Plant-based synthetic ester environment-friendly impregnant as well as preparation method and application thereof

Abstract

This invention belongs to the field of capacitor processing technology, specifically relating to a plant-based synthetic ester environmentally friendly impregnating agent, its preparation method, and its application. The plant-based synthetic ester environmentally friendly impregnating agent provided by this invention comprises: an ester obtained by esterification of an organic alcohol and a plant-based fatty acid; wherein the organic alcohol is a straight-chain or branched alcohol; the straight-chain or branched alcohol has 4 to 10 carbon atoms; the plant-based fatty acid is composed of plant-based carboxylic acids, including one or more of plant-based saturated fatty acids and unsaturated fatty acids. This plant-based synthetic ester environmentally friendly impregnating agent has a high flash point, low pour point, good dielectric strength and volume resistivity, low dielectric loss, and excellent impregnation properties. It also features environmental degradability, renewable raw material sources, non-toxicity and harmlessness to humans, and excellent high-temperature performance, meeting the technical requirements of a new generation of high-performance, high-safety, and environmentally friendly capacitors.

Description

Technical Field

[0001] This invention belongs to the field of capacitor processing technology, specifically relating to a plant-based synthetic ester environmentally friendly impregnating agent, its preparation method, and its application. Background Technology

[0002] As a key energy storage and filtering component in power systems and electronic equipment, the core performance and long-term reliability of capacitors largely depend on the impregnating agent used inside. The main function of the impregnating agent is to fill the gaps between solid dielectrics (such as thin films), expel air and moisture, thereby improving dielectric strength, heat dissipation, and suppressing partial discharge.

[0003] Currently, the impregnating agents widely used in medium and high voltage film capacitors are mainly aromatic hydrocarbon compounds, with benzyltoluene (especially MDBT, DBT, etc.) being a prime example. These synthetic liquids have dominated the market for decades due to their high dielectric constant, good impregnation ability, and compatibility with polypropylene films. However, with increasingly stringent global standards for environmental protection, occupational health, and safe equipment operation, traditional impregnating agents, represented by benzyltoluene, have revealed several increasingly serious shortcomings, mainly in the following aspects: Poor environmental performance and persistent pollution risks: Benzyltoluene-like substances are derived from petrochemical synthesis and have poor biodegradability, making them difficult to decompose naturally in the environment. If capacitors are improperly disposed of at the end of their lifespan and leak, or if leakage occurs during operation due to seal failure, these chemicals will remain in the soil and water for a long time, causing persistent environmental pollution. Furthermore, their production process may involve environmentally unfriendly processes. This is inconsistent with the current global trend of advocating green manufacturing and a circular economy.

[0004] Potential toxic risks to human health: Benzyltoluene compounds pose clear toxicological concerns to human health. Studies have shown that long-term or high-concentration exposure may cause irritation to the skin, eyes, and respiratory tract, and has potential toxicity to the central nervous system and liver. Inadequate protection during the production (filling), maintenance, and dismantling and recycling of capacitors may threaten the health of frontline operators. With increasingly stringent workplace safety and health (EHS) requirements, the use of potentially toxic materials has become a significant compliance and ethical hazard.

[0005] Insufficient chemical stability and safety at high temperatures: As power electronic devices develop towards higher power density and miniaturization, the operating temperature of capacitors is increasing. Benzyltoluene-based impregnating agents are prone to thermal decomposition or oxidative degradation under long-term high-temperature operation (e.g., approaching or exceeding their thermal stability limit temperature, typically around 105°C, although improvements have been made, the improvement is limited). This not only leads to deterioration of their electrical properties (such as dielectric loss) and affects capacitor lifespan, but more importantly, the decomposition may produce toxic gases such as benzene and toluene, posing potential safety hazards. Furthermore, their relatively low flash point and ignition point directly affect the overall fire safety rating of the capacitor.

[0006] Disconnected from future regulations and market demands: International regulations such as the EU's REACH and RoHS directives are increasingly stringent in regulating chemicals, restricting or prohibiting the use of specific hazardous substances (SVHCs). While benzyltoluene compounds are not entirely banned, their environmental and toxic properties mean they face the risk of even stricter regulatory restrictions in the future. Meanwhile, end consumers and manufacturers are increasingly inclined to choose "green" and "harmless" electronic products, creating an urgent market demand for high-performance and environmentally friendly capacitors.

[0007] Therefore, the capacitor industry urgently needs to develop a new type of impregnating agent that can maintain or even improve existing electrical properties (such as high dielectric strength, low dielectric loss, and excellent impregnation) while fundamentally solving the core pain points of the aforementioned benzyltoluene-based impregnating agents, such as poor environmental performance, harm to human health, and high high-temperature safety risks. Summary of the Invention

[0008] In view of this, the purpose of this invention is to provide a plant-based synthetic ester environmentally friendly impregnating agent, its preparation method and application. The plant-based synthetic ester environmentally friendly impregnating agent provided by this invention has a high flash point, low pour point, good dielectric strength and volume resistivity, low dielectric loss, and excellent impregnation properties. It also has the characteristics of environmental degradability, renewable raw material source, non-toxic and harmless to the human body, and excellent high-temperature performance, thus meeting the technical requirements of a new generation of high-performance, high-safety, and environmentally friendly capacitors.

[0009] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a plant-based synthetic ester environmentally friendly impregnating agent, comprising: an ester obtained by esterification of an organic alcohol and a plant-based fatty acid; The organic alcohol is a straight-chain or branched alcohol; the straight-chain or branched alcohol has 4 to 10 carbon atoms. The plant-based fatty acids consist of plant-based carboxylic acids, including one or more of plant-based saturated and unsaturated fatty acids.

[0010] Preferably, the straight-chain or branched alcohol comprises at least one even-numbered carbon branched alcohol.

[0011] Preferably, the plant-based fatty acid comprises at least one unsaturated fatty acid.

[0012] Preferably, the straight-chain or branched alcohol is selected from one or more of n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, isobutanol, isopentanol, isohexanol, isoheptanol, isooctanol, isononol, and isodecanol.

[0013] Preferably, the plant-based fatty acid is selected from one or more of oleic acid, linoleic acid, linolenic acid, tung oil acid, palmitic acid, stearic acid, myristic acid, heptadecanoic acid, arachidic acid, behenic acid, heptadecanoic acid, erucic acid, and arachidienoic acid.

[0014] Preferably, the molar ratio of the organic alcohol to the plant-based fatty acid is 0.8 to 1.4:1.

[0015] This invention also provides a method for preparing the plant-based synthetic ester environmentally friendly impregnating agent described in the above technical solution, comprising the following steps: In a protective atmosphere, organic alcohols, plant-based fatty acids and esterification catalysts are mixed and esterification reaction is carried out to obtain the plant-based synthetic ester environmentally friendly impregnating agent. The organic alcohol is a straight-chain or branched alcohol; the straight-chain or branched alcohol has 4 to 10 carbon atoms. The plant-based fatty acids consist of plant-based carboxylic acids, including one or more of plant-based saturated and unsaturated fatty acids.

[0016] Preferably, the esterification catalyst is selected from one of protic acid catalysts, metal oxide catalysts, and organic acid salt catalysts.

[0017] Preferably, the esterification reaction is carried out at a temperature of 180~250℃ and for a reaction time of 20~48h.

[0018] The present invention also provides the application of the plant-based synthetic ester environmentally friendly impregnating agent described in the above technical solution or the plant-based synthetic ester environmentally friendly impregnating agent prepared by the preparation method described in the above technical solution in capacitors.

[0019] This invention provides a plant-based synthetic ester environmentally friendly impregnating agent, comprising: an ester obtained by esterification of an organic alcohol and a plant-based fatty acid; The organic alcohol is a straight-chain or branched alcohol; the straight-chain or branched alcohol has 4 to 10 carbon atoms. The plant-based fatty acids consist of plant-based carboxylic acids, including one or more of plant-based saturated and unsaturated fatty acids.

[0020] The beneficial effects of this invention are: (1) This invention uses ester oil generated by the esterification reaction of acid and alcohol as a capacitor impregnating agent. The raw materials are renewable, the product is non-toxic and harmless and environmentally degradable, which effectively improves the environmental friendliness of the oil and reduces its harm to the human body. (2) The plant-based synthetic ester environmentally friendly impregnating agent of the present invention obtains an ester oil capacitor impregnating agent with excellent performance through the rational selection and reaction of short and medium chain alcohols and plant-based fatty acids. It has good electrical properties such as dielectric strength and volume resistivity, and at the same time has excellent high temperature performance and high flash point, with a flash point exceeding 210℃. (3) The plant-based synthetic ester environmentally friendly impregnating agent in this invention can effectively destroy the crystallization properties of the prepared ester oil through the asymmetric design of the molecular structure, and effectively reduce its pour point; (4) In this invention, the unsaturated fatty acid structure in plant-based synthetic ester oils enhances their gas absorption under the action of an electric field. Under the action of a strong electric field, the generation of microbubbles is reduced or even eliminated, avoiding safety hazards caused by partial discharge and providing potential functional properties of ester oils as impregnating agents. Detailed Implementation

[0021] This invention provides a plant-based synthetic ester environmentally friendly impregnating agent, comprising: an ester obtained by esterification of an organic alcohol and a plant-based fatty acid; The organic alcohol is a straight-chain or branched alcohol; the straight-chain or branched alcohol has 4 to 10 carbon atoms to ensure a relatively low kinematic viscosity of the final ester oil. The plant-based fatty acids consist of plant-based carboxylic acids, including one or more of plant-based saturated and unsaturated fatty acids.

[0022] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0023] In one embodiment, the organic alcohol is a straight-chain or branched alcohol; the straight-chain or branched alcohol has 4 to 10 carbon atoms, with 8 in a specific embodiment; the straight-chain or branched alcohol is selected from one or more of n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, isobutanol, isoamyl alcohol, isohexanol, isoheptanol, isooctanol, isononol, and isodecanol, with isooctanol, isoamyl alcohol, n-butanol, n-nonanol and isoamyl alcohol, n-decanol and isobutanol, or a mixture of n-heptanol, isooctanol, and isohexanol, or a mixture of isononol, n-octanol, and isoheptanol, or a mixture of isooctanol, isobutanol, n-decanol, and n-hexanol; the straight-chain or branched alcohol contains at least one even-numbered carbon branched alcohol. When there are multiple organic alcohols, the present invention does not have a special limitation on the ratio of different types of organic alcohols, and any ratio is acceptable.

[0024] In one embodiment, the plant-based fatty acid is composed of plant-based carboxylic acids, comprising one or more of plant-based saturated and unsaturated fatty acids. In a specific embodiment, it contains at least one unsaturated fatty acid to ensure that the synthesized ester oil has a negative gas evolution tendency (gas absorption property). The plant-based fatty acid is derived from plant fruits. The plant-based fatty acid is selected from oleic acid, linoleic acid, linolenic acid, tung oil acid, palmitic acid, stearic acid, myristic acid, heptadecanoic acid, arachidic acid, behenic acid, and heptadecanoenoic acid. The organic alcohol comprises one or more of erucic acid and arachidonic acid, specifically oleic acid, linoleic acid, tung oil acid, oleic acid and linoleic acid, linoleic acid and behenic acid, a mixture of oleic acid, heptadecanoic acid and heptadecanenoic acid, oleic acid and palmitic acid, a mixture of linolenic acid, stearic acid and palmitic acid, a mixture of stearic acid, erucic acid and arachidonic acid, or a mixture of linolenic acid, oleic acid and myristic acid; the molar ratio of the organic alcohol to the plant-based fatty acid is 0.8~1.4:1, specifically 1.05:1 in this embodiment. When there are multiple plant-based fatty acids, the present invention does not have a special limitation on the ratio of different kinds of plant-based fatty acids, and any ratio is acceptable.

[0025] In one embodiment, the plant-based synthetic ester environmentally friendly impregnating agent contains no other additives and has a kinematic viscosity of 3.5~20.0 mm at 40°C. 2 / s, specifically 4.2~18.8mm in the embodiments. 2 / s, acid value 0.005~0.05mgKOH / g, specifically 0.009~0.027mgKOH / g in the embodiment, open flash point exceeding 210℃, specifically 218~225℃ in the embodiment, ignition point above 240℃, specifically 242~251℃ in the embodiment, pour point below -30℃, specifically -30~-45℃ in the embodiment, breakdown voltage 65~85kV / 2.5mm, specifically 72~75kV / 2.5mm in the embodiment, dielectric loss factor 0.15~3%, specifically 0.92~1.61% in the embodiment, volume resistivity 0.5~150GΩ·m, specifically 12.3~17.1GΩ·m in the embodiment, gas absorption 20~90μL / min, specifically 25.8~68.5μL / min in the embodiment.

[0026] The main component of the plant-based synthetic ester environmentally friendly impregnating agent provided by this invention is synthetic ester oil, but unlike vegetable oil, it is a modified ester oil obtained through an acid-alcohol reaction.

[0027] The plant-based synthetic ester environmentally friendly impregnating agent prepared in this invention uses synthetic esters obtained by reacting plant-based unsaturated fatty acids with short- and medium-chain alcohols. The use of biodegradable ester oils solves the problems of toxicity, harmfulness, and non-degradability associated with commonly used benzyltoluene impregnating agents. It exhibits good dielectric strength and volume resistivity, while also possessing a high flash point and low pour point. This invention uses industrial-grade plant-based fatty acids and short-chain alcohols as raw materials, fully utilizing the green source of the raw acid and the environmentally friendly biodegradable properties of the ester oil product to synthesize an ester oil impregnating agent that balances usability and environmental friendliness. Compared to benzyltoluene impregnating agents, it has better thermal stability and biodegradability, and higher tolerance to water content. The kinematic viscosity of the plant-based synthetic ester capacitor impregnating agent of this invention at 40°C is 3.5~18.8 mm⁻¹. 2 / s, acid value 0.012~0.05mgKOH / g, open flash point over 210℃, ignition point over 240℃, pour point below -30℃, breakdown voltage 65~85kV / 2.5mm, safety performance far superior to traditional aromatic impregnating agents.

[0028] This invention also provides a method for preparing the plant-based synthetic ester environmentally friendly impregnating agent described in the above technical solution, comprising the following steps: In a protective atmosphere, organic alcohols, plant-based fatty acids and esterification catalysts are mixed and esterification reaction is carried out to obtain the plant-based synthetic ester environmentally friendly impregnating agent. The organic alcohol is a straight-chain or branched alcohol; the straight-chain or branched alcohol has 4 to 10 carbon atoms. The plant-based fatty acids consist of plant-based carboxylic acids, including one or more of plant-based saturated and unsaturated fatty acids.

[0029] In one embodiment, the esterification catalyst is selected from one of protic acid catalysts, metal oxide catalysts, and organic acid salt catalysts, with organic acid salt catalysts or metal oxide catalysts being used in specific embodiments; the protic acid catalyst includes sulfuric acid and / or p-toluenesulfonic acid, with p-toluenesulfonic acid being used in specific embodiments; the metal oxide catalyst includes one or more of zinc oxide, magnesium oxide, titanium oxide, and tin oxide, with zinc oxide being used in specific embodiments; the organic acid salt catalyst includes one or more of stannous oxalate, zinc acetate, and tetrabutyl titanate, with stannous oxalate (CAS 814-94-8, Best Chemicals, reagent grade) being used in specific embodiments; the mass of the esterification catalyst is 0.1-1% of the total mass of the organic alcohol, plant-based fatty acid, and esterification catalyst, with 0.1% being used in specific embodiments.

[0030] In one embodiment, the protective gas is an inert gas; the inert gas includes nitrogen, helium or argon, and in a specific embodiment it is nitrogen; the temperature of the esterification reaction is 180~250℃, and in a specific embodiment it is 200~230℃, the reaction time is 20~48h, and in a specific embodiment it is 24~40h, and the pressure is atmospheric pressure.

[0031] In one embodiment, after the esterification reaction, the process further includes: removing the esterification catalyst and impurity components from the system after the esterification reaction, and refining the crude esterification product to obtain the finished product of the plant-based synthetic ester environmentally friendly impregnating agent.

[0032] In one embodiment, the method for removing the esterification catalyst and impurity components from the system after the esterification reaction is to sequentially perform a first physical adsorption and vacuum filtration; the purification method is to sequentially perform vacuum distillation and a second physical adsorption.

[0033] In a specific embodiment of the present invention, the method for removing the esterification catalyst and impurity components in the system after the esterification reaction is to adsorb the impurities with activated carbon and then vacuum filter to obtain crude esterification product, followed by vacuum distillation to remove excess acid or alcohol, and then adding alumina to remove trace amounts of acid for purification.

[0034] In one embodiment, the adsorbent material used for the first physical adsorption is activated carbon; the mass of the activated carbon is 0.1-1% of the total mass of the system after the esterification reaction, specifically 0.5% in this embodiment; the vacuum degree of the vacuum filtration is 0.09-0.098 MPa, specifically 0.09 MPa in this embodiment, and the time is 5-10 min, specifically 5 min in this embodiment.

[0035] In one implementation method, the vacuum distillation is carried out under continuous pressure reduction by a circulating water vacuum pump; the pressure of the vacuum distillation is 0.09~0.098 MPa, specifically 0.09 MPa in this embodiment; the temperature is 160~220℃, specifically 180~200℃ in this embodiment; and the time is 4~12 hours, specifically 4 hours in this embodiment. This invention removes some residual reactants through vacuum distillation.

[0036] In one embodiment, the second physical adsorption involves stirring under the physical adsorption of a porous, weakly alkaline substance. The stirring speed is 120-300 rpm, specifically 120-240 rpm in this embodiment; the stirring time is 1-3 hours, specifically 1-2 hours in this embodiment; and the temperature is 60-100℃, specifically 80℃ in this embodiment. The porous, weakly alkaline substance is zirconium oxide and / or alumina, specifically alumina in this embodiment. The mass of the porous, weakly alkaline substance is 0.5-3% of the mass of the crude esterification product, specifically 2% in this embodiment. This invention removes acidic residual substances through physical adsorption.

[0037] The present invention also provides the application of the plant-based synthetic ester environmentally friendly impregnating agent described in the above technical solution or the plant-based synthetic ester environmentally friendly impregnating agent prepared by the preparation method described in the above technical solution in capacitors.

[0038] This invention does not impose any special limitations on the application of plant-based synthetic ester environmentally friendly impregnating agents in capacitors; any application method known in the art can be used.

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1 A method for preparing a low-pour-point, high-flash-point plant-based synthetic ester environmentally friendly impregnating agent for capacitors is as follows: Isooctanol and oleic acid were mixed at a molar ratio of 1.05:1 to obtain a mixture. The mixture was then added to a reaction vessel, and stannous oxalate catalyst was added. The mass of the catalyst was 0.1% of the total mass of isooctanol, oleic acid, and catalyst. The esterification reaction was carried out at 200℃ for 24 hours under nitrogen protection and atmospheric pressure. After the reaction was completed, 0.5% of the total mass of activated carbon was added to adsorb impurities, and the mixture was vacuum filtered at 0.09 MPa for 5 minutes to obtain crude esterification product. Subsequently, excess isooctanol was separated by vacuum distillation at a pressure of 0.09 MPa, a temperature of 160℃, and a time of 4 hours. Alumina at 2% of the total mass of crude esterification product was added, and the mixture was stirred at 80℃ and 150 rpm for 2 hours to remove trace amounts of residual acid, finally obtaining the purified product.

[0041] Example 2 A method for preparing a low-pour-point, high-flash-point plant-based synthetic ester environmentally friendly impregnating agent for capacitors is as follows: Isooctyl alcohol and linoleic acid were mixed at a molar ratio of 1.05:1 to obtain a mixture. The mixture was then added to a reaction vessel, and stannous oxalate catalyst was added. The mass of the catalyst was 0.1% of the total mass of isooctyl alcohol, oleic acid, and catalyst. The esterification reaction was carried out at 200℃ for 24 hours under nitrogen protection and atmospheric pressure. After the reaction was completed, 0.5% of the total mass of activated carbon was added to adsorb impurities, and the mixture was vacuum filtered at 0.09 MPa for 5 minutes to obtain a crude esterification product. Subsequently, excess isooctyl alcohol was separated by vacuum distillation at a pressure of 0.09 MPa, a temperature of 80℃, and a time of 4 hours. Alumina at 2% of the total mass of the crude esterification product was added, and the mixture was stirred at 80℃ and 150 rpm for 2 hours to remove trace amounts of residual acid, finally obtaining a purified product.

[0042] Example 3 The difference from Example 1 is that oleic acid is replaced with the same molar amount of linolenic acid; all other steps are the same.

[0043] Example 4 The difference from Example 1 is that oleic acid is replaced with the same molar amount of tung oil acid; all other steps are the same.

[0044] Comparative Example 1 Benzyltoluene is an existing impregnating agent for capacitors.

[0045] Comparative Example 2 The difference from Example 1 is that oleic acid is replaced with octanoic acid, but the other steps are the same.

[0046] Performance testing The performance of the plant-based synthetic ester environmentally friendly impregnating agents obtained in Examples 1-4 and the products of Comparative Examples 1-2 was tested, and the results are shown in Table 1: Table 1. Performance of the plant-based synthetic ester environmentally friendly impregnating agents obtained in Examples 1-4 and the products of Comparative Examples 1-2

[0047] As can be seen from Table 1, the plant-based synthetic ester environmentally friendly impregnating agent prepared by this invention has a low pour point and a high flash point, which meets the technical requirements of a new generation of high-performance, high-safety, and environmentally friendly capacitors.

[0048] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A plant-based synthetic ester environmentally friendly impregnating agent, characterized in that, include: Esters obtained by esterification of organic alcohols and plant-based fatty acids; The organic alcohol is a straight-chain or branched alcohol; the straight-chain or branched alcohol has 4 to 10 carbon atoms. The plant-based fatty acids consist of plant-based carboxylic acids, including one or more of plant-based saturated and unsaturated fatty acids.

2. The plant-based synthetic ester environmentally friendly impregnating agent according to claim 1, characterized in that, The straight-chain or branched alcohols comprise at least one even-numbered carbon branched alcohol.

3. The plant-based synthetic ester environmentally friendly impregnating agent according to claim 1, characterized in that, The plant-based fatty acids contain at least one unsaturated fatty acid.

4. The plant-based synthetic ester environmentally friendly impregnating agent according to claim 1 or 2, characterized in that, The straight-chain or branched alcohol is selected from one or more of n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, isobutanol, isopentanol, isohexanol, isoheptanol, isooctanol, isononol, and isodecanol.

5. The plant-based synthetic ester environmentally friendly impregnating agent according to claim 1 or 3, characterized in that, The plant-based fatty acids are selected from one or more of oleic acid, linoleic acid, linolenic acid, tung oil acid, palmitic acid, stearic acid, myristic acid, heptadecanoic acid, arachidic acid, behenic acid, heptadecanoic acid, erucic acid, and arachidienoic acid.

6. The plant-based synthetic ester environmentally friendly impregnating agent according to claim 1, characterized in that, The molar ratio of the organic alcohol to the plant-based fatty acid is 0.8 to 1.4:

1.

7. A method for preparing the plant-based synthetic ester environmentally friendly impregnating agent according to any one of claims 1 to 6, characterized in that, Includes the following steps: In a protective atmosphere, organic alcohols, plant-based fatty acids and esterification catalysts are mixed and esterification reaction is carried out to obtain the plant-based synthetic ester environmentally friendly impregnating agent. The organic alcohol is a straight-chain or branched alcohol; the straight-chain or branched alcohol has 4 to 10 carbon atoms. The plant-based fatty acids consist of plant-based carboxylic acids, including one or more of plant-based saturated and unsaturated fatty acids.

8. The preparation method according to claim 7, characterized in that, The esterification catalyst is selected from one of the following: protic acid catalysts, metal oxide catalysts, and organic acid salt catalysts.

9. The preparation method according to claim 7, characterized in that, The esterification reaction is carried out at a temperature of 180~250℃ for a reaction time of 20~48h.

10. The application of the plant-based synthetic ester environmentally friendly impregnating agent according to any one of claims 1 to 6 or the plant-based synthetic ester environmentally friendly impregnating agent prepared by the preparation method according to any one of claims 7 to 9 in capacitors.

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