Flame-retardant epoxy resin casting material and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and relates to a flame-retardant epoxy resin casting material and a preparation method thereof. The invention provides a preparation method of a flame-retardant epoxy resin casting material, which comprises the following steps: dissolving dimethyl polysiloxane in a lipophilic solvent, then dropwise adding onto aluminum oxide powder while stirring, and heating in a nitrogen atmosphere to obtain PDMS (Polydimethylsiloxane) modified aluminum oxide; mixing epoxy resin and silica powder in vacuum to obtain a resin mixture; mixing silane coupling agent modified DOPO, the PDMS modified aluminum oxide and an anhydride curing agent in vacuum to prepare a curing agent mixture; and performing vacuum mixing on the resin mixture and the curing agent mixture to obtain the castable. The PDMS modified aluminum oxide and the silane coupling agent modified DOPO are adopted, so that the electrical performance and the mechanical performance of the flame-retardant epoxy resin casting material are synergistically improved.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and relates to a flame-retardant epoxy resin casting material and its preparation method. Background Technology

[0002] Epoxy resin casting materials, due to their excellent mechanical strength, electrical insulation properties, chemical corrosion resistance, and moldability, are widely used in the insulation encapsulation of electrical equipment such as high-voltage switches, transformers, and instrument transformers, as well as in the fabrication of structural components in fields such as new energy vehicles and aerospace. They are an indispensable key material in modern industrial systems. However, pure epoxy resin is a flammable polymer with a low oxygen index. When burned, it releases a large amount of heat and toxic fumes and is prone to dripping, which severely limits its application in scenarios with stringent fire safety requirements. Therefore, efficient flame-retardant modification of epoxy resin casting materials has become a core technological direction for expanding its application boundaries. Currently, flame-retardant modification strategies for epoxy resins are mainly divided into two categories: organic flame retardant modification and inorganic flame retardant modification. Organic flame retardants are represented by phosphorus-based, silicon-based, and nitrogen-based compounds. Among them, phosphorus-based flame retardants (such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, i.e., DOPO) have both gas-phase and condensed-phase flame-retardant effects, high flame-retardant efficiency, and are currently a research hotspot. Silicon-based flame retardants (such as polysiloxanes) have the advantages of low smoke, non-toxicity, and environmental friendliness. During combustion, they can form a dense silicon-oxygen carbon layer, blocking heat and oxygen transfer. However, organic flame retardants generally have poor compatibility with epoxy resin matrices, and excessive addition can easily lead to a decrease in the mechanical properties and electrical insulation properties of the material.

[0003] Inorganic flame retardants, represented by alumina, aluminum hydroxide, and silica powder, are characterized by good thermal stability, low cost, and halogen-free environmental friendliness. They not only enhance flame retardancy through physical heat absorption and barrier effects but also improve thermal conductivity and dimensional stability. However, the interfacial properties of inorganic fillers differ significantly from those of the epoxy resin matrix, making them prone to aggregation within the matrix. This leads to uneven material dispersion, resulting in reduced mechanical strength and deteriorated dielectric properties. To address the dispersion issue, current technologies often employ silane coupling agents to modify the surface of inorganic fillers, enhancing the interfacial bonding between the filler and the matrix through chemical bonding. However, the organic coating layer formed during modification often becomes a permanent interfacial layer with weak mechanical properties, easily causing stress concentration under stress and impairing the overall mechanical properties of the composite material. Furthermore, the modification effect of a single flame retardant mechanism is often insufficient to meet the stringent requirements of high-end fields, leading researchers to increasingly focus on constructing multi-component synergistic flame retardant systems. However, existing synergistic flame retardant technologies are mostly simple physical formulations, failing to fully leverage the synergistic effect between different flame-retardant components, and often facing the contradiction between high flame retardant performance and overall performance. To achieve the ideal flame retardant rating, the amount of flame retardant and inorganic filler added needs to be significantly increased, which significantly deteriorates the material's processing fluidity and mechanical strength, limiting its application in precision packaging, structural components, and other scenarios.

[0004] In summary, developing a technology for preparing epoxy resin casting materials that can simultaneously achieve high dispersibility of inorganic fillers, strong interfacial bonding, and construct an efficient synergistic flame-retardant system, and solving the contradiction between dispersibility and interfacial strength, as well as the imbalance between flame-retardant performance and overall performance in traditional modification methods, has become a technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0005] This invention synergistically improves the electrical and mechanical properties of flame-retardant epoxy resin casting materials by using PDMS-modified alumina and silane coupling agent-modified DOPO.

[0006] On one hand, the present invention relates to a method for preparing a flame-retardant epoxy resin casting material, which includes: dissolving dimethyl polysiloxane in a lipophilic solvent, then adding it dropwise onto alumina powder under stirring, and heating it in a nitrogen atmosphere to obtain PDMS modified alumina; A resin mixture was prepared by vacuum mixing epoxy resin and silica powder; a curing agent mixture was prepared by vacuum mixing DOPO modified with silane coupling agent, the PDMS modified alumina and anhydride curing agent. The resin mixture and the curing agent mixture are vacuum-mixed to obtain a casting material.

[0007] Furthermore, in the preparation method of the flame-retardant epoxy resin casting material provided by the present invention, the lipophilic solvent is cyclohexane and / or n-hexane.

[0008] Furthermore, in the preparation method of the flame-retardant epoxy resin casting material provided by the present invention, each 1g of dimethylpolysiloxane is dissolved in 20~40mL of the lipophilic solvent.

[0009] Furthermore, in the preparation method of the flame-retardant epoxy resin casting material provided by the present invention, the mass ratio of dimethyl polysiloxane to alumina powder is 1:5~10.

[0010] Furthermore, in the preparation method of the flame-retardant epoxy resin casting material provided by the present invention, the heating temperature in the nitrogen atmosphere is 120~180℃, and the heating time is 1~2h.

[0011] Furthermore, in the preparation method of the flame-retardant epoxy resin casting material provided by the present invention, the silane coupling agent used in the silane coupling agent modified DOPO is silane coupling agent KH-151.

[0012] Furthermore, in the preparation method of the flame-retardant epoxy resin casting material provided by the present invention, the anhydride curing agent is 3,3',4,4'-benzophenone tetracarboxylic anhydride.

[0013] Furthermore, in the preparation method of the flame-retardant epoxy resin casting material provided by the present invention, the raw materials for preparing the flame-retardant epoxy resin casting material, by weight, consist of 100 parts of epoxy resin, 10-30 parts of silica powder, 10-30 parts of silane coupling agent modified DOPO, 5-15 parts of PDMS modified alumina, and 5-10 parts of acid anhydride curing agent.

[0014] Furthermore, in the preparation method of the flame-retardant epoxy resin casting material provided by the present invention, the fineness of the silicon micro powder is not less than 1250 mesh, and the average particle size of the alumina powder is not higher than 1 μm.

[0015] On the other hand, the present invention relates to a flame-retardant epoxy resin casting material, which is prepared by the aforementioned method for preparing flame-retardant epoxy resin casting materials.

[0016] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: (1) This invention achieves a synergistic improvement in filler dispersibility and interfacial bonding, resolving the contradictions inherent in traditional modification methods. In existing technologies, organic modification layers (such as silane coupling agents or polymer coatings) introduced to improve the dispersibility of inorganic fillers in resins often form a permanent interfacial layer with weak mechanical properties between the filler and the matrix, impairing the final strength of the composite material. This invention uses reactive PDMS as a temporary dispersing agent. In the early stages of processing, its hydrophobicity and rheological properties improve the dispersion of alumina. In the curing stage, the surface silanol groups (Si-OH) provided by silica powder and other materials in the system react thermally with PDMS, thereby dynamically removing this potentially weak interfacial layer and ultimately obtaining a composite material with uniform dispersion and strong interfacial bonding.

[0017] (2) A multi-level, multi-mechanism synergistic flame retardant system was constructed, with high flame retardant efficiency. This invention constructed a synergistic system, where DOPO derivatives provide efficient gas-phase and condensed-phase phosphorus-based flame retardant effects; PDMS itself has flame retardant and smoke-suppressing properties, and during the curing process, the dimethyl silicone small molecules generated are catalytically eliminated, which can play an auxiliary flame retardant role in the gas phase; at the same time, this process promotes the formation of a denser and more stable silicon-phosphorus-carbon composite carbon layer, improving the condensed-phase flame retardant effect. Alumina and silica powder: as inorganic fillers, they can not only improve the thermal stability of the material and reduce its flammability, but also improve the thermal conductivity of the system and avoid local overheating. This organic combination of gas-phase and condensed-phase, organic and inorganic flame retardant elements enables the material to achieve a high flame retardant rating while reducing the amount of flame retardant added, resulting in less negative impact on the electrical and mechanical properties of the material. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a sample of the cured flame-retardant epoxy resin casting material. Detailed Implementation

[0020] The technical solution of the present invention will be described below with reference to embodiments; however, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Unless otherwise specified, all percentages in the following embodiments refer to mass percentage content. Unless otherwise specified, all ratios in the following embodiments refer to mass ratios.

[0021] In the following examples, the epoxy resin is E51 type epoxy resin, the silica powder fineness is 1250 mesh, the average particle size of the alumina powder is 1 μm, and the silane coupling agent KH-151 is vinyltriethoxysilane.

[0022] Example 1

[0023] This embodiment provides a preparation process for a flame-retardant epoxy resin casting material.

[0024] By weight, the raw material ratio is 100 parts epoxy resin, 10 parts silica powder, 10 parts DOPO modified with silane coupling agent, 5 parts PDMS modified alumina, and 5 parts 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0025] Step 1: Dissolve 5g of dimethylpolysiloxane in 100mL of cyclohexane, stir well, and then drop it onto 25g of alumina powder. Heat in a nitrogen atmosphere at 120℃ for 1h to obtain PDMS modified alumina.

[0026] Step 2: Under a nitrogen atmosphere, 5g of DOPO and 10mL of chloroform were stirred evenly, and then 5g of silane coupling agent KH-151 was added dropwise. After stirring evenly, 0.08g of azobisisobutyronitrile was added. The mixture was heated to 75℃ and reacted for 10h. The solvent was removed by rotary evaporation, and finally dried under vacuum to obtain silane coupling agent modified DOPO.

[0027] Step 3: Modify DOPO with silane coupling agent, modify alumina with PDMS and 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and stir intermittently for 3 hours at 55°C and 3 mbar vacuum to obtain a curing agent mixture.

[0028] Step 4: Stir the epoxy resin and silica powder at 55°C and 3 mbar vacuum for 3 hours to obtain the resin mixture.

[0029] Step 5: Mix the resin mixture in a 130℃ oil bath environment according to the ratio, stir for 20 minutes to make the material uniform, and degas the resin mixture under a vacuum of 10mbar for 1 hour while stirring until there are no obvious bubbles.

[0030] Step 6: According to the raw material ratio, add the curing agent mixture obtained in step 4 to the resin mixture obtained in step 5, stir for 3 minutes, and then degas under a vacuum of 10 mbar for 10 minutes while stirring to obtain the flame-retardant epoxy resin casting material.

[0031] Step 7: Pour the flame-retardant epoxy resin casting material obtained in Step 6 into a mold preheated to 120℃ and cure it. The curing temperature profile is: 110℃ for 2 hours, 130℃ for 3 hours, and 175℃ for 2 hours. The cured resin column is shown below. Figure 1 As shown.

[0032] Example 2

[0033] This embodiment provides a preparation process for a flame-retardant epoxy resin casting material.

[0034] By weight, the raw material ratio is 100 parts epoxy resin, 20 parts silica powder, 20 parts DOPO modified with silane coupling agent, 10 parts PDMS modified alumina, and 8 parts 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0035] Step 1: Dissolve 5g of dimethylpolysiloxane in 150mL of n-hexane, stir well, and then drop it onto 35g of alumina powder. Heat in a nitrogen atmosphere at 150℃ for 1.5h to obtain PDMS modified alumina.

[0036] Step 2: Under a nitrogen atmosphere, 5g of DOPO and 10mL of chloroform were stirred evenly, and then 5g of silane coupling agent KH-151 was added dropwise. After stirring evenly, 0.08g of azobisisobutyronitrile was added. The mixture was heated to 75℃ and reacted for 10h. The solvent was removed by rotary evaporation, and finally dried under vacuum to obtain silane coupling agent modified DOPO.

[0037] Step 3: Modify DOPO with silane coupling agent, modify alumina with PDMS and 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and stir intermittently for 3 hours at 55°C and 3 mbar vacuum to obtain a curing agent mixture.

[0038] Step 4: Stir the epoxy resin and silica powder at 55°C and 3 mbar vacuum for 3 hours to obtain the resin mixture.

[0039] Step 5: Mix the resin mixture in a 130℃ oil bath environment according to the ratio, stir for 20 minutes to make the material uniform, and degas the resin mixture under a vacuum of 10mbar for 1 hour while stirring until there are no obvious bubbles.

[0040] Step 6: According to the raw material ratio, add the curing agent mixture obtained in step 4 to the resin mixture obtained in step 5, stir for 3 minutes, and then degas under a vacuum of 10 mbar for 10 minutes while stirring to obtain the flame-retardant epoxy resin casting material.

[0041] Step 7: Pour the flame-retardant epoxy resin casting material obtained in Step 6 into a mold preheated to 120℃ and cure it. The curing temperature curve is: 110℃ for 2 hours, 130℃ for 3 hours, and 175℃ for 2 hours.

[0042] Example 3

[0043] This embodiment provides a preparation process for a flame-retardant epoxy resin casting material.

[0044] By weight, the raw material ratio is 100 parts epoxy resin, 30 parts silica powder, 30 parts DOPO modified with silane coupling agent, 15 parts PDMS modified alumina, and 10 parts 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0045] Step 1: Dissolve 5g of dimethylpolysiloxane in 200mL of lipophilic solvent (100mL cyclohexane + 100mL n-hexane), stir well, and then drop it onto 50g of alumina powder. Heat in a nitrogen atmosphere at 180℃ for 2 hours to obtain PDMS modified alumina.

[0046] Step 2: Under a nitrogen atmosphere, 5g of DOPO and 10mL of chloroform were stirred evenly, and then 5g of silane coupling agent KH-151 was added dropwise. After stirring evenly, 0.08g of azobisisobutyronitrile was added. The mixture was heated to 75℃ and reacted for 10h. The solvent was removed by rotary evaporation, and finally dried under vacuum to obtain silane coupling agent modified DOPO.

[0047] Step 3: Modify DOPO with silane coupling agent, modify alumina with PDMS and 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and stir intermittently for 3 hours at 55°C and 3 mbar vacuum to obtain a curing agent mixture.

[0048] Step 4: Stir the epoxy resin and silica powder at 55°C and 3 mbar vacuum for 3 hours to obtain the resin mixture.

[0049] Step 5: Mix the resin mixture in a 130℃ oil bath environment according to the ratio, stir for 20 minutes to make the material uniform, and degas the resin mixture under a vacuum of 10mbar for 1 hour while stirring until there are no obvious bubbles.

[0050] Step 6: According to the raw material ratio, add the curing agent mixture obtained in step 4 to the resin mixture obtained in step 5, stir for 3 minutes, and then degas under a vacuum of 10 mbar for 10 minutes while stirring to obtain the flame-retardant epoxy resin casting material.

[0051] Step 7: Pour the flame-retardant epoxy resin casting material obtained in Step 6 into a mold preheated to 120℃ and cure it. The curing temperature curve is: 110℃ for 2 hours, 130℃ for 3 hours, and 175℃ for 2 hours.

[0052] Comparative Example 1 This comparative example is the same as Example 3, except that the PDMS-modified alumina in step 5 is replaced with alumina.

[0053] Comparative Example 2 This comparative example is the same as Example 3, except that, by mass, the raw material ratio is 100 parts epoxy resin, 30 parts silica powder, 30 parts DOPO modified with silane coupling agent, 7.5 parts PDMS, 7.5 parts alumina, and 10 parts 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0054] The flame retardant, electrical, and mechanical properties of the products prepared in Examples 1-3 and Comparative Examples 1-2 were tested. The flame retardant properties were tested according to the vertical burning test of UL-94, the electrical properties were tested according to GB / T 1408—2006 and GB / T 1410—2006, and the mechanical properties were tested according to GB / T 2567—2021. The test results are shown in Table 1.

[0055] Table 1 Flame retardant properties, electrical properties, and mechanical properties of the obtained product

[0056] As shown in Table 1, the flame-retardant epoxy resin casting materials prepared in Examples 1-3 all achieved the UL-94 V-0 flame-retardant rating. Furthermore, their electrical properties, such as breakdown strength and volume resistivity, as well as their mechanical properties, such as compressive strength and tensile strength, were significantly superior to those of Comparative Examples 1-2. Example 1 exhibited the best overall performance (breakdown strength 24.15 kV / mm, volume resistivity 144.26 × 10⁻⁶). 13 The flame retardancy of Comparative Example 1 (PDMS-modified alumina replaced with alumina) and Comparative Example 2 (PDMS and alumina added separately) was only at level V-1, and their electrical and mechanical properties were significantly reduced. This indicates that the use of PDMS-modified alumina is crucial for improving the flame retardancy, insulation and mechanical properties of the material. At the same time, it can be seen from the comparison of Examples 1 to 3 that with the increase of the amount of silica powder, silane coupling agent modified DOPO, PDMS-modified alumina and other additives, some properties of the material show a slight downward trend.

[0057] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate preferred embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for preparing a flame-retardant epoxy resin casting material, characterized in that, include: Dimethylpolysiloxane was dissolved in a lipophilic solvent and then added dropwise onto alumina powder with stirring. The mixture was then heated in a nitrogen atmosphere to obtain PDMS-modified alumina. A resin mixture was prepared by vacuum mixing epoxy resin and silica powder; a curing agent mixture was prepared by vacuum mixing DOPO modified with silane coupling agent, the PDMS modified alumina and anhydride curing agent. The resin mixture and the curing agent mixture are vacuum-mixed to obtain a casting material.

2. The preparation method of the flame-retardant epoxy resin casting material according to claim 1, characterized in that, The lipophilic solvent is cyclohexane and / or n-hexane.

3. The method for preparing the flame-retardant epoxy resin casting material according to claim 1, characterized in that, Each 1g of dimethylpolysiloxane is dissolved in 20-40mL of the lipophilic solvent.

4. The method for preparing the flame-retardant epoxy resin casting material according to claim 1, characterized in that, The mass ratio of dimethylpolysiloxane to alumina powder is 1:5~10.

5. The method for preparing the flame-retardant epoxy resin casting material according to claim 1, characterized in that, The heating temperature in a nitrogen atmosphere is 120~180℃, and the heating time is 1~2h.

6. The method for preparing the flame-retardant epoxy resin casting material according to claim 1, characterized in that, The silane coupling agent used in the modification of DOPO is silane coupling agent KH-151.

7. The method for preparing the flame-retardant epoxy resin casting material according to claim 1, characterized in that, The anhydride curing agent is 3,3',4,4'-benzophenone tetracarboxylic anhydride.

8. The method for preparing the flame-retardant epoxy resin casting material according to claim 1, characterized in that, The raw materials for preparing the flame-retardant epoxy resin casting material, by weight, consist of 100 parts epoxy resin, 10-30 parts silica powder, 10-30 parts DOPO modified with silane coupling agent, 5-15 parts PDMS modified alumina, and 5-10 parts acid anhydride curing agent.

9. The method for preparing the flame-retardant epoxy resin casting material according to claim 1, characterized in that, The fineness of the silicon micro powder is not less than 1250 mesh, and the average particle size of the alumina powder is not higher than 1 μm.

10. A flame-retardant epoxy resin casting material, characterized in that, It is prepared by the method of any one of claims 1 to 9 for the preparation of flame-retardant epoxy resin casting material.

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