JPH05154366A - Gas separation film and production thereof - Google Patents

Abstract

PURPOSE:To obtain a gas separation film large in permeation velocity of gas and good in selectivity and low in deterioration with the lapse of time by dissolving silicone into polyolefin which contains a component of superhigh molecular weight in prescribed amount and has the specified distribution of the molecular weight and drying gelatinous composition in a sheet shape and thereafter stretching the gelatinous composition at least in the uniaxial direction. CONSTITUTION:Polyolefin having superhigh molecular weight of >=7X10<5> weight- average molecular weight (Mw), polyolefin wherein the ratio of weight-average molecular weight to number-average molecular weight is 10-300 and silicone are mixed at a rate of >=1wt.%, 10-30wt.% and 90-70wt.%. A solution consisting of 50-99wt.% solvent for 1-50wt.% total of polyolefin and silicone is prepared. Thereafter the same is extruded from a die and cooled to give gelatinous composition. When the gelatinous composition is dried and thereafter stretched at least in the uniaxial direction, silicone is favorably introduced into fine pores in a large amount. In such a way, a gas permeating film is obtained which is large in permeation velocity of gas and good in selectivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas separation membrane composed of a polymer composite membrane and a method for producing the same, and in particular, it has a high gas permeation rate, good selectivity, and little decrease in selectivity over time. TECHNICAL FIELD The present invention relates to a gas separation membrane and a method for manufacturing the same.

[0002]

2. Description of the Related Art Membrane separation methods for separating various mixtures using a membrane having pores include
In recent years, it has become more and more popular as a method of performing energy-saving filtration, and its technique is being applied in various fields. Further, the separation target in the membrane separation method is not only a solid-liquid mixture but also a wide range of liquid-liquid, gas-gas, gas-liquid mixture, and attention is being paid to the development of separation techniques for various mixtures.

In particular, gas separation by the membrane separation method is expected to be used for separating various gases because it is advantageous in terms of energy, has a simple device structure, and is small and lightweight.

Such a gas separation membrane is required to have excellent gas selectivity and a high permeation rate. However, in general, there is a limit to improving the gas selectivity itself, and therefore it is most effective to substantially increase the gas permeation amount, and it is necessary to make the membrane as thin as possible.

Therefore, it is conceivable to use a microporous film made of an ultrahigh molecular weight polyolefin which is excellent in strength, but there is a limit to thinning it.

In order to solve such a problem, a method of coating the pores of the microporous membrane with a substance that improves the separation performance has been proposed. As such a method, for example, a microporous membrane made of ultra-high molecular weight polyolefin is dipped in a solution of silicone to impregnate the porous membrane (JP-A-52-254).
No. 83, No. 53-86684, No. 58-55005), or a method of superposing a thin film obtained by spreading a silicone solution on the water surface and a porous film (JP-A-57-1906065).

However, a gas separation membrane obtained by immersing a microporous membrane made of ultra-high molecular weight polyolefin in a solution of silicone and impregnating the porous membrane causes pinholes and the like when the thickness of the coating film is reduced. However, there is a problem in that the selectivity is significantly reduced. Therefore, it is necessary to increase the film thickness of the coating film. However, this causes the film thickness of the microporous film to be substantially increased, which causes a problem that the gas permeation rate decreases.

Further, the method of superposing a thin film obtained by spreading a silicone solution on the surface of water and a porous film has a problem that the production conditions of the thin film of silicone are not easily controlled and the productivity is greatly deteriorated.

Therefore, the present inventors formed a gel-like sheet from a solution of an ultra-high molecular weight polyolefin, replaced the solvent contained in the gel-like sheet with silicone, and then heat-stretched it to obtain a porous sheet. We proposed a gas selective permeable membrane in which the pores of a thin film were filled with silicone.
(JP-A-61-157325).

By this method, a gas separation membrane having an extremely high selective gas permeability and a high permeation rate can be obtained. However, in the above method, it is difficult to control the content of silicone introduced into the membrane, and since the amount of silicone that can be introduced is limited, it is possible to further improve the selective permeability. desired. Further, it has been found that the gas separation membrane has a high gas selective permeability in the initial stage, but the gas selective permeability tends to decrease when used for a long period of time. If the selective permeability of the gas can be maintained at a high level, the reliability and economy of the gas separation process will be improved.

On the other hand, Japanese Unexamined Patent Publication No. 2-72932 discloses a dimethylsiloxane-based or heat-crosslinking type silicone rubber 60 to 95% by volume.
And a gas separation membrane obtained by extruding a mixture of 40 to 5% by volume of polyethylene having a molecular weight of 100,000 or more under shear conditions and stretching the extrudate.

[0012] However, although the gas separation membrane described above has a good gas selective permeability, since only a thick membrane can be obtained, there is a problem that the gas permeation rate is significantly slow and the separation efficiency is not good. ..

Therefore, an object of the present invention is to provide a gas separation membrane having a high gas permeation rate, good selectivity, and less deterioration in selectivity over time.

Another object of the present invention is to provide a method for producing the above gas separation membrane.

[0015]

As a result of earnest research in view of the above-mentioned object, the present inventor has formed a gel-like sheet from a solution of an ultrahigh molecular weight polyolefin, and uses a solvent contained in the gel-like sheet as silicone. Since the decrease in the selectivity of the gas separation membrane obtained by heating and stretching after the replacement is considered to be due to the decrease in the fixing power of the silicone into the micropores, the silicone is introduced more satisfactorily into the micropores. It was found that it should be done. Further, the present inventors use, as the polyolefin serving as the base material of the separation membrane, a polyolefin containing a predetermined amount of an ultrahigh molecular weight component and having a molecular weight distribution (weight average molecular weight / number average molecular weight) within a predetermined range, By dissolving silicone in a solution of a polyolefin to form a gel-like sheet, drying the gel-like sheet obtained from the solution of this polyolefin + silicone, and then stretching it in at least one axial direction, a large amount of silicone is present in the microporosity. Found to be introduced in. The present invention has been made based on the above.

That is, the gas separation membrane of the present invention contains 1% by weight or more of an ultrahigh molecular weight polyolefin having a weight average molecular weight (Mw) of 7 × 10 ⁵ or more, and the weight average molecular weight / number average molecular weight of the polyolefin is 10 to 300. A gas separation membrane consisting of a porous thin film consisting of -30% by weight and 90-70% by weight of silicone, characterized in that the pores of the porous thin film are substantially closed and filled with silicone. ..

Further, the method of the present invention for producing the above gas separation membrane comprises 1% by weight of a component having a weight average molecular weight of 7 × 10 ⁵ or more.
With respect to the total content of the above-mentioned polyolefin and silicone, 1 to 50% by weight, and 10 to 30 parts by weight of polyolefin having a molecular weight distribution (weight average molecular weight / number average molecular weight) of 10 to 300 and silicone of 90 to 70 parts by weight. , Preparing a solution consisting of 50-99 wt% solvent, extruding the solution through a die, cooling to form a gel composition, and drying the gel composition,
It is characterized in that it is subsequently stretched.

The present invention will be described in detail below. The gas separation membrane used in the present invention has a weight average molecular weight (Mw) of 7 ×
A porous thin film made of a polyolefin containing 10 ⁵ or more ultra-high molecular weight polyolefin in an amount of 1 wt% or more and having a weight average molecular weight / number average molecular weight of 10 to 300 has a structure in which silicone is occluded and filled in the pores. It is a molecular composite membrane.

The weight average molecular weight / number average molecular weight of the polyolefin used as the base material of the polymer composite membrane is 10 to 300, preferably 12 to 250. When the weight average molecular weight / number average molecular weight is less than 10, the high molecular weight component becomes too much, and it becomes difficult to economically form a thin film by stretching, and the effect of fixing silicone described below is not sufficient, and the molecular weight distribution is 30.
When it exceeds 0, the low molecular weight component is broken during stretching and the strength of the entire film is reduced.

The larger the weight average molecular weight / number average molecular weight ratio used as a measure of the molecular weight distribution, the wider the molecular weight distribution.

In the present invention, the weight average molecular weight / number average molecular weight of the polyolefin is set to 10 to 300, which is larger than the weight average molecular weight / number average molecular weight of ordinary ultrahigh molecular weight polyolefin itself (usually about 6). .. As a result, the molecular weight distribution spreads toward the lower molecular weight side,
A highly concentrated polyolefin solution can be prepared.

When the content of the component having a weight average molecular weight of 7 × 10 ⁵ or more in the above-mentioned polyolefin is less than 1% by weight, the entanglement of the molecular chains of the ultrahigh molecular weight polyolefin, which contributes to the improvement of the stretchability, is hardly formed, resulting in high strength. A microporous membrane cannot be obtained. On the other hand, the upper limit of the content of the ultrahigh molecular weight component is not particularly limited, but if it exceeds 90% by weight, it becomes difficult to increase the concentration of the intended polyolefin solution, which is not preferable.

This polyolefin may be either a single polyolefin or 2 if it has the above-mentioned molecular weight and molecular weight distribution.
It may be either a composition of one or more polyolefins.

In the case of a single polyolefin, for example, it contains 1% by weight or more of an ultrahigh molecular weight component having a weight average molecular weight of 7 × 10 ⁵ or more, and has a molecular weight distribution (weight average molecular weight / number average molecular weight) of 10 to 300. It can be produced by multistage polymerization. As the multistage polymerization, it is preferable to produce the ultrahigh molecular weight portion and the low molecular weight portion by two-stage polymerization.

Further, in the case of a polyolefin composition (mixture), an ultrahigh molecular weight polyolefin having a weight average molecular weight of 7 × 10 ⁵ or more and a polyolefin having a weight average molecular weight of less than 7 × 10 ⁵ have a weight average molecular weight / number average molecular weight of It can be obtained by mixing an appropriate amount within the above range.

In the case of the composition, the ultrahigh molecular weight polyolefin has a weight average molecular weight of 7 × 10 ⁵ or more, preferably 1 × 10 5.
⁶ to 15 × 10 ⁶ . Weight average molecular weight is 7 × 10 ⁵
If it is less than the above, the maximum draw ratio is low and the desired microporous membrane cannot be obtained. On the other hand, the upper limit is not particularly limited, but if it exceeds 15 × 10 ⁶ , the moldability is poor in the formation of a gel-like molded product.

Such ultra-high molecular weight polyolefins include ethylene, propylene, 1-butene, 4-methyl-1-
Examples thereof include crystalline homopolymers obtained by polymerizing pentene, 1-hexene and the like, two-stage polymers, copolymers and blends thereof. Of these, ultra high molecular weight polyethylene, particularly high density ultra high molecular weight polyethylene is preferred.

The content of the above ultrahigh molecular weight polyolefin in the polyolefin composition is 1% by weight or more based on 100% by weight of the entire polyolefin composition. When the content of the ultra-high molecular weight polyolefin is less than 1% by weight, the entanglement of the molecular chains of the ultra-high molecular weight polyolefin that contributes to the improvement of the stretchability is hardly formed, and a high-strength microporous membrane cannot be obtained. On the other hand, the upper limit is not particularly limited, but if it exceeds 90% by weight, it becomes difficult to increase the concentration of the intended polyolefin solution, which is not preferable.

The polyolefin other than the ultrahigh molecular weight polyolefin in the polyolefin composition has a weight average molecular weight of less than 7 × 10 ⁵ , but the lower limit of the weight average molecular weight is 1 × 10 ⁴ . Weight average molecular weight is 1 × 10 ⁴
If the amount of the polyolefin used is less than the range, breakage easily occurs during stretching, and the desired microporous membrane cannot be obtained. In particular, it is preferable to add a polyolefin having a weight average molecular weight of 1 × 10 ⁵ or more and less than 7 × 10 ⁵ to the ultrahigh molecular weight polyolefin.

Examples of such polyolefins include ethylene, propylene, 1-butene, 4-methyl-1-pentene,
Examples thereof include crystalline homopolymers obtained by polymerizing 1-hexene and the like, two-stage polymers, copolymers, and blends thereof. High density polyethylene, which is a polymer mainly composed of ethylene, is particularly preferable.

If necessary, the above-mentioned polyolefin may include an antioxidant, an ultraviolet absorber, a lubricant,
Various additives such as anti-blocking agents, pigments, dyes, and inorganic fillers can be added within a range that does not impair the object of the present invention.

In the present invention, silicone is a general term for organopolysiloxanes, which are bonded to at least one carbon atom per silicon, and
It is a polymer compound having -O-) as a repeating unit. The polymerization degree of such silicone is generally 10 or more, and particularly preferably 10 to 10,000.

As the silicone, a polydimethylsiloxane polymer in which a methyl group is bonded to Si in the repeating unit is basically used, and hydrogen, a vinyl group, a hydroxyl group, an amino group, a carboxyl group, an epoxy group, at the terminal or inside thereof, Modified polysiloxane having methacryloxy group, mercapto group, long-chain alkyl group, phenyl group, chlorine or fluorine bonded, and further having non-polysiloxane moiety in the main chain, for example, alkylene oxide modified polysiloxane, silicone modified copolymer , Alkoxysilane-modified polymers and the like. Among these, polymethyl vinyl siloxane, polymethyl phenyl vinyl siloxane, polymethyl fluoro vinyl siloxane, polydimethyl siloxane having a terminal hydroxyl group blocked, etc. Polysiloxane and the like are preferable.

If desired, an adsorbent such as porous silica-alumina, a cross-linking agent, and a reinforcing material may be added to the silicone.

The ratio of the above-mentioned polyolefin to silicone is 90 to 70% by weight of silicone with respect to 10 to 30% by weight of polyolefin. Polyolefin
Below 10% by weight (above 90% by weight of silicone)
However, the amount of silicone becomes too large, and excess silicone oozes out on the surface of the film during heating and stretching, which will be described later, and coats the film, making it difficult to form a thin film. In addition, polyolefin is 30
If it is more than wt% (less than 70 wt% silicone),
The effective cross-sectional area of silicone (ratio of silicone to the membrane area) decreases, and a separation membrane having a sufficient permeation rate cannot be obtained.

Next, a method for producing the gas separation membrane of the present invention composed of the above-mentioned polyolefin and silicone will be described.

First, the polyolefin and silicone are heated and dissolved in a solvent in an amount of 1 to 50% by weight to form a uniform solution. The solvent is not particularly limited as long as it can sufficiently dissolve both polyolefin and silicone.
For example, decalin, decanol, diphenyl ether,
Diphenylmethane, dodecanol, octanol, 1,2,
4-trichlorobenzene, 3,5,5-trimethylhexyl acetate, p-xylene and the like can be mentioned. Of these, decalin is particularly preferable.

The above heating dissolution is carried out with stirring at a temperature at which the polyolefin is completely dissolved in the solvent. The temperature varies depending on the type of polyolefin used and the solvent, but for example, in the case of a high-molecular-weight polyethylene composition, it is 140
~ 250 ° C. In order to obtain a uniform solution, the above-mentioned dissolution is preferably carried out under a nitrogen atmosphere while stirring, if necessary, at a pressure of about 20 atm or less and at a heating rate of 20 ° C./hour or more.

The concentration of the polyolefin + silicone solution is 1 to 50% by weight, preferably 10 to 45% by weight, based on 100% by weight of polyolefin + silicone + solvent. If the concentration is less than 1% by weight, not only is the amount of solvent used large, which is not economical, but the amount of polyolefin becomes too small, so that the strength of the obtained film decreases. On the other hand, the concentration is 50
When it exceeds the weight%, it becomes difficult to prepare a uniform solution. In addition, it is preferable to add an antioxidant in order to prevent the polyolefin from being oxidized during heating and melting.

Next, this heated solution is extruded from a die to be molded. As the die, a sheet die having a rectangular die shape is usually used, but a double cylindrical hollow die,
An inflation die or the like can also be used. When using a sheet die, the die gap is usually 0.1 to 5
mm, which is heated to 140 to 250 ° C during extrusion. At this time, the extrusion speed is usually 20 to 30 cm / min to 2 to
It is 3 m / min.

The solution thus extruded from the die is cooled to form a gel. As a cooling method, a method of directly contacting with cold air, cooling water, or other cooling medium, a method of contacting with a roll cooled with a refrigerant, or the like can be used. Cooling is preferably performed at a rate of 50 ° C./min or more up to at least the gelation temperature.
When the cooling rate is slow, the degree of crystallinity increases, and it is difficult to form a gel-like material suitable for stretching. The solution extruded from the die is 1 to 10, preferably 1 to 5 before or during cooling.
It is preferable to collect at a collection ratio of. When the take-up ratio is 10 or more, neck-in becomes large, and breakage easily occurs during stretching, which is not preferable.

Subsequently, the residual solvent is removed. The solvent may be removed by air drying or hot air drying under normal pressure or reduced pressure. At this time, it is preferable to remove 70% or more of the solvent in the sheet. If the removal rate of the solvent is less than 70%, it is not preferable because foaming occurs due to volatilization of the solvent during stretching.

The drying temperature varies depending on the solvent used, but is generally higher than the freezing point of the solvent and is preferably a temperature of boiling point + 20 ° C. or lower. When the drying temperature is lower than the freezing point of the solvent, the solvent remains in the sheet to reduce the effective permeation area of the stretched membrane, and when the boiling point of the solvent exceeds + 20 ° C, the solvent boils and the sheet foams, which is preferable. Absent. Such drying can be performed by a hot roll, a tenter type hot air dryer, a roll type heating dryer, an air drying method, or the like.

Next, the dried gel-like molded product is stretched. The stretching is carried out by heating a raw material of the gel-like molded product and using a usual tenter method, roll method, inflation method, rolling method or a combination of these methods at a predetermined magnification. Biaxial stretching is preferred, and either longitudinal / transverse simultaneous stretching or sequential stretching may be used, but simultaneous biaxial stretching is particularly preferred.

The stretching temperature is preferably from the crystal dispersion temperature of the polyolefin used to the melting point + 20 ° C. or lower. For example, in the case of multi-stage polymerized polyethylene, the temperature is 90 to 180 ° C, and more preferably 110 to 140 ° C. If the stretching temperature is lower than the crystal dispersion temperature, the softening of the resin is insufficient and the film is easily broken during stretching, and it cannot be stretched at a high magnification. It is not preferable because it cannot be done.

The stretching ratio varies depending on the thickness of the raw fabric, but is at least 2 times or more, preferably 5 times or more in the uniaxial direction, and the surface magnification is 10 times or more, preferably 25 times or more. If the surface magnification is less than 10 times, the stretching is insufficient and a highly elastic and high-strength microporous membrane cannot be obtained. On the other hand, if the areal magnification exceeds 400 times, there are restrictions on the stretching apparatus and the stretching operation. After stretching, heat fixing in a temperature range of crystal dispersion temperature to melting point can improve thermal stability and strength.

The separation membrane of the present invention thus produced has a form in which the pores of a polyolefin microporous membrane are filled with silicone. The silicone is then subjected to a crosslinking treatment. You can If not crosslinked, the silicone will gradually separate, so that not only the durability of the film is insufficient, but also the strength of the film itself can be improved by the crosslinking. As a method of crosslinking, a method of preliminarily blending 0.005 to 5 parts by weight with respect to 100 parts by weight of silicone, such as a thermally crosslinkable silicone, an organic peroxide, or a crosslinking catalyst of a metal compound, and crosslinking at the time of heating and stretching. ,
Alternatively, 0.1 Mrad of ionizing radiation (γ-ray, electron beam, etc.) is applied to the thin film obtained by heating and stretching the gel-like sheet filled with silicone.
Above, preferably, a method of irradiating 0.5 to 20 Mrad, and a method of bringing the thin film after stretching into contact with water, steam or the like to carry out water crosslinking are mentioned.

The thickness of the gas separation membrane of the present invention is preferably 0.1 to 20 μm, more preferably 0.15 to 8 μm. If the film thickness is less than 0.1 μm, the mechanical strength of the supporting film is small and it is difficult to put it into practical use. On the other hand, if it exceeds 20 μm, the gas permeation rate decreases, which is not preferable.

The porosity of the porous thin film is preferably 30 to 95%, particularly preferably 50 to 90%. If the porosity is less than 30%, the gas permeation function per unit area of the membrane is insufficient,
On the other hand, if it exceeds 95%, the mechanical strength of the supporting film becomes small and it becomes difficult to put it into practical use, which is not preferable.

Further, the average through hole diameter is 0.001 to 1 μm.
Is preferred, and 0.005-0.1 μm is particularly preferred. If the average through hole diameter is less than 0.001 μm, the gas permeation rate will decrease,
On the other hand, if it exceeds 1 μm, the separating function is deteriorated. Further, it has a breaking strength of 200 kg / cm ² or more, which is preferable in terms of practicality as a supporting film.

Since the filling amount of silicone basically corresponds to the ratio of polyolefin and silicone,
It becomes 90% by weight.

Although the gas separation membrane of the present invention has been described above, the separation of gas by such a separation membrane of the present invention is 30 kg.
/ Cm ² or less, preferably 0.1 to 20 kg / cm ² is effective under a gas pressure difference, and the gas to be separated has different permeation rates and a large selection coefficient (permeation rate It is effective for separating two or more gases (having a large ratio). Typically, it is effective in separating nitrogen and oxygen, which are the main constituents in the atmosphere.

[0053] For example, the oxygen transmission rate ^{3 × 10 -4 cm 3 / cm} 2 · sec · cmHg or more gas separation membrane of the present invention, the nitrogen permeation rate ^{1.4 × 10 - cm 3 / cm} 2 · sec · cmHg or more, and the selectivity coefficient of oxygen and nitrogen (ratio of permeation rates of oxygen and nitrogen: R O ₂ / RN ₂ ) is 2.2 to 2.4, and the selectivity coefficient after 6 months is 2.1 to 2.3.

[0054]

In the present invention, as the polyolefin serving as the base material of the separation membrane, a polyolefin containing a predetermined amount of an ultrahigh molecular weight component and having a molecular weight distribution (weight average molecular weight / number average molecular weight) within a predetermined range is used. Since a silicone is dissolved in a solution of a polyolefin that becomes a gel-like sheet, and a gel-like sheet obtained from the solution of this polyolefin + silicone is stretched in at least one axial direction, a gas separation membrane is used. High speed, good selectivity, and little decrease in selectivity with time.

Although the reason why such an effect is obtained is not always clear, since the composite film obtained according to the present invention is excellent in film strength, it can be sufficiently thinned and, in addition, polyolefin + It is considered that since the separation membrane is manufactured from the solution of silicone, the silicone can be introduced into the micropores in a large amount and satisfactorily, and the exudation of the silicone membrane surface is significantly suppressed.

[0056]

The present invention will be described in more detail by the following specific examples.

Example 1 1.5 parts by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight (Mw) of 2.0 × 10 ⁶ and a weight average molecular weight (Mw) of 3.9 × 10
Mw / M consisting of ⁵ high density polyethylene 3.0 parts by weight
Raw material resin composition of n = 13 (weight average molecular weight of the composition is 7.0
X10 ⁵ , molecular weight 7.0 x 10 ⁵ or more ratio 40% by weight) 18% by weight and a decalin mixture solution containing 40.5 parts by weight of polymethylvinylsiloxane were charged into an autoclave equipped with a stirrer, -Di-t-butyl-p-cresol ("BHT",
Sumitomo Chemical Co., Ltd.) 0.125 parts by weight, and tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane ("IRGANOX 101
0 ", manufactured by Ciba Geigy) and 0.250 parts by weight as an antioxidant were added and mixed, and heated to 150 ° C and stirred to form a uniform solution.

This solution was filled in a mold and cooled to 15 ° C. to form a gel sheet having a thickness of 1.0 mm. This gel-like sheet was heated to 70 ° C. under a reduced pressure of 10 mmHg to dry and remove decalin contained in the gel-like sheet to obtain a raw sheet having a polymethylvinylsiloxane content of 90% by weight.

The obtained raw fabric sheet was set in a biaxial stretching machine, and simultaneously biaxially stretched 10 × 10 times at a temperature of 120 ° C. and a stretching speed of 0.3 m / min. The thickness of the obtained polymer composite film is 4.
It was 0 μm. This polymer composite film was irradiated with 5 Mrad of γ-ray to crosslink polymethylvinylsiloxane. Table 1 shows the manufacturing conditions of the gas separation membrane.

The gas separation membrane thus obtained was allowed to stand for 6 months in film thickness, rupture strength, oxygen permeation rate, nitrogen permeation rate, selective permeation coefficient of oxygen and nitrogen, and mixed gas. The subsequent selective permeation coefficient of oxygen and nitrogen was measured. The results are shown in Table 2.

Examples 2 to 4 In Example 1, the concentration of polymethylsiloxane was adjusted to the first
A gas separation membrane was manufactured in the same manner except that various changes were made as shown in the table.

The gas separation membrane thus obtained was allowed to stand for 6 months in the thickness, rupture strength, oxygen permeation rate, nitrogen permeation rate, selective permeation coefficient of oxygen and nitrogen, and mixed gas. The subsequent selective permeation coefficient of oxygen and nitrogen was measured. The results are shown in Table 2.

Examples 5 and 6 A gas separation membrane was produced in the same manner as in Example 1, except that the concentration of the polyethylene composition and the concentration of polymethylsiloxane were changed as shown in Table 1.

The gas separation membrane thus obtained was allowed to stand for 6 months in film thickness, rupture strength, oxygen permeation rate, nitrogen permeation rate, selective permeation coefficient of oxygen and nitrogen, and mixed gas. The subsequent selective permeation coefficient of oxygen and nitrogen was measured. The results are shown in Table 2.

Comparative Example 1 2 parts by weight per 100 parts by weight of a solution consisting of 4% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight (Mw) of 2 × 10 ⁶ and 96% by weight of liquid paraffin (64 cst / 40 ° C.) 0.125 parts by weight of 6,6-di-t-butyl-p-cresol (“BHT”, manufactured by Sumitomo Chemical Co., Ltd.) and tetrakis [methylene-3- (3,5-di-t
-Butyl-4-hydroxyphenyl) propionate] methane ("Irganox 1010", manufactured by Ciba Geigy) was added as an antioxidant and mixed, and the mixed solution was charged into an autoclave equipped with a stirrer, and 200 Heated to ℃,
Stir to give a homogeneous solution.

The mold was filled with this solution and cooled to 15 ° C. to form a gel sheet having a thickness of 2 mm. This gel-like sheet was immersed in methylene chloride for 60 minutes. Then, without drying this gel-like sheet, it was immediately transferred to a 10 wt% methylene chloride solution of methyl vinyl silicone oil (NUC Silicone gumstock W-9613 (trade name) manufactured by Nippon Unicar Co., Ltd.) and immersed for 60 minutes. After that, methylene chloride was dried and evaporated while being attached to a smooth plate to obtain a raw sheet having a methyl vinyl silicone oil filling amount of 52.5% by weight and a shrinkage ratio in the thickness direction of 91.6%.

The obtained raw sheet was set in a biaxial stretching machine and subjected to simultaneous biaxial stretching at a temperature of 130 ° C. and a stretching speed of 0.3 m / min at 10 × 10 times. The thickness of the obtained polymer composite film is 4.
It was 0 μm. This polymer composite film was irradiated with γ-rays at 5 Mrad to crosslink the siloxane to obtain a pinhole-free composite film. Table 1 shows the manufacturing conditions of the gas separation membrane.

The gas separation membrane thus obtained was allowed to stand for 6 months in the thickness, rupture strength, oxygen permeation rate, nitrogen permeation rate, selective permeation coefficient of oxygen and nitrogen, and mixed gas. The subsequent selective permeation coefficient of oxygen and nitrogen was measured. The results are shown in Table 2.

Comparative Example 2 A gas separation membrane was produced in the same manner as in Comparative Example 1, except that the concentration of the polyethylene solution was 2.0% by weight.

The gas separation membrane thus obtained was allowed to stand for 6 months in film thickness, rupture strength, oxygen permeation rate, nitrogen permeation rate, selective permeation coefficient of oxygen and nitrogen, and mixed gas. The subsequent selective permeation coefficient of oxygen and nitrogen was measured. The results are shown in Table 2.

Comparative Example 3 In Comparative Example 2, 10% of methyl vinyl silicone oil was used.
A gas separation membrane was produced in the same manner except that the time of immersion in a wt% methylene chloride solution was 30 minutes.

The gas separation membrane thus obtained was allowed to stand for 6 months in film thickness, breaking strength, oxygen permeation rate, nitrogen permeation rate, selective permeation coefficient of oxygen and nitrogen, and mixed gas. The subsequent selective permeation coefficient of oxygen and nitrogen was measured. The results are shown in Table 2.

Table 1 Manufacturing conditions Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Ratio of high molecular weight polyethylene (% by weight) 1.5 1.5 1.5 1.5 1.5 1.5 Ratio of polyethylene (% by weight) 3.0 3.0 3.0 3.0 6.0 9.8 Molecular weight distribution of polyethylene composition (Mw / Mn) 13 13 13 13 95 191 Polymethylvinylsiloxane concentration (wt%) 40.5 25.5 18.0 10.5 30.0 45.2

Table 1 (continued) Manufacturing conditions Comparative example 1 Comparative example 2 Comparative example 3 Ratio of high molecular weight polyethylene (% by weight) 4.0 2.0 2.0 Molecular weight distribution of polyethylene (Mw / Mn) 6.7 6.7 6.7

Table 2 Physical Properties of Separation Membrane Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Polymethylvinylsiloxane content (% by weight) 90 85 80 70 80 80 Film thickness (μm) 1.9 1.5 1.3 1.0 1.7 2.0 Breaking load (kgf / 10mm width) ⁽¹⁾ 860 670 560 410 790 950 Oxygen permeation rate (RO ₂ : cm ³ / cm ² · sec cmHg) Hg, × 10 ^-4 ) ⁽²⁾ 4.11 4.21 3.87 4.29 3.94 4.01 Nitrogen Permeation Rate (RN ₂ : cm ³ / cm ² · sec · cmHg) Hg, × 10 ^-4 ) ⁽³⁾ 1.77 1.83 1.69 1.89 1.72 1.74 Selective Permeability Coefficient (RO ₂ / RN ₂ ) ^{( 4)} 2.32 2.30 2.29 2.27 2.29 2.30 Selective transmission coefficient (RO ₂ / RN ₂ ) after 6 months ⁽⁵⁾ 2.26 2.24 2.23 2.21 2.24 2.25

Table 2 (continued) Physical Properties of Separation Membrane Comparative Example 1 Comparative Example 2 Comparative Example 3 Polymethylvinylsiloxane content (% by weight) ⁽¹⁾ 52.5 68.4 39.8 Film thickness (μm) ⁽²⁾ 2.8 1.6 1.2 Breaking load (kgf / 10mm width) ⁽³⁾ 990 670 230 Oxygen permeation rate (RO ₂ : cm ³ / cm ² · sec · cmHg) Hg, × 10 ^-4 ) ⁽⁴⁾ 0.507 2.25 0.850 Nitrogen permeation rate (RN ₂ : cm ³ / cm ² · sec · cmHg) Hg, × 10 ^-4 ) ⁽⁵⁾ 0.228 1.12 0.419 Selective transmission coefficient (RO ₂ / RN ₂ ) ⁽⁶⁾ 2.22 2.01 2.03 Selective transmission coefficient after 6 months ^{_{(RO 2 / RN 2) (}} 7) 1.65 1.53 1.55

(1) Polymethylvinylsiloxane content ratio: (amount of polyethylene + polymethylvinylsiloxane) / calculated by polymethylvinylsiloxane. (2) Film thickness: The cross section was measured with a scanning electron microscope. (3) Breaking load: The breaking load of a 10 mm wide strip test piece
Measured according to D882. (4) Oxygen transmission rate: Measured with a differential pressure type gas separation membrane performance evaluation device. (5) Nitrogen permeation rate: Measured with a differential pressure type gas separation membrane performance evaluation device. (6) Selective permeation coefficient: Calculated by oxygen permeation rate / nitrogen permeation rate. (7) 6 months after the lapse of the selected transmission coefficient: The gas separation membrane CH ₄
20 mol%, C ₂ H ₆ 15 mol%, C ₂ H ₄ 10 mol%, C ₃
H ₈ 15 mol%, C ₃ H ₆ 15 mol%, H ₂ 20 mol%, N ₂
After leaving it in a mixed gas consisting of 5 mol% for 6 months,
Measured in the same manner as (4) to (6).

As is clear from Table 2, the gas separation membrane of the present invention has a high gas permeation rate and good selectivity,
The selectivity did not decrease with time. On the other hand, in the gas separation membrane of the comparative example, the gas permeation rate was low, and the selectivity was remarkably lowered with time.

[0079]

As described above in detail, in the present invention, the polyolefin serving as the base material of the separation membrane contains a predetermined amount of an ultrahigh molecular weight component and has a molecular weight distribution (weight average molecular weight / number average molecular weight) within a predetermined range. In addition to the above, the silicone is dissolved in a solution of a polyolefin which becomes a gel sheet, and the gel sheet obtained from the solution of the polyolefin + silicone is used for at least 1 at a predetermined temperature.
As the gas separation membrane is made by stretching in the axial direction, it is easy to control the amount of silicone introduced into the micropores, and it is possible to introduce stably, the gas permeation rate is large, and the selectivity is high. Good and little decrease in selectivity with time.

Claims (2)

[Claims] 1. A polyolefin 10 containing 1% by weight or more of an ultrahigh molecular weight polyolefin having a weight average molecular weight (Mw) of 7 × 10 ⁵ or more, and having a weight average molecular weight / number average molecular weight of 10 to 300.
A gas separation membrane consisting of a porous thin film consisting of -30% by weight and 90-70% by weight of silicone, characterized in that the pores of the porous thin film are substantially closed and filled with silicone. Gas separation membrane 2. A component having a weight average molecular weight of 7 × 10 ⁵ or more
10 to 30 parts by weight of a polyolefin containing 10% by weight or more and having a molecular weight distribution (weight average molecular weight / number average molecular weight) of 10 to 300, silicone of 90 to 70 parts by weight, and the polyolefin +
A solution comprising 50 to 99% by weight of a solvent is prepared with respect to 1 to 50% by weight of silicone, the solution is extruded from a die, cooled to form a gel composition, and the gel composition is dried. And then stretching.