A dry-type bushing aluminum foil / epoxy impregnated paper composite and a method for manufacturing the same

Abstract

The application belongs to the technical field of high-voltage electrical equipment manufacturing, and discloses an aluminum foil / epoxy impregnated paper composite material for dry-type bushings and a preparation method thereof, wherein the surface of the aluminum foil is subjected to cleaning pretreatment; then the surface of the aluminum foil is subjected to plasma double treatment: plasma activation is carried out under an oxygen atmosphere with a working pressure of 10-20 Pa, the power of the plasma activation is 80-120 W, and the time is 2-5 minutes; then the atmosphere is switched to argon, plasma etching is carried out under an argon atmosphere with a working pressure of 15-25 Pa, the power of the plasma etching is 120-150 W, and the time is 0.5-1 minute; then an adhesive is coated on the surface of the aluminum foil and the adhesive is pre-cured; the aluminum foil coated with the adhesive after pre-curing is laminated with a fiber paper to obtain a laminated body; the laminated body is subjected to mold pressing forming together with an epoxy resin, and then curing is carried out, so that the aluminum foil / epoxy impregnated paper composite material for dry-type bushings is obtained. The application can improve the interface performance of the aluminum foil and the epoxy impregnated paper composite system, and further improve the long-term stability of the dry-type bushing under the operating environment.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage electrical equipment manufacturing technology, specifically an aluminum foil / epoxy impregnated paper composite material for dry bushings and its preparation method, which is particularly suitable for the manufacturing of dry bushing insulation for 500kV and above. Background Technology

[0002] Dry bushings, as core components of power transmission and transformation equipment, often employ an aluminum foil and epoxy-impregnated paper composite system for their main insulation structure. The quality of the interfacial bonding in this system directly determines the insulation reliability and mechanical stability of the bushing. Weak boundary layers such as oil stains and natural oxide layers on the aluminum foil surface, along with the large surface energy difference and insufficient chemical affinity between the aluminum foil and epoxy materials, result in common defects in traditional composite materials, including low interfacial bonding strength and poor weather resistance. During long-term operation, under the influence of temperature cycling, electric field stress, and environmental humidity, the interface is prone to cracking, delamination, and other failure phenomena, leading to increased partial discharge and dielectric loss. In severe cases, this can cause bushing insulation breakdown, threatening the safe operation of the power system. Current technologies often employ chemical etching or sandblasting to treat the aluminum foil surface. However, chemical etching presents environmental pollution problems, and sandblasting can damage the properties of the aluminum foil itself and result in poor surface modification uniformity.

[0003] With the implementation of the DL / T 1001-2024 standard, the performance requirements for dry bushings have expanded from basic electrical indicators to seven major categories, including mechanical properties and dimensional characteristics. New test items such as earthquake resistance and zero gauge pressure have been added, placing higher demands on the interfacial reliability of composite materials. Plasma surface treatment technology has begun to be applied in the field of material modification; however, in aluminum foil / epoxy impregnated paper composite material systems, simple single-gas plasma treatment has limited effect on improving interfacial performance, especially in terms of insufficient long-term stability under operating conditions. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide an aluminum foil / epoxy impregnated paper composite material for dry bushings and its preparation method. The present invention can improve the interfacial properties of the aluminum foil and epoxy impregnated paper composite system, thereby improving the long-term stability of dry bushings under operating conditions.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an aluminum foil / epoxy impregnated paper composite material for dry bushings includes the following steps: Pre-treatment for cleaning the aluminum foil surface; The aluminum foil surface after cleaning and pretreatment undergoes a dual plasma treatment, specifically including: first, plasma activation is performed in an oxygen atmosphere at a working pressure of 10-20 Pa, with a power of 80-120 W and a time of 2-5 minutes; then, the atmosphere is switched to argon, and plasma etching is performed in an argon atmosphere at a working pressure of 15-25 Pa, with a power of 120-150 W and a time of 0.5-1 minutes. An adhesive is applied to the surface of the aluminum foil after it has undergone dual plasma treatment. After the adhesive is pre-cured, a transitional bonding layer is formed on the surface of the aluminum foil to obtain the coated aluminum foil. The coated aluminum foil is laminated with fiber paper to obtain a laminate. The laminated body is molded with epoxy resin and then cured to obtain the aluminum foil / epoxy impregnated paper composite material for dry sleeve.

[0006] Preferably, the pretreatment process for cleaning the aluminum foil surface includes: sequentially performing alkaline washing, acid washing, and deionized water rinsing.

[0007] Preferably, the alkaline washing uses a NaOH solution with a concentration of 3 wt%-8 wt%, the treatment temperature is 40-60℃, and the treatment time is 5-15 minutes; the acid washing uses a nitric acid solution with a concentration of 5 wt%-10 wt%, and the treatment time is 3-8 minutes.

[0008] Preferably, during plasma activation, the power of plasma activation is 98-102W and the time is 175-185s; During plasma etching, the power is 128-132W and the time is 46-50s.

[0009] Preferably, the adhesive is an epoxy resin system containing phenolic curing agent and polyurethane toughening agent; The amount of phenolic curing agent added is 30%-40% of the weight of epoxy resin, and the amount of polyurethane toughening agent added is 5%-8% of the weight of epoxy resin.

[0010] Preferably, after the aluminum foil surface is treated with plasma and coated with an adhesive, it is cured at 120-140°C for 40-60 minutes to form a transitional adhesive layer on the aluminum foil surface.

[0011] Preferably, the thickness of the adhesive coating on the aluminum foil surface after plasma dual treatment is controlled at 20-30 μm.

[0012] Preferably, the epoxy resin is bisphenol A type epoxy resin E-51, the phenolic curing agent is linear phenolic resin PF-6520, and the polyurethane toughening agent is hydroxyl-terminated polyurethane prepolymer PU-301.

[0013] Preferably, when the laminate is molded with epoxy resin, the hot pressing temperature is 80-100℃, the applied pressure is 0.5-1MPa, and the holding time is 13-17min. The curing process after compression molding adopts a stepped curing process. During curing, the temperature is first heated to 78-82℃ and held for 55-65 minutes, then heated to 118-122℃ and held for 115-125 minutes, then heated to 148-152℃ and held for 115-125 minutes, and then cooled with the furnace. The heating rate is 1-2℃ / min and the cooling rate is 0.5-1℃ / min.

[0014] The present invention also provides an aluminum foil / epoxy impregnated paper composite material for dry bushings, wherein the aluminum foil / epoxy impregnated paper composite material for dry bushings is prepared by the preparation method of the present invention as described above.

[0015] The present invention has the following beneficial effects: This invention discloses a method for preparing an aluminum foil / epoxy impregnated paper composite material for dry sleeves. First, the aluminum foil surface undergoes a cleaning pretreatment, followed by a dual plasma treatment. First, plasma activation is performed in an oxygen atmosphere at a working pressure of 10-20 Pa with a power of 80-120 W for 2-5 minutes. The chemical action of the oxygen plasma removes the weak boundary layer on the aluminum foil surface and introduces oxygen-containing polar functional groups, increasing surface energy and hydrophilicity, and improving chemical affinity with adhesives and epoxy materials. Then, plasma etching is performed in an argon atmosphere at a working pressure of 15-25 Pa with a power of 120-150 W for 0.5-1 minutes. Argon ion physical bombardment removes the residual natural oxide layer, forming a nanoscale micro-rough structure to increase specific surface area and enhance mechanical interlocking. This two-stage synergistic construction of a gradient active layer, compared to a single plasma treatment, yields significantly improved performance. Plasma treatment comprehensively improves the surface properties of aluminum foil. The treated aluminum foil is then coated with an adhesive and cured to form a transitional bonding layer. The coated aluminum foil is then laminated with fiber paper to form a laminate, which is then molded with epoxy resin and cured. The transitional bonding layer alleviates the surface energy difference between the aluminum foil and the epoxy material. The molding and curing processes ensure full impregnation and bonding of each layer, and full cross-linking of the adhesive and epoxy resin, effectively improving the interfacial bonding strength. This solves the defects of traditional composite materials, such as easy cracking and delamination at the interface. Furthermore, the dual plasma treatment eliminates the need for harmful chemical reagents, avoiding the environmental pollution of chemical etching and the damage to the aluminum foil itself caused by sandblasting. The modification only affects a thin layer on the aluminum foil surface, without affecting the bulk properties. The process parameters are clear and operable, enabling the stable preparation of composite materials with reliable interfacial bonding that meet usage requirements, highlighting the technological innovation and practicality. Attached Figure Description

[0016] Figure 1 This is a process flow diagram for preparing the aluminum foil / epoxy impregnated paper composite material for dry sleeves of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0018] The plasma surface treatment technology described in this method is a green and environmentally friendly surface modification method. It can clean, activate and micro-roughen the material surface through the action of high-energy particles. Moreover, the modification only acts on a thin layer of a few nanometers to a few hundred nanometers on the surface and does not affect the material's bulk properties. It provides an effective way to solve the interfacial bonding problem between aluminum foil and epoxy impregnated paper.

[0019] This invention employs a synergistic process of plasma chemical modification and physical etching. By controlling plasma treatment parameters in stages, an active layer with gradient characteristics is constructed on the surface of aluminum foil. Simultaneously, a specific adhesive system and a stepped curing process are used to achieve a comprehensive improvement in interface performance. This method comprises three key technical steps: first, oxygen plasma is used for surface activation, introducing oxygen-containing polar groups onto the aluminum foil surface; then, argon plasma is used for physical etching, forming a uniformly distributed nanoscale surface morphology; finally, a composite material is prepared through an optimized adhesive formulation and a stepped curing process. Key process control points of this invention are: the plasma-treated aluminum foil must be coated with adhesive within 30 minutes to avoid surface functional group attenuation and secondary contamination; during the coating process, the adhesive layer must be uniform, bubble-free, and free of missed areas, with a thickness deviation ≤ ±1 μm; the temperature and time parameters of each curing stage must be strictly controlled, with a deviation not exceeding ±5%, ensuring an epoxy adhesive crosslinking degree ≥90%.

[0020] See Figure 1 The preparation method of the aluminum foil / epoxy impregnated paper composite material for dry sleeves of the present invention includes the following steps: (1) Aluminum foil surface cleaning treatment: Select electrical grade aluminum foil with a thickness of 0.05-0.1mm and perform alkaline washing, acid washing and deionized water rinsing in sequence; specifically, first use a 3 wt%-8 wt% NaOH solution to wash the aluminum foil with alkaline solution at a temperature of 40-60℃ for 5-15 minutes; then use a 5 wt%-10 wt% nitric acid solution to acid wash the aluminum foil after alkaline washing at a temperature of 40-60℃ for 3-8 minutes. After acid washing, rinse the aluminum foil with deionized water 3-5 times until the rinsing water is neutral, and then put it in a vacuum drying oven at 60-80℃ for 20-30 minutes to dry, controlling the surface water content of the aluminum foil to ≤0.1% to avoid residual moisture affecting the interface bonding quality.

[0021] (2) O2 plasma activation: The aluminum foil after surface cleaning is placed in the vacuum chamber of the plasma treatment equipment, the chamber is closed and evacuated to a pressure ≤5Pa. Then, O2 gas with a purity ≥99.9% is introduced, the working pressure in the chamber is adjusted to 10-20Pa, the radio frequency power is set to 80-120W, and the treatment time is 2-5min. Through the chemical action of O2 plasma, organic pollutants on the aluminum foil surface can be oxidized and decomposed, generating gaseous products that detach from the surface. At the same time, oxygen-containing polar functional groups such as -OH and -COOH are introduced, achieving ultra-clean treatment of the aluminum foil surface and introduction of polar functional groups. This reduces the contact angle of the aluminum foil surface from the initial ≥85° to ≤30°, improving surface energy and hydrophilicity.

[0022] (3) Plasma etching: Keep the vacuum chamber of the plasma equipment sealed, switch to the introduction of Ar gas with a purity ≥99.9%, adjust the working pressure to 15-25 Pa, set the RF power supply to 120-150 W, and the etching time to 0.5-1 min. Utilize the physical bombardment effect of Ar ions to remove the natural oxide layer on the aluminum foil surface, forming a uniform micro-rough structure, thereby increasing the surface roughness Ra from 0.02-0.05 μm to 0.1-0.2 μm, increasing the specific surface area to enhance the mechanical interlocking effect.

[0023] (4) Glue Coating: Using precision glue coating equipment, epoxy glue (i.e., an epoxy resin system containing phenolic curing agent and polyurethane toughening agent) is uniformly coated onto the surface of the plasma-etched aluminum foil. During glue coating, the coating thickness is controlled at 20-30 μm, the coating speed is 0.5-1 m / min, and the ambient temperature is maintained at 20-25℃ and the relative humidity is ≤60%. The selected epoxy glue must meet the requirement of volume resistivity ≥1.0×10⁻⁶. 12 Ω The AC breakdown field strength is ≥20kV / mm (1mm thickness) to ensure the insulation performance of the composite material. Specifically, in this epoxy adhesive, the amount of phenolic curing agent added is 30%-40% of the weight of epoxy resin, and the amount of polyurethane toughening agent added is 5%-8% of the weight of epoxy resin. Further, the epoxy resin can be bisphenol A type epoxy resin E-51, the phenolic curing agent can be linear phenolic resin PF-6520, and the polyurethane toughening agent can be hydroxyl-terminated polyurethane prepolymer PU-301.

[0024] (5) Pre-curing: Place the coated aluminum foil in a constant temperature oven for pre-curing. Set the pre-curing temperature to 120-140℃, the holding time to 40-60 min, and the heating rate to 2-3℃ / min to avoid sudden temperature rise that could cause bubbles in the adhesive layer. The pre-curing stage achieves the initial cross-linking of the epoxy adhesive, ensuring that the aluminum foil can be initially bonded and fixed to the epoxy impregnated paper, preventing displacement in subsequent processes. After pre-curing, a transitional adhesive layer is formed on the surface of the aluminum foil, resulting in coated aluminum foil.

[0025] (6) Composite epoxy impregnated paper: After pre-curing, remove the coated aluminum foil and cool it to below 30°C at room temperature. Then, combine the coated aluminum foil with epoxy impregnated paper (such as fiber paper, which can have a basis weight of 80-120 g / m²). 2 Several layers of aramid fiber paper are rapidly and alternately stacked (the bonding must be completed within 30 minutes) to obtain a laminate. The laminate is then further molded using a hot-pressing composite process. During molding, epoxy resin is injected into the mold, and the pressure is maintained for 13-17 minutes at a hot-pressing temperature of 80-100℃ and a hot-pressing pressure of 0.5-1.0MPa to ensure full wetting and tight bonding between the epoxy-impregnated paper and the adhesive layer on the aluminum foil surface, eliminating interfacial gaps. The molding process is then complete.

[0026] (7) Step curing: The composite material obtained by compression molding is placed in a curing oven for step curing treatment: In the first stage, it is heated to 80±2℃ and held for 55-65min to promote the slow cross-linking of epoxy adhesive and reduce internal stress; in the second stage, the temperature is raised to 120±2℃ and held for 115-125min to accelerate the cross-linking reaction of epoxy adhesive; in the third stage, the temperature is raised to 150±2℃ and held for 115-125min to achieve complete cross-linking of epoxy adhesive, thus obtaining the aluminum foil / epoxy impregnated paper composite material for dry sleeves. The total heating rate of step curing is controlled at 1-2℃ / min. After curing, it is cooled to room temperature with the oven (the cooling rate with the oven is about 0.5-1℃ / min) to avoid material deformation or interface cracking due to excessive cooling.

[0027] In the above scheme, the data before ± is the set value of the heat preservation temperature, and the data after ± is the fluctuation value of the curing oven during the heat preservation stage. For those skilled in the art, the technical solution of the present invention is feasible within the range of set value and fluctuation to a certain heat preservation range.

[0028] Example 1 In this embodiment, the experimental materials used were 1060 industrial pure aluminum foil (thickness 0.1 mm, purity ≥ 99.6%) and aramid fiber paper (grammage 100 g / m²). 2 The test was conducted using a Diener Pico plasma cleaner and an INSTRON 5967 universal testing machine (DuPont Kevlar® 49). Specifically, the preparation method of the aluminum foil / epoxy impregnated paper composite material for dry sleeves of this invention includes the following steps: Step 1: Cleaning the surface of the aluminum foil (1) Alkali washing: Immerse the aluminum foil in a 5wt% NaOH aqueous solution (at 50℃) and sonicate for 10 minutes to remove grease and oxides from the aluminum foil surface; (2) Pickling: Transfer the alkaline-washed aluminum foil to an 8wt% nitric acid solution (at 50°C) and soak for 5 minutes to activate the surface; (3) Rinse with deionized water: Rinse the pickled aluminum foil with deionized water until the rinse water is neutral, and then dry it for later use.

[0029] Step 2: Plasma Dual Treatment (1) Oxygen plasma activation: Place the aluminum foil after surface cleaning treatment into the vacuum chamber of the Diener Pico plasma cleaner (vacuum degree 10Pa), introduce oxygen with a purity of 99.8%, work pressure of 15Pa, and start the plasma generator (power set to 100W, time 3 minutes). (2) Argon plasma etching: Switch the atmosphere of the vacuum chamber of the Diener Pico plasma cleaner to argon atmosphere (argon purity 99.99%), adjust the working pressure to 20Pa and the plasma generator power to 130W, process for 0.8 minutes, and form a nano-scale rough surface on the aluminum foil.

[0030] Step 3: Apply adhesive (1) Preparation of adhesive: Take 100g of bisphenol A type epoxy resin (E-51), add 35g of linear phenolic resin (PF-6520) and 6g of hydroxyl-terminated polyurethane prepolymer (PU-301) to the bisphenol A type epoxy resin (E-51), mix evenly to obtain adhesive. (2) Coating and curing: The adhesive is applied to the surface of the aluminum foil after the plasma double treatment in step 2 by scraping method (the coating thickness is 25μm). The coated aluminum foil is placed in an oven and cured at 130℃ for 50 minutes to form a transition adhesive layer on the surface of the aluminum foil, thus obtaining the coated aluminum foil.

[0031] Step 4: Preparation of composite materials (1) Lamination: The coated aluminum foil obtained by the adhesive coating in step 3 is laminated with aramid fiber paper (100 g / m²). 2 Alternately stacked up to 10 layers, a laminated body is obtained; (2) Compression molding: Place the laminate in the compression molding mold, then inject epoxy resin (E-51) into the compression molding mold, apply a pressure of 0.8MPa, and hold the pressure for 15min; (3) Step curing: The molded blank obtained by compression molding is placed in a curing oven, heated to 80±2℃ at 1.5℃ / min and kept at 1h, then heated to 120±2℃ and kept at 2h, then heated to 150±2℃ and kept at 2h, and then cooled to room temperature naturally to obtain the aluminum foil / epoxy impregnated paper composite material for dry sleeve in this embodiment.

[0032] The aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was subjected to mechanical experiments, and the specific process is as follows: The aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was cut into 15mm (transverse) × 100mm (longitudinal) strips, and a single-overlap shear test was performed using an INSTRON 5967 universal testing machine. The overlap length of the sample was 10mm, and the bonded area was calculated to be 15mm × 10mm = 150mm². 2 The test conditions included ambient temperature (25±1℃) and high temperature (85±1℃) environments, with a shear rate set to 2 mm / s (i.e., 120 mm / min). The interfacial shear strength was calculated using the formula:

[0033] Where τ is the interfacial shear strength (MPa), F is the failure load (N), and A is the bonding area (mm²). 2 ).

[0034] The experimental results are shown in Table 1. The room temperature shear strength of the aluminum foil / epoxy impregnated paper composite material obtained in this embodiment is 35.7 MPa (failure load 5355 N, bonding area 150 mm²). 2 The high-temperature shear strength was 30.2 MPa (failure load 4530 N). The fracture surface of the sample was located inside the epoxy resin (cohesive failure rate ≥ 90%), indicating that the interfacial bonding strength was higher than that of the resin bulk.

[0035] Example 2 In this embodiment, the experimental materials used were 1060 industrial pure aluminum foil (thickness 0.1 mm, purity ≥ 99.6%) and aramid fiber paper (grammage 100 g / m²). 2 The test was conducted using a Diener Pico plasma cleaner and an INSTRON 5967 universal testing machine (DuPont Kevlar® 49). Specifically, the preparation method of the aluminum foil / epoxy impregnated paper composite material for dry sleeves of this invention includes the following steps: Step 1: Cleaning the surface of the aluminum foil (1) Alkali washing: Immerse the aluminum foil in a 5wt% NaOH aqueous solution (at 50℃) and sonicate for 10 minutes to remove grease and oxides from the aluminum foil surface; (2) Pickling: Transfer the alkaline-washed aluminum foil to an 8wt% nitric acid solution (at 50°C) and soak for 5 minutes to activate the surface; (3) Rinse with deionized water: Rinse the pickled aluminum foil with deionized water until the rinse water is neutral, and then dry it for later use.

[0036] Step 2: Plasma Dual Treatment (1) Oxygen plasma activation: Place the aluminum foil after surface cleaning treatment into the vacuum chamber of the Diener Pico plasma cleaner (vacuum degree 10Pa), introduce oxygen with a purity of 99.8%, and set the working pressure to 15Pa. Start the plasma generator (power set to 80W, time 3 minutes). (2) Argon plasma etching: Switch the atmosphere of the vacuum chamber of the Diener Pico plasma cleaner to argon atmosphere (argon purity 99.99%), adjust the working pressure to 20Pa and the plasma generator power to 120W, process for 0.8 minutes, and form a nano-scale rough surface on the aluminum foil.

[0037] Step 3: Apply adhesive (1) Preparation of adhesive: Take 100g of bisphenol A type epoxy resin (E-51), add 30g of linear phenolic resin (PF-6520) and 5g of hydroxyl-terminated polyurethane prepolymer (PU-301) to the bisphenol A type epoxy resin (E-51), mix evenly to obtain adhesive. (2) Coating and curing: The adhesive is applied to the surface of the aluminum foil after the plasma double treatment in step 2 by scraping method (the coating thickness is 25μm). The coated aluminum foil is placed in an oven and cured at 130℃ for 50 minutes to form a transition adhesive layer on the surface of the aluminum foil, thus obtaining the coated aluminum foil.

[0038] Step 4: Preparation of composite materials (1) Lamination: The coated aluminum foil obtained by the adhesive coating in step 3 is laminated with aramid fiber paper (100 g / m²). 2 Alternately stacked up to 10 layers, a laminated body is obtained; (2) Compression molding: Place the laminate in the compression molding mold, then inject epoxy resin (E-51) into the compression molding mold, apply a pressure of 0.8MPa, and hold the pressure for 15min; (3) Step curing: The molded blank obtained by compression molding is placed in a curing oven, heated to 80±2℃ at 1.5℃ / min and kept at 1h, then heated to 120±2℃ and kept at 2h, then heated to 150±2℃ and kept at 2h, and then cooled to room temperature naturally to obtain the aluminum foil / epoxy impregnated paper composite material for dry sleeve in this embodiment.

[0039] The aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was subjected to mechanical tests. The experimental procedure was the same as in Example 1. The experimental results are shown in Table 1. The room temperature shear strength of the aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was 32.1 MPa (failure load 4815 N, bonding area 150 mm²). 2 The high-temperature shear strength was 27.4 MPa (failure load 4110 N). The fracture surface of the sample was located inside the epoxy resin (cohesive failure rate ≥ 85%), indicating good interfacial bonding strength.

[0040] Example 3 In this embodiment, the experimental materials used were 1060 industrial pure aluminum foil (thickness 0.1 mm, purity ≥ 99.6%) and aramid fiber paper (grammage 100 g / m²). 2 The test was conducted using a Diener Pico plasma cleaner and an INSTRON 5967 universal testing machine (DuPont Kevlar® 49). Specifically, the preparation method of the aluminum foil / epoxy impregnated paper composite material for dry sleeves of this invention includes the following steps: Step 1: Cleaning the surface of the aluminum foil (1) Alkali washing: Immerse the aluminum foil in a 5wt% NaOH aqueous solution (at 50℃) and sonicate for 10 minutes to remove grease and oxides from the aluminum foil surface; (2) Pickling: Transfer the alkaline-washed aluminum foil to an 8wt% nitric acid solution (at 50°C) and soak for 5 minutes to activate the surface; (3) Rinse with deionized water: Rinse the pickled aluminum foil with deionized water until the rinse water is neutral, and then dry it for later use.

[0041] Step 2: Plasma Dual Treatment (1) Oxygen plasma activation: Place the aluminum foil after surface cleaning treatment into the vacuum chamber of the Diener Pico plasma cleaner (vacuum degree 10Pa), introduce oxygen with a purity of 99.8%, and set the working pressure to 15Pa. Start the plasma generator (power set to 120W, time 3 minutes). (2) Argon plasma etching: Switch the atmosphere of the vacuum chamber of the Diener Pico plasma cleaner to argon atmosphere (argon purity 99.99%), adjust the working pressure to 20Pa and the plasma generator power to 150W, process for 0.8 minutes, and form a nano-scale rough surface on the aluminum foil.

[0042] Step 3: Apply adhesive (1) Preparation of adhesive: Take 100g of bisphenol A type epoxy resin (E-51), add 40g of linear phenolic resin (PF-6520) and 8g of hydroxyl-terminated polyurethane prepolymer (PU-301) to the bisphenol A type epoxy resin (E-51), mix evenly to obtain adhesive. (2) Coating and curing: The adhesive is applied to the surface of the aluminum foil after the plasma double treatment in step 2 by scraping method (the coating thickness is 25μm). The coated aluminum foil is placed in an oven and cured at 130℃ for 50 minutes to form a transition adhesive layer on the surface of the aluminum foil, thus obtaining the coated aluminum foil.

[0043] Step 4: Preparation of composite materials (1) Lamination: The coated aluminum foil obtained by the adhesive coating in step 3 is laminated with aramid fiber paper (100 g / m²). 2 Alternately stacked up to 10 layers, a laminated body is obtained; (2) Compression molding: Place the laminate in the compression molding mold, then inject epoxy resin (E-51) into the compression molding mold, apply a pressure of 0.8MPa, and hold the pressure for 15min; (3) Step curing: The molded blank obtained by compression molding is placed in a curing oven, heated to 80±2℃ at 1.5℃ / min and kept at 1h, then heated to 120±2℃ and kept at 2h, then heated to 150±2℃ and kept at 2h, and then cooled to room temperature naturally to obtain the aluminum foil / epoxy impregnated paper composite material for dry sleeve in this embodiment.

[0044] The aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was subjected to mechanical tests. The experimental procedure was the same as in Example 1. The experimental results are shown in Table 1. The room temperature shear strength of the aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was 33.8 MPa (failure load 5070 N, bonding area 150 mm²). 2 The high-temperature shear strength was 28.9 MPa (failure load 4335 N). The fracture surface of the sample was located inside the epoxy resin (cohesive failure rate ≥ 88%), indicating that the interfacial bonding strength was higher than that of the resin bulk.

[0045] Example 4 In this embodiment, the experimental materials used were 1060 industrial pure aluminum foil (thickness 0.1 mm, purity ≥ 99.6%) and aramid fiber paper (grammage 100 g / m²). 2 The test was conducted using a Diener Pico plasma cleaner and an INSTRON 5967 universal testing machine (DuPont Kevlar® 49). Specifically, the preparation method of the aluminum foil / epoxy impregnated paper composite material for dry sleeves of this invention includes the following steps: Step 1: Cleaning the surface of the aluminum foil (1) Alkali washing: Immerse the aluminum foil in a 5wt% NaOH aqueous solution (at 50℃) and sonicate for 10 minutes to remove grease and oxides from the aluminum foil surface; (2) Pickling: Transfer the alkaline-washed aluminum foil to an 8wt% nitric acid solution (at 50°C) and soak for 5 minutes to activate the surface; (3) Rinse with deionized water: Rinse the pickled aluminum foil with deionized water until the rinse water is neutral, and then dry it for later use.

[0046] Step 2: Plasma Dual Treatment (1) Oxygen plasma activation: Place the aluminum foil after surface cleaning treatment into the vacuum chamber of the Diener Pico plasma cleaner (vacuum degree 10Pa), introduce oxygen with a purity of 99.8%, work pressure of 15Pa, and start the plasma generator (power set to 100W, time 3 minutes). (2) Argon plasma etching: Switch the atmosphere of the vacuum chamber of the Diener Pico plasma cleaner to argon atmosphere (argon purity 99.99%), adjust the working pressure to 20Pa and the plasma generator power to 130W, process for 0.8 minutes, and form a nano-scale rough surface on the aluminum foil.

[0047] Step 3: Apply adhesive (1) Preparation of adhesive: Take 100g of bisphenol A type epoxy resin (E-51), add 40g of linear phenolic resin (PF-6520) and 6g of hydroxyl-terminated polyurethane prepolymer (PU-301) to the bisphenol A type epoxy resin (E-51), mix evenly to obtain adhesive. (2) Coating and curing: The adhesive is applied to the surface of the aluminum foil after the plasma double treatment in step 2 by scraping method (the coating thickness is 25μm). The coated aluminum foil is placed in an oven and cured at 130℃ for 50 minutes to form a transition adhesive layer on the surface of the aluminum foil, thus obtaining the coated aluminum foil.

[0048] Step 4: Preparation of composite materials (1) Lamination: The coated aluminum foil obtained by the adhesive coating in step 3 is laminated with aramid fiber paper (100 g / m²). 2 Alternately stacked up to 10 layers, a laminated body is obtained; (2) Compression molding: Place the laminate in the compression molding mold, then inject epoxy resin (E-51) into the compression molding mold, apply a pressure of 0.8MPa, and hold the pressure for 15min; (3) Step curing: The molded blank obtained by compression molding is placed in a curing oven, heated to 80±2℃ at 1.5℃ / min and kept at 1h, then heated to 120±2℃ and kept at 2h, then heated to 150±2℃ and kept at 2h, and then cooled to room temperature naturally to obtain the aluminum foil / epoxy impregnated paper composite material for dry sleeve in this embodiment.

[0049] The aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was subjected to mechanical tests. The experimental procedure was the same as in Example 1. The experimental results are shown in Table 1. The room temperature shear strength of the aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was 33.8 MPa (failure load 5070 N, bonding area 150 mm²). 2The high-temperature shear strength was 28.9 MPa (failure load 4335 N). The fracture surface of the sample was located inside the epoxy resin (cohesive failure rate ≥ 88%), indicating that the interfacial bonding strength was higher than that of the resin bulk.

[0050] Example 5 In this embodiment, the experimental materials used were 1060 industrial pure aluminum foil (thickness 0.1 mm, purity ≥ 99.6%) and aramid fiber paper (grammage 100 g / m²). 2 The test was conducted using a Diener Pico plasma cleaner and an INSTRON 5967 universal testing machine (DuPont Kevlar® 49). Specifically, the preparation method of the aluminum foil / epoxy impregnated paper composite material for dry sleeves of this invention includes the following steps: Step 1: Cleaning the surface of the aluminum foil (1) Alkali washing: Immerse the aluminum foil in a 5wt% NaOH aqueous solution (at 50℃) and sonicate for 10 minutes to remove grease and oxides from the aluminum foil surface; (2) Pickling: Transfer the alkaline-washed aluminum foil to an 8wt% nitric acid solution (at 50°C) and soak for 5 minutes to activate the surface; (3) Rinse with deionized water: Rinse the pickled aluminum foil with deionized water until the rinse water is neutral, and then dry it for later use.

[0051] Step 2: Plasma Dual Treatment (1) Oxygen plasma activation: Place the aluminum foil after surface cleaning treatment into the vacuum chamber of the Diener Pico plasma cleaner (vacuum degree 10Pa), introduce oxygen with a purity of 99.8%, and set the working pressure to 15Pa. Start the plasma generator (power set to 80W, time 3 minutes). (2) Argon plasma etching: Switch the atmosphere of the vacuum chamber of the Diener Pico plasma cleaner to argon atmosphere (argon purity 99.99%), adjust the working pressure to 20Pa and the plasma generator power to 150W, process for 0.8 minutes, and form a nano-scale rough surface on the aluminum foil.

[0052] Step 3: Apply adhesive (1) Preparation of adhesive: Take 100g of bisphenol A type epoxy resin (E-51), add 35g of linear phenolic resin (PF-6520) and 8g of hydroxyl-terminated polyurethane prepolymer (PU-301) to the bisphenol A type epoxy resin (E-51), mix evenly to obtain adhesive. (2) Coating and curing: The adhesive is applied to the surface of the aluminum foil after the plasma double treatment in step 2 by scraping method (the coating thickness is 25μm). The coated aluminum foil is placed in an oven and cured at 130℃ for 50 minutes to form a transition adhesive layer on the surface of the aluminum foil, thus obtaining the coated aluminum foil.

[0053] Step 4: Preparation of composite materials (1) Lamination: The coated aluminum foil obtained by the adhesive coating in step 3 is laminated with aramid fiber paper (100 g / m²). 2 Alternately stacked up to 10 layers, a laminated body is obtained; (2) Compression molding: Place the laminate in the compression molding mold, then inject epoxy resin (E-51) into the compression molding mold, apply a pressure of 0.8MPa, and hold the pressure for 15min; (3) Step curing: The molded blank obtained by compression molding is placed in a curing oven, heated to 80±2℃ at 1.5℃ / min and kept at 1h, then heated to 120±2℃ and kept at 2h, then heated to 150±2℃ and kept at 2h, and then cooled to room temperature naturally to obtain the aluminum foil / epoxy impregnated paper composite material for dry sleeve in this embodiment.

[0054] The aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was subjected to mechanical tests. The experimental procedure was the same as in Example 1. The experimental results are shown in Table 1. The room temperature shear strength of the aluminum foil / epoxy impregnated paper composite material obtained in this embodiment was 33.8 MPa (failure load 5070 N, bonding area 150 mm²). 2 The high-temperature shear strength was 28.9 MPa (failure load 4335 N). The fracture surface of the sample was located inside the epoxy resin (cohesive failure rate ≥ 88%), indicating that the interfacial bonding strength was higher than that of the resin bulk.

[0055] Comparative Example 1 Compared to Example 1, this comparative example omits the argon etching step and only performs oxygen plasma activation (the remaining process parameters are the same as in Example 1). The mechanical test results of the composite material obtained in this comparative example are shown in Table 1. The interfacial shear strength of the composite material obtained in this comparative example is 28.3 MPa at room temperature (failure load 4245 N) and 22.6 MPa at high temperature (failure load 3390 N), with a high-temperature strength retention rate of 79.9%. The failure mode is complete detachment from the aluminum foil surface, with no resin residue.

[0056] Comparative Example 2 Compared to Example 1, this comparative example omits the oxygen activation step and only performs argon etching (the remaining process parameters are the same as in Example 1). The results of mechanical tests on the composite material obtained in this comparative example are shown in Table 1. The interfacial shear strength of the composite material obtained in this comparative example is 25.1 MPa at room temperature (failure load 3765 N) and 19.8 MPa at high temperature (failure load 2970 N), with a high-temperature strength retention rate of 78.9%. The failure mode is mixed failure, with resin residue and interfacial debonding coexisting in some areas.

[0057] Comparative Example 3 Compared to Example 1, the aluminum foil in this comparative example was directly coated and cured without any plasma treatment (the other process parameters are the same as in Example 1). The results of mechanical tests on the composite material obtained in this comparative example are shown in Table 1. The interfacial shear strength of the composite material obtained in this comparative example is 18.4 MPa at room temperature (failure load 2760 N) and 13.7 MPa at high temperature (failure load 2055 N), with a high-temperature strength retention rate of 74.5%. The failure mode is complete interfacial debonding, and the aluminum foil surface is smooth with no signs of modification.

[0058] Table 1

[0059] As shown in Table 1, the room temperature shear strength of Examples 1-5 (dual plasma treatment) was 31.5-35.7 MPa, significantly higher than that of Comparative Example 1 (28.3 MPa) activated only by oxygen, Comparative Example 2 (25.1 MPa) etched only by argon, and Comparative Example 3 (18.4 MPa) without treatment, demonstrating the synergistic effect of the dual plasma treatment in this invention. The fracture surfaces of the samples in Examples 1-5 were all located within the epoxy resin (cohesive failure ≥85%), indicating that the interfacial bonding strength exceeded the strength of the resin bulk. At a high temperature of 85°C, the strength retention rate of Examples 1-5 (84.6%-85.6%) was significantly better than that of the comparative examples (74.5%-79.9%), exhibiting excellent thermal stability.

[0060] The chemical activation and physical etching synergistic enhancement interface layer constructed by this invention effectively solves the technical problem of weak interface layers in traditional composite materials, significantly improves the interface bonding strength and high temperature stability, and provides key technical support for the reliability of dry bushings in the long-term operation of ultra-high voltage power transmission systems.

[0061] This method can significantly improve the interfacial bonding strength between aluminum foil and epoxy impregnated paper, making the composite material's room temperature shear strength ≥31.5MPa, high temperature shear strength ≥26.8MPa, and performance retention rate exceeding 90% after 1500h aging. The interfacial bonding strength is higher than that of the resin matrix.

[0062] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0063] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions made to the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the present invention. Furthermore, unless otherwise specified, all or part of any embodiment may be used in conjunction with all or part of any other embodiment.

Claims

1. A method for preparing an aluminum foil / epoxy impregnated paper composite material for dry sleeves, characterized in that, The process includes the following: Pre-treatment for cleaning the aluminum foil surface; After cleaning and pretreatment, the aluminum foil surface undergoes a dual plasma treatment, specifically including: firstly, plasma activation is performed in an oxygen atmosphere with a working pressure of 10-20 Pa, with a plasma activation power of 80-120 W and a time of 2-5 minutes. The atmosphere was then switched to argon, and plasma etching was performed in an argon atmosphere with a working pressure of 15-25 Pa. The plasma etching power was 120-150 W and the time was 0.5-1 minute. An adhesive is applied to the surface of the aluminum foil after it has undergone dual plasma treatment. After the adhesive is pre-cured, a transitional bonding layer is formed on the surface of the aluminum foil to obtain the coated aluminum foil. The coated aluminum foil is laminated with fiber paper to obtain a laminate. The laminated body is molded with epoxy resin and then cured to obtain the aluminum foil / epoxy impregnated paper composite material for dry sleeve.

2. The method for preparing an aluminum foil / epoxy impregnated paper composite material for dry sleeves according to claim 1, characterized in that, The pretreatment process for cleaning the aluminum foil surface includes: sequential alkaline washing, acid washing, and deionized water rinsing.

3. The method for preparing an aluminum foil / epoxy impregnated paper composite material for dry sleeves according to claim 2, characterized in that, The alkaline washing uses a NaOH solution with a concentration of 3 wt%-8 wt%, a treatment temperature of 40-60℃, and a treatment time of 5-15 minutes; the acid washing uses a nitric acid solution with a concentration of 5 wt%-10 wt%, and a treatment time of 3-8 minutes.

4. The method for preparing an aluminum foil / epoxy impregnated paper composite material for dry sleeves according to claim 1, characterized in that, When performing plasma activation, the power of plasma activation is 98-102W and the time is 175-185s; During plasma etching, the power is 128-132W and the time is 46-50s.

5. The method for preparing an aluminum foil / epoxy impregnated paper composite material for dry sleeves according to claim 1, characterized in that, The adhesive is an epoxy resin system containing phenolic curing agent and polyurethane toughening agent; The amount of phenolic curing agent added is 30%-40% of the weight of epoxy resin, and the amount of polyurethane toughening agent added is 5%-8% of the weight of epoxy resin.

6. The method for preparing an aluminum foil / epoxy impregnated paper composite material for dry sleeves according to claim 5, characterized in that, After applying an adhesive to the surface of the aluminum foil that has undergone dual plasma treatment, it is cured at 120-140℃ for 40-60 minutes to form a transitional adhesive layer on the aluminum foil surface.

7. A method for preparing an aluminum foil / epoxy impregnated paper composite material for dry sleeves according to claim 5 or 6, characterized in that, The thickness of the adhesive coating on the aluminum foil surface after plasma dual treatment is controlled at 20-30μm.

8. The method for preparing an aluminum foil / epoxy impregnated paper composite material for dry sleeves according to claim 7, characterized in that, The epoxy resin is bisphenol A type epoxy resin E-51, the phenolic curing agent is linear phenolic resin PF-6520, and the polyurethane toughening agent is hydroxyl-terminated polyurethane prepolymer PU-301.

9. The method for preparing an aluminum foil / epoxy impregnated paper composite material for dry bushings according to claim 1, characterized in that, When the laminate is molded with epoxy resin, the hot pressing temperature is 80-100℃, the applied pressure is 0.5-1MPa, and the holding time is 13-17min. The curing process after compression molding adopts a stepped curing process. During curing, the temperature is first heated to 78-82℃ and held for 55-65 minutes, then heated to 118-122℃ and held for 115-125 minutes, then heated to 148-152℃ and held for 115-125 minutes, and then cooled with the furnace. The heating rate is 1-2℃ / min and the cooling rate is 0.5-1℃ / min.

10. An aluminum foil / epoxy impregnated paper composite material for dry bushings, characterized in that, The aluminum foil / epoxy impregnated paper composite material for dry bushing is prepared by any one of the preparation methods of claims 1-9.

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