Capacitor film and preparation method thereof

Abstract

The invention relates to the technical field of capacitor films, and discloses a capacitor film and a preparation method thereof. The capacitor film comprises a polypropylene film, a first poly (4-methyl-1-pentene) film arranged on the upper surface of the polypropylene film, and a second poly (4-methyl-1-pentene) film arranged on the lower surface of the polypropylene film. The polypropylene film comprises polypropylene resin, and the poly (4-methyl-1-pentene) film comprises an antioxidant and poly (4-methyl-1-pentene) resin; based on the total amount of the capacitor film, the content of the polypropylene resin is 50-70 wt%, and the total amount of the antioxidant and the total amount of the poly (4-methyl-1-pentene) resin in the first poly (4-methyl-1-pentene) film and the second poly (4-methyl-1-pentene) film are respectively and independently 15-25 wt%. According to the invention, a two-way stretching process is adopted, and the prepared capacitor film has excellent temperature resistance and compression strength, uniform thickness and good continuous film-forming property.

Description

Technical Field

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

[0002] Currently, polymer films and capacitors thereof are widely used in various electronic fields, but the application of capacitors made from polymer films is limited due to the properties of the films themselves.

[0003] Polypropylene capacitor film, namely biaxially oriented polypropylene film (BOPP) for capacitors, has become the main dielectric material for power capacitors due to its low specific gravity, good heat resistance and stable chemical properties. However, the dielectric loss factor of polypropylene film is only 0.0002, the dielectric heat generation is not high, and the maximum operating temperature can only reach 105°C, which limits the application of polypropylene film capacitors in high temperature environments. In addition, the polypropylene film capacitors in the prior art generally use a single-layer polypropylene capacitor film, the surface and the interior of which are composed of the same raw materials, without a secondary structure (layer structure). The tensile stress on the product is relatively concentrated, and it is very easy to break, causing the film to be scrapped during subsequent processing.

[0004] Compared with polyethylene and polypropylene resins, poly-4-methyl-1-pentene resin has better heat resistance and is widely used in industrial production and food packaging industries. However, the molecular side chains of this material are very large, and the molecular movement is restricted. In the molten state, the viscosity decreases sharply, and it is easy to decompose, break during stretching, and the uniformity of thickness is difficult to control, making it difficult to form a film.

[0005] Therefore, it is of great value to develop a capacitor film with high temperature resistance and high toughness. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems of low temperature resistance and easy breakage of capacitor films in the prior art, and to provide a capacitor film and a preparation method thereof. The capacitor film includes a polypropylene film and a poly-4-methyl-1-pentene film, which improves the temperature resistance and compressive strength of the capacitor film.

[0007] In order to achieve the above object, the first aspect of the present invention provides a capacitor film, wherein the capacitor film comprises a polypropylene film and a first poly-4-methyl-1-pentene film disposed on the upper surface of the polypropylene film and a second poly-4-methyl-1-pentene film disposed on the lower surface of the polypropylene film;

[0008] Wherein, the polypropylene film comprises polypropylene resin, and the poly-4-methyl-1-pentene film comprises an antioxidant and poly-4-methyl-1-pentene resin;

[0009] Based on the total amount of the capacitor film, the content of the polypropylene resin is 50-70wt%, and the total amount of the antioxidant and the poly-4-methyl-1-pentene in the poly-4-methyl-1-pentene film is independently 15-25wt%;

[0010] In the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film, based on the total amount of the poly 4-methyl-1-pentene film, the content of the antioxidant in the poly 4-methyl-1-pentene film is independently 0.1-0.49wt%, and the content of the poly 4-methyl-1-pentene resin is independently 99.51-99.9wt%.

[0011] A second aspect of the present invention provides a method for preparing the capacitor film according to the first aspect, wherein the method comprises the following steps:

[0012] (1) extruding a polypropylene resin, a mixture containing a poly-4-methyl-1-pentene resin and an antioxidant respectively to obtain a sheet-like fluid;

[0013] (2) sequentially forming, longitudinally stretching and transversely stretching the sheet-like fluid to obtain a base film;

[0014] (3) The base film is treated and rolled up, and then subjected to a first aging treatment and a second aging treatment to obtain the capacitor film.

[0015] Through the above technical solution, the present invention can achieve the following technical effects:

[0016] (1) The capacitor film provided by the present invention has a poly-4-methyl-1-pentene film as the upper and lower surface layers of the capacitor film, and a polypropylene film as the middle layer, and is formed by stacking three layers of films. Compared with a single-layer BOPP capacitor film, the capacitor film is conducive to weakening the electrical weak points formed by the raw material metal ash and other impurities, and improving the film's compressive strength;

[0017] (2) The capacitor film provided by the present invention, in a preferred case, is a poly-4-methyl-1-pentene film obtained by using a specific poly-4-methyl-1-pentene resin, which can further increase the plasticity and tensile properties compared with the conventional poly-4-methyl-1-pentene resin, and the capacitor film has good thickness uniformity, a smooth surface, and good film-forming properties;

[0018] (3) The preparation method of the capacitor film provided by the present invention adopts a suitable biaxial stretching production process. In a preferred case, the shaping temperature is higher than the stretching temperature, which reduces the thermal shrinkage rate of the capacitor film and improves the temperature resistance of the capacitor film. DETAILED DESCRIPTION

[0019] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0020] A first aspect of the present invention provides a capacitor film, wherein the capacitor film comprises a polypropylene film and a first poly-4-methyl-1-pentene film disposed on the upper surface of the polypropylene film and a second poly-4-methyl-1-pentene film disposed on the lower surface of the polypropylene film;

[0021] Wherein, the polypropylene film comprises polypropylene resin, and the poly-4-methyl-1-pentene film comprises an antioxidant and poly-4-methyl-1-pentene resin;

[0022] Based on the total amount of the capacitor film, the content of the polypropylene resin is 50-70wt%, and the total amount of the antioxidant and the poly 4-methyl-1-pentene resin in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film is independently 15-25wt%;

[0023] In the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film, based on the total amount of the poly 4-methyl-1-pentene film, the content of the antioxidant is independently 0.1-0.49wt%, and the content of the poly 4-methyl-1-pentene resin is independently 99.51-99.9wt%.

[0024] In the present invention, the capacitor film uses a polypropylene film as an intermediate layer, and a poly-4-methyl-1-pentene film is arranged on the upper surface layer and the lower surface layer of the polypropylene film. The poly-4-methyl-1-pentene film uses a poly-4-methyl-1-pentene resin and an antioxidant as raw materials. The obtained poly-4-methyl-1-pentene film is easier to process. The capacitor film prepared by compounding the polypropylene film with the polypropylene film solves the problems of the traditional single-layer poly-4-methyl-1-pentene film being easy to break during stretching, the thickness uniformity being difficult to control, and the film forming being difficult. The capacitor film has excellent temperature resistance and compressive strength.

[0025] In the present invention, the poly 4-methyl-1-pentene film includes a first poly 4-methyl-1-pentene film and a second poly 4-methyl-1-pentene film, the content of the polypropylene resin is controlled at 50-70wt%, and the total amount of antioxidant and poly 4-methyl-1-pentene in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film is controlled at 15-25wt%, which is beneficial for the obtained capacitor film to have excellent temperature resistance and compressive strength.

[0026] In the present invention, the content of the polypropylene resin is less than 50wt%, the polypropylene film in the capacitor film is too thin, and the poly-4-methyl-1-pentene film is too thick, the capacitor film has good temperature resistance and compressive strength, but the continuous film forming property is reduced, the yield is low, and the raw material cost is high; the content of the polypropylene resin is greater than 70wt%, the polypropylene film in the capacitor film is too thick, and the poly-4-methyl-1-pentene film is too thin, and the improvement of the temperature resistance and compressive strength of the capacitor film is limited.

[0027] In some embodiments of the present invention, preferably, based on the total amount of the capacitor film, the content of the polypropylene resin is 55-65wt%, and the total amount of the antioxidant and poly 4-methyl-1-pentene in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film is independently 17.5-22.5wt%.

[0028] In the present invention, the total amount of poly 4-methyl-1-pentene and the antioxidant in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film can be the same or different. Preferably, the total amount of poly 4-methyl-1-pentene and the antioxidant in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film is the same, which is more conducive to making the obtained capacitor film have excellent temperature resistance and compressive strength.

[0029] In some embodiments of the present invention, preferably, in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film, based on the total amount of the poly 4-methyl-1-pentene film, the content of the antioxidant in the poly 4-methyl-1-pentene film is independently 0.2-0.4wt%, and the content of the poly 4-methyl-1-pentene resin is independently 99.6-99.8wt%.

[0030] In the present invention, the contents of poly 4-methyl-1-pentene resin and antioxidant in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film may be the same or different. Preferably, the contents of poly 4-methyl-1-pentene resin and antioxidant in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film are the same. The obtained capacitor film has excellent temperature resistance and compressive strength, which is beneficial to improving the continuous film forming property of the capacitor film.

[0031] In the present invention, the contents of the poly 4-methyl-1-pentene resin and the antioxidant in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film are controlled within the above-mentioned preferred range, which is more conducive to improving the continuous film forming property of the capacitor film, so that the obtained capacitor film has better temperature resistance and compressive strength.

[0032] In some embodiments of the present invention, preferably, the weight average molecular weight of the polypropylene resin is 200,000-500,000 g / mol, the melt index at 230°C and a load of 2.16 kg is 0.5-3 g / 10 min, the molecular weight distribution index is 4-8, the isotacticity is ≥97.5%, and the ash content is <20 ppm.

[0033] In the present invention, the weight average molecular weight, melt index, molecular weight distribution, isotacticity and ash content of the polypropylene resin are controlled within the above ranges, which is more conducive to improving the continuous production performance of the polypropylene resin, and the capacitor film obtained by stacking it with the poly-4-methyl-1-pentene film has better thickness uniformity, tensile properties and film-forming properties.

[0034] In some embodiments of the present invention, preferably, the antioxidant is selected from hindered phenol antioxidants and / or phosphite antioxidants, preferably selected from pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, 2,2'-thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2 , at least one of 4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, tris[2,4-di-tert-butylphenyl]phosphite, bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite, tris(4-nonphenyl)phosphite, distearyl thiodipropionate, dilauryl thiodipropionate and 4,4'-thiobis(6-tert-butyl-3-methylphenol), more preferably 2,6-di-tert-butyl-p-cresol.

[0035] In the present invention, the antioxidant is combined with poly 4-methyl-1-pentene resin to obtain a poly 4-methyl-1-pentene film, which is arranged on the upper and lower surfaces of the polypropylene film, which is more conducive to inhibiting the oxidation of the polymer and delaying the aging of the poly 4-methyl-1-pentene resin during use.

[0036] In some embodiments of the present invention, preferably, the poly 4-methyl-1-pentene resin includes a poly 4-methyl-1-pentene homopolymer and / or a 4-methyl-1-pentene copolymer.

[0037] In some embodiments of the present invention, preferably, the weight average molecular weight of the poly 4-methyl-1-pentene homopolymer is 200,000-600,000 g / mol, the melt index at 260°C and a load of 5 kg is 10-50 g / 10 min, the molecular weight distribution index is 4-10, the isotacticity is ≥95%, the ash content is <30 ppm, and the melting point is 235-245°C.

[0038] In the present invention, the weight average molecular weight, melt index, molecular weight distribution, isotacticity, ash content and melting point of the poly 4-methyl-1-pentene homopolymer are controlled within the above ranges, which is more conducive to improving the mechanical properties, temperature resistance and film processing properties of the poly 4-methyl-1-pentene resin.

[0039] In some embodiments of the present invention, preferably, the weight average molecular weight of the poly 4-methyl-1-pentene copolymer is 200,000-500,000 g / mol, the melt index at 260°C and a load of 5 kg is 5-30 g / 10 min, the molecular weight distribution index is 5-10, the isotacticity is ≥65%, the ash content is <30 ppm, and the melting point is 220-240°C.

[0040] In the present invention, the weight average molecular weight, melt index, molecular weight distribution, isotacticity, ash content and melting point of the poly (4-methyl-1-pentene) copolymer are controlled within the above ranges, which is more conducive to improving the plasticity and tensile properties of the poly (4-methyl-1-pentene) resin and making the poly (4-methyl-1-pentene) film easier to process during longitudinal and transverse stretching.

[0041] In some embodiments of the present invention, preferably, the poly 4-methyl-1-pentene copolymer is prepared by copolymerizing 4-methyl-1-pentene and α-olefin.

[0042] In the present invention, 4-methyl-1-pentene and α-olefin are copolymerized in the presence of a catalyst to obtain the poly-4-methyl-1-pentene copolymer. The catalyst is a conventional catalyst in the art and may be at least one selected from a Ziegler-Natta catalyst, a metallocene catalyst and a transition metal catalyst.

[0043] In some embodiments of the present invention, preferably, the content of 4-methyl-1-pentene structural units in the poly-4-methyl-1-pentene copolymer is 50-95 wt %.

[0044] In some embodiments of the present invention, preferably, the α-olefin is selected from α-olefins having 2 to 18 carbon atoms, preferably at least one selected from ethylene, propylene, 1-butene, 1-hexene, 1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene and 1-octadecene, more preferably at least one selected from 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene and 1-octadecene, further preferably at least one selected from ethylene, 1-hexene and 1-octene.

[0045] In some embodiments of the present invention, preferably, the capacitor film has a thickness of 4-12 μm, preferably 5.3-10.8 μm.

[0046] In the present invention, the total thickness of the capacitor film is 4-12 μm, the thickness of the polypropylene film in the capacitor film is 2-10 μm, and the thickness of the poly-4-methyl-1-pentene film is 1-5 μm. The above thickness is conducive to making the obtained capacitor film have excellent comprehensive performance; preferably, the total thickness of the capacitor film is 5.3-10.8 μm, the thickness of the polypropylene film in the capacitor film is 2.3-8 μm, and the thickness of the poly-4-methyl-1-pentene film is 1.4-4.3 μm. The preferred thickness range makes the capacitor film have better continuous film forming properties, uniform thickness, and better temperature resistance and compressive strength.

[0047] In the present invention, the capacitor film thickness is tested by a thickness gauge, wherein the thickness gauge may be a thickness gauge of model 1202HR+P2004MA purchased from the German Marr Film Thickness Gauge Company.

[0048] In some embodiments of the present invention, preferably, the thermal shrinkage rate of the capacitor film at 100°C is 0.3-1.2%, and the DC voltage breakdown strength is 622-645V / μm; the thermal shrinkage rate of the capacitor film at 120°C is 1.3-2%, and the DC voltage breakdown strength is 561-596V / μm.

[0049] In the present invention, the capacitor film uses a polypropylene film as the middle layer, and a poly-4-methyl-1-pentene film is arranged on the upper and lower surfaces of the polypropylene film, and is formed by stacking three layers of films. Compared with a single-layer BOPP capacitor film, the capacitor film is conducive to weakening the electrical weak points formed by the raw material metal ash and other impurities, and has higher compressive strength, a heat shrinkage rate of less than 2% at 120°C, and a DC voltage breakdown strength of not less than 561V / μm, and has excellent temperature resistance and compressive strength. In the present invention, the DC voltage breakdown strength is tested by a voltage breakdown strength tester.

[0050] A second aspect of the present invention provides a method for preparing the capacitor film according to the first aspect, wherein the method comprises the following steps:

[0051] (1) extruding a polypropylene resin, a mixture containing a poly-4-methyl-1-pentene resin and an antioxidant respectively to obtain a sheet-like fluid;

[0052] (2) sequentially forming, longitudinally stretching and transversely stretching the sheet-like fluid to obtain a base film;

[0053] (3) The base film is treated and rolled up, and then subjected to a first aging treatment and a second aging treatment to obtain the capacitor film.

[0054] In some embodiments of the present invention, preferably, in step (1), the extrusion temperature of the polypropylene film raw material is 230-255°C, and the extrusion temperature of the poly-4-methyl-1-pentene film raw material is 250-300°C.

[0055] In the present invention, in step (1), polypropylene resin and a mixture containing poly-4-methyl-1-pentene resin and an antioxidant are melted and plasticized respectively, and then extruded through a three-channel composite die to obtain the sheet fluid, wherein the middle layer of the sheet fluid is a polypropylene resin layer, and the upper and lower surface layers of the polypropylene resin layer are both layers of the mixture containing poly-4-methyl-1-pentene resin and an antioxidant.

[0056] In the present invention, the mixture containing poly 4-methyl-1-pentene resin and antioxidant is the raw material of the first poly 4-methyl-1-pentene film and the raw material of the second poly 4-methyl-1-pentene film. The total amount of poly 4-methyl-1-pentene resin and antioxidant in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film can be the same or different. Preferably, the total amount of poly 4-methyl-1-pentene resin and antioxidant in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film is the same; the contents of poly 4-methyl-1-pentene resin and antioxidant in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film can be the same or different. Preferably, the contents of poly 4-methyl-1-pentene resin and antioxidant in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film are the same, which is conducive to making the obtained capacitor film have excellent temperature resistance and compressive strength.

[0057] In the present invention, in step (2), the forming is preferably to form a thick film by casting the sheet fluid obtained in step (1) through a chilled roller and a high-pressure air knife, the temperature of the chilled roller is 95-110°C, and the gas temperature of the high-pressure air knife is 95-110°C.

[0058] In some embodiments of the present invention, preferably, the longitudinal stretching includes longitudinal preheating, stretching and shaping; the conditions of the longitudinal stretching include: preheating temperature of 125-150°C, stretching temperature of 145-155°C, shaping temperature of 150-158°C, and stretching ratio of 3-8 times.

[0059] In some embodiments of the present invention, preferably, the transverse stretching includes stretching and shaping, and the conditions of the transverse stretching include: a stretching temperature of 145-155° C., a shaping temperature of 150-158° C., and a stretching ratio of 5-8 times.

[0060] In the present invention, the setting temperature used is higher than the stretching temperature. The elongation at break of the conventional poly-4-methyl-1-pentene film is reduced at high temperature, and it is difficult to maintain the continuity of stretching, resulting in film breakage during stretching. The continuous production performance and stretching performance of the polypropylene film are good. The present invention sets the poly-4-methyl-1-pentene film on the upper and lower surfaces of the polypropylene film respectively, and sets the longitudinal stretching and transverse stretching temperatures to 145-155°C independently, and sets the longitudinal setting temperature and transverse setting temperature to 150-158°C independently, which can significantly reduce the thermal shrinkage of the film and improve the compressive strength of the capacitor film.

[0061] In some embodiments of the present invention, preferably, in step (3), the treatment includes sequentially cooling, thickness measuring and trimming the base film; the cooling temperature is 25-30°C.

[0062] In the present invention, in step (3), the base film obtained after the transverse stretching treatment is sequentially cooled, thickness measured and trimmed, and the thickness of the capacitor film is tested by the above-mentioned thickness gauge.

[0063] In some embodiments of the present invention, preferably, the film after edge trimming is rolled up, and the rolling tension is 20-30 N / m, and the rolling pressure is 150-200 N / m.

[0064] In some embodiments of the present invention, preferably, the conditions of the first aging treatment include: purification level ≤ 10,000, temperature 25-30°C, humidity < 60%, and aging time 24-72h.

[0065] In some embodiments of the present invention, preferably, the conditions of the second aging treatment include: purification level ≤ 10,000, temperature 25-30°C, humidity < 60%, and aging time 12-24h.

[0066] The present invention will be described in detail below through examples.

[0067] Melt index test: Tested in accordance with ISO1133 "Determination of mass flow rate and volume flow rate of thermoplastic melts" standard, the test conditions are 230℃ / 2.16kg·10min;

[0068] The weight average molecular weight and molecular weight distribution were tested by gel permeation chromatography (GPC);

[0069] Isotacticity was tested by n -heptane extraction;

[0070] Ash content is tested by combustion method;

[0071] The capacitor film thickness is tested using a thickness gauge;

[0072] The breakdown strength of the capacitor film is tested using a voltage breakdown strength tester;

[0073] Thermal shrinkage test of capacitor film: After the capacitor film is placed in an oven at 100°C or 120°C for 15 minutes, the lateral dimensional change of the film is tested.

[0074] Example 1

[0075] (1) Polypropylene resin: weight average molecular weight 480,000 g / mol, melt index 2.9 g / 10 min (2.16 kg, 230° C.), molecular weight distribution index 5.8, isotacticity 97.5%, ash content 15 ppm;

[0076] The poly-4-methyl-1-pentene resin is a 4-methyl-1-pentene homopolymer, with a weight average molecular weight of 400,000 g / mol, a melt index of 20 g / 10 min (5 kg, 260° C.), a molecular weight distribution index of 7.1, an isotacticity of 95.5%, an ash content of 20 ppm, and a melting point of 240° C. The poly-4-methyl-1-pentene resin and a 2,6-di-tert-butyl-p-cresol antioxidant are uniformly mixed to obtain a mixture containing poly-4-methyl-1-pentene and an antioxidant;

[0077] Wherein, based on the total amount of the capacitor film, the mass of the polypropylene resin accounts for 63.6%, the mass of the mixture containing poly-4-methyl-1-pentene and the antioxidant accounts for 36.4%, the content of 2,6-di-tert-butyl-p-cresol antioxidant in the mixture containing poly-4-methyl-1-pentene and the antioxidant is 0.3wt%, and the raw material composition of the first poly-4-methyl-1-pentene film and the second poly-4-methyl-1-pentene film is the same;

[0078] (2) Extrusion: The polypropylene resin, the mixture containing poly-4-methyl-1-pentene and the antioxidant are melted and plasticized respectively, and then extruded through a three-channel composite die head, the extrusion temperature of the polypropylene resin is 255° C., and the extrusion temperature of the mixture is 280° C.;

[0079] (3) chilling roller and high-pressure air knife: the sheet fluid obtained by extrusion in step (2) is cast into a thick sheet by passing it through a chilling roller and a high-pressure air knife, wherein the temperature of the chilling roller is 100° C. and the gas temperature of the high-pressure air knife is 100° C.;

[0080] (4) longitudinal stretching: the thick sheet is longitudinally preheated, stretched and shaped in sequence to obtain a thick film, the preheating temperature is 145° C., the stretching temperature is 155° C., the shaping temperature is 158° C., and the stretching ratio is 5.5 times;

[0081] (5) Transverse stretching: the thick film is sequentially subjected to transverse stretching and shaping to obtain a thin film, the stretching temperature is 150° C., the shaping temperature is 155° C., and the stretching ratio is 7.5 times;

[0082] (6) Cooling, measuring thickness and trimming the film, the cooling temperature is 30° C., and the film is trimmed and measured for thickness; then the film is rolled up after trimming, the rolling tension is 30 N / m, and the rolling pressure is 200 N / m;

[0083] (7) Aging treatment: The rolled film is subjected to a first aging treatment at 30° C., a humidity of less than 60%, and a purification level of 10,000 for 72 hours; then the film after the first aging treatment is subjected to a second aging treatment at 30° C., a humidity of less than 60%, and a purification level of 10,000 for 12 hours to obtain the capacitor film.

[0084] The thickness of the upper and lower surface layers (poly-4-methyl-1-pentene film) and the middle layer (polypropylene film) of the capacitor film, the DC voltage breakdown strength at 100° C. and 120° C., and the thermal shrinkage are shown in Table 1.

[0085] Example 2

[0086] According to the method described in Example 1, the difference is that in step (1), based on the total amount of the capacitor film, the mass of the polypropylene resin accounts for 69.2%, the mass of the mixture containing poly-4-methyl-1-pentene and an antioxidant accounts for 30.8%, and the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris[2,4-di-tert-butylphenyl]phosphite; in step (4), the longitudinal stretching ratio is 6 times. The capacitor film is obtained.

[0087] The thickness of the upper and lower surface layers (poly-4-methyl-1-pentene film) and the middle layer (polypropylene film) of the capacitor film, the DC voltage breakdown strength at 100° C. and 120° C., and the thermal shrinkage are shown in Table 1.

[0088] Example 3

[0089] According to the method described in Example 1, the difference is that in step (1), the mass of the polypropylene resin accounts for 53.8%, the mass of the mixture containing poly-4-methyl-1-pentene and an antioxidant accounts for 46.2%, and the antioxidant is dilauryl thiodipropionate; in step (5), the transverse stretching ratio is 8 times to obtain the capacitor film.

[0090] The thickness of the upper and lower surface layers (poly-4-methyl-1-pentene film) and the middle layer (polypropylene film) of the capacitor film, the DC voltage breakdown strength at 100° C. and 120° C., and the thermal shrinkage are shown in Table 1.

[0091] Example 4

[0092] The method described in Example 1 is followed, except that in step (1), the poly 4-methyl-1-pentene resin is a copolymer of ethylene and 4-methyl-1-pentene, with a weight average molecular weight of 350,000 g / mol, a melt index of 22 g / 10 min (5 kg, 260° C.), a molecular weight distribution index of 6.8, an isotacticity of 75%, an ash content of 25 ppm, and a melting point of 233° C.; in step (5), the transverse stretching temperature is 150° C. and the setting temperature is 155° C.; and the capacitor film is obtained.

[0093] The thickness of the upper and lower surface layers (poly-4-methyl-1-pentene film) and the middle layer (polypropylene film) of the capacitor film, the DC voltage breakdown strength at 100° C. and 120° C., and the thermal shrinkage are shown in Table 1.

[0094] Example 5

[0095] The method described in Example 1 is different in that in step (1), the poly 4-methyl-1-pentene resin is a copolymer of 1-octadecene and 4-methyl-1-pentene, with a weight average molecular weight of 280,000 g / mol, a melt index of 28 g / 10 min (5 kg, 260° C.), a molecular weight distribution index of 8.3, an isotacticity of 68%, an ash content of 25 ppm, and a melting point of 221° C.; in step (4), the longitudinal stretching preheating temperature is 135° C., the stretching temperature is 150° C., the setting temperature is 155° C., and the stretching ratio is 4.5 times; and the capacitor film is obtained.

[0096] The thickness of the upper and lower surface layers (poly-4-methyl-1-pentene film) and the middle layer (polypropylene film) of the capacitor film, the DC voltage breakdown strength at 100° C. and 120° C., and the thermal shrinkage are shown in Table 1.

[0097] Example 6

[0098] The method of Example 1 is used, except that in step (1), the 4-methyl-1-pentene homopolymer has a weight average molecular weight of 200,000 g / mol, a melt index of 35 g / 10 min (2.16 kg, 260° C.), a molecular weight distribution index of 6.9, an isotacticity of 97%, an ash content of 15 ppm, and a melting point of 235° C.; in step (4), the longitudinal stretching preheating temperature is 135° C., the stretching temperature is 145° C., the setting temperature is 150° C., and the stretching ratio is 4 times; in step (5), the transverse stretching temperature is 145° C., the setting temperature is 150° C., and the stretching ratio is 6.5 times; and the capacitor film is obtained.

[0099] The thickness of the upper and lower surface layers (poly-4-methyl-1-pentene film) and the middle layer (polypropylene film) of the capacitor film, the DC voltage breakdown strength at 100° C. and 120° C., and the thermal shrinkage are shown in Table 1.

[0100] Comparative Example 1

[0101] The capacitor film is obtained in the same manner as in Example 1, except that in step (1), based on the total amount of the capacitor film, the mass of the polypropylene resin accounts for 19%, and the mass of the mixture containing poly-4-methyl-1-pentene and an antioxidant accounts for 81%.

[0102] The thickness of the upper and lower surface layers (poly-4-methyl-1-pentene film) and the middle layer (polypropylene film) of the capacitor film, the DC voltage breakdown strength at 100° C. and 120° C., and the thermal shrinkage are shown in Table 1.

[0103] Comparative Example 2

[0104] (1) Polypropylene resin: weight average molecular weight 480,000 g / mol, melt index 2.9 g / 10 min (2.16 kg, 260° C.), molecular weight distribution index 5.8, isotacticity 97.5%, ash content 15 ppm;

[0105] (2) Extrusion: melting, plasticizing and extruding the polypropylene resin, wherein the extrusion temperature is 255° C.;

[0106] (3) chilling roller and high-pressure air knife: the sheet-like fluid obtained by extrusion in step (2) is cast into a thick sheet by passing it through a chilling roller and a high-pressure air knife, wherein the temperature of the chilling roller is 95° C. and the gas temperature of the high-pressure air knife is 95° C.;

[0107] (4) longitudinal stretching: the thick sheet is longitudinally preheated, stretched and shaped in sequence to obtain a thick film, the preheating temperature is 130° C., the stretching temperature is 140° C., the shaping temperature is 145° C., and the stretching ratio is 4.2 times;

[0108] (5) Transverse stretching: the thick film is sequentially subjected to transverse stretching and shaping to obtain a thin film, the stretching temperature is 140° C., the shaping temperature is 145° C., and the stretching ratio is 5 times;

[0109] (6) Cooling, measuring thickness and trimming the film, the cooling temperature is 30° C., and the film is trimmed and measured for thickness; then the film is rolled up after trimming, the rolling tension is 25 N / m, and the rolling pressure is 150 N / m;

[0110] (7) Aging treatment: The rolled film is subjected to a first aging treatment at 30° C., a humidity of less than 60%, and a purification level of 10,000 for 72 hours; then the film after the first aging treatment is subjected to a second aging treatment at 30° C., a humidity of less than 60%, and a purification level of 10,000 for 12 hours to obtain the capacitor film.

[0111] The thickness, DC voltage breakdown strength at 100° C. and 120° C., and thermal shrinkage of the capacitor film (polypropylene film) are shown in Table 1.

[0112] Table 1

[0113]

[0114] It can be seen from the results in Table 1 that the capacitor film prepared by the preparation method of the present invention has excellent heat resistance and compressive strength. It can be seen from Examples 1-6 in Table 1 that the capacitor film provided by the present invention has a heat shrinkage rate of 0.3-1.2% at 100°C, a breakdown strength of 622-645V / μm, a heat shrinkage rate of 1.3-2% at 120°C, a breakdown strength of 561-596V / μm, uniform thickness, good film-forming property, and fully meets the performance requirements of the capacitor; the content of polypropylene resin in Comparative Example 1 is not within the scope of the claims of the present invention. Under the same processing technology, the continuous film-forming property of the prepared capacitor film is poor, the breakdown strength is insufficient, and the shrinkage rate is large; in Comparative Example 2, no poly-4-methyl-1-pentene resin is added, and only polypropylene film is used. The continuous film-forming property of the prepared polypropylene capacitor film is good, but the heat shrinkage rate at 100°C and 120°C is poor, and the breakdown strength at 100°C is obviously insufficient, and it cannot be used at a high temperature of 120°C. Therefore, the capacitor film provided by the present invention has excellent temperature resistance and pressure resistance, good thickness uniformity, and good continuous film forming property during production.

[0115] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A capacitor film, characterized in that: The capacitor film includes a polypropylene film, a first poly-4-methyl-1-pentene film disposed on the upper surface of the polypropylene film, and a second poly-4-methyl-1-pentene film disposed on the lower surface of the polypropylene film; Wherein, the polypropylene film comprises polypropylene resin, and the poly-4-methyl-1-pentene film comprises an antioxidant and poly-4-methyl-1-pentene resin; Based on the total amount of the capacitor film, the content of the polypropylene resin is 50-70wt%, and the total amount of the antioxidant and the poly 4-methyl-1-pentene resin in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film is independently 15-25wt%; In the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film, based on the total amount of the poly 4-methyl-1-pentene film, the content of the antioxidant is independently 0.1-0.49wt%, and the content of the poly 4-methyl-1-pentene resin is independently 99.51-99.9wt%.

2. The capacitor film according to claim 1, wherein: Based on the total amount of the capacitor film, the content of the polypropylene resin is 55-65wt%, and the total amount of the antioxidant and the poly 4-methyl-1-pentene in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film is independently 17.5-22.5wt%; Preferably, in the first poly 4-methyl-1-pentene film and the second poly 4-methyl-1-pentene film, based on the total amount of the poly 4-methyl-1-pentene film, the content of the antioxidant is independently 0.2-0.4wt%, and the content of the poly 4-methyl-1-pentene resin is independently 99.6-99.8wt%.

3. The capacitor film according to claim 1 or 2, wherein: The weight average molecular weight of the polypropylene resin is 200,000-500,000 g / mol, the melt index at 230° C. and a load of 2.16 kg is 0.5-3 g / 10 min, the molecular weight distribution index is 4-8, the isotacticity is ≥97.5%, and the ash content is <20 ppm.

4. The capacitor film according to any one of claims 1 to 3, wherein: The antioxidant is selected from hindered phenol antioxidants and / or phosphite antioxidants, preferably selected from pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, 2,2'-thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,4,6-tri-tert-butyl At least one of 4,4'-thiobis(6-tert-butyl-3-methylphenol), more preferably 2,6-di-tert-butyl-p-cresol, tris[2,4-di-tert-butylphenyl]phosphite, bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite, tris(4-nonphenyl)phosphite, distearyl thiodipropionate, dilauryl thiodipropionate and 4,4'-thiobis(6-tert-butyl-3-methylphenol).

5. The capacitor film according to any one of claims 1 to 4, wherein: The poly 4-methyl-1-pentene resin includes a poly 4-methyl-1-pentene homopolymer and / or a poly 4-methyl-1-pentene copolymer; Preferably, the weight average molecular weight of the poly-4-methyl-1-pentene homopolymer is 200,000-600,000 g / mol, the melt index at 260° C. and a load of 5 kg is 10-50 g / 10 min, the molecular weight distribution index is 4-10, the isotacticity is ≥95%, the ash content is <30 ppm, and the melting point is 235-245° C.; Preferably, the weight average molecular weight of the poly-4-methyl-1-pentene copolymer is 200,000-500,000 g / mol, the melt index at 260°C and a load of 5 kg is 5-30 g / 10 min, the molecular weight distribution index is 5-10, the isotacticity is ≥65%, the ash content is <30 ppm, and the melting point is 220-240°C.

6. The capacitor film according to any one of claims 1 to 5, wherein: The poly-4-methyl-1-pentene copolymer is prepared by copolymerizing 4-methyl-1-pentene and α-olefin; Preferably, the content of 4-methyl-1-pentene structural units in the poly-4-methyl-1-pentene copolymer is 50-95wt%; Preferably, the α-olefin is selected from α-olefins having 2 to 18 carbon atoms, preferably at least one selected from ethylene, propylene, 1-butene, 1-hexene, 1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene and 1-octadecene, more preferably at least one selected from 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene and 1-octadecene, further preferably at least one selected from ethylene, 1-hexene and 1-octene.

7. The capacitor film according to any one of claims 1 to 6, wherein: The thickness of the capacitor film is 4-12 μm, preferably 5.3-10.8 μm; Preferably, the thermal shrinkage of the capacitor film at 100° C. is 0.3-1.2%, and the DC voltage breakdown strength is 622-645 V / μm; the thermal shrinkage of the capacitor film at 120° C. is 1.3-2%, and the DC voltage breakdown strength is 561-596 V / μm.

8. A method for preparing a capacitor film according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: (1) extruding a polypropylene resin, a mixture containing a poly-4-methyl-1-pentene resin and an antioxidant respectively to obtain a sheet fluid; (2) sequentially forming, longitudinally stretching and transversely stretching the sheet-like fluid to obtain a base film; (3) The base film is treated and rolled up, and then subjected to a first aging treatment and a second aging treatment to obtain the capacitor film.

9. The method according to claim 8, wherein: In step (1), the extrusion temperature of the polypropylene resin is 230-255° C., and the extrusion temperature of the mixture containing poly-4-methyl-1-pentene resin and antioxidant is 250-300° C.; Preferably, the longitudinal stretching includes longitudinal preheating, stretching and shaping; the conditions of the longitudinal stretching include: preheating temperature of 125-150°C, stretching temperature of 145-155°C, shaping temperature of 150-158°C, and stretching ratio of 3-8 times; Preferably, the transverse stretching includes stretching and shaping, and the conditions of the transverse stretching include: a stretching temperature of 145-155° C., a shaping temperature of 150-158° C., and a stretching ratio of 5-8 times.

10. The method according to claim 8 or 9, wherein: In step (3), the treatment includes sequentially cooling, thickness measurement and edge trimming the base film; the cooling temperature is 25-30°C; Preferably, the film after edge trimming is rolled up, the rolling tension is 20-30 N / m, and the rolling pressure is 150-200 N / m; Preferably, the conditions of the first aging treatment include: purification level ≤ 10,000, temperature 25-30°C, humidity < 60%, aging time 24-72h; Preferably, the conditions of the second aging treatment include: purification level ≤ 10,000, temperature 25-30°C, humidity < 60%, and aging time 12-24h.

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