JPS5845239A - Preparation of heterogeneous porous film - Google Patents

Abstract

PURPOSE:To obtain a heterogeneous porous film having high water permeability and improved fractionating properties, by dissolving a water-insoluble polyvinyl alcohol polymer in dimethyl sulfoxide, making it into a film in a coagulating medium containing a specific salt. CONSTITUTION:A substantially water-insoluble polyvinyl alcohol polymer (ethylene-vinyl alcohol copolymer having an ethylene content of preferably 15- 60mol% and a saponification degree of preferably >=95mol%) is dissolved in dimethyl sulfoxide, and this polymer solution is made into a film in a coagulating medium consisting of preferably 5-20wt% aqueous solution of a salt (e.g., calcium chloride) shown by the formula M-X (M is Ca, Mg, Cu, Zn, or Al; X is halogen; solubility in water at 20 deg.C is at least 1.0g/dl), to give the desired porous film. USE:Useful for common ultrafiltration, filtration for a solution of an organism, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyvinyl alcohol (hereinafter referred to as PVA) polymer heterogeneous porous membrane having high water permeability and excellent fractionation properties.

Many membranes such as cellulose-based membranes and synthetic 1m membranes have been developed as microfilters such as conventional medical and industrial dialysis membranes, ultrapolar membranes, and ultra-precision membranes. The present inventors have discovered that it has extremely unique hydrophilic properties, has excellent mechanical properties, durability, and chemical stability, and has biocompatibility and anti-hemolytic properties, which are essential elements for medical materials. We have been conducting intensive research on Pv/A polymer membranes, which are expected to have excellent antithrombotic properties.

For example, EVA, which has a homogeneous porous structure using an ethylene-vinyl alcohol copolymer (hereinafter referred to as EVA),
Dialysis membranes have already been published in Japanese Patent Publication No. 1122/1983, and the EVA hollow fiber membranes have already been successfully developed and are now being used for artificial kidneys. This dialysis membrane for artificial field treatment requires moderate water permeability and high urinary sludge permeability, and requires strict control of numerous coagulation membrane development factors for an appropriate membrane structure. 4
! As a result of successive investigation of rfa factors, it was concluded that the above-mentioned homogeneous structure type obtained by wet film formation under relatively slow conditions was effective.

On the other hand, membranes for general off-shore applications, including medical applications, and especially ultrafiltration membranes, differ from this in that they require the highest possible water permeability and clear fractionation, and therefore the appropriate membrane structure is naturally required. different. It is well known that a heterogeneous porous gland having an ultra-thin active compact layer on the membrane epidermis and a sparse pore structure inside is generally effective as this membrane structure.

By the way, the PVA-based polymer referred to in the present invention has not yet been sufficiently investigated as a membrane material with this type of heterogeneous structure. It is difficult to form a layer, and if the water permeability achieved for a given fractionation performance is low, and the water permeability is set high, the fraction size will shift to the large side, and the fractionation performance itself will be poor, and on the contrary, the fractionation If the conditions were changed to improve the properties, there was a problem in that the water permeability had to be significantly reduced.

Therefore, the present inventors investigated in detail how the addition of second and third components to the membrane stock solution or the entire coagulation system affects the expression of membrane structure. We conducted extensive research on a method for manufacturing a heterogeneous porous membrane that forms a dense active layer with a loose interior.As a result, we dissolved a substantially water-insoluble PVA polymer in dimethyl sulfoxide, and created this electropolymer. By forming a film in a coagulation medium consisting of a water bath solution containing a salt represented by lVl = As a result, we have arrived at the present invention.

As the membrane-promoting element in the present invention, a P-vA-based summer compound that is substantially water-insoluble and soluble in dimethyl sulfoxide is preferably used. The substantially water-insoluble PVA-based polymer referred to here is *Specifically, EVA% carbon having an ethylene content of 1 p to 70 mol, preferably 15 to 60 mol, and a degree of oxidation of 5 Oqb or more. is 3 to 2.0 (α-olefin content is 10 to 70 molti in terms of ethylene unit, LtLi, i:
15 to 60 moles tIb)-vinyl alcohol" copolymer, ethylene, hydrophobic monomers other than α-olefins (for example, vinyl chloride s "Veova" RI I (CHsi=CH-0-C-C- R2 where R1, R2,
R3 is a Ct3 to C20 alkyl group)-vinyl alcohol copolymer, acetalized modified PVA (for example, polyvinyl alcohol,
This refers to formalized EVA), as well as etherified and esterified modified PVA using polymeric polymers, and mixtures thereof can also be used. Among these, Ec F2V is preferred as shown in the Examples below.

The EVA used in the present invention is random.

Either a block or a graft copolymer may be used, but if the ethylene content is less than 10 mol%, the mechanical properties in wet conditions will be insufficient, and rr; I-i
If the amount exceeds 70 mol, the biocompatibility and permeability will decrease, which is not preferable. Therefore, 15-60 among 10-70 molti
A molar range is preferred. Such E V A il P
Unlike VA, it is characterized by very little exudate, making it suitable as a hemodialysis membrane material in the medical field. E
If the degree of saponification of VA is not 80 molar or more, the mechanical properties in wet conditions will be insufficient, and a degree of saponification of VA of 95 molar or higher is more preferable. Generally, a material that is substantially completely saponified with a degree of saponification of 99 molar or more is not used. As EVA, for example, methacrylic acid, vinyl fluoride, methyl methacrylate, acrylonitrile, vinyl pyrrolidone, etc. may be copolymerized by a single rodent method that can be copolymerized in a range of 15 molar or less, In addition, EVA (Jj bulk compound, inorganic crosslinking agent or diincyanate) is added before or after film formation.

Formaldehyde, acetaldehyde, butyraldehyde, butylaldehyde, acetaldehyde, butyraldehyde, etc. in which crosslinking has been introduced by multiple treatments with organic crosslinking agents such as dialdehyde, or where the functional hydroxyl group of the vinyl alcohol unit is within 30 molar.
It also includes compounds that are acetalized with aldehydes such as benzaldehyde. EVA used in the present invention was measured by viscosity measurement [concentration 3J] [Measure the viscosity of a dimethyl sulfoxide solution (temperature 30° C.) with a lid with a B-type viscometer. ] It is preferable to use one whose value is in the range of 1.0 to 50 centivoise. If the viscosity is lower than this, that is, if the degree of polymerization is low, the necessary mechanical performance as a membrane cannot be obtained, and if the viscosity is higher than this, the membrane becomes unsatisfactory.

Dimethyl sulfoxide is suitable as a solvent for these PVA-based polymers, especially EVA, and dimethyl sulfoxide is used in addition to other solvents such as acetone, methanol, ethanol, glopanol, impropatol,
Water, methylpyrrolidone, dimethylacedooxide, dimethylacedooxide, etc. can be partially mixed and used, but the mixing ratio is as follows: A coagulation aid consisting of a salt represented by M-X used in the present invention. should be kept to a level that does not impair the effectiveness of the PVA-based polymer in stock solution, coalescence 111
1! The degree is 10 to 30% by weight, preferably 15 to 2%.
It is 5%. At concentrations higher than this range, the membrane performance is extremely low in water permeability, making it unusable, and at concentrations lower than this range, film forming properties are poor. The stock solution temperature during membrane forming is usually 1.
The temperature range is from 0 to 100°C, preferably from 20 to 80°C. Outside this range, it is difficult to develop the desired heterogeneous membrane structure;
Transmission characteristics are impaired.

The coagulation medium in the present invention refers to an aqueous solution containing one or more salts represented by M-X as coagulation aids. Here, M-X is an element of Group ■ or Group ■ of the periodic table, preferably metal, lucium, magnesium, zinc, aluminum, etc., and X is Br0nste.
ad) means an acid residue, preferably a halogen, and M
-X has a solubility of at least 0.5f in water at 20°C
/di, preferably 1. Refers to books that are Of/# or higher. Salts with low bath dissolubility below this level are difficult to exhibit their effects, and among group 0 and LI elements that are unsuitable for use, highly toxic elements such as mercury and cadmium cannot be put to practical use.

As a specific example of M-X, lucium chloride (Ca(
'J2) Calcium bromide (CaBr2), Cal iodide.

Schramm (Cal2), [magnesium chloride (Mrα2)
), magnesium bromide (MfBrz), magnesium iodide (MfIz), zinc chloride (Znα2), zinc bromide (ZnBrz), zinc iodide (Znl1), steel chloride (Cucjz), copper bromide (CuBr2) , aluminum chloride (Ajα3), aluminum bromide (AJBr
s) etc. Among these, lucium chloride is most suitable. The appropriate concentration range for use of M-X cannot be determined uniquely, but is determined in order to express the desired fraction size in correlation with other factors such as the concentration of the stock solution, the temperature of the stock solution, and the temperature of the coagulation medium. The concentration of Oji M-X in the coagulation medium is 3-3
0 tqb, preferably 5 to 20 tqb.

fJLIIIl The coagulation medium containing the coagulation aid is preferably an aqueous system l) 1%-8B methyl alcohol, ethyl alcohol, propatool, impropateol, etc., dimethyl sulfoxide, methylpyrrolidone,
Some organic solvents such as dimethylacetoamide, dimethylacetoamide, acetone, methyl ethyl ketone, and acetic acid ester can also be used in combination.

The membrane forming method of the present invention can be applied to any membrane shape, such as a flat membrane, a tubular membrane, a hollow fiber membrane, or a composite membrane with a support. Useful in manufacturing. As a flat film, the film thickness is about 3 to 2000μ,
The hollow fiber membrane has an outer diameter of 40 to 3,000 microns, more preferably 100 to 2,000 microns, and a membrane thickness of 3 to 1,000 microns, more preferably 10 to 500 microns. In spinning hollow fiber membranes, the coagulation medium is used only as an injected liquid in the hollow fiber membrane for forming hollows, and a normal coagulation bath (such as water or a mixed solution of water and dimethyl sulfoxide) can be used for spinning. . In this case, active dense jfI is formed on the inner surface of the hollow fiber membrane, and if the coagulation medium is used not only for the hollow fiber membrane injection solution but also for the coagulation bath liquid, active w! , a hollow fiber membrane with a dense layer is obtained. Furthermore, inert gas such as nitrogen is introduced into the hollow fiber membrane,
If this coagulation medium is used in a coagulation bath, a hollow fiber membrane having an active dense layer on the surface of the outer layer can be obtained.

As the film forming method of the present invention, in addition to the wet method in which the stock solution exits the die or nozzle which is the stock solution discharge port is immediately immersed in a coagulation bath, the so-called wet-dry method in which the stock solution is immersed in a coagulation bath after passing through the air is applied. be able to.

The appropriate solidification temperature is usually 0 to 40°C, preferably 10 to 35°C. At temperatures lower than this range, sufficient membrane properties, especially water permeability, cannot be obtained, and at higher temperatures, spinning stability is poor and performance is poor.

As a result of observation using a scanning electron microscope, the membrane thus obtained was found to have an extremely thin, uniform active dense layer on the side that came into contact with the coagulation medium, as is clear from Figures 1 and 2. However, it was confirmed that the inside of the membrane on the opposite side had a good so-called ultrafiltration membrane type inhomogeneous porous structure consisting of a sparse void layer (finger-like voids 1-). In addition, the molecular weight cutoff of the obtained membrane was 11,600,000,
Preferably 40,000 to 400,000, within this range 7
It has excellent fractionability.

Further, by subjecting the membrane thus obtained to post-treatments such as stretching and heat treatment, the membrane structure can be stabilized.

As explained in the explanation of EVA above, the obtained PVA-based membrane is further treated with an inorganic cross-linking agent such as a boron compound or an M-organic cross-linking agent having a functional group such as incyanate or aldehyde, if necessary. By introducing crosslinking by means such as radiation irradiation.

It is possible to carry out modification, which can be expected to particularly improve mechanical properties.

The membrane obtained by the present invention can be used not only for general ultrafiltration, but also for
Biological fluid filtration, e.g. p-type artificial kidney1. It can be used as a membrane for concentrating af1M water protein or for fractionating biological neutral white components (for example, for fractionation for plasma processing).

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

Example 1 220f of saponified ethylene-acetate vinyl coelectrolyte (ethylene content: 31 mol, saponified [99.9 mol%)] was dissolved in dimethyl sulfoxide 780 at 90°C f&, 60
The mixture was left to stand at ℃ for defoaming. Using this stock solution, cast on a glass plate placed on a hot plate at 20℃ Ky.
A white film was obtained by immersing the glass plate together with the glass plate in a 101 aqueous solution of Caα2 (solubility of Caα2 in water at 20° C.: 82 t/dj) and performing wet coagulation. When the cross section of the obtained film was observed using a scanning electron microscope, a clear active dense layer was observed on the free surface side. The single serum albumin rejection rate of this membrane was around 9B, and the fractionation was sharp, and the water permeability was at a high level of 112+wJ/♂, hr, and mug. Contains Etile 7 1140 molg, Ken (t[98 mol%) 250
? was dissolved in a mixed solvent of 720 F of dimethyl sulfoxide and 302 F of water, and the following hollow fiber spinning was performed using this as a stock solution.

For the nozzle, we used a single-hole type manufactured by Kasei Nozzle Co., Ltd., with an inner diameter of 600t+ and an outer diameter of 1200μ at the part that extrudes the stock solution.
I used the one from The temperature of the stock solution was maintained at 50°C, and a 10% aqueous solution of Caα2 at 15°C was used as the solution injected into the cavity, and water adjusted to 20°C was used as the coagulation bath. The raw solution transfer speed is a gear pump discharge rate of 5 m//min, and the loose yarn speed is s.
Wet spinning was performed at 8 m/min. The obtained hollow fiber membrane had an outer diameter of 950 μm, an inner diameter of 500 μm, and exhibited an almost perfectly circular cross-sectional shape. The cross-sectional structure of the obtained hollow fiber membrane was examined using scanning electron micrographs.

The electron micrographs are shown in FIGS. 1 and 2.

Figure 1: A cross-sectional view at a magnification of 450, showing that the inner layer has a sparse structure with finger-like void layers, a dense active layer on the inner surface, and a porous layer on the outer surface. 2nd m: This is a sectional view of the inner surface side at a magnification of 9000, and it is clearly seen that there is a microdense layer on the inner surface. This hollow fiber membrane was incorporated into a small module and the performance measurements showed that the water permeability was 105 yse/rl hr, the Hg fragment serum albumin rejection rate was 98%, and the fractionation was 7'C.
1N opening a58-4
523 (5) Comparative Example 1 When only distilled water was used in the coagulation bath under the same conditions as in Example 1, the membrane obtained had a bovine serum albumin rejection rate of 65% and a water permeability of 120ttl/n? , hr, and Hg, and the protein fractionation property for a certain water permeability was significantly inferior.

Example 3 Under the same conditions as in Example 2, a nozzle with an inner diameter of 400 μm and an outer diameter of 800 μm was used, and the same Caα210 aqueous solution as the hollow injection solution was used for the coagulation bath.

When the hollow fiber membrane was observed under a scanning electron microscope, a secret layer was observed in the inner and outer epidermis. The permeation characteristics are good with a protein inhibition rate of 98-99%, but the water permeability is 95W1e/
rl, hr, and Y company's tg were slightly lower.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph at a magnification of 450 showing a cross-sectional view of a hollow fiber membrane obtained according to the present invention, and FIG. 2 is a scanning electron micrograph at a magnification of 9000 showing a cross-sectional view of the inner surface side of the hollow fiber membrane. This is an electron micrograph.

Claims (1)

[Claims] (1) A substantially water-insoluble polyvinyl alcohol polymer is dissolved in dimethyl sulfoxide, and this polymer solution -
1. A method for producing a heterogeneous porous membrane, comprising forming the membrane in a coagulation medium consisting of an aqueous solution containing a salt represented by IM-X. However, M-X is a salt in which M is an element of Group 1 or Group Ⅰ of the periodic table, X is a Brønsted acid residue, and has a solubility in water at 20° C. of at least 0.5 r/min. (2) The method for producing a heterogeneous porous membrane according to claim 1, wherein M-X is calcium, magnesium, zinc, copper, or aluminum, and X is halogen. 3. The method for producing a heterogeneous porous membrane according to claim 1 or 2, wherein (a) M-X has a solubility in water at 20° C. of at least 10 t/m. (41M-, X is calcium chloride. A method for producing a heterogeneous porous membrane according to claim 1. (6) The coagulation medium is an aqueous solution of a salt represented by M-X at a concentration of 5 to 20 weight. Claims 1, 2, and 3 are:
or the method for producing a heterogeneous porous membrane according to item 4. (6) The substantially water-insoluble polyvinyl alcohol copolymer is an ethylene-vinyl alcohol copolymer having an ethylene content of 10 to 70 mol and a saponification degree of 80 mol or more. Range 1st, 2nd, 3rd, 4th
Further, a method for producing a heterogeneous porous membrane according to Expanded Item 5. (Te) The method for producing a heterogeneous porous membrane according to claim 6, wherein the ethylene content is 15 to 60 mol. (8) The method for producing a heterogeneous porous membrane according to claim 5, wherein the substantially water-insoluble polyvinyl alcohol polymer is acetalized polyvinyl alcohol. . (9) The method for producing a heterogeneous porous membrane according to claims 1 to 8, wherein the heterogeneous porous membrane is a hollow fiber membrane.