, in general, when a nonwoven fabric is used to separate fine particles, an activated sludge mixture, or the like, the gap between the fibers of the nonwoven fabric is large and non-uniform, so that the particle size is 5.
There is a problem that it is difficult to separate fine particles of 0 μm or less. Further, when the filter cloth disclosed in JP-A-61-174912 is used for separation for water treatment, when the pore size of the filter cloth surface is larger than the particle diameter of the separation purpose,
There is also a problem that the fine particles penetrate into the inside of the nonwoven fabric, the nonwoven fabric is clogged, and the water permeation speed is rapidly reduced.

Therefore, attempts have been made to densify the surface of the nonwoven fabric by subjecting the surface of the nonwoven fabric to a chemical treatment. JP-A-61-174914 discloses a nonwoven fabric for solid-liquid separation in which a water-repellent substance is coated on a nonwoven fabric made of synthetic fibers, and JP-A-5-62861 discloses a nonwoven fabric made of glass fibers. Examples of surface treatment using a silane coupling agent are disclosed.

However, in order to improve the amount of permeated water of the nonwoven fabric, it is necessary to impart hydrophilicity to the nonwoven fabric. Therefore, the nonwoven fabric coated with the water-repellent substance or the silane coupling agent has a sufficient permeated water amount. There is a problem that can not be.

Japanese Patent Application Laid-Open No. Sho 60-2111764 discloses an example in which at least one surface of a polypropylene nonwoven fabric is covered with glass fibers, or a surface treatment is performed by microwave or plasma irradiation. ,
JP-A-2-304864 discloses examples in which a corona-discharge-treated polyolefin-based fibrous nonwoven fabric is treated with a dispersion liquid of carbon fine particles containing a surfactant or water glass, respectively. However, these methods have a problem in that their production methods are complicated, and thus they are difficult to put into practical use.

On the other hand, when fine particles are separated from a suspension containing fine particles using a nonwoven fabric, fouling or the like is easily caused inside the nonwoven fabric because the entire nonwoven fabric has filtration resistance, and a cake layer is formed on the surface of the nonwoven fabric. Is formed,
There is a problem that the water permeability decreases with time. For this reason, Japanese Unexamined Patent Publication No. Hei 6-210110 discloses a method of spraying compressed air or liquid to separate a cake layer in order to maintain a high water permeation rate. However, there is a problem that the membrane may be broken due to the high-pressure compressed air.

[0009] In the microfiltration separation for removing fine particles having a particle diameter of 5.0 µm or less, a flat membrane type polymer porous membrane is often used. Generally, a flat membrane type porous membrane is one in which a polymer membrane layer is provided on the surface of a support such as taffeta cloth for reinforcing the membrane, and is integrated with the support.

For example, Japanese Patent Application Laid-Open No. 54-14376 discloses an ultrafiltration tubular article in which a sponge layer of an ultrafiltration membrane made of polysulfone is embedded in a polyester nonwoven fabric. . Further, Japanese Patent Application Laid-Open No. 58-9
No. 1733 discloses that after a polymer solution is applied to one side of a porous reinforcing body, a solvent that does not solidify the polymer is applied from the back side of the coated side, and then dipped in a coagulation bath to form a porous membrane on the reinforcing body. A method for producing an asymmetric film characterized by being formed is disclosed.

Japanese Patent Application Laid-Open No. Sho 58-14904 discloses that a part of a porous supporting membrane penetrates into a base cloth, and the porous pore diameter is in a range of 50 Å to 50 μm. And the porosity of the support film is 5
Although it discloses a support sheet for liquid separation characterized by being 0 to 90%, there is no description about the structure of the base fabric, and the structure is completely unknown.

In the case of a porous membrane, if the fiber gap of the base fabric is large, the polymer solution permeates into the base fabric, the filtration resistance in the porous membrane increases, and a high permeation flux cannot be obtained. There is. In addition, the base fabric on which these porous membranes are formed has a problem that when filtration is continued, particles and the like enter the base fabric, and the so-called fouling cannot maintain the permeation flux for a long time. .

Accordingly, the present invention provides a high permeation flux and a high separation performance, furthermore, prevents particles and the like from entering the inside of the nonwoven fabric, suppresses a decrease in permeation flux due to fouling, and provides a machine. It is an object of the present invention to obtain a separation membrane for water treatment which has excellent mechanical strength, enables air backwashing, can maintain a stable permeation flux over a long period of time, and can be manufactured at low cost.

[0014]

Means for Solving the Problems The present inventors have studied the structure, porosity, relationship between the pore size of the surface of the nonwoven fabric and the size of the fine particles to be separated, the maximum and minimum values of the pore size, the distribution and transmission of the pore size. As a result of various studies on the performance, stability of permeation performance, etc., the pore size on the surface of the nonwoven fabric was designed to be smaller than the particle size for the purpose of separation, and the fine particles were blocked on the surface of the nonwoven fabric, preventing the penetration of the fine particles into the nonwoven fabric. By doing so, it was found that the cleaning effect by air, water, a cleaning liquid or the like can be enhanced, and the permeation flux can be maintained stably. In addition, the structure of the nonwoven fabric as a support for the thin film, the porosity, the pore size, the film thickness, etc., the type of composition constituting the polymer porous layer as a thin film, the type of solvent, the method of forming the thin film, especially the polymer porous As a result of various investigations on the method of controlling the thickness, porosity, pore size, etc. of the porous layer, a polymer porous layer was formed on the dense layer under specific conditions using a non-woven fabric with an asymmetric structure having a dense layer on one surface as a support. It has been found that the above problem can be solved by generating, and the present application has been completed.

The separation membrane for water treatment of the present invention comprises a sheet-like support layer in which fibers are cross-collected and entangled and / or adhered, and is integrally supported on one surface of the support layer by the support layer. It is a nonwoven fabric having an asymmetric structure composed of a dense layer, which is formed in a dense manner, has fibers arranged more densely than the support layer, adheres to each other, and has a smaller average pore diameter than the support layer.

The porosity of the dense layer of the present invention is 30 to
80%, average pore size 0.2 to 30 μm, thickness 10 to 5
And the thickness of the entire nonwoven fabric is 3 μm.
It is characterized in that it is 0 μm to 5 mm.

Further, the present invention is characterized in that the pore diameter of the outer surface of the dense layer of the present invention is in the range of 0.1 to 60 μm.

Further, the fiber constituting the nonwoven fabric of the present invention has a fiber diameter of 0.5 to 30 μm. Further, the fibers of the nonwoven fabric of the present invention are made of polyester or polypropylene.

Further, the surface of the dense layer of the nonwoven fabric of the present invention
A thin film composed of a polymer porous layer at least partially embedded in a dense layer is provided.

The thin film of the present invention is formed by a phase inversion method and has a porosity of 20 to 90% and an average pore size of 0.1 to 2%.
0 μm and a thickness in the range of 0.5 to 200 μm.

Further, the thin film of the present invention is a skinless thin film. Further, the skinless thin film of the present invention is characterized in that it is formed of at least one selected from the group consisting of cellulose acetate derivatives, acrylonitrile-based polymers, acrylic polymers and aromatic sulfone-based polymers. Things.

The bubble point of the thin film of the present invention is
490.5 KPa or less.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION A nonwoven fabric in the present invention means a fabric made without weaving, and is defined as a web or a mass of fibers cross-stacked with each other and entangled and / or bonded. You. When the amounts of these webs and fibers increase, the thickness increases and a sheet-like fiber layer, for example, a support layer is formed. As a method of bonding a web or a lump of fibers, a method of mechanically entangled or entangled, a method of using an adhesive, a method of bonding with a self-adhesive fiber, for example, mixing fibers having a lower melting point, And a method using a core-sheath composite fiber in which a high-melting fiber such as a polyester fiber coated with polyethylene is coated with a lower-melting polymer.

The fibers constituting the nonwoven fabric include natural fibers such as cotton, hemp and wool, polyester, polystyrene, polyvinyl chloride, polyvinylidene chloride, poly (meth) acrylate, viscose rayon, and acetic acid. Cellulose, cellulose derivatives such as methylcellulose, polyethylene, polyolefins such as polypropylene, polycarbonate, polyamide, polyesteramide, polyether, polyimide, polyamideimide,
And polyether esters. Further, these copolymers, blends, cross-linked products and the like can be mentioned.
Among them, polyester, polyethylene, polypropylene and polycarbonate are desirable, and polyester and polypropylene are particularly preferred.

The fibers of the non-woven fabric may be used alone or in combination. In addition, a plurality of combinations may be made by combining respective materials in appropriate amounts. The fiber diameter of the fibers constituting the nonwoven fabric is preferably 0.5 to 30 μm, and the basis weight is preferably 20 to 1000 g / m ² . The reason why the fiber diameter is set to 0.5 to 30 μm is that if the fiber diameter is less than 0.5 μm, the mechanical strength decreases, and if it exceeds 30 μm, the filtration resistance increases and the amount of permeated water decreases.

The non-woven fabric having an asymmetric structure used in the present invention is:
A support layer having a large thickness, which is a fiber layer, and a dense layer having a thickness smaller than that of the support layer and having a dense fiber formed integrally on one surface of the support layer. ) Means that the support layer and the dense layer have a specific asymmetric structure in which the thickness and density of the fibers are different. This dense layer is formed only on one surface of the support layer, continuously with the support layer, by mechanical entanglement, pressure processing, heat processing, an adhesive, or the like, or a more dense film-like fiber, such as a wet papermaking method. By laminating the porous polymer film according to (1) above, so that the average pore size is smaller than the average pore size of the support layer.
The non-woven fabric of this asymmetric structure has a dense layer formed of a non-woven fabric (support layer).
By forming the film on the surface, strength and morphological stability as a film are imparted.

The dense layer and the support layer may each be a laminate of 1 to 5 layers. That is, a single dense layer may be formed on one surface of the above-described single support layer, but the outer surface of the single dense layer may be further subjected to thermal processing to increase the fiber density to form a double dense layer. Alternatively, one or two layers having different fiber densities or different material strengths may be used as the support layer.
The layers may be integrally laminated to increase the mechanical strength of the support layer. At this time, it is desirable to decrease the fiber density and increase the average pore diameter toward the permeation side to reduce the filtration resistance of the permeated water. The reason why five layers are used here is that if the number of layers exceeds five, it is not practical due to transmission resistance and workability.

The porosity of the dense layer of the nonwoven fabric is preferably from 30 to 80%, more preferably from 40 to 75%, particularly preferably from 50 to 75%.
~ 70% is most preferred. Here, the porosity is 30 to 80.
The reason is that if the amount is less than 30%, the amount of permeated water decreases, and
%, The rejection rate decreases. In addition, the average pore size of the dense layer is preferably 0.2 to 30 μm, more preferably 0.5 to 10 μm, and particularly preferably 0.5 to 5 μm.
Is most preferable. Here, the average pore size is 0.2 to 3
The reason why the thickness is set to 0 μm is that if it is less than 0.2 μm, the amount of permeated water decreases, and if it exceeds 30 μm, the coating liquid penetrates into the entire nonwoven fabric, so that it becomes impossible to form a porous layer on the surface. The porosity of the support layer is usually preferably 60 to 90%. Further, the average pore size is preferably 0.5 to 200 μm. Here, the porosity is a ratio of the sum of the areas of the holes viewed from the outer surface side (the side on which the thin film is formed) of the dense layer to the total area to be measured, as can be seen from the test method described later. Good, it does not mean the space inside the layer. Similarly, the porosity of the thin film described later is a ratio with respect to the area of the hole portion viewed from the surface of the thin film, similarly to the above.

Further, in order to suppress fouling, the minimum value and the maximum value of each pore diameter of the pores between fibers as viewed from the outer surface of the dense layer of the nonwoven fabric are important. The pore size of the dense layer is 0.
It is preferably in the range of 1 to 60 μm, and in particular, 0.1 μm.
It is preferable to be within the range of 5 to 40 μm. this is,
If the thickness is less than 0.1 μm, the amount of permeated water decreases. On the other hand, if it exceeds 60 μm, the polluted fine particles are liable to be clogged in the dense layer to easily cause fouling, and the rejection rate is lowered and the separation efficiency is lowered.

Further, the narrower the distribution of the pore size distribution of the pores between the fibers as viewed from the outer surface of the dense layer of the nonwoven fabric, the narrower it is preferable. When the number is expressed in terms of the number of pores, the narrower the distribution of pore diameters, the sharper the so-called pore diameter distribution, the more difficult it is for clogging to occur.

The thickness of the dense layer is 10 to 500 μm
Is more preferable, more preferably 10 to 400 μm, and most preferably 10 to 300 μm. Here, the thickness was set to 10 to 500 μm by 10
If it is less than μm, it will be too thin, lack mechanical strength,
If the thickness exceeds 0 μm, handling becomes difficult during module processing.

The porosity and the average pore diameter of the dense layer of the present invention are formed so as to have specific values smaller than the respective values of the support layer that supports the dense layer, so that a high amount of permeated water can be obtained and a high amount of water can be obtained. It is like getting separation performance. The thickness of the entire nonwoven fabric is preferably 30 μm to 5 mm, more preferably 50 μm to 4 mm, and particularly preferably 1 μm to 4 mm.
Most preferably, it is from 00 μm to 3 mm. Here the thickness is 30μ
When the thickness is less than 30 μm, the mechanical strength of the nonwoven fabric is too weak, and when it exceeds 5 mm, the thickness of the support layer becomes too large, handling becomes difficult, and the permeation resistance becomes too large. . Further, the nonwoven fabric may be subjected to a hydrophilic treatment as necessary.

Further, the present invention provides a water treatment method comprising the step of coating a surface of a dense layer of the non-woven fabric having an asymmetric structure with a thin film comprising a polymer porous layer at least partially embedded in the dense layer. A separation membrane is provided. Separation membrane for water treatment of the present invention, in order to enable air backwashing, the thin film consisting of the polymer porous layer, the strength is required not to peel off the asymmetric nonwoven fabric by the air pressure at the time of backwashing, at least A part is buried in the dense layer and covers the outer surface of the dense layer. Preferably, the porous polymer layer is almost completely buried to the extent that the fiber structure on the surface of the dense layer can be seen in a microscopic observation. The thin film is buried only on the outer surface side of the dense layer of the non-woven fabric with asymmetric structure in order to enable air backwashing with low energy, and as thin as possible, the film surface has a skinless structure, that is, it is not smooth on the dense layer Preferably, it is formed into a surface structure. In order to enable air backwashing with low energy, the bubble point of this separation membrane in water by air should be 490.5 ~
It is preferably 1 KPa, more preferably 30 KPa.
0 to 1 KPa. Here, the reason for setting the pressure to 490.5 to 1 KPa is that if the pressure exceeds 490.5 KPa, the power for backwashing becomes too high, and if the pressure is lower than 1 KPa, the cleaning effect is small due to low pressure.

Hereinafter, the characteristics of the thin film comprising the polymer porous layer of the present invention, the composition of the polymer, and the method of producing the thin film will be described in the case of the phase inversion method. The thin film composed of the polymer porous layer formed by the phase inversion method of the present invention preferably has a porosity in the range of 20 to 90%, particularly preferably 30 to 90%.
Most preferably, it is in the range of ~ 80%. The average pore diameter of the thin film is preferably in the range of 0.1 to 20 μm, and most preferably in the range of 0.1 to 5 μm. The thickness of the thin film is preferably 0.5 to 200 μm, more preferably 2 to 50 μm. The method for measuring the characteristics will be described later.

The reason why the porosity is set to 20 to 90% is that if the porosity is less than 20%, the porosity is too small and the amount of permeated water decreases, and if it exceeds 90%, the rejection decreases. In particular, in the present invention, since air backwashing is enabled, a porosity of 40% is required to enhance the backwashing effect.
The above is preferred. Further, the reason why the average pore diameter is set to 0.1 to 20 μm is that if the average pore diameter is less than 0.1 μm, the amount of permeated water decreases, and
If the thickness exceeds μm, the rejection decreases. The reason why the thickness of the thin film is set to 0.5 to 200 μm is that
If it is less than 200 μm, the mechanical strength decreases, and if it exceeds 200 μm, the filtration resistance increases.

The thin film comprising the polymer porous layer of the present invention comprises:
It may be a thin film formed by a casting method or a dipping method.

The polymer porous layer of the present invention is composed of an organic polymer, and usually has a microphase-separated structure. This microphase-separated structure is formed by coagulation of the gel phase separated by the composition change of the cast polymer solution,
The shape of the pores formed during the solidification phase is usually irregular, irregular and non-circular.

Examples of the polymer used in the present invention include cellulose derivatives [cellulose esters (organic acid esters such as cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate phthalate); cellulose nitrate, cellulose sulfate, and phosphoric acid. Inorganic acid esters such as cellulose; mixed acid esters such as cellulose nitrate acetate), cellulose ethers (such as methyl cellulose, ethyl cellulose, isopropyl cellulose, butyl cellulose, benzyl cellulose, hydroxyethyl cellulose, carboxyethyl cellulose, cyanoethyl cellulose, etc.)], polyolefins (polyethylene, Polypropylene, poly 1
-Butene, polyisobutene, polybutadiene, polyisoprene, polyarene, etc.), polyacrylonitriles (polyacrylonitrile, polymethacrylonitrile,
Acrylonitrile-vinylpyrrolidone copolymer, acrylonitrile-vinyl acetate copolymer, acrylonitrile-
Methyl acrylate copolymer, acrylonitrile-acrylic acid copolymer, etc.), polysulfone polymer (polysulfone, polyether sulfone, etc.), polyether ketone, polyether ether ketone, poly (meth) acrylic acid, poly (meth) acrylate (Polymethyl (meth)
Acrylate, polyethyl (meth) acrylate, polybutyl (meth) acrylate, etc.), polyvinyl alcohol, polyallyl alcohol, polyvinyl acetate, polyacetals (polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc.), polyvinyl ketones (polyvinyl methyl ketone, Polymethyl isopropenyl ketone, etc.), polyvinyl halides (polyvinyl chloride, polyvinylidene chloride, polyvinyl bromide, polyvinyl fluoride, polyvinylidene fluoride, etc.), polystyrenes (polystyrene, poly α
-Methylstyrene, poly4-chlorostyrene, etc.), polyoxides (polyoxymethylene, polyoxyethylene, polyoxypropylene, etc.), polyamide, polyesteramide, polyimide, polyamideimide, polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene) Naphthalate), polycarbonate, polyetherester and the like. These polymers can be used alone or in combination of two or more. Preferred polymers include cellulose derivatives,
Acrylonitrile polymers, polyalkyl (meth) acrylates, and polysulfone polymers are included.

The viscosity-average degree of polymerization of the cellulose derivative (eg, cellulose ester) is, for example, 50 to 800, preferably 75 to 500, and more preferably 100 to 250.
(Especially 100 to 200). Viscosity average degree of polymerization 1
Cellulose acetate of about 00 to 190 can also be used effectively.

The viscosity-average degree of polymerization of cellulose esters such as cellulose acetate is determined by the limiting viscosity method of Uda et al. (Uda Kazuo, Saito Hideo, Journal of the Textile Society, Vol. 18, No. 1, 105-105).
120, 1962). That is,
A precisely weighed cellulose ester is dissolved in a mixed solution of methylene chloride / methanol = 9/1 (weight ratio) to prepare a solution having a predetermined concentration C (2.00 g / liter).
This solution is poured into an Ostwald viscometer, and the time (second) t during which the solution passes between the marking lines of the viscometer at 25 ° C. is measured.
On the other hand, the passing time (second) t ₀ of the mixed solvent alone is measured in the same manner as described above, and the viscosity average polymerization degree is calculated according to the following equation. η _{rel =} t / t ₀ [η] = (ln η _rel ) / c DP = [η] / (6 × 10 ^-4 ) (where t is the solution transit time (sec), and t ₀ is the solvent transit) Time (sec), c is the concentration of cellulose ester in the solution (g / liter), η _rel is the relative viscosity, [η] is the intrinsic viscosity, DP
Indicates an average degree of polymerization. )

The average degree of substitution of the cellulose derivative is 1 to 3
You can choose from a range of degrees. For example, in a preferred cellulose acetate, for example, the average acetylation degree is 42 to 62%.
(43-60%), preferably about 42-57%.

The porous thin film of the present invention can be obtained by a micro phase separation method,
For example, it is also possible to produce by a wet phase separation method in which a good solvent solution of a polymer is cast or coated and immersed in a poor solvent for the polymer. Also, the dry phase inversion method, that is,
A uniform dope containing a polymer, a good solvent for the polymer, and a poor solvent for the polymer is cast or applied on the outer surface of the dense layer of the nonwoven fabric serving as a base material, and the solvent is evaporated to obtain a micro dope. It can be produced by causing phase separation. In particular, in the dry phase inversion method, it is important to use a solvent having a higher boiling point than the good solvent (high boiling point solvent) as the poor solvent. In the above-mentioned dry phase inversion process, in order to control the pore size of the porous membrane, it is important to select a good solvent and a poor solvent.

Examples of good solvents include ketones (eg, C _3-5 dialkyl ketones such as acetone, methyl ethyl ketone and methyl propyl ketone, and cyclohexanone) and esters (eg, formic acid C such as ethyl formate) according to the type of polymer.
C _1-4 alkyl esters such as _1-4 alkyl esters, methyl acetate, ethyl acetate, and butyl acetate; C _1-4 alkyl esters such as ethyl propionate and ethyl lactate; ethers (cyclic or chain C _4-6 such as dioxane and dimethoxyethane) Ethers), cellosolves (C _1-4 alkyl cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve), cellosolve acetates (C _1-4 alkyl cellosolve acetates such as methyl cellosolve acetate and ethyl cellosolve acetate), aromatic hydrocarbons (Benzene, toluene, xylene, etc.), halogenated hydrocarbons (methylene chloride, ethylene chloride, etc.), amides (N,
N-dimethylformamide, N, N-dimethylacetamide, etc.), nitriles (acetonitrile, chloroacetonitrile, propionitrile, butyronitrile, etc.), organic acids (formic acid, acetic acid, propionic acid, etc.), organic acid anhydrides (maleic anhydride) , Acetic anhydride, etc.), dimethyl sulfoxide, and mixtures thereof. Good solvents may include nitro compounds (nitromethane, nitroethane, nitropropane, etc.) and lower alcohols (C _1-4 alcohols such as methanol and ethanol, diacetone alcohols, etc.).

Preferred good solvents for the cellulose derivative include:
C _3-5 dialkyl ketones such as methyl ethyl ketone (especially acetone and methyl ethyl ketone), acetic acid C _1-4 alkyl esters such as ethyl acetate (especially methyl acetate and ethyl acetate), and cyclic or chain C ₄ such as dioxane and dimethoxyethane. _-6 ethers, C _1-4 alkyl cellosolves such as methyl cellosolve (especially methyl cellosolve, ethyl cellosolve), and C _1-4 such as methyl cellosolve acetate
Alkyl cellosolve acetates (especially methyl cellosolve acetate, ethyl cellosolve acetate) and the like are included.

Preferred good solvents for the polyacrylonitrile polymer include nitriles (such as chloroacetonitrile, malonitrile, and fumaronitrile), organic acid anhydrides (such as maleic anhydride and acetic anhydride), and amides (N, N-dimethylformamide). , N, N-dimethylacetamide).

Preferred good solvents for the polyalkyl (meth) acrylate include ketones (C _3-5 dialkyl ketones such as acetone, methyl ethyl ketone and methyl propyl ketone, cyclohexanone) and esters (C _1- formic acid such as ethyl formate). ₄ alkyl esters, C1-4 alkyl acetates such as methyl acetate, ethyl acetate, butyl acetate, etc., ethyl propionate, ethyl lactate, etc.), aromatic hydrocarbons (benzene, toluene, xylene, etc.), halogenated hydrocarbons ( Methylene chloride, ethylene chloride, etc.).

Preferred good solvents for the polysulfone-based polymer include N, N-dimethylformamide, dimethylacetamide, dimethylsulfoxide and the like. The boiling point of a good solvent is usually 35 to 200 ° C (for example, 35 to 180 ° C).
° C), preferably 35 to 170 ° C, more preferably 4 ° C.
It is about 0 to 160 ° C.

The poor solvent means a solvent having no solubility or low solubility in a polymer, and any solvent can be used as long as it has a higher boiling point than the above-mentioned good solvent. Therefore, the type of the poor solvent is not particularly limited. Examples of the poor solvent include esters (amyl formate, C _5-8 alkyl formate such as isoamyl formate, amyl acetate, hexyl acetate, C _4-10 alkyl acetate such as octyl acetate,
C _1-4 alkyl benzoates such as methyl benzoate, ethyl benzoate and propyl benzoate), alcohols
(C _4-8 cycloalkanols such as cyclopentanol, cyclohexanol, methylcyclohexanol and dimethylcyclohexanol, C _5-8 alcohols such as amyl alcohol, isoamyl alcohol and hexyl alcohol), ketones (methyl butyl ketone, methyl C _6-10 dialkyl ketones such as isobutyl ketone, methyl pentyl ketone and methyl isopentyl ketone, acetonylacetone, acetophenone and the like; ethers (C _7-10 such as methyl phenyl ether, methoxy toluene, dibutyl ether and benzyl ethyl ether) ether),
And mixtures thereof.

Preferred poor solvents for cellulose derivatives include
At least one solvent selected from C _5-8 alkyl formate, C _1-4 alkyl benzoate, C _4-8 cycloalkanol, C _6-10 dialkyl ketone and C _7-10 ether, in particular at least C _{5- 7} cycloalkanol
(Among others, cyclohexanols).
Cyclohexanols include mono- or di-C _1-2 alkyl substituents such as cyclohexanol, methylcyclohexanol, dimethylcyclohexanol and the like.

Preferred poor solvents for the polyacrylonitrile-based polymer, polyalkyl (meth) acrylate, and polysulfone-based polymer include C _1-4 alkoxy C _3-7 acetate such as 3-methoxybutyl acetate and 3-methoxypentyl acetate. Alkyl, C _4-8 alkoxy C _1-4 alkyl alcohol such as 2-butoxyethanol, 2-hexyloxyethanol,
Ketones (C _6-10 dialkyl ketones such as methyl butyl ketone, methyl isobutyl ketone, methyl pentyl ketone, methyl isopentyl ketone, acetonylacetone,
Acetophenone).

The boiling point of the poor solvent is usually from 100 to 230.
° C, preferably about 120 to 200 ° C. Further, the poor solvent usually has a boiling point higher than the good solvent by 20 ° C. or more, preferably about 30 to 50 ° C.

The ratio between the good solvent and the poor solvent is not particularly limited as long as a homogeneous solution of the polymer can be formed.
The amount of the poor solvent is 1 to 50 parts by weight, preferably 5 to 40 parts by weight, more preferably about 10 to 35 parts by weight with respect to 00 parts by weight.

Further, the content of the polymer in the dope solution can be selected according to the degree of polymerization of the polymer.
%, Preferably about 5 to 25% by weight, particularly about 5 to 20% by weight.

In the coating solution, known additives such as an antifoaming agent, a coating improver, and the like are used as long as the properties of the present invention are not impaired.
Thickener, heat stabilizer, lubricant, UV absorber, antistatic agent,
You may add an anti-blocking agent etc. The dope solution is a conventional casting or coating method, for example, a roll coater, an air knife coater, a blade coater, a rod coater, a bar coater, a comma coater, a gravure coater, a silk screen coater method, etc., one surface of the nonwoven fabric substrate, That is, it is cast or applied on the dense layer surface. In the present invention, a method based on a transfer method is preferable.

[0055]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. First, a performance test method used in the following examples will be described. (1) Porosity and average pore size The thin film or the dense layer is 100 times and / or 10,000
Three places having an area of 2 cm × 2 cm in an electron microscope surface photograph taken at a magnification of 0 were processed by an image processing apparatus, and a porosity and an average pore diameter were calculated. The porosity was (total area of pores / measured area) × 100 (%). The average pore diameter was determined by assuming each pore as a perfect circle, calculating the pore diameter, and averaging.

(2) Thickness The thickness of the dense layer was measured by an electron micrograph, and the thickness of the support layer was measured by subtracting the thickness of the dense layer from the thickness of the entire nonwoven fabric measured by a micrometer.

(3) Pure water permeation flux The pure water permeation flux of the separation membrane has an operating pressure of 0.2 kgf / c.
The permeation flux of deionized water was measured under m ² , and the amount of deionized water permeated per unit operating pressure, unit time, and unit membrane area was defined as pure water permeation flux, It was used as an index of the transmission performance. The unit is liter / (m ² · h · kgf / c
m ² ).

(4) Permeate flux The amount of permeate per unit time and per unit membrane area was measured by measuring the amount of permeate per unit time and permeation area when a filtration experiment was performed on a separation membrane (nonwoven fabric) using an actual filtrate. A bundle was defined as an index of the permeation performance of the filtrate through the separation membrane. The unit is m ³ / (m ² · h).

(5) Rejection rate The solute rejection rate R is defined as R = 1-Cp / Cb from the feed solution concentration Cb and the permeate concentration Cp at the time of the filtration experiment, and is an index of membrane separation performance. And Regarding the concentration of the feed solution and the concentration of the permeate, the α-alumina particle suspension was measured using a spectrophotometer (U-330, manufactured by Hitachi, Ltd.).
Using 0), the light transmittance at a wavelength of 400 nm was measured and determined. On the other hand, regarding the activated sludge solution, the solid content contained in a predetermined volume was filtered by a glass filter, dried, and then weighed to calculate.

Example 1 A non-woven fabric FC3105 having an asymmetric structure (manufactured by Japan Vilene Co., Ltd .; hereinafter, simply referred to as FC3105) was used as a separation membrane for water treatment. FC3105 is
It consists of a polyester fiber with a fiber diameter of 10 μm, a sheet-like support layer in which the fibers are bonded and heated and bonded together, and a polyester fiber with a fiber diameter of 5 to 10 μm,
A single dense layer which is supported by the support layer and is integrally formed on one surface of the support layer, in which fibers are densely arranged from the support layer and adhered to each other to make the average pore diameter smaller than that of the support layer. It is a nonwoven fabric with an asymmetric structure.

The basis weight is 535 g / m ² ,
The maximum pore size of the dense layer is 60 μm, and the minimum pore size is 0.1 μm
And the thickness of the entire nonwoven fabric is 1.78 mm. Table 1 shows the porosity, the average pore diameter, and the thickness of each layer of the dense layer and the support layer of the nonwoven fabric FC3105. Table 2 shows the pure water permeation rate.

Next, a normal cross-flow filtration evaluation apparatus was prepared using a non-woven fabric FC3105, and a single flat membrane filtration cell (effective membrane area: 37.6 cm ² ) was prepared and attached. Using activated sludge treatment wastewater collected at the Purification Center, temperature 20 ° C, operating pressure 2
Cross flow filtration was performed under the conditions of 0 KPa and a supply liquid flow rate of 5 L / hr. The activated sludge treatment wastewater used had an MLSS (Mixed Liquor Suspended Solid) concentration of 5,000 mg / liter and a particle size of 2 to 200 μm. Table 2 shows the permeation flux and the activated sludge rejection during filtration.

As shown in the results in Table 2, the nonwoven fabric FC31
05, the amount of permeated water of the activated sludge treatment wastewater is sufficient,
The rejection of the fine particles was extremely large, 0.95, and the mechanical strength was sufficient, so that it could be used stably for a long period of time. Further, the nonwoven fabric as the separation membrane for water treatment requires less chemical treatment than the polymer porous membrane and can be manufactured at low cost.

(Example 2) Felt B, which is a nonwoven fabric having an asymmetric structure, was used as a water treatment separation membrane. This felt B
Is implanted into a sheet-shaped polyester fiber woven fabric layer by needle punching, using a polyester-core, polyethylene-sheathed fiber having a core-sheath structure with a fiber diameter of 10 μm, and calendering one surface. The fibers are pressurized and fused to form a dense layer, which is an asymmetric structure. The basis weight is 849 g / m ² ,
The maximum pore diameter of the dense layer is 40 μm, the minimum pore diameter is 0.1 μm, and the thickness of the entire nonwoven fabric is 1.68 mm. Table 1 shows the porosity, the average pore diameter, and the thickness of each layer of the dense layer of felt B having an asymmetric structure. Table 2 shows the pure water permeation flux.

Cross-flow filtration (effective membrane area: 37.6 cm ² ) was carried out under the same conditions as in Example 1 using the activated sludge treatment wastewater used in Example 1 as a supply liquid. Table 2 shows the results
Shown in As shown in the results in Table 2, felt B has a sufficient permeation flux of the activated sludge treatment wastewater, a rejection of fine particles of 0.95, and a sufficiently high mechanical strength.
It could be used stably for a long time.

(Embodiment 3) Next, the production of a separation membrane for water treatment used in Embodiment 3 of the present invention will be described. To 100 parts by weight of a 8% by weight solution of cellulose triacetate (acetylation degree 55%, viscosity average polymerization degree 170) in methyl cellosolve (good solvent),
Cyclohexanol (poor solvent) with good stirring 23.
A dope solution was prepared by adding 8 parts by weight. The obtained dope solution was cast to a thickness of about 100 μm using a coater bar so as to cover the outer surface of the dense layer of felt B, and felt B coated with this dope solution was heated at 60 ° C. and 95 ° C.
Dry for 30 minutes under environmental conditions of% RH (relative humidity). Then, it is dried in a dryer at 80 ° C. for 6 hours to evaporate the solvent to cause microphase separation, and a so-called skinless structure without a thin film portion on the dense layer of felt B,
A thin film made of cellulose triacetate (hereinafter referred to as CTA) buried and buried was formed to obtain a separation membrane for water treatment. This is a thin film formation by a dry phase inversion method. The coating thickness of the separation membrane on the surface of the dense layer was about 3 μm, and the embedding thickness in the dense layer was about 10 μm. Table 2 shows various performances of the separation membrane measured by the performance test method. The bubble point in water was 150 KPa.

Next, using this separation membrane, an operating pressure of 0.2
kgf / cm ² , 500 rpm under stirring speed of 500 rpm
mg / liter of α-alumina particles (average particle diameter 0.5
μm, manufactured by Wako Pure Chemical Industries, Ltd.) and a batch type membrane separation device (capacity: 200 ml, effective membrane area: 2)
8 cm ² , manufactured by Amicon). Table 2 shows the permeation flux and the rejection of alumina particles during filtration.

This water treatment separation membrane has excellent separation performance and mechanical strength because a thin film composed of a specific polymer porous layer is formed on the dense layer of felt B. . In addition, the pure water permeation flux and permeation flux are sufficient, the rejection is extremely excellent, and the filter has stable filtration performance even during long-term operation.

(Embodiment 4) Next, the production of a separation membrane for water treatment used in Embodiment 4 of the present invention will be described. Acrylonitrile / N-vinylpyrrolidone copolymer (composition molar ratio 9
8: 2, 20 parts by weight of 3-methoxybutyl acetate (poor solvent) was added to 100 parts by weight of a 13% by weight solution of N, N-dimethylformamide (good solvent) manufactured by Daicel Chemical Industries, Ltd. with good stirring. Thus, a dope solution was prepared. A thin film of an acrylonitrile / N-vinylpyrrolidone copolymer (hereinafter, referred to as DUY) was formed on the dense layer of felt B used in Example 2 in the same manner as in Example 3 by using the obtained dope solution. A separation membrane for processing was obtained. Table 2 shows various performances of the separation membrane measured by the performance test method. The bubble point in water was 180 KPa.

Next, a filtration experiment of a suspension of α-alumina particles of 500 mg / liter was carried out in the same manner as in Example 3 using this separation membrane. Table 2 shows the results. FIGS. 1 and 2 show scanning electron micrographs of the separation membrane surface at a magnification of 100 times and 10,000 times, respectively.

(Embodiment 5) Next, the production of a separation membrane for water treatment used in Embodiment 5 of the present invention will be described. First, polymethyl methacrylate (Scientific Polymer Products
N, N-dimethylformamide (good solvent) 13
100 parts by weight of acetic acid 3
A dope solution was prepared by adding 20 parts by weight of -methoxybutyl (poor solvent). A thin film of polymethyl methacrylate (hereinafter referred to as PMMA) was formed from the obtained dope solution on the dense layer of felt B used in Example 2 in the same manner as in Example 3 to obtain a water-treated separation membrane. Table 2 shows various performances measured by the performance test method. The bubble point in water was 120 KPa.

Next, a filtration experiment of a 500 mg / liter α-alumina particle suspension was carried out in the same manner as in Example 3 using this separation membrane. Table 2 shows the results.

(Embodiment 6) Next, the production of a separation membrane for water treatment used in Embodiment 6 of the present invention will be described. First, using the same PMMA as in Example 4, this acetone (good solvent) 1
To 100 parts by weight of an 8% by weight solution,
90 parts by weight of propanol (poor solvent) was added to prepare a dope solution. A thin film was formed using the obtained dope solution on the dense layer of felt B used in Example 2 in the same manner as in Example 3 to obtain a separation membrane for water treatment. Table 2 shows various performances measured by the performance test method. The bubble point in water was 40 KPa.

Next, a filtration experiment of a 500 mg / liter α-alumina particle suspension was performed in the same manner as in Example 3 using this separation membrane. Table 2 shows the results.

(Example 7) Next, the production of a separation membrane for water treatment used in Example 7 of the present invention will be described. N, N- of polyethersulfone 4800P (manufactured by Sumitomo Chemical Co., Ltd.)
Dimethylformamide (good solvent) 16% by weight solution 10
To 0 parts by weight, 20 parts by weight of 3-methoxybutyl acetate (poor solvent) was added with good stirring to prepare a dope solution.
A thin film of polyethersulfone (hereinafter referred to as PES) was formed from the obtained dope solution on the dense layer of felt B used in Example 2 in the same manner as in Example 3 to obtain a water-treated separation membrane. Table 2 shows various performances measured by the performance test method. The underwater bubble point is 70KPa
Met.

Next, using this separation membrane, a filtration experiment of a 500 mg / liter α-alumina particle suspension was carried out in the same manner as in Example 3. Table 2 shows the results. FIGS. 3 and 4 show scanning electron micrographs of the separation membrane surface at a magnification of 500 times and 10,000 times, respectively.

(Comparative Example 1) Nonwoven fabric MF-180K which is not asymmetric as a water treatment separation membrane, that is, has no dense layer
(Manufactured by Japan Vilene Co., Ltd.) was used. This non-woven fabric MF-1
80K is made of polyester fiber having a fiber diameter of 10 μm, and the porosity, average pore diameter, and layer thickness are shown in Table 1. Table 2 shows the pure water permeation flux. Under the same method and conditions as in Example 1, a filtration experiment (effective membrane area: 37.6 cm ² ) of a 5,000 mg / liter activated sludge solution was performed. Table 2 shows the results. Both the permeation flux and the rejection are insufficient. As can be seen from the comparison between the filtration results of Comparative Example 1 and the filtration results of Example 1 described in Table 2, by setting the porosity, average pore diameter, and thickness of the dense layer of the nonwoven fabric to specific ranges of the present invention. For the first time, a sufficient flux and excellent rejection can be obtained.

(Comparative Example 2) The DUY dope used in Example 4 was formed on the nonwoven fabric MF-180K used in Comparative Example 1 in the same manner as in Example 4 to form a DUY thin film. I got Table 2 shows various performances of the separation membrane measured by the performance test method. The bubble point in water was 190 KPa. Example 3 using this separation membrane
In the same manner as described above, a filtration experiment was performed on a suspension of α-alumina particles at 500 mg / liter. Table 2 shows the results.
As can be seen from a comparison between Comparative Example 2 and Example 4, both the pure water permeation flux and the permeation flux are significantly low, the rejection is low, and both the permeation performance and the separation performance are poor. That is, it can be understood that the nonwoven fabric on which the thin film is formed can have excellent permeation performance and separation performance only when it has the asymmetric structure of the present invention.

(Comparative Example 3) A solution containing 16% by weight of DUY of N, N-dimethylformaldehyde used in Example 4 was coated on a polyester taffeta woven fabric TD220Y (manufactured by Toray Industries, Inc.) to a thickness of about 100 μm using a coater bar. After casting with a thickness, it was immersed in water to obtain a separation membrane for water treatment. This is a thin film formation by a wet phase inversion method. Table 2 shows various performances of the separation membrane measured by the performance test method. Further, since the bubble point in water was 1 MPa or more, measurement was impossible. Using this separation membrane, a filtration experiment of a 500 mg / liter α-alumina particle suspension was carried out in the same manner as in Example 3. Table 2 shows the results. In Comparative Example 3,
It can be seen that the average pore size of the thin film has been greatly reduced, and the water permeability has been significantly reduced.

[0080]

[Table 1]

[0081]

[Table 2]

[0082]

As described above, according to the present invention,
Using a non-woven fabric having a high mechanical strength with an asymmetric structure in which a dense layer is formed on one surface of the support layer, or forming a thin film on the outer surface of the dense layer of the non-woven fabric, particularly a specific porosity, average By forming a polymer porous layer made of a specific polymer having a pore size, film thickness, and a microphase separation structure, a high permeation flux is maintained and fine particles are separated at a high level. It is possible to obtain a separation membrane that can prevent the decrease in permeation flux, can suppress the decrease in permeation flux, has excellent mechanical strength, and has stable filtration performance even during long-term operation.

[Brief description of the drawings]

FIG. 1 is a 100 × scanning electron micrograph (drawing substitute photograph) showing the surface of a separation membrane for water treatment obtained in Example 4.
It is.

FIG. 2 is a scanning electron micrograph (substitute drawing) of 10,000 times showing the surface of the separation membrane for water treatment obtained in Example 4.

FIG. 3 is a scanning electron micrograph (magnification of a drawing) of 500 times showing the surface of the separation membrane for water treatment obtained in Example 7;
It is.

FIG. 4 is a scanning electron micrograph (a drawing substitute photograph) of 10,000 times showing the surface of the separation membrane for water treatment obtained in Example 7.

Claims (10)

[Claims] 1. A sheet-like support layer in which fibers are cross-collected and entangled and / or adhered to each other, and are integrally formed on one surface of the support layer supported by the support layer. A non-woven fabric having an asymmetric structure comprising a dense layer in which fibers are densely arranged and adhered to each other to have an average pore size smaller than that of a support layer. 2. The dense layer has a porosity of 30 to 80%, an average pore size of 0.2 to 30 μm, a thickness of 10 to 500 μm, and a total thickness of the nonwoven fabric of 30 to 5 mm.
The separation membrane for water treatment according to claim 1, wherein: 3. The pore diameter of the outer surface of the dense layer is 0.1 to 60 μm.
3. The separation membrane for water treatment according to claim 1, wherein the value is within the range of m. 4. The fiber constituting the nonwoven fabric has a fiber diameter of 0.
The separation membrane for water treatment according to any one of claims 1 to 3, wherein the separation membrane has a thickness of 5 to 30 µm. 5. The separation membrane for water treatment according to claim 1, wherein the fibers of the nonwoven fabric are made of polyester or polypropylene. 6. A non-woven fabric according to any one of claims 1 to 5, wherein a thin film made of a polymer porous layer at least partially embedded in the dense layer is provided on the surface of the dense layer. Separation membrane for water treatment. 7. A thin film formed by a phase inversion method, having a porosity of 20 to 90%, an average pore diameter of 0.1 to 20 μm, and a thickness of 0.5 to 200 μm. 7. The separation membrane for water treatment according to 6. 8. The separation membrane for water treatment according to claim 6, wherein the thin film is a skinless thin film. 9. The skinless thin film is formed of at least one selected from the group consisting of cellulose acetate derivatives, acrylonitrile polymers, acrylic polymers and aromatic sulfone polymers. The separation membrane for water treatment according to claim 8. 10. The bubble point of the thin film is 490.5
The separation membrane for water treatment according to any one of claims 6 to 9, wherein the separation membrane has a pressure of not more than KPa.