JPH03267131A - Porous polyether sulfone membrane and its production - Google Patents

Abstract

PURPOSE:To obtain the porous polyether sulfone membrane having high- efficiency separation ability and excellent in resistance to heat and chemicals by irradiating a polyether sulfone membrane with a charged particle to cause irradiation damage and then chemically etching the membrane. CONSTITUTION:A polyether sulfone membrane is irradiated with a charged particle to cause irradiation damage. The polyether sulfone membrane consisting of a composite structure consisting of a porous layer and a dense layer is preferably irradiated with the charged particle from the dense layer side. After the irradiation damage is caused, the membrane is chemically etched to form the membrane capable of being used in various fields. An oxidative soln. contg. one kind among potassium permanganate, sulfuric acid and potassium bichromate is used as the etchant for chemical etching. The damaged part is selectively etched by this treatment, and a membrane having a cylindrical bore hole having <=10mum average diameter is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to porous polyether sulfone (hereinafter referred to as PES).
The present invention relates to a porous PES film using an etching method (track-erosion method) and a method for manufacturing the same.

The porous PES membrane according to the present invention is particularly suitable as a vine separation membrane used in microfiltration membranes, ultrafiltration membranes, and the like.

[Conventional technology]

Polymer membranes having a separation function are applied to membrane separation methods such as microfiltration, ultrafiltration, reverse osmosis, dialysis, gas separation, pervaporation, and electrodialysis. Among them, porous membranes are used in a wide range of fields, such as precision filtration membranes and ultrafiltration membranes.

By the way, conventionally, microporous membranes used for separation membranes etc. have been produced by (1) mechanically (incompletely) stretching a polymer membrane (film) or fibrous material, (2) chemically A method that utilizes the solubility difference of molecules, (3) A method of mixing solvent-soluble solid fine particles and then melting, (4) A method of forming a porous membrane by sintering, (5) A method of crushing a bubble-filled polymer sheet. It is manufactured using porous technology such as the method.

The pore forms are diverse, including those with irregular pores such as three-dimensional network, closed cell type, and open-cell type, and those with continuously changing pore size, and the apparent pore size in the porous membrane is also non-uniform. There is a limit to the separation efficiency for purification or removal of target substances.

For example, a stretched film obtained by stretching a partially crystalline polymer film such as polytetrafluoroethylene or polyolefin by a stretching method has a three-dimensional network structure, and the pore size can be controlled by the stretching conditions. As a result, the apparent pore size is non-uniform, and the separation efficiency (selective permeability) in purifying or removing the target separation product is insufficient. For example, for cellulose ester, polyamide, polysulfone, etc., these polymers are dissolved in a solvent, additives are added to make a dope solution, this dope solution is cast on a flat plate, and after a predetermined period of time, the poor solvent is removed. The porous membrane obtained by this method has a dense layer or a porous skin layer, which is an active layer, on the porous layer. In this method, the pore size is controlled by selecting the solvent, precipitant, viscosity modifier, and film forming conditions such as concentration and temperature, so the apparent pore size is non-uniform and there is a limit to separation efficiency.

A sintered film obtained by rolling polytetrafluoroethylene fine particles into a film and sintering it by a sintering method has non-uniform pore diameters and low mechanical strength.

In recent years, polymer films have been irradiated with high-energy charged particles (ions) containing neutrons generated from nuclear reactors to create tracks where polymer chains are cut, and these tracks are treated with etching agents such as alkaline solutions and oxidizing solutions. An etching method for obtaining a porous membrane by chemically etching has been proposed (Japanese Patent Publication No. 52-3987, JP-A-54-11971, JP-A-59-117).
546, etc.).

According to this etching method, a membrane with very uniform, almost completely cylindrical vertical pores (capillary pore membrane) can be obtained, and when used as a separation membrane, it exhibits good separation efficiency.

However, although polycarbonate and polyethylene terephthalate thin films are currently commercially available as porous separation membranes produced by the etching method, their use is limited due to insufficient heat resistance and chemical resistance. Although polyvinylidene fluoride porous membranes produced by the etching method have relatively excellent chemical resistance, they are easily soluble in some organic solvents and have poor radiation resistance, so they cannot be used in harsh environments.

[Problem to be solved by the invention]

The purpose of the present invention is to create a cylindrical shape with a uniform pore diameter.
An object of the present invention is to provide a porous polymer membrane having high separation efficiency and having excellent heat resistance, chemical resistance, and dimensional stability.

As a result of intensive research to overcome the problems of the prior art, the present inventor used PES as a polymer film, irradiated the PES film with charged particles to form irradiation damage, and then chemically It has been found that the above object can be achieved by performing etching treatment.

In addition, PES membranes with a composite structure consisting of a microporous layer (A) and a dense layer (B) obtained by a phase separation method or a lamination method,
If charged particles are irradiated from the dense layer (B) side, the dense layer (B)
), it has been found that a porous PES membrane having cylindrical perforations and excellent separation efficiency can be obtained.

The present invention has been completed based on these findings.

[Means to solve the problem]

Thus, according to the present invention, there is provided a method for producing a porous PES film, which comprises irradiating the PES film with charged particles to form radiation damage, and then chemically etching the film.

Further, according to the present invention, the PES membrane has a microporous porous layer (A
) and a dense layer (B), and is characterized in that it is irradiated with charged particles from the dense layer (B) side to form irradiation damage, and then chemically etched. A method of manufacturing a porous PES membrane is provided.

Furthermore, the present invention provides a porous PES membrane characterized by having cylindrical perforations with an average pore diameter of 10 μm or less.

Furthermore, according to the present invention, there is provided a PES membrane having a composite structure having a microporous layer (A) and a dense layer (B), characterized in that the dense layer (B) has cylindrical perforations. A porous PES membrane is provided.

The present invention will be explained in detail below.

(Polyethersulfone membrane) PES used in the present invention is a thermoplastic resin whose main constituents are the following repeating units.

[ph-Sow -ph-0-].

(However, ph represents p-phenylene units.) Since PES has a high proportion of phenylene units in its main chain, it is a polymer with high rigidity and high heat resistance. Glass transition temperature (T
g) is usually around 220 to 230°C, and is excellent against acids other than concentrated sulfuric acid and concentrated nitric acid, alkalis, oils, gasoline, grease, detergents, alcohols, aliphatic hydrocarbons, etc. It has high resistance to

The PES membrane used in the present invention means a thin film such as a film or a sheet-like material, and the manufacturing method is not particularly limited.
It may be an asymmetric membrane created by a phase separation method or the like, and its thickness may be a size that allows a porous membrane to be formed by an etching method (track-erosion method).

(Method for producing porous membrane) In the present invention, high-energy charged particles (
A porous PES film is manufactured by irradiating the film with ions) to form an irradiation damage and then chemically etching it.

As the charged particles, for example, nuclear fission fragments obtained by nuclear fission, accelerated ions obtained by an ion accelerator, etc. can be used. In addition to charged particles, uncharged particles may be included, such as charged particles containing neutrons generated from a nuclear reactor.

Charged particles are usually irradiated onto the PES film almost perpendicularly to the film, causing radiation damage (tracks) in which polymer chains are cut in the film.Next, this radiation damage is chemically etched. , a porous PES membrane with uniform cylindrical perforations is obtained.

Irradiation with charged particles causes radiation damage to the PES film, but it is necessary that the chemical species generated at this time are easily etched. In order to efficiently generate this chemical species, irradiation can also be performed in an atmosphere of an active gas such as oxygen or ozone. Furthermore, the generation of chemical species is also determined by selecting the type of charged particles and the energy of the charged particles.

Chemical etching treatment usually removes radiation-damaged P.
The ES film is immersed in an etching agent for a predetermined period of time.

As the etching agent, alkaline solutions such as sodium hydroxide and potassium hydroxide; acidic solutions such as sulfuric acid and nitric acid; and oxidizing agents such as potassium dichromate and potassium permanganate can be used. Among them, oxidizing solutions containing potassium permanganate, sulfuric acid, potassium dichromate, etc. are preferred. It is also possible to use these etching agents to which alcohol or surfactant is added.

By performing the etching treatment, damaged portions of the PES film caused by the penetration of charged particles are selectively etched to form perforations.

In order to efficiently form holes, after irradiating the PES film with irradiation damage with ionizing radiation or ultraviolet rays,
Alternatively, chemical etching may be performed while performing irradiation. By re-irradiating with ultraviolet rays or ionizing radiation, such as electron beams or gamma rays, it is possible to change the chemical species to those that are more easily etched, thereby shortening the etching time and making the pore diameter uniform.

The number of holes thus obtained corresponds to the number of charged particles, and the number of holes can be controlled arbitrarily by selecting the irradiation conditions.

Further, the pore diameter can be arbitrarily controlled to 10 μm or less depending on the type of ions to be irradiated and etching conditions.

PES membrane has a composite structure consisting of a microporous layer (A) and a dense layer (B) obtained by phase separation method or lamination method.
An ES film can be used.

PES membranes with such a composite structure can be manufactured using a phase separation method.
It can be obtained by dissolving ES in a soluble solvent, casting this solution onto a flat plate, and contacting it with a poor solvent after a predetermined period of time. According to this method, PE has a structure in which a microporous layer (A) and a dense layer (B) are continuously connected.
An S film is obtained.

Alternatively, a pre-formed microporous layer (A) made of PES
It can also be obtained by laminating a dense layer (B) thereon by a coating method, an interfacial polymerization method, a plasma polymerization method, or the like.

If the PES membrane having the composite structure is irradiated with charged particles from the dense layer (B) side, a porous PES membrane having cylindrical holes in the dense layer (B) can be obtained. Layer compacta (B)
Because the layer is usually thin, charged particles can easily penetrate it, forming a porous layer with a cylindrical shape and short pore lengths. The obtained porous PES membrane has strong strength because it is supported by the microporous porous layer (A), and the cylindrical porous layer with uniform pore diameter is used as the active layer [dense layer (B)]. It has excellent separation efficiency.

(The following is a blank space) [Examples] The present invention will be specifically described below with reference to Examples, but the present invention is not limited only to these Examples.

[Example 1] 35 g of PES was mixed with 90 m of N-methyl-2-pyrrolidone.
℃, dissolved in a mixed solvent of 10 mjl of tetrahydrofuran, coated on a glass plate with a doctor knife to a thickness of 100 μm, and then immersed in a hot water bath at 50°C to form a dense layer (B).
A porous membrane having a continuous structure of a microporous porous layer (A) was obtained. The thickness of the dense layer at this time was 1 μm or less.

The PES film created in this way was irradiated with Cr" ions from the dense layer side using an ion accelerator at a rate of I x 10" ions/
C rrr irradiation was performed to form an irradiation damage.

The membrane thus obtained was mixed with 5 g of potassium dichromate (Kg Cra Ot )/18 g of 30% sulfuric acid (H,
5o4) in a saturated solution of potassium permanganate at 80°C.
Then, it was immersed for 40 hours and chemically etched.

According to an electron microscope observation of the porous PES membrane thus prepared, the pore diameter of the pores formed in the dense layer was 0.
The pore density was 1 μm and the pore density was 1×10”/C.

[Example 2] Using an ion accelerator on a PES film with a thickness of 2 μm, Ar”
I x 10'' ions/crd were irradiated. This film weighs 5 g Kg Cra Ot / 18 g
It was chemically etched by immersing it in a 30% HaSo4 solution at 80° C. for 40 hours.

The porous PES membrane thus obtained had a pore diameter of 0.1 .mu.m and a pore density of I.times.10"/C, as observed by electron microscopy.

[Example 3] Using an ion accelerator on a PE5 film with a thickness of 2 μm, Ar4
*Irradiated with 5×10” ions/c rrr. This film was placed in a saturated potassium permanganate (KMnO,) solution.
A chemical etching treatment was performed by immersing it at 90° C. for 30 hours.

According to electron microscopic observation, the porous PES membrane thus obtained had a pore diameter of 0.1 μm and a pore density of 5×10”/C.
It was Go.

The porous PES membranes obtained in Examples 1 to 3 above have a glass transition temperature as high as 220 to 230°C, which is higher than that of cylindrical porous membranes obtained using commercially available polycarbonate and polyethylene terephthalate. Excellent dimensional stability.

Furthermore, when polycarbonate and polyethylene terephthalate were immersed in a 5N NaOH aqueous solution for 24 hours at 60°C, deterioration of the film itself was observed, but PE of the present invention
There was no equivalent change in the S film.

〔Effect of the invention〕

The porous PES membrane of the present invention has cylindrical perforations with uniform pore diameters, so it is easier to separate and classify objects by size compared to conventional three-dimensional mesh separation membranes. It is effective for use in the medical field for separating viruses, etc., and in various industrial processes where high efficiency separation performance is required.

In addition, compared to commercially available polycarbonate membranes and polyester membranes as such perforated membranes, it has excellent heat resistance and
Since it has excellent dimensional stability even at 00°C, it can also be used for filtration at high temperatures. Except for polar solvents, it has excellent chemical resistance, making it possible to use it with organic solvents, acids, and alkalis, which are difficult to use with conventional porous membranes.

Claims (5)

[Claims] (1) A method for producing a porous polyethersulfone membrane, which comprises irradiating the polyethersulfone membrane with charged particles to form radiation damage, and then chemically etching the membrane. (2) Porous layer with microporous polyether sulfone membrane (A)
2. The manufacturing method according to claim 1, wherein the method has a composite structure having a dense layer (B) and a dense layer (B), and the charged particles are irradiated from the dense layer (B) side. (3) The chemical etching treatment is an etching treatment using as an etching agent an oxidizing solution containing at least one compound selected from potassium permanganate, sulfuric acid, and potassium dichromate. 2. The manufacturing method described in 2. (4) A porous polyethersulfone membrane characterized by having cylindrical perforations with an average pore diameter of 10 μm or less. (5) A polyethersulfone membrane with a composite structure having a microporous porous layer (A) and a dense layer (B), the dense layer (
B) A porous polyethersulfone membrane characterized in that it has cylindrical perforations.