Bopp capacitor film and preparation method thereof

Abstract

The application relates to the technical field of capacitor films, and particularly discloses a BOPP capacitor film and a preparation method thereof. The capacitor film comprises a temperature-resistant layer, a core layer and a light layer arranged in sequence. The temperature-resistant layer comprises 64-81.5 wt% of polypropylene, 8-15 wt% of styrene grafted polypropylene, 10-20 wt% of H type long branched polypropylene and 0.5-1.0 wt% of an antioxidant. The core layer comprises polypropylene. The light layer comprises 99-99.5 wt% of polypropylene and 0.5-1.0 wt% of an anti-blocking agent masterbatch. The BOPP capacitor film can be used for long-term stable work in a high-temperature environment above 100 DEG C, and meanwhile, the BOPP capacitor film can maintain high dielectric breakdown strength, low dielectric loss and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of capacitor film technology, and in particular to a BOPP capacitor film and its preparation method. Background Technology

[0002] Biaxially oriented polypropylene (BOPP) film, with its excellent tensile properties, good transparency, low gas permeability, excellent chemical stability, and resistance to cold and heat, has been widely used in packaging for food, daily necessities, and pharmaceuticals. Furthermore, BOPP film possesses excellent electrical insulation properties, making it a core dielectric material for capacitor manufacturing and holding an irreplaceable position in electronic capacitors, AC motors, and other electronic fields.

[0003] Polypropylene resin is currently the preferred material for preparing high-performance capacitor films due to its inherently low dielectric loss, high dielectric breakdown strength, excellent self-healing properties, and low price. However, the inherent structural characteristics of the polypropylene molecular chain determine that its high-temperature resistance has significant shortcomings: the helical molecular chain segments in the crystalline regions of polypropylene have a motion activation temperature, i.e., an α-relaxation temperature, in the range of 80-100℃. When the operating temperature exceeds 85℃, the molecular chains at the interface between the crystalline and amorphous regions begin to relax significantly, the interfacial bonding force decreases, and this directly leads to an increase in the material's thermal shrinkage rate and an exacerbation of creep. At the same time, polypropylene is a non-polar polymer. Although it has the inherent advantage of low intrinsic dielectric loss, the expansion of the material's free volume at high temperatures causes an exponential increase in carrier mobility, which in turn leads to a significant increase in conductivity and a sharp decrease in breakdown strength. In addition, although the crystallization melting point of polypropylene is about 165℃, and its short-term heat resistance can be supported by the melting point level, its long-term operating temperature is constrained by multiple factors, including the perfection of the crystalline regions, the molecular chain motion characteristics of the amorphous regions, and thermo-oxidative aging behavior. Therefore, the long-term operating temperature of existing ordinary BOPP capacitor films is only 85~90℃. When the operating temperature exceeds 85℃, the dielectric breakdown strength of the BOPP film drops sharply, the dielectric loss increases significantly, and the thermal shrinkage rate increases, leading to a serious deterioration in the overall performance of the capacitor. Especially in extreme applications such as electric vehicles and photovoltaic inverters, the local operating temperature of capacitors often exceeds 100℃, and can even reach above 120℃. This poses a severe reliability challenge and safety hazard to traditional BOPP capacitor films, greatly limiting their application in high-end fields.

[0004] In summary, existing technologies cannot simultaneously achieve the high-temperature resistance, high dielectric breakdown strength, and low dielectric loss of BOPP capacitor films; these three properties present an irreconcilable contradiction. Therefore, developing a BOPP capacitor film capable of long-term stable operation at temperatures above 100°C while maintaining high dielectric breakdown strength, low dielectric loss, and excellent mechanical properties has become a critical technical problem urgently needing to be solved in the development of the power electronics and new energy industries. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a BOPP capacitor film and its preparation method, which can work stably for a long time in a high temperature environment above 100°C, while maintaining high dielectric breakdown strength, low dielectric loss and excellent mechanical properties.

[0006] This invention is achieved through the following detailed technical solutions: A BOPP capacitor film includes a heat-resistant layer, a core layer, and a light layer arranged sequentially; the heat-resistant layer comprises 64-81.5 wt% polypropylene, 8-15 wt% styrene-grafted polypropylene, 10-20 wt% H-type long-chain branched polypropylene, and 0.5-1.0 wt% antioxidant; the core layer comprises polypropylene; the light layer comprises 99-99.5 wt% polypropylene and 0.5-1.0 wt% anti-blocking masterbatch. The styrene grafting rate of the styrene-grafted polypropylene is 2% to 4%. The H-type long-branched polypropylene is prepared by the following method: After the reactor was pretreated by vacuum and nitrogen purging at 70°C, hydrogen was introduced. A catalyst, triethylaluminum heptane solution, diisopropyldimethoxysilane heptane solution, alkenyldimethylchlorosilane heptane solution, and liquid propylene were added. The propylene homopolymerization reaction was carried out at 70°C. The polymerization product was treated with nitrogen atmosphere steam, then dehydrated and condensed, and vacuum dried to obtain the H-type long-branched polypropylene.

[0007] The applicant's research revealed that the failure of BOPP capacitor films under operating conditions above 85℃ mainly stems from two major performance shortcomings: insufficient thermomechanical temperature resistance and long-term thermal aging stability, and rapid degradation of dielectric properties at high temperatures, specifically manifested as a sharp drop in breakdown strength and a surge in conductivity loss. To improve the dielectric temperature resistance of BOPP capacitor films, this invention incorporates styrene-grafted polypropylene into the temperature-resistant layer. The dielectric temperature resistance modification effect originates from the synergistic effect of a dual mechanism: the deep trap effect and the crystal refinement effect. Because the benzene rings on the styrene side groups have a conjugated π-electron structure, it is equivalent to introducing a large number of electron deep traps into the polypropylene backbone. At high temperatures, the charge carriers of thermally excited polypropylene are easily captured by these deep traps, preventing them from participating in conductivity transport. This helps suppress the increase in leakage current of the BOPP capacitor film, thereby improving the dielectric temperature resistance of the BOPP capacitor film at high temperatures. Furthermore, the grafting points in the styrene-grafted polypropylene can serve as heterogeneous nucleation sites, increasing the nucleation density of polypropylene in the temperature-resistant layer, refining the polypropylene spherulite size, improving crystal perfection, enhancing the scattering effect on charge carriers, and further reducing conductivity. Based on the synergistic effect of the above dual mechanisms, styrene-grafted polypropylene can improve the dielectric temperature resistance of the film.

[0008] However, styrene-grafted polypropylene mainly functions for dielectric temperature resistance, but its overall constraint on the molecular chains of the amorphous regions of polypropylene is limited, making it impossible to construct a long-term physically entangled network. Therefore, its creep resistance, dimensional stability, and long-term thermal aging stability under prolonged heating above 85°C remain insufficient. Based on this, to improve the mechanical temperature resistance of the BOPP capacitor film, this invention further introduces H-type long-branched polypropylene into the temperature-resistant layer. The molecular structure of the H-type long-branched polypropylene is as follows: PP-g-(CH2). n -Si(CH3)2-O- Si(CH3)2-(CH2) n -g-PP, where n is 10, 11 or 12.

[0009] The core feature of this component is the construction of a multi-level entangled network based on "H-type units," with Si atoms as branching centers, symmetrically connecting two polypropylene long molecular chains of equal or unequal length, forming an overall "H"-shaped topology. The H-type branching structure can form dense molecular chain entanglement points within the polypropylene matrix, constructing a physical entanglement network. On one hand, it strongly restricts the free movement and free volume expansion of polypropylene amorphous molecular chains, increasing the α-relaxation activation temperature of polypropylene and fundamentally delaying the high-temperature degradation of the polypropylene crystalline-amorphous region interface. Simultaneously, this entanglement network can mitigate polypropylene molecular chain breakage and polypropylene crystallization disintegration during thermal aging, improving the thermomechanical temperature resistance of the film and extending the high-temperature service life of the BOPP capacitor film. On the other hand, the H-type branching points can serve as highly efficient heterogeneous nucleation sites, increasing the polypropylene nucleation density, refining the size of polypropylene spherulites, improving the crystallization perfection of polypropylene, making the polypropylene lamellar stacks more compact, and less prone to slippage and coarsening at high temperatures, further enhancing the heat aging resistance of the BOPP capacitor film.

[0010] In addition, blending styrene-grafted polypropylene with H-type long-branched polypropylene in a specific ratio can also produce a significant synergistic effect. The physically entangled network constructed by H-type long-branched polypropylene can stabilize the crystalline-amorphous region interface, inhibit the disintegration of the crystalline structure and the generation of interface defects at high temperatures, reduce the carrier activation sites caused by structural degradation, and reduce the high-temperature carrier concentration from the source, which is beneficial to improving the dielectric temperature resistance of the film. Meanwhile, styrene-grafted polypropylene can effectively suppress high-temperature conductivity and slow down the continuous erosion of molecular chains and crystalline interfaces by thermal effects, thereby reducing the thermal aging load of H-type long-branched polypropylene, which is beneficial to extending the high-temperature service life of the physically entangled network and improving the thermomechanical temperature resistance. At the same time, the heterogeneous nucleation of the two components forms a superimposed effect, synergistically increasing the nucleation density of polypropylene and refining the spherulite size, which not only further enhances the thermomechanical high-temperature stability of the crystalline structure, but also simultaneously increases the number of microcrystalline scattering interfaces, synergistically strengthening the dielectric temperature resistance.

[0011] The biaxial stretching process can also create a synergistic effect with the aforementioned material compounding system, further amplifying the temperature resistance modification effect. Under the action of longitudinal and transverse tensile stress fields, the H-type long-branched polypropylene in the temperature-resistant layer is synchronously oriented with the matrix molecular chains, forming a directional entanglement network. This significantly strengthens the constraint effect on the molecular chains, and combined with orientation-induced crystallization to stabilize the crystal interface, it improves the high-temperature creep resistance and dimensional stability of the film, and enhances the thermomechanical temperature resistance. The styrene-grafted polypropylene in the temperature-resistant layer is uniformly arranged with the molecular chains, and the electron deep trap distribution is more regular and orderly, improving the carrier capture efficiency. Combined with orientation crystallization, it synergistically enhances the carrier scattering effect, consolidating the dielectric temperature resistance. This invention, through the dual synergistic effect of "temperature-resistant layer material compounding + biaxial stretching process," simultaneously improves the thermomechanical temperature resistance and dielectric temperature resistance of the capacitor film, enabling the BOPP capacitor film to operate stably for a long time in environments above 120°C.

[0012] Furthermore, this invention limits the amount of styrene-grafted polypropylene added to the heat-resistant layer to 8-15 wt%. If the amount of styrene-grafted polypropylene added to the heat-resistant layer is too low, the concentration of grafting sites in the system will be insufficient, failing to effectively improve the dielectric temperature resistance of the BOPP capacitor film. If the amount of styrene-grafted polypropylene added to the heat-resistant layer is too high, the steric hindrance of the excessive styrene side chains will hinder the regular stacking of polypropylene molecular chains and the growth of lamellar crystals, reducing crystallinity and crystal perfection, which may easily lead to film breakage during the subsequent biaxial stretching process, affecting production smoothness. The present invention further limits the addition amount of the H-type long-branched polypropylene in the heat-resistant layer to 10~20wt%. If the addition amount of the H-type long-branched polypropylene in the heat-resistant layer is too low, the molecular chain entanglement point density is insufficient, making it difficult to form a dense physical entanglement network. The constraint effect on the molecular chains in the amorphous region is weak, the free volume expansion at high temperature is obvious, the α relaxation activation temperature increase is limited, and the interface between the crystalline region and the amorphous region is easy to loosen and dissociate, resulting in insufficient thermomechanical temperature resistance and long-term thermal aging stability of the film. If the addition amount of the H-type long-branched polypropylene in the heat-resistant layer is too high, the steric hindrance of a large number of branches will interfere with the regular stacking of polypropylene molecular chains and lamellar growth, reducing the overall crystallinity and crystal perfection. The excessively dense entanglement network will also increase the internal stress of the film. The release of internal stress at high temperature can easily cause dimensional deformation, and the branching points of excessive tertiary carbon structures can easily become weak sites for thermo-oxidative attack. During biaxial stretching, crystal points, uneven thickness, or even film breakage are likely to occur, affecting the appearance quality of the film and the smoothness of production.

[0013] Furthermore, this invention further limits the grafting rate of styrene-grafted polypropylene to 2-4%. At this appropriate grafting rate, it is beneficial to effectively suppress carrier migration in the polypropylene matrix at high temperatures, reduce film conductivity loss, maintain film breakdown strength, and improve the dielectric temperature resistance of BOPP capacitor films. When the grafting rate is too low, the suppression effect on high-temperature conductivity of the film is poor, and it cannot effectively alleviate the problem of dielectric failure caused by a sharp drop in film breakdown strength and a surge in loss above 85°C, resulting in unsatisfactory temperature resistance modification. When the grafting rate is too high, the high-density styrene side chains significantly increase the flow resistance of the polypropylene molecular chains. The lower the melt index of the grafted polypropylene, the easier it is for styrene side chains to locally accumulate and for micro-phase separation between the styrene and polypropylene phases to occur. This leads to greater difficulty in plasticizing and dispersing during blending, and the easy formation of styrene-grafted polypropylene agglomerates. Co-extruded sheets are prone to defects such as crystal points and fisheyes, and during biaxial stretching, problems such as uneven thickness and stretching film breakage are likely to occur.

[0014] Furthermore, the polypropylene in the core layer has an isotacticity of 96%-97%, a melt index of 2.0~3.5g / 10min at 230℃ and 2.16kg, and an ash content of 10ppm~20ppm. These parameters result in high polypropylene crystal regularity, excellent processing fluidity, and extremely low ash content, which effectively reduces dielectric defects and ensures high breakdown strength and processing uniformity of the film.

[0015] Furthermore, the melt index of the styrene-grafted polypropylene is 2~4 g / 10 min under the test conditions of 230℃ and 2.16 kg.

[0016] Furthermore, the styrene-grafted polypropylene is prepared by the following method: Using 91.7~98.4wt% polypropylene powder as the matrix, 0.05~0.20wt% benzoyl peroxide (BPO) as the initiator, and 3.5~8.3wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. Specifically, polypropylene powder is first added to a reactor containing deionized water and stirred to form a suspension; then, initiator BPO is added, followed by styrene monomer; the mixture is stirred at 60°C for 1-3 hours to allow the styrene monomer to penetrate into the powder; then, the temperature is raised to 90°C and nitrogen gas is introduced to initiate the grafting reaction. The product is filtered, vacuum dried, and then extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymer, yielding the styrene-grafted polypropylene. This preparation process facilitates the uniform penetration of styrene monomer into the polypropylene powder, allows for controllable acquisition of the target grafting rate, and ensures stable modification effects. Preferably, in this invention, the polypropylene powder used to prepare the styrene-grafted polypropylene uses polypropylene with the same parameters as the core layer.

[0017] Furthermore, the H-type long-branched polypropylene has a melt index of 2.0~3.0 g / 10 min and a branching point density of 1.0~1.5 / 10000C under the test conditions of 230℃ and 2.16 kg. Selecting H-type long-branched polypropylene within the above parameter range is beneficial for forming a uniform and dense physical entanglement network in the polypropylene matrix, effectively binding the molecular chain movement of polypropylene amorphous regions, significantly increasing the α-relaxation activation temperature of polypropylene, inhibiting the high-temperature free volume expansion of polypropylene, stabilizing the polypropylene crystalline-amorphous region interface, delaying the chain scission of polypropylene molecules and the disintegration of the polypropylene crystalline structure under thermal aging, and significantly improving the thermomechanical temperature resistance and long-term thermal aging stability of BOPP capacitor film. At the same time, an appropriate number of branching points serve as efficient heterogeneous nucleation sites, which can uniformly refine polypropylene spherulites, improve the crystal perfection of polypropylene, make the polypropylene lamellar stack more compact, and prevent slippage and coarsening at high temperatures. In addition, sufficient polypropylene microcrystalline interfaces can enhance the carrier scattering effect, which is also beneficial for reducing the high-temperature conductivity loss of the film and maintaining the film breakdown strength. Together with styrene-grafted polypropylene, it improves the dielectric temperature resistance of BOPP capacitor film. If the branching density is too low, it is difficult to build a dense physical entanglement network in the polypropylene matrix due to insufficient branching points. The improvement in the thermomechanical temperature resistance of the film above 85°C is not significant, and the inhibition effect on the high-temperature electrical conductivity of the film is also weakened. If the branching density is too high, the melt fluidity of H-type long-branched polypropylene decreases. Excessive branching points will bring strong steric hindrance between polypropylene molecular chains. The excessively dense entanglement network will increase the residual internal stress of the BOPP film. At the same time, the tertiary carbon structure on the polypropylene molecular chain with too many branching points is prone to become a weak site for thermo-oxidative attack, accelerating the chain breakage of polypropylene molecular chains and the disintegration of polypropylene crystal structure, which weakens the long-term thermal aging stability of the film. Moreover, defects such as crystal points and fish eyes are easily generated during film processing, and problems such as stretching and film breakage are likely to occur.

[0018] Furthermore, the alkenyl dimethylchlorosilane is one of 9-decenyl dimethylchlorosilane, 10-undecapenyl dimethylchlorosilane, and 11-dodecenyl dimethylchlorosilane.

[0019] Furthermore, the total thickness of the BOPP capacitor film is 6~12μm; wherein the thickness of the heat-resistant layer is 1~2μm.

[0020] Furthermore, the present invention also provides a method for preparing the above-mentioned BOPP capacitor film, comprising the following steps: After the raw materials of each layer are mixed according to the formula, they are added to each extruder. After being metered by the metering pump, the melt of each extruder is merged into a thick sheet at the T-die. The thick sheet is cooled by the quenching roller and then enters the quenching water tank and the blowing chamber. Then it is stretched longitudinally and then enters the transverse stretching area to be stretched transversely to obtain a film. After the film is shaped and corona treated, it is wound up, then aged and cut to obtain the BOPP capacitor film. Detailed Implementation

[0021] To facilitate understanding of the present invention, it will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0022] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0023] The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. In the description of this application, it should be understood that the terms "first," "second," "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0024] Unless otherwise specified, the experimental methods in the following examples or comparative examples are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used are all commercially available from the conventional market unless otherwise specified.

[0025] As one embodiment of the present invention, this embodiment provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light layer arranged sequentially; the heat-resistant layer comprises 64~81.5wt% polypropylene, 8~15wt% styrene-grafted polypropylene, 10~20wt% H-type long-chain branched polypropylene, and 0.5~1.0wt% antioxidant; the core layer comprises polypropylene; the light layer comprises 99~99.5wt% polypropylene and 0.5~1.0wt% anti-blocking masterbatch; The styrene grafting rate of the styrene-grafted polypropylene is 2% to 4%. The H-type long-branched polypropylene is prepared by the following method: After the reactor was pretreated by vacuum and nitrogen purging at 70°C, hydrogen was introduced. A catalyst, triethylaluminum heptane solution, diisopropyldimethoxysilane heptane solution, alkenyldimethylchlorosilane heptane solution, and liquid propylene were added. The propylene homopolymerization reaction was carried out at 70°C. The polymerization product was treated with nitrogen atmosphere steam, then dehydrated and condensed, and vacuum dried to obtain H-type long-branched polypropylene.

[0026] Furthermore, the polypropylene has an isotacticity of 96%-97%, a melt index of 2.0~3.5g / 10min at 230℃ and 2.16kg, and an ash content of 10ppm~20ppm.

[0027] Furthermore, the melt index of the styrene-grafted polypropylene is 2~4 g / 10 min under the test conditions of 230℃ and 2.16 kg.

[0028] Furthermore, the styrene-grafted polypropylene is prepared by the following method: Using 91.6~96.4wt% polypropylene powder as the matrix, 0.05~0.20wt% benzoyl peroxide (BPO) as the initiator, and 3.5~8.3wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. Specifically, polypropylene powder is first added to a reactor containing deionized water and stirred to form a suspension; then initiator BPO is added, and finally styrene monomer is added; the mixture is stirred at 60°C for 1-3 hours to allow the styrene monomer to penetrate into the powder; then the temperature is raised to 90°C and nitrogen gas is introduced to initiate the grafting reaction; after filtration and vacuum drying, the product is extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers to obtain the styrene-grafted polypropylene.

[0029] Furthermore, the H-type long-branched polypropylene has a melt index of 2.0~3.0 g / 10 min and a branching point density of 1.0~1.5 / 10000C under the test conditions of 230℃ and 2.16 kg.

[0030] Furthermore, the alkenyl dimethylchlorosilane is one of 9-decenyl dimethylchlorosilane, 10-undecapenyl dimethylchlorosilane, and 11-dodecenyl dimethylchlorosilane.

[0031] 10-Undecenyldimethylchlorosilane (CAS: 18406-97-8) was purchased from Shanghai Mairui Biochemical Technology Co., Ltd. The above-mentioned 9-decenyldimethylchlorosilane and 11-dodecenyldimethylchlorosilane can be prepared by the following method: Under an inert atmosphere, dried and purified 1,9-decadiene (or 1,11-dodecadiene) and anhydrous toluene are added to a reaction flask (the volume ratio of diene to solvent is 1:0.5-2), and a Karstedt catalyst (platinum effective concentration 1×10⁻⁶) is used. -5Mix 1,9-decadiene (or 1,11-dodecadiene) at a molar ratio of 2.5–3.5:1 to dimethylchlorosilane (g / mL, i.e., approximately 10–50 ppm relative to dimethylchlorosilane). Heat to 50–60 °C and slowly add dimethylchlorosilane dropwise over 1–2 h. After the addition is complete, maintain the reaction temperature at 50–60 °C for 2–4 h. After the reaction is complete, recover the excess diene under reduced pressure (1,9-decadiene bp 169 °C, 1,11-dodecadiene bp 208.6 °C). Collect the target product by high-vacuum distillation to obtain 9-decenyldimethylchlorosilane or 11-dodecenyldimethylchlorosilane.

[0032] Furthermore, the total thickness of the BOPP capacitor film is 6~12μm; wherein the thickness of the heat-resistant layer is 1~2μm.

[0033] Furthermore, the present invention also provides a method for preparing the above-mentioned BOPP capacitor film, comprising the following steps: After the raw materials of each layer are mixed according to the formula, they are added to each extruder. After being metered by the metering pump, the melt of each extruder is merged into a thick sheet at the T-die. The thick sheet is cooled by the quenching roller and then enters the quenching water tank and the blowing chamber. Then it is stretched longitudinally and then enters the transverse stretching area to be stretched transversely to obtain a film. After the film is shaped and corona treated, it is wound up, then aged and cut to obtain the BOPP capacitor film.

[0034] It should be noted that in the embodiments or comparative examples of the present invention, the polypropylene was measured to have a melt index of 3 g / 10 min, an isotacticity of 96.5%, and an ash content of 15 ppm under the conditions of 230℃ and 2.16 kg; the antioxidant was a compound of antioxidant 1010 and antioxidant 168 (the mass ratio of the two was 1:1); the effective component in the anti-blocking masterbatch was silicon dioxide, the particle size of silicon dioxide was 0.2 μm, and the effective content was 6 wt%; all the proportions mentioned are mass percentages, and the components and contents of each layer in the embodiments and comparative examples of the present invention are shown in Table 1 below.

[0035] Table 1

[0036] In the table above, C10, C11, C12, C4, and C16 represent the alkenyl dimethylchlorosilanes used to prepare H-type long-branched polypropylene, namely 9-decenyl dimethylchlorosilane, 10-undenyl dimethylchlorosilane, 11-dodecenyl dimethylchlorosilane, 3-butenyl dimethylchlorosilane, and 15-hexadecenyl dimethylchlorosilane.

[0037] Example 1 This embodiment provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 96.4 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 3.5 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 2.0%, melt index 4.0 g / 10 min at 230°C and 2.16 kg).

[0038] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. 14 mg of MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL of triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL of diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 600 ppm of 9-decenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) were mixed and flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was subjected to homopolymerization of propylene at 70 °C and 200 rpm for 1 h with stirring. After the reaction, residual propylene was slowly released, and the resulting polymer particles were subjected to a process at 100 °C with flowing N2 (0.3 MPa). The product was treated with saturated steam (L / min) for 30 min to hydrolyze the Si-Cl bonds grafted onto the PP chain to Si-OH. After purging with N2 for 10 min, the product was kept at 100℃ for 20 min to allow the grafted PP chains to form Si-O-Si bridges through dehydration condensation of the hydroxyl groups in Si-OH. The resulting product was then dried under vacuum at 70℃ and -0.095 MPa for 24 hours to obtain H-type long-branched polypropylene (branching point density 1.5 / 10000C, melt index 2.0 g / 10 min at 230℃ and 2.16 kg).

[0039] The 9-decenyldimethylchlorosilane used in this embodiment was prepared by the following method: Under argon protection, 82.9 g (0.60 mol, 3 equivalents) of 1,9-decadiene, which was dried with CaH2 and purified by vacuum distillation, and 0.12 g of Karstedt catalyst (Pt content 2wt%, about 12 ppm) were added to a dry 250 mL three-necked flask. The temperature was raised to 55 °C and stirred at a constant temperature. 23.7 g (0.25 mol) of dimethylchlorosilane was slowly added dropwise at a rate of 2–3 mL / min, which was completed in about 30 min. The reaction temperature was maintained at 55 ± 5 °C and the reaction was continued for 3 h. After the reaction was completed, the excess diene was first recovered under reduced pressure, and then the target product was collected by high vacuum distillation.

[0040] Preparation of heat-resistant layer resin: Take 71.2 wt% polypropylene, 8 wt% of the above-mentioned styrene-grafted polypropylene, 20 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0041] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0042] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0043] Each layer of resin raw material is dried before use.

[0044] (2) Preparation of BOPP capacitor film The method for preparing the BOPP capacitor film in this embodiment includes the following steps: After the raw materials of each layer are mixed according to the formula, they are added to each extruder. After being metered by the metering pump, the melt of each extruder is merged into a thick sheet at the T-die. The thick sheet is cooled by the quenching roller and then enters the quenching water tank and the blowing chamber. Then it is stretched longitudinally and then enters the transverse stretching area to be stretched transversely to obtain a film. After the film is shaped and corona treated, it is wound up, then aged and cut to obtain the BOPP capacitor film.

[0045] In the above preparation method, the quenching temperature is 30°C; the extrusion temperature of the heat-resistant layer is 240°C, and the extrusion temperatures of the core layer and the light layer are 250°C; during longitudinal stretching, the longitudinal stretching ratio is 5.0 times, the preheating temperature of the heat-resistant layer is 130°C and the stretching temperature is 132°C, and the preheating temperature and stretching temperature of the light layer are 135°C and 135°C; during transverse stretching, the transverse stretching ratio is 8.0 times, the preheating temperature is 168°C, the stretching temperature is 165°C, and the setting temperature is 165°C.

[0046] The total thickness of the BOPP capacitor film obtained in this embodiment is 10μm, of which the thickness of the heat-resistant layer is 1.5μm, the thickness of the core layer is 8μm, and the thickness of the optical layer is 0.5μm.

[0047] Example 2 This embodiment provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 94.9 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 5.0 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The procedure was as follows: First, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the styrene monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 4.0%, melt index 2.0 g / 10 min at 230°C and 2.16 kg).

[0048] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. 14 mg of MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL of triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL of diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 750 ppm of 11-dodecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) were mixed and flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was subjected to homopolymerization of propylene at 70 °C and 200 rpm for 1 h with stirring. After the reaction, residual propylene was slowly released, and the resulting polymer particles were subjected to a process at 100 °C with flowing N2 (0.3 MPa). The polypropylene was treated with saturated water vapor at a flow rate of L / min for 30 min to hydrolyze the Si-Cl bonds grafted onto the PP chain into Si-OH. After purging with N2 for 10 min, it was kept at 100℃ for 20 min to allow the Si-OH bonds of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70℃ and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000C, melt index 2.2 g / 10 min at 230℃ and 2.16 kg).

[0049] The 11-dodecenyldimethylchlorosilane used in this embodiment was prepared by the following method: Under argon protection, 99.8 g (0.60 mol, 3 equivalents) of 1,11-dodecadiene, which was dried with CaH2 and purified by vacuum distillation, and 0.12 g of Karstedt catalyst (Pt content 2 wt%, about 12 ppm) were added to a dry 250 mL three-necked flask. The temperature was raised to 55 °C and stirred at a constant temperature. 23.7 g (0.25 mol) of dimethylchlorosilane was slowly added dropwise at a rate of 2-3 mL / min, which was completed in about 30 min. The reaction temperature was maintained at 55±5 °C and the reaction was continued for 3 h. After the reaction was completed, the excess diene was first recovered under reduced pressure, and then the target product was collected by high vacuum distillation.

[0050] Preparation of heat-resistant layer resin: Take 74.2 wt% polypropylene, 15 wt% of the above-mentioned styrene-grafted polypropylene, 10 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0051] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0052] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0053] Each layer of resin raw material is dried before use.

[0054] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this embodiment is the same as that in Embodiment 1.

[0055] The total thickness and the thickness of each layer of the BOPP capacitor film in this embodiment are the same as in Embodiment 1.

[0056] Example 3 This embodiment provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0057] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. 14 mg of MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL of triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL of diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm of 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) were mixed and flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was subjected to homopolymerization of propylene at 70 °C and 200 rpm for 1 h with stirring. After the reaction, residual propylene was slowly released, and the resulting polymer particles were subjected to a process at 100 °C with flowing N2 (0.3 MPa). The polypropylene was treated with saturated steam (L / min) for 30 min to hydrolyze the Si-Cl bonds grafted onto the PP chain to Si-OH. After purging with N2 for 10 min, it was kept at 100℃ for 20 min to allow the Si-OH bonds of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70℃ and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000C, melt index 2.1g / 10min at 230℃ and 2.16kg).

[0058] Preparation of heat-resistant layer resin: Take 72.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0059] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0060] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0061] Each layer of resin raw material is dried before use.

[0062] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this embodiment is the same as that in Embodiment 1.

[0063] The total thickness and the thickness of each layer of the BOPP capacitor film in this embodiment are the same as in Embodiment 1.

[0064] Comparative Example 1 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Preparation of heat-resistant layer resin: Take 99.2 wt% polypropylene and 0.8 wt% antioxidant, mix them evenly to obtain heat-resistant layer resin.

[0065] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0066] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0067] Each layer of resin raw material is dried before use.

[0068] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0069] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0070] Comparative Example 2 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The procedure was as follows: First, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the styrene monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0071] Preparation of heat-resistant layer resin: Take 87.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain heat-resistant layer resin.

[0072] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0073] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0074] Each layer of resin raw material is dried before use.

[0075] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0076] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0077] Comparative Example 3 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. 14 mg of MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL of triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL of diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm of 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) were mixed and flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was subjected to homopolymerization of propylene at 70 °C and 200 rpm for 1 h with stirring. After the reaction, residual propylene was slowly released, and the resulting polymer particles were subjected to a process at 100 °C with flowing N2 (0.3 MPa). The polypropylene was treated with saturated steam at a flow rate of L / min for 30 min to hydrolyze the Si-Cl bonds grafted onto the PP chain into Si-OH. After purging with N2 for 10 min, the polypropylene was kept at 100℃ for 20 min to allow the Si-OH bonds of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70℃ and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000C, melt index 2.1g / 10min at 230℃ and 2.16kg).

[0078] Preparation of heat-resistant layer resin: Take 84.2 wt% polypropylene, 15 wt% of the above-mentioned H-type long-branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain heat-resistant layer resin.

[0079] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0080] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0081] Each layer of resin raw material is dried before use.

[0082] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0083] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0084] Comparative Example 4 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0085] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. A mixture of 14 mg MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) was flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was then subjected to a reaction at 70 °C and 200 rpm. Propylene homopolymerization was carried out under stirring for 1 hour. After the reaction was completed, residual propylene was slowly released. The resulting polymer particles were treated at 100°C with flowing N2 (0.3 L / min) carrying saturated water vapor for 30 minutes to hydrolyze the Si-Cl bonds grafted on the PP chain to Si-OH. After purging with N2 for 10 minutes, the mixture was kept at 100°C for 20 minutes to allow the Si-OH of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70°C and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000°C, melt index 2.1 g / 10 min at 230°C and 2.16 kg).

[0086] Preparation of heat-resistant layer resin: Take 80.2 wt% polypropylene, 4 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0087] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0088] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0089] Each layer of resin raw material is dried before use.

[0090] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0091] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0092] Comparative Example 5 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0093] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. A mixture of 14 mg MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) was flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was then subjected to a reaction at 70 °C and 200 rpm. Propylene homopolymerization was carried out under stirring for 1 hour. After the reaction was completed, residual propylene was slowly released. The resulting polymer particles were treated at 100°C with flowing N2 (0.3 L / min) carrying saturated water vapor for 30 minutes to hydrolyze the Si-Cl bonds grafted on the PP chain to Si-OH. After purging with N2 for 10 minutes, the mixture was kept at 100°C for 20 minutes to allow the Si-OH of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70°C and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000°C, melt index 2.1 g / 10 min at 230°C and 2.16 kg).

[0094] Preparation of heat-resistant layer resin: Take 64.2 wt% polypropylene, 20 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0095] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0096] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0097] Each layer of resin raw material is dried before use.

[0098] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0099] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0100] Comparative Example 6 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0101] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. 14 mg of MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL of triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL of diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm of 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) were mixed and flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was subjected to homopolymerization of propylene at 70 °C and 200 rpm for 1 h with stirring. After the reaction, residual propylene was slowly released, and the resulting polymer particles were subjected to a process at 100 °C with flowing N2 (0.3 MPa). The polypropylene was treated with saturated steam (L / min) for 30 min to hydrolyze the Si-Cl bonds grafted onto the PP chain to Si-OH. After purging with N2 for 10 min, it was kept at 100℃ for 20 min to allow the Si-OH bonds of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70℃ and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000C, melt index 2.1g / 10min at 230℃ and 2.16kg).

[0102] Preparation of heat-resistant layer resin: Take 82.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 5 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0103] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0104] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0105] Each layer of resin raw material is dried before use.

[0106] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0107] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0108] Comparative Example 7 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0109] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. A mixture of 14 mg MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) was flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was then subjected to a reaction at 70 °C and 200 rpm. The propylene homopolymer was carried out under stirring for 1 hour. After the reaction was completed, the residual propylene was slowly released. The resulting polymer particles were treated at 100°C with flowing N2 (0.3 L / min) carrying saturated water vapor for 30 minutes to hydrolyze the Si-Cl bonds grafted on the PP chain to Si-OH. After purging with N2 for 10 minutes, the mixture was kept at 100°C for 20 minutes to allow the Si-OH of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70°C and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000°C, melt index 2.1 g / 10 min at 230°C and 2.16 kg).

[0110] Preparation of heat-resistant layer resin: Take 57.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 30 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0111] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0112] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0113] Each layer of resin raw material is dried before use.

[0114] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0115] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0116] Comparative Example 8 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 98.4 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 1.5 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 1.0%, melt index 4.5 g / 10 min at 230°C and 2.16 kg).

[0117] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. A mixture of 14 mg MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) was flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was then subjected to a reaction at 70 °C and 200 rpm. The propylene homopolymer was carried out under stirring for 1 hour. After the reaction was completed, the residual propylene was slowly released. The resulting polymer particles were treated at 100°C with flowing N2 (0.3 L / min) carrying saturated water vapor for 30 minutes to hydrolyze the Si-Cl bonds grafted on the PP chain to Si-OH. After purging with N2 for 10 minutes, the mixture was kept at 100°C for 20 minutes to allow the Si-OH of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70°C and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000°C, melt index 2.1 g / 10 min at 230°C and 2.16 kg).

[0118] Preparation of heat-resistant layer resin: Take 72.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0119] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0120] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0121] Each layer of resin raw material is dried before use.

[0122] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0123] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0124] Comparative Example 9 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 91.7 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 8.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 6.0%, melt index 1.2 g / 10 min at 230°C and 2.16 kg).

[0125] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. A mixture of 14 mg MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) was flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was then subjected to a reaction at 70 °C and 200 rpm. The propylene homopolymer was carried out under stirring for 1 hour. After the reaction was completed, the residual propylene was slowly released. The resulting polymer particles were treated at 100°C with flowing N2 (0.3 L / min) carrying saturated water vapor for 30 minutes to hydrolyze the Si-Cl bonds grafted on the PP chain to Si-OH. After purging with N2 for 10 minutes, the mixture was kept at 100°C for 20 minutes to allow the Si-OH of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70°C and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000°C, melt index 2.1 g / 10 min at 230°C and 2.16 kg).

[0126] Preparation of heat-resistant layer resin: Take 72.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0127] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0128] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0129] Each layer of resin raw material is dried before use.

[0130] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0131] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0132] Comparative Example 10 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0133] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. 14 mg of MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL of triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL of diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm of 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) were mixed and flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was subjected to homopolymerization of propylene at 70 °C and 200 rpm for 1 h with stirring. After the reaction, residual propylene was slowly released, and the resulting polymer particles were subjected to a process at 100 °C with flowing N2 (0.3 MPa). The polypropylene was treated with saturated steam (L / min) for 30 min to hydrolyze the Si-Cl bonds grafted onto the PP chain to Si-OH. After purging with N2 for 10 min, it was kept at 100℃ for 20 min to allow the Si-OH bonds of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70℃ and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 0.5 / 10000C, melt index 2.1g / 10min at 230℃ and 2.16kg).

[0134] Preparation of heat-resistant layer resin: Take 72.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0135] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0136] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0137] Each layer of resin raw material is dried before use.

[0138] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0139] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0140] Comparative Example 11 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0141] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. A mixture of 14 mg MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) was flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was then subjected to a reaction at 70 °C and 200 rpm. The propylene homopolymer was carried out under stirring for 1 hour. After the reaction was completed, the residual propylene was slowly released. The resulting polymer particles were treated at 100°C with flowing N2 (0.3 L / min) carrying saturated water vapor for 30 minutes to hydrolyze the Si-Cl bonds grafted on the PP chain to Si-OH. After purging with N2 for 10 minutes, the mixture was kept at 100°C for 20 minutes to allow the Si-OH of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70°C and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 2.5 / 10000°C, melt index 2.1 g / 10 min at 230°C and 2.16 kg).

[0142] Preparation of heat-resistant layer resin: Take 72.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0143] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0144] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0145] Each layer of resin raw material is dried before use.

[0146] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0147] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0148] Comparative Example 12 This comparative example provides a PP cast film, comprising a heat-resistant layer, a core layer, and a light-reflecting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0149] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. A mixture of 14 mg MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 650 ppm 10-undecenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) was flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was then subjected to a reaction at 70 °C and 200 rpm. Propylene homopolymerization was carried out under stirring for 1 hour. After the reaction was completed, residual propylene was slowly released. The resulting polymer particles were treated at 100°C with flowing N2 (0.3 L / min) carrying saturated water vapor for 30 minutes to hydrolyze the Si-Cl bonds grafted on the PP chain to Si-OH. After purging with N2 for 10 minutes, the mixture was kept at 100°C for 20 minutes to allow the Si-OH of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70°C and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 1.4 / 10000°C, melt index 2.1 g / 10 min at 230°C and 2.16 kg).

[0150] Preparation of heat-resistant layer resin: Take 72.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0151] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0152] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0153] Each layer of resin raw material is dried before use.

[0154] (2) Preparation of PP cast film The preparation method of the PP cast film in this comparative example includes the following steps: After the raw materials of each layer are mixed according to the formula, they are added to each extruder. After being metered by the metering pump, the melt of each extruder is combined into a thick sheet at the T-die. The thick sheet is cooled by the cooling roller and then enters the cooling water tank and the blowing chamber. After being directly treated by corona, it is wound up, and then subjected to aging treatment and slitting to obtain the PP cast film.

[0155] In the above preparation method, the quenching temperature is 30°C; the casting temperature of the heat-resistant layer is 240°C; the casting temperature of the core layer and the light layer is 250°C; and the setting temperature is 165°C.

[0156] The total thickness of the PP cast film obtained in this comparative example is 10 μm, of which the thickness of the heat-resistant layer is 1.5 μm, the thickness of the core layer is 8 μm, and the thickness of the light layer is 0.5 μm.

[0157] Comparative Example 13 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0158] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. 14 mg of MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL of triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL of diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 600 ppm of 3-butenyldimethylchlorosilane heptane solution (0.5 mol / L, based on propylene mass) were mixed and flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was subjected to homopolymerization of propylene at 70 °C and 200 rpm for 1 h with stirring. After the reaction, residual propylene was slowly released, and the resulting polymer particles were subjected to a process at 100 °C with flowing N2 (0.3 MPa). The polypropylene was treated with saturated water vapor at a flow rate of L / min for 30 min to hydrolyze the Si-Cl bonds grafted onto the PP chain into Si-OH. After purging with N2 for 10 min, the polypropylene was kept at 100℃ for 20 min to allow the Si-OH bonds of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70℃ and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 0.8 / 10000C, melt index 3.5 g / 10 min at 230℃ and 2.16 kg).

[0159] Preparation of heat-resistant layer resin: Take 72.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0160] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0161] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0162] Each layer of resin raw material is dried before use.

[0163] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0164] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0165] Comparative Example 14 This comparative example provides a BOPP capacitor film, comprising a heat-resistant layer, a core layer, and a light-emitting layer sequentially arranged. The specific preparation method is as follows: (1) Preparation of capacitor film raw materials Styrene-grafted polypropylene is prepared by the following method: Using 95.6 wt% polypropylene powder as the matrix, 0.1 wt% benzoyl peroxide (BPO) as the initiator, and 4.3 wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. The steps were as follows: first, the polypropylene powder was added to a reactor containing deionized water and stirred to form a suspension; then, the initiator BPO was added, and finally, the styrene monomer was added; the mixture was stirred at 60°C for 2 hours to allow the monomer to penetrate into the powder; then, the temperature was raised to 90°C and nitrogen gas was introduced to initiate the grafting reaction for 4 hours. After filtration and vacuum drying, the product was extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene (grafting rate 3.0%, melt index 3.0 g / 10 min at 230°C and 2.16 kg).

[0166] H-type long-branched polypropylene is prepared by the following method: A 5 L stainless steel high-pressure reactor was vacuum-treated at 70 °C and repeatedly purged with N2 for more than 3 cycles. Then, H2 was introduced at 0.30 MPa. A mixture of 14 mg MgCl2 / TiCl4 / BMMF catalyst (heterogeneous Ziegler-Natta catalyst, Liaoning Xiangyang Chemical Group, China), 5 mL triethylaluminum heptane solution (0.5 mol / L, Albermarle, USA), 1 mL diisopropyldimethoxysilane heptane solution (0.1 mol / L, J&K Scientific), and 600 ppm (by weight of propylene) 15-hexadecenyldimethylchlorosilane heptane solution (0.5 mol / L) was flushed into the reactor with 1 kg of liquid propylene through another feed pipe. The reactor was then subjected to a reaction at 70 °C and 200 rpm. The propylene homopolymer was carried out under stirring for 1 hour. After the reaction was completed, the residual propylene was slowly released. The resulting polymer particles were treated at 100°C with flowing N2 (0.3 L / min) carrying saturated water vapor for 30 minutes to hydrolyze the Si-Cl bonds grafted on the PP chain to Si-OH. After purging with N2 for 10 minutes, the mixture was kept at 100°C for 20 minutes to allow the Si-OH of adjacent chains to dehydrate and condense to form Si-O-Si bridges. After vacuum drying at 70°C and -0.095 MPa for 24 hours, H-type long-branched polypropylene was obtained (branching point density 0.5 / 10000°C, melt index 3.8 g / 10 min at 230°C and 2.16 kg).

[0167] Preparation of heat-resistant layer resin: Take 72.7 wt% polypropylene, 11.5 wt% of the above-mentioned styrene-grafted polypropylene, 15 wt% of the above-mentioned H-type long-chain branched polypropylene and 0.8 wt% antioxidant, mix the components evenly to obtain the heat-resistant layer resin.

[0168] Core layer resin preparation: 100wt% polypropylene was used as the core layer resin.

[0169] Preparation of glossy resin: Take 99.4 wt% polypropylene and 0.6 wt% antiblocking masterbatch, mix them evenly to obtain glossy resin.

[0170] Each layer of resin raw material is dried before use.

[0171] (2) Preparation of BOPP capacitor film The preparation method of the BOPP capacitor film in this comparative example is the same as that in Example 1.

[0172] The total thickness and the thickness of each layer of the BOPP capacitor film in this comparative example are the same as those in Example 1.

[0173] Performance testing (1) Test methods: The thermal shrinkage rate (longitudinal and transverse), dielectric constant, breakdown strength and maximum operating temperature of the films of Examples 1-3 and Comparative Examples 1-14 were tested respectively. The specific standards for performance testing are as follows: Heat shrinkage rate: Test conditions: 120℃*2min, in accordance with GB / T10003-2008 standard; Dielectric constant: Tested at 120℃ and 1kHz according to GB / T1409-2006 standard using a precision impedance analyzer; Breakdown strength: Tested at 120℃, DC electric field, step-up voltage method, according to GB / T1408.2-2016 standard, using flat plate electrodes; Maximum operating temperature: Complies with IEC60216 series standards.

[0174] (2) Test results: The results are shown in Table 2 below.

[0175] Table 2

[0176] The performance test results above show that Examples 1-3 of this invention construct a dual modification system of "material compounding synergy + biaxial stretching orientation synergy" by compounding styrene-grafted polypropylene and H-type long-chain polypropylene in a specific ratio in the heat-resistant layer. Under the action of biaxial stretching molding, a stable oriented entanglement network and oriented crystalline structure are formed. Compared with the comparative examples, the films of Examples 1-3 have lower longitudinal and transverse thermal shrinkage rates, significantly improved breakdown strength at 120°C, and a maximum operating temperature of 129-132°C. They can achieve long-term stable service at temperatures above 100°C, and have both excellent high-temperature dimensional stability and dielectric properties, meeting the requirements for high-temperature capacitor films.

[0177] Comparative Example 1, with its heat-resistant layer lacking styrene-grafted polypropylene and H-type long-chain branched polypropylene, is a conventional modified BOPP film. The film exhibits a longitudinal thermal shrinkage rate of 4.5% and a transverse thermal shrinkage rate of 1.5%, a breakdown strength of only 420 MV / m at 120℃, and a maximum operating temperature of only 86℃. This indicates that the absence of these two modifying components results in insufficient thermomechanical and dielectric heat resistance. It fails to physically constrain the relaxation of molecular chains at high temperatures, stabilize crystal interfaces, or introduce deep electron traps to capture charge carriers. Consequently, structural degradation and conductivity spikes occur simultaneously at high temperatures, making long-term high-temperature operation impossible.

[0178] Comparative Example 2 used a heat-resistant layer with only styrene-grafted polypropylene and no H-type long-chain polypropylene. Compared to Example 1, the longitudinal and transverse thermal shrinkage of the capacitor film increased significantly, the breakdown strength decreased, and the maximum operating temperature dropped to 113°C. This indicates that styrene-grafted polypropylene can improve dielectric temperature resistance through the deep trap effect, but without the physical entanglement network constructed by H-type long-chain polypropylene, it is difficult to effectively constrain the molecular chain movement in the amorphous region and stabilize the crystal interface. The film's mechanical temperature resistance and long-term thermal aging stability are insufficient, and a single component cannot simultaneously meet the dual requirements of thermomechanical and dielectric temperature resistance.

[0179] Comparative Example 3's heat-resistant layer only added H-type long-chain branched polypropylene and did not contain styrene-grafted polypropylene. Compared to Example 1, the film exhibited increased thermal shrinkage, decreased breakdown strength, and a maximum operating temperature of only 120°C. This indicates that although H-type long-chain branched polypropylene can improve thermomechanical temperature resistance through physical entanglement networks, the lack of electron deep trapping effects from styrene side groups fails to effectively suppress high-temperature carrier migration and reduce conductivity losses. Consequently, the improvement in the film's high-temperature dielectric properties is limited, making it difficult to meet the dual-dimensional temperature resistance requirements.

[0180] Comparative Example 4 reduced the amount of styrene-grafted polypropylene to 4 wt%, which is lower than the lower limit of 8 wt% specified in this invention. The film's properties deteriorated compared to Example 1, with the maximum operating temperature dropping to 120°C. This is because the number of grafting sites in the system was insufficient, making it difficult to generate enough deep electron traps, resulting in limited ability to capture high-temperature carriers and failing to achieve the expected modification effect. This verifies that the amount of styrene-grafted polypropylene added should not be too low.

[0181] Comparative Example 5 increased the amount of styrene-grafted polypropylene to 20 wt%, exceeding the upper limit of 15 wt% of this invention. The film's thermal shrinkage increased, its breakdown strength decreased, and the maximum operating temperature dropped to 116°C. Excessive styrene side chains generated strong steric hindrance, hindering the regular crystallization of polypropylene and reducing crystallinity. Simultaneously, it easily caused micro-phase separation, introducing interface defects and impairing high-temperature dielectric properties and dimensional stability, indicating that the amount of styrene-grafted polypropylene added should not be too high.

[0182] Comparative Example 6 reduced the amount of H-type long-branched polypropylene to 5 wt%, which is lower than the lower limit of 10 wt% in this invention. The film's thermal shrinkage increased, and the maximum operating temperature was only 115°C. Insufficient branched component content prevented the construction of a continuous and dense physical entanglement network, resulting in weak binding effect on the molecular chains in the amorphous regions and limited improvement in the film's high-temperature creep resistance and thermal aging stability.

[0183] Comparative Example 7 increased the amount of H-type long-branched polypropylene to 30 wt%, exceeding the upper limit of 20 wt% of this invention. The overall performance of the film declined, and the maximum operating temperature dropped to 110°C. Excessive long branches lead to excessive entanglement, increasing the internal stress of the film, making it prone to dimensional deformation at high temperatures. The numerous tertiary carbon sites in the branches are also more susceptible to thermo-oxidative corrosion, which is detrimental to the long-term high-temperature service of the film.

[0184] Comparative Example 8 used styrene-grafted polypropylene with a grafting rate of 1.0%, which is lower than the preferred grafting rate range. The high-temperature breakdown strength of the film decreased, and the maximum operating temperature was only 120°C. The low grafting rate resulted in insufficient number of styrene side groups in the molecular chain, limited steric hindrance and deep traps, and an inability to fully bind the molecular chain and suppress high-temperature conductivity.

[0185] Comparative Example 9 used styrene-grafted polypropylene with a grafting rate of 6.0%, which is higher than the preferred grafting rate range. The film performance deteriorated significantly, with the maximum operating temperature only reaching 98℃. Excessively high grafting rates can easily lead to local enrichment, phase interface defects, poor melt flowability, increased film formation defects, and deterioration of the film's thermal stability and dielectric properties.

[0186] Comparative Example 10 used H-type long-branched polypropylene with a branching point density of 0.5 / 10000°C, which is below the preferred range. The high-temperature performance of the film was inferior to that of the examples, with a maximum operating temperature of 116°C. The insufficient branching point density makes it difficult to form an effective physical entanglement network, resulting in limited effects on polypropylene molecular chain confinement and heterogeneous nucleation.

[0187] Comparative Example 11 used H-type long-branched polypropylene with a branching point density of 2.5 / 10000°C, which is higher than the preferred range. The film exhibited increased thermal shrinkage, decreased breakdown strength, and a maximum operating temperature of only 96°C. The excessively high branching point density caused excessive entanglement, increased residual internal stress in the film, and accelerated thermal aging due to the large amount of tertiary carbon structures, thus weakening the film's high-temperature stability.

[0188] Comparative Example 12 had the same formulation as Example 3, but used a casting process and did not undergo biaxial stretching. Although the film had a lower thermal shrinkage value, its breakdown strength at 120°C was only 440 MV / m, and its maximum operating temperature was only 95°C. This confirms that the biaxial stretching process is a necessary condition for achieving the orientation synergistic effect; only after biaxial stretching can the modified components be oriented along the stretching direction to form a composite skeleton of "crystalline hard segments + entangled soft segments", thus fully realizing the dual synergistic modification effect.

[0189] Comparative Example 13 used 3-butenyldimethylchlorosilane with a shorter carbon chain length to prepare H-type long-branched polypropylene, with the remaining formulation and preparation process being the same as in Example 3. The longitudinal thermal shrinkage rate of the film reached 4.2%, the transverse thermal shrinkage rate reached 1.1%, the breakdown strength at 120℃ was only 435MV / m, and the maximum operating temperature was only 92℃, which was significantly worse than that of Example 3. When the number of carbon atoms in the spacer arms of H-type long-branched polypropylene is too small, the electron-withdrawing inductive effect of Si atoms directly acts on the terminal olefin double bond, which easily triggers side reactions such as double bond isomerization and polymerization chain transfer, resulting in poor controllability of the branched structure; moreover, the Si-O-Si bridge is too close to the PP main chain, and the steric hindrance will interfere with the PP chain segments to enter the lattice, resulting in a decrease in crystallinity, which in turn weakens the stability of the high-temperature crystallization structure; at the same time, the short spacer arms make the H-type bridge too rigid, restricting the movement of molecular chain segments, reducing the creep toughness of the film, and ultimately causing the thermomechanical properties and dielectric properties to deteriorate simultaneously.

[0190] Comparative Example 14 used 15-hexadecenyldimethylchlorosilane with a longer carbon chain to prepare H-type long-branched polypropylene, with the remaining formulation and preparation process being the same as in Example 3. The longitudinal thermal shrinkage rate of the film was 3.8%, the transverse thermal shrinkage rate was 0.8%, the breakdown strength at 120°C was 465 MV / m, and the maximum operating temperature was only 112°C, which was still significantly lower than that of Example 3. When the number of carbon atoms in the spacer arms of H-type long-branched polypropylene is too high, the copolymerization activity of the alkenyl monomer decreases significantly, the effective branching point density per unit mass is insufficient, and it is difficult to construct a dense and uniform physical entanglement network; at the same time, the excessively long alkyl chains are prone to microphase separation in the PP matrix, forming independent alkyl crystalline microregions, causing film surface defects and resulting in uneven dielectric properties; in addition, the selectivity of the hydrosilylation reaction of long-chain dienes decreases, the double addition byproducts increase, and excessive crosslinking is easily triggered, further weakening the modification effect and limiting the improvement of the film's temperature resistance.

[0191] In summary, compared to existing conventional BOPP capacitor films, this invention, by synergistically compounding styrene-grafted polypropylene and H-type long-chain branched polypropylene in a specific ratio within the heat-resistant layer, and simultaneously matching modified raw materials with appropriate grafting rates and branching point densities with a biaxial stretching molding process, effectively reduces the high-temperature longitudinal and transverse thermal shrinkage rates of the film while retaining its basic mechanical properties and insulation characteristics. This significantly improves the high-temperature breakdown strength and long-term maximum operating temperature, overcoming the shortcomings of conventional BOPP films such as poor high-temperature dimensional stability, rapid degradation of high-temperature dielectric properties, and difficulty in adapting to high-temperature operating conditions. Furthermore, the biaxial stretching film formation process is stable and the production process is smooth and controllable, meeting the high-performance requirements and continuous industrial production needs of BOPP capacitor films for high-temperature power capacitors.

[0192] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A BOPP capacitor film, characterized in that: The product comprises a heat-resistant layer, a core layer, and a glossy layer arranged sequentially. The heat-resistant layer comprises 64-81.5 wt% polypropylene, 8-15 wt% styrene-grafted polypropylene, 10-20 wt% H-type long-chain branched polypropylene, and 0.5-1.0 wt% antioxidant. The core layer comprises polypropylene. The glossy layer comprises 99-99.5 wt% polypropylene and 0.5-1.0 wt% anti-blocking masterbatch. The styrene grafting rate of the styrene-grafted polypropylene is 2% to 4%. The H-type long-branched polypropylene is prepared by the following method: After the reactor was pretreated by vacuum and nitrogen purging at 70°C, hydrogen was introduced. A catalyst, triethylaluminum heptane solution, diisopropyldimethoxysilane heptane solution, alkenyldimethylchlorosilane heptane solution, and liquid propylene were added. The propylene homopolymerization reaction was carried out at 70°C. The polymerization product was treated with nitrogen atmosphere steam, then dehydrated and condensed, and vacuum dried to obtain the H-type long-branched polypropylene.

2. The BOPP capacitor film according to claim 1, characterized in that: The polypropylene in the core layer has an isotacticity of 96%-97%, a melt index of 2.0~3.5g / 10min at 230℃ and 2.16kg, and an ash content of 10ppm~20ppm.

3. The BOPP capacitor film according to claim 1, characterized in that: The styrene-grafted polypropylene has a melt index of 2~4 g / 10 min under test conditions of 230℃ and 2.16 kg.

4. The BOPP capacitor film according to claim 3, characterized in that, The styrene-grafted polypropylene is prepared by the following method: Using 91.6~96.4wt% polypropylene powder as the matrix, 0.05~0.20wt% benzoyl peroxide (BPO) as the initiator, and 3.5~8.3wt% styrene as the monomer, a grafting reaction was carried out in an aqueous dispersion system. Specifically, polypropylene powder is first added to a reactor containing deionized water and stirred to form a suspension; then initiator BPO is added, and finally styrene monomer is added; the mixture is stirred at 60°C for 1-3 hours to allow the styrene monomer to penetrate into the powder; then the temperature is raised to 90°C and nitrogen gas is introduced to initiate the grafting reaction; after filtration and vacuum drying, the product is extracted with ethyl acetate to remove unreacted monomers and polystyrene homopolymers, yielding styrene-grafted polypropylene.

5. The BOPP capacitor film according to claim 1, characterized in that: The H-type long-branched polypropylene has a melt index of 2.0~3.0 g / 10 min and a branching point density of 1.0~1.5 / 10000C under the test conditions of 230℃ and 2.16 kg.

6. The BOPP capacitor film according to claim 1, characterized in that: The alkenyl dimethylchlorosilane is one of 9-decenyl dimethylchlorosilane, 10-undecapenyl dimethylchlorosilane, and 11-dodecenyl dimethylchlorosilane.

7. The BOPP capacitor film according to claim 1, characterized in that: The total thickness of the BOPP capacitor film is 6~12μm; wherein, the thickness of the heat-resistant layer is 1~2μm.

8. A method for preparing a BOPP capacitor film according to any one of claims 1 to 7, characterized in that, Includes the following steps: After the raw materials of each layer are mixed according to the formula, they are added to each extruder. After being metered by the metering pump, the melt of each extruder is merged into a thick sheet at the T-die. The thick sheet is cooled by the quenching roller and then enters the quenching water tank and the blowing chamber. Then it is stretched longitudinally and then enters the transverse stretching area to be stretched transversely to obtain a film. After the film is shaped and corona treated, it is wound up, then aged and cut to obtain the BOPP capacitor film.

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