JPS6054403B2 - Method for producing porous isotactic polypropylene hollow fiber - Google Patents

Description

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

A technique for producing a porous film by creating pores inside the film by stretching a film made of polypropylene and a few other crystalline polymers is described in U.S. Pat. No. 3,558,764. It is publicly known. According to this prior art, the obtained porous polypropylene film has interconnected pores with an average pore diameter of 1000 to 2000 A inside the film.
Therefore, this film can be effectively used as a support for gas separation membranes, ultrafiltration membranes, reverse osmosis membranes, and the like. However, when the porous polypropylene film obtained from the prior art is used, for example, as an ultrafiltration membrane (2400W membrane manufactured by Celanese), the water permeation rate is 0.02-0.
03 (yId-min-atm), the flux (the number of gallons of treated liquid per day permeating through a 1-foot square membrane area) is lower than that of conventional ultrafiltration membranes made of cellulose acetate, making it suitable for industrial use. There are cost disadvantages when carrying out water treatment on a large scale.

On the other hand, even with such a low-flux membrane, if the membrane is shaped like a macaroni-shaped hollow fiber, the membrane area per unit volume of the device can be significantly increased, and the amount of water that can be processed per unit volume of the device can be increased, making it suitable for industrial use. It is easy to imagine that it would become economically possible to treat water on a large scale. From this point of view, a porous polypropylene hollow fiber and a method for producing the same have recently been proposed (Japanese Patent Application Laid-Open No. 15627/1983).

However, this porous polypropylene hollow fiber requires a complicated process in which heat treatment is performed for one stitch before and after the drawing process, resulting in high manufacturing costs. At the same time, there were disadvantages in that gas permeability and liquid processing ability were reduced.

The present inventors have conducted intensive research to find a porous polypropylene hollow fiber that does not have these drawbacks and a method for producing the same. As a result, the present inventors have developed a new porous polypropylene fiber with excellent gas permeability and liquid processing properties using a very simplified method. The present invention for manufacturing polypropylene hollow fibers has been completed.

That is, the present invention consists of the following invention. 1. Fiber-forming isotactic polypropylene was melt-spun using a macaroni-type hollow fiber production nozzle so that the hollow fiber had a hollowness ratio of 7% or more, and the fiber-forming isotactic polypropylene was melt-spun at a take-up speed of 2000 Tr1. I
The average pore diameter is 400~ or more, characterized by making it m1n or more.
A method for producing a porous isotactic polypropylene hollow fiber in which pores of 700 to 700 pores account for 50% or more of the total pore volume, and the maximum value of the pore volume fraction curve exists in the average pore diameter range of 400 to 700 A. .

Next, the present invention will be explained in more detail.

In the case of the above-mentioned U.S. patent, an unstretched film for obtaining a porous polypropylene film is obtained by melt-extruding polypropylene at a temperature range of 10 to 40°C higher than its melting point, and then forming the film at a take-up ratio (i.e., draft) in a range of 20 to 180. However, in the case of the present invention, the spinning temperature does not need to be limited to a temperature range of 10 to 40°C higher than the melting point; rather, the spinning temperature should be 210°C or higher. is preferably melt-spun at a temperature which is at least 40° C. above the melting point of the isotactic polypropylene used and which is away from the optimum conditions for the film. In the present invention, the isotactic polypropylene may be a known isotactic polypropylene for fibers or used as it is. The isotactic polypropylene may also contain up to (8) % of additives such as weather resistance improvers, matting agents, flame retardants, dyeability improvers, crystal nucleating agents, and the like. Macaroni-shaped hollow fibers (hereinafter abbreviated as hollow fibers) can be easily obtained by extruding this isotactic polypropylene through a known nozzle for producing macaroni-shaped hollow fibers, such as a C-type or bridge-type nozzle. There are no particular restrictions on the cooling conditions directly below the nozzle, but
In order to increase the cooling efficiency and attainable hollowness of the yarn, the cooling airflow used is at a temperature of 30°C or less and a wind speed of 0.37.
TL. It is preferable that it is equal to or higher than Imin. As a result of intensive research, the present inventors came to the following surprising discovery. In other words, in the case of a polymer that easily crystallizes like polypropylene, when the yarn is taken out after melt spinning,
By increasing the pick-up speed, all the way to the pick-up point,
That is, the oriented crystallization of the yarn progresses significantly between the nozzle and the take-off point, and the yarn itself becomes brittle (brittle), and at the same time the take-up tension, air friction, and shear stress increase, creating voids between crystal lamellae. It is a fact that this is possible, especially in hollow fibers where shear stress tends to be applied relatively uniformly in the radial direction of the yarn.
More specifically, when the hollow fibers are extruded and taken off, the hollowness ratio of the hollow fibers is made to be 7% or more, and the take-off speed is 2000 r! 1. Porous hollow fibers can be obtained simply by making Im1n or more.

Increasing the hollowness ratio of hollow fibers can be achieved by devising the dimension of the hollow fiber production nozzle, adjusting the cooling air volume, or by adjusting the dimension of the hollow fiber production nozzle and cooling air volume in an appropriate combination. It will be realized. It is a known fact that increasing the amount of cooling air increases the hollowness ratio of the hollow fibers. Note that the hollowness ratio of the hollow fiber in the present invention is the value obtained by dividing the area of the hollow portion in the cross section of the hollow fiber by the cross-sectional area surrounded by the outer periphery of the hollow fiber, and multiplying the result by 100. The take-up speed is 2000Tr1. ImIn or more, preferably 4000 to 6000m. It is set to Im1n. Collection speed is 4000~6000TT! ．． 1Mln
Within this range, the pore volume fraction increases significantly. When the take-up speed is less than 2000 mImin, the pore volume ratio on the hollow fiber wall surface decreases rapidly and it cannot be said to be porous. Even in small-angle X-ray scattering patterns, the take-up speed is 200
For hollow fibers with less than 0TrL1min, a pattern indicating the fiber long period does not appear easily, but when the take-up speed is 200
When exceeding 07TLImin, a long fiber period appears. That is, if the take-up speed is less than 2000 m1 m1n, oriented crystallization between the nozzle and the take-off point, which is considered to be an essential condition for realizing the present invention, will not proceed sufficiently. Therefore, if the take-up speed is less than 2000 mImin, porous hollow fibers cannot be produced. On the other hand, if the take-off speed exceeds 6000 TrL/min, thread breakage occurs frequently during spinning, making it difficult to take off the yarn stably. Therefore, it is actually very difficult to produce porous hollow fibers at a take-up speed exceeding 6000 mImin. On the other hand, if the hollow fiber has a hollowness ratio of less than 7%, the pore volume ratio will be less than 5% even if the fiber is taken at the above-mentioned take-up speed, and it cannot be said to be porous. The present inventors have found that when the hollow fiber has a hollowness ratio of 7% or more, when the hollow fiber is taken at the take-up speed within the above range, the pore volume ratio is significantly higher than when the hollow fiber has a hollowness ratio of less than 7%. was found to increase.

In other words, it is highly likely that the high shear stress applied to the yarn during high-speed pulling is more likely to be applied uniformly in the radial direction of the yarn in the case of hollow fibers than in the case of solid yarns. At least 7 in the range of shear stress developed at drawing speed
% hollowness is necessary in order to apply shear stress that is relatively uniform in the radial direction of the yarn and sufficient to create voids between crystal lamellae. In order to realize the present invention, the outer diameter of the hollow fibers is particularly preferably 5μ or more and 200μ or less.

When the outer diameter is less than 5μ, the spun yarn becomes very thin.
It becomes very difficult to perform stable winding at a take-up speed of 00 m1 min or more. On the other hand, the outer diameter is 200μ
If it exceeds this, it is necessary to make the hollowness ratio extremely high in order to apply shear stress uniformly in the radial direction of the spun yarn, which is extremely difficult to achieve. Micropores in porous isotactic polypropylene hollow fibers produced according to the present invention were measured by mercury intrusion method [The measuring device was a mercury intrusion pore measuring device (CARLOE).
(manufactured by RBA)], the average pore size (diameter) was 4.
It has become clear that pores of 00 to 700A account for 50% or more, especially 60% or more of the total pore volume, and that the maximum value of the pore volume fraction curve exists in the range of average pore diameter of 400 to 700A. (See Figure 1).

Such pore diameter and pore distribution are described in the above-mentioned Japanese Patent Application Laid-Open No. 52-15627.
This is a new porous polypropylene hollow fiber which is clearly different in pore diameter and pore distribution state from the porous polypropylene hollow fiber obtained by post-spinning stretching and two-stage heat treatment described in the above publication.

That is, the hollow fiber manufactured by the method described in JP-A-52-15627 is
As shown in Figure 2 of the same publication, the stretching ratio is 50~
In the case of 200%, pores with a pore radius in the range of 400 to 1000 A (diameter 800 to 2000 A) account for 50% or more of the total pore volume, and the pore volume fraction curve is in the range of the pore radius. There is a maximum value of , and the stretching ratio is 300~
In the case of 400%, pores with a pore radius in the range of 1500 to 7000A account for 50% or more of the total pore volume, and the maximum value of the pore volume fraction curve exists in the range of the pore radius. ing. As is clear from this, the micropores in the hollow fiber obtained by the present invention are
The pore diameter is substantially smaller than the micropores in the hollow fiber described in Publication No. 7, and the majority of the pores have a small diameter of 400 to 700A and are concentrated in a narrow pore diameter range (see Figure 1).
. The pores in the hollow fiber according to the present invention include both interconnected continuous pores (open pores) and independent pores (closed pores), but the majority are open pores. Therefore, it has an excellent function as a membrane material that can be applied to fields such as gas separation, ultrafiltration, and reverse osmosis. The greatest advantage of the present invention is that the above-mentioned functional porous hollow fibers can be produced all at once using only the spinning process, but if necessary, some stretching treatment may be performed after spinning.

However, in this case, it is necessary to set the stretching ratio as small as possible. As the drawing ratio increases, the diameter of the pores increases, and the pore volume fraction curve shifts to the larger diameter side. The rate curve will be different and the Asspun yarn will have the disadvantage of lower Vegas permeability and liquid handling capacity (flux). Therefore, it is better to avoid stretching after spinning. The method for producing porous isotactic polypropylene hollow fibers according to the present invention is different from conventionally known production methods in that 1) there is no need for stretching treatment 2) there is no need for heat treatment 3) the production speed is very high 4) production cost It can be said to be a groundbreaking manufacturing method, as it has many advantages, including extremely low oxidation.

Further, in the present invention, it is also possible to provide a heating zone between the nozzle and the take-up point for heat treatment. Due to its hydrophobic nature, isotactic polypropylene does not allow water to pass through it unless it is brought into contact with high-pressure water. Therefore,
When operating at low pressures such as ultrafiltration membranes, it is necessary to make the polypropylene hydrophilic. Hydrophilization can be divided into two methods: pre-treatment and post-treatment. In the case of pre-treatment, the isotactic polypropylene to be melt-extruded is made hydrophilic in advance by a known method, and in the case of post-treatment, is made into porous polypropylene hollow fibers, which are then made hydrophilic by chemical or physical treatment.
The method of grafting acrylic acid or maleic anhydride to make it hydrophilic can be applied to both pre-treatment and post-treatment methods. On the other hand, a method of making it hydrophilic using a surfactant or the like can be effectively used as a post-treatment. In the present invention, when it is desired to impart dyeability to the porous isotactic polypropylene hollow fiber, in particular, as a dyeability improver, JP-B No. 46-5213
Publication No. 46-5218 and Special Publication No. 1973
It is recommended to use the copolymer of aminoalkyl acrylate and ethylene described in Japanese Patent No. 5219.

Because this dyeability improver has the property of localizing around micropores, it improves dyeability much better than the effect of the dyeability improver on conventional isotactic polypropylene fibers that do not have micropores. There are things that are effective. Next, the present invention will be explained in more detail using Examples.

Example 1 Isotactic polypropylene ([η] = 14.0 at 35°C in tetralin) produced by a conventional method,
C-type nozzle (outer diameter 1.60Wr!Ft) with a spinning temperature of 260℃, a single hole discharge rate of 2y1min, and a nozzle hollowness ratio of 65%.
Polypropylene hollow fibers were produced using the following conditions: take-up speed: 4000TrLImin1; cooling air velocity: 0.3TrLImjn.

The obtained hollow fibers had an outer diameter of 32.1 μm and a hollow ratio of 23%, and were measured using a mercury intrusion method [the measuring device was a mercury pressure pore measuring device (CARLO)].
ERBA)], the pore size distribution is found to be 510A.
There is a maximum value of the pore volume fraction curve near 530-45
More than 60% of all pores were present in the 0A range. The pore volume fraction with a pore diameter of 510 was approximately 35%. In FIG. 1, the relationship between pore diameter and pore volume fraction is shown by a solid line.

Comparative Example 1 A solid yarn spun under the same conditions as in Example 1 except that the nozzle was changed from a C-shaped nozzle to a circular solid nozzle (hole diameter 0.3w1) was spun by the mercury intrusion method. When the pore size distribution was measured, no pores having a pore diameter of 200 to 6000 A were observed.

Example 2 A hollow fiber (outer diameter 28.5
When measuring the pore size distribution using the mercury intrusion method, the maximum value of the pore volume fraction curve is found to be around 560A, and more than 60% of the total pores exist in the range of 610 to 470A. was.

The pore volume fraction at a pore diameter of 560A was about 39%. The relationship between pore diameter and pore volume fraction is shown in FIG. 1 by a dashed line.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the pore diameter and pore volume fraction of two types of porous polypropylene hollow fibers produced according to the present invention, with the vertical axis in normal scale and the horizontal axis in logarithmic scale.

Claims (1)

[Scope of Claims] 1 Fiber-forming isotactic polypropylene is melt-spun using a macaroni-type hollow fiber manufacturing nozzle so that the fiber-forming isotactic polypropylene becomes 7% or more of the hollow fiber, and the take-up speed is 2000 m/mi.
Average pore diameter of 400 to 700, characterized by being greater than or equal to n
A method for producing a porous isotactic polypropylene hollow fiber, in which pores with a diameter of 1.5 Å account for 50% or more of the total pore volume, and a maximum value of a pore volume fraction curve exists in the range of an average pore diameter of 400 to 700 Å. 2. The method for producing porous polypropylene hollow fibers according to claim 1, wherein the take-up speed is 4000 to 6000 m/min.