JPS6329006B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing porous polypropylene hollow fibers.

Porous hollow fibers, which are made of polymeric materials and have a large number of fine pores formed in their peripheral walls, are used in various substance separation devices such as plasma separation and ultrafiltration in the medical field. It is used as.

Porous hollow fibers can be manufactured by, for example, forming a polymeric material in which an easily soluble substance is mixed and dispersed into a hollow fiber, and then dissolving and removing the easily soluble substance with a solvent to form a material on the peripheral wall of the hollow fiber. Methods such as forming a large number of fine pores are known, but in recent years, the peripheral wall of the hollow fiber is formed by forming a thermoplastic crystalline polymer material into a hollow fiber, heat-treating it, and then stretching it. A method of creating a porous body by generating pores in the part has also become common. Polyolefins, polyamides, polyesters, and similar copolymers are known as thermoplastic crystalline polymer materials used for such purposes, but polypropylene (a homopolymer of propylene or Copolymers with other monomers) are considered to be excellent polymeric materials for porous hollow fibers because of their excellent moldability, strength, and chemical resistance.

Regarding porous hollow fibers using polypropylene as a polymer material and their manufacturing method,
52-15627, JP 52-137026, JP 53-38715, JP 54-34418,
Disclosures include JP-A-54-68414, JP-A-54-120735, JP-A-54-138623, JP-A-55-1314, and JP-A-57-5914.
Most of the methods for manufacturing porous polypropylene hollow fibers disclosed in these documents first heat-treat spun, undrawn polypropylene hollow fibers, and then stretch them at a temperature around room temperature to generate pores. This method is basically a method of heat-setting the porous body by making it into a porous body and then performing heat treatment again.

Considering the purpose of use of porous polypropylene hollow fiber, the fine pores in the peripheral wall should be as homogeneous as possible.
and the desired density (which can be expressed as porosity)
It is preferable that it is formed by. Methods for manufacturing porous polypropylene hollow fibers with such excellent properties are disclosed in JP-A-54-34418, JP-A-54-68414, JP-A-54-138623, etc. A method is known in which the crystal orientation of undrawn polypropylene hollow fibers is enhanced by heat treatment under specific conditions, and then the fibers are drawn to make them porous. On the other hand, as a method for manufacturing porous polypropylene hollow fibers with excellent properties without requiring such complicated processing steps, Japanese Patent Application Laid-open No. 1314/1983 discloses a method for drawing polypropylene hollow fibers. It discloses a method for improving the properties of the resulting porous polypropylene hollow fibers by performing operations such as increasing the degree of crystal orientation by setting the previous spinning conditions within a specific range.

That is, in the conventional method as described above, in order to improve the quality of the porous polypropylene hollow fibers obtained, it was common to perform an operation to increase the crystal orientation of the undrawn polypropylene hollow fibers in advance. . Therefore, there still remains the problem that the manufacturing process for porous polypropylene hollow fibers tends to become complicated as a whole.

The present inventor conducted research aimed at improving the manufacturing method of polypropylene hollow fibers using the conventional technology as described above, and found that when polypropylene hollow fibers are stretched using a specific medium under extremely low temperature conditions. Excellent crazing effect appears, and even if the polypropylene hollow fiber does not have a high degree of orientation, that is, even if the draft ratio is low, this crazing effect effectively acts to create a porous hollow fiber with excellent properties. We have discovered that this is the case, and have arrived at the present invention.

Therefore, the present invention provides a method for producing a porous hollow fiber, which includes a step of forming a large number of fine pores in the peripheral wall of the hollow fiber by drawing a polypropylene hollow fiber, in which the drawing step is performed using nitrogen, oxygen, argon, The stretching is carried out in a medium selected from the group consisting of carbon monoxide and methane, and the stretching temperature is higher than the freezing point of the medium and lower than or equal to a temperature 50°C higher than the boiling point of the medium. The present invention provides a method for producing porous polypropylene hollow fibers characterized by the following.

The present invention uses polypropylene with a low draft ratio, which has been difficult to produce hollow fibers with excellent properties using conventional methods, because the porosity is made using a specific medium under extremely low temperature conditions. Even if this is the case, uniform pores can be formed and porous polypropylene hollow fibers with high porosity can be manufactured. Therefore, the production of undrawn polypropylene hollow fibers does not require complicated operations unlike conventional methods.

Next, the present invention will be explained in detail.

In the present invention, since the conditions for making the porous material are completely different from those of conventional methods, there are no particular restrictions on the polypropylene used; propylene homopolymers, block copolymers of polypropylene and other monomers or oligomers, Random copolymers of propylene and other monomers or oligomers (in the present invention, when polypropylene is written without any particular limitation, the expression polypropylene means a generic term for these things), etc. can be used. There are no restrictions on what can be used as the other monomers or oligomers as long as they can be copolymerized, and examples thereof include ethylene and oligomers derived from ethylene.

In addition, the melt flow index (MFI) of the polypropylene used does not need to be particularly limited, but in consideration of efficiency and productivity during spinning, it is recommended to use a melt flow index (MFI) of 1 to 40 g/10 min. preferable.

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

In the present invention, first, polypropylene as described above is spun into undrawn polypropylene hollow fibers according to a known hollow fiber manufacturing method. Spinning conditions can be appropriately selected from known techniques. for example,
The spinning temperature may be above the temperature at which polypropylene can be discharged and below the thermal decomposition temperature of polypropylene, and is usually 170 to 300°C, preferably 190 to 270°C. Further, there is no particular limitation on the draft ratio (ratio between the take-up speed of the undrawn yarn and the discharge speed from the nozzle: take-up speed/discharge speed), which is a guideline for crystal orientation. However, when using undrawn polypropylene hollow fibers with a draft ratio of zero or extremely small, that is, unoriented or with extremely low orientation, even if subjected to the cryogenic drawing step of the present invention, the resulting porous It tends to be difficult to impart satisfactory properties to polypropylene hollow fibers. Therefore, considering the characteristics such as the porosity and average pore diameter of the micropores of the obtained porous polypropylene hollow fiber, and considering factors such as productivity, the draft of the undrawn polypropylene hollow fiber used in the present invention It is desirable that the ratio is in the range of 10-6000.

The undrawn polypropylene hollow fibers may be heat treated before being subjected to the drawing step. By performing this heat treatment before stretching, the crystallinity of the unstretched polypropylene hollow fibers can be increased, so that the properties of the porous polypropylene hollow fibers obtained by stretching are further improved.

The above heat treatment is carried out by heating the unstretched polypropylene hollow fibers in air heated to, for example, 100 to 155°C for 3 seconds or more.

The stretching step in the present invention is performed in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, and methane at a temperature in a range higher than the freezing point of the medium and 50°C higher than the boiling point of the medium. It is characterized by being carried out under certain conditions.

In the 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
-133℃ range, when using argon, -
The temperature is in the range of 189°C to -136°C, when using carbon monoxide, the range is -205°C to -141°C, and when using methane, the temperature is in the range of -182°C to -112°C. .

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.

The crazing effect according to the present invention occurs because elongation appears when the medium is stretched at an extremely low temperature.In ordinary media other than the above, the hollow fiber becomes a glass state at an extremely low temperature and elongates. is cut off without appearing, and no crazing action occurs.

The stretching step in the present invention can be carried out at a temperature in the range of higher than the freezing point of the medium used and 50°C higher than the boiling point of the medium, but generally the stretching is carried out at a temperature around the boiling point of the low temperature liquid. It is advantageous to carry out the process at a certain temperature in terms of manufacturing control and in keeping the properties of the resulting porous polypropylene hollow fibers constant.

The stretching ratio in the above cryogenic stretching process is:
Generally 1 to 1 for unstretched polypropylene hollow fibers
The value is in the range of 200%. However, the preferred stretching ratio is in the range of 10 to 150%. At stretch ratios within these ranges, the number of through holes tends to increase as the stretch ratio increases, and by utilizing this tendency,
It is also possible to adjust the number of pores and porosity of the resulting porous polypropylene hollow fibers depending on the purpose.

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

Unlike the conventional drawing process near room temperature, the polypropylene hollow fibers are made porous by using a drawing process under cooling at an extremely low temperature in a specific medium of the present invention. It also acts effectively on hollow fibers, resulting in excellent porous polypropylene hollow fibers with uniform pores and high porosity.

The polypropylene hollow fibers made porous through a drawing process at an extremely low temperature in the above specific medium are then
Preferably, it is subjected to heat treatment. The main purpose of this heat treatment is heat fixation to maintain the formed fine pores. This heat treatment
Polypropylene hollow fibers made porous while maintaining their stretched state at extremely low temperatures are heated to 110 to 155°C, preferably
This is carried out by heating for 3 seconds or more in air heated to 130 to 155°C. The heating temperature is 155
If the temperature is above 110°C, the formed micropores may close, and if the temperature is lower than 110°C or the heating time is shorter than 3 seconds, heat fixation is likely to be insufficient, and the pores may be closed later. It closes and is prone to heat shrinkage due to temperature changes during use. The cryogenic stretching and heat treatment 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 treatment.

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

[Example 1] Polypropylene (UBE-PP-J130G, product name: manufactured by Ube Industries, Ltd., MFI = 30 g/10 minutes) was used with a hollow fiber manufacturing nozzle equipped with a gas supply pipe with a diameter of 8 mm and an inner diameter of 7 mm. The spinning temperature was 210°C, the take-up speed was 200 m/min, and the draft ratio was 726.
The obtained polypropylene hollow fibers were heat-treated in a heated air bath at 145°C for 30 minutes, and then heated with liquid nitrogen (−
The polypropylene hollow fibers were stretched by 20% of their initial length at 195°C), and heat treated for 15 minutes in a heated air tank at 145°C while maintaining the stretched state to produce porous polypropylene hollow fibers.

The outer diameter of the obtained porous polypropylene hollow fiber is
200 μm, and the inner diameter was 150 μm.

In addition, mercury intrusion method (measurement is performed using POROSIMETRO SERIES manufactured by CARLOERBA (Italy))
I did it using 1500. The average pore diameter was 0.1 μm, and the porosity was 3.1%.

When the peripheral wall of the above porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Comparative Example 1] A porous polypropylene hollow fiber was produced in the same manner as in Example 1 except that the stretching temperature was changed to room temperature and the stretching atmosphere was changed to air.

The outer diameter of the obtained porous polypropylene hollow fiber is
The inner diameter was 148 μm.

The average pore diameter was 0.01 μm, and the porosity was 2.5%.

[Example 2] The stretching ratio was changed to 20%, and liquid methane (-160°C)
A porous polypropylene hollow fiber was produced in the same manner as in Example 1 except that .

The outer diameter of the obtained porous polypropylene hollow fiber is
The diameter was 198 μm, the inner diameter was 149 μm, the average pore diameter was 0.03 μm, and the porosity was 3%.

When the peripheral wall of the above porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Example 3] Porous polypropylene hollow fibers were produced in the same manner as in Example 1, except that the unstretched polypropylene hollow fibers were not heat-treated.

The average pore diameter of the obtained porous polypropylene hollow fibers was 0.1 μm, and the porosity was 2.8%.

When the peripheral wall of the above porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Comparative Example 2] Polypropylene hollow fibers were stretched and heat-set in the same manner as in Example 3, except that the stretching temperature was changed to room temperature and the stretching atmosphere was changed to air.

When the peripheral wall of the polypropylene hollow fiber subjected to the above stretching and heat treatment was observed using an electron microscope, almost no through holes were observed in the peripheral wall.

[Example 4] Take-up speed is 50 m/min and draft ratio is 27
A porous polypropylene hollow fiber was produced in the same manner as in Example 1 except that the following procedure was performed.

The average pore diameter of the obtained porous polypropylene hollow fibers was 0.1 μm, and the porosity was 2.3%.

When the peripheral wall of the above porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Comparative Example 3] Polypropylene hollow fibers were stretched and heat-set in the same manner as in Example 4, except that the stretching temperature was changed to room temperature and the stretching atmosphere was changed to air.

When the peripheral wall of the polypropylene hollow fiber subjected to the above-described stretching and heat-setting treatment was observed using an electron microscope, almost no through holes were observed in the peripheral wall.

[Example 5] Polypropylene was converted into a propylene block copolymer (UBE-PP-709K, trade name: manufactured by Ube Industries, Ltd.)
A porous polypropylene hollow fiber was produced in the same manner as in Example 1 except that the MFI was changed to 9 g/10 min).

The outer diameter of the obtained porous polypropylene hollow fiber is
The diameter was 199 μm, the inner diameter was 150 μm, the average pore diameter was 0.1 μm, and the porosity was 3.0%.

When the peripheral wall of the above porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Example 6] Random copolymer of polypropylene and propylene (UBE-PP-S309K, product name: Ube Industries, Ltd.)
A porous polypropylene hollow fiber was produced in the same manner as in Example 1, except that the polypropylene fiber was changed to (MFI = 9 g/10 min).

The average pore diameter of the obtained porous polypropylene hollow fibers was 0.08 μm, and the porosity was 3.0%.

When the peripheral wall of the above porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Example 7] MFI=9g/10min polypropylene (UBE-
Porous polypropylene hollow fibers were produced in the same manner as in Example 1, except that PP-J109G (trade name: manufactured by Ube Industries, Ltd.) was used.

The average pore diameter of the obtained porous polypropylene hollow fibers was 0.09 μm, and the porosity was 5.2%.

When the peripheral wall of the above-mentioned porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Example 8] Polypropylene (UBE-PP-F109K, product name: Ube Industries, Ltd., MFI = 9 g/10 minutes) was processed using a hollow fiber manufacturing nozzle equipped with a gas supply pipe with a diameter of 30 mm and an inner diameter of 25 mm. The spinning temperature was 210°C, the take-up speed was 116 m/min, and the draft ratio was 3790.
The obtained polypropylene hollow fibers were heat treated in a heated air bath at 145°C for 30 minutes, then stretched to 20% of the initial length at -180°C in liquefied argon, and heated at 145°C while maintaining the stretched state. Heat treatment was performed in an air bath for 15 minutes to produce porous polypropylene hollow fibers.

The average pore diameter of the obtained porous polypropylene hollow fibers was 0.08 μm, and the porosity was 5.8%.

When the peripheral wall of the above porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Example 9] Porous polypropylene hollow fibers were produced in the same manner as in Example 8, except that the stretching ratio was changed to 40% and the stretching atmosphere was changed to liquid/gaseous carbon monoxide (-141°C).

The average pore diameter of the obtained porous polypropylene hollow fibers was 0.08 μm, and the porosity was 8.8%.

When the peripheral wall of the above porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Example 10] Polypropylene (UBE-PP-J109G, product name: manufactured by Ube Industries, Ltd., MFI = 9 g/10 minutes), diameter 8
Using a hollow fiber manufacturing nozzle equipped with a gas supply pipe with an internal diameter of 7 mm, the spinning temperature was 210°C, and the take-up speed was 200°C.
Porous polypropylene hollow fibers were produced in the same manner as in Example 9, except that the fibers were spun at a draft ratio of 726 m/min and stretched at a draw ratio of 40% in liquid oxygen (-132°C).

The average pore diameter of the obtained porous polypropylene hollow fibers was 0.07 μm, and the porosity was 6.3%.

When the peripheral wall of the above-mentioned porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of through holes were uniformly formed in the peripheral wall, and the diameter of the through holes was almost constant throughout. There were many of them.

[Example 11] Undrawn polypropylene hollow fibers spun in the same manner as in Example 1 were heat-treated in a heated air tank at 145°C for 30 minutes, and then heated in liquid nitrogen (-195°C) to reduce the initial length by 20%. Stretched and heated to 145℃ while maintaining the stretched state.
Heat treatment was carried out for 15 minutes in a heated air bath.

The average pore diameter of the obtained porous polypropylene hollow fibers was 0.1 μm, and the porosity was 3.1%.

This porous propylene hollow fiber was stretched again by 20% in liquid nitrogen, and then the stretched state was maintained.
Heat treatment was performed for 15 minutes in a heated air bath at 145°C.
After repeating this operation consisting of stretching in liquid nitrogen and stretching treatment twice in total, the average pore diameter of the resulting porous polypropylene hollow fiber was measured to be 0.16 μm, and the porosity was 28%. It was hot.

When the peripheral wall of the above-mentioned porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of relatively large pores were uniformly formed in the peripheral wall, and the diameter of the pores was also approximately constant throughout.

[Example 12] Porous polypropylene hollow fibers were produced in the same manner as in Example 11, except that the number of repetitions of the stretching process in liquid nitrogen was changed to 18 times, and the stretching ratio for each time was changed to 10%. did.

When the average pore diameter of the obtained porous polypropylene hollow fiber was measured, it was 0.70 μm, and the porosity was 64%.

When the peripheral wall of the above porous polypropylene 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 also approximately constant throughout.

[Example 13] Stretching ratio in the stretching process in liquid nitrogen was 10%
Example 11 except that between each stretching process, heat setting by heating was not performed, the operation was simply returned to room temperature in air, and the number of repetitions of the stretching process was changed to four times. Porous polypropylene hollow fibers were produced in a similar manner.

When the average pore diameter of the obtained porous polypropylene hollow fiber was measured, it was 0.10 μm and the porosity was 20.0%.

When the peripheral wall of the above-mentioned porous polypropylene hollow fiber was observed using an electron microscope, it was found that a large number of relatively large pores were uniformly formed in the peripheral wall, and the diameter of the pores was also approximately constant throughout.

[Comparative Example 4] Polypropylene hollow fibers were tried to be stretched in the same manner as in Example 1, except that the stretching temperature was changed to -100°C and the stretching atmosphere was changed to nitrogen gas, but the polypropylene hollow fibers were cut and However, it was not possible to obtain porous polypropylene hollow fibers.

[Comparative Example 5] Polypropylene hollow fibers were tried to be stretched in the same manner as in Example 1, except that the stretching temperature was changed to -190°C and the stretching atmosphere was changed to helium gas.
The polypropylene hollow fibers were cut, and porous polypropylene hollow fibers could not be obtained.

Claims (1)

[Scope of Claims] 1. A method for producing a porous hollow fiber, which includes a step of forming a large number of fine pores in the peripheral wall of the hollow fiber by drawing a polypropylene hollow fiber, in which the drawing step is performed using nitrogen, oxygen, or argon. , in a medium selected from the group consisting of carbon monoxide and methane, and under conditions where the stretching temperature is higher than the freezing point of the medium and lower than or equal to a temperature 50° C. higher than the boiling point of the medium. A method for producing porous polypropylene hollow fibers. 2. The method for producing porous polypropylene hollow fibers according to claim 1, characterized in that the polypropylene hollow fibers are heat-treated at a temperature in the range of 100 to 155°C before being subjected to the stretching step. 3. The method for producing porous polypropylene hollow fibers according to claim 1, characterized in that the polypropylene hollow fibers subjected to the stretching step are heat-treated at a temperature in the range of 110 to 155°C. 4 The draft ratio of unstretched polypropylene hollow fiber is
10 to 6,000, the method for producing porous polypropylene hollow fibers according to claim 1. 5. The method for producing porous polypropylene hollow fibers according to claim 1, characterized in that the stretching step under cooling is repeated two or more times.