Breakthrough-resistant metallized film and preparation process thereof

Abstract

The invention relates to the technical field of metallized films, in particular to a breakdown-resistant metallized film and a preparation process thereof, and the breakdown-resistant metallized film comprises a modified polypropylene film and a metal layer located on the surface of the modified polypropylene film; wherein the modified polypropylene film is prepared from the following components in percentage by mass: 0.01-0.1% of 2, 2 '-methylene-bis (4, 6-di-tert-butyl phenyl phosphate) aluminum phosphate, 0.01-0.1% of a coupling agent, 0.01-0.1% of a coupling agent, 0.01-0.1% of an antioxidant, 0.01-0.1% of a lubricant and the balance The mass fraction of the 1, 3: 2, 4-bis (3, 4-dimethyl benzal)-D-sorbitol is 0.05-0.25, and the mass fraction of the 1, 3: 2, 4-bis (3, 4-dimethyl benzal)-D The mass fraction of the long-chain branched polypropylene is 99.65 to 99.94. Due to the flexibility of the long-chain branches, the sphere density of the long-chain branched polypropylene is increased. Wherein the unit cell size of the NA-21 matrix and the unit cell size of the long-chain branched polypropylene melt can be well matched, so that the initial nucleation density of the modified film is higher. As the crystallinity is reduced, the dielectric constant and loss of the long-chain branched polypropylene are relatively large, and the dielectric constant of the modified film is reduced. By introducing a long-chain branch chain and adding a nucleating agent, the conductivity loss of the modified film is reduced, and the breakdown strength and the energy storage density are improved.

Description

Technical Field

[0001] This invention relates to the field of metallized thin film technology, specifically to a breakdown-resistant metallized thin film and its preparation process. Background Technology

[0002] In applications such as high-voltage direct current (HVDC) transmission, hybrid electric vehicles (HEVs), oil and gas exploration, and aerospace, metallized film capacitors (MFCs) require long-term stable operation in high-temperature environments above 100°C. Currently, polypropylene (PP) is widely used as a key dielectric material in MFCs due to its high breakdown strength, low dielectric loss, and good self-healing properties. However, the rated operating temperature of ordinary PP materials typically does not exceed 85°C, and its electrical properties deteriorate significantly under high-temperature conditions. Specifically, its conductivity increases sharply, and its breakdown strength decreases drastically, leading to reduced capacitor charging and discharging efficiency, accelerated insulation aging, decreased energy density, and increased failure risk. This severely restricts its reliability in high-temperature, high-field applications.

[0003] From a microscopic perspective, the degradation of electrical properties in polypropylene (PP) at high temperatures is mainly attributed to intensified thermal motion of molecular chains, resulting in increased free volume and a higher mean free path for charge carriers, thus reducing breakdown strength. Simultaneously, charge carriers in trapped energy levels are more easily excited into free charge carriers, leading to a significant increase in conductivity. To improve the heat resistance of PP, existing technologies have proposed modification methods involving the introduction of long-chain branched structures. By increasing the entanglement density between molecular chains, the thermal motion resistance of chain segments is enhanced, thereby improving the material's thermal stability. Long-chain branching can also promote heterogeneous nucleation, increase crystal density, and introduce deep-level traps, which helps reduce high-temperature conductivity loss and improve breakdown strength. However, long-chain branching has a dual impact on crystallization behavior: on the one hand, it promotes heterogeneous nucleation, increasing the number of crystal nuclei; on the other hand, it inhibits spherulite growth due to increased melt viscosity, making it difficult to achieve precise control of crystal morphology solely through long-chain branching, thus limiting further improvement in its dielectric properties.

[0004] Therefore, based on the above-mentioned problems existing in the prior art, we propose a breakdown-resistant metallized thin film and its preparation process. Summary of the Invention

[0005] The purpose of this invention is to provide a breakdown-resistant metallized thin film and its preparation process, which solves the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A breakdown-resistant metallized thin film and its preparation process, comprising a modified polypropylene film and a metal layer located on the surface of the modified polypropylene film; The modified polypropylene film is prepared from the following components: 0.01-0.1 mass fraction of aluminum 2,2'-methylene-bis(4,6-di-tert-butylphenyl phosphate); 0.05-0.25 mass fraction of 1,3:2,4-bis(3,4-dimethylbenzyl)-D-sorbitol; Long-chain branched polypropylene with a mass fraction of 99.65-99.94%.

[0007] A breakdown-resistant metallized thin film and its preparation process are disclosed. The preparation process includes the following steps: S1. Raw material mixing and preliminary plasticization: Mix long-chain branched polypropylene and nucleating agent in a two-roll mill at 175-200℃ for 10-30 minutes; S2. Hot pressing: The mixture is hot pressed at 175-200℃ and 18-25MPa for 2-5 minutes. S3, Pressure holding and cooling: Cool the film to 120°C under a pressure of 18-25 MPa.

[0008] Preferably, the polypropylene film is a biaxially oriented polypropylene film with a thickness of 1 mm. 15μm.

[0009] Preferably, the metal layer is one or a combination of aluminum or zinc.

[0010] Preferably, the polypropylene metallized film is obtained by forming a metal layer on the surface of the modified polypropylene film using a vacuum evaporation or sputtering deposition process.

[0011] Preferably, the hot pressing temperature in step S2 is the same as the mixing temperature of the twin-roll mill in step S1.

[0012] Preferably, the holding and cooling pressure in step S3 is the same as the hot pressing pressure in step S2. By means of the above technical solution, the present invention provides a breakdown-resistant metallized thin film and its preparation process, which has at least the following beneficial effects: (1) Due to the flexibility of the long-chain branches, the spherical density of the long-chain branched polypropylene increases. The addition of different nucleating agents promotes the crystallization of the long-chain branched polypropylene. Among them, the cell size of the NA-21 matrix and the long-chain branched polypropylene melt can be well matched, so the initial nucleation density of the modified film is higher.

[0013] (2) Due to the reduced crystallinity, the dielectric constant and loss of the long-chain branched polypropylene are relatively large. The nucleating agent induces crystallization, thus reducing the dielectric constant of the modified film. By introducing long-chain branches and adding a nucleating agent, the conductivity loss of the modified film is reduced, and the breakdown strength and energy storage density are improved. At 125℃, the breakdown strength of the modified film with added NA-21 increased by 108.6 kV / mm, and the energy storage density increased by 66.1%.

[0014] (3) The long-chain branches of the present invention hinder the thermal motion of the chains and promote heterogeneous nucleation, thereby improving the dielectric properties at high temperatures. The addition of nucleating agents increases the nucleation density of the film and shortens the mean free path of charge carriers. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] Phase 1: Preparation of modified biaxially oriented polypropylene film.

[0017] The goal of this stage is to produce thin film substrates with uniform thickness, high crystallinity, and smooth surface.

[0018] Step S1: Raw material mixing and preliminary plasticization; 1. Preparation of materials: Accurately weigh 0.01-0.1% by mass of 2,2'-methylene-bis(4,6-di-tert-butylphenyl phosphate) aluminum phosphate, 0.05-0.25% by mass of 1,3:2,4-bis(3,4-dimethylbenzyl)-D-sorbitol, and 99.65-99.94% by mass of long-chain branched polypropylene.

[0019] 2. Preheating: Heat the two rollers of the two-roll mill to a set temperature of 175℃-200℃. The temperature of 175-200℃ is much higher than the melting point of long-chain branched polypropylene, ensuring that the long-chain branched polypropylene is fully melted and has the best fluidity, which facilitates the dispersion of nucleating agents.

[0020] 3. Feeding and Mixing: Add the mixture of long-chain branched polypropylene and nucleating agent to the preheated two-roll mixing machine and mix for 10-30 minutes. Sufficient time is necessary to achieve uniform mixing. If the time is too short, the nucleating agent will not disperse evenly, leading to film performance defects; if the time is too long, it may cause polymer molecular chain degradation, affecting performance.

[0021] 4. Plasticization: Utilizing the shearing and frictional forces generated by the relative rotation of two rollers, the material is repeatedly squeezed, torn, and kneaded. This process completely melts and plasticizes the polypropylene, and uniformly disperses the nucleating agent into the polypropylene melt. The powerful shearing force of the two-roll mill is ideal for efficiently dispersing powders and granular additives into the polymer melt.

[0022] Step S2: Hot pressing; 1. Removal of material: Remove the uniformly mixed molten material from the two-roll mill in step S1.

[0023] 2. Mold loading: Place it into the mold of the preheated flat vulcanizing machine.

[0024] 3. Hot Pressing: Close the mold and apply a high pressure of 18-25 MPa, maintaining this pressure and temperature at 175-200℃ for 2-5 minutes. The extremely high pressure of 18-25 MPa is mainly used to remove air bubbles and compress the melt, expelling air that may have been trapped during mixing and preventing porosity in the film. Simultaneously, it allows the melt to flow and fill the mold cavity, obtaining a pre-formed thick sheet with uniform thickness and a dense structure. This ensures that the material is heated evenly within the mold, fully completing the melting and initial crystallization process, preparing for the next step of cooling and shaping.

[0025] Step S3: Pressure holding and cooling; 1. Pressure holding: After hot pressing is completed, do not release the pressure, but maintain a pressure of 18-25MPa.

[0026] 2. Cooling: Activate the cooling system (cooling water) of the flat vulcanizing machine. While maintaining high pressure, forcefully and slowly cool the mold and the molten sheet inside to 120°C. Maintaining high pressure during cooling helps to: suppress product deformation and shrinkage, ensuring the flatness of the sheet; and promote crystallization. High pressure provides the driving force for the ordered arrangement of polypropylene molecular chains, which, combined with the action of nucleating agents, forms numerous, small, and uniform spherulitic structures. 120°C is below the crystallization temperature range of PP. Slow cooling to this temperature ensures that the crystallization process is fully and completely completed under high pressure, thus locking in this excellent microstructure. This structure determines the final high gloss, high transparency, high rigidity, and good dimensional stability of the film.

[0027] 3. Removing the sheet: After reaching 120℃, the pressure can be released, the mold opened, and the shaped multi-layer composite sheet can be removed.

[0028] Subsequently, the multilayer composite thick sheet undergoes a biaxial stretching process. The thick sheets obtained after S1-S3 processes still need to undergo a biaxial stretching process to become the final BOPP film. The specific steps are as follows: Longitudinal stretching: The thick sheet is stretched along the machine direction at a temperature slightly below its melting point by passing it through a set of heated rollers; Transverse stretching: The longitudinally stretched sheet is fed into a tenter frame, clamped on both sides, and stretched transversely in hot air; 3. Heat setting: The stretched sheet is treated at a higher temperature for a short time to eliminate internal stress and stabilize dimensions. Through biaxial stretching, the molecular chains are highly oriented in both the longitudinal and transverse directions, greatly improving the mechanical strength, barrier properties, and surface gloss of the film, and reducing its thickness to a final specification of 1-15μm.

[0029] Second stage: Surface metallization; This stage involves depositing an extremely thin metal layer on the aforementioned high-performance biaxially oriented film. The specific steps are as follows: 1. Base film pretreatment and unwinding: The biaxially stretched film roll is mounted on the unwinding shaft in the vacuum chamber. The film surface may need to be corona treated to improve wettability and adhesion.

[0030] 2. Vacuuming: The vacuum chamber is evacuated to a high vacuum state to remove air molecules and provide a pure environment for metal evaporation and deposition.

[0031] 3. Metal evaporation: The metal is heated in a crucible by resistance heating or electron beam heating, causing it to melt rapidly and evaporate into metal vapor.

[0032] 4. Deposition and film formation: Metal vapor atoms move in a straight line in a vacuum. When they encounter a continuously passing biaxially stretched thin film surface with a lower temperature, they condense on it to form a uniform and bright metal layer with a thickness of nanometer to micrometer.

[0033] 5. Rewinding and post-processing: The metal-plated film is rewound in preparation for post-processing such as protective coating.

[0034] Example 2 Metallized thin films are prepared by the above steps, wherein the raw materials are 0.1 mass fraction of 2,2'-methylene-bis(4,6-di-tert-butylphenylphosphine)aluminum phosphate, 0.25 mass fraction of 1,3:2,4-bis(3,4-dimethylbenzyl)-D-sorbitol and 99.65 mass fraction of long-branched polypropylene; In step S1, the operating temperature of the open mill is 190℃, and the mixing time is 10 minutes; The hot pressing temperature in step S2 is the same as that in step S1, which is 190℃. The pressure in step S2 is 20MPa and the hot pressing time is 3 minutes. The pressure for holding and cooling in step S3 is the same as in step S2, which is 20 MPa; The thickness of the film after bistretching is 2.5 μm.

[0035] Example 3 Metallized thin films are prepared by the above steps, wherein the raw materials are 0.03 mass fraction of 2,2'-methylene-bis(4,6-di-tert-butylphenyl phosphate) aluminum phosphate, 0.05 mass fraction of 1,3:2,4-bis(3,4-dimethylbenzyl)-D-sorbitol and 99.92 mass fraction of long-branched polypropylene; In step S1, the operating temperature of the open mill is 190℃, and the mixing time is 10 minutes; The hot pressing temperature in step S2 is the same as that in step S1, which is 190℃. The pressure in step S2 is 20MPa and the hot pressing time is 3 minutes. The pressure for holding and cooling in step S3 is the same as in step S2, which is 20 MPa; The thickness of the film after bistretching is 2.5 μm.

[0036] Example 4 Metallized thin films are prepared by the above steps, wherein the raw materials are 0.05 mass fraction of 2,2'-methylene-bis(4,6-di-tert-butylphenyl phosphate) aluminum phosphate, 0.15 mass fraction of 1,3:2,4-bis(3,4-dimethylbenzyl)-D-sorbitol and 99.80 mass fraction of long-branched polypropylene; In step S1, the operating temperature of the open mill is 190℃, and the mixing time is 10 minutes; The hot pressing temperature in step S2 is the same as that in step S1, which is 190℃. The pressure in step S2 is 20MPa and the hot pressing time is 3 minutes. The pressure for holding and cooling in step S3 is the same as in step S2, which is 20 MPa; The thickness of the film after bistretching is 2.5 μm.

[0037] Comparative Example 1 Metallized thin films are prepared through the above steps, wherein the raw material is long-branched polypropylene. In step S1, the operating temperature of the open mill is 190℃, and the mixing time is 10 minutes; The hot pressing temperature in step S2 is the same as that in step S1, which is 190℃. The pressure in step S2 is 20MPa and the hot pressing time is 3 minutes. The pressure for holding and cooling in step S3 is the same as in step S2, which is 20 MPa; The thickness of the film after bistretching is 2.5 μm.

[0038] Comparative Example 2 Metallized thin films are prepared through the above steps, wherein the raw material is polypropylene; In step S1, the operating temperature of the open mill is 190℃, and the mixing time is 10 minutes; The hot pressing temperature in step S2 is the same as that in step S1, which is 190℃. The pressure in step S2 is 20MPa and the hot pressing time is 3 minutes. The pressure for holding and cooling in step S3 is the same as in step S2, which is 20 MPa; The thickness of the film after bistretching is 2.5 μm.

[0039] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A puncture resistant metallized film characterized by: The modified polypropylene film and a metal layer on the surface of the modified polypropylene film; The modified polypropylene film is prepared from the following components: 0.01-0.1 mass fraction of aluminum 2,2'-methylene-bis(4,6-di-tert-butyl phenyl phosphonic acid) phosphate; 0.05-0.25 mass fraction of 1,3:2,4-bis(3,4-dimethylbenzylidene)-D-sorbitol; 99.65-99.94 mass fraction of long-chain branched polypropylene.

2. A process for preparing a breakdown-resistant metallized thin film, used to prepare the breakdown-resistant metallized thin film according to claim 1, characterized in that, The method comprises the following steps: S1, raw material mixing and preliminary plasticization; the long-chain branched polypropylene and the nucleating agent are mixed in a double roller at 175-200℃ for 10-30min; S2, hot pressing; the mixture is hot pressed at 175-200℃ and 18-25MPa for 2-5min; S3, pressure holding and cooling; the film is cooled to 120℃ under the pressure of 18-25MPa.

3. The process for the preparation of a puncture resistant metallized film according to claim 2, characterized in that: The polypropylene film is a biaxially stretched polypropylene film having a thickness of 1 15 μm.

4. The process for making a puncture resistant metallized film according to claim 2, wherein: The metal layer is one or a combination of aluminum metal layer or zinc metal layer.

5. The process for making a puncture resistant metallized film according to claim 2, wherein: The polypropylene metallized film is obtained after the metal layer is formed on the surface of the modified polypropylene film by vacuum evaporation or sputtering coating process.

6. The process for the preparation of a puncture resistant metallized film according to claim 2, characterized in that: The hot pressing temperature of step S2 is the same as the mixing temperature of the double roller in step S1.

7. The process of claim 2, wherein the process is characterized by: The pressure holding and cooling pressure in step S3 is the same as the hot pressing pressure in step S2.