A kind of polypropylene capacitor film and preparation method thereof

Abstract

The present invention relates to the technical field of polypropylene roughening film, specifically a polypropylene capacitor film and a preparation method thereof, including the following process: melt extrusion of polypropylene particles, chilling casting, forming a sheet; then synchronous stretching, obtaining a polypropylene capacitor film; or hot pressing and melting of polypropylene particles, isothermal crystallization, cooling, forming a sheet; then biaxial stretching, obtaining a polypropylene capacitor film; the polypropylene particles include: by mass, 78 to 82 parts of polypropylene and 18 to 22 parts of cycloolefin polymer; cycloolefin polymer includes the following preparation components: 5-norbornene-2,3-dianhydride, amino-containing brominated benzocycloolefin and chlorosilane. The present invention enhances the heat resistance and mechanical properties of polypropylene through the compounding of polypropylene and cycloolefin polymer, improves the dielectric properties of polypropylene capacitor film, reduces its dependence on temperature, and enables it to maintain dielectric medium loss in high frequency regions.

Description

Technical Field

[0001] The invention relates to the technical field of polypropylene roughening films, in particular to a polypropylene capacitor film and a preparation method thereof. Background Art

[0002] Biaxially oriented polypropylene (BOPP) roughened film is an ideal dielectric material for oil-immersed power capacitors. With the deepening of the construction of the national grid, the demand for roughened film has also increased, and the quality and performance requirements of the roughened film have become higher and higher. For roughened film for oil-immersed capacitors, the degree of roughening is an important indicator that affects the metal evaporation and winding of the film, and the thermal shrinkage rate is an important parameter for high-temperature operation of the capacitor. Polypropylene is a semi-crystalline material with poor mechanical properties and a low glass transition temperature, which will affect the dielectric properties of the film at high temperatures. Therefore, we propose a polypropylene capacitor film and a preparation method thereof. Summary of the invention

[0003] The object of the present invention is to provide a polypropylene capacitor film and a preparation method thereof to solve the problems raised in the above background technology.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for preparing a polypropylene capacitor film, comprising the following processes:

[0005] The polypropylene particles are melted and extruded, and then quenched and cast to form a sheet; and then biaxially stretched to obtain a polypropylene capacitor film;

[0006] Alternatively, polypropylene particles are hot-pressed and melted, isothermally crystallized, and cooled to form a sheet; and then biaxially stretched to obtain a polypropylene capacitor film.

[0007] Furthermore, the heating temperature for melt extrusion is 200-250°C.

[0008] Furthermore, in the chilling casting process, the melt is rapidly cooled to 80-110°C to form a glassy casting, and then cooled to below 60°C to crystallize to obtain a sheet. The temperature of the cooling water in the chilling roller is 30±0.5°C.

[0009] Furthermore, the biaxial stretching is simultaneous biaxial stretching, and the process conditions are: preheating temperature 165-175°C, stretching temperature 155-165°C, and stretching ratio (4-5)×(4-5).

[0010] Furthermore, the biaxial stretching is followed by shaping: the shaping temperature is 145 to 175° C., and the shaping time is 2 to 8 minutes.

[0011] Furthermore, after the polypropylene capacitor film is prepared, it is subjected to corona treatment, which can improve the surface polarity of the film, increase the surface tension strength of the film, and improve the wettability of the polymer; and then it is rolled up and aged to eliminate static charge stress.

[0012] Furthermore, the hot pressing melting process is as follows: temperature 210-220° C., pressure 5 MPa, and time 10-15 min.

[0013] Furthermore, the isothermal crystallization process is: temperature 120-130° C., pressure 5 MPa, and time 30-45 min.

[0014] Furthermore, the thickness of the sheet is 0.15-0.25 mm; the thickness of the polypropylene capacitor film is 8-12 μm.

[0015] In the above technical scheme, the polypropylene capacitor film is formed by melting, hot pressing, crystallizing, and then synchronously biaxially stretching the polypropylene particles. In the hot pressing process, the polypropylene particles melt, cast into a film, and form a sheet material containing more β crystals; then placed at an isothermal crystallization temperature, the β crystals have a faster formation speed and maintain a longer crystallization time, which is conducive to the formation of more β crystals. If the isothermal crystallization temperature is too low, the sheet cools too quickly, which is not conducive to the formation of β crystals; if the temperature is too high, it is not conducive to the subsequent stretching process. At the same time as isothermal crystallization, the sheet can also be preheated so that it can be quickly heated to the stretching temperature, so that the transformation of β crystals to α can only be carried out during stretching, which promotes the ideal coarsening effect on both sides of the film (polypropylene capacitor film). Finally, biaxial stretching is performed so that the polypropylene molecular chains are oriented in a direction parallel to the surface of the film to achieve orderly arrangement. The stretching temperature is controlled between the melting point of the β crystal and the melting point of the α crystal, and all the β crystals are converted into α crystals, so that the film has a better coarsening effect on both sides. If the stretching temperature is too low, it is not conducive to the complete melting of the β crystals. Some β crystals will be mechanically damaged by the tensile force during the stretching process, and no crystal transformation will occur, making the film surface smoother; if the stretching temperature is too high, it is easy to cause film breakage, affecting the normal production of the film. Heat setting eliminates the internal stress generated by stretching, and sets the α crystals, stabilizes the molecular chain structure, and sets the roughened surface of the film.

[0016] Furthermore, the polypropylene particles include, by mass, 78 to 82 parts of polypropylene and 18 to 22 parts of cycloolefin polymer.

[0017] Furthermore, the polypropylene is electrical grade polypropylene with an ash content of less than 30 ppm.

[0018] In the above technical scheme, the film-making raw materials include polypropylene and cycloolefin polymer. Polypropylene is a semi-crystalline material with a low glass transition temperature. In an environment exceeding 85°C, the capacitor film made of polypropylene is very prone to operating failures. Cycloolefin polymer is an amorphous transparent polymer material with a ring structure on the molecular chain. It has the characteristics of high transparency, low birefringence, high heat resistance, low water absorption, chemical resistance, low shrinkage, dimensional stability, low dielectric constant and dielectric loss; the rigid ring structure on the main chain of the molecule limits the bending of the molecular chain, making the main chain structure rigid, thereby presenting a higher glass transition temperature, which can enhance the heat resistance and mechanical properties of polypropylene, improve the dielectric properties of the polypropylene capacitor film, reduce its dependence on temperature, and enable it to maintain dielectric dielectric loss in the high frequency region.

[0019] Further, the cycloolefin polymer is prepared by the following process:

[0020] S1. Mix 5-norbornene-2,3-dianhydride and a catalyst in tetrahydrofuran, and place the mixture at a constant temperature of 40-45°C in a nitrogen atmosphere for 24 hours; cool the mixture to room temperature in air, concentrate it, and dissolve and precipitate it using dichloromethane and methanol solution, repeat this process 3 times, and place the mixture at a temperature of 22-27°C and vacuum dry it for 48 hours to obtain polynorbornene;

[0021] S2, polynorbornene and tetrahydrofuran are mixed, glacial acetic acid is added, the temperature is raised to 120-125°C, amino-containing brominated benzocycloolefin is slowly added, and the reaction is stirred for 5-6 hours; the mixture is cooled to room temperature, the reaction is quenched with ethyl acetate, and tetrahydrofuran and methanol are used to dissolve and precipitate, and the mixture is repeated 3 times, and the mixture is placed in a vacuum dryer at 22-27°C for 48 hours to obtain polynorbornene-benzocycloolefin;

[0022] S3, mixing magnesium and iodine, slowly adding polynorbornene-benzocycloolefin and tetrahydrofuran in a nitrogen atmosphere within 30 minutes, raising the temperature to 65-70° C., and reacting under reflux stirring for 60-120 minutes;

[0023] Cool to room temperature, slowly add chlorosilane, and add it within 30 minutes; raise the temperature to 65-70°C, reflux and stir to react for 120-150 minutes; filter, wash with water, dry, take the organic phase, wash with water, rotary evaporate, and distill under reduced pressure to obtain a cycloolefin polymer.

[0024] Further, in S1, the ratio of 5-norbornene-2,3-dianhydride to tetrahydrofuran is 12 g / 100 mL;

[0025] The catalyst is Grubbs catalyst: Grubbs second generation catalyst, derived from Anaiji Chemical, and the dosage is 1% of the mass of 5-norbornene-2,3-dianhydride.

[0026] Further, in S2, the ratio of polynorbornene, glacial acetic acid, and tetrahydrofuran is 3 g:50 mL:100 mL;

[0027] The mass ratio of polynorbornene to amino-containing brominated benzocycloolefin is 1.2 to 1.4;

[0028] Furthermore, in S2, the amino-containing brominated benzocycloolefin is a mixture of one or more of 4-bromobicyclo[4.2.0]oct-1,3,5-triene-7-amine (CAS No.: 1784682-45-6), 5-2,3-dihydro-1H-indene-2-amino (CAS No.: 321352-53-8), and 7-bromo-tetrahydronaphthyl-1-amine (CAS No.: 865472-04-4).

[0029] Further, in S3, the ratio of polynorbornene-benzocycloolefin and tetrahydrofuran is 12 g / 100 mL;

[0030] The mass ratio of polynorbornene-benzocycloolefin and chlorosilane is 10:(3.1-14.2);

[0031] The mass ratio of polynorbornene-benzocycloolefin, magnesium and iodine is 10: (0.72-0.78): (7.1-7.7);

[0032] The chlorosilane is a mixture of one or more of dimethylvinylchlorosilane, n-pentyldimethylchlorosilane, chlorodimethyloctylsilane, decyldimethylchlorosilane, dodecyldimethylchlorosilane, dimethylhexadecylchlorosilane, dimethyloctadecylchlorosilane, n-triacontyldimethylchlorosilane, n-triacontyldimethylchlorosilane, 2-(di-n-octylmethylsilyl)ethyldimethylchlorosilane, 2-(di-n-octylmethylsilyl)ethyldimethylchlorosilane, 7-octenyldimethylchlorosilane, 5-hexenyldimethylchlorosilane, 1-enylundecyldimethylchlorosilane and octadecyldiethoxychlorosilane.

[0033] Further, when the chlorosilane is one of dimethylvinyl chlorosilane, n-pentyldimethylchlorosilane, chlorodimethyloctylsilane, decyldimethylchlorosilane, dodecyldimethylchlorosilane, dimethylhexadecylchlorosilane, dimethyloctadecylchlorosilane, n-triacontyldimethylchlorosilane, n-triacontyldimethylchlorosilane, 2-(di-n-octylmethylsilyl)ethyldimethylchlorosilane, and 2-(di-n-octylmethylsilyl)ethyldimethylchlorosilane, the polypropylene particles are prepared by the following process:

[0034] In a nitrogen atmosphere, polypropylene, cycloolefin polymer and antioxidant are mixed, melt-blended at 215-230° C., extruded and granulated to obtain polypropylene particles.

[0035] Furthermore, the antioxidant is a compound of antioxidants 1010 and 168, with a mass ratio of 1:1; the amount of the antioxidant is 0.10% to 0.25% of the total mass of the polypropylene and cycloolefin polymer.

[0036] In the above technical scheme, the norbornene structure of 5-norbornene-2,3-dianhydride undergoes a ring-opening metathesis polymerization reaction to synthesize a main chain polymer based on norbornene, which is recorded as polynorbornene. Then, the polynorbornene is reacted with amino-containing brominated benzocycloolefin to react its dianhydride structure with the amino group, and the brominated benzocycloolefin is introduced to obtain polynorbornene-benzocycloolefin. Finally, magnesium and iodine are used to react the benzyl bromide in the polynorbornene-benzocycloolefin with the chlorine group in the chlorosilane to obtain a polynorbornene-benzocycloolefin-silyl alkane with an alkyl chain, which is the product cycloolefin polymer; it can effectively improve the compatibility and tensile stability between the cycloolefin polymer and polypropylene, improve the processing performance of the sheet, and prevent the film from breaking; and the movement of the polypropylene molecular chain segment under the co-extrusion high temperature is suppressed, thereby improving the heat resistance of the film; while maintaining the β crystal conversion ability, it can improve the molecular chain entanglement, promote its homogeneous nucleation, and stabilize the β crystal. The addition of benzocycloolefin structure can increase the content of cycloolefin structure in cycloolefin polymer, further reduce its dielectric constant, and improve the dielectric properties and heat resistance of the film.

[0037] The selection of long-chain alkane segments by chlorosilane helps to promote the microphase separation of the prepared cycloolefin polymer in the film; during the hot pressing and melting process, polypropylene and long-chain alkane segments are preferentially melted and mixed, which inhibits the chain movement of the cycloolefin structure (polynorbornene-benzocycloolefin) and causes it to tend to self-assemble, thereby improving the surface roughness of the film without introducing impurities or affecting the electrical properties of the film.

[0038] Further, when the chlorosilane is octadecyldiethoxychlorosilane, the polypropylene particles are prepared by the following process:

[0039] In a nitrogen atmosphere, mix polypropylene and tetrahydrofuran, stir at 30-60°C for 30-60 minutes; add cycloolefin polymer, raise the temperature to 120-140°C, and react for 3-4 hours;

[0040] Cool down to 68-93°C, add distilled water, stir and hydrolyze for 30-45 minutes; wash and dry;

[0041] Add an antioxidant, melt blend at 215-230° C., extrude, and granulate to obtain polypropylene particles.

[0042] Furthermore, the antioxidant is a compound of antioxidants 1010 and 168, with a mass ratio of 1:1; the amount of the antioxidant is 0.10% to 0.25% of the total mass of the polypropylene and cycloolefin polymer;

[0043] The ratio of polypropylene, tetrahydrofuran and distilled water is 100 g / (15-30) mL / (50-100) mL.

[0044] In the above technical solution, when the chlorosilane is octadecyldiethoxychlorosilane, the cycloolefin polymer contains silicon-oxygen bonds, which undergo hydrolysis and cross-linking during the process of preparing polypropylene particles; the degree of microphase separation in the film increases, resulting in an increase in the surface roughness. However, due to the position of the silicon-oxygen bonds in the chain segments, the steric effect leads to a low degree of cross-linking.

[0045] Further, when the chlorosilane is one of 7-octenyldimethylchlorosilane, 5-hexenyldimethylchlorosilane, and 1-alkenylundecanyldimethylchlorosilane, the polypropylene particles are prepared by the following process:

[0046] In a nitrogen atmosphere, mix polypropylene and tetrahydrofuran, stir at 30-60°C for 30-60 min; add cycloolefin polymer and initiator, heat to 120-140°C, react for 3-4 h; add antioxidant, melt blend at 215-230°C, extrude, and granulate to obtain polypropylene particles.

[0047] Further, the initiator is tert-butyl perbenzoate, and the amount used is 3.5% to 4.3% of the mass of polypropylene;

[0048] The antioxidant is a compound of antioxidants 1010 and 168, with a mass ratio of 1:1; the amount of the antioxidant is 0.10% to 0.25% of the total mass of polypropylene and cycloolefin polymer;

[0049] The ratio of polypropylene to tetrahydrofuran is 100 g / (15-30) mL.

[0050] In the above technical scheme, when chlorosilane is selected as olefin silane, in the preparation of polypropylene particles, tetrahydrofuran is used to swell and dissolve polypropylene and cycloolefin polymer, and an initiator is added to initiate the crosslinking of double bonds to construct a crosslinking network, which can further improve the mechanical properties and heat resistance of the film. Affected by the compatible chain segments in polypropylene and cycloolefin polymer, the molecular chains of the two segments interpenetrate and entangle, the crystallization temperature is increased, and the crystallization of polypropylene is induced; it can inhibit the violent movement of polypropylene molecular chains and slow down its entanglement tendency, thereby promoting the generation and transformation of polypropylene β crystals. The initiator selects a high-temperature and low-viscosity initiator, and under the action of stirring, the probability of contact with the material is relatively high.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1. The preparation method of a polypropylene capacitor film described in the present invention enhances the heat resistance and mechanical properties of polypropylene through the compounding of polypropylene and cycloolefin polymer, improves the dielectric properties of the polypropylene capacitor film, reduces its dependence on temperature, and enables it to maintain dielectric loss in the high frequency region.

[0053] 2. The method for preparing a polypropylene capacitor film described in the present invention prepares a cycloolefin polymer with an alkyl chain by using 5-norbornene-2,3-dianhydride, amino-containing brominated benzocycloolefin, chlorosilane, etc., which can effectively improve the compatibility and tensile stability between the cycloolefin polymer and polypropylene, improve the processing performance of the sheet, and prevent the film from rupture; and while maintaining the β crystal conversion ability, it can improve the entanglement of molecular chains, promote its homogeneous nucleation, and stabilize the β crystal. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] In the following specific implementations,

[0056] The catalyst is Grubbs catalyst: Grubbs second generation catalyst, from Anaiji Chemical,

[0057] The antioxidant is a compound of antioxidants 1010 and 168, with a mass ratio of 1:1;

[0058] Polypropylene: FC01: Ash 10×10 -6 , from Henan Zhongyuan Petrochemical Company;

[0059] The thickness of the sheet is 0.2 mm; the thickness of the polypropylene capacitor film is 11 μm;

[0060] The following "parts" are all parts by mass;

[0061] The following process is a small-scale laboratory test, and its material ratio can be expanded in equal proportions.

[0062] Embodiment 1: A method for preparing a polypropylene capacitor film, comprising the following process:

[0063] Step 1, S1, 12g of 5-norbornene-2,3-dianhydride and 0.12g of catalyst are mixed in 100mL of tetrahydrofuran, and the mixture is placed at 40°C for constant temperature reaction for 24h in a nitrogen atmosphere; the mixture is cooled to room temperature in air, concentrated, and dissolved and precipitated using dichloromethane and methanol solution, and the mixture is repeated 3 times; the mixture is placed at 22°C and vacuum dried for 48h to obtain polynorbornene;

[0064] S2, 12g polynorbornene and 400mL tetrahydrofuran were mixed, 200mL glacial acetic acid was added, the temperature was raised to 120°C, 14.4g amino-containing brominated benzocycloolefin (4-bromobicyclo[4.2.0]octa-1,3,5-triene-7-amine) was slowly added, and the reaction was stirred for 5h; the mixture was cooled to room temperature, the reaction was quenched with ethyl acetate, and tetrahydrofuran and methanol were used to dissolve and precipitate, and the mixture was repeated 3 times, and the mixture was placed in a vacuum dryer at 22°C for 48h to obtain polynorbornene-benzocycloolefin;

[0065] S3, 0.9g magnesium and 8.5g iodine were mixed, and 12g polynorbornene-benzocycloolefin and 100mL tetrahydrofuran were slowly added in a nitrogen atmosphere within 30min, and the temperature was raised to 65°C, and the reaction was refluxed and stirred for 120min;

[0066] Cool to room temperature, slowly add 11.5g of chlorosilane (dimethyloctadecylchlorosilane), and add it within 30 minutes; heat to 65°C, reflux and stir to react for 120 minutes; filter, wash with water, dry, take the organic phase, wash with water, rotary evaporate, and distill under reduced pressure to obtain a cycloolefin polymer;

[0067] Step 2, in a nitrogen atmosphere, 82 parts of polypropylene, 18 parts of cycloolefin polymer, and 0.10 parts of antioxidant were mixed, melt-blended at 215° C., extruded, and granulated to obtain polypropylene particles;

[0068] Step 3, take polypropylene pellets, melt and extrude at a temperature of 220°C, and chill cast sheets. In the chill casting process, the melt is quickly cooled to 90°C to form a glassy cast sheet; cooled to 50°C for crystallization for 30 minutes, and the temperature of the cooling water in the chill roller is 30°C to form a sheet;

[0069] Then, synchronous biaxial stretching was performed, and the process conditions were: preheating temperature 170°C, stretching temperature 160°C, stretching ratio 5×5; heat setting: setting temperature 170°C, setting time 3 minutes, to obtain a polypropylene capacitor film.

[0070] Embodiment 2: A method for preparing a polypropylene capacitor film, comprising the following process:

[0071] Steps 1 and 2 are the same as those in Example 1 to obtain polypropylene particles;

[0072] Step 3, hot pressing and melting the polypropylene particles, the hot pressing and melting process is: temperature 210°C, pressure 5MPa, time length 10min; isothermal crystallization, the isothermal crystallization process is: temperature 120°C, pressure 5MPa, time length 30min; cooling to form a sheet;

[0073] Then, synchronous biaxial stretching was performed, and the process conditions were: preheating temperature 165°C, stretching temperature 155°C, stretching ratio 5×5; heat setting: setting temperature 145°C, setting time 5 minutes, to obtain a polypropylene capacitor film.

[0074] Embodiment 3: A method for preparing a polypropylene capacitor film, comprising the following process:

[0075] Step 1, S1, 12g of 5-norbornene-2,3-dianhydride and 0.12g of catalyst are mixed in 100mL of tetrahydrofuran, and the mixture is placed at 42°C for constant temperature reaction for 24h in a nitrogen atmosphere; the mixture is cooled to room temperature in air, concentrated, and dissolved and precipitated using dichloromethane and methanol solution, and the mixture is repeated 3 times; the mixture is placed at 25°C for vacuum drying for 48h to obtain polynorbornene;

[0076] S2, 12g polynorbornene and 400mL tetrahydrofuran were mixed, 200mL glacial acetic acid was added, the temperature was raised to 122°C, 15.6g amino-containing brominated benzocycloolefin (5-2,3-dihydro-1H-indene-2-amino) was slowly added, and the reaction was stirred for 5.5h; the mixture was cooled to room temperature, the reaction was quenched with ethyl acetate, and tetrahydrofuran and methanol were used to dissolve and precipitate, and the mixture was repeated 3 times, and the mixture was placed under vacuum drying at 25°C for 48h to obtain polynorbornene-benzocycloolefin;

[0077] S3, 0.9g magnesium and 8.9g iodine were mixed, 12g polynorbornene-benzocycloolefin and 100mL tetrahydrofuran were slowly added in a nitrogen atmosphere within 30min, the temperature was raised to 68°C, and the mixture was refluxed and stirred for 90min;

[0078] Cool to room temperature, slowly add 7.9g of chlorosilane (1-alkenyl undecyl dimethyl chlorosilane), and add it within 30 minutes; raise the temperature to 68°C, reflux and stir to react for 135 minutes; filter, wash with water, dry, take the organic phase, wash with water, rotary evaporate, and distill under reduced pressure to obtain a cycloolefin polymer;

[0079] Step 2, in a nitrogen atmosphere, take 80 parts of polypropylene and tetrahydrofuran, mix them, stir them at 45°C for 45 minutes; add 20 parts of cycloolefin polymer and 3.2 parts of initiator tert-butyl perbenzoate, heat to 130°C, and react for 3.5 hours; add 0.18 parts of antioxidant, melt blend at 220°C, extrude, and granulate to obtain polypropylene particles; the ratio of polypropylene to tetrahydrofuran is 100g / 30mL;

[0080] Step 3: hot-press and melt the polypropylene particles, the hot-press and melt process is as follows: temperature 215°C, pressure 5MPa, and duration 12min; isothermal crystallization is as follows: temperature 125°C, pressure 5MPa, and duration 38min; cooling to form a sheet;

[0081] Then, synchronous biaxial stretching was performed, and the process conditions were: preheating temperature 170°C, stretching temperature 160°C, stretching ratio 5×5; heat setting: setting temperature 145°C, setting time 5 minutes, to obtain a polypropylene capacitor film.

[0082] Embodiment 4: A method for preparing a polypropylene capacitor film, comprising the following process:

[0083] Step 1, S1, 12g of 5-norbornene-2,3-dianhydride and 1.2g of catalyst are mixed in 100mL of tetrahydrofuran, and the mixture is placed at 45°C for constant temperature reaction for 24h in a nitrogen atmosphere; the mixture is cooled to room temperature in air, concentrated, and dissolved and precipitated using dichloromethane and methanol solution, and the mixture is repeated 3 times; the mixture is placed at 27°C for vacuum drying for 48h to obtain polynorbornene;

[0084] S2, 12g polynorbornene and 400mL tetrahydrofuran were mixed, 200mL glacial acetic acid was added, the temperature was raised to 125°C, 16.8g amino-containing brominated benzocycloolefin (7-bromo-tetrahydronaphthyl-1-amine) was slowly added, and the mixture was stirred for 6h; the mixture was cooled to room temperature, the reaction was quenched with ethyl acetate, and the mixture was dissolved and precipitated with tetrahydrofuran and methanol, and the mixture was repeated 3 times, and the mixture was placed under vacuum and dried at 27°C for 48h to obtain polynorbornene-benzocycloolefin;

[0085] S3, 0.9g magnesium and 9.2g iodine were mixed, and 12g polynorbornene-benzocycloolefin and 100mL tetrahydrofuran were slowly added in a nitrogen atmosphere within 30min, and the temperature was raised to 70°C, and the mixture was refluxed and stirred for 60min;

[0086] Cool to room temperature, slowly add 12.5g of chlorosilane (octadecyldiethoxychlorosilane), and add it within 30 minutes; heat to 70°C, reflux and stir to react for 120 minutes; filter, wash with water, dry, take the organic phase, wash with water, rotary evaporate, and distill under reduced pressure to obtain a cycloolefin polymer;

[0087] Step 2, in a nitrogen atmosphere, take 78 parts of polypropylene and 20 mL of tetrahydrofuran, mix, stir at 60°C for 30 minutes; add 22 parts of cycloolefin polymer, heat to 140°C, react for 3 hours; cool to 70°C, add 75 mL of distilled water, stir and hydrolyze for 40 minutes; wash and dry; add 0.25 parts of antioxidant, melt blend at 230°C, extrude, and granulate to obtain polypropylene particles;

[0088] Step 3, melt extrusion of polypropylene particles, chilling casting, rapidly cooling the melt to 95°C to form a glassy casting; cooling to 50°C for crystallization; the temperature of cooling water in the chilling roller is 30°C to form a sheet;

[0089] Then, synchronous biaxial stretching was performed, and the process conditions were: preheating temperature 175°C, stretching temperature 165°C, stretching ratio 5×5; heat setting: setting temperature 145°C, setting time 5 minutes, to obtain a polypropylene capacitor film.

[0090] Comparative Example 1: A method for preparing a polypropylene capacitor film, comprising the following processes:

[0091] Step 1, S1, 12g of 5-norbornene-2,3-dianhydride and 0.12g of catalyst are mixed in 100mL of tetrahydrofuran, and the mixture is placed at 40°C for constant temperature reaction for 24h in a nitrogen atmosphere; the mixture is cooled to room temperature in air, concentrated, and dissolved and precipitated using dichloromethane and methanol solution, and the mixture is repeated 3 times; the mixture is placed at 22°C and vacuum dried for 48h to obtain polynorbornene;

[0092] S2, 12g polynorbornene and 400mL tetrahydrofuran were mixed, 200mL glacial acetic acid was added, the temperature was raised to 120°C, 9g amino-containing brominated benzocycloolefin (bicyclo[4.2.0]octa-1,3,5-triene-7-amine (CAS: 61599-85-7)) was slowly added, and the reaction was stirred for 5h; the mixture was cooled to room temperature, the reaction was quenched with ethyl acetate, and tetrahydrofuran and methanol were used for dissolution and precipitation, and the mixture was repeated 3 times, and the mixture was placed under vacuum and dried at 22°C for 48h to obtain a cycloolefin polymer;

[0093] Steps 2-3 are the same as those in Example 1 to obtain a polypropylene capacitor film.

[0094] Comparative Example 2: A method for preparing a polypropylene capacitor film, comprising the following process:

[0095] Step 1, 12g of 5-norbornene-2,3-dianhydride and 0.12g of catalyst are mixed in 100mL of tetrahydrofuran, and reacted at 40°C in a nitrogen atmosphere for 24h; cooled to room temperature in air, concentrated, dissolved and precipitated with dichloromethane and methanol solution, repeated 3 times, and dried in vacuum at 22°C for 48h to obtain polynorbornene;

[0096] 12 g of polynorbornene and 400 mL of tetrahydrofuran were mixed, 200 mL of glacial acetic acid was added, the temperature was raised to 120°C, 19.7 g of octadecylamine was slowly added, and the mixture was stirred for 5 h; the mixture was cooled to room temperature, the reaction was quenched with ethyl acetate, and tetrahydrofuran and methanol were used for dissolution and precipitation, and the mixture was repeated 3 times, and the mixture was placed under vacuum and dried at 22°C for 48 h to obtain a cycloolefin polymer;

[0097] Steps 2-3 are the same as those in Example 1 to obtain a polypropylene capacitor film.

[0098] Comparative Example 3: A method for preparing a polypropylene capacitor film, comprising the following processes:

[0099] In a nitrogen atmosphere, 82 parts of polypropylene, 18 parts of cycloolefin polymer (9506F-500, from Polyplastics Co., Ltd.), and 0.10 parts of an antioxidant were mixed, melt-blended at 215°C, extruded, and granulated to obtain polypropylene pellets;

[0100] The melt is rapidly cooled to 95°C to form a glassy sheet; it is cooled to 50°C for crystallization; the temperature of the cooling water in the chilling roller is 30°C to form a sheet;

[0101] Then, synchronous biaxial stretching was performed, and the process conditions were: preheating temperature 170°C, stretching temperature 160°C, stretching ratio 5×5; heat setting: setting temperature 170°C, setting time 3 minutes, to obtain a polypropylene capacitor film.

[0102] Experiment: The polypropylene capacitor films obtained in Examples 1-4 and Comparative Examples 1-3 were used to prepare samples, and their performance was tested respectively with reference to GT / T13542.2 and the test results were recorded:

[0103]

[0104] According to the data in the above table, we can clearly draw the following conclusions:

[0105] The polypropylene capacitor films obtained in Examples 1-4 are compared with the polypropylene capacitor films obtained in Comparative Examples 1-3. The test results show that the polypropylene capacitor films obtained in Examples 2-4 have higher tensile strength, roughening degree, breakdown strength and lower thermal shrinkage data than those in Example 1 and the comparative example. This fully demonstrates that the present invention achieves the improvement of the mechanical properties, heat resistance and dielectric properties of the prepared polypropylene capacitor film.

[0106] Compared with Example 2, the preparation process of the polypropylene capacitor film in Example 1 is different; the cycloolefin polymer in Comparative Example 1 is prepared from 5-norbornene-2,3-dianhydride and bicyclo[4.2.0]octa-1,3,5-triene-7-amine; the cycloolefin polymer in Comparative Example 2 is prepared from 5-norbornene-2,3-dianhydride and octadecylamine; the cycloolefin polymer in Comparative Example 3 is a commercially available film product. The tensile strength, roughness, and breakdown strength of the polypropylene capacitor film obtained in Comparative Examples 1-3 decreased, and the thermal shrinkage rate data increased. It can be seen that the setting of the cycloolefin polymer component and its process of the present invention can promote the comprehensive improvement of the mechanical properties, heat resistance and dielectric properties of the polypropylene capacitor film.

[0107] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process method article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process method article or device.

[0108] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a polypropylene capacitor film, characterized in that: Including the following processes: The polypropylene particles are melted and extruded, and then quenched and cast to form a sheet; and then biaxially stretched to obtain a polypropylene capacitor film; Or take polypropylene particles and heat-press and melt them, isothermally crystallize them, and cool them to form sheets; Then, biaxial stretching is performed to obtain a polypropylene capacitor film; The polypropylene particles include: by mass, 78 to 82 parts of polypropylene and 18 to 22 parts of cycloolefin polymer; The cycloolefin polymer comprises the following preparation components: 5-norbornene-2,3-dianhydride, amino-containing brominated benzocycloolefin and chlorosilane; The cycloolefin polymer is prepared by the following process: S1, 5-norbornene-2,3-dianhydride and a catalyst are mixed in tetrahydrofuran, and reacted at a constant temperature of 40-45° C. for 24 hours in a nitrogen atmosphere to obtain polynorbornene; S2, mixing polynorbornene and tetrahydrofuran, adding glacial acetic acid, heating to 120-125° C., slowly adding amino-containing brominated benzocycloolefin, stirring and reacting for 5-6 hours to obtain polynorbornene-benzocycloolefin; S3, mixing magnesium and iodine, slowly adding polynorbornene-benzocycloolefin and tetrahydrofuran in a nitrogen atmosphere within 30 minutes, raising the temperature to 65-70° C., and reacting under reflux stirring for 60-120 minutes; Cool to room temperature, slowly add chlorosilane, and add it within 30 minutes; raise the temperature to 65-70°C, reflux and stir to react for 120-150 minutes to obtain a cycloolefin polymer; When the chlorosilane is one of 7-octenyldimethylchlorosilane, 5-hexenyldimethylchlorosilane and 1-enylundecyldimethylchlorosilane, the polypropylene particles are prepared by the following process: In a nitrogen atmosphere, polypropylene and tetrahydrofuran are mixed and stirred at 30-60°C for 30-60 minutes; cycloolefin polymer and initiator are added, the temperature is raised to 120-140°C, and the reaction is carried out for 3-4 hours; antioxidant is added, melt blending is carried out at 215-230°C, extrusion is carried out, and granulation is carried out to obtain polypropylene granules; When the chlorosilane is octadecyldiethoxychlorosilane, the polypropylene particles are prepared by the following process: In a nitrogen atmosphere, mix polypropylene and tetrahydrofuran, stir at 30-60°C for 30-60 minutes; add cycloolefin polymer, raise the temperature to 120-140°C, and react for 3-4 hours; Cool down to 88-93°C, add distilled water, stir and hydrolyze for 30-45 minutes; wash and dry; Add an antioxidant, melt blend at 215-230° C., extrude, and granulate to obtain polypropylene particles.

2. The method for preparing a polypropylene capacitor film according to claim 1, characterized in that: The hot pressing and melting process is as follows: temperature 210-220° C., pressure 5 MPa, and duration 10-15 min.

3. The method for preparing a polypropylene capacitor film according to claim 1, characterized in that: The isothermal crystallization process is as follows: temperature 120-130° C., pressure 5 MPa, and duration 30-45 min.

4. The method for preparing a polypropylene capacitor film according to claim 1, characterized in that: The biaxial stretching is synchronous biaxial stretching, and the process conditions are: preheating temperature 165-175°C, stretching temperature 155-165°C, stretching ratio (4-5)×(4-5); and setting temperature 145-175°C.

5. The method for preparing a polypropylene capacitor film according to claim 1, characterized in that: The amino-containing brominated benzocycloolefin is a mixture of one or more of 4-bromobicyclo[4.2.0]octa-1,3,5-triene-7-amine, 5-2,3-dihydro-1H-indene-2-amino, and 7-bromo-tetrahydronaphthyl-1-amine.

6. The method for preparing a polypropylene capacitor film according to claim 1, characterized in that: When the chlorosilane is one of dimethylvinyl chlorosilane, n-pentyldimethylchlorosilane, chlorodimethyloctylsilane, decyldimethylchlorosilane, dodecyldimethylchlorosilane, dimethyloctadecylchlorosilane, n-triacontyldimethylchlorosilane, and 2-(di-n-octylmethylsilane)ethyldimethylchlorosilane, the polypropylene particles are prepared by the following process: In a nitrogen atmosphere, polypropylene, cycloolefin polymer and antioxidant are mixed, melt-blended at 215-230° C., extruded and granulated to obtain polypropylene particles.

7. A polypropylene capacitor film, characterized in that: The method is prepared by any one of claims 1 to 6.

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