JP7400556B2 - Porous fibers, adsorption materials and purification columns - Google Patents

Description

Related to porous fibers, adsorption materials and purification columns.

Conventionally, beads have often been used as an adsorbent material for removing a substance to be removed from a liquid to be treated by adsorption. Patent Document 1 is an invention related to porous beads, and in particular, by making the beads porous, the inside of the pores are utilized as adsorption sites to improve adsorption performance. The reason why beads are used is that bead-shaped adsorption carriers can be easily packed uniformly into a purification column, which has the advantage of less bias in flow and ease of column design.

Fibers can be used as adsorbents other than beads, such as those in which many fibers are inserted in a straight shape parallel to the longitudinal direction of the column case, or those in which high-quality fibers are inserted into knitted fabrics, non-woven fabrics, etc. Examples include those that have been further processed. In order to increase the contact area of such fibers with the liquid to be treated, in addition to making them porous, it is also possible to change the normally circular cross section of the fibers to a different shape, that is, to make the fibers have irregular cross sections. Conceivable. However, as the degree of irregularity of the fibers increases, the strength and elongation of the fibers significantly decreases, and the unevenness of fiber diameters called draw resonance increases, which makes it difficult. For example, Patent Document 2 describes that solid fibers with irregular cross sections are preferable.

Patent Document 3 discloses an invention of a hollow fiber having an irregular cross section. However, the main focus is on suppressing fouling by complicating and disrupting the flow on the outer surface of the hollow fibers.

Patent Document 4 has an invention in which a porous irregular cross-section yarn is obtained by devising the composition of the spinning dope, the shape of the spinneret, and the like.

Patent Document 5 discloses an invention in which cooling air conditions are improved in order to suppress unevenness in the fineness of clothing fibers.

Special Publication No. 2015-530969 Japanese Patent Application Publication No. 6-296860 Japanese Patent Application Publication No. 2012-40464 International Publication No. 2017/18110 Japanese Patent Application Publication No. 2007-63679

Kazuhiko Ishikiriyama et al. ; JOURNAL OF COLLOID AND INTERFACE SCIENCE, 171, 103-111, (1995) Kazuhiko Ishikiriyama et al. ; JOURNAL OF COLLOID AND INTERFACE SCIENCE, 173, 419-428, (1995) Abstracts of the 38th Pore Diameter Calorimetry Symposium 38-39

In the technology using beads as in Patent Document 1, one way to improve adsorption performance is to increase the surface area per volume of the adsorption carrier. However, when the adsorption carrier is bead-shaped, the flow path of the liquid to be treated tends to be complicated and curved, and when the bead diameter is made smaller in order to increase the surface area per volume of the adsorption carrier, the gaps between each bead are reduced. becomes noticeably narrower. Therefore, the flow path resistance becomes high and the pressure loss increases, making it difficult to stably process the liquid to be processed. Furthermore, since the beads used as adsorption carriers are spherical, they have the smallest surface area per volume. That is, even if there is adsorption capacity inside the beads, those adsorption sites are often not effectively utilized.

In the technique described in Patent Document 2, for example, Patent Document 2 states that solid fibers with irregular cross sections are preferable, but the disclosed examples relate only to circular yarns. Furthermore, since the pores are formed by stretching the melt-spun fibers, the micro-crack structure is stretched during the stretching process, and pores of various sizes are formed, resulting in a wide distribution of pore diameters. When the pore size distribution is wide, pores having a pore size smaller than the size of the substance to be removed cannot contribute to adsorption, so there are many pores that do not contribute to adsorption. Furthermore, it is easy to imagine that non-specific adsorption will also increase. Furthermore, since a crystalline portion is required for the stretched pores, there are restrictions such as the support material being limited to crystalline polymers.

In the technique disclosed in Patent Document 3, short protrusions are provided on the outer periphery of the fiber for a purpose different from the present invention. In particular, the idea of suppressing fouling is the opposite idea to the adsorption column idea of adsorbing solutes to fibers as in the present invention. Therefore, there is no concept of improving adsorption performance by increasing the surface area per volume. Therefore, examples of shapes that cannot be said to have a relatively high degree of irregularity are shown. Furthermore, since the spinning raw material contains organic matter and inorganic fine particles as a pore-forming agent, multiple steps are essential to dissolve and wash and remove them. It is not easy to completely remove these substances that exist in pores on the order of nanometers or micrometers.

In the case of irregular cross-section fibers as described in Patent Document 4, there is a problem that unevenness tends to occur in the openings on the fiber surface between convex portions and concave portions, and the pores inside the fibers cannot be fully utilized. The main mechanism by which the surface aperture ratio decreases is that when the structure of a spinning dope containing a supporting component such as a resin and a second component that ultimately becomes pores is fixed, the surface of the dope is in an energetically high state. This is because the supporting components aggregate and the pores on the fiber surface are closed. In order to prevent this and maintain the open state, the fluid spinning stock solution must be cooled promptly after being discharged from the spinneret to reduce the mobility of the supporting components and prevent agglomeration. Cooling using gas or liquid can be considered as a means for efficiently cooling the spinning dope that is continuously discharged. When a liquid is used, its composition needs to be a poor solvent for the supporting component, but contact with the poor solvent before structure fixation is not preferable because aggregation of the supporting component will occur. Therefore, cooling with cold air is often used. Patent Document 4 also uses cooling with cold air and describes the results of measuring the aperture ratio of the fiber surface, but there is no evaluation of uneven apertures between concave portions and convex portions, or any idea to suppress it. Furthermore, there was no detailed description of cold air cooling conditions. Therefore, since the convex portions of the irregular cross-section fibers are less likely to be directly hit by cold air than the concave portions, cooling may have been insufficient, and the surface aperture ratio may have been particularly low in the concave portions. It is believed that there is still room for improvement in the performance of such fibers and purification columns incorporating bundles of these fibers as adsorption materials.

Patent Document 5 is an invention that attempts to improve fineness unevenness by improving the cooling method in spinning multifilament yarns of thermoplastic fibers, but there are no working examples and there is no specific setting of cold air conditions. was also not done. In addition, the purpose of this method was to eliminate unevenness between non-porous circular cross-section fibers, which was far different from the idea of eliminating uneven opening within a single fiber of irregularly shaped cross-section fibers as in the present application.

Therefore, the problem to be solved by the present invention is to provide a purification column incorporating porous fibers and a bundle of the fibers used as an adsorption material, which has excellent removal performance for substances to be removed.

In order to solve the above problems, the present invention has the following configuration.
That is, it is a porous fiber that has pores and one or more protrusions on the outer periphery and satisfies the following requirements (A) to (D).
(A) The degree of pore size distribution of the pores is 1.0 or more and 2.8 or less (B) In the cross section, if the diameter of the inscribed circle is Di and the diameter of the circumscribed circle is Do, the degree of irregularity Do/ Di is 1.35 or more (C) The pore volume of the pores is 0.20 cm ³ /g or more (D) The aperture ratio ratio X expressed by the following formula is 6.0 or less (Formula) Opening ratio Ratio X=surface aperture ratio of convex portions/surface aperture ratio of concave portions The adsorption material is also used as a fiber bundle containing 50% or more of the porous fibers.

Further, the present invention is a medical purification column in which the adsorption material is arranged in a straight shape in the axial direction of the case in a plastic casing, and an inlet port and an outlet port for a liquid to be treated are attached to both ends of the casing.

According to the present invention, it is possible to obtain porous fibers capable of efficiently adsorbing a substance to be removed in a liquid to be treated, and a purification column incorporating porous fibers.

It is a figure which shows the fiber cross section for demonstrating an inscribed circle and a circumscribed circle. FIG. 3 is a diagram showing a central region of a cross section and a region near an outer surface. It is a figure explaining protrusion thickness ω. FIG. 3 is a diagram of a die for producing fibers with two protrusions, and is a diagram illustrating each part of the die. FIG. 3 is a diagram of a die for producing fibers with two protrusions. FIG. 3 is a diagram of a die for producing fibers with three protrusions. FIG. 2 is a diagram of a die for producing fibers with four protrusions. FIG. 3 is a diagram of a die for producing fibers with five protrusions. FIG. 3 is a diagram of a die for producing fibers with six protrusions. FIG. 2 is a diagram of a die for producing fibers with 8 protrusions.

The present invention has the following configuration. It is a porous fiber that has pores and one or more protrusions on the outer periphery and satisfies the following requirements (A) to (D).
(A) The degree of pore size distribution of the pores is 1.0 or more and 2.8 or less (B) In the cross section, if the diameter of the inscribed circle is Di and the diameter of the circumscribed circle is Do, the degree of irregularity Do/ Di is 1.35 or more (C) The pore volume of the pores is 0.20 cm ³ /g or more (D) The aperture ratio ratio X expressed by the following formula is 6.0 or less (Formula) Opening ratio Ratio X=surface aperture ratio of convex portions/surface aperture ratio of concave portions The present invention also relates to an adsorption material used as a fiber bundle containing 50% or more of the porous fibers.

The present invention also relates to a medical purification column comprising a plastic casing, in which the adsorption material is arranged in a straight shape in the axial direction of the case, and an inlet port and an outlet port for a liquid to be treated are attached to both ends of the casing. .

<Porous fiber>
The porous fibers of the present invention may be in the shape and form of porous fibers that do not have hollow portions, which are called solid fibers, or hollow fibers that have hollow portions. In the case of solid fibers, the liquid to be treated can be brought into contact with the outside of the fiber, and in the case of hollow fibers, the liquid to be treated can be brought into contact with the inside or outside of the fiber, or both sides thereof. In the case of hollow fibers, it is somewhat difficult to evenly distribute the flow rate between the inside and outside of the fibers, and flow unevenness tends to occur, so solid fibers are more preferable. However, in the case of hollow fibers, the ends of the fibers can be sealed with resin and used as a hollow fiber membrane type filter, as in an artificial kidney.

Moreover, it is preferable that the fiber is a single fiber, that is, a monofilament. Although it is possible to form a multifilament by tying together a plurality of monofilaments, this is not preferable because the entangled portions are difficult to contact with the liquid to be treated and there is a high possibility that the surface area cannot be used effectively for adsorption. In addition, for fibers with uneven opening on the fiber surface, it is possible to reduce the effect of uneven opening by making the yarn thinner and making it a multifilament, but the fiber of the present invention has sufficient performance even with monofilament. Able to demonstrate

<Porous fiber protrusions>
The porous fiber according to the present invention has a shape in which protrusions are present on the outer periphery of the fiber. The term "protrusion" as used herein refers to a protrusion existing on the outer periphery of the cross section of the fiber. By having protrusions, the adsorption performance can be expected to be improved as a result of the protrusion being irregularly shaped and increasing the surface area per volume. Moreover, it is preferable that the protrusions exist continuously in the longitudinal direction of the fiber. Further, it is preferable that the protrusions continue linearly in the longitudinal direction of the fiber. Such protrusions are preferable because they facilitate the formation of a linear flow path for the liquid to be treated and can reduce flow path resistance. A form in which the protrusions are continuous in a spiral manner is also conceivable, but physical interference with adjacent threads tends to be large. For this reason, there is a possibility that the filling rate will be significantly reduced when the yarn is bundled and packed into a column.

The number of protrusions that the porous fiber of the present invention has on its outer periphery is one or more. It is preferable that the number of protrusions is one or more because as described above, the protrusions are irregularly shaped and the surface area per volume is increased, so that an improvement in adsorption performance can be expected. Further, the number of protrusions is preferably 24 or less, more preferably 16 or less, still more preferably 8 or less, even more preferably 4 or less. When the number of protrusions is 24 or less, the gaps between the protrusions are narrowed and the surface area per volume decreases, and the liquid to be treated does not easily come into contact between the protrusions, which is preferable.

<Deformity of porous fiber>
The degree of irregularity of the porous fiber is expressed by the ratio of the diameters of the inscribed circle and the circumscribed circle when observing the cross section of the fiber, that is, the ratio Do/Di of the diameter Di of the inscribed circle and the diameter Do of the circumscribed circle. The shape of the irregular cross section may be a shape that maintains symmetry such as line symmetry or point symmetry, or it may be asymmetric, but it is a shape that is generally symmetrical in terms of having uniform fiber properties. It is preferable that there be. When it is judged that the irregular cross section maintains approximately line symmetry and point symmetry, the inscribed circle is the circle that is inscribed in the curve that forms the outline of the fiber in the fiber cross section, and the circumscribed circle is the circle that is inscribed in the curve that forms the outline of the fiber in the fiber cross section. It is a circle circumscribing the curve that forms the outline of . FIG. 1 shows the circumscribed circle, inscribed circle, and diameters Do and Di of a fiber having an irregular cross section with three protrusions.

On the other hand, when it is determined that the irregular cross section has a shape that does not maintain line symmetry or point symmetry at all, the inscribed circle and circumscribed circle are defined as follows. The inscribed circle is inscribed in at least two points with the curve that forms the outline of the fiber, and is the maximum possible range that exists only inside the fiber and the circumference of the inscribed circle and the curve that forms the outline of the fiber do not intersect. Let it be a circle with a radius. A circumscribed circle is a circle that circumscribes at least two points on a curve showing the fiber outline, exists only outside the fiber cross section, and has the smallest possible radius within the range where the circumference of the circumscribed circle and the fiber outline do not intersect. shall be.

In the case of hollow fibers, the inscribed circle has the smallest diameter among the circles that touch at least two points on the curve that outlines the outer periphery of the fiber, and the circumscribed circle has the smallest diameter among the circles that touch at least two points on the curve that outlines the outer periphery of the fiber. It has the largest diameter among the circles touching at . Note that the shape of the hollow portion of the hollow fiber in the present application is not particularly limited, and a circular shape, a polygonal shape, a multilobal shape, etc. are suitably employed depending on the purpose. Among these, a circular type is preferable because it is easy to form and control the hollow portion. If the degree of irregularity is 1.35 or more, it becomes possible to increase the ability of the fiber to adsorb the substance to be removed. In general, as the degree of irregularity increases, the surface area per volume increases, so adsorption performance can be improved, which is preferable. Therefore, the lower limit of the preferable degree of irregularity is 1.35. The degree of irregularity is more preferably 1.60 or more, still more preferably 1.90 or more, even more preferably 2.20 or more. On the other hand, if the degree of irregularity increases too much, another problem may arise. That is, the center of the fiber cross section and the protrusions become elongated and the strength and elongation of the fibers decreases, making it easier for the protrusions to bend or break. As a result, problems such as a decrease in spinning stability and difficulty in maintaining the fiber shape arise. Further, when the spinning dope is quickly cooled using wind or liquid before being formed into fibers, the protrusions obstruct the flow of the wind or liquid. As a result, there is a concern that unevenness may occur in the fiber shape and microstructure such as pores and surface openings. For this reason, it is good to set a certain upper limit to the degree of irregularity, and in the present invention, it is set to 5.50 or less, preferably 4.70 or less, more preferably 4.00 or less, and still more preferably 3.50 or less. It is.

To measure the degree of irregularity, both ends of the fiber to be measured are fixed under a tension of 0.1 g/mm ² and cut at random positions. Thereafter, the cut surface is enlarged and photographed using an optical microscope, for example, DIGITAL MICROSCOPE DG-2 manufactured by Scala. When photographing, the scale is also photographed at the same magnification. After the image is digitized, the diameter Do of the circumscribed circle and the diameter Di of the inscribed circle of the cross section of the fiber are measured using, for example, the image analysis software "Micro Measure ver. 1.04" by Scala Co., Ltd. . Then, the degree of irregularity of each fiber is determined by the following formula. This measurement is performed at 30 locations, the values are averaged, and the value rounded to the second decimal place is defined as the degree of irregularity.
(Formula) Degree of irregularity = Do/Di
<Average pore radius of porous fiber>
Moreover, the porous fiber in the present invention has pores inside. The average pore radius of the pores is preferably 0.5 nm or more and 90 nm or less. In the present invention, the average pore radius is expressed as a primary average pore radius. The primary average pore radius of the pores is preferably 0.5 nm or more, more preferably 1.5 nm or more, particularly preferably 2.0 nm or more. On the other hand, it is preferably 90 nm or less, more preferably 40 nm or less, particularly preferably 25 nm or less. Even if the inside has pores, if the average pore radius is small, the substance to be removed will not enter the pores, which may reduce adsorption efficiency. On the other hand, if the pore radius is too large, the substance to be removed will not be adsorbed in the voids, which may conversely reduce the adsorption efficiency. Within the above range of pore radius, there is an optimum pore radius depending on the size of the substance to be removed. Therefore, if the pore radius is selected incorrectly, the substance to be removed may not be sufficiently adsorbed.

<Pore volume of porous fiber>
In order to adsorb the substance to be removed, the porous fiber of the present invention has a large pore volume, thereby increasing the number of adsorption sites and improving adsorption performance. Therefore, the pore volume is 0.01 cm ³ /g or more, preferably 0.2 cm ³ /g or more, more preferably 0.5 cm ³ /g or more, still more preferably 0.7 cm ³ /g or more, and particularly preferably is 1.0 cm ³ /g or more. On the other hand, if the pore volume is too large, the mechanical strength will be insufficient, so the pore volume is preferably 5.6 cm ³ /g or less, more preferably 4.5 cm ³ /g or less, even more preferably It is 3.6 cm ³ /g or less, particularly preferably 2.9 cm ³ /g or less.

<Pore size distribution degree of porous fiber>
The porous fiber of the present invention has a pore size distribution of 1.0 or more and 2.8 or less. The pore size distribution degree is 2.8 or less, and the upper limit is preferably 2.4 or less, more preferably 2.1 or less, still more preferably 1.9, particularly preferably 1.6 or less. If it is 2.8 or less, it is possible to make the pore size distribution uniform and reduce the number of pores that make a small contribution to adsorption, that is, pores that are too small or too large for the substance to be adsorbed. can. Further, size selectivity of the adsorbed substance can be imparted. If it exceeds 2.8, size selectivity decreases and nonspecific adsorption increases, which is not preferable. On the other hand, if the pore size distribution degree is 1.0 or more, the above-mentioned size selectivity can be sufficiently imparted.

<Measurement of pore characteristics of porous fibers>
The average pore radius, pore volume, and pore size distribution of porous fibers can be determined by measuring the degree of freezing point depression due to capillary aggregation of water in the pores using a differential scanning calorimeter (DSC). The radius, that is, the average pore radius in this application is determined. Specifically, the adsorption material is rapidly cooled to -55°C, then heated to 5°C at a rate of 0.3°C/min, measured, and calculated from the obtained curve. For details, refer to the description in Non-Patent Document 1. Further, the i-th average pore radius is determined from the following (Formula 1) in Non-Patent Document 3 based on (Formula 2) in Non-Patent Document 2.

<Structure of fiber cross section of porous fiber (homogeneous structure, heterogeneous structure)>
The porous fiber according to the present invention may have a structure in which the cross section of the fiber is heterogeneous or homogeneous. In particular, it is preferable for fibers with a homogeneous structure to have a homogeneous porous structure in the cross-sectional direction of the fibers, since the adsorption area can be further secured. However, in order to reduce the diffusion resistance toward the fiber center, it is possible to have a slightly gradient structure in which the pores are made larger on the outer periphery of the fiber and gradually shrink toward the fiber center. good. Furthermore, under conditions where the pores on the outermost surface of the fiber are completely clogged due to fouling over time, having such a gradient structure reduces the risk that the pores inside the fiber will also be clogged. As a result, it is also possible to suppress the phenomenon in which the diffusibility of the substance to be removed to the fiber center decreases. In such a homogeneous structure, the average pore radius in the region near the outer surface of the fiber (average pore radius in the region near the outer surface/average pore radius in the center region) is greater than the average pore radius in the center region of the fiber. The ratio is preferably 0.50 times or more and 3.00 times or less, more preferably 0.75 times or more and 2.00 times or less, and even more preferably 0.85 times or more and 1.50 times or less.

Next, a method for determining a homogeneous structure in the present invention will be explained. First, porous fibers are thoroughly moistened and then immersed in liquid nitrogen to instantly freeze the moisture within the pores with liquid nitrogen. Thereafter, the fibers are quickly folded, and while the fiber cross section is exposed, the frozen water is removed in a vacuum dryer at 0.1 torr or less to obtain a dried sample. Thereafter, a thin film of platinum (Pt), platinum-palladium (Pt--Pd), or the like is formed on the surface of the sample by sputtering to obtain an observation sample. A cross section of the sample is observed using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, S-5500). Here, a radius passing through the center point 8 of the fiber cross section is arbitrarily selected, and as shown in FIG. The region including the center point is defined as the center region 6, and the side closest to the outer periphery is defined as the outer surface vicinity region 7. The equivalent circular diameters of the pores existing in the central region and the region near the outer surface are determined, and the average pore diameter in each region is obtained. To calculate the average pore diameter in each region, arbitrarily select 20 areas of 2 μm x 2 μm using a scanning electron microscope (50,000x magnification), measure the entire pore in the photograph, and calculate the average. The pore diameter shall be calculated. To measure the pore diameter, a transparent sheet is placed on top of a printed electron microscope image, and the pores are painted black using a black pen or the like. Then, by copying the transparent sheet onto a blank sheet of paper, the pore areas are clearly distinguished as black and the non-porous areas as white, and the pore diameter is determined using image analysis software.

<Three-dimensional network structure of porous fibers>
Furthermore, it is preferable that the porous fiber used in the present invention has a three-dimensional network structure. The three-dimensional network structure herein refers to a structure in which the pore shape index Dxy is controlled.
Pore shape index Dxy in the cross section in the fiber axis direction = (pore diameter in the longitudinal direction of the fiber) / (pore diameter in the cross-sectional direction of the fiber)
The lower limit of Dxy is preferably 0.2 or more, more preferably 0.4 or more, and still more preferably 0.6 or more. The upper limit of Dxy is preferably 6.0 or less, more preferably 4.0 or less, and even more preferably 2.5 or less. Fibers produced by a stretching method or the like have a characteristic orientation structure in the longitudinal direction of the fibers, which generally results in a structure with a very high Dxy, and therefore cannot be said to be preferable.

The method for measuring Dxy is shown below. Double-sided tape is attached to a plastic plate such as polystyrene, and the fiber to be measured is fixed onto it. Cut the pasted fibers in the longitudinal direction with a single blade to expose the longitudinal cross-section of the fibers, and attach this to the sample stage of a scanning electron microscope using double-sided tape. Be careful because if the hole is crushed by cutting, it will not be possible to obtain an accurate image. Thereafter, a thin film of Pt, Pt--Pd, or the like is formed on the fiber surface by sputtering and used as an observation sample. This cross-section in the longitudinal direction of the fiber is observed at a magnification of 50,000 times using a field emission scanning electron microscope (for example, S-5500 manufactured by Hitachi High-Technologies Corporation), and 10 arbitrarily selected images are imported into a computer. . The size of the captured image is preferably 640 pixels x 480 pixels. Five holes are arbitrarily extracted from the obtained one-point image, and for each hole, the hole diameter in the fiber longitudinal direction, the hole diameter in the fiber axis direction, and the ratio of the two are determined. This is done for the above 10 images to find the above ratio for a total of 50 holes, the average value is calculated, and the value rounded to the second decimal place is set as Dxy.

<Spinning of porous fibers>
The spinning method for obtaining fibers in the present invention may be either melt spinning or solution spinning, but in solution spinning, only the solvent is quickly removed from a state in which the supporting component is uniformly dissolved in the solvent. This is preferable because porous fibers having a uniform structure can be easily obtained. Therefore, the spinning dope preferably consists of a supporting component such as a resin and a good solvent that can dissolve it. A third component such as fine particles can be mixed as a pore-forming material or dispersion material, but this may cause problems such as reduced cleaning efficiency and the need for post-crosslinking immobilization depending on the usage conditions. . In the case of melt spinning, there is a method in which such a third component is removed in a post-spinning process to form pores, and there is also a method in which pores are drawn and opened, but pores of various sizes are formed. Therefore, the specific surface area decreases. Furthermore, since the pore size distribution tends to become wider, pores having a smaller pore size than the size of the substance to be removed cannot contribute to adsorption. That is, within the volume of the pores, there is a portion of the area that does not contribute to adsorption. Furthermore, since the pores are formed by stretching, the supporting component is limited to a crystalline polymer.
In the case of hollow fibers, it can be obtained by using a double tube cap, introducing gas or liquid into the core from the inner circular tube, and discharging the membrane forming stock solution from the outer slit. As the material for forming the core, it is preferable to use a gas, since the liquid requires a subsequent step of removal and cleaning.

Conditions for fixing the fiber structure are important for controlling the aperture ratio of the fiber surface. Particularly in the case of solution spinning, controlling the structure of the fiber surface in the dry spinning section is important. In solution spinning, the fluid spinning solution is brought into contact with a poor (non-)solvent or cooled in order to fix the structure (solidify) and form a fiber shape. It refers to the part where the stock solution travels after it is discharged from the nozzle until it enters a bath consisting of a poor solvent, or until its structure is completely fixed by cooling. When the structure of the spinning dope is fixed, the energy near the surface of the dope is high, so when it comes into contact with a poor solvent or moisture contained in the air, supporting components such as resin aggregate, causing the fiber surface to It is thought that the pores are blocked. Therefore, the pore structure needs to be determined to some extent before the spinning dope comes into contact with the poor solvent, that is, in the drying section. Specifically, it is necessary to quickly induce phase separation after discharging the stock solution to allow the pore structure to grow and expand sufficiently before contact with the poor solvent, and to increase the viscosity of the stock solution by cooling the fibers in the drying section. It is important to suppress aggregation by reducing the mobility of the supporting component. To achieve this, control of the dry section is important.

We have found that sufficient residence time and cooling air velocity conditions at residence time are important. Specifically, a method for producing a porous fiber having pores and one or more protrusions on the outer periphery, the step of fixing the structure of a spinning dope includes the following step. It's a method.
(1) Dry section residence time expressed by the following formula is 0.1 seconds or more (formula) Dry section residence time (seconds) = Dry section length (m) / Winding speed (m/second)
(2) The dry part has a strong wind part and a weak wind part, and the dry part has a strong wind part that occupies a length of 1.5% or more from the starting point, and then a strong wind part that occupies a length of 5.0% or more from the starting point. (3) The ratio of the cooling wind speed of the strong wind section to the cooling wind speed of the weak wind section is within the range of 3:1 to 19:1. means a process of forming a porous fiber structure from a spinning solution and fixing it in that state.
Here, the residence time is 0.10 seconds or more, preferably 0.30 seconds or more, and more preferably 0.50 seconds or more. The residence time is calculated from the following formula as described above.
(Formula) Dry section residence time (seconds) = Dry section length (m) / Winding speed (m/second)
Further, in the dry section, it is preferable to forcibly cool the dry section using cooling air. Furthermore, we found that the openings on the surface can be made uniform by controlling the proportion of strong and weak winds in the cooling air. Specifically, the first 1.5 to 21.0% of the length of the dry section passage portion is a strong wind section, and 5.0% or more following the strong wind section, preferably 15.0% or more, particularly preferably It is important that 30.0% or more be the weak wind portion. The ratio of the cooling wind speed in the strong wind section to the cooling wind speed in the weak wind section shall be in the range of 3:1 to 19:1. The mechanism is not clear, but if there is only a strong wind, the strings are agitated and it is difficult to cool them for a long time, and uneven openings tend to occur between the areas where the cooling air was first blown and the areas where it was not. On the other hand, in the case of only weak winds, the mobility of the spinning stock solution is not sufficiently lowered due to low cooling efficiency, and it is thought that agglomeration of the supporting components in the stock solution occurs. That is, it is considered important that the cooling air in the drying section quickly lowers the mobility of the spinning dope in the first strong wind section, and stably and evenly cools the entire circumference of the fiber in the weak wind section. The absolute value of the cooling air velocity should be set appropriately depending on the winding speed and the viscosity of the spinning dope, but if it is too high, the cross-sectional shape may be deformed, so the upper limit of the cooling air velocity should be set. In the strong wind portion, the wind speed is 24.0 m/s or less, more preferably 15.0 m/s or less, and still more preferably 11.0 m/s or less. The weak wind portion is 10.0 m/s or less, more preferably 3.0 m/s or less, even more preferably 0.7 m/s or less. Furthermore, it is preferable to lower the temperature of the cooling air as much as possible. The temperature is preferably 18°C or lower, more preferably 12°C or lower, even more preferably 8°C or lower, particularly preferably 4°C or lower. On the other hand, if the temperature is below freezing, there is a concern that water droplets may condense, so it is preferable that the temperature exceeds 0°C. In addition, the method of determining the boundary between the strong wind section and the weak wind section is to measure the cold wind speed along the yarn path from the mouthpiece toward the downstream, and measure the cold wind speed from the first 1.5 to 21 The boundary is defined as a point within the range of .0% and where the cold air velocity has decreased to 1/3.

Furthermore, for fibers with protrusions and a high degree of irregularity as in the present application, the cold air in the drying section is blown onto the protrusions, making it easier for the yarn to rotate during the drying section, resulting in less uneven cooling of the cold air. You can also expect some positive effects.

To measure the aperture ratio of the fiber surface, the fiber surface obtained using the same method as the observation sample prepared for the homogeneous structure determination described above was observed using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, S Observe at 50,000x magnification (-5500) and import the image into a computer. The size of the captured image is preferably 640 pixels x 480 pixels. The SEM image is cut out into a 6 μm×6 μm range at an arbitrary position, and image analysis is performed using image processing software. Through the binarization process, a threshold value is determined so that the structure part has bright brightness and the other parts have dark brightness, and an image is obtained in which the bright brightness part is white and the dark brightness part is black. If the contrast difference in the image is small and it is not possible to separate the structure part from the other parts, divide the image into parts with the same contrast range, binarize each part, and then restore the original image. to create a single image. Alternatively, image analysis may be performed by filling in black parts other than the structure part. The image contains noise, and since it is difficult to distinguish between noise and holes in dark and bright areas where the number of consecutive pixels is 5 or less, the image is treated as a bright and bright area as a structure. A method for eliminating noise is to exclude dark brightness areas where the number of consecutive pixels is 5 or less when measuring the number of pixels. Alternatively, the noise portion may be filled in with white. The number of pixels in the dark brightness area is measured, and the percentage of the total number of pixels in the analysis image is calculated to determine the aperture ratio. The same measurement is performed on 30 images and the average value is calculated.

The aperture ratio ratio X, which indicates the aperture unevenness on the fiber surface, is expressed by the following formula and is 6.0 or less.
The upper limit of the aperture ratio ratio X = convex aperture ratio/concave aperture ratio is more preferably 5.6 or less, particularly preferably 5.2 or less. The lower limit is preferably 0.35 or more, more preferably 0.40 or more, particularly preferably 0.45 or more. If the open area ratio X is large, the pores inside the fibers cannot be fully utilized for adsorption, leading to a decrease in adsorption performance. Furthermore, by having a portion with few openings on the fiber surface, there is an increased concern that substances with large molecular weights such as albumin and globulin will be non-selectively adsorbed on the fiber surface. There is also a similar concern because the possibility of locally forming areas with a high aperture ratio increases. Here, when the centers of the circumscribed circle and the inscribed circle are the same as the convex portions and concave portions, a circle having the same center and a diameter expressed by the following formula is drawn, and the fiber surface portion included inside this circle is is the concave portion, and the surface portion included on the outside is the convex portion.
{(circumscribed circle diameter - inscribed circle diameter)/2} + inscribed circle diameter If the centers of the circumscribed circle and inscribed circle are different, a circle with the same center as the circumscribed circle and a diameter expressed by the following formula The fiber surface portion included inside this circle is defined as a concave portion, and the surface portion included outside this circle is defined as a convex portion.
{(circumscribed circle diameter - inscribed circle diameter)/2} + (distance of the straight line connecting the center of the circumscribed circle and the center of the inscribed circle)
Note that it is preferable that the center of the circumscribed circle and the center of the inscribed circle be the same. This is because when different fibers are made into a fiber bundle, the gaps between the fibers tend to be large and non-uniform depending on the orientation of the cross-sectional shape of the fibers.

In addition, the cooling efficiency of the discharged fibers decreases, and the degree of irregularity decreases because it becomes difficult to maintain the shape of the fibers, resulting in the fibers entering the coagulation bath containing a poor solvent without being sufficiently cooled. There is. In this case, supporting components such as polymers near the surface tend to aggregate and precipitate, resulting in a decrease in surface aperture ratio. On the other hand, the lower limit of the equivalent circle diameter is preferably 10 μm or more, more preferably 30 μm or more, particularly preferably 50 μm or more. If the equivalent circle diameter is too small, the strength of the fiber decreases, resulting in poor spinning stability, productivity, and brittleness of the fiber, which is not preferable. Furthermore, if the volume per surface area is too small, the adsorption sites may become easily saturated.

Further, the protrusions of the fibers are defined by a protrusion index Y, which is the protrusion width ω divided by the equivalent circle diameter. If Y is too large, the tips of the protrusions become enlarged, making it difficult for the cooling air in the dry section or the liquid to be treated to come into contact with the recesses of the protrusions, which is not preferable. On the other hand, if it is too small, there is an increased risk that the protrusion will break due to physical impact, which is undesirable. Therefore, the upper limit is preferably 0.9, more preferably 0.8, particularly preferably 0.7. On the other hand, the lower limit is preferably 0.01, more preferably 0.05, particularly preferably 0.10.
To measure the equivalent circular diameter of the cross section, both ends of the fiber to be measured are fixed and cut under a tension of 0.01 to 0.1 g/mm ² . The cut surface is then enlarged and photographed using an optical microscope. At that time, the scale will also be photographed at the same magnification. After digitizing the image, for example, using the image analysis software "Micro Measure ver. 1.04" by Scala Co., Ltd., trace the outer periphery of the fiber cross section to calculate the cross-sectional area S, and calculate the cross-sectional area S using the following formula. Calculate the circle equivalent diameter of each opening. Calculate the average of the 30 measured values and round to the first decimal place.
Equivalent circle diameter of cross section = 2 x (S/π) ^1/2
The protrusion width ω is also the average of the measured values at 30 points.

The material for the porous fibers in the present invention is not particularly limited, but organic materials are preferably used from the viewpoint of ease of molding and cost, such as polymethyl methacrylate (hereinafter referred to as PMMA), polyacrylonitrile, etc. (hereinafter referred to as PAN), polysulfone, polyether sulfone, polyarylether sulfone, polypropylene, polystyrene, polycarbonate, cellulose, cellulose triacetate, ethylene-vinyl alcohol copolymer, and the like. Among these, it is preferable to include a material that is hydrophobic to some extent and has the property of adsorbing proteins, such as PMMA, PAN, and the like. PMMA and PAN are also typical examples of fibers having a uniform structure in the thickness direction, and are preferable because they are easy to obtain a structure with a homogeneous structure and a sharp pore size distribution. Further, a polymer containing an ester group is preferable because it has excellent biocompatibility and can easily exhibit functions by controlling the terminal group. In particular, PMMA is an amorphous polymer, has excellent moldability and cost, and is also highly transparent, so it is relatively easy to observe the internal state of the fibers, making it easy to evaluate the fouling state. Additionally, the porous fibers may have a negative charge. It has also been reported that containing a negatively charged functional group in at least a portion of the material increases its hydrophilicity and tends to cause fine dispersion (that is, the formation of many fine pores). Examples of negatively charged functional groups include materials with substituents such as sulfo groups, carboxyl groups, phosphoric acid groups, phosphorous acid groups, ester groups, sulfite groups, hyposulfite groups, sulfide groups, phenol groups, and hydroxysilyl groups. can be mentioned. Among these, at least one selected from a sulfo group, a carboxyl group, and an ester group is preferred. Those having a sulfo group include vinylsulfonic acid, acrylsulfonic acid, methacrylsulfonic acid, parastyrenesulfonic acid, 3-methacryloxypropanesulfonic acid, 3-acryloxypropanesulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid. and their sodium salts, potassium salts, ammonium salts, pyridine salts, quinoline salts, and tetramethylammonium salts. The amount of negative charge is preferably 1 μeq or more and 50 μeq or less per gram of dry fiber. The amount of negative charge can be measured using, for example, a titration method.

In the production of porous fibers according to the present invention, the viscosity of the spinning dope is important for producing porous fibers. That is, if the viscosity is too low, the fluidity of the stock solution is high and it is difficult to maintain the desired shape. Therefore, the lower limit of the viscosity of the stock solution is 100 poise or more, more preferably 200 poise or more, still more preferably 400 poise or more, particularly preferably 800 poise or more. On the other hand, if the viscosity is too high, the pressure loss during discharge of the stock solution increases, resulting in decreased discharge stability and difficulty in mixing the stock solution. Therefore, the upper limit of the viscosity of the stock solution at the temperature of the spinneret is 10,000 poise or less, more preferably 5,000 poise or less.

The viscosity is measured according to JIS Z 8803 (2011 edition) using a falling ball method in a constant temperature bath set at the spinning temperature. Specifically, it is determined by filling a viscosity tube with an inner diameter of 40 mm with a spinning stock solution, dropping a steel ball with a diameter of 2 mm (material is SUS316) into the stock solution, and measuring the time required for the ball to fall 200 mm. The temperature during measurement is 92°C.

In order to produce the porous fiber according to the present invention, it is important to control the shape of the ejection opening of the spinneret in addition to the composition of the spinning dope and the dry section. In particular, the porous fibers in the present invention have a very high degree of irregularity. Therefore, with a die that has a shape similar to the cross section of the fiber to be obtained, as seen in the conventional die design concept, the draft in the dry section becomes large due to the large cross-sectional area of the die outlet, which is called draw resonance. Unevenness in fiber diameter and irregularity tends to occur, making spinning difficult. That is, as shown in FIGS. 4 and 5, the shape of the spinneret discharge port preferably has a central circular portion, a slit portion, and a tip circular portion. Further, it is necessary to appropriately design the center circle diameter D, slit width W, slit length L, and tip circle diameter d.

The slit portion is important in determining the degree of irregularity, and by increasing the value L/W obtained by dividing L by W, the degree of irregularity can be improved. Therefore, the lower limit of L/W is preferably 1.9 or more, more preferably 2.8 or more, still more preferably 5.5 or more, particularly preferably 9.5 or more. On the other hand, if L/W is too large, the shape of the protrusions of the fibers becomes elongated and unstable, and adhesion of the protrusions within the single filament is likely to occur. Therefore, the upper limit of L/W is 50 or less, particularly preferably 20 or less.

The tip diameter d is preferably larger than a certain value in order to obtain an irregular cross-sectional shape, and by changing d, it is possible to control the width of the protrusion. If the value of W is too small, problems may occur, such as an increase in pressure loss at the mouthpiece, a greater influence of the balancing effect, and difficulty in processing the mouthpiece itself. Therefore, the lower limit of W is 0.005 mm, more preferably 0.010 mm, and even more preferably 0.030 mm. On the other hand, if it is too large, the cross-sectional area of the discharge section becomes large, the draft in the dry section becomes large, and unevenness in fiber diameter and irregularity, called draw resonance, tends to occur, making spinning difficult. The upper limit of W is 1.00 mm or less, more preferably 0.50 mm or less, still more preferably 0.25 mm or less. The center circle 9 is preferably used to control the cross-sectional shape of the irregular cross-section fiber. That is, by providing the center circle 9, the flow rate at the center of the entire spinneret can be increased, and spinning stability can be further improved.

The porous fibers of the present invention have a wide variety of uses, and can be used in various fields such as medicine, water treatment, and purification. In particular, in medical applications, it is suitably used to remove disease-causing proteins, bacteria, viruses, cells, etc. from blood, plasma, and body fluids. Pathogenic proteins include MMP3 (matrix metalloproteinase 3), cytokines, chemokines, β ₂ -microglobulin (β ₂ -MG), IgG, IgA, IgM, immune complexes, cholesterol, myoglobin, hemoglobin, and the like. In particular, MMP3 is an enzyme associated with pain in joints, etc., and is an important substance to be removed that is directly linked to improving the QOL of patients. However, its molecular weight is 55,000, which is close to 66,000 of the useful substance albumin, which will be described later. In order to selectively remove MMP3, it is important to control the pore size distribution and the surface aperture ratio X as in the present application. In addition, when used in water treatment applications, it is suitably used to remove humic substances, metal corrosives, etc.

If the adsorption performance per volume of the porous fiber is low, it is not preferable as an adsorption material and will not exhibit good adsorption performance even when packed in a column or the like. In order to ensure adsorption performance, it is necessary to increase the number of packed fibers, which leads to an increase in column volume, resulting in increased costs and reduced ease of handling. In particular, when blood is used as the liquid to be treated, the amount of blood taken out of the body increases, which may cause serious side effects such as a drop in blood pressure.Therefore, the adsorption capacity per volume of fiber is When MMP3 is used, it is preferably 1000 μg/cm ³ or more, more preferably 2000 μg/cm ³ or more, even more preferably 4000 μg/cm ³ or more, particularly preferably 6000 μg/cm ³ or more.

The method for measuring the adsorption performance of MMP3 is as follows. First, it is added to fetal bovine serum (manufactured by BioWest) so that the MMP3 concentration is 450 μg/L, and stirred. Further, cut the fibers into bundles of 3 cm in length, place them in a 2 mL tube made by Eppendorf, for example, so that the volume of the fibers is 0.10 ^cm3 , add 1.5 mL of the fetal bovine serum, and use a seesaw shaker. For example, using Wave-SI manufactured by TAITEC, the scale is set to 38, the angle is set to the maximum (one round trip in 1.7 seconds), and the mixture is stirred at 37° C. for 2 hours. To measure the MMP3 concentration C1 (μg/mL) of fetal bovine serum before adding fiber and the MMP3 concentration C2 (μg/mL) after adding fiber and stirring, take samples and store them in a freezer at -20°C or below. . MMP3 concentration is measured by ELISA method, and adsorption performance is calculated from the following formula.
(Formula) MMP3 adsorption performance (μg/cm ³ )=(C1-C2)×1.5/0.10.

Furthermore, using the same test system, the albumin adsorption rate can also be determined. To measure the albumin concentration C3 (g/L) of fetal bovine serum before adding fiber and the albumin concentration C4 (g/L) after adding fiber and stirring, take samples and store them in a freezer at -20°C or below. . The albumin concentration is measured by the BCG method, and the adsorption performance is calculated from the following formula.
(Formula) Albumin adsorption rate (%) = (C3-C4)/C3×100.

The albumin removal rate is preferably low. This is because albumin is an important substance that controls osmotic pressure regulation and substance transport within the body when used for blood purification purposes. The upper limit of the albumin removal rate is preferably 45% or less, more preferably 35% or less, particularly preferably 25% or less.

The porous fibers of the present invention can be used as a purification column by being built into a casing having an inlet and an outlet for the treatment liquid.

As for the shape of the casing, both ends are open ends, and examples thereof include rectangular cylinders such as square cylinders and hexagonal cylinders, and cylindrical bodies, among which cylinders, particularly cylinders with a perfect circular cross section, are preferable. This is because the casing does not have corners, so blood can be prevented from stagnation at the corners. Furthermore, by having both sides open, the flow of the processing liquid is less likely to become turbulent, and pressure loss can be minimized. Moreover, it is preferable that the casing is a device made of plastic, metal, or the like. In the case of plastic, for example, a thermoplastic resin having excellent mechanical strength and thermal stability is used. Specific examples of such thermoplastic resins include polycarbonate resins, polyvinyl alcohol resins, cellulose resins, polyester resins, polyarylate resins, polyimide resins, cyclic polyolefin resins, polysulfone resins, and polyether sulfone resins. Examples include polyolefin-based resins, polyolefin-based resins, polystyrene resins, polyvinyl alcohol-based resins, and mixtures thereof. Among these, polypropylene, polystyrene, polycarbonate, and derivatives thereof are preferred in terms of moldability and radiation resistance required for the casing. In particular, resins with excellent transparency such as polystyrene and polycarbonate are convenient for ensuring safety because they allow you to check the internal state during perfusion of blood, etc., and resins with excellent radiation resistance are useful when irradiating with radioactive materials during sterilization. This is because it is preferable. The resin is manufactured by injection molding using a mold or by cutting the material. Among these, plastics are preferably used from the viewpoints of cost, moldability, weight, blood compatibility, etc.

The purification column has its ends sealed with a member, such as a header or a header cap, which ultimately becomes an inlet/outlet port for the liquid to be treated.

A method for arranging the adsorbent material in the casing includes a method in which the casing has a mesh or a partition at at least one end, and the adsorbent material is partitioned and arranged within the casing by the mesh or partition. Here, "compartment" refers to arranging the adsorbent material within the casing using a mesh or partition, but does not necessarily mean completely fixing it to the mesh or partition. do not have. If the adsorbent material can be confined in a closed space by the casing and the mesh or the partition wall, it will meet the purpose of "compartmenting". On the other hand, it is also possible to physically press and fix the adsorbent material by providing the mesh with protrusions extending in the column axis direction. Further, when the partition wall portion is formed of resin, a method of fixing the adsorption material at the partition wall portion can also be adopted. Both of these are included in the meaning of "divide."
When a partition wall is provided, a through hole that penetrates the partition wall and communicates between the inside and outside of the casing can be provided to serve as an inlet for the liquid to be treated. In addition, the through hole is an opening that penetrates the partition wall in the longitudinal direction of the porous fibers. That is, it is a hole that exists in the partition wall and passes through it, communicating the inside and outside of the casing. Further, when the adsorption material is a hollow fiber, the hollow portion is used as a flow path for the liquid to be treated, and the partition wall portion does not need to be provided with through holes.
When the adsorption material is a solid fiber, a method of arranging a mesh is preferably used. This is because the process is easier than the method of forming partition walls, and the dispersibility of the liquid within the column is also high. Furthermore, for the purpose of further increasing the dispersibility of the liquid to be treated in the column, a part of the mesh may be provided with a mesh having a large pressure loss or a plate called a baffle plate that blocks the flow.
On the other hand, when the adsorption material is a hollow fiber, it is preferable to form a partition part. This is because by forming the partition wall, the opening of each hollow fiber tends to be perpendicular to the flow direction of the liquid to be treated, and the inside of each hollow fiber can be used effectively.

If the casing length of the purification column is too long, it may be difficult to insert the porous fibers into the column, or it may become difficult to handle when actually used as a purification column. Moreover, if it is too short, problems may occur, such as being disadvantageous when forming a partition wall, and lacking in handling when formed into columns. Therefore, the casing length of the purification column is 1 cm or more and 500 cm or less, more preferably 3 cm or more and 50 cm or less. Here, the casing length refers to the length of the cylindrical casing in the axial direction before undergoing processes such as attaching a partition wall or attaching a cap.

The shape of the fibers when incorporated in the column is preferably straight, and it is preferable to insert the straight fibers in parallel to the longitudinal direction of the column case. Straight-shaped porous fibers make it easy to secure a flow path for the liquid to be treated, so it is easy to distribute the liquid to be treated evenly within the column. Furthermore, since the flow path is linear, pressure loss can be reduced, and even when highly viscous blood is used as the liquid to be processed, the risk of coagulation within the casing can be kept to a minimum. Porous fibers can be processed into knitted fabrics, woven fabrics, nonwoven fabrics, etc., and can also be finely chopped into pieces of less than 5 mm. However, since large tension and stress are applied to the fibers during processing and shredding, there are restrictions such as the inability to increase the porosity of the fibers. Furthermore, processing the fibers increases the number of steps and costs. Furthermore, if the liquid to be treated contains a large amount of solutes and has high viscosity, this is not very preferable because it is likely to cause an increase in pressure within the column.

The number of straight fibers inserted into the column is preferably about 1,000 to 500,000. Further, the upper limit of the fiber filling rate in the casing is preferably 70% or less, more preferably 65%, particularly preferably 62% or less. The lower limit of the filling rate is 30% or more, more preferably 45% or more, particularly preferably 52% or more. If the packing rate is too high, the insertion into the case will be poor, while if it is too low, the fibers will tend to become uneven within the case, resulting in uneven flow within the column.

The filling rate is the ratio of the casing volume (Vc) calculated from the cross-sectional area and length of the casing to the fiber volume (Vf) calculated from the fiber cross-sectional area, casing length, and number of fibers, and is calculated as follows. It will be done.
Vc = cross-sectional area of casing body × effective length,
Vf = fiber cross-sectional area x number of fibers x effective length,
(Formula) Vf/Vc×100 (%).
Note that the cross-sectional area of the casing body is the cross-sectional area at the center of the casing if the casing has a taper.

Vc here does not include the volume of members that do not contain fibers, such as members called headers and header caps, which serve as inlet and outlet ports for the liquid to be treated. Further, regarding Vf, when spacer fibers or the like are used to prevent fibers from adhering to each other within the case, the volume thereof is also included. The effective length of the fiber is the length of the casing minus the length of the partition wall, but the upper limit of the effective length of the fiber is that pressure loss increases when the fiber is curved or formed into columns. From the viewpoint of compatibility, etc., the length is preferably 5000 mm or less, more preferably 500 mm or less, particularly preferably 210 mm or less. On the other hand, if it is too short, the amount of fibers to be discarded increases when cutting excess fibers protruding from the column in order to make the length of the fibers uniform, which is undesirable because productivity decreases. Further, there are drawbacks such as difficulty in handling the fiber bundle. Therefore, the lower limit of the effective length of the fiber is preferably 5 mm or more, more preferably 20 mm or more, particularly preferably 30 mm or more. As a method for measuring the effective length of a fiber, in the case of a fiber that has been crimped, such as a crimp, the length of the fiber is measured in a straight state with both ends of the fiber stretched. Specifically, one piece of fiber taken out from the column was fixed with tape or the like and hung vertically, and the other piece was given a weight of about 8 g per cross-sectional area (mm2) of the fiber, so that the fiber became straight. Measure the total length immediately. This measurement is performed on 30 randomly selected fibers in a column, etc., and the average value of the 30 fibers is calculated in mm, and the value is rounded to the first decimal place.

When used as a fiber bundle, it is preferable that the bundle contains a large amount of the porous fibers of the present invention. The proportion of the porous fibers of the present invention in the fiber bundle is 50% or more, more preferably 65% or more, still more preferably 80% or more, particularly preferably 90% or more. The fiber bundle thus obtained can be suitably used as an adsorption material having high adsorption performance.

Such fiber bundles and purification columns incorporating them have a wide variety of uses, and can be used for water treatment, purification, medical treatment, and the like. Among these, in the case of medical applications, processing methods include direct perfusion of whole blood and methods of separating plasma or serum from blood and then passing the plasma or serum through a column. It can also be used in methods.

Furthermore, when used as a medical device, it is preferable to incorporate it into an extracorporeal circulation circuit and perform online adsorption and removal from the viewpoints of one-time throughput and ease of operation. In this case, the purification column of the invention is used alone. Although it is conceivable to use it in combination with other medical devices such as an artificial kidney, it is not preferable because there is a possibility that the performance of the purification column of the present invention will be degraded by eluates from other devices.

Specific manufacturing examples of the porous fiber and the purification column incorporating the same according to the present invention will be described below.

<Manufacture of porous fiber>
Prepare a spinning stock solution in which the polymer is dissolved in a solvent. At this time, the lower the concentration of the stock solution (concentration of the substance in the stock solution excluding the solvent), the larger the pore diameter of the fiber can be, so by appropriately setting the concentration of the stock solution, the pore diameter and pore volume can be controlled. Is possible. In addition, the pore diameter and pore volume can be controlled by using a polymer having a negatively charged group. From this viewpoint, the concentration of the stock solution in the present invention is preferably 30% by weight or less, more preferably 27% by weight or less, still more preferably 24% by weight or less. Further, when using a polymer having, for example, methacrylsulfonic acid/parastyrene sulfonic acid as a negatively charged group, the proportion of the polymer having methacrylsulfonic acid/parastyrene sulfonic acid in the total polymer is preferably 10 mol % or less. The fibers are prepared using a nozzle with a discharge port of irregular cross section as shown in Fig. 5 (D = 0.20 mm, W = 0.10 mm, L = 1.0 mm, d = 0.25 mm), and the undiluted solution is spread over a certain distance. It is obtained by passing it through a dry air section and then discharging it into a coagulation bath consisting of a poor solvent such as water or a non-solvent. From the above viewpoint, the lower limit of the fiber passage (residence) time in the dry section is as described above. Further, if the temperature of the discharged fibers decreases in the dry section and the structure is quickly fixed, such as gelling or coagulating, cooling air can be blown in the dry section to promote gelation. Further, as described above, by using both the strong wind section and the weak wind section, it is possible to reduce the unevenness of openings on the fiber surface. Thereafter, the discharged spinning dope is coagulated in a coagulation bath. The coagulation bath usually consists of a coagulant such as water or alcohol, or a mixture with a solvent that constitutes the spinning dope. Water is usually used.

Next, the fibers are washed to remove the solvent adhering to the coagulated fibers. The means for washing the fibers is not particularly limited, but a method of passing the fibers through a bath filled with water in multiple stages (referred to as a washing bath) is preferably used. The temperature of the water in the washing bath may be determined depending on the properties of the polymer constituting the fibers. For example, in the case of fibers containing PMMA, a temperature of 30 to 50°C is used.

Further, in order to maintain the pore size of the pores after the water washing bath, a step of adding a moisturizing component to the fibers may be included. The term "moisturizing component" as used herein refers to a component capable of maintaining the humidity of the fibers or a component capable of preventing a decrease in the humidity of the fibers in the air. Representative examples of moisturizing ingredients include glycerin and its aqueous solution.

After washing with water and applying moisturizing ingredients, in order to increase the dimensional stability of highly shrinkable fibers, it is also possible to pass through a bath (referred to as a heat treatment bath) filled with a heated aqueous solution of moisturizing ingredients. The heat treatment bath is filled with a heated aqueous solution of moisturizing ingredients, and when the fibers pass through this heat treatment bath, they are subjected to thermal action and shrink, making it difficult for them to shrink in subsequent steps and improving the fiber structure. It can be stabilized. The heat treatment temperature at this time varies depending on the fiber material, but in the case of fibers containing PMMA, it is preferably 50°C or higher, more preferably 80°C or higher. Further, the temperature is preferably set to 95°C or lower, and more preferably 88°C or lower.

<Preparation of purification column>
An example of a means for making a purification column using the obtained fibers is as follows. First, a plurality of fibers are cut to the required length, and after the required number of fibers are bundled, they are placed into a plastic casing that will become the cylindrical part of the purification column so that the fiber bundle is straight in the axial direction of the case. The number of columns is determined depending on the purpose of the purification column, but is preferably about 500 to 250,000 columns. Thereafter, both ends of the fibers are cut with a cutter or the like so that the fibers fit within the casing, and mesh filters cut to the same diameter as the inner diameter are attached to the inlets of the liquid to be treated on both end faces of the column. Further, instead of the mesh filter, a partition made of resin may be provided. Finally, a purification column can be obtained by attaching inlet and outlet ports for the liquid to be treated, called header caps, to both ends of the casing.

Furthermore, when used as a medical tool, ie, a medical adsorption column, it is preferable to sterilize or sterilize the product. Examples of sterilization and sterilization methods include various sterilization and sterilization methods, such as high-pressure steam sterilization, gamma ray sterilization, electron beam sterilization, ethylene oxide gas sterilization, chemical sterilization, ultraviolet sterilization, and formalin sterilization. Among these methods, gamma ray sterilization, electron beam sterilization, high pressure steam sterilization, and ethylene oxide gas sterilization are preferable because they have less influence on sterilization efficiency and materials.

[Example 1]
<Preparation of porous fiber>
31.7 parts by mass of syn-PMMA with a mass average molecular weight of 400,000, 31.7 parts by mass of syn-PMMA with a mass average molecular weight of 1.4 million, and 16.7 parts by mass of iso-PMMA with a mass average molecular weight of 500,000. , 20 parts by mass of a PMMA copolymer with a molecular weight of 300,000 containing 1.5 mol % of sodium p-styrene sulfonate was mixed with 376 parts by mass of dimethyl sulfoxide, and the mixture was stirred at 110° C. for 8 hours to prepare a spinning stock solution. The resulting spinning stock solution had a viscosity of 1080 poise at 92°C. The obtained spinning dope was discharged into the air at a rate of 0.7 g/min from a nozzle kept at 92°C and having the shape shown in FIG. 3 and a discharge port with the dimensions shown in Table 1. After running for 500 mm, the fiber was introduced into a coagulation bath and passed through the bath to obtain a solid fiber. In the dry section, cooling was performed using cooling air for the purpose of suppressing a decrease in the fiber surface aperture ratio due to aggregation of the supporting components. Specifically, the first 10% of the 1.8 second residence time in the drying section is a strong wind section, and the cooling air speed is set at 3.5 m/min in order to quickly increase the viscosity of the stock solution and reduce the mobility of PMMA. did. Further, the 40% following the strong wind section was a weak wind section, and the cooling air speed was set to 0.5 m/min in order to stably and evenly cool the entire circumference of the fiber. The ratio of cooling air speed between the strong wind section and the weak wind section was 6:1, and there were no thread breaks. Further, the temperature of the cooling air was set to 1° C. in order to maximize cooling efficiency. Water was used in the coagulation bath, and the water temperature (coagulation bath temperature) was 42°C. After washing each fiber with water, it was introduced into a bath consisting of an aqueous solution containing 60% by weight of glycerin as a humectant, then passed through a heat treatment bath at a temperature of 85°C to remove excess glycerin, and then rolled at 16 m/min. I took it.
Regarding the obtained fibers, the degree of irregularity, circle equivalent diameter, average pore radius, pore volume, pore size distribution, pore shape index, convex opening ratio, recess opening ratio, opening ratio X, MMP3 adsorption performance, albumin adsorption The ratio was measured using the method described above. The results are shown in Tables 1 and 2.

[Example 2]
Fibers were produced under the same conditions as in Example 1, except that a die having the shape shown in FIG. 4 and a discharge port having the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Example 3]
Fibers were produced under the same conditions as in Example 1, except that a die having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Example 4]
Fibers were produced under the same conditions as in Example 1, except that a die having the shape shown in FIG. 6 and the ejection opening with the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Example 5]
Fibers were produced under the same conditions as in Example 1, except that a die having the shape shown in FIG. 7 and a discharge port having the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Example 6]
Fibers were produced under the same conditions as in Example 1, except that a die having the shape shown in FIG. 8 and a discharge port having the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Example 7]
A cap having the shape shown in FIG. 8 and a discharge port having the dimensions shown in Table 1 was used, except that there was a circular gas inlet with a diameter of 0.10 in the center circle to form the hollow part. The fiber was produced under the same conditions as in Example 1 except for the above conditions. Note that nitrogen was flowed as the injection gas. The results are shown in Tables 1 and 2.

[Example 8]
A mouthpiece having the shape shown in FIG. 5 and the dimensions shown in Table 1 was used, except that it had a circular gas injection tube with a diameter of 0.10 in the center circle to form the hollow part. The fiber was produced under the same conditions as in Example 1 except for the above conditions. Note that nitrogen was flowed as the injection gas. The results are shown in Tables 1 and 2.

[Example 9]
A nozzle having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. Fibers were produced under the same conditions as in Example 1, except that the cooling air speed in the weak wind section was 1.0 m/s. The results are shown in Tables 1 and 2.

[Example 10]
A nozzle having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. Fibers were produced under the same conditions as in Example 1, except that the cooling air speed in the strong wind section was 5.5 m/s. The results are shown in Tables 1 and 2.

[Example 11]
A nozzle having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. Fibers were produced under the same conditions as in Example 1, except that the proportion of the strong wind portion was 5% and the proportion of the weak wind portion was 40% as the cooling air. The results are shown in Tables 1 and 2.

[Example 12]
A nozzle having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. Fibers were produced under the same conditions as in Example 1, except that the proportion of the strong wind portion was 20% and the proportion of the weak wind portion was 5% as the cooling air. The results are shown in Tables 1 and 2.

[Comparative example 1]
A nozzle having the shape shown in FIG. 3 and a discharge port having the dimensions shown in Table 1 was used. Fibers were produced under the same conditions as in Example 1, except that the cooling air was 20% strong and 20% weak. The results are shown in Tables 1 and 2.

[Comparative example 2]
Fibers were produced under the same conditions as in Comparative Example 1, except that a die having the shape shown in FIG. 4 and a discharge port having the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Comparative example 3]
Fibers were produced under the same conditions as in Comparative Example 1, except that a die having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Comparative example 4]
Fibers were produced under the same conditions as in Comparative Example 1, except that a die having the shape shown in FIG. 6 and a discharge port having the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Comparative example 5]
Fibers were produced under the same conditions as in Comparative Example 1, except that a die having the shape shown in FIG. 7 and the ejection opening with the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Comparative example 6]
Fibers were produced under the same conditions as in Comparative Example 1, except that a die having the shape shown in FIG. 8 and a discharge port having the dimensions shown in Table 1 was used. The results are shown in Tables 1 and 2.

[Comparative Example 7]
A cap having the shape shown in FIG. 8 and having a circular gas injection tube of φ0.10 in the center circle and a discharge port having the dimensions shown in Table 1 was used to form the hollow part. A fiber was produced under the same conditions as in Comparative Example 1 except for the above. Note that nitrogen was flowed as the injection gas. The results are shown in Tables 1 and 2.

[Comparative example 8]
A fiber with a circular cross section was produced under the same conditions as in Example 1 except that a die with a circular discharge port of φ0.3 was used. The results are shown in Tables 1 and 2.

[Comparative Example 9]
A nozzle having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. Fibers were produced under the same conditions as in Comparative Example 1, except that the proportion of the strong wind portion was 10% as the cooling air. The results are shown in Tables 1 and 2.

[Comparative Example 10]
A nozzle having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. Fibers were produced under the same conditions as in Comparative Example 1, except that the cooling speed in the strong wind section was 5.5 m/min. The results are shown in Tables 1 and 2.

[Comparative Example 11]
A nozzle having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. An attempt was made to produce fibers under the same conditions as in Comparative Example 1, except that the proportion of the strong wind portion was 50% as the cooling air, but fibers could not be obtained due to thread breakage.

[Comparative example 12]
A mouthpiece having the shape shown in FIG. 8 and the dimensions shown in Table 1 was used, except that it had a circular gas injection tube with a diameter of 0.10 in the center circle to form the hollow part. The fiber was produced under the same conditions as in Example 1 except for the above conditions. Note that nitrogen was flowed as the injection gas. The results are shown in Tables 1 and 2.

[Comparative Example 13]
A double tube cap was used to form the hollow part, the inner diameter was circular with a diameter of 0.10 mm, the gas was injected in a circular shape, and the outer slit part serving as the resin discharge port had an outer diameter of a circular diameter of 0.25 mm and an inner diameter of a circular diameter of 0.20 mm. The fiber was produced under the same conditions as in Example 1 except for the above conditions. Note that nitrogen was flowed as the injection gas. The results are shown in Tables 1 and 2.

[Comparative example 14]
A nozzle having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. Fibers were produced under the same conditions as in Example 1, except that the cooling air speed in the weak wind section was 0.1 m/s. The results are shown in Tables 1 and 2.

[Comparative Example 15]
A nozzle having the shape shown in FIG. 5 and a discharge port having the dimensions shown in Table 1 was used. Fiber production was attempted under the same conditions as in Example 1, except that the cooling air speed in the strong wind section was 30 m/s and the cooling speed in the weak wind section was 4.3 m/s, but fiber breakage occurred. No fibers were obtained.

[Comparative Example 16]
High-density polyethylene was melt-spun using a spindle with a circular discharge port of φ0.3 at a spindle temperature of 150 to 190° C., a polyethylene discharge rate of 20 g/min, and a winding speed of 500 m/min or less. The obtained polyethylene thread was cold-stretched to 2 times at 60° C., then hot-stretched to 2 times at 130° C., and then stretched and split to obtain circular porous solid fibers.
The results are shown in Tables 1 and 2.

The following points can be seen by comparing the Examples and Comparative Examples.
In Examples 1 to 7 and Comparative Examples 1 to 7, it can be seen that the influence on the aperture ratio X due to the difference in cooling air conditions is understood. The aperture ratio X was low at 0.4 to 5.5 under the conditions in which both the strong wind section and the weak wind section were used in the example, but it was high at 6.1 to 9.7 in the comparative example, indicating that the aperture unevenness was large. Recognize. Furthermore, the MMP3 adsorption performance also tended to be somewhat low.
In Examples 1 to 6 and Comparative Example 8, the influence of changing the number of protrusions and degree of irregularity can be understood. Since the circular fibers of Comparative Example 8 had the smallest surface area per volume, they tended to have low MMP3 adsorption performance.
Examples 3, 9 to 12 and Comparative Examples 3, 9 to 11, 14, and 15 are the results of studies regarding cooling air conditions. In Comparative Example 9, the weak wind section of Example 3 was eliminated, but the aperture ratio tended to be low, and the MMP3 adsorption performance also tended to be low. Furthermore, in Examples 3, 9, and 10 and Comparative Example 14, the ratio of the cooling air speed in the strong wind section to the cooling air speed in the weak wind section was changed from 3.5:1 to 35:1. At conditions of .5:1 to 18:1, fibers with low X and good MMP3 adsorption performance were obtained, but under the condition of 35:1, X was 6.1, which resulted in large opening unevenness and poor MMP3 adsorption performance. In Comparative Example 10, the cooling rate in the strong wind portion was increased compared to Comparative Example 3, but the aperture ratio X was high. In Comparative Example 11, the conditions were such that the proportion of the strong wind portion was increased compared to Comparative Example 3, but yarn breakage occurred frequently and fibers could not be obtained. In Comparative Example 15, the cooling rate in both the strong wind section and the cold wind section was increased compared to Example 3, but thread breakage occurred frequently and fibers could not be obtained. In Examples 3, 11, and 12, the proportions of strong wind portions and weak wind portions are changed. In the range where the proportion of the strong wind part was 5 to 20% and the proportion of the weak wind part was 5 to 40%, X was low and the MMP3 adsorption performance was good. Examples 7 and 8 and Comparative Examples 12 and 13 are conditions in which the degree of irregularity of the hollow fibers and the number of protrusions are changed. As described above, the MMP3 adsorption performance tended to decrease as the degree of irregularity and the number of protrusions decreased. Example 7 and Comparative Example 12 are the results when the number of protrusions is constant and the degree of irregularity is changed for hollow fibers. Particularly in the case of hollow fibers, when the degree of irregularity was less than 1.35, X increased significantly and uneven opening was noticeable. This mechanism is not clear, but in the case of hollow fibers, the protrusions are closer to the outer periphery and the height difference between the concave and convex parts is small, so it is difficult for the fibers to rotate when exposed to cold air in the dry section. It was thought that this may occur because it is difficult to cool the entire circumference of the fibers evenly. Comparative Example 12 also had a high albumin adsorption rate, and it was thought that pinhole-like pores were formed on the surface because cold air was blown concentrated on a portion of the fiber. These results show that fibers with a controlled aperture ratio X can only be obtained by selectively using the strong wind section and the weak wind section.

Moreover, Comparative Example 16 is a fiber created by stretching and splitting a melt-spun yarn. It can be seen that the fibers produced by this method have a high pore size distribution and a high pore shape index. When compared with Comparative Example 8, which has a low pore size distribution and a low pore shape index, it can be seen that the MMP3 removal performance is low and the albumin removal rate is high, indicating that fibers with such properties have poor selectivity for adsorption targets.
Note that in Tables 1 and 2, cells marked with "-" or "/" indicate that there is no data.

1 Circumscribed circle 2 Inscribed circle 3 Diameter Do of the circumscribed circle
4 Diameter Di of the inscribed circle
5 Concentric circles passing through the points that divide the radius line segment into 5 equal lengths 6 Center area 7 Area near the outer surface 8 Center of the inscribed circle 9 Tip of the protrusion 10 Connect the center of the inscribed circle and the tip of the protrusion Point 11 where the connecting straight line intersects the inscribed circle Protrusion width ω
12 Center circle part 13 Slit part width W
14 Slit length L
15 Tip circular part

Claims (15)

A porous fiber that has pores inside the fiber and 2 to 8 protrusions on the outer periphery of the fiber , and satisfies the following requirements (A) to (D).
(A) The degree of pore size distribution of the pores is 1.0 or more and 1.6 or less (B) In the cross section, where the diameter of the inscribed circle is Di and the diameter of the circumscribed circle is Do, the degree of irregularity Do/ Di is 1.35 or more and 3.50 or less
(C) The pore volume of the pores is 0.20 cm ³ /g or more and 2.9 cm ³ /g or less
(D) The aperture ratio ratio X expressed by the following formula is 0.40 or more and 6.0 or less (Formula) Aperture ratio ratio X = Surface aperture ratio of convex parts/Surface aperture ratio of concave parts
(E) The center of the circumscribed circle and the center of the inscribed circle in the cross section are the same The porous fiber according to claim 1 , wherein the protrusions are continuous in the longitudinal direction of the outer peripheral portion. The porous fiber according to claim 1 or 2 , which is a monofilament. The porous fiber according to any one of claims 1 to 3 , which is a solid fiber. The porous fiber according to any one of claims 1 to 3 , which is a hollow fiber. The porous fiber according to any one of claims 1 to 5 , wherein the pores have an average pore radius of 0.5 nm or more and 90 nm or less. The porous fiber according to any one of claims 1 to 6 , which has a three-dimensional network structure and a homogeneous pore structure in a cross-sectional direction. The porous fiber according to any one of claims 1 to 7 , comprising an ester group-containing polymer. An adsorption material used as a fiber bundle containing 50% or more of the porous fiber according to any one of claims 1 to 8 . The adsorption material according to claim 9 , having a matrix metalloproteinase-3 (MMP3) adsorption performance expressed by the following formula of 1000 μg/cm ³ or more.
(Formula) MMP3 adsorption performance (μg/cm ³ )=(C1-C2)×1.5/0.10
(Here, C1 is the MMP3 concentration of fetal bovine serum before adding fiber, and C2 is the MMP3 concentration of fetal bovine serum after adding fiber and stirring.) The adsorption material according to claim 9 or 10 , wherein the albumin adsorption rate expressed by the following formula is 45% or less.
(Formula) Albumin adsorption rate (%) = (C3-C4)/C3×100
(Here, C1 is the albumin concentration of fetal bovine serum before adding fiber, and C2 is the albumin concentration of fetal bovine serum after adding fiber and stirring.) It has a casing, an inlet port and an outlet port for the liquid to be treated,
The adsorbent material according to any one of claims 9 to 11 is arranged in a straight shape in the axial direction of the casing,
A purification column, wherein an inlet port and an outlet port for the liquid to be treated are respectively attached to both ends of the casing. The purification column according to claim 12 , wherein the casing has a mesh at at least one end, and the adsorption material is partitioned by the mesh. The purification column according to claim 12 , wherein the casing has a partition at at least one end, and the adsorption material is partitioned by the partition. The purification column according to any one of claims 12 to 14 , which is for medical use.

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