JPH0143565B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a composite membrane, and more particularly, to an improved production method for a composite membrane having a porous support layer and a polyorganosiloxane polymer layer in close contact with the porous support layer. It is about the method.

A composite membrane having a porous support layer and a polyorganosiloxane polymer layer in close contact with the porous support layer is useful as a gas separation membrane. In other words, a two-layer composite membrane consisting of a porous support layer and a polyorganosiloxane polymer surface layer can be used not only as a separation membrane to obtain slightly oxygen-enriched air, but also as a separation membrane for obtaining slightly oxygen-enriched air. It is also used as a separation membrane to obtain highly oxygen-enriched air by laminating highly selective thin membranes to form a multilayer composite membrane.

Conventionally, two methods have been proposed for forming such a composite film. One is a method in which a porous support is immersed in a chlorinated solvent solution of a dimethyl silicone monomer and a crosslinking agent and then crosslinked by heating (see Japanese Patent Application Laid-Open No. 82380/1983). This method involves simply adhering a thin layer formed by spreading a solution of a polymer in an aqueous insoluble solvent on a water surface to a porous support (see, for example, US Pat. No. 3,874,986).

However, the former method has the disadvantage that the amount of gas permeation through the composite membrane is reduced due to the formation of crosslinked polymers within the pores of the porous support, and the latter method has the disadvantage that the amount of gas permeation through the composite membrane is reduced. The drawback was that it had poor properties and could not withstand long-term operation under high pressure conditions.

The present inventors, as a result of extensive research based on recognition of the above problems, have found that in the latter method, a thermally crosslinkable polyorganosiloxane polymer composition is used in place of the polyorganosiloxane polymer. However, by performing heat crosslinking treatment after adhesion rather than just adhesion, the above problems are resolved, and a composite membrane with high gas permeability, excellent durability, and ability to withstand long-term operation under high pressure conditions is created. We have obtained the knowledge that it is possible to form

The present invention has thus been completed based on the above findings, and includes a method for producing a composite membrane having a porous support layer and a polyorganosiloxane polymer layer in close contact with the porous support layer. A step of forming a thin film by spreading a solution of a non-aqueous solvent of a thermally crosslinkable polyorganosiloxane polymer composition on a water surface, adhering it to a porous support on the water surface, and then subjecting it to thermal crosslinking treatment. The object of the present invention is to provide a novel method for manufacturing a composite membrane, which is characterized in that it is carried out by passing through at least once.

In the present invention, the porous support preferably has a fine structure that can exclude at least 80% of albumin, from the viewpoint of increasing the effectiveness of the composite membrane as a gas separation membrane. Such suitable porous supports are made from polysulfone, polyethersulfone, polyacrylonitrile, a blend of cellulose nitrate and cellulose acetate, etc.
It can be produced by casting the organic solvent solution and gelling it under appropriate conditions. The organic solvent and gelling conditions are appropriately selected depending on the material of the raw material. For example, in the case of polysulfone and polyacrylonitrile, solvents such as dimethylformamide and N-methyl-2-pyrrolidone and gelling conditions at 5 to 30°C are used. When the temperature is a blend of cellulose nitrate and cellulose acetate,
Solvents such as acetone, methyl ethyl ketone and 5
Gelation temperatures of ~40°C can be employed. Also, non-porous materials such as glass plates, plastic sheets, or films can be used as the casting substrate, but if a porous material such as woven or non-woven fabric is used, it can be used as a backing material for the porous support. It has the advantage that it can be used as a material.

In the present invention, it is important that the polyorganosiloxane polymer layer is formed by thermally crosslinking a thermally crosslinkable polyorganosiloxane polymer composition. This imparts durability to the composite membrane.

The thermally crosslinkable polyorganosiloxane polymer composition in the present invention is a composition containing a polyorganosiloxane polymer having a crosslinking site and a crosslinking agent used in combination as necessary. Here, the crosslinking site is preferably one that is not deactivated by contact with water, and hydroxyl groups, amino groups, epoxy groups, unsaturated bonds, active hydrogen, etc. can be preferably employed.
In addition, as a backbone polymer having such a portion,
In addition to polyorganosiloxane, various copolymers containing polyorganosiloxane segments and other polymer segments such as polycarbonate, polystyrene, polyurethane, and fluorine-containing polymers can also be used.

A crosslinking agent is used in combination as appropriate depending on the form of the crosslinking site. For example, when the crosslinking site is a hydroxyl group,
Even with simple heating, crosslinking proceeds through a dehydration condensation reaction, so there is no need to use a crosslinking agent together. However, a multihydroxy compound or a combination of this with an acid catalyst is effective as a crosslinking agent, and it is also possible to In the case of saturated bonds, radical generating substances such as peroxides and azo compounds are effective as crosslinking agents.

In the present invention, the conditions for the thermal crosslinking treatment are not particularly limited, but are usually 40 to 200°C, preferably 60 to 180°C.
℃ degree temperature and 0.5 to 60 minutes, preferably 1 to 30 minutes
It is possible to adopt a time of about minutes.

In the present invention, a layer of the above-mentioned thermally crosslinkable polyorganosiloxane polymer composition on a porous support is formed by spreading a solution of the composition in a water-insoluble solvent on the water surface. It is important that the thin film is attached to the porous support above the water surface. This maintains the high permeability of the composite membrane.

Methods for spreading the above solution on the water surface include dropping small droplets of the solution onto the water surface, or installing a pair of partition rods on the water surface and spreading the solution within the area separated by these. A method in which the distance between partition rods is increased as the solution is dripped (see Japanese Patent Application Laid-open No. 89564/1987), or a movable surface such as a rotating roll is passed through a solution reservoir installed below the water surface, and the solution is deposited on that surface. A method of forcibly spreading the solution on the water surface by pulling it upward (U.S. Patent No.
3767737), various methods can be adopted, but in that a homogeneous film can be obtained stably for a long period of time, spreading by controlling the relative liquid surface position of the aqueous phase and the solution phase is preferred. Preferably, a method of forcing the user to do so can be adopted.

A preferred spreading method in the present invention will be explained based on FIG. 1. FIG. 1 is a cross-sectional view showing a typical example of an apparatus suitable for carrying out the present invention. In this figure, a bathtub 1 is divided into an aqueous phase part 2 and a solution phase part 3 by a partition plate 11, and another partition plate 12 is provided in the solution phase part 3 , which allows a solution outlet part to be separated. 4 and a solution reservoir 14. First, water is injected into the aqueous phase portion 2 until overflow over the partition plate 11 is observed. Next, the solution is injected into the solution reservoir 14 until the water/solution interface at the solution outlet 4 is located between the top of the partition plate 11 and the bottom of the partition plate 12. Next, water is poured into the solution reservoir 14 to form a water layer 13 on the solution surface. Due to the formation of the water layer 13, the water/solution interface at the solution outlet 4 is pushed up and finally reaches the top of the partition plate 11, forming a solution/air interface, which allows the thin layer of solution to spread smoothly on the water surface. The extension will begin.

The pushing up of the water/solution interface at the solution outlet 4 can be achieved by increasing the amount of solution injected into the solution reservoir 14 instead of forming the water layer 13, or by inserting a partition plate 12 with the illustrated volume into the solution reservoir 14 or an inert object, e.g. This can be carried out by various means, such as immersion of solid lumps, mercury droplets, etc., or by making the solution reservoir 14 a sealed structure and increasing the pressure in the gas phase, or by pushing down the sealing lid. layer 1
The method of forming No. 3 can be preferably adopted from the viewpoint of preventing volatilization of the solvent during the operation and simplifying the operation.

The amount of solution flowing out per unit time during film forming operation is very small, but in order to operate for a long time, it is necessary to always maintain a solution/air interface above the solution outlet 4. There is. The means for doing so is not particularly limited, and various methods applicable to pushing up the water/solution interface at the solution outlet portion 4 described above can be employed. In this case as well, increasing the amount of water in the water layer 13 can be preferably adopted from the viewpoint of operational simplicity.

Next, a specific aspect of thin film attachment to the porous support will be explained based on FIG. 1 as well. The thin layer of solution spread on the water surface is desolvated during spreading to form an ultra-thin layer 5.
form. The membrane is brought into contact with the porous support 6 fed out from the feed roll 8 via a contact roll 9 on the water surface, adheres to the porous support 6, and is wound up on a take-up roll 10 as a laminated membrane 7. In this case, if a contact roll 9 of a desired diameter is used and the supporting material 6 is held around it by appropriate means, such as double-sided adhesive tape, and the operation is carried out, an ultra-thin film corresponding to the number of rotations can be formed. It is possible to obtain composite membranes in which the number of layers is superimposed. A similar operation is possible by using an endless belt, and in this case,
It is also possible to carry out thermal crosslinking of ultra-thin film layers continuously by means such as providing a heating zone within the running path of an endless belt.

The thickness of the polyorganosiloxane polymer layer formed as described above should be 500 to 10,000 Å, especially 1,000 Å, because if it is too large, the amount of permeation will decrease, and if it is too small, the separation performance will decrease.
It is desirable that the thickness be approximately 5000 Å. Further, the above-mentioned crosslinking operation can be carried out each time an ultra-thin film layer is deposited, or it can be carried out after several layers are stacked.

In the present invention, the non-aqueous solvent used is one that has a higher density than water and has appropriate volatility under operating conditions. Such solvents include methylene chloride, chloroform, carbon tetrachloride, chlorinated solvents such as 1,1,1-trichloroethane, or trichlorotrifluoroethane,
A variety of fluoro-based solvents such as tetrachlorodifluoroethane, as well as mixtures of these with each other or other solvents, can be used, and it is desirable to select an appropriate solvent in consideration of the solubility of the polymer used, operating conditions, etc. .

The water that forms a thin film on its surface may be not only simple water but also water containing various inorganic or organic substances. For example, water containing salt such as common salt can be used. Of course, the addition of these additives to water must not make the water containing them mutually soluble with the solution solvent.

The present invention has a polyorganosiloxane polymer crosslinked layer on a porous support layer, a highly selective layer on top of the crosslinked layer, and optionally a polyorganosiloxane polymer, etc. on top of the crosslinked layer. It is also applicable to the production of multilayer composite membranes, such as those having a highly permeable layer consisting of.

Here, the material of the highly selective layer is appropriately selected depending on the use of the composite membrane. For example, poly-4-methylpentene-1, polyphenylene oxide, vinyl pivalate polymers and copolymers, cellulose nitrate, etc. are used to separate oxygen from nitrogen, and polyphenylene oxide is used to separate helium from oxygen. , polystyrene, etc., and for separating helium from methane, polystyrene, polycarbonate, etc. can be preferably employed.

Highly selective materials such as those mentioned above have gas permeability of 1/10 to 1/1 that of polyorganosiloxane polymers.
100, which is extremely low, so if a high amount of gas permeation is expected, it is used as an ultra-thin film of 1000 Å or less, particularly about 50 to 500 Å. When such an ultra-thin membrane layer is formed directly on a porous support, it is difficult to avoid the formation of defects in the ultra-thin membrane during the production and use of the composite membrane, and therefore the composite membrane thus obtained has poor separation performance and It can only be of inferior durability. On the other hand, the multilayer composite membrane having a structure in which a polyorganosiloxane polymer layer is interposed in the middle obtained by the present invention has the advantage of having excellent separation performance and durability.

In the present invention, when manufacturing a multilayer composite membrane,
The highly selective layer described above or the highly permeable layer that may be further provided thereon can be formed by various methods, but the method used to form the polyorganosiloxane polymer layer described above is Preferably adopted. However, in this case, the thermal crosslinking treatment step is not necessarily necessary.

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. In the following Examples and Comparative Examples, a porous asymmetric polysulfone membrane having a nonwoven fabric backing layer obtained by the following method was used as the porous support.

A mixture of 82 parts by weight of dimethylformamide and 18 parts by weight of polysulfone (P-3500, manufactured by Union Carbide, USA) was stirred at room temperature all day and night, and then filtered to obtain a homogeneous polysulfone solution. Width this solution
A nonwoven fabric backing layer was formed by casting on a 30 cm, 110 μm thick polyester nonwoven fabric (manufactured by Nippon Vilene Co., Ltd.) at a speed of 3 m/min through a coater, and then immersing it in water maintained at 15°C to gel. A porous asymmetric polysulfone membrane (total thickness 150 μm) was obtained. The surface structure of this film
In SEM observation, the presence of coarse pores with a pore diameter of 100 Å or more was not observed.

Example 1 2% by weight Freon mixed solvent of polydimethylsiloxane having some hydroxyl groups (tetrachlorodifluoroethane/trichlorotrifluoroethane weight ratio
30/70) solution was prepared, and an ultra-thin film of polydimethylsiloxane was formed on the porous substrate using the apparatus shown in FIG. 1, and crosslinked by heat treatment at 150° C. for 15 minutes. By repeating this operation 10 times, a composite membrane having a polydimethylsiloxane crosslinked layer with a thickness of about 0.5 μm adhered to the support was obtained.

A disk-shaped test piece with a diameter of 10 cm was cut out from the composite membrane thus obtained, set in a measurement cell, and subjected to pressure.
When we checked the oxygen enrichment performance by passing air through a 10Kg/cm ² gauge and at a temperature of 25℃, we found that the oxygen concentration was 33.8.
%, and an oxygen permeation rate of 2.5 m ³ /m ² ·hr · atm, and no decrease in oxygen concentration was observed even after a one-week durability test.

Example 2 2% by weight of a polyphenylene oxide/polydimethylsiloxane-polycarbonate copolymer blend (weight ratio 80/20) was applied onto the two-layer composite film obtained in Example 1 using the apparatus shown in FIG. An ultra-thin layer of the blend was deposited using a fluorocarbon mixed solvent (same as in Example 1) solution, and this operation was repeated four times to form a highly selective surface layer made of the blend with a thickness of approximately 0.1 μm. At least a three-layer composite membrane was obtained.

When the oxygen enrichment performance of the thus obtained composite membrane was tested in the same manner as in Example 1, the oxygen concentration was 46.3.
%, oxygen permeation rate is 0.30m ³ /m ²・hr・atm,
Even after a one-week durability test, no decrease in oxygen concentration was observed.

Example 3 In the same manner as in Example 2, the material of the surface high selectivity layer was changed to a poly-4-methylpentene-1/polydimethylsiloxane-polycarbonate copolymer blend (weight ratio 80/20). A layered composite membrane was obtained.

The oxygen enrichment performance tested in the same way was determined by the oxygen concentration
44.9%, and an oxygen permeation rate of 0.45 m ³ /m ² ·hr · atm, and no deterioration in performance was observed even in a one-week durability test.

Example 4 A blend of polydimethylsiloxane partially containing vinyl groups and benzoyl peroxide in an amount equivalent to 0.5 parts by weight per 100 parts by weight of the polymer was used as a thermally crosslinkable polyorganosiloxane polymer composition. A crosslinked polyorganosiloxane layer was formed in the same manner as in Example 1, except that the heating crosslinking treatment conditions were 120°C for 10 minutes, the number of coating operations was 5 times, and the thickness of the polyorganosiloxane polymer layer was approximately 0.2 μm. A composite membrane was obtained.

The oxygen enrichment performance of the composite membrane thus obtained was as follows: oxygen concentration 33.1%, oxygen permeation rate 3.8m ³ /m ² hr atm
No deterioration in performance was observed even after a one-week durability test.

Example 5 Example 2 was applied on the two-layer composite membrane obtained in Example 4.
A three-layer composite membrane was obtained by forming a highly selective surface layer similar to the above.

The oxygen enrichment performance of the composite membrane thus obtained was as follows: oxygen concentration: 45.7%, oxygen permeation rate: 0.42 m ³ /m ² hr.
ATM, and there was no change in performance even after one week.

Comparative Example 1 In the manufacturing process of the two-layer composite membrane of Example 1, the heating crosslinking process was omitted.

In this case, the initial oxygen enrichment performance of the composite membrane is: oxygen concentration 32.7%, oxygen permeation rate 2.6m ³ /m ² hr atm
However, one week later, the oxygen concentration had dropped to 29.8%.

Comparative Example 2 A highly selective surface layer similar to that in Example 2 was formed on the two-layer composite membrane of Comparative Example 1 to obtain a three-layer composite membrane.

In this case, the oxygen enrichment performance is determined by the oxygen concentration being at the initial value.
43.9%, and 39.5% after one week, which was not only inferior to the composite membrane of Example 2 in the initial value, but also extremely poor in durability.

Comparative Example 3 A porous support was directly immersed in the solution prepared in Example 1 at a speed of 0.1 m/min for about 5 minutes, and then heated at 150°C.
Heat crosslinking treatment was performed for 15 minutes. Then, a highly selective surface layer similar to that in Example 2 was formed thereon to obtain a three-layer composite membrane.

Although the oxygen enrichment performance of the composite membrane thus obtained was quite high at an oxygen concentration of 45.5%, the oxygen permeation amount was only 0.15 m ³ /m ² ·hr · atm.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an apparatus suitable for carrying out the method of the invention. Bathtub... 1 , Aqueous phase...2, Solution phase... 3 , Outlet...4, Partition plate...11, Ultra-thin film...5, Porous support...6.

Claims (1)

[Scope of Claims] 1. In a method for producing a composite membrane having a porous support layer and a polyorganosiloxane polymer layer in close contact with the porous support layer, the formation of the polyorganosiloxane polymer layer is performed using a thermally crosslinkable polyorganosiloxane polymer layer. This is carried out by passing through at least one step of attaching a thin film produced by spreading a non-aqueous solvent solution of a siloxane polymer composition on a water surface to a porous support on the water surface, and then subjecting it to heat crosslinking treatment. A method for manufacturing a composite membrane characterized by a method of manufacturing a composite membrane. 2. The method according to claim 1, wherein the porous support has a microstructure with an albumin exclusion rate of 80% or more. 3. The method according to claim 1, wherein the water-insoluble solvent has a higher density than water and has appropriate volatility.