JPH051049B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to a method for producing a gas-selective permselective composite membrane, and more specifically to a method for supporting a polyetherimide asymmetric pore diameter membrane whose surface has been treated and modified with a silane coupling agent or a silicone primer. The present invention relates to a method for manufacturing a gas selectively permeable composite membrane, in which a plasma polymerized membrane is first deposited on the body, and then a thin film of organopolysiloxane is laminated thereon. "Conventional technology and problems" In recent years, gas selective permeable membranes have been actively developed. In actual use, the gas selectively permeable membrane must have not only excellent gas selective permeability (high selectivity and high permeability) but also excellent heat resistance, chemical resistance, and mechanical strength. It is difficult to satisfy these characteristics with a single membrane made of the same material, so a composite membrane with shared functions becomes effective. Structural formula; Polyetherimide, which is composed of repeating units represented by the following formula, is a material with aromatic imide providing mechanical strength, ether bond providing excellent fluidity and processability, and excellent heat resistance and chemical resistance. This polyetherimide asymmetric pore membrane or a composite membrane formed by laminating a thin polymer film such as a plasma polymerized membrane on the densely structured surface layer of the asymmetric pore membrane can be an excellent gas selective permeability membrane. is described in JP-A-59-115738. However, the content of the invention does not specify a structure or manufacturing method that fully brings out the functions of a plasma polymerized membrane having extremely high gas selectivity in forming a composite membrane using an asymmetric pore membrane as a support. That is, in the example of forming a composite film, a method for forming a two-layer composite film in which only a plasma polymerized film is deposited;
Alternatively, a method for forming a three-layer composite membrane in which a silicone rubber thin film is laminated on an asymmetric pore membrane and a plasma polymerized membrane is deposited thereon is exemplified, but the selectivity of the resulting composite membrane is dependent on the support It does not exceed the inherent value of polyetherimide. Plasma polymerized membranes generally have a highly crosslinked/branched structure and exhibit excellent gas selectivity, but on the other hand, they have the disadvantage of being brittle and prone to defects. Furthermore, it is known that the function of a plasma polymerized film is strongly influenced by the chemical and physical structure of the substrate on which the plasma polymerized film is deposited and grown. It is necessary to create a composite membrane with sufficient consideration to the properties of such a plasma polymerized membrane in order to bring out its excellent gas selectivity. "Means for Solving the Problems" As a result of intensive study on improvements to the above invention, the inventors of the present invention have determined that the surface layer of the polyetherimide asymmetric pore membrane on the side having a dense structure is coated with a silane coupling agent or a silicone primer. After treatment and modification, the inventors discovered that by depositing a plasma polymerized membrane and then laminating a thin film of organopolysiloxane, an extremely excellent composite membrane with gas selective permeability could be obtained, and the present invention was completed. Furthermore, it has been found that it is more suitable to use an organosilicon compound containing a nitrogen atom or an organosilicon compound containing at least one double bond or triple bond for forming a plasma polymerized film. "Function" The method for producing a gas selectively permeable composite membrane of the present invention includes:
Basically, it can be divided into the following four steps. (1) Wet-form a polyetherimide asymmetric pore membrane. (2) The asymmetric pore size membrane is dried, and at this time, a solution containing a silane coupling agent or a silicone primer is applied to the surface layer on the side having a dense structure, and the surface is modified by heating and drying. (3) Depositing a plasma polymerized membrane on the densely structured side of the surface-modified asymmetric pore membrane. (4) Subsequently, a solution containing organopolysiloxane is applied and cured by heating to laminate a thin organopolysiloxane film on the plasma polymerized film. Each step will be explained in detail below. The polyetherimide used in step (1) is A polymer consisting of repeating units represented by 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane anhydride and metaphenylenediamine obtained by a condensation reaction .
Of course, the carboxy and phenooxy positions are 3,3';
It may be 4,4';3,4' or a mixture thereof, and propane has the most preferred structure of -C( _CH3 ) _2- , but other _{-CH2 -CH2}
−CH ₂ −,

[Formula] may be used, and furthermore, n may be in the range of 1 to 8 among -C _o H _2o other than propane. This asymmetric pore membrane using polyetherimide is produced by casting a solution containing the resin into a film or hollow fiber, and then immediately or after partially evaporating the solvent from the surface, it is placed in a coagulation bath mainly consisting of a non-solvent. It can be obtained by soaking it in water and gelling it. Good solvents for polyetherimide include chlorinated solvents such as methylene chloride and chloroform, dimethylformamide, and N-methyl-2-pyrrolidone, with dimethylformamide and N-methyl-2-pyrrolidone being particularly preferred. In addition, a solvent exhibiting relatively good solubility such as tetrahydrofuran may also be used in combination. The pore size of the asymmetric pore membrane can also be controlled by adding polyhydric alcohol, inorganic salt, etc. to the solution. These additives are commonly called swelling agents. The solution concentration is usually prepared in the range of 10% to 40% by weight. When the solution concentration is low, the resulting asymmetric pore membrane has a high porosity and gas permeability, but on the other hand, its mechanical strength is decreased. On the other hand, when the solution concentration is high, the resulting asymmetric pore membrane has a denser overall structure and is stronger, but its gas permeability is reduced. The solution, which has been thoroughly stirred and dissolved, is passed through a precision sieve to defoam. Next, the solution is cast into a film using, for example, a doctor knife, or into a hollow fiber using a tubular nozzle. Immediately after casting or after partially evaporating the solvent in the cast solution from the surface, it is immersed in a coagulation bath mainly consisting of a non-solvent to form a gel. The coagulant is, for example, water, methanol, ethanol, acetone, or a mixture of these non-solvents with a portion of the good solvent used in solution preparation. The coagulation bath composition and coagulation bath temperature also affect the structure of the asymmetric pore membrane,
Affects pore size. In general, when conditions with a slow solidification rate are selected, the resulting asymmetric pore membrane tends to have a more dense overall structure. For example, the coagulation rate can be slowed down by increasing the ratio of good solvent in the coagulation bath or lowering the coagulation bath temperature. After gelation, the membrane is immersed in a non-solvent until the solvent remaining in the membrane is sufficiently replaced with the non-solvent. Once the solvent removal is completed, proceed to the next step (2). Step (2) is an important step that characterizes the present invention. That is, to dry the asymmetric pore membrane formed in step (1), a solution containing a silane coupling side or a silicone primer is applied to the surface layer on the side having a dense structure, and then dried by heating. Of course, after semi-drying or drying, a solution containing a silane coupling agent or silicone primer may be applied and dried again. Silane coupling agents have hydrolyzable groups such as alkoxy groups, chloro groups, acetoxy groups, alkylamino groups, and propenoxy groups, and functional groups such as vinyl groups, epoxy groups, methacrylic groups, amino groups, and mercapto groups. , is widely used as a surface modifier. Silicone primers are composed of condensates of silane coupling agents caused by reactions between organic functional groups, co-hydrolysis reactions between hydrolyzable groups, etc., and have the same effects as silane coupling agents, but the difference is that The silicon primer has film-forming ability. In any case, the main focus of this step is to modify the surface of the asymmetric pore membrane with the silane coupling agent or silicone primer. The purpose of surface modification is related to the next step (3), plasma polymerized film deposition. The properties of plasma polymerized films are strongly influenced by the chemical and physical properties of the substrate. The present inventors have discovered that when a plasma polymerized membrane is deposited after treating the surface of an asymmetric pore membrane with a silane coupling agent or a silicone primer, the gas selective permeation function is further improved compared to the case without treatment. The reason for this is not clear, but it is presumed that the chemical structure of the interface changes due to the difference in the adsorption reaction and chemical reaction between the substrate surface and the monomer during the initial stage of polymerization. In addition, in the case of silicon primers, the higher-order structure such as the pore morphology or smoothness of the asymmetric pore membrane surface is also changed, which is thought to have a positive effect on gas selective permeability. Typical silane coupling agents include vinyltriethoxysilane, diphenyldimethoxysilane, γ-chloropropyltrimethoxysilane, and γ-chloropropyltrimethoxysilane.
-aminopropyltriethoxysilane, N-(β
-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and silicone A primer is obtained. The silane coupling agent or silicone primer is used after being diluted with a suitable solvent. Of course, a solvent that dissolves or swells polyetherimide cannot be used. Alcohols are generally preferred. The asymmetric pore membrane is treated with a solution containing a silane coupling agent or silicone primer and then heated to dry or cure. If the temperature at this time is low, the bonding of the silane coupling agent or silicone primer to the asymmetric pore membrane will be insufficient, and if it is too high, the porous structure of the asymmetric pore membrane will be deformed. Generally processed at temperatures between 60°C and 180°C. In the next step (3), a plasma polymerized membrane is deposited on the surface layer of the modified dense structure side of the polyetherimide asymmetric pore membrane. Plasma polymerized membranes introduce monomers in the form of vapor under reduced pressure.
Applying an electric field to activate monomers into radicals or ions through inelastic collisions of high-speed electrons,
This is a polymerization method that increases the molecular weight by sequentially bonding. Its characteristics include the ability to obtain a homogeneous, ultra-thin film without pinholes, the molecular structure rich in branched and crosslinked structures, and the fact that it is amorphous. Such a molecular structure acts as a molecular sieve and exhibits a high degree of gas selectivity, and the amorphous nature has an advantageous effect on permeability and results in a thin film with excellent heat resistance and chemical resistance. The vast majority of organic monomers can be polymerized in this way and are applicable to the present invention, but especially organosilicon compounds containing nitrogen atoms or containing at least one double or triple bond. was found to provide extremely excellent gas selective permeability. In general, organosilicon compounds have high polymerizability and tend to form high-quality polymer thin films under a wide range of operating conditions. On the other hand, nitrogen atoms are relatively easily incorporated into polymers in plasma and exhibit hydrophilic and adhesive functions. In addition, double bonds and triple bonds easily become active sites in plasma, promoting a highly cross-linked structure. For these reasons, plasma-polymerized membranes made from organosilicon compounds containing nitrogen atoms or at least one double bond or triple bond adhere to surface-modified polyetherimide asymmetric pore membranes. Also, a thin film with a highly cross-linked structure is formed, resulting in a composite film with gas selectivity that far exceeds the gas selectivity inherent to polyetherimide. Deposition of plasma-polymerized membranes results in a surface-modified, densely structured side of the asymmetric pore membrane;
Glow discharge is performed by exposing to a reduced pressure atmosphere of 5 torr or less, preferably 2 torr or less, containing a monomer.
The monomer can be used alone or with an inert gas such as He or Ar,
It is supplied in coexistence with non-polymerizable gases such as H ₂ , N ₂ , O ₂ , and CO. The conditions for glow discharge need to be changed depending on the monomer used, the shape of the electrode and reaction tube, etc., but generally the discharge output is 5 to 200 W and the discharge time is 10 to 3600 seconds. Other operating conditions being the same, the plasma polymer film thickness is approximately proportional to the discharge time. If the discharge output is too low, the polymer produced will have a low molecular weight, and if it is too high, it will damage the substrate and the deposited plasma polymerized film due to etching and heat generation effects. After surface-modifying the densely structured surface layer of the polyetherimide asymmetric pore membrane with a silane coupling agent or silicone primer, a plasma polymerized membrane is deposited to create a composite membrane with excellent gas selective permeability. However, by further laminating a thin film of organopolysiloxane on this composite membrane in step (4), a stable gas selectively permeable composite membrane is obtained.
The main functions of the organopolysiloxane thin film are:
This is a protective film for a plasma polymerized film with a high degree of gas selectivity. Although the highly branched and crosslinked structure of plasma polymerized membranes increases gas selectivity, it leads to the disadvantage of being brittle and lacking in flexibility. Further, in order to increase permeability, it is desirable to make the plasma polymerized membrane as thin as possible within the range where the selective function can be expressed. Therefore, a two-layer composite membrane in which a plasma-polymerized membrane is deposited on a modified surface layer of a polyetherimide asymmetric pore membrane is difficult to handle during film production or when assembling gas-selective permselective membranes into modules. , and even during the actual gas separation operation using the module.
It is easy to generate minute defects, which often leads to variations or rapid decline in gas selection performance. The organopolysiloxane layered on the plasma-polymerized film seals minute defects in the plasma-polymerized film and dramatically improves subsequent handling. The specific operation of step (4) is to add a vulcanizing agent if necessary to the organopolysiloxane solution diluted with a solvent, and use methods such as dip coating, spray coating, roll coating, knife coating, etc.
It is coated on the composite film obtained in steps up to (3) and then heated and cured to form an organopolysiloxane thin film. Organopolysiloxane has excellent heat resistance and chemical resistance, and is a material with high gas permeability, so even if thin films thereof are laminated, the gas permeability of the composite membrane will hardly decrease. Specific examples of organopolysiloxanes include dimethylpolysiloxane, methylvinylpolysiloxane, methylphenylpolysiloxane, trifluoropropylmethylpolysiloxane, and polysiloxanes modified with amino groups, alkylaryl groups, etc. Silicone oil, It is commercially available as silicone rubber, silicone varnish, or silicone primer. Furthermore, copolymers containing a siloxane structure, such as polydimethylsiloxane-bisphenol A carbonate copolymers, can also be used.
A solution is prepared by dissolving these organopolysiloxanes in a suitable solvent and adding a vulcanizing agent if necessary. A solvent that dissolves or swells the polyetherimide support cannot be used. Alcohols such as ethyl alcohol, isopropyl alcohol and t-butyl alcohol, or freonne are used as the main solvent.
Lamination thickness is mainly controlled by solution concentration. After coating, it is cured by heating drying or heating vulcanization. The heating temperature is limited to below the heat distortion temperature of polyetherimide. The present invention will be explained below with reference to Examples. The gas permeation rate and gas selectivity shown in the examples were determined based on the ASTM method (pressure method) by separating and detecting permeated components using a gas chromatograph and quantifying them. The unit of gas permeation rate is
cm ³ (STP)/cm ² Sec·cmHg, and gas selectivity is the ratio of the permeation rates of each gas. Furthermore, the measurements were conducted in an atmosphere of 100°C. Example 1 Polyetherimide (ULTEM; sold by Engineering Plastics Co., Ltd.) was dissolved in N-methyl 2-pyrrolidone to prepare a 25% by weight solution. Spread this solution onto a smooth glass plate using a doctor knife until thick.
The glass plate was cast in a 5% aqueous solution of N-methyl 2-pyrrolidone at a temperature of 5°C. After the membrane was coagulated and peeled off, it was washed in running water for 24 hours. After applying a solution of γ-methacryloxypropyltrimethoxysilane, isopropyl alcohol, and distilled water in a weight ratio of 10:80:10 to the surface of the densely structured side of the obtained wet asymmetric pore membrane. , a surface-modified asymmetric pore membrane was obtained by drying in an atmosphere of 120°C.
This film is placed in a Bergier type plasma reactor,
After evacuating the inside of the device to below 0.01 torr, 1,1,3,3 tetramethyldisilazane and N ₂ gas were introduced at a ratio of 2:1, and glow was performed for 15 minutes at an output of 60 W while adjusting the system pressure to 0.45 torr. A discharge was applied to deposit a plasma polymerized film on the modified surface layer of the asymmetric pore size film. The device has a 13.56MHz high-frequency power source and is equipped with parallel plate capacitively coupled electrodes. Next, a 5% by weight Freon solution of a two-component liquid silicone rubber (SE6721, manufactured by Toray Silicone Co., Ltd.) was spray coated on the plasma polymerized film.
The film was stood vertically, excess solution was removed, and the film was cured by heating at 120°C to form a thin film. The gas selectivity of the resulting composite membrane having a substantially three-layer structure was as follows. Helium permeation rate QHe; 1.8×10 ^-5 Nitrogen permeation rate QN ₂ ; 6.8×10 ^-8 He/N ₂ selectivity; 265 Comparative example 1 A silane coupling agent was used to dry a wet asymmetric pore membrane. without processing
The gas selective permeability of the three-layer composite membrane prepared under the same conditions as in Example 1 except that it was dried in an atmosphere of 120°C was as follows. QHe; 2.0×10 ^-5 QN ₂ ; 1.8×10 ^-7 He/N ₂ selectivity; 111 Example 2 Polyetherimide was dissolved in dimethylformamide, a 30% by weight solution was prepared, and a thickness was The film was cast to a thickness of 300μ, left in an atmosphere of 30°C and 50% relative humidity for 1 minute, and then immersed in distilled water at a temperature of 10°C. After the film solidified and peeled off, it was washed under running water for 24 hours. After applying a 50% t-butyl alcohol solution of silicone primer (ME151; manufactured by Toshiba Silicone Corporation) to the surface layer of the densely structured side of the obtained asymmetric pore membrane in a wet state, it was heated in an atmosphere of 140°C. A surface-modified asymmetric pore membrane was obtained by drying with . A plasma polymerized film and an organopolysiloxane thin film were formed on this film using the same procedure as in Example 1. The plasma polymerization conditions were to supply methyltrivinylsilane and _N2 gas at a ratio of 4:1, and to reduce the system pressure.
It was 0.45torr, output 30W, and reaction time 15 minutes. Example 1 Formation of organopolysiloxane thin film
It was carried out under the same conditions. The gas selective permeability of the obtained composite membrane was as follows. QHe; 1.4×10 ^-5 QN ₂ ; 4.5×10 ^-8 He/N ₂ selectivity; 311 Comparative example 2 Composite membrane prepared under the same conditions as in Example 2, except that surface modification with silicon primer was not performed. The gas selective permeability of was as follows. QHe; 2.0×10 ^-5 QN ₂ ; 2.3×10 ^-7 He/N ₂ selectivity; 87 "Effects of the present invention" The method for producing a gas selectively permeable composite membrane according to the present invention has heat resistance, chemical resistance, A polyetherimide asymmetric pore membrane with excellent mechanical strength and relatively excellent gas selectivity is used as a support, and a plasma polymerized membrane with a high degree of gas selective permeability and an organopolysiloxane with a protective function are used as a support. In addition to laminating thin films to produce a composite membrane with excellent gas selective permeability, the surface layer on the side with a dense structure of the asymmetric pore membrane is treated with a silane coupling agent or silicone primer to modify the surface. In this way, the interfacial properties between the surface and the plasma polymerized membrane are improved, and as a result, a gas selectively permeable composite membrane exhibiting even better gas selectivity is provided.

Claims (1)

[Claims] 1 Structural formula; A film is formed from a solution containing a polyetherimide consisting of repeating units represented by the formula and a solvent and, if necessary, a swelling agent, and is brought into contact with a coagulant, and after removing the solvent, a film containing a silane coupling agent or a silicone primer is formed. After applying the solution, it is heated and dried to obtain a polyetherimide asymmetric pore membrane with a modified surface layer on the side having a dense structure, and then the asymmetric pore membrane is introduced into a reduced pressure atmosphere of 5 torr or less containing a polymerizable monomer. , depositing a plasma polymerized membrane on the densely structured modified surface layer of the asymmetric pore membrane by glow discharge, followed by a solution comprising an organopolysiloxane, a solvent and, if necessary, a vulcanizing agent. 1. A method for producing a gas selectively permeable composite membrane, which comprises coating the membrane, curing it by heating drying or heating vulcanization, and laminating an organopolysiloxane thin film. 2. The method for producing a gas selectively permeable composite membrane according to claim 1, characterized in that plasma polymerization is carried out by glow discharge using an organosilicon compound containing a nitrogen atom as a polymerizable monomer. 3. Production of a gas-selective permselective composite membrane according to claim 1, characterized in that an organosilicon compound containing at least one double bond or triple bond is used as a polymerizable monomer and plasma polymerized by glow discharge. Method.