JPS62184108A - Polymeric porous hollow fiber - Google Patents

Abstract

PURPOSE:To provide a hollow fiber having innumerable pores having specific diameter and extending from the inner wall face to the outer wall face of the fiber and exhibiting excellent performance in filtration or separation, etc., of ions, low-molecular substances, minute particles, etc., in a liquid phase. CONSTITUTION:The objective hollow fiber contains innumerable pores having an average pore diameter of 0.02-10mum and extending from the inner wall face to the outer wall face of the hollow fiber. The opening ratio of the pore in the wall surface is >=10% (preferably 40-80%). A part having smallest average pore diameter, a part having larger pore diameter and a part having smallest pore diameter are distributed along the thickness of the wall in the order. The hollow fiber can be produced e.g. by extruding a homogeneous solution of cuprammonium cellulose having an average molecular weight of 5X10<4>-3X10<5> through a ring nozzle while introducing a coagulant liquid into the extruded filament and introducing the obtained filament into a coagulation bath. A mixture of acetone, ammonia and water is used as the coagulant liquid and coagulation bath to induce a microscopic phase separation in the extruded fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a porous polymer hollow fiber comprising numerous intramembrane through-holes. More specifically, by imparting a new structure to the through-holes in the membrane, it is possible to achieve excellent performance in terms of rejection rate, etc. when passing through and separating substances such as ions in the liquid phase, low-molecular substances, and microparticles. The present invention relates to a porous polymer hollow fiber having the following properties.

[Conventional technology]

Membrane separation using hollow fibers is known as a means for separating substances such as ions, low-molecular substances, and microparticles in a liquid phase from a dispersion thereof. For example, ■concentration at low temperatures,
Fields that require purification and recovery (food, biochemical industry fields) ■ Fields that require sterility and dust-free conditions (pharmaceutical and therapeutic institutions, electronic industry) ■ Concentration and recovery of trace amounts of expensive substances (nuclear power, heavy metal fields) ), ■ Special small quantity separation field (pharmaceutical field),
■Hollow fibers are used in energy-intensive separation fields (alternative to distillation).

Conventionally, as a hollow fiber for separation, the entire cross section and longitudinal section made of cellulose are at most 200X (0.02
Hollow fibers for artificial kidneys having microscopic pores of less than micrometers are known (Japanese Patent Application Laid-open No. 134920/1983). Furthermore, hollow fibers made of polyacrylonitrile, cellulose acetate, polyethylene, polypropylene, polysulfone, polyimide, etc., which are used for ultrafiltration or precision f, are known.

[Problem that the invention seeks to solve]

However, these hollow fibers are either in the inner or outer layer.

Alternatively, the in-plane average pore diameter of both is less than 0.02 μm, or there is no plane parallel to the outer wall surface of the wall layer where the in-plane average pore diameter is extremely small, or even if it exists, there is only one plane. When such hollow fibers are used to filter ions, low-molecular substances, and microparticles in the liquid phase, there is a problem that the rejection rate is insufficient. Furthermore, if hollow fibers with a small average pore diameter are used in order to obtain a sufficient rejection rate, there is a drawback that the flow rate becomes low.

The object of the present invention is to overcome the drawbacks of the above-mentioned hollow fibers for separation,
Filtration of ions, low molecular substances, microparticles, etc. in the liquid phase,
The object of the present invention is to provide a hollow fiber that exhibits excellent performance when used in separation.

[Means for solving problems]

An object of the present invention is to calculate the pore diameter in a plane perpendicular to the membrane thickness direction from the inner wall surface to the outer wall surface of the hollow fiber in terms of the in-plane average pore diameter in a polymer porous hollow fiber comprising numerous through-holes in the membrane. When expressed, the in-plane average pore diameter at the inlet and outlet of the membrane through-hole is in the range of 0.02 μm to 10 μm, and the in-plane average pore diameter is an extremely small portion, a portion larger than the extremely small portion, and an extremely small portion. At least one set of structures arranged in the order of parts exists in the membrane thickness direction of the hollow fiber, and further, the in-plane porosity in all planes perpendicular to the membrane thickness direction of the hollow fiber is 10 or more. This is achieved by a polymeric porous hollow fiber characterized by:

By using the polymer porous hollow fiber according to the present invention having the above-mentioned structure, it is possible to increase the rejection rate of substances and to increase the filtration rate compared to conventionally known hollow fibers. On the other hand, in the case of conventional porous hollow fibers that do not have two or more extremely small portions in terms of in-plane average pore diameter, the permeation rate must be reduced in order to achieve a rejection rate of 99.994 or higher. do not have. In addition, in the above structure, the in-plane average pore diameter of the part larger than the minimum part is 1 of the in-plane average pore diameter of the minimum part.
It is preferable that it is 0 times or less. If it exceeds 10 times, dead space will be created and recovery of R liquid will be poor.

Moreover, it is preferable that the average porosity is 40 or more, since the filtration rate is greatly increased and the amount of throughput is also increased. However, when the average porosity is 8"0% or more, the mechanical properties of the hollow fibers are significantly deteriorated, and the frequency of pinholes increases. Therefore, if the average porosity is 40% or less and less than 80%, It is more preferable.

In addition, in a plane including the membrane thickness direction of the hollow fiber in a region in which the in-plane average pore diameter is arranged in the order of the smallest part, the part larger than the smallest part, and the smallest part in the plane perpendicular to the film thickness direction. Preferably, the shape is substantially circular or elliptical. By providing through-holes in the membrane having such a shape, excellent mechanical strength can be imparted to the porous hollow fibers.

Polymers or copolymers such as polyolefins, polysulfones, polyvinyl chloride, polyamides, cellulose and cellulose derivatives, and polyacrylonitrile can be used as the polymeric substances for the porous hollow fibers of the present invention. In particular, from the hydrophilic aspect of porous hollow fibers, the average molecular weight of fasxtOB
It is preferable to use the above copper ammonium cellulose. If this type of porous hollow fiber is used, pretreatment such as wetting treatment of the hollow fiber can be made unnecessary when processing an aqueous solution such as separation and concentration of particles dispersed in water. Furthermore, regenerated cellulose hollow fibers made from cellulose spring conductor have the property of being brittle in a dry state, but as the molecular weight increases, the strength of the hollow fibers increases and brittleness is improved. If the brittleness is improved, handling of the hollow fiber becomes easier and the breakage rate of the hollow fiber decreases. For this purpose, when copper ammonium cellulose is used, its average molecular weight is preferably 5 x 10 or more. Note that the influence of the average molecular weight on the film properties tends to become saturated as the average molecular weight increases. Therefore, it is preferable to use copper ammonium cellulose having an average molecular weight of 5 x 10' or more and 5 x 105 or less in terms of practical ease of handling. The preferred range is 5.5X10~
It is 3×1O. Porous hollow fibers made of ammonium cellulose having an average molecular weight of 5×10' or more have sufficient mechanical properties even in a dry state without a swelling agent such as glycerin.

Next, a method for producing porous hollow fibers according to the present invention will be explained.

Microphase separation occurs during the formation process of porous hollow fibers using the microphase separation method (described later).During this phase separation, if the dilute polymer produced is dispersed in the form of particles, porous hollow fibers The pore structure formed in this case has a structure consisting of a series of spheres or ellipsoids. The porous hollow fibers formed in this manner have excellent mechanical strength.

Therefore, as a method to obtain the maximum in-plane average pore diameter between two extremely small parts, it is possible to adopt conditions that create a microphase separation state in which the diluted polymer is dispersed in the form of particles during the formation of the hollow fiber. good. However, this has not been achieved with conventional film forming methods, and even a working hypothesis for forming such spherical or ellipsoidal holes has not been established. The present inventors discovered a method for producing the present invention through research on the relationship between phase separation conditions and pore shape, and as a result,
The present invention has been achieved by expressing the unique effects of the present invention.

That is, in the process of making a homogeneous solution of a polymer/solvent into a spinning dope, extruding it from an annular spinning opening, coagulating it, and washing it with water, the spinning dope is transferred from an outer annular spinning opening to a central spinning opening. A coagulating liquid (hereinafter abbreviated as "hollow agent") is discharged from the spinning dope, and the discharged hollow fibrous material is immersed in a liquid (coagulant) that has coagulability for the spinning stock solution. Before solidification of the fibrous material, microphase separation is induced from the inside and outside of the hollow fibrous material. Here, microphase separation means a state in which a concentrated phase or a dilute phase of a polymer is dispersed and stabilized as particles having a diameter of 0.01 to several μm in a solution. Specifically, when making regenerated cellulose porous hollow fibers, for example, cellulose copper ammonia solution is used as a spinning stock solution, acetone/ammonia/water mixture is used as a coagulation bath and hollowing agent, and the process is performed by spinning, coagulating, and then regenerating with sulfuric acid, etc. It can be obtained by However, in the process of forming porous hollow fibers by the microphase separation method, the composition of the spinning dope is such that the polymer concentration increases sequentially from the outside and inside of the hollow fibers toward the inside of the membrane. It is necessary to select the agent and coagulant composition and spinning conditions.

During the formation of the porous hollow fibers of the present invention, the composition of the polymer/solvent system becomes the critical composition at at least two locations in the film thickness direction at the temperature and pressure during the formation of the hollow fibers, and as a result, the final formation It is believed that the porous hollow fiber of the present invention has a novel structure having at least two minimum in-plane average pore diameters.

Next, before describing examples of the polymer porous hollow fiber according to the present invention, definitions of various technical terms (physical property values) used in this specification and methods for measuring them will be shown below.

◎ Minimum in-plane average pore diameter, maximum in-plane average pore diameter, and in-plane porosity Replace the moisture inside the hollow fibers in a wet state with acetone,
After that, the hollow fibers obtained by air drying were embedded in acrylic resin, and then the thickness was measured from the outer wall surface along the wall thickness direction using a glass knife attached to an ultramicrotome (Model 18800 Ultratome manufactured by LKB (Sweden)). Samples of approximately 1 μm in size are sequentially cut out. After deembedding the sample sections in chloroform, electron micrographs are taken of each section. The hole radius is (1) to (r+
The number of holes present in dr) is denoted as N(r)dr. 3
The second and fourth order average pore radii (r3 and r4, respectively) are defined by the following equations.

The average pore diameter is 2' 8 cm and is calculated from equations (1) and (2). From the electron micrograph of each section, the average pore diameter is calculated from equation (2). As shown in the figure, the minimum average pore diameter and the maximum average pore diameter are determined based on the distance from the inner wall surface to the average pore diameter in the plane.

Further, the in-plane porosity is defined by the following formula.

The pore size distribution function N(r) is determined from a II electron micrograph of a sample section as follows. That is, a scanning electron micrograph of a portion where the pore size distribution is to be evaluated is enlarged and printed to an appropriate size, for example, 20 m x 20 cm, and 40 test lines (straight lines) are drawn at equal intervals on the obtained photograph. Each straight line crosses a number of holes. The length of the straight line existing in the hole when it crosses the hole is measured, and the frequency distribution function of this length is used to calculate, for example, stereology (for example, Quantitative Morphology #1 by Norio Suwa, published by Iwanami Shoten, pp. 185-272). Find N (r) using the method described in (see).

◎ Average porosity The moisture inside the hollow fibers in a wet state is replaced with acetone,
Thereafter, the hollow fibers obtained by air drying are dried in a vacuum to reduce the moisture content to 0.5% or less. The inner diameter of the hollow fiber after drying is R1
(cln) r The outer diameter is Ro (ctn), the length of the hollow fiber is 1 cm + the weight is w (i), and ρ is the density of the polymer constituting the porous polymer hollow fiber, then the average porosity is It is given by the following formula.

◎ Calculate the average molecular weight fl (viscosity average molecular weight) Mv by substituting the ``intrinsic viscosity number [η] CILt/I') measured in a copper ammonia solution (20°C) into the following formula (5). do.

Mv= (η)

Example 1 Cellulose linter (viscosity average molecular weight 2.43X105
6.) in a copper ammonia solution with an ammonia concentration of 6.8% by weight and a copper concentration of 3.1% by weight, which was prepared by a known method.
It was dissolved at 0% by weight and subjected to excessive defoaming to obtain a spinning stock solution. The spinning dope is transferred to the outer spinning port of the annular spinneret (outer diameter 2W).
φ) from 2.0 m and 41 minutes, while the ratio of water to acetone as a hollow agent was 67.3% by weight.

A mixed solution with a water to ammonia ratio of 0.9 weight and 1% (hereinafter referred to as hollow agent) is placed at the central spinning spout (outer diameter 0.6 mφ).
Then, in 1 minute at 5.0 rttt, the water was directly discharged into a mixed solution in which the ratio of water to acetone was 67.3% by weight and the ratio of water to ammonia was 0.9% by weight, and 10 m
It was wound up at a speed of /min. In addition, the transparent blue-like fibrous material immediately after discharge gradually turns white, causing microphase separation,
Coagulation continued and the fiber shape was maintained. Thereafter, it was regenerated with a 2% by weight aqueous sulfuric acid solution, and then washed with water and dried.

The average in-plane pore diameter of each part of the through-holes in the membrane of the hollow fiber in this example is as follows: When viewed in the direction from the inner wall surface to the outer wall surface, the in-plane average pore diameter at the entrance of the inner wall surface is Dl, and the in-plane average pore diameter of the smallest portion is Dl. The in-plane average pore diameter is D
x, hThe in-plane average pore diameter of the part larger than the small part is 03
, the in-plane average pore diameter of the smallest portion is D4s, and the in-plane average pore diameter at the outlet of the outer wall surface is D, then DI is 1.268 μm,
DB is 1.14 μm, and D! /D2 is 1.36, D
3/D4 is 1.31. In addition, the minimum value of the in-plane porosity in all planes perpendicular to the wall thickness direction of the hollow fiber in this example is 24.6%, and the average porosity in the entire wall thickness direction is 56.4'%. there were. A colloidal silica particle filtration experiment was conducted using this hollow fiber. The filtration experiment is
The colloidal silica (Ca
The particle size of taloid S I 80 P) is 700
It was 1-900X. The rejection rate of colloidal silica was calculated from the concentration ratio of the stock solution and r solution by atomic absorption spectrometry (quantification of Si). The results are shown in Table 1. Further, as a result of spraying the P solution onto the mesh and checking the presence or absence of particles using an electron microscope, no colloidal silica particles were observed.

A scanning electron micrograph in the film thickness direction is shown in FIG. (
1) is the outer wall part, (2) is the part of x = 16 pm (minimum part), (3) is the part of x = 1014 m (maximum part), (4
) is a portion of x==4 μm (minimum portion), and (5) is an inner wall portion. Here, X indicates the distance from the inner wall in the film thickness direction.

Example 2゜7.5wt of cellulose linter (average molecular weight: 2.43 x 105) was added to the same copper ammonia solution as in Example 1.
% concentration, filtered and defoamed to obtain a spinning stock solution. From this spinning stock solution, regenerated cellulose hollow fibers were obtained under the same conditions as in Example 1. Dl of this hollow fiber is 0
．． 514 μm, DB was 0.51 μm. 03
/D2 was 1.4, and D3/D4 was 1.4.

In addition, the minimum value of in-plane porosity in all planes perpendicular to the membrane thickness direction of the hollow fiber in this example is 20.8%, and the average porosity in the entire wall thickness direction is 48.4%. There was. A filtration experiment similar to that in Example 1 was conducted using this hollow fiber. The particle size of colloidal silica (Catalyst Chemical Industry Co., Ltd. “! Rcatalo Umbrella 1d SI 45 P) is 350X to 550X
Met. The results of the filtration experiments are shown in Table 1. Furthermore, a scanning electron micrograph taken in the wall thickness direction is shown in FIG. (1) is the outer wall part, (2) is the part where Fix = 15.1 μm (minimum part), (3) is the part where x = 10.3 μm (maximum part)
, (4) is the part where x = 5.4 μm (minimum part), (5)
is the inner wall. Here, X indicates the distance from the inner wall in the film thickness direction.

The comparative spinning stock solution was cellulose diacetate with an acetylation degree of 54.2% and a polymerization degree of 190, a mixed solvent of acetone and methanol in a ratio of 5:1, calcium chloride as a metal compound, and cyclohexanol as an additive solvent. Hollow fibers were obtained under the spinning dope composition and spinning conditions shown in Table 2. Dl of hollow fiber is 0.5
2 μm, and DB was 0.54 μm. In addition, there was one portion with a minimal in-plane average pore diameter. Using this hollow fiber, we conducted a filtration experiment similar to that in the example, and the results are shown in the first example.
[Table 1] [Table 2] [Effects of the invention] The porous hollow fiber of the present invention has two or more minimum in-plane average pore diameters and one or more maximum pore diameters in the wall thickness direction. Since it has an average in-plane pore diameter, when used as a support membrane for an impregnated liquid membrane, the retention of the drug substance is significantly improved. In addition, the existence of at least two extremely small portions allows substances such as ions, low-molecular substances, and microparticles to pass through in the liquid phase.

Contributes to a higher rejection rate during separation - therefore, tan tJ? Separation and removal of viruses and bacteria, including Rickettsia, Chlamydia, Mycobacterium japonica, etc., dispersed in an aqueous solution that dissolves lytes and electrolytes.

Or is it better than an aqueous solution containing microbial particles? It can be used as a separation membrane to separate and concentrate substances.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph showing the structure of the fiber at the following points in the wall thickness direction of the porous hollow fiber in Example 1. (1) is the outer wall (2) is the x = 16 μm portion (minimum portion), (3) is x = 10 μm (maximum portion), (4) is the 4 μm portion (maximum portion), (5)
FIG. 2 is a scanning electron micrograph showing the structure of the fiber at the following points in the wall thickness direction of the porous hollow fiber in Example 2. (1) is the outer wall, (2) is x
=15. l#1 part (minimum part), (3) is 3C=l
O, 3μm part (maximum part), (4) is x = 5.4μ
The part m (minimum part) (5) is the inner wall part.

Claims (1)

[Claims] 1. In a polymer porous hollow fiber comprising countless through-holes in the membrane, the pore diameter in a plane perpendicular to the membrane thickness direction from the inner wall surface to the outer wall surface of the hollow fiber is defined as the in-plane average diameter. When expressed in terms of pore diameter, the in-plane average pore diameter at the entrance and exit of the membrane through-hole is in the range of 0.02 μm to 10 μm, and the in-plane average pore diameter is an extremely small portion, and a portion larger than the extremely small portion. , at least one set of structures arranged in the order of the smallest portion exists in the thickness direction of the hollow fiber, and further, the in-plane porosity of the hollow fiber in all planes perpendicular to the thickness direction is 10%. A porous polymer hollow fiber characterized by the above. 2. In a plane including the film thickness direction of the hollow fiber in a region in which the in-plane average pore diameter in the plane perpendicular to the film thickness direction is arranged in the order of a part with a minimum, a part larger than the minimum part, and a minimum part. 2. The porous polymer hollow fiber according to claim 1, wherein the shape of the porous hollow fiber is substantially circular or elliptical. 3. The polymer porous hollow according to claim 1, wherein the in-plane average pore diameter of the portion larger than the extremely small portion in the structure is 10 times or less of the in-plane average pore diameter of the extremely small portion. thread. 4. The porous polymer hollow fiber according to claim 1, which has an average porosity of 40% or more. 5. The average molecular weight of the polymeric substance constituting the hollow fiber is 5×10
The polymeric porous hollow fiber according to claim 1, which is copper ammonium cellulose having a carbon content of ^4 or more.