JPS5857963B2 - Manufacturing method of composite permeable membrane - Google Patents

Description

[Detailed description of the invention] The present invention relates to a composite permeable membrane.

In recent years, separation treatment of solutions, emulsions, etc. using permeable membranes has come into practical use in various fields.

It is desirable for such permeable membranes to have high permeability to solvents and dispersion media, high blocking properties to specific substances, as well as excellent pressure resistance, chemical resistance, and stain resistance. It is difficult to provide a permeable membrane formed by coalescence with all of these desirable physical properties.

In order to solve these problems, it has been proposed to form a composite permeable membrane with a multilayer structure consisting of layers of different types of polymers having different physical properties so as to have desirable physical properties.

However, a film-forming solution containing one kind of polymer is first applied onto a substrate such as a glass plate or a stainless steel tube, and then a film-forming solution containing a different kind of polymer is applied thereon. According to the method, since the lower film-forming liquid layer has high fluidity,
The film-forming solution may diffuse into each other, or uneven coating may occur.
It is difficult to apply two types of film-forming solutions onto a substrate as layers of substantially uniform thickness.

Therefore, conventionally, a composite permeable membrane with a multilayer structure consisting of layers of different types of polymers has been produced by bonding another dry membrane made of a different type of polymer onto a previously produced dry membrane made of one type of polymer, or Alternatively, it is manufactured by applying a film-forming liquid containing a different type of polymer onto one dry film and forming a film.

However, according to the former method, the adhesive layer interposed between the two types of membranes blocks the pores of the permeable membrane, reducing water permeability, and according to the latter method, the membrane forming solution Because it dissolves the underlying permeable membrane or invades and blocks the micropores,
There is a problem of decreasing water permeability.

In order to solve this problem, a casting bob with a special structure is used to simultaneously apply a layer of two or more film-forming solutions containing different polymers onto the inner surface of a cylindrical tube with sufficient strength. , a method of configuring a membrane module is proposed in Japanese Patent Laid-Open No. 156778/1983.

However, this method cannot essentially be applied to sheet-like substrates, and the problems in the sequential application of the film-forming liquid described above remain unsolved.

That is, as long as metal pipes or synthetic resin pipes are used as the base material,
When the film-forming liquid is applied sequentially, the lower layer of the film-forming liquid flows, causing diffusion and uneven coating between the film-forming liquids, making it difficult to coat each layer with a uniform thickness. However, it is difficult to obtain a composite permeable membrane having uniform physical properties over the membrane mass.

In order to solve the various problems mentioned above, the present inventors
As a result of extensive research, we found that by using a fibrous porous base material, the membrane-forming liquid applied first forms a stable layer on the base material that does not substantially flow. We discovered that by applying the No. 20 membrane-forming solution to a membrane and forming a membrane, it is possible to obtain a composite permeable membrane in which different types of polymers form a multilayer structure with each layer having a substantially uniform thickness. This led to an invention.

That is, the composite permeable membrane according to the present invention is produced by coating and impregnating a fibrous porous base material with a membrane-forming solution containing a type of polymer, so that the membrane-forming solution does not substantially flow into the base material. A first layer of a stable film-forming solution is formed, and then a second layer is formed by coating a film-forming solution containing a different type of polymer on top of the first layer, and then a coagulation solvent is applied. It is characterized in that it is immersed and formed into a film to form a two-layer structure of substantially uniform thickness using different polymers.

That is, an important feature of the present invention is that by applying and impregnating a highly fluid membrane-forming liquid onto a fibrous porous base material and allowing at least a portion of the membrane-forming liquid to penetrate into the structure of the base material. The method consists of stably fixing the polymer solution in a layer, and then casting or spraying a different kind of polymer solution on top of the fixed polymer solution layer.

Therefore, in order to obtain a membrane having a desired thickness and porosity, the concentration and viscosity of the membrane-forming liquid are appropriately selected, and furthermore, in order to stably fix the first membrane-forming liquid to the fibrous base material, It goes without saying that physical properties such as porosity, thickness, and permeability of the base material should also be considered.

The fibrous porous base material used in the present invention is preferably a woven fabric or non-woven fabric made of polyethylene, polypropylene, polyvinyl chloride, polyester, etc., but also various natural fiber woven fabrics, glass fiber fabrics, carbon Fiber cloth etc. can also be used.

The shape of such a base material is preferably sheet-like or tubular, and sheet-like and tubular composite permeable membranes can be obtained from each of the squares.

The polymer used as a film-forming substance in the present invention is not particularly limited as long as it has film-forming ability.

Cellulose organic acid esters such as cellulose acetate, polysulfone, polyethersulfone, polyvinyl chloride, polyacrylonitrile, polyvinyl alcohol, ethylene-
An appropriate polymer is selected from polymers conventionally used for producing permeable membranes, such as saponified vinyl acetate copolymer, polyamide, and polyimide, depending on the required physical properties of the membrane.

For example, in order to improve compression resistance, polysulfone, polyethersulfone, etc. are selected as the polymer forming the first layer of the membrane forming solution.

Specifically, for example, "polysulfone known as Needel P3500J (Union Carbide Corporation)"
Polyether sulfone 200P (manufactured by 1, C, I, Inc.) and the like are suitable.

Moreover, in order to improve organic solvent resistance, polyimide, polyimide amide, polyamide, etc. are selected as the first layer.

Usually, the viscosity of the film-forming liquid used to form the first layer is preferably in the range of 50 to 1000 poise, but it is not necessarily limited to this range and depends on the type of substrate. It may have a wider range of viscosities.

Moreover, the thickness of the first layer after film formation is preferably 50 μm or less.

This is because if the thickness exceeds 50μ, it may become difficult to stably fix the first layer to the base material.

There are no particular restrictions on the film-forming liquid for forming the second layer, as long as it can be applied uniformly onto the first layer stably fixed on the fibrous base material.

For example, a film-forming liquid with a viscosity of 10 to 1000 poise can be uniformly applied using a roll coater, knife coater, etc.

Even a film-forming liquid with a viscosity of several poise can be uniformly applied using a gravure coater, spraying, etc.

The film forming solution is prepared according to a conventional method.

That is, a suitable selected polymer is dissolved in an organic solvent or an aqueous organic solvent.

If necessary, a film forming solution may be prepared by uniformly dissolving an inorganic swelling agent such as lithium chloride or lithium nitrate or an organic swelling agent such as ethylene glycol or glycerin in a solvent together with the polymer.

The solvent is also not particularly limited.

For example, one or a mixture of two or more of acetone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, formamide, aliphatic lower alcohol, a mixed solvent of these and water, etc. are used as appropriate.

Note that the solvent in the first film-forming liquid layer and the solvent in the twenty-th film-forming liquid layer may be the same or different.

When a membrane-forming liquid is applied and impregnated onto a fibrous porous substrate, the membrane-forming liquid forms a stable first layer that does not substantially flow.

This fixes the film-forming liquid to the base material.

Therefore, even if a film-forming solution containing a different type of polymer is immediately applied onto this first layer, diffusion of the film-forming solutions into each other may occur in a limited area at the interface. , which does not occur throughout the film-forming solution, unexpectedly allows a second layer that is clearly distinguishable from the first layer to be formed on the substrate with a uniform thickness.

By immersing the base material coated with film-forming liquids containing different polymers in layers in water or a coagulating solvent mainly composed of water, the above-mentioned two methods can be applied in the process of coagulating the polymer. The layer structure is preserved, thus forming a membrane structure consisting of two layers of different polymers.

Incidentally, the membrane forming liquid may be applied in two layers, and after partially evaporating the solvent from the membrane forming liquid, the membrane forming liquid may be immersed in a coagulating solvent.

Furthermore, before forming the first film-forming liquid layer on the base material, the base material is impregnated with water or an appropriate organic solvent in advance to adjust the amount of impregnation of the base material with the first film-forming liquid. , it is also possible to increase the water permeation rate of the resulting permeable membrane.

As described above, according to the method of the present invention, two types of membrane-forming liquids containing different types of polymers are applied in directly overlapping layers to create a two-layer structure in which each layer has a substantially uniform thickness. The membrane can be integrally formed.

Therefore, unlike methods such as bonding two types of dry membranes with adhesive or casting a membrane-forming solution on dry membranes, the membrane's micropores are not clogged, and polysulfone and polyethersulfone Since the dry film is not attacked by organic solvents,
Not only does the resulting composite permeable membrane have high water permeability, but by appropriately selecting the polymer, it is possible to design a membrane that provides desired physical properties.

Furthermore, the production of the composite permeable membrane according to the present invention does not require any special equipment or instruments, and has the advantage that it can be equally applied to sheet-like substrates and tubular substrates.

Examples are given below, but the present invention is not limited thereto.

In addition, parts indicate parts by weight. Example 1 17 parts of polysulfone "Needel P3500J (manufactured by Union Carbide) was added to a mixed solvent consisting of 50 parts of N-N-dimethylacetamide and 33 parts of dimethyl sulfoxide, and dissolved by heating to a temperature of 60 ° C. Film forming solution (
A) (viscosity 100 poise/25°C) was prepared.

Separately, add saponified ethylene-vinyl acetate copolymer (vinyl acetate content 70 mol%, degree of saponification 99% or more, molecular weight approximately 4.
0000) was added and dissolved by heating to a temperature of 80°C to prepare a film forming solution (B) (viscosity: 30 poise/20°C).

The above film-forming solution (4) was applied onto the polyester woven fabric "Polyester Gose" (manufactured by Toshi Co., Ltd.) using a roll gap 15.
Immediately after coating at a roll gap of 0μ, the above film-forming liquid layer was coated thereon at a roll gap of 200μ.

Next, this woven fabric was immersed in O'G water for 2 hours to form a film.

FIG. 1 shows an electron micrograph (100x magnification) showing the cross-sectional structure of the composite permeable membrane thus obtained.

Obviously, the first layer, polysulfone, forms a matrix layer of fibers on the surface layer of the fiber base material, forming a film.
The saponified ethylene-vinyl acetate copolymer, which is the second layer, is formed into a layered film on the first layer.

Further, a dense skin layer is formed on the surface of the second layer film.

Example 2 Cellulose acetate (398-6 manufactured by Eastman Kodak) in a mixed solvent of 45 parts of acetone and 30 parts of formamide
Add 25 parts of film forming solution (C) and heat to 30°C.
A viscosity of 800 poise/25°C) was prepared.

A composite permeable membrane was obtained in the same manner as in Example 1, except that the above membrane-forming liquid (C) was used instead of the membrane-forming liquid (B).

The cross-sectional structure of this composite membrane is shown in an electron micrograph (magnification: 0x) in Figure 2.

Example 3 Polyether sulfone (I, C11, 200P manufactured by Co., Ltd.) 2
0 part was added to 80 parts of dimethylformamide and heated to a temperature of 70°C to uniformly dissolve it to prepare a film forming solution 0 (viscosity 70 poise/25°C).

Separately, ■.2.3.4-butanetetracarboxylic acid and 4.
4'-diaminodiphenyl ether and N-methyl-2
- A polyimide solution was obtained by condensation polymerization in pyrrolidone according to the method disclosed in Japanese Patent Application No. 52-139383.

The composition of this solution was 66 parts of N-methyl-2-pyrrolidone,
The mixture was adjusted to contain 17 parts of polyimide and 17 parts of diethylene glycol (as a swelling agent) to prepare a film forming solution.

In exactly the same manner as in Example I, a film-forming solution (D) was first applied to a polyester woven fabric, and then a film-forming solution with a mouth viscosity of 250 poise/
25° C.) and then immersed in water to form a film.

The cross-sectional structure of the obtained composite permeable membrane is shown in the electron micrograph (100x magnification) in FIG.

Example 4 12 parts of aromatic polyamide (Nomex manufactured by DuPont),
Film forming solution F was prepared by heating 5 parts of lithium chloride, 73 parts of dimethyl sulfoxide, and 10 parts of dimethyl acetamide to a temperature of 70°C to make them uniform.

Except for using the film-forming liquid (6) instead of the film-forming liquid (B),
A film was formed in exactly the same manner as in Example 1.

This permeable membrane also had a two-layer structure of polymers, as in the previous example.

Example 5 Pure water at 20° C. was supplied to the permeable membrane obtained in Example 1 under various pressures, and the amount of water permeated was determined.

The results are shown in FIG. 4 as a solid line.

As a comparative example, film forming liquid B) was used as "Polyester Gose".
Coated on top with a roll gap of 300μ, then 0
A film was formed by immersing it in water at ℃ for 2 hours.

The amount of pure water permeated through this permeable membrane was measured in the same manner as described above, and is shown in FIG. 4 by a dotted line.

Obviously, the amount of water permeated in the permeable membrane according to the present invention increases in proportion to the operating pressure, but in the permeable membrane of the comparative example, the amount of water permeated does not increase in proportion to the operating pressure.

That is, since the permeable membrane of the present invention has polysulfone with a hard skeleton as the first layer, the compression resistance is significantly improved.

In addition, as a solute, the average molecular weight 2
An aqueous solution containing polyethylene glycol of 0.0000 at a concentration of 0.1% by weight was supplied at 20° C. at 14 kg/crA to examine changes in water permeability over time.

The results are shown in FIG. 5 as a solid line. As a comparative example, a 300μ roll of film-forming solution
The film was formed by coating in a gap and then immersing in water at 0°C for 2 hours.

The change in water permeability over time of this permeable membrane measured in the same manner as above is shown in FIG. 5 by a dotted line.

Compared to the permeable membrane of the present invention, the permeable amount of water in the permeable membrane of the comparative example decreased significantly over time.

That is, the permeable membrane according to the present invention has ethylene as the second layer.
It has excellent stain resistance because it has a saponified vinyl acetate copolymer layer.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are electron micrographs showing the cross-sectional structure of the composite permeable membrane according to the present invention, and Figure 4 shows the change in water permeation rate with respect to the supply pressure of the stock solution for the composite permeable membrane according to the present invention. (solid line) together with a comparative example (dotted line), and FIG.

Claims (1)

[Scope of Claims] 1. A membrane-forming solution containing polysulfone or polyethersulfone is applied to and impregnated onto a fibrous porous base material so that the membrane-forming solution is stable and does not substantially flow on the base material. A first layer of a film-forming solution is formed, and then a film-forming solution containing a polymer different from the above is applied onto the first layer to form a second layer, and then solidified. 1. A method for producing a composite permeable membrane, which comprises immersing the membrane in a solvent to form a membrane, and forming a two-layer structure of substantially uniform thickness using different polymers. 2. The method for producing a composite permeable membrane according to claim 1, wherein the fibrous porous base material is a woven fabric or a nonwoven fabric.