JP3499993B2 - Method for producing porous membrane and porous membrane - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separation membrane used for microfiltration, cleaning of foods, industrial materials such as battery separators, bandages, materials for medical materials such as disposable diapers, and rain clothing. The present invention relates to a medical material such as gloves and the like, a pharmaceutical material such as a film capable of accommodating a drug in a hole, a porous film which can be preferably used for optical materials and electronic materials, and a method for producing the porous film.

[0002]

2. Description of the Related Art As a porous membrane, one having a pore structure such as a capillary (straight tubular shape), a sponge or a pie is known. Polymers, metals, ceramics and the like are used as materials for forming such a porous film, but polymers are particularly widely used because they can be manufactured efficiently.

The polymer porous membrane is obtained by casting a solution prepared by dissolving the polymer in an organic solvent on a glass plate or the like, and forming a suitable gelling liquid (which is compatible with the solvent and the polymer is insoluble). It can be obtained by a method (phase conversion method) in which fine pores are formed by immersing in a different organic solvent, water, etc.) and utilizing the phenomenon of two-phase separation that occurs at that time. The shape of the resulting pores is
It is usually sponge-like or pie-like (a structure in which a large number of thin layers having many holes are stacked) and penetrates, but is not a capillary-like through hole (straight through hole). As the polymer, cellulose acetate, polysulfone, polycarbonate, polyvinyl alcohol, polyamide or polyvinylidene fluoride is used. Alternatively, it can be obtained by heating and dissolving a polymer in a solvent that functions as a solvent at a high temperature but becomes a non-solvent at a low temperature, form a film, and then rapidly solidify (melt-quenching method). The above-mentioned phase inversion method and melt-quenching method are used for “membrane” (18 (5),
4-270, 1993). As a simple method for producing a porous polymer film, for example, a large amount of fine inorganic powder is added to a polymer such as polypropylene (usually,
(50% by volume or more with respect to the polymer), then a film is formed by extrusion or the like, and further stretched in a uniaxial or biaxial direction at a high ratio to form a fracture hole at the interface with the inorganic fine powder. The method is known. However, since the amount of the inorganic fine powder is too large with respect to the polymer, there is a problem that the excellent properties inherent to the polymer film such as good flexibility and high strength are impaired.

Straight through-hole (capillary through-hole)
The polymer porous film having
A polymer film such as polycarbonate having a thickness of about m is irradiated with an electron beam (charged particles) to form loci of particles on the film, and the loci are expanded by etching with a solvent to form fine holes. A polymer film with through holes obtained by applying (eg, Nuclepore
Membrane) is known. However, such a polymer film has a problem that it is difficult to form a thick film, the production is complicated, and a high degree of control is required. In addition, Japanese Patent Publication No. 6-84448 discloses a method of producing a porous sheet by irradiating a resin sheet with a laser beam to form linear through holes, but the same as above. There are problems that it is difficult to form a thick film and the manufacturing is complicated.

As described above, most of the porous membranes made of polymers have a sponge-like or pie-like structure and are widely manufactured and used. Such a sponge-like or pie-like polymer porous membrane is an asymmetric membrane having different pore sizes on the front and back sides of the membrane.
When used for microfiltration, the particles to be filtered enter into the pores, so that when the pores are clogged, the particles cannot be removed by the regeneration treatment. In addition, such a sponge-like polymer porous film is easily scratched because there are many thin portions of the film between the pores, and unexpectedly large pores tend to be formed. The liquid generally has a broad particle size distribution. On the other hand, a polymer porous membrane having linear through-holes is generally a symmetric membrane, and when used for microfiltration, the pore diameter distribution on the surface is narrow, so particles with a diameter larger than that will be captured, and the accuracy Good filtration is possible. Further, since the porous membrane having the linear through holes is of a type in which the fine particles are captured on the surface of the membrane as described above, it is relatively easy to remove the particles by the regeneration treatment. However, since such a porous membrane is complicated to manufacture as described above, it is rarely used except for filtration which requires particularly high accuracy.

[0006] For example, in the field of microfiltration, the sponge-like or pie-like porous membrane is mainly used.
If you want to improve the durability such as scratch resistance, pinholes, etc., or the accuracy of filtration, a porous membrane with linear through-holes is useful, and a linear membrane that can be efficiently manufactured is used. The advent of polymeric porous membranes with through holes is desired.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a porous membrane which can efficiently produce a polymer porous membrane having a large number of linear through holes. is there. Another object of the present invention is to provide a polymer porous membrane having a large number of substantially vertically formed through holes having a small surface pore size.

[0008]

According to the present invention, a polymer solution prepared by dissolving a polymer in a solvent is cast on a support,
This is immersed in a coagulation bath consisting of a poor solvent for the polymer cooled to a temperature lower than the temperature of the support by 50 ° C. or more to form a coagulation layer of the polymer on the support, and then a support having a coagulation layer. After peeling off the coagulation layer from the body and taking out the coagulation layer from the coagulation bath, or after taking out the support having the coagulation layer from the coagulation bath and peeling off the coagulation layer from the support, by drying, By forming a polymer layer having a large number of pores formed substantially vertically inside, and removing the surface layers on both sides of the polymer layer from the polymer layer,
It is a method for producing a porous membrane, which comprises obtaining a polymer film having a large number of through holes formed substantially perpendicular to the surface.

A preferred embodiment of the method for producing the above-mentioned porous membrane is as follows. 1) The temperature of the support when casting the polymer solution is 20 to
It is 60 ° C. 2) The temperature of the poor solvent in the coagulation bath is -80 to 0 ° C. 3) The viscosity of the polymer solution is 100 to 8000 at 20 ° C.
cps (preferably 100-5000 cps, especially 20
0-5000 cps). 4) The polymer solution contains the polymer in the range of 5 to 30% by weight (preferably in the range of 5 to 20% by weight). 5) The surface layer is removed by plasma treatment. 6) The polymer is polysulfone, polyurethane, polyvinylidene fluoride, polyvinyl alcohol, polycarbonate, polyamide or triacetyl cellulose. 7) The solvent in which the polymer is dissolved is at least one selected from the group consisting of N-methyl-2-pyrrolidone, methyl acetate, ethyl acetate, methyl ethyl ketone, dimethylacetamide, formic acid, methylene chloride, chloroform, dimethyl sulfoxide and dimethylformamide. . 8) The poor solvent is at least one selected from the group consisting of alcohols (eg, methanol, ethanol and isopropyl alcohol) and water. 9) The shape of the through holes of the polymer film is symmetrical. 10) The thickness of the polymer film is 50 to 500 μm. 11) The average pore diameter (at the 1/2 layer thickness position) of the through holes of the polymer film is 5 to 100 μm. 12) The number of through holes (on the film surface) of the polymer film is 50 to 10,000 / mm ² . 13) The hole diameter of the through holes on both surfaces of the polymer film is the same as or smaller than the hole diameter at the 1/2 thickness position in the thickness direction.

A polymer film having a large number of through holes formed substantially perpendicular to the surface by the above-mentioned manufacturing method, wherein the diameter of the through holes on both surfaces of the film is
It can be advantageously manufactured by a porous membrane characterized by having a pore diameter smaller than the 1/2 thickness position in the thickness direction.

The preferred embodiments of the above-mentioned porous membrane are as follows. 1) The thickness of the polymer film is 50 to 500 μm. 2) The average hole diameter of the through holes (at the 1/2 layer thickness position) is 5 to 1
It is 00 μm. 3) The number of through holes (on the film surface) is 50 to 10,000
The number of pieces / mm ² . 4) The shape of the through hole is symmetrical. 5) The polymer is polysulfone, polyurethane, polyvinylidene fluoride, polyvinyl alcohol, polycarbonate, polyamide or triacetyl cellulose.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The method for producing the porous membrane of the present invention can be performed, for example, as follows. First, a polymer solution is prepared by dissolving a polymer in a solvent. The temperature of the obtained polymer solution is generally higher than the ambient temperature due to the mixing operation at the time of preparing the solution and the like, but it may be heated so as to facilitate the casting. The polymer solution is cast onto a support that has been warmed to about the same temperature as the solution.

Examples of the polymer used in the polymer solution include polysulfone, polyurethane, polyvinylidene fluoride, polyvinyl alcohol, polycarbonate,
Mention may be made of polyamides and triacetyl cellulose. Polysulfone is preferred. The solvent for dissolving the polymer can be used without particular limitation as long as it can dissolve the polymer. Examples of such a solvent include N-methyl-2-pyrrolidone, methyl acetate, ethyl acetate, methyl ethyl ketone, formic acid, methylene chloride, chloroform, dimethylacetamide, dimethylsulfoxide and dimethylformamide. For example, N-methyl-2-pyrrolidone is suitable for polysulfone, methyl acetate for polyurethane, dimethylacetamide for polyamide,
Dimethylsulfoxide and dimethylformamide are preferred, and for triacetylcellulose dimethylacetamide is preferred. In addition, addition of a small amount of water as a solvent (generally 5% by weight or less of the total amount of solvent) is preferable for promoting the formation of pores.

The above polymer solution contains 5 to 30 polymer.
It is preferably contained in an amount of 5% by weight, particularly 5 to 20% by weight. The viscosity of the polymer solution is 10 at 20 ° C.
0-8000 cps is preferable, and further 100-500
0 cps is preferable, and 200 to 5000 cps is particularly preferable.

As described above, the support is preferably heated to about the same temperature as the polymer solution, and the temperature range is preferably 20 to 60 ° C, particularly preferably 20 to 40 ° C. The heating can be performed by applying hot air or warm air to the support, applying infrared rays, or bringing the support into contact with a heated roll. The casting of the polymer solution onto the support is generally performed using an extrusion die, a doctor blade or the like.

The polymer solution layer cast on the support is cooled immediately (generally within 10 seconds after casting) to a temperature lower than the temperature of the support by 50 ° C. or more (a poor solvent for the polymer). It is immersed in a coagulation bath consisting of a liquid in which the polymer dissolves little or not at all. When the polymer solution layer is rapidly cooled, a finger structure structure (a structure having pores having a small pore size at the tip and a large pore size inside) is formed in the layer, and the solvent is condensed in the pores. The poor solvent of the polymer in the coagulation bath penetrates into this portion, and is mostly replaced with the good solvent to complete the finger structure structure (the coagulated layer composed of the polymer and the poor solvent). The polymer solution layer generally has a coagulation bath content of 10
It is soaked for 10 seconds to 10 minutes. It is preferably 20 to 60 seconds. In order for the polymer solution layer to easily form the finger structure structure as described above, it is particularly advantageous that the polymer solution layer has the polymer content and the viscosity as described above.

As the poor solvent, any liquid can be used as long as the polymer is insoluble or almost insoluble. Examples thereof include alcohols (eg, methanol, ethanol and isopropyl alcohol) and water. You can The temperature of the poor solvent in the coagulation bath is −
80 to 0 ° C is preferable, and -80 to -20 ° C is particularly preferable.

The coagulation layer (a small amount of the solvent of the polymer solution is contained) coagulated and coagulated in the coagulation bath is either stripped from the support in the coagulation bath and taken out, or after being taken out from the coagulation bath, It is peeled off from the support. It is then dried to form a polymer layer whose surface is pore-free (has very fine pores) but which has a large number of pores of finger structure inside. The drying is generally 30 to 60 ° C.
At 1 to 60 minutes (preferably 5 to 30 minutes). Before drying, it is preferable to remove the residual solvent in the solidified layer by immersing the solidified layer in water or a poor solvent at room temperature to 30 ° C. In particular, it is effective and preferable when the solvent used has a high boiling point. A schematic view of a cross section of the obtained polymer layer is shown in FIG. In the polymer layer 11, a large number of holes 12 having a finger structure structure (having a small hole diameter at the tip end and a large hole diameter inside) are formed substantially perpendicular to the surface. These pores are not seen near the surface, but strictly speaking, there are very small pores near the surface as well, through which solvent invades and escapes or evaporates during layer formation.

Then, the surface layer having no holes on both sides thereof is removed from the polymer layer (film) having no holes on the surface but having a large number of holes having a finger structure structure inside. Examples of the method for removing the surface layer include plasma treatment, polishing treatment and the like. Plasma treatment is preferred.

By removing the surface layer from the polymer layer in this manner, a polymer film (porous film) having a large number of through holes can be obtained. As shown in FIG. 1, in the polymer layer before the removal of the surface layer, the pores have a small pore size at the tip and a large pore size inside, so that the surface layer is removed so that the tip remains. The porous membrane of the invention can be obtained.

A schematic view of a cross section of the porous membrane of the present invention is shown in FIG. A large number of pores 22 are formed in the porous film 21 substantially perpendicular to the surface. The average diameters (pore diameters) a1 and a2 of the pores on the surface of the porous membrane 21 are smaller than the average pore diameter b at the ½ thickness position in the thickness direction. The average pore diameter on the surface is generally 0.05 to 0.95 times the average pore diameter at the 1/2 thickness position in the thickness direction, and can be appropriately changed depending on the application.

When the surface layer is removed so that the tips of the pores of the polymer layer are completely removed, a porous membrane having a large number of pores having a uniform pore size can be obtained. A schematic view of a cross section of such a porous membrane is shown in FIG. Porous membrane 3
First, a large number of pores 32 are formed substantially perpendicular to the surface. The diameter of the pores (pore diameter) of the porous membrane 21 is almost the same at any position in the cross section, and it can be said that this porous membrane is a symmetrical membrane. It can be seen that the porous film is densely formed with a large number of through holes (pores) substantially perpendicular to the surface. The thickness of such a porous membrane (polymer film) is generally 10 to 500 μm, and 50 to 500 μm.
Is preferred. The average pore diameter of the through-holes in the thickness of ½ of the film is preferably 1 to 100 μm, particularly 5 to 10 μm.
0 μm is preferable. The number of through holes on the film surface is preferably 50 to 10,000 / mm ² , and particularly 10
0 to 8000 pieces / mm ² is preferable. The porous membrane of the present invention shown in FIG. 2 has a similar shape. The shape of the through hole, the composition and viscosity of the polymer solution, the temperature of the support,
It is determined by the temperature of the coagulation bath.For example, in order to reduce the pore size and increase the number of through holes, the viscosity of the polymer solution should be increased, the temperature of the solution and support should be low, and the temperature of the coagulation bath should be low. It is effective to adjust the value higher.

Both the above-mentioned porous membrane having a large number of small pores and the porous membrane having a large number of pores having a small pore size on the surface can completely trap particles having a desired diameter or more. It has the feature that it can. Further, when unfiltered particles are clogged, they are clogged on the surface of the pores, so that the particles can be easily removed by the regeneration treatment, and there is an advantage that they can be used for a long period without clogging. Further, a thick film can be easily obtained, and such a film has excellent durability. Alternatively, as another application, when a drug is injected into the pores of the film and the injected drug is discharged at a necessary place (site), the discharge amount can be controlled by the size of the surface pore size. Therefore, it can be advantageously used as a drug injecting medium. Further, since such a film has a large number of substantially vertical pores, it can also be used in an optical field where light is transmitted through the film and only linear light is extracted. Particularly, the porous membrane having a large number of small pores formed on the surface of the present invention is easy to regenerate after use for filtration and is suitable as a drug injection medium.

[0024]

【Example】

Example 1 140 parts by weight of polysulfone, N-methyl-
860 parts by weight of 2-pyrrolidone and 10 parts by weight of water were mixed to dissolve polysulfone to prepare a polymer solution (viscosity at 20 ° C .: 500 cps). The solution was warmed to 40 ° C. 4. Add the polymer solution at 40 ° C. to 4
Polyethylene terephthalate (PE
T) cast on a film at a casting amount of 150 g / m ² ,
Two seconds later, it was immersed in a coagulation bath of methanol at -50 ° C for 60 seconds, peeled off from the PET film in the coagulation bath, and then the coagulation layer was taken out from the coagulation bath. The solidified layer is immersed in warm water at 30 ° C. to remove the solvent, and then dried at 60 ° C. for 30 minutes to obtain a surface layer having no pores (having extremely fine pores) and a finger structure. A polymer layer (film) having the inside of the structure was obtained. An electron micrograph of this cross section is shown in FIG. 4 (magnification: 350 times). This is a structure corresponding to FIG. 1.

Both sides of the obtained polymer layer (film) were etched with oxygen plasma (conditions: 150 W for 2 minutes) to obtain a porous membrane of the present invention having the structure of FIG.
An electron micrograph of this section is shown in FIG. 5 (magnification: 350).
Times).

[Embodiment 2] A porous material was prepared in the same manner as in Embodiment 1 except that etching by oxygen plasma was carried out for a longer time (1.2 times longer) than that in Embodiment 1. A film was obtained. An oblique electron micrograph of the obtained porous film is shown in FIG. 6, and an electron micrograph of a cross section thereof is shown in FIG. 7 (magnification: 350 times) and FIG. 8 (magnification: 600 times). The obtained porous membrane was a membrane having pores with a substantially uniform pore size as shown in FIGS. 6 to 8. FIG. 3 is the corresponding structure.

[Reference Example 1] A porous material was prepared in the same manner as in Example 1 except that the temperature of the polymer solution was 25 ° C. and the coagulation bath of methanol at −50 ° C. was a coagulation bath of water at 0 ° C. A film was obtained. The pores of the obtained porous membrane were formed in various shapes such as an elliptical cross section, and it was not possible to obtain substantially vertical pores having a uniform pore diameter. No etching treatment was performed. An electron micrograph of this section is shown in FIG. 9 (magnification: 350 times). Furthermore, an electron micrograph of a cross section of a porous film commercially available as a 10 μm filter is shown in FIG.
Is shown (magnification: 200 times).

The physical properties of the porous film obtained above were measured as follows. 1) Average pore diameter and number of through holes Measured using an electron micrograph. 2) Porosity The porous membrane was dipped in a poor solvent, and the porosity was calculated from the increased weight. 3) Porosity calculated using an electron micrograph of the surface. 4) By specific surface area nitrogen adsorption method. The ratio of the actual surface area to the surface area of the cylinder was determined. 5) Light Transmittance One surface of the porous film was irradiated with light, the amount of transmitted light was measured from the opposite surface, and the ratio between the amount of irradiated light and the amount of transmitted light was determined. 6) The brightness of the linearly transmitted light was measured at a distance of 10 cm and a distance of 20 cm, and shown as a percentage of the ratio of the brightness at a distance of 20 cm to the brightness at a distance of 10 cm.

The above results are shown in Table 1 below.

[0030]

[Table 1]                                   Table 1 ────────────────────────────────────                       Example 1 Example 2 Reference example 1 ──────────────────────────────────── Film thickness (μm) 135 125 170 Average pore size [1/2 thickness] 15 15 --- (Μm) [surface] 10 −−−− Number of through holes 1380 1450 --- Porosity (%) 65 70 68 Porosity (%) 20 26 --- Specific surface area ratio 3.2 3.2 --- Light transmittance (%) 50 76 --- Light straightness (%) 65 72 --- ────────────────────────────────────

Example 3 A comparative experiment of filtration was carried out using the porous membrane obtained in Example 2 and the porous membrane commercially available as the 10 μm filter shown in FIG. Figure 11
In a container shown in Fig. 5, a 5% by weight aqueous dispersion 2 of SiO ₂ ground particles was added.
00 cc was charged, and filtration was performed using a porous membrane (area: 1.13 cm ² ) attached to the lower part of the container while pressurizing with 0.5 kg / cm ² air from the upper part.

The diameter of the particles contained in the filtrate was measured with a laser type particle size distribution measuring device. When the porous membrane of Example 2 (average pore size: 15 μm) was used, all particles of 20 μm or larger were cut. On the other hand, when a commercially available filter was used, 20% of particles of 10 μm or more were present, but all particles of 35 μm or more were cut. FIG. 12 shows the respective particle size distributions of a 5% by weight aqueous dispersion of pulverized particles of SiO _{2 as a} raw material, a filtrate using the porous membrane of Example 2, and a filtrate using a commercially available filter. Show.

[0033]

As is apparent from the above examples and reference examples, the porous membrane obtained by the simple production method of the present invention has a large number of through holes substantially perpendicular to the surface. The quality membrane is an advantage of a symmetrical membrane having a through hole, and is characterized by being less likely to be scratched and less likely to cause pinholes when used for microfiltration. Further, since the pore diameters are well aligned and densely formed, it is possible to perform filtration so as to almost completely remove the medium having a desired particle diameter or more. Furthermore, a thick film can be easily obtained by the above production method, and such a film is further excellent in durability. Further, the porous film having a large number of substantially vertical through holes formed on the surface of the present invention in which the surface layer is partially removed is
Since the pore diameter of the surface layer is small, especially when the particles that are not filtered are clogged, the pore surface is likely to be clogged, so that the particles can be easily removed by a regeneration treatment, and there is an advantage that they can be used for a long period of time. Alternatively, as another application, when a drug is injected into the pores of the film and the injected drug is discharged at a necessary place (site), the discharge amount can be controlled by the size of the surface pore size. Therefore, it can be advantageously used as a drug injecting medium. Further, since such a film has a large number of substantially vertical pores, it can be used also in the field of optics where light is transmitted through the film and only linear light is extracted.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross section of a polymer layer which has no holes on the surface but has many holes having a finger structure structure inside.

FIG. 2 shows a schematic view of a cross section of a porous membrane of the present invention.

FIG. 3 shows a schematic view of a cross section of a porous membrane in which the tip of the pores of the polymer layer before the removal of the surface layer are completely removed.

FIG. 4 is an electron micrograph of a cross section of a polymer layer having no holes on the surface but having a large number of holes having a finger structure structure inside.

FIG. 5 shows an electron micrograph of a cross section of a porous film of the present invention.

FIG. 6 shows an electron microscope photograph from an oblique direction of a porous film in which the tips of the pores of the polymer layer before the removal of the surface layer are completely removed.

7 is an electron micrograph (35) of a cross section of the porous membrane of FIG.
(0 times).

8 is an electron micrograph (60) of a cross section of the porous membrane of FIG.
(0 times).

FIG. 9 shows an electron micrograph of a cross section of the porous film obtained in Reference Example 1.

FIG. 10 shows an electron micrograph of a cross section of a commercially available 10 μm filter.

11 shows a cross-sectional view of the device used in the filtration test of Example 3. FIG.

FIG. 12: Particle size distributions of 5% by weight aqueous dispersion of pulverized SiO ₂ particles as a raw material, a filtrate using the porous membrane of Example 2, and a filtrate using a commercially available filter It is a graph which shows.

[Explanation of symbols]

11 Polymer Layers 12, 22, 32 Pore 21, 31 Porous Membrane a1, a2 Mean Pore Diameter (Pore Diameter) b on the Surface of Porous Membrane b Mean Pore Diameter at 1/2 Thickness Position in Thickness Direction

Claims (7)

(57) [Claims] 1. A coagulation of a poor solvent for the polymer, which is obtained by casting a polymer solution in which a polymer is dissolved in a solvent on a support and then cooling the solution to a temperature lower than the temperature of the support by 50 ° C. or more. After immersing in a bath to form a coagulated layer of a polymer on the support, and then peeling the coagulated layer from the support having the coagulated layer and taking out the coagulated layer from the coagulation bath, or the support having the coagulated layer is removed. After being taken out from the coagulation bath, the coagulation layer was peeled from the support, and then dried to form a polymer layer having a large number of pores formed substantially perpendicular to the surface inside, and the polymer layer on both sides thereof. A method for producing a porous membrane, which comprises removing the surface layer to obtain a polymer film having a large number of through holes formed substantially perpendicular to the surface. 2. The method for producing a porous membrane according to claim 1, wherein the temperature of the support when casting the polymer solution is 20 to 60 ° C. 3. The method for producing a porous membrane according to claim 1, wherein the temperature of the poor solvent in the coagulation bath is −80 to 0 ° C. 4. The polymer solution has a viscosity of 10 at 20 ° C.
The method for producing a porous membrane according to claim 1, wherein the production rate is 0 to 5000 cps. 5. The method for producing a porous film according to claim 1, wherein the surface layer is removed by plasma treatment. 6. A polymer film having a large number of through-holes formed substantially perpendicular to the surface, wherein the diameter of the through-holes on both surfaces of the film is ½ of the thickness direction.
A porous membrane characterized by being smaller than the pore diameter at the thickness position. 7. The polymer film has a thickness of 50-5.
The average hole diameter of the through holes at the 1/2 thickness position of the film is 5 to 100 μm, and the number of the through holes per area of the film surface is 50 to 10,000.
The number of particles / mm ² is the porous membrane according to claim 6.