JP2899903B2 - Polyvinylidene fluoride porous membrane and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention has excellent chemical resistance and excellent filtration performance and excellent mechanical properties made of polyvinylidene fluoride resin,
The present invention also relates to a porous membrane having a three-dimensional homogeneous porous structure including fine pores and a method for producing the same.

[Conventional technology]

Polyvinylidene fluoride resin is expected as a material for a porous film having various properties excellent in chemical resistance, heat resistance, and mechanical properties.

Although several techniques have been disclosed for the porous membrane made of polyvinylidene fluoride resin, most of these porous membranes are heterogeneous porous membranes made by a wet film forming method and having a skin layer. Japanese Patent Application Laid-Open No. 60-97001 discloses a method for obtaining a porous membrane having a network structure,
Since it is a wet film forming method, there is a problem in mechanical strength. JP
JP-A-58-93734 discloses a method of mixing a polyvinylidene fluoride resin with an organic liquid and a hydrophilic inorganic fine powder and melt-molding the mixture to obtain a porous film. There is a problem that many voids (coarse pores) are present, the elongation at break is small, and it cannot withstand use at high temperature and high pressure.

As described above, in the related art, a porous membrane having a two-dimensional homogeneous porous structure excellent in mechanical strength could not be obtained.

[Problems to be solved by the invention]

An object of the present invention is to provide a polyvinylidene fluoride resin porous membrane in which the above problems have been solved and a method for producing the same.

[Means for solving the problem]

The present inventors have conducted intensive studies to achieve the above object, and as a result, completed the present invention.

That is, the present invention is made of polyvinylidene fluoride resin, has a porosity of 40 to 90%, does not substantially contain macrovoids of 10 μ or more inside, the average pore diameter of the surface layer is 0.05 μm or more and less than 5 μm, and The ratio of the average pore diameter of the surface layer to the average pore diameter of the membrane cross section has a three-dimensional network structure composed of homogeneous communication holes of 0.5 to 2.0, and the ratio of the maximum pore diameter to the average pore diameter is 1.2 to 2.5. Has a breaking strength of 70-200 kg / cm ² , a breaking elongation of 100-
The present invention relates to a porous membrane made of polyvinylidene fluoride resin of 500%.

Further, the present invention provides a method for producing a porous membrane, comprising mixing a polyvinylidene fluoride resin with an organic liquid and an inorganic fine powder, followed by melt molding, and then extracting the organic liquid and the inorganic fine powder from the molded product. A method for producing a polyvinylidene fluoride porous membrane, comprising using hydrophobic silica having a methanol MW value of 30% or more as an inorganic fine powder, and using an organic liquid having an SP value of 8.4 to 10.5. It is about.

As an inorganic fine powder, the average primary particle diameter is 0.005 to 0.5
It is preferable to use hydrophobic silica having a μ, specific surface area of 30 to 500 m ² / g, and a volume percentage (MW value) of methanol at which the powder is completely wetted is 30% or more. As the organic liquid, it is preferable to use an organic liquid having a solubility parameter (SP value) in the range of 8.4 to 10.5.

 Hereinafter, the present invention will be described in detail.

Examples of the polyvinylidene fluoride resin used in the present invention include vinylidene fluoride homopolymer and vinylidene fluoride copolymer, and examples of the vinylidene fluoride copolymer include vinylidene fluoride, ethylene tetrafluoride, and propylene hexafluoride. , Ethylene trifluoride, or a copolymer with at least one selected from ethylene is used, and vinylidene fluoride homopolymer is preferably used. These polymers can be mixed at any time.

The vinylidene fluoride copolymer used in the present invention preferably has a weight average molecular weight (w) of 100,000 to 1,000,000. More preferably, it is 150,000 to 500,000. When a vinylidene fluoride copolymer having a w of less than 100,000 is used, the resulting porous membrane has a small elongation of 50% or less and is brittle, and cannot be put to practical use. When a vinylidene fluoride copolymer having a w of more than 1,000,000 is used, since the fluidity at the time of melting is small, the thin film moldability by T-die extrusion molding and the moldability of a molded article by injection molding are deteriorated. Furthermore, the average pore size on the surface of the network structure formed by the vinylidene fluoride copolymer is less than 0.05 μ, the open area is reduced, the porosity is also reduced, and the permeability is undesirably reduced.

The membrane of the present invention has a three-dimensional network structure composed of homogeneous communication holes. The membrane of the present invention has the same structure at any 10 μ square in the porous membrane. FIG. 1 (a) to (c)
Shows a typical electron micrograph of the outer surface, inner surface and cross section of the film of the present invention. The average pore size of the membrane of the present invention (calculated by weighting the average of the major axis and minor axis of 200 pores observed in a scanning electron micrograph of the porous membrane surface) is 0.05 μm or more and 5 μm or more.
Is less than. If the average pore size is less than 0.05 μm, the pore size is too small to exhibit the properties of the porous membrane intended in the present invention.
On the other hand, if the average pore diameter is 5μ or more, it corresponds to a pinhole defect,
The membrane function cannot be maintained.

Further, the film of the present invention does not substantially contain macrovoids of 10 μm or more inside (the term “inside” in the present invention refers to a cross section of a porous film cut off). Furthermore, the ratio of the average pore diameter of the surface layer (outer surface and inner surface) to the average pore diameter of the membrane cross section is 0.5 to
It has a three-dimensional network structure consisting of uniform communication holes at 2.0. This structure is achieved by melt-molding a polyvinylidene fluoride resin, an organic liquid material, and a raw material of hydrophobic silica to form a film. The membrane of the present invention has a narrow ratio of 1,2 to 2.5 between the maximum pore size (measured by the bubble point method of ASTM F316-70 and E128-61) and the average pore size (measured by the half dry method of ASTM F316-70). It has a pore size distribution, and has excellent filtration performance and excellent fractionation characteristics. Further, the porosity of the membrane of the present invention (porosity = pore volume / porous membrane volume × 10
0, pore volume = water content-absolute weight) is 40 to 90%. If the porosity exceeds 90%, the resin is too small and the strength is low, and if the porosity is less than 40%, it is unsuitable for obtaining a membrane having excellent permeability.

Further, the film of the present invention is formed by a melt molding method, the entanglement of the molecules of polyvinylidene fluoride resin is achieved by a high degree of breaking strength by 70-200Kg /.
cm ² , elongation at break is 100 to 500%, and the material has mechanical properties with dramatically improved elongation. Breaking strength 70Kg / cm ²
If the elongation at break is less than 100%, or the elongation at break is less than 100%, the mechanical strength is weak and cannot be put to practical use. Further, in the present production method, a material having a breaking strength exceeding 200 kg / cm ² and a material having a breaking elongation exceeding 500% were not obtained.

 The manufacturing method of the present invention will be described.

The organic liquid used in the present invention is extracted from a molded product and imparts porosity to the molded product. The organic liquid material is required to be liquid at the time of melt molding and inert. Further, the organic liquid preferably has a solubility parameter (SP value) in the range of 8.4 to 10.5. More preferably, it is 8.4 to 9.9.

By using those in this range, during melt molding,
The organic liquid material is appropriately dissolved in the polyvinylidene fluoride resin, and when cooled and solidified, most of the organic liquid material is in a state of being adsorbed on the surface of the inorganic fine powder. As a result, a porous material having good moldability, extractability, and mechanical strength can be obtained. Furthermore, the SP value of the organic liquid
By selecting from the range of 8.4 to 10.5, it is possible to adjust the average pore diameter of the polyvinylidene fluoride resin porous body to be between 0.05 and 5 μm.

When the SP value of the organic liquid exceeds 10.5, the solubility in the polyvinylidene fluoride resin increases, and microphase separation hardly occurs during cooling. As a result, the fusion of the melt is sufficiently performed, and while the mechanical strength is improved, the porosity of the organic liquid material is reduced, and the average pore diameter of the polyvinylidene fluoride resin porous material is 0.05 μ or less, and the organic When the liquid and the inorganic fine powder are extracted, the shrinkage is large, the porosity decreases, and the appearance deteriorates.

On the other hand, if the SP value is less than 8.4, the solubility in the resin is reduced and the resin is released during molding. For this reason, welding between the resins is hindered, moldability is deteriorated, and the average pore diameter of the network structure of the polyvinylidene fluoride resin becomes coarse to 5 μ or more, and the strong elongation is reduced.

Examples of the organic liquid having an SP value of 8.4 to 10.5 used in the present invention include phthalate esters and phosphate esters such as diethyl phthalate (DEP), dibutyl phthalate (DBP), and dioctyl phthalate (DOP). Is mentioned. Of these, dioctyl phthalate, dibutyl phthalate, and mixtures thereof are particularly preferred.

The inorganic fine powder used in the present invention has a function as a carrier for holding an organic liquid material, and further has a function as a nucleus for microphase separation. That is, to prevent release of the organic liquid during melt molding, to facilitate molding,
As a core of microphase separation, the organic liquid is highly micro-dispersed, and has a function of highly preventing aggregation of the organic liquid.
Further, it has a function of being extracted to form voids.

The inorganic fine powder used in the present invention is hydrophobic silica. Hydrophobic silica is silica obtained by chemically reacting silanol groups on the surface of hydrophilic silica with an organosilicon compound such as dimethylsilane or dimethyldichlorosilane, and replacing the surface of the hydrophilic silica with methyl groups or the like to make it hydrophobic. I say
The hydrophobic silica used in the present invention has an average primary particle size of 0.1.
Hydrophobic silica having a 005 to 0.5 μm and a specific surface area of 30 to 500 m ² / g, and having a volume percentage (MW value) of 30% or more of methanol to completely wet the powder is preferable.

In addition, the volume percentage of methanol at which the powder is completely wetted is a value measured by a methanol wettability method.

By using hydrophobic silica, aggregation of silica is eliminated, and affinity with hydrophobic polyvinylidene fluoride resin and organic liquid material is increased as compared with the case of using hydrophilic silica. It is considered that a high degree of microdispersion is achieved, and as a result, the formation of macrovoids is prevented, and a porous polyvinylidene fluoride resin having a fine and uniform three-dimensional porous structure without macrovoids is generated.

When hydrophilic silica is used, the moldability deteriorates, the resulting molded article has many macrovoids, the network structure of the polyvinylidene fluoride resin becomes uneven, and the strong elongation decreases. .

In addition, when hydrophobic silica is used, a high degree of micro-dispersion of the inorganic fine powder is achieved, and as a result, the formation of macrovoids is prevented. Is possible.

 The method for producing a porous membrane of the present invention will be described in more detail.

First, a polyvinylidene fluoride resin, an organic liquid, and hydrophobic silica are mixed. The mixing ratio of the polyvinylidene fluoride resin is 10 to 60% by volume, preferably 15 to 40% by volume, the organic liquid is 30 to 75% by volume, preferably 50 to 70% by volume, and the hydrophobic silica is 7 to 42% by volume, preferably 10-20% by volume.

If the polyvinylidene fluoride resin is less than 10% by volume, the amount of the resin is too small, resulting in low strength and poor moldability. 60% by volume
If it exceeds, a porous film having a high porosity cannot be obtained, which is not preferable.

When the content of the organic liquid is less than 30% by volume, the contribution of the organic liquid to the formation of pores is reduced, and the porosity of the obtained porous membrane is 40%.
%, It is not possible to obtain a porous membrane which is substantially effective. If it exceeds 75% by volume, molding becomes difficult, and a porous film having high mechanical strength cannot be obtained.

If the amount of the hydrophobic silica is less than 7% by volume, an organic liquid material necessary for forming an effective porous membrane cannot be adsorbed, and the mixture cannot maintain a powder or granule state, which makes molding difficult. On the other hand, if it exceeds 42% by volume, the fluidity at the time of melting is poor, and the obtained molded product is brittle and cannot be put to practical use.

In addition, the volume% of methanol (MW
Value) is less than 30%, the silica aggregates with each other, and the affinity for the hydrophobic polyvinylidene fluoride resin and the organic liquid is lower than that of the case where the hydrophilic silica is used. The resulting molded article has many macrovoids, which lowers the mechanical properties of the film.

In addition, it is difficult to form a thin film due to the above-mentioned drawbacks, and furthermore, there are many macrovoids, which causes pinholes, resulting in poor productivity (yield of good products).

The composition used in the present invention is mainly composed of a polyvinylidene fluoride resin, hydrophobic silica, and an organic liquid. However, other additives such as lubricants, antioxidants, ultraviolet absorbers, plasticizers, molding aids, etc. may be added as needed without significantly impairing the effects of the present invention.

A Henschel mixer, V-
An ordinary mixing method using a blender such as a blender or a ribbon blender is sufficient. The mixing order of the three components is 3
Rather than mixing the components at the same time, first, the hydrophobic silica and the organic liquid are mixed, the organic liquid is sufficiently adsorbed on the hydrophobic silica, and then the polyvinylidene fluoride resin is mixed and mixed. This is effective in improving the properties and the porosity and mechanical strength of the obtained porous material.

This mixture is kneaded by a melt kneading device such as an extruder, a Banbury mixer, a two-roll mill, or a kneader. The resulting kneaded material is molded by a melt molding method. Examples of the melt molding method used in the method of the present invention include extrusion molding such as T-die method, inflation method, and method using a hollow die, calender molding, and compression molding. , Injection molding and the like.
Further, the mixture can be directly molded by an apparatus having both functions of kneading and extrusion, such as an extruder and a kneader.

By these molding methods, the three-component mixture is 0.025 to 2.5 mm
Into a thick film. 0.025-2.5mm film, especially
Extrusion molding is particularly effective for forming a thin film of 0.025 to 0.30 mm. The shape of the membrane may be hollow fiber, tube, flat membrane, or the like.

The organic liquid is extracted from the obtained film using a solvent. The solvent used for the extraction is capable of dissolving the organic liquid, but must not substantially dissolve the polyvinylidene fluoride resin.

The extraction is easily performed by a general method for extracting a film-like substance such as a batch method or a multi-stage countercurrent method. Examples of the solvent used for the extraction include methanol, acetone and the like.
Halogen hydrocarbons such as 1,1-trichloroethane and trichloroethylene are preferred. In addition, the organic liquid is allowed to remain in the porous membrane from which extraction has been completed, as long as the performance of the substance is not impaired. However, a large residual amount is not preferable because the porosity of the porous membrane decreases. The remaining amount of the organic liquid in the porous membrane is 3% by volume or less, preferably 1% by volume.
It is as follows.

The solvent may be dried on the semi-extracted porous membrane from which the extraction of the organic liquid has been completed, if necessary. Next, the hydrophobic silica is extracted with a solvent of the hydrophobic silica. Prior to the extraction, the semi-extracted porous membrane is immersed in a 50 to 100% aqueous ethyl alcohol solution and then immersed in water to be absorbed in water, so that the extraction is performed more efficiently and evenly. The extraction can be easily completed within a few seconds to several tens of hours by a general extraction method such as a batch method or a countercurrent multistage method.

As a solvent used for extracting the hydrophobic silica, an aqueous alkali solution such as caustic soda and caustic potash is used. There is no particular limitation as long as it does not substantially dissolve the polyvinylidene fluoride resin and dissolves the hydrophobic silica. Further, in the porous membrane after completion of the extraction, hydrophobic silica is allowed to remain within a range that does not impair the performance of the product. However, a large residual amount is not preferable because the porosity of the porous membrane decreases. The remaining amount of the hydrophobic silica in the porous membrane is 3% by volume or less, preferably 1% by volume or less.

Further, it is also possible to simultaneously extract the organic liquid and the hydrophobic silica using an alcohol solution of caustic soda or the like. However, it is preferable to extract the organic liquid and the hydrophobic silica in this order.

In addition, in order to increase the pore diameter or increase the porosity, the porous membrane from which one or both of the organic liquid material and the hydrophobic silica is extracted may be uniaxially or biaxially stretched.

The porous membrane according to the present invention is made of a polyvinylidene fluoride resin having excellent chemical resistance, and has a narrow pore size distribution and a complicated network structure, thereby providing a microfilter having excellent water permeability and air permeability, and high filtration performance. It will be realized.

The porous membrane according to the present invention can be used for refining vegetable oils such as sunflower oil and rapeseed oil by utilizing its excellent chemical resistance and mechanical properties. Further, it can be used for purification of mineral oil, recovery of valuables from fermentation broth, purification of chemicals, and the like. Further, it can be used as a microfilter for removing a large amount of fine particles in water.

〔Example〕

Next, examples will be described. Various physical properties shown in this example were measured by the following measurement methods.

Weight average molecular weight (w) Molecular weight in terms of polystyrene by GPC, GPC measurement device: Toyo Soda LS-8000, column: GMHX
L, solvent: DMF, column temperature: 40 ° C.

Composition ratio (% by volume) It was calculated from the value obtained by dividing the added weight of each composition by the true specific gravity.

Porosity (%) Porosity (%) = (pore volume / porous membrane volume) × 100, pore volume = water-containing weight−absolute dry weight.

Specific surface area (m ² / g) Measured by BET adsorption method.

Average pore size (μ) (calculated from electron micrographs) Calculated as the weighted average of the major axis and minor axis of the 200 pores observed in the scanning electron micrograph of the surface of the porous membrane.

Average pore size (μ) (half dry method) Measured according to ASTM F316-70.

Maximum pore size (μ) (bubble point method) Measured according to ASTM F316-70 and E128-61.

Water permeability (l / m ² · hr · atm · 25 ° C) Measured at 25 ° C and differential pressure 1Kg / cm ² .

Breaking strength (Kg / cm ² ), breaking elongation (%) Measured with an Instron type tensile tester according to ASTM D882 (strain rate 2.0 mm / mm · min).

Dissolution parameter (SP value) Calculated by the following formula (Small's formula) SP value = dΣG / M, d: specific gravity, G: molar index constant.

The volume% (MW value) of methanol in which the powder is completely wetted Collect 0.2 g of silica in a beaker and add 50 ml of pure water. Methanol is added below the liquid surface with electromagnetic stirring, and the point at which no silica is observed on the liquid surface is defined as the end point, and is calculated from the required amount of methanol by the following equation.

 MW value = X / (50 + X) × 100, X: methanol consumption (ml).

Example 1 Hydrophobic silica [Aerosil R-972 (trade name)] having an MW value of 50%, an average primary particle diameter of 16 mμ and a specific surface area of 110 m ² / g, 14.8% by volume, and 48.5% by volume of dioctyl phthalate (SP value: 8.9) And 4.4% by volume of dibutyl phthalate (SP value: 9.4) were mixed in a Henschel mixer, and 32.3% by volume of polyvinylidene fluoride (Kureha KF polymer # 1000 (trade name)) with w = 242,000 was added thereto. And mixed.

The mixture was mixed with a 30 mmφ twin screw extruder to form pellets. The pellet was formed into a hollow fiber shape by a hollow fiber manufacturing apparatus equipped with a 30 mmφ twin screw extruder and a hollow fiber spout. The molded hollow fiber was immersed in 1,1,1-trichloroethane at 60 ° C. for 1 hour to extract dioctyl phthalate and dibutyl phthalate, and then dried.

Next, the hollow fiber was immersed in a 50% ethyl alcohol aqueous solution for 30 minutes, transferred to water, and immersed for 30 minutes to hydrophilize the hollow fiber. After further immersing in a 20% aqueous solution of caustic soda at 70 ° C. for 1 hour to extract hydrophobic silica, it was washed with water and dried.

The performance of the obtained polyvinylidene fluoride porous membrane depends on the outer diameter.
2.00mm, inner diameter 1.10mm, porosity 66.0%, average pore diameter of outer surface, inner surface and cross section calculated from electron micrographs are 1.87μ, 0.86μ and 1.05μ, respectively. The ratio of the average pore diameter of the cross section was 1.78, and the ratio of the average pore diameter of the inner surface to the average pore diameter of the membrane cross section was 0.82. The average pore diameter by the half dry method was 0.59 μm, the maximum pore diameter by the bubble point method was 0.91 μm, and the ratio of the maximum pore diameter to the average pore diameter was 1.54. The water permeability was 7000 l / m ² · hr · atm · 25 ° C, the breaking strength was 115 kg / cm ² , and the breaking elongation was 300%.

Electron micrographs of the outer surface, inner surface and cross section of the obtained porous membrane are shown in FIGS. 1 (a) to (d), respectively. This porous membrane had a three-dimensional network structure consisting of homogeneous communication holes, and no macrovoids of 10 μm or more were found inside.

Comparative Example 1 Hydrophilic silica having an MW value of 0%, an average primary particle size of 16 mμ, and a specific surface area of 280 m ² / g [Nipsil LP (trade name)] was used as the silica.
A polyvinylidene fluoride porous membrane was obtained in the same manner as in Example 1 except that

Performance of the resulting polyvinylidene fluoride porous membrane has an average pore size of 0.40μ by the half-dry method, a maximum pore size 1.00Myu, water permeability ^{2500l / m 2 · hr · atm} · 25 ℃ by the bubble point method
The breaking strength was 60 kg / cm ² , and the breaking elongation was very low at 50%. FIG. 2 shows an electron micrograph of a cross section of the obtained porous membrane. Many macro voids are seen in the porous membrane,
It had an uneven structure.

Example 2 Pellets were prepared in the same manner as in Example 1, and the obtained pellets were formed into a film by a film manufacturing apparatus in which a T-die having a width of 450 mm was attached to a 30 mmφ twin screw extruder.

The formed film was immersed in 1,1,1-trichloroethane at 60 ° C. for 1 hour to extract dioctyl phthalate and dibutyl phthalate, and then dried.

Then, the film was immersed in a 50% ethyl alcohol aqueous solution for 30 minutes, further transferred to water and immersed for 30 minutes to hydrophilize the film. After further immersing in a 20% aqueous solution of caustic soda at 70 ° C. for 1 hour to extract hydrophobic silica, it was washed with water and dried.

The performance of the obtained polyvinylidene fluoride porous membrane depends on the film thickness.
110μ, porosity 64.0%, average pore diameter of outer surface, inner surface and cross section calculated from electron micrographs are 1.55μ, 1.
The ratio of the average pore diameter of the outer surface to the average pore diameter of the membrane cross section was 1.17, and the ratio of the average pore diameter of the inner surface to the average pore diameter of the membrane cross section was 0.91. The average pore diameter by the half dry method was 0.67 μm, the maximum pore diameter by the bubble point method was 1.01 μm, and the ratio of the maximum pore diameter to the average pore diameter was 1.51. The water permeability was 15,000 l / m ² · hr · atm · 25 ° C, the breaking strength was 120 kg / cm ² , and the breaking elongation was 340%.

An electron micrograph of the obtained porous membrane had a three-dimensional network structure composed of homogeneous communication holes, and no macrovoids of 10 μm or more were found inside.

Comparative Example 2 16% by weight of polyvinylidene fluoride [Penwalt, Kynar301F (trade name), w = 460,000], 64% by weight of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), 10% by weight of cyclohexanone, and polyvinylpyrrolidone [ Wako Pure Chemical, K
−30 (molecular weight: 40,000)] A stock solution of 10% by weight was prepared and cast on a glass plate. Leave it in the air for 5 minutes,
After the casting membrane became sufficiently cloudy, it was immersed in a water washing bath to obtain a polyvinylidene fluoride porous membrane.

The performance of the obtained polyvinylidene fluoride porous membrane depends on the film thickness.
130μ, average pore diameter 0.63μ by half dry method, maximum pore diameter 1.90μ by bubble point method, water permeability 14,000l / m ²
· Hr · atm · 25 ° C, the breaking strength was 13 kg / cm ² , and the breaking elongation was very weak at 35%, which was not practical.

Comparative Example 3 A membrane-forming stock solution was prepared in the same manner as in Comparative Example 2, and immediately after casting on a glass plate, NMP 70% by weight and methanol 15% by weight.
The cast film was immersed in a coagulation bath consisting of 15% by weight of water and 15% by weight of water, and 2 minutes after the cast film became cloudy, was immersed in a washing bath to obtain a polyvinylidene fluoride porous film.

The performance of the obtained polyvinylidene fluoride porous membrane depends on the film thickness.
80μ, average pore size 0.19μ by half dry method, maximum pore size 0.78μ by bubble point method, water permeability 260l / m ²・ hr
It was atm at 25 ° C, the breaking strength was 23 kg / cm ² , and the breaking elongation was 2%, which was very weak and could not be put to practical use.

Examples 3 and 4 A polyvinylidene fluoride porous film was obtained in the same manner as in Example 1 except that the mixing ratio of polyvinylidene fluoride, hydrophobic silica, dioctyl phthalate, and dibutyl phthalate was changed. The performance of the obtained polyvinylidene fluoride porous membrane was
It is shown in the table. Elongation at break was all large.

Example 5 Diheptyl phthalate (SP value: 9.1) was used as the organic liquid, and the mixing ratio of polyvinylidene fluoride, hydrophobic silica, and the organic liquid was 31.3% by volume, 12.5% by volume, and 56.2% by volume, respectively. A polyvinylidene fluoride porous membrane was obtained in the same manner as in Example 1. Table 2 shows the performance of the obtained polyvinylidene fluoride porous membrane.

Example 6 A polyvinylidene fluoride porous membrane was prepared in the same manner as in Example 1 except that a hydrophobic silica having a MW value of 60%, an average primary particle size of 16 mμ, and a specific surface area of 75 m ² / g was used. I got

Performance of the resulting polyvinylidene fluoride porous membrane has an average pore size of 0.65μ by the half-dry method, a maximum pore size 1.10Myu, water permeability of ^{8,500l / m 2 · hr · atm} · 25 ℃ by the bubble point method
The breaking strength was 100 kg / cm ² and the breaking elongation was 250%.

An electron micrograph of the obtained porous membrane had a three-dimensional network structure composed of homogeneous communication holes, and no macrovoids of 10 μm or more were found inside.

[Effects of the Invention] The present invention has excellent chemical resistance, excellent filtration performance, excellent mechanical physical properties, and has a uniform porous structure composed of fine pores, and the elongation at break is dramatically improved. Thus, the obtained polyvinylidene fluoride porous film can be obtained.

[Brief description of the drawings]

1 (a) to 1 (d) are electron micrographs showing the surface shape of the polyvinylidene fluoride hollow fiber produced according to Example 1, and FIG. 1 (a) shows the shape of the outer surface of the hollow fiber (see FIG. 1 (a)). FIG. 1 (b) shows the shape of the inside surface of the hollow fiber (3000 ×), and FIG. 1 (c) shows the shape of the cross-sectional surface of the hollow fiber (3000 ×). Figure (d) shows the shape (200 times magnification) of the cross-sectional surface of the hollow fiber. FIG. 2 is an electron micrograph showing the cross-sectional surface shape (magnification: 200 times) of the polyvinylidene fluoride hollow fiber fiber produced in Comparative Example 1.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-97001 (JP, A) JP-A-59-16503 (JP, A) JP-A-58-59072 (JP, A) JP-A-58-590 93734 (JP, A) JP-A-48-56261 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08J 9/26-9/28 102

Claims (2)

(57) [Claims] 1. A surface layer comprising a polyvinylidene fluoride resin having a porosity of 40 to 90%, containing substantially no macrovoids of 10 μm or more inside, and having an average pore diameter of 0.05 μm or more and less than 5 μm in a surface layer. The ratio of the average pore diameter of the membrane to the average pore diameter of the membrane
It has a three-dimensional network structure consisting of 2.0 homogeneous communication holes,
A porous membrane made of a polyvinylidene fluoride resin having a pore size distribution in which the ratio of the maximum pore size to the average pore size is 1.2 to 2.5, a breaking strength of 70 to 200 kg / cm ² , and a breaking elongation of 100 to 500%. 2. A method for producing a porous membrane, comprising mixing a polyvinylidene fluoride resin with an organic liquid and an inorganic fine powder, followed by melt molding, and then extracting the organic liquid and the inorganic fine powder from the molded product. A method for producing a polyvinylidene fluoride porous membrane, comprising using hydrophobic silica having a methanol MW value of 30% or more as an inorganic fine powder, and using an organic liquid having an SP value of 8.4 to 10.5. .