JPH01115406A - Permselective membrane - Google Patents

Abstract

PURPOSE:To prevent the title permselective membrane from being charged and to obviate the deterioration in the performance due to static electricity by forming >=1 layer of the composite membrane with an electrically conductive layer. CONSTITUTION:A conductive layer is provided on the back of at least a porous supporting membrane of the composite membrane consisting of the porous supporting membrane and a functional membrane. A material consisting essen tially of a surfactant is used for the conductive layer, and the surface resistivity is controlled to <=1X10<10>OMEGA. Any porous formed article can be used as the porous supporting membrane, and the microporous supporting membrane having 0.005-0.1mu pore diameter and permeable to air is preferably used. A material capable of separating a gaseous and liq. material to be separated, especially capable of separating an oxygen/nitrogen mixture, is used as the functional membrane. Since the conductive layer is brought into contact with the functional membrane surface when the composite membrane is wound, the layer of the surfactant is preferably used as the conductive layer, because the functional membrane is not damaged by such a conductive layer and the gas separability is not deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a selectively permeable membrane having excellent gas separation properties and liquid separation properties.

[Prior Art] Many proposals have been made in recent years regarding methods of separating and concentrating a specific gas or liquid from a mixed gas or mixed liquid using a selectively permeable membrane. It has a composite form with a functional membrane attached to it. Since these gas and liquid separations are carried out on an industrial scale, the membranes used for this purpose are manufactured either continuously by coating a solution of functional membrane material on a porous support membrane, or by continuous production. A method (G
, Company E, LJSP, Specification No. 3767737). In these continuous manufacturing methods, a large amount of static electricity is generated due to unwinding of the porous support membrane, contact of the membrane with a transport roll, winding of the composite membrane, etc., and the surface potential of the charged membrane reaches several + kV. . Since the thickness of a typical functional film is about 1 μm or less, such a high charge causes dielectric breakdown, which causes a problem in that the separability of the composite film deteriorates. Furthermore, when the module is incorporated into a module and operated continuously for a long period of time, charging of the membrane surface due to the permeated gas and liquid can lead to a decrease in performance.

[Problems to be Solved by the Invention] An object of the present invention is to provide a selectively permeable membrane with excellent gas separation properties and liquid separation properties, with less deterioration in performance due to static electricity.

[Means for Solving the Problems] The present invention has the following configuration to achieve the above object.

"In a composite membrane consisting of at least a porous support membrane and a functional membrane, 1. A permselective membrane characterized in that the composite membrane has one or more conductive layers." In the present invention, the porous support membrane is: Any molded product may be porous, and preferably the diameter of micropores on one side of the support membrane is 0.001 to 5.0μ, preferably 0.00μ.
A supporting membrane having a thickness of 5 to 0.1 μm and having an air permeable structure is preferable. Among these, a porous support membrane with an asymmetric structure is most desirable because the pore size of the micropores is small and the membrane has sufficient air permeability.

As such a porous support membrane, “Office of
Salihsi Water Research and Development Progress Report” No. 359 (
Examples include polysulfone porous support membranes, polyimide porous support membranes, cellulose acetate porous support membranes, polyvinyl chloride porous support membranes, etc., obtained according to the method described in 1968). Alternatively, the support film may be formed using a base fabric such as taffeta or nonwoven fabric.

The functional membrane in the present invention is a thin film made of a material that has separation properties for gas and liquid objects to be separated, particularly a material that has oxygen/nitrogen separation properties. Examples of the material include the following: .

Silicone polymers such as polydimethylsiloxane, polydimethylsiloxane/polycarbonate copolymer, polydimethylsiloxane/polystyrene copolymer, and zvfJW polydimethylsiloxane.

Polystyrene, poly-α-methylstyrene, polyvinyl acetate, polyethylene, polypropylene, polybutene, poly-4-methylpentene, poly-1-hexene, poly-
Synthesized from vinyl polymers such as 1-octene, polymethyl methacrylate, polybutadiene, polyacrylonitrile, polyvinyltrimethylsilane, polyallyltrimethylsilane, polyvinyldimethylphenylsilane, their derivatives, and the monomers that make up these polymers. copolymer. Condensation polymers such as polycarbonate, polysulfone, polyethersulfone, poly(2,6-dimethylphenylene oxide), cellulose acetate, cellulose nitrate, cellulose diacetate, cellulose triacetate, polyethylene terephthalate, polybutylene terephthalate, etc., or their derivative.

The functional film may be a thin film made of a blend of two or more of the above materials, or may have a structure in which a plurality of thin films made of different materials are laminated.

It is desirable that the thickness of the functional film be as thin as possible, but if it becomes thin, problems will occur such as the generation of pinholes and pressure resistance, so it is desirable that the thickness be about 0.0'lμ to 0.5μ.

A method for producing a composite membrane consisting of at least the porous support membrane and the functional membrane is (a) a method in which a solution of the functional membrane material dissolved in a solvent is directly applied onto the porous support membrane, and the solvent is dried. and (a) a method in which the solution is cast onto a water surface, and a thin film in which the solvent has evaporated from the solution spread on the water surface is pressed against a porous support membrane to form a composite. In method (a), the solvent used must be selected from among those that are non-solvents for the porous support membrane and are good solvents for the functional membrane material.

Examples of the conductive layer include a layer made of vapor-deposited metals such as Af, Zn, and Sn, and a layer made of a surfactant, but since the conductive layer comes into contact with the functional film surface when the composite film is rolled up A layer composed of a surfactant is preferable because it does not easily damage the surface of the functional membrane and does not reduce gas separation properties.

Surfactants are classified into anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants, but with the exception of nonionic surfactants, they have no antistatic effect as a component of the conductive layer. big.

Among these, cationic surfactants are preferred in terms of durability and static neutralizing properties. Cationic surfactants can be used as primary amine salts, secondary amine salts, tertiary amine salts, or
Although it is classified as a quaternary ammonium salt, the quaternary ammonium salt is the most desirable in terms of static elimination properties.

In the present invention, the surface resistance of the conductive layer is 1X1Q 1o
Ω or less is preferable, and when it is 1 × 101” Ω or less, the antistatic effect is extremely large, and it becomes possible to suppress performance deterioration due to static electricity of the composite film. 1 × 1
If it exceeds 0.010 Ω, charging will be large and the performance of the composite membrane will tend to deteriorate.

The surface resistance of a conductive layer with a surface resistance of 1 x 10 IQΩ or less is measured using a super megohmmeter (vE-40) manufactured by Kawaguchi Electric.
Connect the room temperature measurement box (RC-02> to 20℃, 60%
Applied voltage 100 in a constant temperature and humidity room controlled by RH
This is a value measured at V.

The conductive layer can be provided on the upper surface of the functional membrane layer of the composite membrane, on the interface between the functional membrane and the porous support membrane, or on the back surface of the porous support membrane, but it may be necessary to In order to prevent charging without causing damage, it is desirable to provide a conductive layer on the back surface of the porous support membrane.

The thickness of the conductive layer is desirably thin, since a thicker layer increases the transmission resistance, but it is preferable that the conductive layer has a surface resistance of 1.times.10" .OMEGA. or less and a thickness that does not impair transparency.

As a method for providing a conductive layer on the back surface of a porous support membrane, when a surfactant is used as a constituent component, a method is used in which a solution of the surfactant dissolved in a solvent is applied to the back surface of the porous support membrane and dried. The solvent must not attack the porous support membrane, and examples thereof include water, methanol, and ethanol. The solution concentration is O, O1t% to 5. Qw
t% is desirable. Coating methods include gravure coater,
It is desirable to apply the coating quantitatively and uniformly using a general coater such as a reverse coater or a slit die coater.

Note that it is desirable to provide the conductive layer on the porous support membrane before the functional membrane is composited, since this prevents damage to the functional membrane surface when the conductive layer is provided.

The conductive layer of the present invention refers to one formed continuously or discontinuously.

The conductive layer being on the back side of the porous support membrane means that the conductive layer is on the back side of the support membrane or is formed from the back side. That is, the term "porous support membrane" refers to non-contrastive porous support membranes, including those in which a conductive layer is formed in the pores of the support membrane. Furthermore, in the case of a porous support membrane formed using a base fabric such as taffeta or nonwoven fabric, the conductive layer includes those formed in the gaps and pores of the support membrane including the base fabric.

[Method of Measuring Characteristics and Method of Evaluating Effects] The method of measuring characteristic values and the method of evaluating effects of the present invention are as follows.

(1) Gas permeability, gas separation properties Across the composite membrane, the pressure on the downstream side is 2 atm and the pressure on the secondary side is 'l atm, and the permeation rate of gas (oxygen or nitrogen) that has permeated through the composite membrane. Precision membrane flow meter 5F-101
(manufactured by Standard Technology). The oxygen permeation rate was defined as the gas permeation performance, and the separation coefficient, which is the ratio of the oxygen permeation rate to the nitrogen permeation rate, was used as the evaluation standard for the gas separation performance.

(2) Surface resistance of the conductive layer A room temperature measurement box (RC-02) was connected to a new super megohmmeter (VE-40) manufactured by Kawaguchi Electric, and the surface resistance was measured in a constant temperature and humidity room controlled at 20°C and 60% RH. Measurement was performed with an applied voltage of 100V.

(3) Chargeability of composite membrane The surface potential was measured using a static electricity meter, Statylon TH, manufactured by Shishido Electrostatic Co., Ltd.

(4) Decrease in membrane performance due to dielectric breakdown 10 long lengths of composite membrane whose membrane performance was measured immediately after film formation
M was wound around a core (or paper tube) and left as it was at room temperature for 15 days, after which the membrane performance was evaluated.

[Example code] The present invention will be explained based on examples.

Example 1 A polysulfone/dimethylformamide 15.6 wt% solution was coated on polyester taffeta to a wet thickness of 50 μm, and the coated film was immersed in a water coagulation bath to obtain a polysulfone porous support membrane. A quaternary ammonium salt cationic surfactant (“Fcol 70
A 1 wt % methanol solution (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) was applied in an amount of 100 μm using a slit die coater and dried. The surface resistance of the conductive layer was 1.9×10 9 Ω.

Poly(2,6-dimethyl-1,4-phenylene oxide) 6.10 was dissolved in 400 ml of anhydrous tetrahydrofuran, and 8.5 ml of N,N,N',N'-tetramethylethylenediamine and n-butyllithium were dissolved at room temperature. A n-hexane solution (1,58M>28ml) was added and stirred for 80 minutes. Next, 5.9ml of trimethylchlorosilane and 1.3ml of triethoxychlorosilane were added to the reaction solution.
The mixture was added, W1 stirring was continued for another 1 hour, the resulting reaction solution was poured into 2Q methanol, and the precipitated polymer was collected by filtration. This polymer was purified again by methanol reprecipitation, dried under reduced pressure, and 7.
4 g of polymer [polymer (■)] was obtained. In the infrared spectrum of this polymer, absorption derived from the trimethylsilyl group is seen at 125 Qcm-1, and roughly according to the proton magnetic coexistence vector, the trimethylsilyl group accounts for 25% of the repeating units. It was confirmed that triethoxysilyl groups were introduced into 4% of the units.

This polymer is dissolved in trichlorotrifluoroethane to prepare a 1 wt % solution. This solution is quietly and continuously supplied onto the water surface using a dropping funnel, and the thin film formed on the water surface is continuously composited onto a polysulfone porous support membrane provided with a conductive layer on the side opposite to the polymer liquid supply side. Come, length 10
A long composite membrane of m length was prepared.

Table 1 shows the composite membrane performance and surface potential immediately after preparation.

The long composite membrane was wound around a core and stored at room temperature for 15 days,
Composite membrane performance and surface potential were measured. Display the measurement results.
Shown in 1. As can be seen from Table 1, it can be seen that deterioration in composite membrane performance and charging were suppressed.

Comparative Example 1 The polymer [I] prepared in Example 1 was dissolved in trichlorotrifluoroethane to make a 1 wt% solution, and the mixture was composited onto a polysulfone porous support membrane without a conductive layer according to the method of Example 1. A long composite membrane was created. Table 1 shows the performance and surface potential of the composite membrane immediately after preparation.

The long composite membrane was wound around a core and stored at V temperature for 15 days, and the performance and surface potential of the composite membrane were measured. Display the measurement results.
Shown in 1. As can be seen from Table 1, the composite membrane without a conductive layer had a large decrease in performance and large charge.

Example 2 Polydimethylsiloxane with silanol groups at both ends (
9.5 parts by weight (number average molecular weight approximately 50,000), 0.4 parts by weight of tetra(dimethylketoxime)silane, and 0.1 parts by weight of dibutyltin diacetate were dissolved in trichlorotrifluoroethane to obtain a solid content of 0.5 parts by weight. Adjust to %. This dilute solution was applied to the polysulfone porous support membrane prepared in Example 1 using a slit diecoder to a wet thickness of 25 μm, and was dried by heating at 120° C. for 1 minute to obtain a composite membrane (I). The surfactant used in Example 1 was applied to the taffeta side of the composite membrane (I).
100μ of a 1wt% methanol solution was applied and dried to obtain a composite film (I[>). Trichlorotrifluoroethane, the polymer (I) used in Example 1, was applied on the silicone layer side of the composite film <II). Coat 25μ of 0.5wt% solution with a slit die coater, dry at 120°C, and then form a composite film (III).
The 10m long product is 14. Composite membrane immediately after creation (III)
performance and surface potential were measured. The measurement results are shown in Table-1. The long composite membrane (I) was wound around a core and stored at room temperature for 15 days, and its performance and surface potential were measured. The results are shown in Table-1. As can be seen from Table 1, it can be seen that performance deterioration and charging are suppressed.

Comparative Example 2 25μ of a 0.5wt% trichlorotrifluoroethane solution of the polymer (I) used in Example 1 was applied to the composite membrane (I) of Example 2 using a slit die coater, and after drying at 120'C, A 10 m long crystal of the composite film (IV) was obtained. The performance and surface potential of the composite film (N) immediately after preparation were measured. The measurement results are shown in Table 1. The performance and surface potential were measured after being rolled up and stored at room temperature for 15 days, and the results are shown in Table 1.As seen from Table 1, the composite membrane (II7) without a conductive layer showed a decrease in performance and charging. It can be seen that the is large.

[Effects of the invention] Since the selectively permeable membrane of the present invention has a conductive layer, charging of the selectively permeable membrane is suppressed, there is less deterioration of membrane performance due to static electricity, and gas and liquid separation and permeability are improved. It has excellent practical properties.

Claims (4)

[Claims] (1) A selectively permeable membrane comprising at least a porous support membrane and a functional membrane, characterized in that the composite membrane has one or more conductive layers. (2) The permselective membrane according to claim (1), wherein the conductive layer has a surface resistance value of 1×10^1^0Ω or less. (3) The permselective membrane according to claim (1), wherein the conductive layer is at least on the back surface of the porous support membrane. (4) The permselective membrane according to claim (1), wherein the conductive layer consists of a surfactant as a main component.