JPH0262294B2 - - Google Patents

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a gas selectively permeable composite membrane and a method for producing the same, and more specifically to a method for applying plasma to a porous tetrafluoroethylene resin membrane as a support. The present invention relates to a gas selectively permeable composite membrane formed by laminating a polymeric membrane and a thin film made of organopolysiloxane, and a method for manufacturing the same.

"Conventional Technology and Problems" In recent years, from the standpoint of energy conservation, the use of gas selectively permeable membranes for gas separation and purification processes has been actively studied. In other words, attempts are being made to selectively permeate oxygen from air to obtain oxygen-enriched air and use it for medical treatment or combustion systems, or to use coal, natural gas, oil sands, etc. as raw materials for processing such as steam reforming or thermal decomposition. Synthesis gas obtained by applying
Alternatively, hydrogen is selectively permeated from waste gas from coke ovens in steel plants, etc., separated and purified from gases such as carbon monoxide and methane, and basic chemicals such as methanol and ethanol are manufactured using these gases as starting materials. There have also been attempts to recover helium from natural gas by selective permeation.

The characteristics required for gas selectively permeable membranes expected for these applications are high gas selectivity and gas permeability, and 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. Tetrafluoroethylene resin is
Because it has excellent heat resistance, chemical resistance, and mechanical strength, gas selective permeability composite membranes based on porous membranes are being developed. Special request 1987-
64506 (see Japanese Unexamined Patent Publication No. 180205/1983), a plasma polymerized membrane of a silane compound containing at least one double bond or triple bond is deposited on a porous tetrafluoroethylene resin membrane or on a tetrafluoroethylene resin porous membrane. An example of a gas selectively permeable composite membrane is disclosed, which is deposited on a composite membrane in which a thin polymer film is laminated onto a porous membrane. Also,
Patent application No. 1982-132859 (see Japanese Patent Application Publication No. 62-60933)
This article discloses examples of gas-selective permselective membranes with a three- or four-layer structure in which a thin polymer film with high gas permeability that performs a mechanical protection function is laminated on a composite membrane on which a plasma polymerized membrane is deposited. There is. However, among these composite membranes, when a plasma polymerized membrane is directly deposited on a porous tetrafluoride resin membrane, the composite membrane has excellent gas permeability but low gas selectivity. be. This is not due to the gas selection function of the plasma polymerized membrane, but is considered to be a problem at the interface between each layer in the composite membrane. In other words, although tetrafluoroethylene resin has excellent properties as mentioned above, it has poor adhesion with other materials due to its chemical inertness, and it has poor adhesion during the process of forming a composite film and during actual use. It is thought that this induces damage and deformation of the plasma polymerized membrane portion, which leads to a decrease in 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 developed an organosilicon compound containing nitrogen atoms on the surface of a polytetrafluoroethylene resin porous membrane having an average pore size of 0.1μ or less. A composite membrane consisting of essentially a three-layer structure, in which a plasma polymerized film mainly composed of is deposited, and then a thin film of organopolysiloxane containing a silane coupling agent or a silicone primer is laminated, is an extremely excellent gas selection material. The present invention was completed by discovering that a gas-selective permeable composite membrane that exhibits permeability and has excellent heat resistance, chemical resistance, and mechanical strength can be obtained.

"Function" In the gas selectively permeable composite membrane according to the present invention, the tetrafluoroethylene resin porous membrane plays the role of a support. Methods for producing the porous tetrafluoroethylene resin membrane include, for example, a nonwoven fabric method, an extraction method, a stretching method, etc., and are not particularly limited, but the stretching method is advantageous from the viewpoint of controlling the pore size and strength characteristics. That is, the most important characteristic required of the porous support of the present invention is the pore diameter. It must be large enough to exhibit the gas selection function of the plasma polymerized film deposited thereon. This means that the plasma polymerized membrane should substantially occlude the surface of the porous support. If the pore diameter of the porous support is large, the plasma polymerized membrane that should be used to block it will become thicker, which will not only reduce gas permeability but also cause cracking and peeling of the plasma polymerized membrane, which has poor flexibility, and will cause problems in gas selection. Sex also disappears. In other words, in order for the plasma polymerized membrane to substantially close the pores of the porous support and to exhibit a high degree of gas selection function in conjunction with the organopolysiloxane layer laminated on the plasma polymerized membrane, the average pore diameter of the porous support must be must be 0.1μ or less. As for other porous properties, the higher the porosity, the better the gas permeability, but on the other hand, the mechanical strength decreases. range. Further, the cross-sectional structure of the porous membrane is more preferably a so-called asymmetric structure in which the surface area of the pores is finer and the inside is larger, but the structure is not limited thereto.

Next, plasma polymerization will be explained. 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. . 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. Furthermore, since high-speed electrons and ions also act on the substrate surface, the adhesion between the plasma polymerized film and the substrate is generally excellent, but the tetrafluoroethylene resin used in the present invention has non-adhesive properties. It has been found that the organic compounds that can be deposited with sufficient adhesion on the polytetrafluoroethylene resin porous membrane substrate are limited because of the high adhesion. After conducting extensive research on organic compounds that can be used to create plasma-polymerized membranes that have superior gas selective permeability in addition to superior adhesive properties, it was discovered that organosilicon compounds containing nitrogen atoms were suitable for this purpose, and the present invention was completed.

Generally, organosilicon compounds are highly polymerizable 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 the polymer in plasma and provide polarity.
For this reason, the plasma-polymerized membrane of an organosilicon compound containing nitrogen atoms adheres well to the porous tetrafluoroethylene resin membrane of the substrate, forming a membrane surface with excellent gas selective permeability.

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-trimethylsilylimidazole, hexamethyldisilazane, 1,1,3,3-
Tetramethyldisilazane, 1,1,3,3,5,
Examples include 5-hexamethylcyclotrisilazane, trimethylsilyl isocyanate, dimethylsilyl diisocyanate, vinylmethylsilyl diisocyanate, and tetraisocyanate. The present invention may be carried out using a single plasma polymerized film of these compounds, but other compounds may also be included. Although many organic compounds may be mentioned, particularly suitable compounds are organosilicon compounds containing at least one double bond. Double and triple bonds are easily activated in plasma, and plasma-polymerized membranes obtained from compounds containing them have highly crosslinked and branched structures, and exhibit excellent gas selective permeability.
Specific examples of these compounds include trimethylvinylsilane, dimethyldivinylsilane, methyltrivinylsilane, tetravinylsilane, dimethylvinylchlorosilane, allyltrimethylsilane, ethynyltrimethylsilane, divinyltetramethyldisiloxane, and dimethylphenylvinylsilane. .

In the present invention, after depositing these plasma polymerized films on a porous tetrafluoroethylene resin film, a thin film of organopolysiloxane containing a silane coupling agent or a silicon primer component is further laminated thereon. The first function of this thin film is as a protective film for the plasma polymerized film having a high degree of gas selective permeability, and the second function is as a repair film for defective parts of the plasma polymerized film. It physically protects the rigid and brittle plasma polymerized membrane grown on the porous membrane, and also provides an infiltration coating for areas where the plasma polymerized membrane does not completely close the pores of the porous membrane or where minute cracks have occurred. The plasma polymerized membrane maintains a high degree of gas selective permeability. By stacking thin films of organopolysiloxane, the high gas selective permeability exhibited by the plasma polymerized film is stabilized, and subsequent handling properties are dramatically improved.

Organopolysiloxane has excellent heat resistance and chemical resistance, and is a material with high gas permeability, so even when thin films thereof are laminated, the gas permeability hardly decreases compared to before lamination. Specific examples of organopolysiloxanes include dimethylpolysiloxane, methylvinylpolysiloxane, methylphenylpolysiloxane, trifluoropropylmethylpolysiloxane, and polysiloxanes modified with amino groups, alkylaryl groups, etc. Silicone oil, silicone rubber, silicone varnish,
Alternatively, it is commercially available as a silicone primer. Additionally, copolymers containing siloxane structures, such as polydimethylsiloxane-bisphenol A
Carbonate copolymers and the like can also be used.

When this organopolysiloxane thin film is laminated on a plasma polymerized film, a silane coupling agent or a silicone primer is used to improve adhesion at the interface. It is desirable that the adhesion of this interface is also excellent in order to maintain a stable gas selective permeation function.

Silane coupling agents are silanes that have hydrolyzable groups such as alkoxy groups, chloro groups, acetoxy groups, alkylamino groups, and propenoxy groups, and organic functional groups such as vinyl groups, epoxy groups, methacrylic groups, amino groups, and mercapto groups. A compound that improves adhesion at interfaces. Silicone primers are mainly composed of condensates of these silane compounds and are also effective in adhesion. It was discovered that this silane coupling agent or silicone primer improves the adhesion between the plasma polymerized film and the organopolysiloxane interface, and furthermore, the silane coupling agent and silicone primer containing amino groups as organic functional groups improve the adhesion between the plasma polymerized film and the organopolysiloxane interface. It was confirmed that it has a higher effect on gender. Specific examples include γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, or combinations thereof. Examples include condensates with epoxysilane.

Next, the method for manufacturing the gas selectively permeable composite membrane of the present invention will be described in detail.

The method for producing the porous tetrafluoroethylene resin membrane is not particularly limited, but a stretching method can generally be suitably used.
The basic process is disclosed in Japanese Patent Publication No. 42-13560, which involves mixing fine powder of tetrafluoroethylene resin with a liquid lubricant, forming it into a sheet or tube shape using a paste method, and then stretching it in an unfired state. In this method, a porous membrane is obtained by subsequently firing the porous membrane. This method has undergone several improvements since then, but
In any case, the most important step in creating porosity is stretching, and the porous properties are controlled by factors such as stretching temperature and stretching ratio. Furthermore, the blending ratio of liquid lubricant, the load pressure during molding, etc. also affect the porous properties. By controlling these operating factors, the average pore size
A porous polytetrafluoroethylene resin membrane with a thickness of 0.1μ or less is formed.

A plasma polymerized film is then deposited on this porous film. The porous membrane is introduced into a reactor under reduced pressure of 5 torr or less, preferably 2 torr or less, and a glow discharge is generated while vapor of an organosilicon compound containing nitrogen atoms or a mixture of this and other monomers is sent to the reactor. , depositing the plasma polymerized membrane on the porous membrane. An inert gas such as He or Ar, or a non-polymerizable gas such as H ₂ , N ₂ , O ₂ or CO may be used together with the monomer as a carrier gas or a diluent gas for the monomer.

Glow discharge conditions need to be changed depending on the monomer used, the shape of the device/electrode, etc., but generally the discharge output is 5 to 500 W and the discharge time is 10 seconds or more.
It takes place for 3600 seconds. If other conditions are the same, the film thickness of the plasma polymer 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, the substrate and the deposited plasma polymer film will be damaged by etching and heat generation effects.

After depositing the plasma polymerized film, a thin film of organopolysiloxane comprising a silane coupling agent or silicone primer component is then deposited. If necessary, a vulcanizing agent is added to the organopolysiloxane solution diluted with a solvent, and the plasma polymerized film is applied to the deposited tetrafluoroethylene resin porous film by dipping, spraying, rolling, knife coating, etc. Subsequently, it is heated and cured to form an organopolysiloxane thin film. The solution concentration and coating thickness are adjusted so that the thickness of the thin film is 50μ or less, preferably 20μ or less. There are two ways to use a silane coupling agent or a silicone primer. One is to apply a solution of a silane coupling agent or silicone primer diluted with an appropriate solvent, heat and cure it, then apply a solution containing organopolysiloxane, heat and cure it, and laminate an organopolysiloxane thin film. It's a method. The other method is to blend a silane coupling agent or a silicone primer into a solution containing organopolysiloxane to form a homogeneous solution, which is then applied, followed by heating and curing to form an organopolysiloxane thin film. It is.

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
cm ³ (STP)/cm ² ·sec·cmHg, and gas selectivity is the ratio of the permeation rates of each gas. Also, the measurement
The test was carried out in an atmosphere of 100℃.

Example 1 27 parts by weight of a liquid lubricant (DOSB, manufactured by Ciel Chemical Co., Ltd.) was mixed with 100 parts by weight of tetrafluoroethylene resin fine powder (manufactured by Daikin Industries, Ltd., F104), and the mixture was molded at a molding pressure of 50 kg/ ^cm2. It was preformed into a cylindrical shape with an outer diameter of 50 mm and an inner diameter of 12 mm, and then extruded into a tube with an outer diameter of 1.3 mm and an inner diameter of 0.3 mm using a ram extruder. The tube was immersed in trichlorethylene to extract and remove the liquid lubricant. Next, it was fed into a furnace at 400°C at a linear speed of 5 m/min, stretched and fired while applying 80% stretching, and the outer diameter was φ1.1 mm and the inner diameter was φ0.2.
A porous tube of tetrafluoroethylene resin having a diameter of 0.08 μm, an average pore diameter of 0.08 μm, and a porosity of 31% was obtained. This porous tube was loaded onto the unwinding drum 10 of the supply chamber 9 of the continuous plasma processing apparatus shown in the figure, and its tip was wound around the winding drum 11. After reducing the pressure inside the device to 0.01 torr, 1,1,3,3-tetramethyldisilazane 5c.c./min, methyltrivinylsilane 2c.c./min, and Ar gas 4c.c are supplied from the raw material gas supply port 7. ./min of mixed gas was introduced, the operating pressure was 0.3 torr, and the discharge power was
A glow discharge was generated by applying 40 W, and the porous tube was moved through the cylindrical reaction tube 3 at a speed for 5 minutes. Note that output electrode 1 has 13.56M.
A Hz high frequency power source (not shown) is connected via a matching box (not shown). Starting with the porous tetrafluoroethylene resin tube on which this plasma polymerized film was deposited, the weight ratio of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane was 10, isopropyl alcohol was 80, and distilled water was 10. It was coated by dipping into a solution uniformly dissolved in water, heated and dried at 120°C, and then mixed with 15% toluene of a two-night mixing type liquid silicone rubber (manufactured by Torre Silicone, SE6721).
After coating the solution by dipping, it was cured by heating at 170°C to form an organopolysiloxane thin film on the composite film. The gas selective permeability of the resulting three-layer composite membrane was evaluated and found to be as follows.

Hydrogen permeation rate QH ₂ ; 1.5×10 ^-5 Carbon monoxide permeation rate QCO ; 1.7×10 ^-7 H ₂ /CO selectivity; 88 “Effects of the present invention” Gas selective permeability composite membrane according to the present invention and method for manufacturing the same uses a porous tetrafluoroethylene resin membrane with an average pore size of 0.1μ or less as a support, deposits a plasma polymerized membrane mainly composed of an organosilicon compound containing nitrogen atoms on this, and then applies silane coupling on top of it. By laminating thin films made of organopolysiloxane containing agents or silicone primer components, we can create composite membranes that exhibit excellent heat resistance, chemical resistance, and mechanical strength, as well as extremely high gas selective permeability. will give.

[Brief explanation of the drawing]

The figure is a schematic diagram of a continuous plasma processing apparatus used in Example 1 of the present invention. In the figure, 1 is an output electrode connected to a high frequency power source (not shown), 2a, 2b
3 is a ground electrode, 3 is a cylindrical reactor, and 4 is an exhaust hole connected to a vacuum pump (not shown). 5 is a polytetrafluoroethylene resin porous tube of the object to be treated, 6a,
6b is a guide roller, 7 is a raw material gas supply port, 8 is a winding chamber, 9 is a supply chamber, 10 is an unwinding drum, 11
is the winding drum.

Claims (1)

[Scope of Claims] 1. A plasma polymerized film mainly composed of an organosilicon compound containing nitrogen atoms is deposited on the surface of a porous tetrafluoroethylene resin film having an average pore size of 0.1μ or less, and a silane coupling is applied thereon. 1. A gas selectively permeable composite membrane, characterized in that thin films made of organopolysiloxane containing a component of a silicone primer or a silicone primer are laminated. 2. The plasma polymerized film mainly composed of an organosilicon compound containing a nitrogen atom is characterized in that it consists of a mixture of an organosilicon compound containing a nitrogen atom and an organosilicon compound containing at least one double bond or triple bond. A composite membrane according to claim 1. 3. The composite membrane according to claim 1, wherein the silane coupling agent or silicone primer contains an amino group. 4 Monomer is supplied to the surface of a polytetrafluoroethylene resin porous membrane having an average pore diameter of 0.1 μ or less in an atmosphere of 5 torr or less, and plasma polymerization is performed under glow discharge to form an organosilicon compound containing nitrogen atoms as the main component. After depositing the plasma-polymerized film, a mixed solution of a silane coupling agent or a silicone primer and an organopolysiloxane is applied, or a solution containing a silane coupling agent or a silicone primer is first applied and then heated and dried. A method for producing a gas selectively permeable composite membrane, which comprises applying a solution containing an organopolysiloxane thereon and laminating a thin film by heating and drying or heating and vulcanizing. 5. To deposit a plasma-polymerized film mainly composed of an organosilicon compound containing nitrogen atoms, a vapor of an organosilicon compound containing nitrogen atoms and a vapor of an organosilicon compound containing at least one double bond or triple bond are used. 5. The manufacturing method according to claim 4, wherein the coexistence is caused by glow discharge and plasma polymerization. 6. The manufacturing method according to claim 4 or 5, characterized in that a silane coupling agent or silicone primer containing an amino group is used.