JP2021176629A - Resin composition manufacturing method, porous film manufacturing method, and porous film - Google Patents

Abstract

To provide a resin composition manufacturing method by which a resin composition containing a large amount of α crystals of PVDF or a porous film can be easily manufactured, and a porous film manufacturing method.SOLUTION: According to this resin composition manufacturing method, a stock solution, which contains a polyvinylidene fluoride and two or more kinds of good solvents in which 10% or more by mass of the polyvinylidene fluoride can be dissolved, is prepared, and the stock solution and a coagulant are brought into contact with each other. According to this porous film manufacturing method, a membrane-forming stock solution, which contains a polyvinylidene fluoride and two or more kinds of good solvents in which 10% or more by mass of the polyvinylidene fluoride can be dissolved, is prepared, and the membrane-forming stock solution and a coagulant are brought into contact with each other, thereby obtaining a porous film precursor.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a resin composition, a method for producing a porous membrane, and a porous membrane.

As a method for producing a film containing polyvinylidene fluoride (PVDF), a non-solvent induced phase separation method (NIPS, hereinafter may be abbreviated as "NIPS method") and a heat-induced phase separation method (Thermally). Induced Phase Separation, TIPS, hereinafter, may be abbreviated as "TIPS method") is known.

It is known that the TIPS method can produce a film containing a large amount of α crystals of PVDF (for example, see Patent Document 1). Further, also in the NIPS method, it is known that a film containing a large amount of α crystals can be produced by adding a salt such as lithium bromide (LiBr) to a film-forming stock solution in which PVDF is dissolved (for example, Patent Documents). 2).

JP-A-2018-171557 Japanese Unexamined Patent Publication No. 2018-069115

When PVDF contains a large amount of α crystals, a film having excellent weather resistance, chemical resistance, and heat resistance can be obtained. Therefore, various attempts have been made in the past to produce a film containing a large amount of α crystals of PVDF. Although the film produced by the TIPS method contains a large amount of α crystals, there is a problem that the film is inferior in water permeability as compared with the film produced by the NIPS method. Further, in the NIPS method, it is known that the proportion of α crystals is increased by adding a salt to the membrane-forming stock solution in which PVDF is dissolved. However, when a coagulating liquid containing a salt is used, a step of removing the salt from the film after the film formation is required, which causes a problem that the manufacturing process becomes complicated.

The present invention has been made in view of the above circumstances, and is a method for producing a resin composition containing a large amount of α crystals of PVDF or a method for producing a resin composition capable of easily producing a porous film, and a method for producing a porous film. The challenge is to provide.
Another object of the present invention is to provide a porous membrane containing a large amount of α crystals of PVDF.

The configuration of the present invention that achieves the above problems is as follows.
[1] A stock solution containing polyvinylidene fluoride and any two or more of good solvents capable of dissolving the polyvinylidene fluoride in an amount of 10% by mass or more is prepared.
A method for producing a resin composition, in which the undiluted solution and the coagulating solution are brought into contact with each other.
[2] A membrane-forming stock solution containing polyvinylidene fluoride and any two or more of good solvents capable of dissolving the polyvinylidene fluoride in an amount of 10% by mass or more is prepared.
A method for producing a porous membrane, wherein the membrane-forming stock solution and the coagulation liquid are brought into contact with each other to obtain a porous membrane precursor.
[3] The porous membrane according to [2], wherein after removing a part or all of the solvent remaining in the porous membrane precursor, the porous membrane precursor is dried to obtain a porous membrane. Production method.
[4] It contains polyvinylidene fluoride, and the polyvinylidene fluoride is unoriented in one direction.
The crystal structure obtained from the absorption intensity of the polyvinylidene fluoride infrared absorption spectrum is the ratio of the absorbance derived from the α crystal in the polyvinylidene fluoride to the total absorbance derived from the α crystal and the β crystal in the polyvinylidene fluoride ( A porous film having an absorbance derived from α-crystal / total of absorbance derived from α-crystal and absorbance derived from β-crystal) of 25% or more and 100% or less.
[5] Containing polyvinylidene fluoride, the polyvinylidene fluoride is non-oriented in one direction.
The crystal structure obtained by the X-ray diffractometry of polyvinylidene fluoride is the ratio of the peak area ratio derived from α crystal in vinylidene fluoride to the peak area ratio derived from α crystal, β crystal and γ crystal in vinylidene fluoride. The ratio to the total (total of peak area ratio derived from α crystal / peak area ratio derived from α crystal, peak area ratio derived from β crystal and peak area ratio derived from γ crystal) is 15% or more and 100% or less. Is a porous film.
[6] The porous membrane according to claim [4] or [5], wherein the orientation parameter calculated by Raman spectroscopy in polyvinylidene fluoride is less than 1.5.
[7] The porous membrane according to claim [4] or [5], wherein the orientation parameter calculated by the X-ray diffraction method in polyvinylidene fluoride is 0.4 or less.
[8] The porous membrane according to any one of [4] to [7], wherein the content of the plasticizer is 1% by 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 of the porous membrane to the other surface.
[10] The porous membrane according to any one of [4] to [9], wherein the content of the inorganic salt is 1% by mass or less.

According to the present invention, it is possible to provide a resin composition containing a large amount of α crystals of PVDF or a method for producing a resin composition capable of easily producing a porous film, and a method for producing a porous film.
Further, according to the present invention, it is possible to provide a porous membrane containing a large amount of α crystals of PVDF.

It is a figure which shows the infrared absorption spectrum of PVDF in the porous membrane of an Example and a comparative example. It is a figure which shows the X-ray diffraction spectrum of PVDF in the porous membrane of an Example and a comparative example.

An embodiment of the porous membrane of the present invention will be described.
It should be noted that the present embodiment is specifically described in order to better understand the gist of the invention, and is not limited to the present invention unless otherwise specified.

1. 1. Porous Membrane The porous membrane of the present embodiment contains polyvinylidene fluoride, polyvinylidene fluoride is unidirectionally unoriented, and the proportion of α crystals in polyvinylidene fluoride is dissolved in a single good solvent of the past. The stock solution is higher than the porous membrane obtained by using the NIPS method. Specifically, in the porous membrane of the present embodiment, the ratio of α crystals to the total crystal ratio of polyvinylidene fluoride is higher than 15%.

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

Examples of vinylidene fluoride copolymers include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, and vinylidene fluoride-tri. Fluoroethylene copolymers, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene ternary copolymers, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene ternary copolymers, and mixtures of two or more of these Can be mentioned.

In these vinylidene fluoride copolymers, the copolymerization ratio of the comonomer is preferably 20 mol% or less, and 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. If the copolymerization ratio of the comonomer becomes too high, the vinylidene fluoride copolymer loses its crystallinity and becomes an elastomer.

The mass average molecular weight of PVDF (hereinafter referred to as "Mw") is preferably 100,000 or more and 2,000,000 or less. When Mw is 100,000 or more, the mechanical strength of the porous membrane of the present embodiment tends to be good, and when Mw is 2,000,000 or less, the solubility in a solvent described later is good. It tends to be. The lower limit of Mw is more preferably 300,000 or more, and the upper limit of Mw is more preferably 1.5 million or less.

PVDF can be produced by a suspension polymerization method or an emulsion polymerization method. In the emulsification polymerization method, vinylidene fluoride alone or a comonomer such as vinylidene fluoride and hexafluoropropylene is emulsified in an aqueous medium using a chemically stable fluorine-based emulsifier. Next, polymerization is carried out using an inorganic peroxide, an organic peroxide, an organic percarbonate compound or the like as a polymerization initiator. After emulsion polymerization, fine latex in the submicron unit is precipitated by a coagulant and aggregated, so that PVDF can be recovered as particles having an appropriate size.

<Materials other than polyvinylidene fluoride>
In producing the porous membrane of the present embodiment, in addition to PVDF, the membrane-forming stock solution contains, for example, monool-based, diol-based, triol-based, and polyvinylpyrrolidone represented by polyethylene glycol for the purpose of controlling phase separation and the like. Hydrophilic polymer resins such as, etc. can be used. These can be appropriately selected and used as needed, but polyvinylpyrrolidone is preferable because it is excellent in thickening effect.

1.2 Orientation of PVDF The PVDF contained in the porous membrane of this embodiment is non-oriented in one direction. Examples of the form of the porous membrane of the present invention include a flat membrane and a hollow fiber membrane. Here, the one direction of PVDF is, for example, the thickness direction of the flat membrane when the porous membrane is a flat membrane, and the fiber shaft of the hollow fiber when the porous membrane is a hollow fiber membrane. It is the direction.

The fact that PVDF is unoriented in one direction means that the orientation parameter calculated by Raman spectroscopy in PVDF is less than 1.5. Further, the fact that PVDF is non-oriented in one direction means that the orientation parameter calculated by the X-ray diffraction method in PVDF is 0.4 or less. When PVDF is non-oriented in one direction, it is easy to prepare a membrane having an asymmetric inclined structure, and high water permeability and blocking rate can be achieved at the same time.

The method for measuring the orientation parameter by Raman spectroscopy is, for example, as follows. The porous hollow fiber membrane is sectioned by cutting with a microtome in a cross section along the longitudinal direction of the porous hollow fiber membrane. While observing the sections thus obtained with an optical microscope, laser Raman measurement is performed at 1 μm intervals along the longitudinal direction of the hollow fiber. The Raman band near 1270 cm ^{-1 of} _{PVDF belongs to the coupling mode of CF 2} (fluorocarbon) expansion and contraction vibration and CC (carbon-carbon) expansion and contraction vibration. The vibration direction of these vibrations is a mode parallel to the molecular chain. On the other hand, the vibration direction of the Raman band near ^{840 cm -1 of PVDF is perpendicular to the molecular chain.} Since Raman scattering is strongly obtained when the vibration direction of the molecular chain and the polarization direction of the incident light match, the ratio of the scattering intensity of these vibration modes changes in correlation with the degree of orientation. Therefore, the orientation parameter can be calculated by the following equation (1). The orientation parameter ν has a larger value as the orientation of the porous hollow fiber membrane in the longitudinal direction is higher, and is 1 when the porous hollow fiber membrane is not oriented, and is smaller than 1 when the orientation in the lateral direction is high.
Orientation parameter ν = (I1270 / I840) parallel / (I1270 / I840) vertical (1)
In the above formula (1), parallel condition: the longitudinal direction of the porous hollow fiber membrane and the polarization direction are parallel. Vertical condition: The longitudinal direction of the porous hollow fiber membrane and the polarization direction are orthogonal. I1270cm ^-1 parallel: The strength of the Raman band of ^{1270cm -1 under parallel conditions.} I1270cm ^-1 Vertical: The strength of the Raman band of ^{1270cm -1 under vertical conditions.} I840cm- ¹ parallel: The strength of the Raman band of ^{840cm-1 under parallel conditions.} I 840 cm ^-1 Vertical: The strength of the Raman band of ^{840 cm -1 under vertical conditions.}

1.3 Crystallinity of PVDF PVDF is known as a highly crystalline resin, and it is known that there are roughly three types of crystal structures, α crystal, β crystal and γ crystal. Has been done.

In the porous membrane of the present embodiment, the ratio of α crystals to the ratio of crystals in the entire PVDF contained in the porous membrane is higher than 15%. By setting the ratio of α crystals to 15% or more, the chemical durability of the porous membrane to alkali is improved.

The ratio of α crystals to the ratio of crystals of PVDF contained in the porous film in PVDF is higher than 15%. The crystal structure obtained by X-ray diffraction (XRD) of PVDF is α crystal, β crystal and When the total peak area ratio derived from γ crystal is 100%, the ratio of peak area ratio derived from α crystal is 15% or more and 100% or less, and the total ratio of peak area ratio derived from β crystal and γ crystal is 100%. It means that it 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.

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).

The specific measurement method is as follows.

From the X-ray diffraction pattern of PVDF obtained from XRD, the peak area from 18.7 ° to 26.5 ° derived from α crystal and the area of peak from 20.7 ° to 41.2 ° derived from β crystal. , And the area of the peak 20.3 ° to 39.4 ° derived from the γ crystal is determined. That is, the start and end points of each diffraction pattern corresponding to each crystal are connected by a straight line, and the area thereof is obtained.

As described above, the proportions of α-crystals correspond to the area of the peak at 18.7 ° corresponding to the α-crystal and 26.5 °, the area of the peak at 20.7 ° corresponding to the β-crystal, and 20 corresponding to the γ-crystal. . Obtain the area of the peak at 3 ° and calculate it by the following formula (2).
As described above, the proportion of β crystals is as follows: the area of the peak of 18.7 ° corresponding to the α crystal, the area of the peak of 20.7 ° corresponding to the β crystal, and the peak of 20.3 ° corresponding to the γ crystal. The area of is calculated by the following formula (3).
As described above, the proportion of γ crystals is as follows: the area of the peak of 18.7 ° corresponding to the α crystal, the area of the peak of 20.7 ° corresponding to the β crystal, and the peak of 20.3 ° corresponding to the γ crystal. The area of is calculated by the following formula (4).

Percentage of α crystals = (18.7 ° peak area + 26.5 ° peak area) / (18.7 ° peak area + 26.5 ° peak area + 20.7 ° peak area +20 .3 ° peak area) x 100 (%) (2)
β crystal ratio = 20.7 ° peak area / (18.7 ° peak area + 26.5 ° peak area + 20.7 ° peak area + 20.3 ° peak area) x 100 (%) (3)
Percentage of γ crystals = 20.3 ° peak area / (18.7 ° peak area + 26.5 ° peak area + 20.7 ° peak area + 20.3 ° peak area) x 100 (%) (4)

The ratio of α crystals to the ratio of crystals of PVDF contained in the porous film in PVDF is higher than 15% because the crystal structure obtained from the absorption intensity by the infrared absorption spectrum of PVDF is derived from α crystals and β crystals. When the total absorbance is 100%, the lower limit of the absorption intensity derived from α crystals is 25% or more, preferably 28% or more, more preferably 30% or more, and the upper limit of the above ratio is 100. % Or less, the lower limit of the total ratio of the absorption intensity derived from β crystals is 0% or more, and the upper limit of the total ratio is 75% or less, preferably 72% or less, more preferably 70% or less. Means.

The absorption intensity of α crystal and β crystal in PVDF can be calculated from the infrared absorption spectrum obtained by Fourier transform infrared spectroscopy (FT-IR).

The specific measurement method is as follows.

The crystal ratio in PVDF is calculated from the peak intensity ratio derived from the polymorph on the low wavenumber side in the infrared absorption spectrum of PVDF. The β crystal uses a peak of ^{840 cm -1} , and the α crystal ^{uses a peak of 764 cm -1.} Using the following formula (5), the intensity ratio is corrected using the absorption coefficient at each absorption, and the β crystal ratio F (β) in the formed crystal is calculated. In the following formula (5), the absorbance at the A _beta 840 cm ^-1, the absorbance at the _A α 764cm ^-1, K β is extinction coefficient at ^{840cm -1 (7.7 × 10 4 cm} 2 mol -1), K α represents an extinction coefficient ^{(6.1 × 10 4 cm 2 mol} -1) at 764cm ^-1.

1.4 Plasticizer The porous membrane of the present embodiment may contain a plasticizer, but the content of the plasticizer is preferably 1% by mass or less, and preferably 0.5% by mass or less. More preferred. When the content of the plasticizer is 1% by mass or less, the amount of the plasticizer that dissolves into the treated water is small when the porous membrane is used, and the water quality of the treated water can be maintained at a high level.

The plasticizer is not particularly limited, and examples thereof include caprolactone such as ε-caprolactone.

1.5 Inorganic substance The porous membrane of the present embodiment may contain an inorganic substance, but the content of the inorganic substance is preferably 1% by mass or less, and more preferably 0.5% by mass or less. When the content of the inorganic substance is 1% by mass or less, the amount of the inorganic substance dissolved into the treated water is small when the membrane is used, and the water quality of the treated water can be maintained at a high level.

Inorganic substances are those used in the production of porous membranes. Examples of the inorganic substance include, but are not limited to, silica, calcium silicate, aluminum silicate, magnesium silicate, calcium carbonate, magnesium carbonate, calcium phosphate, metal oxide, metal hydroxide, salts and the like. Further, examples of the metal oxide include oxides such as iron and zinc. Examples of the metal hydroxide include hydroxides such as iron and zinc. Examples of salts include salts such as sodium, potassium, and calcium.

1.6 Pore The porous membrane of this embodiment has pores. In the porous membrane of the present embodiment, the inner diameter of the pores of the porous membrane gradually changes from one surface of the porous membrane to the other surface. 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 means that the inner diameter of the pores gradually changes from one surface of the porous membrane to the other surface. This includes increasing the size and gradually reducing the inner diameter of the pores from one surface to the other surface of the porous membrane. As a result, the side with a small pore diameter has a separation function, and the side with a large pore diameter can reduce the pressure loss with respect to water. Membranes can be prepared. As long as high water permeability can be maintained, a portion where the inner diameter of the pores gradually increases and a portion where the inner diameter of the pores gradually increases may coexist from one surface of the porous membrane to the other surface.

The average pore size of the pores in the porous membrane is preferably 1 nm or more and 1200 nm or less because it can be used for removing bacteria and viruses, purifying proteins or enzymes, or for clean water. When the average pore diameter of the pores is 1 nm or more, there is a tendency that a high hydraulic pressure is not required when treating water. When the average pore size of the pores is 1200 nm or less, bacteria, viruses and suspended solids in the clean water tend to be removed.

The average pore size of the pores in the porous membrane of the present embodiment is determined by using a scanning electron microscope (manufactured by JEOL Ltd., product name: JSM-7400) on the outer surface portion of the porous membrane of the present embodiment. The average pore diameter obtained by actually measuring the longest diameter of the pores.

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. When the thickness is 10 μm or more, it has high elasticity and tends to be satisfactory in durability. If the thickness is 1000 μm or less, it tends to be produced at low cost. When the porous membrane is a flat membrane, the lower limit of the thickness is more preferably 20 μm or more, and further preferably 30 μm or more. The upper limit of the thickness is more preferably 900 μm or less, and further preferably 800 μm or less.

When the porous membrane of the present embodiment is a flat membrane, examples of the internal structure of the membrane include an inclined structure in which the pore size is reduced in a specific direction in the cross section of the membrane or a structure having uniform pores.

When the porous membrane of the present embodiment is a flat membrane, the membrane can have a macrovoid or spherulite structure.

<Hollow fiber membrane>
When the shape of the porous membrane of the present 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. If the outer diameter of the porous film is 20 μm or more, thread breakage tends to be less likely to occur during film formation. Further, when the outer diameter of the hollow fiber membrane is 3500 μm or less, it is easy to maintain the hollow shape, and it tends to be difficult to flatten even when an external pressure is applied. The lower limit of the outer diameter of the hollow fiber membrane is more preferably 30 μm or more, and further preferably 40 μm or more. The upper limit of the outer diameter of the hollow fiber membrane is more preferably 3200 μm or less, and further preferably 3000 μm or less.

<Support>
The porous membrane of the present embodiment may be composed of only the above-mentioned porous membrane, but has this porous membrane on a hollow support because excellent mechanical strength can be obtained. Is particularly preferable. Although the term “on the support” is used here to clarify the positional relationship between the porous film and the support, the porous film may be impregnated inside the support through the voids of the support. ..

As the support, as long as it has high mechanical strength and can be integrated with the porous membrane, it can be appropriately selected and used, and although it is not particularly limited, the manufacturing cost is low and it is flexible. A braided cord is preferable because it can achieve both properties and shape stability (roundness) of a cross section and is also excellent in adhesiveness to a porous film. Above all, a hollow braided cord in which one thread made of multifilament is circularly knitted is preferable.
In this case, the porous membrane and the support (hollow braid) do not necessarily have to be in close contact with each other, but if their adhesiveness is low, they will separate when the hollow fiber membrane is pulled, and the porous membrane will be porous. The membrane may slip out of the nest.
Therefore, in the porous membrane of the present embodiment, a part of the porous membrane can be infiltrated into the braid through the stitches of the hollow braid to integrate the porous membrane and the hollow braid. preferable.

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

1.8 Performance 1.8.1 Water Permeability The water permeability can be calculated from the relationship between the amount of water permeation and the film area obtained under a predetermined pressure in a module having a predetermined shape. Since the small pore size side has a separation function and the large pore size side can reduce the pressure loss against water, a membrane with a high water permeability is prepared while maintaining the fractionation compared to a homogeneous membrane with a small change in pore size. can.

1.8.2 Chemical resistance The chemical resistance is measured by immersing the porous membrane in sodium hydroxide for a long time. α-crystals are considered to be the most thermodynamically stable crystal structure. It is considered that this is because the hydrogen atom and the fluorine atom are delocalized in the α crystal structure as compared with the β crystal structure, and the charge bias is small. That is, it is considered that excellent chemical resistance can be exhibited when the hydrogen atom and the fluorine atom are localized and the α crystal structure having a relatively low polarity exists in a higher ratio than the β crystal structure having a relatively high polarity. Due to the large proportion of α crystals, it is preferable when used in a separation membrane for treating oil or the like. Treatment of water containing a large amount of oil causes a problem that oil-derived substances are clogged on the surface of the separation membrane, etc. However, in general, treatment with sodium hydroxide or the like can be saponified and washed away. A PVDF film having a large total ratio of β crystals and γ crystals may be damaged by sodium hydroxide and deteriorate. Therefore, a PVDF film containing a large amount of α crystals is preferable.

2-1. Method for producing a porous film In the method for producing a porous film of the present embodiment, a film-forming stock solution (C) in which polyvinylidene fluoride (PVDF) is dissolved in a mixed good solvent containing two or more kinds of good solvents is used as a coagulating solution. Contact.

As an example of the method for producing the porous membrane of the present embodiment, the following method can be mentioned.
First, a membrane-forming stock solution (C) containing PVDF and two or more good solvents is applied to a support and brought into contact with the coagulating solution to coagulate to obtain a porous membrane precursor.
After that, a part or all of the solvent remaining in the porous membrane precursor is washed and removed, and the washed porous membrane precursor is dried to obtain the porous membrane of the present embodiment.

<Undiluted film-forming solution (C)>
The film-forming stock solution (C) contains PVDF and two or more good solvents.
The film-forming stock solution (C) may further contain a resin other than polyvinylidene fluoride, for example, polyvinylpyrrolidone, polyethylene glycol, cellulose acetate, an acrylic resin and the like. These polymer materials may be added when controlling the compatibility and viscosity of the film-forming stock solution (C).

A good solvent is a solvent capable of dissolving PVDF in an amount of 10% by mass or more.
The good solvent to be mixed is excellent in compatibility with each other, and when the good mixture solvent is used, it is not particularly limited as long as it is excellent in the solubility of PVDF. Examples of such a good solvent include acetone, propylene carbonate (PC), γ-butyrolactone (γ-BL), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (N-methylpyrrolidone). NMP), cyclohexanone (CHN), hexamethylphosphoric acid triamide (HMPA), tetramethylurea (TMU), triethyl phosphate (TEP), trimethyl phosphate (TMP) and the like.

As the mixed good solvent, among the above-mentioned good solvents, propylene carbonate (PC), γ-butyrolactone (γ-BL), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), etc. It is preferable to use two or more selected from cyclohexanone (CHN), hexamethylphosphoric acid triamide (HMPA), and triethylphosphate (TEP).

More specifically, as a good mixing solvent, dimethylacetamide (DMAc) / propylene carbonate (PC), dimethylacetamide (DMAc) / γ-butyrolactone (γ-BL), N-methylpyrrolidone (NMP) / propylene carbonate (PC) ), And a combination of N-methylpyrrolidone (NMP) / γ-butyrolactone (γ-BL) is preferred.

When preparing a mixed solvent, it is preferable to mix DMAc or NMP as a main solvent and PC or GBL as a secondary solvent.

When DMAc or NMP is used as the main solvent and GBL is used as the auxiliary solvent, the content ratio of GBL is preferably 1% by mass or more, more preferably 2% by mass or more, further preferably 3% by mass or more, and 5% by mass. Is more preferable, 8% by mass or more is particularly preferable, and 10% by mass or more is most preferable. Further, 49% by mass or less is preferable, 40% by mass or less is more preferable, and 30% by mass or less is more preferable.

When DMAc or NMP is used as the main solvent and PC is used as the auxiliary solvent, the content ratio of GBL is preferably 1% by mass or more, more preferably 2% by mass or more, further preferably 3% by mass or more, and 5% by mass. Is more preferable, 8% by mass or more is particularly preferable, and 10% by mass or more is most preferable. Further, 49% by mass or less is preferable, 40% by mass or less is more preferable, and 30% by mass or less is more preferable.

As the mixed solvent, PVDF (Head-Tail) (Head-) appearing in the vicinity of -93 to -94 ppm when the membrane-forming ^{stock solution containing the mixed solvent was subjected to 19} F NMR measurement by Bruker's "Avance 300". It is preferable that the mixed solvent has a broader fluorine peak in the Head) bond than in the case of a single DMAc. Being broad refers to a phenomenon in which about two peak tops, which are seen in the case of a single DMAc, are seen as almost one peak. The standard for chemical shift is that the peak of hexafluorobenzene is -164.7 ppm, the number of integrations is 64, and the measurement temperature is room temperature.

The film-forming stock solution (C) may be dispersed without partially dissolving PVDF, or may be in a dispersed state as long as it is uniform and the uniformity can be maintained.

The content of PVDF in the film-forming stock 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 film-forming stock solution (C). When 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 also at a practical level. Further, when the content of PVDF is 30 parts by mass or less, a porous membrane having high water permeability can be obtained because it has a sufficient porosity.
The lower limit of the PVDF content is more preferably 10 parts by mass or more, and further preferably 12 parts by mass or more. The upper limit of the PVDF content is more preferably 25 parts by mass or less, and further preferably 20 parts by mass or less.

The content of the solvent in the film-forming stock solution (C) is preferably 50 parts by mass or more and 93 parts by mass or less, and 60 parts by mass or more and 90 parts by mass with respect to 100 parts by mass of the total amount of the film-forming stock solution (C). The following is more preferable.

<Coagulation>
The membrane-forming stock solution (C) and the coagulation solution are brought into contact with each other to obtain a porous membrane precursor. The coagulating liquid used to obtain the porous film precursor is a non-solvent water (distilled water), an aqueous solution containing the same solvent as the solvent contained in the film-forming stock solution (C) and water (distilled water). Can be used, and it is preferable to use an aqueous solution. The concentration of the solvent is preferably 0% by mass or more and 50% by mass or less in the coagulating liquid.

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

<Washing>
It is preferable to remove the solvent from the obtained porous membrane precursor by immersing it in hot water at 40 ° C. or higher and 100 ° C. or lower and washing it. When the temperature of hot water is 40 ° C. or higher, a high cleaning effect on the porous membrane precursor tends to be obtained. When the temperature of hot water is 100 ° C. or lower, the porous membrane precursor tends to be difficult to fuse.

<Drying>
The washed porous membrane precursor is preferably dried at 60 ° C. or higher and 120 ° C. or lower for 1 minute or longer and 24 hours or shorter. When the drying temperature of the porous membrane precursor after washing is 60 ° C. or higher, the drying treatment time is short and the production cost can be suppressed, which is preferable in industrial production. Further, if the drying temperature of the porous membrane precursor after washing is 120 ° C. or lower, the porous membrane precursor tends not to shrink too much in the drying step, and minute cracks occur on the outer surface of the membrane. It tends to happen, which is preferable.

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 brought into contact with a coagulating liquid and coagulated to obtain a porous membrane precursor. In the porous membrane obtained by drying the porous membrane precursor, PVDF is non-oriented in one direction, and the ratio of α crystals in PVDF is a stock solution dissolved in a conventional single good solvent, and the NIPS method is used. Higher than the porous membrane obtained using. Further, 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 kinds of good solvents is used, combined with the good solvent to be used, and a blending ratio. It is also possible to control the proportion of α crystals contained in PVDF by adjusting.

2-2. Method for Producing Resin Composition In the method for producing the resin composition of the present embodiment, a stock 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 coagulating solution. do.

As an example of the method for producing the resin composition of the present embodiment, the following method can be mentioned.
First, a stock solution (C') containing PVDF and two or more kinds of good solvents is dropped into the coagulation liquid, and the stock solution (C') is coagulated by contacting with the coagulation liquid to obtain a pellet-shaped resin composition. ..
After that, a part or all of the solvent remaining in the pellet-shaped resin composition may be washed and removed, and the washed resin composition may be dried and used.
The resin composition obtained by the method for producing the resin composition of the present embodiment can be molded into any form.

<Undiluted solution (C')>
The undiluted solution (C') contains PVDF and two or more kinds of good solvents in the same manner as the above-mentioned film-forming undiluted solution (C).
The undiluted solution (C') may further contain a resin other than polyvinylidene fluoride, for example, polyvinylpyrrolidone, polyethylene glycol, cellulose acetate, acrylic resin and the like. These polymer materials may be added when controlling the compatibility and viscosity of the undiluted solution (C').

The undiluted solution (C') can be prepared in the same manner as the undiluted film-forming solution (C) in the above-mentioned method for producing a porous membrane. The same applies to <coagulation>, <washing>, and <drying>.

According to the method for producing a resin composition of the present embodiment, a stock solution (C') containing PVDF and two or more good solvents is brought into contact with a coagulating solution and coagulated to obtain a resin composition. In the molded product obtained by drying and molding the product, PVDF is non-oriented in one direction, and the ratio of α crystals in PVDF is a stock solution dissolved in a conventional single good solvent, using the NIPS method. Higher than the resulting porous membrane. Further, according to the method for producing a resin composition of the present embodiment, a stock solution (C') in which PVDF is dissolved in a mixed good solvent containing two or more kinds of good solvents is used, combined with the good solvent to be used, and the compounding ratio is adjusted. By adjusting, the ratio of α crystals contained in PVDF can also be controlled.

3. 3. Applications The porous membrane of this embodiment can be used for microfiltration, ultrafiltration, and the like. In particular, as a filtration membrane used for water treatment, it can be preferably used because it removes stains adhering to the surface of the filtration membrane and has high resistance to washing with alkali.
The resin composition obtained by the method for producing the resin composition of the present embodiment can be used as a battery separator, a coating material, or the like for a lithium ion battery. In particular, it can be suitably used as a battery separator for a lithium ion battery.

4. Effect Since the method for producing a porous film of the present embodiment can produce a film containing a large amount of α crystals, a porous film having high chemical resistance can be obtained.
Since the method for producing a resin composition of the present embodiment can produce a resin composition containing a large amount of α crystals, various molded articles having high chemical resistance can be obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Further, in the following, "parts" and "%" indicate "parts by mass" and "% by mass", respectively.

[Example 1]
Dimethylacetamide (DMAc) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade) 94 parts and γ-butyrolactone (GBL) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade) 11 parts are mixed to prepare a good mixing solvent. Prepared. The mass ratio of DMAc to GBL ((mass of DMAc) / (mass of GBL)) in the obtained mixed good solvent was 89/11.
Then, the mixed good 80 parts solvent, PVDF homopolymer (trade name: KF polymer ♯1100, Kureha Co., Mw = 2.8 × ¹⁰ 5) were dissolved 20 parts of film-forming solution of (C-1) Prepared.
The obtained film-forming stock solution (C-1) was allowed to stand at room temperature for one 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. and solidified to prepare a coating film laminate.
After the coating film laminate was left in a coagulation bath for 3 minutes, the obtained flat film-shaped porous film was dried at room temperature and atmospheric pressure to obtain the porous film of Example 1.

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

[evaluation]
(Measurement of crystal ratio of porous membrane by infrared absorption spectrum)
The PVDF contained in the porous membranes obtained in Example 1 and Comparative Example 1 was subjected to Fourier transform infrared spectroscopic analysis by a Fourier transform infrared spectrophotometer (FT-IR). IR Prestige-21 manufactured by SHIMADZU was used for FT-IR measurement. The ATR method was used as the measurement method, and MIRACLE ^TM single reflection ATR manufactured by PIKE technologies was used. The specific measurement method is as described above.
^{The absorbance of the peak of 764 cm -1} derived from the α crystal of PVDF is set ^{to 1, and the absorbance of the peak of 840 cm -1} derived from the β crystal of PVDF is calculated, and the crystal of the α crystal is calculated based on the above formula (5). The ratio was calculated. The results are shown in Table 1.
Further, FIG. 1 shows an infrared absorption spectrum of PVDF in which the absorbance of the peak of ^{764 cm -1} derived from the α crystal of PVDF is set to 1.

From the results shown in Table 1, it was confirmed that the proportion of α crystals in 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 is unoriented in one direction, and the proportion of α crystals in PVDF is higher than the proportion of β crystals.
On the other hand, it was confirmed that the proportion of α crystals in 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 is oriented in one direction, and the proportion of α crystals in PVDF is smaller than the proportion of β crystals.

[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. A good mixed solvent was prepared by mixing so as to have the mass ratio shown in 2.
Next, 20 parts of PVDF homopolymer (trade name: KF polymer # 1100, manufactured by Kureha Corporation, Mw = 2.8 × 105) was dissolved in 80 parts of a good mixed solvent to prepare a film-forming stock solution.
The obtained film-forming stock solution was allowed to stand at room temperature for one 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. and solidified to prepare a coating film laminate.
After the coating film laminate was left in a coagulation bath for 3 minutes, the obtained flat film-shaped porous film was dried at room temperature and atmospheric pressure to obtain the porous film of Example 2.

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

[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 Kasei Kogyo Co., Ltd.) was used as the secondary solvent. The mixture was mixed so as to prepare a good mixed solvent.
Next, 20 parts of PVDF homopolymer (trade name: KF polymer # 1100, manufactured by Kureha Corporation, Mw = 2.8 × 105) was dissolved in 80 parts of a good mixed solvent to prepare a film-forming stock solution.
The obtained film-forming stock solution was allowed to stand at room temperature for one 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. and solidified to prepare a coating film laminate.
After the coating film laminate was left in a coagulation bath for 3 minutes, the obtained flat film-shaped porous film was dried at room temperature and atmospheric pressure to obtain the porous films of Examples 3 to 5.

[evaluation]
(Measurement of crystal ratio of porous membrane by X-ray diffraction method)
This was done in the same manner as in Example 2 described above. The results are shown in Table 2.

[Example 6]
N-Methylpyrrolidone (NMP) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako First 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. A good mixed solvent was prepared by mixing so as to have the mass ratio shown in Table 2 below.
Next, 20 parts of PVDF homopolymer (trade name: KF polymer # 1100, manufactured by Kureha Corporation, Mw = 2.8 × 105) was dissolved in 80 parts of a good mixed solvent to prepare a film-forming stock solution.
The obtained film-forming stock solution was allowed to stand at room temperature for one 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. and solidified to prepare a coating film laminate.
The coating film laminate was left in a coagulation bath for 3 minutes, and then the obtained flat film-shaped porous film was dried at room temperature and atmospheric pressure to obtain the porous film of Example 6.

[evaluation]
(Measurement of crystal ratio of porous membrane by X-ray diffraction method)
This was done in the same manner as in Example 2 described above. The results are shown in Table 2.

[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.
Further, the measurement of the crystal ratio of the porous film by the X-ray diffraction method was also carried out in the same manner as in Example 2. The results are shown in Table 2.

[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.
Further, the measurement of the crystal ratio of the porous film by the X-ray diffraction method was also carried out in the same manner as in Example 2. The results are shown in Table 2.

Further, FIG. 2 shows XRD spectra of PVDF peaks derived from α crystals from 18.7 ° to 26.5 ° and peaks derived from γ crystals from 20.3 ° to 39.4 °.

From the results shown in Table 2, it can be confirmed that the ratio of α crystals contained in PVDF can be controlled by adjusting the compounding ratio using a film-forming stock solution in which PVDF is dissolved in a mixed good solvent containing two kinds of good solvents. rice field.
Further, it was confirmed that the ratio of α crystals in 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 PVDF was high.

Claims (10)

A stock solution containing polyvinylidene fluoride and any two or more of good solvents capable of dissolving the polyvinylidene fluoride in an amount of 10% by mass or more was prepared.
A method for producing a resin composition, in which the undiluted solution and the coagulating solution are brought into contact with each other. A membrane-forming stock solution containing polyvinylidene fluoride and any two or more of good solvents capable of dissolving the polyvinylidene fluoride in an amount of 10% by mass or more was prepared.
A method for producing a porous membrane, wherein the membrane-forming stock solution and the coagulation liquid are brought into contact with each other to obtain a porous membrane precursor. The method for producing a porous membrane according to claim 2, wherein after removing a part or all of the solvent remaining in the porous membrane precursor, the porous membrane precursor is dried to obtain a porous membrane. It contains polyvinylidene fluoride, and the polyvinylidene fluoride is non-oriented in one direction.
The crystal structure obtained from the absorption intensity of the polyvinylidene fluoride infrared absorption spectrum is the ratio of the absorbance derived from the α crystal in the polyvinylidene fluoride to the total absorbance derived from the α crystal and the β crystal in the polyvinylidene fluoride ( A porous film having an absorbance derived from α-crystal / total of absorbance derived from α-crystal and absorbance derived from β-crystal) of 25% or more and 100% or less. It contains polyvinylidene fluoride, and the polyvinylidene fluoride is non-oriented in one direction.
The crystal structure obtained by the X-ray diffractometry of polyvinylidene fluoride is the ratio of the peak area ratio derived from α crystal in vinylidene fluoride to the peak area ratio derived from α crystal, β crystal and γ crystal in vinylidene fluoride. The ratio to the total (total of peak area ratio derived from α crystal / peak area ratio derived from α crystal, peak area ratio derived from β crystal and peak area ratio derived from γ crystal) is 15% or more and 100% or less. Is a porous film. The porous membrane according to claim 4 or 5, wherein the orientation parameter calculated by Raman spectroscopy in polyvinylidene fluoride is less than 1.5. The porous membrane according to claim 4 or 5, wherein the orientation parameter calculated by the X-ray diffraction method in polyvinylidene fluoride is 0.4 or less. The porous membrane according to any one of claims 4 to 7, wherein the content of the plasticizer is 1% by mass or less. The porous membrane according to any one of claims 4 to 8, wherein the inner diameter of the pores of the porous membrane gradually changes from one surface of the porous membrane to the other surface. The porous membrane according to any one of claims 4 to 9, wherein the content of the inorganic salt is 1% by mass or less.

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