High-dielectric low-loss intrinsic polyimide film as well as preparation method and application thereof

Abstract

The invention relates to a high-dielectric low-loss intrinsic polyimide film as well as a preparation method and application thereof. The film is prepared from a diamine system and a dianhydride system through copolymerization-imidization, the diamine system comprises the following components in molar ratio: 40 to 60 mol percent of high dipole metal coordination diamine and 40 to 60 mol percent of cyano functional diamine; the dianhydride system comprises 50 to 80 mol% of fluorine-containing rigid dianhydride and 20 to 50 mol% of auxiliary rigid dianhydride according to a molar ratio. According to the intrinsic polyimide film, the dielectric constant, the breakdown strength and the tensile strength can be improved at the same time, dielectric loss cannot be increased, the intrinsic polyimide film can serve as a base material of an automobile film capacitor, a 5G / 6G base station high-frequency packaging body and a flexible electronic device, inorganic filler does not need to be added in the preparation process, and film interface defects are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular dielectric materials, in particular to a high-dielectric low-loss intrinsic polyimide film, a preparation method and application thereof. BACKGROUND

[0002] Polyimide (PI) film is widely used in 5G / 6G communication, electric vehicle battery management system and other fields due to its excellent thermal stability, mechanical properties and insulation. However, the dielectric constant of intrinsic PI film is generally less than 5 at a test frequency of 150 kHz, which is difficult to meet the demand of high energy storage density devices such as supercapacitors and film capacitors for a dielectric constant greater than 10. If polar groups (such as urea groups and cyano groups) are introduced to improve the dielectric constant, the dielectric loss (Df) will increase to more than 0.005, and the breakdown voltage and mechanical properties will decrease significantly.

[0003] In the prior art, the mainstream scheme for improving the dielectric constant of intrinsic PI film is inorganic filler modification, such as adding BaTiO3 and TiO2 nanoparticles, which can make the dielectric constant reach more than 20, but has the following defects: (1) poor interface compatibility between the filler and the PI matrix, resulting in high dielectric loss and decreased breakdown voltage; (2) uneven dispersion of the filler can cause stress concentration, leading to decreased tensile strength of the film; (3) ultrasonic dispersion and surface modification are required, and the composite process is complex, resulting in high production cost and difficulty in large-scale production.

[0004] In summary, there is a lack of intrinsic PI film that can simultaneously improve the dielectric constant, breakdown strength and tensile strength without increasing the dielectric loss in the prior art. SUMMARY

[0005] Therefore, it is necessary to provide a high-dielectric low-loss intrinsic polyimide film, a preparation method and application thereof to simultaneously improve the dielectric constant, breakdown strength and tensile strength without increasing the dielectric loss.

[0006] In a first aspect, the present application provides a high-dielectric low-loss intrinsic polyimide film prepared from a diamine system and a dianhydride system by copolymerization-imidization. The diamine system includes, by mole ratio, 40-60 mol% of high-dipole metal coordination diamine and 40-60 mol% of cyano functional diamine. The dianhydride system includes, by mole ratio, 50-80 mol% of fluorine-containing rigid dianhydride and 20-50 mol% of auxiliary rigid dianhydride.

[0007] Preferably, the high-dipole metal coordination diamine is selected from at least one of o-phenanthroline-copper (II) coordination diamine, o-phenanthroline-nickel (II) coordination diamine and o-phenanthroline-cobalt (II) coordination diamine.

[0008] Preferably, the cyano-functional diamine is selected from at least one of 2,6-diaminobenzonitrile and 3,5-diaminobenzonitrile.

[0009] Preferably, the fluorine-containing rigid dianhydride is selected from at least one of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 2,2'-bis(trifluoromethyl)-4,4'-biphenyl dianhydride. The auxiliary rigid dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0010] In a second aspect, the present application provides a preparation method of a high-dielectric low-loss intrinsic polyimide film, comprising the following steps: Step 1, synthesis of polyamic acid: under the protection of inert gas, high-dipole metal coordination diamine and cyano-functional diamine are dissolved in N-methylpyrrolidone, and stirred at 25-35℃ for 30-60min; Then, the fluorine-containing rigid dianhydride and the auxiliary rigid dianhydride are added, and stirred at 35-45℃ for 4-6h, to obtain a polyamic acid solution with a solid content of 15-20wt% and a viscosity of 8000-12000cP; Step 2, casting film formation: the polyamic acid solution is coated on a stainless steel substrate, and dried at 40-60℃ for 2-4h to obtain a pre-film; Step 3, ladder imidization: the pre-film is sequentially heated at 120℃ / 1h, 180℃ / 1h, 250℃ / 1h and 310-340℃ / 0.5h, and peeled after cooling to obtain a high-dielectric low-loss intrinsic polyimide film.

[0011] Preferably, the casting gap in step 2 is 50-100μm, and the pre-film thickness is 20-50μm.

[0012] In a third aspect, the present application further provides applications of the above high-dielectric low-loss intrinsic polyimide film or the high-dielectric low-loss intrinsic polyimide film prepared by the above preparation method in preparing automobile film capacitors, 5G / 6G base station high-frequency packaging bodies and flexible electronic devices.

[0013] Preferably, the high-dielectric low-loss intrinsic polyimide film is used as a substrate of an automobile film capacitor, a 5G / 6G base station high-frequency packaging body and a flexible electronic device.

[0014] The present application has the following advantages: (1) The high dielectric and low loss intrinsic polyimide film of the present invention has high polarizability of metal ions such as Cu²⁺, Ni²⁺ and Co²⁺ in the molecular structure of the high dipolar metal coordinated diamine, which can significantly improve the dielectric constant. The rigid ring of o-phenanthroline can restrict dipole relaxation and reduce dielectric loss. The low polarizability of fluorine atoms in the fluorinated rigid dianhydride can suppress dielectric loss. The rigid biphenyl or hexafluoroisopropylene structure can improve the film density and enhance the breakdown voltage and tensile strength. The cyano functional diamine can help improve the dielectric constant. The addition of trace amounts can avoid the increase in loss caused by dipole agglomeration. The auxiliary rigid dianhydride can further enhance the rigidity of the main chain and improve the mechanical strength and thermal stability of the film. (2) The high dielectric and low loss intrinsic polyimide film of the present invention does not require the addition of inorganic fillers during preparation, thus avoiding defects at the film interface. The film has excellent uniformity and the preparation process is compatible with existing casting-imidization industrial equipment, which can be directly mass-produced. (3) The high dielectric and low loss intrinsic polyimide film of the present invention has a dielectric constant ≥20, dielectric loss ≤0.002, DC breakdown voltage ≥200V / μm, and tensile strength ≥100MPa at a test frequency of 150Hz. The film of the present invention can simultaneously improve dielectric constant, breakdown strength and tensile strength without increasing dielectric loss. Detailed Implementation

[0015] To facilitate understanding of the present invention, a more comprehensive description will be given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0016] In one embodiment, a high-dielectric-low-loss intrinsic polyimide film is prepared by copolymerization-iminoization of a diamine system and a dianhydride system.

[0017] The diamine system, measured by molar ratio, includes 40-60 mol% of a high-dipolar metal-coordinated diamine and 40-60 mol% of a cyanofunctional diamine; the dianhydride system, measured by molar ratio, includes 50-80 mol% of a fluorinated rigid dianhydride and 20-50 mol% of an auxiliary rigid dianhydride.

[0018] Specifically, the high-dipolar metal-coordinated diamine is selected from at least one of o-phenanthroline-copper(II)-coordinated diamine, o-phenanthroline-nickel(II)-coordinated diamine, and o-phenanthroline-cobalt(II)-coordinated diamine. The high-dipolar metal-coordinated diamine molecular structure contains metal ions such as Cu²⁺, Ni²⁺, and Co²⁺, which exhibit high polarizability, significantly improving the dielectric constant of polyimide films. Furthermore, the rigid o-phenanthroline ring restricts dipole relaxation, reducing dielectric loss.

[0019] The cyanofunctionalized diamine is selected from at least one of 2,6-diaminobenzonitrile and 3,5-diaminobenzonitrile. The cyano group (-CN, dipole moment 3.9D) can help improve the dielectric constant, and its addition in small amounts can avoid increased losses caused by dipole aggregation.

[0020] The fluorinated rigid dianhydride is selected from at least one of 4,4'-(hexafluoroisopropene)phthalic anhydride and 2,2'-bis(trifluoromethyl)-4,4'-biphenyl dianhydride; the auxiliary rigid dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride. The low polarizability of fluorine atoms in the fluorinated rigid dianhydride can suppress dielectric loss, and the rigid biphenyl / hexafluoroisopropene structure can improve film density, breakdown voltage, and mechanical strength. The auxiliary rigid dianhydride further enhances the rigidity of the main chain, improving mechanical strength and thermal stability.

[0021] The high-dielectric-low-loss intrinsic polyimide film of this embodiment can simultaneously improve dielectric constant, breakdown strength and tensile strength without increasing dielectric loss.

[0022] In one embodiment, a method for preparing a high-dielectric-low-loss intrinsic polyimide film includes the following steps: Step 1: Polyamic acid synthesis; Under inert gas protection, a high-dipolar metal-coordinated diamine and a cyano-functionalized diamine are dissolved in N-methylpyrrolidone and stirred at 25-35°C for 30-60 min. Nitrogen is preferred as the inert gas.

[0023] Then, fluorinated rigid dianhydride and auxiliary rigid dianhydride are added, and the mixture is stirred at 35~45℃ for 4~6 hours to obtain a polyamic acid solution with a solid content of 15~20wt% and a viscosity of 8000~12000cP.

[0024] Step 2: Casting film; Coat a polyamic acid solution onto a stainless steel substrate and dry at 40~60℃ for 2~4 hours to obtain a pre-formed film.

[0025] Specifically, in step 2, the casting gap is 50~100μm and the pre-film thickness is 20~50μm.

[0026] Step 3, stepwise imidization: The pre-formed film is heated in the following order: 120℃ / 1h, 180℃ / 1h, 250℃ / 1h, 310~340℃ / 0.5h. After cooling, it is peeled off to obtain a high dielectric and low loss intrinsic polyimide film.

[0027] The high dielectric and low loss intrinsic polyimide film preparation method of this embodiment does not require the addition of inorganic fillers, thus avoiding film interface defects. The film has excellent uniformity and the preparation process is compatible with existing casting-imidization industrial equipment, which can be directly mass-produced.

[0028] In one embodiment, the high-dielectric-low-loss intrinsic polyimide film described above or the high-dielectric-low-loss intrinsic polyimide film prepared by the above preparation method is used in the preparation of automotive film capacitors, 5G / 6G base station high-frequency packages, and flexible electronic devices.

[0029] Specifically, high-dielectric- and low-loss intrinsic polyimide films are used as substrates for automotive film capacitors, 5G / 6G base station high-frequency packages, and flexible electronic devices.

[0030] The following are specific examples.

[0031] Example 1 The high-dielectric-low-loss intrinsic polyimide film of this embodiment is prepared by copolymerization-iminolation of a diamine system and a dianhydride system. The total molar amount of the diamine and dianhydride systems is 100 mmol. The diamine system consists of 30 mol% o-phenanthroline-copper(II) coordinated diamine and 20 mol% 2,6-diaminobenzonitrile; the dianhydride system consists of 28 mol% 4,4'-(hexafluoroisopropene)phthalic anhydride and 22 mol% 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0032] The method for preparing high-dielectric- and low-loss intrinsic polyimide films in this embodiment includes the following steps: (1) Synthesis of polyamic acid: Under inert gas protection, o-phenanthroline-copper(II) coordinated diamine and 2,6-diaminobenzonitrile were dissolved in N-methylpyrrolidone and stirred at 30°C for 45 min; Then 4,4'-(hexafluoroisopropene) phthalic anhydride and 3,3',4,4'-biphenyltetracarboxylic anhydride were added, and the mixture was stirred at 30°C for 5 hours to obtain a polyamic acid solution with a solid content of 18 wt% and a viscosity of 8000~12000 cP. (2) Casting film: The polyamic acid solution was coated onto a stainless steel substrate and dried at 50°C for 3 hours to obtain a pre-cast film; the casting gap was 80 μm.

[0033] (3) Stepwise imidization: The pre-formed film is heated in the order of 120℃ / 1h, 180℃ / 1h, 250℃ / 1h, and 320℃ / 0.5h, and then peeled off after cooling to obtain a high dielectric and low loss intrinsic polyimide film.

[0034] Example 2 The other features in this embodiment are basically the same as those in Embodiment 1, except that: The diamine system consists of 20 mol% o-phenanthroline-copper(II) coordinated diamine and 30 mol% 2,6-diaminobenzonitrile; the dianhydride system consists of 35 mol% 4,4'-(hexafluoroisopropene) phthalic anhydride and 15 mol% 3,3',4,4'-biphenyltetracarboxylic dianhydride; and the polyamic acid solution has a solid content of 18 wt%.

[0035] The casting gap is 80 μm, the pre-drying temperature is 50℃, and the time is 3 h.

[0036] Example 3 The other features in this embodiment are basically the same as those in Embodiment 1, except that: The diamine system consisted of 28 mol% o-phenanthroline-nickel(II) coordinated diamine and 22 mol% 3,5-diaminobenzonitrile; the dianhydride system consisted of 32 mol% 2,2'-bis(trifluoromethyl)-4,4'-biphenyl dianhydride and 18 mol% 3,3',4,4'-biphenyltetracarboxylic dianhydride; and the polyamic acid solution had a solid content of 17 wt%.

[0037] The casting gap was 90 μm, the pre-drying temperature was 45℃, and the time was 3.5 h; the imidization program was: 120℃ (1 h) → 180℃ (1 h) → 250℃ (1 h) → 330℃ (0.5 h).

[0038] Example 4 The other features in this embodiment are basically the same as those in Embodiment 1, except that: The diamine system consists of 25 mol% o-phenanthroline-cobalt(II) coordinated diamine and 25 mol% 3,5-diaminobenzonitrile; the dianhydride system consists of 40 mol% 4,4'-(hexafluoroisopropene) phthalic anhydride and 18 mol% 3,3',4,4'-biphenyltetracarboxylic dianhydride; and the polyamic acid solution has a solid content of 19 wt%.

[0039] The casting gap was 85 μm, the pre-drying temperature was 55℃, and the time was 2.5 h. The imidization process was: 120℃ (1 h) → 180℃ (1 h) → 250℃ (1 h) → 310℃ (0.5 h).

[0040] Example 5 The other features in this embodiment are basically the same as those in Embodiment 1, except that: The diamine system consists of: 20 mol% o-phenanthroline-copper(II) coordinated diamine, 15 mol% o-phenanthroline-nickel(II) coordinated diamine, and 15 mol% 2,6-diaminobenzonitrile; the dianhydride system consists of: 30 mol% 4,4'-(hexafluoroisopropene) phthalic anhydride and 20 mol% 3,3',4,4'-biphenyltetracarboxylic dianhydride; the polyamic acid solution has a solid content of 18 wt%.

[0041] The casting gap is 85 μm, the pre-drying temperature is 55℃, and the time is 2.5 h.

[0042] Example 6 The other features in this embodiment are basically the same as those in Embodiment 1, except that: The diamine system consists of: 20 mol% o-phenanthroline-nickel(II) coordinated diamine, 10 mol% o-phenanthroline-cobalt(II) coordinated diamine, and 20 mol% 3,5-diaminobenzonitrile; the dianhydride system consists of: 25 mol% 2,2'-bis(trifluoromethyl)-4,4'-biphenyl dianhydride and 25 mol% 3,3',4,4'-biphenyltetracarboxylic dianhydride; the polyamic acid solution has a solid content of 16 wt%.

[0043] The casting gap was 85 μm, the pre-drying temperature was 55℃, and the time was 2.5 h. The imidization process was: 120℃ (1 h) → 180℃ (1 h) → 250℃ (1 h) → 340℃ (0.5 h).

[0044] Comparative Example 1 In the comparative example, a polyimide film was prepared using a cyanide-containing polyimide scheme. It was prepared by copolymerization-imidization of 20 mol% 2,6-diaminobenzonitrile, 80 mol% 4,4'-diaminodiphenyl ether, and 100 mol% 3,3',4,4'-biphenyltetracarboxylic dianhydride. The preparation method was the same as in Example 1.

[0045] The polyimide films prepared in Examples 1-6 and Comparative Example 1 were tested for film thickness, dielectric constant, dielectric loss, breakdown voltage, glass transition temperature and tensile strength. The test results are shown in Table 1 below.

[0046] The dielectric constant (εᵣ) and dielectric loss (Df) were measured using an impedance analyzer (Agilent 4294A) at a frequency of 150 Hz and a temperature of 25 °C. The DC breakdown voltage was measured using a breakdown voltage tester (Keithley 2410) at a voltage ramp rate of 50 V / s and a temperature of 25 °C. Tensile strength was measured using a universal testing machine (Instron 5969) at a tensile rate of 5 mm / min, according to GB / T 13022-2013.

[0047] Table 1. Test results of different properties of different polyimide films As shown in Table 1 above, the intrinsic polyimide films obtained in Examples 1-6 of this invention have a dielectric constant ≥20, dielectric loss ≤0.002, DC breakdown voltage ≥200V / μm, and tensile strength ≥100MPa at 150Hz. Compared with the prior art cyanide-containing intrinsic polyimide films that improve dielectric constant, the dielectric constant is significantly improved, while the dielectric loss is only about half that of Comparative Example 1, and the breakdown voltage is also significantly improved. The high dielectric and low loss intrinsic polyimide film of this invention can simultaneously improve dielectric constant, breakdown strength, and tensile strength without increasing dielectric loss.

[0048] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high-dielectric low-loss intrinsic polyimide film, characterized by, Prepared by copoly-imidization of a diamine system and a dianhydride system; The diamine system comprises, in terms of molar ratio, 40-60 mol% of a high-dipole metal coordination diamine and 40-60 mol% of a cyano-functional diamine; The dianhydride system comprises, in terms of molar ratio, 50-80 mol% of a fluorine-containing rigid dianhydride and 20-50 mol% of an auxiliary rigid dianhydride.

2. The high-dielectric low-loss intrinsic polyimide film according to claim 1, characterized by, The high-dipole metal coordination diamine is selected from at least one of phenanthroline-copper (II) coordination diamine, phenanthroline-nickel (II) coordination diamine and phenanthroline-cobalt (II) coordination diamine.

3. The high-dielectric low-loss intrinsic polyimide film according to claim 2, characterized by, The cyano-functional diamine is selected from at least one of 2,6-diaminobenzonitrile and 3,5-diaminobenzonitrile.

4. The high-dielectric low-loss intrinsic polyimide film according to claim 3, characterized by, The fluorine-containing rigid dianhydride is selected from at least one of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride and 2,2'-bis(trifluoromethyl)-4,4'-biphenyl dianhydride; The auxiliary rigid dianhydride is 3,3',4,4'-biphenyl tetracarboxylic dianhydride.

5. A method for preparing a high-dielectric-low-loss intrinsic polyimide film, characterized in that, Comprising the following steps: Step 1, polyamic acid synthesis: under inert gas protection, the high-dipole metal coordination diamine and the cyano-functional diamine are dissolved in N-methyl pyrrolidone, stirred at 25-35℃ for 30-60 min; Then the fluorine-containing rigid dianhydride and the auxiliary rigid dianhydride are added, stirred at 35-45℃ for 4-6 h, to obtain a polyamic acid solution with a solid content of 15-20 wt% and a viscosity of 8000-12000 cP; Step 2, casting film formation: the polyamic acid solution is coated on a stainless steel substrate, dried at 40-60℃ for 2-4 h to obtain a pre-film; Step 3, stepwise imidization: the pre-film is sequentially heated at 120℃ / 1h, 180℃ / 1h, 250℃ / 1h and 310-340℃ / 0.5h, and peeled after cooling to obtain a high-dielectric low-loss intrinsic polyimide film.

6. The method of claim 5, wherein the method further comprises the step of: The casting gap in step 2 is 50-100 μm, and the pre-film thickness is 20-50 μm. ​ 7. Use of the high-dielectric low-loss intrinsic polyimide film of any one of claims 1 to 4 or the high-dielectric low-loss intrinsic polyimide film prepared by the preparation method of claim 5 in the preparation of an automotive film capacitor, a 5G / 6G base station high-frequency package and a flexible electronic device.

8. Use according to claim 7, characterized in that, The high-dielectric low-loss intrinsic polyimide film is used as a substrate for an automotive film capacitor, a 5G / 6G base station high-frequency package and a flexible electronic device.

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