Porous film

Abstract

To provide a method for manufacturing a resin composition and a method for manufacturing a porous film capable of manufacturing a resin composition containing many PVDF α crystals or a porous film.SOLUTION: This porous film containing a polyvinylidene fluoride is manufactured only by a nonsolvent induction phase separation method (NIPS method). The polyvinylidene fluoride is non-oriented in one direction. A crystal structure obtained from the absorption intensity by the infrared absorption spectrum of the polyvinylidene fluoride is such that the ratio of absorbance derived from α crystals in the polyvinylidene fluoride to total absorbance derived from α and β crystals in the polyvinylidene fluoride (absorbance derived from α crystals / total amount of absorbance derived from α crystals and absorbance derived from β crystals) is 25%-100%.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a resin composition, a method for producing a porous membrane, and a porous membrane. [Background technology]

[0002] There are two methods for producing membranes containing polyvinylidene fluoride (PVDF): the nonsolvent induced phase separation method (NIPS, hereafter sometimes abbreviated as "NIPS method") and the thermally induced phase separation method (TPS). TIPS (Induced Phase Separation, hereafter sometimes abbreviated as "TIPS method") is known.

[0003] It is known that the TIPS method can produce a membrane containing a large amount of α-crystals of PVDF (for example, see Patent Document 1). It is also known that the NIPS method can produce a membrane containing a large amount of α-crystals by adding a salt such as lithium bromide (LiBr) to a membrane-forming solution in which PVDF is dissolved (for example, see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-171557 A [Patent Document 2] JP 2018-069115 A Summary of the Invention [Problem to be solved by the invention]

[0005] When PVDF contains a large amount of α-crystals, a membrane with excellent weather resistance, chemical resistance, and heat resistance can be obtained. Therefore, various attempts have been made to produce a membrane with a large amount of α-crystals of PVDF. Although the membrane produced by the TIPS method contains a lot of α crystals, it has a problem of inferior water permeability compared to the membrane produced by the NIPS method. It is also known that in the NIPS method, the proportion of α crystals increases by adding salt to the membrane-forming solution in which PVDF is dissolved. However, when a coagulation solution containing salt is used, a process of removing salt from the membrane after the membrane is formed is required, which is a problem of making the manufacturing process complicated.

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a method for producing a resin composition that can easily produce a resin composition or a porous membrane containing a large amount of PVDF α crystals, and a method for producing a porous membrane. Another object of the present invention is to provide a porous membrane containing a large amount of α crystals of PVDF. [Means for solving the problem]

[0007] The present invention, which achieves the above object, is configured as follows. [1] A stock solution containing polyvinylidene fluoride and two or more of good solvents capable of dissolving 10% by mass or more of the polyvinylidene fluoride is prepared; The method for producing a resin composition comprises contacting the raw solution with a coagulation liquid. [2] A film-forming solution is prepared containing polyvinylidene fluoride and two or more of good solvents capable of dissolving the polyvinylidene fluoride in an amount of 10 mass % or more; The method for producing a porous membrane comprises contacting the membrane-forming solution with a coagulation liquid to obtain a porous membrane precursor. [3] The method for producing a porous membrane according to [2], comprising removing a part or all of the solvent remaining in the porous membrane precursor, and then drying the porous membrane precursor to obtain a porous membrane. [4] A polyvinylidene fluoride film comprising the polyvinylidene fluoride, the polyvinylidene fluoride being non-oriented in one direction; A porous membrane, in which the crystal structure of the polyvinylidene fluoride determined from the absorption intensity in an infrared absorption spectrum has a ratio of the absorbance originating from α crystals in the polyvinylidene fluoride to the sum of the absorbance originating from α crystals and β crystals in the polyvinylidene fluoride (absorbance originating from α crystals / sum of absorbance originating from α crystals and absorbance originating from β crystals) of 25% or more and 100% or less. [5] A polyvinylidene fluoride film comprising the polyvinylidene fluoride, the polyvinylidene fluoride being non-oriented in one direction; A porous membrane, in which the crystal structure of the polyvinylidene fluoride determined by X-ray diffraction method has a ratio of the peak area ratio originating from α crystals in the polyvinylidene fluoride to the sum of the peak area ratios originating from α crystals, β crystals and γ crystals in the polyvinylidene fluoride (peak area ratio originating from α crystals / peak area ratio originating from α crystals, sum of the peak area ratio originating from β crystals and the peak area ratio originating from γ crystals) of 15% or more and 100% or less. [6] The porous membrane of claim [4] or [5], wherein the orientation parameter of the polyvinylidene fluoride calculated by Raman spectroscopy is less than 1.5. [7] The porous membrane described in claim [4] or [5], wherein the orientation parameter of the polyvinylidene fluoride calculated by X-ray diffraction method is 0.4 or less. [8] The porous membrane according to any one of [4] to [7], wherein the plasticizer content is 1 mass % or less. [9] The porous membrane according to any one of [4] to [8], wherein the inner diameter of the pores of the porous membrane gradually changes from one surface to the other surface of the porous membrane.

[10] The porous membrane according to any one of [4] to [9], having an inorganic salt content of 1 mass % or less. Effect of the Invention

[0008] According to the present invention, it is possible to provide a resin composition or a method for easily producing a porous membrane containing a large amount of α crystals of PVDF, and a method for easily producing a resin composition and a porous membrane. Furthermore, according to the present invention, a porous membrane containing a large amount of α crystals of PVDF can be provided. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram showing infrared absorption spectra of PVDF in the porous membranes of the examples and comparative examples. [Diagram 2] FIG. 2 is a diagram showing X-ray diffraction spectra of PVDF in the porous membranes of the examples and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of the porous membrane of the present invention will be described. It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0011] 1. Porous membrane The porous membrane of the present embodiment contains polyvinylidene fluoride, the polyvinylidene fluoride is non-oriented in one direction, and the ratio of α crystals in polyvinylidene fluoride is higher than that of a porous membrane obtained by using a conventional stock solution dissolved in a single good solvent and applying the NIPS method. In detail, the porous membrane of the present embodiment has a ratio of α crystals to the total crystal ratio of polyvinylidene fluoride that is higher than 15%.

[0012] 1.1 Material <Polyvinylidene fluoride> In the porous membrane of this embodiment, polyvinylidene fluoride (PVDF) means a homopolymer of vinylidene fluoride and a vinylidene fluoride copolymer containing vinylidene fluoride as a main component.

[0013] Examples of vinylidene fluoride copolymers include vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-chlorotrifluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymers, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene terpolymers, and mixtures of two or more of these.

[0014] In these vinylidene fluoride copolymers, the copolymerization ratio of the comonomer is preferably 20 mol % or less, more preferably 10 mol % or less. When the copolymerization ratio of the comonomer is 20 mol % or less, the vinylidene fluoride copolymer becomes a thermoplastic resin having crystallinity. When the copolymerization ratio of the comonomer is too high, the vinylidene fluoride copolymer loses crystallinity and becomes an elastomer.

[0015] The mass average molecular weight (hereinafter referred to as "Mw") of PVDF is preferably 100,000 or more and 2,000,000 or less. If Mw is 100,000 or more, the mechanical strength of the porous membrane of the present embodiment tends to be good, and if Mw is 2,000,000 or less, the solubility in a solvent described below tends to be good. The lower limit of Mw is more preferably 300,000 or more, and the upper limit of Mw is more preferably 1,500,000 or less.

[0016] PVDF can be produced by suspension polymerization or emulsion polymerization. In emulsion polymerization, vinylidene fluoride alone or vinylidene fluoride and a comonomer such as hexafluoropropylene are emulsified in an aqueous medium using a chemically stable fluorine-based emulsifier. Polymerization is then carried out using an inorganic peroxide, an organic peroxide, an organic percarbonate compound, or the like as a polymerization initiator. After emulsion polymerization, the submicron-sized latex is precipitated and coagulated using a coagulant, and PVDF can be collected as particles of an appropriate size.

[0017] <Materials other than polyvinylidene fluoride> In producing the porous membrane of the present embodiment, in addition to PVDF, hydrophilic polymer resins such as monools, diols, triols, polyvinylpyrrolidone, etc., typified by polyethylene glycol, can be used in the membrane forming solution for the purpose of controlling phase separation, etc. These can be appropriately selected and used as needed, but among them, polyvinylpyrrolidone is preferred because of its excellent thickening effect.

[0018] 1.2 Orientation of PVDF The PVDF contained in the porous membrane of the present embodiment is non-oriented in one direction. The form of the porous membrane of the present invention can be, for example, a flat membrane and a hollow fiber membrane. Here, the one direction of PVDF refers to, for example, the thickness direction of the flat membrane when the porous membrane is a flat membrane, and refers to the fiber axis direction of the hollow fiber when the porous membrane is a hollow fiber membrane.

[0019] "PVDF is non-oriented in one direction" means that the orientation parameter of PVDF calculated by Raman spectroscopy is less than 1.5. "PVDF is non-oriented in one direction" means that the orientation parameter of PVDF calculated by X-ray diffraction is 0.4 or less. When PVDF is non-oriented in one direction, it is easy to prepare a membrane having an asymmetric gradient structure, and high water permeability and rejection can be achieved at the same time.

[0020] The method for measuring the orientation parameter by Raman spectroscopy is, for example, as follows. The porous hollow fiber membrane is sliced ​​by cutting the cross section along the longitudinal direction of the porous hollow fiber membrane with a microtome. The slice thus obtained is observed with an optical microscope and laser Raman measurement is performed at 1 μm intervals along the longitudinal direction of the hollow fiber. -1 The Raman band around 840 cm belongs to the coupling mode between CF2 (fluorocarbon) stretching vibration and CC (carbon-carbon) stretching vibration. The vibration direction of these vibrations is parallel to the molecular chain. On the other hand, the 840 cm of PVDF-1 The vibration direction of the Raman band near is perpendicular to the molecular chain. Since Raman scattering is strong when the vibration direction of the molecular chain coincides with the polarization direction of the incident light, the ratio of the scattering intensity of these vibration modes changes in correlation with the degree of orientation. For this reason, the orientation parameter can be calculated using the following formula (1). The orientation parameter ν increases as the orientation in the longitudinal direction of the porous hollow fiber membrane increases; it is 1 when there is no orientation, and is smaller than 1 when the orientation in the transverse direction is high. Orientation parameter ν=(I1270 / I840)parallel / (I1270 / I840)perpendicular (1) In the above formula (1), the parallel condition is that the longitudinal direction of the porous hollow fiber membrane is parallel to the polarization direction. The perpendicular condition is that the longitudinal direction of the porous hollow fiber membrane is perpendicular to the polarization direction. -1 Parallel: 1270cm when parallel -1 Intensity of the Raman band at I1270cm -1 Vertical: 1270cm when vertical -1 Intensity of the Raman band at I840cm -1 Parallel: 840cm when parallel -1 Intensity of the Raman band at I840cm -1 Vertical: 840cm when vertical -1 is the intensity of the Raman band.

[0021] 1.3 Crystallinity of PVDF PVDF is known as a highly crystalline resin, and its crystal structure is roughly classified into three types: α-crystal, β-crystal, and γ-crystal.

[0022] In the porous membrane of the present embodiment, the proportion of α crystals in the total crystals of the PVDF contained in the porous membrane is higher than 15%. By making the proportion of α crystals 15% or more, the chemical durability of the porous membrane, particularly against alkali, is improved.

[0023] The ratio of α crystals to the total crystal ratio of PVDF contained in a porous membrane in PVDF is higher than 15%, which means that, when the total of the peak area ratios attributable to α crystals, β crystals, and γ crystals in the crystal structure of PVDF determined by X-ray diffraction (XRD) is taken as 100%, the ratio of the peak area ratio attributable to α crystals is 15% or more and 100% or less, and the total ratio of the peak area ratios attributable to β crystals and γ crystals is 0% or more and 90% or less. The ratio of the peak area ratio derived from α crystals is preferably 15% or more, and more preferably 25% or more.

[0024] The peak area ratios of α-, β-, and γ-crystals in PVDF can be calculated by comparing the area ratios of the peaks corresponding to each crystal structure using X-ray diffraction (XRD).

[0025] The specific measurement method is as follows.

[0026] From the X-ray diffraction pattern of PVDF obtained by XRD, the areas of the peaks from 18.7° to 26.5° and the peaks derived from α crystals, the areas of the peaks from 20.7° to 41.2° derived from β crystals, and the areas of the peaks from 20.3° to 39.4° derived from γ crystals are calculated. In other words, the areas are calculated by drawing a straight line connecting the start and end points of each diffraction pattern corresponding to each crystal.

[0027] The proportion of α crystals is calculated as described above by determining the areas of the peaks at 18.7° and 26.5° corresponding to α crystals, the areas of the peaks at 20.7° corresponding to β crystals, and the areas of the peaks at 20.3° corresponding to γ ​​crystals, using the following formula (2). The proportion of β crystals is calculated by determining the area of ​​the 18.7° peak corresponding to α crystals, the area of ​​the 20.7° peak corresponding to β crystals, and the area of ​​the 20.3° peak corresponding to γ ​​crystals, as described above, and using the following formula (3). The proportion of gamma crystals is calculated by determining the area of ​​the 18.7° peak corresponding to α crystals, the area of ​​the 20.7° peak corresponding to β crystals, and the area of ​​the 20.3° peak corresponding to gamma crystals, as described above, and using the following formula (4).

[0028] Percentage of α crystals = (area of ​​the peak at 18.7° + area of ​​the peak at 26.5°) / (area of ​​the peak at 18.7° + area of ​​the peak at 26.5° + area of ​​the peak at 20.7° + area of ​​the peak at 20.3°) × 100 (%) (2) Percentage of β crystals = area of ​​the peak at 20.7° / (area of ​​the peak at 18.7° + area of ​​the peak at 26.5° + area of ​​the peak at 20.7° + area of ​​the peak at 20.3°) x 100 (%) (3) Percentage of γ crystals = area of ​​the peak at 20.3° / (area of ​​the peak at 18.7° + area of ​​the peak at 26.5° + area of ​​the peak at 20.7° + area of ​​the peak at 20.3°) × 100 (%) (4)

[0029] The ratio of α crystals to the total crystal ratio of PVDF contained in a porous membrane in PVDF is higher than 15%, which means that, when the total absorbance derived from α crystals and β crystals in the crystal structure of PVDF determined from the absorption intensity in the infrared absorption spectrum is taken as 100%, the lower limit of the absorption intensity derived from α crystals is 25% or more, preferably 28% or more, and more preferably 30% or more, and the upper limit of said ratio is 100% or less, the lower limit of the total absorption intensity derived from β crystals is 0% or more, and the upper limit of said total ratio is 75% or less, preferably 72% or less, and more preferably 70% or less.

[0030] The absorption intensities of α- and β-crystals in PVDF can be calculated from infrared absorption spectra obtained by Fourier transform infrared spectroscopy (FT-IR).

[0031] The specific measurement method is as follows.

[0032] The crystal ratio in PVDF is calculated from the peak intensity ratio of polymorphs on the low wavenumber side in the infrared absorption spectrum of PVDF. -1 , α crystal is 764 cm -1The intensity ratio is corrected using the absorption coefficients in the respective absorptions using the following formula (5) to calculate the β crystal ratio F(β) in the formed crystals. β is 840cm -1 Absorbance at, A α is 764cm -1 Absorbance at, K β is 840cm -1 The absorption coefficient at (7.7×10 4 cm 2 Mol -1 ), K α is 764cm -1 The absorption coefficient at (6.1×10 4 cm 2 Mol -1 )

[0033]

number

[0034] 1.4 Plasticizers The porous membrane of the present embodiment may contain a plasticizer, but the content of the plasticizer is preferably 1% by mass or less, more preferably 0.5% by mass or less. If the content of the plasticizer is 1% by mass or less, the amount of the plasticizer dissolved in the treated water during use of the porous membrane is small, and the quality of the treated water can be maintained at a high level.

[0035] The plasticizer is not particularly limited, but examples thereof include caprolactones such as ε-caprolactone.

[0036] 1.5 Inorganic substances The porous membrane of the present embodiment may contain an inorganic substance, but the content of the inorganic substance is preferably 1 mass% or less, more preferably 0.5 mass% or less. If the content of the inorganic substance is 1 mass% or less, the amount of the inorganic substance dissolved in the treated water during use of the membrane is small, and the water quality of the treated water can be maintained at a high level.

[0037] The inorganic substance is used when manufacturing the porous membrane. The inorganic substance is not particularly limited, but examples thereof include silica, calcium silicate, aluminum silicate, magnesium silicate, calcium carbonate, magnesium carbonate, calcium phosphate, metal oxides, metal hydroxides, and salts. Examples of the metal oxides include oxides of iron and zinc. Examples of the metal hydroxides include hydroxides of iron and zinc. Examples of the salts include salts of sodium, potassium, and calcium.

[0038] 1.6 Pore The porous membrane of this embodiment has pores. In the porous membrane of this embodiment, the inner diameter of the pores of the porous membrane gradually changes from one surface to the other surface of the porous membrane. The gradual change in the inner diameter of the pores of the porous membrane from one surface to the other surface of the porous membrane includes the gradual increase in the inner diameter of the pores from one surface to the other surface of the porous membrane, and the gradual decrease in the inner diameter of the pores from one surface to the other surface of the porous membrane. This allows the membrane to have a separation function on the side with a small pore size and to reduce the pressure loss to water on the side with a large pore size, so that a membrane with a high water permeability can be prepared while maintaining fractionation compared to a homogeneous membrane with a small pore size change. As long as high water permeability can be maintained, the membrane may have a mixture of parts where the inner diameter of the pores gradually increases and parts where the inner diameter of the pores gradually decreases from one surface to the other surface of the porous membrane.

[0039] The average pore size of the pores in the porous membrane is preferably 1 nm or more and 1200 nm or less in terms of usability for removing bacteria and viruses, purifying proteins or enzymes, or for drinking water applications. If the average pore size of the pores is 1 nm or more, high water permeation pressure tends not to be required when treating water. If the average pore size of the pores is 1200 nm or less, it tends to be possible to remove bacteria, viruses, and suspended solids in drinking water.

[0040] The average pore diameter of the pores in the porous membrane of this embodiment refers to the average pore diameter obtained by actually measuring the longest diameter of the pores in the outer surface portion of the porous membrane of this embodiment using a scanning electron microscope (manufactured by JEOL Ltd., product name: JSM-7400).

[0041] 1.7 Shape <flat membrane> When the porous membrane of the present embodiment is a flat membrane, the thickness is preferably 10 μm or more and 1000 μm or less. If the thickness is 10 μm or more, it tends to have high elasticity and satisfactory durability. If the thickness is 1000 μm or less, it tends to be produced at low cost. In addition, when the porous membrane is a flat membrane, the lower limit of the thickness is more preferably 20 μm or more, and even more preferably 30 μm or more. The upper limit of the thickness is more preferably 900 μm or less, and even more preferably 800 μm or less.

[0042] When the porous membrane of this embodiment is a flat membrane, the internal structure of the membrane may be, for example, a gradient structure in which the pore size decreases in a specific direction in the cross section of the membrane, or a structure having uniform pores.

[0043] When the porous membrane of the present embodiment is a flat membrane, it may have a macrovoid or spherulite structure in the membrane.

[0044] <Hollow fiber membrane> When the shape of the porous membrane of this embodiment is a hollow fiber membrane, the outer diameter of the hollow fiber membrane is preferably 20 μm or more and 3500 μm or less. When the outer diameter of the porous membrane is 20 μm or more, thread breakage during membrane production tends to be less likely to occur. Furthermore, when the outer diameter of the hollow fiber membrane is 3500 μm or less, the hollow shape is easily maintained, and in particular, even when external pressure is applied, the hollow fiber membrane tends to be less likely to become flattened. The lower limit of the outer diameter of the hollow fiber membrane is more preferably 30 μm or more, and even more preferably 40 μm or more. Furthermore, the upper limit of the outer diameter of the hollow fiber membrane is more preferably 3200 μm or less, and even more preferably 3000 μm or less.

[0045] <Support> The porous membrane of the present embodiment may be composed of only the above-mentioned porous membrane, but it is particularly preferable that the porous membrane is on a hollow support, because it can obtain excellent mechanical strength.In addition, in this embodiment, it is expressed as on the support to clarify the positional relationship between the porous membrane and the support, but the porous membrane may be impregnated into the support through the voids of the support.

[0046] The support may be appropriately selected and used as long as it has high mechanical strength and can be integrated with the porous membrane, and is not particularly limited, but a knitted cord is preferred because it has low manufacturing costs, can achieve both flexibility and cross-sectional shape stability (roundness), and has excellent adhesion to the porous membrane. Among them, a hollow knitted cord made by circularly knitting a single thread made of multifilament is preferred. In this case, the porous membrane and the support (hollow braid) do not necessarily need to be in close contact with each other, but if their adhesion is low, they may separate when the hollow fiber membrane is pulled, causing the porous membrane to come loose. Therefore, in the porous membrane of this embodiment, it is preferable that a portion of the porous membrane penetrates into the hollow braid through the stitches of the braid, and the porous membrane and the hollow braid are integrated together.

[0047] The total thickness of the porous membrane and the support of the hollow fiber membrane is preferably 5 μm or more and 500 μm or less. If the total thickness of the porous membrane and the support of the hollow fiber membrane is 5 μm or more, thread breakage is less likely to occur during membrane production. If the total thickness of the porous membrane and the support of the hollow fiber membrane is 500 μm or less, the hollow shape tends to be easily maintained. The lower limit of the total thickness of the porous membrane and the support of the hollow fiber membrane is more preferably 10 μm or more, and even more preferably 15 μm or more. The upper limit of the total thickness of the porous membrane and the support of the hollow fiber membrane is more preferably 450 μm or less, and even more preferably 400 μm or less.

[0048] 1.8 Performance 1.8.1 Water permeability Water permeability can be calculated from the relationship between the amount of water permeable and the membrane area obtained under a certain pressure in a module with a certain shape. Since the small pore side has a separation function and the large pore side can reduce the pressure loss for water, it is possible to prepare a membrane with high water permeability while maintaining fractionation compared to a homogenous membrane with small pore size change.

[0049] 1.8.2 Chemical resistance Chemical resistance is measured by immersing the porous membrane in sodium hydroxide for a long time. The α crystal is considered to be the most thermodynamically stable crystal structure. This is thought to be because the α crystal structure has delocalized hydrogen and fluorine atoms and has less charge imbalance than the β crystal structure. In other words, it is thought that excellent chemical resistance can be exhibited when the α crystal structure, which has relatively low polarity, is present at a higher ratio than the β crystal structure, which has relatively high polarity and localized hydrogen and fluorine atoms. The high ratio of α crystals makes it preferable for use in separation membranes that treat oil, etc. When treating water containing a lot of oil, there is a problem of oil-derived substances clogging the separation membrane surface, etc., but generally, when treated with sodium hydroxide, etc., the oil-derived substances are saponified and can be washed away. A PVDF membrane with a high total ratio of β crystals and γ crystals is likely to be corroded and deteriorated by sodium hydroxide, so a PVDF membrane containing a large amount of α crystals is preferable.

[0050] 2-1. Manufacturing method of porous membrane In the method for producing a porous membrane of this embodiment, a membrane-forming solution (C) in which polyvinylidene fluoride (PVDF) is dissolved in a mixed good solvent containing two or more kinds of good solvents is brought into contact with a coagulation liquid.

[0051] As an example of a method for producing the porous membrane of this embodiment, the following method can be mentioned. First, a membrane-forming solution (C) containing PVDF and two or more good solvents is applied to a support and solidified by contacting with a solidifying liquid to obtain a porous membrane precursor. Thereafter, a part or all of the solvent remaining in the porous membrane precursor is removed by washing, and the washed porous membrane precursor is dried to obtain the porous membrane of this embodiment.

[0052] <Membrane forming stock solution (C)> The membrane-forming solution (C) contains PVDF and two or more good solvents. The membrane-forming solution (C) may further contain a resin other than polyvinylidene fluoride, such as polyvinylpyrrolidone, polyethylene glycol, cellulose acetate, acrylic resin, etc. These polymer materials may be added to control the compatibility and viscosity of the membrane-forming solution (C).

[0053] A good solvent is a solvent that can dissolve 10% by mass or more of PVDF. The good solvents to be mixed are not particularly limited as long as they are mutually compatible and, when combined into a mixed good solvent, have excellent solubility for PVDF. Examples of such good solvents include acetone, propylene carbonate (PC), γ-butyrolactone (γ-BL), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), cyclohexanone (CHN), hexamethylphosphoric triamide (HMPA), tetramethylurea (TMU), triethyl phosphate (TEP), and trimethyl phosphate (TMP).

[0054] As the mixed good solvent, it is preferable to use two or more kinds selected from the above-mentioned good solvents: propylene carbonate (PC), γ-butyrolactone (γ-BL), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), cyclohexanone (CHN), hexamethylphosphoric triamide (HMPA), and triethyl phosphate (TEP).

[0055] More specifically, it is preferable to use, as the mixed good solvent, a combination of dimethylacetamide (DMAc) / propylene carbonate (PC), dimethylacetamide (DMAc) / γ-butyrolactone (γ-BL), N-methylpyrrolidone (NMP) / propylene carbonate (PC), and N-methylpyrrolidone (NMP) / γ-butyrolactone (γ-BL).

[0056] When preparing a mixed solvent, it is preferable to mix DMAc or NMP as a main solvent and PC or GBL as a sub-solvent.

[0057] When DMAc or NMP is used as the main solvent and GBL is used as the auxiliary solvent, the content of GBL is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, even more preferably 5% by mass or more, particularly preferably 8% by mass or more, most preferably 10% by mass or more, and is preferably 49% by mass or less, more preferably 40% by mass or less, and more preferably 30% by mass or less.

[0058] When DMAc or NMP is used as the main solvent and PC is used as the auxiliary solvent, the content of GBL is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, even more preferably 5% by mass or more, particularly preferably 8% by mass or more, most preferably 10% by mass or more, and is preferably 49% by mass or less, more preferably 40% by mass or less, and more preferably 30% by mass or less.

[0059] In addition, the mixed solvent is preferably a mixed solvent that, when a film-forming stock solution containing the mixed solvent is subjected to 19F NMR measurement using Bruker's "Avance 300," the fluorine peak in the (Head-Tail)(Head-Head) bond of PVDF, which appears around -93 to -94 ppm, becomes broader than that in the case of DMAc alone. "Broadening" refers to the phenomenon in which the peak tops that are roughly two in the case of DMAc alone are seen as almost one peak. The chemical shift standard is set to -164.7 ppm for the hexafluorobenzene peak, the number of integrations is 64, and the measurement temperature is room temperature.

[0060] The membrane-forming solution (C) may be in a dispersed state even if some of the PVDF is not dissolved and dispersed, so long as the solution is homogeneous and the homogeneity can be maintained.

[0061] The content of PVDF in the membrane-forming solution (C) is preferably 7 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the total amount of the membrane-forming solution (C). If the content of PVDF is 7 parts by mass or more, it is easy to form a porous membrane, and the mechanical properties of the obtained porous membrane are at a practical level. In addition, if the content of PVDF is 30 parts by mass or less, a porous membrane having sufficient porosity and therefore high water permeability can be obtained. The lower limit of the PVDF content is more preferably 10 parts by mass or more, and even more preferably 12 parts by mass or more. The upper limit of the PVDF content is more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less.

[0062] The content of the solvent in the membrane-forming solution (C) is preferably 50 parts by mass or more and 93 parts by mass or less, and more preferably 60 parts by mass or more and 90 parts by mass or less, per 100 parts by mass of the total amount of the membrane-forming solution (C).

[0063] <Coagulation> The membrane-forming solution (C) is brought into contact with a coagulation solution to obtain a porous membrane precursor. The coagulation solution used to obtain the porous membrane precursor can be a non-solvent such as water (distilled water) or an aqueous solution containing the same solvent as that contained in the membrane-forming solution (C) and water (distilled water), and is preferably an aqueous solution. The concentration of the solvent in the coagulation solution is preferably 0% by mass or more and 50% by mass or less.

[0064] The temperature of the coagulation liquid is preferably 10° C. or higher and 90° C. or lower. If the temperature of the coagulation liquid is 10° C. or higher, the water permeability of the porous membrane of the present embodiment tends to be improved. If the temperature of the coagulation liquid is 90° C. or lower, the mechanical strength of the porous membrane of the present embodiment tends not to be impaired.

[0065] <Cleaning> The obtained porous membrane precursor is preferably immersed in hot water of 40° C. to 100° C. and washed to remove the solvent. If the temperature of the hot water is 40° C. or higher, a high washing effect on the porous membrane precursor tends to be obtained. If the temperature of the hot water is 100° C. or lower, the porous membrane precursor tends to be less likely to fuse.

[0066] <Drying> The porous membrane precursor after washing is preferably dried at 60°C or more and 120°C or less for 1 minute or more and 24 hours or less. If the drying temperature of the porous membrane precursor after washing is 60°C or more, the drying process time can be short, and the production cost can be reduced, which is preferable for industrial production. In addition, if the drying temperature of the porous membrane precursor after washing is 120°C or less, the porous membrane precursor tends not to shrink too much in the drying process, and microcracks tend not to occur on the outer surface of the membrane, which is preferable.

[0067] According to the method for producing a porous membrane of the present embodiment, a membrane-forming stock solution (C) containing PVDF and two or more good solvents is solidified by contacting with a solidification solution to obtain a porous membrane precursor, and the porous membrane obtained by drying the porous membrane precursor has PVDF non-oriented in one direction, and the proportion of α-crystals in PVDF is higher than that of a porous membrane obtained by using a stock solution dissolved in a conventional single good solvent and the NIPS method. In addition, according to the method for producing a porous membrane of the present embodiment, a membrane-forming stock solution (C) in which PVDF is dissolved in a mixed good solvent containing two or more good solvents is used, and the proportion of α-crystals contained in PVDF can be controlled by adjusting the combination or compounding ratio of the good solvents used.

[0068] 2-2. Manufacturing method of resin composition In the method for producing a resin composition of the present embodiment, a raw solution (C') in which polyvinylidene fluoride (PVDF) is dissolved in a mixed good solvent containing two or more kinds of good solvents is brought into contact with a coagulation liquid.

[0069] As an example of a method for producing the resin composition of the present embodiment, the following method can be mentioned. First, a raw solution (C') containing PVDF and two or more good solvents is dropped into a coagulation liquid, and the raw solution (C') is coagulated by contacting with the coagulation liquid to obtain a pellet-shaped resin composition. Thereafter, the solvent remaining in the pelletized resin composition may be partially or entirely removed by washing, and the washed resin composition may be dried before use. The resin composition obtained by the method for producing a resin composition of the present embodiment can be molded into any shape.

[0070] <Standard solution (C')> The raw solution (C') contains PVDF and two or more good solvents, similar to the above-mentioned membrane-forming raw solution (C). The raw solution (C') may further contain a resin other than polyvinylidene fluoride, such as polyvinylpyrrolidone, polyethylene glycol, cellulose acetate, acrylic resin, etc. These polymer materials may be added when controlling the compatibility or viscosity of the raw solution (C').

[0071] The raw solution (C') can be prepared in the same manner as the raw solution (C) for membrane formation in the above-mentioned method for producing a porous membrane. The same also applies to <coagulation>, <washing> and <drying>.

[0072] According to the method for producing a resin composition of this embodiment, a stock solution (C') containing PVDF and two or more good solvents is brought into contact with a coagulation liquid to coagulate the resin composition, and the resin composition is dried and molded to obtain a molded product in which PVDF is non-oriented in one direction, and the proportion of α crystals in PVDF is higher than that of a porous film obtained by dissolving PVDF in a conventional stock solution in a single good solvent using the NIPS method. In addition, according to the method for producing a resin composition of this embodiment, a stock solution (C') in which PVDF is dissolved in a mixed good solvent containing two or more good solvents is used, and the proportion of α crystals contained in PVDF can be controlled by adjusting the combination or compounding ratio of the good solvents used.

[0073] 3.Applications The porous membrane of the present embodiment can be used for microfiltration, ultrafiltration, etc. In particular, as a filtration membrane used in water treatment, it is suitable for use because it has high resistance when washed with an alkali to remove dirt attached to the surface of the filtration membrane. The resin composition obtained by the method for producing a resin composition according to the present embodiment can be used as a battery separator for a lithium ion battery, a coating material, etc. In particular, the resin composition can be suitably used as a battery separator for a lithium ion battery.

[0074] 4.Effects The method for producing a porous film according to the present embodiment can produce a film containing a large amount of α crystals, and therefore a porous film with high chemical resistance can be obtained. The method for producing a resin composition according to the present embodiment can produce a resin composition containing a large amount of α crystals, and therefore can provide a variety of molded articles with high chemical resistance. EXAMPLES

[0075] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0076] In the following description, "parts" and "%" indicate "parts by mass" and "% by mass", respectively.

[0077] [Example 1] A mixed good solvent was prepared by mixing 94 parts of dimethylacetamide (DMAc) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade) and 11 parts of γ-butyrolactone (GBL) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade). The mass ratio of DMAc to GBL in the obtained mixed good solvent ((mass of DMAc) / (mass of GBL)) was 89 / 11. Next, 80 parts of the mixed good solvent was diluted with PVDF homopolymer (product name: KF Polymer #1100, manufactured by Kureha Corporation, Mw = 2.8 × 10 5 20 parts of the above was dissolved in water to prepare a film-forming solution (C-1). The obtained film-forming solution (C-1) was left to stand at room temperature for a day, then coated on a glass substrate using a spin coater and treated at 1000 rpm for 10 minutes to obtain a thin film. The thin film was immersed in a large amount of deionized water at 22°C to solidify, and a coating film laminate was produced. The coating laminate was left in the coagulation bath for 3 minutes, and then the resulting flat porous membrane was dried at room temperature under atmospheric pressure to obtain the porous membrane of Example 1.

[0078] [Comparative Example 1] A membrane-forming stock solution (C-2) containing only dimethylacetamide (DMAc) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade) as a good solvent was prepared, and the porous membrane of Comparative Example 1 was obtained in the same manner as in the Examples, except that the membrane-forming stock solution (C-2) was used.

[0079] [evaluation] (Measurement of the crystalline ratio of porous membranes by infrared absorption spectroscopy) The PVDF contained in the porous membranes obtained in Example 1 and Comparative Example 1 was subjected to Fourier transform infrared spectroscopy analysis using a Fourier transform infrared spectrophotometer (FT-IR). For the FT-IR measurement, an IR Prestige-21 manufactured by SHIMADZU was used. The measurement method was the ATR method, and the MIRacle manufactured by PIKE Technologies was used. TM A single reflection ATR was used. The specific measurement method was as described above. 764cm originating from α-crystal of PVDF -1 The absorbance of the peak at 840 cm originating from the β crystal of PVDF is taken as 1. -1 The absorbance of the peak was calculated, and the crystal ratio of α crystals was calculated based on the above formula (5). The results are shown in Table 1. In addition, Fig. 1 shows the 764 cm -1 The infrared absorption spectrum of PVDF is shown, with the absorbance of the peak being set to 1.

[0080] [Table 1]

[0081] From the results shown in Table 1, it was confirmed that the proportion of α-crystals in the PVDF contained in the porous membrane of Example 1 was 32.5%, which was 25% or more. As a result, it can be said that the PVDF contained in the porous membrane of Example 1 was non-oriented in one direction, and the proportion of α-crystals in the PVDF was greater than the proportion of β-crystals. On the other hand, it was confirmed that the proportion of α crystals in the PVDF contained in the porous membrane of Comparative Example 1 was 23.5%, which was less than 25%. As a result, it can be said that the PVDF contained in the porous membrane of Comparative Example 1 was oriented in one direction, and the proportion of α crystals in the PVDF was less than the proportion of β crystals.

[0082] [Example 2] Dimethylacetamide (DMAc) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade) was used as the main solvent, and γ-butyrolactone (GBL) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade) was used as the secondary solvent. They were mixed in the mass ratio shown in Table 2 below to prepare a mixed good solvent. Next, 80 parts of the mixed good solvent was diluted with PVDF homopolymer (product name: KF Polymer #1100, manufactured by Kureha Corporation, Mw = 2.8 × 10 5 ) was dissolved to prepare a film-forming solution. The obtained film-forming solution was left to stand at room temperature for a day, then coated on a glass substrate using a spin coater and processed at 1000 rpm for 10 minutes to obtain a thin film. The thin film was immersed in a large amount of deionized water at 22°C to solidify, and a coating film laminate was produced. The coating laminate was left in the coagulation bath for 3 minutes, and then the resulting flat porous membrane was dried at room temperature under atmospheric pressure to obtain the porous membrane of Example 2.

[0083] [evaluation] (Measurement of the crystalline ratio of porous membranes using X-ray diffraction method) The PVDF contained in the porous membrane obtained in Example 2 was subjected to X-ray diffraction (XRD) measurement using an X-ray diffractometer. For the X-ray diffraction measurement, a Rigaku "MiniFlex II" was used. X-rays used were Cu·Kα rays (tube voltage: 30 kv, direct current: 15 mA), and the measurement was performed using the θ, 2θ method (scan speed: 2 to 10° / min). The specific measurement method was as described above. From the X-ray diffraction pattern of PVDF obtained by XRD, the area of ​​the peak from 18.7° to 26.5° derived from α crystals, the area of ​​the peak from 20.7° to 41.2° derived from β crystals, and the area of ​​the peak from 20.3° to 39.4° derived from γ crystals were obtained, and the crystal ratio of α crystals was calculated based on the above formula (2). The results are shown in Table 2.

[0084] [Examples 3 to 5] Dimethylacetamide (DMAc) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade) was used as the main solvent, and propylene carbonate (PC) (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the auxiliary solvent. They were mixed in the mass ratios shown in Table 2 below to prepare mixed good solvents. Next, 80 parts of the mixed good solvent was diluted with PVDF homopolymer (product name: KF Polymer #1100, manufactured by Kureha Corporation, Mw = 2.8 × 10 5 ) was dissolved to prepare a film-forming solution. The obtained film-forming solution was left to stand at room temperature for a day, then coated on a glass substrate using a spin coater and processed at 1000 rpm for 10 minutes to obtain a thin film. The thin film was immersed in a large amount of deionized water at 22°C to solidify, and a coating film laminate was produced. The coating laminate was left in the coagulation bath for 3 minutes, and then the resulting flat porous membrane was dried at room temperature under atmospheric pressure to obtain the porous membranes of Examples 3-5.

[0085] [evaluation] (Measurement of the crystalline ratio of porous membranes using X-ray diffraction method) The same procedure was carried out as in Example 2. The results are shown in Table 2.

[0086] [Example 6] N-methylpyrrolidone (NMP) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Grade 1) was used as the main solvent, and γ-butyrolactone (GBL) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade) was used as the auxiliary solvent. They were mixed in the mass ratio shown in Table 2 below to prepare a mixed good solvent. Next, 80 parts of the mixed good solvent was diluted with PVDF homopolymer (product name: KF Polymer #1100, manufactured by Kureha Corporation, Mw = 2.8 × 10 5 ) was dissolved to prepare a film-forming solution. The obtained film-forming solution was left to stand at room temperature for a day, then coated on a glass substrate using a spin coater and processed at 1000 rpm for 10 minutes to obtain a thin film. The thin film was immersed in a large amount of deionized water at 22°C to solidify, and a coating film laminate was produced. The coating laminate was left in the coagulation bath for 3 minutes, and then the resulting flat porous membrane was dried at room temperature under atmospheric pressure to obtain the porous membrane of Example 6.

[0087] [evaluation] (Measurement of the crystalline ratio of porous membranes using X-ray diffraction method) The same procedure was carried out as in Example 2. The results are shown in Table 2.

[0088] [Comparative Example 2] A porous membrane of Comparative Example 2 was obtained in the same manner as in Example 2, except that no auxiliary solvent was used. The crystal ratio of the porous film was also measured by X-ray diffraction in the same manner as in Example 2. The results are shown in Table 2.

[0089] [Comparative Example 3] A porous membrane of Comparative Example 3 was obtained in the same manner as in Example 6, except that no auxiliary solvent was used. The crystal ratio of the porous film was also measured by X-ray diffraction in the same manner as in Example 2. The results are shown in Table 2.

[0090] FIG. 2 shows an XRD spectrum of PVDF with peaks from 18.7° to 26.5° originating from α crystals and peaks from 20.3° to 39.4° originating from γ crystals.

[0091] [Table 2]

[0092] From the results shown in Table 2, it was confirmed that the proportion of α crystals contained in PVDF can be controlled by using a film-forming solution in which PVDF is dissolved in a mixed good solvent containing two types of good solvents and adjusting the blending ratio. It was also confirmed that the proportion of α-crystals in the PVDF contained in the porous membranes of Examples 2 to 6 was 15% or more. As a result, it was confirmed that the PVDF contained in the porous membranes of Examples 2 to 6 was non-oriented in one direction, and the proportion of α-crystals in the PVDF was high.

Claims

1. A stock solution containing polyvinylidene fluoride and two or more of good solvents capable of dissolving the polyvinylidene fluoride at 10 mass % or more is prepared; The method for producing a resin composition comprises contacting the raw solution with a coagulation liquid.

2. preparing a film-forming solution containing polyvinylidene fluoride and two or more of good solvents capable of dissolving the polyvinylidene fluoride in an amount of 10 mass % or more; The method for producing a porous membrane comprises contacting the membrane-forming solution with a coagulation liquid to obtain a porous membrane precursor.

3. The method for producing a porous membrane according to claim 2 , further comprising the steps of removing a part or all of the solvent remaining in the porous membrane precursor, and then drying the porous membrane precursor to obtain a porous membrane.

4. The polyvinylidene fluoride is non-oriented in one direction, A porous membrane, in which the crystal structure of the polyvinylidene fluoride determined from the absorption intensity in an infrared absorption spectrum has a ratio of the absorbance originating from α crystals in the polyvinylidene fluoride to the sum of the absorbance originating from α crystals and β crystals in the polyvinylidene fluoride (absorbance originating from α crystals / sum of absorbance originating from α crystals and absorbance originating from β crystals) of 25% or more and 100% or less.

5. The polyvinylidene fluoride is non-oriented in one direction, A porous membrane, in which the crystal structure of the polyvinylidene fluoride determined by X-ray diffraction method has a ratio of the peak area ratio originating from α crystals in the polyvinylidene fluoride to the sum of the peak area ratios originating from α crystals, β crystals and γ crystals in the polyvinylidene fluoride (peak area ratio originating from α crystals / peak area ratio originating from α crystals, sum of the peak area ratio originating from β crystals and the peak area ratio originating from γ crystals) of 15% or more and 100% or less.

6. The porous membrane according to claim 4 or 5, wherein the polyvinylidene fluoride has an orientation parameter calculated by Raman spectroscopy of less than 1.

5.

7. The porous membrane according to claim 4 or 5, wherein the polyvinylidene fluoride has an orientation parameter of 0.4 or less as calculated by an X-ray diffraction method.

8. The porous membrane according to any one of claims 4 to 7, wherein the plasticizer content is 1% by mass or less.

9. The porous membrane according to any one of claims 4 to 8, wherein the inner diameter of the pores of the porous membrane changes gradually from one surface to the other surface of the porous membrane.

10. The porous membrane according to any one of claims 4 to 9, wherein the content of inorganic salt is 1% by mass or less.

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