JP2000288369A - Gas separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas separation membrane for a gas-permeable tube or the like that is hardly permeated by steam and has excellent breaking elongation and gas permeability. SOLUTION: This separation membrane is made of a polymer blend containing styrenic thermoplastic elastomer and polyolefin and the example of the styrenic thermoplastic elastomer includes a (S)-(EB)-(S) triblock copolymer comprising styrene polymer (S) and hydrogenated butadiene polymer (EB) or a (S)-(BU)-(S) triblock copolymer comprising styrene polymer (S) and butadiene polymer (BU); and a hydrogenated random copolymer of styrene monomer and butadiene monomer or a random copolymer of styrene monomer an butadiene monomer; and the likes.

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 for selectively separating oxygen, nitrogen and the like from a mixed gas, or a gas separation membrane which is dissolved in a liquid such as alcohol, water, printing ink and ink jet printer ink. Gas (oxygen, nitrogen, etc.)
A gas separation membrane for degassing the gas.

[0002]

2. Description of the Related Art As materials for conventional gas-permeable tubes, for example, thermoplastic segmented polyurethane, poly-4-methylpentene-1, polytetrafluoroethylene, and silicone rubber are known (Japanese Patent Laid-Open No. 2-1644).
No. 25, No. 5-267149, No. 8-153675
Nos. 8-243306, 9-57008, 9
187602, 8-124825, etc.).

[0003]

Among the above materials, silicone rubber and thermoplastic segmented polyurethane are:
Large water vapor transmission coefficient. Therefore, when oxygen or nitrogen is separated from air containing water vapor using a tube made of silicone rubber or thermoplastic segmented polyurethane, water vapor permeates to the membrane permeation side (pressure reduction side), and water vapor condensation easily occurs. For example, if water vapor is mixed into the pressure reducing pump, the pressure reducing pump may fail.

Among the above materials, poly-4-methylpentene-1 has a glass transition temperature of about 30 ° C. and is in a glassy state at a low temperature (for example, room temperature (20 ° C.)). Generally, poly 4-methylpentene at room temperature (20 ° C.)
The elongation at break of the tube made of No. 1 in tension is about 50 to 100% of the sample length, depending on the wall thickness, and is lower than that of the polymer tube in a rubber state.

FIG. 2 is a graph showing a stress-strain curve of a tube made of poly-4-methylpentene-1. Yield stress 1, yield elongation 2, breaking stress 3, breaking elongation 4
(50 to 100%) is indicated by each symbol. As can be seen from this graph, the tube made of poly-4-methylpentene-1 breaks immediately above the yield point. That is, when used as a separation membrane, the yield stress 1
The ability to absorb the tensile stress exceeding elongation by elongation is insufficient, and is not sufficient in terms of the durability in actual use.

Among the above materials, polytetrafluoroethylene has an oxygen permeability coefficient at 20 ° C. of 3.75 × 10
^{-14 to} 7.5 × 10 ^-14 cm ³ (STP) · cm / (cm ² · sec · Pa). Therefore, when a tube is used, its gas permeation flux is low, and the gas permeation performance is insufficient for use as a separation membrane. In addition, polytetrafluoroethylene is more expensive than other materials.

The present invention has been made in order to solve the problems of the prior art, and it is difficult to transmit water vapor, is excellent in elongation at break against tensile strength and gas permeation performance, and is inexpensive. It is intended to provide a separation membrane.

[0008]

The above object of the present invention is achieved by a gas separation membrane comprising a polymer blend of a styrene-based thermoplastic elastomer and a polyolefin.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

The gas separation membrane of the present invention is obtained from a polymer blend of a styrene-based thermoplastic elastomer and a polyolefin. Specifically, both are melt-blended and formed into a desired shape such as a tubular shape (hollow tubular shape) or a flat film shape.

The morphology of this polymer blend is as follows: when the styrene-based thermoplastic elastomer and the polyolefin have a co-continuous structure (phase structure close to mutual penetration);
There may be a two-phase structure in which one is the sea and the other is the island.

The gas permeability is mainly borne by the styrene thermoplastic elastomer. Here, a co-continuous structure is preferable in that there is a continuous gas permeation path from the front to the back of the gas separation membrane. On the other hand, in applications where degassing is performed in liquid, if the liquid to be degassed has high affinity with the styrene-based elastomer, the bicontinuous structure easily swells with the liquid to be degassed from front to back, that is, chemical resistance May be inferior in sex.
Therefore, when the affinity between the liquid to be degassed and the styrene-based elastomer is high, the sea-island two-phase structure is preferable because the degree of swelling can be reduced. However, the bicontinuous structure is
Since the gas permeable path is hard to be interrupted, it is excellent in gas permeability.

As described above, the morphology of the gas separation membrane of the present invention may be appropriately selected from a co-continuous structure, a sea-island two-phase structure, and the like according to the use and the like, and there is no particular limitation on the morphology.

Typical examples of the styrene thermoplastic elastomer used in the present invention include the following triblock copolymer [a] and random copolymer [b].

[A] (S)-comprising a polymer (EB) obtained by hydrogenating a styrene polymer (S) and a butadiene polymer.
(EB)-(S) triblock copolymer or styrene polymer (S) and butadiene polymer (BU)
(S)-(BU)-(S) triblock copolymer, [b] a polymer obtained by hydrogenating a random copolymer composed of a styrene monomer and a butadiene monomer, or a styrene monomer and a butadiene Random copolymer with monomer.

Commercial products of the triblock copolymer [a] include, for example, Kraton G, manufactured by Shell Chemical Co., Ltd.
Is mentioned. Commercial products of the random copolymer [b] include, for example, HSBR (trade name, manufactured by Nippon Synthetic Rubber Co., Ltd.). In the copolymers [a] and [b], the hydrogenation rate is preferably 80% or more. By increasing the hydrogenation rate in this way, the light resistance of the molded product is improved. It has been conventionally known that both Clayton G and HSBR have a large hydrogenation rate of 90 to 99%.

The polyolefin used in the present invention is preferably a low-density, low-crystalline polyolefin having a glass transition temperature lower than room temperature, since a tube having high flexibility and high gas permeability can be obtained. Specifically, the density of the polyolefin is preferably 0.92 g / cm ³ or less, and the crystallinity is preferably 50% or less. Such polyolefins include, for example, linear low density polyethylene (liner low de polyethylene).
nsity polyethylene, manufactured by Mitsui Chemicals, Inc. under the trade name of Ultex, etc.) and very low density polyethylene with very many branches based on metallocene catalyst (very low density polyethylene,
Dupont Dow Elastomer Co., Ltd., brand name ENGAGE
Etc.), atactic polypropylene and the like. Further, a copolymer of ethylene and propylene (trade name: Tuffmer, manufactured by Mitsui Chemicals, Inc.) may be used.

By blending the styrenic thermoplastic elastomer and polyolefin, and molding the polymer blend into a desired shape such as a tube,
Oxygen permeability coefficient at room temperature (20 ° C.) is 3.75 × 10
^{-13 cm 3 (STP) · cm} / (cm 2 · sec · Pa) ~2.25 × 10 -12 cm 3 (S
A gas separation membrane exhibiting excellent oxygen permeation performance of (TP) · cm / (cm ² · sec · Pa) can be obtained.

The thickness (thickness in the case of a tube) of the gas separation membrane is not particularly limited, but is preferably 50 μm or more from the viewpoint of ensuring practical pressure resistance (1 MPa or more). Further, it is preferable that the oxygen permeation flux is 500 μm or less (7.5 × 10 ⁻¹² cm ³ (STP) / (cm ^2.
sec · Pa) or more).

As described with reference to FIG. 2, the tube made of poly-4-methylpentene-1 which is in a glassy state at room temperature has a low breaking elongation (50 to 100%) and a tensile stress exceeding the yield stress. When added, the ability to absorb the stress by elongation is insufficient, and it is easy to break, which is insufficient in terms of the durability in actual use.

On the other hand, since the gas separation membrane of the present invention uses a styrene-based thermoplastic elastomer as one of the materials, the polymer chains present in the styrene-based thermoplastic elastomer and in a rubber state at room temperature are: A tensile stress exceeding the yield stress is absorbed by elongation, and a high breaking elongation (200% or more) is obtained. FIG. 1 shows the stress-strain of the gas separation membrane (gas permeable tube) of the present invention.
It is a graph showing a curve. As can be seen from this graph, the gas separation membrane (gas permeable tube) of the present invention does not break immediately even after exceeding the yield point, and has excellent durability in actual use.

Further, since the gas separation membrane (gas permeable tube) of the present invention uses polyolefin as one of the raw materials, as shown in the graph of FIG.
The ress-Strain curve shows a behavior close to that of a tube made of poly-4-methylpentene-1, and the yield stress is
The value is almost the same as that of the tube made of methylpentene-1.

As described above, the gas separation membrane (gas permeable tube) of the present invention can have a breaking elongation of 200% or more of the sample length, and at the same time, has a flexibility close to that of silicone rubber or thermoplastic segmented polyurethane. Can also be given.

Further, the gas separation membrane of the present invention has a water vapor transmission coefficient of 1 × 10 ⁻² g · m / (m ² · day) or less, which is as low as about 1/100 of that of silicone rubber or thermoplastic segmented polyurethane. Can be. As a result, the problem of water vapor mixing into the decompression pump, which is one of the problems of the prior art, can be solved.

The composition ratio of the styrene-based thermoplastic elastomer to the polyolefin may be determined as desired in consideration of the above-mentioned points, and is not particularly limited in the present invention. However, the styrene-based thermoplastic elastomer is preferably 20 to 95 parts by weight and the polyolefin is preferably 80 to 5 parts by weight, and the styrene-based thermoplastic elastomer is 40 to 90 parts by weight, and the polyolefin 6 is based on 100 parts by weight of both components.
More preferably, the amount is 0 to 10 parts by weight.

The shape of the gas separation membrane of the present invention is not particularly limited, and may be formed into a tube shape, a flat film shape, or any other desired shape as required. For example, in the case of forming a gas-permeable tube, the polymer blend may be extruded in a molten state from a hollow die, cooled, wound up, or the like, and may be molded according to a conventionally known method. The gas permeable tube is a gas separation membrane having a non-porous and hollow cylindrical shape.

The gas separation membrane of the present invention is used, for example, for selectively separating oxygen, nitrogen and the like from a mixed gas, or
It is useful for various gas separation applications such as applications for degassing gases (oxygen, nitrogen, etc.) dissolved in liquids such as alcohol, water, printing inks and ink jet printer inks.

[0028]

The present invention will be described in more detail with reference to the following examples. In the following description, “parts” means “parts by weight” unless otherwise specified.

In the following examples, the oxygen permeability coefficient is A
The water vapor permeability coefficient was measured according to ASTM E96 according to STM D-1434 and D-2684. The degassing efficiency (%) is calculated by the following formula.

[0030]

(Equation 1) It calculated according to.

<Example 1> As a styrene-based thermoplastic elastomer, Kraton G-, trade name, manufactured by Shell Chemical Co., Ltd.
1652 and Clayton G-16
57 as 80 parts, and as polyolefin, ENGAGE8400 (trade name, manufactured by Dupont Dow Elastomer Co., Ltd.)
870 g / cm ³ ) were weighed and melt-blended with a twin-screw kneader. This melt-blended polymer (glass transition temperature Tg = −45 ° C.) was extruded from a hollow die at 190 ° C. and wound up at a draft ratio of 600 to obtain a gas-permeable tube.

The dimensions (inner diameter, outer diameter, wall thickness) of this gas-permeable tube, oxygen permeability at room temperature (20 ° C., the same applies hereinafter), nitrogen permeability at room temperature, oxygen permeation flux at room temperature, Table 1 shows the nitrogen permeation flux, water vapor transmission coefficient at room temperature, elongation at break at room temperature, and the results of degassing experiments for dissolved oxygen in water.

Further, a slice was cut out on a plane perpendicular to the longitudinal direction of the tube, stained with RuO ₄ , and observed with a transmission electron microscope. As a result, the morphology of the styrene thermoplastic elastomer was sea and that of the polyolefin was islands ( It is known that a styrene-based thermoplastic elastomer is dyed black by RuO ₄ ).

Example 2 As a styrene-based thermoplastic elastomer, HSBR13 (trade name, manufactured by Nippon Synthetic Rubber Co., Ltd.)
90 parts of 90P (styrene content 30% by weight) and 10 parts of ENGAGE8400 (trade name: 0.870 g / cm ³ ) manufactured by Dupont-Dow Elastomer Co., Ltd. as a polyolefin were weighed and melt-blended by a twin-screw kneader. This melt blend polymer (glass transition temperature Tg = -45 ° C)
Was extruded from a hollow die at 190 ° C. and wound up at a draft ratio of 800 to obtain a gas-permeable tube. Table 1 shows the results of evaluation performed in the same manner as in Example 1. Further, in the tube of this example, as in Example 1, the morphology was such that the styrene-based thermoplastic elastomer was sea and the polyolefin was islands.

Example 3 MK (trade name, manufactured by Dainippon Plastics Co., Ltd.) which is commercially available as a polymer blend comprising a styrene-based thermoplastic elastomer and polypropylene
Using resin MK-2F, this polymer blend (T
g = −35 ° C., composition ratio = (S)-(EB)-(S) triblock consisting of a styrene polymer (S) and a hydrogenated polymer (EB) of a butadiene polymer as a styrene thermoplastic elastomer 50 parts of a polymer and 50 parts of atactic polypropylene as a polyolefin) are extruded at 190 ° C. from a hollow die and wound up at a draft ratio of 700,
A gas permeable tube was obtained. Table 1 shows the results of evaluation performed in the same manner as in Example 1.

When the tube of this example was observed with a transmission electron microscope in the same manner as in Example 1, the morphology of the styrene-based thermoplastic elastomer and the polyolefin was a bicontinuous structure.

<Comparative Example 1> The oxygen permeation coefficient of a tube made of tetrafluoroethylene incorporated in a deaerator (trade name Nitosep) manufactured by Nitto Denko Corporation was measured to be 3.75 × 10 ^-14 cm. ³ (STP) · cm / (cm ² · cmHg · Pa). Water is flowed at a flow rate of 1 L / min. Into the inside of the tube made of tetrafluoroethylene, and 1.
When degassing was attempted while maintaining the pressure at 3 × 10 ⁴ Pa, the efficiency of removing dissolved oxygen after degassing was about 1%, and most of dissolved oxygen remained dissolved in water even after degassing.

Comparative Example 2 Poly-4-methylpentene-1
(Inner diameter: 24 μm, outer diameter: 43 μm, wall thickness: 10 μm). The oxygen transmission flux of this tube is 2.0 × 10 ⁻⁹ cm ³ (STP) / (cm ² · cmHg · Pa), oxygen transmission flux / nitrogen transmission flux = 3.7, breaking elongation 93%, pressure resistance 0 It was 0.7 MPa. Using this tube (length: 10 cm, number of tubes: 1,000), water (water temperature: 20 ° C.) is flowed into the tube at a flow rate of 5 L / min, and the outside of the tube is maintained at 1.3 × 10 ⁴ Pa to remove the tube. When I tried to do that, there were countless cracks in the tube wall.

Comparative Example 3 A tube made of silicone rubber (inner diameter 100 μm, outer diameter 300 μm, wall thickness 100 μm)
m) was prototyped. The oxygen permeation flux of this tube is 4.5 × 10 ⁻⁹ cm ³ (STP) / (cm 2 · sec · Pa), oxygen permeation flux / nitrogen permeation flux = 1.3, elongation at break 250
% And a withstand pressure of 1 MPa. This tube (length 10
cm, 1000 pieces) and flow rate 5
Water (water temperature: 20 ° C.) was flowed at L / min., And degassing was attempted while maintaining the outside of the tube at 1.3 × 10 ⁴ Pa. The degassing time was 30 minutes, and the degassing efficiency was 65%. The water vapor coefficient of the tube was 1.8 × 10 ⁻¹ g · m / (m ² · day).

COMPARATIVE EXAMPLE 4 A thermoplastic segmented polyurethane, trade name T from Themedics Inc.
Ecoflex EG80A tube (1 inner diameter)
(00 μm, outer diameter 300 μm, wall thickness 100 μm). The oxygen permeation flux of this tube is 4.5 × 10
^-11 cm ³ (STP) / (cm ² · sec · Pa), oxygen transmission flux / nitrogen transmission flux = 4.0, elongation at break 250%, pressure resistance 1
It was 0 kg / cm ² . Using this tube (length 10 cm, number 1000), water (water temperature 20 ° C.) is flowed inside the tube at a flow rate of 5 L / min., And 1.3 × 10 ⁴ outside the tube.
Degassing of dissolved oxygen in water was attempted while maintaining the pressure at Pa. The deaeration time was 30 minutes, and the deaeration efficiency was 70%. The water vapor coefficient of this tube was 3.0 × 10 ⁻¹ g · m / (m ² · day).

[0041]

[Table 1]

[0042]

As described above, the gas separation membrane (permeable tube etc.) of the present invention is inexpensive and has excellent gas permeation performance as compared with a tube made of a fluororesin such as polytetrafluoroethylene. . Furthermore, compared with a tube made of silicone rubber or thermoplastic segmented polyurethane, the water vapor permeability is low, and the water vapor condensation on the membrane transmission side is reduced. In addition, compared to a tube made of poly-4-methylpentene-1, it has a high elongation at break with respect to tension and is flexible, so it is excellent in pressure resistance, and has a high breaking stress, so that it is safe and reliable. Excellent in terms of sex.

[Brief description of the drawings]

FIG. 1 shows the gas separation membrane (gas permeable tube) of the present invention.
It is a graph which shows a stress-strain curve.

FIG. 2 is a graph showing a stress-strain curve of a conventional tube made of poly-4-methylpentene-1.

[Explanation of symbols]

 1 Yield stress 2 Yield elongation 3 Breaking stress 4 Elongation at break

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA32 GA41 KE02P KE08Q KE12P KE13P KE16P KE28P MA02 MA03 MA30 MA31 MA33 MB03 MB04 MB16 MC22X MC23X MC24X MC68X MC81 MC83 MC84 MC87 NA21 PA01 PB17 PB19 PB63 PB62

Claims (6)

[Claims] 1. A gas separation membrane comprising a polymer blend of a styrene-based thermoplastic elastomer and a polyolefin. 2. An (S)-(EB)-(S) triblock copolymer, wherein the styrene-based thermoplastic elastomer comprises a hydrogenated styrene polymer (S) and a butadiene polymer (EB). 2. The gas separation membrane according to claim 1, wherein the gas separation membrane is an (S)-(BU)-(S) triblock copolymer composed of a styrene polymer (S) and a butadiene polymer (BU). 3. A polymer obtained by hydrogenating a random copolymer comprising a styrene monomer and a butadiene monomer, or a random copolymer of a styrene monomer and a butadiene monomer. The gas separation membrane according to claim 1, wherein the gas separation membrane is combined. 4. The gas separation membrane according to claim 1, wherein the elongation at break against tensile is 200% or more of the sample length. 5. A water vapor transmission coefficient of 1 × 10 ⁻² g · m / (m ² ·
day) or less, and the oxygen permeability coefficient at room temperature is 3.75 ×
10 ^-13 cm ³ (STP) cm / (cm ² sec Pa)-2.25 x 10 ^-12 c
The gas separation membrane according to any one of claims 1 to 4, wherein m ³ (STP) · cm / (cm ² · sec · Pa). 6. The gas separation membrane according to claim 1, which is in the form of a tube.