Electric breakdown-resistant high-performance polypropylene electrical membrane and preparation method thereof

Abstract

The invention relates to the technical field of polypropylene electrical membranes, in particular to an electric-breakdown-resistant high-performance polypropylene electrical membrane and a preparation method thereof. The invention provides a preparation method of a high-performance polypropylene electrical membrane, which comprises the following steps: mixing polypropylene powder, styrene, a crosslinking aid and a compatilizer, performing melt extrusion granulation, and performing hot pressing, cold pressing, two-way stretching, cooling shaping, trimming and corona treatment to obtain the polypropylene electrical membrane, wherein the cross-linking auxiliary agent is prepared by taking maleic anhydride, 2, 4, 6-triaminotoluene and allyl isocyanate as raw materials and carrying out reaction on the maleic anhydride, the 2, 4, 6-triaminotoluene and the allyl isocyanate; the compatilizer is obtained by reacting maleic anhydride and polypropylene. The prepared polypropylene electrical membrane is good in combustion performance, high in mechanical strength and high in electric breakdown resistance at high temperature.

Description

Technical Field

[0001] The invention relates to the technical field of polypropylene electrical films, in particular to an electrical breakdown resistant high-performance polypropylene electrical film and a preparation method thereof. Background Art

[0002] In recent years, as the demand for clean energy has gradually increased, renewable green energy such as wind and solar energy has accounted for an increasing proportion in power generation. As a key device for energy storage, filtering and voltage stabilization, capacitors are widely used in all aspects of the power system. Compared with electrolytic capacitors, film capacitors have the advantages of high rated voltage, strong surge resistance and light weight.

[0003] With the continuous development of new energy technologies, the domestic lithium battery separator industry has also developed rapidly. Among many polyolefin materials, polypropylene has the advantages of light weight, cleanliness, high rigidity, good heat resistance, and low dielectric loss coefficient. After biaxial stretching, it can be used to manufacture electrical films with small thickness and high mechanical properties, which are used in the manufacture of capacitors and lithium battery separators. However, under high temperature conditions, the breakdown field strength of polypropylene film decreases. The low breakdown field strength makes the polypropylene film prone to insulation breakdown, and produces gas due to thermal decomposition, which in turn causes capacitor bulging, explosion and other failures. Therefore, it is necessary to modify the existing technology. Summary of the invention

[0004] The object of the present invention is to provide a high-performance polypropylene electrical film resistant to electrical breakdown and a preparation method thereof, so as to solve the problems raised in the above-mentioned background technology.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a high-performance polypropylene electrical film resistant to electrical breakdown and a preparation method thereof, comprising the following steps:

[0006] Step 1:

[0007] Weigh polypropylene powder, dibenzoyl peroxide, styrene, a crosslinking aid, and a compatibilizer, mix them, heat them for a reaction of 10 to 15 minutes, melt and plasticize them to obtain a molten fluid melt; filter the molten fluid melt to remove impurities and unmelted materials in the melt, and extrude and granulate them;

[0008] Step 2:

[0009] After hot pressing the particles, the temperature is reduced and cold pressed to obtain flakes;

[0010] Step 3:

[0011] The sheet is biaxially stretched, and the biaxially stretched film is sequentially cooled, shaped, trimmed and corona treated to obtain a polypropylene electrical film.

[0012] Furthermore, in step 1, the reaction temperature is 190-200°C.

[0013] Furthermore, in step 1, the melt plasticizing temperature is 260-270°C.

[0014] Furthermore, in step 1, the extrusion granulation temperature is 250-260°C.

[0015] Furthermore, in step 1, the contents of the components, by weight, are 100 to 120 parts of polypropylene powder, 0.03 to 0.05 parts of dibenzoyl peroxide, 1 to 2 parts of styrene, 3 to 4 parts of a cross-linking aid, and 1 to 2 parts of a compatibilizer.

[0016] Furthermore, in step 1, the preparation method of the cross-linking auxiliary agent is: take maleic anhydride and 2,4,6-triaminotoluene and disperse them in 1,4-dioxane, under nitrogen protection, heat to 85-90°C, heat to reflux and stir to react for 2-3 hours, then cool to 50-60°C, add allyl isocyanate and continue to react for 1-2 hours, remove 1,4-dioxane by rotary evaporation, wash the solid precipitate with ethanol, and vacuum dry.

[0017] Furthermore, the molar ratio of maleic anhydride, 2,4,6-triaminotoluene and allyl isocyanate is 1:1:2.

[0018] Furthermore, in step 1, the preparation method of the compatibilizer is as follows: polypropylene powder and maleic anhydride are dispersed in xylene by weight, heated and stirred to 120-130° C. under nitrogen protection, dibenzoyl peroxide is added to react for 3-5 hours, the product is precipitated with acetone, washed with clean water, and dried.

[0019] Furthermore, the amount of each component, by weight, is 45-50 parts of polypropylene powder, 5-7 parts of maleic anhydride dispersed in xylene, and 0.01-0.015 parts of dibenzoyl peroxide.

[0020] Furthermore, in step 1, the preparation method of polypropylene powder is: taking CONSISTA catalyst, activator triethylaluminum, and external electron donor cyclohexylmethyldimethoxysilane into the Unipol process circulating gas pipeline, and reacting in the Unipol process reactor; wherein the molar ratio of aluminum / titanium of the activator triethylaluminum and the CONSISTA catalyst is (12-48):1; the molar ratio of silicon / titanium of cyclohexylmethyldimethoxysilane and the CONSISTA catalyst is (1-4):1; the reaction temperature in the polymerization stage is 70-75°C, and the isotacticity of polypropylene is ≥98wt.%.

[0021] Furthermore, in step 2, the hot pressing temperature is 200-210° C., the hot pressing pressure is 10-15 MPa, and the hot pressing time is 10-15 min; the cold pressing temperature is 25-35° C., the cold pressing pressure is 10-15 MPa, and the cold pressing time is 10-15 min.

[0022] Furthermore, in step 2, the thickness of the sheet is 100 to 120 μm.

[0023] Furthermore, in step 3, the longitudinal stretching ratio is 3 to 5 times, the transverse stretching ratio is 5 to 10 times, and the stretching is performed in both directions simultaneously.

[0024] Furthermore, in step 3, the thickness of the polypropylene electrical film is 2 to 4 μm.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the present invention provides a method for preparing a high-performance polypropylene electrical film, specifically, the polypropylene powder, styrene, a cross-linking aid, and a compatibilizer are mixed, melt-extruded and granulated, and then subjected to hot pressing, cold pressing, biaxial stretching, cooling and shaping, trimming, and corona treatment to obtain the polypropylene electrical film. The polypropylene electrical film prepared by the present invention has good performance, is not easy to burn, and has strong electrical breakdown strength at high temperatures.

[0026] The present invention uses maleic anhydride, 2,4,6-triaminotoluene and allyl isocyanate as raw materials to react and synthesize a crosslinking aid. The crosslinking aid contains two unsaturated carbon-carbon double bonds, which can react with styrene monomer under the action of an initiator to prepare long-chain branched polypropylene. The long-chain branched structure can enhance the entanglement between polypropylene molecular chains, inhibit the thermal motion of polypropylene molecular chains at high temperatures, reduce the influence of temperature on free volume, and improve dielectric properties. Generally, the ash in polypropylene is ionized to generate carriers under the action of an electrothermal composite field, and the carrier migration causes an increase in conductivity loss and a decrease in breakdown field strength. In the present invention, styrene and the crosslinking aid are both aromatic compounds, which can introduce deep traps on the long branched chains, limit the carrier migration characteristics, and thus achieve the enhancement of the dielectric properties of the film; in addition, the benzene ring structure has a strong electron affinity and stability (having a similar effect to voltage stabilization), and the polypropylene matrix after the benzene ring is grafted is more likely to capture high-energy electrons, while inhibiting the damage of high-energy electrons to the polyolefin molecular chains, so the material has a stronger resistance to electrical breakdown.

[0027] In addition, the present invention also prepares a compatibilizer for improving the compatibility of each component. Wherein, the compatibilizer is obtained by reacting maleic anhydride and polypropylene. The compatibilizer and the crosslinking aid in the present invention are both polar materials, which weaken the effect of interfacial polarization and make it show more excellent dielectric properties. The maleic anhydride in the compatibilizer and the benzene ring produce a synergistic effect, further increasing the trap depth, significantly inhibiting the accumulation of space charges in polypropylene, increasing the breakdown field strength, thereby inhibiting the migration of charges, so that the addition of the compatibilizer enables polypropylene to obtain good electrical properties and mechanical properties. DETAILED DESCRIPTION

[0028] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0029] Materials and sources used in the present invention: CONSISTA catalyst comes from GRACE Company, USA, model CONSISTA 602.

[0030] Embodiment 1: A high-performance polypropylene electrical film resistant to electrical breakdown and a preparation method thereof, comprising the following steps:

[0031] Step 1:

[0032] Maleic anhydride and 2,4,6-triaminotoluene are dispersed in 1,4-dioxane, and the temperature is raised to 85°C, heated to reflux and stirred for reaction for 2 hours under nitrogen protection, and then the temperature is lowered to 50°C, allyl isocyanate is added and the reaction is continued for 1 hour, 1,4-dioxane is removed by rotary evaporation, and the solid precipitate is washed with ethanol and vacuum dried to obtain a cross-linking agent; wherein the molar ratio of maleic anhydride, 2,4,6-triaminotoluene and allyl isocyanate is 1:1:2;

[0033] Step 2:

[0034] Disperse 50g of polypropylene powder and 5g of maleic anhydride in xylene, heat and stir to 120°C under nitrogen protection, add 0.013g of dibenzoyl peroxide and react for 3h, precipitate the product with acetone, wash with water and dry to obtain a compatibilizer;

[0035] Step 3:

[0036] S1: Weigh 120kg of polypropylene powder, 0.03kg of dibenzoyl peroxide, 1kg of styrene, 3kg of a crosslinking aid, and 1.5kg of a compatibilizer, mix them, heat them to 190°C for reaction for 10min, heat them to 260°C for melt plasticization, and obtain a molten fluid melt; filter the molten fluid melt to remove impurities and unmelted materials in the melt, and extrude and granulate them at 250°C;

[0037] S2: hot pressing the particles at 200°C and 10 MPa for 10 min, cooling to 25°C, and cold pressing at 10 MPa for 10 min to obtain a sheet with a thickness of 120 μm;

[0038] S3: The thin film is biaxially stretched, with a longitudinal stretching ratio of 5 times and a transverse stretching ratio of 6 times, and the biaxial stretching is performed simultaneously; the biaxially stretched film is sequentially cooled, shaped, trimmed and corona treated to obtain a polypropylene electrical film with a thickness of 4 μm.

[0039] The preparation method of the above-mentioned polypropylene powder is: add CONSISTA catalyst, activator triethylaluminum, and external electron donor cyclohexylmethyldimethoxysilane into the Unipol process circulating gas pipeline, and react in the Unipol process reactor; wherein the molar ratio of aluminum / titanium of the activator triethylaluminum and the CONSISTA catalyst is 45:1; the molar ratio of silicon / titanium of the cyclohexylmethyldimethoxysilane and the CONSISTA catalyst is 3.4:1; the reaction temperature in the polymerization stage is 70°C, and the isotacticity of the polypropylene is ≥98wt.%.

[0040] Embodiment 2: A high-performance polypropylene electrical film resistant to electrical breakdown and a preparation method thereof, comprising the following steps:

[0041] Step 1:

[0042] Maleic anhydride and 2,4,6-triaminotoluene are dispersed in 1,4-dioxane, and the temperature is raised to 90°C, heated under reflux and stirred for reaction for 2.5 hours under nitrogen protection, and then the temperature is lowered to 55°C, allyl isocyanate is added, and the reaction is continued for 1.5 hours, and 1,4-dioxane is removed by rotary evaporation, and the solid precipitate is washed with ethanol and vacuum dried to obtain a crosslinking auxiliary agent; wherein the molar ratio of maleic anhydride, 2,4,6-triaminotoluene and allyl isocyanate is 1:1:2;

[0043] Step 2:

[0044] Disperse 50g of polypropylene powder and 5g of maleic anhydride in xylene, heat and stir to 125°C under nitrogen protection, add 0.013g of dibenzoyl peroxide and react for 4h, precipitate the product with acetone, wash with water and dry to obtain a compatibilizer;

[0045] Step 3:

[0046] S1: Weigh 120kg of polypropylene powder, 0.03kg of dibenzoyl peroxide, 1.5kg of styrene, 3.5kg of a crosslinking aid, and 1.5kg of a compatibilizer, mix them, heat them to 195°C for reaction for 12min, heat them to 265°C for melt plasticization, and obtain a molten fluid melt; filter the molten fluid melt to remove impurities and unmelted materials in the melt, and extrude and granulate them at 255°C;

[0047] S2: The particles were hot pressed at 205°C and 13 MPa for 12 min, cooled to 30°C, and cold pressed at 12 MPa for 14 min to obtain a sheet with a thickness of 120 μm;

[0048] S3: The thin film is biaxially stretched, with a longitudinal stretching ratio of 5 times and a transverse stretching ratio of 6 times, and the biaxial stretching is performed simultaneously; the biaxially stretched film is sequentially cooled, shaped, trimmed and corona treated to obtain a polypropylene electrical film with a thickness of 4 μm.

[0049] The preparation method of the above-mentioned polypropylene powder is: add CONSISTA catalyst, activator triethylaluminum, and external electron donor cyclohexylmethyldimethoxysilane into the Unipol process circulating gas pipeline, and react in the Unipol process reactor; wherein the molar ratio of aluminum / titanium of the activator triethylaluminum and the CONSISTA catalyst is 45:1; the molar ratio of silicon / titanium of the cyclohexylmethyldimethoxysilane and the CONSISTA catalyst is 3.4:1; the reaction temperature in the polymerization stage is 72°C, and the isotacticity of the polypropylene is ≥98wt.%.

[0050] Embodiment 3: A high-performance polypropylene electrical film resistant to electrical breakdown and a preparation method thereof, comprising the following steps:

[0051] Step 1:

[0052] Maleic anhydride and 2,4,6-triaminotoluene are dispersed in 1,4-dioxane, and the temperature is raised to 90°C, heated under reflux and stirred for reaction for 3 hours under nitrogen protection, and then the temperature is lowered to 60°C, allyl isocyanate is added, and the reaction is continued for 2 hours, and 1,4-dioxane is removed by rotary evaporation, and the solid precipitate is washed with ethanol and vacuum dried to obtain a crosslinking auxiliary agent; wherein the molar ratio of maleic anhydride, 2,4,6-triaminotoluene and allyl isocyanate is 1:1:2;

[0053] Step 2:

[0054] Disperse 50g of polypropylene powder and 5g of maleic anhydride in xylene, heat and stir to 130°C under nitrogen protection, add 0.013g of dibenzoyl peroxide and react for 5h, precipitate the product with acetone, wash with water and dry to obtain a compatibilizer;

[0055] Step 3:

[0056] S1: Weigh 120kg of polypropylene powder, 0.03kg of dibenzoyl peroxide, 2kg of styrene, 4kg of a crosslinking aid, and 1.5kg of a compatibilizer, mix them, heat them to 200°C for reaction for 15min, heat them to 270°C for melt plasticization, and obtain a molten fluid melt; filter the molten fluid melt to remove impurities and unmelted materials in the melt, and extrude and granulate them at 260°C;

[0057] S2: hot pressing the particles at 210°C and 15 MPa for 15 min, cooling to 35°C, and cold pressing at 15 MPa for 15 min to obtain a sheet with a thickness of 120 μm;

[0058] S3: The thin film is biaxially stretched, with a longitudinal stretching ratio of 5 times and a transverse stretching ratio of 6 times, and the biaxial stretching is performed simultaneously; the biaxially stretched film is sequentially cooled, shaped, trimmed and corona treated to obtain a polypropylene electrical film with a thickness of 4 μm.

[0059] The preparation method of the above-mentioned polypropylene powder is: add CONSISTA catalyst, activator triethylaluminum, and external electron donor cyclohexylmethyldimethoxysilane into the Unipol process circulating gas pipeline, and react in the Unipol process reactor; wherein the molar ratio of aluminum / titanium of the activator triethylaluminum and the CONSISTA catalyst is 45:1; the molar ratio of silicon / titanium of the cyclohexylmethyldimethoxysilane and the CONSISTA catalyst is 3.4:1; the reaction temperature in the polymerization stage is 70-75°C, and the isotacticity of the polypropylene is ≥98wt.%.

[0060] Comparative Example 1: No crosslinking agent was added, and other parameters were the same as those in Example 1.

[0061] Step 1:

[0062] Disperse 50g of polypropylene powder and 5g of maleic anhydride in xylene, heat and stir to 120°C under nitrogen protection, add 0.013g of dibenzoyl peroxide and react for 3h, precipitate the product with acetone, wash with water and dry to obtain a compatibilizer;

[0063] Step 2:

[0064] S1: Weigh 120kg of polypropylene powder, 0.03kg of dibenzoyl peroxide, 1kg of styrene, and 1.5kg of a compatibilizer, mix them, heat them to 190°C for reaction for 10min, heat them to 260°C for melt plasticization, and obtain a molten fluid melt; filter the molten fluid melt to remove impurities and unmelted materials in the melt, and extrude and granulate them at 250°C;

[0065] S2: hot pressing the particles at 200°C and 10 MPa for 10 min, cooling to 25°C, and cold pressing at 10 MPa for 10 min to obtain a sheet with a thickness of 120 μm;

[0066] S3: The thin film is biaxially stretched, with a longitudinal stretching ratio of 5 times and a transverse stretching ratio of 6 times, and the biaxial stretching is performed simultaneously; the biaxially stretched film is sequentially cooled, shaped, trimmed and corona treated to obtain a polypropylene electrical film with a thickness of 4 μm.

[0067] The preparation method of the above-mentioned polypropylene powder is: add CONSISTA catalyst, activator triethylaluminum, and external electron donor cyclohexylmethyldimethoxysilane into the Unipol process circulating gas pipeline, and react in the Unipol process reactor; wherein the molar ratio of aluminum / titanium of the activator triethylaluminum and the CONSISTA catalyst is 45:1; the molar ratio of silicon / titanium of the cyclohexylmethyldimethoxysilane and the CONSISTA catalyst is 3.4:1; the reaction temperature in the polymerization stage is 70°C, and the isotacticity of the polypropylene is ≥98wt.%.

[0068] Comparative Example 2: No benzene ring structure is introduced (melamine is used instead of 2,4,6-triaminotoluene to prepare the crosslinking auxiliary agent, and styrene is not introduced), and the other parameters are the same as those in Example 2.

[0069] Step 1:

[0070] Maleic anhydride and melamine are dispersed in 1,4-dioxane, and the temperature is raised to 90°C, heated under reflux and stirred for reaction for 2.5 hours under nitrogen protection, and then the temperature is lowered to 55°C, allyl isocyanate is added, and the reaction is continued for 1.5 hours, and 1,4-dioxane is removed by rotary evaporation, and the solid precipitate is washed with ethanol and vacuum dried to obtain a crosslinking auxiliary agent; wherein the molar ratio of maleic anhydride, melamine and allyl isocyanate is 1:1:2;

[0071] Step 2:

[0072] Disperse 50g of polypropylene powder and 5g of maleic anhydride in xylene, heat and stir to 125°C under nitrogen protection, add 0.013g of dibenzoyl peroxide and react for 4h, precipitate the product with acetone, wash with water and dry to obtain a compatibilizer;

[0073] Step 3:

[0074] S1: Weigh 120kg of polypropylene powder, 0.03kg of dibenzoyl peroxide, 3.5kg of crosslinking aid, and 1.5kg of compatibilizer, mix them, heat them to 195°C for reaction for 12min, heat them to 265°C for melt plasticization to obtain a molten fluid melt; filter the molten fluid melt to remove impurities and unmelted materials in the melt, and extrude and granulate them at 255°C;

[0075] S2: The particles were hot pressed at 205°C and 13 MPa for 12 min, cooled to 30°C, and cold pressed at 12 MPa for 14 min to obtain a sheet with a thickness of 120 μm;

[0076] S3: The thin film is biaxially stretched, with a longitudinal stretching ratio of 5 times and a transverse stretching ratio of 6 times, and the biaxial stretching is performed simultaneously; the biaxially stretched film is sequentially cooled, shaped, trimmed and corona treated to obtain a polypropylene electrical film with a thickness of 4 μm.

[0077] The preparation method of the above-mentioned polypropylene powder is to add CONSISTA catalyst, activator triethylaluminum, and external electron donor cyclohexylmethyldimethoxysilane into the Unipol process circulating gas pipeline and react in the Unipol process reactor; wherein the molar ratio of aluminum / titanium of the activator triethylaluminum and the CONSISTA catalyst is 45:1; the molar ratio of silicon / titanium of the cyclohexylmethyldimethoxysilane and the CONSISTA catalyst is 3.4:1; the reaction temperature in the polymerization stage is 72°C, and the isotacticity of the polypropylene is ≥98wt.%.

[0078] Comparative Example 3: No compatibilizer was added, and the other parameters were the same as those in Example 3.

[0079] Step 1:

[0080] Maleic anhydride and 2,4,6-triaminotoluene are dispersed in 1,4-dioxane, and the temperature is raised to 90°C, heated under reflux and stirred for reaction for 3 hours under nitrogen protection, and then the temperature is lowered to 60°C, allyl isocyanate is added, and the reaction is continued for 2 hours, and 1,4-dioxane is removed by rotary evaporation, and the solid precipitate is washed with ethanol and vacuum dried to obtain a crosslinking auxiliary agent; wherein the molar ratio of maleic anhydride, 2,4,6-triaminotoluene and allyl isocyanate is 1:1:2;

[0081] Step 2:

[0082] S1: Weigh 120kg of polypropylene powder, 0.03kg of dibenzoyl peroxide, 2kg of styrene, 4kg of a crosslinking aid, and 1.5kg of a compatibilizer, mix them, heat them to 200°C for reaction for 15min, heat them to 270°C for melt plasticization, and obtain a molten fluid melt; filter the molten fluid melt to remove impurities and unmelted materials in the melt, and extrude and granulate them at 260°C;

[0083] S2: hot pressing the particles at 210°C and 15 MPa for 15 min, cooling to 35°C, and cold pressing at 15 MPa for 15 min to obtain a sheet with a thickness of 120 μm;

[0084] S3: The thin film is biaxially stretched, with a longitudinal stretching ratio of 5 times and a transverse stretching ratio of 6 times, and the biaxial stretching is performed simultaneously; the biaxially stretched film is sequentially cooled, shaped, trimmed and corona treated to obtain a polypropylene electrical film with a thickness of 4 μm.

[0085] The preparation method of the above-mentioned polypropylene powder is: add CONSISTA catalyst, activator triethylaluminum, and external electron donor cyclohexylmethyldimethoxysilane into the Unipol process circulating gas pipeline, and react in the Unipol process reactor; wherein the molar ratio of aluminum / titanium of the activator triethylaluminum and the CONSISTA catalyst is 45:1; the molar ratio of silicon / titanium of the cyclohexylmethyldimethoxysilane and the CONSISTA catalyst is 3.4:1; the reaction temperature in the polymerization stage is 75°C, and the isotacticity of the polypropylene is ≥98wt.%.

[0086] Experiment: The performance of the polypropylene electrical films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was tested.

[0087] Tensile performance test: refer to GB / T 12802.2-2004 to test the tensile strength and elongation at break of the samples. Each group of samples is tested 5 times and the average value is calculated.

[0088] Dielectric strength test: Place the sample on the ball plate electrode and apply voltage at a rate of 0.5 kV / s until the film breaks down. The test temperature is 100°C. Each group of samples is tested 5 times and the average value is calculated and recorded as the DC breakdown voltage.

[0089] The experimental results are shown in Table 1.

[0090] Table 1. Test results of various properties of polypropylene electrical film

[0091]

[0092] Conclusion: The data of Examples 1 to 3 show that the polypropylene electrical film prepared by the present invention has good performance. The data of Example 1 and Comparative Example 1 show that after adding the crosslinking aid, since the crosslinking aid contains two unsaturated carbon-carbon double bonds, it can be grafted with styrene to the polypropylene side chain to form a branched long chain, thereby improving the electrical breakdown resistance of the polypropylene electrical film at high temperature. The data of Example 2 and Comparative Example 2 show that after the introduction of the benzene ring structure, the electronic energy band structure of the polypropylene matrix is ​​different. After the benzene ring structure is grafted onto the polypropylene, a deep trap site will be formed inside the polypropylene, thereby improving the breakdown performance. The data of Example 3 and Comparative Example 3 show that when a compatibilizer is added, since the compatibilizer and the crosslinking aid are polar, the grafting rate of styrene in polypropylene can be increased. At the same time, the two will also produce a synergistic effect, which increases the trap depth, thereby inhibiting the migration of charges, effectively hindering the accumulation of spatial charges in polypropylene, and improving the electrical breakdown strength.

[0093] Finally, it should be noted that the above description 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 high-performance polypropylene electrical film resistant to electrical breakdown, characterized in that: The following steps are involved: Step 1: Take polypropylene powder, dibenzoyl peroxide, styrene, crosslinking aid and compatibilizer, mix them, heat them to 190-200°C for reaction for 10-15 minutes, heat them to 260-270°C for melting and plasticizing to obtain a molten fluid melt; filter the molten fluid melt to remove impurities and unmelted materials in the melt, and extrude and granulate them at 250-260°C; Step 2: hot pressing the particles and then cooling and cold pressing them to obtain flakes; Step 3: biaxially stretch the sheet, and sequentially cool, shape, trim and corona treat the biaxially stretched film to obtain a polypropylene electrical film.

2. The method for preparing a high-performance polypropylene electrical film resistant to electrical breakdown according to claim 1, characterized in that: In step 1, the content of each component, by weight, is 100 to 120 parts of polypropylene powder, 0.03 to 0.05 parts of dibenzoyl peroxide, 1 to 2 parts of styrene, 3 to 4 parts of cross-linking aid, and 1 to 2 parts of compatibilizer.

3. The method for preparing a high-performance polypropylene electrical film resistant to electrical breakdown according to claim 1, characterized in that: In step 1, the preparation method of the cross-linking auxiliary agent is as follows: maleic anhydride and 2,4,6-triaminotoluene are dispersed in 1,4-dioxane, and the temperature is raised to 85-90° C. under nitrogen protection, and the mixture is refluxed and stirred for reaction for 2-3 hours, and then the temperature is lowered to 50-60° C., allyl isocyanate is added, and the reaction is continued for 1-2 hours, 1,4-dioxane is removed by rotary evaporation, and the solid precipitate is washed with ethanol and dried in vacuo.

4. The method for preparing a high-performance polypropylene electrical film resistant to electrical breakdown according to claim 3, characterized in that: The molar ratio of maleic anhydride, 2,4,6-triaminotoluene and allyl isocyanate is 1:1:

2.

5. The method for preparing a high-performance polypropylene electrical film resistant to electrical breakdown according to claim 1, characterized in that: In step 1, the preparation method of the compatibilizer is as follows: by weight, 45 to 50 parts of polypropylene powder and 5 to 7 parts of maleic anhydride are dispersed in xylene, heated and stirred to 120 to 130° C. under nitrogen protection, 0.01 to 0.015 parts of dibenzoyl peroxide are added to react for 3 to 5 hours, the product is precipitated with acetone, washed with clean water, and dried.

6. The method for preparing a high-performance polypropylene electrical film resistant to electrical breakdown according to claim 1, characterized in that: In step 1, the preparation method of polypropylene powder is: adding CONSISTA catalyst, activator triethylaluminum, and external electron donor cyclohexylmethyldimethoxysilane to the Unipol process circulating gas pipeline, and reacting in the Unipol process reactor; wherein the molar ratio of aluminum / titanium of the activator triethylaluminum and the CONSISTA catalyst is (12-48):1; the molar ratio of silicon / titanium of the cyclohexylmethyldimethoxysilane and the CONSISTA catalyst is (1-4):1; the reaction temperature in the polymerization stage is 70-75°C, and the isotacticity of the polypropylene is ≥98wt.%.

7. The method for preparing a high-performance polypropylene electrical film resistant to electrical breakdown according to claim 1, characterized in that: In step 2, the hot pressing temperature is 200-210° C., the hot pressing pressure is 10-15 MPa, and the hot pressing time is 10-15 min; the cold pressing temperature is 25-35° C., the cold pressing pressure is 10-15 MPa, and the cold pressing time is 10-15 min.

8. The method for preparing a high-performance polypropylene electrical film resistant to electrical breakdown according to claim 1, characterized in that: In step 2, the thickness of the sheet is 100 to 120 μm.

9. The method for preparing a high-performance polypropylene electrical film resistant to electrical breakdown according to claim 1, characterized in that: In step 3, the longitudinal stretching ratio is 3 to 5 times, the transverse stretching ratio is 5 to 10 times, and the stretching is performed in both directions simultaneously; the thickness of the polypropylene electrical film is 2 to 4 μm.

10. The polypropylene electrical film prepared by the preparation method according to any one of claims 1 to 9.

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