JPH06246140A - Production of heterogeneous hollow yarn membrane - Google Patents

Abstract

PURPOSE:To obtain a heterogeneous membrane with a thin dense layer even in the case of no pinholes or a few pinholes in the dense layer and to produce a heterogeneous hollow yarn membrane having a high rate of gas permeation. CONSTITUTION:A crystalline thermoplastic polymer is melt-spun into hollow yarn, crystallization is accelerated by heat treatment if necessary and the hollow yarn is drawn at above a drawing factor at which the oxygen/nitrogen separation factor of the hollow yarn after drawing begins to lower in accordance with the increase in the drawing factor. The drawn hollow yarn is then heat- fixed at a temp. above (drawing temp.+10) deg.C while being shrunk at above a shrinkage at which the oxygen/nitrogen separation factor of the hollow yarn after heat fixing begins to increase in accordance with increase in the shrinkage at the time of heat fixing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a separation membrane, an improved method for producing a hollow fiber heterogeneous membrane, and a method for producing a hollow fiber heterogeneous membrane having an improved gas permeation rate. The hollow fiber heterogeneous membrane produced according to the present invention can be used for, for example, production of oxygen-enriched air, production of nitrogen-enriched air, gas separation such as concentration of carbon dioxide, and also membrane oxygenator, diaphragm oxygen for fish tanks. Supply,
Dissolution of gas into liquid such as absorption of carbon dioxide in a membrane, removal of dissolved gas in liquid such as degassing of water, deoxygenation of water, decarbonation of water, and removal of organic solvent from water, for example It is used for perforation and defoaming.

[0002]

2. Description of the Related Art Hollow, which is composed of a crystalline thermoplastic polymer, has a dense layer which is substantially non-porous on the surface of the membrane or inside the membrane, and has other portions inside the membrane which are continuous and porous. A method for producing a heterogeneous membrane of yarn, that is, a hollow-fiber-type heterogeneous membrane, in particular, having a dense layer of substantially nonporous on the outer surface, the inside of the membrane is continuous porous, and the inner surface has fibers. Regarding the method for producing a hollow fiber heterogeneous membrane in which pores surrounded by a plurality of plate crystals extending in the direction perpendicular to the axis and a plurality of fibrils connecting the crystals are open, for example, a gas separation membrane is characterized by JP-A-59-196706 and JP-A-59-229320
Japanese Patent Application Laid-Open No. 63-258605
Japanese Patent Laid-Open No. 1-104271 regarding a diaphragm for artificial lung,
Regarding these general films, JP-A-4-210216
Is disclosed in.

In the method for producing a hollow fiber heterogeneous membrane by melt molding described in these prior art documents, a crystalline thermoplastic polymer is melt-spun into a hollow fiber shape, and heat-treated as necessary for crystallization. This is a method of advancing and stretching and then heat-fixing if necessary. The stretching step in this manufacturing method is an essential step for making the inside of the membrane porous, but if the stretching ratio is increased, the dense layer on the membrane surface is also cleaved, and
(Holes penetrating the dense layer) are generated. In order to obtain a heterogeneous film having a high gas permeation rate, it is necessary to form a thin dense layer having no pinholes and a porous support layer having a high porosity. However, when the draw ratio is increased for the purpose of improving the gas permeation rate, that is, for making the dense layer thin and increasing the porosity of the porous support, pinholes are generated and the gas separation coefficient is lowered. Has resulted in.

Therefore, the draw ratio cannot be increased. In some cases, multistage drawing at different temperatures was adopted to increase the draw ratio while preventing breakage of the hollow fibers, but there was a limit. Further, it has been known that the stretched hollow fiber is heat-fixed by exposing the stretched yarn to a high temperature under a constant length condition, a free shrinkage condition, a restricted shrinkage condition or the like in order to impart dimensional stability.

[0005]

In the field of gas separation membranes and gas-liquid gas exchange membranes, gas permeation performance is improved, that is, gas permeation rate is improved without lowering the gas separation coefficient. That is an eternal task. The present inventors have conducted a study on a production method for achieving a high gas permeation rate for a hollow fiber heterogeneous membrane made of a crystalline thermoplastic polymer, and as a result, carry out stretching and heat setting under specific conditions. As a result, they have found that high gas permeability can be realized, and arrived at the present invention.

[0006]

The summary of the present invention is as follows.
After melt-spinning the crystalline thermoplastic polymer into a hollow fiber shape, heat treatment is performed if necessary to promote crystallization, and then the oxygen / nitrogen separation coefficient of the hollow fiber after drawing decreases with an increase in draw ratio. After stretching beyond the starting draw ratio, the oxygen / nitrogen separation coefficient of the hollow fiber after heat setting increases at a temperature of (stretching temperature +10) ° C. or higher as the shrinkage amount during heat setting increases. A method for producing a hollow fiber heterogeneous membrane is characterized by heat-setting while shrinking beyond a starting shrinkage amount.

The present invention will be described in more detail below. The polymer used in the present invention is a crystalline thermoplastic polymer. The crystalline polymer referred to in the present invention has an ultimate crystallinity of 3
It means 0% or more. Among the crystalline thermoplastic polymers, a polyolefin-based polymer is preferable because it has high crystallinity and a high crystallization rate. Among them, a poly (4-methyl-1-pentene) -based polymer has a gas permeability. Due to its high velocity and high oxygen / nitrogen separation coefficient, it is particularly suitable for producing membranes intended for the production of oxygen-enriched air or nitrogen-enriched air.

Poly (4-methyl-1) used in the present invention
-Pentene) -based polymer is a homopolymer of 4-methyl-1-pentene or 55% of 4-methyl-1-pentene.
It is a copolymer or mixture containing the above. In the production method of the present invention, first, a crystalline thermoplastic polymer is added to Tm to (Tm +
100) ° C. (however, Tm represents the crystal melting temperature of the polymer), preferably (Tm + 20) to (Tm + 50) ° C., extruded from a hollow fiber nozzle, and a draft ratio (= take-off speed / discharge linear speed) of 50- 1500, preferably 20
A gas, preferably air, while taking in from 0 to 1200
Melt spinning is performed by cooling with nitrogen or carbon dioxide.

The obtained spun yarn is heat-treated as necessary (hereinafter referred to as heat treatment step). The heat treatment may be omitted depending on the type of polymer, the size of the hollow fiber and the spinning cooling conditions, but it is preferably carried out to produce a high performance heterogeneous membrane. Heat treatment is (Tg + 10) ° C or higher (however,
Tg represents the glass transition temperature of the polymer), preferably (Tm-60) ° C or higher, and more preferably (Tm-4).
It can be carried out by a method of keeping the temperature at 0) ° C. or higher for a certain time. The upper limit of the heat treatment temperature is Tm. The heat treatment can be carried out by a method in which the fluid at that temperature, for example, an air atmosphere is retained, or a method such as infrared heating.

Next, the spun yarn or the heat treated spun yarn (hereinafter referred to as undrawn yarn) is drawn. The first feature of the manufacturing method of the present invention is the draw ratio in this step (hereinafter referred to as the drawing step). In the present invention,
The draw ratio in the drawing step is set to exceed the draw ratio at which the oxygen / nitrogen separation coefficient of the drawn yarn begins to decrease. In the drawing step, when the draw ratio is increased, the hollow fiber after drawing (that is, the hollow fiber immediately after drawing, which is not subjected to post-treatment such as heat setting, up to a certain draw ratio. Hereinafter, this is referred to as a drawn yarn. ), The oxygen / nitrogen separation coefficient is constant (or slightly increased), but if it exceeds a certain value, pinholes are generated in the dense layer, and the oxygen / nitrogen separation coefficient begins to decrease.

The draw ratio at which the oxygen / nitrogen separation coefficient begins to decrease varies depending on other conditions such as the type of polymer, spinning conditions, heat treatment conditions, drawing temperature, drawing speed, etc., and is therefore expressed as an absolute value. Although it is difficult, it can be easily obtained by an experiment in which the draw ratio is changed. When the stretching ratio is further increased, the oxygen / nitrogen separation coefficient is reduced accordingly, and finally converges to 0.935 (oxygen / nitrogen separation coefficient of the porous membrane having fine pores). In the range so far, the oxygen permeation rate increases with an increase in the draw ratio.
When the stretching ratio is further increased, the oxygen permeation rate is decreased due to the collapse of the porous structure. At this time, the oxygen / nitrogen separation coefficient may increase again.

The first feature of the manufacturing method of the present invention is the draw ratio in the drawing step. In the present invention, the draw ratio in the drawing step is set to exceed the draw ratio at which the oxygen / nitrogen separation coefficient of the drawn yarn begins to decrease. Therefore, the oxygen / nitrogen separation coefficient of the drawn yarn is smaller than the oxygen / nitrogen separation coefficient of the raw material polymer and is 0.935 or more. Although there is no particular restriction on the upper limit of the draw ratio, there is a limit naturally because the hollow fiber is broken. Hollow fiber breakage occurs at any of the above-mentioned circumstances. That is, when the oxygen / nitrogen separation coefficient starts to decrease, the oxygen / nitrogen separation coefficient starts to decrease, and when it breaks before reaching 0.935, the oxygen / nitrogen separation coefficient breaks at 0.935. In this case, the oxygen permeation rate may start to decrease again and then break.

When the breakage of the hollow fiber occurs
It depends on the type of polymer, the gel content of the polymer, uneven spinning, heat treatment conditions, stretching temperature, stretching speed, and the like. In the present invention, the stretching temperature can be adjusted so that breakage of the hollow fiber does not occur before the oxygen / nitrogen separation coefficient begins to decrease. It is difficult to indicate the draw ratio in the drawing step in the absolute draw ratio range as described above, but if the approximate range is shown, it is 1.2 or more and less than 5, and 1.3 or more and less than 3.5. preferable. Further, the stretching ratio in the stretching step in the present invention is 1.0 to 1.0 of the stretching ratio at which the oxygen / nitrogen separation coefficient of the hollow fiber after stretching starts to decrease.
It is preferably 2.5 times, more preferably 1.05 to 1.7.

The stretching may be one-stage stretching or multi-stage stretching,
Multi-stage stretching, especially multi-stage stretching in which the temperature is sequentially increased, is preferable in that a required stretching ratio can be obtained without breaking and a film with excellent performance is obtained. In the case of multi-stage stretching, the stretching ratio is the total stretching ratio in the stretching process. In addition, the stretching step is performed at temperatures (Tg + 10) to (Tg
m-60) ° C. (where Tg is the glass transition temperature of the polymer,
Tm is preferably one-step or multi-step drawing including drawing at the crystal melting temperature of the polymer), and one-step or multi-step drawing in which the total draw ratio of the drawing in the temperature range is 1.2 to 3.0. Is more preferable.

By carrying out the stretching in this range, it is possible to increase the stretching ratio while preventing breakage of the hollow fiber and structural change of the porous layer. In measuring the oxygen permeation rate and oxygen / nitrogen separation coefficient of the drawn yarn, it is necessary to measure the drawn yarn while keeping it at a constant length without shrinking. Upon contraction, these gas permeation properties may change.
The oxygen / nitrogen separation coefficient referred to here is a value obtained by dividing the oxygen permeation rate by the nitrogen permeation rate. The second feature of the present invention is that the drawn yarn is heat-set under a specific condition (hereinafter, this step is referred to as a heat-setting step).

In heat setting, when heat-fixing while shrinking the hollow fiber, when the heat-setting temperature is kept constant and the shrinkage amount is gradually increased from zero (that is, the constant length condition), the heat-set hollow The oxygen / nitrogen separation coefficient of the yarn (hereinafter referred to as heat setting yarn) has the same value as that of the drawn yarn at first, but increases as the amount of shrinkage increases. When the heat setting temperature was gradually increased from the drawing temperature while keeping the shrinkage constant, the value was initially the same as that of the drawn yarn, but the oxygen / nitrogen separation coefficient of the heat set yarn increased as the temperature increased. To increase. That is, the diameter of the pinhole becomes smaller or the number of pinholes decreases. Where temperature and /
Alternatively, the maximum value of the oxygen / nitrogen separation coefficient when the shrinkage ratio is maximized may be the oxygen / nitrogen separation coefficient of the polymer or may be lower than that.

That is, pinholes may remain even if the temperature and / or the shrinkage ratio are maximized. In the present invention, the heat setting is characterized in that the temperature and shrinkage conditions are sufficiently high so that the oxygen / nitrogen separation coefficient of the heat setting yarn is higher than the oxygen / nitrogen separation coefficient of the drawn yarn, that is, the temperature and shrinkage amount are sufficiently high. Is. More specifically, in the present invention, at a temperature of (stretching temperature + 10) ° C. or higher, the oxygen / nitrogen separation coefficient of the hollow fiber after heat setting begins to increase as the shrinkage amount during heat setting increases. Heat setting while shrinking beyond the amount of shrinkage.

If the temperature is (stretching temperature + 10) ° C. or higher, the oxygen / nitrogen separation coefficient is sufficiently increased by shrinking. Furthermore, the heat setting temperature is (Tm-50)
To Tm ° C. are preferable, and (Tm-30) to (Tm-10)
C is even more preferred. Further, the shrinkage amount during heat setting in the present invention is not constant under the influence of the processing conditions up to the heat setting step, the heat setting temperature, and the heat setting time, but is usually 10 to 40.
%. Furthermore, at a temperature of (Tm-50) to Tm ° C, preferably (Tm-30) to (Tm-10) ° C,
Most preferred is a single-stage or multi-stage heat setting, including heat setting that causes 10 to 30% shrinkage. In particular, in the case of producing a film having a high oxygen / nitrogen separation coefficient, it is preferable that the temperature and shrinkage conditions are heat set in order to sufficiently increase the oxygen / nitrogen separation coefficient.

When the heat treatment conditions are set within this range, it is presumed that the pinhole generated in the drawing step is closed and fused. The gas separation coefficient of the hollow fiber heterogeneous membrane produced according to the present invention is a membrane in which the oxygen / nitrogen separation coefficient is the separation coefficient of the polymer as the raw material, that is, a membrane in which there are virtually no pinholes in the dense layer. It is most effective in the case of, but it is also effective when there are some pinholes in the dense layer. That is, the present invention can be applied to a heterogeneous membrane having an oxygen / nitrogen separation coefficient of 0.940 or more, and is more effective in the case of a membrane having an oxygen / nitrogen separation coefficient of 1.1 or more.

The structure of the hollow fiber heterogeneous membrane in which the present invention is effective is not particularly limited, and may be the structure described in JP-A-59-196706. That is, when the dense layer is on the outer surface of the hollow fiber membrane, on the inner surface of the hollow fiber membrane, or inside the membrane, the dense layer is not observed as a clear layer, but the gas that permeates the membrane has one or more non-porous layers. This is the case when a part is permeated by a dissolution diffusion mechanism.
The dimensions of the hollow fiber heterogeneous membrane produced by the present invention are not particularly limited, but the outer diameter is preferably 40 μm to 3 mm, more preferably 100 to 500 μm. Film thickness is 5μ
The thickness is preferably m to 1 mm, more preferably 10 to 50 μm.

[0021]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. [Measurement method of oxygen transmission rate and oxygen / nitrogen separation coefficient]
The stretched yarn is fixed on a wire or other fixing jig without shrinking, and is sampled. With the hollow fiber membrane kept at a fixed length, the drawn yarn is inserted into the module case and sealed,
Make a mini module for measurement. The length of the hollow fiber used as a sample is not particularly limited, but if it is 3 m or more, the fluctuation is averaged, which is preferable. The mini module for measurement is AST
According to MD-1434, it measures by a pressure method or a volume method. At this time, the gas pressure difference is in the range of 1 to ³ kgf / cm ² . The hollow fiber membrane after heat setting is measured in the same manner as in the case of the stretched yarn except that the operation of keeping the length constant is not performed.

[Example 1] Melt index (AST
MD-1238, 260 ° C., 5 kg) 26 poly (4-methyl-1-pentene) (Tm = 240 ° C.) was melt extruded at 285 ° C. from an annular nozzle having a diameter of 6 mm, After cooling with a cross wind of 2 m / sec and passing through a spinning cylinder with a length of 4 m, the take-up speed was 1 at a position 5.5 m below the nozzle.
It was wound on a bobbin with a draft 350 at 20 m / min. This spun yarn is continuously heat-treated by passing it through a hot air oven having a temperature of 210 ° C. for a residence time of 5 seconds in a roller system,
C., cold stretching at a draw ratio of 1.2, and hot stretching at 150.degree. C. and a draw ratio of 1.6 (the draw ratio combined with the cold draw is 1.9.
2), and then the first stage heat setting is performed in which the hot air oven at 210 ° C. is shrunk by 5% and the residence time is 3 seconds, and then at 70 ° C. for 6 hours under a free length condition. It was dipped (2nd stage heat setting). By aging, 16% of the length before aging contracted.

On the other hand, when the stretching ratio of hot stretching was changed at 150 ° C. to prepare a sample without heat setting and the gas permeation rate and the gas separation coefficient were measured, the stretching ratio at which the separation coefficient began to decrease was 1. 4 (1.6 with cold drawing
8) and a draw ratio of 2.1 (2.5 together with cold drawing.
The hollow fiber was broken in 2). The obtained hollow fiber membrane has an outer diameter of 29.
3 μm, inner diameter 223 μm, film thickness 35 μm, SEM
No pores were observed on the outer surface, and crystals extending long in the fiber axis direction were laminated in the fiber direction on the outer surface, and fibrils were connected between the laminated crystals. However, the portion surrounded by crystals and fibrils was observed as elliptical pores elongated in the fiber axis direction, and the average diameter of the pores was about 0.05 μm.

Further, the cross section of the hollow fiber membrane cut off diagonally is
It had a porous structure with a pore size of about 0.1 μm. This hollow
Oxygen permeation rate is 2.1 ×
10 ^-Five[Cm³/ Cm²・ S ・ cmHg], oxygen / nitrogen content
The separation coefficient was 4.2 [-].

[Example 2] Stretching temperature is 100 at the stretching step.
℃, the draw ratio of 1.8, single-stage stretching, the first stage heat setting treatment time is 1 second, the second stage heat setting conditions,
A hollow fiber heterogeneous membrane was produced in the same manner as in Example 1 except that the free length was 70 ° C. and 6 hours. At this time, in the second stage heat setting, the hollow fiber length after the first stage heat setting is 2
Shrink 8%. On the other hand, in addition to this, an experiment was conducted to change the draw ratio in the drawing process.
The draw ratio at which the nitrogen separation coefficient began to decrease was 1.4.

When the obtained film was observed by SEM, a small number of pores having a pore size of about 0.05 μm were observed on the outer surface, and the dimensions, outer surface shape, inner surface shape, and cross-sectional shape of Example 1 were obtained. Was almost the same as. The gas permeation characteristics of this hollow fiber heterogeneous membrane are such that the oxygen permeation rate is 1.3 × 10 ^−4.
[Cm ³ / cm ² · s · cmHg] and the oxygen / nitrogen separation coefficient were 1.15 [−].

[Example 3] Hollow by the same method as in Example 1 except that the draw ratio of heat drawing is 1.5 and the heat setting is one stage under the conditions of 180 ° C and 25% shrinkage. A yarn heterogeneous film was prepared. A small number of pores having a pore size of about 0.05 μm were observed on the outer surface of the obtained membrane. The inside and the inside surface of the film were the same as in Example 1. The gas permeation characteristic of this hollow fiber heterogeneous membrane is that the oxygen permeation rate is 2.4 × 10 ⁻⁵ [cm ³ /
cm ² · s · cmHg], and the oxygen / nitrogen separation coefficient is 3.4.
It was [-].

[Example 4] The spinning temperature was 300 ° C, the stretching temperature was 150 ° C and the stretching ratio was 2.1, and the heat setting step was 190 ° C for 5 seconds and 10% shrinkage conditions. A hollow fiber heterogeneous membrane was produced in the same manner as in Example 1 except that the two-step heat setting was performed under the conditions of 150 ° C., 30 seconds, and 20% shrinkage. On the other hand, when an experiment for changing the draw ratio in the drawing step was conducted, the draw ratio at which the oxygen / nitrogen separation coefficient of the drawn yarn started to decrease was 1.6.

No pores were observed on the outer surface of the obtained film. The inside of the membrane is porous and the inner surface has a pore size of about 0.
The pores of 3 μm were open. The gas permeation characteristics of this hollow fiber heterogeneous membrane were such that the oxygen permeation rate was 1.5 × 10 5.
^-5 [cm ³ / cm ² · s · cmHg], and the oxygen / nitrogen separation coefficient was 4.2 [-].

[Comparative Example 1] The heat draw ratio is 1.3.
A hollow fiber heterogeneous membrane was prepared in the same manner as in Example 1 except that
It was Observation of this film with a SEM revealed that it had an outer surface and a film cross section.
The inner surface of the film was the same as that of the film obtained in Example 1. This
The gas permeability of the hollow fiber heterogeneous membrane of
1.2 x 10^-Five[Cm ³/ Cm²・ S ・ cmHg], oxygen
/ The nitrogen separation coefficient was 4.2 [-].

[Comparative Example 2] Heat setting at 210 ° C. for 10 seconds,
Same as Example 1 except that only one step of 5% shrinkage condition is used.
In this way, a hollow fiber heterogeneous membrane was produced. This film with SEM
Observation revealed that the outer surface, the cross section of the film, and the inner surface of the film were
It was similar to the membrane obtained in Example 1. This hollow fiber heterogeneous membrane
As for the body permeability characteristics, the oxygen transmission rate is 1.0 x 10^-Four[Cm ³
/ Cm².S.cmHg] and the oxygen / nitrogen separation coefficient is 1.
It was 1 [-].

[Comparative Example 3] The thermal draw ratio was 1.3.
And, heat setting is 210 ° C, 10 seconds, 5% shrinkage condition
Hollow in the same manner as in Example 1 except that there is only one stage
A yarn heterogeneous film was prepared. This film was observed by SEM.
B, the outer surface, the cross section of the membrane, and the inner surface of the membrane were the membranes obtained in Example 1.
Was similar to. Gas permeation characteristics of this hollow fiber heterogeneous membrane
Has an oxygen transmission rate of 1.0 × 10^-Five[Cm ³/ Cm²・ S
-CmHg] and oxygen / nitrogen separation coefficient is 4.2 [-]
It was.

[0033]

[Effect] The present invention can provide a hollow fiber having a high gas permeation rate, which can obtain a heterogeneous membrane having a thin dense layer, whether the dense layer has no pinholes or some pinholes. A method for manufacturing a heterogeneous film can be provided.

Claims (6)

[Claims] 1. A crystalline thermoplastic polymer is melt-spun into a hollow fiber and then heat-treated as necessary to promote crystallization,
Then, the oxygen / nitrogen separation coefficient of the stretched hollow fiber starts to decrease with an increase in the stretch ratio, and the hollow fiber is stretched at a temperature of (stretching temperature + 10) ° C. or higher and then heat-set. A method for producing a hollow fiber heterogeneous membrane, characterized in that the oxygen / nitrogen separation coefficient of the hollow fiber is heat-set while shrinking beyond the amount of shrinkage that begins to increase as the amount of shrinkage during heat setting increases. 2. The stretching ratio in the stretching is 1. The stretching ratio at which the reduction of the oxygen / nitrogen separation coefficient of the hollow fiber after stretching starts.
The production method according to claim 1, which is 0 to 2.5 times. 3. The stretching is carried out at a temperature (Tg + 10) to (Tm−).
60) The single-stage or multi-stage stretching including the stretching at the temperature range of 1.2, and the total stretching ratio in the temperature range is 1.2.
The manufacturing method according to claim 1 or 2, wherein 4. The heat setting is performed at a temperature (Tm-50) to Tm ° C.
2. The production method according to claim 1, wherein the heat shrinkage is one-stage or multi-stage heat-setting including heat-setting, and the total shrinkage amount of the one-stage or multi-stage heat setting is 10 to 40%. 5. The production method according to claim 1, wherein the crystalline thermoplastic polymer is a polyolefin-based polymer. 6. The polyolefin polymer is poly (4-
The method according to claim 5, which is a methyl-1-pentene) -based polymer.