JPH0262604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing porous thermoplastic resin hollow fibers.

[Background of the Invention] Porous thermoplastic resin hollow fibers (porous thermoplastic resin hollow fibers), which are composed of hollow fibers made of polymeric material with a large number of fine pores formed therein, are used, for example, in water treatment, etc. It is used in various fields as filtration membranes or separation membranes, separation membranes used in artificial lungs, plasma separation, etc.

The method for manufacturing porous thermoplastic resin hollow fibers is as follows:
For example, a method is known in which a polymer material in which an easily soluble substance is mixed and dispersed is formed into a hollow fiber, and then the easily soluble substance is dissolved and removed using a solvent to form a large number of fine pores in the hollow fiber. ing.

In recent years, a method has also been developed in which a thermoplastic crystalline polymer material is molded into hollow fibers, heat treated, and then stretched to generate pores in the hollow fibers to form porous bodies. It is becoming common.

[Description and problems of the prior art] Porous thermoplastic resin hollow fibers using polymeric materials and their manufacturing method are described, for example, in
Publication No. 52123, Japanese Unexamined Patent Publication No. 55-107507, Japanese Unexamined Patent Publication No. 1987-107507
It is disclosed in JP-A No. 57-66117, Japanese Patent Application Laid-Open No. 57-5914, etc. Most of the porous thermoplastic resin hollow fibers and their manufacturing methods disclosed in the above-mentioned publications first heat-treat the molded thermoplastic resin hollow fibers, and then heat-treat the molded thermoplastic resin hollow fibers at around room temperature or at a secondary temperature of the thermoplastic resin used. Stretching at a temperature higher than that temperature (for example, -100°C or higher when using polyethylene) to generate pores and make it a porous body;
The gist of this method is to heat-fix the formed holes by heat-treating them again.

Generally, using known methods such as those mentioned above,
In order to obtain porous thermoplastic resin hollow fibers with uniform and large fine pores and high porosity, the undrawn thermoplastic resin hollow fibers used must have high orientation or high elastic recovery rate (Elastic
recovery) is necessary. Methods for adjusting such undrawn thermoplastic resin hollow fibers include a method of molding the hollow fibers under specific conditions, or a method of heat-treating the undrawn thermoplastic resin hollow fibers to improve the degree of crystallinity. etc. are used. In other words, in conventional methods, in order to improve the quality of the porous thermoplastic resin hollow fibers obtained, it is common to add an operation to increase the crystallinity of the undrawn thermoplastic resin hollow fibers in advance. . Therefore, there has been a problem that the manufacturing process of the porous thermoplastic resin hollow fiber tends to become complicated as a whole.

[Object of the Invention] An object of the present invention is to provide a method for producing a porous thermoplastic resin hollow fiber having a high porosity, a large average pore diameter, and uniform pores. In particular, the present invention has a high porosity, a large average pore diameter, and uniform pores even if undrawn thermoplastic resin hollow fibers made of a thermoplastic resin with a low elastic recovery rate or a low draft ratio are used. An object of the present invention is to provide a method for producing porous thermoplastic resin hollow fibers.

[Summary of the Invention] The present invention provides polyethylene, poly(4-methyl-
A porous thermoplastic resin hollow fiber comprising a step of forming a large number of fine pores in the hollow fiber by drawing a thermoplastic resin hollow fiber made of pentene-1), polyvinylidene fluoride, or ethylenetetrafluoroethylene copolymer. In the method for producing yarn, the drawing step is carried out in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane and ethane, and the drawing temperature is -100°C or lower. Provided is a method for producing porous thermoplastic resin hollow fibers, characterized in that the process is carried out at a temperature in the range of higher than the freezing point of the medium and 50° C. higher than the boiling point of the medium.

The present invention also provides polyethylene, poly(4-methyl-pentene-1), polyvinylidene fluoride,
Or, in a method for producing a porous thermoplastic resin hollow fiber comprising a step of forming a large number of fine pores in the hollow fiber by drawing a thermoplastic resin hollow fiber made of an ethylenetetrafluoroethylene copolymer, the drawing step () In a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane and ethane, and at a stretching temperature of -100°C or lower, () stretching the hollow fibers at a temperature in the range above the freezing point and 50° C. above the boiling point of the medium; and () after the cryogenic stretching step, the hollow fibers are subjected to melting of the thermoplastic resin. Polyethylene, poly(4
-Methyl-pentene-1), polyvinylidene fluoride, or ethylenetetrafluoroethylene copolymer.

The present invention exhibits an excellent crazing effect when a hollow fiber of a thermoplastic resin such as polyethylene is stretched in a specific medium such as liquid nitrogen at extremely low temperatures;
This crazing effect was developed based on the knowledge that even if the thermoplastic resin hollow fiber does not have a high elastic recovery rate or draft ratio, it acts to become a porous thermoplastic resin hollow fiber with excellent properties. be. That is, in the present invention, the formation of porous fibers is carried out using a specific medium under extremely low temperature conditions, which made it difficult to produce porous thermoplastic resin hollow fibers with particularly excellent properties using conventional methods. Even if a thermoplastic resin with a low elastic recovery rate is used, uniform pores can be formed, and porous thermoplastic resin hollow fibers with a high porosity can be manufactured. Therefore, when producing undrawn thermoplastic resin hollow fibers, there is no particular need for complicated operations to improve the elastic recovery rate or draft ratio, unlike conventional methods.

[Detailed Description of the Invention] The present invention provides a thermoplastic resin in a specific medium.
It is necessary to stretch (hereinafter also referred to as cryogenic stretching) at a temperature of 100°C or less, which is higher than the freezing point of the medium and 50°C higher than the boiling point of the medium. It is.

Examples of thermoplastic resins used in the present invention include:
Examples include high-density polyethylene, poly(4-methyl-pentene-1), polyvinylidene fluoride, and ethylenetetrafluoroethylene copolymer, and these can be used alone or in combination.

Furthermore, the melt viscosity [melt flow index (MFI) or melt index (MI)] of the thermoplastic resin used does not need to be particularly limited as long as it is within the range that allows spinning of hollow fibers. When using polyethylene, it is preferable to use polyethylene having an MI of 0.5 to 40 g/10 min, considering the efficiency or productivity of hollow fiber spinning.

In addition, thermoplastic resins containing additives (materials) such as plasticizers, colorants, flame retardants, and fillers can also be used.

In the present invention, the above thermoplastic resin is first spun into undrawn thermoplastic resin hollow fibers according to a known hollow fiber spinning method. Such spinning conditions can be appropriately selected from known techniques. For example, the spinning temperature can be within a range of a temperature higher than the temperature at which the thermoplastic resin used can be discharged and lower than the thermal decomposition temperature of the resin. For example, when using high-density polyethylene, the temperature is usually 150-300℃, preferably 160-300℃.
270℃, when using poly(4-methyl-pentene-1), usually 260 to 330℃, preferably 270 to 300℃, when using ethylenetetrafluoroethylene copolymer, usually 290~350
℃, preferably 190 to 280℃, and when polyvinylidene fluoride is used, the temperature is usually 190 to 300℃, preferably 190 to 280℃.

Furthermore, there is no particular limitation on the elastic recovery rate (or draft ratio) of the undrawn thermoplastic resin hollow fibers obtained by spinning. However, when using undrawn thermoplastic resin hollow fibers with an elastic recovery rate (or draft ratio) of zero (%) or extremely low, that is, undrawn thermoplastic resin hollow fibers with extremely low crystal orientation, this Even in the cryogenic stretching process of the invention, it may be difficult to impart satisfactory properties to the resulting porous thermoplastic resin hollow fibers. Therefore, it is preferable to set the spinning conditions for the undrawn hollow fibers in consideration of the characteristics such as the porosity and the average diameter of the fine pores of the resulting porous thermoplastic resin hollow fibers.

As mentioned above, there is no particular limit to the elastic recovery rate of the undrawn thermoplastic resin hollow fiber, but for the above reasons, the elastic recovery rate of the drawn thermoplastic resin hollow fiber at 25°C,
For example, when using polyethylene, the elastic recovery rate at 50% elongation at 65% relative humidity is preferably 20% or more, and productivity when using normal molding equipment is also important. Taking this into account, it is particularly preferable that it is in the range of 30 to 95%.

Elastic recovery rate (%) = [Length at stretching - Length after stretching] ÷
[Length when stretched - Length of original hollow system] x 100 In addition, considering the above requirements and factors such as productivity, the draft ratio of the unstretched thermoplastic resin hollow fiber used in the present invention (unstretched For example, when polyethylene is used, the ratio of the take-up speed of the thermoplastic resin hollow fiber to the discharge speed from the nozzle (take-up speed/discharge speed) is Preferably in the range 10-6000.

The unstretched thermoplastic resin hollow fibers may be heat treated before being subjected to the stretching process. By performing this heat treatment before stretching, the crystallization of the unstretched thermoplastic resin hollow fibers can be enhanced, so that the properties of the porous thermoplastic resin hollow fibers obtained by stretching are further improved.

The above heat treatment can make the undrawn thermoplastic resin hollow fibers, for example, 30 to
It is carried out by heating for 3 seconds or more in air heated to a temperature 5°C lower.

The stretching step in the present invention is carried out in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane and ethane, at a stretching temperature of -100°C or lower and below the boiling point of the medium. It is necessary to conduct the test under conditions where the temperature is within a range of 50°C or less.

In the cryogenic stretching step of the present invention, the above-mentioned media can be used alone or in combination.

Examples of preferred stretching temperatures when using the above media are -209°C to -209°C when nitrogen is used.
Range of 146°C, -218°C to -218°C with oxygen
-132℃ range, when using argon, -
When using carbon monoxide, the range is -205°C to -141°C. When using methane, the range is -182°C to -111°C. When using ethane, the range is -189°C to -140°C. If it is, it is in the range of -183℃ to -100℃. If the stretching temperature is higher than -100°C, for example, when unstretched hollow fibers with a low elastic recovery rate are used, the rate of effective formation of pores by stretching will be low. Note that, in the present invention, a temperature of 50° C. higher than the boiling point or lower does not mean a temperature range lower than exactly 50° C. higher than the boiling point, but a temperature of approximately 50° C. higher than the boiling point or lower.

At such extremely low temperatures, the medium becomes liquid,
The medium is in a liquid/gaseous state or a gaseous state, and the stretching process of the present invention can be carried out even if the medium is in any of the above states.

It is presumed that the above-mentioned stretching according to the present invention occurs due to the crazing effect of stretching at extremely low temperatures using the medium. In ordinary media other than those mentioned above, the hollow fibers of the thermoplastic resin become glassy at extremely low temperatures, are cut without elongation, and no crazing action occurs.

The cryogenic stretching temperature of the present invention is -100°C or lower, and is carried out under conditions that are higher than the freezing point of the medium used and lower than 50°C higher than the boiling point of the medium. However, in general,
It is advantageous to perform the stretching at a temperature near the boiling point of the low-temperature liquid, both in terms of manufacturing control and in keeping the properties of the resulting porous thermoplastic resin hollow fibers constant.

The stretching ratio in the above-mentioned cryogenic stretching process is generally 1 to 200 for the unstretched thermoplastic resin hollow fiber.
The value is in the range of %. However, the preferred stretching ratio is in the range of 10 to 50%. At stretching ratios within these ranges, the number of pores tends to increase as the stretching ratio increases, and this tendency can be used to determine the average pore diameter and porosity of the resulting porous thermoplastic resin hollow fiber. It is also possible to adjust accordingly.

The cryogenic stretching process described above can be repeated two or more times until the desired average pore diameter and porosity are obtained.

In the specific medium of the present invention, the porous structure of the thermoplastic resin hollow fiber using the drawing process under cooling at an extremely low temperature differs from the conventional drawing process at around room temperature. To provide an excellent porous thermoplastic resin hollow fiber that acts effectively even on thermoplastic resin hollow fibers whose elastic recovery rate from strain of % is less than 40%, has uniform pores, and has a high porosity. Can be done.

It is preferable that the thermoplastic resin hollow fibers made porous through the drawing process at an extremely low temperature in the specific medium are then subjected to a heat setting treatment. The main purpose of this heat setting treatment is heat setting to maintain the formed fine holes. This heat setting treatment is carried out by heating the porous thermoplastic resin hollow fibers in air heated to a temperature 70 to 5° C. lower than the melting temperature of the thermoplastic resin used for 3 seconds or more. For example, when using high density polyethylene, the specific heating temperature is usually 70 to 125°C, preferably 80 to 120°C, and when using poly(4-methyl-pentene-1), Normally 150-210℃, preferably 160-200℃
℃, when using an ethylenetetrafluoroethylene copolymer, it is usually 180 to 240℃, preferably 200 to 230℃, and when using polyvinylidene fluoride, it is usually 100 to 165℃, preferably
The temperature is 110-160℃. Note that if the heating temperature is significantly higher than the upper limit of the listed temperature, the formed micropores may close, and if the temperature is significantly lower than the lower limit or the heating time is shorter than 3 seconds, heat fixation may occur. is likely to be insufficient, the formed through holes may close later, and heat shrinkage is likely to occur due to temperature changes during use. The cryogenic stretching and heat setting treatments described above can be repeated until a desired average pore diameter and porosity are obtained. That is, the temperature of the hollow fiber can be returned to room temperature and subjected to a process including repeated cryogenic stretching (and heat setting treatment). By repeatedly performing cryogenic stretching, the number of through holes formed can be increased, and the average through hole diameter can be increased.

The porous thermoplastic resin hollow fiber prepared as described above has a large average pore diameter and a high porosity and exhibits good properties. By subjecting it to the process, its properties are further improved.

The hot stretching process of the thermoplastic resin hollow fibers, which have been made porous through at least one stretching process at an extremely low temperature, is carried out as follows. This hot stretching process is carried out mainly for the purpose of expanding the diameter of the fine holes formed at extremely low temperatures. This hot stretching process involves stretching the porous thermoplastic resin hollow fibers from 90 to 90 degrees above the melting temperature of the thermoplastic resin
This is carried out by stretching in air heated to a temperature 5° C. lower. For example, when using high-density polyethylene, the temperature is usually 70 to 125℃.
Preferably 80 to 120°C, and when poly(4-methyl-pentene-1) is used, usually 150 to 120°C.
210℃, preferably 160-200℃, when using ethylenetetrafluoroethylene copolymer,
The temperature is usually set at 180 to 240°C, preferably 200 to 230°C, and when polyvinylidene fluoride is used, the temperature is usually set at 100 to 165°C, preferably 110 to 160°C. Note that if the heating temperature is higher than the upper limit of the above temperature, the formed micropores may close, and if the temperature is lower than the lower limit, the expansion of the pore diameter by stretching may be insufficient. There is.

The stretching ratio in this hot stretching process is usually 10 to 700%, preferably 50 to 550% of the length of the hollow system (initial length) before being subjected to the ultra-low stretching process.
It is. If the stretching ratio is lower than 10%, the expansion of the pores may be insufficient, and if the stretching ratio is higher than 700%, the hollow fibers may be cut.

Note that this hot stretching step is performed alternately with the above-mentioned cryogenic stretching step, or after completing at least one cryogenic stretching step.

The hollow fibers made porous by this stretching process are
It is desirable to perform a heat setting treatment between the stretching steps. The main purpose of this heat setting treatment is to heat set the through holes formed through the hot stretching process.

This heat-setting treatment usually involves placing porous thermoplastic resin hollow fibers in the air for 30 minutes while maintaining their stretched state.
20 seconds or more than the melting temperature of the thermoplastic resin used
It is carried out by a method of heating to a temperature lower by ~5°C. The specific heating temperature is, for example, usually 70 to 125°C, preferably 80 to 120°C when using high-density polyethylene, and usually 150 to 210°C when using poly(4-methyl-pentene-1). °C, preferably 160-200 °C, usually 180-240 when using ethylenetetrafluoroethylene copolymer
°C, preferably 200 to 230 °C, and when polyvinylidene fluoride is used, the temperature is usually 100 to 165 °C, preferably 110 to 160 °C.

It is desirable that this heat setting treatment be performed in the same manner on the hollow fibers that have undergone all the stretching steps.

If the heating temperature is higher than the above upper limit temperature, the formed through holes may close, and if the temperature is lower than the above lower limit temperature or the heating time is shorter than 3 seconds, heat fixation is likely to be insufficient, and later The hole closes,
Furthermore, thermal shrinkage is likely to occur due to temperature changes during use.

Next, Examples and Comparative Examples of the present invention will be shown.

Example 1 High-density polyethylene (Shorex F6080 trade name: manufactured by Showa Denko K.K., MI = 8 g/10 minutes) was spun using a hollow fiber production nozzle equipped with a gas supply pipe of 8 mm in diameter and 7 mm in inner diameter. Spinning was carried out at a temperature of 190°C, a take-up speed of 200 m/min, and a draft ratio of 726.
The obtained polyethylene hollow fibers were heat treated in a heated air bath at 110°C for 30 minutes, and then heated with liquid nitrogen (-195°C).
The film was stretched by 20% of its initial length in a heated air bath at 110°C for 15 minutes while maintaining the stretched state.

This hollow fiber was hot-stretched by 300% in an air atmosphere at 110°C, and then heat-treated for 15 minutes in a heated air tank at 110°C while maintaining the stretched state to produce a porous polyethylene hollow fiber.

The average pore diameter of the obtained porous polyethylene hollow fiber was measured by mercury intrusion method (measurement was carried out using POROSIMETRO SERIES 1500 manufactured by CARLOERBA (Italy). The same applies hereinafter), and it was 0.32 μm. The porosity was 68%.

When the peripheral wall of the above-mentioned porous polyethylene hollow fiber was observed using an electron microscope, it was found that many large pores were uniformly formed in the peripheral wall, and the diameter of the pores was almost constant throughout.

Example 2 Poly(4-methyl-pentene 1) (TPX RT18
(Product name: Mitsui Petrochemical Co., Ltd.) using a hollow fiber production nozzle equipped with a gas supply pipe with a diameter of 8 mm and an inner diameter of 7 mm, at a spinning temperature of 280°C and a take-up speed of 200 m/min.
The fibers were spun at a draft ratio of 726. The obtained poly(4-methyl-pentene 1) hollow fiber was heated at 180°C.
Heat treated in a heated air bath for 30 minutes, then stretched 20% of the initial length in liquid nitrogen (-195℃).
15 minutes in a heated air tank at 180℃ while maintaining the stretched state.
Heat treatment was performed for 1 minute.

This hollow fiber was heat-stretched by 80% in an air atmosphere at 180°C, and then heat-treated for 15 minutes in a heated air bath at 180°C while maintaining the stretched state to form porous poly(4-methylpentene 1). A hollow fiber was manufactured.

The resulting porous poly(4-methylpentene 1)
When the average pore diameter of the hollow fibers was measured by mercury intrusion method, it was found to be 0.1 μm, and the porosity was 40%.

When the peripheral wall of the above porous poly(4-methylpentene 1) hollow fiber was observed using an electron microscope, it was found that a large number of pores were uniformly formed in the peripheral wall, and the pore diameter was almost constant throughout. Was.

Example 3 Ethylenetetrafluoroethylene copolymer (Afron COP product name: manufactured by Asahi Glass Co., Ltd.) was prepared with a diameter of 8 mm.
Using a hollow fiber manufacturing nozzle equipped with a gas supply pipe with an inner diameter of 7 mm, the spinning temperature was 330°C and the take-up speed was 50 m/min.
The fibers were spun at a draft ratio of 181. The obtained ethylenetetrafluoroethylene copolymer hollow fibers were heat-treated in a heated air bath at 220°C for 30 minutes, and then heated in liquid nitrogen (-195°C) to reduce the initial length by 20 minutes.
%, and heat-treated in a heated air tank at 220° C. for 15 minutes while maintaining the stretched state.

This hollow fiber was heat-stretched by 80% in an air atmosphere at 220°C, and then heat-treated for 15 minutes in a heated air tank at 145°C while maintaining the stretched state to form a porous ethylene-tetrafluoroethylene copolymer hollow fiber. produced yarn.

The average pore diameter of the obtained porous ethylene/tetrachloroethylene hollow fiber was measured by mercury intrusion method, and was found to be 0.06 μm, and the porosity was 30%.

When the peripheral wall of the above porous ethylene tetrafluoroethylene copolymer hollow fiber was observed using an electron microscope, it was found that a large number of pores were uniformly formed in the peripheral wall, and the pore diameter was almost constant throughout. was.

Claims (1)

[Scope of Claims] 1. By stretching a thermoplastic resin hollow fiber made of polyethylene, poly(4-methyl-pentene-1), polyvinylidene fluoride, or ethylenetetrafluoroethylene copolymer, a large number of In a method for producing a porous thermoplastic resin hollow fiber including a step of forming fine pores, the drawing step is performed in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane and ethane, and the stretching temperature is -100°C or less, higher than the freezing point of the medium and lower than 50°C higher than the boiling point of the medium. , poly(4-methyl-
A method for producing a porous thermoplastic resin hollow fiber comprising pentene-1), polyvinylidene fluoride, or ethylenetetrafluoroethylene copolymer. 2. The method for producing a porous thermoplastic resin hollow fiber according to claim 1, wherein the stretching step under cooling is repeated two or more times. 3. During the drawing process and after the final drawing process, the thermoplastic resin hollow fibers are heat-set at a temperature 70 to 5°C lower than the melting temperature of the thermoplastic resin. A method for producing a porous thermoplastic resin hollow fiber according to item 1 or 2. 4. By stretching a thermoplastic resin hollow fiber made of polyethylene, poly(4-methyl-pentene-1), polyvinylidene fluoride, or ethylenetetrafluoroethylene copolymer, a large number of fine pores are formed in the hollow fiber. A method for producing a porous thermoplastic resin hollow fiber comprising the step of: () stretching the hollow fiber in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, and methane and ethane; and the stretching temperature is −100°C or less,
higher than the freezing point of the medium and 50° higher than the boiling point of the medium
and () after the stretching step at extremely low temperatures, the hollow fibers are stretched at a temperature in the range of 90 to 5°C lower than the melting temperature of the thermoplastic resin. Polyethylene, poly(4
-Methyl-pentene-1), polyvinylidene fluoride, or ethylenetetrafluoroethylene copolymer. A method for producing a porous thermoplastic resin hollow fiber. 5. The method for producing a porous thermoplastic resin hollow fiber according to claim 4, wherein the cooling stretching step and the hot stretching step are each repeated two or more times. 6. A patent characterized in that the thermoplastic resin hollow fibers are heat-set between each stretching process and after being subjected to the final stretching process within a temperature range of 70 to 5°C lower than the melting temperature of the thermoplastic resin. A method for producing a porous thermoplastic resin hollow fiber according to claim 4 or 5.