High tracking resistance flame retardant epoxy resin insulating shield and its casting process

Abstract

The application discloses a high tracking resistance and flame-retardant epoxy resin insulating shield and a casting forming process thereof, and relates to the technical field of electrical insulating materials.The method comprises the following steps: mold design and manufacturing, mold pretreatment, epoxy resin mixture preparation, casting, curing, demolding and post-treatment; and the insulating shield is composed of an epoxy resin matrix, a flame-retardant system, a tracking resistance modifier, a flexible chain modifier, a silane coupling agent and a curing agent.The application aims to solve the problems that the existing epoxy resin insulating material is difficult to meet the comprehensive requirements of high tracking resistance and flame-retardant performance, and lacks a casting forming process for the insulating shield, and improves the tracking resistance and flame-retardant performance from the molecular structure through phosphorus-nitrogen synergistic flame-retardant and organic silicon chemical bonding modification.

Description

Technical Field

[0001] This invention relates to the field of electrical insulation materials technology, and in particular to a high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover and its casting process. Background Technology

[0002] Epoxy resin, as an important thermosetting polymer material, is widely used in electrical insulation, electronic packaging, aerospace, and composite materials due to its excellent adhesion, mechanical strength, chemical resistance, and electrical insulation properties. With the development of power equipment towards high voltage and large capacity, the performance requirements for epoxy resin insulation materials are increasing, especially in outdoor electrical equipment, transformers, and insulating bushings, where epoxy resin insulation products face stringent environmental challenges.

[0003] Tracking is a significant issue in electrical insulation. Under the influence of an electric field, conductive channels form on the surface of insulating materials due to contamination, moisture, and other factors, gradually developing and eventually leading to insulation breakdown. High-resistance epoxy resin insulation materials with excellent tracking resistance are crucial for ensuring the safe operation of electrical equipment. Simultaneously, flame retardancy is a fundamental requirement for electrical insulation materials, especially in applications with high fire risks. Currently, domestic and international research on epoxy resin modification mainly focuses on improving toughness, reducing chlorine content, improving heat resistance, and reducing costs. This emphasis on improving single properties lacks a comprehensive solution that simultaneously satisfies both high tracking resistance and flame retardancy, and it also neglects the casting molding process for insulating covers.

[0004] In summary, this invention proposes a high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover and its casting process. Summary of the Invention

[0005] The purpose of this invention is to provide a high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover and its casting process, in order to solve the problem that existing epoxy resin insulating materials cannot simultaneously meet the comprehensive requirements of high resistance to tracking and flame retardancy, and lack a casting process for insulating covers.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover is prepared from the following components in parts by weight:

[0008] The composition comprises 100 parts epoxy resin matrix, 15 to 35 parts flame retardant system, 5 to 20 parts tracking-resistant modifier, 8 to 15 parts flexible segment modifier, 1 to 3 parts silane coupling agent, 30 to 50 parts curing agent, and 0.2 to 2.0 parts accelerator; wherein the flame retardant system comprises a compound of phosphorus-based flame retardant and nitrogen-based flame retardant, and the mass ratio of phosphorus-based flame retardant to nitrogen-based flame retardant is 1:2 to 2:1; the tracking-resistant modifier is an organosilicon compound containing an aromatic structure.

[0009] By employing a compound system of phosphorus-based and nitrogen-based flame retardants, and utilizing the synergistic flame-retardant mechanism of phosphorus and nitrogen, a dense char layer is formed during the curing process of epoxy resin, effectively suppressing heat release and smoke generation during combustion. Simultaneously, the introduction of organosilicon compounds containing aromatic structures, through the bridging effect of silane coupling agents, chemically bonds organosilicon segments into the three-dimensional network structure of epoxy resin, forming an island-like silicon phase structure. This silicon phase structure can effectively suppress the generation and growth of electrical trees under an electric field, significantly improving the material's resistance to tracking. Furthermore, the introduction of flexible segment modifiers increases the flexibility of the cured epoxy resin, alleviates internal stress, and improves the material's impact resistance.

[0010] Preferably, the epoxy resin matrix is ​​at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, or phenolic epoxy resin, with an epoxy value of 0.50 to 0.95 mol / 100g. The phosphorus-based flame retardant is at least one of triphenyl phosphate, tricresyl phosphate, diphenyl phosphate, or red phosphorus. The nitrogen-based flame retardant is at least one of melamine, cyanurate, or guanidine salt.

[0011] Preferably, the organosilicon compound containing an aromatic structure is at least one of phenyl silicone oil, phenyl silicone resin, or phenylmethylsilane, and its viscosity is 100 to 1000 mPa·s at 25°C. This organosilicon compound is chemically bonded to the epoxy resin using γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane as a silane coupling agent. The flexible segment modifier is at least one of polyether polyol, polyester polyol, or hydroxyl-terminated liquid nitrile rubber, and its number average molecular weight is 500 to 3000.

[0012] Preferably, the silane coupling agent is at least one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and its amount is 1% to 3% of the weight of the epoxy resin matrix.

[0013] Preferably, the curing agent is at least one selected from methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, tung oil anhydride, or a polyamide curing agent. It also includes an accelerator, which is at least one selected from 2-methylimidazole, 2-ethyl-4-methylimidazole, or benzyldimethylamine, used in an amount of 0.5% to 2% of the weight of the curing agent.

[0014] According to the present invention, the insulating cover exhibits excellent resistance to tracking and flame retardancy, while also possessing good mechanical strength and chemical corrosion resistance. Due to the adoption of a phosphorus-nitrogen synergistic flame retardant system, a stable charred protective layer is formed during combustion, achieving a flame retardancy rating of UL94 V-0. The introduction of organosilicon compounds containing aromatic structures creates uniformly dispersed silicon phase particles within the three-dimensional network structure of the epoxy resin. These silicon phase particles effectively inhibit the initiation and growth of electrical trees, enabling the material to achieve a tracking resistance rating of CTI 600V or higher according to the IEC 60112 standard. This insulating cover is suitable for the insulation protection of high-voltage electrical equipment, transformer bushings, insulators, and other power equipment.

[0015] Preferably, the flame retardant performance of the insulating cover meets the UL94 V-0 requirement, with a limiting oxygen index greater than or equal to 32%.

[0016] Preferably, the tracking resistance of the insulating cover meets the requirement of a CTI value greater than or equal to 600V in the IEC 60112 standard.

[0017] Preferably, the volume resistivity of the insulating cover is greater than or equal to 1×10^15Ω·cm, and the dielectric strength is greater than or equal to 20MV / m.

[0018] Preferably, the flexural strength of the insulating cover is greater than or equal to 80 MPa, and the impact strength is greater than or equal to 15 kJ / m².

[0019] Preferably, the heat resistance rating of the insulating cover is F (155°C) or H (180°C).

[0020] This invention provides a casting process for a high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover, comprising the following steps:

[0021] P10: Mold design and manufacturing. Based on the size and structural requirements of the insulating cover, design and manufacture a metal mold with appropriate draft angle, injection port and vent. The mold material is high-quality carbon structural steel and the surface roughness Ra of the mold is not greater than 1.6μm.

[0022] P20: Mold pretreatment, thoroughly clean the mold to remove oil, rust and residue, then apply release agent and preheat the mold to the set temperature;

[0023] P30: Preparation of epoxy resin mixture: According to the preset formula ratio, epoxy resin matrix, flame retardant system, tracking modifier, flexible segment modifier, and silane coupling agent are added to the mixing equipment in sequence and mixed at the set temperature and speed. Then, curing agent and accelerator are added, and mixing is continued and vacuum degassing is performed to obtain casting material.

[0024] P40: Casting. The casting material prepared in step P30 is transferred to the casting equipment and injected into the preheated mold under vacuum or pressure assistance. During the casting process, the material temperature, casting speed and pressure are controlled.

[0025] P50: Curing. After filling the mold, transfer it to the curing oven and carry out the curing reaction according to the set heating curve and holding time to make the epoxy resin completely cured and molded.

[0026] P60: Demolding and post-processing. After curing, the mold is cooled to an appropriate temperature for demolding. The product is then deburred, dimensionally corrected, surface-treated, and its performance tested.

[0027] According to this invention, by precisely controlling every parameter in the casting process, including mold design, pretreatment temperature, mixing process, casting parameters, and curing curve, stable quality insulating shield products are ensured. The draft angle in the mold design is set to 3 to 5 degrees for easy demolding; the design of the injection port position and number ensures that the casting material can fill the cavity uniformly and quickly; the design of the venting port removes gas from the mold, avoiding the formation of bubbles and defects. Vacuum assistance or pressure assistance during the casting process can improve filling efficiency and reduce internal defects. Optimization of the curing process ensures a smooth curing reaction, reduces internal stress, and improves the dimensional accuracy and performance stability of the product.

[0028] Preferably, in step P10, the draft angle of the mold is 3 to 5 degrees, the injection port diameter is 8 to 15 mm, the vent diameter is 2 to 5 mm, and the mold parting surface adopts a labyrinth-type sealing structure.

[0029] Preferably, in step P20, the release agent is an organosilicon release agent, and the coating method is spraying or brushing. After coating, it is preheated at 80 to 100°C for 10 to 20 minutes to form a uniform film of release agent.

[0030] Preferably, in step P30, the mixing device is a vacuum planetary mixer with a mixing speed of 200 to 500 rpm, a vacuum degree of -0.08 to -0.095 MPa, and a total mixing time of 45 to 90 minutes.

[0031] Preferably, in step P40, the casting equipment is a vacuum casting machine or a pressure casting machine, the material temperature is controlled at 40 to 50°C, the casting speed is 10 to 50 g / s, and the casting pressure is 0.01 to 0.05 MPa.

[0032] Preferably, in step P50, the curing oven is a hot air circulating oven or an oil bath heating oven, with a temperature control accuracy of ±2℃.

[0033] Preferably, in step P60, the demolding temperature is 60 to 80°C, and the demolding method is mechanical ejection or air pressure ejection; the post-processing includes deburring, dimensional correction, cleaning, and surface spraying.

[0034] Preferably, the process also includes a quality inspection step, which involves visual inspection, dimensional measurement, electrical performance testing, and mechanical performance testing of the insulating cover after demolding. The electrical performance testing includes volume resistivity, dielectric strength, and tracking resistance testing, while the mechanical performance testing includes bending strength, impact strength, and hardness testing.

[0035] To improve the tracking resistance of epoxy resin, the tracking resistance modifier is an organosilicon compound containing an aromatic structure. The organosilicon compound containing an aromatic structure is chemically bonded to the three-dimensional network structure of epoxy resin through a silane coupling agent to form uniformly dispersed silicon phase particles.

[0036] According to the present invention, by introducing organosilicon segments containing aromatic structures into the epoxy resin molecular chain, the excellent electrical insulation properties and low dielectric constant of organosilicon compounds can effectively disperse and suppress the concentration of electrical stress under the action of an electric field. Simultaneously, the introduction of organosilicon segments forms a microphase separation structure after the epoxy resin is cured, with silicon phase particles uniformly dispersed in the continuous epoxy resin phase. These silicon phase particles have high volume resistivity and low dielectric constant, effectively preventing the initiation and growth path of electrical trees, thereby significantly improving the material's resistance to tracking. Furthermore, the presence of aromatic structures increases the thermal stability and flame retardancy of the organosilicon compounds, forming a synergistic effect with the flame-retardant system.

[0037] Preferably, the organosilicon compound containing an aromatic structure is phenyl silicone oil, phenyl silicone resin, or phenylmethylsilane, and its addition amount is 5% to 20% of the weight of the epoxy resin matrix.

[0038] Preferably, the silane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane, and its amount is 10% to 20% of the weight of the organosilicon compound.

[0039] Preferably, the chemical bonding reaction is carried out simultaneously during the epoxy resin curing process, with a curing temperature of 150 to 180°C and a curing time of 6 to 12 hours.

[0040] The insulating cover adopts a phosphorus-nitrogen synergistic flame retardant system, which includes a compound system of phosphorus-based flame retardants and nitrogen-based flame retardants. Utilizing the phosphorus-nitrogen synergistic flame retardant mechanism, a dense carbonized layer is formed during the epoxy resin curing process.

[0041] According to the present invention, a synergistic flame-retardant effect is utilized by combining phosphorus-based and nitrogen-based flame retardants. When heated, the phosphorus-based flame retardant decomposes to produce phosphoric acid, polyphosphoric acid, and other phosphoric acid-containing substances. These substances catalyze the dehydration and carbonization of epoxy resin, forming a carbonized layer on the material surface. The nitrogen-based flame retardant decomposes upon heating to produce non-flammable gases such as ammonia and nitrogen. These gases dilute the concentration of flammable gases and simultaneously assist the carbonized layer produced by the phosphorus-based flame retardant in expanding and foaming, forming a denser foamed carbonized layer. This carbonized layer has a low thermal conductivity, effectively blocking heat transfer and inhibiting further combustion of the material. The phosphorus-nitrogen synergistic effect significantly improves the flame-retardant efficiency compared to using phosphorus-based or nitrogen-based flame retardants alone. It achieves better flame-retardant effects at the same dosage while reducing the total amount of flame retardant added, thus minimizing adverse effects on the mechanical properties of the epoxy resin.

[0042] Preferably, the phosphorus-based flame retardant is triphenyl phosphate, tricresyl phosphate, or red phosphorus, and the amount added is 5% to 15% of the weight of the epoxy resin matrix.

[0043] Preferably, the nitrogen-based flame retardant is melamine, cyanurate, or guanidine salt, and the amount added is 10% to 20% of the weight of the epoxy resin matrix.

[0044] Preferably, the mass ratio of the phosphorus-based flame retardant to the nitrogen-based flame retardant is 1:2 to 2:1.

[0045] Preferably, the system also includes a synergistic flame retardant, wherein the synergistic flame retardant is at least one of zinc oxide, magnesium oxide or aluminum hydroxide, and the amount added is 5% to 10% of the total weight of the flame retardant system.

[0046] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0047] This invention utilizes the phosphorus-nitrogen synergistic flame retardant mechanism by combining phosphorus-based and nitrogen-based flame retardants to form a dense char layer during the epoxy resin curing process. This results in excellent flame retardant performance, with a limiting oxygen index greater than or equal to 32% and a flame retardant rating reaching UL94 V-0.

[0048] This invention utilizes an organosilicon compound containing an aromatic structure to chemically bond to a three-dimensional network structure of epoxy resin via a silane coupling agent, forming uniformly dispersed silicon phase microparticles. This effectively inhibits the initiation and growth of electrical trees, significantly improves resistance to tracking, and achieves a CTI value greater than or equal to 600V.

[0049] This invention increases the flexibility of epoxy resin cured products by introducing flexible segment modifiers, relieves internal stress during the curing process, and improves the impact resistance and dimensional stability of the products.

[0050] This invention achieves a smooth, high-density, and stable insulating shield product through optimized control of casting process parameters, including precise control of mold design, pretreatment temperature, mixing process, casting parameters, and curing curve.

[0051] The insulating cover provided by this invention has high resistance to tracking, flame retardancy, good mechanical properties and chemical corrosion resistance. It is suitable for insulation protection of power equipment such as high voltage electrical equipment, transformer bushings, and insulators, and has broad application prospects. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the composition of the high-resistance tracking and flame-retardant epoxy resin insulating cover provided in the embodiments of the present invention;

[0053] Figure 2 This is a schematic diagram of the casting process for a high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover provided in an embodiment of the present invention. Detailed Implementation

[0054] 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 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Example 1

[0056] Please refer to Figure 1 The high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover provided in this embodiment comprises the following components by weight: 100 parts of bisphenol A type epoxy resin, 15 parts of modified phenyl silicone oil, 12 parts of polyether polyol, 8 parts of triphenyl phosphate, 12 parts of melamine, 1.5 parts of γ-aminopropyltriethoxysilane, 40 parts of methylhexahydrophthalic anhydride, and 0.8 parts of 2-methylimidazole.

[0057] The specific parameters of the raw materials are as follows:

[0058] Bisphenol A type epoxy resin: epoxy value 0.51 mol / 100g;

[0059] Phenyl silicone oil: viscosity 500 mPa·s (25℃), phenyl content 20%;

[0060] Polyether polyols: number average molecular weight 2000;

[0061] Triphenyl phosphate: purity ≥99%;

[0062] Melamine: Purity ≥ 99.5%;

[0063] γ-aminopropyltriethoxysilane: purity ≥98%;

[0064] Methylhexahydrophthalic anhydride: acid value ≥650mgKOH / g;

[0065] 2-Methylimidazole: Purity ≥99%.

[0066] Preparation method:

[0067] Weigh each component according to the formula. 100g of phenyl silicone oil and 12g of γ-aminopropyltriethoxysilane were stirred and reacted at 70℃ under nitrogen protection for 2 hours, followed by vacuum distillation to obtain modified phenyl silicone oil. Bisphenol A type epoxy resin was heated to 70℃, and 15 parts of modified phenyl silicone oil, 12 parts of polyether polyol, 8 parts of triphenyl phosphate, and 12 parts of melamine were added. The mixture was stirred at 300rpm for 45 minutes and then degassed under vacuum for 15 minutes. 40 parts of methylhexahydrophthalic anhydride and 0.8 parts of 2-methylimidazole were added, and the mixture was stirred at 200rpm for 15 minutes and then degassed under vacuum for 8 minutes. The mold was preheated to 50℃, coated with a release agent, and poured under a vacuum of -0.09MPa at a material temperature of 45℃. Curing process: 90℃ / 3h → 130℃ / 6h → 160℃ / 3h. An insulating shield was obtained after demolding.

[0068] Example 2

[0069] This embodiment provides a high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover, which, by weight, comprises the following components: 100 parts of bisphenol F type epoxy resin, 18 parts of modified phenyl silicone resin, 10 parts of polyester polyol, 10 parts of tricresyl phosphate, 15 parts of cyanurate, 1.8 parts of γ-glycidyl etheroxypropyltrimethoxysilane, 45 parts of methyltetrahydrophthalic anhydride, and 0.9 parts of 2-ethyl-4-methylimidazole.

[0070] The specific parameters of the raw materials are as follows:

[0071] Bisphenol F type epoxy resin: epoxy value 0.65mol / 100g.

[0072] Phenyl silicone resin: viscosity is 800 mPa·s.

[0073] Polyester polyol: Number average molecular weight 1500.

[0074] Trimethylbenzene phosphate: Industrial grade.

[0075] Cyanurate: Industrial grade.

[0076] γ-glycidyl etheroxypropyltrimethoxysilane: purity ≥98%.

[0077] Methyltetrahydrophthalic anhydride: Acid value ≥ 650 mg KOH / g.

[0078] 2-Ethyl-4-methylimidazole: Purity ≥99%.

[0079] The preparation method is the same as in Example 1, except that: the pretreatment temperature is 75℃ and the stirring time is 2.5 hours; during mixing, the flame retardant system is first premixed with the flexible segment modifier, and the mixing operation is carried out at a temperature of 45℃ for 20 minutes; the curing process is: 100℃ / 2.5h → 140℃ / 5h → 170℃ / 2.5h.

[0080] Example 3

[0081] This embodiment provides a high resistance to tracking and flame retardant epoxy resin insulating cover, which, by weight, comprises the following components: 100 parts phenolic epoxy resin, 12 parts modified phenylmethylsilane, 14 parts hydroxyl-terminated liquid nitrile rubber, 5 parts red phosphorus, 18 parts melamine, 1.2 parts γ-aminopropyltriethoxysilane, 48 parts tung oil anhydride, and 0.5 parts benzyl dimethylamine.

[0082] The specific parameters of the raw materials are as follows:

[0083] Phenolic epoxy resin: epoxy value 0.85mol / 100g.

[0084] Phenylmethylsilane: Industrial grade.

[0085] Hydroxyl-terminated liquid nitrile rubber: number average molecular weight 2500.

[0086] Red phosphorus: Microencapsulated red phosphorus.

[0087] Tung oil anhydride: acid value ≥ 680 mg KOH / g.

[0088] Benzyldimethylamine: Purity ≥ 99%.

[0089] The preparation method is the same as in Example 1, and the curing process is: 85℃ / 4h→125℃ / 7h→155℃ / 4h.

[0090] Example 4

[0091] This embodiment provides a high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover, which, by weight, comprises the following components: 70 parts of bisphenol A epoxy resin, 30 parts of bisphenol F epoxy resin, 15 parts of modified phenyl silicone oil, 12 parts of polyether polyol, 8 parts of triphenyl phosphate, 12 parts of melamine, 1.5 parts of γ-aminopropyltriethoxysilane, 42 parts of methylhexahydrophthalic anhydride, and 0.63 parts of 2-methylimidazole.

[0092] The raw material parameters are the same as in Examples 1 and 2. The preparation method is the same as in Example 1.

[0093] Example 5

[0094] This embodiment provides a high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover, which, by weight, comprises the following components: 100 parts of bisphenol A type epoxy resin, 16 parts of modified phenyl silicone oil, 13 parts of polyether polyol, 9 parts of triphenyl phosphate, 14 parts of melamine, 1.5 parts of zinc oxide, 1.6 parts of γ-aminopropyltriethoxysilane, 42 parts of methylhexahydrophthalic anhydride, and 0.63 parts of 2-methylimidazole.

[0095] The zinc oxide particles were 50 nm in diameter. The preparation method was the same as in Example 1.

[0096] Comparative Example 1

[0097] This comparative example provides an epoxy resin insulating cover without a flame-retardant system, comprising the following components by weight: 100 parts bisphenol A type epoxy resin, 15 parts modified phenyl silicone oil, 12 parts polyether polyol, 1.5 parts γ-aminopropyltriethoxysilane, 40 parts methylhexahydrophthalic anhydride, and 0.8 parts 2-methylimidazole. The preparation method is the same as in Example 1, except that triphenyl phosphate and melamine are not added in the second step.

[0098] Comparative Example 2

[0099] This comparative example provides an epoxy resin insulating shield without added tracking-resistant modifier, comprising the following components by weight: 100 parts bisphenol A type epoxy resin, 12 parts polyether polyol, 8 parts triphenyl phosphate, 12 parts melamine, 1.5 parts γ-aminopropyltriethoxysilane, 40 parts methylhexahydrophthalic anhydride, and 0.8 parts 2-methylimidazole. The preparation method is the same as in Example 1, except that no modified organosilicon compound is added in the second step.

[0100] Comparative Example 3

[0101] This comparative example provides an epoxy resin insulating shield that uses ordinary silicone oil instead of organosilicon compounds containing aromatic structures. By weight, it comprises the following components: 100 parts bisphenol A type epoxy resin, 15 parts ordinary dimethyl silicone oil modified with γ-aminopropyltriethoxysilane, 12 parts polyether polyol, 8 parts triphenyl phosphate, 12 parts melamine, 1.5 parts γ-aminopropyltriethoxysilane, 40 parts methylhexahydrophthalic anhydride, and 0.8 parts 2-methylimidazole. The preparation method is the same as in Example 1, except that ordinary dimethyl silicone oil is used instead of phenyl silicone oil in the first step.

[0102] Example 1 V-0 34 650 2.1×10^15 22 88 16 F Example 2 V-0 35 680 1.8×10^15 23 85 17 F Example 3 V-0 36 720 2.5×10^15 24 82 15 H Example 4 V-0 33 620 1.9×10^15 21 90 18 F Example 5 V-0 38 660 2.0×10^15 22 86 16 F Comparative Example 1 No grade 24 580 2.3×10^15 23 92 14 F Comparative Example 2 V-0 35 380 2.0×10^15 22 87 15 F Comparative Example 3 V-0 34 420 1.9×10^15 21 88 16 F

[0103] Test Methods: UL94 rating is tested according to UL94-2013 standard; limiting oxygen index is tested according to GB / T2406.2-2009 standard; CTI value is tested according to IEC 60112 standard; volume resistivity is tested according to GB / T1410-2006 standard; dielectric strength is tested according to GB / T 1408.1-2006 standard; flexural strength is tested according to GB / T 9341-2008 standard; impact strength is tested according to GB / T 1843-2008 standard; heat resistance rating is tested according to GB / T 11021-2015 standard.

[0104] According to the test results in the table above, the insulating covers prepared in Examples 1 to 5 of this invention have excellent flame retardant properties and resistance to tracking. Comparative Example 1, without the addition of a flame retardant system, has a limiting oxygen index of only 24%, failing the UL94 V-0 rating test, indicating that the addition of a flame retardant system is crucial for improving the flame retardant properties of epoxy resin. Comparative Example 2, without the addition of a tracking-resistant modifier, has a CTI value of only 380V, indicating that the addition of a tracking-resistant modifier is crucial for improving the tracking-resistant properties of epoxy resin. Comparative Example 3, using ordinary dimethyl silicone oil instead of an organosilicon compound containing an aromatic structure, has a CTI value of only 420V, indicating that an organosilicon compound containing an aromatic structure has a significant effect on improving tracking-resistant properties, and ordinary silicone oil cannot achieve the same modification effect.

[0105] Examples 1 to 5 all have a CTI value greater than or equal to 600V, meeting the CTI 600V requirement of the IEC 60112 standard; their limiting oxygen index is greater than or equal to 32%, and their flame retardancy rating reaches UL94 V-0. Furthermore, Examples 1 to 5 have a volume resistivity greater than or equal to 1×10^15 Ω·cm, dielectric strength greater than or equal to 20MV / m, flexural strength greater than or equal to 80MPa, and impact strength greater than or equal to 15kJ / m², and a heat resistance rating of F (155℃) or H (180℃). Their basic performance meets the requirements for use as insulating covers for high-voltage electrical equipment.

[0106] Example 6

[0107] Please refer to Figure 2 Mold design for casting molding process: In the casting molding process of insulating covers, mold design is a crucial step in ensuring product quality. The following examples illustrate the key points of mold design.

[0108] Mold Design and Manufacturing: The insulating cover mold consists of three parts: an upper mold, a lower mold, and a mold sleeve. The mold material is high-quality carbon structural steel with a surface roughness Ra of 1.2μm. The draft angle of the mold is designed to be 4 degrees for easy demolding. Two injection ports, each 12mm in diameter, are located at the top center of the insulating cover. Six vents, each 3mm in diameter, are evenly distributed along the edges of the mold. The mold parting surface employs a labyrinth-type sealing structure to ensure sealing performance.

[0109] Mold pretreatment: Thoroughly clean the mold to remove oil, rust, and residue. Then apply an organosilicon release agent by spraying to a thickness of 12 μm. After coating, preheat at 90°C for 15 minutes to allow the release agent to form a uniform film.

[0110] Preparation of epoxy resin mixture: According to the preset formula ratio, such as any ratio in Examples 1 to 5, the epoxy resin matrix, flame retardant system, tracking modifier, flexible segment modifier, and silane coupling agent are sequentially added to a mixing device. The tracking modifier is an organosilicon compound containing an aromatic structure, which is chemically bonded to the three-dimensional network structure of the epoxy resin through the silane coupling agent to form uniformly dispersed silicon phase particles. The mixing device is a vacuum planetary mixer with a stirring speed of 300 rpm, a vacuum degree of -0.09 MPa, and a total mixing time of 60 minutes. Then, the curing agent and accelerator are added, and mixing continues followed by vacuum degassing to obtain the casting material.

[0111] Casting: Transfer the prepared casting material to the casting equipment, using a vacuum casting machine or a pressure casting machine. The material temperature is controlled at 45℃, the casting speed is 25g / s, and the casting pressure is 0.03MPa. Under vacuum assistance, the casting material is injected into a preheated mold, maintaining a vacuum level of -0.09MPa inside the mold. After casting, the mold is kept under vacuum for 8 minutes to remove dissolved gases.

[0112] Curing: Transfer the filled mold to a curing oven, which is a hot air circulating oven with a temperature control accuracy of ±2℃. Perform the curing reaction according to the following segmented temperature rise curve:

[0113] Heat from room temperature to 90°C at a rate of 2°C / min, and hold for 3 hours;

[0114] Continue to increase the temperature to 130℃ at a rate of 1.5℃ / min, and hold for 6 hours;

[0115] Finally, the temperature is increased to 160℃ at a rate of 0.8℃ / min and held for 3 hours.

[0116] After curing, it is cooled to below 60°C in the oven.

[0117] Demolding and post-processing: After curing, cool the mold to the demolding temperature of 60-80℃ and demold using mechanical or pneumatic ejection. Post-processing of the product: remove burrs, correct dimensions, clean, and apply a surface coating, including a moisture-proof and insulating coating, followed by performance testing.

[0118] Surface treatment: The insulating cover after demolding undergoes surface treatment, as follows:

[0119] Surface Treatment Example 1: After the insulating cover was demolded, its surface was sanded and cleaned, and then a layer of silicone sealant was applied as a moisture-proof and insulating coating. The coating was applied by brushing, and the coating thickness was 30 μm. After application, it was cured at room temperature for 24 hours.

[0120] Surface Treatment Example 2: After sanding and cleaning the surface of the demolded insulating cover, a layer of polyurethane anti-corrosion coating is applied as a moisture-proof and insulating coating. The coating is applied by spraying and has a thickness of 40 μm. After coating, it is cured at 80°C for 2 hours.

[0121] In this quality inspection example, the quality inspection of the insulating cover is carried out as follows:

[0122] Visual inspection: Inspect the surface of the insulating cover for defects such as bubbles, cracks, and missing material. The insulating covers prepared in Examples 1 to 5 have smooth surfaces with no visible defects.

[0123] Dimensional Measurement: Measure the critical dimensions of the insulating cover, including inner diameter, outer diameter, and height. Dimensional deviations should be controlled within ±0.5mm.

[0124] Electrical performance testing included volume resistivity testing, dielectric strength testing, and tracking resistance testing. The insulating covers prepared in Examples 1 to 5 all met the requirements.

[0125] Mechanical performance tests included bending strength, impact strength, and hardness testing. The insulating covers prepared in Examples 1 to 5 all met the requirements.

[0126] The precisely controlled casting process described above, including mold design and pretreatment, vacuum-assisted casting, segmented temperature curing, post-treatment, and quality inspection, produces an insulating cover with high density, low internal stress, excellent dimensional stability, and reliable electrical insulation performance, fully meeting the comprehensive requirements of high-voltage electrical equipment for insulating covers.

[0127] Based on the test results of Examples 1 to 5 and Comparative Examples 1 to 3, the high tracking resistance and flame-retardant epoxy resin insulating cover provided by this invention exhibits excellent flame-retardant properties, tracking resistance, and comprehensive mechanical properties. By introducing an organosilicon compound containing an aromatic structure into the epoxy resin system and utilizing a silane coupling agent to achieve chemical grafting between the compound and the epoxy resin molecular chain, uniformly dispersed silicon phase particles can be formed in the cured three-dimensional network structure, thereby effectively suppressing tracking and electrical treeing, and significantly improving the CTI value of the material. Simultaneously, the phosphorus-based flame retardant and the nitrogen-based flame retardant form a synergistic flame-retardant system, effectively enhancing the flame-retardant performance of the material, enabling the resulting insulating cover to achieve a UL94 V-0 flame-retardant rating. The addition of a flexible segment modifier further reduces the internal stress during the material curing process, improving the bending strength, impact strength, and dimensional stability of the product. By adopting vacuum casting and segmented curing processes, the internal bubbles and defects of the product can be effectively reduced, and the density, electrical insulation performance and molding stability of the insulating cover can be improved, so that it can meet the usage requirements in the field of insulation protection for high-voltage electrical equipment.

[0128] Furthermore, the mold structure design in Example 6 further improves the product molding quality. By setting up an upper mold, lower mold, and mold sleeve combination structure, and adopting a labyrinth-type parting surface sealing structure, the sealing performance during the casting process can be effectively improved, reducing resin leakage and air ingress. The mold surface roughness is controlled at Ra1.2μm, and with a 4-degree draft angle design, the demolding smoothness can be effectively improved, reducing surface scratches and edge defects on the product. By setting two 12mm diameter injection ports at the center of the top of the mold and six 3mm diameter vents evenly distributed along the edge of the mold, the uniformity of resin flow and venting efficiency can be effectively improved, reducing internal air bubbles, shrinkage cavities, and localized material shortages in the product, thereby improving the overall density and dimensional accuracy of the insulating cover.

[0129] Regarding the casting process, this invention employs a vacuum planetary mixer to mix the epoxy resin system, controlling the stirring speed at 300 rpm, the vacuum degree at -0.09 MPa, and the mixing time at 60 minutes. This effectively improves the dispersion uniformity of the flame retardant system, tracking-resistant modifier, and flexible segment modifier in the epoxy resin, preventing filler agglomeration. Furthermore, the use of a vacuum casting process, controlling the material temperature at 45℃, the casting pressure at 0.03 MPa, and the casting speed at 25 g / s, effectively reduces air bubble entrainment and uneven local curing during casting, improving the internal structural uniformity and electrical insulation performance of the product.

[0130] Regarding the curing process, this invention employs a staged heating and curing method, combined with a hot air circulating oven for precise temperature control, achieving a temperature control accuracy of ±2℃. This staged curing process effectively reduces the internal stress and curing shrinkage caused by the rapid cross-linking of epoxy resin, improving the dimensional stability and structural integrity of the product and reducing defects such as cracking and warping. Simultaneously, in subsequent surface treatment, coating the surface of the insulating cover with silicone sealant or polyurethane anti-corrosion coating further enhances the product's moisture resistance, corrosion resistance, and surface insulation properties, ensuring that the insulating cover maintains stable and reliable insulation protection even in high humidity, high salt spray, and complex outdoor operating environments.

[0131] In summary, through the synergistic combination of material system design, mold structure optimization, vacuum casting process, segmented curing process, and surface protection treatment, this invention not only effectively improves the flame retardant performance, tracking resistance, and mechanical properties of the insulating cover, but also significantly improves the internal density, dimensional stability, and long-term service reliability of the product, making it more suitable for insulation protection of high-voltage switchgear, cable branch boxes, ring main units, and other high-voltage electrical equipment.

[0132] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover, characterized in that, The product comprises the following components in parts by weight: 100 parts epoxy resin matrix, 15 to 35 parts flame retardant system, 5 to 20 parts tracking resistant modifier, 8 to 15 parts flexible segment modifier, 1 to 3 parts silane coupling agent, 30 to 50 parts curing agent, and 0.2 to 2.0 parts accelerator; wherein the flame retardant system includes a compound of phosphorus-based flame retardant and nitrogen-based flame retardant, with a mass ratio of phosphorus-based flame retardant to nitrogen-based flame retardant of 1:2 to 2:1; the tracking resistant modifier is an organosilicon compound containing an aromatic structure.

2. The high resistance to tracking and flame retardant epoxy resin insulating cover according to claim 1, characterized in that, The epoxy resin matrix is ​​at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, or phenolic epoxy resin, and its epoxy value is from 0.50 to 0.95 mol / 100g.

3. The high resistance to tracking and flame retardant epoxy resin insulating cover according to claim 1, characterized in that, The phosphorus-based flame retardant is at least one of triphenyl phosphate, tricresyl phosphate, diphenyl phosphate, or red phosphorus; the nitrogen-based flame retardant is at least one of melamine, cyanurate, or guanidine salt.

4. The high resistance to tracking and flame retardant epoxy resin insulating cover according to claim 1, characterized in that, The organosilicon compound containing an aromatic structure is at least one of phenyl silicone oil, phenyl silicone resin, or phenylmethylsilane, and its viscosity is 100 to 1000 mPa∙s at a temperature of 25°C; the flexible segment modifier is at least one of polyether polyol, polyester polyol, or hydroxyl-terminated liquid nitrile rubber, and its number average molecular weight is 500 to 3000.

5. The high resistance to tracking and flame retardant epoxy resin insulating cover according to claim 1, characterized in that, The organosilicon compound containing an aromatic structure is chemically bonded to the three-dimensional network structure of the epoxy resin through a silane coupling agent to form uniformly dispersed silicon phase particles; the silane coupling agent is at least one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

6. The high resistance to tracking and flame retardant epoxy resin insulating cover according to claim 1, characterized in that, The accelerator is at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole or benzyldimethylamine, and is used in an amount of 0.5% to 2% of the weight of the curing agent.

7. A casting process for a high-resistance, tracking-resistant, flame-retardant epoxy resin insulating cover as described in any one of claims 1-6, characterized in that, Includes the following steps: P10: Mold design and manufacturing. Based on the size and structural requirements of the insulating cover, design and manufacture metal molds with draft angles, injection ports and vents. P20: Mold pretreatment, cleaning the mold to remove oil and residue, then applying a release agent and preheating the mold to the set temperature; P30: Preparation of epoxy resin mixture: According to the preset formula ratio, epoxy resin matrix, flame retardant system, tracking modifier, flexible segment modifier, and silane coupling agent are added to the mixing equipment in sequence and mixed at the set temperature and speed. Then, curing agent and accelerator are added, and mixing is continued and vacuum degassing is performed to obtain casting material. P40: Casting. The casting material prepared in step P30 is transferred to the casting equipment and injected into the preheated mold under vacuum or pressure assistance. During the casting process, the material temperature, casting speed and pressure are controlled. P50: Curing. The mold after filling is transferred to the curing oven and the curing reaction is carried out according to the set temperature rise curve and holding time. P60: Demolding and post-processing. After curing, the mold is cooled to an appropriate temperature for demolding. The product is then deburred, dimensionally corrected, surface-treated, and its performance tested.

8. The casting process for the high tracking resistance and flame retardant epoxy resin insulating cover according to claim 7, characterized in that, In step P10, the draft angle of the mold is 3 to 5 degrees, the injection port diameter is 8 to 15 mm, and the venting port diameter is 2 to 5 mm.

9. The casting process for the high tracking resistance and flame retardant epoxy resin insulating cover according to claim 7, characterized in that, In step P30, the mixing equipment is a vacuum planetary mixer with a mixing speed of 200 to 500 rpm, a vacuum degree of -0.08 to -0.095 MPa, and a total mixing time of 45 to 90 minutes.

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