JPS61118106A - Production of anisotropic filtering membrane - Google Patents

Abstract

PURPOSE:To increase the anisotropy of a filtering membrane suitable for the selective filter such as the precision filter and the ultrafiltration by bringing preliminarily a nonsolvent, a bad solvent or a swelling agent of specified quantity into contact with a side part of supporting base material of a membrane and thereafter forming it into the membrane by a wet process. CONSTITUTION:A nonsolvent, a bad solvent or a swelling agent of a polymer forming a membrane is preliminarily imparted on a supporting base material such as metal, glass, plastics, paper, woven cloth and nonwoven fabric by means of the coating, the immersion or the spraying. A membrane is formed on the supporting body by a wet process by using a membrane-formable polymer of 5-30wt% concn. a coagulating liquid which nondissolves practically the membrane-formable polymer and is excellently mixable with the used solvent is adopted and the supporting body is immersed therein 0-80 deg.C temp. for about 30sec-5min.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention provides an improved method for producing an anisotropic filtration membrane suitable for selective permeation such as precision filtration or ultrafiltration for filtering microparticles. It is related to.

The anisotropic filtration membrane produced according to the present invention is used in industry for clarification filtration, stabilizing sterilization of liquid foods such as beer, wine, sake, and juice, air purification, sterilization of pharmaceutical products, protein filtration, and microbial filtration. It is used in various fields such as detection, analysis, inspection of industrial and domestic wastewater, and removal of pyrogens (heating factors).
It is expected to have excellent effects.

(Prior Art) As permeable membranes used for the above-mentioned purposes, various polymers having the property of forming a thin film having a network structure have been used, but in general, the selectivity of particle filtration of these permeable membranes is determined by is the pore with the smallest diameter on the surface of the membrane, and microscopically the pore diameter of the surface layer of the membrane is almost the same as the pore diameter of the supporting layer that supports it. Alternatively, they were called symmetric membranes, and those in which the pore diameter on the surface layer was smaller than the pore diameter in the support layer were distinguished by being called anisotropic or asymmetric membranes.

Generally, in order to reduce the resistance to fluid flow and obtain a high filtration rate, it is advantageous to have a thinner minimum pore size layer, so anisotropic membranes are considered to be superior in terms of filtration rate. has been done.

Traditionally, this anisotropic film has been produced using a wet method (called "wet method"), in which the film is cast to a uniform thickness onto a support base material, and after an evaporation process is performed as necessary, the support base material is coated with a coagulating liquid. The method consisted of the steps of immersing the membrane in the membrane to diffuse the coagulation liquid into the membrane, and then peeling off the formed membrane from the supporting substrate or using it as it is.

During this immersion, only the surface of the cast dope film on the side opposite to the supporting substrate comes into contact with the coagulation liquid, but a surface layer with small pores is first formed on that surface. It is explained that inside the surface layer, pores with a coarse pore size are formed by contact with the coagulating liquid that has sequentially diffused from the surface layer.

(Problem to be solved by the invention)
However, these conventional methods for producing anisotropic permeable membranes may not provide sufficient anisotropy, and in order to increase this anisotropy, the ratio of nonsolvent to polymer solution must be increased to just before phase separation. It is known, for example, from JP-A-56-154051, that the dope becomes extremely unstable and good results cannot be expected. Furthermore, for the purpose of adjusting the diffusion rate of the coagulating liquid into the film, there is a method in which several percent of the same type of solvent used for dope preparation is added to the coagulating liquid in advance, for example, as described in JP-A No. 59. Although it has been proposed in the specification of No. 80305, no good results were obtained in the limited trials.

[Structure of the invention]

(Means and effects for solving the problems) The present invention was proposed for the purpose of overcoming the above-mentioned technical difficulties in manufacturing an anisotropic permeable membrane by a wet method, and the details thereof are as follows. The following is a general explanation: In other words, the mechanism for generating anisotropy in a permeable membrane by the conventional wet method is as described above. As a result of various experiments, we came up with the idea that if a non-solvent, a poor solvent, or a swelling agent is brought into contact with the material and then immersed in the conventional method, the pore diameter of that area would change. , ■ The amount of non-solvent, poor solvent, or swelling agent that gives the maximum pore size value to the membrane portion on the supporting base material side varies depending on the composition of the dope and the type of non-solvent, poor solvent, or swelling agent used. ■When a dope of a certain composition is cast onto a support base material, the membrane pore diameter on the side in contact with the support base material changes depending on the amount of non-solvent, poor solvent, or swelling agent applied onto the support base material. It has been found that there is a tendency that maximum pore size values can be obtained at a constant application amount. This knowledge had not been known to anyone in the past.

Here, the supporting substrate used in the present invention is the same as in the case of the conventional wet method, and for example, metal, glass, plastic, paper, etc. in the form of a plate, film, or tube with a smooth surface are used. Alternatively, porous materials such as woven fabrics and non-woven fabrics can also be used. Adding a non-solvent, poor solvent or swelling agent to the material in advance means that coating, impregnation, spraying, adsorption, dew condensation, etc. This means that it is added by means.

The film-forming polymer that can be used in the present invention is polyacrylonide* similar to that used in conventional wet methods.
※※You can choose from among Ryl, polysulfone, polyethersulfone, acetyl cellulose, polyamide, polyimide, polyvinyl alcohol, polyvinylidene fluoride, polyvinyl chloride, regenerated cellulose, etc.

(Note) * indicates repeating unit. ※※ is repeating unit: It is a compound of

Dimethylformamide, dimethylacetamide, N-methyl-2-
It is appropriately selected from among pyrrolidone, dimethyl sulfoxide, methylene chloride, cyclohexanone, acetone, etc. depending on the type of polymer.

The concentration of the film-forming polymer dissolved in the solvent is usually 5 to 3.
It is 0% by weight, preferably 8 to 15% by weight; if this concentration is too high, the water permeability of the resulting membrane will be low, while if the concentration is too low, a membrane with sufficient strength will not be obtained.

The conditions for the coagulating liquid used in the present invention are such that it does not substantially dissolve the film-forming polymer and has good miscibility with the solvent used. The coagulating liquid may be different or the same type of liquid, but in practice water is most commonly used.

In summary, in addition to the above-mentioned new findings (1) and (2), the present invention provides the following advantages: Preferably, (1) a method of applying water by placing the support base material in an environment of constant humidity and allowing it to absorb moisture is suitable for controlling the amount of water applied, and (2) it is preferable that the support base material is a hydrophilic polymer material. This was achieved through knowledge.

Immersion of supporting base Murakami's dope in water as a coagulating solution is 0
It is sufficient to sufficiently diffuse water into the membrane at a temperature of ~80°C for about 30 seconds to 5 minutes, and after that, it can be thoroughly washed and stored in water, or completely dried and stored, and used when necessary. do.

Example 1 A dope at 30°C consisting of 10 parts by weight of polyether sulfone, 32 parts by weight of dimethyl sulfoxide and 58 parts of polyoxyethylene octylphenol ether was hygroscopically absorbed in advance at a temperature of 30°C in an atmosphere of relative humidity (RH) of 58%. The mixture was poured onto a vinylon film as a supporting base material having a ratio of 9%, and was smoothed to a uniform thickness using a glass rod on its side.

Next, after weighing in an atmosphere at a temperature of 30°C for 3 minutes, the Nivinylon film was immersed in water at 30°C to solidify. After further immersion for 5 minutes, the vinylon film was peeled off, washed with water, and dried.

Example 2 Tracing paper as a support substrate has a moisture absorption rate of 9% in an atmosphere with a temperature of 30°C and a relative humidity of 65°C.
And so. A dope having the same composition as in Example 1 was cast onto this tracing paper, and treated in the same manner as in Example 1.

Example 3 A support base made of a dope at 30°C consisting of 10 parts by weight of polyether sulfone, 60 parts by weight of dimethyl sulfoxide and 30 parts of diethylene glycol with a moisture absorption rate of 10% in an atmosphere at a temperature of 30°C and a relative humidity of 65%. The mixture was poured onto a vinylon film as a material and treated in the same manner as in Example 1.

The pore sizes on the surface layer and the support layer supporting it obtained in Examples 1 to 3 above were treated in the same manner as in the example after the support substrate had previously absorbed moisture under the conditions specified separately. The pore diameters obtained are shown below as a comparative example.

However, the dope compositions of Comparative Examples 1 to 4 are the same as Example 1, and the dope compositions of Comparative Examples 5 and 6 are the same as Example 3.

Table (Effects of the Invention) From the results shown in the table above, in the case of the dope compositions used in Examples and Comparative Examples, the amount of water that should be applied in advance as a non-solvent to the supporting substrate is determined by the moisture absorption rate. It was confirmed that only in a narrow range of about 9 to 10 inches, the pore size in the supporting layer is larger than that on the surface layer. As explained at the beginning, permeable membranes are expected to exhibit excellent furnace-specific performance in various industrial fields.

(Percentage applicant: Kurashiki Boseki Co., Ltd.) (Agent: Patent attorney Yasu Kasuya)

Claims (1)

[Claims] 1. A wet method in which a permeable film-forming polymer is dissolved in a solvent and cast to a uniform thickness onto a support base material, and the support base material is immersed in a coagulation liquid for a certain period of time. A method for producing an anisotropic filtration membrane, which comprises applying a non-solvent, a poor solvent, or a swelling agent in advance to the surface of a supporting base material that comes into contact with the polymer solution. 2. The method for producing an anisotropic filtration membrane according to claim 1, wherein the permeable membrane-forming polymer is polysulfone or polyethersulfone. 3. Claims 1 and 3, characterized in that the non-solvent, poor solvent or swelling agent that is applied in advance to the surface of the supporting base material that will come into contact with the polymer solution is water together with the coagulating liquid that is subsequently immersed. 2. A method for producing an anisotropic filtration membrane according to item 2. 4. Claim 1, characterized in that the water applied in advance to the supporting base material is based on moisture absorption from the air, and the supporting base material is made of a hydrophilic polymer.
, the method for producing an anisotropic filtration membrane according to items 2 and 3. 5. Anisotropy according to claims 1, 2, 3, and 4, wherein the supporting base material is a sheet-like material of a hydrophilic polymer containing polyvinyl alcohol, cellulose polymer, etc. Manufacturing method of filtration membrane.