JP6447623B2 - Composite microporous membrane and filter using the same - Google Patents

Description

  The present invention relates to a microporous membrane suitable for water treatment applications represented by a membrane separation activated sludge method (membrane bioreactor: MBR) and the like.

  Microporous membranes made of polyvinylidene fluoride (PVDF) are widely used as air filters, bag filters, and liquid filtration filters because of their excellent chemical resistance and heat resistance. The PVDF microporous membrane can be produced by a non-solvent induced phase separation method (by preparing a solution in which a polymer is dissolved in a good solvent and immersing this solution thinly on a glass plate or the like in a non-solvent. For example, a method of inducing phase separation to obtain a microporous membrane) (for example, Patent Document 1).

  Since the PVDF microporous membrane is hydrophobic, it needs to be subjected to a hydrophilization treatment by coating it with a hydrophilizing agent such as polyvinyl alcohol (PVA) or by replacing it with ethanol in order to use it for water treatment. (For example, Patent Document 2). However, the hydrophilized microporous membrane obtained by this method has poor persistence of the hydrophilizing effect, and the hydrophilizing effect is lost when all of PVA and ethanol are eluted. Moreover, there exists a problem that PVA mixes in a filtrate or a pore is clogged with PVA.

International Publication No. 10/032808 Pamphlet Japanese Patent Laid-Open No. 05-023557

  In view of the above, the object of the present invention is to provide a composite microporous membrane for water treatment that has no permanent clogging due to coating with a hydrophilizing agent and has permanent hydrophilicity, and a filter using the same. There is to do.

The inventors of the present invention have made extensive studies in order to solve the above problems. As a result, a composite microporous membrane obtained by using a microporous membrane containing a polyvinylidene fluoride resin with an optimized surface structure and covering the surface with a SiO ₂ glass layer solves the above-mentioned problems The present invention has been completed based on this finding.

The composite microporous membrane according to the first aspect of the present invention is characterized in that a SiO ₂ glass layer is coated on the surface of at least one side of a microporous membrane containing a polyvinylidene fluoride resin. When configured in this manner, in addition to heat resistance and chemical resistance possessed by polyvinylidene fluoride resin, because the resulting hydrophilic effect with the SiO ₂ glass layer, exhibits excellent performance as a filtration membrane.

  The composite microporous membrane according to the second aspect of the present invention is the composite microporous membrane according to the first aspect of the invention, wherein the microporous membrane containing the polyvinylidene fluoride resin is a non-solvent induced phase. It is produced by a separation method. With this configuration, the skin layer in which the pore diameter changes in the thickness direction of the membrane (see the left side of FIG. 8), and the pores larger than the pores supporting the skin layer and the skin layer in which the pores are formed are formed. Since it has the structure provided with the formed support layer, the filtration accuracy is maintained by the skin layer, and the permeability can be secured by the support layer.

The composite microporous membrane according to the third aspect of the present invention is the composite microporous membrane according to the first or second aspect of the invention, wherein the microporous membrane containing a polyvinylidene fluoride resin is An asymmetric membrane, comprising a skin layer in which micropores are formed and a support layer in which pores larger than the micropores are formed to support the skin layer, the skin layer having a plurality of spherical bodies, A plurality of linear binders extend from each of the spherical bodies in a three-dimensional direction, and the adjacent spherical bodies are connected to each other by the linear binders, and a three-dimensional network having the spherical bodies as intersections. Form a structure.
FIG. 1 shows an example of a three-dimensional network structure according to the present invention. FIG. 1 is a scanning electron microscope (SEM) photograph of the skin layer surface. The “skin layer” refers to the layer from the surface to the macro void in the cross section of the microporous membrane containing the polyvinylidene fluoride resin, and the “support layer” refers to the fine layer containing the polyvinylidene fluoride resin. A layer obtained by removing the skin layer from the entire porous membrane. “Macrovoid” refers to a huge cavity that occurs in a support layer of a microporous membrane and has a minimum size of several μm and a maximum size approximately the same as the thickness of the support layer. The “spherical body” is a sphere formed at the intersection of the three-dimensional network structure, and is not limited to a perfect sphere, but includes almost a sphere. With this configuration, the gap between the sphere and the sphere is partitioned by a linear binder, making it easy to form micropores of uniform shape and size, and a skin layer with excellent permeability. Can be formed. Since the linear binding material also serves to crosslink the spherical body, the spherical body does not fall off and the filtering medium itself can be prevented from being mixed into the filtrate. Furthermore, since a spherical body exists at the intersection of the three-dimensional network structure, the skin layer can be prevented from being crushed by pressure when used as a filtration membrane. That is, the pressure resistance is high. Furthermore, the three-dimensional network structure as shown in FIG. 1 using a spherical body and a linear binder makes the skin layer voids smaller than conventional microporous membranes containing a polyvinylidene fluoride resin having the same pore size. Therefore, the passage is maintained, and the voids are more uniformly and three-dimensionally arranged.

  The composite microporous membrane according to the fourth aspect of the present invention is the composite microporous membrane according to the third aspect of the present invention, wherein the spherical particles have a width within ± 10% of the average particle size. In the range of 50% or more. If comprised in this way, the spherical body which a skin layer has will become the thing with the equal particle size. Therefore, a void having a uniform pore diameter is easily formed between the spherical body and the spherical body.

  The composite microporous membrane according to the fifth aspect of the present invention is the composite microporous membrane according to the third aspect or the fourth aspect of the present invention, wherein the length of the binder is ± the average length. It has a frequency distribution of 50% or more in a range of 30% width. If comprised in this way, the spherical body which a skin layer has will be disperse | distributed more uniformly. Therefore, a void having a uniform pore diameter is easily formed between the spherical body and the spherical body.

  The composite microporous membrane according to the sixth aspect of the present invention is the composite microporous membrane according to any one of the third to fifth aspects of the present invention, wherein the spherical body is 0. It has an average particle size of 0.05 to 0.5 μm. If comprised in this way, a micropore will be easily formed between a spherical body and a spherical body with the spherical body which has the average particle diameter in the said range, and the linear binding material which connects a spherical body.

  The composite microporous membrane according to the seventh aspect of the present invention is the composite microporous membrane according to any one of the third to sixth aspects of the present invention, wherein the thickness of the skin layer is 0.5 to 5 μm, and the thickness of the support layer is 20 to 500 μm. With this configuration, since the skin layer is a layer (functional layer) that removes impurities in the asymmetric membrane, the thinner it is within the range that does not hinder the formation of the three-dimensional network structure with the spherical body as an intersection, the lower the filtration resistance. Since it can be made small, it is preferable. The support layer occupying most of the microporous membrane hardly contributes to the removal of impurities, but can be avoided by a support layer that is sufficiently thicker than the skin layer because it can be broken only by an extremely thin skin layer. it can.

A composite microporous membrane according to an eighth aspect of the present invention is the composite microporous membrane according to any one of the third to seventh aspects of the present invention, wherein the base supporting the support layer is provided. A material layer is provided.
If comprised in this way, a base material layer will become a reinforcing material and will be able to endure a higher filtration pressure. In addition, in the application during film formation, it is possible to prevent a raw material solution obtained by dissolving a resin as a raw material in a solvent from flowing out carelessly. This is particularly effective when the raw material liquid has a low viscosity. A part of the support layer is mixed with the base material layer, and the boundary between them is not so clear. When there are too few mixed parts of a support layer and a base material layer, a support layer may become easy to peel from a base material layer.

The composite microporous membrane according to the ninth aspect of the present invention is the composite microporous membrane according to the first to eighth aspects of the present invention, wherein the weight-average molecular weight (Mw) of the polyvinylidene fluoride resin is the same. ) Is 600,000 to 1,000,000.
When configured in this manner, the polyvinylidene fluoride resin having the weight average molecular weight includes a skin layer having a three-dimensional network structure in which the spherical bodies and the spherical bodies formed by a linear binder that cross-links the spherical bodies are crossed. A microporous film containing a polyvinylidene fluoride resin can be easily formed.

  The composite microporous membrane according to the tenth aspect of the present invention is the composite microporous membrane according to any one of the first to ninth aspects of the present invention, wherein the average pore size is 5 ~ 500 nm. If the average flow hole diameter is 5 nm or more, an increase in pressure loss due to clogging during filtration can be minimized, and if it is 500 nm or less, transmission of coarse impurity particles can be suppressed. The filtration performance is shown.

  The composite microporous membrane according to the eleventh aspect of the present invention shows a flat membrane shape in the composite microporous membrane according to any one of the first to tenth aspects of the present invention. . When configured in this way, compared to the hollow fiber, when a module in which a plurality of filtration membranes are combined is created, impurities are less likely to accumulate between the membranes, and an increase in pressure loss can be suppressed. Excellent filtration performance.

  A filter according to a twelfth aspect of the present invention is a filter characterized by using the composite microporous membrane according to any one of the first to eleventh aspects of the present invention. If comprised in this way, the composite microporous film excellent in hydrophilic property and permeability | transmittance can be utilized as a filter. When this filter is used, since impurities are not eluted from the composite microporous membrane, it exhibits excellent performance in terms of energy efficiency and treated water quality, and thus can be suitably used for water treatment applications such as MBR.

A method for producing a composite microporous membrane according to a thirteenth aspect of the present invention is a method for producing a composite microporous membrane according to any one of the first to eleventh aspects of the present invention. Te, after forming the coating film of the silica precursor on at least one side of the microporous film containing polyvinylidene fluoride resin, by the conversion of the silica precursor to SiO ₂ glass, to form a SiO ₂ glass layer , A production method for obtaining a microporous film containing a polyvinylidene fluoride resin at least one side coated with SiO ₂ glass. When configured in this manner, it is possible to form a uniformly SiO ₂ glass layer on the surface of the microporous film containing polyvinylidene fluoride resin, it is possible to obtain an excellent hydrophilizing effect.

The method for producing a composite microporous membrane according to the fourteenth aspect of the present invention is the method for producing a composite microporous membrane according to the thirteenth aspect of the present invention, wherein the silica precursor is polysilazane. This is a method for producing a microporous membrane. When configured in this manner, it is possible to proceed with the conversion to SiO ₂ glass layer having a dense structure with ease.

  The method for producing a composite microporous membrane according to the fifteenth aspect of the present invention is the method for producing a composite microporous membrane according to the eighth aspect of the present invention, wherein the polyvinylidene fluoride resin is used as a good solvent. An application step of applying the raw material solution dissolved in the base material layer on the base material layer, and an immersion step of immersing the base material layer and the applied raw material solution in a non-solvent after the application step. If comprised in this way, it will be the manufacturing method of the microporous film | membrane which contains the polyvinylidene fluoride type-resin which is an asymmetrical film | membrane, and a skin layer has a some spherical body. The spherical bodies included in the skin layer are cross-linked with each other by a linear binder to form a three-dimensional network structure with the spherical bodies as intersections. Since the spherical bodies are more uniformly dispersed in a uniform size, the pores of the skin layer are uniformly dispersed and have excellent permeability.

A method for producing a composite microporous membrane according to a sixteenth aspect of the present invention is a method for producing a composite microporous membrane according to the ninth aspect of the present invention, wherein the polyvinylidene fluoride resin is used as a good solvent. An application step of applying the dissolved raw material liquid onto a base material layer or a support and an immersion step of immersing the base material layer and the applied raw material liquid in a non-solvent after the application step are provided.
With this configuration, since the polyvinylidene fluoride resin suitable for forming the three-dimensional network structure of the skin layer is used as a material, the spherical bodies are cross-linked by a linear binder, and the spherical bodies are crossed. The three-dimensional network structure can be easily formed on the skin layer.

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

FIG. 1 is a photograph of the surface of a skin layer of a microporous film containing a polyvinylidene fluoride resin in the present invention. FIG. 2 is a photograph of a conventional filtration membrane made of polyvinylidene fluoride. FIG. 3 is a flowchart showing a method for producing a composite microporous membrane according to the present invention. 4 is a photograph of the surface of the skin layer of the composite microporous membrane of Example 1. FIG. FIG. 5 is a photograph of the surface of the skin layer that the microporous membrane of Comparative Example 1 has. 6A is a cross-sectional photograph of the composite microporous membrane of Example 1. FIG. FIG. 6B is an enlarged photograph of a cross-sectional portion of the skin layer. FIG. 7 is a photograph of the surface of the skin layer of the composite microporous membrane of Example 1, and is a photograph used to measure the particle size of the spherical body and the length of the linear binder. FIG. 8 is a schematic diagram showing a cross-sectional view (left) of the asymmetric membrane and a cross-sectional view (right) of the symmetric membrane. (Source: JPO Homepage / 2005 Standard Technology Collection Water Treatment Technology / 1-6-2-1 Symmetric Membrane and Asymmetric Membrane)

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same or similar reference numerals, and redundant description is omitted. Further, the present invention is not limited to the following embodiments.

The composite microporous membrane in the present invention will be described. The composite microporous membrane of the present invention has a structure in which the surface of a microporous membrane containing a polyvinylidene fluoride resin is covered with a SiO ₂ glass layer, and the SiO ₂ glass layer contains a hydrophobic polyvinylidene fluoride resin. It serves to impart hydrophilicity to the microporous membrane.
The SiO ₂ glass layer is preferably formed by impregnating and coating the silica precursor solution over the entire pores of the microporous membrane containing the polyvinylidene fluoride resin, but the air permeability required for the composite microporous membrane In consideration of the necessity of maintaining liquid permeability, the polyvinylidene fluoride resin is contained so that at least one side of the surface of the microporous film containing the polyvinylidene fluoride resin is covered with the SiO ₂ glass layer. A SiO ₂ glass layer may be formed on at least one side of the microporous film.

Examples of the polyvinylidene fluoride resin used in the present invention include resins containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer. As the polyvinylidene fluoride resin, a plurality of types of vinylidene fluoride homopolymers having different physical properties (viscosity, molecular weight, etc.) may be contained. Alternatively, a plurality of types of vinylidene fluoride copolymers may be included. The vinylidene fluoride copolymer is not particularly limited as long as it is a polymer having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and other fluorine-based monomers. And a copolymer of one or more fluorine-based monomers selected from vinyl fluoride, ethylene tetrafluoride, propylene hexafluoride, and ethylene trifluoride chloride and vinylidene fluoride. Particularly preferred is a vinylidene fluoride homopolymer (polyvinylidene fluoride).
The microporous film containing the polyvinylidene fluoride resin used in the present invention can be constituted by using the above-mentioned polyvinylidene fluoride resin, but may further contain other components. Further, the microporous film containing the polyvinylidene fluoride resin used in the present invention may be a microporous film made of a polyvinylidene fluoride resin. In this case, other components may be included as long as the effects of the present invention are not hindered. Examples of other components include polymers other than polyvinylidene fluoride resins and additives such as antibacterial agents for imparting other characteristics.

  The composite microporous membrane of the present invention has an asymmetric structure in which the pore diameter changes in the thickness direction of the membrane (see the left side of FIG. 8), the pore diameter of the layer (skin layer) near the surface of the membrane is the smallest, and goes to the back surface. As the hole diameter increases. The skin layer has a pore size necessary for separation characteristics and functions as a functional layer. The remaining portion is a layer that functions as a support layer, has a large pore size and a small permeation resistance, and maintains the flow path and membrane strength. The thickness of the skin layer is preferably 0.5 to 5 μm, and the thickness of the support layer is preferably 20 to 500 μm.

FIG. 1 is a part of a photograph of the surface (skin layer side) of the composite microporous membrane of the present invention taken with a scanning electron microscope (SEM). As shown in FIG. 1, the skin layer has a plurality of spherical bodies 1, and a plurality of linear binders 2 extend from each spherical body 1 in a three-dimensional direction. They are connected by a linear binder 2 to form a three-dimensional network structure with the spherical body 1 as an intersection, and the generated voids are holes. Therefore, a hole is easily formed in the skin layer, and the hole is not easily deformed. An asymmetric membrane has a dense thin layer called a skin layer, and this layer generally has few pores, so it is extremely effective to improve permeability by opening many holes that are difficult to deform in this layer. It is. In the composite microporous membrane according to the third embodiment, the permeability is greatly improved by the spherical body 1 included in the skin layer and the linear bonding material 2 connecting them. Therefore, it can have higher permeability than the conventional microporous membrane having the same average flow pore diameter. Here, the “average flow pore size” is a value obtained by ASTM F316-86, and when a composite microporous membrane is used as a filtration membrane, its inhibition particle size is greatly affected. In the present invention, the average flow pore size of the composite microporous membrane is preferably 5 to 500 nm, more preferably 5 to 450 nm, and most preferably 10 to 400 nm. If the average pore size of the composite microporous membrane is 5 nm or more, an increase in pressure loss due to clogging during filtration can be minimized, and if it is 500 nm or less, transmission of coarse impurity particles is suppressed. Is preferable.
Furthermore, as shown in FIG. 1, the spherical bodies 1 are almost uniform in size and are dispersed almost uniformly. Therefore, a skin layer is formed in which the shape and size of the gap formed between the spherical body 1 and the spherical body 1 are uniform. The space between the spheres 1 is delimited by a linear binder 2 that bridges the adjacent spheres 1, and the resulting holes are egg-shaped or almost egg-shaped with no dents on the outer periphery curve. Thus, a microporous membrane having a uniform pore shape is obtained.

  Even if the surface of the conventional filtration membrane made of polyvinylidene fluoride has the “spherical body” or the “binding material” as used in the present invention, the effect of the present invention cannot be obtained. . For example, a polyvinylidene fluoride filtration membrane having only a portion corresponding to the “binding material” in the present invention needs to be thickened in order to maintain a strength sufficient to be used as a filtration membrane. Therefore, it is difficult to make the hole fine because it is not linear but is planar. FIG. 2 is a scanning electron micrograph of a conventional polyvinylidene fluoride filtration membrane having such a structure as an example.

The average particle diameter of the spherical body of the skin layer of the composite microporous membrane of the present invention is preferably 0.05 to 0.5 μm. More preferably, it is 0.1-0.4 micrometer, More preferably, it is 0.2-0.3 micrometer. Most of the spherical particles have a value close to the average particle size and have a uniform size. Further, the average particle diameter varies depending on the produced microporous membrane, and the value has a range as described above. Therefore, various microporous membranes having different pore sizes formed in the skin layer and different average flow pore diameters can be obtained.
As for the particle size of the spherical body, at least 50 arbitrary spherical bodies were photographed using a scanning electron microscope (SEM) or the like at such a magnification that the spherical body could be clearly confirmed on the skin layer side surface of the composite microporous membrane. It can be obtained by measuring the particle size and averaging the number. Specifically, it is as described in the examples. As shown in FIG. 7, the “particle diameter” is the diameter of a perfect circle when the outer periphery of the spherical body is surrounded by a perfect circle having the maximum diameter that does not include the surrounding holes. In order to make the shape of the pores of the skin layer more uniform, the shape of each spherical body is preferably close to a perfect sphere, and the size of the spherical body is preferably small in variation.

  The particle diameter of the spherical body preferably has a frequency distribution of 50% or more in the range of ± 10% width of the average particle diameter in the frequency distribution. More preferably, it is 55% or more, More preferably, it is 60% or more. When the frequency of 50% or more is distributed in the range of the width of ± 10% of the average particle diameter, the spherical body of the skin layer has a more uniform shape and size, and the pore size between the spherical body and the spherical body Can form uniform (aligned) voids.

The average length of the linear binding material of the skin layer of the composite microporous membrane of the present invention is preferably 0.05 to 0.5 μm. More preferably, it is 0.1-0.4 micrometer, More preferably, it is 0.2-0.3 micrometer. Most of the lengths of the linear binders are close to the average length, and the length is uniform. Further, the average length varies depending on the produced microporous membrane, and the value has a width as described above. Therefore, various composite microporous membranes having different pore sizes formed in the skin layer and different average flow pore diameters can be obtained.
The average length of the linear binder is at least 100 by taking a photograph using a scanning electron microscope (SEM) or the like at a magnification at which the linear binder can clearly confirm the skin-side surface of the composite microporous membrane. It can be obtained by measuring the length of an arbitrary linear binding material of a book and averaging the number. Specifically, it is as described in the examples. As shown in FIG. 7, the “length of the linear binding material” is the distance between the perfect circles when the outer periphery of the spherical body is surrounded by a perfect circle having the maximum diameter so as not to include the surrounding holes. is there.

  The length of the linear binder preferably has a frequency distribution of 50% or more in the range of ± 30% of the average length in the frequency distribution. More preferably, it is 55% or more, More preferably, it is 60% or more. When the frequency of 50% or more is distributed in the range of the average length ± 30%, the spherical bodies of the skin layer are more uniformly dispersed, and voids with a uniform or uniform pore diameter are formed between the spherical bodies and the spherical bodies. Can be formed.

  The ratio of the average particle diameter of the spherical body to the average length of the linear binder is preferably between 3: 1 and 1: 3. When the average particle size of the spherical body is smaller than three times the average length of the linear binder, the opening on the skin layer surface of the composite microporous membrane becomes large, and a high permeation amount can be obtained more remarkably. . In addition, if the average particle size of the spheres is larger than one third of the average length of the binder, the number of binders that can be connected to one sphere increases, so there is little dropout of the filter media and high pressure resistance. Features can be obtained more prominently.

The weight average molecular weight (Mw) of the polyvinylidene fluoride resin is preferably 600,000 to 1,000,000. More preferably, it is 700,000-950,000, More preferably, it is 790,000-900,000. The higher the weight average molecular weight (Mw) of the polyvinylidene fluoride resin, the easier it is to form spherical bodies and linear binders, and the fine particles containing the polyvinylidene fluoride resin with a skin layer having a three-dimensional network structure. A porous membrane can be easily obtained. Thereby, the selection range of a good solvent and a poor solvent, which will be described later, is widened, and it becomes easier to further increase the permeability and film strength of the microporous film containing the polyvinylidene fluoride resin. Moreover, since the viscosity of the raw material liquid can be suppressed by making the weight average molecular weight (Mw) not much higher than 1 million, it becomes easy to apply uniformly, and the support layer and the base material layer This is preferable because a mixed portion is more easily formed.
In addition, in order to increase the adhesion to other materials and the film strength within a range not impeding the effects of the present invention, a polyvinylidene fluoride resin having a weight average molecular weight (Mw) outside this range may be mixed.

  Here, the good solvent is a liquid capable of dissolving a required amount of the polyvinylidene fluoride resin under a temperature condition for applying the raw material liquid. The non-solvent is a solvent that does not dissolve or swell the polyvinylidene fluoride-based resin under temperature conditions that replace the good solvent in the coating film with a non-solvent. The poor solvent is a solvent that cannot dissolve the required amount of the polyvinylidene fluoride resin, but can dissolve or swell less than that amount.

  Good solvents include N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide, N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, phosphorus Examples include lower alkyl ketones such as trimethyl acid, esters, amides, and the like. These good solvents may be used as a mixture, and may contain a poor solvent and a non-solvent as long as the effects of the present invention are not impaired. When film formation is performed at room temperature, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, and N, N-dimethylformamide are preferable.

Non-solvents include water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, low molecular weight polyethylene glycol and other aliphatic hydrocarbons, aromatic hydrocarbons, chlorine Chlorinated hydrocarbons or other chlorinated organic liquids. The non-solvent needs to be dissolved in a good solvent and is preferably mixed with the good solvent in a free ratio. A good solvent or a poor solvent may be intentionally added to the non-solvent.
Since the substitution rate of the good solvent and the non-solvent affects the expression of the three-dimensional network structure in the present invention, the combination thereof is also important. As the combination, NMP / water, DMAc / water, DMF / water, and the like are preferable from the viewpoint of easy expression of a three-dimensional network structure, and a combination of DMAc / water is particularly preferable.

  In addition to the polyvinylidene fluoride resin as a raw material and its good solvent, it is preferable to add a porosifying agent that promotes porosity to the raw material liquid for film formation. The porous agent is not limited as long as it does not inhibit the dissolution of the polyvinylidene fluoride resin in a good solvent, dissolves in a non-solvent, and promotes the microporous membrane to become porous. Absent. Examples include organic high-molecular substances or low-molecular substances, such as water-soluble polymers such as polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone, and polyacrylic acid, and sorbitan fatty acid esters. Low ethylene oxide, such as ester of polyhydric alcohol such as (mono, triester, etc.), ethylene oxide low molar adduct of sorbitan fatty acid ester, ethylene oxide low molar adduct of nonylphenol, pluronic ethylene oxide low molar adduct Mole adducts, polyoxyethylene alkyl esters, alkylamine salts, surfactants such as sodium polyacrylate, polyhydric alcohols such as glycerin, tetraethylene glycol, triethylene glycol, etc. Mention may be made of the recall class. These may be used alone or in a mixture of two or more. These porous agents preferably have a weight average molecular weight (Mw) of 50,000 or less, more preferably 30,000 or less, and still more preferably 10,000 or less. If the weight average molecular weight of the porosifying agent is within the above range, it is preferable because it is uniformly dissolved in the polyvinylidene fluoride resin solution. This porous agent is considered to remain in the microporous membrane containing the polyvinylidene fluoride resin for a relatively long time as compared with the good solvent when the good solvent is extracted in the non-solvent and the structural aggregation occurs. In the case of using water as the non-solvent, the porous agent is particularly preferably polyethylene glycol, and more preferably having a weight average molecular weight of 200 to 1000, since these functions are easily exhibited.

  When a porosifying agent is used, since the porosizing agent is extracted after the structural aggregation accompanying the good solvent extraction becomes gentle, the obtained porous resin containing the polyvinylidene fluoride resin has porosity. Get higher. The resulting structure depends on the type of porous agent, molecular weight, added amount, and the like. The porosifying agent is preferably added in an amount of 0.1 to 2 times, more preferably 0.5 to 1.5 times the weight of the polyvinylidene fluoride resin. If the addition amount of the porosifying agent is within the above range, it is preferable that macrovoids generated in the support layer do not become too large and the film strength does not decrease.

The method for producing the composite microporous membrane of the present invention is as follows. FIG. 3 shows a rough flow of the manufacturing method.
(1) Raw material liquid preparation step (S01):
First, a polyvinylidene fluoride resin, which is a raw material for a microporous membrane, is dissolved in a solvent, which is a good solvent, together with a porous agent to make a raw material solution.
Specifically, for example, 5 to 20 parts by weight of polyvinylidene fluoride is used as the polyvinylidene fluoride resin, and 0.1 to 2 times the amount of polyethylene glycol is used as the porosifying agent with respect to the material weight. Then, 70 to 90 parts by weight of dimethylacetamide (DMAc) is used as a solvent and dissolved therein at room temperature to 100 ° C. to obtain a raw material liquid. In addition, a raw material liquid is normally used after returning to normal temperature.
Examples of the polyvinylidene fluoride resin include Arkema's polyvinylidene fluoride “Kyner HSV900”, “Kyner HSV800”, “Kyner 761A”, Solvay “Solef6020”, and Kureha “W # 7200”.
(2) Porous process (S02):
Next, a nonwoven fabric as a base material layer is placed on a glass plate as a support, and a raw material liquid is applied thereon. In addition, you may apply | coat directly on a glass plate, without placing a nonwoven fabric etc., In that case, it becomes a microporous film containing the polyvinylidene fluoride resin without a base material layer. Moreover, it is preferable to apply | coat so that the thickness after film forming may be 10-500 micrometers. Immediately after coating, or after standing for a certain time, the whole support is immersed in a non-solvent for polyvinylidene fluoride resin for 3 minutes to 12 hours. When providing the leaving time after application | coating, about 5 to 60 second is preferable. If the standing time is taken longer, the average flow hole diameter becomes larger, but if it is taken too long, pinholes are generated and the effects of the present invention may not be sufficiently obtained. A good solvent and a non-solvent are mixed, and the solubility of the polymer in the good solvent is reduced due to the mixing of the non-solvent, so that the polymer is precipitated and becomes porous. Specifically, a polyester nonwoven fabric is placed on a glass plate and a raw material solution is applied. For the application, a baker applicator, a bar coater, a T die, or the like can be used. After soaking in a non-solvent, the glass plate as a support is removed to obtain a microporous membrane.
(3) Cleaning / drying step (S03):
Next, the microporous membrane is washed in a water tank by replacing water (ultra pure water) as a non-solvent several times. In general, DMAc is less likely to evaporate than water, and therefore incomplete cleaning may cause the solvent (DMAc) to concentrate and the resulting pore structure to dissolve again, so multiple cleanings are preferred. In order to reduce the amount of drainage and increase the washing speed, warm water may be used for washing, or an ultrasonic washing machine may be used. After washing, the microporous membrane may be dried. Drying may be natural drying, a hot air drier or far-infrared drier may be used to increase the drying speed, and a pin tenter type to prevent shrinkage and undulation of the microporous membrane during drying. A dryer may be used.
(4) SiO ₂ glass layer forming step (S04)
Finally, a SiO ₂ glass layer is formed on the surface of the microporous film containing the polyvinylidene fluoride resin obtained in the cleaning / drying step (S03). Examples of the method for forming the SiO ₂ glass layer include a sol-gel method in which polyorganosiloxane is infiltrated and adhered to a microporous film containing a polyvinylidene fluoride resin and converted by a method such as heating. it can.
Specifically, a solution in which a hydrolyzable silicon-containing organic compound is partially gelled by reacting with water is applied to the surface of a microporous film containing a polyvinylidene fluoride resin by a technique such as coating or spraying. After making it adhere, it can be made to react with water and completely gel, and further heat dried at a suitable temperature usually in the range of 25 to 120 ° C. to obtain a composite microporous membrane. In addition, a solution (polysilazane solution) mainly composed of a polysilazane compound having a structural unit represented by the following formula (A) is attached to a microporous film containing a polyvinylidene fluoride resin by a technique such as coating or spraying. Examples thereof include a polysilazane method in which a composite microporous film is obtained by being converted into a SiO ₂ glass layer through treatment with air heating, hot water, water vapor or the like.

In the formula (A), each R independently represents hydrogen or alkyl having 1 to 22 carbon atoms.
In order to obtain the composite microporous membrane of the present invention, the polysilazane method using polysilazane as the silica precursor is most preferable. The polysilazane method is easy to obtain a high-strength composite microporous membrane by relatively easy conversion to a SiO ₂ glass layer having a dense structure, and there is little elution of impurities derived from crosslinking agents, catalyst residues, etc. preferable.

The polysilazane used in the present invention is preferably a polysilazane that can be converted into SiO ₂ glass at a low temperature. Examples of such polysilazane include a solution containing polysilazane having a Si—H bond described in JP-A No. 2004-155834, a silicon alkoxide-added polysilazane described in JP-A No. 5-23827, and the like. And glycidol-added polysilazane described in JP-A-6-122852, and acetylacetonato complex-added polysilazane described in Japanese Patent No. 3307471. The polysilazane solution can be obtained, for example, as “AQUAMICA” manufactured by AZ Electronic Materials Co., Ltd.
The method for applying the polysilazane solution to the microporous film 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 polysilazane solution is applied to and adhered to the microporous film, and then the solvent is evaporated by pre-drying to produce a polysilazane layer. Further, the polysilazane layer is converted into a SiO ₂ glass layer by a method such as heating, hot water immersion, or steam exposure to form a microporous film. Incidentally, after winding in a state of forming a polysilazane layer, it may be converted to SiO ₂ glass layer is subjected to processing such as winding body for each heating or steam exposure.

As in the porosification step (S02), a base material layer may be provided during film formation. When the base material layer is provided, the raw material liquid can be prevented from inadvertently flowing out during the application of the raw material liquid. This is particularly effective when the raw material liquid has a low viscosity. Furthermore, the base material layer functions as a reinforcing material during filtration, and the membrane can withstand the filtration pressure. As the base material layer, non-woven fabrics, woven fabrics, porous plates and the like obtained by papermaking, a spunbond method, a melt blow method, and the like can be used. Polyester, polyolefin, ceramic, and the like can be used as the material. Among them, a polyester nonwoven fabric, a polypropylene nonwoven fabric, and a polyphenylene sulfide nonwoven fabric are preferable because of excellent balance of flexibility, lightness, strength, heat resistance, and the like. In the case of using a nonwoven fabric, the basis weight is preferably in the range of 15~150g / ^{m 2,} more preferably in the range of 30~90g / ^{m 2.} When the basis weight exceeds 15 g / m ² , the effect of providing the base material layer is sufficiently obtained. On the other hand, when the basis weight is less than 150 g / m ² , post-processing such as bending and heat bonding becomes easy.

In the step of forming the SiO ₂ glass layer (S04), the concentration of the polysilazane solution is preferably in the range of 0.1 to 20 parts by weight, and more preferably in the range of 0.5 to 10 parts by weight. When the polysilazane concentration exceeds 0.1 parts by weight, a sufficient hydrophilic effect can be obtained. When the polysilazane concentration is less than 20 parts by weight, the SiO ₂ glass layer does not block pores, so that sufficient permeability can be secured.
In addition, in the process of attaching the polysilazane solution, the filter performance can be further improved by adding an appropriate filler to the polysilazane solution as long as the chemical resistance and heat distortion resistance of the microporous membrane are not hindered. Can do. Examples of fillers include fine particles such as zinc oxide, titanium dioxide, barium titanate, barium carbonate, barium sulfate, zirconium oxide, zirconium silicate, alumina, magnesium oxide and silica, as well as silicon carbide, silicon nitride and carbon. Can be mentioned. The carbon includes fine particles composed of activated carbon, carbon nanotubes and the like in addition to graphite carbon fine particles. At least one of these fillers adheres to the microporous membrane together with the polysilazane and is firmly fixed in the SiO ₂ glass layer, whereby a composite porous membrane that does not fall off can be obtained.
The concentration of the filler in the polysilazane solution is usually 0 to 20% by weight, preferably 0 to 10% by weight. In such a concentration range, the performance as a filter can be further improved.

As described above, the composite microporous membrane of the present invention has a high hydrophilicity because the surface layer is coated with the SiO ₂ glass layer, and the microporous membrane contains a polyvinylidene fluoride resin based on the SiO ₂ glass layer. Since there is no blockage of micropores in the membrane, it is possible to maintain high permeability. Moreover, since the polyvinylidene fluoride resin is used as the film material, it can have excellent chemical resistance and a high heat resistance temperature (˜120 ° C.). Furthermore, since the skin layer has a three-dimensional network structure composed of a homogeneous spherical body and a linear binder, the pore size and the pore diameter of the skin layer are uniform, and high permeability (for example, high water permeability and high liquid permeability) is achieved. Can be realized. That is, since the size and shape of the pores are more uniform, a membrane with a narrower pore size distribution is obtained, and unprecedented permeability can be obtained while maintaining the particle blocking rate. Furthermore, since it is a microporous film having the above three-dimensional network structure, it is easy to apply the polysilazane solution uniformly to the entire film, and the hydrophilic effect of the SiO ₂ glass layer can be effectively exhibited. The composite microporous membrane of the present invention can be used for applications such as a chemical solution holding material used for adhesive bandages, a sanitary material surface material, a battery separator, etc., in addition to a filter application such as a filtration membrane.

  Hereinafter, the present invention will be described in more detail with reference to examples and the like. However, the scope of the present invention is not limited by these descriptions.

[Used materials]
For the polyethylene glycol 600 (weight average molecular weight 600), which is a porous material, reagent grade 1 manufactured by Wako Pure Chemical Industries, Ltd. was used.
As the solvent, N-dimethylacetamide, a reagent special grade manufactured by Wako Pure Chemical Industries, Ltd. was used.
As the polyvinylidene fluoride, Arkema's polyvinylidene fluoride “Kyner HSV900” (weight average molecular weight 800,000, number average molecular weight 540,000) was used.
As the base material layer, a card nonwoven fabric (H-8007, basis weight 70 g / m ² ) manufactured by Japan Vilene was used as the polyester nonwoven fabric.
As the support, a glass plate (size 20 cm × 20 cm) was used.
As the water, ultrapure water having a specific resistance value of 18 MΩ · cm or more manufactured by “DirectQ UV” (trade name) manufactured by Millipore was used.

〔Evaluation method〕
The physical property values of the microporous membranes obtained in Examples and Comparative Examples were measured by the following methods.
1) Average molecular weight of polymer The number average molecular weight and weight average molecular weight were determined by dissolving the polymer in dimethylformamide (DMF), using Shodex Asahipak KF-805L as a column, and using gel permeation chromatography (GPC) method with DMF as a developing agent. It was determined by measuring and converting to polystyrene.
2) Thickness of skin layer and thickness of support layer As shown in FIG. 6, a cross section of the obtained composite microporous membrane was photographed with a scanning electron microscope (SEM), and the photograph was image-analyzed. The length until the macro voids exist was defined as “skin layer thickness”, and the value obtained by subtracting the skin layer thickness from the total thickness of the composite microporous membrane was defined as “support layer thickness”.
3) Average flow hole diameter The average flow hole diameter was determined according to ASTM F316-86 using "Capillary Flow Porometer CFP-1200AEX" manufactured by PMI.
4) Flux The obtained composite microporous membrane is cut to a diameter of 25 mm, and is set in a filter sheet holder having an effective filtration area of 3.5 cm ² for each of the case where the composite microporous membrane is immersed in an appropriate amount of ethanol and the case where it is not immersed. Pressurization was performed at a pressure of 50 kPa to allow 5 mL of water to pass through, and the time required for passing water was measured. The flux was determined by the following formula (1).
Flux (10 ⁻⁹ m ³ / m ² / Pa / sec) = Water flow rate (m ³ ) ÷ Effective filtration area (m ² ) ÷ Filtration pressure (Pa) ÷ Time (sec) (1)
5) Number of spherical bodies, average particle diameter, frequency distribution The skin layer surface of the composite microporous membrane was photographed with a scanning electron microscope at a magnification of 20,000 times. Then, as shown in FIG. 7, for the spherical body having a central portion in the region of 4 μm length × 6 μm width in the center of the photograph, the outer periphery of the spherical body is surrounded by a perfect circle with the maximum diameter so that the surrounding holes are not included. The diameter of the perfect circle was taken as the particle size of the spherical body. However, since the number of the linear binding materials to be connected is 3 or less is difficult to distinguish from the linear binding materials, it was not regarded as a spherical body. And the average value of the diameter of all the spherical bodies contained in this area | region was made into the average particle diameter. Further, the number distribution of particles within a range of ± 10% of the average particle diameter was counted from all the spherical bodies, and the number was divided by the total number of particles of the spherical body to obtain a frequency distribution.
6) Number of binders, average length, frequency distribution As shown in FIG. 7, all the binders between the spheres included in the region (when two spheres are connected by a plurality of binders) The number and length of only one of them were measured, and the number and average length of all binders were determined. Moreover, the frequency distribution was calculated | required by counting the number of the binders included in the range of the width | variety of +/- 30% of the average length among them, and dividing the number by the number of all the binders.

[Example 1]
[Preparation process of raw material liquid]
The total amount of the raw material liquid is 100 parts by weight, 86 parts by weight of dimethylacetamide, 7 parts by weight of polyvinylidene fluoride “Kyner HSV900 (weight average molecular weight 800,000)”, 7 parts by weight of polyethylene glycol, these are mixed, Dissolved at ° C. It was returned to room temperature to obtain a raw material solution.
[Porosification process]
A polyester nonwoven fabric was placed on a glass plate, and the raw material liquid was applied thereon with a thickness of 250 μm using a Baker applicator. Immediately after application, the film was made porous to make it porous. The water was changed several times and washed, and the membrane was taken out of the water and dried to obtain a microporous membrane containing a polyvinylidene fluoride resin.
[SiO ₂ glass layer forming step]
As a polysilazane solution, a microporous material containing a polyvinylidene fluoride-based resin that has been subjected to a porous process using “AQUAMICA (registered trademark) model number NAX121-01 (polysilazane concentration: 1.0 part by weight)” manufactured by AZ Electronic Materials Co., Ltd. After dipping and removing the membrane, it is allowed to stand in a fume hood for about 30 minutes until the solvent completely evaporates, placed in an oven maintained at 130 ° C., heat-treated for 1 hour, and then allowed to stand at room temperature for 1 week. And a composite microporous membrane was obtained.

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

As can be seen by comparing the scanning electron micrographs of the skin layers of FIGS. 4 and 5, the skin layer of the composite microporous membrane of Example 1 has a three-dimensional network structure composed of a spherical body and a linear binder. Even when compared with the skin layer of the single-layer microporous film of Comparative Example 1, it can be seen that the micropores are not blocked by the SiO ₂ glass layer. As shown in Table 1, it can also be seen that the inside of the microporous membrane is not clogged from the fact that the average flow pore diameter also shows the same value. Moreover, since Example 1 shows a very high flux even without ethanol treatment compared with Comparative Example 1, it can be seen that the hydrophilicity is very high due to the formation of the SiO ₂ glass layer.

  Tables 2 to 3 show the particle diameters (perfect circle diameters) of the spherical bodies 1 obtained from scanning electron micrographs of the composite microporous membrane of Example 1.

  Table 4 shows the particle size characteristics of the spherical bodies of Example 1. The skin layer of the composite microporous membrane of Example 1 has a spherical average particle size of 0.190 μm. Further, 112 spheres corresponding to 62% of the spheres have a particle diameter within a range of ± 10% of the average particle diameter.

  Table 5 shows a frequency distribution table of the particle sizes of the spherical bodies. The particle size is concentrated within a width of 0.05 μm (0.15 to 0.20 μm), and it can be seen that the spherical body has a uniform particle size.

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

  Table 11 shows the characteristics of the linear binder of Example 1. In the skin layer of the composite microporous membrane of Example 1, the average length of the linear binder is 0.219 μm. Furthermore, the length of 259 binders, which is 61% of the binder, is in the range of ± 30% of the average length.

  Table 12 shows a frequency distribution table of the lengths of the linear binders. The frequency distribution increases and decreases so that the range of 0.20 to 0.25 μm peaks, and it can be seen that the length of the binder is concentrated in a specific range.

DESCRIPTION OF SYMBOLS 1 Spherical body 2 Linear binding material 3 Thickness of the whole film (support layer thickness = whole-skin layer)
4 Macrovoid 5 Skin layer thickness

  Since the composite microporous membrane of the present invention exhibits high water permeability without hydrophilic treatment such as alcohol substitution, it is possible to produce a filter having excellent chemical resistance and heat resistance possessed by a polyvinylidene fluoride resin. . For this reason, the membrane bioreactor, the water purification membrane, the medicine for which the high temperature sterilization process is essential, and the use for the food use can be used particularly effectively.

Claims (14)

A skin layer composed of a SiO ₂ glass layer is provided on at least one surface of a microporous film containing a polyvinylidene fluoride resin having a weight average molecular weight (Mw) of 790,000 to 900,000 , A composite microporous membrane for water treatment , comprising a three-dimensional network structure, wherein the SiO ₂ glass layer covers a skin layer in a state where micropores of the three-dimensional network structure are not blocked . A microporous membrane containing a polyvinylidene fluoride resin is an asymmetric membrane, and includes a skin layer in which micropores are formed and a support layer in which pores larger than the micropores are formed, which support the skin layer. The skin layer has a plurality of spherical bodies, and a plurality of linear binders extend from each of the spherical bodies in a three-dimensional direction, and the adjacent spherical bodies are formed by the linear binders. The composite microporous membrane according to claim 1, which is connected to each other to form a three-dimensional network structure having the spherical bodies as intersections. The composite microporous membrane according to claim 2 , wherein the spherical particles have a frequency distribution of 50% or more in a range of ± 10% of the average particle size. The composite microporous membrane according to claim 2 or 3 , wherein the length of the binder has a frequency distribution of 50% or more in a range of ± 30% of the average length. The composite microporous membrane according to any one of claims 2 to 4 , wherein the spherical body has an average particle diameter of 0.05 to 0.5 µm. The composite microporous membrane according to any one of claims 2 to 5 , wherein the skin layer has a thickness of 0.5 to 5 µm, and the support layer has a thickness of 20 to 500 µm. The composite microporous membrane according to any one of claims 2 to 6 , further comprising a base material layer that supports the support layer. The composite microporous membrane according to any one of claims 1 to 7 , wherein an average flow pore size of the composite microporous membrane is 5 to 500 nm. The composite microporous membrane according to any one of claims 1 to 8 , wherein the composite microporous membrane has a flat membrane shape. A filter using the composite microporous membrane according to any one of claims 1 to 9 . The method of manufacturing the composite microporous membrane according to any one of claims 1 to 9 to form a coating film of silica precursor on at least one side of the microporous film containing polyvinylidene fluoride resin Thereafter, by converting the silica precursor into SiO ₂ glass, a SiO ₂ glass layer is formed, and a microporous film containing a polyvinylidene fluoride resin at least one side coated with SiO ₂ glass is obtained. A method for producing a composite microporous membrane. The method for producing a microporous film according to claim 11 , wherein the silica precursor is polysilazane. 7. The method for producing a composite microporous membrane according to claim 6 , wherein a coating solution in which a raw material solution in which the polyvinylidene fluoride resin is dissolved in a good solvent is applied on the base material layer and after the coating step, The manufacturing method of a composite microporous film | membrane provided with the immersion process which immerses the said base material layer and the apply | coated said raw material liquid in a solvent. It is a manufacturing method of the composite microporous film | membrane of Claim 7 , Comprising: The application | coating process which apply | coats the raw material liquid which melt | dissolved the said polyvinylidene fluoride resin in the good solvent on a base material layer or a support body, and the said application | coating process Then, the manufacturing method of a composite microporous film | membrane provided with the immersion process which immerses the said base material layer or a support body and the apply | coated said raw material liquid in a non-solvent.

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