JPS61103521A - Selective permeable compound film for gas and its preparation - Google Patents

Abstract

PURPOSE:To prepare a compound film having superior selective permeability for gas, heat resistance and chemical resistance by forming a thin film of a plasma polymer on the surface of a dense layer of an asymmetric film of polyetherimide, then laminating a thin film of organosiloxane. CONSTITUTION:A polyetherimide film as expressed by the formula having asymmetric pore size distribution is used. An extremely thin film of a plasma polymer having excellent gas selective permeability is deposited on a surface layer at a denser side of the polyetherimide. By the deposition of the plasma polymer, pores having <=0.1 micron mean pore size are clogged. Preferred material for the plasma polymn. is an organosilicon compd. having N atom and that having an unsatd. bond. A thin film of organopolysiloxane is further deposited on the plasma polymer film. The film serves as a protecting film of the plasma polymer thin film.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a gas-selective permselective composite membrane and a method for producing the same, and more specifically, it relates to a gas selectively permeable composite membrane and a method for producing the same. The present invention relates to a gas selectively permeable composite membrane in which a thin film is deposited and then a thin film of organopolysiloxane is laminated thereon, and a method for manufacturing the same.

"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. Polyetherimide consisting of repeating units represented by the structural formula;
The aromatic imide provides mechanical strength, the ether bond provides excellent fluidity and processability, and the material also has excellent heat resistance and chemical resistance. This polyetherimide asymmetric pore membrane or a composite membrane made by laminating a thin polymer film such as a plasma polymer on the densely structured surface layer of the asymmetric pore membrane becomes an excellent gas selective permeability membrane. is published in Japanese Unexamined Patent Publication No. 59-11
5738.

However, the content of the invention is that the asymmetric pore size membrane is
In forming a composite membrane using a single support, the authors have not clearly demonstrated a configuration that fully brings out the functions of a plasma polymer thin film with extremely high gas selectivity. In other words, in the examples of composite membrane formation, a two-layer composite membrane in which only a plasma polymer thin film is deposited, or a three-layer composite membrane in which a silicone rubber thin film is laminated on an asymmetric pore size membrane and a plasma polymer thin film is deposited on top of the silicon rubber thin film is laminated on an asymmetric pore diameter membrane. Although exemplified, the selectivity does not exceed the inherent value of the polyetherimide support.

Plasma polymers generally have a highly cross-linked/branched structure and exhibit excellent gas selectivity, but have the disadvantage of being brittle and prone to defects.

It is important to construct a composite membrane by fully considering the characteristics of this plasma polymer.

"Means for Solving the Problems" As a result of intensive study on improvements to the above-mentioned invention, the present inventor first applied a plasma polymer thin film to the surface layer of the densely structured polyetherimide asymmetric pore membrane. The three-layer composite film obtained by depositing and then laminating a thin film of organopolysiloxane becomes a composite film with extremely excellent gas selective permeability and excellent mechanical strength. The present inventors have discovered that these properties can be further improved by using an organosilicon compound containing at least one double bond or triple bond, and have completed the present invention.

"Function" In the eight-layer composite membrane according to the present invention, the polyetherimide asymmetric pore membrane serves as a support. The polyetherimide used in the present invention is a polymer consisting of repeating units represented by 2
, 2-bis (4-(3,4-dicarboxyphenoxy)phenyl)propane anhydride and metaphenylenediamine.

Of course, the positions of carboxy and phenoxy are a, a'; 4
, 4'; 3 , 4' or a mixture thereof, and the structure of propane is most preferably -C(CH3)2-, but other structures such as CH3 -CH2-CH2-CH2-, - It may be CH2-CH-, and furthermore, n of -CnHgH other than propane
= may be in the range of 1 to 8.

Polyetherimide has excellent heat resistance, chemical resistance, mechanical strength, and high gas selectivity, but on the other hand, permeability is somewhat lacking. Therefore, the present invention uses polyetherimide as an asymmetric pore membrane and uses it as a support with excellent gas permeability.

An extremely thin film of plasma polymer with extremely excellent gas selective permeability is deposited on the surface layer of the densely structured side of this asymmetric pore membrane.

The larger the average pore diameter of the asymmetric pore membrane, the higher the gas permeability, but the loss of force selectivity and the difficulty of clogging by the plasma polymer thin film deposited thereon. In order to sufficiently occlude with the plasma polymer and develop a high degree of gas selective permeability through its compositing, it is preferable that the average pore diameter of the surface layer on the side having a dense structure is 0.1 μm or less. Plasma polymerization is a polymerization method in which monomers are introduced in the form of vapor under reduced pressure, an electric field is applied, and the monomers are activated into radicals or ions by inelastic collisions of high-speed electrons, which are sequentially bonded to increase the molecular weight. be.

Its characteristics include being able to obtain a homogeneous and pinhole-free ultrathin film, having a molecular structure rich in branched and cross-linked structures νζ, and being of poor quality. Such a molecular structure has a molecular structure of 5 and σ1, and exhibits a high degree of gas selectivity, and its low quality has an advantageous effect on permeability, and results in a thin film with excellent heat resistance and chemical resistance. Furthermore, the majority of plasma polymers that generally have excellent adhesion to substrates can be polymerized by this method and are applicable to the present invention, but in particular, organosilicon compounds containing nitrogen atoms and at least one It has been found that organosilicon compounds containing more than one double or triple bond provide extremely good gas selective permselectivity. 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,
Contributes to wood-loving and adhesive functions. In addition, double and triple bonds easily become active sites in plasma, promoting a highly cross-linked structure. For these reasons, plasma polymers made from organosilicon compounds containing nitrogen atoms or having at least one double or triple bond have a strong adhesion to polyetherimide asymmetric pore membranes and highly It is presumed that this results in the formation of a thin film with an advanced cross-linked structure, resulting in a composite film with gas selectivity that far exceeds the gas selectivity inherent to polyetherimide.

Specific examples of organosilicon compounds containing a nitrogen atom include bis(dimethylamino)dimethylsilane, bis(dimethylamino)methylsilane, bis(dimethylamino)methylvinylsilane, methyltris(dimethylamino)silane, bis(ethylamino)dimethylsilane, trimethylsilyldimethylamine, 1-trimethylsilylimidazolehexamethyldisilazane, 1,1,3,3-tetramethyldisilazane, 1,1,3,3,5.5-hexamethylcyclotrisilazane, and at least one As an embodiment of an organosilicon compound containing two or more double bonds or triple bonds, trimethylvinylsilane, dimethyldivinylsilane, methyltrivinylsilane, tetravinylsilane, dimethylvinylchlorosilane, allyltrimethylsilane, ethynyltrimethylsilane, divinyltetramethyl Examples include disiloxane and dimethylphenylvinylsilane.

The present invention deposits these plasma polymer thin films onto a polyetherimide asymmetric pore size membrane, and then further laminates an organopolysiloxane thin film thereon. The primary function of the film is a protective coating for plasma polymer thin films with a high degree of gas selectivity. The highly branched-crosslinked structure of plasma polymers
Although it improves gas selectivity, it has the disadvantage of being brittle and lacking in flexibility. Further, in order to increase permeability, it is desirable to make the plasma polymer as thin as possible within the range where the selective function can be expressed. Therefore, a two-layer composite membrane in which a plasma polymer thin film is deposited on a polyetherimide asymmetric pore membrane can be used during film production or during handling when assembling gas-selective permeable composite membranes into modules, and even during actual processing by modules. During gas separation operations, microscopic defects are likely to occur, often leading to variations or rapid decline in gas selection performance.

The organopolysiloxane laminated on the plasma polymer thin film seals minute defects in the plasma polymer thin film and further improves subsequent handling properties dramatically. Organopolysiloxane has excellent heat resistance and chemical resistance, and is a material with high gas permeability, so even if these thin films are laminated, the gas permeability will decrease compared to before lamination. Never. Specific examples of organopolysiloxanes include dimethylpolysiloxane, methylvinylpolysiloxane, methylphenylpolysiloxane, trifluoropropylmethylpolysiloxane, polysiloxanes modified with amino groups, alkylaryl groups, etc., silicone oil, silicone rubber, It is commercially available as silicone oil or silicone primer.

Furthermore, copolymers containing a siloxane structure, such as polydimethylsiloxane-5 bisulfonol A carbonate copolymers, can also be used.

Next, the method for manufacturing the gas selectively permeable composite membrane of the present invention will be described in detail. A polyetherimide asymmetric pore membrane is produced by casting a solution containing the resin in the form of a film or hollow fibers, that is, after evaporating a portion of the solvent, and then immersing it in a coagulation bath mainly consisting of a non-solvent. After gelation and sufficient extraction of the solvent, drying is performed to obtain an asymmetric pore membrane. During this casting, the side that is in contact with the outside air, that is, when it is cast in the form of a film onto a flat plate such as a glass plate, the side opposite to the side that is in contact with the flat plate will have a dense structure, and when spinning hollow fibers, the outer peripheral side will have a dense structure. .

Good solvents for polyetherimide are methylene chloride,
Chlorinated solvents such as chloroform, dimethylformamide,
N-methyl-2-pyrrolidone and the like are preferably used, particularly dimethylformamide and N-methyl-2-pyrrolidone. In addition, a solvent exhibiting relatively good solubility such as tetrahydrofuran may also be used in combination. It is also possible to adjust the pore diameter of the asymmetric pore membrane by adding polyhydric alcohol, inorganic salt, etc. to the solution. These additives are commonly called swelling agents. The solution concentration is usually 10% by weight to 40% by weight.
Adjusted in weight percentage range. When the solution concentration is low, gas permeability increases, but the average pore size increases and mechanical strength also decreases. When the solution concentration is high, the overall structure becomes denser and the mechanical strength increases, but the permeability decreases. The solution is thoroughly degassed through a precision sieve. Next, the solution is cast into a film using, for example, a doctor knife or into a hollow fiber using a tubular nozzle. If dissolved after casting or in the cast solution, it is water, methanol, ethanol,
It is acetone, or it is made by mixing these non-solvents with a good solvent used in solution preparation. Coagulation bath composition and coagulation bath temperature also influence the structure and pore size of asymmetric pore membranes.

After gelation, the film is immersed in a non-solvent until the solvent remaining in the film is sufficiently replaced by the non-solvent, and then dried at a temperature below the heat distortion temperature of polyetherimide. Next, the plasma polymerization operation will be described. Place the polyetherimide asymmetric pore membrane described above in a reduced pressure atmosphere of 5 torr or less, preferably 2 jorr or less, containing a polymerizable monomer,
A glow discharge is applied to deposit a thin plasma polymer film on the surface layer of the densely structured side of the asymmetric pore membrane. The polymerizable monomer may be used alone or with an inert gas such as He or Ar, H2,
NZ, 02. It is introduced into the reaction system together with a non-polymerizable gas such as Co. The conditions for glow discharge need to be changed depending on the monomer used, the device, the shape of the electrode, etc., but generally the discharge output is 5 to 200 W and the discharge time is 10 seconds 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 resulting polymer will have a low molecular weight, and if it is too high, it will damage the polyetherimide asymmetric pore membrane that is the base.

After depositing the plasma polymer film, a thin organopolysiloxane film is then laminated. If necessary, add a vulcanizing agent to the organopolysiloxane solution diluted with a solvent, immerse it,
A thin plasma polymer film is applied to the deposited polyetherimide asymmetric pore membrane by spraying, roll, knife coating, etc.

Subsequently, it is dried or cured by vulcanization to form an organopolysiloxane thin film. The solution concentration and coating thickness are adjusted so that the thickness of the thin film is 50 μm or less, preferably 20 μm or less. Further, the solvent used here is preferably one that does not dissolve or swell the polyetherimide, and for example, alcohols and Freon are preferably used.

The present invention will be explained below with reference to Examples. The gas permeation rate and gas selectivity shown in the examples were determined by separating and detecting permeated components using a gas chromatograph and quantifying them based on the ASTM method (pressure method).The unit of gas permeation rate is α3 (STP). 7cm2-5 e(-CI
! LHJl, and gas selectivity is the ratio of the permeation rates of each gas.

Further, the measurement was carried out in an atmosphere of 80°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 to a thickness of 3 cm using a doctor knife.
After the film was coagulated and peeled off, it was washed with water for 6 hours, and then dried by heating at 110° C. for 1 hour to obtain an asymmetric pore membrane with a thickness of about 150 μm.

When the gas permeation properties of this membrane for helium and nitrogen were evaluated, the following values were obtained.

He permeation rate; 5. s Tetramethyldisilazane and Ar gas
:1 ratio, and the system pressure was 0.45 torr.
) Glow discharge was performed for 20 minutes at an output of 60 W while adjusting the temperature to deposit the surface layer on the densely structured side of the asymmetric pore membrane and the plasma polymer thin film. The device is 13.5
It has a 6 MHz high frequency power source and is equipped with parallel plate capacitively coupled electrodes. The gas permeation characteristics of the two-layer structure film deposited with this plasma polymer thin film were as follows.

He permeation rate; 1.20 X 1O-5N2 permeation rate; 6 Xl0-8He//'NQ selectivity; 2
00 Next, a two-component mixed liquid silicone rubber (
SE6721. ) - After spray coating with a 5% by weight Freon solution of Ray Silicone (manufactured by Co., Ltd.),
Stand the membrane vertically, remove excess solution, and incubate at 120'C.
A thin film was formed by heating and curing. Electron microscopic observation of the cross section after film formation confirmed that the thickness of this thin film was 15 μm. The gas permeation properties of this three-layer membrane, in which a plasma polymer thin film was deposited on this polyetherimide asymmetric pore membrane and then a silicone rubber thin film was laminated thereon, were as follows.

He permeation rate; 1.15 X 1O-5N2 permeation rate; 4 Xl0-8He7'N 2 selectivity; 2
88 Example 2゜Polyetherimide was dissolved in dimethylformamide,
A 30% by weight solution was prepared, and following the same procedure as in Example 1,
An asymmetric pore membrane with a thickness of 175μ was obtained.

Its gas permeation properties were as follows.

He permeation rate; 2.4 The thin film and organopolysiloxane thin film were laminated in this order. Plasma polymerization uses bis(dimethylamino)methylsilane as a monomer and N2 gas as a coexisting gas at a pressure of 0.38 torr.
r, the reaction was carried out for 15 minutes at a discharge output of 40W.

The organopolysiloxane thin film was formed by diluting a silicone primer (ME151; manufactured by Toshiba Silicone Co., Ltd.) with t-butanol and coating and drying to form a film with a thickness of 2 μm. The gas permeation properties of the three-layer composite membrane thus obtained were as follows.

He permeation rate, 7.4 A plasma polymer thin film and an organopolysiloxane thin film were laminated in this order on the surface layer under the following conditions. The plasma polymerization conditions were methyltrivinylsilane and N
2 Gas is supplied at a ratio of 5:1, and the system pressure is 0.
The temperature was 50 torr, the output was 20 W, and the reaction time was 15 minutes.

In addition, regarding the organopolysiloxane thin film, 6% by weight of t-butanol was added to the same two-component liquid silicone rubber as in Example 1.
After applying the solution by dip coating and removing excess solution, 120℃, 3
A film was formed by heating for 0 minutes. The gas permeation properties of the obtained three-layer membrane were as follows.

He permeation rate; 1.3 x 1O-5N2 permeation rate; 6xlO-8 He/1'J2 selectivity; 217 "Effects of the present invention" The gas selectively permeable composite membrane and its manufacturing method according to the present invention are as follows:
By using polyetherimide as the support material, which itself has relatively high gas selectivity, and depositing a plasma polymer thin film on the densely structured surface layer of the asymmetric pore membrane, excellent gas selective permeability can be achieved. By developing it and then layering a thin organopolysiloxane film on top of it,
A composite membrane exhibiting higher and more stable gas selective permeability is provided.

In particular, by forming the plasma polymer thin film with an organosilicon compound containing nitrogen atoms or an organosilicon compound containing at least one 2-type or 3-type packing, heat resistance and resistance properties with extremely high gas selectivity can be achieved. A gas selectively permeable composite membrane with excellent chemical properties and mechanical strength can be provided.

Claims (6)

[Claims] (1) Structural formula: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ An asymmetric pore membrane made of polyetherimide having the repeating unit shown by is used as a support, and the surface layer on the side with a dense structure is coated with glow discharge. A gas selectively permeable composite membrane characterized by laminating a plasma polymer thin film and then an organopolysiloxane thin film. (2) The gas selectively permeable composite membrane according to claim 1, wherein the plasma polymer thin film produced by glow discharge is made of an organosilicon compound containing nitrogen atoms. (3) The gas selectively permeable composite membrane according to claim 1, wherein the plasma polymer thin film produced by glow discharge is made of an organosilicon compound containing at least one double bond or triple bond. (4) In the gas selectively permeable composite membrane according to claim 1, a polyetherimide consisting of a repeating unit represented by the structural formula;
A solution comprising a solvent and, if necessary, a swelling agent is formed into a membrane, contacted with a coagulant, the solvent removed, and dried to obtain an asymmetric pore membrane, which is then heated at 5 Torr containing a polymerizable monomer. A thin plasma polymer film is deposited on the surface layer of the densely structured side of the asymmetric pore membrane by placing it in a reduced pressure atmosphere and causing a glow discharge, then the organopolysiloxane is coated with a solvent and, if necessary, a vulcanizing agent. 1. A method for producing a gas selectively permeable composite membrane, comprising applying a solution comprising the above-mentioned gas and curing it by drying or vulcanization. (5) A method for producing a gas selectively permeable composite membrane according to claim 4, characterized in that plasma polymerization is performed by glow discharge using an organosilicon compound containing a nitrogen atom as a monomer. (6) A gas selectively permeable composite membrane according to claim 4, characterized in that an organosilicon compound containing at least one double bond or triple bond is used as a monomer and plasma polymerized by glow discharge. Production method.