TW201536406A - Composite microporous film, its manufacturing method and filter using the same - Google Patents

Abstract

The invention acquires a composite microporous film which not only retains high permeability but also has hydrophilicity. The composite microporous film of the invention is the composite microporous film using SiO2 glass layer to cover the surface of microporous film with polyvinylidene fluoride resin. The composite microporous film is hydrophilized by covering SiO2 glass layer on the surface. The composite microporous film of the invention excludes the microporous clogging of the surface of the composite microporous film, besides it realizes high permeability and hydrophilicity.

Description

Composite microporous membrane and filter using the same

The present invention relates to a microporous membrane suitable for water treatment purposes represented by a membrane separation activated sludge process (membrane bioreactor (MBR)).

A microporous membrane containing polyvinylidene fluoride (PVDF) is excellent in chemical resistance and heat resistance, and is used as an air filter, a bag filter, and a filter for liquid filtration. Widely used. The PVDF microporous membrane is prepared by a nonsolvent induced phase separation method (a solution obtained by dissolving a polymer in a good solvent, and applying the solution to a glass plate or the like thinly. A method in which an adult is immersed in a non-solvent to cause phase separation to obtain a microporous membrane or the like (for example, Patent Document 1).

Since the microporous membrane of PVDF is hydrophobic, it is necessary to coat the surface with a hydrophilizing agent such as polyvinyl alcohol (PVA) or to perform hydrophilization treatment in order to be used for water treatment (for example, Patent Document 2) ). However, the hydrophilized microporous membrane obtained by this method lacks the hydrophilization effect. In the case of continuous release, in the case where PVA or ethanol is completely dissolved, the hydrophilization effect disappears. Further, there is a problem in that PVA is mixed into the filtrate or the pores are clogged by PVA.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] International Publication No. 10/032808

[Patent Document 2] Japanese Patent Laid-Open Publication No. 05-023557

In view of the above, an object of the present invention is to provide a composite microporous membrane which does not have pore blocking due to coating of a hydrophilizing agent and which has a hydrophilic property, and a filter using the same. .

The inventors of the present invention have repeatedly conducted active research in order to solve the above problems. As a result, it has been found that a microporous film containing a polyvinylidene fluoride-based resin which optimizes the surface structure and a composite microporous film obtained by coating the surface with a SiO ₂ glass layer can solve the above problem. And the present invention has been completed based on this finding.

A composite microporous membrane according to a first aspect of the invention is characterized in that at least one of the surfaces of the microporous membrane containing the polyvinylidene fluoride-based resin is coated with a SiO ₂ glass layer. When it is configured as described above, in addition to the heat resistance and chemical resistance of the polyvinylidene fluoride-based resin, the hydrophilization effect of the SiO ₂ glass layer is obtained, so that the filter film exhibits excellent performance. .

The composite microporous membrane of the second aspect of the present invention is the first aspect of the invention A composite microporous membrane according to the first aspect, wherein a microporous membrane containing a polyvinylidene fluoride-based resin is produced by a non-solvent-induced phase separation method. If it is configured in the above manner, it has an asymmetrical structure in which the pore diameter changes in the thickness direction of the film (refer to the left of FIG. 8), and has a surface layer including the micropores formed, and the formation of the surface layer is supported by the micropores. Since the support layer of the larger pores has a structure, the surface layer can be used to maintain the filtration precision, and the support layer can be used to ensure the permeability, so that excellent filtration performance is exhibited.

The composite microporous membrane according to the third aspect of the present invention is the composite microporous membrane according to the first aspect or the second aspect of the invention, and the microporous material containing the polyvinylidene fluoride resin. The film is an asymmetric film, and includes a surface layer formed with micropores and a support layer supporting the surface layer to be formed with a larger pore than the micropores, and the surface layer has a plurality of spheroids, a plurality of lines The shaped bonding material extends in three directions from each of the spherical bodies, and the adjacent spherical bodies are connected to each other by the linear bonding material to form a three-dimensional network structure in which the spherical body is used as an intersection.

Fig. 1 shows an example of a three-dimensional network structure of the present invention. Figure 1 is a scanning electron microscope (SEM) photograph of the surface of the surface layer. In addition, the term "surface layer" refers to a layer from the surface to the micropores in the cross section of the microporous film containing the polyvinylidene fluoride resin, and the "support layer" means self-containing polyvinylidene fluoride. A layer in which the surface layer is removed from the entire microporous film of the resin. The term "microporous" refers to a large void which is generated on the support layer of the microporous membrane and has a minimum of several μm and a size which is substantially the same as the thickness of the support layer. The "spherical body" refers to a spherical shape formed at the intersection of the three-dimensional network structure, and is not limited to a completely spherical shape, and includes a substantially spherical shape. If it is constructed in the manner described, it becomes a ball. The gap between the spheroid and the spheroid is separated by a linear bonding material, so it is easy to form a shape. Micropores of the same size can form a surface layer excellent in permeability. Since the linear bonding material also functions to crosslink the spheroids, the spheroids do not fall off, and the filter material itself can be prevented from being mixed into the filtrate. Further, since the spherical body exists at the intersection of the three-dimensional network structure, it is possible to prevent the surface layer from collapsing due to pressure when used as a filter film. That is, the pressure resistance is high. Further, by using a three-dimensional network structure as shown in FIG. 1 formed of a spherical body and a linear bonding material, the voids of the surface layer and the conventional microporous resin containing polyvinylidene fluoride resin having the same degree of pore diameter. Since the film ratio is increased, the passage is maintained, and the voids are more homogeneous and three-dimensionally arranged, so that the permeability is excellent.

The composite microporous membrane of the fourth aspect of the invention is the composite microporous membrane according to the third aspect of the invention, wherein the spheroid has a particle diameter of ±10% of the average particle diameter. Within the range of the amplitude, it becomes a frequency distribution of 50% or more. According to the above configuration, the spherical body of the surface layer has the same particle diameter. Therefore, it is easy to form a void having a uniform pore diameter between the spheroid and the spheroid.

The composite microporous membrane of the fifth aspect of the invention is the composite microporous membrane according to the third aspect or the fourth aspect of the invention, wherein the length of the bonding material has an average length A frequency distribution of 50% or more in the range of ±30% of the amplitude. When it is configured as described above, the spherical body of the surface layer is more uniformly dispersed. Therefore, it is easy to form a void having a uniform pore diameter between the spheroid and the spheroid.

The composite microporous membrane of the sixth aspect of the present invention is the composite microporous membrane according to any one of the third aspect to the fifth aspect of the present invention, wherein The spheroid has an average particle diameter of 0.05 μm to 0.5 μm. According to the above configuration, the spherical body having the average particle diameter within the range and the linear bonding material connecting the spherical bodies are easily formed between the spherical body and the spherical body. hole.

The composite microporous membrane of the seventh aspect of the invention is the composite microporous membrane according to any one of the third aspect to the sixth aspect of the invention, wherein the thickness of the surface layer is The thickness of the support layer is from 0.5 μm to 500 μm from 0.5 μm to 5 μm. According to the configuration described above, since the surface layer is a layer (functional layer) in which impurities are removed in the asymmetric film, the thinner layer can be formed as long as it does not interfere with the formation of the three-dimensional network structure in which the spherical body is the intersection point. It is preferred to reduce the filter impedance. The majority of the support layer of the microporous membrane is substantially unhelpful for the removal of impurities, but if only the very thin surface layer is broken, a sufficiently thick support layer can be used to avoid this.

The composite microporous membrane of the eighth aspect of the present invention is the composite microporous membrane according to any one of the third aspect to the seventh aspect of the present invention, which is provided with the support The substrate layer of the layer.

When it is configured as described above, the base material layer becomes a reinforcing material and becomes resistant to a higher filtration pressure. Further, in the application during film formation, it is possible to prevent the raw material liquid obtained by dissolving the resin which is a raw material in a solvent inadvertently. It is especially effective in the case of a low viscosity raw material liquid. Further, a part of the support layer is in a form mixed with the substrate layer, and the boundaries between the two are not so clear. If the mixed portion of the support layer and the base material layer is too small, the support layer may be easily peeled off from the base material layer.

The composite microporous membrane of the ninth aspect of the invention is as described in the invention The composite microporous membrane according to the first aspect to the eighth aspect, wherein the polyvinylidene fluoride-based resin has a weight average molecular weight (Mw) of 600,000 to 1,000,000.

According to the above configuration, in the polyvinylidene fluoride-based resin having a weight average molecular weight, a microporous film containing a polyvinylidene fluoride-based resin including a spherical body and a surface layer can be easily formed. The surface layer has a three-dimensional network structure in which a spherical body is formed as an intersection point by a linear bonding material in which the spherical bodies are cross-linked to each other.

The composite microporous membrane of the tenth aspect of the invention is the composite microporous membrane according to any one of the first aspect to the ninth aspect of the invention, wherein the average pore diameter is 5 nm. ~500nm. When the average pore diameter is 5 nm or more, the increase in pressure loss accompanying clogging at the time of filtration can be minimized, and when it is 500 nm or less, the transmission of coarse foreign particles can be suppressed, and thus excellent filtration performance is exhibited.

The composite microporous membrane of the eleventh aspect of the invention is a composite microporous membrane as described in any one of the first aspect to the tenth aspect of the invention, which exhibits a shape of a flat membrane . When it is configured as described above, when a module in which a plurality of filtration membranes are combined is formed as compared with a hollow fiber, it is difficult to deposit inclusions between the membrane and the membrane, and an increase in pressure loss can be suppressed, so that performance is exhibited. Excellent filtration performance.

A filter according to a twelfth aspect of the present invention is characterized in that the composite microporous membrane according to any one of the first aspect to the eleventh aspect of the invention is used. According to the above configuration, a composite microporous membrane having excellent hydrophilicity and permeability can be used as the filter. For the use of this filter Since the impurities are not eluted from the composite microporous membrane, the energy efficiency and the treated water quality are excellent, so that it can be suitably used for water treatment applications such as MBR.

The method for producing a composite microporous membrane according to the thirteenth aspect of the present invention is the method for producing the composite microporous membrane according to any one of the first aspect to the eleventh aspect of the present invention. After the coating film of the ceria precursor is formed on at least one side of the microporous film containing the polyvinylidene fluoride-based resin, the ceria precursor is converted into SiO ₂ glass, thereby forming SiO ₂ glass. In the layer, a microporous film containing a polyvinylidene fluoride-based resin in which at least one side thereof is coated with SiO ₂ glass is obtained. According to the above configuration, the SiO ₂ glass layer can be uniformly formed on the surface of the microporous film containing the polyvinylidene fluoride resin, and thus an excellent hydrophilization effect can be obtained.

A method for producing a composite microporous membrane according to a thirteenth aspect of the present invention, wherein the ceria precursor is polyfluorene Azane. When it is configured as described above, the conversion to the SiO ₂ glass layer having a dense structure can be easily performed.

A method for producing a composite microporous membrane according to a fifteenth aspect of the present invention is the method for producing the composite microporous membrane according to the eighth aspect of the present invention, comprising: a coating step which causes the a raw material liquid obtained by dissolving a polyvinylidene fluoride-based resin in a good solvent is applied onto the base material layer; and a immersing step of immersing the base material layer in a non-solvent after the coating step The raw material liquid applied. When it is configured as described above, it is a method for producing a microporous film containing a microporous film of a polyvinylidene fluoride-based resin as an asymmetric membrane and having a plurality of spherical bodies in the surface layer. The spheroids of the surface layer are cross-linked with each other by a linear bonding material to form a spherical shape. The body acts as a three-dimensional network of intersections. The spheroids are more uniformly dispersed in a more uniform size, so that the micropores of the surface layer are dispersed in the same manner and have excellent permeability.

A method for producing a composite microporous membrane according to a sixteenth aspect of the present invention, which is a method for producing a composite microporous membrane according to the ninth aspect of the present invention, comprising: a coating step which causes a mixture a raw material liquid obtained by dissolving a difluoroethylene resin in a good solvent is applied onto a substrate layer or a support; and a dipping step, after the coating step, immersing the substrate layer in a non-solvent and The raw material liquid applied.

According to the above configuration, a polyvinylidene fluoride-based resin suitable for forming a three-dimensional network structure of the surface layer is used as a material. Therefore, the spherical bodies are crosslinked by a linear bonding material, and the surface layer can be easily formed. The three-dimensional network structure in which the spheroid is used as an intersection.

The composite microporous membrane of the present invention is a composite microporous membrane comprising a microporous membrane containing a polyvinylidene fluoride-based resin, and the microporous membrane containing the polyvinylidene fluoride-based resin has a membrane surface Since the SiO ₂ glass layer is coated with a regular three-dimensional network structure, it is excellent in heat resistance and chemical resistance, and has high porosity and permanent hydrophilicity.

1‧‧‧ spheroid

2‧‧‧Line-shaped bonding materials

3‧‧‧The thickness of the film as a whole (thickness of the support layer = overall - surface layer)

4‧‧‧Microporosity

5‧‧‧ Surface thickness

Fig. 1 is a surface photograph of a surface layer of a microporous film containing a polyvinylidene fluoride-based resin of the present invention.

Fig. 2 is a photograph of a conventional polyvinylidene fluoride filter membrane.

Fig. 3 is a flow chart showing a method of producing a composite microporous membrane of the present invention.

4 is a surface photograph of a surface layer of the composite microporous film of Example 1.

Fig. 5 is a surface photograph of a surface layer of the microporous membrane of Comparative Example 1.

The left side of Fig. 6 is a cross-sectional photograph of the composite microporous membrane of Example 1. The right side of Fig. 6 is an enlarged photograph of a section of the surface layer.

Fig. 7 is a photograph showing the surface layer of the surface layer of the composite microporous film of Example 1, and is a photograph for measuring the particle diameter of the spherical body and the length of the linear bonding material.

Fig. 8 is a schematic view showing a cross-sectional view (left) of an asymmetric film and a cross-sectional view (right) of a symmetric film. (Source: Japan Patent Office Homepage / 2005 Standard Technology Collection Water Treatment Technology / 1-6-2-1 Symmetrical Film and Asymmetric Membrane)

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or similar components are designated by the same or similar reference numerals, and the repeated description is omitted. Further, the present invention is not limited to the following embodiments.

The composite microporous membrane of the present invention will be described. Composite microporous membrane of the present invention comprises a surface comprising a polyvinylidene fluoride resin microporous film of SiO ₂ or glass layer coated structure, SiO ₂ glass layer containing a hydrophobic play polyvinylidene fluoride The resin-containing microporous membrane imparts a hydrophilic effect.

The SiO ₂ glass layer is preferably formed by impregnating the entire pores of the microporous film containing the polyvinylidene fluoride resin and coating the ceria precursor solution, but it is also required to maintain the composite microporous film. The necessity of the air permeability and the liquid permeability is as long as at least one of the surfaces of the microporous film containing the polyvinylidene fluoride-based resin is coated with the SiO ₂ glass layer to contain the polyvinylidene fluoride. The SiO ₂ glass layer may be formed on at least one side of the microporous film of the vinyl resin.

The polyvinylidene fluoride-based resin used in the present invention may be a resin containing a vinylidene fluoride homopolymer and/or a vinylidene fluoride copolymer. The polyvinylidene fluoride-based resin may contain a plurality of vinylidene fluoride-based homopolymers having different physical properties (viscosity, molecular weight, etc.). Alternatively, it may contain a plurality of vinylidene fluoride copolymers. The vinylidene fluoride copolymer is not particularly limited as long as it has a structure having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and a fluorine-based monomer other than the above. A copolymer of one or more fluorine-based monomers selected from the group consisting of vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and chlorotrifluoroethylene and vinylidene fluoride. Particularly preferred is a vinylidene fluoride homopolymer (polyvinylidene fluoride).

The microporous film containing a polyvinylidene fluoride-based resin used in the present invention may be formed by using the polyvinylidene fluoride-based resin, or may further contain other components. Further, the microporous membrane containing the polyvinylidene fluoride-based resin used in the present invention may be a microporous membrane containing a polyvinylidene fluoride-based resin. In this case, other components may be contained as long as it does not impair the effects of the present invention. Examples of the other component include a polymer other than the polyvinylidene fluoride-based resin or an additive such as an antibacterial agent for imparting other properties.

The composite microporous membrane of the present invention has an asymmetrical structure in which the pore diameter changes in the thickness direction of the membrane (see left in Fig. 8), and the pore layer (surface layer) near the surface of the membrane has the smallest pore diameter, and the pore diameter becomes larger as it goes toward the back surface. The surface layer has an aperture required for separation characteristics and functions as a functional layer. The rest is played as a support layer The functional layer has a large aperture and a small transmission impedance to maintain the flow path and film strength. The thickness of the surface layer is preferably from 0.5 μm to 5 μm, and the thickness of the support layer is preferably from 20 μm to 500 μm.

FIG. 1 is a part of a photograph obtained by photographing the surface (surface side) of the composite microporous membrane of the present invention by a scanning electron microscope (SEM). As shown in FIG. 1, the surface layer has a plurality of spherical bodies 1, and the plurality of linear bonding materials 2 extend in three directions from the respective spherical bodies 1, and the adjacent spherical bodies 1 are connected by the linear bonding material 2 to form The three-dimensional network structure in which the spheroid 1 is used as an intersection point produces a void which becomes a hole. Therefore, it is easy to form a hole in the surface layer, and the hole is difficult to be deformed. The asymmetric membrane has a dense and thin layer called a surface layer, which usually has few pores, so opening a large number of pores which are difficult to deform on the layer is extremely effective for improving permeability. The permeability of the composite microporous membrane of the third embodiment is greatly improved by the spherical bodies 1 provided in the surface layer and the linear bonding material 2 which is connected to each other. Therefore, it is possible to have higher permeability than the existing microporous membrane having the same average flow pore diameter. Here, the "average flow pore diameter" is a value obtained by ASTM F316-86, and when a composite microporous membrane is used as a filtration membrane, it has a large influence on the particle size. In the present invention, the average pore diameter of the composite microporous membrane is preferably from 5 nm to 500 nm, more preferably from 5 nm to 450 nm, most preferably from 10 nm to 400 nm. When the average pore diameter of the composite microporous membrane is 5 nm or more, the increase in pressure loss accompanying clogging at the time of filtration is minimized. Therefore, when it is 500 nm or less, the passage of coarse foreign particles can be suppressed. Therefore, it is preferred.

Further, as shown in Fig. 1, the spherical body 1 has substantially the same size and is substantially uniformly dispersed. Therefore, the shape of the gap formed between the spherical body 1 and the spherical body 1 is formed. A surface layer of uniform shape and size. The voids between the spherical bodies 1 are divided by the linear bonding material 2 which crosslinks the adjacent spherical bodies 1, and as a result, the pores formed are egg-shaped or substantially egg-shaped in which the outer peripheral curve has no depression. As described above, the shape of the pores is a homogeneous microporous membrane.

The surface of the conventional polyvinylidene fluoride filter membrane has only one of the "spherical body" or "bonding material" in the present invention, and thus the effect of the present invention is not obtained. For example, a polyvinylidene fluoride filter membrane having only a portion corresponding to the "bonding material" in the present invention is required to have a thickness corresponding to the "bonding material" in order to maintain the strength which can be used only as a filter membrane. Therefore, since it is not a linear shape but a planar shape, it is difficult to make a hole fine. Fig. 2 is a scanning electron micrograph of a conventional polyvinylidene fluoride filter membrane having the above configuration as an example.

The average particle diameter of the spheroids of the surface layer of the composite microporous membrane of the present invention is preferably from 0.05 μm to 0.5 μm. More preferably, it is 0.1 μm to 0.4 μm, and particularly preferably 0.2 μm to 0.3 μm. The particle diameter of the spherical body is often a value close to the average particle diameter, and is a uniform size. Further, the average particle diameter differs depending on the microporous membrane to be produced, and as described above, the value exists in a range. Therefore, a plurality of microporous membranes having different pore sizes and average pore diameters formed in the surface layer can be obtained.

The particle diameter of the spheroid can be determined by clearly checking the magnification of the spheroid, and taking a photograph of the surface side surface of the composite microporous film using a scanning electron microscope (SEM) or the like, and measuring at least The particle size of 50 arbitrary spheroids was averaged. Specifically, it is described in the examples. In addition, the so-called "particle size" is As shown in Fig. 7, the outer circumference of the spherical body is surrounded by a perfect circle that does not include the maximum diameter of the hole around it, and the diameter of the perfect circle. In order to make the shape of the pores in the surface layer more uniform, the shape of each of the spherical bodies is preferably close to a complete sphere, and the size of the spherical bodies is preferably less uneven.

The particle diameter of the spheroid is preferably a frequency distribution of 50% or more in the range of ±10% of the average particle diameter in the frequency distribution. More preferably, it is 55% or more, and particularly preferably 60% or more. If more than 50% of the frequency is distributed within the range of ±10% of the average particle diameter, the spheroid of the surface layer has a more uniform shape. The size can form a uniform (uniform) gap between the spheroid and the spheroid.

The average length of the linear bonding material of the surface layer of the composite microporous membrane of the present invention is preferably from 0.05 μm to 0.5 μm. More preferably, it is 0.1 μm to 0.4 μm, and particularly preferably 0.2 μm to 0.3 μm. Most of the length of the linear bonding material is a value close to the average length and becomes a uniform length. Further, the average length differs depending on the microporous membrane to be produced, and as described above, the value exists in a range. Therefore, a plurality of composite microporous membranes having different pore sizes and average pore diameters formed in the surface layer can be obtained.

The average length of the linear bonding material can be obtained by clearly photographing the magnification of the linear bonding material, and taking a photograph of the surface side surface of the composite microporous film using a scanning electron microscope (SEM) or the like. The length of at least 100 arbitrary linear bonding materials was measured and averaged. Specifically, it is as described in the examples. The "length of the linear bonding material" is a distance between the perfect circles when the outer circumference of the spherical body is surrounded by a perfect circle that does not include the largest diameter of the hole around the spherical body as shown in FIG. 7 .

The length of the linear bonding material in the frequency distribution preferably has a frequency distribution of 50% or more in the range of ±30% of the average length. More preferably, it is 55% or more, and particularly preferably 60% or more. When a frequency of 50% or more is distributed over a range of an average length of ±30%, the spheroids of the surface layer are more uniformly dispersed, and a void having a uniform or uniform pore diameter can be formed between the spheroid and the spheroid.

The ratio of the average particle diameter of the spheroid to the average length of the linear bonding material is preferably between 3:1 and 1:3. When the average particle diameter of the spherical body is less than 3 times the average length of the linear bonding material, the opening portion of the surface layer surface of the composite microporous film becomes large, and a high permeation amount is more remarkably obtained. Further, when the average particle diameter of the spherical body is larger than one third of the average length of the bonding material, the number of bonding materials that can be connected to one spherical body is increased, so that the filter material is less likely to be peeled off and resistant. High pressure characteristics.

The weight average molecular weight (Mw) of the polyvinylidene fluoride-based resin is preferably from 600,000 to 1,000,000. More preferably 700,000 to 950,000, especially 790,000 to 900,000. The higher the weight average molecular weight (Mw) of the polyvinylidene fluoride-based resin, the easier the formation of the spherical body and the linear bonding material, and the polyvinylidene fluoride-containing system including the surface layer having a three-dimensional network structure can be easily obtained. A microporous membrane of resin. Thereby, the selected range of the good solvent or the poor solvent mentioned later is wide, and it is easy to further improve the permeability and film strength of the microporous film containing the polyvinylidene fluoride resin. Further, since the weight average molecular weight (Mw) is not excessively more than 1,000,000, the viscosity of the raw material liquid can be suppressed, so that it is easy to apply uniformly, and it is easier to form a mixed portion of the support layer and the base layer. .

Further, in order to improve the adhesion to other materials or the film strength within a range that does not impair the effects of the present invention, a polyvinylidene fluoride-based resin having a weight average molecular weight (Mw) within the above range may be mixed.

Here, the good solvent is a liquid which can dissolve a necessary amount of a polyvinylidene fluoride-based resin under the temperature condition of applying the raw material liquid. In addition, the non-solvent is a solvent which does not dissolve or swell the polyvinylidene fluoride-based resin under the temperature condition in which the good solvent in the coating film is replaced with the non-solvent. Further, the poor solvent is a solvent which does not dissolve the necessary amount of the polyvinylidene fluoride-based resin, but can be dissolved or swollen in an amount smaller than this.

Good solvents include N-methyl-2-pyrrolidone (NMP), dimethyl hydrazine, and N,N-dimethyl acetamide. , DMAc), N, N-dimethylformamide (DMF), methyl ethyl ketone, acetone, tetrahydrofuran, tetramethyl urea, trimethyl phosphate and other lower alkyl ketones, esters , guanamine and so on. These good solvents may be used in combination, and may contain a poor solvent or a non-solvent within a range that does not impair the effects of the present invention. In the case of film formation at normal temperature, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide are preferred.

Examples of the non-solvent include aliphatic hydrocarbons such as water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, and low molecular weight polyethylene glycol, and aromatic hydrocarbons. , chlorinated hydrocarbons, or other chlorinated organic liquids. The non-solvent must be dissolved in a good solvent, preferably in a free ratio with a good solvent. A good solvent or a poor solvent may also be intentionally added to the non-solvent.

In the present invention, the replacement rate of the good solvent and the non-solvent affects the performance of the three-dimensional network structure, so the combination is also important. In terms of ease of performance of the three-dimensional network structure, the combination is preferably NMP/water, DMAc/water, DMF/water, etc., particularly preferably a combination of DMAc/water.

In the raw material liquid for film formation, in addition to a polyvinylidene fluoride-based resin which is a raw material and a good solvent thereof, it is preferable to add a porous agent which promotes porosity. The porous agent is not limited as long as it does not inhibit the dissolution of the polyvinylidene fluoride-based resin in a good solvent and is dissolved in a non-solvent and has a property of promoting the porosity of the microporous membrane. Examples thereof include a polymer material or a low molecular substance of an organic substance, and specific examples thereof include water solubility such as polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, and polyacrylic acid. An ester of a polyhydric alcohol such as a polymer, a sorbitan fatty acid ester (monoester, triester, etc.), an ethylene oxide low molar addition of a sorbitan fatty acid ester, or a nonylphenol Ethylene oxide low molar addition, Pluronic ethylene oxide low molar addition, ethylene oxide low molar addition, polyoxyethylene alkyl ester, alkylamine A surfactant such as a salt or a sodium polyacrylate; a polyhydric alcohol such as glycerin; or a glycol such as tetraethylene glycol or triethylene glycol. These compounds may be used alone or in combination of two or more. These porous agents are preferably 50,000 or less, more preferably 30,000 or less, and still more preferably 10,000 or less, in terms of weight average molecular weight (Mw). When the weight average molecular weight of the porous agent is within the above range, it is preferably dissolved in the polyvinylidene fluoride-based resin solution. It is considered that when a good solvent is extracted in a non-solvent to cause structural agglomeration, the porous agent remains relatively long in a polyvinylidene fluoride-based resin as compared with a good solvent. In the pore membrane. The porous agent in the case where water is used for the non-solvent is particularly preferably polyethylene glycol, and particularly preferably has a weight average molecular weight of 200 to 1,000 because it is easy to exhibit these functions.

When the porous agent is used, the structure agglomerates accompanying the extraction with the good solvent becomes slow, and the porous agent is extracted. Therefore, the porosity of the obtained porous resin containing the polyvinylidene fluoride-based resin is improved. The structure obtained depends on the type, molecular weight, addition amount, and the like of the porous agent. The amount of the porous agent is preferably 0.1 to 2 times the weight of the polyvinylidene fluoride resin, and more preferably 0.5 to 1.5 times. When the amount of the porous agent to be added is within the above range, the micropores generated in the support layer do not become excessively large, and the film strength does not decrease, which is preferable.

The method for producing the composite microporous membrane of the present invention is as follows. In addition, FIG. 3 shows a rough flow of the manufacturing method.

(1) Preparation step of raw material liquid (S01):

First, a polyvinylidene fluoride-based resin which is a raw material of the microporous membrane is dissolved in a solvent which is a good solvent together with a porous agent to prepare a raw material liquid.

Specifically, for example, 5 parts by weight to 20 parts by weight of polyvinylidene fluoride is used as the polyvinylidene fluoride-based resin, and 0.1 to 2 times the amount of polyethylene glycol is used as the porous agent with respect to the weight of the raw material. Further, 70 parts by weight to 90 parts by weight of dimethylacetamide (DMAc) was used as a solvent, and dissolved therein at a normal temperature to 100 ° C, whereby a raw material liquid was obtained. In addition, the raw material liquid is usually used after returning to normal temperature.

Examples of the polyvinylidene fluoride-based resin include: polyvinylidene fluoride (Kynar HSV900) and "Kynar HSV800" manufactured by Arkema. "Kynar 761A", "Solef6020" made by Solvay, "W#7200" by Kureha.

(2) Porosification step (S02):

Then, a non-woven fabric as a base material layer was placed on a glass plate as a support, and a raw material liquid was applied thereon. In addition, it may be directly applied to a glass plate without placing a nonwoven fabric or the like, and in this case, a microporous film containing a polyvinylidene fluoride-based resin having no base material layer. Moreover, it is preferable to apply so that the thickness after film formation may be 10 micrometer - 500 micrometer. Immediately after coating or immediately after standing for a certain period of time, it is immersed in a non-solvent for the polyvinylidene fluoride-based resin together with the support for 3 minutes to 12 hours. In the case where the standing time after coating is set, it is preferably about 5 seconds to 60 seconds. When the standing time is extended, the average flow pore diameter becomes large, but if it is excessively elongated, pinholes may occur and the effects of the present invention may not be sufficiently obtained. The good solvent is mixed with the non-solvent, and the solubility of the polymer in the good solvent is lowered by the incorporation of the non-solvent, and the polymer is precipitated and becomes porous. Specifically, a polyester nonwoven fabric was placed on a glass plate, and a raw material liquid was applied. At the time of coating, a Baker applicator, a bar coater, a T die, or the like can be used. After immersing in a non-solvent, the glass plate as a support was removed, and the microporous film was obtained.

(3) Cleaning. Drying step (S03):

Then, in the water tank, water (ultra-pure water) as a non-solvent was replaced several times, and the microporous membrane was washed. In general, DMAc is more difficult to evaporate than water. Therefore, if the cleaning is incomplete, the solvent (DMAc) may be concentrated, and the formed pore structure may be dissolved again. Therefore, it is preferred to carry out multiple washings. In order to reduce the amount of water, speed up the clearance Washing speed, warm water can be used for cleaning, and ultrasonic cleaning machine can also be used. After washing, the microporous membrane can also be dried. Drying can be natural drying. In order to speed up the drying speed, a hot air dryer or a far infrared dryer can also be used. In order to prevent shrinkage or undulation of the microporous film during drying, a pin tenter can also be used. Dryer.

(4) Step of forming a SiO ₂ glass layer (S04)

Finally, in the cleaning. The surface of the microporous film containing the polyvinylidene fluoride-based resin obtained in the drying step (S03) forms a SiO ₂ glass layer. The method of forming the SiO ₂ glass layer is, for example, a sol-gel method in which a polyorganosiloxane is infiltrated and adhered to a microporous film containing a polyvinylidene fluoride-based resin, and is converted by heating or the like.

Specifically, a method in which a solution in which a hydrolyzable cerium-containing organic compound is reacted with water and partially gelled by a method such as coating or spraying is attached to a microporous layer containing a polyvinylidene fluoride-based resin. After the surface of the plasma membrane is allowed to react with water to completely gel, it is usually dried by heating at a preferred temperature in the range of 25 ° C to 120 ° C to obtain a composite microporous membrane. In addition, a polyazide method such as a polyazide-based compound having a constituent unit represented by the following formula (A) as a main component (polyazide nitrogen) by a method such as coating or spraying is used. The alkane solution is attached to a microporous membrane containing a polyvinylidene fluoride-based resin, and then converted into an SiO ₂ glass layer by air heating, hot water treatment, or steam treatment to obtain a composite microporous membrane.

[Chemical 1]

In the formula (A), R independently represents hydrogen or an alkyl group having 1 to 22 carbon atoms.

In order to obtain the composite microporous membrane of the present invention, a polyazide method using polyazane as a precursor of cerium oxide is preferred. Since the polyazide method is relatively easy to convert to a SiO ₂ glass layer having a dense structure, it is easy to obtain a high-strength composite microporous film, and since impurities derived from a crosslinking agent or a catalyst residue are less eluted, Preferably.

The polyazane used in the present invention is preferably a polyazane which can be converted into SiO ₂ glass at a low temperature. An example of such a polydiazolidine is a solution containing a polyazide having a Si-H bond as described in JP-A-2004-155834, or a method described in JP-A-H05-238827.矽 氧化物 加 加 加 加 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 6-1 Polyazane and the like. Further, the polyazide solution can be obtained, for example, as "Aquamica" manufactured by AZ Electronic Materials Co., Ltd.

The method of applying the polyazide solution to the microporous membrane is not particularly limited, and examples thereof include known methods such as roll coating, gravure coating, blade coating, spin coating, bar coating, and spray coating. . The polyazide solution was applied onto the microporous membrane, and after adhering, the solvent was evaporated by pre-drying to prepare a polyazide layer. Further, the polyaziridine layer is converted into a SiO ₂ glass layer by heating, hot water immersion, steam exposure or the like to form a microporous film. Further, it may be wound in a state in which a polyaziridine layer is formed, and then subjected to treatment such as heating or vapor exposure together with the wound body to be converted into a SiO ₂ glass layer.

As described in the porosification step (S02), a substrate layer may be provided during film formation. When the base material layer is provided, it is possible to prevent the raw material liquid from flowing out inadvertently during the application of the raw material liquid. Especially for the case of low viscosity raw material liquid. Further, the base material layer functions as a reinforcing material at the time of filtration, so that the membrane can withstand the filtration pressure. As the base material layer, a nonwoven fabric, a woven fabric, a porous board, or the like obtained by a spunbonding method, a melt flow method, or the like can be used, and a polyester, a polyolefin, a ceramic, or the like can be used as the material. Among them, polyester nonwoven fabric, polypropylene nonwoven fabric, and polyphenylene sulfide nonwoven fabric are preferable in terms of excellent balance of flexibility, light weight, strength, heat resistance and the like. Further, in the case of using a non-woven fabric, the basis weight thereof is preferably in the range of 15 g/m ² to 150 g/m ² , and particularly preferably in the range of 30 g/m ² to 90 g/m ² . If the basis weight is higher than 15 g/m ² , the effect of providing the substrate layer is sufficiently obtained. Further, when the basis weight is less than 150 g/m ² , post-processing such as bending or thermal bonding becomes easy.

In the step (S04) of forming the SiO ₂ glass layer, the concentration of the polyazirane solution is preferably in the range of 0.1 part by weight to 20 parts by weight, particularly preferably in the range of 0.5 part by weight to 10 parts by weight. When the polyazide concentration is more than 0.1 part by weight, a sufficient hydrophilization effect is obtained, and if it is less than 20 parts by weight, the SiO ₂ glass layer does not block the pores, so that sufficient permeability can be ensured.

Further, in the process of attaching the polyazulane solution, by adding an appropriate filler to the polyazide solution without impeding the chemical resistance and heat deformation resistance of the microporous membrane, further Improve performance as a filter. Examples of the filler include, in addition to zinc oxide, titanium oxide, barium titanate, barium carbonate, barium sulfate, zirconium oxide, zirconium silicate, aluminum oxide, magnesium oxide, and cerium oxide, cerium carbide, cerium nitride, and the like. Microparticles such as carbon. As the carbon, in addition to the graphite carbon fine particles, fine particles composed of activated carbon, carbon nanotubes, or the like are also included. At least one of these fillers adheres to the microporous membrane together with the polyazide, and is firmly fixed to the SiO ₂ glass layer, whereby a composite porous membrane which does not fall off can be obtained.

The concentration of the filler in the polyazane solution is usually from 0% by weight to 20% by weight, preferably from 0% by weight to 10% by weight. If it is the said concentration range, the performance as a filter can further be improved.

As described above, the microporous composite membrane of the present invention since the surface layer is coated with a glass layer of SiO _2, and therefore has a high hydrophilicity, comprising a polyvinylidene fluoride resin microporous by SiO ₂ glass layer caused by The clogging of the pores of the plasma membrane is also absent, so that high permeability can be maintained. Further, since a polyvinylidene fluoride-based resin is used as the film material, it has excellent chemical resistance and high heat resistance temperature (~120 ° C). Further, since the surface layer has a three-dimensional network structure formed of a homogeneous spherical body and a linear bonding material, the pore size or pore diameter of the surface layer is uniform, and high permeability (for example, high water permeability and high liquid permeability) can be achieved. That is, since the size or shape of the pores is more uniform, a film having a narrower pore diameter distribution is formed, and not only the particle blocking ratio but also the permeability which was not previously obtained can be obtained. Further, since it is a microporous film having a three-dimensional network structure as described above, it is easy to uniformly apply the polyazirane solution to the entire film, and the hydrophilization effect of the SiO ₂ glass layer can be effectively exhibited. The composite microporous membrane of the present invention can be used for a filter such as a filter membrane, a chemical liquid retaining material used for a plaster or the like, a surface material of a sanitary material, and a battery separator.

[Examples]

Hereinafter, the present invention will be further described in detail with reference to the embodiments and the like. However, the scope of the invention is not limited by the description.

[components used, etc.]

Polyethylene glycol 600 (weight average molecular weight: 600) as a porous material is a reagent grade 1 manufactured by Wako Pure Chemical Industries, Ltd.

As a solvent, N-dimethylacetamide is a reagent grade manufactured by Wako Pure Chemical Industries Co., Ltd.

Polyvinylidene fluoride is a polyvinylidene fluoride "Kynar HSV900" manufactured by Arkema (weight average molecular weight is 800,000, and the number average molecular weight is 540,000).

The polyester nonwoven fabric as the base material layer was a card nonwoven (H-8007, basis weight: 70 g/m ² ) manufactured by Japan Vilene.

The support was a glass plate (20 cm x 20 cm in size).

The water is manufactured using the "DirectQ UV" (trade name) manufactured by Millipore to have a specific resistance value of 18 MΩ. Ultrapure water above cm.

[Evaluation method]

The physical property values of the microporous membranes obtained in the examples and the comparative examples were measured by the following methods.

1) Average molecular weight of the polymer

The number average molecular weight and the weight average molecular weight were determined by dissolving the polymer in dimethylformamide (DMF), using Shodex Asahipak KF-805L as a column, and using DMF as a developing solvent. It was measured by Gel Permeation Chromatography (GPC) method and converted to polystyrene.

2) Thickness of the surface layer and thickness of the support layer

As shown in FIG. 6, a photograph of a cross section of the obtained composite microporous membrane was taken by a scanning electron microscope (SEM), and the photograph was subjected to image analysis, and the length from the surface to the micropores was taken as "the thickness of the surface layer. The value obtained by subtracting the thickness of the surface layer from the thickness of the entire composite microporous film is referred to as the "thickness of the support layer".

3) Average flow aperture

The average flow aperture was determined using a "Capillary Flow Porometer CFP-1200AEX" manufactured by PMI Corporation according to American Society for Testing Material (ASTM) F316-86.

4) Stream

The obtained composite microporous membrane was cut into a diameter of 25 mm, and was placed in an appropriate amount of ethanol and not impregnated, respectively, in a filter sheet holder having an effective filtration area of 3.5 cm ² . In the above, pressurization was carried out at a filtration pressure of 50 kPa, and 5 mL of water was passed, and the time required for water supply was measured. The stream is obtained by the following formula (1).

Stream (10 ^-9 m ³ /m ² /Pa/sec) = water flow (m ³ ) ÷ effective filtration area (m ² ) ÷ filtration pressure (Pa) ÷ time (sec)...(1)

5) Number, average particle size, and frequency distribution of spheroids

A photograph was taken on the surface of the surface of the composite microporous membrane by a scanning electron microscope at a magnification of 20,000 times. Further, as shown in FIG. 7, the spherical body having the center portion in the region of 4 μm in length × 6 μm in width in the center of the photograph surrounds the outer circumference of the spherical body with a perfect circle having the largest diameter of the hole surrounding the same. The diameter of the perfect circle is taken as the particle diameter of the spherical body. However, the number of the linear bonding materials to be connected is 3 or less, and it is difficult to distinguish them from the linear bonding materials, and thus is not considered to be a spheroid. Further, the average value of the diameters of all the spheroids contained in the region is defined as the average particle diameter. Further, the particles contained in the range of ±10% of the average particle diameter are counted from all the spheroids, and the number is divided by the total number of particles of the spheroid to determine the frequency distribution.

6) The number, average length and frequency distribution of the combined materials

As shown in Fig. 7, all the bonding materials between the spheroids contained in the region are measured (in the case where the two spheroids are connected by a plurality of bonding materials, only one of them) The number and length of the composite materials were determined for the number and average length of the combined materials. In addition, within the range of ±30% of the average length thereof The number of bonding materials contained is divided by the number of all bonding materials to determine the frequency distribution.

[Example 1]

[Preparation step of raw material liquid]

The total amount of the raw material liquid was set to 100 parts by weight, and 86 parts by weight of dimethyl acetamide was used, and polyvinylidene fluoride "Kynar HSV900 (weight average molecular weight: 800,000)" was 7 weight. The mixture and polyethylene glycol were 7 parts by weight, and they were mixed and dissolved at 90 °C. This was returned to normal temperature as a raw material liquid.

[Porousization step]

A polyester nonwoven fabric was placed on the glass plate, and a raw material liquid was applied thereto at a thickness of 250 μm using a Baker applicator. Immediately after coating, it was placed in water to make the membrane porous. The water was washed several times for washing, and the film was taken out from the water and dried to prepare a microporous film containing a polyvinylidene fluoride-based resin.

[SiO ₂ glass layer forming step]

"Aquamica (registered trademark), model NAX121-01 (polyxane concentration of 1.0 part by weight) manufactured by Anzhi Electronic Materials Co., Ltd." was used as a polyazoxide solution, and the impregnation and porosification step was completed. The microporous membrane containing the polyvinylidene fluoride-based resin was taken out and left to stand in a ventilating chamber for about 30 minutes until the solvent was completely evaporated, and placed in an oven maintained at 130 ° C for 1 hour. The mixture was allowed to stand at room temperature for 1 week to obtain a composite microporous membrane.

[Comparative Example 1]

A single-layer microporous membrane was obtained in the same manner as in Example 1 except that the SiO ₂ glass layer forming step was omitted.

Comparing the scanning electron micrographs of the surface layers of FIG. 4 and FIG. 5, it is understood that the surface layer of the composite microporous membrane of Example 1 has a three-dimensional network structure including a spherical body and a linear binder, even in comparison with the comparative example. The surface layer of the single-layer microporous membrane of 1 was compared, and the micropores were not blocked by the SiO ₂ glass layer. As shown in Table 1, the average pore diameter also showed the same value, and therefore it was also found that the inside of the microporous membrane was not blocked. Further, in Example 1, compared with Comparative Example 1, even if the ethanol treatment was not performed, a very high flow was observed. Therefore, it was found that the hydrophilicity was extremely high by the formation of the SiO ₂ glass layer.

In Tables 2 to 3, the particle diameter (a perfect circle diameter) of the spherical body 1 obtained by the scanning electron micrograph of the composite microporous membrane of Example 1 is shown.

The characteristics of the particle diameter of the spheroid of Example 1 are shown in Table 4. The average particle diameter of the spherical body of the surface layer of the composite microporous membrane of Example 1 was 0.190 μm. Further, the particle diameter of 112 spheroids corresponding to 62% of the spheroids is within ±10% of the average particle diameter.

Table 5 shows the frequency distribution table of the particle diameter of the spheroid. It can be seen that the particle diameter is concentrated in a width of 0.05 μm (0.15 μm to 0.20 μm), and the spheroid has a uniform particle diameter.

Tables 6 to 10 show the length (length between perfect circles) of the linear bonding material 2 obtained by the scanning electron micrograph of the composite microporous film of Example 1.

The characteristics of the linear bonding material of Example 1 are shown in Table 11. The average length of the linear bonding material of the surface layer of the composite microporous film of Example 1 was 0.219 μm. Further, the length of the 259 bonding materials corresponding to 61% of the bonding material was within ±30% of the average length.

A frequency distribution table showing the length of the linear bonding material is shown in Table 12. It can be seen that the frequency distribution is increased and decreased in such a manner that the range of 0.20 μm to 0.25 μm becomes a peak, and the length of the bonding material is concentrated in a specific range.

[Industrial availability]

The composite microporous membrane of the present invention is not subjected to hydrophilization such as alcohol replacement Since it exhibits high water permeability, it is possible to produce a filter excellent in chemical resistance and heat resistance of a polyvinylidene fluoride-based resin. Therefore, it can be used particularly effectively in the use of a membrane bioreactor or a water-purifying membrane, and a pharmaceutical or food application in which a step of high-temperature sterilization is required.

1‧‧‧ spheroid

2‧‧‧Line-shaped bonding materials

Claims (16)

A composite microporous membrane characterized in that at least one surface of a microporous membrane containing a polyvinylidene fluoride-based resin is coated with a SiO ₂ glass layer. The composite microporous membrane according to claim 1, wherein a microporous membrane containing a polyvinylidene fluoride-based resin is produced by a non-solvent-induced phase separation method. The composite microporous membrane according to claim 1 or 2, wherein the microporous membrane containing the polyvinylidene fluoride-based resin is an asymmetric membrane, and includes a surface layer formed with micropores and a support Forming a support layer having a larger pore than the micropores, the surface layer having a plurality of spherical bodies, and a plurality of linear bonding materials extending from the respective spherical bodies in a three-dimensional direction, adjacent to each other The spheroids are connected to each other by the linear bonding material to form a three-dimensional network structure in which the spheroids are used as intersections. The composite microporous membrane according to claim 3, wherein the spherical body has a particle diameter of 50% or more in a range of ±10% of the average particle diameter. The composite microporous membrane according to claim 3, wherein the length of the binder has a frequency distribution of 50% or more in a range of an amplitude of ±30% of an average length. The composite microporous membrane according to any one of claims 3 to 5, wherein the spheroid has an average particle diameter of 0.05 μm to 0.5 μm. The composite micro-multiple as described in any one of claims 3 to 6 The porous film, wherein the surface layer has a thickness of 0.5 μm to 5 μm, and the support layer has a thickness of 20 μm to 500 μm. The composite microporous membrane according to any one of claims 3 to 7, which comprises a substrate layer supporting the support layer. The composite microporous membrane according to any one of claims 1 to 8, wherein the polyvinylidene fluoride-based resin has a weight average molecular weight (Mw) of 600,000 to 1,000,000. The composite microporous membrane according to any one of claims 1 to 9, wherein the composite microporous membrane has an average pore diameter of 5 nm to 500 nm. The composite microporous membrane according to any one of claims 1 to 10, wherein the composite microporous membrane is in the shape of a flat membrane. A filter comprising a composite microporous membrane according to any one of claims 1 to 11. A method for producing a composite microporous membrane, which is a method for producing a composite microporous membrane according to any one of claims 1 to 11, which is characterized in that it contains polyvinylidene fluoride After at least one of the resin-containing microporous membrane forms a coating film of the cerium oxide precursor, the cerium oxide precursor is converted into SiO ₂ glass, thereby forming a SiO ₂ glass layer, and at least one side is obtained. A microporous film containing a polyvinylidene fluoride-based resin coated with SiO ₂ glass. The method for producing a microporous membrane according to claim 13, wherein the ceria precursor is polyazane. A method for producing a composite microporous membrane, which is manufactured as a patent application The method of the composite microporous membrane according to the eighth aspect of the invention, comprising: a coating step of applying a raw material liquid obtained by dissolving the polyvinylidene fluoride-based resin in a good solvent; And a immersing step of immersing the substrate layer and the applied raw material liquid in a non-solvent after the coating step. A method for producing a composite microporous membrane, which is a method for producing a composite microporous membrane according to claim 9, characterized in that it comprises a coating step for causing the polyvinylidene fluoride to be a raw material liquid obtained by dissolving a resin in a good solvent on a substrate layer or a support; and a dipping step of immersing the substrate layer or the support and the non-solvent in the non-solvent after the coating step The raw material liquid coated.