JPS61254203A - Microporous membrane - Google Patents

Abstract

PURPOSE:To obtain a microporous membrane showing sharp fractional characteristics and having a large void ratio, by using a microporous membrane having narrow pore size distribution wherein a void ratio is a specific value or more and the inhibiting ratio of monodisperse latex particles is a specific value. CONSTITUTION:For example, polystyrene is used as a spherical phase and polyhydroxybutyrate is used as a continuous phase to respectively prepare chloroform solutions and the solution mixture of both of them is formed into a film to evaporate a solvent. Next, the obtained film is immersed in dimethylformamide being the solvent to polystyrene but the non-solvent to polyhydroxybutyate and subsequently washed with water and dried by air. Thus obtained membrane has a void ratio of 25% or more and an inhibiting ratio of monodisperse latex particles, which has a particle size 1/5 the diameter of monodisperse latex particles showing an inhibiting ratio of 95%, of 10% or less and shows sharp fractional characteristics and a high filtrate transmitting speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Sedentary Use] The present invention relates to a microporous membrane with a narrow pore size distribution suitable for ultrafiltration, semi-filtration, etc.

[Conventional technology]

Ultrafiltration membranes and precision filtration membranes are widely used in water treatment, food industry, pharmaceutical industry, medical field, etc., but these membranes have various pore sizes depending on the particle size of the target material to be fractionated. However, the membrane is required to have a high filtration rate and sharp fractionation characteristics.

Conventional microporous membranes are made by dissolving all polymers in a solvent, shaping the resulting solution into a film, tube, or inner-walled thread, and then immersing it in a non-solvent for the polymer. A method for obtaining a microporous membrane by precipitation, a method for obtaining a microporous membrane by dissolving a polymer in a mixture of a solvent and a non-solvent, and evaporating the mixture after shaping; It was obtained by a method such as mixing all the inorganic salts, shaping, and then extracting with a polymer of 10,000 or a solvent of 7,700 inorganic salts.

[Problems to be solved by the invention]

The membrane of cn et al. has a large porosity and may be able to obtain a high permeation rate, but the membranes of cn et al. obtained by these methods have broad fractionation characteristics, and it is not possible to obtain a membrane that exhibits sharp fractionation characteristics. No.

It is incorrect to think that this t'L is due to the non-uniformity of the pore diameters of the pores present in the microporous membrane. When the pore size distribution is measured using the mercury intrusion method, some products show an apparently sharp pore size distribution, but the mercury intrusion method only provides a guideline for the pore size distribution and does not indicate practical performance. Figure 1 (aJ
It draws a curve as shown in (n), and does not show a sharp pore size distribution in practical use.

On the other hand, as a microporous membrane with sharp fractionation characteristics among conventional technologies, the polymer film is fully irradiated with high-energy charged particles generated from a nuclear reactor, and then the polymer decomposed in the charged envelopes is extracted by alkali etching etc. There is Eucribore (trade name, manufactured by GEi) that is created using this method. However, due to the constraints imposed by its manufacturing method, it is difficult to form a large number of pores in this @, and the porosity is at most 20.
%, and the disadvantage is that the permeation rate is low! Therefore, there is a need for a membrane with a sharp pore size distribution and high porosity, which is one of the factors that determines the filtration rate, in practical use.

An object of the present invention is to provide a microporous membrane that exhibits sharp fractionation characteristics and has a large porosity.

[Means for solving problems]

The gist of the present invention is to have a porosity tM of 25% or more and a rejection rate of 95.
The microporous membrane has a narrow pore size distribution in which the blocking wheel of monodisperse latex particles having a particle size of 115% of the diameter of the monodisperse latex particles showing %7 is 10% or less.

The porosity is the total volume of pores in the membrane, V, relative to the total volume of the membrane, VM.
Porosity can generally be measured by mercury porosimetry, but a simple method is to measure it using a liquid that does not swell the polymer that makes up the membrane. It is also possible to fill the pores in the membrane and determine the porosity from the weight change before and after filling.

A method for measuring the rejection of monodisperse latex particles as an indicator of the fractionation properties of a membrane is fully described. Using a dilute suspended aqueous solution of monodisperse latex, stir the aqueous solution t''F near the membrane surface using a magnetic stirrer, and measure the latex particle concentration (af, 0p, respectively) before and after r. ,
The rejection rate can be calculated from equation (2). Determine the rejection rate using latex of various particle sizes, draw a fractionation curve from this,
What is necessary is to find the particle size at 95% inhibition and the rejection rate for the particle size of 115%.

In the case of a hollow fiber or tubular membrane, the measurement may be performed by stirring the liquid outside the membrane so that the membrane surface is exposed to turbulent flow and filtering it.

The rejection rate of the monodispersed latex particles of the microporous membrane of the present invention can be selected from various values depending on the purpose, and it is preferable that the particle size of the particles exhibiting a 95 rejection rate is 0.1 to 50 μm.

The present invention will be explained below using the drawings.

Figure 1 is a curve showing the rejection rate of monodisperse latex particles of a certain particle size, curves (1)) and (e) are the measurement results of the membrane of the present invention, and curve (a) is the mercury intrusion These are the results of measuring a membrane using the conventional method, in which the pore size fraction was found to be sharp. From Fig. 1, when the particle diameter is 'eXIX' which gives a blocking rate of 95%, the blocking rate of particles with a particle size of 0.2 and (12') is shown by the curve (al, approximately 50%, (b) 10%,
In (C), it is a little less than 5%, indicating that the membrane of the present invention has sharp fractionation characteristics.

Next, a preferred method for manufacturing the membrane of the present invention will be described.

Even if polymers with poor compatibility are mixed, phase separation [-] will occur, but if a mixed solution of both is made using a solvent that can dissolve both, a uniform polymer mixed solution will be obtained. When the solvent is evaporated after shaping this n', phase separation of the polymer solution occurs as the solvent evaporates. In this case, if the mixing ratio of both polymers is appropriately selected, one polymer becomes a continuous phase and the other polymer becomes spherical and dispersed to form a phase-separated structure.

The diameter of the spherical pores varies depending on the evaporation rate of the solvent, the evaporation temperature, the viscosity of the spherical phase, the continuous phase, the molecular weight of the polymer in the spherical pores, etc. For example, if the evaporation rate of the solvent is increased, the diameter of the sphere becomes smaller, and the evaporation temperature is increased. If it is lower, the spherical pores will not associate with each other, and a large number of spherical phases with uniform diameters will be obtained.

As for a careful combination of polymers to obtain such a structure with kW, the absolute value Δδ of the difference in solubility parameters between the two should be 113 or more, preferably 15 or more, more preferably 1.0 or more. The larger Δδ is, the easier it is to obtain a spherical phase with uniform diameter.

When polystyrene is selected as the spherical phase as a combination of such polymers, the polymers forming the continuous phase are polyhydroxybutyrate (hereinafter referred to as PHB), polylactide, cellulose acetate, polyvinylidene chloride, and PAN.
Examples include polymers of various types. Conversely, these polymers can be made into a spherical phase and polystyrene can be made into a continuous phase.

In the case of these combinations, low boiling point halogenated hydrocarbons such as chloroform and methylene chloride are preferably used as the solvent.

If ΔJ is α3 or more, there is a solvent that can dissolve both of them to form a uniform solution, and there is a solvent that completely dissolves them and becomes a non-solvent for the other, if the polymer is assembled, Any combination can be used without being limited to one or the other polystyrene.

In order to form a spherical phase and obtain a membrane with a large porosity, the mixing ratio of polymers is preferably such that the weight ratio of spherical phase polymer/continuous phase polymer is 12 to 1.3. , 15
The concentration when both polymers are dissolved in a solvent is preferably [15 to 1.2].
It is preferable that it be 0%. If the concentration is too high, a uniform solution will not be obtained, and if it is too low, the amount of solvent and the cost for solvent evaporation will increase, which is undesirable.

By treating the thus obtained excipient consisting of a continuous phase in which the above-mentioned spherical phase is dispersed, using a solvent that has the ability to dissolve the spherical phase and is a non-solvent for the continuous phase. After all the spherical phases are selected and dissolved, a membrane with uniform pore diameter and high porosity can be obtained by drying.

This selective solubility'! When the spherical phase is polystyrene, the solvent used is MffiK, cyclohexane, DMF.
, THF, aromatic hydrocarbons, and the like, which do not completely dissolve the polymer constituting the continuous phase may be appropriately selected. In the case of water-soluble polymers, water can be mentioned.

When the spherical phase is dissolved and removed, a small amount of the polymer of the spherical phase is mixed in the continuous phase, so in addition to the spherical phase, extremely small pores may also be present in the continuous phase. However, the pores in this continuous phase are significantly smaller than the pores produced by removal of the spherical phase, so they do not substantially affect the separation performance of the membrane.

Those skilled in the art can easily realize that the membrane of the present invention can be formed not only into a film but also into tubes and hollow fibers. Furthermore, in order to improve the separation efficiency, it is preferable to make the membrane thickness as thin as possible, and the membrane thickness is preferably from several μm to several tens of μm.

By the method of the present invention, it is possible to obtain a membrane that can sharply separate latex vagina particles with a particle size of 0.1 μm to several tens of μm, and a membrane with a porosity of 25% or more and a permeation rate. A large film can be obtained.

〔Example〕

The present invention will be explained in more detail below using examples.

Example 1 Polyhydroxybutyrate (P) with a viscosity average molecular weight of 500,000
H! Glazed monodisperse polystyrene (P
Prepare a 13w chloroform solution of st, ) and mix in equal amounts, Pat/PHB = 1
(D a Base m solution! l!! L7c. This mixed solution r;c was transparent and uniform. This mixed solution was placed in a glass Petri dish so that the thickness of the film after solvent evaporation was 50 μm. The evaporation rate of the solvent cannot be controlled.
To IeI Holm! I let it emanate. Note that the evaporation rate of the solvent was measured as follows. Pour the solution into a desiccator with a diameter of about 20 mm.Pour the solution into a glass petri dish.

7 tons of desiccator? Shita. The solution was poured into a desiccator and completely dried. In this experiment, 9 air volume was controlled using 70 meters, and 200WLt/m1n was used at room temperature.
The evaporation temperature was room temperature (approximately 25°C) at a flow rate of . The obtained film-like excipient t-PstK is a solvent, but P
HBIC uses dimethylformamide (DMF), a non-solvent.
), the film was washed with water and air-dried. Obtained: rL7
1 = The surface of the film is photographed when observed with a full electron microscope (3
), it is possible to obtain a membrane having a large number of all pores with uniform pore diameters that are nearly circular. Table 1 shows the porosity and water permeation rate of the obtained n-film.

The porosity is 6 after immersing the dry membrane in butanol for 30 minutes.
Weight (Wl) when the surface is wiped with gold, weight after drying this f'L' at 60°C in a vacuum dryer for one day and night (W2),
Density of the polymer (ρp, 1,250 for PHB),
Photo 3 shows the surface condition of the membrane of Experiment No. 4, which was determined using Equation 3 from the density ρB of butanol at the weight measurement temperature.

Each particle size (LaO2, (L913.1.091.2.9
5.4.31, i7, &9.11.9.1&7 Monodisperse polystyrene, polyvinyltoluene, or styrene-divinylbenzene polymer latex 111% aqueous solution was used to determine the fractionation curve of these membranes, and the fraction From the curve, the rejection rate at a particle size of 175 (Rd
15) t-calculated. The results are shown in Table 1.

Table 1 Example 2 Same as Example 1 except that a thiamin Petri dish was used instead of a glass Petri dish in the polymer assembly of Experiment No. 004 of Example 1, and the film thickness after drying was adjusted to 10 μm. Microporous membranes were prepared in the same manner, and particle sizes [1L605, α7, [1L804, α91
3.1.091.2.95.4.31, i7, &8.1
1.9.1 & 7 monodispersed latex α 1% aqueous solution was used, and the evaporation rate was determined by Nitkido t-DIl.
250 mA/m at 1nxFX membrane 300 mt/m
The same method as in Example 1 was carried out except that the temperature was changed to "in". A fractionation curve was determined. After further irradiation with high-energy charged particles, an alkaline curve was determined. These are shown in FIG. The flow diameter showing the 95% rejection rate of these membranes ((1), part 11
Rejection W at a particle size of 5 = RA15. The porosity is shown in Table 2.

Table 2: This product name: 70-bore (manufactured by Sumitomo Electric) As is clear from Figure 2, the membrane G (curve?) had a broad fractionation curve, and the desired fractionation characteristics could not be obtained. As is clear from
It can be seen that while the overspeed is small, the membrane of the present invention has sharp fractionation characteristics and a large porosity.

Example 3 A chloroform solution of (L 3 wt%) of monodisperse polystyrene (weight average molecular weight 570,000) and monodispersed polystyrene (weight average molecular weight 570,000) were prepared and mixed in equal amounts. P
Example 2 A mixed solution of st/PLLA = 1 was prepared.
In the same manner as above, the entire solution was cast onto a Teflon Petri dish, and after evaporating the solvent, it was immersed in DMP, washed with water, and dried to obtain a 10 pm thick 'It-N semipermeable membrane. The fractionation characteristics of the obtained membrane were measured in the same manner as in Example 2, and the particle size was z9μ showing a porosity of 63% and a rejection rate of 95%.
The membrane exhibited excellent fLt fractionation characteristics with a rejection rate of 2 at m1CL of 58 μm, and had a large porosity.

Example 4 PHB of Example 1 and polymethyl methacrylate) (PM
(abbreviated as MA, weight average molecular weight 28,000) and monodisperse polystyrene as PHB: PMMA: Pst=1:α5
:(L5 (weight ratio) was mixed to prepare a 1 wt% chloroform solution. Film formation was performed in the same manner as in Example 3,
Microporous membrane surface with a thickness of 20μ. The fractionation characteristics of this membrane were measured using monodispersed latex in the same manner as in Example 3, and the particle size was 2.7 μm, showing a porosity of 59% and a rejection rate of 95%.
4゜The rejection rate at the 175 diameter was 0%.

〔Effect of the invention〕

When the membrane obtained by the present invention is used as an ultrafiltration or microfiltration membrane, it exhibits sharp fractionation characteristics.
In addition, since the porosity of the membrane is large, the permeation rate of the P liquid is also high, and it is possible to process a predetermined amount of the liquid to be filtered with a small membrane area.

It has a pore form. It is clear that the pore diameter of the membrane of the present invention is uniform, and compared to photograph (2), the number of pores per unit membrane area (ie, porosity) is large. In addition, the fractionation characteristics of the membrane examined using a latex aqueous solution are as follows: In the case of the membrane of the present invention, the throat is low (Figures 1(b) and (C)), whereas the characteristics of the conventional membrane (Figures 1(a) and 2) are low. (t)] exhibits sharper characteristics.

The membrane of the present invention exhibits excellent separation properties as described above, and the particle sizes are relatively close to each other, making it possible to effectively use the membrane for separating particles.

[Brief explanation of drawings]

FIG. 1 is a model diagram of curves showing the fractionation characteristics of a microporous membrane, where curve a is a conventional membrane curve and curve c is a membrane curve of the present invention. FIG. 2 is a graph showing the results of Example 2. Curves d and e are the membranes of the invention, and curves f and f are commercially available membranes. Photos (1) and (2) are scanning electron micrographs of the pore morphology on the surface of a commercially available membrane, and Photo (3) is a scanning electron micrograph of the pore morphology on the surface of the microporous membrane of the present invention. be. Completion - @ Analysis (wave) Kitsune - @ Screen (subject) Engraving of the drawing (no change in content) P 73 Engraving of the 4-page drawing (no change in content) Amendment of procedure for five-year prisoner 1986 5 Patent Application No. 281261 filed in 1981 by the Commissioner of the Japan Patent Office Michibe Uga on August 27th, Name of the invention Relationship to the microporous membrane amendment case Patent applicant: 2-3-19 Kyobashi, Chuo-ku, Tokyo No. (603) Akio Kawasaki President and Director of Mitsubishi Rayon Co., Ltd. to correct. 2) “Photo (1), Photo (2)” on page 17, line 7 of the specification
" should be corrected to "Figures 3 and 4." 3) Correct "Photo (3)" in line 8 to "Figure 5." 4) Correct photos 1 to 3 of the drawings according to the 5J1 paper.

Claims (1)

[Claims] 1. Narrow pore size distribution with a porosity of 25% or more and a rejection of 10% or less for monodisperse latex particles with a particle size of 1/5 of the diameter of the monodisperse latex particles exhibiting a rejection of 95% Microporous membrane.