A method for preparing maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film

Abstract

The present invention discloses a method for preparing a maleic anhydride-grafted polypropylene / magnesium oxide nanocomposite capacitor film, comprising the following steps: step (1) preparing modified porous nanomagnesium oxide; step (2) preparing maleic anhydride-modified porous nanomagnesium oxide; and step (3) melt-blending the maleic anhydride-grafted polypropylene, an antioxidant, dicumyl peroxide, and the maleic anhydride-modified porous nanomagnesium oxide, extruding, rolling, stretching, and shaping to obtain the maleic anhydride-grafted polypropylene / magnesium oxide nanocomposite capacitor film. This solution utilizes a silane coupling agent and maleic anhydride-modified nanomagnesium oxide to enable them to be better dispersed in the maleic anhydride-grafted polypropylene, thereby improving the overall performance of the composite capacitor film.

Description

Technical Field

[0001] The present invention relates to the field of power capacitors, and in particular to a method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film. Background Art

[0002] Polypropylene is commonly used to prepare capacitor films. Due to its low dielectric loss, high breakdown field strength, and excellent thermal stability, it is widely used in high-frequency circuits, power systems, and new energy equipment. However, with the development of society, the performance of current pure polypropylene films has gradually failed to meet market demand, and modified composite films often suffer from unstable quality and reduced mechanical properties. CN 107987390 B provides a high-energy storage density polypropylene-maleic anhydride-grafted polypropylene-nano-zirconia composite material and its preparation method. Pure polypropylene, maleic anhydride-grafted polypropylene, and nano-zirconia are melt-blended in a certain proportion, wherein the polypropylene is isotactic polypropylene; the grafting rate of the maleic anhydride-grafted polypropylene is 1%; the nano-zirconia particles have a diameter of 10 to 30 nm, and the surface has been treated with KH570 silane coupling. A composite film is then prepared using this composite material. However, the nanoparticles used are not modified, so agglomeration is inevitable, and the mechanical properties are questionable. Summary of the Invention

[0003] In order to solve the above problems, the present invention proposes a method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film, which uses a silane coupling agent and maleic anhydride to modify nano-magnesium oxide so that it can be better dispersed in maleic anhydride grafted polypropylene, thereby improving the overall performance of the composite capacitor film.

[0004] To achieve the above object, the technical solution of the present invention is:

[0005] A method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film comprises the following steps:

[0006] Step (1): adding 50-70 parts of magnesium salt, 3-5 parts of maltodextrin, 5-8 parts of corn starch and 0.5-1 part of polyethylene glycol to 100 parts of water by mass, heating and stirring until completely gelled, then adjusting the pH to 8-9 under stirring, drying, calcining at 600-700°C, dispersing, and then adding together with 0.5-2 parts of silane coupling agent to a 60% by volume ethanol aqueous solution, adjusting the pH to 4-5, soaking under negative pressure stirring for 2-3 hours, filtering, washing, vacuum drying, and dispersing to obtain modified porous nano-magnesium oxide;

[0007] Step (2): dissolving 4-5 parts of maleic anhydride in 40-50 parts of anhydrous toluene by mass, adding 0.3-0.5 parts of initiator, and then adding 20-30 parts of modified porous nano-magnesium oxide, stirring at 100-120° C. under nitrogen atmosphere for 2-3 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide;

[0008] Step (3): melt-blending 50-60 parts by mass of maleic anhydride grafted polypropylene, 0.1-0.5 parts by mass of antioxidant, 0.1-0.2 parts by mass of diisopropylbenzene peroxide and 1-2 parts by mass of maleic anhydride modified porous nano-magnesium oxide, extruding, rolling, stretching and shaping to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0009] This solution utilizes the fact that corn starch and polyethylene glycol are dissolved under heating conditions to form a colloidal substance with a three-dimensional spatial structure, and the hydroxyl groups of the dissolved maltodextrin and the Mg 2+ Forming a coordination bond, when adjusting the pH, guiding magnesium carbonate or magnesium hydroxide to grow along the maltodextrin molecular chain, forming a three-dimensional network structure, and then forming a porous precursor, through the synergistic effect of maltodextrin carbonization and magnesium carbonate or magnesium hydroxide decomposition during the calcination process, porous nano-magnesium oxide can be generated, and further modified by a silane coupling agent to obtain modified porous nano-magnesium oxide, which has good dispersibility in step (2) and can improve the grafting effect with maleic anhydride. At the same time, the free radicals generated by the thermal decomposition of the initiator promote the combination of the anhydride group of maleic anhydride with the modified porous nano-magnesium oxide, thereby obtaining maleic anhydride-modified porous nano-magnesium oxide. After the surface of the maleic anhydride-modified porous nano-magnesium oxide is double-modified with KH570 and maleic anhydride, it has Si-O-Mg and anhydride groups, has excellent compatibility with maleic anhydride-grafted polypropylene, can significantly improve the mechanical and electrical properties, and has certain flame retardancy.

[0010] In step (3), the extrusion film-making process includes extrusion, roller shaping, preheating, stretching, heat preservation and shaping, corona treatment and other processes according to actual needs. The maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film prepared in this scheme can be obtained through conventional production processes. For example, the extrusion temperature can be controlled at 165-185°C. During the roller shaping process, the upper roller temperature can be set at 60-70°C and the lower roller temperature at 50-60°C. The stretching process can be selected to be synchronous or asynchronous stretching, and finally the film is heat-insulated and shaped at 100-120°C.

[0011] Preferably, in step (1), the magnesium salt is magnesium chloride or magnesium nitrate, and the silane coupling agent is KH570.

[0012] If magnesium chloride is selected, the mass proportion of chloride ions in the modified porous nano-magnesium oxide must be less than 0.3%.

[0013] Preferably, in step (1), the substance used to adjust the pH is one or more of sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide.

[0014] Preferably, in step (1), the heating and stirring temperature is 80-95°C.

[0015] Preferably, in step (1), on the basis of the calcination conditions at 600-700°C, a low-temperature calcination process is added, specifically, calcination at 350-450°C in an oxygen-free state for 2-3 hours, followed by heating to 600-700°C in an oxygen-enriched state for 30-60 minutes at a heating rate of 2-5°C / min, wherein the oxygen-enriched calcination condition is an oxygen volume concentration of 20-25%.

[0016] Heating too quickly may result in incomplete decomposition, while heating too slowly may cause the porous structure to collapse. Oxygen-rich conditions are primarily intended to fully react the residual carbon, converting it into carbon dioxide for removal. A two-stage calcination is preferred because the primary outflow from the first stage is water, leaving the magnesium carbonate undecomposed. The residual carbon is oxidized in the second stage to release carbon dioxide, potentially improving the dispersibility of the magnesium carbonate.

[0017] Preferably, in step (2), the initiator is dicumyl peroxide.

[0018] Preferably, in step (3), the grafting rate of the maleic anhydride grafted polypropylene is 1%-1.5%.

[0019] Preferably, in step (3), the antioxidant is antioxidant 1010.

[0020] Preferably, in step (3), 0.1-0.3 parts by mass of polyethylene glycol and 0.05-0.1 parts by mass of styrene are further included.

[0021] Polyethylene glycol is a dispersant, and styrene is a chain transfer agent that inhibits the self-polymerization of maleic anhydride.

[0022] Compared with the existing technology, the technical advantages of this solution are:

[0023] 1. This proposal proposes a method for preparing a maleic anhydride-grafted polypropylene / magnesium oxide nanocomposite capacitor film. Nanomagnesium oxide is modified with a silane coupling agent and maleic anhydride to enable it to be better dispersed in maleic anhydride-grafted polypropylene, thereby improving the overall performance of the composite capacitor film.

[0024] 2. This scheme utilizes the fact that maltodextrin, corn starch and polyethylene glycol can form a colloidal solution after being dissolved in water. When the pH is adjusted, magnesium carbonate or magnesium hydroxide is guided to grow along the maltodextrin molecular chain to form a three-dimensional network structure, thereby forming a porous precursor. Through the synergistic effect of maltodextrin carbonization and magnesium carbonate or magnesium hydroxide decomposition during the calcination process, further, through two modifications, maleic anhydride-modified porous nano-magnesium oxide that can be dispersed in maleic anhydride-grafted polypropylene is obtained. DETAILED DESCRIPTION

[0025] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0026] Example 1

[0027] A method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film comprises the following steps:

[0028] Step (1): 60 parts of magnesium nitrate, 4 parts of maltodextrin, 7 parts of corn starch and 0.8 parts of polyethylene glycol (PEG 1000) are added to 100 parts of water by mass, heated and stirred at 85°C until completely gelled, then slowly added with sodium carbonate under stirring to adjust the pH to 8, dried, calcined at 650°C for 3 hours, dispersed, and then added together with 1 part of silane coupling agent KH570 to a 60% by volume ethanol aqueous solution, adjusted the pH to 4.5, stirred and soaked under negative pressure for 3 hours, filtered, washed, vacuum dried, and dispersed to obtain modified porous nano-magnesium oxide;

[0029] Step (2): dissolving 4 parts of maleic anhydride in 45 parts of anhydrous toluene by mass, adding 0.4 parts of diisopropylbenzene peroxide, and then adding 25 parts of modified porous nano-magnesium oxide, stirring at 110°C under a nitrogen atmosphere for 2.5 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide;

[0030] Step (3): By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant 1010, 0.15 parts of diisopropylbenzene peroxide and 1.5 parts of maleic anhydride modified porous nano-magnesium oxide are melt-blended, extruded, rolled, stretched, and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0031] Example 2

[0032] A method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film comprises the following steps:

[0033] Step (1): by weight, 60 parts of magnesium chloride, 4 parts of maltodextrin, 7 parts of corn starch and 0.8 parts of PEG1000 are added to 100 parts of water, heated and stirred at 85°C until completely gelled, then slowly added with stirring sodium hydroxide powder to adjust the pH to 8, dried, calcined at 650°C for 3 hours, dispersed, then added together with 1 part of silane coupling agent KH570 to a 60% by volume ethanol aqueous solution, adjusted the pH to 4.5, stirred and soaked under negative pressure for 3 hours, filtered, washed, vacuum dried, dispersed, and obtained modified porous nano-magnesium oxide; the chloride ion mass ratio of the modified porous nano-magnesium oxide is 0.21%;

[0034] Step (2): dissolving 4 parts of maleic anhydride in 45 parts of anhydrous toluene by mass, adding 0.4 parts of diisopropylbenzene peroxide, and then adding 25 parts of modified porous nano-magnesium oxide, stirring at 110°C under a nitrogen atmosphere for 2.5 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide;

[0035] Step (3): By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant 1010, 0.15 parts of diisopropylbenzene peroxide and 1.5 parts of maleic anhydride modified porous nano-magnesium oxide are melt-blended, extruded, rolled, stretched, and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0036] Example 3

[0037] Step (1): by weight, add 60 parts of magnesium nitrate, 4 parts of maltodextrin, 7 parts of corn starch and 0.8 parts of PEG1000 to 100 parts of water, heat and stir at 85 ° C until completely gelled, then slowly add sodium carbonate powder under stirring to adjust the pH to 8 until the pH is 8, dry, calcine at 400 ° C for 2 hours in anoxic conditions, then calcine at 650 ° C for 45 minutes at a heating rate of 3 ° C / min, the oxygen-enriched calcination condition is that the oxygen volume concentration is 23%, disperse, then add together with 1 part of silane coupling agent KH570 in a 60% by volume ethanol aqueous solution, adjust the pH to 4.5, soak with negative pressure stirring for 3 hours, filter, wash, vacuum dry, disperse, and obtain modified porous nano-magnesium oxide;

[0038] Step (2): dissolving 4 parts of maleic anhydride in 45 parts of anhydrous toluene by mass, adding 0.4 parts of diisopropylbenzene peroxide, and then adding 25 parts of modified porous nano-magnesium oxide, stirring at 110°C under a nitrogen atmosphere for 2.5 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide;

[0039] Step (3): By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant 1010, 0.15 parts of diisopropylbenzene peroxide and 1.5 parts of maleic anhydride modified porous nano-magnesium oxide are melt-blended, extruded, rolled, stretched, and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0040] Example 4

[0041] Step (1): 60 parts of magnesium nitrate, 4 parts of maltodextrin, 7 parts of corn starch and 0.8 parts of PEG1000 are added to 100 parts of water by mass, heated at 85°C with stirring until completely gelled, then slowly added with stirring sodium carbonate powder to adjust the pH to 8, dried, calcined at 400°C in anoxic conditions for 2 hours, then calcined at 650°C in oxygen-enriched conditions for 45 minutes at a heating rate of 3°C / min, wherein the oxygen-enriched calcination condition is an oxygen volume concentration of 23%, dispersed, then added together with 1 part of silane coupling agent KH570 in a 60% by volume ethanol aqueous solution, adjusted to pH 4.5, stirred and soaked at negative pressure for 3 hours, filtered, washed, vacuum dried, dispersed, and modified porous nano-magnesium oxide was obtained;

[0042] Step (2): dissolving 4 parts of maleic anhydride in 45 parts of anhydrous toluene by mass, adding 0.4 parts of diisopropylbenzene peroxide, and then adding 25 parts of modified porous nano-magnesium oxide, stirring at 110°C under a nitrogen atmosphere for 2.5 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide;

[0043] Step (3): By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant, 0.15 parts of diisopropylbenzene peroxide, 0.2 parts of PEG 1000, 0.08 parts of styrene and 1.5 parts of maleic anhydride modified porous nano-magnesium oxide are melt-blended, extruded, rolled, stretched, and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0044] Comparative Example 1

[0045] The difference from Example 1 is that the film was produced using only maleic anhydride grafted polypropylene with a grafting rate of 1%.

[0046] Comparative Example 2

[0047] The difference from Example 1 is that nano magnesium oxide particles are directly added:

[0048] By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant 1010, 0.15 parts of dicumyl peroxide and 1.5 parts of nano-magnesium oxide were melt-blended, extruded, rolled, stretched and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0049] Comparative Example 3

[0050] The difference from Example 1 is that in the preparation process of step (1), maltodextrin, corn starch and PEG1000 are not used to prepare nano magnesium oxide:

[0051] A method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film comprises the following steps:

[0052] Step (1): 60 parts of magnesium nitrate are added to 100 parts of water by mass, heated and stirred at 85°C until completely gelled, then slowly added with stirring to adjust the pH to 8, dried, calcined at 650°C for 3 hours, dispersed, then added together with 1 part of silane coupling agent KH570 to a 60% by volume ethanol aqueous solution, adjusted to pH 4.5, stirred and soaked under negative pressure for 3 hours, filtered, washed, vacuum dried, dispersed, and obtained modified porous nano-magnesium oxide;

[0053] Step (2): dissolving 4 parts of maleic anhydride in 45 parts of anhydrous toluene by mass, adding 0.4 parts of diisopropylbenzene peroxide, and then adding 25 parts of modified porous nano-magnesium oxide, stirring at 110°C under a nitrogen atmosphere for 2.5 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide;

[0054] Step (3): By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant 1010, 0.15 parts of diisopropylbenzene peroxide and 1.5 parts of maleic anhydride modified porous nano-magnesium oxide are melt-blended, extruded, rolled, stretched, and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0055] Comparative Example 4

[0056] The difference from Example 1 is that, in the preparation process of step (1), KH570 was not used for modification:

[0057] A method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film comprises the following steps:

[0058] Step (1): by weight, add 60 parts of magnesium nitrate, 4 parts of maltodextrin, 7 parts of corn starch and 0.8 parts of PEG1000 to 100 parts of water, heat and stir at 85°C until completely gelled, then slowly add sodium carbonate under stirring to adjust the pH to 8, dry, calcine at 650°C for 3 hours, disperse, then add to water, adjust the pH to 4.5, stir and soak under negative pressure for 3 hours, filter, wash, vacuum dry, disperse, and obtain modified porous nano-magnesium oxide;

[0059] Step (2): dissolving 4 parts of maleic anhydride in 45 parts of anhydrous toluene by mass, adding 0.4 parts of diisopropylbenzene peroxide, and then adding 25 parts of modified porous nano-magnesium oxide, stirring at 110°C under a nitrogen atmosphere for 2.5 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide;

[0060] Step (3): By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant 1010, 0.15 parts of diisopropylbenzene peroxide and 1.5 parts of maleic anhydride modified porous nano-magnesium oxide are melt-blended, extruded, rolled, stretched, and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0061] Comparative Example 5

[0062] The difference from Example 1 is that in the preparation process of step (2), maleic anhydride modification is not used:

[0063] A method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film comprises the following steps:

[0064] Step (1): 60 parts of magnesium nitrate, 4 parts of maltodextrin, 7 parts of corn starch and 0.8 parts of PEG1000 are added to 100 parts of water by mass, heated and stirred at 85°C until completely gelled, then slowly added with stirring to adjust the pH to 8, dried, calcined at 650°C for 3 hours, dispersed, then added together with 1 part of silane coupling agent KH570 to a 60% by volume ethanol aqueous solution, adjusted the pH to 4.5, stirred and soaked under negative pressure for 3 hours, filtered, washed, vacuum dried, dispersed, and obtained modified porous nano-magnesium oxide;

[0065] Step (2): By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant 1010, 0.15 parts of diisopropylbenzene peroxide and 1.5 parts of modified porous nano-magnesium oxide are melt-blended, extruded, rolled, stretched, and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0066] Comparative Example 6

[0067] The difference from Example 1 is that the calcination temperature in step (1) is too high and the holding time is too long:

[0068] A method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film comprises the following steps:

[0069] Step (1): 60 parts of magnesium nitrate, 4 parts of maltodextrin, 7 parts of corn starch and 0.8 parts of PEG1000 are added to 100 parts of water by mass, heated at 85°C with stirring until completely gelled, then slowly added with sodium carbonate under stirring to adjust the pH to 8, dried, calcined at 800°C for 3.5 hours, dispersed, then added together with 1 part of silane coupling agent KH570 to a 60% by volume ethanol aqueous solution, adjusted the pH to 4.5, stirred and soaked under negative pressure for 3 hours, filtered, washed, vacuum dried, dispersed, and obtained modified porous nano-magnesium oxide;

[0070] Step (2): dissolving 4 parts of maleic anhydride in 45 parts of anhydrous toluene by mass, adding 0.4 parts of diisopropylbenzene peroxide, and then adding 25 parts of modified porous nano-magnesium oxide, stirring at 110°C under a nitrogen atmosphere for 2.5 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide;

[0071] Step (3): By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant 1010, 0.15 parts of diisopropylbenzene peroxide and 1.5 parts of maleic anhydride modified porous nano-magnesium oxide are melt-blended, extruded, rolled, stretched, and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0072] Comparative Example 7

[0073] The difference from Example 1 is that the calcination temperature in step (1) is too low and the holding time is too short:

[0074] A method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film comprises the following steps:

[0075] Step (1): 60 parts of magnesium nitrate, 4 parts of maltodextrin, 7 parts of corn starch and 0.8 parts of PEG1000 are added to 100 parts of water by mass, heated and stirred at 85°C until completely gelled, then slowly added with stirring to adjust the pH to 8, dried, calcined at 550°C for 2 hours, dispersed, then added together with 1 part of silane coupling agent KH570 to a 60% by volume ethanol aqueous solution, adjusted the pH to 4.5, stirred and soaked under negative pressure for 3 hours, filtered, washed, vacuum dried, dispersed, and obtained modified porous nano-magnesium oxide;

[0076] Step (2): dissolving 4 parts of maleic anhydride in 45 parts of anhydrous toluene by mass, adding 0.4 parts of diisopropylbenzene peroxide, and then adding 25 parts of modified porous nano-magnesium oxide, stirring at 110°C under a nitrogen atmosphere for 2.5 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide;

[0077] Step (3): By weight, 55 parts of maleic anhydride grafted polypropylene with a grafting rate of 1%, 0.3 parts of antioxidant 1010, 0.15 parts of diisopropylbenzene peroxide and 1.5 parts of maleic anhydride modified porous nano-magnesium oxide are melt-blended, extruded, rolled, stretched, and shaped to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

[0078] The steps (3) of Examples 1-4 and Comparative Examples 1-7, including extrusion after blending, rolling, stretching, and shaping, are all the same, specifically, extrusion at 165-185°C, and during rolling shaping, the upper roller temperature is 65°C, the lower roller temperature is 55°C, the longitudinal stretching temperature is 130°C, the stretch ratio is 5.5, the transverse stretching temperature is 165°C, the stretch ratio is 9.5, and finally, the shaping is performed at 110°C under heat preservation conditions.

[0079] Performance testing:

[0080] 1. Breakdown Test: Referring to ASTM-D149 and ASTM-D3755, a DC breakdown test was conducted on the film in silicone oil using a hemispherical electrode with a diameter of 12.7 mm at a voltage ramp rate of 500 V / s. At least 30 effective breakdown points were obtained for each sample. Weibull statistical analysis was performed on these at least 30 breakdown field strength data. The scale parameter of the Weibull distribution, that is, the breakdown field strength at a breakdown probability of 63.2%, was selected as the characteristic breakdown field strength for evaluation.

[0081] 2. Dielectric test: Spray gold (gold ion sputtering) on ​​the surface of the sample, with an electrode diameter of 30mm. Test at room temperature (25℃) and 1kHz frequency range to obtain the dielectric constant and dielectric loss of the sample;

[0082] 3. Mechanical properties test: refer to ASTM D638 test.

[0083] The test results are shown in Table 1.

[0084] Table 1

[0085]

[0086] From the results of Examples 1-4 and Comparative Examples 1-8, it can be seen that Examples 1-4 of this solution can obtain better mechanical and electrical properties. Compared with Example 1-3, Example 4 has better control over the temperature during the preparation of porous nano-magnesium oxide, and a dispersant is added during the film formation process of step (3), thereby obtaining the best performance. Compared with Example 1-2, Example 3 has better control over the temperature during the preparation of porous nano-magnesium oxide, thereby obtaining better performance. Example 2 may be affected by residual chloride ions. Chloride ions are typical mobile ionic impurities that are prone to migration under an external electric field, forming ion currents, resulting in increased dielectric loss and leakage current. This ion migration will lead to additional energy loss and may also cause local charge accumulation, destroying the uniformity of the electric field. Migration will produce micro defects (such as micropores and cracks) inside the film or at the interface. These defects become electric field concentration points, resulting in a decrease in breakdown field strength and mechanical properties. Therefore, the presence of low concentrations of chloride ions in Example 2 leads to slightly lower performance than that of Example 1.

[0087] Comparative Example 1 was a blank control group in which nano-magnesium oxide was not added and was considered as an intrinsic characteristic.

[0088] The difference between Comparative Example 2 and Example 1 is that unmodified magnesium oxide is directly added in Comparative Example 2. The unmodified magnesium oxide particles agglomerate, which easily forms problems such as electrical conduction paths and stress concentration, resulting in a decrease in overall performance.

[0089] The difference between Comparative Example 3 and Example 1 is that Comparative Example 2 does not use maltodextrin, corn starch and polyethylene glycol to prepare nano-magnesium oxide, that is, it lacks a network structure and lacks organic matter to act as a pore-forming agent. The surface of the nano-magnesium oxide becomes smoother and the porosity is insufficient, resulting in weak defect shielding ability and reduced polarization interface.

[0090] The difference between Comparative Example 4 and Example 1 is that the nano-magnesium oxide is not modified with KH570 coupling agent, resulting in poor maleic anhydride modification effect and poor affinity with the maleic anhydride-modified polypropylene film matrix, which easily causes interface defects and increased interface polarization loss.

[0091] The difference between Comparative Example 5 and Example 1 is that maleic anhydride is not used to further modify the nano-magnesium oxide, which has poor affinity with the maleic anhydride-modified polypropylene film matrix, easily causing interface defects and increased interface polarization loss.

[0092] The difference between Comparative Example 6 and Example 1 is that, during the preparation of nano-magnesium oxide, the calcination temperature is too high and the time is too long. Excessive calcination causes the pores of the magnesium oxide to collapse and the grains to coarsen. The surface of the nano-magnesium oxide becomes smoother and the porosity is insufficient, resulting in weak defect shielding ability and reduced polarization interface.

[0093] The difference between Comparative Example 7 and Example 1 is that, during the preparation of nano-magnesium oxide, the calcination temperature is too low and the time is too short, mainly because carbon, organic matter or magnesium carbonate are not fully decomposed, resulting in a strong breakdown field and an increase in carriers causing dielectric loss.

Claims

1. A method for preparing a maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film, characterized in that: The following steps are involved: Step (1): adding 50-70 parts of magnesium salt, 3-5 parts of maltodextrin, 5-8 parts of corn starch and 0.5-1 part of polyethylene glycol to 100 parts of water by mass, heating and stirring until completely gelled, then adjusting the pH to 8-9 under stirring, drying, calcining at 600-700°C, dispersing, and then adding together with 0.5-2 parts of silane coupling agent to a 60% by volume ethanol aqueous solution, adjusting the pH to 4-5, soaking under negative pressure stirring for 2-3 hours, filtering, washing, vacuum drying, and dispersing to obtain modified porous nano-magnesium oxide; Step (2): dissolving 4-5 parts of maleic anhydride in 40-50 parts of anhydrous toluene by mass, adding 0.3-0.5 parts of initiator, and then adding 20-30 parts of modified porous nano-magnesium oxide, stirring at 100-120° C. under nitrogen atmosphere for 2-3 hours, filtering, washing with acetone, vacuum drying, and dispersing to obtain maleic anhydride-modified porous nano-magnesium oxide; Step (3): melt-blending 50-60 parts by mass of maleic anhydride grafted polypropylene, 0.1-0.5 parts by mass of antioxidant, 0.1-0.2 parts by mass of diisopropylbenzene peroxide and 1-2 parts by mass of maleic anhydride modified porous nano-magnesium oxide, extruding, rolling, stretching and shaping to obtain a maleic anhydride grafted polypropylene / magnesium oxide nano-composite capacitor film.

2. The method for preparing the maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film according to claim 1, wherein: In step (1), the magnesium salt is magnesium chloride or magnesium nitrate, and the silane coupling agent is KH570.

3. The method for preparing the maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film according to claim 1, wherein: In step (1), the substance used to adjust the pH is one or more of sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide.

4. The method for preparing the maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film according to claim 1, wherein: In step (1), the temperature of the heating and stirring is 80-95°C.

5. The method for preparing the maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film according to claim 1, wherein: In step (1), on the basis of the calcination conditions at 600-700°C, a low-temperature calcination process is added, specifically, calcination at 350-450°C in an oxygen-free state for 2-3 hours, and then heating to 600-700°C in an oxygen-enriched state for 30-60 minutes at a heating rate of 2-5°C / min, wherein the oxygen-enriched calcination condition is an oxygen volume concentration of 20-25%.

6. The method for preparing the maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film according to claim 1, wherein: In step (2), the initiator is dicumyl peroxide.

7. The method for preparing the maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film according to claim 1, wherein: In step (3), the grafting rate of the maleic anhydride grafted polypropylene is 1%-1.5%.

8. The method for preparing the maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film according to claim 1, wherein: In step (3), the antioxidant is antioxidant 1010.

9. The method for preparing the maleic anhydride grafted polypropylene / magnesium oxide nanocomposite capacitor film according to claim 1, wherein: In step (3), 0.1-0.3 parts of polyethylene glycol and 0.05-0.1 parts of styrene are also included, by weight.

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