Vinylidene fluoride polymer solution

Abstract

The present invention addresses the problem of providing a vinylidene fluoride polymer solution obtained by dissolving a vinylidene fluoride polymer in a solvent that imposes a small burden on the environment and that can be easily handled. A vinylidene fluoride polymer solution that solves said problem contains a vinylidene fluoride polymer and a solvent. The solvent has a molecular weight of 100 or more and includes an affinitive solvent having at least one structure selected from ether, ketone, and ester. The vinylidene fluoride polymer satisfies a specific requirement.

Description

Technical Field

[0001] The present invention relates to a vinylidene fluoride polymer solution.

Background Art

[0002] Vinylidene fluoride polymers are used in a wide range of applications because of their excellent weather resistance and chemical resistance. However, vinylidene fluoride polymers are difficult to dissolve in common solvents. Therefore, when it is necessary to dissolve a vinylidene fluoride polymer, such as in a paint or a coating agent, N-methylpyrrolidone (NMP) or acetone is used as a solvent.

[0003] However, acetone has a low flash point and boiling point, making it difficult to handle. On the other hand, NMP can easily dissolve vinylidene fluoride polymers and has a high boiling point, but in recent years, its toxicity has been a concern and legal regulations have become stricter. On the other hand, hexamethylphosphoramide and dimethyl sulfoxide are also known as solvents that can dissolve vinylidene fluoride polymers. However, these solvents also have relatively high freezing points and are not easy to handle.

[0004] Here, Patent Document 1 describes a coating composition in which an acrylic resin and a vinylidene fluoride polymer are dissolved in cyclohexanone or the like.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, as a result of intensive studies by the present inventors, it has been revealed that when the vinylidene fluoride polymer described in Patent Document 1 is to be dissolved in a solvent alone, its solubility in the solvent is not sufficient and it takes a very long time to dissolve. That is, in the conventional technology, it has been very difficult to dissolve a vinylidene fluoride polymer in a solvent with a low environmental load and good handleability.

[0007] The present invention has been made in view of the above problems. An object of the present invention is to provide a vinylidene fluoride polymer solution in which a vinylidene fluoride polymer is dissolved in a solvent with a low environmental load and easy handling.

Means for Solving the Problems

[0008] The present invention provides a vinylidene fluoride polymer solution containing a vinylidene fluoride polymer and a solvent, wherein the solvent contains an affinity solvent having a molecular weight of 100 or more and having at least one structure selected from ether, ketone, and ester, and the vinylidene fluoride polymer satisfies the following (A) to (C). (A) containing a structural unit derived from vinylidene fluoride and a structural unit derived from a fluorine-containing alkyl vinyl compound (B) having a peak top in the range of 60 ° C or more and less than 100 ° C of the DSC curve obtained by differential scanning calorimetry according to ASTM D3418 (C) In the X-ray diffraction pattern obtained by X-ray diffraction measurement, it has at least one maximum value in the range of a diffraction angle of 10 ° or more and 19.9 ° or less, and the maximum diffraction intensity in the range of a diffraction angle of 22.5 ° or more and 30 ° or less is the maximum diffraction intensity in the range of a diffraction angle of 10 ° or more and 19.9 ° or less or less.

Effects of the Invention

[0009] According to the present invention, a vinylidene fluoride polymer solution in which a vinylidene fluoride polymer is dissolved in a solvent with a low environmental load and easy handling can be obtained.

Brief Description of the Drawings

[0010]

Figure 1

Mode for Carrying Out the Invention

[0011] As described above, general vinylidene fluoride polymers were difficult to dissolve in solvents such as ethers, ketones, and esters, which have a low environmental load and are relatively easy to handle. On the other hand, in the vinylidene fluoride polymer solution of the present invention, a vinylidene fluoride polymer satisfying the following requirements (A) to (C) and an affinity solvent having a molecular weight of 100 or more and having at least one structure selected from ethers, ketones, and esters are combined. Thereby, the vinylidene fluoride polymer can be easily dissolved in the above solvent, and its stability is also improved. Hereinafter, each component in the vinylidene fluoride polymer solution will be described.

[0012] ·Vinylidene fluoride polymer The vinylidene fluoride polymer contained in the vinylidene fluoride polymer solution of the present invention contains a structural unit derived from vinylidene fluoride and a structural unit derived from a fluorine-containing alkyl vinyl compound (requirement (A)).

[0013] The vinylidene fluoride polymer may contain at least a structure derived from vinylidene fluoride and a structure derived from one or more fluorine-containing alkyl vinyl compounds, and may be a binary copolymer of vinylidene fluoride and a fluorine-containing alkyl vinyl compound, or may be a terpolymer of vinylidene fluoride, a fluorine-containing alkyl vinyl compound, and still another compound. Further, additives such as a polymer modifier may be added to these copolymers. However, it is preferable that the total of the structural units derived from vinylidene fluoride and the structural units derived from the fluorine-containing alkyl vinyl compound is 90% by mass or more, more preferably 95% by mass or more, and still more preferably 97% by mass or more, based on all the structural units of the vinylidene fluoride polymer. When the total amount of the structural units derived from vinylidene fluoride and the structural units derived from the fluorine-containing alkyl vinyl compound is within this range, the solubility of the vinylidene fluoride polymer in the solvents described below is likely to increase.

[0014] Here, when the total of the structural units derived from vinylidene fluoride and the structural units derived from the fluorine-containing alkyl vinyl compound is 100% by mass, the amount of the structural units derived from vinylidene fluoride in the vinylidene fluoride polymer is preferably 40 to 75% by mass, more preferably 51 to 70% by mass, and still more preferably 55 to 68% by mass. When the amount of the structural units derived from vinylidene fluoride in the vinylidene fluoride polymer is 40% by mass or more, the physical properties derived from vinylidene fluoride are likely to be exhibited. On the other hand, when the amount of the structural units derived from vinylidene fluoride in the vinylidene fluoride polymer is 75% by mass or less, the amount of the structure derived from the fluorine-containing alkyl vinyl compound becomes sufficiently large, and the solubility in the solvents described below is likely to increase. The amount of the structural units derived from vinylidene fluoride in the vinylidene fluoride polymer can be specified, for example 19 by analysis using 19F-NMR or the like.

[0015] On the one hand, when the total of the structural unit derived from vinylidene fluoride and the structural unit derived from the fluorine-containing alkyl vinyl compound is 100% by mass, the amount of the structural unit derived from the fluorine-containing alkyl vinyl compound in the vinylidene fluoride polymer is preferably 25 to 60% by mass, more preferably 30 to 49% by mass, and even more preferably 32 to 45% by mass. When the amount of the structural unit derived from the fluorine-containing alkyl compound in the vinylidene fluoride polymer is 25% by mass or more, the solubility in the solvent described below becomes good. On the other hand, when the amount of the structural unit derived from the fluorine-containing alkyl vinyl compound in the vinylidene fluoride polymer is 60% by mass or less, the amount of the structure derived from vinylidene fluoride becomes sufficiently large, and the physical properties derived from vinylidene fluoride are likely to be exhibited. The amount of the structural unit derived from the fluorine-containing alkyl vinyl compound in the vinylidene fluoride polymer can be specified, for example, 19 by analysis using 19F-NMR or the like.

[0016] The above-mentioned fluorine-containing alkyl vinyl compound may be any compound having a vinyl group and a fluorine-containing alkyl group. The vinylidene fluoride polymer may contain only one kind of constitutional unit derived from the fluorine-containing alkyl vinyl compound, or may contain two or more kinds. Examples of the fluorine-containing alkyl vinyl compound include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, fluoroalkyl vinyl ether, and perfluoroalkyl vinyl ether typified by perfluoromethyl vinyl ether. Among these, tetrafluoroethylene, chlorotrifluoroethylene, and hexafluoropropylene are preferable, and hexafluoropropylene is particularly preferable from the viewpoint of easily satisfying the requirements (B) and (C) described below.

[0017] Also, as described above, the vinylidene fluoride polymer may have a structural unit derived from a monomer other than vinylidene fluoride and the fluorine-containing alkyl vinyl compound (hereinafter, also referred to as "other monomer"). Examples of the other monomer include unsaturated carboxylic acids and unsaturated carboxylic acid esters.

[0018] The unsaturated basic acid may be an unsaturated carboxylic acid or its derivative. Examples thereof include compounds in which one or more carboxyl groups are bonded by a linear or branched unsaturated alkylene group having 1 to 6 carbon atoms. More specific examples of the unsaturated basic acid include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and citraconic acid.

[0019] The unsaturated basic acid ester is an ester compound derived from the above unsaturated basic acid. Specific examples thereof include methyl acrylate, methyl methacrylate, monomethyl maleate, monoethyl maleate, dimethyl maleate, monomethyl citraconate, and monoethyl citraconate.

[0020] Here, the above vinylidene fluoride polymer has a peak top in the range of 60°C or higher and lower than 100°C in the DSC curve obtained by differential scanning calorimetry in accordance with ASTM D3418 (requirement (B)).

[0021] The DSC curve is a curve obtained by performing differential scanning calorimetry while changing the temperature in accordance with ASTM D3418. The temperature range during the measurement can usually be 20°C to 230°C. In this specification, a group of measurement values that are convex on the endothermic side with respect to the baseline is regarded as a peak. The definition of the baseline in differential scanning calorimetry is shown below. Calculate the average value of the heat flux and the average value of the temperature of a plurality of measurement points in the range of 40°C or higher and 41°C or lower, respectively. Similarly, calculate the average value of the heat flux and the average value of the temperature of a plurality of measurement points in the range of 120°C or higher and 121°C or lower, respectively. A straight line connecting the two points, which are the average values of the plurality of measurement points in the range of 40°C or higher and 41°C or lower and the average values of the plurality of measurement points in the range of 120°C or higher and 121°C or lower calculated in this way, is taken as the baseline. In differential scanning calorimetry, it is desirable to perform the measurement so that there are three or more measurement points in each temperature range (40°C or higher and 41°C or lower, and 120°C or higher and 121°C or lower).

[0022] Here, when the vinylidene fluoride polymer has a peak top in the range of 60°C or higher and less than 100°C in the above DSC curve, the vinylidene fluoride polymer is likely to soften or melt at 60°C or higher and less than 100°C. That is, since the diffusion movement of the molecular chains of the vinylidene fluoride polymer becomes faster in this temperature range, swelling and dissociation in the solvent are promoted, and it becomes easier to dissolve in the solvent described later. Incidentally, it is more preferable that the vinylidene fluoride polymer has a peak top in the range of 60°C or higher and less than 90°C in the above DSC curve.

[0023] In order to adjust the vinylidene fluoride polymer so that the DSC curve has a peak top in the range of 60°C or higher and less than 100°C, it is preferable to adjust the amount of the structural unit derived from vinylidene fluoride and the amount of the structural unit derived from the fluorine-containing alkyl vinyl compound in the vinylidene fluoride polymer to the above-mentioned ranges.

[0024] Further, the above vinylidene fluoride polymer has at least one maximum value in the range of a diffraction angle of 10° or more and 19.9° or less in the X-ray diffraction pattern obtained by X-ray diffraction measurement, and the maximum diffraction intensity in the range of a diffraction angle of 22.5° or more and 30° or less is equal to or less than the maximum diffraction intensity in the range of a diffraction angle of 10° or more and 19.9° or less (requirement (C)).

[0025] Here, the above X-ray diffraction measurement is performed based on JIS K0131:1996. In this specification, having at least one maximum value in the range where the diffraction angle is 10° or more and 19.9° or less means that the X-ray diffraction pattern has a peak and the maximum value of the peak is in the range where the diffraction angle is 10° or more and 19.9° or less. Whether the X-ray diffraction pattern has a peak is determined as follows. First, as shown below, a baseline is specified. Then, the diffraction intensity at a point on the baseline is compared with the diffraction intensity on the X-ray diffraction pattern at the same diffraction angle. When the diffraction intensity on the X-ray diffraction pattern shows a value that is 1.5 times or more the diffraction intensity on the corresponding baseline for 5 or more consecutive points, it is determined that the X-ray diffraction pattern has a peak. Also, the maximum value in the group of measurement values where the diffraction intensity on the X-ray diffraction pattern is 1.5 times or more the diffraction intensity on the baseline for 5 or more consecutive points is specified, and it is determined whether the maximum value falls within the range where the diffraction angle is 10° or more and 19.9° or less.

[0026] In this specification, the baseline in the X-ray diffraction measurement is defined as follows. The average value of the diffraction angles and the average value of the diffraction intensities of a plurality of measurement points in the range where the diffraction angle is 10.0° or more and less than 10.1° are calculated respectively. Similarly, the average value of the diffraction angles and the average value of the diffraction intensities of a plurality of measurement points in the range where the diffraction angle is 30.0° or more and less than 30.1° are calculated respectively. Then, the straight line connecting these two points of the diffraction angle - diffraction intensity values calculated in this way is taken as the baseline. From the perspective of measurement accuracy, it is desirable to use the average value of 5 or more measurement points for calculating the baseline, that is, the average value of the measurement points in the range where the diffraction angle is 10.0° or more and less than 10.1°, and the average value of the measurement points in the range where the diffraction angle is 30.0° or more and less than 30.1°. Also, when the sample weight used in the measurement is 0.1 g or more, accurate measurement values are easily obtained.

[0027] The X-ray diffraction pattern of the vinylidene fluoride polymer represents the crystallization state of the vinylidene fluoride polymer. Also, the position of the maximum value of the diffraction intensity of the X-ray diffraction pattern varies depending on the type of crystal structure.

[0028] For example, like the vinylidene fluoride polymer D (a homopolymer of vinylidene fluoride) in the examples described later, when it has a large number of maxima in the region where the diffraction angle is 10° or more and 30° or less, it can be said that the vinylidene fluoride polymer contains many crystal structures (see Fig. 1). To dissolve such a vinylidene fluoride homopolymer in a solvent, a large amount of energy is required. Further, according to the studies by the present inventors, in particular, when the vinylidene fluoride polymer contains many crystal structures appearing in the range where the diffraction angle is 22.5° or more and 30° or less, it has been clarified that the solubility in the solvents described later is low.

[0029] On the other hand, like the vinylidene fluoride polymer G in the examples described later, when there are no maxima in the X-ray diffraction pattern, the vinylidene fluoride polymer has no crystal structure and becomes rubbery (see Fig. 1). In such a vinylidene fluoride polymer, it is difficult for a solvent to penetrate into its interior, and the solubility of the vinylidene fluoride polymer in the solvent is low.

[0030] In contrast, for a vinylidene fluoride polymer having at least one maximum in the range where the diffraction angle is 10° or more and 19.9° or less, and the maximum diffraction intensity in the range where the diffraction angle is 22.5° or more and 30° or less is equal to or less than the maximum diffraction intensity in the range where the diffraction angle is 10° or more and 19.9° or less, the solubility in the solvents described later is significantly increased. In such a vinylidene fluoride polymer, there are few crystal structures with low solubility in the above-mentioned solvents, and the solvent can penetrate in appropriately, so it is considered that the solubility in the solvent is high.

[0031] Here, the vinylidene fluoride polymer satisfying the above requirement (C) can be easily obtained by adjusting the amounts of the structural units derived from vinylidene fluoride and the structural units derived from the fluorine-containing alkyl vinyl compound in the vinylidene fluoride polymer to the above-mentioned ranges. Further, it is preferable to prepare the vinylidene fluoride polymer or perform post-preparation treatment under conditions that do not break the crystal structure in which a maximum appears in the range where the diffraction angle is 10° or more and 19.9° or less. For example, examples of the treatment for breaking the above crystal structure include the treatment of dissolving the prepared vinylidene fluoride polymer in a solvent such as acetone.

[0032] The weight-average molecular weight of the vinylidene fluoride polymer satisfying the above requirements (A) to (C) is preferably 10,000 or more and 2,500,000 or less, more preferably 50,000 or more and 2,000,000 or less, and even more preferably 100,000 or more and 1,500,000 or less. The above weight-average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). When the weight-average molecular weight of the vinylidene fluoride polymer is within the above range, the vinylidene fluoride polymer is more likely to be dissolved in the solvent described below.

[0033] The vinylidene fluoride polymer satisfying the above requirements (A) to (C) can be prepared by copolymerizing vinylidene fluoride, a fluorine-containing alkyl vinyl compound, and, if necessary, other compounds by a known method. Examples of the method for copolymerizing these include suspension polymerization, emulsion polymerization, solution polymerization, etc. Here, emulsion polymerization is preferable from the viewpoint that a vinylidene fluoride polymer satisfying the above requirements (B) and (C) can be easily obtained. The vinylidene fluoride polymer copolymerized by emulsion polymerization has a small primary particle diameter, so it is easy to disperse and the stability after dispersion is improved.

[0034] · Solvent The solvent contained in the vinylidene fluoride polymer solution only needs to have a molecular weight of 100 or more and contain at least an affinity solvent having at least one structure selected from ether, ketone, and ester, and may partly contain other solvents as long as the object and effect of the present invention are not impaired. However, the amount of the affinity solvent with respect to the total amount of the solvent is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0035] When the molecular weight of the above affinity solvent is 100 or more, even a solvent having polar groups of ether, ketone, and ester has an appropriately reduced polarity, so the affinity with the above vinylidene fluoride polymer is increased. The molecular weight of the affinity solvent is preferably 100 or more and 251 or less, more preferably 100 or more and 201 or less, and even more preferably 100 or more and 161 or less.

[0036] Further, the affinity solvent may have only one of ether, ketone, and ester, or may contain two or more thereof. Further, the solvent may contain only one kind of affinity solvent, or may contain two or more kinds.

[0037] Here, the octanol / water partition coefficient LogP of the above-mentioned affinity solvent is preferably 0 or more, more preferably 0 or more and 4 or less, still more preferably 0 or more and 3 or less, and even more preferably 0.5 or more and 2.9 or less. When the octanol / water partition coefficient of the affinity solvent is 0 or more, the water content of the vinylidene fluoride polymer solution becomes low, and the stability of the vinylidene fluoride polymer solution is likely to increase. The octanol / water partition coefficient LogP is the common logarithm value (Log(Co / Cw)) of the ratio of the concentration Co of the affinity solvent in the octanol phase and the concentration Cw of the affinity solvent in the water phase when the affinity solvent is dissolved in a two-phase system of octanol and water and equilibrated at 25°C.

[0038] Here, specific examples of the affinity solvent include ketones such as diisobutyl ketone (molecular weight: 142, LogP: 2.56), methyl isobutyl ketone (molecular weight: 100, LogP: 1.31), isophorone (molecular weight: 138, LogP: 1.67); esters such as ethyl methyl carbonate (molecular weight: 104, LogP: 1.21), amyl acetate (molecular weight: 130, LogP: 2.18), ethyl butyrate (molecular weight: 116, LogP: 1.85), butyl butyrate (molecular weight: 144, LogP: 2.8), isopropyl acetate (molecular weight: 102, LogP: 1.3), ethyl propionate (molecular weight: 102, LogP: 1.21); solvents containing esters and ethers such as 2-butoxyethyl acetate (molecular weight: 160, LogP: 1.51), etc.

[0039] Among the above, from the viewpoint of handleability, etc., as the affinity solvent, isophorone, diisobutyl ketone, methyl isobutyl ketone, amyl acetate, isopropyl acetate, ethyl butyrate, butyl butyrate, and ethyl propionate are preferable.

[0040] · Other components The vinylidene fluoride polymer solution may contain components other than the vinylidene fluoride polymer and the solvent, according to its intended use and within a range that does not impair the object and effect of the present invention. For example, it may further contain other types of resins such as acrylic resins, fillers such as inorganic fillers, and various additives.

[0041] · Physical properties The concentration of the vinylidene fluoride polymer in the vinylidene fluoride polymer solution is not particularly limited, but the concentration is preferably 30% by mass or less. When the concentration of the vinylidene fluoride polymer is within this range, it is difficult for undissolved vinylidene fluoride polymer to occur, and the stability of the vinylidene fluoride polymer is likely to increase. Furthermore, it becomes easier to use the vinylidene fluoride polymer solution for various applications.

[0042] The haze value of the vinylidene fluoride polymer solution is preferably 18% or less, more preferably 15% or less, and even more preferably 10% or less. When the haze value of the vinylidene fluoride polymer solution is 18% or less, it can be said that the vinylidene fluoride polymer is sufficiently dissolved in the solvent. Also, when the haze value is 18% or less, precipitation or separation of the vinylidene fluoride polymer is less likely to occur even over time.

[0043] The haze value of the vinylidene fluoride polymer solution was measured using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with ISO 14782. The haze value in this specification is a value calculated based on the following formula by measuring the diffused light transmittance Td (%) and the total light transmittance Tt (%) of each vinylidene fluoride polymer solution placed in a quartz cell. Haze value = (Td / Tt) × 100 (%)

[0044] · Preparation method The method for preparing the vinylidene fluoride polymer solution is not particularly limited, and it can be prepared by mixing a vinylidene fluoride polymer and a solvent in a known method to dissolve the vinylidene fluoride polymer. The vinylidene fluoride polymer and the solvent are preferably mixed at a temperature of 40°C or higher and 150°C or lower, and more preferably at a temperature of 60°C or higher and 100°C or lower. When the temperature is 60°C or higher, the vinylidene fluoride polymer is likely to soften or dissolve. On the other hand, when the temperature is 100°C or lower, the solvent is less likely to volatilize excessively, and a vinylidene fluoride polymer solution with a desired composition can be easily obtained.

[0045] In addition, when mixing the vinylidene fluoride polymer and the solvent, it is preferable to stir with a known device. Also, the mixing time (stirring time) is preferably 3 minutes or more and 3 hours or less from the viewpoint of production efficiency, and more preferably 5 minutes or more and 2 hours or less. In the present invention, since a vinylidene fluoride polymer satisfying the above requirements (A) to (C) and a solvent containing the above affinity solvent are combined, it does not take time to dissolve the vinylidene fluoride polymer in the solvent, and furthermore, the stability of the obtained vinylidene fluoride polymer solution can be improved.

[0046] · Use The use of the above vinylidene fluoride polymer solution is not particularly limited, and it can be used for various applications such as paints, coating agents, various binders for non-aqueous electrolyte secondary batteries and all-solid-state batteries.

Examples

[0047] Hereinafter, specific examples of the present invention will be described together with comparative examples, but the present invention is not limited thereto.

[0048] 1. Preparation of vinylidene fluoride polymer Vinylidene fluoride polymers A to G were prepared by the following method.

[0049] · Preparation of vinylidene fluoride polymer A 0.2 parts by mass of disodium hydrogen phosphate (Na2HPO4) and 330 parts by mass of water were placed in an autoclave. After degassing, 0.003 parts by mass of polyoxyethylene alkylene alkyl ether, 0.1 parts by mass of ethyl acetate, 8.7 parts by mass of vinylidene fluoride (VDF), and 38.0 parts by mass of hexafluoropropylene (HFP) were added. Then, the temperature inside the autoclave was raised to 80 °C with stirring, and 0.06 parts by mass of ammonium persulfate (APS) was added to initiate polymerization. The initial pressure at this time was 2.5 MPa, and 53.3 parts by mass of VDF was continuously added so that the pressure was maintained at 2.5 MPa. Then, when the pressure dropped to 1.5 MPa, the polymerization reaction was terminated, and a latex of a copolymer of vinylidene fluoride and hexafluoropropylene (VDF-HFP copolymer) was obtained.

[0050] The resin concentration of the latex was 20.6% by mass, and the average particle diameter of the VDF-HFP copolymer in the latex was 221 nm. The average particle diameter of the VDF-HFP copolymer was a value derived by integrating 50 times using DelsaMaxCORE of Beckman Coulter (detector angle: 90 degrees).

[0051] Thereafter, the latex was frozen with liquid nitrogen and further vacuum-dried for 8 hours under a reduced pressure of 30.0 Pa or less using a freeze dryer to obtain particles of a copolymer of vinylidene fluoride and hexafluoropropylene (vinylidene fluoride polymer A). Incidentally, 19 The mass ratio of vinylidene fluoride to hexafluoropropylene derived by 19F-NMR was 63:37.

[0052] · Preparation of vinylidene fluoride polymer B 0.2 parts by mass of disodium hydrogen phosphate (Na2HPO4) and 330 parts by mass of water were placed in an autoclave. After degassing, 0.003 parts by mass of polyoxyethylene alkylene alkyl ether, 0.1 parts by mass of ethyl acetate, 5 parts by mass of vinylidene fluoride (VDF), and 47.0 parts by mass of hexafluoropropylene (HFP) were added. Then, the temperature inside the autoclave was raised to 80 °C with stirring, and 0.3 parts by mass of ammonium persulfate (APS) was added to initiate polymerization. The initial pressure at this time was 2.5 MPa, and 48 parts by mass of VDF was continuously added so that the pressure was maintained at 2.5 MPa. After that, when the pressure dropped to 1.5 MPa, the polymerization reaction was terminated, and a latex of a copolymer of vinylidene fluoride and hexafluoropropylene (VDF-HFP copolymer) was obtained.

[0053] The resin concentration of the latex was 20.6% by mass, and the average particle diameter of the VDF-HFP copolymer in the latex was 100 nm. The average particle diameter of the VDF-HFP copolymer was a value derived by integrating 50 times using DelsaMaxCORE of Beckman Coulter (detector angle: 90 degrees). Thereafter, the latex was frozen with liquid nitrogen and further vacuum-dried for 8 hours under a reduced pressure of 30.0 Pa or less using a freeze dryer to obtain particles of a copolymer of vinylidene fluoride and hexafluoropropylene (vinylidene fluoride polymer B). 19 The mass ratio of vinylidene fluoride to hexafluoropropylene derived by 19F-NMR was 55:45.

[0054] · Preparation of vinylidene fluoride polymer C 0.2 parts by mass of disodium hydrogen phosphate (Na2HPO4) and 330 parts by mass of water were placed in an autoclave. After degassing, 0.003 parts by mass of polyoxyethylene alkylene alkyl ether, 0.1 parts by mass of ethyl acetate, 13 parts by mass of vinylidene fluoride (VDF), and 24 parts by mass of hexafluoropropylene (HFP) were added. Then, the temperature inside the autoclave was raised to 80 °C under stirring, and 0.06 parts by mass of ammonium persulfate (APS) was added to initiate polymerization. The initial pressure at this time was 2.5 MPa, and 63 parts by mass of VDF was continuously added so that the pressure was maintained at 2.5 MPa. Then, when the pressure dropped to 1.5 MPa, the polymerization reaction was terminated, and a latex of a copolymer of vinylidene fluoride and hexafluoropropylene (VDF-HFP copolymer) was obtained.

[0055] The resin concentration of the latex was 20.9% by mass, and the average particle diameter of the VDF-HFP copolymer in the latex was 180 nm. The average particle diameter of the VDF-HFP copolymer was a value derived by integrating 50 times using DelsaMaxCORE of Beckman Coulter (the detector angle was 90 degrees). Thereafter, the latex was frozen with liquid nitrogen and further vacuum-dried for 8 hours under a reduced pressure of 30.0 Pa or less using a freeze dryer to obtain particles of a copolymer of vinylidene fluoride and hexafluoropropylene (vinylidene fluoride polymer C). 19 The mass ratio of vinylidene fluoride to hexafluoropropylene derived by 19F-NMR was 80:20.

[0056] · Preparation of vinylidene fluoride polymer D 0.2 parts by mass of disodium hydrogen phosphate (Na2HPO4) and 330 parts by mass of water were placed in an autoclave. After degassing, 0.003 parts by mass of polyoxyethylene alkylene alkyl ether, 0.1 parts by mass of ethyl acetate, and 30 parts by mass of vinylidene fluoride (VDF) were added. Then, the temperature inside the autoclave was raised to 80 °C with stirring, and 0.06 parts by mass of ammonium persulfate (APS) was added to initiate polymerization. The initial pressure at this time was 2.5 MPa, and 70 parts by mass of VDF was continuously added so that the pressure was maintained at 2.5 MPa. Then, when the pressure dropped to 1.5 MPa, the polymerization reaction was terminated, and a latex of a homopolymer of vinylidene fluoride (VDF homopolymer) was obtained.

[0057] The resin concentration of the latex was 20.9% by mass, and the average particle diameter of the VDF homopolymer in the latex was 150 nm. The average particle diameter of the VDF homopolymer was a value derived by integrating 50 times using DelsaMax CORE of Beckman Coulter (the detector angle was 90 degrees). Thereafter, the latex was frozen with liquid nitrogen and further vacuum-dried for 8 hours under a reduced pressure of 30.0 Pa or less using a freeze dryer to obtain particles of a vinylidene fluoride homopolymer (vinylidene fluoride homopolymer D).

[0058] · Preparation of vinylidene fluoride polymer E 0.3 parts by mass of disodium hydrogen phosphate (Na2HPO4) and 380 parts by mass of water were placed in an autoclave. After degassing, 0.003 parts by mass of polyoxyethylene alkylene alkyl ether, 0.1 parts by mass of ethyl acetate, 25 parts by mass of vinylidene fluoride (VDF), and 10 parts by mass of hexafluoropropylene (HFP) were added. Then, the temperature inside the autoclave was raised to 80 °C with stirring, and 0.2 parts by mass of ammonium persulfate (APS) was added to initiate polymerization. The initial pressure at this time was 4.01 MPa, and 65 parts by mass of VDF was continuously added so that the pressure was maintained at 2.5 MPa. Thereafter, when the pressure dropped to 1.5 MPa, the polymerization reaction was terminated, and a latex of a copolymer of vinylidene fluoride and hexafluoropropylene (VDF-HFP copolymer) was obtained.

[0059] The resin concentration of the latex was 20.9% by mass, and the average particle diameter of the VDF-HFP copolymer in the latex was 129 nm. The average particle diameter of the VDF-HFP copolymer was a value derived by integrating 50 times using DelsaMaxCORE of Beckman Coulter (detector angle: 90 degrees). Thereafter, the latex was frozen with liquid nitrogen and further vacuum-dried for 8 hours under a reduced pressure of 30.0 Pa or less using a freeze dryer to obtain particles of a copolymer of vinylidene fluoride and hexafluoropropylene (vinylidene fluoride polymer E). Incidentally, 19 The mass ratio of vinylidene fluoride to hexafluoropropylene derived by 19F-NMR was 91:9.

[0060] · Preparation of vinylidene fluoride polymer F 0.2 parts by mass of disodium hydrogen phosphate (Na2HPO4) and 330 parts by mass of water were placed in an autoclave. After degassing, 0.003 parts by mass of polyoxyethylene alkylene alkyl ether, 0.2 parts by mass of ethyl acetate, 8 parts by mass of vinylidene fluoride (VDF), and 32 parts by mass of hexafluoropropylene (HFP) were added. Then, the temperature inside the autoclave was raised to 80 °C with stirring, and 0.3 parts by mass of ammonium persulfate (APS) was added to initiate polymerization. The initial pressure at this time was 2.5 MPa, and 60 parts by mass of VDF was continuously added so that the pressure was maintained at 2.5 MPa. Then, when the pressure dropped to 1.5 MPa, the polymerization reaction was terminated, and a latex of a copolymer of vinylidene fluoride and hexafluoropropylene (VDF-HFP copolymer) was obtained.

[0061] The resin concentration of the latex was 20.9% by mass, and the average particle diameter of the VDF-HFP copolymer in the latex was 210 nm. The average particle diameter of the VDF-HFP copolymer was a value derived by integrating 50 times using DelsaMaxCORE of Beckman Coulter (detector angle: 90 degrees). Thereafter, the latex was frozen with liquid nitrogen and further vacuum-dried for 8 hours under a reduced pressure of 30.0 Pa or less using a freeze dryer to obtain particles of a copolymer of vinylidene fluoride and hexafluoropropylene. 5 parts by mass of acetone was added to 1 part by mass of the copolymer granulated particles and dissolved. After adding 10 parts by mass of hexane to this acetone solution and stirring, it was filtered to obtain a rubbery precipitate. The rubbery precipitate was dried with a vacuum dryer to obtain particles of a copolymer of vinylidene fluoride and hexafluoropropylene (vinylidene fluoride polymer F). 19 The mass ratio of vinylidene fluoride to hexafluoropropylene derived by 19F-NMR was 70:30.

[0062] · Preparation of vinylidene fluoride polymer G Into an autoclave with a volume of 5 L having a stirrer and an external temperature control jacket, 1 kg of deionized and deoxygenated water, 2.4 g of ammonium persulfate, 4.0 g of ammonium perfluorooctanoate, and 0.8 g of sodium acid sulfite were charged, and further 0.2 g of sodium hydroxide was added. After replacing the inside of the autoclave with nitrogen gas three times, 170 g of vinylidene fluoride (VDF), 80 g of tetrafluoroethylene (TFE), and 90 g of hexafluoropropylene (HFP) were charged, and polymerization was carried out at 60 °C for 7 hours while stirring. The polymer was coagulated, the polymer was filtered off, washed with water, then washed with n-hexane, and further dried in a vacuum dryer to obtain 160 g of a white powdery vinylidene fluoride polymer G. The composition of the vinylidene fluoride polymer G was VDF:TFE:HFP (mass ratio) of 61:24:15.

[0063] ·Measurement of physical properties of vinylidene fluoride polymer For the vinylidene fluoride polymers A to G obtained by the above method, DSC curves and X-ray diffraction patterns were obtained based on the following method.

[0064] (DSC curve) For each vinylidene fluoride polymer, differential scanning calorimetry was performed in the range from 20 °C to 230 °C using a METTLER STARe DSC1 (apparatus) in accordance with ASTM D3418 to create a DSC curve. The heating rate was 10 °C / min, and the measurement was carried out under a nitrogen flow of 50 mL / min. In addition, a group of measured values convex on the endothermic side with respect to the baseline was regarded as a peak, and the measured value corresponding to the maximum value of the curve formed by the group of measured values was taken as the peak top. The baseline was specified as follows. For three measurement points in the range of 40 °C or more and 41 °C or less and three measurement points in the range of 120 °C or more and 121 °C or less, the average value of the heat flux and the average value of the temperature in each temperature interval were calculated. A straight line connecting two points, which are the average values of each measurement point in the range of 40 °C or more and 41 °C or less and the average values of each measurement point in the range of 120 °C or more and 121 °C or less calculated in this way, was taken as the baseline.

[0065] (X-ray diffraction measurement) As the device, X'Pert-PRO manufactured by Philips was used. The optical system was a Bragg-Brentano type focusing optical system. For the generation of X-rays, a Cu tube was used, with a voltage value of 45 kV and a current value of 40 mA. The X-rays were monochromatized using a Ni filter, and a movable slit (irradiation area: 1 cm × 1 cm) was used. When it was necessary to fix the sample, a polyimide Kapton tape was used. Under the above device conditions, X-ray diffraction measurements of each vinylidene fluoride polymer were carried out based on JIS K0131:1996. The measurement range in each measurement was from 10.00° to 60.00°, the number of scan steps was 0.026 per degree, and the Time per step was 86.19 / s. Also, the X-ray diffraction patterns of each vinylidene fluoride polymer are shown in Figure 1. In the obtained X-ray diffraction patterns, it was confirmed whether there was a maximum value in the range where the diffraction angle was 10° or more and 19.9° or less, and whether the maximum diffraction intensity in the range where the diffraction angle was 22.5° or more and 30° or less was less than or equal to the maximum diffraction intensity in the range where the diffraction angle was 10° or more and 19.9° or less.

[0066] Specifically, the average value of the diffraction angles and the average value of the diffraction intensities of a plurality of measurement points in the range where the diffraction angle in the X-ray diffraction measurement was 10.0° or more and less than 10.1° were calculated respectively. Similarly, the average value of the diffraction angles and the average value of the diffraction intensities of a plurality of measurement points in the range where the diffraction angle was 30.0° or more and less than 30.1° were calculated respectively. Then, a straight line connecting these two points of the diffraction angle and diffraction intensity values calculated in this way was used as the baseline. Then, the diffraction intensity of the points on the baseline was compared with the diffraction intensity on the X-ray diffraction pattern at the same diffraction angle. When the diffraction intensity on the X-ray diffraction pattern continuously showed a value of 1.5 times or more of the diffraction intensity on the baseline for 5 or more points, it was determined that the X-ray diffraction pattern had a peak. Furthermore, the maximum value in the group of measurement values where the diffraction intensity on the X-ray diffraction pattern continuously became 1.5 times or more of the diffraction intensity on the baseline for 5 or more points was specified, and it was specified whether the maximum value fell within the range where the diffraction angle was 10° or more and 19.9° or less.

[0067] According to the specific method, for example, in the X-ray diffraction patterns of vinylidene fluoride polymers F and G, there is no point where the diffraction intensity of the measured value is 1.5 times or more the diffraction intensity of the corresponding baseline in the range of diffraction angles from 10° to 19.9°. Therefore, it was determined that there is no maximum value. The results are shown in Table 1.

[0068]

Table 1

[0069] 2. Preparation of vinylidene fluoride polymer solution 2-1. Preparation of solvent Solvents with the physical properties shown in Table 2 below were prepared. Each physical property value shown in Table 2 is a literature value.

Table 2

[0070] 2-2. Preparation of vinylidene fluoride polymer solution The above vinylidene fluoride polymer and the above solvent were mixed in the combinations shown in Tables 3 and 4 to obtain a vinylidene fluoride polymer solution. The vinylidene fluoride polymer and the solvent were stirred and mixed at 70°C and 700 rpm for 3 hours. The concentration of the vinylidene fluoride polymer in the solution at this time is represented as the solution concentration. Then, for the vinylidene fluoride polymer solution, the state of the solution, the haze value, and the fluidity were measured as follows. The results are shown in Tables 3 and 4.

[0071] (State of the solution) Each vinylidene fluoride polymer solution was visually confirmed to check whether separation, turbidity, precipitation, or gelation occurred.

[0072] (Measurement of haze) The haze was measured with an NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. Each vinylidene fluoride polymer solution was placed in a quartz cell, and the diffused light transmittance Td (%) and the total light transmittance Tt (%) were measured, and the haze value was calculated as follows. Haze value = (Td / Tt) × 100 (%) During the measurement, the haze of the solvent used in each example and each comparative example was set to 0, and the haze of the sample was derived. When separation was observed in the sample or when it was in an undissolved state, accurate haze could not be derived, so the measurement was considered impossible (indicated as "-" in Table 4).

[0073] (Fluidity) Each vinylidene fluoride polymer solution was added to a screw bottle, and the screw bottle was tilted to an angle of 45 degrees. Whether a horizontal plane could be seen in the vinylidene fluoride polymer solution inside the tilted screw bottle was visually confirmed based on the following criteria. 〇: A horizontal plane could be confirmed, and no phase separation or sedimentation was observed. ×: A horizontal plane could not be confirmed, or even if a horizontal plane was confirmed, phase separation occurred in the vinylidene fluoride polymer solution and partial sedimentation occurred.

[0074]

Table 3

Table 4

[0075] As shown in Table 3 above, when a vinylidene fluoride polymer satisfying the above requirements (A) to (C) was combined with a solvent containing the above-mentioned compatible solvent, the resulting vinylidene fluoride polymer solution was transparent and had good fluidity. Furthermore, the haze value was also low (Examples 1 to 21). As shown in Table 4, even if the vinylidene fluoride polymer satisfied the above requirements (A) to (C), when the solvent did not contain a compatible solvent, specifically, when the molecular weight of the solvent was less than 100, even if it was a solvent having ether, ketone, or ester, due to its excessively high polarity and low affinity with the above-mentioned polymer, the primary particles aggregated and cloudiness occurred (Comparative Example 11). Also, even for a solvent having a molecular weight of 100 or more, a solvent not containing any of ether, ketone, or ester had an excessively low polarity and the polymer did not dissolve (Comparative Examples 17 and 18).

[0076] In Comparative Examples 2, 7, 13, 20, and 23 using vinylidene fluoride polymer D that did not satisfy requirement (A), precipitation and separation easily occurred. This is presumably because it was not sufficiently compatible with the solvent. Also, in Comparative Examples 1, 3, 6, 8, 12, 14, 19, and 25 using vinylidene fluoride polymer C or E that did not satisfy requirement (B) even though it satisfied requirement (A), gelation and separation occurred. In this case as well, it is considered that it could not be sufficiently compatible with the solvent. Furthermore, in Comparative Examples 4, 5, 9, 10, 15, 16, 21, 22, 24, and 26 using vinylidene fluoride polymer F that did not satisfy requirement (C) although it satisfied requirements (A) and (B), or vinylidene fluoride polymer G that did not satisfy requirements (B) and (C), undissolved matter occurred depending on the solvent. Vinylidene fluoride polymers F and G are rubbery, and this is presumably because it was difficult for the solvent to penetrate inside.

[0077] This application claims priority based on Japanese Patent Application No. 2021-164151 filed on October 5, 2021. All of the content described in the specification and drawings of the said application is incorporated herein by reference.

Industrial Applicability

[0078] According to the present invention, a vinylidene fluoride polymer solution in which a vinylidene fluoride polymer is completely dissolved in a solvent with low environmental impact and easy handling can be obtained. The said vinylidene fluoride polymer solution can be used in various fields.

Claims

1. A vinylidene fluoride polymer solution containing a vinylidene fluoride polymer and a solvent, wherein the solvent has a molecular weight of 100 or more and contains an affinity solvent having at least one structure selected from ether, ketone, and ester, and the vinylidene fluoride polymer satisfies the following (A) to (C): A vinylidene fluoride polymer solution. (A) Containing a structural unit derived from vinylidene fluoride and a structural unit derived from a fluorine-containing alkyl vinyl compound (B) Having a peak top in the range of 60 °C or more and less than 100 °C of the DSC curve obtained by differential thermal analysis in accordance with ASTM D3418 (C) In the X-ray diffraction pattern obtained by X-ray diffraction measurement, having at least one maximum value in the range of a diffraction angle of 10 ° or more and 19.9 ° or less, and the maximum diffraction intensity in the range of a diffraction angle of 22.5 ° or more and 30 ° or less is equal to or less than the maximum diffraction intensity in the range of a diffraction angle of 10 ° or more and 19.9 ° or less

2. The octanol / water partition coefficient LogP of the affinity solvent is 0 or more, The vinylidene fluoride polymer solution according to Claim 1.

3. The solvent contains at least one selected from the group consisting of isophorone, diisobutyl ketone, amyl acetate, ethyl butyrate, butyl butyrate, and ethyl propionate, The vinylidene fluoride polymer solution according to Claim 1.

4. The fluorine-containing alkyl vinyl compound is hexafluoropropylene, The vinylidene fluoride polymer solution according to any one of Claims 1 to 3.

5. The concentration of the vinylidene fluoride polymer is 30% by mass or less, The vinylidene fluoride polymer solution according to any one of Claims 1 to 3.

6. The haze value is 18% or less, The vinylidene fluoride polymer solution according to any one of Claims 1 to 3.

7. The haze value is 18% or less, The vinylidene fluoride polymer solution according to Claim 4.

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