JPS59202237A - Production of porous polymer membrane - Google Patents

Abstract

PURPOSE:To produce a porous polymer membrane having a controlled pore structure, by forming a membrane from a dope prepared by dissolving a membrane-forming polymer in a specified solvent and controlling the period of time from the beginning of the membrane formation to the immersion in a soiidifying liquid. CONSTITUTION:A membrane having a desired shape is formed from a dope of a concentration of 10-40w/v%, obtained by dissolving a water-insoluble, membrane-forming polymer substance, e.g., acrylonitrile/styrene copolymer, in a solvent of a solubility parameter delta (J<1/2>.m<-3/2>) of 18-25, e.g., dimethyl-formamide. This membrane is left standing in an atmosphere at 0-30 deg.C so that log to is 0-5 (wherein t (sec) is the period of time from the beginning of the membrane formation to the immersion in a solidifying liquid), and is solidified by immersion in a solidifying liquid comprising an aqueous solution containing 20-40vol% solvent of delta>=25, e.g., dimethylformamide, and heat-treated by immersion in water at 60-90 deg.C to obtain a porous polymer membrane of a pore diameter of 100-5,000Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a porous polymer membrane by a cane wetting method.

Porous membranes made of polymer compounds have been effectively used as membranes with a substance separation function, such as IV close-contact ultrafiltration membranes and reverse osmosis membranes.

On the other hand, the application of porous polymer membranes is extremely wide, as the use of thin supporting membranes, sound tracing membranes, or moisture absorption/desorption membranes having the ability to separate gas and liquid is also considered. The membrane obtained by utilizing the polymer-solvent-nonsolvent phase separation in the porous polymer lll1Jc can be used as a support membrane to give mechanical strength to the separation functional membrane, and also as a separation functional layer and its separated substance. It is particularly effective as a composite B@ (asymmetric I membrane) that is integrated with a permeable portal layer that has almost no resistance to the membrane.

However, in the production of porous polymer membranes using such phase separation, factors such as the preparation of the stock solution, casting conditions, selection of solidification liquid, and post-treatment of the membrane have a rough influence. However, the current situation is that the structure and function of the membranes obtained vary significantly depending on the manufacturing method. Numerous studies have been conducted to date on what steps determine the porous structure of membranes, but no clear answer has been given regarding the causal relationship. In addition, a membrane that is actually effectively used must be satisfactory from an economic point of view.

Therefore, an object of the present invention is to provide a simple and economical method for producing a porous polymer membrane having a controlled porous structure.

Further objects of the invention will be apparent from the description below.

The present invention 4 uses a solvent having a solubility parameter within a predetermined range in a film forming method that utilizes phase separation of polymer-solvent-non-solvent, from immediately after film formation until immersion in a solidifying liquid. The present invention was completed based on the discovery that a polymer membrane having a controlled porous structure can be obtained by controlling the time.

The porous structure of the porous polymer membrane obtained by the method of the present invention has a finger-shaped structure in which the stock solvent is eluted from only one side of the formed film, or a sponge-shaped structure consisting of normal open cells. and the pore size on the membrane surface is about 51111
It is characterized by being controlled within the afL range up to OA.

The method for producing a crystalline molecular porous a-a membrane according to the present invention includes the following steps: 1.
6 亦子q14. When r is dissolved 1fMj I□2.2□-k-a (=J' ``m!) (J/% molar cohesive energy, mremol represents the molecular volume) is 187'r
Dissolve the stock solution in a solvent within the range of 7. A step of forming a desired shape using the stock solution, and a step of immersing the formed membrane in a solidifying solution, and the vagina obtained from membrane formation Iv9> The time t (seconds) until immersion in the solidified liquid of 10gt is 0 to 5.
To 2, the structure of the porous Si is controlled by adjusting I and Z.

The polymeric substance %j of L is soluble in a solvent whose solubility jW parameter δ is in the range of 18 to 5, and water (/
(1) Insoluble polymers are used, such as cellulose acetate, cellulose nitrate, acetic acid-resistant cellulose, polystyrene, polyacrynitrile, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyethylene Examples include organic polymeric substances such as terephthalate and copolymers of monomers constituting these polymers. Preferred polymeric substances include polypropylene, rylonitrile, styrene copolymer, and vinyl chloride-vinyl acetate copolymer. Polyacrylonitrile-styrene copolymer is particularly preferred.

Examples of solvents in which δ is in the range of 18 to 5 include dimethylformamide (DMF), dimethylsulfoxide, N-methylpyrrolidone, 3-ethylphosphoric acid, dimethylacetamide, and acetic acid.

Organic solvents such as dioxane, ethyl lactate, acetone, ethyl chloride, propylene oxide and tetrahydropyran may be mentioned, with dimethylformamide and dimethylacetamide being preferred.

Solvents with δ of 18 or less have low water solubility, so
When water or an aqueous solution is used in the method of the present invention as an assimilate liquid, a porous membrane cannot be obtained.

Further, a solvent in which δ is 25 Pl is not suitable for use in the present invention because the solubility of the polymer is low.

), iI+41. [il: liquid polymer 4 times jI′i
7 always 10 to 40% (shuit/Akuashi 1 (W/V%)
4, preferably 110~:lal VV/
It is also within V%σJ. If the polymer concentration is lower than 1 (IW/V%), the viscosity of the stock solution will be low, and if a membrane is applied, 11
G-shape cannot be maintained. On the other hand, if it exceeds 40% (W/V), is it a polymer? Either the 7th substance is not sufficiently dissolved in the aqueous medium, or even if it is dissolved, the 1ψ is too high and the 11th bullet cannot be drawn. This 4 degree also affects the structure of the surface layer of the film.

The film's ti
The structure can be changed significantly. To obtain a porous membrane, the logarithm is: Nakamiya 0 to 5. Preferably 0-35. More preferably, it is 0 to 3.0. Especially 20
In the case of less than 0 μm1 F, it is preferable to control logt within the range of 0 to 3.5. Depending on the time taken and the δ value of the solvent used for the stock solution, the optimum l
The value is given to og.

For example, when using a solvent with δ of 18 to 21, Jo
g t is mouth or 3.0. Especially 0 to 2,0. A porous membrane with a sponge-like structure is obtained between
．． When it exceeds 0, it becomes a homogeneous film. On the other hand, δ is 21 to 5
When using a solvent of
A porous membrane with a guiding structure is obtained, and A! When og t is 3.0 to 3.5, a porous membrane with a sponge-like structure can be obtained.

It is preferable that the formation of the 41 film of the above-mentioned stock solution and the leaving until immersion in the assimilation solution are carried out in an atmosphere in which the temperature and humidity are kept substantially constant. The temperature range is usually an ambient temperature of 0° to 30°C, and the humidity is not particularly limited.

By standing for a certain period of time, the solvent evaporates over time. This membrane is then gelled by immersing it in a solidifying solution.

Examples of the assimilation liquid include water; an aqueous solution of the solvent used in the stock solution, such as an aqueous dimethylformamide solution; and an aqueous solution of a solvent with a δ of 5 or more, such as an aqueous alcohol solution; Dissolve the solvent used in
1F solvent, solution I$: A mixture or solution is used.

Preferred is an aqueous solution of the solvent or solvent mixture used in the stock solution. 18 degrees of the stock solvent in the solidified solution is 0'fr to 4
By maintaining the O degree at a constant value within the range of 0 volume, preferably within the range of 0 to 40 volumes, it is possible to control the degree of occlusion of pores on the membrane surface.

s> By adjusting IQ within the range of Δ)k to 40% IRII, the pore diameter on the membrane surface can be adjusted from 100 to 50%.
(1) When the solvent concentration is controlled within the range of IA and the added volume is increased to π, the membrane surface layer becomes a dense layer having pores with a diameter of 100 A or more. The assimilation liquid immersion time depends on the class of the polymer material, the film thickness, the axial tilt of the assimilation liquid, the temperature, etc., but is usually 11.1-(a) minutes.

Next, the 1 grass solidified in this way is added to 6 () if desired.
0 to 90°C 90° C The membrane shape can also be fixed and/or the substance permeability of the membrane can be improved by subjecting it to a chemical treatment in which the membrane is soaked for minutes.

Next, the present invention will be explained in detail using examples.

Example 1: Acrylonitrile-styrene copolymer (Asahi Dabi 20.4) was added to tetrahydrofuran, ethyl formate, acetone, and dioxane in an atmosphere with a temperature of 15°C and a humidity of 50℃, respectively. (W/V) to prepare a stock solution and cast it on a flat glass plate to form a film. ', 5ec)
After adjusting t in the range of 0 to 3.5, the membrane was immersed in water at 15°0 for 60 minutes. Thereafter, the solidified membrane was fixed on a glass plate and immersed in water at 70°C for 10 minutes. Observe the porous structure of this membrane using a scanning electron microscope. log
When t was between 0 and 3.0, a sponge-like porous 11th layer was obtained. The porous bamboo structure of the membrane changed with 10 g of t.

When log t was 30 or more, a transparent homogeneous film was obtained.

Example 2: δ of 22.0 and 24 as solvent, respectively
7 in the same manner as in Example 1 except that dimethylacetamide and dimethylformamide were used. I lamented. When logt was between 0 and 3.0, a porous a-film was obtained. 10g When t was between 3.0 and 3.5, the porous membrane of Kesuhonjihiro was fabricated.If logt was 35 or more, polymers were precipitated in some places on the glass plate. , the porous structure of the membrane changed significantly from 10 g t K, although the shape of the membrane was not obtained.

Figure @1 shows the phase diagram of the polymer porous-homogeneous membranes prepared in Rice Examples 1 and 2. In Figure 11, DME! 'Ni-dimethylformamide, DMA n-dimethylacetamide,
13 (JX Nidioxane, AT: Acetone, gF:
Ethyl formate, THF: represents tetrahydrofuran.

Figure 2 shows that dioxane (IX) or dimethylformamide (DMF) was used as the solvent for the stock solution in Examples 1 and 2.
A scanning electron micrograph of a typical porous structure of a molecular membrane prepared using the method is shown. In Figure 2, photo AI, A2
．． BIQ and B2 are micrographs of membrane samples AI, A2, B1 and B2 shown in the graph of FIG. 1, respectively.

Example 3: Using the same acrylonitrile-styrene copolymer used in Example 1 and dimethylformamide as a solvent, the temperature was 4 times 10.15° and % (W/V)
A film was formed using the same method as in Example 2 with ilogt set to 0. A folded porous membrane was obtained in each case, but the surface layer of the membrane was different depending on the 4 degree change in the stock solution.

Figure 3 shows the structure of the folded porous membrane obtained. The surface layer was different on the front side of the membrane (the side in contact with the assimilate fluid) and the back side (the side in contact with the glass plate). The surface layer of the membrane using the stock solution with a concentration of 10% had elongated pores with a diameter of 100 to 100 mm on the front side, and pores with a diameter of 1 ft of 1 to 2 μm on the side. When using a stock solution with a concentration of '/'%, the surface layer of the membrane was a dense layer.Actual Example 4: The same acrylonitrile-styrene co-component and solvent used in Example 1. Using dimethylformamide as an assimilate solution, 12.10 g of an aqueous solution containing dimethylformamide at a concentration of 21) and 40% (V/V) was prepared from the stock solution with a concentration of 10 and 9%. The film was formed by the '+ method.The inside of the film is a finger)W
Although it had a porous a structure, the surface layer of pus, the cylindrical molecules of the undiluted solution,
'1 degree and the solvent of the assimilate solution changed by 4 degrees.

FIGS. 4 and 5 show changes in the membrane surface 1ri'i (the front side and the back side, respectively) depending on the polymer 4 degree of the stock solution and the solvent concentration of the villization solution, as shown by electron microscope surface images of typical membranes. If the polymer concentration of the stock solution is varied from 10% to 2% and the solidified solution solvent concentration is varied from 1% to 40%, the pores on the membrane surface, especially on the front side, can be reduced from 1 to 5n (1 flA). It is possible to control the polymer porous structure σ) by controlling the polymer porous structure σ) if the polymer in the stock solution changes by -5!% from 0 to 40%.
However, when the concentration exceeds 40%, the solution becomes extremely viscous, making it difficult to form a membrane.Example 5: The porous solution prepared in Example 2 using dimethylformamide as the solution solvent The gas permeability of the membrane was measured in this example.

The results are shown in Table 1. The gas permeation rate of the finger-shaped porous membrane is smaller than that of the sponge-type porous membrane. This dense layer was present on the front and back sides of the membrane. The gas permeation rate of the membrane from which the m-dense layer on the back side was removed was greater than that before removal. Without removing the dense layer of the folded porous membrane, the membrane was immersed in ethanol with δ reaching 1O.
Soaked for minutes. The gas permeation rate of the membrane treated with ethanol was significantly higher than that before treatment with ethanol.

It was confirmed from the 'er J analysis results of the membrane that the ethanol treatment removed the hydrocarbons, styrene derivatives, and additives contained in the polymeric substance contained in the m-dense layer.

The porous polymer membrane obtained by the method of the present invention with a controlled porous structure has surface pores with a diameter smaller than HIOA and can be used for #i gas separation membranes, reverse osmosis membranes, dehumidification membranes, etc. The membrane according to the present invention can be used as a support membrane for a separation mirror layer or as a separation layer. It can also be used as a composite membrane integrated with a permeable functional layer.

[Brief explanation of the drawing]

The first factor is the phase diagram of the porous polymer membrane-homogeneous membrane prepared in Examples 1 and 2. , FIG.
%15% and w%), and Figures 4 and 5 show the front and back sides of the folded polymer porous membrane prepared in Example 4, respectively. This is a scanning electron micrograph of the surface.

Claims (8)

[Claims] (1) Solubility parameter δu, −
5 (J2 mz) is prepared by dissolving it in a solvent in the range of 18 to δ, forming a film of the desired shape using the stock solution, and immersing the obtained sliding door in the solidifying solution. process, and controls the porous structure of the membrane by adjusting the time t (seconds) from immediately after membrane formation to immersion of the obtained membrane in the assimilated liquid within the range of 7ogt ( ) to 5. Cylindrical molecular porous) J! , The manufacturing method of grief. (2) The polymer concentration of the stock solution is 10 Yr and 40% (
The manufacturing method according to claim 1, which is listed in IIQ of the following patent claims. (3) The manufacturing method according to claim 1 or 2, wherein the solidification solution has a solvent strength of up to 40% (volume/volume). (4) Set the polymer diameter of the stock solution to 10 to 2), set the solvent concentration of the solidified solution to 40%, and set the pore diameter on the membrane surface to 11) OA 7Ir-50.
The manufacturing method according to any one of claims 1 to 3, wherein the manufacturing method is controlled within the range of 011A. (5) The manufacturing method according to any one of claims 1 to 4, wherein each step is carried out in an atmosphere where the temperature and humidity are kept substantially constant. (6) After immersing the membrane in the solidifying solution, the temperature is 60 to 90'0.
of? The manufacturing method according to any one of claims 1 to 5, which involves a heat treatment step of immersing I@mochi in water at a constant temperature. (7) The manufacturing method according to any one of claims 1 to 6, wherein the membrane is immersed in a solidifying liquid and then subjected to a chemical treatment in which δ is immersed in a solvent of 25 or more. (8) The method according to any one of claims 1 to 7, wherein the polymeric substance is an acrylonitrile-styrene copolymer.