Low-heat-release epoxy insulating resin and preparation method thereof

Abstract

The application belongs to the technical field of epoxy insulation materials, and particularly relates to a low-heat-release high-toughness epoxy insulation resin and a preparation method thereof. The preparation method takes epoxy resin, a chain extender, a compounded catalyst and an acid anhydride curing agent as raw materials. The compounded catalyst is used for synergistic regulation in the chain extension stage, so that the molecular structure design is realized by mainly linear chain extension and moderately branched chain extension, the epoxy value is reduced, and the toughness is improved. In the curing stage, the difference in starting temperature of the two catalysts is used to realize step-by-step curing, so that the heat release peak value and internal stress are effectively reduced. Finally, the chain extension-curing two-stage synergistic regulation is realized, and the obtained cured product has high glass transition temperature, excellent electrical insulation performance and good mechanical toughness, and is suitable for large-thickness and large-size casted electrical insulation components.

Description

Technical Field

[0001] This invention belongs to the technical field of epoxy insulation materials, specifically relating to a low-heat, high-toughness epoxy insulation resin and its preparation method. Background Technology

[0002] Epoxy resin, as an important thermosetting polymer material, is widely used in high-voltage electrical insulation fields due to its excellent mechanical properties, electrical insulation properties, and chemical corrosion resistance. Examples include ultra-high voltage (UHV) insulation components and pot-type insulators in gas-insulated switchgear (GIS). With the development of power equipment towards UHV and large capacity, the application of epoxy resin as an insulating material is receiving increasing attention, especially in large cast-molded insulating components where the performance requirements for epoxy resin are becoming increasingly stringent. Traditional bisphenol A type epoxy resins (such as E51) typically have a high epoxy value, which, while beneficial for forming a dense cross-linked network, also leads to a violent reaction during curing, releasing a large amount of heat. This violent exothermic reaction generates a large temperature difference within the resin, inducing internal stress and causing cracks or fissures in the insulating components during curing. These cracks not only affect insulation performance but also significantly reduce the mechanical properties and long-term reliability of the insulating components, and in severe cases, may even lead to insulation failure, affecting the safe operation of power equipment.

[0003] In existing technologies, traditional epoxy resin modification techniques primarily reduce the heat released during curing by lowering the epoxy value of the epoxy resin. Industrially, bisphenol A is commonly used for chain extension modification of epoxy resins. Through the reaction of some epoxy groups with bisphenol A, the epoxy value of the resin is reduced, thereby reducing the total heat release during curing and alleviating internal stress. Such modified resins (such as Huntsman's 5531 long-chain epoxy resin) have been used in large-scale insulation equipment. However, simple chain extension modification, while reducing the epoxy value, often significantly reduces the crosslinking density of the material, leading to a decrease in heat resistance, mechanical strength, and insulation performance. Especially when the epoxy value decreases to a certain level, key properties such as the glass transition temperature (Tg), toughness, and volume resistivity may deteriorate significantly, making it difficult to meet the comprehensive requirements of high-performance insulation materials. Therefore, current modified resins cannot synergistically solve the problem of reducing the epoxy value without compromising the material's heat resistance, mechanical strength, and insulation strength. Summary of the Invention

[0004] In view of this, one objective of the present invention is to provide a method for preparing a low-exothermic, high-toughness epoxy insulating resin. This method utilizes a dual-catalyst formulation and controlled dosage to achieve a molecular structure design with linear chain extension as the primary pathway and moderate branching as a secondary pathway during the chain extension stage, thereby reducing the epoxy value and improving toughness. During the curing stage, the difference in the initiation temperatures of the two catalysts is used to achieve stepwise curing, reducing the exothermic peak and minimizing defects caused by internal stress during curing. By controlling the synergistic effect of the chain extension and curing stages through dual-catalyst formulation, the problem of simultaneously achieving both toughness and low exothermicity in existing technologies is solved.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a low-heat, high-toughness epoxy insulating resin, comprising the following steps: (1) Mix 100 parts by weight of epoxy resin, 10-30 parts by weight of chain extender and 0.01-0.08 parts by weight of compound catalyst, and carry out chain extension reaction under heating conditions to obtain modified epoxy resin with reduced epoxy value; the compound catalyst is a combination of quaternary ammonium salt catalyst and phosphorus catalyst in a mass ratio of (0.25-4):1. (2) The modified epoxy resin obtained in step (1) is mixed with 30 to 60 parts by weight of curing agent, and heated, stirred and vacuum degassed to obtain a uniform resin mixture. (3) Pour the resin mixture into the mold, heat and cure it in stages, and demold it after cooling to obtain the epoxy insulating resin.

[0006] Further improvements to the preparation method of low-heat, high-toughness epoxy insulating resin: Preferably, the epoxy resin is selected from one or a combination of two or more of bisphenol A type epoxy resin and bisphenol F type epoxy resin.

[0007] Preferably, the chain extender is a bisphenol chain extender.

[0008] Preferably, the bisphenol chain extender is bisphenol A.

[0009] Preferably, the composite catalyst is a combination of quaternary ammonium salt catalyst and phosphorus catalyst in a mass ratio of (0.25~4):1.

[0010] Preferably, the quaternary ammonium salt catalyst is benzyltriethylammonium chloride, and the phosphorus catalyst is triphenylphosphine.

[0011] Preferably, the curing agent is selected from one or more combinations of acid anhydride curing agents.

[0012] Preferably, in step (1), the chain extension reaction temperature is 80~160℃ and the reaction time is 1~8 hours; the epoxy value of the modified epoxy resin is 0.20~0.40 eq / 100g.

[0013] Preferably, in step (2), the mixing temperature is 80~120℃, the mixing time is 0.5~1.5 hours, and the vacuum degassing pressure is not less than -0.1 MPa.

[0014] Preferably, the curing in step (3) is carried out in three stages: the first stage is cured at 80~110℃ for 2~5 hours; the second stage is cured at 110℃~130℃ for 2~5 hours; and the third stage is cured at 130~150℃ for 8~12 hours.

[0015] A second objective of this invention is to provide a low-heat, high-toughness epoxy insulating resin prepared by any of the above-described preparation methods.

[0016] A third objective of this invention is to provide an application of the aforementioned low-heat, high-toughness epoxy insulating resin in the preparation of insulating components for electrical equipment.

[0017] The advantages of this invention compared to the prior art are as follows: (1) The present invention relates to a method for preparing a low-heat, high-toughness epoxy insulating resin, wherein the raw materials of the epoxy insulating resin include epoxy resin, chain extender, compound catalyst and curing agent; wherein the compound catalyst is composed of a first catalyst and a second catalyst, and is used to synergistically regulate the chain extension modification process of epoxy resin, and is introduced into the chain extension modification stage and remains in the resin system to synergistically regulate the subsequent curing reaction path and the formation of crosslinking network.

[0018] The first catalyst mainly promotes linear chain extension and can induce the formation of a suitable amount of branched structure. The degree of branching can be moderately controlled by adjusting its dosage. The second catalyst also mainly promotes linear chain extension, but its branching ability is weaker and it has a higher start-up temperature in the curing stage, which can initiate the curing reaction step by step and effectively reduce instantaneous exothermic reaction.

[0019] Figure 1This is a schematic diagram illustrating the preparation mechanism of a low-exothermic, high-toughness epoxy insulating resin according to the present invention. The present invention employs a combination of a first catalyst and a second catalyst with different reaction selectivity and catalytic activity to achieve precise construction of the epoxy resin molecular structure during the chain extension modification stage, primarily using linear chain extension while introducing an appropriate amount of branched structures. This strategy effectively reduces the epoxy value and decreases the total heat of curing. Simultaneously, the introduced branched structure molecules, due to their typically greater than 2 effective functionality, can construct a more diverse and uniform cross-linked network topology during curing, contributing to uniform stress distribution and avoiding localized stress concentration. The flexible segments introduced in the branched structure can effectively absorb and dissipate mechanical energy under external force through segment movement, slippage, and conformational changes, significantly inhibiting crack initiation and propagation, thereby achieving a significant improvement in toughness without reducing the overall strength of the material.

[0020] During the preparation process, the residual composite catalyst in the system continues to exert a catalytic effect in the subsequent anhydride curing stage. The two catalysts have different initiation temperatures and catalytic pathways in the curing reaction, inducing stepwise, orderly ring-opening of epoxy groups and the gradual construction of a cross-linked network. This moderates the exothermic rate of the curing reaction, reducing the instantaneous exothermic peak and the resulting internal thermal stress. This regulation of curing kinetics avoids micro-defects caused by excessively rapid curing and synergistically improves the mechanical toughness, glass transition temperature, and electrical insulation strength of the cured product. Its overall performance is superior to single-catalyst modified systems and traditional commercial long-chain epoxy resins.

[0021] (2) The low-heat-exothermic and high-toughness epoxy insulating resin obtained in this application has a high glass transition temperature (Tg not lower than 120℃), excellent electrical insulation performance and good mechanical toughness. It is suitable for casting and molding of electrical equipment insulation components with large thickness and large size, including but not limited to basin insulators, ultra-high voltage insulation pillars, dry transformer winding insulation and insulation bushings in gas-insulated switchgear (GIS). Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the preparation mechanism of a low-heat, high-toughness epoxy insulating resin according to the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] Example 1

[0025] This embodiment provides a method for preparing a low-heat, high-toughness epoxy insulating resin, comprising the following steps: (1) Chain extension modification: 100 g of bisphenol A type epoxy resin (DER331, epoxy value 0.53 eq / 100g), 20 g of bisphenol A chain extender (BPA) and 0.06 g of compound catalyst were mixed, heated to 150℃ to completely dissolve bisphenol A, and reacted for 3 hours under mechanical stirring at 300 rpm to obtain modified epoxy resin with reduced epoxy value. The compound catalyst consists of 0.03 g of triethylbenzylammonium chloride (TEBAC) and 0.03 g of triphenylphosphine (PPh3).

[0026] (2) Preparation of resin mixture: The modified epoxy resin obtained in step (1) was mixed with 42.4 g of methyltetrahydrophthalic anhydride (MeTHPA) curing agent at 100°C and stirred at 300 rpm for 30 minutes. Then, the mixture was degassed under a vacuum of -0.1 MPa for 30 minutes until no visible bubbles were found in the system, resulting in a homogeneous resin mixture.

[0027] (3) Curing and molding: The resin mixture was poured into a mold preheated to 100°C and placed in an oven for curing according to the following procedure: first, pre-curing at 100°C for 4 hours, then increasing the temperature to 120°C and curing for 4 hours, and finally continuing to cure at 140°C for 10 hours. After curing, the mixture was allowed to cool naturally to room temperature and then demolded to obtain the epoxy insulating resin.

[0028] Example 2

[0029] This embodiment provides a method for preparing a low-heat, high-toughness epoxy insulating resin. The specific steps are the same as in embodiment 1, except that the compound catalyst in step (1) is composed of 0.045 g of triethylbenzylammonium chloride (TEBAC) and 0.015 g of triphenylphosphine (PPh3).

[0030] Finally, a low-heat-exothermic, high-toughness epoxy insulating resin was obtained.

[0031] Example 3

[0032] This embodiment provides a method for preparing a low-heat, high-toughness epoxy insulating resin. The specific steps are the same as in embodiment 1, except that the epoxy resin in step (1) is a bisphenol F type epoxy resin (NPEF-170, epoxy value 0.58 eq / 100g).

[0033] Finally, a low-heat-exothermic, high-toughness epoxy insulating resin was obtained.

[0034] Example 4

[0035] This embodiment provides a method for preparing a low-heat, high-toughness epoxy insulating resin. The specific steps are the same as in embodiment 1, except that methyl hexahydrophthalic anhydride (MeTHPA) curing agent is used in step (2).

[0036] Finally, a low-heat-exothermic, high-toughness epoxy insulating resin was obtained.

[0037] Example 5

[0038] This embodiment provides a method for preparing a low-heat, high-toughness epoxy insulating resin. The specific steps are the same as in embodiment 1, except that in step (3), the resin is first pre-cured at 80°C for 4 hours, then heated to 120°C for 4 hours, and finally cured at 140°C for 10 hours. After curing, the resin is naturally cooled to room temperature and demolded to obtain the epoxy insulating resin.

[0039] Example 6

[0040] This embodiment provides a method for preparing a low-heat, high-toughness epoxy insulating resin. The specific steps are the same as in embodiment 1, except that 30g of bisphenol A (BPA) chain extender is added in step (1).

[0041] Finally, a low-heat-exothermic, high-toughness epoxy insulating resin was obtained.

[0042] Example 7

[0043] This embodiment provides a method for preparing a low-heat, high-toughness epoxy insulating resin, comprising the following steps: (1) Chain extension modification: 100 g of bisphenol A type epoxy resin (DER331, epoxy value 0.53 eq / 100g), 10 g of bisphenol A chain extender (BPA) and 0.01 g of compound catalyst were mixed, heated to 80℃ to completely dissolve bisphenol A, and reacted for 1 hour under mechanical stirring at 300 rpm to obtain modified epoxy resin with reduced epoxy value. Its epoxy value was measured to be 0.38 eq / 100g. The compound catalyst consists of 0.002 g benzyltriethylammonium chloride (TEBAC) and 0.008 g triphenylphosphine (PPh3), with a mass ratio of 0.25:1.

[0044] (2) Preparation of resin mixture: The modified epoxy resin obtained in step (1) was mixed with 30 g of methyltetrahydrophthalic anhydride (MeTHPA) curing agent at 80°C and stirred at 300 rpm for 1.5 hours. Then, the mixture was degassed under a vacuum of -0.1 MPa for 30 minutes until no visible bubbles were visible in the system, resulting in a homogeneous resin mixture.

[0045] (3) Curing and molding: The resin mixture was poured into a mold preheated to 80°C and placed in an oven for curing according to the following procedure: first, pre-curing at 80°C for 2 hours, then increasing the temperature to 110°C and curing for 2 hours, and finally continuing to cure at 130°C for 8 hours. After curing, the mixture was allowed to cool naturally to room temperature and then demolded to obtain the epoxy insulating resin.

[0046] Example 8

[0047] This embodiment provides a method for preparing a low-heat, high-toughness epoxy insulating resin, comprising the following steps: (1) Chain extension modification: 100 g of bisphenol A type epoxy resin (DER331, epoxy value 0.53 eq / 100g), 30 g of bisphenol A chain extender (BPA) and 0.08 g of compound catalyst were mixed, heated to 160℃ to completely dissolve bisphenol A, and reacted for 8 hours under mechanical stirring at 300 rpm to obtain modified epoxy resin with reduced epoxy value. Its epoxy value was measured to be 0.22 eq / 100g. The compound catalyst consists of 0.064 g benzyltriethylammonium chloride (TEBAC) and 0.016 g triphenylphosphine (PPh3) in a mass ratio of 4:1.

[0048] (2) Preparation of resin mixture: The modified epoxy resin obtained in step (1) was mixed with 60 g of methyltetrahydrophthalic anhydride (MeTHPA) curing agent at 120°C and stirred at 300 rpm for 1.5 hours. Then, the mixture was degassed under a vacuum of -0.1 MPa for 30 minutes until no visible bubbles were visible in the system, resulting in a homogeneous resin mixture.

[0049] (3) Curing and molding: The resin mixture was poured into a mold preheated to 110°C and placed in an oven for curing according to the following procedure: first, pre-curing at 110°C for 5 hours, then increasing the temperature to 130°C and curing for 5 hours, and finally continuing to cure at 150°C for 12 hours. After curing, the mixture was allowed to cool naturally to room temperature and then demolded to obtain the epoxy insulating resin.

[0050] Comparative Example 1

[0051] This comparative example provides a method for preparing a low-heat, high-toughness epoxy insulating resin. The specific steps are the same as in Example 1, except that the compound catalyst in step (1) is replaced with 0.06 g of triphenylphosphine (PPh3).

[0052] Comparative Example 2

[0053] This comparative example provides a method for preparing a low-heat, high-toughness epoxy insulating resin. The specific steps are the same as in Example 1, except that the compound catalyst in step (1) is replaced with 0.06 g of triethylbenzylammonium chloride (TEBAC).

[0054] Comparative Example 3

[0055] This comparative example provides a method for preparing an epoxy insulating resin, comprising the following steps: (1) Preparation of resin mixture: 100 g of Huntsman 5531 epoxy resin and 42.4 g of curing agent methyltetrahydrophthalic anhydride (MeTHPA) were mixed at 100°C and stirred at 300 rpm for 30 minutes. Then, the mixture was degassed under a vacuum of -0.1 MPa for 30 minutes until no visible bubbles were visible in the system, resulting in a homogeneous resin mixture.

[0056] (2) Curing and molding: The resin mixture was poured into a mold preheated to 100°C and placed in an oven for curing according to the following procedure: first, pre-curing at 100°C for 4 hours, then increasing the temperature to 120°C and curing for 4 hours, and finally continuing to cure at 140°C for 10 hours. After curing, the mixture was allowed to cool naturally to room temperature and then demolded to obtain the epoxy insulating resin.

[0057] Performance testing

[0058] This experimental example uses the epoxy insulating resins provided in Examples 1-6 and Comparative Examples 1-3 as test samples for performance testing, including thermodynamic and mechanical property tests. Dynamic thermomechanical analysis (DMA) was performed using a TA Instruments DMA850 dynamic mechanical analyzer, employing a single cantilever beam mode, a frequency of 1 Hz, and a heating rate of 2℃ / min. Volume resistivity testing was conducted according to national standard GB / T 1408.1-2016, using a 100 mm diameter, 1 mm thick sample, with a voltage increase rate of 2 kV / s. Impact strength testing was performed according to national standard GB / T 2567-2021. The test results are shown in Table 1.

[0059] Table 1 Performance tests of epoxy resin samples prepared in Examples 1-6 and Comparative Examples 1-3

[0060] The performance test results show that the epoxy insulating resins prepared in Examples 1-6, with their dual-catalyst synergistic regulation, exhibit superior overall performance compared to Comparative Examples 1-3 in terms of impact strength, volume resistivity, and glass transition temperature (Tg). This demonstrates that the combination of TEBAC and PPh3 achieves synergistic regulation in both chain extension and curing stages, effectively optimizing the crosslinked network structure and thus synergistically improving the material's mechanical properties, electrical insulation properties, and heat resistance.

[0061] It should be noted that long-chain resins have lower crosslinking density due to reduced epoxy value and reactivity, and their Tg is usually lower than that of high-epoxy-value E51 type epoxy resins. This is an inherent characteristic of this type of material. The "high Tg" achieved in this invention is relative to conventional long-chain resins (such as commercially available 5531 resin), and reflects the improved heat resistance obtained through catalyst blending and structural regulation under the same low epoxy value conditions.

[0062] Specifically, the glass transition temperature (Tg) of Comparative Example 1 (using only PPh3) was significantly lower than that of Comparative Example 2 (using only TEBAC) and the Example. This indicates that while a single catalyst system can improve specific properties to some extent, it is difficult to construct a dense cross-linked network with high thermal stability while reducing the heat of curing. In particular, the lack of a high Tg in Comparative Example 2 may be related to the predominance of linear chain extender structure formed under PPh3 catalysis and the limited network cross-linking density.

[0063] In contrast, Examples 1-8, through the combination of TEBAC and PPh3, synergistically controlled the ratio of linear and branched structures during the chain extension stage. TEBAC promoted the formation of an appropriate amount of branched structures, improving the effective functionality of the resin; while PPh3 ensured the linear extension of the main framework. The residual catalysts from both further exerted a synergistic effect in the subsequent curing stage: TEBAC initiated curing at a lower temperature, moderating the exothermic reaction; while PPh3 continued to catalyze at the subsequent high temperature stage, promoting complete reaction and ultimately constructing a cured system with higher crosslinking density and a superior network topology. This collectively resulted in the examples (such as Example 1) achieving a significantly higher glass transition temperature while maintaining excellent impact strength and volume resistivity.

[0064] The properties of Comparative Example 3 (commercial resin 5531), especially impact strength and Tg, were significantly lower than those of most examples. This further demonstrates that while traditional chain extension methods that simply reduce epoxy value can reduce exothermic reactions, they come at the cost of sacrificing the integrity of the crosslinking network and thermomechanical properties. In contrast, the "structure regulation-curing synergy" strategy achieved through catalyst blending in this invention can reconstruct and strengthen the crosslinking network while reducing epoxy value and controlling exothermic reactions, thereby fundamentally surpassing the performance limitations of traditional commercial resins.

[0065] The above embodiments and comparative examples are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0066] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for preparing a low-heat, high-toughness epoxy insulating resin, characterized in that, Includes the following steps: (1) Mix 100 parts by weight of epoxy resin, 10-30 parts by weight of chain extender and 0.01-0.08 parts by weight of compound catalyst, and carry out chain extension reaction under heating conditions to obtain modified epoxy resin with reduced epoxy value; the compound catalyst is a combination of quaternary ammonium salt catalyst and phosphorus catalyst in a mass ratio of (0.25-4):

1. (2) The modified epoxy resin obtained in step (1) is mixed with 30 to 60 parts by weight of curing agent, and heated, stirred and vacuum degassed to obtain a uniform resin mixture. (3) Pour the resin mixture into the mold, heat and cure it in stages, and demold it after cooling to obtain the epoxy insulating resin.

2. The method for preparing the low-heat, high-toughness epoxy insulating resin according to claim 1, characterized in that, The epoxy resin is selected from one or more of bisphenol A type epoxy resin and bisphenol F type epoxy resin.

3. The method for preparing the low-heat, high-toughness epoxy insulating resin according to claim 1 or 2, characterized in that, The chain extender is selected from bisphenol chain extenders.

4. The method for preparing the low-heat, high-toughness epoxy insulating resin according to claim 1 or 2, characterized in that, The quaternary ammonium salt catalyst is benzyltriethylammonium chloride, and the phosphorus catalyst is triphenylphosphine.

5. The method for preparing the low-heat, high-toughness epoxy insulating resin according to claim 1, characterized in that, The curing agent is selected from one or more combinations of acid anhydride curing agents.

6. The method for preparing the low-heat, high-toughness epoxy insulating resin according to claim 1, characterized in that, In step (1), the chain extension reaction is carried out at a temperature of 80~160℃ and for a reaction time of 1~8 hours; the epoxy value of the modified epoxy resin is 0.20~0.40 eq / 100g.

7. The method for preparing the low-heat, high-toughness epoxy insulating resin according to claim 1 or 6, characterized in that, In step (2), the mixing temperature is 80~120℃, the mixing time is 0.5~1.5 hours, and the vacuum degassing pressure is not lower than -0.1MPa.

8. The method for preparing the low-exothermic, high-toughness epoxy insulating resin according to claim 1 or 6, characterized in that, The curing in step (3) is carried out in three stages: the first stage is cured at 80~110℃ for 2~5 hours; the second stage is cured at 110℃~130℃ for 2~5 hours; and the third stage is cured at 130~150℃ for 8~12 hours.

9. A low-heat, high-toughness epoxy insulating resin prepared by the preparation method according to any one of claims 1-8.

10. The use of the low-heat-exothermic, high-toughness epoxy insulating resin of claim 9 in the preparation of insulating components for electrical equipment.

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