Gas barrier sheet and tank

Abstract

Provided is a gas barrier sheet containing a vinylidene fluoride polymer and having both high gas barrier properties and high flexibility. The gas barrier sheet of the present invention contains a vinylidene fluoride polymer, and an alkyl quaternary ammonium sulfate or an alkyl quaternary ammonium sulfite. The content of the alkyl quaternary ammonium sulfate and the alkyl quaternary ammonium sulfite is 0.7 parts by mass or more and 5.0 parts by mass or less relative to the 100.0 parts by mass of the vinylidene fluoride polymer. The ratio of the α crystal form relative to all crystal forms of the vinylidene fluoride polymer is 30% or less, and the ratio of the β crystal form relative to all crystal forms of the vinylidene fluoride polymer is 20% or more.

Description

Gas barrier sheet and tank

[0001] The present invention relates to a gas barrier sheet and a tank.

[0002] Since vinylidene fluoride polymer has high crystallinity, it improves the gas barrier property of a molded article. On the other hand, high crystallinity of vinylidene fluoride polymer makes it difficult to increase the flexibility of the molded article. Although the flexibility of the molded article can be increased by increasing the amount of comonomer in the vinylidene fluoride polymer, increasing the amount of comonomer may decrease crystallinity and lower gas barrier properties. As described above, it is not easy to achieve both gas barrier properties and flexibility in a molded article containing vinylidene fluoride polymer.

[0003] Patent Document 1 describes that when a resin composition obtained by mixing a vinylidene fluoride polymer and an onium salt is subjected to compression molding or the like, the tensile elastic modulus decreases and the tensile elongation at break improves.

[0004] It is known that vinylidene fluoride polymer has three crystal forms: α crystal, β crystal and γ crystal. Non-Patent Document 1 describes a method for measuring the ratio of α crystal, β crystal and γ crystal in vinylidene fluoride polymer.

[0005] US Patent Application Publication No. 2008 / 0281031 Specification

[0006] Cai et al., "A critical analysis of the α, β and γ phases in poly(vinylidene fluoride) using FTIR", RSC Advances, 2017, No. 7, p. 15382-15389

[0007] Gas barrier sheets are used, for example, as liners for hydrogen tanks. Such gas barrier sheets require flexibility to withstand repeated filling and depressurization of high-pressure hydrogen without rupturing. While vinylidene fluoride polymers enhance the gas barrier properties of molded bodies, they do not easily improve flexibility. Therefore, vinylidene fluoride polymers have had the problem of being difficult to apply to gas barrier sheets used in applications where contact with high-pressure air and pressure drops are repeated. As described in Patent Document 1, attempts have been made to improve the flexibility of molded bodies containing vinylidene fluoride polymers using onium salts. However, simply adding onium salts has not been sufficient to produce gas barrier sheets that achieve a high degree of both gas barrier properties and flexibility.

[0008] The present invention has been made in view of the above problems, and aims to provide a gas barrier sheet containing a vinylidene fluoride polymer that has both high gas barrier properties and flexibility, and a tank using the same.

[0009] One embodiment of the present invention for solving the above problems relates to the gas barrier sheet and tank described in [1] to [8] below. [1] A gas barrier sheet comprising a vinylidene fluoride polymer and an alkyl quaternary ammonium sulfate or alkyl quaternary ammonium sulfite, wherein the content of the alkyl quaternary ammonium sulfate and alkyl quaternary ammonium sulfite is 0.7 parts by mass or more and 5.0 parts by mass or less per 100.0 parts by mass of the vinylidene fluoride polymer, the ratio of α crystals to the total crystalline form of the vinylidene fluoride polymer is 30% or less, and the ratio of β crystals to the total crystalline form of the vinylidene fluoride polymer is 20% or more. [2] The gas barrier sheet according to [1], wherein the ratio of α crystals to the total crystalline form of the vinylidene fluoride polymer is 10% or more and 30% or less, and the ratio of β crystals to the total crystalline form of the vinylidene fluoride polymer is 20% or more and 80% or less. [3] The gas barrier sheet according to [1] or [2], wherein the ratio of the β crystals to the α crystals (β crystals / α crystals) is 2.0 or more and 10.0 or less. [4] The gas barrier sheet according to any one of [1] to [3], wherein the ratio of γ crystals to the total crystalline form of the vinylidene fluoride polymer is 80% or less. [5] The oxygen permeability coefficient at 23°C is 6.0 [cm] ３ mm / (m) ２ A gas barrier sheet as described in any of [1] to [4], wherein the birefringence Δn is 0.001 × 10⁻¹⁰. －３ 30 x 10 －３ The following gas barrier sheets are those described in any of [1] to [5]: [7] A gas barrier sheet described in any of [1] to [6] having a yield strain of 13% or more in a tensile test. [8] A tank containing a gas barrier sheet described in any of [1] to [7] as a liner. [9] A hydrogen tank as described in [8].

[0010] According to the present invention, a gas barrier sheet containing a vinylidene fluoride polymer and having high gas barrier properties and flexibility, and a tank using the same are provided.

[0011] Figure 1A is a schematic cross-sectional view showing the general configuration of a hydrogen tank having a gas barrier sheet as a liner according to this embodiment. Figure 1B is a schematic cross-sectional view showing the layer configuration of the hydrogen tank.

[0012] 1. One embodiment of a gas barrier sheet relates to a gas barrier sheet comprising a vinylidene fluoride polymer and an alkyl quaternary ammonium sulfate or alkyl quaternary ammonium sulfite (hereinafter also simply referred to as "alkyl quaternary ammonium sulfate, etc.").

[0013] Due to its high crystallinity, vinylidene fluoride polymer enhances the gas barrier properties of gas barrier sheets. Specifically, vinylidene fluoride polymer is a polymer whose main constituent units are derived from vinylidene fluoride, and more precisely, it is a polymer in which the content of vinylide-derived constituent units is 50 mol% or more.

[0014] The vinylidene fluoride polymer may be a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride and other monomers. Examples of monomers copolymerizable with vinylidene fluoride include 1-chloro-1-fluoroethylene, 1-chloro-2-fluoroethylene, trifluoroethylene, chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), tetrafluoropropene, hexafluoropropylene (HFP), and perfluoroalkyl vinyl ethers. From the viewpoint of increasing the crystallinity of the vinylidene fluoride polymer and improving its gas barrier properties, a homopolymer of vinylidene fluoride is preferred.

[0015] The content of constituent units derived from vinylidene fluoride in the vinylidene fluoride polymer may be 50 mol% or more relative to the total constituent units of the vinylidene fluoride polymer, preferably 80 mol% to 100 mol%, and more preferably 90 mol% to 100 mol%. The content of constituent units derived from monomers other than vinylidene fluoride in the vinylidene fluoride polymer may be 50 mol% or less relative to the total constituent units of the vinylidene fluoride polymer, preferably 0 mol% to 20 mol%, and more preferably 0 mol% to 10 mol%. The higher the content of constituent units derived from vinylidene fluoride, the higher the gas barrier properties can be.

[0016] The vinylidene fluoride polymer preferably has an Inherend viscosity of 0.75 dl / g or more and 1.30 dl / g or less, more preferably 0.80 dl / g or more and 1.20 dl / g or less, and even more preferably 0.80 dl / g or more and 1.10 dl / g or less. The lower the Inherend viscosity (lower degree of polymerization), the faster the crystallization rate during cooling and the easier it is for crystal growth to proceed, thus increasing the gas barrier properties. The higher the Inherend viscosity (higher degree of polymerization), the easier it is for the gas barrier sheet to be stretchable.

[0017] The inherent viscosity of vinylidene fluoride polymer is measured in accordance with JIS K 7367-1:2002. Specifically, 80 mg of vinylidene fluoride polymer is dissolved in 20 ml of N,N-dimethylformamide, and the viscosity η of the polymer solution is determined using an Ubbelohde viscometer in a 30°C constant temperature bath. Then, the viscosity η of the polymer solution and the viscosity η of the N,N-dimethylformamide used as the solvent are measured. ｏ Based on the concentration C (g / dl) of the solution, the inherent viscosity η is calculated using the following formula. ｉ Calculate (dl / g). η ｉ =(1 / C)・ln(η / η ｏ Here, the concentration of the solution is 0.4 (g / dl).

[0018] The vinylidene fluoride polymer is crystallized within the gas barrier sheet.

[0019] Vinylidene fluoride polymers can exist in three crystalline structures: α-crystal, β-crystal, and γ-crystal. Of these, when molten vinylidene fluoride polymer is cooled, the α-crystal is usually formed. Stretching the α-crystal at low temperatures yields the β-crystal, and heat-treating the α-crystal at high temperatures yields the γ-crystal. According to our new findings, the flexibility of gas barrier sheets can be improved by lowering the proportion of α-crystals and increasing the proportion of β-crystals in the vinylidene fluoride polymer.

[0020] However, stretching the gas barrier sheet to increase the proportion of β crystals reduces its flexibility. Therefore, from the viewpoint of improving the flexibility of the gas barrier sheet, it is desirable to increase the proportion of β crystals without stretching. The inventors diligently investigated this issue and found that a film-like molded article obtained by melting and rapidly cooling a resin composition containing an alkyl quaternary ammonium sulfate or the like added to a vinylidene fluoride polymer exhibits high gas barrier properties, a high proportion of β crystals, and high flexibility even without stretching. This is thought to be because crystal growth is finely controlled by the alkyl quaternary ammonium sulfate or the like.

[0021] Even if the proportion of β crystals is increased, the flexibility of the gas barrier film will not be sufficiently increased if a large amount of α crystals are also generated. Therefore, in this embodiment, the gas barrier sheet has a ratio of α crystals to the total crystalline form of the vinylidene fluoride polymer of 30% or less. The proportion of α crystals of the vinylidene fluoride polymer can be reduced by adding alkylquaternary ammonium sulfate or the like to the vinylidene fluoride polymer. The ratio of α crystals to the total crystalline form of the vinylidene fluoride polymer is preferably 10% to 30%, and more preferably 10% to 20%.

[0022] Further, in the gas barrier sheet, the ratio of β-crystals to the total crystal forms of the vinylidene fluoride polymer is 20% or more. By melting a resin composition obtained by adding an alkyl quaternary ammonium sulfate or the like to a vinylidene fluoride polymer and then quenching the melt, the ratio of β-crystals in the vinylidene fluoride polymer can be increased without stretching. The ratio of β-crystals to the total crystal forms of the vinylidene fluoride polymer is preferably 20% or more and 80% or less, more preferably 40% or more and 80% or less, and still more preferably 50% or more and 80% or less.

[0023] In the gas barrier sheet, the ratio of the ratio of β-crystals to the ratio of α-crystals (β-crystals / α-crystals) is preferably 2.0 or more and 10.0 or less, and more preferably 4.0 or more and 6.0 or less. This allows the flexibility of the sheet to be sufficiently improved.

[0024] Note that in the gas barrier sheet, the ratio of γ-crystals to the total crystal forms of the vinylidene fluoride polymer is preferably 80% or less, more preferably 0% or more and 40% or less, and still more preferably 10% or more and 30% or less. According to the findings of the present inventors, when an alkyl quaternary ammonium sulfate or the like is added, the vinylidene fluoride polymer tends to form γ-crystals. In contrast, by adjusting cooling conditions and the like to reduce the ratio of γ-crystals, the ratio of β-crystals can be increased.

[0025] Further, the gas barrier sheet has a birefringence Δn of 0.001×10 －３ -3 or more and 30×10 －３ -3 or less, preferably 0.010×10 －３ -3 or more and 20×10 －３ -3 or less, more preferably 0.010×10 －３ -3 or more and 10×10 －３ -3 or less, and even more preferably within this range. By forming the sheet without stretching, the birefringence Δn falls within the above range. As the birefringence Δn increases, polymer chains are oriented and the flexibility of the gas barrier sheet tends to decrease. As the birefringence Δn decreases, polymer chains are randomly arranged, so the gas barrier properties tend to decrease. By setting the birefringence Δn within the above range, a gas barrier sheet that achieves both flexibility and gas barrier properties can be obtained.

[0026] The birefringence Δn is affected by the sheet manufacturing method. For example, if the sheet is stretched during manufacturing, the birefringence Δn will increase to 30 × 10⁻⁶. －３ It exceeds this. In press molding with low resin flow, the birefringence Δn is 0.001 × 10 －３ ~0.009 x 10 －３ To what extent, in blow molding or injection molding, the birefringence Δn is 0.010 × 10⁻¹⁰. －３ ~10 x 10 －３ It will be to that extent.

[0027] Furthermore, the gas barrier sheet preferably has a crystal melting enthalpy ΔH of 30 J / g or more and 70 J / g or less, more preferably 36 J / g or more and 60 J / g or less, and even more preferably 36 J / g or more and 54 J / g or less. The higher the crystal melting enthalpy ΔH, the higher the gas barrier properties of the gas barrier sheet. On the other hand, increasing the crystal melting enthalpy ΔH reduces the flexibility of the gas barrier sheet, but by adjusting the ratio of crystal forms as described above, the flexibility of the molded body can be increased even when the crystal melting enthalpy ΔH is high.

[0028] Alkyl quaternary ammonium sulfates are compounds represented by the following formula (1). Alkyl quaternary ammonium sulfites are compounds represented by the following formula (2).

[0029]

[0030] In equations (1) and (2), R １ ~R ４ R is an alkyl group having 1 to 10 carbon atoms. １ ~R ４ Examples of alkyl groups in R include methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, and octyl groups. １ ~R ４ The total number of carbon atoms in the alkyl group is preferably 6 to 30, more preferably 6 to 24, and even more preferably 8 to 20.

[0031] In equations (1) and (2), R ５R is an alkyl group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a hydrogen atom. ５ Examples of alkyl groups in R include methyl and ethyl groups. ５ Examples of fluoroalkyl groups in this context include CF ３ and C ２ F ５ This includes R. ５ It is preferably hydrogen.

[0032] Examples of alkylquaternary ammonium sulfates include (C ２ H ５ ) ４ N ＋ , (C ３ H ７ ) ４ N ＋ , (C ４ H ９ ) ４ N ＋ , and (C ５ H １１ ) ４ N ＋ Alkyl quaternary ammonium cations such as and CF ３ SO ４ － ,CH ３ SO ４ － , and HSO ４ － These include salts with anions such as [specific anions]. These compounds can be used individually or in combination of two or more.

[0033] The alkyl quaternary ammonium sulfate is preferably an alkyl quaternary ammonium hydrogen sulfate. Examples of alkyl quaternary ammonium hydrogen sulfates include tetraethylammonium hydrogen sulfate, tetrapropylammonium hydrogen sulfate, tetrabutylammonium hydrogen sulfate, tetrapentylammonium hydrogen sulfate, and tetrahexylammonium hydrogen sulfate.

[0034] It is believed that alkyl quaternary ammonium sulfates and the like interact with the fluorine atom and cation of the C-F bond in the vinylidene fluoride polymer, and with the hydrogen atom and anion of the C-H bond in the vinylidene fluoride polymer. Due to these interactions, alkyl quaternary ammonium sulfates and the like inhibit the formation of a trans-gauche-trans-gauche' structure (TGTG) in the vinylidene fluoride polymer when the resin composition is cooled, and promote the formation of an all-trans structure (TTTT), thereby suppressing the growth of α crystals and generating more β crystals. As a result, alkyl quaternary ammonium sulfates and the like increase the proportion of β crystals in the molded product and improve the flexibility of the gas barrier sheet.

[0035] Furthermore, from the viewpoint of more effectively generating the interaction between the cations and anions and the vinylidene fluoride polymer, thereby sufficiently suppressing the growth of α-crystals and increasing the proportion of β-crystals, it is desirable that sufficient separation of anions and cations occurs during the molding of the gas barrier sheet. Here, since alkyl quaternary ammonium sulfates and the like have a low melting point of around 170°C, they separate sufficiently at the temperature required to melt the vinylidene fluoride polymer. Therefore, it is considered that alkyl quaternary ammonium sulfates and the like more effectively generate the combined action between the cations and anions and the vinylidene fluoride polymer, thereby sufficiently suppressing the growth of α-crystals and increasing the proportion of β-crystals.

[0036] The amount of alkylquaternary ammonium sulfate, etc. is not particularly limited, but is preferably 0.1 parts by mass or more and 5.0 parts by mass or less per 100.0 parts by mass of vinylidene fluoride polymer, more preferably 0.3 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.7 parts by mass or more and 5.0 parts by mass or less, even more preferably 1.0 part by mass or more and 5.0 parts by mass or less, even more preferably 1.8 parts by mass or more and 5.0 parts by mass or less, even more preferably 2.8 parts by mass or more and 5.0 parts by mass or less, and particularly preferably 3.8 parts by mass or more and 5.0 parts by mass or less. The more alkylquaternary ammonium sulfate, etc. is used, the more the microstructure of the vinylidene fluoride polymer is appropriately controlled, and thus the flexibility of the molded article increases. When the amount of alkylquaternary ammonium sulfate, etc. is 5.0 parts by mass or less, the alkylquaternary ammonium sulfate, etc. and the vinylidene fluoride polymer can be sufficiently mixed during the production of the molded article.

[0037] Furthermore, the gas barrier sheet may contain antioxidants, ultraviolet absorbers, light stabilizers, lubricants, mold release agents, antistatic agents, flame retardants, reinforcing agents, nucleating agents, and bluing agents.

[0038] The thickness of the gas barrier sheet is not particularly limited, but is preferably 50 μm or more and 5 mm or less, more preferably 100 μm or more and 3 mm or less, and even more preferably 500 μm or more and 2 mm or less. The thicker the sheet, the higher the gas barrier properties.

[0039] 2. Method for Manufacturing Gas Barrier Sheets Gas barrier sheets can be manufactured by forming a film from a resin composition containing the above-mentioned vinylidene fluoride polymer and alkylquaternary ammonium sulfate, etc., using a known molding method.

[0040] The molding method is not particularly limited. Examples of molding methods include extrusion molding, injection molding, blow molding, and press molding. In extrusion molding, the resin composition is melted and kneaded in a kneader, then extruded from a T-die and cooled by contacting it with a cooling roll. In injection molding, the resin composition is melted and kneaded in a kneader, then injected into a mold having a sheet-shaped cavity, and then cooled. In blow molding, the resin composition is melted and kneaded in a kneader, then extruded or injected in a ring shape to form a parison, air is blown into the inside of the parison in a mold to expand it into a hollow cylindrical shape, and then cooled. It is then injected into a mold and cooled. In press molding, the resin composition placed inside a mold is heated and melted, pressed, and then cooled.

[0041] The resin composition can be manufactured by melt-kneading a vinylidene fluoride polymer and an alkylquaternary ammonium sulfate, etc., and then cooling it. The shape of the resin composition is not particularly limited and may be any shape such as pellets, flakes, or powder. Alternatively, the melt-kneaded resin composition may be injected directly into a mold and then cooled.

[0042] The mixing temperature should be higher than the melting point of the vinylidene fluoride polymer, preferably between 190°C and 260°C, and more preferably between 200°C and 220°C. The higher the temperature during melt mixing, the more thoroughly the vinylidene fluoride polymer can be melted and mixed. Keeping the melt mixing temperature below 220°C can suppress the increase in oxygen permeability and decrease in flexibility caused by the decomposition of alkylquaternary ammonium sulfates, etc.

[0043] The rotation speed of the screw during kneading is preferably 50 rpm to 200 rpm, and more preferably 100 rpm to 150 rpm. Setting the rotation speed within the above range allows for efficient dispersion of alkyl quaternary ammonium sulfates and the like in the vinylidene fluoride polymer.

[0044] In either method, the resin composition is melted during molding. The melting temperature should be higher than the melting point of the vinylidene fluoride polymer, preferably between 190°C and 260°C, and more preferably between 200°C and 220°C. The higher the melting temperature during kneading, the more thoroughly the vinylidene fluoride polymer can be melted and kneaded. Keeping the melting temperature below 220°C suppresses the increase in oxygen permeability and decrease in flexibility due to the decomposition of alkylquaternary ammonium sulfates, etc. Note that the melting temperature during kneading is the set temperature of the device that heats the resin composition in contact with it, such as the cylinder temperature of the kneader or the heating temperature of the compression molding machine.

[0045] Next, the molten resin composition is cooled. In this embodiment, the resin composition is rapidly cooled. The cooling rate is preferably 40°C / min to 200°C / min, more preferably 50°C / min to 150°C / min, and even more preferably 60°C / min to 100°C / min. When the molten resin composition is cooled in contact with a cast roll or the like, the surface temperature of the cast roll is preferably 20°C to 120°C, more preferably 40°C to 100°C, and even more preferably 60°C to 100°C. By rapidly cooling the resin composition containing vinylidene fluoride polymer and alkylquaternary ammonium sulfate, the proportion of α-crystals and the proportion of β-crystals of the crystallized vinylidene fluoride polymer can be reduced.

[0046] The cooling method is not particularly limited; any cooling method appropriate to the molding method should be adopted.

[0047] 3. Applications of Gas Barrier Sheets The applications of gas barrier sheets are not limited and can be used as liners for hydrogen tanks, liners for fuel tanks, and films for packaging materials. Of these, applications requiring high gas barrier properties and flexibility (especially resistance to yielding during deformation) are preferred, such as liners for hydrogen tanks.

[0048] Figure 1A is a schematic cross-sectional view showing the general configuration of a hydrogen tank having a gas barrier sheet as a liner according to this embodiment. Figure 1B is a schematic cross-sectional view showing the layer configuration of the hydrogen tank.

[0049] The hydrogen tank 100 can be, for example, a substantially cylindrical sealed container having a liner 110, a pressure-resistant layer 120, and an outer layer 130. Furthermore, at both ends of the hydrogen tank 100 in the longitudinal direction, there are fittings 142 and 144 that function as openings for injecting or releasing hydrogen, and as mounting parts for attaching pipes and valves.

[0050] Liner 110 constitutes the innermost layer of the hydrogen tank 100 and is positioned in contact with hydrogen gas to prevent leakage of hydrogen gas. Liner 110 is formed from the gas barrier sheet described above. Liner 110 can be manufactured, for example, by injection molding or blow molding of a resin composition containing the vinylidene fluoride polymer and alkylquaternary ammonium sulfate described above.

[0051] The pressure-resistant layer 120 is a layer that covers the outside of the liner 110 to prevent the tank from rupturing due to high-pressure hydrogen gas. The pressure-resistant layer 120 is made of fiber-reinforced resin or the like. The pressure-resistant layer 120 may have a configuration in which multiple layers of carbon fiber-reinforced resin or glass fiber-reinforced resin are arranged. The pressure-resistant layer 120 can be manufactured by welding a tape-shaped fiber-reinforced resin to the liner 110, to which the nozzles 142 and 144 are attached, using a method such as filament winding.

[0052] The outer layer 130 is a layer that covers the outside of the pressure-resistant layer 120 to protect the liner 110 and the pressure-resistant layer 120 from external friction and impact, and to prevent deterioration of the liner 110 and the pressure-resistant layer 120 due to ultraviolet rays, etc. The outer layer 130 can be manufactured by known coating methods or the like.

[0053] Such a hydrogen tank 100 has a liner 110 that has high gas barrier properties and is highly flexible, making it resistant to yielding even when deformed. Therefore, even if pressure changes due to the injection and release of hydrogen gas are repeated, damage to the liner 110 is unlikely to occur. As a result, it has higher durability than conventional hydrogen tanks 100.

[0054] 1. Preparation of Materials Two types of vinylidene fluoride polymers were prepared as follows: • PVDF1: A vinylidene fluoride homopolymer produced by the same method as Example 4 of International Publication No. 2006 / 061988. • PVDF2: KF#1000 (vinylidene fluoride homopolymer) manufactured by Kureha Corporation.

[0055] The following three types of quaternary organic compound salts were prepared: • TBAHS: Tetrabutylammonium bisulfate (melting point 170-175°C) • TAP: Tetrabutylammonium perchlorate (melting point 211-215°C) • BTPC: Benzyltriphenylphosphonium chloride (melting point 323-332°C)

[0056] 2. Preparation of molded articles of resin composition 100.0 parts by mass of PVDF1 was mixed with TBAHS at a ratio of 1.0 part by mass. Then, the mixture was extruded using a co-screw extruder (TEM-26, manufactured by Toshiba Machine Co., Ltd.) at a cylinder temperature of 200°C and a screw rotation speed of 120 rpm to obtain pelletized resin composition 1.

[0057] The obtained pelletized resin composition 1 was extruded using an extrusion molding machine (Union Plastics, BO-1) at a cylinder temperature of 230°C. Next, the molten resin was taken up by a cast roll at a set temperature of 60°C to produce a sheet-like molded body 1. The thickness of the molded body was measured five times per sample using a linear gauge (Ono Sokki Co., Ltd., DG-925) and the average value was calculated. This average value was taken as the thickness of the molded body.

[0058] Molded bodies 2 to 17 were prepared by changing the type of vinylidene fluoride polymer, the type and amount of the quaternary organic compound salt, and the cooling method.

[0059] Table 1 shows the types of vinylidene fluoride polymers, the types and amounts of quaternary organic compound salts used in the preparation of molded bodies 1 to 17, and the cooling methods. The amount of quaternary organic compound salt added is the amount added per 100.0 parts by mass of vinylidene fluoride polymer. In experiments where slow cooling was used, the cast roll temperature was set to 160°C.

[0060]

[0061] 3. Evaluation of Molded Products 3-1. Ratio of Crystal Forms The obtained molded products were subjected to FT-IR measurements by the ATR method using a Fourier transform infrared spectrophotometer (FT / IR-4100 type A, JASCO Corporation) and a polarized single-reflection ATR (ATR PRO610P-S, JASCO Corporation). The obtained FT-IR spectra were measured from 400 to 1500 cm⁻¹. －１ Within this range, absorption peaks characteristic of α, β, and γ crystals were identified. The characteristic peak of the α crystal was 614 cm⁻¹. －１ and 763 cm －１ The characteristic peak of the β crystal appears at 1275 cm⁻¹. －１ The characteristic peak of the γ crystal appears at 1234 cm⁻¹. －１ These peaks appear. The presence of each phase was confirmed based on these peaks. Next, the height of the absorption peak was measured. 1275 cm －１ and 1234cm －１ The peaks were 1260 cm each. -1 Nearby and 1220 cm -1 The difference in height between the valleys (lowest points) appearing nearby and each peak was calculated, and based on this, the ratio of β crystals F(β) was calculated using formula (1) and the ratio of γ crystals F(γ) was calculated using formula (2) using the P2VHR method described in Non-Patent Document 1.

[0062]

[0063]

[0064] Note that in equations (1) and (2), ΔH Β’ 1275 cm －１ The difference in height between the peak and the valley, ΔH γ’ 1234 cm－１ This shows the difference in height between the peak and the valley. Also, F ＥＡ This represents the overall proportion of the electroactive phase (β-crystal and γ-crystal), and was calculated using formula (3).

[0065]

[0066] In formula (3), I ＥＡ 840cm －１ Absorption intensity, I ７６３ 763cm －１ Absorption intensity, K ８４０＊ and K ７６３ Each is 840 cm －１ and 763 cm －１ This is the absorption coefficient.

[0067] Then, the values ​​obtained by subtracting F(β) and F(γ) from 100% were defined as the proportion of α crystals.

[0068] Then, from the obtained ratios of α-crystals and β-crystals, the ratio of β-crystals to α-crystals (β-crystal / α-crystal) was calculated.

[0069] 3-2. The phase difference of the molded body obtained using an orientation phase difference / elliptic deflection measuring device (KOBRA-HBR, manufactured by Oji Instruments Co., Ltd.) is measured, and the phase difference (R) at a measurement wavelength of 589 nm is determined. ５８９ Using the ) and the thickness of the molded body, the birefringence (Δn) was calculated using the following formula: Birefringence (Δn) = R ５８９ [nm] / Molded body thickness [μm]

[0070] 3-3. Oxygen Permeability Coefficient The oxygen permeability of the obtained molded body was measured using an oxygen permeability measuring device (OX-TRAN2 / 22, manufactured by MOCON Corporation) in accordance with JIS K-7126-2. At this time, the measurement temperature was set to 23°C and the measurement humidity to 0%RH, and the average value of five points after equilibrium was reached was taken as the oxygen permeability. Using the obtained oxygen permeability and the thickness of the molded body, the oxygen permeability coefficient was calculated using the following formula: Oxygen permeability coefficient [cm ３ mm / m ２ ・day・atm] = oxygen permeability [cm ３ / m ２ [day / atm] × Molded body thickness [mm]

[0071] 3-4. Yield point strain The obtained press sheet was punched out into the shape of ASTM D638 Type 4 to produce dumbbell pieces. The obtained dumbbell pieces were subjected to a tensile test at room temperature using a Shimadzu Autograph AGS-1KNJ at a tensile speed of 50 mm / sec.

[0072] Table 2 shows the evaluation results for molded bodies 1 to 17.

[0073]

[0074] As is clear from Tables 1 and 2, a gas barrier sheet containing a vinylidene fluoride polymer and an alkyl quaternary ammonium sulfate or alkyl quaternary ammonium sulfite, wherein the content of the alkyl quaternary ammonium sulfate and alkyl quaternary ammonium sulfite is 0.7 parts by mass or more and 5.0 parts by mass or less per 100.0 parts by mass of the vinylidene fluoride polymer, the ratio of α-crystals to the total crystalline form of the vinylidene fluoride polymer is 30% or less, and the ratio of β-crystals is 20% or more, exhibited high gas barrier properties and was resistant to yielding even when deformed.

[0075] This application claims priority to Japanese Patent Application No. 2025-056408, filed on 28 March 2025. The matters described in the original specification, claims and drawings of said application are incorporated herein by reference.

[0076] According to the present invention, a gas barrier sheet is provided that has high gas barrier properties and high durability even when subjected to repeated deformation.

[0077] 100 Hydrogen tank 110 Liner 120 Pressure layer 130 Outer layer 142, 144 Valve

Claims

1. A gas barrier sheet comprising a vinylidene fluoride polymer and an alkyl quaternary ammonium sulfate or alkyl quaternary ammonium sulfite, wherein the content of the alkyl quaternary ammonium sulfate and alkyl quaternary ammonium sulfite is 0.7 parts by mass or more and 5.0 parts by mass or less per 100.0 parts by mass of the vinylidene fluoride polymer, the ratio of α-crystals to the total crystalline form of the vinylidene fluoride polymer is 30% or less, and the ratio of β-crystals to the total crystalline form of the vinylidene fluoride polymer is 20% or more.

2. The gas barrier sheet according to claim 1, wherein the ratio of α-crystals to the total crystalline form of the vinylidene fluoride polymer is 10% or more and 30% or less, and the ratio of β-crystals to the total crystalline form of the vinylidene fluoride polymer is 20% or more and 80% or less.

3. The gas barrier sheet according to claim 1, wherein the ratio of the β crystals to the α crystals (β crystals / α crystals) is 2.0 or more and 10.0 or less.

4. The gas barrier sheet according to claim 1, wherein the ratio of γ crystals to the total crystalline form of the vinylidene fluoride polymer is 80% or less.

5. The oxygen permeability coefficient at 23°C is 6.0 [cm²]. ３ mm / (m) ２ The gas barrier sheet according to claim 1, wherein the temperature is less than or equal to [day / atm].

6. The birefringence Δn is 0.001 × 10⁻⁶ －３ 30 x 10 －３ The gas barrier sheet according to claim 1, which is as follows:

7. The gas barrier sheet according to claim 1, wherein the yield strain in a tensile test is 13% or more.

8. A tank comprising a gas barrier sheet as a liner according to any one of claims 1 to 7.

9. The tank according to claim 8, which is a hydrogen tank.

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