A high-thermal-conductivity fluoropolymer piezoelectric film and a method of making the same

Abstract

The application relates to a high-thermal-conductivity fluorine-containing polymer piezoelectric film, which comprises a fluorine-containing polymer with a piezoelectric effect and isocyanate surface-modified montmorillonite, and the mass ratio of the fluorine-containing polymer to the montmorillonite is (50-95):(5-50). The fluorine-containing polymer piezoelectric film not only effectively improves the thermal conductivity and reduces the thermal resistance, but also is highly oriented and has more excellent electric insulation performance, and can be widely applied to capacitors, refrigeration, sensing and other fields.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymers, in particular to a high-thermal-conductivity fluoropolymer piezoelectric film and a preparation method thereof. BACKGROUND

[0002] At present, power equipment and electronic devices are developing towards high power density and high integration, especially the semiconductor industry, which is developing at a speed faster than Moore's Law. During the operation and working process of power equipment and electronic devices, a large amount of heat will be generated. If this heat cannot be efficiently transferred out, it will seriously affect the working efficiency, reliability and service life of the equipment and devices. Polymers are widely used as dielectric materials in power equipment and electronic devices, but most of the polymer materials have low thermal conductivity, which seriously restricts the improvement of the thermal management capability of various equipment.

[0003] At present, vinylidene fluoride-based dielectric materials are closely watched due to their high dielectric constant, but they have too high dielectric loss, which leads to intense heat release during use, and low thermal conductivity, which is easy to be melted and broken down. In the prior art, a large amount of inorganic, metal or carbon-based thermal conductive fillers are usually added to the polymer dielectric material to improve its thermal conductivity.

[0004] Japanese patent JP2021088621A discloses a thermal conductive resin composition using boron nitride as a filler. Metal nitride has high thermal conductivity, good electrical insulation performance, excellent high-temperature resistance and excellent dielectric performance, but it is expensive and can easily cause problems such as increased resin viscosity and decreased processing performance.

[0005] US20170005026 discloses a nanoparticle thermal interface agent for reducing thermal conductive resistance, which enhances the thermal conductivity of the material by adding gold or silver nanorods or nanowires with large aspect ratio. However, metal nanowires are expensive and not resistant to breakdown.

[0006] Chinese patent CN109593218A discloses a preparation method of a composite dielectric material and the composite dielectric material, which is obtained by compounding modified inorganic particles and grafted modified polyvinylidene fluoride-based copolymer, and has high dielectric constant, breakdown field strength, energy storage density and energy release efficiency. However, the inorganic particles in the dielectric material are uniformly and compatibly dispersed in the polymer matrix, which cannot effectively improve the thermal conductivity.

[0007] At present, the low thermal conductivity of fluoropolymers affects the further application of fluoropolymers in thin film capacitors.

[0008] The prior art technical solutions for adding fillers to increase thermal conductivity are either not uniformly dispersed, have poor compatibility, are high in cost, reduce processing performance, or cause degradation of electrical performance, and thus cannot be used as dielectric materials. In order to realize large-scale commercialization of the vinylidene fluoride-based dielectric material, it is urgent to find a technical method that can ensure electrical performance and improve thermal conductivity. SUMMARY

[0009] To solve the above problems, the present application provides a fluorine-containing polymer piezoelectric film with high thermal conductivity, which not only effectively improves the thermal conductivity and reduces the thermal resistance, but also has high orientation and excellent electrical insulation performance, and can be widely used in thin film capacitors.

[0010] The purpose of the present application is achieved by the following technical solutions:

[0011] A fluorine-containing polymer piezoelectric film with high thermal conductivity, comprising a fluorine-containing polymer with piezoelectric effect and montmorillonite surface modified by isocyanate, and the mass ratio of the fluorine-containing polymer to the montmorillonite is (50-95):(5-50).

[0012] The montmorillonite surface modified by isocyanate in the present application forms urethane with isocyanate, changes the original polarity of the surface of the montmorillonite, reduces the surface energy of the montmorillonite, makes the montmorillonite change from oil-repellent to oil-wet, and has better compatibility with the fluorine-containing polymer. The montmorillonite surface modified by isocyanate is highly oriented, forms a high-orientation chain connected to each other, and the montmorillonite can construct a continuous thermal conduction network in the fluorine-containing polymer matrix, so that heat can be conducted through the network, thereby significantly improving the thermal conductivity of the fluorine-containing polymer piezoelectric material while ensuring excellent electrical insulation performance. Specifically, the thermal conductivity of the fluorine-containing polymer piezoelectric film is >1 W / (m·K), the dielectric constant is >10, the breakdown field strength is >500 MV / m, and the energy release efficiency is ≥90%.

[0013] The thickness of the fluorine-containing polymer piezoelectric film is 1-1000 μm; preferably, the thickness of the fluorine-containing polymer piezoelectric film is 5-100 μm; more preferably, the thickness of the fluorine-containing polymer piezoelectric film is 10-30 μm.

[0014] The construction of the thermal conduction network and the types of polymer matrix, inorganic particles, modification method, and preparation method are all closely related. Similar inorganic particles and modification methods will exhibit different structures in different polymer matrices, so it is impossible to realize the construction of the thermal conduction network by simple analogy.

[0015] The amount of montmorillonite in the fluoropolymer piezoelectric film has an effect on the performance of the fluoropolymer piezoelectric film. Too high amount of montmorillonite will result in the mechanical performance of the fluoropolymer piezoelectric film being reduced and the film being unable to be formed. Too low amount of montmorillonite will result in the montmorillonite being unable to build a heat conduction path and the thermal conductivity of the fluoropolymer piezoelectric film being insufficiently improved. Preferably, the mass ratio of the fluoropolymer to the montmorillonite in the fluoropolymer piezoelectric film is (65-85):(15-35).

[0016] The fluoropolymer has a piezoelectric effect. Preferably, the fluoropolymer is at least one selected from polyvinylidene fluoride, poly(vinylidene fluoride-trifluoroethylene) or poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene). More preferably, the fluoropolymer is poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene).

[0017] The application further provides a preparation method of the fluoropolymer piezoelectric film.

[0018] S1. Surface modification of montmorillonite: under the protection of inert gas, the montmorillonite is activated and then reacted with isocyanate in organic solvent I to obtain surface-modified montmorillonite.

[0019] S2. Preparation of fluoropolymer-montmorillonite mixed solution: the surface-modified montmorillonite prepared in step S1, the fluoropolymer and organic solvent II are mixed to obtain a fluoropolymer-montmorillonite mixed solution.

[0020] S3. Preparation of fluoropolymer piezoelectric film: the fluoropolymer-montmorillonite mixed solution prepared in step S2 is used to prepare a fluoropolymer piezoelectric film by using a doctor blade method, the base temperature of the doctor blade platform is 30-120℃ and the moving speed of the doctor blade is 1-100 mm / s.

[0021] In the preparation method of the fluoropolymer piezoelectric film, specifically, in step S1, the montmorillonite has a sheet structure and an average diameter of 5-200 nm, preferably 10-50 nm; the isocyanate is preferably toluene-2,4-diisocyanate or diphenylmethane diisocyanate; the mass ratio of the montmorillonite to the isocyanate is 1:(1-0.1), preferably 1:(0.5-0.1), more preferably 1:(0.4-0.2). The inert gas is at least one selected from nitrogen, helium and argon; the organic solvent I is at least one selected from anhydrous toluene, benzene and n-hexane. If the reaction temperature of step S1 is too low, the isocyanate will not react with the montmorillonite. Specifically, the reaction temperature is 50-150℃, preferably 70-120℃, more preferably 80-100℃. The surface-modified montmorillonite by the isocyanate has a brown color from the original white color, indicating that the modifier isocyanate is coated on the surface of the montmorillonite.

[0022] In the step S2, the organic solvent II is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide or acetone. In order to make the fluoropolymer-montmorillonite mixture uniform, the isocyanate surface modified montmorillonite and fluoropolymer are dissolved in the organic solvent II respectively, and then mixed.

[0023] In the step S3, the base temperature of the doctor blade platform is 30-120℃, preferably 60-100℃, and the moving speed of the doctor blade is 1-100mm / s, preferably 5-20mm / s.

[0024] The fluoropolymer piezoelectric film prepared by the method has uniform thickness and is not easy to break.

[0025] The application further provides the application of the fluoropolymer piezoelectric film, which can be applied in the fields of capacitor, refrigeration, sensing, etc., and is particularly suitable for thin film capacitor.

[0026] Compared with the prior art, the application has the beneficial effects that:

[0027] 1. The fluoropolymer piezoelectric film effectively improves the thermal conductivity, reduces the capacitor interface thermal resistance, and is highly oriented.

[0028] 2. The fluoropolymer piezoelectric film has excellent electrical insulation and can be widely applied in thin film capacitor. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 (a) is the SEM picture of montmorillonite, Figure 1 (b) is the SEM picture of isocyanate surface modified montmorillonite;

[0030] Figure 2 (a) is the cross-sectional photo of the fluoropolymer piezoelectric film prepared in Example 1, Figure 2 (b) is the in-plane transmission diagram of heat flow in the fluoropolymer piezoelectric film prepared in Example 1;

[0031] Figure 3 is the temperature change curve diagram of the capacitor device under the use of 10kHz alternating current. DETAILED DESCRIPTION

[0032] The application will be further described in conjunction with specific examples, but the application is not limited to these specific examples. Those skilled in the art should realize that the application covers all alternatives, improvements and equivalents included in the scope of the claims.

[0033] Example 1

[0034] S1. Surface modification of montmorillonite (MMT): Put the montmorillonite into a three-necked flask, and heat to 250℃ under nitrogen protection for 2h; then add the activated montmorillonite and diphenyl methane diisocyanate (MDI) with a mass ratio of 1:0.3 under nitrogen protection, stir and mix in a certain amount of anhydrous toluene for 30min, and then heat to 90℃. After the reaction is completed, the three-necked flask is naturally cooled in air; then the sample in the container is washed with anhydrous toluene for 3 times, vacuum filtration, and finally the sample is vacuum dried at 40℃ to obtain the surface-modified montmorillonite (MDI@MMT);

[0035] S2. Preparation of fluoropolymer-montmorillonite mixed solution: 25 parts by weight of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) is added to 75 parts by weight of solvent N,N-dimethylformamide (DMF) and stirred at room temperature for 12h to obtain a P(VDF-TrFE-CTFE) solution; 1.91 parts by weight of MDI@MMT prepared in step S1 is mixed with 20 parts by weight of solvent N,N-dimethylformamide (DMF) and ultrasonicated for 20-40min, and then mixed with 80 parts by weight of the P(VDF-TrFE-CTFE) solution and stirred for 20-40min;

[0036] S3. Preparation of fluoropolymer piezoelectric film: The substrate temperature of the doctor blade platform is set to 70℃, the doctor blade moving speed is set to 10mm / s, then the uniformly stirred MDI@MMT / P(VDF-TrFE-CTFE) mixed solution is dropped in front of the doctor blade, and a 25μm thick fluoropolymer piezoelectric film is prepared by doctor blade drying.

[0037] Example 2

[0038] Example 2 is prepared according to Example 1, except that the weight ratio of P(VDF-TrFE-CTFE) to MDI@MMT used in step S2 is 83.3:16.7.

[0039] Example 3

[0040] Example 3 is prepared according to Example 1, except that the weight ratio of P(VDF-TrFE-CTFE) to MDI@MMT used in step S2 is 75.9:24.1.

[0041] Example 4

[0042] Example 4 is prepared according to Example 1, except that the weight ratio of P(VDF-TrFE-CTFE) to MDI@MMT used in step S2 is 68.9:31.3.

[0043] Example 5

[0044] Example 5 was prepared as in Example 1, except that toluene-2,4-diisocyanate was used instead of MDI.

[0045] Comparative Example 1

[0046] S1. Preparation of P(VDF-TrFE-CTFE) solution: 25 parts by weight of P(VDF-TrFE-CTFE) was added to 75 parts by weight of DMF, stirred at room temperature for 12 h to obtain a P(VDF-TrFE-CTFE) solution;

[0047] S2. Preparation of fluoropolymer piezoelectric film: the substrate temperature of the doctor blade platform was set to 70°C, the moving speed of the doctor blade was set to 10 mm / s, then the P(VDF-TrFE-CTFE) solution was dropped in front of the doctor blade, and a 25 μm thick fluoropolymer piezoelectric film was prepared by doctor blade drying.

[0048] Comparative Example 2

[0049] S1. Preparation of P(VDF-TrFE-CTFE) solution: 25 parts by weight of P(VDF-TrFE-CTFE) was added to 75 parts by weight of DMF, stirred at room temperature for 12 h to obtain a P(VDF-TrFE-CTFE) solution;

[0050] S2. Preparation of MMT / P(VDF-TrFE-CTFE) mixture: 1.91 parts by weight of MMT was mixed with 20 parts by weight of DMF for 20-40 min, then mixed with 80 parts by weight of the P(VDF-TrFE-CTFE) solution prepared in step S1, and stirred for 20-40 min;

[0051] S3. Preparation of fluoropolymer piezoelectric film: the substrate temperature of the doctor blade platform was set to 70°C, the moving speed of the doctor blade was set to 10 mm / s, then the uniformly stirred MMT / P(VDF-TrFE-CTFE) mixture was dropped in front of the doctor blade, and a 25 μm thick fluoropolymer piezoelectric film was prepared by doctor blade drying.

[0052] Comparative Example 3

[0053] Comparative Example 3 was prepared as in Example 1, except that KH550 silane coupling agent was used instead of MDI.

[0054] Comparative Example 4

[0055] Comparative Example 4 was prepared as in Example 1, except that dopamine was used instead of MDI.

[0056] Comparative Example 5

[0057] Preparation of Comparative Example 5 is the same as Example 1, except that trimethylol aminomethane is used instead of MDI.

[0058] Comparative Example 6

[0059] Preparation of Comparative Example 6 is the same as Example 1, except that silver nanowires are used instead of MMT.

[0060] Comparative Example 7

[0061] Preparation of Comparative Example 7 is the same as Example 1, except that polyurethane is used instead of P(VDF-TrFE-CTFE).

[0062] Comparative Example 8

[0063] Preparation of Comparative Example 8 is the same as Comparative Example 2, except that polyurethane is used instead of P(VDF-TrFE-CTFE).

[0064] The thermal conductivity of the films prepared in Examples 1-5 and Comparative Examples 1-8 is tested at room temperature using a Hot Disk thermal constant analyzer, and the test results and film components are shown in Table 1.

[0065] Table 1, film components and thermal conductivity of films prepared in Examples 1-5 and Comparative Examples 1-8

[0066]

[0067] As can be seen from Table 1, by comparison, the thermal conductivity of the films prepared in Examples 1-5 is significantly higher than that of Comparative Example 1, indicating that the thermal conductivity of the film with the addition of isocyanate surface modified montmorillonite is significantly improved compared with pure P(VDF-TrFE-CTFE); by comparing Example 1 and Comparative Example 2, it is shown that the montmorillonite modified by the method disclosed in the present application has a significantly better effect than the unmodified montmorillonite; Comparative Examples 3-5 show that modification of montmorillonite by KH550 silane coupling agent, dopamine, and trimethylol aminomethane cannot achieve the effect of increasing thermal conductivity; Comparative Example 6 shows that fillers such as silver nanowires cannot be used in the capacitor field; Comparative Examples 7 and 8 show that the isocyanate surface modified montmorillonite and the unmodified montmorillonite according to the present application do not have an improving effect on the thermal conductivity of polyurethane.

[0068] The energy storage performance of the films prepared in Example 1 and Comparative Example 1 is tested, and the results are shown in Table 2.

[0069] Table 2, energy storage performance of films prepared in Example 1 and Comparative Example 1

[0070]

[0071] As can be seen from Table 2, the thin film prepared in Example 1 has a significantly improved thermal conductivity, and a certain improvement in breakdown field strength, energy storage density and energy efficiency compared with the thin film prepared in Comparative Example 1.

[0072] In addition, the actual use temperature of the thin film capacitors prepared in Example 1 and Comparative Example 1 and a commercial polypropylene thin film capacitor (PP thin film capacitor) was tested under an alternating current of 10 kHz, and the results are shown in Table 3. Figure 3 The thin film capacitor prepared in Comparative Example 1 has a low thermal conductivity, and heat cannot be transferred in time, resulting in a rapid increase in temperature, which exceeds 100°C within 5 seconds. The thin film capacitor prepared in Example 1 has almost no increase in temperature within 5 seconds, and the temperature increases slightly after a long time of work, and the increase is smaller than that of the commercial PP thin film capacitor.

Claims

1. A high thermal conductivity fluoropolymer piezoelectric film, characterized by: The fluoropolymer piezoelectric film comprises a fluoropolymer having a piezoelectric effect and an isocyanate surface-modified montmorillonite, and the mass ratio of the fluoropolymer to the montmorillonite is (50-95):(5-50).

2. The fluoropolymer piezoelectric film according to claim 1, wherein: The fluoropolymer piezoelectric film has a thermal conductivity >1 W / (m·K), a dielectric constant >10, a breakdown field strength >500 MV / m, and an energy release efficiency ≥90%.

3. The fluoropolymer piezoelectric film according to claim 1, wherein: The fluoropolymer piezoelectric film has a thickness of 1-1000 μm.

4. The fluoropolymer piezoelectric film according to claim 1, wherein: The fluoropolymer is selected from at least one of polyvinylidene fluoride, poly(vinylidene fluoride-trifluoroethylene) or poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene).

5. A method of producing the fluoropolymer piezoelectric film according to claim 1, characterized by: The preparation method comprises the following steps: S1. Surface modification of montmorillonite: under inert gas protection, the montmorillonite is activated and then reacted with isocyanate in organic solvent I to obtain surface-modified montmorillonite; S2. Preparation of fluoropolymer-montmorillonite mixed solution: the surface-modified montmorillonite prepared in step S1, the fluoropolymer and organic solvent II are mixed to obtain a fluoropolymer-montmorillonite mixed solution; S3. Preparation of fluoropolymer piezoelectric film: the fluoropolymer-montmorillonite mixed solution prepared in step S2 is used to prepare a fluoropolymer piezoelectric film by using a doctor blade method, the base temperature of the doctor blade platform is 30-120 ℃, and the moving speed of the doctor blade is 1-100 mm / s.

6. The method for preparing a fluoropolymer piezoelectric thin film according to claim 5, characterized in that: In step S1, the montmorillonite has a sheet structure and an average diameter of 5-200 nm; the isocyanate is toluene-2,4-diisocyanate or diphenylmethane diisocyanate; and the organic solvent I is selected from at least one of anhydrous toluene, benzene and n-hexane.

7. The method for preparing a fluoropolymer piezoelectric thin film according to claim 5, characterized in that: In step S1, the reaction temperature is 50-150 ℃.

8. The method for preparing a fluoropolymer piezoelectric thin film according to claim 5, characterized in that: In step S2, the organic solvent II is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide and acetone.

9. Use of the fluoropolymer piezoelectric film according to claim 1, characterized in that: The fluoropolymer piezoelectric film is applied to the fields of capacitors, refrigeration and sensing.

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