JPS6245318A - Preparation of gas separation membrane - Google Patents

Abstract

PURPOSE:To obtain a composite membrane having an ultrathin active layer free from a pinhole, by applying coating to a homogenous non-porous support before making said support porous by stretching. CONSTITUTION:A thermoplastic crystalline polymer with an arrival crystallization degree of 20% or more is formed into a hollow yarn shape at melting temp. of Tm-Tm+100 deg.C (wherein Tm is a crystal m.p.) by melt spinning. A draft ratio is set to 5-10,000. The formed hollow yarn is cooled in a temp. range of glass transition temp. Tg-50 deg.C-Tm-50 deg.C and subsequently subjected to heat treatment at temp. of Tg+20 deg.C-Tm-5 deg.C. A substance forming a polymer film is applied to the surface of the obtained membrane in a thickness of 0.001-50mum. The viscosity of the coating solution is 0.5-500cp and the concn. of the polymer is 0.01-10wt%. This membrane is subjected to cold stretching at a stretching magnification of 1.05-3 at temp. of Tg-50 deg.C-Tm-10 deg.C. A stretching speed is pref. 1-10,000%/sec. Thereafter the stretched membrane is thermally set for 0.1sec or more at temp. of cold stretching temp.-Tm at a stretching magnification rate of 0.9-2.

Description

[Detailed Description of the Invention] <Industrial Application Field> In recent years, the separation of mixed gases using membranes, that is, the gas diaphragm separation technique, has been widely used for energy saving, separation devices, etc. Made by IY+
It has attracted attention in many respects, including oxygen enrichment from air, production of indoor air, fractional recovery of CO7, CO from combustion gas, f( , Removal of NO2 and S02 from waste gas, Purification and adjustment of H,/Co- of synthesis gas in C1 chemistry, He from natural gas
Its use in the fields of separation and recovery of inert gases such as This has become a key point for its widespread use, and there is a strong need for the development of membranes that are excellent in these respects.

The present invention responds to such requirements, and the gas minute v
The object of the present invention is to provide a method for efficiently manufacturing a membrane that has high R capacity, high permeation rate, and excellent mechanical properties.

<Prior Art> In the technical field of gas diaphragm separation, as mentioned above, there is a demand for good gas separation performance and at the same time, for reasons such as economical efficiency, a high overflow rate. In order to rapidly achieve this goal, it is essential to reduce the thickness of the knee material having gas separation nf: to a thickness of several micrometers or less, thereby making it possible to achieve a reasonable gas permeation rate. However, since such a thin film has very low mechanical strength, it is usually used in the form of a so-called composite membrane in which the thin film is formed on a porous support. Methods for manufacturing composite membranes include liquid surface development method (e.g., JP-A No. 57-107204), solution coating method (e.g., JP-A-57-122906), plasma polymerization method (e.g., JP-A-56-24018), Interfacial polymerization methods (for example, JP-A No. 59-59221) are known, and have a structure similar to that of a composite membrane, but consist of a porous layer and a non-porous layer made of the same material. Wet method (
For example, JP-A-59-59209) and the melting method (for example, JP-A-59-196706 and JP-A-229320 filed by the present applicant) are known.

The solution application method (coating method) is described, for example, in Japanese Patent Application Laid-Open No. 1987-
As described in Publication No. 41958, this method forms a non-porous layer on the surface of a porous membrane by applying a solution of a material with gas separation ability to the porous membrane and drying it. It has the following advantages compared to membrane manufacturing methods.

In other words, ■ There are fewer restrictions on the porous membrane that serves as the support and coating materials, so there is a wide range of choices, so it is easy to create separation membranes that suit the purpose. ■ Existing coating technology can be applied. ■ Manufacturing equipment costs are low. High productivity due to high production rate; ■Easy to manufacture hollow fiber type composite membranes with large membrane surface area.

However, the disadvantage of the coating method is that when the coating thickness is reduced to improve gas permeability, the pores of the support are not completely covered, resulting in pinholes.
The problem is that this results in a decrease in the gas separation coefficient. Therefore, in order to obtain a practical separation factor, the coating layer must be thick (
However, this method has the disadvantage that only a membrane with inferior gas permeability can be obtained compared to other composite membrane manufacturing methods.

<Problems to be Solved by the Invention> The present invention aims to establish a method for manufacturing a composite film that possesses the advantages of the above-mentioned coating method and overcomes the trade-offs between preventing pinholes and thinning the film. be.

<Means for Solving the Problem> As a result of detailed studies on the method for manufacturing composite membranes by the coating method, the present inventors found that the difficulty in improving membrane performance by the coating method is that the porous support is By determining that the pores must be completely blocked, and by avoiding this essential difficulty, we have discovered that it is possible to form an ultra-thin film layer without pinholes, and have completed the present invention. That is, the feature of the present invention is that before making the support porous, a separation active substance is coated on the support, and then only the support is made porous.

A similar idea to the present invention, which solves the difficulty of completely blocking the pores of a porous support, is disclosed in, for example, JP-A-59
It can also be seen in No. -49802 and No. 59-120211. That is, in these methods, a supporting porous membrane is pre-impregnated with water or a bath agent to make it appear non-porous, a coating operation is performed, and then the impregnating liquid is removed.

However, in these methods, the surface state of the porous material impregnated with liquid is unstable not only when the impregnating liquid is a volatile liquid, but even when it is a non-volatile liquid, It is quite difficult to achieve a uniform coating.Furthermore, these methods require a subsequent removal operation of the impregnating liquid, especially when using a non-volatile impregnating liquid on a hollow fiber type support. When using , this operation is extremely difficult and practically impossible.

On the other hand, the manufacturing method of the present invention does not have all of the above-mentioned drawbacks, since a homogeneous non-porous support is coated and then the support is made porous by stretching.

In addition, in general, coating films are stretched after the coating layer is formed.
Cars with thinner ^ are known. For example:
No. 8470 states that a thin coating layer without pinholes can be obtained by stretching the film in the machine direction, then coating it, and then stretching it in the transverse direction. However, in this method, the extent to which the coating is thinned by stretching is at most the reciprocal of the stretching ratio, and it is not possible to achieve essentially thin coatings at all.

In the present invention, during coating, the support is made into a non-porous material with a smooth surface, and only the support layer is made porous through a stretching process after coating, which is a technical concept different from that of conventional technology. I stood on it. Therefore, the present invention makes it possible to overcome the difficulty in coating technology of completely blocking the pores of porous materials, and as a result, it is possible to form a very thin coating layer, which is not simply the reciprocal of the stretching ratio. do not have.

In the present invention, it is surprising that even if the support is made porous by stretching and cleavage occurs, the coating layer thereon remains non-porous without tearing and does not peel off. That's a thing.

The gist of the present invention is that a thermoplastic crystalline polymer is
(1) Melting@Temperature Tm ~ (Tm+100)℃ (However, Tm
is crystal melting point), draft ratio Df is 50≦Df≦100
00 conditions to form a hollow fiber-like or film-like precursor, (2) the precursor
A coating layer is formed by using a support as a support and coating the surface thereof with a coating material that does not create penetrating microporosity in the subsequent stretching process, and (3) forming a support with this coating layer at (Tg+20). ~(Tm-5)℃(
However, Tg is the glass transition temperature), or (6') heat treatment in step (3) is performed prior to step (2), and (4) thereafter (Tg-10) to (T
m-10) Stretched at a temperature of 0C, (5) then heat-set at a temperature of (previous stretching temperature + 10) to Tm℃ to form micropores only in the support, thus forming microporous supports. This is a method for producing a gas separation membrane, characterized in that the membrane is coated with a non-porous coat IM on its surface.

The crystalline polymer used in the present invention is a thermoplastic crystalline polymer having an ultimate crystallinity of 20% or more, such as polyethylene, polypropylene, poly-6-methyl-butene-1
, polyolefins such as poly-4-methyl-pentene-1, polystyrene, vinyl polymers such as poly-methyl methacrylate, fluorine such as polyvinylidene fluoride, polyvinyl fluoride ethylene/H)q fluorinated ethylene copolymers, etc. Polyamides such as nylon 6, nylon 66, and nylon 12, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, BoIJ-4.4'-dioxydiphenyl-2,2- Examples include polycarbonates such as 7'lovan carbonate, polyethers such as polyoxymethylene and polymethylene sulfide, polythioethers, polyphenylene oxides, polyphenylene sulfether ketones (PFJEK), and the like. Further, a blend or copolymer of these polymers may have an attained crystallinity of 20% or more. Furthermore, compositions containing 70% or more of the above polymers, such as blends with other amorphous polymers or blends with inorganic substances, can also be used in the present invention, and antioxidants, antistatic agents, and antifungal agents can also be used in the present invention. , lubricant,
A suitable amount of a surfactant or the like can be contained as required.

Melt spinning temperature of hollow fiber (or bath melt extrusion temperature of film) (Hereinafter, to simplify the explanation, unless otherwise specified, we will discuss the case of hollow fiber membranes.The story is similar in the case of film extrusion and inflation. ) is higher than the melting point Tm of the polymer (it is preferable not to exceed the melting point by 100°C or more).

The suitable spinning temperature varies depending on the crystallization rate of the polymer, the molecular weight of the polymer, the cooling conditions, the spinning speed and draft ratio, and the processing conditions of subsequent steps. When using a low molecular weight polymer, when the spinning speed and draft ratio are relatively low, (Tm+1
A low temperature of 0) to (Tm+50)°C is preferred. At a temperature 100° C. or more higher than one point, it is difficult to obtain a membrane with a high gas permeation rate.

The draft ratio (=take-up speed/discharge speed) is 5 to 1ooo.

is preferred. 5 to 20 in the case of high molecular weight polymers with a melt viscosity of 7000 voids or more at the spinning temperature.
A relatively low draft ratio of 0 is suitable, but 50 or higher is generally preferred. Sometimes, when using a low molecular weight polymer with a melt viscosity of 1000 voids or less, a high draft of 500 voids or higher is required. Additionally, in general, when the discharge yarn is rapidly cooled, the draft ratio can be lowered compared to when it is slowly cooled.

Although it is possible to produce the membrane of the present invention even when the draft ratio is outside this range, high gas permeation performance cannot be expected and, in addition,
The disadvantage is that manufacturing becomes difficult.

The extrusion speed can be chosen relatively arbitrarily. If the thread is too slow or too fast, thread breakage is likely to occur, but this can be determined depending on the equipment requirements.

As the hollow fiber spinning nozzle, a conventional hollow fiber spinning nozzle such as an annular type, a horseshoe type, a bridge type, etc. can be used. As the die for film extrusion, a commonly used film or sheet die such as a T die or an annular die for inflation can be used.

The outer diameter of the hollow fiber varies from 5 to 5 depending on the nozzle dimensions, draft, etc.
It is preferable to set it to 5000 μm. If the thickness is less than 5 μm or more than 5000 μm, it becomes difficult to obtain a membrane with a large permeation rate. It is preferable that the thickness of the hollow fiber or film is similarly set to 1 to 1000 μm. Outside this range, it is difficult to form a good porous membrane and the gas permeation rate becomes low.

When using the membrane produced according to the present invention as a gas separation membrane, a hollow fiber having a larger surface area is advantageous than a film (flat membrane), and its outer diameter is 20 to 500 μm.
Pa7! f- is more preferably 1 to 50 μm.

The thread extruded from the nozzle is cooled and solidified. Cooling is done automatically by the discharge thread running through the air,
It is more preferable to further add an active cooling operation. As a cooling method, in addition to blowing air, ordinary cooling methods such as cooling with a chill roll or water (or hot water) can be used. The cooling temperature depends on the crystallization rate of the polymer, but is generally (
Tg-50) to (Tm-50)°C is preferred.

The hollow fibers obtained as described above are subjected to heat treatment. In the case of polymers with a fast crystallization rate such as polyolefins, crystallization progresses during the spinning process under slow cooling conditions.
Heat treatment is not necessarily necessary, but it is necessary for polymers that crystallize slowly, such as polyester. Even in the case of polyolefin, it is advantageous in terms of membrane performance and product uniformity to perform cooling during spinning conditions and heat treatment as a separate step. The appropriate heat treatment temperature is (Tg+20) to (Trn-5)°C. Outside this range, a membrane with a high permeation rate cannot be obtained.

In the present invention, ζ coating, in which a coating substance is applied to the hollow fiber or film obtained by the above method, can also be performed before heat treatment.

In the present invention, the coating substance refers to a substance that forms a polymer coating film by coating or a combination of coating and other means. , polymerizable monomers that polymerize under the action of light, radiation, etc. to form a coating film.

However, such a coating material must not produce through-hole microporosity during the subsequent stretching process.

The coating material may also be natural or synthetic. Synthetic materials include both addition and condensation polymers. Typical examples of useful materials that may constitute coatings are substituted or unsubstituted polymers that are solid or liquid under gas separation conditions, such as synthetic rubber, natural rubber, relatively high molecular weight and/or high boiling point polymers, etc. liquids, organic prepolymers, poly(siloxanes) (silicone polymers), polysilazane, polyurethanes, poly(ebichlorohydrin), polyamines, polyimines, polyamides, acrylonitrile-containing copolymers, polyesters (including polylactams), poly(alkyl) acrylates) and poly(alkyl methacrylates), polysepersades, polysuccinates and alkyd resins, terpenoid resins, cellulose polymers, polysulfones, poly(alkylene glycols) and others, poly(alkylene) polysulfates, polypyrrolidones, polyolefins such as poly(ethylene) ,
Poly(propylene), poly(butadiene), poly(2,
6-dichlorobutadiene), poly(isoprene), poly(chloroprene), poly(styrene) and copolymers, poly(vinyl alcohol), poly(vinyl aldehyde) [
poly(vinyl formal) and poly(vinyl butyral)], poly(vinyl ketones) [e.g. poly(methyl vinyl ketone)], poly(vinyl esters) [e.g. poly(vinyl benzoate)], poly(vinyl halides) [e.g. (vinyl bromide)], poly(vinylidene halide), poly(vinylidene carbonate), poly(N-vinylmaleimide), poly(methyl isopropenyl ketone), fluorinated ethylene copolymer, polyarylene oxide), polycarbonate, polyphosphate, and any copolymer containing the block copolymer described above! <
Examples include coalescence, grafting and blending. These polymers may be polymerized in advance and applied as a solution to the hollow fiber or film, or monomers or prepolymers may be applied as they are or in the form of a solution and then polymerized. The coating material can also contain appropriate amounts of surfactants, antioxidants, antistatic agents, plasticizers, ultraviolet absorbers, colorants, etc. depending on the purpose.

Preferably, the coating layer is not so thick that it adversely affects the performance of the membrane, for example by causing an undue reduction in flow. The coating layer is approximately 1], 001
It may have an average thickness in the range of ~50 microns. In some cases, the average thickness of the coating layer is less than about 1 micron, and may be less than about Q, 5 microns. The coating may be a single layer or may consist of at least two separate layers of the same or different materials.

The coating is applied to at least one, preferably one surface of the hollow fiber or film. Particularly when the membrane is ultimately used as a separation membrane, it is desirable that the side opposite to the coated side be kept under a low absolute pressure.

The coating may be applied by any suitable method, such as spraying, brushing, dipping into an essentially liquid substance containing the coating material, or other coating operation. As mentioned above, when the coating material is specified, it is preferably used as a solution in a solvent that is liquid in nature and substantially non-solvent for the hollow fiber or film.

The viscosity of the coating liquid measured with a capillary viscometer is preferably 15 to 500 centipoise, more preferably 3 to 50 centipoise at the coating temperature. When the coating liquid is a polymer solution, it is preferable that the concentration of the polymer is adjusted to have the above-mentioned bath liquid viscosity. Preferably, 4 degrees is thick (depending on the degree of polymerization of the polymer, but it is cL01 to 10 weight percent, more preferably a1 to 2 weight percent).

The film or hollow fiber coated with the coating liquid is dried, polymerized, or crosslinked to form a solid coating layer. Drying may be performed using air blowing, heat, infrared rays, or any other method. For polymerization or crosslinking, methods such as heating, ultraviolet irradiation, visible light irradiation, contact with a reactive gas or liquid, and plasma treatment can be used.

When the coating operation is performed before the heat treatment referred to in the present invention, the heat treatment can also serve as the solidification operation of the coating layer by heating. In addition, when the coating operation is performed after the heat treatment in the present invention (5-%), the solidification operation of the coating layer is performed during or after the cold stretching.
8 is also possible. However, in any case, it is not preferable to touch the roller in an unsolidified state because this will result in a significant decrease in the separation coefficient.

In addition, prior to the coating operation, the hollow fiber or film may be pretreated with acid or alkali treatment, or coated with a surfactant, or the coating operation may be repeated multiple times to suppress the occurrence of pinholes. It is also preferable to do so.

The hollow fiber or film subjected to the above treatment is stretched to generate voids in the olfactory interior and to form a porous structure (this process is referred to as a cold stretching process). A suitable stretching ratio is 105 to 3.0. The cold stretching temperature is (
'rg-50) to (Tm-10)°C is preferred. In this temperature range, when the ultimate crystallinity of the polymer is low, or when crystals are not sufficiently developed due to cooling and heat treatment conditions, cold stretching must be performed at a lower temperature. Although it varies depending on the type of polymer, generally speaking, if the degree of crystallinity is about 60% or less, it is necessary to cold stretch at Tg+10°C or less. Stretching at higher temperatures does not create voids and
High gas permeability cannot be achieved.

On the other hand, the crystallization rate is fast and the crystallinity reached is high, making the polymer (
For example, in the case of isotactic polypropylene) or in the case of relatively sufficient heat treatment, it is preferable to stretch at Tg or higher. Stretching at low temperatures tends to cause breakage of the hollow fiber or film. Further, the stretching temperature is preferably higher than the Tg of the coating material.

In order to further increase the gas permeability, stretching may be performed at a temperature higher than the cold stretching temperature (Tm or lower) without loosening the tension following the cold stretching (this process will be referred to as the hot stretching process). ).The hot stretching can be performed in one stage or in multiple stages.The appropriate stretching ratio DR for the cold stretching and hot stretching is t1 to 5.0.

In the case of a film, the cold/hot stretching may be free width-axial stretching, constant width uniaxial stretching, or the hollow fiber or film may be continuously stretched with a roller. Generally, the stretching speed is preferably 1 to 100%/sec. In addition, in continuous stretching, it is possible to fix the stretching point or narrow the stretching range by shortening the stretching section, using rollers with a small diameter, using a stretching bar, etc. to make the product uniform. It is advantageous in this respect.

The cross-sectional area of the hollow fiber or film hardly decreases depending on the cold/hot stretching. Therefore, the apparent density will decrease. This indicates that voids were created inside the membrane, making it porous.

Heat setting is performed so that the pores in the support produced by cold/hot stretching remain fixed even after the stress is released. The heat setting temperature needs to be higher than the cold stretching temperature +10°C and lower than Tm. The heat setting time is preferably 0.1 seconds or more and the stretching ratio is preferably 19 to 2.0. When hot stretching is performed under heat setting conditions, heat setting is not necessarily necessary. In this case, the hot stretching process is heat setting. In addition, when hot stretching is performed, there is little deterioration in performance even if heat setting is performed under no tension (free shrinkage conditions).

The shape of the membrane of the present invention can be arbitrarily selected depending on the intended use. For example, it can be in the form of a hollow fiber or a tubular 1 flat membrane. In addition, various forms can be made as necessary, such as by introducing a structure to improve the film strength or by changing the film thickness. The appropriate outer diameter of the hollow fiber (including tubular fibers) is 5 to 5000 μm, and 2
More preferably 0 to 500 μm. Although it is possible to produce a hollow fiber-like heterogeneous membrane with an outer diameter of 5 μm or less or 5000 μm or more, the production cost, membrane performance, etc. are inferior, and there is no advantage.

The appropriate film thickness is 1 to 1000 μm. If it is less than 1 μm, it is difficult to obtain mechanical strength, and if it is more than 1000 μm, the transmittance will decrease. Regarding the film thickness, the same applies to the case of a flat film.

Function: When attempting to separate (including concentration and removal) a selected gas from a mixture of two or more gases using a diaphragm separation method, the performance of the separation device should be favorable gas selectivity, good concentration ratio, and high Permeation rate, etc. are required, but these performances are largely determined by the performance of the separation membrane. The membrane of the present invention has good performance as a gas separation membrane.

Gas separation threads in which the membrane of the present invention can be used include, for example, production of oxygen-enriched air or nitrogen-enriched air from air, separation and recovery of CO1, Co, H,
recovery, removal of NO, SO, from waste gas, C010
, separation of H, /C0 separation, separation of Htlot, He
Examples include, but are not limited to, separation and recovery of inert gases such as, methane/ethane separation, etc.

The membrane of the present invention can also selectively remove gases from liquids,
Used for separation and concentration realized by permeation through a non-porous thin membrane, such as selective dissolution of a selected gas in a mixed gas into a liquid, separation of a selected liquid from a mixed liquid (so-called harperation), etc. be able to.

<Example> The present invention will be explained in more detail by showing Examples and Comparative Examples below, but the present invention is not limited to these Examples. Example 1 Polypropylene (ASTM
D-1238 (melt index 6.0) was spun from a nozzle with a diameter of 9n at a temperature of 230°C and a winding speed of 250.
The fibers were spun at a speed of m/min and a draft ratio of 500 to obtain hollow fibers with an outer diameter of 214 μm and a membrane thickness of 2α5 μm. This unstretched hollow fiber was heat treated at 140° C. for 30 minutes under constant length conditions. The outer and inner surfaces of the obtained hollow fibers (observed by cutting them at an angle) were observed using a scanning type Naoko Microscope (SGG), but no pores were observed (the resolution of the SEM was approximately 1ooX). This hollow fiber was continuously immersed using a roller system in a 15% toluene solution of polystyrene having an average molecular weight of 320,000, and then dried with hot air at 100°C. This coating operation was repeated 6 times, and the resulting composite hollow fiber was heated to 105°C.
Stretching was carried out continuously using a roller system so that the stretching ratio (DR) was 2.0. Next, while maintaining the stretched state, it was continuously introduced into a hot air circulation constant temperature oven at 140° C., and was retained in the oven for 1 minute to perform heat fixation. This hollow fiber is S
When observed by EM, pores with a major axis of 15 μm and a minor axis of about a2 μm were observed on the inner surface, but no pores were observed on the outer surface.

The oxygen and nitrogen permeability and separation coefficient of the manufactured hollow fiber were measured. Is the measurement condition 1 kl? /ar? The outside of the hollow fiber was subjected to X pressure at a pressure of −a, and the pressure rise rate inside the hollow fiber was measured after the pressure was reduced to 11 torr or less. The membrane area was determined from the micrograph Nff1ffl of the cross section of the hollow fiber. As a result, oxygen permeability Q (Ot) = 9.1 x 10-'
(R(S TP )/cri-sea-cyt*Hg
), oxygen/nitrogen separation coefficient α(0,/N, ): 5.
It was 9.

Comparative Example 1 A hollow fiber membrane was produced in the same manner as in Example 1, except that the polystyrene coating was not applied after heat treatment, but instead after heat setting. When the hollow fiber before coating (after heat fixation) was observed by SEM, pores with a major diameter of about C15 μm and a short diameter of about A1 μm were observed on both the inner and outer surfaces of the hollow fiber. The results of the gas permeation test of the membrane after coach ink were as shown in Table 1.

Under conditions where the pores (pinholes) are completely blocked by coating, the gas permeability can be reduced by one order of magnitude or more compared to Example 1.

, / / / /'' Table 1 1 (1511942,4X10zu2 (17G,94 2.8x10-'3 tO
tl 1. lX10-'4 1.5 5. Ot
9 x 10-' 5 2.5 5.9 7.7 The hollow fibers obtained by spinning at a draft ratio of 1000 were continuously introduced into a hot air oven at 145° C. using a roller yarn at a draw ratio of 10 (constant length), and heat-treated for a residence time of 30 seconds. was continuously immersed in a 100.8% poly-4 methylpentene cyclohexene solution (45°C) using a roller system, and then dried with hot air at 80°C.

This coating operation was repeated 6 times, and the resulting composite hollow fiber was cold-stretched at 65°C with a stretching ratio of 1.2, and then
Hot stretching was carried out at 40°C at a stretching ratio of t5, and further heat setting was carried out at 145°C for 10 seconds at a stretching ratio of to. The gas permeation properties of the composite hollow fibers obtained were as shown in Table 2.

Table 2 1 N, t7X10-5
t02 Ar 2.0X10-'
t13 Co 3.1x
10-5 1.8402 6.5X
10” 3.75 H62,3
X 10-' 13.16 Co
, 3.4x10-' 19.6
7 1-it4.1x10-' 2
3.4 Comparative Example 2 A hollow fiber membrane was manufactured in the same manner as in Example 2 except that coating was performed after heat treatment (after heat setting).The hollow fibers before coating (after heat setting) were
When observed with M, the long diameter CL of both the inner and outer surfaces of the hollow fiber is 4 μm.
, pores with short diameter α1 μm were observed. The results of the gas permeation test of the membrane after coating were as shown in Table 3. It can be seen that coating the porous hollow fibers and completely closing the pores (pinholes) requires multiple coating operations, and that only a membrane with low gas permeability can be obtained.

Table 3 1 3 α94 7.7x10-32 5 1
:L94 2. lX10-'3 7 1.0
4.8X10-'4 10 3.7 6.0X10
-'Suishikatou example 2
6.7 6.5X10-' Comparative Example 6 When a commercially available polypropylene fissured porous hollow fiber (Polyplastics Juraguard 6112) was observed with an SEM, both the inner and outer surfaces were thin with a long diameter of 15 μm and a short diameter of 0.1 μm. A hole was observed. Table 4 shows the results of the gas permeation test of the composite hollow fiber obtained by coating this hollow fiber in the same manner as in Example 2.

It turns out that it is difficult to obtain a high-performance gas separation membrane by coating a commercially available porous membrane.

Table 4 1 3 [194a2X10-'2 5 α9
4 4.8X10-33 7 (1943,1
x10-'4 10 α96 7.6X10""
5 15 3.7 5.5x10
-'Example 3 Poly-4-methylpentene-1 (ASTM D-123
Melt index 26) according to 8 was spun from a nozzle with a diameter of 5rtrx at a temperature of 300°C and a winding speed of 400*
/min, and the draft ratio was 2000. A 5% toluene solution of poly(dimethylsiloxane) was applied to the hollow fibers, and the coating process was repeated three times at 50°C.
Heat treatment was performed for 1 minute. Next, it was continuously stretched using a roller system at a stretching ratio of 13 times the original length at room temperature, then stretched at a stretching ratio of t6 at 150°C, and then heated at 180°C for 10 seconds at a constant length condition. Fixed.

When the oxygen and nitrogen permeability of this hollow fiber was measured in the same manner as in Example 1, Q (Ot) = 2. IX10-
'(cm'(s'rp)/Ma・5ee−α■ω,α
=2.1.

Example 4 Poly-4-methylpentene-1 (ASTM D-123
Melt index 26) according to 8 was spun 11Z from a nozzle with a diameter of 5n.

Yarn temperature 280°C, winding speed 100 m/min, drag 7
The hollow fibers spun with OO were heat-treated at 200° C. for 1 minute.

This hollow fiber was continuously immersed in a 15% cyclohexene solution of poly-4-methylpentene-1 at 40°C using a roller system, and then immediately dried with hot air at 50°C, and then dried for 3
At 5°CK, stretch by the draw ratio (DR) t3, then continue to 1
DR12 stretching at 50°C and further D stretching at 190°C.
Heat fixation was carried out at R195 with a residence time of 10 seconds.

The oxygen and nitrogen permeability of this hollow fiber is Q (Oz) = 7.2
X10-', Q (Nt)=2. OX 10-' (c
m' (STP)/iseccmHg).

Example 5 Melt index (ASTM D-1238) 5.5
High-density polyethylene was spun using a circular nozzle with a diameter of 9tIL at a spinning temperature of 150°C and a winding speed of 900m/mi.
The fibers were spun at a draft ratio of 2000 to obtain hollow fibers with an outer diameter of 184 μm and a membrane thickness of 1×2 μm. This hollow fiber was heat-treated at 110°C for 1 minute using a roller system, and then continuously immersed in a polysiloxane derivative chloroform solution for 60 minutes.
Dry with hot air at °C, stretch by DRt3 at room temperature,
Subsequently, the film was stretched at 100° C. by 1) Rt 6, and then heat-set at a constant length of 110° C. for 10 seconds. The gas permeation property of the obtained hollow fiber is Q(02)=tOXl
0-'(i(STP)7cm"aec・cmHg),
α(02/Nt) = 2.3.

Example 6 Hollow fibers were produced in the same manner as in Example 1, except that a 15% polyvinyl acetate solution in methyl ethyl ketone was used as the coating agent. The measured value of this film property is P(0,)
=2.8X10-'(c&(STP)/cm'
sec・cmHg) α=6.6.

〔Effect of the invention〕

As shown in the examples above, according to the production method of the present invention, an ultra-thin film with no pinholes can be produced, which was difficult to achieve with conventional methods such as coating a porous film due to contradictory properties. It becomes possible to manufacture composite membranes with layers. Therefore, it becomes possible to produce a separation polymer 5 having both a high separation coefficient and permeation rate, and it becomes possible to produce a polymer membrane having excellent performance in gas separation and organic liquid separation.

Depending on the intended system, the required membrane performance (e.g. gas permeability, separation coefficient, pressure resistance, heat resistance, corrosion resistance, etc.)
However, in the production method of the present invention, the hollow fiber crystalline polymer that serves as the support and the coating material that serves as the separation active layer can be selected independently and relatively freely, so the membrane can be selected according to the purpose. Can be designed and manufactured.

Claims (1)

[Claims] 1. A thermoplastic crystalline polymer having (1) a melting temperature Tm~
(Tm + 100)°C (where Tm is the crystal melting point) and a draft ratio Df of 50≦Df≦10000 to form a hollow fiber-like or film-like precursor; A coating layer is formed by coating the surface of the support with a coating material that does not create penetrating microporosity in the subsequent stretching process, and (3) the support having this coating layer is coated with (T
(3') above (2).
Prior to the step (3), heat treatment is performed to obtain (
4) Then stretched at a temperature of (Tg-10) to (Tm-10)°C, (5) then (stretching temperature of the previous stage + 10) to Tm
Production of a gas separation membrane characterized by forming micropores only in the support by heat-setting at a temperature of °C, thereby obtaining a membrane in which a non-porous coating layer is laminated on the surface of the microporous support. Method. 2. The method according to claim 1, wherein the thermoplastic crystalline polymer is polypropylene, polyethylene, poly-4-methylpentene-1 or polyoxymethylene.