A polypropylene resin composition, a high-temperature resistant polymer film containing the same, and a preparation method and application thereof

Abstract

The present invention provides a polypropylene resin composition, a high-temperature resistant polymer film containing the same, and a preparation method and application thereof. By mass percentage, the polypropylene resin composition includes 79.7-98.9% of polypropylene resin, 1-20% of cycloolefin copolymer, and 0.1-0.3% of radiation crosslinking agent; the glass transition temperature of the cycloolefin copolymer is 120-160 °C; in the present invention, the film including the polypropylene resin composition has a high heat distortion temperature and a low thermal shrinkage rate, good high-temperature resistance, does not affect the dielectric properties of the film capacitor, has a small dielectric loss, can be biaxially stretched at a high draw ratio, and has a low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of capacitor materials, and particularly relates to a polypropylene resin composition, a high-temperature resistant polymer film containing the same, and a preparation method and application thereof. Background Art

[0002] Film capacitors are widely used in various fields such as wind power converters, photovoltaic inverters, new energy vehicle inverters, and high-voltage direct current power transmission due to their non-polarity, high insulation impedance, excellent frequency characteristics, and small dielectric loss. Polypropylene film is the main dielectric material of film capacitors due to its high breakdown field strength, small dielectric loss, excellent self-healing property, high energy storage density, ultra-thin ability, and low cost, and has a wide range of applications in modern electronic and electrical equipment; among them, biaxially oriented polypropylene film is the primary choice as the dielectric material for capacitors. However, the biaxially oriented polypropylene film has poor high-temperature resistance. The upper limit of the operating temperature of the existing polypropylene film capacitors is about 110°C. When the operating temperature of the capacitor exceeds 85°C, most of the film properties decline, such as the sharp decrease in the breakdown strength and the sharp increase in the leakage conductance loss, which easily leads to the operation failure of the capacitor and affects the safe and stable operation of the entire equipment system.

[0003] In the prior art, the heat resistance of polypropylene film is often improved by adding additives, inorganic particles, or cycloolefin copolymers to polypropylene. After adding additives and inorganic particles to polypropylene to form a film, the dielectric constant difference between the additives and inorganic particles and the polymer matrix in the film is too large, which will increase the local electric field and lead to a decrease in the electrical strength of the film and a significant increase in the dielectric loss, seriously affecting the dielectric properties of the capacitor film; in addition, to effectively improve the related properties of polypropylene film, various additives are usually added to the formulation and a relatively high content of additives is added. However, too many types or contents of additives will result in poor dispersion and uneven distribution of the additives in the system, and impurities are easily generated, further reducing the dielectric properties of the polypropylene film and affecting the use of the polypropylene film; after adding cycloolefin copolymer to polypropylene resin to form a film, although no physical defects will appear in the polymer capacitor film, the addition of cycloolefin copolymer can only slightly improve the temperature resistance of the capacitor film, and the improvement of the temperature resistance of the polypropylene film is limited. This is because the compatibility of cycloolefin copolymer with polyethylene and polypropylene is poor, and phase separation will gradually occur during long-term use, resulting in a decrease in the heat resistance of the material and affecting the product quality.

[0004] Cyclic olefin copolymer is an amorphous transparent polymer material with a cyclic olefin structure. It has the advantages of high transparency, good dimensional stability, low water absorption rate, excellent airtightness, chemical corrosion resistance, heat resistance, easy processing and molding, etc., and is widely used in optical resins and films, biomedicine, polyolefin modification and other fields. However, the high brittleness caused by the high glass transition temperature of cyclic olefin copolymer makes it have great limitations in processing. For example, when using cyclic olefin copolymer as raw material to make capacitor film, the high brittleness of cyclic olefin copolymer makes it very difficult or impossible to perform biaxial stretching on the cyclic olefin copolymer capacitor film. Therefore, the capacitor film formed by cyclic olefin copolymer can only be prepared on a special machine and cannot be stretched at a high draw ratio, which is not conducive to the preparation of capacitor film.

[0005] The published patent CN116368175A discloses a capacitor comprising a biaxially stretched film as a dielectric, and the biaxially stretched film comprises a mixture of polypropylene and a cyclic olefin polymer, wherein the proportion of the cyclic olefin polymer in the mixture is 3-18% by weight. The film prepared by this patent has high temperature resistance and high dielectric strength at room temperature, but the compatibility between polypropylene and the cyclic olefin polymer is poor, and phase separation will gradually occur in the film prepared by blending the two, affecting the running stability of the film and easily causing capacitor failures, threatening the safe operation of power electronic equipment.

[0006] The published patent CN103448254A discloses a method for preparing a polypropylene capacitor film, which includes the following steps: stretching and forming a polypropylene raw material composition with the following weight ratio: 100 parts of polypropylene resin, 0.05-0.15 parts of photoinitiator, 3-5 parts of crosslinking agent, and 0.25-0.35 parts of hindered phenol antioxidant, and then irradiating with ultraviolet (UV). The film after the irradiation crosslinking post-treatment is sent to a rewinder for winding to obtain a finished film. Although the heat resistance and breakdown strength of the polypropylene film prepared by this process have been improved, the types and amounts of additives in the film preparation process of this patent are both excessive, which easily causes problems of impurity generation and uneven distribution, thereby reducing the dielectric properties of the polypropylene film and affecting the use of the polypropylene film.

[0007] Therefore, it is an urgent problem to be solved in the field to develop a resin composition of polypropylene-cyclic olefin copolymer that maintains unchanged dielectric properties, has good high temperature resistance, low thermal shrinkage rate, and can be biaxially stretched, and is used to prepare a biaxially stretched film capacitor. Summary of the Invention

[0008] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a polypropylene resin composition, a high-temperature resistant polymer film containing the same, and a preparation method and application thereof. The film including the polypropylene resin composition has a high heat distortion temperature, a low thermal shrinkage rate, good high-temperature resistance, stable dielectric properties, low dielectric loss, can be biaxially stretched at a high draw ratio, and has a low cost, etc.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a polypropylene resin composition. In terms of mass percentage, the polypropylene resin composition includes 79.7-98.9% of polypropylene resin, 1-20% of cycloolefin copolymer, and 0.1-0.3% of radiation cross-linking agent; the glass transition temperature of the cycloolefin copolymer is 120-160°C.

[0011] In the present invention, 79.7-98.9% of polypropylene resin can be, for example, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, etc.

[0012] In the present invention, 1-20% of cycloolefin copolymer can be, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0013] In the present invention, 0.1-0.3% of radiation cross-linking agent can be, for example, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, etc.

[0014] In the present invention, the glass transition temperature of the cycloolefin copolymer is 120-160°C, and can be, for example, 120°C, 122°C, 125°C, 128°C, 130°C, 132°C, 135°C, 138°C, 140°C, 142°C, 145°C, 148°C, 150°C, 152°C, 155°C, 158°C, 160°C, etc.; preferably 150-160°C.

[0015] In the present invention, when the glass transition temperature of the cycloolefin copolymer is within the above-defined range, the high-temperature resistance of the film can be improved. After mixing the cycloolefin copolymer into the polypropylene resin, the film-forming processing conditions of the polymer will not be changed. At the same time, the obtained film can be biaxially stretched, which is beneficial to the preparation of biaxially stretched film capacitors.

[0016] In the present invention, the cycloolefin copolymer comprises repeating unit A and repeating unit B; the repeating unit A comprises a repeating unit having the structure shown in General Formula I; the repeating unit B comprises at least one repeating unit having the structure shown in General Formula II and / or at least one repeating unit having the structure shown in General Formula III; the molar ratio of the repeating unit A to the repeating unit B is 1:(0.77 - 1.33).

[0017] General Formula I.

[0018] General Formula II.

[0019] General Formula III.

[0020] Among them, the dotted lines in General Formula I, General Formula II, and General Formula III each independently represent the connection site of the repeating unit.

[0021] In the formula, R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 , R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 , R 28 , R 29 , R 30 , R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 , R 38 each independently represents any one of a hydrogen atom, a halogen, an alkyl group, a cycloalkyl group, or an aryl group.

[0022] In the present invention, the alkyl group includes an alkyl group having 1 or more carbon atoms, for example, it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, etc.; the cycloalkyl group includes a cycloalkyl group having 3 or more carbon atoms, for example, it can be 3, 4, 5, 6, 7, 8, 9, 10, etc.; the aryl group includes an aryl group having 6 or more carbon atoms, for example, it can be 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, etc.

[0023] In the formula, m1, m2, n1, and n2 are each independently selected from integers greater than or equal to 0, for example, they can be 0, 1, 2, 3, 4, 5, 6, etc.; preferably, m1, m2, n1, and n2 are each independently selected from 0 or 1.

[0024] In the present invention, a cycloolefin copolymer with a specific structure is adopted, that is, the cycloolefin copolymer includes a repeating unit A (general formula I) derived from an olefin, and a repeating unit derived from a cyclic non-conjugated diene shown in general formula II, and / or a repeating unit derived from a cyclic olefin shown in general formula III, having a rigid ring structure, which can improve the temperature resistance of the capacitor film, and controlling the content of the cycloolefin copolymer within a specific range is not only beneficial to improving the high-temperature resistance of the capacitor, but also has good dielectric properties and low cost, and can prepare a biaxially stretched film capacitor.

[0025] In the present invention, the molar ratio of the repeating unit A to the repeating unit B is 1:(0.77 - 1.33), where the specific values in (0.77 - 1.33) can be, for example, 0.77, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.33, etc.

[0026] In the present invention, the repeating unit B includes any one of a combination of at least one repeating unit having the structure shown in general formula II and at least one repeating unit having the structure shown in general formula III, at least one repeating unit having the structure shown in general formula II, or at least one repeating unit having the structure shown in general formula III. When the repeating unit B includes a combination of at least one repeating unit having the structure shown in general formula II and at least one repeating unit having the structure shown in general formula III, the molar ratio of the repeating unit having the structure shown in general formula II to the repeating unit having the structure shown in general formula III is (10 - 55):1, where the specific values in (10 - 55) can be, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, etc.

[0027] In the present invention, the radiation crosslinking agent includes triallyl isocyanurate and / or trimethylolpropane trimethacrylate.

[0028] In the present invention, the polypropylene resin includes a capacitor-grade polypropylene resin, and the melting point of the polypropylene resin is 155 - 175°C, for example, it can be 155°C, 160°C, 165°C, 170°C, 175°C, etc.

[0029] In a second aspect, the present invention provides a high-temperature resistant polymer film, and the material of the high-temperature resistant polymer film includes the polypropylene resin composition according to the first aspect.

[0030] In the present invention, the heat distortion temperature of the high-temperature resistant polymer film is 145 - 160°C, for example, it can be 145°C, 146°C, 147°C, 148°C, 149°C, 150°C, 151°C, 152°C, 153°C, 154°C, 155°C, 156°C, 157°C, 158°C, 159°C, 160°C, etc.

[0031] In a third aspect, the present invention provides a preparation method of the high-temperature resistant polymer film according to the second aspect, and the preparation method includes the following steps:

[0032] (1) Melting the polypropylene resin composition, extruding and casting to obtain a blended polypropylene film;

[0033] (2) Biaxially stretching and heat setting the blended polypropylene film obtained in step (1) to obtain a biaxially stretched polypropylene film;

[0034] (3) Irradiating and crosslinking the biaxially stretched polypropylene film obtained in step (2) to obtain the high-temperature resistant polymer film.

[0035] In the present invention, in the preparation method, after melting, extruding and casting, and biaxially stretching the polypropylene resin composition, irradiation crosslinking is carried out to achieve crosslinking enhancement, and the addition of the radiation crosslinking agent can increase the crosslinking degree of the film prepared in the present invention, improve the compatibility and stability between the cycloolefin copolymer and polypropylene, and further improve the high-temperature resistance of the material.

[0036] In the present invention, the preparation method of the polypropylene resin composition in step (1) includes: mixing the polypropylene resin with a cycloolefin copolymer to obtain the polypropylene resin composition.

[0037] In the present invention, the method of irradiation crosslinking in step (3) includes irradiation crosslinking with γ rays.

[0038] In the present invention, the dose of irradiation crosslinking is 15 to 45 kGy, and for example, it can be 15 kGy, 16 kGy, 17 kGy, 18 kGy, 19 kGy, 20 kGy, 21 kGy, 22 kGy, 23 kGy, 24 kGy, 25 kGy, 26 kGy, 27 kGy, 28 kGy, 29 kGy, 30 kGy, 31 kGy, 32 kGy, 33 kGy, 34 kGy, 35 kGy, 36 kGy, 37 kGy, 38 kGy, 39 kGy, 40 kGy, 41 kGy, 42 kGy, 43 kGy, 44 kGy, 45 kGy, etc.

[0039] In the present invention, within a specific range of the irradiation dose, the obtained film has a higher heat distortion temperature, a lower thermal shrinkage rate, and better high-temperature resistance; and it can ensure that the dielectric properties of the film are not affected.

[0040] In the fourth aspect, the present invention provides a film capacitor, and the base film of the film capacitor is made of the polypropylene resin composition described in the first aspect or the high-temperature resistant polymer film described in the second aspect.

[0041] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges not listed. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] The polypropylene resin composition provided by the present invention uses a cycloolefin copolymer with a specific glass transition temperature and an irradiation crosslinking agent to be compounded with the polypropylene resin, improving the compatibility and stability between the cycloolefin copolymer and polypropylene, being beneficial to increasing the heat distortion temperature of the film capacitor, reducing the thermal shrinkage rate of the film capacitor, improving its high-temperature resistance, and not affecting the dielectric properties of the film capacitor, with low dielectric loss; it can prepare a biaxially stretched film capacitor, and at the same time, the material cost is low. Specific Embodiments

[0044] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0045] The materials used in the present invention are as follows:

[0046] Polypropylene resin (PP)

[0047] Capacitor-grade polypropylene resin: Borclean™ HC318BF, with a melting point of 165 °C and a melt flow index of 3.2 g / 10 min (230 °C, 2.16 kg).

[0048] Cycloolefin copolymer (COC)

[0049] In the present invention, the raw materials for synthesizing COC include the compounds shown in the general formula II and / or the compounds shown in the general formula III, as follows. Specifically, it may include compound IIa, compound IIIb, compound IIIa, etc.; the compound IIa, compound IIIb, and compound IIIa can all be prepared from the existing compounds in the prior art, such as using dicyclopentadiene (A), ethylidene norbornene (B), norbornene (C), etc. as raw materials for preparation.

[0050] In the present invention, the reaction routes for preparing the compound IIa and compound IIIa are as follows.

[0051]

[0052]

[0053] The specific steps include: in the presence of a solvent (toluene, the amount used is sufficient to dissolve the compound), reacting compound A and compound B, or, compound A and compound C at 240 °C for 60 min respectively, and obtaining compound IIa or compound IIIa with a purity greater than 99% by vacuum distillation.

[0054] In the present invention, the reaction route for preparing the compound IIIb is as follows.

[0055]

[0056]

[0057] The specific steps include: mixing compound A with a Ru catalyst, introducing hydrogen into it, with the molar ratio of hydrogen to compound A being 1:1, and performing selective hydrogenation to obtain compound D. Then, in the presence of a solvent (hexane, the amount used is sufficient to dissolve the compound), reacting compound A and compound D at 230 °C for 60 min, and obtaining compound IIIb with a purity greater than 99% by vacuum distillation.

[0058] COC-1: The structural formula is ; The molecular structure contains repeating unit A (ethylene repeating unit) and repeating unit B (IIa repeating unit and ethylidene norbornene repeating unit); the molar ratio of repeating unit A to repeating unit B is 1:1.27; in repeating unit B, the molar ratio of IIa repeating unit to ethylidene norbornene repeating unit is 13:1, and the glass transition temperature (Tg) is 150 °C.

[0059] The preparation method of COC-1 used in the present invention comprises the following steps:

[0060] Add 500 mL of toluene solvent into a reaction kettle fully replaced with nitrogen, and add compound IIa and ethylidene norbornene according to the formula amount. Introduce ethylene gas at a rate of 60 L per hour. After maintaining at 20 °C for 10 min, add 5 mg of methylaluminoxane and a toluene solution (mass concentration is 50%) of 0.005 mg of dichloro·ethylenebis(indenyl)zirconium into the reaction kettle. Polymerize for 1 h under the conditions of 20 °C and normal pressure, and then add isopropanol to stop the polymerization. Subsequently, add a large amount of methanol / acetone mixed solvent (volume ratio is 1:1) to the polymer solution to precipitate the polymer. Dry the precipitated polymer in a vacuum oven at 120 °C for 24 h to obtain the cycloolefin copolymer COC-1.

[0061] COC-2: The structural formula is ; The molecular structure contains repeating unit A (ethylene repeating unit) and repeating unit B (IIa repeating unit and norbornene repeating unit); the molar ratio of repeating unit A to repeating unit B is 1:1.13; in repeating unit B, the molar ratio of IIa repeating unit to norbornene repeating unit is 16.7:1; Tg is 140 °C. The preparation method of COC-2 is the same as that of COC-1, except that the types and ratios of raw materials are different.

[0062] COC-3: The structural formula is ; The molecular structure contains repeating unit A (ethylene repeating unit) and repeating unit B (IIIa repeating unit and ethylidene norbornene repeating unit); the molar ratio of repeating unit A to repeating unit B is 1:1.17; in repeating unit B, the molar ratio of ethylidene norbornene repeating unit to IIIa repeating unit is 53:1; Tg is 147 °C; the preparation method of COC-3 is the same as that of COC-1, except that the types and ratios of raw materials are different.

[0063] COC-4: The structural formula is ; The molecular structure contains repeating unit A (ethylene repeating unit) and repeating unit B (IIa repeating unit); the molar ratio of repeating unit A to repeating unit B is 1:1.33; Tg is 160 °C; the preparation method of COC-4 is the same as that of COC-1, except that the types and ratios of raw materials are different.

[0064] COC-5: The structural formula is ; The molecular structure contains repeating unit A (ethylene repeating unit) and repeating unit B (IIIb repeating unit and ethylidene norbornene repeating unit); The molar ratio of repeating unit A to repeating unit B is 1:0.96; In the repeating unit B, the molar ratio of ethylidene norbornene repeating unit to IIIb repeating unit is 11.25:1; Tg is 142 °C; The preparation method of the COC-5 is the same as that of COC-1, except that the types and ratios of raw materials are different.

[0065] COC-6: The structural formula is the same as that of COC-4, the difference is that the molar ratio of repeating unit A to repeating unit B is 1:0.77; Tg is 120 °C; The preparation method of the COC-6 is the same as that of COC-1, except that the types and ratios of raw materials are different.

[0066] COC-7: The structural formula is the same as that of COC-3, the difference is only that the molar ratio of repeating unit A to repeating unit B is 1:0.12; In the repeating unit B, the molar ratio of ethylidene norbornene repeating unit to IIIa repeating unit is 5:1; Tg is 58 °C. The preparation method of the COC-7 is the same as that of COC-1, except that the types and ratios of raw materials are different.

[0067] COC-8: The structural formula is the same as that of COC-3, the difference is only that the molar ratio of repeating unit A to repeating unit B is 1:0.375; Tg is 40 °C. The preparation method of the COC-8 is the same as that of COC-1, except that the types and ratios of raw materials are different.

[0068] COC-9: The structural formula is the same as that of COC-5, the difference is that the molar ratio of repeating unit A to repeating unit B is 1:0.12; Tg is 80 °C; The preparation method of the COC-9 is the same as that of COC-1, except that the types and ratios of raw materials are different.

[0069] In the present invention, the cyclic olefin copolymer used contains crosslinkable groups, has good moldability and solubility, and can improve the product yield. In addition, the cyclic olefin copolymer also has good heat resistance, mechanical properties and dielectric properties.

[0070] Examples 1 to 6 and Comparative Examples 1 to 5 respectively provide a polypropylene resin composition. By mass percentage, its formula is shown in Table 1; The preparation method of the polypropylene resin composition includes: mixing polypropylene resin, cyclic olefin copolymer and radiation crosslinking agent.

[0071] Table 1

[0072]

[0073] For the application examples of the present invention, biaxially stretched high-temperature resistant polymer films with a thickness of 6 μm are manufactured using the polypropylene resin compositions provided in Examples 1 to 6 and Comparative Examples 1 to 5.

[0074] Application Example 1

[0075] This application example provides a high-temperature resistant polymer film. The preparation method of the high-temperature resistant polymer film includes the following steps:

[0076] (1) Heat and melt the polypropylene resin composition (Example 1) at 250 °C, filter and extrude it onto a casting roll at a temperature of 120 °C, and blow it with an air knife to adhere vertically to the roll to obtain a blended polypropylene film;

[0077] (2) Biaxially stretch the blended polypropylene film obtained in step (1). Among them, the stretching temperature for longitudinal stretching is 155 °C and the stretching ratio is 5; the stretching temperature for transverse stretching is 165 °C and the stretching ratio is 7. The biaxially stretched film is heat-set at 165 °C to obtain a biaxially stretched polymer film;

[0078] (3) Irradiate and crosslink the biaxially stretched polymer film obtained in step (2) with γ-rays having a radiation dose of 45 kGy to obtain the high-temperature resistant polymer film.

[0079] Application Example 2

[0080] This application example provides a high-temperature resistant polymer film. The difference from Application Example 1 is only that the polypropylene composition is the composition shown in Example 2, and the irradiation dose in step (3) is adjusted to 18 kGy, and other preparation methods are the same as those in Example 1.

[0081] Application Example 3

[0082] This application example provides a high-temperature resistant polymer film. The difference from Application Example 1 is only that the polypropylene composition is the composition shown in Example 3, and the irradiation dose in step (3) is adjusted to 15 kGy, and other preparation methods are the same as those in Example 1.

[0083] Application Example 4

[0084] This application example provides a high-temperature resistant polymer film. The difference from Application Example 1 is only that the polypropylene composition is the composition shown in Example 4, and the irradiation dose in step (3) is adjusted to 40 kGy, and other preparation methods are the same as those in Example 1.

[0085] Application Example 5

[0086] This application example provides a high-temperature resistant polymer film, which is only different from Application Example 1 in that the polypropylene composition is the composition shown in Example 5, and the irradiation dose in step (3) is adjusted to 25 kGy, and other preparation methods are the same as those in Example 1.

[0087] Application Example 6

[0088] This application example provides a high-temperature resistant polymer film, which is only different from Application Example 1 in that the polypropylene composition is the composition shown in Example 6, and the irradiation dose in step (3) is adjusted to 25 kGy, and other preparation methods are the same as those in Example 1.

[0089] Application Example 7

[0090] This application example provides a high-temperature resistant polymer film, which is only different from Application Example 3 in that in the preparation method, the irradiation dose in step (3) is adjusted to 10 kGy, and other materials and step parameters are the same as those in Application Example 3.

[0091] Comparative Application Examples 1 - 3

[0092] Comparative Application Examples 1 - 3 respectively provide a high-temperature resistant polymer film, which is only different from Application Example 3 in that the polypropylene resin compositions are the polypropylene resin compositions provided in Comparative Examples 1 - 3 respectively, and other steps, parameters, and preparation methods are the same as those in Application Example 3.

[0093] Comparative Application Example 4

[0094] This comparative application example provides a high-temperature resistant polymer film, which is only different from Application Example 1 in that in the preparation method, step (3) is not carried out, and other materials and step parameters are the same as those in Application Example 1.

[0095] Comparative Application Example 5

[0096] This comparative application example provides a high-temperature resistant polymer film, which is only different from Application Example 3 in that the polypropylene resin composition is the polypropylene resin composition provided in Comparative Example 4, and other materials and step parameters are the same as those in Application Example 3.

[0097] Comparative Application Example 6

[0098] This comparative application example provides a high-temperature resistant polymer film, which is only different from Application Example 5 in that the polypropylene resin composition is the polypropylene resin composition provided in Comparative Example 5, and other materials and step parameters are the same as those in Application Example 5.

[0099] Comparative Application Example 7

[0100] This comparative application example provides a high-temperature resistant polymer film, which is only different from Application Example 5 in that the polypropylene resin composition is the polypropylene resin composition provided in Comparative Example 5; in the preparation method, the irradiation dose in step (3) is adjusted to 50 kGy, and other materials and step parameters are the same as those in Application Example 5.

[0101] Performance Test

[0102] The following performance tests were carried out on the films obtained from Application Examples 1 to 7 and Comparative Application Examples 1 to 7:

[0103] (1) Heat distortion temperature: Tested in accordance with GB / T 1634.2-2019;

[0104] (2) Heat shrinkage rate: Measure the transverse and longitudinal dimensions of the film before and after heating at 120 °C for 10 min, and calculate the heat shrinkage rate; the heat shrinkage rate in the transverse or longitudinal direction = (dimension before heating - dimension after heating) / dimension before heating × 100%;

[0105] (3) Dielectric constant: Tested in accordance with the method of GB / T31838.6-2021;

[0106] (4) Dielectric loss factor: Tested in accordance with GB / T1409-2006, and the test conditions are 23 °C and 50 Hz.

[0107] The specific test results are shown in Table 2, where " / " indicates that no irradiation cross-linking was carried out.

[0108] Table 2

[0109]

[0110] As can be seen from Table 2, the polypropylene resin composition provided by the present invention, with a specific raw material composition and film-making process, results in a polymer film with a high heat distortion temperature and a low heat shrinkage rate; the heat distortion temperature reaches 135-160 °C, and even can reach 145-160 °C; the transverse heat shrinkage rate ≤ 0.3%, and the longitudinal heat shrinkage rate ≤ 1.3%; and it does not affect the dielectric properties of the film.

[0111] It can be seen from the comparison between Application Example 3 and Comparative Application Examples 1 to 3 and Comparative Application Example 5 that the repeating unit ratio and Tg of the cycloolefin copolymer are not within a specific range, and the temperature resistance of the film after blending is only slightly higher than that of the film made of a single capacitor-grade polypropylene, but it is much lower than that of the blend film made of the specific cycloolefin copolymer and capacitor-grade polypropylene of the present invention.

[0112] It can be seen from the comparison between Application Example 1 and Comparative Application Example 4 that without the specific film-making process of the present invention, the temperature resistance of the film becomes worse.

[0113] It can be seen from the comparison between Application Example 3 and Comparative Application Example 5 that the temperature resistance of the film made only of capacitor-grade polypropylene is much lower than that of the blend film made of polypropylene and cycloolefin copolymer.

[0114] It can be seen from the comparison between Application Example 5 and Comparative Application Example 6 that the crosslinking density of the polypropylene composition film without adding an irradiation crosslinking agent is relatively low. Compared with Comparative Application Example 5, it can only slightly improve the temperature resistance of the film and cannot further improve the temperature resistance of the blend film. However, the film provided by Application Example 5 has a high crosslinking density, thus significantly improving the temperature resistance of the film.

[0115] It can be seen from the comparison between Application Example 7 and Application Example 3 that when the polypropylene-cycloolefin copolymer blend film is irradiated with a radiation dose lower than the limit defined in the present invention, the crosslinking degree of the blend film is relatively low, resulting in a relatively high thermal shrinkage rate of the film, and the temperature resistance is lower than that of the high-temperature-resistant film made with the specific radiation dose of the present invention.

[0116] It can be seen from the comparison between Application Example 5 and Comparative Application Example 7 that after the polypropylene-cycloolefin copolymer blend film is irradiated with a high radiation dose without adding an irradiation crosslinking agent, the blend film degrades, resulting in a relatively high thermal shrinkage rate of the blend film and a significant reduction in temperature resistance.

[0117] In summary, in the present invention, for the polypropylene resin composition, by adding a cycloolefin copolymer with a specific Tg and an irradiation crosslinking agent and compounding them with polypropylene in a specific ratio, the film including the polypropylene resin composition has good high-temperature resistance and basically does not affect the dielectric properties of the film; further, by blending the polypropylene resin composition and combining with a γ-ray irradiation process, it helps to further improve the temperature resistance of the film. The high-temperature-resistant polymer capacitor film obtained by the present invention by controlling the raw material ratio, irradiation dose, and content of the irradiation crosslinking agent has a high heat distortion temperature and a low thermal shrinkage rate, which can not only ensure that the dielectric constant of the film remains unchanged but also enhance the high-temperature resistance of the film.

[0118] The above specific embodiments have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-temperature resistant polymer film, characterized in that, The material of the high-temperature resistant polymer film comprises a polypropylene resin composition; By mass percentage, the polypropylene resin composition comprises 79.7 - 82% polypropylene resin, 16 - 20% cycloolefin copolymer, and 0.2 - 0.3% irradiation crosslinking agent; The glass transition temperature of the cycloolefin copolymer is 150 - 158 °C; The heat distortion temperature of the high-temperature resistant polymer film is 152 - 160 °C; The high-temperature resistant polymer film is prepared by the following method, and the method comprises the following steps: (1) Melting the polypropylene resin composition and extruding and casting to obtain a blended polypropylene film; (2) Biaxially stretching and heat setting the blended polypropylene film obtained in step (1) to obtain a biaxially stretched polypropylene film; (3) Irradiation crosslinking the biaxially stretched polypropylene film obtained in step (2) to obtain the high-temperature resistant polymer film; The method of irradiation crosslinking in step (3) comprises irradiation crosslinking with γ-rays; The dose of the irradiation crosslinking is 15 - 45 kGy; The cycloolefin copolymer comprises repeating unit A and repeating unit B; The repeating unit A comprises a repeating unit having the structure shown in general formula I; The repeating unit B comprises at least one repeating unit having the structure shown in general formula II, or, the repeating unit B comprises at least one repeating unit having the structure shown in general formula II and at least one repeating unit having the structure shown in general formula III; General formula I; General formula II; General formula III; Wherein, the dotted lines in general formula I, general formula II, and general formula III each independently represent the connection site of the repeating unit; R1, R2, R3, R4, R5, R6, R7, R8, R9, R 10 、R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 、R 18 、R 19 、R 20 、R 21 、R 22 、R 23 、R 24 、R 25 、R 26 、R 27 、R 28 、R 29 、R 30 、R 31 、R 32 、R 33 、R 34 、R 35 、R 36 、R 37 、R 38 each independently represents a hydrogen atom; m1, m2, n1, n2 each independently selected from 0 or 1; The molar ratio of the repeating unit A to the repeating unit B is 1:(0.77 - 1.3).

2. The high-temperature resistant polymer film according to claim 1, characterized in that, The repeating unit B comprises at least one repeating unit having the structure shown in general formula II and at least one repeating unit having the structure shown in general formula III, and the molar ratio of the repeating unit having the structure shown in general formula II to the repeating unit having the structure shown in general formula III is (10 - 55):

1.

3. The high-temperature resistant polymer film according to claim 1, wherein The irradiation crosslinking agent comprises triallyl isocyanurate and / or trimethylolpropane trimethacrylate; The polypropylene resin comprises a capacitor-grade polypropylene resin, and the melting point of the polypropylene resin is 155 - 175 °C.

4. A method for preparing a high-temperature resistant polymer film according to any one of claims 1 to 3, characterized in that, The preparation method comprises the following steps: (1) Melting the polypropylene resin composition and extruding and casting to obtain a blended polypropylene film; (2) Biaxially stretching and heat setting the blended polypropylene film obtained in step (1) to obtain a biaxially stretched polypropylene film; (3) Irradiation crosslinking the biaxially stretched polypropylene film obtained in step (2) to obtain the high-temperature resistant polymer film.

5. The preparation method according to claim 4, wherein The preparation method of the polypropylene resin composition in step (1) comprises: mixing the polypropylene resin with the cycloolefin copolymer and the irradiation crosslinking agent to obtain the polypropylene resin composition.

6. A thin-film capacitor, characterized in that, The base film of the film capacitor is made of the high-temperature resistant polymer film according to any one of claims 1 - 3.

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