JPH03202132A - Preparation of porous membrane and mist generator used therein - Google Patents

Abstract

PURPOSE:To easily prepare a porous membrane having pores with a pore size of about 0.05mum or more provided to the surface thereof by shielding the gaseous atmosphere above a coagulation bath through which a film forming raw solution passes from the outside gaseous atmosphere and controlling the temp. in the gaseous atmosphere so as to make the same lower than the temp. of the coagulation bath. CONSTITUTION:A film forming raw solution 1 composed of a polymer solution forming a film is cast to be passed through the gaseous atmosphere containing the mist composed of the non-solvent of the polymer and subsequently guided to a coagulation bath 9 composed of the non-solvent of the polymer or the liquid mixture of the non-solvent and a solvent to gel the polymer. The gaseous atmosphere containing the mist of the non-solvent immediately before the film forming raw solution 1 is introduced into the coagulation bath 9 is shielded from the outside gaseous atmosphere and the temp. of the shielded gaseous atmosphere is controlled so as to be lower than that of the coagulation bath 9. The vapor of the non-solvent constituting the coagulation bath 9 present in the internal gaseous atmosphere is condensed by this temp. control.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a novel method for producing a porous membrane, and more specifically, a porous membrane having a high surface porosity and excellent water permeability. This relates to a manufacturing method.

[Prior art and problems to be solved by the invention] Substance separation methods using porous membranes with a selective permeation function are generally called membrane separation technologies, and are used in the desalination of seawater, the electronic industry, etc. It is widely used in various fields including water production, food industry processes, and industrial wastewater treatment.

Conventionally, porous membranes have been created by forming a polymer solution (dope) in which a raw material polymer is dissolved in an organic solvent by casting, etc., and then coagulating a non-solvent of the polymer that is compatible with the organic solvent. A method called a phase transformation method, in which the dope is gelled by immersing it in a bath, is preferably used. In this phase transformation method, the structure and pore size of the porous membrane can be varied over a wide range of ways depending on the target substance and separation method by examining various factors such as the composition of the dope, the composition of the coagulation bath, and the evaporation process of the solvent. It has the advantage of being adjustable.

However, when the material polymer is a polysulfone-based polymer, it is difficult to control the pore system because the intermolecular cohesive force is too strong compared to cellulose acetate or the like. In particular, with regard to porous membranes with relatively large surface pore diameters, which are the object of the present invention, specifically, with micropores with a pore diameter of 0.05 μm or more on the surface, there are several problems with conventionally known film forming methods. A point is left.

For example, a method is known in which an extractable substance is mixed with a dope and extracted and removed after film formation.For example, for polysulfone polymers, the use of polyethylene glycol as an extractant is disclosed in Japanese Patent Application Laid-Open No. 5785906. ing. However, it takes a lot of effort and time to completely perform the extraction, and depending on the conditions, the generated micropores may not penetrate, resulting in insufficient extraction, which not only reduces filtration performance but also There are many disadvantages such as a significant decrease in specific heat resistance and mechanical strength.

In addition, a method is known in which a dope is maintained at a liquid temperature below the temperature at which phase separation occurs (critical temperature), and then cooled to a temperature near or below the critical temperature after casting to cause phase separation to form a film. For example, it is disclosed in Japanese Patent Laid-Open No. 56-154051 and Japanese Patent Laid-Open No. 59-58041. However, in this method, if the critical temperature is higher than room temperature, it is necessary to maintain the dope solution temperature above the critical temperature at all times until film formation, which increases energy costs.

Further, when the critical temperature is below room temperature, equipment is required to cool the dope after casting to a critical temperature below room temperature, and in this case as well, equipment costs and energy costs increase.

It is also known to add a good bathing agent or a poor bathing agent to the coagulation tower. For example, regarding polysulfone polymers, JP-A No. 56-152704 and JP-A No. 59-1.85
Publication No. 239 can be mentioned. However, the amount of liquid used in the coagulation bath is generally large, and in order to obtain the porous membrane targeted by the present invention, the amount added must be at least 50% or more, in fact 70% or more. It is difficult to industrialize it due to the cost.

[Means for Solving the Problems] As a result of extensive research in order to overcome the drawbacks of the known manufacturing methods described above, the present inventors have found that it is possible to easily and inexpensively form pores with a diameter of 0.05μ or more on the surface. The present invention was achieved by discovering a method for manufacturing a porous membrane having micropores.

That is, in the present invention, a membrane-forming stock solution consisting of a solution of a polymer constituting a membrane is cast, and after passing through a gaseous atmosphere containing a mist consisting of a non-solvent of the polymer, a non-solvent or non-solvent of the polymer is cast. In a porous membrane manufacturing method in which a polymer is gelled by introducing it into a coagulation bath consisting of a mixture of solvents and solvents, a mist consisting of the non-solvent is used to remove the gas atmosphere from the outside immediately before the membrane forming stock solution is introduced into the coagulation bath. This is caused by condensation of non-solvent vapor constituting the coagulation bath existing in the gas atmosphere inside the shield, which is generated by shielding from the gas atmosphere of the shield and controlling the temperature of the gas atmosphere inside the shield to be lower than that of the coagulation bath. A method for producing a porous membrane characterized in that the porous membrane is further arranged on a coagulation bath to shield it from an external gas atmosphere and to control the temperature of the gas atmosphere inside the shield to be lower than that of the coagulation bath. The present invention provides a mist generating device used in the method for manufacturing a porous membrane described above, which has a cooling jacket and generates a non-solvent mist constituting a coagulation bath inside the cooling jacket.

The polymer constituting the membrane in the present invention includes cellulose-based, polyamide-based, polyacrylonitrile-based, polysulfone-based polymers, or copolymers thereof, etc.
In short, any polymer can be used as long as it can be formed into a film using a phase transformation method. Further, the present invention also provides two mutually compatible
This does not preclude the use of a blend of more than one type of polymer. Among them, it has excellent heat resistance and chemical resistance.
It is desirable to use polysulfone-based polymers. As polysulfone-based polymers, the following formulas (i) to (2) are used.
An aromatic polysulfone polymer having the following structure is typical, but the benzene nucleus may have a substituent.

1@-5o2-@+ (2) The film-forming stock solution in the present invention is prepared by dissolving the above polymer in a suitable solvent. The polymer concentration used here is 5-30% by weight, preferably 10-20% by weight. A good solvent for the polymer can be appropriately selected and used as the solvent, but it is necessary to select a solvent that is compatible with the non-solvent for the polymer used in the coagulation bath, and preferably one that can be mixed in an arbitrary ratio. be. In addition, good solvents are used alone or in appropriate mixtures, and inorganic salts,
Swelling agents and non-solvents for the polymer, such as low-molecular organic substances and polymer additives, are preferably added to the above-mentioned good solvent.

In the present invention, any suitable non-solvent for the polymer can be used as the coagulation bath without any particular limitation, but from the viewpoint of ease of handling and cost, water is preferably used industrially. Further, a good solvent or a poor solvent for the polymer may be mixed with the non-solvent.

The production method of the present invention involves passing a film-forming stock solution through a gaseous atmosphere containing a mist made of a non-solvent of the polymer, and then immersing it in a coagulation bath to create a gaseous atmosphere containing a non-solvent mist. The method is characterized in that it shields the gas atmosphere above the coagulation bath through which the film-forming stock solution passes from the external gas atmosphere, and controls the temperature inside the coagulation bath to be lower than that of the coagulation bath, thereby reducing the non-solvent vapor in the coagulation bath. is brought into a saturated state and a non-solvent mist is generated inside. This method is also advantageous in that the concentration of the non-solvent mist can be easily controlled by the temperature of the gas atmosphere. This allows the target surface to have a pore size of 0.05
Porous membranes with micropores larger than μ can be created. Although the mechanism by which this effect is expressed is not known in detail, it is thought to be as follows. 2. In the gas atmosphere, the non-solvent of the polymer exists in the form of vapor (gas) and mist (liquid), and the film-forming stock solution passing through this atmosphere removes the non-solvent from its surface as vapor. Since it is absorbed in the form of a mist, gelation is thought to progress extremely on the surface.

However, gelation in this case is clearly different from gelation in a coagulation bath. In other words, the amount of non-solvent supplied from the gaseous atmosphere is overwhelmingly smaller than that during coagulation bath, so the rate of gelation progresses is slow, and gelation progresses in the coagulation bath due to the exchange of good solvent and non-solvent. On the other hand, in a gas atmosphere, only non-solvent enters, so the porosity of the surface structure becomes high, with a pore size of 0.05 μm.
It is thought that the above micropores are formed.

Further, although any specific means for generating mist may be used, a jacket type mist generator is used as an embodiment thereof. The refrigerant passed through the jacket may be either gas or liquid, but for example, water at a temperature sufficiently lower than the coagulation bath may be used for convenience.

The gas in the gas atmosphere in the present invention can be appropriately selected from gases that are inert to the membrane forming stock solution and the coagulation bath, but air is particularly preferred from the viewpoint of ease of handling and cost.

In the present invention, the non-solvent constituting the mist can be selected appropriately from among the non-solvents for the membrane material polymer, and can be used alone or in a mixture of two or more. It is desirable that the non-solvent be the same as the non-solvent in the coagulation bath in that it can create an atmosphere.

['Effects of the Invention] According to the present invention, the means for generating a gas field containing non-solvent mist is a very simple and low-cost method, and the method has micropores with a pore diameter of 0.05μ or more on the surface. Porous membranes can be easily produced. The membrane thus obtained can be used for sterilization,
It can be used as a precision filtration membrane for separating and purifying valuable substances such as proteins, or as a blood processing membrane for separating specific components from plasma, such as plasma separation.

[Example] The present invention will be explained in more detail with reference to Examples below.

Example 1 Polyether sulfone, Pictrex
x) 12 parts by weight of 4800P (trade name manufactured by ICI), 2 parts by weight of polyethylene oxide having an average molecular weight of 900,000, and 86 parts by weight of 2-pyrrolidone were dissolved to prepare a stock solution for film formation.

In the continuous flat membrane film forming machine shown in Figure 1, the top of the coagulation bath consisting of 60°C hot water is covered with a cover equipped with a temperature control jacket, and 10°C water is circulated through the jacket to cool the inside. and generated a water mist.

Apply the above film-forming stock solution to a thickness of 300 μm on a polyester nonwoven fabric.
It was passed through a cover in which water mist was generated and immersed in a coagulation bath. When the surface structure of the membrane thus obtained was observed with a scanning electron microscope, it was found that the pore size was O11~
Micropores of 0.5 μm were open. In addition, the pure water permeability of this membrane is 253 mB/cJ ・min -kg/a
It was t.

Comparative Example 1 A film was formed in the same manner as in Example 1 except that 60° C. water was circulated through the jacket of the cover. At this time, no water mist was observed inside the cover. The surface structure of the obtained membrane was observed using a scanning electron microscope, and the pore size was 0.05μ.
No micropores larger than m were found.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a continuous flat film forming apparatus used in an example of the present invention. 1... Stock solution for film forming, 2... Stock solution reservoir for film forming, 3...
- Knife coater, 4... Nonwoven fabric roll, 5... Nonwoven fabric, 1 2 6... Jacket type cover, 7... Jacket inlet, 8... Jacket outlet, 9... Coagulation bath, 10.・
- Winding roll, 11...Pulley 12...Support roll, 13...Roll. Figure 1

Claims (2)

[Claims] (1) After casting a film-forming stock solution consisting of a solution of a polymer constituting a membrane and passing it through a gas atmosphere containing a mist consisting of a non-solvent for the polymer, In a method for producing a porous membrane in which a polymer is gelled by introducing it into a coagulation bath consisting of a mixture of solvents, a mist consisting of the non-solvent is used to transform the gas atmosphere immediately before the membrane-forming stock solution is introduced into the coagulation bath into an external gas. This is caused by the condensation of non-solvent vapor constituting the coagulation bath existing in the gas atmosphere inside the shield, which is generated by shielding it from the atmosphere and controlling the temperature of the gas atmosphere inside the shield to be lower than that of the coagulation bath. A method for producing a porous membrane, characterized by: (2) The method for producing a porous membrane according to claim 1, wherein the non-solvent constituting the mist and the coagulation bath is water. (3) It has a cooling jacket placed above the coagulation bath to shield it from the external gas atmosphere and to control the temperature of the gas atmosphere inside the shield to be lower than that of the coagulation bath, and the coagulation bath is formed inside the cooling jacket. 2. A mist generator used in the method for producing a porous membrane according to claim 1, wherein the mist generator generates a non-solvent mist.