JPS62163705A - Hollow yarn membrane made of ethylene-vinyl alcohol copolymer - Google Patents

Abstract

PURPOSE:To reduce the diameter, to increase the amt. of water to be permeated, to permeate low molecular substances, and to exclude high molecular substances by forming a particle binding layer having 0.01-2mum thickness at the next to the surface of an EVA copolymer hollow yarn membrane with a dense active layer on the surface. CONSTITUTION:An ethylene-vinyl alcohol copolymer is dissolved in a polar org. solvent to obtain a spinning soln. The soln. is spinned while introducing a coagulable liq. into the hollow part, and coagulated in a gaseous atmosphere under 3-30 times draft. When the coagulation temp. at this time is expressed as T and the polymer concn. as C, the relational expression, -15<=T<=(C/4)+10, must be satisfied at 15<=C<=40. Consequently, a three-layered EVA hollow yarn membrane consisting of a dense active layer 1 on at least one of the membrane surfaces, an internal binding layer 3 of particles 2 having 0.01-2mum particle diameter at the next to both surfaces, and further an internal homogeneous layer 4 wherein a particulate structure is not substantially recognized can be obtained.

Description

Detailed Description of the Invention The present invention relates to a hollow fiber membrane made of ethylene-vinyl alcohol (EVAJ-based copolymer). The present invention relates to an EVA-based hollow fiber membrane.

Single-selective permeability membranes, especially hollow fiber membranes, are becoming widely used in the medical field such as hemodialysis and the industrial field such as ultrafiltration of various solutions. The EVA-based copolymer membrane developed by the present inventors has excellent biocompatibility, and membrane performance such as water permeability and permeability to medium-molecular weight substances quickly decreases, so it has been recognized for its usefulness in various fields. There is.

The present inventors have already provided several types of EVA-based copolymer membranes. JP-A No. 52-152877 discloses an EVA-based polymer membrane in which the entire membrane has a structure in which particles with a particle size of 100 to 10.0 (10"A) are bonded to each other, and the linear membrane is used for hemodialysis. In addition, in Japanese Patent Application No. 108251/1987, a hatropic membrane made of BVA copolymer compositions with different ethylene contents and consisting of continuous cylindrical voids and spherical voids in micron units was developed. The wire membrane is also excellent as a dialysis membrane.
The wire membrane discloses an anisotropic membrane having a porous support layer with vacuoles having a long axis length of ~99% and a porosity of 60 to 90%, and the wire membrane is suitable for ultrafiltration applications, etc. Excellent as a filtration membrane.

As mentioned above, it is possible to obtain membranes with various structures by changing the manufacturing conditions of EVA copolymers, and it is recognized that they are particularly excellent as membrane materials.

As a result of extensive research, the present inventors succeeded in producing an EVA-based hollow fiber membrane having a structure different from that described above, and completed the present invention.

That is, the present invention provides a hollow fiber membrane made of an EVA-based copolymer, which has a dense active layer on at least one of the inner and outer surfaces of the hollow fiber membrane in electron microscopic observation of a dried membrane.
and an EVA system having a 3m structure consisting of a particle bonding layer formed by bonding particles with a particle diameter of 01 to 2μ in contact with both surfaces, and a homogeneous layer with virtually no particle structure existing roughly inside the layer. It is a hollow fiber membrane.

The membrane according to the present invention is characterized in that it has an active layer on at least one surface of the membrane, and has a three-layer structure consisting of a particle binding layer and a homogeneous layer inside. Conventionally known EVA-based copolymer membranes are broadly classified into those having a substantially homogeneous structure throughout the membrane, and those having an anisotropic structure consisting of an active layer and a porous support layer therebelow. In contrast, although the membrane of the present invention has an active layer, there is no known porous support layer underneath it, but a particle binding layer and a homogeneous layer, which are considered to have the structure of a conventional homogeneous membrane, are laminated. It has a 3m structure. As will be described later, the hollow fiber membrane of the present invention has higher water permeability, permeability to low-molecular heavy substances such as urea, and permeability to medium-molecular mineral substances such as VB and 2 than conventional EVA dialysis membranes. Furthermore, it has extremely excellent performance with high extraction of polymeric substances such as proteins and dextran, that is, sharp fractionation (7). Regarding the relationship between such performance and membrane structure, Although it has not yet been elucidated by the present inventors, it is certain that the structure clearly different from the conventional EVA homogeneous membrane mentioned above is the cause of the excellent membrane performance.The EVA-based copolymer shown in the present invention The structure of the membrane is new and has not been previously announced not only for EVA-based membranes but also for membranes made of any other material.

The EVA copolymer used in the present invention has an ethylene content of 1
Dimethyl sulfoxide (DM80) with a concentration of 0 to 90 mol%, more preferably 10 to 60 mol%, and a concentration of triple point %
A solution having a viscosity of 1.0 to 50 centiboise at 30°C is used.

As will be described in more detail later, it also includes copolymers with other copolymerizable monomers and those that are crosslinked with a crosslinking agent such as a polyvalent or polyvalent aldehyde or diisocyanate after film formation.

Figure 41 is an electron micrograph (3,600x magnification) showing an example of an EVA-based copolymer film according to the present invention. FIG. 2 is a schematic diagram thereof. The membrane shown in FIG. 2 has an active layer 1 on one outer surface, and a particle bonding layer 3 in which a large number of particles 2 are bonded in contact with the active layer 1-. Roughly speaking, the inner surface 5 may be either an active layer or a layer with micropores, and has a particle bonding layer 3' in which a large number of particles 2' are bonded in contact with the inner surface, and the particle bonding layer 3.3 There exists a homogeneous layer 4 in which no grain structure is actually seen even in an electron micrograph of 12,000 times magnification. If this homogeneous h''!J4 has a gii dense structure similar to the active layer, it cannot exhibit the high water permeability waves and solute permeability mentioned above, and it is thought that it has some kind of different structure, but at present it is The majority of the particles have a particle size in the range of 0.01 to 2μ, preferably 0.01μ to 2μ.
The particle size is in the range of 0.05 to 1 μm, and the particle size is larger near the membrane surface and becomes smaller toward the inside. If the particle size is smaller than this, the water permeability, solute permeability, etc. will be too small, making it undesirable as a membrane. Further, a structure in which each grain size is 2 μ or more cannot be manufactured by the method of the present invention. The thickness of the particle bonding layer and the homogeneous layer can be changed as necessary from 4 to 4. When the thickness of the particle bonding layer in contact with the outer surface is 1, the thickness of the homogeneous layer is 1 to 15.
．． More preferably 2 to 8 - a particle binding layer in contact with the inner surface (
Yo0.2~3. More preferably 0.2-2. The active layer on the membrane surface is an extremely thin layer.

The surface was observed under an electron microscope (+2.00□ magnification) and no fine pores or gaps were observed. The active layer exists on at least one of the outer and inner surfaces, and if the active layer is too thin, the membrane performance will be greatly reduced.

The obtained hollow fiber membrane has an outer diameter of about 50 to 3000 μm and a membrane thickness of about 5 to 500 μm, and can be made into any thickness as required.

FIG. 3 is an electron micrograph (2,400 times) showing a hollow fiber membrane with a homogeneous structure disclosed in JP-A-52-152877, and the structure of a conventional kVA homogeneous membrane. This is clearly different from the membrane of the present invention.

Note that the film structure in the present invention is observed by a first-order method. A dried film obtained by the manufacturing method described below is frozen in liquid nitrogen and broken to create a fractured surface.

Next, gold was deposited on the fractured surface to a thickness of about 10 OA, and this was observed using a Hitachi FS electron microscope model 11 FS-2.

The hollow membrane of this Q-Mei is manufactured by using a hollow fiber spinneret with a spinning stock solution in which an ethylene-vinyl alcohol copolymer is dissolved in a solvent containing dimethyl sulfoxide, dimethylacetamide, pyrrolidone, N-methylpyrrolidone, or a mixture thereof as a main component. It is produced by spinning the yarn while introducing a coagulable liquid into the middle part of the yarn, passing the spun yarn in a gas atmosphere so as to receive a draft of 3 to 30 times, and then coagulating it in a coagulation bath in the temperature range shown below. I can do it.

When X5=C≦40-15≦T≦−〇+I 0 where C is the polymer concentration (vrt, %) and T is the coagulation temperature (°C)
In addition to those mentioned above, the EVA copolymer used in the present invention may be one in which other copolymerizable heptamers are copolymerized in an amount of 15 mol % or less. Seven polymers that can be copolymerized
Examples include methacrylic acid, vinyl chloride, methyl methacrylate, acrylonitrile, vinylpyrrolidone, and the like. In addition, EVA is used before or after spinning.
Crosslinking is introduced by treating a copolymer with an inorganic crosslinking agent such as a boron compound, or an organic crosslinking agent such as diisocyanate or dialdehyde.

Alternatively, up to 30 mol% of the functional hydroxyl groups of the vinyl alcohol unit may be acetalized with an aldehyde such as formaldehyde, acetaldehyde, butyraldehyde, or benzaldehyde.

Monohydric and polyhydric alcohols such as methanol, ethanol, ethylene glycol, and propylene glycol - phenol, metacresol, methylpyrrolidone, formic acid, and hydrated products thereof are known as solvents for dissolving EVA copolymers. 1. In order to manufacture the membrane targeted by the present invention.

Dimethyl sulfoxide, dimethyl acetamide.

Preferably, pyrrolidone, N-methylpyrrolidone or mixtures thereof are used. Particularly preferred is dimethyl sulfoxide, which exhibits high solubility in EVA-based Kobo U7-. E
When dissolving the Vp and copolymers in these solvents, the concentration is 15 to 40%, more preferably 18%.
A range of 30% to 30% solidity is desirable. The temperature of the polymer solution is preferably 0 to 1200C, preferably 20 to 80C. Humidities higher than this are not desirable because the polymer may deteriorate in quality, and temperatures lower than this are undesirable because the solution viscosity becomes too high or the polymer gels, making spinning difficult.

The spinning stock solution prepared as described above is spun into a hollow fiber using a hollow fiber spinneret such as a circular cane nozzle. In the present invention, it is necessary to perform spinning while introducing a coagulating liquid into the polymer solution from the middle of the spinneret. The coagulable liquid causes coagulation on the inner surface side of the hollow fiber membrane, forming a particle binding layer in contact with the inner surface. Further, an active layer can be formed on the inner surface depending on the conditions and degree of coagulation.

The coagulable liquid includes water alone, a solution of water and a water-miscible organic solvent, and a solution of water and a salt such as glauber's salt. Yu%
Particularly preferred are solutions containing.

The coagulating ability of this solution makes it particularly suitable for forming membrane structures.

The yarn spun from the spinneret first passes through a gas atmosphere. Since the spinning dope retains its fluidity in a gas atmosphere, the spinning yarn is stretched out to form a round and uniform membrane wall.

Furthermore, the spun yarn is subjected to drafting in a gas atmosphere, and the drafting conditions are also an important factor in the present invention. That is, in order to achieve roundness and uniform film thickness, especially thinning of the film, it is desirable that the draft ratio be large. However, if the draft is too large, the overall film thickness becomes thinner, and pinhole-like film destruction tends to occur more easily.

On the other hand, if the draft ratio is too small, the resulting membrane will not have sufficient fractionation properties or permeation performance for fluxes, etc., and will also deteriorate practically necessary mechanical properties such as strength and dimensional stability.

Generally speaking, the three-layer structure seen in the membrane of the present invention is thought to be formed by the interaction between the draft in the gas atmosphere and the coagulation in the coagulation bath, but the phenomenon of shaking has been observed in the hollow fiber membrane manufacturing method. This was something that the inventors could not have predicted at all. In the present invention, it is desirable that the spinning yarn is subjected to a draft of 3 to 30 times, more preferably 5 to 20 times.

The distance between the nozzle and the surface of the coagulation bath is preferably about 3 to 50 mm.

The gas atmosphere is normally an open space, but if the evaporation of the solvent is to be controlled, a shield of any shape such as a cylindrical tube is provided, and the atmosphere is filled with vapor from the coagulation bath or vapor supplied separately. Alternatively, the atmosphere may have a controlled air flow.

The spun yarn is then introduced into a coagulation bath and undergoes coagulation.

Although a wide range of compositions and temperatures can be considered for the coagulation bath, as a result of studies conducted by the inventors of the present invention, they have found that it is desirable to have the same composition as the coagulating liquid introduced into the middle part. That is, an aqueous solution of the solvent used in the spinning dope is preferable, and an aqueous solution of dimethyl sulfoxide is particularly preferable.

The richness of each component should be selected depending on the conditions such as the coagulable liquid introduced into the middle part and the coagulation temperature.
Determined experimentally from the range of % weight.

Furthermore, the solidification temperature is 15≦C, which forms the membrane structure of the present invention.
≦40, 15≦T≦-C+10, where C is the frimer concentration (wt, %), and T is the coagulation temperature (C°C). Membrane performance 2 (mechanical performance) can be adjusted by performing moist heat stretching or the like. Also monoaldehydes such as formaldehyde, acetaldehyde, chloroacetaldehyde, and benzaldehyde, glutaraldehyde, and glyoxal.

It is also possible to acetalize the vinyl alcohol moiety with a dialdehyde such as PVA dialdehyde, and to introduce ester crosslinking with a diisocyanate such as phenylene diisocyanate or tolylene diisocyanate, or ether crosslinking with epichlorohydrin. In particular, crosslinking with dialdehydes such as glutaraldehyde greatly improves heat resistance, chemical resistance, strength, dimensional stability, etc.

preferable.

The hollow-based membrane according to the invention can be used as a wet or dry membrane. In the drying method, water contained in the hollow system is removed using an organic solvent (e.g.
acetone, methanol, tetrahydrofuran, etc.) and then removing the organic solvent by heating or the like, or treatment with a polyhydric aliphatic alcohol (e.g., ethylene dalicol, diethylene glycol, glycerin) during or after film formation, After that, a method of heating and drying at a relatively low temperature, or a freeze-drying method of freezing the moist pleura containing water with liquid nitrogen, etc., and then removing the water under reduced pressure using a sublimation phenomenon, etc. You can take it.

The diameter of the hollow fiber membrane according to the present invention can be easily reduced.

When used in an artificial kidney a or the like, it is advantageous because the priming volume can be made small. In addition, it has a large amount of water permeability, and compared to conventional homogeneous EVA membranes, it is particularly permeable to low-molecular weight substances such as urea, and has a high rejection rate of high-molecular weight substances such as proteins, making it suitable for hemodialysis and body fluid reduction. Useful as a membrane.

The present invention will be explained below with reference to Examples.

Examples 1 to 6 and Comparative Example 1 Ethylene-containing ht 33 mol% ethylene-vinyl 7
/l/ Cole copolymer was heated and dissolved in dimethyl sulfoxide to obtain a solution having a concentration of 22%. This was left at 70°C overnight to defoam. An annular nozzle with a nozzle hole diameter of 1.5 mm, a needle outer diameter of 1.13 mm, and a needle inner diameter of 0.87 mm was installed in 20 groups above the coagulating liquid surface.
．． 96/0.610.311rr! n nozzle],
Dimethyl sulfoxide and water (45/s
s wt/vt) mixed solvent at 1,3 cc/rn
While injecting the mixture with water, the degassed stock solution was extruded from the outside at a rate of 1.1 cc/min and spun vertically downward into a coagulation bath of a dimethyl sulfoxide-water mixed solution, and the spinning speed was set at 30 m. /m1n. The obtained wet hollow fibers had an outer diameter of 250 μm, a film thickness of 25 μm, and a nearly perfect circular cross-sectional shape [7, diameter over 1 km of anchor fiber length.

The fibers had excellent uniformity with almost no unevenness in film thickness. Comparative Example 1 is a method of spinning directly into a coagulation bath without passing through the air.

Details are shown in Table 1.

The following margins are Example 7 and Comparative Example 2.3 The hollow fiber obtained in Example 6 has a membrane area of 1
．． It is modularized so that it becomes 0, and the flow rate on the blood side is 1.
0077Le, pressure 1001MIRQ, dialysate side flow kk
The water permeability of 1 molecule of dextran was measured using Okikushima and Okikushima. The solution was prepared to have a dextran concentration of 0.1% and measured. The Okikushi distance referred to here was calculated using the formula below.

Comparative Example 2 is a hollow fiber obtained in Comparative Example 1, and Comparative Example 3 is a regenerated cellulose-based hollow fiber membrane (Cuprophan manufactured by Enka Co., Ltd.,
A similar experiment was conducted using a film having a wet film thickness of 30 to 35 μm.

The results are shown in Table 2.

Table 2 'OF R (Tnl!Ar-ranHg) Dextran (M, W, 10,000) F5 Kushima Example 7
6.7 55 Comparative Example 2
4.3 49tt3 2.9
75

[Brief explanation of drawings]

FIG. 1 is an electron micrograph showing the cross-sectional structure of an example of an EVA-based hollow fiber membrane according to the present invention, and FIG. 2 is a schematic diagram thereof. FIG. 3 is an electron micrograph showing the cross-sectional structure of a conventional EVA-based hollow fiber membrane.

Claims (1)

[Claims] A hollow fiber membrane made of an ethylene-vinyl alcohol copolymer, which has a dense active layer on at least one of the inner and outer surfaces of the hollow fiber membrane when observed by electron microscopy of a dry membrane, and is in contact with both surfaces. Ethylene having a three-layer structure including a particle bonding layer formed by bonding particles having a particle size of 0.01 to 2μ, and a homogeneous layer with substantially no particle structure existing inside the particle bonding layer. - Vinyl alcohol hollow fiber membrane.