JPS6238221A - Porous membrane for separation - Google Patents

Abstract

PURPOSE:To obtain the titled membrane developing excellent separation trans missivity and also excellent in dynamical characteristics or thermal dimensional stability, by using a thermoplastic polymer wherein a crystal orientation degree is 90% or more, an X-ray dispersion half power angle of diffraction is 0.28 deg. or less and a void orientation degree is 70% or more. CONSTITUTION:In a method for continuous multistage orientation of a non- stretched thermoplastic polymer utilizing the speed ratio of rotors, neck stretching is performed by using dielectric heating in the first stage of multistage stretching divided by a tension separator and, at least in the second stage, dielectric heating and external heating are continuously used to perform stretching. By this method, a separation porous membrane comprising a thermoplastic polymer, wherein a dispersion half power angle of diffraction in the equator direction of void scattering according to an X-ray small angle scattering method is 0.28 deg. or less, a void orientation degree is 70% or more and a crystal orientation degree measured by X-ray wide angle scattering method is 90% or more, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a porous separation membrane made of a polymer that has both excellent separation permeability and mechanical performance. For more details,
The present invention relates to a porous separation membrane made of a thermoplastic polymer and suitable for gas separation, particularly for separating gases consisting of small molecules such as hydrogen and helium from gases consisting of large molecules.

(Prior Art) The performance of a porous membrane for separation is required to have both processing ability and separation ability. Increasing the throughput depends on how many pores are present in the membrane. On the other hand, increasing the separation ability depends on having uniform pores with controlled size and shape in the membrane. Therefore, in the production of porous membranes for separation, efforts have traditionally been made to ensure that as many uniform pores as possible are present in the membrane, and a number of methods have been tried. Method using phase separation of substances (U.S. Pat. No. 3,133,132)
), methods for sintering powders (Herr ing, C.,
, J. Appff, Phys., 21.301 (1
950), or a method of mixing easily removable components and removing them after film formation (Swiss Patent No. 7,718,76)
5 etc.) are known.

On the other hand, stretching or superstretching is one of the methods that has been used for a long time to improve the mechanical performance of thermoplastic polymers. For polyoxymethylene, industrial material 32
(4), 92 (1984) describes an example in which dielectric heating was used to enable superstretching and a stretched body exhibiting high tensile modulus and high tensile strength was obtained. It is also described that polyethylene can be ultra-stretched by gel-spinning ultra-high molecular weight polyethylene, thereby producing a stretched body having high tensile modulus and high tensile strength.

(Problems to be solved by the invention) In recent years, as the uses of porous membranes for separation have expanded, the required mechanical properties have become stricter. There is an increasing demand for membrane strength such as resistance to cleaning (backwashing, etc.) (for example, Japanese Patent Laid-Open No. 58-223). Particularly in the field of gas separation, there are strict requirements regarding pore size distribution and shape, so it is extremely difficult to improve the mechanical properties of a porous membrane for separation while simultaneously satisfying both separation capacity and processing capacity. ing. For example, for the purpose of improving the strength of porous membranes, Japanese Patent Laid-Open No. 52-85525,
A method of forming a membrane into a hollow fiber is proposed in Japanese Patent No. 144416 and the like. However, the tensile strength of these hollow fibers is 0.4 GPa or less, and cannot meet the recent requirements for the strength of porous membranes for separation.

An object of the present invention is to provide a porous membrane for separation that has high separation capacity and processing capacity, and has extremely excellent mechanical properties.

(Means for Solving the Problems) In order to achieve the above object, the present inventors have developed a mechanism for generating voids (vacancies) in thermoplastic polymers and a method for improving the strength in thermoplastic polymers. As a result of extensive studies, the present inventors discovered that when a porous membrane has a microstructure related to voids in a certain region, the porous membrane has excellent gas and liquid separation functions and excellent mechanical properties, and has arrived at the present invention. .

That is, the present invention provides a method in which the dispersion half-value diffraction angle in the equator direction of void scattering measured by small-angle X-ray scattering is 0.28° or less, the degree of void orientation is 70% or more, and the crystal orientation measured by wide-angle X-ray scattering is The present invention is characterized in that it is a porous membrane for separation made of a thermoplastic polymer having a polycarbonate of 90% or more.

In the present invention, the polymer forming the porous membrane must be a thermoplastic polymer. With thermosetting polymers, it is difficult to produce a film by melt molding, and the degree of orientation cannot be increased by heating and stretching.

The thermoplastic polymer in the present invention may have any composition and any polymerization method may be used as long as it can be molded into a film.

Preferred thermoplastic polymers are polyoxymethylene, polyethylene, polypropylene, polyester, etc., which can be stretched or superstretched, or those that generate heat by dielectric heating,
They are dielectric polymers that generate voids, and non-dielectric polymers that contain dielectric materials. Examples of the dielectric polymer include polyethers such as polyoxymethylene, polyamides, polyesters, polycarbonates, polyvinyl chloride, polymethacrylates, and the like. Dielectric materials include titanium oxide, lead titanate, barium titanate,
Examples include inorganic dielectric substances such as alumina, copper oxide, silicone carbide, and barium sulfate, and various organic dielectric substances.

The most preferred thermoplastic polymers are polyoxymethylene and polyethylene terephthalate, which can generate heat by dielectric heating and obtain excellent mechanical properties by stretching or superstretching.

A particularly important feature of the porous membrane of the present invention is that it has a novel microstructure. This fine structure will be discussed below.

FIG. 1 shows the results of the small-angle X-ray scattering method of the porous membrane of the present invention.
FIG. 3 is a diagram schematically showing a diffraction intensity distribution curve in the equatorial direction with respect to the stretching axis. Details of the measurement of this diffraction intensity distribution curve will be described later. The dispersive half-value diffraction angle α is a diffraction angle that exhibits a half-value diffraction intensity A/2 of the diffraction intensity A when the diffraction angle (2θ)=0.2, as shown in FIG. In the present invention, the dispersion half-power diffraction angle α in the equator direction must be 0.28° or less. The diffraction intensity distribution curve in FIG. 1 shows the distribution of diffraction intensity due to void scattering, and means the distribution of void sizes in the diffraction scanning direction. If α is larger than 0°28°, the size distribution of voids will be excessive, resulting in a decrease in separation performance and strength, and voids in the porous membrane will likely become non-penetrating, making it difficult to obtain a sufficient permeation flow rate. It disappears.

Diffraction intensity A when the diffraction angle (2θ) = 0.2° of the small-angle X-ray diffraction intensity distribution curve in the equatorial direction with respect to the stretching axis direction as shown in Figure 1, and the small-angle X-ray diffraction in the same meridian direction From the diffraction intensity B when the diffraction angle (2θ) of the intensity distribution curve is 0.2°, the void orientation degree ■0 is calculated using the following equation. In the present invention, this ■0 (%)
must be 70% or more. (2) The smaller 0 is, the more spherical the void becomes, and the larger VO is, the flatter the void is in the direction of the stretching axis. If the VO content is less than 70%, the voids are likely to deform during gas separation or liquid separation, which reduces the processing capacity and impairs practicality. The preferred range of VO is 80% or more.

In the present invention, the degree of crystal orientation CO must be 95% or more. CO is related to the mechanical properties and thermal properties of porous membranes, and these properties tend to deteriorate when CO is low. If the degree of crystal orientation is less than 95%, the porous membrane has a small tensile modulus and a tendency to yield. Because the stress is small, it expands due to the pressure of the gas or liquid to be separated, and because of its poor dimensional stability against heat, it partially shrinks due to the heat treatment applied when manufacturing the separation module, resulting in a decrease in separation ability. This results in a decrease in the temperature of the membrane, making it unsuitable as a separation membrane. In order to have good mechanical and thermal properties, the degree of crystal orientation CO of the porous membrane should preferably be 98% or higher.

An example of a method for producing the porous membrane for separation of the present invention having the above-mentioned novel microstructure is a method in which an unstretched body of a thermoplastic polymer is continuously stretched in multiple stages using the speed ratio of a rotating body. In multi-stage stretching separated by tension separation devices, neck stretching is performed using dielectric heating in the first stage,
Examples include a method in which dielectric heating and external heating are used successively or external heating is used to carry out stretching in at least the second stage.

FIG. 2 is an explanatory diagram showing an embodiment of the apparatus for producing a porous membrane for separation according to the present invention by two-stage stretching. This device operates between a feeder 3 consisting of a pair of nip rolls a% a' and a first take-up machine 6 consisting of a pair of nip rolls b, b'', using the speed ratio of the two to A first stage stretching area where stretching is carried out and a second pulling machine 10 consisting of a first pulling machine 6 and nip rolls c and c" in which a second stage stretching is performed using the speed ratio of both. It consists of a two-stage stretching area.

The first puller 6 corresponds to a tension separating device, and the tension on both sides thereof is independently controlled. In the figure, an unstretched body 2 of thermoplastic polymer wound around a winding drum 1 is sent to a first stage stretching area by a payout ta3, and is heated in a first stage dielectric heating furnace 6 disposed there. Immediately, the first stage of stretching, that is, neck stretching, is carried out, and at the same time it is taken up by the first drawing machine 6, which is a tension separation device, it is sent to the second stage stretching area, and the The temperature is raised in a two-stage dielectric heating furnace 7 and an external heating furnace 8, and a second stage of stretching is performed. Subsequently, the stretched thermoplastic polymer 11 is taken up by a second take-up machine 10 and then wound up by a take-up machine 12. Note that 4 and 9 in the figure indicate the first stage and second stage tension detectors, respectively.

In the multi-stage stretching method described above, the neck stretching ratio in the first stage is in the range of 1 to 1.5 times the so-called natural stretching ratio, and the stretching stress in the first stage is set to a value greater than 4.5 kg/mrd. Furthermore, in the second stage, the total stretching ratio is 1.1 to 6 times the natural stretching ratio, preferably 1. It is preferable to stretch the film by 1 to 5 times. If the stretching conditions are outside the above range, the gas separation ability, processing ability, or mechanical performance of the resulting porous membrane may be impaired, and the object of the present invention may not be achieved.

The porous membrane for separation of the present invention may be in the form of a flat membrane or in the form of hollow filaments (the membrane thickness is preferably 0.5 mm or less. In the case of the membrane thickness in the form of hollow filaments, the It is preferable that the striated body has a hollow part having a uniform shape and size over the entire length, with a ratio of the cross-sectional area of the hollow part being 0.1 or more.The ratio of the cross-sectional area of the hollow part to the total cross-sectional area is 0.
．． When the film thickness is less than 1 or greater than 0.5 w,
The separation and permeability of the porous membrane may be impaired because the amount of gas or liquid processed per unit time may be reduced, or the amount of permeation may be reduced due to an increase in membrane resistance. In addition, porous membranes whose hollow parts are uneven in shape and size not only result in uneven separation permeability, but also pose problems in pressure resistance during separation and backwashing, making them unsuitable as porous membranes for separation. I can't say that. More preferably, the cross-sectional area of the hollow portion is 0.3 or more with respect to the total cross-sectional area, and the film thickness is 0°1 fl or less.

A method for measuring a microstructure and a method for measuring various physical properties in the present invention will be described below.

(1) Dispersion half-value diffraction angle α Based on small-angle X-ray scattering method. The X-ray small-angle diffraction intensity curve was measured using an ultra-powerful X-ray diffractometer (Geigerflex RA) manufactured by Rigaku Denki Co., Ltd.
D-γA), position sensitive detector (PSPC-10),
Using position analysis circuit and multi-channel analyzer,
CuKα rays made monochromatic with a nickel filter (λ=1.5
418 people).

The X-ray generator was operated at 30 KV and 180 mA, and the first pinhole slit was 0.2 mm in diameter, the second pinhole slit was 0.2 mm in diameter, and from the first pinhole slit to the second pinhole slit. The distance from the second pinhole slit to the sample is 40 m, the distance from the sample to the position-sensitive detector is 4001 m, and the diffraction angle (2θ )=0° position,
The line beam stopper was installed so that the centers of the line beam stoppers with a width of 1.5 cranes coincided with each other.

The porous membrane was installed so that the stretching axis of the porous membrane was perpendicular to the X-ray diffraction plane, and the small-angle X-ray diffraction intensity in the equator direction with respect to the stretching axis was measured. The thickness of the sample is approximately 1.0 am
Then, the porous membrane was installed with its stretching axes aligned. The intensity curve obtained is schematically shown in FIG. The intensity obtained by subtracting the intensity curve obtained by measuring without a sample, that is, the baseline intensity, from the intensity measured with the sample attached is the true X-ray small-angle diffraction intensity of the sample. be. In FIG. 1, the diffraction angle at which the half-value diffraction intensity A/2-t- of the true diffraction intensity A when the diffraction angle (2θ)=0.2° is taken as the dispersive half-value diffraction angle α.

(2) Void orientation degree ■0 Measured under the same conditions as the measurement of the dispersion half-value diffraction angle α. However, the porous membrane is installed so that the stretching axis of the sample is parallel to the X-ray diffraction surface. The intensity curve obtained is therefore a small-angle X-ray diffraction intensity curve in the meridian direction with respect to the stretching axis. In this intensity curve, diffraction angle (2θ) = 0.2°
Let B be the diffraction intensity when . The degree of void orientation ■O is defined by the following equation using the above-mentioned diffraction intensity A and the above-mentioned diffraction intensity B.

(3) Crystal orientation degree CO Based on X-ray wide-angle diffraction method. Measuring the degree of crystal orientation of porous membranes is
Rigaku Denki's ultra-strong X-ray diffraction device (Geigerflex RAD-γA), fiber sample measuring device (FS-3), goniometer (SG-9), a synnarration counter in the meter, and a pulse height analyzer in the counting section. The measurement is performed using CuKα rays (λ=1.5418), which are made monochromatic with a nickel filter.

The thermoplastic polymers of the porous film of the present invention each have a characteristic diffraction intensity in the range of a diffraction angle (2θ) of 10 to 40° in the equator direction with respect to the stretching axis direction.

The reflection with the lowest angle of 20 in its diffraction intensity curve is used. The 2θ reflection used is determined from the equatorial diffraction intensity curve.

The X-ray generator operates at 30KV and 180mA. Attach the sample to the fiber sample measuring device so that the single yarns are parallel to each other. The thickness of the sample is 0.5111
<It is appropriate to make it leprosy. The goniometer is set to the 2θ value determined from the equatorial diffraction intensity curve. Using the symmetrical transmission method, the azimuth direction is set to -30°~
Scan +30° and record the diffraction intensity in the azimuthal direction. Furthermore, the diffraction intensities in the azimuth directions of −180° and +180° are recorded. At this time, the scanning speed is 4°/811
, chart speed 10 dragon/11. Time constant 1 second, collimator double layer φ, receiving slit w width t.

911, and the width is 3.51.

From the obtained diffraction intensity curve in the azimuthal direction, the degree of crystal orientation CO
To obtain this, take the average value of the diffraction intensities obtained at ±180', draw a horizontal line, and use it as a base line.

Draw a perpendicular line from the top of the peak to the baseline and find the midpoint of its height. A horizontal line passing through the midpoint is drawn, the distance between the intersection of this horizontal line and the diffraction intensity curve is measured, and the value obtained by converting this value into an angle (°) is defined as the orientation angle H.

The degree of crystal orientation is expressed by the following formula %formula% given by.

(4) Film thickness d When the porous film is a flat film, it is measured using a conventionally known micrometer. Further, when the porous membrane is a hollow filament, the hollow filament is cut in the cross-sectional direction using a conventionally known microtome, and the film thickness is measured under the field of view of an optical microscope.

(5) Strength: Place the sample in a normal tensile testing machine with a grip length of 10 cm, and perform a tensile test at a tensile speed of 10 cm.

Divide the force with which the sample is cut by the cross-sectional area of the sample and use that value as the strength.

(6) Gas Permeability Coefficient FIGS. 3(a) and 3(b) schematically show the state in which the porous membrane is attached when measuring the permeability coefficient of the porous membrane. When the porous membrane is a flat membrane, C in Figure 3
a'), and when it is in the form of a hollow striatum, the third
As shown in (b) of the figure, the porous membrane 21 is attached to the stainless steel tube 22 with epoxy resin 23. Particularly in the case of a hollow filament form, one end of the sample is sealed with epoxy resin. temperature 2
0℃, high pressure side pressure cuff 6coaHg, low pressure side pressure IQc+
Permeate the permeate gas (hydrogen or nitrogen) at nl (g).

From the permeated gas flow rate at that time, the gas permeability coefficient P is calculated from the following equation.

(7) Separation coefficient S The ratio of the above gas permeability coefficients is defined as separation coefficient S, which is defined by the following formula.

S A/B = PA /PB S A/B : Separation coefficient of gas component A with respect to gas component B PA : Permeability coefficient of gas component A PB : 〃 B 〃 (Example) Example 1 Polyoxy as a thermoplastic polymer Methylene (Tenac (registered trademark) 3010, manufactured by Asahi Kasei Industries, Ltd.) was selected, and an unstretched film made of this was stretched under various conditions using the two-stage stretching device shown in Figure 2, and the final stretching ratio was 28. A porous membrane for separation consisting of a stretched polyoxymethylene film was obtained. The stretching conditions are shown in Table 1.

Table 1: The porous separation membrane made of stretched polyoxymethylene film is in the form of a flat membrane, and its thickness, parameters representing the microstructure, and mechanical strength such as tensile strength and initial The tensile modulus is shown in Table 2.

Table 2 Using the present polyoxymethylene flat membrane type porous membrane for separation,
N2 and N2 gas were permeated respectively. Transmission method,
The conditions are as described above. The permeability coefficient and separation coefficient of each sample are shown in Table 3.

Table 3 As is clear from Table 2, the porous membrane for separation of the present invention has the following properties:
It can be seen that it has excellent mechanical properties and excellent gas separation processing ability as shown in Table 3.

Example 2 As the thermoplastic polymer, the same polyoxymethylene as in Example 1 was selected, and a 4-frame outer diameter and 0.0 mm thickness was constructed from it.
A 75-n hollow unstretched tube was stretched using the same stretching device as in Example 1. The stretching conditions are shown in Table 4.

Table 4 The polyoxymethylene stretched tubes obtained had a final stretching ratio of 20.
At a magnification of 25.28 times, all of them had the form of hollow striae with uniform through holes. Table 5 shows the outer diameter, thickness, parameters representing the microstructure, bow tensile strength, and initial tensile modulus of each sample.

The permeation performance of the present porous membrane for polyoxymethylene hollow filament type separation was investigated according to the method and conditions described above. The results are shown in Table 6.

The porous membrane for separation in the form of hollow filaments according to the present invention has excellent mechanical strength as shown in Table 5, and is also extremely excellent in terms of pressure resistance required as a material for separation. As can be seen from Table 6, excellent performance is exhibited in terms of gas separation processing capacity.

Example 3 A porous membrane for separation was obtained in the same manner as in Example 2, except that a hollow unstretched polyoxymethylene tube having an outer diameter of 3 fl and a thickness of 0.251 m was used. Tables 7 and 8 show the stretching conditions, the outer diameter, thickness, microstructure, and mechanical strength of the samples.

As shown in Table 7, Table 8, and Table 8, it can be seen that even if the thickness of the sample is only 0.095 mm, the mechanical strength of the sample maintains excellent performance. Table 9 shows the permeability performance, and both the permeability coefficient and separation coefficient were excellent. Furthermore, by reducing the membrane thickness, the separation processing capacity was significantly increased.

Table 9 Comparative Example 1 The same unstretched polyoxymethylene tube as used in Example 2 was stretched using the same stretching device as in Example 1.

The stretching conditions are shown in Table 10.

Table 10 In Table 10, Sample No. 8 was stretched under the conditions listed in the table, so its outer diameter and thickness were non-uniform in the stretching direction. For this reason, it was extremely unsuitable as a separation material.

On the other hand, Samples 9 and 10 are polyoxymethylene stretched tubes with a final stretching ratio of 28 times, and the outer diameter, thickness, microstructural parameters, tensile strength, and initial tensile modulus are as shown in Table 11. Ta.

Table 11 From the above table, both Samples 11h9 and 10 have dispersion half-value diffraction angles larger than 0.28°, void orientation degrees are much smaller than 70%, and crystal orientation degrees are also less than 95%. It turns out that it is outside the scope of the invention.

In addition, the mechanical strength is also slightly reduced. Sample disease 9.10
When H2 and N2 gases were permeated using the same method as in Example 2, the permeation coefficients of both gases decreased significantly, and the gas separation processing ability decreased.

Example 4 Polyethylene terephthalate was selected as the thermoplastic polymer, and a material made of it had an outer diameter of 3.5 n+, a thickness of l,
A hollow unstretched tube of Q mm was stretched using the same stretching apparatus as in Example 1 under the conditions shown in Table 12.

Table 12 The polyethylene terephthalate stretched tube obtained is as follows:
The final stretching ratio was 7.8 times, and the film had a hollow filament shape with uniform through holes. Further, when the cross section of the stretched tube was observed with a scanning electron microscope, it was found that the surface layer was composed of a dense layer and the inner layer was porous. 1st
Table 3 shows the outer diameter, thickness, parameters representing the microstructure, tensile strength, and initial tensile modulus of the sample.

Table 13 Table 14 shows the permeability of the polyethylene terephthalate hollow filament type porous membrane for separation.

Table 14 The porous membrane for separation of hollow filaments has excellent mechanical properties as shown in Table 13, and excellent gas separation processing ability as shown in Table 14.

Comparative Example 2 A porous membrane in the form of hollow filaments made of cellulose acetate was prepared according to the method described in JP-A-52-85525, and its strength was measured and found to be 0.3 GPa or less. When compared with the strength of the porous separation membrane of the present invention, it is clear that its mechanical strength is considerably inferior. Moreover, even when compared with the mechanical strength required for a porous membrane for separation, the value is not sufficiently satisfactory.

(Effects of the Invention) The porous membrane for separation made of a thermoplastic polymer having a novel microstructure of the present invention reflects its unique microstructure and exhibits excellent separation permeability, regardless of its form. Moreover, it also has extremely excellent mechanical properties required for a porous membrane for separation. This is not only favorable in terms of performance of the separation membrane material, but also has thermal dimensional stability, which improves stability against heat treatment during separation module fabrication, and even reduces permeation. It also has excellent processability, handling properties, and durability, such as pressure resistance and durability against backwashing, and is also advantageous in terms of cost.

The porous separation membrane of the present invention can be widely used not only for gas separation but also as a separation porous membrane for liquid separation and so-called filtration.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a diffraction intensity distribution curve in the equatorial direction with respect to the stretching axis, obtained by small-angle X-ray scattering of the porous membrane of the present invention;
FIG. 2 is an explanatory diagram showing one embodiment of the stretching device used in the present invention, and FIGS. 3(a) and (b) are explanatory diagrams showing the state in which a sample is attached when measuring the permeability coefficient of a porous membrane. be. 1... Unstretched body winding drum, 2... Unstretched body, 3.
... Feeding machine, 4... First stage tension detector, 5... First
Stage external heating furnace, 6... First take-up machine, 7... Second stage dielectric heating furnace, 8... External heating furnace, 9... Second stage tension detector, 10... Second stage Pulling machine, 11...stretched body, 12
... Winder, 13... Microwave oscillator, 14...
- Coupling waveguide, 15... Applicator, 16... Dielectric heating furnace inlet, 17... Dielectric heating furnace outlet, 18...
Microwave reflection conditioner. Agent Patent Attorney Takeshi Kawakita (a) (b) 23 Nepoxy Resin Procedural Amendment Spring - November 7, 1985 1. Case description 1985 Patent Application No. 178282 2. Title of invention Separating pores Membrane 3, Relationship with the case of the person making the amendment Patent applicant address 1-2-6 Dojimahama, Kita-ku, Osaka-shi, Osaka Name (003) Asahi Kasei Industries Co., Ltd. Representative Masaomi Seko 4, Agent Address 103 Nihombashi Kayabacho-chome 11-8-6, Chuo-ku, Tokyo
,? 7. Contents of the amendment (1) In the brief explanation of the drawings in the specification (1) on page 28, line 11 of the specification, "winding machine" is changed to "winding machine." (1) “13...” on page 28, lines 11-14 of the specification
...Microwave reflection adjuster. ”. that's all

Claims (1)

[Claims] (1) Made of a thermoplastic polymer, the dispersion half-value diffraction angle in the equator direction of void scattering measured by small-angle X-ray scattering is 0.28° or less, the degree of void orientation is 70% or more, and
A porous membrane for separation, characterized in that the degree of crystal orientation measured by wide-angle line scattering is 95% or more.