JPH0549877A - Production of composite filter membrane - Google Patents

Abstract

PURPOSE:To increase the membrane permeating flux at the time of filtering a raw fluid contg. suspended matter by using a composite filter membrane having an anisotropic structure. CONSTITUTION:A filter membrane forming liq. is cast over a continuously traveling support consisting of filter paper, nonwoven fabric, woven fabric and glass fiber through a casting coater to form a filter liq. membrane, the support is traveled so that the liq. membrane is brought into contact with the surface of a liq. coagulant to solidify the liq. membrane. Consequently, a composite filter membrane with the diameter of the hole of the filter membrane changed continuously or discontinuously in the membrane thickness direction and having an anisotropic structure in which the diameter of the hole on one surface of the precision filter membrane is different from that on the other surface is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a microfiltration membrane, and more particularly to a drug in the pharmaceutical industry, an alcoholic beverage in the food industry, an electronic device for fine processing including the above-mentioned manufacturing industry and semiconductor manufacturing industry. It is used for filtration of purified water, pure water, etc. for the production of ultrapure water used in industrial fields and laboratories of various industries, and other microfiltration, and fine particles and microorganisms of submicron order of 10 μm or less, especially 1 μm or less. The present invention relates to a microfiltration membrane that efficiently filters water. Microfiltration membranes obtained by the production method of the present invention, various polymers, microorganisms, yeast,
It can be applied to separation, purification, recovery, concentration, etc. of a liquid containing or suspending fine particles, and especially when it is necessary to separate the fine particles from a liquid containing fine fine particles that requires filtration. For example, it is also applied to separate fine particles from various suspensions containing fine particles, fermentation broth, culture solution, etc., as well as to separate fine particles from pigment suspension, and to remove clad from condensate of nuclear power generation. .. In addition, with the rapid development of biotechnology in recent years, production of biochemical substances by culture, fermentation, enzyme reaction, etc. has become popular in many fields such as pharmaceuticals, foods, and chemical products. Although the added value of these produced substances is increased by refining, the refining operation is currently expensive. The microfiltration membrane obtained by the production method of the present invention is particularly effective in these fields. For example, high-density culture is carried out by continuously removing a reaction-inhibiting substance from the culture broth, extracellular enzyme-producing bacteria. When the enzyme is used, the enzyme is continuously recovered, the enzyme is recovered from a solution obtained by crushing the intracellular enzyme-producing bacteria, and the enzyme is removed from the culture solution obtained in a batch method.

[0002]

2. Description of the Related Art Conventionally, as a technique for separating a suspended substance from a raw liquid containing a suspended substance using a membrane, for example, a reverse osmosis method using pressure as a driving force, an ultrafiltration method, a microfiltration method,
There are an electrodialysis method using a potential difference as a driving force, a diffusion dialysis method using a concentration difference as a driving force, and the like. These methods are capable of continuous operation, and can be separated, purified or concentrated without greatly changing the temperature and pH conditions during the separation operation, and particles,
A wide range of molecules, ions, etc. can be separated,
It is economical because it can keep the processing capacity of a small plant large, the energy required for the separation operation is small, and it is possible to process low concentration raw liquid that is difficult with other separation methods. There is. Furthermore, with the progress of biotechnology, high purity, high performance,
High precision is required, continuous operation is possible instead of conventional centrifugal separation and diatomaceous earth filtration, and large-scale processing is possible, and no addition of filter aid or coagulant is required.
Separation efficiency is independent of the difference in specific gravity between the cells and the suspension, a clear filtrate can be obtained regardless of the physical properties of the culture fluid and the type of cells, high-concentration culture is possible, and production efficiency is improved. The application field of microfiltration or ultrafiltration technology is expanding for the reasons that it is possible to do so, there is no leakage of bacteria, the cells can be washed after concentration, scale-up is easy and economical is high.

Membranes used in the above separation techniques include polymer membranes mainly composed of organic polymers such as cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone, polyacrylonitrile, polyamide and polyimide (for example, Japanese Patent Publication No. 48-40050, JP-A-58-37.
842, JP-A-58-91732, JP-A-56-1.
No. 54051) and porous ceramic membranes having excellent durability such as heat resistance and chemical resistance. When mainly filtering colloid, an ultrafiltration membrane is used, In microfiltration intended for filtration, a microfiltration membrane having suitable micropores is used. Such a microfiltration membrane has a so-called isotropic membrane in which the pore size of the micropores existing therein does not substantially change and the pore sizes on both surfaces of the membrane do not substantially change, and the pore size in the film thickness direction is It is classified as having a structure called a so-called anisotropic film, which changes continuously or discontinuously, and the pore size of one surface of the membrane is different from the pore size of the other surface. Among these, the isotropic membrane is
As described in JP-A-58-98015, the entire membrane exhibits a large resistance to the flow of fluid during filtration, and only a small flow velocity can be obtained (that is, per unit area,
Only a small flow rate can be obtained per unit time and unit differential pressure), and there are drawbacks such as easy clogging, short filtration life, and no blocking resistance. On the other hand, an anisotropic film has a layer having a small pore size, which is called a dense layer described in JP-B-55-6406 and JP-A-56-154051, on one surface of the film or inside the film, and It has large holes or extremely large finger voids from the inside of the membrane to the other surface. Suspended substances are trapped on the surface of the microporous membrane when using an isotropic membrane or when the raw liquid is supplied to the side of the anisotropic membrane with a smaller pore size, while the suspended material is trapped on the side of the anisotropic membrane with a larger pore size. When supplying a liquid, the suspended matter is trapped inside the microporous membrane. That is, when the suspended substance is blocked on the surface of the microfiltration membrane, the suspended substance becomes a very large filtration resistance and the permeation flow velocity is rapidly reduced, resulting in a decrease in the total filtration amount. Is a so-called anisotropic membrane having a structure in which the pore size changes continuously or discontinuously in the film thickness direction so that the pore size on one surface of the microfiltration membrane and the pore size on the other side are different from each other on the raw liquid side. When used for the purpose, suspended substances can be prevented inside the microfiltration membrane, and thus a large total filtration amount can be obtained.

[0004]

As described above, the microfiltration membrane has a structure in which the pore size changes continuously or discontinuously in the film thickness direction, and the pore size on one surface of the microfiltration membrane and the pore size of the other differ from each other. By using the so-called anisotropic membrane having a large surface pore size facing the raw liquid side, it is possible to prevent suspended substances inside the microfiltration membrane and obtain a large total filtration amount. However, when the concentration of the compressive suspended substance is very high, such as the fermentation broth or the culture medium, it is necessary to disperse the suspended substance in a large amount and evenly in the fault direction inside the membrane. There was a problem that a sufficiently high permeation flux could not be obtained only with an anisotropic membrane. Further, when backwashing is performed periodically, a large load is applied to the filtration membrane during backwashing, and when the strength of the filtration membrane is weak, cracks occur in the filtration membrane. In order to solve these problems, it has hitherto been attempted to form a filtration membrane on a support such as a filter paper or a nonwoven fabric to increase the strength of the filtration membrane or to enhance the trapping effect with the filter paper or the nonwoven fabric. The method for integrating the filtration membrane and the non-woven fabric, etc. may be carried out by dot-shaped or linear adhesive bonding or heat-sealing, but when the filtration membrane is formed as in JP-B-45-13931. It is more effective to cast the undiluted solution of the filtration membrane directly onto a non-woven fabric or the like to form a porous structure in a state where the filtration membrane partially penetrates into the non-woven fabric or the like. However, when the filtration membrane has an isotropic structure, the above composite filtration membrane can be obtained relatively easily, but when a filter paper or a non-woven fabric is formed on the side of the anisotropic membrane having a large pore size, the composite membrane is not formed at the interface with the non-woven fabric. Since a dense layer having a small pore size was formed, a continuous anisotropic structure was not obtained, and as a result, the sufficient effect of the anisotropic film was not obtained.

[0005]

The present invention has been made in order to solve the above-mentioned problems in the prior art, and has a high trapping property of suspended substances, that is, a high permeation flux and a high strength. It is an object of the present invention to provide a novel membrane forming technology of a high filtration membrane. Hereinafter, the present invention will be described in detail.
The composite filtration membrane of the present invention has a composite structure in which a microfiltration membrane and filter paper, non-woven fabric, woven fabric or glass fiber are integrated, and by making the non-woven fabric side the undiluted solution side, the trapping property of the suspended substance and backwashing Cleanability is enhanced. In particular, when the particle size distribution of the suspended substance is wide, a large suspended substance is trapped inside the nonwoven fabric and a small suspended substance is trapped inside the porous filtration membrane, which is very effective. A general method for producing a composite filtration membrane is prepared by casting a stock solution of a filtration membrane on a support through a casting coater, and then immersing it in a coagulation bath filled with a poor solvent for the polymer. In the case of a film-forming method in which a filtration membrane stock solution is cast on a support such as a non-woven fabric, when forming an isotropic membrane, it does not affect the structure of the filtration membrane even if it is cast on the support and then immersed in a coagulation solution. However, when forming an anisotropic membrane, dipping in a coagulation liquid affects the filtration membrane structure. That is, the anisotropy of the filtration membrane is such that, in the process of being immersed in the coagulation liquid, the diameter of the pores on the side where the cast filtration liquid film comes into contact with the coagulation liquid, that is, the side where the coagulation liquid penetrates is small, and the anisotropy of the coagulation liquid penetrates in the depth direction. The pore size gradually increases. Conventionally, the filtration membrane stock solution was cast on a glass plate or a plain film, but in the method of casting the filtration membrane stock solution on the filter paper, the nonwoven fabric, the woven fabric, and the glass fiber of the present invention, from the support side when immersed in the coagulating solution. Also, since the coagulation liquid invades, a dense layer having the smallest pore size is formed at two locations on the interface between the surface of the filtration membrane and the support. That is, not only the effect of the anisotropic membrane disappears, but also the pure water permeation flux of the composite filtration membrane extremely decreases.

The membrane forming method of the present invention is characterized in that, when the filtrate film is coagulated with the coagulating liquid, the coagulating liquid does not enter from the support side but only from the filtrate film side. That is, it can be achieved by casting a filter membrane stock solution on filter paper, a non-woven fabric, a woven fabric and glass fiber, and then transporting the solution with the filter membrane stock solution side in contact with the coagulation solution. The coagulation time varies depending on the types of the filtration membrane stock solution and the coagulation solution, but basically, the filtration membrane stock solution may coagulate, and is generally 10 seconds or more, preferably 30 seconds or more. The filter paper, the non-woven fabric, the woven fabric or the glass fiber of the support used in the present invention has different ability to prevent suspended substances depending on the thickness, porosity and thickness of the fibers forming them. That is, the thinner the fiber and the lower the porosity, the finer suspended substances can be blocked, and the thicker the fiber, the more suspended substances can be blocked. The thickness of the fiber correlates with the surface pore size of the filtration membrane with which the non-woven fabric or the like contacts. That is, it is preferable that the substantial pore size of the non-woven fabric or the like is substantially the same as or slightly larger than the surface pore size of the filtration membrane with which the non-woven fabric or the like contacts. The thickness of the fibers of the non-woven fabric or the like so that the pore size becomes substantially continuous at the interface between the filtration membrane and the non-woven fabric is 0.5 times or more and 5 times or less the pore size of the filtration membrane surface. That is, when the average pore diameter on the surface of the filtration membrane is 2 μm, the fiber thickness of the nonwoven fabric or the like is preferably 1 μm or more and 5 μm or less. If the porosity of the non-woven fabric is extremely low, the filtration resistance becomes large, and if it is too high, the suspended solids are not blocked. Therefore, it is usually preferably 50% or more and 90% or less, more preferably 60% or more and 75% or less. .. Further, if the thickness of the non-woven fabric or the like is thin, the effect of trapping suspended matter cannot be obtained, and it is preferably 1/2 or more of the thickness of the filtration membrane. The material of the non-woven fabric is not particularly limited, but generally polyester, polypropylene, polyamide, stainless steel or the like is used.

The film-forming polymer used in the present invention can be selected depending on the application of the porous film and other purposes. Examples of such polymers include cellulose acetate, nitrocellulose, polysulfone, sulfonated polysulfone, polyether sulfone, polyacrylonitrile, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, saponified ethylene-vinyl acetate copolymer, polyvinyl alcohol, polycarbonate, and organo. Examples thereof include siloxane-polycarbonate copolymer, polyester carbonate, organopolysiloxane, polyphenylene oxide, polyamide, polyimide, polyamideimide, and polybenzimidazole.

Inorganic electrolytes, organic electrolytes, polymers or their electrolytes called swelling agents for controlling the porous structure are polyvinylpyrrolidone, sodium chloride, lithium chloride, sodium nitrate, potassium nitrate, sodium sulfate, zinc chloride. Inorganic acid metal salts such as, sodium acetate, sodium formate and other organic acid metal salts, polyethylene glycol, polyvinylpyrrolidone and other polymers, sodium polystyrene sulfonate, polyvinylbenzyltrimethylammonium chloride and other polymer electrolytes, dioctylsulfosuccinic acid Sodium, a good solvent for the film-forming polymer that can include ionic surfactants such as sodium alkylmethyl taurate, is usually a solvent for the film-forming polymer, and is rapidly mixed with the coagulating liquid when immersed in the coagulating liquid. Will be replaced The are used can be selected depending on the kind of the film forming polymer. When the film-forming polymer is polysulfone, N-methyl-2-pyrrolidone, dioxane, tetrahydrofuran, dimethylformamide, dimethylacetamide or a mixed solvent thereof is suitable, and when polyacrylonitrile is used, dioxane, N-
Methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, etc., in the case of polyamide, dimethylformamide, dimethylacetamide, etc .; in the case of cellulose acetate, acetone,
Dioxane, tetrahydrofuran, N-methyl-2-pyrrolidone and the like are suitable.

Examples of the non-solvent in the present invention include water, cellosolves, methanol, ethanol, propanol, acetone, tetrahydrofuran, polyethylene glycol, glycerin and the like. The polymer concentration of the stock solution for film formation is 5% by weight or more and 35% by weight or less, preferably 10% by weight or more and 30% by weight or less. If it exceeds 35% by weight, the water permeability of the obtained microfiltration membrane is so small as to have no practical meaning, and if the concentration is lower than 5% by weight, a microfiltration membrane having a sufficient separation function cannot be obtained. Further, the addition amount of the swelling agent is not particularly limited as long as the uniformity of the stock solution for film formation is not lost by the addition, but it is usually 0.5% by volume or more and 10% by volume or less with respect to the solvent. The ratio of the non-solvent to the good solvent may be any range as long as the mixed solution can maintain a uniform state, but is preferably 5% by weight or more and 50% by weight or less. As the coagulation bath, water, alcohols such as methanol, ethanol and butanol are used. Any glycol ether such as ethylene glycol and diethylene glycol, aliphatic hydrocarbons such as n-hexane and n-heptane, and glycerols such as glycerin can be used as long as they do not dissolve the polymer. Preferred is water, alcohols or a mixed liquid of two or more kinds of these liquids.

Next, a method for producing the composite filtration membrane of the present invention will be described with reference to the drawings. FIG. 1 shows a conventional film forming machine in which a stock solution of a filtration membrane is cast on a support and immersed in a coagulating liquid, and the coagulating liquid enters from both the liquid film side and the support side. Therefore, the completed filtration membrane has a dense layer on both the liquid membrane side surface and the support side. FIG. 2 shows the manufacturing method of the present invention.
The coagulation liquid enters and coagulates only from the liquid film side. for that reason,
The completed filtration membrane has a dense layer on the liquid membrane side, and a so-called anisotropic membrane whose pore size increases toward the support side is formed in a form integrated with the support.

[0011]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto. Example 1 15 parts of polysulfone (P3500 manufactured by Amoco), 15 parts of polyvinylpyrrolidone and 3 parts of water are dissolved in 67 parts of N-methyl-2-pyrrolidone to obtain a stock solution for film formation. A polypropylene non-woven fabric having a porosity of 70% and a thickness of 150 μm that was continuously run was cast with a liquid film thickness of 180 μm through a casting coater, and the liquid film surface was cast at 25 ° C. and a relative humidity of 45.
% Of air was applied at 2 m / sec for 5 seconds, and immediately thereafter, it was conveyed for about 60 seconds so that the liquid film was in contact with the water surface of the coagulating liquid tank filled with water. The obtained composite filtration membrane had an anisotropic structure, the pore size gradually increased from the surface, and it was bonded to the nonwoven fabric, and the average pore size was 2.0 μm. Comparative Example 1 Under the same conditions as in Example 1, the film was conveyed while being immersed in a coagulation bath to form a filtration membrane. The obtained composite filtration membrane has a dense layer on the surface and the interface with the non-woven fabric, and has an average pore diameter of 0.5.
became μm. The average pore size shown here is ASTM-
It is measured by the 316-80 method.

[0012]

INDUSTRIAL APPLICABILITY According to the present invention, a composite filtration membrane having an anisotropic structure can be easily obtained, and by using it, a high membrane permeation flux can be obtained, whereby liquids containing various suspended substances can be obtained. Separation, recovery, purification, concentration, etc. of each suspension component are performed very efficiently and economically. Further, the process can be continued and the device can be downsized, and the selectivity of the membrane can be used to continuously and selectively separate only the target substance, which can be applied to bioreactors such as yeast and cells. It can be applied and has various effects such as easier operation management than the conventional technology.

[Brief description of drawings]

FIG. 1 shows a conventional film forming machine immersed in a coagulating liquid.

FIG. 2 shows a film forming machine of the present invention.

[Explanation of symbols]

 1 Filtration Membrane Undiluted Liquid 2 Support Feeding Roll 3 Casting Gisers 4 Coagulation Liquid Tank 5 Coagulation Liquid 6 Coagulation Liquid Penetration Direction 7 Coagulation Liquid Surface 8 Composite Filtration Film Transport Direction 9 Filtration Liquid Membrane 10 Support 11 Nonwoven Part Cross Section 12 Different Partial cross section of isotropic film 13 Partial cross section of dense layer

Claims (3)

[Claims] 1. A filtration membrane stock solution is cast on a continuously running support through a casting coater to form a filtration fluid film, and the liquid membrane is conveyed so as to be in contact with the surface of the coagulation liquid to coagulate the liquid film. A method for producing a composite filtration membrane, comprising: 2. The composite filtration membrane according to claim 1, wherein the support is a filter paper, a non-woven fabric, a woven fabric or glass fiber, and a part of the liquid membrane impregnates the support. Production method. 3. The filtration membrane has a pore size which continuously or discontinuously changes in the film thickness direction, has an anisotropic structure in which one surface pore diameter of the microfiltration membrane and the other surface pore diameter are different, The method for producing a composite filtration membrane according to claim 1, wherein a non-woven fabric, a woven fabric, or a glass fiber is present on the side having a large pore diameter.